Laboratory investigation on morphology response of submerged artificial sandbar and its impact on beach evolution under storm wave condition

The Submerged Artificial sandBar (SAB), recognized as one of the nature-based solutions for beach protection and restoration, has become increasingly popular in coastal engineering applications. However, its morphological response to waves and the resulting impacts on beach evolution are yet not well understood. Here, laboratory experiments are conducted considering different background profiles and various SAB designs. Morphological evolution of the SAB and berm are inspected from the measured beach profile data in the wave flume. Results show that the SAB migrates onshore with its bar shape decaying, providing a paradigm shift away from the traditional understanding that the net subaqueous sediment transport is always offshore directed under storm wave conditions. SAB can alter the beach state and berm behavior by triggering onshore sediment transport locally and temporarily. The stability of the SAB is controlled by its seaward slope and the ratio of crest water depth to the bar height. A morphological coupling is found between the SAB and berm, and an empirical relationship is proposed to quantitatively capture it. Finally, the experiment results are used to validate a process-based beach profile evolution numerical model, and an explanation for the morphological coupling is provided from the perspective of wave energy dissipation.