Eective control of nonpoint source pollution from contaminants transported by runo requires information about the source areas of surface runo. Variable source hydrology is widely recognized by hydrologists, yet few methods exist for identifying the saturated areas that generate most runo in humid regions. The Soil Moisture Routing model is a daily water balance model that simulates the hydrology for watersheds with shallow sloping soils. The model combines elevation, soil, and land use data within the geographic information system GRASS, and predicts the spatial distribution of soil moisture, evapotranspiration, saturation-excess overland ยฏow (i.e., surface runo), and interยฏow throughout a watershed. The model was applied to a 170 hectare watershed in the Catskills region of New York State and observed stream ยฏow hydrographs and soil moisture measurements were compared to model predictions. Stream ยฏow prediction during non-winter periods generally agreed with measured ยฏow resulting in an average r 2 of 0 . 73, a standard error of 0 . 01 m 3 /s, and an average Nash-Sutclie eciency R 2 of 0 . 62. Soil moisture predictions showed trends similar to observations with errors on the order of the standard error of measurements. The model results were most accurate for non-winter conditions. The model is currently used for making management decisions for reducing non-point source pollution from manure spread ยฎelds in the Catskill watersheds which supply New York City's drinking water.