Hydromechanical factors influencing erosion and recession of compacted sandy bluffs under random waves actions

Abstract

The recession of a sandy bluff was investigated in a controlled laboratory wave flume, replicating the complex interactions between hydrodynamic forcing, sediment transport processes, and bluff slope stability. A comprehensive monitoring approach measured water levels, pore water pressures, moisture content, and detailed bathymetric-topographic data, providing a thorough understanding of the governing mechanisms and their interrelationships within the beach-bluff system. Bluff recession occurred through notch formation at the bluff toe, followed by a series of minor and major episodic bluff failures. Pore-water pressure variations within the bluff were closely linked to morphological changes on the beach and the bluff's instability. The final beach profile exhibited distinct characteristics: near the shoreline, it was steeper than the equilibrium beach profile due to the sediment supplied by bluff recession. Cross-spectral analysis between water level fluctuations and pore water pressure signals revealed a strong coupling between incident wave energy and pore water pressure responses within the beach-bluff system. The rapid rise in saturation, along with the formation and expansion of the notch, contributed to bluff instability and episodic failure events.