SAMPLING TECHNIQUES FOR SUSPENDED SEDIMENT

1. SAMPLING TECHNIQUES FORSUSPENDED SEDIMENT Introduction to Sediment Sampling USGS Technical training in Support of Native American Relations (TESNAR) 2013 Siletz, Coquille, Umatilla, and Cowlitz Tribes Siletz, OR May 20-23, 2013

2. SAMPLING TECHNIQUES • Why a suspended-sediment sampler? • Standardization of instrumentation among investigators • Tool for obtaining a representative sample

3. The Colorado River SamplerUsed until the mid-1940’s

4. SAMPLING TECHNIQUESStandardization Jaukowsky Suspended-Sediment Sampler (FISP, 1940, p. 131)

5. Deploying the Jaukowsky Suspended-Sediment Sampler from a boat in the Yellow River near Zhengzhou, China May 17, 2002 (FISP, 1940, p. 131)

6. Deploying the Jaukowsky Suspended-Sediment Sampler (FISP, 1940, p. 131) in the Yellow River near Zhengzhou, China Zhang L. dumping sample

7. SAMPLING TECHNIQUES • Standardized instruments • Isokinetic sample collection • Velocity- or discharge-weighted samples

8. SAMPLING TECHNIQUES • Representative sample • Site selection -- characteristic of reach? • Temporal variability • Spatial variability • Sampling frequency

9. Streamflow Constrictions

10. SAMPLING TECHNIQUES • Site selection • Uniform flow in x-sectoin • Well-mixed flow • Ability to sample range of flows, most importantly medium-and-high flows • Availability of historical data

11. SAMPLING TECHNIQUES • Temporal variability • Sediment transport variability over time • Event hydrograph • Seasonal hydrograph • Annual hydrograph

13. SAMPLING TECHNIQUES • Spatial variability • Site specific • Variability over the width of the channel cross section • Variability in each sampled vertical • Basin characteristic • Higher versus lower elevation sites • Northern versus southern exposures

17. SAMPLING TECHNIQUES • Sampling frequency • Generally dictated by the study approach and level of funding • Less critical to collection of a discrete representative sample than site selection, and temporal and spatial variability

18. SAMPLING TECHNIQUES • Sample collection methods • Depth-integrated sampling • Point-integrated sampling • Point sampling • Grab or dip sampling • Pumped samples * • Single-stage samples * *will be covered in separate lecture

19. SAMPLING TECHNIQUES • Depth-integration techniques • Equal-width increment (EWI) method • Equal-discharge increment (EDI) method • Single-vertical sample (Box sample)

21. Key for Previous Chart 1) US DH-48 2) US DH-59 3) US DH-76 4) US DH-81 5) US DH-95 6) US DH-2 7) US D-74 8) US D-74AL 9) US D-95 10) US D-96 11) US D-96A1 12) US D-99 13) US P-61A1 14) US P-63 15) US P-72

22. SAMPLING TECHNIQUES • Equal-width increment (EWI) method • Cross section divided into (~8-20) equal-width increments • Sampling transit rate for all sample verticals determined at the deepest/fastest vertical • Collect velocity-weighted sub-samples from the mid-point vertical in each width increment • Composite all sub-samples for analysis

24. EWI

25. Transit Rate Ratios for Nozzle/Bottle Combinations

26. SAMPLING TECHNIQUES • Equal-discharge increment (EDI) method • Stream discharge divided into (4-9) equal increments of discharge • Collect velocity- and discharge-weighted samples from the centroid vertical of each discharge increment • Vary the transit rate among verticals to obtain equal sample volumes • Analyze samples individually or composited

28. EDI

29. EDI Centroids

31. Why the different number of verticals • Why sometimes 5 verticals • Why sometimes 20 verticals • Assumption made • Sample collected at the center of the centroid represents the mean concentration for that centroid • If, not, must increase number of verticals

32. SAMPLING TECHNIQUES • Single-vertical sample • Use EDI method to determine sample vertical location • Sample vertical should be at the point in the cross section where the mean sediment concentration occurs over the largest range in stage • Use the slowest transit rate possible without overfilling the sample bottle • Duplicate samples are typically collected

33. SAMPLING TECHNIQUES • Point-integration technique • Necessary in depths >15 feet (total sampler traverse >30 feet) • A point-integrating sampler is necessary • Used in conjunction with EWI or EDI method • Transit rates determined by EWI or EDI method • Descending traverse matched by ascending traverse • Single-vertical sub-samples composited for analysis

35. SAMPLING TECHNIQUES • Point sampling • Use a point-integrating sampler • Samples represent discrete points in the sampled cross section and/or verticals • Samples may be velocity-weighted over an interval equal to the fill time for the nozzle/bottle combination • Samples may be instantaneous snap shots of sediment transport at a point without consideration for velocity

36. SAMPLING TECHNIQUES • Grab or dip sampling • Flow conditions or other unusual circumstances generally render standard samplers unusable • Sediment is well mixed spacially • Samples are not integrated • Samples are seldom representative

37. Grab or Dip Sampling

38. Site selection- characteristic of reach, uniform flow, well mixed, sample full range of flows, H/L elev, N/S exposure, any historical data Temporal variability- event, seasonal, annual Variations in X-sec and w/i sampling vertical, sediment sizes (coarse,sand,silt,clay) will vary How frequent sample- depends on objectives EWI- equal width & transit rate, volume not equal, first set transit rate at thalweg EDI- volume equal, width and transit rate not equal; need Q meas, divide by 10,30,50,70,90 % Technique Points to Remember

39. A Good Reference Field Methods for the Measurement of Fluvial Sediment http://pubs.usgs.gov/twri/twri3-c2/