Evaluating the relationship between hydrological extremes and groundwater in Luvuvhu River Catchment, South Africa

Abstract

Extreme hydrological events have been reported to be on an increase in terms of magnitude and frequency in southern Africa. Groundwater in this area plays a significant role in domestic water supply and agriculture. The aim of this study is to evaluate the relationship between groundwater levels and hydrological extremes in north-eastern South Africa. An index-based approach was used to determine the drought and flood events over the study period while the Water Table Fluctuation approach was used to determine groundwater recharge. Flow duration curves were further employed to determine the exceedance period of high and low flows in the study area. Mann-Kendall and Sequential Mann-Kendall were used to detect trends and the point of change. Both floods and drought were found to have occurred in the study area at different magnitudes, however both the Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSI) found that majority of these were not categorized as mild to near normal conditions. Specific yield determined using the simple linear regression method ranged between 0.04 and 0.06. Groundwater recharge estimates ranged between 1.1 and 11.5 % of mean annual rainfall ranging between 167–1000 mm/a. About 60 % of the stations (i.e. rainfall, streamflow, and groundwater) show significantly decreasing trend. This therefore indicates that there is a decreasing trend in groundwater levels, streamflow, and rainfall over the study area. Based on the trend analysis findings, it suggests that extreme events in the catchment influences groundwater resources.