The main objective of this research was to create a two dimensional and three dimensional Environmental Fluid Dynamics Code (EFDC) model using Aberdeen Pool of the Tennessee-Tombigbee Waterway for the purpose of determining the differences in their ability to address sediment transport. These objectives were reached in the results with comparisons of water levels, sediment concentrations, shear stress, and bed change. The models produced very similar results for the majority of the sediment transport throughout both models with the overall trend being deposition except in the upper limits of the Tombigbee River. The main differences between the two models are produced from the 2D model being depth averaged and the 3D being able to transport sediment vertically. The results show the 2D model tends to erode less and deposit more whereas the 3D model tends to follow the same pattern except for less deposition with more erosion.

Sediment is a leading contributor to nonpoint source (NPS) pollution in streams and rivers. Sources and sinks of sediment movement were identified for a 121-hectare watershed located in Webster County, Mississippi in order to evaluate the impact of forest harvesting on water quality and sedimentation rates. In a completely randomized design containing three replications of two treatments (unharvested vs. harvested) and two slopes (≤9% vs. >9%), twelve sub-watersheds were randomly selected for intensive measurement of the sources and sinks of sediment after precipitation events. In-stream, bank and forest road sediment movement were also monitored pre- and post-harvest. Total suspended sediment (TSS) in runoff from forest roads ranged from 36-188 g/L with a consistent trend of decreasing sediment concentrations with increasing distance from the road. Within the watershed, erosional processes dominated however there was little net change in soil elevation one year post-harvest.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Vita. / Bibliography : leaves 138-142. / Ph.D.

Yes / In the research on environmental hydraulics, its turbulence and sediment transport, constant challenges have been faced. The complexity of hydraulic impacts towards sediment morphology and turbulent flow properties makes research in this area a difficult task. However, due to pressure from climate change and the mounting issue of pollution, environmental flow studies are more crucial than ever. Bedforming within rivers is a complex process that can be influenced by the hydraulics, vegetated field, and various suspended and bedload transports. Changes in flow conditions due to rain and flood can further complicate a hydraulic system. To date, the turbulence, morphologic, and bedforming characteristics of natural environmental flows are still not well understood. This book aims to bring together a collection of state-of-the-art research and technologies to form a useful guide for the related research and engineering communities. It is useful for authorities and researchers interested in environmental and civil engineering studies, as well as for river and water engineers to understand the current state-of-the-art practices in environmental flow modelling, measurement and management. It is also a good resource for research, post-, or undergraduate students who wish to know about the most up-to-date knowledge in this field.

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This thesis investigates the influence of bed material shape on sediment transport in gravel-bed rivers. The approach involves a combined series of field and laboratory experiments. Magnetic tracing experiments were carried out at three experimental sites in two Pennine gravel-bed streams. The specific aim of these experiments was to quantify the selective transport of different shapes of coarse river gravel and determine their spatial sorting within a natural stream channel. A total of 900 tracers in three size groups (32- 64 mm, 64-128 mm and greater than 128 mm) and four shape classes (spheres, blades, rod and discs) were prepared for each of the three sites. In die laboratory, tilting table experiments were carried out to clarify the mechanistic behaviour of different particle shapes, sizes and orientations on a variety of artificial and naturally formed bed roughnesses. Using strobe-light photography visualization experiments were undertaken with natural and artificially-moulded gravel-size particles of differing shape, size and weight in order to investigate the influence of shape on settling, grain impact, initial motion and transport paths of gravel-size particles. Results of the magnetic tracing experiments showed that there was both size and shape selectivity in bedload transport. Preferential movement occurred in die small and medium particle size classes with tracers concentrated along the channel thalweg. Sphere-shaped particles were transported the greatest distance and in greatest numbers. Rods also moved preferentially, while discs showed a lesser degree of transport and blades hardly moved at all. Results from the tilting table experiments highlight the importance of roundness as well as particle form and particle orientation in continuing thresholds of entertainment. In terms of size, friction angle was found to depend on the ratio of the diameter of the test particle to be moved to that it rests upon (d/D). Shape and orientation were found to be important parameters influencing friction angles. On a given bed roughness and for a constant size non-spherical test particles showed greater friction angles than spherical ones. A very clear difference was found in friction angle distibutions between sphere, transverse rod and other flat-shaped particles, namely, blades with parallel and transverse orientations, disc, and rod with parallel orientations. Visualisation experiments indicated that shape is an important particle characteristic that has a significant effect on settling rates and also the mode of near bed transport. These effects increase with greater particle sizes. The departure of a particle from a sphere leads to a decrease in its settling velocity, Experiments, across a range of test sizes showed that when compared to a sphere of equivalent weight and density, sphere and rod-shaped particles tend to settle the fastest and move by rolling. Discs and blades showed slower settling rates and, in most instances, moved by sliding. Experiments carried out with irregularly-shaped, natural particles show greater variability in settling behaviour and irregular patterns of motion. For every size group, sphere and rod shaped particles have lower critical angles of initial motion flian blade and disc-shapes. Regardless of shape, greater bed roughness, or decreasing particle size results in an increase in the critical angle for motion.

Particle Image Velocimetry, Laser Induced Fluorescence, pressure transducers and wetting front digital image measurements were made for two steep immobile beaches with different roughness and permeability (1.5mm and 10mm sediment).  The experimental results proved valuable in revealing the interaction mechanisms between the swash and the subsurface flow, in particular, showing the significant role of entrapped air.  The comprehensive dataset was used for the development and validation of a numerical model of swash consisting of a surface and subsurface flow model. The surface flow model, capable of simulating the movement of a steep bore over a permeable coarse-grained beach, is based on the non-linear shallow water equations solved using the Godunov-type finite volume ADER scheme.  The subsurface flow model simulates the vertical movements of the wetting front and the horizontal movement of air and groundwater within a beach.  Vertical movement is simulated as downwards or upwards piston-like flow, with the drag term parameterised by the Forchheimer equation.  Air and groundwater flow are simulated using simple Darcian modules. The experimental and numerical results reveal the distinctly different behaviour of filtration and pressure within the beach for the two types of sediment.  The considerable build-up of air pressure, induced by entrapped air below the wetting front in the unsaturated region of the 1.5mm sediment, minimise the loss of surface water to the beach by reducing infiltration rates.  Moreover it causes the flow within the bed to reverse and induce exfiltration.  Conversely, the build-up of air pressure in the 10mm beach is considerably lower, resulting in higher infiltration rates and a greater exchange of water from surface flow to the subsurface.

Modeling sediment erosion is important in a wide range of environmental problems. The effects of various environmental factors on erosion rates have been studied, but the effects of surface slope on erosion rates of a wide range of sediments have not been quantified. The effects of surface slope, both in the direction of flow (pitch) and perpendicular to the flow (roll), on erosion rates of quartz particles were investigated using the Sediment Erosion at Depth Flume (Sedflume). / US Navy (USN) author.

Thesis advisor: Gail C. Kineke / This study characterizes the bed of the Connecticut River estuary in terms of grain size and bedforms, and relates these to river discharge, tidal currents, and sediment transport. Over four field excursions, sediment cores were collected, in addition to bathymetry surveys, and water column measurements. A three-dimensional circulation and sediment transport model calculated boundary shear stress over the same time. The bed of the estuary is composed mostly of sand, with small amounts of fine sediments. Deposition of fine sediments is limited by the landward extent of the salt intrusion. Large bedforms are oriented seaward. The critical shear stress for the median grain size is exceeded each tidal cycle. Bedload transport is dominantly seaward during high discharge conditions, but varies during low discharge. Bathymetry surveys from previous studies and this study show consistent bedform fields over 25 years. Bedforms observed in the field reflect typical conditions rather than extreme events. / Thesis (MS) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.