Maximum equilibrium scour depths, equilibrium scour volumes, and induced equilibrium movements at isolated obstacles on river beds were investigated in clear-water scour. The research was achieved by a systematic flume study based on the results of dimensional analysis of local scour. The main tested obstacles for local scour were cubes. Local scour at a circular cylinder of aspect ratio 1 and a sphere were also examined for comparison with scour at cubes. Each obstacle was placed on a flat movable bed and oriented normal to the incident flow. Non-cohesive uniform medium sand and very fine gravel were used as movable beds. The tested flow conditions were controlled to give many combinations of the relevant dimensionless parameters for local scour: the flow Froude Number, relative obstacle size, and relative roughness of bed material. Water surface profiles and longitudinal velocity profiles along the plane of symmetry, as well as the horizontal velocities near the bed around isolated obstacles on a fixed bed were examined in several runs. For a slightly submerged cube, the path of maximum velocity downstream of the cube moves from the water surface into the lower part of the flow. At a greater distance downstream, the path of maximum velocity tends to move upward toward the water surface. An increase of flow Froude Number leads to a hydraulic jump behind the cube. The relative longitudinal velocity near the bed is increased in this region. The decrease of relative water depth or the increase of flow Froude Number can lead to increased average relative horizontal velocity (V/u) near a cube. The cube has the highest average V/u value, as compared to flow near a circular cylinder and a sphere. The local scour processes and equilibrium scour patterns at isolated cubes on movable beds were also examined. There is not a unique equilibrium scour pattern for clear-water scour at a cube on a movable bed. Equations were developed to predict the maximum equilibrium scour depth and scour volume and the critical condition for incipient motion of bed material at a cube in clear-water scour. As the water becomes relatively deep, the shape effect of the circular cylinder and the sphere become negligible. The major equilibrium movement of a cube on a movable bed due to scour involves longitudinal displacement, vertical settlement, and longitudinal inclination. Equations were developed to predict the equilibrium movement and the critical condition for incipient upstream movement of a cube in clear-water scour. / Graduation date: 1991

No description available.

No description available.

Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 227-250).

The main objective of this research is to estimate the sizes of riprap (loose rock) on highway or railroad embankments approaching bridges, that would be stable in major floods. Two assumptions about the flow direction were made: one horizontal to the bridge abutment and the other normal to the projection of the bridge abutment. Three dynamic conditions of stability of riprap were observed and classified as shaking, some movement, and large movement (washing out). Shaking is the most conservative criteria for design because it indicates more stability than is necessary, requires larger rock, and is less cost efficient. Some movement suggests a conservative design criteria and is the most desirable because it requires smaller riprap and is therefore less expensive. Large movement or washing out means the least stable condition; it may leave the structure as well as human lives exposed to danger.

The first objective of this investigation was to derive and compare scour depth equations in a long contraction using the most widely used sediment transport equations and a variety of other equations. The second objective was to determine a procedure to find an equivalent rectangular section which would convey the same water discharge and sediment load at same slope as an irregular, natural channel in order to simplify numerical computations of scour depth and to allow appropriate application of long contraction scour theory. Some of the transport equations were manipulated algebraically to develop equations for scour depth and slope in a long contraction; others were manipulated using computer programs written especially for each equation, thus deriving scour depth equations. A computer program was written to compare characteristics of a non-rectangular section with rectangular sections of different widths in order to derive a procedure to find an equivalent rectangular transport section (a triangular section was used in this investigation) but the procedure is equally valid for any irregular, natural section. This investigation indicated that depth in the contraction is greater than in the wider approach channel. How much greater depended on which sediment-transport equation was used. Most of the derived scour equations, based on the different sediment transport equations, predicted that the y₂/y₁ ratio decreases as slope, velocity, c, and τₒ'/τ(c) or √τ/ρ)/ω increase; a few do not. Most of the analysis predicted S₂ < S₁, but a few do not. Field and experimental data provided extra evidence that the depth in the contracted section is greater than in the approach reach and how much greater. The evidence that the slope is flatter is not sufficient to be completely convincing. The equivalent rectangular transport section which can carry the same water and sediment discharge at the same slope as the natural section has a depth which is a large fraction of the deepest part of the original section, and the width is considerably narrower than the top width of the original section. Results of the investigation also indicated that the slope, velocity, sediment concentration, and sediment size have little effect on the geometry of the equivalent rectangular section.

No description available.

Thesis (Ph.D.)--University of Western Australia, 2007.

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.