Bismarck News

Inside the Garrison Dam

Inside the Garrison Dam

Monday's opening of spillway gates at the Garrison Dam demonstrated that there are three ways to move water from Lake Sakakawea into the Missouri River channel.
Through the power plant, through the regulating tunnels that were used over the past couple of months, and through the spillway gates.
That's what we see from the outside.
But there's a lot going on with the Garrison Dam Project we don't normally see.
Jim Olson takes us on a tour, inside the Garrison Dam.

We'll begin here - at the intake structure that sits on the reservoir side of the dam.

(Dale Evenson, Garrison Dam Maintenance & Operations Manager) "There are eight tunnels that move water. Five of them for the power plant. And the three on this end are what we call the regulating tunnels."

Five primary tunnels - known as penstocks one through five - feed the power plant. There are ten massive bulkhead gates - each weighing 100 tons - that regulate how much water goes through the penstocks. And they can be slammed shut if needed.

(Dale Evenson, Garrison Dam Maintenance & Operations Manager) "If there needed to be an emergency shutdown of water going through the penstock, this is one way to do that."

The penstocks penetrate the earthen dam to this spot - more than 150 feet below the surface of the water in the lake in the bowels of the power plant - and feed cold water from the bottom of the reservoir into the turbines that spin smoothly. They look like this up top - as they produce electricity that serves hundreds of thousands of customers.

In high water years - like this year - the three regulating tunnels - penstocks 6, 7, and 8 - move water from the lake through the embankment directly into the river, without producing any electricity. They are key to the dam's ability to minimize flooding.

And finally, there's the spillway that was the focus of attention this week. 

(Todd Lindquist, Garrison Dam Project Manager) "The spillway sat there for 50+ years and was never used."

That changed in 2011 when it was first used to deal with record water levels in the system. And it changed again Monday when nine of its 28 gates were opened one foot to demonstrate the flexibility the six-decades-old system has to keep doing its job - using what we can see and what's inside the Garrison Dam.

The two-mile-long embankment that forms Lake Sakakawea makes Garrison the 5th largest earthen dam in the world.


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