The construction of coastal defence structures to keep people’s feet dry can have severe consequences on the coastal ecosystem if the project is not well designed. The construction of breakwaters for coastal protection requires a better understanding of the ecological impact on local coral reefs.
In an interesting study published in SN Applied Sciences, Stender et al. indicated that though breakwaters are suitable for coastal protection, very little effort has been made to understand the ecological impact of their constructions on the local coral reefs in Hawai’i. The authors revealed that the design of the commercial harbour in Hawai’i, which takes into consideration ecological and environmental factors as well as engineering principles, could serve as a model for environmentally friendly harbour development.
The researchers employed different methodologies to evaluate environmental conditions and reef community composition at the proposed site. The features of the lower ecological zone were assessed using a towed drop camera system to relate to biological factors. In addition, detailed visual surveys were carried out at the existing breakwater, the proposed site, the unaltered surrounding habitat, and within and outside the shipping channel. Finally, water quality at the different sites was measured to derive information about prevailing environmental conditions.
The authors show that the breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. Their results also indicate that a deep area characterized by unconsolidated sublayers and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an ideal environment for coral to flourish while at the same time protecting the harbour from large ocean waves. They also found that surfaces on shallow sloping hard bottoms receive higher levels of sunlight that benefits coral growths and that optimal movement of water facilitates sediment removal and enhances coral recruitment and growth.
It is clear from this study that an integrated approach that combines coastal hazard protection and coral reef resilience is vital for adaptive coastal communities in the face of changing climate and its associated impact. By combining ecological, environmental, and engineering aspects of coastal defence structure this interdisciplinary project can be used by policymakers as guidelines for harbour development and shoreline modification throughout the tropics.
Stender, Y., Foley, M., Rodgers, K. et al. Evaluating the feasibility and advantage of a multi-purpose submerged breakwater for harbor protection and benthic habitat enhancement at Kahului Commercial Harbor, Hawai‘i: case study. SN Appl. Sci. 3, 167 (2021). https://doi.org/10.1007/s42452-020-04072-4