Enviro Facts - River Catchments



41) RIVER CATCHMENTS Estuaries are silting up, inland wetlands are disappearing, some perennial rivers are drying up, and rivers, lakes and dams are polluted! Water bodies in southern Africa clearly suffer from many problems - all of which are linked to the way in which the catchment area is used. WHAT IS THE RIVER CATCHMENT The river catchment, or drainage basin, is all the land from the mountain to to the seashore, drained by a single river and its tributaries. 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. THE IMPORTANCE OF PLANTS In catchments which have not been cultivated or developed, the ground cover or vegetation is still in place. Ground cover is important for the following reasons: * 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. DISTURBED CATCHMENTS Where plant cover in river catchments has been disturbed by farming, industry and settlements, soil erosion increases. In addition, without plants, runoff increases and the supply of water to aquafers is reduced because less water soaks into the ground. Consequently rivers do not have a continuous supply of water from the aquafers and flow only in the rainy season. Much of the deposition of silt into estuaries results from erosion of riverbanks. When riverbank vegetation is remove, the banks are at the mercy of the erosive forces of flood waters which scour away the riverbank allowing the adjacent slope to collapse. CATCHMENT CONSERVATION A catchment conservation programme should include: * protection of wetlands such as vleis and marshes; * sound conservation practices on agricultural and forestry lands, eg. all ploughing and planting should be on the contour; riverbank vegetation should not be disturbed; lands should be strip cropped; * prevention of water pollution from informal settlements, industry or agriculture; * protection of riverbank vegetation. COORDINATING LOCAL ACTION A catchment is ideally suited to coordinated planning and management, requiring cooperation between the many land owners and residents in the catchment. A first step in encouraging collective action is the formation of a catchment management committee, with representatives of all major land users (eg. farmers, municipal and government officials), which is guided by regional planners. This management committee should survey the catchment, and investigate with specialists the best methods of controlling problems. 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. WHAT YOU CAN DO * Alert your local land use authority to misuse of a catchment. * 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." FURTHER READING THE BIOLOGY AND CONSERVATION OF SOUTH AFRICA'S VANISHING WATERS. B.R.Davies and J.A.Day. CEMS, University of Cape Town and the Wildlife Society of Southern Africa, 1986. 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". USEFUL ADDRESSESS Regional offices of the Dept. of Africulture. 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.
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