On July 2, 2011, Copenhagen became a lake when a storm cloud deposited 135 millimetres of water over the course of just a few hours, resulting in 4.9 billion kroner in damages.
The incident spurred the City Council to action, looking into ways to make the city more resilient to flash storms. A first set of projects was agreed to in 2013, and this April, the Council approved 11 new projects costing 391 million kroner.
The ambition is to draw as much water as possible from homes and businesses using diversion canals and flood basins. The strategy is a more cost-effective alternative to increasing the capacity of sewers to drain water from the streets.
“We could dig up Copenhagen and install larger sewers, but that would cost around 20 billion kroner and only benefit the city when it rains heavily,” deputy mayor for technical and environment affairs Morten Kabell told Politiken.
The drainage basins are designed to double as green areas that city residents can enjoy at all times of the year. One of them would be formed by widening the banks of Skt. Jørgens Sø, an inner city lake. The deepest of the city’s lakes, the plan would lower its baseline water level, thereby increasing its capacity when it rains. Surplus water would then run over the banks into new green areas.
The council warns the project will take several years to be developed, as the lake is a protected landmark.