Breaking waves over a mild gravel slope: Experimental and numerical analysis

An experimental and numerical study of the effects of a gravel slope on wave shoaling and breaking is presented herein. In the laboratory experiments, fluid velocities, pressure and water surface elevations were measured. Experiments were conducted for both spilling and plunging breakers and for gravel slopes with different gravel sizes. Since gravel slopes caused additional energy dissipation, wave heights in the shoaling zone as well as at the breaking point were reduced. On the other hand, the mean free surface setup inside the surf zone increased. It was also observed that the gravel slope had a stronger influence on the vertical profile of undertow under spilling breaker than on that under a plunging breaker. Moreover, the undertow became weaker over a gravel slope with a larger gravel size. Outside the surf zone, turbulent velocities near the gravel slope were relatively high because of the bottom roughness and percolation. Inside the surf zone, turbulence generated by wave breaking dominated over the gravel bed generated turbulence. The vertical flow induced by the gravel slope changed the turbulence pattern only at cross sections very close to the shoreline. Numerical simulations of the wave breaking processes over a gravel slope were performed. The numerical model was tested by comparing numerical results with experimental data. The model accurately simulated the mean flow quantities. The magnitude of turbulence and turbulence characteristics were also simulated reasonably well.