Culmback Dam

Culmback Dam

The reservoir, Spada Lake, seen from the air, with the dam on the left end of the lake
Location Snohomish County, Washington
Coordinates 47°58′31″N 121°41′11″W / 47.9753°N 121.6865°W / 47.9753; -121.6865Coordinates: 47°58′31″N 121°41′11″W / 47.9753°N 121.6865°W / 47.9753; -121.6865
Construction began 1960
Opening date 1965
Operator(s) Snohomish County PUD
City of Everett
Dam and spillways
Impounds Sultan River
Height 262 ft (80 m)
Length 640 ft (200 m)
Elevation at crest 1,450 ft (440 m)[1]
Reservoir
Creates Spada Lake
Total capacity 165,774 acre·ft (204,479,000 m3)
Catchment area 84 sq mi (220 km2)
Surface area 1,870 acres (760 ha)[2]
Power station
Commission date 1983
Hydraulic head 1,165 ft (355 m)
Turbines 2x 47.5 MW Pelton
2x 8.4 MW Francis
Installed capacity 112 MW
Annual generation 418 million KWh

The Culmback Dam (also known as the George Culmback Dam or the Snoqualmie National Forest Dam)[3] is a large rockfill hydroelectric and water supply dam on the Sultan River, a tributary of the Skykomish River, in Washington. Built in 1965,[4] the dam is 640 feet (200 m) long at the crest and 262 feet (80 m) high. Its reservoir, Spada Lake, provides water for 70 to 75 percent of Snohomish County, and the powerhouse downstream of the dam produces 112 megawatts. Some critics charge that the dam has strongly impacted the runs of salmon and other migratory fish in the Sultan River by depleting gravel and sediment needed to line the riverbed.[5] The dam’s operator counters that Culmback Dam dramatically reduces flooding events, benefiting fish populations and the surrounding communities. The dam was named in honor of George Culmback, a former mayor of Everett.[4]

The Dam is co-owned by the Snohomish County PUD and the City of Everett and is operated by the PUD. Water from Spada Lake is diverted through a pipeline to a powerhouse further downstream on the Sultan River. From the powerhouse, some water is returned to the river, and some is diverted to Lake Chaplain, where the water enters the Everett water supply system.[6][7]

Construction

Prior to 1917 the City of Everett received its water supply from Woods Creek, a tributary of the Snohomish River. Because of increasing water needs of large paper mills and factories, the city switched its water supply to the Sultan River basin via the tributary Chaplain Creek. The Chaplain Reservoir was created in 1929 with the completion of an earthfill dam, and later raised in 1942. This supply proved insufficient as well, so engineers looked to tap the main stem of the Sultan River, where an excellent dam site had been identified.

The Culmback Dam was built in two stages, or phases. Phase 1, which began in 1960 and ended in 1965, involved building the dam to a height of 200 feet (61 m), impounding a 40,000-acre-foot (49,000,000 m3) reservoir. The construction done during this phase served to replace the smaller, 22-foot (6.7 m) diversion dam 6.5 miles (10.5 km) downstream[4] on the Sultan River. Phase 2, completed in 1984, involved raising the dam 62 feet (19 m) to its present height, quadrupling the reservoir capacity. The second phase also included the pipeline connecting Spada Lake to a new hydroelectric powerhouse and from there to the Chaplain Reservoir.[8]

Site

The Sultan River at Sultan, Washington.

Culmback Dam and Spada Lake received water from a drainage basin of 84 square miles (220 km2) on the west slope of the Cascade Range.[9] Although the broad valley in which the reservoir now lies predates the last Ice Age, the canyon in which the dam was built was formed only about 1 million years ago, when the Sultan River was interrupted by the 1-mile (1.6 km) thick Laurentide ice sheet, which rerouted the river from its original watershed, the Pilchuck River. The river eroded a narrow gorge to empty into the Skykomish River, forming an ideal dam site.[5]

The Sultan River, formed by the convergence of the North Fork of the Sultan River and Elk Creek, enters the lake from the east. Additional major contributors are the South Fork, which forms an arm of the lake close to Stickney Ridge, and Williamson Creek, which enters from the north at the base of Big Four Mountain.

Water supply and power

Spada Lake is part of the water supply of the City of Everett, Washington. This water supply consists of two lakes, the other being the much smaller, 17,000-acre-foot (21,000,000 m3) Lake Chaplain on Chaplain Creek, a tributary of the Sultan River. Most of the flow of the Sultan River is diverted at the dam into a 8-mile (13 km) penstock that flows to the 112 megawatt (MW) Jackson powerhouse further downstream, with an elevation drop of 1,165 feet (355 m). At the powerhouse, the water feeds four turbine/generator units, consisting of two 47.5 MW Pelton-type turbines, and two 8.4 MW Francis turbines. The water from the Pelton turbines is released directly into the Sultan River, while the rest of the water is piped to Lake Chaplain.[1]

From Lake Chaplain, the water flows in four 4-foot (1.2 m) diameter pipes towards Everett. During flood events, water is also discharged back into the Sultan River through Chaplain Creek and the Sultan River Fresh-water Return Line.[7] The Culmback Dam is able to discharge water through an inverted-bell spillway that has a capacity of 62,000 cubic feet (1,800 m3) per second,[2] which is sufficient to handle the 100-year flood flow of the Sultan River, which is calculated at 47,000 cubic feet (1,300 m3) per second.[10]

References

  1. 1 2 "Everett Water System-Culmback Dam". Archived from the original on September 5, 2008. Retrieved 2009-02-20.
  2. 1 2 "Jackson Hydro Project-History". Archived from the original on November 21, 2007. Retrieved 2009-02-21.
  3. ↑ "Culmback Dam". Geographic Names Information System. United States Geological Survey. Retrieved 2009-02-22.
  4. 1 2 3 "Everett, Washington Water Supply- Culmback Dam". Retrieved 2009-02-20.
  5. 1 2 "Foundation for Water and Energy-Testing the waters". Retrieved 2009-02-20.
  6. ↑ "Snohomish County PUD- Jackson Hydro Project". Retrieved 2009-02-12.
  7. 1 2 "City of Everett Water Supply". Retrieved 2009-02-20.
  8. ↑ "History Lesson in Everett". Retrieved 2009-02-21.
  9. ↑ "EverettWashington.org- Sultan River". Retrieved 2009-02-21.
  10. ↑ "Sultan River Flood Flows" (PDF). Retrieved 2009-02-21.
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