When flooding cannot be avoided, plan the flooding.
One of the first constructions with storm water management at the source and fauna passage in Denmark is localised in Bækrenden at Vallensbæk Landsby. It was constructed in 2005.
The creek, Bækrenden, receives large amounts of storm water from the connecting system. It has a limited capacity and at large flows Vallensbæk Landsby may be flooded. This happened often before the storm water management facility was established.
Modeling made by the municipality’s advisor showed that discharges to the village pond above approx. 800 l/s would result in flooding the village.
Upstream of the village lies a field/meadow, whose areas near the creek side can withstand being flooded.
In 2005 a Mosbaek Double Baffle with fauna passage and integrated emergency overflow was installed at the meadow limiting the flow to the village to max. 800 l/s. The flow regulator is located at the inlet to the road bridge at Højrupgårdsvej.
It was dimensioned for a discharge up to 2 m3/s. At that time that was an 18-years occurrence.
At flows above 800 l/s to the flow regulator the resistance in the regulator increases and the water level increases accordingly upstream of the regulator resulting in flooding of the creek side. When the available volume on the creek side is used, the water level is so high that it enters the regulator’s integrated emergency overflow (at level 3.03)
Since 2005 adjustments of the surrounding terrain have been made giving a storage volume of approx. 1100 m3 at level 3.03.
When receiving 2 m3/s the Mosbaek Double Baffle is designed so the water level is approx. 25 cm below the level of the road, which is approx. 3.50.
The municipality is currently working on further storm water management in the area.