Numerical Groundwater flow Modelling of Gur Catchment, Central Ethiopia
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Date
2023-09
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Addis Ababa University
Abstract
This study focuses on the numerical modeling of groundwater system in the Gur catchment, located in central Ethiopia. The catchment covers an area of 530 km2 and exhibits diverse topographic features, including gorges, flatlands, and ridges, with elevations ranging from 1402 to 3341 m. The climatic classification of the catchment falls on Dega (Alpine vegetated zones), Woina Dega (temperate zone), and Kola (hot zone) climatic zones, with mean annual rainfall ranging from 1029 to 1198 mm and average temperatures ranging from 14.4 to 16.5 °C. Land cover analysis reveals that approximately 83% of the study area is covered by cropland. The geological formations in the study area comprise Mesozoic sedimentary rock units, Tertiary volcanic rock units, and Quaternary superficial sediments. The hydrogeological units identified in the catchment include moderately productive porous aquifers, moderately productive fissured aquifers, and aquicludes consisting of gypsum and mudstone. Two methods, namely the Chloride Mass Balance and WetSpass Model, were employed to derive groundwater recharge estimates, yielding an average value of 104.5 mm/year. Groundwater recharge estimation using the WetSpass Model indicates that the catchment receives an annual runoff of 426 mm (39% of precipitation), evapotranspiration of 561 mm (51% of precipitation), and groundwater recharge of 106 mm (10% of precipitation). The numerical groundwater flow model developed for the Gur catchment demonstrates satisfactory calibration results, with simulated hydraulic heads closely matching observed values. The model predicts a total inflow water balance of 246974 m3/day and an outflow of 246972.7 m3/day, with a small discrepancy of 1.3 m3/day. Scenario analysis reveals that increased groundwater extraction leads to a decline in water levels, while reduced recharge results in a significant decrease in hydraulic heads. Combining decreased recharge and increased groundwater abstraction intensifies the decline in water levels. These findings provide valuable insights into the hydrogeological dynamics of the Gur catchment and contribute to sustainable groundwater management in the region.
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Keywords
Gur Catchment, Groundwater Recharge, Numerical Groundwater Flow Model, Central Ethiopia