Channel Reshaping and Adaptive Management of Inland Tail-End Deltas Under River–Lake Interaction: Model Experiments and Empirical Evidence from the Comprehensive Regulation of the Ganjiang Tail-End Delta

Intensive human activities are reshaping inland tail-end deltas. Based on hydrological and sediment data from 1950 to 2023 and physical model experiments, this study examines the Ganjiang tail-end delta to analyze channel evolution, driving mechanisms, and management pathways. Results indicate that the Wan’an Reservoir and large-scale sand mining are the dominant drivers of flow-sediment regime shifts and channel reshaping. Sand mining has caused severe riverbed incision, with a local maximum depth of 16.5 m. During the dry season, the flow diversion ratio of the West Branch exceeds 90%, fundamentally altering the flow distribution pattern. Although riverbed incision has enhanced local flood conveyance, the overall flood discharge capacity of the tail-end delta remains limited due to backwater from Poyang Lake, introducing new flood risks. Reduced sediment supply and hydrological changes have exacerbated wetland shrinkage and eutrophication. Physical model experiments show that the comprehensive regulation project can raise dry-season water levels by approximately 5 m through sluice operation, optimize flow diversion, and increase wetland surface water area by 56%. This project integrates flood control, ecological protection, and water resource utilization, representing a proactive exploration of adaptive management for deltas and providing scientific references for understanding evolution and guiding management in similar inland tail-end deltas.