Hydropower is a more environmental friendly way of producing electric power than many other alternatives today. Though, the effects of constructing mega dams are much tangible for the local eco systems in addition to changing many people’s lives forever. In order to prevent floods, riverbank erosions or landslides, proper investigations of the environmental impact from dam constructions must be performed. One of the key parameters in such investigations is the flow discharge velocity. This master thesis treats experimental measurements and numerical simulations of the velocity downstream a model of Xiluodu dam. The Xiluodu dam is a mega dam under construction in China and will have a total capacity of 12 600 MW when completed. The model is in scale 1:100 and the experiments have been performed at Department of Hydraulic Engineering, Tsinghua University, Beijing, China. The velocity profile shows that the velocity in the middle of the river is larger than the velocity at the surface and near the riverbank. The comparison between the measured and the simulated velocities shows a difference of less than 20 percent in almost all points which can be considered as a good result. In those points where the difference is more than 20 percent, this is believed to be due to the position of these points. Some of them were located near a vortex and others very close to the bottom. This is a problem when sparsely measured topography in combination with linear interpolation makes the boundaries of the simulations incorrect. In order to perform better simulations, more densely topography data and better flow boundary conditions should be used. More measuring points of the velocity could also improve the result.

Submitted by Socorro Pontes (socorrop@ufersa.edu.br) on 2017-01-19T14:02:26Z No. of bitstreams: 1 JoséHRA_DISSERT.pdf: 4845272 bytes, checksum: 6462e3cce9165dbc00d428bf9d3352e5 (MD5) / Made available in DSpace on 2017-01-19T14:02:26Z (GMT). No. of bitstreams: 1 JoséHRA_DISSERT.pdf: 4845272 bytes, checksum: 6462e3cce9165dbc00d428bf9d3352e5 (MD5) Previous issue date: 2016-01-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The erosion of a riverbank is a natural phenomenon, being it very dynamic and capable of being accelerated by human activities. The understanding of riverbank erosion is crucial for studies related to fluvial geomorphology, because this phenomenon causes environmental disturbances, thus it can lead to problems of social and economic order. Most of the studies on riverbanks erosion were developed in temperate regions and in small watersheds of rivers. In Brazilian territory, some work was carried out in the Paraná River basin. In semi-arid regions such as the Northeast Brazil, few studies like these were developed. In rivers located in semi-arid regions, the erosive processes are observed with greater magnitude in above average rainy seasons, which favors the occurrence of the level of full riverbanks, contributing to the widening of the canal. This is quite different from rivers located in more humid regions in which the flow and rainfall are more regular, thus the widening of the river is most common. This study aims to analyze the dynamics of riverbank erosion in the Jaguaribe River, in its lower course, precisely in Quixeré town. The Jaguaribe River is one of the main rivers of Ceará, it is a semiarid river and it has its subsidiaries controlled by dams. For that it have been selected over a stretch of 10 km of the river in nine sections which were grouped into three areas types, that is: preserved areas, partially preserved areas and degraded areas. The setbacks of the monitored riverbanks were followed monthly via the pin method. Also, some soil samples were collected to determine the root density at the riverbanks, besides the application of an Infiltration test based on Maia (2014). Satellite images from 1980 and 2014 were worked for checking the uses and land use in the study area, and to analyze the morphological changes of the river. The results showed that the volume eroded in the sections monitored was considered low, degraded areas have higher volumes eroded, comparing the conserved and partially preserved areas. For the study period (June / 2014 to May / 2015) the main factor responsible for riverbank erosion was the precipitation, even this have been below the historical average. Flow rates and the change in river levels have been not decisive for erosion during the study period. Among the uses observed in the fluvial plains, pastures and irrigated agriculture stand out, suppressing the riparian forest that acts in the stability of the riverbanks. The main erosion observed in the stretch under study has been the laminar riverbank erosion, corrosion, collapse by shearing and the collapse by tipping. With this, it was found that the ciliary vegetation contributes strongly on the stability of riverbanks, minimizing erosion. The low erosive rates are related to reduced rainfall occurred in the area and it may have very high volumes in more rainy years and with higher flow rates / A erosão das margens de um rio é um fenômeno natural, sendo o mesmo muito dinâmico e passível de ser acelerado pelas atividades humanas. O entendimento da erosão marginal é fundamental, para os estudos relacionados a geomorfologia fluvial, pois além de proporcionar desequilíbrios ambientais, este processo pode acarretar problemas de ordem social e econômica. A maioria dos estudos sobre erosão de margens foram desenvolvidos em rios de regiões temperadas e em rios de pequenas bacias de drenagem, no território brasileiros alguns trabalhos foram realizados na bacia do rio Paraná, em regiões semiáridas, como é o caso da região do Nordeste brasileiros, poucos trabalhos nesta linha foram desenvolvidos. Em rios situados em regiões semiáridos, os processos erosivos são observados com maior magnitude em épocas de chuvas acima da média, o que favorece a ocorrência do nível de margens plenas, contribuindo, para o alargamento do canal. Isto é completamente diferente dos rios localizados em regiões mais úmidas no qual as vazões e precipitações são mais regulares, desta forma o alargamento do rio é mais frequente. O presente estudo tem como objetivo analisar a dinâmica dos processos de erosão de margens no rio Jaguaribe, no seu baixo curso, precisamente no município de Quixeré. O rio Jaguaribe é um dos principais mananciais do Estado do Ceará, o mesmo é um rio semiárido e apresenta suas vazões controladas por açudes. Para isto foram selecionadas ao longo de um trecho de 10 km do rio nove seções que foram agrupadas em três tipos áreas, ou seja, áreas conservadas, áreas parcialmente conservadas e áreas degradadas. Os recuos das margens monitoradas foram acompanhados mensalmente, através do método dos pinos. Também foram coletadas amostras de solo para determinar a densidade de raiz nas margens, além da aplicação de um teste de Infiltração baseado em Maia (2014). Imagens de satélite de 1980 e 2014 foram trabalhadas para verificações dos usos e ocupações do solo na área de estudo, e analisar as mudanças morfológicas do rio. Os resultados obtidos mostram que o volume erodido nas seções monitoradas foi considerado baixo, as áreas degradadas apresentaram maiores volumes erodidos, comparadas as áreas conservadas e parcialmente conservadas. Para o período avaliado (junho/2014 a maio/2015) a principal condicionante responsável pela erosão marginal foram as precipitações, mesmo estas terem ficado abaixo da média histórica. As vazões e a variação do nível do rio não foram determinantes para erosão no período estudado. Entre os usos observados na planície fluvial, as pastagens e agricultura irrigada se destacam, suprimindo a vegetação ciliar que atua na estabilidade das margens. Os principais processos erosivos observados no trecho em estudo foram a erosão laminar das margens, a corrosão, desmoronamento por cisalhamento e o desmoronamento por basculamento. Com isso, verificou-se que a vegetação ciliar contribui fortemente na estabilidade das margens, minimizando os processos erosivos. As baixas taxas erosivas estão relacionadas as reduzidas precipitações ocorridas na área, podendo apresentar volumes bem elevados em anos mais chuvosos e com vazões mais elevadas / 2017-01-18

Asian countries are urbanizing at an unprecedented rate, which has led to significant demand for sand. While sand mining fuels infrastructure development, creates livelihoods, and stimulates local economic activity, it also drives a series of environmental and socio-economic consequences which cannot be ignored. These include erosion, the destruction of habitats and loss of biodiversity, the deterioration of traditional livelihoods, forced displacement of communities, and damage to homes and infrastructure. On the one hand, this thesis uses mixed methods to study the multifaceted impacts of sand mining along the Red River in China, near the Vietnamese border. On the other hand, using qualitative methods, it explores how these impacts unfold along the Mekong River in Cambodia, near Phnom Penh. Using a political ecology approach, it identifies the actors involved in sand mining, their motives, and their impacts on the environment and local communities. The extractivism framework is used to describe sand mining activities and practices. In doing so, this thesis contributes to the literature on the understudied sand mining industry and its far-reaching impacts.