State of the Environment: Cape Metropolitan Area: Theme: Water : Health of rivers, vleis and wetlands

Water

ISSUE: Health of rivers, vleis and wetlands

The health of rivers, vleis and wetlands in the CMA is under threat mainly due to deteriorating water quality.

Increased urbanisation in river catchments in the CMA leads to a number of impacts on the health of rivers, wetlands and vleis. These include:

canalisation and encroachment of urban development into the floodplain;
poor water quality as a result of sewage and industrial effluents and stormwater run off;
increased flows leading in some cases to changes in flow regimes of the river, from seasonal to perennial;
removal of indigenous riparian vegetation and encroachment of invasive alien vegetation; and,
dumping of litter and rubble.

Deteriorating water quality in dams and aquifers, which in turn affect the health of rivers, vleis and wetlands. In addition, over-abstraction of water from rivers on the outskirts of the CMA flowing through rural and peri-urban areas leads in many cases to changes in flow regime.

Of the 10 major catchments in the CMA, six currently receive effluent from sewage treatment works. Nine percent of treated effluent is currently reused for industrial purposes.

Rivers are categorised according to six ecological status classes. These classes indicate the percentage of a river’s potential ecological value (or naturalness) that remains. The total length of rivers in the CMA is 353.82 km and, in 1998, were categorised as follows:

Class 1 (100% of potential value; unmodified, natural): 46.7 km
Class 2 (80-99% of potential value; largely natural with few modifications): 17.65 km
Class 3 (60-79% of potential value; moderately modified): 72.98 km
Class 4 (40-59% of potential value; largely modified): 147.71 km
Class 5 (20-39% of potential value; seriously modified): 68.21 km
Class 6 (0-19% of potential value; modifications have reached a critical level and there has been an almost complete loss of natural habitat and biota.): 0 km

The specific state of rivers varies greatly between catchments in the CMA, depending mostly on the degree of urbanization in the catchment. In 1998, the majority of river reaches where accorded an ecological class status of four (40 – 59% of potential value), with nine river reaches regarded as having high rehabilitation potential.

Of the 11 coastal lakes/estuaries assessed in 1998, four were accorded class 3 status while five were accorded class 4 status. Two, namely Wildevoëlvlei and Zeekoeivlei, were accorded only class 5 status, where severe water quality problems exist due to eutrophication. Most wetlands in the CMA display undesirably high trophic levels. There were two toxic algal bloom episodes recorded in 1998. Both occurred at Wildevoëlvlei during the summer months.

The protozoan parasite Giardia has been detected in certain dams supplying the CMA with potable water as well as a number of recreational vleis, namely Zeekoeivlei, Little Princess Vlei and Wildevoëlvlei.

Faecal coliform levels exceeding European Union guidelines have been reported in the Black River, Vygekraal River below Athlone Wastewater Treatment Works, and the Big Lotus River.

Nine reaches of rivers assessed display rehabilitation potential. The majority of those were classified as Class 3 status. Of the 11 coastal lakes/estuaries studied, four were considered borderline in terms of their ecological status. The class status of Wildevoëlvlei (Class 5) and Zandvlei (Class 4) could be improved with very little intervention. Conversely, the eutrophic and hypertrophic lakes of Zeekoeivlei (Class 5) and Princessvlei (Class 4) require considerable effort to improve their ecological status class. A relatively small increase in negative factors would, however, force them into a lower class.

Water quality in catchments is variable and is generally good in mountain streams, becoming degraded in rivers flowing through urban areas. Water quality tends to improve in the major vleis due to dilution of the various chemical constituents in the larger water bodies, e.g. ammonia and phosphorus. The higher levels of soluble reactive phosphorous in some catchment areas can be linked to runoff from fertilised market gardens.

The following responses are underway by the CMC:

Integrated Catchment Management has been adopted as a process and a Catchment Management Department has been established. Integrated Catchment Management results in the drafting of Catchment Management Plans and the establishment of broadly representative Catchment Management Forums to prioritise catchment management issues and strategies. Such forums have been established for the Khayelitsha Wetlands, Noordhoek Valley (Wildevoëlvlei), Kuils River, Black River, Sand River, Disa River and Big Lotus River catchments.

A study is being undertaken, in conjunction with South Peninsula Municipality, to upgrade the Wildevoëlvlei Waste Water Treatment Works. Extensions to these works are being constructed and will incorporate improved nutrient removal processes.

A reporting system to monitor the state of rivers in the CMA is being developed. This will be consistent with the DWAF river health reporting system.

A Geographical Information System is being established and will be designed specifically to manage catchment-related information generated within the CMA.

An Environmental Significance Mapping Project has been commissioned, which will include an ecosystem map of the CMA.

Aquatic weed control and river maintenance activities in the CMA are being co-ordinated.

Do not litter or dump any solid or liquid wastes into rivers, vleis and wetlands.
Do not throw any chemicals and other harmful substances down the drain.
Notify the authorities if you see anyone dumping waste into rivers, water bodies or stormwater drains.
Join an NGO or CBO that is involved in monitoring and rehabilitating river and vlei environments.