RUN-OFF ESTIMATION AND ASSESSING WATER HARVESTING ZONE FOR IRRIGATION PRACTICES IN KELETA WATERSHED, AWASH BASIN, ETHIOPIA

Abstract

The world water demand is growing twice as fast as the population. On the other hand, Food supply is the greatest challenge faced by humankind in the 21st century. The communities in the study area are facing acute water shortage for crop production during dry seasons, where Rainwater harvesting is vital means of survival. The purpose of this study was to assess water harvesting zone for irrigation practices by considering socioeconomic and biophysical factors. This was performed through integrated Geographic Information Science, Soil Water Assessment Tool model, fuzzy logic, and Analytical hierarchy process model. The parameters used for rainwater harvesting site selection were rainfall, drainage density, surface runoff, percentage of clay content, land use land cover, slope, lithology, lineament, and Euclidean distance to settlement and road. The Soil Water Assessment Tool model was used to compute run-off, Analytical hierarchy process was used to drive the weight of each influential factor, fuzzy membership to standardize the input factor, and gamma fuzzy overlay weighted was used to aggregate factors together. Statistical performance of the Soil Water Assessment Tool model was revealed with R2 of 0.79 and NSE of 0.77 for monthly calibration and R2 of 0.81 and NSE of 0.75 for monthly validation periods. Rainwater harvesting potential suitability class coverage of the study area was very highly Suitable (16.91%), highly suitable (27.6%), moderately suitable (20.23%), low suitable (13.1%), not suitable (6.43%), and constraints (15.73%). Finally, surface irrigation land suitability class coverage was highly suitable (7.8%), moderately (22.8%), marginally (58.6%), and unsuitable (10.8%). The study result could assist policy makers for better decisions during development of irrigation projects in the Keleta watershed and for better identification of profitable and sustainable irrigation investment opportunities in the watershed