Evaluation of Groundwater Resource Potential in Borkena River Catchment, Awash Basin

Abstract

The main aim of this study was to understand the groundwater potential of Borkena river catchment for domestic and agricultural uses. Water qualitative analysis and recharge estimation of groundwater resource for sustainable use and groundwater flow modeling were conducted in the catchment. The fast population growth, uncontrolled urbanization and industrialization, poor sanitary situation, uncontrolled solid and liquid waste disposal, oil fuel etc. caused series quality degradation of the river and borehole waters in the catchment. Therefore, evaluation of physico chemical parameters of the river water and boreholes in the catchment of Borkena was conducted. In this study, EC, Temperature, pH, Na + , K + , Mg 2+ , Ca 2+ , F- , Cl - , NO 3 - , SO4 2- and HCO3 - of 7 water samples were analyzed from rivers and boreholes that across the town and industrial sites of the study area. The results of the physico-chemical parameter analysis shown that the rivers and boreholes for industrial areas were characterized by their maximum mean levels of pH, temperature, EC, Na + , K + Mg 2+ , Ca 2+ , F - , Cl - , NO3 - , HCO 3 - , and SO4 2- with 8.5, 32°C, 944 µS/cm, 112.4 mg/l, 18.5 mg/l, 11.65 mg/l, 19 mg/l, 1.2 mg/l, 36.61 mg/l, 1.92 mg/l, 8.4 mg/l, 7.93 mg/l respectively. The amount of natural groundwater recharge is a pre-requisite for efficient groundwater resource evaluation and water balance approaches were used to estimate the annual groundwater recharge of the area. It was found to be 133mm/year which is 11.5% of the total precipitation of the catchment. Processing MODFLOW Pro is useful in confirming the distribution of recharge when used in combination with a water balance model but relies on the correct assumptions on the hydrogeological model. PMWIN Pro proved to be a very useful tool for the analysis of the water budget of the catchment. The model was calibrated for steady state condition by matching simulated and observed hydraulic head data for different periods. Model calibration was carried out by trial and error calibration method using groundwater contours constructed from heads collected for 11 wells. The calibration showed small error of simulated heads and the overall root mean square errors for simulated hydraulic heads was found to be 3.96m.