Garden owners and municipality find stormwater solution

In spring 2011, 28 garden owners along the suburban street Lindevang in Brøndby Strand were asked if they would like to participate in a series of demonstration projects that would test various environmentally friendly stormwater solutions in practice.

"The idea behind the demonstration projects is to give us some visible and concrete experience on how to use rainwater locally, which we can then demonstrate. This will make it possible for us to give the public advice that has been tested, and it will also give us some documentation that can be used to plan the scale of future initiatives", said Søren Hansen, project manager at Avedøre Wastewater Services.
The philosophy behind the Lindevang project is that the challenges presented by the increase in extreme events of heavy rain are best met through cooperation and a combination of regional and local solutions: If more garden owners along the street join forces, it will be possible to divert large amounts of stormwater away from the combined sewer system and thereby take pressure off the system.

The project is dimensioned for a five-year rainfall event. A total of about 2200 m² of roofing area has been decoupled. In addition, the project has included the road that receives runoff water from the gardens. The road water is treated and permeates through a series of roadside infiltration beds that function as speed-reducing chicanes and planted areas at the same time.

Out of the 28 potential detached-house gardens, 15 became demonstration projects. The remaining gardens were either judged to be unsuitable due to flat roofs, unsuitably sloped ground plots, lack of space, or because the garden owners did not wish to participate for other reasons.

"We experienced great support for the project right from the start. I think that the extreme rainstorms of recent years have caused people to believe that the stormwater problem is best solved through cooperation. We also saw that the residents already were interested in and knew relatively much about the problems and the solutions to them" Søren Hansen said.

Before the project started, the garden owners took interested visitors around their gardens to give the project a visible demonstration value.
"We now have 15 powerful ambassadors who are proud to participate in the project, and who gladly share their experience with people, over the hedge and in the badminton club. In fact, we have had garden owners asking when they can expect more visitors. The experience gained here spreads like ripples in the water, so to say", Søren Hansen said.

The stormwater solutions in the 15 gardens comprise a combination of subsurface dry wells, rain beds and lowered areas on lawns, but no two gardens are the same. The combination that was chosen for each specific garden was chosen after a team comprised of people with various technical backgrounds had looked at the gardens and spoken with the garden owners and assessed what could be done on each property.

"Both gardens and garden owners are different, and the water needs to meet with the residents' requirements, so to say. For example, some people were not interested in having a lowered area in their lawn, while others thought it was fine to do away with the lawn mowing and have a rain bed instead. One of the basic ideas behind the project is 'The right solution in the right place'", Søren Hansen said.

The demonstration project on the private properties is partially financed with the approx,. DKK 23,000 that each garden owner can be reimbursed for by their water supplier for decoupling his/her stormwater from the sewer system. Brøndby Wastewater Services has financed the remainder. Søren Hansen does not wish to give an estimate of the real cost of establishing these solutions for a garden owner because this depends on the layout of the property and the level of ambition one has.

"The solutions in themselves are not so difficult to establish. Basically it's all about bending drainpipes and digging holes, but people need technical advice on where the holes should be dug, how deep they need to be and not least to disconnect correctly so that we don't get problems with rats."

• Cooperate across technical specialisations and organisations
• Work on the basis of common goals
• Back words up with action
• Include local practical knowledge
• Use combined solutions: "both-and" instead of "either-or".