UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION CIRCULAR No. 250 July, 1922 MEASUREMENT OF IRRIGATION WATER ON THE FARM BY H. A. WADS WORTH CONTENTS PAGE Introduction 2 Units of measurement and equivalents 3 Weirs 4 Rectangular weirs 7 Cipolletti weirs 9 90-degree triangular-notch weirs 11 Weir construction 12 Submerged orifices 14 Submerged orifices of fixed dimensions 18 Construction of submerged orifices of fixed dimensions 20 Computations if tables are not available 20 Adjustable submerged orifices 21 Theory of inch box measurement 23 Riverside box 24 Anaheim Union Water Company measuring box 25 Santa Ana Valley Irrigation Company miner's inch box 26 Azusa hydrant 27 Division boxes 29 Mechanical devices for measuring water volumetrically 31 Reliance meter 32 Dethridge meter 33 Other measuring devices 34 Lyman meter 34 Sentinel meter 34 Venturi meter 34 Venturi flume 35 Summary 35 TABLES 1. Discharge table for rectangular weirs , 8 2. Discharge table for Cipolletti weirs 10 3. Discharge table for triangular notch 12 4. Weir board dimensions 13 5. Dimensions for weir boxes 14 6. Discharge table for submerged orifices of fixed dimensions 19 7. Dimensions for boxes for submerged orifices of fixed dimensions 20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION INTRODUCTION The aim of this circular is to make available in a single publi- cation the tables, and in some cases the formulae, necessary for the measurement of irrigation water under the varying conditions found in California. In order to avoid confusion, only those methods which are in common use have been considered in detail. Even with this limitation, it has been necessary to include a considerable number of methods of measurement. This is due to the variation in conditions under which irrigation water is delivered. As an example, in the Orland area in the Sacramento Valley, where field ditches are built on fairly steep grades, small weirs are used almost exclusively to measure irrigation water to the water user. In other areas where canal grades are much flatter and where the head of water in the canal is subject to wide fluctuations, the sub- merged orifice is used as a measuring device. In general these ori- fices are so built that the size of the orifice can be increased or de- creased as the changing head demands. In Imperial Valley, the submerged orifice has come into general use, largely because the water from the Colorado River is so heavily charged with silt that the use of weirs is unsatisfactory. The measurement of water in terms of the miner's inch is prac- tically universal in most of the foothill and citrus orchard sections of the state. In these areas, where irrigation water is bought and paid for on the basis of the miner's inch, special devices are in gen- eral use by which a flow can be measured directly in that unit with- out the necessity of transposing from the more common units of the other parts of the state. Where individual pumping plants are in use water is commonly measured in terms of gallons per minute. The common method of payment for irrigation water in an area has had a great influence in determining the method of measure- ment in that area. In most cases that method of measurement is used which can be most readily changed into the terms necessary for the computation of the water charges. In addition to descriptions of the devices used with these com- mon methods of measurement, which are familiar to most users of irrigation water, descriptions of a few unusual devices have been included, either because of the different theory involved, or because the devices seem well suited to a greater use in California. CIRCULAR 250] MEASUREMENT OF IRRIGATION WATER 3 The tables for weir discharge and for flow through submerged orifices of fixed openings are the most recent and the most reliable that are available. The United States Reclamation Service and the United States Department of Agriculture, Division of Irrigation In- vestigations, have willingly furnished tables. UNITS OF WATER MEASUREMENT AND EQUIVALENTS Cubic foot per second. — This unit represents an exact and definite quantity of water, viz : the equivalent of a stream one foot wide and one foot deep flowing at the rate of one foot per second. 24-hour second foot. — This is one cubic foot per second, running continuously throughout a 24-hour period. It is equivalent to ap- proximately two (exactly 1.9834) acre-feet. Acre-Foot. — This is the equivalent of a body of water one acre in area and one foot deep, or 43,560 cubic feet. One cubic foot per second, or fifty southern California inches, or forty California statute inches, running continuously for twenty-four hours will supply ap- proximately two (exactly 1.9834) acre-feet. Acre-Inch. — This is one-twelfth of one acre-foot, or the equivalent of a sheet of water one acre in area and one inch deep. It is the unit sometimes used instead of the acre-foot, especially in express- ing quantities of less than one acre-foot. One cubic foot per second running continuously for one hour will supply approximately one acre-inch. Gallon. — As many irrigators receive their water supply from pumps and as pump manufacturers usually estimate discharges in gallons per minute or per second, this is sometimes a convenient unit to use. One cubic foot is approximately equal to iy 2 gallons (ex- actly 7.4805) and one cubic foot per second is approximately equiva- lent to 450 gallons per minute or 7% gallons per second. One thousand gallons. — This unit is quite common in irrigation practice in San Diego County, California. Inch. — This is a variable unit having different meanings in dif- ferent states and even in different sections of the same state. The old miner's inch of California was the quantity of water flowing freely through an opening one inch square, the center of which was four inches below the surface of the water standing above the open- ing; it is equivalent to a flow of nine gallons per minute or 1/50 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION cubic foot per second. The present statute inch of California is denned as a flow of one and one-half cubic feet per minute. It is measured through an orifice one inch square under a six-inch pressure and is equivalent to a flow of 11% gallons per minute or 1/40 cubic foot per second. While the meaning of the inch varies with local prac- tice, it is not a stream of water one inch deep and one inch wide, regard- less of pressure. Where its meaning is clear, the inch is a convenient unit for measuring small streams up to, say 50 to 100 inches, and is quite frequently used for such streams, particularly on many of the southern California systems. For larger streams its use is generally discarded in favor of the more definite unit, cubic foot per second. 24-hour inch. — This is a very common unit, especially in southern California, and is, as its name implies, one inch (the exact amount of which varies with locality and local custom) running for twenty- four hours. Variations of this unit found on some California irri- gation systems are the one-hour inch and the twelve-hour inch. The following table will be found useful in changing the ex- pression of a quantity of water from one of these units to another: Southern California miner's inch Statute miner's inch Gallons per minute Cubic feet per second Acre- inch Acre- foot 1 southern Cali- fornia miner's inch equals.... 1.25 9.0 fco 1 in 50 hours 1 in 600 hours 1 Stat, miner's inch equals.... 0.80 11.25 Ko 1 in 40 hours 1 in 480 hours 1 gallon per minute equals tt ill. 25 ^450 1 in 450 hours 1 in 5400 hours 1 cubic foot per second equals 50 40 450 1 in 1 hour 1 in 12 hours WEIES A weir is one of the simplest and most accurate means of meas- uring irrigation water on the farm. The weir of the irrigation farmer is simply a bulkhead or wall placed across a stream, with an opening cut in the top through which the water is allowed to pass. This opening is commonly called the "weir notch." The depth of the water pouring through the weir notch is the measure of the amount of water in the stream. By gauging this depth and consult- ing the weir table for the kind and length of the weir notch used the amount of water passing over the weir is obtained. Circular 250] MEASUREMENT OF IRRIGATION WATER In some cases the weir bulkhead is placed in a short section of flume, called a weir box; in others it is placed directly across an earth ditch and is independent of any other structure. (Fig. 1.) The theory and method of weir measurement remain the same in either case. There are certain conditions which must be observed before a weir can be used for the accurate measurement of water. In general Fig. 1. Rectangular field weir in use. it may be said that the "weir crest" or bottom of the weir notch should be short enough so that the amount of water to be measured will never give a depth of less than two inches over the crest, and long enough so that the depth will never be more than one-third of the length of the crest. Care should also be taken to see that the weir crest is long enough so that the water can pour through the notch without having to back up in the channel to a greater height than can be done with safety to the ditch bank. A number of other conditions are usually laid down as necessary for the weir. The most important of these are as follows : 1. The weir crest or bottom of the weir notch must be absolutely level. 6 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 2. The water passing over the weir must have a free "over-fall." If the water in the ditch below the weir is allowed to rise to such a height that this free fall is not possible, the weir is said to be sub- merged. Measurements made on a submerged weir are unreliable unless complicated corrections are introduced. 3. The distance from the crest of the weir to the bottom of the canal or to the floor of the weir box above the weir crest need only be great enough to check the velocity of water flowing in the bottom of the stream, say about 0.5 foot for small weirs. 4. The distance from the ends of the weir crest to the sides of the weir box or canal or ditch should be about twice the depth of the water on the weir, or, say from ten to twelve inches in the case of a weir with an eighteen-inch crest measuring about two cubic feet per second. 5. The bottom and sides of the weir notch should have a narrow edge. The use of a galvanized iron crest to give such a narrow edge is quite common and very satisfactory but not necessary. Sometimes thin pieces of strap iron are fastened on the up-stream side of the weir notch. In other cases the board in which the weir notch is cut is merely beveled on the down-stream side to a crest thickness of one-eighth or one-quarter of an inch. 6. Water should not be allowed to approach the weir with a ve- locity exceeding six inches per second. Also, it should flow to the weir in a smooth stream free from eddies or swirls. Both of these conditions are most easily met by placing the weir in a straight sec- tion of the ditch and, when necessary, by placing baffle boards across the channel. 7. The depth of water on the weir crest must be measured suffi- ciently above the weir to be free from the downward curve of the water as it passes over the weir. For convenience in making this measurement of depth a stake with its top level with the crest of the weir is usually set at one side of the ditch two or three feet above the weir, the measurements of depth being made from the top of this stake to the surface of the water. It will be noted from these conditions that the weir is not a suit- able means of measuring water under all conditions. In ditches where the grade is very slight, placing a bulkhead across a stream and raising the level of the water above the weir often results in a break in the ditch bank. In such cases it is also difficult to keep the weir from becoming submerged. In streams heavily laden with silt the weir is not a practical means of measurement. Reducing the velocity of the water to the Circular 250] MEASUREMENT OF IRRIGATION WATER point necessary for weir measurements soon precipitates such a quan- tity of solid matter above the weir that suitable weir conditions no longer exist. By itself, a weir, measures a rate of flow and does not indicate the total quantity delivered. In conjunction with a water register, which keeps a graphic record of the changing depth of water over the weir, a permanent record is obtained from which the total quan- tity of water can be easily computed. WEIE NOTCHES There are three types of weir notches in common use, viz: rec- tangular weirs, Cipolletti weirs, and triangular weirs. Special tables have been devised for each of these. It is of course essential that the proper table be used for the weir crest selected.* Fig. 2. Two foot rectangular weir notch. RECTANGULAR WEIRS The name is taken from the shape of the weir notch, shown in figure 2. This weir is also known sometimes as the Francis weir. It is one of the earliest forms of weirs used and is the type from which all other forms have been developed. Because of the simplicity, ease of construction, and accuracy with which the crest and sides may be set with the implements ordinarily at hand, this type of weir should be used more widely than it has been in the past. It is as accurate as the other types. The crest is placed in a horizontal position and the sides extend vertically above the crest. A right angle is therefore formed, which permits the weir to be made and set easily and accu- rately by means of a carpenter's square and level. The sides must be placed carefully to give the desired length along the crest. Table 1 gives the discharge over rectangular weirs from one to four feet in length, computed from the corrected formula: * The discussion of " rectangular weirs," "Cipolletti weirs'' and "90-degree triangular notch weirs," together with the discharge tables for these weir notches, is copied largely from Farmers' Bulletin No. 813, entitled "Construc- tion and Use of Farm Weirs, ' ' by Victor M. Cone. UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION TABLE 1 Discharge Table for Rectangular Weirs Discharge in cubic feet per second Discharge in cubic feet per second Head Head for crests of various lengths Head Head for crests of various lengths in in in in feet inches feet inches lfoot 1.5 feet 2 feet 3 feet 4 feet lfoot 1.5 feet 2 feet 3 feet 4 feet 0.20 2% 0.291 0.439 0.588 0.887 1.19 .86 10ft « 2.46 3.72 5.01 7.59 10.19 .21 2*4 .312 .472 .632 .954 1.28% .87 10ft 6 2.50 3.79 5.10 7.72 10.36 .22 2% .335 .505 .677 1.02 1.37 .88 10ft 6 2.54 3.85 5.18 7.85 10.54 .23 2% .358 .539 .723 1.09 1.46 .89 lOlfte 2.58 3.92 5.27 7.99 10.71 .24 2% .380 .574 .769 1.16 1.55 .90 lOHie 2.62 3.98 5.35 8.12 10.89 .25 3 .404 .609 .817 1.23 1.65 .91 lOHis 2.67 4.05 5.44 8.25 11.07 .26 3« .428 .646 .865 1.31 1.75 .92 Il*'l6 2.71 4.11 5.53 8.38 11.25 .27 3% .452 .682 .914 1.38 1.85 .93 lifts 2.75 4.18 5.62 8.52 11.43 .28 3% .477 .720 .965 1.46 1.95 .94 11*4 2.79 4.24 5.71 8.65 11.61 .29 3*4 .502 .758 1.02 1.53 2.05 .95 11% 2.84 4.31 5.80 8.79 11.79 .30 3% .527 .796 1.07 1.61 2.16 .96 11*4 2.88 4.37 5.89 8.93 11.98 .31 3% .553 .836 1.12 1.69 2.26 .97 11% 2.93 4.44 5.98 9.06 12.16 .32 3Hi« .580 .876 1.18 1.77 2.37 .98 11% 2.97 4.51 6.07 9.20 12.34 .33 3 Hi 6 .606 .916 1.23 1.86 2.48 .99 11% 3.01 4.57 6.15 9.34 12.53 .34 4*i 6 .634 .957 1.28 1.94 2.60 1.00 12 3.06 4.64 6.25 9.48 12.72 .35 4ft 6 .661 .999 1.34 2.02 2.71 1.01 12*4 4.71 6.34 9.62 12.91 .36 4% 6 .688 1.04 1.40 2.11 2.82 1.02 12ft 4.78 6.43 9.76 13.10 .37 4fi 6 .717 1.08 1.45 2.20 2.94 1.03 12% 4.85 6.52 9.90 13.28 .38 4ft 6 .745 1.13 1.51 2.28 3.06 1.04 12*4 4.92 6.62 10.04 13.47 .39 4 Hi 6 .774 1.17 1.57 2.37 3.18 1.05 12% 4.98 6.71 10.18 13.66 .40 4i?i 6 .804 1.21 1.63 2.46 3.30 1.06 12% 5.05 6.80 10.32 13.85 .41 41% 8 5*i 6 .833 .863 1.26 1.30 1.69 1.75 2.55 2.65 3.42 3.54 1.07 1.08 12Hie 12Hi 6 5.12 5.20 6.90 6.99 10.46 10.61 14 04 .42 14.24 .43 5?i 6 .893 1.35 1.81 2.74 3.67 1.09 13*i 6 5.26 7.09 10.75 14.43 .44 5*i 5% 5*4 5% 5% 5% 6 .924 .955 .986 1.02 1.05 1.08 1.11 1.40 1.44 1.49 1.54 1.59 1.64 1.68 1.88 1.94 2.00 2.07 2.13 2.20 2.26 2.83 2.93 3.03 3.12 3.22 3.32 3.42 3.80 3.93 4.05 4.18 4.32 4.45 4.58 1.10 1.11 1.12 1.13 1.14 1.15 1.16 13ft 6 13ft 6 13ft 6 13ft 6 13 Hi e 13Hie 13 Hi e 5.34 5.41 5.48 5.55 5.62 5.69 5.77 7.19 7.28 7.38 7.47 7.57 7.66 7.76 10.90 11.04 11.19 11.34 11.48 11.64 11.79 14.64 .45 14.83 .46 15.03 .47 15.22 .48 15.42 .49 15.62 .50 15.82 .51 6*4 6*i 6% 6*4 1.15 1.18 1.21 1.25 1.73 1.78 1.84 1.89 2.33 2.40 2.46 2.53 3.52 3.62 3.73 3.83 4.72 4.86 4.99 5.13 1.17 1.18 1.19 1.20 14*i 6 14ft 6 14*i 14% 5.84 5.91 5.98 6.06 7.86 7.96 8.06 8.16 11.94 12.09 12.24 12.39 16.02 .52 16.23 .53 16.43 .54 16.63 .55 6% 1.28 1.94 2.60 3.94 5.27 1.21 14*4 6.13 8.26 12.54 16.83 .56 6% 1.31 1.99 2.67 4.04 5.42 1.22 14% 6.20 8.35 12.69 17.03 .57 6 Hi 6 1.35 2.04 2.74 4.15 5.56 1.23 14% 6.28 8.46 12.85 17.25 .58 6 Hi 6 1.38 2.09 2.81 4.26 5.70 1.24 14% 6.35 8.56 12.99 17.45 .59 7*i 6 7ft 6 1.42 1.45 2.15 2.20 2.88 2.96 4.36 4.47 5.85 6.00 1.25 1.26 15 15*4 6.43 8.66 13.14 13.30 17.65 .60 17.87 .61 7ft 6 1.49 2.25 3.03 4.59 6.14 1.27 15*4 13.45 18.07 .62 7ft 6 1.52 2.31 3.10 4.69 6.29 1.28 15% 13.61 18.28 .63 7ft 6 1.56 2.36 3.17 4.81 6.44 1.29 15*4 13.77 18.50 .64 7 Hi e 7 Hi e 7 Hi e 8ft 6 8ft e 1.60 1.63 1.67 1.71 1.74 2.42 2.47 2.53 2.59 2.64 3.25 3.32 3.40 3.47 3.56 4.92 5.03 5.15 5.26 5.38 6.59 6.75 6.90 7.05 7.21 1.30 1.31 1.32 1.33 1.34 15% 15% 15 Hi e 15Hie 161i6 13.93 14.09 14.24 14.40 14.56 18.71 .65 18.92 .66 19.12 .67 19.34 .68 19.55 .69 8V 4 8% 1.78 1.82 2.70 2.76 3.63 3.71 5.49 5.61 7.36 7.52 1.35 1.36 16ft 6 16ft 6 14.72 14.88 19.77 .70 19.98 .71 8*4 1.86 2.81 3.78 5.73 7.68 1.37 16ft 6 15.04 20.20 .72 8% 1.90 2.87 3.86 5.85 7.84 1.38 16ft 6 15.20 20.42 .73 8% 1.93 2.93 3.94 5.97 8.00 1.39 16Hi 6 15.36 20.64 .74 8% 9 1.97 2.01 2.99 3.05 4.02 4.10 6.09 6.21 8.17 8.33 1.40 1.41 16 Hi e 16 Hi 6 15.53 15.69 20.86 .75 21.08 .76 9*4 2.05 3.11 4.18 6.33 8.49 1.42 17*i 6 15.85 21.29 .77 9*i 2.09 3.17 4.26 6.45 8.66 1.43 17ft 6 16.02 21.52 .78 9% 2.13 3.23 4.34 6.58 8.82 1.44 17*4 16.19 21.74 79 9*4 2 17 3 29 4 42 6 70 8 99 1 45 17% 16.34 21.96 80 9% 2 21 3 35 4 51 6 83 9 16 1.46 17*4 16.51 22.18 .81 9% 2.25 3.41 4.59 6.95 9.33 1.47 17% 16.68 22.41 .82 9 HI e 2.29 3.47 4.67 7.08 9.50 1.48 17% 16.85 22.64 83 9 Hi s 2 33 3 54 4 75 7 21 9 67 1 49 17% 17.01 22.85 .84 10*i « 2.37 3.60 4.84 7.33 9.84 1.50 18 17.17 23.08 .85 10ft. 2.41 3.66 4.92 7.46 10.01 Circular 250] MEASUREMENT OF IRRIGATION WATER CIPOLLETTI WELES This type of weir is trapezoidal in shape, the name "Cipolletti" being that of the Italian engineer who proposed its use. As shown in figure 3, the crest of the weir, or bottom of the weir notch, must be level, and the sides placed on a slope of one to four, meaning one unit horizontal to four units vertical. The notch therefore is larger than a rectangle with the same crest length. It is readily seen that the Cipolletti type of weir, or in fact any weir having sloping sides, is not so easy either to construct or to check for accurracy as is the rectangular weir. The great popular- ity of the Cipolletti weir is due somewhat to its having been proposed 1 , ~>r>l/" ~l r% T L 24*-$$$ J ^ Yfe^Tf-r . 7T^1 L K J> Fig. 3. Two foot Cipolletti weir notch. at a time when the use of weirs for measuring irrigation water was being considered, but principally because the angle which the sides make with the crest was supposed to make the flow over the weir proportional to the length of the crest. In other words, the flow for a certain head on a two-foot weir was supposed to be twice the flow over a one-foot weir for the same depth of water, which would re- quire but a simple weir table for field use. Recent experiments, however, prove that the flow over Cipolletti weirs is not proportional to the length of the crest, which apparently refutes the principal argument in its favor. However, if the sides are placed properly with respect to the crest, and other conditions are observed fully, the flow can be measured as accurately over a Cipolletti weir as over a rectangular weir, by use of the accompanying weir tables, or formula. It is all right, therefore, to use a Cipolletti weir if built properly, but where a weir is to be constructed, the rectangular should be chosen in preference to the Cipolletti type. Table 2 gives the discharge over Cipolletti weirs from one to four feet in length, computed from the corrected formula. 10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE 2 Discharge Table for Cipolletti Weirs Head in inches Discharge in cubic feet per second for crests of various lengths 2% 2*4 2% 231 2% 3 3% 3% 3*4 3% 3% 31?'l6 3 15 'l6 4*ie 43'i6 49l6 4?16 4%e 4Hie 4i?i6 41%6 5*ie 59ie 5% 5% 5*4 5% 5% 5% 6 6*4 6% 614 6% 6% 6^16 6^16 71'l6 7%6 79'l6 7 7 /l6 791e 7H'i6 7i?i 6 71%6 8116 89ie 8*4 8% 814 8% 8% 8% 9 914 914 994 914 9% 9% 9»9'l6 9^16 1011s 109*6 1 foot 1.5 feet 2 feet 0.30 .32 .35 .37 .39 .42 .45 .47 .50 .53 .56 .59 .61 .64 .67 .70 .73 .77 .80 .83 .87 .90 .93 .97 1.00 1.04 1.07 1.11 1.15 1.18 1.22 1.26 1.30 1.34 1.38 1.42 1.46 1.50 1.54 1.58 1 1 1 1 1 1 1.89 1.93 1.98 2.02 2.07 2.12 2.16 2.21 2.26 2.31 2.36 2.41 2.46 2.51 2.56 2.61 2.66 2.71 2.77 2.82 0.45 .48 .52 .55 .59 .63 .67 .70 ..74 .79 .83 .87 .91 .95 1.00 1.04 1.09 1.13 .1.18 1.23 1.28 1.32 1.37 1.42 1.47 1.53 1.58 1.63 1.68 1.74 1.79 1.85 1.90 1.96 2.02 2.07 2.13 2.19 2.25 2.31 2.37 2.43 2.49 2.55 2.62 2.68 2.75 2.81 2.87 2.94 3.01 3.07 3.14 3.21 3.28 3.35 3.42 3.49 3.56 3.63 3.70 3.77 3.84 3.92 3.99 4.07 0.60 .64 .69 .74 .79 .84 .89 .94 .99 1.04 1.10 1.15 1.21 1.27 1.32 1.38 1.44 1.50 1.57 1.63 1.69 1.76 1.82 1.89 1.95 2.02 2.09 2.16 2.23 2.30 2.37 2.44 2.51 2.59 2.66 2.74 2.81 2.89 2.97 05 13 20 28 ■il 45 53 61 3.70 3.79 3.87 3.95 4.04 4.13 4.22 4.31 4.40 4.49 4.58 4.67 4.76 4.85 4.95 5.04 5.14 5.23 5.33 3 feet 0.90 .97 1.04 1.11 1.18 1.25 1.33 1.40 1.48 1.56 1.64 1.73 1.80 1.89 1.98 2.07 2.16 2.25 2.34 2.43 2.53 2.62 2.72 2.81 2.91 3.01 3.11 3.21 3.32 3.42 3.53 3.64 3.74 3.85 3.96 4.07 4.18 4.30 4.41 4.53 4.64 4.76 4.88 5.00 5.12 5.24 5.36 5.48 5.61 5.73 5.86 5.99 6.12 6.24 6.38 6.51 6.64 6.77 6.90 7.04 7.18 7.31 7.45 7.59 7.73 7.87 4 feet 1.20 1.29 1.38 1.47 1.57 1.67 1.77 1.87 1.97 2.08 2.19 2.30 2.41 2.52 2.64 2.75 2.87 2.99 3.11 3.24 3.36 3.49 3.61 74 .87 .01 14 .28 .41 55 3. 3. 4. 4. 4. 4. 4. 4.69 4.83 4.97 5.12 5.26 5.41 5.56 5.71 5.86 6.01 6.17 6.32 6.47 6.63 6.79 6.95 7.11 7.28 7.44 7.61 7.77 7.94 8.11 8.28 8.45 8.62 8.80 8.97 9.15 9.33 9.51 9.69 9.87 10.05 10.23 10.42 Head in feet .86 .87 .88 .89 .90 .91 .92 .93 .94 .95 .96 .97 .98 .99 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32 1.33 1.34 1.35 1.36 1.37 1.38 1.39 1.40 1.41 1.42 1.43 1.44 1.45 1.46 1.47 1.48 1.49 1.50 Head nches lCYie 10%6 lOTie lOHle 10'% 6 ioiy 16 lllie 11316 1111 U% 11*4 11% 1194 11% 12 12H 1214 1294 1214 12% 1294 1219! e 1219'ie 1311c 13916 13916 13?16 139ie 13H' 16 131916 13^16 14*16 149.6 1414 14% 1414 14% 1494 14% 15 1514 1514 1594 1514 15% 1594 151916 15^16 16116 16916 1691e 16?i 8 169ie 16H16 16*946 16^16 17*1 6 17916 17*4 17% 17*4 17% 1794 17% 18 Discharge in cubic feet per second for crests of various lengths lfoot 1.5 feet 2 feet 3 feet 4 feet 2.87 2.93 2. 98 3.04 3.09 3.15 3.20 3.26 3.32 3.37 3.43 3.49 3.55 3.61 3.67 4.14 4.22 4.29 4.37 4.45 4.53 4.60 4.68 4.76 4.84 4.92 5.00 5.09 5.17 5.25 5.33 5.42 5.50 5.59 5.67 5.76 5.84 5.93 6.02 6.11 6.20 6.29 6.37 6.46 6.56 6.65 6.74 6.83 6.93 7.02 7.11 7.20 7.30 7.40 7.49 5.43 5.52 5.62 5.72 5.82 5.92 6.02 6.13 6.23 6.33 6.44 6.55 6.64 6.75 6.86 6.96 7.07 7.18 7.29 7.40 7.51 7.62 7.73 7.84 7.96 8.07 8.18 8.29 8.41 8.53 8.65 8.76 8.88 9.10 9.12 9.24 9.36 9.48 9.60 9.72 8.01 8.15 8.30 8.44 8.59 8.73 8.88 9.03 9.17 9.32 9.48 9.62 9.78 9.93 10.08 10.24 10.40 10.55 10.71 10.87 11.03 11.18 11.35 11.51 11.68 11.84 12.00 12.16 12.33 12.50 12.67 12.84 13.01 13.18 13.35 13.52 13.69 13.87 14.04 14.21 14.39 14.56 14.74 14.92 15.11 15.29 15.46 15.64 15.82 16.01 16.19 16.37 16.57 16.75 16.94 17.13 17.31 17.51 17.70 17.89 18.08 18.28 18.47 18.66 18.85 10.60 10.79 10.98 11.17 11.36 11.55 11.74 11.94 12.13 12.33 12.53 12.72 12.92 13.12 13.32 13.53 13 . 73 13.94 14.15 14.35 14.56 14.76 14.98 15.19 15.41 15.62 15.84 16.04 16.26 16.48 16.70 16.93 17.15 17.37 17.59 17.81 18.03 18.27 18.49 18.71 18.95 19.17 19.41 19.65 19.88 20.12 20.34 20.58 20.82 21.06 21.29 21.53 21.78 22.02 22.27 22.51 22.75 23.01 23.26 23.50 23.75 24.01 24.26 24.50 24.75 Circular 250] MEASUREMENT OF IRRIGATION WATER 11 90-DEGEEE TEIANGULAE-NOTCH WEIRS This type of weir (Fig. 4) deserves to be more widely used than at present for the measurement of small quantities of water to the irrigator. If sufficient fall is available it may be used for flows as great as fourteen second-feet, which would be obtained with a depth of practically two feet of water above the vertex, or lowest point, of the angle formed by the sides. However, conditions usually are not favorable for its use for such large heads, and table 3 gives the discharge for heads up to 1.25 feet. Since the sides meet at a point with no length of crest, a small flow of water that would not pass over one of the other weirs without adhering to the crest and therefore making the measurement worthless, will flow free in the ninety-degree Fig. 4. 90° weir notch. triangular notch and may be measured accurately. The ninety-degree triangular notch is especially applicable from small flows up to two or three cubic feet per second. Because of the greater depth of water required for this type of weir to discharge a given quantity of water, and the consequent greater loss of head, one of the other types of weirs usually will be better adapted to large quantities of water. Experi- ments have shown that the rectangular and Cipolletti weirs with six- inch crest lengths do not follow the same laws of discharge as the longer weirs, and the discharge formulae given in this circular for these weirs do not apply to weirs with a crest length of six inches or less. Therefore, where only a small flow of water is to be measured the use of the ninety-degree triangular notch is especially recom- mended. The sides of the ninety-degree triangular notch may be set read- ily by means of a carpenter's square and level. The notch can be marked out properly by placing the point of the angle between the arms of a carpenter's square at a point which is to be the bottom of the notch and adjusting the square so that the same figures on 12 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION both arms of the square are at the edge of the board, then if the board is set level the notch will be in the proper position. The sides, therefore, have the same slope. Table 3 gives the discharge over the ninety-degree triangular notch, computed from the corrected formula: TABLE 3 Discharge Table for 90° Triangular Notch Discharge Discharge Discharge Head in Head in in second- Head in Head in in second- Head in Head in in second- feet inches feet (Q) feet inches feet (Q) feet inches feet (Q) 0.20 2% 0.046 0.55 6% 0.564 0.90 101?'l6 1.92 .21 2*4 .052 .56 6% .590 .91 ioiy, 6 1.97 .22 2% .058 .57 6^8 .617 .92 lUie 2.02 .23 2% .065 .58 m* .644 .93 11%6 2.08 .24 2% .072 .59 . 7Via .672 .94 11% 2.13 .25 3 .080 .60 7%6 .700 .95 11% 2.19 .26 3% .088 .61 7%a .730 .96 n% 2.25 .27 3% .096 .62 7yi 6 .760 .97 n% 2.31 .28 3% .106 .63 7%6 .790 .98 n% 2.37 .29 3*4 .115 .64 7Hi 6 .822 .99 n% 2.43 .30 3% .125 .65 7Mia .854 1.00 12 2.49 .31 3% .136 .66 7Hia .887 1.01 12% 2.55 .32 3i?ic .147 .67 8Vi 6 .921 1.02 12% 2.61 .33 3^16 .159 .68 8%8 .955 1.03 12% 2.68 .34 4H« .171 .69 8*4 .991 1.04 12% 2.74 .35 4%6 .184 .70 8% 1.03 1.05 12% 2.81 .36 4 , 3&V ■ ' Fig. 14. Photograph of Azusa miner's inch box. Taken from above. 13). The orifices for the desired amounts to be turned out are opened and the others closed with slides. By adjusting the gate under the spillway the water can be brought to the crest of the spillway. If the water rises above the spillway a large part of the excess will be carried back to the supply line over the spillway, but any increase in depth on the orifices will also increase the amount turned out. The Azusa hydrant as shown has walls six inches thick, all sides being vertical. The forms required in making it are therefore simple. The box contains 78.3 cubic feet of concrete. This can be made of Circular 250] MEASUREMENT OF IRRIGATION WATER 29 one part cement and four parts coarse sand. As the walls are six inches thick it is better to add some gravel (not larger than iy 2 inches) to the sand where this can be obtained cheaply, but the pro- portion of one part cement to four parts of aggregate should be maintained. The concrete for this box including forms will cost from $18.00 to $20.00 under a large contract and about $30.00 if made singly. The plate with the openings and slides can be bought already made for $12.50 from foundries in the vicinity of the places the hydrant is used. The gate can be any of the usual types of slide gate. The average of a number of tests made of this hydrant at Davis showed the amounts in inches being carried through the openings to be one per cent more than their area in square inches. This dif- ference includes all errors in the measurements so that these openings are seen to be very accurate. The tests showed all openings or com- binations of openings to be equally accurate. The box will there- fore measure as accurately as is required. The openings are not as closely adjustable to the amounts turned out, however, as they are in the case of the box of the Riverside Water Company. Errors to be avoided in the use of this hydrant result from allowing the water to pass through the openings unevenly, which produces a swirling motion of the water as it rises to the openings ; also from not so ad- justing the gate under the spill-crest as to keep the flow over the spill to a thin film of water. DIVISION BOXES In some places in California, as well as in other western states, the waters in small streams are so allotted that an individual user is entitled to a definite proportion of the entire flow of that stream. This proportion is usually fixed by consideration of the number of irri- gable acres each owner farms and the age of the established water rights. Canal companies in areas where this method of proportional delivery is common have at times adopted division boxes for the divi- sion and distribution of their supply. In such cases the company is commonly organized as a stock company and the stock purchased by the water users. One share of stock usually represents one acre of irrigable land. If, for instance, 100 shares of stock have been sold in a ditch company and one user owns ten shares, that user is entitled to 10/100 of the entire flow of the canal. Many types of division boxes have been designed in an effort to make this propor- tionate division just and accurate. All of these devices are based upon the principle that for a given head the discharge over two weir 30 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION crests set at the same elevation is approximately proportional to the length of those weir crests. In the example given above the water user is entitled to 10/100 of all the water in the canal. Such a division might be made by set- ting two weirs at the same elevation in the canal near the farmer's turnout. If, for example, one of the weirs has a crest ten inches long and discharges its water into the farmer's lateral, and the other weir with a crest ninety inches long empties its water into the com- pany's ditch, this proportionate division would be equitably accom- plished, since the lengths of the weir crests would have the same ratio as that required by the conditions of the diversion. No matter how much water came down the canal, the user would receive 10/100 of the entire flow. These division weirs are subject to the conditions already given for other weirs. These conditions are usually difficult to obtain throughout the length of a canal. The users at the upper end of the canal do not contribute toward the payment for water lost by seepage below them in the canal and the whole charge for this loss falls on the users at the lower end. Several structures have been designed to obviate these difficul- ties, but in most cases this has been done at the sacrifice of accuracy in the division. An isometric drawing of one of these devices is shown in figure 15. With this structure the water enters the flume at the left, is divided into the required proportion by the vertical cutwater, and is discharged into the user's flume which leads off to the right or runs out of the flume and into the company's ditch again. A flat crested weir set across both divisions of the flume and about three feet back from the entering end aids in the just division. In a struc- ture of this sort the dividing partition in the flume is so set that its distance from the water user's side of the box holds the same propor- tion to the whole width as the number of shares of stock owned by the water user holds to the number of shares below him plus those he holds himself. In the case as given above the user owned ten shares of stock. One hundred shares had to be served by the water in the canal. The partition in his box would then be built so that it stood 10/100 of the way across the box. He, of course, would re- ceive the water pouring through the narrower compartment. The hinged gate at the beginning of the user's flume will allow him to turn water into his ditch or back into the company's canal at will. Such a structure assumes that water flows with an equal velocity at all points in a stream. This is never or very seldom the case, for the water near the banks is necessarily slowed down by weeds, rocks Circular 250] MEASUREMENT OF IRRIGATION WATER 31 or irregular earth work of the banks and bottom. With such a box the water user will usually receive less water than he is entitled to, for his share is taken from an area of reduced velocity while the water running past him comes from the fastest-flowing part of the stream. A box such as that described above contains about 650 board feet of lumber. Note: Gate to bo 'at this ■post U**3'6' Fig. 15. Drawing of proportional division box. MECHANICAL. DEVICES FOR MEASURING WATER VOLUMETRICALLY It frequently is desirable that a measuring device should record the volume of water delivered to irrigators, rather than the rate of flow. Numerous mechanically recording devices have been designed to accomplish this, several of these being described below. Without discussing the individual merits of these devices, it may be said that although several of them are in use in California and are believed by those using them to be giving more or less satisfactory service, there are many practical difficulties involved in operating devices of this nature. It would, therefore, seem that when a mechanical device is selected for measuring individual farmer's deliveries of irrigation water, the practical limitations of the device chosen should be under- stood. This is desirable in order that care may be taken to provide the conditions necessary for satisfactory measurements, and also that the need for occasional tests of the operating accuracy of the devices may be appreciated. 32 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION EELIANCE METER The Reliance meter consists of a brass vane, shaped something like a propeller wheel, set in a throat, and a brass rod which connects the vane to the recording head. This recording head contains gear- ing which is connected with a counter. The figures in this counter show the number of acre-feet of water which have passed through the device. Fig. 16. Photograph of Reliance meter. This apparatus is set so that the water to be measured pours be- tween a series of plates or vanes and on to the propeller shaft in the throat. It can be used in either open ditches or concrete pipe lines. The great advantage of such a device lies in the fact that it shows at a glance how many acre-feet of water have passed through the meter. With most other devices some computations are necessary to change the expression of the flow in cubic feet per second into terms of acre-feet. Figure 16 is a photograph of a Reliance meter installed on a con- crete pipe line. Circular 250] MEASUREMENT OF IRRIGATION WATER 33 DETHRIDGE METER In the Keliance meter only a part of the stream hits the propeller wheel and turns it. In the Dethridge meter (Fig. 17) the whole flow of the stream is directed against the wheel. The wheel in this case is a large sheet-iron drum, three feet, four inches in diameter and two feet, six inches wide. Attached to the outer surface of this drum are a series of heavy blades which extend ten inches beyond the circumference of the drum. Fig. 17. Photograph of Dethridge meter. This drum turns in hardwood bearings attached to the concrete base. When the wheel turns the projecting blades fit closely into a depression in the concrete floor of the device. Water, when turned into the device, presses successively against the blades on the cylinder and turns it in the bearings. A counter can easily be arranged to record these revolutions. With a Dethridge meter of the size described above, the discharge per revolution is about 30.5 cubic feet of water, regardless of the speed at which the wheel revolves. Each wheel installed should be accurately calibrated to determine the quantity of water discharged by the wheel per 34 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION revolution. The Dethridge meter has been very popular in Australia where a large number are in use. The device has never been used for the practical measurement of water in California. A description of the Dethridge meter is included in this circular because it involves a new principle. OTHER MEASURING DEVICES The Lyman meter. Many mechanical devices have been invented and patented by which the flow over weirs can be read as a quantity in terms of acre-feet, in place of as a rate of flow as in cubic feet per second. One of the more recent of these devices is the Lyman meter. The Lyman meter consists of a small, delicately balanced brass turbine wheel, enclosed in a brass shell. This shell is attached to the down-stream face of a weir bulkhead and must be so set that a hole bored through the weir bulkhead and leading into the turbine shell shall have a fixed relation with the weir notch. On the up- stream side of the weir board is a brass tube in which carefully placed openings have been cut. This brass tube connects at its base with a short length of pipe which passes through the weir bulkhead and into the turbine shell. The holes in the brass tube on the up-stream side of the weir bulkhead are of such varying diameters that they separate a cer- tain definite proportion of the water from the stream going over the weir, no matter at what height the water may stand above the weir. This small flow passes down the tube, through the bulkhead and into the turbine shell, where it revolves the small turbine wheel. This wheel is geared to a counter in such a way that the quantity can be read directly on the face of the counter. Different sizes of turbine wheels and different calibrations on the up-stream tube are necessary for use with weirs of various types and various lengths of crest. The Sentinel meter. This meter is mounted in a 2-foot section of steel pipe designed to be set in an irrigation pipe line, the size of the meter and of the steel section depending on the size of such pipe line. A wheel or turbine set in the steel section turns as the water passes through the pipe line, the revolutions of the wheel being indicated by a counter set in a dial above the steel section, the gearing being so arranged that the quantity of water passing is directly indicated by the counter. CIRCULAR 250] MEASUREMENT OF IRRIGATION WATER 35 The Vcnturi meter. The Venturi meter is a device for the ac- curate measurement of relatively large flows of water. This device, in irrigation systems, is confined to large diversions from main canals into laterals and not to the measurement of water from the lateral to the individual user. The Venturi flame. The Venturi flume is similar to the Venturi meter in theory. "Water in an open ditch is led into a structure through a narrow throat and out into the original channel. In pass- ing through this constricted cross-section, a difference in head above the device and in the throat always results. This difference in head, which may be determined as in the submerged orifice, is the measure of the amount of water which passes through the device. Tables and curves have been prepared to aid in determining the amount of water passing through the Venturi flume when the difference iu water level above and below the device is known. The difference in head which results when a stream of water passes through the Venturi flume may be so small that it is very difficult to measure it accurately. SUMMAEY Common devices for measuring irrigation water in California in- clude rectangular, Cipolletti, and triangular weirs, submerged ori- fices with fixed and with adjustable openings, various miner 's-inch boxes and hydrants, and numerous mechanical devices for registering the volume of water that passes through them. In cases where the water to be measured is free from silt and where the grade of the ditch is sufficient to allow for the required backing up of the stream, some type of weir is undoubtedly the most satisfactory device. A weir is accurate, cheap, easily installed and has no moving parts to get out of order. For small heads of water, a triangular or "V" notch weir is most accurate. For larger heads a rectangular weir is most satisfactory. A Cipolletti weir seems to have no ad- vantage over a rectangular weir; it is harder to construct and for this reason is liable to be more inaccurate than the simple rectangular weir. If the ditch grade at the required point of measurement is so flat that the necessary fall over a weir crest can not be provided, or if the water to be measured is so heavily charged with silt that a weir pond would rapidly fill up, a submerged orifice may be con- sidered the most satisfactory device. 36 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION A submerged orifice of fixed dimensions, if carefully installed and with careful measurements for the difference in head, will give fairly accurate results. Accuracy is necessarily sacrificed when wide fluc- tuations in the stream to be measured make it necessary to install an adjustable orifice. With the adjustable orifice the coefficient "C, M which is used in determining the discharge, varies with the area of the opening. Besides this indefinite value of "C" there is an added complication due to variation in individual boxes. The skill of the carpenter who builds the device may affect its discharge to a con- siderable extent under given conditions. At times an adjustable sub- merged orifice is the only device at all suited to the conditions which must be met. Miner 's inch boxes are used chiefly in the foothill orchard sec- tions and in the citrus sections of southern California. These are usually installed by the company furnishing the water. If carefully installed and proper conditions of measurement are maintained, they will give approximately correct results.