The drought is affecting the Zandvlei estuary in two major ways: the water quality and quantity as a potential source of water.
The important message here is that Zandvlei is under stress, like all other local wetlands, due to the low water levels from the drought. The nutrients that have accumulated in wetland systems over time can now be expected to be manifested in algae blooms , excessive plant growth and in this case a new weed species coming to the fore. Wetland systems can be expected to manifest water quality issues in response to the stress imposed upon them by years of city runoff, pollutants and the drought conditions. What we are seeing are symptoms of underlying stresses placed upon our wetlands.
The condition of the Zandvlei estuary is currently a cause for closer monitoring. It is not as dire as some may suggest, considering what it has to accommodate:
1. There is a larger than usual amount of stringy algae. This is due to the hot temperatures, and also a nutrient build up because there is not enough flow to flush the system, because of the extreme drought. Lower water levels concentrate nutrients already in the system – high temperatures spurn algal growth.
2. The drought also means that there is a larger build-up of nutrients higher up in the catchment. When rain does come it washes large amounts of nutrients off the catchment into the estuary in one or two events, as opposed to continued rain with small amounts of nutrients over a long period.
3. The biggest challenge the system currently faces is sediment build up which is impairing the functioning of the estuary as a nursery. The annual maintenance dredging has been redirected to drought emergency measures.
4. The mouth opening depends on flow into the system to manage the salinity, and the flow has been low due to the extreme drought. The build-up of sand in the mouth of the estuary means that when there is tidal interchange the amount of water exchanged with the sea is limited. In addition, the budget for this is also constrained due to drought emergency measures. The sand bar, coupled with the long drought, means a decrease in sea water exchange and a decrease in flushing of the system. Thus the conditions seem to be set for poor water quality issues in the summer ahead.
The top priority of the ZPAAC currently is to dredge the estuary. While this will have a positive impact on the nutrient balance and hence pond weed growth, the pond weed management is not the main topic under scrutiny. Any help obtaining funds or assistance in getting any amount of dredging done will be welcomed.
There has been reports of water being extracted from the estuary. It is illegal (see below), but people removing water by hand from Zandvlei wouldn’t be a huge ecological disaster; there may be health consequences but this would probably be out of the ambit of the City to resolve.
In terms of the Marina; the first 2m of water is owned by the adjacent property and is not Council property. Thus Council permission is not needed as they are not the land owners. The person however still needs a water use licence from National Government and be registered as a water user.
The Zandvlei water has a high salt content (about half sea water) so it won’t be too good as drinking water.
Below is an extract of the present legislation – it is old and outdated but still in effect. If you witness water extraction, please call the reserve ranger staff (24/7) at 083 499 1717 (please note this is for ENVIRONMENTAL emergencies only).