R--The Hydrologic Modeling System (HEC-HMS)

This contract action was accomplished using other than competitive procedures because there is only one responsible source as this is a follow-on contract, and no other supplies or services will satisfy agency requirements (FAR 6.302-1). See posted J&A for further information. The Hydrologic Modeling System (HEC-HMS) currently has no grid-based routing scheme to simulate overland flow and surface soil erosion. This Performance Work Statement provides for the addition of a new 2-D diffusion wave surface routing method and the addition of a grid-based surface soil erosion method to HEC-HMS. The grid-based surface soil erosion capability will be based on the Rangeland Hydrology and Erosion Model (RHEM). The grid-based erosion model requires commensurate surface hydrology capable of calculating the shear stress within each grid cell. The existing ModClark transform method, while grid-based, is only quasi-distributed and cannot compute shear stress. In order to support the development of the new erosion method, a new transform method will be created that can provide the required surface hydraulic information. The new transform method will be based on the 2-D Diffusion Wave Routing method used in the HEC-RAS 2-D solver engine. A previous work effort converted the RHEM source code to the Java language and implemented it as a beta version of RHEM in HEC-HMS. The RHEM code will need to be modified to work with the new 2-D Diffusion Wave Routing method.