Walla Walla Groundwater

Science Center Objects

The Issue: Within the states of Washington and Oregon, the 1,777 mi2 Walla Walla River Basin (WWRB) is a complex hydrogeologic system with long-term water-level declines in regional aquifers and insufficient instream flows required for threatened and culturally important fish populations. The public and state resource management agencies need an improved understanding of the WWRB hydrogeologic system to manage and protect this valuable resource.

How USGS will help: In close cooperation with water-resource agencies and stakeholders from Oregon and Washington, the USGS will collect new hydrologic data and aggregate data from past studies to better understand (a) the extent and connectivity of groundwater in the basin, (b) the impacts of pumping on groundwater levels, and (c) the locations of gaining and losing stream reaches and the volume of water being exchanged in those reaches. These data are necessary for the eventual development of a basin-wide numerical groundwater flow model to evaluate forward-looking scenarios and predict outcomes for water-management decisions.

Walla Walla Groundwater

Walla Walla Groundwater

(Public domain.)

Problem: The Walla Walla River Basin (WWRB) is a complex hydrogeologic system with long-term water-level declines in regional aquifers and insufficient instream flows required for fish populations listed as threatened under the Endangered Species Act and other culturally important fish species. Surface water is over appropriated, and groundwater level declines are impacting groundwater availability for some users and may be impacting the limited summer streamflow.

Irrigated agriculture accounts for the largest use of groundwater in the basin, but it is used for industrial, domestic, and livestock needs as well.

Past studies have provided a general understanding of the groundwater flow system in the WWRB, however changes in groundwater use, evolving water rights law, and the scope and scale of earlier studies have left gaps in understanding of the hydrogeologic system. In particular, an improved and quantitative understanding of the relationship between groundwater in the Columbia River Basalt, the overlying sedimentary units, and surface water is crucial to holistic water resource management in the WWRB.

Objectives: The primary water-resource management agencies for Washington (Ecology) and Oregon (Oregon Water Resources Department (OWRD)), along with the Confederated Tribes of the Umatilla Indian Reservation (CTUIR) and USGS Oregon and Washington Water Science Centers have begun planning a transboundary study of the groundwater system in the WWRB to inform planning and water management decisions at a basin-wide scale. In this first year of study, the USGS is compiling existing hydrologic information, identifying and filling gaps in water-level monitoring, and collecting reconnaissance level geochemical information to guide the development of a more comprehensive workplan for a multi-year investigation of the WWRB groundwater hydrology.