No description available.

Himalayan glaciers are key components of earth's cryosphere, acting as hydrological reservoirs vital to many human and natural systems. Most Himalayan glaciers are shrinking in response to changing climate, which will potentially impact water resources, natural hazards, sea level rise, and many other aspects. However, there is much uncertainty regarding the state of these glaciers, as direct field data are difficult to obtain. Accordingly, long-timespan remote sensing techniques are needed to measure changing glaciers, which have memory and often respond to climate on decadal timescales. This study uses declassified historical imagery from the Hexagon spy satellite database to fulfill this requirement. A new highly-automated, computer-vision based solution is used to extract historical terrain models from Hexagon imagery, which are used as a baseline to compute geomorphic change for glaciers in the Kingdom of Bhutan and Tibet Autonomous Region of the eastern Himalayas. In addition to glaciers, the new method is used to quantify changes resulting from the Thistle Creek Landslide (surface elevation changes resulting from the landslide show an average elevation decrease of 14.4 ± 4.3 meters in the source area, an increase of 17.6 ± 4.7 meters in the deposition area, and a decrease of 30.2 ± 5.1 meters resulting from a new roadcut) and Mount St. Helens eruption in western North America (results show an estimated 2.48 ± 0.03 km3 of material was excavated during the eruption-triggered debris slide). These additional results illustrate the applicability of Hexagon imagery to a variety of landscape processes. Regarding the primary application in the Himalayas, all studied glaciers show significant ice loss. Futhermore, the multi-decadal timespan reveals important aspects of glacier dynamics not detectable with temporally shorter datasets. Some glaciers exhibit inverted mass-balance gradients due to variations in debris-cover, while enhanced ice losses are prominent on glacier toes terminating in moraine-dammed proglacial lakes, resulting from calving caused by thermal undercutting. Remarkably, debris-covered glaciers show significant thinning despite insulating effects of the debris, likely due to poorly-understood ice cliff and melt pond mechanisms. The mean annual geodetic mass balance of 22 studied glaciers over a 32-year period is estimated to be -0.16 ± 0.03 m yr-1 water equivalent. Thus, these glaciers are not in equilibrium with current climate, and appear to be losing significant amounts of ice regardless of debris-cover.

O estudo de bacias hidrográficas no meio tropical úmido, tem adquirido grande importância nas últimas décadas, devido a crescente demanda por planejamento de recursos hídricos. Entretanto, muitos desses trabalhos têm confundido o conceito de bacias hidrográficas, acreditando ser esta, uma mera rede de canais interconectados que formam a hidrografia dos terrenos, portanto, tomando-a como simples unidade cartográfica de estudo. Este fato tem banalizado em muito o uso de conceitos relacionados aos estudos de bacias, provocando sérios equívocos nas produções acadêmicas atuais. Partindo do princípio de que as bacias hidrográficas são espaços territoriais de circulação vertical e horizontal dágua, tendo a rede interconectada de canais, como um dos seus principais elementos, que escolhemos a bacia hidrográfica do Rio Benevente para estudo da relação entre a dinâmica fluvial desta e os seus condicionantes estruturais e morfológicos. Fundamentado no método da associação e indeterminação geomorfológica de Leopold e Langbein (1970), e, através de informações oriundas dos procedimentos técnico-operacionais de compartimentação geomorfológica e compilação de dados de parâmetros hidrográficos, foi possível descobrir que os sub-sistemas de drenagem que compõem a hidrografia total da bacia, evoluem condicionados por litoestruturas cristalinas e tectônicas do proterozóico, portanto, de organização antiga, e, que, aparentemente, demonstram não sofrer reativações modernas, a ponto de intervir na evolução dos sub-compartimentos de relevo regionais e na evolução hidrográfica da rede de canais. Chega-se desta forma, à conclusão de que os processos de encaixamento da drenagem, capturas fluviais, seccionamento de litoestruturas, gênese de knickpoints e evolução dos perfis longitudinais fluviais estão associados à dinâmica de processos geomórficos diferenciais, sob litoestruturas de forte natureza anisotrópica e complexa organização geotectônica. Fato que responde pela diversidade de sub-compartimentos de relevo e configuração evolutiva dos sistemas fluviais de dinâmicas diferenciais. / The study of watersheds in the humid tropical environment, has acquired great importance in recent decades due to growing demand for water resources planning. However, many studies have confused the concept of watersheds, believing that this was simply a network of interconnected channels that form the hydrography of the land, thus making it as simple cartographic unit of study. This commonplace is the use of concepts related to the studies of basins, causing serious confusion in the current academic productions. Assuming that the basins are territorial spaces of vertical and horizontal movement of water, the interconnected network of channels, as one of its main elements, we chose the basin of Rio Benevente to study the relationship between the dynamics of this river and its structural and morphological constraints. Based on the method of the Association and indeterminacy in geomorphologic Leopold and Langbein (1970), and through information from the technical and operational procedures of geomorphological partitioning and compilation of data from hydrographic parameters, could find that the sub-drainage systems that make up the total of the hydrographic basin, driven by evolving litoestruturas crystal and the tectonic proterozóico, therefore, the old organization, and that, apparently, show not suffer reactivations modern as to intervene in the evolution of sub-compartments of regional importance and the evolution of the network of river channels. Enough is thus concluded that the processes to fit the drainage, catch river, sectioning of litoestruturas, gênesis of knickpoints and evolution of longitudinal river profiles are associated with the dynamic of geomorphic processes differential,under litoestruturas of strong anisotropic nature and complex organization geotectônica. Fact responsible for the diversity of sub-compartments of important configuration and evolutionary dynamics of river systems of differential.

A travers une approche systémique, l’objectif de cette thèse est de préciser les modes et les rythmes d’ajustement du continuum glacio-fluvial au changement climatique post-Petit Âge Glaciaire. À partir de la datation lichénométrique et de la quantification des réponses des systèmes glaciaire et fluvioglaciaire de quinze émissaires et sandurs sud-islandais, nous explorons l’éventail des scénarios d’ajustements observés, testons l’hétérogénéité et le caractère asynchrone des réponses glaciaires et fluvioglaciaires et cernons les variables de contrôle susceptibles d’expliquer la diversité des réponses mesurées. Sur la base des données collectées, traitées et analysées, nous avons pu : (1) mettre en évidence une asynchronie du maximum PAG glaciaire et une forte hétérogénéité de l’intensité de recul post-PAG des émissaires sud-islandais reflétant la nature fondamentalement complexe des ajustements glaciaires ; (2) suggérer l’existence de processus marginaux de contrôle des flux hydrosédimentaires s’apparentant à la criticalité auto-organisée ; (3) identifier un mode dominant d’ajustement fluvioglaciaire post-PAG pour les sandurs de type I et mettre en évidence l’indépendance relative des sandurs de jökulhlaup vis-à-vis des fluctuations glaciairesgh / Based on a systemic approach, this study intends to characterize the patterns and the temporal rhythms of the glacio-fluvial continuum adjustment to the post-Little Ice Age climate change. According to lichenometric dating and quantification of the glacial and fluvioglacial responses of fifteen glaciers tongues and sandurs in south-Iceland, the range of observed adjustments scenarios is explored. The heterogeneous and asynchronous nature of responses are tested and the variables controlling the observed adjustment variability are identified. Based on the collected and analyzed data sets: (i) we highlight the asynchronous LIA maximum extent of south-Icelandic glaciers and the significant heterogeneity in glacier fronts retreat intensity which both reflect the complex nature of glacier response to climate change; (ii) we suggest the existence of marginal processes akin to self-organized criticality which control sediment transport efficiency and water discharges; (iii) we identify a prevailing pattern for the post-LIA fluvial adjustment of sandur type I and the independent response of jökulhlaup sandur (type III) to glacier front fluctuations.

Made available in DSpace on 2017-07-10T17:30:53Z (GMT). No. of bitstreams: 1 Leonel.pdf: 6347803 bytes, checksum: 7d336a55689271653876d5cb0037c7f0 (MD5) Previous issue date: 2016-05-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This dissertation seeks to understand the evolution of landforms in the sector between Fartura Mountain and the River Chapecó (Abelardo Luz - SC), located on the geomorphological surface of Abelardo Luz, Plateau of Araucárias. Therefore it follows two research fronts: the characterization of the materials that make up the superficial formation representative of the area and fluvial-morphometric analysis of the current drainage. To achieve the objective of the research analysis in the field, in the laboratory and in the cabinet were carried out. In the field description was identified the horizons of superficial formation through color, texture, structure and consistency. In laboratory granulometric, routine chemistry, particle density, analytical chemistry (10 leading oxide), iron content (free, total, amorphous) and mineralogy by X-ray diffraction analyzes were performed. The superficial formation is ten meters thick, and of these, six meters and half are exposed in roadblock and three and a half meters were described by manual probing with Dutch auger. The horizons have been identified: Ap (0-30 cm); AB (30 - 70 cm); BA (70 - 140 cm); Bw1 (140-420 cm); Bw2 (420-700 cm); BC (700-860 cm); CB (860-950 cm) and C (950-1000 cm). Through the physical and chemical routine characteristics, the solum may be classified as Oxisoil, aluminum character. The routine chemical analysis shows that there is not an increasing order of basic cations in depth, thus showing to be an allochthonous soil, in the most superficial part (up to about 6m). The chemical analysis confirms the routine chemistry data, demonstrating that not increasing order of depth basis. The Ki and Kr values attest well weathered formation from the base, indicating again allochthonous material in the superficial part and autochthonous in the base. Data from iron analyzes by Fed-Feo / Fet reason show that the weathering of the superficial formation is evolved. Mineralogical by X-rays showed mineral quartz type, hematite, magnetite, gibbsite, anatase, cristobalite and goethite and clay minerals of the kaolinite and vermiculite and / or chlorite type. The presence of gibbsite in any Solum, indicates that there is partial desilicatization (monosialitization) up to a total desilicatization (alitização). The fluvio-morphometric analysis of drainage indicates movement blocks in the study area, and the Serra da Fartura is characterized as a rising block. Subsident block is found from this point up to the channel of river Chapecó. Finally, the analysis results indicate the occurrence of overlap of models etchplanation and pediplanation and that the superficial formation has more than one polygenetic genesis in the study area. / A presente dissertação busca compreender a evolução das formas de relevo no setor entre a Serra da Fartura e o rio Chapecó (Abelardo Luz SC), localizada na superfície geomorfológica de Abelardo Luz, VI, Planalto das Araucárias. Para tanto seguiu-se duas frentes de investigação: a caracterização dos materiais que compõem a formação superficial representativa da área e a análise fluviomorfométrica da drenagem atual. Para atingir o objetivo da pesquisa foram realizadas análises em campo, em laboratório e gabinete. Na descrição de campo identificou-se os horizontes da formação superficial através da cor, textura, estrutura e consistência. Já em laboratório foram realizadas análises granulométricas, química de rotina, densidade de partículas, química analítica (10 principais óxidos), teores de ferro (livre, total e amorfo) e a mineralogia por difração de raios-X. A formação superficial possui dez metros de espessura, sendo que destes, seis metros e meio estão expostos em corte de estrada e três metros e meio foram descritos através de sondagem manual com trado holandês. Foram identificados os horizontes: Ap (0 30 cm); AB (30 70 cm); BA (70 140 cm); Bw1 (140 420 cm); Bw2 (420 700 cm); BC (700 860 cm); CB (860 950 cm) e C (950 1000 cm). Através das características físicas e químicas de rotina, o solum pode ser classificado como Latossolo Vermelho Distrófico, caráter Alumínico. A análise da química de rotina mostra que não há um ordenamento crescente dos cátions básicos em profundidade, demonstrando assim ser um solo alóctone na parte mais superficial (até aprox. 6 m). A química analítica confirma os dados da química de rotina, demonstrando este não ordenamento crescente das bases em profundidade. Os valores Ki e Kr atestam uma formação bem intemperizada desde a base, indicando novamente material alóctone na parte superficial e autóctone na base. Os dados das análises de ferro através da razão Fed-Feo/Fet demonstram que o estágio de intemperismo da formação superficial é evoluído. A mineralogia por difração de raios-X apresentou minerais do tipo quartzo, hematita, magnetita, gibbsita, anatásio, cristobalita e goetita, e argilominerais do tipo caulinita e vermiculita e/ou clorita. A presença da gibbsita em todo o solum, indica que há dessilicatização parcial (monossialitização) até a dessilicatização total (alitização). A análise fluviomorfométrica da drenagem indica movimentação de blocos na área de estudo, sendo que a Serra da Fartura se caracteriza como bloco ascendente e deste a calha do rio Chapecó tem-se bloco subsidente. Por fim, os resultados das análises indicam ocorrência de justaposição dos modelos de etchplanação e pediplanação e que a formação superficial possui mais que uma gênese (poligenético) na área de estudo.

Made available in DSpace on 2017-05-12T14:42:23Z (GMT). No. of bitstreams: 1 Leonel.pdf: 6347803 bytes, checksum: 7d336a55689271653876d5cb0037c7f0 (MD5) Previous issue date: 2016-05-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This dissertation seeks to understand the evolution of landforms in the sector between Fartura Mountain and the River Chapecó (Abelardo Luz - SC), located on the geomorphological surface of Abelardo Luz, Plateau of Araucárias. Therefore it follows two research fronts: the characterization of the materials that make up the superficial formation representative of the area and fluvial-morphometric analysis of the current drainage. To achieve the objective of the research analysis in the field, in the laboratory and in the cabinet were carried out. In the field description was identified the horizons of superficial formation through color, texture, structure and consistency. In laboratory granulometric, routine chemistry, particle density, analytical chemistry (10 leading oxide), iron content (free, total, amorphous) and mineralogy by X-ray diffraction analyzes were performed. The superficial formation is ten meters thick, and of these, six meters and half are exposed in roadblock and three and a half meters were described by manual probing with Dutch auger. The horizons have been identified: Ap (0-30 cm); AB (30 - 70 cm); BA (70 - 140 cm); Bw1 (140-420 cm); Bw2 (420-700 cm); BC (700-860 cm); CB (860-950 cm) and C (950-1000 cm). Through the physical and chemical routine characteristics, the solum may be classified as Oxisoil, aluminum character. The routine chemical analysis shows that there is not an increasing order of basic cations in depth, thus showing to be an allochthonous soil, in the most superficial part (up to about 6m). The chemical analysis confirms the routine chemistry data, demonstrating that not increasing order of depth basis. The Ki and Kr values attest well weathered formation from the base, indicating again allochthonous material in the superficial part and autochthonous in the base. Data from iron analyzes by Fed-Feo / Fet reason show that the weathering of the superficial formation is evolved. Mineralogical by X-rays showed mineral quartz type, hematite, magnetite, gibbsite, anatase, cristobalite and goethite and clay minerals of the kaolinite and vermiculite and / or chlorite type. The presence of gibbsite in any Solum, indicates that there is partial desilicatization (monosialitization) up to a total desilicatization (alitização). The fluvio-morphometric analysis of drainage indicates movement blocks in the study area, and the Serra da Fartura is characterized as a rising block. Subsident block is found from this point up to the channel of river Chapecó. Finally, the analysis results indicate the occurrence of overlap of models etchplanation and pediplanation and that the superficial formation has more than one polygenetic genesis in the study area. / A presente dissertação busca compreender a evolução das formas de relevo no setor entre a Serra da Fartura e o rio Chapecó (Abelardo Luz SC), localizada na superfície geomorfológica de Abelardo Luz, VI, Planalto das Araucárias. Para tanto seguiu-se duas frentes de investigação: a caracterização dos materiais que compõem a formação superficial representativa da área e a análise fluviomorfométrica da drenagem atual. Para atingir o objetivo da pesquisa foram realizadas análises em campo, em laboratório e gabinete. Na descrição de campo identificou-se os horizontes da formação superficial através da cor, textura, estrutura e consistência. Já em laboratório foram realizadas análises granulométricas, química de rotina, densidade de partículas, química analítica (10 principais óxidos), teores de ferro (livre, total e amorfo) e a mineralogia por difração de raios-X. A formação superficial possui dez metros de espessura, sendo que destes, seis metros e meio estão expostos em corte de estrada e três metros e meio foram descritos através de sondagem manual com trado holandês. Foram identificados os horizontes: Ap (0 30 cm); AB (30 70 cm); BA (70 140 cm); Bw1 (140 420 cm); Bw2 (420 700 cm); BC (700 860 cm); CB (860 950 cm) e C (950 1000 cm). Através das características físicas e químicas de rotina, o solum pode ser classificado como Latossolo Vermelho Distrófico, caráter Alumínico. A análise da química de rotina mostra que não há um ordenamento crescente dos cátions básicos em profundidade, demonstrando assim ser um solo alóctone na parte mais superficial (até aprox. 6 m). A química analítica confirma os dados da química de rotina, demonstrando este não ordenamento crescente das bases em profundidade. Os valores Ki e Kr atestam uma formação bem intemperizada desde a base, indicando novamente material alóctone na parte superficial e autóctone na base. Os dados das análises de ferro através da razão Fed-Feo/Fet demonstram que o estágio de intemperismo da formação superficial é evoluído. A mineralogia por difração de raios-X apresentou minerais do tipo quartzo, hematita, magnetita, gibbsita, anatásio, cristobalita e goetita, e argilominerais do tipo caulinita e vermiculita e/ou clorita. A presença da gibbsita em todo o solum, indica que há dessilicatização parcial (monossialitização) até a dessilicatização total (alitização). A análise fluviomorfométrica da drenagem indica movimentação de blocos na área de estudo, sendo que a Serra da Fartura se caracteriza como bloco ascendente e deste a calha do rio Chapecó tem-se bloco subsidente. Por fim, os resultados das análises indicam ocorrência de justaposição dos modelos de etchplanação e pediplanação e que a formação superficial possui mais que uma gênese (poligenético) na área de estudo.

O estudo de bacias hidrográficas no meio tropical úmido, tem adquirido grande importância nas últimas décadas, devido a crescente demanda por planejamento de recursos hídricos. Entretanto, muitos desses trabalhos têm confundido o conceito de bacias hidrográficas, acreditando ser esta, uma mera rede de canais interconectados que formam a hidrografia dos terrenos, portanto, tomando-a como simples unidade cartográfica de estudo. Este fato tem banalizado em muito o uso de conceitos relacionados aos estudos de bacias, provocando sérios equívocos nas produções acadêmicas atuais. Partindo do princípio de que as bacias hidrográficas são espaços territoriais de circulação vertical e horizontal dágua, tendo a rede interconectada de canais, como um dos seus principais elementos, que escolhemos a bacia hidrográfica do Rio Benevente para estudo da relação entre a dinâmica fluvial desta e os seus condicionantes estruturais e morfológicos. Fundamentado no método da associação e indeterminação geomorfológica de Leopold e Langbein (1970), e, através de informações oriundas dos procedimentos técnico-operacionais de compartimentação geomorfológica e compilação de dados de parâmetros hidrográficos, foi possível descobrir que os sub-sistemas de drenagem que compõem a hidrografia total da bacia, evoluem condicionados por litoestruturas cristalinas e tectônicas do proterozóico, portanto, de organização antiga, e, que, aparentemente, demonstram não sofrer reativações modernas, a ponto de intervir na evolução dos sub-compartimentos de relevo regionais e na evolução hidrográfica da rede de canais. Chega-se desta forma, à conclusão de que os processos de encaixamento da drenagem, capturas fluviais, seccionamento de litoestruturas, gênese de knickpoints e evolução dos perfis longitudinais fluviais estão associados à dinâmica de processos geomórficos diferenciais, sob litoestruturas de forte natureza anisotrópica e complexa organização geotectônica. Fato que responde pela diversidade de sub-compartimentos de relevo e configuração evolutiva dos sistemas fluviais de dinâmicas diferenciais. / The study of watersheds in the humid tropical environment, has acquired great importance in recent decades due to growing demand for water resources planning. However, many studies have confused the concept of watersheds, believing that this was simply a network of interconnected channels that form the hydrography of the land, thus making it as simple cartographic unit of study. This commonplace is the use of concepts related to the studies of basins, causing serious confusion in the current academic productions. Assuming that the basins are territorial spaces of vertical and horizontal movement of water, the interconnected network of channels, as one of its main elements, we chose the basin of Rio Benevente to study the relationship between the dynamics of this river and its structural and morphological constraints. Based on the method of the Association and indeterminacy in geomorphologic Leopold and Langbein (1970), and through information from the technical and operational procedures of geomorphological partitioning and compilation of data from hydrographic parameters, could find that the sub-drainage systems that make up the total of the hydrographic basin, driven by evolving litoestruturas crystal and the tectonic proterozóico, therefore, the old organization, and that, apparently, show not suffer reactivations modern as to intervene in the evolution of sub-compartments of regional importance and the evolution of the network of river channels. Enough is thus concluded that the processes to fit the drainage, catch river, sectioning of litoestruturas, gênesis of knickpoints and evolution of longitudinal river profiles are associated with the dynamic of geomorphic processes differential,under litoestruturas of strong anisotropic nature and complex organization geotectônica. Fact responsible for the diversity of sub-compartments of important configuration and evolutionary dynamics of river systems of differential.

En zone méditerranéenne, d’intenses précipitations automnales sont responsables de crues particulièrement violentes : les crues « éclair ». L’intensité et la variabilité des précipitations ainsi que la complexité des processus hydrologiques responsables de la production des écoulements sur ces bassins limitent la prédictibilité de ces phénomènes. Une meilleure compréhension des processus impliqués dans les réponses hydrologiques des bassins versants et responsables de la variabilité spatio-temporelle des chemins de l’eau peut permettre d’améliorer les modélisations de ce type d’évènement. S’insérant dans le cadre de l’hydrologie spatialisée, cette thèse se propose d'étudier l'apport des potentialités satellitales, et notamment des produits 3D à très haute résolution pour la caractérisation spatiale des bassins et de leurs réseaux hydrographiques, afin d’étudier les origines géomorphologiques des variations spatio-temporelles des réponses hydrologiques et en vue d’améliorer la compréhension des mécanismes responsables des épisodes de crue. Pour cela, ce travail s’articule autour de deux axes. Le premier consiste à caractériser, à partir de données spatiales, le drain « potentiel » représentant le réseau géomorphologique sec formé par la suite continue des lignes de thalweg des bassins. Un algorithme original utilisant une structure de MNT sous forme triangulaire (TIN) a été développé spécifiquement dans ce but, afin d’obtenir un tracé des réseaux fidèle à leur tracé réel et de fournir des éléments sur leur géomorphologie ainsi que sur celle des bassins. Le deuxième axe concerne l’étude de la dynamique drain en eau ou « réel ». Il s’agit d’améliorer la compréhension des dynamiques spatiales de mise en eau des drains à travers différents épisodes de crue. Dans ce cadre, un réseau spatialisé de capteurs légers a été distribué sur deux bassins expérimentaux (< 1Km²) situés sur le Gardon d’Anduze afin de suivre les variations spatio-temporelles des dynamiques hydrologiques au sein des réseaux en eau. La confrontation des caractéristiques géomorphologiques et des réponses hydrologiques observées a permis de confirmer la prédominance des écoulements sub-surfaciques sur les bassins étudiés, de mettre en évidence deux types de réseaux aux fonctionnements différenciés (le réseau principal et le réseau secondaire), l’importante influence des pentes et de leur changement sur l’initiation et la pérennité des écoulements au sein des réseaux, et de proposer des hypothèses de fonctionnements différenciés en fonction des épisodes. / In Mediterranean areas, heavy rainfalls can generate flash floods during fall season. The rainfall intensities and their high spatial variability combined with complex processes of run-off generation reduce drastically the predictability of these phenomena. Although rainfall intensities monitoring techniques are progressing, another way to better understand and predict the hydrological responses of the catchments is to better understand the hydrological processes underlying the spatial and temporal variability of water pathways on upstream elementary catchments where concentrated flows begin. In the framework of spatial hydrology, this PhD proposes to study the potentialities of remote sensing, in particular the emergent high spatial resolution 3D products, to characterize catchments drainage elementary networks in order to relate some derivated geomorphologic traits to the observed hydrological responses all over catchments. This permits to identify the involved hydrological processes during flow dynamics on upstream mountainous catchments. This work is organized in two axes. The first one consists in characterizing, from 3D satellite data, the “potential” drain corresponding to the dry morphological network of a basin, formed by the continuum of thalweg lines within a catchment. An original algorithm, based on a TIN DEM structure, has been specifically designed for this purpose. This algorithm allows the delineation of thalwegs networks and provides geomorphological traits of catchments and networks. The second axe concern the study of the spatial dynamic of the “real” drain, which is the drain with effective flow. The goal is to enhance the understanding of flow networks spatial dynamics during rainfall events. A specific sensor network has been specially distributed on two experimental sub-catchments of the Gardon d’Anduze watershed in order to monitor the spatio-temporal variations of flow and network dynamics. The relationship between computed geomorphologic features and observed hydrological responses along networks tends to confirm the prevalence of sub-surface flows on the studied catchments. This exhibits two types of hydrographic networks, showing two distinct hydrological behaviors (the principal and secondary networks). Results also show the great influence of slopes and their variations on flow initiation and durability, and to propose hypothesis of hydrological mechanisms, in function of the observed events.

>Magister Scientiae - MSc / Globally climate variability and anthropogenic effects are causing more perennial rivers to become non-perennial rivers. Non-perennial rivers are distinguished by their isolated pools which serve as refugia for aquatic organisms, water birds, and riparian vegetation. The literature on non-perennial rivers demonstrates that pools are poorly understood in terms of their location, nature, and geomorphic persistence. Therefore, this study examines the relationships between the spatial distribution, morphology, and substrate characteristics of pools in reaches of the Prins and Touws rivers in the Klein Karoo. A greater understanding of pools will facilitate better management, monitoring, and restoration strategies for pool ecology since the geomorphology of pools provides a key part of the ecological template. Worldview-2 satellite imagery (2017) and orthorectified aerial photography (2014, 2013, and 1944) were used to assess the effects of major flooding events on pools over time. A DGPS (Differential Global Positioning System) was used to survey the pool widths, lengths, depths, and valley widths, cross-sections, and longitudinal profiles of the river. Sediment samples and Wolman pebble counts were used to assess the grain size and organic matter content of each pool in the study area. Detailed descriptions of the characteristics of each pool in terms of position in the channel, valley form, and obstruction presence and type were also assessed. Results indicate that most of the large pools occur at bedrock outcrops of the valley margins, and smaller pools are associated with Vachellia karroo debris bar features. Larger and highly persistent pools are associated with valley confinement and smaller less persistent, scour pools occur mid-channel where the valley expands. Analysis of the results shows that the valley width is the dominant control on these forced pools. The type of obstruction also plays a role in the formation of the pool as large woody debris results in smaller pools whereas, bedrock outcrops result in larger sized pools. A significant relationship was found between the grain size and organic matter content of pools. Aerial photography of the spatial distribution of the pools revealed that before a major flood, the pools were small and patchy, whereas afterward, they were larger and more elongated. It is suggested that at the bedrock outcrops, major scouring and eddy processes drive the formation of larger pools during large flood events, whereas pool dissection by sediment deposits prevails during intervening intermediate to low flow periods. The results are discussed in terms of the geomorphic controls (valley width, pool dimensions, morphology, substrate, and obstruction characteristics) on the formation and maintenance of pools in dryland settings. A conceptual model is proposed to explain the geomorphic changes of the pools in the four geomorphological zones of non-perennial rivers.

No description available.