LaPrele Dam to be demolished before spring runoff to avoid ‘catastrophe’

DOUGLAS — The 140-foot-high concrete LaPrele Dam,  at 115 years old, is in its end of days sooner than expected and will be demolished prior to the upcoming spring 2025 runoff season, following orders by the Wyoming State Engineer and Gov. Mark Gordon.

The dam is located 20 miles west of Douglas. It creates the LaPrele Reservoir and sits above Natural Bridge Park. Completed in 1909, it is the oldest and tallest open front dam in the nation.

Wyoming State Engineer Brandon Gebhart on Nov. 1 issued an order to “breach the dam.” That order requires the dam to be demolished by spring.

Converse County and state officials, as well as the LaPrele Irrigation District – which owns the dam – have been monitoring its structural integrity for several years following the discovery of cracks and other issues.

After ongoing monitoring and a recent, thorough inspection, the discovery of a large, new crack above the dam’s outlet works, the deterioration of previously identified structural deficiencies and the operational limitations of the existing dam led to the decision, according to a release issued by Gordon’s office Sunday.

Gordon said he commends Gebhart and his staff for recognizing the significant risks of a potential dam failure and proactively addressing the situation before a disaster occurs.

“This decision was not made lightly and we recognize the impact this will have on those who rely on that water for irrigation,” he said.

The deteriorating conditions of the dam had been identified and monitored by multiple entities, eventually leading Gebhart to issue orders restricting water storage behind the dam in 2019.

“This dam has significant structural deficiencies and has reached the end of its life,” Gebhart told the Budget during a previous interview.

This week, he said there is “currently no risk or danger to the public downstream, because there is little to no water stored, and the outlets are able to pass inflows to prevent new storage.

“However, continued use of the dam to store water could cause catastrophic failure, which poses a threat to life and property. These threats need to be mitigated before the spring runoff, when flows are expected to exceed the dam’s ability to pass inflows.”

Gordon said he greatly appreciates the collaboration of all involved parties to work together, identify and address such a significant threat.

Given the age and condition of the structure, LaPrele Dam was already scheduled for replacement in the coming years and planning for the replacement is already underway. Those plans included demolition of the dam, which was set to occur as part of the replacement project, so this order moves up that timetable considerably.

“I appreciate (Gebhart’s) foresight and agency expertise to detect a risk and prevent failure. A dam failure could have had major impacts to I-25 and other transportation infrastructure like bridges and underpasses,” WYDOT Director Darin Westby said. “We will be monitoring the impacts of the decommissioning on all impacted WYDOT infrastructure.”

The LaPrele Irrigation District expressed its appreciation via a statement for the collaborative efforts the state has undertaken to address the dam’s issues.

“. . . We also hold paramount our responsibility as owners of this high hazard dam to mitigate the threat it currently poses to life, property and natural resources downstream. We are grateful for the support and collaboration of the State Engineer’s Office and the Water Development Office in addressing the issue,” the statement said. “We continue our unwavering commitment to replacing the LaPrele Dam with a renewed sense of urgency.”

Converse County Commission Chairman Jim Willox said the commissioners are disappointed in the decision to breach LaPrele Dam, but they understand it.

“A catastrophic failure would be devastating,” Willox said. “The commissioners have been following the discussions surrounding the dam for a while and have been fully aware of what is taking place and the condition of the dam.”

“We’ve been proactive. We know the dam is old and we’ve been trying to jump through all of the hoops to build a new dam. This was a little earlier than what we’d expected,” said LaPrele Irrigation District Chairman Gary Shatto. “We knew the dam couldn’t last forever so we’ve been trying to build a new one, working with consultants, the state, Wyoming Water Development (Commission). It’s a slow process to build something this massive and of this magnitude.”

Shatto added that losing the dam is a strain on shareholders.

“For the past 100 years they have been depending on that water to improve their land, their livestock,” he said. “They thought they’d have that water forever.”

The irrigation district is not sure how the dam demolition will affect shareholders’ groundwater, Shatto said.

“New generations have taken over and they depend on the water, too. It irrigates 11,400 acres,” he said. “People think it just affects a few ranchers and farmers, but it’s much bigger than that. Think about all those shareholders, their families and kids, hired help, full-time employees, managers, the full and part-time jobs. It’s close to 1,000 people this is going to directly or indirectly affect and that’s going to have a domino effect within our community.”

Shatto said the district will finish the design of a new dam and get started on construction by 2026, with a goal of completing it in late 2028.

This story was published on November 6, 2024.