Characterizing the Ground Water Resources Potential in Omo Gibe River Basin

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Addis Ababa University


Groundwater characterization and potential assessment across a river basin plays a vital role in quality control, occurrence, extraction and management of the groundwater resources. In this study a three dimensional (3D) steady state FEM based groundwater modeling code (TAGSAC) was used to characterize and assess the groundwater potential and the groundwater aquifer system in omo gibe river basin. This model needs the hydro geologic, recharge and boundary conditions as its input. Thus a simplified one layer conceptual model is created by the perennial rivers in the basin as constant head boundary, omo gibe catchment divided and bottom boundary as no flow boundary, and the top surface as a recharge boundary. This conceptual groundwater model includes the geologic map of the basin as input, so that its hydro geologic parameters were adjusted manually to bring about inventoried well hydraulic heads. In the calibration 603 boreholes, protected spot springs, dug wells, springs and shallow wells were used. The calibration was made to a level of 10m, root mean square error value. The result has 6.56m, 7.8m and 0.9986 mean errors mean absolute error and correlation coefficient between the measured and computed hydraulic head respectively. The calibrated model clearly shows the groundwater flow direction follows the general topography of the basin. Besides by looking into the porosity of the geologic medium in the basin, the monthly groundwater tables and stream flow variation the groundwater potential is about 4.38 billion m3. The groundwater resources variation shows that the minimum groundwater recharge occurs in January and the maximum groundwater recharge occurs in August. The limitation of the groundwater model developed to represent the basin by FEM has the same element dimensions (3 km by 3 km) which is very large and one groundwater model layer having large thickness, which uses equivalent porous medium approach to determine the hydraulic property of the geologic medium & gives the same hydraulic property for the geologic medium from the surface up to the bottom boundary conditions. Keywords: - groundwater resources potential, Hydraulic head, OGRB, TAGSAC, groundwater model,Omo Gibe ,Ethiopia



Groundwater Resources Potential, Hydraulic Head, OGRB, TAGSAC, Groundwater Model, Omo Gibe, Ethiopia