Regional hydraulic controls on flood wave propagation post-impoundment: Insights from the Three Gorges Reservoir for regulated river systems

Study region The Three Gorges Reservoir (TGR), a large channel-type reservoir on the Yangtze River, extends 595.6 km from Cuntan to the dam and is strongly influenced by longitudinal backwater. Study focus This study investigated how impoundment alters flood-wave propagation and travel time in the TGR, using a calibrated 1D hydrodynamic model combined with a physically based wave celerity framework under multi-scenario conditions. New hydrological insights for the region Impoundment shifted the dominant control of flood propagation from discharge (kinematic-wave behavior pre-impoundment) to reservoir water level (dynamic-wave behavior under backwater). Near-dam wave celerity increased to ∼19 m/s at high levels, reducing mean travel time from ∼39 h (pre-impoundment) to ∼15 h at 175 m. The proposed celerity formulation agreed well with model results (R² = 0.61), and improved significantly (R² = 0.90) when using model-derived pre-impoundment celerity. These findings provide a physical basis for flood travel time estimation in regulated rivers and support forecasting and reservoir operation.