EFFECTS OF BAR FORMATION ON CHANNEL STABILITY AND SEDIMENT LOADS IN AN URBAN WATERSHED

Abstract

This study investigates channel adjustment due to urbanization in the Little Paint Branch creek of the Anacostia River watershed. In the past 15 years, large gravel bars have formed in the channels, more than doubling the active channel width of some reaches. Field data was collected to analyze downstream hydraulic geometry and the effects of gravel bars on shear stress, turbidity, and morphological change. The watershed was gauged at three locations to document the contributions of discharge and sediment to the downstream Anacostia Estuary. The results indicate that Little Paint Branch Creek generates proportionally more runoff per basin area than the watershed does as a whole, even though the impervious surface area is lower in the upstream tributaries, like Little Paint Branch Creek. Bar formation induces channel widening, which decreases flow depth and thus shear stress for bankfull and higher stages. This shoaling limits bed transport and will eventually limit bank erosion.