Morphodynamic Modeling of a Flood Event at a Restored Alpine River Reach

Morphodynamic models are essential tools for estimating sediment dynamics along river reaches. A wide range of bedload transport equations is available, and applying these models to river restoration projects and river widenings requires simplifying assumptions about slope effects, secondary currents, and bank failure, introducing significant uncertainties. This study evaluates morphological changes during a flood event in the restored section between Stams and Rietz on the Inn River in Tyrol, Austria, using the 2D hydrodynamic model Telemac2D coupled with the morphodynamic model Gaia. As the flood occurred shortly after the completion of the restoration works, vegetation had not yet developed, allowing the influence of vegetation to be neglected in the numerical model. To enhance the applicability to similar restoration projects, the simulations were solely hydraulically calibrated and only relied on default morphodynamic calibration parameters. A comprehensive sensitivity analysis tested multiple bedload transport equations and key model parameters. The results suggest that the Meyer‐Peter & Müller and Hunziker equations effectively replicate erosional and depositional patterns, with volume estimates within a factor of two compared to the survey data. Transport rates varied significantly across all tested equations, underscoring the limitations of existing formulas for rivers characterized by coarse and broad gravel‐dominated particle size distributions and immobile coarse particle fractions. The sensitivity analysis also highlights the critical role of slope effects. While accounting for secondary currents and bank failure improved the model results, their impact was comparatively smaller. Overall, this study demonstrates that morphodynamic modeling can be a valuable tool for planning river restoration projects, particularly in estimating sediment budgets and predicting erosional and depositional patterns.