One of the most important areas for protecting water quality in Flathead Lake is the Flathead River corridor and associated floodplain and shallow aquifer in the Evergreen area.
What is the shallow aquifer?
As glaciers receded ten thousand years ago, the meltwater became a river many times larger than the Flathead River of today. The glaciers and ancient river left behind a huge area of gravels permeated by water that forms a shallow alluvial aquifer, often referred to as the Evergreen Aquifer. We may not see it today, but water still moves underground between the Flathead River and the aquifer.
This aquifer is located between the Flathead River to the east and Whitefish River to the west, and between Badrock Canyon to the north and the confluence of the Flathead and Whitefish rivers to the south. The depth to groundwater in this area is generally less than 50 feet and for much of the area less than five feet.
Why is this aquifer important?
Research by the Flathead Lake Biological Station at Yellow Bay has shown that these gravels are penetrated by groundwater that originates in the Flathead River and returns to the river with high flow rates through the gravel. Any materials that get in the groundwater in this area (such as oil and gas, heavy metals, and tire residue from parking lots) easily percolate into the acquifer and are rapidly transported to the river. Ric Hauer, a biological station scientist, told us that because of this, we would be hard pressed to find a worse place in western Montana to locate intensive commercial development.
The shallow alluvial aquifer contains a complex network of organisms that naturally cleanse the waters. But pollution entering the alluvial aquifer can contaminate the aquifer and damage or destroy the natural cleansing system, jeopardizing groundwater supplies. Polluted groundwater can then move into the Flathead River and flow down to Flathead Lake.
During floods, water from the river can saturate the aquifer and cause surface flooding before the river overflows its banks. To reduce the risk of flooding and groundwater contamination, it is important to build in upland areas where the groundwater is not so shallow and limit the density of any development over the aquifer.
Shallow Aquifer Map
The Flathead Lakers contracted with the Flathead Lake Biological Station to produce a map showing depth to groundwater in the Evergreen Aquifer area. Click on this link for a larger version of the map at the top of this page.