| This thesis concerns primarily the computation of flow in meandering streams. The work is intended as a contribution towards the development of a computationally efficient, and yet accurate, morphological model for the determination of meandering bed deformation. Considering this, this thesis is also used as an opportunity to gain insight into aspects of the bed deformation and its modeling. It is assumed that the centreline of the stream follows a sine-generated curve; the flow is turbulent and subcritical; the width-to-depth ratio is large.; A method is developed for the computation of flow in meandering streams having a specified bed geometry. The model rests on the simultaneous solution of the vertically-averaged equations of motion and continuity. In the present formulation, the consideration of the bed shear stress and the turbulence stresses is replaced by that of a single local resistance factor cM. This is determined, among others, by the local channel curvature and the local longitudinal bed slope. The introduction of cM leads to a considerable simplification of the equations of motion. It is shown that the expression proposed in this thesis for the evaluation of cM renders the computed flows compatible with experimental flow pictures.; In order to gain insight into the mechanics of bed deformation and assess some of the current modeling practices, the present flow model is combined with a sediment transport algorithm. The resulting bed deformation model is used to perform two series of numerical runs. It is found that the vertically-averaged flow is capable of producing the required bed topography without any need to invoke cross-circulation for values of the width-to-depth ratio >≈ 10. It is concluded that in the vicinity of the banks the shape of the deposition bars is largely determined by the bank effect. The results of the runs also suggest that the existing equations for cross-circulatory velocity---developed from experiments in circular channels---overestimate the intensity of cross-circulation in natural meandering streams. |
