Morphodynamic Effects and Fish Habitat Assessment at an Idealized Bifurcation: A Numerical Experiment

ABSTRACT River bifurcations impact the surrounding area in a plethora of ways, namely, redistributing flow of water, sediment, and nutrients throughout a watershed and delta. In addition to this, fish habitat can also be altered by these bifurcation structures. In the Yangtze River, anthropogenic interventions such as dam construction and navigation channel improvements have altered the natural bifurcated morphology. In this paper, geometric features of river bifurcation were analyzed using 36 remote sensing images, and seven bifurcation structures were generalized. A framework system coupling hydrodynamics, sediment transport, and fish habitat was developed to simulate the evolution of hydraulic conditions and fish habitat of bifurcated channels with the four major Chinese carps of the Yangtze River. The simulation results show that bifurcation geometry considerably influences flow velocity, sediment transport, and fish habitat availability. The angle of bifurcation is directly proportional to the velocity difference between the two channels on either side of the river; when the bifurcation angle reaches 90°, the velocity increases by approximately 30%. Moreover, the velocity and water depth increase with different flow configurations, and this change is also influenced by the combined effects of the bifurcation angle, channel symmetry, and the curvature of the upstream river. The fish habitat quality peaked at moderate flows, declining under both low and extreme flow conditions. The upstream meandering river channel structure has, to a certain extent, mitigated the erosion of fish habitats caused by long‐term high flows and has improved by 20% compared to the control experiment. These findings highlight the importance of bifurcation geometry in shaping flow dynamics and habitat suitability, providing valuable insights for river management and conservation efforts.