GSSHA: Model To Simulate Diverse Stream Flow Producing Processes

The need to simulate surface water flows in watersheds with diverse runoff production mechanisms has prompted the Department of Defense to invest in the development of a new, physically based hydrologic model, called the Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) model. GSSHA is a reformulation and enhancement of the two-dimensional, physically based model CASC2D. The GSSHA model simulates stream flow generated by both infiltration-excess and saturation-excess mechanisms, as well as exfiltration, and groundwater discharge to streams. The model employs mass-conserving solutions of partial differential equations and closely links the hydrologic components to assure an overall mass balance. Testing of the model on a watershed with diverse runoff mechanisms indicates that the model is useful for investigating the important streamflow producing processes at the watershed scale and determining the contributions of surface water, saturated groundwater, and unsaturated groundwater to the overall water balance. Split-sample tests indicate that the model is capable of reproducing both observed hourly and total discharge at the test basin outlet.