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Retreat, defend, attack

The threat of rising sea levels around the British coastline means the country must soon decide what approach it will take towards the possibility of serious flooding. Jo Stimpson reports.

Climate change scientists agree that sea levels have risen over the past century and will continue to rise as a result of land-based ice melting, ocean warming and an increase in storm frequency and intensity.

The latest research by the UN Intergovernmental Panel on Climate Change predicts sea level rises, by the year 2100, of up to 590mm. Further independent research by the Helsinki University of Technology and Potsdam Institute for Climate Impact Research shows there is a chance levels could even rise by as much as 1.9m. A study by Durham University also suggests that landmass subsidence in parts of England, Wales and Southern Ireland could add between 10% and 33% to projected rises.

It all spells trouble for the British Isles, says Royal Institute of British Architects think tank Building Futures chair Dickon Robinson. “In an era of unknown unknowns, this is a known known. This is going to happen,” he says. “This is an issue that we need to engage with now. We cannot put it off − the scale of the issue is too great.”

Target areas

Significant areas along the UK’s 12,429km coastline are under threat and flooding does not discriminate between urban communities and rural ones, says Environment Agency national coastal policy advisor Nick Hardiman.

“It could have a real impact, not just in terms of rural areas but in terms of cities like Portsmouth, Hull and London. We need to be prepared for the outside chance of that happening,” he says.

The ICE and Building Futures have just launched a report and touring exhibition to provoke discussion of the subject.

Facing up to Rising Sea Levels: Retreat, Defend, Attack? looks at Portsmouth and Kingston upon Hull. It suggests flood response systems for the year 2100, based on three different options: Retreat, Defend and Attack.

Hull and Portsmouth

Hull and Portsmouth were chosen as case studies because they are typical examples of coastal cities at risk, says Hardiman. The group considered looking at fictional cities, but decided that using real situations gives the report more focus, and drives home the reality of the threat.

Studio Egret West partner and urban designer David West is a member of the team behind the report. While many Britons are all too aware of the need for flood planning, many more are not, he says. “There are so many people out there who probably don’t think about this. We wanted to get some simple messages out there.”

West says the UK perspective on flood planning is too negative and unmotivated. Instead he feels it should be proactive, with recognition of the opportunities and possibilities of the three approaches proposed by the new report. “Actually there is no sadness here, there are no sad stories,” he says. “All three bring something positive.”

The most exciting possibilities lie in the Attack option of using stilted and floating structures to build out into the water, extending the city outwards.

“What we’re talking about protecting here is 25% of our food stock. This is something we should worry about”

Peter Dawe, The Wash Tidal Barrier Corporation

Such projects are already happening with land reclamation in Dubai, the Louvre in Abu Dhabi, amphibious homes in The Netherlands and stilted houses designed for the rebuilding of New Orleans. But that kind of thinking is not in common parlance in the UK yet.

“In 20 years’ time it’ll be something that’s actually pretty normal,” West says. “We don’t have that debate here, we don’t see it as a positive.”

Attack solutions demonstrate perfectly the secondary benefits that can come from flood mitigation.
For Portsmouth, the team envisaged large piers that have two tiers and link into existing infrastructure and streets.

The lower tiers would be used for traffic, with pedestrianised upper tiers offering mixed-use streetscapes incorporating residential, commercial and recreational spaces. “People live in Portsmouth to enjoy the watery experience. So why not take that further?” says West.

Hull: A city on stilts

In Hull, an Attack strategy could mean building static platforms and floating structures created from re-used marine infrastructure. Linked together and connected to onshore infrastructure, these rigs would be developed into residential, recreational and commercial spaces, says the report.

The Attack designs not only alleviate pressure on the cities’ ever-expanding populations but also provide opportunities for new employment and revenue streams, and could become tourist attractions in themselves.
“I’d really want to go to Hull to experience this,” says West. “It’s a straightforward maritime living experience.”

Similarly, the less appealing Retreat option could generate tourism. The Retreat design for Hull saw it renamed New Hull and conceived as “something similar to Venice”, with the historic city centre defended as an island and the surrounding area flooded.

The idea could “really create that excitement, that sense of “wow’,” says Arup rivers and coastal director David Wilkes. “I think it could create a fantastic potential destination.”

“There are so many people out there who probably don’t think about flood planning. We wanted to get some simple messages out there.”

David West

“Retreat is really about letting water in among these urban spaces,” says Halcrow maritime project director Ben Hamer, describing the creation of new natural habitats and water storage. “It’s often seen as a controversial, negative approach, almost giving up - but it needn’t be.”

The Defend approach is familiar: building defences to prevent sea water from entering the existing built environment. It is an expensive solution - but the report strove to find ways to make it financially viable. The new twist in the report is inhabited defence structures. The key is thinking about what needs to be done within the schemes to attract new investment, says Hamer. “Yes, let’s get the water out, but let’s generate new revenue streams.”

In Hull, small reservoirs were designed behind a sea defence wall, with twice-daily drainage allowing for the energy to be generated from tidal power. The reservoir has wide enough walls for art exhibitions and recreational activities - canoeing, for example - to take place on top of them. Some reservoirs could also be used for grey water storage and reed beds.

Hull strategy

The ICE has identified three possible responses to the threat of coastal flooding.

The Attack option involves building elevated urban structures in the sea, ready to cope with incoming storm surges.

Defence is the second option. This more familiar approach involves building coastal protection structures to hold off the sea and protect land based structures.

The Retreat option accepts the reality of rising sea levels and the need to migrate inland away from flood risk areas.

 

The team designed tide gates for Portsmouth to protect the harbour from extreme tidal surges. “We’ve pinched the idea of these nice rotating gates from Rotterdam,” explains Hamer.

Meanwhile, a living wall was designed to defend the seafront. Segments of the thick wall would be sold out to be developed and maintained, with street level units for shops and offices.

The design team has let its imagination loose on the scenarios in the report - they were approached idealistically, as if there were no financial or bureaucratic limitations, says Hamer - but the reality is different.

Portsmouth design challenges

Portsmouth City Council coastal strategy manager Bret Davies was quick to point out that the existing constraints and limitations are a real challenge.

Meanwhile, the same problems are faced by the rural coastline. The Wash Estuary on England’s east coast is one of the areas most vulnerable to coastal flooding, and is characterised by low-lying agricultural land.

Local resident and The Wash Tidal Barrier Corporation founder Peter Dawe has taken it upon himself to publicise the dangerous sea level rises that he believes threaten the Wash. He says discussions on coastal flooding neglect rural areas. “There is not enough focus on the Fens. Because it’s dispersed it never gets the attention that cities do,” he says

Dawe says the Wash area is crucial for food security in Britain. “What we’re talking about protecting here is 25% of our food stock,” he says. “This is something we should worry about.”

Like those in the ICE/Building Futures report, Dawe’s ideas are big. His campaign promotes the construction of an 80km tidal barrier stretching from Hunstanton to Skegness, protecting the Wash area from rising sea levels and storm surges.

Portsmouth strategy

For Portsmouth to defend itself, the design team found simple but effective solutions.

Positioning tidal gates at the narrow entrances to the harbours would negate the need to defend their extensive inner perimeters, and would protect against tidal surges. The sea facing coastline would be defended by walls which could be sold as real estate for commercial, residential and recreational developments.

The Attack option has the city extending outwards onto inhabited “rigs” in the water, while Retreat sees inhabitants moving north to new developments in the hills and the city’s fringes converted to saltmarsh sheep farming land.

 

Dawe too expects coastal defences to bring benefits. He estimates that his barrier could generate over 1GW in tidal energy, would create an enclosed and protected area of sea for leisure use and would create an opportunity to build a protected deep water port to serve the Midlands and North Sea offshore wind farms, such as those licensed for Round 3. “The barrier would self-fund,” he says. “It would actually be a very profitable venture.”

Still only an idea, Dawe hopes that discussions with consultants, the Crown Estate and the Environment Agency will go some way towards raising the profile of rural coastal areas under threat.

The debate is timely given the upcoming review of the second generation of Shoreline Management Plans (SMP2s. Due to be completed by March, the SMP2s will help local authorities and decision makers to address future coastal management issues, including sea level rise.

Plans in place

The SMP2s will identify the best approach to managing coastal risks in the short-term (0 years to 20 years), mediumterm (20 years to 50 years) and long-term (50 years to 100 years), says the Environment Agency.

They will also include an action plan for managing coastal processes into the future, which will form the basis for deciding upon and delivering flood risk management schemes and erosion monitoring.

What the ICE/Building Futures report really emphasises - albeit in an ambitious and perhaps even unrealistic way - is the potential scale of the problem of coastal flooding, and the scale of response that will be required if climate predictions are right.

That message must get across to the public and those producing and using the SMP2s if adequate schemes are to be enacted early enough, says Wilkes. “The real stumbling block is that the general British public doesn’t see how serious the problem is”, nor how large the economic returns could be, he says. “That is the greatest challenge.”

  • The full project, including sketches and details of the proposed new cities, will be exhibited at the Building Centre, London until 29 January, before travelling to Portsmouth from 15 to 27 February and Kingston upon Hull from 15 to 28 April. The report can be downloaded at theBuilding Futures website

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