FLOW PATTERNS, BANK EROSION AND PLANIMETRIC CHANGES IN MEANDERING STREAMS: AN EXPERIMENTAL STUDY

Abstract

This work focuses on the coupling between channel geometry, flow, bank erosion and planimetric changes in meandering streams. The study has the following three objectives: 1- to gain insight into how the flow patterns in meandering streams are affected by the stream geometry and flow conditions; 2- to evaluate existing equations for the determination of bank erosion rates; and 3- to seek an explanation for why some meandering streams remain regular (or symmetric) in plan shape while evolving in plan, while other acquire irregular shapes. The thesis is also used as an opportunity to introduce a new technique to immobilize the movable boundary and present a series of tests to assess the structural integrity of the coating layer and its roughness (Chapter 2). Chapter 3 presents a series of laboratory tests carried out to investigate the effect of different geometric characteristics and hydraulic conditions on the pattern of the initial flow in sine-generated meandering streams. The most significant finding of the work is that it demonstrates that the meander wavelength plays a considerable role in determining the location in flow plan of the convergence-divergence zone of flow. Chapter 4 presents an experimental study involving a meandering stream with a fixed bed and movable banks. The initial flow at the beginning of the test is detailed with the aid of Acoustic Doppler Velocimetry. The natural deformation of the bank under the action of flow is closely monitored and recorded. The location of maximum bank erosion is found to be between that of maximum bed deformation (or maximum downstream gradients of flow velocity) and maximum flow velocity. This intrinsic shift between the locations in plan of maximum velocity gradient (where maximum bed deformation occurs) and the location of maximum bank erosion appears as a likely mechanism leading to deviations from regular meandering plan shapes.