Overtopping Reduction By Artificial Reefs

Abstract

Artificial or Engineered reefs are primarily developed for enhancing the ecological system. In Guidelines for the Placement of Artificial Reefs (UNEP, 2009) they are described as "An artificial reef is a submerged structure deliberately constructed or placed on the seabed to emulate some functions of a natural reef such as protecting, regenerating, concentrating, and/or enhancing populations of living marine resources." Often these artificial reefs have either a complex shape inspired by biomimicry (e.g. Coastruction) or a more regular shape, designed to function as modular blocks that can be easily placed on top of each other (e.g. Reefy). In many parts of the world, application of these engineered elements on top of existing shallow reefs may be a solution to not only enhance the ecosystem but also to increase the safety level of the hinterland. Also, in light of climate change and further increasing water levels, the artificial reefs may be a valuable alternative to reduce wave overtopping and prevent the land for extreme flooding. To quantify the possible effect of such artificial reefs in more shallower areas, physical model testing have been performed in which both overtopping was measured with and without the use of engineered elements. Shallow water depths have been chosen here, since the reef should induce wave breaking, resulting in the wave energy to decrease. The performance of these engineered elements in relation to its submergence has been investigated and a reduction coefficient has been developed.