Traditionally, runoff has been managed via underground pipes. However, due to urbanization and climate change in particular, we now need to build open green-blue solutions in our cities that delay runoff locally. Green-blue solutions can contribute many added values to the city, but implementing solutions often requires collaboration and new ways of working.
“Many different actors must work together to achieve sustainable runoff management. RISE has extensive experience as an objective partner for successful collaboration,” says Beatrice Nordlöf, project manager for climate adaptation at RISE.
The two main reasons why we cannot manage runoff solely through underground pipes are urbanization and climate change. Urbanization has meant that cities have more and more hard surfaces that do not allow water to pass through and fewer green areas where rainwater can infiltrate and flow down to the groundwater.
Climate change means that precipitation is changing and total precipitation in Sweden will increase. We will see more droughts in the summer and more heavy rainfall. The increased precipitation, combined with the fact that we have more hard surfaces in cities, means that the water cannot be accommodated in the drainage system and instead runs off the surface, causing flooding.
To reduce the risk of flooding, measures are needed to safely divert and delay water. This could involve, for example, building green roofs or rain gardens where water is delayed locally, raising the level of a street so that water is diverted away from buildings, or creating a bowl-shaped park so that large amounts of water can be collected there without causing damage.
Read more about Climate-proof solutions for urban areas.
Plans for runoff management begin to be implemented
All municipalities are at risk of flooding during heavy rainfall, but municipalities have progressed at different rates when it comes to planning and implementing measures.
"Some municipalities have progressed further than others. This is often because they have been exposed to heavy rainfall and flooding in the past, which tends to bring climate adaptation issues into focus and secure funding," explains Beatrice Nordlöf.
One municipality that has been severely affected by heavy rainfall and flooding is Vellinge, which has now built several different facilities to manage runoff sustainably. Among other things, they have constructed so-called rain gardens or biofilters, which are small plantings where rainwater is directed, delayed, and to some extent even purified.
Another municipality that has invested heavily in local solutions is the City of Malmö. In the Augustenborg area, an open runoff system was introduced in the late 1990s as a measure against regular basement flooding. Following these measures, the area has become more resistant to flooding. When Malmö was hit by heavy rainfall in 2014, the buildings in Augustenborg fared relatively well compared to the surrounding areas.
Runoff should be viewed as a shared resource in our cities
Responsibility spans multiple actors and multiple administrations
Responsibility for managing runoff and heavy rainfall is divided among several different actors and involves several of the municipality's administrations. This sometimes creates uncertainty about who is responsible for what and how costs should be allocated, which can make it difficult to implement measures in practice.
“Several different administrations must collaborate, finance, and plan for sustainable runoff management together. Other actors, such as private property owners, may also need to be involved. This is especially true in our larger cities, where there is already a shortage of space. Here, RISE is a good partner for collaboration,” says Beatrice Nordlöf.
RISE has worked on collaboration around runoff and heavy rainfall management in a number of research and innovation projects. In addition, since 2016, RISE has had a test bed for evaluating runoff technology. Here, technology suppliers of runoff solutions can test their products in a real environment. Some examples of technologies that can be evaluated in the test bed are biofilters, overflow surfaces, skeleton soils, delay reservoirs, and filter solutions and filter materials.
Precipitation is clean water that we could utilize
Water that comes from the sky in the form of precipitation is relatively clean water. If handled correctly, we could use it for irrigation.
"In order for runoff to be used as a resource, cooperation and joint planning within the municipality are required. It is also a matter of increased consensus and understanding of the management of runoff as a resource when handled correctly. This could involve a high curb built to facilitate snow removal but which prevents rainwater from being diverted to a park or other suitable area for delaying runoff. It also involves an administration, such as the parks and nature administration, needing water for irrigating the city's parks, but which today is forced to use clean drinking water instead of runoff collected in the water and sewage administration's facilities. Runoff needs to be seen as a shared resource in our cities that is included early on in the planning process and plays a central role in all other planning," says Beatrice Nordlöf.
The issue of sustainable runoff management is particularly complex in the existing built environment. Many areas have been built without consideration for flood risks, while climate change is increasing these risks.
"In existing buildings, it is currently difficult to implement local solutions. There are greater opportunities in new developments, where it is important that the issue of sustainable runoff management is not lost along the way. It is important that runoff is valued based on the resource it represents when properly managed, the ecosystem services it provides, and the social values it can contribute. This could change the approach to and planning of runoff management," concludes Beatrice Nordlöf.