An experimental study of wave-induced flow and bottom topographical changes in tidal flats

Abstract

Artificial tidal flat construction has been increasing to replace the environmental functions performed by natural ones that have been destroyed. However, remarkable topographical changes in constructed tidal flats have occurred due to wave-induced flow and the tides. Therefore, from a coastal engineering standpoint, understanding the mechanisms behind these topographical changes is essential to designing future tidal flats. In this paper, three-dimensional fixed and movable bed model experiments were conducted to elucidate the topographical change mechanisms of a constructed tidal flat that includes a submerged breakwater on its offshore side. The experiments revealed that three-dimensional circulation flows formed in the fixed bed model around the uneven submerged breakwater. The intensity of this flow depended upon the wave steepness and the crest depth to wave height ratio. The movable bed model experiments used models with two different bottom slopes (horizontal and 1/100). Attention in these experiments focused upon the effect of bed material grain size, the tide, and the submerged breakwater shape on the topographical change of the constructed tidal flat. As expected, the results showed that small grain sizes produce larger topographical changes than large grain sizes. The results also revealed that bottom topographical changes in artificial tidal flats can be classified into three categories. Finally, it was found that tide level variations reduce the bottom topography deformation intensity of the constructed tidal flat.