Hedevænget. Can the rainwater be diverted? Pilot project

Hedevænget – Pilot area for infiltration in Gladsaxe Municipality.

Gladsaxe Municipality has been affected on several occasions by heavy rain events, resulting in lots of flooding of both basements and the terrain – most recently in the summer of 2007. In 2008, a major survey began into where the problems were greatest, and what measures could be implemented in order to reduce the risk of flooding. This survey was based on the municipality's records of flooded basements since 2001 and hydraulic modelling of the entire sewer system. The model identifies areas with a risk of flooding over the terrain at less than a 10-year rain.

One measure involves separation of rainwater from the community sewer by means of infiltration on private land. Hence a map showing the potential for infiltration throughout the entire municipality has been compiled. Historical maps which identify a range of earlier and current marsh, river and lake areas where infiltration was not advised were used when compiling this infiltration map. The map shows that infiltration is feasible throughout much of the municipality, but the potential is greatest in the northern and north-easterly parts of the municipality. The major challenge with this initiative is that it is not possible to offer citizens the opportunity to establish an infiltration system on their own land. The initiative will have no appreciable effect if citizens choose to establish infiltration only sporadically.

The municipality has worked on the basis of the infiltration map, the hydraulic modelling and the statistics to identify a pilot area for infiltration, known as "Hedevænget." All 429 landowners in the area were asked about their interest in infiltration via a questionnaire-based survey. Before the questionnaire was sent out, the municipality held an information meeting about water in basements, and information was provided on the questionnaire at this meeting.

This project description will be updated when new results have been achieved within the project.

Statement from Kristoffer Amlani Ulbak, Gladsaxe Municipality: "Involving citizens in the solution for rainwater management on their own land has been an exciting process. We have been very surprised by how committed people are and have been to the process. A better environment has really provided a strong incentive for people."

Finance
The municipality is offering to repay a connection charge for rainwater amounting to DKK 20,800
Establishment costs for soakaways. Estimate from contractor: DKK 9,000 to 15,000

Recipient
The solution will reduce the discharge of untreated waste water to Lyngby Lake via the Bagsværd trench. At present the municipality is complying with requirements for overflow to Lyngby Lake.

Location
Hedevænget, DK-2800 Kongens Lyngby (Gladsaxe Municipality)

Contact person
Name: Keld Rehder
Organisation: Gladsaxe local authority, Vand- og afløbskontoret (Water and drainage office)
E-mail: tmfkre@gladsaxe.dk
Phone: +45 39 57 58 93