African liveability

How will climate change affect Cape Town's coastlines?

A wave engulfs the pier at Kalk Bay, by Greg Oelofse and City of Cape Town

As a city, Cape Town is embraced by 300km of coastline. This precious natural resource is an essential part of our city’s past and its identity today, but it is also highly vulnerable to the effects of global warming and rising sea levels. Gregg Oelofse, conservation biologist, surfer and head of environmental policy and strategy for the City of Cape Town, explains how climate change will affect our shores and what we can do about it.

Imagine cutting Cape Town out with a cookie cutter and putting it in the middle of the Karoo – it would hardly be Cape Town, would it? I believe our coastline is fundamental to our identity as a city. It’s our biggest asset, central to our economy, identity and sense of place. As Cape Town has urbanised we sometimes forget this, but at its heart Cape Town is a port city, a coastal city and a fishing city. It was established as part of a shipping route, so little wonder that much of our cultural heritage is linked to the sea. This is our legacy, and with it comes the responsibility to look after our coastline as a precious natural resource.

The city’s mandate ends at the high-water mark, so we handle the beaches. Of course, nature doesn’t make that distinction, so we try to look at these things holistically. Our work includes dealing with law enforcement around poaching, shark spotting, dune management, wrecks, coastal pollution, development and coastal policy and much else too – basically how people interact with the coastline.

About four years ago we looked at climate change and sea rise in coastal areas, to try to get a handle on the risk our coastal areas face. We found that compounding factors make the risk significant, in other words many things combined substantially increase the overall risk. The risk of climate change is a compound of several factors: a small mean sea level rise associated with bigger and more frequent storms, these storms happening in an environment in which the shoreline has been fixed due to human development, the fact that the shoreline being fixed means that the coastline cannot recover as quickly as it should do and therefore the coastline is made more vulnerable to the next storm.

Rising sea levels

Climate change predicts that there will be a rise in sea levels due to thermal expansion. Put simply: warmer water means more volume. In addition, melting glaciers in Greenland, the Arctic and the Antarctic will also add volume to the sea. Experts agree that sea level will rise, but the predicted rate and extent of that rise vary hugely: from 30cm to 6m (in which case the Maldives will disappear). We are already seeing raised readings, although whether that is due to climate change or about natural variation no one can say at present. The current consensus is that by 2100, the mean sea level rise would be around 76cm.

Bigger storms

The earth’s atmosphere is warming; this means there will be an increase in energy, which means bigger storms. So we’ll have more frequent storms, and also more severe storms. You know the huge waves you see breaking over the Sea Point Promenade? Imagine that but far, far bigger. These “discrete storm events”, as we call them, last between 8 and 36 hours, and are highly destructive because massive energy is released onto our shoreline.

The first two elements combined cause added risk: the higher sea level and more frequent and severe storms means that we have compounded risk.

Waves batter the Seapoint Promenade, Cape Town

Waves batter the Seapoint Promenade, Cape Town

Vulnerable coastlines

Coastal systems are by their nature very dynamic. In Cape Town, with its two large bays, complex systems govern sand movement and sediment transfer. What increases the risk for the city is that we have fixed our coastline, which means it is more vulnerable. For example, sand is deposited on our False Bay beaches during winter and in summer the southeaster blows that sand inland. These systems are an adaptable and appropriate way of buffering against the coastal storms we experience but they require space to operate. In places like Sea Point this buffer zone is no longer in place due to the way we have developed the shoreline. The sea hits the promenade, and there is no buffer to the energy. In the case of a big storm the natural systems would be able absorb and recover from the storm but because we have fixed the coastline it no longer recovers, or it recovers slowly. As a result the next storm is even more destructive and the shoreline is made progressively more vulnerable.

Development in Hout Bay on the sand dune, then and now.

Development in Hout Bay on the sand dune, then and now.

So what can we do?

Thankfully we have now defined a coastal edge, which has been included in the projected framework of the city. Once our proposed legislation is passed it will help to ensure that no inappropriate infrastructure is built to the seaward side of this line. This will help to protect the spaces where we retain the natural functioning dune systems. This is the best way to protect our natural environment and also to protect the city and its assets in the future.

In a broad sense we need to ensure that the coastal edge is defined and that those areas are protected. We should stop developing properties too close to the water’s edge. We also need to manage informal access to the beaches better, as it can result in the dunes systems being damaged. We need to recognise that these are essential to the health of our coastal systems.

One thing that we as individuals can do is never to litter; most of the litter we see on our beaches, which can be incredibly harmful to both animals and the environment, is left there by humans. Most importantly, we must get out there and enjoy our beaches. We are blessed to have such a beautiful coastline so close to our city and it is all of ours to enjoy.

City Views June 2013

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This article first appeared in the June 2013 issue of City Views: Cape Town’s water stories. Read it online.
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