Abstract
A new type of block, which is named "Moses block", was proposed to improve the functions of a submerged breakwater: wave reduction and mean water level suppression. The block, from a plane view, is an equilateral triangle with legs at each apex. The blocks are placed on the crown of the submerged breakwater, adjacent to each other and spaced apart, facing one side of the triangle toward the offshore along the breakwater. The block height should be less than the freeboard of the breakwater in order to preserve the visible environment. The wave reduction is expected to be obtained mainly by increasing the crown height of the breakwater with the blocks. The suppression of the mean water level rise behind the breakwater is expected to be obtained by inducing stronger outward flow. This induction might be caused by the difference of the flow resistance between the inward and outward directions because of the asymmetric shape of the block arrangement.
In this study, to confirm whether the block can actually have the expected effects, model experiments were conducted using a two dimensional wave tank. The experimental results led to the following important findings: 1) the block should be set on the onshore side on the crown of the submerged breakwater to maximize its effects. 2) When the blocks are arranged in multiple lines, wave reduction and mean water level suppression are further improved.
