228 THE IRRIGATION AGE. 



much above the level on which it is first struck, you have a reservoir 

 in which the dam is generally friction instead of masonry. But it is 

 none the less a reservoir. Too many taps cannot be made in it nor 

 can too many be left open. Much of the development made this year 

 will represent pockets or channels of water connected with the source 

 of supply by some small thread of gravel through which water moves 

 very slowly. If exhausted it may take a long time after the next wet 

 winter to fill them again. In many cases the very fact they are now 

 full shows that they have no outlet to the sea. From this it is quite 

 easy to understand how the inlet to them may be very small. For if 

 it were very large the channel would probably go clear through to 

 the ocean. , The expression inexhaustable well has become quite 

 common. But all wells are inexhaustable as long as you do not 

 exhaust them. The test will come after many weeks, months or even 

 years of pumping, when you have planted your orchard or alfalfa and 

 expanded out on the strength of the new supply. Many develop- 

 ments will stand it but it is quite as certain that many more will not. 

 In case of wells, which will be the principal means of develop- 

 ment, keep a careful record of the material passed through, so that 

 you will know whether you are on gravel channel which is probably a 

 stream or only in a sponge which will feed the well by seepage. 

 Seepage is unreliable for heavy and continuous work. It may do for 

 the windmill but generally 'the engine that is throwing much of a 

 stream. 



MUST BE ON AN UNDERGROUND STREAM 



or a few weeks or even a few days may find the bottom of the well 

 dry soon after the engine starts up. At first the well fills readily 

 when pumped out but a cone of depression forms around it as soon as 

 the pump begins. At first the sides of this are steep and when the 

 pump stops the water soon fills it to the general level of the stratum 

 of water in the sand or gravel. Day after day the edges of this cone 

 spread farther away from the well, the slopes forming the sides 

 become longer and more nearly a level. The water having farther to 

 travel through resisting material comes in more slowly while the 

 general level of the stratum of water is constantly falling to the level 

 of the bottom of the pump. Once down there it may take several 

 weeks, months or even years to fill again. The time cannot even be 

 guessed at for you know nothing of the mode of supply and perhaps 

 not even its source. Such is quite certain to be the case with wells 

 sunk in decayed granite if a heavy draft is made on them. Even 

 though the water comes in from crevices they cannot long be 

 depended on. 



THE PASSAGE OF WATER THROUGH FINE MATERIAL IS VERY SLOW. 



You all know springs in the hills that flow without weakening 

 for at least seven months after the last rain and yet where it is much 



