Experimental Observation on Beach Evolution Process with Presence of Artificial Submerged Sand Bar and Reef

For observation on the influence mechanism of environmentally and aesthetically friendly artificial submerged sand bars and reefs in a process-based way, a set of experiments was conducted in a 50 m-long flume to reproduce the cross-shore beach morphodynamic process under four irregular wave conditions. The beach behavior is characterized by the scarp (indicating erosion) and the breaker bar (indicating deposition), respectively, and the scarp location can be formulated as a linear equation regarding the natural exponential of the duration time. Overall, main conclusions are: (1) the cross-shore structure of significant wave height and set-up is mainly determined by the artificial reef (AR); (2) the cross-shore distribution of wave skewness, asymmetry, and undertow (indicating shoaling and breaking) is more affected by the artificial submerged sand bar (ASB); (3) the ASB deforms and loses its sand as it attenuates incident waves, which leads to a complex sediment transport pattern; (4) the scarp retreat is related to the beach state, which can be changed by the AR and the ASB; (5) the AR, the ASB, and their combination decrease wave attack on the beach. In conclusion, this study proves positive effects of the AR and the ASB in beach protection through their process-based influences on beach behaviors and beach states for erosive waves.

Experimental Study of the Changes of Morphodynamic Process Caused by the Hong Kong-Zhuhai-Macao Bridge

In order to predict the effects on the hydrodynamic environment caused by the Hong Kong-Zhuhai-Macao Bridge, the physical model is built to analyze the changes of morphodynamic process. The experimental results show that the drag force on flow is increased and the flow section area is decreased by the two large artificial islands built in the sea. The opposite side of the artificial islands, there is the recirculation zone with many vortexes in different scales, which have the periodic change from formation to disappearance. Near both ends of the artificial islands, the velocities of tidal currents increase, then the seabed has obvious erosion trend. Affected by the topography, hydrodynamic conditions, as well as by the position, shape and scale of the artificial islands, the changes of morphodynamic process caused by both the west artificial island and the east one is similar in the change rules and different in the forms.