ASSESSMENT OF SURFACE WATER POTENTIAL AND WATER DEMANDS: IN CASE OF GOGARA RIVER-CATCHMENT, OMO GIBE BASIN ETHIOPIA

Abstract

Water resources are vital components for a country's development important to the country's growth and transformation. .The abstraction of water from the river without proper basin plan as well as without considering middle stream and downstream water users. The main aim of this study was to conduct surface water potential assessment and evaluation of water demands of Gogara watershed. The Gogara river sub-basin receives an estimate mean annual precipitation of = 873.464 mm. HEC-HMS evaluates surface water resources availability by analyzing their presence and quantity. WEAP assesses factors affecting water availability, identifying optimal allocation policies based on changes in demand, development activities, and climate conditions for efficient water management. CROPWAT calculates crop water requirements by considering factors like crop type, weather, soil characteristics, and irrigation methods, ensuring optimal growth and development. The estimated mean annual runoff in the whole watershed is 159.2MCM which is correspond to mean annual depth of surface runoff is mean annual precipitation. The mean annual water balance shows that the significant number of the mean annual precipitation (69.4%) received by the watershed were lost via evapotranspiration. The remaining parts of annual precipitation (172.2mm which accounts about 15.9%) received by the watershed infiltrates to the soil to recharge GW aquifers as well as to contribute to base flow (24.2mm as lateral flow and about 140.35mm as return flow). The model was calibrated and validated by using 1995 to 2007 and 2008 and 2014 respectively years stream flow data. The performance was found good during calibration [correlation coefficient, R 2 = 0.6, Nash-Sutcliffe efficiency, NSE = 0.658) and validation R 2=0.6, NSE = 0.609). The mean annual future surface water resources potential of the catchment was estimated as 267.75MCM and 318.35MCM under RCP4.5 and RCP8.5 respectively. The estimated surface water potential was 159.609 MCM. The scenarios were developed to evaluate the future demands based on different sets of “what if” situations up to the 2030. The environmental flow requirement is required more detailed studies of water allocation patterns within the basin.