Quantity of Water Consumed in Irrigation. 39 



have been more, but this will not be found materially to 

 affect the result), and using the same symbols as in Ap- 

 pendix B, the following results are obtained : — 



D = 4668 c. ft. per second ) 794,794 ^ 



A = 794,794 acres } a = -4GG8~ = 1 '° acreS 



Q = 4668 x 86,400 = 403 million c. ft. 



q = 152 Q -r- A = 77,132 c. ft. per acre. 



The area of wetted surface (M) over which the loss took 

 place may have been less in 1868-69 than in 1875-76, since 

 there was a less length (by nearly 300 miles) of distributaries 

 in the former year ; but probably the larger area irrigated 

 necessitated more village watercourses being in operation, 

 while many of these, doubtless, having been quickly and 

 carelessly formed on an emergency, and used for the rirst 

 time, the loss in them would be greater than in ordinary 

 years. On the whole, then, perhaps it will be safe to 

 estimate the loss (Qa) as in both years the same, that is, 192 

 million cubic feet daily. Then q a = 152 Q a -r- A = 36,740 

 cubic feet per acre, leaving q c = 40,392 cubic feet per acre, 

 which would represent a depth of about 11 inches. Allow- 

 ing 3 J inches per watering (see par. 13), it would appear 

 that a little over three waterings, on the average, were 

 given, which is probably correct. Taking a greater number 

 of days (than 152) for the season would increase the values 

 of q and q c ; but, if irrigation went on for a longer period, 

 it would be only fair to assume that more waterings would 

 be given to some of the fields ; this would increase the 

 average number of waterings as well as the consumption of 

 water per acre without altering the " duty." It is evident 

 from Colonel Brownlow's remarks that fewer waterings were 

 given at the ordinary time; the above calculation gives 

 corresponding results, and so far supports the author's pre- 

 vious deductions. 



27. In the second instance the result — 65,000 cubic feet 

 per acre (q) — may be distributed in the following manner : 

 — D = 12 cubic feet per second = 432,000 cubic feet in 10 

 hours, the consumption daily. Mean distance of the fields 

 from the tank was two miles ; though as much as two miles 

 of distributary and ten village watercourses, each say half a 

 mile long, would be running at one time to irrigate 20 acres 

 daily, on the average. Then the area over which loss has 

 to be distributed was : — 



