Evaluation of Recharge and Groundwater flow Dynamics in Beles Basin, Upper Blue Nile Basin, Northwestern Ethiopia
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Date
2023-10
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Addis Ababa University
Abstract
The demand for groundwater is growing, leading to the identification of this valuable resource as the focal point for investigation, administration, and preservation. The Beles basin's groundwater resources and groundwater dynamics have been both quantitatively and qualitatively analyzed in this work. Therefore, evaluating groundwater recharge and groundwater flow dynamics utilizing Wetspass,baseflow separation and chloride mass balance approaches was the primary goal of the current research project.
The annual recharge of the basin is predicted to be 223.40 mm/year based on the results of the Wetspass model, which corresponds to around 13.86% of the annual rainfall that infiltrates into the aquifer. The model also shows that around 36.35% of the total annual precipitation is accounted for by direct runoff.
Furthermore, the Main Beles River at Beles Bridge and the Gilgel Beles river catchments near Mandura town were selected as the primary rivers for assessing the recharge process within the Beles basin. Through baseflow separation, it was determined that the basin experiences an annual recharge of 203.52 mm/year, accounting for 12.63% of the total annual rainfall that replenishes the aquifer. Interestingly, the basin exhibits higher baseflow during the summer months due to increased precipitation and higher evapotranspiration rates. The baseflow index, which indicates the contribution of groundwater to rivers, is highest during the rainy season and lowest during the dry season.
Lastly, the chloride mass balance method was employed to estimate groundwater recharge in the area. The findings revealed chloride concentrations of 0.74 mg/L in rainfall and 4.93 mg/L in groundwater. As a result, the CMB method determined that the groundwater recharge in the Beles catchment is approximately 241.9 mm/year, which corresponds to 15% of the annual precipitation that infiltrates into the groundwater reservoir.
By examining groundwater level readings from 3 boreholes, 12 shallow wells, 16 hand-dug wells, and information from 89 springs, the groundwater flow dynamics is controlled by surface morphology and structures and flows from the northeast towards the west, aligning with the flow of the Beles River.
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Keywords
Baseflow Separation, Chloride Mass Balance, Groundwater Flow Dynamics, Recharge Evaluation, Wetspass