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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