Suction removal of sediment from between armor blocks. III: Breaking waves

When a sediment beach covered by stones or an armor layer is exposed to breaking waves, the turbulence generated by the breaking waves can cause mobilization and removal of the sediment underneath the stones. In two earlier studies by the Technical University of Denmark (DTU)-group, the suction removal of sediments from between armor blocks has dealt with the case of steady current and nonbreaking waves.

The present study is an extension of these studies and the results will be presented in a similar way. The critical conditions for removal of sediment are determined. It is found that the onset of removal of sediment is governed by three parameters: (1) the sediment mobility (based on the sediment size, wave height, and wave period), (2) the ratio between the sediment size and the stone size, d=D, and (3) surf similarity parameter, ξ ¼ tanðβÞ=ðH0=L0 Þ0.5.

The variation of the critical mobility number for removal of sediment as function of d=D and ξ is determined for the range 0.001 < d=D ≤ 1.0 and 0.15 < ξ < 6.00. The experiments were made on 1∶2, 1∶14, and 1∶30 slopes. Spilling, plunging, and surging breakers were used in the experiments. Both one and two layers of armor stones and rectangular blocks were studied.