Zandvlei Trust

ZIMP - Salinity

Opening the mouth of the Zandvlei estuary.

Zandvlei estuary mouth opened.

 

Zandvlei Estuary mouth planned opening and closing dates -
rubble weir is 0.7m above M.S.L.  updated 10/10/2011
Day. Date
Open.		 Day. Date
Close.		 Tide Datum
 in metres.		 M.S.L
 in metres.
- - Fri 30/09/2011 1.86 1.017
Mon 24/10/2011 Fri 28/10/2011 1.92 1.077
Mon 21/11/2011 Fri 25/11/2011 1.89 1.047
Fri 20/01/2012 Tues 24/01/2012 1.77 0.927
Mon 06/02/2012 Fri 10/02/2012 1.82 0.977
Mon 05/03/2012 Fri 09/03/2012 1.89 1.047
Wed 04/04/2012 Mon 09/04/2012 1.78 0.937
Tues 03/05/2012 Mon 07/05/2012 1.83 0.987
Mon 04/06/2012 - - 1.81 0.967
- - Thur 18/09/2012 1.92 1.077
Fri 12/10/2012 Mon 18/10/2012 1.81 0.967
Mon 12/11/2012 Fri 16/11/2012 1.80 0.957
Mon 10/12/2012 Fri 14/12/2012 1.87 1.027

 

General notes.

  • The above tables are supplied by City of Cape Town - Stormwater Catchment Management and are planned dates for opening and closing the mouth. Note - these are planned dates and could change with weather conditions.

  • 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.

  • The Sand River Catchment Forum and Zandvlei Action Committee (City of Cape Town officials and other interested parties) 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 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. This is available from the Roads and Stormwater Department –  Catchment, Stormwater and River Management Branch.
    ph 021 400 1205 or csrm.secretary@capetown.gov.za

  • This pamphlet sets out the background information in priority order for;
    Flooding
    Salinity
    Revetment stability (concrete walls around the vleis edge)
    Fish migration
    Recreation

         

This graph indicates the monthly average or mean salinity collected at 2 points in Zandvlei.
The readings are taken weekly.

  • This information was collected and supplied by Timm Hoffman. It is only part of the information and should not be used to draw any conclusions or make deductions.

  • The data may not indicate the current months readings but will be updated regularly.

  • Royal Road bridge about 50 meters from the mouth of Zandvlei as it enters the sea, and

  • Rutter Road about 2 kms away near the confluence of the Westlake and Keysers Rivers on the western side of the railway line. This water body is fresh, it is located out of the main river flow entering the main water body.

Long-term salinity trends in Zandvlei estuary (Western Cape, South Africa) and implications for dominant macroalgae. by S Muhl, JJ Bolton (corresponding author) and TM Hoffman.

Read the reference document.       new 10/10/2011.

                                                                                                                                               

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