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John A. Weeks III
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Highways, Byways, And Bridge Photography
Forbay Canal
Saint Louis River Water Project
Thomson, MN

Forbay Canal

• Location: River Miles 26 To 29
• Canal Length: 2.0 Miles
• Canal Width: Varies, 75 Feet To 115 Feet On Average
• River Elevation (Entrance): 1,051 Feet
• River Elevation (Exit): 1,050 Feet
• Date Built: 1907
The Forbay Canal is part of the giant Thomson Hydro Project located between River Miles 24 and 30. The canal was built to move water from Thomson Reservoir near the top of the bluffs down to the Thomson Power Plant which is near the bottom of the bluffs. Having the reservoir dam and the hydro power plant located in two different locations is an unusual configuration. The advantage is that much more hydro power can be generated due to the water not losing energy as it cascades down toward the bottom of the bluffs. The disadvantage is that the spectacular rapids and waterfalls on the river channel see only a fraction of their historic water volume.

The canal starts at the southeast corner of the Thomson Reservoir. There is a head house that blocks the reservoir and contains the valves and controls that regulate the amount of water flowing into the canal. The canal is 2 miles long overall. The first 1,500 feet of the canal between the head house and the Thomson Road Bridge were blasted out of rock. The next 2000 feet from the road bridge to just past the Munger Trail Bridge was excavated. The next 3,500 feet followed an old stream bed, while the final 3,500 feet used the existing Forbay Lake. The canal ends at an intake building. Here, water from the canal flows through another set of valves and into three large pipes. The pipes run down the steepest part of the bluff, ending at the bottom in a pair of large surge tanks. Water flows from the surge tanks through the power plant and exits back into the Saint Louis River.

The Thomson Dam pool is at 1,069 feet above sea level. Lake Superior is at 602 feet above sea level. This leaves a potential drop of 467 feet for generating hydro power. The canal leaves the reservoir at 1,051 feet and enters the intake at 1,050 feet. The river level is at 680 feet. This means that the actual hydro power realized is from a drop of 370 feet. The Fond du Lac dam just downstream picks up another 78 feet of the drop, which means that 448 feet of the 467 feet of hydro potential is used. There are also three more dams upstream of the Thomson Hydro Project that captures another 79 feet of hydro potential.

The Forbay Canal runs 2 miles, and the water pipes are another mile, for a total distance of 3 miles. This Saint Louis River channel takes 5 miles to cover this same distance. The photo above is a typical section of the Forbay Canal, located just downstream from the Willard Munger Trail Canal Bridge, as seen from the south shore of the canal looking northeast.

A storm of historic proportions hit the Duluth area on June 19-20, 2012, dropping 11 inches of rain in some areas. The Thomson Dam overtopped causing extensive flooding in the city of Thomson. Large amounts of debris fouled the gates at the gate house and intake house resulting in extensive damage to the structures. The power plant flooded causing a need to shut down the turbines, and the water damaged much of the electrical equipment. Later, the south wall of the Forbay Canal failed, causing the lake to drain cutting a new river channel through Jay Cooke State Park. This resulted in a long section of highway MN-210 washing out. In addition, MN-210 was washed out near the Fond du Lac Dam and in front of the Thomson Dam. It took two years of work to bring the first generator back on line (unit #6), and considerable work remains to be completed as this update was written in late 2015. A few photos of the flood aftermath are included below.

Forbay Canal
The photo above is a rock pile located on the south side of the canal near the Thomson Dam Gate House. This section of canal just downstream of the Gate House was blasted from rock known as slate and greywacke. The rock that was blasted out of the canal was simply piled up on the south bank of the canal. The rock formed from mud and sand beds in an ancient sea about 1.9-billion years ago. The rock was later uplifted causing it to fold and fracture, resulting in long rock ridges that are exposed at the surface through the Thomson Reservoir and Jay Cooke State Park area. The photo below is the Gate House as seen from the reservoir side of the structure.

Forbay Canal
Forbay Canal
These two photos are views looking upstream towards the Thomson Dam Gate House from the Thomson Road Bridge. The photo above is from early autumn just as the trees were turning colors, while the photo below is from summer. The Gate House is located 1,550 feet northwest of the bridge.

Forbay Canal
Forbay Canal
These two photos are looking downstream towards the old railroad bridge that carries the Munger Trail over the Forbay Canal. The photo above is an autumn view, while the photo below is from early summer. The bridge is about 1,100 feet from this vantage point.

Forbay Canal
Forbay Canal
The photo above is looking downstream from the west end of the Munger Trail bridge over the Forbay Canal as the canal makes a turn to the east. This is the only significant direction change for the canal. The photo below is looking upstream from the Thomson Dam Intake at the far east end of the canal. The canal flows through an old lake at this point, resulting in the canal being over 400 feet wide in places. That is in contrast to a spot that is only 28 feet wide less than a mile upstream of this spot.

Forbay Canal
Forbay Canal
These two photos are views of the upstream side of the Thomson Dam Intake at the east end of the Forbay Canal. The water flows into large penstock pipes to carry it down the 370 foot drop into the power plant. The photo above is the north side of the channel, while the photo below is the south side of the canal. The Lake Superior Hiking Trail crosses the canal over this structure and follows the south shore of the canal.

Forbay Canal
Forbay Canal
These two photos, and the six that follow, are views of the Forbay Canal after the 2012 flood. They were taken in the summer of 2013 when repair work was just starting to get underway (the complexity required design time and lead time to start the manufacture of custom parts). The photo above is the downstream side of the gate house (Upper Intake) at the start of the canal. The photo below is the first half mile of the canal between the gate house and Thomson Road.

Forbay Canal
Forbay Canal
The photo above is the nearly dry canal as it passes under the Thomson Road Bridge. The photo below is looking downstream from the Thomson Road Bridge towards the Munger Canal Bridge.

Forbay Canal
Forbay Canal
The photo above is the canal as it makes a turn towards the east with the Munger Canal Bridge in the background. The pipe on the right side of the canal is a telecommunications cable that runs from the dam structure down to the control room in the power plant. The photo below is the blowout in the south bank of the canal. There are several landslides on the far side of the canal wall, plus a smaller breach just upstream of the main breach.

Forbay Canal
Forbay Canal
These two photos are views of the Intake house (Lower Intake). The photo above is looking downstream from inside the canal. The photo below is a view from the north bank of the canal. Crews had to get heavy equipment into the lower level to remove debris, and then the gate valves had to be replaced due to damage from the debris.

Forbay Canal

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