Groundwater availability of the Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho

Professional Paper 1817
Groundwater Resources Program
By: , and 



The Columbia Plateau Regional Aquifer System (CPRAS) covers about 44,000 square miles of southeastern Washington, northeastern Oregon, and western Idaho. The area supports a $6-billion per year agricultural industry, leading the Nation in production of apples, hops, and eight other commodities. Groundwater pumpage and surface-water diversions supply water to croplands that account for about 5 percent of the Nation’s irrigated lands. Groundwater also is the primary source of drinking water for the more than 1.3 million people in the study area. Increasing competitive demands for water for municipal, fisheries/ecosystems, agricultural, domestic, hydropower, and recreational uses must be met by additional groundwater withdrawals and (or) by changes in the way water resources are allocated and used throughout the hydrologic system. As of 2014, most surface-water resources in the study area were either over allocated or fully appropriated, especially during the dry summer season. In response to continued competition for water, numerous water-management activities and concerns have gained prominence: water conservation, conjunctive use, artificial recharge, hydrologic implications of land-use change, pumpage effects on streamflow, and effects of climate variability and change. An integrated understanding of the hydrologic system is important in order to implement effective water-resource management strategies that address these concerns.

To provide information to stakeholders involved in water-management activities, the U.S. Geological Survey (USGS) Groundwater Resources Program assessed the groundwater availability as part of a national study of regional systems (U.S. Geological Survey, 2008). The CPRAS assessment includes:

  1. The present status of groundwater resources,
  2. How these resources have changed over time, and
  3. Development and application of tools to estimate system responses to stresses from future uses and climate variability and change.

This effort builds on previous investigations, especially the USGS Columbia Plateau Regional Aquifer-System Analysis study (CP-RASA). A major product of this new assessment is a numerical groundwater-flow model of the system. The model was used to estimate water-budget components of the hydrogeologic units composing the groundwater system, and to evaluate groundwater availability under existing land- and water-use conditions and a possible future climate scenario representing an increase in pumpage demand due to a warming climate. Information from this study also allowed for analysis of:

  1. The CPRAS for predevelopment times (pre-1920),
  2. Variations from 1920 through 2007,
  3. Conditions during 1985–2007 (referred to as “existing conditions”), and
  4. Changes in the system from predevelopment times.

The model also is a useful tool for investigating water supply, water demand, management strategies, groundwater-surface water exchanges, and potential effects of changing climate on the hydrologic system.

Suggested Citation

Vaccaro, J.J., Kahle, S.C., Ely, D.M., Burns, E.R., Snyder, D.T., Haynes, J.V., Olsen, T.D., Welch, W.B., and Morgan, D.S., 2015, Groundwater availability of the Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho: U.S. Geological Survey Professional Paper 1817, 87 p.,

ISSN: 2330-7102 (online)

ISSN: 1044-9612 (print)

Study Area

Table of Contents

  • Foreword
  • Executive Summary
  • Introduction
  • Background
  • Description of Study Area
  • Hydrogeologic Units
  • Hydraulic Characteristics
  • Hydrologic Toolbox
  • Groundwater-Flow Model
  • Predevelopment Water Budget
  • Existing-Conditions Water Budget
  • Changes to the Water Budget between Predevelopment and Existing Conditions
  • Climate Variability and Climate Change
  • Groundwater Availability and Sustainability
  • Monitoring the Hydrologic System
  • Future Uses of Model and Challenges to Assessing Groundwater Availability
  • Acknowledgments
  • References Cited
  • Appendix 1. An Overview of Water Law in Washington, Oregon, and Idaho
  • Appendix 2. Sources of Information for “Dry” Season Water-Availability Map
Publication type Report
Publication Subtype USGS Numbered Series
Title Groundwater availability of the Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho
Series title Professional Paper
Series number 1817
ISBN 978-1-4113-3928-6
DOI 10.3133/pp1817
Year Published 2015
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center, Washington Water Science Center
Description xi, 87 p.
Country United States
State Idaho, Oregon, Washington
Other Geospatial Columbia Plateau Regional Aquifer System
Online Only (Y/N) N
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details