Diverting Underground Waters 



305 



Then, again, in steep valleys, where the streams carry plenty 

 of water, but too far below the surface to be diverted, it fre- 

 quently happens that at the foot of a terrace water may be 

 flowing very near the surface toward the river channel, and by 

 ditching or tunneling here this may be diverted to the surface 

 when that in the river must be pumped. 



Another method of utilizing the waters which have fallen 

 below the surface in the valley gravels is by building what is 

 called a submerged dam across the valley, excavating to bed 



Fig. G6. Submerged dam at San Fernando, California. 



rock and erecting a water-tight dam, which shall hold the under- 

 flow back until it has filled the gravels above the dam and flows 

 over it at the surface high enough to be taken away in cement 

 ditches, flumes or pipes to the land it is desired to irrigate. 

 One such submerged dam is shown in Fig. 66, built near San 

 Fernando, California. It was not, however, sufficiently well built 

 to hold the water back until it could be made to overflow, and 

 they were, in 1896, using two gasoline engines with pumps to 

 lift the water held back by the dam, instead of depending upon 

 gravity, as planned. 



