Eklutna River - The Upper Dam

The Upper Dam

Military expansion in Anchorage during the 1940s stressed the capacity of the Eklutna power generation system and it was upgraded several times. In 1948 the Bureau of Reclamation recommended the construction of a new dam to raise the level of Eklutna Lake to an elevation of 875 feet (267 m) above sea level with a tunnel intake at 830 feet (250 m). Construction was completed in 1955. The new system replaced the aging storage dam at the lake outlet with a new dam that diverted water through a 4.5-mile (7.2 km) long, 9-foot (2.7 m) diameter concrete lined tunnel with a capacity of 640 cubic feet (18 m3) per second (18 m³/s) to a turbine house on the south bank of the Knik River. The dam, as modified, is an earth- and rock-filled structure, 555 feet (169 m) long and contains approximately 5,000 cubic yards (3,800 m3) of material. This new plant used essentially the entire storage capacity of Eklutna Lake and no water was made available to operate the existing plant at Eklutna.

The 1964 Good Friday Earthquake severely damaged the dam. Because of this, a new storage dam was built downstream from the existing storage dam at the lake outlet. The new Eklutna Dam (referred to as the Upper Dam) is an earth and rockfill structure 815 feet (248 m) long and 51 feet (16 m) high containing 85,000 yd³ (65,000 m³) of material. The spillway is a rectangular concrete conduit through the dam with an uncontrolled overflow crest. The maximum capacity of the spillway is 3,315 ft³/s (94 m³/s). There are no outlet works through the dam, as the power tunnel serves in that capacity. As the Upper Dam impounds 100% of the flow from Eklutna Lake, the river's volume immediately downstream is zero.