RESEARCH BULLETIN NO. 47 OCTOBER 1960
Measurement of Water
Over Silted-In Weirs
G. L. COREY and ROBERT McFALL
AGRICULTURAL EXPERIMENT STATION
Department of Agricultural Engineering
UNIVERSITY OF IDAHO
College of Agriculture
The research reported in this bulletin was
sponsored in part by Western Regional Research
Project W-32, twelve Western States,
and U.S. Department of Agriculture cooperating.
Measurement of Water Over
Stilted-In Weirs
G. L. COREY and ROBERT MCFALL*
ACCURATE water measurement is essential for proper management
of this valuable natural resource. There is increasing need
for adequate measurement and control as the water demands of our
country increase. Hydrologists, engineer s, irrigation and power
companies as well as many other agencies are interested in accurate
measurement of water.
There are many devices to measure water flow. The quant ity of
watet passing a given point can be expressed as the product of the
velocity of flow and the cross-sectional area of flow. Most measurement
devices take advantage of t his simple fact. The weir, orifice,
Parshall and type-H flumes are all devices which restrict the flow
to a known cross section and, since the velocity is a function of the
f low depth it is possible to determine discharge through them. Another
popular means of measuring discharge is to determine the
velocity with a current meter through any known cross-section.
This method is especially adaptable to large stream flow. There are
many other devices for measuring water in closed conduits. Since
this publication deals with open channel f low they will not be referred
to here.
The weir is the oldest and most common device for measuring
water discharge in small open channels. James Richno Francis f irst
presented his now classical weir formulas in 1852. (2). This device
consists of a bulkhead placed across the channel and provided with
a notch through which the water pours. One might consider the
weir as an orifice flowing part full. If the channel is rectangular
and the bulkhead has a sharp crest extending the full width of the
channel the weir has no end contractions and is called a suppressed
weir. If the crest width is less than the channel width, the weir has
side or end cont ractions and is referred to as a contracted we1r.
~ost weirs are of the latter type.
Weirs provide an accurate means of measuring water if certain
standard conditions are met (3). One of these is that the velocity
of approach to the weir should be less than I/2 feet per second. In
order to meet this condition a relatively large weir pond must be
provided ahead of the weir so that the velocity of approach will be
negligible. Since the velocity is low in a weir pond it is an ideal
location for sediments to be deposited. The velocity of approach increases
as silt is deposited and standard weir formulas may no
longer be accurate.
•Associate Professor and former graduate student. respectively. Department of Agricul·
tural Engineering, University of Idaho.
(1)
2 IDAHO AGRICULTURAL EXPERIMENT STATION
Formulation has been developed for determining discharge when
the velocity of approach is greater than lf2 fps. ( 4). However, the
procedure is laborious. Several research workers have demonstrated
that, when a flat rod is held vertically in a flowing stream, the
height of the pile-up on the upstream face of the rod is directly
r elated to the velocity of approach. Wilm and Storey (5) reported
on such a rod in 1944. This rod was triangular in cross section and
was first held with the apex or sharp edge upstream, then turned
to present the flat edge upstream. The difference between the
water height on the apex and the flat side of the rod was related to
velocity. They found good correlation between rod reading and velocity
for velocities between 1 and 8 feet per second. Much earlier in
1921, Steward (6) developed a rod to measure flow over a weir. His
rod operated much the same as that described with the Wilm and
Storey rod. Much of his work is obscure and details on development
and accurary are lacking. The Clausen Weir Rule Company (1) has
developed a rule which is held on the weir crest. The flow rate for a
given weir width is obtained directly from a scale on the rule.
It was the purpose of this research to determine the relationships
between readings taken with a rod held on a weir crest and
the discharge flowing over the weir. If a reliable relationship exists
then many weirs which have become silted-in can again be used
as measuring devices without r econstructing adequate weir ponds.
There are many weirs in Idaho, especially in the mountainous areas,
which have become inoperative because of silt.
Methods and Materials
The problem involves flow of water over a bulkhead placed in an
open channel. The complete study required analysis of the flow resulting
from a great many variable conditions. For this reason the
work was performed in the irrigation laboratory where variables
could be accurately controlled.
THEORY
A weir operating under ideal conditions must have a negligible
approach velocity. Also the height of the weir crest above the upstream
channel floor must be at least twice the maximum depth of
flow over the weir (3). It is logical to assume that neither of these
conditions will be met if the weir pond becomes silt laden. In fact,
the crest height is an indication of the amount of silting that has
taken place and the approach velocity is somewhat dependent upon
it. Therefore, the crest height was given consideration in the experiment.
Water flowing over a weir, with a gage held on the crest, is illustrated
in Figure 1. To examine this flow experimentally the sup-
MEASURING WATER OVER SILTED-IN WEIRS 3
) ) )).>> -
Figure !.- Gravity flow over a sharp crested weir with a gage held on
the crest.
pressed weir was treated separately from the weir with end coni
ractions because of the additional variable, weir length, which was
considered with the contracted weir.
SUPPRESSED WEIR: The important variables that describe
1.he flow over a suppressed silted-in weir are q, v, H, D, and g.
Where q discharge per unit length of weir in ft2/ sec.
v approach velocity in ft/ sec.
H depth of f low over weir crest as measured with
a gage held on the crest in ft.
D = crest height above upstream channel floor in
ft.
g = acceleration due to gravity in ft/ sec.2
There are other variables such as viscosity, surface tension,
and density which might affect the flow. However, in this type of
open channel flow their effect can justifiably be assumed negligible.
The assumption was made that the amount of pile-up on the
gage, (H+ D-h) Figure 1, is a function of the velocity. The velocity,
then was eliminated as a variable leaving q, H, D, and g to be
studied. One possible combination of dimensionless groups or parameters
for these four variables is :
qh/ gD3 and H/ D
The relationship between these two parameters can be obtained experimentally
by varying them so that a range of values for each is
obtained and presenting the results graphically.
~ IDAHO AGRICULTURAL EXPERIMENT STATION
Of course, the shape and dimensions of the weir rod will affect
the value of H. However, for a given shape and dimension the above
analysis is valid.
CONTRACTED WEIR: The Contracted weir differs from the
suppressed weir in that there is nonuniform flow over the crest
length because of the end contractions. The contractions effectively
shorten the crest length. This effect varies with the number of contractions
and the depth of flow past the weir. Francis (2) proposed
correcting for this condition in the following way:
Let L' L- O.lOn H
Where L' effective crest length.
L measured crest length.
n number of contractions, usually two.
H depth of flow over weir crest.
The variables describing the flow over the contracted weir are
the same as those over the suppressed weir with the addition of the
effective length. This factor was, therefore, introduced in the analysis.
Discharge per unit length of weir crest is meaningless since it is
not uniform over the crest. Total discharge over the weir must,
therefore, be reported. The dimensionless grouping of the variables
becomes:
Where
PROCEDURE
Q/ L' ygD3 and H/ D
Q = total discharge over the weir in ft:J / sec.
L' = effective weir length in ft = L - 0.2H
To determine relationships between the variables affecting
flow, the dimensionless parameters developed in the theory varied
through a reasonable range of values. This was accomplished by
varying the controllable factors which combine to make up the
dimensionless number.
With the suppressed weir q/ y gD:J was varied from 0.04 to 35.00
while H/ D varied from 0.20 to 15.00. These were obtained by:
Varying
Varying
Varying
D from 0.02 ft to 0.35 ft.
q from 0.05 cfs/ ft to 0.35 cfs/ ft.
H from 0.065 ft to 0.220 ft.
With the contracted weir Q/ L'y gD3 was varied from 0.05 to
MEASURING WATER OVER SILTED-IN WEIRS 5
40.00 and H/ D from 0.20 to 15.00. These variations were obtained
by:
Varying
Varying
Varying
D from 0.02 ft to 0.40 ft.
Q from 0.08 cfs to 0.36 cfs.
H from 0.13 ft to O.R2 ft.
A r ange of approach velocities from 1 to 3 feet per second resulted
from the many combinations of tests made.
A special tilting flume was constructed for this study. It was
constructed of marine plywood and was 7 feet long, 2 feet wide and
1 foot deep. The tilting feature of the flume allowed a variation of
approach velocities for any given discharge.
Weir plates were installed in the end of the flume. The plates
were constructed of brass and cut to provide the above mentioned
variations in crest height, D. The suppressed weir, of course, extended
over the complete flume width of 2 feet. The contracted
weir was 8 inches long leaving 8 inch contractions on either side of
the weir. Figures 2 and 3 show the flume and weirs in operation.
Figure 2.-Gage reading being taken on suppressed weir.
The flume was installed over the existing large laboratory f lume
in order to utilize the recirculating system. Water was pumped
from the sump beneath the laboratory floor, through the test flume,
6 IDAHO AGRICULTURAL EXPERIMENT STATION
Figure 3.-Gage reading being taken on contracted weir.
into the permanent flume and hence into the sump. Discharge was
controlled by a gate valve between the pump and the flume entrance.
It was accurately measured through a calibrated water
meter.
The important measurement considered was the depth of flow
over the weir as measured with a gage held on the weir crest. The
gage used was constructed of wood and lf2 inch square in cross section.
A scale was placed on one face of the gage which allowed
readings to the nearest 0.01 feet. In operation, the gage was held
vertically on the crest and a reading made on the upstream face of
the gage at the point of maximum water rise. Of course, t his reading
(H) was greater than the true depth because it consisted of the
pile-up due to velocity as well as the true depth. The actual depth
of flow over the weir was measured with a point gage placed directly
over the weir crest. Figures 2 and 3 illustrate the method of
reading the gage height. The point gage at the weir can also be
seen.
DATA COLLECTION
One complete trial consisted of operating the apparatus with a
given weir in place and with a given discharge over the weir while
the flume was at a given slope. Water was turned into the flume
and the flow rate was adjusted to the desired amount with the gate
valve. After the flow had become stabilized; discharge, Q, and gage
MEASURING WATER OVER SILTED-IN WEIRS 7
height, H, measurements were taken. At each flow condition, f ive
readings were taken on these items. The recorded value was the
average of these readings. The value of q (discharge per foot of weir
length) for the suppressed weir was calculated by dividing total
discharge, Q, by the weir length, L.
Data collected with the suppressed weir included operating t he
flume at 4 different slopes, using 6 separate discharge rates artd 5
weir heights. This involved 120 separate tests with this weir. When
these data were plotted it was found. that there was a great deal of
duplication. The number of t rials with t he contracted weir was
therefore reduced to 3 weir heights on 3 slopes with 4 discharge
rates making a total of 36 individual tests.
Experimental Results
The dimensionless grouping of variables, discussed in the theory,
were calculated from the data. Each particular test-run produced
one set of dimensionless numbers. After all tests had been calculated
the results were plotted. Figure 4 shows this information for the
suppressed weir while Figure 5 represents the contracted weir.
Figure 4.-Relationship of dimensionless grouping of variables for suppressed
weir flow.
e
H
20.0
10.0
8.0
60
IDAHO AGRICUL TURAL EXPERIMENT STATION
0 2.0
0.2
Figure 5.-Relationship of dimensionless grouping of variables for contracted
weir flow.
These plots demonstrate the extremely close r elationship between
the parameters. In fact, the data plotted in a straight line
on logrithmic paper indicating an exponential relationship between
the variables. It was t herefore possible to develop equations relating
discharge to t he other variables. The resulting equations were as
f ollows:
Suppressed weir
Contracted weir
q
Q
3.310 D -o.oog H 1.549 (1)
3.584 (L - 0.2H) D o.oo9 H 1.
597 (2)
These equations were found by the multiple regression method
r ather t han the graphicial method because of the inaccuracies involved
in t he latter. The value of the weir crest height, D, above t he
channel floor has a very small effect on the discharge as measured
with t he gage because, regardless of the value of D, when it is taken
to such a small power t he result approaches 1. Neglecting D in t he
equations would r esult in an error of less than two percent. The
accuracy of any operating weir is undoubtedly no better t han t his.
Omitting D as a variable in t he analysis was therefore justified.
This was done and a direct relationship between discharge and
depth of flow was obtained. These r elationships appear in Figures
6 and 7 and t he equations r esulting from multiple regression were
as f ollows :
•
::
:r
~
Q... 0 ..
"0 '
C>
.. ::
:r
~
Q... 0 ..
"0 '
C>
MEASURING WATER OVER SILTED-IN WEIRS 9
0.20
0.10
0.08
0.06
0.0 4
0.02 0.0 4 0.06 0.08 0.10
Discharge q cfs/ ft
Figure 6.-Gage depth-discharge relationship for flow over a suppressed
weir .
0.10
0.02 0.04
Discharge Q L-0.2 H cfs/ ft
Figure 7 .-Gage depth-discharge relationship for flow over a contracted
weir.
10 IDAHO AGRICULTURAL EXPERIMENT STATION
Suppressed weir
Contracted weir
q
Q
3.369 H 1.
549
3.496 (L - 0.2H) H 1.
593
(3)
(4)
In order to determine the accuracy obtainable with these four
equations a con·elation was made between calculated discharge and
measured discharge. The resulting correlation coefficients were:
Weir Type Equation Coefficient
Suppressed 1 0.999
Suppressed 3 0.988
Contracted 2 0.998
Contracted 4 0.990
It is obvious that very little is gained by using equations 1 and 2
when 3 and 4 are almost as accurate. Equations 3 and 4, then, represent
discharge over a weir which has an appreciable approach
velocity. The discharge (q) in equation 3 r epresents the discharge
per foot of weir length while the discharge (Q) in equation 4 represents
the total discharge over a weir of length L. The value of the
depth of flow H was measured with a gage held on the weir crest.
This depth was measured with a gage which was square in cross
section being lh inch by 1;2 inch. These fonnulas are not valid if
a gage of any other size or configuration is used.
Tables 1 and 2 have been calculated and are presented in order
that this method of measurement can be used without laboriously
using the fonnula for each specific flow. Information on four weir
widths is presented. It will be noticed that values of H greater than
one-third the crest length are not given. It has been found that for
greater depths than this the contractions are not complete and
measunnents are inaccurate unless special precautions are taken.
Since this study did not involve measurements at these depths it is
doubtful that these fonnulas apply.
MEASURING WATER OVER SILTED-IN WEIRS 11
Summary
Weirs that have silted-in no longer operate as standard weirs.
The velocity of approach becomes greater than lh fps and is greater
than standard conditions. The weir crest height above the channel
bottom is reduced. For these reasons the usual method of measurement
over them is inaccurate.
This study has demonstrated that it is possible to ut ilize these
weirs as accurate measuring devices if the depth of flow is measured
with a gage held on the weir crest. The value of the depth measured
in t his manner includes the true depth of flow and a certain amount
of pile-up on the gage face caused by the approach-velocity.
The study related the depth of flow measured with a lf2 inch
square gage to the discharge over the weir. It was found that for
the method of measurement used, the crest height above the channel
floor has very little effect on the measurement and may be
eliminated as a variable.
Equations were developed relat ing discharge to gage depth and
tables which may be used to determine discharge are presented.
Table I.- Discharge over suppressed rectangular weirs in cubic feet per second. Depth measured with lh inch square gage t-.>
held on the weir crest. •
Gage Depth Crest Length of Weir (ft) Gage Depth Crest Length of Weir (ft)
(ft) 1.0 1.5 2.0 3.0 (ft) 1.0 1.5 2.0 3.0
....
0.05 0.033 0.050 0.067 0.100 0.55 ····------ -----·----- 2.670 4.005 tl
;t:.
0:06 0.043 0.065 0.086 0.129 0.56 ---- -- ---- -----····· 2.746 4.119 :I:
O.Q7 0.055 0.082 0.110 0.164 0.57 --------- ---------- 2.822 4.233 0
0.08 0.067 0.101 0.134 0.202 0.58 ---------- ---------- 2.898 4.347 ;t:.
0.09 0.081 0.121 0.162 0.242 0.59 2.976 4.464
Q
---------- ---------- ::tJ
0.10 0.095 0.143 0.190 0.286 0.60 3.054 4.581 .... ---------- ---------- (')
0.11 0.110 0.165 0.221 0.331 0.61 ········-- -----··· -· 3.134 4.701 c::
0.12 0.126 0.190 0.253 0.379 0.62 3.213 4.820
t"'
-----··--- ---------- '"3
0.13 0.143 0.214 0.285 0.428 0.63 ---------- -------··· 3.294 4.941 c::
::tJ
0.14 0.160 0.240 0.320 0.481 0.64 ---------- .......... 3.374 5.061 ;t:.
0.15 0.178 0.268 0.357 0.535 0.65 ---------- ---------- 3.457 5.186 t"'
0.16 0.197 0.296 0.394 0.591 0.66 3.540 5.310 t>J ---------- ---------- ~
0.17 0.217 0.325 0.433 0.650 0.67 ---------- ---------- 3.623 5.435 .,
0.18 0.237 0.355 0.473 0.710 0.68 3.708 5.561
t>J
---------- ---------- ::tJ
0.19 0.257 0.385 0.514 0.770 0.69 5.689 ....
---------- ---------- ---------- ~
0.20 0.278 0.4 7 0.557 0.835 0.70 ---------- ---------- ---------- 5.817 t>J
0.21 0.300 0.450 0.599 0.899 0.71 5.946 ~ ---------- ---------- ---------- '"3
0.22 0.323 0.486 0.646 0.968 0.72 ---------- ---------- ---------- 6.076 tr.l
0.23 0.346 0.5.:.8 0.691 1.037 0.73 ---------- ---------- ---------- 6.207 ;'"t:3.
0.24 0.369 0.554 0.738 1.107 0.74 ---------- ---------- ---------- 6.339 .'"..3.
0.25 0.393 0.5!W 0.786 1.179 0.75 ---------- ---------- ---------- 6.473 0
0.26 0.418 0.628 0.837 1.255 0.76 6.607 ~ ---------- ---------- ·---------
0.27 0.413 0.665 0.886 1.329 0.77 ---------- ····-···-- --------·- 6.741
0.28 0.469 0.701 0.938 1.407 0.78 ------···- ---------- -·-······· 6.878
0.29 0.495 0.743 0.990 1.485 0.79 ---------- ·--------- ---------- 7.015
0.30 0.522 0.783 1.014 1.566 0.80 .......... ---------- ..........
.....
7.153
0 .31 0.549 0.824 1.098 1.647
0 .32 0 .576 0.864 1.152 1.728
0 .33 0.(l05 0.908 1.210 1.815
0 .34 0.633 0.950 1.266 1.899
0.35 ··-------- 0.995 1.326 1.989
0.36 ---------- 1.038 1.384 2.076
0.37 --------- 1.083 1.444 2.166
0.38 --------- 1.130 1.506 2.259
0.39 ---------- 1.176 1.568 2.352
0.40 ---------- 1.223 1.630 2.445
0.41 ---------- 1.269 1.692 2.538
0.42 ---------· 1.319 1.758 2.637
0.43 --········ 1.367 1.822 2.733
0.44 ---------- 1.418 1.890 2.835
0.45 ---------- 1.467 1.956 2.934
0.46 ·····----- 1.5 "8 2.024 3.036
0.47 ---------- 1.568 2.090 3.135
0.48 ---------- 1.620 2.160 3.240
0.49 ----·----- 1.673 2.230 3.345
0 .50 --------.-- 1.727 2.303 3.454
0.51 ----··-·-- ··-···---- 2.375 3.562
0.52 ··-------- -----·--- 2.446 3.669
0.53 -----··· --·· ····· 2.519 3.779
0 .54 ---------- ......... 2.594 3.891
•computed with the formula Q = 3.369 L H•·'·'"
0.81 ·--------- ----------
0.82 ----------
0.83 ---------- ----------
0.84 ---------- ----------
0.85 - -------- ----------
0.86 ---------- ----------
0 .87 ---------- ----------
0.88 ---------- ----------
0.89 ---------- ----------
0.90 ---------- ----------
0.91 ---------- ----------
0.92 --------·· ----------
0.93 ---------- ---------
0.94 ·········· ----------
0.95 ··-------- ········--
0.96 ---------- ----------
0.97 -·--·----- ------·---
0.98 - -~----- . ----------
0.99 ---------- -----·----
1.00 ········-- ------·-··
··------- 7.292
-----····· 7.432
---------- 7.573
---------- 7.713
---------- 7.858
---- ~- --- 8.009
---------- 8.146
---------- 8.291
---------- 8.438
---------- 8.584
------·--- 8.733
---------- 8.882
--------· 9 .022
oooooouoo 9.183
.......... 9.335
-------~-~ 9.487
·---·-··-- 9.641
···------- 9.796
---·····-- 9.951
----- ---- 10.107
Ei:
t>J
;t.
tn c::
.~...
~
Q
~
;t.
>-3
t>J
~
0
<:::
t>J
~
t..n..
t"'
>-3
t>J
t1
..I ..
~
~
.t>..J.
~
tn
....
c..>
~
Table 2.-Discha rge over contracted rectangular we irs in cubic feet per second. Depth measured with % inch squa re gage """
held on the weir crest. •
Gage Depth Crest Length of Weir (ft) Gage Depth Crest Length of Weir (ft)
( ft) 1.0 1.5 2.0 3.0 (ft) 1.0 1.5 2.0 3.0 .....
0.05 0.029 0.044 0.059 0.088 0.55 2.549 3.898 t:J ---------- ---------- :t>
0.06 0.039 0.059 0.079 0.118 0.56 ·-·------- ---------- 2.621 4.009 ::z:
0.07 0.050 0.075 0.100 0.151 0.57 2.693 4.121 0 ---------- ---------- :t>
0.08 0.062 0.093 0.124 0.187 0.58 ··-······- ---------- 2.75! 4.217 Q
0.09 0.074 0.112 0.150 0.225 0.59 ---------· ----· ·--- 2.839 4.347 ~.....
0.10 0.087 0.132 0.177 0.266 0.60 ---------- ---------- 2.913 4.462 ()
0.11 0.102 0.154 0.205 0.309 0.61 2.987 4.578 c::
---------- ---------- t"'
0.12 0.116 0.176 0.236 0.355 0.62 ---------- ---------- 3.063 4.695 >-3 c::
0.13 0.132 0.200 0.268 0.403 0.63 ---------- ---------- 3.138 4.813 ~
0.14 0.148 0.225 0.301 0.453 0.64 ---------- ---------- 3.215 4.932 t:t">'
0.15 0.165 0.250 0.335 0.506 0.65 ---------- --------·- 3.291 5.052 t>l
0.16 0.183 0.277 0.371 0.560 0.66 ---------- ---------- 3.369 5.172 ::><:
0.17 0.201 0.305 0.409 0.616 0.67 3.447 5.294 .,
---------- ········-- t>l
0.18 0.219 0.333 0.447 0.675 0.68 ---------- ---------- 3.525 4.417 ~.....
0.19 0.239 0.363 0.487 0.735 0.69 ---------- ---------- ---------- 5.540 Ei:
0.20 0.258 0.393 0.528 0.797 0.70 5.665 t>l
---------- ---------- -------- <:
0.21 0.279 0.424 0.570 0.861 0.71 --------- ---------- ____.., _ __ 5.790 >-3
0.22 0.300 0.456 0.613 0.926 0.72 5.916 til --------·· ---------- -------·· >-3
0.23 0.321 0.489 0.657 0.994 0.73 --------- --------- -·------· 6.044 :t>
>-3
0.24 0.343 0.523 0.703 1.062 0.74 ---------- ---------- ····-····· 6.172 .....
0
0.25 0.365 0.557 0.749 1.133 0.75 ---------- ---------- --------- 6.301 <:
0.26 0.388 0.592 0.796 1.205 0.76 ---------- ---------- ···------ 6.441
0.27 0.411 0.628 0.845 1.279 0.77 ---------- ---------- ---------- 6.561
0.28 0.434 0.664 0.895 1.355 0.78 ---------- ---------- ........ 6.693
0.29 0.458 0.702 0.945 1.432 0.79 ---------- ---------· .......... 6.825
0.30 0.483 0.740 0.996 1.510 0.80 ---------- -··-·-···- -------·-· 6.958
0.31 0.508 0.778 1.049 1.590
0.32 0.533 0.817 1.102 1.671
0.33 0.558 0.857 1.156 1.754
0.34 0.584 0.898 1.211 1.838
0.35 ·--------- 0.939 1.267 1.924
0.36 --------- 0.981 1.324 2.011
0.37 ·--------- 1.023 1.382 2.099
0.38 ---------- 1.066 1.440 2.188
0.39 ---------- 1.109 1.499 2.279
0.40 --------- 1.153 1.559 2.372
0.41 --·------ 1.198 1.620 2.465
0.42 ·-------· 1.243 1.682 2.560
0.43 ---------- 1.289 1.744 2.656
0.44 ······---- 1.335 1.807 2.753
0.45 --------- 1.382 1.871 2.851
0.46 --------- 1.429 1.936 2.951
0.47 --------- 1.476 2.001 3.051
0.48 ---------- 1.525 2.067 3.153
0.49 --·------ 1.573 2.134 3.256
0.50 ---------- 1.622 2.202 3.361
0.51 --------- ---------- 2.270 3.466
0.52 ---------- --------- 2.339 3.572
0.53 --------- ---------- 2.408 3.680
0.54 --------- ---------- 2.479 3.789
• computed with the formula Q = 3.496 (L . 0.2H) H •·=
0.81 ---------- ..........
0.82 -----·---- ----------
0.83 --------- ----···---
0.84 ---------- ----------
0.85 ---------- ····-----
0.86 ·-·------ ---------~
0.87 ---------- ----------
0.88 ····----- ---------
0.89 ..... -- ----------
0.90 ----····-- ----------
0.91 ---------- ----------
0.92 ---------- --------··
0.93 ---------- ----------
0.94 ---------· ---------
0.95 ---------- ----------
0.96 ---------- ----------
0.97 ---------- ----------
0.98 ---------- ----------
0.99 ---------- ----------
1.00 ---------- ----------
---------- 7.092
--------·- 7.227
---------- 7.363
---------- 7.500
---------- 7.637
-----·---- 7.775
---------- 7.914
---------- 8.051
---------- 8.194
---------- 8.335
---------- 8.477
··--·----- 8.620
---------- 8.764
---------- 8.908
---------- 9.053
---------- 9.199
---------- 9.345
---------- 9.492
~- - --- --- 9.640
----·----- 9.789
~
t>:1
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16 IDAHO AGRICULTURAL EXPERIME:VT STATION
References
I. Clausen Weir Rule Co., 'Mea suring I rrigation Water": Phoenix, Arizona; 1950.
2. Fra ncis, J . R.; "Lowell Hydraulic E xper iments"; D. Van Nostrand Co.; 1883.
3. J e nsen, Max C. and Kulp, Mark R .; "Farm Wa t e r Measurement"; Univer sity of
Idaho Extension Bulletoin No. 170; Moscow, Idaho: May 1948.
4. King, H. W., " Handbook of Hydraulics"; McGraw Hill Book Compa ny; New York 1954
(4th ed .) .
5. Wilm, H. G. and Storey, H. C. ; " Velocity Head Rod Ca libr a te d for Me a suring Stream
Flow"; Civil Enginee r ; Vol. 14; 475·476, 1944.
6. Stewar d. W. H. and Coffin, E . H.; " E asy Method of De te rmining Disch arge Over Weir
Ha ving Ve locity of Approach" Reclamation Record 276·277; Denver, Color ado; J une
1921.