The freshwater resources on which the Durban Metropolitan Area (DMA) depends are under pressure from a range of human activities. The growing need for potable freshwater has resulted in five main channel dams (i.e dams are built across the main channel of the river) being constructed on DMA rivers. In addition, seven rivers have been subjected to canalisation in their lower reaches. The DMA's growing water consumption has resulted in the production of increasing volumes of sewage requiring disposal. Much of this is treated and discharged either to the sea or into nine DMA rivers. Estuarine reaches are negatively affected by catchment malpractices such as soil erosion, soil loss and siltation, runoff from informal housing and from illegal discharges from industrial activities.

Growing needs for potable freshwater

Main channel dams on Durban's rivers

Shongweni - 7x106m3 (1927) Umlaas Nagle - 25x106m3 (1950) Umgeni Midmar - 177x106m3 (1962) Umgeni Albert Falls - 293x106m3 (1976) Umgeni Inanda - 250x106m3 (1987) Umgeni Hazelmere - 40x106m3 (1977) Umdloti

The growth of the Durban Metropolitan Area has increased the demand for potable freshwater. In order to meet these needs, five dams have been built on the main channels of two large DMA rivers. The Shongweni dam, built in 1927, is no longer used to supply water to Durban because of the poor water quality, high siltation and because it is no longer economical. This form of channel regulation significantly alters the quantity and pattern of water flow in these rivers and the amount reaching the estuaries.

The supply of water to users outside a donor river catchment can also significantly alter the flow regimes of rivers. Treated potable water from the Umgeni system (donor river) is supplied to residential areas in other river basins such as the neighbouring Umbilo and Ohlanga (recipient rivers). Much of the water from the donor river may ultimately reach the recipient rivers as treated waste water (return flows) unless it is diverted into a marine disposal pipeline. These return flows can substantially increase the water flow in the recipient rivers and their estuaries, particularly where the waste water treatment works discharge volume is large relative to the river flow (eg Ohlanga and Little Amanzimtoti). Click here to view a map of the DMA rivers and dams.

Flood protection for urban development

Rivers which are partially canalised

Isipingo .................3 - 4km Umlaas................... 3 - 4km Umbilo ................... 3 - 5km Umhlatuzana........... 2 - 3km Amanzimnyama ... 3 - 4km Umgeni .................. 1 - 2km

The expansion and intrusion of the DMA's urban and industrial development onto wetlands and flood plains has resulted in a need to ensure that flooding does not occur. Extensive canalisation of the lower reaches of the DMA's main rivers is a flood protection measure for the infrastructure in these low-lying areas. This has significant impacts on the natural functioning of the coastal reaches of these rivers. The artificial river structure leads to loss of natural habitat and results in a rapid transfer of pollutants and silt from the upper catchment to the recipient system - normally to the detriment of an estuarine component (eg sediment- impacted parts of Durban Bay).

Soil erosion
Poor agricultural practices and some urban developments have resulted in soil erosion and soil loss from the catchment. This has led to increased siltation of some of the DMA's river systems with significant implications for flow regimes and river morphology.

Growing volumes of sewage requiring disposal
The volume of sewage requiring treatment and disposal is increasing as the DMA's population increases. In addition, a higher proportion of residents are using water-borne sanitation as informal settlements are being upgraded. Many wastewater treatment plants discharge their final return flows into the main channel of the nearest river. The largest wastewater treatment works (Central Sewage Works and Southern Sewage Works) dispose of effluent to the sea through submarine pipelines. This results in the loss of freshwater but also a gain in nutrients for a nutrient deficient marine environment.
Click here to view a map showing the location of the different works in the DMA.