Assessment Of Surface Water Potential And Current Water Demand: The Case Of Holetta River Catchment, Awash River Basin, Ethiopia

Abstract

Nowadays, the need of water for different purpose is dramatically increasing. The source of this water may be surface water or ground water. There are various ways how to allocate the available water, but the challenge is to find an optimal way. An important purpose of water management is to balance the demand for water with its availability, through suitable water allocation arrangements. Therefore, assessing the surface water potential of a river catchment and allocating the available water resources becomes crucial concern of different researchers. Currently the surface water potential of Holetta river catchment is not studied well and users of the river are facing the problem of sharing the available water during dry season due to scarcity. This paper was initiated with an objective of assessing surface water potential and current water demand of Holetta River catchment. Soil and Water Assessment Tool (SWAT) was used to determine the surface water potential. Sensitivity analysis, model calibration and validation were done by using SWAT_CUP SUFI2 algorithm while Water Evaluation and Planning (WEAP) tool was used to determine water demand for the current year 2019 G.C. Statistical model performance measures, coefficient of determination (R 2 ) and Nash– Sutcliffe simulation efficiency (NSE), indicated good performance of the model simulation on monthly time step both on calibration and validation with a value of 0.89 and 0.74 for calibration and 0.87 and 0.65 respectively for validation. PBIAS value during calibration and validation were -7.3 and -6.4 respectively indicating model over prediction. The catchment receives mean annual precipitation of 1213.5 mm. The monthly surface runoff volume for the months of January, February, March, April, May, and December were 0.582, 1.192, 2.556, 1.947, 2.080 and 0.342 Mm3 respectively which accounts a total surface runoff volume of 8.699 Mm3 . Four demand sites were considered and given equal priorities regardless of the differences in financial returns expected from each site. The WEAP21 model result showed that the current water demand, during dry season, for irrigation, livestock, urban and rural domestic demand sites were 6.6, 0.012, 1.767 and 4.698 Mm3 respectively which accounts a total water demand of 13.077 Mm3 . The current base year 2019 water allocation result revealed that the demand is much higher than the available water and hence, there is unmet demand with a deficit volume of 1.046, 0.93, 0.497, 0.921, 0.073, and 0.911 Mm3 respectively in the dry months. Therefore, to overcome water scarcity during the dry season, it is important to store the available water in the rainy season by constructing artificial water storage.