Tokyo, by the Sumida river

Cities that tame floods

Posted on 15 April 2015.

Cities around the world are riding the innovation wave and embracing flooding. An urban challenge for a better environment…

Flood threats and cities – taming, not fighting, the rising waters

What do Buenos Aires, Los Angeles and Tokyo have in common? Rising sea levels. With global warming, even more cities could soon be coping with floods. According to the United Nations, floods will threaten 233 cities worldwide - from New York to Rio. Although the risk of natural disaster is increasing, cities are getting prepared. Some are even trying to tame rather than fight the waters – that’s what Popsu, the urban project and strategy observation platform, have concluded... Published by Parenthèses, the book Villes inondables compares the approaches studied through its Europe program, under the leadership of the architect Jean-Jacques Terrin. And in his opinion, "flooding is now a natural event that we certainly need to protect against, but it’s also something we can take advantage of!" All over the Old Continent, cities are embracing aquatic panoramas. Looking at all the solutions that have been devised, landscape architect Nicolas Gilsoul came to this somewhat surprising conclusion: to protect against floods, there are only five standard strategies - no more! "Innovative measures are not about new strategies, but about reinterpreting and combining existing models," he explains.

An arch, a wall or a sponge?

He says cities have a choice of five solutions: an arch, a wall, a sponge, stilts or deviation. The arch strategy means the city floats – for example in Germany, where Hamburg has transformed itself into an architecture testing ground on a floodplain by installing exhibition areas and non-floodable offices in the old port areas. The wall strategy is based on the dike principle, made ever higher and thicker to keep urban areas safe. The sponge approach focuses on absorbing water in urban environments - urban planners are attempting to improve absorption capacity by developing new public spaces. For example in Toulouse, Grand Parc Garonne seeks to free itself from its dikes and bring people into contact with the river by taking back and constructing 32 km of embankments... Building on stilts will raise a city out of the water, and finally deviation divides the flow of water to reduce its power: in Angers the city is endeavoring to get closer to the water by creating a green and blue ecological web beginning with the low valleys leading into Angers and extending as far as the Loire river... What do all these innovative developments have in common? Walking the tightrope between risk and attractiveness, they rely on the appeal of new landscapes in symbiosis with the water...