210 IRRIGATION. 



Where a more substantial construction is needed, or 

 where the current is so swift that loose earth would be 

 carried away, the method of construction will be differ- 

 ent. Crib work would then be required, or else the pil- 

 ing should be continued to the end, and should be of a 

 substantial character. The piling, or the cribs, should be 

 connected by stringers and cross-ties, and the vacancies 

 may be filled with brush and stone. It is not always 

 necessary that the dam be absolutely tight, as if it were 

 one of the usual kind ; if it diverts a sufficient quantity 

 of water, that is all that is required. But a tight dam 

 may be made in this manner, if the cribs, or the space 

 between the piles are filled with brush and stone, and 

 earth be thrown upon the inner side of the dam. Then 



Fig. 100. CROSS- WING DAM. 



the cribs, or piling, serve as supports to the dam, and the 

 earth serves to confine the water. In some cases wing 

 dams of a different form may be used. "Where, for in- 

 stance, a longitudinal dam would need to be of extreme 

 length, because of the inadequate fall of the stream, and 

 where it is desirable to avoid closing the stream entirely, 

 cross-wing dams maybe constructed in the manner shown 

 at fig. 100. Here partial dams of crib work, or piles, 

 filled in with stone ; or dams of logs, brush, and earth, 

 are thrown into the stream, from each side, but not upon 

 the same line, so that when each reaches the middle, an 

 open space it left through which a portion of the water 

 escapes in a rapid. The distance between the ends of 



