Longmont will directly benefit from the biggest public works project to be completed on the Front Range in more than 50 years.
Just west of Carter Lake, construction is underway for Chimney Hollow Reservoir, meant to hold 90,000 acre-feet of water as part of the Windy Gap Firming Project, which is expected to yield Longmont enough water for roughly 15,000 households.
Longmont Water Resources Manager Ken Huson explained that back in the 1960s, Longmont and some other northern Colorado water users sought out water rights on the West Slope, coming from the headwaters of the Colorado River.
That led to the construction of the Windy Gap Reservoir in Grand County, which was meant to deliver 48,000 acre-feet of water per year.
However, there is limited storage for that water, meaning that it might not be possible to keep all that water in high moisture years. Because these are junior water rights, that also means there might be no water in low moisture years, Huson explained.
“We’ve always known we’ve needed to firm up the water,” Huson said. “Storage is absolutely critical in Colorado for water supply. That’s what the Windy Gap project does.”
The Chimney Hollow reservoir is where water from high moisture years will be stored. Known as the Windy Gap Firming Project because it solidifies this water supply, the $650 million project will yield 30,000 acre-feet of water annually.
There are 12 northern Colorado participants in the project, of which Broomfield will be the largest beneficiary. Longmont will see 7,500 acre-feet, equal to about 8.3% of the yield.
Other participants include the Platte River Power Authority, Loveland, Greeley, Erie, the Little Thompson Water District, Superior, Louisville, Fort Lupton, Lafayette and the Central Weld County Water District. While these public entities are funding the project, Northern Water is the agency ensuring the completion of this ambitious undertaking.
“What we’re seeing is really highly variable precipitation,” explained Jeff Stahla, public information officer for Northern Water. “Some years we’ll have a ton of snow and some years we won’t. The reason why we’re building this reservoir is we think it would behoove us to capture that water when there’s a bunch of it so in the years that there’s not, we don’t have to freak out.”
Additional storage of the Windy Gap water has been contemplated since the original dam was built in 1985 just below the confluence of the Fraser and Colorado rivers near Granby. It took decades of planning, including a 15-year permitting process and a lawsuit from environmental groups challenging that permit, to finally break ground on the project last August.
Huson explained that Longmont’s water planning goal is to ensure that citizens will still have water even during a 100 year drought, which typically lasts about seven years. This project helps the town toward that goal.
“Windy Gap sets up the city well for its future water demands,” Huson said.
At build out, Longmont plans to have one third of its water supply from West Slope sources, including the Windy Gap, and two-thirds from its native basin, the St. Vrain Creek watershed. Huson said growth has not quite caught up with water, so Longmont’s not yet at that ratio.
With the growing concerns about drought and the health of West Slope watersheds, especially the Colorado River, water users are beginning to contribute to environmental mitigation whether they know it or not.
“It’s something that affects northern Colorado, but northern Colorado folks are actually starting to open up their wallets. They’re seeing it in their utility bills,” Stahla said. “Part of their utility bill is going towards addressing some of the issues you may have heard about on the Colorado River.”
While the Windy Gap Firming Project itself will cost about $500 million to construct, another $150 million is going toward mitigation. Because the valley where the reservoir will go was not a significant waterway, Chimney Hollow Reservoir’s environmental impacts are relatively minimal.
Instead, most of that money is going toward the West Slope.
As part of the lawsuit settlement between Northern Water and environmental groups, Longmont and the other participants in this project have contributed $15 million to the Grand Foundation for projects aimed at improving water quality, river health and fish habitat in Grand County where Chimney Hollow will get its water.
Other previously negotiated work means the participants are also contributing to the Colorado River Connectivity Channel, also known as the Windy Gap bypass, which is meant to improve the health of the Colorado River where the Windy Gap Reservoir cuts off fish movement and sediment flows.
Participants are additionally contributing to wastewater treatment plant improvements in Grand County, which will improve the health of the river and the quality of water eventually being pumped to the Front Range.
With all these concerns about the Colorado River, Huson said that good stewardship of water is a priority for Longmont. In 2003, the city set a goal that 10% of water demand be met through conservation, and the city is now close to realizing and even surpassing that target.
“We really have been able to keep our total treated water use for the city fairly flat for about 15 years now,” Huson said. “We’re using about the same amount of water we used 15 years ago, even though the city has grown.”
He credited the citizens and groups in Longmont for their conservation efforts to help reach this goal.
Along with storing the water needed to meet Longmont’s growth, Chimney Hollow will also be a public recreation space just 25 minutes from town. The reservoir will be just a little smaller than Carter Lake, but Stahla said the docks will be hand-launch only, making it an ideal spot for those wanting wake-free water recreation.
Additionally, Larimer County will be managing the open space around the lake with a trail system planned for the area.
So far, Stahla said the Chimney Hollow Reservoir is on schedule and on budget with roughly three and a half years of construction to go.
