Turbulent transport dynamics in open-channel floodplains for different submergence conditions

Floodplains are side regions of river channels characterized with low velocities that have a high depositional potential for contaminants transported by the flow, which can be resuspended during floods and mobilized downstream. The resuspension process is determined by the bed stresses, and transport is driven by the shear layer at the interface between the floodplain and the main channel. The temporal and spatial structure of the shear-stress distribution and the coherent-structure dynamics of the shear-layer strongly depends on the submergence ratio between the water depth of the main channel H, and the floodplain h. To provide a further understanding of the underlying physics of the exchange processes for different submergence conditions, we perform high-resolution numerical simulations using the detached-eddy simulation (DES) approach. We test four different submergence ratios, from shallow to deep-water regimes (h/H = 0.13, 0.25, 0.5, 0.62), and simulation results are validated with experimental data. We study the role of large-scale vortical structures and velocity fluctuations at the interface for different regimes by providing a comprehensive description of the effects of flow submergence on the spatial and temporal dynamics of the coherent structures of the shear-layer.