Guidance for Collecting Discharge-Weighted Samples in Surface Water Using an Isokinetic Sampler. For the entire report see sw99.01.pdf
Date: Tue, 03 Nov 1998 08:55:39 -0500
From: Nana Frye
To: "A - Division Chief and Staff",
"B - Branch Chiefs and Offices",
"DC - All District Chiefs",
"S - Special Distribution for Research",
"FO - State, District, Subdistrict and other Field Offices",
"PO - Project Offices",
wqspecs@usgs.gov, owq@usgs.gov
Cc: " WRD Archive File, ",
Nana Snow
Subject: OWQ 99.02/OSW 99.01--Guidance for Collecting Discharge-Weighted Samples in Surface Water Using an Isokinetic Sampler
In Reply Refer To: October 28, 1998
Mail Stop 412 or
Mail Stop 415
OFFICE OF WATER QUALITY TECHNICAL MEMORANDUM 99.02
OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM 99.01
Subject: Guidance for Collecting Discharge-Weighted Samples in Surface
Water Using an Isokinetic Sampler
PURPOSE AND SCOPE
The purpose of this memorandum is to provide guidance for collecting
discharge-weighted, depth-integrated samples in surface water using
isokinetic samplers. Tables 4-15 and 17-24 in Appendix 4 quantify
acceptable ranges of reeling and transit rates for rigid-bottle and bag
isokinetic samplers when used with standard reels. This memorandum also
reviews common terminology to provide a better understanding of
surface-water sampling procedures.
This memorandum does not provide guidance on other sampling techniques
such as point sampling, area-weighted sampling, or non-isokinetic
sampling. The techniques may be useful and/or desirable depending on the
sampling design and objectives of a project.
BACKGROUND
Under most field conditions, isokinetic, depth-integrated sampling
techniques must be used to collect discharge-weighted samples.
Constituent concentrations determined from discharge-weighted samples
are used to compute the discharge of any constituent. The discharge of
any constituent is the product of the stream discharge and the
discharge-weighted concentration of the constituent.
The Office of Surface Water and the Office of Water Quality recognize
that the uses and limitations of depth-integrating samplers are not well
documented. Consequently, samples that must be collected using
discharge-weighted, depth-integrated, isokinetic sampling techniques are
sometimes being collected under depth and velocity conditions that are
outside the range where isokinetic samples are obtainable with available
samplers. The following information is presented to better define and
document the operational ranges of the most commonly used
depth-integrating samplers used by the U.S. Geological Survey. Similar
information is presented in Chapters A2, A4, and A6 of Techniques of
Water-Resources Investigations book 9, "National Field Manual for the
Collection of Water-Quality Data," by Wilde and others, eds., in press.
GUIDANCE FOR COLLECTING DISCHARGE-WEIGHTED SAMPLES
IN SURFACE WATER USING AN ISOKINETIC SAMPLER
Many factors can affect whether the concentration of a constituent
(property) in a discharge-weighted sample adequately represents the
discharge-weighted concentration of that constituent in the stream at
the time of sampling. This memo primarily discusses the inherent
physical limitations of commonly used depth-integrating samplers. These
samplers collect isokinetic samples under a relatively narrow set of
conditions that need to be understood by those collecting the sample.
The operational ranges of commonly used samplers are presented in tables
4 through 15 and 17 through 24 in Appendix 4. If water samples are
obtained within these operational ranges, the sample can be reasonably
assumed to be representative of the stream at the time of sampling.
Equal-Discharge-Increment and Equal-Width-Increment Sampling Methods:
Uses and Limitations
Isokinetic sampling is necessary to discharge-weight (velocity-weight)
samples and to accurately collect the sand fraction of suspended
sediment. Equal-discharge-increment (EDI) and equal-width-increment
(EWI) sample-collection methods are specifically designed to result in
the collection of discharge-weighted, depth-integrated, isokinetic
samples (Appendixes 2 and 3). If used correctly, and samples are taken
within the limitations of the sampler used, both methods result in
samples that have the same concentration of constituents.
EDI is the most universally applicable discharge-weighted sampling
method. This method can be used to collect a single composite sample or
a series of samples representing each increment of discharge. The basic
assumption that must be made for the EDI method to be properly used is
that the concentration of any constituent collected at the centroid of
the equal increment of discharge represents the mean concentraton in
that entire increment of discharge. When using the EDI method and
compositing the sample, the total composite sample volume can be
estimated on-site before sampling begins because an approximately equal
volume (at least the minimum volume shown for the deepest vertical) of
water is collected at each increment of discharge. The total composite
volume can be estimated by multiplying the volume collected at the
deepest vertical by the number of increments of equal discharge sampled.
When using the EDI method and not compositing, the samples at each
vertical are analyzed separately. The volume collected at each vertical
can be any volume from within the isokinetic range of the sampler for
that vertical. The total constituent discharge is the sum of the
products at the individual increment stream discharge and the
constituent concentration from that increment.
The EDI method can be used to collect discharge-weighted samples at
water velocities less than about 1.5 feet per second in nonstratified
streams. Although the samplers do not collect true isokinetic samples at
flows less than about 1.5 feet per second, a lack of suspended sand
makes it unnecessary to collect fully isokinetic samples under these
conditions (Office of Water Quality Technical Memorandum 76.17, "Water
Quality--Sampling Mixtures of Water and Suspended Sediment in Streams,"
May 12, 1976, states that a velocity of 2 feet per second is required to
transport sand). The EWI method cannot be used under these low velocity
conditions since this method assumes isokinetic sampling in each
vertical, which is not possible at velocities less than about about 1.5
feet per second.
The EWI method is broadly applicable to streams in which the cross
section has a relatively uniform depth and water velocity. EWI is more
limited in application than is the EDI method, primarily because of the
requirement to use only one transit rate and because of sampler
limitations. All EWI samples must be collected within the isokinetic
range of the sampler because EWI samples are by definition
discharge-weighted samples and the isokinetic collection ability of the
sampler is used to discharge weight the sample. All EWI water-quality
samples must be composited.
The EWI method cannot be used if a significant number of verticals in
the cross section require transit rates slower than the transit rate
used at the deepest, fastest vertical because of the one-transit-rate
requirement. Tables 7, 11, 15, 20, and 24 in Appendix 4 provide transit
rates for a range of stream depths and velocities for several bottle and
nozzle combinations. To determine if the slower velocity verticals can
be sampled at the same transit rate as the faster velocity verticals,
compare the slowest transit rate that will fill the bottle at the
deepest (highest velocity) vertical with the maximum rate allowable at
the slowest vertical. When using a bottle sampler, the full reeling or
transit rate at the deepest, fastest vertical will usually exceed the
fastest allowed rate at one or two verticals near the streambank. The
difference in constituent concentration in a composite sample caused by
this error may be insignificant because (a) the cumulative discharge
associated with slow and shallow sections is usually negligible with
respect to the total discharge, and (b) the sample volume collected
isokinetically from these sections is negligible with respect to the
total sample volume. Also, there may be compensating errors of excessive
transit rates and oversampling in slow water velocities.
Currently available bottle samplers generally are not designed to
collect samples isokinetically at water velocities of less than about
1.5 feet per second. Currently available bag samplers generally do not
collect samples isokinetically at water velocities of less than about 3
feet per second. Thus, the EWI method cannot be used at cross sections
at which all, or large parts, of the sampling cross section have
velocities of less than about 1.5 feet per second when using a bottle
sampler, or less than 3 feet per second when using a bag sampler.
Usable Range of Bottle Samplers
Generally, bottle samplers (see Appendix 1, "Definitions") can collect
isokinetic samples in streams up to 15 feet deep, at water velocities
greater than about 1.5 feet per second, as long as the sampler does not
fill above the outlet of the nozzle, or the transit rate does not exceed
0.4 times the mean stream velocity at the sampling vertical (see
Appendix 3).
Common errors observed in the use of a 3-liter bottle sampler include
excessively fast transit rates and its use in streams that are too
shallow. A clear indication that the transit rate is too fast is the
absence of bubbles from the exhaust port when the sampler is lowered, or
an insufficient volume of water in the sampler after a round-trip
transit has been completed (see Appendix 4, tables 4 through 24.
Usable Range of Bag Samplers
Currently available bag samplers may collect samples isokinetically to
any depth that the bag capacity is not exceeded by the minimum
round-trip sample volume (Appendix 4, table 16) if (1) the temperature
is greater than about 8 degrees Celsius, (2) the mean velocity at
verticals is more than about 3 feet per second, and (3) the transit rate
is less than 0.4 times the mean stream velocity at the sampling vertical
(see Appendix 4, tables 17-24). Because several factors can affect the
sampling efficiency of bag samplers, it is recommended that a field
calibration of the bag samplers hydraulic efficiency be done on-site
before each set of samples is collected.
Sampling Streams Less Than 15 Feet Deep
Container selection
There is no substantial difference in the range of depths and velocities
that can be sampled with different 1- and 3-liter sample bottle and
nozzle combinations. However, transit rates can differ substantially for
different 1- and 3-liter bottle and nozzle combinations. The 1-liter
bottle sampler is the best choice for isokinetic sampling for water
chemistry in streams less than 15 feet deep. The 1-liter sampler has a
smaller unsampled zone and requires much smaller minimum volumes for
each vertical than the 3-liter bottle sampler.
The 3-liter bottle sampler has an unsampled zone of at least 7 inches
and should not be used in streams less than about 2 to 3 feet deep when
(1) the EWI method is being used or (2) sand is to be analyzed as part
of the sample and the stream velocity is sufficient to transport sand.
The 3-liter bottle sampler requires very slow transit rates in slow to
moderate stream velocities.
Currently available bag samplers can be used for depth-integrated,
isokinetic water-quality sampling of streams less than 15 feet deep and
provide a much wider isokinetic range in depth and velocity than do
bottle samplers. Bag samplers require water temperatures above about 8
degrees Celsius, velocities greater than 3 feet per second, strict
attention to transferring all the sand out of the bag, and clean
sampling techniques when appropriate. The D-77 bag sampler can be used
in streams as shallow as 2 to 3 feet deep. Frame-type bag and bottle
samplers require deeper streams in order to minimize the effect of the
unsampled zone. For deep, swift streams (greater than about 7 feet per
second) a heavily weighted frame-type bag or bottle sampler would be a
reasonable choice for water-quality sampling.
Sampling Streams More Than 15 Feet Deep
Point samplers, as described in Edwards and Glysson (1998), are the
preferred samplers to collect isokinetic, depth-integrated samples in
streams deeper than about 15 feet. Point samplers are known to
contaminate trace-element samples and cannot be easily sterilized so
that if samples are to be analyzed for trace elements or bacteria, bag
samplers must be used.
Nozzle selection
For 1-liter bottles, the 5/16-inch nozzle for shallow depths and the
1/4-inch nozzle for greater depths provide adequate ranges in transit
and reeling rates. For 3-liter bottles, even the 5/16-inch nozzle
requires excessively slow transit rates at shallow depths. For a bottle
sampler, larger nozzles provide greater range between the slowest and
fastest isokinetic transit rates (in feet per second). Smaller nozzles
provide a larger difference between the slowest and fastest, total
round-trip transit time. These statements may seem counter intuitive but
examination of the tables for bottle transit rates and reeling rates
will clarify the statement. Smaller nozzles require slower transit
rates. Nozzle size has little effect on minimum sample volumes. For a
pint bottle, the 3/16-inch nozzle increases the isokinetic depth
capabilities from 9 feet for the 1/4-inch nozzle to 15 feet for the
3/16-inch nozzle. No substantial increases in depth capabilities are
provided by reducing the nozzle size for any other bottle.
Nozzles 3/16 inch and larger are recommended for sampling suspended
sediment.
For bag samplers, smaller nozzles may be preferred because they provide
isokinetic sampling in greater depth and velocity ranges and smaller
minimum volumes than do larger nozzles. Smaller nozzles also provide a
greater range between the slowest and fastest, total round-trip transit
time. And, as opposed to bottle samplers, smaller nozzles also provide
greater range between the slowest and fastest isokinetic transit rates.
LOCATION AND DESCRIPTION OF OTHER INFORMATION
In the public ftp depot on srv3rvares.er.usgs.gov/, the directory
contains Excel workbook files that
include tables 3 through 24 of Appendix 4 and additional workbook files
for different bottle, bag, and nozzle sizes. The workbooks can be
printed as is or can be modified to meet user needs.
SELECTED REFERENCES
Edwards, T.K., and Glysson, G.D., 1998, Field methods for measurement of
fluvial sediment: U.S. Geological Survey Techniques of Water-Resources
Investigations, book 3, chap. C2, 80 p.
Federal Interagency Sedimentation Project, 1952, The design of improved
types of suspended-sediment samplers--Interagency Report 6: Minneapolis,
Minnesota, St. Anthony Falls Hydraulic Laboratory, 103 p.
Wilde, F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T., eds., in
press, Selection of equipment for water sampling, chapter A2 of National
Field Manual for the Collection of Water-Quality Data: U.S. Geological
Survey Techniques of Water-Resources Investigations, book 9, chap. A2.
Wilde, F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T., eds., in
press, Collection of water samples, chapter A4 of National Field Manual
for the Collection of Water-Quality Data: U.S. Geological Survey
Techniques of Water-Resources Investigations, book 9, chap. A4.
Wilde, F.D., and Radtke, D.B., eds., in press, Field Measurements,
chapter A6 of National Field Manual for the Collection of Water-Quality
Data: U.S. Geological Survey Techniques of Water-Resources
Investigations, book 9, chap. A6.
Thomas H. Yorke, Jr. /s/ Janice R. Ward /s/
Chief Acting Chief
Office of Surface Water Office of Water Quality
4 attachments
Keywords: Isokinetic, EDI, EWI, sampler, depth-integrated sample,
discharge-weighted sample, area-weighted sample, surface-water quality,
transit rate, reeling rate, suspended sediment.
Distribution: A, B, DC, S, FO, PO
District Water-Quality Specialists
Regional Water-Quality Specialists
OWQ Staff
Appendix 1.
DEFINITIONS
Isokinetic sampling: "To sample in such a way that the water-sediment
mixture moves with no change in velocity as it leaves the ambient flow
and enters the sampler intake." (ASTM)
Discharge-weighted sample: A sample that contains an equal volume from
each unit of discharge sampled.
Depth-integrated sample: A sample that is collected so that each
vertical portion of the stream depth is represented in the sample in
proportion to the desired sampling scheme.
Depth integration (for a discharge-weighted sample as defined by ASTM):
"A method of sampling at every point throughout a given depth (the
sampled depth) whereby the water-sediment mixture is collected
isokinetically so that the contribution from each point is proportional
to the stream velocity at the point. This process yields a sample with
properties that are discharge weighted over the sampled depth." (ASTM)
Depth integration to collect a discharge-weighted sample:
"Depth-integrated sample--a discharge-weighted (velocity-weighted)
sample of water-sediment mixture collected at one or more verticals in
accordance with the technique of depth integration; the discharge of any
property of the sample expressible as a concentration can be obtained as
the product of the concentration and the water discharge represented by
the sample." (ASTM)
Equal-width-increment (EWI) and equal-discharge-increment (EDI)
sample-collection methods: Sampling methods that are specifically
designed to result in the collection of discharge-weighted,
depth-integrated, isokinetic samples. The procedures for collecting EWI
and EDI samples are described in Edwards and Glysson (1998). When
either method is used properly, the resulting samples contain the same
property concentrations.
Bottle samplers: Samplers that have rigid sample containers. Because
these bottles are rigid, they do not instantly transmit the ambient
pressure to the interior of the sample container and have neither
pressure compensation nor opening and closing valves. Point samplers
described in Edwards and Glysson (1998) use rigid bottles but have
pressure compensation and opening and closing valves and are not
considered bottle samplers for the purposes of this document. The tables
in Appendix 4 were not designed for use with point samplers. Point
samplers should perform as bottle samplers if held open from before the
sampler enters the water to until the sampler leaves the water.
Bag samplers: Samplers that have sample containers (bags) that instantly
transmit the ambient pressure to the interior of the sample container
and do not have opening or closing valves.
Transit rate: The rate at which the sampler is passed through the water
from the stream surface to the streambed or from the streambed to the
surface.
Unsampled zone: The part of the sampling vertical, usually assumed to be
the zone from the streambed to the sampler intake. Sampler intakes are
generally 4 to 7 inches above the streambed, depending on the type of
sampler used.
Increment: Refers to the subdivisions of the stream cross section made
based on equal widths (using EWI) or equal discharge (EDI).
Vertical: Refers to that location within the increment at which the
sampler is lowered and raised through the water column.
Centroid: The vertical within the increment at which discharge is equal
on both sides.
Appendix 2. Some uses and advantages of the equal-width-increment (EWI)
and equal-discharge-increment (EDI) sampling methods
EWI method
USE EWI WHEN:
· Information required to determine locations of sampling verticals for
the EDI method is not available.
OR
· The stream cross section has relatively uniform depth and velocity.
AND ESPECIALLY WHEN:
· The location of EDI sampling verticals changes significantly at the
same discharge from one sampling time to another. This situation occurs
frequently in sand bed streams.
Advantages of the EWI method
· The EWI method is easily learned and used for small streams.
· Generally, less time is required on site if the EWI method can be used
and information required to determine locations of sampling verticals
for the EDI method is not available.
EDI method
USE EDI WHEN:
· Information required to determine locations of sampling verticals for
the EDI method is available.
AND ESPECIALLY WHEN:
· Small, non-homogeneous increments need to be sampled separately from
the rest of the cross section. The samples from those verticals can be
analyzed separately or appropriately composited with the rest of the
cross-sectional sample. (Have your sampling scheme approved.)
OR
· Flow velocities are less than the isokinetic transit-rate range
requirement. A discharge-weighted sample can be obtained, but the sample
will not be isokinetic.
OR
· The EWI sampling method cannot be used. For example, isokinetic
samples cannot be collected because stream velocities and depths vary so
much that the isokinetic requirements of the sampler are not met at
several sampling verticals.
OR
· Stage is changing rapidly. (EDI requires less sampling time than EWI,
provided the locations of sampling verticals can be determined quickly.)
Advantages of the EDI method
· Fewer increments are necessary, resulting in a shortened collection
time (provided the locations of sampling verticals can be determined
quickly and constituents are adequately mixed in the increment).
· Sampling during rapidly changing stages is facilitated by the shorter
sampling time.
· Subsamples making up a sample set may be analyzed separately or may be
appropriately composited with the rest of the cross-sectional sample.
· The cross-sectional variation in constituent discharge can be
determined if sample bottles are analyzed individually.
· A greater range in velocity and depth can be sampled isokinetically at
a cross section.
· The total composite volume of the sample is known and can be adjusted
before sampling begins.
Appendix 3. Isokinetic, depth-integrating water-quality samplers and
sampler characteristics
This table could not be converted to text. The table is in Framemaker
and is in the attached Framemaker file.
Appendix 4.
TABLES
Tables 3 through 24 provide guidelines for using bag and bottle samplers
to collect discharge-weighted, depth-integrated, isokinetic samples.
Tables of reeling rates and transit rates (tables 4-15 and 17-24) list
the theoretically defined minimum and maximum reeling rates (in seconds
per turn) and transit rates (in feet per second) for various stream
depths and velocities for commonly used nozzles and bottle or bag
combinations when using an A, B, or E reel. In the tables, the minimum
values are defined as "full" to indicate that when using a listed rate,
the bottle will be full after one round-trip transit; the maximum values
are defined as "fastest" to indicate the fastest reeling rate or transit
rate that can be used for the isokinetic range of the sampler. The
tables also list the volumes that should be in the samplers after one
complete round-trip transit. The sample volumes, reeling rates, and
transit rates assume one complete round-trip vertical transit of a
sampler that, starting empty, goes from the stream surface to the
streambed and returns to the surface at a sampling vertical of specified
depth and mean velocity for a given bottle and nozzle combination. All
depths shown in tables 3 through 24 are water depth minus the unsampled
zone. A key assumption used here and in previously published work is
that the velocity distribution at each vertical is that described in
Edwards and Glysson (1998) in which the water velocity at the deepest
point in the transit is 0.5 of the mean stream velocity in the vertical.
The information provided in the tables is not new, but rather is a
tabular representation of the information presented in the following
references: Edwards and Glysson, 1998; Federal Interagency Sedimentation
Project (FISP), 1952; and a written communication (distributed with each
US D-77 sampler) from Hydrologist-in-Charge, Federal Inter-Agency
Sedimentation Project, 2/21/79, Operating Instructions D-77 Suspended
Sediment Sampler or similar identically computed information for newer
samplers. The values in these tables were computed at each depth and
velocity from the minumum and maximum transit rate ratios shown in
figures similar to 39, 40, and 41 of Edwards and Glysson (1998) for the
applicable nozzle and bag or bottle combination.
The utility of the tables of reeling and transit rates may be enhanced
if used with a vertical transit pacer VTP 74 (available from FISP).
The mean velocity and depth of a sampling vertical must be known to use
the tables and assure that 1- and 3-liter bottle samplers are used
within their isokinetic range. The mean velocity of a vertical can be
estimated adequately for sampling purposes by dividing 10 by the seconds
required for a floating object to travel 11.6 feet at the sampling
vertical. (Timing a peanut passing an 11.6-foot length of flagging
trailing from a suspension cable works quite well.)
Tables For Bottle Samplers
Tables 3 through 15 in Appendix 4 apply to specific bottle, cap, and
nozzle combinations and apply to samplers when that bottle, cap, and
nozzle combination is used with the sampler. For example, the table for
a 1-liter bottle and 5/16-inch nozzle applies to any of the approved
samplers (such as US DH-81, US DH-95, US D-95) when that bottle, cap,
and nozzle are used in the sampler. The range of velocities on the
tables may exceed the velocity of a stream in which some samplers are
stable. (An aluminum D-77 sampler is unstable in stream velocities
greater than 3.5 feet per second, but the 3-liter table shows reeling
and/or transit rates for 9 feet per second.)
Table 3 lists the minimum volume that must be in the sample bottle after
the first transit of the sampler from the stream surface to the
streambed and return to the surface, at a sampling vertical of specified
depth for a given bottle and nozzle combination. If the volume of sample
in the bottle is less than that listed in table 3, the sample was not
collected isokinetically. A volume equal to or greater than that listed
and less than the maximum volume indicates, but does not guarantee, that
the sample was collected isokinetically. Further indication that a
sample was collected isokinetically is obtained by comparing the volume
in the sampler with the volume computed from the product of nozzle area,
mean stream velocity, and total transit time at the vertical.
The volumes in table 3 were calculated for each size sample bottle using
the minimum allowable transit rate for that bottle, nozzle, and depth
combination. The minimum required volume depends only on the stream
depth, bottle size, and atmospheric pressure and is independent of
stream velocity and transit rate. The volumes listed in table 3 are for
sea level and should be increased by about 4 percent for each 1,000 feet
of elevation.
When a sampler filled to the maximum (full) volume is tipped down from
the horizontal, water will spill out of the nozzle; this spillage might
increase the concentration of sand in the sample. When using the EWI
method, sample spillage would result in underrepresentation of that
vertical in the composited sample. In some conditions the maximum depth
of sampling should be limited because the "full" volume of the sampler
needs to be limited to a volume such that water will not be spilled when
the sampler is used. For bottle samplers, the tables provide reeling and
transit rates designated as "-10 tip." When these or faster rates are
used, the sampler will not spill if tipped 10 degrees down from
horizontal. A 10-degree-down tip reduces the operational depth of 1- and
3-liter bottle samplers about 3 feet because of the reduced maximum
sample volume.
When a sampler is filled to a volume exceeding the -10 tip volume, watch
carefully to assure that the sampler has not overfilled. When a sampler
is filled to the maximum (full) volume it is difficult to determine that
it has not overfilled and spilled back to the maximum (full) volume.
Tables 4, 5, and 6 list the minimum (full), -10 tip, and maximum
(fastest) reeling rates (in seconds per turn) for various depths and
velocities for a 1-liter bottle, cap, and 1/4-inch nozzle combination
when using an A, B, or E reel.
Table 7 lists the full, -10 tip, and fastest transit rates (in feet per
second) for various depths and velocities for a 1-liter bottle, cap, and
1/4-inch nozzle combination.
Tables 8,9, and 10 list the full, -10 tip, and fastest reeling rates (in
seconds per turn) for various depths and velocities for a 1-liter
bottle, cap, and 5/16-inch nozzle combination when using an A, B, or E
reel.
Table 11 lists the full, -10 tip, and fastest transit rates (in feet per
second) for various depths and velocities for a 1-liter bottle, cap, and
5/16-inch nozzle combination.
Tables 12, 13, and 14 list the full, -10 tip, and fastest reeling rates
(in seconds per turn) for various depths and velocities for a 3-liter
bottle, cap, and 5/16-inch nozzle combination when using an A, B, or E
reel.
Table 15 lists the full, -10 tip, and fastest transit rates (in feet per
second) for various depths and velocities for a 3-liter bottle, cap, and
5/16-inch nozzle combination.
Appendix 4.--Table 1. List of tables for bottle samplers
Table Type Bottle Nozzle Reel Units
4 Reeling 1 L 1/4 A seconds/turn
5 Reeling 1 L 1/4 B seconds/turn
6 Reeling 1 L 1/4 E seconds/turn
7 Transit 1 L 1/4 any feet/second
8 Reeling 1 L 5/16 A seconds/turn
9 Reeling 1 L 5/16 B seconds/turn
10 Reeling 1 L 5/16 E seconds/turn
11 Transit 1 L 5/16 any feet/second
12 Reeling 3 L 5/16 A seconds/turn
13 Reeling 3 L 5/16 B seconds/turn
14 Reeling 3 L 5/16 E seconds/turn
15 Transit 3 L 5/16 any feet/second
Tables for Bag Samplers
Table 16 lists the minimum (full) volume that must be in a bag sampler
after the first complete transit from the surface of the stream to the
streambed and return to the surface, at any sampling vertical of
specified depth for the specified nozzle. If there is less sample in the
sampler than listed in table 16, the sample was not collected
isokinetically, possibly because the transit rate exceeded four-tenths
the mean stream velocity at that vertical. (Four tenths the mean stream
velocity at a vertical is the maximum (fastest) transit rate allowed
for isokinetic sampling.)
The depths and velocities in the tables are arbitrary but focus on
typical conditions that may frequently be encountered. There are many
configurations for bag samplers and only the field personnel will know
the stable range of their bag-sampler configuration.
There is no single, exact volume for a bag sampler because each bag
installation results in a slightly different volume. The full volumes
used to develop tables for bag samplers assume the sampler is not
allowed to spill and the nozzle is not tipped below horizontal. The
maximum usable volume of a 3-liter bag sampler is estimated to be 2.6
liters based on USGS field experience.
Tables 17, 18, and 19 list the minimum (full) and maximum (fastest)
reeling rates (in seconds per turn) for various depths and velocities
for a 3-liter bag, cap, and 1/4-inch nozzle combination when using an A,
B, or E reel.
Table 20 lists the minimum and maximum transit rates (in feet per
second) for various depths and velocities for a 3-liter bag, cap, and
1/4-inch nozzle combination.
Tables 21, 22, and 23 list the minimum and maximum reeling rates (in
seconds per turn) for various depths and velocities for a 3-liter bag,
cap, and 5/16-inch nozzle combination when using an A, B, or E reel.
Table 24 lists the minimum and maximum transit rates (in feet per
second) for various depths and velocities for a 3-liter bag, cap, and
5/16-inch nozzle combination.
Appendix 4.--Table 2. List of tables for bag samplers
Table Type Bag Nozzle Reel Units
17 Reeling 3 L 1/4 A seconds/turn
18 Reeling 3 L 1/4 B seconds/turn
19 Reeling 3 L 1/4 E seconds/turn
20 Transit 3 L 1/4 any feet/second
21 Reeling 3 L 5/16 A seconds/turn
22 Reeling 3 L 5/16 B seconds/turn
23 Reeling 3 L 5/16 E seconds/turn
24 Transit 3 L 5/16 any feet/second
Appendix 4.--Table 3. Minimum volumes for bottle samplers
This table could not be converted to text. The table is in Framemaker
and is in the attached Framemaker file.