Drifting Behavior of Organic Debris Clouds and Their Interaction with Flow Structures in Mountainous Navigable River Channels

Abstract

Navigable river channel construction increasingly emphasizes balance of ecological sustainability and waterway transportation. Dike structures are widely applied as they enhance habitat complexity and promote nutrient cycling, yet the mechanisms governing organic debris advection, dispersion, and cloud diffusion in complex hydrodynamics remain unclear. This study focuses on Chaotianmen–Fuling reach of the upper Yangtze River to investigate flow structures and the diffusion behaviors of floating leaves and their grouped clouds within engineered habitats between dikes. Settling experiments on eight common leaf species in static water were first conducted, followed by flume tests and three-dimensional hydrodynamic simulations under different dike configurations. In addition, the leaf drifting process in a natural river was simulated using a Euler–Lagrange approach. Results indicate that recirculation zones with a length-to-width ratio of 3:1 optimize leaf retention, while increased channel constriction enhances turbulence and leaf entry into pools; submerged bars reduce retention efficiency. Moreover, numerical simulation revealed that turbulence and secondary circulation accelerate dispersion of both floating debris and granular clouds, whereas dikes create localized retention zones forming nutrient-rich microhabitats. Application to the real fluvial reach confirmed that the proposed design-channel constriction ratio of 0.33 and bar spacing three times the bar length-improves retention and aggregation of organic and granular matter. These findings provide a scientific basis for integrating habitat restoration with navigation channel construction, offering a model for ecological waterway development in large rivers.