The Eklutna River is a 22 mile (35 km) long river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 located in the Southcentral region of the U.S. state

U.S. state

A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

 of Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

. A degraded anadromous stream of glacial

Glacier

A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

 origin, it originates at Eklutna Glacier and flows through Eklutna Lake and a canyon up to 350 feet (107 m) deep, emptying into the Knik Arm of Cook Inlet

Cook Inlet

Cook Inlet stretches from the Gulf of Alaska to Anchorage in south-central Alaska. Cook Inlet branches into the Knik Arm and Turnagain Arm at its northern end, almost surrounding Anchorage....

 approximately 17 miles (27 km) northeast of Anchorage

Anchorage, Alaska

Anchorage is a unified home rule municipality in the southcentral part of the U.S. state of Alaska. It is the northernmost major city in the United States...

. It has one significant tributary, Thunderbird Creek, which enters the south bank about 1 km (0.6 mi) upstream from where the river exits the canyon and forms an alluvial fan

Alluvial fan

An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...

. Due to water impoundments on the Eklutna River for power generation, Thunderbird Creek is currently the main source of water in the river. The river is located entirely within the limits of the Municipality of Anchorage.

The lower dam

Anchorage was largely electrified

Electricity

Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 by the late 1920s, but as demand increased, Eklutna was selected as a power source because of the hydroelectric

Hydroelectricity

Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

 potential of the river, then known as Eklutna Creek, and Eklutna Lake. In 1927, the City of Anchorage contracted with the Anchorage Light and Power Company to construct what is now called the Old Eklutna Hydroplant. Construction included a low-head storage dam at the outlet of Eklutna Lake and a 68 feet (20.7 m) high concrete arch diversion dam (known as the Lower Dam) in the river canyon 8 miles (12.9 km) downstream of the lake. The diversion dam diverted water through a 1/4 mile-long tunnel to a turbine house near the village of Eklutna

Eklutna, Alaska

Eklutna is a native village within the Municipality of Anchorage in the U.S. state of Alaska. The Tribal Council estimates the population at 70; many tribal members live in the surrounding communities....

. Since its construction, the Lower Eklutna Dam has been a barrier to fish movement upstream. When the Upper Dam was brought online, the Lower Dam was shut down as a result and the Lower Eklutna Dam was allowed to fill with gravel. This dam is no longer operational and is currently completely backfilled with sediment to a depth of approximately 68 feet (20.7 m) at the upstream face of the 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 (266.7 m) above sea level with a tunnel intake at 830 feet (253 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 miles (7.2 km) long, 9 feet (2.7 m) diameter concrete lined tunnel with a capacity of 640 cubic feet (18.1 m³) per second (18 m³/s) to a turbine house on the south bank of the Knik River

Knik River

The Knik River is a 25-mile-long river in the U.S. state of Alaska. Its source is at Knik Glacier, from which it flows northwest and west and empties into the head of Cook Inlet's Knik Arm, near the mouth of the Matanuska River....

. The dam, as modified, is an earth- and rock-filled structure, 555 feet (169.2 m) long and contains approximately 5000 cubic yards (3,822.8 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

Good Friday Earthquake

The 1964 Alaska earthquake, also known as the Great Alaskan Earthquake, the Portage Earthquake and the Good Friday Earthquake, was a megathrust earthquake that began at 5:36 P.M. AST on Good Friday, March 27, 1964...

 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 (248.4 m) long and 51 feet (15.5 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

Outlet works

A set of outlet works is a device used to release and regulate water flow from a dam. Such devices usually consist of one or more pipes or tunnels through the embankment of the dam, directing water usually under high pressure to the river downstream...

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.

Eklutna Lake Road

The winding and rolling road leading to Eklutna Lake from the Glenn Highway was recently paved as it was previously primarily dirt and gravel. The result of this has been a massive influx of motorcycle riders that treat the road as if it were their own racetrack. Many crashes and even a few fatalities have occurred since the amount of rubbish dragged onto the road by ATV towing trucks makes for very hazardous riding conditions. Additionally, the pavement quickly cracked and was repaired with numerous tar strips. This has also accounted for several accidents and destroyed motorcycles. Motorcycles aren't the only ones with mishaps on this particular stretch of asphalt as several automobiles have also driven off of the road into the woods feet below. At least one instance was a suicide.