To combat water shortages, Berlin is building giant reservoirs

A gaping hole 20 meters deep guts the heart of Berlin. Within two years, this titanic project will give birth to the largest reservoir in the German capital, capable of collecting water that has become scarce. “Before, the goal was to evacuate rainwater and walk through the city without rubber shoes», jokes the spokesman for Berlin’s water department, Stephan Natz, a construction helmet bolted to his head on the edge of a concrete crater. But the metropolis has changed course and is now working to store rainwater where it falls to reduce flooding and combat drought.

This is the “mushroom city” concept, theorized in the 1970s and adopted in 2018 by Berlin. In the United States, China, and Europe, many urban centers have switched to this approach, which proposes to absorb, collect, drain, and reuse runoff water. Climate change causes”a more patchy distribution of precipitation, meaning drought followed by heavy rain, and ever-increasing warming that increases evaporation” explains Mr. Natz.

Five times the capacity of an Olympic pool

A symbol of ongoing transformation: a giant water reserve under construction in the center of the capital, less than two kilometers from the iconic Brandenburg Gate. The 40-meter-diameter pool holds nearly 17,000 cubic meters of water, five times the capacity of an Olympic pool, stores it, and then sends it to a treatment plant. Because with a 150-year-old sewage system and more extreme weather than in the past, the city is no longer able to manage both wastewater and rainwater: “in case of heavy rain, the waters mix and overflow into the Spree River, causing fish kills and visual pollution“, explains Stephan Natz.

Berlin, even though it is built on former marshes, has been struggling with a serious water shortage for several years. According to data from the Leibniz Institute for Freshwater Ecology and Fisheries, after five years of drought, groundwater levels have still not returned to normal levels. “In Berlin, we are slowly realizing the value of water. It is one of the driest places in Germany», points out Darla Nickel, director of the German capital’s Rainwater Management Agency, created to support the city’s transformation into a sponge. Every new real estate project must now apply this strategy by developing rainwater harvesting techniques.

Exemption from license fee

The 52 degrees north area, which appeared about 5 years ago, in the southwest of the city, carefully applies the new rules. Around three large pools in a row, where the wind blows through the reeds, young parents with prams, children and the elderly wave. Rainwater iscollects on green roofs and in these tanks. The water evaporates and creates more pleasant air” explains Darla Nickel. Greenways are also sloped to allow water to soak into the soil more easily. “You see it can be really simple!» calls Mrs. Nickel. But the challenge is also to increase this type of measure in the heart of the city, even though Berlin is half as dense as Paris. “We progressed much more slowly with the existing building than with the new construction,” admits Darla Nickel.

In the historic district of Berlin, for example, a square is being reconstructed where rainwater is collected and injected into the groundwater. The Stormwater Management Agency supports more than thirty projects associated with the “mushroom city”. The municipality also encourages individuals to install water collectors or green roofs by exempting them from rainwater management and treatment fees. However, local officials are aware that it will take several generations for Berlin to truly become a “sponge”. “Whether climate change will give us time remains to be seen.“, notes Stephan Natz.

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