MODELING CHANGE

MODELING CHANGE: LOCATING OPPORTUNITIES FOR LID In Urban Areas California State Polytechnic University Pomona, Department of Landscape Architecture, Studio 606

Spring 2011

Jake Aalfs Megan Dreger Eric Whitemyer Sina Yousefi

Unless otherwise indicated images throughout the text have been generated by the 606 team

Modeling Change: Locating Opportunities for LID In Urban Areas

Studio 606 Team: Jake Aalfs Megan Dreger Eric Whitemyer Sina Yousefi

Faculty Advisors: Lee-Anne Milburn, MLA, Ph.D., ASLA, CELA, LEED-AP Susan MulleY, MA, MLA, Ph.D. Karen Hanna, MA, FASLA, FCELA

Studio 606 Department of Landscape Architecture cal poly pomona Spring 2011

Executive Summary

Executive Summary

This document is a study of the highly-urbanized Upper San Antonio River (USAR) Watershed in central Texas. The study is focused on the use of geospatial technology to create an analytical tool to identify priority locations for Low Impact Development (LID) redevelopment or retrofit projects in urban areas. The strategic placement of LID projects in urbanized watersheds allows municipalities and regional planning agencies to focus their limited resources on locations with the greatest possible environmental impact. Thus, the ultimate goal of the modeling process presented in this document is to reduce stormwater runoff and improve water quality, minimize the negative effects of existing developments and maximize the environmental and experiential quality of urban areas within the USAR Watershed.

LOW IMPACT DEVELOPMENT LID is an environmental design approach which strives to maintain or recreate the natural hydrological characteristics of

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undeveloped terrain (Perrin et al. 2009, Housing and Urban Development [HUD] 2003, EPA 2000, EPA 1999, Prince George’s County Department of Environmental Resources [PGDER] 1999). It differs from traditional stormwater management, which seeks to drain water off a site as quickly as possible and deliver it to a receiving waterbody via the storm drain system (EPA 1999). LID addresses stormwater runoff as close to its source as possible, thereby reducing the downstream collection of runoff and the concentration of nonpoint source (NPS) pollutants in receiving waterbodies (EPA 2007). It promotes on-site storage, infiltration, and cleansing of stormwater using subtle changes in topography, planted surfaces, and a variety of built forms (County of Los Angeles 2009). Traditional stormwater management is typically centralized, utilizing large end-of-pipe control measures in order to treat as much water as quickly as possible (Perrin et al. 2009). By comparison, LID is a decentralized, localized approach to managing stormwater runoff (Perrin et al. 2009).

This document is primarily concerned with NPS pollution, hydrological function and related water quality and quantity issues in existing urban areas. LID can have the greatest benefits when combined with land use planning regulations that promote high-density, small footprint buildings--which result in less runoff from storm events (EPA 2006).

Although this study is focused on existing developed areas, it is important to note that this is only one stage of regional LID planning and implementation. This study recommends a three-part approach to implementing LID at the regional scale: 1. Protect: Provide adequate protection of existing natural resources and undeveloped lands, 2. Prevent: Create policies that help prevent urban sprawl, habitat degradation and other environmental factors contributing to waterbody contamination, and

LID IN THE UPPER SAN ANTONIO RIVER WATERSHED The San Antonio area has several unique environmental and cultural factors that affect LID implementation. Some are technical challenges such as the amount of rainfall and projected population growth; other issues are due to the regulatory environment in the jurisdictions within the USAR Watershed.

Despite these challenges, there are numerous examples of projects that demonstrate typical LID principles and strategies in the San Antonio metropolitan area and the surrounding region. This document provides a brief overview of several of these, including the Pearl redevelopment project and Phil Hardberger Park--two noteworthy examples in the City of San Antonio.

TOOLS FOR LID: CONCEPTUAL MODEL 3. Mitigate: Reduce environmental effects of impervious surfaces and sources of NPS pollution in existing urban areas.

Thus, the first steps for local government and planning bodies should be to review policies regarding development in the Edwards Aquifer recharge zone and near sink holes, intact forests, wetlands, riparian corridors and other sensitive environmental resources--and to introduce the incentives and regulations necessary to reduce such development. Once adequate conservation and pollution prevention policies are in place, the next step is retrofitting existing developments with appropriate Best Management Practices (BMPs). Since this is an enormous task in an urban area, the conceptual model presented in this document is a useful tool for determining areas to focus mitigation efforts.

The scope of this project is limited to the USAR Watershed, but the framework and conceptual model are tools that can be applied elsewhere.

The conceptual model described in this document is a relatively simple method for determining priority locations for LID redevelopment or retrofit projects in urban areas. The model uses various factors indicative of urban environmental quality, such as population density; prevalence of residential and commercial parcels (specifically, the type and density of these land uses); degree of impervious surface cover; location in drainage catchments that outfall to polluted waterbodies; soil type; proximity to water bodies; and presence of sensitive natural resources (such as aquifer recharge zones). Each

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of the factors is given equal importance in the sample results presented in Section 5, but their modeling weight can be adjusted for more detailed analysis and for specific circumstances.

designs are presented as illustrations of LID implementation in these various contexts.

NEXT STEPS Through the overlay and analysis of geospatial data, the model identifies the most beneficial locations for placement of future LID projects in existing urban areas of the USAR Watershed.

Municipalities and regional planning bodies can further develop the model’s analytical criteria and build upon the preliminary methodology presented in this document. The resulting tool will help to focus resources on already developed urban sites with the greatest possible environmental impact.

TOOLS FOR LID: DESIGN STRATEGIES Urban land uses such as residential and commercial/industrial development are the two greatest contributors to bacterial NPS pollution in the USAR Watershed (TCEQ 2007c).

Thus, this document examines the typical opportunities and constraints associated with the implementation of LID projects in such contexts, describing general strategies and specific structural BMPs that can be applied to similar development types within the USAR Watershed. The document highlights LID opportunities for development in the dense urban core, post-industrial redevelopment, residential retrofit, and new residential development. The first three development types are studied based on their association with important indicators of NPS pollution, such as high levels of impervious surfaces, population density and residential land use. New residential development is studied primarily because of its current prevalence in the San Antonio region. Finally, several site

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The document concludes by describing possible incentives and education/outreach programs that can be used to encourage LID projects, as well as a list of the geospatial data sets necessary for future study and model development. Though LID is often conceptualized primarily in terms of the placement of structural BMPs, the implementation of nonstructural BMPs is in many ways a more critical component of the approach, since such policies are usually directed at reducing the extent of impervious surfaces and/or eliminating sources of NPS pollution. Educational programs aimed at increasing residents’ understanding of the environmental consequences of urban stormwater runoff--and the implications of their individual actions and collective behavior--are an important part of a regional LID strategy.

CONCLUSION For the USAR Watershed, the opportunities presented by LID are especially crucial due to the region’s high degree of urbanization, its relatively arid climate, its vulnerability to both flash floods and droughts, its reliance on the environmentally sensitive Edwards Aquifer, and its projected population growth.

LID implementation in high priority redevelopment and retrofit sites within the existing urban areas of the USAR Watershed creates opportunities to minimize NPS pollution, improve the aesthetic quality of urban spaces and create increased societal awareness of water quality and quantity issues.

Acknowledgments

Acronyms

The authors of this document would like to thank the following individuals and institutions for their generous financial support, logistical help, and intellectual guidance:

BMP CN CWA EAA GCD GIS GMA HSG LID MS4 MEP NPDES

Julia Raish and the Lady Bird Johnson Wildflower Center Steve Graham and the San Antonio River Authority The City of San Antonio Planning Department Dr. Michael Barrett of the University of Texas, Austin The Cal Poly Pomona Landscape Architecture Department Studio 606 Faculty: Professor Karen Hanna, Dr. Lee-Anne Milburn and Dr. Susan Mulley

NPS O&M PGMA SARA SAWS SWMP TCEQ

TMDL TOD TPDES TSS TWDB UDC USAR

Best Management Practice Curve Number Clean Water Act Edwards Aquifer Authority Groundwater Conservation District Geographic Information System Groundwater Management Area Hydrologic Soil Group Low Impact Development Municipal Separate Storm Sewer System Maximum Extent Practicable National Pollution Discharge Elimination System Nonpoint Source Pollution Operation and Maintenance Priority Groundwater Management Area San Antonio River Authority San Antonio Water System Storm Water Management Program Texas Commission on Environmental Quality (formerly TNRCC Texas Natural Resource Conservation Commission) Total Maximum Daily Load Transit Oriented Development Texas Pollutant Discharge Elimination System Total Suspended Solids Texas Water Development Board Unified Development Code Upper San Antonio River

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Table of Contents List of Figures List of Tables

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Table of Contents Executive Summary acronyms Table of Contents List of Figures List of Tables

i iv vii ix xii

3. A Case for LID

1. Introduction 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

Project Overview Regional Importance of Water Overview of Stormwater and Nonpoint Source Pollution Introduction to LID Project Partner Purpose and Significance Issues Goals and Objectives

2 4 5 6 8 9 10 10

3.1 Overview of LID 3.2 LID Principles 3.3 Best Management Practices (BMPs) 3.4 LID and BMPs 3.5 Advantages and Challenges of LID 3.6 Economics of LID 3.7 Attributes That Affect LID 3.8 Effects of Climate on LID 3.9 Studies on LID Effectiveness 3.10 Philosophy

48 48 49 50 51 52 52 53 53 54

2. Background 2.1 Description of Project Area 2.2 Geomorphology 2.3 Topography and Slope 2.4 Soils 2.5 Climate 2.6 Surface Hydrology: Rivers 2.7 Subsurface Hydrology: Aquifers 2.8 Flooding 2.9 Drought 2.10 Stormwater and Flood Control 2.11 Water Quality 2.12 Vegetation 2.13 Wildlife 2.14 Population Demographics 2.15 Land Cover 2.16 Land Use 2.17 Parks and Open Space 2.18 Riverwalk

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15 17 17 18 21 22 23 25 26 27 28 30 34 37 39 42 43 44

4. implementing lid 4.1 4.2 4.3 4.4

Overview Planning and Policy Context Regional Precedents of LID How to Apply LID in San Antonio

58 59 61 65

5. LID LOcator model 5.1 5.2 5.3 5.4 5.5 5.6

Watershed Modeling Overview Pollutants of Concern Modeling Methodology Summary of Findings Limitations Next Steps

68 69 72 75 76 77

9. Conclusion

6. LID Development Types 6.1 6.2 6.3 6.4 6.5 6.6

Overview of Development Types Dense Urban Core Redevelopment Post-Industrial Redevelopment Residential Retrofit Residential New Development Selection of Structural BMPs

80 81 82 84 85 87

7. LID in action 7.1 7.2 7.3 7.4 7.5 7.6

Introduction to Design Sites Dense Urban Core Redevelopment Post-Industrial Redevelopment Residential Retrofit Residential New Development Regional Significance of Proposed Designs

Education and Outreach Potential Incentives for LID Conceptual Model Leadership

Significance LID in the USAR Watershed Conceptual Model Implications

94 98 117 135 159 177

186 187 187 188

references References Images

8. Next Steps 8.1 8.2 8.3 8.4

9.1 9.2 9.3 9.4

192 201

Appendices Appendix A : Appendix B : Appendix C : Appendix D : Appendix E :

Resources Plants Model Details Runoff Calculations Profiles

A-1 B-1 C-1 D-1 E-1

180 181 182 183

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List of Figures All images and graphics created by the 606 Studio Team, except those noted in References Fig. 1.1 Images of San Antonio Fig. 1.2 River Collage: San Antonio River Fig. 1.3 San Antonio Water System Customer Demand Fig. 1.4 Conventional Storm Drain System Fig. 1.5 Impervious Development In San Antonio Fig. 1.6 LID Explanation Diagram Fig. 1.7 Impervious Infrastructure in San Antonio Fig. 1.8 Broadway Street, San Antonio Fig. 1.9 Downspout in Downtown San Antonio Fig. 1.10 Open Lot in San Antonio Fig. 1.11 Pedestrian Bridge Over Stormwater Channel Fig. 1.12 College Street, San Antonio Fig. 1.13 Freeway Driving in San Antonio Fig. 2.1 San Antonio, Texas Context Map Fig. 2.2 San Antonio River and the USAR Watershed Fig. 2.3 Cities Within City of San Antonio Fig. 2.4 Different Watershed Definitions Fig. 2.5 Section Depicting the Edwards Plateau Fig. 2.6 Map of Topography Fig. 2.7 Map of Soil Infiltration Fig. 2.8 Map of Soil Drainage Fig. 2.9 Annual Average And Monthly Average Rainfall Fig. 2.10 Average Monthly Humidity And Temperature Fig. 2.11 The Blue Hole Fig. 2.12 Springs at the Headwaters of the San Antonio River Fig. 2.13 Sink Hole in Recharge Zone Fig. 2.14 Edwards Aquifer Recharge Zone Fig. 2.15 Edwards Aquifer Section Fig. 2.16 Edwards and Carrizo Recharge and Artesian Zones, Regional Map Fig. 2.17 Rainfall Intensity Comparison Fig. 2.18 Historical Floods in San Antonio Showing Cost of Flood Related Damage Fig. 2.19 Historical Droughts Fig. 2.20 Conventional Stormwater System Fig. 2.21 Map of Point Source Permits Fig. 2.22 Map of Impaired Waterbodies Fig. 2.23 Map of Monitoring Stations Fig. 2.24 Ecoregions Fig. 2.25 Vegetation Fig. 2.26 Habitat Connectivity

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2 3 4 5 6 7 7 7 8 8 9 9 11 14 15 16 16 17 18 19 20 21 21 22 22 23 24 24 24 25 25 26 27 28 29 30 31 32 35

Fig. 2.27 Animal Species Fig. 2.28 Recommended Conservation Areas Fig. 2.29 Population Growth in San Antonio Fig. 2.30 New Development in San Antonio Fig. 2.31 City Boundary Growth Fig. 2.32 County Growth And Projections Fig. 2.33 Population Density Fig. 2.34 Growth and Development, Interstate-410 Fig. 2.35 Impervious Area Fig. 2.36 Hydrological Change Related To Development Fig. 2.37 Different Land Use Types Fig. 2.38 Land Use Map Fig. 2.39 Residential Land Use Fig. 2.40 Land Value Map Fig. 2.41 San Antonio Greenways Fig. 2.42 San Antonio Riverwalk Fig. 2.43 San Antonio Riverwalk Fig. 3.1 Sand Filter Fig. 3.2 LID Chart Fig. 3.3 View of San Antonio River Fig. 4.1 Pearl Redevelopment, San Antonio, Texas Fig. 4.2 Phil Hardberger Park, San Antonio, Texas Fig. 4.3 Cistern, Redbud Center, Austin, Texas Fig. 4.4 Swale and Shade structure, Redbud Center, Austin, Texas Fig. 4.5 Model of the Lower Colorado River, Redbud Center, Austin, Texas Fig. 4.6 Parking Area, Redbud Center, Austin, Texas Fig. 4.7 Rainwater Harvesting, Redbud Center, Austin, Texas Fig. 4.8 Livestrong Foundation Entrance, Austin, Texas Fig. 4.9 Livestrong Foundation Sign, Austin, Texas Fig. 4.10 Salvaged Walls at the Livestrong Foundation, Austin, Texas Fig. 4.11 Planting Area, Livestrong Foundation, Austin, Texas Fig. 5.1 Streams in San Antonio Fig. 5.2 Pet Waste Bag Dispenser Fig. 5.3 Losoya Street, Downtown San Antonio Fig. 5.4 Storm Drain, Downtown San Antonio Fig. 5.5 Impaired Streams and Potential Source Subwatersheds Fig. 5.6 Model Methodology Diagram Fig. 5.7 Model Overlay Diagram Fig. 5.8 Model Output: Priority Areas for LID Fig. 5.9 Detailed Sample Model Output

35 36 37 37 38 38 39 39 40 40 41 41 42 43 44 45 45 50 51 55 61 61 62 62 63 63 63 64 64 64 65 69 70 71 71 72 73 74 75 76

Fig. 6.1 Fig. 6.2 Fig. 6.3 Fig. 6.4 Fig. 6.5 Fig. 7.1 Fig. 7.2 Fig. 7.3 Fig. 7.4 Fig. 7.5 Fig. 7.6 Fig. 7.7 Fig. 7.8 Fig. 7.9

San Antonio’s Dense Urban Core Post-Industrial Sites in San Antonio Post-Industrial Site in San Antonio Images Of Single-Family Homes In San Antonio Typical San Antonio Residential Development Context Map For Site Designs Dense Urban Area Context Map Context Map Of Selected Dense Urban Core Area Image of Commerce Street Image of Navarro Street Peacock Alley Pressa Street Bridge City Section Showing Dry-Season Water Flow in River Section Showing the Flow of Contaminants into the San Antonio River Fig. 7.10 Section Showing Historical Flood Risk Fig. 7.11 Analysis Maps of Dense Urban Core Fig. 7.12 Analysis Maps of Dense Urban Core Fig. 7.13 Downspouts from Rooftops Fig. 7.14 Green Roof Section Fig. 7.15 Green Roof Open Space Fig. 7.16 Roofs of San Antonio Fig. 7.17 Parking Lots in Downtown San Antonio Fig. 7.18 Parking Lot Design Series Fig. 7.19 LID Parking Lot Design Fig. 7.20 Parking Lot Current Condition Fig. 7.21 Proposed Parking Lot With Trees And Subsurface Storage Fig. 7.22 Broadway Street Plan Fig. 7.23 Broadway Street Current Conditions Fig. 7.24 Broadway Street After Implementation Fig. 7.25 Broadway Street Section Before Implementation Fig. 7.26 Broadway Street Section After Implementation Fig. 7.27 Current Losoya Street Fig. 7.28 Losoya Street With Permeable Pavement Fig. 7.29 Section Showing Water Filtration At Traffic Intersections Fig. 7.30 Intersection With Filtration And Water Storage Looking East on Houston Street Fig. 7.31 Intersection With Filtration and Water Storage Looking West on Houston Street Fig. 7.32 Runoff Volumes from 1.5” Design Storm for Dense Urban Area

81 82 83 85 86 95 98 99 99 99 100 100 101 101 101 102 103 104 104 104 105 106 107 108 109 109 110 111 111 112 112 113 113 114 115 115 116

Fig. 7.33 Fig. 7.34 Fig. 7.35 Fig. 7.36 Fig. 7.37 Fig. 7.38 Fig. 7.39 Fig. 7.40 Fig. 7.41 Fig. 7.42 Fig. 7.43 Fig. 7.44 Fig. 7.45 Fig. 7.46 Fig. 7.47 Fig. 7.48 Fig. 7.49 Fig. 7.50 Fig. 7.51 Fig. 7.52 Fig. 7.53 Fig. 7.54 Fig. 7.55 Fig. 7.56 Fig. 7.57 Fig. 7.58 Fig. 7.59 Fig. 7.60 Fig. 7.61 Fig. 7.62 Fig. 7.63 Fig. 7.64 Fig. 7.65 Fig. 7.66 Fig. 7.67 Fig. 7.68 Fig. 7.69

Filtered Volumes from 1.5” Design Storm for Dense Urban Area Big Tex Grain Company Site Context Big Tex Grain Company Site Context: Walking Distances Big Tex Grain Company Site Context: Key Features Existing Structures in Big Tex Grain Company Site Existing Impervious Surfaces in Big Tex Grain Company Site View of the Big Tex Grain Company Site from Across the River Recreational Uses of the Eagleland Hike and Bike Trail Big Tex Grain Company Site Context: Parcel Zoning Big Tex Grain Company Site: Drainage and Access Big Tex Grain Company Site: Impervious Surfaces and Existing Structures Local Post-Industrial LID Precedents Big Tex Grain Company Site Conceptual Design Uses of New Buildings in Big Tex Grain Company Site Construction Rubble in Big Tex Grain Company Site Reuse of Broken Concrete as Permeable Pavement Section of Public Plaza and Stormwater Features The Main Ruin Perspective of Public Plaza and Swale Section of Restored Prairie: Before and After LID Perspective of Restored Prairie and Sculpture Park Runoff Volumes From a 1.5” Design Storm for the Big Tex Grain Company Site Filtered Volumes From a 1.5” Design Storm for the Big Tex Grain Company Site Tobin Hill Neighborhood Context Map Dead End Streets Look onto the 281 Freeway Map Showing a Portion of the Tobin Hill Neighborhood Zoning Map of Tobin Hill Neighborhood Narrow Streets in the Tobin Hill Neighborhood Drainage Map of the Tobin Hill Neighborhood The Only Storm Drain in the Tobin Hill Neighborhood Concrete Channels For Stormwater Outflow Concrete Channel Directs the Stormwater to a Swale Site Analysis Maps Residential Yard Showing Soil Buildings, Streets and Parking Lots Create Large Impervious Areas Vacant Lot One of the Many Parking Lots in the Area

116 118 119 120 121 121 122 122 123 124 124 125 127 128 129 129 130 131 131 132 133 134 134 136 137 137 138 138 139 139 139 139 140 140 140 141 141

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Fig. 7.70 Fig. 7.71 Fig. 7.72 Fig. 7.73 Fig. 7.74 Fig. 7.75 Fig. 7.76 Fig. 7.77 Fig. 7.78 Fig. 7.79 Fig. 7.80 Fig. 7.81 Fig. 7.82 Fig. 7.83 Fig. 7.84 Fig. 7.85 Fig. 7.86 Fig. 7.87

View of Oak Canopy Near Terry Court Natural Area Conceptual Design of Tobin Hill Neighborhood Mistletoe Avenue Showing Existing Drainage Patterns Conceptual Design for Mistletoe Avenue and New Drainage Pattern Section Showing Existing Mistletoe Avenue Section Showing Mistletoe Avenue With Swales Added Section of Residential Front Yard Residential Lot Showing Existing Drainage Pattern Conceptual Design and New Drainage Pattern Residential Lot With Rain Garden and Permeable Paving Section of Residential Rain Garden Russell Place Showing Existing Drainage Pattern Russell Place Conceptual Design for Russell Place Park and New Drainage Pattern Existing Vacant Lot Looking East from St. Mary’s Street View of Russell Place Park Section Showing Existing Vacant Lot and Width of Russell Place Section of Russell Place Park Showing Park Features and Street Alterations Fig. 7.88 Terry Court and Existing Drainage Pattern Fig. 7.89 Mature Oak Trees Adjacent to Vacant Lot Fig. 7.90 Conceptual Design and New Drainage Pattern for Terry Court Fig. 7.91 Canopy of Oak Trees Adjacent to Terry Court Fig. 7.92 Section of Terry Court Showing Proximity of Freeway Embankment Fig. 7.93 Section of Terry Court Showing Boardwalk Extended above Swale Fig. 7.94 Section of Terry Court Showing Vacant Area and Proximity to Freeway Fig. 7.95 Section of Terry Court Showing Stormwater Biofiltration Area with Trail Fig. 7.96 Runoff Volumes From a 1.5” Design Storm for the Tobin Hill Neighborhood Fig. 7.97 Filtered Volumes From a 1.5” Design Storm for the Tobin Hill Neighborhood Fig. 7.98 Typical San Antonio Greenfield Development Fig. 7.99 Alon Area Zoning Fig. 7.100 Point A, View of Alon Greenfield - Looking Northeast Fig. 7.101 Point B, View of Alon Greenfield - Looking Southwest Fig. 7.102 Alon Greenfield Fig. 7.103 Point C, View Looking West at Existing Stormwater Detention Area Fig. 7.104 Storm Drain Outlet from Commercial Area Fig. 7.105 Alon Area 100-Year Floodplain Fig. 7.106 Alon Area Drainage Fig. 7.107 Points of Interest Around Alon Greenfield Fig. 7.108 Alon Area Conventional Development Lot Layout Fig. 7.109 LID Design for Alon Greenfield Fig. 7.110 High Density Apartments Fig. 7.111 Single Family Housing Aesthetics Fig. 7.112 Ephemeral Creek Section Fig. 7.113 Ephemeral Creek in Alon Greenfield

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142 143 144 145 147 147 148 148 149 149 149 150 151 151 152 152 153 153 154 154 155 155 156 156 157 157 158 158 160 161 162 162 162 163 163 164 164 165 166 168 169 169 170 170

Fig. 7.114 Ephemeral Creek and Community Trail Fig. 7.115 Existing Native Vegetation in Alon Greenfield Fig. 7.116 LID Design Residential Street Fig. 7.117 Residential Street Section in Alon Greenfield Fig. 7.118 Residential Street Showing Single Loaded Lot and BMPs Fig. 7.119 Closeup of Roadside Swale Fig. 7.120 LID Design Residential Lot Fig. 7.121 Residential Lot Section Fig. 7.122 Example of a LID Residence with BMPs Fig. 7.123 KB Homes Typical Lots and Home Designs Fig. 7.124 Runoff Volumes from a 1.5” Design Storm for the Alon Area Fig. 7.125 Filtered Volumes from a 1.5” Design Storm for the Alon Area Fig. 8.1 The San Antonio Riverwalk Fig. 9.1 View of the San Antonio River Fig. 9.2 LID Impacts the River, the People and the Economy of San Antonio Fig. A.1 Comparison of Selected LID Manuals Fig. B.1 Clasping Coneflower Fig. B.2 Plants for Rain Gardens: Edges of The Rain Garden Fig. B.3 Plants for Rain Gardens: Base of The Rain Garden Fig. C.1 Screen Shot of ModelBuilder Flowchart Showing Selection of Industrial Zoned Areas Fig. C.2 Screen Shot of Sample Model to Clip and Select Land Use Data Types Fig. C.3 ArcToolbox from ArcMap Screen Shot Fig. C.4 Environmental Settings Dialog Box Screen Shot Fig. C.5 Sample ModelBuilder Flowchart Showing Implementation of the Model Fig. C.6 Parameter Dialog Box Screen Shot Fig. C.7 Model Results for USAR Fig. C.8 Detailed Model Results Fig. D.1 Drainage Map of the Dense Urban Area Fig. D.2 Runoff Volumes From a 1.5” Design Storm in the Dense Urban Area Fig. D.3 Filtered Volumes From a 1.5” Design Storm in the Dense Urban Area Fig. D.4 Drainage Map of Big Tex Grain Company Site Fig. D.5 Runoff Volumes From a 1.5” Design Storm in the Big Tex Grain Site Fig. D.6 Filtered Volumes From a 1.5” Design Storm in the Big Tex Grain Site Fig. D.7 Drainage Map of Tobin Hill Neighborhood Fig. D.8 Runoff Volumes From a 1.5” Design Storm in the Tobin Hill Area Fig. D.9 Filtered Volumes From a 1.5” Design Storm in the Tobin Hill Area Fig. D.10 Drainage Map of Alon Area Fig. D.11 Runoff Volumes from a 1.5” Design Storm for the Alon Area Fig. D.12 Filtered Volumes from a 1.5” Design Storm for the Alon Area

171 171 172 172 173 173 174 174 175 175 176 176 183 188 189 A-4 B-1 B-2 B-4 C-2 C-2 C-4 C-4 C-5 C-7 C-8 C-8 D-2 D-3 D-3 D-4 D-5 D-5 D-6 D-7 D-7 D-8 D-9 D-9

List of Tables

Table 1.1 Table 4.1 Table 4.2 Table 6.1 Table 6.2 Table C.1

Five Leading Sources of Water Pollution City Residential Street Width Requirements in USAR Watershed Sample Evaluation of San Antonio’s Municipal Code Chart of Structural BMPs Examples of Swales in Seattle, Washington and Salt Lake City, Utah Table of Inputs, Their Relevance, Source and Notes

5 60 65 88 91 C-3

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1. Introduction 1.1 Project Overview 1.2 Regional Importance of Water 1.3 Overview of Stormwater and Nonpoint Source Pollution 1.4 Introduction to LID 1.5 project partner 1.6 Purpose and Significance 1.7 Issues 1.8 Goals and Objectives

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1. Introduction

1.1 Project Overview Urbanization brings dramatic changes to the land. These changes cause increased stormwater runoff, beginning a chain of events that includes erosion, stream channel alteration, pollution, and ecological damage. If left unchecked, these changes result in degraded systems no longer capable of providing good drainage, healthy habitat, or natural pollutant processing.

Figure 1.1

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Images of San Antonio

Figure 1.2

The City of San Antonio is highly urbanized, which has significantly altered the natural environmental processes.

It serves as an example of the effects of urbanization, and therefore an example of possible solutions (See Figure 1.1).

Low Impact Development (LID) is a design strategy that addresses environmental issues related to urbanization, including water quality, urban runoff, and aquifer recharge.

Although LID can be implemented anywhere, a method for prioritizing the projects is needed in large urban areas such as San Antonio. This prioritization is critical in order to effectively use available funding and ensure that remediation and retrofit projects will provide maximum benefit.

This document describes a framework for the environmentally responsible placement and design of (re)development projects in the Upper San Antonio River (USAR) Watershed (See Figure 1.2). The framework identifies priority areas for LID projects in existing urban areas based on physical and social

River Collage: San Antonio River

factors. The priority areas can then be assessed for site level design.

The project has four primary stages: (1) geospatial analysis and modeling, (2) the identification of areas contributing to nonpoint source (NPS) pollution, (3) the development of LID development types, and (4) the creation of site designs to provide practical examples of LID implementation in the USAR Watershed. Each stage of the project builds upon the findings of the preceding stage, and all are founded upon the interrelationships between biological, environmental, and sociocultural factors analyzed during modeling.

The project process will incorporate three scales of analysis and design: the watershed, the development type, and the site.

At the watershed scale, the project will create a systematic process using the ArcGIS model builder tool for identifying probable sources of targeted NPS pollutants in the USAR Watershed. The development type scale will consist of general

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strategies that can be applied to similar sites anywhere. At the site scale, sample designs will provide guidance for unique site-specific LID solutions. The project thus progresses from larger to smaller scales of analysis, presenting a multi-tiered tool for municipal and regional decision making.

The analysis and modeling phase is the cornerstone of this project because of the importance of prioritizing LID projects.

This ensures that funding and administrative resources can be focused on strategic projects within the existing urban fabric with the greatest anticipated impact. This is a critical step in the decision-making process and so the conceptual model is designed to be replicated and used elsewhere, potentially having a broader regional impact.

To facilitate the urban site design decisions that must be made following the identification of potential project sites in the USAR Watershed, this document provides design recommendations for various development types. Likewise, this document presents several detailed designs as a means of illustrating site-specific LID strategies, and the broader regional solutions that would link individual projects.

This additional groundwater pumping contributed to the San Antonio River running completely dry in 1900 during a sustained drought (Glennon 2002), a dramatic example of the effects of development on the area’s finite water supply.

San Antonio is the largest city in the United States completely dependent on groundwater (Glennon 2002). The water is pumped from the Edwards Aquifer, which is vast yet prone to fluctuations in recharge rate. If the recharge rate equals or exceeds the pumping rate, the aquifer remains in equilibrium, resulting in flows to wells and springs (Kaiser and Phillips 1998). However, removing as little as five percent of the total volume of the Edwards Aquifer can result in the drying of local springs, with disastrous affects on local wildlife (Eckhardt 2010).

The area’s water supply is limited, but the population is increasing. Bexar County’s current population is 1,525,587,

0.23% 4.22%

0.2%

Residential Commercial

1.2 Regional Importance of Water 15.49%

Water is critical to San Antonio. Native Americans called the area “Yanaguana,” meaning “refreshing waters” (Fisher 1996).

Spanish colonists founded the City of San Antonio in 1691 and began harnessing the water for agriculture using aqueducts and irrigation ditches, or “acequias” (Glennon 2002). As San Antonio prospered and grew, the city began pumping groundwater to meet the needs of its increasing population.

Apartment

54.92% 23.74%

SAWS Metered Wholesale

Figure 1.3

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CoSA

San Antonio Water System Customer Demand

but is projected to reach 2,253,060 by 2040 (Texas State Data Center 2009). This additional pressure on limited resources makes environmental planning and the management of natural resources all the more important.

Trunk Line

Catch Basin Feeder Line

Discharge

Drain Inlet

The San Antonio Water System (SAWS) supplies the area’s water. Currently, almost 70% of San Antonio’s water supply goes to houses or apartments (See Figure 1.3). With the increase in population, SAWS has forecasted increased water demand, particularly during droughts. SAWS proposes to meet future demand by decreasing water usage and increasing water reserves (San Antonio Water System [SAWS] 2009).

1.3 Overview of Stormwater and Nonpoint Source Pollution Figure 1.4

Conventional Storm Drain System

Stormwater runoff occurs when the precipitation falling on an urban environment flows across impervious surfaces (including

RANK

RIVERS & STREAMS

LAKES, PONDS & RESERVOIRS

ESTUARIES

GREAT LAKES SHORELINE

OCEAN SHORELINE

1

Agriculture

Agriculture

Municipal point sources

Atmospheric deposition

Urban runoff / storm sewers

2

Hydromodification

Hydromodification

Urban runoff / storm sewers

Discontinued discharges from pipes

Land disposal

3

Urban runoff / storm sewers

Urban runoff / storm sewers

Atmospheric deposition

Contaminated sediment

Municipal point sources

4

Municipal point sources

Municipal point sources

Industrial discharges

Industrial discharges

Spills

5

Resource extraction

Atmospheric deposition

Agriculture

Urban runoff / storm sewers

Industrial discharges

Table 1.1

Five Leading Sources of Water Pollution

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

5

roads, parking lots, sidewalks, and building rooftops) instead of percolating into the ground. In an urban area, the volume of runoff can be considerable. The conventional approach has been to direct the runoff into storm drains, which carry the water into an extensive network of pipes, channels, and other conveyances in order to carry the untreated runoff to be discharged into a river or lake (See Figure 1.4). This approach has kept stormwater runoff “out of sight” and therefore “out of mind” (Wong and Eadie 2000). Stormwater drains do not typically channel water to treatment facilities, but carry runoff directly into streams, rivers, and lakes.

Nonpoint source (NPS) pollution of stormwater occurs as runoff travels across these impervious surfaces, collecting chemicals and other pollutants (See Figure 1.5 and Figure 1.7 - Figure 1.13). Examples of NPS pollution sources include fertilizers and pesticides, greases and oils, fecal matter and heavy metals. As a result, urban runoff and storm drains are considered one of the leading sources of water pollution in the United States (Environmental Protection Agency [EPA] 1994) (See Table 1.1).

via the storm drain system (EPA 1999). LID promotes on-site storage, infiltration, and cleansing of stormwater using subtle changes in topography, planted surfaces, and a variety of built forms (PGDER 1999). While some LID strategies utilize the natural filtration functions of vegetation and permeable soils to help remove contaminants from stormwater runoff, other LID strategies are planning policies designed to prevent or diminish the water runoff and pollution (HUD 2003).

The fundamental objectives of LID designs are to: • • • • •

Slow stormwater runoff (HUD 2003) Increase soil infiltration (and reduce outfall discharge) Increase contact time with the landscape (by increasing flow lengths) Prevent soil erosion (EPA 1999) Conserve existing soil and vegetation (by minimizing

1.4 Introduction to LID The primary goal of Low Impact Development (LID) is to maintain or recreate the natural hydrological characteristics of undeveloped terrain (Perrin et al. 2009, Housing and Urban Development [HUD] 2003, EPA 2000, EPA 1999, Prince George’s County Department of Environmental Resources [PGDER] 1999). This approach differs from conventional stormwater management, which seeks to drain water off a site as quickly as possible and deliver it to a receiving waterbody Figure 1.5

6

MODELING CHANGE

Impervious Development In San Antonio

• •

grading) (Perrin et al. 2009) Concentrate development on flatter slopes Minimize and cluster development footprints (Perrin et al. 2009)

There is significant overlap between the principles of LID and those of other sustainability frameworks such as The Sustainable Sites Initiative™ (SITES™) and the Leadership in Energy and Environmental Design (LEED) standard (Leadership in Energy and Environmental Design 2011, Sustainable Sites Initiative 2010). However, an important difference between LID and other frameworks is that its principles can be applied at a variety of scales, from an individual property to a regional watershed. Thus, LID is defined not so much by the tools and strategies it employs, but rather by a hydrology-focused approach to the location and design of urban development (See Figure 1.6).

Figure 1.7

Impervious Infrastructure in San Antonio

Low Impact Development

DESIGN STRATEGIES

BEST MANAGEMENT PRACTICES (BMPs)

ROAD WIDTH CLUSTERING DEVELOPMENT

NON-STRUCTURAL

STRUCTURAL

MINIMUM BUILDING FOOTPRINT

POLICIES & ORDINANCES

SWALES

SIDEWALK PLACEMENT

PUBLIC EDUCATION

FILTER STRIPS

FORM BASED CODES

OVERLAY DISTRICTS

INFILTRATION TRENCHES

URBAN GROWTH BOUNDARY

DETENTION BASINS CONSTRUCTED WETLANDS

Figure 1.6

Figure 1.8

LID Explanation Diagram

Broadway Street, San Antonio

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

7

1.5 Project Partner The Lady Bird Johnson Wildflower Center proposed this project as part of their Texas LID Initiative (Texas LID 2010).

The Center’s stated mission is to “increase the sustainable use and conservation of native wildflowers, plants and landscapes,” and the organization’s programs emphasize the linkages between storm water management, the creation of wildlife habitat, the protection and restoration of plant biodiversity, and pollution reduction (Lady Bird Johnson Wildflower Center 2011). In 2006, the Center joined with the American Society of Landscape Architects (ASLA) and the U.S. Botanical Garden to develop the Sustainable Sites Initiative, a series of voluntary incentives intended to serve as a common standard for the design and construction of “large campuses, public parks, conservation areas, private resorts, recreation areas or transportation and utility corridors” (Lady Bird Johnson Wildflower Center 2011).

Figure 1.9

8

MODELING CHANGE

Downspout in Downtown San Antonio

The Center’s over-arching interest in resource conservation and environmental stewardship, as well as its important role in the development of the Sustainable Sites Initiative, makes it a suitable institution for the exploration of LID planning and implementation strategies for the City of San Antonio. The Center has provided guidance and acted as liaison with the San Antonio River Authority (SARA) and the City of San Antonio, which have provided most of the geospatial data used during the analysis phase of the project.

The Center’s primary objective for this project is to develop a conceptual model that can be used to prioritize potential LID sites in the San Antonio region’s existing urban areas. Thus, the project is mainly focused on opportunities for retrofit and redevelopment, rather than greenfield development.

Figure 1.10

Open Lot in San Antonio

1.6 Purpose and Significance

redevelopment. This maximizes water quality and minimizes the quantity of urban stormwater runoff.

Responsible development is critical to the future of both San Antonio and Texas. By 2060, the State’s population is expected to more than double while the demand for water is expected to increase by 27 percent (Texas Water Development Board [TWDB] 2007). Since San Antonio relies almost exclusively on groundwater, this expansion will put additional pressure on the city’s water supply (SAWS 2009). Both water quantity and water quality will become intensely critical issues.

Thus, San Antonio must go beyond standard flood and erosion control practices and address the issues of existing urban stormwater runoff quality and quantity. This can be done through multifaceted LID projects designed to improve water quality, increase the urban landscape’s hydrological and ecological functions, and avoid urban sprawl and other negative aspects of conventional development.

Population growth often brings a corresponding increase in development. If not carefully planned, this new development can occur in environmentally sensitive areas and lessen the amount of undeveloped open land. This results in reduced open space for recreation and reduced habitat available to local wildlife. While new development should utitlize LID practices, existing development impacts can also be mitigated by application of LID principles through retrofit and

The successful implementation of LID projects will result in improved water quality, reduction of the amount of runoff, improved riparian habitats for wildlife and increase recreational opportunities. These factors contribute to both public health and the quality of life, creating healthy livable spaces. The economic benefits of LID include increases in property values and possible increases in tourism (MacMullan and Reich 2007).

Figure 1.11

Pedestrian Bridge Over Stormwater Channel

Figure 1.12

College Street, San Antonio

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

9

The USAR Watershed is home to almost 500,000 people, with an additional 800,000 people elsewhere in the city (Census Bureau 2000). As an urbanized watershed, the area must balance the needs of its residents with the need to maintain a healthy environment. LID is a design approach that can help to do both. LID can enhance property values and improve the quality of life, while protecting San Antonio’s vital water resources and improving biodiversity, conservation, and recreational opportunities.

1.8 Goals and Objectives

1.7 Issues

OBJECTIVES

Like many cities, San Antonio has experienced rapid growth that has defined its physical form. Conventional development methods have encouraged this expansion but at the cost of various bio-physical and socio-cultural factors.

Develop a conceptual model for the application of LID, which creates a planning framework for: •

Improving the quality of ground and surface water;

Bio-physical issues • Reduced water quality • Habitat degradation • Habitat loss • Ground water scarcity and reduced aquifer recharge

•

Reducing stormwater runoff;

•

Mitigating the environmental effects of increased urbanization and expanding development;

•

Identifying undeveloped areas suitable for preservation;

•

Protecting drinking water supplies from the potentially negative impacts of future development; and

•

Improving habitat quality and connectivity.

Socio-cultural issues • Reduced public health • Reduced quality of life • Lack of public awareness

10

MODELING CHANGE

GOAL Develop an analytical tool to identify priority urban retrofit and redevelopment locations for LID projects in order to reduce stormwater runoff and improve water quality, minimize the negative effects of proposed and existing development and maximize the environmental and experiential quality of the watershed.

Develop conceptual designs for the implementation of LID, which will describe strategies for: •

Improving the experiential and aesthetic quality of the landscape;

•

Revealing and celebrating natural processes as a means of increasing public awareness;

•

Creating multifunctional spaces that serve a variety of purposes - including recreation and habitat; and

•

Creating designs that reflect and celebrate San Antonio’s distinct identity.

SCOPE LIMITATIONS While the concept of LID includes broad issues such as energy usage, the primary focus of this document is the management of stormwater, including issues related to water quantity and quality issues.

Figure 1.13

The document’s data analysis, modeling, and design recommendations focus specifically on the Upper San Antonio River Watershed (as defined by the USDA), but the modeling methodology and framework structure may be applicable to other areas in Texas. The conceptual geospatial model presented in this document is intended to serve as a starting point for further research and analysis. The model is focused on locating LID opportunities in existing urban areas rather than identifying potential areas for greenfield development.

This is mainly due to the needs expressed by the client and project partners. Although this document addresses LID strategies that may be applied to greenfield developments, the anticipated findings of the conceptual model can not be utilized to prioritize sites for such development.

Although this document focuses specifically on water quantity and NPS pollution, the successful implementation of LID principles must go beyond the mere placement of structural BMPs and actually address the ways in which a city grows, the demarcation of areas for development and preservation, the management of natural resources and the engagement of private landowners and members of the general public in the planning process.

Freeway Driving in San Antonio

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

11

12

MODELING CHANGE

2. Background 2.1 Description of Project Area 2.2 Geomorphology 2.3 Topography and Slope 2.4 Soils 2.5 Climate 2.6 Surface Hydrology: Rivers 2.7 Subsurface Hydrology: Aquifers 2.8 Flooding 2.9 Drought 2.10 Stormwater and Flood Control 2.11 Water Quality 2.12 Vegetation 2.13 Wildlife 2.14 Population Demographics 2.15 Land Cover 2.16 Land Use 2.17 Parks And Open Space 2.18 RiverWalk

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

13

2. Background

LOcation

Hydrologic soil Groups Oklahoma

Arkansas

New Mexico

Louisiana

San Antonio An

TEXAS AS +T

Mexico Gulf of Mexico

Figure 2.1

14

MODELING CHANGE

San Antonio, Texas Context Map

2.1 Description of Project Area The Upper San Antonio River (USAR) Watershed is located in central Texas. It is one of several watersheds that make up the larger San Antonio River Watershed, which flows southeast toward the Gulf of Mexico (See Figure 2.1).

The USAR Watershed is located at the headwaters of the San Antonio River and covers approximately 530 square miles within Bexar County (Texas Commission on Environmental Quality [TCEQ] 2007c). It extends from the north end of Bexar County to just south of the 410 freeway (USDA 2009).

The watershed is almost entirely within San Antonio’s city limits, and includes the jurisdictions of Alamo Heights, Balcones Heights, Castle Hills, Leon Valley, Olmos Park, Shavano Park, and Terrell Hills (See Figure 2.2 & Figure 2.3).

The USAR Watershed is the project boundary used for data analysis and design throughout this document. Although a watershed is demarcated by topography in which all of the water drains to the same place, there can be variations in watershed boundaries. The authors have chosen to use the watershed boundary defined in the Watershed Boundary Dataset’s (WBD) 10-digit (5th-level) hydrologic unit codes (HUCs). See Figure 2.4 for a comparison of USAR Watershed boundaries.

Gulf of Mexico Figure 2.2

San Antonio River and the USAR Watershed

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

15

The watershed is characterized by varying land use types ranging from open space to dense urban and industrial areas, but most of the watershed is comprised of urban development. Because it is the source of the San Antonio River, it does not receive flow from upstream, which makes it relatively self-contained. This makes the USAR Watershed an ideal location for the study of NPS pollution and the contribution of conventional development methods to water quality problems, as well as a good “laboratory� for studying

the effectiveness of Low Impact Development strategies in preventing and mitigating NPS pollution in urban settings.

These characteristics also suggest that LID implementation in the watershed can have a significant effect on downstream water quality. The USAR watershed presents an opportunity to develop a model which can identify priority locations for urban retrofit and redevelopment using LID principles. It can also be used to demonstrate ways in which BMP applications can improve water quality and reduce the quantity of stormwater runoff.

Shavano Park

Hollywood Park Castle HIlls Alamo Heights

Leon Valley

Olmos Park

Balcones Heights

Kirby Terrell Hills

Lackland AFB

Upper San Antonio River Basin (USGS)

Watershed Boundary Dataset (WBD) 8 Digit HUCs (12100301)

San Antonio River Watershed (SARA)

Watershed Boundary Dataset (WBD) 10 Digit HUCs (1210030102)

N 0

5

10 Miles

Bexar County USAR Watershed

Figure 2.3

16

MODELING CHANGE

Cities Within City of San Antonio

Figure 2.4

Different Watershed Definitions

2.2 Geomorphology The USAR Watershed is located just south of the Balcones Escarpment, a series of cliff and cliff-like structures separating the higher altitudes of the Edwards Plateau to the northwest from the Gulf Coastal Plain to the southeast. The base of the Balcones Escarpment is marked by the Balcones Fault Zone, a series of faults extending from southwest Texas near Del Rio to north central Texas around Waco (University of Texas n.d.).

Over time, the Balcones Fault and water movement have acted upon the ancient layers of subsurface limestone, resulting in the formation and development of the Edwards Aquifer (Eckhardt 2010). Called a karst aquifer because of

its water-bearing, soluble limestone layers, it is characterized by sinkholes and fissures at the surface and subterranean voids connected by conduits of varying sizes (Eckhardt 2010) (Figure 2.5).

2.3 Topography and Slope The topography and slope of the land are important indicators of the movement of surface water. As slope increases, there is also a rise in runoff velocity, erosion and sediment transport (Baldwin & Shelton 2003). Erosion and flooding can also increase in relation to the length of slope, which increases the accumulation of runoff and scouring of soil (Baldwin & Shelton 2003) (Figure 2.5).

A A B LC BA CONES ESCAR AR RPM MEN ENT NT

A’

SINK HOL OLES E ES KA ARS RST LI RST LIME MEST ME ST TO ON NE

A’

ARTE AR TESI TE S AN A SPR PRIN NG KARS KA R T AQUI RS AQU AQ UIIFE ER

Figure 2.5

Section Depicting the Edwards Plateau

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

17

The USAR Watershed is relatively flat, with the exception of the hills of the Balcones Escarpment to the north. The elevation ranges from a high of 1080 feet in the north to the lowest point of 415 feet, where the San Antonio River flows out of the Watershed and converges with the Medina River.

The slope is also relatively low, with the majority of land sloped less than 3%. Bexar County includes small areas in the Edwards Plateau with slopes measuring more than 24%; however, within the USAR Watershed, only a few hill and riverbank areas have steep slopes (See Figure 2.6).

2.4 Soils Soils are a critical component of stormwater management (Pitt and Chen 1999). As water travels across the soil, it may percolate into the soil or run off the surface, depending on the soil’s properties. The infiltration capacity of soils affects the rate and amount of runoff as well, as the rate of groundwater recharge (Scheyer and Hipple 2005). It can also decrease the amount of NPS pollution that is carried into surface waterbodies (Pitt and Chen 1999).

N 0

5

10 Miles

City of San Antonio USAR Watershed Figure 2.6

18

MODELING CHANGE

Map of Topography

As urban areas grow, the properties of the soil change. Some soil is covered by impervious surfaces such as buildings, roads, and parking lots. Other soil remains in place but is changed due to compaction, reordering of the soil layers, removal of topsoil, additions (such as construction debris) and other processes (Scheyer and Hipple 2005). This changes

the behavior of the soil and can reduce infiltration rates (Pitt and Chen 1999). Thus, there is generally more runoff in urban areas because of the impervious surfaces and compacted soils (Scheyer and Hipple 2005). This increased runoff causes erosion and carries pollutants such as pesticides, oil, and gas (Scheyer and Hipple 2005) and can also lead to flooding as water volumes are increased (EPA 2000).

High infiltration rates can be problematic when they allow contaminants to leach into groundwater without sufficient treatment. Some pollutants, such as certain pesticides, are water-soluble and so move through the soil easily. This allows them to enter the groundwater and adversely affect water quality.

Bexar County varies in soil properties, particularly between the north and south. Figure 2.7 shows hydrologic soil groups (HSG), which are indicators of infiltration. The categories range from A, which indicates rapid infiltration, to D, which indicates that rainwater generally runs off the surface. Bexar County has moderate to high infiltration rates in the southern portion of the county, but the majority of the county has slow or very slow infiltration. The USAR Watershed has predominantly very slow infiltration rates with some slow to moderate infiltration (National Resources Conservation Service [NRCS] 1995).

1 0

5

10 Miles

A=High infiltration rates B=Moderate infiltration rates C=Slow infiltration rates D=Very slow infiltration rates USAR Watershed Figure 2.7

Map of Soil Infiltration

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

19

Figure 2.8 shows the drainage characteristics of the county.

Most of the county is moderately to well drained, and the southern portion is somewhat excessively well drained. The USAR Watershed is moderately well drained to well drained.

Drainage is an important factor for LID, determining the type of intervention that would be most appropriate. For example, an infiltration BMP may not function properly in a poorly draining soil. This could result in unwanted standing water without proper engineering and consideration.

1 0

5

10 Miles

Somewhat excessively drained Well drained Moderately well drained USAR Watershed

Figure 2.8

20

MODELING CHANGE

Map of Soil Drainage

2.5 Climate The climate of the USAR Watershed is “modified subtropical” due its unique location at the junction of the higher altitudes of the Edwards Plateau to the northwest and the lower altitudes of the coastal plains to the southeast (National Weather Service [NWS] 2010). This location between extremes contributes to a high variation in precipitation.

10.0

52.5

7.5 Inches

Inches

Annual Monthly Average

70.0

35.0

17.5

5.0

2.5

0

0 2000 2001

2002

2003 2004 2005

Figure 2.9

2006

Jan

2007 2008 2009 2010

Feb Mar

Apr

May

Jun

July Aug Sep Oct

San Antonio, TX

San Antonio, TX

Seattle, WA

Seattle, WA

Nov Dec

Annual Average And Monthly Average Rainfall

Average monthly Humidity

Monthly Temperature Range

80

100

60

75

Degrees F

Percent

Average daytime temperatures in San Antonio range from 50 to 80°F, with summer high temperatures generally above 90°F and occasionally reaching more than 100°F (NWS 2010). High temperatures in the summer months are often accompanied by high humidity. Historically there have been at least 300 days of sunshine per year (San Antonio Convention and Visitors Bureau 2010) and only an average of 20 days with temperatures below freezing (NWS 2010) (See Figure 2.10).

Total Annual average 2000-2010

http://www.srh.noaa.gov/images/ewx/sat/satmonrain.pdf http://www.weather.gov/climate/index.php?wfo=sew

Average annual precipitation is approximately 30 inches, though actual annual precipitation ranges from 10 to 50 inches (San Antonio Convention and Visitors Bureau 2010). Most precipitation is in the form of rain; however, infrequent snowfall may occur in small amounts (NWS 2009). On average, most rainfall occurs during the months of May and September, while the driest months are December through March (See Figure 2.9). Given the high variability of precipitation, large rain events can happen at any time and result in amounts exceeding five inches in the span of a few hours, occasionally causing flash floods (National Oceanic and Atmospheric Administration 2010, NWS 2010).

Rainfall

40

20

50

25

0

0 Jan

Feb Mar

Apr

May

Jun

July Aug Sep Oct

Nov Dec

Jan

Feb Mar

Apr

Average Relative humidity

May

Jun

July Aug Sep Oct

Nov Dec

Average max Mean Average Min

Figure 2.10

Average Monthly Humidity And Temperature

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

21

2.6 Surface Hydrology : Rivers The USAR Watershed includes the headwaters of the San Antonio River, which begins as a collection of springs that are produced by artesian pressure forcing water up from the Edwards Aquifer. The water from several major spring outlets and hundreds of small springs converges to create the creeks, which in turn join to create the San Antonio River. The largest of the springs, known as the Blue Hole (See Figure 2.11 and Figure 2.12), and many of the smaller springs are now protected in a preserve area known as the Headwaters Sanctuary, which was established in 2006 (Eckhardt 2010).

San Pedro Springs San Antonio Springs

!

! ! !

The springs are dependent on the water level of the aquifer and so the flow of the springs varies considerably. During

N 0

1.5 6.0

6.0 Miles

USAR Rivers & streams !

Figure 2.11

22

MODELING CHANGE

The Blue Hole

Spring

Figure " 2.12

Springs at the Headwaters of the San Antonio River

dry periods when the aquifer level is low, some springs may not flow at all. Thus, the flow of the San Antonio River is dependent upon both rainfall and the water level of the Edwards Aquifer.

As the river meanders through San Antonio, it collects water from several creeks that carry water from across the city and from springs. Because the watershed is highly urbanized, the river, creeks and tributaries have become important flood control channels. While some of these have remained naturalized drainage courses, others are now engineered earthen channels, concrete channels, or culverts (City of San Antonio n.d.).

The river flows out of the USAR Watershed at the confluence with the Medina River. It then flows through the plains until eventually joining the Guadalupe River and emptying into the Gulf of Mexico over 100 miles away.

surface directly down to subterranean conduits and caverns, similar to underground rivers (Eckhardt 2010). It is also a “confined” or “artesian” aquifer because the water-bearing limestone layer is covered by relatively impervious confining layers (See Figure 2.15).

The aquifer consists of three main zones: the Contribution or Drainage Zone, the Recharge Zone, and the Artesian Zone (See Figure 2.15). The Contribution or Drainage Zone is relatively nonporous, which directs the water downhill into the more porous Recharge Zone (See Figure 2.14). In the Recharge Zone, an outcropping of porous limestone allows water to enter an underground network of conduits.

In fact, almost all surface water in the Recharge Zone flows underground, except in times of extreme precipitation (Eckhardt 2010). Finally, the Artesian Zone, shown in Figure 2.16, is where the confined water is forced to the surface due to pressure from the impervious bedrock surrounding

2.7 Subsurface Hydrology : Aquifers The Edwards Aquifer is a critical source of drinking water for the population of San Antonio. The EPA has designated it as a “sole source” aquifer, meaning that it is the sole or principal source of drinking water for the area (EPA 2008b). Its water level is regularly reported by the local news media, which has brought widespread awareness to residents (S. Graham, personal communication, 11 November 2010).

The Edwards Aquifer is classified as a karst aquifer, meaning that it is made up of limestone that allows water to flow through sinkholes (See Figure 2.13) and swallow holes from the Figure 2.13

Sink Hole in Recharge Zone

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

23

USAR Watershed

0

N

15

30

USAR Watershed

60

Edwards Aquifer Recharge Zone

miles

Drainage Zone

0

15

30

N

60 miles

Edwards Aquifer Artesian Zone

Recharge Zone

Carrizo-Wilcox Aquifer Recharge Zone

Artesian Zone

HAYS

Carrizo-Wilcox Aquifer Artesian Zone

COMAL

BEXAR

BEXAR KINNEY

Figure 2.14

UVALDE

MEDINA

Edwards Aquifer Recharge Zone

DRAINAGE ZONE

Figure 2.16

ARTESIAN ZONE

RECHARGE ZONE

the aquifer. Thus, water from the Recharge Zone presses on the confined water in the Artesian Zone and forces it to the surface, forming the artesian springs that feed local watercourses (Eckhardt 2010).

ARTESIAN SPRING

BALCONES ESCARPMENT

EDWARDS AQUIFER

SAN ANTONIO RIVER SOURCE: ADAPTED FROM SARA

Figure 2.15

24

MODELING CHANGE

Edwards Aquifer Section

Edwards and Carrizo Recharge and Artesian Zones, Regional Map

As the City of San Antonio continues to expand to the north, urban development increasingly falls within the Edwards Aquifer Recharge Zone. This trend could have adverse longterm consequences because the Recharge Zone is essentially made up of direct conduits to the aquifer, which allows urban runoff to enter the aquifer unimpeded. This could allow polluted urban runoff into the aquifer and therefore into San Antonio’s drinking water supply.

2.8 Flooding

5.00

San Antonio is at the southern end of what has been called “Flash Flood Alley.” The Hill Country to the north of the USAR Watershed is especially prone to flash flooding because of its thin soils, large areas of exposed bedrock, and relatively sparse vegetation (Votteler 2002) (See Figure 2.17).

Inches

3.75

2.50

1.25

0

1 2

3 4

5 6

7

As areas such as San Antonio become increasingly urbanized, flood hazards can become a greater threat because the land loses the capacity to slow down and store rainwater (Konrad 2005). With less storage capacity for water in urban watersheds and swifter runoff, urban streams rise more quickly during storms and have higher peak discharge rates than do rural streams. Also, the total volume of water discharged during a flood tends to be larger for urban streams than for rural streams (Konrad 2005).

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hours

Figure 2.17

Wettest Day in San Antonio During 2002 Flood. July 1, 2002

9.52 In. Total

Wettest day in Seattle Oct. 20 2003

5.01 In. Total

Rainfall Intensity Comparison

d an n on us i l io o il ill M Th M 2 .5 9 $8 $7 $1

Source: NOAA & NWS

on

0

M

n n io io n on ill o ill i i M M ill ill 5 M M 7.

10 $1 $1 $4 $1

h”

uc

“M

$3

M

ill

io

n n on n lli io io ill ow Mi ill M kn 0 B 0 3 $1 $4 Un $5

n

Severity of Storm

$2

i ill

Figure 2.18

2010

2000

1990

1980

1970

1960

1950

1940

1930

1920

1910

Catastrophic Storm Major Storm

Historical Floods in San Antonio Showing Cost of Flood Related Damage

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

25

LOcation

In the last century San Antonio has been subject to several significant floods. The floods also caused significant property damage. During this period San Antonio residents alone received $14,864,976.29 for flood related damages (USGS n.d.) (See Figure 2.18).

Hydrologic soil Groups Oklahoma

Arkansas

New Mexico

TEXAS

Because flooding is a regional issue, the state created special governmental units called River Authorities to serve regional areas roughly equivalent to river basins. The San Antonio River Authority (SARA) was created in 1937 and its jurisdiction extends 3,658 square miles - including all of Bexar, Wilson, Karnes, and Goliad counties (SARA 2010).

Louisiana

San an Antonio

+

Mexico Gulf of Mexico

2.9 Drought LOcation

Hydrologic soil Groups Oklahoma

Texas is known for being water rich or water poor. Droughts are intermittent but can be lengthy and severe. The Drought of Record was in 1950 and lasted until 1957, which forced some ranchers and farmers out of the state (Votteler 2002) (See Figure 2.19).

Arkansas

New Mexico

TEXAS

Today the population of Texas is double what it was in 1950, and as cities such as San Antonio grow, water scarcity poses an even greater threat as supply is forced to stretch further (Votteler 2000). The effects of drought are exacerbated by

Louisiana

San an Antonio An

+

Mexico Gulf of Mexico

SOURCE: US DROUGHT MONITOR D2- Severe Drought

Figure 2.19

26

MODELING CHANGE

Historical Droughts

2010

2000

1990

1980

1970

1960

1950

1940

1930

1920

1910

D3- Extreme Drought D4- Exceptional Drought

urban sprawl because it allows less infiltration and ground water recharge (Otto et al. 2002). Thus, planning for future growth is critical, particularly in the aquifer recharge zones.

Several measures have already been taken. For example, in 2005 San Antonio adopted a water conservation ordinance (City of San Antonio 2005). Another recent strategy to alleviate the effects of drought has been to store water. Because of the porous nature of the Edwards Aquifer’s karst formations and the terrain characteristics, traditional reservoirs have not proven to be a viable option in San Antonio. They have also been opposed by landowners and conservationists because vast expanses of productive land and natural habitat would be submerged (Votteler 2000, TWPD n.d.). Instead, the Aquifer Storage and Recovery system is used (Eckhardt 2010). This pumps water below ground into a sand aquifer, and because water flows through sand at such a slow rate compared to karst aquifers, the water can be stored. The water is then pumped back out when needed. The Twin Oaks Aquifer Storage and Recovery project was completed in 2004 and provided a substantial amount of water storage underground (Eckhardt 2010). By 2006 the facility held 20,000 acre feet and provided relief during the drought that occurred that year (Eckhardt 2010).

of peak discharge management and storage volumes (Wanielista and Yousef 1993). Stormwater was collected by various inlets (e.g. curb openings, gutters, or catch basins) and then transported away in ditches, channels, or storm drains. Although effective in terms of conveyance and flood control, this strategy removed the stormwater from the hydrologic cycle, which in turn led to increases in water pollution, a slowing of groundwater recharge, and other environmental problems (EPA 2010).

San Antonio has an extensive stormwater conveyance network, which includes almost 500 miles of underground stormwater drainage channels and more than 400 miles of above ground drainage channels. There are also over 1400 acres of other types of above ground drainage channels (City of San Antonio n.d.).

Trunk Line

Catch Basin Feeder Line

Discharge

Drain Inlet

2.10 Stormwater and Flood Control Stormwater has traditionally been viewed simply as a problem whereby excess runoff was disposed of as quickly and efficiently as possible (EPA 2010) (See Figure 2.20). Flood control was the primary consideration for most urban areas and, as a result, stormwater management was approached as an issue Figure 2.20

Conventional Stormwater System

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

27

2.11 Water Quality SOURCES OF POLLUTION Water pollution in the United States is categorized as either point source or NPS pollution. Point source pollution originates at an identifiable localized source, such as a factory or a sewage treatment plant (EPA 2010 B). NPS pollution, by contrast, comes from a variety of sources, not from a single discharge pipe. Most NPS pollution is a direct result of stormwater runoff, which picks up and carries away small amounts of pollutants from a large number of dispersed sources (EPA 2010 b). It is thus often difficult to pinpoint the origin of NPS pollutants. Common NPS pollutants include oil and grease, sediment, nutrients, and bacteria. Most surface pollutants are collected during the initial phase of a storm and referred to as the “first flush” (TCEQ 2007c). In a traditional stormwater management system like San Antonio’s, runoff is typically channeled through pipes directly into rivers, lakes, and streams without any treatment (TCEQ 2007c).

$

! " Î ;

$

$

! " Î ; ! " Î ;

$ ! " Î ; ! " ; Î

$

N 0

1.5 6.0

6.0 Miles

$ ! " ; Î

$ USAR Rivers & Streams

$ $

Municipal Solid Waste Site

! " ; Î

Wastewater Outfall

Permitted Industrial & Hazardous Waste

Figure 2.21

28

MODELING CHANGE

Map of Point Source Permits

Point source pollutants, which come from a single definable point such as a pipe, are regulated by permit under the Texas Pollutant Discharge Elimination System (TPDES). There are several point sources in the USAR Watershed, most of which are permitted, and have a disinfection requirement that must be reached prior to discharge. Of the five point sources in our study area listed in the TCEQ report, three are controlled by the San Antonio Water System (SAWS). The other point source is not under permit and discharges substantial concentrations of bacteria (TCEQ 2007c).

Another potential source of contaminants is municipal solid waste facilities (landfills) and Superfund sites. Although these are monitored and regulated, their location should be considered

when siting projects, particularly if infiltration is planned. See Figure 2.21 for locations of these sites. Although urban areas contribute a significant amount of pollutants, other activities also create problems. For example, some of the sources of water quality impairment in surface waters are agriculture, forestry, and mining (EPA 2002).

SURFACE WATER QUALITY According to the 2010 San Antonio River Basin Highlights Report, sections of the Upper San Antonio River do not meet the contact recreation use designation due to elevated levels of bacteria. Figure 2.22 shows the tributaries of the Upper San Antonio River that have also been identified as not meeting the contact recreation use designation. These tributaries are Apache Creek (Segment 1911B), Alazรกn Creek (Segment 1911C) and San Pedro Creek. All of these tributaries are unclassified waterbodies.

Other pollutants were also found. Nutrients such as nitrate (NO3N) and total phosphorus (TPO4) were elevated at many locations throughout the Upper San Antonio watershed. San Pedro Creek and Apache Creek were identified as having concerns for dissolved oxygen grab screening levels. SARA has made daily water quality data available through their website http://www.riverrec.com.

In recent years contact recreation in the USAR has been discouraged because of a concern for the high number of bacteria counts found during water quality testing. The Texas Natural Resource Conservation Commission stated in a 1996 report on water quality that the EPA had disapproved the standards of east Texas streams in general and that appropriate revisions were underway in order to comply with

N 0

1.5 6.0

6.0 Miles

USAR Rivers & streams Alazan Creek Apache Creek San Antonio River

"

San Pedro Creek

Figure 2.22

Map of Impaired Waterbodies

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

29

! ! ! ! ! ! !

!

! !

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!

1.5 6.0

! ! !

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! !

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!

!

!

0

2.12 Vegetation

!! !! !!

!!

N

6.0 Miles !

!

! ! ! !

! ! !! !

! !!

!

! !

! !

USAR Rivers & Streams Monitoring Stations

Figure 2.23

30

MODELING CHANGE

Native vegetation plays an important role in the natural hydrological system, and is an important component of LID strategies as it intercepts, slows, and filters stormwater runoff (SARA n.d.). However, the native vegetation of the USAR Watershed has largely been replaced by development and non-native plant species.

!

!

!

!

Later testing, which targeted E. coli and fecal coliform organisms, was managed by the San Antonio River Authority (SARA). In 2007 the TCEQ concluded that attaining federal water quality standards on this portion of the San Antonio River would require a 50 percent reduction in NPS pollution loading, a 30 percent reduction in urban stormwater loading, and a 99.9 percent reduction in baseflow loading from the San Antonio Zoo (TCEQ 2007). Monitoring stations can be seen in Figure 2.23.

!

! !

federal regulations regarding the Clean Water Act (TNRCC 1996). The river was first designated as “impaired� due to bacteria in the Texas Water Quality Inventory and 303(d) List (TCEQ 2000).

Map of Monitoring Stations

! !!! !!

! ! ! ! !

The land cover of Bexar County historically belonged to three ecoregions, as defined by the Texas Park and Wildlife Department (2010): the Balcones Canyonlands of the Edwards Plateau in higher elevations, the Texas Blackland Prairie in mid elevations, and the lower elevation South Texas Plain (See Figure 2.24). Although there is some overlap, each ecoregion is largely characterized by several key plant species (See Figure 2.25). In the Balcones Canyonlands, they are Live Oak (Quercus fusiformis & Quercus virginiana), Ashe Juniper

Edwards Plateau

ashe Ashe juniper Juniper

Live Oak

Blackland Prairie

Bluewood

Mesquite

South Texas plain

Post Oak

A A

A’

A’ Figure 2.24

Ecoregions

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

31

Live Oak

Ashe Juniper

Opuntia

Edwards Plateau Blackland Prairie South Texas plain Post Oak

Sabel Palm

Figure 2.25 32

MODELING CHANGE

Big Bluestem

Vegetation

Little Bluestem

Honey Mesquite

Indian Grass

Texas Persimmon

Purple Coneflower

Bald Cypress

Texas Redbud

Silver Bluestem

Blue Grama Grass

Pale-leaf Yucca

Sideoats Grama

Desert Willow

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

33

(Juniperus ashei) and Mesquite (Prosopis sp.). In the remnant Blackland Prairie, they are Mesquite, Live Oak, and Bluewood (Condalia hookeri var. hookeri). The Southern Post Oak Savanna’s key plant species are Post Oak (Quercus stellata) and native grasses.

In addition to the key plant species, typical riparian corridor species were once common along the creeks and rivers. Such vegetation can still be found in certain stretches of the San Antonio River, such as near the historic Mission San Juan Capistrano (SARA n.d.). Important riparian plant species include: Black Willow (Salix nigra) Cedar Elm (Ulmus crassifolia) Hackberry (Celtis occidentalis) Pecan (Carya illinoensis) Texas Sycamore (Platanus glabrata) Bluewood (Condalia hookeri var. hookeri) Arrowhead (Sagittaria latifolia) Pickerelweed (Pontederia cordata) Scarlet Sage (Salvia coccinea) Blue Grama (Bouteloua gracilis) (SARA n.d.)

Of the three ecoregion types, the Blackland Prairie has been most dramatically affected by the urban and agricultural development around San Antonio (TPWD 2005). However, plant species throughout the area have been affected. Today, Bexar County contains six rare or threatened plant species listed by TPWD (2011), including:

34

MODELING CHANGE

Big Red Sage (Salvia pentstemonoides) Bracted Twistflower (Streptanthus bracteatus) Correll’s False Dragon-head (Physostegia correllii) Elmendorf’s Onion (Allium elmendorfii) Hill Country Wild-mercury (Argythamnia aphoroides) Parks’ Jointweed (Polygonella parksii) Sandhill Woollywhite (Hymenopappus carrizoanus) While these plant species are unlikely to occur within Bexar County’s urban environment, they may be found along the margins of the City of San Antonio, such as the areas north of the City in which new development is gradually expanding.

See Appendix B: Plants for resources and lists of appropriate plant species for the San Antonio area.

2.13 Wildlife Wildlife has also been adversely affected by urbanization and the loss of native vegetation. For example, the amount of impervious land cover in traditionally developed watersheds is typically correlated with reduced fish populations in streams and rivers (Wang, Lyons, Kanehl and Bannerman 2001, Limburg and Schmidt 1990). Other animal species are also affected as there are numerous species found within Bexar County that are considered endangered or threatened by the state and federal governments (See Figure 2.27).

Several bird species are listed and this reflects the intricate ecological relationship with native plant species, particularly the Golden-cheeked Warbler (Dendroica chrysoparia), which nests in older stands of Ashe Juniper and uses the mature tree’s bark to construct its nests (TPWD 2011a). Thus,

Zone Tail Hawk Green Jay

Mexican Free Tail Bat

Gray Wolf Texas Horned Toad

Golden Cheeked Warbler White Faced Ibis

Black capped Vireo

N 0

1.5

6.0

12.0 Miles

Heavily Wooded Parks Rivers & Creeks

INTRODUCTION INTRODUCTION

" Figure 2.26

Habitat Connectivity

Figure 2.27

Animal Species

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

35

the habitat destruction or modification resulting from urban development is a major concern for the health of both plant and animal species populations. Interspecies competition and the presence of invasive species is also a major concern, as in the case of the Black-capped Vireo, which is threatened by “nest-site parasitism� from cowbirds (City of San Antonio 2010b).

Two species of bats are also threatened: the Ghost-faced Bat (Mormoops megalophyllaare) and the Cave Myotis Bat (Myotis velifermost rele) (TPWD 2011a). San Antonio and surrounding cities (including Austin) have a history of accommodating and recognizing the ecological importance of bat populations, as demonstrated by the existence of several historic bat roosts in this region (Figure 2.27). The continued existence of a bat colony beneath the Interstate 35 Bridge over the San Antonio River is indicative of the adaptability of some local wildlife species and suggests that there may be ways in which the urban built environment can accommodate their presence.

Other endangered or threatened species of note within Bexar County are three species of eye-less beetles and six species of cave-dwelling arachnids (essentially eye-less spiders and harvestmen), which are found in areas north and northwest of San Antonio (TPWD 2011a). Uniquely adapted to karst features, these species are particularly significant due to their role as indicator species for water quality and quantity (TPWD 2011a).

N 0

1.5

6.0

12.0 Miles

Recommended Preservation Areas Impervious Surfaces Figure 2.28

36

MODELING CHANGE

Recommended Conservation Areas

LID strategies can play an important role in improving the quality of existing habitats. Though the connectivity of native vegetation and wildlife habitat patches is typically not a major component of LID, it is important to explore the potential role

that LID projects may have in improving habitat linkages. For example, the City’s North Sector Plan identifies the areas north of the City as having the greatest amount of potential habitat for endangered or threatened wildlife species (City of San Antonio 2010b). Thus, any projects in that area can address habitat issues along with more general LID principles.

Many areas along the western edge of the City of San Antonio are categorized as “heavily wooded,” forming a peripheral arc of habitat patches (See Figure 2.26). Likewise, certain stretches of the Leon and Salado Creeks and the San Antonio River can likely support diverse wildlife populations, and serve as habitat corridors extending through the urban area and linking the undeveloped pastures and woodlands north and south of the city. Recommended conservation areas, based on the aquifer recharge zone and heavily wooded land use, can be seen in Figure 2.28.

2.14 Population Characteristics NPS pollution is sometimes called “people pollution” because much of it is the result of people’s activities. Population density is thus a particularly important factor to consider when analyzing sources of NPS pollution; as the population of an area increases, there is also an increase in NPS pollution (EPA 1993).

Bexar County’s population is primarily concentrated within the City of San Antonio, which has a population of 1,319,492 (US Census Bureau 2009). This area has seen tremendous growth since the original 36 square mile city had a population of 3,488 in 1850 (See Figure 2.31). Beginning in the 1940’s, the San Antonio area began rapid growth, both in population and in expanding city boundaries. Figure 2.30 shows an example of new development in San Antonio. Figure 2.29 shows the rapid increase in city population and Figure 2.31 shows the corresponding expansion of city limits.

1,000,000

800,000

600,000

400,000

Figure 2.29

Population Growth in San Antonio

Year

2000

1990

1980

1970

1960

1950

1940

1930

1920

1910

1900

1890

1880

1870

1860

200,000

1850

Population

1,200,000

Figure 2.30

New Development in San Antonio

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

37

Original

1970s

1940s 70 sq.mi.

1950s 161 sq.mi.

1960s 184 sq.mi.

263 sq.mi.

1980s 342 sq.mi.

1990s 430 sq.mi.

Present

1,500,000

1,000,000

Figure 2.32

MODELING CHANGE

County Growth And Projections

Year

2040

2030

2020

2010

2000

1990

1980

1970

1960

1950

1940

1930

1920

1910

1900

1890

1880

0

1870

500,000

1860

The population density in the county increases dramatically from the rural areas to the denser urban areas. The population density within the Upper San Antonio River Watershed is approximately 3,238 people per square mile (See Figure 2.33).

2,000,000

1850

The San Antonio area is projected to continue to grow significantly in population (See Figure 2.32). Bexar County currently has a population of 1,392,931 and is projected to grow by about 35% by 2040, to a total of 1,884,509 people (Texas State Data Center 2009). Planning for this growth is critical and the city’s Master Plan includes several growth management goals designed to address this additional population (City of San Antonio 1997).

38

552 sq.mi.

City Boundary Growth

Population Population

Figure 2.31

36 sq.mi.

Figure 2.34

Growth and Development, Interstate-410

2.15 Land Cover Impervious cover includes anything that prevents or impedes water from soaking into the ground (EPA 2011b). Typically this includes driveways, roads, parking lots, rooftops, and sidewalks (See Figure 2.34). These impervious surfaces prevent rain and snow from soaking into the ground, turning it into stormwater runoff. Under natural conditions, a portion of the water is absorbed into the soil and vegetation. This process slows the water and partially filters it before it reaches groundwater or other waterbodies.

1 0

5

10 Miles

1 Dot = 100 People USAR Watershed Figure 2.33

When land is developed and impervious surfaces are added, the natural systems are no longer able to intercept the runoff (EPA 2011b). As the impervious cover increases, the volume of runoff increases (See Figure 2.36). The annual volume of runoff can increase by 2 to 16 times the pre-development rates (Schueler 1995). For example, a one acre parking lot

Population Density

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

39

10-20% IMPERVIOUS

NATURAL GROUND COVER 40%

38%

10%

42%

50%

35-50% IMPERVIOUS

75-100% IMPERVIOUS

15%

35%

SOURCE: ADAPTED FROM US EPA

N 0

Figure 2.36

1.5 6.0

6.0 Miles

USAR

Impervious Percentage High : 100 Low : 0 Figure 2.35

40

55%

30%

30%

35%

20%

MODELING CHANGE

Impervious Area

Hydrological Change Related To Development

produces about 16 times more stormwater runoff than an undeveloped one-acre meadow (Schueler 1995).

This increase in runoff results in less water infiltrating into the soil, which means there is less water available to recharge groundwater (NRCS 2005). The water that is able to percolate through the soil generally carries increased quantities of pollutants, which can lead to groundwater quality issues (Pitt, Clark, and Parmer 1994) (See Figure 2.36).

Figure 2.37

Different Land Use Types

San Antonio’s most impervious areas are at the city center and along major transportation corridors. The majority of the impervious surfaces are north of the city center, which coincides with the city limits (See Figure 2.35). The areas with the least amount of impervious cover are outside the city.

Residential Commercial Streets Agriculture Golf Courses Other Open Space Waterbodies USAR Watershed

0

1.5 6.0

Figure 2.38

6.0 Miles

N

Land Use Map

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

41

2.16 Land Use Land use is another key factor in NPS pollution. For example, urban areas may contribute rubber fragments and heavy metals while agricultural land may add higher levels of nutrients and sediment (Tong and Chen 2002). Although different land uses can produce pollution, some land uses are associated with particular pollutants. This is important for studying current pollutant loads as well as for future land use planning. As land use changes, the levels of contaminants will change, particularly if undeveloped land becomes urban development or agriculture (Tong and Chen 2002).

$ +

! " ; Î

Land use within the USAR Watershed is largely urban, with 80% of the land designated commercial/industrial, residential, or street (See Figure 2.37 & Figure 2.38). The residential category alone makes up 43% of the Watershed. This is further broken down by density in Figure 2.39.

$ +

$ +

USAR Watershed

! " ; Î

Residential greater than 1 acre Single family 1 acre Single family 1/2 acre Single family 1/3 acre Single family 1/4 acre

! " ; Î

Single family 1/8 acre

$ + ! " Î ;

LAND VALUES

! " Î ;

One of the important drivers of land use is the landowner’s ability to maximize the value of the land (Elliott 2008). Land value is affected by many factors, such as topography, zoning, and access. Because land prices are high, property owners are concerned with any changes that could potentially lower their property value (Elliott 2008). LID’s effect on property values should therefore be considered (See Figure 2.40). See Section 3 for addition information on the economics of LID.

$ + $ + ! " ; Î $ + 0

1.5

Figure 2.39

42

MODELING CHANGE

3

6 Miles

N

Residential Land Use

2.17 Parks and Open Space In 2009, San Antonio had a population of 1,328,984 and approximately 19,620 acres of parks--including the 835- acre San Antonio Missions National Historical Park (Trust for Public Land 2009). This equates to approximately 14.8 acres of park space per 1,000 residents, ranking below several cities with similar population sizes and densities, such as San Diego, Phoenix, and Dallas (Trust for Public Land 2009). Thus, residents could benefit from multifunctional LID projects that have a recreational component, contributing to increased quality of life and improved public health. $0 - $200,000 per acre $200,100 - $400,000 per acre $400,100 - $600,000 per acre $600,100+ per acre USAR Watershed

The Leon Creek, Medina River, North Salado Creek and South Salado Creek Greenways are noteworthy because they serve stormwater management and habitat connectivity functions in addition to acting as recreational amenities. The existing greenway system consists of 1,100 acres of acquired property and 23 miles of trails, with plans for the construction of another 14 miles of trails in the near future (City of San Antonio 2011).

The future expansion of the Leon Creek, North Salado Creek and South Salado Creek Greenways will allow the creation of habitat corridors extending through the urban area, linking habitat patches on the northern and southern peripheries of the city (See Figure 2.41).

$0 - $200,000 per acre $200,100 - $400,000 per acre $400,100 - $600,000 per acre

0

per acre6 1.5$600,100+ 3 Miles USAR Watershed

Figure 2.40

N

Recreation in and along the San Antonio River itself is somewhat limited. The urban Downtown and Museum Reach areas are reserved for tourist boat traffic. Paddling is allowed in the Eagleland Reach of the river, just south of the Downtown, though there is limited access. The stretch of river to the south is currently unavailable for paddling due to a weir and also because of construction currently taking

Land Value Map

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

43

place on the Mission Reach of the river. When construction is finished, the mission reach will increase paddling opportunities (SARA 2011). Some fishing opportunities exist on the river at Brackenridge Park and Espada Lake.

2.18 Riverwalk San Antonio is perhaps best known for its popular Riverwalk, a growing stretch of pedestrian walkways along the banks of the river. The Riverwalk was developed in the 1930’s by the Works Project Administration (WPA) and grew over time to assume its currrent form. Today the Riverwalk is a major attraction offering a variety of restaurants, hotels, shops, boat tours, popular nightclubs, and seasonal festivities (See Figure 2.42 & Figure 2.43).

The Riverwalk has proven to be an important economic driver for San Antonio as the number of restaurants, hotels, and retail shops has steadily increased. Local voters have passed a series of bond measures in order to help fund improvements to the Riverwalk. Most recently, the San Antonio River Improvements Project (SARIP), completed extensive renovations and extended the Riverwalk north into the Museum Reach, with improved pedestrian access along the River (SARA 2011).

N 0

1.5

6.0

12.0 Miles

Parks Greenway (Existing & Planned) Rivers & Creeks USAR Watershed

" Figure 2.41

44

MODELING CHANGE

San Antonio Greenways

Figure 2.42

San Antonio Riverwalk

Figure 2.43

San Antonio Riverwalk

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

45

46

MODELING CHANGE

3. A Case for LID 3.1 Overview of LID 3.2 LID Principles 3.3 Best Management Practices (BMPs) 3.4 LID and BMPs 3.5 Advantages and Challenges of LID 3.6 Economics of LID 3.7 Attributes that Affect LID 3.8 Effects of Climate on LID 3.9 Studies on LID Effectiveness 3.10 Philosophy

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

47

3. A Case for LID

3.1 Overview of LID LID is a stormwater management concept that strives to maintain the pre-development hydrologic response of a landscape, including infiltration, storage, evapotranspiration and groundwater replenishment (EPA 2000). In addition to LID, there are numerous stormwater management concepts with varying terminology but essentially similar goals, including SUDS (Sustainable Urban Drainage Systems), WSUD (Water Sensitive Urban Design) and LIUDD (Low Impact Urban Design and Development) (Construction Industry Research and Information Association n.d., Melbourne Water n.d., van Roon and van Roon 2005).

3.2 LID Principles LID design and implementation measures are intended to reduce impervious surfaces on a site, thereby decreasing the

48

MODELING CHANGE

volume of runoff, slowing its flow across the site, temporarily or permanently storing it, filtering it and encouraging its infiltration into the soil (EPA 2000). However, the LID approach focuses not only on water quantity, quality and hydrological function, but also seeks to address other related environmental issues (PGDER 1999). LID differs from conventional stormwater management in its goals, methods and effectiveness (National Research Council [NRC] 2009).

the approach is most effective when implemented at an earlier phase in the design process, which allows for the most appropriate use of design strategies, non-structural Best Management Practices (such as public education or household hazardous materials disposal) and finally structural Best Management Practices (such as vegetated swales, vegetated detention areas, rooftop gardens and permeable paving) (HUD 2003).

LID differs from a conventional design approach by attempting to address stormwater runoff as close to its source as possible and mimic or recreate pre-development hydrology, thereby reducing the downstream collection of large volumes and the concentration of NPS pollutants in the receiving waterbody.

Conventional stormwater management implements largerscale control measures to mitigate the quantity and quality of runoff, and is generally more centralized and located at the end-of-pipe, in order to treat as much water as quickly as possible.

LID can have the greatest benefits when combined with land use planning regulations that promote high-density, small footprint buildings, which result in less runoff from storm events (EPA 2006). Thus, LID should ideally be part of an integrated land use planning process, resulting in more concentrated development, less disturbance to existing landscapes and the construction of fewer roads and other paved impervious surfaces (EPA 2006). LID complements such larger-scale land use planning because site-scale BMPs fit within available open spaces and manage the reduced stormwater runoff.

On the other hand, LID implementation has been linked with increased pollutant removal, reduced flow volumes and reduced peak flow rates (Dietz and Clausen 2006, Dietz and Clausen 2005, Davis, Shokouhian, Sharma and Minami 2001, EPA 2000). While both LID and conventional stormwater management achieve the same basic function (drainage), LID succeeds in attenuating some of the detrimental effects associated with conventional development.

As a design approach, LID is applicable to a variety of project types, including redevelopment in the dense urban core, new development (greenfields) and the conversion of former industrial sites (brownfields) (Perrin et al. 2009). However,

3.3 Best Management Practices (BMPS) In the context of stormwater management, the term Best Management Practices (BMPs) refers to the various policies and structures used at the site, neighborhood and city scales to achieve various management goals, such as improving water quality, promoting aquifer recharge and preventing flooding (EPA 1999). While the term LID refers to a general approach or set of principles, BMPs are highly specific strategies adapted to certain site conditions and management purposes (Field 2006). Over time, the materials and construction techniques of detention and retention basins,

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

49

swales and other BMPs have become largely standardized (Ice 2004). Although there are important functional differences between various BMPs, they all work together to slow, detain, cleanse and infiltrate water on-site (Perrin et al. 2009).

Due to the dispersed nature of NPS pollution, management strategies vary depending on factors such as location, land use and target pollutant. BMPs, which are also sometimes referred to as Stormwater Control Measures (SCMs), are designed to prevent or minimize the amount of NPS pollution generated in various situations (NRC 2009). BMPs are often categorized by function, such as sediment reduction (or filtration in general), infiltration and water capture and storage. The implementation of BMPs often requires a balance between the reduction of NPS pollution and the need for an affordable and practical solution (Ice 2004).

3.4 LID and BMPs The term LID refers to a multi-scale planning and design process, and BMPs are the tools implemented in the final stages of this process to achieve the intended goals (See Figure 3.2) (HUD 2003). Since BMPs are specific welldefined methods, they can be utilized in a more conventional stormwater management system as well, independent of the overarching goals of LID. Indeed, a conventional stormwater management system may use structural BMPs to convey water as quickly as possible to storm drains, which in turn drain to streams. What makes a project conform to the principles of LID is not the presence of BMPs, but rather the extent to which BMPs function collectively to achieve the goals of LID (PGDER 1999).

There are two types of BMPs: structural and non-structural.

Structural BMPs are physical devices or methods used in the landscape, such as a sand filter. Non-structural BMPs consist of planning and policy techniques, such as education, street sweeping programs or city ordinances. Non-structural BMPs focus on the prevention of NPS pollution while structural BMPs mitigate the effects of stormwater-related impacts (EPA 1999).

Most structural BMPs are small-scale and placed on a site as space permits; their goal is to treat most stormwater runoff onsite but it may be necessary for larger sub-regional and even regional structural BMPs to handle excessive flow. Figure 3.1 shows an example of a sand filter, one type of structural BMP.

Figure 3.1

50

MODELING CHANGE

Sand Filter

3.5 Advantages and Challenges of LID Compared to conventional stormwater management techniques, LID has advantages and challenges. The advantages of LID are a result of LID being a holistic design philosophy with the goal of maintaining pre-development hydrology. The challenges of implementing LID are related to treatment limitations, implementation and maintenance (Perrin et al. 2009, HUD 2003, PGDER 1999).

LID is scalable and can be implemented from the regional watershed level down to the site scale. Conversely, conventional methods emphasize larger scale structures for collecting and conveying stormwater. LID removes pollutants and reduces the volume of runoff, benefiting both humans and wildlife in the affected area. Conventional methods emphasize drainage, and removal of pollutants is a secondary consideration. LID is more cost-effective than conventional stormwater management methods (EPA 2007, Alexander and Heaney 2002).

It is necessary to understand the challenges of LID. Initial issues include lack of design information related to size, safety, cost and vegetation (Adair 2010, Miccio 2010, Perrin et al.

2009). These issues are further complicated by slow approval processes (Adair 2010). Finally all aspects of maintenance including management, inspections and upkeep suffer from lack of experience (Godwin, Parry, Burris and Chan 2008).

Given clear LID installation policies and reasonable levels of pollutants and enlightened maintenance, the advantages far outweigh the disadvantages of implementing LID.

LID cannot completely replace all conventional stormwater management techniques due to several challenges. LID implementation requires detailed knowledge of sites, including exact measurements of areas and slopes in order to implement LID methods. LID may not treat all the effluent generated by a site, thus requiring further treatment downstream. Also, many LID methods require maintenance at shorter intervals than conventional management practices and failure to complete regular maintenance degrades effectiveness of the BMPs. Sites with concentrated pollutants such as automobile repair facilities are not suitable for LID implementation since the level of pollution may overwhelm the biological capacity of filtration BMPs and render them useless.

Low Impact Development

DESIGN STRATEGIES

BEST MANAGEMENT PRACTICES (BMPs)

ROAD WIDTH CLUSTERING DEVELOPMENT

NON-STRUCTURAL

STRUCTURAL

MINIMUM BUILDING FOOTPRINT

POLICIES & ORDINANCES

SWALES

SIDEWALK PLACEMENT

PUBLIC EDUCATION

FILTER STRIPS

FORM BASED CODES

OVERLAY DISTRICTS

INFILTRATION TRENCHES

URBAN GROWTH BOUNDARY

DETENTION BASINS CONSTRUCTED WETLANDS

Figure 3.2

LID Chart

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

51

3.6 Economics of LID

3.7 Attributes That Affect LID

There are a growing number of studies that investigate the economic implications of LID implementation, most of which compare LID costs to conventional stormwater management methods (Revitt, Scholes and Ellis 2008, EPA 2007, MacMullan and Reich 2007, HUD 2003). Several studies have shown how LID projects could benefit developers by lowering the costs of stormwater control infrastructure (EPA 2007).

However, some studies point out cases where LID BMPs increased the cost of development (EPA 2007, MacMullan and Reich 2007).

Determining the best location for LID projects in an area is a complex process, with multiple inputs and variable determinants. The application of structural BMPs relies on multiple variables, including the land’s physical characteristics, land use (which determines degree of imperviousness), amount of available space, the location of sources of pollutants, the depth of groundwater, the costs of land acquisition and BMP construction and management (Perrin et al. 2009, Lai, Dai, Zhen, Riverson, Alvi and Shoemaker 2007, Tong and Chen 2002). To make matters more complicated, it is sometimes necessary to first monitor the quality and quantity of runoff in an area in order to determine the management goals and the most suitable BMPs for the site (Lai et al. 2007).

To truly determine the economic consequences of utilizing LID, it is important to look beyond initial construction costs and consider long-term operation and management (O&M) costs and to compare these to those of conventional controls.

Sample et al. (2003) suggest evaluating stormwater BMPs using life-cycle-cost (LCC) analysis. LCC analysis includes the initial capital expenditures for construction and planning as well as the present value of lifetime O&M costs and the salvage (or residual) value at the end of the BMP’s useful lifespan (Revitt, Scholes and Ellis 2008). In addition, the opportunity cost of land (alternative values for the land based on different uses) can be included the cost analysis (Revitt, Scholes and Ellis 2008). Larger-scale BMPs that occupy more land area typically have a higher opportunity cost valued at the next-best use for the land, e.g., residential value (MacMullan and Reich 2007).

In general LID projects are more cost effective due to a combined reduction in site grading, preparation, stormwater infrastructure, paving and landscaping (EPA 2007).

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Physical properties of the land determine the efficiency of specific structural BMPs (Lai, Shoemaker and Riverson 2005). For example, the soil type determines the rate of infiltration, while slope affects the speed of runoff. The depth of subsurface groundwater beneath the land limits the depth of retention and detention basins. The physical properties of the land also determine the volume and speed of run-off, the rate of infiltration and the collection of surface water in receiving waterbodies (Lai et al. 2005). Land use is an important factor since it determines the level of imperviousness; land used for human activity such as residential, commercial or industrial uses generally result in a higher proportion of impervious surfaces (relative to total land area), which contributes to increased runoff (Wang, Lyons, Kanehl and Bannerman 2001, Hollis 1975). Land use areas with high amounts of transportation-related uses, such as a fast food restaurant with drive-thru or automotive service center, may negate the use

of certain LID BMPs such as porous pavement due to high buildup of oil and brake-dust sediment.

Water quantity and quality can be determined (using sensors or modeling) prior to placing LID BMPs. However, substantial time and financial resources are necessary to place, monitor and maintain sensors. Modeling also requires heavy use of resources in order to ensure that the targeting of BMPs is as accurate as possible (Lai et al. 2005). Thus, it is important to consider cost when determining the best location for BMPs, as well as possible benefits. The implementation of individual BMPs also has associated costs based on their type and size (EPA 2007). Finally, knowing how to weigh the importance of each variable is also important. Ultimately, the best location to place structural BMPs is where space is available, where they will address the most environmental issues and cost the least amount of money (EPA 2009b, EPA 2007, Lai et al.

2005). Determining this location requires an understanding of complex interactions between many variables, and is the purpose of Section 5 of this document.

3.8 Effects of Climate on LID Climate affects the implementation of LID in several ways.

LID is affected by the amount of precipitation, temperature and humidity in a region. LID implementation methods have biological and physical components that may be affected by climate. Many BMPs filter stormwater function via contact with vegetated material. Climate can affect the health of the vegetation and thus the effectiveness of the BMP (Roseen et al. 2009). Unfortunately, little research has been conducted regarding the role of native vegetation in BMP success.

The effectiveness of LID in cold climates with freezing temperatures has been questioned due to the dormancy of vegetation and the possible freezing of below ground infiltration zones (Roseen et al. 2009).

3.9 Studies on LID Effectiveness Since the early 1990s, LID has evolved from an intuitive concept for handling stormwater to a structured, detailed approach (Lai et al. 2007, EPA 2000, PGDER 1999). The choice between implementing LID and utilizing a conventional stormwater management system is greatly facilitated by recent research and case studies which demonstrate the effectiveness of LID design principles (on-site water storage, treatment and infiltration). Case studies initially provided the first evidence of the approach’s effectiveness and more recent research papers have detailed the complexity of its components, proving its ability to reduce runoff volume and to reduce pollutant loads (EPA 2000).

Low Impact Development (LID) A Literature Review (2000), concludes that bioretention areas were effective at reducing the amount of runoff and removing lead, copper and zinc, as well as phosphorous, total nitrogen, ammonium and nitrate (EPA 2000). Further research studies have shown increased imperviousness correlates with increased local stream flow and that LID can significantly reduce the impact on waterways (Davis, Hunt, Traver and Clar 2009, Dietz and Clausen 2008, Jennings and Taylor 2002).

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3.10 Philosophy The overarching philosophy uniting the various phases of this project is: Protect, Prevent and Mitigate.

structural and non-structural BMPs to capture and cleanse stormwater, as well as to encourage its infiltration. Priority should be directed towards sites near streams and wetlands, in recharge zones, or within highly impervious, dense urban areas.

Protect Before local planning agencies consider the implementation of LID projects, they should take steps to protect existing natural resources, including aquifer recharge zones, sink holes, large habitat patches, stands of mature trees, wetlands and stream corridors. While it is challenging to balance conservation efforts with the economic benefits of increased development, it is critical to incentivize infill development and regulate greenfield development that threatens natural resources.

Prevent Once appropriate conservation measures are implemented, the next priority should be to identify land uses contributing to NPS pollution and to prevent the pollution generation of these areas. This requires the implementation of non-structural BMPs and other planning policies intended to prevent NPS pollution, habitat fragmentation and urban sprawl. To achieve this, sustainable site design strategies that reduce the amount and connectivity of impervious surfaces are necessary.

Mitigate After conservation and prevention policies have been considered, a planning body should mitigate the environmental effects of existing impervious surfaces and sources of NPS pollution. This requires the selection and installation of

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The conceptual model presented in this document is intended to help developers and planners prioritize LID sites in existing urban areas. Thus, this document is mainly focused on the Mitigation aspect of the project philosophy, due to the needs of the project partners. The project philosophy demonstrates how the conceptual implementation tools presented in this document fit into a broader LID process, and emphasizes the need for appropriate natural resource protection and NPS prevention measures before the consideration of specific LID implementation sites.

Figure 3.3

View of San Antonio River

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4. implementing lid 4.1 4.2 4.3 4.4

Overview Planning and Policy Context Regional Precedents of LID How to Apply LID in San Antonio

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4. implementing lid

4.1 Overview The San Antonio area has unique environmental and cultural factors that affect LID implementation. Some are technical challenges such as the amount of rainfall and the projected population growth described in Section 2. Other issues are due to the regulatory environment in the jurisdictions within the Upper San Antonio River (USAR) Watershed. In many cities across the country there are institutional barriers to LID such as restrictive zoning or code requirements (Low Impact Development Center 2005, Nelson, Nowacek, and Petchenik 2003); therefore, it is important to understand any laws or regulations that could impede LID projects in the USAR Watershed.

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4.2 Planning and Policy Context REGULATORY FRAMEWORK The Texas Commission on Environmental Quality (TCEQ) is the state’s primary environmental regulatory agency. Other state agencies, such as the Texas Water Development Board (TWDB), are responsible for water supply planning and other water-related issues. In Texas, water is managed and regulated under two separate categories: surface water and groundwater (Texas Water 2011).

OWNERSHIP Generally, the landowner “owns” the surface water on his/ her property. However, after it enters a clearly defined watercourse, it becomes state water (Kaiser 2005). The Rule of Capture governs groundwater and gives landowners the right to capture the water beneath their property (Texas Water 2011). However, although considered private property, water may still be regulated.

SURFACE WATER REGULATION The Clean Water Act, the cornerstone of the EPA’s surface water quality protection, addresses both point source and nonpoint source pollution (EPA 2008a). The TCEQ administers the state’s stormwater management program (TCEQ 2011c).

Under the CWA, the Total Maximum Daily Load (TMDL) is the maximum amount of a pollutant that a given surface water body can receive and still maintain its uses (EPA 2008a). A

surface water body is considered impaired if it does not meet the criteria for one or more of its beneficial uses, as defined in the Texas Surface Water Quality Standards. Impaired waters are identified every two years in the Texas Integrated Report for Clean Water Act Sections 305(b) and 303(d) (TCEQ 2011b).

Point source pollution is regulated through permits. The EPA’s National Pollutant Discharge Elimination System (NPDES) controls discharges of pollutants to surface waters. In Texas, this oversight has been transferred to the TCEQ and is called the Texas Pollutant Discharge Elimination System (TPDES).

The TPDES applies to all permitted discharges except those associated with oil, gas, and geothermal exploration and development activities, which are regulated by the Texas Railroad Commission (TCEQ 2011c).

The TCEQ grants permits to cities with Municipal Separate Storm Sewer Systems (MS4s), which are the systems designed or used to collect or convey stormwater (including storm drains and pipes). The permit requires that the cities prevent or prohibit pollutant discharge to the Maximum Extent Practicable (MEP). To accomplish this, the cities are required to implement an approved Storm Water Management Program (SWMP) (TCEQ 2009).

Other surface water management issues are handled by the one of the twenty-three River Authorities. The boundaries of each of these river authorities usually include the watershed of that particular river, such as the San Antonio River Authority (SARA), which covers the San Antonio River Watershed. The River Authorities are generally responsible for issues related to water supply and distribution, flood control, and water quality

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control. They are overseen by the TCEQ (Texas State Senate Committee on Natural Resources 2009).

Authority (EAA), responsible for managing and regulating the aquifer area (Edwards Aquifer Authority 2011).

GROUNDWATER REGULATION

Finally, the Texas Groundwater Protection Committee, which is made up of ten state agencies and an association of Groundwater Districts, implements the state’s groundwater protection policy (TGPC n.d. a).

Groundwater is handled separately from surface water.

Although the same state agencies are involved, primarily the TCEQ and TWDB, the smaller administrative units differ significantly.

The state is divided into sixteen Groundwater Management Areas (GMAs), which define the Desired Future Conditions for each aquifer (TWDB 2011). The Desired Future Conditions are included in the framework of groundwater management plans, regional water plans, and the granting of permits.

An area can also be designated a Priority Groundwater Management Area (PMGA) if critical groundwater problems exist or are predicted within twenty-five years (TCEQ 2011a).

Protecting groundwater quality and quantity are the central tasks of these state agencies and management areas (TGPC n.d. b).

Much of the regulation, including the placement and production of wells on private property, is done by Groundwater Conservation Districts (GCDs). GCDs are units of local government empowered to manage and protect groundwater.

Each of the almost 100 GCDs creates a Groundwater Management Plan outlining goals for the use and conservation of groundwater (Lesikar, Kaiser and Silvy 2008). These goals must be approved by the TWDB. The Edwards Aquifer area has additional oversight. It has been designated as a Sole Source Aquifer, which provides specific protection under federal law (EPA 2011b). The aquifer also has a special groundwater district, the Edwards Aquifer 60

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LOCAL ORDINANCES Before any LID project can be implemented, a thorough investigation of the relevant city ordinances is required. These ordinances can have a significant impact on LID projects. For example, some city codes require minimum street widths,

City

Minimum Width

Code

Alamo Heights

No minimum width

Alamo Heights, TX, Code of Ordinances, § 17-27 (2010)

Balcones Heights

Minimum pavement width for Local A (Residential) is 30’ (with 50’ ROW)

Balcones Heights, TX, Code of Ordinances, § 152.16 (2010)

Castle Hills

No minimum width

Castle Hills, TX, Code of Ordinances, § 23.301 (2010)

Leon Valley

No minimum width

Leon Valley, TX, Code of Ordinances, § 10.02.301 (2009)

Olmos Park

Minimum width for Minor Street is 36’ (with 60’ ROW)

Olmos Park, TX, Code of Ordinances, Ch. 24.5, Art. IV § 1 (2010)

San Antonio

Minimum width for Local Type A Street is 28’ (with 50’ ROW)

San Antonio, TX, Unified Development Code, Art. V, Div. II, § 35-506 (2010)

Shavano Park

No minimum width

Shavano Park, TX, Code of Ordinances, Ch. 28, App. A, § 35-A201 (2010)

Terrell Hills

No minimum width

Terrell Hills, TX, Code of Ordinances, § 14-1 (2007)

Table 4.1

City Residential Street Width Requirements in USAR Watershed

which conflicts with LID’s emphasis on narrow streets. Other impediments found in city codes include minimum driveway size, setbacks, frontages, parking codes, and whether curbs and gutters are required (Center for Watershed Protection n.d.). See Appendix A: Resources for a list of municipal code evaluation tools.

The USAR Watershed falls within several jurisdictions, each with its own regulations. To illustrate the differences, Table 4.1 is a comparison of the regulations regarding minimum residential street width. While some cities have no specified width requirement, others vary from 28 feet to 36 feet.

Within the City of San Antonio, the Pearl redevelopment project in Midtown features several LID strategies, such as the adaptive reuse of existing structures, material reuse, rainwater harvesting, bioswales, and the use of permeable pavement (Sustainable Sites Initiative 2008). Mixed-use infill sites such as the Pearl concentrate development in existing urban areas and help to prevent sprawl, and are therefore an important component of a regional LID strategy (See Figure 4.1).

Phil Hardberger Park is a multipurpose park in San Antonio, which includes both active and passive recreation areas, an

4.3 Regional Precedents of LID Despite the challenges, there are numerous examples of projects that demonstrate typical LID principles and strategies in San Antonio and the surrounding area.

Figure 4.1

Pearl Redevelopment, San Antonio, Texas

Figure 4.2

Phil Hardberger Park, San Antonio, Texas

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off-leash dog park, and preserved and restored vegetation throughout (See Figure 4.2). With its vision of “cultivated wild,” the park focuses on environmental education through programs and on-site classrooms (Phil Hardberger Park Conservancy 2011). Some of the LID features include the preservation of native vegetation and the permeable surfaces of parking areas.

The City of Austin is particularly rich in LID projects, serving as an excellent example of what is possible in the San Antonio area. Since Austin’s climate, soil types and native vegetation are very similar to those of the San Antonio area, these projects can serve as regional templates.

The Redbud Center in Austin is the headquarters of the Lower Colorado River Authority (LRCA) and includes numerous LID

Figure 4.3

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Cistern, Redbud Center, Austin, Texas

Figure 4.4

Swale and Shade structure, Redbud Center, Austin, Texas

Figure 4.5

Model of the Lower Colorado River, Redbud Center, Austin, Texas

Figure 4.6

Parking Area, Redbud Center, Austin, Texas

Figure 4.7

Rainwater Harvesting, Redbud Center, Austin, Texas

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features (See Figure 4.3 - Figure 4.7). Water conservation is a focus of the design as well as the educational mission.

For example, rainwater and air conditioning condensate are harvested in the large cisterns that are prominent on the site.

This water is reused for irrigation and toilet flushing. This and other features allow this LEED certified building to use significantly less water for the building and landscape than similar buildings (LRCA 2011).

Lance Armstrong’s Livestrong Foundation in Austin is a LEED Gold certified building which made extensive use of existing materials on the site (See Figure 4.8 - Figure 4.11).

The landscape features native, drought tolerant plants, a permeable parking lot, and salvaged concrete walkways and low walls (Ten Eyck Landscape Architects 2011). These features reduce both construction waste and water use.

Figure 4.9

Figure 4.8

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Livestrong Foundation Entrance, Austin, Texas

Figure 4.10

Livestrong Foundation Sign, Austin, Texas

Salvaged Walls at the Livestrong Foundation, Austin, Texas

4.4 How to Apply LID in San Antonio In order for an LID project to be successful, an in-depth analysis of relevant ordinances will be necessary. The sample designs in this document fall within the City of San Antonio, which has a number of municipal code requirements that must be considered. Table 4.2 shows a sample analysis of San Antonio’s municipal code using the Center for Watershed Protection’s Code and Ordinance Worksheet (n.d.) as a guide.

Based on this analysis, LID projects face some institutional obstacles, such as minimum parking ratio requirements that make it difficult to use less car-centered design approaches.

In other areas, however, the city is less restrictive and even outlines alternatives such as shared parking and pervious pavement for spillover parking. This is important for the future of LID in the city because fewer regulatory restrictions result in fewer barriers to successful LID projects. See Section 8 Next Steps for details about additional analysis needed.

Is the minimum parking ratio for a professional office building less than 3 spaces per 1000 ft2 of gross floor area)?

No. The minimum is 1 spot per 300 sq ft [San Antonio, TX, Unified Development Code, Art. V, Div. 6 § 35-526 (2010)].

Is the minimum required parking ratio for single family homes (per home) less than or equal to 2 space?

Yes. Only one space is required per detached dwelling [San Antonio, TX, Unified Development Code, Art. V, Div. 6 § 35-526 (2010)].

Are parking ratios reduced if shared parking arrangements are in place?

Yes. Shared parking is allowed to reduce the number of spaces required on mixed use parcel [San Antonio, TX, Unified Development Code, Art. V, Div. 6 § 35-526 (2010)].

Is the minimum stall width for a standard parking space 9 feet or less?

Yes. The minimum parking stall width is 9 feet [San Antonio, TX, Unified Development Code, Art. V, Div. 6 § 35-526 (2010)].

Are at least 30% of the spaces at larger commercial parking lots required to have smaller dimensions for compact cars?

Not required, but allowed. Up to thirty (30) percent of the required parking spaces may be designated for use by compact vehicles with minimum dimensions of eight (8) feet in width and sixteen (16) feet in length [San Antonio, TX, Unified Development Code, Art. V, Div. 6 § 35-526 (2010)].

Can pervious materials be used for spillover parking areas?

Yes. Vehicle parking spaces may exceed the maximum number of spaces permitted if the additional spaces are designed as pervious pavement [San Antonio, TX, Unified Development Code, Art. V, Div. 6 § 35-526 (2010)].

Is the minimum sidewalk width allowed in the community 4 feet or less?

Yes. Sidewalks shall be four (4) foot in width with a planting strip or six (6) foot in width without a planting strip [San Antonio, TX, Unified Development Code, Art. V, Div. 6 § 35-506 (2010)].

If forests or specimen trees are present at residential development sites, does some of the stand have to be preserved?

Yes. There are standards and procedures listed for tree preservation [San Antonio, TX, Unified Development Code, Art. V, Div. 5 § 35-523 (2010)].

Figure 4.11

Planting Area, Livestrong Foundation, Austin, Texas

Table 4.2

Sample Evaluation of San Antonio’s Municipal Code

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5. LID LOcator model 5.1 5.2 5.3 5.4 5.5 5.6

Watershed Modeling Overview Pollutants of Concern Modeling Methodology Summary of Findings Limitations Next Steps

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5. LID LOcator model

5.1 Watershed Modeling Overview Watershed modeling is a critical element of any long-term environmental planning process, as it simulates complex natural processes. There are many different existing models, each serving different purposes and applicable to different scales. The conceptual model described in this document is intended to be easy to learn and use, and is focused on priority placement of LID sites in existing urban areas in order to determine the highest impact areas for retrofit and redesign.

The team began by investigating existing watershed models.

This was done initially to explore the possibility of using or adapting an existing model. Once this possibility was eliminated, the team researched the methodology and data inputs of the existing models to inform choices for the Upper San Antonio River (USAR) Watershed LID model.

Many models were examined and rejected based on usability requirements for one or all of the following reasons:

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1. Model did not prioritize location for placement of LID. 2. Model was difficult to learn.

3. Model was overly complex and difficult to use.

were used, this research was a critical step in determining the team’s data needs and initial modeling methodology.

The following models were examined:

5.2 Pollutants of Concern

•

Creeks in urban watersheds are affected by a number of nonpoint source (NPS) pollutants, including: bacteria, nutrients, heavy metals, hydrocarbons (oil and grease) and Total Suspended Solids (TSS) in terms of water quality (See Figure 5.1, Figure 5.3 and Figure 5.4) (Perrin et al. 2009). This document focuses specifically on bacteria and nutrients, the pollutants highlighted in the Total Maximum Daily Load (TMDL) report for the Upper San Antonio River (TCEQ 2007).

• • • • •

Structural BMP Prioritization and Analysis Tool (SBPAT) (SBPAT 2011) Watershed Assessment Model (WAM) (EPA 2011f) Generalized Watershed Loading Function (GWLF) (Penn State Institutes of Energy and Environment 2009) Storm Water and Management Model (United States Geological Survey [USGS] 2010) Better Assessment Science Integrating point & Non-point Sources (BASINS) (EPA 2011a) System for Urban Stormwater Treatment and Analysis INtegration Model (SUSTAIN) (EPA 2011e)

Other models, such as Watershed Treatment Model (WTM) (Center for Watershed Protection 2011), were user-friendly but required extensive local knowledge and data and so were not practical for this project. Although none of these models

Figure 5.1

BACTERIA In urban areas, waterbody impairments caused by bacteria are often associated with high population densities of people, domesticated animals and/or wildlife (EPA 2004). In an urban watershed, an imbalanced microbial stream ecosystem contributes to the high concentrations of bacteria (EPA 2004).

Streams in San Antonio

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collection of domestic animal waste are an important first step in improving stream water quality and reducing bacteria impairment (See Figure 5.2) (EPA 2004). Likewise, the creation of alternative habitat areas or wildlife-specific structures (such as bat roosts or constructed wetlands) may reduce the dependence of local wildlife on stream channels and their associated built environments.

The analysis of NPS pollutants is complicated by the fact that certain pollutants accentuate the impairment effects of others.

For example, there is a link between bacteria impairment and the concentrations of Total Suspended Solids (TSS), with bacteria levels generally rising with turbidity and the increased presence of sediment in a waterbody (EPA 2004). Thus, BMP practices that promote settling of TSS or “inhibit resuspension during high flow events” can help control bacteria levels as well (EPA 2004, p.20). Constructed wetlands promote both settling and predation by bacterivores, and are particularly effective in removing bacteria from urban runoff (EPA 2004).

Figure 5.2

Pet Waste Bag Dispenser

In the case of the Upper San Antonio River, the TCEQ report, Three Total Maximum Daily Loads for Bacteria in the San Antonio Area, estimates that septic systems are not a significant source of bacteria impairment in the San Antonio River (TCEQ 2007c). However, land uses associated with urban development were identified as the predominant source of bacteria, with “the combined commercial, industrial, and residential loads account[ing] for about 68.1 percent of the average annual load” (TCEQ 2007c, n.p.). Both domestic animals and urban wildlife may be significant sources of bacteria (Miertschin, James & Associates, Inc., and Parsons, Inc. 2006). Thus, non-structural BMPs that promote the

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NUTRIENTS Commercial fertilizers applied to lawns and landscaped areas are a common source of the nutrients (nitrogen and phosphorus) entering urban waterways. In terms of water quality, the most significant effect of such nutrients is eutrophication and the resulting algae blooms, which reduce dissolved oxygen (DO) levels (EPA 2011c). The resulting “eutrophication-induced hypoxia and anoxia” poses a great risk to fish populations (EPA 2011c, n.p.). Landscaping practices such as “the reduction of high maintenance turf grass and integration of native plants into the landscape” can “lower nutrient runoff potential by limiting fertilizer application” (Southern California Stormwater Monitoring Coalition 2010, p. 53).

HEAVY METALS Heavy metals such as copper, lead and zinc (and to a lesser extent, cadmium and chromium) are common NPS pollutants associated with transportation, as well as industrial and commercial land uses (EPA 2011c). Such pollutants pose a threat to humans since they may contaminate groundwater and bio-accumulate in fish (EPA 2011c).

HYDROCARBONS Hydrocarbons derived from petroleum products are a common pollutant associated with vehicular transportation. Because of their “high affinity for sediment,� hydrocarbons can collect and persist in the bottom sediments of waterbodies (EPA 2011c, n.p.). The environmental effects of hydrocarbons are

Figure 5.3

Losoya Street, Downtown San Antonio

accentuated by elevated levels of TSS, demonstrating the interrelationships between various NPS pollutants and the need for a comprehensive stormwater treatment strategy.

TOTAL SUSPENDED SOLIDS The term Total Suspended Solids (TSS) includes both sediments and other organic and inorganic materials suspended in water (North Dakota Department of Health [NDDH] 2011). The increased concentration of TSS in waterbodies is a direct result of development and the creation of continuous networks of impervious surfaces, since the increased runoff volume and flow velocity associated with increased imperviousness leads to higher levels of erosion (Schueler 1995). This higher concentration of suspended solids increases turbidity, raises water temperature and

Figure 5.4

Storm Drain, Downtown San Antonio

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reduces light penetration and the presence of submerged aquatic vegetation (EPA 2011c). Water oxygen content decreases, since less photosynthesis occurs and the warmer temperature decreases the water’s capacity to hold oxygen (NDDH 2011). Such changes can have drastic impacts on aquatic life. Even when TSS settling occurs in a waterbody, the effects still have cascading environmental effects that can drastically affect aquatic life, decreasing larval survival and reducing microhabitat availability (NDDH 2011).

5.3 Modeling Methodology The goal of the conceptual model is to identify the best locations for LID projects in existing urban areas in order to determine areas for retrofit and redevelopment. ESRI’s ArcMap tool is used to build and run the model. ArcMap is a Geographic Information Systems (GIS) software package that includes analysis tools suited to the requirements of the model. Further, ArcMap is the industry standard GIS software package. As such, many government agencies publish relevant data in ArcMap file formats.

ArcMap software allows the user to view, manipulate and process maps based on data objects. Each data object has a shape component along with an associated data table. The Modelbuilder tool within ArcMap is used to build and save processing instructions which can be used to analyze any watershed.

N 0

1.5 6.0

USAR Potential Source Subwatersheds Subwatersheds

"

Impaired Streams

Figure 5.5

The basic methodology of the model is to identify and map factors that are related to the generation of NPS pollution and the efficacy of LID. These factors include items directly

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6.0 Miles

Impaired Streams and Potential Source Subwatersheds

Sample Model Instance

PARAMETERS

INPUT

TYPE

WEIGHT

WATERSHED

BOUNDARY

IMPAIRED WATERBODIES

LID FACTOR

1

LID FACTOR

1

LID FACTOR

1

LID FACTOR

1

LID FACTOR

1-4

LID FACTOR

1

AQUIFER ZONES

LID FACTOR

-1

CITY OWNED LAND

LID FACTOR

1

LOCAL WATERBODIES BUFFER

1/4 MILE

SOIL SURVEY IMPERVIOUSNESS LIMIT

20%

POPULATION DENSITY PARCEL ZONING

COMMERCIAL

RESULTS Figure 5.6

Model Methodology Diagram

related to where NPS pollution is generated or reported, such as impaired streams (See Figure 5.5), or to the operation of BMPs, such as soil infiltration. The factors also include indirect items such as whether a piece of land is owned by the City of San Antonio. Next, parameters for selected factors are set by the user; for example, the user can enter the buffer size placed around local waterbodies. The user then sets a weighting for each factor, in order to specify its significance relative to other factors. Factors deemed important are weighted higher (greater than one), while factors to be ignored are weighted with a zero and factors that the user decides adversely affect LID are weighted negatively (less than zero) (See Figure 5.6).

Each input factor, also referred to as a layer, is converted to a raster representation, multiple grid cells each measuring 30 meters by 30 meters. Then all layers are summed for each grid cell (See Figure 5.7). The resulting sum for each grid cell is a combination of all weighted factors. Grid cells with higher final summed point values indicate areas where layers overlap and are the ideal locations for both structural and nonstructural BMP implementation based on factors, parameters and weighting (See Figure 5.8).

Each time the model is run is known as an instance. Each instance is defined by a set of inputs, parameters and weights.

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Aquifer Recharge Zones

Well Drained Soil

COSA Owned Land

Riparian Buffer

Imperviousness

Model

Suspect Subwatersheds

Output Population Density

Figure 5.7

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Model Overlay Diagram

For each unique instance there is a unique solution as defined by the user inputs. This methodology allows the user to use the model in many ways. For example, in order to find priority locations on undeveloped land the user would choose “Open Space’ as the parameter for the parcel zoning input and weight this input significantly higher than other inputs. The results for this instance would be areas zoned as “Open Space”, a combination of pasture, meadow and other descriptors. With limited modifications, the conceptual model can be used to identify priority locations for greenfield development, in addition to redevelopment and retrofit sites. However, this document is focused on identifying LID opportunities for existing urban areas in order to determine priority locations for retrofit and redevelopment as specified by The Ladybird Johnson Wildflower Center.

Ideal location for both structural and non-structural BMP implementation

The model is implemented using the ModelBuilder tool, an optional part of the ArcMap program. Complete model details and an example are shown in Appendix C.

5.4 Summary of Findings The conceptual model provides a relatively simple way to gather appropriate data, process the data and graphically display results. The model is informed by research literature concerning NPS pollutants, LID requirements and the geospatial analysis of constraints and opportunities. Figure 5.8 shows output of the model, highlighting sample locations deemed suitable for LID implementation, with the darker hue corresponding to higher priority areas. The sample model results show the existence of several distinct priority areas, shown in detail in Figure 5.9.

N 0

1.5 6.0

6.0 Miles

USAR 8 of 9 Points 7 of 9 Points

"

6 of 9 Points

Figure 5.8

Model Output: Priority Areas for LID

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5.5 Limitations It is difficult to gauge the accuracy of the model without conducting additional tests, and the results of the model should be confirmed by local site reconnaissance efforts (including soil testing). The areas indicated as high priority sites for LID implementation must be further scrutinized to confirm their significance. Furthermore, the inclusion of additional or more detailed data sets in the modeling methodology may produce more refined model results. Likewise, since the sample model results presented in this section were based on the parameters summarized in Figure 5.6, altering these parameters (for example, by assigning alternate weighting) will yield different priority areas.

N 0

USAR 8 of 9 Points 7 of 9 Points

"

It is important to point out limitations of the data. The output map consists of a grid with a cell size of 30 meter by 30 meters. Therefore, it is not accurate enough to make assumptions regarding areas smaller than this size. Also, the soil data used in the model is not valid for scales less than 1:24,000, requiring a local soil survey.

The implementation of this model requires specific software, ArcMap with Spatial Analyst extension, and experience using the software. The model was developed using ArcMap 9.3.1; however, as of publication, the newer version (ArcGIS 10) is available. Due to the complexity and many details of this software package, it is advisable to seek assistance from experienced professionals for further development of this model.

This section outlines the basic ideas and methods for developing a model to prioritize the placement of LID in an

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1.5 6.0

6 of 9 points Figure 5.9

7 of 9 points

Detailed Sample Model Output

8 of 9 points

6 of 9 Points

6.0 Miles

urban watershed. However, the complete description of every detail of the model is beyond the scope of this document.

Parties interested in further exploration of the ideas and methods presented in this document should contact the authors.

5.6 Next Steps In order to gain a more complete picture of the local conditions affecting the placement and implementation of LID strategies, interested parties in the San Antonio area (and elsewhere) should consider the collection and distribution of the following data sets (most of which, unfortunately, were not available during the production of this document): 1. Storm drain network, showing the locations and sizes of individual drains, catchments and discharge outlets in receiving waterbodies.

2. Local soil infiltration rate data and which local soil types are suitable for certain structural BMPs. 3. Locations of regional sink holes in order to protect the underlying aquifer from NPS pollution.

In order to address LID placement for new development, additional dataset inputs should be investigated and added to the model. Particular emphasis should be placed on investigating the use of 4-band Color InfraRed (CIR) from the National Agriculture Imagery Program (NAIP). See Appendix C for more information.

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6. LID Development Types 6.1 6.2 6.3 6.4 6.5 6.6

Overview of Development Types Dense Urban Core Redevelopment Post- Industrial Redevelopment Residential Retrofit Residential New Development Selection of Structural BMPs

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6. LID Development Types

6.1 Overview of Development Types Since urban land uses such as residential and commercial/ industrial development are the two greatest contributors to NPS pollution in the Upper San Antonio River (USAR) Watershed (TCEQ 2007c), it is important to examine the typical opportunities and constraints associated with the implementation of LID projects in each context. The goal of this section is to present recommendations that illustrate not only the challenges and opportunities that a developer or designer may encounter at a specific site, but also to indicate more general BMPs and design strategies that can be applied to similar land uses within the USAR Watershed. While each site is unique and requires a distinct solution, the authors hope to facilitate the design decision-making process by highlighting the key information that must be considered in residential and commercial/industrial types of development.

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6.2 Dense Urban Core Redevelopment Dense urban cores are typically almost entirely developed or paved, with higher amounts of continuously impervious surfaces than other parts of a metropolitan area. Such high amounts of impervious surfaces have been shown to be linked to the NPS contamination of rivers. Implementing LID in the dense urban core adds a filtering function to the city’s infrastructure systems, so stormwater is cleansed before it enters the waterways. From a LID perspective, redevelopment in the dense urban core has the additional benefit of reducing development pressure elsewhere in an urban region.

A major obstacle to LID implementation in the dense urban core is the limited available surface area (See Figure 6.1). In a dense area, LID implementation measures must fit into areas that already have large amounts of automobile and bicycle traffic, as well as pedestrian flow. This means that some of the areas that have the greatest need of structural BMPs are often also the most difficult areas in which to implement LID. Thus, LID projects in dense urban areas often require either sub-surface applications (e.g. underground cisterns) or the utilization of buildings (e.g. green roofs, above-ground cisterns).

Because of the limited space available for LID retrofit or redevelopment in dense urban areas, street and sidewalk widths are an important consideration when planning an LID project in such a setting. Since sidewalks may contain underground utilities, it is necessary to consult as-built plans before proposing LID modifications. Municipal codes further complicate the matter. Most municipalities have minimum sidewalk and street width requirements, as well as traffic standards that require a certain number of traffic lanes.

Figure 6.1

San Antonio’s Dense Urban Core

Before the installation of structural BMPs in a dense urban area, typical traffic volume and pedestrian access must be analyzed, as well as parking requirements. In order to minimize conflict with public transportation routes, bus stop locations may also be considered.

Although it is often difficult to find space for structural BMPs in dense urban areas, there are a number of structural BMPs that can typically be implemented in this setting (EPA 2010, Matel 2010). Some of the most common structural BMPs found in dense urban areas are permeable pavement, green roofs, bioretention cells, infiltration trenches, swales and sand filters (See Section 6.6). Green roofs are appropriate for the dense urban core because they can provide much-needed open space in areas that typically have limited access to parks, in addition to filtering stormwater runoff.

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Non-structural BMPs (such as programs encouraging alternative transportation, or street sweeping) are particularly important in dense urban areas because of the limited opportunities for structural BMPs. Indeed, due to the link between transportation and NPS pollution, public programs that help to reduce the need for vehicular transportation and surface parking will likely have important stormwater management benefits as well.

6.3 Post - Industrial Redevelopment As a region with a rich industrial heritage, the San Antonio metropolitan area has a wealth of former industrial properties that can be converted to future commercial and/or residential

Figure 6.2

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Post-Industrial Sites in San Antonio

developments (See Figure 6.2 and Figure 6.3). The inclusion of LID design features in such redevelopment projects can provide much-needed stormwater storage and treatment, serve as an open space amenity and improve habitat connectivity for native birds and insects.

The greatest challenge to LID implementation in post-industrial sites is most likely to be soil and groundwater contamination, making thorough testing of site soil and water a necessity (Stormwater Monitoring Coalition 2010).

Post-industrial sites provide a number of opportunities for planners and designers, such as the adaptive reuse of existing buildings, a unique industrial aesthetic, the recycling of materials (such as broken-up concrete, railroad ties, etc.), proximity to transportation infrastructure and relatively large

size. Because of these characteristics, many post-industrial sites are well-suited for mixed-use developments with both residential and commercial components, as well as TOD (Transit Oriented Development) projects. While such projects will likely increase local impervious surfaces to a certain degree, the “breaking up” of these surfaces during the site design process and the inclusion of structural BMPs can help reduce the amount of runoff. Since post-industrial projects are often examples of “infill” development, they have the additional benefit of concentrating development closer to urban cores, and helping to reduce regional urban sprawl. This can have a positive impact on water quality and quantity, by reducing impervious surfaces and increasing soil infiltration.

As demonstrated by a number of redevelopment projects in the San Antonio area - including the Pearl, the Blue Star Complex and the CAMPstreet Residences - the iconic structures often associated with post-industrial sites can become important local landmarks and help strengthen neighborhood identities. The inclusion of stormwater management features in such high-visibility projects can in turn expose a larger number of users to LID principles, particularly if educational signage is utilized and if such features are treated as landscape amenities.

Information that should be considered for LID projects in postindustrial sites include: (1) soil type and drainage class; (2) the type, location and depth of possible soil and groundwater contaminants; and (3) topography (especially for the construction of flow-type BMPs such as bioswales).

A post-industrial site’s land area and its degree of pollution will determine the most suitable stormwater management Figure 6.3

Post-Industrial Site in San Antonio

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structural BMPs. If a site is fairly large, as many industrial properties tend to be, and if contamination is minimal, a wider range of structural BMPs can be utilized, including infiltration-type BMPs (depending on the native soil). In larger post-industrial sites, constructed wetlands can be utilized to remove a variety of pollutants from both stormwater and soil (via phytoremediation), with the additional benefit of providing wildlife habitat (Southern California Stormwater Monitoring Coalition 2010).

However, if contamination is detected, infiltration-type BMPs should be avoided, since they may “mobilize pollutants in the soil”, possibly resulting in the spread of contaminants to groundwater (Southern California Stormwater Monitoring Coalition 2010, p. 36). If infiltration-type BMPs such as bioretention cells or permeable pavers are used in this context, they should include an impermeable liner and underdrain, in order to ensure that treated stormwater is directed to a storm sewer (Southern California Stormwater Monitoring Coalition 2010).

Likewise, it may be advisable to locate new buildings and paved surfaces on top of “contamination hotspots”, to prevent infiltration in these areas (Southern California Stormwater Monitoring Coalition 2010, p. 36). In contaminated brownfields, LID implementation should focus on minimizing runoff (by minimizing impervious surfaces), as well as utilizing detention-type BMPs to store stormwater and flow-type BMPs to cleanse it (Southern California Stormwater Monitoring Coalition 2010).

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6.4 Residential Retrofit Existing residential development is one of the most prevalent land use types in the USAR Watershed. It is an important development type to address because it is a significant source of NPS pollutants such as bacteria and nutrients (TCEQ 2007c, Bannerman, Owens, Dodds, and Hornewer 1993). The retrofit of existing residential structures and landscapes can reduce the stormwater runoff and pollutant loads generated by such areas.

Existing residential development presents unique challenges and opportunities for LID implementation (See Figure 6.4). Since such areas are already built up, there is often little land available for LID projects--particularly in San Antonio’s older, denser historic neighborhoods. In spite of this, there are opportunities for adding BMPs at both the individual lot and neighborhood scale.

The small scale structural BMPs typically used in residential areas differ from many others because they are located on private property and require the participation of the homeowners. This can be a challenge due to the public’s possible lack of knowledge regarding stormwater and NPS pollution, lack of expertise in installing and maintaining structural BMPs, and the perception that the BMPs are unattractive (Echols 2008, Bartlett 2005, Nelson, Nowacek and Petchenik 2003). Although such structural BMPs are relatively inexpensive, the expense involved in retrofitting existing landscapes can be a significant obstacle to public participation as well.

Cities can help alleviate this through a number of nonstructural BMPs such as education and outreach, incentives or rebates and subsidized products such as rain barrels. See Section 8: Next Steps for more discussion of these options.

There are also opportunities for LID projects at the street or neighborhood scale. For example, a swale along the street could be designed to take runoff from the residential lots as well as runoff from the street. These larger-scale solutions are not necessarily unique to residential areas, but are an important part of a design focused on reducing the amount of runoff and treating the water on site.

Important information to consider when planning LID implementation in existing residential areas includes lot and neighborhood topography, the locations of underground utilities, and parking needs. In historic neighborhoods, it is important to consult local planning agencies regarding additional codes and regulations.

Some of the most common BMPs found in residential retrofit situations are cisterns (capture and reuse), rain gardens (bioretention cells), and permeable pavement (See Section 6.6). Swales, bioretention cells and other street modifications may also be appropriate.

6.5 Residential New Development New residential development on a greenfield site presents a difficult situation with respect to the implementation of LID (See Figure 6.5). From a LID perspective, the undeveloped land is best left untouched, in order to maintain hydrological Figure 6.4

Images Of Single-Family Homes In San Antonio

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Successful LID implementation in greenfield sites relies on a thorough understanding of present conditions, local ordinances and LID principles. As with all design endeavors, an initial inventory is absolutely necessary. Since the land is undeveloped, it is imperative to document all natural resources on the site. Particular care should be taken to recognize specimen trees, existing tree stands, endangered species habitat, aquifer features and natural drainage patterns. The inventory of the surrounding land is also important in order to locate destinations and understand future transportation demands.

Figure 6.5

Typical San Antonio Residential Development

functions, minimize impervious surfaces, and prevent NPS pollution. Undeveloped land has the potential to infiltrate stormwater (depending on soil type), is likely covered with existing native vegetation and provides habitat and migration corridors for local wildlife. Given all these reasons, the first option should be to avoid new development on greenfield sites. However, given population trends, private land ownership and the lack of local ordinances restricting urban sprawl, greenfield residential development will likely continue in the future. Thus, it is important to propose ways in which such development can incorporate LID design strategies and BMPs, while minimizing its impact on natural resources and hydrological processes.

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The next step is to understand local development policies and ordinances. For example, the City of San Antonio has recently implemented a Unified Development Code (UDC) which contains policies and regulations outlining development procedures, standards and options (City of San Antonio 2011). Newer zoning regulations may define overlays which provide alternative development strategies and regulations that San Antonio area cities should continue to investigate. The City of San Antonio currently has an example of this development type, referred to as a conservation subdivision (Arendt 1996). This special subdivision allows variances to the standard policy if certain requirements are met (City of San Antonio 2011).

After inventory and the review of local ordinances, LID principles should be addressed. Building on undeveloped land allows implementation of basic LID principles that minimize the detrimental effects of development. For example, the first priority should be to minimize impervious cover by minimizing street width, building pad size and other paved infrastructure. Streets should be aligned parallel

with existing contours to reduce grading and decrease sheet flow runoff. Design considerations such as using pervious materials and massing buildings should also be part of greenfield development. Vegetated swales should be used to capture runoff and route it to natural drainage pathways. Areas should be set aside in order to place detention and retention ponds. Successful implementation of LID principles will negate the need for engineered stormwater solutions.

Runoff calculations should be made in order to determine predevelopment runoff. Post development calculations based on the amount of impervious cover are used to determine the amount of water storage and infiltration if applicable. Further calculations are needed to determine storage necessary to capture the first flush of rain events--determined to be 1.5� in San Antonio (North Central Texas Council of Governments 2010).

Residential BMPs such as rainwater harvesting and rain gardens can be installed by the developer and serve as the first opportunity to capture and store rainwater. Vegetated swales that drain excessive runoff to natural drainage ways are also suggested, however there are issues with regard to long-term maintenance that will have to be addressed by the developer or Homeowners Association (England 2010).

New residential development offers several design opportunities that are typically not applicable to existing residential areas, such as incorporating green roofs into building design. Greenfield development is suitable for many structural BMPs, since it lacks the constraints imposed by previously developed sites. Recommended structural BMPs

include cisterns, bioretention cells on each lot and vegetated swales which drain to local detention basins. See Section 6.6 for a list of structural BMPs, including capabilities and constraints.

6.6 Selection of Structural BMPs The selection of structural BMP applications for a site is affected by a number of factors, including the application’s necessary surface and subsurface area, its effectiveness in removing target NPS pollutants, its long-term costs (See Table 6.1) and maintenance requirements, and its runoff treatment or storage capacity (Perrin et al. 2009). Site-specific factors such as native soil type, upstream land uses, and slope of adjacent areas also play an important role in structural BMP selection (Perrin et al. 2009, California Stormwater Quality Association 2003).

Although they require large amounts of space, constructed wetlands are inexpensive (relative to unit area treated), capable of removing a wide range of NPS pollutants, and can serve as wildlife habitat (Perrin et al. 2009). If constructed wetlands are combined with the creation of restored riparian buffers, the resulting stormwater management system will also serve important ecological and recreational functions, and will increase regional habitat connectivity and the amount of public open space. However, since constructed wetlands may require the input of additional water during dry periods, their use must be balanced with other environmental considerations and human needs (California Stormwater Quality Association 2003).

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BMP Type

NPS Pollutant Removal Effectiveness (CA BMP)

Treatment Area Size

Suitable Soils (source: NC LID + NC BMP)

Medium

M (NC BMP)

All

High

High

M - L (NC BMP)

All

High

High

High

S-M (NC LID) S (NC BMP)

All Upstream soil stability necessary

Low (NC BMP)

Medium

Medium

Medium

S-L (NC LID)

Clay OK; sand better Upstream soil stability necessary

High

High

High

High

High

S (NC LID)

All, including low perm. soils

Constructed Wetland

High

Medium

High

High

High

M-L (NC LID)

Clay is better

Vegetated Buffer / Filter Strip

Low

Low

High

Medium

High

M (NC BMP)

All Upstream soil stability necessary

Vegetated Swale

Low

Low

Medium

Medium

Medium

M-L (NC LID)

All

Green Roof

Low (NC BMP)

Low (NC BMP)

Low

Low

Low

N/A

N/A

Infiltration Device Infiltration Trench Infiltration Basin Dry Well

High

High

High

High

High

M (NC LID) S-M (NC BMP)

Sand & permeable soils are best Not good for poorly drained soils Upstream soil stability necessary

Sand / Media Filter

Medium

Medium

High

High

High

S-M (NC LID)

All

Restored Riparian Buffer

Medium (NC BMP)

Medium

Medium

Medium

Medium

S-M (NC BMP)

All

Bacteria

Nutrients

Metals

Sediment

Oil/Grease

Dry Extended Detention Basin

Medium

Low

Medium

Medium

Wet Extended Detention Basin

High

Medium

High

Bioretention Cell

High

Medium

Permeable Pavement

Low (NC BMP)

Capture / Reuse (Retention + Irrigation)

NOTES: Treatment Area Size: Small (S) (less than ¼ acre), Medium (M) (~1 acre), Large (L) (~5 acre) Cost/Unit Areat Treated = Cost relative to unit area of watershed treated It is best to avoid constructing large “end-of-pipe” facilities because of their “high cost, maintenance requirements, consumption of land, and disruption of the landscape” (NCDENR 2007, p.4-2). * Rating derived from several sources Table 6.1

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Chart of Structural BMPs

Cost / Unit Area Treated (source: NC LID)

Construction Cost (source: NC BMP)

Maintenance Requirements & Issues (source: CA BMP & SoCal LID)

Maintenance Burden

Additional LID Functions (source: NC BMP)

NA

Low

Vegetation maintenance; vector control; debris removal Slope maintenance; sediment removal every 5-25 years

Low-Medium (NC BMP) Medium (SoCal LID)

Recreation/open space (b/w storms) Peak runoff attenuation; volume capture

N/A

Medium

Odors (algae); codes may require fencing Annual vegetation harvesting

Medium (NC BMP) Medium (SoCal LID)

Peak runoff attenuation Medium wildlife habitat

Medium

Medium - High

Clogging; vegetation maintenance Mulch replacement (to prevent accumul. of metals)

Medium-High (NC BMP) Low-Medium (SoCal LID)

Peak runoff attenuation Medium wildlife habitat

High

High

Semi-annual vacuuming & inspection

Low-Medium (NC BMP)

N/A

High

N/A

Sediment accumulation; vector control Mechanical maintenance; emptying b/w storms

Low (SoCal LID)

Irrigation (but not for edible plants)

Low

Medium

Maintaining water level during dry periods; veg. maint.; removal of floating debris

Medium (NC BMP) High (SoCal LID)

Peak runoff attenuation; volume reduction High wildlife habitat

N/A

Low

Vegetation maintenance

Low (NC BMP) Low-Medium (SoCal LID)

Medium wildlife habitat

Low

Low

Vegetation maintenance

Low (NC BMP) Low-Medium (SoCal LID)

N/A

Very High

High

Vegetation maintenance

Medium (SoCal LID)

N/A

Medium

Medium - High

Groundwater contamination; “fail relatively quickly�

Metals accumulation; volunteer vegetation removal Clogging (need veg. buffer for sediment removal) Infiltration monitoring and vector control

Medium (NC BMP) Trench: Large (SoCal) Basin: Medium-High (SoCal) Dry Well: Large (SoCal)

Groundwater recharge (which supports dry-weather flow)

High

High

Debris removal; clogging; need veg. buffer/ swale Anoxic conditions (poor drainage) = Increased nutrients

High (NC BMP) Medium (SoCal LID)

N/A

N/A

Medium

Vegetation & trail maintenance Control of invasives

Low (NC BMP)

Erosion control; water temperature control Recreation/open space; high wildlife habitat

SOURCES NC BMP: North Carolina Division of Water Quality Stormwater Best Management Practices Manual (NCDENR 2007) NC LID: Low Impact Development: A Guidebook for North Carolina (Perrin et al. 2009) CA BMP: California Stormwater BMP Handbook: Municipal Handbook (California Stormwater Quality Association 2003) SoCal LID: Low Impact Development Manual for Southern California: Technical Guidance & Site Planning Strategies (Southern California Stormwater Monitoring Coalition 2010)

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Vegetated swales, buffers and filter strips are relatively inexpensive to build and require less maintenance than other structural BMPs, but are generally not very effective in reducing bacteria or nutrient levels (California Stormwater Quality Association 2003). However, they are effective in treating heavy metals, as well as oil and grease, and are thus particularly suitable for landscaped areas adjacent to transportation corridors (California Stormwater Quality Association 2003).

Bioretention cells are very effective in removing a variety of NPS pollutants, and can be applied to various urban settings, including the dense urban core (California Stormwater Quality Association 2003). They require some regular maintenance (such as the periodic replacement of mulch to prevent the accumulation of metals) and are moderately expensive to construct, but are nonetheless good options to consider, especially because of their aesthetic potential (California Stormwater Quality Association 2003).

Stormwater harvesting techniques directed at capturing and reusing rainwater are effective at treating a variety of NPS pollutants, with various applications ranging in size (and cost) from simple rain barrels to expensive underground cisterns (California Stormwater Quality Association 2003). Such applications typically have a high cost per unit area treated and typically require regular inspection and maintenance (Perrin et al. 2009, California Stormwater Quality Association 2003).

Green roofs are the most expensive structural BMPs, in terms of unit cost per treatment area (Perrin et al. 2009).

However, green roofs can have important benefits in addition to stormwater treatment--such as reduced energy use and

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the reduction of Urban Heat Island effect--and can serve as open space gathering areas (Southern California Stormwater Monitoring Coalition 2010). Green roofs are expensive and may require extensive structural modifications, and therefore may not be appropriate in all cases.

Infiltration trenches and dry wells are effective in removing a wide range of NPS pollutants from stormwater runoff, but they are generally not suitable for poorly drained soils and tend to clog over time--particularly if no upstream vegetated buffer strip is utilized (Perrin et al. 2009, California Stormwater Quality Association 2003). Sand or media filters can be susceptible to clogging as well. Although they are typically not effective in treating nutrients, they are quite effective in treating oil and grease (California Stormwater Quality Association 2003). Sand and media filters tend to be expensive to construct and may require careful monitoring (California Stormwater Quality Association 2003), however, they are well suited for some applications.

A summary of common structural BMPs is provided in Table 6.1. There are also a number of LID manuals available that can be consulted for detailed information regarding the use of specific structural BMPs for stormwater management.

See Appendix A: Resources for more information on these manuals.

Table 6.2

Examples of Swales in Seattle, Washington and Salt Lake City, Utah

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7. LID in action 7.1 Introduction to Design Sites 7.2 Dense Urban Core Redevelopment 7.3 Post-Industrial Redevelopment 7.4 Residential Retrofit 7.5 Residential New Development 7.6 Regional Significance of Proposed Designs

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7. LID in action

7.1 Introduction to Design Sites The site designs presented in this document were informed by both the initial outputs of the conceptual model (described in detail in Section 5 and Appendix C) and the project philosophy described in Section 3.10. While the model findings presented in Section 5 represent the highest priority areas for LID implementation in the USAR Watershed, the sites explored in this section were selected partially according to the project philosophy—Protect, Prevent, Mitigate. This philosophy places a strong emphasis on natural resource conservation and preventative measures that minimize new sources of NPS pollution, and regards the installation of structural BMPs as a final means of addressing existing pollutants.

The dense urban development and post-industrial redevelopment types studied in this section are prioritized based on their typically high levels of impervious surfaces, as well as their potential for reducing urban sprawl and habitat loss elsewhere in the region—assuming the introduction

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of appropriate incentives (as described in Section 8.2).

Residential retrofit is studied because older, denser residential areas represent one of the largest land use types in the USAR Watershed. Since population density and residential land use are both important indicators of NPS pollution, it is important to consider such older residential areas when identifying regional LID opportunities.

Residential New Development

On the other hand, greenfield or new residential development is studied because it is currently one of the most common types of development, and is often implemented in a way that is contrary to the philosophy of this project. Thus, this document seeks to demonstrate ways in which a new residential development can be designed to minimize disturbances to native vegetation, wildlife, and existing hydrology.

Residential Retrofit Dense Urban

This section’s focus on new residential development is therefore largely due to the project philosophy, whereas the other three types of development being studied are informed by the outputs of the conceptual model (See Figure 7.1). The model, detailed in Section 5, focuses on LID opportunities in existing urban areas, and therefore does not indicate possible locations for new greenfield development; however, since such development will likely continue to occur in the future, it is important to study it from a LID perspective.

This document recommends that future LID implementation projects in the USAR Watershed prioritize the sites identified via a geospatial modeling process (such as that described in Section 5), which include land uses not represented by the site designs in this section, such as existing multifamily residential and commercial developments. The following conceptual

Post-Industrial

Figure 7.1

Context Map For Site Designs

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site designs are intended to serve as examples of how LID implementation can enhance an area’s environmental or aesthetic quality, strengthen its local identity, or improve its connections to surrounding areas.

Each conceptual design responds to unique conditions at specific locations, but also demonstrates general strategies and specific structural BMPs that can be applied to similar sites elsewhere. The designs utilize a range of BMPs to optimize the filtration and cleansing of stormwater, increase temporary detention and soil infiltration, and reduce runoff.

Often, such LID features also have additional potential benefits, such as beautification and increased property values.

These conceptual site designs serve as examples of good LID practice and the application of structural BMPs to typical conditions, such as the dense urban core, post-industrial redevelopment, residential retrofit, and residential greenfield development. They thus demonstrate what is possible for future LID projects in the San Antonio region.

For the most part, the site designs presented in this document utilize uniform data sets (such as 2’-0” contours provided by the City of San Antonio) and a standard landscape architectural design approach, beginning with site analysis and progressing through stormwater runoff calculation and design development. For the purposes of stormwater runoff calculation, this document utilizes a 1.5” design storm and the NRCS Runoff Curve Number method, as described by the Texas Department of Transportation Hydraulic Design Manual (2009). The selection of the 1.5” water quality design storm is based on the use of a similar methodology by the City of Dallas (North Central Texas Council of Governments 2009). Appendix D provides additional information regarding

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the use of the NRCS Runoff Curve Number method and the 1.5” design storm for the calculation of expected runoff and treatment volumes.

7.2 Dense Urban Core Redevelopment

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Dense Urban Core Redevelopment 34.2 ACRES

N Figure 7.2

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MODELING CHANGE

0

500

1000 Feet

Dense Urban Area Context Map

Br oa dw ay

Taylor T ylor St

Jefferson J fferson St. Je St

Navarro Navarro St. St. Martin Mart St. t

Pecan an St. St

1 TTravis avis SSt.

2

Houston ouston St. St

Figure 7.4

Image of Commerce Street

Figure 7.5

Image of Navarro Street

College ll St.

C rockett ock o oc ckett tt SSt St. Crockett

3 E. Com merce St.

N Figure 7.3

0

250

1

TRAVIS PARK

2

INTERSTATE 37

3

RIVERWALK

500 Feet

Context Map Of Selected Dense Urban Core Area

INTRODUCTION In most large cities, dense urban cores pose significant challenges for LID implementation. Downtown San Antonio contains some of the region’s most dense and impervious areas. Since NPS pollutant loads typically increase as the amounts of impervious surface increase, Downtown San Antonio is an ideal location for LID implementation. See

Section 6.2 for more information about the opportunities and challenges for LID projects in dense urban areas.

In dense urban areas, limited space is the greatest obstacle to LID implementation. Urban infrastructure is composed of a number of complex systems, such as transportation, underground utilities, water conveyance, bike lanes, and public transit routes. As LID is a relatively new approach to

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99

managing stormwater, it can be difficult to find implementation sites in a highly urban environment not originally designed to accommodate LID. For example, if cleansing stormwater is determined to be a priority, vegetated swales may require space that would otherwise be used for widened sidewalks or a bike line.

However, despite limited space, there are numerous opportunities for LID implementation in dense urban areas.

This can help weave natural systems into the urban fabric, creating multifunctional infrastructure systems that help filter

Figure 7.6

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MODELING CHANGE

Peacock Alley

stormwater and serve as a means of beautification. Flood control is another important benefit of LID implementation.

Although the Downtown area has become much less flood prone in recent years due to extensive flood control measures, nonstructural BMPs can help to slow runoff and ease the burden on an aged stormdrain system that may back up during heavy rains. Structural BMPs such as biofiltration cells, swales and underground cisterns are a few examples of the LID implementation measures that can collect and treat stormwater runoff in dense urban areas.

Figure 7.7

Pressa Street Bridge

Figure 7.8

City Section Showing Dry-Season Water Flow in River

0

50

100 Feet

0 Figure 7.9

50

100

Section Showing the Flow of Contaminants Into The San Antonio River

Fee et

Figure 7.10

Section Showing Historical Flood Risk

0

100 Feet

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sidewalk space, street intersections present a better opportunity for structural BMP installation.

SITE ANALYSIS In order to develop a strategy for LID implementation in Downtown San Antonio, understand existing systems and identify opportunities for structural BMPs, a thorough site analysis is necessary. Many of the sidewalks in Downtown contain utilities and in some cases are located over basements or elevators used for deliveries. Thus, LID implementation in sidewalk areas may be impractical. Because of limited

INTERSECTIONS INTERSECTIONS

Figure 7.11

102

MODELING CHANGE

PARKING LOTS PARKING LOTS

Analysis Maps of Dense Urban Core

It is essential to gain an understanding of the stormdrain system and to identify locations where interception of stormwater is possible. Bus traffic determines areas that may not be feasible for permeable paving. On the other hand, street parking areas can serve as excellent areas for permeable paving, allowing the infiltration of stormwater. Roof

STORM DRAINS STORM DRAINS

DRAINAGE DRAINAGE

space that is mostly flat and contains few obstructions can also provide opportunities for extensive green roofs. However, any green roof installation requires a thorough structural evaluation and engineering report prior to design and implementation.

STORM DRAIN SYSTEM STORM DRAIN SYSTEM

Figure 7.12

ROOF OPPORTUNITIES ROOF OPPORTUNITIES

BUS TRAFFIC BUS TRAFFIC

STREET PARKING STREET PARKING

Analysis Maps of Dense Urban Core

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GREEN ROOFS

hold larger plant material, such as shrubs and small trees.

Some green roofs contain both intensive and extensive components. Green roofs have been found to provide insulation and longevity to a roof membrane, as well as to help reduce urban heat island effect. In the dense urban core, green roofs can also create additional public or private open space as well as serving as LID retrofits.

The University of Texas at Austin is currently conducting research to determine the effectiveness of green roof implementation in the San Antonio area. Green roofs provide another way to cleanse stormwater, as well as to reduce and slow runoff. Green roofs are divided into two main categories: intensive and extensive. Extensive green roofs are typically characterized by a shallow soil depth and accommodate small plants, such as sedum. On the other hand, intensive green roofs have more substantial soil depths and are designed to

Figure 7.13

Downspouts from Rooftops

Figure 7.14

Green Roof Section

Figure 7.15

Green Roof Open Space

0

50

100 Feet

104

MODELING CHANGE

Figure 7.16

Roofs of San Antonio

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PARKING LOTS Parking lots comprise vast impervious surfaces in most urban cores, collecting and conveying large amounts of runoff quickly to the storm drain system, and thus concentrating NPS pollutants and sediment. For this reason, structural BMPs associated with parking areas should address water quantity and quality. Parking lots also offer an opportunity to collect water into underground cisterns, where it can be recycled or allowed to percolate into the groundwater table. In addition, biofiltration swales create opportunities to filter stormwater as it flows through vegetation and is exposed to natural microbial processes that help to break down contaminants.

Figure 7.17

106

MODELING CHANGE

Parking Lots in Downtown San Antonio

Current Island Areas: The current islands in the parking lot are excavated, and stormwater is directed into them.

Most are not currently vegetated but could be converted into runoff-catching swales, allowing filtration to occur.

Extention of Islands and Biofiltration Swales: To allow maximum interception of stormwater, additional narrow swales are created where possible to connect the excavated islands and to create more biofiltration opportunities. This essentially develops a more extensive filter network to cleanse more runoff.

Subsurface Water Storage and Infiltration: All swales are then connected via underground storage areas. Water is directed to the vegetated swales and then overflows into the storage areas under the pavement. This slows runoff, cleanses stormwater, and allows percolation into the groundwater table.

Figure 7.18

Parking Lot Design Series

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Trees Another addition are trees. Trees provide shade to protect cars from the heat and help to counter the urban heat island effect.

Figure 7.19

LID Parking Lot Design

1

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MODELING CHANGE

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100 Feet

Figure 7.20

Parking Lot Current Condition

Trees for shade and water absorbtion

A more extensive network of water catchment and interception

Underground water storage

Figure 7.21

Proposed Parking Lot With Trees And Subsurface Storage

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STREETS/ STREET PARKING

with native prairie grasses that are drought tolerant, yet able to handle short periods of water inundation. The sides of the street are transformed to support street parking and bioretention cells. Permeable pavement is used in the strips of parking and bioretention cells are used where possible to treat stormwater before it enters the storm drain system. These areas also provide room for street trees, which help to soften the urban environment in addition to slowing runoff.

Br

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Many streets in downtown San Antonio can be challenging sites for LID implementation because of their limited space.

However, some streets, such as Broadway, contain enough room to place LID BMPs. This requires reconfiguring street parking and taking advantage of median space. In this example, the median pavement is removed and replaced

Median of Prairie Species Street Parking

Bioretention Cells

0

50

100 Feet

Figure 7.22 110

MODELING CHANGE

Broadway Street Plan

1

Figure 7.23

Broadway Street Current Conditions

Figure 7.24

Broadway Street After Implementation LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

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BROADWAY STREET BEFORE LID

Sidewalk

Figure 7.25

Traffic Lanes

Traffic Lanes

Sidewalk

Broadway Street Section Before Implementation

BROADWAY STREET AFTER LID

Sidewalk

Traffic Lanes

Biofiltration Cell

Sidewalk

Traffic Lanes

Native Grasses

Biofiltration Cell 0

Figure 7.26

112

MODELING CHANGE

Broadway Street Section After Implementation

25

50 Feet

Figure 7.27

Current Losoya Street

Figure 7.28

Losoya Street With Permeable Pavement

The map above shows the locations of street parking. The images to the right illustrate the potential use of permeable paving at these locations. Street trees are also used to add aesthetic and environmental value.

Shade Trees

Permeable Paving

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FILTERSECTIONS The streets of San Antonio are the primary conveyance surface for stormwater before it enters the stormdrain system. In urban spaces that are too small or crowded to accommodate bioinfiltration cells or swales, other opportunities may exist.

The existing clusters of storm drains at intersections suggests that these are good locations for LID implementation. Water is currently directed to intersections, but this design transforms each cross walk into an underground sand filter with decorative drainage grate. During a storm event, runoff flows through the grate and is directed into voids under the sidewalk, where it is then filtered through a sand matrix. The filtered water is then directed into the storm drain system before it reaches the San Antonio River.

H C

Figure 7.29

Section Showing Water Filtration At Traffic Intersections

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MODELING CHANGE

Figure 7.30

Intersection With Filtration And Water Storage Looking East On Houston Street

Figure 7.31

Intersection With Filtration and Water Storage Looking West on Houston Street

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Although 1.4 acre feet of runoff is now able to be kept on site, helping to restore predevelopment hydrological cycles, even more water is being filtered of pollutants. The filtration and storage capacity of each of the traffic intersections throughout the site, combined with bioinfiltration swales and permeable pavement, enables the slowing and filtering of all runoff produced in a 1.5 inch storm. See Appendix D for calculations.

BENEFITS Some of the benefits of this design include:

116

•

Reduced runoff

•

Increased infiltration

•

Stormwater storage and reuse

•

Reduced pollutant loading

•

Beautification

•

Improved pedestrian infrastructure

•

Increased property value

MODELING CHANGE

PREDEVELOPMENT

EXISTING

AFTER LID Figure 7.32

PREDEVELOPMENT

EXISTING

AFTER LID

Figure 7.33 Area

.004 Acre Feet

3.3 Acre Feet 1.4 Acre Feet

Runoff Volumes from 1.5” Design Storm for Dense Urban Area

FILTERE D

By implementing LID throughout this area stormwater runoff was reduced from 3.3 acre feet to 1.4 acre feet. This is due, in large part to the storage capacity beneath ground level parking lots.

RUNOFF

STORMWATER

4.27 Acre Feet .21 Acre Feet 4.27 Acre Feet

Filtered Volumes from 1.5” Design Storm for Dense Urban

7.3 Post-industrial Redevelopment

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t

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Post-industrial RedevelopmenT 7.5 acres

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Figure 7.34

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MODELING CHANGE

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Big Tex Grain Company Site Context

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Lone Star Bou

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INTRODUCTION The San Antonio area has numerous post-industrial sites that are currently ready for redevelopment--several of which are located along the San Antonio River. The inclusion of LID design features in such redevelopment projects can provide much-needed stormwater storage and treatment, serve as an open space amenity and improve habitat connectivity for native birds and insects. Post-industrial sites provide a number of opportunities in terms of LID implementation, including the adaptive reuse of existing structures, the recycling of materials, and proximity to existing transportation infrastructure.

Blue Star Arts Complex 0.4 mi

0.3 mi

La Tuna Restaurant

Like development in dense urban cores, post-industrial redevelopment should be prioritized because of its potential to reduce development pressure elsewhere in the region.

This is especially true if appropriate incentives are in place to encourage redevelopment in denser urban areas, helping to reduce regional urban sprawl and concentrate development closer to urban cores. See Section 6.3 for more information regarding LID opportunities and challenges in post-industrial redevelopment projects.

SITE CONTEXT

0.25 mi

Brackenridge High School

N Figure 7.35

0

400

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Big Tex Grain Company Site Context: Walking Distances

The 7.5 acre site on Blue Star Road is located between the San Antonio River and the Southern Pacific railroad tracks, near the intersection of Probandt and Alamo Streets (See Figure 7.34). The adjacent Eagleland Hike and Bike Path runs along the east side of the site, before crossing over a pedestrian bridge to the opposite bank of the River and the relatively dense King William neighborhood (See Figure 7.36).

To the northwest of the site is the Blue Star Contemporary Arts

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HISTORIC DISTRICT

1

HIKE and BIKE TRAIL

2

PEDESTRIAN BRIDGE

3

RAILROAD

4

ACCESS ROAD

4

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N Figure 7.36

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MODELING CHANGE

0

400

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800 Feet

Big Tex Grain Company Site Context: Key Features

Complex, which contains a number of galleries, a restaurant, and residential lofts. Brackenridge High School is located just across the pedestrian bridge, in King William (See Figure 7.35).

Along with the historic neighborhoods of King William and La Vaca, the Blue Star Arts Complex forms the cultural core of Southtown, a burgeoning arts district characterized by colorful murals and the adaptive reuse of historic structures. A monthly First Friday Art Walk centered on South Alamo Street helps define the district’s identity. The area surrounding the Big Tex Grain Company reflects this local identity, as well as the area’s industrial heritage, as demonstrated by the Blue Star Arts Complex and the nearby La Tuna restaurant (across Probandt Street).

SITE HISTORY

Figure 7.37

Existing Structures in Big Tex Grain Company Site

Figure 7.38

Existing Impervious Surfaces in Big Tex Grain Company Site

While the Big Tex Grain Company site takes its name from its former use as a grain processing facility, between 1961 and 1989 it also served as an industrial manufacturing site for vermiculite ore containing a dangerous form of asbestos (Avatar Environmental 2011). Following environmental sampling of the site and its immediate surroundings--including the Eagleland Hike and Bike Trail--the US EPA began excavation operations on the site, during which “predetermined grids were excavated to a depth of six inches” (EPA 2009, p.

1-2).

The site clean-up operations were completed by December 2008 and the site and its buildings were judged “ready for reuse” by January 2009 (EPA 2009, p. 2). Since asbestos contamination is typically found at the soil surface, and

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Figure 7.39

View of the Big Tex Grain Company Site from Across the River

since remediation has already occurred, LID strategies that encourage stormwater infiltration are most likely appropriate for the site.

SITE ANALYSIS Most of the industrial and agricultural structures that existed on the Big Tex Grain Company site have been removed, leaving behind numerous concrete pads of varying elevation (See Figure 7.38). The remaining structures consist of 18 detached silos and two grain elevators with attached silos (See Figure 7.37). The largest of these, referred to as “the Main Ruin” in this document, is around six stories tall, and is the site’s most distinctive feature (See Figure 7.50).

Figure 7.40

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MODELING CHANGE

Recreational Uses of the Eagleland Hike and Bike Trail

Because of the concrete pads remaining on the site, approximately one third of the site currently consists of impervious surfaces (See Figure 7.43). While the site does not appear to receive a significant amount of runoff from surrounding areas (most likely due to the train tracks on the south-west edge), there is apparently enough runoff generated on the site to necessitate the installation of three large drains, all near the Main Ruin. Thus, there is an obvious need for LID implementation on the site.

The existing topography and hydrology are fairly simple. Most of the site is flat, with the exception of several mounds on the south-west edge, which appear to be man-made and the result of former industrial uses or excavation. There is a prominent drainage area on the northern edge of the site, near the Main Ruin, which is where all three of the existing drains are located (See Figure 7.42). This portion of the site appears to receive the majority of the runoff.

N

0

Figure 7.41

800

1600 Feet

Big Tex Grain Company Site Context: Parcel Zoning

Mixed Use (Infill) Zone Industrial Zone Residential Zone Commercial Zone

The site is accessible to pedestrians and bicyclists along most of its north-east edge, which is adjacent to the Eagleland Bridge and the Hike and Bike Trail. Vehicular access is possible only via Blue Star Road, on the north side of the site, because of the railroad (See Figure 7.36 and Figure 7.42).

There are a small number of small or medium-sized trees on the site, most of which appear to be volunteers. Two larger trees are located outside the site, along the Hike and Bike Trail, near the Main Ruin.

The site is surrounded by a variety of land uses, including single family residential, mixed-use infill, and industrial uses (See Figure 7.41).

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ACCESS

DRAINAGE

VEHICULAR ACCESS

DRAIN RUNOFF

DRAIN BE RM

DRAIN

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Figure 7.42

400

800 Feet

Big Tex Grain Company Site: Drainage and Access

EXISTING STRUCTURES

IMPERVIOUS SURFACES

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Figure 7.43

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MODELING CHANGE

400

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Big Tex Grain Company Site: Impervious Surfaces and Existing Structures

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DESIGN PRECEDENTS

PLANNED DEVELOPMENT

The San Antonio area offers several examples of postindustrial redevelopment projects. Some of these sites, such as the Pearl mixed-use redevelopment project in Midtown, utilize LID features such as stormwater cisterns (See Figure 7.44). However, the Pearl, the Blue Star Arts Complex in Southtown, and the CAMPstreet Residences are especially noteworthy because of their successful programming, combining multiple land uses and incorporating both private and public elements. By providing community amenities such as educational programs for local students, a weekly farmer’s market, and a public park with interactive landscape features, these projects create pedestrian-oriented destinations and encourage changes in local lifestyles. They demonstrate the importance of social programming as well as structural BMP utilization for the creation of a truly multi-faceted LID project.

The site is currently owned by Lifshutz Companies, the developer of the Blue Star Arts Complex. A mixed-use residential/commercial development is planned for the site, with approximately 121 multifamily residential units, 12 townhouses, an unspecified number of live/work units, and about 50,000 sq.ft. of commercial retail space (Alamo Architects 2011).

Figure 7.44

LID DESIGN The proposed design for the Big Tex Grain Company site modifies the developer’s planned mixed-use program in order to incorporate more open space and increase opportunities for BMP implementation (See Figure 7.45). While the design is first and foremost an example of the application of LID principles to the design of a mixed-use development, it also

Local Post-Industrial LID Precedents

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125

seeks to demonstrate how such a project can enhance local identity and improve regional connectivity (both in terms of pedestrian access and wildlife habitat).

Although it would likely be possible to create a LID design to match the developer’s planned program in terms of the number of residential units and amount of commercial retail, an analysis of the surrounding land uses and zoning codes suggests that the site’s neighborhood would benefit from increased open space. While the Eagleland Hike and Bike Trail and Roosevelt Park are nearby recreational resources, the redevelopment of numerous post-industrial sites in the area (currently zoned as “Infill Development”) may necessitate additional open space to meet the needs of the expanding local population.

The design seeks to strengthen Southtown’s arts district’s identity and to complement the existing facilities at the Blue Star Arts Complex by providing additional opportunities to create, display and sell artwork. The Blue Star currently contains approximately 16 live/work lofts, as well as a number of galleries and retail spaces. The proposed design for the Big Tex Grain Company site seeks to expand this creative community. The creation of additional live/work units and galleries at the Big Tex Grain Company site will be combined with commercial retail and loft residences, creating a more varied community and attracting a wider range of visitors to the site.

The proposed design for the Big Tex Grain Company site will create an additional 30 live/work units, 20 residential lofts, and 40,000 sq.ft. of commercial development (See Figure 7.46).

The Main Ruin will be refurbished and used as a cafe and art

126

MODELING CHANGE

gallery, in order to minimize new construction. The existing silos along the Hike and Bike Trail will be relocated to the narrow area between the Blue Star Arts Complex and the Big Tex Grain Company site and used as commercial kiosks. This will help to unite the two sites and draw visitors from one to the other.

By utilizing podium structures with underground parking, the proposed design minimizes the need for surface parking, and thus has less impervious surfaces than conventional development (See Figure 7.46). The ground floor of the proposed buildings will contain commercial space and the “work” component of live/work units. Second and third stories will contain residential lofts and the “live” component of live/ work units. The placement of building footprints creates public plazas that are intimate, yet linked to the Hike and Bike Trail.

These public plazas unite the various program uses.

The design’s two main programmatic areas are the Public Plaza and the Restored Prairie (See Figure 7.45). Both are envisioned as multifunctional spaces, in that they serve important recreational and hydrological functions, in addition to providing outdoor exhibition and performance spaces for local artists. In the Public Plaza area, a “critical mass” of residents and visitors is created through concentrated development, while in the Restored Prairie, native vegetation and elevated platforms provide opportunities for individual exploration and contemplation.

DESIGN

Hike and Bike Trail

BUIL

Cistern

DING

Biofiltration Runnel

BUIL

DING

Drain

Rain Garden

Public Plaza

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Swale

RU

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Elevated Boardwalk Path

8’ Gabion Wall Elevated Stage

Permeable Pavement

Restored Prairie ands Sculpture Park

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200

400 Feet

Figure 7.45

Big Tex Grain Company Site Conceptual Design

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FLOOR 3: Residential Lofts

FLOOR 2: Residential Lofts and “Live” Component of Live/Work Units

FLOOR 1: Retail and “Work” Component of Live/Work Units UNDERGROUND: Parking

LID SOLUTIONS

N

Figure 7.46

Uses of New Buildings in Big Tex Grain Company Site

The concentration of development is a common LID design strategy, since it minimizes impervious surfaces and reduces disturbance to existing hydrological systems, soils and native vegetation (Southern California Stormwater Monitoring Coalition 2010). The design proposed for the Big Tex Grain Company site utilizes this approach, partially for the abovementioned reasons, but also in order to bring about the “critical mass” of residents and visitors often necessary for the creation of vibrant urban spaces.

In accordance with the principles of LID, existing drainage patterns are preserved and complemented by new swales and interconnected basins that allow the temporary detention and filtration of stormwater. New paved surfaces are concentrated near the site’s vehicular access point, in order to minimize road extension into the site (See Figure 7.45). Linking the new development to the Hike and Bike Trail will help reduce

128

MODELING CHANGE

the need for vehicular transportation. The proposed design takes advantage of the large quantities of concrete on the site (See Figure 7.47). This material can be broken up and used to fill the gabion baskets used in retaining walls or to construct permeable pavement paths (See Figure 7.48).

In the Public Plaza area, cisterns capture the stormwater from building roofs, storing it until it can be reused for irrigation. The public plaza itself directs stormwater to a biofiltration runnel (essentially a gravel swale) that helps to filter runoff and deliver it to the vegetated swale (See Figure 7.49). In the vegetated swale and its interconnected basins, runoff is further filtered before entering the River (See Figure 7.51).

Figure 7.47

Construction Rubble in Big Tex Grain Company Site

Figure 7.48

Reuse of Broken Concrete as Permeable Pavement

In the Restored Prairie area, the creation of elevated platforms and boardwalk paths minimizes the amount of impervious surfaces, helping to reduce runoff. Likewise, the restoration of native prairie grasses encourages the infiltration of stormwater that once flowed directly across the site and into the River (See Figure 7.52). Since many prairie grasses have deep root systems, the infiltration capacity of the restored area can be expected to improve over time, as the grasses grow (See Figure 7.53). Thus, it is an example of how landscape restoration can support the stormwater management goals of LID, while providing both recreational opportunities and wildlife habitat.

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BEFORE LID

Existing Structure

Existing Structure

Hike and Bike Trail

AFTER LID

Biofiltration Runnel

Underground Parking

Swale

0

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Figure 7.49

130

MODELING CHANGE

Section of Public Plaza and Stormwater Features

Figure 7.50

The Main Ruin

Figure 7.51

Perspective of Public Plaza and Swale

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BEFORE LID

Concrete Platform

Existing Structure

AFTER LID

Elevated Platform

Elevated Path

Restored Prairie

0

50

100 Feet

Figure 7.52

132

MODELING CHANGE

Section of Restored Prairie: Before and After LID

Figure 7.53

Perspective of Restored Prairie and Sculpture Park

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It is possible to estimate the pre-development hydrology of the Big Tex Grain Company site using the Curve Number Method, as well as to compare its current stormwater runoff to the expected quantity following the implementation of the proposed LID design.

Prior to development, a 1.5” storm would have produced about 0.004 acre feet of runoff from the site. By comparison, at the height of the site’s industrial and agricultural uses, the same

1.5” storm could have produced as much as 0.24 acre feet of runoff, due to the increase in impervious surfaces. Since most of these impervious surfaces still exist on the site, a similar amount of runoff may be expected today.

As a result of the described LID design, the runoff generated by the site following a 1.5” storm can be almost entirely eliminated. The combination of swales, biofiltration runnels, and permeable pavement can reduce the runoff resulting from a 1.5” storm to about pre-development levels. See Appendix D for calculations.

RUNOFF

STORMWATER

PREDEVELOPMENT

BENEFITS EXISTING

Some of the benefits of this design include: Reduced runoff

•

Increased infiltration

•

Restored native vegetation

•

Stormwater storage and reuse

•

Reduced pollutant loading

•

Diversified housing types

•

Increased property value

•

Beautification

AFTER LID

.24 Acre Feet

.004 Acre Feet

Figure 7.54 Runoff Volumes From a 1.5” Design Storm for the Big Tex Grain Company Site

PREDEVELOPMENT

EXISTING

AFTER LID

FILTERED

•

.004 Acre Feet

.93 Acre Feet .61 Acre Feet

Figure 7.55 Filtered Volumes From a 1.5” Design Storm for the Big Tex Grain Company Site

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MODELING CHANGE

.93 Acre Feet

7.4 Residential Retrofit

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Brackenridge Golf Course

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1 Figure 7.56

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MODELING CHANGE

500

1000 Feet

Tobin Hill Neighborhood Context Map

Fre

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INTRODUCTION Existing residential neighborhoods present a challenge because there is little land available for stormwater projects. In addition, many BMPs such as rain gardens require the participation of the individual property owners.

In spite of these challenges, it is important to look for LID retrofit opportunities because residential areas are a significant source of bacteria and other pollutants in the USAR Watershed (TCEQ 2007). See Section 6.4 for more information about the opportunities and challenges for LID projects in residential areas.

Mistletoe Avenue

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Woodlawn Avenue

28

This primarily residential area is part of the Tobin Hill Neighborhood and is located about 1.5 miles north of downtown San Antonio (See Figure 7.56).

Craig Place

Largely built before World War II, it was once part of a larger neighborhood that extended to the San Antonio River. However, in the 1970s the 281 Freeway was built and split the neighborhood, creating a series of dead end streets and disconnected access points (See Figure 7.57 and Figure 7.58).

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Russell Place

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Valdez Avenue

Although less than 200 feet from the open space of the Brackenridge Golf Course, views are obstructed by the 281 Freeway which gives the area a more urban character (See Figure 7.56).

French Place

Ter r

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1 Figure 7.57

Dead End Streets Look onto the 281 Freeway

0

Figure 7.58

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Map Showing a Portion of the Tobin Hill Neighborhood

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Commercial

250

500 feet

N

Figure 7.60

Narrow Streets in the Tobin Hill Neighborhood

Residential Golf Course

Figure 7.59

Zoning Map of Tobin Hill Neighborhood

The neighborhood is just under 25 acres and is primarily residential, although there is a commercial corridor along St. Mary’s Street (See Figure 7.59). Most of the residential lots are 1/8 acre with a single family home.

138

MODELING CHANGE

As an older neighborhood, it was built before many of today’s standards for street widths and sidewalks (See Figure 7.60).

Several of the streets are quite narrow, which affects traffic patterns and parking.

N

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500 Feet

Catchment areas Storm drain Direction of flow

Figure 7.61

Figure 7.62

The Only Storm Drain in the Tobin Hill Neighborhood

Figure 7.63

Concrete Channels For Stormwater Outflow

Figure 7.64

Concrete Channel Directs the Stormwater to a Swale

Drainage Map of the Tobin Hill Neighborhood

Stormwater drainage is also handled differently than on newer streets. There is only one traditional storm drain; most of the stormwater flows instead to the ends of the streets where it is diverted into a swale that runs alongside the 281 Freeway (See Figure 7.61 - Figure 7.64). Local residents have identified the area as having drainage problems (See Figure 7.65) (City of San Antonio 2008).

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SITE ANALYSIS

There are a number of important factors to consider when implementing LID projects.

Because this area is developed, the LID solutions will largely be limited to retrofitting existing spaces with appropriate BMPs. Soil infiltration rates are critical in designing BMPs that require infiltration. The soil data presented here is general and onsite soil tests should be conducted before beginning any detailed design work.

Other issues and opportunities include the location of impervious surfaces, known drainage problems, vacant land, and parking lots (See Figure 7.65 Figure 7.69).

Figure 7.66

140

MODELING CHANGE

Residential Yard Showing Soil

SOIL INFILTRATION

IMPERVIOUS AREAS 10 acres

SOIL INFILTRATION

Very slow Infiltration

Moderate Infiltration

Figure 7.65

Site Analysis Maps

LID Design Analysis: • Place BMPs according to infiltration requirements • In areas with poor infiltration, additional engineering may be needed to allow infiltration

Figure 7.67

LID Design Analysis: • Disconnect impervious areas • Convert to permeable surfaces where possible • Utilize impervious areas such as rooftops for rainwater harvesting

Buildings, Streets and Parking Lots Create Large Impervious Areas

DRAINAGE PROBLEMS Drainage Problems Buildings

"

OPEN / VACANT LAND

PARKING LOTS

3 acres

5 acres

OPEN / VACANT LAND 3 acres

LID Design Analysis: • Install BMPs to address runoff volume

Figure 7.68

Vacant Lot

LID Design Analysis: • Install neighborhood scale stormwater features

Figure 7.69

LID Design Analysis: • Convert to permeable pavements • Install rainwater harvesting cisterns underground • Redesign to reduce size

One of the Many Parking Lots in the Area

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141

DESIGN In urban areas, it is difficult to restore developed land to pre-developed hydrologic conditions. However, significant improvements can be made through creative and efficient use of the land available.

Although the area is developed, there are still a number of opportunities for LID projects. Because LID focuses on dealing with the water on site, these opportunities can be grouped by scale, beginning with the residential lot (See Figure 7.71).

Using these opportunities as a basis for design, the stormwater runoff can be reduced or eliminated. However, for an LID design in a residential neighborhood to be successful, it must address more than just stormwater. It must also be designed for the people living and visiting the area, including issues such as maintenance, aesthetics, and usability.

This design accommodates the stormwater while offering attractive swales, medians, and biofiltration areas. It also provides areas for people to use and enjoy, including a park, a natural area, and a walking trail connecting the two.

Residential Lot: • Rainwater harvesting via cistern or rain barrel • Diverting residential rainwater into a rain garden • Disconnecting downspouts Commercial Lot: • Rainwater harvesting via cistern under parking lots • Parking lot converted to permeable paving Street: • Controlling where the stormwater flows once it reaches the street via swales Neighborhood: • Creating large biofiltration areas to store and filter water that was not handled on site Figure 7.70

142

MODELING CHANGE

View of Oak Canopy Near Terry Court Natural Area

Design

Mistletoe Avenue

Residential Lot

Russell Place Park

Terry Court Natural Area

Stormwater Features (2 acres total): • Biofiltration Areas • Vegetated Swales

Converted Parking Lots (2+ acres total): • Permeable Paving • Underground Storage for Rainwater

1

0

Figure 7.71

250

500 Feet

Walk/Jog Trail (.5 mi)

Conceptual Design of Tobin Hill Neighborhood

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143

MISTLETOE AVENUE

This portion of Mistletoe Avenue once extended further west, but is now a 225 foot long cul-de-sac due to the construction of the 281 Freeway. It is unusually wide with an 18 foot median (See Figure 7.72 and Figure 7.74).

wide, it is too narrow to accommodate both a parked car and a moving car. The median is planted with turf along with several trees and palms. It is currently graded so that it drains onto the street.

The street collects the runoff from the adjacent lots and directs the water to a concrete channel at the end of the street where the water flows over the edge and into a swale below.

St

.M

ar

y’s

St

.

A’

The median separates the avenue into two one-way streets, each with on-street parking. Since each section is only 15 feet

Existing large median with palm trees

A

Existing concrete channel outflow

Existing swale for 281 Freeway drainage

0

1 Figure 7.72

144

MODELING CHANGE

25

50

28

1F

wy .

Existing vacant lot

100 Feet

Mistletoe Avenue Showing Existing Drainage Patterns

This area suffers from drainage problems, according to area residents (See Figure 7.65) (City of San Antonio 2008).

LID SOLUTIONS By installing various stormwater BMPs and regrading the streets, the drainage pattern can be significantly improved (See Figure 7.73 and Figure 7.75). Runoff from adjacent lots is directed into swales rather than into the streets. The median is narrowed by two feet in order to provide an extra foot to

Median is converted to large swale

A’

St y’s ar .M St

Street is widened and regraded to drain into median

.

There is currently an irregularly shaped 0.08 acre vacant lot on the south side of the street that is an opportunity for addressing drainage problems as well as stormwater runoff (See Figure 7.72).

Existing concrete channel outflow is removed to direct water into biofiltration area

5’ swales drain runoff from residential lots

A

Biofiltration area can accommodate runoff from 1.5” storm

28

1F

wy .

Overflow drains to prevent flooding in major storm events

1

0

Figure 7.73

25

50

100 Feet

Conceptual Design for Mistletoe Avenue and New Drainage Pattern

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145

each of the streets, making them slightly wider for easier passage.

The streets and median can be regraded so that the north side of the street drains into the median and all other runoff drains into the biofiltration area installed on the vacant lot.

Because the soils in this area may have poor infiltration rates, additional steps must be taken to ensure adequate filtration in the biofiltration area. For example, the area may need excavation and use of engineered soil. Additional soil tests are necessary in order to determine requirements.

These changes not only accommodate the runoff from a 1.5� storm, but allow the water to be filtered as it infiltrates through the soil. The design of the median, swale, and biofiltration area enables them to become attractive amenities rather than merely functional infrastructure. This makes the street and neighborhood more inviting and increases property values.

146

MODELING CHANGE

BEFORE LID

Sidewalk

A

Figure 7.74

AFTER LID

4’

Sidewalk

5’

15’ One way street w/ parking

18’ Median

15’

5’

A’

4’

One way street w/ parking

5

Section Showing Existing Mistletoe Avenue

Sidewalk

Swale

Swale

Sidewalk

A 4’ Rain garden

5’

16’ One way street w/ parking

16’ Median w/ bioswale

16’ One way street w/ parking

5’

A’

4’ Biofiltration area 5

Figure 7.75

10 Feet

Section Showing Mistletoe Avenue With Swales Added

10 F Feet

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147

A’

RESIDENTIAL LOT

A

67 6’

Although residential lots vary in size and configuration, most have room for small scale BMPs such as cisterns and rain gardens. Using a small lot as an example, the amount of stormwater runoff leaving the site can be dramatically reduced.

67 4’

This approximately 1/8 acre corner lot is currently draining runoff to the street (See Figure 7.76 and Figure 7.77). It has a traditional front yard of turf bisected by the impervious surfaces of the driveway, sidewalk, and walkways.

Although this lot produces a relatively small volume of runoff, there are hundreds of similar lots and so the total runoff from residential lots becomes significant when considering the larger area.

0

20

1 Figure 7.77

40 Feet

Residential Lot Showing Existing Drainage Pattern

LID SOLUTIONS A

A’ Turf

Turf 10

Figure 7.76

148

MODELING CHANGE

Section of Residential Front Yard

Feet

By adding a cistern and rain garden, and converting the impervious surfaces to permeable concrete or pavers, the amount of runoff can be reduced to almost nothing (See Figure

A’

Replace turf with drought tolerant groundcover

A

Rain gardens

Figure 7.79

Residential Lot With Rain Garden and Permeable Paving

Cistern to capture rainwater

0

1 Figure 7.78

20

40 Feet

Conceptual Design and New Drainage Pattern

7.78 - Figure 7.80). The rainwater harvested in the cistern can later be used for irrigation. This allows the water to be filtered as it infiltrates into the soil rather than flowing into the street.

A

A’ Rain Garden

Groundcover 5

Figure 7.80

Section of Residential Rain Garden

10 Feet

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149

RUSSELL PLACE PARK

Russell Place is a narrow street that connects with Craig Place to the north (See Figure 7.81). Originally an alley, Russell Place is between residential lots to the north and commercial lots to the west and south (See Figure 7.82).

Russell Place currently has no sidewalks or curbs. The existing drainage flows east along Russell Place where it enters a storm drain to the north. The area suffers from

drainage problems, according to area residents (See Figure 7.65) (City of San Antonio 2008).

There is a long, narrow vacant area on the south side of Russell Place currently zoned for commercial use (See Figure 7.81 and Figure 7.86). Using this vacant land as an opportunity, this design assumes that the parcel could be rezoned for park space.

Craig Place

A’

St

.M

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y’s

St

.

Existing drainage flows into storm drain

Russell Place

Figure 7.81

150

MODELING CHANGE

50

100 Feet

Russell Place Showing Existing Drainage Pattern

Fwy

0

1

281

A

Existing vacant lot

LID SOLUTIONS The neighborhood has identified a desire for additional park space through the creation of pocket parks and identifying vacant land to convert to parks (City of San Antonio 2008).

By converting the vacant lot into a park which incorporates stormwater features, the drainage pattern can be changed and runoff reduced significantly.

One reason this area is vacant may be that Russell Place is such a narrow street that access is problematic. The street is only 14 feet wide and has no sidewalks. In order to make the best use of this space for both stormwater treatment and Figure 7.82

Russell Place

Parking lot converted to permeable paving with underground cistern

Biofiltration area created by closing Russell Place

Hammerhead-style turnaround for emergency vehicles

y’s

St

A’

.

Turf areas for recreation

St

.M

ar

Russell Place is widened from 14’ to 20’ and now includes a sidewalk Biofiltration area

1

0

Figure 7.83

50

100 Feet

281 F

wy

A

Parking area with 20 spaces using permeable paving

1/2 mile walk/jog trail connecting to Terry Court Natural Area

Conceptual Design for Russell Place Park and New Drainage Pattern

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151

parkland, this design drastically alters Russell Place by making it wider, adding a sidewalk and swale, and converting it to a dead end street (See Figure 7.83 Figure 7.87).

Changing Russell Place to a dead end street allows a portion of the former loop street to be converted to a stormwater biofiltration area that serves Craig Place to the north. A hammerhead-style turnaround is used in order to accommodate emergency vehicles.

The park features swales and biofiltration areas, which treat the stormwater while serving as landscape amenities. They also help to define the large turf areas provided for recreation. In addition, there is a parking lot designed with permeable pavers which drains into the swales.

Figure 7.84

Existing Vacant Lot Looking East from St Mary’s Street

Figure 7.85

View of Russell Place Park

There is also a trail that circles the park, taking the walkers and joggers through turf and trees as well as across the biofiltration areas so that all areas of the park are highlighted. The trail leaves the park to connect to the Terry Court Natural Area to the south.

152

MODELING CHANGE

BEFORE LID

A

14’

100’

Russell Place

Vacant Lot

A’ 5 5

0

Figure 7.86

10 10 F Feet Feet

Section Showing Existing Vacant Lot and Width of Russell Place

AFTER LID

A

A’ 20’ Russell Place

5’ Swale

4’ Biofiltration Area New Sidewalk

Figure 7.87

Turf

Trail

0

5

10 Feet

Section of Russell Place Park Showing Park Features and Street Alterations

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153

The southern end of the neighborhood includes a one acre parcel that was once part of the Brackenridge Golf Course, but was cut off when the 281 Freeway was built (See Figure 7.88).

TERRY COURT NATURAL AREA

The existing drainage flows along Terry Court and eventually into the swale alongside the 281 Freeway, bypassing this site. Residents have expressed an interest in converting it to a park (City of San Antonio 2008), but its location is somewhat problematic because it is on a dead end loop street that becomes quite narrow in sections. It also lacks visibility from the major intersection at St. Mary’s Street, which makes it rather isolated.

Currently, there is no connection between French Place and this area

French Place A

A’

Currently the only access is from Terry Court. There is no connection to the neighborhood from French Place to the north because the residential lots extend to the swale alongside the 281 Freeway (See Figure 7.88 and Figure 7.92), thus preventing any sidewalk or trail connecting the areas.

Mature oak trees

B

B’

Ter ry 0

1 Figure 7.88

154

MODELING CHANGE

50

100

Cou

rt

Feet Terry Court and Existing Drainage Pattern

Figure 7.89

Mature Oak Trees Adjacent to Vacant Lot

LID SOLUTIONS This is an ideal location for a neighborhood scale stormwater project because it is at the low point of the area (See Figure 7.90 - Figure 7.95).

A

Trail connecting to Russell Place Park

Due to its relative isolation, this site is less suited to be an active park, but it is an ideal location for a natural area that focuses on stormwater and wildlife habitat. It is adjacent to a stand of mature oak trees (See Figure 7.89 Figure 7.91), which can form the backbone of a native Blackland Prairie plant palette.

Local wildlife experts should be consulted in order to identify the appropriate species to target. This would help to guide the planting design, as plant species and locations would be determined by the seasonal needs of the wildlife.

Figure 7.91

A’

Additional trees

Biofiltration area, with vegetation chosen for habitat value B

0

1 Figure 7.90 Terry Court

B’

50

100 Feet

Conceptual Design and New Drainage Pattern for

Canopy of Oak Trees Adjacent to Terry Court

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

155

BEFORE LID Access can be improved by creating a trail linking this area to French Place and Russell Place Park to the north. This requires a boardwalk to extend out over the swale that lies between the residential lots and the 281 Freeway (See Figure 7.92 and Figure 7.93).

A House

With its focus on both stormwater treatments and wildlife habitat, the Terry Court Natural Area can serve educational goals through interpretive signs about both the native plants and stormwater benefits.

A’ Swale w/ underdrain

Embankment

281 Freeway 5

10 Feet t

Figure 7.92

AFTER LID

Section of Terry Court Showing Proximity of Freeway Embankment

Boardwalk

Additional plantings

A House

A’ Swale w/ underdrain

Embankment

281 Freeway 5

10 Feet

Figure 7.93

156

MODELING CHANGE

Section of Terry Court Showing Boardwalk Extended above Swale

BEFORE LID

B’

B Terry Court

281 Freeway

Swale w/ underdrain

Vacant Area

0

25

50 Feet

Figure 7.94

Section of Terry Court Showing Vacant Area and Proximity to Freeway

Structural diversity of vegetation for wildlife habitat

AFTER LID

B’

B Terry Court

Trail

Stormwater Biofiltration Area

Trail

Swale w/ underdrain

281 Freeway 0

25

50 Feet

Figure 7.95

Section of Terry Court Showing Stormwater Biofiltration Area with Trail

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157

STORMWATER

BENEFITS Some of the benefits of this design include: •

Reduced runoff

•

Increased infiltration

•

Restored native vegetation

•

Stormwater storage and reuse

•

Reduced pollutant loading

•

Improved pedestrian infrastructure

•

Increased property value

•

Increased public awareness

By implementing the design described here, the area would produce almost no runoff from a 1.5” storm (See Figure 7.96).

Instead, the water would be retained on site and treated by filtration as it travels through the soil and vegetation (See Figure 7.97). See Appendix D for calculations.

RUNOFF

Today, the area is approximately 40 percent impervious cover (See Figure 7.65). The same 1.5” storm results in 1.4 acre

feet of water running off the site. This is a significant increase from the pre-development conditions

PREDEVELOPMENT

.004 Acre Feet

EXISTING

1.4 Acre Feet

AFTER LID

.004 Acre Feet

Figure 7.96 Runoff Volumes From a 1.5” Design Storm for the Tobin Hill Neighborhood

PREDEVELOPMENT

EXISTING

AFTER LID

FILTERED

The quantity of stormwater flowing across this area has been drastically altered by its development. Before the area was built up, a small storm would result in very little runoff because the water was held by the soil and vegetation. A 1.5” storm would create .004 acre feet of water flowing off site and down into the San Antonio River.

3 Acre Feet 1.7 Acre Feet 3 Acre Feet

Figure 7.97 Filtered Volumes From a 1.5” Design Storm for the Tobin Hill Neighborhood 158

MODELING CHANGE

7.5 Residential New Development

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159

Residential New Development 61 acres

Lo

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y wa rk Pa h ac

y

hwa

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Mili

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N Figure 7.98

160

MODELING CHANGE

0

500

1000 Feet

Typical San Antonio Greenfield Development

INTRODUCTION Residential new development, also referred to as greenfield development, offers many opportunities for successful implementation of LID. Greenfield development allows designers to reduce runoff by applying simple LID principles such as reduced road widths, alignment of road widths existing contours, clustering structures, minimizing lot size, establishing conservation areas and specifying pervious building materials. Similarly, water quality issues can be addressed by bioretention gardens, filter strips, roadside swales and biofiltration areas. Greenfield development is unique in that the design principles can be fully utilized and be an integral part of the development. Residential new development allows a designer to incorporate all LID principles and BMPs at an early stage, making a successful LID implementation more likely. See Section 6.5 for more information about the opportunities and challenges for LID projects in new residential development.

The Alon greenfield is being developed by KB Homes as the next phase in the Woods of Alon subdivision. Based on existing homes from the first phase, lot sizes are expected to be 6,000 to 8,000 square feet with houses from 1,500 to 3,500 square feet and prices from $200,000 to $300,000. Figure 7.98 outlines the 61.1 acres of the greenfield. KB Homes is currently clearing the land for infrastructure and roads. The pictures presented in this section show the site before any clearing. All design options will be presented based on a completely undeveloped site.

Commercial

Phil Hardberger Park

ALON GREENFIELD This greenfield is surrounded by residential and commercial areas that have been developed over the last 10 years (See Figure 7.98) . It is bordered on the north by a brand new commercial area anchored by a HEB supermarket. Directly south is a new residential neighborhood being developed

by KB Homes. To the east is Phil Hardberger Park, which contains 311 acres of multi-use trails, picnic facilities, playgrounds, access to Salado Creek Greenway, sports fields and a dog park. The immediate area is referred to as Alon, with the shopping center and new residential incorporating Alon into their names. This area is located approximately eight miles north of downtown San Antonio and is within city limits.

KB Homes Phase I

N

0

1000

Commercial Figure 7.99

Residential

2000 Feet

Park

Alon Area Zoning

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

161

thw

Nor y

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A

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162

Figure 7.100 Northeast

Point A, View of Alon Greenfield - Looking

Figure 7.101

Point B, View of Alon Greenfield - Looking Southwest

MODELING CHANGE

0

Figure 7.102

250

500 Feet

Alon Greenfield

The site is almost completely covered with vegetation.

General vegetation communities include live oak woodlands, live oak/ashe juniper woodlands, live oak/mixed deciduous woodlands and live oak/cedar elm woodlands containing live oak, ashe juniper, cedar elm, Texas persimmon and mesquite.

There are a substantial number of prominent trees that are at least 24” diameter at breast height (DBH). The site has sporadic understory grasses, opuntia and yucca. There are a few areas without trees that contain grasses (See Figure 7.92 through Figure 7.102).

The soils on site are typical for this part of Texas, a mixture of clay loam, silty clay, cobbly clay and extremely stoney clay loam resulting in very slow infiltration. Bedrock is between 40” and 200” below the surface. This site is in the transition zone of the Edwards Aquifer and may contain sinkholes or other conduits that drain directly to the underlying aquifer.

Stormwater from the commercial area directly north of the site is drained onto the site via two 24” storm drain pipes (See Figure 7.95 and Figure 7.106). Considerable erosion is evident immediately below the storm drain outlets, however runoff is quickly slowed and erosion is not evident at a distance

Figure 7.103

Figure 7.104

Storm Drain Outlet from Commercial Area

Point C, View Looking West at Existing Stormwater Detention Area

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

163

0 94

from the outlet. Stormwater flows from the outlet pipes to drains and detention areas as shown in Figure 7.95, Figure 7.104 and Figure 7.106.

0 93

0 92 0 91

The elevation on site ranges from a high of approximately 926 feet in the northern area to a low of 870 feet in the southwest (See Figure 7.106). Slope on the site ranges between 1 and 10 percent with most slopes at less than 5 percent. There is little evidence of high water flow on site and any water flowing off site drains to the existing detention area to the south or storm drains to the west and southwest. The site is not within the 100-year floodplain of an Olmos Creek tributary (See Figure 7.105).

0 90 0 89 0 88

N 0 87 0 86

0

250

500 Feet Contour Interval: 2 Feet

Catchment Boundary Figure 7.106

Storm Drain

Concentrated Offsite Drainage

Alon Area Drainage

SITE ANALYSIS There are certain factors that must be considered when designing LID for new residential development. Any new impervious infrastructure will cause additional runoff that must be handled on site. Further, removal of existing vegetation will decrease the existing infiltration.

N

0

1000

2000 Feet

100-Year Floodplain Figure 7.105

164

MODELING CHANGE

Alon Area 100-Year Floodplain

Soil infiltration rates are important when selecting BMPs, specifically infiltrating BMPs. Soil information presented is for the general area and may not represent soils on site. Soil testing should be performed before LID design is started on any new residential development.

In Terms of LID implementation, the site provides both opportunities and constraints. Opportunities include the existing infiltration function of wooded areas and the existing drainage patterns, including the detention area to the south.

Constraints include the detrimental effects of vegetation removal on soil infiltration and wildlife habitat.

LID DESIGN OPTIONS: • Retain as much wooded land as possible • Use pervious materials when possible • Collect runoff for each lot using bioretention rain gardens and cisterns • Collect and divert runoff to vegetated swales • Design and build detention BMPs as needed

Existing Walkway to Shopping Area

CONVENTIONAL DEVELOPMENT Conventional development of new residential areas greatly alters the physical appearance and functionality of the landscape. Typical conventional development consists of storm drains, wide roads with gutters, complete development of all land, cul-de-sac arrangement of streets and clearing of most existing vegetation (See Figure 7.108) (Perrin et al.

2009). This type of development replaces pervious areas with impervious areas and removes existing vegetation, both of which contribute to water quantity and quality issues (Dietz and Clausen 2008).

Existing Trail

N 0

Park Entrance

Existing Retention Basin

250

Existing Detention Basins

500 Feet

Existing Stormwater Areas Figure 7.107

Points of Interest Around Alon Greenfield

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

165

Office Building

Conventional Development

Pedestrian Walkway

th-

Nor

Existing Drain to Stormwater Pipe

rk

wa

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HEB Supermarket

ay

ighw

ry H

ilita

tM

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Pa

Existing Drain to Stormwater Pipe

6,000 - 8,000 Square Foot Lots

Existing Retention Pond

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Existing Detention Ponds

el

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N Figure 7.108

166

MODELING CHANGE

0

250

220 Units

500 Feet

Alon Area Conventional Development Lot Layout

LID DESIGN

CONVENTIONAL VS LID DESIGN:

New residential development offers many opportunities to implement LID methods.

• •

Conventional: ~220 Units LID design: 90 Single Family and ~230 Apartment Units

Conservation subdivision: • 50% of original land conserved • Reduced lot size • Reduced road width • Single loaded streets • Community trail system

• •

Conventional: Lots mostly scraped and cleared LID design: Retain existing vegetation in conservation areas and on individual lots

• •

Conventional: Increased impervious areas LID design: Minimization of impervious areas

Residential streets: • Impervious sidewalks with vegetated swale buffer • Impervious materials used for parking areas

• •

Conventional: Increased runoff LID design: Goal is to maintain pre-development runoff

• •

Conventional: Increased NPS pollution LID design: Runoff treated by many small BMPs on site, cleansing stormwater and removing NPS pollutants

• •

Conventional: Native species, plant and animal, removed LID Design: Native habitat conserved

Engineered ephemeral creek: • Provides conveyance and storage for drainage from existing commercial area and constructed impervious areas Residential lots: • Rainwater harvesting cistern • Bioretention rain garden • Vegetated swales • Retain wooded areas • Single loaded - residences only on one side of street

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

167

Nor

Office Building Permeable Parking Areas

est Mili

LID Design

thw

Detention Area

tary

Pedestrian Walkway

y wa

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Hig Existing Drain Outfalls to Ephemeral Creek

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HEB Supermarket

W ur

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High Density Housing

Existing Drain to Stormwater Pipe and Outfall to Ephemeral Creek

High Density Apartments

Detention Area Community Trail System Ephemeral Creek

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4,000 Square Foot Lots

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Existing Retention Pond

Existing Detention Ponds

N Figure 7.109

168

MODELING CHANGE

0

250

90 Single Family and 230 Apartment Units

500 Feet

LID Design for Alon Greenfield

Figure 7.110

High Density Apartments

Figure 7.111

Single Family Housing Aesthetics

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169

EPHEMERAL CREEK An ephemeral creek starts from the northern stormwater drainage outlet and follows natural contours, terminating at a detention area in the southern portion of the site. The creek provides stormwater conveyance and storage during rain events. Drainage from lots and streets will be channeled to the creek via swales. The creek serves as the primary conservation area and design feature for the development.

This area has multiple benefits including treatment and storage of stormwater, recreation and potential for ecological restoration of plant and animal species.

A

A’

Figure 7.113

Ephemeral Creek in Alon Greenfield

A 20’

A’

6’ 10

Ephemeral Creek with Underdrain Figure 7.112

170

MODELING CHANGE

Ephemeral Creek Section

Community Trail

Feet

Ephemeral Creek Figure 7.114

Ephemeral Creek and Community Trail

Figure 7.115

Existing Native Vegetation in Alon Greenfield

Community Trail

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

171

RESIDENTIAL STREET

A

A’

The residential streets in Alon Greenfield are specifically designed to be as narrow as possible in order to reduce the amount of impervious surface in the subdivision. The streets do not have curbs, but instead they are bordered by a vegetated swale (See Figure 7.117, Figure 7.118 and Figure 7.119). The swale collects, filters and conveys stormwater to the central ephemeral creek. There is a sidewalk on only one side of the street which is built with pervious materials.

Figure 7.116

LID Design Residential Street

A

A’ Rain Garden

Figure 7.117

172

MODELING CHANGE

6’

4’

22’

Sidewalk

Swale

Residential Street

Residential Street Section in Alon Greenfield

5

10 Feet

Single Loaded Residential Permeable Driveway Reduced Road Width

Roadside Swale

Figure 7.118

Residential Street Showing Single Loaded Lot and BMPs

Figure 7.119

Closeup of Roadside Swale

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173

RESIDENTIAL LOT

A

A’

Each residential lot has a minimum area of 4,000 square feet. Minimum lot width is 40 feet and setback restrictions for a conservation subdivision allow houses to be placed on one edge of the lot without setback. The maximum home footprint is 60% of lot size or 2400 square feet. Residents are encouraged to build up. Each lot is required to have bioretention rain gardens and a cistern. Residents are also required to abide by subdivision covenants, conditions and restrictions (CC&Rs) that prohibit development that would remove local vegetation or increase impervious areas. The conservation subdivision would differ from other residential development in the area, where all existing vegetation was cleared prior to home construction (See Figure 7.123).

Figure 7.120

LID Design Residential Lot

A

A’

Total Lot Length: 100’ Undisturbed Oak Woodlands

Cistern

Rain Garden 10 Feet

Figure 7.121

174

MODELING CHANGE

Residential Lot Section

4,000 sq. ft. Lot

Cistern

Existing Vegetation

Figure 7.122

Example of a LID Residence with BMPs

Figure 7.123

KB Homes Typical Lots and Home Designs

Rain Garden

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175

STORMWATER

Undeveloped, the area has no discernible impervious areas.

A traditional subdivision would result in approximately 40% impervious surfaces and the clearing of almost all trees and vegetation.

By implementing the LID design described here, the area would produce almost no runoff from a 1.5” storm. Instead, the water would be retained on site and treated by filtration as it travels through the soil and vegetation. See Appendix D for calculations.

RUNOFF

This area generates a small amount of runoff in its predevelopment form (See Figure 7.124 for quantities).

PREDEVELOPMENT

CONVENTIONAL

BENEFITS Reduced runoff

•

Increased infiltration

•

Protected existing natural areas

•

Reduced pollutant loading

AFTER LID Figure 7.124

PREDEVELOPMENT

•

Stormwater storage and reuse

•

Diversified housing types

•

Beautification

•

Improved pedestrian infrastructure

CONVENTIONAL

AFTER LID

Figure 7.125

•

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Increased property value

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3.1 Acre Feet

.2 Acre Feet

Runoff Volumes from a 1.5” Design Storm for the Alon Area

FILTERED

•

.2 Acre Feet

7.4 Acre Feet

4.5 Acre Feet 3 7.4 Acre Feet

Filtered Volumes from a 1.5” Design Storm for the Alon Area

7.6 Regional Significance of Proposed Designs When considering the designs presented in this chapter, it is important to note that a single LID design must be replicated many times, across an urban area, in order to have a significant impact on regional water quality and quantity. In order to have a truly regional impact, there must be a concerted effort on the part of multiple jurisdictions and communities to implement LID projects across the urban landscape. While the total number of LID projects implemented is critical (as demonstrated by Kansas City’s 10,000 Rain Gardens initiative), the selection of individual sites is important as well, since some locations may have a greater contribution to NPS pollution and stormwater runoff than others. Institutions interested in achieving regional LID goals should thus focus on: (1) the replication of a specific set of LID designs: and (2) the identification of sites that have the greatest potential contribution to pollutant loads and local stormwater runoff.

This document provides a conceptual basis for both design replication and site prioritization. In terms of the replication of LID designs across the urban landscape, this document presents several design strategies that can be reproduced relatively easily. For example, Section 7.2 details street intersection sand filters, retrofitted parking lots, and street median modifications that can be implemented across Downtown San Antonio. The replication of these proposed changes will multiply the post-LID runoff reduction value identified in Section 7.2. Likewise, Section 7.3 provides numerous examples of LID retrofit strategies for existing residential areas. Since older residential areas represent one

of the largest land use types in the USAR Watershed, the LID implementation measures presented in Section 7.3 can be replicated at a larger scale, resulting in a multiplied reduction in stormwater runoff.

In terms of the prioritization of implementation sites, the conceptual model presented in this document will provide interested parties a means of identifying sites with the greatest possible contribution to NPS pollution and stormwater runoff mitigation. The conceptual model’s output is described in Section 5, and represents a starting point for the identification of existing urban areas that should be prioritized for further study and LID implementation. By identifying priority areas for LID and BMP application, there can be a signifcant regional impact on both water quality and quantity.

Since the model is focused on locating LID opportunities in existing urban areas, it does not identify potential areas for greenfield development. This is mainly due to the project’s philosophy (Protect, Prevent, Mitigate), which prioritizes the regional protection of undeveloped lands and the prevention of additional sources of NPS pollution over site-scale mitigation strategies (such as the use of structural BMPs). However, it is important to develop a modeling methodology specific to greenfield development, since such development is likely to continue in the future. Thus, further research and geospatial analysis is necessary in order to develop a model that identifies priority sites for new residential development that uses LID methods.

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8. Next Steps 8.1 8.2 8.3 8.4

Education and Outreach Potential Incentives for LID Conceptual Model LEADERSHIP

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8. Next Steps

8.1 Education and Outreach LID is often thought of in terms of the placement of structural BMPs; however, non-structural BMPs are often a more critical component of successful LID implementation. Policies are usually directed at reducing the extent of impervious surfaces and/or eliminating sources of NPS pollution, rather than cleansing the affected runoff. Educational programs aimed at increasing residents’ understanding of the environmental consequences of urban stormwater runoff--and the implications of their individual actions and collective behavior--are an important part of a regional LID strategy.

Kansas City’s 10,000 Rain Gardens Initiative is an excellent example of the educational potential of LID projects, and a good model for the integration of community outreach in stormwater management (Sustainable Cities Institute 2005).

The initiative to build 10,000 rain gardens draws upon a wide range of stakeholders, including local residents, students, businesses, non-governmental organizations (NGO) and

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municipal government agencies (Sustainable Cities Institute 2005). The resulting projects are intended to increase public awareness of issues relating to water quality, water quantity and the use of native plants. An example of the initiative’s awareness-raising measures is the planned distribution of “garden kits with design concepts, instruction manual, registration form, and [a] garden sign” (Sustainable Cities Institute 2005, p. 3). This rain garden initiative and similar ones in other cities (such as Milwaukee) have provided residents with discounted plants as an additional means of encouraging public participation (Water Environment Research Foundation [WERF] 2011). As demonstrated by the Kansas City initiative, the creation of awards or other types of public recognition for local LID projects--such as front yard signs--is another important means of outreach (EPA 2009c).

8.2 Potential Incentives for LID Aside from education/outreach programs and special awards, there are numerous ways in which San Antonio area municipalities can encourage LID in urban planning and design. As highlighted by the US EPA Water Quality Scorecard (2009d), municipalities seeking to adopt sustainable stormwater management policies can: (1) remove existing barriers to LID implementation, (2) adopt incentives for specific forms and types of development and (3) enact regulations. In addition to promoting the implementation of LID principles at the site scale, such incentives have the added benefit of creating pedestrian-friendly mixed-use districts and aesthetically pleasing neighborhoods with a myriad of landscape amenities (EPA 2009c) .

According to the EPA’s Managing Wet Weather with Green Infrastructure: Incentive Mechanisms (2009c) municipal handbook, the two most common types of incentives used by many cities to promote LID are (1) a discounted stormwater service fee based on reduced impervious area and (2) tax credits or financing programs that reduce the installation cost of specific practices. Some cities, such as Chicago, New York, Philadelphia and Portland, Oregon, also provide development incentives during the permitting process, which can include: “zoning upgrades, expedited permitting, reduced stormwater requirements and increases in floor to area ratios” (EPA 2009c, p. 1).

While San Antonio area municipalities already utilize many of these strategies--often without the specific aim of encouraging LID--a thorough policy review is necessary in each jurisdiction to determine additional opportunities. The EPA Water Quality Scorecard (2009d) highlights numerous planning policies that can be used to incentivize LID, including the following: •

Accelerating permitting and streamlining plan review for brownfields, infill redevelopments and projects utilizing green infrastructure practices.

•

Reducing the number of vehicle parking spaces required for developments that provide pedestrian/bicycle circulation systems, have narrow driveways, contain a minimum number of bicycle parking spaces, or incorporate vehicle sharing mechanisms.

•

Reducing parking space requirements for mixed-use and Transit-Oriented Developments (TOD).

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•

Sharing the cost of pervious pavement installations and reducing street width and parking requirements for developments that use it.

•

Excluding parking structures with green roofs from a site’s allowable floor to area ratio.

•

Reducing stormwater utility rates based on the use of green infrastructure practices, such as rainwater harvesting/reuse.

•

Offering financial incentives for the purchase and planting of trees.

One of the main challenges in incentivizing LID is overcoming the apparent conflict between density bonuses (granted for the development of a brownfield or greyfield, or for the preservation of an increased number of existing trees) and the general principle of reducing impervious surfaces. While some of the above-mentioned incentives seek to reduce impervious surface area, others appear to effectively increase it at the site scale. Infill and mixed-use redevelopment of abandoned or underutilized sites is a critical component of LID at the regional scale, but there should be a balance between more dense development in one portion of a site and the incorporation of LID design strategies or structural BMPs in another portion.

This may require the review and revision of Floor to Area Ration (FAR), building setback, and minimum open space requirements to allow both greater density and the inclusion of LID features.

Another approach would be to encourage developers to convert abandoned or vacant lots to permanent community

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open space in exchange for more dense development opportunities elsewhere in the same watershed (WERF 2011).

Such “vacant lot stabilization” programs could possibly improve adjacent property values and provide increased recreational opportunities (WERF 2011, n.p.).

Though many of the incentives described above are intended mainly for new development or redevelopment projects, the retrofit of existing residential and commercial sites is an important aspect of a comprehensive LID strategy as well. This is because, in urbanized watersheds, “existing development is still responsible for the majority of poor water quality issues” (WERF 2011, n.p.). Many of the incentives utilized for existing developments are the same as those used for new developments, including BMP installation subsidies, a “stormwater fee reduction based on the amount of stormwater runoff managed on-site” and “fast track permit review” (WERF 2011, n.p.). Other strategies are more specific to retrofit projects, such as the combination of grants and municipal funds used by Burnsville, Minnesota to develop public rightof-way rain gardens “on the edge of the private properties of the 85 percent of residents that agreed to help” (WERF 2011, n.p.)--which are then maintained via easements.

8.3 Conceptual Model This project has focused on LID redevelopment and retrofit projects in existing urban areas. However, there is also a need to analyze and plan for LID projects in currently undeveloped areas due to the expected growth in the region. These greenfield development sites should be studied carefully in order to ensure that they are located and designed to minimize the negative environmental impact of additional growth.

In order to plan for future greenfield developments, the model can be expanded to include relevant factors such as vegetation. See Section 5.6 and Appendix C for more information.

8.4 Leadership As demonstrated by the Riverwalk, the San Antonio area has a history of creating innovative urban spaces that help define a distinct local identity and provide various societal and economic benefits. However, due to the region’s increasing development and the resulting effects on environmental quality, a new approach is necessary. In order to grow in a sustainable manner, San Antonio area cities must protect vital natural resources such as the Edwards Aquifer. They must also guide development to areas that are already urbanized, in order to minimize regional impervious surfaces and the loss of wildlife habitat.

By adopting regulations and incentives that promote LID implementation, cities in the San Antonio region can increase the pace of structural BMP installation and focus development on existing urban areas with the greatest potential water quality and quantity benefits. In doing so, the San Antonio region can once more demonstrate leadership in urban planning and also gain national recognition for an innovative approach to stormwater management, NPS pollution mitigation and redevelopment.

Figure 8.1

The San Antonio Riverwalk

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9. Conclusion 9.1 9.2 9.3 9.4

significance LID IN THE USAR WATERSHED conceptual Model IMPLICATIONS

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9. Conclusion

9.1 Significance The Upper San Antonio River (USAR) Watershed is a highly developed urban area, with a large amount of impervious surfaces, such as roads, parking lots, and buildings. The conventional development approach that allowed the area to grow and prosper has drastically changed the natural hydrologic cycle by creating networks of impervious surfaces to collect stormwater runoff as quickly as possible and deliver it untreated to a hidden drain system.

As the San Antonio metropolitan area continues to grow, there will be additional impacts on the environment. There will likely be development in the Edwards Aquifer Recharge Zone and other undeveloped areas, which will increase the amount of impervious surface and could lead to groundwater depletion during periods of drought and increased risk of water pollution from NPS pollutants. Since San Antonio relies almost exclusively on groundwater for its drinking water, future urban expansion will put additional pressure on its water supply.

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Given the San Antonio area’s relatively arid climate, its vulnerability to both flash floods and droughts, its reliance on the environmentally sensitive Edwards Aquifer, and its projected population growth, a different approach to managing regional water quality and quantity is necessary.

9.2 LID in the USAR Watershed LID is a design approach focused on managing stormwater as close to its source as possible in order to decrease NPS pollution, reduce runoff volumes, and improve ecological functions. While LID can be applied to both new and existing development, this project focuses on the existing urban areas of the USAR Watershed.

It is important to note, however, that this is only one stage of regional LID planning and implementation. This study recommends a three-part approach to implementing LID at the regional scale: 1. Protect: Provide adequate protection of existing natural resources and undeveloped lands; 2. Prevent: Create policies that help prevent urban sprawl, habitat degradation and other environmental factors contributing to waterbody contamination; and, 3. Mitigate: Reduce environmental effects of existing impervious surfaces and sources of NPS pollution.

Thus, this project is focused primarily on the third stage of regional LID planning: mitigation. This includes redeveloping

or retrofitting areas with appropriate BMPs. This is an enormous task in an urban setting, so this document provides additional tools for analyzing and implementing LID in developed areas.

The conceptual model is a useful tool for determining urban areas in which to focus mitigation efforts. The development types describe the unique issues and opportunities for different land use classifications. Finally, the site designs provide examples of BMP implementation in a variety of contexts.

9.3 Conceptual Model The conceptual model described in this document is a relatively simple method for determining priority locations for LID redevelopment and retrofit projects. It uses several key factors to analyze the USAR Watershed, although the model could easily be applied to any watershed by adjusting the data inputs.

The model uses various factors indicative of urban environmental quality, such as population density; prevalence of residential and commercial parcels (specifically, the type and density of these land uses); degree of impervious surface cover; location in drainage catchments that outfall to polluted waterbodies; soil type; proximity to water bodies; and presence of sensitive natural resources (such as aquifer recharge zones). Each of the factors is given equal importance in the sample results presented in Section 5, but their modeling weight can be adjusted by future users for more detailed analysis.

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Through the overlay and analysis of geospatial data, the model identifies the most beneficial locations for placement of future LID projects in the USAR Watershed. Municipalities and regional planning bodies can further develop the model’s analytical criteria and build upon the preliminary methodology presented in this document. The resulting tool will help to focus resources on sites with the greatest possible environmental impact.

and other metropolitan areas continue to be examined. Thus, the tools presented in this document are part of a larger effort to bring positive change to urban infrastructure.

9.4 Implications This document is a study of the highly-urbanized Upper San Antonio River (USAR) Watershed in central Texas. It recommends the development of a segmented, decentralized, multifunctional infrastructure used for capturing, storing and filtering runoff--as well as providing wildlife habitat linkages and recreational opportunities.

The implementation of LID projects can increase local property values and improve residents’ quality of life by providing landscape amenities. LID projects can also complement existing park and trail systems, enhance recreational opportunities, and in turn, improve public health. At the same time, the strategic placement of LID projects can improve habitat connectivity, reduce urban areas’ susceptibility to flooding, and improve regional water quality through the reduction of NPS pollution.

The scope of this project is limited to the USAR Watershed, but the analytical framework and conceptual model are tools that can be applied elsewhere. Their versatility enables these tools to be shared and developed as the San Antonio region Figure 9.1

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View of San Antonio’s River

Figure 9.2

LID Impacts the River, the People and the Economy of San Antonio

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references References Images

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Santhi, C., Srinivasan, R., Arnold, J.G., & Williams, J.R. (2006). A Modeling Approach to Evaluate the Impacts of Water Quality Management Plans Implemented in a Watershed in Texas. Environmental Modelling & Software, 21(8) 1141-1157.

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MODELING CHANGE

Texas Commission on Environmental Quality (TCEQ). (2011b).

Texas Integrated Report for Clean Water Act Sections 305(b) and 303(d). Retrieved from http://www.tceq.texas.gov/waterquality/ assessment/305_303.html Texas Commission on Environmental Quality (TCEQ). (2011c). What is the “Texas Pollutant Discharge Elimination System (TPDES)”?

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Texas Commission on Environmental Quality (TCEQ). (2007c). Three Total Maximum Daily Loads for Bacteria in the San Antonio Area, 2007. Retrieved from http://www.tceq.texas.gov/assets/public/ implementation/water/tmdl/34uppersa/34-uppersanantoniotmdladopted.pdf

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Texas Parks & Wildlife Department (TPWD). (2010). Level III Ecoregions from Omernik, J. M., Ecoregions of the Conterminous United States (Map Supplement), Polygon Coverage. Retrieved from http://www.tpwd.state.tx.us/landwater/land/maps/gis/data_ downloads/

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van Roon, M. & van Roon, H. (2005). Low Impact Urban Design and Development Principles for Assessment of Planning, Policy and Development Outcomes. (Working Paper 51). Retrieved from http://www.landcareresearch.co.nz/research/built/liudd/documents/ WkP051Principles.pdf Votteler, T.H. (2002). Flood. Texas Parks & Wildlife 2002. Retrieved from http://www.edwardsaquifer.net/pdf/flood.pdf Votteler, T.H. (2000). Drought. Retrieved from http://www. edwardsaquifer.net/pdf/drought.pdf Wang, L., Lyons, J. Kanehl, P., & Bannerman, R.T. (2001). Impacts of Urbanization on Stream Habitat and Fish Across Multiple Spatial Scales. Environmental Management, 28(2), 255–266.

Wanielista, M.P. & Yousef, Y.A. (1993). Stormwater Management, J. Wiley and Sons, New York.

Water Environment Research Foundation. (2011). Stormwater BMP Retrofit Policies. Retrieved from http://www.werf.org/ livablecommunities/toolbox/retrofit_pol.htm Wong, T. & Eadie, M. (2000). Water Sensitive Urban Design- a Paradigm Shift in Urban Design. Paper presented to Water Sensitive Urban Design in the Australian Context Conference, Melbourne, August 30, 2000. Retrieved from http://gabeira. locaweb.com.br/cidadesustentavel/biblioteca/%7B30788FE698A8-44E5-861E-996D286A78B3%7D_Wong1.pdf

Images All images and graphics created by 606 Studio Team, except: FIGURE 2.11 THE BLUE HOLE Sarider1: http://www.flickr.com/photos/83379080@ N00/2419720491/in/photostream/ FIGURE 2.25 VEGETATION Andrew C: http://www.flickr.com/photos/thors_elemnt/4506382657/ (Texas Redbud) Carlo Abbruzzese: http://www.ci.austin.tx.us/water/live_oak.htm (Quercus fusiformis) City of Austin: http://www.ci.austin.tx.us/growgreen/plantguide/ viewdetails.cfm?plant_id=192 (Big Muhly) John Frisch: http://www.flickr.com/photos/johnfrisch/2870170041/ (Indian Grass) Jordan Valley Conservation Gardens Foundation: http:// conservationgardenpark.org/plants/259/blue-grama/ (Blue Grama Grass) Karen and Brad Emerson: http://www.flickr.com/photos/ karenandbrademerson/5681256417/ (Desert Willow) Lawrence Gilbert: https://picasaweb.google.com/lawrencegilbert0/ BrackenridgeFieldLaboratoryNaturalHistory# (Silver Bluestem) Steinbrink Landscaping & Greenhouses: http:// www.steinbrinklandscaping.com/proddetail. php?prod=orngrasses-00449 (Little Bluestem) Texas A & M: http://botany.csdl.tamu.edu/FLORA/301Manhart/ Monocots/Commel/Poa/Poa.html (Big Bluestem)

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Texas A & M: http://uvalde.tamu.edu/herbarium/dite.htm (Texas Persimmon) Toledo Metropolitan Area Council of Governments: http://www. tmacog.org/BP_11/March_11/03_2011_native_plants.htm (Purple Coneflower) Zach Hollandsworth: http://www.flickriver.com/photos/ zhollandsworth/tags/clouds/ (Honey Mesquite) FIGURE 5.1 STREAMS IN SAN ANTONIO Google maps: http://maps.google.com/

FIGURE B.2 PLANTS FOR RAIN GARDENS: EDGES OF THE RAIN GARDEN Big Bluestem Prairie: bigbluestemprairie.com (Big Bluestem) East Tennessee Wildflowers: easttennesseewildflowers.com (Marsh Fleabane) Free Flower Pictures: freeflowerpictures.net (Plains Coreopsis)

FIGURE 6.5 TYPICAL SAN ANTONIO RESIDENTIAL DEVELOPMENT James Bond Agent 007: http://forum.skyscraperpage.com/ showthread.php?p=2498150

Justing Seed Co.: justinseed.com (Clasping Coneflower)

FIGURE 7.15 GREEN ROOF OPEN SPACE Trendir: http://www.trendir.com/green/2008-green-roof-award-ofexcel.html

Lafayette Report: http://lafayettereport.blogspot.com/2010/08/ desmanthus-illinoensis.html (Illinois Bundleflower)

FIGURE 7.111 SINGLE FAMILY HOUSING AESTHETICS Design Milk: http://design-milk.com/images/2008/ MM/2942069688_f636880c53.jpg Urban IPM: http://3.bp.blogspot.com/-oACxnjQG5vo/ TcqQeYA8QLI/AAAAAAAAAOY/8OqnqQ4mc4g/s320/ P5100026.JPG FIGURE 9.1 VIEW OF THE SAN ANTONIO RIVER Dremle: http://www.flickr.com/photos/dremle/3524697603/sizes/l/ in/set-72157618034205884/ FIGURE 9.2 LID IMPACTS THE RIVER, THE PEOPLE AND THE ECONOMY OF SAN ANTONIO Cheap Air: http://blog.cheapoair.com/image.axd?picture= 2011%2f3%2fsa1.jpg

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FIGURE B.1 CLASPING CONEFLOWER Sage to Meadow: http://swamericana.wordpress.com/2010/05/30/ (Clasping Coneflower)

MODELING CHANGE

Kiss of Sun: http://kissofsun.blogspot.com/2009/10/october-bloomday.html (Gulf Coast Muhly)

Mark Zimmermann: http://zhurnaly.com/ (Black-eyed Susan) Mellocutie: http://www.mellocutie.com/2010_04_01_archive.html (Pink Evening Primrose) Melody Lytle: http://www.wildflower.org/gallery/result.php?id_image=19889 (Prairie Wildrye) Mike: https://picasaweb.google.com/KE4ROP/EasternGamagrass#5362838369728851202 (Eastern Gamagrass) Rock Rose: http://wwwrockrose.blogspot.com/2011_04_01_archive.html (Cut-Leaf Daisy) Sally and Andy Wasowski: http://www.wildflower.org/gallery/result. php?id_image=23668 (Brazos Penstemon)

Sam Strickland: http://www.wildflower.org/gallery/result.php?id_image=16850 (Big Muhly)

Fossil Creek Nursery: http://www.fossilcreeknursery.com/grasses/ switchgrass-dallas-blues (Switchgrass)

Santa Monica Mountains Trails Council: http://www.smmtc.org/ plantofthemonth/plant_of_the_month_201003_Crimson_Pitcher_Sage.php (Pitcher Sage)

Greg Jordan: http://www.utas.edu.au/dicotkey/dicotkey/AST/ast/ zBrachys_cardiocarpa.htm (Water Daisy)

WaterWise Landscapes Inc: http://www.waterwiselandscapesnm. com/plants-02.htm (Deer Muhly) Wildseen Farms: aggie-horticulture.tamu.edu (Scarlet Sage) FIGURE B.3 PLANTS FOR RAIN GARDENS: BASE OF THE RAIN GARDEN Bill Drummond: https://picasaweb.google.com/lh/photo/pW1dR5B_ zRwNRBBNZcNu0w (Salt Marsh Mallow) California Flora Nursery: http://www.calfloranursery.com/pages_ plants/pages_h/helang.html (Swamp Sunflower) Campbell and Lynn Loughmiller: http://www.wildflower.org/gallery/ result.php?id_image=8410 (Marsh Obedient Plant) Charlotte Garden: http://acharlottegarden.blogspot.com/2010/09/ shallotte-wildflowers.html (White-topped Sedge) Chris Kleymeer: http://www.flickr.com/photos/kleydev/3831262964/ (Inland Sea Oats)

Mahonia Vineyards & Nursery: http://www.mahonianursery.com/ grasses-sedges/slender-rush-native.html (Slender Rush) Mike: https://picasaweb.google.com/KE4ROP/EasternGamagrass#5362838369728851202 (Eastern Gamagrass) Ohio Nature: http://www.ohio-nature.com/red-and-orange-wildflowers.html (Swamp Milkweed) Plano Prairie Garden: http://planobluestem.blogspot.com/2010/07/ prairie-fireworks.html (Frogfruit) Powell Gardens: http://powellgardens.blogspot.com/2010_09_01_ archive.html (Maximilian Sunflower) Sally and Andy Wasowski: http://www.wildflower.org/gallery/result. php?id_image=23119 (Cardinal Flower) Sally and Andy Wasowski: http://www.wildflower.org/gallery/result. php?id_image=23771 (Fall Obedient Plant) Scriptor Senex: http://scriptorsenex.blogspot.com/2008_09_01_archive.html (Soft Rush)

Conscious Gardening: http://consciousgardening.blogspot. com/2010/07/its-cool-cool-summer-gbbd.html (Gregg’s Mistflower)

Shon Scott: http://wildflowers.jdcc.edu/Wooly_Rose_Mallow.html (Wooly Rose Mallow)

Downtowngal: http://commons.wikimedia.org/wiki/File:Horsetail_ plants.jpg (Horsetail)

Shotaku: http://www.fotopedia.com/items/flickr-2699362289 (Scarlet Rose Mallow)

Florida Nature: http://www.floridanature.org/species. asp?species=Andropogon_glomeratus (Bushy Bluestem)

Sunland Water Gardens: http://www.sunlandwatergardens. com/2011/04/water-clover/ (Water Clover)

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

205

A-1

MODELING CHANGE

Appendices Appendix A: Resources LID Manuals Municipal Code Evaluation Tools

Appendix B: plants Recommended Readings Plants for Rain Gardens: Edges of the Rain Garden Plants for Rain Gardens: Base of the Rain Garden

APPENDIX C: MODEL DETAILS Introduction Tools and Processing Environment Inputs Setup ModelBuilder Flowchart Starting the Model Results Next Steps ModelBuilder Tutorial Data Resources Contact Information for Questions about The Model

appendix D: Runoff Calculations Methodology Calculations for Calculations for Calculations for Calculations for

Dense Urban Core Redevelopment Post-Industrial Redevelopment Residential Retrofit Residential New Development

appendix E: profiles Faculty Profiles Student Profiles

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

A-2

Appendix A: Resources

LID Manuals There are many LID manuals available. Several were selected based on their relevance to this project. These are listed below and compared on the facing page.

Los Angeles County. (2009). County of Los Angeles Low Impact Development Standards Manual. Retrieved from http://ladpw.org/wmd/LA_County_LID_Manual.pdf Low Impact Development Center Inc. (2010). Low Impact Development Manual for Southern California: Technical Guidance and Site Planning Strategies. Retrieved from http://www.casqa.org/LinkClick.aspx?fileticket=zhEf2cj4Q% 2fw%3d&tabid=218 MacAdam, James, for Watershed Management Group, (2010). Green Infrastructure for Southwest Neighborhoods.

Retrieved from. http://www.watershedmg.org/sites/default/ files/greenstreets/WMG_GISWNH_1.0.pdf

A-3

MODELING CHANGE

Perrin, C., Milburn, L., Szpir, L., Hunt, W., Bruce, S., McLendon, ... Eaker, W. (2009). Low Impact Development: A Guidebook for North Carolina (AG-716). NC Cooperative Extension Service, NC State University. Retrieved from http://www.ncsu.edu/WECO/LID Sustainable Sites Initiative. (2009). Sustainable Sites Initiative: Performance Guidelines and Benchmarks. Retrieved from http://www.sustainablesites.org/report/Guidelines%20 and%20Performance%20Benchmarks_2009.pdf U.S. Green Building Council. (2009). LEED 2009 for New Construction and Major Renovations Rating System. Retrieved from http://www.usgbc.org/ShowFile. aspx?DocumentID=8868

LI D C ar ol in a

G

N or th

C ou nt y An ge le s Lo s

C al ifo rn ia

N ew LE ED

So ut he rn

C on st ru ct io n

In iti at iv e Si te s Su st ai na bl e

Planning

G ui de re bo fo en ok r S In ou fra th str w uc es tu t N re ei gh bo rh oo ds

Guidebook Comparison Based on Relevance to LID and Texas

Large Scale Planning Consideration of Site Selection

Non-Structural BMPs

Working with Regulations

Site Development

Structural BMPs

Site Design/Process

Vegetation Recommendations DEPTH & RELEVANCE Maintenance of Structural BMPs Weak Case Studies

Strong

References Year Published

Figure A.1

Moderate

2009

2009

2010

2009

2009

2010

Comparison of Selected LID Manuals

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

A-4

Municipal Code Evaluation Tools Addison County Regional Planning Commission. (n.d.). Low Impact Development Review: Does Your Town Plan and Your Bylaws Support LID? (Bristol, Vermont). Retrieved from http://207.136.225.66/Downloads/Other/LID_review_ Bristol.pdf Center for Watershed Protection. (n.d.). Code and Ordinance Worksheet. Retrieved from http://www.cwp.org/documents/ cat_view/77-better-site-design-publications.html New England Environmental Finance Center. (n.d.). 5 Things You Can Do to Promote LID In Your Local Regulations. In Promoting Low Impact Development In Your Community.

Retrieved from http://efc.muskie.usm.maine.edu/docs/ lid_fact_sheet.pdf New Jersey Department of Environmental Protection. (2004).

New Jersey Stormwater Best Management Practices Manual: Appendix B Municipal Regulations Checklist.

Retrieved from http://www.njstormwater.org/tier_A/pdf/ NJ_SWBMP_B.pdf

A-5

MODELING CHANGE

Appendix B: plants

Figure B.1

Clasping Coneflower

Recommended Readings City of Austin. (1995). Rain Garden Plants. Retrieved from http:// www.ci.austin.tx.us/growgreen/raingardenplants.htm

Lady Bird Johnson Wildflower Center. (2011). Plant Database.

Retrieved from http://www.wildflower.org/plants/

City of San Antonio. (2007). San Antonio Recommended Plant List--All Suited to Xeriscape Planting Methods. Retrieved from https://webapps1.sanantonio.gov/dsddocumentcentral/upload/ Appendix%20E.pdf

Nokes, J. (2001). How to Grow Native Plants of Texas and the Southwest. Austin, TX: University of Texas Press.

Cox, P.W. & Leslie, P. (1988). Texas Trees: A Friendly Guide. San Antonio, TX: Corona Publishing Company.

Damude, N. & Bender, K.C. (1999). Texas Wildscapes: Gardening for Wildlife. Austin, TX : Texas Parks and Wildlife Department.

Mattiza, D.B. (1993). 100 Texas Wildflowers. Tucson, AZ: Southwest Parks and Monuments Association.

Miller, G.O. (2006). Landscaping with Native Plants of Texas. St. Paul, MN: Voyageur Press.

Powell, A.M. & Powell, S.A. (2005). Native Plants in Landscaping: Trees, Shrubs, Cacti and Grasses of the Texas Desert and Mountains. Marathon, TX: Iron Mountain Press.

San Antonio Water System (SAWS). (2011). SAWS Approved Landscape Plant List. Retrieved from http://www.saws.org/ conservation/h2ome/landscape/plantlist.cfm Wasowski, S. & Wasowski, A. (1997). Native Texas Plants: Landscaping Region by Region. Houston, TX: Gulf Publishing Company.

Welsh, D., Welch, W.C., & Duble, R.L. (2007). Xeriscape...Landscape Water Conservation. (Texas A & M AgriLIFE Extension E-447).

Retrieved from https://agrilifebookstore.org/

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

B-1

Plants for Rain Gardens: Edges of The Rain Garden A rain garden is a shallow recessed garden designed to catch and store rainfall for short periods and then dry out. Plants selected must tolerate short periods of inundation, but not require constant standing water.

Black-eyed Susan

Big Muhly Figure B.2 B-2

MODELING CHANGE

Brazos Penstemon

Big Bluestem Plants for Rain Gardens: Edges of The Rain Garden

Edges of rain garden: These plants can tolerate wet soil conditions for at least 24 hours (See Figure B.2). They prefer soil conditions that are a bit drier and that drain more quickly than the plants suggested for the bottom of a rain garden.

Adapted from the City of Austin’s Rain Garden Plants (1995).

Clasping Coneflower

Cut-leaf Daisy

Deer Muhly

Illinois Bundleflower

Marsh Fleabane

Pink Evening Primrose

Eastern Gamagrass

Pitcher Sage

Gulf Coast Muhly

Plains Coreopsis

Scarlet Sage

Prairie Wildrye

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

B-3

Plants for Rain Gardens: Base of The Rain Garden

Bottom of the rain garden: These plants can tolerate partial inundation and wet soil conditions for two days or more (See Figure B.3). They prefer moist soil most of the year; however they can tolerate periods when the soil is dry. Adapted from the City of Austin’s Rain Garden Plants (1995).

A rain garden is a shallow recessed garden designed to catch and store rainfall for short periods and then dry out. Plants selected must tolerate short periods of inundation, but not require constant standing water.

Marsh Obedient Plant

Bushy Bluestem Figure B.3 B-4

MODELING CHANGE

Maximilian Sunflower

Eastern Gamagrass

Plants for Rain Gardens: Base of The Rain Garden

Salt Marsh Mallow

Horsetail

Scarlet Rose Mallow

Island Sea Oats

Cardinal Flower

Swamp Milkweed

Fall Obedient Plant

Swamp Sunflower

Slender Rush

Water Clover

Soft Rush

Gregg’s Mistflower

Frogfruit

Water Daisy

Switchgrass

Wooly Rose Mallow

White-topped Sedge

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

B-5

APPENDIX C: MODEL DETAILS Introduction

Tools and Processing Environment

This appendix provides details on data inputs, operation of the model, how to interpret the results and suggestions on how to expand the model. Basic understanding of ArcMap software is assumed.

This model is created using ArcMap 9.3.1, a Geographic Information Systems (GIS) software package available from Environmental Systems Research Institute (ESRI). ArcMap is also a de facto standard and existing published data is usually available in ArcMap formats. ArcMap provides the ability to map, analyze and display data. Some tools referenced in this section may require special extensions. It is beyond the scope of this document to provide instruction in using the software, however, some resources are listed at the end of this Appendix. Please contact the authors for more information.

The goal of the model is to determine the best location for the placement of LID projects in an urban area. The basic operation of the model is based on mapping areas that: • • • • • •

contain pollutants contribute to nonpoint source pollution support LID functionality are buffers around waterbodies are environmentally sensitive areas are owned by local government

It is important to emphasize this model is based on general principles of LID functionality and NPS pollution generation.

The model operation is based entirely on user input of parameters and weighting and therefore meaningful results are dependant on proper selection of inputs and parameters.

The model is intended to be a simple starting point for the placement of LID in an urban area.

C-1

MODELING CHANGE

ModelBuilder is a separate tool in the Spatial Analyst extension. It is used to build all models described hereafter.

ModelBuilder allows inputs, processes and output to be described using a simple flowchart (See Figure C.1) and the ModelBuilder interface allows the definition of parameters and model specific variables. Finally, a complete ModelBuilder model (See Figure C.2) can be named, saved, distributed and used by others.

Inputs

Zoning

Each input is described in Table C.1 with details on why the input is relevant and source(s) for the data. Note that some inputs are built from base data sources and require preprocessing, which is described conceptually. Some of this preprocessing is incorporated into separate ModelBuilder models. Users of this document are encouraged to include new inputs as needed in order to customize the model results.

USAR

Clip Bexar Land Use

Clip

Land Use Clipped

Select Commercial

Commercial Land Use

Zoning_Clip_USAR Select All Residential

Residential Land Use

Select Industrial

Select All Open Land

Open Land

Zoning_Select _Industrial

Select Streets

Streets

USAR

Figure C.1 Screen Shot of ModelBuilder Flowchart Showing Selection of Industrial Zoned Areas

Figure C.2

Screen Shot of Sample Model to Clip and Select Land Use Data Types

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

C-2

Input

Relevance

Source

Notes

Watershed Boundary

Limit of model

United States Department of Agriculture (USDA) http://datagateway.nrcs.usda.gov/ or http://viewer.nationalmap.gov/viewer/

Select watershed boundary based on hydrologic unit codes (HUC)

Impaired Waterbodies

Where NPS pollution is located

EPA or State Environmental Protection Agency http://water.epa.gov/lawsregs/lawsguidance/cwa/ tmdl/index.cfm

Texas Commission on Environmental Quality (TCEQ) has TMDL reports for some watersheds.

Local Waterbody Buffer

Protect local waterbodies, the buffer United States Geological Survey (USGS), National provides an area to intercept pollutants Hydrography Dataset (NHD) http://nhd.usgs.gov/data.html

Use viewer to determine watershed boundary datasets (WBD)

Soil Infiltration Rate

Good for infiltration BMPs

Natural Resources Conservation Service, Soil Survey Geographic (SSURGO) database. http://soildatamart.nrcs.usda.gov/

Extensive preprocessing necessary to get maps of hydrologic soil groups (with soil infiltration rate)

Imperviousness Limit

More impervious equals more runoff

Multi-Resolution Land Characteristics Consortium (MRLC), National Land Cover Database (NLCD) http://www.mrlc.gov/

30 meter x 30 meter resolution

Population Density

NPS pollution associated with people

Census Bureau http://www.census.gov/geo/www/tiger/

Extensive preprocessing necessary to map population density by block groups

Land Use Zoning

Target specific land use

Land use zoning data is made by city governments May have to use city zoning if land and is a combination of city zoning and land use use is not available. Appraisal data is also good reference

Aquifer Recharge Zones

Sensitive areas

Local, State and Federal Agencies EPA: http://www.epa.gov/geospatial/ TCEQ: http://www.tceq.texas.gov/gis/boundary.html EAA: http://www.edwardsaquifer.org/

Did not find central repository for aquifer data, datasets differed slightly between sources

City Owned Land

Opportunity to install BMPs

City or county appraisal data.

Obtained from City of San Antonio for this example

Slope

Constraint on placement of BMPs

United States Geological Survey (USGS), Digital Elevation Model. http://www.gis.ttu.edu/center/ DataCatalog/Download.php?County=Bexar

Preprocessing necessary using slope tool (spatial analyst / surface)

Table C.1 C-3

Table of Inputs, Their Relevance, Source and Notes

MODELING CHANGE

Setup Models are made and stored in the ArcToolbox. See Figure C.3 for the ArcToolbox display and notice the six models listed under LID Model. Double-click on any model to start it. First, it is necessary to set up variables that apply to the whole model.

These variables, called environment settings, are details that apply to the operation of the ArcMap program and determine how processing is performed. See Figure C.4 for an example of these settings. This dialog box is accessed by opening the “model properties� and clicking the Environments tab. It is important to set up specific settings on this dialog box including the Snap Raster and Cell Size. These settings allow all datasets to be sized and aligned to a common raster grid.

ModelBuilder Flowchart Figure C.3

ArcToolbox from ArcMap Screen Shot

Figure C.4

Environmental Settings Dialog Box Screen Shot

Figure C.5 shows the Modelbuilder flowchart used to determine priority locations for LID projects within the Upper San Antonio River (USAR) Watershed. This flowchart is adapted from the actual ModelBuilder flowchart. The flowchart shows inputs under the Data column. Inputs are datasets which may result from extensive preprocessing. The next column, Calculations, shows the application of parameters set by the user to further define the input data. When the model is started the user will be prompted to enter parameters. The Processing column shows the conversion of all datasets into a common grid raster. The next column, Weighting, shows the application of user defined weighting to individual factors.

The user is prompted for weighting when the model is started.

Finally, the weighted factor for each grid cell is summed and the results are displayed.

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

C-4

DATA

calculations

SOIL SOURCE: NRCS SSURGO

SELECT SOIL GROUPS A+B

OUTPUT FEATURE

IMPERVIOUS COVER

SELECT AREAS > 20%

OUTPUT FEATURE

NORMALIZE BY AREA TO GET DENSITY

OUTPUT FEATURE

CREATE 1/4 MI BUFFER

OUTPUT FEATURE

RUN SUBWATERSHED TOOL

OUTPUT FEATURE

SOURCE: MRLC NLCD

POPULATION SOURCE: CENSUS BUREAU

RECHARGE ZONE SOURCE: EAA

RIVERS + STREAMS SOURCE: NHD

RUN HYDROLOGY TOOL TO FIND UPSTREAM WATERSHEDS

IMPAIRED WATERBODY SOURCE: TCEQ

DIGITAL ELEVATION MODEL SOURCE: USGS

ZONING SOURCE: COSA

SELECT LAND USE (E.G. COMMERCIAL)

CITY OWNED LAND SOURCE: COSA Figure C.5

C-5

MODELING CHANGE

Sample ModelBuilder Flowchart Showing Implementation of the Model

OUTPUT FEATURE

OUTPUT FEATURE

PROCESSING

WEIGHTING

CONVERT TO RASTER

OUTPUT RASTER

DEFINE WEIGHT

OUTPUT RASTER

CONVERT TO RASTER

OUTPUT RASTER

DEFINE WEIGHT

OUTPUT RASTER

CONVERT TO RASTER

OUTPUT RASTER

DEFINE WEIGHT

OUTPUT RASTER

CONVERT TO RASTER

OUTPUT RASTER

DEFINE WEIGHT

OUTPUT RASTER

CONVERT TO RASTER

OUTPUT RASTER

DEFINE WEIGHT

OUTPUT RASTER

RESULTS

SUM

CONVERT TO RASTER

OUTPUT RASTER

DEFINE WEIGHT

OUTPUT RASTER

CONVERT TO RASTER

OUTPUT RASTER

DEFINE WEIGHT

OUTPUT RASTER

CONVERT TO RASTER

OUTPUT RASTER

DEFINE WEIGHT

OUTPUT RASTER

RESULTS

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

C-6

Starting the Model Starting the model by double-clicking on the model name will bring up a parameter dialog box (See Figure C.6). This dialog box prompts the user to enter all parameters and weightings, for example buffers around waterbodies. Once all parameters are entered and the OK button is pressed the processing begins.

Results The results consist of a grid of cells, each containing the sum of all the weighted factors. The user has options on how to display the results. Figure C.7 shows the entire grid for the USAR. Cells with darker red have a higher sum and therefore

are the priority location for the placement of LID. The user has the option to display cells in many ways. The user can zoom in and see specific areas where the model indicates priority locations (See Figure C.8).

Next Steps There are many steps that can be taken to improve the model.

Several inputs can be investigated and added. Weighting of individual inputs can be further refined in order to improve performance. Finally, the accuracy of the model needs to be verified and vetted through real-life testing.

Currently the lowest resolution dataset is the impervious cover, sized at 30 meters by 30 meters. Improving the resolution of this data would increase the resolution of the model overall.

ModelBuilder Tutorial GISTutor http://www.gistutor.com/esri-arcgis/18-advanced-arcgistutorials/43-arcgis-model-builder.html Data Resources Additional data sources that may be of use are listed below.

Reach Address Database (RAD): http://epamap32.epa.gov/radims/ Geospatial One-Stop (GOS): http://gos2.geodata.gov/wps/portal/gos

Figure C.6

C-7

MODELING CHANGE

Parameter Dialog Box Screen Shot

0

750 Feet

N Figure C.8

Detailed Model Results

National Hydrography Dataset (NHD) Viewer: http://viewer.nationalmap.gov/viewer/nhd.html?p=nhd

N 0

1.5 6.0

6.0 Miles

EPA Impaired Water Bodies: http://water.epa.gov/lawsregs/lawsguidance/cwa/tmdl/index. cfm Texas GIS Data: http://www.gis.ttu.edu/center/DataCatalog/CntyDownload.php

Figure C.7

Model Results for USAR

4-Band Color Infrared Imagery: http://www.tnris.state.tx.us/datadownload/quad. jsp?Quad=Losoya&ScrollY=649

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

C-8

Contact Information for Questions about The Model Jake Aalfs jaalfs@yahoo.com 310.425.6340 Megan Dreger mmdreger@gmail.com Eric Whitemyer ericwhitemyer@gmail.com Sina Yousefi syousefi@yahoo.com 606 Studio Department of Landscape Architecture College of Environmental Design California State Polytechnic University, Pomona 3801 West Temple Avenue, Bldg 7 Pomona, CA 91768 la@csupomona.edu 909.869.2673

C-9

MODELING CHANGE

appendix D: Runoff Calculations

Methodology For the purposes of stormwater runoff calculation, this document utilizes a 1.5� design storm and the National Resources Conservation System (NRCS) Runoff Curve Number (RCN) method, as described by the Texas Department of Transportation Hydraulic Design Manual (2009). The selection of the 1.5� water quality design storm is based on the use of a similar methodology by the City of Dallas (North Central Texas Council of Governments 2009).

The RCN method approximates the amount of direct runoff by subtracting infiltration and other losses empirically determined and based on soil type and vegetated cover (Texas Department of Transportation 2009).

Where: R = accumulated direct runoff (in.)

P = accumulated rainfall (potential maximum runoff) (in.)

Ia = initial abstraction including surface storage, interception, and infiltration prior to runoff (in.). Generally, Ia can be estimated as: Ia = 0.2S S = potential maximum retention (in.), which can be calculated as: S= 10 *

100 RCN

-1

The equation is:

R=

(P-Ia)2 (P-Ia) + S

The Hydraulic Design Manual (2009) includes charts to determine the appropirate RCN figure to use for various vegetated cover and soil types.

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

D-1

Calculations for Dense Urban Core Redevelopment Below are the calculations for the Dense Urban Core Redevelopment described in Section 7.2. This area contains Hydrologic Soil Group B (moderate infiltration rate). The area was calculated as a single catchment area due to the lack of available data about the storm drain system (See Figure D.4). The total volume of rainfall in a 1.5� storm is 4.27 acre feet.

PREDEVELOPMENT Area Description Sagebrush/grass

Acres

RCN

34.2

55

RUNOFF (acre feet) .004

EXISTING CONDITIONS: RUNOFF VOLUME Area Description Impervious area Open (good)

Acres

31.2 3

RCN

98 69

Runoff (acre feet) 3.1 .21

TOTAL RUNOFF (acre feet) 3.3 Figure D.1

D-2

MODELING CHANGE

Drainage Map of the Dense Urban Area

Permeable Paving Green Roofs Swales and Infiltration Areas Parking Lots w/ Underground Storage

Runoff Now Retained on Site (acre feet) .07 .06 .13 1.58

1.9

TOTAL RUNOFF* (acre feet) 1.4

PREDEVELOPMENT

EXISTING

AFTER LID

Figure D.2

*Total runoff = existing runoff - runoff now retained on site

AFTER LID: FILTRATION The amount of water either filtered or infiltrated.

Filtered or Infiltrated (acre feet) Existing Infiltration Permeable Paving Green Roofs Swales and Infiltration Areas Sand Filters at Intersections Parking Lots w/ Underground Storage

.24 .07 .06 .13 2.19 1.58

TOTAL (acre feet)

PREDEVELOPMENT

EXISTING

4.27

AFTER LID

Figure D.3 Area

.004 Acre Feet

3.3 Acre Feet 1.4 Acre Feet

Runoff Volumes From a 1.5” Design Storm in the Dense Urban Area

FILTERED

BMPs

RUNOFF

AFTER LID: RUNOFF VOLUME The volume of water retained on site due to the BMPs listed.

4.27 Acre Feet .21 Acre Feet 4.27 Acre Feet

Filtered Volumes From a 1.5” Design Storm in the Dense Urban

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

D-3

Calculations for Post-Industrial Redevelopment Below are the calculations for the Post-Industrial Redevelopment described in Section 7.3. This area contains Hydrologic Soil Group B (moderate infiltration rate). It is a single catchment area (See Figure D.7). The total volume of rainfall in a 1.5� storm is .94 acre feet.

PREDEVELOPMENT Area Description

Acres

RCN

RUNOFF (acre feet)

Grassland (good)

7.5

61

0.004

EXISTING CONDITIONS: RUNOFF VOLUME Area Description Building Roofs Concrete Pads Dirt Road Open Space (fair)

D-4

MODELING CHANGE

Acres

0.36 1.46 0.57 5.11

RCN

98 98 82 69

Runoff (acre feet) 0.038 0.156 0.016 0.03

TOTAL RUNOFF (acre feet) Figure D.4

0.24

Drainage Map of Big Tex Grain Company Site

PROPOSED DEVELOPMENT

1.56 1.84 0.35 0.1 3.65

Runoff (acre feet)

98 92 98 85 61

0.166 0.123 0.037 0.004 0.002

RUNOFF (acre feet)

0.33

AFTER LID: RUNOFF VOLUME OF PROPOSED DEVELOPMENT The volume of water retained on site due to the BMPs listed.

BMPs

Cisterns Swales and Basins Infiltration Areas

Runoff Now Retained on Site (acre feet) 0.25 0.62 0.06

0.93

PREDEVELOPMENT

TOTAL RUNOFF* (acre feet)

EXISTING

.004

AFTER LID

*Total runoff = existing runoff - runoff now retained on site

Figure D.5 Grain Site

AFTER LID: FILTRATION The amount of water either filtered or infiltrated.

Filtered or Infiltrated (acre feet) Existing Infiltration Swales and Basins Infiltration Areas

.40 .51 .02

RUNOFF

Building Roofs Paved Plaza Paved Road Elevated Platforms/Stage Open Space (good)

RCN

PREDEVELOPMENT

TOTAL (acre feet)

EXISTING

.93 AFTER LID

Figure D.6 Grain Site

.004 Acre Feet .24 Acre Feet

.004 Acre Feet

Runoff Volumes From a 1.5” Design Storm in the Big Tex

FILTERED

Area Description

.93 Acre Feet .61 Acre Feet

.93 Acre Feet

Filtered Volumes From a 1.5” Design Storm in the Big Tex

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

D-5

Calculations for Residential Retrofit Below are the calculations for the Residential Retrofit area described in Section 7.4. This area is primarily Hydrologic Soil Group D, with a small area of Group B in the southeast corner. All calculations were done using Group D (very poor infiltration rate) in order to be more conservative with the design. There are five catchment areas (See Figure D.10). The total volume of rainfall in a 1.5� storm is 3.09 acre feet.

PREDEVELOPMENT Area Description Sagebrush/grass

Acres

RCN

RUNOFF (acre feet)

24.7

55

.004

A B

EXISTING CONDITIONS: RUNOFF VOLUME Catchment

A (2 acres)

Area Description Commercial Open (good) Street Residential

Acres

.89 .38 .36 .37

RCN

95 80 98 87

Runoff (acre feet) .07 .008 .04 .02

TOTAL RUNOFF (acre feet)

C

.1

D E

B (2.8 acres)

Street Commercial Residential

0.4 1.32 1.08

98 95 87

.04 .11 .05

.2 Figure D.7

D-6

C (5.2 acres)

Street Commercial Open (poor) Residential

1 1.9 1.45 0.85

98 95 89 87

.1 .12 .08 .04

D (7 acres)

Street Commercial Open (good) Residential

1.53 0.72 0.48 4.27

98 95 80 87

.16 .06 .01 .2

E (7.7 acres)

Street Commercial Open (good) Residential

0.7 0.7 0.95 5.35

98 95 80 87

.07 .06 .02 .24

MODELING CHANGE

.3

.4

.4

1.4

Drainage Map of Tobin Hill Neighborhood

Runoff Now Retained on Site (acre feet) .38 1.01 0

1.4

.004 Acre Feet

EXISTING

1.4 Acre Feet

.004 AFTER LID

*Total runoff = existing runoff - runoff now retained on site. **This is the minimum amount required. Larger volumes of stormwater (up to 8.3 acre feet) can be retained on site, depending on design.

AFTER LID: FILTRATION The amount of water either filtered or infiltrated.

Filtered or Infiltrated (acre feet) Existing Infiltration Cisterns and Rain Gardens** Swales and Infiltration Areas**

PREDEVELOPMENT

1.70 .38 1.01

Figure D.8 Area

PREDEVELOPMENT

TOTAL (acre feet)

EXISTING

AFTER LID

3.09

**This is the minimum amount required. Larger volumes of stormwater can be filtered or infiltrated, depending on design.

Figure D.9 Area

.004 Acre Feet

Runoff Volumes From a 1.5” Design Storm in the Tobin Hill

FILTERED

Cisterns and Rain Gardens** Swales and Infiltration Areas** Parking Lots w/ Underground Storage**

TOTAL RUNOFF* (acre feet)

RUNOFF

AFTER LID: RUNOFF VOLUME The volume of stormwater retained on site due to the BMPs listed.

3 Acre Feet 1.7 Acre Feet 3 Acre Feet

Filtered Volumes From a 1.5” Design Storm in the Tobin Hill

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

D-7

Calculations for Residential New Development Below are the calculations for the Residential New Development described in Section 7.5. This area is entirely Hydrologic Soil Group D (very poor infiltration rate). There are three catchment areas (See Figure D.13). The total volume of rainfall in a 1.5” storm is 7.63 acre feet.

PREDEVELOPMENT Area Description Oak-aspen—mountain brush Poor - 79, Good - 48, Selected - 66

Acres

RCN

RUNOFF (acre feet)

61

66

0.2

A B C

CONVENTIONAL DEVELOPMENT (1/8 acre - 1/4 acre lots) Catchment

A (3.4 acres)

Area Description Oak-aspen (15%) Street (20%) Residential (65%)

Acres

0.51 0.68 2.21

RCN

66 98 87

Runoff (acre feet) 0.002 0.98 0.77

TOTAL RUNOFF (acre feet) .17 Figure D.10

D-8

B (28.5 acres)

Oak-aspen (15%) Street (20%) Residential (65%)

4.28 5.7 18.5

66 98 87

0.014 0.61 0.83

1.45

C (29.1 acres)

Oak-aspen (15%) Street (20%) Residential (65%)

4.37 5.82 18.9

66 98 87

0.014 0.62 0.84

1.48

MODELING CHANGE

3.1

Drainage Map of Alon Area

CONSERVATION SUBDIVISION (< 1/8 acre lots) Acres

RCN

Runoff (acre feet)

TOTAL RUNOFF (acre feet)

A (3.4 acres)

Oak-aspen (56.8%) Street (15%) Residential (%)

1.93 0.51 0.96

66 98 92

0.006 0.05 0.06

0.1

B (28.5 acres)

Oak-aspen (56.8%) Street (15%) Residential (%)

16.2 4.3 8.0

66 98 92

0.05 0.46 0.54

1.0

C (29.1 acres)

Oak-aspen (56.8%) Street (15%) Residential (%)

16.5 4.4 8.2

66 98 92

0.05 0.47 0.55

1.1

2.2

AFTER LID: RUNOFF VOLUME OF CONSERVATION SUBDIVISION The volume of stormwater retained on site due to the BMPs listed.

Runoff Now Retained on Site (acre feet) Cisterns and Rain Gardens**

.72

TOTAL RUNOFF* (acre feet)

PREDEVELOPMENT

CONVENTIONAL

2

.2 AFTER LID

Swales, Ephemeral Creek and Detention Areas**

1.28 Figure D.11 Alon Area

*Total runoff = conservation subdivision runoff - runoff now retained on site. **This is the minimum amount required. Larger volumes of stormwater (up to 5.52 acre feet) can be retained on site, depending on design.

AFTER LID: FILTRATION The amount of water either filtered or infiltrated.

Existing Infiltration Cisterns and Rain Gardens Swales, Ephemeral Creek and Detention Areas

RUNOFF

Area Description

PREDEVELOPMENT

Filtered or Infiltrated (acre feet) 5.43 .72 1.28

TOTAL (acre feet)

7.4

CONVENTIONAL

AFTER LID

Figure D.12 Alon Area

.2 Acre Feet 3.1 Acre Feet

.2 Acre Feet

Runoff Volumes from a 1.5” Design Storm for the

FILTERED

Catchment

7.4 Acre Feet

4.5 Acre Feet 3 7.4 Acre Feet

Filtered Volumes from a 1.5” Design Storm for the

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

D-9

appendix E: profiles Faculty Profiles Karen Hanna, MA, FASLA, FCELA Professor of Landscape Architecture California State Polytechnic University Pomona 3801 W. Temple Avenue, Pomona, CA 91768 Work Phone: 909.869.4897 Email: kchanna@csupomona.edu Professor Karen Hanna has been involved in higher education for the past twenty years, following fifteen years as a practicing landscape architect. Her first use of Geographic Information Systems (GIS) was in 1972, when she worked on the Smith River Highway Visual Analysis Study for the US Forest Service, a double award winning project. Since then Professor Hanna has advanced her GIS work through a Fulbright Award to the Netherlands, grants with the American Battlefield Protection Program of the National Park Service, and her teaching at the graduate and undergraduate levels. She has written two books on the subject: GIS in Site Design (John Wiley & Sons, 1998) and GIS for Landscape Architects (ESRI Press, 1999). Professor Hanna currently teaches planning and design courses involving GIS at Cal Poly Pomona.

E-1

MODELING CHANGE

Lee-Anne S. Milburn, MLA, Ph.D., ASLA, CELA, LEED-AP

Dr. Susan J. Mulley, MA, MLA, Ph.D.

Associate Professor and Chair, Department of Landscape Architecture California State Polytechnic University Pomona 3801 W. Temple Avenue, Pomona, CA 91768 Work Phone: 909.869.6814 Email: lsmilburn@csupomona.edu

Assistant Professor, Department of Landscape Architecture California State Polytechnic University Pomona 3801 W. Temple Avenue, Pomona, CA 91768 Work Phone: 909.869.2673 Email: sjmulley@csupomona.edu

Lee-Anne Milburn is the chair of the Department of Landscape Architecture. She is the past associate director of the School of Architecture, associate professor and program coordinator for the Landscape Architecture and Planning Program, and Acting Director of the Natural Energies and Advanced Technologies (NEAT) laboratory at the University of Nevada Las Vegas. She was co-editor of Low Impact Development: A Guidebook for North Carolina for which she and her team won the 2010 Marvin Collins Outstanding Planning Award. She is registered landscape architect, and holds a masterâ&#x20AC;&#x2122;s degree in Landscape Architecture, and a Ph.D. in Rural Studies â&#x20AC;&#x201C; Environmental Design and Rural Development from the University of Guelph, Ontario, Canada.

Dr. Mulley has a BSc (Env Sci), a MA in History, a Masters in Landscape Architecture, and a PhD in Rural Studies. Her postdoctoral fellowship was at the University of Guelph where she researched stewardship and conservation attitudes and behaviors of rural landowners of Southern Ontario which informed the creation of a Southern Ontario Agricultural Greenbelt. She is currently an assistant professor of landscape architecture at California State Polytechnic University, Pomona, and teaches in both the graduate and undergraduate programs with a focus on social and environmental justice, environmental planning and design, advanced ecosystem design, community design issues, research methods and historic landscapes. Her research deals with linked human and natural systems issues including design for human health, ecological and social function of urban, rural and wildland interface landscapes, urban agriculture and food security, and participatory action research. She is founding director of a new interdisciplinary research and applied practice center at Cal Poly Pomona, the California Center for Land and Water Stewardship (C-CLAWS).

C-CLAWS enables community and academic collaboration to examine critical issues facing California today, develops new and innovative projects, and encourages interdisciplinary community collaborations and creative methods to examine and solve environmental and social justice issues in the State of California.

LOCATING OPPORTUNITIES FOR LID IN URBAN AREAS

E-2

Student Profiles Jake Aalfs

jaalfs@yahoo.com

ericwhitemyer@gmail.com

Jake graduated from the Masters of Landscape Architecture program at California State Polytechnic University, Pomona in 2011. He received a B.S. In Electrical and Computer Engineering from Cal Poly Pomona and spent many years developing innovative consumer products before returning to graduate school. He returned to graduate school in order to integrate his passion for urban design, transportation, water conservation and the environment. A native of the Los Angeles area, he has seen the explosive population growth and impacts on local ecosystems. He is interested in the appropriate application of technology in order to evaluate impacts, design solutions and educate the public.

Eric graduated from Masters of Landscape Architecture program at California State Polytechnic University, Pomona in 2011. He graduated with a B.S. in Ornamental Horticulture from BYU-Idaho and became more familiar with issues in the realm of landscape maintenance as an account manager for a commercial landscape management company in San Diego, CA. His interest in improving water conservation through proper plant selection and design led him to pursue a degree in Landscape Architecture. He has interned with the City of Chino Planning Department and has been interested in the landscape as it is linked to the environment, to people, and to public health.

Megan Dreger

Sina Yousefi

mmdreger@gmail.com

Megan graduated from the Masters of Landscape Architecture program at California State Polytechnic University, Pomona in 2011. She is interested in our relationship with water in the urban landscape. She earned a B.A. in Art History from the University of Oregon as well as an M.S. in Library Science from the University of North Carolina, Chapel Hill. She worked as an academic librarian for a number of years before deciding to return to school in order to pursue her interests in urban design, water use and water conservation.

E-3

Eric Whitemyer

MODELING CHANGE

syousefi@yahoo.com

Sina received a B.S. in Genetics and a M.S. in Community Development from the University of California, Davis, before graduating from the Masters of Landscape Architecture program at California State Polytechnic University, Pomona in 2011. He was drawn to the program at Cal Poly Pomona by its simultaneous emphasis on ecological functionality and social responsibility. While at Cal Poly Pomona, he has developed a wide range of academic interests, including the study of cultural landscapes and the improvement of habitat connectivity through ecological design. He hopes to gain experience in the design of urban open space as a professional landscape architect. Sina has complemented his studies with travel in Europe, North Africa and Southwest Asia, as well as throughout the United States.

MODELING CHANGE: LOCATING OPPORTUNITIES FOR LID In Urban Areas

This document is an analysis of the Upper San Antonio River Watershed in Texas focusing on Low Impact Development (LID) in the existing urban environment.

It was prepared as part of a year-long comprehensive landscape planning and ecological design studio in the Department of Landscape Architecture at Califonia State Polytechnic University, Pomona. The projectâ&#x20AC;&#x2122;s focus is a conceptual geospatial model developed to locate priority areas for LID implementation.

It also seeks to promote LID and specific Best Management Practices (BMPs) in the San Antonio area.

Jake Aalfs, Megan Dreger, Eric Whitemyer, Sina Yousefi - Spring 2011 Lee-Anne Milburn, Ph.D., MLA, ASLA, CELA, LEED-AP; Susan Mulley, Ph.D., MLA, MA; Karen Hanna, MA, FASLA, FCELA