Large joint climate change adaptation project along the Store Vejle Å watercourse west of Copenhagen

About the project

Simple technical solutions have prepared neighbours to Store Vejle Å, a watercourse in the suburban district of Vestegnen west of Copenhagen, for more extreme rainfall events in the future.

Furthermore, part of the riparian zone has been upgraded with more natural areas and recreational opportunities. Six municipalities and four utility companies joined forces to provide climate protection along the watercourse.

A more than ten-year-long project was completed in November 2017.

The event was marked by five mayors from the Vestegnen district pushing the start button for two large pumps in Ishøj where Store Vejle Å flows into Køge Bay.

The opportunity to adapt Store Vejle Å to climate change came about in 2007 when the Danish Parliament agreed to establish a railway line between Copenhagen and Ringsted.

Rail Net Denmark had to expropriate part of Vallensbæk Lake to make way for the railway.

The affected municipalities and the two local utility companies spent the financial compensation from Rail Net Denmark on climate protection of the entire course of Store Vejle Å.

The first part of the project was inaugurated in spring 2016. The final part at the end of 2017.

The established facilities have worked as intended with only a few technical adjustments needed since their inauguration.

The neighbours to Store Vejle Å have never been directly affected by floodwater during major flooding events. However, the water has been inches away on several occasions.

The financial compensation from Rail Net Denmark, enabled the local communities to take preventive action in advance.

“It’s not rocket science," said director of collaboration and green growth at HOFOR Frank Brodersen about the project at Store Vejle Å.

This was a deliberate choice on the part of the municipalities and utilities, because they wanted a resilient solution above all else.

The wastewater treatment facilities along Store Vejle Å start with three new retention basins upstream from Høje-Taastrup, and then continue with periodically wet marshes in Albertslund.

Together, these facilities can retain a total of about 78,000m³ rainwater.

The facilities direct the water to Store Vejle Å, which runs into Tueholm Lake and Vallensbæk Lake.

The lakes also serve as retention basins and can hold back about 450,000m3 water. The lakes are a natural part of the landscape and serve as places for recreation.

From the lakes, the water is led back into the Store Vejle Å watercourse. Emergency spillways have been established to allow for overflow of water from Vallensbæk Lake into Tranegilde/Vallensbæk Marsh, which then acts as an emergency retention basin. The marsh can retain 900,000m3 water.

From Vallensbæk lake the water is led into Store Vejle Å via another spillway that is controlled automatically based on flood gauges that have been strategically placed downstream from the estuary.

A pumping station in Vallensbæk Marsh was renovated as part of the project. The emergency pumping station is equipped with digital gauges for better stormwater management.

Furthermore, emergency pumps were procured so that the marsh can be emptied quickly when acting as an emergency retention basin.

Some of the houses close to Vallensbæk Marsh have been fitted with dikes to protect against intruding water when the marsh acts as an emergency retention basin.

Store Vejle Å flows into Køge Bay at the habour of Ishøj. Here, a pumping station with two large pumps was built into the dike at the harbour. Each pump can pump 2,000 litres of water per second.

The pumps are needed for situations with extensive water from land combined with high sea levels or a storm surge in Køge Bay.

The pumps have already been in operation and proven their worth several times since their establishment in November 2017.

In September 2017, the system was put to the test when heavy rain made it necessary to diverge water from Vallensbæk Lake into the emergency retention basin in Vallensbæk Marsh.

According to Frank Brodersen from HOFOR, the continuously variable control of the gates near the outlet from Vallensbæk Lake had not been installed at this point in time. The gates had to be controlled manually, and the response team was only just able to prevent water from damaging some of the houses in the area.

The Store Vejle Å climate change adaptation project has been designed to withstand a 100-year event.

Surplus soil from the retention basins was used to build a sound barrier along the motorway and railway line.

Treatment of the rainwater is much improved in the new basins and periodically wet marshes, benefitting water quality in Store Vejle Å and Tueholm Lake and Vallensbæk Lake.

The risk of houses and roads being flooded has been reduced. And the public now has fine new recreational areas and nature.

Residents and road users along the Store Vejle Å watercourse have a far lower risk of experiencing floods in connection
with extreme rain.

Even during storm surges with high sea levels in Køge Bay, the watercourse system can now manage all of the water.

The new retention basins in the climate change adaptation project treat the contaminated stormwater runoff from the roads before it is led into Store Vejle Å and Tueholm Lake and Vallensbæk Lake. Treatment is now seven to eight times better than previously.

Surplus soil from the newly established basins was used to build a 300-meter-long noise barrier along the nearby motorway and Copenhagen-Ringsted railway line.

Finally, the neighbourhoods surrounding the lakes in Vallensbæk, Høje-Taastrup and Albertslund now have natural and recreational areas with vegetation, birds, insects and a system of hiking paths.

The project was financed by DKK 40 million from Rail Net Denmark provided as compensation for expropriation of part of Vallensbæk Lake. DKK 10 million came from the utility companies in Ishøj, Vallensbæk and Brøndby.

Rail Net Denmark established an agreement with the affected utility companies on compensation of DKK 40 million for the reduction in the water volume in Vallensbæk Lake and the associated installations.

The pumping station at Ishøj Harbour was established as a co-financed project at a cost of DKK 10 million. The utility companies are each paying their share of this cost based on how much basin capacity the individual company has established.

The DKK 10 million has been financed by a 25-year loan. The citizens of the respective municipalities are repaying the loan over their water utility bill.

many years of collaboration is now more anchored

The climate change adaptation project for Store Vejle Å was made possible with the decision to build a railway line between Copenhagen and Ringsted. The actual climate change adaptation project commenced in 2014 when it was adopted by the local authority in the six municipalities affected.

The climate change adaptation project for Store Vejle Å was made possible with the decision to build a railway line betwThe current climate change adaptation project marked the beginning of an even deeper collaboration between the utility companies, which meet regularly in a steering committee. The important principles in this collaboration are unanimity, openness and trust.

The project has political backing through authorisations and approvals in all six of the affected local authorities, and political involvement at mayor level from start to end.

Furthermore, there has been a number of community meetings.

Collaboration between utility companies, politicians and citizens has been good. There were some technical difficulties at the beginning. But otherwise the challenges with regard to Store Vejle Å have mostly had to do with communication.

The six local authorities have been supportive, and collaboration between the utility companies has been good.

The citizens affected by the project are making good use of the new natural areas.

However, it has been difficult to communicate to citizens that the new areas are actually wastewater treatment facilities designed to flood, and that they may have to accept that a ten-minute bicycle trip to work could become a 90-minute trip after a cloudburst event, because then the entire natural area will have been flooded and cyclists will have to find a new route home.

The utility companies are planning a solution to this problem, which involves a text message service for citizens so that they can be notified when water levels are high.