The study of fluvial geomorphology is one of the critical sciences in the 21st Century. The previous century witnessed a virtual disregard of the hydro and morphodynamic processes occurring in rivers when it came to design of transportation, flood control, and water resources infrastructure. This disregard, along with urbanization, industrialization, and other land uses has imperiled many waterways. New technologies including geospatially referenced data collection, laser-based measurement tools, and increasing computational powers by personal computers are significantly improving our ability to represent these complex and diverse systems. We can accomplish this through both the building of more sophisticated models and our ability to calibrate those models with more detailed data sets. The effort put forth in this dissertation is to first introduce the accomplishments and challenges in fluvial geomorphology and then to illustrate two specific efforts to add to the growing body of knowledge in this exciting field. First, we explore a dramatic phenomenon occurring in the Middle Rio Grande River. The San Marcial Reach of the Rio Grande River has experienced four events that completely filled the main channel with sediment over the past 20 years. This sediment plug has cost the nation millions of dollars in both costs to dredge and rebuild main channels and levees, along with detailed studies by engineering consultants. Previous efforts focused on empirical relations developed with historical data and very simple one dimensional representation of river hydrodynamics. This effort uses the state-of-the-art three-dimensional hydro and morphodynamic model Delft3D. We were able to use this model8to test those hypotheses put forth in previous empirical studies. We were also able to use this model to test theories associated with channel avulsion. Testing found that channel avulsions thresholds do exist and can be predicted based on channel bathymetric changes. The second effort included is a simple yet sophisticated model of river meander evolution. Prediction of river meandering planform evolution has proven to be one of the most difficult problems in all of geosciences. The limitations of using detailed three dimensional hydro and morphodynamic models is that the computational intensity precludes the modeling of large spatial or temporal scale phenomenon. Therefore, analytical solutions to the standard Navier-Stokes equations with simplifications made for hydrostatic pressure among others, along with sediment transport functions still have a place in our toolbox to understand and predict this phenomenon. One of the most widely used models of meander propagation is the Linear Bend Model that employs a bank erosion coefficient. Due to the various simplifications required to find analytical solutions to these sets of equations, efforts to build the stochasticity seen in nature into the models have proven useful and successful. This effort builds upon this commonly used meander propogation model by introducing stochasticity to the known variability in outer bank erodibility, resulting in a more realistic representation of model results.

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.

Stochastic modelling of river morphology and its potential in present-day river management practice is the topic of this thesis. In summary, this thesis shows how to analyse the stochastic nature of river morphology by means of Monte Carlo Simulation. It provides insight into the uncertainty sources that contribute most to the stochastic morphodynamic river behaviour. Furthermore, three applications illustrate the potential of a stochastic model approach in river management practice. The conclusion can be drawn that the use of this 'computation-intensive' approach adds value to river engineering and management practice

Around the world, many people live, work and recreate in river, estuarine and coastal areas, systems which are also important wildlife habitats. It is imperative to understand the physics of such systems. A key element here is morphodynamics: the mutual interaction and adjustment of landform topography and fluid dynamics involving the motion of sed

This book provides a comprehensive overview of the recent developments on river, coastal and estuarine morphodynamics through a collection of review papers written by well-recognized experts in the field. Apart from geoscientists it is also of special interest to people involved in fluid mechanics who want to understand near wall turbulence and the effects of coherent structures on the mechanisms of sediment transport. Though aimed at geomorphologists and sedimentologists the terminology employed in the book makes it generally accessible to engineers, physicists and applied mathematicians at the postgraduate level. The contributions are well illustrated with splendid pictures of various morphodynamic natural patterns.

The proceedings of the 4th Symposium on River, Coastal and Estuarine Morphodynamics offers the latest research results concerning quantitative modelling of the interaction of water and sediment and the shapes this interaction makes in rivers, watersheds, estuaries, the coast, the continental shelf and the deep sea. Morphodynamics is the study of the evolution of landscape and seascape features, from small scale to large.