Long-term salinity changes in the Crocodile river catchment upstream of Hartebeespoort dam

Abstract

This research study investigated the changes in the salinity composition and fluctuation of the Crocodile river and its catchment upstream of the Hartbeespoort dam covering the period of 1985 to 2015. By analysing the 35-year long-term data sets of nine monitoring stations in the study area’s catchment, various trends and patterns emerged. Maucha diagrams and various graphs were drawn by utilising the above-mentioned data sets. These Maucha diagrams and graphs indicated the changes that took place in the salt composition of the water sources in the catchment of the study area over the 35-year study period. The following three salts, TDS, SO₄ and TAL, showed the biggest margin of change while the other salts remained fairly stable over the study period. Thus, the study focussed on these three salts. The five-yearly average of the TDS, SO₄ and TAL concentration, loads as well as the volume of water coming down the catchment were calculated. By interpreting the results, it was clear which sub-catchments were responsible for the specific salinity changes identified, as well as the possible sources of those changes in the salinity composition and fluctuation. Both the Jukskei river and the Bloubankspruit had significant impacts on the salt composition, concentration and loads in the Crocodile river although the nature of their impacts differed. The main drivers of salinity changes in the Crocodile river catchment were found to be anthropogenic sources such as increased run-off resulting from urbanisation, the progressive expansion of hard surfaces, increase in economic and industrial activities with their corresponding pollution sources, population growth, water transfer from outside the study area’s catchment and an increase in the volume of water deposited study area’s catchment. The importance of continued monitoring and sampling programmes were emphasised during this research study.