Nature-based flood protection: the efficiency of vegetated foreshores in reducing wave run-up.

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Vincent Vuik, Sebastiaan N. Jonkman, Bas W. Borsje, Tomohiro Suzuki, Isabella Kratzer, Tjeerd J. Bouma

Chair(s): Mark van Koningsveld

Monday 29 june 2015

14:50 - 15:05h at Antarctica (level 0)

Themes: (T) Special session, (ST) Building with nature

Parallel session: 2D. Special Session: Building with Nature

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It is generally recognized that vegetation fields can dissipate wave energy, authorizing the statements that vegetated foreshores can reduce the wave loads on coastal dikes. This paper actually quantifies the efficiency of vegetated foreshores in reducing the wave run-up on the outer slope of coastal dikes. The spectral wave model SWAN, which is used to compute the wave transformation over vegetated foreshores, has been validated using recent measurements of wave propagation over several salt marshes in the Netherlands under severe storm conditions. This article shows that in case that vegetated foreshores are present along coastal dikes, the wave run-up height on the outer slope of the dike is substantially reduced during storm conditions with large water depths and high waves. Vegetated foreshores are more effective in reducing wave loads on the dike than bare foreshores with the same geometry, even when vegetation in their fragile winter state is compared with a bottom on which ripples have been formed. Because the required crest height of a dike is strongly related to the wave run-up height, a reduction in wave run-up height allows for lower crests and more slender dike bodies. We conclude that the construction of vegetated foreshores can be considered as a sound alternative for traditional dike reinforcement methods.