Experiences of nature-based solutions for mitigating ship-induced erosion in confined coastal waters

Abstract

Hydrodynamic forces from ships operating in sheltered, confined fairways can result in increased wave impact and sediment transport leading to loss of land and habitats. Nature-based solutions (NBS) offer the potential to mitigate ship-induced erosion and increase biodiversity and ecosystem services. The aim of this study is to evaluate the performance of NBS in a sheltered, confined fairway located in a cold, temperate region. The case study presents the results of a 2.5-year study of the morphologic response at two sites where NBS was implemented to mitigate bluff erosion and at one site where NBS was implemented to mitigate the retreat of a reed belt. Moreover, a qualitative assessment was made of the vegetation development at the sites. The results showed that fine sediments with planted vegetation could not withstand the hydrodynamic forces induced by the ships. However, by adding sills as stabilizing structures, the forces were sufficiently attenuated for the vegetation to establish. The vegetation, which reduced the ship-generated waves and currents, was especially important during high water-level events when the energy dissipation by the sill decreased. Moreover, a small-scale nourishment was successfully applied to mitigate bluff erosion without negatively affecting sediment supply to an adjacent sandy beach. This study demonstrates that NBS can be implemented to retain erodible sediment and favour vegetation growth in fairways experiencing primary and secondary waves produced by large, ocean-going ships.