Agency Says February Floods Worst In 22 Years

North Idaho’s February floods were the worst to hit the area in 22 years and approached the “100 year” mark - flooding that might be expected only once in a century.

That’s the conclusion of a study by the U.S. Geological Survey. It was based on water measurements and estimates of peak flows Feb. 8 or 9.

In early February, a powerful storm swept into the Pacific Northwest from the Pacific Ocean. Strong, warm winds, several inches of rainfall on heavy mountain snowpack and ice-jammed river channels caused severe floods throughout the Coeur d’Alene, St. Joe, Palouse and other northern Idaho river basins.

Lake Coeur d’Alene rose more than eight feet above its normal summer level. The floods forced evacuation of many low-lying areas. Fifteen northern Idaho counties were declared flood disaster areas.

The 100-year flood peak is one that has a 1 percent chance of occurring any given year.

The Geological Survey said at several places, peak Feb. 9 flows nearly reached the 100-year mark. Record flows at those points were on Jan. 16, 1974.

On the North Fork of the Coeur d’Alene River at Enaville, the flow was measured at 56,600 cubic feet per second. The 100-year standard is 58,400 cfs.

Mean February flow at that point is 2,016 cfs, with the flood reaching 28 times that flow.

At Cataldo, the Coeur d’Alene River hit 68,300 cfs, about 27 times normal flow.

The St. Joe River at Calder was measured at 38,700 cfs. Normal flow is 1,495.

The Palouse River near Potlatch was measured at 14,600 cfs, above the 100-year mark of 14,000. That was 27 times normal flow.

The U.S. Geological Survey also found that the floods moved large quantities of trace mineral-enriched sediment through the lower Coeur d’Alene River and into the lake.