• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 18
  • 10
  • 4
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 45
  • 45
  • 9
  • 8
  • 8
  • 8
  • 7
  • 6
  • 5
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

An Integrated Wind Erosion Modelling System with Emphasis on Dust Emission and Transport

Lu, Hua, Mathematics, UNSW January 2000 (has links)
In this thesis, an integrated wind erosion assessment and prediction system has been developed. This system couples a physically based dust emission scheme, a high resolution limited area weather prediction model, a dust transport model, and a high resolution GIS (Geographic Information System) database. A simple expression for particle threshold velocity has been derived by considering the force balance of a single particle resting on the surface. Theoretical analyses have been performed to confirm that the main mechanism for dust uplifting is sand saltation bombardment rather than direct aerodynamic entrainment. A new model for dust emission by saltation bombardment is proposed and validated against experimental data. Preliminary sensitivity tests for the new dust emission model have been carried out by examining the dependence of dust emission rate on a range of parameters. The transport of airborne dust is modelled by using the particle mean concentration equation. The time-dependent advection terms are discretized and solved numerically by a multi-dimensional wave-propagation slope-limiter scheme. Some computational features of the integrated model are discussed in terms of its coupling, module decomposition, data handling and efficiency. A systematic sub-grid treatment is designed to extract soil surface parameters from the GIS database for large scale modelling. The integrated system is applied to investigate the February 1996 dust storms over the Australia continent. The simulated wind erosion pattern and intensity are in good agreement with available meteorological records and satellite images. It reveals that the system can be used to identify areas and periods under wind erosion threat as well as the responsible environmental factors.

Modelling Land Susceptibility to Wind Erosion in Western Queensland, Australia

Mr Nicholas Webb Unknown Date (has links)
No description available.

Bedload transport of mixed-sized sediments by wind /

Shaw, Susan Calder. January 1994 (has links)
Thesis (Ph. D.)--University of Washington, 1994. / Vita. Includes bibliographical references (leaves [227]-238).

Characterising and mapping of wind transported sediment associated with opencast gypsum mining /

Van Jaarsveld, Francis. January 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

The Factors Affecting Wind Erosion in Southern Utah

Ozturk, Mehmet 01 August 2019 (has links)
Wind erosion is a global issue and affecting millions of people in drylands by causing environmental issues (acceleration of snow melting), public health concerns (respiratory diseases), and socioeconomic problems (costs of damages and cleaning public properties after dust storms). Disturbances in drylands can be irreversible, thus leading to natural disasters such as the 1930s Dust Bowl. With increasing attention on aeolian studies, many studies have been conducted using ground-based measurements or wind tunnel studies. Ground-based measurements are important for validating model predictions and testing the effect and interactions of different factors known to affect wind erosion. Here, a machine-learning model (random forest) was used to describe sediment flux as a function of wind speed, soil moisture, precipitation, soil roughness, soil crusts, and soil texture. Model performance was compared to previous results before analyzing four new years of sediment flux data and including estimates of soil moisture to the model. The random forest model provided a better result than a regression tree with a higher variance explained (7.5% improvement). With additional soil moisture data, the model performance increased by 13.13%. With full dataset, the model provided an increase of 30.50% in total performance compared to the previous study. This research was one of the rare studies which represented a large-scale network of BSNEs and a long time series of data to quantify seasonal sediment flux under different soil covers in southern Utah. The results will also be helpful to the managers for controlling the effects on wind erosion, scientists to choose variables for further modeling or local people to increase the public awareness about the effects of wind erosion.

Dust emissions from undisturbed and disturbed soils: effects of off-road military vehicles

Xu, Youjie January 1900 (has links)
Master of Science / Department of Biological & Agricultural Engineering / Ronaldo G. Maghirang / Military training lands can be significant sources of fugitive dust emissions due to wind erosion. This study was conducted to determine dust emission potential of soils due to wind erosion as affected by off-road military vehicle disturbance. Multi-pass traffic experiments using two types of vehicles (i.e., wheeled and tracked) were conducted on six soil textures at four military training facilities: Fort Riley, KS; Fort Benning, GA; Yakima Training Center, WA; and White Sands Missile Range (WSMR), NM. Prior to and after the preselected number of vehicle passes, soil samples at three locations were collected with minimum disturbance into trays. Adjacent to the location where tray samples were collected, a Portable In-Situ Wind Erosion Lab (PI-SWERL) was used to measure dust emission potential. The tray samples were tested in a laboratory wind tunnel (with sand abrader) for dust emission potential using a GRIMM aerosol spectrometer and gravimetric method with filters. Comparison of the PI-SWERL (with DustTrak™ dust monitor) and wind tunnel (with GRIMM aerosol spectrometer) measurement results showed significant difference in measured values but high correlation, particularly for soils with high sand content. Wind tunnel tests results showed that sampling locations significantly affected dust emissions for the tracked vehicles but not for the light-wheeled and heavy-wheeled vehicles. Also, soil texture, number of vehicle passes, and vehicle type significantly affected dust emissions. For the light-wheeled vehicles, dust emissions increased as the number of vehicle passes increased. From undisturbed conditions to 10 vehicle passes, there was a significant (P<0.05) increase in dust emissions (297%) on average for all light-wheeled vehicle tests. From 10 to 25 passes and 25 to 50 passes, an additional 52% and 62% increments were observed. For the tracked vehicle, for the straight section sampling location, dust emission increased as the number of vehicle passes increased. However, for the curve section, dust emissions at any level of pass were significantly higher than initial condition; beyond the first pass, no significant increase was observed.

Use of bentonite to stabilize sandy soil material in a wind tunnel study

Diouf, Babou. January 1986 (has links)
Call number: LD2668 .T4 1986 D56 / Master of Science / Agronomy

Candidate halophytic grasses for addressing land degradation: Shoot responses of Sporobolus airoides and Paspalum vaginatum to weekly increasing NaCl concentration

Pessarakli, Mohammad, Breshears, David D., Walworth, James, Field, Jason P., Law, Darin J. 28 February 2017 (has links)
In many arid and semiarid regions worldwide, high levels of soil salinity is a key driver of land degradation, as well as a key impediment to re-establishing plant cover. Combating land degradation and erosion associated with soil salinity requires experimental determination of plant species that can grow in soils with high levels of salinity and can be used to re-establish plant cover. Herein, we evaluated the responses of untested candidate cultivars of two halophytic grass species to high soil salinity: alkali sacaton (Sporobolus airoides Torr.) and seashore paspalum (Paspalum vaginatum Swartz). We evaluated the growth responses of both species in a greenhouse under control (no-salt) and various levels of NaCl salinity (EC 8, 16, 24, 32, 40, and 48dSm(-1)) using Hoagland solution in a hydroponics system in a randomized complete block design trial. At all salinity levels, sacaton grass had a greater shoot height, shorter root length, lower shoot fresh and dry weights, and poorer color and general quality compared to seashore paspalum. The shoot fresh and dry weights of both grasses were greatest at the low to medium levels of salinity, with the greatest response observed at EC 16dSm(-1). At the highest level, salinity significantly reduced shoot fresh and dry weights of both grasses. Because growth of both halophytic species exhibited high tolerance to salinity stress and were stimulated under low to medium levels of salinity, both species could be considered suitable candidates for re-establishing plant cover in drylands to combat desertification and land degradation associated with high levels of soil salinity.

Studie zur Beurteilung des Winderosionsschutzes durch Erstaufforstung, Gehölzstreifen und Ackerbau im Nordraum Leipzig

Ziemann, Astrid, Arnold, Klaus, Schönfeldt, Hans-Jürgen 05 December 2016 (has links) (PDF)
In der vorliegenden Studie wird einerseits die Winderosion und der damit verbundene Sedimenttransport hinter ausgedehnten Waldgebieten, die in ihrer Zusammensetzung typisch für den Nordraum von Leipzig sind, und hinter schmalen Gehölzschutzstreifen untersucht. Als Ergebnis dieser Analyse lassen sich Empfehlungen für die günstigsten Eigenschaften von Windschutzanpflanzungen hinsichtlich einer maximalen Schutzwirkung vor Sedimenttransport ableiten. Andererseits wird die Häufigkeit möglicher erosiver Ereignisse am Beispiel einer für das Untersuchungsgebiet repräsentativen meteorologischen Station geprüft. Kritische meteorologische Randbedingungen für erosive Prozesse treten entsprechend einer statistischen Datenanalyse zweimal pro Jahr auf. / On the one hand, the wind erosion and the associated sediment transport behind extensive forest areas, which are typically for the northern area of Leipzig, and behind narrow shelterbelts were examined in this study. Recommendations for the favourable properties of such protective arrangements with reference to the maximal shelter effect against sediment transport follow from this analyses. On the other hand, the :frequency of the potential occurrence of erosion will be proofed by data of a representatively meteorological station. Critically meteorological conditions appear two times per year corresponding to the statistical analyses.

Fugitive dust emissions from off-road vehicle maneuvers on military training lands

Meeks, Jeremy C. January 1900 (has links)
Master of Science / Department of Biological and Agricultural Engineering / Ronaldo G. Maghirang / Military installations in the United States may be large sources of fugitive dust emissions. Off-road vehicle training can contribute to air quality degradation resulting from increased wind erosion events as a result of soil disruption; however, limited information exists regarding the impacts of off-road vehicle maneuvering. This study was conducted to determine the effects of soil texture and intensity of training with off-road vehicles on fugitive dust emission potential due to wind erosion at military training installations. Multi-pass trafficking experiments, involving wheeled and tracked military vehicles (i.e., M1A1 Abrams tank, M925A1 water tanker and various HMMWV models), were conducted at three military training facilities with different climate and soil texture (i.e., Fort Riley, KS; Fort Benning, GA; and Yakima Training Center, WA). Dust emissions were measured on site using a Portable In-Situ Wind Erosion Laboratory (PI-SWERL) coupled with a DustTrak™ dust monitor. In addition, a top layer of soil was collected in trays and tested in a laboratory wind tunnel for dust emission potential. In wind tunnel testing, the amount of emitted dust was measured using glass-fiber filters through high-volume samplers. Also, the particle size distribution and concentration of the emitted dust were measured using a GRIMM aerosol spectrometer. Comparison of the PI-SWERL (with DustTrak™ dust monitor) and wind tunnel test (with GRIMM aerosol spectrometer) results showed significant difference and little correlation. Also, comparison of the filter and GRIMM aerosol spectrometer data showed significant difference but high correlation. The dust emission potential (as measured with the GRIMM spectrometer) was significantly influenced by soil texture, vehicle type and number of passes. For the light-wheeled vehicle, total dust emissions increased from 66 mg m-2 for undisturbed soil to 304 mg m-2 (357%) and 643 mg m-2 (868%) for 10 and 50 passes, respectively. For the tracked vehicle, an average increase in total dust emission of 569% was observed between undisturbed conditions and 1 pass, with no significant increase in emissions potential beyond 1 pass. For the heavy-wheeled vehicle, emissions increased from 75 mg m-2 for undisturbed soil to 1,652 mg m-2 (1,369%) and 4,023 mg m-2 (5,276%) for 10 and 20 passes, respectively. Soil texture also played an important role in dust emission potential. For all treatment effects, there was a 1,369% difference in emissions between silty clay loam soil and loamy sand soil.

Page generated in 0.0573 seconds