| A sound understanding of river planform evolution and bank erosion control, together with the integration of expertise from several disciplines (engineering, geomorphology, ecology, among others), is required for the development of predictive models for river naturalization. Both, basic and applied researches are needed to cover the wide range of spatial- and time-scales found in rivers. Therefore, this study is organized into fundamental and applied topics. Related to fundamental topics, my research advances the knowledge of the effects of bend orientation on the hydrodynamics and morphodynamics of transitional meandering channels. Among the hydrodynamic effects, it is observed that downstream skewed configurations produce fully-developed secondary flows around the bend apex, while upstream-skewed configuration results in non-developed secondary flow. The Hydraulic Transitional Region (HTR) is used to describe the development of the three-dimensional flow structure along meandering channels. The upstream-skewed condition produces a shear layer with high turbulence intensity around the bend apex, while the downstream-skewed condition produces a similar shear layer downstream of the bend apex, suggesting several implications on bed morphodynamics. Among the morphodynamic effects, it was observed that by having a downstream-skewed bend configuration, a higher erosional power is found at the outer bank. The latter is linked to the fully developed secondary flow found previously. The Morphodynamic Transitional Region (MTR) is used to define the development of bed morphology response to local curvature. It was demonstrated that under steady hydraulic conditions, the bed morphodynamics presents an unsteady (fluctuations) component related to the migration of bedforms. For the upstream-skewed condition, it is clear that bedforms are not as developed (in size and shape) as their counterparts for the downstream-skewed condition. Due to bedform progression, sediment transport rates, and bed morphology are constantly changing and modifying the local flow structure, which consequently produces high shear stresses along the bed and on the banks promoting fluvial erosion. These pulsations on shear stresses exerted on the banks are much higher than those values observed when steady bed configurations are considered. Overall my research explains the details of the hydrodynamics and morphodynamics at transitional channels, which could be of great importance for geological studies, river restoration projects such as the use of instream structures for bank erosion control, among others. Related to applied topics, a study on the hydrodynamics of meander bends with bendway weirs (for streambank protection) is present. Field measurements (Sugar creek, Illinois) and numerical simulations were performed to validate the Computational Fluid Dynamic (CFD) model at low-flow conditions. Then, additional simulations were carried out for medium- and high-flow conditions where bendway weirs are completely submerged. Results indicate that flow patterns at high-flow condition produces high shear stresses over the top of weirs that implies bank retreat, thus producing a shelf along the base of the outer bank as observed in the field. |
