Urban runoff has traditionally been handled via underground pipelines. However, due to urbanisation and climate change, we must now instead build open blue green infrastructure solutions in our cities that divert runoff locally. Unfortunately, the change towards more sustainable runoff management is moving at a slow pace.
“There are frequent conflicts over the management of runoff,” says Helene Sörelius, Environmental and Hydraulic Engineer at RISE. “There is no single authority or agency able to handle the issue alone, many different operators need to cooperate. RISE has extensive experience of being an objective partner for successful collaboration.”
Urbanisation and climate change are the two main reasons we can no longer manage runoff as in the past, i.e. via pipelines underground. As a result of urbanisation, impervious surfaces – hard surfaces through which water cannot pass – are covering increasingly large areas in cities, with fewer and fewer green areas for water to infiltrate and flow down to the groundwater. Climate change is causing precipitation patterns to change, and Sweden will see higher total precipitation. We will experience drier summers with heavier downpours. The higher precipitation combined with more impervious surfaces in cities is preventing rainwater infiltration and causing flooding.
Runoff plans need to be implemented
Municipalities are responsible for keeping track of waterways, their capacity, and where risks of flooding exist.
“Some municipalities are better than others when it comes to sustainable runoff management,” says Sörelius. “It’s often the case that they have previously been affected by torrential rain and flooding. Only then do runoff projects receive focus and funding. And it usually requires another heavy downpour to show that the project has had an effect.”
One municipality that has been hard hit by torrential rains and flooding is Vellinge, which has now built several different facilities to sustainably manage the runoff. Among other things, they have built bioretention facilities (also referred to as rain gardens), which are small, landscaped sites where the rainwater is led, diverted and even purified to some extent. Another municipality that has invested heavily in local solutions is the City of Malmö. In the neighbourhood of Augustenborg, an open runoff system was established in the late ’90s to tackle recurring basement flooding. Since the measure was introduced, there has been no flooding in the area, despite heavy downpours such as the one that hit the city in 2014 and submerged much of the city centre.
Runoff should be viewed as a shared resource in our cities
Area of responsibility spans several administrations
Unfortunately, there are frequent conflicts related to municipal runoff planning. In addition to shortcomings in current legislation, one cause of conflict is that responsibility for runoff management rests with a single administration, but multiple administrations need cooperate in order to resolve the issue.
“It is primarily the water and sewage administration that is responsible for runoff management in a municipality, but they are seldom able to handle it themselves,” says Sörelius. “A number of different administrations need to cooperate, provide funding and jointly plan for sustainable runoff management. Especially in our major cities where there is already a shortage of space. In this, RISE serves as a good partner for collaboration.”
RISE is state-owned and has extensive experience of assuming an objective role in projects to support collaborations between government agencies and private and public operators. In addition, RISE has had a test bed since 2016 for evaluating runoff technologies and techniques, in which providers of runoff solutions can test their products in a real-world environment. Examples of technologies and techniques that can be evaluated in the test bed include biofiltration, silage surfaces, structural soils, and water retention systems, as well as filter solutions and filter materials.
Rain is clean water we could use
Water that falls to the ground in the form of rain is relatively clean. Properly managed, we could use it as potable water and for irrigation.
“Making runoff a usable resource requires cooperation and joint planning in municipalities,” says Sörelius. “There also needs to be greater consensus and understanding of how to use runoff as the resource it could provide if properly managed. It may have to do with a tall edge that was built to facilitate snow clearing but which does not divert rainwater to a park or other appropriate surface such as a football field. Another example is an administration, such as a parks and environment board, that needs water to irrigate the city’s parks but which is currently forced to use clean drinking water instead of runoff collected in the water and sewage administration’s facilities. Runoff should be viewed as a shared resource in our cities and should be addressed early on in the planning process and play a central role in all other planning. More incentives are needed to ensure sustainable runoff management, and municipalities must be able to set requirements.”
An organisational issue
At present, the issue of sustainable runoff management is addressed late in the planning phase of Swedish cities. Or it is addressed early but decreases in priority as time goes by.
“The circumstances today make it difficult – or almost impossible – to push through local solutions. New developments offer greater opportunities, but plans for sustainable runoff management all too often fall by the wayside. If runoff was valued according to the resource it would provide if properly managed, the ecosystems it would add and the social factors it would contribute, the approach to and planning of runoff could be changed,” concludes Helene Sörelius.