Steady State Numerical Ground Flow Modeling of Ada’a Plain Aquifer Upper Awash Basin
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Date
2022-06
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Addis Ababa University
Abstract
The Ada’a plain is located within the upper awash basin, East of Addis Ababa City, Central Ethiopia. The Steady state Numerical groundwater flow modelling was carried out to understand present groundwater conditions in the Ada’a Plain and to help estimate groundwater availability and water levels in response to present withdrawal and potential future development. In this thesis a WetSpass modeling was used to estimate the groundwater recharge. Results of the study showed that the total groundwater recharge in the study area is 119mm/year (13.45% of the mean annual rainfall).The study area was modelled with a grid of 266 columns x 301 rows with one-layer unconfined aquifer extending up to 450m depth. All the grid size has uniform lateral dimensions of 200m by 200m. Natural recharge due to rainfall and groundwater inflow from specified flux formed the main input to the aquifer system and the output was made of abstraction from pumping wells and base flow to the south eastern direction towards the rift valley. The simulation was carried out using Visual MODFLOW software and calibrated for the 2007 groundwater levels at 69 observation wells. The Water levels in the model are most sensitive to recharge and the horizontal hydraulic conductivity. The computed groundwater level contours have been following the trend of observed ones. The numerical simulation model developed was applied to assess the responses of the Ada’a plain aquifer water level under different pumping scenarios during the next 20 years. Analysis of two different development schemes were formulated to predict the future response of the aquifer under long-term water stress. The computed groundwater budget based on analysis of two different groundwater abstraction scenarios that were formulated to predict the future response of the aquifer under long-term water stress is indicated that the groundwater pumping declined groundwater level and groundwater storage of the plain. Natural recharge due to rainfall and groundwater inflow from specified flux it is an important factor for the sustainability of the groundwater of the plain; however, the intensive abstraction of aquifer decreases the groundwater out flow to the rift valley.
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Groundwater, Numerical Modelling, Groundwater Recharge, Ada’a Plain Aquifer, Model Calibration