Sediment Field Methods March 2014 Castle Rock, WA John Gray landers@usgs 678-924-6616

1. Bedload Samplers and Sampling Sediment Field Methods March 2014 Castle Rock, WA John Gray landers@usgs.gov 678-924-6616 Federal Interagency Sedimentation Project water.usgs.gov/fisp

2. Bedload: Sediment that moves by sliding,rolling, or bouncing along on or very near the streambed.http://gallery.usgs.gov/videos/289#.UzEEN_ldU3Y

3. Early Non-Standard Samplers

4. Early Non-Standard Samplers

5. One of the fundamental features of bedload movement is the extreme variation of the transport rate even when the streamflow is constant.

6. Examples of possible distribution of mean bedload transport rates in a cross section. A, Discharge varies uniformly. B, Discharge is uniformly consistent. C, Discharge is erratic with varying tendencies. D, Discharge is an unpredictable combination of varying tendencies.

7. Temporal variation of bedload transport rates for 120 consecutive bedload samples from a stream with constant water discharge (Carey, 1985).

8. The difference between bedload and unmeasured load when dealing with bedload or total load data.

9. Zones sampled by suspended-sediment and bedload samplers and the unmeasured zone.

10. Bed Load Sampling efficiency:The mass of sediment collected by the sampler divided by the mass of sediment that would have passed the nozzle area had the sampler not been there.

11. Bedload samplers can be grouped into four categories: Box or basket (Trap) Pressure difference Slot or pit samplers

12. Bedload Traps http://water.usgs.gov/fisp/docs/091221_Bunte_and_Abt_Trap_HS_comparison_and_adjustment_functions_final.pdf

13. Bedload Traps: Limitations • Stream must be wadeable at all stages • Bedload must be gravel and cobble size • Bedload rates are low enough to allow for deployment and retrieval without over filling the bag. • Streambed must be stable during bedload transport period.

14. Bedload samplers can be grouped into four categories: Box or basket (Trap) (2) Pressure difference Slot or pit samplers

15. Bedload Sampler: Pressure Difference Nozzle Ratio equals Outlet Area Inlet Area

16. US BL-84

17. FISP TM US BLH-84

18. TR-2

19. Helly Smith

20. Some Pressure-Difference Type Bedload Samplers

21. Nozzle size: No established criteria exist for the selection of nozzle size. However, the USGS recommends that the nozzle opening be at least twice the size of the largest particle likely to be in motion at the time the sample is collected.

22. Acceptable Conditions: • The following physical conditions exist: • The bed material is firm enough physically to support the sampler without is sinking into the streambed; • The streambed is smooth enough for the nozzle to lay flat on the bottom; • The stream velocity is low enough to allow the sampler to sit properly on the streambed; and • Neither organic nor mineral deposits clog the bag to the extent that flow through the sampler is restricted.

23. Depending on the relative magnitude of the temporal and spatial variability of the bedload transport, different sampling methods are optimal when making a bedload-discharge measurement.

24. Variation in maximum probable errors with number of sampling traverses at 4 and 20 equally spaced verticals at cross sections with different bedload transport rates (modified from Hubbell and Stevens, 1986). A, Fairly uniform transport rates. B, Skewed transport rates.

25. Sampling Procedure: • Tetherlines: • Cross-sectional procedure: • Single Equal Width Increment (SEWI) method • Multiple Equal Width Increment (MEWI) method • Unequal Width Increment (UWI) method • Sampling time: Sample times normally range from 30 to 60 seconds.

26. Single equal-width-increment bedload-sampling method.

27. Multiple equal-width-increment bedload-sampling method.

28. Unequal-width-increment bedload-sampling method.

29. Sampling Procedure (cont.): • Particle-size analysis: It is recommended that particles size analysis of the bedload and suspended load material be made. • Sample compositing: • Only samples collected with the same sampling times and width increments can be composited. • Until the varibility of bedload distribution at the sampling section is defined, samples should not be composited.

30. Analysis: • Computation of bedload discharge: Depends on sampling procedure. • Sampler efficiency: All bedload data stored in NWIS should not be adjusted for sampling efficiency. • Documentation:

31. Total cross-section method for computing bedload discharge from samples collected with a Helley-Smith bedload sampler.

32. K = Conversion Factor • K = seconds * ton * foot day grams Nw Nw = Width of Sampler nozzle in feet 3 inch; K = 0.381 6 inch; K = 0.190 (see page 78 TWRI)

33. Midsection method for computing bedload discharge from samples collected with a Helley-Smith bedload sampler.

34. Mean-section method for computing bedload discharge from samples collected with a Helley-Smith bedload sampler.

35. Analysis: • Computation of bedload discharge: Depends on sampling procedure. • Sampler efficiency: All bedload data stored in NWIS should not be adjusted for sampling efficiency. • Documentation:

36. Mandatory Data: • Date and Location • Start and Ending Times • Time of Composite • Hydrologic Conditions Code • Remarks on the Quality of the Measurement • Instantaneous Stream Discharge • Bedload Transport Rate

37. Mandatory Data (cont.): • Number of Samples in Composite • Number of Verticals in Composite • Location in Cross-Section • Width Increment of Samples in Composite • Sampling Time of Each Sample • Type of Sampler • Sampling Methodology

38. Mandatory Data (cont.): • Bedload Sampler Bag Mesh Size • Tetherline Used, Yes or No • Bedload Particle-Size Distribution • Suspended Sediment Concentration • Suspended Sediment Particle-Size Distribution • Bed Material Particle-Size Distribution • Stream Temperature

39. Hydrologic Event Gage Height Stream Velocity Stream Width Stage Condition Sample Purpose Optional Data: