The complete absence or presence of scanty and unreliable historical hydro-meteorological data has been the primary constraint in the planning and design of water resources development projects in Eritrea. The available data possess considerable gaps in the time series making hydrologic analysis and design impractical. To make matters worse, many of the existing hydro-meteorological stations are non-functional. Thus, the authors have attempted to test the applicability of geomorphologic instantaneous unit hydrograph (GIUH) coupled with Nash modell in one of the major Eritrean basins for the derivation of unit hydrograph.