A method is presented which enables the computation of the bed-load transport as the product of the saltation height, the particle velocity and the bed-load concentration. The equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity. Experiments with gravel particles (transported as bed load) are selected to calibrate the mathematical model using the lift coefficient as a free parameter. The model is used to compute the saltation heights and lengths for a range of flow conditions. The computational results are used to determine simple relationships for the saltation characteristics. Measured transport rates of the bed load are used to compute the sediment concentration in the bed-load layer. A simple expression specifying the bed-load concentration as a function of the flow and sediment conditions is proposed. A verification analysis using about 600 (alternative) data shows that about 77% of the predicted bed-load-transport rates are within 0.5 and 2 times the observed values.

Sediment transport; Part I, Bed load transport

A method is presented which enables the computation of the suspended load as the depth-integration of the product of the local concentration and flow velocity. The method is based on the computation of the reference concentration from the bed-load transport. Measured concentration profiles have been used for calibration. New relationships are proposed to represent the size gradation of the bed material and the damping of the turbulence by the sediment particles. A verification analysis using about 800 data shows that about 76% of the predicted values are within 0.5 and 2 times the measured values.

Sediment Transport, Part II: Suspended Load Transport

Data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size, t* c 50 . Calculated t* c 50 values were stratified by initial motion definition, median grain size type (surface, subsurface, or laboratory mixture), relative roughness, and flow regime. A traditional Shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition; t* c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel Shields curves, with the latter generally underlying the former; values derived from competence functions define a separate but poorly developed field, while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous, rather than time-averaged, critical shear stresses. The available data indicate that for high critical boundary Reynolds numbers and low relative roughnesses typical of gravel-bedded rivers, reference-based and visually based studies have t* c50 ranges of 0.052-0.086 and 0.030-0.073, respectively. The apparent lack of a universal t*50 for gravel-bedded rivers warrants great care in choosing defendable t* c50 values for particular applications.

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A systematic analysis of eight decades of incipient motion studies, with special reference to gravel-bedded rivers

A method is presented that makes the classification of bed forms, the prediction of the bed‐form dimensions and the effective hydraulic roughness of the bed forms feasible. The proposed relationships are based on the analysis of reliable flume and field data. A verification analysis using about 1,500 (alternative) reliable flume and field data shows good results in predicting the hydraulic roughness (friction factor). For field conditions, the proposed method yields considerably better results than previously proposed methods, which are reviewed here. The proposed method has also been used to predict the flow depth and the total bed‐material load.

Sediment Transport, Part III: Bed Forms and Alluvial Roughness

The flow of water in straight open channels with prismatic complex cross-sections is considered. Lateral distributions of depth-mean velocity and boundary shear stress are derived theoretically for channels of any shape, provided that the boundary geometry can be discretized into linear elements. The analytical model includes the effects of bed-generated turbulence, lateral shear turbulence and secondary flows. Experimental data from the Science and Engineering Research Council (SERC) Flood Channel Facility are used to illustrate the relative importance of these three effects on internal shear stresses. New experimental evidence concerning the spatial distribution of Reynolds stresses τyx and τzx is presented for the particular case of compound or two-stage channels. In such channels the vertical distributions of τzx are shown to be highly nonlinear in the regions of strongest lateral shear and the depth-averaged values of τyx are shown to be significantly different from the depth mean apparent shear stresses. The importance of secondary flows in the lateral shear layer region is therefore established. The influence of both Reynolds stresses and secondary flows on eddy viscosity values is quantified. A numerical study is undertaken of the lateral distributions of local friction factor and dimensionless eddy viscosity. The results of this study are then used in the analytical model to reproduce lateral distributions of depth-mean velocity and boundary shear stress in a two stage channel. The work will be of interest to engineers engaged in flood channel hydraulics and overbank flow in particular.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112091001246

Turbulent open-channel flows with variable depth across the channel

The relationship of sediment transport to fluid flow is considered. Physical reasoning leads to dimensionless groupings of the variables which are different for coarse sediment and for fine sediment, because of dissimilar modes of transport. This concept provides a basis for a new analysis of data from flume experiments, and a method for dealing with transitional sizes of sediment is suggested. The analysis of experimental data supports the theory put forward and predictive equations are derived which relate total sediment flux to measurable properties of flow. A preliminary comparison is made with observations from other sources, including natural rivers.

Sediment Transport: New Approach and Analysis

Rational regime relationships for the width, depth and slope of a channel in equilibrium are developed using the Ackers and White sediment transport formulae and the White, Paris and Bettess friction relationships, together with the principle of maximum sediment transporting capacity. Favorable comparisons are made with data from sand and gravel channels and with existing empirical regime relationships.

Analytical Approach to River Regime

The resistance of alluvial channels depends upon flow and sediment characteristics. This paper considers the bed features and alluvial resistance that occur at, and close to, the transition zone between the upper and lower flow regimes. New flume and river data are published and the results are analyzed to provide satisfactory predictive techniques covering the lower, transition, and upper regimes for use by river engineers. The bed features that occur in the transition regime are shown to be washed‐out dunes that diminish rapidly in height and steepness with increasing shear stress. The increase in depth with increasing unit discharge is much reduced in the transition regime due to lower hydraulic resistance. In certain circumstances, depths in the transition region can decrease with increasing unit discharge. A criterion for the upper limit of the transition regime corresponding to a moving flat bed is proposed by the writers.

Alluvial resistance in transition regime

Closure to “Sediment Transport: New Approach and Analysis”

Sediment tests were carried out with the ultimate aim of providing design data for flat-vee weir installations in alluvial channels. The model study was of an idealized nature but did serve to indicate those variables which are important and the type of conditions where shoaling in the approach channel is likely to occur. Correlation with initial movement theory was established and the results were used to predict prototype bed formations in terms of sediment properties and flow conditions.

William Rodney White

Papers

Sediment Transport: New Approach and Analysis

Analytical Approach to River Regime

Alluvial resistance in transition regime

Closure to “Sediment Transport: New Approach and Analysis”

Flat-Vee Weirs in Alluvial Channels