GANNETT.] AMOUNT OF WATEE USED IN. IRRIGATION. 321 



grounds ougbt to receive 200 inches of water, or six times the total 

 amount of precipitation, during the growing season." In Egypt ("Man 

 and Nature," page 380) about 17^ inches, applied during 150 days, suf- 

 fice. The report of the Commissioner of Agriculture for 1871 gives 

 (page 280) the amount of water applied in France, from the Marseilles 

 Canal, as one cubic foot per second for 70 acres. This is equivalent to 

 an annual precipitation of 122.4 inches. 



In the same report the following facts regarding the usage in Italy 

 are given. For rice lands the equivalent of 16.2 inches per month, or of 

 an annual precipitation of 194.4 inches is used ; for summer meadows, 

 7.2 inches per month, or 86.4 per year j for maize, 2.4 per mouth, or 28.8 

 ■per year. 



In the sub-Himalayan districts the practice is to allow one cubic foot 

 per second for 218 acres, and this is very nearly the result to which 

 Marsh arrives. (See report U. S. Geol. Survey, 1870, page 260.) This 

 is equivalent to an annual precipitation of 39.36 inches. This, however, 

 is far below the amount used in the West at present, but I have no defi- 

 nite comparable data on the subject. 



This allowance of water takes into account roughly the amount wasted 

 by evaporation and absorption by the bottom and sides of the ditches ; 

 an amount which, of course, differs in every case, and of which no cer- 

 tain estimate can be made. 



The rain fall is of so uncertain, variable, and sudden a nature, that I 

 do not consider it best to ta.ke it into account in making estimates of 

 arable land ; particularly as the amount of water allowed is, as stated 

 above, much below the practice at present, and as, iii some localities, 

 the rain-fall may, in any year, be absolutely nothing. 



In a " Report on the Irrigation of the San Joaquin, Tulare, and Sac- 

 ramento Valleys of California," the following facts concerning the amounu 

 of water per acre are given : The commissioners estimate that, on an 

 average of crops and soils, one cubic foot per second will irrigate 200 

 acres, and quote the following statements: "In North India one cubic 

 foot per second irrigates five acres per day. Taking the interval of 

 irrigation at 40 days, we have the duty of 200 acres for one foot a second, 

 for cereals. In Grenada, a canal for the Genii irrigates of wheat, barley, 

 and vines, 240 acresDcr cubic foot. In Valencia, * * * about 200 

 acres per foot. In Bfcbe, where water is very scarce, a cubic foot goes 

 so far as to irrigate 1,000 acres. * * * Eice fields in different parts 

 of the earth vary from 30 to 60 or even 80 acres to the cubic foot. In 

 the heavy monsoons of India, 90 acres per foot is irrigated. * * * 

 The grants for six recent canals in Spain run from 70 to 260 acres per 

 cubic foot." 



PROPER SEASON FOR GAUaiNG STREAMS. 



Before giving any facts regarding the amount of the discharge of 

 streams, with relation to their irrigating capacity, I wish to call atten- 

 tion to the fact that these measurements amount to very liltle, except 

 as very general indications. The volume of water carried to-day is 

 little indication of what it may be to-morrow. A heavy shower or a 

 warm day in the mountains may temporarily double the discharge. At 

 the time of the spring floods, in June, the amount discharged may be 

 five, ten, or even twenty times that sent down in November, when the 

 streams arQ at their lowest. 



The proper time for gauging, with reference to the irrigating capacity 

 of the stream, is at the end of July or early in August, about the close 

 21 a 



