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Water

Pathfinder Modification accepts construction bids

Casper – Upon the completion of the Pathfinder Modification project, which will raise the spillway 2.4 feet, Pathfinder Reservoir will be returned from its current 1.16 million acre-feet capacity back to its original 1.7 million acre-feet appropriation.
“The history of this project has been amazing,” says Wyoming Water Development Commission Director Mike Purcell of the modification project. “In the 1980s the State of Wyoming wanted to construct Deer Creek Dam for supplemental supplies for North Platte municipalities and in ’86 Nebraska sued Wyoming, as they thought the construction of Deer Creek Dam was a violation of the Decree.”
Purcell says there were simultaneous negotiations for an endangered species program. “That came to a head in the mid-’90s. We always knew the Endangered Species Act would come front and center on anything new, but in the mid-’90s it became apparent that we needed to address the endangered species issues even if we wanted to improve existing facilities.”
“Ultimately we solved the lawsuit and the endangered species were handled through the Platte River Recovery Implementation Plan, and all parties agreed we’d substitute the Pathfinder Modification project for Deer Creek Dam, and that’s how Nebraska, Colorado, Wyoming and the Department of the Interior came to embrace the modification project,” says Purcell.
Under the endangered species plan, water captured in Pathfinder will move down to Lake McConaughy in central Nebraska, where the U.S. Fish and Wildlife Service will release water as needed for the species.
“We’re up here modifying a reservoir to get water for endangered species some 500 miles downstream,” says Bureau of Reclamation Wyoming Area Manager John Lawson. “The whole goal of the program is to provide 130,000 to 150,000 acre-feet of flow to improve the target species in the Central Platte.”
Only in its first 13-year increment, the project’s ultimate goal is 417,000 acre-feet of water. Lawson says some will come from the Pathfinder Modification as Wyoming’s contribution, some will come from Lake McConaughy and some will come from the Tamarack Project, an underground reservoir, in eastern Colorado.
“We split the 54,000 acre-feet, and 30,000 of it became the environmental account – Wyoming’s contribution to the Platte River Recovery on behalf of our water users, who are all users faced with endangered species consultations, including the Bureau of Reclamation, municipalities and irrigation districts,” says Purcell.
After that was settled, the modification had to go before Congress to get the federal authorization changed for the water use, it had to go through the Wyoming Legislature for an $8.5 million appropriation and back again for perimission to export water to Nebraska. A mitigation plan for fisheries was put in place with the Wyoming Game and Fish Department and the Bureau of Reclamation had to go before the Board of Control for a water right amendment expended to municipal and environmental uses.
The modification project also had to go through negotiations with upstream water users in Carbon County. “In essence, the 54,000 acre-feet of water rights say we get to store water under that priority, but it can’t make calls,” says Purcell. “it cannot call out the upper basin, where those users were concerned about potential additional water rights administration upstream.”
“The culmination of all this is that we’re accepting construction bids,” says Purcell, noting that the spillway has been “high and dry” for 26 years, and now that contractors will be on the spillway, “Mother Nature has decided to give us some grief.”
Running over Pathfinder’s existing spillway is a walkway, and under that is the existing low dam, or weir, used to raise the level of water upstream and regulate its flow.
“The weir is what we use to judge how much water is being passed downstream,” says Lawson. “We know by every tenth of a foot how much water is being passed downstream, and it worked rather well.”
“What the modification amounts to is building a new weir 2.4 feet higher than the existing,” says Lawson. “The amazing thing is that 2.4 feet will store 54,000 acre-feet of water.”
He puts that into perspective by noting that Guernsey Dam, further down the system, only holds 45,000 acre-feet of water maximum.
The new weir will be extended somewhat, allowing for a longer weir area that will allow the spillway to meet its requirements of what it needs to pass in a probable maximum flood. “By having a longer weir we have more surface area to pass water over, and in addition to that we’ll have a considerable amount of work with regard to rock removal and getting the spillway area cleared out for friction,” says Lawson.
Instead of a rough concrete block, the new weir will also be shaped with the dynamics of an airplane wing so more water can be passed over with less pressure.
“We told the contractors in the bid package that this spillway has to be operational again by April 1, 2011, because we don’t know what the future brings for next year,” says Purcell. “You’d have to suggest, with all the water we have right now, and the fact there’s not much demand on the system, a spill is very potential for next year.”
The contractors can start in August, get out in April and begin work again August 2011, if need be.
“The first thing they’ll do is blasting, because that will immediately increase the capacity of the spillway,” says Purcell. “And John Lawson and the Bureau of Reclamation need to know how much water spills, so we can’t really have a situation where half the new weir is in. It has to be an integral controlled area in preparation for next year.”
Christy Hemken is managing editor of the Wyoming Livestock Roundup and can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..