SMORMOD - A GIS-INTEGRATED RAINFALL-RUNOFF MODEL

The Soil Moisture-based Runoff Model (SMoRMod), is a cell-based rainfa ll-runoff model which is integrated into the GRASS (Geographic Resourc es Analysis Support System) Geographic Information System (GIS). The u se of current GIS technology enables construction of strong physically based models that are entirely spatially referenced, within which all parameters, results, and intermediates retain their physical meaning. The model consists of soil moisture balance and runoff generation/tra nsport submodels. The soil moisture balance submodel functions on a da ily time step and provides the initial conditions for the runoff gener ation submodel. The latter operates with a short time step (30 min for this study) and features an infiltration function in which the increm ental abstraction is derived directly from the soil moisture status. T he formulation of the infiltration function accounts for both infiltra tion excess and saturation excess types of runoff generation. The mode l uses only readily available watershed characteristic data, e.g., soi ls, topography, and land use, and requires minimal calibration. Model results compare favorably with recorded streamflows for 77 rainstorms on the WD-38 watershed in east-central Pennsylvania. The 77 storms enc ompass a wide variety of rainfall amounts, rainfall intensities, and a ntecedent moisture conditions.