Evolution of the Deep Channels in the Hechangzhou Anabranching Reach Under the Regulation of Submerged Dikes

The Hechangzhou Anabranching Reach is a typical tidal anabranching segment of the Yangtze River with intense riverbed evolution driven by altered water-sediment regimes and channel regulation. Submerged dikes stabilize river regimes and navigation yet trigger differential local clear-water scour; most prior studies only adopt short-term bathymetric data and lack long-term quantitative analysis across diverse hydrological scenarios, so the synergistic geomorphic mechanism under the control of the submerged dike group remains unclear. This study integrates the 2002–2025 flow division ratio series and multi-period bathymetric data from 2018 to 2026 to quantify spatiotemporal deep-channel adjustments, scour-deposition patterns and cross-sectional deformation of the two anabranches, and evaluate morphological effects of river training structures and relevant potential scour risks. The submerged dike group regulates diversion patterns and keeps the left anabranch’s flow division ratio below 70%. The right anabranch deep channel undergoes persistent vertical incision and reverses its historical deposition trend, while the left anabranch features spatially uneven scour: intense scour zones migrate within the SD1–SD2 reach, and persistent landward erosion occurs between SD2 and SD3. The reach’s polarized evolution of intensified scour and attenuated deposition arises from the joint control of the submerged dike group, bank protection and reduced basin sediment supply. This study reveals the spatially differentiated riverbed evolution driven by engineering-induced hydrodynamic redistribution, offering scientific support for refined waterway management and scour prevention in analogous tidal anabranching rivers.