>Magister Scientiae - MSc / Gully erosion and headcut migration has been at the crux of wetland degradation in South Africa. The resulting erosion and draining effect has seen more than 50% of wetlands in the country degraded. This study investigated the degradation of indigenous Palmiet, peat forming, wetlands through headcut erosion. This was done by exploring the relationship between headcut migration rate and morphodynamic characteristics through the use of multiple regression analysis. Wetlands investigated in this study occurred in the Kromme River catchment and Nuwejaars River catchment, in the Eastern Cape and Western Cape respectively. Morphodynamic characteristics assessed include headcut dimensions, gully characteristics, soil characteristics and drainage basin characteristics. These parameters were determined either through infield assessment, image analysis or laboratory analysis. Three headcut migration rate types were calculated through a combination of infield measurements and image analysis techniques executed within ArcGIS. These migration rate types include apex advancement (m/a), gully expansion (m2/a) and volume erosion (m3/a). Statistical analysis revealed significant relationships between morphodynamic characteristics and both volume erosion and gully expansion. Morphodynamic characteristics such as drop height, apex width, gully width, drainage rate and sand content were found to have a direct relationship with migration rates, whereas characteristics such as average drainage basin slope, clay content, silt content, SOM content and soil saturation were found to have an indirect relationship with headcut migration rates. Results provide insight into the headcut migration process, its influencing factors and the potential for headcut migration rate prediction. An evaluation of these results using WET-Health found that the wetland management tool captures wetland geomorphic controls to an accuracy of 68% and 70%. Furthermore, the influence of morphodynamic characteristics on migration rates contributes to the wetland rehabilitation process as it allows for the identification of headcut sites most susceptible to erosion. This will then allow for timely wetland rehabilitation, decreasing the rate of net wetland degradation and improving the management and efficiency of wetland restoration.

Ultrasonic descalers are used in dentistry to remove calculus and other contaminants from teeth. One mechanism which may assist in the cleaning is cavitation generated in cooling water around the descaler. The spatial distribution of cavitation around three designs of descaler tips and under three load conditions has been observed using sonochemiluminescence from a luminol solution and compared with the vibratory motion of the tips in a water bath, characterised by scanning laser vibrometry. The type of cavitation was confirmed by acoustic emission analysed by a ‘Cavimeter’ supplied by NPL. Surface profilometry and SEM of eroded hydroxyapatite pellets was performed to quantitatively study the erosion caused by a descaler tip in both contact and non-contact modes. Densitometry was used to study the erosion of black ink from a glass microscope slide, and determined that under the majority of conditions, no erosion was demonstrated via cavitation, by descalers operating in non-contact mode, although significant erosion was demonstrated with the tip in contact with the slide.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Orientador: Roger Augusto Rodrigues / Banca: Marcilene Dantas Ferreira / Banca: Heraldo Luiz Giacheti / Resumo: Países com clima tropical sofrem frequentemente com o fenômeno da erosão. Devido às condições climáticas, que variam entre longos períodos de seca e chuvas intensas, em conjunto com a ação antrópica, este fenômeno tem seu efeito acelerado e pode causar graves consequências para o meio ambiente. Apesar do grande número de trabalhos publicados sobre o fenômeno erosivo, pouco deles aborda esse assunto sobre uma perspectiva da Mecânica dos Solos Não Saturados, muito comum nas regiões de clima tropical. Esta dissertação apresenta uma caracterização hidromecânica de um solo não saturado coletado de uma microbacia da cidade de Bauru-SP afetada por um processo erosivo hídrico e, conjuntamente, avalia o mecanismo de erodibilidade ocorrido na área. Os parâmetros hidráulicos foram obtidos pelos de retenção da água no solo e permeabilidade. Os parâmetros mecânicos foram obtidos pelos ensaios de compressão triaxial e edométricos, ambos com sucção controlada. Os resultados desses ensaios mostraram a influência da sucção tanto nos parâmetros de resistência ao cisalhamento do solo quanto nos de compressibilidade. A avaliação do mecanismo de erodibilidade foi realizada com base nos resultados encontrados nos ensaios de compressão triaxial e Inderbitzen, sendo esse último disponível no histórico de informações da microbacia. Essa avaliação constatou que o aumento da sucção pode contribuir contra o efeito da erosão uma vez que interfere na sua resistência através do intercepto de coesão. Entret... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Countries with tropical climate often suffer from the erosion phenomenon. Due to the climatic conditions, which vary between long periods of drought and intense rains, together with the anthropic action, this phenomenon has its effect accelerated and can cause serious consequences for the environment. In spite of the great number of published works on the erosive phenomenon, few of them approach this subject on a perspective of the Mechanics of Unsaturated Soils, very common in the regions of tropical climate. This dissertation presents a hydromechanical characterization of an unsaturated soil collected from a microbasin of Bauru-SP city affected by an erosive water process and, together, evaluates the mechanism of erodibility occurred in the area. The hydraulic parameters were obtained by the soil-water retention and permeability. The mechanical parameters were obtained by triaxial and edometric compression tests, both with controlled suction. The results of these tests showed the influence of suction on both the shear strength and the compressibility parameters. The evaluation of the erodibility mechanism was carried out based on the results found in the triaxial and Inderbitzen tests, the latter being available in the history of the microbasin information. This evaluation found that increased suction may contribute to the erosion effect since it interferes with its resistance through the cohesion parameter. However, if there is heavy rainfall in the area, this contribution... (Complete abstract click electronic access below) / Mestre

Reservoir sediment flushing is increasingly considered beneficial to reduce sedimentation of reservoirs and maintain sediment supply downstream of impounded rivers. Nevertheless, flushing of the accumulated sediments downstream of the dam also bears numerous negative impacts. In this study, first the most important downstream impacts of fine sediment releases of flushing were identified based on previously published research of twenty case studies in eleven countries. The results showed that the long-term as well as short term biological and physical impacts decreased with distance from the dam. The temporal scale of impacts on macro-invertebrates could span from few weeks or a month to several months while the effect on fish could last for a number of years. The impacts on downstream vegetation dynamics is driven by many years of flushing activities. The study also enabled proposing generic management strategies aimed to reduce the impacts. Second, fine sediment transport in coarse immobile bed, which is a common phenomenon downstream of dams during flushing releases, dam removal and also in many mountain and canyon rivers, was investigated. Particularly, the dynamics of the downstream erosion and transport of fine sediments released during sediment flushing was investigated based on a series of flume experiments that were carried out in immobile gravel bed and using a one-dimensional (1-D) suspended sediment transport model developed in the present study. In the framework of the flume experiment, firstly gravel bed roughness, porosity and roughness density were exclusively extracted from gravel surface elevation data in which developing a spatial filter to overcome elevation errors was carried out. Secondly a new technique to acquire fine sediment erosion in immobile coarse bed in running water condition was developed. The method proved to be the back bone of all fine sediment erosion experiments conducted in the present study and could be used for similar studies. This study presents a first work of direct measurement of erosion rate and characterizing its spatial heterogeneity in gravel bed. The experimental data of erosion rate of fine sediments showed that it varied spatially with high erosion rate on the stoss side of gravels and less on the lee side conforming to sweeps and ejections characteristics in coherent flow structure of gravel bed flows. Erosion rate was significantly affected by increase in roughness of immobile gravel bed with high erosion rate noticed when sand level was reduced although the effect on stream-wise velocity was not significant. The vertical profile of erosion rate was found to decrease linearly and showed an exponential decay in time in the gravel matrix. Third, a new non-equilibrium erosion rate relation is proposed. Drag force profile in the interfacial sublayer of clean gravel bed was found to be scaled well with roughness density and allowed predicting the effective shear stress distribution available for fine sediment entrainment with an empirical equation. vi The new relation is a modified version of the pick-up rate function of van Rijn (1984b) in which the predicted shear stress in the roughness layer was implemented. The most important finding was that if the shear stress distribution in the interfacial sublayer is predicted, a relation for sand bed condition can be applied to predict fine sediment erosion rate in immobile gravel bed. This approach is conceptually superior to previous approaches where erosion rate in sand bed condition was scaled empirically for various fine sediment bed level within the interfacial sublayer. Finally, the effect of the interaction between hydrodynamic and sediment wave dynamics of sediment flushing on spatial pattern of sediment deposition was investigated. The 1-D model was developed to include major processes observed in sediment flushing: sediment wave celerity correction, variable bed roughness, bed exchange in immobile bed, hindered settling velocity and rough bed porosity. The proposed erosion rate relation showed encouraging results when implemented in the 1-D model. The wave celerity factor did not show significant effect on the spatial lag in immobile bed condition although was significant in sand bed condition. Variable bed roughness modified both the flow field and sediment deposition in which larger length of sediment deposit was noted. The immobile bed porosity allowed modelling clogged depth of fine sediments. The model was also found to be very valuable to investigate flushing scenarios that reduce significant deposition through the analysis of the dependence of deposition on peak-to-base flow and intermittence of releases. The highest peak-to-base flows produced the longest and thickest region of deposition while those with the lowest ratio produced the shortest and thinnest. A single flushing release followed by clear water release reduced area or length of sediment deposition more than intermittent flushing followed by inter- and post-flushing clear water releases. In the latter case, the peak of concentration reduced but remained higher for longer duration than the former, which suggests that a large quantity of clear water release has to be available. Overall, the present research represents a step forward in understanding relevant processes involved in the downstream transport of fine sediments released during sediment flushing and the associated impacts that can help the development of better management strategies and predictive tools.

Orientador: José Augusto de Lollo / Resumo: A erosão, especialmente do tipo acelerada, é um fenômeno com grande potencial de causar degradação ambiental, diminuindo a produção de alimentos, provocando a desertificação de áreas, o assoreamento de rios, o deslizamento de solo, entre outros. Dessa forma, o estudo dos processos erosivos e suas consequências é de fundamental importância em diversas áreas do conhecimento, exatamente para que possam ser propostas formas de remediar os casos já existentes e prevenir possíveis próximas ocorrências. Dentre os tipos de erosão existentes destaca-se a hídrica, e os parâmetros envolvidos nesse cenário podem ser diversos, envolvendo tanto fatores naturais, como as propriedades do solo, o clima e o relevo, quanto antropogênicos, como a ocupação do solo e técnicas de manejo. Além disso, uma ferramenta muito utilizada nos estudos de suscetibilidade à erosão é o SIG, ou Sistemas de Informações Geográficas, devido à sua capacidade de armazenar, manipular, analisar e apresentar dados distribuídos espacialmente e georreferenciados. O uso dessa ferramenta proporciona tanto a melhora na precisão dos valores obtidos, quanto diminui o tempo consumido durante os cálculos. Assim, o objetivo deste trabalho foi avaliar os resultados de diferentes abordagens de avaliação do potencial de ocorrência de erosão na Bacia Hidrográfica do Córrego do Jaú, em Aparecida D’Oeste – SP, envolvendo diversos parâmetros naturais e antrópicos, e utilizando sistemas de informações geográficas, de forma a verificar a ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Erosion, especially the accelerated type, is a phenomenon with high potential to cause environmental degradation, declining food production, causing desertification of areas, siltation of rivers, landslides, among others. Thus, the study of erosion and its consequences is of fundamental importance in many areas of knowledge, so that ways to remedy existing cases of it and prevent possible subsequent occurrences can be proposed. Among the existing types of erosion, the one caused by water stands out, and the parameters involved in this scenario may be diverse, involving both natural factors, such as soil properties, climate and relief, and anthropogenic ones, such as soil occupation and management. In addition, a tool widely used in erosion susceptibility studies is GIS, due to its ability to store, manipulate, analyze and present spatially distributed and geo-referenced data. The use of this tool provides both the improvement in the accuracy of the values obtained and the reduction of time consumed during calculations. So, the objective of this study was to evaluate the results of different approaches to assess the potential for erosion occurrence in the Córrego do Jaú watershed, in Aparecida D'Oeste – SP, involving several natural and anthropic parameters, and using geographic information systems, in order to verify the applicability of these methods in the study basin. For the proposed study, the methods of the Natural Vulnerability to Erosion (VNE) and adaptations of the U... (Complete abstract click electronic access below) / Mestre

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / A bacia hidrogrÃfica do rio Jaibaras localiza-se na porÃÃo centro-norte do Estado do CearÃ, banhando nove municÃpios, à uma importante subbacia da bacia hidrogrÃfica do rio Acarau. Para a anÃlise dos recursos naturais foi considerado a bacia hidrogrÃfica como unidade territorial para o desenvolvimento do estudo, fundamentando-se com base teÃrico-metodologica na teoria geral dos sistemas e na anÃlise geosistÃmica, onde foram avaliados seus processos de sua evoluÃÃo, determinado a vulnerabilidade à erosÃo. Com a utilizaÃÃo tÃcnicas de sensoriamento remoto e geoprocessamento foi levado em consideraÃÃo à dinÃmica territorial, baseada nos processos de morfogÃnese e pedogÃnese. Com a anÃlise de paisagem foram estabelecidas cinco categorias de meios morfodinÃmicos, sendo considerando a cobertura vegetal como fator estabilizador da paisagem, possibilitando assim, determinar o grau da vulnerabilidade de cada subsistema. A bacia hidrogrÃfica do rio Jaibaras possui uma diversidade paisagÃstica que refletem diretamente nas suas condiÃÃes de uso e ocupaÃÃo, essas diversidades foram compartimentadas em quatro sistemas ambientais, DepÃsitos QuarternÃrios, DepressÃo Sertaneja, MaciÃos Residuais e Planalto Sedimentar de Ibiapaba, e esses sistemas foram subdivididos em dez subsistemas, cada um com suas caracterÃsticas naturais que possuem certo grau de homogeneidade fisionÃmica, sendo observadas as condiÃÃes de uso e ocupaÃÃo, configurando os principais impactos ambientais na bacia. / The river basin Jaibaras located in north-central portion of the state of Ceara, bathing nine municipalities, is an important subbacia the river basin AcaraÃ. For the analysis of natural resources was considered a watershed as the basic unit for the development of the study, basing himself on the basis of theoretical and methodological in general systems theory and analysis Geosystems were evaluated in their processes of evolution, given the vulnerability erosion. By using remote sensing and GIS has been taken into consideration the territorial dynamics, based on the processes of morphogenesis and pedogenesis. With the analysis of landscape were established five categories of morphodynamic means, and considering the vegetation as a stabilizing factor of the landscape, making possible to determine the degree of vulnerability of each subsystem. The river basin has a diverse landscape Jaiba that directly reflect the conditions governing their use and occupation, these differences were compartmentalized into four environmental systems, Deposits QuarternÃrios Depression Sertaneja, Solid Waste and Plateau sedimentary Ibiapaba, and these systems were subdivided into ten subsystems, each with its natural characteristics that have some degree of homogeneity of countenance, and observing the conditions of use and occupation, setting the main environmental impacts in the basin.

Seedbanks provide many ecosystem services that support wildlife and regulate soil function. The fate of arable seeds is vital in shaping the aboveground composition of plant communities in agroecosystems. Understanding seed fate informs seedbank dynamics with multi-species interactions, as well as safeguarding arable biodiversity and food security. While many seed fate pathways are well known, the role of myxospermy in temperate agricultural soils is rarely addressed. Mucilage released by myxospermous seeds can modify the soil physical, hydraulic and microbial environment surrounding the seed. The principle biophysical mechanisms underlying the redistribution of weed seeds in eroded soils are unknown. It is possible that myxospermy delivers crucial services at the field scale, such as soil stability and water retention. However, modifications of the soil physical environment have been investigated using only a single-species approach and are often tested with extracted mucilage rather than seeds in-situ. As multiple taxa produce myxospermous seeds, the effects of a single species cannot be generalised. As seeds co-exist in the soil as multi-species communities, a multi-species approach is needed to further understand the functionality of seed mucilage and their implications for soil, relative to the wider seedbank. This thesis focussed on examining the mechanisms responsible for the adhesive interactions between soil and myxospermous seeds and discusses the ecological function and behaviour at the soil particle scale.

Excessive delivery of fine sediment from agricultural river catchments to aquatic ecosystems can degrade chemical water quality and ecological habitats. Management of accelerated soil losses and the transmission of sediment-associated agricultural pollutants, such as phosphorus, is required to mitigate the drive towards sustainable intensification to increase global food security. Quantifying soil erosion and the pathways and fate of fine-grained sediment is presently under-researched worldwide, and particularly in Ireland. This thesis established a sediment monitoring network upon an existing catchment study programme (Agricultural Catchments Programme) in five instrumented catchments (~10 km2) across Ireland. The research used novel, high quality measurement and analysis techniques to quantify sediment export, determine controls on soil erosion and sediment transport, and identify sediment contributions from multiple sources in different agricultural systems over time to evaluate approaches to fine sediment management. Results showed suspended sediment measurement using a novel ex situ methodology was valid in two of the study catchments against in situ and direct depth-integrated cross-section methodologies. Suspended sediment yields in the five intensive agricultural catchments were relatively low compared to European catchments in the same climatic zone, attributed to regionally-specific land use patterns and land management practices expressed in terms of ‘landscape complexity’ (irregular, small field sizes partitioned by abundant hedgerows and high drainage ditch densities) resulting in low field-to-channel connectivity. Variations in suspended sediment yield between catchments were explained primarily by soil permeability and ground cover, whereby arable land use on poorly-drained soils were associated with the largest sediment yields. Storm-event sediment export and sediment fingerprinting data demonstrated that sediment connectivity fluctuations resulted from rainfall seasonality, which in turn regulated the contrasting spatial and temporal extent of surface hydrological pathways. Increased transport occurred when and where sediment sources were available as a result of hillslope land use (low groundcover) or channel characteristics. Field topsoils were most vulnerable when low groundcover coincided with surface hydrological pathways; frequently on poorly-drained soils and following extreme rainfall events on well-drained soils as storage decreased. Although well-drained soils currently demonstrate low water erosion risk, past sugar beet crops exposed freshly drilled soils during periods of greater rainfall risk and soil removal during crop harvesting. Sediment loss from grassland catchments dominated by poorly-drained soils and extensive land drainage (sub-surface and surface) primarily derived from channel banks due to the delivery of high velocity flows from up-catchment drained hillslopes. Catchment specific soil erosion and sediment loss mitigation measures are imperative to cost-effectively preserve or improve soil and freshwater ecosystem quality worldwide.

Klarälven är en av Sveriges längsta älvar och är unik i Skandinavien för sitt karaktäristiska meanderlopp. Det unika i Klarälvens fall är att älvfåran är instängd mellan två bergssidor. Klarälvens meanderlopp innebär erosion och förändringar i älvens lopp. Syftet med studien är att jämföra och analysera hur erosionen längs en sträcka av Klarälven har förändrats över tid. Underlaget består av en historisk karta från 1883 samt ortofoton från 1961 och 2014. Studien är avgränsad till en 25 km lång sträcka norr om Ekshärad i Värmland. Metoder som används omfattar georeferering av den historiska kartan samt skärmdigitalisering av samtliga data. Därefter granskades och jämfördes resultaten genom överlagringsanalys uppdelat i två perioder samt alla perioder på en gång. Resultatet visar att omfattande erosion och avlagring har skett. I älvens ytterkurvor där vattnets hastighet är som högst har störst erosion skett och i innerkurvorna där vattnet rinner långsammare har det eroderade materialet avlagrats. De största skillnaderna är uppmätta mellan åren 1883 och 1961. Men erosionsförändring i mindre skala har skett även mellan 1961 och 2014. / River Klarälven is one of Sweden's longest rivers and is unique in Scandinavia because of its characteristic meander course.  The uniqueness in the case of Klarälven is that the riverbed is trapped between two mountain sides. The meandering course of Klarälven means major changes in its path due to extensive erosion along some reaches. The purpose of this study is to compare and analyze how some reaches of River Klarälven have changed over time. The data consists of a historical map from 1883 as well as orthophotos from 1961 and 2014. The study is limited to a 25 km meandering reach north of the town Ekshärad in northern Värmland. Methods involved are georeferencing of the historical map and screen digitizing of all data. Subsequently, the results were reviewed and compared by overlay analysis divided into two periods and all periods at once. The result shows that extensive erosion and deposit have taken place. In the river's outer curves where the velocity of the water is highest is also the place where most erosion occurs. In the inner curves where the water velocity is slower, the eroded material is deposited. The largest differences were measured between the years 1883 and 1961. However, erosion changes on a smaller scale also occurred between 1961 and 2014.