An experimental study of the cross-shore evolution of artificial submerged sand bars

Artificial submerged sand bars have been used as an alternative soft engineering structure for shore protection. To successfully implement the sand bar in an economically beneficial manner, more knowledge is required concerning the evolution of a sand bar under different conditions. A series of experiments is presented to quantify the sediment transport that is induced by artificial submerged sand bars in a wave-driven beach environment. Artificial movable sand bars of various initial geometries were tested on various fixed, inclined bottom slopes by using different incoming regular wave conditions. A new, beneficial parameter, the cumulative transport rate, is defined by integrating the time-dependent cross-shore sediment transport rate from an initial deposition to a quasi-equilibrium state of a sand bar migration. From many tests and analyses, it has been found that the cumulative transport rate of the sand bar is highly dependent on the local Shields number being related to the bed-load transport. Additionally, the Shields-dependent relation is compared to previous field sand bar evolution projects to determine if the sand bar actively migrates onshore or remains stable. An optimal initial bar geometry is suggested to pursue an efficient onshore sediment transport. The effects of the bottom slope on the cumulative transport rate are also discussed.