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Chapter 4 Transport of Sediment by Water

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Chapter 4 Transport of Sediment by Water I Contents Symbols ................................................................................. 4-1 I Terms ................................................................................... 4-3 General ................................................................................. 4-4 Factors affecting sediment transport ......................................................... 4-4 Characteristics of water as the transporting medium .......................................... 4-4 Laminarsublayer ....................................................................... 4-4 Characteristics of transportable materials ................................................... 4-5 Mechanism of entrainment ................................................................. 4-5 Forces acting on discrete particles .......................................................... 4-5 Tractiveforce ........................................................................... 4-5 Determining critical tractive stress ......................................................... 4-6 Determining critical velocity .............................................................. 4-6 Hydraulicconsiderations ................................................................... 4-8 Fixedboundaries ........................................................................ 4-8 Movableboundaries ...................................................................... 4-8 Movement ofbedmaterial .................................................................. 4-9 Schoklitschformula ...................................................................... 4-10 Meyer-Peterformula ..................................................................... 4-10 Haywoodformula ........................................................................ 4-11 Meyer-Peter and Muller formula ........................................................... 4-11 Einsteinbedloadfunction ................................................................. 4-11 Engelund-Hansen procedure ............................................................... 4-12 Colby procedure for relating mean velocity to sand transport ................................... 4-15 Using the graphs to determine the discharge of sands ......................................... 4-15 Application and limitations of formulas ...................................................... 4-18 . Comparison of predictive methods ........................................................... 4-20 / Example of a channel problem .............................................................. 4-24 Summary of procedures for evaluation of bed material transport problems ......................... 4-27 Transportofsuspendedsediment ............................................................ 4-29 Suspensionmechanism ................................................................... 4-29 Sampling and laboratory procedures ........................................................ 4-29 Sediment-rating curve and flow-duration curve method of computing suspended-sediment load ....... 4-31 References ............................................................................... 4-35 Appendix ................................................................................ 4-36 Figures Page 4-la Critical shear stress for quartz sediment in water as a function of grain size .................. 4-7 4-lb Critical water velocity for quartz sediment as a function of mean pain size ................... 4-8 L 4-2 Sediment load classification ........................................................... 4-9 4-3 Relationship between grain roughness (T') and form drag (T") and total bed shear (T~)........... 4-12 4-4 Relationship between dimensionless forms of bed shear (8 and 8') ............................ 4-13 4-5 Graphical solution to and 4 in the Engelund-Hansen procedure .................. 4-14 V<Ss - l>gda 4-6 Relationship of discharge of sands to mean velocity for six median sizes of bed sand, four depths of flow. and a water temperature of 60" F ............................................... 4-16 4-7 Approximate correction factors for the effect of water temperature and concentration of fine sedi- ment (4-7a) and sediment size (4-7b) on the relationship of discharge of sands to mean velocity . 4-17 4-8 Characteristics of bed material ......................................................... 4-18 4-9 Sediment rating curves for Mountain Creek near Greenville. S.C., according to several formulas compared with measurements .......................................................... 4-21 4-10 Sediment rating curves for Niobrara River near Cody. Nebr., according to several formulas com- pared with measurements ............................................................. 4-22 4-11 Sediment rating curves for Colorado River at Taylor's Ferry. Ariz., according to several formulas compared with measurements .......................................................... 4-23 4-12 Vertical distribution of sediment in Missouri River at Kansas City. Mo ....................... 4-30 4-13 Sediment rating curve. Cottonwood Creek. any State ...................................... 4-32 4-14 Flow-duration curve. Cottonwood Creek. any State .............................. ....... 4-33 4-15 Form-drag friction factor in sand-bed channels. f"b. as a function of Rdd,, and FD = -'U ..... 4-38 a0 4-16 Friction-factor predictor for flat-bed flows in alluvial channels ..............................4-39 4-17 Depth-discharge relationships obtained by Alam-Kennedy technique ......................... 4-39 Tables Page 4-1 Discharge data for example channel problem. high flow ....................................4-24 4-2 Sediment transport computed for various flows ...........................................4-25 4-3 Discharge data for example channel problem. lower flow ...................................4-25 4-4 Sediment transport computed for lower flows .............................................4-26 4-5 Checklist of procedures for solving bed-material transport problems ..........................4-28 4-6 Factor A for computing sediment in milligrams per liter by Equation 4.6 .....................4-31 4-7 Computation of average annual suspended-sediment load. Cottonwood Creek. any State ......... 4-34 Chapter 4 Transport of Sediment by Water Symbols Symbol Description -Unit Acceleration due to Feet per Area of flow, cross Feet gravity, 32.2 second L1A section per second or b Channel width or water Feet Meters per surface width second per Depth of flow Feet second Median size of sediment Millimeters, Representative grain Feet (letter d with numerical inches, or feet size subscript denotes parti- Water discharge Cubic feet per cle size in sediment for second which the percentage by Bedload discharge Tons per day weight corresponding to or pounds per subscript is finer, e.g., second d, is size for which 84 Water discharge effec- Cubic feet per percent of sediment by tive in transporting second weight is finer). bedload Effective diameter of the Feet or Total bed-material Tons per day bed material millimeters discharge or pounds per Particle size Millimeters, second (unspecified) inches, or feet Unit water discharge Cubic feet per ~roudenumber; equal to Dimensionless second per u foot of chan- m nel width Darcy-Weisbach friction Dimensionless Unit water discharge Cubic feet per coefficient 8gRS just sufficient to move second per u2 bed material foot channel width Unit bedload discharge Tons per day Difference between the Pounds per per foot or specific weight of sedi- cubic foot pounds per ment and that of water L second per Thickness of laminar Feet foot of chan- sublayer nel width A form of the bed shear, Dimensionless Unit bed-material Tons per day To discharge per foot or Kinematic viscosity Square feet pounds per per second second per Dynamic viscosity Pound-seconds foot of chan- per square nel width foot Hydraulic radius Feet Density of water Slugs per Hydraulic radius with Feet cubic foot respect to the bed Density of sediment Slugs per Reynolds number; equal Dimensionless cubic foot to UD or 4UR A parameter indicating Dimensionless v v the ability of a flow to Boundary Reynolds Dimensionless dislodge a given particle number; equal to 4U d v size (Einstein) (Shields) A parameter describing Dimensionless Hydraulic radius with Feet the intensity of respect to the grain transport of bed material Hydraulic radius with Feet in a given size range respect to dunes and (Einstein) bars Total bed shear stress Pounds per Slope Feet per foot square foot Water surface slope or Feet per foot Critical tractive stress Pounds per I, hydraulic gradient associated with begin- square foot Bed slope Feet per foot ning of bed movement Energy gradient Feet per foot (Shields) Specific gravity of Dimensionless Shear stress associated Pounds per sediment with grain resistance square foot Water temperature Degrees Shear stress associated Pounds per Fahrenheit or with irregularities in square foot degrees bed and banks Celsius Shear velocity (gDSelM Feet per second Shear velocity associated Feet per with grain roughness second Mean velocity Feet per second Fall velocity of sediment Feet per particles second Unit weight of water, Pounds per 62.4 cubic foot or or 1.0 Grams per cubic centimeter Unit weight of sediment, Pounds per dry cubic foot Terms Antidunes. Bed forms that occur if the water suspended particles is continuously supported by velocity is higher than that forming dunes and the fluid (see wash load). plane beds. Antidunes
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