Groundwater flow modeling of Kwa Ibo river watershed, Southeastern Nigeria

Abstract

Groundwater flow modeling of Kwa Ibo River Watershed in Abia State of Nigeria is presented in this paper with the aim of assessing the degree of interaction between the Kwa Ibo River and the groundwater regime of the thick sandy aquifer. The local geology of the area, called Benin Formation, is of Quaternary to Recent age. Potential aquifer zones earlier delineated using the geoelectrical resistivity soundings and well inventory in the area formed the basis for groundwater flow modeling. The watershed has been modeled with a grid of 65 rows x 43 columns and with two layers Lateral inflow from the north has been simulated with constant heads at the Government College Umuahia and outflow at Usaka Elegu in the south. The Kwa Ibo River traverses the middle of the watershed from north to south. The river stage data at Umudike, Amawom, Ntalakwu and Usaka Elegu have been used for assigning surface water levels and riverbed elevations in the model. Permeability distribution was found varying from 3 to 14.5 m/day. Natural recharge due to rainfall formed the main input to the aquifer system and abstraction from wells, the output. A steady-state groundwater flow simulation was carried out and calibrated against the May 1980 water levels using 26 observation wells. The model computations have converged after 123 iterations. Under the transient-state calibration, the highest rainfall (and hence groundwater recharge) over the ten-year study period was recorded in 1996, while the lowest was recorded in 1991. The computed groundwater balance of 55274m³/day was comparable to that estimated from field investigations. Results from the modeling show that abstraction is very less compared to groundwater recharge. Hence there is the possibility for additional groundwater exploitation in the watershed through drilling of bore holes.

Keywords: groundwater, modeling, permeability, recharge, Kwa Ibo River

Global Journal of Geological Sciences Vol. 3(2) 2005: 169-177