Experimental investigation on wave roller area evolution in the surf zone

In the surf zone, breaking waves generate an air-entraining turbulent region ahead of the wave crest, known as the wave roller, which plays a crucial role in nearshore dynamics. Using image-based techniques, measurements of wave roller areas and their relationships with wave properties were obtained in a laboratory wave tank. The results indicated a positive correlation between wave roller area and both wave height and wavelength. The ratio of roller area to the product of wave height and wavelength varied with factors such as slope, wave steepness, and degree of roller development. A predictive formula for roller area was then developed using a genetic programming model. Furthermore, the fraction of breaking dissipation feeding wave roller energy revealed a gradual decrease along the direction of wave propagation in the surf zone. A substantial portion of breaking dissipation feeds into roller energy in the outer surf zone, while wave rollers stabilize and draw minimal energy from breaking dissipation in the inner surf zone. The measurements and analysis in this study could enhance the understanding of momentum flux caused by wave rollers, improving numerical predictions of hydrodynamics and material transport in the nearshore ocean.