Abstract

The study was conducted to know the impact of LULC changes on stream flow and sediment yield in Gibe III watershed, Omo-Gibe basin Ethiopia under the LULC conditions of 1994, 2006 and 2018 by applying SWAT model with discharge data of 21 years (1990-2010) and sediment estimation from rating curve. SWAT satisfactorily estimated flow and sediment yield at the Abelti sub-watershed with R², NSE and BIAS of 0.90, 0.87 and -5.8% during calibration and 0.82, 0.77 and 14.8% during validation of stream flow while 0.87, 0.86 and -6.0% during calibration and 0.75, 0.73 and 10.9% during validation of sediment. The mean monthly observed and simulated flow amount of 218.75 m³/s and 231.79 m³/s at calibration while 226.37m³/s and 192.92m³/s at validation respectively was obtained. In Gojeb sub-watershed, R², NSE and PBIAS of 0.81, 0.80 and 0.0% during calibration period and 0.78, 0.76 and 9.7% during validation for stream flow respectively while R2, NSE and PBIAS of 0.73, 0.73 and 5.4% during calibration and 0.60, 0.60 and 2.1% during validation respectively were obtained. Using transfer of best calibrated parameter of SWAT model to un-gauged sub-watershed, the mean annual stream flow at Gibe III watershed was obtained as 614.29 m³/s, 446.09 m³/s and 515.93 m³/s was obtained during 1994, 2006 and 2018 respectively which indicate high reduction in flow from 1994 to 2018. The annual sediment load during 2018 at Gibe III was estimated as 88.2 Mton indicating 67.8 Mm³ storage volume of reservoir being filled with sediment per year that need well organized community based watershed management.

Keywords: Annual cycle; Climate models; CORDEX; Inter-annual variability; RCMs