Shutting off a super-sized spigot
Moving water from mountain reservoirs to household taps is never easy. For the next several months, Denver Water will be doing it with the equivalent of one hand tied behind its back.
A series of major maintenance and construction projects will require Denver Water to, essentially, shut down the entire north side of its collection, delivery and treatment system, and rely wholly on the southern end to supply 1.5 million people with water as the utility heads into the colder seasons.
The work has required a Colorado Ballet level of choreography to move water around the system months in advance in preparation for a rare set of circumstances.
“Shifting all that water here and there, it’s a lot to keep straight, a lot to think about, a lot to juggle,” said Nathan Elder, manager of water supply for Denver Water. “And it all comes on top of watching the weather to see what it might — or might not — bring us as far as precipitation.”
Denver Water is conducting several projects that required the utility to turn off the spigot on its north side supply system late this summer. Those include:
- Replacing a massive grate at the bottom of Gross Dam that prevents heavy debris from finding its way into the pipes and valves that calibrate water releases at the base of the dam. The project is so complex it requires specially trained diving crews working hundreds of feet under the reservoir surface.
- Replacing concrete at the Moffat Canal near the east portal of the Moffat Tunnel. The freeze-thaw cycle at 9,200 feet has taken a toll and allowed for water to seep underneath concrete and create the potential for damaging erosion.
- Repairing deteriorated concrete within the Moffat Tunnel caused by years of scour within the tunnel.
- Replacing key structures at Ralston Reservoir along Highway 93 near Golden. The work to replace equipment that regulates the way water is carried through the dam will allow for safer operation of reservoir releases. Replacing that equipment requires draining the reservoir.
- A project to connect the emerging Northwater Treatment Plant to Denver Water’s distribution system. This work, the overarching reason for shutting down north side flows, also requires taking the existing Moffat Treatment Plant offline for modifications related to the Northwater connections.
All that north side work means Denver Water will have to rely almost fully on supplies from its southern end that gather water from the South Platte River as well as from Dillon Reservoir in Summit County.
This north side shutdown is even more complicated than the maneuverings required in the summer of 2020, when Denver Water had to undertake big shifts in how it moved water through its system due to repair work that closed the Roberts Tunnel for two months, closing off access to water from Dillon Reservoir.
That orchestration was hard enough. Planning for the current shutdown began months ago when engineers decided to coordinate several projects to contain the treatment and delivery disruptions to a single fall and winter cycle.
“Doing it this way made the most sense,” explained Jennifer Gelmini, a senior engineer at Denver Water who is coordinating the projects. “We realized we were going to have a long outage for the work needed for the Northwater plant connections and Moffat modifications and looked at how we could take advantage of this big shutdown and what other projects could fit into that timeframe.”
That plan made it critical to maintain as much water as possible in Dillon Reservoir to help with supplies in the late summer and fall, while also keeping levels high at Cheesman and Marston reservoirs so they can be relied on over the upcoming winter months.
Anglers and Sunday drivers may have noticed big flows in the North Fork of the South Platte River, too, in late summer, as the utility moved more water than usual from Dillon, through the Roberts Tunnel under the Continental Divide and into the North Fork. At times, late summer flows reached 450 cubic feet per second, compared to a more typical September flow of one-third that volume.
“We’ve been setting the stage on this for months,” Elder said. “Taking the north end out of the equation means we have to set up our southern end for all the heavy lifting for nearly an eight-month span. It’s a highly unusual and tricky undertaking.”
Ralston Reservoir near Golden must be drained completely to replace the outlet works at the base of the earthen dam. That reservoir holds nearly 11,000 acre-feet and will be out of commission until the beginning of runoff season in April 2022, creating a dramatic gap in Denver Water’s typical water delivery and treatment pattern.
Because the 84-year-old Moffat Treatment Plant also will be offline for that period, all the water treatment needs are pushed to the utility’s Marston and Foothills plants in the southwest side of the region.
Further complicating such an extended dance: Denver Water this summer had to release large volumes of water from two West Slope reservoirs (Williams Fork and Wolford Mountain) to make up for a water debt it owed on the other side of the Continental Divide.
While those releases weren’t tied to the projects on the north end, it was another factor water managers had to keep in mind as they ensured Denver Water met all its many obligations, both to its customers and to agreements related to Colorado River flows.
“This year has been unusual,” Elder said. “No year is ever the same in water supply, but between a pretty dry winter, then a wet spring and early summer, followed by another dry stretch as we try to set the system up for these construction projects, there were a lot of details to sweat.”
The good news: Come spring, a lot of key projects will be wrapped up, and water managers will once again have more flexibility to manage water between its north and south systems.
Just in time for spring runoff season.