The Zandvlei estuary mouth is manually managed to support flushing of nutrients and sediment out of the system and to manage the salinity levels. This is in compliance with conditions of the Zandvlei Estuary Mouth Maintenance Management Plan: DEADP Reference E12/2/4/7 – A5/328 – CJ2142/11.
The vlei mouth is opened and closed mechanically at full moon and spring tides where the tide is generally in excess of 1,8 meters.This is to get as much sea water into the estuary as possible. The rainfall in the catchment is monitored electronically. With telemetry the responsible Managers are notified of the rising and falling water levels in the catchment rivers.
Mouth will remain open in the winter months, unless there is very little rainfall. Officials monitor the forecasts daily.
Mouth openings are subject to weather conditions which may necessitate adjustments to planned dates or the introduction of additional dates.
The Zandvlei Catchment Forum and Zandvlei Protected Areas Advisory Committee (City of Cape Town, Provincial and National government officials and other interested stakeholders) regularly review in and out flows of Zandvlei, as there are a number of critical factors which have to be maintained. ie. water levels for flood management for the residents and waterbody user groups, also the salintity levels need to be maintained so that the estuary may function to an optimum for aquatic fauna and flora.
Martin Thompson has produced a pamphlet: Zandvlei – Factors concerning Water Level Management. (Link: Zandvlei Trust website, archive, PDF of web page)
This pamphlet sets out the background information in priority order for
- Revetment stability (concrete walls around the vleis edge)
- Fish migration