IRRIGA TION WORK IN IDAHO. 



257 



forming squares eight feet between centers. These 

 sills were bedded in the loose rock without other 

 preparation than leveling up the trenches in which 

 they were laid. From the crest of the dam the water 

 drops vertically fifteen feet to the apron, which is a 

 heavy timber flooring covering the down stream half 

 of the loose rock foundation. 



The crest of the dam is level with the bottom of 

 the canal, and the required depth of water at the 

 head gates is secured by the use of flash boards. 



building the timber superstructure was carried on 

 with total disregard of the river flowing beneath it. 

 But an accumulation of anchor ice, which cemented 

 the loose rock as tight as masonry for nearly twenty- 

 four hours and raised the river over the foundation of 

 the superstructure, delayed the construction for about 

 a day. Charges of dynamite exploded on the face of 

 the rock filling would send the accumulated waters 

 roaring through the foundation, but the channels thus 

 opened were almost instantly closed by the ice, and 



VIEW OF VALLEY AND MAIN CANAL. 



These are supported by posts projecting above the 

 crest, and carrying at their upper ends a set of iron 

 brackets. Upon these brackets is laid the footwalk 

 from which the flash boards are worked. Massive 

 masonry abutments and wing walls, which are ten 

 feet higher than the crest of the dam, connect it with 

 the canyon slopes. 



During the construction of the dam the flow of the 

 river passed through the interstices of the rock fill- 

 ing, leaving its top perfectly dry, and the work of 



the only relief came from a change in the weather and 

 the melting of the ice. r~~i 



After the completion of the dam the foundation 

 was made water tight by gravel dumped from a flat 

 boat upon the face of the rock filling. There is no 

 appreciable displacement or settlement in the dam 

 after two years of use, and the loose rock foundation 

 has served as perfectly as solid rock. The flood of the 

 past spring was the highest ever known on the Bru- 

 neau, and it was passed without damage to the dam. 



