WATER RETENTION AND LOCALISED RAINWATER DRAINAGE (LRD)
Climate change and increased precipitation are making water retention and rainwater drainage key elements of future construction. When it rains heavily, our sewage system cannot cope, which can result in flooding. Sedum roofs can be part the solution here. The roof’s green plants and growth media can absorb large quantities of precipitation and delay runoff, so the sewers are able to cope better.
Green roofs are therefore the roofs of the future, and can be part of the solution for managing increased precipitation and localised rainwater drainage (LRD).
And that’s not just something we say. We have participated in comprehensive studies, where our roofs were tested for their ability to retain rainwater. And these studies show that sedum roofs can make an even bigger difference than people have so far believed.
Testing of sedum roofs’ water retention
DHI and Nature Impact have jointly studied water retention on sedum roofs in a project that ran for more than three years. Absorption and delay of rainwater were measured under different weather conditions at several locations.
Because full-scale measurements were taken in real time, the results are figures that are to be reckoned with in the real world. And the results were positively surprising. It was shown that sedum roofs retain significantly more rainwater than people have so far believed.
Sedum roofs are the future solution to rainwater management
Depending on the weather conditions, a sedum roof can retain up to 50% of all rainwater annually – up to 90% during the summer. This means that the sedum roof’s retention of rainwater will be able to even out the effect of climate change when rainwater and sewage systems are dimensioned.
The study also shows that sedum roofs provide better protection against heavy rainfall than expected. Heavy rainfall can produce up to 100 ml of water in a very short space of time, and the study showed that the sedum roof could retain up to 20 mm of rainwater and delay runoff to a significantly greater extent than expected.
Thus sedum roofs can assist with both rainwater management in everyday life and significant water retention after heavy rainfall. This is already a major gain today, and will be so all the more in the future, when the level of precipitation is expected to increase by up to 25% by 2100.
Runoff and retention of rainwater have been studied
The study of water retention on green roofs has been carried out by Nature Impact A/S in collaboration with DHI and Grontmij (now part of Sweco). The study was funded by Realdania. Testing and measuring programmes continue with data analysis by Niels Eisum from Huginn Consult and inputs and analyses from Krüger.
The water retention is calculated from ongoing measurements in the roof’s drainage gully combined with a magnetic inductive flow meter and software for data collection and analysis.
