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1
Durán, Orencio. "Vegetated dunes and barchan dune fields." [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-29639.
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Kiki, Sandoungout Serge Nahed. "Caractérisation de la morphologie des dunes dans des écoulements unidirectionnels et alternatifs." Thesis, Brest, 2019. http://www.theses.fr/2019BRES0045/document.
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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<br>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
3
Diniega, Serina. "Modeling Aeolian Dune and Dune Field Evolution." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195665.
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sand hops and bounces -see the dunes grow, run, collide -form the field's pattern.Aeolian sand dune morphologies and sizes are strongly connected to the environmental context and physical processes active since dune formation. As such, the patterns and measurable features found within dunes and dune fields can be interpreted as records of environmental conditions. Using mathematical models of dune and dune field evolution, it should be possible to quantitatively predict dune field dynamics from current conditions or to determine past field conditions based on present-day observations.In this dissertation, we focus on the construction and quantitative analysis of a continuum dune evolution model. We then apply this model towards interpretation of the formative history of terrestrial and martian dunes and dune fields. Our first aim is to identify the controls for the characteristic lengthscales seen in patterned dune fields. Variations in sand flux, binary dune interactions, and topography are evaluated with respect to evolution of individual dunes. Through the use of both quantitative and qualitative multiscale models, these results are then extended to determine the role such processes may play in (de)stabilization of the dune field. We find that sand flux variations and topography generally destabilize dune fields, while dune collisions can yield more similarly-sized dunes. We construct and apply a phenomenological macroscale dune evolution model to then quantitatively demonstrate how dune collisions cause a dune field to evolve into a set of uniformly-sized dunes. Our second goal is to investigate the influence of reversing winds and polar processes in relation to dune slope and morphology. Using numerical experiments, we investigate possible causes of distinctive morphologies seen in Antarctic and martian polar dunes. Finally, we discuss possible model extensions and needed observations that will enable the inclusion of more realistic physical environments in the dune and dune field evolution models.By elucidating the qualitative and quantitative connections between environmental conditions, physical processes, and resultant dune and dune field morphologies, this research furthers our ability to interpret spacecraft images of dune fields, and to use present-day observations to improve our understanding of past terrestrial and martian environments.
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Ripley, Bradford Sherman. "The ecophysiology of selected coastal dune pioneer plants of the Eastern Cape." Connect to this title online, 2001. http://eprints.ru.ac.za/18/.
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Poizat, Marine. "Observation et modélisation de la répartition géographique des dunes de neige et de la rugosité de surface en Antarctique." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALU026.
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Les dunes sont des modelés éoliens que l'on rencontre fréquemment dans les déserts de sable, les lits de rivière, les régions polaires et même sur d'autres planètes, comme Mars. Formées par l'interaction complexe entre le vent et les sédiments de surface, les dunes présentent une grande variété de formes et de tailles. Si les dunes de sable ont suscité un intérêt scientifique considérable, leurs homologues les dunes de neige, ont reçu moins d'attention, bien que leur présence ait été signalée depuis les années 1900 en Antarctique. Par conséquent, des questions fondamentales sur les processus de dépôt et d'accumulation de la neige restent sans réponse, ce qui a un impact sur la compréhension de la redistribution de la neige et de la variabilité du bilan de masse en surface dans l'Antarctique et, plus généralement, sur le transport éolien d'un matériau cohésif.Pour combler ces lacunes, nous avons réalisé la première carte complète de l'Antarctique documentant la présence et les orientations des dunes de neige hectométriques (100-1000 m de long) en utilisant les images satellites. Nous avons retrouvé l'orientation et la présence des dunes en appliquant l'autocorrélation spatiale sur toutes les images satellites disponibles (Sentinel-2 et Landsat-8). Les résultats présentés dans cette thèse révèlent que ces dunes sont omniprésentes et stables en Antarctique, et que leur orientation est parallèle à la direction moyenne du vent dans la plupart des régions. Pour expliquer ceci, nous avons appliqué une théorie bien établie, développée à l'origine pour les dunes de sable. Cette théorie relie l'orientation des dunes à la disponibilité des sédiments pour le transport par le vent et au régime des vents. Nous montrons que cette théorie peut être étendue avec succès aux dunes de neige pour expliquer les orientations observées. En outre, la prédominance des dunes alignées parallèlement à la direction du vent, plutôt que perpendiculairement, indique une faible disponibilité en neige pour le transport par le vent en Antarctique. Il s'agit d'un résultat contre-intuitif pour le continent le plus venteux et presque entièrement recouvert de neige de notre planète.Nous avons appliqué la même méthodologie au Groenland et obtenu des résultats similaires. Les dunes de neige linéaires sont omniprésentes sur la calotte glaciaire. Cependant, contrairement à l'Antarctique, la théorie développée pour les dunes de sable s'est avérée inadéquate pour expliquer les orientations observées. Nous suggérons que cette différence est due aux processus de frittage, qui empêchent les dunes de s'adapter à la variabilité de la direction du vent. Par conséquent, ces orientations sont peut-être représentatives de courts évènements plutôt que de régimes de vent annuels.Enfin, nous avons examiné la dynamique et la morphologie de dunes beaucoup plus petites, les barchans, dont la longueur varie entre 1 à 10 mètres. En utilisant des images acquises toutes les heures à la station Concordia, en Antarctique, nous avons identifié les évènements de formation et de migration de barchans. Nous avons orthorectifié les images et mesuré les paramètres morphologiques des barchans. Afin de comprendre les conditions météorologiques influençant la formation et la migration des barchans, nous avons étudié les données météorologiques mesurées in-situ. La vitesse de migration et la taille des barchans ont été comparées à la relation établie pour les barchans de sable, ce qui a donné des résultats cohérents.Ces résultats démontrent que les dunes de neige sont des objets importants qui devraient être pris en compte dans les modèles polaires ou l'interprétation des mesures réalisées par télédétection en Antarctique. Nos résultats ont des implications majeures pour les mesures in situ du bilan de masse de la surface, mais aussi pour l'interprétation des carottes de glace, car ils mettent en évidence l'hétérogénéité spatiale de la surface enneigée<br>Dunes are bedforms that are frequently encountered in sand desert, river beds, polar regions and even on planets, like Mars. Formed through the intricate interplay between wind and surface sediment, dunes exhibit a variety of shapes and sizes. While sand dunes have garnered considerable scientific interest, their counterparts, snow dunes, have received comparatively less attention, despite their presence being reported since the 1900s in Antarctica. As a result, fundamental questions about the processes of deposition and accumulation of snow remain unanswered, impacting the understanding of snow redistribution and surface mass balance variability in Antarctica and, more generally, the eolian transport of a cohesive material.To address these knowledge gaps, we provide the first comprehensive Antarctic-wide map documenting the presence and orientations of long dunes (100-1000 m in length) across Antarctica using satellite imagery. We retrieve dune orientations and presence using 2D spatial autocorrelation on all available optical satellite imagery (Sentinel-2 and Landsat-8). The results reveal that these dunes are ubiquitous and stable in Antarctica, and that their orientation is mainly parallel to the mean wind direction across most regions. To explain this fact, we applied a well-established theory originally developed for sand dunes. This theory relates dune orientation to the availability of sediments for wind transport and the wind regime. We show that this theory could successfully be extended to snow dunes to explain the observed orientation. Furthermore, the predominance of long dunes aligned parallel to the wind direction, rather than perpendicular, indicates a scarcity of mobile snow available for transport in Antarctica. This is a counter-intuitive result for the most windy and almost completely snow-cover continent of our planet.We applied the same methodology to Greenland and obtained similar results. Linear snow dunes were found to be ubiquitous across the ice sheet. However, unlike in Antarctica, the theory developed for sand dunes proved inadequate in explaining the observed orientations. We propose that this discrepancy is attributed to sintering processes, which hinder the dunes from reflecting the variability of wind directions. Consequently, these orientations may be indicative of short-term events rather than annual wind regimes.To further understand this, we investigated the temporal evolution of dune orientations in Terre Adélie, Antarctica. We showed that dune orientations vary every few months, following events of significant precipitation and strong winds. In addition,the new orientations observed align well with theoretical predictions when applied during precipitation events. However, despite these variations, no migration is observed. Therefore, we argue this lack of migration is due to the rapid sintering of snow dunes. Furthermore, to explain the orientation observed in Greenland, it might be important to consider the last significant precipitation event rather than relying only on the annual wind regime.Finally, we examined the dynamics and morphologies of small crescent-shaped bedforms, barchans, (1 – 10m in length). Using hourly images acquired at Concordia Station, Antarctica, we identified events involving barchans. By orthorectifying the images, we retrieved their morphological parameters. The events were correlated with in-situ weather data to understand the conditions influencing barchan formation and migration. Their migration speed and size were compared to the relationship established for sand dunes, showing consistent results.These findings demonstrate that snow dunes are significant objects which should be accounted for in polar models or remote sensing interpretation over Antarctica. Our results have major implications for in-situ surface mass balance measurements but also ice core interpretation, as they highlight the spatial heterogeneity of the snow surface
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Avis, Anthony Mark. "Coastal dune ecology and management in the Eastern Cape." Thesis, Rhodes University, 1993. http://hdl.handle.net/10962/d1003753.
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The importance of understanding the ecological functioning of coastal dune systems is emphasized as being fundamental to the correct management of the dune landscape. Dune vegetation along the Eastern Cape coastline, from Cape St Francis in the west to Kei Mouth in the east was described in terms of the distribution and phytochorological affinities of the taxa. At a regional scale species distribution was strongly influenced by both the climate, particularly rainfall, and the phytochorological affinities of the taxa. Seven communities were defined using TWINSPAN, and the interrelationships between these communities in anyone area appeared to be linked to a successional gradient. Dune Slacks are thought to play a key role in this successional sequence, and a temporal study of this community led to a conceptual model of plant succession in these dunefields. Climate, particularly rainfall and wind, are major factors influencing plant succession. Wind-borne sand causes the slacks to migrate in an easterly direction under the influence of the predominantly westerly winds, although easterly winds, mainly in summer months may reverse these trends. Autogenic changes appeared to be important in this succession, and a comparative study of a good example of a primary succession at Mtunzini in Natal was undertaken to elucidate the main mechanism of change. Eight communities that were identified here were concluded to be distnbuted along a gradient of increasing age, with successional changes predictable, linear and directional. Species were grouped in distinct zones along the continuum and edaphic changes (decrease in soil pH, increase in organic matter and exchangeable bases) were related to the community based changes in species composition. The mechanism of change supported the facilitation model of plant succession which is a modification of the original Clementsian concept. Similar results were found in the Eastern Cape, but due to the harsh environment, multiple pathways of succession exist. Data from this study lent support to the model of plant succession developed earlier, and confinned that the dune slacks played an important role in this facilitation by acting as centres of diversity. The foredunes were found to have an indirect role in protecting these slacks from salt spray and sand movement. The central theme of the management studies was to investigate the ecological consequences of recreational pressure within the dune environment. Current levels of beach utilization at East London were lower than other beaches in South Africa, but a general trend of increasing utilization due to sociopolitical changes can be expected. The suitability of questionnaire surveys to assess aspects such as the adequacy of facilities, perceptual carrying capacity and the beach users opinion of natural vegetation and preference for particular beaches was demonstrated. The dune vegetation was found to be sensitive to human trampling, but at current levels, the ecological carrying capacity will not be exceeded since results of the aerial census counts and questionnaire survey revealed that few people entered sensitive zones such as the coastal forest. More detailed long term studies on the susceptibility of dune vegetation to both trampling and off-road vehicle impacts revealed a low resilience of dune plant communities to these effects. Although susceptibility differed between the three communities tested, generally the greatest amount of damage occurred after the first few passages, and vehicles caused a more significant decrease in height when compared to trampling. Recovery rates were slow and low levels of repeated damage were sufficient to retard or prevent the recovery of the plants. Stricter control of vehicle use on beaches is therefore required, and in high use zones the ecological carrying capacity should be increased by providing access tracks if possible, or if not possible, by restricting access. A historical account of the process of dune stabilization showed that although first initiated in 1845, indigenous species were only used in the past three decades. The use of alien species has resulted in problems such as a reduction in the ecological integrity and aesthetic appeal of coastal systems. The techniques applied in the stabilization of drift sands with indigenous vegetation have been successful, as revealed by a quantitative survey of 17 sites in the Eastern Cape. Sites were grouped by multivariate analysis on the basis of their species composition, and variability between sites was dependent on the types of species planted. Selection of suitable species is therefore important and is discussed with respect to their natural distribution along the coast. The long term objective of stabilization should be the creation of functional, diverse, aesthetic ecosystems, since the intrinsic and economic value of the dune landscape for tourism lies therein. However, detailed studies should be undertaken prior to implementing a manipulative process such as dune stabilization, since ecological processes may be disrupted. An understanding of such processes is therefore important if one wishes to effectively manage the dune landscape.
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Ogor, Julien. "Design of algorithms for the automatic characterization of marine dune morphology and dynamics." Thesis, Brest, École nationale supérieure de techniques avancées Bretagne, 2018. http://www.theses.fr/2018ENTA0005/document.
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Les dunes marines sont de grandes structures sédimentaires qui, ensemble, couvrent de larges zones appelées champs de dunes. Des dunes ont été découvertes dans tous les océans, de la côte jusqu'aux talus continentaux. Leur forme et mobilité sont des témoins du lien étroit qui existe entre le transport sédimentaire, l'hydrodynamique (courants marins) et la topographie du fond. L'étude des dunes est intéressante scientifiquement parlant, mais elle est également motivée par des enjeux économiques et environnementaux. Les dunes peuvent être étudiées de deux manières : La modélisation et l'analyse de données de terrain (granulométrie, courantométrie, données sismiques, données bathymétriques). Ces deux approches sont très différentes mais complémentaires. Avec l'amélioration des données Sondeur Multi-Faisceaux (SMF), il est maintenant possible de visualiser la morphologie des dunes et de suivre leur évolution de manière plus détaillée. Plusieurs méthodes automatiques d'analyse de la morphologie et de la dynamique des dunes ont été développées pour analyser les Modèles Numériques de Terrain (MNTs) construits à partir de ces données SMF. Pourtant, aucun ne permet d'estimer les valeurs de descripteurs morphologiques et dynamiques pour chaque dune. L'analyse et l'évaluation de ces descripteurs restent régionales avec le découpage des MNTs en régions rectangulaires. Seul un traitement manuel permet d'estimer ces descripteurs pour chaque dune. L'objectif de cette thèse est de développer des algorithmes automatiques permettant de quanti er la morphologie et la dynamique de chaque dune. Pour ce faire, une représentation des données SMF sous forme d'une tessellation triangulaire a été préférée au classique MNT régulier. Tout d'abord, les dunes doivent être extraites de la topographie du fond marin. Un algorithme par accroissement de régions avec adaptation de l'échelle d'analyse, issu de la géomorphométrie est proposé. Les crêtes de dunes sont d'abord extraites en combinant un algorithme de simplification de tessellations avec un algorithme d'extraction de lignes de crête. La résolution de la tessellation est adaptée par l'algorithme de simplification afin de faciliter l'extraction des lignes de crête. Les lignes de crête sont des objets bien définis en géométrie différentielle. Leur extraction s'appuie sur l'interprétation de cette définition appliquée à des modèles discrets du fond (tessellations). Les crêtes servent d'embryons à l'algorithme d'extraction des dunes. L'estimation des paramètres morphologiques des dunes (longueur, largeur, hauteur, etc.) découle de l'extraction automatique des dunes. L'utilisation d'une méthode de recalage non rigide (isométrique) pour la quantification de la dynamique est discutée. Des tessellations représentant la topographie d'un même champ de dunes à différents moments sont analysées par l'algorithme d'extraction des dunes. Ensuite, une dune est associée à une dune d'une autre tessellation qui lui correspond (même dune à un autre instant). La dynamique de chaque dune est quantifiée à partir des résultats de l'algorithme de recalage : les transformations permettant d'aligner différentes représentations d'une dune<br>Marine dunes are large sedimentary mounds often organized in dunefields. Theyhave been discovered in oceans all around the globe, from continental rises to nearshore areas. These mobile seafloor structures reflect the unique and complex relationship between the sediment, the seafloor topography and the hydrodynamics (currents). Dunes are not only interesting at a scientific level. In fact, their study is also motivated by economic, safety and environmental reasons. The study of dunes can be divided into two complementary approaches: Modelling and analysis of in situ data (granulometry, current, bathymetric data).The increased quality of MultiBeam EchoSounder (MBES) data allows scientists to monitor and visualize the complexity of, both, dune morphology and dynamics. Au-tomatic methods to characterize dune morphology and dynamics using Digital TerrainModels (DTMs) have already been proposed. But, none does it at the dune scale. Mor-phological and dynamical descriptors are estimated for patches of the dunefield. Today, the evaluation of such descriptors for each dune can only be achieved manually.The objective of this thesis is to design automatic algorithms for the quantification of dune morphology and dynamics. A representation of MBES data as triangular meshes has been preferred to the usual gridded DTMs. The first stage consists of delineating dunes in the seafloor. A scale adaptative, region growing algorithm based on geomorphometry is proposed. The combination of mesh implification and crest extraction algorithms enables to accurately recover dune crest lines. The mesh simplification facilitates the crest extraction by adapting the mesh resolution. Crest extraction is based on the discrete interpretation of the definition of crest lines in differential geometry. The crests are, then, used as seed regions by the dune extraction algorithm
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Barwell, Lauriston. "Integrity assessment procedure for buffer dune systems on the Cape South Coast, South Africa." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6524.
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Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011.<br>ENGLISH ABSTRACT: The hypothesis postulated in this research, namely that the effectiveness of natural and
constructed buffer dune systems can be assessed by a set of indicators that defines the
integrity of the dune system and triggers informed management decisions, was evaluated
and proved to be essentially true.
Two key objectives, namely (1) the identification of key indicators that define the buffer
dune integrity; and (2) the development of a scientifically defendable and practical
checklist-based method of gathering qualitative information on the identified key indicators
so as to guide decision-making at municipal level formed the core of the study.
The six dune integrity indicators that collectively define the risk profile of a particular site
along the Southern Cape coastline are (1) the degree of protection from prevailing wave
energy, (2) the characteristics of the dominant winds and sand supply during the dry
season, (3) the relative height of the foredune, (4) the degree of pressure on the buffer
dune due to humans, (5) the vulnerability of the type of coastline to erosion, and (6) the
coastline stability considering the prevailing coastal processes.
The first two indicators relate to the natural (permanent) characteristics of the site and can
be defined by experts and presented in the form of a risk and vulnerability atlas layer for
direct use by non-experts. The third and fourth indicators relate directly to the
implementation of proactive assessment and appropriate management actions to ensure a
high level of buffer dune integrity. The last two indicators allow for management
intervention to reduce the vulnerability but may entail costly engineering solutions and
require expert input.
A conceptual risk profile assessment procedure and a decision support guideline
incorporating these indicators were developed and evaluated for relevance and practicality
through a series of workshops with municipal officials along the south coast of South Africa.
It was seen that although some initial basic training may be required, carrying out rapid
assessments of the environmental status of key components of an identified human–nature
system, such as a buffer dune, is practical and achievable by non-experts.<br>AFRIKAANSE OPSOMMING: Die hipotese wat in hierdie navorsing gepostuleer is, naamlik dat die doeltreffendheid van
natuurlike en geboude bufferduinstelsels geassesseer kan word deur ’n stel aanwysers wat
die integriteit van die duinstelsel bepaal en ingeligte bestuursbesluite tot gevolg het, is
getoets en bewys hoofsaaklik waar te wees.
Twee sleuteldoelwitte, naamlik (1) die identifisering van sleutelaanwysers wat die
bufferduinintegriteit bepaal; en (2) die ontwikkeling van ’n praktiese kontrolelys-gebaseerde
metode wat wetenskaplik verdedigbaar is om kwalitatiewe inligting oor die geïdentifiseerde
sleutelaanwysers in te samel ten einde besluitneming op munisipale vlak te bevorder, vorm
die kern van die studie.
Die ses duin-integriteitsaanwysers wat gesamentlik die risikoprofiel van ’n bepaalde terrein
langs die kuslyn bepaal, is (1) die graad van beskerming teen die heersende golfenergie,
(2) die kenmerke van die dominante winde en sandbron gedurende die droë seisoen, (3)
die relatiewe hoogte van die voorduin, (4) die graad van druk op die bufferduin as gevolg
van mense, (5) die eroderingskwesbaarheid van die soort kuslyn, en (6) die kuslynstabiliteit
met inagname van die kusprosesse.
Die eerste twee aanwysers het betrekking op die natuurlike (permanente) eienskappe van
die terrein en kan deur kundiges bepaal word en in die vorm van ’n kaart in ’n risiko-enkwesbaarheidsatlas
aangebied word vir direkte gebruik deur niedeskundiges. Aanwysers 3
en 4 hou direk verband met die implementering van tydige en deurlopende proaktiewe
assessering en gepaste bestuursaksies om ’n hoë vlak van bufferduinintegriteit te verseker.
Aanwysers 5 en 6 bevorder bestuursaksies om kwesbaarheid te verminder, maar kan
moontlik duur ingenieursoplossings inhou en kundige insette benodig.
’n Konseptuele risikoprofielassesseringsprosedure en ’n besluitondersteuningsriglyn wat die
aanwysers insluit, is ontwikkel en geëvalueer vir toepaslikheid en uitvoerbaarheid deur ’n
reeks werkswinkels met munisipale amptenare aan die suidkus van Suid-Afrika. Hoewel
aanvanklike basiese opleiding nodig kan wees, bly dit dat vinnige assessering van die
omgewingstatus van sleutelkomponente van ’n geïdentifiseerde mens–natuurstelsel, soos ‘n
bufferduin, prakties en haalbaar deur niedeskundiges is.
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Cocks, David. "Mathematical modelling of dune formation." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442818.
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This study is concerned with the mathematical modelling of the formation and subsequent evolution of sand dunes, both beneath rivers (fluvial) and in deserts (Aeolian). Dunes are observed in the environment in many different shapes and sizes; we begin by discussing qualitatively how and why the different forms exist. The most important aspect of a successful model is the relationship between the bed shape and the shear stress that the flow exerts on the bed. We first discuss a simple model for this stress applied to fluvial dunes, which is able to predict dune-like structures, but does not predict the instability of a flat bed which we would hope to find. We therefore go on to look at improved models for the shear stress based on theories of turbulent flow and asymptotic methods, using assumptions of either a constant eddy viscosity or a mixing length model for turbulence. Using these forms for the shear stress, along with sediment transport laws, we obtain partial integrodifferential equations for the evolution of the bed, and we study these numerically using spectral methods. One important feature of dunes which is not taken into account by the above models is that of the slip face - a region of constant slope on the downwind side of the dune. When a slip face is present, there is a discontinuity in the slope of the bed, and hence it is clear that flow separation will occur. Previous studies have modelled separated flow by heuristically describing the boundary of the separated region with a cubic or quintic polynomial which joins smoothly to the bed at each end. We recreate this polynomial form for the wake profile and demonstrate a method for including it into an evolution system for dunes. The resulting solutions show an isolated steady-state dune which propagates downstream. From the asymptotic framework developed earlier with a mixing length model for turbulence, we are able, using techniques of complex analysis, to model the shape of the wake region from a purely theoretical basis, rather than the heuristic one used previously. We obtain a Riemann-Hilbert problem for the wake profile, which can be solved using well-known techniques. We then use this method to calculate numerically the wake profile corresponding to a number of dune profiles. Further, we are able to find an exact solution to the wake profile problem in the case of a sinusoidally shaped dune with a slip face. Having found a method to calculate the shear stress exerted on the dune from the bed profile in the case of separated flow, we then use this improved estimate of the shear stress in an evolution system as before. In order to do this efficiently, we consider an alternative method for calculating the wake profile based on the spectral method used for solving the evolution system. We find that this system permits solutions describing an isolated dune with a slip face which propagates downstream without changing shape. All of the models described above are implemented in two spatial dimensions; the wind is assumed to blow in one direction only, and the dunes are assumed to be uniform in a direction perpendicular to the wind flow. While this is adequate to explain the behaviour of transverse dunes, other dune shapes such as linear dunes, barchans, and star dunes are by nature three-dimensional, so in order to study the behaviour of such dunes, the extension of the models to three dimensions is essential. While most of the governing equations generalize easily, it is less obvious how to extend the model for separated flow, due to its reliance on complex variables. We implement some three-dimensional evolution models, and discuss the possibility of modelling three-dimensional flow separation.
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Momiji, Hiroshi. "Mathematical modelling of the dynamics and morphology of aeolian dunes and dune fields." Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249363.
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Purvis, Kelly Grant. "Assessment of beach access paths on dune vegetation and implications for dune path planning and management." Thesis, College of Charleston, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1545049.
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<p> The impact of beach access paths on dune vegetation was investigated on the Isle of Palms, SC. Understanding the impacts of the most direct form of disturbance in this system (beach access paths) is of increasing importance from ecological and economic perspectives. Vegetation characteristics were measured along transects in foredune, mid dune and back dune communities at set distances from beach access paths. Survey was conducted to allow comparisons between path types and materials. Results indicate that beach access paths have a significant impact on beach dune vegetation. Sand paths cause greater reductions in vegetative cover than wooden paths and wooden paths raised at least 0.7m from the sand surface cause the least reduction in vegetation cover. Closely spaced paths reduce the species richness and percent of vegetative cover more than paths spaced at least 40 m apart. Current regulations can be minimally altered to improve dune vegetation and dune stability. Regulations requiring construction of raised wooden paths and disallowing private sand paths would greatly improve dune vegetation continuity. Additionally, voluntary path sharing of neighboring properties could significantly reduce the number of paths per mile of coastline while creating minimal inconvenience for beachfront homeowners and visitors.</p>
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Baddock, Matthew. "Airflow dynamics in transverse dune interdunes." Thesis, University of Northampton, 2005. http://nectar.northampton.ac.uk/2994/.
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Aeolian dune interdunes have been relatively ignored when compared with the research attention on the morphodynamics of the dune bodies themselves. This neglect is in spite of the possible significance of interdune dynamics for the geomorphology of the sand dune system as a whole, especially with regard to dune spacing. This project involved the collection of geomorphologically relevant airflow data for four relatively simple transverse dune interdunes. The study locations were chosen in order to sample interdunes with different size and surface type characteristics, the dynamics of which were investigated for when incident flow was normal to the upwind crest. The findings confirm existing models of aeolian dune lee-side flow in terms of flow re-attachment length and recovery attributes. A consistent pattern of increasing near-surface velocity downwind of re-attachment provides a mechanism for interdunes as sand-free features. Where studies for comparison from other aeolian examples are limited, the field-measured turbulence shows the importance of the shear layer as a source of turbulence, and agrees with studies from subaqueous bedforms. The importance of shear stress variability and the possible contribution of turbulence structures to the maintenance of sediment transport at re-attachment where velocity and mean stress is low or negative is also emphasised. At the downwind edge of interdunes, the mean and turbulent velocity properties, and therefore morphodynamics, vary according to the interdune size. In this case, interdune length leads to greater recovery, and a balance exists in this region between the recovering flow at the surface, dissipating wake from above and the obstacle effect of the dune. The flow dynamics are characterised for the different types of interdune observed. Dynamics accordant with the flow response model are seen to characterise the interdune setting with the closest spacing. The occurrence of other “extended” aeolian interdunes with a length well over that for flow separation demanded the development of a new descriptive model to characterise the dynamics therein. In this model, the variation in near-surface flow allowed process zones to be identified through the interdune. The geomorphological significance of the processes dominating each zone are discussed and comparisons are made between the flow response case and the new interdune model from this study
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Robertson-Rintoul, M. J. "The morphology and dynamics of parabolic dunes within the context of the coastal dune systems of mainland Scotland." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371712.
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Burns, Michael Edmund Reid. "A synecological study of the East London coast dune forests." Thesis, Rhodes University, 1987. http://hdl.handle.net/10962/d1006134.
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Quantitative community descriptions, based on point quarter sample data, are made for a number of dune forest units along the East London coast. These are supported by multivariate classifications and ordinations which illustrate the inter community variation between the sampled seaward, landward and dune valley sites. Climax valley forest is floristically most characteristic and can be clearly distinguished from the seaward and landward thicket communities which tend to show a degree of similarity. Within-forest community differences are shown to be more significant than variation along the coast. This appears to indicate that climoedaphic gradients established laterally to the coast induce a greater floristic response than the rainfall gradient within the study area. The state of developnent within the dune soil profile and the rate and effect of salt spray deposition are considered to be important factors influencing dune forest succession and are discussed in some detail. An overview of certain other climatic variables as well as the geological features within the study area is also given. A phenology study of the dune forest, scrub-thicket and strand plant cornnunities shows some general patterns of flowering and fruiting phenorhythms. Although much variation was observed, there appears to be a bimodal hyperactive phenophase response which is thought to be related to rainfall or periods of favourable soil moisture conditions. A brief discussion of some of the positive and negative human influences on the coastline is given. This includes a description of the management activities carried out in the area as well as the demands placed on ·the coastal resource.
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Knevel, Irma Cornelia. "The life history of selected coastal foredune species of South Africa." Thesis, Rhodes University, 2002. http://hdl.handle.net/10962/d1003776.
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South African dune fields are severely threatened by human expansion and in the long run the stabilisation of many dunes will be necessary. The alien grass Ammophila arenaria is the most important drift sand stabiliser at present in South Africa. Although not invasive, the current impact of A. arenaria on the dune systems of South Africa is considerable, and thus the stabilising benefit of the grass seemed to may be outweighed by its negative consequences. It is therefore preferable to use indigenous sand stabilising species. In order to define guidelines for the application of indigenous plants for stabilisation, their autecology should be studied first to enhance the chance of successful stabilisation results. The main aim of the present thesis was to gather information on the life history processes of selected indigenous, sand stabilising foredune species. To investigate the growth of foredune pioneer species, the common pioneer Scaevola plumieri was followed over a three-year period to determine the growth season and leaf phenology. Soil-borne pathogens are known to influence the growth and vegetation dynamics of foredune species. To examine this effect on the South African foredunes the rhizosphere soil and the roots of several species were studied. To test the effect of the nematode fauna on succeeding plant species a transplantation experiment was carried out. The seed stage is the only life-cycle stage that can survive unfavourable conditions. Therefore, the seed ecology of several foredune species was studied extensively to determine the reproductive season, the seed production, the fate of seeds after shedding (germination, seawater dispersal), germination requirements and seed bank strategy. Seeds of the species Arctotheca populifolia, Ipomoea pes-caprae, Myrica cordifolia, and Scaevola plumieri were subjected to germination trials, field observations on seedling survival, and scarification and stratification experiments. This was done to obtain information about the germination requirements and to determine the reproductive season and growth season. The seed bank strategy of the foredune species, as well as the seed bank density, was determined by extensive sampling along the Cape coast. The species S. plumieri thrived under sand accretion situations, which makes it a good candidate for stabilisation purposes. The growth of S. plumieri was seasonal, with the highest leaf production during spring and summer. The stem position on the foredune had a strong effect on the overall performance of S. plumieri , with the stems situated on the landward face of the foredune showing higher leaf and seed production. Theiii nematode survey of soil and roots of several foredune species showed that all plant species featured a specific nematode fauna in the rhizosphere soil and the roots. The specific nematode fauna affected the growth of foreign plant species in the transplantation experiment, resulting in a lower root and/or shoot biomass production. Most of the foredune species produce seeds from spring to late summer. For S. plumieri the position of the stem on the dunes, as well as the predation of unripe seeds affected the number of seeds produced. The highest production was found for the landward faced stems. The S. plumieri seeds were able to float on seawater for at least three months without losing viability, as was observed for seeds of I. pes-caprae. The seeds of M. cordifolia, however, sank after a few days, but their viability was not affected. The rhizome fragments of A. arenaria and S. virginicus floated for 120 days, whereas the fragments of E. villosa sunk after one day. The viability of S. virginicus fragments was affected by the duration in seawater by an increase in sprouting time. The seeds of all species tested germinated readily under controlled conditions, except S. plumieri seeds which required a long lag-phase before germination. In the field the seeds of A. populifolia, I. pes-caprae and S. plumieri germinated, producing many seedlings. Only the seedlings of A. populifolia and S. plumieri survived. Of the species found in the foredunes 57% was represented in the soil seed bank. For most species, the seeds that were found in the seed bank showed viability of at least 40%. Many of the seeds found were older than one year, suggesting a short-term persistent seed bank. The present study is a start in filling the gap in information on dune pioneer and foredune species. The conclusion was that in general all species in the present study were easy to grow under controlled conditions, and thus could be used for stabilisation purposes. When the more rapidly growing pioneer species are planted in combination with succeeding foredune species, a functional and aesthetic ecosystem could be created.
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Domínguez, Acosta Miguel. "The Pluvial Lake Palomas-Samalayuca Dune systems." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Ripley, B. S. "The ecophysiology of selected coastal dune pioneer plants of the Eastern Cape." Thesis, Rhodes University, 2002. http://hdl.handle.net/10962/d1003791.
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Understanding the mechanisms and adaptations that allow only certain species to thrive in the potentially stressful foredune environment requires a knowledge of the basic ecophysiology of foredune species. Ecophysiological measurements were conducted on the foredune pioneer species Arctotheca populifolia (Berg.) Norl., Ipomoea pes-caprae(L.) R. Br. and Scaevola plumieri (L.) Vahl. and showed significant differences among species with respect to the physiology associated with biomass production, water and nutrient relations. Differences related to CO₂ assimilation included differences in photosynthetic and respiratory rates, susceptibility to light stress and leaf and stem non-structural carbohydrate concentrations. These resulted in differences in primary production rates of shoots. Mechanisms leading to the differences in CO₂ assimilation among species included differences in stomatal behaviour, carboxylation efficiencies, efficiencies of utilisation of incident photosynthetic photon flux density (PPFD) and rates of ribulose-1,6-bisphosphate (RuBP) regeneration. Correlated with differences in photosynthetic capacity were differences in chlorophyll contents but not differences in leaf nitrogen content. Differences in interspecific stomatal behaviour resulted in significantly different transpiration rates which in combination with differences in assimilation rates resulted in differences in water-use efficiency. The absolute amounts of water transpired, although significantly different among species, were moderate to high in comparison with species from other ecosystems and were typical of mesophytes. Transpiration rates in combination with plant hydraulic conductances and soil water availability resulted in leaf water potentials that were not very negative and none of the investigated species showed evidence of osmotic adjustment. The volume of water transpired by each of the species per unit land surface area was estimated from the relationship between abiotic factors and plant water loss. These relationships varied among species and had varying degrees of predictability as a result of differences in stomatal behaviour between the three species. The water requirements of A. populifolia and S. plumieri were adequately met by the water supplied by rainfall and the water stored in the dune sands. It was therefore not necessary to invoke the utilisation of ground water or the process of internal dew formation to supply sufficient water to meet the requirements. However, I. pes-caprae despite its lower transpiration rates and due to its higher biomass, lost greater volumes of water per unit dune surface area than either A. populifolia or S. plumieri. This resulted in periods of potential water limitation for I. pes-caprae. Incident light was the most important determinant of leaf photosynthetic CO₂ assimilation and transpiration, particularly as a linear relationship between incident PPFD and atmospheric vapour pressure deficit (VPD) could be demonstrated. Whole plant photosynthetic production by S. plumieri was shown to be light limited as a result of mutual shading despite high incident and reflected PPFD occurring in the foredune environment. The leaf hair-layer of A. populifolia was shown to be important in reducing transmitted UV and hence reducing photoinhibition but it also caused reduced transpiration rates because of the thicker boundary layer and thus increased leaf temperatures. The nutrient content of above-ground plant parts of the investigated species were typical of higher plants despite the low nutrient content measured for the dune soils. With the possible exception of nitrogen the nutrient demand created by above-ground production was adequately met by the supply of nutrients either from sand-water or from aquifer-water transpired by the plants. Differences in the volumes of water transpired, and hence the quantity of nutrients potentially taken up via the transpiration stream, resulted in interspecific differences in above-ground plant macronutrient content. The reallocation patterns of nutrients differed both between the various nutrients measured and interspecifically. Standing biomass and the density of plants per unit land area was low in comparison to that of other ecosystems and was different among investigated species. This may be important in maintaining the adequate supply of resources (water, nutrients and light). As a result of the interspecific differences in biomass when production was expressed per unit land surface area the resultant productivity was not dissimilar among species. Productivity was high when comparisons were made with species from other ecosystems. No single resource (water, nutrients or light) could be identified as the controlling factor in the foredune environment and a combination of both resource stress and environmental disturbance are likely to be involved. Physiology, production, growth and growth characteristics conveyed certain adaptive advantages to these species in respect to both resource stress and environmental disturbance. Interspecific differences in these adaptations can be used to offer explanations for the observed microhabitat preferences of the three investigated species. Furthermore features common to all three species offer some explanations as to why these species and not others are able to inhabit the foredunes.
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Caldeira, Ana Eugénia Calha Grave. "Viver da Ria : a requalificação da Ilha da Culatra." Master's thesis, Universidade de Lisboa. Faculdade de Arquitetura, 2015. http://hdl.handle.net/10400.5/8929.
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Garcia-Lozano, Carla. "Els sistemes dunars de la costa catalana. Evolució històrica, estat actual i potencial de restauració." Doctoral thesis, Universitat de Girona, 2019. http://hdl.handle.net/10803/668331.
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Human developed coasts in Catalonia show a high-degraded dune landscape. Along the last decades, dunes have disappeared from 60% of the beaches studied, whereas 30% of dunes have been reduced in extension, and only 10% have suffered fewer changes.Currently, more than 800 beaches compose the Catalan shoreline of which only 127 host some type of dune morphology. Regardless of their volume and extension, the Catalan coastal dunes reflect, in general, an advanced status of degradation related to the lack of management focused on maintaining and restoring dune morphologies. The application of the indexes proposed in this Thesis allowed to classify beaches of Catalonia in three groups according to the most suitable management measures: dune conservation, dune restoration, dune recovery and renaturalization of the dry beach. The results verify that the most part of studied beaches presents higher values in dune restoration potential index.<br>Les costes humanitzades de Catalunya presenten un paisatge dunar fortament degradat. Al llarg de les darreres dècades, les dunes han desaparegut al 60% de sistemes platja-duna; mentre que el 30% n’han vist reduïda la superfície dunar; i, tan sols, el 10% de les platges conserven els sistemes dunars ben conservats. Actualment, 800 platges conformen el litoral català i només 127 presenten algun tipus de morfologia dunar. Al marge del seu volum i extensió, les dunes de la costa catalana presenten, de forma generalitzada, un estadi de degradació molt avançat vinculat a l’escassa gestió enfocada a la conservació i recuperació de les formacions dunars. L’aplicació dels indicadors elaborats en aquesta tesi permeten classificar les platges de Catalunya en quatre grups segons les mesures de gestió que cal implementar: conservació dunar, restauració dunar, recuperació dunar, renaturalització de la platja. La major part dels casos estudiats presenten un notable potencial de restauració dunar.
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O'Malley, Paul W. "Understanding Formation and Evolution of Dune Fields by Spatial Mapping and Analysis: Upper Muskegon River Valley, Michigan." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1557841176226706.
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Bell, James Clayton. "An aeolian transport model for the selection of dune restoration alternatives." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4788.
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The landfall of hurricane Claudette in 2003 damaged and eroded most Texas
coastal counties. The residents of Pointe San Luis on the west end of Galveston Island,
Texas lost their protective dune front and experienced significant shoreline erosion.
Following the storm, the Pointe San Luis Property Owner's Association contacted Texas
A&M University to design a dune restoration strategy. The greatest natural contributor
to dune reconstruction is the available sand delivered by aeolian transport. During the
course of the study it became apparent that no model or software existed capable of
demonstrating the effectiveness of available dune restoration alternatives. Building
Beaché, a coastal aeolian sand transport simulator, was developed in response to this
need. Based on discrete dynamics and requiring a minimum of technical input, the
software allows coastal property owners, consultants, and coastal developers to
graphically model the effectiveness of several dune restoration options including sand
fence, planted vegetation, geo-textiles, and other solid protective barriers. The graphical
output of Building Beaché enables the user to compare approximations of the
performance of different restoration strategies to select the most effective option for a
particular beach.
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Mohd-Said, Mohd Nizam. "Effects of anthropogenic nitrogen inputs on dune grassland." Thesis, Bangor University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285519.
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Jackson, Derek William Thomas. "Aeolian entrainment of surface beach and dune settlements." Thesis, University of Ulster, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242047.
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Graham, Stuart Andrew. "Conservation of U.K. dune system native Lacertidae species." Thesis, Bangor University, 2018. https://research.bangor.ac.uk/portal/en/theses/conservation-of-uk-dune-system-native-lacertidae-species(b591154e-a7a1-48a3-975f-b2efa913a2c9).html.
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After years of decline, resulting in the extinction of the sand lizard Lacerta agilis in Wales, the species has now been returned to several dune system sites which also contain the viviparous lizard Zootoca vivipara. As dune system habitats are becoming an increasingly important habitat type in the UK for L. agilis, providing a relatively safe haven for these and Z. vivipara populations from anthropogenic change, it is time to ensure the long-term survival of these populations. In this study, environmentally advantageous conditions for detection of both species were established for three dune system sites in North-West Wales. Surface temperature, UV, cloud cover and wind speed were identified as being the most influential detection parameters, with cloud cover and wind speed noted as having a negative influence on detection. Furthermore, favoured habitat was identified and ‘suitable habitat’ modelled for both species. Across the research sites both species were found to utilise habitats of a similar composition with reintroduced L. agilis favouring specific habitat features such as basking direction and degree of angle of their basking position. Habitat and site utilisation models indicate that for highly mobile dune systems L. agilis dispersal across a site is not of concern. For static or eroding dune systems, large, connected areas of favoured habitats are absent. In this situation, L. agilis dispersal (from introduction locations) is limited. Mean yearly L. agilis dispersal distances of 19.64 m – 28 m represents an approximate trend across the three research sites. The physical presence of L. agilis alone, however, does not constitute a successful reintroduction. Genetic diversity of the reintroduced populations was observed to be lower than those calculated in naturally occurring British populations. This is a matter of conservation concern, with a number of targeted mitigatory measures proposed to improve the genetic integrity, reducing the chance of population extinction(s). Mean time to extinction estimates indicate that for populations on highly mobile dune systems population survival times of between 11.4 yrs and 63.1 yrs could be expected. This is reduced for static or eroding dune system sites. The implications of these findings for the conservation of L. agilis and Z. vivipara are discussed in the context of current challenges and future management requirements. It is hoped that this thesis will help guide the future development of the reintroduction program, and in addition, provide a sound scientific basis for the future management of reintroduction sites and species monitoring.
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Paarlberg, Andries Jan. "Modelling dune evolution and dynamic roughness in rivers." Enschede : University of Twente [Host], 2008. http://doc.utwente.nl/59778.
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Livingstone, I. "The dynamics of sand transport on a Namib linear dune." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375978.
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Sturgess, Peter William. "Post-felling vegetation changes on three afforested sand-dune systems." Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363340.
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Wu, Jianzhao. "Numerical simulation of wind erosion : application to dune migration." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC016/document.
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L’érosion éolienne est un phénomène complexe avec des interactions entre la couche limite atmosphérique, le transport des particules et la déformation des dunes. Dans cette thèse des simulations numériques de transport de particules solides sur des dunes fixes ou déformables sont effectuées. L’écoulement turbulent est calculé par des simulations des grandes échelles (LES) couplée avec une méthode de frontières immergées. Les particules solides sont tractées par une approche Lagrangienne. L’entraînement des particules, leur interaction avec la surface et leur dépôt sont pris en compte par des modèles physiques complets d’érosion. D’un point de vue numérique, une méthode de frontières immergées a été introduite pour simuler les écoulements turbulents sur des frontières mouvantes. Le nouveau solveur a été validé en effectuant des comparaison avec les résultats expérimentaux de Simoens et al. (2015) dans le cas d’une colline Gaussienne. D’un point de vue physique, des modèles complets ont été développés pour l’érosion éolienne en se basant sur les forces agissant sur les particules. Des modèles instantanés pour l’envol, le roulement et le glissement des particules sont développés pour initier le mouvement des particules. Leur rebond et le splash sont également pris en compte. Des équations Lagrangiennes sont utilisées pour simuler la trajectoire des particules solides dans l’air. Une équation de transport d’un lit de particules a également été développée pour les cas de glissement et de roulement des particules sur la surface. La déformation de la dune est effectuée en faisant le bilan des particules qui s’envolent et se déposent. Ces modèles ont été validés en comparant les résultats de simulation avec les résultats expérimentaux de Simoens et al. (2015) sur les profils de concentration autour d’une colline Gaussienne. Enfin, des simulations numériques d’une dune sinusoïdale déformable sont effectuées. La forme de la dune simulée est comparée avec les résultats expérimentaux de Ferreira and Fino (2012). Un bon agrément est obtenu a t = 2.0 min, par contre la hauteur de la dune est sous-estimée entre 4.0 min et 6.0 min. Les résultats numériques montrent que la zone de recirculation diminue progressivement quand la dune se déforme. L’érosion, due à l’envol et au splash, est important a l’avant de la dune tandis que les particules se déposent a l’arrière de la dune. Le modèle de splash a été modifié pour prendre en compte l’effet de la pente, ce qui a permis une meilleure estimation de la hauteur de la dune a t = 4.0 min<br>Wind erosion is a complex dynamic process consisting in an atmospheric boundary layer, aeolian particle transport, sand dune deformation and their intricate interactions. This thesis undertakes this problems by conducting three-dimensional numerical simulations of solid particle transport over a fixed or deformable sand dune. Turbulent flow is calculated by a developed numerical solver (Large-eddy simulation (LES) coupled with immersed boundary method (IBM)). Solid particle trajectories are tracked by a Lagrangian approach. Particle entrainment, particle-surface interactions and particle deposition are taken into account by physical comprehensive wind erosion models. Firstly, a new numerical solver has been developed to simulate turbulent flows over moving boundaries by introducing the IBM into LES. Two canonical simulation cases of a turbulent boundary layer flow over a Gaussian dune and over a sinusoidal dune are performed to examine the accuracy of the developed solver. Recirculation region characteristics, mean streamwise velocity profiles, Reynolds stress profiles as well as the friction velocity over the dune are presented. In the Gaussian case, a good agreement between experimental data and simulated results demonstrates the numerical ability of the improved solver. In the sinusoidal case, the developed solver with wall modeling over the immersed boundary shows a better performance than the pure one, when a relatively coarse grid is used. Secondly, physical comprehensive modeling of wind erosion is described in detail, based on the forces acting an individual particle. An instantaneous entrainment model for both lifting and rolling-sliding modes is proposed to initialize particle incipient motions. Lagrangian governing equations of aeolian particle motion are presented and used to simulate the trajectories of solid particles. Particularly, Lagrangian governing equations of bed-load particle motion are originally deduced and applied to model the particle rolling-sliding movement on the bed surface. In addition, particle-surface interactions are taken into account by probabilistic rebound/splash models. Thirdly, numerical simulations of particle transport over a fixed Gaussian dune and over a deformable sinusoidal dune are carried out. In the fixed Gaussian case, an overall good agreement on the particle concentration profiles over the dune between the simulated results and the experimental data of Simoens et al. (2015) preliminarily validates the ability and accuracy of the developed numerical solver coupled with physical comprehensive wind erosion models. In the deformable sinusoidal case, the simulated dune shapes are compared with the experimental ones of Ferreira and Fino (2012). A good agreement between them is observed at t = 2.0 min and an obvious underestimate of the dune shape is shown at t = 4.0 min and t = 6.0 min. By analyzing the simulated results, it is shown that the recirculation zone behind the dune is gradually reduced as the dune deforms and that windward erosion and lee side deposition is observed. It is also shown after testing that the splash entrainment is important for the lee side erosion. Moreover, a preliminary attempt is presented to apply an improved splash model with accounting for the bed slope effect to the simulation of sand dune deformation. A better performance on the simulated dune shape is achieved at t = 4.0 min in comparison with the experimental one
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Kirschner, Audrey. "Planting Density Effects on the Growth of Dune Grasses." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6068.
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Coastal dune vegetation plays a key role in dune formation and stabilization through sediment trapping and erosion control. To restore degraded dunes, revegetation of dune building species is critical. Planting density has been found to effect growth of marsh species, with closer plantings alleviating stress through facilitation. As coastal dunes are high stress environments, it is expected that dune species may also exhibit facilitative interactions based on the Stress Gradient Hypothesis. Therefore, planting grasses in clumped configurations may lead to more successful dune revegetation. The objective of this research was to determine how planting density affects the growth of two dominant dune grasses along the US Atlantic coast, Ammophila breviligulata and Uniola paniculata, through field surveys of natural distribution, density, and a manipulation study of planting densities. Natural distribution differed between the two species with A. breviligulata occurring at lower dunes and U. paniculata occurring at higher dunes. Ammophila breviligulata occurred more densely than U. paniculata. Planting density of U. paniculata had an effect on growth parameters (shoot length, stem number, and ramet number) but not survival with dispersed plantings (50 cm apart) having higher growth than clumped plantings. The effect of density planting on growth parameters may impact dune building processes. Sparsely planted U. paniculata may have greater sediment capture compared to densely planted U. paniculata due to greater stem number and biomass resulting in taller, steeper dunes.
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Buck, Mitchell Arthur. "Experiments and numerical model for berm and dune erosion." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 190 p, 2008. http://proquest.umi.com/pqdweb?did=1456291111&sid=6&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Costas, Vázquez Iria [Verfasser], and Christian [Akademischer Betreuer] Betzler. "Climate Archive Dune / Iria Costas Vázquez. Betreuer: Christian Betzler." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://d-nb.info/1050239075/34.
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Monge, Jackie Ann. "CONVERGENCE OF DUNE TOPOGRAPHY AMONG MULTIPLE BARRIER ISLAND MORPHOLOGIES." UKnowledge, 2014. http://uknowledge.uky.edu/geography_etds/19.
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Wave-dominated and mixed tidal and wave energy barrier islands are assumed to have characteristic dune topographies that link to their macroscale form. However, there has been no systematic attempt to describe the linkage between barrier island macroscale form and dune topography. The goal of this thesis was to investigate how dune topographies correspond to a number of barrier island morphologies found along the southeastern U.S. Atlantic coast. Macroscale process-form variables were used to classify 77 islands into seven morphologic clusters. Islands from each cluster were selected and sites characteristic of the range of dune topographies within islands were characterized using three methods: the frequency distribution of elevations, directional spatial autocorrelation of elevation at different distance classes, and FRAGSTATS indices summarizing the patch structure of elevations. Variables derived from each of these methods peaked in their ability to discriminate among barrier island morphologies when the islands were aggregated into three groups. An ordination of those variables revealed a two or three-fold grouping of barrier island dune types that approximated the traditional wave dominated and mixed energy barrier island morphologic classification. These findings suggest that dune topographies converge upon two to three configurations even within the heterogeneity in macroscale island morphology.
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Greipsson, Sigurdur. "Population studies on the dune-building grass Leymus arenarius." Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303369.
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Smyth, Thomas Andrew George. "Airflow and sediment transport dynamics in coastal dune blowouts." Thesis, Ulster University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.646398.
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Blowouts are erosional depressions that occur on pre-existing vegetated sand deposits. Their morphodynamic behaviour can reflect changes in anthropogenic activity, climatic conditions and animal behaviour; however patterns of deflation are poorly understood as near-surface airflow is complex. Previous research has indicated that flow is topographically manipulated as it moves through the landform, causing steering, reversal and jetting of the airflow. However, empirical data on these effects have been limited due to inadequacies in anemometer and sediment trap deployments. As a consequence knowledge of flow behaviour inside blowouts is limited to crude conceptual approaches. This study used ultrasonic three-dimensional anemometry (50 Hz) to validate a three dimensional computational fluid dynamics (CFD) model. This enabled a detailed description and explanation of near surface wind flow within a bowl blowout from a variety of wind direction and wind speeds up to hurricane force. Three-dimensional anemometry complemented by a CFD simulation was used to quantify wind conditions, whilst high resolution (25 Hz) electronic load cell traps and saltation impact responders, measured sediment transport within a trough blowout. The results demonstrate that considerable flow streamline compression, expansion, steering and reversal occur within trough and saucer blowouts. Airflow within blowouts alters with incident wind direction but does not change structurally with wind speed. Sediment transport flux and intermittency vary considerably within the landform, whilst the best correlation between wind flow and sediment transport varies between wind speed and turbulent kinetic energy (TKE). Where wind speed correlates best with TKE, the optimum averaging interval is much lower than those locations which correlate best with wind speed.
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Costas, Vázquez Iria Verfasser], and Christian [Akademischer Betreuer] [Betzler. "Climate Archive Dune / Iria Costas Vázquez. Betreuer: Christian Betzler." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://nbn-resolving.de/urn:nbn:de:gbv:18-67065.
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Carrasco, Martínez Juan Carlos. "Probing CPT breaking induced by quantum decoherence at DUNE." Master's thesis, Pontificia Universidad Católica del Perú, 2019. http://hdl.handle.net/20.500.12404/14341.
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We consider a beyond standard physics scenario, where neutrino is considered
as an open quantum system. In order to have that consideration we
use the Lindblad master equation, which introduce the quantum phenomena
called decoherence. In that context we explore one of the most exotic
of its consecuences, the CPT violation. We work in three
avor generation
case where making the SU(3) decomposition of the operators we encounter
that there exist fteen parameters in the decoherence matrix that explicitly
violate CPT. Regarding four of those parameteres we choose one case of
decoherence which will be tested at DUNE.<br>Trabajo de investigación
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Savage, Christopher Jon. "Implications of Dune Pattern Analysis for Titan's Surface History." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/3077.
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Analyzing dune parameters such as dune width and spacing can be useful in determining the reaction of dunes to changes in atmospheric and sedimentary conditions currently and in the recent geologic past. Dune parameters, dune width and spacing, were measured for linear dunes in regions across Saturn's moon Titan from images T21, 23, 28, 44 and 48 collected by Synthetic Aperture RADAR aboard the Cassini spacecraft in order to reconstruct the surface history of Titan. Dunes in the five study swaths are all linear in form, but lack superimposed or flanking dunes. They have a mean width of 1.3 km and mean crest spacing of 2.7 km, wider and farther apart on average than similar terrestrial dunes in the Namib and Agneitir Sand Seas though larger linear dunes exist on Earth. Because of the lack of superimposed and flanking dunes and their size, Titan's dunes are classified as very large simple linear dunes. The large size, spacing and uniform morphology are all indicators that Titan's dunes are very mature and long-lived features. The ratio of dune width to spacing for Titan's dunes is similar to that found in terrestrial dunes in that dune spacing tends to be twice dune width. In addition to being similar in size, this is further evidence that terrestrial dunes can be used as analogues for Titan's dunes and vice versa and that the essential dune-forming processes are the same on both bodies. Dune width and spacing decrease northward, which is attributed to, but not limited to, increased maturity of dune fields to the south or increased sediment stabilization to the north. Sediment stabilization may be caused by Titan's asymmetric seasons and a net transport of moisture from south to north. The majority of dunes have spacings consistent with an upper limit of 2 to 4 km established by the atmospheric boundary layer, further evidence they are mature. Dunes are more widely spaced in the south are evidence they have been growing toward a steady state for a longer period of time than those in the north. Titan's large linear dunes have long reconstitution times. This is in part due to the fact that winds sufficient for saltation are reached only near the Titan equinox every 14 Earth years. Based on rates for similar terrestrial dunes the reconstitution time for Titan's dune is 600,000 Earth years or more, and therefore substantial changes in dune form should not be observable over Cassini's lifetime. Cumulative probability plots of dune parameters measured at different locations across Titan indicate there is a single population of dunes on Titan. This suggests that, unlike analogous dunes in the Namib and Agneitir Sand Seas, dune-forming conditions that currently exist on Titan are either the only dune-friendly conditions in the moon's history, or the current conditions have been stable and active long enough to erase any evidence of past conditions.
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Whitaker, Lindsey M., Ph D. Matthew Ritter, Ph D. Scott J. Steinmaus, and Jonathan Hall. "The Preservation and Protection of Native Biodiversity in the Guadalupe Nipomo Dunes Complex." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1715.
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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.
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Al-Hinai, Khattab Ghalib. "Quaternary aeolian sand mapping in Saudi Arabia using remotely sensed imagery." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/7772.
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VICENZI, MATTEO. "A GRAIN of SAND for DUNE: Development of simulations and reconstruction algorithms for the liquid Argon target of the SAND detector in DUNE." Doctoral thesis, Università degli studi di Genova, 2023. https://hdl.handle.net/11567/1105305.
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Neutrinos are the most abundant of known matter particles in the Universe and the study of their properties has produced many surprises, including the evidence for physics beyond the Standard Model of particle physics. In particular, the phenomenon of neutrino oscillations, transitions in flight between the different types of neutrinos, provides compelling evidence that neutrinos have small, but non-zero, masses and that their mass states are mixtures of their flavor states. The field of neutrino physics has advanced rapidly and there is currently a good understanding of most experimental results in the context of neutrino oscillations. Presently, the focus of current and future experiments has therefore shifted to making precise measurements of the oscillation parameters and trying to understand the nature of neutrino masses.
The Deep Underground Neutrino Experiment (DUNE) is a future neutrino oscillation experiment that is designed to achieve the sensitivity required to finally solve long-standing open questions in neutrino physics, such as finding the ordering of neutrino mass states and measuring the possible matter-antimatter asymmetry in this sector of the Standard Model. The latter would be a very important step in our understanding of the Universe: current observations show in fact a large asymmetry, with matter strongly dominating over antimatter from the small to the large structures of the cosmos, despite our cosmological models predicting that the Big Bang should have created equal amounts of matter and antimatter. If an intrinsic asymmetry exists within the laws of physics, it would explain why the balance was broken in favor of matter, rather than antimatter. A small asymmetry has already been found in the quark sector of the Standard Model, but it is still not sufficient to explain the observations. A precise measurement of the same effect in the neutrino sector is therefore crucial.
DUNE will be employing a high-intensity neutrino beam produced at the Fermi National Accelerator Laboratory (Fermilab) in Illinois (US) and directed towards an underground detector at the Sanford Underground Research Facility (SURF) in South Dakota (US). Neutrino oscillations are measured by comparing recorded neutrino events between two detectors at the near and far sites. The Far Detector will consist of a modular 68 kt liquid argon time projection chamber, by far the largest liquid argon neutrino detector ever built. Neutrinos cannot be detected directly, but charged articles resulting from their interactions in liquid argon produce two signals, vacuum ultraviolet (VUV) light from the excitation of Ar atoms and electric charge from their ionization. Both these signals are collected and used to achieve a complete reconstruction of the neutrino interaction. The Near Detector will instead be a suite of three detectors, as it needs to address some of the most important challenges of the experiment. Apart from characterizing the unoscillated neutrino beam, the precision needed to achieve DUNE goals requires to carefully constrain the systematic uncertainties of the measurement. The Near Detector is therefore expected to fulfill this task by providing corrections for extrapolating the beam to the far site, measuring ν-Ar cross-sections and tuning the interaction models.
SAND (System for on-Axis Neutrino Detection) will be one of the three components of the Near Detector complex, acting as the primary beam monitor of the experiment. It will be a magnetized detector, equipped with a high resolution tracker to measure the momentum of particles by their curvature and a high performance electromagnetic calorimeter. Moreover, it will also host several different targets to study neutrino interactions on different nuclei. In particular, since the presence of Ar targets in the Near Detector is essential for comparison with the Far Detector, SAND will contain a small (1 t) liquid argon cryostat inside its magnetic volume called GRAIN (Granular Argon for Interaction of Neutrinos). GRAIN is not foreseen simply as a passive target, but it will also be instrumented to actively contribute to the reconstruction of neutrino interactions occurring inside. In principle, liquid argon provides information via scintillation light and ionization charge. However, given the high rate environment and the shape of the cryostat, collecting ionization charge as it is done in the Far Detector will not be feasible. On the other hand, equipping GRAIN with photodetectors only will allow to measure the total energy released in the medium and give a time reference to the event, but the spatial reconstruction ability would still be limited. The proposed improvement to recover the spatial reconstruction is to place imaging devices on the inner walls of GRAIN to take pictures of neutrino interactions. Such devices are an innovative concept for liquid argon detectors, as scintillation light has never been exploited to this extent. Since the VUV wavelength and the cryogenic environment rule out commercially available cameras, a custom-made solution is being pursued. The active photosensor will be a 2D array of Silicon PhotoMultipliers (SiPMs), each acting as an independent pixel, while two technologies are currently being investigated for the imaging element of the camera: coded aperture masks and lenses.
The purpose of this thesis has been the study of the lens-based option and its performance for the reconstruction of ν-Ar interactions in SAND. An optimized device was designed to address the challenges derived from operating in liquid argon and validated using Monte Carlo simulations, leading to the definition of a preliminary geometrical configuration of these cameras in GRAIN. An optical simulation of GRAIN was then developed to simulate its response to neutrino interactions within the SAND framework. This software package includes a full description of the scintillation mechanism and light propagation, returning as output the set of images recorded by each camera. A preliminary reconstruction algorithm was also developed to analyze these 2D images and combine them together to obtain a 3D reconstruction of the event. The overall reconstruction performance was then studied by integrating together information coming from all SAND subsystems. In addition to the simulation efforts, the first camera prototype was built and tested in a warm environment, showing agreement with the expectations, while cold tests are in preparation for the near future. Despite more development being needed, this innovative optical readout for GRAIN is expected to provide a significant contribution to the selection of ν-Ar samples and the fulfillment of the Near Detector goals.
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Cotte, Philippe. "Le projet WA105 : un prototype de chambre à projection temporelle à argon liquide diphasique utilisant des détecteurs LEMs." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS246/document.
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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<br>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
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Junior, Daniel Rodrigues do Nascimento. "\"Morfologia e sedimentologia ao longo do sistema praia-duna frontal de Ilha Comprida, SP\"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/44/44140/tde-15032007-161706/.
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A Ilha Comprida, localizada no litoral sul do Estado de São Paulo, é uma ilha-barreira arenosa holocênica de 63 km de comprimento por até 5 km de largura, limitada a SW pela desembocadura de Cananéia, e a NE, pela desembocadura de Icapara. Seu sistema praia - duna frontal teve grande variação no tempo, como evidenciado por sucessivos truncamentos de cordões litorâneos. Em escala de tempo mais restrita, dentro dos últimos 200 anos, coberta pelo registro histórico e cartográfico e por fotografias aéreas, as mudanças morfológicas mais significativas concentram-se no extremo nordeste da ilha. Incluem a variação de largura na área hoje caracterizada pelo máximo estrangulamento da ilha, a formação de um pequeno campo de dunas transgressivo nesta mesma área, o surgimento em 1943 de uma projeção da linha de costa, atualmente em estágio avançado de erosão, e o aparecimento intermitente e sucessivo de embaiamentos lagunares no setor adjacente da ilha de Iguape. A abertura do canal artificial do Valo Grande, em 1852, atuou de modo direto ou indireto em pelo menos parte destas mudanças. O aumento de vazão, de retrabalhamento de sedimentos arenosos e portanto de aporte de carga de fundo, devido ao Valo Grande, induziu o surgimento de ilhas arenosas e a formação de ?manchas de areia? no fundo do canal lagunar, bem como a intensificação da dinâmica de meandramento da desembocadura de Icapara, implicando possível aceleração na migração desta desembocadura rumo NE e no próprio crescimento longitudinal da barreira. O sistema praia - duna frontal da Ilha Comprida apresenta também grande variação no espaço, evidenciada pela alternância ao longo de sua extensão de morfologias diferentes, o que pode ser atribuído à intercalação entre setores de caráter deposicional e erosivo. As extremidades da barreira caracterizam-se pela ocorrência marcante de pequenos campos de nebkhas sobre terraços baixos de dunas frontais (<0,5 m). A presença dessas feições pode ser relacionada à contínua progradação próximo às desembocaduras lagunares de Icapara e de Cananéia. A zona erosiva mais evidente encontra-se na extensão centro-sul da praia, como evidenciado pela ocorrência de cordões antigos truncados pela linha de costa atual, e pela redução em tamanho de dunas frontais ativas incipientes e estabelecidas, as quais aparecem por vezes com falésias vivas associadas. Na mesma região, a morfodinâmica muda de regime dissipativo para intermediário, com presença de cúspides de espraiamento e berma. Esta região, ademais, concentra a mais alta variabilidade e complexidade de morfologia de dunas (i.e. cordões de dunas incipientes e estabelecidas obliquamente amalgamadas), além de uma concentração maior de dunas do tipo rampa. No restante do sistema, predomina ampla face de praia de baixa declividade (média de 0,66o), com tendência para formas mais estáveis de dunas frontais (terraços e cordões). Medidas estatísticas de distribuição granulométrica (diâmetro médio, desvio-padrão e assimetria) obtidas através do método dos momentos de Pearson, permitiram inferir, pela regra de McLaren, duas células de deriva litorânea longitudinal principais. A célula nordeste, dirigida para NE, abrange aproximadamente 53 km, e a célula sudoeste toma em sentido oposto (SW) os restantes 10 km. As duas zonas de pólo deposicional de deriva são caracterizadas por amplos e baixos terraços de dunas frontais incipientes progradacionais. A zona de divergência entre as células de deriva coincide com a região de erosão costeira mais intensa. A distribuição em massa de minerais pesados é concordante com o transporte longitudinal verificado. Responde a isso a tendência de aumento de minerais de menor equivalente hidráulico (em geral, quimicamente mais instáveis) a despeito da redução de minerais de equivalente hidráulico mais alto (em geral, quimicamente mais estáveis) no rumo de transporte. A integração dos resultados obtidos por análise morfológica (fotointerpretação e estudo de feições de campo) e sedimentológica (granulometria e minerais pesados) permitiu estabelecer um modelo morfodinâmico para o sistema praia - duna frontal recente da Ilha Comprida. Neste modelo, a fase final de evolução da ilha é atribuída tanto à superação do obstáculo ao crescimento longitudinal exercido pelo morro de Icapara, quanto ao incremento de carga sedimentar na desembocadura de Icapara, induzido pela abertura do Valo Grande.<br>Ilha Comprida is a Holocene sandy barrier-island located on the south coast of São Paulo State, 63 km long and 2 to 5 km wide. Its transverse boundaries are Cananéia and Icapara inlets, at the SW and NE, respectively. The beach-foredune system of Ilha Comprida have experienced intense morphological variation in time, as showed by the successive truncations of littoral ridges. In a more restricted time-scale (at least 200 years) as covered by historical and cartographic records and aerial photographs, the most relevant changes have occurred on the northeast extremity of the island. These changes include: i) variation in width at the present most narrow region; ii) formation of a little transgressive dunefield (2 km2) in the same region; iii) initiation (in 1943) of a projection in the coastline, actually in advanced erosional state; iv) intermittent and successive appearing of lagoonal embayments at the neighboring sector of the Iguape island. The opening of the Valo Grande artificial channel, in 1852, acted either directly and indirectly on these changes. The increase of sedimentary bed-load supply induced the appearance of sand islands and submerged sand patches along the lagoonal channel. Beside this, the increasing meandering of Icapara inlet forced its rapid migration to the NE, and the longitudinal growing of the barrier. The beach-foredune system also shows great variability alongshore, observed on the morphologic alternance of depositional and erosional sectors. The tips of the barrier are characterized by the marked occurrence of small nebkha fields on foredune terraces (up to 0.5 m high). These aeolian morphological features can be related with a continuous progradation nearly Icapara and Cananéia inlets. The most-evidenced erosional zone stays at the mid-southwestern portion of the beach, as observed on the truncation of former beach and foredune ridges by the present coastline, and on the reduction in size of active incipient and established foredunes (that often appears with active cliffs). In the same region, the coastal morphodynamics changes from dissipative to intermediary beach, with presence of swash cusps and berm. Moreover, this site concentrates the highest variability and complexity of dune morphology (e.g. obliquely amalgamated incipient and established foredune ridges), beyond a increasing occurrence of ramp foredunes. In the remains of the beach-dune system, large shorefaces of low declivity (0.66o in mean), with tendency to more stable shapes of foredunes (terraces and ridges), are dominant. Statistical measures on the distribuition of granulometric frequencies (mean diameter, standard deviation, skewness), calculated through the Pearson?s moments method, indicate according to the McLaren rule two main longshore drift cells. The northeastern cell, oriented towards the NE, comprises about 53 km. The southwestern cell, comprising the remaining 10 km, is oriented towards the SW. The two depositional poles of longshore drift cells are characterized by wide and flat progradational, incipient foredune terraces. The divergence zone among these longshore cells drift coincides with the zone of the most intense coastal erosion. The mass distribution of heavy minerals is in agree with the deduced directions of longshore transport. This fact is confirmed by the tendency of increasing concentration of minerals with minor hydraulic equivalence (usually, more unstable minerals) in despite of reduction of minerals with high hydraulic equivalence (usually, more stable minerals) along the net longshore drift direction. The integration of data obtained by morphologic analysis (interpretation of aerial photographs and field features) and sedimentology (grain size, heavy minerals), allowed to postulate a morphodynamic model for the recent beach-foredune system of Ilha Comprida. According to this model, the late phase of barrier evolution is related both to the surpassing an obstacle to longitudinal growth (Icapara hill), and to the increasing sedimentary input at the Icapara inlet, favored by the opening of the Valo Grande channel.
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Todd, Colleen Barbara. "A comparison of the reproductive strategies of key species of a prograding dune system in the Mlalazi Nature Reserve, Natal." Thesis, Rhodes University, 1995. http://hdl.handle.net/10962/d1003800.
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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.
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Boehme, Nicole F. "A Comparison of Antlions, Bees, Darkling Beetles and Velvet Ants Across Sand Dune and Non-Sand Dune Habitats at Ash Meadows National Wildlife Refuge." DigitalCommons@USU, 2014. https://digitalcommons.usu.edu/etd/2078.
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Insects fulfill important roles within all ecosystems, including deserts, and interact directly and indirectly with the endemic and endangered species at the Ash Meadows National Wildlife Refuge (AMNWR). Here I investigate the variability of species richness, diversity, abundance and community composition of four insect groups between stabilized sand dune habitats, unstabilized sand dune habitats and non-sand dune habitats. The insects examined in this thesis include antlions (Myrmeleontidae), bees (Apiformes), darkling beetles (Tenebrionidae) and velvet ants (Mutillidae). As the impact and interactions of two of the insect groups, antlions and velvet ants, are largely unknown within any ecosystem, this thesis also includes a faunal study of velvet ants at AMNWR and their spatial and temporal variation at the refuge. Generalized linear mixed models were used to identify significant differences in richness, diversity and abundance for each insect group between the stabilized sand dune, unstabilized sand dune and non-sand dune habitats. Species richness differed between habitats for antlions, beetles and velvet ants over the study period. Diversity differed between habitats for antlions and beetles, and abundance differed between habitats for all groups over the study period. Nearly every habitat supported some unique species. The faunal survey of velvet ants revealed minor variation in flight times between species and a unique pattern of temporal niche partitioning in one species. Habitat preferences were observed for seven of 42 velvet ant species at AMNWR. In a comparison of the diversity of velvet ants between AMNWR and the Nevada Test Site (NTS), six velvet ant species that occurred at the NTS were not found at AMNWR. Diagnoses and a key are provided for the velvet ants of AMNWR. This thesis increases the number of known terrestrial invertebrates at the refuge and provides a comparison of terrestrial insect distribution and habitat use at AMNWR. These investigations contribute to the goals and objectives of the U. S. Fish and Wildlife Service to obtain basic inventories and understand the terrestrial habitat use of invertebrates at AMNWR.
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Pries, Alexander James. "Hurricane impacts on coastal dunes and spatial distribution of Santa Rosa beach mice (Peromyscus polionotus leucocephalus) in dune habitats." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013415.
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Isvén, Ulrika. "Sanddynsmorfologi och kusterosion i Laholmsbukten, Hallands län." Thesis, Stockholms universitet, Institutionen för naturgeografi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-123318.
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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.<br>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.
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Peter, Craig Ingram. "Water requirements and distribution of Ammophila arenaria and Scaevola plumieri on South African coastal dunes." Thesis, Rhodes University, 2000. http://eprints.ru.ac.za/38/.
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Fauver, Laura A. "Toward predicting barrier island vulnerability simple models for dune erosion /." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001055.
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Irizarry, Adella. "The amtal rule| Testing to define in Frank Herbert's Dune." Thesis, Florida Atlantic University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1524501.
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<p> In this project, I focus on the function of the “amtal,” or test of definition or destruction, in Frank Herbert's <i>Dune</i>. It is my argument that these tests “to destruction” determine not only the limits or defects of the person being tested, but also—and more crucially—the very limits and defects of the definition of humanity in three specific cultural spheres within the novel: the Bene Gesserit, the Fremen, and the Faufreluches. The definitions of “amtal” as well as “humanity,” like all definitions, are somewhat fluid, changing depending on usage, cultural context, and the political and social needs of the society which uses them. Accordingly, <i>Dune</i> remains an instructive text for thinking through contemporary and controversial notions about the limits of humanism and, consequently, of animalism and posthumanism. </p>
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Plassmann, Katharina. "Effects of grazing and nitrogen deposition on sand dune systems." Thesis, Bangor University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433686.
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