Green-blue climate corridor Kamen - Disconnection of rainwater from sewage systems to prevent urban flooding
Full Solution
Restored Heerener Mühlbach in Kamen, DE
Lippeverband
The green-blue corridor project in Kamen, Germany was developed to improve the urban climate and restore the nature water supply in the area, thereby reducing flood risk. In conjunction with 2 km of ecologic improvement and stream restoration, rainwater from around 80 adjoining buildings and properties was diconnected from the sewage system. Residents were involved in the project and were responsible in some cases for the implementation of individual adaptation measures on their own properties.
Last update: 10 Mar 2021
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Context
Challenges addressed
The Heerener Mühlbach was a canalized water body used as an open wastewater system, creating ecological and social challenges. The poor quality of the water in a concrete bed damaged local biodiversity, significantly reduced the ecosystem’s resilience and led especially in summer to a disturbing smell within the neighborhood. Extreme rainfall events became more frequent leading to flood events and endangering adjoining private and industrial properties. Finally, the physical form of the banks made it dangerous to use the area recreationally.
Location
Kamen, Germany
West and South Europe
Process
Summary of the process
The ecological improvement of the Heerener Mühlenbach brook by “Transforming the water body to nature-like banks” (BB3) in combination with the disconnection of storm water of the nearby paved areas is ready to make a significant contribution to weakening the potential impacts of climate change. If the effects of climate change do not come true as expected, the “Selection of no-regret adaptation measures” (BB2) will still allow for a number of benefits. Local inhabitants enjoy better living conditions with the recreational purposes the river now offers. “Engaging private citizens to implement adaptation measures” (BB1) is also a great opportunity to raise their general awareness of the water cycle and own responsibility for sustainable development. This was strongly supported by the “Communication strategy to increase understanding and support on flood prevention“ (BB4). At the level of the municipality, the city has become more attractive due to the ecological innovations. For the water board Lippeverband, such a no-regret measure is also a way to attain the EU Water Framework Directive, to reach better flood resilience and to allow for a more cost-effective water treatment.
Building Blocks
Engaging private citizens to implement adaptation measures
Successful implementation of EbA sometimes necessitates the involvement and support of private actors in cases where the measures are to take place on their land. This can create a challenge as the process of convincing individual stakeholders to participate in implementation activities often requires significant time investments, financial resources, and public outreach efforts. In the case of Kamen, it was necessary to determine the value of decoupling private citizens’ rainwater from the sewage system and then to convey this information in a convincing manner to those involved. Two public information meetings were followed by one-on-one planning sessions in which a technician visited individual homes and drafted catered solutions for disconnection that met the needs of each citizen. Furthermore, financial incentives were provided to the residents in the form of expenses per decoupled square meter to motivate participation.
Enabling factors
The project’s success can be credited to the participation and engagement of private citizens. Their support for decoupling rainwater from the sewage system emerged from a combination of several factors: outreach and awareness raising activities, public funding, voluntariness, provision of targeted and bilateral on-site expert advice, and a reduction in fees for disconnected households.
Lesson learned
Given the high importance of citizen support and participation in the project, significant efforts and resources were invested in motivating participation. The approaches taken underscore the value of investing time in one-on-one sessions, in which information and arguments for participation are tailored to each stakeholder. As a consequence of these efforts, most of the property owners in the area were aware of the project of the need to adapt to climate change, and understood the value of their contribution as single actor. This has led the residents to be highly accepting of the implemented EbA measures and develop a sense of ownership, as well as to be open towards and even encourage the pursuit of further adaptation initiatives in the future in order to reach climate change adaptation goals and produce additional co-benefits for themselves and the environment.
Selection of no-regret adaptation measures
Given the many uncertainties associated with climate change, political and community support for so-called ‘no-regret’ adaptation measures can often be higher than for alternative approaches whose (cost-)effectiveness depends on the degree of future climate change. The no-regret approach focuses on maximizing positive and minimizing negative aspects delivered by EbA, and selecting actions that yield a range of benefits even in the absence of such change. In the case of the Kamen green-blue-corridor, the ecological improvement of the stream in combination with disconnecting the storm water from surrounding properties was determined to have positive impacts regardless of whether rainfall will increase in the long-term or not. Should rainfall intensify and become more frequent, flood risks will be reduced; if temperatures increase in the summer, the stored water will benefit the mircroclimate. Regardless of climate, however, the EbA measures can be considered as ‘no-regret’ as they create amenity and recreational benefits for the community and visitors, increase awareness levels, contribute to the EU Water Framework Directive and biodiversity conservation, and reduce water discharge fees for local inhabitants.
Enabling factors
In order to gain political and public support for such measures, it is 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 disseminated via targeted awareness raising campaigns to highlight the potential environmental, societal and economic benefits and thereby foster greater recognition of the value of EbA, increase public support, and lead to
Lesson learned
A range of obstacles can serve as potential barriers to implementing no-regret EbA actions, such as (i) financial and technology constraints; (ii) lack of information and transaction costs at the micro-level; and (iii) institutional and legal constraints (as outlined on the European Union’s Climate-Adapt platform). It is thus important to conduct assessments of the (cost-)effectiveness of the no-regret option as well as of other available measures in order to facilitate informed decision-making and steer appropriate communication campaigns. In Kamen, such comparative data was gathered and presented in group meetings and bilateral discussions to community members who were considering decoupling their rainwater from the sewage system. Given the reliance on private citizen support for a successful implementation, it was of particular importance to highlight the ‘no-regret’ character of the EbA measures alongside the personal benefits which could be expected.
Transforming the water body to nature-like banks
Given the history of the Ruhr region, the Heerener Mühlbach was a canalised water body used as an open wastewater system. Conducting a mixture of waste and storm water in a straight concrete bed, the water body got classified as heavily modified according to the EU Water Framework Directive and required that a number of problems be resolved. Discharges of wastewater in the stream derogated the ecosystem tremendously and the concrete bed of the water body and the specific management of the banks harmed biodiversity. Another problem was the dangerous shape of the canal which prohibited the recreational use of the water body. And finally, bad smell regularly disturbed the neighbourhood. As a first essential step towards ecologic enhancement, a sewer pipe was placed underground along the river. The concrete bed was then removed (apart from few exceptions, e.g. under bridges), which led the river to flow on a new sole that was higher and wider than before and meander where possible. The hard banks were converted into nature-like banks. The initial plantation is complemented by wild and natural vegetation: green plants have the chance to flourish along the blue water body.
Enabling factors
A precondition for the nature-like development of the water body was the separation from waste water and clean surface water. Thus, the construction of the underground sewer was the absolute necessary first step. For the development of biodiversity, it was important to give as much room to the water body as possible; adjoining property was thus included in the creation of wetlands. Ultimately, the support of the community and decision-makers made the planning and implementation possible.
Lesson learned
In other locations where water bodies were 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 has now developed into a balanced ecosystem with the water body and adjoining wetlands.
Communication strategy to increase understanding and support on flood prevention
From 2007 to 2010, severe flash floods occurred in different cities in the Emscher- and Lipperegion due to extreme rainfall events. In the public discussion that followed, the question of responsibility came up. Citizens formulated the demand that the public bodies, particularly the municipalities and water boards, had to guarantee a full protection against future flood events. In further developing this demand, it quickly became clear that this would not be possible without paying a high price. Questions arose like: How high should the dikes be, and how big should the waste water sewers be dimensioned to protect people against any extreme event? How much energy and money would that cost? This would speak against all efforts regarding climate protection and reducing greenhouse gas emissions. A communication strategy was thus necessary to change citizen perspectives and develop support for a reasonable solution. The goals was to convince the population that there is no solution by public authorities which can offer 100% protection against the impacts of climate change, and that there will always remain a degree of personal responsibility. This was the starting point when people began to ask the question: What can I do?
Enabling factors
The fact that people were concerned about their wellbeing supported the communication strategy. Without the extreme rainfall events. It would have been much more difficult to come into a mutual dialogue with people about possible approaches on how to face the impacts of climate change. Talking about climate, there is no “polluter-pays-principle”, but rather open discussions about “who can do what” were needed.
Lesson learned
Communication strategies built around stories intended to scare the audience are not successful. Neither policy makers nor people like to act on the assumption that their world will be flooded and damaged. However, informing citizens in an open and factual way, complemented by highlighting the potential positive impacts of adaptation measures can be a strong and successful approach. Here, highlighting the benefits of an enhanced living quality, improved recreation facilities and a sound ecosystem convinced stakeholders and citizens to start taking acting themselves and support the planned EbA measures.
Impacts
The project achieved a long-term and cost-effective adaptation of the local water infrastructure, an improved microclimate, and increased ecosystem resilience. Pressure on the mixed canalization system and thus flood risk were significantly reduced during severe rainfall periods, while enabling the maintenance of water bodies during the summer. The diversification of rainwater into the naturally designed stream resulted in a restoration of the natural water supply and balances, support of diverse biotopes and increased amenity and recreational values for residents.
Beneficiaries
The residents of Kamen enjoy reduced flood risk, increased recreational opportunities and amenity values and improved microclimate offered by the restored corridor area. The area’s biodiversity also benefited from improved water quality and balance.
Sustainable Development Goals
SDG 11 – Sustainable cities and communities
SDG 13 – Climate action
Story
Ecological Restoration of Heerener Mühlbach
(c) Anke Althoff
The idea of “no-regret measures”: In view of the uncertainties of climate change, so-called no-regret measures were the solution: Most anticipatory options are not only beneficial for climate change adaptation but also for other sectors such as economic growth. Even if climate change impacts do not occur as expected, the measures will still be beneficial and cost-effective.
According to the long-term rainfall measurements of the water board Lippeverband, no significant trend towards climate change could be observed. But it can also not be sure that rainfall will not increase. The ecological improvement of the stream in combination with the disconnection of storm water of the nearby paved areas is ready to make a significant contribution to weakening the impacts of potential climate change, no matter in which dimension this will happen. In case of more intense and frequent heavy rainfall, it reduces the flood risks since the water run-off is slowed down by means of meandering and infiltration through the natural bed and banks. Also, the ecological improvement and the sustainable use of rainwater can reduce floods because the sewer system does no longer have to cope with the same amount of rainwater. With rising temperatures in summer the water bodies tend to dry out. Due to the use of rainwater for the open water body the water cycle remains sound even in dry periods and evaporation creates a better micro- climate. While combining water management measures with green corridors, the climate in the urban surrounding is enhanced.
Communication – a key to motivation
Especially the storm water disconnection on the private grounds needed special communication. At the start of the project, inhabitants were not really aware of the coherences 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.
