Sea change: Resilient Flooding Schemes

Portsmouth Island elephant cage

Portsmouth is the only European island city outside of Venice, and is extremely vulnerable to climate-change-induced sea level rises. £60m has been earmarked for improvements to the city’s currently barely adequate sea defences, but the existing engineering-led proposal includes a sheer wall on the landside, in places as much as 3m high, severing access to the sea and views out of the city.

Architect Walter Menteth felt that the city council and government agencies might achieve better value and benefit from more holistic and collaborative thinking. With his procurement organisation Project Compass CIC and the Dutch foundation Architectuur Lokaal, a two-and-a-half-day Anglo-Dutch ‘elephant cage’ competition was organized.

In this form of innovative ‘parallel commissioning’ competitively selected, mixed and multi-disciplinary teams of 17 young UK and Dutch architects, engineers and landscape architects, were mentored by seven international coastal design experts and supported by Masters students from Portsmouth School of Architecture in a competition to explore a range of innovative solutions along the Portsmouth and Southsea frontage.

Team A’s solution, Awake, Asleep, Dreamer, proposed three separate walls, one under the sea, one on the waterfront and a third inland. The first dissipates storm energy while promoting marine ecology and creating a family-friendly sheltered lagoon; the second would be used for inhabited infrastructure including beach huts, lidos, kiosks and tunnels; and the third acting as a last resort, would also be used to create gardens, amphitheatres, play spaces and skate parks.

Portsmouth Island elephant cage

Team B’s proposal, The New Common, was for a super dike, intended to protect the site from even once-in-4,000-year superstorms. It would entail raising the level of Southsea Common to provide an improved and naturalised landscape incorporating pedestrian and cycle routes accessing a replenished beach with subterranean activities located beneath that would contribute to city-centre regeneration. Eastney Beach to the east would be consolidated and extended using material dredged from the harbour.

Team C’s proposition for appropriate and incremental interventions, postulated a dynamic, Dancing Coastline, which would change over time, requiring delivery of salient ‘precision work’, engaging with both defend and retreat strategies, utilising multiple modes and approaches engaging stakeholders. This would harness natural processes to mitigate the impact of rising sea levels, protecting Portsmouth’s coastal forts and allowing them to become islands during storms.

In March in the Netherlands, the second stage will occur when the schemes will be developed, further supported by Dutch experts, The proposals will then feature in an exhibition in Portsmouth over the summer of 2017.

Designing a resilient community

In 2013, White Arkitetker, working with Arup and Gensler, beat 116 other international teams in a US-run competition to design a new, resilient seafront neighbourhood, which could be a desirable new home for the hurricane afflicted community of Arverne East, on the Rockaway peninsula, south side of Long Island.

Rockaway’s 32ha were abandoned in the Fifties, and its only current inhabitants are wildlife. In the competition brief, the environment agency suggested that the left-hand side of Rockaway should remain a nature reserve, but White’s scheme places nature reserve elements around the site to deflect storm impact, reduce flooding and enrich the landscape. A large section of nature reserve becomes an ecological zone just beyond the shore, protected by a deep sandbar, which should reduce wave impact, further out to sea.

Two V-shaped nature reserves extend along the town centre, creating green routes and recreation space for residents, but also acting as floodwater detainment and retention sites.

Designing a resilient community

Along the Atlantic-facing beach, a sweeping raised boardwalk acts as public space, designed to promote swimming, hospitality and leisure activities. The boardwalk and its tributaries are kinked in order to reduce the force of the waves and this gives the landscape a distinctive character as well as offering opportunities for pocket parks to sprout between pathways and buildings. Further out from the city centre, family housing blocks are raised above street level, with shared back gardens creating play and social space for residents and families, but also ensuring that rapid draining of floodwaters can be directed away from housing.

Social resilience is also factored into the urban design, with key public buildings set back from the boardwalk and grouped to form a strong urban centre. A dense but attractive, socially varied mix of housing fringes the shared civic and community spaces, retail and commercial buildings, in order to weave social engagement and interaction opportunities into everyday life.

The New Hondsbossche Dunes

Research from the last three decades has provided sound methods to quantify dune strength for coastal safety assessments. This has subsequently led to the development of soft and dynamic dune engineering methods, which are capable of creating a robust coastal defence of a predetermined strength.

Sand based coastal management strategies are clearly effective, sustainable and flexible. Research and experience have shown that sandy coasts, although soft and dynamic, can in fact be engineered to provide predefined safety levels while supporting other functions as well

In The Netherland’s New Hondsbossche Dunes, the principle of ‘building with nature’ is fully exploited. Working closely with the consultant team, West 8 designed a natural dunal landscape as an alternative to a dike. Intended to strengthen the Dutch coastline, the landscape intervention also strengthens the identity of the region, enhances and embraces the natural environment, improves accessibility and bolsters recreational activities in the area.

The New Hondsbossche Dunes

By connecting the Schoorl and Pettemer dunes one of the longest uninterrupted dunescapes in the Netherlands is created. Designed to complement the existing dunes, the new landscape features varied topography, native vegetation, young drifting dunes, an enclosed ecologically significant dune valley, a sculptural memorial to the ‘drowned villages’ of Petten, and a south-facing lagoon at Camperduin which features an open connection to the sea.

The new 10km beach varies in width and culminates with a 25m-high dune, with panoramic lookout in Petten. The highly technical, carefully engineered solution for the new dune volumes efficiently uses sand, and minimizes dune erosion to meet the dual goals of coastal protection and environmental quality. The intervention begins a new chapter in the Dutch art of landmaking, one that unites a technical solution with a poetic narrative.

Pickering prevention measures

The pretty market town of Pickering in North Yorkshire has had 10 floods in 12 years. Arup was recently called in by the Environment Agency and Ryedale Local Authority to help put the town out of its misery. Arup saw an opportunity to apply a little holistic thinking, working together with local environmental partners such as the Forestry Commission to come up with a more integrated and site-sensitive solution. David Wilkes, Arup’s global flood resilience leader, says: ‘A boring flood protection scheme would see you putting walls and embankments along the river and destroying the charm of the relationship between market town and river.

Pickering prevention measures

Instead, we are trying to slow the flow, storing water in the North York Moors within the landscape, using otter- and beaver-friendly woody, leaky dams (provided by The Forestry Commission), encouraging more and more water to stay up in the hills for a longer period of time. Just above the town of Pickering there is a large, flat, flood plain. And so we have gone for a bit of harder engineering and put a landscaped dam across that flood plain with a small opening for the river. And we have tuned that so that as a flood coming off the hills starts to get close to the speed of flow which would cause flooding in the town, it can’t get through the bottleneck in the dam.

In this way, the excess floodwater starts to build up behind the dam, and we end up with hopefully a temporary lake of water, and a dry, safe town.’ Already these measures have been successfully tried and tested, with the town staying dry through 2016’s hurricanes Frank and Angus.

Governors Island - a floodproof park

When West 8 won the 2006 competition for the masterplanning and design of Governors Island, nobody had predicted the arrival or impact of 2012’s Hurricane Sandy, which left 305,000 homes damaged or destroyed and amounted to $19bn in losses. The island, just a seven-minute ferry ride from Manhattan, had lain barely used for decades since its decline as a US Army base. But West 8’s masterplan helped to drive interest in and enthusiasm for the 35ha site, as a destination and landmark, offering unique vistas onto New York Harbour.

It combined desirable mixed use development potential within its northern Historic District with the chance to experience the tranquillity of nature in a 16ha park by the sea, as well as a 3.5km Great Promenade around its entire perimeter. Construction on this previously ‘flat as a pancake’ site had already started when Sandy hit, in 2012.

Fortunately, New York- and Rotterdam- based West 8 director Adriaan Geuze had already persuaded the Governors Island client team, led by mayor Leslie Koch, to spend a quarter of the budget to ‘lift’ the park 2.7m (normal storm surges around New York push sea levels up by 2.4m, but superstorms as much as 4.3m). As soon as the storm hit, and the entire New York Harbour area was evacuated, the newly built landforms of Governors Island were used to save equipment and machinery.

Nothing was lost, apart from a handful of mature trees. (The West 8 design team took care to populate the island with young, native trees, planted much earlier in their life cycle so that they would grow up to be able to withstand the island’s extremes of wind and salty air.)

From its soft opening in 2015 to last year’s formal launch, Governor’s Island park has proved a massive hit; in the four months after its soft opening in 2015, the island welcomed 450,000 people — more than most of New York’s major cultural institutions.

Governors Island - a floodproof park

Its unique blend of ‘heightened reality’ landscaping is as much about embedding narratives and drama as it is about making the island safe. Along the edges, walking paths are outlined in thick white concrete kerbs that rise and fall, like a giant doodle, from pavement to seating height; these will help channel any moderate water surges away from the more populated centres. But most spectacular are the four new hills which loom in the near distance, luring the visitor deeper into the park, then parting to reveal the Statue of Liberty.

Each hill has its role: from the top of Outlook Hill, the highest of them all at 21.3m, visitors can see across the harbour to Liberty Island, but also the Brooklyn Bridge, lower Manhattan and Jersey City. Discovery Hill is thickly wooded, and contains a site-specific ‘cabin’ sculpture by Rachel Whiteread. Slide Hill, to the east, offers thrills in the form of a 15m slide; and Grassy hill in the north offers a 7.6m roll down, and space for picnics and play.

All these hills were conjured from a combination of landfill, demolished buildings and a specific soil recipe, though a large chunk of Outlook Hill is made from pumice, to avoid overloading the island’s fragile footings. Officially opened in 2016, Governors Island has proved such a prudent and popular design, says Geuze, that its double-whammy of storm-proofed ingenuity and public-facing appeal ‘is now used as the prototype resilient park approach.’

Milford-on-Sea beach huts

Snug Architects won a New Forest District Council competition, together with Ramboll consulting engineers, to replace 119 beach huts damaged in winter storms, with the proviso that the replacements should be able to weather a once-in-1200 year storm event.

Milford-on-Sea beach huts

Snug’s solution was to use precast concrete for the hut structures, but bring the promenade up onto their roofs, transforming the public realm while preserving the traditional seafront appearance of the town. Construction of the £12m project is currently under way.

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