Next month, the Town of Estes Park Board of Trustees will be presented with the results of the Big Thompson River and Fall River Capacity Improvement Study, after ongoing updates at study sessions starting on Sept. 10, 2024.
The study recommends infrastructure improvements in the downtown corridor, including lowering the river channels by several feet, to mitigate future flooding along the Big Thompson and Fall Rivers.
The paths of these two rivers as they flow through Estes Park, especially through the downtown corridor, have resulted in significant property damage during flood events, most recently with the 100-year-plus flood of Sept. 2013.
Over a seven-day period, more than 17 inches of rain fell on the Front Range of Colorado, from Colorado Springs to Fort Collins, according to John Batka, a project engineer with the Colorado Division of Water Resources. The rain caused both the Big Thompson and Fall Rivers to swell, quickly exceeding their banks. The flood waters passed through Estes Park and other Front Range mountain communities before going downriver to inflict more than $4 billion of damage, statewide.
Locally, large sections of roads and bridges were completely washed out along both Highways 36 and 34; and Highway 7 was heavily damaged. The canyons closed with National Guard members posted at the mouths of each to prevent motorists from unwittingly driving off into oblivion. Estes Park was isolated from the rest of the world for 36 hours before contact was restored.
The sound of Chinook helicopters rescuing stranded people and bringing in supplies filled the air for weeks. About a month after the flood, the Federal Government shut down in a standoff over the budget. Up until then, the only way to reliably get in and out of Estes Park had been to drive over the Divide on Trail Ridge Road in Rocky Mountain National Park.
Sometime during the 16 days of government shutdown, RMNP closed Trail Ridge Road for the season. U.S. Highway 36, which was the first to reopen, was closed from Lyons to Estes Park for 30 days. Repairs on the Big Thompson Canyon took much longer. It was nearly five years until U.S. Highway 34 from Estes Park to Loveland was completely repaired. In total, nine lives were lost in the 2013 Front Range Flood.
The Big Thompson Flood of 1976 killed 144 people as it roared through the canyon on a crowded camping day on July 31. An estimated 2,500 people were in the Big Thompson along the Highway 34 Canyon that night, residents and those who came to celebrate Colorado Day the same year the state celebrated its centennial.
A thunderstorm stalled over Estes Park, producing 12 inches of rain in an estimated seven-hour period. The narrow canyon between Estes Park and Loveland funneled the flood into a wall of water, traveling at 32,000 cubic feet per second for nearly an hour. The speed was estimated from a stream gauge at Drake that was ultimately demolished in the surge. Almost 50 years later, five people remain missing from the Big Thompson Flood.
The Lawn Lake Flood of 1982 was caused by a dam break. Years before RMNP was established, area ranchers had installed an earthen dam at Lawn Lake. When this dam drastically failed, it created the Roaring River, the Alluvial Fan, and joined Fall River to send about three feet of water cascading into Estes Park via the path of least resistance — West Elkhorn Avenue, straight through downtown.
Unfortunately, the flood had already killed three people who were tent-camping in the Park’s Aspenglen Campground.
The flow rate of this flood was estimated at 18,000 cubic feet per second, said Jennifer Waters, the Town’s Water Engineer.
Modeling suggests that during a 100-year flood, water would reach 3,010 cfs at the Visitor’s Center, said the Town’s Public Works Director/Stormwater Manager. Greg Muhonen. This confirms Batka’s 2014 calculation that Colorado will experience a major flood event once every 16 years.
Flash floods are especially powerful in rocky, dry climates and while notification capabilities have improved since 1976, 1982, and then 2013, the floods were expensive and disruptive to Estes Park. And in all cases, deadly.
Before Estes Park was established in 1917, the Big Thompson River meandered through the Estes Valley just as it does today in Moraine Park, RMNP. It was a wide and shallow river, flanked on both sides with lush growth and willows, fed from the Big Thompson’s frequent flooding in the spring and summer months.
The Big Thompson River combines with Fall River at Confluence Park in the heart of downtown Estes Park before heading east and down the Big Thompson Canyon along Highway 34.
This beautiful water feature was capitalized on by early settlers of Estes Park. They straightened the river channels and constructed buildings close to the water’s edge to create the town’s quaint downtown. When the floods came, they damaged these buildings and tore out infrastructure, each time.
The Town developed a stormwater master plan which was adopted in 2017. It “identified $79 million worth of improvements that were needed in the community to become more resilient and capable of handling the next significant flood when it comes through town,” said Muhonen. Several possibilities were explored to pay for these improvements, but “instead we came up with a three-legged strategy,” he said.
Voters approved a 10-year 1% sales tax last year; 28% of that income is slated for stormwater improvements.
In addition, grant funding and the Town’s General Fund all combine to pay for the design and construction of the improvements recommended by the Big Thompson River and Fall River Capacity Improvement Study.
It covers the “logical first phase” of improvements, said Muhonen, starting from downstream and working west. “We’re trying to keep this thing in digestible sections, considering not only the cost of the package, but the disruption associated with the packages, because these are going to be impactful projects,” he said.
By April 20, “GEI Consulting will have furnished the deliverables, which are a technical report and 30% design drawings,” said Waters, who is the project manager for this study, at the Jan. 28 Town Board Study Session.
“When and if the town chooses to do so, this package may be submitted with an application for a construction grant to completely design and build the capacity improvements, modeled to mitigate flooding by decreasing the coverage of the Special Flood Hazard Area in the vicinity of East Elkhorn Avenue and the Fall River Corridor up to the Moraine Bridge,” said Waters.
This extensive study was funded primarily by a grant from the Federal Emergency Management Administration, only 25% or $136,000 will be paid by the Town, Waters said.
Construction on this project will not start until 2028, or later, said Muhonen. Batka’s flood frequency prediction says we’re due for another flooding event by 2029.
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