THE KITIMAT STORY — CROOME 359 



upstream filter layers perform a similar function with respect to the upstream 

 blanket of quarry-run rock. The downstream filters comprise three layers; im- 

 mediately downstream from the Impervious core a layer of sand % inch and 

 smaller; next crushed rock or gravel, 3 inches: and. finally, adjoining the main 

 rock-fill a layer of 10-inch selected rock. The upstream filter is similar but in 

 the reverse sense. 



Below the impervious core, effective cut-off is assured by a grout curtain. This 

 was developed by grouting the upper 25 feet of rock at pressures of about 20 lb. 

 per square inch, then continuing to the necessary depth by deep holes drilled 

 through the consolidated upper zone, using higher pressures. 



Another point worth noting is that the original l-in-1.5 slope of 

 the upstream face was increased to l-in-2.5 during the model tests at 

 the University of California, as an additional safety measure. In 

 view of the dam's elaborate and scientific packing, the claim that its 

 life will be measured "in geological, not historical time" is probably 

 justified. 



On October 8, 1952, the diversion tunnel above the dam was closed 

 and the storage reservoir began filling. The water has been rising ever 

 since. The 2,800-foot-elevation level should be reached in 1957. 



Coloring an account of the construction of this, the world's largest 

 rock-fill dam nearly 3,000 feet up in the mountains, there should be 

 a sense of the acute inaccessibility of the region and the human hard- 

 ships that this must bring. Nechako Canyon is nearly 100 miles 

 from the nearest railway station. To bring the heavy equipment and 

 the men to the site a heavy motor road had to be driven 60 miles 

 through virgin country. The Canadians did this in 12 weeks flat. 



THE POWER TUNNEL 



The storage capacity of the reservoir permits a regulated flow esti- 

 mated at 6,920 cubic feet per second for the powerhouse turbines. But 

 first the water had to be thrust 10 miles through solid rock to reach 

 those turbines. 



The boring of the tunnel started on October 22, 1951, from the west- 

 ern shores of Tahtsa Lake. On November 4 the bore into the mountain 

 from the seaward side began. Two further mining crews attacked 

 from a midway shaft driven into Mount DuBose at Horetzky Creek; 

 one of these crews bored eastward from this point, the other west- 

 ward. 



Mining operations on the western mountain face were complicated 

 by the need to start drilling half a mile up a heavily wooded and al- 

 most cliff-steep slope. An overhead-cable railway solved this problem. 

 The cable car, weighing 9 tons itself, could convey 20 tons of machinery 

 or 60 men per trip. 



Within the tunnel highly coordinated teamwork operating a newly 

 developed large-scale drilling technique chewed through the rock 



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