Using Fine-Grained Sediment and Wave Attenuation as a New Measure for Evaluating the Efficacy of Offshore Breakwaters in Stabilizing an Eroded Muddy Coast: Insights from Ca Mau, the Mekong Delta of Vietnam

Thai Thanh Luom,Nguyen Tuan Anh,Tran Anh Duong,Nguyen Thanh Tung,Nguyen Tan Phong,Le Xuan Tu

doi:10.3390/su13094798

Abstract

Offshore breakwaters can be effective in reducing the energy of incident waves through dissipation, refraction or reflection. Breakwaters are increasingly constructed to stabilize eroded muddy coasts, particularly in developing countries. Accumulation of fine-grained sediment and wave attenuation are two attributes of a stable muddy coast. Effective interventions in stabilizing eroded muddy coasts include two important elements: accumulation of fine-grained sediment and wave reduction. The efficacy of offshore breakwaters in stabilizing eroded muddy coasts is, however, not yet adequately understood. A crucial question needing attention is whether accumulation of fine-grained sediment and wave attenuation should be used in evaluating the efficacy of these offshore breakwaters in stabilizing eroded muddy coasts. To address this issue, a pile-rock offshore breakwater in Huong Mai, Tieu Dua of Ca Mau, Vietnam was selected as an appropriate example in this regard. Accumulation of fine-grained sediment and wave attenuation were tested as means to investigate the efficacy of the Huong Mai structure in stabilizing the eroded muddy coast. The study was undertaken using field-based measurements and semi-structured interviews in three stages between October 2016 and December 2020. We found that this structure has had limited efficacy in stabilizing the eroded muddy coast. The structure was effective in dissipating the energy of incident waves, but we found no evidence of fine-grained sediment accumulation due to an inappropriate structural design. There was also no monitoring system in place, leading to difficulties in evaluating its efficacy in terms of wave attenuation and accumulation of fine-grained sediment. The gaps between the shoreline and the structure have not been adequately explained, resulting in substantial challenges in replicating the structure elsewhere. The Huong Mai structure should be strengthened using supplementary measures and granulometric tests in order to improve the efficacy in stabilizing eroded muddy coasts. The methods in this study provide new insights in this regard.

Highlights

Offshore breakwaters aim to manage shoreline change or eliminate erosion by reducing the energy of incident waves through dissipation, refraction and/or reflection [1]
Offshore breakwaters have been recently constructed in combination with transplantation of mangrove seedlings to control eroded muddy coasts, in developing countries such as Malaysia [8,9], Thailand [10] and Vietnam [11,12]
The HMS has been of limited efficacy in stabilizing the eroded muddy coast in Huong Mai, Tieu Dua, Ca Mau

Summary

Introduction

Offshore breakwaters aim to manage shoreline change or eliminate erosion by reducing the energy of incident waves through dissipation, refraction and/or reflection [1]. Sustainability 2021, 13, 4798 at a certain distance from the shoreline [1,2] They include geo-tubes, tubular structures, reef balls (concrete artificial reef modules), stable underwater mud berms [3], emergent and low-crested structures and detached breakwaters [1]. To date, these offshore breakwaters are frequently evaluated on the basis of economic viability or the physical impacts caused by their construction. Effective intervention to stabilize eroded muddy coasts includes two important elements: accumulation of fine-grained sediment and wave attenuation [15]

Objectives

Methods

Results

Discussion

Conclusion