Groundwater assessment in relation to climatic variation: case study of the Lightenburg Karst Aquifer

Abstract

Monitoring and assessment of groundwater resources in the karst belt in South Africa has been conducted by the Department of Water and Sanitation (DWS) for several years as a special monitoring program as it was considered as a vulnerable aquifer. This was done to determine the groundwater potential for bulk water supply and also the impact of climatic variation and over abstraction on the availability of groundwater in the area. The impact of climatic variation on the Lichtenburg dolomitic aquifer was assessed based on the declining water table from 2013 to 2017. The study analysed previous studies conducted in relation to past drought events in Southern Africa. The study established that climatic variation alone did not result in the decline of groundwater table. Over abstraction was also contributed to the decline of the water table owing to high demand in water use. The standardized precipitation index (SPI) calculated in 2015 corresponds with the declining groundwater table. The groundwater quality of the aquifer was not impacted by climatic variation. The 20 years groundwater quality data indicated that there was no major difference in water quality over different climatic conditions beside slightly elevated sodium in the September 2016 results. The main water facies was represented by Ca-Mg-HCO3 type water. The stable isotope results indicated the possibility of mixing with deep circulating karstic springs and also that evaporation took place before infiltration in some part of this aquifer. The conceptual model indicates quantitative values and findings determined by the study.