Abstract: Hydrological exchange between a river and its floodplain plays a critical role in maintaining river ecosystem. Herein, a state-of-art hydrodynamic model (AdH) was applied in modeling flood events in the Truckee River at lower McCarran ranch in Nevada. The hydrologic connectivity between main channel and floodplains is examined in details through flow field characteristics, trans-boundary flux, and particle tracing analysis. Results reveal substantial spatial variations of main channel-floodplain flux exchanges in both magnitude and direction. During a flood peak, up to 60% of its total discharge flows into floodplain, or about 1.52 times as much as that in main channel. Trans-boundary flux can be affected by both the river morphology and discharge magnitude. Particle-tracing shows that a large majority of particles (>85%) passed over the boundaries for at least one time, revealing a strong flux exchange at the interface of main channel and floodplains during flood events. The particle trajectory and residence time distribution also reflected a spatial and temporal heterogeneity of hydraulic interactions in a main channel-floodplain system.