“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 Tuesholm 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.