NUMERICAL GROUNDWATER FLOW MODELING OF THE CENTRAL MAIN ETHIOPIAN RIFT LAKES BASIN

Abstract

A three dimensional steady·state finite difference numerical groundwater flow model (MODFLOW) was used to study the groundwater.surface water interactions in the C..entral Main Ethiopian Rift lakes basin. Special emphasis is given to quantifying the groundwater fluxes and the subsurface hydraulic connection of the rift valley lakes. The result shows that despite the geographic proximity of the lakes the groundwater flux is highly variable, mainly owing to geologic factors. The net groundwater flux ranges fr<:?m 7,011 m 3 / day for Lake Abiyata to 651,022 m 3/ day for Lake Shala. The groundwater flow converges from all sides of the basin to the center of the rift where the lakes are clustered, and ultimately to the tenninal Lake Shala. Local, intermediate and regional flow systems were identified. The direction and magnitude of the faults have strong bearing on the occurrence and movement of the groundwater.
The major flow systems and groundwater flux into the lakes are controlled strongly by rift faults.