Pollution Prevention - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 457

TABLE 13.2
Opportunities for Stormwater Storage and Diversion at the Micro-Topographic Scale

Microscale
Landscape Feature Opportunities for Storage/Diversion

Branches Certain tree canopy shapes (such as beech) act to funnel water downward to zones

containing more permeable soil near the main root zone (Mosley 1982)

Leaves Conifers have generally higher interception capacity (Cape et al. 1991)

Soil Increasing the organic content of soil increases its water retention capacity (Hudson 1994)

Median strips Concave or flat median strips can increase stormwater storage

Surface depressions Downspouts can be routed to slight depressions to increase infiltration, instead of

discharging to paved surfaces. These areas can also delay stormwater from entering the
pipe network

Root buttresses Roots from larger trees and shrubs create friable soil more capable of infiltrating water

(Bartens et al. 2008)

Flat rooftops Can become storage areas with the addition of vegetation or rooftop cisterns

Swales Store overland flow and prevent entry into street drains

Downspouts Should be disconnected from footing drains and routed to cisterns or natural depression

storage areas for infiltration or use as graywater; “in-line” storage bins can store up to
100 gal per downspout

Driveways Use porous pavement to reduce runoff

Sidewalks Use porous pavement

maximum surface temperatures averaged 6°C higher in the winter and more than 19°C
lower in the summer (DeNardo et al. 2005).
Downspout diversion provides excellent potential for stormwater flow reduction in
highly urbanized communities lacking available space for large-scale detention facilities.
In the Beecher Water District, a highly urbanized area near Flint, Michigan, a downspout
diversion program was implemented from 1996 to 1997. Here, downspouts were connected
to footing drains and into sanitary sewer pipes, resulting in frequent sanitary sewer pipe
overflows during wet weather. Downspout diversion contributed to a reduction of over
35% in the mean flow volumes within the sanitary sewer collection network and reduced
overtime costs associated with overflow maintenance (Kaufman and Wurtz 1997). A simi-
lar reduction of 35% was also achieved in Dearborn, Michigan (Montrief, pers. com. 2010).
In Portland, Oregon, the Downspout Disconnection Program has disconnected 50,000
downspouts, and these disconnections are removing more than 1 billion gallons of storm-
water annually from the combined sewer system (City of Portland 2010). Where down-
spouts are already disconnected, many can be rerouted to prevent direct discharge onto
paved surfaces.
The construction of large-scale CSO basins in several areas (e.g., Boston, Atlanta, Detroit)
represents a major investment (Figure 13.13). Using source control to keep stormwater out
of the sewer pipes before constructing these basins—as Portland has done—may help
reduce infrastructure costs.
It may not be practical or affordable to convert driveways and sidewalks to porous pave-
ment. There are, however, opportunities for some conversions whenever homeowners and
commercial establishments repave their driveways and parking lots.

13.4.1.5.1.1 Elimination of Pollutants As with point sources, the elimination of chemicals
should focus on contaminants with high CRFs. Many lake associations ban the use of