476 NATIONAL RECLAMATION OF ARID LANDS. 



the stream about 60 feet, and its length is about 625 feet. The con- 

 crete core wall is built upon a solid rock foundation throughout the 

 entire length of the dam, and at each end reaches to within about 11 

 feet of the top of the earth and rock part of the dam, while through 

 the central portion its top is 44 feet below the crest of the dam. On 

 top the dam is 25 feet wide, and the bottom width averages about 300 

 feet. The downstream part of the dam is built of loose rocks of 

 large size, the minimum weight being 1,000 pounds, the central part 

 of gravel and small rocks, increasing in size toward the large rocks 

 on the lower side, and the upstream part of earth and gravel with 

 riprap covering on the upper portion. The volume of this portion 

 of the structure is 101,000 cubic yards. 



At the south end of the earth and rock dam is a concrete spillway 

 built ui^on solid rock for nearly half a mile in length. This spillway 

 follows along a broken undulating ridge of lava that has been previ- 

 ously mentioned as extending across the river at the dam site. The 

 spillway is therefore very sinuous in its course, following as it does 

 the highest portion of this ridge, and is of varying height, the maxi- 

 mum being 14 feet. In two or three short spaces it is discontinuous, 

 as the surface of the ridge rises above the maximum elevation of the 

 water in the reservoir. The elevation of the crest of this spillway is 

 10 feet below the top of the dam, 48 feet above the bottom of the 

 sluiceway, 7 feet above the gate sills of the north side canal, 6 feet 

 above sills of the gate of the south side canal. This structure con- 

 tains over 4,000 cubic yards of concrete. 



At the south end of the concrete spillway or weir are located the 

 headworks of the south side canal, built of reenforced concrete and 

 having 12 cast-iron gates, each 5 feet wide by 6 feet. There were 

 used in this structure about 250 cubic yards of concrete. From this 

 point an earth embankment about 800 feet in length and averaging 

 10 feet in height completes the necessary inclosure of the reservoir 

 above the dam. 



The channel of Snake River was closed by the rock fill in April, 

 1906, and the entire flow was discharged through the regulating 

 gates. The flood flow of this stream was somewhat above normal, 

 the maximum discharge at this point, amounting to 24,292 second- 

 feet, occurring June 20, 1906. 



The natural conditions are usually favorable for the development 

 of power. A very good site for a power house exists on the north 

 side of the river immediately below the dam. The foundation 

 will be blasted out of solid rock and the water will be delivered to 

 the wheels by means of steel conduits and a supply canal about 150 

 feet in length. Up to July 15 the natural flow of the stream will be 

 about 5,400 cubic feet per second. With storage at the headwaters 

 this flow can be maintained throughout the year and all of it utilized 



