Tuesday, February 07, 2023

What's up with the lake?

by Brian Walker
| December 23, 2010 8:00 PM

COEUR d'ALENE - If Lake Coeur d'Alene seems high for December, it is.

Patrick Maher, Avista Utilities' senior hydro operations engineer, said the lake's level on Wednesday was 2,127.17 feet. Recent levels are as high as the lake has been in December since 1995.

"We have gone above 2,128 (the summer level) in December just 15 years in the last 105 years," Maher said.

Maher said the lake level reached a high of 2127.58 so far this December.

The highest elevation recorded in December was 2,139 on Christmas Day in 1933. In 1995, the previous highest year, the lake went as high as 2,132.5 feet in December.

Maher said the lake's high level this year can be attributed to record snowfall in November, followed by a brief thaw and rain earlier this month.

Avista, which operates the Post Falls hydroelectric dam that controls the lake level, continually monitors the level in case of an extended thaw and flood threats on the Coeur d'Alene and Spokane rivers.

"There is always a potential for flooding as Mother Nature can send us a bunch of rain and warm weather at any time," Maher said. "However, in the current 15-day forecast, no major weather events are projected."

The utility watched particularly close last week with the rain.

"The Coeur d'Alene Basin is a low elevation basin subject to rapid snow melts," Maher said. "After receiving record snowfall ... in November, there was a large amount of snow residing at low elevations around the basin. During a weeklong period from Dec. 8 to Dec. 14 we also received a significant amount of rain (about 1.6 inches) while temperatures were above normal."

Maher said the flow in the Coeur d'Alene River went from 1,500 cubic feet per second (cfs) on Dec. 12 to 19,000 cfs on Dec. 14, which was just below flood stage.

While the lake rose with high inflows in November and December, there wasn't any danger of the lake going above 2,128 feet during the December runoff, Maher said.

"Avista had plenty of room to allow enough water past Post Falls and the outlet restriction on the lake could allow enough water to escape the lake," he said.

Maher said the level typically continues to decrease throughout December and added that there is not an optimal elevation for the lake this time of year.

"Avista annually draws down the lake over a several-month period, with a goal of letting enough water pass by Post Falls such that if there is a sudden melt or high rainfall event, the lake is in a natural state with respect to the outlet restriction at the mouth of the Spokane River," he said.

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