With thunderstorms unleashing heavy rains across the region Tuesday afternoon, a 90-mile-long reservoir behind Libby Dam was raised above its maximum operating pool to reduce the risk of flooding in Bonners Ferry.
Under an agreement worked out between the U.S Army Corps of Engineers and their Canadian counterparts, the Koocanusa Reservoir is a couple inches above its typical high-water mark. Depending on weather conditions, reservoir levels could rise by up to 2 feet over the next few days to reduce downstream flows in the Kootenai River.
The higher-than-normal pool doesn’t pose safety risks for downstream residents, but it could lead to flooding of roads and marinas above the dam in Montana and British Columbia, said Matt Rabe, a corps spokesman.
The Kootenai River Basin broke rainfall records in June, with some areas receiving four times the average amount of precipitation. Bonners Ferry had 5.24 inches of rain in June, compared to a typical accumulation of 1.66 inches for the month. The river snakes back and forth across the international border, so the heavy runoff has created challenges for dam operators in both countries.
BC Hydro is operating its dams to reduce high water in Kootenay Lake. At Queen’s Bay near Nelson, B.C., the lake is at its highest level since 1974.
At Bonners Ferry, the river is about 2 feet above flood stage. The dikes along the Kootenai River Inn near downtown are sandbagged to reduce damage from high flows.
The decision to raise Libby Dam’s reservoir followed extensive flooding in the Kootenai River Valley in 2006, which saturated agricultural fields and drowned high-value crops.
“We had less advance notice of the 2006 event, which was shorter and quicker,” said Rabe, the corps spokesman. “This time around, it was more drawn out, with storm after storm after storm. We had more opportunity to coordinate with Canada and it seems to have been a successful engagement.”
Libby Dam was built as part of the 1964 Columbia River Treaty, which governs hydropower and flood control operations along the 1,200-mile river and its tributaries. Changes to the dam’s flood control activity require coordination between the U.S. and Canada.
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