RAINFALL-RUNOFF MODELING OF HAWASAA CATCHMENT

Abstract

The SWAT model is hydro-dynamic and physically-based model for application in complex and large basins. Model inputs are as follows: rainfall, air temperature, soil cbaracteristics, topography, vegetation, bydrogeology and other relevant physical parameters and. The Soil and Water Assessment Tool 2005(SWAT2005) was developed by the Agricultural Research Service of the United States Department of Agriculture and distributed by the US Environmental Protection Agency for watershed management. The main objective of this study is to estimate over all flow yield of Hawasaa catchment which is located in the Main Ethiopian Rift valley in Ethiopia. After the data quality test, meteorological and hydrological data for calibration and validation were used to estimate the parameters in the SWAT model. The evaluation of the SWAT model response to rainfall-run of relationship from sensitive analysis we take the most ten sensitive flow parameter which affect the rainfall runoff relationship of the catchment. Among the sensitive flow parameters the soil evaporation Compensation factor (ESCO) were found to be more sensitive parameter to runoff. While Threshold water depth in the shallow aquifer for flow (GWQMN), Base flow Alpha Factor (ALPHA-BF), threshold water for water in the shallow aquifer for flow "revamp" percolation to deep aquifer to accrue (REVAPMN), Soil depth in meter (SOL Z) and SCS runoff curve number (CN-2) the most influential flow parameter of the catchment and other flow parameter less influence than other. The mean monthly and annual water yield simulated for a base period found to be 25.8mm and 309.0mm, respectively. Seasonal water yield simulation resulted 56.6mm, 89.7mm and 155.0mm for dry, intermediate and wet seasons respectively. Water yield is the total amount of water leaving the HRU and entering main channel during the time step. (WYLD) = SURQ + LATQ +GWQ TLOSS. From our result, the total amount of water leaving the HRU and entering main channel

during the time step (WYLD) is 769.8 mm H2O. The predicted hydrograph was calibrated

against observed one and the model parameters were optimized for good simulation. The

calibration and validation result show that the coefficient of determinations (R^) and the NashSutcliffe simulation efficiency (ENS) are 0.76 and 0.72 for calibration and 0.77 and 0.73 for

validation this shows it is good simulation.