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Geologists study potential dam site on Weiser

Published on February 24, 2012 3:01AM

Last changed on March 23, 2012 7:10AM

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Rare site has 'potential to provide benefits across state'


Capital Press

Work is underway to determine the geologic feasibility of a proposed large reservoir on the Weiser River, which proponents say would benefit irrigators statewide.

Officials are coordinating access routes with landowners and finalizing details of a drilling plan for a $1.5 million geologic study. Core sample drilling is on track to commence in early summer, with study results due by the year's end, said Cynthia Bridge Clark, Idaho Department of Water Resources staff engineer.

The board is revisiting a 1990s feasibility study by the Army Corps of Engineers, calling for a 300-foot-tall rock-fill embankment that would inundate up to 6,918 acres and have a 900,000-acre-foot storage capacity. The so-called Weiser-Galloway Dam would be 13.5 miles east of the city of Weiser, upstream from the Snake River confluence.

Aside from direct irrigation, recreational and flood-control benefits, the dam could free volume for Snake River water users upstream of Hell's Canyon, Clark said. The state and Bureau of Reclamation must dedicate an annual average of 427,000 acre-feet of Snake River flows to aid Columbia Basin salmon. Located on a Snake River tributary, the Weiser project could fill the flow requirement instead.

Clark considers the project unique because most U.S. sites with potential for large dams have already been taken.

"It's also an interesting site because it has the potential to provide benefits across state, not just the basin it's in," she said.

If drilling reveals no seismic or other geologic risks, a $500,000 cost-benefit study is scheduled in 2013 to analyze issues including how reduced flows could affect a reach of the Snake.

"If the study comes back and says a dam would work there, one of our top priorities would be to get that dam built," said Roger Chase, vice chairman of the Idaho Water Resource Board. "Of all the sites we've looked at (for a dam) it's the one that looks the best."

Idaho Power Co., which hasn't taken a position on the issue, could be affected by reduced flows to its Snake River hydroprojects. Mark Stokes, manager of power-supply planning, said the utility plans to offer input "on the possible benefits of hydroelectric development at the site ... and potential impacts to Idaho Power's existing hydroelectric resources."

Awaiting project study results, Trout Unlimited also hasn't taken a formal position.

"In general, I would say a new dam of that size on an undammed river is going to be a heavy lift for a number of reasons," said Peter Anderson, with Trout Unlimited in Boise.

Responding to a 2008 legislative directive to pursue more water storage, the board completed an analysis in March 2011 outlining 181 information gaps to update in a new Weiser-Galloway proposal. Geologic and cost-benefit studies were named as the top priorities.

Based on the Legislature's request, the board also initiated three other dam studies, exploring possible new storage options on the Henry's Fork and Boise River and a potential expansion of Minidoka Dam on the Snake River.

Hearing planned on dam

POCATELLO -- The Twin Lakes Canal Co. has a hearing March 5-9 to seek approval of additional water rights for its planned dam on the Bear River.

The meeting will be conducted at Clarion Inn, 1399 Pocatello Bench Road, by James Cefalo, watermaster of the Eastern Region with the Idaho Department of Water Resources.

The canal company has applied with the Federal Energy Regulatory Commission for a license to build a dam within the Oneida Narrows of Franklin County. It would inundate nearly 4 miles of the river for water storage and hydropower.


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