The transboundary floodplain corridor extending from Prek Kdam Bridge and Khsach Kandal in Cambodia to the Vietnamese Mekong Delta represents a critical component of the Lower Mekong Basin’s hydrological and socio-ecological system. Seasonal inundation within this corridor underpins agricultural production, sustains capture fisheries, and supports the livelihoods of millions of rural households. However, this natural flood regime is increasingly disrupted by multiple interacting pressures, including upstream hydropower development, rapid land use transformation, and the emerging impacts of climate variability. These drivers are reshaping hydrodynamic conditions, intensifying flood risks, and complicating the governance of shared water resources. To examine these dynamics, this study applies a two-dimensional hydrodynamic model (HEC-RAS) to simulate peak flood events in 2022 across the corridor. The model integrates a digital terrain data (12m×12m) with observed boundary conditions to represent key hydraulic parameters, including water depth, velocity, and water surface elevation (WSE). Calibration against observed water levels produced an RMSE of 0.58, NSE of 0.71 and PBIAS of 14.21% demonstrating satisfactory predictive skill and reliability for flood assessment in this complex setting. Simulation results highlight pronounced spatial heterogeneity in flood characteristics. Deep river channels (5–15 m) function as critical aquatic habitats and dry-season refugia but also exacerbate bank erosion and increase exposure to fluvial hazards. Floodplain areas with moderate depths (1–5 m) sustain rice cultivation and sediment deposition processes, yet prolonged inundation in these zones threatens crop yields and rural livelihoods. The results are setting out inundation characteristic hydrodynamic properties of the flood plain.