Groundwater–lakewater interactions: an evaluation of the impacts of climate change and increased abstractions on groundwater contribution to the Volta Lake, Ghana

A 3D steady state groundwater flow model has been calibrated for the Afram Plains portion of the Southern Voltaian Sedimentary Basin. The model was based on data of hydraulic parameters of the aquifer in the area, and regional groundwater recharge estimates conducted by various researchers using a variety of methods. Model calibration was conducted using hydraulic head data of 43 boreholes in the area. Although the groundwater system in the area appears to receive some amount of recharge from the Volta Lake, the net groundwater outflow into the lake currently outstrips the volumes received from the Lake. The net effect, as suggested by the calibrated model is that groundwater outflows into the Volta Lake amount to approximately 465 m ³ /day (169,725 m ³ /year). However, with increasing groundwater abstractions at a rate of 2.5%, consistent with annual population projections, a reversal of flow is predicted by 2030 if groundwater recharge remains at the 2015 rates. This would lead to a net lake discharge of approximately 9755 m ³ /day into the aquifer system to sustain abstraction rates by 2050. This is predicted to increase further if there is a reduction in groundwater recharge as suggested by regional hydroclimatological data. A 25% reduction in groundwater recharge rate by 2050 will induce a net lake discharge of approximately 11,000 m ³ /day into the aquifer system to sustain abstractions for domestic consumption. Lateral outward/environmental flows will reduce from 5200 m ³ /day to 2700 m ³ /day under the 2015 recharge conditions, and 1300 m ³ /day under conditions of reduced recharge by 2050. Groundwater in the area does not appear to hold promise for commercial abstraction for irrigation purposes, especially under climate change conditions.