Flow and Turbulence at Rubble-Mound Breakwater Armor Layers under Solitary Wave

Abstract

This paper presents the results of an experimental investigation of the flow and turbulence at the armor layer of rubble-mound breakwaters during wave action. The study focused on the details of the flow and turbulence in the armor layer and on the effect of the porous core on flow and stability. To isolate the processes involved with the flow in the porous core, experiments were conducted with increasing complexity. Specifically, three parallel experiments were performed including (1) an impermeable smooth breakwater slope, (2) an impermeable breakwater slope with large roughness elements added to the breakwater, and (3) a porous breakwater where the porous core was added below the breakwater front. One breakwater slope of 1:1.5 was applied. In this paper the focus is on the details of a single sequence of wave approach, run-up, and rundown. To isolate this sequence the experiments were performed applying a solitary wave. The individual sources of turbulence generation were distinguished using Laser Doppler anemometry measurements, and the effect of the armor layer and porous core was described in terms of a reduced impact of the rundown process, production of lee wake turbulence, and less transport of turbulence above the armor layer. The shear stresses were evaluated from the measurements of turbulence, and they were associated with the run-up and rundown phases. The Shields parameter, determined from the shear stresses, was found to be reduced by 30% as a result of the porous core material.