SURFACE WATER POTENTIAL ASSESSMENT AND DEMAND SCENARIO ANALYSIS IN MEKI WATERSHED, ETHIOPIA

Abstract

Water resource available was not well managed due to rainfall variability and unavailability, insufficient knowledge about available water resource and coordination in water resource management, population growth, expansion of irrigation. and environmental requirements, particularly during low flow periods. These clearly show that there was a need to analyze the water balance of the river basin and formulate water allocation strategies and principles for the present and future. To achieve this general objective Soil and Water Assessment Tool (SWAT) model was used to determine the surface water potential. The types of data that used to achieve this objective were Digital Elevation Model (DEM), land use and land cover (LuLc), Soil data, Meteorological data, Hydrological data, population data irrigation data, annual water use rate, and crop types. After sensitivity analyses, calibration and validation of the model by SWAT-CUP the Water evaluation and Planning (WEAP) model was used to analysis current and future water demand and under scenario development. The result revealed that an estimated mean annual precipitation was 144.11mm. Total surface water potential from the watershed was 350.76 million-cubic meter (Mm 3 ) annually during the current account year (2021). The model was calibrated and validated by using 18-year (1996- 2013) stream flow data. The performance was found good during calibration (R2 = 0.83), Nash-Sutcliffe efficiency (NSE)=0.69, and PBIAS=-19%, while validation (R2= 0.86, NSE=0.76, and PBIAS=-18%). In the base year 109.47Mm 3 of water was required by both consumptive use and non-consumptive use (environmental flow requirement). In the base year (2021) there was no unmet water demand annually. The estimated total annual consumption water demand may be expected to be for reference scenario, high population growth scenario, increase irrigation area scenario, and increase water demand scenario were 82.44Mm 3 , 161.4Mm 3 , 173.2Mm 3 , and 210.6Mm 3 respectively. High flow during rainy season and low or no flow during dry season hence, congestive use of water is recommended