Grid-based digital elevation models (DEMs) are used to simulate overland flow paths in hydrological models. The accuracy of these drainage patterns are dependent upon how well the DEM represents the terrain features that control runoff patterns. Often regional DEMs are not produced at scales small enough to represent rural infrastructure. The scale of runoff patterns that can be accurately modeled is, therefore, restricted, particularly when the terrain is relatively flat. The RIDEM (Rural Infrastructure Digital Elevation Model) model is presented that utilizes commonly available ancillary data to downscale grid-based runoff patterns. The resulting drainage patterns reflect drainage modifications imposed by rural infrastructure including: roads, ditches, culverts, and irrigation canals. Downscaling runoff patterns enables the completion of runoff studies at smaller scales. The model was implemented with the Oldman River watershed, Alberta, Canada to determine the spatial patterns of potential runoff contributing areas in three agricultural watersheds regularly contaminated by pathogens. / vii, 170 leaves : ill. (some col.) ; 29 cm.