Sampling techniques for suspended sediment
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SAMPLING TECHNIQUES FOR SUSPENDED 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. SAMPLING TECHNIQUES. Why a suspended-sediment sampler?

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Sampling techniques for suspended sediment

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


Sampling techniques

SAMPLING TECHNIQUES

  • Why a suspended-sediment sampler?

    • Standardization of instrumentation among investigators

    • Tool for obtaining a representative sample


The colorado river sampler used until the mid 1940 s

The Colorado River SamplerUsed until the mid-1940’s


Sampling techniques standardization

SAMPLING TECHNIQUESStandardization

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


Sampling techniques for suspended sediment

Deploying the Jaukowsky

Suspended-Sediment

Sampler from a boat

in the

Yellow River

near Zhengzhou, China

May 17, 2002

(FISP, 1940, p. 131)


Sampling techniques for suspended sediment

Deploying the Jaukowsky Suspended-Sediment Sampler

(FISP, 1940, p. 131)

in the Yellow River near Zhengzhou, China

Zhang L. dumping sample


Sampling techniques1

SAMPLING TECHNIQUES

  • Standardized instruments

    • Isokinetic sample collection

    • Velocity- or discharge-weighted samples


Sampling techniques2

SAMPLING TECHNIQUES

  • Representative sample

    • Site selection -- characteristic of reach?

    • Temporal variability

    • Spatial variability

    • Sampling frequency


Streamflow constrictions

Streamflow Constrictions


Sampling techniques3

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


Sampling techniques4

SAMPLING TECHNIQUES

  • Temporal variability

    • Sediment transport variability over time

      • Event hydrograph

      • Seasonal hydrograph

      • Annual hydrograph


Sampling techniques5

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


Sampling techniques6

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


Sampling techniques7

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


Sampling techniques8

SAMPLING TECHNIQUES

  • Depth-integration techniques

    • Equal-width increment (EWI) method

    • Equal-discharge increment (EDI) method

    • Single-vertical sample (Box sample)


Key for previous chart

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


Sampling techniques9

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


Sampling techniques for suspended sediment

EWI


Transit rate ratios for nozzle bottle combinations

Transit Rate Ratios for Nozzle/Bottle Combinations


Sampling techniques10

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


Sampling techniques for suspended sediment

EDI


Edi centroids

EDI Centroids


Why the different number of verticals

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


Sampling techniques11

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


Sampling techniques12

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


Sampling techniques13

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


Sampling techniques14

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


Grab or dip sampling

Grab or Dip Sampling


Technique points to remember

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


A good reference

A Good Reference

Field Methods for the Measurement of Fluvial Sediment

http://pubs.usgs.gov/twri/twri3-c2/


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