Africa Center of Excellence for Water Management

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Browsing Africa Center of Excellence for Water Management by Subject "Aquifer Characterization"

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    Groundwater Recharge Estimation and Aquifer Characterization. a Case Study of Walga Catchment Upper Gibe Basin, Central Ethiopia
    (Addis Ababa University, 2020-11-24) Wakjira, Tekalign; Azagegn, Tilahun (PhD)
    Groundwater is mainly used for irrigation and water supply in Walga catchment as other parts of the country. The main objective of this study is to quantify the amount of groundwater recharge using WetSpass model and characterization of aquifers using Aquifer test in the upper Omo-Ghibe basin of Walga catchment. Meteorological data like rainfall, wind speed, temperature, relative humidity, sunshine hours were collected from meteorological stations located within the catchment and nearby area. Potential evapotranspiration was calculated using Penman-Montieth based FAO CROPWAT software. Slope and topography map were generated from Shuttle Radar Topographic Mission elevation data while Land use land cover were prepared from Landsat OLI8 satellite images downloaded from United States Geological Earth Explorer. Parameter table (dbf data) and grid maps were prepared for WetSpass model input with the help of ArcMap 10.4. Using the model the mean annual recharge of the catchment was found to be 7.5% of the precipitation whereas surface runoff was 38.25% of the annual precipitation. The aquifer hydraulic properties were estimated from the pumping test by fitting mathematical models (type curves) to response data (water level changes) through computer software known as AQUIFER TEST. Yield or discharge of bore holes values range from 0.15 l/sec. to 61 l/sec, whereas Transmissivity ranges from 3.5 x10-4 m2/day to 290 m2/day with an average of 50.94 m2/day. Hydraulic conductivity values ranges from 0 to 16.04 m/se with mean values of 1.2 m/s. The sum of the yield from 72 boreholes is 430 l/s (119.4 m3/hr), this gives a total of 37152000 liters per day. 65.8% of Walga catchment coverage is under Satisfactory ground water potential while 0.72% is classified under very good groundwater potential. The mean descriptive statics value of groundwater quality of Walga catchment is below WHO limit and also good for irrigation water quality. The study area is characterized by lowest groundwater recharge relative to surface runoff and actual evapotranspiration due to effect of impermeable soils, morphology of the land and land use land cover of the area. The lowest transmissivity value is indicative of the poor permeability in the pyroclastic lithologic formations and low discharge to wells. It also implies that it will take a considerable time for the aquifers to replace water into wells removed during pumping.