Culmback Dam

Culmback Dam
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[1]
Construction began	1965
Dam and spillways
Height	262 ft (80 m)
Length	640 ft (200 m)
Impounds	Sultan River
Reservoir
Creates	Spada Lake
Capacity	165,774 acre feet (204,479,000 m3)
Surface area	1,870 acres (7.6 km2)[2]

The Culmback Dam (also known as the George Culmback Dam or the Snoqualmie National Forest Dam)^[1] is a large rockfill hydroelectric and water supply dam on the Sultan River, a tributary of the Skykomish River, in Washington. Built in 1965,^[3] the dam measures 640 feet (200 m) long at the crest and 262 feet (80 m) high. The elevation of the crest is 1,450 feet (440 m) above sea level.^[4] 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.^[3]

The Dam is co-owned by the Snohomish County PUD and the City of Everett and is operated by the PUD. In 1965, it was built to a height of 200 feet (61 m). The dam was raised to its present height of 262 feet (80 m) in 1984, which increased the surface area of Spada Lake by four times. 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, the second stage in the water supply system.^[6]

The Sultan River's basin covers a total of 84 square miles (220 km²). It has an average annual rainfall of 165 inches (4,200 mm) per year.^[7]

Construction

Prior to the construction of the Culmback Dam the City of Everett received its water supply from Wood Creek, a tributary of the Snohomish River, from 1898 to 1917. In 1917, because of increasing water needs of large paper mills and factories, the city switched its water supply to the Sultan River. The Chaplain Reservoir was created in 1929 with the completion of an earthfill dam on Chaplain Creek, and later raised in 1942.

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 reservoir approximately 1/4 the size of current Spada Lake, or 467.5 acres (189.2 ha). 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^[3] on the Sultan River. Phase 2, completed in 1984, involved raising the dam 62 feet (19 m) to its present height, increasing the reservoir capacity to 50 billion US gallons (190,000,000 m³); building the powerhouse and pipeline; and constructing a pipeline to the Chaplain Reservoir.^[8]

Geography

The Sultan River at Sultan, Washington.

Culmback Dam is located in the basin of the Sultan River, which covers approximately 84 square miles (220 km²) on the west slope of the Cascade Range.^[9] The valley was formed approximately 1 million years ago during the last ice age. The Sultan River was forced to its present course by a 1-mile (1.6 km) thick sheet of ice, which rerouted the river from its original watershed, the Pilchuck River. The river formed a gorge to the Skykomish River as it needed a new course. The Culmback Dam was built in this valley in 1965.^[5]

The inflow of Spada Lake occurs primarily from the North Fork Sultan River, which is formed by the convergence of the North Fork of the Sultan River and Elk Creek. Additional major contributors are the South Fork, which enters the lake close to Stickney Ridge, and Williamson Creek, 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, 722,446,440 cubic feet (20,457,405 m³) Lake Chaplain, built 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) pipe that flows to the 112-megawatt Jackson powerhouse further downstream, with an elevation drop of 1,165 feet (355 m). At the powerhouse, the water feeds four turbine/generator units. Two are 47.5 megawatt Pelton-type turbines, and the other two are 8.4 MW Francis turbines. The water from the Pelton turbines are released directly back into the Sultan River, while the rest of the water is piped to Lake Chaplain.^[4]

From Lake Chaplain, the water flows in four identical pipes each with a diameter of 4 feet (1.2 m) towards Everett. During periods of high water, 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. ^ ^{a b} "Culmback Dam". Geographic Names Information System, U.S. Geological Survey. http://geonames.usgs.gov/pls/gnispublic/f?p=gnispq:3:::NO::P3_FID:1531308. Retrieved 2009-02-22. 
2. ^ ^{a b} "Jackson Hydro Project-History". http://www.prism.washington.edu/crystal/EverettHistory.html. Retrieved 2009-02-21. ^{[dead link]}
3. ^ ^{a b c} "Everett, Washington Water Supply- Culmback Dam". http://www.everettwa.org/WFPVirtTour/-1-Culmback.html. Retrieved 2009-02-20. 
4. ^ ^{a b} "Everett Water System-Culmback Dam". http://www.prism.washington.edu/crystal/Everett'sSystem.html. Retrieved 2009-02-20. ^{[dead link]}
5. ^ ^{a b} "Foundation for Water and Energy-Testing the waters". http://www.fwee.org/news/getStory?story=1110. Retrieved 2009-02-20. 
6. ^ "Snohomish County PUD- Jackson Hydro Project". http://www.snopud.com/water.ashx?p=1819. Retrieved 2009-02-12. 
7. ^ ^{a b} "City of Everett Water Supply". http://www.ci.everett.wa.us/Get_PDF.aspx?pdfID=1399. Retrieved 2009-02-20. 
8. ^ "History Lesson in Everett". http://www.everettwa.org/default.aspx?ID=84. Retrieved 2009-02-21. 
9. ^ "EverettWashington.org- Sultan River". http://www.everettwa.org/WFPVirtTour/-1-SultanRiver.html. Retrieved 2009-02-21. 
10. ^ "Sultan River Flood Flows" (PDF). http://www.ci.sultan.wa.us/City_Hall/City_Boards_and_Commissions/Planning_Board/2009/2009-01-06/attachments/D-1_FEMA_Flood_Restudy_1-6-09.pdf. Retrieved 2009-02-21.