Co-author of the paper Chris Spray is Professor of Water Science and Policy at the University of Dundee, in Scotland. He explains that natural flood management is all about “slowing the flow” by diverting and temporarily storing ’excess’ flood water. Tree planting, re-meandering of rivers, installing ’leaky dams’ and log restrictors, creating temporary flood storage ponds, and more all come into the mix.
“Such measures have only been shown to work in small experimental catchment areas, and there is lack of evidence for their effectiveness over larger areas. In the paper, we looked at the combined effect of NBS measures across much larger land areas. Based on our very detailed research in the Eddleston catchment, we extend the findings into the bigger picture through modelling.”
The scientists find that NBS-enriched landscapes do have the capacity to slow down powerful floods as they move down the river. This increase in the lagtime between heavy rain falling and river levels rising gives downstream communities precious time to respond to the imminent danger. In addition, the NBS measures will typically help reduce flood peaks by spreading the water across a larger area.
These effects of NBS are fairly modest, typically reducing flood damages by 5 to 10%. However, the positive effect will remain year on year. And this level of reduction remains constant, even under the most severe events. When you look at the long-term expected return on investment, NBS therefore generate significant value.
Chris Spray explains that natural flood management works at all scales because of its expandable nature. Simply put, the floodplain can soak up and store a larger body of water during more severe events.