Figure 7 Variation of current velocity on submerged breakwater

(2) Steady Current Occurred in Irregular Waves

Figure 8 shows the velocity and direction of the steady current around the submerged breakwater in regular, uni-directional random, and mult-directional random waves. The irregularity and directionality of incident waves give little influence on the direction and velocity of steady current. The current direction at the surface layer and that at the bottom layer agree with each other. At the backward of the submerged breakwater, strong current is induced by waves in any cases.

Figure 8 Steady current component

5. TRACER MOVEMENT ON SUBMERGED BREAKWATER

(1) Criteria of Tracer Movement

The tracers of which diameter is 0.8mm and specific gravity is 1.20 are put at the 8 points on the submerged breakwater as shown in Fig. 1. The characteristic of the tracer movement is observed in photograph analysis 30s after the wave start.

Table 1 shows the definition of the tracer movement scale proposed in this study. Figure 9 shows the relation between the wave height on the submerged breakwater

Table 1 Tracer movement scale

Figure 9 Relation between wave height and sand movement level

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