The coastline in Ca Mau and Kien Giang provinces on Mekong Delta has been severely eroded in recent years. The Pile-Rock Breakwater (PRBW) was selected as predominant structure to construct widely more than 30 km on the west coast of Ca Mau. This structure shows the effectiveness of wave reduction, stimulating sediment accumulation and facilitating restoration of mangrove forest. However, this breakwater had been designed on the basis of best-engineering practice, lacking sufficient scientific background with regard to the structural design, capacity of wave reduction, working conditions. This study is to investigate the interaction of crest width, working states (submerged, transition and emerged) and the wave transmission coefficient, wave reflection coefficient and wave energy dissipation of PRBW by experiment in the laboratory and derive the empirical formulas for this construction under different sea states and crest widths. The results show a significant influence of width dimensions on the above coefficients. The findings revealed that the crest width of the breakwater is inversely proportional to the wave transmission coefficient (Kt) under emerged state. The crest width is also proportional to the wave reduction efficiency and wave energy dissipation in both working states (submerged and emerged states). The front wave disturbance coefficient is proportional to the reflected wave coefficient and the wave height in front of the structure can increase by 1.4 times in the emerged state. It is especially important to note when designing this structure to reduce the erosion in the structure toe due to the reflected waves. The empirical equations including linear and non-linear formulas have also developed and compared with previous studies for different breakwaters. This is necessary to be considered to calculate the structure and stability of breakwater. The results of this study serve as the basis for the design of pile-rock breakwater to reduce the waves under different natural conditions in the coastal area of the Mekong Delta.

The coastline of the Ca Mau and Kien Giang provinces in the Vietnamese Mekong Delta has been severely eroded in recent decades. Pile–Rock Breakwaters (PRBWs) are among the most widely adopted structures for controlling shoreline erosion in this region. These structures are effective for wave energy dissipation, stimulating sediment accumulation, and facilitating the restoration of mangrove forests. These breakwaters are generally considered to be the best-engineering practice; however, there is currently insufficient scientific evidence with regard to specific structural design aspects. This can lead to PRBW structures being compromised when deployed in the field. This study used a physical model of a PRBW in a laboratory to investigate several design parameters, including crest width and working states (i.e., submerged, transition, and emerged), and investigated their relationship with the wave transmission coefficient, wave reflection coefficient, and wave energy dissipation. To investigate these relationships further, empirical formulas were derived for PRBWs under different sea states and crest widths to aid the design process. The results showed that the PRBW width had a significant influence on the wave energy coefficients. The findings revealed that the crest width of the breakwater was inversely proportional to the wave transmission coefficient (Kt) under the emerged state. The crest width was also proportional to the wave reduction efficiency and wave energy dissipation in both working states (i.e., the submerged and emerged states). The front wave disturbance coefficient (Kf) was found to be proportional to the wave reflection coefficient, and the wave height in front of the structure was found to increase by up to 1.4 times in the emerged state. The wave reflection coefficient requires special consideration to reduce the toe erosion in the structure. Lastly, empirical equations including linear and non-linear formulas were compared with previous studies for different classes of breakwaters. These empirical equations will be useful for understanding the wave transmission efficiency of PRBWs. The findings of this study provide important guidance for PRBW design in the coastal area of the Mekong Delta.

The coastline in the Ca Mau and the Kien Giang provinces of the Vietnamese Mekong Delta has been severely eroded in recent decades. Pile-Rock Breakwaters (PRBW) are one of the most widely adopted structures for controlling shoreline erosion in this region. These structures are effective for wave energy dissipation, stimulating sediment accumulation, and facilitating the restoration of mangrove forests. These breakwaters are generally considered to be best-engineering practice however there is currently insufficient scientific evidence with regard to specific structural design aspects. This can lead to PRBW structures being compromised when deployed in the field. This study uses a physical model of a PRBW in a laboratory to investigate several design parameters, including crest width and working states (i.e. submerged, transition, and emerged), and investigates their relationship with the wave transmission coefficient, wave reflection coefficient, and wave energy dissipation. To investigate these relationships further, empirical formulas were derived for PRBWs under different sea states and crest widths to aid the design process. The results showed that PRBW width had a significant influence on the wave energy coefficients. The findings revealed that the crest width of the breakwater is inversely proportional to the wave transmission coefficient (Kt) under the emerged state. The crest width is also proportional to the wave reduction efficiency and wave energy dissipation in both working states (i.e., submerged and emerged states). The front wave disturbance coefficient (Kf) was found to be proportional to the wave reflection coefficient, and the wave height in front of the structure was found to increase by up to 1.4 times in the emerged state. The wave reflection coefficient requires special consideration to reduce the toe erosion in the structure. Lastly, empirical equations including linear and non-linear formulas were compared with previous studies for different classes of breakwaters. These empirical equations will be useful for understanding the wave transmission efficiency of PRBWs. The findings of this study provide important guidance for PRBW design in the coastal area of the Mekong Delta.