# Discharge Assessment in Straight and Meandering Compound Channels

Wark, James Binning (1993) Discharge Assessment in Straight and Meandering Compound Channels. PhD thesis, University of Glasgow.

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## Abstract

The conveyance capacity of compound channels is investigated. Initially the case of straight compound channels is examined and a novel approach to calculating the lateral distribution of flow across channel widths is derived and verified against a wide range of laboratory and field data. Secondly a similar exercise for the case of meandering compound channels is carried out. A new procedure for calculating the discharge capacity of meandering two stage channels is derived and verified against the available data. Thus the work presented in this thesis is specifically directed towards providing improved methods of estimating the overall conveyance capacity of compound channels. In the past a considerable amount of work has been carried out in to the behaviour of compound channels. Much of this work has concentrated on particular aspects of the hydraulics of compound channels. Recent work has stressed the practical importance of compound channels to river engineers. The general approach followed in deriving these new methods is as follows. The mathematical formulation of river flows is examined. The 3-D turbulence equations are depth integrated to obtain the shallow water equations. A novel approach to the approximation to both bed friction and lateral shear stress terms was followed. The relationship between the shallow water equation and the 1-D St Venant equations is explored. This review of the mathematical aspects of river and floodplain flows provides the physical and theoretical basis of much of the following work on compound channels. A literature search is presented into flow mechanisms in straight compound channels. The important flow mechanisms are identified and possible techniques of accounting for their effects on the conveyance capacity of straight compound channels are identified. A simplification of the 2-D shallow water equations results in the technique called the Lateral Distribution Method (LDM). A suitable finite difference technique was applied to the basic differential equation and combined with the most promising lateral eddy viscosity model, based on bed shear stresses. The available laboratory and field data are used to investigate the performance of the LDM and the range of non-dimensional eddy viscosities. The LDM is compared with methods developed by other authors. A literature search into flow mechanisms in meandering compound channels is presented. The important flow mechanisms are identified and strategies for accounting for the effects on the conveyance capacities of meandering channels are identified. A semi-empirical analysis of the best laboratory data available is carried out and improved methods of discharge estimation for meandering channels are derived. These new methods were verified against independent laboratory and field data. Strategies for future research are presented. These should concentrate on the collection of reliable field data to confirm findings based on laboratory data and the development of sophisticated numerical models, which may then be used to extend the detailed understanding of the complex mechanisms present during compound channel flows. In summary the author has derived and developed an improved version of the lateral distribution model for discharge estimation in straight compound channels. This model is shown to be superior in many respects to existing models. Laboratory and field data used to investigate the behaviour of possible lateral viscosity models and the use of a single value of non-dimensional eddy viscosity is found to be adequate in a wide range of situations. The author has also derived two new models for discharge estimation in meandering compound channels. These models are verified against the available laboratory and field data and are shown to be superior to the existing methods.

Item Type: Thesis (PhD) Doctoral Adviser: D A Ervine Civil engineering, Hydraulic engineering 1993 Enlighten Team glathesis:1993-75709 Copyright of this thesis is held by the author. 19 Nov 2019 18:32 19 Nov 2019 18:32 http://theses.gla.ac.uk/id/eprint/75709