358 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



Kenney Dam is practically 5,500 square miles. A further 290-square- 

 mile watershed, that of the Nanika-Kidprice Lakes, can eventually be 

 diverted into the main system. When the storage reservoir has risen 

 to its scheduled level it will have a capacity of 873X10 9 cubic feet, 

 although the rise in level will only be 15 feet in the Tahtsa Lake, at 

 the western end. The reservoir surface area will then be 358 square 

 miles, double that of the original lakes ; even so the depth of water at 

 the upstream face of the dam will be little more than 300 feet. The 

 full reservoir surface level will stand at 2,800 feet above sea level, with 

 the inlet to the power tunnel nearly 100 feet below this surface. 



The Nechako Canyon site of the main dam was too deep and narrow 

 for the usual cofferdam procedure for drying out the channel where 

 the dam was to go. A new river channel was therefore drilled into 

 the bank upstream, carried 1,539 feet inside the mountain in a sweep- 

 ing arc, and the water debouched again into the river well below the 

 dam site. This diversion tunnel was cut and completed in two months 

 during the summer of 1951. 



The thousand men working on this section of the development were 

 now able to start clearing the river bed. Canyon walls and water 

 channel were stripped down to the solid bedrock. A concrete slab, 150 

 by 82 feet and 10 feet thick, was spread on the cleared reservoir floor. 

 Upon this, the placement of the rock of which the dam was to be 

 formed began to rise on May 20, 1952. 



The rock came from quarries in the surrounding mountains. Four 

 million cubic yards of filling rock was used. It took the 1,000-man 

 labor force six months to shift and place this material. At 45-second 

 intervals throughout those summer months one of a fleet of trucks 

 dumped its load on the dam, its drivers' movements radio-controlled 

 from a central tower. 



The construction of the rock-fill dam is of special interest in the 

 case of the Kenney Dam since it holds a highly critical position at the 

 head of a major tributary of the Fraser Kiver. Here is the technical 

 description of the Chief Engineer of the Power Department of Alu- 

 minium Laboratories Ltd., 3 F. L. Lawton, who has been closely as- 

 sociated with Kitimat: 



. . . the load-carrying element is a heavy rock-fill thoroughly sluiced, support- 

 ing on the upstream slope an impervious section of rolled-earth construction en- 

 closed between suitable filter layers. The upper section is loaded with quarry- 

 run rock to retain the filter layers and impervious core, and resist wave erosion. 

 The impervious core extends from a cut-off trench in sound rock to near the top 

 of the dam. 



The function of the downstream filter layers is to prevent the impervious core 

 material from being forced into the rock-fill by the water pressure, whereas the 



3 Aluminium Laboratories Limited is a subsidiary of Aluminium Limited in the 

 same group of companies as Alcan. 



