EQUIPMENT & SUPPLIES--Bedload samplers; use of Helley-Smith sampler



In Reply Refer To:                              October 2, 1979 
EGS-Mail Stop 412

QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 79.17

Subject: EQUIPMENT & SUPPLIES--Bedload samplers; use of 
                               Helley-Smith sampler

Through the years, the Geological Survey has provided leadership 
in the research and development of procedures for collection and 
analysis of water data. In the field of suspended-sediment 
sampling, for example, the Survey has played a dominant role in 
the development of standard sampling equipment and procedures that 
are now in use throughout the United States and in many foreign 
countries. The Water Resources Division feels that the Survey has 
a similar responsibility to show leadership in the development of 
bedload samplers and sampling techniques and in the reporting and 
interpretation of bedload information. In order to assist Division 
personnel in planning and programming for measurement of bedload 
discharge, the Quality of Water Branch periodically will issue 
updated guidelines on the use of the Helley-Smith sampler as new 
evidence regarding sampling efficiency, accuracy, and precision of 
the sampler becomes available.

The development of the Helley-Smith sampler (a modified version of 
the Arnhem or Dutch sampler) in 1971 by Helley and Smith (1971) 
constituted the Geological Survey's first effort to develop a 
bedload sampler. Considerable field use of this sampler as well as 
field research has been conducted since it's development. 
Virtually all of the documented field research has been conducted 
at the bedload-transport research facility at East Fork River near 
Pinedale, Wyoming (See Emmett, 1979, copy attached). Research on 
the hydraulic characteristics of the original Helley-Smith sampler 
and a double-size version of the sampler has been carried out at 
our Gulf Coast Hydroscience Center at Bay St. Louis, Mississippi 
(Druffel and others, 1976). More recently, extensive laboratory 
testing of the original Helley-Smith sampler design, as well as 
several modifications of the original design plus other new 
samplers, has been started by WRD researchers at the St. Anthony 
Falls Hydraulics Laboratory, University of Minnesota.

The purpose of this memorandum is to present revised guidelines 
for the use of this sampler, based largely on conclusions stated 
in Emmett's rcport. Please refer to the following previous 
memoranda issued on this subject:

1. QW Branch Technical Memorandum No. 76.04
2. WRD Memorandum No. 77.60
3. QW Branch Technical Memorandum No. 77.07

Restrictions given in the above-mentioned memoranda reflect a 
conservative philosophy regarding use of the Helley-Smith sampler. 
Because of the fact that multi-million dollar river engineering 
projects are being designed at least in part on the basis of 
models calibrated with bedload data obtained by the Geological 
Survey using this sampler, we will continue to maintain a 
conservative philosophy until we have more definitive information 
from the research being conducted at the St. Anthony Falls 
Hydraulic Laboratory on the efficiency of the sampler.

Revised Conditions for use of Helley-Smith Sampler--The field-
calibration tests reported by Emmett indicate that the original 
sampler (76.2 x 76.2 mm opening) used at the East Fork River 
research site had a trap efficiency of near 100% for particles in 
the size range 0.5 to 16 mm. There remains some question about the 
trap efficiency for particles in the 8 to 16 mm size class, 
however, because of the paucity of particles in that size range 
trapped in the sampler during the East Fork River studies (Emmett, 
1979, p. 26).

Quality of Water Branch Technical Memorandum No. 77.07 gave as an 
optimum condition for use of the sampler a range of median 
diameter of bed material (d50) rather than giving the actual size 
of particles moving into the sampler. In that memorandum a range 
in d50 of 2 to 8 mm was given as a criterion or optimum condition 
for use of the sampler.

Use of the d50 of bed material still appears to be a logical basis 
for deciding whether the sampler should be used. However, on the 
basis of the East Fork River data and until further laboratory 
tests are completed, the principal criterion for most efficient 
use of the original Helley-Smith sampler (76.2 x 76.2 mm opening) 
is changed to require that the median diameter of the bed material 
at the location to be sampled be within the range of 1 to 8 mm. 
Using this range as a guide will mean that generally the size of 
most of the particles moving as bedload will be within the range 
of 0.5 to 32 mm, the size range for which we have some assurance 
at this time that the sampler has acceptable sampling 
characteristics.

Until further guideliues are issued the Helley-Smith sampler with 
a 76.2 mm opening should not be considered for use in

a) streams in which the median diameter of the bed material is 
smaller than about 1.0 mm. (Exception: If the median diameter is 
smaller than 1.0 mm but the content of material finer than about 
0.25 mm is no greater than 10-15 percent, the sampler may still be 
used.

b) streams in which the median diameter of the bed material is 
larger than about 8 mm. (Exception: If the median diameter is 
laFger than 8 mm but the content of material larger than 32 mm is 
no greater than about 10 percent, the sampler may still be used.)

c) streams in which the quantity of fine material, particularly 
organic material, is great enough to clog the sampler bag.

d) streams in which large particles or irregular bed 
configurations are likely to interfere with a good fit of the 
sampler to the streambed. Dune bed forms having a length:height 
ratio of less than about 20 may fall in this category.

Sampling technique--Emmett's field-calibration studies indicated 
that the technique used in the collection of samples with the 
Helley-Smith sampler may be as significant as the actual 
efficiency of the sampler. Therefore, upon receipt of this 
memorandum and until further notice, the following sampling 
technique should be used. This technique, used with the standard 
76.2 x 76.2 mm Helley-Smith sampler and for material in the size 
range specified above, will be considered a provisional method of 
the Geological Survey for measurement of bedload discharge. 
Measurements made using this method should be documented and 
referred to as having been collected by the provisional USGS 
method (for bedload sampling using the standard Helley-Smith 
sampler).

Provisional method

1. Samples will be collected at a minimum of 20 equally-spaced 
sampling stations in the cross section.

Variations--For wide cross sections, sampling stations should not 
be spaced greater than 15 meters (50 ft) apart. For narrow cross 
sections, sampling stations need not be closer than about 0.5 
meters apart.

2. The sampling duration will be the same at each sampling station 
(for each sample in the cross section). The sampling duration will 
depend upon the rate of filling of the bag, and probably will vary 
from 30 to 60 seconds. If more than 60 seconds is required to 
collect an appreciable quantity of material, the transport rate 
generally is insignificant.

The correct procedure would be to collect a sample at a high-
velocity location in the cross section to see whether there is 
bedload moving and to select a sampling duration that will assure 
that the bag does not fill to more than about 40 percent at any 
sampling station (Druffel, 1976).

3. One sample will be collected at each sampling station starting 
from one bank and proceeding across to the other bank. Each sample 
will be placed in a separate bag and labeled. Return to the 
beginning sampling station and repeat the sampling, collecting a 
second sample at each of the same stations sampled during the 
first pass across the river. Each sample will be placed in a 
separate bag and labeled.

4. Depending upon the objective of the sampling program, (l) each 
sample will be analyzed individually, or (2) a composite of the 
two samples collected at each sampling station will be analyzed. 
It is recommended that analyses always include a determination of 
particle-size distribution in each sample or composite.

5. Results will be reported in terms of mass per unit time per 
unit width, such as pounds per second per foot (of width) or 
kilograms per second per meter. The unit bedload discharge 
reported will be a widthweighted average for the cross section.

6. If possible, the bed should be sampled to determine the size 
distribution of the bed material, and suspended-sediment samples 
should be collected so that total sediment discharge can be 
calculated (Hubbell, 1964, pp 7-19). Note that this is not a 
simple calculation.

Publication of data--WRD Memorandum No. 77.60 prohibited the 
publication of Helley-Smith bedload data in the annual basic-data 
report series, thereby limiting publication to special reports. We 
will be studying this question again in the near future based on 
the current state of knowledge and would appreciate receiving 
recommendations from any district or project office on publication 
format, needed changes in publication policy, or new parameter 
codes needed if data are to be published in the basic-data 
reports. Parameter codes currently are available for sieve 
diameters of bedload ranging from 0.062 mm to 128 mm--codes 80226 
through 80238. There also is a code for Sediment Discharge, 
Bedload (Tons/day), 80225.

Finally, Quality of Water Branch Technical Memoranda Nos. 76.04 
and 77.07 both requested that the Branch be kept informed by the 
districts of their use of the Helley-Smith sampler as an aid in 
our determination of the applicability of this sampler. To date, 
we have received no information from any district office. I repeat 
this request. Specific information about the accuracy, precision, 
and limits of practical applicability of any sampler is absolutely 
necessary before we can recommend its designation as a standard 
sampler.



                               R. J. Pickering

Attachment

Distribution: A(Regional Hydrologist only), FOL


References

Druffel, L., Emmett, W. W., Schneider, V. R., and Skinner, J. V., 
1976, Laboratory hydraulic calibration of the Helley-Smith bedload 
sediment sampler: U.S. Geol. Survey Open-File report 76-752, 63 p.

Emmett, W. W., 1979, A field calibration of the sediment-trapping 
characteristics of the Helley-Smith bedload sampler, 96 p.

Helley, E. J., and Smith, W., 1971, Development and calibration of 
a pressure-difference bedload sampler: U.S. Geol. Survey Open-File 
report, 18 p.

Hubbell, D. W., 1964, Apparatus and techniques for measuring 
bedload: U.S. Geol. Survey Water-Supply Paper 1748, 74 p.