AbstractThis paper presents case study applications for the hydraulically‐based geomorphologic Instantaneous Unit Hydrograph (IUH), developed by Diaz‐Granadoset al.(1986). This IUH was derived as a function of watershed geomorphology and stream response to lateral inflows. This response was determined by solving one‐dimensional linearized equations of motion including a simple infiltration expression approximated by an infiltration coefficient multiplied by the streamflow discharge. Three gauged watersheds in Saudi Arabia are selected as case studies. A procedure for estimating the stream response parameters (the flow depth, the flow velocity, and the infiltration coefficient) is provided. A comparison is made between the observed and computed hydrographs and an evaluation of the IUH results and limitations is pro