By Brandi Smith
Avista recently sent out the latest issue of the Spokane River Newsletter, a quarterly publication that keeps subscribers informed about our activities in and around the Spokane River. Below is an article from the newsletter that describes how we operate the Post Falls Dam during the winter season. Check out the latest issue
and learn more about what Avista has been up to.
Winter river flows and Coeur d’Alene Lake levels
People commonly think floods occur in the spring. But did you know many of the highest levels recorded for Coeur d’Alene Lake have occurred in the winter? For example, on Christmas day in 1933 the lake reached an all-time peak of roughly eleven feet over its summer level.
Coeur d’Alene Lake is a natural lake with an outlet that naturally restricts its outflow. The primary sources of water into the lake are the St. Joe, St. Maries and Coeur d’Alene rivers. The water then flows through the outlet to create the Spokane River. Avista’s Post Falls Hydroelectric Dam is on the Spokane River, nine miles downstream of the lake’s outlet. The dam affects Coeur d’Alene Lake elevation for about half of the year. During winter and spring, lake levels are controlled entirely by the natural outlet restriction and inflows.
The winter months are generally the wet season in our region. Fluctuating temperatures, rain that occurs on top of snow, or extended heavy rain can increase flows rapidly, which in turn can result in quickly-rising river and lake elevations.
Avista’s goal each year is to draw Coeur d’Alene Lake down six to seven feet below the summer level by early January. This allows Post Falls Dam to generate electricity while providing capacity in the lake for later precipitation and runoff. Natural inflows usually exceed our turbine capacity early in the year, letting Coeur d’Alene Lake and the Spokane River find their naturally occurring levels with no influence by the dam. This free flow condition typically continues through spring run-off until late May, June or early July.
River and lake levels can change quickly. We want you to stay safe, so always use caution on the water and comply with all posted notices and closures, especially in the vicinity.
Avista has a 24-hour telephone information line that provides notification of anticipated elevation changes on Coeur d’Alene Lake, Lake Spokane and the Spokane River.
In Idaho, call (208) 769-1357, in Washington call (509) 495-8043
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