Flood inundation is a major natural hazard that can have very severe socio-economic consequences. This thesis presents an enhanced numerical model for flood simulation. After setting the context by examining recent large-scale flood events, a literature review is provided on shallow flow numerical models. A new version of the hyperbolic horizontal variable density shallow water equations with source terms in balanced form is used, designed for flows over complicated terrains, suitable for wetting and drying fronts and erodible bed problems. Bed morphodynamics are included in the model by solving a conservation of bed mass equation in conjunction with the variable density shallow water equations. The resulting numerical scheme is based on a Godunov-type finite volume HLLC approximate Riemann solver combined with MUSCL-Hancock time integration and a non-linear slope limiter and is shock-capturing. The model can simulate trans-critical, steep-fronted flows, connecting bodies of water at different elevations. The model is validated for constant density shallow flows using idealised benchmark tests, such as unidirectional and circular dam breaks, damped sloshing in a parabolic tank, dam break flow over a triangular obstacle, and dam break flow over three islands. The simulation results are in excellent agreement with available analytical solutions, alternative numerical predictions, and experimental data. The model is also validated for variable density shallow flows, and a parameter study is undertaken to examine the effects of different density ratios of two adjacent liquids and different hydraulic thrust ratios of species and liquid in mixed flows. The results confirm the ability of the model to simulate shallow water-sediment flows that are of horizontally variable density, while being intensely mixed in the vertical direction. Further validation is undertaken for certain erodible bed cases, including deposition and entrainment of dilute suspended sediment in a flat-bottomed tank with intense mixing, and the results compared against semi-analytical solutions derived by the author. To demonstrate the effectiveness of the model in simulating a complicated variable density shallow flow, the validated numerical model is used to simulate a partial dam-breach flow in an erodible channel. The calibrated model predictions are very similar to experimental data from tests carried out at Tsinghua University. It is believed that the present numerical solver could be useful at describing local horizontal density gradients in sediment laden and debris flows that characterise certain extreme flood events, where sediment deposition is important.

Submitted by Claudia Rocha (claudia.rocha@udesc.br) on 2018-03-21T14:23:46Z No. of bitstreams: 1 PGCA17MA228.pdf: 726282 bytes, checksum: 40f271b726c358d9c09eb5ec50c81604 (MD5) / Made available in DSpace on 2018-03-21T14:23:46Z (GMT). No. of bitstreams: 1 PGCA17MA228.pdf: 726282 bytes, checksum: 40f271b726c358d9c09eb5ec50c81604 (MD5) Previous issue date: 2017-06-22 / Capes / Nitrogen (N) participates in several metabolic processes in the plant and is directly related to the accumulation of dry matter of the pasture, thus reflecting increases in the overall productivity of the system. In this sense, the Ncritical (lower concentration of N for a given species to perform its maximum growth potential) in multispecies pastures may change depending on the species that compose it. The objective of this work was to evaluate the NNI (Nitrogen Nutrition Index) in three perennial winter grasses (oatgrass - Arrhenatherum elatius, cocksfoot - Dactylis glomerata - and tall fescue - Festuca arundinacea) cultivated as monocultures or intercropped throughout the four seasons of the year. The experimental area was located in Lages, SC, containing 12 paddocks of 45 m2 each where the four treatments (the three pure cultivated species and the mixture) were distributed through a completely randomized design with three replicates. The cut height at each treatment was determined by the time the swards intercept 95% of the incident light during the vegetative stage of the pastures, being lowered by 50% of this height. Fertilization was carried out with the equivalent of 50 kg / N / ha every 40 days, totaling 450 kg of N / ha / year. The forage mass was determined in pre-cut, and thus evaluated the N contents in the forage mass and the N contents in the 10 cm of the upper part of the canopy for the species pure and individually for each species in the consortium. The Ncritical was estimated by the equation: Ncritical = 4,8 x W-0,32, where W is the mass of forage above the level of the soil. A second experiment was carried out with the objective of evaluating the effect of the management adopted on the N dilution curve, in which two methods were performed to determine the N dilution curve, one performed with the management adopted in the experiment (starting from a residual height of 10 cm) and another with the management proposed by the literature starting from the ground level. Statistical analyzes were performed using the MIXED procedure of the SAS statistical program (version 9.02) with 5% significance. Regression analyzes were performed using the SigmaPlot(R) statistical package. In general, the NNI actually observed did not reach the critical values (Experiment I), however, when corrected (disregarded the percentage of dead material in the sample) NNIs were satisfactory for all species at all times. Throughout the manuscript inferences are discussed on the ways to evaluate the INN in perennial pastures under lenient grazing, due to the changes in the dilution of nitrogen, due to the high percentage of dead material at the beginning of pasture growth. The height control was important in the coexistence of the species in the consortium, since it allowed the entrance of luminosity, decisive factor in the absorption of N / O nitrogênio (N) participa de diversos processos metabólicos na planta e está diretamente relacionado com o acúmulo de matéria seca do pasto, refletindo, assim, em aumentos em produtividade global do sistema. Neste sentido, o Ncrítico (menor concentração de N para que uma determinada espécie desempenhe seu máximo potencial de crescimento) em pastagens multiespecíficas pode mudar em função das espécies que o compõem. Dessa forma, o objetivo desse trabalho foi avaliar o INN (índice de nutrição nitrogenada) em três espécies perenes de inverno (Aveia perene - Arrhenatherum elatius-, Dáctilis - Dactylis glomerata- e Festuca - Festuca arundinacea) cultivadas puras e em consórcio ao longo das quatro estações do ano. A área experimental foi implantada em Lages, SC, contendo 12 piquetes de 45 m2 cada onde foram distribuídos os quatro tratamentos (as três espécies cultivadas puras e o consórcio entre elas) por meio de um delineamento inteiramente casualizado com três repetições. A altura de corte em cada tratamento foi determinada pelo momento em que os mesmos interceptarem 95% da luz incidente durante o estádio de desenvolvimento vegetativo dos pastos, sendo rebaixados em 50% desta altura. As adubações foram realizadas com o equivalente a 50 kg/N/ha a cada 40 dias, totalizando 450 kg de N/ha/ano. Foi determinada a massa de forragem em pré-corte, e, assim avaliados os teores de N na massa de forragem e os teores de N nos 10 cm da parte superior do dossel para as espécies puras e individualmente para cada espécie no consórcio. O Ncrítico foi estimado pela equação: Ncrítico = 4,8 x W-0,32, onde W é a massa de forragem acima do nível do solo. Foi realizado um segundo experimento, com o objetivo de avaliar o efeito do manejo adotado na curva de diluição do N, no qual foram executados dois métodos para determinar a de curva de diluição do N, uma realizada com o manejo adotado no experimento (partindo de uma altura residual de 10 cm) e outra com o manejo proposto pela literatura partindo do nível do solo. As análises estatísticas foram realizadas por meio do procedimento MIXED do programa estatístico SAS (versão 9.02) com 5% de significância. As análises de regressão foram realizadas utilizando-se o pacote estatístico SigmaPlot (R). De modo geral, os INN efetivamente observados não alcançaram os valores críticos (Experimento I), no entanto, quando corrigidos (desconsiderados os porcentuais de material morto da amostra) os INN foram satisfatórios para todas as espécies em todas as épocas. Ao longo do manuscrito inferências são discutidas sobre as formas de se avaliar o INN em pastos perenes sob pastejo leniente, devido às alterações na diluição do nitrogênio, consequência da alta porcentagem de material morto no início do crescimento dos pastos. O controle de altura foi importante na coexistência das espécies no consórcio, pois permitiu a entrada de luminosidade, fator decisivo na absorção de N

Les taillis à courte rotation (TCR) permettent de produire de la biomasse ligneuse, alternative aux combustibles fossiles. L'intégration d’espèces d’arbres fixateurs d'azote atmosphérique en mélange avec les essences à croissance rapide peut être un moyen de limiter le risque d'appauvrissement des sols dans les TCR. Le succès d'un tel mélange va dépendre des interactions entre les deux espèces : facilitation, compétition ou complémentarité pour la lumière et les ressources du sol (eau, nutriments). L’objectif de cette étude était d’évaluer l’impact du mélange peuplier / robinier, sur la croissance, la production de biomasse et l'acquisition de l'azote d'une plantation à courte rotation. Un dispositif instrumenté composé de monocultures de peuplier et robinier et le mélange des deux espèces a été étudié pendant quatre ans. La quantification répétée des biomasses aériennes et souterraines associée au suivi des dimensions des arbres a permis de mettre en évidence que la présence des robiniers n'avait pas d'influence sur la croissance, la production et l'allocation de biomasse des peupliers à l'échelle de l'arbre comme à l'échelle du peuplement. En revanche, les robiniers souffraient de la compétition interspécifique : mortalité augmentée, croissance et production de biomasse diminuée. De plus, une approche isotopique (15N) couplée à l'analyse des minéralomasses a montré que les teneurs en azote des robiniers dans le mélange étaient plus faibles que dans la monoculture dues à une fixation de l'azote atmosphérique réduite. Le stock global d'azote dans le milieu était comparable dans les mélanges et les monocultures de chaque espèce. Le mélange n'a pas montré d'intérêt sur la période d'étude en raison notamment des conditions pédoclimatiques inappropriées (en particulier pour le robinier) et d'une incompatibilité entre les deux espèces sur ce site / Biomass from short rotation coppice (SRC) plantations may help reducing fossil fuel consumption. The development of mixed-species plantations, introducing a nitrogen-fixing species could be a solution to reduce the risk of fertility decline in SRC. Nevertheless, the success or failure of the mixture will depend on the competition and complementarity processes, for light and soil resources (water and nutrients), between both species. The objectives of this study were to determine the impact of a mixture of poplar and black locust, on growth, biomass production and nitrogen uptake in the plantation. Instrumented monocultures and mixed plantations of both species have been studied during four years. Repeated above-and belowground biomass estimations associated with tree dimension monitoring have shown that the presence of black locust affected neither growth, nor biomass production and allocation of poplar trees both at tree and plot level. On the other hand, the black locusts trees suffered from interspecific competition: high mortality, decrease in growth and biomass production. Moreover, an isotopic approach (15N) coupled with mineralomass analyses allowed to highlight that nitrogen concentration in black locust trees in the mixture was lower than in the monoculture due to a reduction of the percentage of nitrogen derived from atmospheric fixation. The total nitrogen contents were close in the mixture and in the monocultures of each species. No advantage of the mixture was found during the study period because of inappropriate pedoclimatic conditions (especially for the black locust) and incompatibility between both species on this site