Overtopping flow velocity (OFV) and overtopping layer thickness (OTL) are essential parameters in breakwater design. Several empirical equations to predict these parameters are available in many works of literature, but most of the equations were derived based on impermeable structures such as sea dikes. In this study, we experimented with overtopping waves over a composite breakwater with tetrapod armor units. In the experiments, wave overtopping was generated from regular waves. We used a digital image-based velocimetry method, bubble image velocimetry (BIV), to measure the OFV and digitize the corresponding image to obtain the OLT. The patterns of OFV and OTL with respect to time steps, wave conditions, and corresponding events were provided and discussed. The application of the widely used empirical equations for sea dike to breakwater was also tested by calibrating the coefficients. New empirical coefficients and roughness factors were suggested to reduce the difference between predicted and measured OFV and OLT on breakwater through the bootstrap resampling technique. This study provides modified empirical equations on wave overtopping, which is further applicable to breakwater design.

The safety of pedestrians on a breakwater structure or seawall is significantly influenced by two essential factors: the wave overtopping flow velocity (OFV) and the overtopping layer thickness (OLT). The main issue, however, is that most studies have predominantly focused on impermeable structures rather than composite breakwaters. This study conducted 55 physical experiments to investigate the OFV and OLT on a composite breakwater. The non-intrusive bubble image velocimetry (BIV) technique was employed to measure the OFV and OLT, as well as the plunging distance on the rear side of the structure. Empirical equations with two sets of dimensionless variables, the wave steepness and relative crest freeboard, were proposed as predictors. The results show that these two dimensionless variables perform well for both OFV and OLT estimation. The comparison between the proposed empirical equation and the available empirical equation in the literature is also presented. Finally, the proposed empirical equations were used to estimate the maximum instantaneous wave overtopping discharge and plunging distance. The findings of this research offer insights into the physical mechanisms of wave overtopping, providing an initial exploration into the design of composite breakwaters.

Adibhusana, M.N.; Lee, J.-I., and Ryu, Y., 2021. Wave overtopping plunging on the rear side of composite breakwater. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 574–578. Coconut Creek (Florida), ISSN 0749-0208. In this study the behavior of overtopping water falling on the rear side of composite breakwater were investigated through physical experiment. A series of regular wave with various wave period and wave height were used as wave parameters while velocity at the rear edge of breakwater, plunging location, and plunging velocity were used as the parameters of wave overtopping behavior on the rear side of composite breakwater. The geometry of the composite breakwater was kept constant through the experiment. The Bubble Image Velocimetry (BIV) and digital image analysis were applied to measure the velocity in the aerated region of overtopping water falling on the rear side of breakwater and the plunging location. The rear edge velocity was linearly increased as the wave parameter increased. The increment value of plunging location shows a logarithmic trend as wave period and wave height increased. The front velocity of overtopping flows right before plunging the rear water surface shows a linear trend with those wave parameters.

Plastic pollution poses a growing threat to benthic ecosystems in coastal waters, yet assessments often emphasize surface accumulation while overlooking seasonal variability and seafloor impacts. This study evaluates the spatial and seasonal variability of plastic pollution levels in benthic...