EPA-430/1-78-003
EVALUATION OF FLOW MEASUREMENT INSTALLATIONS
IN WASTEWATER TREATMENT FACILITIES
TRAINING MANUAL
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF WATER PROGRAM OPERATIONS

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EPA-4J0/ l-78-00i
March 1978
EVALUATION OF FLOW MEASUREMENT INSTALLATIONS
IN WASTEWATER TREATMENT FACILITIES
U. S. ENVIRONMENTAL PROTECTION AGENCY
Office of Water Program Operations
National Training and Operational Technology Center

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DISCLAIMER
Reference to commercial products, trade names, or
manufacturers is for purposes of example and illustration.
Such references do not constitute endorsement by the
Office of Water Program Operations, U. S. Environmental
Protection Agency.

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CONTENTS
Title or Description	Outline Number
Measurement of Wastewater Flows: Sharp-Crested Weirs	1
Measurement of Wastewater Flows: Parshall Flumes	2
Flow Sensing, Recording, and Totalizing Devices	3
Evaluation of Flow Installations	4
Appendix A - Section VI of the NPDES Compliance
Sampling Inspection Manual

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MEASUREMENT OF WASTEWATER FLOWS: SHARP-CRESTED WEIRS
I Genera] Considerations
A A weir is an overflow structure built
across an open channel, usually to
measure the rate of flow of the liquid
being carried in the channel. There
are two broad categories of weirs.
1	Sharp-crested weirs, made of
a thin plate having a sharp up-
stream corner or edge so formed
that the overflowing liquid springs
clear of the weir crest. These
are quite commonly used to meas-
ure wastewater flow in treatment
plants.
2	Weirs not sharp-crested. Also
referred to as broad-crested
weirs. The overflowing liquid
does not spring clear of the crest
of these weirs. Although flow
rates can be measured accurately
• by means of a broad-crested weir,
they have not been used in this
country as extensively as thin
plate weirs and Parshall flumes
for flow measurement, and will
rarely, if ever, be found in a
wastewater flow measurement
application.
This outline deals only with the sharp-
crested weir as a primary flow measur-
ment device. When the term "weir" is
used herein, a sharp-crested weir is
meant.
B A weir is one of the oldest, simplest and
most reliable structures that can be used
to measure flows in canals, ditches,
flumes, and other open channels. Weirs
have several advantages in comparison
with other measuring devices, among
which are:
1 They are relatively simple to
construct and install. This does
not imply that lack of care and
precision in their construction
and installation is tolerable.
2 A considerable data base exists
for these devices.
C Main disadvantages of sharp-crested weirs are:
1	Solids will collect behind the weir plate
and can seriously affect the accuracy
of the measurement.
2	Their use involves an appreciable head
loss. Usually a fall of at least 0. 5 feet
must be available in the channel in whi ch
the weir is installed.
3	They are relatively difficult to maintain
if used for long periods. The crest, for
example, is likely to become dulled, rusted,
or damaged, with loss of accuracy resulting.
II Definitions and Terminology
A A section through a weir installation is shown
in Figure 1. Pertinent definitions are given
below:
Weir Crest - The edge of the weir over which the
the liquid flows.
Nappe - The overflowing sheet of water.
Head - The depth of water over the crest of
the weir. For a specific weir operating under
steady-state free-flow conditions and a proper
weir-to-pool relationship, only one depth of
water (H) can exist in the upstream ;ool for
a given discharge.
Channel of Approach - The channel leading up
to the weir.
Velocity of Approach - The mean velocity in
the channel.of approach.
Free Flow (Free discharge) - A condition of
flow existing when the nappe discharges into
the air.
EN. FM. 1.5. 78
1-1

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Measurement of Wastewater Flows: Sharp-Crested Weirs
STAFF
FIG. 1
SHARP-CRESTED WEIR INSTALLATION
Submerged Flow (Submerged discharge) -
A condition of flow existing when the
nappe discharges partially under water
(Figure 2), due to the liquid level down-
stream of the weir being at the same
elevation, or higher than, the weir
crest. Accurate measurements cannot
be made of submerged weir discharges
because of lack of extensive, accurate
experiments for determining the discharge
coefficients (1).
FIG. 2
SUBMERGED DISCHARGE
Drawdown - The drop in the elevation of
the liquid surface as it approaches the
weir.
Staff Gage - A measuring device, used for
determining the head on weir.
Nappe Contraction - Formation of the nappe
into a jet narrower than the weir opening as
the liquid passes over the weir crest. It re-
sults from the liquid having to assume a
curved flow path as it approaches the crest.
When approach conditions allow complete con-
tractions, the weir is called a contracted weir.
Weir Configurations
A A weir can be made in any shape desired,
however, those most commonly used to
measure flow (so-called "standard" weirs)
are shown in Figure 3.
These are:
1	The rectangular weir: either with
end contractions, or suppressed.
2	The V-notch weir, most often having
a 90° notch angle.
1-2

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Measurement of Wastewater Flows: Sharp-Crested Weirs
HEAD MEASURING
POINT
FLOW
»////////>'///////
(A) CONTRACTED
RECTANGULAR
WEIR
(B) SUPPRESSED
RECTANGULAR
WEIR
HEAD MEASURING
POINT
FLOW
////////////////>>///
(C) 90° V-NOTCH WEIR
(D) CIPPOLETTI WEIR
B = CHANNEL WIDTH H = HEAD
L = CREST LENGTH	p - CREST HEIGHT
A = CONTRACTION
FIG. 3 - WEIR CONFIGURATIONS
3 The Cippoletti or trapezoidal weir.
In wastewater applications, the rectangular
and V-notch weirs are most frequently used,
the Cippoletti weir may occasionally be
found.
/
B The weir itself should be made of a hard,
durable material, most often metal of an
appropriate type. A plate can be cut to
any of the forms shown in Fi gure 3, or
in some cases a bulkhead can be built to
the proper shape and used as a support
for a narrow metal strip constituting the
weir proper. (Figure 4)
However the weir itself is constructed,
the weir crest should be from 0. 03-0. 08 inch
thick (about 1-2 mm) and have a sharp
upstream edge, as shown in Figure 5.
The crest should not be formed by cutting
it as a knife edge, this being unnecessary
in the first place, and secondly being con-
siderably more difficult to maintain in
satisfactory condition than the edge formed
as shown in Figure 5.

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Measurement of Wastewater Flows: Sharp-Crested Weirs
METAL STRIP
FIGURE. 4
TYPICAL SHARP CRESTED WEIRS
SHARP
CORNER
90° ANGLE
0.03 - 0.08"
45° CHAMFER IF
PLATE THICKNESS >0.08"
FIG. 5
WEIR CREST DETAIL
1-4

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Measurement of Wastewater Flows: Sharp-Crested Weirs
These weir configurations are so frequent-
ly used because of the extensive data base
that is available in terms of their head-
discharge relationships, and conditions of
operation. Equations and tables are readi-
ly available which can be used with con-
fidence, provided that the weir is installed
and maintained in conformity with the con-
ditions prevailing when the data base was
developed. These conditions are discuss-
ed further below.
IV Rectangular Weirs
A The rectangular weir with two end contractions
(Figure 3a), and the rectangular suppressed weir
(Figure 3b) are in common use. A number of
equations for the head-discharge relation for
these weirs have been proposed by different
investigators. Comparative discussions of the
various formulations will be found in the litera-
ture (2).
B The Francis formulas are frequently used:
For the suppressed weir: Q = 3. 33 LH3^2... (a)
E Significant errors can also be introduced
by neglecting to take velocity of approach
into consideration. (The velocity of
approach is the average velocity of the
liquid in the approach channel just upstream
of the weir.) Examples of the magnitude
of these errors are shown in Table 111(4).
Table III
Velocity of Approach
ft. /sec.
Measured Head-ft.
.0, 2
0. 6
1.0
error in Q, %
0.5
1.0
1.5
2.7
9. 8
20.8
0. 9
3.4
7. 5
0. 6
2. 2
4.7
In developing this Table the Francis equation
was used, and velocity of approach was ignored.
The data shows that approach velocities have
to be well below 0. 5 ft. /sec. before the error
becomes negligible at low heads. In general,
moderate velocities of approach with low heads
on the weir produce large errors, whereas
comparatively high velocities of approach with
large heads on the weir produce small errors.
For the contracted weir:	F
3/2
Q = 3. 33 (L-0. 2H)H ..(b)
where Q = discharge, ft3/sec.
L = crest length, ft.
H = measured head, ft.
Tables of discharge are available (1, 2, 3) which
provide the solution for these equations for
various combinations of L, and H. A portion
of a table for a contracted weir is shown in
Table I, and for a suppressed weir in Table II.
C The Francis equations should not be used
for weirs which are not fully contracted.
To ensure full contraction of the nappe,
the dimensions A and P in Figure 3a must
be at least 2H, and in no case less than
1 foot. The same applies to dimension P
in Figure 3b.
D The Francis equations should not be used
for heads greater than one-third of the
crest length, even if such results appear
in published tables. Significant errors
can result. Similarly, heads less than
0. 2 feet should not be used.
If velocity of approach is included in the Francis
equations, they become:
For the suppressed weir:
Q' = 3. 33 L[(H+h)3/2-h3/2]	(c)
For the contracted weir:
Q' = 3. 33 (L-0. 2H) [ (H+h)3^2-h3/2] ...(d)
Where Q' = discharge, ft.3sec., considering
velocity of approach;
L = crest length, ft.
H = measured head, ft.
h = head on the weir in feet due to the
velocity of approach
2
= Z— where v is the velocity of approach.
2g
G When using the Francis equations, correction
for velocity of approach is usually made by
trial, as follows:
1 Measure H. Determine Q, using formula
(a) or (b) without velocity of approach
considered.
1-5

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Measurement of Wastewater Flows: Sharp-Crested Weirs
TABLE 1
FLOW THROUGH RECTANGULAR WEIRS
WITH END CONTRACTIONS
Formula CFS = 3.33(L-0.2H)H^Z MGD = CFS X .646317
Head
Fi
LENGTH OF WF.IR CREST IN 1 tUT
1
IVi
2
3
4
5
CFS
MGD
CFS
MGD
CFS
MGD
crs
MGD
CFS
MGD
crs
MGD
.01
.003
.002
.005
.003
.007
.005
.010
.006
.013
008
017
.011
.02
.009
.006
014
.009
019
.012
.028
.018
038
.025
.047
.030
.03
.017
011
.026
.017
035
.023
.052
.034
.069
.045
.086
.056
.04
.026
.0J7
.040
.026
.053
.034
080
.052
.106
.069
.133
.086
.05
.037
024
.055
036
.074
048
111
.072
.149
.096
.186
.120
.06
048
.031
073
.047
.097
.063
.146
.094
.195
.126
.244
.158
.07
.061
.039
.092
.059
122
.079
184
.119
.246
.159
.307
198
.08
.074
.048
.112
.072
.149
.096
.225
.145
.300
.194
.376
.243
.09
.088
.057
.133
086
.178
.115
.268
.173
.358
.231
.448
290
.10
.103
.067
156
.101
.209
.135
.314
.203
.419
.271
.524
.339
.11
.119
.077
.180
.116
.240
.155
.362
.234
.483
.312
.605
391
12
.135
.087
.204
.132
.274
.177
.412
.266
.550
.355
.689
.445
.13
.152
.098
.230
.149
.308
199
.464
.300
.620
.401
.776
.502
.14
.170
.110
.257
.166
344
222
.518
.335
.693
.448
.867
.560
.15
.188
.122
.284
.184
.381
.246
.575
.372
.768
.496
.961
.621
.16
.206
.133
.313
202
.419
.271
.633
.409
.846
547
1.059
.684
17
225
.145
342
.221
.459
.297
692
.447
926
.598
1.159
.749
.18
245
.158
372
.240
.499
.323
754
487
1.008
.651
1.262
.816
.19
.265
.171
.404
260
.541
.350
.817
.528
1.093
.706
1.368
.884
.20
.286
.185
.435
.281
.584
.377
.882
.570
1.179
762
1.477
.955
.21
.307
j 98
.468
302
627
405
.948
.613
1.268
.820
1.589
1.027
.22
.329
.213
.501
323
.672
434
1 016
.657
1 359
878
1.703
1.101
.23
.350
.226
.534
.345
.718
.464
1 085
.701
1 452
.938
1.820
1.176
.24
.373
.241
.568
.367
.764
494
1.156
.747
1.547
1.000
1.939
1.253
.25
.395
.255
.604
.390
.812
.525
1.228
.794
1.644
1.063
2.060
1.331
.26
.419
.271
639
413
.860
.556
1 301
.841
1.743
1.127
2.184
1.412
.27
.442
.286
.676
437
.909
588
1.376
.889
1.844
1.192
2.3)1
1.494
.28
.466
.301
.712
460
.959
.620
1.453
.939
1.946
1.258
2.439
1.576
.29
490
.317
750
.485
1 010
653
1.530
.989
2.050
1.325
2.570
1 661
.30
.514
.332
788
.509
1.062
.686
1.609
1.040
2.156
1.393
2.703
1.747
.31
.539
.348
.827
.535
1.114
720
1.689
1.092
2.263
1.463
2.838
1.834
.32
564
.365
.866
.560
1 167
.754
1.770
1.144
2.373
1.534
2.975
1.923
.33
.590
.382
.905
.585
1.221
.789
1.852
IJ97
2.483
1.605
3.115
2.013
.34
.615
.397
.945
.611
1.275
824
1.936
1.251
2.596
1.678
3.256
2 104
-.35
641
.414
.986
.637
1.331
.860
2.020
1.306
2.710
1.752
3.399
2.197
IEUPOID & STEVENS. INC.
STEVENS WATER RESOURCES DATA BOOK 2nd ED
TABLE 2
FLOW PER FOOT OF LENGTH THROUGH RECTANGULAR
WEIRS WITHOUT END CONTRACTIONS
Formula CFS = 3.33L H3/2	MGD = CFS x .646317
Head
Ft.
.00
01
.02
03
04
.05
.06
07
0
J
.0"
*
CFS
MGD
CFS
MGD
CFS
MGD
CFS
MGD
CFS
MGD
CFS
MGD
CFS
MGD
CFS
MGD
CFS
MGD
CFS
MCL
0.0
I
4
5
.6
.7
.8
.9
1.0
1.1
1.2
1 3
1.4
1 1
.00
.11
.30
55
.84
1.18
1	55
1.95
2	38
2.84
3.33
3.84
4.38
4.94
5	52
6	1?
00
07
.19
.36
54 .
76
1.00
1.26
1	54
1.84
2.15
2	48
2.83
3.19
3	57
196
.00
.12
.32
.57
.87
1.21
1 59
1.99
2.43
2.89
3.38
3 89
4.43
4.99
5.58
6 18
00
08
.21
37
56
.78
1	03
1.29
1.57
1.87
2.18
2	51
2.86
3.23
3.61
3	99
.01
.14
.34
.60
.91
1.25
1.63
2.03
2.47
2.94
3 43
3	95
4	49
5.05
5.63
6 24
.01
.09
22
39
.59
.81
1.05
1.31
1 60
1	90
2.22
255
2	90
3.26
3.64
4 03
.02
.16
.37
.63
94
1.28
1.67
2.08
2 52
2	99
3	48
4	00
4	54
5	11
5.69
6.30
6l
.10
24
.41
.61
83
1.08
1.34
1	63
193
2	25
2 59
2.94
3.30
3.68
4 07
.03
17
.39
.66
97
1.32
1	70
2.12
2	56
3.03
3.53
4.05
4	60
5	17
5	75
6	36
.02
11
25
43
.63
.85
1	10
1.37
1.6S
1.96
2.28
2	62
2.97
3.34
3	72
4	11
04
.19
.42
.69
1.01
1.36
1.75
2.16
261
3.08
3 58
4.11
4.65
5 22
5.81
643
.03
.12
27
.45
.65
88
1.13
1 40
1.69
1.99
231
2.66
3.01
3.37
3	76
4	16
.05
.21
.44
.72
1.04
1	40
1.79
2	21
2.66
3.13
3.63
4.16
4 71
5.28
5.87
6 49
.03
.14
.28
.47
67
90
1.16
1.43
1.72
2.02
2.35
2.69
3.04
3.41
3.79
4.19
.06
.23
47
75
1.07
1	43
1.83
2	25
2.70
3.18
3	69
4.21
4.77
5.34
5.93
6.55
04
.15
.30
.48
.69
92
1.18
1.45
1.75
2.06
2.38
2 72
3.08
3.45
3.84
4.23
08
.25
.49
.78
I 11
1.47
1.87
2.29
2.75
3.23
3.74
4.27
4,82
5.40
6.00
6.61
.05
.16
.32
.50
.72
95
1.21
1.48
1.78
2.09
2.42
2.76
3.12
3.49
3.88
4.27
.09
.28
.52
.81
1.14
1.51
1.91
2.34
2.80
3.28
3.79
4.32
4.88
5.46
6.06
6.68
06
.18
.34
.52
74
98
1.23
Ml
1.81
2.12
2 45
2.79
3.15
3J3
3.92
4.32
IEUPOID & STEVENS. INC.
STEVENS WATER RESOURCES DATA BOOK. 2nd ED
1-6

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Measurement of Wastewater Flows: Sharp-Crested Weirs
2	Compute velocity of approach, v = Q, "A'
being the cross-sectional area of the
approach channel in square feet.
3	Compute velocity of approach head, h
v2	o
h = ^_= 0.0156 v2
2g
4	Compute effective head on weir, D
D = [ (H t h)3'2 - h3'2]
5	Substitute "D" for "H" in formula used and
calculate Q'.
6	The second approximation to the true value
of Q, as obtained in step 5 above, is always 1
sufficiently close for practical purposes.
H Using the above method of correcting for
velocity of approach it will be seen that;
Q' _ D
Q
3/2
3/2
= C, or Q' = CQ
(e)
H
where Q
discharge considering velocity
of approach
Q = discharge neglecting velocity
of approach
D = effective head on weir crest
considering velocity of approach
H = measured head on weir crest
C = a coefficient
Values of C appear in Table IV for velocities
of approach from 0. 4 to 3,0 ft. / sec. The
table is used as follows:
1	Compute velocity of approach as
described in G1 and G2 above.
2	Determine "C" from table for the
applicable combination of v and H values.
3	Use formula (e) to obtain Q1.
An improved formula for computing discharges
for rectangular weirs has been developed by
Kindsvater and Carter. This equation is
coming into more frequent use and is consid-
ered by some to be more accurate than the
Francis formulations. Direct, accurate,
simple computations quickly yield the rate
of flow with correction factors for approach
velocity and approach channel width and depth
included.
The basic equation is:
3/2
Q - Cg Lg
(f)
Table IV -Diichara* correction coefficient, C, (or determining effect of velocity of approach to weirt. Computed
Q'
from the formula C— q-= jyj/j'



//
f
k
02
0 4
0 l>
(1 »
1 0
1 5
20
2 5
3 0
3 5
4 0
5 0
0.4
0 0025
0 0002
1 014
1 007
I 004
1 004
1 004
1.002
1 0U2
1 002
1.001
1 001
1 001
1 001
.5
UU9
.ouai
1 027
1 on
1 OIK)
1 000
1 006
1 004
1 003
1 002
1 002
i no2
1 001
1.001
.6
0050
<1006
1 037
1 019
t 013
( 009
1 OOH
1 IMti
) 0O4
I 003
) 003
1 002
1 002
1.002
,7
nurr,
0007
i.n*w
1 02fi
I 017
1.013
LOU
1 007
1 006
1 004
1 0D4
1 003
1 003
1 002
M
ouyj
.omo
1 004
1 ou
1 022
1 Olfi
1 014
1 OUV
1 007
1 006
1 005
1 004
1.003
1 003
.«
.0125
0UI4
1 0*2
1 012
i 
1 0)3
} Oil
) 009
1 008
1 007
1.3
02m
0041
1 10J
1 OK4
1 057
1 (M3
1 035
1 024
1 018
1 015
1 012
1 011
1.009
1 008
1.010
1 4
.rcro
0051
1 IKf,
1 090
1 OjG
i (tyi
1.011
1 028
1 021
1 017
1 014
1 012
1 Oil
1. &
0350
JIM
1 208
1 109
1 075
1 057
1 047
1 032
1 024
1 019
1 016
1.014
1 012
1.011
1.012
1 6
0398
0079
1 225
1 122
1 0H4
1 005
1 052
1 035
1 027
1.022
1 018
1 01 6
1 014
1 7
.IM49
0095
1 2A4
1 13%
1 09.1
1 071
1 059
1 040
1 031
1 025
1 071
1 OIK
1 0IC
I 014
) 0)6
1 8
0504
0111
1 277
1 149
1 104
1 OH)
1 065
1 045
1 0.M
1 027
1 023
1 (120
1 0)7
1.0
0501
0172
1 308
1. 165
1 115
1 089
1 072
1 049
1 038
1 0J0
1 020
1 022
1 Oltf
1 017
20
,0(32
0154
1 335
1 181
1 126
J 097
1 079
I (155
1 042
1 031
1 028
1 025
1 021
1.019
1 021
1 023
1.025
1 027
2. 1
0fi8T,
0179
1 3TwJ
1 197
1 13?
1 IOC
1.087
1 0G0
1 046
1.037
I rui
1 027
I 024
2.2
0752
0200
1.391
1 213
1 149
1 118
1 094
1 065
1 050
1 039
1 0J4
1 029
1 02ft
2.3
OKII
0235
1 420
1 231
1 161
1 124
1 102
1 071
1 054
1 044
1 037
1 032
1 028
1 030
2.4
0K95
.WW
1 449
1 248
1 I7fi
1 134
1. 110
I 077
1 059
1 047
1 0<0
1 034
2.5
.0972
rtim
1.480
1 206
1 IM7
1 145
1 119
I 083
1 OTvt
1 051
1 043
I 037
1.033
1 035
1 079
1 032
1.034
1 03 R
1.039
2. 6
. toil
OHO
I 5| 1
1 285
) 2110
J 155
1 128
1 OHM
1 OAS
1 055
1 046
1 040
2.7
. 1133
torn
1 542
1 JU1
1 213
1 IfiTi
1 137
1 (195
1 073
1 059
I osn
1 043
1 038
2.8
1710
0420
1 573
I 322
1 22H
1 178
1 140
1 100
1.078
1 OK)
1 053
1 04 ft
1 041
1 043
2.0
1307
0472
J.fiOfi
1 341
1 242
1 189
1 155
1 108
1 08J
1 0G7
1 057
1 049
3.0
.1399
0524
1 (137
1 361
1 2M
1 199
1. 165
1 115
1.088
1 072
I or.i
1 053
1 04ft
1 041
1-7

-------
Measurement of Wastewater Flows: Sharp-Crested Weirs














-0.003
0	0 20 0 40 0.60 0 80 100
L/B
FIGURE 6.
VALUES OF Kb FOR KINDSVATER-CARTER EQUATION



L/B =
10 >

Ce
- 3 22
+ 0.40h
/px
Ix





X09





0.8

A



0.6





0 4
V
N0 2

0 0 4 0.8 1.2 1.6 2.0 2.8
H/P
FIGURE 7.
VALUES OF Ce FOR KINDSVATER-CARTER EQUATION
1-8

-------
Measurement of Wastewater Flows: Sharp-Crested Weirs
D
where Ce = a discharge coefficient, obtained
from Figure 7
Lg = L + and
He = H + kh = H + 0.003
In these relationships
Q = discharge, ft. /sec.
H = head above weir crest, ft.
L = length of weir crest, ft.
B = width of approach channel, ft.
k k = a correction factor to obtain the
effective weir length Le (Figure 6)
k ^ = a correction factor to obtain the
effective head Hg
This method is particularly useful for in-
stallations where full crest contractions
or full end contractions are difficult to
achieve, and should be used for determining
the discharge of rectangular weirs not fully
contracted, or when H is greater than 1/3
of the crest length. In these cases, large
errors can be involved if the Francis formula
is used. The Kindsvater-Carter formula is
not applicable to V-notch or Cippoletti weirs.
V V-Notch Weir
A These are particularly useful for low flows.
Standard contraction requirements are the
same as for rectangular weirs. Probably the
most commonly-used weir of this type is the
90° V-notch weir, for which the Cone formula
Q = 2.49	- is usually employed. Table
V shows the head-discharge relationship for
a 90° fully contracted V-notch weir using this
formula.
Weirs notched at angles other than 90° will
sometimes be encountered. Tables are available
(3) for weirs having angles of 60°, 45°, and
22-1/2°.
B The Kindsvater-Sten equation (5) valid for any
notch angle is
Q = (8/15)(2g)1/2 Ce tan (6/2)h 3/2	(g)
Q = discharge, ft. 3/ sec.
g = gravity constant
Ce = a coefficient (Figs. 8 & 9)
(Note that values of C shown on Figure 9
are for 90°, V-notch weirs only, incom-
pletely contracted Corrections for other
notch angles are not available.)
6 = notch angle
Hg = measured head plus (Figure 10)
Ordinarily, V-notch weirs are not appreciably
affected by velocity of approach. If the weir
is installed with complete contractions, the
velocity of approach will be low.
The Kindsvater-Sten and Cone formulas give
results within about 0. 5% of each other for
fully contracted 90° V-notch weirs. If con-
tractions are incomplete, the Kindsvater-Sten
equation should be used with the correction as
shown above.
WATER MEASUREMENT MANUAL
Tabic V —Diichars* of 90° V-notch wcirt In wcond-fett. Com-
pvtcd from the formula Q—2.49 H1 u
Head in
fttt
Discbarge
in second-
feet
LI pad in
feet
Discharge
in second-
fret
~cad in
feet
Discharte
ia second-
feet
0 JO
0 046
0 55
0 564
0 90
1.92
il
05J
VI
590
91
1 97
22
058
57
017
92
2 02

005
58
.
-------
Measurement of Wastewater Flows: Sharp-Crested Weirs
0.60
0.58
0.561						
0 20	40	60	80	100 120
NOTCH ANGLE, DEGREES
FIGURE 8.
VALUES OF Ce FOR KINDSVATER-SHEN EQUATION,
FULLY CONTRACTED V-NOTCH WEIRS
1
¦
P/B = l.C
V 0.8
1
/°6
i
I
0.3^
0.2
1
1
1
i
i
01
I
0	0.2 0.4	0.6	0.8	1.0	1-2
H/P
FIGURE 9.
VALUES OF Ce FOR KINDSVATER-SHEN EQUATION,
90° V-NOTCH WEIRS WITH INCOMPLETE
CONTRACTIONS
0.012
0.008
x
*
0.004
0 						
0	20 40	60	80 100 120
NOTCH ANGLE, DEGREES
FIGURE 10.
VALUES OF K, FOR KINDERSVATER-SHEN EQUATION
n
1-10
-------
Measurement of Wastewater Flowp: Sharp-Crested Weirs
E The angle at which the notch is cut should
be measured accurately. A change of only
lc for a nominal 90° notch would introduce
an error of almost 2% in measured flow rate.
VI Cippoletti Weir
A This must also be installed as a fully con-
tracted weir if reasonably correct and
consistent discharge measurements are
to be obtained. The accuracy of measure-
ments with this weir, however, is less
than that obtainable with rectangular and
V-notch weirs but is acceptable when no
great precision is required (1, 2).
B The formula for this weir, neglecting
velocity of approach is
Q = 3. 367 LJ-r^2	(h)
where Q, L, and 1-1 have the same meanings
as for rectangular weirs.
C With velocity of approach included, discharge
can be obtained from the formula.
Q' = 3. 367 L (I I + 1.		(i)
where the symbols have the same meanings
as for rectangular weirs. The velocity-of-
approacli correction can be applied, as in
the Francis formula, with fair results.
VII Setting Standard Weirs (1)
A Rectangular, V-notch, and Cippoletti weirs
are sometimes referred to as "standard"
weirs when set so that the nappe is fully
contracted. Extensive experiments on weirs
and long experience with their use dictate
that the following conditions are necessary
for accurate measurement of flow with
standard contracted weirs.
1	The upstream face of the bulkhead
should be smooth and in a vertical
plane perpendicular to the axis of
the channel.
2	The upstream face of the weir plate
should be smooth, straight, and flush
with the upstream face of the bulkhead.
3	The entire crest should be a level,
plane surface which forms a sharp,
right-angled edge where it inter-
sects the upstream face. The thick-
ness of the crest, measured in the
direction of flow, should be between
0.03 and 0.03 inch (about 1 to 2'mm).
Both side edges of rectangular weirs
should be truly vertical and of the same
thickness as the crest.
4	The upstream corners of the notch must be
sharp. They should be machined or filed
perpendicular to the upstream face, free of
burrs or scratches, and not smoothed off
with abrasive cloth or paper. Knife edges
should be avoided because they are difficult
to maintain.	/
5	The downstream edges of the notch
should be relieved by chamfering if the
plate is thicker than the prescribed crest
width. This chamfer should be at an angle
of 45° or more to the surface of the crest.
6	The distance of the crest from the bottom
of the approach channel (weir pool) should
preferably be not less than twice the depth
of water above the crest and ui no case
less than 1 foot.
7	The distance from the sides of the weir
to the sides of the approach channel should
preferably be no less than twice the depth
of water above the crest and never less
than 1 foot.
8	The overflow sheet (nappe) should touch
only the upstream edges of the crest
and sides.
9	Air should circulate freely both under
and on the sides of the nappe.
10	The measurement of head on the weir
should be taken as the difference in
elevation between the crest and the water
surface at a point upstream from the
weir a distance of four times the maximum
head on the crest.
11	The cross-sectional area of the approach
channel should be at least 8 times that of
the overflow sheet at the crest for a dis-
tance upstream from 15 to 20 times the
depth of the sheet.
1-11
-------
Measurement of Wastewater Flows: Sharp-Crested Weirs
12 If the weir pool is smaller than de-
fined by the above criteria, the
velocity of approach may be too
high and the staff gage reading
too low. The head should be corrected
by increasing it as explained earlier.
B In addition, for the suppressed weir
1	The sides of the approach channel
should be coincident with the sides
of the weir, and should extend down-
stream beyond the crest to prevent
lateral expansion of the nappe.
2	Special care must be taken to secure
proper aeration beneath the nappe
at the crest.
VIII Selection of Weirs (1)
A In general, for best accuracy, a rectangular
suppressed weir or a 90° V-notch weir should
be used. Cippoletti weirs and contracted
rectangular weirs, although useful in many
applications, have not been investigated ex-
perimentally as thoroughly as the suppre ssed
rectangular and V-notch weirs.
B Usually, the range of flows to be measured
can be fairly well estimated in advance, and
the following points considered:
1	The minimum head should be at least
0. 2 foot to prevent the nappe from
clinging to the crest, and because
at smaller depth it is difficult to get
sufficiently accurate gage readings to
calculate reliable discharges.
2	The length of rectangular and Cippoletti
weirs should be at least three times
the head.
3	The 90° V-notch weir is the best type
for measuring discharges less than
1 ft. 3/sec. It is as accurate as other
types for flows from 1-10 ft. ^/sec.
4	If possible, the crests should be placed
high enough so the liquid will fall
freely, leaving an air space under
and around the nappe. If submergence
is permitted, special computations and
reduced flow measurement accuracy may
be expected.
C Capacities of standard weirs are shown
in Table VI.
Table VI—Capacities of standard wctrs in iccond-f«et.
Length
In reel
Contracted rectan-
gular
Suppressed rectan-
gular
Clpollettl







Maximum
Minimum
Maximum
Minimum
Maximum
Minimum
1 0
1	5
2	0
2 5
0	500
1	65
3 M
5 87
0 286
435
584
.732
0 631
1.77
3 65
6 30
0 208
447
. 506
744
0.638
1.70
3 60
6.37
0 303
452
.602
753
3 0
3	6
4	0
4 5
9	32
13 8
10	1
25 7
881
1 03
1 18
1 33
10 0
14.8
20.4
27 5
803
1.04
1 10
1 34
10 1
15 0
20 6
27 8
003
1 05
1 20
1 35
3 0
5	5
6	0
0
8-0
0.0
33 5
42 3
52 7
77.4
108 5
145.3
1.48
1.63
1	78
2	07
2 37
2 67
36 0
45 3
56 6
82 9
116.2
165.0
1 40
1.64
1	79
2	08
2 38
2 68
36 4
46 8
57 3
83 8
117.5
157 6
1 51
1	66
1.81
2	11
2 a
2 71
10 0
12 0
14 0
16.0
18 0
188 S
298 4
439 1
612 0
822 4
2 07
3.56
4 16
4 75
6.35
202 4
320 0
470 4
056 6
882.0
2.08
3.67
4 17
4 76
5.36
204.6
3216
476 6
663 8
801.8
3.01
3 61
4.21
182
0.42
Note—Limits follow the prescribed practice of A>0.2 foot and &<
IX Care of Weirs
A A weir installation requires some maintenance
and care to ensure continued accuracy of the
measurement being made.
1	The weir and the channel upstream of the
weir should be kept free of trash, debris,
& excessive sediment build-ups.
2	Sediment should be removed from the
channel upstream of the weir as it
accumulates.
3	The crest should be checked periodically
to be sure it is absolutely level.
4	A periodic check should be made to ensure
that the zero of the gage is at the same
elevation as the crest.
5	Any leakage which may occur around the
weir should be immediately eliminated.
6	Great care must be taken to avoid damage
to the weir notch itself, as even small nicks
or dents can reduce the accuracy of an
otherwise good installation. Dress any
nicks and dents that do occur with a fine-
cut file or stone, but only to remove any
metal that may protrude above the normal
surfaces. Under no circumstances should
the upstream corners of the notch be rounded
or chamfered, nor should an attempt be
1-12
-------
Measurement of Wastewater Flows: Sharp-Crested Weirs
made to completely remove an imperfection
if the shape of the weir opening is thereby
changed. Erosion, rusting, and wear can
produce rounding of the weir crest, or
unacceptable changes in the shape of the
notch. Badly eroded weirs should be
replaced.
This outline was prepared by C. E. Sponagle,
Sanitary Engineer, National Training &
Operational Technology Center, MOTD, OWPO,
USEPA, Cincinnati, Ohio 45268
Bibliography
1	Water Measurement Manudl. Bureau of
Reclamation, U.S. Dept. of the Interior,
Second Ed., revised reprint, 1974, Ch 2,
pp 7-42. Order from U.S. Government
Printing Office, Washington, D. C. 20402.
$5.80. Stock No. SN2403-0027, Cat. No. I
27.19/2:W 29/2
2	King, H. W. Handbook of Hydraulics. 3rd Ed.,
McCraw-Hill, N.Y. 1939.
3	Stevens Water Resources Data Book. 2nd Ed.
Leupold & Stevens, Inc. P. O. Box 688,
Beaverton, Oregon 97005. $4.00
4	A Guide to Method & Standards for the
Measurement of Water Flow. NBS Special
Publication 421. National Bureau of Standards
U.S. Dept. of Commerce, May 1975, Order
from U.S. Government Printing Office,
Washington, D. C. 20402. SD Catalog
No. C13.10:421. $1.65
5	British Standards Institution, Standard No.
3680-4A, Methods of Measurement of Liquid
Flow in Open Channels: Part 4A, Thin Plate
Weirs and Venturi Flumes, 1965 Order from
American National Standards Institute, 1430
Broadway, New York, N.Y. 10018. $9.50
6	Johnson, J. W. The Aeration of Sharp Crested
Weirs, Civil Engineering, 5. 3.1935. pp 177-8.
7	Gibson, A. H. Hydraulics and its Applications.
1925 Constable & Co., Ltd., London, England.
1-13
-------
MEASUREMENT OF WASTEWATER FLOW: PARSHALL FLUME
I Background and Description
A The Parshall Flume is a specific type
of venturi flume, named for its principal
developer, the late Mr, Ralph L. Parshall.
It was developed in the late 1920's, primarily
to measure irrigation water, but is also now
frequently used to measure wastewater flows.
B Configuration of the Flume is shown in
Figure 1, standard sizes and dimensions
appear in Table 1. It is essential that
these dimensions be strictly adhered to,
when using standard H-Q relationships.
For the smallest flume sizes, tolerances
of 1/64 inch for the throat and 1/32 inch
elsewhere have been suggested (1). In a
1 -inch flume a throat width difference of
even 1/64 inch will result in a 1.5% error,
unless corrected as explained in V-C below.
C Referring to Figure 1 it can be seen that
the flume proper consists of three sections:
1	A converging section in which the
entering flow is accelerated.
2	A constricted throat, producing a
differential head that can be related
to discharge
3	A diverging section in which liquid
is carried away from the throat.
D Wing walls are provided (a) at entrance,
(b) at exit, or (c) at both entrance and
exit from the flume when the channel
width exceeds dimension C or D in
Figure 1. These can be either straight
or curved as shown, and provide a gradual
smooth transition of the flowing liquid
into and away from the flume.
E The crest of the flume is the floor of
the converging section. It must be level
in all directions if accurate measurements
are to be made.
F Flume sizes are designated by the throat
• width W, Figure 1.
G Flumes can be built of wood, concrete,
galvanized sheet metal, or other suitable
materials. They can be constructed as
an integral part of the channel in which
they are situated, or purchased as pre-
fabricated structures to be installed in
one piece.
II Measuring Flow
A Discharge through the flume can occur for
two conditions of flow
1	Free flow, which occurs when there is
insufficient backwater depth to reduce
the discharge rate.
2	Submerged flow, which occurs when the
water surface downstream of the flume
is far enough above the elevation of the
flume crest to reduce the discharge.
B For free flow only the head at the upstream
gage location (Ha, Figure 1) is needed to
determine the discharge from a standard
table.
C For submerged flows both the upstream and
downstream heads (Ha and Hb.- Figure 1) are
needed to determine the discharge,
III Free-flow Measurements
A In free flow the discharge depends solely on the
throat width and the depth of the liquid at the
gaging point in the converging section (Ha,
Figure 1). This depth must be measured at
the point shown in the plan view of the flume.
Figure 1, which is upstream of the throat at
a distance equal to 2/3 the length of the con-
verging section.
B Once Ha is known, the discharge for the size
flume being used can be obtained from a table.
See Table II.
EN. FM. 2a. 5. 78
2-1
-------
Measurement of Wastewater Flow; Par shall Flume
PLAN
	B	
- F-
— G —
FLOW
LEVEL
FLOOR
i. SUBMERGED
. FLOW
, 1 i
H^FREE FLOW
CR EST *1	|
r'xi"xi/8"
ANGLE
/
l"xl"xl/8"
ANGLE
SECTION L-L
LEGEND-
W Size of flume, in inches or feet.
A Length of side wall of converging section.
2/3A Distance back from end of crest to gage point.
B Axial length of converging section.
C Width of downstream end of flume.
D Width of upstream end of flume.
E Depth of flume.
F Length of throat.
G Length of diverging section.
K Difference in elevation between lower end of flume and crest.
N Depth of depression in throat below crest.
R Radius of curved wing wall.
M Length of approach floor.
P Width between ends of curved wing walls.
X Horizontal distance to gage point from low point in throat.
Y Vertical distance to gage point from low point in throat.
FIGURE 1. Configuration and Standard Nomenclature of Parshall Flumes
2-2
-------
Measurement of Wastewater Flow: Parshall Flume
TABLE I. STANDARD PARSHALL FLUME DIMENSIONS AND CAPACITIES
Widths
Aaial Lengths
Wal 1
Depth in
Con-
verging
Section
E
Vertical Distance
Below Crest
Con-
Gage
f*o 1 nts

Free Flow
Capac1 ties
Size;
Throa t
Width
W
Up-
stream
End
0
Down-
s tream
End
C
Con-
verging
Section
B
Throat
Section
F
01verg1ng
Sec tion
G
Dip at
Throat
N
Lower
End of
F 1 ume
K
verglng
Wall
Length
A*
Ha. Dist
lfn< t r#Aff!
Hb
Mln
Max
Up 3 * * Cfl"1
of Crest**
X
y
Inches
Fee t
Feet
Feet
Feet
Fee t
Feet
Feet
Feet
Feet
Feet
Feet
Feet
cfs
cfs
1
0.549
0.105
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
. 700
.443
1 .33
.375
.83
0.50-0.83
.141
.073
1.36
.91
.052
.083
.01
.30
3
.849
.583
1.50
.500
1 .00
1.00-2.00
.188
.083
1.53
1.02
.083
.125
.03
1.90
6
1.30
1 .29
2.00
1 .00
2.00
2.0
.375
.25
2.36
1 .36
.167
.25
.05
3.90
9
1.88
1.25
2.83
1.00
1.50
2.5
.375
.25
2.88
1.93
.167
.25
.09
8.90
Feet














1.0
2.77
2.00
4.41
2.0
3.0
3.0
.75
.25
4.50
3.00
.167
.25
.11
16.1
1.5
3. 36
2. 50
4.66
2.0
3.0
3.0
.75
.25
4 . 75
3.17
.167
.25
.15
24.6
2.0
3.96
3.00
4.91
2.0
3.0
3.0
.75
.25
5.00
3.33
.167
.25
.42
33.1
3.0
5.16
4. 00
5.40
2.0
3.0
3.0
.75
.25
5.50
3.67
.167
.25
.61
50.4
4.0
6 35
5.00
5.88
2.0
3.0
3.0
.75
.25
6.00
4.00
.167
.25
1 .30
67.9
5.0
7.55
6.00
6.38
2.0
3.0
3.0
.75
.25
6.50
4.33
.167
.25
1.60
85.6
6.0
8.75
7.00
6.86
2.0
3.0
3.0
.75
.25
7.0
4.67
.167
.25
2.60
103.5
7.0
9.95
8.00
7. 35
2.0
3.0
3.0
.75
.25
7.5
5.0
.167
.25
3.00
121.4
8.0
11.15
9.00
7.84
2.0
3.0
3.0
.75
.25
8.0
5.33
.167
.25
3.50
139.5
10
15.60
12.00
14.0
3.0
6.0
4.0
1.12
.50
9.0
6.00


6
300
12
18.40
14.67
16.0
3.0
8.0
5.0
1.12
. 50
10.0
6.67


8
520
15
25.0
18. 33
25.0
4.0
10.0
6.0
1 .50
.75
11.5
7.67


e
900
20
30.0
24.00
25.0
6.0
12.0
7.0
2.25
1 .00
14.0
9.33


10
1340
25
35.0
29.33
25.0
6.0
13.0
7.0
2.25
1.00
16.5
11 .00


15
1660
30
40.4
34.67
26.0
6.0
14.0
7.0
2.25
1 .00
19.0
12.67


15
-1990
40
50.8
45.33
27.0
6.0
16.0
7.0
2.25
1.00
24.0
16.00


20
2640
50
60.8
56.67
27 . 0
6.0
20.0
7.0
2.25
1.00
29.0
19.33


25
3280
For sizes 1" to 8" . A ¦ W/2 ~ 4.
Ha located 2/3 A distance from crest for all sizes; distance is nail length, not axial.
Notes:
1. Flume sizes 3 Inches through S feet have approach aprons rising at a 1:4 slope "JJ?1!0?!?' 'IJVfSIl;
rounding*: 3 through 9 inches, radius • 1.33 feet; 1 through 3 feet, rtdluf • 1.67 f««t. 4 through B f««t.
Z.
3.
roundings: 3 through
radius ¦ 2.00 feet.
To maximize clarity, equivalent St units are not glv#n.
Table preparad by Kllpatrlck.
2-3
-------
TABLE II
FREE FLOW DISCHARGE TABLE FOR PARSHALL MEASURING FLUME
SEC.-FT X €46317 « M.6 D.
M G D X i 54723¦ SEC-FT
SEC-FT X 4 4 8.831 * G P M
G P M. X .002228 ¦ SEC -FT
HEAD
6"
9"
12"
IB"
24"

HEAD
6"
9"
12"
18"
24"
FT.
IN.
SEC-FT
G PM.
M.G.O
s£gft:
0. PM.
M GO
5£C FT
6 PM. I
MGD
SEC-FT
G P.M. 1
M.GD
SECFT
G PM. f
MGD

FT
IN
SEC.FT
G PM.
M.G.O
SECFT
G P M
MGD
SEC F T
OPM
MGD
SEC-FT
G. PM
M G 0
SECFT
G PM
MGD
010

005
27.4
0032
0.05 J
•'.0.4 ,
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54^6
" 585
WATER & SEWAGE WORKS, REFERENCE AND DATA SECTION, 1954 P. R-277.
-------
Measurement of Wastewater Flow: Parshall Flume
C The basic head-discharge equation for the
Parshall Flume is:
Q = CHan
Where
O
Q = discharge, ft /sec
Ha = upstream head, ft.
C and n are constants, which vary with the
size of flume. Values of these constants
are given in Table III.
Table III
Free Flow Values of C and n for Parshall Flumes
Flume Throat, W	C	n
Free-flow discharge is not reduced until
the submergence exceeds the values
shown in Table IV.
Table IV
Critical Submergence for Parshall Flumes
(Data from Ref. 4)
Critical	Critical
Flume Size Submergence Flume Size Submergence
1 in
0.56
3 ft
0. 68
2 in
0.61
4 ft
0. 70
3 in
0.64
5 ft
0.72
6 in
0.55
6 ft
0. 74
9 in
0.63
7 ft
0. 76
1.5 ft
0. 64
10 to 50 ft
0. 80
2 ft
0.66


effect of submergence on discharge is
m in Figure 2. It can be seen that
1 in
0. 338
1. 55
2 in
0.676
1.55
3 in
0.992
1. 55
6 in
2.06
1. 58
9 in
3.07
1. 53
1 ft
4W (*)
1. 52
1.5 ft
n
1!
2 ft
f i
tl
3 ft
n
It
4 ft
11
11
5 ft
>1
It
6 ft
n
It
7 ft
11
II
8 ft
11
It
10 ft
39. 38
1.6
12 ft
46.75
1.6
15 ft
57. 81
1. 6
20 ft
lO
CM
CO
r-
1. 6
25 ft
94.69
1.6
30 ft
113.13
1.6
40 ft
150.00
1.6
50 ft
186.88
1. 6
* W in feet


T
si
2$*
026
D To determine if the flume is operating in the
free-flow condition the submergence can be
calculated. Submergence (S) is defined as
S=^b
H
x 100
USEFUL RANGE FOR
SUBMERGED FLOW FROM
67 TO 95 PERCENT
NO REDUCTION
IN DISCHARGE
\
J
O
z
Ul
O
*
O
<
D
u
<
100
90
80
70
60
50
40
30
20
10
O
\
DISCHARGE BEGINS TO
MEASURABLY REDUCE
AT 67 - 70%
SUBMERGENCE. ^
/!

PRACTICAL UPPER LIMIT ~
FOR SUBMERGENCE = 95%
Where S = % submergence
H = upstrean1 head, ft.
0 10 20 30 40 50 60 70 80 90 100
SUBMERGENCE, ^ , in PERCENT
Ha
Typical Discharge Reduction caused
by Submergence in l-to-8 foot Parshall
Flumes
FIGURE 2
H, = downstream head, ft.
b
2-5
-------
Measurement of Wastewater Flow: Parshall Plume
for 1 to 8 foot flumes the reduction in
discharge does not become significant
below 70% submergence, then increases
rapidly above this value. The 95%
submergence point on the curve is of
practical interest. This is considered
to be the point when the Parshall Flume
ceases to be an effective measuring de-
vice because the head differential between
H and becomes so small that any
sSght inaccuracy in either head reading
results in a large error in flow measure-
ment.
E In many cases a determination as to whether
or not the free-flow condition exists can be
more simply made. Under free-flow con-
ditions a hydraulic jump or "standing wave"
will be observed downstream of the flume,
or in the converging section, or even in the
throat section. The formation of this jump
is a certain indication of free-flow conditions.
IV Submerged-flow Measurements
A When submergence exceeds the percentages
shown in Table IV, it is necessary to measure
both H and H, in order to determine the
discharge, and also to make a correction
to the free-flow discharges appearing in
standard tables. These procedures are
discussed below for 6-inch to 8-foot flumes.
B When 6-inch and 9-inch flumes are operating
with a submergence greater than shown in
Table IV, the flow can be obtained by using
Figure 3 (for a 6-inch flume) or Figure 4
(for a 9-inch flume). First H& and are
determined and the submergence calculated.
The intersection of the horizontal line
corresponding to this value of submergence with
with the appropriate "upstream Head" line
is found. A vertical line dropped from this
point intersects the "Discharge" axis at the
discharge value.
C For 1-foot flumes, Figure 5 can be used to
estimate the flow when submergence exceeds
the values of Table IV,
1 Measure H& and H^, calculate
submergence.
2	Using measured value of H , go
horizontally to right to intersect
the,appropriate "Percentage of
Submergence" curve.
3	Drop vertically from this point to
"correction" scale. Read correction.
4	From Table I, obtain free-flow correspond-
ing to measured H .
cl
5	Subtract the correction determined in
step 3 from the free-flow discharge.
This gives the submerged flow discharge.
D For 1 1/2-foot to 8-foot flumes follow the
above procedure, except that the correction
has to be multiplied by the factor "M" for
the size flume being used. This multiplying
factor appears in the box on the right-hand
side of Figure 5.
E Flumes larger than 8 feet will rarely be
encountered in wastewater flow applications.
Corrections for larger flumes are discussed
in Reference 1.
V Sources of Error in Flume Use
A Head-discharge relation
1 Published tables are apparently all based
on the original experiments of Parshall.
There might be uncertainties of up to 5%
in thesevalues.lt is therefore necessary
that flumes be calibrated in place if great-
er accuracy is desired.
B Errors in Head Measurement
1 The percentage error in head measurement
is multiplied by about 1. 5 to determine its
contribution to the percentage error in flow
rate.
C Departures from Standard Geometry
1 Width
a For slight differences in throat width
from the standard dimension it has been
recommended (1) that the standard flow
2-6
-------
Measurement of Wastewater Flow: Parshall Flume
UP STREAM head ho, FEET
PIG. 3 —Diagram for determining rale ol submerged flow for a 6-mch Parshall Hume. 103-D-897. (Courtesy U.S.
Soil Conservation Service.)
UPSTREAM Hi&o Ho. F£f T
5 5	6 0
FIG. 4—Diagram for determining rate of submerged flow for a 9-inch Parshall flume 103-D-898. (Courtesy U.S.
Soil Conservation Service.)
2-7
-------
2 S
UJ
u
0
1
0
<
UJ
1
2
<
ui
tr
K
(/>
Q.
3

NOTE Correction i» u$#d directly for I"
foot flumes For lorg»r sues fhe
correction equal* the value from the
chart multiplied by sue factor, M
.06 .07.08.09.10 12 .14 .16.18.20
.25 .30 .35 40.45.50 . 60 .70 80.90 1.0 1 2 1 4 1.6 IB 2.0 2.5
CORRECTION, SECOND-FEET
3.5 4 4 5 5
8 9 10
FIG. 5—Did 3rd m for determining correction to be subtracted from free-discharge flow to obtain rate of submerged flow
through Parshall flumes 1 to 8 feet wide. 103-D-875. (Courtesy U.S. Soil Conservation Service.)
-------
Measurement of Wastewater Flow: Par shall Flume
rate be changed proportionately.
Use of this correction should be
restricted to throat change widths
of a few percent only.
b For flumes which are not of
standard dimensions but which
have the correct sidewall con-
vergence angle, and for flumes
in which only the location of the
depth measurement is incorrect,
corrections can be mad® by the
method of Davis (2), which is sum-
marized in the Appendix of this outline.
2	Level
a There are no guidelines for
adjusting the standard flow-
rate for flumes which are
not level longitudinally.
.b If flume is slightly out of level
transversely use the standard
H-Q curves only if an average
H is used.
3	Length
a Shortening the converging section
of the flume will affect the per-
formance.
b Lengthening the converging
section produces no discernible
effect, but the head should be
measured at the standard point
in the converging section (2/3 A,
Figure 1).
c There is reportedly no difference
in performance between straight
and curved entrance wingwalls
(Figure 1) although the curved
wall appears to ensure smooth
flow at the head measuring point.
D Velocity Distribution
1 Situations which distort the entering
flow should be avoided, eg
a Placement of flume immediately
downstream of a bend without
allowing sufficient straightening
length.
b Discharging from a narrower
conduit into a wider flume
without providing enough entrance
length for the flow to become
evenly distributed across the
section. A transition section
is helpful here if available length
is restricted.
2 It is best to provide a long and regular
entrance channel to the flume where
possible, as experimental evidence
regarding the flume's ability to flatten
non-uniform velocity distributions is
lacking. Where conditions are such
that distorted velocity distributions
are expected in the approach flow, only
in-place calibration can inspire confidence
in use of the standard H-Q curves.
E Other Entrance Effects
1	The flume should not be placed at a lower
elevation than that of the channel being
measured because of the danger of inducing
a hydraulic jump within the flume (Figure 6).
Large errors in measurement can result.
2	If a hydraulic jump occurs in the approach
channel, a check should be made to insure
that the jump is sufficiently 'ar upstream
to permit adequate smoothing of the flow
at entrance. A minimum distance of 20
channel widths upstream of the flume has
been suggested (3).
3	Weak hydraulic jumps upstream of the
flume, characterized by long-lasting
standing waves downstream, should in
particular be avoided. These will lead to
erroneous measurements.
F Submerged Flow
1 In wastewater measurement applications,
flumes should operate in free-flow.
Significant errors can be introduced if
submergence ratios even slightly in excess
of the values shown in Table IV are not
taken into account. Figure 7 illustrates
the magnitude of such errors for a 1-foot
flume. Here, an error as large as 10%
can occur at low heads for uncorrected
submergence of 70% while at higher sub-
mergences the error becomes intolerable
under all conditions.
2-9
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Measurement of Wastewater Flow: Parshall Flume
POSSIBLE FLOW
Potential Hydraulic. Jump Development in a Parshall Flume.
Figure 6
HEAD, FT.
Errors in 1 —ft. Parshall Flume Measurements if uncorrected
for Submergence. Figure 7
2-10
-------
Measurement of Wastewater Flow: Parshall Flume
2 Even when the submergence correction
is properly made, errors in flows can
be introduced if the depth measurements
are in error. For example, in a 1-foot
flume operating at 85% submergence
(Ha = 1 foot, = 0. 85 foot), an error
of +_ 1% in the depth measurements could
introduce an error as large as 5% in the
discharge. This illustrates the desirability
of having flume installations operate in
the free-flow condition.
VI Maintenance
A Although the Parshall flume was originally
designed to pass moderate sediment loads,
heavy debris will settle out and affect per-
formance. Periodic cleaning may be necessary
in wastewater applications.
B Periodic calibrations of float gages, recorders
and checks on flume level, are also necessary
to maintain accuracy of measurement.
5	A Guide to Methods and Standards for the
Measurement of Water Flow. NBS Special
Publication 421. U. S. Dept. of Commerce,
National Bureau of Standards, Washington,
D. C. 20234. 1975. Order from Supt. of
Documents, U. S. Govt. Printing Office,
Washington, D. C. 20402, Catalog No.
C13.10:421. $1.65
6	Sewer Flow Measurement: A State-of-
the-Art Assessment. EPA-400/2-75-
-27. USEPA, Cincinnati, Ohio 45268.
Nov. 1975
7 Parker, H. K. and Bowles, F. D. Adaptation
of Venturi Flumes to Flow Measurement in
Conduits. Transactions, ASCE, Vol 101 (1936)
pp. 1195-1216.
Bibliography
j Water Measurement Manual. Bureau of
Reclamation, U. S. Dept. of the Interior,
Second Ed., revised reprint, 1974, Ch
2, pp 7-42. Order from U. S. Govern-
ment Printing Office, Washington, D. C.
20402. $5.80. Stock No. SN2403-0027,
Cat. No. I 27. 19/2:W 29/2
2	Davis, S. Unification of Parshall Flume
Data. ASCE Proceedings, 87, IR4,
Dec. 1961, pp. 13-26.
3	British Standards Institution, Standard
No. 3680-4A, Methods of Measurement
of Liquid Flow in Open Channels, Part
4A; Thin-Plate Weirs and Venturi Flumes.
1965.
4	Design & Calibration of Submerged Open
Channel Flow Measurement Structures,
Part 2 - Parshall Flumes. Skogerboe,
G.V; Hyatt, M. L. ; English, J. D., and
Johnson, J. R. Rep. No. WG 31-3,
Utah Water Research Lab., Utah State
Univ., Kogan, Utah, 84321 $0.25
This outline was prepared by C. E. Sponagle,
Sanitary Engineer, National Training &
Operational Technology Center, MOTD,
OWPO, USEPA, Cincinnati, Ohio 45268.
2-11
-------
APPENDIX
Unification of Parshall Flume Data
In his paper by this title (2) Davis states
. . dimensional methods have been used
to develop a semi-theoretical equation re-
lating flow and depth for all flumes from 1
inch to 50 feet. Excellent agreement between
this equation and all published data is found.
This will permit using flumes of non-standard
sizes and will broaden the field of application
for this type of measuring device."
He derived the following equation, which he
states closely fits all data published on Parshall
flumes and can be used for calculating the
flow for flumes of any size. It can also be
used for correcting the calibration curves
of standard size flumes that do not conform
with the specified dimensions of throat width
or upstream measuring distance.
Qn2	0.645
yQ + 2	2 = 1. 351 Q
2yo(l+0.4xo)	o
y
where yQ = non-dimensional depth
b
y^ = depth at measuring section
(see Figure A-l)
9
— ^ ^ —
. b .
Figure A-l
The Davis equation can be used only with
flumes having a side angle 9 = ^tan"* 0. 2 = 11° 19',
and a drop down angle = tan 0. 375 =
20° 33'. The effects of varying these angles
have not been investigated. All standard
Parshall flumes, with dimensions as shlown
in Table I, have these angles.
*1
J,
b = throat width (see Figure A-l)
Qq= non-dimensional discharge
"1/2 5/2
g b
g = acc11 due to gravity
Q = discharge
x = non-dimensional distance, 1
T
Xj = distance from throat crest
to measuring section (see
Figure A-l)
Figure A-l shows the important dimensions
referred to in'the above equation.
The non-dimensional factors in the equation
can be eliminated by substituting dimensional
factors, and the equation then will be
1
Q
0.4409 Q
7= .1.613
0. 645
2g byj (b + 0. 4 x ) b
For a particular flume installation, all variables
in the above equation, except Q, will be known.
Substituting the known values (.y , b, g, x.),
the equation becomes
2 0.645
A + BQ = CQ
Where A, B, and C would be constants for the
particular installation. This equation can then
be written
A + BQ2 - C Q°* 645 - F
Several values of Q can be assumed, and the
corresponding values of F obtained. The values
of Q vs F can be plotted, and the plotted line
extended to intersect the F - Axis (F=0). The
corresponding value of Q would be the flow.
-------
FLOW SENSING, RECORDING, AND TOTALIZING DEVICES
I Measurement of Head
A When primary flow measurement devices
such as weirs and flumes are used to
measure open channel flow, discharge (Q)
is related to a head (H), or depth of flowing
liquid, measured at a specific point upstream
of the crest.
B Since there is a definite H-Q relationship in
these cases, varying with the primary device
used, changes in Q can be obtained by observ-
ing changes in H.
C Several methods of measuring and recording
changes in H are considered in this outline.
II Staff gage; Float gage
A Frequently a staff gage (Figure 1) is used
to measure H, This is a graduated scale,
usually installed vertically at the point where
the depth of the liquid is to be measured.
'-S
9-s
si
J!
11
FIG. 1 - STAFF
GAGE SECT ON
Commercially-available gages are made of
18-gage metal coated with a substantial
thickness of porcelain enamel. Face of the
gage is white, numerals and graduations are
black. Gages are available in several styles,
in widths from 2 1/2 to 4 inches, in lengths
from 1 to 5 feet. A metric gage is also avail-
able in 1 meter sections, graduated in centi-
meters and decimeters.
The gage is usually installed so that the
bottom of the gage is at the same level as
the crest of the primary measuring device.
The head can then be read directly, being
the gage division at which the liquid surface
intersects the gage. From time-to-time the
installation should be checked to be surp that
the gage bottom is at crest level.
D When surges with flow or oscillations in the
water surface are such as to make the accur-
acy of a head reading questionable from a
gage installed in the flowing liquid, use of a
stilling well will substantially reduce or
eliminate this difficulty.
1	A stilling well (sometimes called a
float well) is a chamber that has a
small inlet connecting it to the channel
in which the liquid to be measured is
flowing. Sudden waves or surges
in the flow will not appear in the
well. The quiet water in the well
will nevertheless follow all the
steady fluctuations of the flow.
Such conditions are very necessary
to obtain good records of water levels,
particularly for float-operated devices.
2	Stilling wells can be made of wood or re-
inforced concrete, rectangular or square;
of round metal pipe, cement or vitrified
sewer pipe. The well must have a bottom
and be practically water tight except for
the liquid inlet.
3	Size of the well depends on the equipment
to be installed, although in installations
where considerable suspended materials
are carried in the flow it is advisable to
make the well large enough for cleaning.
4	In order to effectively eliminate wave action
and surges, the area of the liquid inlet
should be about 1/ 1000 the area of the well.
Where a pipe connects the well with the
liquid, it can be somewhat larger than where
connection is by a mere hole in the wall. If
the inlet is placed at considerable depth, it
can be considerably larger than if near the
surface. Some suggested relationships are
shown below. (1)
Diameter of
Float Well
16 inches
24 inches
36 inches
x 3'
x 4'
Diameter of Diameter of Inlet
Inlet Hole Pipe 20-30 Ft. Long
3'
3'
1/2 inch
3/4 inch
1 1/4 inch
1 1/4 inch
1 1/2 inch
3/4 inch
1	inch
2	inches
2	inches
3	inches
EN. FM. 3. 5. 78
3-1
-------
Flow Sensing, Recording, and Totalizing Devices
5 In wastewater applications, provisions
must be made for frequent cleaning of
stilling wells or levels in them will not
be representative. Another problem is
that the inlet to the well can be quickly
clogged with sediment or grease. Routine
maintenance is necessary to prevent errone
ous flow records from being obtained as a
result of these conditions.
Another simple device used to indicate water
levels is the float gage (Figure 2).
(Fig. 2 )
This can usefully be employed in stilling
wells, when it would be difficult or im-
possible to accurately read a staff gage.
1	A float gage consists of:
a A graduated stainless steel tape
attached to a copper float.
b A guide pulley mounted on a
standard having an adjustable
index, and
c A couterpoise attached to the
other end of the tape.
The tape is graduated to read in feet,
tenths and hundredths, or meters,
decimeters and centimeters.
2	As for the staff gage, tape readings
on the float gage must be referenced
to the crest of the weir or flume.
Ill Instantaneous vs. Continuous Discharge
Measurements
A A staff gage or float gage installation can
be used, in conjunction with a primary
flow measuring device, to read instantane-
ous flows, or, by means of frequent read-
ings, to estimate average flows over a
desired period of time.
B In many cases, however, a continuous
record of flow is desired. More sophisticat-
ed sensing and recording instrumentation is
then required, although a staff or float gage
should ideally be a part of any such installa-
tion, so that operation of the automatic
equipment can readily be checked.
IV Secondary Devices
A A number of automatic flow sensing and
recording devices are commercially
available. These may be called flowmeters
by their manufacturers, but in actuality
they are secondary devices for measuring
liquid depth. They must be used with some
sort of primary device, such as a weir or
flume, before true flow measurement can
be made. A brief discussion of these devices
is given below along generic lines.
1 As is the case with all secondary
devices, there are three basic types
of information that can be provided,
either separately or in combination.
These are an indication of flow rate
(typical units are cfs, gph, mgd, etc.;
such devices are sometimes referred
to as indicators); a running total of
flow to the observed moment (typical
units are cu. ft., gal., m. g., etc.;
such devices are sometimes called
totalizers); and a record, ranging
from a curve drawn in ink with a pen
to a magnetic tape recording, of the
rate of flow with time over some suitable
period (hour, day, week, etc.; such
devices are termed recorders). Additional
features may include the ability to transmit
the flow data to a remote site (transmitters,
the corresponding instruments at the other
end being termed receivers), the ability
to operate in digital versus analog form,
etc.
3-2
-------
Flow Sensing. Recording, and Totalizing Devices
B Float-in- Well. This is probably the oldest
type of secondary device in existence. It
is applied in a stilling well connected to the
gage point of the primary device (weir, flume,
etc.). The float-tn-well essentially consists
of a float of some suitable shape (sized for
compatibility with the dimensions of the well)
connected via a cable to a wheel and counter-
balanced in some fashion so that the cable
remains taut. As the float rises or falls
with changes in water level, the cable rotates
the wheel, which is connected either mechan-
ically or electronically to the readout, recorde
. or whatever. Discharge is determined by the
use of cams, electronic circuits, etc. , that
are characterized for the primary device
involved.
C Float-in-Flow. In this type of secondary
device, the float rides on the actual surface
of the flow, directly sensing its level rather
than indirectly sensing it as with a stilling
well. Float shapes range from spherical,
to scow or ski shaped, the latter being de-
signed to minimize disturbances of the liquid
surface, fouling by trash or debris, oscilla-
tions in the instrument, etc. The float is
attached to a hinged arm that is directly or
indirectly (e.g., by cable) connected to the
main body of the instrument. Directly-
connected designs should be immersion proof
if they are to be used in storm or combined
sewers with any history of surcharging.
In indirectly-connected designs, where
the main body of the instrument can be
located above the nigh water level, it
need not necessarily be immersion proof,
but this feature never hurts.
Advantages of float-in-flow devices
include: freedom from the requirement
for a stilling well and purge system;
direct (rather than indirect) sensing of
the liquid level; and avoidance (in some
designs) of cables, counterweights, etc.,
typical of float-in-well devices. Dis-
advantages include: possible fouling by
trash or debris (which can result in er-
roneous readings or even physical damage);
broad chart records in some instances due
to the lack of damping of water surface
oscillations that some stilling wells provide;
and a more limited range due to the restric-
tions on arm length necessary at some
installations.
D Bubbler. In this type secondary device,
a pressure transducer senses the back-
pressure experienced by a gas which is
bubbled at a constant flow rate through a .
tube anchored at an appropriate point with
respect to the primary device. This back-
pressure can be translated into water depth
and subsequently related to discharge.
Advantages include a lack of moving parts
or mechanisms, a sort of self-cleaning
action arising from the gas flow, and
virtually no obstruction to the flow. One
of its main disadvantages is that if the exit
end base of the bubble tube becomes appreci-
ably reduced due to build-up of contaminants
from the flow, erroneous readings will
result even though the instrument may appear
to be functioning normally. "Aspiration effects
due to the velocity of the flow may also pre-
sent problems.
E Electrical. These secondary devices make
use of some sort of change in electric circuit
characteristics in order to indicate the liquid
level. Most designs utilize a probe or some
similar sensor which is immersed in the flow
at the gage point. This sensor is a part of an
electrical circuit, and its behavior in the
circuit is a function of its degree of immer-
sion. For example, the sensor could basically
be an admittance-to-current transducer,
providing a measure of depth based on
the small current flowing from the sensor
to the grounded stream. Changes in any
electrical property (capacitance, resistance,
etc.) can be used to sense liquid depth.
Advantages are the absence of any moving
parts, floats, cables, stilling wells, gas
supplies, purge requirements and the fact
that they cannot plug and are usually un-
affected by build-up of sludge, algae, slime,
mud, etc. The major disadvantage is the
requirement for the sensing element to
physically be in the flow. The presence of
appreciable foam or floating oil and grease
can cause errors in most designs.
In a somewhat different design belonging to
this class, the probe is not actually in the
stream but is periodically lowered, via a
motor-pulley-cable arrangement, until it
makes contact with the water surface, which
completes a microampere circuit through
the liquid to a ground return.
3-3
-------
Flow Sensing, Recording, and Totalizing Devices
This signal reverses the motor, raising the
probe above the surface of the liquid. As in
the case with a float, the amount of cable
paid out is the measure of stage. Although
this design does not require immersion of
the sensor in the flow, it does involve mechanical
complexities and moving parts not characteristic
of the other electrical secondary devices.
F Acoustic. This type of secondary device is
growing in popularity as prices decrease.
Requiring no physical contact with the liquid,
they enjoy all of the advantages listed for
electronic designs. They were covered in
the discussion of acoustic primary devices
and will not be redescribed here. However,
a few precautionary words will' be given. For
applications where space is restricted as in
some manholes and small meter vaults, problems
due to false echos may be encountered. This
problem may be overcome at some sites by
shielding the transducer, but accurate readings
{at low flows at least) should not be expected
for flows in round pipes or deep, narrow channels
from most designs. Also, good results should
not be expected if the surface of the flow is highly
turbulent or foam covered as the reduced return
signal may not be properly detected.
Bibliography
1	Stevens Water Resources Data Book, 2nd Ed.,
Leupold & Stevens, Inc. P.O. Box 688,
Beaverton, OR 97005. $4.00
2	Sewer Flow Measurement: A State-of-the-Art
Assessment. EPA-600/2-75-027. Order from
National Technical Information Service,
SDrinefield, Virginia 22161.
This outline was prepared by C. E.
Sponagle, Sanitary Engineer, National
Training & Operational Technology Center,
MOTD, OWPO, USEPA, Cincinnati, Ohio
45268
3-4
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evaluation of flow installations
I evaluation of existing flow
MEASUREMENT INSTALLATIONS
INVOLVES THE EVALUATION OF
A The primary measuring device
1	Is it installed in conformance with the
requirements for the particular device?
2	Is it accurately measuring the flow?
B The secondary devices (if any) for sensing
and recording the flow
1 Are these functioning properly and
recording the correct values of flow?
II PRIMARY MEASURING DEVICE
A A check list should be prepared listing all
pertinent features of the installation which
require examination and documentation
1 Example check lists for weirs and
the Parshall flume are included in
this outline.
I SECONDARY DEVICES
A Compare value of recorded flow obtained
by independent means.
1	Comparison may be made based on
one or several instantaneous measure-
ments.
2	A separate recording device can be set
up, and comparable results compared
over a longer period of time.
This outline was prepared by C. E. Sponagle,
Sanitary Engineer, National Training &
Operational Technology Center, MOTD, OWPO,
USEPA, Cincinnati, Ohio 45268.
B Channel conditions upstream and downstream
of the device should be observed for obstruc-
tions, turbulence, etc. Any condition which
might influence performance should be noted.
1 Such conditions should be eliminated to
the extent possible, prior to calibration
of the device.
C Measure flow by an independent means, and
compare results with these obtained from
existing installation.
1 The most appropriate independent
method of measuring flow will depend
on the characteristics of the installa-
tion. Three methods commonly used are-
a Current meter traverse
b Dilution methods
c Thin-plate weir
EN. FM. 4.5. 78
4-1
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CHECKLIST FOR EXISTING FLOW MEASUREMENT DEVICES
Name of Industry or Municipality
Name of Contact
Datej_	
Permit Discharge Number:
Type of Wastes:			
Type of Discharge: Batch	, 	Hrs/Batch, 	Number/Day
Continuous	, 	Hrs/Day
Type of Measurement Device:
Dimensions (e.g.. Length of Weir)	
Capacity of Device	 (max-min mgd)
Range of Flows			
Is Device Properly Installed	Yes	Xo
If no, specify reasons installation is not correct:
When was device last calibrated by permittee:	
Type of Stage Recording Device (Manufacturer, model, etc.)
Relation Between Recording Device and Measuring Device	
Is Recorder Device Properly Installed:	Yes	No
If no, specify reasons installation is not correct:	
Is Recording Device Functioning Properly:	Yes	.No
If no, specify reasons for malfunctions-.	
Remarks
Date
By
(Signature)
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CHECK LIST
Suppressed Rectangular Weir
YES NO
1.	Bulkhead (or weir Plate)
a.	Upstream face smooth
b.	Upstream face vertical
c.	Upstream face perpendicular to axis of channel
d.	Is weir plate smooth, straight, flush with upstream
face of bulkhead
e.	Any leakage around bulkhead
2.	Weir Crest
a.	Level
b.	Upstream edge forms a sharp right angle at inter-
section with upstream face
c.	Thickness 0.03-0.08 inches (1-2 mm.)
d.	Downstream edge properly chamfered
e.	Crest minimum of 1 foot or 2 Hmax above
bottom of channel
f.	Any nicks, dents, rust, or deformation of weir shape
3.	Nappe
a.	Touches only upstream edge of crest
b.	Free discharge into atmosphere
c.	Proper ventilation provided
d.	Sides of channel extend downstream of weir
4.	Head
a.	Measured at proper location
b.	Measuring device zeroed to crest level
c.	Head remains between 0. 2 ft and 1/3 L ft.
5.	Approach Conditions
a.	Excessive solids deposits in weir pool
b.	Weir pool dimensions satisfactory*
c.	Velocity-of-approach correction indicated
REMARKS
*Area of flow at least 8 times that of overflow sheet at crest for a distance upstream from 15-20 times
depth of overflow sheet.
Other remarks or pertinent observations: (Use back of sheet)
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CHECK LIST
Rectangular Weir with End Contractions
YES NO REMARKS
1.	Bulkhead (or weir plate)
a.	Upstream face smo *tn
b.	Upstream face vertical
c.	Upstream face perpendicular to axis of channel
d.	Is weir plate smooth, straight, flush with upstream
face of bulkhead
e.	Any leakage around bulkhead
2.	Weir Notch
a.	Crest level
b.	Sides vertical
c.	Upstream edge forms a sharp right angle at inter-
section with upstream face
d.	Thickness 0.03-0.08 inches (1-2 mm.)
e.	Downstream edge properly chamfered
f.	Crest minimum of 1 foot or- 2 Hn . above
bottom of channel
g.	Sides minimum of 1 foot or 2 H	from sides
& max.
of channel
3.	Nappe
a.	Touches only upstream edge of crest and sides of
notch
b.	Free discharge into atmosphere
4.	Head
a.	Measured at proper location
b.	Measuring device zeroed to crest level
c.	Head remains between 0. 2 ft and L/3 ft
5.	Approach Conditions
a.	Excessive solids deposits in weir pool
b.	Weir pool dimensions satisfactory*
c.	Velocity-of-approach correction indicated
-Area of flow at least 8 times that of overflow sheet at crest for a distance upstream from 15-20 times
depth of overflow sheet.
Other remarks or pertinent observations: (Use back of sheet)
-------
2.
3.
CHECK LIST
V-Notch Weir
YES
NO
REMARKS
1.
Bulkhead (or weir plate)
a.	Upstream face smooth
b.	Upstream face vertical
c.	Upstream face perpendicular to axis of channel
d.	Is weir plate smooth, straight, flush with
upstream face of bulhead
e.	Any leakage around bulkhead
Weir Notch
a. Is top of weir level
Notch angle cut accurately
b.
c.
d.
e.
f.
g.
h.
i.
Vertical through bottom of notch bisects
notch angle
Upstream edge forms a sharp right angle at
intersection with upstream face
Thickness 0. 03-0.08 inches (1-2 ml)
Downstream edge properly chamfered
Bottom of notch minimum of 1 foot or 2 H
above bottom of channel
max.
At Hmax , intersection of liquid surface with
notch a minimum of 1 foot or 2 H™,v from sides
of channel
'may.
Any nicks, dents, rust, or deformation of
weir shape
Nappe
a.	Touches only upstream edge of notch
b.	Free discharge into atmosphere
Head
a.	Measured at proper location
b.	Measuring device zeroed to bottom of notch
c.	Minimum head no less than 0. 2 ft
Approach Conditions
a.	Excessive solids deposits in weir pool
b.	Weir pool dimensions satisfactory*
c.	Velocity-of-approach correction indicated
*Area of flow at least 8 times that of overflow sheet at crest for a distance upstream from 15-20 times
depth of overflow sheet.
Other remarks or pertinent observations: (Use back of sheet)
5.
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CHECK LIST
Parshall Flumes
'ES
NO
1.	Is channel upstream of flume free of debris or deposit.
2.	Does flow entering flume appear reasonably well dis-
tributed across the channel ^nd free of turbulence, boils,
or other distortions
3.	Are cross-sectional vclociti 3 at e trance relatively
uniform
4.	Is flume clean and free of debris or deposits
5.	is crest level in all directions
6.	Are all dimensions accurate
7.	Are side walls vertical and smooth
8.	Are sides of throat vertical and parallel
9.	is head being measured at proper location
10.	Is head measurement zeroed to flume crest
11.	Is flume of proper size to measure range of flows
existing
12.	Is flume operating under free-flow conditions over
existing range of flows
13.	Is channel downstream of flume free of debris or
deposits
REMARKS
PARSHALL FLUME DIMENSIONS AND CAPACITIES
Widths
» Aifat Lengtns
wall
Oepth In
Vertical Distance
Below Crest
Con-
verglna
Hal!
Length
k*
6ag«
Points
Free
Capac
Flow
1 ties
Slit;
ThrO*t
Width
W
Up.
streaa
End
0
0o*n*
streaa
End
C
Con-
verging
Section
B
Throet
Section
F
Diverging
Section
G
Con-
verging
Section
E
Dip at
Throat
H
Lower
End of
FIum
K
Ha, Dlst
Upstrean
of Crest**
Hb
Mln
Max
X
y
Inctiei
Feet
Feet
Feet
Feet
Feet
Feet
Feet
Feet
Feet
Feat
Ftet
Feit
eft
eft













































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APPENDIX A
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SECTION VI
WASTEWATER FLOW MEASUREMENT
A. Introduction
The measurement of flow in conjunction with wastewater
sampling is essential to almost all water pollution control
activities. All activities such as NPDES permit compliance
monitoring, municipal operation and maintenance, planning and
research rely on accurate flow measurement data. The importance
of obtaining accurate flow data cannot be overemphasized,
particularly with respect to NPDES compliance monitoring
inspections, since these data should be usable for enforcement
purposes. NPDES permits limit the quantity (mass loading) of a
particular pollutant that may be discharged. The error involved
in determining these mass loadings is the sum of errors from flow
measurement, sample collection, and laboratory analyses. It
should be obvious that measurement of wastewater flow should be
given as much attention and care in the design of a sampling
program as the collection of samples and their subsequent
laboratory analyses.
The basic objectives of this chapter are:
(1)	To discuss basic wastewater flow measurement systems;
(2)	To outline what is expected of field personnel with
respect to wastewater flow measurement during NPDES
compliance monitoring activities; and
53-
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(3) To present acceptable wastewater flow measurement
techniques commonly used.
A. complete discussion of all available flow measurement
techniques and the theory behind them is beyond the scope of this
manual. Most of the common techniques in current use are
covered, however, in rather general terms. A comprehensive list
of references is included at the end of this chapter for those
who desire a more detailed discussion.
B. Wasterwater Flow Measurements Systems
Flow data may be collected on an instantaneous or a
continuous basis. A flow measurement system is required for the
collection of continuous data. A typical continuous system
consists of a primary flow device, a flow sensor, transmitting
equipment, a recorder, and possibly, a totalizer. Instantaneous
flow data can be obtained without using such a system.
The heart of a typical continuous flow measurement system,
as shown in Figure VI-1, is the primary flow device. This device
is constructed such that it has predictable hydraulic responses
which are related to the flowrate of water or wastewater through
it. Examples of such devices include weirs and flumes which
relate water depth (head) to flow, Venturi and orifice type
meters which relate differential pressure to flow, and magnetic
flow meters which relate induced electric voltage to flow. A
standard primary flow device has undergone detailed testing and
experimentation and its accuracy has been verified.
-54-
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FIGURE VI-1
COMPONENTS OF FLOW MEASURING SYSTEMS
aj"
,
H
-p
CO
Primary
Flow
Device
i
Ul
m
i
.signal	*
(electrical,
mechanical or ^
pneumatic)

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A flow sensor is required to measure the particular
hydraulic responses of the primary flow device and transmit them
to the recording system. Typically, sensors include floats,
pressure transducers, capacitance probes, differential pressure
cells, electromagnetic cells, etc.
The sensor signal is generally conditioned by using
mechanical, electromechanical, or electronic systems. These
systems convert the signal into units of flow which are recorded
on a chart or put into a data system. Those systems which
utilize a recorder are generally equipped with a flow totalizer
which displays the total flow on a real time basis.
NPDES permits that necessitate continuous flow measurement
require a complete system. Permits that require instantaneous
flow measurement do not necessarily dictate the use of any
portion of such a system. Techniques are available (described
later in this chapter) for measuring instantaneous flow with
portable equipment.
An important consideration during sampling inspections for
NPDES compliance purposes is that the investigator may want to
obtain continuous flow data at a facility where only
instantaneous flow data is required by permit monitoring
conditions. If an open channel primary flow device is utilized
for making instantaneous measurements, only the installation of a
portable field sensor and recorder is necessary. If, on the
other hand, the facility being investigated does not utilize a
primary flow device, and a continuous flow record is desired, the
-56-
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investigator's job becomes more difficult. A portable primary
flow device will have to be installed. Generally, the
investigator is limited to the installation of open channel
equipment, since the installation of closed-conduit flowmeters is
more complex and time-consuming. This chapter does not cover in
detail the installation of primary flow devices, but many of the
references cited treat this area quite adequately. The USDI
Water Measurement Manual (1) is an excellent reference for
details on checking the installation of primary flow devices.
The accuracy of wastewater measurement systems varies
widely, depending principally upon the primary flow device used.
The total error inherent in a flow measuring system is, of
course, the sum of each component part of the system. However,
any system that can not measure the wastewater flow within ~ 10%
is considered unacceptable for NPDES compliance purposes.
C. Field Verification Of Flow Measurement Systems
The responsibility of the investigator during NPDES
compliance sampling inspections includes the collection of
accurate flow data during the inspection, as well as the
validation of such data collected by the permittee for self-
monitoring purposes.
The investigator must insure that the flow measurement
system or technique being used measures the entire wastewater
discharge as described by the NPDES permit. A careful inspection
should be made to determine if recycled wastewaters or wastewater
-57-
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diversions are present upstream of the system. The investigator
should note any anomalies on the inspection report form or in a
bound field notebook.
The investigator1s second task is to verify that the system
being used is accurate. In cases where the discharger is making
instantaneous flow measurements to satisfy permit requirements,
the specific method used should be evaluated. If a primary flow
device is used, the device should be checked for conformity with
recognized construction and installation standards. Any
deviation from standard conditions should be well documented.
Where there are significant deviations, accuracy of the primary
flow device should be checked by making an independent flow
measurement.
All components of continuous flow measuring systems should
be verified. The primary flow device should be checked for
conformity with recognized construction and installation
standards (where possible). The flow sensing and recording
devices are usually checked simultaneously. The procedure most
often used is to make an independent flow measurement utilizing
the primary flow device, obtaining the flow rate from an
appropriate hydraulic handbook and comparing this flow rate with
the recorded value. Since most primary flow devices do not have
linear responses, several checks should be made over as wide a
flow range as is possible. The accuracy of the recorder timing
mechanism may be checked by marking the position of the recorder
indicator and checking this position after an known elapsed time
-58-
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interval. Flow totalizers are easily checked by integrating the
area under the curve. If the investigator has the proper
equipment and knowledge, electronic recorders and totalizers may
be checked by inducing known electric current to simulate flow.
The accuracy of closed conduit flow measurement systems can be
verified by making independent flow measurements at several
different flowrates or by electrically, mechanically or
hydraulically inducing known flowrates. Specific techniques for
making independent flow measurements are given later in this
section.
If the discharger*s flow measurement system is accurate
within ~ 10 percent, the investigator is encouraged to use the
installed system. If the flow sensor or recorder is found to be
inaccurate, determine if it can be corrected in time for use
during the inspection. If the equipment cannot be repaired in a
timely manner, the investigator should install a portable flow
sensor and recorder for the duration of the investigation. The
installation and use of such equipment is preferred over attempts
to correct erroneous flow measurement systems. The inspector
should note the action taken in the inspection report and inform
the permittee that the equipment should be repaired as soon as
possible. If non-standard primary flow devices are being used,
it is the responsibility of the discharger to supply data
supporting the accuracy and precision of the method being
employed.
-59-
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The inspector should evaluate and review calibration and
maintenance programs for the discharger's flow measurement
system. The permit normally requires that the calibration of
such systems be checked by the permittee on a regular basis. The
lack of such a program should be noted in the inspection report.
The compliance inspection report should contain an
evaluation of the discharge flow measurement system.
Inadequacies may be discussed with the permittee during the
inspection and deficiencies noted in the report so that follow-up
activity can be conducted. Any recommendations to the permittee
should be made in such a manner that any subsequent enforcement
will not be jepordized.
D.. Wasterwater Flow Measurement Methods
This section outlines and familiarizes the field
investigator with the most commonly used methods of wastewater
flow measurement and the primary devices that will be encountered
during NPDES compliance sampling inspections. Volumetric and
dilution techniques are presented at the beginning of this
chapter, since they are applicable to both open-channel and
closed-conduit flow situations. The remaining methods are
grouped under categories dealing with open channels and closed-
conduits. The general method of checking individual primary flow
devices is given, where applicable. Several estimation
techniques are presented. However, it should be recognized that
flow estimates do not satisfy NPDES permit monitoring
-60-
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requirements unless the permit specifically states that this is
permissible.
1. Volumetric Techniques
Volumetric flow techniques are among the simplest and
most accurate methods for measuring flow. These techniques
basically involve the measurement of volume and/or the
measurement of time required to fill a container of known size.
(a)	Vessel Volumes
The measurement of vessel volumes to obtain flow data
is particularly applicable to batch wastewater discharges. An
accurate measurement of the vessel volume(s) and the frequency
that they are dumped is all that is required. An accurate
engineering tape measure to verify vessel dimensions and a stop
watch are the only required field equipment. The equations for
calculating the volumes of various containers is given in Figure
VI-2.
(b)	Pump Sumps
Pump sumps may be used to make volumetric wastewater
flow measurements. This measurement is made by observing the
sump levels at which the pump(s) cut on and off and calculating
the volume contained between these levels. This volume, along
with the number of pump cycles, will give a good estimate of the
daily wastewater flow. One source of error in this measurement
is the quantity of wastewater that flows into the sump during the
pumping cycle. This error may be particularly significant if the
-61-
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FIGURE VI-2
EQUATIONS FOR CONTAINER VOLUMES
SPHERE
Total Volume
V	= 1/6 ttDj = 0.523598D3
Partial Volume
V	= 1/3 (3/2 D-d)
RIGHT CYLINDER
Total Volume
V	= 1/4 ttDzH
Partial Volume
V	= 1/4 ?rDzh
ANY RECTANGULAR CONTAINER
r







y
w'

>
H

Total Volume
V	= HLW
Partial Volume
V	= hLW
-62-
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FIGURE VI-2 (CONTINUED).
FRUSTUM OF A CONE
Case 1
Case 2
Total Volume
V	= n/12 H (D22 + Dx D2 + D22)
Partial Volume
V	= tt/12 h (Diz + Di d + d2)
CONE
Case 1
Case 2
Partial Volume
V	= 1/12 tt dzh
Total Volume
V	= 1/12 it D^H
Partial Volume
V	= 1/12 tt CD^H
(case 1)
(case 2)
d2h)
PARABOLIC CONTAINER
, D'
/L


u
;

1^
Case 1
Case 2
1
U:
+ i H

Partial Volume
V	= 2/3 hdL
Total Volume
V	= 2/3 HDL
Partial Volume
V	= 2/3 (HD - hd) L
-63-
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sump is large, the rate of inflow is highr and/or the pumping
cycle is long. This error may be accounted for if the inflow is
fairly constant, by measuring the time required to fill the sump
and adding this additional flow for each pump cycle. The number
of times that the pump cycles during a measurement period may be
obtained by using a counter on the pump or using a stage recorder
to indicate the number of pump cycles.
(c) Bucket and Stopwatch
The bucket and stopwatch technique is particularly
suited to the measurement of small wastewater flows. It is
accurate and easy to perform. The only equipment required to
make this measurement are a calibrated container (bucket, drum,
tank, etc.) and a stop watch. The container should be calibrated
carefully, using primary standards, or other containers which
have been calibrated using such equipment. Ordinarily, this
measurement is made at the end of a pipe; however, using some
ingenuity, a bucket and stopwatch flow measurement may be made in
ditches and other open channel locations. Short sections of pipe
may be used to channel or split flows into measurable portions.
A shovel is often needed to dig a hole under a pipe or in an open
channel to get the container under the wastewater stream that is
to,be measured. As with all flow measurement techniques, it is
important to insure that all of the wastewater stream is
measured. This method is limited by the amount of flow that can
practically be measured in a reasonably sized container. A five
gallon bucket filled to_capacity, for example, would weigh U2
-64-
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pounds. Also, the filling time of the container should be
sufficiently long so that the calibrated container can be moved
in and out of the wastestream without spilling the contents or
overflowing the bucket. A minimum filling time of 10 seconds is
recommended. If the container is hand-held, the practical limit
of container size is what can be comfortably handled, about five
gallons. Therefore, with a 5-gallon container, the maximum flow
that could practically be measured would be 30 gpm. At least
three consecutive measurements should be made, and the results
averaged.
(d) Orifice Bucket
The orifice bucket permits the investigator to measure
higher wastewater flows than is possible by using a bucket and
stopwatch. An orifice bucket is a metal container (bucket) that
has been modified by cutting holes (orifices) in the bottom. The
bucket is calibrated by plugging the orifices with rubber
stoppers and using bucket and stopwatch measurements to calibrate
the bucket. The calibration curve relates the depth of the water
in the bucket, for various combinations of orifices, to the
flowrate. This method is usable over a flow range of 7 to 100
gpm. Construction of the orifice bucket and directions for its
use is given by Smoot (3).
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2* Dilution Methods
Dilution methods for water and wastewater flow are based on
the color, conductivity, fluorescence, or other quantifiable
property of an injected tracer. The dilution methods require
specialized equipment, extreme attention to detail by the
investigator, and are time consuming. However, these techniques
offer the investigator:
A method for making instantaneous flow measurements
where other methods are inappropriate or impossible to
use;
A reference procedure of high accuracy to check in
situ those primary flow devices and flow measurement
systems that are nonstandard or are improperly
installed; and
A procedure to verify the accuracy of closed conduit
flow measuring systems.
Thfe tracer may be introduced as a slug
(instantaneously) or on a continuous flow basis. The constant
rate dilution method is performed by injecting a tracer at a
constant rate into a wastewater stream at an upstream location
and measuring the resulting tracer concentration at a downstream
location. The method is based on the following continuity
equation;
Q = qlC^-C^/CC-s-Co) (1)
Where:	Q = Flowrate of the stream to be measured
q = Constant flowrate of injected tracer
-66-
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Cj = Concentration of injected tracer
C2 = Concentration of tracer in the stream
at downstream sampling location
C0 = Background tracer concentration
upstream from the tracer injection
site.
If the flowrate and background concentration of the injected
tracer are negligible when compared to the total stream
characteristiesr this equation reduces to:
Q = qCj/C2	(2)
Where Q# q, Ct and C2 are as previously defined for equation
a).
The use of this method requires that the following
conditions be attained:
t The injection rate of the tracer (q) must be precisely
controlled and must remain constant over the
measurement period;
•	The tracer used must not degrade, sorb, or be changed
in basic characteristics by environmental factors or
the wastestream to which it is added;
•	The location of injection and sampling sites must be
judiciously selected and located such that the dye is
well mixed across the cross-section, so that a
concentration plateau is reached during the
measurement period; and
-67-
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The tracer used must be capable of being analyzed
precisely.
In practice, many tracers have been used for dilution flow
measurements including sodium chloride, lithium chloride, and
fluorescent dyes. Fluorescent dyes and fluorometric analyses
have been widely employed in dilution measurements and are
particularly convenient. The tracer is normally injected into
the wastestream by'using a piston type chemical metering pump.
The use of this type of pump is almost mandatory to maintain a
constant injection rate. Automatic samplers are widely used to
collect samples during the period of measurement. If fluorescent
dyes are used, a submersible pump may be used in conjunction with
a flow-through fluorometer and recorder to provide a continuous
record of the dye concentration at the sampling point.
The flowrate may also be determined by making a1 slug
(instantaneous) injection of tracer and measuring the resultant
concentration at the downstream location during the entire time
of passage of the tracer. The principle' of the slug injection
method is expressed in the following4equation:
Q =	x V/0/»(C2-C0)dt	(3)
Where:	V = Volume of tracer injected
t = time
Q» q# C0r Clr C2 are as previously defined
for equation (1).
The principal advantage of this method is that sophisticated
equipment is not required to inject the tracer. The
-68-
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disadvantages of the method are that it may not be used for
unsteady flow situations and the entire tracer pulse must be
sampled. The latter problem is easily solved by using
fluorescent dyes and a flow-through fluorometer and recorder.
The denominator of equation (3) may then be obtained by simply
integrating the fluorometer recorder chart (after allowing for
the background concentration, C0) for the measurement period.
A graphical comparison of the constant rate and slug
injection methods is given in Figure VI-3. The use of dilution
techniques is covered in detail in the references (1, 3, 4). The
monograph available from the Turner Design Company (4) is a
particularly valuable reference for the use of fluorescent dyes
and fiuorometers in dilution flow measurement work. Experience
indicates that accuracies of +3 percent are achievable utilizing
the dilution method under field conditions.
3. Open Channel Plow Measurements
The measurement of wastewater flow in open channels is the
most frequently encountered situation in field investigations.
An open channel is defined as any open conduit such as a ditch or
flume or any closed conduit such as a pipe, which is not flowing
full. The most commonly encountered methods and primary flow
devices used in measuring open channel wastewater flow are
described in this section. Several flow estimation techniques
are also presented.
-69-
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TIME
CONCENTRATION-TIME. CURVE FOR
CONSTANT-RATE INJECTION METHOD
IS FLOW RATE OF STREAM
IS FLOW RATE OF CHEMICAL
IS BACKGROUND CONCENTRATION OF
STREAM
IS CONCENTRATION OF CHEMICAL
INJECTED
IS CONCENTRATION OF STREAM PLATEAU
t
"«a:
Oc
o
<_>
TIME
b. CONCENTRATION-TIME CURVE FOR
SLUG-INJECTION METHOD.
v C-
Q =
r (c-cjdt
Q	IS FLOW RATE OF STREAM
v	IS VOLUME OF CHEMICAL INJECTED
C	IS BACKGROUND CONCENTRATION OF
0	STREAM
C,	IS CONCENTRATION OF CHEMICAL
1	INJECTED
C	IS INSTANTANEOUS STREAM
CONCENTRATION
FIGURE VI-3
CONSTANT RATE AND SLUG INJECTION METHODS (10)
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The measurement accuracies quoted in this section apply only
to the specific method or to the primary flow device being
discussed. The total error involved in a continuous flow
measurement system, which is the sum of the errors of each
component, is beyond the scope of this discussion. The reader is
referred to the list of references at the end of this chapter for
such a discussion.
(a) Velocity-Area Method
(i) Introduction
The velocity-area method is the established method of
making instantaneous flow measurements in open channels. This
method is particularly useful where the flow is too large to
permit the installation of a primary flow device. It is also
useful for checking the accuracy of an installed primary flow
device or other flow measurement method. The basic principle of
this method is that the flow (Q) in a channel is equal to the
average velocity (V) times the cross-sectional area of the
channel (A) at the point where the average velocity was measured,
i.e., Q = V x A. The velocity of water or wastewater is
determined with a current meter; the area of the channel is
calculated by using an approximation technique in conjunction
witfy a series of velocity measurements.
While the velocity-area method is an instantaneous flow
measurement method, it can be used to develop a continuous flow
measurement system. This is accomplished by making a number of
individual measurements at different flow rates and developing a
-71-
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curve or curves that relate water depth (head) to discharge
(generally referred to as a rating curve). This curve can then
be utilized along with a stage recorder to provide a continuous
flow record.
This method requires some experience and good judgement in-
practice. A complete description of the equipment needed and the
basic measurement methods are given in the references (1, 3, 5).
Before attampting to use current meters or the velocity-area
method, the neophyte investigator should accompany an experienced
field professional during the conduct of several such
measurements.
The accuracy of this method is directly dependent on the
experience of the investigator, the strict adherence to
procedures outlined in the references, and the care and
maintenance of the equipment used. An experienced field
investigator can make flow measurements using current meters that
are accurate within a + 10 percent.
(ii) Current Meters
There are two. types of current meters, rotating element and
electromagnetic. Conventional rotating element current meters
are of two general types—the propeller type with the horizontal
axis as in the Neyrpic, Ott, Hoff, and Haskell meters (Figure VI-
and the cup-type instrument with the vertical axis as in the
Price A-A and Pygmy meters (Figure VI-5).
In comparison with horizontal-axis (propeller) meters, the
vertical axis (cup type) meters have the following advantages:
-72-
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FIGURE VI—4
OTT TYPE HORIZONTAL AXIS CURRENT METER
-73-
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ASSEMBLY
LIST OF PARTS;
CAP FOR CONTACT CHAMBER
CONTACT CHAMBER
INSULATING BUSHING FOR CONTACT BINDING POST
SINGLE-CONTACT BINDIN6 POST
PENTA-CONTACT BINDING POST
PENTA GEAR
SET SCREWS
YOKE
HOLE FOR HANGER SCREW
TAILPIECE
BALANCE WEIGHT
12.	SHAFT
13.	BUCKET-WHEEL HUB
14.	BUCKET-WHEEL HUB NUT
15.	RAISING NUT
16.	PIVOT BEARING
17.	PIVOT
18.	PIVOT ADJUSTING NUT
19.	KEEPER SCREW FOR PIVOT ADJUSTING NUT
20.	BEARING LUG
21.	BUCKET WHEEL
FIGURE VI-5
ASSEMBLY DRAWING OF PRYCE TYPE AA CURRENT METER (10)
-------
(1)	Their threshold velocities are usually
lower;
(2)	The lower pivot bearing operates in an air
pocket, so the likelihood of silt
intrusion is reduced;
(3)	The meter, in particular the Price type,
has earned a reputation for sturdiness an
-------
of the moving parts of the meter, it should be reconditioned and
recalibrated.
(iii) Field Practice
The two principal methods for determining mean velocities in
a vertical section with a current meter are the two-point method
and the six-tenths-depth method. The two-point method consists
of measuring the velocity at 0.2 and then at 0.8 of the depth
from the water surface, and using the average of the two
measurements. The accuracy obtainable with, this method is high
and its use is recommended. The method should not be used where
the depth is less than two feet and should always be used at
depths greater than two and one-half feet.
The six-tenths-depth method consists of measuring the
velocity at 0.6 of the depth from the water surface, and is
generally used for shallow depths where the two-point method is
not applicable.
Current meters should be carefully checked before each
measurement. It is good field practice to periodically check
each current meter against one known to be in calibration^ When,
making a measurement, the cross-section of the stream or Channel
should be divided into vertical sections, such that there will be
no more than 10 percent, and preferably not more than 5 percent,
of the discharge between any two adjacent vertical segments.
This, of course, is possible only in open conduits. When making
measurements through a manhole, it is rarely possible to obtain
more than one section (at the center of the channel, normally).
-76-
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This particular situation can be a significant source of error.
Appropriate velocity measurements are made and the depth is
measured at each vertical in the cross-section by using a current
meter and wading rod or special sounding line and current meter
assembly. Depths and velocities are recorded for each section,
(iv) Area and Flow Calculations
The midsection method and Simpson*s parabolic rule are two
methods for computing flow from current meter measurements. Both
are based on the summation of discharges from each section
measured.
If the two-point method of determining mean velocities is
used, the formula for computing the discharge of an elementary
area by the midsection method is:
V, + V-
(L2 - Lt) * (I3 - L2)
CO
q =
Where
Llr L2, and L3 = distance in feet from the initial point, for any
three consecutive verticals,
d2 = water depth in feet at vertical L2r
Vj and V2 = velocities in feet per second at 0.2 and 0.8 of
the water depth, respectively, at vertical L2, and
q = discharge in cubic feet per second through section
of average depth d2.
-77-
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The formula for computing the discharge for each pair of
elementary areas by Simpson*s parabolic rule is:
a+4b+c
Where	V +4V.+V
i _ a be
q
-r
(5)
3
arb,and c = The water depths in feet at three consecutive
verticals,
V , V , and V = The respective mean velocities in feet per
a b	c
second at these verticals,
L = The distance in feet between the consecutive
verticals (note-this distance is not measured
from the initial point as in equation (4)),
q'= The discharge in cubic feet per second for
the pair of elementary areas.
Typical current meter notes and computations for the
midsection method are shown in Figure VI-6.
(b) Weirs
A weir is an obstruction built across an open channel or in
a pipe flowing partially full over which water flows. The water
usually flows through an opening or notch, but may flow over the
entire weir crest. The theory of flow measurement utilizing
weirs involves the release of potential (static) energy to
kinetic energy. Equations can be derived for weirs of specific
geometry which relate static head to water flow (discharge).
Weirs are generally classified into two general categories: broad
crested and sharp crested.
-78-
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FIGURE VI-6
FIELD NOTES FOR THE MID-SECTION METHOD
* JO JO M M	M	M	.TO	.n
Rirc it—
i>
Dto.
Initial
pobl
Width
Depth
i!
Rrr-
ctu-
tiong
Tin*
m
NC*
aod>
VELOCITY
Adjusted
for her.
anflw or
Am
Diacfauie
At
point
Man
la ver-
tical














0.5
0

-
-
-
-

-
-













2
1.0
l
6
30
\l
1.4
1.4

1.0
1.40













3
1.0
2
2
40
i 2
1.4
LI. 3j

2.0
2.68




8
30
52
1.2
j




4"
1.0
1.5
2
50
55
1.9
3 1.'
'5
1.5
2.63




8
30
43
1.5
1




5
1.0
1.4
6
30
40
1.6
5 l.<
.3
1.4
2.28













6
1.0
1. 3
6
20
60
. 74
I . 7.
-2
1.3
0.96













7
1.0
0.8
6
15
47
.71
1 . 7.
.2
0.8
0.57
o












8
0.5
0

-
-
-
-

-
-


7 n








10.32











cfs








































































































































































.0 .10 ,t» JV	M	M	M	M	.7*
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(i)	Broad Crested Weirs
Broad crested weirs are normally incorporated into hydraulic
projects as overflow structures. However, they can be used to
measure flow. Typical broad crested weir profiles are shown in
Figure VI-7. The equation for a broad crested weir takes the
following form:
Q = C L H 3/2	(6)
Where
Q = discharge
L = length of weir crest
H = head on weir crest, and
C = coefficient dependent on the shape of
the crest and the head.
Values of the coefficient for various shapes of broad
crested weirs are given in hydraulic handbooks (6,7). When these
structures are used to measure wastewater flow, they should be
calibrated using independent flow measurements (refer to
techniques later in chapter). A discharge table based on these
measurements should be prepared for each installation.
(ii)	Sharp Crested weirs
A sharp crested weir is one whose top edge (crest) is thin
or beveled and presents a sharp upstream corner to the water
flow. The water flowing over the weir (the weir nappe) does not
contact any portion of the downstream edge of the weir, but
springs past it. Sharp crested weirs may be constructed in a
wide variety of shapes (Figure VI-8). A great deal of work has
-80-
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FLOW
FLOW
FIGURE VI-7
BROAD-CRESTED WEIR PROFILES (10)
-------
been performed with sharp crested weirs and certain of these
weirs are recognized as primary flow devices. If such weirs are
constructed and installed in accordance with standard criteria,
they can be used in the field without calibration.
The advantages of sharp crested weirs are accuracy and
relatively low cost of fabrication and installation. The
principal disadvantages are maintenance problems if the
wastewater contains corrosive materials, trash or floating
solids. These weirs can also cause undesirable settling of
solids behind the weirs in the quiescent waters of the weir pool.
The nominal accuracy of a standard, properly installed, sharp
crested weirs in good condition, is approximately + five percent
(3,8,9,10).
(1) Standard Sharp Crested Weir Shapes
The most commonly encountered sharp crested weirs are the V-
notch, rectangular, and Cippoletti. Typically, V-notch weirs are
limited to measuring lower flows, while rectangular weirs are
used to measure higher flows. When a rectangular weir is
constructed with sharp crested sides, it is said to be
contracted; when such a weir extends from one side of the channel
to the other, and the smooth sides of the channel form the weir
sides, the weir is said to be suppressed. Cippoletti weirs
combine the features of both the contracted rectangular and V-
notch weirs and are used to measure highly variable flows. These
weirs and their equations are shown in Figure VI-9.
-82-
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RECTANGULAR
2a
TRIANGULAR OR V-NOTCH
2a
TRAPEZOIDAL (INCLUDING
CIPOLLETTI)
2a
INVERTED TRAPEZOIDAL
POEBING
TY
APPROXIMATE EXPONENTIAL

APPROXIMATE LINEAR
PROPORTIONAL OR SUTRO
FIGURE VI-8
SHARP CRESTED WEIR PROFILES (10)
83
-------
0 - 3.33 (L-0.2H)H3/2(CONT.
Q = 3.33 LH3/2 (SUP.)
Q - 3.367 LH3/2
90 - Q = 2.50 H2-50
Q = 2.49 H2-48
60 -Q =1.443 H2-50
45 -Q=1.035H2-50
22.5 - Q = 0.497 H2-50
4:l slope
CIPOLLETTI WEIR
~ X—I
TRIANGULAR OR
V-NOTCH WEIR
L at least 3Hmax
X at least 2Hmax

Max Level 1
«*- X
I JjJmax

1

_iy

L
1 i
X
RECTANGULAR WEIR
i
max
i
FIGURE VI-9
THREE COMMON TYPES OF SHARP CRESTED WEIRS AND THEIR EQUATIONS (15)
-84~
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Occasionally a proportional or "Sutro" weir is encountered
in field installations. These weirs are generally used as
velocity control devices for municipal sewage treatment plant
grit chambers. Flow through these weirs is directly proportional
to the head, and the use of sophisticated flow recording
equipment is not required. This type of weir is not generally
considered to be a primary flow device. The design and
construction of these weirs is given in most standard hydraulic
handbooks. The remaining sharp crested shapes shown in Figure
VI-8 are rarely encountered.
(2)	Standard conditions
The profile of a sharp crested weir is shown on Figure VI-
10, along with the standard sharp crested weir nomenclature.
Table VI-1 summarizes the standard conditions used for the
construction and installation of these weirs.
(3)	Field Inspection
All weirs installed by the investigatory agency or those
installed by the facility being investigated should be checked
for conformance with the standard conditions given in Table VI-1.
It should be noted that the dimensions for placement of the weir
in the flow channel and the point at which the head is measured
are in terms of the maximum head that can be measured for a
particular weir. In actual practice, the maximum head expected
-85-
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TABLE VI-I
STANDARD CONDITIONS FOR SHARP-CRESTED WEIRS
(See Figure VI-10)
1.	The weir should be installed so that it is perpendicular to
the axis of flow. The weir plate should be level. The
sides of rectangular contracted weirs should be truly
vertical. V-notch weir angles must be cut precisely.
2.	The thickness of the weir crest should be less than 0.1
inch. The downstream edges of the crest or notch should be
relieved by chamfering at a 45° angle (or greater) if the
weir plate is thicker.
3.	The distance from the weir crest to the bottom of the
approach channel should not be less than twice the maximum
weir head and never less than one foot. The distance from
the sides of the weir to the sides of the approach channel
should be no less than twice the maximum head and never less
than one foot (except for the suppressed rectangular weir).
4.	The nappe (overflow sheet) should touch only the upstream
edges of the weir crest or notch.
5.	Air should circulate freely under, and on both sides of, the
nappe.
6.	The measurement of head on the weir should be made at-a
point at least four (4) times the maximum head upstream from
the weir crest.
7.	The cross-sectional area of the approach channel should be
at least eight times that of the nappe at the weir crest for
a distance of 15-20 times the maximum head upstream from'the
weir. The approach channel should be straight and uniform ...
upstream from the weir for the same distance.
8.	If the criteria in Items 3 and 7 are not met, the velocity
of approach corrections will have to be made.
9.	Heads less than 0.2 feet (2.4 inches) should not be used
under ordinary field conditions, because the nappe may not
spring free of the crest.
10.	All of the flow must pass through the weir and no leakage at
the weir plate edges or bottom should be present.
-86-
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X = APPROX.
0.1" |JUj JJL.J
i
00
I
POINT TO
MEASURE
DEPTH, H
^ I
20 H
max
STRAIGHT I
INLET RUN
or
SHARP - CRESTED WEIR
1
4!
V
max
disch
level

FIGURE VI-10
SHARP CRESTED WEIR NOMENCLATURE (15)
-------
during the measurement period should be used. Any deviation from
standard conditions should be noted on the field sheet.
Any trash, slime, or debris should fce removed from the weir
crest before proceeding with a flow measurement. The head on a
sharp crested weir can be measured by knowing the depth of the
weir notch from the top of the weir and measuring the head
approximately four times the maximum head upstream using, the top
of the weir as a reference. The head is the difference in these
two measurements. A carpenter's level, straight edge and framing
square are invaluable for making this measurement. An
engineering level and level rod can also be used. The
carpenter's level can also be used to plumb the weir. A
measuring tape is necessary to check the dimensions of weirs.
A problem frequently encountered when using suppressed
rectangular weirs is the lack of ventilation of the weir nappe.
When the weir nappe is not ventilated it will stutter or jump
erratically. In permanent installations, provisions should be
made for a vent to maintain atmospheric pressure behind the
nappe. In field installations, flexible plastic tubing can be
used for this purpose.
The pool upstream of the weir should be quiescent with
approach velocities much less than one foot per second.
Generally, excessive approach velocities are not a problem with
V-notch weirs. However, if all the standard conditions outlined
in Table VI-1 are not met or some other condition is encountered,
it is possible to encounter excessive approach velocities when
-88-
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using rectangular weirs. When approach velocities exceed one
foot per second, a correction should be applied to the observed
measurements. One method of making such a correction is given in
Table VI-2.
(4) Use of Weir Tables
The most convenient method for translating weir head
measurements to flow is a set of weir tables. The use of weir
formulas and curves in the field is not recommended, since this
is a cumbersome procedure and leads to numerous computational
errors. Excellent weir tables are included in the USDI Water
Measurement Manual (1) and the Stevens Water Resources Data Book
(11). The explanatory material accompanying these tables should
be read thoroughly before they are used. In some cases, flow
data are tabulated which are outside the useful range for a
particular weir.
(c) Flumes
Flumes are widely used to measure wastewater flow in open
channels. They are particularly useful for measuring large
flowrates.
(i) Parshall Flumes
The Parshall flume is the most widely used open channel,
primary flow device for wastewater flow measurement. Parshall
flumes are available in a wide range of sizes and flow
capacities", and are available to fit almost any open-channel,
flow measuring application. These flumes operate with relatively
low head loss, are insensitive to the velocity of approach, and
-89-
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TABLE VI-2
SHARP CRESTED RECTANGULAR WEIRS
VELOCITY OF APPROACH CORRECTION
1.	Compute the Velocity of Approach from: V = Q/A
Where: V = Velocity of Approach in feet per second
Q = Discharge in cfs (from weir formula)
A = Cross-sectional area of approach channel
2.	Enter the following table with the velocity of approach (V)
and head (H) and obtain the coefficient (C} from the table:
r
A
h*l*

0.2
0.4
0 6
0.8
1.0
1.5
0.4
0.0025
1). 00112
1.014
1.007
1.004
1.01)4
1.004
1.002
.5
.1)039
.0003
1.027
1 013
1.009
l.OOfi
1 006
1.004
. A
.0051.
.0005
1.037
1 019
1 013
1.009
1 008
1 005
.7
.0076
.01107
1.0SQ
1 020
1.017
1.013
1 on
1.U07
.X
.0099
.0010
1.064
1.033
1.022
1.016
1.014
1 009
.9
.0126
.0014
1.082
1 042
1.029
1.021
1.018
1.012
1.0
. 0155
.0019
1.008
1.051
1 034
1.027
1.022
1.015
1.1
.0188
.0025
1.122
1.062
1 041
1.(131
1.026
1.1117
1.2
.0224
.0(133
1.141
1 072
1.049
1.037
1 031
1 021
1.3
.0203
.0041
1.163
1 084
1.057
1.043
1.036
1.024
1.4
.0.105
.0051
1.186
1.096
1. 0j6
1.050
1.041
1.028
1.5
.0350
.0064
1.208
1 109
1.075
1.057
1.047
1.032
1.6
.0393
. 0079
1.225
1.122
1.084
1 065
1 052
1 035
1.7
.0449
.01)95
1.2M
1.135
1.093
1.071
1.059
1.040
1.8
.0504
.0111
1 277
1.149
1.104
1 080
1.065
1.045
1.9
.0561
.0132
1.308
1.165
1.115
1.089
1.072
1.049
2.0
.0622
.0154
1.335
1.181
1 126
1.097
1.079
1 055
2.1
.0686
. 0t79
1.363
1.197
1.137
1.106
1.087
1.060
2.2
0752
.0206
1.3S1
1.213
1.149
1.118
1.094
1.065
2.3
.0822
.0235
1.420
1.231
1.161
1.124
1.102
1.071
2.4
.0895
.0268
1.449
1.248
1. 176
1.134
1.110
1 077
2. S
.0972
.0303
1. 4SO
1.266
1.187
1.145
1.119
1.083
2.6
.1051
.0340
1.511
1.285
1.200
1.155
1.128
1.088
2.7
.1133
.0381
1.542
1.303
1.213
1.166
1.137
1.095
2.8
.1219
.0426
1.573
1.322
1.223
1.178
1.146
1.100
2.9
. 1307
.0472
1.606
1.341
1.242
1.189
1.155
1.108
3.0
.1399
.0524
1.637
1.361
1.256
1.199
1..165
1.115
//
2.0
1.002
1.003
i m
1.000
1.007
1.009
1.0)1
1.013
1.016
1.018
1.021
1.024
1.027
1.031
I 034
1.038
1.042
1.046
1.050
1.054
1.059
1.063
1.063
1.073
1.078
1.083
1.088
2.5
1.002
1 002
1.003
1.004
1.006
1.007
1.0Q9
1.011
1.013
1.015
1.017
1.019
1.022
1.025
1 027
1.030
1 034
1.037
1.039
1.044
1.047
1.051
1.055
1.059
1.063
1.067
J. 072
3.0
1.001
1 002
j.003
1.01)4
1.005
1.006
1.007
1.009
1.011
1 012
1.014
i.oifi
1.01H
1.021
1.023
1.02a
I 028
1.031
1.034
1.037
1.040
1.043
1.046
1.050
1.053
1.057
1.061
3.5
1.001
1.002
1.002
1.003
1.004
1.00.5
1.000
1.008
1.009
1.011
1.012
1.014
1.016
1.018
1.020
1.022
1.025
1.027
1.029
1.032
1.034
1.-037
1.040
1.043
1.046
1 049
1.053
4.0
1.001
T. 001
1.002
1.003
1.003
1 005
1.005
1.007
1.008
1.009
1.011
1.012
1.014
1.016
1.017
1.019
1.021
I 024
1.026
1.028
1.030
I 033
1.035
1.038
1.041
1.043
1.046
5.0
1.001
1.001
1.002
1.002*
1.003
1.004
1.005
1.006
1.007
1.008
1.010
1.011
1.012
1.014
1.016
1.017
1.019
1.021
1.023
1.025
1.027
1.029-
1.032
1.034
1.036
1.039
1.041
3. The correct flow then = CxQ
For example: V = 1 fps, Q = 6.31 cfs, H = 1 ft,
then C = 1.022 and corrected Q = 1.022 x 6.31 = 6.45 cfs
Note: Method and Table from Water Measurement Manual (1)
-90-
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are self-cleaning in most applications. The accuracy of a
Parshall flume in a good field installation is recognized to be
approximately ~ 5 percent (3,8,9,10)..
(1) Parshall Flume Structure and Nomenclature
A Parshall flume consists of a converging section, throat
section, and diverging section, as shown in Figure VI-11. The
size of the flume is determined by the width of the throat
section. All dimensions for various Parshall flume sizes are
given in the USDI Water Measurement Manual (1). Tolerances for
Parshall flume dimensions, as given by this manual, are + 1/64
inch for the throat width and ~ 1/32 for the. remaining sections.
The head (Ha) is measured at the point 2/3 of the length of
the converging section (wingwall), upstream from the throat
section. During conditions of free-flow, this is the only
measurement required to determine flow. Occasionally, back water
exists which causes some flooding of the diverging section of the
flume. In those cases, it is necessary to check the head at an
additional location (Hb) between the throat and diverging
sections as shown in Figure VI-11. The ratio of the measured
heads (Hb/Ha) is known as the submergence. Flumes can be used to
accurately measure flow without correction until the following
limits are reached for each indicated size of flume:
-91-
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NOTE: 7.6cm (3in) TO 2.4m (8 ft) FLUMES HAVE
hi~

t
-F —
T
s
" ll
i i' ii ^
FLOW
ll H

CREST
I
,	M	H
.	II	II
f	H	|| LEVEL FLOOR „
Vvl"Xl"X 1/8"
ANGLE
SECTION L-L
— G —
¦| SUBMERGED
l|^ FLOW
-FREE FLOW
ANGLE
LEGEND:
H	Size of flume, 1n Inches or feet.
A	Length of side wall of converging section.
2/3A Distance back from end of crest to gage point.
B	Axial length of converging section.
C	Width of downstream end of flume.
D	Width of upstream end of flume.
E	Depth of flume.
F	Length of throat.
G	Length of diverging section.
K	Difference 1n elevation between lower end of flume and crest.
N	Depth of depression 1n throat below crest.
R	Radius of curved wing wall.
H	Length of approach floor.
P	Width between ends of curved wing walls.
X	Horizontal distance to Hb gage point from low point 1n throat.
Y	Vertical distance to gage point from low point in throat.
FIGURE VI-11
CONFIGURATION AND STANDARD NOMENCLATURE FOR PARSHALL FLUME (10)
-92-
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Hb/Ha (X)
50
lr 2, 3 inches
Flume Size
60
6, 9 inches
70
1-8 feet
80
8-50 feet
When the submergence exceeds 95 JS, the flume is not usable
for flow measurement purposes. A detailed description of
Manual (1) .
Although the Parshall flume is relatively insensitive to
approach velocities, influent flow should be evenly distributed
across the channel as it enters the converging section. These
flumes should not be installed immediately downstream from
transition sections in order to assure such an even distribution.
As a practical matter, a uniform channel should be provided
upstream from the flume as far as is practical. A minimum
distance of 15-20 channel widths or pipe diameters is
recommended.
During compliance sampling inspections, flumes should be
inspected to determine if entrance conditions provide a uniform
influent flow distribution, the flume dimensions conform to those
given in the OSDI Water Measurement Manual (1) , the flume
converging throat section flow is level, and the throat.section
walls are vertical. Useful tools for checking Parshall flumes
include a carpenter's level, framing square and tape. The. flume ,
submergence corrections is given in the USDI Water Measurement
(2) Field Inspection and Flow Measurement
-93-
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should be closely examined to determine if it is discharging
freely. If there is any question about free discharge, the
downstream head (Hb) should be measured. A staff gage is useful
for making head measurements. Any problems observed during the
inspection should be noted on the field sheet.
A set of flume tables is necessary for calculating flows.
Both the USDI Water Mea surement Manual (1) and the Stevens Water
Resources Data Book (11) contain a complete set of tables. The
explanatory material accompanying these tables should be: read and
understood before they are used. In many cases, tabulated flow
values are given for measured heads that are not within the
usable measurement range.
The most frequently encountered problems with facility
installed flumes include:
•	Poor entrance and exit hydraulics that cause poor flow
distribution or submergence,
•	Improper installation, out of level, throat sidewalls
not vertical, improper throat dimensions, or
•	Improper location of head measuring points,
(ii) Palmer-Bowlus Flumes
Palmer-Bowlus flumes depend upon existing conduit slopes and
a channel contraction (provided by the flume) to produce
supercritical flow. Several different shapes of this flume ar£
in use and are shown in Figure VI-12. These flumes are beinig"
increasingly used as primary flow devices for measuring flow in
circular conduits. Their principal advantage lies in simplicity
-91-
-------
Longitudinal mid sections
Vertical
Horizontal
VS/SS/SS/s)
T

WAVYfo
t
I i mi ^7A4Kf&C(7* nr
FIGURE VI - 12
VARIOUS CROSS - SECTIONAL SHAPES OF PALMER-
BOWLUS FLUMES (15)
-95^
-------
of construction and ease of installation through manholes. There
is a paucity of data on the accuracy of this flume, although one
reference reports that the performance of these flumes can be
theoretically predicted to within 3 percent when used in U-shaped
channels, so long as the upstream depth does not exceed 0.9D
(where D is the diameter of the circular conduit leading into the
flume) (3). A complete description of the theory of these flumes
and their use is given in the references (3,10,12).
(iii) Other Flumes
A number of other flumes have been developed to solve
specific flow measurement problems, including cutthroat,
trapezoidal with bottom slope, critical depth, H, etc.
(1,3,9,10). These flumes are seldom used for wastewater flov$
measurement purposes.
(d) Open Channel Flow Nozzles
The open channel flow nozzle is a combination of flume and
sharp crested weir. Unlike sharp crested weirs, these devices
operate well with wastewaters that contain high concentrations of
suspended solids; however, they have poor head recovery
characteristics. These devices are designed to be attached to
the end of a conduit, flowing partially full, and must have a
free fall discharge. Open channel flow nozzles are designed so
there is a predetermined relationship between the depth of liquid
within the nozzle and the flowrate. The Kennison nozzle has a
cross-sectional shape such that the relationship between the
flowrate and head is linear. These nozzles require a length of
-96-
-------
straight conduit immediately upstream from the nozzle, and the
slope of the conduit must be within the limits of the nozzle
calibration specifications. The profile of a parabolic and a
Kennison type open flow nozzle is shown in Figure VI-13.
Open flow nozzles are factory calibrated and are ordinarily
supplied as part of a flow measurement system. Calibration and
installation data for each nozzle should be supplied by/or
obtained from the manufacturer. The accuracy of these devices is
reported to be often better than + 5 percent of the indicated
flow (10).
(e) Slope - Area Method
The slope-area method consists of using the slope of the
water surface, in a uniform reach of channel, and the average
cross-sectional area of that reach, to estimate the flowrate of
an open channel. The flowrate is estimated from the Manning
formula:
Q
1.486/n AR2/3S»/2
(7)
Where
Q = discharge in cfs
A = average area of the wetted channel
cross-section in square feet
R = average hydraulic radius of the wetted
channel in feet. (Average cross-
sectional area divided by
the average wetted perimeter.)
S
slope of the water surface, and
-97-
-------
a. Linear (Kennison) Nozzle Profile (Q * H)
b. Parabolic Nozzle Profile (Q H^)
FIGURE VI-13
OPEN CHANNEL FLOW NOZZLE PROFILES (10)
-98-
-------
n = a roughness factor depending on
the character of the channel lining.
A long straight section of channel should be used for this
estimation technique. Values of n may be obtained from hydraulic
handbooks (6,7). It should be remembered that the slope in the
equation is of the water surface and not the channel invert,
(f) Measurement by Floats
A crude but simple method of estimating flow in an open
channel is by using floats. A straight reach of channel with
uniform slope is necessary for this method. Three cross-sections
are used. The purpose of the middle section is to provide a
check on the velocity measurements between the beginning and end
sections. The velocity is obtained by measuring the length of
the reach and timing the passage of the float with a stopwatch.
The flowrate is obtained by multiplying the resulting velocity by
the average cross-sectional area of the section of channel used.
Since surface velocities are higher than the average velocity of
the channel, the velocities obtained by the float method should
be corrected using the empirical factors presented in the USDI
Water Measurement Manual(1).
U. Closed Conduit Flow Me a sure me nt s
Closed conduit flow measurement systems present a special
challenge to the field investigator. These systems, once
installed, generally cannot be visually inspected, nor can the
-99-
-------
hydraulic responses of the systems be as easily evaluated as is
the case with most open channel systems. One procedure for
verifying the accuracy of closed conduit flow measurement systems
in the field is to make an independent flow measurement at an
acceptable location. The constant injection dilution technique,
or the velocity area method, both of which were described earlier
in this section, would be acceptable for this purpose. Another
procedure includes inducing known pressures or voltages on the
sensing system and verifying recorder response.
Some of the most commonly used closed conduit primary flow
devices are presented and discussed briefly in this section.
Several flow estimation techniques are also presented. The
measurement accuracies quoted in this section apply only to the
specific method or to the primary flow device being discussed.
The total error involved in continuous flow measurement systems,
which is the sum of the errors of each component, is beyond the
scope of this discussion. The reader is referred to the list of
references at the end of this chapter for such a discussion.
(a) Venturi Meter
The Venturi meter is one of the most accurate primary flow
devices for measuring flowrates in pipes. Basically, the Venturi
meter is a pipe segment (Figure VI-14) consisting of a converging
section, a throat and a diverging section. A portion of the
static head is converted in the throat section to velocity head.
Thus, the static head in the throat of the Venturi is lower than
in the converging section. This head differential is
-100-
-------
proportional to the flowrate. One of the advantages of the
Venturi meter is that it has a low head loss.
The meter must be installed downstream from a straight and
uniform section of pipe, at least 5-20 pipe diameters, depending
upon the pipe diameter to throat diameter ratio. The accuracy of
the Venturi is affected by changes in density, temperature,
pressure, viscosity, and by pulsating flow. When used to measure
flow in wastestreams containing high concentrations of suspended
solids, special provisions must be made to insure that the
pressure measuring taps are not plugged. The typical accuracy of
Venturi meters is given at 1 to 2 percent (3,8,10).
There are a number of variations of the Venturi meter,
generally called flow tubes, presently being used (10). Their
principle of operation is similar to that of the Venturi, and
they will not be discussed.
(b) Orifice Meters
The Orifice meter is one of the oldest flow measuring
devices. Flow is measured by the difference in static head
caused by the presence of the orifice plate. The differential
pressure is related to the flowrate. The thin plate orifice is
the most common variety, and consists of a round hole in.a thin
plate, which is generally clamped between a pair of flanges ^t a
point in a pipe. The most common orifice plate consists of a
sharp 90-degree corner on the downstream edge. Some orifice
plates have a rounded edge facing into the direction of flow, and
perhaps a short tube with the same diameter as the orifice
-101-
-------
FIGURE VI - 14
VENTURI METER (15)
-------
opening facing downstream. Pressure measuring taps are located
upstream and downstream of the orifice plate to facilitate
differential pressure measurements. Only one pressure tap is
required if the orifice plate is located at the end of a pipe
discharging at atmospheric pressure.
Orifice meters are of limited usefulness in measuring
flowrates in wastestreams containing high suspended solids, since
solids tend to accumulate upstream of the orifice plate. Orifice
meters produce the highest head loss of any of the closed conduit
flow devices, and are quite sensitive to upstream disturbances.
It is not uncommon to need from ^0 to 60 pipe diameters of
straight pipe upstream of the installation. They can be quite
accurate, 0.5*, although their usable range is small (5:1) unless
rated in place (10).
(c) Flow Nozzles
A flow nozzle may consist of designs that approach the
Venturi meter in one extreme and the orifice meter in the other.
The basic principle of operation is the same as that of the
Venturi meter. Typically, a flow nozzle has an entrance section
and a throat, but lacks the diverging section of the Venturi (a
typical flow nozzle is shown in Figure VI-15). A major advantage
of the flow nozzle over the Venturi meter is that the flow nozzle
can be installed between pipe flanges. They are intermediate in
head loss between the Venturi and orifice meters. Like orifice
meters, they are sensitive to upstream disturbances and 20 or
more pipe diameters of straight pipe are required upstream from
-103-
-------
HIGH
PRESSURE TAP
LOW PRESSURE TAP
ENTRANCE
CONE ~
THROAT
FIGURE VI-15
FLOW NOZZLE IN PIPE (10)
-------
the flow nozzle for successful operation. Some flow nozzles are
not recommended for use in measuring flowrates in high suspended
solids wastestreams. Flow nozzle accuracies can approach those
of Venturi meters (10).
(d)	Electromagnetic Flowmeter
The electromagnetic flowmeter operates according to
Faraday's Law of Induction. Namely, the voltage induced by a
conductor moving at right angles through a magnetic field will be
proportional to the velocity of the conductor through the field.
In the electromagnetic flowmeter, the conductor is the liquid
stream to be measured and the field is produced by a set of
electromagnetic coils. A typical cross-section of an
electromagnetic flowmeter is shown in Figure VI-16. The induced
voltage is subsequently transmitted to a converter for signal
conditioning.
Electromagnetic flowmeters have many advantages; they are
very accurate (within ~ 1 percent of full scale), have a wide
flow measurement range, introduce a negligible head loss, have no
moving parts, and the response time is rapid (10). However, they
are expensive. Buildup of grease deposits or pitting by abrasive
wastewaters can cause error. Regular checking and cleaning of
the electrodes is necessary.
(e)	Acoustic Flowmeters
Acoustic flowmeters operate on the basis of the difference
in transit time between upstream and downstream directed sonic
pulses. The difference in transit time is caused by the velocity
-105-
-------

INSULATING
LINER
ELECTRODE
ASSEMBLY
MAGNET COILS
POTTING COMPOUND
STEEL METER
BODY
FIGURE VI - 16
ELECTROMAGNETIC FLOW METER (15)
-106-
-------
of the water in the conduit. This time lag is proportional to
the velocity, and hence the flowrate. Manufacturers employ
various methods to take advantage of this principle. Some
flowmeters use the acoustic doppler principle. According to the
manufacturers, accuracies of one percent of full scale are
achievable (3,10).
(f) Trajectory Methods
A. number of methods for estimating the flowrate from the end
of a pipe with a free discharge are available. All of these
methods, whether theoretically or empirically derived, have in
common the measurement of the issuing stream coordinates (Figure
VI-17) in the vertical and horizontal directions. It should be
emphasized that all of these methods are estimates—none of them
is accurate enough for NPDES compliance purposes.
The California pipe method (Figure VI-17) uses a straight
level section of pipe at least six pipe diameters in length as
the primary flow device. The pipe must have a free discharge and
must be only partially full. The distance from the crown of the
pipe to the water surface (a) at the end of the pipe is related
to the flowrate by the following equation:
Q = 8.69 (1-a/d)	d*.««	(8)
Where
Q = flowrate in cfs
d = diameter of pipe in feet
-107-
-------
a. CALIFORNIA PIPE METHOD
FIGURE VI-17
TRAJECTORY METHODS (10)
-108-
-------
It is recommended that a/d be restricted to values greater than
0.5. The experiments from which the above equation was derived
used pipe diameters of from 3 to 10 inches (1,3,10).
The Purdue method involves the measurement of the horizontal
(x) and the vertical (y) coordinates of the issuing stream at the
end of a pipe, and the use of a set of curves that empirically
relate these coordinates to the discharge. Curves for pipes 2,
3, 4, 5r and 6 inches are available (1,3).
If the water jet is treated as a freely falling body with
constant horizontal velocity, the following equation results (3):
Q = A(g/2y) o.s x	(9)
Where
Q = flowrate in cfs
A = cross-sectional area of the issuing stream
X & Y = horizontal and vertical trajectory coordinates
measured as shown in Figure VI-17
(g) Pump Curves
Pump curves, supplied by pump manufacturers, have been used
extensively to estimate flows in closed conduits. Where pumps
are operated on a cyclic basis, a timer hooked to a pump gives an
estimate of the total flow. However, there are so many variables
present in pump and piping installations that it is likely that
most pump curves are not accurate enough for NPDES compliance
purposes. When pump curves are used for NPDES compliance
wastewater flow measurements, these curves should be verified by
making an independent flow measurement.
-109-
-------
(h) Use of Water Meters
Municipal and process water meters have been used to
estimate industrial wastewater flows when all other methods have
failed or are not usable. The use of water meters should be
viewed with caution. All consumptive uses of water must be
accounted for and subtracted from the meter readings. Also,
water meters are often poorly maintained and their accuracy is
questionable, when water meters have to be used, the
municipality or utility that has responsibility for the meters
should be consulted as to when the meters were last serviced or
calibrated.
-110-
-------
REFERENCES - SECTION VI
1.	"Water Measurement Manual", Second edition, revised. United
States Department of Interior, Bureau of Reclamation, 1974.
Available from the U.S. Government Printing Office,
Washington, D.C. 20402.
2.	Smoot, C. W., "Orifice Bucket for Measurement of Small
Discharges from wells", Water Resources Division Bulletin,
Illinois Water Survey, Champaign, Illinois, November 1963.
3.	"A Guide to Methods and Standards for the Measurement of
Water Flow", U.S. Department of Commerce, National Bureau of
Standards, NBS Special Publication 121, May 1975.
4.	"Fluorometric Facts, Flow Measurements", Monograph, 1976.
Available from the Turner Designs Company, 224 7A Old
Middlefield Way, Mountainview, California 94043.
5.	"Discharge Measurements at Gaging Stations", Hydraulic
Measurement and Computation, Book I, Chapter 11, United
Stated Department of Interior, Geological Survey, 1965.
6.	King, H. W., and Brater, E. F., "Handbook of Hydraulics",
Fifth Edition, McGraw-Hill, New York (1963).
7.	Davis, C. V., and Sorenson, K. E., "Handbook of Applied
Hydraulics", Third Edition, McGraw-Hill, New York (1969).
8.	American Society of Testing Materials, "1976 Annual Book of
ASTM Standards", Part 31 - Water, American Society of
Testing Materials, 1916 Rose Street, Philadelphia,
Pennsylvania 19103.
9.	"Use of Weirs and Flumes in Stream Gaging", Technical Note
No. 117, World Meteorological Organization, Technical Note
No.117, United Nations, New York, N.Y. 1971.
10.	"Sewer Flow Measurement A State-Of-The-Art Assessment",
Municipal Environmental Research Laboratory, Office of
Research and Development, U.S. Environmental Protection
Agency, Cincinnati, Ohio 45268.
11.	"Stevens Water Resource Data Book", Second Edition, Leopold
Stevens, Inc., P.O. Box 688, Beaverton, Oregon.
12.	Wells, E.A. and Gotaas, H.B., "Design of Venturi Flumes in
Circular Conduits", American Society of Civil Engineers, 8 2,
Proc. Paper 928, April 1956.
-111-
-------
13.	"Fluid Meters--Their Theory and Application", Sixth Edition,
1971, American Society of Mechanical Engineers, New York,
N.Y.
14.	"Field Manual for Research in Agricultural Hydrology",
Agricultural Handbook No. 224, Soil and Water Conservation
Research Division, Agricultural Research Service, United
States Department of Agriculture, Washington, D.C. 20402.
15.	"Handbook for Monitoring Industrial Wastewater", Technology
Transfer Publication, United States Environmental Protection
Agency, 1973.
-112-
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Form Approved
OMB No. 15B-R0073
NPDES COMPLIANCE INSPECTION REPORT (Coding Instructions on back of last page)
TRANSACTION
CODE
NPDES
u l=J
_J	2_
JLL
INSPEC-	FAC
YR MO OA TYPE TOH	TYPE
I I I I I I I u u	u
J2	17 1ft 19	20
TIME
I p.m.
REMARKS
LLl
2J	
I I I I

£5_
70
ADDITIONAL
SECTION A - Permit Summary
NAME AND ADDRESS OF FACILITY jInclude County, State and ZIP code)
EXPIRATION DATE
ISSUANCE DATE
RESPONSIBLE OFFICIAL
TITLE
PHONE
FACILITY REPRESENTATIVE
TITLE
PHONE
SECTION B ¦ Effluent Characteristics (Additional sheets attached .
PARAMETER/
OUTFALL
MINIMUM
AVERAGE
MAXIMUM
ADDITIONAL
SAMPLE
MEASUREMENT
PERMIT
REQUIREMENT
SAMPLE
MEASUREMENT
PERMIT
REQUIREMENT
SAMPLE
MEASUREMENT
PERMIT
REQUIREMENT
SAMPLE
MEASUREMENT
PERMIT
REQUIREMENT
SAMPLE
MEASUREMENT
PERMIT
REQUIREMENT
¦SECTION C - Facility Evaluation (S= Satisfactory, U - Unsatisfactory, N/A = Not applicable)

EFFLUENT WITHIN PERMIT REQUIREMENTS

OPERATION AND MAINTENANCE

SAMPLING PROCEDURES

RECORDS AND REPORTS

COMPLIANCE SCHEDULE

LABORATORY PRACTICES

PERMIT VERIFICATION

FLOW MEASUREMENTS

OTHER:
fe
ECTION D • Comments
ECTION E - Inspection/Review
• SttFORCI«**t«T .
MVWO*
uoeomly
SIGNATURES
AGENCY
DATE
INSPECTED BY


C0MP1IAWKJE atATUft
~ COIlM'UANCE
0 fcQNCOWf AMC* ¦
INSPECTED BY


REVIEWED BY


PA FORM 3560-3 (9-77)
REPLACES EPA FORM T-51 (9-76) WHICH IS OBSOLETE.
PAGE 1 OF 4
-------
Form Approved
OMB No. I58-R0073
Sections F thru L: Complete on all inspections, as appropriate. N/A = Not Applicable
SECTION F - Facility and Permit Background
PERMIT NO.
ADDRESS OF PERMITTEE IF DIFFERENT FROM FACILITY
{Including City, County and ZIP code)
DATE OF LAST PREVIOUS INVESTIGATION BY EPA/STATE
FINDINGS
SECTION G - Records and Reports
records and reports maintained as REQUIRED by permit. Dyes Dno ~ N/A (Further explanation attached _
)
DETAILS-





(a) ADEQUATE RECORDS MAINTAINED OF:
(i) SAMPLING DATE, TIME, EXACT LOCATION
~
YES
~
NO
~ n/a
(ii) ANALYSES DATES, TIMES
~
YES
~
NO
~ n/a
(ii|) INDIVIDUAL PERFORMING ANALYSIS
~
YES
~ NO
~ n/a
(iv) ANALYTICAL METHODS/TECHNIQUES USED
~
YES
~
NO
~ n/a
(v) ANALYTICAL RESULTS {e.g., consistent with self-monitoring report data)
~
YES
~
NO
~ n/a
(b) MONITORING RECORDS (e.g.,flow, pH, D.O., etc.) MAINTAINED FOR A MINIMUM OF THREE YEARS





including all origi nal strip CHART RECORDINGS (e.g. continuous monitoring instrumentation,





calibration and maintenance records).
~
YES
~
NO
~ n/a
(c) LAB EQUIPMENT CALIBRATION AND MAINTENANCE RECORDS KEPT.
~
YES
~
NO
~ n/a
(d) FACILITY OPERATING RECORDS KEPT INCLUDING OPERATING LOGS FOR EACH TREATMENT UNIT.
~
YES
~
NO
~ n/a
(e) QUALITY ASSURANCE RECORDS KEPT.
~
YES
~
NO
~ n/a
(f) records maintained OF MAJOR CONTRIBUTING INDUSTRIES (and their compliance status) USING




~ N/A
PUBLICLY OWNED TREATMENT WORKS.
u
YES
u
NO
SECTION H - Permit Verification
INSPECTION OBSERVATIONS VERIFY the PERMIT. Dyes ~ NO ~ N/A (Further explanation attached

)

DETAILS:





(a) CORRECT NAME AND MAILING ADDRESS OF PERMITTEE.
~
YES
~
NO
~ N/A
(b) FACILITY IS AS DESCRIBED IN PERMIT.
~
YES
~
NO
~ n/a
(c) PRINCIPAL PRODUCT(S) AND PRODUCTION RATES CONFORM WITH THOSE SET FORTH IN PERMIT





APPLICATION.
~
YES
~
NO
~ n/a
(d) TREATMENT PROCESSES ARE AS DESCRIBED IN PERMIT APPLICATION.
~
YES
~
NO
~ n/a
(e) NOTIFICATION GIVEN TO EPA/STATE OF NEW, DIFFERENT OR INCREASED DISCHARGES.
~
YES
~
NO
~ n/a
(f) ACCURATE RECORDS OF RAW WATER VOLUME MAINTAINED.
~
YES
~
NO
~ n/a
(g) NUMBER AND LOCATION OF DISCHARGE POINTS ARE AS DESCRIBED IN PERMIT.
~
YES
~
NO
~ n/a
-------
Form Approved
OMB No. 158-R0073

>ERMIT NO.
1


SECTION J - Compliance Schedule)
PERMITTEE IS MEETING COMPLIANCE SCHEDULE. DYES DnO ~ N/A (Further explanation attached

— V
CHECK APPROPRIATE PHASE(S)'





~ (a) THE PERMITTEE HAS OBTAINED THE NECESSARY APPROVALS FROM THE APPROPRIATE
AUTHORITIES TO BEGIN CONSTRUCTION.





~ (b) PROPER ARRANGEMENT HAS BEEN MADE FOR FINANCING (mortgage commitments, grants, etc.).




~ (c) CONTRACTS FOR ENGINEERING SERVICES HAVE BEEN EXECUTED.





~ (d) DESIGN PLANS AND SPECIFICATIONS HAVE BEEN COMPLETED.





~ (el CONSTRUCTION HAS COMMENCED.





~ (f) CONSTRUCTION AND/OR EQUIPMENT ACQUISITION IS ON SCHEDULE.





~ (g) CONSTRUCTION HAS BEEN COMPLETED.





~ (h) START-UP HAS COMMENCED.





~ (i) THE PERMITTEE HAS REQUESTED AN EXTENSION OF TIME.





SECTION K - Self-Monitoring Program
Part 1 - Flow measurement (Further explanation attached 	J





PERMITTEE FLOW MEASUREMENT MEETS THE REQUIREMENTS AND INTENT OF THE PERMIT.
DETAILS.
~
YES
~
NO
~ N/A
(a) PRIMARY MEASURING DEVICE PROPERLY INSTALLED.
~
YES
~
NO
~ N/A
TYPE OF DEVICE: DwEIR ~ PARSHALL FLUME DmaGMETER ~ VENTUR1 METER ~ OTHER (Specify^

)
(b> CALIBRATION FREQUENCY ADEQUATE. (Date of last calibration 1
~
YES
~
NO
~ n/a
(c) PRIMARY FLOW MEASURING DEVICE PROPERLY OPERATED AND MAINTAINED.
~
YES
~
NO
~ n/a
(d)SECONDARY INSTRUMENTS (totalizers, recorders, etc.) PROPERLY OPERATED AND MAINTAINED.
~
YES
~
NO
~ n/a
(e) FLOW MEASUREMENT EQUIPMENT ADEQUATE TO HANDLE EXPECTED RANGES OF FLOW RATES.
~
YES
~
NO
~ n/a
Part ~> — Sampling (Ftirthpr pxplnnafirw nttarhpd 1





PERMITTEE SAMPLING MEETS THE REQUIREMENTS AND INTENT OF THE PERMIT.
~
YES
~
NO
~ n/a
DETAILS-





(a) LOCATIONS ADEQUATE FOR REPRESENTATIVE SAMPLES.
~
YES
~
NO
~ n/a
(b> PARAMETERS AND SAMPLING FREQUENCY AGREE WITH PERMIT.
~
YES
~
NO
~ n/a
(c) PERMITTEE IS USING METHOD OF SAMPLE COLLECTION REQUIRED BY PERMIT.
IF NO. DgRAB ^MANUAL COMPOSITE ~ AUTOMATIC COMPOSITE FREQUENCY
~
YES
~
NO
~ n/a
(d) SAMPLE COLLECTION PROCEDURES ARE ADEQUATE.
~
YES
~
NO
~ n/a
(i) SAMPLES REFRIGERATED DURING COMPOSITING
~ yes
~ NO
~ n/a
(it) PROPER PRESERVATION TECHNIQUES USED
~
YES
~
NO
~ n/a
(iii) FLOW PROPORTIONED SAMPLES OBTAINED WHERE REQUIRED BY PERMIT
~
YES
~
NO
~ n/a
(iv) SAMPLE HOLDING TIMES PRIOR TO ANALYSES IN CONFORMANCE WITH 40 CFR 136.3
~
YES
~
NO
~ n/a
(e) MONITORING AND ANALYSES BEING PERFORMED MORE FREQUENTLY THAN REQUIRED BY
PERMIT
~
YES
~
NO
~ n/a
If) IF 
-------
Form Approved
OMB No 158-R0073
PERMIT NO.
SECTION L ¦ Effluent/Receiving Water Observations (Further explanation attached	)
outfall no.
OIL SHEEN
GREASE
TURBIDITY
VISIBLE
FOAM
VISIBLE
FLOAT SOL
COLOR
OTHER
















































(Sections M and N: Complete as appropriate for sampling inspections)
SECTION M - Sampling Inspection Procedures and Observations (Further explanation attached	)
~	GRAB SAMPLES OBTAINED
~	COMPOSITE OBTAINED
~	FLOW PROPORTIONED SAMPLE
~	AUTOMATIC SAMPLER USED
~	SAMPLE SPLIT WITH PERMITTEE
~	CHAIN OF CUSTODY EMPLOYED
~	SAMPLE OBTAINED FROM FACILITY SAMPLING DEVICE
COMPOSITING FREQUENCY 	 PRESERVATION
SAMPLE REFRIGERATED DURING COMPOSITING: ~ YES DnO
SAMPLE REPRESENTATIVE OF VOLUME AND NATURE OF DISCHARGE	
SECTION N - Analytical Results (Attach report if necessary)
EPA Form 3560-3 (9-77)
PAGE 4 OF 4
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Instructions
for Completion of the
NPDES Compliance Inspection Report
(EPA Form 3550-3)
Overview
The intent of the NPDES Compliance Inspection Report
form is to provide standard, reviewable information about an
inspection to Enforcement. All inspections will be conducted
and all reports will be completed as if they may lead to
enforcement action. The form defines the minimum amount of
information that Enforcement should receive. Regional and
State inspectors may elect to include additional information,
as the circumstances warrant.
Both Compliance Evaluation Inspections (CEIs) and
Compliance Sampling Inspections (CSIs) of municipal and non-
municipal facilities will be conducted using the same type
of Compliance Inspection Report form (EPA Form 3560-3).
Using the same form and format will minimize the reporting
burden on inspectors and permittees because identical elements
of compliance (e.g., permittee records and self-monitoring
program, etc.) are examined in both CEIs and CSIs. Although
the form may be used for either inspection, a completed form
will be credited in only one category of the Formal Program
Reporting System (FPRS). A completed form contains all the
information appropriate to the accomplished inspection. A
completed form is, by definition, also what will be accepted
by the Enforcement Director of the agency responsible for
enforcing the permit. Procedures for the distribution of
the completed form should be planned with the Enforcement
Director. Users should note that the top of page 1 serves
as a coding sheet for entries into the Water Enforcement
National Data Base (WENDB).
The Compliance Inspection Report consists of two major
parts. The first part, sections A-L, is completed for all
inspections, as appropriate. The second part, sections
M-N, is completed only for CSIs. For the checklists,
•sections G through K, each lead statement will summarize
deficiencies covered in the section. Each item in the
checklist (except Section I items (n) & (o)) is written so
that a "yes" answer is positive, indicating some degtee of
permit compliance. If there are no problems in a section,
all the answers will be yes (with the exceptions noted
above).
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Throughout the form, numerous opportunities exist to
attach additional explanations. These explanations should
be attached only when necessary. Although a narrative is
not appropriate when a simple yes, no, or N/A will do,
inspectors must adequately document their observations.
However, lengthy narratives will defeat the purpose of the
checklists. Nonetheless, if further explanation is deemed
necessary, it should be attached and noted on the form.
A brief review of each section follows. For further
explanation of Compliance Inspections, consult the appro-
priate manuals. (NPDES Compliance Evaluation Inspection
Manual - U.S. EPA, Office of Water Enforcement ar.d NPDSS
Compliance Sampling Manual - U.S. EPA, Office of Water
Enforcement).
Keypunch Summary
This lead information is used to identify the facility
and the inspection date, type and agency. The data can be
keypunched on one card and entered directly into the Water
Enforcement National Data Base (WENDB). Entries in WEND3
will assist tracking of inspection results and will be usee
for reporting in FPRS. To be part of the WENDS, the data
should be reported as follows:
Column 1	Transaction Code - Use N, C, or D for
New, Change or Delete. All inspections
will be new unless there is an error in
the data keypunched into KEND3.
Column 2	Card Code - always 5 for this card.
Columns 3-11
Columns 12-17
NPDES - The NPDES permit number. (The
State permit number may be accommodated
in the remarks or additional spaces).
Inspection Date - entered in the year/
month/day format (e.g. 77/06/30 = June
1977).
Column 18
Inspection Type - An inspection will
fall into one of two possible categories
•C' for Compliance Evaluation or 'S* for
Compliance Sampling.
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Column 19	Inspector Code - P.n inspection may be
performed by the Region, State or NEIC
(U.S. EPA National Enforcement Investi-
gations Center). It may also be the
result of a joint effort. (Credit in
FPR5 for a joint inspection is given to
th$ lead agency.) Acceptable codes for
WEND3 are: •
R - EPA Regional inspections
S - State inspections
J - Joint EI"A and State inspections -
EPA lead
T - Joint EPA and State inspections -
State lead
N - NEIC inspections
Column 20	Facility Type - This code describes the
type of facility that was inspected.
Acceptable codes ^re:
1	- Municipal - Publicly-Owned Treat-
ment Works (POTWs) with 1972 Standard
Industrial Classification (SIC) 4952
2	- Industrial - Other than Municipal,
Agricultviral, and Federal facilities.
3	- Agricultural - Those facilities
classified with 1972 SIC Olli-0971.
4	- Federal - Those facilities identi-
fied as Federal by EPA Regional
officq.
Columns 21-70 Remarks - This remarks field provides
the inspector with a vehicle to store
descriptive information about the in-
spection. There is no set format within
this 50-pqsition field. Individual
Regions or States may choose to set
aside portions of this field for their
own specific needs.
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The "Tine" and "Additional" boxes can also describe th
inspection, but will not be keypunched. Supplementary in-
formation that the performing agency or Region needs may be
entered in the Additional box, e.g., STORET numbers, basin
codes, etc.
Section A - Permit Summary
This section provides the summary information required
to further identify the inspected facility. Most of the
elements are self explanatory; however, the last two lines
iaay require explanation. "Responsible Official" is the
individual required to sign the Discharge Monitoring Report
or is responsible for wastewater management at the facility.
"Facility Representative" is the individual who acted as a
contact during the inspection.
Section B - Effluent Characteristics
Effluent Characteristics contains a.summary, of those
parameters (e.g. BOD, pH, flow) that are regulated by the
permit and any other parameters that are measured but not
regulated by the permit. If more than one outfall is
inspected, the parameter and outfall should be indicated and
additional sheets attached as required. If the inspection
will not include samples, it may be advisable, but is not
.required, to substitute the data from the latest Discharge
Monitoring Report in the "Sample Measurement" row before
performing the inspection. However, if self-monitoring data
are entered in the spots for sampling data, they should be
clearly identified as such to avoid confusing the reviewer.
The column marked "Additional" is for the performing agency's
or Region's own requirements, e.g., design data, comments or
explanations of the measurements.
Section C - Facility Evaluation
The Facility Evaluation provides a summary evaluation
of the inspection results. The evaluations made in this
section should be documented and supported by notation in
the appropriate checklist portions of the form and by any
additional comments as required. .
Section D - Comments
Little space is allowed for comments here. Rather than
fragmenting the narrative detailing comments and possible
recommendations, the form allows detailed comments in an
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attachment, on the back of the form, or in Section H. The
Section D comments should be used to flag lengthy comments
(e.g. "Recommendations on p.4") or used for those inspections
which only merit abbreviated comments. Procedures for
making recommendations and comments should be worked out
with the Enforcement Director of the organization responsible
• for the permit. All comments or recommendations that are
made should.be documented and supported by the checklist
portions of the form.
Section E - Inspection Review
This section provides the inspector's and reviewer's
names and agencies. Compliance status should be determined
only by the Enforcement personnel.
Section F - Facility and Permit Background
If the permittee's address is different from that of
the facility/ it should be so indicated. If the facility
was inspected previously, the date and findings summary
should be noted before performing the current inspection.
Section G - Records and Reports
This portion of the form documents that the records and
reports maintained by the permittee are in coir.pliance with
permit requirements. As mentioned earlier, if the checklist
does not adequately represent the situation, further expla-
ation should be attached and so indicated.
Section H - Permit Verification
Each inspection should identify discrepancies, if any,
between the issued permit and actual conditions. Again, if
further explanation is necessary, it should be provided and
so indicated.
Section I - Operation and Maintenance
Each inspection of an operating facility should evaluate
its operation and maintenance. Operating facilities include
those on final limits and those in the process of being
upgraded.
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Section J - Compliance Schedule
The compliance schedule progress should be evaluated
when the permittee is on a compliance schedule. Any grant-
related inspections of facilities should be coordinated with
Regional Construction Grants personnel. The current phase
of compliance schedule status should be marked on the form.
Section K - Self-Monitoring Program
The permittee's flow measurement, sampling, and labora-
tory procedures should be checked, as appropriate, on all
inspections. If deficiencies are noted, additional pertinent
information should be provided, if necessary. For example,
if the laboratory is not calibrating or maintaining the
equipment satisfactorily, the calibration or maintenance
intervals should be noted. If parameters other than those
required by the permit are analyzed, the parameters and
analytical methods should be noted. If the permittee
laboratory, flow-measurement, or sampling procedures are not
inspected, an explanation should be provided (e.g., contract
lab off the premises).
Section L - Effluent/Receiving Water Observations
Visual observations made during the inspection should
be noted, as applicable, for each outfall. The inspector's
observations are subjective and qualitative, but serve to
focus attention oh potential treatment problems. Discharge
of floating solids or visible foam in other than trace
amounts is prohibited by the permit. Thus, observations of
greater than trace amounts represent permit violations and
indicate poor treatment.
Section M - Sampling Inspection Procedures and Observations
The performing agency's or Region's sampling procedures
should be noted for each sampling inspection. Details docu-
menting the procedures should be provided (e.g., the composite
time interval).
Section N - Analytical Results
If the analytical results or laboratory report from a
sampling inspection provides more information than can be
inserted in Section C, the additional information should be
noted in this part or attached to the report form. This
section also offers more space for comments or additional
materials (e.g. flow diagrams) as the situation merits.
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