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Sediment Transport Outline 1.Incipient motion criteria for unisize and mixed-size sediments 2.Modes of sediment transport 3.Bedload transport 4.Suspended.

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Presentation on theme: "Sediment Transport Outline 1.Incipient motion criteria for unisize and mixed-size sediments 2.Modes of sediment transport 3.Bedload transport 4.Suspended."— Presentation transcript:

1 Sediment Transport Outline 1.Incipient motion criteria for unisize and mixed-size sediments 2.Modes of sediment transport 3.Bedload transport 4.Suspended load 5.Bedforms

2 Incipient Motion

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

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

5 (Miller et al., 1977) Motion SmoothTransitionalRough No Motion

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

7 Entrainment of mixed-size sediment Due to: 1.Relative Protrusion 2.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 and m quartz-density particles in a mixture with D 50 = m? Using Shields for unisize sediment 0.7 Pa 7.3 Pa

13 Sediment Transport

14 (Leeder, 1999) Modes of sediment transport

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

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

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

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

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

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

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

23 (c) Ackers and White [1973] equation by d i (a) Meyer-Peter and Müller [1948] equation by d 50ss (b) Meyer-Peter and Müller equation by d i (d) Bagnold equation by d mss (e) Bagnold equation by d mqb (g) Parker et al. [1982] equation by d i (Parker et al. hiding function) (h) Parker et al. [1982] equation by d i (Andrews [1983] hiding function) (Barry et al., 2004) Predicting bedload transport

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

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

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

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

28

29 Ripples Dunes Upper-stage plane beds Bedload sheet

30 Bedform Stability

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

32 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

33 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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