Low Impact Development Guidebook Prepared for the City of Midwest City
Low Impact Development Guidebook Prepared for the City of Midwest City
Created by Eric Sabin Master of Landscape Architecture Student
Project Committee Sarah Little Ph.D., PLA - Advisor Jason Vogel Ph.D., P.E. - Committee Member Bryce Lowery Ph.D. - Committee Member Special Thanks to: Robert Bettes: Stormwater Manager, City of Midwest City Brady Wright: Stormwater Technician, City of Midwest City My family and classmates for all their support
TABLE OF CONTENTS 1 INTRODUCTION 3 THIS GUIDEBOOK 5 TOOLKIT 7 DOWNSPOUT DISCONNECTION 9 RAINWATER HARVESTING 11 GREEN ROOF 13 PERMEABLE PAVERS 15 PERVIOUS CONCRETE 17 GRAVEL PAVERS 19 BIORETENTION SWALE 21 GRASS BIORETENTION SWALE 23 CURB MANIPULATION 25 BOX PLANTERS 27 DETENTION PONDS 29 RAIN GARDENS 31 RETENTION PONDS 33 CONSTRUCTED WETLANDS 35 CHANGING THE WAY WE SEE LOW IMPACT DEVELOPMENT 36 DIFFERENCES BETWEEN TRADITIONAL AND LOW IMPACT DEVELOPMENT 37 COMMERCIAL VERSUS RESIDENTIAL APPLICATIONS 39 MIDWEST CITY 42 STRATEGY TO DETERMINE LOCATIONS 47 CONCLUSION
April 2018
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LOW IMPACT DEVELOPMENT GUIDEBOOK | ii
LOW IMPACT DEVELOPMENT BENEFITS
INTRODUCTION
The use of LID for urban stormwater solutions has many benefits which include:
WHAT IS LOW IMPACT DEVELOPMENT? Low Impact Development (LID) is an approach to sustainably utilize the landscape to absorb stormwater, and reduce the amount of off site flow. This method of stormwater management is also called green infrastructure because of its use of landscape features instead of traditional stormwater management systems. LID utilizes techniques in an effort to reduce runoff flow from the site that may contribute to flooding, and increased infrastructure costs. The ability for LID to mimic the hydrological patterns that existed before development allow stormwater flow to slow down, as well as have the opportunity for sediment and pollutants to be filtered. LID strategies can be used to support native and designed landscapes through diversion and slowing of the stormwater runoff.
channels and pipes, LID Design tools are WHY SHOULD WE USE LOW IMPACT often best applied close to the source, which reduces runoff volume of during a storm, DEVELOPMENT? and supports landscape vegetation on site. LID can be utilized to supplement, and The use of LID practices can be applied sometimes reduce, the need for traditional to a wide range of land use types, project stormwater management systems usually scales, and budgets. However, they should seen in today’s infrastructure. Because not be installed within a flood plane. the conventional methods of stormwater This guidebook focuses on LID tools that management are to move water off specific look at processes such as water filtration, sites as quickly as possible through use of 1 | LOW IMPACT DEVELOPMENT GUIDEBOOK
infrastructure.
• Shade and insulation of buildings from wide temperature swings, decreasing the • Added environmental and economic energy needed for heating and cooling. benefits from investments, in comparison to traditional stormwater management • Improved air quality as vegetation approaches that literally bury the absorbs gaseous air pollutants and absorbs particulates. investments out of sight.
• Reduction of stormwater quantity and simultaneously increasing water quality, thereby reducing the burden and demand • Effective counteraction of the urban on existing infrastructure. heat island by substituting hard, heat • Beneficial aspects of the natural absorbing materials common in urban environment by providing shade, wind areas, for soils and vegetation creating breaks, and noise barriers. shade, and emitting water vapor. • Cost savings in comparison to traditional TRADITIONAL STORMWATER PRACTICES
Image: GreenWorks, P.C.
Image: City of Monterey, CA.
LOW IMPACT DEVELOPMENT PRACTICES
30% Evapotranspiration
movement, infiltrating and percolation, storage, and evapotranspiration. The guidebook shows many design interventions that can be utilized, and these elements are shown in their principal components. This book shows examples of tools supported by the Environmental Protection Agency (EPA) in its Municipal Separate Storm Sewer System (MS4) requirements. (Environmental Protection Agency, 2014)
• Increased property values with trees and other vegetation, providing private benefits to homeowners, increased property tax revenue, and more livable communities.
38% Evapotranspiration
20% Runoff
55% Runoff 15% Infiltration
Impervious ‘hard’ surfaces such as roofs, roads, large areas of pavement, and asphalt parking lots increase the volume and speed of stormwater runoff. This swift surge of water erodes streambeds, reduces stormwater infiltration, and delivers many pollutants and sediment to downstream waters.
42% Infiltration
Pervious ‘soft” surfaces such as green roofs, rain gardens, grass paver parking lots, and other LID tools that allow infiltration help decrease volume and speed of stormwater runoff. The slowed water infiltrates into the ground, recharges the water table, and filters out pollutants and sediment before they arrive in downstream waters. LOW IMPACT DEVELOPMENT GUIDEBOOK | 2
THIS GUIDEBOOK
VARIATIONS FROM SUGGESTED IMPLEMENTATION Many of the LID techniques found in this guidebook have multiple variations and/or site specific adaptations. These require special understanding and care when implementing these techniques. Within the appropriate site and project context, LID tools can be effectively deployed to achieve the city’s stormwater management goals.
SETTING While LID can be scaled and installed in all types of development that create stormwater runoff, this guidebook focuses on a few potential tools. Midwest City, OK was selected as an example site to demonstrate the process of selecting appropriate LID options. The tools and techniques presented in this guidebook can be applied to existing and new development.
Other context and site related issues that must be considered when applying the LID guidebook suggestions to stormwater management are:
SCOPE OF GUIDEBOOK
• Knowledge of local codes and regulations.
There are three main components of this guidebook, which are:
• Anticipation of high intensity storms that exceed the capacity of the LID guidebook’s designs.
• The introduction which explains the benefit of LID tools. • The LID toolkit in section two which includes a user-friendly catalogue of tools including a description, site selection, installation, and management suggestions regarding each of the LID principles discussed in this booklet. • Geographic information system (GIS) analysis of Midwest City stormwater system, practices, and analysis of potential LID sites.
• Intermittent rainfall requiring vegetation to have supplemental irrigation.
HOW CAN THIS BOOK BE USED • Learn about LID tools that can be used to improve stormwater management. • Encourage the implementation of LID tools. • Educate developers, businesses, and residents about the benefits and
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advantages of LID practices. • Enhance the built environment by the use of ecologically friendly and aesthetically pleasing design solutions that will provide multiple benefits for the community. Image: Used with Permission by Deeproot
• Periods of drought and/or extreme heat requiring adapted and highly tolerant vegetation. Image: Project 180 Downtown OKC by Deeproot
* The LID Guidebook is not intended to address all of the requirements or local, state, regional, and other codes, regulations and standards. This document is intended for educational purposes only. Additional research and analysis will be required for each project, feature and site. Refer to a qualified professional before beginning any project LOW IMPACT DEVELOPMENT GUIDEBOOK | 4
TOOLKIT
TOOLS
Each tool is organized by its context within a site or system, and which action(s) the tool is intended to perform with respect to the stormwater it manages. Before implementing these suggestions it is recommended to consult a professional in design and construction of similar projects. Tools described in this document are those that are appropriate in developed or developing areas in Midwest City and the surrounding region.
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Infiltrate
Convey
Store
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LOW IMPACT DEVELOPMENT DIAGRAM
Reuse Evapotranspiration
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ORIGIN OF STORMWATER RUNOFF WITHIN AN URBAN SETTING
MANAGEMENT METHOD OF STORMWATER RUNOFF
STREETS & PARKING LOTS
FILTER
STRUCTURE RUNOFF
INFILTRATE
CONVEY
LANDSCAPED AREAS
STORE
HARDSCAPE AREAS
REUSE
OTHER SOURCES
EVAPOTRANSPIRATION
ACTIONS TO MANAGE STORMWATER RUNOFF TOOLS
This guidebook is not intended to be all-inclusive, however, it is intended to be a reference for educational purposes to provide general descriptions of LID intervention tools that may be utilized throughout the Oklahoma City metro region.
Low
ACTION
The techniques and suggestions included in this document have been collected, reviewed, and refined from many sources including research of professional organizations, on-site observation and research, as well as data provided by the City of Midwest City and other resources. The EPA has published multiple guides to LID that describe various LID methods that have been developed and implemented.
Category Tool Rooftop Manipulation Downspout Disconnection Rainwater Harvesting Green Roof Permeable Surfaces Permeable Pavers Permeable Concrete Gravel Pavers Conveyance Bioretention Swale Grass Bioretention Swale Curb Cuts Detention and filtration Box Planters Detention Pond Rain Gardens Water Retainment Retention Ponds Constructed Wetlands
Management Method Impact:
SOURCE
SOURCES
TOOL MANAGEMENT BENEFITS
ROOFTOP MANIPULATION
PERMEABLE SURFACES
CONVEYANCE
DETENTION AND FILTRATION
WATER RETAINMENT
Downspout Disconnection
Permeable Pavers
Bioretention Swale
Box Planters
Retention Ponds
Rainwater Harvesting
Permeable Concrete
Green Roof
Gravel Pavers
Grass Bioretention Swale
Detention Pond Rain Gardens
Constructed Wetlands
Curb Cuts
*The low impact development tools described within this guidebook are the most commonly utilized within Oklahoma. Other low impact development tools and techniques can be implemented, but are not described in this guidebook. 5 | LOW IMPACT DEVELOPMENT GUIDEBOOK
LOW IMPACT DEVELOPMENT GUIDEBOOK | 6
DOWNSPOUT DISCONNECTION DESCRIPTION Disconnecting or redirecting one or more downspouts on a building is a simple way to reduce the amount of stormwater runoff entering conventional storm systems. Typically, a downspout directs storm water toward a drain—in many urban environments, the downspout goes directly into the ground, where it moves the water to a gray infrastructure storm system. In some cases, the downspout is open at the base of the building and water flows over impervious surface on its way to the sewer, unable to be absorbed into the ground and picking up pollutants on its way.
Image Right: Used with permission wikimedia commons.
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Water from downspouts can be redirected to permeable surfaces such as lawn or planted area. This not only insures that the water enters the natural groundwater filtration system, but also reduces the demand on the municipal sewage system. Note that downspout disconnection can be part of a larger stormwater plan that might include a rain barrel, rain garden, bioswale, or detention pond.
SITE SELECTION
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Not every site is capable of having disconnected downspouts. You need enough green space on the property to drain water into the ground naturally. Having water cause issues for neighbors, or creating conditions that may be unsafe such as areas where ice may be a hazard is not ideal. It is important to slope the drain to move water away from the building foundation. Standing water near the foundation can seep into concrete slabs, which can cause interior damage. Managing erosion at the end of the downspout is important. Erosion can create unstable conditions. Drain water at least 5 feet from the foundation and property line. Do not disconnect downspouts within 10 feet of a retaining wall. Creating a splash zone where water initially exits the downspout can create an aesthetically pleasing solution to this problem. Gravel or cobble rock can be installed to reduce erosion.
INSTALLATION
MANAGEMENT
Understanding where the water will drain before making drainage changes is essential to prevent foundation damage. Disconnecting includes cutting the downspout, attaching elbows, extensions, and splashblocks to direct the water to flow away from the house, and capping the standpipe, if needed.
Clean gutters and downspouts twice a year, and check that they are properly draining. Inspect area for any erosion that has occurred and address any issues. Inspect for standing water after storm event and ensure that water is draining properly away from foundations.
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RAINWATER HARVESTING
Roof Washer
DESCRIPTION Rain barrels are a type of rainwater harvesting technique for small scale use, and they are often seen at residential sites. Cisterns are utilized when additional stormwater can be captured and utilized. Rainwater harvesting systems collect rainfall running off a roof and store it for future use, such as watering flowers and garden plants when the weather turns dry. Rain water can be better for plants than water pumped from a well or piped through a city water main. It’s not chlorinated, fluoridated, or loaded with dissolved salts. Rainwater is mildly acidic, which helps plants take up important minerals from the soil. Rain barrels are usually about 40-60 gallons. Using rain barrels to temporarily store and reuse rainwater can conserve drinking water by providing an alternative water source for gardens. Rain barrels can also reduce peak summer utility water bills. Collecting water can help protect the quality of our streams and groundwater. The simplest rainwater harvesting setup requires a storage tank, a secure lid, a basket strainer or screen, a roof washer
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First Flush Diverter
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Lid and Screen Overflow
Storage Tank
Sedement from first flush captured Slow Release Valve
Hose Spigot
to deflect large debris, an overflow drain, and a spigot or drain valve. Water flows off of the roof into the gutter, then enters the downspout and pours through the basket strainer attached to the lid of the barrel.
can be directed to the desired location. An overflow device on your water barrel should carry overflow water into additional rain barrels or to a safe distance from your foundation. Although this system Rainwater can be retrieved directly from is highly effective, there are still many rainwater harvesting accessories which can the spigot at the bottom of the barrel, or a improve its gathering, storage, and delivery hose can be attached by which the water capabilities.
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SITE SELECTION
INSTALLATION
MANAGEMENT
Rainwater harvesting systems are installed at downspouts and need a level area for the barrel. If disconnecting the downspout from an underground drainage system, ensure that water from the overflow on the barrel is directed into the underground system to deter any potential area flooding or structural damage.
Make sure you are setting up your container in a level place. If it is not a level location, like a deck or patio surface, use leveling blocks underneath it, such as paving stones, so as to provide a safe spot for draining underneath, and a sturdy base to prevent tipping.
Properly maintained rainwater harvesting systems do not provide breeding sites for mosquitoes or other pests.
Always keep your rain barrels and cisterns covered to keep mosquitoes and larvae from reproducing, and to discourage exploration from curious pets or children.
Clean gutters once a year to keep them clear of debris.
Rainwater harvesting interventions can collect up to 600 gallons of water per 1000 square feet of roof surface for a one inch rain event. Collection of all rainfall on every storm may not be feasible.
Cover the downspout and drainage spots with netting or wire mesh to prevent mosquitoes and debris from getting in your water. Position your rain barrel or cistern so that the overflow valve is facing away from your home’s foundation, a splashblock or additional piping may be required to prevent erosion or foundational damage.
Wash out storage containers and check washers for integrity every spring. Algae buildup may occur, and steps may need to be taken to remove and prevent buildup.
Empty the storage container and disconnect prior to first freeze to prevent damage. Images: Left: Used with permission by D. Mittleider, Center: Used with permission by Jason Vogel Right: Photo by Polymart, permission pending
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GREEN ROOF DESCRIPTION Green Roofs incorporate plants into the design of the roofing system. This method reduces the impact of stormwater runoff by decreasing the impervious surface on the roof. The most common example of rooftop manipulation is green roofs. Green roofs are vegetated layers that sit on top of the conventional waterproofed roof surface. Green roofs can help by retaining a portion of rainfall, and delaying and decreasing the peak runoff rate from a site. Green roofs can also have other beneficial outcomes such as increasing air quality, water quality, and reducing the urban heat island effect, among others. Discharge from downspouts should be routed to another LID practice such as vegetated filter strips, rain gardens or rain barrels for reduction in runoff. Studies have shown that green roofs can retain over 50% of the total precipitation, and reduce runoff.
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Vegetation
Growing
Filter Fabric Drain a ge S tructu Water re proofi n g Me mb
Media
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MANAGEMENT Green roof plants rapidly lose water following irrigation after which water loss rates decline. Early drought is very detrimental to the survival and establishment of green roof plants, particularly those in shorter growing media. Supplemental water is needed during establishment and dry periods to maintain healthy plant growth. Regular watering intervals should be maintained throughout the growing season to ensure plant health.
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SITE SELECTION
INSTALLATION
Before doing any green roof or rooftop manipulation project, the structure of the roof should be verified by a licensed engineer for structure stability. Sites will require access for management. All rooftop manipulation will require maintenance.
Installing green roof systems is very different from installation of landscapes on the ground. Contractors should be trained and experienced before beginning any project. An understanding of weight and growing medium used on green roofs is essential to its success.
If using a tray system, debris should be cleared between and under trays to help prevent stormwater runoff carrying debris downstream. Images: Left: Sandridge Energy Commons, Oklahoma City, OK, Photo by Greenshade Trees. Right: Greenroof in Oklahoma City, Photo by Greenshade Trees
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PERMEABLE PAVERS DESCRIPTION Permeable pavers are designed to allow rain and snow melt to pass through them, thereby reducing runoff from the site and promoting groundwater recharge. Permeable paving materials are alternatives to conventional pavement surfaces such as concrete and asphalt. Permeable pavers may include concrete paving blocks, poured in place concrete grids, and cobblestone pavers.
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Geotextile Fabric
Always follow manufacturer’s installation instructions when installing paver systems. Excavation is required to include subgrade depth that will allow for water storage and infiltration. An open grade subbase reservoir should be installed as a base layer. A secondary reservoir layer is placed atop the first layer with smaller aggregate to help with stability of the paver bedding course and still give adequate void area.
Evapotranspiration and Heat Island Reduction
Overdrain (If needed)
Permeable pavers allow stormwater to infiltrate into underlying soils, promoting pollutant treatment and groundwater recharge
A bedding course may be placed directly below the paver layer to stabilize pavers and create a level course for pavers. Edge treatment should be determined and put into place to ensure pavers do not shift along edge. Image Right: Used with Permission Conservation Design Forum
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**Follow paver manufacturers specifications
SITE SELECTION Permeable pavers can be installed where traditional concrete or asphalt paving normally occurs. Pavers can be installed as roadways, driveways, sidewalks, and pathways. Site selection should always consider the common use of the area. Pavers used in areas with automotive traffic should always be designed by a licensed professional.
Because permeable pavers require excavation, utility locations (call Okie 811) and structure foundations should be considered when planning and installing.
MANAGEMENT Inspect pavers regularly for settlement and broken pavers. Replace broken pavers to maintain structural stability. Pavers may be removed individually if needed. Do not pressure wash pavers, this reduces stability between pavers. Images: Upper Left: Town Center Plaza in Midwest City photo by Eric Sabin. Lower Left: Photo used with per mission by Edmonton. Right: Myriad Gardens in Oklahoma City photo by Eric Sabin
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PERVIOUS CONCRETE DESCRIPTION Pervious concrete has functionality and workability similar to that of regular concrete, however, the mix contains little sand or other fine particles. This creates a significant number of voids, through which water flows relatively unobstructed. Pervious concrete can be used in place of traditional concrete or asphalt and can aid in reducing stormwater infrastructure needed on site. Permeable concrete has many benefits over typical concrete such as recharging groundwater, reducing stormwater infrastructure, reducing urban heat island effect, and maintaining traction better when wet. Pervious concrete pavement is a Portland cement-based, rigid permeable pavement that serves not only as the surface layer of a stormwater management system, but also as a vital part of a water filtration system. Beneath the pervious concrete is the second layer of the stormwater system, the base rock, which is an open-graded, stone layer that is used for temporary stormwater detention. When rain falls, the pervious concrete allows on-site infiltration of stormwater. It also filters sediments and pollution from stormwater deposited on the pavement surface.
rain Underd
Pervious concrete systems replenish the ground water table while at the same time decreasing the amount of runoff and pollution entering streams during large storm events, significantly reducing the potential for downstream flooding events.
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This pavement technology can lower overall project costs and create more efficient land use by eliminating the need for retention ponds, swales, and other storm water management devices. Porous concrete can have an average life of 20 years.
SITE SELECTION
INSTALLATION
MANAGEMENT
Drainage of all unpaved areas should be directed away from the pervious concrete pavement. If areas are allowed to drain onto the pavement, suspended materials may wash into the void structure and reduce the porosity and compromise its service life.
It is strongly recommended to have a Certified Pervious Concrete Craftsman on site during installation.
Visual inspection to ensure pavement is clean of debris and sediment can determine when pavement should be cleaned. If ponding or puddles form, cleaning is The subsurface layers of permeable required. Because this permeable surface concrete is essential for proper function. Pervious concrete should be based according is a filter and filters water as it travels through the concrete layers, routine vacuum Adjacent areas that do drain to to proper design techniques, according sweeping is needed quarterly. Deicing the pavement should be kept seeded to the National Ready Mixed Concrete treatments should not be used. and maintained to minimize sediment Association (NRMCA). In following these deposition which may increase the guidelines, permeable concrete will allow In properly designed and installed frequency of cleanings needed. Landscape adequate drainage for typical storm events. pervious concrete pavements water drains contractors should be advised of the special The subgrade reservoir should allow for through to the underlying draining layers precautions required to avoid debris buildup drainage to the stormwater system through and soil and water will not be retained in on the pavement surface. Additionally, it is its void structure. However, if the pervious underdrain tile or piping. This is especially recommended that informational signage concrete is completely saturated and is important if the subgrade does not allow be posted to identify the pervious pavement adequate infiltration. subjected to freezing, the water has no place as being part of a stormwater management to go. This can result in pressure on the thin Because pervious concrete requires system and that particular care should be cement paste that coats the aggregates and excavation, utility locations (call Okie taken to maintain its peak performance. can cause deterioration of pervious concrete 811) and structure foundations should be installations. Porous pavement is recommended considered when planning and installing. for sites that have low traffic applications Images: Left: Demonstration of permeable concrete by such as areas of parking lots, driveways, Topmix Concrete in Texas Right: Maintaining permeable concrete walkways, and bike paths. by the National Ready Mixed Concrete Association LOW IMPACT DEVELOPMENT GUIDEBOOK | 16
GRAVEL PAVERS DESCRIPTION Gravel pavers utilize a grid like system to add support to gravel infill that creates a structured system that allows for strength and durability to support automobiles. The porous paving allows rainwater to percolate through the pavement’s surface and back into the ground. Because these systems promote natural stormwater infiltration and reduce runoff, they can reduce the need for other stormwater interventions. A series of grids, most commonly rectangular or circular, gives support to the gravel contained within. The grid system allows load pressure to be transferred through the grid to the fill material and onto the base layer.
Gravel Aggregate
Gravel Paver System Grid
INSTALLATION
Geotextile Fabric Proper Edging to Contain Gravel Base Layer Compacted Subgrade
Many gravel paver system manufacturers also have products that allow for grass pavers to be utilized. Grass paver systems have many of the same stormwater properties and often are similar in structural makeup and support. The use of grass paving systems can be utilized to enhance landscapes by giving support to low use access roads or driveways, creating a seamless transition from traditional turf areas. Images: Right: Photo of Geopave system, by Presto, permission pending
Underdrain (If Needed)
**Follow Manufacturers Specifications
Gravel paving systems should be installed according to manufacturers instructions. Preparation of subbase depends on the permeability of underlying soils. The soil may need to be amended to achieve desired infiltration. Subgrade soils with poor permeability may require underdrain. Slope for subgrade should allow for sheet flow, and should be prepared prior to installation of the gravel paver system. Open course road base type aggregate should be installed SITE SELECTION as base to allow for adequate stormwater Gravel paving systems can be utilized in infiltration. Geotextile fabric is used to deter driveways, parking lots, alleyways, fire lanes, the top layer of aggregate from mixing with bike, pedestrian, and equestrian trails. Areas open course gravel base. The gravel paver that experience low speed traffic are optimal system grid should be installed atop the for gravel pavers. Because of the low speeds base and filled with fine angular aggregate gravel is not displaced and the surface to allow adequate void space for infiltration. requires minimum management. Compaction of gravel fill is recommended. It is often recommended to have top or grid show upon completion. Because gravel pavers require
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excavation, utility locations (call Okie 811) and structure foundations should be considered when planning and installing. MANAGEMENT Seasonally check rings in high traffic areas and entrance lanes for lower levels of fill and replace by sweeping gravel from other areas to bring it to level. Additional gravel fill may be required after long use. Potholes will appear only if base course has not been compacted properly before installation. Leaves and other debris should be raked or vacuumed and not allowed to decay. Organic matter will stimulate weed growth and reduce porosity. Porous pavement thaws faster than conventional pavements because it allows water to flow directly through pavement and increases temperature within the gravel layers. Images: Left: National Garden in Washington DC used with permission by Invisible Structures. Right: GravelRings system, used with permission by GreenBlue Urban
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BIORETENTION SWALE Evapotransporation
DESCRIPTION A bioswale is typically a vegetated channel with a parabolic or trapezoidal cross section that can be used in place of a ditch or as an alternative runoff conveyance system to piped storm sewers. Bioswales are categorized by the type of vegetation used. Grassed swales are common and are lined with turfgrass that is mowed. These provide a manicured look, however they demonstrate less effective slowing of stormwater runoff than those with taller plants. Vegetated bioswales can be planted with ornamental grasses, shrubs, perennials, or a combination. Mulch or stone is used to protect soils where plant cover is not present. Larger stone can be used to break up concentrated flow of water, reduce velocity, and increase infiltration and filtration characteristics. Vegetated bioswales’ largest benefit is reducing contaminants from stormwater runoff. The slope of the bioswale allows the water to drain slowly, thus increasing its filtering time. The vegetation in a bioswale filters the stormwater runoff and provides an attractive vegetated area. Vegetation also aids in slowing water and helps prevent erosion. Soil preparation and soil type are
Contaminated Stormwater Runoff Non-Permeable Geotextile Fabric
Sto Ca rmwa ptu t re a er Ru nd noff Filt rati on
Biological Treatment Peak Flow Reduction Detention and Infiltration
rain falls in natural areas The water is absorbed and filtered by soil and plants When
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factors in water infiltration. Vegetated swales help to improve water quality by allowing water to infiltrate from the first flush of stormwater runoff. Because bioswales are long and often run alongside of the road they do not take up large amounts of space and can be used in urban, suburban, or rural settings.
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Underdrain May Be Needed
Non-Permeable Geotextile Fabric
SITE SELECTION
INSTALLATION
MANAGEMENT
For best results, enhance and utilize existing natural drainage swales whenever possible. Existing swales can be enhanced with native plants. The thicker and heavier the grasses, the better the swale can filter out contaminants. Additionally, subgrade drains and amended soils may be needed to facilitate infiltration. Avoid soil compaction during installation. Swales should be sized to convey a 10- year storm. Storm size data can be found through the United States Geological Survey (USGS) Water-Resources Investigations Report 99-4232.
Native plants or well adapted noninvasive exotics with a deep root system are preferred to prevent erosion. They also help slow water to promote water infiltration and minimize maintenance. Soil conditions should be evaluated and amended to allow greater infiltration in order to drain within one day. Shredded hardwood mulch is discouraged due to erosion and mulch restricting drainage ways downstream. An underdrain is recommended if the soil does not allow water to drain within one day.
Once established, bioswales require less maintenance than turfgrass because they need less water and no fertilizer. Supplemental irrigation may be required to help initially with vigorous plant establishment as well as in time of drought. Removal of sediment may be required depending on surrounding conditions to allow swale to retain shape and volume capacity. Vegetation within the swale may require regular management such as removal of debris and occasional pruning.
Because bioretention swales are sunken areas within the landscape, utility locations (call Okie 811) and structure foundations should be considered when planning and installing.
Images: Upper Left: Rob Flemming Park in Spring Texas. Photo by Clark Condon Lower Left: Main Street, Little Rock AR by Eric Sabin Right:Houston Texas Right of way. Photo by Houston Chronicle
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GRASS BIORETENTION SWALE DESCRIPTION Bioretention swales are shallow, vegetated, landscaped depressions with sloped sides. They are designed to capture, treat and infiltrate stormwater runoff as it moves downstream. Swales are less expensive to build but use more space for infiltration and conveyance than planters, and can handle low to moderate flows of runoff. They are often linear in design. They provide an alternative to traditional piped storm sewer systems. Grass swales are often located along sides of roadways. Street runoff is often directed into the swale through curb cuts, or sheet flow. Swale storage opportunities allow small storm volumes to be captured and to infiltrate within the bioswale. Where soils are poorly drained, underdrain systems may be used to help with peak flows and force water stored within the swale through a filter media before continuing in conventional stormwater systems. In most cases, grass swales are fairly shallow, and generally less than 2 feet in depth and do not pose major safety risks even in the event of incursion by people walking or by motor vehicles. The level bottom area of a swale provides space for maintenance crews to stand while working.
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Cont a
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SITE SELECTION
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Detention and Infiltration
Underdrain may be needed
swales, the surface should be protected using a suitable erosion control product Grass bioretention swales may be utilized while seed is being established to avoid as more than simply a tool for conveyance erosion. Sod is acceptable as well, and it may depending on soil type, groundwater be easier and cheaper to install than a seed table, size of area it serves, and soil and erosion control matting combination. imperviousness It is also acceptable to have trees planted The basic design parameters for swale within the swale area. These trees should systems are storage volume, character, tolerate prolonged periods of submersion. permeability rate of its planting soil bed, and Grass Bioretention Swales require the capacity of an underdrain, if needed. The excavation, utility locations (call Okie system must have sufficient storage volume 811) and structure foundations should be above the surface of the bed to contain the considered when planning and installing. design runoff volume without overflow. Permeability of soils should be that water will drain within 48 hours. Deep rooted grass should be utilized. When installing the grass swale, care should be taken to avoid compaction of the drainage area soil. Side slopes greater than 4:1 become difficult to maintain and have increased chance for erosion. For grassed
MANAGEMENT It is important that the storage capacity and functional integrity of the bioswale be maintained through regular monitoring and maintenance of grass. Mowing and/or trimming of vegetation must be performed on a regular schedule based on specific site conditions. Vegetated areas must be inspected annually for erosion and scour. Vegetated areas should also be inspected at least annually for unwanted growth, which should be removed with minimum disruption to the planting soil bed and remaining vegetation. Regular inspection should be conducted to identify erosion, trash debris buildup, or excessive sedimentation. Images: Photos by Eric Sabin
LOW IMPACT DEVELOPMENT GUIDEBOOK | 22
CURB MANIPULATION
Evapotransporation
DESCRIPTION Altering the conveyance of stormwater along streets can have beneficial effects on stormwater quality. Strategies such as curb cuts, or curb removal can be used where water is allowed to flow off the street and into landscaped areas.
Stormwater Runoff Capture and Filtration
Curb cuts convey stormwater into vegetated areas such as roadside swales, parking lot islands, rain gardens, or bioretention areas. They are effective in moving stormwater to landscaped areas. Curb cuts are often used to convey stormwater into another LID practice. Curb cuts do not perform any pretreatment, however, they can minimize erosion by creating diffuse flow into other stormwater control measures.
Peak Flow Reduction Biological Treatment Detention and Infiltration Overflow Drain
Infiltration
Curb cuts can also be installed to redirect stormwater into a grassy field. While this is not directly considered a LID practice, it does reduce stormwater quantity in the receiving water body. Roadside curb cuts usually intercept perpendicular stormwater flow and in many cases, multiple curb cuts are needed to adequately collect and move stormwater. Image: Right: EPA Permission Pending
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d nate off tami n Con ater Ru w m r Sto
SITE SELECTION There are many potential sites for curb manipulation, many of which can easily be retrofitted. Curb manipulation and can be used in residential or commercial land use areas. Roadside curb manipulations are best when used on crested streets that have their highest point in the center of the street and carry stormwater to either side. Prior to design, a site visit during a rainfall event is helpful to note flow patterns that may affect stormwater flows into the site where future curb manipulation is proposed. Locate curb openings at low points and space openings according to stormwater velocity and volume, as well as the capacity of the area behind the curb for detention or infiltration. Curb cuts can have either vertical or angled side slopes. The design intent is to create a smooth transition from the paved surface to full curb height.
Multiple small notches can be used in place of larger openings to allow similar flow. Curb cuts work well with relatively shallow stormwater facilities that do not have steep side slopes that may erode with large amounts of stormwater flow. Rip-rap type rock can be used to slow water down after it has passed through curb cuts as well as reduce erosion of landscaped area. Alternatives to utilizing rock are to allow for sheet flow instead of channelizing the water in through certain areas. This could be done by utilizing parking bumper style alternatives to traditional curbs.
MANAGEMENT Regularly clear curb cuts of debris and sediment that prevent the flow of stormwater into facility (1-2 times a year) and after large storms. Annually inspect the structure and rip rap areas, if applicable, for signs of erosion damage. Repair and reinforce as necessary. Images: Left: Curb Cut in Oklahoma City. Photo by SixTwelve Right: Curb Cut in Plano TX by Eric Sabin
Local Ordinances: It should be noted that city or county codes and ordinances will likely require approval from the city before any ground can be broken for curb cut construction. Because curb manipulation often requires excavation, utility locations (call Okie 811) should be considered when planning and installing.
LOW IMPACT DEVELOPMENT GUIDEBOOK | 24
BOX PLANTERS DESCRIPTION Planter boxes are sometimes referred to as tree boxes. They are a bioretention treatment control measure that is completely contained within an impermeable surrounding. Planter boxes are often placed adjacent to or near buildings or other structures, however, they are most common within sidewalks. Planter boxes are ideal for space limited sites in dense urban areas and as a streetscaping element. They often consist of a mulch layer, bioretention amended soil, observation and cleanout pipes, underdrain pipes, a street tree or other plantings, and a grate cover.
Pervious Filter Fabric
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A planter box consists of three primary components: a chamber, soil media, and plants. The underground storage chamber typically contains a specially formulated soil media and support structure to filter the stormwater. Tree boxes are small biofiltration systems that perform pollutant removal via filtration and absorption. The planter box is specifically designed to connect to the existing stormwater network and help reduce peak runoff flow. Box planters are filled with specially designed soil media that is designed for rapid infiltration. Right: Photo used with permission by GreenBlue Urban
25 | LOW IMPACT DEVELOPMENT GUIDEBOOK
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**Follow system manufacturers specifications
SITE SELECTION
INSTALLATION
MANAGEMENT
The versatility of a planter box is the ability to be installed in dense urban areas as well as residential and suburban areas; regardless of land use. Box planters are designed to capture and treat small drainage areas. Box planters generally capture and treat stormwater runoff from small frequently-occurring storms but are not designed to capture runoff from large storms or extended periods of rainfall.
The system is planted with one or more trees or shrubs and shredded hardwood mulch is applied.
Management consists of annual maintenance of mulch, clearing litter and pruning of trees. Performance efficiency is correlated with proper management.
The site should be associated with an entity that will be responsible for and perform the maintenance required. To encourage maintenance, the site should be easily accessible. The cost of management should be considered when selecting sites for implementation. All installations should have maintenance agreements in place guaranteeing access to and maintenance of the tree box. Because box panters are below grade, utility locations (call Okie 811) and structure foundations should be considered.
The top of the chamber typically has a tree grate that protects the system from vegetation disturbance. This grate is primarily a safety feature, but also serves to filter pollutants from entering the top of the planter box.
Images: Left: Photo used with permission by Greenshade Trees Right: Photo used with permission of the City of Edmondton Below: Photo used with permission by GreenBlue Urban
The majority of the runoff entering the system will occur at an inlet located on the side of the chamber, or from sheet flow from nearby hardscape areas. Stormwater filtrates through the system, absorbs to the media, infiltrates in open systems, or exits to the piping system in closed systems. The ponding area in box planters should be designed with adequate ponding depth to reduce peak runoff and to drain ponded water within 24 hours.
LOW IMPACT DEVELOPMENT GUIDEBOOK | 26
DETENTION PONDS DESCRIPTION Detention ponds are used for flood prevention by temporarily storing stormwater runoff, thereby reducing the peak rate of runoff to a stream or storm sewer. They help to prevent localized flooding and, if designed to do so, provide some water quality benefits and reduce stream bank erosion downstream.
Outlet Structure
Filtration
SITE SELECTION
Detention ponds are often utilized in conventional stormwater management practices. An understanding of the benefits they provide when designed correctly allow for LID benefits to take place also. Welldesigned and maintained pond areas can offer aesthetic, amenity, and ecological benefits to the urban landscape, particularly as part of public open spaces. During a storm, runoff drains from impervious surfaces directly to storm sewers or waterways. Large storm events contribute a significant volume of runoff moving at an increased rate, which raises the potential for erosion and flooding downstream. Detention ponds are basins that receive and hold runoff for release at a predetermined rate, thereby reducing the peak runoff delivered to storm sewers and streams. Detention ponds are designed to release all captured runoff over time and do
Evapotranspiration
Detention Level
Due to their ability to contain a substantial volume of runoff, detention ponds may be suited for placement at a variety of sites, including large sites. Berm
Sedementation Infiltration
not allow for permanent pooling of water.
tool because they do not provide a large number of benefits, however reduction of In addition to increased groundwater peak flow, the ability to reduce sediment, recharge, detention ponds can improve water quality during smaller, more frequent and the increase of the aesthetics of the landscape are a few reasons why we storm events. In addition to removing consider it a viable alternative to gray sediments coming off paved areas, infrastructure. Though these ponds do not pollutants can also be removed through absorption into plantings and evaporation. return areas to their natural hydrological cycle, the alternatives to these ponds make Some do not consider detention ponds use of this tool beneficial. to be viable as a low impact development
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INSTALLATION
MANAGEMENT
Planting native vegetation on the bottom of the basin and slope embankments is recommended. Grass is most commonly planted. Ensure that water will properly drain within 48 hours after the end of storm Location of the basin should be events. This will help reduce mosquito downstream of developed areas on site. When possible, utilizing additional LID tools larvae. to help with stormwater quality and quantity Because detention ponds are sunken have been shown to aid in the function of areas within the landscape, utility locations detention ponds. (call Okie 811) and structure foundations should be considered when planning and installing. Before starting construction of a detention pond check local and state regulations on sizing and other requirements.
Plantings should get supplemental irrigation until established. Ponds should drain completely within 48 hours of a storm event. Drainage structure or pipe should be regularly checked for debris or sediment buildup and cleared as needed. The space around the drainage area and the inlet area should be checked regularly for erosion. There is often no need to the fertilize pond area, as sediment brought into the pond is often sufficient. Images: Left: Rose State College in Midwest City photo by Eric Sabin Right: Detention Pond in Charlotte, NC by Metrolina Landscape
LOW IMPACT DEVELOPMENT GUIDEBOOK | 28
RAIN GARDENS DESCRIPTION A rain garden is a sunken or lowered area within the landscape that allows rainwater to be collected from a roof or paved surface and detains the water, allowing it to soak into the ground. Rain gardens can be a cost effective and aesthetically pleasing way to reduce rainwater runoff from a property. In semiarid regions like Oklahoma, native plants are drought resistant and hearty. They require little to no maintenance once established if planted in correct conditions. Rain gardens also act as a natural filter by removing pollutants within the stormwater runoff. They also can provide food and shelter for butterflies, birds, and other wildlife. They can also provide shade and aesthetic benefits.
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Stormwater Capture and Filtration
Create Habitat
SITE SELECTION
Peak Flow Reduction
Biological Treatment
Rain gardens meet public landscaping requirements as well as provide stormwater benefits. The ability for rain gardens to slow runoff and be utilized as an aesthetic landscape feature make this tool a common intervention at the residential scale. Depending on soil makeup, the infiltration rate may vary. The typical soil in Oklahoma is clay or clay-loam, which does not allow for water to infiltrate as quickly as other soils, however, this may vary between site locations. Because rain gardens are sunken areas within the landscape, utility locations (call Okie 811) and structure foundations should be considered when planning and installing.
INSTALLATION
MANAGEMENT
Determining the design of the rain Fertilizing may not be necessary (except garden is essential to prevent standing water maybe during plant establishment) because from being present after 24 hours of rainfall. runoff of other nutrients should contain nutrients to sustain vegetation. Plant selection will minimize
maintenance and reduce additional water If large amounts of sediment are needs. Plant information may be found deposited within the rain garden, it should through regional extension sources. be removed to maintain the rain gardens Shredded hardwood mulch can be added capture volume. Weeding may be required. to help reduce evapotranspiration rate. Irrigation may be needed in the first growing Images: Rain Garden by Watershed Texas season to help plants become established. LOW IMPACT DEVELOPMENT GUIDEBOOK | 30
RETENTION PONDS DESCRIPTION Retention ponds are ponds or pools designed with additional storage capacity to attenuate surface runoff during rainfall events. They consist of a permanent pond area with landscaped banks and surroundings to provide additional storage capacity during rainfall events. They are created by using an existing natural depression, by excavating a new depression, or by constructing embankments. Existing natural water bodies should not be used due to the risk that pollution events and poorer water quality might disturb/damage the natural ecology of the system. Retention ponds can provide both stormwater attenuation and water quality treatment by providing additional storage capacity to retain runoff and release this at a controlled rate. Ponds can be designed to control runoff from all storms by storing surface drainage and releasing it slowly once the risk of flooding has passed. Runoff from each rain event is detained and treated in the pond. The retention time and calm water promote pollutant removal through sedimentation, while aquatic vegetation and biological uptake mechanisms offer additional treatment. Retention ponds have good capacity to remove urban pollutants and improve the quality of surface runoff. Retention ponds are often utilized in conventional stormwater management
Limit of Detention Area Evapotranspiration
Outlet Structure
Outlet Elevation Level of Permanent Pool
SITE SELECTION Retention Ponds should contain the following zones: • A permanent pool which will remain wet throughout the year and is the main treatment zone Sedmentation
practices. An understanding of the benefits they provide when designed correctly allow for LID benefits to take place. Welldesigned and maintained ponds can offer aesthetic, amenity, and ecological benefits to the urban landscape, particularly as part of public open spaces. They are designed to support emergent and submerged aquatic vegetation along their shoreline. They can be effectively incorporated into parks through good landscape design.
• A temporary storage volume for flood attenuation, created through landscaped banks to the permanent pool
of the permanent pool to support wetland planting, providing ecology, amenity and safety benefits. • A sediment forebay or other form of upstream pre-treatment system (i.e. as part of an upstream management train of sustainable drainage components)
MANAGEMENT Debris should be collected and disposed of on a frequent basis. Dredging of ponds may be required with sediment buildup. Images: Left: Tinker Bicentennial Park, Photo by Eric Sabin Right: Retention Pond in Yukon, OK, Photo by Eric Sabin
Additional pond design features should include an emergency spillway for safe overflow when storage capacity is exceeded, • A shallow zone or aquatic bench maintenance access, a safety bench, and which is a shallow area along the edge appropriate landscaping.
Image Right: Used with permission by Paroramio.
31 | LOW IMPACT DEVELOPMENT GUIDEBOOK
LOW IMPACT DEVELOPMENT GUIDEBOOK | 32
CONSTRUCTED WETLANDS DESCRIPTION Constructed wetlands are treatment systems that use natural processes involving wetland vegetation, soils, and their associated microbial assemblages to improve water quality. If planned and maintained properly, treatment wetlands can provide wastewater treatment and also promote water reuse, wildlife habitat, and public use benefits. Potentially harmful environmental impacts, such as the alteration of natural hydrology, introduction of invasive species and the disruption of natural plant and animal communities can be avoided by following proper planning, design, construction and operating techniques. Image Right: Used with permission by Panoramio.
Wildlife Habitat Slow flowing Water Depth
Natural Plantings
Extended Biological Treatment
Non-Evasive Plantings Sedementation
Evapotranspiration
SITE SELECTION Construct treatment wetlands on uplands and outside floodplains in order to avoid damage to natural wetlands and other aquatic resources.
INSTALLATION
MANAGEMENT
Design for minimal maintenance. Use a gradual slope to move water. Design the wetland with the landscape, not against it. Integrate the design with the Consider the role of treatment wetlands natural topography of the site. Avoid overwithin the watershed such as potential water engineering the design with rectangular quality impacts, surrounding land uses and basins, rigid structures and channels, and regular morphology. Mimic natural systems. local wildlife corridors relations. Give the system time. Wetlands do not Examine site-specific factors, such necessarily become functional overnight and as soil suitability, hydrology, vegetation, several years may pass before performance and presence of endangered species or reaches optimal levels. Strategies that critical habitat, when determining an appropriate location for the project in order try to short-circuit the process of system development or to over manage often fail. to avoid unintended consequences, such as destruction of habitats. Do not design in a Design the system for function, not form. floodplain. For instance, if initial plantings fail, but the overall function of the wetland, based on Use water control measures that will initial objectives, is intact, then the system allow easy response to changes in water has not failed. quantity, quality, depth, and flow.
Wetlands must be managed if they are to perform well. Water level management is the key to determining the success of vegetation. While wetland plants can tolerate temporary changes in water depth, care should be taken not to exceed the tolerance limits of desired species for extended periods of time. Ensure that water reaches all parts of the wetland area to establish and maintain healthy plant growth. Inspect and clean inlet and outlet structures yearly, if installed. Removal of sediment accumulation may be needed to maintain desired water level. Images: Left: Used with permission by Jason Vogel Center Right: Photo used with permission from The Gathering Place in Tulsa, OK
Create and follow a long-term management plan that includes regular inspections, monitoring and maintenance. 33 | LOW IMPACT DEVELOPMENT GUIDEBOOK
LOW IMPACT DEVELOPMENT GUIDEBOOK | 34
CHANGING THE WAY WE SEE LOW IMPACT DEVELOPMENT
DIFFERENCES BETWEEN TRADITIONAL AND LOW IMPACT DEVELOPMENT
Longevity of impervious surfaces such as concrete and asphalt have changed the way we as a society live. We have been able to make huge strides in travel innovations which has increased the demand for more paved parking spaces, more lanes on the highway, and more convenience in everything we do from drive through grocery pickup and banking, to fast food restaurants and dry-cleaning pickup. We are driven by convenience. With this convenience, we have sacrificed green space and techniques that were the normal practice before the automobile. Common practice is no longer ditches and streams to carry stormwater, instead we have put gray infrastructure into place, placing pipes and drains at many locations. We take down trees and pave over fields, so we can keep our desire for convenience met. Conventional stormwater techniques are simple; get the water that falls on a specific site off the site as quickly as possible. Within my research in this section I look at many different variables, such as impervious surfaces, location of existing stormwater
In planning and landscape architecture, we often focus on what will benefit the
most people, or where interventions that we propose will have the greatest impact on the largest number of people. We often look at the cost-benefit analysis to determine our decisions. What if we looked beyond what the final number of a project would be, and instead looked at what would best help the environment. This study focuses on potential Midwest City stormwater tool implementations and how stormwater can be improved.
TRADITIONAL STORMWATER PRACTICES
These suggestions are in no way meant to limit where any of the tools may be implemented. The LID tools presented in the previous section may be installed at locations other than those suggested in
35 | LOW IMPACT DEVELOPMENT GUIDEBOOK
this section. The purpose of this section is to demonstrate the need for LID tool implementation throughout Midwest City, and where those implementations could have an impact on water quality benefits that could help bring the hydrological cycle closer to its natural state.
Image below: Used with Permission by Integration and Application Network
LOW IMPACT DEVELOPMENT PRACTICES
30% Evapotranspiration
outfalls, inlets, and waterways.
Most residents do not even think of stormwater or stormwater infrastructure except for when it is a problem, such as a clogged drain making us have to park yet a few spots farther away from a store entrance, or accidentally dropping our keys down the storm drain.
38% Evapotranspiration
20% Runoff
55% Runoff 15% Infiltration
Impervious ‘hard’ surfaces such as roofs, roads, large areas of pavement, and asphalt parking lots increase the volume and speed of stormwater runoff. This swift surge of water erodes streambeds, reduces stormwater infiltration, and delivers many pollutants and sediment to downstream waters.
42% Infiltration
Pervious ‘soft” surfaces such as green roofs, rain gardens, grass paver parking lots, and other LID tools that allow infiltration help decrease volume and speed of stormwater runoff. The slowed water infiltrates into the ground, recharges the water table, and filters out pollutants and sediment before they arrive in downstream waters. LOW IMPACT DEVELOPMENT GUIDEBOOK | 36
COMMERCIAL VERSUS RESIDENTIAL APPLICATIONS
RESIDENTIAL APPLICATIONS Residential sites lend themselves to the utilization of certain LID tools more than others, such as but not limited to: • Downspout Disconnection • Rainwater Harvesting • Permeable Pavers • Curb Manipulation • Rain Gardens
The LID tools presented in this guidebook can be implemented in many different settings, however, some are more favorable to be implemented within certain land uses. COMMERCIAL APPLICATIONS Commercial, institutional and industrial settings such as retail centers and schools lend themselves to utilization of certain LID tools more than others, such as but not limited to: • Green Roofs • Permeable Pavers • Pervious Concrete • Gravel Pavers • Bioretention Swale • Grass Bioretention Swale • Curb Manipulation • Box Planters • Detention Ponds • Retention Ponds • Constructed Wetlands This does not exclude other LID tools and practices or change the effectiveness of any LID tool implementation within residential applications. The utilization of these above practices is more commonly found in commercial, institutional and industrial situations more often than in residential type settings. 37 | LOW IMPACT DEVELOPMENT GUIDEBOOK
This does not exclude other LID tools and practices or change the effectiveness of any LID tool implementation within residential applications. The tools listed above are often thought of as LID practices that can be implemented more easily by homeowners or contractors at residential sites.
Rainwater Harvesting Downspout Disconnection
Rain Garden Permeable Pavers
All LID tools have the ability to provide stormwater benefits. The ability to reduce the impact development has had on a site and the effort to return closer to the natural hydrological cycle is the reason LID tools are recommended.
Box Planters Curb Cuts
Permeable Pavers
Pervious Concrete
Curb Removal
LOW IMPACT DEVELOPMENT GUIDEBOOK | 38
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Images: Below: Basemap used with permission from Esri, DigitalGlobe, GeoEye, Earthstar Geographics, ONES/Airbus DS, EDSA, USGS, AeroGRID, IGN, and the GIS User Community
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The City of Midwest City has a large amount of impervious surfaces, a few of the larger areas include Heritage Park Mall, Rose State College, Hudiberg Auto Group,
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The entire city drains into the North Canadian River Watershed. There are multiple creeks and waterways within the
Town Center Plaza, Home Depot, Walmart, and Sam’s Club. These surfaces contribute to a large amount of stormwater runoff. There are many opportunities to implement LID tools throughout the city, through new development or redevelopment projects.
Silv
Midwest City, Oklahoma is part of the Oklahoma City metropolitan area. The city was established in 1943 and has quickly grown to be home to over 50,000 residents. The city covers over 24 square miles.
city. Kulman Creek flows in the southwest corner, joining with Crutcho Creek shortly after leaving the city limits. Soldier Creek flows through the middle of the city and meets up with Crutcho Creek in the north. Silver Creek and Choctaw Creek are in the north and east of the city.
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Midwest City is largely residential as shown in the map above. There are areas of commercial development as well as industrial scattered throughout the city. The residential development largely
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dominates the city, due to the large number city’s golf course, regional park, and trail of employees of Tinker Air Force Base living systems. There are multiple commercial within the city. corridors that are found in the city. These areas are good sites for larger scale LID The city has developed a large parkway system along Soldier Creek that includes the interventions.
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0 Esri, DigitalGlobe, 0.5 1GeoEye, Earthstar Geographics, 2 Miles Source: CNES/Airbus DS, USDA, USGS, AeroGRID,
LOW IMPACT DEVELOPMENT GUIDEBOOK | 40
This study of the stormwater system of Midwest City compares many factors that influence stormwater quality. The factors presented within the following pages show
Potential LID interventions can take place almost anywhere. There are considerations to take when identifying potential LID tool implementation. These
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interventions can be implemented at other locations besides those identified, and should be kept in consideration when determining potential sites for LID tools. It is highly recommended to not place inground LID practices within the flood plain. The map below shows the waterways within Midwest City and the 100-year floodplain associated with these waterways.
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Peter Chawaga, Water Online November 28, 2016
multiple techniques to determine LID tool intervention locations. Other factors might need to be considered before installing LID tools.
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“That is why many communities are turning to green infrastructure for stormwater management, like rain gardens, porous pavement, and green roofs. It can play a vital role in meeting stringent stormwater regulations, managing volatile water supplies in the face of longterm drought, and creating more sustainable places to live.”
STRATEGY TO DETERMINE LOCATIONS
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“Conventional stormwater infrastructure simply moves runoff away from densely populated areas, oftentimes overwhelming sewer systems and contaminating local waterways in the process. Impervious concrete carries stormwater to streams and lakes, picking up urban pollutants along the way. This infrastructure also keeps the water from entering groundwater supplies, exacerbating drought issues.
2 Miles
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Impervious surfaces are directly linked to inlets. The more impervious surface
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development. There are many potential LID possibilities in these areas because stormwater is handled so traditionally.
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you have, the more inlets are required to manage stormwater. We see an increase of impervious surfaces along major roads throughout the city due to commercial
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IMPERVIOUS SURFACE STUDY
After determining the areas with a greater concentration of buffer zones, locations within public property close to these zones were located and deemed best areas for interventions.
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2 Miles
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These layers of data were analyzed by creating a buffer around each point, followed by placing each layer atop of one another and performing an analysis of determining how many buffer areas cover each area. The areas with more buffer zones covering them determined could have more LID tool benefits if they were implemented.
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The studies of locations of specific stormwater structures, namely pond outlets, stormwater inlets, and impervious surfaces as well as the overarching understanding that in-ground LID tools are not recommended within the floodplain are compiled within this section.
ON SO
S WESTMINSTER RD
S POST RD
S DOUGLAS BLVD
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ree
S ANDERSON RD
N POST RD
N DOUGLAS BLVD
N AIR DEPOT BLVD
N MIDWEST BLVD S MIDWEST BLVD
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S AIR DEPOT BLVD
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NE 10TH ST
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C Low : ~15% Impervious per 1/2 awMile
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N SOONER RD
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High : ~50% Impervious per 1/2 Mile
tary
Value
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Impervious Surface Density
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The ability to understand what currently is happening when storm events take place allows for an understanding of how to improve the stormwater system. Utilizing Geographic Information Systems (GIS) data of Midwest City, this study provided insight into where potential locations for LID tool interventions could take place and have a great benefit.
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MWC City Limits
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Legend
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UTILIZING GEOGRAPHIC INFORMATION SYSTEMS
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This study is one way to determine potential sites, and does by no way limit LID tool interventions to be placed within these zones, nor does it lower the need to have sites evaluated by a knowledgeable professional LOW IMPACT DEVELOPMENT GUIDEBOOK | 44
STORMWATER INLET STUDY
Midwest City limits. The recently redeveloped original mile and car A stormwater inlet is a drain in which dealerships, as well as Rose State College’s stormwater is moved towards and allows the parking lots all contribute to this increased water to enter the underground pipe. These density. Other areas of high density inlets can be in areas such as parking lots, or curb are City Hall and surrounding areas. and gutter situations. Utilizing inlet data study and comparing this There are over 1,700 inlets within
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SE 29TH ST
S WESTMINSTER RD
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ry
S POST RD
S DOUGLAS BLVD
Soldier Cre
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6
0.5
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e
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7 N ANDERSON RD
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Ch
ribu kT
o Ch
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S ANDERSON RD
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Ku lh
S MIDWEST BLVD
SE 15TH ST
m
1
2 Miles
k
Mid-Del Technology Center, and locations surrounding the Reed Conference Center. Ponds are most commonly used for These listed locations are a few larger areas, flood reduction. Pond outlets may include amongst many potential sites for improving retention ponds, detention ponds, or stormwater runoff before it arrives at the When viewing concentrated points not wetland outlets. The study utilized this data pond, which could benefit stormwater to determine where potential improvements located in the floodplain there are multiple quality. of existing LID practices could take place. It clusters that are noticeable, namely Midwest Regional Medical Center and City Hall, 45 | LOW IMPACT DEVELOPMENT GUIDEBOOK
N POST RD
N DOUGLAS BLVD
N MIDWEST BLVD
N AIR DEPOT BLVD
Crutc ho
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tary
ut
was also noted that these current outlets are aiding in peak runoff reduction by utilizing a system in which water is being detained and thus reducing peak runoff flow.
Streets
Inlets
2 Miles
k
POND OUTLET STUDY
North
Cre aw Ch
oct
N ANDERSON RD
N SOONER RD
S WESTMINSTER RD 1
NE 10TH ST
S AIR DEPOT BLVD
ee Cr
0.5
Waterways
NE 23RD ST
S SOONER RD
an
0
6
MWC City Limits
100 Year Floodplain
S ANDERSON RD
N POST RD S POST RD
S DOUGLAS BLVD
ry
NE 36TH ST
k
m
SE 29TH ST
ek Tr ib
Legend
e Cre
S MIDWEST BLVD
Soldier Cre
e Cre
r
ier Sold
S AIR DEPOT BLVD
C
a
S SOONER RD
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ta hoc
ut
Ku lh
ek
N DOUGLAS BLVD
N MIDWEST BLVD
N AIR DEPOT BLVD
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E RENO AVE
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SE 15TH ST
ry 7
ta ribu T k
ve Ri
reek
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100 Year Floodplain
tary
Pond Outlets
NE 23RD ST
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Waterways
reek
North
MWC City Limits
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dataset to the impervious surfaces showed where impervious surface concentration was high and allowed for a better understanding of what inlets could potentially be diverted to LID tool techniques to allow less stormwater to directly enter the storm sewer system during a storm event.
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LOW IMPACT DEVELOPMENT GUIDEBOOK | 46
CONCLUSION Stormwater runoff impacts the environment. The potential benefits of low impact development tools are to reduce peak runoff and pollution, benefit plant and animal life by helping create habitat, reduce the urban heat island, encourage evapotranspiration, and infiltration. These are a few reasons why LID is beneficial
over current industry standards when considering stormwater solutions. The ability to move closer to the natural hydrological cycle is essential to make these suggestions have an impactful change. Utilizing the tools suggested in this guidebook are one way of making a small impact on our most valuable resource, water. The ability for simple changes to be made that have such a broad impact cannot be overlooked.
47 | LOW IMPACT DEVELOPMENT GUIDEBOOK
The studies given of potential locations for LID interventions utilizing GIS analysis show that there are many potential sites to implement suggested tools. The ability to go beyond this analysis and find other locations for these interventions is encouraged and will allow for an even greater impact. The studies shown give great insight into just how many factors can influence stormwater. Below: Photo used with permission by Reed Coffman