Foto: The water body after measure was completed – People's gardens are extended by the green, Lippeverband
Green-blue Climate Corridor – Disconnection of Rainwater from Sewage Systems
In Kamen, Germany, a green-blue climate corridor has been created to improve the urban climate and restore the nature water supply in the area, reducing the risk of flooding. The corridor includes the restoration of a stream, as well as disconnecting rainwater coming from 80 buildings from the sewage system. Owing to this project, the residents of the area experience less flooding and a more stable microclimate, and they now benefit from a more attractive and natural environment with new opportunities to enjoy themselves. In addition, some residents have been inspired to create their own adaptation projects in their homes, and the wildlife now has access to improved water quality, helping to support biodiversity.
The Adaptation Journey
The positive impact
The green-blue climate corridor can be considered a ‘no-regret’ adaptation measure, which involves the selection of measures which bring a range of benefits to people, nature and the economy, even beyond climate change adaptation. This is considered ‘maximising the positive and minimising the negative’. For example, disconnecting rainwater from the properties and improving the ecology of the river will have a positive impact whether rainfall increases in the long-term or not.
Overall, the project achieved a long-term and cost-effective adaptation of local water infrastructure, an improved microclimate and increased ecosystem resilience. The original ‘mixed canalised system’ of rainwater and sewage led to a higher risk of flooding during storms, whereas now high rainfall doesn’t cause as much flooding, and areas of water are protected during the summer. By channelling rainwater into the restored stream, the natural balance of water supply has been improved, supporting local wildlife and providing better spaces of recreation for residents.
How does it work?
Disconnection of waste water and clean rainwater
A precondition for the nature-like development of the water body was the separation from waste water and clean surface water. The construction of the underground sewer was the absolute necessary first step, therefore a sewer pipe was placed underground along the river. In case of more intense and frequent heavy rainfall due to climate change, this change reduces the flood risks, since the water run-off is slowed down by means of meandering of the stream and infiltration through the natural bed and banks. In addition, the ecological improvement and the sustainable use of rainwater can reduce floods because the sewer system no longer has to cope with the same amount of rainwater. With rising temperatures in summer, the water bodies also tend to dry out. Due to the use of rainwater for the open water body the water cycle remains balanced even in dry periods, while evaporation creates a better micro- climate.
The concrete bed of the stream was removed (apart from few exceptions, e.g. under bridges), which led the river to flow on a new bed that was higher and wider than before and meander where possible. The hard banks were converted into nature-like banks. The initial plantation was complemented by wild and natural vegetation: green plants have the chance to flourish along the blue water body. For the development of biodiversity, it is important to give as much room to the water body as possible, so adjoining properties were included in the creation of the wetlands. Ultimately, the support of the community and decision-makers made the planning and implementation possible.
The stream, Heerener Mühlbach, was a canalised water body used as an open wastewater system, creating ecological and social challenges. The straight concrete bed of the water body contained a mixture of waste and storm water, and was classified as heavily modified by the EU Water Framework Directive, which triggered problems to be resolved.The poor water quality in the concrete bed damaged local biodiversity and reduced the resilience of the ecosystem, as well as leading to a bad smell in the neighbourhood. Extreme rainfall became more frequent leading to flooding, and endangering nearby private and industrial property. Adding to this, the dangerous shape of the canal which prohibited the recreational use of the water body.
Communication was a key to motivation for the project, in particular, the storm water disconnection on the private grounds needed special communication. At the start of the project, inhabitants were not fully aware of the connection between climate change and their own property. A communication strategy to inform about the project and to motivate people for disconnection was set up in combination with an individual assistance. By the end of the project most of the property owners at the Heerener Mühlbach were aware of the need to adapt to climate change and understood how every individual can make his/her contribution. People were encouraged to take action for a better city climate and against climate change.
In order to gain political and public support for such measures, it was also key to have sound scientific evidence of the potential benefits which can be created regardless of climate change and to compare these to other approaches. The outcomes of such comparative analyses can be shared through targeted awareness raising campaigns to highlight the potential environmental, societal and economic benefits and thereby foster greater recognition of the value of adaptation measures and increase public support.
Obstacles and challenges
In some locations where water bodies have been ecologically enhanced by the water board, too much initial vegetation was planted shortly after completion of the construction works. As nature develops itself as soon as the conditions are good, the vegetation grew to such an extent that the trees and shrubs required almost the full amount of water coming from the water body, turning the habitat into a purely green corridor without open water. The green-blue corridor in Kamen has now developed into a balanced ecosystem with the water body and adjoining wetlands.
How much did it cost?
The costs for the planning and construction were shared by the district and the environmental department MA 22 and the private owner, who is responsible for the maintenance. Financial resources for the guideline, including content creation, print and publication were planned in the annual project budget from the environmental department – MA22. There were no additional funds.
Revitalization of water elements Family and apartment houses Urban greenery Water purification and recycling Use of rainwater Flood control measures Biodiversity Floods and torrential rainfall Lack of water and drought