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Highways, Byways, And Bridge Photography
Garrison Dam
Missouri River Hydroelectric Dam
Riverdale, ND

Garrison Dam

• Location: River Mile 1,389.9
• Structure Type: Earth Fill
• Structure Width: 11,300 Feet
• River Elevation (Pool): 1,838 Feet
• River Elevation (Outflow): 1,674 Feet
• Waterfall: 180 Feet
• Date Built: Built 1946 To 1955
At 2-1/2 miles wide and 210 feet tall, the Garrison Dam is the fifth largest earthen dam on the planet. The reservoir behind the dam, named Lake Sakakawea, stretches across 178 miles and contains enough water to cover the entire state of North Dakota six inches deep. The dam was built for flood control, hydroelectric power, and irrigation. While the first two goals were met, the irrigation project was never finished. Canals running long distances across the state remain empty due to a 22 mile section of canal that was never completed. The million new acres of irrigated farmland never materialized, and the best farmland in the state was flooded out when the dam was closed off, including nearly all tillable land allotted to Indian tribes. As a result, local tribes refer to the Garrison Dam as the unfinished dream.

The photo above is looking east towards the dam from the west end of the structure. The powerplant is located on the near right side of the photo, while the intakes are on the near left side. The spillway is located on the east end of the dam, some 3 miles in the distance.

Garrison Dam
Garrison Dam
The photo above is the power plant intake. Water flows into this structure, though pipes under the dam, and into the powerhouse. There are 8 intakes in total. Five are for the five power power turbines, and three are for flood control. The flood control intakes bypass the powerplant and flow directly into the river downstream. The intake pipes are 24-feet in diameter, while the flood control pipes vary between 22-feet and 26-feet in diameter. The water is approximately 180 feet deep at this location.

The photo below is looking downstream at the power plant and the tail channel flowing away form the dam. There are ten large tanks on top of the power plan building. These are surge tanks. They act like buffers to briefly hold the water flowing into the power turbines. This tends to smooth out the flow, which keeps the pressure on the turbine blades more even, resulting in much longer life.

Garrison Dam
Garrison Dam
The photo above is another view of the power plant and electrical power substation. The power plant has five turbine generating units capable of generating 515 megawatts of power, though typical operation is about half that amount.

The photo below is looking east along the highway that runs across the dam. The lake is to the left, and the downstream face of the dam is to the right. The base of the dam is 2,050 feet thick, and it tapers to a width of only 60 feet wide at the top.

Garrison Dam
Garrison Dam
The photo above is taken from the lower service road looking up towards the top of the face of the dam. The main highway is on top of the dam, some 200 feet higher in elevation. The dam is planted with grass and mowed at least twice a year. Mowing the grass is essential to keeping weeds and brush down, and to be able to see any wet spots due to leakage long before it becomes a problem.

Below is another view looking east across the dam. The highway across the top of the dam has several curves connected by long stretches of straight highway.

Garrison Dam
Garrison Dam
The photo above is another view looking east along the highway at the top of the dam. We are getting very close to the spillway. The red and white rock riprap on the left side of the photo is the edge of the lake and part of the wall between the lake and the spillway. The red layer is normally above lake level, while the white section is normally below water. The height of the white rock shows how far down the lake is in late 2007 when this photo was taken.

The photo below shows the downstream side of the emergency spillway. The spillway is used in the event of a major flood where the lake is low, and the power plant cannot pass enough water to prevent the dam from over-topping. An over-top situation could lead to dam failure, so the spillway is needed to divert flood waters though the dam. There are a total of 28 gates, each of which are 40 feet wide and 29 feet tall. Under normal operation, the spillway is dry.

Garrison Dam
Garrison Dam
Here are two views of the highway bridge over the spillway. Both photos are looking east. The upper photo is entering the bridge from the west end. The lower photo is exiting the bridge on the far east end of the dam.

Garrison Dam

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