Flow Patterns around a Marginal Bank under the Action of Unsteady Flow

Unsteady flow represents one of the most prevalent and intricate forms of fluid motion in nature. The erosion and damage caused by water flow to slope protection blocks are issues of significant concern. Understanding the hydrodynamic structures near slopes is crucial for enhancing the protection of these blocks. This study primarily focuses on the tidal flats along the main waterways in the middle and lower reaches of the Yangtze River. The analysis includes the distribution of water surfaces, velocity distribution, average flow velocity, and their variations near these beaches. The results indicate that the water flow near the beaches can be divided into four main regions: the rising water area, the falling water area, the backflow area, and the maximum flow velocity area. The slope of the beach has a noticeable impact on the water’s surface profile. Within a certain range, the area of flow velocities above 0.35 m/s is linearly inversely correlated with the beach angle. In terms of longitudinal water surface profiles, the shallowest water level occurs at the widest part of the beach, and the location of maximum flow velocity is about one-fourth of the beach length from the head of the beach. Steep changes in the water surface are more likely to occur at the junction of steep slopes and the riverbed. Near the backflow area, the flow velocity is approximately zero, and in longitudinal sections other than the backflow area, the maximum flow velocity is 1.3–1.8 times the minimum flow velocity.