Once the risk analysis is complete, it will help guide decisions on where and how to build. Development is already restricted in some stretches of river floodplains and may soon be in others. But with population continuing to rise, there’s great pressure to develop tracts of low-lying areas like those in the southwest polder. And besides, defying the sea is a point of patriotic pride. “It is our culture to cope with water,” says Chris Zevenbergen, director of business development at the construction company Dura Vermeer and a professor at the Unesco-IHE Institute for Water Education in Delft. “Retreat would give a very bad signal to the world. Suppose we are not building; this will have an enormous impact on the climate for foreign investment. And from a technological point of view, [construction] is feasible. We need to adapt to that kind of development.”
To demonstrate what is possible, Dura Vermeer has built a floating housing development in a hamlet called Maasbommel, in the rural province of Gelderland, near the center of the country. There, 46 amphibious houses are perched on the outer edge of a dike that holds back the River Maas, adjacent to a marina. Sixteen are floating at the river’s edge, in conjoined pairs, with sealed hollow basements providing buoyancy. Between each pair of houses are two vertical concrete piles (one pile is shown below); if water levels rise, the houses rise around the piles. Flexible water, sewer, and electrical connections are unaffected. Thirty similar houses sit on slightly higher ground, on concrete slabs a meter or so above the waterline. They, too, have piles and hollow basements that will let them float if necessary. All 46 houses can tolerate a four-meter rise in water levels. (Video of the floating houses.)Though the houses have been finished since 2006, the higher ones have not yet faced a flood high enough to test them. “Everybody wants to see it happen. Including the builder and the architect,” jokes Cees Westdijk, who owns one of the houses. His two-bedroom house offers beautiful water views; on the downside, an algae bloom last year made for a nasty, if temporary, smell.
The Netherlands has designated 15 areas near riverbeds as possible sites for amphibious developments, including variations on the Maasbommel prototype. For the southwest polder, researchers at Delft Hydraulics and Wageningen University have already produced the first risk maps, showing which areas within its 50 square kilometers are most vulnerable. National planners “look inside the dike ring and make zones for how the water comes–fast and deep, fast and undeep, slow,” says Bloemen of the National Spatial Planning Agency. Buildings could be customized accordingly; some might always float, others might rise and fall if needed, and still others might simply be built to survive inundation without sustaining major damage. “You [could] have building restrictions appropriate to the relative dangers and flooding probabilities within each subzone,” Bloemen says.