The design of permeable structures aimed at rehabilitating mangroves

Abstract

Mangrove forests are highly valuable environments that offer numerous ecosystem services, including carbon storage, serving as nurseries for fish and shrimp, and providing timber. Additionally, these ecosystems offer coastline protection against erosion and flooding by attenuating waves and trapping sediment. Despite the crucial role of mangrove ecosystems, global mangrove cover has significantly declined in recent decades, with deforestation and coastal erosion being one of the contributing factors, launching a variety of initiatives for mangrove rehabilitation. To rehabilitate mangroves along eroding coastlines, permeable structures are designed as a solution. These structures dissipate incoming waves and reduce current strength, creating low-energy areas behind them that are conducive to sediment deposition. However, these structures frequently prove ineffective in the rehabilitation of mangroves, possibly due to the absence of clear design guidelines, and a lack of understanding regarding the influence of design parameters on the performance of these structures.

This study, therefore, aimed to develop an integrated design guideline for permeable structures aimed at rehabilitating mangrove habitat along eroding coastlines by combining scientific knowledge with insights gleaned from pilot projects conducted globally. Furthermore, the research aimed to deepen understanding of the influence of design parameters on the performance of these permeable structures by conducting simulations of various structure configurations in a numerical, process-based model, and evaluating the performance of each configuration in reducing bed shear stress across the sheltered areas behind them. A nested model was employed in Delft3D-4, configuring the flow and wave modules to be coupled in order to incorporate the interaction between waves and currents.

The developed conceptual framework and design guideline as well as the identified correlations between design parameters and structure performance in this study contribute to enhancing the design process of permeable structures aimed at rehabilitating mangrove habitat. It provides preliminary insights, highlights significant knowledge gaps and provides recommendations for further research, thereby opening up opportunities to expand knowledge surrounding the design of permeable structures aimed at morphodynamic restoration of mangrove habitat.