STREAM FLOW AND SEDIMENT YIELD MODELING, THE CASE OF GIDABO WATERSHED

Abstract

Soil and Water Assessment Tool (SWAT) Model provides important planning tools that can be used in water resource and management of land which can be used in the understanding of dynamic process and prediction of the existing process. In this study, SWAT-CUP was used to calibrate and validate a hydrologic component on Gidabo river discharges at gauging station and predict stream flow and sediment yield of Gidabo watershed. Sensitivity analysis, model calibration for the year 1997-2002 and for validation period 2003-2005 were also performed to assess the model performance. Highly sensitive parameters were identified of which curve number (CN2) factor was the most sensitive one for stream flow and Sensitive parameters for sediment flow in the watershed includes USLE support practice factor (USLE_P). The coefficient of determination (R 2 ) and Nash-Sutcliffe (ENS) was used to evaluate model calibration and validation. The results found were satisfactory for the gauging station (for stream flow R 2 = 0.78 and. ENS = 0.75 for calibration period and R 2 = 0.75 and. ENS = 0.74 for validation and sediment yield R 2 = 0.72 and ENS = 0.71 for calibration and R 2 = 0.67 and ENS = 0.63 for validation period. Gidabo at the existing condition generates a maximum annual average sediment yield of 15.8 ton/ha, this was attributed due to the topographic slope and land use of this subbasin.in general the highly eroded and sediment generating sub basin are those having about 75-85 % of agricultural land coverage. This can be reduced by using sediment yield intervention strategies such as land slope stabilization, construction bench terraces, changing the land use of steep area and afforestation.