A new model is being developed to describe the water balance of a small mountainous catchment that is subject to snow accumulation and snow melt. Surface elevation across the catchment is determined from a digital elevation model. The distributed water storage capacity is calculated by combining depth-to-bedrock data with soil porosity data. At the surface, the complete energy balance is calculated using standard meteorological input. The snowpack, if present, is represented by two state variables: water equivalence and energy content (similar to the Utah Energy Balance Snow Accumulation and Melt Model). Lateral subsurface flow above the bedrock is calculated using the Boussinesq equation. Saturation-excess surface runoff is moved to neighboring cells assuming instantaneous redistribution. The model is tested in the Boise-Front Experimental Watershed, Boise, Idaho.