INSTITUTE OF TECHNOLOGY, FACULTY OF BIO-SYSTEMS AND WATER RESOURCES ENGINEERING, DEPARTMENT OF WATER RESOURCES AND HYDRAULIC ENGINEERING

Abstract

The goal of this study was to assess the groundwater potential zone in a Deme watershed area of the Omo-Gibe basin, Ethiopia, where data availability was poor. In this study, a number of data from a variety of sources have been used, including climate, stream flow, and spatial thematic layers including land use maps, soil maps, drainage density maps, geology maps, slope maps, lineament density maps, and geomorphology maps. In order to estimate the recharge amount and its spatio temporal fluctuation in the watershed, Soil and Water Assessment Tool model was utilized. At the Orata Alem location within the Deme watershed, several modeling techniques, sensitivity analysis, calibration beginning from 1991 to 2001, and validation 2002 to 2006 periods, were applied. As a result, the results of the calibration and validation phases showed that the model can accurately and reasonably reproduce the stream flow pattern and the various hydrograph responses, as indicated by the Nash-Sutcliffe efficiency(ENS) values of 0.78 and 0.74 and the coefficient of determination(R 2) values of 0.81 and 0.76, respectively. The watershed's mean annual recharge rate is estimated to be 214.5 mm/y, with the northern top section of the watershed experiencing a recharge rate of 233.77 mm/y, the middle of the watershed experiencing a recharge rate of 214.72 mm/y, and the lower part of the watershed experiencing a recharge rate of 194.51 mm/y. Analytical Hierarchical Process was used to rank the various layers based on a pair-wise comparison matrix in order to estimate the final normalized weights of thematic map layers. Groundwater flow direction was determined by the Surfer model. GIS-based Multi-Criteria Decision Analysis was applied for mapping of groundwater potential zones and its results were used to identify three Groundwater Potential Zone: low, moderate and high, with area coverage of 26.3664 Km2 ,744.1776 Km2 and 271.9179 Km2 correspondingly. Around 71.4% of the region has a moderate groundwater potential, and 26.084% has a high potential. Lastly, groundwater well inventory data for 35 wells dispersed around the region were used to validate the Groundwater Potential Zone map in order to evaluate the model's efficacy. The validation results confirmed that 84.44% the study Ground water potential zone match with ground water well points in the Deme watershed, so that the applied approach provides well reasonable results that can help in planning, management and sustainable utilization of the groundwater resources in this water-stressed area.