Author(s): Jiaming Liu; Yang Xiao; Saiyu Yuan; Carlo Gualtieri
Linked Author(s): Carlo Gualtieri, Saiyu Yuan, Yang Xiao, Jiaming Liu
Keywords: Compound channel Unsteady flow Flood inundation Numerical modeling Secondary flow
Abstract: Compound channels exhibit complex hydrodynamic behaviors during flood events, especially when water levels fluctuate between bankfull and overbank conditions. While previous studies have explored steady flows and fully inundated conditions, the transitional processes of floodplain inundation and recession remain poorly understood. This study employs a validated combined 2D/3D numerical approach to investigate the hydrodynamic characteristics during these critical transitions. A laboratory-scale compound channel (20m×1.2m) with a 0.2m bankfull depth is modeled. The 2D shallow water equations model provides boundary conditions for the 3D RANS-RSM-VOF model. Multiple scenarios with varying peak discharge (10-50 L/s), period (1-10 min), and rising time are simulated to examine the inundation-recession process. Results reveal distinct flow patterns during three key phases: (1) Pre-inundation phase with confined main channel flow; (2) Inundation phase characterized by lateral expansion and momentum exchange; and (3) Recession phase showing preferential drainage paths and residual floodplain storage. The main channel-floodplain interaction exhibits strong temporal variation in velocity distribution, turbulence structure, and lateral exchange. Secondary currents near the main channel-floodplain interface reorganize significantly during transitions. Wall shear stress peaks occur during different times for the main channel bed versus the floodplain edge. This research provides new insights into compound channel hydraulics during flood transitions, with implications for improving flood routing models and floodplain management strategies.
Year: 2025