Multiple intertidal bars are common sedimentary landforms found on low-gradient sandy coasts exposed to low to moderate wave energy with significant tidal ranges. Their formation and evolution are closely tied to contemporary challenges such as climate change, sea-level rise, and reduced sediment supply, making them crucial for coastal defense and ecological protection. However, understanding their dynamics is often challenging due to limited high-resolution field data and tools for bedform analysis.
In this study, we employed a multifaceted approach to investigate the morphology of intertidal bars at two adjacent tidal beaches on the north and south coasts of a small estuary along the Lianyungang coast of China. Our approach included repeated real-time kinematic global positioning system (RTK-GPS) leveling, unmanned aerial vehicle (UAV) surveys, surface sediment sampling, satellite remote sensing analysis, and automated bedform analysis. Field observations covered the period from September 2020 to July 2024.
Our findings revealed that the north coast featured low-amplitude ridges (also known as ridge and runnel). This coast exhibited 2–5 oblique, asymmetrical, and dynamic bars that migrated landward from the seaward end of the intertidal zone, eventually attaching to the steep beach at the landward end, thus completing a full life cycle. Quarterly observations from April 2023 to April 2024 showed seasonal variations in these bars: during the summer (April to October), they migrated landward at a near-constant rate of approximately 5 m per month. In contrast, during the winter (October to April of the following year), the positions of the bars remained stable.
On the south coast, we observed 6–9 parallel, continuous, symmetrical, and stable sand bars, commonly referred to as “sand waves”, occupying the lower part of the intertidal zone. These bars showed minimal change in their positions and shapes throughout the observation period.
Given the nearly identical hydrodynamic background, alongshore variability in sediment supply is suggested as a key factor driving and influencing these distinct types of bars. The south coast benefits from abundant sediment due to southward transport and river input, leading to a broader, gentler intertidal zone with stable sand waves. In contrast, the north coast, with limited sediment from upstream sources and sand mining, has a narrower, steeper intertidal zone with migrating low-amplitude ridges. This research highlights the critical role of sediment supply in bar morphology, suggesting that southerly sediment transport is key to these differences. Further studies could emphasize the importance of sediment supply in coastal geomorphology.
 

Multiple intertidal bars,Sandy beach,Morphodynamics