U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008–3086

September 2008

Ground-Water Resources Program

Printed on recycled paper

Ground-Water Availability Assessment for the Columbia Plateau 

Regional Aquifer System, Washington, Oregon, and Idaho

Ground Water is a Critical 

Resource in the Region

The Columbia Plateau covers more 

than 60,000 square miles within the 

Columbia River Basin in Washington, 

Oregon, and Idaho (fig. 1). More than 

10 million acres support a $5 billion per 

year agricultural industry, among the 

most productive in the Nation. Water 

supplied from the Columbia River 

system and the basalt and overlying 

unconsolidated aquifers is essential to 

nearly 2 million acres of irrigated land 

(fig. 1). Water also is important for growing 

rural and urban populations and ecological

needs, and ground-water availability is 

a primary consideration for balancing

the conjunctive use of surface-water and

ground-water supplies throughout the region.

Figure 1. Land use and cover in the Columbia Plateau study area.

Part of a National Effort to 

Assess Ground-Water 

Availability

The U.S. Geological Survey (USGS)

is assessing the availability and use 

of the Nation’s water resources to 

gain a clearer understanding of the 

status of our water resources and the 

land-use, water-use, and climatic 

trends that affect them. The goal 

of the National assessment is to 

improve our ability to forecast water 

availability for future economic and 

environmental uses. Assessments 

will be completed for regional 

aquifer systems across the Nation to 

help characterize how much water 

we have now, how water availability 

is changing, and how much water 

we can expect to have in the future 

(Reilly and others, 2008).

Water availability is a function of 

many factors, including the quantity 

and quality of water, and the 

laws, regulations, economics, and 

environmental factors that control 

its use. The focus of the Columbia 

Plateau regional ground-water 

availability assessment is to improve 

fundamental knowledge of the 

ground-water balance of the region, 

including the flows, storage, and 

ground-water use by humans. An 

improved quantitative understanding 

of the region’s water balance not 

only provides key information 

about water quantity, but also can 

serve as a fundamental basis for 

many analyses of water quality and 

ecosystem health.

River

River

River

Columbia

Yak ima

Columbia

Snake River

Umatila River

Deschutes River John Day River

Palouse River

Walla Walla River

Grand Ronde River

River

Columb ia

Coeur 

d'Alene

Lake

Potholes 

Reservoir

Moses 

Lake

Banks

Lake

Pasco

Yakima

Tacoma

Olympia

Seattle

Spokane

Walla Walla

Pendleton The Dalles

"

"

Pullman

Moscow

0 20 40 60 80 100 Miles

0 20 40 60 80 100 Kilometers

OREGON

WASHINGTON IDAHO

EXPLANATION

Land cover classification

Developed/barren/other

Dryland agriculture

Irrigated agriculture

Shrub and grassland

Study area boundary

Forest

Water

MONTANA

122° 120° 118° 116°

48°

47°

46°

45°

Agriculture in the Quincy Valley (Photograph taken 

by David Putnam, July 2006.)
What are the depths, thicknesses, 

extents, and characteristics of the major 

aquifer units?

Most ground water used in the Columbia 

Plateau comes from layers of basalt 

collectively known as the Columbia 

River Basalt Group, a complex aquifer 

system made up hundreds of individual 

basalt flows. As part of this study, 

maps depicting the regional extent and 

geometry of the major basalt aquifers 

will be updated using geologic data 

from a wide variety of sources. The 

resulting three-dimensional “geomodel” 

will integrate data and interpretations 

from recent studies in many parts of the 

Columbia Plateau and will serve as the 

framework for a simulation model of the 

ground-water flow system.

Ground-Water Modeling: A Tool 

for Assessing Water Availability

Ground-water models attempt to simulate 

the behavior of a ground-water system 

using a mathematical counterpart. Models 

typically are used to evaluate changes to 

the water budget of an aquifer caused by 

pumping, land-use changes, and climate, 

and how these changes affect groundwater storage, streamflow, lake levels, 

and other environmental variables.

The ground-water model developed 

during this study will be used to answer 

questions about how the ground-water 

system works, and to forecast the 

effects of regional water management 

alternatives and effects of drought and 

climate change. The regional model

will also serve as a starting point for more

For More Information:

Visit the project web page at: http://

wa.water.usgs.gov/projects/cpgw

Or contact David S. Morgan

 USGS Oregon Water Science Center

 Ph: 503-251-3263 dsmorgan@usgs.gov

Richard S. Dinicola

 USGS Washington Water Science Center

 Ph: 253-552-1603 dinicola@usgs.gov

James R. Bartolino

 USGS Idaho Water Science Center

 Ph: 208-387-1392 jrbartol@usgs.gov

refined local models that can be developed

within the boundaries of the regional 

model, saving time and resources.

Working with Partners

Many State, Federal, and non-governmental 

agencies, as well as Tribal organizations, 

have responsibilities or interests in water 

resource management in the Columbia 

Plateau. The USGS is collaborating with 

many of these agencies and organizations 

to build a better understanding of the 

region’s water resources, expand existing 

monitoring and data collection networks, 

and develop tools that will better inform 

resource management decisions.

Reference Cited:

Reilly, T.E., Dennehy, K.F., Alley, W.M., and 

Cunningham, W.L., 2008, Ground-water 

availability in the United States: U.S. 

Geological Survey Circular 1323, 70 p.

http://pubs.usgs.gov/circ/1323/

Banner photograph taken by David Putnam, 

July 2006.

1960 1970 1980 1990 2000 2010 

DEPTH TO WATER, IN FEET BELOW LAND SURFACE140

160

180

200

220

240

260

280

1,500-foot deep basalt well in Umatilla County, Oregon Ground-water pumping has removed 

water from storage in the basalt aquifers 

and resulted in maximum water-level 

declines of 300 feet and declines of more 

than 100 feet over extensive areas (fig. 2), 

placing important agricultural sectors 

at risk. Streamflow in many subbasins 

currently is inadequate for certain fish 

listed under the Endangered Species 

Act and ground-water depletion has 

contributed to adverse environmental 

effects. Declining ground-water levels 

have measurably reduced streamflows 

and have contributed to loss of wetlands 

and degradation of aquatic habitat. 

Developing Tools and 

Understanding to Support 

Resource Management Decisions

Several questions must be answered 

to adequately assess water availability 

within the Columbia Plateau regional 

aquifer system:

What is the hydrologic budget 

(inflows, outflows, and change in 

storage) for the regional aquifer system 

and how have its components changed 

over time?

The study will estimate key components 

of the ground-water budget (recharge, 

pumping, exchange with surface water) 

and evaluate how changes over time 

have affected ground-water storage and 

availability.

How have indicators such as 

ground-water levels and streamflow 

responded to changes in hydrologic 

stresses, such as pumping, irrigation 

return flow, and climate? 

Ground-water level data collected from 

hundreds of wells monitored by State, 

Federal, local agencies, Tribes, and the 

USGS will be compiled and analyzed 

to define the current status of storage in 

the ground-water system and evaluate 

temporal and spatial trends that can be 

correlated with changes in pumping and 

recharge to the system. 

Figure 2. Pumping has removed water from storage in basalt aquifers and caused 

declines in many areas of the Columbia Plateau.

Wood duck pair at McNary Wildlife Refuge, 

Washington (Photograph taken by Janet Barrett, 

January 2008.)