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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2953

Title: NUMERICAL GROUNDWATER FLOW MODELING OF THE KOBO VALLEY: NORTHERN ETHIOPIA
Authors: Getaneh, Kinfu Hailu
Advisors: Tenalem Ayenew (Prof.)
Copyright: Jun-2010
Date Added: 10-May-2012
Publisher: AAU
Abstract: The study aims to get better understanding of the groundwater flow system of the Hormat- Golina basin using numerical groundwater flow modeling under steady-state condition. The basin comprises inter-mountain valley (Kobo Valley) which is the most fertile irrigable land. The basin is part of the western escarpment of Afar Rift and measures about 811 km2. The study was ambitious in the sense that the modeling was conducted with limited data particularly for the highland volcanic part of the basin. Two aquifer units: the fractured basalt and the valley fill sediments aquifer were identified in the basin. The fractured basalt aquifer forms the highland part and underlies the alluvial sediments aquifer. The two-aquifer systems were assumed to be hydraulically connected. Deep groundwater circulation was assumed for the highland volcanic aquifer, because of the absence of shallow groundwater features such as springs and base flow of the rivers. The groundwater flow system in the two aquifers of the basin was modeled using PMWIN Pro (Chiang et al., 1998) as pre-and post processor for MODFLOW (McDonald and Harbaugh, 1988). The model was run for steady-state conditions in unconfined aquifer. The grid cell size of the model was taken 250 x 250m and 500m x 500m for the valley part and the highland volcanic aquifer respectively. Model area and the layer top elevation were delineated by the ASTER DEM processing and use of topographic maps. The hydraulic conductivity values were determined from pumping test data analysis and literature review for the alluvial sediment aquifer and the fractured volcanic aquifer respectively. Recharge was estimated from water balance method. The model was calibrated using observed hydraulic heads from 37 wells. The model was calibrated to the root mean square error (RMSE) of about 6m and it was sensitive to recharge and hydraulic conductivity. The model simulated water budget showed that the basin receives a total recharge of (in-flow) 48mmy-1 and discharge it to the river for steady state condition. Similarly, the model generated total in-flow for the highland volcanic aquifer and the alluvial sediments aquifers were 54mmy-1 and 52mmy-1 respectively. The model result showed that the valley fill sediment receives more in-flow from horizontal flux (40mmy-1) than other recharge sources. In this study, the model was calibrated but not verified. Thus, the model results obtained should not be interpreted as a perfect simulation rather as system response for reasonable model input parameters.
URI: http://hdl.handle.net/123456789/2953
Appears in:Thesis - Earth Sciences

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