Cette thèse traite de la forme et de la mobilité des dunes dans l’eau sous un écoulement turbulent. L’état d’équilibre des dunes en régime stationnaire puis le retour à l’équilibre après un changement de sens de l’écoulement sont caractérisés. On examine la variation des paramètres de forme (hauteur, longueur, rapport d’aspect) et de la vitesse de migration des dunes en fonction de la masse du sédiment m0 et de la vitesse de l’écoulement. Cette étude est menée expérimentalement dans un chenal fermé et étroit et les résultats sont comparés aux prédictions d'un modèle de dunes 2D tenant compte du processus de relaxation du transport. À l’équilibre, ce modèle prédit suivant la masse de la dune un régime « petite dune » et un régime « grande dune » où la hauteur est proportionnelle respectivement à m0 et à √m0. Un régime de transition où la hauteur est fonction de m0 à une puissance comprise entre 0,5 et 1 les sépare. Ces régimes sont identiques à ceux prédits par le modèle de Kroy et al. (2002) pour les barkhanes éoliennes. Expérimentalement, seuls les régimes de transition et « grande dune » sont observés. Cet accord permet d’évaluer la longueur de saturation du transport. Le résultat obtenu est cohérent avec la longueur de dépôt proposée par Lajeunesse et al. (2010). Pour le retour à l’état d’équilibre suite au changement du sens de l’écoulement, deux scénarios transitoires sont observés. Le premier est une contraction suivie d’une élongation de la dune. Le second présente une contraction supplémentaire liée à une élongation de la dune au-delà de sa longueur d'équilibre initiale. Dans ces deux cas, le temps de retour à l’équilibre n’est pas proportionnel à la masse de la dune. / This thesis deals with the morphodynamics of subaqueous dunes under a turbulent flow. The equilibrium State of the dunes under stationary flow, and then the return to equilibrium state after a change in the flow direction are characterized. The variation of the shape parameters (height, length, aspect ratio) and the migration speed of dunes are examined as a function of the mass m0 of sediment and the flow rate. This study is conducted experimentally into a narrow, closed flume and the results are compared to predictions of a 2D dune model that takes into account the transport relaxation process. For steady dunes, this model predicts a "small dune" and a "large dune" régime where the dune height respectively increases as m0 and √m0. These regimes are separated by a transitional régime where the dune height is proportional to m0 with an exponent ranging from 0.5 to 1. These régimes are identical to those predicted by the model of Kroy et al. (2002) for æolian barchans.Experimentally, the steady dunes range from the “transition” to the "large dune" régime as the mass increases. This agreement allows to assess the saturation length of the transport. The result is consistent with the deposition length proposed by Lajeunesse et al. (2010). Concerning the return to the steady-state shape after changing in the flow direction, two transient scenarios are identified. The first one is a contraction followed by an elongation of the dune shape. In the second one, there is an additional contraction phase associated with an elongation of the dune beyond its initial equilibrium length. For either scenarios, the return-to equilibrium time is not proportional to the mass of the dune.

The dune field at White Sands, New Mexico, shows a well-defined pattern of dunes and interdune areas, as well as spatial variations in this pattern. The purpose of this research is to determine which measured pattern parameters are most consistent across the dune field and to determine the cause of depositional spatial variability. This was accomplished using an airborne LiDAR generated digital-elevation model (DEM) collected in June 2007 and covering 39 km² of the dune field. Properties of the dune field are defined by measurements from three dune populations: 1) 110 randomly selected dunes, 2) 247 dunes along transects oriented in the net transport direction, and 3) 171 dunes from three zones within the field where differences in pattern are visible. Measurements of eight common dune parameters show that the lowest coefficients of variation occur with dune orientation and crestline sinuosity, which largely define the field pattern. Cross-plotting of parameters shows generally poor correlations, which is thought to reflect variation around field-scale means that are comparable to other dune fields globally. Removing the dunes from the LiDAR DEM reveals a depositional substrate with breaks in slope interpreted as three paleoshorelines associated with Pleistocene Lake Otero. The paleoshorelines are antecedent boundary conditions that exert the primary control on spatial variability within the dune pattern. / text

Thesis (M. Sc. (Botany))--Rhodes University, 2000.

Thesis (M.A.)--Humboldt State University, 2006. / Includes bibliographical references (leaves 36-38). Also available via Humboldt Digital Scholar.

The succession on the dunes of the Mlalazi Nature Reserve represents a classical example of primary succession. The reproductive strategies of eight key species were compared to determine some of the mechanisms affecting the community dynamics, at the population level, in the early stages of succession. There is a temporal separation in the flowering and fruiting phenologies. Passerina rigida, Stipagrostis zeyheri and Imperata cylindrica produced small seeds with a low fruit/seed mass ratio within a short cycle. The seeds are suitable for wind-dispersal. The animal-dispersed species; Eugenia capensis, Mimusops caffra and Scaevola plumieri, produced large fleshy seeds with a high fruit/seed mass ratio within cycles of six months and more. Chrysanthemoides monilifera, also an animal-dispersed species, produced a large quantity of small fleshy seeds throughout the year. The fern, Microsorium scolopendrium produced spores throughout the year. The staggered fruiting and flowering phenology ensures a year-round availability of fruit in the dunefield. The key species formed less than half of the species composition of the soil seed bank. The size and range of the soil seed bank differed between the species. P. rigida and S. plumieri formed a high proportion of the seeds in the soil with a wide distribution along the successional gradient. The other species had low soil seed densities with short distribution ranges, or were not present. P. rigida and S. plumieri are easily dispersed species, whereas the other species may have a more restricted and clumped distribution due to the effect of foragers. A high density of P. rigida and E. capensis seeds were found under the parent trees. Only seeds of P. rigida and S. zeyheri were found in the soil in the open. Seeds of P. rigida, S. zeyheri, E. capensis and M. caffra were found under the canopies of P. rigida, E. capensis and M. caffra. No seeds of C. monilifera and I. cylindrica were found in the soil, possibly due to predation. The period of the study (September 1991 to November 1992) was in a dry or drought cycle with only 56.8% of the mean annual rainfall falling. Seed germination and seedling survival of all the species were affected by these dry, warm climatic conditions. The species had seedling densities of less than 4 seeds/m². The environmental conditions along the successional gradient also had an effect on seed germination and seedling survival. Environmental factors of soil pH, light intensity and surface soil temperatures were higher in the open than under canopy. Soil pH and the understorey cover decreased as the light intensity decreased from under the canopy of P. rigida to M. caffra . Litter cover and plant height increased. E. capensis had measurements intermediate to the two species, but had higher surface soil temperatures and plant height than P. rigida. Seedlings of P. rigida in the open and under the canopy of the parent plants had died by the end of the monitoring period. 50% of the seedlings of S. zeyheri under the canopy of P. rigida and M. caffra died. The mortality rate of the seedlings of E. capensis was lower under M. caffra than under the parent plants. I. cylindrica may be propagated vegetatively. However, the mortality of the propagules was greater under the canopy of E. capensis than under P. rigida. M. caffra only germinated under the canopy of E. capensis with a 100% mortality of the seedlings. M. scolopendrium only produced propagules through vegetative propagation under the canopy of E. capensis and M. caffra. The mortality of the young ferns was less than 50% and less under M. caffra than under E. capensis. No seedlings of C. monilifera or S. plumieri were found. The seed distribution range, seed germination requirements and the effect of the environmental conditions on the germination of the seeds and seedling establishment of the species appear to important factors of the reproductive strategies regulating the size of the species populations along the successional gradient.

Le projet WA105/ProtoDUνE-DP est une expérience de prototypage qui a pour objectif de tester la technologie de Chambre à Projection Temporelle à Argon Liquide Diphasique (DLArTPC) à grande échelle dans le but de l'utiliser dans la future expérience de physique des neutrinos DUνE. Prévue fin 2026 aux USA, DUνE vise à déterminer l'ordre des masses des neutrinos ainsi que la violation de CP dans le secteur leptonique. Le travail de cette thèse s'oriente dans un premier temps autour des tests et simulations effectués sur les éléments de détection et d'amplification des détecteurs de WA105. Dans un second temps, la thèse s'oriente autour de l'analyse des traces de muons cosmiques vues par un premier prototype de 4t, opéré en 2017 au CERN. La technologie DLArTPC est une variante de la technologie LArTPC permettant une amplification des électrons extraits de la phase liquide à la phase gazeuse. Les amplificateurs d'électrons (LEMs) sont des plaques de PCB de 50x50cm² épais de 1mm, percés de 400k trous de 500 microns de diamètre, recouvertes de chaque côté par une mince couche de cuivre. Une différence de potentiel de l'ordre de 3kv permet d'atteindre un gain supérieur à 10. Une partie du travail de cette thèse a consisté à simuler la dérive des électrons à travers ces LEMs afin d'étudier les efficacités de collection de charge. Une autre partie de cette thèse a consisté à mesurer les caractéristiques importantes (épaisseur, tenue en tension) des amplificateurs destinés au démonstrateur de 300t de WA105, dont la mise en route a été effectuée fin août 2019 au CERN. Le gain est une des caractéristiques principales d'une DLArTPC, et il a été étudié dans le prototype de 4t grâce à la détection de muons cosmiques. Des comparaisons sont effectuées avec les résultats d'un prototype de 3L datant de 2014, et un programme de reconstruction de trace dédié a été développé pour traiter certains événements bruités. Le travail effectué dans cette thèse a permis de mieux comprendre le fonctionnement des DLArTPCs, notamment en ce qui concerne l'aspect multiplication et dérive des électrons. Ces connaissances seront importantes lors de l'opération du démonstrateur de 300t au CERN, ainsi que lors de l'exploitation du module DLArTPC de DUνE. / The WA105/ProtoDUνE-DP project is a prototyping experiment which goal is to test the Double Phase Liquid Argon Time Projection Chamber (DLArTPC) technology at large scale, to use it in the future neutrinos physics experiment DUνE. Scheduled for the end of 2026 in the USA, DUνE aims at measuring the neutrinos mass ordering and the leptonic CP symetry violation. The first part of this thesis is dedicated to tests and simulations of the detection and amplification elements of the WA105 detectors. The second part is focused on the analysis of cosmic muon tracks seen by a first prototype of 4t, operated at CERN in 2017. The DLArTPC technology is a variation of the LArTPC technology allowing for the amplification of the electrons extracted from the liquid phase to the gas phase. The Large Electron Amplifiers (LEMs) are 50x50cm² PCB plates with a thickness of 1mm, pierced by 400k holes of 500 microns diameter, covered on each side by a thin layer of copper giving a gain superior to 10. Part of this thesis work is about the simulation of electrons drifting through those LEMs to study the charge collection efficiencies. Another part of this thesis is about the measurement of important caracteristics (thickness, voltage stability) of the LEMs that are used in the 300t demonstrator of WA105, which commissionning was done in the end of August 2019. The gain is one of the main caracteristics of a DLArTPC, and it has been studied in the 4t prototype by detecting cosmic muons. Comparisons are done with previous results from 2014 from a smaller prototype of 3L, and a dedicated reconstruction program was created to analyse noisy events. The work done in the thesis allowed for a better understanding of DALrTPCs, mainly on the multiplication and drift of electrons. This knowledge will be important during the operation of the 300t demonstrator at CERN, and during the operationg of the DLArTPC module of DUνE.

The Guadalupe Nipomo Dunes Complex (GNDC) is located within the California Floristic Province, a biodiversity hotspot characterized by high rates of endemism and exceptional loss of habitat. In 1980, the US Fish and Wildlife Service described the GNDC as, “the most unique and fragile ecosystem in the State of California,” and ranked it first on a list of 49 habitat areas needing state protection. It is the largest coastal dune area in California and it is one of the last remaining, relatively intact ecosystems of its type and size in the western United States. The growing recognition of species decline and the limited number of dollars allocated to conservation and restoration have led to development of new conservation planning software and conservation strategies. Marxan and Zonation were selected for this project due to their worldwide acceptance in biodiversity conservation planning as well as their specialization in identifying priority zones for conservation. This document describes the unique use of conservation planning software to select areas for resource allocation. It outlines the process of selecting conservation targets, the habitats and species important to overall health of an ecosystem, by using the expert involvement approach. Most importantly, this document outlines areas of high biodiversity that will later be used to allocate resources for the preservation and protection of biodiversity within the Guadalupe Nipomo Dunes Complex. Introduced species are the second-leading cause (after habitat degradation/loss), causing or contributing to the decline in species abundance and diversity. Ehrharta calycina Smith has become highly invasive in the coastal dune communities of Central and Southern California and currently holds a “high” CAL-IPC inventory rating, defined as a species with severe ecological impacts on physical processes, plant and animal communities and vegetation structure as well as reproductive biology and other attributes conducive to moderate to high rates of dispersal and establishment. Ehrharta calycina is a prolific seeder and stores its seeds annually in the soil, collecting a substantial seedbank. Little is known about E.calycina outside its native range, as its invasion into California coastal ecosystem is fairly recent. A field experiment in the Guadalupe Nipomo Dunes Complex assessed the contribution of seeds originating from the seedbank as compared to seeds from above ground either dropping from maternal plants or blown in from outside the plots to the establishment of new E. calycina cover. After a nine month perios, new E. calycina cover from both sources was not significantly different. Visible coverage of E. calycina began 77 days (November 24, 2015) after plot installation. After nine months of surveying, coverage reached 19% in the Seedbank Present treatment and 21% in the Seedbank Absent treatment. There was no significant effect associated with the slope and aspect of the experimental locations. This experiment will aid in management of this invasive species by educating land managers to focus on preventing current seed production of established individuals as those sources of seed were as important as those originating in the seedbank. Stimulating germination of seeds from the seedbank with a concomitant management strategy such as herbicide application or physical removal will likely be the most effective methods for dealing with seeds in the seedbank.

This research paper was submitted to the Department of Geography in fulfillment of the requirements of Geography 4C6. / There are marked differences in the morphology and vegetation of the west (Dune du Nord) and east (Dune du Sud) coast dunes of Les Iles-de-la-Madeleine in the southern Gulf of St. Lawrence. The west coast dunes consist mainly of blown-out foredunes succeeded inland by large parabolic dunes. Vegetation is dominated by Ammophila breviligulata with <40% cover, except for the rich flora of cranberry bog communities that occur in deflation hollows at the base of the parabolic scarps. One section of Dune du Nord has more stable, heath-covered dunes that have been extensively modified by deflation, creating a complex topography. On the east coast, the stable dunes support species rich heath and grassland vegetation with higher cover (60-100%). The southern part is a wide complex of progradational ridges, now being overridden on the seaward side by a narrow blown-out strip dominated by A. brevliligulata. To the north, the topography is simple, with A. brevliligulata on the foredune that is quickly succeeded by grassland vegetation on a narrow dune flat. This contrast in morpho-ecological conditions between the two coasts is related to the differences in wave energy described by Owens (1977), wind regime, and existing topography. The present research paper provides a Canadian example of Hesp's (1988) model of the surfzone and wave energy interaction with dune morphology and ecology. / Thesis / Bachelor of Science (BSc)

The following study investigates how a sand dune system in the central part of Laholm Bay (Laholmsbukten) in Halland County, Sweden, has evolved over the time period 1947 to 2014. Effort was made to contribute to improved knowledge of how geomorphological variations and anthropogenic activity in the area have been influenced by each other over time. The study is aiming to provide an improved science basis for further development of coastal management in the area. Initial focus points were to investigate the correlation over time between changes in dune system morphology, vegetation distribution and anthropogenic influence. Furthermore connections were made as to how climate has influenced the development and how climate change during the 21st century might affect the area. Methods used during the course of this study entailed fieldwork and remote sensing of aerial photographs. Changes in dune system dynamics, land cover and human impact on the area over time were analyzed. The result demonstrates that the area has undergone dynamic changes, affected by climatological aspects, human activities as well as vegetation changes. Decreasing topographic variations in the southern part of the dune system compared to the north is identified to be dependent on variations in soil fractions. This combined with the identified changes in vegetation distribution over time has an affect on erosion and deposition processes within the area. Future climate change during this century may further increase the dynamic behavior of the dune system, an important aspect to consider within local coastal management. / Följande studie utreder hur ett sanddynsområde i de centrala delarna av Laholmsbukten i Hallands län utvecklats under tidsperioden 1947-2014. Syftet var att skapa en uppdaterad kunskapsbild av områdets geomorfologiska utveckling och hur den antropogena aktiviteten i området har påverkat denna, för att, om möjligt bidra med underlag till en utveckling av förvaltningsarbetet i kustområdet. Fokus låg på att utreda sambanden mellan förändringar av landskapets morfologi, vegetationens utbredning och antropogen påverkan. Vidare undersöks hur klimatet under tidsperioden kan ha bidragit till den geomorfologiska utvecklingen och hur området kan komma att förändras fram till sekelskiftet år 2100. Arbetet innefattade fältarbete och fjärranalys av flygbilder. Faktorer såsom dynsystemets dynamik, areella förändringar i marktäcke och mänsklig påverkan på området analyserades. Resultatet påvisar att sanddynsområdet genomgått dynamiska förändringar över tid som kan antas bero på klimatologiska aspekter i kombination med mänsklig aktivitet och vegetationsförändringar. Dynområdets minskande relief i nord-sydlig riktning och variationer i dynkantens förskjutning över tid är beroende av det dynbildande materialets sammansättning. I kombination med identifierade variationer i vegetationens utbredning påverkar detta erosions- och ackumulationsförutsättningarna i området. Klimatförändringar under detta sekel kan komma att påverka de faktorer som reglerar dynsystemets uppbyggnad vilket kan öka dynamiken i systemet ytterligare. En aspekt som är viktig att ta hänsyn till i förvaltningen av dynområdet.

Grain size distribution, porosity, and hydraulic conductivity from over 400 unlithified sediment samples were analized. The measured hydraulic conductivity values were then compared to values calculated using 20 different empirical equations commonly used to estimate hydraulic conductivity from grain size analyses. It was found that most of the hydraulic conductivity values estimated from the empirical equations correlated very poorly to the measured hydraulic conductivity values. Modifications of the empirical equations, including changes to special coefficients and statistical off sets, were made to produce modified equations that considerably improve the hydraulic conductivity estimates from grain size data for beach, dune, off shore marine, and wadi sediments. Expected hydraulic conductivity estimation errors were reduced. Correction factors were proposed for wadi sediments, taking mud percentage and the standard deviation (in phi units) into account.