Reinforcement of vegetated and unvegetated dunes by a rocky core: A viable alternative for dissipating waves and providing protection?

Abstract

Coastal dunes can provide protection from flooding during extreme weather events. As such, consideration should be given to strengthening the protective mechanisms of dunes. Vegetation has recently been seen as an important factor influencing erosion processes on dunes. Another means of dune reinforcement is the installation of internal structures within dune systems. The purpose of this work is to investigate the potential utility of both vegetation and an internal rocky structure as reinforcing factors on dunes, and explain how they differentially dissipate wave energy and influence the morphodynamic response of the dune profile. This work consists of a series of experiments on dune profiles, with and without an inner rocky structure, and with two different distributions of live Ipomoea pes-caprae plants of the same density, under storm conditions. The results showed that when vegetation was at forward positions on the dune, it decreased run-up, increased reflected energy and transferred it to low frequency bands, and reduced the eroded volume on the exposed dune face. When the vegetation was placed on the leeside of the dune, it retarded and prevented overwash, but not as efficiently as the internal rocky structure did. In summary, plants are better to dissipate waves and provide protection during the initial swash and collision stages of a storm, while a rock structure is better to prevent overwash and dune destruction during the final stages. While it is possible to use both means together, for maximum protection, dune managers should weigh the financial and ecological costs according to each unique project location.