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.