A review of the braided-river depositional environment

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

A Symposium entitled "Classification of Large-Scale Flow-Transverse Bedforms" was convened at the 1987 Mid-Year Meeting of SEPM in Austin, Texas with the purpose of examining the problems involved in classifying large subaqueous flow-transverse bedforms developed in fluvial, intertidal, and marine environments, and recommending changes in nomenclature. The consensus of the participants is that despite the wide spectrum of morphologies of large-scale flow-transverse bedforms (excluding antidunes), they all occupy a similar position in the lower-flow-regime sequence between ripples and upper plane bed. The wide variety of forms is a reflection of secondary effects such as channelization, fluctuating water levels, and unsteady and reversing flows. The bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1,000 m. The symposium panel proposes, therefore, that they should have only one name, DUNE. Dune is preferred as it has historical precedence over other terms in use, such as megaripple and sand wave. The term "dune" should be modified by primary descriptors of shape (i.e., 2-D or 3-D) and size based on spacing (small (0.6-5 m), medium (5-10 m), large (10-100 m) or very large (> 100 m) and the adjective subaqueous when it is important to distinguish them from eolian dunes. The panel recommends a morphologically based classification that is descriptive, with an underlying genetic rationale. Second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature.

Classification of large-scale subaqueous bedforms; a new look at an old problem

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.

/pdf/a-systematic-analysis-of-eight-decades-of-incipient-motion-4jq1z95rbv.pdf

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

/pdf/summary-of-alluvial-channel-data-from-flume-experiments-1956-3j5yoji50z.pdf

Summary of alluvial channel data from flume experiments, 1956-61

________________________________________ Introduction. ______________________________________ Problem and scope_______._____--_--__--_-____ Drag concepts________________________________ Shear drag_________________--_-_-___-_-_-__ Pressure drag-_____________---_--__--_-_-__ Total drag.________________--_--_-_-____-__ Historical development of drag concepts.__________ Mathematical development-_________________ Experimental development.__________________ Acknowledgments___ _ _________________________ Fall behavior parameteis____________________________ Variables affecting particle behavior.______________ Fluid variables._________________-----___-_Variables associated with particle motion. _____ Geometric variables_______________________ Dimensional analysis.___________________________ Coefficient of drag versus Reynolds number____ Shape factor._________________-_--------___ Frequency numbers.________________________ Stability numbers_________________________ Force number._______-_____-_--_----_-_____ Page Cl 1 1 2 2 2 2 3 3 3 5 5 5 5 5 7 7 8 9 9 9 10 Page Fall behavior parameters Continued Choice of characteristic diameters and velocities.___ CIO Particle steadiness______________________________ 11 Particles, liquids, equipment, and procedure__________ 12 Particles___________________________________ 12 Liquids_ _____________________________________ 12 Equipment__ _ _ _______________________________ 13 Procedure__ _ __-_--___-_-_-_-_________________ 15 Experimental results-_______________________________ 16 Description of findings._________________________ 16 Spheres ____________________________________ 16 Disks.---_____________________ 17 Oblate spheroids____________________________ 27 Cylinders__________________________________ 27 Prolate spheroids-__________________________ 31 Comparison of behavior among all particles ________ 31 Interpretation of results_________________________ 32 Parametric relationships.____________________ 32 Patterns of fall___________________________ 32 Shape factors_____________________________ 33 Summary and conclusions._________________________ 35 References cited.----_------_--_----________________ 36

/pdf/the-behavior-of-large-particles-falling-in-quiescent-liquids-3pr4aisp4t.pdf

H.P. Guy

Papers

Summary of alluvial channel data from flume experiments, 1956-61

The behavior of large particles falling in quiescent liquids