IMPLEMENTATION OF THE SEDIMENT IMPACT ASSESSMENT MODEL (SIAM) IN HEC-RAS

Abstract: A sediment impact assessment model is being incorporated as part of the Hydrologic Engineering Center's River Analysis System (HEC-RAS) through a joint research and development effort between HEC and the U.S. Army Engineer Research and Development Center’s (ERDC) Coastal and Hydraulics Laboratory (CHL). The sediment impact assessment model (SIAM) was initially developed through CHL research activities conducted with Colorado State University. The reach based sediment accounting model has been embedded in the Hydraulic Design module of HEC-RAS, and will provide users with an expedient means of determining average annual sediment impacts for stream networks. The stream network of HEC-RAS provides the conceptual framework for the application of SIAM, and the HEC-RAS user interface expedites data entry. HEC-RAS hydraulic and sediment transport calculations are coupled with user defined bed material and wash material descriptions, sediment sources, and flow duration information to compute reach averaged sediment supply, transport capacity, and local balance by grain size. Input data include bed material gradation, flow duration representative of an average annual hydrologic cycle, sediment properties, sediment source loading by grain size, and reach averaged hydraulic parameters. Results are reported by grain size and in total for each reach, and include local bed material balance, average annual sediment transport capacity, bed material and wash material supply, and local source supply. Use of the HEC-RAS interfaces to generate and execute SIAM runs will be discussed and illustrated