Answers to silt explored by Willwood/DEQ

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Willwood Irrigation District is actively seeking potential solutions to avoid massive releases of silt from behind Willwood Dam in the future.   

District leaders met with various government agencies — including the Wyoming Department of Environmental Quality — on Thursday, Dec. 1 in Casper.

The agencies met to find solutions to a buildup of silt behind the dam, some of which washed into the Shoshone River downstream when the pool behind the dam was lowered for repair work in October. The silt release killed fish and raised the ire of sportsmen and landowners downstream.

It’s not the first time that silt releases from behind the dam have caused environmental problems in the area.

Representatives from the U.S. Bureau of Reclamation, Wyoming Game and Fish Department, Park County Commission, Wyoming Water Development Commission, State Engineer’s Office and Rep. Dave Northrup, R-Powell, attended last week’s meeting. No staff from Gov. Matt Mead’s office were present. 

“It was a good, positive meeting,” said Todd Singbeil, Willwood Irrigation District manager

In the short term, the district sought a flushing-flow study to determine the volume of water necessary to flush away the silt that was deposited downstream of the dam, Singbeil said. A flushing flow would require requesting additional water from the Bureau of Reclamation, the agency that controls the flow from Buffalo Bill Dam.

Flushing flows are a means to wash away sediment on riverbeds to improve aquatic habitat.

Dirk Miller, Game and Fish deputy chief of fisheries in Cheyenne, said he believes a flushing flow would help, but he does not know the quantity of water necessary to remove the sediment. Nor, he said, does he know at this time whether a flushing flow would remove all the silt.

The district agreed to invest $10,000 in a University of Wyoming flushing flow study, Singbeil said.

Flushing flows are conducted on the North Platte and Wind rivers, Miller said. Calculating how much liquid energy emanating from the Buffalo Bill Dam is necessary to push sediment is where the UW study comes in. Increasing dam releases also must be accomplished without flooding users downstream.

The Bureau of Reclamation prefers to release a fixed amount during the winter to prevent the accumulation of excess ice that can damage facilities downstream, Miller said.

There had been some early discussions about digging up and removing the estimated 800,000 cubic yards of silt that’s still stacked up behind the dam, but it now seems that’s not a viable option, said Park County Commissioner Joe Tilden, who attended the meeting.

For one thing, a dredging operation would be pricey.

“Right now, it looks like the only potential long term solution is to allow the irrigation district to go back to how they operated prior to 1950,” Tilden said.

Willwood officials estimate that, if they were allowed to increase the Shoshone River’s turbidity during certain parts of the year — as the DEQ allowed them to do decades ago — “within 20 to 25 years, they could not only flush the yearly accumulation of silt, but they could eat away and get rid of that 800,000 cubic yards,” explained Commissioner Lee Livingston.

Livingston said the idea seems to make sense.

The DEQ will look at Willwood’s current turbidity limit, whether that is the correct standard and whether the current limit could be raised without impacting aquatic life, said Keith Guille, DEQ public information officer in Cheyenne.

“There’s still an awful lot of unanswered questions out there,” said Tilden. “One of the biggest questions is ... the Game and Fish Department has to determine how much silt a trout can live with — which they don’t know.”

“That’s crazy they don’t know that,” Commissioner-elect Jake Fulkerson interjected at the commission’s Tuesday meeting.

A followup meeting with the district, DEQ and others is scheduled for after the holidays, Singbeil said.

By then, more information from the UW study may be available, Miller said.

Everyone at last Thursday’s meeting, including district representatives, wanted the fix to be permanent, Miller said.

Although the solution will not be simple, Game and Fish’s goal is preserving the fishery now and finding a long term solution, Miller said.

“Let’s figure out how to avoid this in the future,” he said.

Thursday’s discussion also included examining the potential to address non-point source sediment (sediment from unknown sources) upstream of the dam, Guille said.

DEQ is paying attention to public comments and will continue to do so, Guille said. “We remain committed to working with the Willwood Irrigation District.”

Livingston said he considered Thursday’s discussion to be a “great meeting” and hopes there will be some good action that comes out of it.

(CJ Baker contributed reporting to this article.)

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