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Denmark’s largest wastewater basin helps prevent flooding

Photo: COWI

​By expanding capacity and incorporating innovative designs, the country’s largest wastewater basin will help protect homes, businesses and the environment in two suburban Copenhagen towns

​Denmark’s on-going efforts to adapt to climate change took a step forward on 6 October when BIOFOS officially opened the country’s largest wastewater basin. The newly renovated facility can now hold 78,000 cubic metres of water (or the equivalent of 20 centimetres of water spread over 57 football pitches) in the event of a torrential downpour.

The basin is situated in a suburban greenspace known as Den Grønne Kile, located in the municipality of Brøndby Kommune. During heavy downpours, the basin will be able to hold on to excess runoff from Brøndby and neighbouring Glostrup Kommune until there is capacity in the sewerage system.

Climate adapted

In recent years, intense downpours have on occasion delivered more water than Brøndby’s sewerage system could handle. During such events, wastewater flows out of the system and into homes, businesses and natural areas along the coast. That risk has now been greatly reduced thanks to the 10,000 cubic metre expansion of the existing basin’s capacity, as well as adjustments to the local wastewater treatment plant itself.

Brøndby Mayor Ib Terp said: “We are relieved to know that we have more capacity to hold back what the heavens dump on us. This is an important step in our efforts to address the challenges that climate change poses.”

In addition to being built to protect against the effects of climate change, the basin is itself protected against climate change: its base is thicker than the previous basin’s was, which will allow it to stand up increased groundwater pressure expected to be caused by rising sea levels and increasing precipitation amounts.

Using and securing resources

In addition, the basin can be divided into two sections, a smaller and a larger, that makes operation of the facility more flexible.

“Under normal operations you only need to use the smaller section but you can expand it to include both sections if necessary," says Finn Kofoed Jensen, a COWI project director who was involved in the design of the basin.

Bo Brask Helleberg, a COWI hydrogeologist, added:

“The previous basin had a drain and pumping station in the bottom. The new basin has a heavy, tightly packed clay base that is stabilised using chalk and cement. That helps protect it against cracking under increased groundwater pressure, and it also protects the groundwater from being contaminated by the runoff that collects in the basin. By not having to include a drain or pumping station we also cut back on maintenance.”

The team involved in designing the renovation sought to incorporate existing resources to the extent possible during construction. Clay dug up during excavation was included in the base of the new basin. Likewise, lightly contaminated soil from the previous basin was incorporated into construction of the base of the new basin after it had been stabilised using chalk and cement. Excess soil removed during excavation was used to build a noise barrier along a near-by motorway.

 

By Anja Basilio Fabech, afj@cowi.com
Published 13.10.2014

LAST UPDATED: 17.09.2016