170 



THE IRRIGATION AGE. 



Reinforced concrete 



ultimately an ex- 

 ample of any ir- 

 rigation measur- 

 ing device of mer- 

 it may be seen 

 installed under 

 practical field 

 conditions on the 

 University Farm. 



There are va- 

 rious units of 

 water measure- 

 ment, which fig- 

 ure in experi- 

 ments such as are 

 here described. 

 These water 

 m e a s u r ement 

 units include : 



The Inch. - 

 This is a variable 

 unit having dif- 

 ferent meanings 

 in different 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 1 inch 

 square, the center of which was 

 4 inches below the surface of 

 the water standing above the 

 opening, and which is equiva- 

 lent to a flow of 9 gallons per 

 minute or 1/50 cubic foot per 

 second. The present statute 

 inch of California is defined as 

 a flow of one and one-half 

 cubic feet per minute. It is 

 measured under a 6-inch pres- 

 sure 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 practice, it is 

 not a stream of water 1 inch 

 deep and 1 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 com- 

 monly used for such streams, 



particularly on many of the southern California sys 

 terns. For larger streams its use is generally discarded 

 in favor of the more definite cubic foot per second. 

 The 24-Hour Inch. This is a very common unit, 

 especially in southern California, and is, as its name 

 implies, 1 inch (the exact amount of which varies 

 with locality and local custom) running for 24 

 hours. Variations of this unit found on some Cali- 

 fornia irrigation systems are the 1-hour inch and the 

 12-hour inch. 



The Cubic Foot per Second. This unit repre- 

 sents an exact and definite quantity of water, viz. : 

 the equivalent of a stream 1 foot wide and 1 foot 



Davis Field Labors 



A water register. Experimenters at the Davis 

 Laboratory declare tliest instruments require too 

 much care and are too expensive for use in 

 making delivery of water to farms. 



deep flowing at 

 the rate of 1 foot 

 per second. It 

 is therefore the 

 most satisfactory 

 unit for streams 

 of one or more 

 cubic feet per 

 second. 



The 24-Hour 

 Second Foot. 

 This is one cubic 

 loot per second, 

 running contin- 

 uously through- 

 out a 24-hour pe- 

 riod. It is equiv- 

 alent to approx- 

 imately 2 (exact- 

 ly 1.9834) acre- 

 feet. 



The A c r e - 



'ory. Foot. - - This is 



the equivalent of 

 a body of water 1 acre in area 

 and 1 foot deep, or 43,560 cubic 

 feet. As already stated, one 

 cubic foot per second, or 50 

 southern California inches, or 

 40 California statute inches, 

 running continuously for 24 

 hours will supply approxi- 

 mately 2 (exactly 1.9834) acre- 

 feet. 



The Acre-Inch. This is one- 

 twelfth of 1 acre-foot, or the 

 equivalent of a sheet of water 

 1 acre in area and 1 inch deep. 

 It is the unit sometimes used 

 instead of the acre-foot, espe- 

 cially in expressing quantities 

 of less than 1 acre-foot. 



The Gallon. As many irri- 

 gators receive their water sup- 

 ply from pumps, and as pump 

 manufacturers usually esti- 

 mate discharges in gallons per 

 minute or gallons per second, 

 this is sometimes a convenient 

 unit to use. One cubic foot is 

 approximately equal to 7y> 

 gallons ('exactly 7.4805) and 1 

 cubic foot per second is ap- 

 proximately equivalent to 450 gallons per minute or 

 7]/2 gallons per second. 



Otic Thousand Gallons. This unit is quite com- 

 mon in irrigation practice in San Diego County, 

 C'al., where the cost of irrigation water is perhaps 

 higher than anywhere else in the United States. 



In addition to the various measuring devices 

 subsequently described, the Davis laboratory con- 

 sists of the following elements : 



(1) Reinforced concrete lined reservoir 96 

 feet long, 16.5 feet wide, and 5.5 feet deep, with side- 

 slopes of 1 to 1, and with elevation of 94.8 feet 

 (Continued on page 188.) 



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