Wave reduction efficiency for three classes of breakwaters on the coastal Mekong Delta

Abstract

This study presents a laboratory scale implementation of breakwaters and their ability to mitigate extreme wave erosion on the coast of Mekong Delta. Three classes of breakwaters are tested in this study: Hollow Triangle breakwaters (HTBW), pile-Rock breakwaters (PRBW), and semi-circular breakwaters (SBW) using physical models in the laboratory. The investigation includes 210 experimental tests using a physical model under various incident waves and water levels. The experimental results show that the SBW has the lowest wave transmission coefficient (Kt). The HTBW has the highest Kt. The Kt of SBW, PRBW and HTBW in the submerged state (Rc/Hm0,i < 0) varies between 0.45 – 0.73; 0.55 – 0.73 and 0.64 – 0.82, respectively. The wave reflected coefficient of the PRBW is found larger than SBW and HTBW. The SBW demonstrates the largest wave energy dissipation capacity. The wave reflection coefficients (Kr) in the submerged state for SBW, PRBW and HTBW have a similar range of Kr with varying range i.e., 0.16 – 0.30, 0.16 – 0.27 and 0.16 – 0.28, respectively. Meanwhile, the Kr of the HTBW and the SBW in the emerged state (Rc/Hm0,i > 0) varies in a range, 0.17 – 0.35 and 0.19 – 0.33, respectively, while the Kr of the PRBW has a larger variation with a range of 0.22 – 0.48. From the field measurements, the Kt and wave spectrum is verified with the physical model results. The average wave dissipation capacity of the three breakwaters is obtained about 54-80% for PRBW, 75-81% for HTBW, and 51-90% for SBW, respectively. The observed Kt for the field scale breakwaters shows non-linearity rather than the physical models due to the large variability of incident wave conditions in the East and West Seas. HTBW and SBW are highly efficient in dissipating the longer period waves peak, while PRBW is highly efficient in dissipating the short period waves peak. The results indicate that three breakwaters particularly the PRBW have a great capacity to dissipate wave energy under the different sea states in the Mekong Delta.