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Sediment Transport

Sediment Transport. Outline Incipient motion criteria for unisize and mixed-size sediments Modes of sediment transport Bedload transport Suspended load Bedforms. Incipient Motion. Forces Acting on Stationary Grain. (Middleton and Southard, 1984). Threshold of Motion.

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Sediment Transport

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  1. Sediment Transport Outline • Incipient motion criteria for unisize and mixed-size sediments • Modes of sediment transport • Bedload transport • Suspended load • Bedforms

  2. Incipient Motion

  3. Forces Acting on Stationary Grain (Middleton and Southard, 1984)

  4. Threshold of Motion (Shields,1936; Julien, 1998) (Middleton and Southard, 1984)

  5. Smooth Transitional Rough Motion No Motion (Miller et al., 1977)

  6. Sample Calculation What is c for D = 0.005 mm quartz-density particle?

  7. Entrainment of mixed-size sediment • Due to: • Relative Protrusion • Pivoting angle

  8. Relative Protrusion

  9. Pivoting Angle

  10. Threshold of Motion for a Stationary Grain (Unisize or Graded Sediment) Wiberg and Smith (1987), Bridge and Bennett (1992), + many others

  11. Entrainment of mixed-size sediment

  12. Sample Calculation What is c for 0.001 and 0.010 m quartz-density particles in a mixture with D50 = 0.005 m? Using Shields for unisize sediment 0.7 Pa 7.3 Pa

  13. Sediment Transport

  14. Modes of sediment transport (Leeder, 1999)

  15. Criteria for Sediment Transport Modes • Bedload: • Suspended bed material: • Washload: D 0.063 mm

  16. Modes of sediment transport Washload: D 0.063 mm (Bridge, 2003)

  17. Bedload Transport Equations Meyer-Peter and Muller (1948) Bagnold (1966)

  18. Measuring bedload transport Bedload traps (K. Bunte) Helley-Smith sampler

  19. Bedload Transport Observations HS trap Gravel-bed streams (Bunte et al., 2004) Gravel-bed stream (Cudden & Hoey, 2003) HS

  20. Bedload Transport Equations Wilcock & Crowe (2003) Reference threshold condition Hiding function Reference dimensionless shear stress for median size base don fraction of sand Transport rate based on t/tri

  21. Bedload Transport Equations Barry et al. (2004) Meyer-Peter and Muller (1948) Abrahams and Gao (2006; following Bagnold, 1966, 1973) Bagnold (1966)

  22. Predicting bedload transport Abrahams and Gao (2006) following Bagnold (1966, 1973) Barry et al. (2004)

  23. (a) Meyer-Peter and Müller [1948] equation by d50ss (b) Meyer-Peter and Müller equation by di (d) Bagnold equation by dmss (c) Ackers and White [1973] equation by di (e) Bagnold equation by dmqb (e) Bagnold equation by dmqb (g) Parker et al. [1982] equation by di (Parker et al. hiding function) (h) Parker et al. [1982] equation by di (Andrews [1983] hiding function) Predicting bedload transport (Barry et al., 2004)

  24. Suspended Sediment • Simple criterion for suspension: (van Rijn, 1993)

  25. Measuring suspended load transport DH59 – Hand line Sampler DH48 – Wading Sampler D74 – Hand line Sampler Others: Super-critical flumes, ISCO, OBS, Acoustics

  26. Suspended Sediment • Sediment-diffusion balance (equilibrium): downward settling + upward diffusion Total suspended load • Rouse equation:

  27. Suspended sediment profiles and Rouse equation Z (van Rijn, 1993)

  28. Ripples Dunes Bedload sheet Upper-stage plane beds

  29. Bedform Stability

  30. Suspended Load Observations Mobile orbital ripples with acoustic probes, P. Thorne Mobile river dunes with acoustic probe, Wren et al. (2007) Stochastic simulation, Man (2007)

  31. Sediment Transport and Stream Restoration • Deficient or excessive sediment transport based on design discharge will result in erosion or deposition, which can redirect flow and threaten infrastructure and ecologic indices • Sediment transport prediction depends on grain size, gradation, and bed topography • Uncertainty can be large • Excludes bank erosion and wash load • Use multiple relationships

  32. Sediment Transport Conclusions • Threshold conditions defined by Shields criterion • Modes of sediment transport depend on Shields criterion and grain size • Bedload and suspended load transport treated separately • Load is modulated by bedforms

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