In estuaries containing cohesive sediment, flocculation and break-up of the suspended particles during the tidal cycle has implications for the monitoring and modelling of sediment transport. Monitoring of suspended sediment concentration using in situ optical or acoustic instruments is problematic since the amount of light or sound scattered from the suspended sediment is proportional to both the suspended concentration and the size of the particles. Numerical sediment transport models are heavily reliant upon such concentration data. Particle size variation also directly affects model parameterisation by influencing the settling velocity. A critical review of current particle sizing techniques shows that in situ imaging offers the best option in terms of cost, accuracy and versatility. This thesis presents a new, low cost video-based instrument for measuring the in situ particle size distribution. The system uses two CCTV cameras to view a total size range of 4 to 3000 microm. Illumination is provided by miniature microsecond flash units. These allow blur-free images of particles to be obtained in current speeds of up to 1.4 ms-1, which are saved to hard disk at a frame rate of up to 10 s-1. The instrument package is designed for small-boat operation and deployment in profile mode. Calculation of size and shape parameters is accomplished in software using automated image-processing algorithms. An efficient and accurate edge coincidence technique is developed to detect in focus particles. Instrument performance is evaluated through a case study of the Blyth estuary (Suffolk, UK). Particle size data from a small reach of the estuary are presented for both a spring and neap tide. The process of flocculation is clearly shown, and a semi-empirical model of particle size variation is derived based on turbulent intensity and suspended sediment concentration. The modelled sizes are used to derive settling velocity data for a 2DH model of sediment transport using a simplified model of floe density. Model output is improved in comparison to using a fixed value of settling velocity. Two distinct particle size subpopulations are observed which affect both the settling velocity and the calibration of ADCP backscatter data for sediment concentration between flood and ebb. In addition, rapid resuspension of bed material at the beginning of the flood tide is successfully simulated using a two-layer bed model. It is concluded that the new instrument is a valuable aid to monitoring and modelling of sediment transport.

The movement of individual clasts over a water-lain gravel substrate is investigated in a series of flume experiments. The effects of three experimental variables (mobile clast size, flow condition and release pocket) on the characteristics of extracted transport parameters (step length, step velocity, pathway sinuosity and rest period) are examined using a novel facsimilie of a real gravel bed. As the mobile clast size is increased the mean step length and mean step velocity of individual steps increases. The sinuosity of individual pathways increases with mobile clast size. The release pocket, which determines the region of the substrate over which the clast can move, was also found to influence the transport parameters. In general, mobile clasts exhibit shorter step lengths and more sinuous pathways over substrates that have a number of large clasts present in the bed surface. The mean rest period was found to be dependent on the mobile clast size and the release pocket. Mobile clasts equal to and greater in size than the median (of the gravel substrate) exhibited longer rest periods when their pathways coincided with areas in which large obstacle clasts were present. In contrast, mobile clasts smaller than the median exhibited longer rest periods when their pathways coincided with areas devoid of the influence of large obstacle clasts. Examination of the tracer pathways identified a number of areas that operate as trap areas or transport routes for mobile clasts. Trap areas were identified in a number of different topographical locations, in both the of and upstream, on the stoss side of, large clasts. In general, compared to the rest of the bed, the trap areas exhibit lower than average streamwise velocities, mean vertical velocities away from the boundary and a dominance of turbulent structures away from the boundary. The ability of the trap areas to trap mobile clasts was found to decrease with increasing mobile clast size. Furthermore, this effect was found to be greater at stronger flows. In general, compared to the rest of the bed, the transport routes exhibit higher than average streamwise velocities, mean vertical velocities towards the boundary and a dominance of turbulent structures towards from the boundary. In total, these observations contribute to an understanding of the elementary parameters of transport and are therefore of substantial value to the future development of models that deal with the prediction of bedload transport rates and simulations of bedform development.

The primary purpose of this work was to study the morphological change of river-bed sediment surfaces over time using wavelet transform analysis techniques. The wavelet transform is a rapidly developing area of applied mathematics in both science and engineering. As it allows for interrogation of the spectral made up of local signal features, it has superior performance compared to the traditionally used Fourier transform which provides only signal averaged spectral information. The main study of this thesis includes the analysis of both synthetically generated sediment surfaces and laboratory experimental sediment bed-surface data. This was undertaken using two-dimensional wavelet transform techniques based on both the discrete and the stationary wavelet transforms. A comprehensive data-base of surface scans from experimental river-bed sediment surfaces topographies were included in the study. A novel wavelet-based characterisation measure - the form size distribution ifsd) - was developed to quantify the global characteristics of the sediment data. The fsd is based on the distribution of wavelet-based scale-dependent energies. It is argued that this measure will potentially be more useful than the traditionally used particle size distribution (psd), as it is the morphology of the surface rather than the individual particle sizes that affects the near bed flow regime and hence bed friction characteristics. Amplitude and scale dependent thresholding techniques were then studied. It was found that these thresholding techniques could be used to: (1) extract the overall surface structure, and (2) enhance dominant grains and formations of dominant grains within the surfaces. It is shown that assessment of the surface data-sets post-thresholding may allow for the detection of structural changes over time.

Most sedimentary deposits are inherently anisotropic due to their natural deposition in horizontal layers. This inherent anisotropy highlights the fact that the response of soils to loading is depending on both stress magnitude and its direction. Most of the field problems in geotechnical engineering are three-dimensional, and a soil is more likely to subject an anisotropic stress state (σ1 ≠ σ2 ≠ σ3), together with rotation of the principal axes. It is therefore essential that the soil behaviour under such realistic and general loading conditions is to be well understood, so that engineers can devise appropriate geotechnical design and analysis in practical situations. The Small-Strain Hollow Cylinder Apparatus (SS-HCA), developed by GDS Instruments Ltd. has been used to study drained anisotropic behaviour of sand under generalized stress conditions. In particular, the anisotropic stress-strain-strength characteristics, volume change behaviour, non-coaxiality and combined effects of α and b are studied. Three testing programs composed of two main types of stress paths (e.g. monotonic loading with different inclinations of the major principal stress and cyclic rotation of principal stress axes) were conducted. Inherently anisotropic behaviour of sands is clearly illustrated by deformation response that is strongly dependent on the loading direction in the monotonic shear tests. For a given loading direction, the mechanical response of sands is affected by the material density, the particle properties and the loading history. Non-coincidence of principal directions of stress and strain increment is observed and shear band inclinations in hollow cylindrical specimens follow the theoretical predictions. Results also clearly show the effects of intermediate principal stress on the deformation response of sand. This is seen in variation of stress-strain response and peak friction angle with differing b-values. A significant plastic deformation is induced during rotational shear despite the magnitudes of principal stresses remaining constant. Volumetric strain during rotational shear is mainly contractive and the amount of the volumetric strain increases with the increase in the stress ratio. Most of the contractive volumetric strain occurred during the first 20 cycles and its accumulation rate tended to decrease as the number of cycles increases. When principal stress rotation continues, the sand samples appear to be stabilized and the strain trajectory in the deviatoric plane approaches an ellipse. The test results also demonstrate that the mechanical behaviour of sand under rotational shear is generally non-coaxial, and the stress ratio has a significant effect on the non-coaxiality. The larger the stress ratio, the lower degree of non-coaxiality is induced. It was also observed that parameter b is not a negligible factor for the sand deformation during rotational shear, but has significant impact. The larger the b-value, the more the volumetric strain is accumulated.

Potentially harmful elements (PHEs) have been researched in a wide variety of disciplines, including pedology, chemistry, pollution science and medicine. Within the scientific community, emphasis has usually been placed on the toxic elements, such as cadmium, chromium, lead and arsenic, but rarely has there been consideration of interactions between PHEs, the sediment matrix and processes occurring in the sediments. Dredging of canals is needed for navigability purposes and consequently testing of dredged sediments (to assess whether sediments are hazardous) and landfilling can be costly for British Waterways facing constantly changing regulations and reduction in government grants. PHE mobility and availability in canal sediments can be affected by oxygen availability, pH and Redox. Remediation is thus becoming a priority for British Waterways to limit their operational costs. Zeolites, a type of remediation tool, have been widely studied in the past 30 years due to their attractive properties, such as molecular-sieving, high cation exchange capacities and their affinity for PHEs. The pilot study to investigate the efficiency of the clinoptilolite showed that there was a concentration difference between PHEs adsorbed by the clinoptilolite and the PHE concentration lost from the sediments from three sites in the West Midlands. Thorough characterisation of the sediments was needed to understand the speciation of the PHEs and the secondary processes occurring in the sediments. The different components of the sediments were analysed using various analytical methods, such as X-Ray Fluorescence spectroscopy (XRF), particle size and X-ray Diffraction (XRD) for the solid-inorganic phase, Ion Chromatography (IC) and Inductively Coupled Plasma-Optical Emissions Spectroscopy (ICP-OES) for the liquid phase (pore water), Gas Chromatography-Mass Spectrometry (GC-MS) and organic loss on ignition for the organic phase, pH and Redox for the electrochemistry of the sediments and Scanning Electron Microscope with Energy Dispersive X-Ray analysis (SEM-EDX) for microscopy and imaging. The British Geological Survey (BGS) sequential extraction method was used to investigate the different phases in the sediments. pH remained near neutral for all three sites and Redox remained anoxic. Organic contents for all three sites were around 30% and contained most of the polycyclic aromatic hydrocarbons considered hazardous. Pore water showed only high concentrations of sulphates but low concentrations of PHEs, suggesting PHEs were not mobile. Sequential extraction confirmed the other results showing that PHEs were mainly associated with stable phases, such as iron and manganese oxides or sulphides. The results have been taken into consideration to design a new remediation strategy to maximise efficiency of the zeolite.

Le but de cette thèse est d'étudier le transport et le dépôt de particules solides dans les écoulements à travers les fractures. Dans un premier temps, l'écoulement monophasique à travers les fractures est étudié afin d'évaluer la validité de la loi cubique locale comme modèle de l'écoulement. Des canaux à parois sinusoïdales à géométrie variable sont utilisés pour représenter différents types de fractures. Un premier développement analytique montre que l'ouverture hydraulique de la fracture diffère de son ouverture moyenne lorsque la rugosité des parois est élevée. La méthode des éléments finis est ensuite utilisée pour résoudre les équations de continuité et de Navier-Stokes et comparer les solutions numériques aux prédictions théoriques de la loi cubique locale sur une gamme relativement étendue de nombres de Reynolds Re. Pour de faibles Re, typiquement inférieurs à 15, la loi cubique locale décrit raisonnablement l'écoulement, surtout lorsque la rugosité et le déphasage entre les parois sont relativement faibles. Dans un deuxième temps, les écoulements chargés de particules sont étudiés. Une approche analytique est d'abord développée pour montrer comment des particules distribuées dans un écoulement stationnaire et laminaire à travers une fracture peuvent être transportées sur de longues distances ou au contraire se déposer à l'intérieur. Plus précisément, une équation simple décrivant la trajectoire d'une particule est établie. Sur la base de cette équation, il est démontré que, quand l'inertie des particules est négligeable, leur comportement dépend directement de la géométrie de la fracture et d'un nombre adimensionnel W qui relie la vitesse de sédimentation des particules à la vitesse moyenne de l'écoulement. L'équation proposée est vérifiée en comparant ses prédictions à des simulations numériques de suivi de particules prenant en compte l'inertie des particules et résolvent complètement les équations de Navier-Stokes. Il est montré que l'équation est valide lorsque l'inertie du fluide est faible. Des diagrammes de régimes, permettant de prévoir le comportement des particules à travers la fracture sont proposés. Enfin, un appareil expérimental conçu dans le but d'effectuer une évaluation pratique du modèle analytique est présenté et les résultats préliminaires sont discutés. Les résultats expérimentaux préliminaires tendent valider le modèle analytique. De façon plus générale, les résultats obtenus à travers ce travail de thèse font progresser nos connaissances du comportement des petites particules transportées dans les écoulements de fractures. Potentiellement, ce travail devrait permettre d'améliorer notre prévision de la pollution souterraine, et peut avoir des applications dans le développement de nouvelles techniques de filtration de l'eau et de séparation des minéraux / The aim of the present thesis is to study the transport and deposition of small solid particles in fracture flows. First, single-phase fracture ow is investigated in order to assess the validity of the local cubic law for modeling ow in corrugated fractures. Channels with sinusoidal walls having different geometrical properties are considered to represent different fracture geometries. It is analytically shown that the hydraulic aperture of the fracture clearly deviates from its mean aperture when the walls roughness is relatively high. The finite element method is then used to solve the continuity and the Navier-Stokes equations and to simulate fracture ow in order to compare with the theoretical predictions of the local cubic law for Reynolds numbers Re in the range 0.067-67. The results show that for low Re, typically less than 15, the local cubic law can properly describe the fracture ow, especially when the fracture walls have small corrugation amplitudes. For Re higher than 15, the local cubic law can still be valid under the conditions that the fracture presents a low aspect ratio, small corrugation amplitude, and moderate phase lag between its walls. Second, particle-laden flows are studied. An analytical approach has been developed to show how particles sparsely distributed in steady and laminar fracture flows can be transported for long distances or conversely deposited inside the channel. More precisely, a rather simple particle trajectory equation is established. Based on this equation, it is demonstrated that when particles' inertia is negligible, their behavior is characterized by the fracture geometry and by a dimensionless number W that relates the ratio of the particles sedimentation terminal velocity to the ow mean velocity. The proposed particle trajectory equation is verified by comparing its predictions to particle tracking numerical simulations taking into account particle inertia and resolving the full Navier-Stokes equations. The equation is shown to be valid under the conditions that ow inertial effects are limited. Based on this trajectory equation, regime diagrams that can predict the behavior of particles entering closed channel flows are built. These diagrams enable to forecast if the particles entering the channel will be either deposited or transported till the channel outlet. Finally, an experimental apparatus that was designed to have a practical assessment of the analytical model is presented. Preliminary experimental results tend to verify the analytical model. Overall, the work presented in this thesis give new insights on the behavior of small particles in fracture flows, which may improve our prediction and control of underground contamination, and may have applications in the development of new water filtration and mineral separation techniques