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A very draining experience — followed by a 'full-filling' one

Denver Water drained, refilled Ralston Reservoir to do much-needed upgrades.

When you’re a 104-year-old utility, you don’t get a lot of firsts. But when you do, they’re amazing — and sometimes complicated.

Such was the case late last year when Denver Water drained Ralston Reservoir, located off Highway 93 north of Golden, to provide some much-needed infrastructure upgrades at the bottom of the reservoir. 

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Empty reservoir
The bottom of Ralston Reservoir in February 2022, the first time the reservoir off Highway 93 north of Golden has been drained of water in nearly 90 years. Photo credit: Denver Water.

It was the first time Ralston was drained since the reservoir was completed in 1937. 

“Nobody (around today) has ever seen the bottom of Ralston Reservoir before we drained it,” said Ryan Haas, a senior project manager at Denver Water. “So, we weren’t sure what we were going to find.”

Most of the upgrades were to the reservoir’s original, aging infrastructure. 


Read more about the work Denver Water does to deliver water to 1.5 million people. 


“Redundancy is important when working with the flow control of a dam,” Haas says. “You should have multiple ways to control the flow of water through the dam. And this project brought that redundancy back to Ralston.”

The biggest piece of the project required building a new intake structure upstream of the existing one. 

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Crane holds concrete gate
Ralston Dam’s new knife gate, which helps control the flow of water through a dam, being lowered into place by crane. Photo credit: Denver Water.

That new intake structure includes a 66-inch upstream control valve with a 6-inch bypass valve, to better control water flow through the dam. That existing 4-foot-by-5-foot slide gate also was refurbished to provide redundancy in controlling the reservoir’s flow.

“A lot of that infrastructure was nearly 90 years old,” Haas says. “It served us well, but this new intake structure will help us operate the dam much more effectively.”

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Two men stand near concrete gate
Lance Paplow, left, a senior construction inspector at Denver Water, and Ryan Haas, a senior construction project manager, give perspective to the size of the new knife gate installed at the base of Ralston Dam as part of the infrastructure upgrades. Photo credit: Denver Water.

So where did all that water go? This project was a long time in planning, so there was ample opportunity to keep a lot of water out of Ralston last summer, and then to use most of its existing contents before draining. 

With the work now completed, Denver Water has started filling Ralston again. Once runoff season is finished by late spring, there should be plenty of water once again covering up all that shiny new infrastructure -- that we expect to last for another 90 years or so. 

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Dam inlet structure
Ralston Reservoir’s new knife gate and inlet structure, completed and ready for many more decades of service. Photo credit: Denver Water.