Experimental observation on wave propagation and geomorphological evolution in a sandbar-lagoon system

Abstract

The sandbar-lagoon coast, one of the most productive and valuable ecosystems, has been strongly exposed to severe degradation. Excessive erosions aggravate the fragility of sandbar-lagoon systems. In order to seek adaptable solutions for ecological restoration, it is essential to study the hydrodynamic and morphodynamic characteristics. In this study, a series of flume experiments are conducted to investigate the wave propagation and geomorphological evolution in a typical sandbar-lagoon system. The time-series of swell and infragravity waves are obtained by a simple time-domain separation method, where wave reflection coefficient, skewness and asymmetry are calculated separately. The following conclusions can be drawn. To quantitatively assess the experimental results, a critical parameter ζ is introduced involving the incident wave height, the water depth and the sandbar freeboard. There is a linear relationship between wave attenuation and ζ. Further, a linear dependence on the maximum erosion thickness of foredune is achieved, and the maximum erosion thickness of sandbar increases with the increasing incident wave height by a superb linear correlation. Additionally, the shape transition of foredune scarp is significantly correlated with the dramatic change of the water level rise in the lagoon and the infragravity wave reflection. These findings promote better understanding for the morphodynamics of typical sandbar-lagoon systems and provide fundamental and scientific evidences on further coastal engineering.