26 Aug 2024 RISING SEAS, SINKING SHORES — HOW THE V&A WATERFRONT IS BRACING FOR IMPACT Rising sea levels and increased storm events are increasingly threatening coastlines worldwide, and Cape Town, with its extensive coastline, may be particularly vulnerable. Coastal tourism, a vital part of the city’s economy, is expected to be significantly affected in the years leading up to 2050 and beyond. [As published on Daily Maverick, 22 August 2024 – here.] Cape Wheel and Victoria Wharf showing coastal erosion as well as the rock armour on Granger Bay. The Cape Wheel located on the water’s edge at the V&A Waterfront, may come under threat in the future as a result of sea level rise. With this looming threat, the V&A Waterfront, one of Cape Town’s most prominent landmarks, is preparing to deal with sea level rise (SLR) in the short and long term, as well as impacts on its coastal tourism development. The threat of sea level rise Projections indicate that the impact of sea level rise will become more severe in the V&A Waterfront precinct, and larger Cape Town, by 2050 and beyond. In a Cape of Storms study done by the University of Cape Town’s African Centre for Cities, the Stockholm Environment Institute and partner institutions – working closely with the City of Cape Town to explore ways to manage changing coastal risks in the Mother City – it is stated that the oceans have become a greater potential risk for three reasons: As the ocean warms, it swells, making the sea level rise. As ice over land masses in places like Greenland and Antarctica melt, it adds more water to the ocean, which causes the sea level to rise further. As storms become fiercer, the coastline takes a greater pounding. This is particularly severe when intense storms coincide with spring tides, when the natural high tide peaks. One short storm surge can leave devastation in its wake. These factors combined create a scenario where even a storm surge could cause significant damage along the coastline. For the V&A Waterfront, this means they not only have to prepare for a gradual rise in sea levels, but also for acute impacts of fiercer storms. Immediate and long-term planning Donald Kau, communications manager for the V&A Waterfront, said that their regular risk assessments had not identified its coastline as specifically under threat of SLR in the short term, but the Waterfront experienced natural tidal erosion along its seafront and on an annual basis, based on regular inspection, routinely reinforced the existing coastal protection. The weather is also monitored, and Kau said that, depending on prediction, portions of the Waterfront such as the Tour Bus Parking and Boardwalk would be closed to the public. Speaking of long-term vulnerability, Kau said that their overall urban planning considered the widely acknowledged and projected rise in sea levels (2mm every year) to future-proof new developments to the best of their collective knowledge. In recognising the need for a more comprehensive solution for this projection in the longer term, the V&A Waterfront has applied thorough environmental impact studies around Granger Bay for significant increase in coastal protection in the form of rock armour revetment (also known as dolosse, which are wave-dissipating concrete blocks) and other coastal protection measures to reinforce existing protections against surging tides. Ocean view of the V&A Waterfront precinct showing coastal erosion as well as the rock armour on Granger Bay. Sea level rise in the 20th and 21st centuries is driven mainly by the warming-linked expansion of the ocean and the slow melting of the ice sheets. The latter’s increasing contribution is accelerating the rate of SLR. Professor Pedro Monteiro from the School for Climate Studies at Stellenbosch University warned the impacts of sea level rise were not the apparently modest rises (±0.5m) in sea level, but rather the amplification that the SLR trend exerts on the variability peaks of other drivers such as equinox spring tides (±1m above mean sea level), extreme storm wave surges (±2m above mean sea level) and storm low-pressure sea level bulge (±1m). Thus, according to the UN’s Intergovernmental Panel on Climate Change (IPCC), a once-in-a-century extreme flood could become an annual or more frequent event from 2050 onwards, with the frequency dependent on emission scenarios. In the case of the V&A Waterfront, the precinct is protected from extreme storm wave sets by the breakwaters and piers, but Monteiro said it remains exposed to the risks of the convergence of the impacts of a very low-pressure winter cold front and late March and late September spring tides, amplified by the ±0.4-0.5m sea level rise. “Together these could, for 1-2 days, overtop the wharf level and block the stormwater drains that could lead to significant flooding under conditions of heavy rainfall and strong run-off from the urban areas,” he said. Monteiro said that the loss and damage would be further enhanced by the increased frequency of these compound extreme events. Considerable impacts of SLR on V&A Waterfront and coastal tourism The major concerns will be the floating jetties, boats and ships tied alongside the Waterfront and commercial facilities, like the Cape Wheel, at the wharf level and potentially power, water and waste systems. Monteiro said the main concerns of SLR for the V&A Waterfront will begin to emerge more strongly towards the end of the 21st century when SLR of 1m is likely under high emission scenarios. Sea level rise is referred to as the supertanker of climate change because even after we reach net zero greenhouse gas emissions, the sea level will continue to rise because the ocean will continue to take up the excess heat. Monteiro said this would happen under all emission scenarios, but the magnitude of warming and hence sea level rise is scenario-dependent. Thus, he said, even if we stop additional warming we are committed to a long 100-300-year emission scenario-dependent period of rising sea levels. This may be amplified to 5-15m with the as-yet unpredictable collapse of one of the major ice sheets. According to the IPCC Working Group 1 assessment, this possibility cannot be excluded in the long term. Anton Cartwright told Daily Maverick that at the beginning of the century, scientists thought sea level rise risk would be quite modest up to 2100, but as they continue to study and understand the phenomenon, the estimates of mean sea level rise continue to go up as a warmer ocean expands and terrestrial ice melts more quickly than anticipated. “Sea level rise is one of these phenomena that the more we understand, the more we recognise that this is a very significant climate change risk,” he said. Cartwright is an economist focused on Africa’s urban transition, infrastructure and services, green finance, environmental degradation and poverty alleviation. He was also lead author of South Africa’s Just Urban Transition Framework, lead author on Chapter 4 of the IPCC’s Special Report on 1.5°C of warming released in 2018, and a contributing author to the IPCC’s 6th Assessment Report. “We think there has been 10-15cm of sea level rise around Cape Town since the mid-1900s,” says Cartwright. He said that these were estimates, making the point that the seas were never level; there were tides, storms, high-pressure and low-pressure cells, so the historical data set is quite difficult to pronounce on. Most vulnerable places The intensity and frequency of storms are increasing as the atmosphere warms up, but it is the combination of more intense storms approaching our coastlines off a raised mean sea level rise platform that is already causing damage in Cape Town and in other coastal cities. “When you get a storm surge striking the coast off a raised platform, you really do disrupt the long-term coastal equilibrium and you suddenly get water encroaching on areas it hasn’t been before. That’s when severe coastal erosion takes place and the most damage happens. “We’ve seen an increase in these events in the last 10 to 15 years at Three Anchor Bay, the Atlantic Seaboard – even the Sea Point promenade and at Strand. One of the things that we try to track is how much money the City of Cape Town is having to spend on simply maintaining places such as the Sea Point promenade,” Cartwright said. Cape Town is already experiencing impact, but the major mean sea level rise impacts are expected in 2050 and beyond. These have been locked in by the atmospheric warming that has already taken place, so it will be very difficult to prevent these events. For now, the most vulnerable places are those that are exposed to storm surges associated with low-pressure cells generating southwest swells that roll in from the deep Atlantic Ocean. Cartwright said this is when we get the big hits and worst damage. This has been seen at Strand, Seapoint Promenade and Milnerton lagoon areas, which are massively exposed. The V&A Waterfront, because it’s in a bay and protected by the harbour walls, is sheltered from those southwest swells. It is located on reclaimed land, but is also part of a highly engineered built environment and harbour infrastructure, complete with dolosse and breakwaters. Cartwright said it’s quite plausible that by 2040, the V&A Waterfront would have to add to the height of the breakwater due to the mean sea level having increased and the risk of waves washing over the top during extreme high tides. At the moment, the breakwater and dollose dissipate all the wave energy that comes into the harbour so it’s not the most exposed area. And by 2050, when the area is more severely exposed, Cartwright said that because it’s already a very engineered environment, adding another metre of dollose would not be difficult. Much harder to protect than the Waterfront are the natural, less engineered habitats that would have to be evacuated. “What’s very interesting is that when the Cape Town harbour was built, it changed the currents in the bay, causing new patterns of coastal erosion in the bay. This erosion, together with sea-level rise, has become a problem for places such as Milnerton and Paarden Island in the last 20 years,” Cartwright said. The City of Cape Town is aware of this and has done a lot to protect the sandbar between the sea and the Milnerton Lagoon, for example. It’s not about trying to predict the impact and then fix the problem. Rather, it’s about being aware of the issue and being prepared to adapt to several different scenarios. Cartwright added that it was important to implement social and institutional responses (including early warnings and public awareness), biological responses, and physical engineering responses to mitigate these risks and keep people and infrastructure out of harm’s way. Social and institutional responses should be the first option, followed by biological options — rehabilitating the dunes, kelp beds, and protecting coastal marine ecology to ensure that ecological infrastructure provides as much natural buffer as possible. The engineering option, such as sea walls, should be the last resort. Cartwright said that the V&A Waterfront did not have the biological option as it was not a natural habitat, so there was no kelp bed or sand dune they could rehabilitate. It was a highly engineered coastal interface, so they had to do the physical engineered protection — raising the pier and installing dollose. Cartwright said that what had been learned elsewhere was that this option had to go together with early warning systems and public awareness to ensure buildings and people were not put in harm’s way.
