As of: 08/26/2021 4:26 p.m.
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Not only since the July flood has been considered how cities can better cope with heavy rain. One idea: the “sponge city”. Offenbach, for example, has been working on active water management since 2017.
In the Offenbach district of Bieber, they are now used to it: the small, concreted-in river repeatedly overflows its banks when it rains heavily. The result: flooded paths and water that sloshes into the cellars of neighboring houses. And because heavy rain leads to traffic disruptions and disaster relief elsewhere in Offenbach, too, they decided in 2017 to not only focus on climate protection, but also on climate adaptation – with active water management, among other things.
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“A lot has to happen to make heavy rain manageable in any form,” says Heike Hollerbach, head of the city’s environmental agency. “That means we have to deal with our sealed area in the city center. Every building that is being built now has to be designed for heavy rain events.” By this she means that the infrastructure of a house can no longer be damaged by the water.
So-called heavy rain maps are the basis for this new type of water management. These are maps on which, after a detailed analysis, it is precisely drawn where there is a risk of flooding, where the water has enough space to expand and where the ground is possibly too built up.
A heavy rain map of Offenbach – this shows where there is a risk of flooding.
Photo: Marcus Pfeiffer / HR
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Expert: Cities should become “sponge cities”
The latest analyzes by the German Weather Service (DWD), the Federal Office for Civil Protection and Disaster Aid (BBK) and other authorities show that this is necessary. When comparing rain radar images and fire brigade operations, the experts found that instead of extensive continuous rain, local heavy rain events are becoming more and more frequent – and they are particularly dangerous where the earth is sealed and the water cannot run off. One possible solution: unsealing, wider green areas, rain retention basins.
For Peter Jakubowski from the Federal Institute for Building, Urban and Urban Planning, one thing is clear: the cities should develop into so-called sponge cities. “Ultimately, every cubic meter of water must be prevented from condensing into a flash flood. That is the task that sounds easy, but is quite complex to implement in an urban context.”
Jakubowski said it was a task of the century in terms of effort and investment. “The dilemma is that we don’t have that much time and, at the same time, we need concerted action from the federal, state and local governments. And of course support from science.”
Work on a climate concept for 2050
In Offenbach you are already one step further on the way towards Sponge City. Last year they adopted the climate concept for 2035, and they are currently continuing their climate adaptation concept until 2050. And not just with politics alone, but with the participation of the people in Offenbach, for example through workshops.
One solution, according to Heike Hollerbach: move the beavers.
Photo: Marcus Pfeiffer / HR
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They have already found a solution so that the beavers will soon no longer overflow their banks so much, explains Hollerbach, the head of the environmental department. “We are laying the beavers over a length of around 1.8 kilometers and giving them bows and bows so that they have more space and people are no longer so endangered.”
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