Modeling Watershed and Riverine Sediment Processes with HEC-HMS and HEC-RAS

Sediment yield and transport capabilities have recently been added the Hydrologic Engineering Center's (HEC) Hydrologic Modeling System (HEC-HMS) and River Analysis System (HEC-RAS). HEC-HMS computes watershed sediment yield using the Modified Universal Soil Loss Equation (MUSLE) and includes several empirical assumptions that translate a total event load into a sediment time-series by grain class. Multiple methods for modeling sediment transport and erosion/deposition within the channel are available as well. HEC-HMS sediment output can provide sediment load boundary conditions for more detailed, mobile boundary, open channel, sediment routing simulations using the sediment transport module in HEC-RAS. This paper will cover the approaches and methodologies used in these sediment models and focus on the features and assumptions included to facilitate integrated watershed-riverine modeling with both programs.