Influence of Waves and Currents on Sediment Erosion and Deposition Based on In-situ Observation: Case Study in Baisha Bay, China

摘要

The dynamics of sediment erosion and deposition have been investigated in the Baisha Bay, China featured by a sandy bed. The wave elements, tide level, velocity and direction of the currents, seabed height change were measured by the underwater anti-subsidence in-situ tripod in December 2013. During the observations, the tripod installed with steel clump weights and needle-like piles can keep itself from subsiding vertically and moving horizontally. Both the observation results and shear stress analysis show that the contribution of waves to sediment erosion and deposition surpasses that of currents. On the whole, the seabed height change (approximately 1 millimeter [mm]) caused by currents is about one order smaller than that (0.8 centimeter [cm] to 2.2 cm) caused by high waves. The maximum wave-induced shear stress can reach up to 1.56 Pascal (Pa) and the mean wave-induced shear stress is approximately 10 times greater than mean current-induced shear stress. Even so, the influence of currents on sediment erosion and deposition cannot be arbitrarily ignored. Besides, the waves are responsible for sediment erosion and deposition only during episodic high waves and currents constantly cause sediment erosion and deposition. Despite the difference in deposition amount, the episodic high waves lead to sediment deposition with centimeter scale during the observation. While the sediments are eroded during flood tidal currents and deposited during ebb tidal currents with millimeter scale.