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Feedback Relationship in Wave Erosion of Laboratory Rocky Coast

Two kinds of model experiments were conducted: one was done in a wave tank and the other in a wave basin. In the former test, a model cliff was placed at an angle of 90° to the input wave direction, while in the latter, an identical cliff was installed at an angle of 60°. Erosional process in the wave tank experiment was characterized by a closed-loop system, while that in the wave basin test by an open-loop system. In the former system, the erosive force of the input waves was modified by the action of sand deposited at the cliff base: the sand intensified the erosive force by acting as an abrasive or it moderated the force by acting as an obstacle. This feedback-control system was analyzed by applying the automatic control theory. A result showed that the maximum erosive force, intensified by sand, was 4.5 times as great as the erosive force having no sand effect.