Winter water release planned for Painted Rocks Reservoir

by Michael Howell

As a result of the unusual weather conditions and warm temperatures experienced so far this winter, officials at Painted Rocks Reservoir are planning on an unprecedented wintertime draw down of the reservoir waters starting this month.

The state owns the dam at Painted Rocks Reservoir and leases water saved up in the dam to two parties with different interests. Montana Department of Fish, Wildlife and Parks (FWP) owns the right to 15,000 acre feet while the Painted Rocks Water Users Association (PRWUA) owns the right to 10,000 acre feet. The distribution is a coordinated balancing act that usually begins in mid-summer once the reservoir is filled and ends on September 31. Dam Tender and Bitterroot River Water Commissioner J. R. Iman works closely with Department of Natural Resources and Conservation Civil Engineering Specialist Larry Schock to coordinate the release of the contract water.

Storage at full pool is 32,362 acre feet of water. At the end of the season, when the 25,000 acre feet of contracted water has been expended, about 7,000 acre feet of base water is left in the reservoir and the outflows from the dam are set to match the inflows. Spring melt water is then generally captured starting near the end of March or early April to bring the reservoir back up to full pool.                                 

The problem this winter, according to Iman, is that Mother Nature isn’t following her usual plan. Due to the atmospheric river that is dropping unusual amounts of moisture combined with unusually warm weather, the reservoir is already half-full. Iman said the moisture in winter is generally stored on the mountain tops as snow. He said the Sno-tel levels near the top of the mountain are about 90% of average right now. But the snow on the lower slopes is melting off or coming down in the form of rain and running off. The danger, he said, is that if the reservoir is full when the spring melt-off surges there will be no way to manage the flows and it will all go over the top of the dam. 

“It’s not just here,” said Iman,” it’s happening all over the Northwest.” He said Libby has lost two road bridges and Flathead Lake is filling up as well. He said they like to keep Flathead Lake 5 feet below flood level and right now they are at 3 inches. He said in his experience over the last 15 to 20 years he has not seen a wintertime drawdown like this before.

Right now, we are close to holding about 15,000 acre feet in the reservoir,” said Iman. “We would like to get it down to 12,000.” He said they started letting out about 20 cubic feet per second last week. That’s about 40 acre feet of drawdown per day.

“So, for all of you river watchers out there, you can expect to see the water levels in the river coming up over the next one or two months as we get set for the spring surge.”