1. Flow Energy PE + KE = constant between any two points  PE (loss) =  KE (gain) Rivers are non-conservative; some energy is lost from the system and can not do mechanical work H1 H2 Datum PE = mgh

2. Available Energy is Used To: Overcome Viscous shear and turbulence (internal friction within the fluid); Overcome friction at the channel boundaries; Erode sediment from the channel boundaries; Transport the sediment once it has been eroded.

3. Flow Energy Rate of potential energy loss along the channel can be determined by the slope of the water surface – commonly referred to as the energy- grade line. H1 H2 Datum PE = mgh

4. Flow Types Laminar vs. Turbulent Laminar: –Water particles move along paths that do not disrupt the movement of neighboring particles. –Most resistance is caused by intermolecular viscous forces. –Resistance is  to velocity Turbulent Flow –Water particles move in all directions and velocity constantly fluctuates –Most resistance is generated along channel perimeter; related to channel shape, particle size, and concentration. –Resistance is  to square of velocity

5. Velocity Distribution in Open Channels Modified from Wolman, 1955; Figure from Ritter et al., 2002

6. Flow Types Steady/Uniform Flow Uniform/non-uniform: velocity is constant/variable with position; Steady/unsteady: velocity is constant/variable with time at any given location

7. Manning Equation Describes Flow and Resistance in Open Channels V = 1.49(R 2/3 )(S 1/2 )/n n = Manning’s roughness Coefficient Slope = water surface slope Assumes English units; remove 1.49 from equation for metric

8. Influence of Manning’s n on Resistance and Suspended Sediment

9. Sediment Transport Terminology Entrainment: the processes that initiate the motion of a particle. Competence: the size of the largest particle a stream can entrain under any give set of hydraulic conditions. Capacity: the maximum amount of sediment that the stream can carry given the current hydraulic conditions. Load: amount of sediment that is actually carried by the stream. Sediment discharge: time rate of movement through a cross-section (weight/time; tons/day)

10. Load Types Classification Based on Mode of Transport Suspended Load: Particles transported mainly or entirely in suspension through the supporting action of turbulence. Bedload: Sediment which moves by skipping, sliding, and rolling along the channel bed. Remains within a few grain diameters of the channel bed.

11. Types of Sediment Load Chernicoff S., Fox, HA., and Venkatakrishnan, R., 1997, Essentials of Geology, Worth Publishers, Fig. 13-13, pg. 261

12. Load Types Classification Based on Bottom Sediment Characteristics Wash Load: Particles so fine that they are not found in appreciable amounts in the channel bed. Bed Material Load: Particle sizes that are found in great quantities in the stream bed. – Most bed material load is actually transported in suspension.

13. Methods Used to Describe Entrainment Critical Bed Velocity –Impact or momentum of the water mass on the exposed part of the particle. –6th power law: Size of particle entrained increases with the 6th power of the velocity. –Very difficult to measure Velocity (V) Water 

14. Methods Used to Describe Entrainment Critical Tractive Force –Dragging force is exerted on the exposed part of the particle. –  = γ DS (Duboy’s Equation) –Fairly Easy to measure  Depth (D) Water Surface Slope (S)

15. From Knighton, 1998, Fluvial Forms and Processes, Arnold, Figure 4.4a, page 108.

16. Shield’s Dimensionless Values Dimensionless Shear Stress  =  ( γ f - γ s ) d Dimensionless Reynolds Numbers R * = V*dV*d  V * = (gRS) 1/2 d = Intermediate grain diameter R = Hydraulic Radius γ - Specific weight of solid and fluid

17. Dimensionless Shields Plot

18. Hjulstrom Plot

19. Stream Power  = γ QS  = γ wdvS  /w = (( γ dS)v)/w  /w =  v

20. East Fork River Bedload Trap Flow Bedload Trap