Geomorphology

This study reports on as series of laboratory wind tunnel experiments aimed at furtheringour understanding of aggregate breakdown and dust release during aeolian transport, and thereby, has implications for air quality and the management of dust emission through water application. Particles aggregates 500 um in diameter were formed and isolated by the wetting, drying, and screening of playa sediments collected from Owens Lake. They were then released into a boundary-layer flow within the Trent Environmental Wind Tunnel (TEWT), whereupon they either slid, rolled and/or saltated downwind. The concentration of PM10 and the particle size of the aggregates were monitored throughout each test along the central axis of the tunnel. The results confirm that aggregate breakdown did occur, resulting in the production and emission of dust. The relative efficiency of aggregate abrasion in the production of silt sized particles during aeolian transport was calculated using normalized indices, providing a starting point for the modelling of similar systems in a natural setting. The results indicate that for every metre of transport, the abrasion of a 500 um aggregate formed from playa sediment may release a volume of dust roughly equivalent to that of a single silt particle that is 60 um diameter. Conversely, aggregate formation is found to produce 1-4% of dust as compared to an equivalent volume of disaggregated silt when exposed to a given airflow above the threshold for saltation.

Author Keywords: Aeolian abrasion, Aggregate breakdown, Owens Lake, PM10, Saltation, Wind Tunnel

A key knowledge gap in aeolian transport research concerns the adjustment of saltation processes to the extreme conditions found within high-latitude regions. A series of wind tunnel experiments were carried out under full climate control and over a wide range in humidity. Particle entrainment and transport within shearing flows of varied wind speed were monitored over beds of varied temperature, and ice content to determine their affect on 1) particle trajectory, 2) saltation cloud height, 3) particle velocity, 4) surface erosivity, 5) mass transport rate and 6) vertical dust flux. Particles were found to have higher velocities over cold beds than dry beds. With a 3% increase in bed moisture content, a significant increase in particle velocity was measured. Fewer particles are ejected from a bed with moisture than a dry bed. The mass transport rate was measured to be 23% higher at -10 degrees Celsius compared to 30 degrees Celsius.

Author Keywords: Aeolian processes

A wind tunnel study was conducted to investigate aeolian impact ripples in sand beds of varied texture from coarsely skewed to bimodal. Experimental data is lacking for aeolian megaripples, particularly in considering the influence of wind speed on ripple morphometrics. Additionally, the modelling community requires experimental data for model validation and calibration.

Eighteen combinations of wind speed and proportion of coarse mode particles by mass were analysed for both morphometrics and optical indices of spatial segregation. Wind tunnel conditions emulated those found at aeolian megaripple field sites, specifically a unimodal wind regime and particle transport mode segregation. Remote sensing style image classification was applied to investigate the spatial segregation of the two differently coloured size populations.

Ripple morphometrics show strong dependency on wind speed. Conversely, morphometric indices are inversely correlated to the proportion of the distribution that was comprised of coarse mode particles. Spatial segregation is highly correlated to wind speed in a positive manner and negatively correlated to the proportion of the distribution that was comprised of coarse mode particles. Results reveal that the degree of spatial segregation within an impact ripple bedform can be higher than previously reported in the literature.

Author Keywords: Aeolian, Impact Ripples, Megaripple, Self-organization, Wind Tunnel

This thesis presents a palaeotopographic reconstruction of the Burleigh Bay region of Stony Lake (Kawartha Lakes Region, Ontario) from 12,600 cal BP to present. The paleotopographic reconstructions are used to model paleoshoreline locations and archaeological site potential for the Late Paleoindian and early Archaic periods. Isostatic rebound following the end of the last glacial period has altered the topography in the region and water levels are now artificially managed by dams constructed in the 1830s. I completed a high-resolution bathymetric survey using a kayak equiped with a GPS coupled single-beam sonar. Utilizing GIS technology and isostatic rebound response surface models, I created paleotopographic reconstructions for 12,600 cal BP, 11,500 cal BP, 7,000 cal BP, 5,700 cal BP, and present. Results show that water levels in Burleigh Bay have been regressing over time until dam construction. Early site potential is centered in northern inland areas. Site potential following 7,000 cal BP is concentrated in northern areas flooded by the dam. Based on the reconstructions, surveys in lacustrine granite shield regions that follow the Ontario Standards and Guidelines for Consultant Archaeologists risk missing areas of high archaeological potential for early sites in these environments. Paleolandscape reconstructions would alleviate this issue by modeling paleoshoreline changes over time.

Author Keywords: Canadian Shield, Early Archaic, Isostatic Rebound, Kawartha Lakes, Late Paleoindian, Paleolandscape

Aeolian transport of sand particles is an important geomorphic process that occurs over a significant portion of the earth's land surface. Wind tunnel simulations have been used for more than 75 years to advance the understanding of this process; however, there are still several principles that lack validation from direct sampling of the sand particles in flight. Neither the three-dimensional dispersion of, nor the momentum carried by particles in flight have been properly measured. This has resulted in the inability to validate numerical particle dispersion models and the key boundary-layer momentum partitioning model that serves as the framework for understanding the air-sand feedback loop. The primary impediment to these measurements being made is a lack of tools suited for the task. To this end, this PhD aims to improve existing particle tracking technology, thus enabling the collection of particle measurements during wind tunnel experiments that would address the aforementioned knowledge gaps.

Through the design and implementation of the Expected Particle Area Searching method, a fully automated particle tracking velocimetry system was developed with the capability to measure within ½ grain diameter of the bed surface under steady state transport conditions. This tool was used to collect the first 3-D data set of particle trajectories, from which it was determined that a mere 1/8th of sand transport is stream aligned and 95% is contained within ± 45o of the mean wind direction. Particles travelling at increasing spanwise angles relative to the stream aligned flow were found to exhibit different impact and ejection velocities and angles. The decrease in the number of particles with increasing height in the saltation cloud, very close to the bed is observed to transition from a power to a linear relation, in contrast to previous literature that observed an exponential decay with coarser vertical resolution.

The first direct measurements of particle-borne stress were captured over a range of wind velocities and were compared with earlier fluid stress measurements taken using Laser Doppler Anemometry. In support of established saltation theory, impacting particle momentum is found to contribute strongly to particle entrainment under equilibrium conditions. In opposition to established theory, however, particle-borne stress was found to reach a maximum above the surface and does not match the change in air-borne stress with increasing distance from the surface. Near surface splashed particles, measured herein for the first time, appear to play a greater role in stress partitioning than previously thought. This study suggests that research is needed to investigate the role of bed load transport on stress partitioning, to differentiate between airborne trajectory types, and to develop particle tracking tools for field conditions.

Author Keywords: Aeolian Transport, Eolian Transport, Particle Tracking Velocimetry, Saltation, Stress Partitioning, Wind Tunnel Simulation