A futuristic project released by think tank Building Futures and the Institution of Civil Engineers (ICE) warns that the future of coastal cities is in jeopardy due to rising sea levels, sinking landmasses and an increase in storm frequency.

Focusing on Kingston-upon-Hull and Portsmouth, two of the UK's highest flood risk areas, the research proposes three options to cope with the threat: retreat (or managed realignment), defend, and attack.

The first option, managed realignment, would see the line of defence moved inland, allowing flood water to occupy previously protected city areas. This is based on the premise that hard engineering defences are no longer sustainable or affordable.

The feasibility of the second option depends on making flood defence systems commercially viable to attract private investment. There is a growing deficit on flood defences which public funding is not covering, but the benefits of preventing water entering the existing cities still outweigh the costs.

The third option “attack“ would mean building out into the water via stilted floating structures, proposed as an attractive option to alleviate pressure inland.

This has been proven successful overseas, and due to high demand for space the public and private sector are both willing to invest in expanding seaward.

Chair of the ICE steering group, Ben Hamer, said, ˜A proactive and united, almost war-like approach is needed if we are to win the battle against what is set to be our biggest challenge in the next century, the “water invasion.

˜Some very difficult decisions need to be made in the near future, and to do this we need integrated thinking. The UK must urgently change the way it plans, builds and designs at-risk communities.”

The scenarios were master-minded by a group of top architects, civil engineers, city designers, planners, developers, policy-makers, ecologists and futurologists.

Building Futures is a think tank of the Royal Institute of British Architects (RIBA).