Technical Report

Sponsor: GWRI

Start Date: 1999-03-01; Completion Date: 2000-02-29;

Keywords: Climate and Hydrologic processes, Geomorphological and Geochemical processes, Sediments, Models

Problem and Research Objectives:

Continued development in urban watersheds without adequate controls on sediment production from construction activities contributes sediment load to urban streams that may affect its sediment regime. Subsequent deposition of the sediment chokes the benthic aquatic habitat, and affects storage in the channel and floodplain and thus the flooding potential of the stream. In addition, urbanization creates a greater volume of runoff and higher peak flows with a different timing than exists prior to urbanization. These higher flows may contribute to bank erosion in some stream reaches and deposition further downstream. The result is again a change in geometry and sediment regime of the natural stream with consequent adverse affects on aquatic habitat and stream water quality. Furthermore, the deposited finer-grained sediments from urbanized areas may carry with them attached contaminants that are subject of resuspension during subsequent flood conditions. While much work has been done on urban hydrology to predict changes in runoff characteristics due to urbanization, much less attention has been paid to the closely related sediment effects and the changes that they cause in flooding potential and water quality of the recieving stream over the entire watershed. The research project provides a case study of an urban stream to distinguish sediment contributions from watershed development and bank erosion, resultant changes in floodpain and channel storage, and the final effect on flood routing and thus flooding potential as well as movement of sediment-bound contaminants through the watershed system. In addition, a methodology has been developed that can be applied to other urban streams to predict the effects of urban development not just on the hydrology of the watershed, but on its sedimentology as well. As a result of the study, recommendations will be made on the relative efficacy of specific control measures such as best-management practices on contruction sites to limit sediment yield, artificially-created wetlands for aditional floodplain and sediment storage, streambank stabilization, vegetative buffer zones along the stream, and strict constols on development of the floodplain. This methodology allows decision makers to make more informed watershed-wide decisions rather than piecemeal approval and disapproval of particular development projects.