Meandering rivers provide fresh water and important aquatic ecosystem services, yet at the same time induce flood and erosion hazards. In the face of ongoing development pressure and changing climate, growing concern for meandering rivers has increased the demand to model accurately the flow and predict the sediment transport in a meandering river channel. Calibration and validation of these models based on comparable field-based data, as opposed to laboratory-scale experimental data, may decrease uncertainty and improve understanding of complex flow structures in natural meandering rivers. In this thesis, spatially intensive field data are utilized to develop appropriate calibration and validation methods for 3D meandering river models. Validated models are then applied to the study of morphodynamic processes and the influence of channel change on fish habitat availability in meandering rivers. This study presents a novel methodology for use of three-dimensional (3D) velocity for improved calibration of a 3D hydro-morphodynamic model. A natural tortuously meandering river was simulated using the Delft3D hydrodynamic model. A spatially intensive acoustic Doppler current profiler (ADCP) survey was conducted throughout the study river, providing fully 3D distributed velocities for model calibration. For accurate and realistic comparison of the fully 3D predicted and measured velocities, an algorithm was developed to match the location of each ADCP bin with 3D model grid points. The results suggest that different calibration approaches can result in different calibration parameterizations whose simulated results can differ significantly. It is shown that the model which was calibrated based on the proposed 3D calibration approach had the best model performance. Depending upon the nature and objectives of the numerical modelling exercise, the results demonstrate the importance of model calibration with spatially intensive field data. Given the importance of pressure gradients in driving secondary flow, it is worth studying how the modelled flow structures in a natural river bend can be impacted by the assumption of hydrodynamic pressure. Accordingly, the performance of hydrostatic versus non-hydrostatic pressure assumption in the Delft3D hydrodynamic modelling of a tortuously meandering river was studied. An Acoustic Doppler Velocimeter (ADV) was employed to measure the 3D flow field at a section in a sharp bend of the simulated river at two different flow stages. The field-based ADV data were employed to validate the simulated hydrodynamic models. The results indicate the surprisingly superior performance of the hydrostatic over non-hydrostatic Delft3D modelling of the secondary flow. It was determined that the non-hydrostatic routine employed in Delft3D was not mass conservative, which diminished model accuracy. Despite several decades of intensive study of the morphological changes in meandering rivers, less attention has been paid to confined meanders. This thesis includes a study of the meandering behavior of a semi-alluvial cohesive bed river over a 10-year period. We employed a paired sub-reach study approach, wherein one sub-reach is freely meandering and the second adjacent sub-reach is confined by a railway embankment. Channel migration and morphological changes of the channel banks along each of these sub-reaches were analyzed by comparing the historical aerial photography, light detection and ranging (LIDAR) data, bathymetric data obtained from a total station survey, and field examination. Moreover, two different spatially intensive ADCP surveys were conducted in the study area to find the linkage between the hydrodynamics and morphological changes in the two different sub-reaches. The unconfined sub-reach displayed a typical channel migration pattern with deposition on the inner bank and erosion on the outer bank of the meander bend. On the other hand, the confined sub-reach showed greater bank instabilities than the unconfined sub-reach. In the confined sub-reach, an irregular meandering pattern occurred by the evolution of a concave-bank bench, which was caused by reverse flow eddies. The results of this study could shed light on the potential impacts of channel confinement on bank retreat and river migration in comparable case studies. It is reasonable to expect that hydro-morphodynamic processes in rivers can affect fish habitat availability and quality, but the impact of river morphological changes on fish habitat is not well studied. Herein, we investigate the impact of morphological development of a cohesive meandering creek on the quality of fish habitat available for juvenile yellow perch (Perca flavescens) and white sucker (Catostomus commersonii). A 3D morphodynamic model was first developed to simulate the hydro-morphodynamics of the study creek over a 1-year period. Total station topographic surveys were conducted to provide bathymetric change data for calibration of the morphodynamic module. Successful calibration efforts indicated that the developed model could be reasonably employed to predict the hydro-morphodynamics of the study creek. Two fish sampling surveys were carried out at the beginning and the end of the study period to determine habitat utilization of each fish species in the study reach. ANOVA multiple comparison tests indicate that morphological development of the river was a significant factor for the habitat utilization of juvenile yellow perch, whereas juvenile white sucker habitat utilization was not significantly impacted by the changes in the creek morphology. It is shown that flow depth, depth-averaged velocity, and suspended sediment transport also significantly influenced presence of the juvenile yellow perch at the 5% significant level. As for the juvenile white sucker, the only significant factor was the depth-averaged velocity. The results of the developed 3D hydro-morphodynamic model were fed into a fish habitat model. Comparison of the predicted fish habitat map of the juvenile yellow perch with the results of fish sampling surveys confirms that the habitat quality was better predicted when the impact of morphological changes was taken into account in the fish habitat modelling. The results of the proposed methodology could provide some insights into the impact of sediment transport processes on the fish community. This has important implications for effective river management.

Puisque l’altération des habitats d’eau douce augmente, il devient critique d’identifier les composantes de l’habitat qui influencent les métriques de la productivité des pêcheries. Nous avons comparé la contribution relative de trois types de variables d’habitat à l’explication de la variance de métriques d’abondance, de biomasse et de richesse à l’aide de modèles d’habitat de poissons, et avons identifié les variables d’habitat les plus efficaces à expliquer ces variations. Au cours des étés 2012 et 2013, les communautés de poissons de 43 sites littoraux ont été échantillonnées dans le Lac du Bonnet, un réservoir dans le Sud-est du Manitoba (Canada). Sept scénarios d’échantillonnage, différant par l’engin de pêche, l’année et le moment de la journée, ont été utilisés pour estimer l’abondance, la biomasse et la richesse à chaque site, toutes espèces confondues. Trois types de variables d’habitat ont été évalués: des variables locales (à l’intérieur du site), des variables latérales (caractérisation de la berge) et des variables contextuelles (position relative à des attributs du paysage). Les variables d’habitat locales et contextuelles expliquaient en moyenne un total de 44 % (R2 ajusté) de la variation des métriques de la productivité des pêcheries, alors que les variables d’habitat latérales expliquaient seulement 2 % de la variation. Les variables les plus souvent significatives sont la couverture de macrophytes, la distance aux tributaires d’une largeur ≥ 50 m et la distance aux marais d’une superficie ≥ 100 000 m2, ce qui suggère que ces variables sont les plus efficaces à expliquer la variation des métriques de la productivité des pêcheries dans la zone littorale des réservoirs. / As freshwater fisheries become increasingly prone to habitat alteration, it is critical we identify the components of habitat that greatly influence fisheries productivity metrics. Using fish habitat modeling, we compared relative contributions of three types of habitat variables to explain variation in abundance, biomass and richness metrics, and identified habitat variables most effective at explaining these variations. During the summers of 2012 and 2013, fish communities in 43 littoral sites were sampled from Lac du Bonnet, a reservoir in southeastern Manitoba (Canada). Seven different sampling scenarios, consisting of different sampling methods, years and time periods, were used to measure relative abundance, biomass and richness metrics for all species combined per site. Three types of habitat variables were measured: local (i.e. within site), lateral (i.e. shore characterization) and contextual (i.e. position relative to landscape attributes) variables. Together local and contextual habitat variables explained on average 44% R2adj of the variation across fisheries productivity metrics, while only 2% R2adj of the variation was explained by lateral habitat variables. Specifically, macrophyte coverage, distance to tributaries ≥ 50 m wide, and distance to marshes ≥ 100,000 m2 ranked most significant across metrics, suggesting these habitat variables may be most effective at explaining variation in fisheries productivity metrics in the littoral zone of reservoirs.