Investigating groundwater and surface water interactions in the Uthukela Catchment, KwaZulu-Natal, South Africa.

Abstract

Groundwater-surface water (GW-SW) interactions are not fully explored in South Africa. This study investigated the interaction between GW-SW in the uThukela Catchment, located in KwaZulu Natal, South Africa. Understanding the complex interactions of the GW-SW is very important for water resources and water quality management, thus making it essential to investigate the factors that control these interactions. The widely referred factors include topography, geology (lineament and dykes), climate and land use. The research employed stable isotopes of oxygen-18 (δ¹⁸O) and deuterium (δ²H), piezometric analysis, baseflow analysis, in situ measurements of radioactive radon isotope (222Rn), and hydrochemical parameter of Temperature, pH and electrical conductivity (EC). Rainfall δ¹⁸O and δ²H were sampled across altitudinal transect and precipiation gradient at five locations; Catchment 6 (1921 masl, 1273 mm), Mike Pass (1621 masl, 1236 mm), Winterton (1103 masl, 833 mm), Pietermarzitburg (627 masl, 825 mm), and Eshowe (522 masl, 800 mm). The δ¹⁸O and δ²H revealed a weak altitude effect limiting its use to trace regional scale movement of groundwaters.The role of groundwater was investigated across three spatial scales: hillslope, catchment, and regional. A total of 470 samples were collected and analysed during the dry and wet seasons. These included 39 groundwater samples, 28 wetland samples, 363 surface water samples, and 40 spring samples. At the hillslope scale, stable isotope data and EC measurements indicate that groundwater plays a dominant role in runoff generation both during rainfall events and periods of no rainfall. At the catchment scale, stable isotopes and EC measurements shows mountain front aquifers are recharged from losing streams. Additionally, at the regional scale, ²²²Rn and baseflow analysis indicate substantial groundwater contributions to streamflow in the upper uThukela Catchment. However, there is no clear evidence of deep regional groundwater flow.