The Spokane River is hydrologically connected to the Spokane Valley-Rathdrum Prairie (SVRP) Aquifer.
Photo credit: Sierra Club. Low flow in the lower Spokane River, August 2015, at Bowl and Pitcher, Riverside State Park. This section of the river receives water from the aquifer. However, during the drought of 2015, flow here was still extremely low.
The Aquifer underlies about 370 square miles in two states. It has one of the fastest flow rates in the United States, flowing as much as 60 feet per day in some areas. The volume of the entire Aquifer is about 10 trillion gallons, making it one of the most productive aquifers in the country. Note, however, that the Aquifer is not simply an "underground river” — a common misconception. It is a combination of gravels, cobbles, and boulders — the result of the rapid draining of Glacial Lake Missoula when ice dams broke. Water from adjacent lakes, mountain streams, the Spokane River, and precipitation flow through these flood deposits supplying the Aquifer.
The SVRP Aquifer is the sole source of water for over 600,000 people in Spokane and Kootenai counties. As the sole source of water for most people in Spokane County in Washington and Kootenai County in Idaho, the Aquifer was designated as a "sole source aquifer” by the EPA in 1978. it was the second Aquifer in the nation to receive this special designation, and it increased public awareness for Aquifer protection and supported the development of special management practices by local agencies. Practices such as eliminating septic tanks and pre-treating stormwater over the Aquifer have greatly improved water quality over the last forty years.
We know the river is the largest source of recharge for our water supply, providing 43% of aquifer inflow annually. The aquifer is also an important source of water for the river, contributing 60% of its annual outflow. The surface outlet for Lake Coeur d'Alene is the Spokane River, which is the only watercourse over the Aquifer that remains on the surface for an extended distance. Only Hangman Creek and the Little Spokane River flowing out of the surrounding highlands actually reach the Spokane River. Other streams contact the coarse, gravelly soils overlying the Aquifer and disappear, percolating downward.
In this graph from 2015 you can see that river flows increase dramatically when city pumping slowed down, without any changes from upstream sources or rainwater input. The red line shows that flows over Post Falls Dam remained fairly consistent into September, yet the river flows are slowly increasing.
The Spokane River is more than a beautiful sight – it is a place of recreation, a natural habitat for many species of fish and invertebrates in our region, and a prominent symbol in Spokane’s cultural heritage. Water flowing into the river from the aquifer provides cool clean water that native fish need to survive.
In the drought year of 2015, the Department of Ecology studied the influence pumping from the SVRP aquifer has on the Spokane River. When water is drawn from the SVRP aquifer, the amount of water flowing in the Spokane River decreases.
The more water Spokane takes from the aquifer, the more likely the recreation and ecology of the river will be threatened. Therefore, the need to address water conservation in our city is vital for the future of our river, and all that it supports.
Check out the science from the 2015 drought here. Check out the 2018 Water Forum for more info on river/aquifer interaction and perspectives on conservation here.
LEARN MORE
Learn more about the Spokane Valley-Rathdrum Aquifer, and its connection to the Spokane River in the Aquifer Atlas by Spokane Joint Aquifer Board
You can also learn more about what an aquifer is, and how our aquifer functions from Spokane Aquifer Joint Board.