Skip to content

Search

Menu

 

 

Sludge removal at Rondevlei to improve biodiversity, health of wetland<p>​The operation is part of the City’s maintenance and management plan for wetlands, and entails the use of heavy machinery for the sludge removal. </p><p>The work commenced on 5 January 2022 and once complete, the sluice gates at Rondevlei will be opened and allowed to drain. The drawdown will take about four months and other water in the vlei will naturally evaporate in the summer conditions.</p><span> <figure class="subtopic-fullsize-img"> <img class="responsive" src="https://resource.capetown.gov.za/cityassets/Media%20Centre/Rondevlei1.jpg" alt="" style="width:951px;" /> </figure><p>‘The sludge is a very fine sediment that consists mainly of old organic matter such as dead reeds, algae, and pondweed, but heavy metals and plastic waste, washed in by stormwater runoff and trapped in the dead organic matter, could also be present. High nutrients have a negative impact on wetlands because all of the special indigenous organisms in our wetland systems are adapted to low nutrient conditions. Thus, by removing the organic sludge the City is improving the overall health, biodiversity, and water quality of the wetland,’ said Alderman Eddie Andrews, the City’s Deputy Mayor and Mayoral Committee Member for Spatial Planning and Environment.</p><span> <figure class="subtopic-fullsize-img"> <img class="responsive" src="https://resource.capetown.gov.za/cityassets/Media%20Centre/Rondevlei2.jpg" alt="" style="width:951px;" /> </figure>​​</span><span>​​ ​With the sludge removed, the outflow from Rondevlei will be significantly better. This means the water level will lower and most of Rondevlei will dry out over the next four months or so.</span></span><p>The water levels of wetlands in the Western Cape are influenced by the climate with low levels during our dry summers and high levels in winter, during our rainy season. However, given the urbanised nature of Rondevlei the wetland often remains full all year.</p><span> <figure class="subtopic-fullsize-img"> <img class="responsive" src="https://resource.capetown.gov.za/cityassets/Media%20Centre/Rondevlei4.jpg" alt="" /> </figure>​‘By facilitating an effective drawdown, we replicate a natural system where the wetland should have a low water level during the summer months when Cape Town has little rainfall. Once the water level has lowered, wading bird species that migrate to Southern Africa in the summer months will feed along the shallow shorelines. One of the main reasons that Rondevlei was listed as a Ramsar site is because it provides a habitat for these migrating bird species which usually stay away when the water levels are too high,’ said Alderman Andrews.</span><p> </p><p>Given that much of the vlei will dry out, it will be easier to remove the water hyacinth, a Schedule 1 Alien Invasive Species which is often described as the world’s worst invasive plant. </p><p>‘Water hyacinth grows at a rapid rate, doubling itself every 14 days in ideal conditions. It floats on top of water and smothers water bodies by killing off species trapped underneath it. Water hyacinth also prevents animals from accessing their habitat. Thus, this maintenance operation will assist to protect and enhance our biodiversity,’ said Alderman Andrews.</p><p>Excavator machines are currently on site and most of the sludge will be removed by truck.</p><p>‘We are grateful to the False Bay Nature Reserve’s Protected Area Advisory Committee and the Friends of Zeekoevlei and Rondevlei who have visited the site after we have informed them about the sludge removal operation. They assisted us with water hyacinth control operations in the past and I want to thank them for their continued support. Unlike Zeekoevlei, there are no residents living along the Rondevlei shoreline, but it is popular with visitors. With a healthier natural system, we will see wading birds returning which will be ideal for birdwatching. </p><p>‘During this time, the resident hippo family at Rondevlei will move to another wetland in the nature reserve, which will not be affected by the drawdown,’ said Alderman Andrews. </p><p>It is important to mention that scouring naturally happens during flood events where the high velocity and volume of water erodes the bottom of the wetland system as it washes everything with it downstream and ultimately to the sea. In natural river systems a lot of scouring happens in the fast flowing upper reaches and there would be a deposition of sediment in the lower reaches of the river as the gradient drops and the water slows down.</p><p>Cape Town’s recreational waterbodies are all situated on the flatter bottom sections of inflowing rivers which aggravates sludge build-up. Thus, we simulate natural scouring through a drawdown. </p><p>Captions:</p><ul><li>Alderman Eddie Andrews (in the white t-shirt), the City’s Deputy Mayor and Mayoral Committee Member for Spatial Planning and Environment, visited the Rondevlei, situated in the False Bay Nature Reserve, where the City is busy removing the sludge. The work commenced on 5 January 2022 and once complete, the sluice gates at Rondevlei will be opened and allowed to drain. The drawdown will take about four months and other water in the vlei will naturally evaporate in the summer conditions.</li><li>Alderman Eddie Andrews (in the white t-shirt), the City’s Deputy Mayor and Mayoral Committee Member for Spatial Planning and Environment, visited Rondevlei, situated in the False Bay Nature Reserve, where the City is busy removing the sludge. The work commenced on 5 January 2022 and once complete the sluice gates at Rondevlei will be opened and allowed to drain. The drawdown will take about four months and other water in the vlei will naturally evaporate in the summer conditions.</li><li>Given that much of the Rondevlei will dry out it will be easier to remove the water hyacinth, a Schedule 1 Alien Invasive Species which is often described as the world’s worst invasive plant.</li><li>Ald. Eddie Andrews, the City’s Deputy Mayor and Mayoral Committee Member for Spatial Planning and Environment, visited the Rondevlei, situated in the False Bay Nature Reserve where the City is busy removing the sludge. With the sludge removed, the outflow from Rondevlei will be significantly better. This means the water level will lower and most of Rondevlei will dry out over the next four months or so.</li></ul><p> <br>End<br></p>2022-01-15T22:00:00ZGP0|#1d539e44-7c8c-4646-887d-386dc1d95d70;L0|#01d539e44-7c8c-4646-887d-386dc1d95d70|City news;GTSet|#62efe227-07aa-45e7-944c-ceebacca891dGP0|#25f3316a-6921-4d78-86de-5117d756102e;L0|#025f3316a-6921-4d78-86de-5117d756102e|rondevlei;GTSet|#2e3de6c1-9951-4747-8f53-470629a399bb;GP0|#aebd769e-785e-4b86-aa68-3176fd6d892f;L0|#0aebd769e-785e-4b86-aa68-3176fd6d892f|Wetlands;GP0|#a6695739-564f-4371-9249-88d212fc205c;L0|#0a6695739-564f-4371-9249-88d212fc205c|false bay nature reserve10

You have disabled JavaScript on your browser.
Please enable it in order to use City online applications.