Numerical Groundwater Flow Modeling of the Meki River Catchment, Central Ethiopia
No Thumbnail Available
Date
2011-10
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
The Meki river catchment aquifer is located in the central Ethiopian rift valley. This unconfined aquifer is one of the most important groundwater reservoirs of the country. A total catchment of 2319 km2 was selected to study the groundwater flow system using a numerical groundwater flow model (Processing Modflow Pro (Version 8.0.15)). A three dimensional steady-state finite difference groundwater flow model is used to quantify the groundwater fluxes and analyze the subsurface hydrodynamics in the Meki river catchment by giving emphasis to the well field that supplies water to the community. The area is characterized by Quaternary volcanics covered with lacustrine, alluvial, talus, and pyroclastic deposits. The model is calibrated using head observations from 95 wells. The simulation is made in a one layer unconfined aquifer with spatially variable recharge and hydraulic conductivities under well-defined boundary conditions. The calibrated model is used to forecast groundwater flow pattern, the interaction of groundwater and surface water, and evaluate the behavior of the groundwater system under possible future utilization scenarios . A sensitivity analysis conducted indicates that the model is more sensitive to decrease in recharge and increase in hydraulic conductivity but less sensitive to increment or decrement of pumpage.
The simulation result indicates that the groundwater flows from western escarpment to east directions finally join Lake Ziway. Lakes and rivers play important role in recharging the aquifer. Simulations made under different possible future utilization scenarios including increase in pumping rate results in substantial regional groundwater level decline, which will lead to the drying of springs, and shallow hand dug wells. It has also implications of reversal of flow from contaminated rivers in to productive aquifers close to main river courses; decrease in recharge caused more inflow from Lakes as well as increase stream flow but decrease drains, and disappearance of Lake Tuffa results in increased recharge and groundwater outflow through springs. The sensitivity and scenario analysis provided important information on the data gaps and the specific sites to be selected for monitoring that may be of great help for transient model development. This study has laid the foundation for developing detailed predictive groundwater model, which can be readily used for groundwater management practices.
Keywords: Central Ethiopian, Meki, Modeling, Modflow, Volcanic aquifer, groundwater management
Description
Keywords
Central Ethiopian, Meki, Modeling, Modflow, Volcanic Aquifer, Groundwater Management