Groundwater Resource Potential Assessment in the Upper Guder Catchment, West Shoa, Central Ethiopia
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Date
2024-09
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Addis Ababa University
Abstract
The purpose of this research is to assess the upper Guder subbasin's groundwater resource potential using hydrometeorological, hydrogeological, and hydro chemical data analysis. The Guder Catchment, which is the main tributary of the Abay Sub-basin, is located between latitudes 1011758mN and 962477mN and longitudes 321928mE and 405109mE. The watershed spans roughly 2200 km2. Extremely rough terrain, a dendritic drainage pattern, and a tropical to tropically wet and dry climate are its defining characteristics. The area elevations range from 1700 to 3300 m.a.s.l. The catchment's annual precipitation is estimated to be 1267.2 mm/year using the long-term mean monthly rainfall data. The estimated PET values, derived from the Penman and Thornthwaite method, are 995.83 mm/year and 738.77 mm/yr. AETs of 774 mm/year and 733.48 mm/year have been determined using the Turc and soil-water balance approaches, respectively.
According to water balance and chloride mass balance methods, the yearly groundwater recharge was estimated to be 148 mm/year and 236.89 mm/year, respectively. The Actual evapotranspiration, surface runoff, and average annual long-term groundwater recharge in the catchment have all been modeled by the wetSpass model. The findings show that the annual results are 558.4 mm/year,340.5mm/year, and 298 mm/year, respectively. The catchment contains the following lithologic units: Jima lower basalts and Tarmaber formation; Tertiary volcanics (Lower Basalts, Guder-Babicha basalts and Upper basalt, Alaji Rhyolite and plugs); Quaternary sediment (Alluvial and Eluvium); and Mesozoic (Abay beds, sandstone). The most extensive lithology in the study area is found in tertiary volcanic rocks. The basin is classified as a local aquifer, extensive and moderately productive porous aquifers, extensive and highly productive fissure aquifer, extensive and highly productive porous/fissured aquifer, low productive fissured/porous aquifer, and aquitards based on qualitative and quantitative
analysis of aquifer/aquitard characteristics. The primary water-bearing component of the catchment is the weathered and fractured volcanic rocks. Higher discharge, hydraulic conductivity, and transmissivity values are mapped at or near fractured areas and towards the outlet based on the available borehole data.
The regional groundwater flow is typically northward, and water moves from the surrounding highlands to the discharge areas along a low hydraulic gradient.
According to the hydro chemical analysis, the predominant cation is Ca, and the predominant anion is HCO3. According to graphical plots, the predominant water types in the region are Ca-HCO3 and Ca-Na/Mg-HCO3, which have low TDS and EC values in highland areas (recharge zone) and relatively high TDS and EC values relative to the recharge area. The majority of water sample results indicate that the area is suitable for irrigation and residential use.
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Keywords
Transmissivity, Aquifer, Upper Guder Catchment, Groundwater, Evapotranspiration