Application of GMS - MODFLOW to Investigate Groundwater Development Potential in River Meme Catchment, Kogi State, Nigeria

Groundwater modelling is an important tool that can be used to determine appropriate management strategies for groundwater conditions. It is useful in monitoring groundwater levels due to extensive exploitation as is presently done in the Otokiti area on the River Meme catchment, Lokoja, Nigeria. A conceptual model was developed using Groundwater Modelling System (GMS) software. The model was calibrated both in steady and transient states. The steady state calibration was done for March 2009, aquifer performance data while the transient model was calibrated for March 2016 aquifer data. Results from calibration showed values of hydraulic conductivity varying from 0.02 to 25.6 m/d while the recharge rates varied from 0.0001 to 0.0007 m/d. A predictive run was done from 2016 to 2026 where the model examined the response of the aquifer to abstractions under three different schemes. In Scheme A, the abstractions remained the same as that of the current year 2016. In Schemes B and C, abstractions were increased by 20% and 60% respectively over the 2016 rates. The results showed that there was very little decline in head for locations near the rivers at the eastern and western parts of the catchment. However, for locations in the central part of the study area, which were mostly residential, there was a gradual decrease in head of up to 6 m for scheme A, 6.5 m for scheme B and 6.8 m for scheme C. The implies that even if the rate of abstraction is increase by up to 60% i.e. at 122 m3/d, the groundwater system would still be sustainable as a main source of supply for domestic consumption. The volumetric budget of the study area for the three abstraction schemes also showed that the groundwater abstraction was generally less than the annual groundwater recharge. Consequently, more water is available in the formation which can be abstracted for future development without any appreciable loss of head.