Evaluation of the Effectiveness of Low-Impact Development Practices
Project Number: BQY25
Project Chief: William R. Selbig
Project Topics: xxxc
Cooperators: Wisconsin Department of Natural Resources
Period of Project: July 1998–September 2007
A detention pond (foreground) serves as one stormwater-runoff control device during construction of a residential subdivision using low-impact development practices in Dane County, Wis.
Problem
Farmland in Wisconsin is rapidly being converted to urban land uses. This urban development, with the associated increase in impervious area, generally impacts the water quality and increases the runoff volume that is delivered to the receiving water body. When new site plans are proposed, many of the plans use “end-of-pipe” structural best-management Practices (BMPs) such as wet and dry detention ponds. However, these structural BMPs are primarily designed to reduce the flood peak of a runoff event. They have limited water quality and quantity benefits.
Low-impact development is designed to reduce the volume and improve the quality of runoff while attempting to preserve the natural hydrology of the site. Low-impact practices include the reduction of impervious surfaces and installation of infiltration devices, such as rain gardens.
Approach
Test and control sites have been selected in Cross Plains, Wisconsin. The control site, which was developed from 1988 to 1991, used traditional urban design practices such as storm sewers, curbs and gutters, and a wet detention basin. The second site began development in May 1999 and is implementing low-impact development practices. Both sites are finger valleys that are approximately a quarter mile apart.
Equipment at both sites is maintained to continuously monitor water level, precipitation, and water temperature, and is housed in a monitoring station that has phone telemetry and electrical power. An automated water-quality sampler at each site is programmed to take flow-proportional samples from runoff-producing storm events.
Comparisons in the performance of BMPs in the control and study area will be made based on unit-area runoff and unit-area loads. Trends in water quality and quantity will also be analyzed to further characterize the construction cycle (from platting to site closeout).
Progress
All event summary statistics were computed for the test sites at Cedar Hills and the north detention pond for the period 1998 – 2005. A regression was created using dye tracer data to estimate discharge at the control site on Bourbon Road for the period 1998-2005. Removal of monitoring equipment was initiated.
Plans
The remainder of instrumentation will be removed and the site restored to natural conditions. Event statistics for the control site at Bourbon Road will be computed and compared to the test site. All data will be tabled and summarized for inclusion in draft report.
Publications and Reports
Selbig, W.R. and Bannerman, R.T., 2008, A comparison of runoff quantity and quality from two small basins undergoing implementation of conventional- and low-impact development (LID) strategies: Cross Plains, Wisconsin, water years 1999–2005, U.S. Geological Survey Scientific Investigations Report 2008-5008, 57 p.
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