A dimensionless equation is developed which describes the flow profile in rectangular channels with spatially varied flow. This equation is solved for various slopes and rates of discharge. The results show that when the slope and roughness are constant the dimensionless profiles are also constant over a very wide range of discharge. Once the dimensionless profile is established the water surface curve may be rapidly and accurately determined. Tests were conducted in the laboratory which reasonably verified the validity of the dimensionless profiles. / Master of Science

As the world's population shifts toward living in cities, urbanization and its deleterious effects on the environment are a cause of increasing concern. The hyporheic zone is an important part of stream ecosystems, and here we focus on the effect of urbanization on the hyporheic zone from ten first-to-second-order streams within the Virginia Piedmont. We use sediment hydraulic conductivity and stream geomorphic complexity (vertical undulation of thalweg, channel sinuosity) as metrics of the potential for hyporheic exchange (hyporheic potential). Our results include bivariate plots that relate urbanization (e.g., total percent impervious) with hyporheic potential at several spatial scales. For example, at the watershed level, we observed a decrease in horizontal hydraulic conductivity with urbanization and an increase in vertical hydraulic conductivity, which ultimately results in a negligible trend from conflicting processes. Vertical geomorphic complexity increased with total percent impervious cover. This trend was somewhat unexpected and may be due to erosion of legacy sediment in stream banks. At the reach level, hydraulic conductivity increased and sinuosity decreased as the riparian buffer width increased; these trends are weak and are essentially negligible. The hydraulic conductivity results conform to expected trends and are a product of aforementioned concomitant processes. Our results emphasize the complexity of hydrologic and geomorphic processes occurring in urban stream systems at multiple scales. Overall, the watershed level effects enhancing hyporheic exchange, which is contrary to expectations. Given the importance of hyporheic exchange to stream function, further study is warranted to better understand the effects of urbanization. / Master of Science

M.S.

Sediment and microplastic accumulation in stream systems occur when particulates entrained in overbank flow are retained by the floodplain. Despite overbank flow conditions dictating sediment and microplastic accumulation, the spatial distribution of accumulation within floodplains remains poorly understood. Difficulty quantifying hydraulic flow conditions is due to spatial variation introducing erroneous error. This study hypothesized floodplain sediment and microplastic accumulation would be closely correlated with topographic, vegetative, and hydraulic conditions. To test this hypothesis, sediment and microplastic accumulation were measured along a 1.25 km stretch of Stroubles Creek in Blacksburg, Virginia. Sediment accumulation was measured using tiles with a surface area of 144cm² at 75 locations. Tiles accumulated 4,782g over their two-year deployment. Microplastic accumulation was assessed by taking 15cm3 soil grab samples from 40 locations. Microplastics were identified using FTIR spectroscopy and were found to have a concentration of approximately 7MPm-3. Topographic and vegetative variables were measured using digital elevation and canopy height models, while hydraulic variables were calculated with an unsteady flow model in HEC-RAS. Sediment and microplastic accumulation were both found to be significantly influenced by terrain and hydraulic conditions. Sediment accumulation yielded an MLR model with an R2 of 0.72, with a confidence level between 97% - 99%, while the microplastic model yielded an R2 of 0.26 and with a confidence level between 95% - 98%. Differences in sediment and microplastics particle density resulted in hydraulic conditions being more influential on microplastic accumulation with an R2 81.5% greater than any its terrain components. This research identified floodplain accumulation process drivers which could help to guide future management decisions regarding sediment storage and monitoring microplastic accumulation. / Master of Science / Streams act as natural thoroughfares, with the potential to transport materials beneficial and harmful to biological and environmental processes. During flood events, the material carried by stream flow is often deposited in areas adjacent to the main channel. These adjacent areas are called floodplains and contribute to the accumulation of sediment and small pieces of plastic in stream systems. Spatial patterns in floodplain accumulation are believed to be the result of site-specific terrain, vegetation, and flow conditions within a stream system. In the context of a stream system, descriptive characteristics of terrain, vegetation, and flow conditions are heavily confounded making their relationship with floodplain accumulation difficult to interoperate. This study aims to understand the accumulation of sediment and plastics in the Stroubles Creek floodplain by evaluating the terrain, vegetative, and flow conditions believed to influence systematic patterns in accumulation. Floodplain sediment and plastic accumulation were measured along a 2 km reach of Stroubles Creek at 75 and 40 sampling locations. Terrain, vegetative, and flow conditions at each of the sediment (75) and plastic (40) sampling locations were determined to be the characteristics driving their relative accumulation process. The distance and change in elevation of the sampling locations from the channel, flow velocity of water, arrival time and duration of time each location experienced floodwaters were observed to have the most significant impact on accumulation processes. However, the degree to which each of these variables affected sediment and plastic accumulation differed. These findings suggest that sediment and plastic accumulation are both heavily influenced by terrain and flow conditions; however, the processes by which sediment and microplastics accumulate in the floodplain are likely to differ.

Hydraulic tomography is a cost -effective technique for characterizing the heterogeneity of hydraulic parameters in the subsurface. During hydraulic tomography surveys, a large number of hydraulic heads (i.e., aquifer responses) are collected from a series of pumping or injection tests in an aquifer. These responses are then used to interpret the spatial distribution of hydraulic parameters of the aquifer using inverse modeling. In this study, we developed an efficient sequential successive linear estimator (SSLE) for interpreting data from transient hydraulic tomography to estimate three-dimensional hydraulic conductivity and specific storage fields of aquifers. We first explored this estimator for transient hydraulic tomography in a hypothetical one-dimensional aquifer. Results show that during a pumping test, transient heads are highly correlated with specific storage at early time but with hydraulic conductivity at late time. Therefore, reliable estimates of both hydraulic conductivity and specific storage must exploit the head data at both early and late times. Our study also shows that the transient heads are highly correlated over time, implying only infrequent head measurements are needed during the estimation. Applying this sampling strategy to a well -posed problem, we show that our SSLE can produce accurate estimates of both hydraulic conductivity and specific storage fields. The benefit of hydraulic tomography for ill -posed problems is then demonstrated. Finally, to affirm the robustness of our SSLE approach, we apply the SSLE approach to transient hydraulic tomography in a hypothetical two- dimensional aquifer with nonstationary hydraulic properties, as well as a hypothetical three-dimensional heterogeneous aquifer.

Hydraulic tanks have a variety of different tasks. The have to store the volume of oil needed for asymmetric actors in the system as well as to supply the system with preconditioned oil. This includes the deaeration as air contamination is affecting the overall system performance. The separation of the air in the tank is being realized mainly by passive methods, improving the guidance of the air and oil flow. The use of CFD models to improve the design of hydraulic tank is recently often discussed. In this paper, a design method for hydraulic tanks using CFD is presented and discussed. First the different requirements on a hydraulic tank are described as well as the motivation changing the tank designs. Additionally, a quick overview on different calculation models for the behavior of air in oil as well as the capabilities of CFD to reproduce them is given. After this the methodology of tank design applying CFD is presented. The method is then used in an example.

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The primary aim of the research was to determine the optimum diversion location in a curved channel to minimise the abstraction of sediment. The secondary aim was to determine the optimum diversion angle for a diversion channel located on the outside of a bend at the optimum diversion location. The velocity distribution in the curved channel was investigated to try obtain a better understanding of curvilinear flow. The scour patterns in the channel were monitored in order to compare them with the measured velocity distributions. Simulations were carried out with the DELFT 3D (hydrodynamics) and Mike21C (sediment dynamics) modelling programmes and compared with the results obtained from laboratory experiments and with existing empirical formulas. The optimum diversion location was found to be located on the outside of the bend in the downstream section of the bend. Three main scour zones were identified with the third scour zone at the location of the maximum velocity. The location of the maximum velocity was found to be relatively constant with varying Froude numbers, but moving in the downstream direction with increasing radius of curvature-to-width ratio. The velocity distributions in the horizontal and vertical planes are well defined and correspond to descriptions in the literature. It is evident that the diverted discharge ratio increases with an increase in the diversion angle while it decreases with an increase in Froude number. Higher Froude numbers in the curved channel lead to more favourable conditions for the diversion of water. The diversion does not influence the secondary flow patterns (for the range of Diversion Discharge Ratio’s tested) and that the maximum velocity zone stayed in the same location as in the tests without a diversion. The hydrodynamics of the laboratory experiments were well simulated with the DELFT 3D hydrodynamic model, using three-dimensional and two-dimensional formulations. Mike21C was used to simulate the sediment dynamics of some of thelaboratory experiments that gave relatively good agreement with experimental data. A two-dimensional depth averaged model could therefore be used with reliability to simulate field conditions in relatively shallow rivers, and is preferred to empirical methods to predict maximum scour that were calibrated under very specific hydraulic conditions. / AFRIKAANSE OPSOMMING: Die primêre doel van navorsing was om die optimum uitkeer-posisie in ‘n draai te bepaal om sodoende sediment onttrekking te minimiseer. Die sekondêre doel was om die optimum uitkeringshoek vir ‘n uitkeerkanaal te bepaal wat geleë is aan die buitekant van ‘n draai by die voorgestelde optimum uitkeer-posisie. Die snelheidsverspreiding in die draai was ook ondersoek om te probeer om spiraalvloei beter te verstaan. Die uitskuurpatrone in die kanaal is ook gemonitor om dit te kon vergelyk met die gemete snelheidsverspreiding. Numeriese simulasies is gedoen met DELFT 3D (hidrodinamika) en Mike21C (sediment dinamika) modelleringsprogrammatuur en is vergelyk met die resultate van die laboratorium eksperimente asook met die van bestaande empiriese vergelykings. Daar is gevind dat die optimum uitkeer-posisie aan die buitekant van ‘n draai aan die stroomaf-kant van die draai geleë is. Drie hoof uitskurings-areas is gevind terwyl die derde area ooreenstem met die posisie van maksimum snelheid. Die posisie waar die maksimum snelheid voorkom is relatief konstant met ‘n verandering in Froude-getal, maar beweeg in die stroomaf-rigting met ‘n styging in die radius-tot-wydte verhouding. Die vertikale en horisontale snelheidsverspreiding is goed gedefinieer en stem ooreen met soortgelyke beskrywings in die literatuur. Die uitkeer-vloei verhouding styg met ‘n stygende uitkeerhoek terwyl dit daal met ‘n styging in Froude-getal. Daar is ook gevind dat groter Froude-getalle meer gunstige omstandighede skep vir die uitkeer van water. Die uitkeer-kanaal beïnvloed nie die sekondêre vloei-patrone nie (vir die reeks van uitkeer vloei-verhoudings wat getoetsis) en die sone van maksimum snelheid bly in dieselfde omgewing vir hierdie toetse as vir die toetse sonder ‘n uitkeer kanaal. Die hidrodinamika van die laboratorium eksperimente is goed gesimuleer m.b.v die DELFT 3D numeriese program, terwyl Mike21C gebruik is om die sedimentdinamika te simuleer. Die resultate van die Mike21C simulasies vergelyk relatief goed met die eksperimentele data en kan met ‘n redelike graad van vertroue aangewend word om veldkondisies te simuleer in relatiewe vlak riviere. Dit word aanbeveel bo die empiriese vergelykings om maksimum uitskuring te voorspel aangesien die empiriese vergelykings gekalibreer is vir baie spesifieke hidroulise kondisies.

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Local scour is the erosion of a riverbed resulting from the flow of the river around an obstacle. It is a principal cause of failure of bridges and other hydraulic structures. Current design practice relies on the use of empirical formulae that are often extremely inaccurate, or on the use of physical models that are very expensive. Recent advances in the power of microcomputers have however made numerical simulation increasingly attractive. One obstacle to numerical simulation though is that there is no general agreement on the concept of incipient motion, that critical point at which motion - and hence scour - begins. In this dissertation, the unit stream power model developed by Rooseboom (1992) is extended to handle the complex three-dimensional flow conditions that pertain close to the riverbed in the vicinity of an obstacle. The relationship between unit stream power (the dissipation function) and the Movability Number (the ratio of the shear velocity to the terminal settling velocity of the critical sediment particles) is clearly indicated. Since incipient motion is probabilistic in nature, a relationship was established between the Movability Number and the intensity of motion with allowance for bed-slope and relative depth. An extension of this work resulted in a new bed-load transportation equation that could be used to determine the rate of scour development. Physical modelling in a laboratory flume aided the selection of suitable critical conditions for the onset of scour. The usefulness of the above-mentioned relationships was then demonstrated through the construction of a simple mathematical model of scour and deposition around a structure. This model was used in conjunction with commercially available computational fluid dynamics (CFD) software to predict the scour potential around typical engineering structures. Physical model data was obtained for four situations, and the measured scour was compared with that predicted by the numerical model. There was reasonable agreement between the different models and such differences as there were could be readily attributed to constraints on the numerical model, in particular the lack of a free-surface routine and the coarseness of the grid. This dissertation has opened up a new method for the prediction of local scour that could be readily extended to include all types of scour. With the advent of increasingly fast computers, it could become a useful engineering tool that would assist engineers in the design of safe and cost-effective foundations for hydraulic structures. / AFRIKAANSE OPSOMMING: Plaaslike uitskuring is die erosie van 'n rivierbed as gevolg van vloei verby 'n obstruksie. Dit is 'n belangrike oorsaak van die swigting van brfïe en ander hidrouliese strukture. Bestaande ontwerppraktyk berus op empiriese vergelykings wat dikwels hoogs onakkuraat is, of op fisiese modelle, wat baie duur is. Numeriese simulasie het die afgelope tyd 'n al hoe meer aantreklike opsie geword danksy die snelle toename in die kapasiteit van mikro-rekenaars. 'n Struikelblok met numeriese simulasies is die gebrek aan konsensus oor die konsep van begin-van-beweging, daardie kritieke toestand waarby beweging en derhalwe uitskuring begin. In hierdie proefskrif is die eenheidstroomdrywing model, ontwikkel deur Rooseboom (1992), uitgebrei om die komplekse drie-dimensionele vloeitoestande, wat teenaan die rivierbodem verby 'n obstruksie heers,te hanteer. Die verwantskap tussen Eenheid Stroomdrywing (Dissipasiefunksie) en die Beweeglikheidsgetal (verhouding tussen sleursnelheid en die ewewigvalsnelheid van die kritieke sedimentpartikels ) is duidelik uitgewys. Aangesien begin van beweging probabilisties van aard is, is die verwantskap bepaal tussen die Beweeglikheidsgetal en die Intensiteit van Beweging, met voorsiening vir bodernhelling en relatiewe diepte. Verdere uitbreiding het gelei tot 'n nuwe bedvrag vervoervergelyking wat gebruik kan word om die tempo van uitskuring te bepaal. Kritieke toestande, waarby uitskuring begin, is met fisiese modelle in die laboratorium gekwantifiseer. Die bruikbaarheid van bogenoemde verbande is gedemonstreer deur die ontwikkeling van 'n eenvoudige wiskundige model van uitskuring en afsetting rondom 'n struktuur. Hierdie model is saam met bestaande kommersiële sagteware vir vloeidinamika berekenings (CFD) ingespan om uitskuringspotensiaal rondom tipiese ingenieurstrukture te voorspel. Fisiese modelmetings van uitskuring vanaf vier uitlegte is vergelyk met die numeries voorspelde waardes. Bevredigende ooreenkoms is gevind en verskille kon geredelik gewyt word aan beperkings van die numeriese model, veral die gebrek aan' n vryvlakroetine en die growwe maas. Die proefskrif stel 'n nuwe metode vir die voorspelling van uitskuring daar wat geredelik uitgebrei kan word na ander vorms van uitskuring. Met die ontwikkeling van al vinniger rekenaars kan dit 'n nuttige hulpmiddel vir ingenieurs word om veilige en koste-doeltreffende fondamente in waterlope te ontwerp.

The objective of this study is to estimate 2-D spatial distribution of hydraulic conductivity (Ks) of Zhuoshui River alluvial fan, Taiwan, using groundwater level data from 88 wells and stream stage data from 4 gauging stations. In order to accomplish this analysis, wavelet analysis is first carried out to investigate the periodic cycles of groundwater level, precipitation, and stream stage. The results of the analysis show that variations of groundwater level and stream stage are highly correlated in terms of seasonal and annual periods. Subsequently, seasonal variations of groundwater level in response to stream stage variation are utilized to estimate the Ks spatial distribution by spatiotemporal cross correlation analysis, cokriging, and river stage tomography. Prior to applications of these methods to the alluvial fan, performances of each approach are evaluated and compared with reference field of a noise free synthetic experiment. It is found that all of the approaches could yield similar general spatial pattern of Ks. Nevertheless, river stage tomography seems to reveal a higher resolution of spatial Ks distribution. When the geologic zones are provided in river stage tomography analysis as prior information, the accuracy of estimated Ks values improves. Finally, results of the applications to data of the alluvial fan reveal that the apex and southeast of the alluvial fan are regions with relative high Ks and the Ks values gradually decrease toward the shoreline of the fan. These two areas are considered as the possible main recharge regions of the aquifer. It is also observed that Ks at northern alluvial fan is slightly larger than that at southern. These findings seem consistent with the geologic evolution of this alluvial fan.

<p>QC 20170306</p>