We investigate evolution of mountain channel morphology and riverbed surface roughness by conducting laboratory experiments. The experimental flume is 4m long by 0.1m wide with a working length of 2.5m. We control initial sediment size distribution, flume slope, water discharge, and sediment feed rate. Measurements include topographic profiles, flow depth, surficial grain-size distribution, sediment transport rate, and sediment size distribution. Experiments begin with a gravel bed of a broad sediment size distribution, at two initial flume slopes: 8.2% and 12.4%. Discharge is held constant until transport rates and topographic changes indicate the system is at near steady state. Coarse sand is then fed into the channel at 1,000 g/min as a means to perturb the system. Sediment feed is held constant until the perturbed bed reach steady-state conditions. The feed is subsequently ceased and measurements continue until sediment transport rates and topography stabilize. These laboratory experiments provide first-hand observations of channel systems evolving after perturbations. Transport rates decay exponentially following perturbations and remain very low when the channel bed is stabilized. The introduction of coarse sand acts to smooth the channel bed by filling in topographic lows in the 8.2% sloped channel. At a 12.4% slope, increased mobility of sand allows steady state conditions to be met with little smoothing of the bed. The sand also increases the mobility of coarser sediment that was previously stable, likely due to local surface smoothing at grain scale. The increased fraction of surface sand cover maintains increased scouring and mobilization of coarser grains. These post-perturbation mechanisms are interpreted to be responsible for topographic adjustments as the system readjusts towards new steady-state conditions. Surface sorting and transporting distributions reflect high sand fractions well after perturbations have ceased. This suggests that brief pulses of fine sediment can increase coarse sediment mobility for prolonged periods. / text

abstract / Earth Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / Geography and Geology / Master / Master of Philosophy

The objective of this research is to identify the circulation patterns of the water and sediment fluxes in coastal and estuarine zones, where the shoaling processes correlate with tide generating flow patterns. The research provides a better understanding of the characteristics of spatial and temporal variability of currents. An important deviation from previous research is the inclusion of the baroclinic term, which becomes very important in density driven flows. The understanding of this process provides a basis for determining how the water circulation three-dimensionally controls the hydrodynamics of the system and ultimately transports the suspended and soluble materials due to combined currents and waves. A three-dimensional circulation model is used to calculate the water circulation. The model is based on the three-dimensional (3D) version of Advanced Circulation (AD-CIRC) Hydrodynamic Model with extending the Sediment Transport module. The model is based on the finite element method on unstructured grids. The output of the hydrody-namic model is used to estimate spatial and temporal advections, dispersions and bottom shear stress for the erosion, suspension, deposition and transport of sediment. The model development includes extending the existing three-dimensional (3D) ADCIRC Model with (1) baroclinic forcing term and (2) transport module of suspended and soluble materials. The transport module covers the erosion, material suspension and deposition processes for both cohesive and non-cohesive type sediments. The inclusion of the baroclinic demonstrates the potential of over or underpredicting the total net transport of suspended cohesive sediment under influence of currents. The model provides less than 6% error of theoretical mass conservation for eroded, suspended and deposited sediment material. The inclusion of the baroclinic term in stratified water demonstrates the prevailing longshore sediment transport. It is shown that the model has an application to the transport of the cohesive sediments from the mouth of the Mississippi River along the north shore of the Gulf of Mexico towards and along the Texas coast. The model is also applicable to determine the design erosion thickness of a cap for isolating contaminated dredged material and to evaluate the appro-priate grain size of cap sediments to minimize the erosion.

Bed load transport measurements were made in a small urban stream in Decatur, GA, from which thresholds for motion were calculated using methodologies from the published literature. These methodologies are discussed in terms of their limitations and assumptions. Mobility frequencies were calculated for single grains of each grain size fraction to illustrate the transition from size selective transport to equal mobility. In general, urban streams behave differently than many gravel rivers in non-urban settings because of differences in the availability and character of sediment sources and altered flow hydrographs. This comparison allows for discussion about the way sediment is transported in urban streams versus typical gravel-bed, armored channels.

No description available.

An understanding of the clogging of fine sediments within gravel substrates is advanced through the use of dimensional analysis and macro-analysis of clogging experiments in hydraulic flumes. Dimensional analysis is used to suggest that the dimensionless clogging depth can be collapsed using the original and adjusted bed-to-grain ratios, substrate porosity, roughness Reynolds number, and Peclet number. Macro-analysis followed by statistical analysis of 146 experimental test results of fine sediment deposition in gravel substrates suggests that the dimensionless clogging depth can be collapsed using the substrate porosity and roughness Reynolds number reflecting the processes of gravity settling and turbulence induced fluid pumping between substrate particles. In addition, a clear cutoff of fine sediment unimpeded static percolation and sediment clogging is found using the adjusted bed-to-grain ratio. Thereafter, a physics-based approach is used to predict the clogging depth of fine sediment in gravel and in turn approve upon the preliminary findings in the empirical analysis. A momentum-impulse model that accounts for the critical impulse of a particle bridge is balanced with a fluid pulse resulting from turbulent pumping. The momentum-impulse model reduces the number of unknown parameters in the clogging problem and increases the model predictability as quantified using k-fold validation and model comparison with the empirical approach. A nomograph derived from applying the momentum-impulse model is provided herein, which will be useful for stream restoration practitioners interested in estimating embeddedness. Also, prediction of the clogging profile is shown using the clogging depth predicted with the momentum-impulse model.

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.

Graduation date: 2000

Emergent spatial signals which may be interpreted in the context of fluvial sediment transport processes are detected through the use of reflectance spectroscopy in the sand-sized sediments of the Towamba River, southeastern New South Wales. Reflectance spectroscopy of sufficiently fine spectral resolution represents a technique for mineral composition analysis which is complementary to X-ray diffraction, with advantages in terms of ease of sample preparation and rapidity of measurement. Instrumentation is available allowing high-quality spectrum acquisition in the field and from airborne and satellite-borne instruments. The former allows mineral analyses to more easily be incorporated into sediment tracing studies as an additional variable. The latter offers large scale, repeatable areal coverage of a dynamic system in which sediments are exposed to the sky. The Towamba River drains a catchment of c. 1000 km [square] in extensively altered granitic terrain along the south coast of New South Wales, and carries significant quantities of sand-sized sediment through much of the system. Pervasive but spatially variable chlorite, epidote, and sericite have been described in local and neighbouring terrain. These are spectrally active in the SWIR wavelength region in which the PIMA portable spectrometer operates. The airborne HyMap instrument is sensitive through this range as well as through the visible and near-infrared regions. Conventionally such channel sediments would represent a single class in the context of the broader landscape, and comparatively they represent a domain of restricted variance. In this study of samples of sediment were collected for analysis with the PIMA, the results of which supported the efficacy of such an exercise in a conventional tracing context and supported analysis of HyMap imagery. Although issues related to reduction of HyMap-detected radiance to reflectance prevented effective analysis of the shorter wavelengths sensitive to the presence of ferrous and ferric iron, the consideration of absorption feature depths and the application of a matched filtering operator revealed gross-scale spatial patterns which were interpreted as two populations of sand in the main channel. This interpretation is consistent with bank erosion occurring during two very large magnitude flow events in the 1970s, with minor ongoing perturbation of the sediment signal in the main channel by the contribution of sediment from tributaries. The presence of a definite spatial signal having been established, routes for further investigation are suggested. A noisy signal hypothesised on the basis of imagery may be used to better direct a field sampling program for a conventional sediment tracing study. The signal to noise ratio may be improved for example through calibration of radiance to reflectance and removal of atmospheric interference and improved field sampling schemes, after which more rigorous, quantitative exercises such as geostatistical ???field??? trial or spatial series analysis may be performed. Connections to process through sediment transport models are enabled through the use of GIS.