Understanding the cause of abrupt climate change in the geologic past can help assess the potential magnitude and variability of future changes in regional and global climate. The research presented here focuses on some of the first records of hydrologic variability in the central North American continent during an interval of Marine Isotope Stage 3 (24-57 thousand years before present (ka)). Sediment core MD02-2551 from the Orca Basin, northern Gulf of Mexico, is used to document the first detailed melting history of the southern margin of the Laurentide Ice Sheet (LIS) during MIS 3, and to record terrestrial inputs from the Mississippi River related to changes in evaporation-precipitation over the mid-continent, from 28-45 ka.Paired measurements of oxygen isotopes and Mg/Ca-SST on the planktonic foraminifera Globigerinoides ruber (pink) are used to calculate the oxygen isotopic composition of seawater and test one of the key hypotheses for abrupt climate change. Five rvals of freshwater input from 28-45 ka do not match the abrupt Dansgaard-Oeschger temperature oscillations recorded in Greenland ice. Rather, summer melting of the LIS may have occurred during Antarctic warming and likely contributed to sea-level variability during MIS 3. A detailed assessment over one of the meltwater events, using the oxygen and carbon isotopic composition of G. ruber and the deeper dwelling Neogloboquadrina dutertrei, demonstrate that meltwater was confined to the surface layers and likely had an impact on the biological pump in the Gulf of Mexico. A similar oxygen isotopic composition of seawater record determined from the year-round white G. ruber suggests that melting was not limited to the warmest summer months. The timing of LIS meltwater input is decoupled from an interval of enhanced wet conditions over the North American continent and increased Mississippi River discharge, as shown by a suite of organic and sedimentologic proxies. Increasing summer insolation on the orbital scale may have led to a northward migration of the Intertropical Convergence Zone and an intensification and westward shift in the conical position of the Bermuda High, which shuttles moisture to the North American continent and contributes to flooding in the Mississippi River drainage basin.

This thesis relates fluvial morphology to those hydraulic conditions identified as being ideal for the rearing of juvenile Atlantic salmon. The suitability of flow depths and velocities were obtained from published habitat preference curves in order to compute the percent area (percent usable area - PUA) and average width (average usable width - AUW) of reaches providing ideal rearing habitat for juvenile Atlantic salmon at 2 typical summer discharge levels, in the Ste. Marguerite River. / By dividing reaches into smaller, morphologic unit's, in order to make the conditions more uniform, it was noticed that the wetted width and the amplitude of the vertical oscillation of riffles and pools (riffle-pool amplitude) provided the strongest hydraulic and morphologic relationships with the amount of usable habitat at the morphologic unit scale. Two regression models were produced to estimate the AUW of morphologic as a function of hydraulics and morphology, respectively. / The historic flood in July 1996 also provided an opportunity to examine some of the impacts of a large magnitude flood on channel morphology: localized bed and bank erosion, the destruction of riparian vegetation, the enhancement and destruction of individual bars, and localized changes in the hydraulic and morphologic character (induced by large sediment inputs).

[Truncated abstract] Runoff generation behaviour and flooding in a lake dominated catchment are nonlinear, threshold-driven processes that result from the interactions between climate and various catchment characteristics. A complicating feature of the rainfall to runoff transformation, which may have implications for the flood frequency, is that the various surface and subsurface flow pathways are dynamic, heterogeneous and highly nonlinear, consisting of distinct thresholds. To understand the impact of threshold nonlinearities on the rainfall-runoff transformation in such catchments, a systematic examination was carried out to investigate runoff generation behaviour of the catchment itself, the overflow behaviour of a lake in combination with the catchment draining into it, as well as the lake organisation within a lake chain network. Three storage based thresholds were considered: the catchment field capacity storage governing catchment subsurface stormflow, total storage capacity governing catchment surface runoff, and lake storage capacity governing lake-overflow. ... Through these investigations, this thesis has provided valuable insights into the process controls of lake-overflow events and the associated flood frequency behaviour in lake dominated catchments. In particular, the relative roles of climate, soil depth, the soil?s drainage capacity, as well as the relative geometry of the lake vis a vis the contributing catchment, in the determination of the dynamic characteristics of lake-overflow events and associated flood frequency behaviour have been highlighted. In addition, the importance of lake organization, as expressed in terms of the average ratio of catchment area to lake area and the spatial variability of this ratio from upstream to downstream, and their impact upon connectivity and flood frequency have also been explored. The outcomes of this study highlight the importance of thresholds governing flood frequency, and provide insights into the complex interactions between rainfall variability and the various threshold nonlinearities in the rainfall-runoff process, which are shown to have a significant impact on the resulting flood frequency curves. The improved understanding of these process controls will be useful in assisting the 1 management of the catchment-lake system in the study region, and in regions elsewhere. In particular, the outcome of this study can provide guidance towards the adoption of various management strategies for lake chain systems by illustrating the effects of potential flow interruption and retardation as ways to assist in flood prevention and mitigation, whether it is aimed at decreasing the frequency of occurrence of lake overflows, or merely decreasing the flow magnitude for a given return period.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references (p.100-101).

Teilw. zugl.: Paris 3, Univ., Diss. / Literauturverz. S. 321 - 344. - Webliogr. S. 344 - [345]

Thesis (M.S.)--University of Tennessee, Knoxville, 2008. / Title from title page screen (viewed on Sept. 23, 2009). Thesis advisor: John S. Schwartz. Vita. Includes bibliographical references.

Dissolved oxygen (DO) is an important water quality parameter that is used to assess the health of aquatic ecosystems. Typically physically-based numerical models are used to predict DO, however, these models do not capture the complexity and uncertainty seen in highly urbanised riverine environments. To overcome these limitations, an alternative approach is proposed in this dissertation, that uses a combination of data-driven methods and fuzzy numbers to improve DO prediction in urban riverine environments. A major issue of implementing fuzzy numbers is that there is no consistent, transparent and objective method to construct fuzzy numbers from observations. A new method to construct fuzzy numbers is proposed which uses the relationship between probability and possibility theory. Numerical experiments are used to demonstrate that the typical linear membership functions used are inappropriate for environmental data. A new algorithm to estimate the membership function is developed, where a bin-size optimisation algorithm is paired with a numerical technique using the fuzzy extension principle. The developed method requires no assumptions of the underlying distribution, the selection of an arbitrary bin-size, and has the flexibility to create different shapes of fuzzy numbers. The impact of input data resolution and error value on membership function are analysed. Two new fuzzy data-driven methods: fuzzy linear regression and fuzzy neural network, are proposed to predict DO using real-time data. These methods use fuzzy inputs, fuzzy outputs and fuzzy model coefficients to characterise the total uncertainty. Existing methods cannot accommodate fuzzy numbers for each of these variables. The new method for fuzzy regression was compared against two existing fuzzy regression methods, Bayesian linear regression, and error-in-variables regression. The new method was better able to predict DO due to its ability to incorporate different sources of uncertainty in each component. A number of model assessment metrics were proposed to quantify fuzzy model performance. Fuzzy linear regression methods outperformed probability-based methods. Similar results were seen when the method was used for peak flow rate prediction. An existing fuzzy neural network model was refined by the use of possibility theory based calibration of network parameters, and the use of fuzzy rather than crisp inputs. A method to find the optimum network architecture was proposed to select the number of hidden neurons and the amount of data used for training, validation and testing. The performance of the updated fuzzy neural network was compared to the crisp results. The method demonstrated an improved ability to predict low DO compared to non-fuzzy techniques. The fuzzy data-driven methods using non-linear membership functions correctly identified the occurrence of extreme events. These predictions were used to quantify the risk using a new possibility-probability transformation. All combination of inputs that lead to a risk of low DO were identified to create a risk tool for water resource managers. Results from this research provide new tools to predict environmental factors in a highly complex and uncertain environment using fuzzy numbers. / Graduate / 0543 / 0775 / 0388

Au cours du XXe siècle, les lits de nombreuses rivières ont été sujets à l'installation de végétation alluviale. Dans le cas des rivières aménagées, cette tendance est souvent associée à des altérations géomorphologiques directes (extractions de granulats, endiguements, etc.) ainsi qu'à des modifications anthropiques de leur régime hydrologique et sédimentaire conduisant à une stabilisation du lit qui permet l'installation de la végétation. Cette végétation augmente le risque d'inondation en diminuant les vitesses d'écoulement et en augmentant les niveaux d'eau en crue. Par ailleurs la biodiversité est dégradée par la diminution des habitats pionniers caractéristiques de ces environnements. Manipuler artificiellement le régime hydrologique d'une manière qui pourrait limiter l'installation de végétation sur les bancs est une option considérée par les gestionnaires. Dans ce contexte, ce projet de thèse a pour objectif de comprendre les impacts des crues d'amplitude variable sur la destruction de végétation, et d'identifier les mécanismes associés. Le site d'étude sur lequel cette thèse se focalise est l'Isère en Combe de Savoie, une rivière à galets très aménagée des Alpes françaises.Dans le cadre de cette étude, la destruction de végétation a été étudiée à l'échelle du tronçon à partir d'une analyse des données hydrologiques, des photos aériennes, et des données topographiques disponibles pour la période 1996-2015. À l'échelle du banc, un suivi de terrain avant et après les événements hydrologiques marquants entre avril 2014 et septembre 2015 nous a permis d'étudier l'action des crues sur la mobilité sédimentaire et sur la végétation. Ces observations ont été complétées par une modélisation numérique bidimensionnelle de l'écoulement en crue.À l'échelle du tronçon (20 km), nous avons trouvé une corrélation très forte entre les volumes d'eau ayant transité dans le chenal sur une période donnée, et la destruction de végétation associée au cours de la période 1996-2015. Les débits associés à des temps de retour infra-annuels semblent permettre la destruction de végétation. Le mécanisme de destruction le plus efficace que l'on observe à cette échelle est l'érosion latérale ; les mécanismes prenant place à la surface des bancs sont très minoritaires. Cependant, les surfaces détruites sont modestes ; 3,4 % de la surface végétalisée est détruite annuellement en moyenne. À l'échelle du banc, la période de suivi de terrain a couvert une série de crues fréquentes (temps de retour < 1 an) et une crue de temps de retour 10 ans. Seule cette crue a partiellement détruit la végétation pionnière sur les bancs suivis. La destruction de végétation ligneuse jeune a eu lieu par le biais de quatre mécanismes : 1) déracinement par érosion de surface supérieure à 20 cm, 2) enfouissement sous une couche de sédiment grossiers supérieure à 30 cm, 3) déracinement par une combinaison d'érosion et de dépôt, et 4) érosion latérale en marge des bancs. La destruction de végétation est toujours associée à une mobilité sédimentaire importante.Ces résultats montrent qu'une crue très importante est nécessaire pour détruire la végétation par la mobilisation de la surface des bancs sur ce site. Par contraste, les débits forts mais non exceptionnels (temps de retour infra-annuel) sont en mesure de détruire la végétation par érosion latérale. Dans le cas de l'Isère en Combe de Savoie, il semble que l'utilisation de crues artificielles ne peut pas seule permettre de maintenir la largeur inter-digues libre de végétation. Pour la suite, on propose de s'intéresser à la destruction de végétation dans le contexte de la dynamique des bancs alternés plus ou moins végétalisés, en prenant en compte les apports et le transport des sédiments en plus de l'hydrologie. / Many rivers worldwide have seen vegetation establish within their beds throughout the 20th century. In the case of managed rivers, this trend is usually linked to direct geomorphological alterations (sediment mining, diking, etc.) as well as anthropic alterations of flow regime and sediment supply. These pressures have stabilized river beds, allowing vegetation to establish permanently. This vegetation increases the risk of flooding by decreasing flow velocities and increasing water levels. In addition, the associated reduction in availability of pioneer habitats characteristic of these stabilized environments typically degrades biodiversity. Managing hydrology in a way that would limit vegetation establishment on bars presents an interesting management option. In this context, our study was aimed at understanding the impacts of floods of varying magnitude on vegetation removal, as well as identifying and quantifying the underlying mechanisms. This work focused on the Isère River, a heavily managed gravel bed river located in the western French Alps.Vegetation removal was studied at the reach scale using hydrological data, aerial photographs, and topographic data available between 1996 and 2015. At the bar scale, field monitoring before and after floods from april 2014 to september 2015 allowed us to document the impact of floods on sediment mobility and vegetation. A 2D numerical model was used to document fine scale hydraulics.At the reach scale, we found a strong correlation between water volume flowing through the river channel and the amount of vegetation removal. Discharges with return intervals of less than one year seem to have an impact on vegetation removal. The main mechanism observed from aerial photographs was lateral erosion; surface processes were negligible in comparison. However, global vegetation removal was modest: since 1996, on average 3,4 % of vegetated area was removed annually. At the bar scale, our study period permitted monitoring of a series of high frequency floods (return interval < 1 year) and a 10-year food event. Only the largest flood partially removed pioneer vegetation from bars. Young vegetation removal occurred through four different mechanisms: 1) uprooting by surface scour > 20 cm, 2) burial under a thick layer of coarse sediments > 30 cm, 3) uprooting by a combination of surface scour and sediment deposition resulting in no net topographic change, and 4) lateral erosion of bars. Vegetation removal was always associated with significant sediment mobility.We conclude that on the Isere River a very important flood is required to remove vegetation by mobilizing bar surfaces. In contrast, high but not exceptional flows (return interval < 1 an) are capable of removing vegetation through lateral erosion. However, artificial floods alone are unlikely to maintain the full width of the channelized bed of the Isere River free of vegetation. In the future, vegetation removal needs to be studied in the context of alternate bar dynamics with or without vegetation. It seems necessary to consider sediment transport as well as hydrology to understand the overall dynamics of the bed.

Floods are a natural phenomenona that normally occur during Summer of every year and sometimes extraordinarily at any time in Huancané, damaging enormous areas near the lake due to lake transgressions and the overflowing of de Ramis and Huancané rivers. This origins uncountable losses to peasants’ patrimony, such as cultigens, cattle, housing, etcétera. As it is expected, this brings the assistance of both public and private institutions, to assure the surviving of the people damnified.The most serious floods took place in 1986 and 2003 that interrupted all means of comunication to the city of Huancané. As usual, the government attention to these terrible problems, consisted in short time actions to cap the moment, without any understanding of the real causes of these phenomenona, which are the filled beds of the fluvial beds and the shallowness of Lake Titicaca in the outflet of the Ramis river that collects the water from the chain of mountains at the N and NW of the Peruvian Altiplano. / Las inundaciones como fenómenos naturales se presentan anualmente en cada verano y extraordinariamente cada cierto tiempo en Huancané, afectando enormes áreas de planicies contiguas al lago. Son el resultado de la transgresión lacustre y desbordamientos de los ríos Ramis y Huancané; y causan cuantiosas pérdidas patrimoniales de los campesinos: cultivos, ganado, viviendas, etcétera. Como es de esperarse, esto pone en acción el apoyo de instituciones privadas y públicas para asegurar la sobrevivencia de la población damnificada.Las dos inundaciones más graves fueron en 1984-1986 y 2003 que interrumpieron las carreteras de conexión a la ciudad de Huancané. Los esfuerzos del gobierno incidieron en respuestas momentáneas, sin comprender que la verdadera causa de estos fenómenos se encuentra en la colmatación de los lechos fluviales y del fondo del lago Titicaca, en la desembocadura del río Ramis que recibe las aguas pluviales desde las cordilleras de la parte N y NO del altiplano peruano.

As inundações urbanas apontam como um dos exemplos de desastres naturais que vêm causando sérios danos e prejuízos à população, registrando, em nível mundial, tanto o aumento como a intensidade de ocorrências. Uma das consequências disso é o aumento dos impactos econômicos causados por estes eventos e a mensuração de danos associados a eventos precisa ser mais explorada para auxiliar na melhoria do sistema de planejamento e gestão de áreas que ofereçam risco à população. Com o intuito de contribuir com esta discussão, este trabalho acadêmico objetivou encontrar alternativas para mensurar o custo dos danos de inundações visando a obtenção de parâmetros econômicos para fins de auxílio à tomada de decisão em relação ao planejamento urbano. A hipótese proposta foi testar se o custo do risco de inundações é crescente e se os valores encontrados são significativos o suficiente para auxiliar a tomada de decisões que envolvam o planejamento urbano, utilizando como método a função marginal. Para utilização desta metodologia foram necessários os seguintes dados: a obtenção de dados hidrológicos, diagrama de permanência e o tempo de retorno dos níveis máximos hidrológicos, base de dados altimétricos, prejuízo histórico de inundações, planta de valores mobiliários, valor produção industrial, valor produção comercial e número de transbordos efetuados. A aplicação do método foi realizada através de uma função marginal, obtendo para cada variação do nível de inundação um custo marginal correspondente, representando os dados através dos gráficos de cota/prejuízo. A disponibilidade de dados existentes sobre as últimas maiores inundações ocorridas em Porto Alegre, nos anos de 1967 e 1941, descritas em detalhes pelo Estudo de Viabilidade Técnico Econômica das Obras de Defesa de Porto Alegre e Canoas contra as inundações, elaborado na década de 60, pelo Departamento Nacional de Obras de Saneamento (D.N.O.S.) foram determinantes para a escolha do estudo de caso. Como resultados dos custos dos riscos de inundações podemos sinalizar que, considerando danos diretos e indiretos para as áreas residencial, industrial e de transporte público, numa inundação atingindo uma cota entre 3,10m e 3,20m para os bairros Centro Histórico, Floresta, Humaitá, Praia de Belas e São Geraldo seriam na ordem de R$ 11,5 bilhões. A partir deste montante podemos refletir sobre a importância dos sistemas de proteção contra inundações para segurança da população e quanto ao uso de áreas de risco, que exigem soluções que merecem ser pensadas e planejadas a partir de múltiplos olhares e saberes. Quanto a aplicação do método, podemos concluir que é de fácil acesso e utilização, tendo a hipótese confirmada a partir da obtenção de valores crescentes a cada cota incremental e um montante expressivo o suficiente para justificar que este é um assunto que precisa ser considerado no que se refere a aplicação dos instrumentos legais de planejamento urbano e principalmente na tomada de decisão. / Urban floods are pointed as one of the examples of natural disasters that are causing serious damages to the population, it is recording, worldwide, both increase and intensity of occurrences. One of those occurences consequences is the increase of the economical impact of these events, so that the measuring of the damages associated to this situations must be more explored to help in a management and planning system of areas that offer risk to population. We tryed to contribute with this discussion, so that this scholary work aimed to find alternatives to measure the costs of floods damages, and also tried to obtain economic parameters to help to urban planning. The proposed hypothesis was to test whether the cost of the risk of flooding is increasing and the values found are significant enough to assist decision-making involving urban planning, using as method the marginal function. To use this methodology the following data were needed: hydrological data, permanence diagram and retorn time of the maximum hydrological levels, altimetric data bases, historical flood damages, real estate value plant, industrial production value, comercial production value and made transshipment numbers. The method was applied through a marginal function, so that we obtained to each flood level variation a corresponding marginal cost, the data were represented through quota/loss graphics. The existent data from the lats biggers floods at Porto Alegre, in 1967 and 1941, that were described in details by the Thecnical Economical Viability Study of Porto Alegre and Canoas Defense Works against floods, made at 60´s, by the National Department of Sanitation Works (DNOS) were determinant to choose case study. The results found about the cost of floods can signal that the damage, considering direct and indirect damages to residential, industrial and public transport areas, in a flood that can reach a dimension between 3,10m ad 3,20m, at “Centro Histórico”, “Floresta”, “Humaita”, “Praia de Belas” and “São Geraldo” regions, could be about R$11,5 billion. From this amount we can reflect about the importance of flood protection systems to the security of the population and about the use of risk areas, which requires solutions that deserve to be thought and planned from multiple perspectives and knowledges. As the application the method, we can conclude that it is easy to access and use, and the hypothesis confirmed from obtaining increased amounts each incremental dimensions and a significant amount enough to justify that this is an issue that needs to be considered in refers to application of the legal instruments of urban planning and especially in decision making.