ABSTRACT
Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) Model: A Model for Simulating Diverse Streamflow-Producing Processes
Charles W. Downer, Fred L. Ogden, Justin Neidzialek, and Siqing Liu
The Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) model is a reformulation and enhancement of the two-dimensional, physically based Hortonian (Horton, 1933) model CASC2D (Ogden and Julien, 2002). In addition to Hortonian runoff (infiltration excess), the GSSHA model is capable of simulating streamflow generated from saturated source areas, exfiltration, and groundwater discharge to streams. GSSHA is intended to provide watershed analysis capability in a wide range of hydrologic conditions, and provides an alternative to lumped-parameter models such as HEC1 (HEC, 1985), for use in complex catchments where heterogeneities and predictions of flow path are important. GSSHA also provides an alternative to the use of closely coupled surface water groundwater models capable of solving complex groundwater and flow and transport problems, such as ADH (Howington et al., 1997), WASH123D (Yeh et al., 1998) or MODHMS (Panday and Huyakorn, 2004). The complexity of these closely coupled models comes with a large computational burden and input data requirements. Furthermore, the use of models with multidimensional representations of the unsaturated zone may suffer problems with aspect ratio when applied to simulate infiltration and associated hydrologic fluxes (Talbot et al., 2002). GSSHA is a comparatively simpler and faster, robust, physically based hydrologic model that can perform watershed analysis in regions with varied flow-generating processes.
