464 Irrigation and Drainage 



well, as in Fig. 150, into which the main drain, A, 

 discharges, and from which there is an overflow, B, 

 to the reservoir. The object of the well is to place 

 the pump under conditions where it will not freeze in 

 the severest weather, and thus prevent the ground from 

 becoming over- saturated at any season. The water may 

 be made to discharge through an under- ground drain 

 connected directly with the pump, as at C, or a flume- 

 box above ground may be used, as is most convenient. 



It might even be practicable to have this drainage 

 water discharged into a reservoir and used for irriga- 

 tion at a lower level during the dry season of the 

 year, or it would be practicable to discharge it into a 

 series of tiles laid 2 feet below the surface on a 

 section of higher ground which is naturally well 

 drained, and thus sub -irrigate this at the same time 

 the low place is being drained, the two systems caring 

 for themselves continuously. 



LANDS WHICH MUST BE SURFACE DRAINED 



There are many ancient lake bottoms now consti- 

 tuting wide stretches of very flat country underlaid by 

 heavy deposits of a very close lacustrian clay, through 

 which water percolates with extreme slowness. Such 

 lands must generally be surface drained, not only 

 because it is difficult to find adequate fall for proper 

 outlets for underdrains, but because the water would 

 not reach underdrains quickly enough to meet the 

 demands of crops unless the lines were laid closer 

 together than could be afforded. 



