Wednesday, March 23, 2016

Let's talk science: What the 2015 drought taught us about flows in the Spokane River

by Brook Beeler, communications

As the state suffered a historic “snowpack drought” last year, winter temperatures were 4.7 degrees warmer than normal and streamflows dropped to unheard lows across the state. The Spokane River was low, but it wasn’t the lowest the region had seen.


The Spokane is a complex river system and its flow is influenced by a variety of factors
Seasonal weather, groundwater use, and operation of hydropower facilities all play out on the river.

The red line shows water flowing from Lake Coeur d’ Alenethrough the Post Falls dam. In July Avista locked in the flowat 500 cfs as a minimum required in the 2009 FERC license.The green line shows Spokane River flows just below downtown Spokane.
Something was different during last year’s drought. Flows were higher out of Lake Coeur d’ Alene through the Post Falls dam operated by Avista.

Since 2009, Avista is required to maintain a minimum flow of 500 cubic feet per second at the Post Falls dam under a Federal Energy Regulatory Commission (FERC) license. That’s 200 cubic feet per second higher than historical low-flows.

Due to drought conditions, the minimum flow was locked into place starting in July

Because the flow coming out of Post Falls dam remained constant until mid-October, scientists were able to “see” the hydrologic connection between groundwater pumping and Spokane River flows for the first time in 100 years of data collection. Under normal flow conditions, it is difficult to observe this relationship because dam operations and typical summer rain events inhibit scientists' ability to observe this trend.

Aquifer levels (pink) began to increase in late August and Spokane River flows (blue) began to increase shortly after in September as seasonal groundwater pumping (red) decreases. Flow from the Post Falls dam remains constant.

In the hottest, driest part of summer data shows that Spokane River flows hovered right around 700 cubic feet per second.

By comparing river flow and groundwater pumping data, scientists could see river flows increase as seasonal groundwater pumping decreased.

Despite record-low snowpack in the watershed, flows in the Spokane River were low, but not at their all-time low because the FERC license worked.

Flows in the river were below our recently adopted rule to protect the Spokane River. But it is important to note that instream flow rules do not add water to the river — they are a regulatory threshold to determine whether there is water available for new uses.

For more drought related information from around the state check out our 2015 drought response.

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