Snowpack in Idaho helps replenish Spokane aquifer
Snowpack in the mountains of the Idaho panhandle is near-normal this month, according to the Natural Resources Conservation Service. Come spring, that could be very good news for the groundwater aquifer that provides Spokane’s drinking water.
The Spokane Valley-Rathdrum Prairie (SVRP) aquifer is a large, crescent-shaped area of gravel, cobbles and boulders deposited during the great Missoula glacial floods 18,000 to 12,000 years ago. SVRP underlies parts of Spokane and Kootenai counties, and – crucially – it is the sole source of drinking water for half a million people.
Having a substantial snowpack in the panhandle mountains now can help bolster the aquifer and its surface water siblings, said Toni Taylor, an education specialist with Spokane County Water Resources.
“Snowpack is important,” Taylor said. “What it does is, it fills our river and our lakes. It’s filling those surface waters that actually contribute to our aquifer more than anything else.”
The Spokane River not only flows atop the aquifer, it’s also the single biggest contributor to the underground water supply, Taylor said. Smaller creeks and streams also contribute, because their water sinks directly into the aquifer’s overlying soils.
“The Spokane River contributes roughly 45 percent of the aquifer’s water. The lakes add another 25 to 30 percent,” Taylor said. “So filling those things is important. They provide the bulk of the aquifer recharge.”
After some early season snowfall in October, snowpack in Idaho remained “alarmingly low” until mid-December, NCRS said. The agency reported a big increase in the amount of water that fell as snow in the second half of December.
But good snowpack isn’t the only key to replenishing the SVRP aquifer. How swiftly the spring thaw sets in is another important factor, Taylor said. If the weather warms too quickly, much of the snow will melt and evaporate before its water can be fully absorbed.
“You can have a great snowpack, but it’s not as valuable when it melts quickly,” Taylor said. “And it’s not just the aquifer that suffers…the whole ecosystem can suffer, because that water moves through our region and on out into the Columbia [watershed].”
A mild, slow spring is ideal for a snow melt rate that introduces the maximum amount of water into the Spokane River, Coeur d’Alene Lake and ultimately, into the aquifer. NCRS reported moisture content in Idaho improved in December, which should help improve the effectiveness of the spring melt.