Tena, Alamirew (PhD)Dangenet, Sultan (PhD) Co- AdvisorKedir, Hassen2021-04-012023-11-282021-04-012023-11-282020-01http://etd.aau.edu.et/handle/12345678/25897This paper presents an application of surface rainfall run-off simulation using the Hydrologic Modelling System (HEC-HMS). A case study was carried out for the Dechatu watershed, a Rainfall is classified as “bi-modal” with the first significant rains from March to May and the second rains from is July to Septembertypical semi-arid and sub-humid geo-climatic region in eastern Ethiopia Awash River basin. The modeling schemes using mechanism of models provided by HEC-HMS for runoff volume. The modeling results were compared with historical observation data. Several River Basins (Watershed) across the world have been simulated using hydrological models to understand hydrological processes and the availability of water resource. Some of these basins are ungauged. In this study in order to evaluate the hydrological process of Dechatu Watershed for sustainable management; HEC-HMS 4.2 hydrologic model (with CN) is used to simulate its runoff (Watershed Modelling) was used as an interface to delineate the watershed and generate some input (basins parameters). The CNparameters are computed in HEC-GeoHMS using land use and soil type data.Using the Chi-Squared test ranking, Dengego rainfall data fits Lognormal 3 parameter distribution. Annual Maximum Daily Rainfall (mm) for selected return periods50years were used for the meteorological inputs. The results showed a total volume of runoff 150.20MM3 during the fifty years of the simulation. The peak discharge was found to be 2,528.7m 3 /s and the model evaluation has showed, indicating that the results of the simulation are satisfactory.en-USRainfall-Run-OffModelingSimulationDechatu WatershedThesis