Characterizing the Groundwater Potential of Wabi Shebelle River Basin
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Date
2015-10
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Addis Ababa University
Abstract
Water is one of the limiting factors for development in the Wabi Shebelle basin area. The overall
quantity of water available in the basin is very insufficient. In addition, the difficult access of
water resources in the basin severely restricts their utilization. With an area of some 191146 km2,
the WSRB basin mainly comprises the south eastern highlands of the Arsi Bale. The basin is
endowed with abundant groundwater resources that require proper management if they are to be
wisely utilized in a sustainable manner. With the Wabi Shebelle River as the major resource, the
WSRB is the most undeveloped. The groundwater potential in the basin is seldom estimated.
The objective of this study is to investigate the regional groundwater characteristics and to assess
the groundwater resource potential of Wabi Shebelle river basin. To achieve this objective, a
three dimensional groundwater model (TAGSAC) that uses finite element method were applied.
Ground water models provide a scientific and predictive tool for determining appropriate
solutions to water allocation, surface water – ground water interaction, landscape management or
impact of new development scenarios. The model can also be used to simulate possible future
changes to hydraulic-head or groundwater-flow rates as a result of future changes in stresses on
the aquifer system.
The numerical model was calibrated by trial-and-error methods where by hydrogeological
parameters like hydraulic conductivity and the recharge amount are adjusted. The relatively
small span of physically possible values of head was not considered sufficient to justify the effort
required to implement inverse calibration methods. Calibration results provided the estimate on
the regional distribution of hydraulic conductivity values, which range from 8.64 x 10-8 m/s to
7.7 x 10-4 m/s over 36 zones resulting in a greater reliability of the spatial and temporal evolution
of state variables for simulations. Best model performance achieved, resulted in a mean absolute
error of 8.77 m and a root mean square error of 15.30 m (R2 = 0.9992). From this work the
estimated replenish able groundwater potential of the study area is about (8700 MCM). Results
show that groundwater head have an immediate effect on hydraulic conductivity of the aquifer.
And the amount of recharge also has its own effect on the model simulation.
Keywords: Numerical Groundwater Flow Models; Finite Element Method, Wabi Shebelle
River Basin, Wabi Shebelle River, TAGSAC, Ethiopia
Description
Keywords
Numerical Groundwater Flow Models, Finite Element Method, Wabi Shebelle River Basin, Wabi Shebelle River, TAGSAC, Ethiopia