ABSTRACT

Flow. around artificial seaweed was computed by the Reynolds equation. Further, the effect of sway of artificial seaweed is considered in the basic equation. Sediment concentration is computed by the turbulent diffusion equation with a time-dependent turbulent diffusion coefficient which depends on the flow velocity. Sediment concentration at the reference level is evaluated by the author's model(1986), which is a modification of the Kalkanis" model(1965). Near the artificial seaweed, flow is distorted shoreward at the boundary of vegetation. The organized vortex generated at the boundary of vegetation is closely associated with the transport of Reynolds stress. Moreover, the vortex produced near the boundary of vegetation carries its momentum by the sweep-like events down to the bottom. The agreement between computed results and experimental ones is satisfactory for the flow profile and the displacement of swaying. Temporal concentration of sediment at the point where the artificial seaweed is attached has four peaks, two of which are strong and the others weak, and the phase lag between the strong and weak peaks is approximately rr/2. The function of artificial seaweed is to facilitate shoreward sand movement near the boundary of vegetation and also to accelerate the accumulation of sand at both the fore and lee side of the attached point.

1. Introduction

So far such rind structures as groins and detached breakwaters have contributed more or less to the erosion control of sandy beaches. After the advocacy of maintenance and servicing of waterfront environment including the landscape, a waves/sand drift control system that can replace the rind structures has remained as a future possibility. With this background, a flexible structure using artificial seaweed has been proposed as a system that controls not merely the wave and sand drift but has an influence on the ecosystem.

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