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Highways, Byways, And Bridge Photography
Penstock Bridge
MN-210 Saint Louis River Highway Crossing
Thomson, MN

Penstock Bridge

• Structure ID: NBI: 91366
• Location: River Mile 26.0 (Approximate)
• River Elevation: 990 Feet
• Highways: MN-201
• Daily Traffic Count: 610 (2004)
• Bridge Type: Steel Culvert, 3 Tubes
• Bridge Length: 93 Feet, 21 Foot Longest Span
• Bridge Width: 28 Feet (Estimated), 2 Lanes
• Navigation Channel Width: Non-Navigable
• Height Above Water: 0 Feet
• Date Built: 1975
The huge Thomson Energy Center, also known as the Thomson Water Project, generates 70-Megawatts of hydroelectric power. That is enough electricity to light up a city of 100,000 people. That electrical power is generated when water descends 370 feet through three parallel mile-long penstock pipes. The penstock pipes are up to 20 feet in diameter. They run from the Thomson Dam Intake, which is at the east end of the Forbay Canal, and they connect to a power house on the north bank of the Saint Louis River. There, the water re-enters the Saint Louis River after passing through the turbines in the power house.

The highway MN-210 bridge over the penstock pipes is not visible from the surface, rather, it is completely buried. The bridge consists of three steel culverts, one placed around each penstock. The largest of these culverts is 21 feet in diameter. The Penstock Bridge is listed as being built in 1975. Given that the Thomson Dam was built in 1907, I suspect that the bridge was rebuilt, possibly as part of a project to replace or upgrade the penstock pipes. They would have been almost 60 years old at that point in time.

The photo above is looking downhill towards the surge towers near the power plant along the path of the three penstock pipes. The vantage point is the Thomson Dam Intake. The photo below is looking westbound down the length of the Penstock Bridge.

Penstock Bridge
Penstock Bridge
The photo above is looking southwest towards the uphill side of the Penstock Bridge. The photo below is looking northwest towards the downhill side of highway MN-210. It is difficult to make out the paths of the pipes in these ground level views despite them showing up so clearly in the views from the top of the hill. The dark section of grass in the foreground of the photo above is the side of the mound covering the pipe. The eastern of the three pipes is located just beyond the highway sign in the photo below.

Penstock Bridge

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