An experimental study on the evolution of a submerged berm under the effects of regular waves in low-energy conditions

Abstract

Reduced-scale mobile-bed flume tests are conducted on the evolution of a submerged berm under the effects of regular waves in low-energy conditions. Twenty-three flume tests are performed on a profile model of a submerged berm under different combinations of wave heights and wave periods. The profile shapes and water elevations along the profile are recorded during the tests. Comprehensive analyses are conducted on the profile evolution and the wave parameters along the profile of the submerged berm model. In all cases the crest of the submerged berm moves onshore and the profile shape become asymmetrical. Overall analyses are conducted on the evolution-related parameters such as the moving distance of the centroid ( D lc ), the change of skewness of the profile shape ( C sk ), the change of the crest elevation of the submerged berm ( C cl ) and the irregularity parameter of the profile shape ( K rms ). The effects of wave height and wave period on these parameters are discussed. An Empirical Orthogonal Function (EOF) analysis of the test results indicates two major evolution patterns of the submerged berm, onshore migration and onshore inclining of the crest, both of which are controlled by wave height. The velocity skewness, wave height and local water depth are the major factors that impact the onshore sediment transport under low energy conditions. No obvious connections can be found between acceleration skewness and sediment transport in this experimental study. However, large acceleration skewness would reduce the values of velocity skewness and impact the sediment transport indirectly. This paper proposes new insights on the morphodynamics of submerged berms under low-energy conditions and provide validation data for numerical models. • The evolution of a submerged berm under low-energy conditions are studied via a series of flume tests. • A general portrait on the feature of the evolution of a submerged berm under low energy conditions is given. • The effects of wave height and wave period on the shape-changing of the submerged berm are analyzed quantitatively. • Two major evolution patterns of the submerged berm in this case are onshore migration and onshore inclining of the crest. • The velocity skewness, wave height and local water depth dominate the onshore sediment transport under low energy conditions.