Urban Stormwater Management in the United States (2009) / Chapter Skim
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5 Stormwater Management Approaches
5 Stormwater Management Approaches
Pages 339-474
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From page 339... ...
The committee's statement of task asks for an evaluation of the relationship between different levels of stormwater pollution prevention plan implementation and in-stream water quality. As discussed in the last two chapters, the state of the science has yet to reveal the mechanistic links that would allow for a full assessment of that relationship.
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From page 340... ...
. But while hardening and enlarging natural channels is a cost-effective solution to erosion and flooding, the modified channel increases downstream peak flows and it does not provide habitat to support a healthy aquatic ecosystem.
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From page 341... ...
Ordinances started appearing in the early 1970s, requiring developers to reduce the peaks of different size storms, such as the 10year, 24-hour storm. The ordinances were usually intended to prevent future problems with peak flows by requiring the installation of flow control structures, such as detention basins, in new developments.
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From page 342... ...
This is accomplished with infiltration practices, functional grading, open channels, disconnection of impervious areas, and the use of fewer impervious surfaces. Much of the LID focus is to manage the stormwater as close as possible to its source -- that is, on each individual lot rather than conveying the runoff to a larger regional SCM.
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From page 343... ...
Documentation of elevated concentrations of conventional pollutants and potentially toxic pollutants, however, required intensive collection of water quality samples during runoff events. Samples collected from storm sewer pipes and urban streams in the Menomonee River watershed in the late 1970s clearly showed the concentrations of many pollutants, such as heavy metals and sediment, were elevated in urban runoff (Bannerman et al., 1979)
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From page 344... ...
The term encompasses such diverse actions as using more conventional practices like basins and wetland to installing stream buffers, reducing impervious surfaces, and educating the public. REVIEW OF STORMWATER CONTROL MEASURES Stormwater control measures refer to what is defined by EPA (1999)
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From page 345... ...
However, because of the substantial knowledge gap about the effect of a particular stormwater discharge on a particular receiving water (see Chapter 3 conclusions) , surrogate goals are often used by state stormwater programs in lieu of water quality standards.
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From page 346... ...
The relative positions of the cost curves indicate that achieving any specific designated use will be more costly in situations with a higher percentage of the watershed in impervious cover. All cost curves are upward sloping, reflecting the fact that incremental improvements in designated uses will be increasingly costly to achieve.
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From page 347... ...
Yet, promising what cannot be realistically achieved may act to undermine public support for urban stormwater programs. Increasing costs without significant observable improvements in ambient water conditions or achievement of water quality standards could ultimately reduce public commitment to the program.
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From page 348... ...
Common State Stormwater Goals Most states do not and have never had an overriding water quality objective in their stormwater program, but rather have used engineering criteria for SCM performance to guide stormwater management. These criteria can be loosely categorized as: Erosion and sedimentation control, Recharge/base flow, Water quality, Channel protection, and Flooding events.
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From page 349... ...
However, it presumes that there will be some water quality benefits in receiving waters; that is, phosphorus and fecal coliform might be captured by the TSS requirement. Similarly water quality criteria may be expressed as credits for good practices, such as using LID, street sweeping, or stream buffers.
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From page 350... ...
Some states require a reduction in runoff volume for these events to match preconstruction levels. Others may require that the average annual duration of flows that are large enough to erode the streambank be held the same on an annual basis under pre- and postdevelopment conditions.
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From page 351... ...
Both of these flow control goals are thought to also have water quality benefits. The goal for existing urban areas is an annual reduction in TSS loads.
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From page 352... ...
Role of SCMs in Achieving Stormwater Management Goals One important fundamental change in SCM design philosophy has come about because of the recent understanding of the roles of smaller storms and of impervious surfaces. This is demonstrated by Box 3-4, which shows that for the Milwaukee area more than 50 percent of the rainfall by volume occurs in storms that have a depth of less then 0.75 inch.
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From page 353... ...
Stormwater Control Measures SCMs reduce or mitigate the generation of stormwater runoff and associated pollutants. These practices include both "structural" or engineered devices as well as more "nonstructural measures" such as land-use planning, site design, land conservation, education, and stewardship practices.
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From page 354... ...
354 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES TABLE 5-1 Summary of Stormwater Control Measures -- When, Where, and Who Stormwater Control When Where Who Measure National, state, Product Substitution Continuous Regulatory agencies regional Watershed and Land- Local planning agen Planning stage Watershed Use Planning cies Conservation of Natural Site and watershed Developer, local Site, watershed Areas planning stage planning agency Impervious Cover Developer, local Site planning stage Site Minimization review authority Developer, local Earthwork Minimization Grading plan Site review authority Erosion and Sediment Developer, local Construction Site Control review authority Reforestation and Soil Site planning and Developer, local Site Conservation construction review authority Pollution Prevention Operators and local Post-construction SCMs for Stormwater Site and state permitting or retrofit Hotspots agencies Runoff Volume Developer, local Post-construction Reduction -- Rooftop planning agency or retrofit Rainwater harvesting and review authority Runoff Volume Developer, local Post-construction Reduction -- Site planning agency or retrofit Vegetated and review authority Runoff Volume Developer, local Post-construction Reduction -- Site planning agency or retrofit Subsurface and review authority Developer, local Peak Reduction and Post-construction Site planning agency Runoff Treatment or retrofit and review authority Developer, local Post-construction Runoff Treatment Site planning agency or retrofit and review authority Developer, local Planning, construcAquatic Buffers and planning agency tion and post- Stream corridor Managed Floodplains and review author construction ity, landowners Local planning Stream Rehabilitation Postdevelopment Stream corridor agency and review authority continues next page
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From page 355... ...
What is possible is to describe their basic hydrologic and water quality objectives and make a general comparative assessment of what is known about their design, performance, and maintenance as of mid-2008. This broad technology assessment is provided in Table 5-2, which reflects the committee's collective understanding about the SCMs from three broad perspectives: Is widely accepted design or implementation guidance available for the SCM and has it been widely disseminated to the user community?
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From page 356... ...
TABLE 5-2 Current Understanding of Stormwater Control Measure Capabilities Hydrologic Water Available Performance Defined SCM Control Quality Design Studies Maintenance Objectives Objectives Guidance Available Protocols Product Substitution NA Prevention NA Limited NA Watershed and Land-Use Planning All objectives Prevention Available Limited Yes Conservation of Natural Areas Prevention Prevention Available None Yes Impervious Cover Prevention and Minimization Prevention Available Limited No reduction Earthwork Minimization Prevention Prevention Emerging Limited Yes Erosion and Sediment Prevention and Prevention Control Available Limited Yes reduction and removal Reforestation and Soil Prevention and Prevention Conservation Emerging None No reduction and removal Pollution Prevention SCMs for Hotspots NA Prevention Emerging Very few No Runoff Volume Reduction -- Rainwater Reduction NA Emerging Limited Yes harvesting Runoff Volume Reduction -- Vegetated (Green Reduction and some peak Removal Available Limited Emerging Roofs, Bioreten attenuation tion, Bioinfiltration, Bioswales) Runoff Volume Reduction -- Subsurface (Infil- Reduction and some peak Removal Available Limited Yes tration Trenches, attenuation Pervious Pavements)
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From page 357... ...
Key: Hydrologic Objective Water Quality Objective Available Design Guidance? Prevention: Prevents Prevention: Prevents genera- Available: Basic design or implementa generation of runoff tion, accumulation, or wash- tion guidance is available in most Reduction: Reduces volume of off of pollutants and/or areas of the country are readily avail runoff reduces runoff volume able Treatment: Delays runoff Removal: Reduces pollutant Emerging: Design guidance is still delivery only concentrations in runoff by under development, is missing in Peak Attenuation: Reduction of physical, chemical, or many parts of the country, or peak flows through detention biological means requires more performance data Defined Maintenance Performance Data Available?
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From page 358... ...
. Many of these are compiled in the Center for Watershed Protection's National Pollutant Removal Performance Database for Stormwater Treatment Practices (http://www.cwp.org/Resource_Library/Center_Docs/SW/bmpwriteup_092 007_v3.pdf)
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From page 359... ...
The level of control afforded by product substitution is quite high if major reductions in emissions or deposition can be achieved. The difficulty is that these reductions require action in another environmental regulatory arena, such as air quality, hazardous waste, or pesticide regulations, which may not see stormwater quality as a core part of their mission.
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From page 360... ...
Elements of Better Site Design: Single-Family Residential o Maximum residential street width o Maximum street right-of-way width o Swales and other stormwater practices can be located within the rightof-way o Maximum cul-de-sac radius with a bioretention island in the center o Alternative turnaround options such as hammerheads are acceptable if they reduce impervious cover o Narrow sidewalks on one side of the street (or move pedestrian pathways away from the street entirely) o Disconnect rooftops from the storm-drain systems o Minimize driveway length and width and utilize permeable surfaces o Allow for cluster or open-space designs that reduce lot size or setbacks in exchange for conservation of natural areas o Permeable pavement in parking areas, driveways, sidewalks, walkways, and patios
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From page 361... ...
. Several monitoring studies have documented a major reduction in stormwater runoff from development sites that employ various forms of impervious cover reduction and LID in the United States and Australia (Coombes et al., 2000; Philips et al., 2003; Cheng et al., 2005)
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From page 362... ...
This element is an important, but often under-utilized component of local erosion and sediment control plans. Numerous researchers have documented the impact of mass grading, clearing, and the passage of construction equipment on the compaction of soils, as measured by increase in bulk density, declines in soil permeability, and increases in the runoff coefficient (Lichter and Lindsey, 1994; Legg et al., 1996; Schueler, 2001a,b; Gregory et al., 2006)
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From page 363... ...
Most erosion and sediment control manuals provide design guidance on the capacity and ability of swales to handle runoff without eroding, on the design of flow paths to transport runoff at non-erosive velocities, and on the dissipation of energy at pipe outlets. Examples include rock energy dissipaters, level spreaders (see Figure 5-11)
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From page 364... ...
. SOURCES: Top, EPA NPDES Menu of BMPs (available at http://cfpub.epa.gov/npdes/storm water/menuofbmps/index.cfm?
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From page 365... ...
STORMWATER MANAGEMENT APPROACHES 365 FIGURE 5-9 Sediment basin. SOURCE: EPA NPDES Menu of BMPs (available at http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?
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From page 366... ...
BOX 5-3 Recommended Construction Stormwater Control Measures 1. As the top priority, emphasize construction management SCMs as follows: • Maintain existing vegetation cover, if it exists, as long as possible.
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From page 367... ...
widely applied in many communities, and most states have some level of design guidance or standards and specifications. Nonetheless, few communities have quantified the effectiveness of a series of construction SCMs applied to an individual site, nor have they clearly defined performance benchmarks for individual practices or their collective effect at the site.
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From page 368... ...
The project title is Studies to Evaluate the Effectiveness of Current BMPs in Controlling Stormwater Discharges from Small Construction Sites and was conducted for the Alabama Water Resources Research Institute, Project 2001AL4121B, by Drs. Robert Angus, Ken Marion, and Melinda Lalor of the University of Alabama at Birmingham.
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From page 369... ...
vegetation. Mean total solids in samples collected below silt fences and a 15-foot-wide vegetated buffer zone were about 20 percent lower, on average, than those samples collected only below the silt fence.
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From page 370... ...
. At this time, there are few monitoring data to assess the degree to which land reforestation or soil amendments can improve the quality of stormwater runoff at a particular development site, apart from the presumptive watershed research that has shown that forests with undisturbed soils have very low rates of surface runoff and extremely low levels of pollutants in runoff (Singer and Rust, 1975; Johnson et al., 2000; Chang, 2006)
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From page 371... ...
For all of these measures, the amount of runoff volume to be captured depends on watershed goals, site conditions including climate, upstream nonstructural practices employed, and whether the chosen SCM is the sole management measure or part of a treatment train. Generally, runoff-volume-reduction SCMs are designed to handle at least the first flush from impervious surfaces (1 inch of rainfall)
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From page 372... ...
In retrofit situations, capture amounts as small as 1 cm are a distinct improvement. It should be noted that there are important, although indirect, water quality benefits of all runoffvolume-reduction SCMs -- (1)
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From page 373... ...
. In some areas it might be possible to use the water for drinking, showering, or washing, but treatment to potable water quality would be required.
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From page 374... ...
. Bioretention generally refers to a constructed sand filter with soil and vegetation growing on top to which stormwater runoff from impervious surfaces is directed (Figure 5-17)
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From page 375... ...
. FIGURE 5-17 Bioretention during a storm event at the University of Maryland.
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From page 376... ...
FIGURE 5-19 Retrofit bioinfiltration at Villanova University immediately following a storm event. SOURCE: Robert Traver, Villanova University.
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From page 377... ...
The results from 10 recent studies are given in Table 5-3, which shows the runoff reduction capability of bioretention. As can be seen, the reduction in runoff volume achieved by these practices is impressive -- ranging from 20 to 99 percent with a median reduction of about 75 percent.
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From page 378... ...
(2008) BOX 5-5 th Bioswale Case Study 110 Street Cascade, Seattle, Washington A recent example of the ability of SCMs to accomplish a variety of goals was illustrated for water quality swales in Seattle, Washington.
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From page 379... ...
. Water quality data were also extremely encouraging, as shown in Table 5-4.
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From page 380... ...
BOX 5-6 SCM Evaluation Through Monitoring: Villanova Bioinfiltration SCM The Bioinfiltration Traffic Island located on the campus of Villanova University in Southeastern Pennsylvania is part of the Villanova Urban Stormwater Partnership (VUSP) BMP Demonstration Park (see Figure 5-21)
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From page 381... ...
Copyright by Villanova Urban Stormwater Partnership. During construction two curb cuts were created to direct runoff into the SCM.
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From page 382... ...
Research on this site is currently examining water quality benefits and groundwater interactions. When evaluating the pollutant removal of bioinfiltration, it is critical to consider flow volumes and pollutant levels together.
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From page 383... ...
Copyright by Villanova Urban Stormwater Partnership. continues next page
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From page 384... ...
SOURCE: Reprinted, with permission, from VUSP. Copyright by Villanova Urban Stormwater Partnership.
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From page 385... ...
In most urban areas, there is so much impervious cover that it would be
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From page 386... ...
Thus, like vegetated SCMs, these SCMs provide benefits for groundwater recharge, water quality, stream channel protection, peak flow reduction, capture of the suspended solids load, and filtration through the soil (Ferguson, 2002)
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From page 387... ...
STORMWATER MANAGEMENT APPROACHES 387 FIGURE 5-28 Schematic of a seepage pit.
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From page 388... ...
388 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES FIGURE 5-30 A retrofitted infiltration trench at Villanova University. SOURCE: Reprinted, with permission, from VUSP.
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From page 389... ...
The pavement infiltrates runoff from most storm events for one-third of the impervious area on the half-acre site. SOURCE: Courtesy of Wenk Associates.
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From page 390... ...
They are designed to capture the first portion of a rainfall event and to treat the runoff from a few hundred square meters of impervious cover.
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From page 391... ...
The final storage bed has an overflow that connects to the existing storm sewer. The beds are approximately 4 feet deep and are filled with stone, producing about 40 percent void space within the beds.
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From page 392... ...
392 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES BOX 5-7 Continued FIGURE 5-34 Infiltration bed under construction. Pervious concrete has functionality and workability similar to that of regular concrete.
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From page 393... ...
Besides hydrologic plots, water quality plots also show the benefits of permeable concrete (Kwiatkowski et al., 2007)
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From page 394... ...
394 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES BOX 5-7 Continued FIGURE 5-35 Rainfall and corresponding outflow from the weir of the SCM. SOURCE: Reprinted, with permission, from VUSP.
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From page 395... ...
By holding a volume of stormwater runoff for an extended period of time, extended detention SCMs can achieve both water quality improvement and reduced peak flows. Generally the goal is to hold the flows for 24 hours at a minimum to maximize the opportunity of settling, adsorption, and transformation of pollutants (based on past pollutant removal studies)
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From page 396... ...
grass swales, education Somerset Heights, USA Grass swale, bioretention, and roof- 45% Cheng et al.
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From page 397... ...
Note that the traditional watershed shows the delay and peak reduction from the detention basins, while the LID watershed has almost no runoff. The LID watershed was found to reduce runoff volume by 74 percent by increasing infiltration over preconstruction levels.
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From page 398... ...
Note that concentrations of TSS and nutrients are increased in the LID subdivision (left-hand panel) ; this is because swales and natural systems are used in place of piping as a "green" drainage system and because only larger storms leave the site.
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From page 399... ...
. FIGURE 5-41 Retrofitted stormwater wetland at Villanova University.
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From page 400... ...
The first step in treatment is the settling of larger particles in the sediment forebay. Next, for wet ponds a permanent pool of water is maintained so that, for smaller storms, the new flows push out a volume that has had a chance to interact with vegetation and be "treated." This volume is equivalent to an inch of rain over the impervious surfaces in the drainage area.
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From page 401... ...
or a continuous water source is needed to sustain wet ponds and stormwater wetlands. Maintenance requirements for extended detention basins and wetlands include the removal of built-up sediment from the sediment forebay, harvesting of grasses to remove accumulated nutrients, and repair of berms and structures after storm events.
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From page 402... ...
Finally, in some cases these SCMs are specifically designed to reduce peak flows in addition to providing water quality benefits by introducing elements that make them similar to detention basins; this is particularly the case for sand filters. The sand filter is relied on as a treatment technology in many regions, particular those where stream geomorphology is less of a concern and thus peak flow control and runoff volume reduction are not the primary goals.
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From page 403... ...
STORMWATER MANAGEMENT APPROACHES 403 FIGURE 5-45 Austin sand filter. SOURCE: Robert Traver, Villanova University.
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From page 404... ...
With the exception of some types of sand filters, the strengths of water quality SCMs are that they can be placed within existing infrastructure or under parking lots, and thus do not take up land that may be used for other purposes. They make excellent choices for retrofit situations.
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From page 405... ...
The Wet Weather Flow Technologies Pilot was established as part of the ETV program to verify commercially available technologies used in the abatement and control of urban stormwater runoff, combined sewer overflows, and sanitary sewer overflows. Ten proprietary SCMs were tested under the ETV program (see Figure 5-47)
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From page 406... ...
It would be relatively easy for state and local agencies to review the benefits of each installation if the efficiency curves were incorporated into urban runoff models, such as WinSLAMM or P8. Stormwater 360 Hydrodynamic Separator.
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From page 407... ...
STORMWATER MANAGEMENT APPROACHES 407 Bay Seperator.
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From page 408... ...
At the present time, there are no data to support an optimum width for water quality purposes. The beneficial impact of riparian forest cover is less detectable when watershed impervious cover exceeds 15 percent, at which point degradation by stormwater runoff overwhelms the benefits of the riparian forest (Roy et al., 2005, 2006; Walsh et al., 2007)
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From page 409... ...
notes that improvement of biological diversity of urban streams should still be considered an experiment, since it is not always clear what hydrologic, water quality, or habitat stressors are limiting. Larson et al.
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From page 410... ...
The only revegetation performed was to seed the area for erosion control. SOURCE: Courtesy of Wenk Associates.
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From page 411... ...
. While a great deal of design guidance on urban stream rehabilitation has been released in recent years (FISRWG, 2000; Doll and Jennings, 2003; Schueler and Brown, 2004)
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From page 412... ...
. The basic finding is that regular street sweeping has a low or limited impact on stormwater quality, depending on street conditions, sweeping frequency, sweeper technology, operator training, and on-street parking.
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From page 413... ...
Field experience in conducting outfall surveys does indicate that illicit discharges may be present at 2 to 5 percent of all outfalls at any given time. Given that pollutants are being introduced into the receiving water during dry weather, illicit discharges may have an amplified effect on water quality and biological diversity.
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From page 414... ...
. Residential Stewardship This SCM involves municipal programs to enhance residential stewardship to improve stormwater quality.
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From page 415... ...
Both the federal and several state industrial and construction stormwater general permits have standard requirements for visual inspections following a major storm event. Visual observations of an SCM by themselves do not provide information on runoff reduction or pollutant removal, but rather only that the device is functioning as designed.
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From page 416... ...
Other indicators of problems would include erosion downstream of the SCM, algal blooms, invasive species, poor water clarity, and odor. For water quality and manufactured devices, visual inspections after a storm event can determine whether the SCM is functioning properly.
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From page 417... ...
It requires integration of flow and water quality data creating both a hydrograph and a polutograph for a storm event as shown in Figure 5-53. The creation of these graphs requires continuous monitoring of the hydrology of the site and multiple water quality samples of the SCM inflow and outflow, the vadose zone, and groundwater.
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From page 418... ...
One advantage of these data recording systems is that they can be connected to water quality probes and automated samplers to provide a flowweighted sample of the event for subsequent laboratory analysis. Field calibration and monitoring of these systems is required.
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From page 419... ...
Finally groundwater wells can be used to establish the effect of the SCM on the groundwater depth and quality during and after storm events. Performance monitoring of extended detention SCMs is difficult because the inflows and outflows are variable and may extend over multiple days.
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From page 420... ...
and the Center for Watershed Protection's National Pollutant Removal Database (CWP, 2000b, 2007b)
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From page 421... ...
Until such information is available, it will be virtually impossible to predict that an individual SCM can accomplish a certain level of treatment and thus prevent a nearby receiving water from violating its water quality standard. DESIGNING SYSTEMS OF STORMWATER CONTROL MEASURES ON A WATERSHED SCALE Most communities have traditionally relied on stormwater management approaches that result in the design and installation of SCMs on a site-by-site basis.
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From page 422... ...
With the relatively recent recognition of unacceptable downstream impacts and the regulation of urban stormwater quality has come a rethinking of the design of traditional stormwater systems. It is becoming rapidly understood that stormwater management should occur on a watershed scale to prevent flow control problems from occurring or reducing the chances that they might become worse.
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From page 423... ...
The last category is broken out because the suite of SCMs needed is substantially different than for urban redevelopment. Each type of development has a different footprint, impervious cover, open space, land cost, and existing stormwater infrastructure.
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From page 424... ...
Redevelopment in these areas is typically much denser than the original use. The resulting increase in impervious area, and typically the inadequacy of existing stormwater infrastructure serving the site often results in significant development costs for on-site detention and water quality treatment.
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From page 425... ...
STORMWATER MANAGEMENT APPROACHES 425 TABLE 5-7 Applicability of Stormwater Control Measures by Type of Development Low-Density Intense Stormwater Control Urban Greenfield Industrial Measure Redevelopment Residential Redevelopment Product Substitution Watershed and Land-Use Planning Conservation of Natural Areas Impervious Cover Minimization Earthwork Minimization Erosion and Sediment Control Reforestation and Soil Conservation Pollution Prevention SCMs Runoff Volume Reduction -- Rainwater Harvesting Runoff Reduction -- Vegetated Runoff Reduction -- Subsurface Peak Reduction and Runoff Treatment Runoff Treatment Aquatic Buffers and Managed Floodplains Stream Rehabilitation Municipal Housekeeping NA IDDE Stormwater Education Residential Stewardship NA NOTE: , always; , often; , sometimes; , rarely; NA, not applicable.
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From page 426... ...
Some SCMs are useful at all scales, such as product substitution and impervious cover minimization. Choosing Among On-Site, Distributed SCMs and Larger, Consolidated SCMs There are distinct advantages and disadvantages to consider when choosing to use a system of larger, consolidated SCMs versus smaller-scale, on-site SCMs that go beyond their ability to achieve water quality or urban stream health.
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From page 427... ...
This choice may be guided by regional water quality priorities (such as nutrient reduction in the Chesapeake Bay or Neuse River watersheds) or may be an outgrowth of the total maximum daily load process where there is known water quality impairment or a listed pollutant.
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From page 428... ...
428 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES BOX 5-11 Examples of Communities Using Consolidated versus Distributed SCMs Stapleton Airport New Community This is a mixed-use, mixed-density New Urbanist community that has been under development for the past 15 years on the 4,500-acre former Stapleton Airport site in central Denver. As shown in Figures 5-55 and 5-56, the stormwater system emphasizes surface conveyance and treatment on individual sites, as well as in consolidated regional facilities.
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From page 429... ...
Consolidated stormwater treatment areas and surface conveyances define more traditional park recreation and play areas. SOURCE: Courtesy of the Stapleton Redevelopment Foundation.
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From page 430... ...
. Water quality treatment is being provided for a combined area of over 660 acres that includes the 100-acre project area and over 500 acres of adjacent neighborhoods.
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From page 431... ...
STORMWATER MANAGEMENT APPROACHES 431 FIGURE 5-58 Natural drainage system methods have been applied to a 34-block, 1,600unit mixed-income housing redevelopment project called High Point. Shown on top, vegetated swales, porous concrete sidewalks, and frontyard rain gardens convey and treat stormwater on-site.
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From page 432... ...
432 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES BOX 5-11 Continued Pottsdammer Platz This project, in the heart of Berlin, Germany, illustrates the potential for stormwater treatment in the densest urban environments by incorporating treatment into building systems and architectural pools that are the centerpiece of a series of urban plazas. As shown in Figure 5-59, on-site, individual SCMs are used to collect stormwater and use it for sanitary purposes.
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From page 433... ...
FIGURE 5-60 Illustrations show consolidated treatment areas in proposed parks. The top image illustrates the fair weather condition, the center image the water quality capture volume, and the bottom image the 100-year storm event.
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From page 434... ...
. If the receiving water is too sensitive to meet these goals, one should consider adjustments to zoning and development codes to reduce the amount of impervious cover.
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From page 435... ...
This usually requires a watershed approach to stormwater management to ensure that quality and quantity control are integrated together, with an emphasis on the connection and effective use of conveyance channels, streams, riparian buffers, and floodplains. Establishing Community Objectives for the Publicly Owned Elements of Stormwater Infrastructure The stormwater infrastructure in a community normally occupies a considerable surface area of the landscape once all the SCMs, drainage easements, buffers, and floodplains are added together.
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From page 436... ...
Summary Taking all of the elements above into consideration, the emerging goal of stormwater management is to mimic, as much as possible, the hydrological and water quality processes of natural systems as rain travels from the roof to the stream through combined application of a series of practices throughout the entire development site and extending to the stream corridor. The series of SCMs incrementally reduces the volume of stormwater on its way to the stream, thereby reducing the amount of conventional stormwater infrastructure required.
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From page 437... ...
STORMWATER MANAGEMENT APPROACHES 437 TABLE 5-8 From the Roof to the Stream: SCMs in a Residential Greenfield SCM What it Is What it Replaces How it Works Map and plan submitted at earliest stage of development review Early site Doing SWM design Land-Use Planning showing assessment after site layout environmental, drainage, and soil features Preservation of priority forests and Conservation of Maximize forest Mass clearing reforestation of turf Natural Areas canopy areas to intercept rainfall Construction practices to Earthwork Conserve soils Mass grading and conserve soil structure Minimization and contours soil compaction and only disturb a small site footprint Narrower streets, permeable driveways, Impervious Cover Better site de- Large streets, lots clustering lots, and Minimization sign and cul-de-sacs other actions to reduce site IC Runoff Volume A series of practices to Reduction -- Utilize rooftop Direct connected capture, disconnect, Rainwater runoff roof leaders store, infiltrate, or Harvesting harvest rooftop runoff Grading frontyard to treat Positive drainage Frontyard roof, lawn, and from roof to bioretention driveway runoff using Runoff Volume road shallow bioretention Reduction -- Vegetated Shallow, well-drained Curb/gutter and bioretention swales Dry swales storm drain located in the street pipes right-of-way Long, multi-cell, forested Peak Reduction Large detention wetlands located in and Runoff Linear wetlands ponds the stormwater Treatment conveyance system Aquatic Buffers Active reforestation of Stream buffer Unmanaged and Managed buffers and restoration management stream buffers Floodplains of degraded streams Note: SCMs are applied in a series, although all of the above may not be needed at a given residential site. This "roof-to-stream" approach works best for low- to medium-density residential development.
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From page 438... ...
438 URBAN STORMWATER MANAGEMENT IN THE UNITED STATES TABLE 5-9 From the Roof to the Outfall: SCMs in an Industrial Context SCM What it What it Is How it Works Category Replaces Analysis of the locations and connections of the stormwater Drainage mapping No map and wastewater infrastructure from the site Systematic assessment of runoff Hotspot site Visual problems and pollution Investigation inspection prevention opportunities at the site Use of alternative roof surfaces or Uncontrolled Rooftop coatings to reduce metal runoff, rooftop management and disconnection of roof runoff runoff for stormwater treatment Special practices to reduce dis Exterior maintenance Routine plant charges during painting, practices maintenance powerwashing, cleaning, sealcoating and sandplasting Extending covers over susceptible Exposed Extending roofs for loading/unloading, fueling, hotspot no exposure outdoor storage, and waste operations management operations Pollution prevention practices Uncontrolled Vehicular pollution applied to vehicle repair, vehicle prevention washing, fueling, and parking operations operations Pollution Prevent rainwater from contact Prevention Outdoor pollution Outdoor with potential pollutants by prevention materials covering, secondary practices storage containment, or diversion from storm-drain system Exposed Improved dumpster location, Waste management dumpster or management, and treatment to practices waste prevent contact with rainwater or streams runoff Develop and test response to Spill control plan and spills to the storm-drain system, No plan response train employees, and have spill control kits available on-site Routine Reduce use of pesticides, landscape fertilization, and irrigation in Greenscaping and turf pervious areas, and conversion maintenance of turf to forest Regular ongoing training of Lack of storm Employee employees on stormwater water aware stewardship problems and pollution ness prevention practices Regular sweeping, storm-drain Site housekeeping Dirty site and cleanouts, litter pickup, and and stormwater unmaintained maintenance of stormwater maintenance infrastructure infrastructure Filtering retrofits to remove Runoff Stormwater No stormwater pollutants from most severe Treatment retrofitting treatment hotspot areas Monitoring of outfall quality to IDDE Outfall analysis No monitoring measure effectiveness Note: While many SCMs are used at each individual industrial site, the exact combination depends on the specific configuration, operations, and footprint of each site.
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From page 439... ...
STORMWATER MANAGEMENT APPROACHES 439 TABLE 5-10 From the Roof to the Street: SCMs in a Redevelopment Context SCM Category What it Is What it Replaces How it Works Designing redevelopment footprint to restore natuImpervious Cover Site design to Conventional site ral area remnants, mini Minimization prevent pollution design mize needless impervi ous cover, and reduce hotspot potential Use of green rooftops to Treatment on the Traditional rooftops reduce runoff generated roof from roof surfaces Runoff Volume Use of rain tanks, cisterns, Reduction -- Rooftop runoff Directly connected and rooftop Rainwater treatment roof leaders disconnection to capture, Harvesting and store, and treat runoff Vegetated Use of foundation planters Runoff treatment in Traditional and bioretention areas to landscaping landscaping treat runoff from parking lots and rooftops Reducing runoff from compacted soils through tilling and compost Runoff reduction in Impervious or amendments, and in pervious areas compacted soils Soil Conservation some cases, removal of and unneeded impervious Reforestation cover Providing adequate rooting Increase urban tree volume to develop Turf or landscaping canopy mature tree canopy to intercept rainfall Use of permeable pavers, porous concrete, and Runoff Increase permeabil- similar products to Hard asphalt or Reduction -- ity of impervious decrease runoff concrete Subsurface cover generation from parking lots and other hard sur faces. Use of expanded tree pits, Runoff Sidewalks, curb dry swales and street Runoff treatment in Reduction -- and gutter, and bioretention cells to fur the street Vegetated storm drains ther treat runoff in the street or its right-of-way Use of underground sand Underground treat- Catch basins and filters and other practices Runoff Treatment ment storm-drain pipes to treat hotspot runoff quality at the site Targeted street cleaning Municipal on priority streets to re Street cleaning Unswept streets Housekeeping move trash and gross solids Stormwater retrofits or restoration projects Off-site stormwater elsewhere in the waterWatershed treatment or On-site waivers shed to compensate for Planning mitigation stormwater requirements that cannot be met on site Note: SCMs are applied in a series, although all of the above may not be needed at a given redevelopment site.
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From page 440... ...
COST, FINANCE OPTIONS, AND INCENTIVES Municipal Stormwater Financing To be financially sustainable, stormwater programs must develop a stable long-term funding source. The activities common to most municipal stormwater programs (such as education, development design review, inspection, and enforcement)
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From page 441... ...
Municipal stormwater programs can use separate fees to finance inspection activities. For instance, inspection fees can be charged to cover the costs of ensuring that SCMs are adequately planned, installed, or maintained (Debo and Reese, 2003)
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From page 442... ...
given up by society to achieve a particular outcome. In the case of stormwater control, opportunity costs include direct costs necessary to control and treat runoff such as capital and construction costs and the present value of annual operation and maintenance costs.
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From page 443... ...
In general the cost of SCMs is incompletely understood and significant gaps exist in the literature. More systematic research has been conducted on the cost of conventional stormwater SCMs (wet ponds, detention basins, etc.)
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From page 444... ...
Based on estimates from Wossink and Hunt (2003) , the total present value of maintenance costs over 20 years can range from 15 to 70 percent of total capital construction costs for wet ponds and constructed wetlands and appear generally consistent with percentages reported in EPA (1999)
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From page 445... ...
For example, nutrients from anthropocentric sources are an increasing water quality concern for many fresh and marine waters. Some states (e.g., Virginia, Maryland, and North Carolina)
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From page 446... ...
. As discussed earlier in the chapter, stormwater runoff can be reduced and managed through better site design to reduce impervious cover.
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From page 447... ...
Credit payments are typically made based on the volume of water detained. For example, as part of Portland, Oregon's Clean River Rewards program, residents and commercial property owners can reduce their stormwater utility fee by as much as 35 percent by reducing stormwater runoff from existing developed properties (Portland Bureau of Environmental Services, 2008a)
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From page 448... ...
Finally, impact fees on new developments can be structured in a way to create incentives to reduce stormwater runoff volumes. Charges based on runoff volume (or a surrogate measure like impervious surface)
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From page 449... ...
Congress provided no start-up or upgrade financial assistance, unlike what it did for municipally owned and operated wastewater treatment plants after the promulgation of the NPDES permit program under the Clean Water Act in 1972. Local governments have been reluctant to tax residents or create stormwater utilities.
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From page 450... ...
Concerns over assigning responsibility to individual residential landowners or homeowners associations include insufficient technical and financial resources to conduct consistent maintenance and a lack of inspection to require maintenance. A recent survey of municipal stormwater programs found that less than one-third perform regular maintenance on stormwater detention ponds or water quality SCMs in general residential areas (Reese and Presler, 2005)
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From page 451... ...
Such research is critical to understanding the longterm cost obligation that is being assumed by municipal stormwater programs that are responsible for managing a growing number of SCMs. At the present time, the maintenance schedule for many of the proprietary and non-proprietary SCMs is poorly defined.
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From page 452... ...
For example, design guidance is lacking or just emerging for many of the non-traditional SCMs, such as conservation of natural areas, earthwork minimization, product substitution, reforestation, soil restoration, impervious cover reduction, municipal housekeeping, stormwater education, and residential stewardship. Some LID techniques are better covered, such as the standards for pervious concrete from the American Concrete Institute and the National Ready Mixed Concrete Association.
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From page 453... ...
For example, often out-of-date rainfall distributions, methods, or standards are required in the code that do not apply to the newer focus on smaller storms and volume reduction. If methods that include Modified Rational or TR55 are used, it is difficult if not impossible to show the benefits in peak flow reduction gained through volume reduction devices.
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From page 454... ...
In California, which does not have a uniform policy for groundwater management and groundwater rights, authority over groundwater quality management falls to several regional and local agencies. For example, the Upper Los Angeles River Area (ULARA)
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From page 455... ...
. They acknowledge the importance of protecting natural resources to maintain quality of life and have established water quality as an important consideration in city building.
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From page 456... ...
Municipalities may have to consider the added cost of vector control and public health when implementing stormwater quality management programs. With larger consolidated and regional extended detention facilities, concerns about the safety of children who may be attracted to such SCMs and ensuing liability must be considered.
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From page 457... ...
CONCLUSIONS AND RECOMMENDATIONS SCMs, when designed, constructed, and maintained correctly, have demonstrated the ability to reduce runoff volume and peak flows and to remove pollutants. However, in very few cases has the performance of SCMs been mechanistically linked to the guaranteed sustainment at the watershed level of receiving water quality, in-stream habitat, or stream geomorphology.
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From page 458... ...
Performance characteristics are starting to be established for most structural and some nonstructural SCMs, but additional research is needed on the relevant hydrologic and water quality processes within SCMs across different climates and soil conditions. Typical data such as long-term load reduction efficiencies and pollutant effluent concentrations can be found in the International Stormwater BMP Database.
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From page 459... ...
Rather, EPA and the states should encourage the development of regional design guidance that can be readily adapted and adopted by municipal and industrial permittees. As our understanding of the relevant hydrologic, environmental, and biological processes increases, SCM design guidance should be improved to incorporate more direct consideration of the parameters of concern, how they move across the landscape, and the issues in receiving waters.
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From page 460... ...
I, Urban Stormwater Characteristics, Con stituent Sources, and Management by Street Sweeping: Chicago, U.S.
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From page 461... ...
Earth Surface Processes and Landforms 13:355-367. CASQA (California Stormwater Quality Association)
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From page 462... ...
Water Resources Research, doi:10.1029/2007WR006343. CWP (Center for Watershed Protection)
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From page 463... ...
2007b. Urban stormwater retrofit practices.
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From page 464... ...
1999. Preliminary Data Summary of Urban Stormwater Best Manage ment Practices.
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From page 465... ...
2007. Reducing Stormwater Costs Through Low Impact Development (LID)
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From page 466... ...
2002. Costs of Urban Stormwater Control.
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From page 467... ...
utilizing per vious concrete. Journal of the American Water Resources Association 43(5)
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From page 468... ...
2. Pre pared for the EPA Chesapeake Bay Program and Urban Stormwater Work ing Group.
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From page 469... ...
2006. Costs of urban stormwater control practices.
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From page 470... ...
2004a. National Stormwater Quality Da tabase.
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From page 471... ...
2003. Costs of best management practices and associated land for urban stormwater controls.
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From page 472... ...
2007. Urban Stormwater Retrofit Practices: Urban Stormwater Restoration Manual 3.
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From page 473... ...
1991. Costs of Urban Nonpoint Source Water Pollution Control Measures.
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From page 474... ...
1986. Cost of Urban Stormwater Runoff Controls.
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Key Terms
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