Portage Mountain Intake Structure and Facilities

Portage Mountain Project, 600-ft high earth dam creates a reservoir of 57,000,000 acre-ft. The free standing water intake towers rise 115 ft above the rocks to support the bridge. For the first three units the intake sill is 110 ft lower than for the other units to enable generation in the first year. The principal forces considered were ice at 30 kips per lineal foot at the water surface with full reservoir and earthquake of modified Mercalli intensity between VII and VIII. For this earthquake, reinforcement is provided so that, with a ductility factor of 1.56, the steel will be stressed to the yield point of 60,000 psf. The deck is anchor bolted to the towers. Large earthquakes shear the anchor bolts allowing the deck to slide on lubrite plates. The deck is restrained from walking off the towers by neoprene cushions. The factor of safety against overturning is 1.9 on uncantilevered towers.