During a heavy rainfall, the impervious surfaces of urban environments—roadways, rooftops, and sidewalks—generate excess storm water runoff that can cause a long list of negative environmental impacts. These impacts can radiate throughout an entire watershed. Storm water runoff accelerated by impervious surfaces prevents the natural infiltration of rainfall into the soil and can dissolve and move contaminants, such as lawn chemicals, animal wastes, and rooftop and auto trace metals (copper, zinc, and nickel), into nearby streams. Large-scale engineering proposals for storm water controls are often rejected by taxpayers because of their cost and complexity.

National Risk Management Research Laboratory (NRMRL) sustainable technology scientists are testing an alternative, multidisciplinary control program in the Shepherd Creek watershed near Cincinnati, Ohio. This program offers property owners the opportunity to voluntarily cooperate in the management of excess storm water runoff through natural diversion, infiltration, and small-scale detention methods. Implemented in significant numbers within the watershed, this decentralized approach can restore watershed ecology to less-impaired conditions at a reasonable cost.

Background

The Shepherd Creek watershed is approximately two square kilometers of mixed residential and commercial zones, forested parkland, and established homes built between 1960 and 1980. Previous NRMRL research identified five sub-watersheds with varying proportions of impervious surfaces, ranging from 12 to 20 percent. Stream conditions are known to decline more rapidly above 10 to 15 percent, and NRMRL research data confirmed the heaviest impairments to Shepherd Creek streams at those sites with the highest percentages of impervious surfaces.

Two chief goals of the program were to reduce immediate water quantity by mitigating the volume of storm water runoff, and to enhance water quality by reducing the potential for pollutants to be dissolved and transported. By infiltrating runoff, there is greater opportunity for the recharge of groundwater and the natural cleansing of pollutants in soil, both of which help arrest major runoff impacts on waterways.

From a number of Best Management Practices (BMPs) available for the watershed project, the NRMRL team selected rain barrels, or cisterns, and rain gardens to reduce storm water runoff from rooftops, driveways, and lawns. The choice of BMPs was determined in part by the relatively high proportion of rooftops and driveways (50 to 72 percent) that comprise total amounts of impervious area of the sub-watersheds. Rain barrels detain runoff until owners use it to water gardens, for example. Rain gardens (intentional infiltration areas typically planted with native, water-tolerant plants) infiltrate surface runoff before it becomes unmanageable farther downstream. These source-reduction strategies, set on individual properties, allow for flexible distribution throughout a watershed, with the added advantages of ease of installation and maintenance.

Legal and economic issues associated with private property rights were addressed through the adoption of a voluntary system, wherein homeowners bid at auction to participate and to specify their desired level of compensation. Researchers set a first-round goal of 150 properties as the threshold number whose impervious areas were likely sources of a variety of environmental impairments. About 120 rain barrels, or cisterns, and 50 rain gardens were installed during the summer of 2007. Planning continues for a second auction in 2008 to study its potential to recruit more participants to reduce their storm water runoff contribution.

Evaluation of this program will compare baseline data with data collected for three years after installation of the BMPs to determine whether these management measures had an effect on water quantity, water quality, and the ecological integrity of the streams that drain the watershed. The cost-effectiveness of the auction as an economic incentive will also be measured. For details on the auction system through which volunteer participants are selected and other information about the Shepherd Creek project, contact Patricia Schultz, NRMRL Office of Public Affairs, (513) 569-7966.