Downstream face of the main Thomson Dam on the St. Louis River in 2017
|Location||Carlton County, Minnesota, U.S.|
|Built by||Great Northern Railway|
|Dam and spillways|
|Type of dam||Earth Embankment, Concrete Gravity, Arch|
|Impounds||Saint Louis River|
|Height||Main: 15 ft (4.6 m) |
Canal: 45 ft (14 m)
|Length||Main: 1,600 ft (490 m) |
Canal: 3,500 ft (1,100 m)
|Spillway capacity||60,000 cu ft/s (1,700 m3/s)|
|Total capacity||4,352 acre⋅ft (5,368,000 m3)|
|Catchment area||9,154 sq mi (23,710 km2)|
|Surface area||649 acres (263 ha)|
|Hydraulic head||375 ft (114 m)|
|Installed capacity||72 MW|
|Annual generation||280 GWh|
Thomson Dam, also known as the Thomson Hydro Stationor Thomson Water Project, is an embankment and concrete gravity dam on the Saint Louis River near the town of Thomson in northeastern Minnesota, United States. It consists of a 1600-foot (488 m) long primary structure and multiple supplementary dams which, together with precambrian rock outcrops known as the Thomson formation, impound the river to create Thomson Reservoir. The tallest dam in the complex is 51.6 feet (16 m) and the longest is 3500 feet (1067 m). A series of gate houses, a canal, forebay, and underground penstocks supply a hydropower plant located 3 miles away in Jay Cooke State Park. With an installed capacity of 72 MW and an annual generation of approximately 280 GWh, the Thomson project is the largest hydroelectric facility in the state.
An embankment dam is a large artificial dam. It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay, or rock. It has a semi-pervious waterproof natural covering for its surface and a dense, impervious core. This makes such a dam impervious to surface or seepage erosion. Such a dam is composed of fragmented independent material particles. The friction and interaction of particles binds the particles together into a stable mass rather than by the use of a cementing substance.
A gravity dam is a dam constructed from concrete or stone masonry and designed to hold back water by primarily using the weight of the material alone to resist the horizontal pressure of water pushing against it. Gravity dams are designed so that each section of the dam is stable, independent of any other dam section.
The Saint Louis River is a river in the U.S. states of Minnesota and Wisconsin that flows into Lake Superior. The largest U.S. river to flow into the lake, it is 192 miles (309 km) in length and starts 13 miles (21 km) east of Hoyt Lakes, Minnesota. The river's watershed covers 3,634 square miles (9,410 km2). Near the Twin Ports of Duluth, Minnesota and Superior, Wisconsin, the river becomes a freshwater estuary. The lower St. Louis is the only river in the state with whitewater rafting opportunities.
Thomson Dam was completed in 1907 by Great Northern Power, an operating division of the Great Northern Railway. The generating station was expanded in 1914 with the addition of Unit 4.Unit 5 was added in 1918 and Unit 6 in 1948. Railroad tracks built into the generator floor allowed for installation and maintenance of the equipment. The complex was later transferred to the Saint Louis Power Company. Today it is owned by Minnesota Power, a division of Allete, Inc.
The Great Northern Railway was an American Class I railroad. Running from Saint Paul, Minnesota, to Seattle, Washington, it was the creation of 19th-century railroad entrepreneur James J. Hill and was developed from the Saint Paul & Pacific Railroad. The Great Northern's (GN) route was the northernmost transcontinental railroad route in the U.S.
Heavy rains in June 2012 created an historic flood in the region which overtopped the dam, breached the forebay canal and severely damaged the hydroelectric station. Following $90 million in reconstruction and upgrades, including the addition of a new emergency spillway, the facility came back online in November, 2014. Additional upgrades will continue through 2018, including removal of the original 46kV transmission line equipment in favor of other, higher voltage equipment that was added later.
The most visible part of Thomson Dam is the primary structure straddling the Saint Louis River channel near Minnesota State Highway 210. However, the Thomson Project is actually composed of multiple dams and control structures, several of which have been rebuilt and merged over the years. Today the United States Army Corps of Engineers National Inventory of Dams (NID) counts 18 structures as part of the complex, with 14 formally listed as separate.
Minnesota State Highway 210 (MN 210) is a state highway in west-central, central, and northeast Minnesota, which runs from North Dakota Highway 210 (ND 210) at the North Dakota state line, and continues east to its eastern terminus at its intersection with MN 23 in Duluth near the Saint Louis River.
The United States Army Corps of Engineers (USACE) is a U.S. federal agency under the Department of Defense and a major Army command made up of some 37,000 civilian and military personnel, making it one of the world's largest public engineering, design, and construction management agencies. Although generally associated with dams, canals and flood protection in the United States, USACE is involved in a wide range of public works throughout the world. The Corps of Engineers provides outdoor recreation opportunities to the public, and provides 24% of U.S. hydropower capacity.
|Dam ID||Other ID||Name||Height||Width||Type|
|MN00604||–||Thomson Dam||15 ft (4.6 m)||1,600 ft (490 m)||Embankment and concrete gravity|
|MN00604||S010||Thomson Canal Dam||45 ft (14 m)||3,500 ft (1,100 m)||Embankment|
|MN83020||S011||Thomson Dam #1-1/2||10 ft (3.0 m)||90 ft (27 m)||Embankment|
|MN83021||S001||Thomson Dam #2A, 2B||23 ft (7.0 m)||530 ft (160 m)||na|
|MN83022||S012||Thomson Dam #2-1/2||9 ft (2.7 m)||130 ft (40 m)||Concrete gravity|
|MN83023||S002||Thomson Dam #3|
(Nos 2-3/4, 3, 3A, 4, 4A)
|38 ft (12 m)||1,322 ft (403 m)||Concrete gravity|
|MN83024||S003||Thomson Dam #5||23 ft (7.0 m)||100 ft (30 m)||Concrete gravity|
|MN83025||S013||Thomson Dam #5-1/2||23 ft (7.0 m)||115 ft (35 m)||Concrete gravity|
|MN83026||S004||Thomson Dam #6||51.6 ft (15.7 m)||125 ft (38 m)||Concrete arch|
|MN83027||S005||Thomson Dam #8||12 ft (3.7 m)||100 ft (30 m)||na|
|MN83028||S006||Thomson Dam #9||11 ft (3.4 m)||100 ft (30 m)||Concrete gravity|
|MN83029||S007||Thomson Dam #10||11 ft (3.4 m)||80 ft (24 m)||Concrete gravity|
|MN83030||S008||Thomson Dam #11|
(Nos. 11, 11-1/2 and Upper Gate House)
|17 ft (5.2 m)||365 ft (111 m)||Concrete gravity|
|MN83031||S009||Thomson Dam #12||12 ft (3.7 m)||450 ft (140 m)||Embankment|
Hydropower or water power is power derived from the energy of falling water or fast running water, which may be harnessed for useful purposes. Since ancient times, hydropower from many kinds of watermills has been used as a renewable energy source for irrigation and the operation of various mechanical devices, such as gristmills, sawmills, textile mills, trip hammers, dock cranes, domestic lifts, and ore mills. A trompe, which produces compressed air from falling water, is sometimes used to power other machinery at a distance.
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