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AMERICAN FORK CANYON — Nestled high in the mountains above several northern Utah County communities, the Silver Lake Flat Dam could fail in an earthquake, sending gushing waters down the canyon and likely killing a couple thousand people.
Should the 1970s-era dam crumble apart, two schools would be in jeopardy, as would dozens upon dozens of homes, multiple highways and businesses.
The U.S. Department of Agriculture's Natural Resources Conservation Service is heading up a $5.5 million dam restoration project, funded through a trio of partners that include the federal agency, the state and the local water provider, the North Utah County Water Conservancy District.
"This will extend the life of the dam, improve irrigation, improve recreation and improve wildlife use," said project engineer Aimee Rohner. "It is a fantastic project."
The reservoir was drained to a mere puddle in work that began in mid-July. Contractor RSCI out of Meridian, Idaho, is working at an elevation of 7,500 feet via access provided on a narrow, gravel road filled with switchbacks and sheer drop-offs. The goal is to get the project done before snow flies, with an ambitious deadline set for Halloween.
"We can't have a half-finished project come spring runoff," said Bronson Smart, the state engineer for the Natural Resources Conservation Service in Utah.
Over the years, the agency has built 45 dams in Utah with local partners such as water conservancy districts. The dams went in during the 1960s or 1970s and were designed for a 50-year life.
Kristin Murphy/Deseret News
Smart said many of those dams are now at risk of failure, which will jeopardize lives, communities, water storage and recreation.
With the help of $12 million in funding approved in the last session of the Utah Legislature, the Utah Natural Resources Conservation Service was able to tap into a huge chunk of national money available for dam rehabilitation — $37 million.
The 2014 Farm Bill made $262 million available for the rehabilitation of 151 dams in 26 states.
Utah has 22 dams that will receive seismic retrofits so they are able to withstand a 7.5-magnitude earthquake. Silver Lake Dam is the first recipient of the do-over, with Tibble Fork and Millsite scheduled for next year.
"We are actively working on the design phase for these dams that range from Washington County to Weber County," Smart said.
At Silver Lake Flat, the dam will be raised 4 feet and an elaborate new spillway is being constructed. Engineers also put in a layer of sand in an earthen reconfiguration designed to improve resiliency in the event of a large temblor.
Both Tibble Fork and Silver Lake Flat reservoirs are extremely popular destinations up American Fork Canyon.
"Recreation is huge up here," Smart said, adding that about a quarter of a million people use the lower reservoir each year.
This will extend the life of the dam, improve irrigation, improve recreation and improve wildlife use. It is a fantastic project.
–Aimee Rohner, project engineer
"This is the most visited per-square mile Forest Service district in the nation," he said.
Over time, sediment has sloughed into both reservoirs, not only leading to a diminished recreation experience for visitors but causing problems for water delivery systems along the way.
Tibble Fork Dam will be raised by 17 feet in the restoration project next year to help dissipate some of the sludge, and crews are installing sediment traps and monitoring systems to detect excess silt.
Hunt Willoughby, chairman of the North Utah County Water Conservancy Board, said the dam restoration project at Silver Lake Flat has been on the wish list of the organization for years.
"For years the district has been going to do something and going to do something, and then we got this funding," Willoughby said.
Smart said the federal government kicked in 65 percent of the money, the state contributed 30 percent and the district was responsible for 5 percent of the costs.
With Silver Lake Flat drained and the area full of heavy equipment, the project has required some closures and resulted in travel delays on certain trailheads and roads.
Rohner said they've had to chase some people off for their safety, but errant visitors have been understanding.
"Once you explain it to them that it will be bigger and better, they like that," she said.
Contributing: Jed Boal
