A laboratory study on wave Attenuation by oyster reefs-mangrove system

In a coastal ecological project aimed at wave attenuation through mangroves, incorporating oyster reefs as a complementary component to establish an “oyster reefs + mangrove” wave attenuation system could enhance the survival probability of mangroves, as well as improve the overall effectiveness of wave attenuation. This study investigates and proposes an innovative wave attenuation system consisting of oyster reefs and mangroves with various configurations. Laboratory experiments were conducted in a wave flume using artificial models of mangroves and oyster reefs to examine the impact of the system on wave attenuation, thereby providing a scientific foundation for coastal ecological restoration projects. The findings demonstrate that the wave attenuation coefficient exhibited a positive correlation with both the significant wave height and oyster reef height, as well as with mangrove density. Conversely, it displayed a negative association with water depth and period. Notably, oyster reefs substantially affected the wave attenuation. When three layers of oyster reefs are integrated with staggered dense mangroves, the system demonstrates optimal wave attenuation, with coefficients ranging from 0.38 to 0.42. The incorporation of oyster reefs within mangroves significantly enhances the capacity of wave attenuation, resulting in an increase of up to 0.26 in the wave attenuation coefficient. Moreover, although the combined wave attenuation coefficient of the individual mangroves and oyster reefs was higher than that of the system, the system’s overall wave attenuation surpassed that of either component. A theoretical equation has been formulated to quantify wave attenuation in the oyster reefs-mangrove system, aiming to provide practical guidance for coastal restoration projects. Maximizing the height of oyster reefs in areas with low water depth and pairing them with staggered dense mangroves is recommended to reduce wave energy in coastal restoration projects. The most effective wave reduction strategy for areas with high water depth is a combination of tall oyster reefs and staggered or in-line clusters of dense mangroves.