O adequado projeto de obras fluviais requer o conhecimento das condições sob as quais um curso d\'água natural atinge seu estado de equilíbrio. Para que este estado de equilíbrio seja determinado analiticamente é necessário utilizar um número de equações compatível com a quantidade de incógnitas do sistema, denominadas de graus de liberdade. Em um curso d\'água escoando sobre leito aluvionar não coesivo é possível admitir até quatro graus de liberdade, que são: a largura, a profundidade, a declividade e o traçado em planta do canal. Neste trabalho são apresentados alguns métodos que permitem avaliar as condições de estabilidade de um canal através do uso de relações puramente empíricas, ou através da aplicação de equações derivadas dos princípios físicos que regem a Hidráulica Fluvial, sendo possível ainda combinar o uso das duas abordagens no mesmo método. / The properly design of river improvements depends on the knowledge of the conditions under which a natural river becomes stable. This state of equilibrium is determined analytically if the number of equations is enough to describe the unknown system factors, called degrees of freedom. In an alluvial stream, it\'s possible to consider four degrees of freedom, they are: width, depth, channel slope and the variations in plan-form stream. This text presents some methods to evaluate the stability condition of a channel using empirical relationships, equations based on theoretical principles of Fluvial Hydraulics or both of these approaches in the same method.

Changes in sediment morphology on the West Florida Shelf is investigated over a 14-year time period using multibeam bathymetry and backscatter in water depths between 10 m and 20 m, off the coast of Indian Rocks Beach, Pinellas County, Florida. Bathymetric surveys collected in 2002 (Kongsberg EM 3000 at 300 kHz) and 2016 (Reson 7125 at 400 kHz) were processed using CARIS Hips and Sips to create bathymetric maps and backscatter images. These data were then interpreted and compared in order to test hypotheses and answer questions related to sediment migration and sediment volume change. The following questions prompted this study: A. How mobile is the sediment on the limestone? B. What sedimentary changes occurred following the 2002 and 2003 deployments of mines for an Office of Naval Research project? C. How much sediment was removed during dredging and how closely does it compare to the Army Corps of Engineers’ reported estimate during the beach renourishment of Sand Key in 2012? In order to answer these questions, hypotheses were proposed: Hypothesis A: The sediment ridges in the study site have not migrated significantly over the limestone hard bottom during the 14-year time period (Hafen, 2001; Edwards et al. 2003). Hypothesis B: There is no change in sediment volume where the mine-like object were placed and removed after the ONR mine burial experiment (Wolfson 2005 Wolfson et al. 2007). Hypothesis C: Changes in sediment volume between 2002 and 2016 will match the amount estimated by the Army Core of Engineers who dredged the area. Results show that the sediment ridges in the study area had some migration over the limestone hard bottom during the 14-year time period. The results also found that there was a sediment volume change where mine-like objects were placed and removed during the Office of Naval Research mine burial experiment because of a dredging operation in 2012 that dredged sediment from the experimental area. Specific areas investigated that surround the dredging area showed significant loss of sediment, with the change in hydrodynamics from dredging influencing this sediment loss. The volume of sediment removed from the aforementioned dredging cut was found to be within 16% of that estimated in the Army Corps of Engineers report prior to the dredging. Geologic interpretations of the backscatter images interpreted strong backscatter returns as limestone, mid strength returns as coarse shell hash and weak returns as fine to medium-grained sediments. The weak returns were found primarily on the sediment ridges. The dredging cut showed stronger returns than the surrounding ridge, indicating that underlying coarse sediments were most likely compacted and composed of shell hash. Using satellite remote sensing as a way to gather continual repeat coverage at high resolution (2 m) data to determine absolute depth in these water depths is investigated and preliminary results suggest that processed 250 m pixel MERIS data will give a similar depth range as multibeam bathymetry. The higher-resolution 0.5 m pixel raw WorldView 2 data shows NW-SE trending structure, suggesting the seafloor morphology will be more visible.

Storms play a significant role in beach morphodynamics. Storm-induced beach-profile changes and their longshore variations are investigated in this study. The impacts of four summer tropical storms and two series of winter storms over the last 10 years along the coast of Treasure Island were documented. Tropical storms Alberto in 2006, Fay in 2008, Debby in 2012, Hermine in 2016 and winter storms in winter seasons of 2014 and 2015 are discussed in this study. In general, the Treasure Island beach experienced more erosion generated by tropical storms with greater intensity, but shorter duration, as compared to winter storms due to lower waves, weaker wind and smaller storm surge. Winter storms typically do not generate high storm surge and generally do not cause erosion at the dune and back beach unless the pre-storm beach is very narrow. Based on pre- and post-storm beach-profile surveys along the coast of Treasure Island, the northern end of the barrier island, located directly downdrift of the John’s Pass tidal inlet, experienced erosion along the entire profile during the storms. Along the middle part of Treasure Island, dry beach suffered erosion during both the tropical storms and winter seasons while the nearshore zone suffered erosion during the tropical storms and experienced deposition during the winter seasons. Sunset Beach at the southern end experienced severe erosion during tropical storm Debby, but not during other storms. Winter seasons caused relatively small changes to the morphology of Sunset Beach. Deposition happened in the nearshore zone along Sunset Beach during winter storms. Survey line R143 at the very south end of Treasure Island suffered erosion in tropical storm Alberto, Debby and Hermine. Beach profile changes induced by Tropical storm Fay was different as compared to other tropical storms. Considerably less beach erosion occurred due to the large distance of the storm path from the study area. Overall, Sunshine Beach, bounded by John’s Pass inlet at northern end of Treasure Island, was influenced both by wave conditions and the tidal flows. Sediment transport was to the north along the coast of Sunshine Beach when wind direction was from south, e.g. during tropical storm Fay. However the northward sediment transport was blocked by the John’s Pass jetty. Therefore, deposition occurred at Sunshine Beach during tropical storm Fay. When wind direction was from north (e.g. during tropical storms Alberto and during the winter seasons), southward sediment transport was generated. Erosion occurs during the northerly approaching storms. The morphodynamics of the middle section of Treasure Island are influenced by the sand supply at the attachment point of John’s Pass ebb delta. Sunset Beach experienced various levels of erosion during the tropical storms not only because of the high wave, strong wind and high water level generated by storms, but also due to the higher waves associated with an offshore dredged pit.

This study investigates the relation between channel instability and sediment transport along an 80 km reach of lower Fraser River, British Columbia. The major processes governing instability, bank erosion and sedimentation were investigated by analyzing the patterns of morphologic change along the river over the last century. Morphologic changes were documented using historical maps and air photographs. The method of approach can be considered a "macroscopic" one since the investigation focused primarily on the gross patterns of change that occurred over periods of years to decades. It was found that this interval is the most appropriate time scale for investigating channel instability and sedimentation processes on a large stream such as the Fraser River. This is because the major features governing instability and sedimentation also develop over comparatively long time periods. Several examples are presented to illustrate how sequences of major channel instability have propagated along the river over periods of 10 to 30 years. These disturbances often initiated new patterns of sedimentation, local erosion and subsequent channel instability further downstream. The most common diagnostic feature associated with these travelling disturbances are relatively large, low amplitude, linguoidal-shaped "gravel sheets" that attach to more stable lateral bars and islands. These bars may cause strong flow impingement against previously stable banks and islands. As a result, rapid scour and erosion may be initiated even during periods of low discharge. Four different approaches were used to estimate the long term gravel transport rate along the river. These methods included direct measurements using trap samplers (carried out by Water Survey of Canada over a period of 12 years), a sediment budget calculation which related changes in transport through a reach to changes in the volume of sediment stored in the channel determined by surveys, a morphologic approach which used a simple model of sediment transfers through a reach, and finally theoretical bed load formulae. It was found that the sediment budget and the morphological model provided the most reliable and most generally applicable results. This was because the methods rely on observations of sediment movement over periods of years or decades. It was found that on Fraser River, the time scales of the major processes governing gravel bed load transport were also measured in years or decades. As a result, short term measurements such as from bed load trap samplers show only a poor correlation between transport rate and flow variables. Therefore, to estimate long term transport rates with these data, a very large number of observations is required to integrate the transport rates over time. / Arts, Faculty of / Geography, Department of / Graduate

Shippagan Gully is a highly dynamic tidal inlet located on the Gulf of St-Lawrence near Le Goulet, New Brunswick. This tidal inlet is highly unusual due to the fact that the inlet has two open boundaries with phase lagged tidal cycles that drives flow through the inlet. Over the past few decades, the shipping activities through the inlet have been threatened due to the narrowing of the navigation channel caused by deposited sediment on the east side of the channel. Many engineering projects have been undertaken at Shippagan Gully in order to try and mitigate the deposition problem. However, these attempts have either been unsuccessful or the engineered structures have deteriorated over the years. This study uses the CMS-Flow and CMS-Wave numerical models to provide guidance concerning the response of the inlet to various potential interventions aimed at improving navigation safety.

This study set out to investigate the shear stress behaviour at the bed under combined wave and current action. The intention of the study was to make experimental measurements to determine how wave and current shear stresses combine, so that theoretical models describing the combined flow condition could be proposed. Two types of experiment were conducted, and theoretical models for the combined flow were assessed. One set of experiments attempted to use a shear plate to make direct measurements of the combined flow shear stress, and of the shear stresses for the component waves and steady currents. This approach failed because the large correction terms introduced by the non-uniform wave pressure field could not be accurately estimated. The second set of experiments used a laser doppler anemometer to make detailed velocity profile measurements over flat sediment beds. The onset of sediment motion was used as a criterion to carefully control the experiments. It is assumed that the threshold of sediment motion represents a specific shear stress intensity at the bed for sediments of narrow size ranges. As the shear stresses can be determined from the velocity fields under waves and currents, their additive nature under combined flow conditions could be investigated. For each sediment size range, it is shown that the same maximum velocity very near the bed can be used to specify the threshold of sediment motion condition for all flow types, be they under waves, currents, or combined waves and currents. It is also shown that the near-bed velocity under a laboratory wave can be predicted accurately from second order wave theory and that the velocity under a current can be predicted from combining Manning's relation with the universal log velocity law. It is further shown that the near-bed velocity under a combined wave and current can be described by the vectorial addition of the maximum component wave velocity and the average component current velocity. The shear stress for the onset of motion is calculated for the steady current using Manning's relation, for the wave by combining the oscillatory shear stress formula with Kamphuis's rough turbulent friction factor relation, and for the combined wave and current by the simple vectorial addition of the component shear stresses, and is shown to be comparable with Shields's threshold criterion for nearly all conditions tested. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Turbidity currents, both continuous flow and surge-type, have been detected with acoustic sounders operating at 42.5, 107 and 200, kHz. The turbidity currents are associated with the discharge of mine tailing into Rupert Inlet. A linear relation is obtained between the backscattered acoustic signal at 200 kHz and the one-half power of suspended particulate concentration from 10 to 1000 mg 1⁻¹. This relation is consistent with Rayleigh scattering theory in form and (relative to a standard target) amplitude, and is used to generate a cross-sectional profile of sediment concentration in the discharge plume. Estimates of surge speeds from the acoustic records based on a universal shape for density current heads range from 30 to 120 cm s⁻¹. The excess density of one surge was estimated from the reverberation amplitude to be 0.12 g cm⁻³. The additional attenuation of sound waves by suspended particles is important in turbidity currents and may be used to estimate suspended particulate concentration. Thermal processes contribute very little to the additional attenuation by particles with the grain densities of common minerals. A leveed submarine channel extended from the point of the tailing discharge (outfall) over the surface of the tailing deposit as early as 1974. The upper reach of this system was buried in 1978, and by late 1979 a new channel had developed. In 1976-77, the original channel consisted of: (1) a left-hooking upper reach with an average slope of 2.2°, (2) a middle reach (1° slope) with pronounced meanders (700-1100 m wavelengths) "increasing in curvature with distance downstream and (3) a straight lower reach (0.5° slope). The cross-sectional area of the channel decreased with distance downstream, excepting an increase in the first 100-200 m, until the channel disappeared about 5.5 km from the outfall. Acoustic records of the discharge plume in bends indicate overspill from the outer bank and an upward tilt of the upper interface away from the centre of bend curvature. The interfacial slope is steeper than indicated by the cross-channel difference in levee heights. These records together with observed tidal currents suggest that the left hook in the upper reach is caused by a mechanism similar to that which has been suggested for deep-sea channels. Turbidites in gravity cores from the levees are present as layers of vertically-graded, Cu-rich and Fe-poor sand and silt, some of which have load-casted flame-structures or load-pockets at their basai contacts. These layers comprise more of the sediment column with distance down-channel, suggesting that levee-building by overbank spillage from continuous flow becomes less important, and that most of the material transported through the lower reach is carried by turbidity surges. Surge recurrence intervals of 2-5 d are obtained from the number turbidites per core and the local deposition rate. The latter ranged from 0.3-4 m yr⁻¹, as given by changes in water depth, in tailing thickness from seismic reflection surveys, and in diatom frustule abundance in the cores. A model of continuous turbidity flow in submarine channels including entrainment is applied to the Rupert Inlet channel. Results are consistent with a sediment budget based on changes in the tailing deposit volume, and with turbidity surge recurrence intervals. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Coastal bays and salt marshes are buffer zones located at the interface between land and ocean, and provide ecologically and commercially important services worldwide. Unfortunately, their location makes them vulnerable and sensitive to sea-level rise (SLR), reduced sediment loads and anthropogenic modifications of the shoreline. Sediment budget and sediment availability are direct metrics for evaluating the resilience of salt marshes and coastal bays to various stressors (e.g. SLR). Salt marshes requires adequate sediment inputs to maintain their elevation with respect to sea level. Understanding sediment trajectories, sediment fluxes and sediment trapping capacities in different geomorphic unit facilitates efficient restorations and coastal management. In this research I used remote sensing, field observations and numerical modelling in the Plum Island Sound in Massachusetts, USA, to explore mechanisms controlling sediment dynamics and their feedbacks with SLR. The analysis of remote-sensed suspended sediment concentrations (SSC) reveals that a 5-year record (2013-2018) is sufficient to capture a representative range of meteorological and tidal conditions required to determine the main drivers of SSC dynamics in hydrodynamically-complex and small-scale coastal bays. The interplay between river and tidal flows dominated SSC dynamics in this estuary, whereas wind-driven resuspension had a more moderate effect. The SSC was higher during spring because of increased river discharge due to snowmelt. Tidal asymmetry also enhanced sediment resuspension during flood tides, possibly favoring deposition on marsh platforms. Together, water level, water-level rate of change, river discharge and wind speed were able to explain > 60% of the variability in the main channel SSC, thereby facilitating future prediction of SSC from these readily available variables. To determine the fate of cohesive sediments and spatial variations of trapping capacity in the system, a high-resolution (20 m) numerical model coupled to a vegetation module was developed. The results highlight the importance of the timing between sediment inputs and tidal phase and show that sediment discharged from tidal rivers deposit within the rivers themselves or in adjacent marshes. Most sediment is deposited in shallow tidal flats and channels and is unable to penetrate farther inside the marshes because of the limited water depths and velocities on the marsh platform. Trapping capacity of sediment in different intertidal subdomains decreases logarithmically with the ratio between advection length and the typical length of channels and tidal flats. Moreover, sediment deposition on the marsh decreases exponentially with distance from the channels and marsh edge. This decay rate is a function of settling velocity and the maximum value of water depth and velocity on the marsh platform. Bed sediment compositions were generated to further explore feedbacks between SLR, sediment dynamics and morphological changes. The results show SLR increases tidal prism and inundation depth, facilitating sediment deposition on the marsh platform. At the same time, SLR enhances ebb-dominated currents and increases sediment resuspension, reducing the sediment-trapping capacity of tidal flats and bays, leading to a negative sediment budget for the entire system. This bimodal distribution of sediment budget trajectories will have a profound impact on the morphology of coastal bays, increasing the difference in elevation between salt marshes and tidal flats and potentially affecting intertidal ecosystems. The results also clearly indicate that landforms lower with respect to the tidal frame are more affected by SLR than salt marshes. Therefore, Salt marshes, shallow bays, tidal flats, and barrier islands are inherently and physically connected systems, and evaluating the effect of SLR on salt marshes should involve all these units.

Thesis advisor: Gail C. Kineke / An observational study was conducted from 2013 to 2016 to investigate suspended-sediment transport processes in the stratified Connecticut River estuary. Time-series measurements of velocity and suspended-sediment concentration from the upper estuary were analyzed to determine the relative importance of different processes driving sediment flux under highly-variable river discharge. Results indicate that under high discharge the salt intrusion is forced towards the mouth causing large seaward sediment fluxes throughout the water column. Seaward fluxes are dominated by mean advection, with some contribution due to tidal pumping. Under low discharge the salt intrusion extends to the upper estuary, advancing as a bottom salinity front during each flood tide. Stratification and strong velocity shear during the ebb tide cause the upper and lower water column to become dynamically decoupled. Sediment flux near the bed is landward throughout the tidal cycle despite the net seaward depth-integrated flux, and is almost fully attributed to the mean estuarine circulation. River discharge is the primary factor affecting the magnitude and direction of sediment flux because of its high variability and direct connection to the salt-wedge dynamics. A generalized three-phase conceptual model describes suspended-sediment transport in shallow, stratified estuaries with low trapping efficiencies. First, fine sediment bypasses the estuary during high river flows and exports to the coastal ocean where a portion of this sediment is temporarily deposited outside the mouth. Second, during low discharge offshore mud deposits are reworked by wave- and tidally-driven currents and some sediment is advected back into the estuary with the advancing salt intrusion that transports sediment landward. Third, spatial salinity gradients facilitate sediment transport from the main channel to channel margins, marshes and off-river coves where it is retained and deposited long-term, as demonstrated in prior studies. This re-introduction and trapping of recycled sediment under low-discharge conditions can have important implications for pollutant transport, shoaling of navigation channels and harbors, and salt marsh accretion in the face of rising sea levels. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Ice regime plays a significant role in River hydraulics and morphology in Northern hemisphere countries such as Canada. The formation, propagation and recession of ice cover introduce a dynamic boundary layer to the top of the stream. Ice cover affects the water velocity magnitude and distribution, water level and consequently conveyance capacity. A stable ice cover also tends to reduce bed shear and associated sediment transport, but bank scour and ice jamming events can increase sediment entrainment. These effects are even more intense during the ice cover break-up period when extreme conditions such as ice-jamming and release and mechanical ice cover break-up can locally accelerate the flow, and ice can mechanically scour the river bed and banks. The presence of ice has some important implications for hydro-electrical power generation operations too. The ice cover changes the channel conveyance capacity (and therefore increases the flood risk), may increase sediment transport and causes scouring, and is likely to block water intakes and turbines. The rate of water release should, therefore, be adjusted in the presence of the ice cover to avoid unwanted consequences on the dam structure and equipments as well as on the downstream channel and the environment. Even though the influence of ice cover on rivers is widely recognized, large gaps still exist in our understanding of ice cover processes in rivers. Two main reasons for such a shortage are the difficulty and danger involved in collecting hydraulic and sediment transport data under ice cover, especially during the unstable periods of freeze-up and break-up. In the absence of sufficient data, the applicability of available formulae and theories on hydraulic processes in ice-covered rivers cannot be extensively tested and improved. The purpose of this research mainly is a) to perform a continuous, in-situ monitoring of water velocity profiles, sediment loads and ice-cover condition during several years through winter field campaigns at a section of the Lower Nelson River, Manitoba, Canada.The Lower Nelson River is a regulated river (Manitoba Hydro). It receives augmented flow from the Churchill River Diversion, and is subject to operation of many hydro-electricity facilities, one of which is currently under construction, while others are planned to be constructed in the future. Due to the geographical location of the study reach, it is covered by ice and experiences severe ice condition for several months during the year. b) Analysis of the collected data in order to study the impact of ice cover on the hydraulic properties and sediment conveyance capacity at the study reach and c) using the insight gained from the field data analysis to improve a river ice simulation model to apply in the study of Lower Nelson River ice regime. The selection of the Lower Nelson river is motivated by intention of Manitoba Hydro (MH) ,as the industrial partner in this research, to study the winter flow regime at the Lower Nelson River. Manitoba Hydro operates several dams on the Lower Nelson River and is considering more hydropower developments in the future. This study is composed of six steps as are described in the following main steps. Step 1: Selection of potential study sites and data collection techniques: The particular study site for this research is located immediately upstream of Jackfish Island, between Limestone generating station and Gillam Island in Lower Nelson River, Manitoba, Canada. River width at the study site location is about 1km. Water depth at the deployment site varies between 10-12 meters depending on both the time of year and the time of day due to hydropeaking fluctuations. Given the low accessibility to the field during winter time and considering the type of the required data, acoustic techniques were selected as the main approach for the field measurements. Two types of acoustic instruments, Acoustic Doppler Current Profiler (ADCP) and Shallow Water Ice Profiling Sonar (SWIPS) are selected for field investigations in this study. Both of them were planned to be deployed in the river for an extended period of time in order to record necessary data during the ice cover and open water periods. Step 2: Data acquisition. After the site selection and defining the appropriate techniques, data acquisition has been started through a series of annual field measurement campaigns starting from winter 2012. Measured data mainly consist of water velocity and sediment suspension during various ice cover stages, including river ice break-up. The velocity profiles are analyzed to determine dynamic changes in boundary shear stress and hydraulic resistance and stresses in the flow during the both open water and ice cover periods. Step 3: Data analysis and development/testing of roughness and sediment transport formulas. Several aspects of river-ice interactions are covered in the recorded data including ice cover condition and cover thickness variation, river hydraulic characteristics such as depth and velocity and finally information about the concentration of suspended particles. These data are analyzed to define the behavior of the ice cover and river during different ice stages. Ice effect on river conveyance capacity is also evaluated . The accuracy of common assumptions in composite roughness calculations in rivers is estimated and a new approach is developed and validated using the field observations and measurements. Ice cover influence on suspended sediment concentration is also studied as the other part of this research. Considering the type of the river sediment load (mostly bed load) available methods for sediment transport simulation are studied and applied for estimation of the sediment transport under ice cover condition. According to the results, the most suitable methods were planned to be a part of the river ice numerical simulation model, developed in this study. Turbulent characteristics in ice covered flows are also studied through two years of data recordings. Acoustic Doppler Current Profiler employed in this study is programmed for appropriate recording of the water velocity for this purpose. Results are analyzed and turbulent structures in the river are studied in this research as well. Step 4: Testing of Hatch-MH’s river ice simulation model. A numerical model has been selected in order to simulate the river ice process at the study site (LNR). ICESIM, a steady state, one-dimensional river ice process model originally developed in 1973 by Acres International Limited (now Hatch), is selected for this study.ICESIM is originally developed in FORTRAN and is capable of predicting the progression and stabilization of river ice cover. Step 5: Improvement of Hatch-MH’s river ice simulation model: ICESIM model is converted to Matlab as the first step of the model improvements. A Graphical User Interface (GUI) is designed for the program which facilitates the assessment of model performance during the simulation leads to a more user-friendly model to operate. The new model, ICESIMAT is calibrated and evaluated based on the conducted field studies. Simulation capabilities of ICESIMAT are improved in the form of extended or additional subroutines to enhance its capabilities in the simulation of river ice processes and sediment transport. The current version of ICESIMAT is a steady state model, capable of simulating river ice , river hydrodynamic characteristics and sediment transport along the study reach. Though the model is restricted in the terms of the dimensions of the simulation (only one dimensional) its lower computational cost, permits a longer study reach to be simulated (in the scale of hundred kilometers instead of couple hundred meters in three dimensional simulation). ICESIM model is unable to simulate the break-up period which reduces the model capability in the simulation of the complete cycle of river ice. New subroutines are designed and added to extend the model capability to include simulation of ice processes during the ice cover break-up and finally to calculate the sediment transport under the ice cover. Step 6: As the final step, the new subroutines are adjusted and linked to the main improved code, providing a new framework for dynamic ice cover simulation, more prepared for further future improvements both in terms of conceptual and programming aspects of the river ice modeling . The new Matlab basis of the code facilitates upgrading the model to include more complicated processes like river ice jam simulations. As the general result of this thesis, we have a better understanding of hydraulics and sediment transport processes in ice covered rivers ( direct and indirect measurements of river hydraulics characteristics), improved formulas for these processes (including more involving parameters) and a better version of the river ice simulation model (capable of simulating the complete river ice processes) for the contributors to this study in the industry.