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 (Shields,1936; Julien, 1998) (Middleton and Southard, 1984)

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

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

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

Relative Protrusion

Pivoting Angle

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

Entrainment of mixed-size sediment

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

Sediment Transport

Modes of sediment transport (Leeder, 1999)

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

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

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

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

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

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

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

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

Predicting bedload transport (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)

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

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

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

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

Ripples Dunes Bedload sheet Upper-stage plane beds

Bedform Stability

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)

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

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