THE ART OF IRRIGATION. 



147 



If the land-owner could have got them 

 during the six months of summer he would 

 have either wasted them or have extended 

 his acreage. Or if he had the place in 

 alfalfa he might have used them all to ad- 

 vantage on the ten acres. But very few 

 companies either public or private could 

 run on such a principle without too great 

 an expense for the water and the size of 

 the aqueducts for its delivery or too great 

 a clash of interest among the irrigators. 

 For an inch of water means the equivalent 

 of an inch for a year taken in heads accord- 

 ing to rules for the convenience of all con- 

 sumers and one of the first of these gener- 

 ally is that one cannot exceed thirty 

 twenty-four inches a month. Daring the 

 other six months he could have had the 

 other one hundred and eighty-five twenty- 

 four-hour inches. Had he used them he 

 could have extended his acreage or used less 

 water on the piece he actually irrigated as 

 shown in the chapter on winter irrigation. 

 But he preferred to take his chances on 

 the clouds doing their duty and let them 

 go to the sea unused a clear waste of 

 public wealth. If the clouds failed to do 

 their duty then he would need more than 

 thirty inches a month for the summer ; but 

 he not only could not get any more, but 

 he might under the rules have to take less; 

 for no ditch can be successfully managed 

 even by the landowner's without making 

 all take shortage sometimes. 



MORE ABOUT DUTY OF WATER. 



Be careful now and follow me closely 

 for this subject has puzzled many a head. 



During the six months the water was 

 used on this ten acre tract it was used at 

 the rate of three hundred and sixty-five 

 twenty-four hour inches for the year. But 

 the actual business was done by one hun- 

 dred and eighty twenty- four hour inches. 

 But as during the six months of actual use 

 it was applied at the rate of an inch to ten 

 acres it is called an inch to ten. The 

 absurdity of this is more apparent by sup- 

 posing it had been only once, say thirty 

 inches in July. Because used at the rate 

 of an inch it is still called an inch to ten, 

 whereas the quantity actually put upon 

 the ground is but one-sixth of what it was 

 before. According to this in a country 

 needing so little irrigation that once a year 

 would suffice the duty of water would be 

 about the same as in one needing it all 

 the time. 



But how are we to get at the duty any 

 other way? Well, at present it is not 

 easy. It is certain that the effectiveness 

 of any water system, as a system, can be 

 tested only by what it will do during that 

 period of the year when most water is 

 needed and vegetation will suffer most if 

 not quickly and fully supplied. That is 

 the way this method of computation arose 

 and remains in fashion. If a stream will 

 furnish a thousand feet a second during 

 the winter when it is not needed, or if 

 people think it is not needed, which for 

 this purpose is the same thing, but will 

 furnish only one hundred feet during the 

 three summer months when the water is 

 most needed and the full capacity of the 

 stream is in demand every day, it is clear 

 that the power of that stream as an irri- 

 gating resource is measured almost en- 

 tirely by what it will furnish during that 

 time. 



On the other hand it is just as certain 

 that had the owner of the ten acre tract 

 above mentioned put upon the ground the 

 one hundred and eighty-five twenty-four 

 hour inches that went to the sea the other 

 one hundred and eighty would have done 

 more duty than they did. The one hun- 

 dred and eighty-five would have covered the 

 tract about nine inches deep, which would 

 in effect have been equal to about eighteen 

 inches of rain as it generally comes here 

 in winter. Added to the regular rainfall, 

 which at that place is about twenty inches, 

 it would have put the ground in such con- 

 dition that almost anything but oranges, 

 lemons, berries and a few such things 

 would give a good yield without any irri- 

 gation in summer. When water becomes 

 valuable enough to make people store it 

 in the ground if they cannot afford to 

 store it above, the duty of water will be 

 estimated by the depth of water put upon 

 the tract during the year. Until then it 

 will be estimated by the rate for the irri- 

 gating season because the great majority 

 of the canals of the country depend upon 

 the flow of streams that are lower during 

 that time. 



If ' ' the season " were everywhere the 

 same we might compute in this way. But 

 as it varies continually with locality and 

 products you will never unravel the tangle 

 of opinions on the duty of water until you 

 understand the following figures: 



A miner's inch under four-inch pressure 

 will cover about fourteen and a quarter 



