Palouse Basin

Palouse Hills (credit: Stephen Penland 2010)

As early as 1897, concerns were raised over the sustainability of Palouse Basin water supplies. The first wells drew water from surficial loess layers and shallow Wanapum basalts and sediments. In the 1950's, dramatically declining water levels in the Wanapum wells prompted the first well-drilling into the deeper Grande Ronde basalts. Water levels in the Grande Ronde wells have consistently declined 1-2 feet per year since.

Pullman's first artesian well, 1884
Pullman's first artesian well, 1884

Water taken from Grande Ronde wells is 10,000–20,000 years old. Soil research shows that little, if any, area precipitation is able to recharge the deep basalt layers from which we draw our water. Rain and snow travel horizontally to streams and rivers that carry it out of our basin. The water we're currently consuming may have seeped into the Grande Ronde basalts during the last ice age, when the Palouse was covered with water; thus, the deep aquifer may effectively be a non-renewable resource under current conditions.

Basin Description

The physical extent of the Palouse Basin has been defined in various ways by different organizations depending on the scope or intent of their studies. In the broadest sense, the Palouse Basin can be thought of as the area of land lying within the Palouse River Watershed. The Washington State Department of Ecology has identified "Watershed Resource Inventory Areas" or "WRIAs" to refer to the state's major watershed basins; WRIA 34 corresponds to the Palouse River watershed (WRIA34 map).

The Palouse Basin Aquifer Committee (PBAC) has defined the Palouse Basin on the basis of groundwater and location of the primary pumping entities; PBAC does not delineate precise boundaries for the basin, but defines a general working boundary for the groundwater basin (PBAC map).

Palouse Basin CWIS mapFor the purpose of this website, we define the Palouse Basin both in terms of surface water and groundwater resources. Specifically, we are focusing on the area of greatest population and water demand in the region: the North Fork and South Fork sub-watersheds of the Palouse River (and underlying groundwater systems), which lie upstream of the town of Colfax, Washington (map).