48 THE 1RRIGA TION A GE. 



will only equal five hundred yards of storage space. So that to have 

 storage space for thirteen thousand yards of water at $130 an inch in 

 place, you will need twenty -six cubic yards in the dam. If these con- 

 ditions hold out you would have a dam containing twenty-six thousand 

 yards of masonry at $5 a yard, costing $130,000, and holding one 

 thousand inches of water continuous flow for two hundred days. 



There are few basins in Southern California that will fulfill these 

 conditions, and they are none too plenty in any country. And in this 

 we have not allowed for the evaporation, which will . be about three 

 feet for the irrigating season of two hundred days. Seepage and loss 

 in transit cannot be estimated, but generally that loss is trifling. 



This does not consider any of the other expenses of the reservoir 

 or the aqueduct or the maintenance of both. It is merely a basis from 

 which to estimate the chief item of expense in reservoir systems. 

 And upcn this comes the fact, now proved, that we must carry ahead 

 water for at least two seasons and, for real safety, enough for two 

 and a half or perhaps three if there is much of a town dependent on it. 



These are unpleasant facts yet they are stubborn. But they by 

 no means prove the reservoir system a failure. There are sections 

 that can well afford to pay even on this basis, others where cheaper 

 dams may be built, others where the reservoir may be merely supple- 

 mentary to a stream that most of the year supplies enough water, 

 while in other cases thorough winter irrigai ion with cultivation will 

 make the draught on a reservoir in summer very light. Yet we must 

 face the fact that good reservoir sites are rare and that the first thing 

 to do is what is generally reserved to the last estimate the first cost 

 of the water in place back of the dam. 



This applies to reservoirs to be filled only once a \ o:ir or once in 

 two years, Basins that are flat enough and wide enough, with a 

 mouth narrow enough for a cheap dam, with foundation suitable for a' 

 safe one, yet with a watershed of sufficient size and rain-fall, but not 

 so large as to have a huge river to fight or a vast wash of sand to fill 

 up the reservoir, are very scarce in any country. But where there is 

 a very large one it will pay to spend considerable on it rather than re- 

 sort to small ones that are cheaper. For they are quite apt to be 

 cheaper in appearance only. The rule is that the smaller ihe reser- 

 voir is the more expensive is the water. This is certain to be so in 

 nine out of ten of small basins that look very fine, and in all of them 

 there is apt to be more uncertainly about the supply when badly 

 needed. 



A reservoir to be tilled more than once a year, as is the case with 

 most of those in -the Atlantic states, is a different affair, and so is one 

 hero to be filled from another source than its own watershed. For 

 reservoiring an irrigating head several times during the irrigating 

 season much more expense will often be justified Most of the small 

 reservoirs we see made for this purpose will repay their cost because 



