Catchment areas vary greatly in size - a big river may have a catchment area of several thousand square kilometres, whereas a smaller tributary will have a catchment area of only a few hectares.
Catchments are separated from each other by watersheds. The characteristics of any river (physical, chemical, biological) are determined by the nature of the catchment and the activities , both human and natural, that take place in it.
* Plants slow down water as is flows over the land (runoff) allowing much of the rain to soak into the ground and replenish pools of underground water. Water seeps from these aquafers into rivers which are therefore usually perennial (flow throughout the year).
* Plants prevent soil erosion as their root hold soil in position, preventing it from being washed away. IN addition plants break the impact of a raindrop before it hits the soil, thus reducing its erosive potential. Rivers running through an undisturbed catchment are clean, erosion is slow, and limited to periods of very high rainfall.
* Vegetation in wetlands and on the banks of rivers is of particular importance. The roots of the reeds, sedges, trees, shrubs and grasses growing in wetlands and next to rivers bind the soil of the riverbank and prevent erosion whilst cleaning the water and regulating its flow.
* prevention of water pollution from informal settlements, industry or agriculture;
* protection of riverbank vegetation.
It is important that all people in the catchment are involved in each stage of the conservation programme, from planning to execution, as they will be responsible for its success or failure. Catchment management committees, which may be private, provincial or national, are active in both rural and urban areas, eg. Umgeni Water in KwaZulu/Natal and the Braamfontein Spruit Trust in Gauteng.
* Start a catchment conservation project for a river in your area.
* Take part in the "Rivers and Ridges" competition run by the Wildlife Society in Gauteng.
* Read "The Biology and Conservation of South Africa's Vanishing Waters" (see below) which includes a very useful chapter entitled "What you can do."
INDIGENOUS AFFORESTATION OF DEGRADED WATER COURSES. Wildlife Management Technical Guide, Natal Parks Board, 1990.
MANAGING THE WATER RESOURCES OF SOUTH AFRICA. Dept. Water Affairs, 1986.
All books are available from Russel Friedman Books, PO Box 73, Halfway House, 1685. Tel. 011-7022300/1.
Enviro Facts: "Precious Water", "Wetlands", "Estuaries".
Local nature conservation authority.
Dept. Environment Affairs anf Tourism. P/Bag X447, Pretoria, 0001. Tel. 012-310 3425.
Wildlife Society of Southern Africa. Head Office, PO box 44344, Linden, 2104. Tel. 011-486 3294/5 or 0938.
Share-Net. Wildlife Society, PO Box 394, Howick, 3290. Tel. 0332-303931. Produces resource materials.
Project W.A.T.E.R. (Water Awareness Through Educational Responce.) PO Box 9, Pietermaritzburg, 3200. Tel. 0331-454365.