Este estudo trata da caracterização hidromorfodinâmica de um setor paulista da planície fluvial meândrica do rio Ribeira de Iguape, abordando-se os três níveis da pesquisa geomorfológica de acordo com a concepção de HART (1986), a saber: (a) o nível descritivo da morfologia; (b) o nível descritivo dos materiais superficiais e solos; e (c) o nível analítico interpretativo dos processos, que, no caso, são hidrodinâmicos. Os resultados possibilitaram compreensão da hidromorfodinâmica das planícies fluviais meândricas em ambientes tropicais úmidos e, principalmente, da planície de inundação, podendo servir de subsídios no planejamento físico territorial regional, tendo em vista a importância da ocupação humana dentro desses setores. / The objective of this research is the hydromorphodynamic characterization of the Paulista River Ribeira de Iguape sector, approaching three levels of the geomorphology research according HART (1986), to know: (a) the morphology descriptive level; (b) the superficial materials and ground descriptive level; and (c) the processes interpretation analytical level, or hydrodynamic processes. With these surveys and systematization was possible the partially understanding humid tropical environments hidromorphodynamics trends and, mainly, of the flooding plain, which can be used in the regional territorial physical planning, in view of the importance of the occupation human being on these sectors.

Um modelo paramétrico regional tridimensional da Corrente do Brasil (CB) foi construído com o objetivo de investigar se o meandramento frontal da CB domina a variabilidade subinercial na Bacia de Campos. A parametrização da CB normal à costa seguiu a formulação proposta por Schmidt et al. [2007]. Os parâmetros da CB foram estimados a partir dos perfis de velocidade quase-sinóticos durante a amostragem do cruzeiro OCEANO SUDESTE II (OCSEII) da Marinha do Brasil. A frente térmica costeira (FTC), facilmente detectado na superfície do mar por imagens de satélite, é tida como a fronteira costeira do CB com velocidades desprezíveis. A FTC padrão é, então, inferida pelo método do gradiente máximo em uma data escolhida. Com a localização da FTC, várias radiais são projetadas normalmente à frente e os perfis de velocidades da CB são ajustados a estas radiais. O próximo passo é interpolar objetivamente o campo de velocidade para obter uma CB tridimensional. A variabilidade espacial da CB neste mapa é, portanto, unicamente devido à arqueamento da velocidade/ FTC, e os padrões de velocidade são devidos apenas ao meandramento frontal. Estes foram identificados nas séries temporais das FTC e o modelo foi computado para dois eventos separados no inverno de 2007 e comparados com os dados de ADCPs da PETROBRAS montados em quatro plataformas de petróleo. A comparação foi feita usando compósitos semanais e médias para isolar movimentos de mesoescala. Isso mostra que há um acordo muito favorável entre o modelo e as medições de velocidade de mar aberto em ambas as magnitudes e direções. Este assegura que os meandros frontais, ou mais especificamente, o meandro de São Tomé domina a variabilidade subinercial ao longo do talude continental e do platô de São Paulo. A única exceção é para o ADCP montado sobre uma plataforma de petróleo em plataforma continental. O modelado e as observações in situ discordam e indicam que outros fenômenos, tais como ondas de plataforma, devem ser contabilizados na parte costeira / A regional three-dimensional parametric model of the Brazil Current (BC) was built with the goal of investigating whether or not the BC frontal meandering dominates the subinercial current variability in the Campos Basin. The BC cross-stream parametrization followed the formulation proposed by Schmidt et al. [2007]. The BC parameters were estimated from quasi-synoptic velocity profiling sampled during the Brazilian Navy cruise OCEANO SUDESTE II (OCSEII). The surface inshore thermal front (ITF),easily detected in sea surface temperature satellite images, is taken as the inshore border of the BC jet with negligible velocities. The ITF spatial pattern is then inferred by the maximum gradient method on a chosen date or period. With the ITF location, several BC cross-strem profiles are projected normally to it. The next step is to objectively interpolate the velocity field to obtain a three-dimensional BC. The spatial variability of the BC in this map is therefore solely due to the arching of the velocity/ITF front, and therefore, the velocity patterns are due to frontal meandering only. Meandering events were identified in the IFT time series, the model computed the BC frontal patterns for two separate events in the winter of 2007 and compared with PETROBRAS\' ADCP records mounted on four oil rigs. The comparison was done using weekly composites and averages to isolate mesoscale motions. It shows that there is a very favorable agreement between between the model and the open sea velocity measurements in both magnitude and direction. This reassures that the frontal meandering, or more specifically, the S~ao Tom´e Meander formation dominates the subinertial variability over the continental slope and the S~ao Paulo Plateau. The only exception is for the ADCP mounted on an oil rig on the continental shelf. The modeled and in situ observations disagree and indicate that other phenomena, such as shelf waves, should be accounted in the coastal ocean in addition to the BC meandering.

Early 1960's meander rectification of the Ste-Marguerite River, Quebec, Canada, was undertaken in order to facilitate highway construction along the valley bottom. Through analysis of thalweg elevation and grain size data, the fourfold response of the river since rectification has been determined: (1) 1 m of bed incision in the upper 4 km and 2m of bed aggradation in the lower 2 km of the 6 km straightened reach; (2) coarsening (up to 20 mm) of the pavement D50 and D84 in the area of maximum degradation; (3) lateral erosion of the channel into three high terraces; and (4) regrowth of three meanders within the reach. / Estimations indicate that reprofiling and pavement coarsening have been most important in reducing the disequilibrium in gravel transport rates due to rectification. Model simulations of the response to rectification have been validated against field data and the half-time scale of response has been estimated at 10 years. A further 10 cm of degradation upstream, 17 cm of aggradation downstream and 10 mm of pavement coarsening is predicted for the next century.

The wandering river pattern represents one of the last remaining river patterns that are not well understood. Many aspects of these rivers are not well known, particularly the processes of their creation and maintenance. The term wandering describes gravel or cobble bedded rivers, transitional between braided and meandering, with multiple channel sections around semi-permanent islands connected by single channel sections. This dissertation investigates the controls on the characteristics of wandering rivers within the Miramichi region of New Brunswick through time and at three nested spatial scales. / At the scale of rivers, three factors appear to be needed for wandering to occur: (1) wide valleys, (2) channel energy between braiding and meandering, and (3) avulsion triggers, frequent overbank flows caused by icejams in the Miramichi. Principal component analysis showed that larger wandering rivers displayed greater anabranching intensity than smaller rivers, perhaps related to higher stage ice jams within larger rivers. / At the scale of channels, the wandering pattern of the Renous River was found to be in a state of dynamic equilibrium, with channel creation balanced by channel abandonment. The anabranch cycle model was developed to illustrate the temporal dynamics of anabranch creation, maintenance and abandonment within wandering rivers. / Also at the channel scale, principal component analysis of channel reaches within the Renous River displayed differences in grain size and hydraulic efficiency between side-channels and main-channels. Energy and sediment mobility within side-channels was related to their formation, maintenance and abandonment. Energy and sediment mobility within main-channels was related to mega bedforms called bedwaves. The apex of some bedwaves occurred at diffluences. / At the scale of channel elements, diffluences are stable where a large bar is formed and accretes upstream, creating a large reservoir of sediment upstream of anabranch channels to buffer their degradation. Where diffluences are unstable, a large bar forms within one anabranch channel to partially block flow and may cause its abandonment. The dissertation illustrates that within wandering rivers, processes occurring at multiple spatial and temporal scales interact to create and maintain the pattern.

Meandering rivers and associated vegetation communities are highly dynamic systems that interact through various geomorphic and successional processes. However, much is still unknown about these interactions. Studies that focus on system integration rather than examining fluvial-related and vegetation dynamics individually will benefit science and the management of river systems. Tree communities in riparian areas, although consisting mainly of bottomland hardwood species, can be very diverse. Diversity has been linked to environmental influences such as meander migration, and changes in elevation and soil texture. This study focused on a single meander bend of the lower Trinity River in southeast Texas. The purpose of this research was to examine interactions between soil texture variation and the establishment and succession of riparian tree communities, as such interactions contribute to the formation of complex riparian landscapes. A bend-scale approach was utilized to provide a detailed study of vegetation pattern and of soil texture resulting from sedimentation processes, to examine for any relationships between them. Aerial imagery was used to assist in interpreting patterns of vegetation succession. The field portion of the study collected species and size class data on trees and soil samples for textural analysis. These data were analyzed separately to understand variations in tree communities and soils, but also together, to determine any relationships between soil texture and what tree communities are able to establish. Mean annual flow data from gauges upstream and downstream of the site were analyzed for changes in flow following dam construction upstream, as river regulation could potentially alter the vegetation establishment regime. Results showed five distinct communities or zones of vegetation. Soils on the site were strongly skewed toward finer sands and high silt and clay content. Zone locations and community structure were not directly related to soil texture; however, given species had clear relationships of relative density or dominance with specific soil textures. No changes in flow were noted between pre- and post- dam construction periods, indicating that the riparian system at this site may operate under near-natural conditions. Further studies in species-soil texture interactions, and for rare and invasive species in particular, may prove beneficial in improving understanding of the complex functioning of riparian systems and in providing valuable information for their management and restoration.

Este estudo trata da caracterização hidromorfodinâmica de um setor paulista da planície fluvial meândrica do rio Ribeira de Iguape, abordando-se os três níveis da pesquisa geomorfológica de acordo com a concepção de HART (1986), a saber: (a) o nível descritivo da morfologia; (b) o nível descritivo dos materiais superficiais e solos; e (c) o nível analítico interpretativo dos processos, que, no caso, são hidrodinâmicos. Os resultados possibilitaram compreensão da hidromorfodinâmica das planícies fluviais meândricas em ambientes tropicais úmidos e, principalmente, da planície de inundação, podendo servir de subsídios no planejamento físico territorial regional, tendo em vista a importância da ocupação humana dentro desses setores. / The objective of this research is the hydromorphodynamic characterization of the Paulista River Ribeira de Iguape sector, approaching three levels of the geomorphology research according HART (1986), to know: (a) the morphology descriptive level; (b) the superficial materials and ground descriptive level; and (c) the processes interpretation analytical level, or hydrodynamic processes. With these surveys and systematization was possible the partially understanding humid tropical environments hidromorphodynamics trends and, mainly, of the flooding plain, which can be used in the regional territorial physical planning, in view of the importance of the occupation human being on these sectors.

Flow mechanisms of compound meandering channels are recognised to be far more complicated than compound straight channels. The compound meandering channels are mainly characterised by the continuous variation of mean and turbulent flow parameters along a meander wavelength; the existence of horizontal shear layer at the bankfull level and the presence of strong helical secondary flow circulations in the streamwise direction. The secondary flow circulations are very important as they govern the advection of flow momentum, distort isovels, and influence bed shear stress, thus producing a complicated and fully three-dimensional turbulent flow structures. A great deal of experiments has been conducted in the past, which explains flow mechanisms, mixing patterns and the behaviour of secondary flow circulations. However, a complete understanding of secondary flow structures still remains far from conclusive mainly because the secondary flow structures are influenced by the host of geometrical and flow parameters, which are yet to be investigated in detail. The three-dimensional Reynolds-averaged Navier-Stokes and continuity equations were solved using a standard Computational Fluid Dynamics solver to predict mean velocity, secondary flow and turbulent kinetic energy. Five different flow cases of various model scales and relative depths were considered. Detailed analyses of the measured and predicted flow variables were carried out to understand mean flow mechanisms and turbulent secondary flow structures in compound meandering channels. The streamwise vorticity equation was used to quantify the complex and three-dimensional behaviour of secondary flow circulations in terms of their generation, development and decay along the half-meander wavelength. The turbulent kinetic energy equation was used to understand energy expense mechanisms of secondary flow circulations. The strengths of secondary flow circulations were calculated and compared for different flow cases considered. The main findings from this research are as follows. The shearing of the main channel flow as the floodplain flow plunges into and over the main channel influences the mean and turbulent flow structures particularly in the crossover region. The horizontal shear layer at the inner bankfull level generates secondary flow circulations. As the depth of flow increases, the point of generation of secondary flow circulations moves downstream. The secondary shear stress significantly contributes towards the generation of streamwise vorticity and the production of turbulent kinetic energy. The rate of turbulence kinetic energy production was found to be higher than the rate of its dissipation in the crossover region, which demonstrates that the turbulence extracts more energy from the mean flu\\' than what is actually dissipated. This also implies that, in the crossover region, the turbulence is always advected downstream by the mean and secondary flows, The strength of geometry induced secondary flow circulation increases with the increase in the relative depth.

An investigation of the flow characteristics and sediment transport processes has been carried out in a two-stage meandering channel. Three phases of experiments have been conducted with various floodplain roughnesses. The dimensions of the flume are 13m long and 2.4m wide with a fixed valley slope of 11500. The meandering main channel has a sinuosity of 1.384 with top width of 0.4m. In each phase of the experiment, hydraulic data pertaining to stage-discharge, bed topography and sediment transport rate were measured at various overbank flow depths. Several flow depths were chosen to measure the three-dimensional velocities by means of Laser Doppler Anemometer and the morphological bedforms were recorded using the Photogrammetric technique. The boundary shear stresses were also measured by means of a Preston Tube and Vane Indicator. The experimental results showed that the presence of the energy losses due to momentum exchange and turbulence, bedforms roughness and floodplain roughness induced additional flow resistance to the main channel flow, particularly for shallow overbank flows. The combination of these losses affected a significant reduction in velocity and boundary shear stress in the main channel which, subsequently led to the reduction of sediment discharge at low relative depth for most tested cases. The reduction was more pronounced when the floodplain roughness increased. The examination of the three-dimensional velocity indicated that the formation of bedforms in the main channel is significantly affected by the flow structures, especially the secondary flow. A new method for predicting velocity and sediment transport rate has been introduced based on the two-dimensional equation (Spooner's) coupled with the self-calibrated empirical transport formula. The proposed method gave accurate prediction for depthaveraged velocity and sediment transport rate for two-stage meandering channel.

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