Retreat, attack or defend? Engineers and architects weigh options for coastal cities

A joint report from the Institute of Civil Engineers (ICE) and RIBA spin-off building future attempts to spark a wider debate by using military metaphor to look at the three broad options – retreat, defend or attack.

Pulling back from the coastline and estuaries to avoid catastrophe is one option, says the report, making a distinction between a managed retreat and abandonment.

Under this option, settlements would move critical infrastructure and housing away from the water’s edge and have soft flood defences that would allow water into previously-protected areas.

The advantages of such solutions are long-term sustainability and cost savings, but of course there are down sides as well – investment in property and infrastructure would be lost and there are real difficulties translating much of this from the drawing board to reality – is it possible to relocate residential areas, for example?

The next option addressed by the report is that of building bigger and better flood defences.

The report questions the practicality of trying to maintain the status quo in a changing environment.

“Many of the hard engineered defences of the 20th century have been criticised for being unsustainable, reducing access to water, damaging to coastal habitats and costly to maintain and improve,” it says.

“However, they have provided protection and reduced risk from flooding, allowing activities to go on uninterrupted in the built environment.”

It suggests that some of the problems might be averted by taking an over-arching view of the problem, rather than addressing localized issues piecemeal.

But the report cautions that this is likely the remain a costly and difficult approach – though imaginative solutions such as allowing developers to build shoreline leisure facilities on top of defences at the price of picking up a share of the bill might offset some of the costs to the public purse.

The final option – attack – on the face of it sounds impractical.

But, according to the report, engineering has moved on since the days of King Canute and there are opportunities to build out into the sea, as demonstrated elsewhere in the world.

“There is massive development potential to be gained for coastal cities by building out onto the water,” says the report.

“This further reduces the need to sprawl into the countryside and ensures their sustained social and economic vitality. Although it leaves parts of the city still vulnerable to flooding, can the long term benefit of new development outweigh this risk?”

It cites examples of how man has lived with water for centuries, from stilted structures to land reclamation.

These strategies of Attack could unlock a vital planning tool and give flexibility to our extremely dynamic 21st century cities,” argues the report.

“Moreover, it could encourage a new breed of developers to fill this gap as demand for the prime waterfront sites grows. This commercial competition will need to be matched in long-term management and responsibility.

“If new development in coastal cities starts to prepare for rising sea-levels now, the livelihood of the city could be maintained for generations to come.”

To illustrate its points, the report also looks at what might happen if two flood-prone coastal cities – Hull and Portsmouth – each chose to retreat, defend or attack.

The full report can be viewed here.

Sam Bond