ASSESSMENT OF SURFACE WATER POTENTIAL AND DEMAND EVALUATION IN TEJI WATERSHED, UPPER AWASH RIVER SUB-BASIN, ETHIOPIA

Abstract

In Teji watershed the livelihoods of the dense population are confirmed on the river streamflow. The competition for water resources between water users has prominently led unbalanced water demand and a limited supply that resulted in serious conflicts between water users. The goal of this study was to assess the surface water potential and evaluate demands using the Soil and Water Assessment Tool (SWAT) and Water Evaluation and Planning (WEAP). The 12.5 m x 12.5 m resolution DEM was used in watershed delineation and multiple slope classification and the 30 m x 30 m land use/cover, soil data, were used to hydrologic response unit classification. The watershed divided into 9 sub-basins, and 123 hydrological response units were identified. The model was calibrated with 2000-2010 data and twelve most sensitive flow parameters which gave very good correlation between observed and simulated streamflow with statistical criteria Coefficient of determination (R2=0.81), Nash-Sutcliffe efficiency (NSE=0.81) and Percent BIAS (PBias=+1.6). The model validation was carried out for the year 2011-2016 data and the model performance was resulted very good correlations between observed and simulated streamflow. The performance criterial of the model, R2, NSE and PBias were 0.77, 0.78 and +2.3 respectively. The mean annual water balance were simulated with a mean precipitation of 1039.30mm. Surface runoff, lateral flow, and groundwater flow were 198.63 mm (19 %), 28.78 mm (2.8%), and 17.53 mm (1.9%), respectively. The mean evaporation losses of the area were estimated as 461.40 mm which accounting for 44.34% of the mean annual water budget. The mean annual surface runoff of the watershed was 130.25 MCM. WEAP model was run to evaluate the current and future water demand under four different scenarios. At the current account year (2021) about 43.22 MCM of water was required for all water demands. The future water demand evaluation shows water supply deficit in all developed scenarios. Scenarios show that in each water demands there would be both monthly and annually unmet water demands. However, the absolute deficits were varied between scenarios.