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Land Use Impacts on Storm Hydrographs and the Effectiveness of Best Management Practices, Coastal Plain, Virginia
Murray, John Twohy
Murray, John Twohy
Abstract
The urbanization of watersheds results in substantial changes to hydrologic regimes. Impervious surfaces increase flow volume and runoff rate causing incision and channel enlargement in natural streams. To prevent these impacts, best management practices (BMP’s) like detention basins are constructed to control storm flow. However, little empirical data is available to assess BMP effectiveness. We installed gauging stations on four streams in small watersheds (~1-2 km?) in Williamsburg, VA and surrounding counties. Although the four basins were similar in geology, elevation and channel slope, they differed in land-use and BMP installation. Land-use was mapped using GIS, which allowed calculations of impervious cover and forest cover. Development ranged from high (25% impervious) to low (13% impervious) in the basins studied. Gauging stations were equipped with stilling wells and dataloggers to measure stage from July 2003 to December 2003. Hydrograph comparisons of response time, time to rise, lag to peak, centroid lag, normalized peak discharge and runoff coefficients were made to understand the effect of land use and BMP implementation on stream hydrology. Results show that Williamsburg streams are greatly affected by the development throughout the region. Lag to peak shortened and normalized peak discharge increased with increased impervious cover. Response time and lag to peak were longer in the least developed for over 60% of the storms compared. The peak discharge of developed basins is on average 3.6 times larger than the peak discharge of the least developed basin. Lag time in the BMP basin was usually shorter than the lag of the two other basins studied. However, centroid lag was typically longer in the BMP. Peak discharge in the BMP basin was on average 3.0 times smaller than the peak discharge of the developed basins.
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2004-01-01
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Geology