Interbasin Groundwater Transfer in Upper Rift Valley Lakes and Upper Awash River Basins
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Date
2005-06
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Addis Ababa University
Abstract
Groundwater models are used to predict the groundwater flow processes using mathematical
equations based on certain simplifying assumptions. Numerical modeling method is used to
investigate the possibility of groundwater transfer (interbasin groundwater flow) between
Upper Awash River basin and Upper Rift Valley Lakes basin. Within the study the
hydrogeology is investigated from previous studies, a conceptual groundwater model is
produced and the numerical model is developed from this. The model conceptualization is
done by idealizing the study area into three models related to the surface water divide and the
main perennial Rivers and lakes. For these three basins the boundary conditions are identified
and incorporated into the models. The boundaries are Upper Awash River, Meki River, Ziway
Lake, and Koka Lake in addition to bottom and top surface of the aquifer in concern. The
models are three dimensional steady state by finite element method. All the study basins are
discretized according to finite element method into equal element dimensions. The elements
are three dimensional. The finite element model used in the study was TAGSAC. The
modeling process was towards estimating the hydraulic head in the model basins of the study
area by a means of finding the hydraulic conductivity of different geological classifications
and estimating surface recharge in terms of some percentage of the rainfall of the study area.
Finally the models are calibrated with the measured hydraulic head for each model basins.
The models results show that the groundwater divide and the surface water divide are not
coincident. There is a clear hydraulic head difference which can make groundwater to flow
from Upper Rift Valley Lakes basin towards Upper Awash basin in the middle of the study
area, along Ziway- Koka Lake and from Upper Awash to Rift Valley Lakes basin at west and
east part of it.
Key Words: Upper Awash River basin, Upper Rift Valley Lakes basin, Interbasin flow,
Groundwater flow Modeling, Hydraulic head, TAGSAK
Description
Keywords
Upper Awash River basin, Upper Rift Valley Lakes basin, Interbasin flow, Groundwater flow Modeling, Hydraulic head, Tagsak