Groundwater flow modelling in the upper Anga’a river watershed, Yaounde, Cameroon

Abstract

The Anga’a River watershed is located within the Yaounde IV district, South-east of Yaounde City, Cameroon. The groundwater flow and particle tracking modelling was carried out to determine in detail the groundwater flow and particle migration in the shallow unconfined aquifer of the Upper Anga’a river watershed. The watershed was modelled with a grid of 106 columns x 68 rows with two layers viz., unconfined and semi-confined aquifers extending up to 50 m depth. The Anga’a river traverses in the central part of the watershed and generally flows North-South. Lateral inflows and outflows were
simulated with constant head. The Anga’a river heads and the Lake levels were simulated using a river package. Natural recharge due to rainfall formed the main input to the aquifer system and the output was made of abstraction from pumping wells, base flow to Anga’a River, lake, springs and Evapotranspiration. A steady state groundwater flow simulation was carried out using Visual MODFLOW software and calibrated for the February, 2008 groundwater levels at 18 observation wells. The model computation has converged after 170 iterations with a convergence criterion of 0.01 m. The
computed groundwater level contours have been following the trend of observed ones. The computed
groundwater balance indicated that the Anga’a river base flows come from the groundwater regime. Groundwater Flow model results indicated that the topography controls groundwater flow in the watershed and that base flow to river is an important factor moderating groundwater movement in the Anga’a river watershed.