2003: Impact of BMP's on Stream Hydrographs

Jerod Randall (Geology) Beloit College

Advisor:  Gregory Hancock

The urbanization of watersheds results in substantial changes to stream hydrologic regimes. With urbanization, natural channels respond to increases in flow volume and runoff rate with incision and channel enlargement. To prevent these impacts, best management practices (BMPs) like detention basins are constructed to reduce flow rates. However, little empirical data is available to assess BMP effectiveness. We have been monitoring water flow in four watersheds in and around Williamsburg. The Williamsburg region is undergoing rapid growth with population more than doubling between 1980-2000. We equipped gauging stations with stilling wells and data loggers to measure stage, and rating curves were established for each site. Rain gauges were installed in each monitored basin to more accurately determine rainfall in each basin. Measurements included lag time, peak discharge, and event flow. These were compared among basins of differing land use and detention basin implementation. Lag times in more highly developed basins were shorter than in lightly developed basins. There were also very distinct differences in discharge between those basins that were highly developed and those that were lightly developed. Peak discharge was up to 5 times higher in the more developed basins than the lightly developed basins, but some lightly developed basins showed peak flows reaching twice as high as more developed ones during smaller storm events.

For additional documentation Jerod Randall provided a PowerPoint Presentation entitled " Impact of BMP's on Stream Hydrographs" provided here in PDF form.