For morphodynamic modelling, riverbed survey data are essential as the basis for the evaluation of temporal riverbed development, mesh creation, and model calibration. To study the effects of uncertain geometry input on these issues, datasets of different spatial resolutions were analysed. As a result, cross-profile data were derived from high-resolution survey data, which are available for a river reach in the Upper Danube in Bavaria for several periods. Finally, the prediction quality of simulations based on cross-profile and high-resolution spatial data was assessed. The analysis of both datasets shows continuous riverbed erosion but of different magnitudes. However, complex riverbed geometry due to, e.g., scours, is depicted poorly by cross-profile data. In more homogenously characterised reaches, cross-profile data significantly more closely represents the riverbed geometry than the high-resolution spatial data base. Local misinterpretation of riverbed geometry by cross-profile data leads to deviations of calibration parameters in the entire study area. Consequently, these deviations in calibration outcome effect the model predictions. In this case, cross-profile calibration generally induces higher transport capacities, leading to more erosion in the study area compared to the model based on high-resolution spatial calibration. The general shape of predicted riverbed geometries is found to be similar but with local deviations, which are not limited to areas with complex river geometry.

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.

The presented work is part of the optimization of the sediment management at the hydroelectric powerplants in Reutte/Höfen in Austria. The weirs of the two powerplants are situated at the alpine river Lech, located about 3 km upstream of the Lechaschau gauge (A=1012.2 km²). Totally five sluice gates and a fixed overflow weir are controlling the upstream reservoir, being subjected to high rates of coarse bed load material. In frame of a coupled approach of physical and numerical modelling, different options to (i) avoid/minimize sediment deposition and (ii) allow improved sediment flushing were tested and optimized. Besides a lowering of energy losses (reduced spilling times) the reduction of depositions downstream close to the turbine outlet were considered.The physical model covers the hydropower and weir system of both power plants within a stretch of 400m / 150m using a model scale of 1:25. Investigated situations covered periods of reservoir sedimentation, flushing of the reservoir and typical flood flow situations (e.g. HQ1 and an unsteady HQ5 event). For model parametrization, sediment samples to quantify size distribution were taken in the field. Sediment inputs to the model were realized dynamically and were required (due to scaling effects) to exclude cohesive fractions having a minimum particle size of 0.5 mm. The full-area surface measurement of the river bed was made by means of airborne laser bathymetry and echo sounding.As part of an optimization of the overall sediment management strategy, the focus of the presented research is on the western located runoff power plant Höfen. Via a lateral water intake, a maximum design flow of 15 m³/s is withdrawn causing that the intake structure is subjected to sediment depositions. Within the described scale model (1:25) and a partial scale model (1:15) covering the western side, several management options and configurations of sediment guiding walls were tested. Erosion and deposition as well as the transported material are assessed by 3D laser scanning and permanent monitoring of transported sediment load entering and leaving the scale model.Complementary, a 2D hydro numerical model using a layer based multi fraction approach for sediment transport is set up for an extended area to simulate the morpho-dynamic behavior. The numerical model covers the whole weir system and 750 m of the upstream part of the Lech. The simulations made were realized at nature scale and allowed to mimic the erosion and deposition pattern obtained within the physical modelling for different tested options. Regardless of a chosen guiding wall setup, the results showed that each one is compromise between sediment defense and the effectiveness of the subsequent flushing processes.

Over the past two centuries, river regulation practices in Europe have significantly altered river systems through straightening, channelization and bedload retention. These modifications, coupled with the implementation of transverse structures such as hydropower facilities, have adversely affected riverine ecosystems, floodplains and sediment dynamics. River widening projects aim to address these challenges by creating more space for rivers, thereby improving the health of these natural systems. In Tyrol, Austria, between Stams and Rietz, a restoration project on the Inn River included the removal of most bank protection, the widening of the river up to 75 meters, and the creation of a dead branch and a side channel. On a length of 3 km, this measure re-established aquatic as well as terrestrial habitats. Shortly after completion, a 50-year flood event caused significant changes along the restoration zone, including the breaching of the dead branch, which subsequently connected to the main channel. These morphodynamic changes were documented using two airborne laser bathymetry (ALB) surveys and an echo-sounding survey for cross-sectional profiles.Morphodynamic models are key tools for understanding sediment transport processes in rivers and providing insights into riverbed dynamics and sediment budgets over time. For this study, the Telemac2D hydrodynamic model, coupled with the Gaia sediment transport module, was employed to simulate the hydrograph of the HQ50 flood event. The model accounted for complex bedload behavior, including lateral slope effects and bank failure, which are essential processes in river restoration. A stable sediment budget with inflow rates equal to outflow rates was assumed due to the uncertainty in bedload inflow rates. A sensitivity analysis was conducted using various transport equations, including Meyer-Peter & Müller, Einstein & Brown, Hunziker, and Wilcock & Crowe. To assess model performance, metrics such as mean change in elevation (MCE), root mean square error (RMSE), and a newly developed erosion and deposition pattern index (EDPI) were analyzed. All transport equations replicated the general survey patterns, with the Meyer-Peter & Müller equation achieving the lowest MCE and RMSE errors and the highest EDPI values. Despite these promising results, unrealistic behavior was observed since none of the transport models accounted for the movement of the coarsest sediment fraction, leading to bed coarsening as fine material was preferentially transported out of the model. Furthermore, the Hunziker and Wilcock & Crowe equations yielded unrealistically low transport rates, resulting in reduced erosion and deposition compared to the Meyer-Peter & Müller and Einstein & Brown equations. These limitations highlight uncertainties in shear stress calculations for alpine rivers characterized by large particle sizes. Further research is recommended to address these issues and enhance the accuracy of sediment transport modeling in similar contexts.

Morphodynamic modelling relies on different types of riverbed surveys. Surveys are essential as the basis of the evaluation of temporal river bed development, mesh creation, and model calibration. Spatial data, for example, obtained by topo-bathymetric airborne laser scanning (ALB) or sonar surveys results in a dense point cloud, providing detailed information on the river bathymetry. However, data gaps can occur due to restrictions in data acquisition (e.g. high water turbidity or water depth for ALB, low water for boat-mounted sonar). In contrast, cross-profiles contain only limited information on the bathymetry strongly dependent on the cross-profile and point spacing.To assess the effect of the two survey data types on river bed development and morphodynamic predictions, the temporal evolution of a river stretch in the upper Danube at Donauwörth was analysed. The study area contains homogeneous river sections and sections with complex river geometry due to scours, bridge foundations, and river mouths. Spatial sonar and ALB surveys were conducted from 2013 to 2020 and give detailed documentation of the river bed development. Cross-profiles with a cross-profile spacing of 200 m were derived from the spatial data. The spatial and cross-profile datasets show continuous river bed erosion. However, in this case, cross-profile data overestimate the overall erosion compared to spatial data. The geometry of homogeneous river stretches is depicted very similarly in the two datasets. For cross-profile data two cases exist for reaches with more complex river bed geometry: (i) The geometry lies in between two cross-profiles and it is missed entirely. (ii) The geometry is covered by a cross-profile and the resulting geometry is smeared in between the cross-profiles due to the interpolation process. Both possibilities result in an unsatisfactory depiction of the riverbed geometry.To analyse the effect of morphological developments two morphodynamic models based either on the spatial or cross-profile datasets were set up. The models were calibrated against the datasets from 2013 to 2020 by adjusting the Strickler value for river sections with a length of 200 m. The Strickler values differ over the entire river stretch and not only in sections where complex river bed geometry occurs, meaning that the calibration errors propagate through the entire study area. Consequently, the deviations in calibration outcomes affect the model predictions, which simulate 7 years. In this case, the general shape of the predicted riverbed is similar, but due to the overestimation of riverbed erosion by cross-profile data, the morphodynamic model overestimates the erosion compared to the spatial data. However, the obtained error is for river reaches with low local variability within an acceptable range. If a project demands a highly accurate depiction of the river bed and the river geometry is known for having complex features, the use of spatial data is strongly advised.