Friday, December 11, 2009

Finding a fix for the Fish Creek Dam

Farmers in the Carey area hope to resurrect 86-year-old dam

Express Staff Writer

Farmers and state officials are looking at ways to restore the Fish Creek Dam, located 11 miles northeast of Carey Photo by Mountain Express

Father Time hasn't been kind to the Fish Creek Dam.

The broad, 92-foot-high by 1,700-foot-wide dam rests forlorn and almost forgotten in the lower Fish Creek drainage in the southern foothills of the Pioneer Mountains, 11 miles northeast of Carey. It has been weakened by more than 80 years of constant exposure to the harsh and unyielding elements. Countless freeze-and-thaw events have steadily deteriorated the hulking structure's concrete construction, engineers from the Idaho Department of Water Resources say.

In 2007, Fish Creek Dam was named by the Association of Dam Safety Officials as one of the four "high-hazard" dams in Idaho. The dam was included on a list of 14 dams in the state considered structurally deficient. The "high-hazard" designation means that if that dam fails, it poses a significant threat to human life.

Farmers in the Carey area hope they've found a way to repair the dam, which was completed in 1923. As with many things, the success or failure of the endeavor will ultimately come down to money. Fixing the dam will not be cheap.

In 2005, Department of Water Resources officials ordered the Fish Creek Reservoir Co. to cut a larger spillway in one side of the multiple-arch dam to keep the maximum water level in the reservoir from rising too high. Today, waters backing up behind the dam rise no higher than 69.2 feet.

Before the new spillway was cut, waters used to rise to a height of 88 feet behind the dam, said Corey Skinner, an engineer with the Department of Water Resources' Twin Falls District.

While the work did help alleviate some of the fears surrounding the dam's structural issues, Skinner said, concerns still remain.

"It's just an old structure. The concrete is deteriorating," he said.


The order from the Department of Water Resources also required the reservoir company to dig a new channel below the spillway to direct flows when water levels crest the maximum.

The amount of irrigation water the dam is now capable of holding back for downstream farmers in the Carey area declined significantly after the spillway work. Where the reservoir once held 12,743 acre-feet of water, it now holds back just 5,500 acre-feet, Skinner said.

An acre-foot is the amount of water required to flood one acre 1 foot deep.

Rights to hold full capacity in the Fish Creek Reservoir won't be reinstated until Department of Water Resources officials deem it safe. Repairs by the reservoir company have been ongoing since 2003. Several years ago, it added a large, concrete vertical patch that helped stabilize things, said Lawrence Kimball, water master for the Fish Creek Reservoir Co.

"It really filled some of the leaks off," Kimball said.

In 2002, Department of Water Resources officials also required the reservoir company to install a dam-failure warning system on state Highway 20, which connects Carey east with the community of Arco.

Kimball said the reservoir company is now developing a phased reconstruction project to address the safety issues of the dam. The Department of Water Resources will have the final say on whether the fix will go forward and whether the company can ever fill the reservoir.

"We've been working with engineers for a decade," Kimball said.

He said there's no estimate yet for how much the work will cost.

The idea is to take a phased approach to stabilizing the dam's vertical columns to make them earthquake proof—one that doesn't break the bank for the owners of the dam, the 40 or so downstream farmers with rights to its irrigation water. The reservoir company is hoping to get some financial help from the Idaho Department of Fish and Game because of the reservoir's value as a fishery.

Kimball said 13 of the irrigators with rights to the water agreed this year to keep some of their allotted water rights in the reservoir to help preserve its respectable fishery. He said there's talk of building campsites around the reservoir in the future if a high enough pool can be maintained.

"Really make a recreational deal out of it," he said.

Kimball said he's been told by Fish and Game officials that the reservoir is one of the best fisheries around. Fish in the impoundment grow large because of the freshwater shrimp that inhabit it.

"None of them are under two pounds," Kimball said.

Jason Kauffman:

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