University of Twente Student Theses


Groundwater flow modelling of Dire Dawa sub-basin, Ethiopia

Gebretsadik, Solomon (2011) Groundwater flow modelling of Dire Dawa sub-basin, Ethiopia.

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Abstract:The study focused on assessment of groundwater resource potential and prediction of the response to future abstractions through steady- state flow modelling in Dire Dawa groundwater sub-basin( eastern Ethiopia) , which is the only source of water for Dire Dawa and Harar areas. Boundary condition was assigned to the model to simulate inflow and outflow terms of the model domain. The model domain was delineated based on a DEM extracted from a SRTM image and a hydrogeological map. The aquifer system was modelled using PMWIN as pre and post processor for MODFLOW (Mc Donald and Harbaugh, 1998). The aquifer was simulated under unconfined condition and represented by a single layer of 74-300 m of variable thickness. Aquifer parameters were assigned by zoning based on analysis of pumping test data and a hydrogeological map. To represent the aquifer parameters in the model spatially grid cells of 200x200 m were taken for the entire area (256 km2) later refined at the groundwater outlet area to 40x 40 m. The recharge condition of the Dire Dawa groundwater sub-basin is characterized by two sources: direct rainfall and inflow water from the upstream areas through the southern boundary. Outflow condition is subsurface lateral outflow and well abstractions. The recharge of the groundwater sub-basin was estimated using chloride mass balance method (CMB) and from simulation of the model. The estimation was 47 m3 y-1 (183 mm) and 50 m3 y-1 (195 mm) respectively. To calibrate the model using observed and simulated hydraulic head trial and error method was used by zoning based on hydrogeological map. The water budget of the Dire Dawa groundwater sub-basin simulated for 2025 reached equilibrium condition with recharge from both direct recharge from rainfall and inflow from the southern boundary of 50 m3y-1, well abstraction of 34.9 m3y-1 (the average water demand up to 2025), and outflow through the general head boundary 15.1 m3 y-1. The calibration of the model was done with one year piezometric head data and needs calibration using more than one year data and verification to say the results obtained from the simulation fully represent the real condition the groundwater sub-basin. Based on the calibrated model results recommendation were made. Key words: Dire Dawa groundwater sub-basin, groundwater modelling, recharge, abstraction
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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