Bridge over rising water

The World’s first road designed to float on water and adapt to flooding by rising and falling with the tide is to be opened in the Netherlands later this month.

The 70m long construction can cope with floods of 30cm above normal while still allowing motorists to drive at up to 50mph.

The design, known as Building Block Over The Water, is part of the Dutch Ministry of Transport and Public Works’ Roads to the Future project, which aims to develop solutions to the low-lying country’s transport problems between now and 2030.

New technologies

The road is one of a number of new technologies that could be used in areas of the Netherlands and the UK at risk from rising tides. Houses built on hydraulic rams, and the use of offshore windfarms to ‘blow’ away high tides, are some of the ideas that have been suggested as a means of future flood defence. However, the most likely option for London and the Thames Estuary is a second barrier stretching from Sheerness to Shoeburyness.

The Dutch scheme, designed by a consortium of Bayards Aluminium Constructions, engineers DHV Environment and Infrastructure, TNO Construction and XX-Architects, is located on the River Maas in Hedel, south Holland, and will be officially opened on 24 September.

‘If high water levels are predicted then the choice can be made to direct water to certain areas, flooding them to protect the dykes and preventing an emergency,’ said project manager Douwe Zijlstra of the Ministry of Transport and Public Works. ‘The floating roads will allow economic centres to remain connected while preventing problems. They will be ideal for connecting floating cities and greenhouses that have been proposed for building and farming in low-lying areas that are often flooded.’

The road has the appearance of a bridge, but instead of using fixed underpinned piers it sits on modular aluminium, catamaran-like pontoons coupled together so that the top side forms a smooth road surface.

Each pontoon is 3.5m long x 8.5m wide and has a weight between 2,000 and 2,700kg.Modules at the road’s end are wider and have a larger surface area to help them bear loads.

Each is also filled with expanded polystyrene (EPS) foam to make it unsinkable, and can be transported to sites by truck.

Unlike previous concrete-shelled fixed floating bridges built in the US and Norway, the EPS filling means that the road does not fill with water if the aluminium casing leaks, removing the need for expensive pumping systems.

To stop horizontal drift, the pontoons are anchored to steel piles driven into the ground below.

A U-shaped hinged aluminium bridge deck forms a 10m-long transition area between the road and more solid ground nearby. The slope of this increases or decreases as the road rises and falls.

The floating roads can be deployed to provide constant access in areas that are regularly cut off by flooding, and can also be used in drier areas where the soil is very soft and has little load bearing capacity. This would allow building to be carried out in areas which are traditionally considered as too wet for development.

Temporary bypasses

Zijlstra said they could also be placed in the country’s canals to form temporary bypasses during large-scale maintenance of bridges and roads.

Boats would then sail alongside traffic, as the pontoons are designed to remain stable when hit by waves.

The scheme has attracted interest from Norway and Eastern Europe, as well as four other possible sites in the Netherlands.

In future, Zijlstra added that it could be possible to fit the constructions’ underside with tunnels able to carry sewage pipes, telephone and electricity cables, though there were no current plans to do this.