Federal reservoir managers plan a $3.7 million seismic retrofit to the dam at Hyatt Lake this summer, shoring up the dam's leaky base to withstand any big shake from an earthquake.
The federal Bureau of Reclamation is finishing up plans for a stabilizing berm and a drain-filter system at the 56-year-old earthen dam's outside base to keep leaking water from pooling and weakening the dam's base.
The work is expected to bring the dam into safety compliance after the seepage issue was discovered during a 2009 inspection of the dam in the Greensprings area east of Ashland.
"It's getting out ahead of some perceived seismic event," said Greg Garnett, the bureau's field office manager in Bend, which oversees operations of the bureau's Rogue Valley projects.
As part of the work, Hyatt Lake will be kept no higher than four feet from full pool this summer, Garnett said. That reduction is to reduce head pressure on any seepage that occurs during construction, he said.
That drop will not impact Talent Irrigation District's ability to store and delivery irrigation water this year, TID Assistant Manager Wanda Derry said.
The lake will have to recharge itself on its own next winter, Garnett said.
The drop in peak lake level, which still remains significantly higher than most years this decade, also will not alter the Oregon Department of Fish and Wildlife's trout-stocking plans for the reservoir, said Dan Van Dyke, Rogue District fish biologist for the Oregon Department of Fish and Wildlife.
"We're going to have better water conditions than during the drought, but we won't get a full reservoir at Hyatt," Van Dyke said.
ODFW plans to stock 10,200 legal-sized trout there this spring and 39,000 larger fingerlings in October, he said.
Bureau engineers are putting the finishing touches on the designs this month and plan to hire a contractor for the work, Garnett said.
The work is expected to begin in mid-May and run into mid-November, he said.
The design calls for creating a French drain-like system at the dam's base that will capture and filter seepage as it moves the water away.
The bureau four years ago considered other options, including putting filters in the dam so water would pass through without threatening its structural integrity.
That's how the bureau dealt with seepage problems in the 1960s and 1980s.
Another option that was earlier considered was dropping the reservoir's maximum elevation to a foot below the seepage point along the upper portion of the dam's southeast corner, according to the bureau.
That option would have reduce the lake's 16,200-acre-foot capacity by about 6,000 acre-feet, bureau statistics show.
Hyatt, Howard Prairie and Emigrant reservoirs comprise a three-tiered system for feeding irrigation water through TID and the Medford and Rogue River Valley irrigation districts.
At over 5,000 feet above sea level, Hyatt's ability to draw on high-elevation snow helps make it TID's ace in the hole during dry years. Also, because of limited canal size and other restrictions at Howard Prairie, Hyatt outflows can be more aggressively altered to control water levels in Emigrant Lake near the valley floor.
TID built the original Hyatt Dam on Keene Creek in the early 1920s. It was taken over by the bureau in 1960 and rehabilitated.