N b assignment2

Source: NYC Environmental Protection

Urban Greening

Flooding + Hydrology: Best Practices and Benefits

Assignment 2 - Question 2 Natural + Built Envrironments: Spring 14 Josh Ellsworth, Jared Pinkus, Cameron Savois, Sam Starr

Contents

Introduction Benefits

flooding and river conditions ecology flood regulation

Best Management Practices

retention systems

detention ponds

permeable pavement greenstreets bioswales

rain gardens

stormwater canals/parks

constructed wetlands

Conclusion

Introduction

source: sitephocus.com As our cities grow and continue the recent trend in the United State of emigration back the urban core, many issue will come to the forefront. Infrastructure will need to reinvent itself and adapt to the changes of the urban environment. As more and more land is developed upon, planners and designers need to create and implement innovative ways to counteract the issues that present itself with growing metropolitan areas. With the continuous development and increasing impervious surfaces, stormwater mitigation and flooding downstream are specific issues that arise in the urban core. An awareness of stormwater and how cities manage and regulate it has become a polarizing topic for designers and city officials. Cities like Portland, Seattle, and New York City have directed investment into green infrastructure and have implemented their plans effectively. These cities have used various approaches to maintain and conserve natural areas while handling storm water in tactical and bucolic ways.

This report will focus on the issue of flooding and the benefits of remediation, ecological, and regulation. These benefits will set the stage for the implementation strategies and best management practices for urban greening that can provide solutions to flooding and stormwater in the urban setting.

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Benefits

Flooding + River Conditions

Source: intechopen.com Individuals who study hydrology acknowledge that rivers are very complex natural structures, whose evolution has helped shaped the surrounding areas. Naturally a river will create bends and meanders as water from the river moves along a downward slope. The deepest part of a river channel is on the outside of each bend, this is where the speed and volume of water is greatest. Sediment is picked up from the outside of the river bend where water flow is the greatest. The sediment is then dropped down stream on the inside bend where the flow is slower. The distribution of sediment from one area of the river to another helps maintain the overall condition of the river (Indiana). N. LeRoy Poff, et al., (1997) explain that river bars and riffle-pools are formed and even maintained by this distribution of sediment (Poff et al., 1997, p. 772). Furthermore, the natural occurrence of flooding allows for the river sediment to displace along the floodplain. Due to the nutrients of these sediments, floodplains tend to be very fertile areas allowing for a vast amount of trees and shrubs to grow (Craft and Casey, 2000, p. 326-331). The natural systems involved in a floodplain promotes an efficient way of reducing the potential impacts of flooding to the surrounding areas.

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Although, erosion and redistribution of sediment

Restoration of natural river characteristics is a

is a natural occurrence, these transformations

very important if not crucial aspect of reducing

are the result of the complex evolution of river

the speed of the water, amount of erosion and

systems. By reengineering rivers from their

peak flows. By implementing a restoration

natural state to those more appropriate for human

project, the natural conditions will significantly

use, we have created conditions that effect the

reduce the likelihood of a damaging flood.

speed and quantity of water flow. Changing the morphology on one section of a river, has a great

The use of river restoration projects can be

impact on the areas surrounding it down stream.

beneficial for the health of the river and also

David Rosgen (1997) presents evidence that

a better way to limit the potential hazards of

development of and around a river relates to

a flood, as compared to manmade structures.

accelerated erosion of the river banks, creating

Previously mentioned, rivers are complex

incised streams. As erosion occurs, the degree

systems and therefore restoring a section

of incision, (lowest height of the bank compared

of a river by creating natural features is also

to the highest) increases, meaning that it takes

very complex. Kondolf et al. (2001) and Smith

a larger magnitude flood to spill over into what

and Prestgaard (2005) explain that in certain

once was the flood plain. Also as the degree

instances, restoration efforts including creating

of incision increases, there is a greater risk

meanders have failed either by being washed

of even more erosion (Rosgen, 1997, p. 1-3).

away or if in fact they do remain stable they may

Wolman, (1967) and Schueler, (1998) explain

not provide any benefit to the natural systems

that by modifying an urban river, the amount of

that surround a river (as cited in Kondolf, 2006,

sediment, runoff volume and peak discharge

p.1). Erskine et al., (2007) argues that vegetation

are increased. Trimble (1997) and Rizzuto et

also needs to be examined when dealing with

al., (2000) argue that these increases result in

restoration projects. Vegetation is not only

more intense erosion and increased channel size

beneficial in the floodplain but also helps to

( as cited in Hession et al., 2003, p.147). It is

limit erosion along the river bank (Eskrine et al.,

evident from these arguments that by changing

2007, p. 88-89). Restoring rivers to their natural

the morphology of a river to fit our needs, we

conditions will help alleviate potential hazards

are affecting not just a specific section of a river

from floods while also improve the health of the

but also affecting a larger area downstream.

river system

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Benefits

Ecology

source: vp-lee_hmbg Ecological Benefits of Streams

conservation buffers especially in the urban/rural

According to Karr (1996), river health is

interface, found that preserving critical freshwater

determined by the intersection of its ecological

systems decreased nutrient loading, decreased

vitality and benefits derived thereof and the

erosion of nutritious topsoil, and increased

human values placed upon rivers. The ecological

biodiversity. By absorbing, filtering, and breaking

Criteria of a healthy stream include sustainability,

down harmful chemicals and pesticides found in

resilience to stress, the capacity to support and

runoff, wetland buffers mitigate eutrophic cycle.

maintain a balanced, integrated, adaptive biologic system having the full range of elements and

Freshwater systems provide stunning amounts of

processes expected in the natural habitat of a

biodiversity and organisms that have important

region (p.10).

ecological and economic functions. These organisms are deeply entrenched in various

Rivers, watersheds, and wetlands provide

food webs that support life outside of their

extensive ecological benefits that have economic

ecosystems. The presence of certain species

considerations for urban planning. Lovewell

or a level of biodiversity can directly indicate

and Sullivan (2005), through their studies of

the health of the freshwater system. According

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to Dr. Ruth Patrick, who founded the “Patrick

helping to curb erosion, improve water quality by

Principle”, a diversity of species holds the key to

exposing water to air, sunlight, vegetation, and

understanding the environmental problems that

soil to help neutralize pollutants, and recreate

affect our world (www.freshwater-science.org).

aquatic habitats and riparian corridors for fish, birds, and vegetation. In terms of economic

Stream Daylight/Deculverting

benefits, daylighting streams can cost less or

Throughout the urbanized world, streams have

marginally more than replacing culverts while

often been culverted or buried underground

allowing for easy monitoring, increase property

to make way for development whether it be

values up to 20%, benefit businesses by creating

roads, cities, or large scale farming (Pinkham,

a new amenity, and create jobs in stream and

2000). Culverted streams have been considered

park construction and maintenance. In terms

problematic because they “exhibit low ecological

of social benefits, daylighting can provide

integrity due to reduced light levels, habitat

new recreational opportunities ranging from

modifications, geomorphological change and

watersports to new multi-use paths, serve as an

increased diffuse and point source pollution,

outside laboratory for schools, beautify parks and

especially misconnections into surface water

neighborhoods, build civic pride, and reconnect

sewers” (Wild, Bernet, Westling & Lemner

people to nature (Pinkham, 2000; Wild et. al.,

2009, p. 412). The process of daylighting or

2009).

deculverting a stream involves bringing a stream back to the surface and restoring the natural

Daylighting streams seeks to integrate

features such as beds and banks.

watersheds back into the fold of the urban

The current literature in the field suggests that

landscape by providing new wildlife habitat,

there are numerous environmental, economic,

provide crucial ecosystem services with flood

and social benefits to daylighting streams. In

control and bioremediation, as well as social and

terms of environmental benefits, daylighting

economic benefits to neighborhoods, businesses,

streams can relieve choke points and flooding

citizens and visitors.

problems caused by under-capacity culverts, increase hydraulic capacity over that of a culvert

Constructed Wetlands

by recreating the floodplain, reduce runoff

Constructed wetlands are “shallow marsh

velocities by reintroducing meanders therefore

systems planed with emergent vegetation

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source: Kongjian Yu that are designed to treat storm water runoff�

In terms of water quality improvement,

which mimic natural wetlands and require only

constructed wetlands use natural processes such

moderate maintenance to function (Department

as biological uptake, microbial decomposition,

of Environmental Protection, 2006). Constructed

settling, natural filtration, volatilization, and

wetlands are designed to carry out two distinct

adsorption to improve water quality. They are

purposes, water quantity control and water quality

extremely effective at removing common storm

improvement. While these are the two direct

water pollutants such as “suspended solids,

purposes, they provide indirect aesthetic and

heavy metals, total phosphorus, total nitrogen,

wildlife habitat benefits.

toxic organics, and petroleum products.

In terms of water quantity control, constructed

As a product that mimics natural processes,

wetlands alleviate peak storm water runoff rates

constructed wetlands is a cost effective tool to

and lower runoff volumes. Constructed wetlands

mitigate the flooding potential of a high intensity

have the ability to retain storm water and act as

weather event and provide bioremediation

a buffer for stream flow especially during severe

services to runoff which greatly improves water

weather events.

quality. (Department of Environmental Protection, 2006; Sample & Wang, 2013; Vymazal, 2010).

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Benefits

Flood Regulation

source: http://papers.risingsea.net Undeniably, floods, and regulating floodplains

of upmost importance that local governments of

play a large role in urban hydrologic systems. In

urban areas understand exactly how floods and

fact, “Global statistics show that floods are the

floodplains work, and what their options are for

most frequently recorded destructive events,

avoiding disaster in a way that doesn’t adversely

accounting for about 30 percent of the world’s

impact the natural hydrologic cycle.

disasters each year” (Types of Disasters and Their Consequences), and it’s becoming more

This should not be confused with the floodway,

pronounced in urban areas. The United Nations

which is a more specific area and known as

Office for Disaster Risk Reduction reports that,

“the channel of a river or other watercourse and

“urban floods will represent the lion’s share of

theadjacent land areas that must be reserved

total flood impact because of infrastructure,

in order to discharge the base flood without

institutions and processes that are not yet up to

cumulatively increasing the water surface

the task ahead” (Singh, 2012). This statistical

elevation more than a designated height”

outlook becomes more alarming when one

(Department of Conservation and Recreation,

considers that over half of the world lives in urban

2013). In times of natural disaster, the floodway

areas, and that number is expected to rise to 70

is the most dangerous part of the floodplain.

percent by 2050 (Singh, 2012). Therefore, it is

Typically, the floodway is the most heavily

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regulated portion of the floodplain because of the

through weirs. However drainage is a very

potential danger it may cause.

difficult aspect of floodplain management in an urban system since urbanization has a significant

One of the two ways that cities can better

effect on the impact of drainage flows on the

manage their floodways is through structural

environment: for example, where rain falls on

measures. The most commonly used structural

impermeable artificial surfaces and is drained by

measures are: Conveyance, Flood Storage,

a system of pipes, it passes much more rapidly

and Drainage systems. As far as conveyance is

to the receiving water body than it would have

concerned, its to provide a route to take potential

done when the catchment was in a natural state.

floodwater away from areas at risk. Traditionally

This causes a more rapid build-up of flows and

this has been seen as a way to remove the

higher peaks, increasing the risk of flooding (and

problem of flooding from the urban environment

pollution) in the receiving water (Jha Bloch and

(Jha, Bloch, and Lamond, 2012). This can be

Lamond, 2012). Moreover, cities in developing

achieved in a number of ways, but is most often

countries struggle with separating wastewater

done through increasing height of the banks, and

and storm water, which quickly evolves into a

the creation of relief channels that redirect water

public health concern.

at peak flow time (Jha Bloch and Lamond, 2012).

Non-structural approaches to integrated flood The second method, flood storage, is also

risk management are just as crucial as structural

paramount to urban hydrological regulation since

approaches, and can also be completed in a

it can aid greatly in attenuating flood flow in a

number of ways. However, the literature will

natural way. Since Storage occurs naturally in

only focus on the impact of zoning on floodplain

a catchment, for example within the floodplain

regulation, as it is the most directly relatable

or, more locally, in ponds, it is typically one of

management tool to the study at hand. As noted

the most economical and environmentally safe

in the Cities and Flooding Guidebook, zoning

means for controlling the floodplain by redirecting

plans are essential to reducing liability, and risk

to a reservoir, and then controlling the outflow of

to people and property. The guidebook further

the redirected water. (Jha Bloch and Lamond,

states that cities can, and should determine land

2012). Drainage is the third structural method,

use in floodplain areas based on a scale

and can be utilized to help transport the water

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regulation, as it is the most directly relatable

management, it is also important to remember

management tool to the study at hand. As noted

that over-regulation can have negative impacts,

in the Cities and Flooding Guidebook, zoning

since maintaining a healthy floodplain is vital for

plans are essential to reducing liability, and risk

the natural ecosystem. In fact, these floodplains,

to people and property. The guidebook further states that cities can, and should determine land use in floodplain areas based on a scale of vulnerability, where one end of the spectrum is occupied by “most vulnerable areas” a where floods can do the

and floods are necessary for the environment, especially since “Flood waters can carry nutrient-rich sediments which contribute to a fertile environment for vegetation”. (Natural and Beneficial Functions of Floodplains, 2014) As well “Floodplains

most damage,

are beneficial

like “mobile

for wildlife by

homes and park

creating a variety

homes intended

of habitats for

for permanent

fish and other

residential use”

animals” (Natural

(Jha, Bloch and

and Beneficial

Lamond, 2012).

Functions of

The other end

Floodplains,

of the land use spectrum created by the zoning

2014). Biodiversity is also fostered in floodplains

would be “water compatible development” (Jha

and hydrologic systems through breeding,

Bloch and Lamond, 2012) and include uses like

nursery, and the provision of feeding grounds

water transmission infrastructure, and sand and

for marine fisheries. Floodplains also offer the

gravel pits. Zoning is also responsible for the

invaluable, but often hard to quantify benefit of

strict prohibition of development on floodways,

mental health and well being to human beings,

which is one of the most common regulations for the prevention of flood damage.

since “Natural floodplains are valuable in providing the “wilderness experience” that is an important part of American culture” (Natural and

While it is important to consider structural and

Beneficial Functions of Floodplains, 2014).

non-structural approaches to floodplain

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Stategies

Descriptions

So now that we have discussed the benefits of remediating and regulating flooding and restoring natural hydrological systems to their ecological equilibrium, we can further discuss the strategies and best practices in the world to achieve these goals. There are many examples of urban greening that can be applied to the issues of stormwater and flooding. The strategies that we will explain are: retention systems, detention ponds, permeable pavement, greenstreets, bioswales, rain gardens, and stormwater canals + parks. All of these strategies are best management practices and are valuable alternatives and solutions to the infrastructure dilemma that exists in our urban environments.

Retention Systems A retention basin is used to manage stormwater runoff to prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. It is implemented as an artificial lake with vegetation buffer zone around it, the stalwart of the design is a permanent pool of water .

Unlike a detention pond, the retention systems do not relaese the water collected.Retention ponds are frequently used for water quality improvement, groundwater recharge, flood protection, and aesthetic improvements to a resinetial or commercial area generally.

They are replacements for the natural systems that were destroyed during development.

Source:http://www.seattlehousing.org/redevelopment/high-point/

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Detention Ponds Source: http://www.tleng.net/Detention_Pond_-_Commerical12_22.jpg

Detention ponds are storm water control features that provide both retention and treatment of storm water runoff and its pollutants. The pond consists of a permanent pool of water into which storm water runoff is directed. As the runoff enters the pond it is detained and treated in the pond until the next storm carries it out. By collecting and retaining stormwater, detention ponds control both storm water quantity and quality. While the water is retained the various natural and engineered systems work to remove pollutants. “Sedimentation processes remove particulates, organic matter, and metals, while dissolved metals and nutrients are removed through biological uptake.” (United States Environmental Protection Agency, 1999, p. 1-2)

Permeable Surfaces Source: http://www.good2golawncare.com/images/turfstone2_wqkf.jpg

Permeable surfaces are paved surfaces that infiltrate, treat, and/or store rainwater where it falls.

There are many different types of materiality permeable surfaces can have such as, “pervious concrete, porous asphalt, permeable interlocking pavers, and several other materials.” (United States Environmental Protection Agency, 1999, p. 1) These pavements are particularly cost effective where land values are high and where flooding or icing is a problem. There is an aesthetic appeal as well, this feature can make parking lots more physically unobtrusive and add character to the area.

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Greenstreets Source: http://landperspectives.files.wordpress.com/2011/05/portland-oregon-green-street-1b.jpg

Green streets and alleys integrate green infrastructure elements into the street and/or alley design design to store, infiltrate, and evapotranspire stormwater. Permeable pavement, bioswales, planter boxes, and trees are among the many green infrastructure features that may be woven into street or alley design. Greenstreets may also be called complete streets, as many different sytems are integrated in the right of way with the lowest impact on the enironment.

Bioswales Source: http://lacreekfreak.files.wordpress.com/2011/05/zoo-ciara-6044.jpg

A bioswale is a vegetated channel that has vegetation that covers tthe slopes and bottom of the depressed area. Bioswales can be a natural occuerenc but also a manmade feature. They are designed to collect the pollutants of stormwater, help catalyze the natural inflitrtation process, and collect water during peak flows of runoff after a storm. Bioswales can serve in liu of comventional storm water systems drainage system and can replace curbs and gutters. Bioswales “are best suited for residential, industrial, and commercial areas with low flow and smaller populations.� (United States Environmental Protection Agency, 1999, p. 1) Bioswales can be used in any location where the climate allows for dense vegetation and ground cover.

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Rain Gardens Source: http://www.maxcohendesign.net/uploads/3/9/0/9/3909649/707163_orig.jpg?836

Rain gardens are shallow vegetated basins that allow the collection and filtration of stormwater runoff.

Rain gardens are a form of biomimicry which emulate the natural systems that filter and absorb water to return it to the soil. Rain gardens are very versatile and can be implemented in any unpaved space.

These features are usually located next to impervious surfaces such as road to collect runoff and are designed to be resilient to heavy amounts of moisture.

Stormwater Canals + Parks Source: http://buildingoursustainablefuture.blogspot.com/2012/09/european-village-in-bo01.html

Stormwater canals are engineered drainage systems that collect the runoff of the the adjacent area and move it downstream to a larger body of water or filterd into the existing sewage stormwater system. These systems are a fascinating feature and an aesthetic improvement to urban environments, giving the impression of natural water systems that citizens are fond of. These sytems work in dense development areas and where the climate is privy to large amounts of rainfall.

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Conclusion As the population's of the world continue to urbanize, it is crucial to acknowledge the mistakes of the past in order to create safer and more healthy communities. Historically, humans have tried to manage and control the natural systems that surround our cities. Unfortunately by doing such things as creating concrete river channels or burying streams, not only is the health of the river and surrounding ecosystem endangered, but these structures are also creating a more dangerous condition for the surrounding populations and manmade developments. There has been a misconception that the natural environment is able to be separated form the built environment, but this is not the case. It has been demonstrated that by deconstructing these unnatural barriers and reintroducing the natural developments both systems can and will mutually benefit each other.

Source: Kongjian Yu

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