Thesis (Ph. D.)--University of Hong Kong, 1973.

No description available.

One of the most important aspects of coastal management and planning programs that needs to be investigated is shoreline dynamics. Long-term coastal analysis uses historical data to identify the sectors along the coast where the shoreline position has changed. Among the information that can be obtained from these studies are the general trend of coasts, either advancing or retreating. The erosion or accretion rates at each location can be used to forecast future shoreline positions. The current techniques used to study shoreline evolution are generally based on transects perpendicular to a baseline at selected points. But these techniques proved to be less efficient along more complex shorelines, and need to be refined. A new and more reliable method, the topologically constrained transect method (TCTM), was developed for this study and tested using data available for three sectors of the Texas Gulf Coast. Output data generated from TCTM also allowed performing shoreline evolution analysis and forecasting based on historical positions. Using topological constrained transects, this study provides a new method to estimate total areas of accretion or erosion at each segment of the coastline. Reliable estimates of future gains or losses of land along the coast will be extremely useful for planning and management decisions, especially those related to infrastructure and environmental impacts, and in the development of coastal models. Especially important is the potential to quickly identify areas of significant change, which eliminates the need for preliminary random sample surveying, and concentrate higher-resolution analyses in the most significant places. The results obtained in this research using the new methodology show that the Texas coast generally experiences erosion, with anthropogenic factors responsible for accretion. Accretion areas are located near coastal infrastructure, especially jetties that block the along shore sediment transport. The maximum erosion rate obtained in the study area is 5.48 m/year. This value helps make us aware of the powerful dynamic of the sector.

Das Studienziel war die Ermittlung der Effizienz von niedrig- bzw. hochkonzentrierten Fluoridpräparaten zum Schutz des Zahnschmelzes gegen Demineralisationen bzw. Erosionen. Es wurde das diagnostische Verfahren der quantitativen lichtinduzierten Fluoreszenz (QLF) angewandt, mit dem sich anhand der Eigenfluoreszenz des Schmelzes Demineralisationsveränderungen im Sinne einer Erosion noninvasiv quantifizieren lassen. Die Effizienz niedrigkonzentrierter Präparate wie Fluor Protector Gel (Gruppe A; 1450 ppm; IvoclarVivadent AG Schaan, Liechtenstein), Tooth Mousse Plus Gel (Gruppe B; 900ppm; GC Deutschland, München, Deutschland), Colgate Total Zahnpasta (Gruppe C; 1450ppm; Colgate-Palmolive, Hamburg, Deutschland) und einem hochkonzentrierten Präparat (Gruppe D; 12500 ppm; Elmex gelée; GABA Lörrach, Deutschland), sowie einer nicht behandelten Kontrollgruppe (Gruppe E) wurde in einem standardisierten, objektiven in-vitro-Aufbau miteinander verglichen. Eine Simulation nahrungsaufnahmebedingter Säureangriffe erfolgte durch das Aufbringen von 0,05 M Zitronensäure (pH=2,3; 6x/Tag) mit zwischenzeitlicher Lagerung in künstlichem Speichel. QLF-Messungen erfolgten zur Baseline (t0), sowie nach 3 Tagen (t1), 7 Tagen (t2), 14 Tagen (t3) und 30 Tagen (t4): Die erfassten Daten wurden nachfolgend analysiert: Für den globalen Vergleich der fünf Gruppen (A-E), als auch separat für jeden Zeitpunkt (Baseline und t(1)-t(4) wurde der Kruskal-Wallis-Test (α=5%) angewandt. Um herauszufinden, zwischen welchen Untersuchungszeitpunkten sich signifikante Unterschiede im Fluoreszenzverlust zeigen, wurden paarweise Vergleiche der Untersuchungszeitpunkte t(1)-t(4) mit der Baseline (t0) mittels Wilcoxon-Test innerhalb der fünf Behandlungsgruppen herangezogen. Es wurde ein Paarvergleich zwischen den Gruppen bzw. zwischen den Zeitpunkten mit dem Mann-Whitney-U-Test durchgeführt. Die Messwerte der erodierten Prüfkörper wurden als durchschnittlicher Fluoreszenzverlust (∆F) erfasst. Aus dem analysierten Fluoreszenzverlust (∆F) geht hervor, dass alle hier getesteten fluoridhaltigen Präparate unabhängig von der Höhe der Fluoridkonzentration eine ähnlich effiziente Schutzwirkung der Zahnhartsubstanz gegen Erosionen im Vergleich zur Kontrollgruppe besitzen: Es ist nach 30 Versuchstagen (t1-t4) kein signifikanter Unterschied innerhalb der einzelnen Fluoridgruppen ersichtlich. Eine signifikante Veränderung im Sinne einer Erosion war nur in der nicht fluoridierten Kontrollgruppe E zu verzeichnen. Schlussfolgernd ist an unfluoridiertem Zahnschmelz bereits innerhalb von zwei Wochen eine Demineralisation im Sinne einer Erosion zu erwarten. Eine Schutzwirkung kann sowohl durch die tägliche lokale Applikation von niedrigkonzentrierten Zahnpasten als auch durch die wöchentliche Anwendung eines hochkonzentrierten Fluoridpräparates erzielt werden,.

Univ., Diss.--Basel, 2001.

Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references (p. 58-59).

Data on erosion processes and other aspects of environmental change in the Himalaya are scarce and unreliable, and consequently policy decisions have been taken in a quantitative vacuum. Published estimates of denudation for large catchments in Nepal vary from 0.51 to 5.14 mm/yr, and indicate a dynamic geomorphological environment A review of the literature on erosion in Nepal revealed a consensus that: (1) mass wasting is the dominant hillslope process; (2) activity is seasonal, with virtually all failures occurring during the monsoon; (3) geological factors are the most important determinants of slope stability; (4) sediment delivery to channels is high; (5) little quantitative evidence exists to link landsliding to deforestation. Although few data exist, loss of forest cover does appear to be related to surface erosion and gullying, and a hypothesis linking the expansion of unmanaged, eroding areas to reduced nutrient subsidies from the forest is proposed. A reconnaissance survey of sediment production and transfer mechanisms in the 122 km² Phewa Valley in the Middle Mountains of Nepal identified a variety of mass movement processes. The commonest events were shallow translational failures on slopes of, typically, 36° to 45°, with volumes ≤1 x 10³ m³ and with recovery taking less than ten years. Larger slides occurred on slopes oversteepened by fluvial action. Flows developed in areas of weak rock and unfavourable structure, and were associated with groundwater discharge. Flow velocities accelerated during the monsoon. The highly fractured and deeply weathered zones around faults were the sites of "mass movement catchments", complex failures responsible for approximately 90% of all sediment production by mass wasting in the watershed. A first estimate of surface lowering by mass movement processes in the Phewa Valley is 2-3 mm/yr. Locally, surface erosion on overgrazed pasture may be 5-6 mm/yr. No data were available on soil losses from cultivated areas, and, similarly, losses due to shallow creep, gullying and solution remain unknown. The fluvial transport system in the valley bottom is unable to transport all the material with which it is supplied. Sediment yield to the lake was not calculated owing to insufficient data. Discharge estimates and intensity-duration-frequency analysis of rainfall records indicate that in Pokhara storms of 275 mm/day have a return period of approximately 10 years. The primary controls on mass movement processes in the Middle Himalaya of Nepal are geological and climatic, and therefore are not amenable to modification by man. However, surface erosion is a consequence of poor land management, and therefore can be controlled, given the right institutional environment / Forestry, Faculty of / Graduate

This research examines the use of remote sensing techniques to quantify rill erosion in two agricultural fields in the Lower Fraser Valley. Soil erosion during the winter is particularly problematic in some of the sloping soils developed from loess over glacio-marine parent materials. New techniques are needed to quantify rill erosion on a timely basis, and this research focuses on measuring the extent and rate of rill erosion from field and aerial photograph measurements. A model which used rill measurements as input, was used to determine the rill plan areas, rill volumes, and thus rill erosion rates in the test area. Using field rillometer measurements of rills as input into the model resulted in a soil loss estimate of 49m³ /ha/yr or 38.4 t/ha/yr for the test site. This soil loss estimate is deemed to be more reliable than erosion plot and Universal Soil Loss Equation estimates of soil loss for the test area. The rill volume and plan area of three main rills, using three different rill measurement methods for input into the model, were compared. Using field measuring tape measurements of rills as input into the model, resulted in a soil loss estimate which was 16 % greater than the estimate from rillometer measurements. Using photo rill width measurements and an estimation of rill depths and bottom widths from field data as model input, resulted in a soil loss estimate which was 22 % less than the estimate from rillometer measurements. Spectral reflection measurements made in rill, interrill and depositional areas were found to be significantly different, confirming that rill erosion could be assessed in a quantitative manner using digital image analysis techniques. The spectral separation was largely due to differences in organic matter, surface roughness and imaging geometry. The latter is of particular importance in creating darker shadowed rill sides opposite bright sun-facing rill sides within a single rill. A maximum likelihood classifier, used as part of the computer based image analysis, determined the rill plan area for a sample area to be 9 % less than the rill plan area obtained from the model using rillometer input. This indicates the potential of digital analysis to quickly determine the plan area of larger rills. Digital elevation and moisture content data confirmed that the topographic shape of the field is important in determining the spatial pattern of rill formation. The combination of such data with image analysis and geographic information systems (GIS) have great potential in the timely quantification of erosion in the future. / Land and Food Systems, Faculty of / Graduate

No description available.

No description available.