Nature Based Flood Defenses - Illusion or Solution?
Nature-based flood defences (NBFD) use natural dynamics and ecosystem services to reduce flood risk. They focus on preserving or restoring ecosystems such as marshes, mangroves, coral reefs and dunes in order to create natural barriers or breakwaters to protect the hinterland from flooding. Having said that this actually have never been put to the test like traditional flood barriers. Perhaps it is time ?
[Music] [Sound of waves] The main problem is that people start living really close to the coast, or even flood plains. So, then you start inhabiting areas that are very vulnerable, but you are also losing the protective function of ecosystems. Good examples of ecosystems that have a protective function are coral reefs. They break waves which is effective and reduced coastal erosion. Mangroves are effective in breaking waves especially if they're really wide. They can reduce storm surge levels. And salt marshes are both effective in attenuating waves but they also accrete a lot of sediments. So it reduces wave setup but also reduces the water depth and thereby the wave height. It has been very clear for a long time that natural systems such as mangroves or salt marshes protect against floods. What is unclear is how much it protects against floods. And we have now taken the next step to quantify that. That is really a step forward. The FAST tool uses images from satellites that give us the status of a foreshore, of a coast, and knowing that status we can quantify, calculate how safe that coastline is against flooding. This screen shows you information on a coastal zone. It shows you the depth of the water, it shows you a green area that is the salt marsh that we're interested in. And it shows you how our numerical model calculated the waves that roll in against the coast and that are attenuated reduced by the salt marsh. And behind the salt marsh you see the dyke. What we are interested now is how during a storm surge from low water to higher water, the salth marsh is protecting the dyke. While we are able to make combined designs for example with a marsh in front of a levy and then we can adjust the levy design top the conditions that are generated by the presence of the marsh. Now, we basically do that by using numerical modelling, but those model function the best under mild conditions. The functions of marshes and magroves becomes really important under extreme conditions. So what we would like to do is to use facilities like the big scale wave basins to validate the models under more extreme conditions. The more results we have, the more conditions we've simulated the more reliable the models will be in future. The fast tool is, of course, as reliable as the information we put into the tool. Part of this information, is the information from for instance flume tests or field testing on how plants interact with wves and currentts. That information is crucial. Therefore, we need ot make certain that these predictions that we do are of the best quality. Our dream is to make clear to the world that these natural coastlines are very important for flood safety. If we make that clear, the restoration and protection of these coasts will be very logical because they contribute to your safety. I think in the ideal situation, we'd be able to conserve ecosystemsm, which means we should be able to predict their function accurately. But also to design with them and maange them in a sustainable way. [Music]
Created in partnership with: Deltares