The Culmback Dam (also known as the George Culmback Dam or the Snoqualmie National Forest Dam) is a large rockfill

hydroelectric Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and ...

and water supply

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, a ...

on the

Sultan River Sultan (; ar, سلطان ', ) is a position with several historical meanings. Originally, it was an Arabic abstract noun meaning "strength", "authority", "rulership", derived from the verbal noun ', meaning "authority" or "power". Later, it ...

, a tributary of the

Skykomish River The Skykomish River is a long river in the U.S. state of Washington which drains the west side of the Cascade Mountains in the southeast section of Snohomish County and the northeast corner of King County. The river starts with the confluence ...

, in

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

. Built in 1965, the dam is long at the crest and high. Its reservoir, Spada Lake, provides water for 70 to 75 percent of

Snohomish County Snohomish County () is a county located in the U.S. state of Washington. With a population of 827,957 as of the 2020 census, it is the third-most populous county in Washington, after nearby King and Pierce counties, and the 75th-most populous ...

and feeds the Jackson Hydro Project, providing 112

megawatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units, International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), ...

s of clean energy to Snohomish county. Some critics charge that the dam has strongly impacted the runs of

salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...

and other migratory fish in the Sultan River by depleting gravel and sediment needed to line the riverbed. 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. The Dam is co-owned by the

Snohomish County PUD The Snohomish County Public Utility District is a public utility agency providing power to over 367,000 customers in Snohomish County and on Camano Island, Washington. It provides water service to about 23,000 customers in the northeast section ...

and the City of Everett and is operated by the PUD. Water from Spada Lake is diverted through a

pipeline Pipeline may refer to: Electronics, computers and computing * Pipeline (computing), a chain of data-processing stages or a CPU optimization found on ** Instruction pipelining, a technique for implementing instruction-level parallelism within a s ...

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.

Construction and other additions

Prior to 1917 the City of Everett received its water supply from Woods Creek, a tributary of the

Snohomish River The Snohomish River is a river in Snohomish County, Washington, formed by the confluence of the Skykomish and Snoqualmie rivers near Monroe. It flows northwest entering Port Gardner Bay, part of Puget Sound, between Everett and Marysville. The ...

. 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 , impounding a reservoir. The construction done during this phase served to replace the smaller,

diversion dam A diversion dam is a dam that diverts all or a portion of the flow of a river from its natural course. Diversion dams do not generally impound water in a reservoir; instead, the water is diverted into an artificial water course or canal, which ...

downstream on the Sultan River. Phase 2, completed in 1984, involved raising the dam 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. In June 2016, the PUD began demolition of the dam's sluiceway to re-open the upper Sultan River basin to spawning fish.

Site

Culmback Dam and Spada Lake received water from a

drainage basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, t ...

of on the west slope of the

Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...

. 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 thick

Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million years a ...

, which rerouted the river from its original watershed, the

Pilchuck River The Pilchuck River ( lut, dxʷkʷiƛ̕əb) is a river in Snohomish County in the U.S. state of Washington. It is a tributary of the Snohomish River. The name is derived from Chinook Jargon ''pilpil'' ("blood", "red") and ''chuck'' ("water"), or " ...

. The river eroded a narrow gorge to empty into the

, forming an ideal dam site. 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 Big Four is a mountain summit in the Cascade Range, located about east of Granite Falls, Washington. It is situated west of Barlow Pass along the Mountain Loop Highway, near the Monte Cristo area, on land administered by the Mount Baker-Sn ...

Water supply and power

Spada Lake is part of the water supply of the City of Everett, Washington, serving 80 percent of

. This water supply consists of two lakes, the other being the much smaller, 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 penstock that flows to the 112

(MW) Jackson powerhouse further downstream, with an elevation drop of . 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 turbine The Francis turbine is a type of water turbine. It is an inward-flow reaction turbine that combines radial and axial flow concepts. Francis turbines are the most common water turbine in use today, and can achieve over 95% efficiency. The proces ...

s. The water from the Pelton turbines is released directly into the Sultan River, while the rest of the water is piped to Lake Chaplain. From Lake Chaplain, the water flows in four 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. The Culmback Dam is able to discharge water through an inverted-bell spillway that has a capacity of per second, which is sufficient to handle the

100-year flood A 100-year flood is a flood event that has a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year. The 100-year flood is also referred to as the 1% flood, since its annual exceedance probability is 1%.Holmes, R.R., Jr. ...

flow of the Sultan River, which is calculated at per second.

Recreation

The area around the dam and Spada Lake is visited by 5,000 people annually for a variety of recreational activities, including boating, hiking, fishing, and kayaking. The lake has two boat launches and prohibits combustion engines.

References

{{stack, {{Portal, United States, Water, Renewable energy Dams in Washington (state) Hydroelectric power plants in Washington (state) Rock-filled dams Buildings and structures in Snohomish County, Washington Dams completed in 1965 Energy infrastructure completed in 1965 1965 establishments in Washington (state)