Experimental assessment of Athabasca river cohesive sediment deposition dynamics.

Polycyclic aromatic hydrocarbons (PAHs) originating from natural sources, and potentially from the Athabasca Oil Sands development, are of concern for the Athabasca River and Lake Athabasca delta ecosystems. In order to model the transport of fine sediments (and associated PAHs), it is important to describe the sediment dynamics within the river system. Flocs possess different settling characteristics compared to individual particles. A key aspect in modelling floc settling behaviour is the mathematical linkage of the floc density to floc size. In this paper, a rotating annular flume is used to determine the settling characteristics of Muskeg River (a tributary of the Athabasca River) sediments under different shear conditions. Simulations of the settling and flocculation behaviour of these sediments were used to calibrate a density vs. floc size model. A relationship of the parameters relating floc size and density with the fractal dimension F shows that as diameter increases flocs become weaker. Recommendations for the practical application of the model are further formulated in this paper. The deposition tests offer a quantitative measure of the relative amount of sediment that is likely to be transported through the river for given flow conditions.Para el rio Athabasca y los ecosistemas deltaicos del lago athabasca, los hidrocarburos Aromaticos policiclicos (HAPs) originados e fuentes naturales y potencialmente por los desarrollos de arenas bituminosas, son una amenaza. Para poder modelar el transporte de sedimentos finos (y HAPs asociados) es importante describir la dinámica de estos dentro del sistema. Los agregados (floculos) que se forman tiene caracteristicas de sedimentación diferentes a las partículas individuales. Un aspoecto importante para modelar la sedimentación de floculos es la relación matemática entre el tamaño de este y su densidad. En este articulo un canal rotatorio circular es usado para determinar las características de sedimentación de sedimentos del río Muskeg(un tributario del Athabasca) para diferentes condiciones de tasa de corte. Un modelo de densidad de los flóculos vs. tamaño de estos fue calibrado con las simulaciones de la sedimentación de esos sedimentos cohesivos. Una relación obtenida entre tamaño de flóculos, densidad y dimensión fractal F muestra que ha medida que su tamaño aumenta se vuelve mas frágil. Recomendaciones para la aplicación práctica del modelo se sugieren en el artículo. Los tests de deposito presentan una medida cuantitativa de la proporción de sedimentos que es posible que sea transportada por el río dada sus condiciones hidrodinámicas.Environment Canada, CONACY

Exploring bacterial pathogen community dynamics in freshwater beach sediments: A tale of two lakes

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154434/1/emi14860.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154434/2/emi14860_am.pd

Erosion characteristics and floc strenght of Athabasca river cohesive sediments: towards managing sediment-related issues

Purpose: Most of Canada’s tar sands exploitations are located in the Athabasca river basin. Deposited cohesive sediments in Athabasca river and tributaries are a potential source of PAHs in the basin. Erosional behavior of cohesive sediments depends not only of fluid turbulence but on sediments structure and particularly the influence of organic content. This research tries to describe this behavior in Athabasca river sediments. Methods: An experimental study of cohesive sediments dynamics in one of the tributaries, the Muskeg river, was developed in a rotating annular flume. Variation of the shear stress allowed the determination of erosional strength for beds with different consolidation periods. Particle size measurements were made with a laser diffraction device operated in a continuous flow through mode. Optical analyses of flocs (ESEM and TEM) were performed with samples taken at the end of the experiments. Results: An inverse relationship between suspended sediment concentration (SS) and the consolidation period was found. The differences are related in this research to the increasing organic content of the sediments with consolidation period. The particle size measurements during the experiments showed differences on floc strength that are also related to changing organic content during different consolidation periods. ESEM and TEM observations confirm the structural differences for beds with different consolidation periods. The effects of SFGL on floc structure and in biostabilization of the bed are discussed. Conclusions: It is recommended in this paper that consolidation period should be taken into account for the modeling of erosion of cohesive sediments in the Athabasca river. Relating to transport models of pollutants (PAHs) it is highly recommended to consider flocs organic content, particularly algae, in the resuspension module.Environment Canada, CONACY

Numerical Modeling Of Flow And Sediment Transport Within The Lower Reaches Of The Athabasca River: A Case Study

This study investigates flow and sediment transport patterns within the lower reaches of the Athabasca River (~250 km) in Alberta, Canada, which are characterized by complex bathymetry, regions of high tortuosity, and variable discharges and bed slopes. Sediment within this reach is primarily sand and gravel, but there is also a high percentage (\u3e10%) of cohesive clay with unique settling properties. A combination of 1D and 2D regional numerical modeling is used here to predict hydrodynamics of the flow and transport of suspended sediment. Bathymetry measurements were obtained from a combination of high resolution 3D Geoswath and ADCP surveys, and detailed 2D cross-section measurements. The 1D model solves the advection-diffusion equation for the cohesive sediment floc concentrations, and uses an explicit flocculation algorithm to calculate their distribution. Regional and high resolution local 2D numerical simulations are also completed using the Environmental Fluids Dynamics Code (EFDC) for the entire reach and a reach near Steepbank River (\u3c20 km) respectively. The high resolution local model helps in understanding the effects of coarse grid resolution and subsequently bathymetry resolution on the predictions. Validation of the model results is completed using field measurements including water surface elevations collected with Global Positioning System (GPS), water velocities collected using a Gurley current meter, and suspended sediment measurements obtained from the Regional Aquatics Monitoring Program

Development of novel 2D and 3D correlative microscopy to characterise the composition and multiscale structure of suspended sediment aggregates.

Suspended cohesive sediments form aggregates or 'flocs' and are often closely associated with carbo, nutrients, pathogens and pollutants, which makes understanding their composition, transport and fate highly desirable. Accurate prediction of floc behaviour requires the quantification of 3-dimensional (3D) properties (size, shoe and internal structure) that span several scales (i.e. nanometre [nm] to millimetre [mm]-scale). Traditional techniques (optical cameras and electron microscopy [EM]), however, can only provide 2-dimensional (2D) simplifications of 3D floc geometries. Additionally, the existence of a resolution gap between conventional optical microscopy (COM) and transmission EM (TEM) prevents an understanding of how floc nm-scale constituents and internal structure influence mm-scale floc properties. Here, we develop a novel correlative imaging workflow combining 3D X-ray micro-computed tomography (μCT), 3D focused ion beam nanotomography (FIB-nt) and 2D scanning EM (SEM) and TEM (STEM) which allows us to stabilise, visualise and quantify the composition and multi scale structure of sediment flocs for the first time. This new technique allowed the quantification of 3D floc geometries, the identification of individual floc components (e.g., clays, non-clay minerals and bacteria), and characterisation of particle-particle and structural associations across scales. This novel dataset demonstrates the truly complex structure of natural flocs at multiple scales. The integration of multiscale, state-of-the-art instrumentation/techniques offers the potential to generate fundamental new understanding of floc composition, structure and behaviour

Sediment-contaminant interactions and transport: a new perspective

Abstract This paper investigates the sediment structural controls over the transport and compartmentalization of Cd, Cu and Pb within flocculated sediments. The compartmentalization of contaminants within flocculated sediment particles demonstrates the complex underlying biogeochemical conttols of sediment contami nant interactions. The aims and objectives of the paper are to demonstrate (a) how the structure of suspended sediment particles will influence the transfer of metals within aquatic systems and (b) how the internal shoicture/composition of the particles promotes compartmentalization of metals in a selective manner

Spatial variability of the erodibility of fine sediments deposited in two alpine gravel-bed rivers: The Isère and Galabre

International audienceIn mountainous environments, high suspended sediment load during runoff or dam flushing events can lead to important amounts of fine deposits in gravel bed rivers. Fine sediment deposits may contribute to bar elevation, riparian vegetation growth and consequently to bar stabilization. Despite their contribution to the morphodynamic of mountain rivers, the erosion properties of fine sediments in this context is not fully understood.In order to investigate the dynamics of re-suspension of these deposits, field monitoring campaigns were performed to explore both the spatial variability and the controlling factors of the erodibility of fine deposits. A cohesive strength-meter (CSM), along with moisture, grain sizes, geographical position and elevation were used to evaluate both the critical bed shear stress for erosion and erosion rate of fine sediment deposits in two rivers of the French Alps: the Isère and Galabre.The results highlight a large variety of fine sediment deposition areas, which are discontinuous compared to those in estuaries and lowland rivers. A high spatial variability of erodibility was observed on the reach, the bar and the metric scale. While no upstream–downstream trend was observed at the scale of both studied reaches, the locations of the deposits, elevation from the river surface and their moisture were inter-related variables and with the highest correlations to erodibility. Measurements showed that both dry and humid deposits located at the highest and lowest elevation from the river surface respectively, were more easily eroded than intermediate deposits with medium moisture