Ploughed upland drains are straight prismatic channels of low aspect ratio. The drains are either uniformly or compositely roughened. In compositely roughened drains the bed and side-walls are differentially roughened although each roughness type is homogeneous. Upland catchments, containing extensive ploughed drainage networks, are particularly prone to flash flooding and increased sediment yield. However, the basic hydraulic data necessary to route flow through the drainage network and improve the engineering design of stable drainage channels are currently unavailable. A logarithmic flow resistance equation is developed for low aspect ratio channels, where the effective Nikuradse equivalent grain size is known. Testing against field data indicates that the relationship successfully predicts the resistance to uniform flow through upland drains. The performance of eight composite roughness formulae to predict the mean velocity in differentially roughened channels is compared. The composite roughness equations involve dividing the cross-sectional flow area into a number of sub-areas. The different methods of cross-sectional area division are considered and their effect on mean velocity prediction examined. Preferences are indicated concerning composite roughness equations which predict the mean velocity in channels of simple cross-sectional shape. Empirical equations are derived to determine the mean bed and side-wall shear stresses in straight symmetrical trapezoidal and rectangular open channels, with uniform or composite roughness. The model proposed is appropriate for stable sub-critical and super-critical flows. The equations are based on data collected from laboratory channels and should be cautiously applied to larger scale channels. Using the mean shear stress model, a design procedure is proposed to improve drainage channel stability.

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The effect of climate on the fluvial system has long been investigated due the significant impact it can have on a river’s hydrological regime and fluvial processes. In recent years this interest has increased as global changes in climate are expected to bring more frequent high magnitude flood events globally and to North West Europe in particular. Despite the knowledge that the frequency and magnitude of floods is to increase, less is known about the geomorphological implications of this for river channels and where channel instability is likely to occur at both the river network and national scale. This is certainly the case in Scotland where increased flooding is expected and large floods have been abundant over the last two decades. To manage Scottish river catchments effectively in the future, in terms of hazard mitigation and nature conservation, river managers need to be able to predict not only how climate will impact flood magnitude and frequency in Scotland but the effect these changes will have on the internal dynamics of river channels in terms of erosion, sediment transport and deposition, and morphological dynamics. Such knowledge will ensure adequate measures are implemented to reduce fluvial risks to humans and to maintain and preserve valuable river habitats and linked species. In this thesis, several novel methods incorporating field, laboratory and GIS-based analysis, have been investigated as a means of predicting how climate change will affect channel stability in Scottish rivers and the implications of this for river management and river ecology. This includes (i) analysing the potential change in the frequency of geomorphologically-active flood flows with climate change; (ii) the use of stream power thresholds to predict changes in channel stability on a national scale with climate change; and (iii) using a Digital River Network developed using geospatial data to predict changes in the rate of bedload transfer and channel stability with climate change. Studies were undertaken on 13 different rivers across Scotland from north to south and east to west. vii As a case study of ecological implications, the thesis also examines how changes in habitat and stability of freshwater pearl mussels (Margaritifera margaritifera) may be altered by increased flooding. Predictions of the frequency of geomorphic activity, channel stability, rate of bedload transfer, and the stability of freshwater pearl mussel habitat with climate change are discussed along with the methods used to obtain these outcomes. The results all suggest an increase in the frequency and rate at which bedload is transferred through the river system and an increased frequency of flood flows resulting in greater channel instability. Morphological responses vary spatially with some river reaches experiencing greater increased erosion and transport potential than others. Climate change effects on the freshwater pearl mussel are: increased occasions of disturbance and transport downstream and the importance of specific populations in more stable environments for ensuring population recovery post flooding is highlighted. It is hoped that the methodologies developed for predicting changes in channel stability with climate change will provide useful screening tools to regulatory agencies which can be developed further to assist management decisions in the future which aim to reduce fluvial hazards and maintain good quality river environments for the species that inhabit it. The approaches used in this study allow for the identification of areas at high risk of morphological and ecological change, and the pro-active planning and management of sediment-related river management issues and nature conservation.

Centrifugal compressors with high pressure ratio are widely used in small aircraft turbine engines and turbocharges. At high rotational speeds they have narrow stable operating region and commonly used impellers with back swept blades are not able to ensure requested stability. In order to achieve wider stable operating region, some other anti-surge measures can be used, such as an Internal Recirculation Channel (IRC) located in compressor impeller inlet. This thesis deals with an investigation of IRC influence on centrifugal compressor operational parameters. As a first, the various recirculation channel geometry was studied by using of CFD analysis on simplified computational models. Those geometry, which indicated best results in terms of mass flow and looses in channel were used for testing on a model test device. Subsequently the same geometry was tested on real centrifugal compressor in experimental turbine engine to verify influence of IRC on compressor performance map – pressure ratio and efficiency. Simultaneously the CFD analyses of IRC with a 3D model of compressor impeller were performed and results compared with those, gained from measurement on model and compressor. In addition the measurement of flow field downstream the recirculation channel outlet slot with using of 3-hole pressure probe was performed and compared with flow velocity profiles evaluated from numerical simulations.

Centrifugal compressors with high pressure ratio are widely used in small aircraft turbine engines and turbocharges. At high rotational speeds they have narrow stable operating region and commonly used impellers with back swept blades are not able to ensure requested stability. In order to achieve wider stable operating region, some other anti-surge measures can be used, such as an Internal Recirculation Channel (IRC) located in compressor impeller inlet. This thesis deals with an investigation of IRC influence on centrifugal compressor operational parameters. As a first, the various recirculation channel geometry was studied by using of CFD analysis on simplified computational models. Those geometry, which indicated best results in terms of mass flow and looses in channel were used for testing on a model test device. Subsequently the same geometry was tested on real centrifugal compressor in experimental turbine engine to verify influence of IRC on compressor performance map – pressure ratio and efficiency. Simultaneously the CFD analyses of IRC with a 3D model of compressor impeller were performed and results compared with those, gained from measurement on model and compressor. In addition the measurement of flow field downstream the recirculation channel outlet slot with using of 3-hole pressure probe was performed and compared with flow velocity profiles evaluated from numerical simulations.

Urbanization increases runoff during storm events due to a reduction in vegetation and an increase in impervious surfaces, which limits the land's capacity to absorb and slow down water. This increase in runoff contributes to channel erosion. While extensive research exists on the hydrologic benefits of various types of stormwater control measures (SCMs), the relationship between urbanization, widespread SCM implementation, and channel stability in headwater streams remains less explored. Additionally, the impact of climate change (CC) on SCMs, with its growing focus due to improved global and regional CC models and data, is a critical area of study. However, most existing studies rely on simplified design storm analyses and unit-area runoff models, and there is a lack of comprehensive research evaluating the long-term, continuous hydrologic response of SCMs under future CC scenarios. This study presents an in-depth evaluation of the effectiveness of SCMs in maintaining channel stability in urbanized headwater streams, with a particular focus on the challenges posed by urbanization and CC. Conducted in a small catchment in Montgomery County, Maryland, USA, the study employs a sequential hierarchical modeling approach integrating the Storm Water Management Model (SWMM) with the Hydrologic Engineering Center's River Analysis System (HEC-RAS). First, the impact of a stormwater management system design following Maryland's Unified Stormwater Sizing Criteria (USSC) on channel stability was investigated. Simulation over 16 years (2004-2020) demonstrated that the majority of storm events were short in duration, with the greatest peak flows resulting from storm events with durations less than 24 hours. However, results indicated that despite the use of multiple SCMs, channel changes, including both degradation and aggradation up to 1.2 m, are likely over a period of 16 years. Study results indicate SCMs should be designed using continuous simulation models to simulate pre- and post-development sediment transport. Secondly, the impact of SCMs and CC on flow regime and channel stability was examined, challenging the previous simplified analyses. The findings highlight that future CC scenarios, characterized by decreased total rainfall but increased intensity, will likely shift watershed hydrology towards a flashier regime, exacerbating channel erosion. To address these shortcomings, a multicriteria design approach for SCMs is required, considering local sediment transport capacity and the complexities of urban catchments under changing climatic conditions. Lastly, evaluation of the impact of proposed stormwater regulations on channel stability using a novel three-step methodology revealed that SCM design goals focused on maintaining pre-development sediment transport or excess shear stress could reduce channel disturbance. Overall, this study illustrates the need for more nuanced and holistic approaches to stormwater management to ensure channel stability, especially in the face of the challenges posed by climatic changes. / Doctor of Philosophy / As cities grow, with more buildings and roads replacing green spaces, managing stormwater becomes a crucial challenge. Without enough soil and plants to absorb it, stormwater rushes over these hard surfaces, contributing to stream erosion. This urban scenario sets the stage for my research, which investigated effective ways to handle stormwater in cities to protect small, local streams. The focus of this study was to understand the performance of stormwater control measures (SCMs), which are engineered structures designed to manage this excessive runoff in urban environments. The key question is: Are SCMs effective, especially as we face the impacts of climate change? This research was conducted in a small watershed in Montgomery County, Maryland, using computer simulations to replicate water flow and stream conditions over a 16-year period. The findings reveal that, despite using SCMs, streams can still experience significant changes. This is especially true during intense, short-duration storms that can rapidly increase stream flow and cause channel erosion. With climate change, these problems may increase. Future weather patterns could lead to less frequent but more intense rainstorms. This study suggests that our approach to designing SCMs needs to be more sophisticated, taking into account not only the amount of water running into streams, but also the amount of coarse sediment moving during floods. In summary, this research highlights the need for comprehensive strategies in urban water management to ensure the stability and health of urban streams amidst the challenges of increasing urban development and climatic changes.

Made available in DSpace on 2017-07-10T17:31:24Z (GMT). No. of bitstreams: 1 Leandro_Neri_Bortoluzzi.pdf: 4120006 bytes, checksum: e870dd7340723061217fb4d7fdece089 (MD5) Previous issue date: 2012-05-03 / The bridges and culverts alter the natural conditions of rivers, causing changes in fluvial processes. The level of stability of river banks and beds around crossing structures was evaluated in the Paraná III watershed, Western region of Paraná State (Brazil), adopting the methodology of Johnson (2006). The study area is characterized by outcrops of basaltic rocks of Cretaceous age. The degree of channel stability was analyzed at 46 structures (18 bridges, 15 culverts box, 7 culverts pipe and 6 small bridges). We selected all crossings structures located in the Paraná Basin III along paved roads, positioned outside the urban area. Among the crossings structure, 14 were classified as excellent level of stability and level 32 as good. There was no point with fair or poor stability. The predominance of soils with low erodibility (Oxisols and Ultisols) derived from basaltic rocks provide greater stability to streams banks which mostly show vertical phases. It was noted that in culverts (box and pipe), the stability of channels tends to lower than the bridges. / As obras de engenharia como pontes, pontilhões, bueiros tubulares de concreto e bueiros celulares de concreto são consideradas estruturas de transposição do talvegue. Elas têm como objetivo permitir a passagem de um curso d água abaixo e alteram as condições naturais dos rios, acarretando mudanças nos processos fluviais. O nível de estabilidade das margens e leitos fluviais em torno das estruturas de transposição do talvegue foi avaliado na bacia hidrográfica do Paraná III, Oeste do Paraná, adotando a metodologia de Johnson (2006). A região é caracterizada pelo afloramento de rochas basálticas de idade cretácea que integra a unidade morfoescultural do Terceiro Planalto Paranaense, sub-dividido na área em apreço em quatro sub-unidades: Planaltos de Cascavel, São Francisco, Campo Mourão e Foz do Iguaçu. O grau de estabilidade do leito e das margens foi analisado em 46 pontos (18 pontes, 15 bueiros em célula de concreto, sete bueiros tubulares de concreto e seis pontilhões). Foram alvo dos levantamentos as estruturas situadas em estradas federais, estaduais e municipais asfaltadas posicionadas fora das áreas urbanas. Dentre os pontos observados, 14 estruturas foram classificadas como de nível excelente de estabilidade e 32 como de nível bom. Não houve nenhum ponto com estabilidade regular ou ruim. O predomínio de Latossolos e Nitossolos na área de estudo proporcionou estabilidade física nas margens dos cursos de água que em sua maioria apresentam fases com 90º de declividade. Com este estudo pode-se identificar as condições de estabilidade das estruturas de transposição do talvegue dentro da bacia do Paraná III. Foi constatado que nos bueiros (tubulares ou celulares), a estabilidade dos canais tende a ser menor do que nas pontes e pontilhões.

Made available in DSpace on 2017-05-12T14:42:52Z (GMT). No. of bitstreams: 1 Leandro_Neri_Bortoluzzi.pdf: 4120006 bytes, checksum: e870dd7340723061217fb4d7fdece089 (MD5) Previous issue date: 2012-05-03 / The bridges and culverts alter the natural conditions of rivers, causing changes in fluvial processes. The level of stability of river banks and beds around crossing structures was evaluated in the Paraná III watershed, Western region of Paraná State (Brazil), adopting the methodology of Johnson (2006). The study area is characterized by outcrops of basaltic rocks of Cretaceous age. The degree of channel stability was analyzed at 46 structures (18 bridges, 15 culverts box, 7 culverts pipe and 6 small bridges). We selected all crossings structures located in the Paraná Basin III along paved roads, positioned outside the urban area. Among the crossings structure, 14 were classified as excellent level of stability and level 32 as good. There was no point with fair or poor stability. The predominance of soils with low erodibility (Oxisols and Ultisols) derived from basaltic rocks provide greater stability to streams banks which mostly show vertical phases. It was noted that in culverts (box and pipe), the stability of channels tends to lower than the bridges. / As obras de engenharia como pontes, pontilhões, bueiros tubulares de concreto e bueiros celulares de concreto são consideradas estruturas de transposição do talvegue. Elas têm como objetivo permitir a passagem de um curso d água abaixo e alteram as condições naturais dos rios, acarretando mudanças nos processos fluviais. O nível de estabilidade das margens e leitos fluviais em torno das estruturas de transposição do talvegue foi avaliado na bacia hidrográfica do Paraná III, Oeste do Paraná, adotando a metodologia de Johnson (2006). A região é caracterizada pelo afloramento de rochas basálticas de idade cretácea que integra a unidade morfoescultural do Terceiro Planalto Paranaense, sub-dividido na área em apreço em quatro sub-unidades: Planaltos de Cascavel, São Francisco, Campo Mourão e Foz do Iguaçu. O grau de estabilidade do leito e das margens foi analisado em 46 pontos (18 pontes, 15 bueiros em célula de concreto, sete bueiros tubulares de concreto e seis pontilhões). Foram alvo dos levantamentos as estruturas situadas em estradas federais, estaduais e municipais asfaltadas posicionadas fora das áreas urbanas. Dentre os pontos observados, 14 estruturas foram classificadas como de nível excelente de estabilidade e 32 como de nível bom. Não houve nenhum ponto com estabilidade regular ou ruim. O predomínio de Latossolos e Nitossolos na área de estudo proporcionou estabilidade física nas margens dos cursos de água que em sua maioria apresentam fases com 90º de declividade. Com este estudo pode-se identificar as condições de estabilidade das estruturas de transposição do talvegue dentro da bacia do Paraná III. Foi constatado que nos bueiros (tubulares ou celulares), a estabilidade dos canais tende a ser menor do que nas pontes e pontilhões.

No description available.