Gauteng is located on the continental divide with some rivers flowing towards the Indian Ocean and others to the Atlantic Ocean. It contains the headwaters of a number of important river systems in an urban environment. Important rivers include the Klip River, Natal Spruit and Blesbok Spruit that forms part of the Vaal River primary catchment, the Jukskei, Hennops, Apies and Pienaars Rivers that form part of the Crocodile River West catchment, and headwaters of the Olifants River primary catchment in the eastern most part of Gauteng.
Rivers, Wetlands and Dams
The rivers and streams in Gauteng represent a relatively fine maize of small seasonal fast, flowing channels that are deceptively dangerous during summer storms. The high flow velocity also causes erosion especially where vegetation cover is removed or the banks of rivers and streams are modified. Seasonal flooding is a real danger in several extensive areas in Gauteng. Canalisations of several rivers in urban as well as rural areas have further negative effects. In the Ekurhuleni area excessive damming of small streams occur for agricultural purposes.
The maintenance of rivers in a natural state is important because artificial habitat types, biological communities and ecosystem processes bear no or little resemblance to natural aquatic systems. The in stream availability and diversity of habitat is important for aquatic invertebrates. A variety of invertebrate organisms (insect larvae, snails, crabs, worms) requires specific aquatic habitat types and water quality for at least part of their lifecycle. Fish (number of species, sensitivity, size and condition) are good indicators of the longer term influences on a river reach and the general habitat conditions. Healthy riverbanks maintain the form of the river channel, provide habitat for species (aquatic and terrestrial) and filter sediment, minerals and light. Water quality includes the chemical, physical and bacteriological properties of water determine its suitability for use.
The categories of condition of rivers as indicated on Figure A11 are:
AB: (blue): Unmodified, natural – this category is virtually absent in Gauteng;
B: (dark green): Largely natural with few modifications – this category is virtually absent in Gauteng;
C: (light green): Moderately modified – a few rivers mainly in the Dinokeng area fall in this category;
D: (orange): Largely modified – most of the rivers in Gauteng fall in this category;
EF.: (red): Seriously or critically modified – most of the rivers, especially headwater and tributaries along the continental divide fall in this category;
Z: Condition modelled as not intact – in a few places where rivers have been transformed (canalisation etc.).
The urban nature of Gauteng (especially the central part) as well as road networks across the province seals natural surfaces in manner that does not allow natural infiltration of rain water into the ground. This high runoff scenario during rainfall events coupled to pollution emanating from the urban environment puts a high level of stress on the river system of Gauteng.
The following are drivers for the poor state of rivers in Gauteng:
Polluted urban runoff, especially sewage that enters the system through the stormwater system;
Effluent from mining activities and mine dumps as well as the release of poor quality water that are pumped from mines;
Sand winning especially along natural river floodplains;
Effluent emanating from heavy industries such as steel mills, paper mills, power stations and large factories;
Erosion caused by overgrazing;
Water running from cultivated fields often contains high levels of salts, nutrients and even pesticides, that damages river health; and
Sewage treatment works that does not function optimally releases poor quality of water with elevated levels of nutrients, salts and bacteria in to the river systems.
Water quality and the state of the rivers in Gauteng constituted the biggest single concern in Gauteng and inter alia includes:
Unacceptably high levels of pollution in almost all rivers from many sources;
Need for new development to incorporate the following planning and design:
Water catchment capacity for foreseen additional urban development;
Sewage capacity and management in respect to exiting and foreseen additional urban development;
The management of erosion and excessive sedimentation in respect to existing and foreseen additional urban development;
The management and remediation of acid mine drainage where it occurs and its impact on the development, production and conservation potential of Gauteng; and
The maintenance of river banks and channels to ensure proper drainage in order to avoid current and likely increased water runoff, especially in urban areas.