Cape Town in mudslide warning

By African News Agency Time of article published Jun 14, 2015

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Cape Town - The City of Cape Town on Sunday warned residents to take precautions against mudslides following the devastating fires which raged on the Cape mountains earlier in the year and which have left mountain slopes in the peninsula treacherously slippy.

In a statement, the City said: “Over the past eight weeks, the City has put in a tremendous effort to limit the impact of possible mudslides in the Southern Peninsula, following the devastating fires that raged on the mountains in this area in March. While this preventative work is still ongoing, the City wants to urge residents to also do their part in protecting their private properties.”

The warning came ahead of the next heavy rains being forecasted for the coming week, and the City of Cape Town urged residents in the Southern Peninsula, in particular those in close proximity to or against mountain slopes, to take protective measures within their property boundaries.

“To date, Transport for Cape Town (TCT), the City’s transport authority, has spent over R2 million on preventative measures in the Southern Peninsula, with another million to be spent by the end of this month. We are trying our best to limit the possibility of damaging mudslides, but residents in this part of the city must also take action,” said the City’s Mayoral Committee Member for Transport, Brett Herron.

Residents needed to ensure that excess flow from heavy rains was directed away from their properties and the City called on those needing more information on what measures to take to contact TCT’s District Office for the South Peninsula on 021 444 3257 or email them at [email protected]

Some of our residents have prior experience of devastating mountain fires in previous years and they will be aware of the serious risks involved due to the lack of vegetation to hold soils in place.

The after-affects thereof can be extremely acute during the rainy season, with severe flooding and debris coming off the mountain. I am urging residents not to underestimate the possibility of mudslides and to report blocked stormwater infrastructure so that we can take immediate action,” said Herron.

During the past eight weeks, TCT had focused on preventative measures along Boyes Drive and Ou Kaapse Weg as these were the main traffic routes that could be affected by heavy rains, the City added.

Some of the preventative measures included:

Silt curtains: these were installed on the mountain slopes to intercept silt that may be washed down the slopes in heavy rains.

The curtain is a 300mm wide geo-fabric strip fixed to short wooden or steel posts hammered into the ground at set intervals.

The geo-fabric material allows water to flow through it but traps the silt.

The silt curtains would remain on the mountain until the vegetation on the slopes had recovered sufficiently to stabilise the soil.

Sandbags: sandbags were mainly used to increase the capacity of the existing drainage system and to redirect stormwater flows away from areas that were at risk of flooding

Gabions: gabions are wire baskets filled with stones with the size and extent being determined by the risk at hand.

Gabions were commonly used within watercourses and other areas of high anticipated run-off to trap silt and debris, as opposed to silt curtains and sandbags which were too fragile to manage the heavy flows from the mountain.

Dragon teeth: these traps made of vertical steel beams are installed in front of the openings at stormwater catch-pits and mountainside stormwater inlet structures to prevent rocks and sticks from entering the stormwater system and blocking the stormwater pipes.

To date, the following measures had been put in place: Approximately 3 000 metres of silt curtains had been installed on the mountain slopes above Boyes Drive, Clovelly, Noordhaven and Belvedere; with another 2 000 metres planned for installation on the slopes above Noordhoek, Tokai and along Ou Kaapse Weg in June.

Approximately 7 000 sandbags had been placed along Boyes Drive and Ou Kaapse Weg, with an additional 3 000 bags to be placed along other roads in the Southern Peninsula where the risk of flooding is high.

One gabion structure has been completed on Ou Kaapse Weg, with a second under construction. Another two gabions would be installed on Boyes Drive within the next three weeks and two were already under construction near Zwaanswyk Road in Tokai.

Dragon teeth were being installed at 11 different stormwater catch-pits and mountainside stormwater inlet structures across the Southern Peninsula.

In the meantime, TCT’s maintenance teams in the Southern Peninsula were continuously monitoring the stormwater inlets, culverts, catch pits, channels and pipe inlets for blockages and regular maintenance is done by contractors, the City added.

The City had already contacted home owners who were considered to be at high risk to advise them about obstructions to water flow on their properties such as boundary walls with inadequate openings, stored or stockpiled materials, and structures that could pose a risk (such as Wendy houses).

“I want to assure our residents that throughout winter we will continue to monitor and analyse the areas that were damaged by the mountain fires. We will ensure that blockages in the stormwater system are cleared as soon as practically possible and, if needed, we will also implement additional measures during the rainy season,” said Herron.

Residents were encouraged to report blockages to stormwater infrastructure to the City’s Transport Information Centre on 0800 65 64 63.

ANA

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