A GIS-based variable source area hydrology model

Effective control of nonpoint source pollution from contaminants transporte d by runoff requires information about the source areas of surface runoff. Variable source hydrology is widely recognized by hydrologists, yet few met hods exist for identifying the saturated areas that generate most runoff in humid regions. The Soil Moisture Routing model is a daily water balance mo del that simulates the hydrology for watersheds with shallow sloping soils. The model combines elevation, soil, and land use data within the geographi c information system GRASS, and predicts the spatial distribution of soil m oisture, evapotranspiration, saturation-excess overland flow (i.e., surface runoff), and interflow throughout a watershed. The model was applied to a 170 hectare watershed in the Catskills region of New York State and observe d stream flow hydrographs and soil moisture measurements were compared to m odel predictions. Stream flow prediction during non-winter periods generall y agreed with measured flow resulting in an average r(2) of 0.73, a standar d error of 0.01 m(3)/s, and an average Nash-Sutcliffe efficiency R-2 of 0.6 2. Soil moisture predictions showed trends similar to observations with err ors on the order of the standard error of measurements. The model results w ere most accurate for non-winter conditions. The model is currently used fo r making management decisions for reducing non-point source pollution from manure spread fields in the Catskill watersheds which supply New York City' s drinking water. Copyright (C) 1999 John Wiley & Sons, Ltd.