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Sediment transport Part 2: transport rate

Sediment transport Part 2: transport rate. GEOL/CE/EEB 8601 Intro to Stream Restoration. Steps in analyzing sediment mobility. Determination of bed sediment characteristics: grain size distribution and texture Will it move? Apply the Shields criterion (Shields diagram)

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Sediment transport Part 2: transport rate

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  1. Sediment transportPart 2: transport rate GEOL/CE/EEB 8601 Intro to Stream Restoration

  2. Steps in analyzing sediment mobility • Determination of bed sediment characteristics: grain size distribution and texture • Will it move? Apply the Shields criterion (Shields diagram) • Estimation of bed-material transport rate • Understanding channel change: watershed, natural history and effects of imposed changes

  3. Bedload: the movie! John Gaffney movie

  4. Measuring bedload Helley-Smith sampler

  5. Estimating bedload: Meyer-Peter & Müller KMPM = 8 in the original formulation; corrected to 4 by Wong & Parker (2005)

  6. Form drag: Smith & McLean Indirect estimate of skin friction component of total stress hbf 

  7. Mixed sizes: definitions Surface layer thickness La [1-2]Ds90 fraction of material in the surface (active) layer in the ith size range = Fi unit bedload transport rate in the ith size range = qbi surface La subsurface

  8. Bedload vs suspension suspension Fw ~ w’ (turbulence) bedload Fw ~ bed (collisions, contact) Turbulent fluctuations w’ ~ u* suspension if u* ~ settling vel ws

  9. Bedload vs suspension Low Ro: turbulence > settling, suspension > bedload; sediment column is well mixed High Ro: turbulence < settling, bedload only; sediment transport confined to bed region Turbulent fluctuations w’ ~ u* suspension if u* ~ settling vel ws

  10. Bedforms

  11. Bedform types: unidirectional flow ripples

  12. Bedform types: unidirectional flow dunes

  13. Bedform types: unidirectional flow plane bed

  14. Bedform types: unidirectional flow antidunes

  15. Bedform stability 0.2 0.4 0.6 1.0 2.0 0.2 0.4 0.6 1.0 2.0 Southard (1991)

  16. Bedform stability 0.2 0.4 0.6 1.0 2.0 0.2 0.4 0.6 1.0 2.0 Southard (1991)

  17. Bedform stability Southard (1991)

  18. Bedform stability Southard (1991)

  19. Bedform stability Southard (1991)

  20. Bedforms - summary • Ripples • D < 0.5 mm •  < 0.3 m • /hbf ~15 • u ~ uc • Upper plane bed • D = any • u>ws • Dunes • D > 0.2 mm • hbf ~ 0.3 h • /hbf >15 • ws> u >> uc • Antidunes • D = any • Fr = U/gh ~ 1

  21. Can you explain this? Pigeon Roost Creek, Mississippi

  22. Total load formulas Engelund-Hansen (1967) Brownlie (1981) K = 1 for lab data = 1.268 for field data r = hydraulic radius (Area/wetted perimeter

  23. Bedload, suspended load, gravel and sand: adding fines to a gravel channel • Establish steady-state slope profile with constant sediment feed Qs_coarse of a fixed coarse grain size, fixed water supply Qw • Double Qs by adding an equal supply rate of a second finer grain size • Measure new steady-state slope with the additive Qs_coarse + Qs_fine John Gaffney, Sarah Baumgardner, Kimberly Hill, Peter Wilcock

  24. Adding fines to gravel channel John Gaffney, Sarah Baumgardner, Kimberly Hill, Peter Wilcock

  25. Adding fines to gravel channel D50 coarse/D50 fine John Gaffney, Sarah Baumgardner, Kimberly Hill, Peter Wilcock

  26. Adding fines to gravel channel John Gaffney, Sarah Baumgardner, Kimberly Hill, Peter Wilcock

  27. Adding fines to gravel channel

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