Plantation Road detention pond flooding risk reduced

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The City of Cape Town’s Road Infrastructure Management Department in collaboration with the Water and Sanitation Department, has done extensive work to the detention pond adjacent to Plantation Road, on the border of Wallacedene and Belmont Park, to mitigate severe future flooding in the area. The work was undertaken after an unforeseen blockage in the outlet system caused the pond to overflow, leaving several houses flooded in Belmont Park last year.

‘We have ponds like this one across the city and their purpose is to control water flow and make the surrounding areas safe. Last year, when we were informed about the flooding, sandbags were provided to residents as a temporary measure, while officials started working on a more permanent solution. The officials have been working on this pond since the incident. I deliberately chose to be here a day after Cape Town experienced severe floods, to see for myself the fruits of their labour and ensure that the pond is secure and functions optimally,’ said the City’s Mayoral Committee Member for Urban Mobility, Councillor Rob Quintas.

The detention pond adjacent to Plantation Road was constructed about 26 years ago to collect and detain stormwater during a flood situation and to let the water out within the 48 hours after the flood, once it is safe to do so. The pond is designed to accommodate a 1:50 year flood event. A normal blockage will clear itself due to the pressure of the water, however, an unknown and unforeseen blockage in the 300mm diameter outlet resulted in the pond overflowing its embankment on 28 June 2021.

Numerous interventions were undertaken to prevent, as far as possible, a reoccurrence of the situation this winter.

Work done to date includes:

  • construction of a new 375mm pipeline to enable the retention pond to drain
  • filling the detention pond embankment with milling to raise the embankment and to channelise the overflow to a specific point
  • ensuring that the existing overflow is functional and working
  • Water and Sanitation Department embarked on a massive clean-up action using specialised mechanical equipment to remove all solid waste from the pond, among which mostly litter that ended up in the pond through the stormwater system
  • Roads Infrastructure Management (RIM) Department cleared the partially blocked outlet structure from the pond which entailed the reconstruction of approximately 10m of outlet pipe and new headwalls
  • numerous inspections and the cleaning of the outlet pipe system downstream from the pond. This pipe system is now recognised and marked as a ‘RED Gulley’ item, meaning that it will be inspected and cleaned before the winter each year
  • RIM has inspected and cleaned the overflow piped system located in the services servitude running south to north from Old Paarl Road to the railway line in 12th Avenue. This pipe system is now also recognised and marked as a ‘RED Gulley’ item and will again be cleaned before the winter
  • RIM has placed a grid at the outlet structure of the Plantation pond. The purpose of the grid is to restrict litter from entering the piped system downstream of the pond
  • RIM has made use of a long-boom excavator to open the earth canal traversing the land that was invaded in June 2020 opposite the racetrack north of Old Paarl Road and south of the Water Sanitation Transfer Station. In sections where mechanical plant access was impossible due to informal housing structures on the embankments, we have used manual labour to remove reeds from our canal
  • Secured the assistance of Catchment Stormwater and River Management Department who will fund and facilitate the modelling of the pond catchment area. This will enable us to re-visit the design and to determine how we can improve the functionality of the pond seeing that the surrounding environment has changed significantly since July 2020 with the invasion of large areas of open land

Furthermore, the City intends to:

  • look at additional measures to address sewerage ingress into our stormwater system, to address solid waste ingress and the removal thereof
  • erect a new fence approximately 4m closer to Old Paarl Road to enable movement of heavy machinery on the embankment of the pond
  • clean all the catchpits in Belmont Park as part of our annual catchpit cleaning programme in preparation for winter. There are more than 22 000 catchpits that are cleaned in this district every year

‘The driving force behind all our activities and interventions is the intention to keep on improving our service delivery, and the safety and wellbeing of residents. The reconstructed pond will significantly reduce run-off and is now able to withstand extreme weather conditions. Belmont Park residents can rest assured that we have done all we can to reduce the risk of flooding in their area.

‘We will continue with our regular maintenance and upgrading, where necessary, to ensure that the heavy rains flow safely. I must also appeal to all to please refrain from dumping litter and objects in our stormwater system. Last year’s incident demonstrated the devastating impact illegal dumping has on surrounding communities,’ said Councillor Quintas.