ASTM D1941-91(1996)

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

• Status: Historical
• Publication Date: 31-Dec-2000
• Technical Committee: D19 - Water
• Drafting Committee: D19.07 - Sediments, Geomorphology, and Open-Channel Flow

Relations

• Replaced By: ASTM D1941-91(2001) - Standard Test Method for Open Channel Flow Measurement of Water with the Parshall Flume
• Effective Date: 01-Jan-2001

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NOTICE: This standard has either been superseded and replaced by a new version or
withdrawn.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 1996)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
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 that is, the flume crest.
3.2.3 hydraulic jump—an abrupt transition from supercriti-
1.1 This test method covers measurement of the volumetric
cal to subcritical flow, accompanied by considerable turbulence
flowrate of water and wastewater in open channels with the
or gravity waves, or both.
Parshall flume.
3.2.4 normal depth—the uniform depth of flow for a given
1.1.1 Information related to this test method can be found in
flowrate in a long open channel of specific shape, roughness,
ISO 1438 and 4359.
and slope.
1.2 This standard does not purport to address all of the
3.2.5 primary instrument—the device (in this case, the
safety concerns, if any, associated with its use. It is the
flume) that creates a hydrodynamic condition that can be
responsibility of the user of this standard to establish appro-
sensed by the secondary instrument.
priate safety and health practices and determine the applica-
3.2.6 scow float—an in-stream flat for depth sensing usually
bility of regulatory limitations prior to use.
mounted on a hinged cantilever.
2. Referenced Documents
3.2.7 secondary instrument—in this case, a device which
measures the depth of flow at an appropriate location in the
2.1 ASTM Standards:
flume. The secondary instrument may also convert the mea-
D 1129 Terminology Relating to Water
sured depth to an indicated flow rate.
D 2777 Practice for Determination of Precision and Bias of
3.2.8 stilling well—a small reservoir connected through a
Applicable Methods of Committee D-19 on Water
D 3858 Test Method for Open Channel Flow Measurement constricted passage to the main channel, that is, the flume, so
that a depth measurement can be made under quiescent
of Water by Velocity-Area Method
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
relation no longer applies and discharge depends on two head
3. Terminology
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.
3.2.2 head—the height of a liquid above a specified point;
4. Summary of Test Method
4.1 Parshall flumes are measuring flumes of specified ge-
1 ometries for which empirical relations of the form
This test method is under the jurisdiction of ASTM Committee D-19 on Water
and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor- n
Q 5 CH (1)
a
phology, and Open-Channel Flow.
Current edition approved Jan. 25, 1991. Published March 1991. Originally
have been established so that the flowrate, Q, can be
e 2
published in 1962. Last previous edition D 1941 – 67 (1975) .
determined from a single depth measurement, H , in free flow.
a
Annual Book of ASTM Standards, Vol 11.01.
If the flow is submerged, an addition downstream depth, H ,
Available from American National Standards Institute, 11 W. 42nd St., 13th b
Floor, New York, NY 10036. must be measured and suitable adjustments made.
D 1941
5. Significance and Use 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
5.1 Flume designs are available for throat sizes of 1 in. (2.54
made at H instead, because disturbances have been observed
cm) to 50 ft (15.2 m) which cover maximum flows of 0.2 to c
3 3 4
at the H location in these sizes ((1) and (2)). See Fig. 2 for the
b
3000 ft /s (0.0057 to 85 m /s) (1) and (2) . They can therefore
relation between H and H .
be applied to a wide range of flows, with head losses that are b c
7.3 Stilling Well and Connector:
moderate.
7.3.1 Stilling wells are recommended for accurate depth
5.2 The flume is self-cleansing for moderate solids transport
measurements; they are required when wire- or tape-supported
and therefore is suited for wastewater and flows with sediment.
cylindrical floats are used or when the liquid surface is
6. Interferences
fluctuating.
6.1 The flume is applicable only to open channel flow and is 7.3.2 The lateral area of the stilling well is governed in part
inoperative under full-pipe flow conditions. by the requirements of the depth sensor. For example, the
6.2 Although the flume has substantial self-cleansing clearance between a float and the stilling-well wall should be at
capacity, it can be clogged by debris or affected by least 0.1 ft (3 cm) and should be increased to 0.25 ft (7.6 cm)
accumulation of aquatic growth and cleaning or debris removal if the well is made of concrete or other rough material, the float
may be required. diameter itself being determined in part by permissible float lag
error (see 11.4.2). Other types of depth sensors may also
7. Apparatus
impose size requirements on the stilling well, and the
7.1 A Parshall flume measuring system consists of the flume maximum size may be limited by response lag.
itself (primary) and a depth-measuring device (secondary). The
7.3.3 Provision should be made for cleaning and flushing
secondary device can range from a simple scale for manual
the stilling well to remove accumulated solids. It may be
readings to an instrument which continuously senses the depth,
necessary to add a small purge flow of tap water to help keep
converts it to flowrate, and provides a readout or record of
the well and any connector pipe and the sensor parts clean. This
instantaneous flowrate or totalized flow, or both.
flow should be small enough for any depth increase in the
7.2 The Flume:
stilling well to be imperceptible.
7.2.1 Parshall flumes are characterized by throat width;
7.3.4 The opening in the flume sidewall connecting to the
dimensions and flowrates for each size are given in Fig. 1 and
stilling well either directly or through a short perpendicular
Table 1, respectively. The dimensions must be maintained
pipe must have a burr-free junction with the wall. The hole or
within 2 %, because the flume is an empirical device and
pipe must be small enough to dampen surface disturbances; an
corrections for non-standard geometry are only estimates. The
area of about 1/1000th of the stilling-well area is considered
inside surface of the flume should be at least as smooth as a
adequate for this purpose. However, the diameter should not be
good quality concrete finish.
so small (or the pipe so long) that it is difficult to keep open or
7.2.2 The measurement location for depth H is shown in
a lag is introduced in the response to changing flows (3); hole
a
Fig. 1. In submerged flow a second depth, H , must be
b and pipe diameters of about ⁄2 in. (1.3 cm) should be
considered a minimum. If changes are made in pipe sizes, they
should be done sufficiently removed from the flume wall that
The boldface numbers in parentheses refer to a list of references at the end of
no drawdown will occur. The intake dimensions cited in this
this test method.
paragraph should be regarded as suggestions only.
7.4 Depth-Discharge Relations:
7.4.1 Free Flow—The values of C and n for use with Eq. 1
are given in Table 2, along with approximate limiting
flowrates. The maximum submergence ratios, H /H , for which
b a
free flow will occur are:
H /H < 0.5, for 1, 2, and 3-in. (2.54, 5.08, and
b a
7.62-cm) flumes;
H /H < 0.6, for 6 and 9-in. (15.24 and 22.86-cm) flumes;
b a
H /H < 0.7, for 1 to 8-ft (30.48 to 243.8-cm) flumes;
b a
H /H < 0.8, for 10 to 50-ft (304.8 to 1524.0-cm) flumes.
b a
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
22.86-cm) flumes in Table 3, Table 4, Table 5, Table 6, and
Table 7 (Table 8, Table 9, Table 10, Table 11, and Table 12),
which were compiled from published curves (2).
7.4.2.2 For all larger flumes, that is, 1 to 50 ft (30.48 to 1524
cm) throat widths, flowrates under submerged-flow conditions
are given as corrections to be subtracted from the free-flow
FIG. 1 Parshall Flume discharge at the same H . These corrections are found in Table
a
D 1941
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 5 1.33
ft; 1 through 3 ft, radius 5 1.67 ft; 4 through 8 ft, radius 5 2.00 ft.
Wall Vertical distance
Widths Axial lengths, ft Gage Points, ft
Depth in below crest, ft
Free-flow Capacities,
Converg-
Con-
ft /s
ing wall
Down- Converg- H , wall
C
verging H
Upstream Throat Diverging Lower end T
length
Throat, stream ing Dip at length
A
end, W , section, section, Section, of flume,
C C ,ft
W end, W , Section, Throat, N upstream
T D
D,ft
ft L L K
T D B ab Minimum Maximum
ft L of crest
C
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 5 W /2 + 4 ft.
T
B
H located ⁄3 C distance from crest for all sizes; distance is wall length, not axial.
C
TABLE 2 Free-Flow Values of C and n for Parshall Flumes
(See Eq. 1)
A B B
Throat Width C Q, min Q, max
n 3
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
NOTE 1—1 ft 5 30.48 cm
A
Listed values of C should be used in Eq. 1 with H in feet to obtain flowrate in
a
FIG. 2 Relation Between H and H for 1, 2, and 3-in. (2.54, 5.08,
b c
cubic feet per second. Listed values of C (metric) should be used with H in
a
and 7.62-cm) flumes (Reference (2))
centimetres to obtain flowrate in litres per second.
B
From Ref (1).
13, Table 14, Table 15, and Table 16 (Table 17, Table 14, Table
18, and Table 16), which were compiled from published curves 7.4.2.3 It is recommended that submergence be avoided if
(2). possible and that ratios not be allowed to exceed 0.95.
D 1941
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
...