Author(s): Élodie Marchand

Abstract: The study investigates the complex hydraulic behavior arising from the interaction between main channels and adjoining floodplains during transient flow events. Laboratory-scale experiments were conducted in a symmetrical compound channel setup, and the results were analyzed using both steady and unsteady flow models based on the Saint-Venant equations. The research aimed to quantify the influence of floodplain width, slope, and roughness on flow conveyance, stage-discharge relationships, and lateral momentum exchange under dynamic conditions. The findings demonstrated that steady-flow assumptions significantly overestimate water surface elevation and conveyance, especially during flood wave propagation. The unsteady model yielded improved predictions, with reduced root-mean-square errors, higher Nash-Sutcliffe efficiency, and better alignment with measured hydrographs. Hysteretic behavior was observed between rising and falling limbs of the hydrograph, attributed to time-dependent momentum transfer and shear redistribution between channel and floodplain zones. Wider floodplains and higher roughness contrasts intensified these unsteady effects, validating the need for transient modeling in compound river systems. The study concludes that unsteady flow analyses provide a more realistic representation of hydraulic performance, offering vital insights for the design of flood protection structures, floodplain management, and hydraulic modeling. Practical recommendations include adopting time-varying roughness coefficients, enhancing field monitoring systems for transient data, and incorporating unsteady simulation tools in flood routing and river restoration projects. The integration of these approaches will enhance the predictive capability of hydraulic models, reduce design uncertainties, and contribute to more sustainable and resilient water resource management.

Pages: 42-48 | Views: 8 | Downloads: 5

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