With reservoirs full, dams open up their gates

The Kootenai River rose more than two feet above flood stage Wednesday at Bonners Ferry, Idaho, prompting a variety of emergency response efforts, and Lake Koocanusa continues to fill even with Libby Dam spilling water at full capacity.

Hungry Horse Dam, too, was releasing high flows since Hungry Horse Reservoir is full.

High flows at Bonners Ferry are expected to continue through the weekend, said Doug Weber, chief of emergency management for the U.S. Army Corps of Engineers in Seattle.

The Corps has a response team providing assistance to Boundary County and the city of Bonners Ferry.

About 300 “super sack” sandbags have been deployed on about 500 feet of riverbank to protect the Kootenai River Inn Casino and Spa, Weber said.

The city’s storm drain system had to be shut down and pumped out, a house on the north side of the river was evacuated, access roads to some homes and businesses have been closed and agricultural land downstream from the city has been swamped.

The last time there was flooding at Bonners Ferry was in 2006, when there was a similar emergency spill situation at Libby Dam.

The dam has been operating at powerhouse capacity of 25,000 cubic feet per second, with an additional 15,000 cfs being released over the dam’s spillway since Monday. Even so, Lake Koocanusa has been rising rapidly, reaching an elevation of 2,455.3 feet Wednesday, less than four feet shy of the full pool elevation of 2,459 feet.

“We filled 1.4 feet in the last 24 hours,” said Scott Lawrence, a public affairs specialist for the Corps. “And we’re still anticipating the reservoir to continue to rise a foot to a foot and a half a day.”

Lake Koocanusa inflows have recently exceeded 70,000 cfs, while outflows are at 40,000 cfs. Lawrence said there is uncertainty about how long the high inflows will continue.

The high flows from Libby Dam, combined with water from downstream tributaries, have driven the Kootenai River at Bonners Ferry to an elevation of 1,766.3 feet on Wednesday. Flood stage is 1,764 feet.

Some degree of spill has been under way for most of the month at Libby Dam, and that will have impacts on fish in the Kootenai River just below the dam, said Brian Marotz, a Montana Fish, Wildlife and Parks biologist who has long been involved in monitoring Libby Dam operations.

“I can tell you right now that we’re going to see a high incidence of gas bubble trauma in fish. Whether it’s lethal or not is the question,” Marotz said.

Dissolved gases created by the spillway releases can cause bubble-like sores on fish, particularly when there is an extended duration of spill. While most fish appear to recover after past spill events, it is unknown if there are long-term impacts that might affect survival.

Fish that get gas bubbles on their eyes, for instance, might appear to recover when the bubbles go away. “But has it affected their vision?” Marotz said, noting that fish are sight-dependent feeders.

There are questions about whether gas bubble trauma causes secondary infections that may be lethal, and if there may long-term effects on reproductive systems, Marotz said.

Montana Fish, Wildlife and Parks will be spot monitoring for fish kills on the river, but Marotz said it’s important to consider that some fish are killed are injured when passing through the dam.

The state is in a “rear-guard position” because nothing can be done to stop the spill operation at Libby Dam, Marotz said. “We’re going to set out to learn as much as we can. There’s nothing else we can do about it.”

Hungry Horse Dam, meanwhile, was releasing 500 cfs through its spillway, 7,000 cfs through its three jet valves and water through its generators for a total discharge of 17,300 cfs Wednesday, said Facility Manager Dennis Philmon.

The reservoir was just over its full pool elevation of 3,560 feet.

“We’re above it and that’s why we are spilling,” Philmon said.

However, inflows into the reservoir have been dropping so discharges from the dam could be curtailed by the middle of next week, he said.

The high flows on the South Fork Flathead River below the dam have contributed to the main stem Flathead River at Columbia Falls reaching minor flood stage Tuesday, but flows are expected to drop off over the next few days.

Reporter Jim Mann may be reached at 758-4407 or by email at jmann@dailyinterlake.com.