Soil erosion within the catchment areas of the Black, Vygekraal and Elsieskraal Rivers (Cape Town, South Africa) results in sediment transport by these rivers, their tributaries, and the stormwater drainage systems which flow into these rivers. This sedimentary material is subsequently deposited in the lower reaches of the Black and Vygekraal Rivers owing to a decrease in the competence of the watercourse in this area. The resultant accumulation of sediment necessitates costly annual dredging of this section of river (referred to in this study as the "dredged area") by the Cape Town City Council. The loss of soil cover within the three catchments is initiated mainly by wind in summer, and by rain in winter. Soil erosion is likely to be of greatest magnitude in the Vygekraal catchment, owing to the extensive exposure of the natural sand cover as a result of poorly vegetated areas. Steep slopes, and construction works linked to urban development, also render the upper parts of the Elsieskraal catchment vulnerable to soil erosion. A relatively insignificant amount of soil loss is believed to occ~_r within the catchment of the Black River. Measurements and estimations of the relative transporting powers of the Black, Vygekraal and · Elsieskraal Rivers showed that the Vygekraal River was likely to have the greatest capacity to transport sediment throughout the year, while the Black River would have the least capacity. Particle size analyses of the watercourse sediments in the study area showed that the sands of the Cape Flats, i.e., within the Vygekraal catchment area, were the most easily transported sediments in the study area, by both water and wind. Finer alluvial sediments in the Tygerberg "Hills region (in the upper Elsieskraal catchment), directly derived from the loam soils of the area, were also found to be easily transported by natural elements. The coarser sediments in the Black River catchment were ·probably transported at a significantly slower rate, than were the fine sediments of the Elsieskraal River, and the medium-grained sands in the Vygekraal catchment area X-ray diffraction analysis of the clay component of the sediments indicated that the sediments accumulating in the extreme lower sector of the dredged area probably had their source in the upper Elsleskraal catchment area. Microscopic studies of the modal sand fractions of the sediments showed that it was likely that the sediments deposited in the upper and middle parts of the dredged area were almost exclusively derived from the catchment of the Vygekraal River, while the sediments in the lower part of the dredged area were equally likely to have originated from either of the three catchments. Multivariate statistical analyses were performed on the data set comprising the variables generated by the particle size analyses. The results from these investigations showed that, for the dredged area as a whole, the largest contribution of sediment came from the Vygekraal River, with the least from the Black River. The proportionate contribution of the Elsieskraal River to the total sediment accumulation in the dredged area · is likely, therefore, to be intermediate to those from the Vygekraal and Black Rivers. Further, more detailed studies of sediment transport and soil loss would be necessary in order to accurately determine the percentage contribution of each of the Vygekraal, Elsieskraal and Black Rivers to the total quantity of sediment accumulating annually in the dredged area.

When we think of floods in the urban environment we also think of damage. We continuously rebuild our infrastructure to alleviate any damage. Although erosion and flooding can be detrimental to our environment, a by-product of the damage is wild nature, offering health and mental benefits and possibly the key to understanding resiliency. Consequently, our perception of nature changes when it pervades our urban environment, becoming a nuisance. As we face rising water levels and urbanization our infrastructure is falling apart more frequently and the role of the landscape architect in designing infrastructure is crucial. How should we design our infrastructure knowing that it will be reworked by water and reclaimed by nature? The thesis proposes the re-design of a road that has been closed several times due to severe flooding and erosion. The road sits within a steep valley in Washington D.C. and acts as the Southern boundary for Rock Creek Park. A creek runs alongside of the path, and the moments of collision are the least accessible to both people and water. The thesis explores the processes of material erosion and deposition, and the movement and power of water and asks: can the process of damage be used to create a more durable path that will enhance connectivity for both water and people? With the goal of enriching the experiential quality of nature in the city, the proposed design exposes the underground processes of water and translates its pattern of movement into a design that reveals, carves, and places a new pedestrian path/dam system that emphasizes the tremendous wildness of stormwater. / Master of Landscape Architecture

No description available.

La thèse est organisée autour du développement d'un modèle numérique d’interaction fluide - structure pour simuler la déformation induite dans un matériau solide lors de l’implosion de bulles de cavitation. Le solveur est développé à partir du code open source SPHYSICS_2D utilisant la méthode des Smoothed Particles Hydrodynamics (SPH). Dans cette thèse, le code 2D a été modifié pour traiter le cas de fluides en conditions 2D-axisymétrique. Le solveur solide SPH a été complètement développé en interne en 2D-axisymétrique avec un nouveau schéma pour résoudre les problèmes apparaissant à proximité de l'axe de symétrie. Une loi de comportement élasto-visco-plastique de type Johnson Cook est implémentée dans le solveur solide afin de prendre en compte l’effet de la vitesse de déformation sur l’écrouissage du matériau.Les applications du solveur FSI traitent le cas d’une bulle unique implosant au voisinage d’une surface solide. Deux cas sont envisagés : celui d’une bulle détachée de la surface solide pour laquelle l’effondrement génère une onde de choc ; et celui d’une bulle au contact de la surface pour lequel un micro-jet de liquide vient impacter la surface solide. Pour une taille de bulle donnée, les résultats montrent que le micro-jet peut produire deux fois solide pour laquelle l’effondrement génère une onde de choc ; et celui d’une bulle au contact de la surface pour lequel un micro-jet de liquide vient impacter la surface solide. Pour une taille de bulle donnée, les résultats montrent que le micro-jet peut produire deux fois plus de déformation plastique que l'onde de choc, réduisant ainsi le temps d'incubation. Par contre, le volume de matière déformée plastiquement dans le cas du micro-jet (cavité attachée) est 800 fois plus petit que celui déformé par l’impact d'une onde de choc (cavité détachée). Par conséquent, la capacité d'érosion d'une cavité détachée est beaucoup plus élevée que celle d'une cavité attachée. Un important résultat de cette étude concerne les cavités détachées où il est montré que la déformation plastique ne se produit pas au centre de l'effondrement mais à un décalage par rapport à l’axe de symétrie. Les résultats montrent également que même si la pression subie par le matériau est la plus élevée au niveau de l’axe de symétrie, la déformation plastique ne sera pas maximale à cet endroit mais dans une zone éloignée du centre. Nous Une étude paramétrique est menée pour quantifier les effets de la distance bulle/paroi, de la pression d’effondrement et du rayon de la bulle. Les résultats montrent que l'énergie totale absorbée et le taux d'érosion devraient être plus élevés pour une cavité détachée que pour une cavité attachée. La densité d'énergie absorbée (d'où le temps d'incubation) et l'énergie totale absorbée (d'où le taux d'érosion) augmentent avec la pression d’effondrement. Le changement du rayon de la bulle tout en gardant les autres paramètres constants n'affecte pas beaucoup l'amplitude de la déformation plastique ni la densité d'énergie absorbée, ce qui suggère que quelle que soit la taille de la bulle de cavitation, le temps d'incubation devrait rester similaire. Cependant, comme le volume de la zone déformée plastiquement varie presque linéairement avec la taille de la bulle, l'énergie totale absorbée ou le taux d'érosion augmente significativement avec la taille de la bulle.Dans le passé, les études similaires n'ont jamais pris en compte la sensibilité à la vitesse de déformation dans le modèle de plasticité. Nos simulations montrent que l'ampleur de la déformation plastique est alors surestimée d'environ 60% pour les cavités détachées présentées dans ce document et d'environ 200% pour les cavités attachées. Nous montrons ainsi que de telles études réductrices fondées sur des modèles de plasticité insensibles à la vitesse de déformation conduisent à une sous-estimation du temps d'incubation et à une surestimation du taux d'érosion. / The thesis is focused on development of a Smoothed Particle Hydrodynamics (SPH) Fluid-Structure Interaction (FSI) cavitation solver to understand the phenomenon of material deformation under cavitation load better. This summary presents a brief overview of the methodology used to solve a fluid-structure interaction simulation of a bubble collapse over a deformable solid medium. The fluid solver and the solid solver are validated against Rayleigh-Plesset spherical bubble collapse case and FEM solver respectively. The fluid solver is developed using an open source SPH code SPHYSICS_2D, the code is changed from 2D to 2D axisymmetric. The solid SPH solver is developed in-house in 2D axisymmetric, a novel scheme is derived to solve typical issues near symmetry axis in the solid axisymmetric SPH solver. The solid solver has the capability to solve for non-linear isotropic hardening with strain rate effects (commonly known as Johnson-Cook plasticity model).A case each for a detached and an attached cavity is simulated using the FSI solver, the results show that for the same magnitude of pressure wave initiating the collapse and the same size of the bubble, the micro-jet can produce twice the maximum plastic deformation compared to a shock wave, hence a micro-jet dominated impact would exhibit a smaller incubation time compared to the detached cavity. It is also observed that the volume of material that is plastically deformed in case of a micro-jet is miniscule compared to a shock wave impact (almost 800 times smaller). This would imply that even though the incubation time for material erosion might be lower for a micro jet collapse, the shock wave can plastify a much larger volume of material and so the erosion rate should be higher for a shock wave impact. Hence it could be inferred that the material erosion ability of a shock wave is much higher than a micro-jet.An important and novel finding in the present study is the response of the material for a detached cavity where plastic deformation does not occur at the center of collapse but at an offset from the center. The results show that even though the pressure experienced by the material is the highest at the center, it does not produce the maximum plastic deformation. This is for the first time that such a phenomenon is reported in cavitation studies, we find that the phenomenon is linked to inertial effects where the material does not respond to the load as the rate of loading and unloading is extremely high. The effect is linked to the high loading and unloading rate near the center of the collapse due to the flat geometry of the solid medium. The study clearly demonstrate that maximum pressure does not always correspond to the location of maximum plastic deformation or material erosion.Fluid-Structure Interaction simulations for different stand-off ratios, driving pressure and bubble radius have been computed. Results show that for varying stand-off ratio while keeping the bubble radius and driving pressure constant, the attached cavities (SR<=1) show a higher plastic strain magnitude and a higher absorbed energy density which would suggest a quicker incubation time. However, the volume of plastic defamation zone is much lower in attached cavities thus the total absorbed energy and the erosion rate would be higher for a detached cavity compared to an attached one.The strain rate effects suggest that the magnitude of plastic strain is over predicted while using plasticity models that do not use strain rate sensitivity. The over prediction of the magnitude of plastic strain of around 60% for detached cavities presented in the paper and around 200% for attached cavities presented in the paper is observed. This would lead to an under prediction of incubation time and over prediction of erosion rate while using strain rate insensitive plasticity models.

No description available.

To further understand bank undercutting processes that occur in the Petitcodiac River estuary (New Brunswick, Canada), the erosion of sediment cores obtained at the base of the estuary banks was studied by testing for the critical shear stress and erosion rates in a laboratory flume. It was found that there is variation in the erodibility of the sediment with depth horizontally into the bank over the depths tested. The bank cores were shown to erode in distinct layers, with the erosion of extremely weak layers occurring at rates that were an order of magnitude higher than the rates of adjacent resistant layers. Bed cores obtained at the toe of the bank were also tested and similar variability in sediment erodibility was found with vertical depth into the bed. Sediment properties of the cores, including particle size distribution, bulk density, water content, and organic content were compared to the erodibility of the sediment. Additional investigations included observations of the Petitcodiac River estuary bank movement through GPS surveys and erosion pin monitoring, as well as testing for the presence of biological sediment-stabilization factors, and changes in particle size and mineralogy on the river bank.

Centrifugal separation is a crucial piece of technology, used in a wide range of industries. In cases where solid particles are included in the working medium, erosive wear of componentsinside a centrifugal separator is one of the reasons limiting its service life. In the present work, erosion of some candidate materials of metals, hard metals and polymers were tested to represent the erosive conditions inside a centrifugal separator, and to study the erosion behavior between different material groups. A literature study was conducted to give an overview of the field of erosion, and to evaluate which erosion parameters to consider for testing. A centrifugal erosion test rig was used for the testing, using natural sand, sieved to a size interval of 500 to 700 µm, as erodent, at both 90° and 30° impact angle. Every material was tested at 100 m/s impact velocity, while only metals and polymers were tested at 70 m/s. The erosion rates, volumes of material removed per mass of impinging erodent, were measured and used to rank the candidate materials within each respective material group. Surface analysis of the eroded surfaces were conducted, using SEM, to determine the mechanism of material removal. Relation between erosion resistance, erosion mechanism and material property were investigated.

Erosion is the action of various natural processes, such as water flow, wind and gravity, that displaces material from one area to another. Creating physically-based models of these complex phenomena has been a major challenge in creating realistic terrain in video games in a fast way, without having a 3D artist model the terrain by hand. There has also been an increasing interest in representing terrain in a more complex way using 3D data, to support more interesting terrains which can contain overhangs, arches and caves. With this new terrain representation there is also a need for new models for terrain generation and modification, to handle the difference in data representation. Combining the work of previous hydraulic erosion models (erosion caused by running water), this thesis proposes a new approach to hydraulic erosion on 3D-SDF data. An efficient shallow-water model combined with making an approximation of the 3D data into multiple “layers” are the main components of this model. The number of layers relates to how the 3D model can represent 3D features such as overhangs and arches. This also enables the model to be mapped to the GPU, for efficient simulation speeds. A performance comparison was carried out on the 3D erosion model, both comparing the difference on the CPU and GPU, as well as the performance compared to it’s 2D counterpart. The terrains were rendered using OpenGL, and the simulation on the GPU was implemented using CUDA. The 3D model took about 2.8 times longer than it’s 2D counterpart for a terrain of size 1024x1024 with 2 layers, with degrading results as the layers needed to represent the 3D terrain increase. The simulation was around 10-15 times faster on the GPU compared to the single core CPU version, also with degrading results as the amount of layers increase. This thesis thus provides a simple and efficient hydraulic erosion model that can be used on 3D-SDF data, which supports overhangs and arches. / Erosion är effekten av ett antal olika naturliga processer, så som vatten flöde av regn, vind och gravitation, som förflyttar material från en plats till en annan. Att skapa verklighets baserade modeller av dessa komplexa fenomen har varit en stor utmaning för att skapa verklighetstrogna terränger för datorspel på ett snabbt vis, utan att behöva en 3D artist som modellerar terränger för hand. Det finns även ett ökat intresse för att representera terräng på mer komplexa sätt med användningen av 3D data, för att stödja mer intressanta terrängen som kan innehålla överhäng, valv och grottor. Med ett nytt sätt att representera terräng behövs det även nya modeller för att generera och modifiera terräng, som tar hänsyn till skillnaden i hur data representeras. Genom att kombinera arbetet från tidigare vatten erosions modeller föreslår denna tes ett nytt sätt för vatten erosion på 3D-SDF data. En effektiv flödesmodell kombinerat med en approximation av 3D data i form av flera lager är huvudkomponenterna av denna modell. Antalet lager relaterar till vilka sorts 3D egenskaper som kan representeras, så som överhäng och valv. Lagrena gör även att modellen kan exekveras på GPU:n, för effektivare simulations hastigheter. En prestanda jämförelse genomföred på 3D erosions modellen, där både skillnaden mellan GPU och CPU jämfördes, samt prestandan jämfört med 2D motsvarigheten. Terrängerna renderades med OpenGL, och simuleringen på GPU:n implementerades med hjälp av CUDA. 3D modellen tog omkring 2.8 gånger så långt tid som 2D motsvarigheten för en terräng med storlek 1024 x 1024 med 2 lager, med degraderande resultat när antalet lager ökades. Simuleringen var omkring 10- 15 gånger så snabb på GPU:n jämfört med en enkärnig CPU version, också med degraderande resultat när antalet lager ökas. Denna tes framför således en simpel och effektiv vattenerosions modell som kan användas på 3D-SDF data, vilket stödjer överhäng, valv och grottor.

Master of Science / Department of Biological & Agricultural Engineering / Trisha L. Moore / Excess sediment is a leading cause of stream impairment in the United States, resulting in poor water quality, sedimentation of downstream waterbodies, and damage to aquatic ecosystems. Numerous case studies have found that accelerated bank erosion can be the main contributor of sediment in impaired streams. An empirically-derived "Bank Assessment for Non-Point Source Consequences of Sediment" (BANCS) model can be developed for a specific hydrophysiographic region to rapidly estimate sediment yield from streambank erosion, based on both physical and observational measurements of a streambank. This study aims to address model criticisms by (1) evaluating the model’s repeatability and sensitivity and (2) examining the developmental process of a BANCS model by attempting to create an annual streambank erosion rate prediction curve for the Central Great Plains ecoregion. To conduct the repeatability and sensitivity analysis of the BANCS model, ten stream professionals with experience utilizing the model individually evaluated the same six streambanks twice in the summer of 2015. To determine the model’s repeatability, individual streambank evaluations, as well as groups of evaluations based on level of Rosgen course training, were compared utilizing Kendall’s coefficient of concordance and a linear model with a randomized complete block design. Additionally, a one-at-a-time design approach was implemented to test sensitivity of model inputs. Statistical analysis of individual streambank evaluations suggests that the implementation of the BANCS model may not be repeatable. This may be due to highly sensitive model inputs, such as streambank height and near-bank stress method selection, and/or highly uncertain model inputs, such as bank material. Furthermore, it was found that higher level of training may improve model implementation precision. In addition to the repeatability and sensitivity analysis, the BANCS model developmental process was examined through the creation of a provisional streambank erosion rate prediction curve for the Central Great Plains ecoregion. Streambank erosion data was collected sporadically from 2006 to 2016 from eighteen study banks within the sediment-impaired Little Arkansas River watershed of south-central Kansas. Model fit was observed to follow the same trends, but with greater dispersion, when compared to other created models throughout the United States and eastern India. This increase in variability could be due to (1) obtaining streambank erosion data sporadically over a 10-year period with variable streamflows, (2) BEHI/NBS ratings obtained only once in recent years, masking the spatiotemporal variability of streambank erosion, (3) lack of observations, and (4) use of both bank profiles and bank pin measurements to calculate average retreat rates. Based on the results of this study, a detailed model creation procedure was suggested that addresses several model limitations and criticisms. Recommendations provided in the methodology include (1) more accurate measurement of sensitive/uncertain BEHI/NBS parameters, (2) multiple assessments by trained professionals to obtain accurate and precise BEHI/NBS ratings, (3) the use of repeated bank profiles to calculate bank erosion rates, and (4) the development of flow-dependent curves based on annually assessed study banks. Subsequent studies should incorporate these findings to improve upon the suggested methodology and increase the predictive power of future BANCS models.

One of the most important aspects of coastal management and planning programs that needs to be investigated is shoreline dynamics. Long-term coastal analysis uses historical data to identify the sectors along the coast where the shoreline position has changed. Among the information that can be obtained from these studies are the general trend of coasts, either advancing or retreating. The erosion or accretion rates at each location can be used to forecast future shoreline positions. The current techniques used to study shoreline evolution are generally based on transects perpendicular to a baseline at selected points. But these techniques proved to be less efficient along more complex shorelines, and need to be refined. A new and more reliable method, the topologically constrained transect method (TCTM), was developed for this study and tested using data available for three sectors of the Texas Gulf Coast. Output data generated from TCTM also allowed performing shoreline evolution analysis and forecasting based on historical positions. Using topological constrained transects, this study provides a new method to estimate total areas of accretion or erosion at each segment of the coastline. Reliable estimates of future gains or losses of land along the coast will be extremely useful for planning and management decisions, especially those related to infrastructure and environmental impacts, and in the development of coastal models. Especially important is the potential to quickly identify areas of significant change, which eliminates the need for preliminary random sample surveying, and concentrate higher-resolution analyses in the most significant places. The results obtained in this research using the new methodology show that the Texas coast generally experiences erosion, with anthropogenic factors responsible for accretion. Accretion areas are located near coastal infrastructure, especially jetties that block the along shore sediment transport. The maximum erosion rate obtained in the study area is 5.48 m/year. This value helps make us aware of the powerful dynamic of the sector.