Willwood Irrigation District scrutinizes silt situation

Posted 2/23/10

Approximately 355,000 cubic yards of silt or sediment encroaching on the dam and sluice gates need to be removed. Built-up silt prevents the operation of two of the three sluice gates, said Travis Conklin, of Engineering Associates, in a PowerPoint …

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Willwood Irrigation District scrutinizes silt situation


With silt running approximately one-quarter the length of the Willwood Dam, the Willwood Irrigation District board and district members debated over a costly fix at the district's annual meeting Feb. 12.The rehabilitation work was based on a study funded by the Wyoming Water Development Commission.

Approximately 355,000 cubic yards of silt or sediment encroaching on the dam and sluice gates need to be removed. Built-up silt prevents the operation of two of the three sluice gates, said Travis Conklin, of Engineering Associates, in a PowerPoint presentation.

Only one gate is operating now.

The dam, more than 80 years old, requires rehabilitation to check the erosion.

The U.S. Bureau of Reclamation owns the actual facilities, but transferred operation, maintenance and repairs to the district after the dam was completed, said John Lawson, Wyoming area manager for the bureau.

The dam is structurally sound, even if the silt rises to the level of the spillway, Lawson said. However, he said that would not be good, because the release of water could not be controlled.

The district is considering two silt-removal options, both of which would be costly. Even doing nothing to remove the silt would require other changes that would cost more than $1 million.

The Wyoming Water Development Commission, which funds water district material costs, has not decided whether it would pitch in for silt removal, Conklin said.

The first option which consists of removing the silt, adding cofferdams to divert the water temporarily, would cost approximately $5 million. If the Wyoming Water Development Commission chips in, the agency would pay $3.35 million, leaving the district to raise $1.65 million.

The second option would dredge the silt using a machine resembling a stubby, old-fashioned riverboat with the paddles mounted fore rather than aft. That option would cost $1.9 million. If the WWDC is willing, it would pay half and the district the other half, said Conklin's slides.

The $1.9 million operation would include the purchase of the boat dredge, and the year-round operation would take two years to complete, said Tom Walker, Willwood District manager.

The district is leaning toward that option, Walker said.

To bankroll the district's cost, Walker said the district would have to increase assessments another $15 per acre annually.

Currently, users are paying $25 per acre.

Shoshone Irrigation District's assessment is $17.10 per acre, and Heart Mountain Irrigation District's is $22.50 per acre.

“A lot of these guys are struggling out here right now,” Walker said.

Walker said essential rehabilitation of the dam, including sluice-gate replacement, could be initiated at a cost of $3.4 million. The district's share would be $1.12 million, with Wyoming Water Development Commission picking up the rest. The dredging and sluice-gate repairs must be done simultaneously, Walker said.

The $1.9 million dredging operation would increase the diltrict's share to just more than $3 million without the Water Development Commission's financial assistance.

“The silt removal,” Walker said, “we might have to shoulder all of that.”

If all three gates can be opened, the district could keep sediment moving downstream, Conklin said.

If the sediment is removed above the gates, more will slough just upstream from the dam. However, if all the silt is removed, both atop the gates and upstream, and all three gates are operating, the silt level would be manageable, Walker said.

If the district does nothing, a retention pond to collect silt would be needed downstream in the canal at an estimated cost of nearly $1.3 million, he said.

Roger Easum, district member, said he wants to see less talk and more action.

“My goal is to get something done about this,” Walker said at the meeting.

Walker said he plans to apply to the Water Development Commission for funding this fall. If funding comes through, dredging could begin in the fall of 2011.

Work to remove the silt could be a collaborative effort that included other water stakeholders, such as the Wyoming Game and Fish Department, other irrigation districts and the Bureau of Reclamation. Discussion needs to be initiated with them, Conklin said.

However, no agencies have stepped forward to help with silt removal up to this point, Walker said.

“I think there should be some responsibility of the dam by the bureau,” District Chairman Keith Murray said.

The bureau does not the have means to assist the district financially, but it would back the district, if it applied for a loan, Lawson said.

With the federal government acting as a sort of cosigner, the district could secure a low interest loan, Lawson said.

Walker said all district members should have a say in any plan when the district is looking at a potential multi-million dollar debt.

According to the district's 2008-09 fiscal report, total revenue was at $372,767. Total fiscal expenses were $344,538.