Restoring Coral Reefs for Flood Protection

We frequently hear in the news about dying coral reefs, and also about the threats of sea level rise and climate change. But there is a key gap: what if we can hit two birds with one stone, and restore damaged ecosystems while providing vital protection against flooding? Our latest research demonstrates how coastal managers and ecologists can join forces to achieve both goals, which may help stretch limited funding further.

I am extremely proud to share Floortje Roelvink’s first scientific paper, “Coral reef restorations can be optimized to reduce coastal flooding hazards“, published in Frontiers of Marine Science. I had the great privilege of sitting on her MSc thesis committee two years ago, and she has been our colleague at Deltares ever since.

Floortje’s work carries on the line of research that I joined in my own master’s thesis: how can we better predict flooding due to waves on reef-lined coasts? Although I briefly tangoed with the topic of coral restoration, Floortje took it to a whole other level in her epic MSc thesis, which formed the basis for this new paper.

For starters, she analyzed an extensive dataset of over 30,000 coral reef bathymetries, which indicate their shape and depth. From there, she used statistical techniques to identify typical four reef shapes that frequently recur in the environment.

An overview of the four characteristic reef types that Floortje identified in her bathymetry analysis (top row), as well as the potential restoration locations that she tested (bottom row). Coral reefs are tremendously diverse not only in terms of ecology, but also in their shape, size, and the ways they respond to waves. Floortje’s approach attempts to boil down all of this complexity to a more manageable set of test cases that we can use to better understand the basic physical principles at work. [Source].

She then simulated a range of representative wave and offshore water level conditions to determine how waves transform as they move across the different types of reef. This gave a baseline estimate for the flooding that could be expected onshore for reefs that have not yet been restored. With that baseline, she then added small rough humps at various locations on the reef to simulate the presence of restored coral. By comparing the expected flooding from restored reefs versus their unrestored counterparts, Floortje determined that best places to strategically place coral.

It turns out that you can most effectively reduce wave-driven flooding by placing restorations on the shallowest parts of the steep forereef slope, or on the flat part of the reef near the shore. However, these are also some of the most energetic places on the reef, which means that the corals planted there need to be extremely tough and resilient to survive. Basically, the coral functions as a sort of living breakwater.

One of the benefits of Floortje’s research is that by showing the powerful potential of coral reef restoration to limit wave-induced flooding, it may also increase funding opportunities for reef conservation. What if instead of building big concrete breakwaters to protect vulnerable islands from hurricanes, we can instead restore the coral reefs there and achieve multiple goals? I think this is something worth fighting for.

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