Group proposes multiple ways to reduce sediment in Shoshone River

Posted 11/29/19

After years of studying and brainstorming, a local working group has come up with a list of ways to help prevent sediment from clogging up the Shoshone River south of Powell.

The group formed …

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Group proposes multiple ways to reduce sediment in Shoshone River


After years of studying and brainstorming, a local working group has come up with a list of ways to help prevent sediment from clogging up the Shoshone River south of Powell.

The group formed after tons of sediment were released from behind Willwood Dam amid repairs to the structure in 2016. The release killed fish downstream of the dam and temporarily turned the Shoshone into a grayish slurry, drawing a public outcry.

Multiple groups formed to prevent a future sediment spill, including Willwood Work Group 3. Charged with coming up with a plan to reduce the amount of sediment that reaches the Willwood Dam, the group is made up of representatives from a variety of organizations with an interest in the river.

They’ve spent parts of three years studying the issue and possible solutions — and group leaders told Park County commissioners last month that there’s much more work still to do.

“This is going to be a long-term effort and it’s going to take coordination among many groups of people,” said Jennifer Zygmunt of the Wyoming Department of Environmental Quality, adding that, “Obviously this is going to be a lift over many, many years.”

During the Oct. 15 meeting, the group laid out seven preliminary recommendations for curbing human-caused sediment upstream of the Willwood Dam; some of the proposed management measures are efforts that have been underway for years.

They include:

Zygmunt said it’s important to understand the watershed “to make sure that you’re planning projects that are going to improve the resource, but also protect the use of the fisheries — and also work with producers to find solutions that are feasible for agriculture.”

While the proposal focuses on reducing human-caused sediment, one of the big unknowns is how much of the sediment is naturally occurring; for instance, group members strongly suspect erosion from the McCullough Peaks is a big contributor.

“We just don’t have the data right now to come up with great answers to that question, but it is a really big important question that we are trying to answer,” Zygmunt said. She said it would take at least five years to gather enough data for a good estimate.

Still, preliminary data has already given some insights. For instance, samples from 2017 and 2018 indicated that Sulphur and Sage creeks carried hundreds of tons of sediment into the Shoshone River on peak days, while Dry Creek and Dry Gulch carried no more than 24 tons.

“... You can see that potentially Sage Creek and Sulphur Creek are high contributors, whereas Dry Creek and Dry Gulch probably aren’t the places to focus for us to get the biggest bang for the buck,” Zygmunt said.

One of the group’s primary recommendations is that the sediment sources continue to be monitored. Zygmunt hopes grants can fund that monitoring and employ a watershed coordinator. “You really need that local champion in the watershed who knows the watershed to make this happen,” she said.

While the dramatic release of silt in 2016 drew attention to the sediment problem, it’s not a new one. Silt has been stacking up for decades behind the dam, as the Willwood irrigation District, which manages the facility, has been restricted in how much sediment it can put downstream.

Since 2016, the district has been allowed to flush a little more sediment, said Willwood Irrigation District Manager Travis Moger. Further, new monitoring equipment alerts managers when turbidity is rising — and there’s now regular communication between the district, regulators and others to avoid a repeat.

“It’s working,” Moger said of the new process, adding, “If it [turbidity] starts to come up, I can kind of shut it down right away and get it calmed down.”

However, Moger said he does think there’s still more sediment arriving at the dam each year than is released downstream.

“I believe we’re probably still building,” he said.

The group’s presentation says that, “Additional repairs [to the Willwood Dam] are going to be necessary in the next five to 10 years, which will require the sluicing or dredging of 360,000 cubic yards of sediment.”

A different group, known as Work Group 2, has been working on ways to better manage the sediment at the dam and evaluate the water quality standards.

As for the members of Work Group 3, they indicated to commissioners that their collaborative efforts to reduce sediment have been rewarding.

“This has been a pretty wild ride, kind of a joyous one. It’s kind of amazing,” said Powell Clarks Fork Conservation District Manager Ann Trosper.

“It didn’t start out too joyous,” interjected Commission Chairman Jake Fulkerson, referring to the 2016 spill.

“No, it didn’t. We were making lemonade out of lemons, trust me,” Trosper said. “But the best part of this is it put a lot of people with very distinct personalities and perspectives together, trying to solve a common problem. And I’m extremely proud of the effort that went into this.”

The working group includes representatives from the Willwood Irrigation District, Wyoming Department of Environmental Quality, Wyoming Game and Fish Department, Bureau of Land Management, the Powell Clarks Fork and Cody conservation districts, Natural Resources Conservation Service, Wyoming Association of Conservation Districts, East Yellowstone Chapter of Trout Unlimited, University of Wyoming Extension, The Nature Conservancy and ag producers.



For more information about work of Willwood Working Group 3 and its efforts to reduce sediment on the Shoshone River, visit to view a presentation outlining the group’s work.

You can also visit to read the group’s “Sediment Watershed Plan for the Shoshone River from Buffalo Bill Reservoir to Willwood Dam.”