BOULDER CANYON PROJECT — NELSON 437 



concrete expanded, due to its increase in temperature to that of the 

 surrounding medium, the concrete was placed in compression and 

 the possibility of future cracking eliminated. Cooling tubing 

 placed in the dam amounted to 582 miles and grouting pipe 180 

 miles. 



How effectively the system of cooling and grouting has worked 

 can best be seen by an examination from one of the numerous in- 

 spection galleries that cross the dam on horizontal and circumfer- 

 ential lines. One of these, the abutment gallery, starts in the dam 

 near the top of an abutment, follows it downward, crosses the river 

 channel within 5 to 30 feet of foundation rock! and ascends along 

 the other abutment to the dam crest. Other galleries pierce the dam 

 in circumferential and radial lines at levels 12, 257, 357, 452, 527, and 

 558 feet below the crest. All, except the lower of the circumferen- 

 tial galleries, contact the two elevator shafts which connect with the 

 dam crest. 



Water that otherwise would percolate past the dam through small 

 crevices and fissures in the rock was halted by injecting water- 

 cement grout into the foundations and abutments. Holes for grout- 

 ing were drilled into the rock at 5-foot intervals the full height of 

 each abutment and across the base, to a depth as great as 150 feet, 

 and grout forced into the rock at pressures as high as 1,000 pounds 

 per square inch. Any water passing the grout curtain will be caught 

 by drainage holes drilled at 10-foot centers from the abutment gal- 

 lery downstream from the curtain. Drainage from the gallery is 

 provided by a passage through the dam to its downstream face. 



The reservoir formed by this high dam will be the largest man- 

 made lake. When filled to capacity, it will contain sufficient water 

 to cover the State of Connecticut 10 feet deep, its shore line will ex- 

 tend 550 miles, and its depth at the dam will be 589 feet. If the 

 entire flow of the river were stopped, the lake would fill in 2 years of 

 mean flow, but owing to the demands for downstream irrigation, at 

 least 3 years will be required. The 30,500,000 acre-foot capacity of 

 the reservoir is allocated to the following uses: The lower 5,000,000 

 to 8,000,000 acre-feet for a silt pocket, the next 12,000,000 to 15,- 

 000,000 for active storage, and the upper 9,500,000 for flood control. 



The two spillways, which take the overflow of the reservoir, are 

 located upstream and off to the sides of the dam. Each spillway 

 channel has a length greater than that of two residence blocks, is a 

 half block wide and a hundred feet deep. A concrete weir, whose 

 unobstructed crest length is 400 feet, forms the upstream part of 

 the channel on its reservoir side, and the downstream end of the 

 channel is connected with the river below the powerhouse by a 

 shaft, which drops downward on an incline a vertical height of 500 



