PROGRAMS AND PLANS--Policy and Guidelines for the Collection and Publication of Bedload Data

In Reply Refer To:
WGS-Mail Stop 415                        July 24, 1990

OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 90.08

Subject:  PROGRAMS AND PLANS--Policy and Guidelines for the
                              Collection and Publication of
                              Bedload Data

One of the fundamental features of bedload movement is the
extreme variation of the transport rate even when the flow is
constant.  The theory of dune movement indicates that an
individual bedload sample may contain a mass of sediment which
ranges from zero to four times that expected from the actual
average bedload of the stream (Hubbell, 1987).  Field data have
shown that both spatial and temporal variability are as large, or
larger than predicted by this theory (Emmett, 1980, Carey, 1985,
Pitlick 1988).  Thus, an individ-ual bedload sample may give no
more than the roughest estimation of the actual average bedload
transport.  Individuals measuring bedload should be well aware of
this variability and of the potential inaccuracy of their data.

The following policy and the attached Guidelines for the
collection, publication, and storage of bedload data were
developed after much discussion within WRD and supersede previous
policy and guideline statements given in the Office of Water
Quality Technical Memorandum Nos. 76.04, 77.07, 79.17, and 80.07,
as well as WRD Memorandum No. 77.60.  A brief summary of the WRD
policy issues is given in this memorandum and detailed Guidelines
for the collection and publication of bedload data are given in
the attachment.

This policy applies to all bedload data being collected except
those for projects investigating bedload-sampling, equipment, or
analytical procedures.

                            POLICY

Acceptable Conditions

It is the WRD policy that samples can be collected wherever
physical conditions will permit sample collection.  Acceptable
physical conditions are defined in the attached Guidelines.

Sampler Selection

   a.  Sampler type:

Samplers should be fabricated exactly to design specifications
because it has been shown that relatively minor variations in
construction can cause significant differences in sampling
efficiency.  Examples of minor variations that affect sampling
efficiency include the thickness of the nozzle wall and locating
the frame mount above the bottom of the nozzle. Schematics of the
Helley-Smith and FIASP samplers are shown in Figure 1 of the
Guidelines. Working drawings of the samplers shown in Figure 1 can
be obtained from the Federal Interagency Project in St. Anthony
Falls, Minnesota.

The sampler type must be recorded as part of the basic data
associated with any bedload measurement.

   b.  Bag mesh size:

Field personnel are to use their own judgment in the selection of
the proper mesh size.  Mesh sizes normally used are 0.25, 0.5,
1.0, and 2.0 mm with the 0.25 mm size being the most common.
Mesh size must be recorded as part of the basic data associated
with the bedload measurement.

   c. Nozzle expansion ratio:

The WRD endorses the use of the 1.40 expansion ratio nozzle,
tentatively recommended by the Technical Committee of the Federal
Interagency Sedimentation Subcommittee, but will continue to
accept data obtained with the standard 3.22 expansion ratio
nozzle.

   d. Nozzle size:

The nozzle should be at least two times the size of the largest
particles likely to be in motion.

Sampling Procedure

   a. Particle-size analyses:

It is mandatory that particle-size analyses of the bedload and
suspended load are made at all bedload sampling sites until
sufficient analyses have been obtained to define the particle size
distribution at the site for the flow in question.  Bed material
size analyses should also be made, if at all possible.

   b. Tetherlines:

The use of tetherlines, often called stay-lines, is strongly
recommended when bedload samples are collected using a cable-
suspended sampler.

   c. Cross-sectional procedures:

The U.S. Geological Survey Open-File Report 86-531 lists three
cross-sectional procedures that can be used.  They are the Single
Equal Width Increment (SEWI) method, the Multiple Equal Width
Increment (MEWI) method, and the Unequal Width Increment (UWI)
method.  The SEWI method actually involves collecting 2 samples at
each of 20 verticals and is the most commonly used procedure.
Sampling procedures should consider spatial (cross-sectional)
variations and temporal (at-a-point) variations.  Because
knowledge of where bedload has occurred in the past does not
necessarily imply where bedload will occur in the future, it is
unlikely that pre-judgment will allow an investigator to
substitute spatial concerns for temporal concerns, or vice versa.
Unless sufficient data have been previously collected at the site
to ensure that spatial and temporal variations are consistent
enough to pre-select an appropriate sampling procedure, enough
samples must be collected at each vertical to establish the mean
and range of values to be expected, and at enough verticals to
define the cross sectional distribution.

It is the responsibility of the field personnel to select the
procedure that is optimal for the local conditions.

   d. Sampling time:

Although a sampling time of less than 10 seconds should be
avoided, the sample bag should never be filled to more than about
half full.  The sampling time should not be so long that a
significant amount of clogging of the bag occurs.

   e.  Sample compositing:

Individual bedload samples can be (1) analyzed individually, or
(2) composited into one or more samples for analyses. Until the
sampling variability for the site is understood, all samples
should be analyzed individually.

Sampler efficiency

Sediment-trapping efficiency is the amount of material trapped in
the sampler relative to the amount of material that would have
passed through the space occupied by the sampler nozzle were the
sampler not in place.  Bedload data stored in WATSTORE should not
be adjusted for sediment-trapping efficiency.

Documentation

Bedload data may be stored in WATSTORE and published in the annual
data reports.  The data will be qualified, however, by storing
with each data set the mandatory information given in Table 1 of
the Guidelines.  Districts should review bedload data stored in
WATSTORE prior to the issuance of this memo-randum and enter as
much of the mandatory and optional information as possible.

In order to gain general knowledge on the subject, it is
recommended that anyone who programs, plans, or executes bedload-
sampling efforts should become familiar with all references given
in the attached Guidelines.

Questions and/or comments concerning this new policy should be
directed to the Chief, Office of Surface Water, 415 National
Center, Reston, Virginia 22092.






                              Charles W. Boning
                              Chief, Office of Surface Water

Attachment (see note below)

WRD DISTRIBUTION:  A, B, FO, PO


Note:  The attachment to this memorandum is long and complex, containing both
figures and tables.  It does, however, include important information, mandantory
requirements, and matters of policy.  If not otherwise available, a copy of this
attachment should be obtained from the Office of Surface Water.