Case

It’s raining frogs – stormwater solution improves biodiversity

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Heavy rain caused multiple sewer overflows in a small Danish town.

Heavy rain events have caused multiple sewer overflows in the small town Lynge, a district of Alleroed Municipality north of Copenhagen. The area was previously a marsh area, which could store large volumes of stormwater but due to drainage, Lynge has lost parts of its natural character over time.

Stable waterflow and reduced risk of overflow

With a combination of landscape-based stormwater solutions and nature improving initiatives, Alleroed Municipality decided to improve stormwater management, increase biodiversity in Lynge and improve conditions for the recipient, Lynge Stream.

The developed stormwater solution holds back stormwater in dry and wet basins and slowly discharges it into Lynge Stream. The result is a more stable waterflow in the stream, a reduction of the risk of combined sewer overflow to the stream, as well as an increase in wet and semi-wet habitats.

Plant species expected to increase
An increase in plant species diversity has been attempted by increasing the overall diversity of growth conditions. Exposure of mineral soil in combination with the addition of stormwater and planting of selected species are expected to increase plant species diversity of the area, and in turn increase the number of food sources for insects.

Furthermore, a new pond was established to attract amphibians. The pond only receives stormwater that has passed through a dual porosity filter implemented centrally in the area.

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