PPL Montana, which operates Kerr Dam, has begun the annual drawdown of the lake, which should be a foot below full pool by the end of this month and two feet below the high mark by the end of October.
Deb Mullowney, spokeswoman for PPL Montana, says the company has received many phone calls from boat owners about its plans for lowering the lake this fall.
“Lowering Flathead Lake during fall, typically a stormy season in Montana, has significant shoreline benefits,” Jon Jourdonnais, PPL Montana's director of hydro licensing and compliance, said. “Erosion, caused by windswept waves that wear at the gravel shoreline, is reduced when the lake elevation is lowered.”
But just a few inches can make a big difference to people who need to pull their boats out of the lake for the winter, especially those who keep their crafts moored in shallow bays on Flathead. This year's drawdown won't be as fast as last year, but will still be significantly quicker than years previous to that, when the lake level averaged 2,892.2 feet on Nov. 1. That's 14 inches higher than it's projected to be this year.
PPL Montana confers with representatives of the U.S. Army Corps of Engineers, the Confederated Salish and Kootenai Tribes, the Bureau of Indian Affairs, the Bureau of Reclamation and the Bonneville Power Administration in determining lake levels.
The lake level is always subject to changing conditions and weather patterns.
“The operation of the project and, in particular, decisions with respect to lake levels, are subject to constant monitoring, re-evaluation and change as weather patterns themselves may rapidly change,” Mullowney said. “Weather conditions will be monitored throughout September and appropriate operational changes will be made, if necessary.”
PPL Montana plans to have the lake down to 2,888 feet, or 5 feet below the full-pool mark of 2,893, by the end of December.
The lake usually reaches its lowest point between March 15 and April 15. Last year, it wound up a full 10 feet below full pool before PPL Montana began refilling it in mid-April by regulating the outflows at Kerr Dam.
“The conditions were just right last year that we could take it lower than usual,” Mullowney explained. “Because of the heavy snowpack, we had to make sure there was plenty of room” for the spring runoff.
During the height of the 2008 spring runoff, Kerr Dam was letting 41,800 cubic feet of water per second pass through. The inflows into the lake, meantime, were consistently above 50,000 cubic feet per second and one day exceeded 60,000.
The current outflow is 6,700 cubic feet per second. August streamflows averaged 108 percent of normal and flows in September have been about 100 percent of normal.
The lake level stood at 2,892.53 feet late Tuesday afternoon.
Reporter Vince Devlin can be reached at 1-800-366-7186 or at vdevlin@missoulian.com.
Track the lake level
You can keep track of the level of Flathead Lake by visiting waterdata.usgs.gov/mt/nwis/uv?formatgif&period7&site_no=12371550.
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