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Channel Geometry Chnages in Response to Development in Williamsburg, VA
David, Gabrielle
David, Gabrielle
Abstract
This study measures variation in stream channel cross-sectional morphology in basins with different extents of development. Channel morphology is influenced primarily by water discharge, velocity, sediment load, channel roughness, and slope. Development in a basin alters runoff pathways, and produces changes in these parameters that may result in channel morphology modifications. Because channel morphology (e.g., width, depth) is determined largely by the dominant discharge, any development that promotes increased runoff typically causes a stream to change its channel shape by increasing its width and depth. This may disrupt vegetation along stream banks, accelerate mass failures along banks and slopes, and damage structures (Rhoads, 1995). To compare stream channel morphology to extent of development, we have surveyed 39 channel cross-sections in 16 small watersheds (1-3 km’). Multiple regressions are used to find the statistically significant factors in changing the channel morphology. Hydraulic radius and channel depth are both found to increase with increasing development. Contrary to previous studies (e.g. Hammer, 1972; Krug and Goddard, 1986), this investigation found that bankfull width does not change significantly in more developed basins. Consequently, streams in Williamsburg are found to incise in response to development as predicted by previous studies, and not to widen or significantly change their cross-sectional area.
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2002-01-01
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Geology