EX
IC O
Y
N EW
U
College of Agriculture and
Home Economics
M
TE
TA
Cooperative Extension Service
S
Estimating Water
Flow From Pipes
N
IV
E RSI
T
Guide A-104
C.H. Hohn, Extension Agricultural Engineer
This publication is scheduled to be updated and reissued 10/02.
In recent years, there have been increased demands
upon our limited water supply by industry, cities and
towns, recreation, and agriculture. So irrigators should use
the available water supply more wisely than ever before.
Proper management takes the guesswork out of the application of irrigation water to the land. Times and
amounts of water applied are just as important as the times
and amounts of seed and fertilizer used.
Irrigation management involves measuring water at delivery points to determine exact amounts going to the field.
The standard term for rate of flow of irrigation water is
cubic feet per second (cfs). A cubic foot per second of water is flowing when a cubic foot volume of water (equal to
one foot wide, one foot long, and one foot high) passes a
given point every second.
A cubic foot of water equals:
• Approximately 405 gallons per minute (gpm).
• Approximately 1 acre-inch per hour.
• Approximately 1 acre-foot per 12 hours.
• Approximately 2 acre-feet per 24 hours.
An acre-inch is the volume of water required to cover
an acre of land one inch deep. An acre-foot is the volume
of water required to cover an acre one foot deep.
The following tables will be helpful to the irrigator in
determining the amount of water being applied to the land
with nothing more than a carpenter’s rule:
DISCHARGE FROM PIPES FLOWING FULL
In Gallons Per Minute
with
Vertical Drop “Y” = 13 Inches
Pipe size
Inside
diameter
2"
2.5"
3"
4"
5"
6"
7"
8"
9"
10"
11"
12"
Area
(Sq. In.)
3.14
4.91
7.07
12.57
19.64
28.27
38.48
50.27
63.62
78.54
95.03
113.10
Horizontal distance “X”
12"
38
59
85
151
236
339
462
603
763
942
1140
1357
14"
44
69
99
176
275
396
539
704
891
1100
1330
1583
16"
50
79
113
201
314
452
616
804
1018
1257
1520
1809
Q=
18"
57
88
127
226
354
509
693
905
1145
1414
1711
2036
20"
63
98
141
251
393
565
770
1005
1272
1571
1901
2262
22"
69
108
156
277
432
622
847
1106
1400
1728
2091
2488
24"
75
118
170
302
471
678
924
1206
1527
1885
2281
2714
26"
82
128
184
327
511
735
1000
1307
1654
2042
2471
2941
28"
88
137
198
352
550
792
1077
1408
1781
2199
2661
3167
3.61 AX Where: A = Cross-sectional area of discharge
√
pipe in square inches
X = Horizontal distances in inches
Y = Vertical distances in inches
30"
94
147
212
377
589
848
1154
1508
1909
2356
2851
3393
32"
100
157
226
402
628
905
1231
1609
2036
2513
3041
3619
34"
107
167
240
427
668
961
1308
1709
2163
2670
3231
3845
36"
113
177
255
453
707
1013
1385
1810
2290
2827
3421
4072
AN APPROXIMATE METHOD OF ESTIMATING
DISCHARGE FROM PIPES FLOWING
PARTIALLY FULL
Rate of flow in gallons per minute
Y
D
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
4
142
128
112
94
75
55
37
21
8
0
Inside diameter of pipe - “D” in inches
6
8
10
12
334
579
912
1310
302
524
825
1185
264
457
720
1034
222
384
605
868
176
305
480
689
130
226
355
510
88
152
240
345
49
85
134
194
17
30
52
74
0
0
0
0
ESTIMATING FLOW FROM
VERTICAL PIPE OR CASING
The approximate flow from vertical pipes or casings can
be determined by measuring the maximum height(h) in
inches to which the water jet rises above the pipe, and inside diameter of the pipe (d) in inches.
The flow in gallons per minute is given in the following
table for different sizes of standard pipe and for different
heights of the water jets.
Guide A-104 • Page 2
H
D
Height (H)
NOMINAL DIAMETER (D) OF STANDARD PIPE (INCHES)
(Inches)
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
8
9
10
12
14
16
18
20
25
30
35
2
29
32
35
38
41
44
47
49
52
54
57
61
65
69
76
83
89
95
101
113
124
134
3
65
72
77
85
92
98
104
109
115
121
126
135
144
153
169
184
197
209
221
249
273
298
4
113
126
135
149
161
172
182
192
202
211
219
236
251
265
294
319
342
364
386
433
476
516
5
180
202
217
238
252
270
286
301
316
331
345
370
396
418
463
502
540
575
607
680
746
810
6
269
291
311
341
369
396
420
444
469
490
509
548
585
621
685
740
796
845
890
998
1095
1175
7
352
396
425
465
503
540
575
606
638
667
700
751
802
850
933
1020
1090
1160
1225
1375
1505
1630
8
460
517
569
626
687
733
779
825
872
913
949
1025
1091
1150
1259
1360
1454
1542
1626
1818
1991
2151
10
797
898
950
1055
1115
1200
1270
1332
1391
1448
1503
1606
1704
1796
1967
2125
2272
2410
2540
2840
3111
3360
12
1148
1293
1416
1530
1636
1735
1829
1918
2003
2085
2164
2313
2454
2586
2833
3060
3272
3470
3658
4090
4480
4839
14
1583
1760
1928
2083
2227
2362
2489
2611
2727
2838
2945
3149
3340
3520
3856
4165
4453
4723
4979
5566
6098
6586
16
2042
2299
2518
2720
2908
3085
3251
3410
3562
3707
3847
4113
4362
4598
5037
5440
5816
6169
6503
7270
7964
8602
40
144
318
551
865
1270
1745
2299
3592
5173
7041
9196
For other pipe sizes and heights of jets. Use the formulae:
Gal. per min. = 5.68 CD2 H
Cu. ft. per sec. = 0.0126 CD2 H
Where
D = inside pipe diameter in inches.
H = jet height in inches.
C = a constant varying from 0.87 to 0.97
for pipes of 2 to 6 inches in diameter
and heights of 6 to 224 inches.
Guide A-104 • Page 3
New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department of Agriculture
cooperating.
Reprinted October 1997
Las Cruces, NM
5C
Guide A-104 • Page 4