ASTM D1941-91(2001)
(Test Method)Standard Test Method for Open Channel Flow Measurement of Water with the Parshall Flume
Standard Test Method for Open Channel Flow Measurement of Water with the Parshall Flume
SCOPE
1.1 This test method covers measurement of the volumetric flowrate of water and wastewater in open channels with the Parshall flume.
1.1.1 Information related to this test method can be found in ISO 1438 and 4359.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D 1941 – 91 (Reapproved 2001)
Standard Test Method for
Open Channel Flow Measurement of Water with the Parshall
Flume
This standard is issued under the fixed designation D 1941; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2.2 head—the height of a liquid above a specified point;
that is, the flume crest.
1.1 This test method covers measurement of the volumetric
3.2.3 hydraulic jump—an abrupt transition from supercriti-
flowrate of water and wastewater in open channels with the
caltosubcriticalflow,accompaniedbyconsiderableturbulence
Parshall flume.
or gravity waves, or both.
1.1.1 Information related to this test method can be found in
3.2.4 normal depth—the uniform depth of flow for a given
ISO 1438 and 4359.
flowrate in a long open channel of specific shape, roughness,
1.2 This standard does not purport to address all of the
and slope.
safety concerns, if any, associated with its use. It is the
3.2.5 primary instrument—the device (in this case, the
responsibility of the user of this standard to establish appro-
flume) that creates a hydrodynamic condition that can be
priate safety and health practices and determine the applica-
sensed by the secondary instrument.
bility of regulatory limitations prior to use.
3.2.6 scow float—an in-stream flat for depth sensing usually
2. Referenced Documents
mounted on a hinged cantilever.
3.2.7 secondary instrument—in this case, a device which
2.1 ASTM Standards:
measures the depth of flow at an appropriate location in the
D 1129 Terminology Relating to Water
flume. The secondary instrument may also convert the mea-
D 2777 Practice for Determination of Precision and Bias of
sured depth to an indicated flow rate.
Applicable Methods of Committee D-19 on Water
3.2.8 stilling well—a small reservoir connected through a
D 3858 Test Method for Open Channel Flow Measurement
constricted passage to the main channel, that is, the flume, so
of Water by Velocity-Area Method
that a depth measurement can be made under quiescent
2.2 ISO Standards:
conditions.
ISO 555 Liquid Flow Measurements in Open Channels—
3.2.9 subcritical flow—open channel flow at a velocity less
Dilution Methods for Measurement of Steady Flow—
than the velocity of gravity waves in the same depth of water.
Constant Rate Injection Method
Subcritical flow is affected by downstream conditions, since
ISO 1438 Liquid Flow Measurement in Open Channels
disturbances are able to travel upstream.
Using Thin-Plate Weirs and Venturi Flumes
3.2.10 submerged flow—a condition where the water stage
ISO 4359 Liquid Flow Measurement in Open Channels—
downstream of the flume is sufficiently high to affect the flow
Rectangular Trapezoidal and U-shaped Flumes
over the flume crest and hence the free-flow depth-discharge
3. Terminology
relation no longer applies and discharge depends on two head
measurements.
3.1 Definitions: For definitions of terms used in this test
3.2.11 supercritical flow—open channel flow at a velocity
method, refer to Terminology D 1129.
greater than that of gravity waves in the same depth, so
3.2 Definitions of Terms Specific to This Standard:
disturbances cannot travel upstream, and downstream condi-
3.2.1 free flow—a condition where the flowrate is governed
tions do not affect the flow.
by the state of flow at the crest overfall and hence can be
3.2.12 throat—the constriction in a flume.
determined from a single upstream depth measurement.
4. Summary of Test Method
This test method is under the jurisdiction ofASTM Committee D-19 on Water
4.1 Parshall flumes are measuring flumes of specified ge-
and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-
ometries for which empirical relations of the form
phology, and Open-Channel Flow.
n
Current edition approved Jan. 25, 1991. Published March 1991. Originally
Q 5CH (1)
a
e 2
published in 1962. Last previous edition D 1941 – 67 (1975) .
Annual Book of ASTM Standards, Vol 11.01.
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 1941 – 91 (2001)
corrections for non-standard geometry are only estimates. The
inside surface of the flume should be at least as smooth as a
good quality concrete finish.
7.2.2 The measurement location for depth H is shown in
a
Fig. 1. In submerged flow a second depth, H , must be
b
measured in the throat as indicated. However, in the 1, 2, and
3-in. (2.54, 5.08, and 7.62-cm) flumes, this measurement is
made at H instead, because disturbances have been observed
c
at the H location in these sizes ((1) and (2)). See Fig. 2 for the
b
relation between H and H .
b c
7.3 Stilling Well and Connector:
7.3.1 Stilling wells are recommended for accurate depth
measurements; they are required when wire- or tape-supported
cylindrical floats are used or when the liquid surface is
fluctuating.
7.3.2 The lateral area of the stilling well is governed in part
by the requirements of the depth sensor. For example, the
clearancebetweenafloatandthestilling-wellwallshouldbeat
least 0.1 ft (3 cm) and should be increased to 0.25 ft (7.6 cm)
FIG. 1 Parshall Flume
ifthewellismadeofconcreteorotherroughmaterial,thefloat
diameteritselfbeingdeterminedinpartbypermissiblefloatlag
have been established so that the flowrate, Q, can be
error (see 11.4.2). Other types of depth sensors may also
determined from a single depth measurement, H , in free flow.
a
impose size requirements on the stilling well, and the maxi-
If the flow is submerged, an addition downstream depth, H ,
b
mum size may be limited by response lag.
must be measured and suitable adjustments made.
7.3.3 Provision should be made for cleaning and flushing
5. Significance and Use the stilling well to remove accumulated solids. It may be
necessary to add a small purge flow of tap water to help keep
5.1 Flumedesignsareavailableforthroatsizesof1in.(2.54
thewellandanyconnectorpipeandthesensorpartsclean.This
cm) to 50 ft (15.2 m) which cover maximum flows of 0.2 to
3 3
flow should be small enough for any depth increase in the
3000 ft /s (0.0057 to 85 m /s) (1) and (2) . They can therefore
stilling well to be imperceptible.
be applied to a wide range of flows, with head losses that are
moderate. 7.3.4 The opening in the flume sidewall connecting to the
stilling well either directly or through a short perpendicular
5.2 The flume is self-cleansing for moderate solids transport
and therefore is suited for wastewater and flows with sediment. pipe must have a burr-free junction with the wall. The hole or
pipe must be small enough to dampen surface disturbances; an
6. Interferences
area of about 1/1000th of the stilling-well area is considered
adequateforthispurpose.However,thediametershouldnotbe
6.1 The flume is applicable only to open channel flow and is
inoperative under full-pipe flow conditions. so small (or the pipe so long) that it is difficult to keep open or
a lag is introduced in the response to changing flows (3); hole
6.2 Although the flume has substantial self-cleansing capac-
ity, it can be clogged by debris or affected by accumulation of and pipe diameters of about ⁄2 in. (1.3 cm) should be
considered a minimum. If changes are made in pipe sizes, they
aquatic growth and cleaning or debris removal may be re-
quired. should be done sufficiently removed from the flume wall that
no drawdown will occur. The intake dimensions cited in this
7. Apparatus
paragraph should be regarded as suggestions only.
7.1 AParshallflumemeasuringsystemconsistsoftheflume
7.4 Depth-Discharge Relations:
itself(primary)andadepth-measuringdevice(secondary).The
7.4.1 Free Flow—The values of C and n for use with Eq 1
secondary device can range from a simple scale for manual
are given in Table 2, along with approximate limiting flow-
readings to an instrument which continuously senses the depth,
rates.Themaximumsubmergenceratios, H /H ,forwhichfree
b a
converts it to flowrate, and provides a readout or record of
flow will occur are:
instantaneous flowrate or totalized flow, or both.
H /H < 0.5, for 1, 2, and 3-in. (2.54, 5.08, and
b a
7.2 The Flume:
7.62-cm) flumes;
7.2.1 Parshall flumes are characterized by throat width;
H /H < 0.6, for 6 and 9-in. (15.24 and 22.86-cm) flumes;
b a
dimensions and flowrates for each size are given in Fig. 1 and
H /H < 0.7, for 1 to 8-ft (30.48 to 243.8-cm) flumes;
b a
Table 1, respectively. The dimensions must be maintained
H /H < 0.8, for 10 to 50-ft (304.8 to 1524.0-cm) flumes.
b a
within 2 %, because the flume is an empirical device and
7.4.2 Submerged Flow:
7.4.2.1 Discharge rates for submerged-flow conditions are
given for 1, 2, 3, 6, and 9-in. (2.54, 5.08, 7.62, 15.24, and
The boldface numbers in parentheses refer to a list of references at the end of
this test method. 22.86-cm) flumes in Table 3, Table 4, Table 5, Table 6, and
D 1941 – 91 (2001)
TABLE 1 Dimensions and Capacities of Standard Parshall Flumes
NOTE 1—Flume sizes 3 in. through 8 ft have approach aprons rising at 25 % slope and the following entrance roundings: 3 through 9 in., radius = 1.33
ft; 1 through 3 ft, radius = 1.67 ft; 4 through 8 ft, radius = 2.00 ft.
Vertical distance be-
Wall
Widths Axial lengths, ft Gage Points, ft
low crest, ft
Free-flow Capacities,
Depth in Converg-
ft /s
Con- ing wall
Down- H , wall H
C T
Upstream Converg- Throat Diverging Lower end
verging length
Throat, stream Dip at length up-
A
end, W , ing Sec- section, section, of flume,
C Section, C ,ft
W end, W , Throat, N stream of
T D
ft tion, L L L K
C T D D,ft B ab Minimum Maximum
ft crest
1 in. 0.549 0.305 1.17 0.250 0.67 0.5–0.75 0.094 0.062 1.19 0.79 0.026 0.042 0.005 0.15
2 in. 0.700 0.443 1.33 0.375 0.83 0.50–0.83 0.141 0.073 1.36 0.91 0.052 0.083 0.01 0.30
3 in. 0.849 0.583 1.50 0.500 1.00 1.00–2.00 0.188 0.083 1.53 1.02 0.083 0.125 0.03 1.90
6 in. 1.30 1.29 2.00 1.00 2.00 2.0 0.375 0.25 2.36 1.36 0.167 0.25 0.05 3.90
9 in. 1.88 1.25 2.83 1.00 1.50 2.5 0.375 0.25 2.88 1.93 0.167 0.25 0.09 8.90
1.0 ft 2.77 2.00 4.41 2.0 3.0 3.0 0.75 0.25 4.50 3.00 0.167 0.25 0.11 16.1
1.5 ft 3.36 2.50 4.66 2.0 3.0 3.0 0.75 0.25 4.75 3.17 0.167 0.25 0.15 24.6
2.0 ft 3.96 3.00 4.91 2.0 3.0 3.0 0.75 0.25 5.00 3.33 0.167 0.25 0.42 33.1
3.0 ft 5.16 4.00 5.40 2.0 3.0 3.0 0.75 0.25 5.50 3.67 0.167 0.25 0.61 50.4
4.0 ft 6.35 5.00 5.88 2.0 3.0 3.0 0.75 0.25 6.00 4.00 0.167 0.25 1.30 67.9
5.0 ft 7.55 6.00 6.38 2.0 3.0 3.0 0.75 0.25 6.50 4.33 0.167 0.25 1.60 85.6
6.0 ft 8.75 7.00 6.86 2.0 3.0 3.0 0.75 0.25 7.0 4.67 0.167 0.25 2.60 103.5
7.0 ft 9.95 8.00 7.35 2.0 3.0 3.0 0.75 0.25 7.5 5.0 0.167 0.25 3.00 121.4
8.0 ft 11.15 9.00 7.84 2.0 3.0 3.0 0.75 0.25 8.0 5.33 0.167 0.25 3.50 139.5
10 ft 15.60 12.00 14.0 3.0 6.0 4.0 1.12 0.50 9.0 6.00 . . 6 300
12 ft 18.40 14.67 16.0 3.0 8.0 5.0 1.12 0.50 10.0 6.67 . . 8 520
15 ft 25.0 18.33 25.0 4.0 10.0 6.0 1.50 0.75 11.5 7.67 . . 8 900
20 ft 30.0 24.00 25.0 6.0 12.0 7.0 2.25 1.00 14.0 9.33 . . 10 1340
25 ft 35.0 29.33 25.0 6.0 13.0 7.0 2.25 1.00 16.5 11.00 . . 15 1660
30 ft 40.4 34.67 26.0 6.0 14.0 7.0 2.25 1.00 19.0 12.67 . . 15 1990
40 ft 50.8 45.33 27.0 6.0 16.0 7.0 2.25 1.00 24.0 16.00 . . 20 2640
50 ft 60.8 56.67 27.0 6.0 20.0 7.0 2.25 1.00 29.0 19.33 . . 25 3280
A
For sizes 1 to 8 ft, C = W /2 + 4 ft.
T
B
H located 2 3 C distance from crest for all sizes; distance is wall length, not axial.
C
/
TABLE 2 Free-Flow Values ofC andn for Parshall Flumes
(See Eq 1)
A B B
Throat Width C Q,min Q, max
n
inch- m 3
3 3 3
ft-in cm SI ft /s ft /s m /s
pound 10 /s
0-1 2.54 0.338 0.0479 1.55 0.01 0.28 0.2 0.0057
0-2 5.08 0.676 0.0959 1.55 0.02 0.56 0.5 0.014
0-3 7.62 0.992 0.141 1.55 0.03 0.85 1.1 0.031
0-6 15.24 2.06 0.264 1.58 0.05 1.42 3.9 0.11
0-9 22.80 3.07 0.393 1.53 0.09 2.55 8.9 0.25
1-0 30.48 4.00 0.624 1.522 0.11 3.1 16.1 0.46
1-6 45.72 6.00 0.887 1.538 0.15 4.2 24.6 0.69
2-0 60.96 8.00 1.135 1.550 0.42 11.9 38.1 0.93
3-0 91.44 12.00 1.612 1.566 0.61 17.3 50.4 1.42
4-0 121.92 16.00 2.062 1.578 1.3 36.8 67.9 1.92
5-0 152.40 20.00 2.500 1.587 1.6 45.3 85.6 2.42
6-0 182.88 24.00 2.919 1.595 2.6 73.6 103.5 2.93
7-0 213.36 28.00 3.337 1.601 3.0 85.0 121.4 3.44
8-0 243.84 32.00 3.736 1.607 3.5 99.1 139.5 3.95
10-0 304.8 39.38 4.709 1.6 6 170 200 5.6
12-0 365.8 46.75 5.590 1.6 8 227 350 9.9
19-0 457.2 57.81 6.912 1.6 8 227 600 17.0
20-0 609.6 76.25 9.117 1.6 10 283 1000 28.3
25-0 762.0 94.69 11.32 1.6 15 425 1200 34.0
30-0 914.4 113.13 13.53 1.6 15 425 1500 42.5
40-0 1219.2 150.00 17.94 1.6 20 566 2000 56.6
50-0 1524.0 186.88 22.35 1.6 25 708 3000 84.9
A
Listed values of C should be used in Eq 1 with H in feet to obtain flowrate in
NOTE 1—1 ft = 30.48 cm a
cubic feet per second. Listed values of C (metric) should be used with H in
a
FIG. 2 Relation BetweenH andH for 1, 2, and 3-in. (2.54, 5.08,
b c
centimetres to obtain flowrate in litres per second.
and 7.62-cm) flumes (Reference (2))
B
From Ref (1).
D 1941 – 91 (2001)
TABLE 3 Flume, 1-in. (2.54-cm), Submerged—Flowrate, ft /s
H ,ft
a
Sub- 0.05 0.06 0.08 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.70 0.80
merged,
%
50 0.0033 0.0044 0.0067 0.0095 0.0180 0.028 0.039 0.052 0.066 0.082 0.097 . . . . .
55 0.0032 0.0043 0.0066 0.0094 0.0180 0.028 0.038 0.052 0.065 0.081 0.096 . . . . .
60 0.0032 0.0042 0.0065 0.0093 0.0179 0.027 0.038 0.051 0.064 0.079 0.094 . . . . .
65 0.0031 0.0041 0.0064 0.0090 0.0173 0.026 0.037 0.050 0.061 0.076 0.091 . . . . .
70 0.0030 0.0040 0.0062 0.0087 0.0165 0.025 0.035 0.047 0.058 0.072 0.087 . . . . .
75 . 0.0038 0.0059 0.0083 0.0156 0.024 0.033 0.044 0.055 0.068 0.081 0.096 . . . .
80 . 0.0036 0.0055 0.0077 0.0145 0.022 0.031 0.040 0.051 0.063 0.074 0.088 0.100 . . .
85 . 0.0032 0.0050 0.0069 0.0130 0.020 0.028 0.036 0.045 0.056 0.066 0.077 0.090 0.100 . .
90 . . 0.0042 0.0060 0.0112 0.017 0.024 0.031 0.038 0.046 0.055 0.064 0.074 0.083 . .
95 . . 0.0034 0.0048 0.0089 0.014 0.018 0.024 0.030 0.037 0.042 0.050 0.056 0.062 0.075 0.090
TABLE 4 Flume, 2-in. (5.08-cm), Submerged—Flowrate, ft /s
H ,ft
a
Sub- 0.06 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.70 0.80 0.90 1.00
merged,
%
50 0.0086 0.0189 0.0350 0.0554 0.080 0.103 0.137 0.165 0.200 0.230 0.271 0.314 . . . .
55 0.0086 0.0188 0.0350 0.0550 0.079 0.103 0.136 0.163 0.198 0.229 0.270 0.314 0.382 . . .
60 0.0085 0.0185 0.0345 0
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.