Urbanization with more paved and other hard surfaces that convey rain- and meltwater instead of absorbing it. Climate change with increased precipitation in the form of rain. These factors can contribute to severe floods, as we have seen in the past year in Gävle, western Germany, Belgium and Japan, among others.
– When there is not much natural drainage where it is easy for the water to infiltrate, there will be consequences. This is a growing problem that needs to be solved. We are trying to find an innovative concept for stormwater storage consisting of a porous material. Our vision is to find a material that can be placed in communities, and that swells and retains water when there is a lot of rain or meltwater, says Maria Viklander, professor of urban water engineering, who leads DRIZZLE – Centre for Stormwater Management, a Vinnova funded competence centre for research in areas of importance for Sweden.
Reduce the risk of floods
The overall goal within DRIZZLE is to develop pioneering research-based stormwater solutions that reduce the risk of floods in cities and minimize the pollution load in lakes and other watercourses.
The idea of a material that can absorb large masses of water in the event of a cloud-burst was raised within DRIZZLE, and researchers in urban water engineering contacted Sofia Larsson, researcher in fluid mechanics, and her colleagues.
After initial data modeling, the researchers are now in the process of testing different types of existing materials in the lab, including hydrogels that are otherwise used for wound dressing.
– As researchers in fluid mechanics, we have a lot of experience of flows through porous materials for different areas of use. In this case, it is about finding a material that can both absorb the water and keep it until the rain subsides. We hope to take steps towards a smarter form of water storage, where the system takes care of itself – you should not have to drain the water manually, says Sofia Larsson.
The scientists work on the basis of three main concepts:
- a, where the material is placed on surfaces such as parking garages and roofs. Similar to sedum roofs, but with even better absorbency.
- b, where the absorbent material is attached vertically around lampposts, bridge pillars and other existing structures.
– The material is placed low and the stormwater is led there. The capillary force causes the water to be sucked upwards and the material to swell, Sofia Larsson explains.
- In the third concept, c, the absorbent material becomes a form of sponge-like installation, which grows during heavy rain.
– It should be a nice and smart addition to the outdoor environment.
What should happen to the absorbed water is a difficult problem to solve.
– We are thinking about how we can dry the material in an efficient way so that the water evaporates and new rain can be absorbed, says Sofia Larsson.
The material that absorbs the rain masses must be durable and not dangerous to humans, animals or the environment. It must not be too heavy when it is filled with water, so that, for example, roof structures are damaged. It must also not obstruct traffic or be a hindrance in other ways.
– We can see that our concepts work in theory in so-called "ten-year rain" or extreme rain. Now we are testing different types of materials in the lab and based on that we have to think about how we proceed with the next step – always with the perspective "what will work in reality".