Basin Extent The physical extent of the Palouse Basin has been defined differently 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 define a general working boundary for the groundwater basin (PBAC map).

For 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 subwatersheds of the Palouse River (and underlying groundwater systems), which lie upstream of the town of Colfax, Washington (map).

Water Resources Management on the Palouse: Areas of Concern

View of the Palouse from Kamiak Butte [J.Hinds]

Understanding and subsequently managing water resources in an effective manner requires knowledge of the dynamic interaction between climate, surface processes, subsurface (aquifer) characteristics, and human impacts.

Key features of each topical area affecting the water budget for the Palouse Basin are as follows:

CLIMATE [more]

• hot, dry summers (very little precipitation, high evaporation/ET)
• cool, wet winters (precipitation occurs as both rain and snow)
• significant spring runoff when snow melt is rapid or rainfall occurs on frozen ground
• effects of climate change are uncertain, but will ultimately determine water availability

SURFACE PROCESSES [more]

• limited surface water present (<2% of the basin is occupied by perennial and intermittent streams, riparian areas, and wetlands)
• low summer streamflows; ephemeral springs
• significant runoff potential and erosion in spring during rapid snowmelt events
• land cover and agricultural practices affect rates of evapotranspiration, runoff, erosion, water quality, infiltration/recharge
• presumably limited surface water/groundwater hydraulic connection

AQUIFER CHARACTERISTICS [more]

• groundwater is the primary source of water used in the basin
• steadily declining water levels (seen both currently and historically)
• uncertainty regarding groundwater-resource sustainability
• shallow Wanapum aquifer (basalts and interbedded sediments) - not a significant producer of water in many parts of the basin
• deeper Grande Rhonde aquifer (mainly basalts) - water is 10,000-20,000 years old; currently may not be receiving recharge
• spatial heterogeneity and compartmentalization make aquifer characterization difficult (uncertainies exist regarding aquifer spatial connectivity, as well as groundwater-surface water connectivity)

HUMAN IMPACTS [more]

• agricultural and urban land-use modifications affect water storage potential (these human impacts typically increase runoff, erosion, and evapotranspiration, and reduce infiltration, riparian areas, and wetlands)
• population growth and urban development create increased water demands
• water demands are high in summer (for lawn and garden irrigation) when surface water availability is most limited
• complex cross-state/cross-county policies, water law, water rights

Additional Background

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.

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; as may thus effectively be a non-renewable resource under current conditions.