Modelling potential groundwater recharge in the Limpopo River Basin with SWAT-MODFLOW

Abstract

Understanding groundwater recharge processes is important for development of water resources in arid and semi-arid regions. This study sought to build a regional-scale surface water-groundwater model with SWAT-MODFLOW for assessing the spatial distribution of annual and seasonal groundwater recharge and interactions with surface water in the Limpopo River Basin (LRB), Africa. The model was calibrated and evaluated for monthly streamflow from 1984 to 2013 in the basin. Due to the lack of reliable measured water table data, water table elevation was compared to estimates of water table depth reported in the literature for the basin. Simulation results from this study suggest an annual average recharge of almost 0–530 mm over the basin while simulations show a range of 1300 m in summer to 1400 m in autumn for groundwater table elevation. Annual and seasonal analysis show high spatial variability in both water table and recharge. Annual recharge along the Limpopo main river and at the outlet of the basin was high compared to other locations in the basin. Groundwater table appears generally shallow in the rainy east region and along the Limpopo River network. Summer months have the highest groundwater recharge with an average of 147 mm/year over the basin, followed by autumn with an average of 27 mm/year, spring with 3.2 mm/year, and winter having the lowest seasonal recharge of 0.3 mm/year during the 30-year study period. The simulations also suggest high spatial variability in groundwater-surface water interactions in the basin's rivers. Rivers in the southern region show input from groundwater discharge while west river channels appeared to seep to the underlying aquifer. The results can assist with groundwater management by providing insights into areas of high recharge and problematic areas susceptible for water quality pollution, especially where groundwater discharge is experienced.