Gravel-bed river morphodynamic processes throughout a large flood with an 80-year return period from numerical modeling: Implications for flood regulation strategies

• The morphodynamic processes occurring in a gravel-bed river throughout a large flood event were simulated. • The time-evolution of morphodynamic processes varies in different morphodynamic units. • Bar growth and bank erosion mainly developed during the rising phase of the flood. • The bedload predictions are more sensitive to variations in flow velocity than in sediment size. • For given flood peak and duration, a briefer rising period can limit flood-induced morphodynamic changes. Due in part to the lack of continuous-in-space-and-time flow and sediment transport data, the river morphodynamic processes during large floods are not fully understood. This study developed a two-dimensional (2-D) morphodynamic model to study the morphodynamic process of a gravel-bed river during a flood event with a return period of 80 years in Calgary, Canada. The model was calibrated against post-flood velocimetry data and post-flood bathymetry data. Temporal and spatial distributions of flow velocity, bedload transport rate, surface sediment sizes, and cumulative morphological changes throughout the flood are presented and analyzed. The results show that the timings of morphological changes during the flood differ for different morphodynamic units (MUs). It is demonstrated that, with the same flood peak and duration, a regulated flood event with a brief rising period, rather than a long-lasting rising period, might result in less bank erosion and bar growth. We also found that bedload transport rates are more sensitive to flow velocities than bed sediment sizes in the Bow River case, due to the greater spatial and temporal variance of velocities during the flood.