Abridgement of thesis (doctoral)--Kyoto University, 1977. / "Translation of Doctoral Dissertation in Japanese."

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Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [172]-180).

Thesis (M.Sc.)--Aberdeen University, 2009. / Title from web page (viewed on Dec. 23, 2009). Includes bibliographical references.

This thesis presents observations from the Bosphorus (Strait of Istanbul), Turkey, made to study the effects of mixing, entrainment and frictionally induced shear on the dynamics of an exchange flow. The well known two-layer structure with an upper layer of brackish Black Sea water over an opposing undercurrent of salty Mediterranean water was observed. It is likely that the exchange was maximal as it seemed to be bounded by two hydraulic controls at the strait's ends; a sill control at the Black Sea was readily identifiable and the exchange also appeared to be controlled at the south exit toward the Sea of Marmara. The lower layer lost 15 to 20% of its volume to the upper layer because of upward mixing caused by interfacial shear and turbulence created at bends and lateral protuberances. The exchange was quasi-steady, except during a so-called Orkoz when strong winds caused a reversal of the upper layer flow. Between the controls the interface sloped steeply throughout the strait indicating that mass and momentum exchange between the layers and friction along the interface and sidewalls were important. The hydraulics of a single layer flow with entrainment is examined with a reduced gravity model. Expressions are derived for the local change of layer thickness and Froude number as function of the entrainment velocity. It is shown that entrainment, like friction, acts to force the flow toward criticality, although the layer thickness can increase if the Froude number is smaller than 1/2. For certain Froude numbers the effects of friction and entrainment on the layer thickness and the hydraulic state of the flow are found to be of comparable magnitude. A two-layer model with entrainment is developed. Predicted and observed interfacial slopes are found to be in reasonable agreement. The classical definition of hydraulic control assumes layers with uniform velocity so that further consideration is required if there is frictionally induced shear as observed in the Bosphorus. If a shear flow preserves the shape of its velocity profile, a standard formula suggests that hydraulic control is achieved when the depth-averaged flow speed is less than ( gh)1/2. On the other hand, shallow water waves have a speed relative to the mean flow of more than (gh)1/2, suggesting that information could propagate upstream. This apparent paradox is solved by showing that the internal stress required to maintain a constant velocity profile depends on flow derivatives, thus altering the wave speed without introducing damping. By contrast, an inviscid shear flow does not maintain the same profile shape, but is shown to exhibit hydraulic control when the depth-averaged speed equals the inviscid long wave speed. In the Bosphorus the similarity assumption was found to approximately hold indicating that hydraulic control could not be defined using classical inviscid theory. / Graduate

This study had three primary aims. Firstly, to establish the flow resistance characteristics of meandering channels in flood with different inner channel sinuosities and morphology. Secondly, to gain a better understanding of the coherent flow structures and energy loss mechanisms present within such flows. Third, to establish a link between the identified energy loss mechanisms and the flow resistance behaviour of channels with different geometry. The study begins with a review of current literature appertaining to three flow systems. These were; Inbank flow through meandering channels, overbank flow through channels comprising a straight channel with straight parallel floodplains, and meandering channels with floodplain flow. The available literature with regards to flooded meandering channels was limited to a handful of studies. It was clear there existed a deficiency in stage-discharge data over a range of inner channel sinuosities, and the flow descriptions given were limited to inner channels of relatively low sinuosity i.e. 1.25 - 1.3, rectangular or trapezoidal cross-section and unrealistically low width to depth (aspect) ratio. In addition, the influence of roughened floodplains also required further study. To address these needs, a small-scale laboratory investigation was undertaken at Aberdeen, together with a large-scale collaborative experimental study centred at the SERC Flood Channel Facility. These two experimental studies, in which two inner channels of sinuosity 1.4 and 2 were investigated in detail, are described. The experimental techniques and data collection procedures used are also described. The data types collected include: stage- discharge data, flow visualisation, flow velocity measurement, water surface profiles and bed shear stress analysis using an erodible bed. The stage-discharge data were used for the following; to establish the relationship between inner channel sinuosity and overall channel flow resistance; to establish the effect of inner channel morphology on overall channel resistance: and to assess the implications of roughened floodplains on resistance behaviour. The analysis of these data, together with existing related overbank data, yielded a number of conclusions; i). Overall flow resistance increases as inner channel sinuosity increases, ii). At deep floodplain flows, a floodplain comprising a trapezoidal inner channel was less efficient than one comprising a smaller natural inner channel, iii). Roughening the floodplains has a significant effect on channel resistance characteristics. The flow description data, of overbank flow, revealed the presence of coherent flow structures in flows over inner channels of sinuosity 1.4 and 2, and at a number of flow depths. It is suggested these coherent flow structures are a source of additional energy loss, and a link is proposed between the vigour and frequency of these structures for several flow conditions and channel geometries, and the overall resistance behaviour. Contour maps of water surface elevation are presented for several flow conditions and channel geometries. An increase in surface relief was observed as floodplain depth, and therefore velocity, increased. These maps and earlier related work were then discussed. Plots of near bed velocities, secondary circulation patterns and erodible bed observations strongly indicated a change in sediment erosion and deposition patterns, and thus a change in inner channel morphology during overbank flow. Implications of this change are proposed and discussed. Finally, suggestions for future work are presented. with particular emphasis on a 3-dimensional numerical model presently under development at the University of Aberdeen.