CHAPTER VII. 



RESERVOIRS AXD POXI>S. 



The fortunate irrigator who has a reservoir of his 

 own has his water supply constantly on tap the reser- 

 voir may also appropriately be called the farmer's savings 

 bank. An irrigation system depending upon storage, 

 when the storage works are judiciously constructed, is 

 the most reliable of all. The reservoirs can hold the 

 waters of a wet year for use in a dry one, and in the pos- 

 sible sequence of several dry years the smaller stored 

 supply gives several months' warning to irrigators, so 

 that water can be husbanded and made to perform a 

 larger duty than usual in order to tide over a period of 

 scarcity. 



The problem of water storage for irrigation is a very 

 different one from that for the domestic supply of a city. 

 In the first place it is important that water for domestic 

 use be as nearly as possible free from mud and organic 

 impurities, while for irrigation such impurities are not 

 only no objection to the water but often materially add 

 to its value by enriching the soil to which it is applied. 

 Waters held in reservoirs and intended for irrigation pur- 

 poses are often rendered much warmer ^than the flowing- 

 waters of streams, and are therefore more beneficial to 

 plant growth when drawn off and applied. The reser- 

 voirs must also be credited with having a salutary effect 

 on the atmosphere of the arid region, and countless num- 

 bers of them scattered here and there over the lands 

 would greatly increase the humidity, and brin^ about a 

 marked meteorological change for the better. In Western 



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