1. 7.8.3 Other Urban Stormwater Management Considerations
      2. 7.9 References

Pennsylvania Stormwater Best Management Practices Manual
Chapter 7
designed to flush and convey debris, makes the urban landscape a significant source of
pollutants that are rapidly conveyed to receiving surface streams. The use of various devices to
intercept and contain these waste materials offers some measure of pollutant reduction, if
maintenance is performed on a regular basis. Street cleaning by vacuum units also presents a
very efficient method of pollutant removal, but purchase cost combined with operation and
maintenance makes this BMP a significant investment for any urban community. In one urban
center (Santa Monica, CA), the street gutters have been formed with porous concrete and
infiltrating underdrains, combined with traps at corner inlets. Less dense residential portions of
the urban community may utilize a variation of this approach, where shallow infiltration can be
accomplished.
Stormwater “hot spots
such as gas stations, industrial areas, vehicle service areas, and public
works storage areas are commonly found in urban communities, especially in the industrial
zones. Smaller facilities, such as fueling islands and dumpster pads, should be treated as
separate sources of pollution, and the runoff should be prevented or segregated from surface
runoff. On the larger scale, a block-by-block strategy may be appropriate in portions of the
community where pollutant-producing activities are concentrated.
7.8.3 Other Urban Stormwater Management Considerations
In many urban areas, local codes and regulations may require designs that are contrary to current
BMP design. For example, local codes may require that all roof leaders be connected directly to
a storm sewer, or that all streets have curbs and gutters. Local code officials may not be familiar
with on-going stormwater management efforts. In these instances, early review of local
requirements and communication to the appropriate officials is necessary to avoid BMP
construction delays or denials. Long-term, review and updating of local ordinances may be
warranted, with model urban guidelines developed by PADEP.
Redevelopment in depressed or blighted communities adds an additional dimension to
stormwater management. These conditions have led some states (such as New Jersey) to
exclude such communities from new stormwater regulations. The imposition of stringent
regulations that are not feasible may serve to direct redevelopment to undeveloped sites outside
the urban center. Brownfield parcels with significant residual contamination must be designed
carefully to assure that any residual pollutants are not mobilized by stormwater BMPs. Highly
contaminated sites may warrant excavation and removal of materials before any BMP can be
installed. Stormwater management must not be detrimental to the economic health of urban
areas, because this would ultimately be more damaging to the overall water resources of an area.
Most of the BMPs described in Chapter 6 can find some application in the urban environment, but
a number of seemingly small measures, not described in separate BMP sections, can have a
cumulative effect if applied to hundreds or thousands of individual residences or small buildings.
These types of measures include:
Reduce Parking Imperviousness -
New parking lots in urban areas can follow the guidelines set
out in Chapter 5 relating to reducing imperviousness, while rehabilitation of existing parking lots
can be designed with some areas of pervious paving, or even re-vegetated areas if the parking
spaces are under-utilized.
Rooftop Downspout Disconnection -
Roof leaders (gutters) in residential, urban areas can be
re-configured to drain into rain barrels or planter boxes, for example. Multiple, smaller stormwater
elements placed around the home/structure can be combined to form a flexible design applicable
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to confined areas. Larger, commercial buildings may have internal drainage systems, which can
still be disconnected into larger stormwater elements such as cisterns, planters, or vertical
storage.
Disconnect from storm sewers -
Disconnecting from existing storm sewers can be
accomplished by either adding another inlet slightly up-gradient from the existing inlet to intercept
the runoff and redirect it into a storm water feature, or closing off the existing inlet and regrading
the area to drain into a stormwater feature, such as an infiltration bed.
Street Sweeping -
Streets, roads, and highways constitute large percentages of urban areas,
and pollutant loadings are usually greatest from these areas. Runoff from streets may end up at
a treatment plant, but is more typically discharged directly to a body of water. Actively sweeping
or vacuuming these surfaces can greatly reduce the amount of pollutants entering inlets, and
possibly reduce the need for other (usually more costly) water quality measures.
Rooftop Runoff Capture & Reuse
Rain barrels can be used to capture runoff originally coming
from roof leaders, and they are small enough to fit in yards often found in urban residential
neighborhoods. Cisterns and vertical storage units can be placed in corners of structured parking
lots, inside buildings, on the outside walls of buildings, in adjacent alleys, alongside elevator
shafts, and other locations deemed feasible by the designer. Vertical storage is very applicable in
urban areas where space is at a premium; the shape and location of this BMP requires very little
horizontal land area.
Vegetated Roof
: A vegetated roof is one of the most effective (both cost and stormwater –
wise) methods to manage stormwater in an urban environment. Many buildings in urban areas
have large flat roofs that can be converted into vegetated roofs
Water Quality Filter
- Filters can be used at the end of a drainage area, or at a “hot spot” to treat
pollutant filled runoff. They have urban area relevance because of their size – filters can provide
substantial water quality treatment in a relatively small container. They are typically used at the
end of a drainage area (before it discharges into a body of water) that did not have room up
gradient for other water quality measures.
Water Quality Insert
- These manufactured devices can be placed in urban area inlets to
address water quality. They’re appropriate where stormwater is discharged without other
treatment and where removing pollutants before they enter the conveyance system is crucial.
They are not appropriate for areas with combined sewers
Use of Parking lots and rooftops, as special detention areas -
Detaining runoff on impervious
surfaces does not have any volume benefit, but does reduce CSO impacts by temporarily holding
the runoff and slowly releasing it so that the treatment plant can properly treat it. Surface storage
can also help reduce the peak rates of a drainage area by increasing the time of concentration for
that specific area. This can be useful in areas that require peak rate reductions, or are subject to
downstream flooding.
7.9
References
AASHTO Highway Subcommittee on Design Task Force for Environmental Design, 1991.
A
Guide for Transportation Landscape and Environmental Design
. American Association of
State Highway and Transportation Officials. Washington, D.C.
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2006
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