The Western Karoo depends entirely on groundwater for domestic and agricultural use. An understanding of the chemical evolution of the groundwater provides insight into the interaction of water with the environment and contributes to better resource management.Descriptive statistics, correlation matrices and factor analysis, together with stable isotope data were used to gain an understanding of the hydrochemical processes of the groundwaters in the fractured rocks around Sutherland in the Western Karoo. The main processes influencing the groundwater chemistry are salinisation, mineral precipitation and dissolution, cation exchange and human activity. The stable isotope data indicate that the infiltration of evaporated water is partly responsible for the occurrence of saline subsurface waters. The ionic, oxygen and hydrogen stable isotope composition of the groundwaters suggests that the effects of localised topography are one of the overriding factors controlling the groundwater chemistry. In higher lying areas, Ca(HCO 3 ) 2 type waters are prevalent, while in topographical flat areas NaCl type waters dominate. In areas where water collects close to or at the surface, saline soils are formed. From these areas salts are leached to the subsurface, during significant recharge periods. These findings are important in that they contribute to the identification of suitable locations for developing groundwater resources that could yield a relatively better quality water. ᭧

No abstract

In South Africa, the flow requirements for maintaining the normal functioning of aquatic ecosystems is termed the "ecological reserve", and these should be determined when a licence application for water allocation is processed. Determination of the ecological reserve entails investigation of the relationship between the major interactive components of the hydrologic cycle, namely groundwater and surface water bodies including rivers, lakes and estuaries. Information on groundwater discharge towards surface water bodies is critical for the water resource manager to make a decision regarding the amount of groundwater allocation that can be licensed without causing a negative impact on aquatic ecosystems. Existing techniques of hydrograph-separation are too subjective either due to the fact that assumptions of the techniques cannot be met in reality or that the parameters used in models do not have physical meanings. This paper presents a geomorphologic framework under which the quantification of groundwater from a hydrograph is discussed. A focus is placed on hydrogeomorphological typing that can be used to guide a process of separating groundwater discharge time series from hydrographs where a monthly groundwater discharge time series is required for comparison with instream flow requirements. For generating monthly groundwater discharge time series, a generic procedure is proposed, which is applied in a case study.

No abstract