Patterns of flow and bed deformation in meandering streams: An experimental study

This thesis concerns primarily the patterns of flow over the flat initial bed surface (at time t = 0) and their relationship to the geometry of the developed beds in meandering streams. The meandering streams are idealized as regular, sine-generated channels conveying a constant flow rate. In agreement with the conditions prevailing in real rivers, the flow is turbulent and sub-critical, and the width-to-depth ratio is "large".; The effect of channel sinuosity on the initial flow pattern is investigated by considering a series of laboratory flow measurements (carried out by da Silva 1995 and Tape 2001) involving the systematic variation of sinuosity (i.e. of the deflection angle theta0). It is found that every different sinuosity has its own convective flow pattern, i.e. its own distribution in plan of (the laterally adjacent L/2-long) convergence-divergence zones of flow. As theta 0 increases, a gradual change in flow pattern is observed. Two expressions defining the observed theta0-variation of the convective flow pattern are introduced.; Movable bed runs are carried out in a 70° sine-generated channel to investigate the geometry of the developed beds. It is found that the erosion-deposition pattern is substantially different from the patterns typical of "small" and "large" sinuosity, and that the location in flow plan of the L/2-long erosion-deposition zones is hardly affected by the width-to-depth ratio.; The location of erosion-deposition zones of the developed beds is found to (approximately) coincide with the location of the convergence-divergence zones of the initial flows for any value of theta 0. The implications of this finding regarding the process of bed deformation and the prediction of bed geometry are explored.; Finally, the flow data collected for the purpose of this thesis and its main findings are used to develop improved methods for the determination of flow-related quantities.