Hydrology of the Columbia Plateau 

Regional Aquifer System, Washington, 

Oregon, and Idaho

By H. H. Bauer and A. J. Hansen, Jr.

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 96-4106

A contribution to the 

REGIONAL AQUIFER-SYSTEM 

ANALYSIS PROGRAM

Tacoma, Washington 

2000
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Geological Survey.

For additional information write to:

District Chief

U.S. Geological Survey

1201 Pacific Avenue, Suite 600

Tacoma, Washington 98402

Copies of this report may be purchased from:

U.S. Geological Survey 

Information Services 

Box 25286 Federal Center 

Denver, Colorado 80225
CONTENTS

Abstract.................................................................................................................................................................................. 1

Introduction ................................................................................. 2

Purpose and scope ....................................................................................................................................................... 4

Description of study area............................................................................................................................................. 4

Hydrogeology........................................................................................................................................................................ 6

Geologic setting........................................................................................................................................................... 6

Basalt. ...........................................................................................................................................................^ 6

Overburden........................................................................................................................................................ 12

Structural features.............................................................................................................................................. 12

Ground-water movement............................................................................................................................................. 12

Basalt units ........................................................................................................................................................ 12

Overburden aquifer............................................................................................................................................ 14

Hydraulic characteristics............................................................................................................................................. 15

Recharge ................................................................................. 15

Pumpage ........................................................................ 16

Simulation of ground-water flow........................................................................................................................................... 16

Model grid and boundary conditions........................................................................................................................... 20

Adjustments to estimates of hydraulic characteristics................................................................................................. 22

Model reliability and sensitivity.................................................................................................................................. 30

Simulated regional flow......................................................................................................................................................... 32

Changes from predevelopment to 1983-85.................................................................................................................. 35

Ground-water budget......................................................................................................................................... 35

Water levels........................................................................................................................................................ 39

Ground-water discharge..................................................................................................................................... 41

Potential future effects of current ground-water development.................................................................................... 41

Potential effects of proposed expansion of the Columbia Basin Irrigation Project (CBIP)........................................ 45

Summary and conclusions..................................................................................................................................................... 54

Selected references................................................................................................................................................................ 57

FIGURES

1-2. Maps showing:

1. Location of the Columbia Plateau regional aquifer system study area and the extents of the

formations of the Columbia River Basalt Group............................................................................................ 3

2. Location of physiographic and cultural features of the Columbia Plateau in the study area......................... 5

3. Diagram showing infrastructure of a basalt flow within a group of basalt flows .................................................... 8

4. Chart showing relation between geologic units, hydrogeologic units, and the computer model layers

of the Columbia Plateau Regional aquifer system................................................................................................... 9

5. Diagrams showing generalized hydrogeologic sections through the Columbia Plateau......................................... 11

6. Map showing locations of major geologic structures within the Columbia Plateau............................................... 13

7-8. Maps showing distribution of estimated recharge within the hydrologic study area for:

7. Predevelopment (1850's) land-use conditions................................................................................................ 17

8. 1980's land-use conditions ............................................................................................................................. 18

9. Map showing distribution of 1983-85 ground-water pumpage............................................................................... 19

10. B oxplots of calculated and calibrated lateral hydraulic conductivities for the model layers.................................. 28

11-12. Maps showing:

11. Contours of simulated and observed 1983-85 water levels for the Wanapum unit........................................ 31

12. Locations of basins and stream reaches for which water budgets are presented............................................ 34

III
13-14. Diagrammatic sections showing the model-calculated:

13. Predevelopment water budget........................................................................................................................ 36

14. 1983-85 time-averaged water budget............................................................................................................. 37

15-20. Maps showing:

15. Simulated water-level changes in the Wanapum unit from predevelopment to current conditions............... 40

16. Simulated future water-level changes in the Wanapum unit from predevelopment to

current conditions........................................................................................................................................... 43

17. Distribution of estimated increase in recharge resulting from proposed expansion of the

Columbia Basin Irrigation Project for Phase 1 .............................................................................................. 46

18. Distribution of estimated increase in recharge resulting from proposed expansion of the

Columbia Basin Irrigation Project for Phases 1 and 2................................................................................... 47

19. Simulated water-level rises in the Wanapum unit under future equilibrium conditions

resulting from the proposed expansion of the Columbia Basin Irrigation Project, Phase 1 .......................... 49

20. Simulated water-level rises in the Wanapum unit under future equilibrium conditions

resulting from the proposed expansion of the Columbia Basin Irrigation Project, Phases 1 and 2............... 50

21-22. Diagrammatic sections showing simulated water-budget changes from future equilibrium conditions 

resulting from the proposed expansion of the Columbia Basin Irrigation Project for:

21. Phase 1 .....................................................................................................................................^ 52

22. Phases 1 and 2................................................................................................................................................ 53

TABLES

1. Summary of selected storage-coefficient estimates for the Columbia Plateau....................................................... 23

2. Comparison of simulated ground-water discharge, estimated recharge, and average

streamflows for drainage basins with streamflow records within the modeled area............................................... 33

3. Regional ground-water budgets based on seven ground-water flow simulations ................................................... 35

4. Comparison of ground-water discharge to selected river reaches for the various simulations............................... 42

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

inch (in.) 25.40 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

square foot (ft2) 0.0929 square meter

acre 0.4047 hectare

s\

square mile (mi ) 2.590 square kilometer

cubic mile (mi3) 4.168 cubic kilometer

inch per year (in/yr) 2.540 centimeter per year

foot per second (ft/s) 0.3048 meter per second

foot per day (ft/d) 0.3048 meter per day

foot squared per second (ft/s) 0.09290 meter squared per second

cubic foot per second (ft3/s) 0.02832 cubic meter per second

pound per square inch (lb/in2) 6.895 kilopascal

Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)--a geodetic 

datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called 

Sea Level Datum of 1929.

IV
Hydrology of the Columbia Plateau 

Regional Aquifer System, Washington, 

Oregon, and Idaho

By H. H. Bauer and A. J. Hansen, Jr.

ABSTRACT

The Columbia Plateau aquifer system underlies 

about 50,600 square miles in Washington, Oregon, 

and a small part of northwestern Idaho. The aquifer 

system is composed primarily of Miocene flood 

basalts of the Columbia River Basalt Group. 

Approximately 4,500 square miles of saturated 

sedimentary deposits (hereafter referred to as the 

overburden aquifer) overlying the basalts, mainly in 

the central part, are also a part of the aquifer system.

A five-layer, numerical finite-difference groundwater model covering 32,688 square miles was used 

to simulate the regional ground-water flow system. 

The uppermost layer represents the overburden 

aquifer, and all other layers represent the various 

basalt formations. The model simulated and was 

calibrated to data from the period 1983-1985 using a 

time-averaged steady-state approach. After the 

time-averaged model was calibrated, the predevelopment (1850's) and hypothetical future flow systems 

were simulated.

Recharge to the aquifer system from natural precipitation and irrigation, estimated by soil-moisture 

budgeting, ranges from zero in low-lying areas that 

receive precipitation of less than 8 inches annually, to 

more than 30 inches per year in the mountainous 

and irrigated areas. Recharge was estimated to be 

6,566 ft3/s (cubic feet per second) under predevelopment conditions and 10,205 ft3/s for 1983-1985

o

conditions. The increase, 3,639 ft/s, is mainly from 

surface-water-supplied irrigation. Most recharge

from precipitation and irrigation follows short flow 

paths and discharges to nearby streams and drains, 

especially in the uplands and in irrigated areas, 

whereas, for low-lying, semiarid areas where no 

nearby major rivers drain the aquifer system, little 

ground water discharges locally. Leakage from 

rivers provides an additional 554 ft3/s of recharge 

under predevelopment and 1983-85 conditions.

Initial mapping of hydraulic conductivities 

derived from specific-capacity data for the basalts 

exhibited little spatial correlation. Such randomness 

was initially assumed also to apply in areas lacking 

data. In order to calibrate the ground-water model, 

however, much smaller, relatively uniform hydraulic 

conductivities had to be assumed for the upland 

areas, and somewhat larger, relatively uniform 

hydraulic conductivities for the low-lying areas near 

major rivers. The model-derived median lateral 

hydraulic conductivity for the overburden aquifer is 

about 5x10~4 ft/s (feet per second). The range is from 

about 5xlO"7 to 1.3xlO"2 ft/s. Basalt conductivities 

range from about IxlO'6 to IxlO"4 ft/s with a median 

of about 1.7x10'5 ft/s.

Few data are available for vertical conductances. 

Model calibration resulted in distributions of vertical 

conductances that were generally less in the upland 

folded areas. Vertical conductances used in the two 

uppermost layers hydraulically connected to major 

rivers are anomalously large immediately beneath 

these rivers. Evidence suggests that such large conductances may be caused by deep erosional channels 

that were backfilled with coarse materials.
Discharge to rivers and drains was simulated to 

be about 2,754 and 3,944 ft3/s for predevelopment 

conditions and about 3,804 and 5,596 ft3/s for 

1983-85 conditions. Discharge from the aquifer 

system for time-averaged conditions also includes 

about 1,135 ft3/s of ground-water pumpage.

Since predevelopment time, water-level rises 

have been more prevalent and widespread than 

water-level declines because the areas of croplands 

irrigated with surface water are larger than those 

irrigated with ground water, and the irrigation application rate is larger in surface-water irrigated areas. 

Water-level rises in excess of 300 feet were simulated 

within the Columbia Basin Irrigation Project, generally east of the Columbia River between Pasco and 

Quincy. Water-level declines as much as about 

200 feet were simulated for the Odessa-Lind area, 

Horse Heaven Hills area, Walla Walla River Basin 

area, the Umatilla area, and in some of the small 

tributary valleys draining to the Yakima River.

A steady-state simulation was made to estimate 

long-term future changes to the aquifer system from 

the 1983-85 period, assuming no changes in the 

1983-85 rates of pumping and recharge. Although 

simulated water-level changes were generally less 

than 10 feet in the overburden aquifer, significant 

declines were simulated in all four basalt units. 

Declines of more than 400 feet in the Wanapum unit 

were centered around large pumping centers in the 

central part of Horse Heaven Hills, whereas similar 

declines in the Saddle Mountains unit were simulated 

in a ground-water-irrigated valley about 8 miles 

northeast of Yakima. More widespread but smaller 

declines of as much as 200 feet in the Wanapum were 

simulated for the Odessa-Lind area. Most other 

areas, even some that are heavily pumped, were 

simulated to have relatively small (less than 50 feet) 

to no water-level declines in any of the basalt units. 

Heavily pumped areas that have small simulated 

declines are located within or adjacent to areas of 

high recharge from either surface-water irrigation or 

precipitation.

Potential effects of two proposed CBIP expansions, Phase 1 and Phases 1 and 2, were simulated. 

Recharge increases of 330 ft3/s and 974 ft3/s were 

estimated for Phase 1 and Phases 1 and 2, respectively, assuming the same average irrigation application rate as in the existing CBIP. Water levels for the 

uppermost aquifers were simulated to rise to land

surface everywhere in the expansion areas. Maximum water-level rises in the basalts of about 400 feet 

and 600 feet for Phase 1 and Phases 1 and 2, respectively, were simulated in the main parts of the 

expansion areas.

INTRODUCTION

The Columbia Plateau aquifer system underlies 

about 50,600 mi2 of the Columbia Plateau of central 

and eastern Washington, north-central and eastern 

Oregon, and a small part of northwestern Idaho 

(fig. 1). The aquifer system consists of Miocene 

basalt belonging to the Columbia River Basalt 

Group, Miocene sedimentary rocks interlayered with 

the basalt, and Miocene to Holocene sediments overlying the basalts. The aquifer system is a major 

source of water for municipal, industrial, domestic, 

and irrigation uses. Concurrent with ground-water 

usage, imported surface water is used to irrigate 

several areas of the plateau. Use of surface water for 

irrigation has caused ground-water-level rises of as 

much as about 300 ft in some areas. Water levels 

have declined as much as about 200 ft in areas of 

ground-water pumpage, and the chemical quality of 

ground water has changed in irrigated areas. An 

improved understanding of the aquifer system, 

especially the movement and direction of groundwater flow, is needed to fully address concerns 

related to these changes.

The Columbia Plateau aquifer system is one of 

several regional aquifers selected for study as part of 

the U.S. Geological Survey's regional aquifer-system 

analysis (RASA) program. The objectives of the 

Columbia Plateau study are to describe (1) the hydrogeologic framework, (2) hydrologic characteristics of 

the hydrogeologic units, (3) the area's water budget, 

(4) the ground-water and surface-water interaction, 

and (5) the water-quality characteristics and waterrock interactions that occur in the study area. In 

order to provide the analytical capabilities for assessment of management alternatives and to allow a 

better understanding of the ground-water flow 

system, a numerical model that simulates groundwater flow was constructed and its reliability was 

tested by comparing the simulated and measured 

water levels and by comparing baseflows of streams 

with computed ground-water discharges (Hansen and 

others, 1994).
122° 116°

48° -

47° -

EXPLANATION

i i i i r

0 20 40 60 80 100 KILOMETERS

Geologic Units

Overburden

Columbia River Basalt Group, undivided

Saddle Mountains Basalt

Wanapum Basalt

Grande Ronde Basalt

Imnaha Basalt

Not mapped

Columbia Plateau aquifer system 

study area boundary

Geologic contact 

State boundary

Index Map of Study Area

Figure 1 . Location of the Columbia Plateau regional aquifer system study area and the extents of the formations 

of the Columbia River Basalt Group.
Purpose and Scope

This report summarizes the results of simulations made using the numerical model of groundwater flow in the aquifer system. Most of the information presented and described in this report is for 

the area (about 32,700 mi2) included within the 

ground-water model boundaries, and is referred to in 

Whiteman and others (1994) and in this study as the 

hydrologic study area. Flow was simulated for the 

averaged conditions (water levels, pumpage, 

recharge) observed or estimated during 1983-85 and 

for predevelopment (1850's) conditions. Hansen and 

others (1994) describe in detail the development and 

calibration of the model for 1983-85 and predevelopment conditions; for a more detailed analysis, interested readers are referred to this report, which 

contains 15 plates that present all relevant items-- 

geologic framework, model grid system, hydraulic 

characteristics, observed and calculated water levels, 

pumpage, recharge, and discharge. In addition to 

summarizing the work of Hansen and others (1994), 

this report also describes simulations of groundwater flow for several possible future conditions:

(1) future equilibrium with 1983-85 stresses and

(2) four proposed expansion scenarios of the Columbia Basin Irrigation Project (CBIP). The effects of 

the expansion were simulated under two proposed 

phases, Phase 1 and Phases 1 and 2. Additionally, 

the phases were simulated using two pumpage 

scenarios 1983-85 pumping rates and reduced 

1983-85 pumping rates. This report includes a 

description of the geologic framework, the hydraulic 

characteristics, ground-water movement, and the 

simulated regional groundtwater flow system 

budgets. More detailed analyses of parts of these 

items is presented in the companion reports of Drost 

and Whiteman (1986), Gonthier (1990), Drost and 

others (1990), Bauer and others (1985), Bauer and 

Vaccaro (1987, 1990), Whiteman (1986), Cline 

and Knadle (1990), Collins (1987), and Lane and 

Whiteman (1989).

Description of Study Area

The Columbia Plateau aquifer system lies 

within the Columbia Intermontane physiographic 

province (Freeman and others, 1945). The study area

is bordered by the Cascade Range on the west, by the 

Okanogan Highlands on the north, and by the Rocky 

Mountains on the east. The southern boundary of the 

aquifer system has no well-defined physiographic 

boundary but is considered to correspond with the 

extent of the mapped Columbia River Basalt Group. 

The deeply incised Grande Ronde River, the Blue 

Mountains, and their western extension, formed by 

the Blue Mountains anticline and delineated by a 

series of outcrops of older pre-Columbia River Basalt 

Group rocks, form a hydrogeologic boundary 

between the basalt aquifers to the north and south. 

This report deals primarily with the more agriculturally developed northern part (the hydrologic 

study area).

The study area has been further divided by 

Myers and Price (1979) into three informal physiographic subprovinces: the Yakima Fold Belt, the 

Blue Mountains, and the Palouse (fig. 1). Together, 

these subprovinces are a structural and topographic 

basin. The Yakima Fold Belt, located in the western 

part of the study area, is characterized by long, 

narrow, east-west-trending anticlinal ridges with 

intervening broad to narrow synclinal basins. The 

Palouse subprovince consists of a gentle, southwest 

sloping, undeformed series of basalt flows under a 

rolling topography of loess deposits. The Blue 

Mountains subprovince, located in the southeastern 

part of the study area, consists of dissected upland 

plateaus; the subprovince also includes the 

Deschutes-Umatilla Plateau in Oregon.

The study area is completely within the drainage 

of the Columbia River. Major tributaries to the 

Columbia River within the study area include the 

Snake, Yakima, John Day, Umatilla, Klickitat, and 

Deschutes Rivers (fig. 2). These tributaries and their 

associated tributaries drain the bordering mountainous areas. Land-surface altitudes and precipitation 

quantities largely determine the types and amounts of 

natural vegetation found in the Columbia Plateau. 

As part of this RASA study, a map of the distribution 

and rate of average annual precipitation for the 

period 1956-77 (Nelson, 1991) was constructed and 

presented by Nelson (1991) and is also presented in 

Whiteman and others (1994). At altitudes from 350 

to 2,000 ft above sea level in the central part of the 

plateau, the precipitation ranges from 6 to 15 inches a 

year, the vegetation is principally sage and
122° 120° 118° 116°

47°

46°

SKAGIT

____I

LINCOLN

SNOHOMISH

\ |

OKANOGAN FERRY S PEND ! LIN(

I JN IORIELLE BONNER ! ~

"> ^ ^^ y\ ^( STEVENS I I hr" I

<- >r5KANO^?S«--^|l-ILANDS > \-, , [ J I

\ fGr^nd Coulee Daro^_ ibfeeiCl / \>VO H l^^l '--vl

/ « . JrT"* _r Tx/,,, \ / ,. £, _ t x_ / \J L_I v

	KJ5&TENAI I \ SANDERS

i

/

 Seattle

SHOSHONE *

ASH.NGT

I / Kll III AS

"ut^-%/ O/ % -, , /

l^tenshurc ^

Z/ F* *± \

, DES0HUTES

20 40 60

I

80 100 MILES

I i I

i i n i r

0 20 40 60 80 100 KILOMETERS

EXPLANATION

Columbia Basin Irrigation Project

Columbia Plateau aquifer system 

study area boundary

State boundary 

County boundary

Index Map of Study Area

Figure 2. Location of physiographic and cultural features of the Columbia Plateau in the study area.
grasslands, and few streams are perennial. At intermediate altitudes (2,000 to 3,500 ft), precipitation 

ranges from 15 to 25 inches where the vegetation 

includes both grasslands and forest. Forest lands 

predominate at altitudes greater than 3,500 ft and 

perennial streams are common.

The predominant economic activities in the 

study area are agriculture and its associated services. 

In 1984, nearly 780 mi2 of cropland were irrigated 

with ground water and about 1,950 mi2 of cropland 

were irrigated with surface water (Cline and Collins, 

1992). More than 8,000 mi2 of sage, grasslands, and 

dryland crop area have the potential for conversion to 

irrigated crops.

Development of water resources and changes in 

land use within the study area have been extensive 

since predevelopment (1850's) time. Numerous 

dams have been constructed throughout the lengths 

of the Columbia and Snake Rivers in the study area, 

and only a few short reaches of these rivers are not 

impounded. The effect of the reservoirs on the 

regional ground-water flow system is probably minimal, however, because these impoundments are still 

areas of ground-water discharge. A much more 

profound effect on the ground-water system is from 

the delivery of irrigation water from the impounded 

river water to large areas. Water-level rises and 

effects on ground-water flow in the 556,000-acre 

CBIP (fig. 2) were described by Tanaka and others 

(1974).

Ground-water pumping for irrigation has lowered water levels in several areas. The effects of this 

pumping in selected areas is discussed by Cline 

(1984), Davies-Smith and others (1988), Packard and 

others (1996), MacNish and Barker (1976), and Lum 

and others (1990).

Other land-use practices have a much less 

pronounced but more widespread effect. Most of the 

current (1980's) agriculture is dryland wheat, which 

generally is fallowed every other year. Calculations 

of recharge quantities indicate that this practice has 

increased consumptive use of water compared with 

that of native vegetation (predevelopment land 

cover), thereby slightly decreasing recharge over 

large areas (Bauer and Vaccaro, 1990).

HYDROGEOLOGY

The Columbia Plateau is underlain by a series of 

layered basalt flows extruded from vents (located 

mainly in southeastern Washington and northeastern 

Oregon) during Miocene time. Collectively, these 

basalt flows are known as the Columbia River Basalt 

Group. Individual basalt flows range in thickness 

from a few inches to as much as 300 ft. Some flows 

probably cover more than half of the study area. 

Smaller flows are confined to the source region and 

(or) mainly fill ancestral river valleys (called intercanyon flows). Generally, the rubbly, vesicular tops 

of flows readily transmit ground water. The massive 

central part of a flow contains some joints and fractures but transmits ground water much less readily 

and impedes the vertical movement of water between 

flow tops.

A variety of sedimentary materials (the "overburden") from Pliocene through Holocene age overlie about 14 percent of the Columbia River Basalt 

Group, mainly in the central part of the study area. 

On average, these materials transmit water more 

readily than the basalts and also compose an 

important aquifer.

Geologic Setting

Basalt

The study area is both a structural and a topographic basin and its lowest point is near Pasco, 

Franklin County, Wash. (fig. 2). The Columbia River 

Basalt Group covers an area of about 63,700 mi and 

has an estimated volume of 42,300 mi (Tolan and 

others, 1989). Basalt flows of the Columbia River 

Basalt Group are intercalated with and overlain by 

sediments collectively assigned to the Miocene-toHolocene-age Ellensburg, Latah, Ringold, Palouse, 

and The Dalles Formations. Along the borders of the 

plateau, the basalts are underlain by Precambrian to 

early Tertiary rock of mostly volcanic and metamorphic origin. Sedimentary rocks underlie the basalts 

in the Yakima Fold Belt and in adjacent parts of the 

plateau to the east, and volcanic and metamorphic 

rocks underlie the basalts in the other subprovinces.
The eruptions of basalt occurred from about 17 

to 6 million years before present (B.P.). Most flows, 

comprising about 42,000 mi3 , were extruded 

between 17 and 14.5 million years B.P. Eruptions 

were less frequent and less voluminous, comprising 

only about 600 mi3 , from 14.5 to 6 million years B.P. 

(Tolan and others, 1989) allowing time for erosion, 

deformation, and increased deposition of sediment 

between eruptions. Basaltic lava was extruded from 

a system of northwest-trending linear vents in southeastern Washington, northeastern Oregon, and western Idaho (Swanson and others, 1975; Hooper, 1982). 

Basin subsidence was concurrent with extrusion, thus 

the lava flows thin progressively outward from the 

central basin.

Extrusion and cooling of individual flows under 

different physical settings resulted in the formation 

of columnar joints, pillow lavas, and brecciated flow 

tops. Individual basalt flows range in thickness from 

a few inches to more than 300 ft and average about 

110 ft. The internal structure of a typical flow generally consists of, from bottom to top, a flowbase, a 

colonnade, an entablature, and a flow top (fig. 3). 

The base of a flow generally has a thin zone of glassy 

basalt, a vesicular zone, and may include a zone of 

pillow basalt. Porous pillow-palagonite complexes, 

caused by underwater cooling, are present at the base 

of some flows. The colonnade consists of nearly 

vertical three- to eight-sided columns of basalt that 

average about 3 ft in diameter and about 25 ft in 

length. The columns were formed by vertical jointing that occurred during the slow cooling and contraction of the flow interior. Columns are commonly 

crosscut by systems of joints. The denser entablature 

consists of small-diameter (averaging less than 2 ft) 

basalt columns in fan-shaped arrangements. Cross 

joints in the entablature are less consistently oriented 

than those in the colonnade. Hackly joints are common in the upper part of the entablature and are often 

vesicular. The flow top generally consists of vesicular basalt with scoria and clinker and averages about 

5 to 10 percent of the total thickness of a single flow 

(fig. 3). The flow top in combination with the superposed flowbase is called the interflow zone.

The Columbia River Basalt Group has been 

stratigraphically subdivided into five formations and 

numerous members (fig. 4) (Swanson and others, 

1979c). The Yakima Basalt Subgroup of the Columbia River Basalt Group is the most extensive and

consists of, from oldest to youngest, the Grande 

Ronde, Wanapum, and Saddle Mountains Basalt 

formations. Pre-Yakima Basalts, which consist of 

the Picture Gorge and Imnaha Basalt formations, 

have been mapped only in scattered locations in the 

southern and southeastern parts of the plateau and 

these outcrops lie mostly outside the modeled area. 

Except for a small part of the Imnaha Basalt, the 

pre-Yakima Basalts were not analyzed in this study 

because of their limited, peripheral extent.

Interbed sediments occur within and between 

basalt formations. These sediments were derived 

from erosion of older rocks surrounding the plateau, 

from erupting volcanoes in the Cascade Range, and 

from the basalt itself. The areal extent, thickness, 

and lithology of interbeds is probably dependent on 

the time between eruptions, Cascade volcanic activity between eruptions, and topographic position.

Hydrologic data generally are not available for 

individual basalt flows, many of which may be individual aquifers, because the open intervals of most 

wells in the study area span more than one basalt 

flow. Moreover, identification and correlation of 

single basalt flows from well log data are not feasible. However, when the groups of flows composing 

the Saddle Mountains, Wanapum, and Grande Ronde 

Basalt formations are considered, much useful data 

are available. Additionally, the laterally extensive 

fine-grained sedimentary interbeds between these 

formations in many areas impose a degree of hydraulic separation, so that it is logical to treat these 

groups of basalt flows as separate composite aquifers. These composite aquifers are referred to in 

this report as "units" and include any intercalated 

sediments.

Structure contour maps of the top of the formations composing the Yakima Basalt Subgroup 

(Swanson and others, 1979 a,b) were modified for 

the Grande Ronde, Wanapum, and Saddle Mountains 

Basalts by Drost and Whiteman (1986) for Washington and by Gonthier (1990) for Oregon. Additionally, thickness maps were constructed during these 

studies for the Saddle Mountains and Wanapum 

Basalts, plus their intercalated sediments. These 

basalt formations and their intercalated sediments are 

herein called the Saddle Mountains and Wanapum 

units to distinguish them from the formations, which 

do not include intercalated sediments. Similarly, the
00

c

(D CO

5"03

C 

£C 

CDa

0)

CT03en

0) 

CQ 

O
(Q

I 

.U

3J 

2L wo'

(D 

(D

3

(Q 

(D 

O. 

O

O* (Q

C 

3

»<

a. 

o

(Q 

CD 

O^

o

o' (Q

03

a.

CD 

o 

o

T3

CD^

3 

o 

a.

I

55

CD

O

0_

c 

3

CTfl)'

o

03

JJ

(D 

o' CO

3

a>

JD

Lower 

to Tertiary 

Precambrian

Basement rocks(

3

o

c

3

cr

33

1 

CD 

8?

91

0

o

MIOCENE

Miocene Upper Miocene Middle Miocene Lower 

GROUP BASALT RIVER COLUMBIA 

003

3 P 

° w 

3!

1

rjj33ff>

^Q-Q.

units Magnetostratigraphic 

Z 33 

0 0 

2 33 H -* -*

'33^

SUBGROUP BASALT YAKIMA 

Wanapum 

Basalt

-D 33 -n m 

riest MembeRapids Member oza t\ renchman Springs Merr ckle Mountain 

^ ffl cr 

3 CD cr ~" 

CD

!

1

u|

1

(E

>

33 

0

3

Q

(D

i

3-

CD

a.

Basalt Mountains Saddle 

> $. c 

Member sotin/ilbur Creek Membe matilla Member

CO 

a.

CD

o

5T

I

3

T3

C

3

5'

sCD

a.

f" o" CD [Tj "D m ^ 

S 3" ^ 3 {O N" 3 

III

0 ? ? 

co tu CD r~ "D ~n c; (D ta o o tu o in °- (D 5f ° o 3 ^ 

3" s; P J= w i. 8 

^2. 0 ^ 2. - § 

2 p' ^ w " 13 - Q. o 

o - 3; w 3) 5 S 

^-03 p 3" O O " 

5 - S" 3 P- = <o 

o p" p" w" E w E2 

^* ^t 1 1 1 O 

^^ ^" ffl m *~ O Si ir ^ ^£. ffl ^ 

o - w 

o cr 

CD C 

g <3 

system aquifer Plateau Columbia 

CD

CO 

CD

CO

n

O

CO

c

~

Q 

1

Q.

CD

33 

0

a

(D

C

^

- Ol

O 

o

|

CO

c

-*

3

ur iapum 

~

CO

O0

5|

CO

c 

g_

CO

Q. 

Q. 

CD

O

1

3

CO

c

ro

o

1

Q. 

CD

1S"

"^

» 

m

JASALT

W

RATIGRAPHY

W

m 

a

^

m

2 

H

W

33

H

Q

33

-a

I

^^

I

a

33 

O

Q

m 

O

O 

Q

O

c

2

-1

GEOLOGI

0

3

^^

i

O 

DO7;

IT

0

DO

0

0

O

O 

~n 

DO

^

m

O

DO7;

^

m c 

|- 03 

> m 

-< DO 

m

DO
Grande Ronde Basalt and intercalated sediments are 

referred to as the Grande Ronde unit; for this study, 

the Grande Ronde unit also includes a small part of 

the Irnnaha Basalt in the southeastern part of the 

study area.

The mapping work was later extended into 

Idaho, and maps describing the geologic framework 

for the Columbia Plateau regional aquifer system 

have been published by Drost and others (1990). The 

areal extent of each unit within the RASA study area 

is shown on figure 1, and a comparison of geologic 

units, hydrogeologic units, and model layers is 

shown on figure 4. Generalized hydrogeologic 

sections (fig. 5) show the configuration of the basalt 

units and the overlying sediments (overburden).

The Grande Ronde unit underlies all of the area 

(fig. 1), and constitutes 85 to 88 percent of the 

volume of the Columbia River Basalt Group (Reidel, 

1982; Tolan and others, 1987). It is exposed mainly 

along the northern, southeastern, and southern 

margins and in a few deeply incised stream channels 

in the central part of the plateau. Its thickness varies 

from a few feet along the northern and southern 

margins, where it pinches out against older rock, to 

greater than 14,000 ft in the central and southwestern 

parts of the study area. The Grande Ronde unit is 

composed of as many as 130 individual flows (Tolan 

and others, 1987); most flows are fine grained with 

microphenocrysts of plagioclase and clinopyroxene. 

Sedimentary interbeds in the Grande Ronde unit are 

rare, generally only a few feet thick, and of small 

lateral extent because of the short time intervals 

between outpourings of successive flows. A laterally 

extensive sedimentary interbed that has been given 

different formation namesun different areas lies 

between the Grande Ronde and Wanapum units. For 

clarity, it has been named the Wanapum-Grande 

Ronde interbed for this regional study (Drost and 

others, 1990; Whiteman and others, 1994). Where 

present, this interbed averages about 25 ft but is 

as much as 100 ft thick, and consists chiefly of 

claystone and siltstone.

A thickness map of the Grande Ronde unit was 

constructed on the basis of available well logs, magnetotelluric data, exposures of the older "basement" 

rocks, and on information from partially penetrating

deep wells (Hansen and others, 1994). The estimated 

thickness distribution generally is smooth throughout 

most of the plateau except in the Blue Mountains, 

where there are deeply eroded valleys. In contrast to 

the Blue Mountains, the Yakima Fold Belt, which 

also has rugged topography principally because of 

anticlinal folding, the thickness distribution was 

smooth.

The Wanapum unit is exposed or is covered by a 

veneer of quaternary sediments throughout most of 

the northern half of the area. In the southern half, the 

unit generally is covered by thick sequences of 

sediments or by the Saddle Mountains unit. The 

Wanapum unit averages about 600 ft in thickness, 

varying from a few feet where it pinches out against 

exposures of the Grande Ronde unit to about 1,200 ft 

in the southwestern part of the area (Drost and others, 

1990; Hansen and others, 1994). The Wanapum unit 

generally contains about 33 flows (Tolan and others, 

1987) and makes up about 6 percent of the volume of 

the basalts. Most Wanapum unit flows are medium 

grained and slightly to moderately plagioclasephyric. Sedimentary interbeds are more common in 

the Wanapum unit than in the Grande Ronde unit, but 

are still rare and only a few feet thick. A sedimentary 

interbed between the Wanapum unit and the overlying Saddle Mountains unit occurs in part of the 

study area, and for this study it is called the Saddle 

Mountains-Wanapum interbed. This interbed is 

as much as 200 ft thick and averages about 50 ft. 

The interbed consists chiefly of clay, silt, claystone, 

or siltstone and minor amounts of sand and conglomerate.

The Saddle Mountains unit underlies only the 

southwestern part of the study area (fig. 1). The unit 

has a maximum thickness of more than 800 ft and 

averages about 600 ft (Drost and others, 1990; 

Hansen and others, 1994). Individual flows in the 

Saddle Mountains unit vary greatly in texture and 

composition. Sedimentary interbeds are common, 

averaging about 50 ft thick. The intercalated Beverly 

Member of the Ellensburg Formation is areally 

extensive and stratigraphically and hydrologically 

important in south-central Oregon and in parts of the 

Yakima Fold Belt.

10
122° 120° 118° 116°

EXPLANATION 

Geologic Unit 

I Overburden 

J Saddle Mountains Basalt 

I Wanapum Basalt 

Grande Ronde Basalt

"1 Pre-Columbia River Basalt 

Group rocks

- Geological contact, 

dashed where queried

Columbia Plateau aquifer 

system study area boundary

State boundary 

County boundary

EAST 

A'

0 50 100 KILOMETERS

VERTICAL SCALE GREATLY EXAGGERATED 

0 50

I

100 MILES

NORTH 

B'

50

\ 

100 KILOMETERS

Figure 5. Generalized hydrogeologic sections through the Columbia Plateau. (From Drost and others,1990.)

11
Overburden

Sediments overlying the Columbia River Basalt 

Group compose the "overburden." These sediments 

include Pliocene through Holocene fluvial, glaciofluvial, eolian, and volcaniclastic sediments. Loess 

occurs at the surface throughout much of the Columbia Plateau, reaching its greatest thickness (as much 

as 250 ft) and continuity in the Palouse subprovince 

of southeastern Washington, where it is called the 

Palouse Formation. Loess deposition was greatest 

during the Pleistocene, with glacial drift and alluvium the major source of silt.

The extent and thickness of the overburden, 

generally greater than 50 ft thick, has been mapped 

and presented by Drost and others (1990), but 

because the thickness of the loess is highly variable 

locally and because it is discontinuous, fine grained, 

and generally not an aquifer, Drost and others (1990) 

did not include the loess in the overburden as part of 

the RASA study. The greatest thickness of the overburden is in excess of 800 ft, and the thickest deposits occur in structural basins and in areas adjacent to 

the Cascade Range. The overburden is herein 

referred to as the overburden aquifer. The overburden aquifer overlies about 4,500 mi2 of the basalts 

(Hansen and others, 1994).

Structural Features

Drost and Whiteman (1986), Gonthier (1990), 

and Drost and others (1990) present detailed descriptions of the Columbia Plateau's geologic structures. 

Geologic structures within the plateau are diverse 

and range from simple monoclines to sharp folds 

with structural relief of as much as several thousand 

feet. The major structural features (fig. 6) impose 

significant controls on the movement of ground water 

in the aquifer system.

The Yakima Fold Belt subprovince is characterized by long, narrow, faulted anticlines (such as 

Umtanum, Yakima, and Ahtanum Ridges, fig. 6) with 

intervening narrow (Wapato) to broad (Kittitas 

Valley) synclines that trend in an easterly to southeasterly direction from the western margin of the 

plateau to its center. The anticlines are generally 

asymmetrical with the steepest limb to the north. 

Most major faults are thrust or reverse faults whose

strikes are similar to the anticlinal fold axes; the 

faults probably are contemporaneous with the folding. Northwest- to north-trending shear zones and 

minor folds commonly transect the major folds.

The Palouse subprovince contains basalt flows 

with a regional dip to the southwest of less than 5 

degrees (Drost and Whiteman, 1986). This subprovince is structurally simple, the largest features 

being broad folds with amplitudes of only a few 

tens of feet.

The Blue Mountains are a broad anticline that 

extends from north-central Oregon into southeastern 

Washington. The anticline is cut by a series of northto northwest-trending faults that are nearly vertical 

(Gonthier, 1990). The basement or core of the 

anticline is composed of folded, faulted, and metamorphosed upper Paleozoic and Mesozoic rocks.

Ground-Water Movement

The generalized description of the occurrence 

and movement of ground water is described in this 

section; more detailed discussions based on results of 

the ground-water model are presented later in the 

section "Simulated Regional Flow." Ground-water 

level contour maps for the four aquifer units were 

constructed and published by Bauer and others

(1985) and for the three basalt units by Whiteman

(1986), and Lane and Whiteman (1989). The last 

report also shows ground-water-level changes from 

spring 1983 to spring 1985. Water-level contours 

representing the average of 1983-85 conditions for 

the overburden aquifer and three basalt units are 

based on these published maps and data used in those 

investigations; these contours for average conditions 

have been further described and presented in Hansen 

and others (1994).

Basalt Units

Ground water in the basalts occurs in joints, 

vesicles, fractures, and in intergranular pores of the 

intercalated sedimentary interbeds. The rubbly flow 

tops generally have the highest permeabilities 

(fig. 4). The denser, more coherent entablature and 

colonnade usually have lower permeabilities. In a 

few areas, saturated sedimentary interbeds are

12
122° 120° 118° 116°

WASHINGTON

 (

PALOUSE 

SUBPROVINCE

YAKIMA 

FOLD

45° -

EXPLANATION

i i i i r

0 20 40 60 80 100 KILOMETERS

Physiographic Subprovinces 

Blue Mountains 

Yakima Fold Belt 

Palouse

Columbia Plateau aquifer system 

study area boundary

Fault - Relative displacement unknown

Strike-slip fault - Arrows show relative 

horizontal movement

Anticline - Shows trace of crestal plane; 

dashed where inferred

 I Syncline - Shows trace of trough

 State boundary ^ j 

 County boundary

Figure 6. Locations of major geologic structures within the Columbia Plateau.

Monocline - Abrupt increase in dip in 

direction of arrows

13
aquifers where they contain coarse-grained materials. 

Few hydrologic data exist for the interbeds, therefore 

in this study their hydraulic characteristics are incorporated into the hydraulic characteristics of the 

basalts. In most areas, water-table conditions exist in 

the uppermost basalt unit. Owing to the wide difference between horizontal and vertical hydraulic con- 

"ductivities, to the presence of sedimentary interbeds, 

and to the presence of fine-grained materials in parts 

of the lower section of the overburden aquifer, the 

deeper basalt units are generally confined. However, 

because the hydraulic connection between units is 

sufficient to allow continuous, vertical movement of 

water between them, the confined units are referred 

to as being semiconfined.

Water-level data indicate that over most of the 

plateau, the vertical component of regional flow in 

basalts is downward except near discharge areas, 

generally along streams and rivers (Lane and Whiteman, 1989). Localized anomalies to this pattern are 

caused primarily by geologic structures of both 

known and uncertain nature and secondarily by 

ground-water pumping and irrigation.

Previous studies of ground-water flow in the 

Columbia River Basalt Group have suggested that 

certain structures affect ground-water movement. 

Newcomb (1961, 1965, and 1969) cites linear 

zones of steepened hydraulic gradients caused by 

lateral-flow impediments such as faulting and (or) 

sharp folding at locations near Walla Walla, Wash., in 

the Cold Creek syncline east of Yakima, Wash., and 

southwest of The Dalles, Oreg. More recent work in 

the Horse Heaven Hills (Packard and others, 1996) 

suggests a linear ground-water impediment, possibly 

associated with shear faulting. Upward groundwater movement occurs in an area where the regional 

flow is downward, and this anomaly is assumed to be 

caused by the impediment. Similarly, a study of the 

ground-water resources of the Umatilla area in 

Oregon (Davies-Smith and others, 1988) found that 

just up-gradient (lateral ground-water flow is northward) of the east-west-trending Willow Creek monocline, the vertical flow gradient is upwards instead of 

the more common downward gradient. Further, the 

lateral hydraulic gradient steepens near the monocline, indicating the structure's effect on groundwater movement.

Under 1983-85 conditions, the potentiometric 

surfaces of the Saddle Mountains, Wanapum, and 

Grande Ronde units (Hansen and others, 1994) 

roughly parallel the land surface in areas where these 

units are exposed at the surface. In these areas, these 

units are directly recharged by precipitation and in 

some areas also by irrigation water. Lateral groundwater flow is generally toward surface-drainage 

features where ground water discharges. Groundwater movement in the deeply buried portions of the 

Wanapum and Grande Ronde units is influenced less 

by minor surface-drainage features. For the Quincy 

Basin (fig. 2), for example, such control was 

described by Lane and Whiteman (1989) and Hansen 

and others (1994) where ground-water movement 

within the Wanapum unit, which is at or near land 

surface, is toward Moses Lake and Potholes Reservoir. Ground-water movement in the underlying 

Grande Ronde unit, however, is virtually unaffected 

by these surface-drainage features, and flow is south 

and west toward the Columbia River, a much larger 

drainage feature. These differences are due to the 

fact that movement of water to and from deeply 

buried portions of the basalts that are not laterally 

connected to the surface must occur by vertical leakage to and from the overlying and underlying units.

In the Palouse subprovince north of the Snake 

River, the regional ground-water flow in both the 

Wanapum and Grande Ronde units is toward the 

southwest, roughly paralleling the land surface and 

the regional dip of the basalts. Regional discharge is 

to the Columbia and Snake Rivers. In the Yakima 

Fold Belt, ground-water movement is downward 

from the anticlinal ridges toward the streams and 

rivers in the intervening synclinal basins. In the Blue 

Mountains subprovince, water moves from the 

uplands or mountains toward the Snake and Columbia Rivers. In addition, the deeply incised John Day 

and Deschutes Rivers provide major control to the 

ground-water flow system, and water moves from the 

intervening uplands to these rivers.

Overburden Aquifer

The overburden in the structural basins readily 

transmits water and comprises water-table aquifers. 

These aquifers are generally coarse-grained and 

highly permeable in their upper sections and

14
fine-grained and less permeable at depth. However, 

where the overburden is thick, such as in the structural basins in the Yakima Fold Belt, extensive 

coarse-grained layers exist deeper in the section and 

function as water-producing zones.

The water-level contours for the overburden 

aquifer roughly parallel land surface (Whiteman, 

1986; Lane and Whiteman, 1989; Hansen and others, 

1994). Recharge is mainly from infiltration of 

applied irrigation water and from precipitation. 

Discharge is to rivers, lakes, drains and waterways, 

wells, and to the underlying basalt unit. Downward 

movement of water to the underlying basalts is 

controlled by intervening fine-grained sedimentary 

layers and by the head difference between the units. 

An example of such control on ground-water flow 

also was described by Hansen and others (1994) in 

the Quincy Basin (fig. 2), where steeper vertical head 

gradients have been noted in areas where large thicknesses of clay-rich materials directly overlie the 

Wanapum Basalt. Where this clay layer is thin or 

absent, the heads in the overburden aquifer and 

Wanapum unit are nearly identical. Additionally, 

with the onset of surface-water irrigation in the 

Quincy Basin, a rapid increase in heads was observed 

in both the overburden aquifer and the Wanapum 

unit. This rapid response to increased recharge was 

not seen in the more deeply buried Grande Ronde 

unit, indicating that the overall hydraulic connection 

between the overburden and the underlying basalt 

unit generally is better than it is between adjoining 

basalt units.

Hydraulic Characteristics

The values of lateral hydraulic conductivity for 

each basalt unit and the overburden aquifer initially 

were estimated from specific-capacity data. The 

modified Theis equation (Theis, 1963) for nonleaky 

artesian aquifers (Ferris and others, 1962, p. 99) was 

first used to estimate transmissivity values from the 

specific-capacity data. In order to estimate a hydraulic conductivity value from a transmissivity value, 

the ratio of the open interval of the well to the unit or 

aquifer thickness is required. For this study, any 

basalt well was assumed to 'effectively' penetrate at 

least one entire basalt flow, and the effective open 

interval is 55 ft greater than the actual saturated open

interval, but not less than 110 ft (the average thickness of one basalt flow; see Hansen and others, 

1994). The calculated lateral hydraulic conductivities for the overburden aquifer and the basalt units 

are shown later in figure 11.

The median lateral hydraulic conductivity for 

the overburden aquifer is roughly two orders of 

magnitude greater than that of the basalt units. The 

smaller median lateral hydraulic conductivity of the 

Saddle Mountains unit, compared with the other 

basalt units, is attributed to the numerous intercalated 

fine-grained interbeds, which generally are absent in 

the Wanapum and Grande Ronde units. The large 

range in values for all units indicates the heterogenous nature of both the overburden and the basalts.

Recharge

The source of water to the aquifer system is 

predominantly from direct recharge from precipitation (Bauer and Vaccaro, 1990). For equilibrium 

conditions, recharge equals discharge to streams, 

rivers, lakes, springs, and seepage faces.

To compute the spatial distribution of recharge 

over the study area, where annual precipitation varies 

from about 6 in/yr to more than 40 in/yr, a daily 

soil-moisture budgeting computer model was developed during this study (Bauer and Vaccaro, 1987). 

The model computes daily quantities of moisture that 

percolate downward beyond the root zone (deep 

percolation) for any specified number of years at any 

specified number of grid cells, within a drainage 

area, using readily available meteorologic, soil, 

land cover, altitude, streamflow, and irrigationapplication-rate data.

Deep percolation was simulated for 53 basins 

and subareas underlain by the aquifer system on a 

daily time step over a 22-year period, 1956 to 1977 

(Bauer and Vaccaro, 1990), and the 22 years of daily 

values were used to calculate a long-term average 

recharge. The 22-year period included a large range 

of climatic variability and therefore was assumed to 

be representative of overall climatic conditions. 

Each of these basins and subareas was divided into 

cells generally ranging from 0.25 to 1 mi2. The 

recharge estimates then were aggregated to cells that 

were 2.5 minutes of latitude by 2.0 minutes of longitude (about 2.88 by 1.62 mi), resulting in an

15
area-weighted average value for recharge. These 

larger cells correspond with the ground-water flow 

model grid system, which is described later in the 

section "Model Grid and Boundary Conditions." 

Predevelopment deep percolation also was simulated 

using climatic data from the same 22-year period, but 

using estimates of predevelopment land cover. A 

detailed description and analysis of the data and 

results can be found in Bauer and Vaccaro (1990).

The modeled basins and subareas included most 

of the irrigated croplands and most of the area with 

annual precipitation less than 11 in/yr. Recharge for 

each of the remaining ground-water model cells was 

then estimated using a polynomial regression equation. The equation related the 22-year averageannual precipitation to the estimated long-term 

average recharge at the approximately 30,000 

recharge-simulation cells of the 53 basins. Figures 7 

and 8 show predevelopment and current estimates of 

recharge for the ground-water model cells (outlines 

of the basins and subareas for which deep percolation 

was simulated are shown on figure 13.)

Long-term, time-averaged estimate of recharge 

for the modeled area for predevelopment land-use 

conditions was calculated to be about 6,600 ft3/s and 

for current land-use conditions about 10,200 ft3/s. 

These estimates of recharge are about 7 to 10 percent 

larger than those reported by Bauer and Vaccaro 

(1990) due to refinements in estimates made in 

areas south of the Columbia River (see Hansen 

and others, 1994).

Pumpage

Estimates of ground-water pumpage for 1984 

have been made for this study by Collins (1987) for 

the Oregon part of the Columbia Plateau, and by 

Cline and Knadle (1990) for the Washington part 

of the plateau and a small part of Idaho. About 

828,300 acre-ft (1,144 ft3/s) of ground water was 

pumped from the entire regional aquifer system in 

1984 from approximately 3,500 high-capacity wells. 

Between 85 and 90 percent was for irrigation and the 

rest for public supply and industrial uses. In 1984, 

nearly 500,000 acres of cropland were irrigated with 

ground water. The relatively small quantity of 

ground water used for domestic purposes and other 

uses, such as stock watering, was not considered in 

this regional analysis.

Cline and Collins (1992) also estimated pumpage for 1983, about 813,000 acre-ft (1,123 ft3/s), and 

averaged these values with the 1984 values (fig. 9). 

For wells that tap more than one unit, pumpage was 

divided proportionally according to the amount of 

saturated thickness per unit open to the well. About 

32 percent of the total pumpage was from the Grande 

Ronde unit, 40 percent was from the Wanapum unit, 

3 percent was from the Saddle Mountains unit, and 

25 percent was from the overburden aquifer. Hansen 

and others (1994) show the pumpage distribution for 

each ground-water model cell of each unit.

The greatest concentrations of pumpage occur 

near Hermiston in Umatilla County, Oregon, (south 

of the Columbia River, east of Willow Creek, west of 

Pendleton, and south of Heppner), and in three areas 

in Washington: (1) southwestern Lincoln and northcentral Adams Counties (herein called the OdessaLind pumping area; this area is east of the CBIP, 

south of Coulee City, Wilbur, and Davenport, west of 

Cow Creek, and north of a line connecting Connell 

and Hooper), (2) the Quincy Basin (Grant County), 

and (3) southern Franklin County.

SIMULATION OF GROUND-WATER FLOW

The movement of ground water in the Columbia 

Plateau aquifer system was simulated using the 

three-dimensional finite-difference ground-water 

flow model of McDonald and Harbaugh (1988). The 

model requires the use of a rectangular grid system 

for discretizing the ground-water system into layers 

of rectangular cells. Values of lateral hydraulic 

conductivity must be specified for each cell, and 

depending on the type of simulation and the flow 

system, storage, recharge, and pumpage also may 

need to be specified. If there is more than one layer, 

vertical conductance between cells of adjacent layers 

must be specified. Conceptually, vertical conductance (VCON) is the vertical hydraulic conductivity 

times the area of the cell, divided by the thickness of 

a low-permeability layer between adjacent aquifer 

layers. Where no such confining layers exist, VCON 

is used to represent the equivalent conductance 

between centers of adjacent layers, in which case 

VCON per unit area can be expressed as a function 

of the thicknesses and anisotropies of the adjacent 

layers.

16
122° 120° 118° 116"

EXPLANATION 

Average recharge, in inches per year _

Assumed zero, area of 

outcropping impermeable 

basement rock

0-0.5 

0.5-1.0

i i i r

0 20 40 60 80 100 KILOMETERS

Columbia Plateau aquifer 

system study area boundary

1.0-2.0 

2.0 - 5.0

j | 5.0-10.0 

^ 1 10.0-28.6

Hydrologic study area 

State boundary

Figure 7. Distribution of estimated recharge within the hydrologic study area for predevelopment (1850's) 

land-use conditions.

17
122° 120° 118° 116°

WASHINGTON

20 40 60

I

80 100 MILES

I i I

EXPLANATION

Average recharge, in inches per year _

Assumed zero, area of 

outcropping impermeable 

basement rock

0-0.5 

0.5-1.0

i i i i i i

0 20 40 60 80 100 KILOMETERS

Columbia Plateau aquifer 

system study area boundary

1.0-2.0 

2.0 - 5.0 

5.0-10.0 

10.0-28.6

Hydrologic study area 

State boundary

Figure 8. Distribution of estimated recharge within the hydrologic study area for 1980's land-use conditions.

18
122° 120° 118° 116°

WASHINGTON 

\

20 40 60 80 100 MILES

46° -

45° 

EXPLANATION

1984 pumpage, in acre-feet; block size is one quarter township 

D 0-49 D 2,000-3,999 

D 50-99 4,000-5,999 

D 100-499 n 6,000-8,999 

M 500-999 9,000-11,000 

D 1,000-1,999

Columbia Plateau aquifer system 

study area boundary

\ r r

0 20 40 60 80 100 KILOMETERS

 State boundary

Figure 9. Distribution of 1983-85 ground-water pumpage.

19
Cell widths, lengths, and, optionally, cell top 

and bottom altitudes also must be specified. Cell 

tops and bottoms are required for layers that are to be 

"convertible," meaning that the cells in such layers 

can be simulated as for either fully saturated (confined) or partially saturated (water table). Boundary 

conditions and an initial-head configuration also 

must be specified for each layer.

The ground-water flow model simulations 

described in this report are for equilibrium predevelopment conditions, average hydrologic conditions 

for the period spring 1983 to spring 1985 "current 

conditions" and several possible future equilibrium 

hydrologic conditions. For equilibrium (steadystate) simulations, the storage parameter is not used. 

All simulations were operated in the "convertible" 

mode for all layers in order to represent the aquifer 

system as realistically as possible. The 1983-85 

period was not at equilibrium, but was treated as such 

by using the average head configuration for the 

period and by incorporating the average rate of 

change of storage for the period into the pumpage 

variable. The average change in storage for 1983-85 

was estimated using the published water-level 

changes (Lane and Whiteman, 1989) for this period. 

Hansen and others (1994) describe this method in 

greater detail.

The boundary condition specified for each cell 

at the perimeter of each layer may be no flow, specified head, specified flux, or head-dependent flux. 

Drains, rivers, and general head boundaries (GHB) 

are specific types of head-dependent flux boundary 

conditions. Drains differ from rivers and GHB's in 

that they are not allowed to supply water to the aquifer and were used for those surface-water features 

that could not supply large quantities of water to the 

aquifer system, such as irrigation drains and small 

streams. GHB's were used to simulate seepage from 

escarpments of units that are completely truncated by 

erosion or uplift. For this application, the GHB head 

is set to the altitude of the bottom of the unit so that 

no inflow occurs.

The model was modified for this study so that 

(1) subtotals of water budgets for specified zones and 

cross sections are calculated, (2) linear features such 

as faults or narrow canyons are more rigorously 

simulated, and (3) vertical flow is allowed directly 

between layers where intervening layers are missing. 

Hansen (1993) describes these modifications in 

detail.

Model Grid and Boundary Conditions

A north-south rectangular grid spacing of 

2.5-minute latitude by 2.0-minute longitude (2.88 by 

1.62 mi, or 4.67 mi on average) was used to discretize the aquifer system. This resulted in 76 rows 

of latitude and 130 columns of longitude. The cell 

size was determined in consideration of the size of 

the study area, available computer storage, data availability, and estimates of the maximum cell size that 

would describe most of the geologic structures. This 

grid was imposed on each of five layers, and is presented in Hansen and others (1994). Numbered from 

youngest to the oldest, the layers representing aquifers and units are:

Layer 1 Overburden aquifer

Layer 2 Saddle Mountains unit + Saddle 

Mountains-Wanapum interbed

Layer 3 Wanapum unit + Wanapum-Grande 

Ronde interbed

Layer 4 Upper 2,000 feet of the Grande 

Ronde unit

Layer 5 Lower part of the Grande Ronde unit 

not included in layer 4.

The Grande Ronde unit was divided into two layers 

to better simulate vertical head gradients within the 

unit, which, overall, is much thicker than any of the 

overlying units.

Generally, the lateral extent of the grid system 

for each layer was constructed to coincide with the 

lateral or hydrogeologic extent (boundary) of the 

corresponding unit (fig. 1). The upper Grande Ronde 

layer covers the widest area and, except for only a 

few locations, forms the outermost edge of the 

model. The lower Grande Ronde layer is defined as 

the part of the Grande Ronde unit lying 2,000 ft or 

more below the top of the Grande Ronde unit.

Wherever a layer pinches out or becomes unsaturated, the peripheral cells are bounded by no-flow 

boundaries. The boundaries for current conditions 

for the overburden aquifer and the Saddle Mountains 

unit covered a wider area than for predevelopment 

conditions because the amount of saturated areas 

increased with the development of surface-water

20
irrigation projects. Boundaries for the Wanapum and 

Grande Ronde units remained the same. For current 

conditions there were 17,899 active cells.

Certain areas of the Columbia River Basalt 

Group were not included in the ground-water model 

because they are hydrologically isolated from the 

main body and would have added little to the analyses of the main regional-flow system. These areas 

are outside of the hydrologic study area and are 

described as follows.

1. The basalts south of the northeast-trending Blue 

Mountains anticline (fig. 6) are hydrologically 

separated from those to the north by the anticline that rises as much as 5,000 ft above the 

relatively flat-lying basalts on either side. The 

Blue Mountains crest coincides approximately 

with the anticlinal axis. Exposures of impermeable crystalline rock in the Blue Mountains indicate an impermeable core through which little 

ground water could move. Thus, the drainage 

divide along the Blue Mountains crest was 

chosen as a no-flow boundary in this area. 

Additionally, much of the area south of the 

anticline is sparsely populated, and there is little 

hydrogeologic information available.

2. West of The Dalles, the Columbia River Basalt 

Group extends along a narrow strip of the 

Columbia River valley to the Pacific Ocean. 

Ground-water flow in this strip follows short 

paths perpendicular to and terminating at the 

Columbia River. This area does not influence 

the main ground-water reservoir, therefore 

layers 3, 4, and 5 (the only layers in this area) 

were made to end along a selected flow line a 

few miles west of the deeply incised Klickitat 

River (fig. 2).

3. A situation similar to that west of the Dalles 

exists east into Idaho along the Clearwater 

River. Layers 3 and 4 north of the Clearwater 

River were made to end along flow lines perpendicular to the Clearwater River east of the confluence (layer 3) and at the confluence (layer 4) 

with the Snake River. The Wanapum unit generally ends as escarpments along the Snake and 

Clearwater Rivers well above river level. This is

represented by GHB cells in layer 3. The 

Grande Ronde unit is partially penetrated by and 

in contact with the rivers. This is represented by 

river cells in layer 4. Other units are not present 

in this area.

4. In the extreme southeastern part of the study 

area, the north-trending Snake River and the 

east-trending Grande Ronde River cut deep 

canyons in excess of 2,000 ft that isolate some 

of the Columbia River Basalt Group to the east 

and south. Because all measured water levels in 

this area are much higher than the river stage 

and also because in some areas impermeable 

crystalline rock is exposed in the canyon 

bottom, it is unlikely that basalt aquifers on one 

side are hydrologically connected to those on 

the other side. Therefore, layer 4 was made to 

end and river cells were placed along the Grande 

Ronde and Snake River Canyons. Other layers 

are not present along these reaches of the 

Grande Ronde and Snake Rivers.

5. Similarly, the Spokane River, at the northeastern 

boundary (fig. 2), cuts through the Wanapum 

unit and deeply into the Grande Ronde unit, in 

places exposing older impermeable crystalline 

rock and isolating areas of the Grande Ronde 

and Wanapum units to the north. Thus, layer 4 

has river cells along the Spokane River and 

layer 3 ends as GHB cells where the Wanapum 

unit is truncated in this area. Additionally, just 

south of this area is a ground-water divide.

6. Moving westward along the Spokane River, then 

westward and southward along the Columbia 

River to Wenatchee (southeastern Chelan 

County), these rivers cut entirely through the 

basalt and are entrenched in older impermeable 

crystalline rock isolating relatively small areas 

of basalt to the north and west. The model 

boundary, however, was not placed at the river 

canyon. Instead, layers 3 and 4 were made to 

end several miles south and west of the canyon, 

corresponding to a low anticlinal ridge and 

ground-water divide. The basalt along this line 

is, for the most part, thinner than on either 

side and in places is absent, exposing older

21
impermeable crystalline rock. Incorporation 

into the model of the "sliver" of basalt between 

the ground-water divide and the irregular course 

of the Columbia River to the north and west 

would have resulted in a complex, fragmented, 

head-dependent flux boundary that, at the grid 

scale employed, would have created untenable 

simulation problems. Layers 3 and 4 are the 

only layers present in this area.

Adjustments to Estimates of 

Hydraulic Characteristics

Hansen and others (1994) describe in detail the 

progression and rationale of adjustments to the initial 

estimates of hydraulic characteristics used in the 

ground-water flow model that were necessary for the 

model to simulate water levels that were in reasonable agreement with observed water levels the 

calibration process. The initial estimates and final 

adjustments are described briefly in this section, 

relating them to the physical interpretations of the 

flow system.

Initial estimates of lateral hydraulic conductivities, discussed in the "Hydraulic Characteristics" 

section, showed little or no spatial pattern within the 

units. This may, in part, be because of where the 

wells are drilled. For example, there are many wells 

in low-lying agricultural and urban areas, where the 

units tend to be relatively flat-lying, whereas areas of 

intense folding and faulting usually coincide with 

steep mountains and (or) ridges upon which few 

wells have been drilled and therefore little is known, 

other than estimates of hydraulic characteristics from 

cursory inspection of outcrops. However, waterlevel data from areas adjacent to certain of these 

structural features suggest that hydraulic conductivities are, in general, lower than those in surrounding 

areas. For example, Frenchman Hills (fig. 6), an 

anticlinal ridge located just south of the Quincy 

Basin and just north of the Royal Slope agricultural 

area, appears to hydraulically separate the Wanapum 

unit of these two areas (Lane and Whiteman, 1989). 

Just to the north of Frenchman Hills, water-level 

contours in the Wanapum unit have a small gradient 

and ground-water flow is generally to the east. 

Whereas, just south of Frenchman Hills, where water 

levels are lower, the gradient is steeper and flow is to 

the south. If hydraulic conductivities were similar

under Frenchman Hills, ground-water flow probably 

would be south across Frenchman Hills, from the 

Quincy Basin to the Royal Slope.

Similar impedances to ground-water flow across 

anticlinal ridges are interpreted wherever sufficient 

water-level data exist. A ground-water flow model in 

the Horse Heaven Hills area of Washington and 

Oregon (see fig. 2; Packard and others, 1996) used 

hydraulic conductivities at anticlines and faults that 

were less by a median factor of 0.0167 than the initial 

gridded values used for these locations. A factor of 

0.0167 was therefore used to adjust the initial values 

at major faults and folds throughout the modeled 

area. For less severely deformed structures, such as 

monoclines, a factor of 0.1 was arbitrarily chosen. In 

order to better simulate these linear impedances to 

flow, Hansen (1993) provided modifications such that 

these reductions could be applied to specified modelcell walls without affecting hydraulic conductivities 

across the other three walls.

For estimating VCON, reported values of vertical to horizontal anisotropy of hydraulic conductivity 

ranged from about 0.0005 to 0.1 (Packard and others, 

1996; Lum and others, 1990; Davies^mith and 

others, 1988). The initial estimate used in the model 

was 0.003. This value was areally adjusted on th^J^ 

basis of the lithology and distribution of interbeds. ~*

For the time-averaged steady-state simulations, 

the change in stored water resulting from water*evel 

declines and rises in each aquifer, and thus the stor^ 

age coefficient, had to be estimated. However, it was 

not necessary to make any estimates of overburden > 

aquifer storage coefficients because virtually no 

changes in water levels in the overburden were 

observed for the time-averaged period. Few data 

exist from which to estimate storage coefficients in 

the project area. Table 1 shows values estimated 

from previous investigations. For the basalts, most of 

the interconnected pore space probably consists of 

fractures and rubbly zones. An average total porosity 

of about 4 percent is indicated by bulk and grain 

densities (Whiteman and others, 1994). In the Horse 

Heaven Hills area, water-level rises in relation to 

estimated quantities of irrigation water that recharged 

the basalt water table suggested a specific storage of 

about 0.015, whereas pumpage and water-level 

decline data suggested a specific storage of about 

0.006 (A. Hansen, U.S. Geological Survey, written 

commun., 1989).

22
Table \.~Summary of selected storage-coefficient estimates for the Columbia Plateau

Geologic unit

Fluvial

Glaciofluvial

Ringold Formation

Touchet Beds

Glaciofluvial

Overburden

Ringold Formation

Glaciofluvial

Basalt

Basalt

Basalt

Basalt

Basalt

Basalt

Basalt

Basalt

Basalt

Basalt

Hydrogeologic unit

Overburden aquifer

~Do--

-Do--

-DO--

-DO--

-DO--

--DO--

-DO--

Wanapum

Saddle MountainsWanapum

Grande Ronde

Mainly Wanapum

Wanapum

Wanapum and

Grande Ronde

WanapumGrande Ronde

Saddle Mountains,

Wanapum, and

Grande Ronde

Saddle Mountains

Not determined

Wanapum and

Grande Ronde to

Storage 

coefficient/ 

specific 

yield

0.20

0.03-0.2

2.0x1 0'4

0.1

0.06-0.2

0.06

0.1

0.15

1.2xlO'4

2.2xlO'5

3.2xlO"2

5.2xlO'4

4.7xlQ-4

9.0xlO'5

4.75xlO'3

2.0xlO'4

6.0xlO"4

1.4xlO'6

1.5xlO'3

2.0x1 0'3

6.0xlO'3

l.OxlO"2

l.OxlO'3

2.5xlO'3

S.lxlO'2

1.9xlO'3

4.6x1 0'4

S.OxlO'5

7.6x1 0'4

S.OxlO'5

Method 1 

of 

determination

Model

AT

Model

AT

AT

AT, Model

AT

Model

Model

AT

AT

AT

Model

Model

AT, Model

AT

AT

References

Bolke and Skrivan, 1981

Newcomb and others, 1972

..........Do -

Prych, 1983

Bierschenk, 1959

.........Do -

Tanaka and others, 1974

.........Do 

Eddy, 1976

 -Do -

A. Smith, U.S. Geological

Survey, written commun., 1984

............Do 

MacNish and Barker, 1976

Price, 1960

LaSala and Doty, 1971

Luzier and Skrivan, 1973

FA. Packard, U.S. Geological

Survey, written commun., 1987

Tanaka and others, 1974

Oregon Water Resources Department from A. Smith, U.S. Geological Survey, written commun.,

1984

Tanaka and others, 1979

1 Model, derived from calibration of numerical ground-water flow model; AT, computed from aquifer test data using 

analytical formula.

23
Given the estimated porosities and specificstorage values and the thickness of the basalt units, a 

storage coefficient of 0.01 was used initially with a 

final derived value of 0.04 for any water-table basalt 

aquifer. Wherever a basalt aquifer is overlain by 

another aquifer, it was assumed to be confined. A 

specific storage that was related to only the compressibility of water and pore space was assumed 

(the compressibility of the skeletal structure of the 

basalt was assumed to be negligible). Using a porosity of 0.04, the specific storage of confined basalt 

aquifers was estimated at about 6xlO"8ft" 1 and was 

used with thickness values to calculate storage coefficients at model cells that had water-level declines 

over the period 1983-85.

The three types of head-dependent boundary 

conditions rivers, drains, and GHB's used in the 

model each require a value of conductance, C. Conceptually, for rivers and drains, the streambed is an 

impeding layer and C is equivalent to streambed 

vertical hydraulic conductivity, times the area of the 

streambed, divided by the thickness of the streambed. 

Initial estimates of vertical conductance for river 

cells were obtained from Packard and others (1996), 

Bolke and Vaccaro (1981), and Prych (1983). A 

value for C of SxlO'V1 was used for all river cells in 

the overburden aquifer, and a value of 7 x 10'V1 was 

used for all river cells in the basalt units.

Initial estimates of C for most drains were made 

on the same basis as for rivers. Values for C in 

agricultural drain areas were estimated according to 

unpublished values used by the authors in a calibrated ground-water flow model during an investigation in the Quincy Basin area of the CBIP. Agricultural drains are spaced at close regular intervals, 

and for any ground-water model cell, a network of 

tile drains may exist. For these areas C-values were 

initially estimated from the drain-line spacings .and 

lengths and the lateral hydraulic conductivity distribution in the water table aquifer. The DupuitForchheimer discharge formula was used in a manner 

similar to that presented in subsequent paragraphs for 

determining equivalent river-leakage conductances.

The observed water levels, in general, exhibit 

downward gradients in successively deeper aquifer 

units within most of the aquifer system. Only close 

to major rivers and streams, locally at large pumping

centers, or at certain geologic structures, are the 

gradients observed to be upward. Moreover, the 

magnitude of the downward gradients is generally 

much larger than of the upward gradients. Downward head differences of more than 400 ft between 

basalt units occur in many areas, but upward differences of more than 100 ft are rare. Generally, computed head differences between units did not initially 

match well with the observed head differences. For 

areas near major discharge features the Columbia, 

Snake, and Yakima Rivers computed upward vertical gradients were generally hundreds of feet too 

large, and downward gradients in most other areas 

were too small. Changes to VCON by global variation of vertical to horizontal anisotropy (FCTR) 

proved futile; any decrease of upward gradient near 

the major discharge areas brought about by reducing 

FCTR would be counteracted by a reduction in 

downward gradient in the other areas. Complete 

head collapse over most of the modeled region 

resulted when FCTR was adjusted to the extent that 

observed upward gradients were matched. Refinements of estimates of the distribution and lithology 

of the interbed material between basalt formations 

and subsequent adjustments to VCON did little to 

improve this situation.

Simulations using larger river-leakage conductances generally reduced the imbalance of head 

differences between the discharge and nondischarge 

areas and led to a different formulation of these 

conductances. The following is a brief discussion of 

a formulation for the river-leakage conductances 

that gives much larger values than were initially 

estimated on the basis of vertical hydraulic conductivities.

All of the major rivers are deeply incised into 

the basalts over most of their lengths within the study 

area and function as major discharge areas. Moreover, it is observed that lateral ground-water-level 

gradients increase precipitously in most locations 

near these discharge areas. This suggested that a 

Dupuit-Forchheimer discharge formulation would be 

more appropriate than the assumption of strictly 

vertical discharge through an impeding streambed 

(McDonald and Harbaugh, 1988). The DupuitForchheimer approximation for discharge to a stream 

was used to estimate an "equivalent" river-leakage

24
conductance. Discharge from a water-table aquifer 

to one side of a reach of a stream (Qj /2) > modified 

from Bear (1979), may be written as

LS K

) -(H-H)'] (1)

where

Hb = the altitude of the streambed, L;

HS = the altitude of the water surface in the

stream, L;

x = distance from the stream, L; 

h = the water level in the water-table aquifer at

distance x from the stream, L; 

K = the lateral hydraulic conductivity, L/T;

and 

LS = the length of the stream reach, L.

If the model cell head value is assumed to be 

approximately equivalent to the aquifer head at a 

distance half way between the stream (lying at the 

center of the cell) and the cell wall ( x ~ Lc /4 for a 

rectangular grid where LC is the cell width), and if 

equation (1) is doubled to account for discharge to 

both sides of the stream, and factored, equation (1) 

becomes

4L.K

+ Hs -2Hb )(h-Hs ) (2

For rivers and streams in the study area, 

HS - Hb is negligible compared with h-Hb and 

generally LS approximately equals LC for most cells. 

Using these simplifications, equation (2) becomes

= 4K(h-Hb )(h-Hs) (3

Thus, four times the lateral hydraulic conductivity 

times the average saturated thickness above the 

streambed for a river cell replaces the streambed 

conductance (C) .

Results of the simulations using the above 

formulation for river-leakage conductance improved 

considerably; however, computed heads were still too 

high at the rivers. Because most of the surface area

of river cells are occupied by large rivers, estimated 

vertical conductance of the streambed multiplied by 

river area was also added to C calculated by equation 

3; this assumes that vertical flow also contributes to 

the total discharge. Later in the calibration process, 

adjustments were made in order to regionalize 

values.

Using these river-leakage conductances gave 

computed heads in agreement with observed heads 

along the major rivers in all aquifers in hydraulic 

connection with rivers. However, upward head 

gradients were still too large between many river 

cells and cells of the layer immediately below in the 

vicinity of the rivers. Trial-and-error experimentation showed that in order to achieve a reasonable 

vertical head gradient match, it became necessary to 

also set the VCON between layers beneath the major 

rivers sufficiently large while not changing VCON 

throughout the remaining modeled area. Thus, it 

appeared that wherever a riverbed was observed to be 

in a particular basalt unit, there was good connection 

between the river, the unit in contact with the river, 

and the next lower basalt unit. Four hypotheses are 

presented here to explain such connection.

1. Riverbeds are probably more deeply entrenched 

into the basalt layers than has been mapped. 

When structure contours of the top of units were 

mapped, outcrops and well logs were used for 

altitude control. Smooth structure contours 

were drawn using these controls, with the 

constraint that land surface is an upper bound. 

Thus, under major rivers where there is no 

control other than streambed altitude, it is 

almost certain that if the river were deeply 

entrenched into the basalt units, it would not 

have been mapped as such. The original assignment of rivers to model layers therefore was 

probably biased toward the upper units, thereby 

introducing a greater simulated impedance for 

discharge from lower units.

2. It is well documented that during Pleistocene 

time there were enormous discharges down the 

Columbia and Snake Rivers from the breaching of prehistoric Lake Missoula and Lake 

Bonneville. These large flood volumes 

(386,000,000 ft3/s; U.S. Geological Survey,

25
1974) scoured and plucked the riverbeds and 

deposited alluvium to great depths. At Wallula 

Gap, for example, just downstream of the 

confluence of the Columbia and Snake Rivers, 

cobbly gravels below the riverbed are reported 

to be more than 250 ft thick (Mackin, 1955).

3. Rivers that cut through basalt flows only at 

scattered locations can increase greatly the 

"apparent" vertical connection between units. 

The impedance to discharge can be decreased 

greatly in such a situation because the lateral 

hydraulic conductivity of basalt is generally 

several orders of magnitude greater than the 

vertical hydraulic conductivity. There actually 

may be much less vertical flow to the rivers than 

has been conceptualized because ground water 

can discharge laterally, probably in places as 

underwater springs, to where the basalt layers 

are cut by the river bed. Because of the large 

spatial scale of this project, many localized cuts 

would not have been accounted for. Such an 

enhancement of vertical conductance from 

bedrock erosion would occur only in areas of 

shallow water levels and therefore in the 

discharge areas. Thus, in upland areas where 

the bedrock topography may be heavily 

dissected, it has little or no effect on "apparent" 

vertical conductances because water levels are 

well below the erosional irregularities.

4. Many of these river cells with large vertical 

conductances overlie the axis of synclines. The 

potential exists that deformation might enhance 

vertical hydraulic conductivity with depth at 

synclines.

Except for (4), the above discussion does not 

apply to the lower Grande Ronde, the top of which is 

far beneath all rivers. During the calibration process, 

the VCON between the upper and lower Grande 

Ronde layers, for lack of any data, was formulated in 

the same manner as that for the VCON between the 

Wanapum unit and the upper Grande Ronde. This 

generally resulted in lower VCON values than for 

those between the upper layers because of the greater 

thicknesses involved. Again, there were high head 

problems in the vicinity of the major discharge areas.

Generally using larger and more nearly uniform 

values of VCON between these two layers throughout the model gave reasonable results. This may be 

justified by the fact that there are few interbeds and 

saprolites between the Grande Ronde Basalt flows to 

impede vertical ground-water flow.

In some of the tightly folded upland areas, it 

was necessary to use values of VCON between the 

Saddle Mountains and Wanapum units and between 

the Wanapum unit and the upper Grande Ronde that 

were smaller than those used for most of the less 

structurally complex areas. The use of median-range 

values could not sustain simulated water levels in the 

uppermost unit, resulting in many desaturated cells. 

Increasing recharge as much as 30 percent did not 

help. This structural relation between anticlines and 

low vertical conductance is not clearly understood. 

A probable reason for this relation is that compressional forces during folding disrupted and closed the 

vertical jointing spaces in the colonnade parts of the 

basalt flows. Evidence for this is seen in exposures 

of anticlines that have been cut deeply by the Yakima 

River, a few miles upstream of the City of Yakima. It 

is difficult to recognize the colonnade structure that is 

so evident in undeformed exposures of basalt flows.

Final values of VCON were regionalized with 

larger values along major rivers, and lower values in 

upland areas. Median values between layers are, 

from top to bottom, 2.6xlO'8 , 2xlO"n, 6xlO' 12, and 

5xlO-n s' 1 .

It was evident early in the calibration process 

that topography would be a major hydrologic control. 

That is, the water-table aquifer is drained by rivers, 

streams, and even some nonperennial streams and 

coulees. Only in the low-lying areas near the center 

of the study area, where the water table is deeper, are 

these topographic controls lacking. Topographic 

control was simulated by using the drain and river 

functions. These functions initially were used only 

along the larger perennial streams and rivers, and as a 

result, higher-than-observed heads were calculated in 

many intervening areas. Even a 60-percent reduction 

of the recharge estimates in these areas did not help; 

the drains received less discharge and heads were 

still much too high. It became evident that more 

topographic control was necessary, especially in the 

upland areas, which receive large quantities of 

recharge, such as the southern flank of the Blue

26
Mountains and the east side of the Cascade Range. 

In order to lower computed heads, it became necessary to use the drain or river functions for almost all 

stream channels.

Another alternative for lowering computed 

heads was to increase lateral hydraulic conductivity 

values to much larger than median values in areas of 

large precipitation. However, such a coincidence of 

large precipitation and large conductivity was not 

physically plausible and this alternative was not 

pursued.

Simulated heads were much lower than 

observed heads in various upland areas that initially 

were assigned median lateral hydraulic conductivities and that receive relatively small quantities of 

precipitation such as in the Yakima Fold Belt, 

eastern Horse Heaven Hills, Beezely Hills, and 

Frenchman Hills (fig. 2). In general, hydraulic 

conductivities in the uplands had to be sufficiently 

reduced to adequately match observed heads in areas 

of low recharge, and these values were assumed to 

prevail in other upland areas that receive more 

recharge. However, specific-capacity data are scarce 

for upland areas, but where available, they do not 

show any consistent differences when compared with 

other areas. A hypothesis is presented below in 

support of smaller hydraulic conductivities in the 

uplands on the basis that upland areas of the Columbia Plateau are known to have numerous faults.

Lateral ground-water flow in basalts is predominantly along the rubbly interflow zones, which 

typically occupy only 5 to 10 percent of basalt flow 

thickness (see fig. 3); thus, even minor offsets of the 

basalt strata would tend to impede lateral flow. On 

a regional scale, an effectively smaller hydraulic 

conductivity would be the consequence of such faulting. Locally, however, the conductivity is unaltered; 

aquifer or specific-capacity tests may not show the 

smaller regional-scale values unless conducted on a 

long-term basis at sufficient pumping rates (most 

wells in the uplands are shallow, small-diameter, 

low-yield domestic wells) to lower water levels at the 

faults and observe boundary effects. Thus, a regional 

ground-water model whose grid spacing is larger 

than fault spacing can only simulate a faulted area 

using smaller hydraulic conductivities.

Later in the calibration process, adjustments 

were made to lateral hydraulic conductivity values 

for all layers in order to regionalize values. The final

model-derived distributions of lateral hydraulic 

conductivity for each layer (presented in Hansen 

and others, 1994) when referenced to the median 

values derived from the specific-capacity data, are 

(1) smaller in the uplands, (2) smaller in the remaining area but larger than the upland values, and 

(3) larger in a few locations. Boxplots of calculated 

and calibrated lateral hydraulic conductivities for the 

model layers (fig. 10) show that, for all units, the 

lower quartile, median, and upper quartile values 

derived during model calibration are less than those 

derived from the specific-capacity data.

In specific areas unusual problems were encountered during the calibration process.

1. Big Bend area: This area lies north of Pasco, 

Wash., and generally encompasses the area 

between the Snake and Columbia Rivers to as 

far north as about 46.5° latitude (fig. 2). 

Ground-water flow in all four basalt units in 

this area generally is southwestward toward 

discharge areas along the Columbia and Snake 

Rivers. Simulated heads in the Wanapum and 

Grande Ronde units were too high, especially in 

the upper Grande Ronde, using a full range of 

reasonable values of lateral hydraulic conductivity and vertical conductances. In order to simulate lower heads in this area, it was necessary to 

use small lateral hydraulic conductivities along 

an east-west-trending strip just upgradient of 

this area. This strip corresponds with areas 

where lateral head gradients in the Wanapum 

and Grande Ronde units are considerably 

steeper than to either the northeast (upgradient) 

or the southwest (downgradient). The physical 

reason for such a low-conductivity strip in this 

relatively flat-lying region is not known. The 

strip appears as an eastward extension of the 

Saddle Mountains anticline into the subsurface, 

although the mapped eastward extension of this 

anticline is short (Tolan and Reidel, 1989). The 

deeper older basalts might have been folded and 

faulted along this strip and later covered by the 

younger, relatively flat-lying Wanapum Basalt 

flows, so that there is now no surficial expression of such structure. However, because the 

Saddle Mountains were being uplifted during 

and after the time of deposition of Saddle 

Mountains Basalt flows, it is likely that the

27
10

-3

10

-2

10

HYDRAULIC CONDUCTIVITY, IN FEET PER DAY 

" 1 1 10 10 2 10 3

10" 

c 

0"O

0

C

O ±±

_0 

"O 

"O 

CO

(f)

Q. ±±

co c

c :D CO

0 

"O

i_ O 

0 CC

s 0

o

Minimum

Lower quartile

Calibrated

Calibrated

Calibrated

Maximum

Upper quartile

Calibrated

Calculated

Calc

Calculate

10" 10"

10

-6

10" b 10"4 10" 13 10"^ 

HYDRAULIC CONDUCTIVITY, IN FEET PER SECOND

10"

Figure 10. Boxplots of calculated and calibrated lateral hydraulic conductivities for the model layers.
Wanapum Basalt should have been displaced as 

well. Perhaps such structures have not been 

mapped because displacements are small and 

outcrops scarce. As was mentioned previously, 

slight vertical displacements of basalt flows can 

decrease regional hydraulic conductivities. 

Alternatively, basalt flow displacement may be 

the result of several intercanyon flow members 

that closely correspond to this strip of the 

Columbia River Basalt Group (Tolan and 

others, 1989).

2. Odessa-Lind ground-water-irrigated area: This 

roughly rectangular area lies south of Crab 

Creek, west of Cow Creek, east of the East Low 

Canal, and north of Lind Coulee, Wash. (fig. 2). 

During the initial time-averaged simulations, a 

large percentage of Wanapum unit cells went 

dry in this area, regardless of reasonable adjustments of hydraulic conductivities and vertical 

conductance. Pumpage from the Wanapum 

unit, which is exposed in this area, is simply too 

great to be supplied by only lateral or upward 

ground-water inflow. As a result, it became 

necessary to increase recharge from the quantities estimated using the deep percolation model. 

The most likely source of such additional 

recharge is the surface water that is present at 

times in the coulees crossing this area. The 

water table is well below the bottoms of these 

coulees, and therefore they do not drain the 

Wanapum unit. In fact, down-gradient flexures 

of the Wanapum water-level contours beneath 

some of the larger coulees suggest recharge 

through the coulees. Moreover, crest-stage 

streamflow data for several of these coulees 

show that for short periods there is a large 

potential for recharge. Providence Coulee 

(fig. 2), for example, flowed at the rates of 

2,160, 650, and 522 ft3/s during 1956,1969, and 

1970, respectively (Williams and Pearson, 

1985). Actual recharge quantities derived from 

the streamflow in the coulees could not be 

estimated, so the smallest quantity of recharge, 

which would keep most cells in this area wet 

during simulations, was added along the coulee 

courses. This amounted to an additional 32 ft3/s 

of recharge along the coulees.

3. Moses Coulee: This coulee is second in size 

only to Grande Coulee in the study area. It cuts 

deeply into the Grande Ronde Basalt on the 

northwest upland, referred to as the Waterville 

Plateau. The Waterville Plateau is bounded on 

the west and north by the Columbia River, on 

the east by Grande Coulee, and on the south by 

Beezely Hills (fig. 2). From the water-level 

contours, it appears that Moses Coulee drains 

the Grande Ronde unit over the entire length 

of the coulee. Jamison Lake, which covers 

620 acres of the coulee bottom in the upper 

reach, has no outlet and yet contains fresh water. 

The model simulated about 37 ft3/s of groundwater discharge to the Douglas Creek drainage 

basin, which is tributary to Moses Coulee, plus 

about 10 ft3/s to the lower part of Moses Coulee. 

However, streamflow records indicate that the 

simulated flow should be much smaller. When 

recharge on the Waterville Plateau is reduced so 

that simulated discharge is more comparable to 

observed or estimated streamflow, calculated 

water levels are much too low using reasonable 

values of lateral hydraulic conductivity. Vertical 

conductance is not relevant, because only the 

upper Grande Ronde is present in this area; 

although the Wanapum unit is present in small 

discontinuous areas, it was considered part of 

the upper Grande Ronde. It is reasonable to 

expect that there may be ground-water outflow 

through highly permeable alluvium lying in 

the coulee bottom. Therefore, ground-water 

discharge to Moses Coulee may be primarily 

into the alluvium, which eventually discharges 

to the Columbia River at the coulee's mouth.

4. Peripheral and upland areas: For many areas at 

high altitudes, simulated heads were considerably lower than observed or estimated heads, 

even after the downward adjustments of lateral 

hydraulic conductivities and vertical conductances. Because most observed upland heads 

are from shallow domestic wells that penetrate 

only the uppermost part of a basalt unit, such 

heads are probably not representative of the 

vertically averaged values of head for the unit, 

unless the unit is relatively thin. In fact, downward vertical gradients are observed virtually

29
everywhere in the uplands wherever sufficient 

data are available. For example, a test well 

drilled on the crest of Rattlesnake Mountain 

(fig. 2) within the Yakima Fold Belt (Raymond 

and Tillson, 1968) shows a downward head 

difference of approximately 830 ft within 

approximately 3,200 ft of thickness of the 

Grande Ronde unit. Thus, if representative 

water-level data were not available and reasonable values of lateral hydraulic conductivity and 

vertical conductance were used, simulated heads 

that were lower than observed were accepted 

(and assumed to be more representative of the 

average head of a unit's thickness) in the 

uplands. In addition to simulating lower heads 

than those observed in some upland areas, many 

peripheral upland cells of the uppermost unit 

would desaturate during simulation. This 

usually happened in areas where the unit was 

thin and (or) recharge was small. For example, 

the entire crest of the Saddle Mountains east of 

the Columbia River, which is in a low-recharge 

area, desaturated. Because there are no wells 

in this area, these dry cells generally were 

accepted as reasonable despite the original 

estimates of water levels presented in earlier 

reports (Bauer and others, 1985; Whiteman, 

1986; and Lane and Whiteman, 1989).

Model Reliability and Sensitivity

The reliability of the ground-water model can be 

judged by comparing the closeness of fit between 

computed and measured water levels for four of 

the five layers (the overburden aquifer, Saddle 

Mountains unit, Wanapum unit, and upper Grande 

Ronde) and by comparing estimates of baseflow of 

streams with computed ground-water discharge for 

certain drainage basins lying completely within the 

modeled area. No comparisons were made for layer 

5 that represents the lower Grande Ronde because 

there were no water-level data. As part of the first 

criterion, differences in water levels between layers 

can also be compared. The second criterion is much 

more subjective because estimates of baseflow of

streams are difficult to make, especially during wet 

periods when shallow subsurface discharge cannot be 

reliably separated from baseflow.

Time-averaged, model-computed and the 

observed water-level contours and cells that desaturated during the simulation are shown for the 

Wanapum unit (fig. 11); Hansen and others (1994) 

present this information for all layers. No data were 

available to verify whether the aquifer is actually 

saturated in areas where the cells desaturated. For 

most areas, the computed and observed water levels 

appear to match reasonably well. Flow directions 

and lateral gradients replicate the natural system on a 

regional scale. Only in certain upland areas are 

computed water levels significantly different from 

contoured water levels (water-level data generally 

were not available for the uplands and water-level 

contours were estimated).

For the overburden aquifer, agreement between 

simulated and observed heads is good (as would be 

expected on a regional scale because the overburden 

aquifer exists only in relatively flat, low-lying areas). 

However, during simulations 79 cells in the overburden desaturated at peripheral locations where the unit 

tends to thin out and turn upward as it pinches out 

against the underlying basalt. For the Saddle Mountains unit, the greatest differences between simulated 

and observed water levels were at the crest of eastern 

Horse Heaven Hills, where computed water levels 

were as much as 400 ft lower than observed. For the 

Wanapum unit, computed water levels at the crest of 

Rattlesnake Hills similarly were 400 ft lower. For 

the upper Grande Ronde, computed water levels were 

as much as 500 ft lower in an upland area south of 

Wenatchee and northeast of Yakima, bounded on the 

east and west by the canyons of the Columbia and 

Yakima Rivers, respectively, and as much as 1,000 ft 

lower between the canyons of the John Day and 

Deschutes Rivers, in the extreme southwest corner of 

the modeled area.

The values, in feet, for the mean residual (MR), 

mean absolute residual (MAR), and root mean square 

(RMS) for all cells between the time-averaged simulation water levels and the contoured observed water 

levels for layers 1 through 4 are as follows.

30
122° 120° 118° 116°

48'

45° -

0 20 40 60 80 100 KILOMETERS

EXPLANATION

I | Extent of ground-water model layer 3

pi Area of thin or absent unit not included in

u ground-water model

1 Cell simulated as unsaturated

 Columbia Plateau aquifer

	system study area boundary

 State boundary

-BOO- Line of equal simulated water level. Interval, 

in feet, is variable. Datum is sea level

-BOO- Line of equal observed water level. Interval, 

in feet, is variable. Datum is sea level

Figure 11. Map showing contours of simulated and observed 1983-85 water levels for the Wanapum unit.

31
Model

layer

1

2

3

4

Mean

residual

-18

-14

-31

-122

Mean

absolute

residual

46

72

81

184

Root

mean

square

71

104

124

292

Number

of cells

900

1,092

4,308

6,977

The values for cells where there are observed water 

levels are as follows.

Model

layer

1

2

3

4

Mean

residual

-0.30

-9.0

-45

-107

Mean

absolute

residual

39

67

88

158

Root

mean

square

58

91

142

253

Number

of cells

74

77

307 -

276

By some standards these residuals are large, but on a 

regional perspective where the overall observed head 

relief is more than 5,000 ft, the model simulates the 

estimated heads reasonably. Accuracy is diminished 

in the high-gradient areas where lateral head differences between adjacent cells approach 600 ft.

Table 2 shows total simulated discharges from 

river, drain, and GHB cells within 27 separate drainage basins for which estimates of baseflow were 

made. Sufficient daily stream discharge data were 

available for 23 of these basins, from which average 

annual discharges were computed and also tabulated. 

These 23 basins are among the 53 basins for which 

recharge simulations were made (see "Recharge" 

section). Only low-flow data were available for the 

other four basins and probably represent minimum 

values of ground-water discharge. Figure 12 shows 

the gridded outlines and locations of these basins. 

There were no major discrepancies between modelsimulated discharge and estimates of baseflow. Simulated ground-water discharges were significantly 

greater than total streamflow in only four basins. 

One of these is Douglas Creek (in Moses Coulee), 

which has already been discussed in the "Adjustments to Estimates of Hydraulic Characteristics" 

section. The reason for the discrepancies at the other 

three basins Wilson Creek, Willow Creek, and 

Ahtanum Creek Basins is not understood at this 

time. A possible explanation is that unrealistic simulation of ground-water flow across small drainage 

basins could result from large cell size and regionalization of parameters. For example, the computed 

discharge for Glade Creek slightly exceeds observed 

annual streamflow; however, in the adjacent basins of 

Pine Creek and Rock Creek, the computed discharge 

is less than estimated baseflow. Considering both the 

uncertainty in estimating baseflow and the regional 

nature of the model, these simulated discharges are 

believed to be reasonable.

Model sensitivity was tested by changing input 

parameters (lateral conductivity, vertical conductance, recharge, and pumpage) uniformly over all 

cells within a range of ±15 to+25 percent. Generally, within the range of changes tested, the sensitivity increases with depth for all inputs. This is mainly 

because the rivers and drains are the major control on 

the water levels in the surficial layer. For example, 

for the 1983-85 simulation, when the lateral hydraulic conductivity was uniformly reduced by 20 percent, the average head rise in layer 5 was 26 ft but in 

layer 1 was only 6 ft; when the vertical hydraulic 

conductance was reduced 20 percent, the average 

decline for layer 5 was 10 ft and for layer 1, 2 ft. 

In general, the head changes resulting from the sensitivity tests were less than the mean absolute residuals 

of the calibrated model (Hansen and others, 1994).

SIMULATED REGIONAL FLOW

The following sections present information on 

regional ground-water flow based on results that 

were simulated by the model. In addition to the 

1983-85 time-averaged model results, information 

for six other simulations are presented, five of which 

represent potential future conditions. These six are 

(1) predevelopment, (2) future equilibrium with 

1983-85 stresses, (3) Phase 1 expansion of the CBIP 

retaining 1983-85 pumpage, (4) Phase 1 expansion of 

the CBIP with reduced 1983-85 pumpage, (5) Phases 

1 and 2 expansion of the CBIP retaining 1983-85 

pumpage, and (6) Phases 1 and 2 expansion of the 

CBIP with reduced 1983-85 pumpage. Each of these 

is described in more detail in the following sections.

32
Table ^.--Comparison of simulated ground-water discharge, estimated recharge, and average streamflows for drainage basins with streamflow records within

the modeled area

[Values in cubic feet per second except where noted; Cr = creek, R = river, S. = south, Wash. = Washington, Oreg. = Oregon, and CBIP = Columbia Basin Irrigation Project]Reference 1 number

1

234567

8

9

10111213

14

15161718

19

2021

222324252627

Basin

Rebel Flat Cr.

Pine Cr.

Bowers CouleeGlade Cr.

S. Fork Palouse R.

Alkali Flat Cr.Alder Cr.DryCr.Rock Cr, Wash.Wilson Cr.Cow Cr.Naneum Cr.Hawk Cr.

Union Flat Cr.

Crab Cr.

Foster Cr.

Douglas Cr.

Rock Cr, Oreg.

Willow Cr.Asotin Cr.Little Klickitat R.

Ahtanum Cr.Touchet R.Walla Walla R.

Satus Cr.

Tucannon R.

Umatilla R.

Drainage 

area, in square 

miles

7966

992427

125158

254

52

415437

543

83

168172

1,015

322598515837

173

287

126

725

132

577

430

2,436

Estimated recharge

predevelopment

17.6

4.4

74.0

5.2

18.3

26.9

19.316.7

36.230.388.452.7

27.9

39.1

129.1

29.944.3

58.534.3

79.9

132.3

104.3164.0151.1

231.3212.2

680.7

1983-85

17.6

4.4

77.522.1

18.3

26.921.7

14.7

37.151.2

80.9

52.727.939.1

106.3

28.636.258.5

104.0

80.0

132.3

108.6148.0

152.3

231.4203.5719.8

Streamflow2

total

..

12.7

9.86.4

36-17.025.2

107

14.5

24

78-35

68-3.15431

78

177

78

172

325287

197

750

estimated baseflow

1.2

6.20.0

1.3

18

1.21.2

7.1

37

0.0

13

46

8.8

0.0

19

2.00.0

7

0.0

442246

0.8

230

134129

328

Predevelopment

0.0

1.6

12.3

0.0

14.5

9.6

11.114.3

21.9

16.9

40.9

23.2

25.9

24.262.8

30.9

43.8

56.5

64.9

75.5

100.8

99.6

124.3159.4162.3174.9

553.5

1983-85 

timeaveraged

0.0

2.0

2.7

7.9

8.6

9.59.6

12.0

21.5

21.6

22.9

23.8

23.824.324.627.437.154.663.2

75.379.0

102.4109.1160.6164.2168.7

556.5

1983-85 

equilibrium

0.0

2.0

1.0

6.4

8.6

9.47.8

12.0

20.7

21.1

11.1

23.8

23.1

23.920.627.436.954.162.075.278.4

102.4109.1160.6

164.0

168.7

549.1

Phase 1 CBIP expansion

1983-85 

pumpage

0.0

2.0

7.36.4

8.6

9.47.8

12.0

20.721.3

12.0

23.823.323.9

23.127.4

37.154.1

62.075.278.4

102.4109.1160.6164.0168.7

549.1

reduced pumpage

0.02.0

8.6

6.4

8.6

9.47.8

12.0

20.7

21.5

12.6

23.823.423.9

23.427.4

37.154.162.0

75.278.4

102.4109.1160.7164.0168.7

549.2

Phases 1 and 2 

CBIP expansion

1983-85 

pumpage

0.0

2.0

254.0

6.4

8.6

9.57.8

12.0

20.721.5

15.0

23.8

23.5

23.923.527.437.154.1

62.075.278.4

102.4109.1160.7164.0

168.7

549.2

reduced 

pumpage

0.0

2.0

314.9

6.4

8.6

9.57.8

12.0

20.7

22.1

18.9

23.823.923.926.1

27.437.254.1

62.075.278.4

102.4109.2160.7164.0

168.7

549.3

1 Reference number shown on figure 12 for location of basin.

2 Average values for periods of record during 1956-77.
122'

48° -

47° -

46° -

45° -

20 40 60 80 100 MILES

EXPLANATION

© Basin reference number

for basins presented on Table 2

n River cell locations for rivers 

presented on Table 4

i i i i r

0 20 40 60 80 100 KILOMETERS

Outline of model cells representing 

a basin

Extent of model

Columbia Plateau aquifer system 

study area boundary

Figure 12. Locations of basins and stream reaches for which water budgets are presented.

34
Changes from Predevelopment 

to 1983-85

Development of water resources and changes in 

land use from predevelopment (1850's) to current 

(1980's) conditions have affected the regional 

ground-water flow system. A major objective of this 

RASA study was to describe and quantify the water 

budget for the aquifer system and to assess the effects 

of development. Ground-water budgets, water 

levels, and ground-water discharge to selected basins 

for predevelopment and 1983-85 conditions are 

compared.

Ground-Water Budget

Simulated flows across the various boundaries, 

recharge from precipitation and irrigation to each 

layer, vertical flow between layers, and pumpage 

from each layer for predevelopment and 1983-85 

time-averaged conditions are shown schematically in 

figures 13 and 14, respectively. Table 3 shows the 

regional ground-water budget including recharge,

change in storage, leakage from rivers, pumpage, and 

discharges to the rivers, drains, and GHB's. This 

information provides the basis for the following 

discussions.

For predevelopment conditions, the largest 

single flow component is 4,131 ft3/s of recharge from 

precipitation to the upper Grande Ronde (fig. 13). 

This is 63 percent of the total recharge from precipitation to the entire system (table 3). Most of this 

recharge to the upper Grande Ronde occurs in the 

peripheral areas where the unit is at land surface 

(fig. 1); these areas correspond with the uplands of 

the Blue Mountains, the foothills of the Cascades, the 

Waterville Plateau, and a narrow strip just south of 

the Columbia River along the northern margin. 

About 2,970 ft /s of the recharge discharges to drains 

and GHB's in the upper Grande Ronde along the 

peripheral outcrop areas. Thus, 72 percent of 

recharge from precipitation to the Grande Ronde unit 

(45 percent of total recharge from precipitation to the 

system) discharges in these peripheral areas. This 

indicates that regional lateral ground-water inflow 

from areas of large precipitation (large recharge) to 

lowland areas is limited.

Table 3.--Regional ground-water budgets based on seven ground-water flow simulations 

[Values in cubic feet per second; CBIP = Columbia Basin Irrigation Project]

Water-budget

component

Recharge 

Leakage from rivers 

Rate of change in

storage

Predevelopment

6,566 

553.6 

0.0

1983-85 

timeaveraged

10,205

556.7 

186.6

1983-85 

equilibrium

10,205

576.5 

0

Phase 1 CBIP expansion

1983-85

pumpage

10,535 

564.0 

0

reduced

pumpage

10,535 

552.6 

0

Phases 1[ and 2

CBIP expansion

1983-85

pumpage

11,179 

553.8 

0

reduced

pumpage

11,179 

538.5 

0

TOTAL IN* 7,120 10,948 10,782 11,099 11,087 11,732 11,717

Leakage to rivers

Leakage to drains

Leakage to generalhead boundaries

Pumpage

TOTAL OUT*

2,753.9

3,944.8

425.5

0.0

7,124

3,804.5

5,595.9

422.6

1,134.7

10,958

3,726.1

5,549.0

420.9

1,095

10,791

3,757.6

5,821.3

424.5

1,104.1

11,107

3,770.4

5,925.9

424.6

974.7

11,096

3,798.0

6,406.8

426.2

1,114.1

11,745

3,846.1

6,609.2

426.6

843.2

11,725

* The totals may not match exactly because they are taken directly from the output of model simulations, which have a certain 

amount of mass balance error due to non-exact closure of the numerical solution.

35
119.3

452.3 ^

912.2 <^ 

11.5 ^

180.3 <^ 

45.0 ^

522.4 <^

44.8 ^

1,139.0 <^

R

R

R

1 J

o>

°° 1 CM

f-'

at'

8 10 1

L j

0)

O)

i

,_A

00

^5 1

f*s» 1

i

i

o

C)

L

1

|°? 

10

 T^ TKi

G>13-9

\148.4 

D > V132.6

o T ^ x^ 

O)

(O "* 

CD

1 r

^ 1

S D ^ 1

1 Mo

(O

1 CO

 Jr

^ t

1 \l

oT !<*

§l t

f2,

Q

p

^> 329.0

^> 877.5

^ 4

G

D

^>

^> 

EXPLANATION 

(Units are cubic feet per second)

119.3

1

452.3 p

912.2 <

D lx

r

^ R

d R

> 148.4

Recharge "HV¥am ^wn

Leakage from rivers ^

Leakage to rivers

T 

Leakage to general- g 

head boundaries °°

Leakage to drains

k

\

Figure 13. Diagrammatic section showing the model-calculated predevelopment water budget.
407.0

1,882.5

274.9

69.5

531.4

71.5

1,115.8

3,202.4

3,202.4

T

R

R

R

R

A \

8Lin I ** 

d

-1"

in

in 

in 1

k j

O5

CO I 

CO 1

285.1

iOL

39.7

O

1

00

in

L

1

1

CO

1 CM 

1 CM

G ^>16.2 

xj ,670.1 

D > T576.7

^^ ^^^^^1

S 11.7 is.

CM

CM 449.2

O

II °

I

^_ T

o

111

T 360

>14.4

> 225'2 T2,267.8

G ^312.2

-8 - 3 D>812'3__ 

en V4,1

8 t G

o 

> I gj 63" 1 °

§1 t

EXPLANATION 

(Units are cubic feet per second)

407.0 R

Recharge 

Leakage from rivers

Upward Downward

1,882.5 <\J R Leakage to rivers

Q r\ 162 Leakage to generalhead boundaries

D > 1 ,670.1 Leakage to drains

CO

I

, 160.6

C^j 

Figure 14. Diagrammatic section showing the model-calculated 1983-85 time-averaged w
For the 1983-85 period (fig. 14), recharge and 

discharge in the upland outcrop areas (drains and 

GHB's) from the upper Grande Ronde are nearly 

equal to the predevelopment values; this occurs even 

though the upper Grande Ronde was pumped at an 

average rate of 361 ft3/s during 1983-85. However, 

downward vertical leakage to the upper Grande 

Ronde in areas that are pumped increased by 206 ft 

while upward vertical flow decreased by 9 ft (figs. 

14 and 15). Most of this pumping generally is not in 

the peripheral outcrop areas (fig. 9), indicating again 

that regional flow from uplands to lowlands is limited. Most of the recharge in the uplands follows 

short flow paths to local discharge areas and is not 

significantly influenced by stresses in the lower-lying 

areas. Thus, the development of ground water from 

the Columbia River Basalt Group may be limited by 

relatively local ground-water recharge that leaks 

downward to the pumped aquifer. This is further 

indicated by the fact that simulated discharge to 

rivers and major streams from the upper Grande 

Ronde decreased by only 23 ft /s (about 2 percent of 

predevelopment river discharge).

For the Wanapum unit, discharge areas (drains 

and GHB's) are not as far from pumping areas as for 

the upper Grande Ronde (Hansen and others, 1994), 

and the effects of pumping on discharge to drains and 

GHB's are more pronounced. For example, drain and 

GHB discharge from the Wanapum unit declined by 

82 ft3/s (7 percent of predevelopment discharge to 

drains and GHB's). Recharge to the Wanapum unit 

increased by 83 ft3/s (figs. 13 and 14). Downward 

leakage from the Wanapum unit to the upper Grande 

Ronde increased by 191 ft3/s (26 percent), and 

upward leakage decreased by 23 ft3/s (3 percent; figs. 

13 and 14). Therefore, it appears that much of the 

additional recharge to the Wanapum unit became 

leakage to the upper Grande Ronde because the head 

in the upper Grande Ronde was lowered by pumping. 

These changes in the water budget indicate that, in 

general, pumping stress in a basalt unit will have a 

larger local effect on other units than it will have on 

the pumped unit at large distances.

The recharge-discharge relations and their 

changes from predevelopment to time-averaged 

conditions for the Saddle Mountains unit and the 

overburden aquifer are quite different from those of 

the Wanapum unit and upper Grande Ronde.

Whereas for the Wanapum unit and upper Grande 

Ronde, most of the discharge is from drains and 

GHB's in the upland areas, in the Saddle Mountains 

unit and overburden aquifer, for predevelopment conditions, most (85 percent for each) of the discharge is 

to the major rivers. This is because precipitation is 

much less in the central part of the region where 

those layers are at the surface, water levels are farther 

below land surface because of lower recharge, and 

ground-water flow is not drained by stream channels, 

as it is in the upland areas. These three conditions 

for the upper two units changed dramatically from 

predevelopment time. Recharge increased from 

119 ft3/s to 3,202 ft3/s to the overburden aquifer and 

from 133 ft3/s to 577 ft3/s to the Saddle Mountains 

unit (see figs. 13 and 14) because of the infiltration 

of irrigation water supplied primarily from the 

Columbia and Yakima Rivers and secondarily from 

the Umatilla and Walla Walla Rivers. As a result of 

this increase in recharge, discharge to drains and 

GHB's increased from 162 ft3/s to 1,686 ft3/s for the

n n

overburden aquifer and from 32 ft /s to 240 ft /s 

for the Saddle Mountains unit. The part of total 

discharge now going to drains and GHB's increased 

from 15 percent to 47 percent for the overburden 

aquifer and from 15 percent to 47 percent for the 

Saddle Mountains unit. Because of the increased 

recharge, and thus higher water levels in these two 

units, much of the additional recharge follows short 

flow paths to local discharge areas (farm drains and 

wasteways).

Both downward and upward flows between the 

overburden aquifer and the underlying basalt unit 

increased dramatically as a result of the large 

increase in recharge from surface-water irrigation. 

Downward flow increased from 82 ft3/s to 500 ft3/s, 

more than six-fold, while upward flow increased 

much less, from 578 ft3/s to 734 ft3/s. Upward flow 

for the predevelopment overburden aquifer was much 

greater than downward flow.

Downward and upward flows have also 

increased for the Saddle Mountains unit because of 

the effects of irrigation: from 88 ft3/s to 321 ft3/s, 

and from 503 ft3/s to 561 ft3/s, respectively. As with 

the overburden aquifer, upward flow for the predevelopment Saddle Mountains unit was much greater 

than downward flow.

38
For both the overburden aquifer and Saddle 

Mountains units, the increase in downward flow was 

much larger than the increase in upward flow. Some 

of the increased downward flow is accounted for by 

pumpage from lower units, and some is accounted 

for as increased discharge to rivers from the Saddle 

Mountains and Wanapum units.

Downward flow from the Wanapum unit to the 

upper Grande Ronde increased from 724 ft3/s to 

915 ft3/s, and upward flow decreased from 708 ft3/s 

to 685 ft3/s, resulting in a net downward leakage 

increase of 191 ft3/s. Virtually all of this increased 

leakage was accounted for by pumpage from the 

upper Grande Ronde, which reduced net discharge 

from and storage in the upper Grande Ronde. Flow 

to and from the lower Grande Ronde did not significantly change from predevelopment conditions.

Water Levels

The changes between simulated water levels for 

the 1983-85 time-averaged and simulated predevelopment water levels for all modeled units are shown 

on maps in Hansen and others (1994). Only a map of 

the Wanapum unit showing these water-level changes 

are presented in this report (fig. 15). For the overburden aquifer, which received the largest increase in 

recharge (3,083 ft3/s), the average simulated waterlevel rise was about 40 ft, equivalent to about 16 mi3 

of additional saturated aquifer. This change was the 

result of infiltration of applied surface water (average 

of about 4 ft/yr) to croplands (Bauer and Vaccaro, 

1990). The largest changes occurred in the CBIP, 

where, in some areas, water levels rose more than 

300 ft. In the wide, low-lying lower Yakima River 

Basin, where water levels already were near land 

surface, which is near river level, extensive surfacewater irrigation has caused water-level rises of only 

about 10 ft. Natural and artificial drains remove most 

of the additional recharge. Similarly, in the surfacewater-irrigated areas of Oregon, water-level rises 

have been small and moderated because land surface 

is near river level. Simulated water-level declines 

caused by pumping occurred in relatively few locations within the overburden aquifer. In the Wenas 

Creek Valley (tributary to the Yakima River), 

declines of only about 10 ft were simulated, but 

declines of as much as 40 ft were simulated along the 

eastern edge of the overburden aquifer in the Walla

Walla River Basin. In the remainder of the overburden aquifer in the Walla Walla River Basin, 

however, simulated rises ranged from 5 to 30 ft.

Water-level rises averaging about 65 ft were 

simulated throughout much of the Saddle Mountains 

unit. The largest rises occurred within the lower 

CBIP north of Pasco, Wash., where, in some areas, 

they exceeded 200 ft. As in the overburden aquifer, 

only small rises occurred in the Saddle Mountains 

unit where it underlies the valley floor in the Yakima 

River Basin; however, larger rises, in some areas 

exceeding 100 ft, occurred along the edges of the 

basin and within tributary valleys of the Yakima 

River where the top of the Saddle Mountains unit is 

well above river level. Rises also occurred along the 

Columbia River in both Oregon and Washington 

between the Umatilla River and Willow Creek. 

Water-level rises, caused by both surface-water 

irrigation and the construction of dams along the 

Columbia River, saturated an additional 23 mi3 of the 

Saddle Mountains Basalt compared with predevelopment conditions. Water-level declines were 

relatively small and localized, mainly in small 

valleys within the Yakima Fold Belt.

Simulated water-level changes in the Wanapum 

unit (fig. 15) were much more widespread than in the 

upper two units, mainly due to the much larger areal 

extent of the Wanapum unit. Again, water levels rose 

in areas of intensive surface-water irrigation~the 

Yakima River Valley, the CBIP, and parts of Oregon 

between the Umatilla River and Willow Creek. 

These rises averaged about 55 ft, but were as much as 

about 300 ft in the northwestern part of Quincy 

Basin. Simulated rises greater than 10 ft covered an 

area of about 3,900 mi2 (about 19 percent of the 

Wanapum unit).

Water-level declines greater than 10 ft were 

simulated over about 7,400 mi2 in the Wanapum unit 

(about 36 percent of the Wanapum unit). Simulated 

declines averaged about 60 ft and were more than 

200 ft in some areas. The largest declines occurred 

in the Odessa-Lind area, in some of the valleys in the 

Yakima Fold Belt, on the southern slope of Horse 

Heaven Hills, near Umatilla in Oregon, and in the 

Walla Walla River Basin. In several areas, the / 

declines were moderated by the rising water levels/m 

nearby surface-water irrigated areas. For example, 

water-level rises in the CBIP offset the water-level 

declines of the Odessa-Lind area just east of the East 

Low Canal. \

\

\

39
122° 120° 118°

48°

47°

46°

45°

116°

ITWASHING

IDAHO

0 20 40 60 80 100 MILES

I III I i I i I

I i i rr i

0 20 40 60 80 100 KILOMETERS

EXPLANATION

I Extent of ground-water model layer 3

n Area of thin or absent unit not included

u in ground-water model

1 Cell simulated as unsaturated

-100- Line of equal simulated water-level change.

Interval, in feet, is variable. Datum is sea level

Columbia Plateau aquifer system 

study area boundary

 State boundary

Figure 15. Simulated water-level changes in the Wanapum unit from predevelopment to current conditions.

40
Water levels in the upper Grande Ronde rose 

and declined over nearly equal areas. Rises averaged 

about 30 ft and declines about 35 ft. Maximum 

simulated rises and declines both exceeded 200 ft. 

The rises occurred in the surface-water-irrigated 

areas and along narrow strips of the dammed parts of 

the major rivers. The largest rises occurred in the 

northwest corner of the Quincy Basin. Declines were 

simulated in areas of ground-water pumping, mainly 

in the Odessa-Lind area in Washington and in the 

Umatilla area in Oregon. Smaller areas of decline 

were simulated in the Pullman-Moscow area and in 

the Horse Heaven Hills area.

The greatest simulated rises for the lower 

Grande Ronde, about 150 ft, were in northwestern 

Quincy Basin. Smaller rises were simulated in other 

surface-water-irrigated areas and along the major 

rivers. Declines as much as 170 ft were simulated for 

the Odessa-Lind area and as much as 50 ft for the 

Umatilla area. The distribution of simulated rises 

and declines for the lower Grande Ronde were similar to the upper Grand Ronde, but their magnitude 

was less. Declines in both layers of the Grande 

Ronde unit spread north and east from the OdessaLind area. The southern extent of simulated declines 

approximately coincides with the narrow east-west 

strip of low conductivity that acts as a barrier to 

ground-water flow, previously discussed.

Where historical water-level information is 

available, the model-calculated and observed waterlevel changes are similar (Hansen and others, 1994). 

It is therefore assumed that the ground-water levels 

in unmonitored areas are also reasonably simulated 

and that the ground-water budgets presented in the 

previous section are also reasonable.

Ground-Water Discharge

Results of the model simulation indicate that 

ground-water discharge to 16 of the 27 selected 

basins with streamflow data (table 2) and 14 of the 16 

selected river reaches (table 4) has changed significantly (more than 1.0 ft3/s change) from predevelopment to 1983-85 conditions.

Simulated discharge to 14 of the selected drainage basins significantly decreased. The largest 

percentage decreases (in excess of 40 percent) in

ground-water discharge were in Cow Creek, Crab 

Creek, Bowers Coulee, and South Fork Palouse River 

Basins. Ground-water discharge in Cow Creek Basin 

decreased from about 41 ft3/s under predevelopment 

conditions to about 23 ft3/s under current conditions. 

Similarly, the discharge in Crab Creek Basin 

decreased by about 38 ft3/s, from 63 ft3/s to 25 ft3/s. 

Only Glade Creek Basin showed percentage increase 

of more than 40 percent, which is due to surfacewater irrigation.

Simulated ground-water discharge to 7 of the 16 

selected river reaches increased by more than 40 

percent because of water development (table 4). 

Ground-water discharge to the upper Yakima River 

increased from 185 ft3/s to 304 ft3/s, and to the lower 

Yakima River, from 45 ft3/s to 425 ft3/s. The upper 

Columbia River received an additional 540 ft3/s 

under 1983-85 conditions when compared to predevelopment conditions; this increase is a direct result 

of the rise in water levels in the CBIP caused by 

surface-water irrigation (its delivery, leakage, and 

application). Simulated discharge in the Rocky 

Ford-Crab Creek area (located in the vicinity of 

Potholes Reservoir and Moses Lake, figs. 2 and 12) 

increased from 11 ft /s to 91 ft /s, and discharge in 

lower Crab Creek increased from 76 ft3/s to 145 ft3/s. 

Again, this increased discharge was due to the delivery, leakage, and application of surface water in the 

CBIP. Unlike the drainage basins, ground-water 

discharge to the stream reaches showed no decreases 

in excess of 40 percent.

Potential Future Effects of Current 

Ground-Water Development

A steady-state simulation was made in order to 

estimate the potential future changes to the 1983-85 

flow system assuming no change in 1983-85 pumpage and recharge. The future equilibrium flow 

system was simulated by eliminating the 1983-85 

rate of ground-water storage change from the pumpage array (see "Simulation of Ground-Water Flow" 

section). No estimates were made of the rate at 

which the long-term changes from 1983-85 to equilibrium conditions will occur. Water-level changes 

are first described below and then the changes in the 

water budget are described.

41
Table ^.--Comparison of ground-water discharge to selected river reaches for the various simulations 

[Values in cubic feet per second; CBIP = Columbia Basin Irrigation Project]

Stream reach

Upper Columbia River 

Snake River

Lower Yakima River

Lower Columbia River

Upper Yakima River 

Klickitat River

Palouse River

Lower Crab Creek

Walla Walla River

Naches River

Rocky-Ford Creek 

Grande Ronde River

Spokane River 

Deschutes River

John Day River 

Moses Coulee

Predevelopment

291.1 

491.1

45.3

383.9

185.4 

217.2

160.4

76.3

72.1

54.7

10.8 

74.0

52.4 

47.4

42.5 

11.5

1983-85 

timeaveraged

831.4 

435.5

424.8

354.1

303.8 

225.7

164.3

145.1

115.3

97.5

90.9 

74.0

51.5 

50.6

45.9 

9.8

1983-85 

equilibrium

827.1 

428.0

417.9

333.6

303.4 

225.7

140.5

140.3

114.6

95.7

87.6 

74.0

51.4 

50.4

45.6 

9.2

Phase 1 CBIP expansion

1983-85

pumpage

840.8 

433.0

418.2

333.7

303.4 

225.7

142.6

144.6

114.8

95.7

98.5 

74.0

51.4 

50.4

45.6 

9.2

reduced

pumpage

842.6 

434.9

418.3

333.7

303.4 

225.7

144.0

146.9

114.9

95.7

104.7 

74.0

51.4 

50.4

45.6 

9.2

Phases 1 and 2

CBIP expansion

1983-85

pumpage

850.6 

449.0

418.9

333.8

303.4 

225.7

150.1

152.2

115.3

95.7

103.1 

74.0

51.4 

50.4

45.6 

9.2

reduced

pumpage

857.4 

456.1

419.4

334.1

303.4 

225.7

158.1

162.8

115.5

95.7

114.3 

74.0

51.4 

50.4

45.6 

9.3

Simulated water-level changes for the four 

basalt units from 1983-85 conditions to potential 

future equilibrium conditions caused by average 

1983-85 stresses indicate large water-level declines 

may occur in the future. Changes for the overburden 

aquifer generally were less than 10 ft and are not 

shown. The greatest simulated declines were in the 

Wanapum unit (fig. 16), and the most widespread 

simulated declines occur about equally in the 

Wanapum unit and upper Grande Ronde throughout 

roughly the same areas.

Although water-level declines were generally 

less than 200 ft, some localized large declines, more 

than 400 ft in the Wanapum unit, were simulated in 

the central part of Horse Heaven Hills, centered 

around large pumping centers. Additionally, three 

Wanapum unit cells and four Saddle Mountains unit 

cells were simulated to desaturate. The probable 

reason for such large declines in this area is that the 

east-west-trending crest of the Horse Heaven Hills 

anticline, which is a barrier to ground-water inflow 

from the north, (fig. 6) lies only 5 to 10 miles north 

and northwest and upgradient from the pumping 

areas. Furthermore, the area to the south and east 

(downgradient) of the pumping centers receives little

recharge and is hydraulically separated from this area 

by a ground-water impediment of uncertain origin 

(Packard and others, 1996). Only to the west and 

northwest are there areas of significant recharge that 

are hydraulically connected to the aquifers in the 

pumping area. About 8 mi northeast of Yakima, in a 

ground-water-irrigated valley, large water-level 

declines in the Saddle Mountains and Wanapum units 

were simulated. Additionally, four pumped cells in 

the Wanapum unit and five pumped cells in the 

Saddle Mountains unit desaturated. The valley is 

bounded to the north and south by sharp east-westtrending anticlines. The anticlines greatly impede 

inflow from all units from the north and south. 

Therefore, inflow must occur mainly upvalley from 

the east and from the flanks of the anticlines rising 

from the valley floor. Because the upgradient 

ground-water drainage area is quite small, local 

recharge is insufficient to replace the quantity 

pumped.

On the basis of the simulations, these two areas 

will have the largest water-level declines in the study 

area, even though the total quantities of pumpage 

from these areas is small compared with other areas 

of concentrated pumping (fig. 9).

42
122° 120° 118° 116°

48°

47°

46°

45°

WASHINGTON

IDAHO

0 20 40 60 80 100 MILES

I i I i I I I i I i I

I i \ rr T

0 20 40 60 80 100 KILOMETERS

EXPLANATION

|| Extent of ground-water model layer 3

n Area of thin or absent unit not included in

u ground-water model

 Columbia Plateau aquifer system 

study area boundary

 State boundary

 -w Line of equal simulated water-level decline

(negative values). Interval, in feet, is variable

 Cell simulated as unsaturated, 

both simulations

* Cell simulated as unsaturated, 1983-85 

predevelopment simulation only

Figure 16. Simulated future water-level changes in the Wanapum unit from predevelopment to current conditions.

43
In other areas where much larger quantities of 

ground water are pumped, no or only slight future 

declines were simulated because of their proximity to 

areas of surface-water irrigation and thus large 

quantities of recharge. During 1983-85, water levels 

appeared to be stable in the Yakima, Pasco, MiltonFreewater-Walla Walla, and Black Sands (Quincy 

Basin) areas. For these areas, no change in storage 

was added to the pumpage term for the timeaveraged simulations, and therefore the future 

equilibrium (steady-state) simulation produced about 

the same water levels. For example, just north and 

west and upgradient of the Black Sands area, which 

lies within the Quincy Basin just west of Potholes 

Reservoir, imported surface water for the CBIP 

provides more than enough recharge to support the 

current pumping rate. A similar situation exists 

along a north-south-trending area fringing the eastern 

extent of the CBIP. Water levels generally are stable 

over most of this fringe area except northwest of 

Connell, where irrigation blocks served by the CBIP 

are fragmented and pumpage is locally large. Unlike 

the Black Sands area, however, the large quantities of 

recharge in the CBIP are generally downgradient 

from the pumped areas. As a consequence, this area 

of large pumpage and stable water levels is much 

narrower than the Black Sands area.

Future simulated water-level declines are small 

in a few areas with relatively large quantities of 

pumpage and no surface-water irrigation. The 

Pendleton area has had water-level declines in the 

past, but simulated water levels stabilized because of 

the area's proximity to the abundant recharge (lateral 

inflow) from the Blue Mountains to the southeast. 

This result is in approximate agreement with estimates made by Davies-Smith and others (1988). For 

the Pullman area, future declines of about 10 ft were 

simulated, suggesting that recharge estimated for the 

Pullman area is sufficient to supply 1983-85 pumping 

rates. These results are in approximate agreement 

with those of Lum and others (1990), who estimated 

rapid adjustments to pumping stresses. Pullman 

is near where the basalts pinch out against lowpermeability crystalline rocks to the east and north, 

and the regional ground-water gradient is to the south 

and west. The area affected by pumping, therefore, 

is small and rapidly approaches steady-state conditions. The area southwest of Spokane has had no 

large water-level declines in the past. Recharge in

this area appears to be adequate to supply most of the 

1983-85 pumping rates. However, areas to the west, 

near Davenport, had simulated declines, probably 

because the basalts tend to pinch out against the 

impermeable basement rocks a few miles to the 

north.

Generally, moderate but areally widespread 

future declines were simulated for two large areas. 

In the Odessa-Lind area, which is east of the stable 

CBIP eastern fringe, a large quantity of ground water 

is used for irrigation (Cline, 1984; Cline and Knadle, 

1990; and Cline and Collins, 1992) and there is a 

demand for additional ground water. In this area, 

simulated declines in the Wanapum unit were generally between 10 ft and 100 ft and occurred mainly 

south of Crab Creek. Locally, declines as much as 

200 ft were simulated and some areas (represented 

by 25 Wanapum cells) desaturated (fig. 16). Simulated future declines in the upper and lower Grande 

Ronde were more areally widespread, but generally 

were less than 50 ft. Declines of about 10 ft in the 

upper and lower Grande Ronde extended to the 

northern boundary of the model.

The second area where moderate but widespread future declines were simulated was the area 

around Hermiston, Oreg. In this area, total ground 

pumping for irrigation is about 113 ft3/s (Collins, 

1987). Declines, ranging between 10 ft and 50 ft, 

were simulated for both the Wanapum unit and the 

upper Grande Ronde. Simulated declines in the 

Saddle Mountains unit were slightly smaller and 

were concentrated more to the north. Although the 

rate of pumping compared with natural recharge 

from precipitation in this area is similar to that of the 

Odessa-Lind area, simulated declines were considerably less because of recharge from surface-watersupplied irrigation from the Umatilla River. In 

addition, 29 ft /s net leakage was simulated from the 

lower Umatilla River into the overburden aquifer, 

through which it moves westward and downward 

into the basalts.

As the aquifer system comes to a new steady 

state under future equilibrium conditions, flows 

between layers and discharge to rivers, drains, and 

GHB's will reach new equilibrium values. Total 

discharge to surface-water bodies was simulated to 

decrease from the estimated 1983-85 rates because 

none of the pumped water will come from storage.

44
Net decrease in discharge to the rivers was simulated 

to be 79 ft3/s, or about 2 percent of the 1983-85 total. 

Decrease in drain and GHB discharge was 47 ft3/s 

(about 1 percent of 1983-85 drain discharge) and 

1.7 ft3/s (less than 1 percent of 1983-85 GHB 

discharge), respectively.

On average, simulated long-term decreases from 

1983-85 stream baseflows due to 1983-85 pumpage 

are small. Locally, however, the simulation results 

indicate that reductions in the baseflow of some 

streams would probably be noticeable. Baseflow in 

the Cow Creek Basin decreased from 23 ft3/s to 

11 ft3/s, which is the greatest relative decrease of 

baseflow of the 43 basins and river reaches analyzed 

(see tables 2 and 4). Simulated ground-water 

discharge in the Crab Creek Basin and the Palouse 

River reach decreased from 25 ft3/s to 21 ft3/s and 

from 164 ft3/s to 140 ft3/s, respectively. These three 

areas are adjacent to and overlap onto the OdessaLind pumping area, which, as previously mentioned, 

was simulated to have future water-level declines 

from the 1983-85 conditions.

Reductions of ground-water discharge to the 

lower Columbia and Snake Rivers ranged from 

354 ft3/s to 334 ft3/s and from 435 ft3/s to 428 ft3/s, 

respectively, and discharge to the Umatilla River 

Basin was reduced from 556 ft3/s to 549 ft3/s, all of 

which are minor quantities in comparison to the 

streamflow in those rivers. Ground-water discharge 

to the remaining 37 basins and river reaches analyzed 

generally was unaffected (tables 2 and 4).

Potential Effects of Proposed Expansion 

of the Columbia Basin Irrigation Project 

(CBIP)

The CBIP originally was authorized for the 

development of 1,095,000 acres of irrigated lands 

that were to receive Columbia River water; about 

556,000 acres are currently developed. Under the 

proposed expansion, the remaining 539,000 acres 

would be developed in two phases, with several 

proposed alternatives for each phase (Water Conservation Steering Committee, 1987). The authors 

chose to simulate the effects of potential development under Alternative A, Phase 1 and Phase 2, 

which adds 160,000 and 379,000 acres, respectively, 

for the total of 539,000 acres. Simulations were

made for Phase 1 and Phases 1 and 2. The total 

expansion area covers most of the Odessa-Lind 

pumping area.

In areas where the CBIP currently furnishes 

water for irrigation, the USER has mandated that 

CBIP water be the only source of irrigation water. 

Therefore, on the basis of prior policy, ground-water 

pumping rates will decline with the proposed expansion as farmers switch over to the new surface-water 

supply. To account for this in the simulations, for 

each cell it was assumed that pumpage will decline in 

proportion to the area served by new CBIP water: 

For example, where the CBIP would serve 25 percent 

of the area represented by a cell, the pumping rate 

was assumed to be 75 percent of the 1983-85 rate. 

Two additional scenarios using the current pumping 

rate also were simulated under Phase 1 and Phases 1 

and 2. Therefore, four simulations are described 

below: Phase 1 with reduced pumpage, Phase 1 with 

the 1983-85 pumping rate, Phases 1 and 2 with 

reduced pumpage, and Phases 1 and 2 with the 

1983-85 pumping rate. The effects on each aquifer 

unit are described but only the effects on the 

Wanapum unit water levels, which had the most 

extensive simulated changes, are presented on a map 

(see fig. 19).

All scenarios were simulated using an annual 

surface-water irrigation application rate of 4.0 ft/yr, 

the recent average rate for the currently operating 

CBIP. Recharge to those cells caused by the infiltration of this surface water was estimated from the 

information presented by Bauer and Vaccaro (1990). 

As a result, it was estimated that recharge would 

increase by about 330 ft3/s for Phase 1 only, and by 

974 ft3/s for both phases. The distribution of the estimates of the increase in recharge for the two phases 

are shown on figures 17 and 18. Additionally, on the 

basis of the observed historical water-level rises in 

the existing CBIP, drains were added at every model 

cell with new surface-water application so that simulated water levels would not rise above land surface. 

Climate and current (1980's) water-development 

practices were assumed to be invariant for the scenarios and, because the simulations were steady state, 

the rate at which the simulated changes occur was 

not estimated. In fact, in the following discussions, 

the simulated changes are not compared with 

1983-85 conditions, but are compared with the future 

equilibrium conditions resulting from current

45
122° 120° 118° 116°

48°

47°

46°

45°

WASHINGTON 

\

fj

rv^'

I ~^ OREGON

J J V_ S

IDAHO

20 40

I

60

I

80 100 MILES

I i I

I I I I I I 

0 20 40 60 80 100 KILOMETERS

EXPLANATION

1 | Extent of ground-water model

Columbia Plateau aquifer system 

study area boundary

State boundary

Additional recharge, 

in inches per year

D 0 to 2

i 2 to 4

i 4 to 8

i 8 to 12

i 12 to 16

I Greater than 16

Figure 17. Distribution of estimated increase in recharge resulting from proposed expansion of the Columbia Basin 

Irrigation Project for Phase 1.

46
122° 120° 118° 116°

48°

47°

46°

45°

WASHINGTON

IDAHO

"V.--,

0 20 40 60 80 100 MILES

I III I i I i I

I 1 \ T \ 1

0 20 40 60 60 100 KILOMETERS

EXPLANATION

Extent of ground-water model Additional recharge,

in inches per year

Columbia Plateau aquifer system n 0 to 2 

study area boundary I 2 to 4

I 4 to 8

State boundary 8 to 12

* I 12 to 16

I Greater than 16

Figure 18. Distribution of estimated increase in recharge resulting from proposed expansion of the Columbia Basin 

Irrigation Project for Phases 1 and 2.

47
(1983-85) stresses. In this way, the future long-term 

effects of additional surface-water irrigation are 

isolated.

The simulated water-level rises (there are no 

declines) from future equilibrium conditions that 

result from the proposed CBIP Phase 1 expansion 

were greatest in the uppermost unit in the newly 

irrigated areas. Simulated water-level rises in the 

overburden aquifer, Saddle Mountains unit, and 

Wanapum unit were virtually identical for both 

pumping scenarios. The quantity of additional 

recharge to these units is far greater than the unit's 

ability to laterally transmit this extra water and the 

quantity of ground water removed by pumping is too 

small to prevent water-level rises; as a result, ground 

water rises to just below land surface, where it 

discharges to drains.

In the overburden aquifer, the largest rises, as 

much as about 50 ft, were simulated in the central 

Quincy Basin. The areal extent of these rises was 

limited to that of the irrigation expansion in this area; 

this is because the surrounding areas currently have 

both surface-water irrigation and farm drains, and the 

water levels are already at or near land surface.

For the Phase 1 expansion scenarios, water-level 

rises of more than 50 ft in the Saddle Mountains unit 

were limited to a small area in the northeastern part 

of the unit and did not exceed about 100 ft. Additionally, 14 model cells in the Saddle Mountains unit 

in the vicinity of this area were simulated to be 

saturated; whereas in the simulation of the future 

equilibrium conditions they were not.

The largest water-level rises occurred in the 

Wanapum unit; maximum water-level rises were 

about 400 ft and roughly coincided with the centers 

of the two main expansion areas of Phase 1 (fig. 19). 

The location of simulated water-level rises in the 

Wanapum unit extended beyond the expansion areas, 

especially in the southeastern part where water-level 

rises of 50 ft or more extended up to about 15 mi 

beyond the expansion area. For the larger northeastern part of the Phase 1 expansion, the areal extent of 

water-level rises in the Wanapum unit was smaller; 

water-level rises of 50 ft or more extended only as 

much as about 7 mi south and east of the expansion, 

and to the north and west of the expansion there were 

almost no rises. To the west, water levels in the 

Wanapum unit were already near land surface, and

any additional inflow of ground water would merely 

discharge to drains. To the north, the Wanapum unit 

is deeply cut by Crab Creek, thereby limiting 

water-level rises north of Crab Creek.

Simulated water levels were almost invariably 

within a few tens of feet of land surface in the unit 

that is closest to land surface in the areas of new 

irrigation. Thus, water logging is likely to occur in 

most areas of the proposed expansion unless farm 

drains also are constructed.

Water-level rises in the underlying upper and 

lower Grande Ronde layers generally were much less 

but more widespread than in the other layers. For 

example, for both pumping scenarios of Phase 1, 

water-level rises of more than 10 ft occurred throughout about twice as much area as for the Wanapum 

unit. However, areas with larger rises in the Grande 

Ronde unit than in the Wanapum unit extend only 

upgradient, to the north and northwest; this is probably because of the east-west strip of low conductivity 

north of the Big Bend area, described previously. For 

the reduced pumping scenario, water-level rises of 

more than 50 ft were less widespread (about half the 

area as for the Wanapum unit). For the 1983-85 

pumping scenario, there were almost no areas of 

water-level rises greater than 50 ft.

For the reduced pumping scenario of Phase 1, 

maximum water-level rises in the upper and lower 

Grande Ronde were about 100 and 50 ft, respectively. For the current pumping scenario, maximum 

water-level rises in the upper and lower Grande 

Ronde were about 50 and 35 ft, respectively. Thus, 

for the Grande Ronde unit, the quantity of pumpage 

is an important control on water levels, even though 

recharge to the overlying units is at its maximum. 

This is because recharge to the unit must move 

through all of the overlying materials and is thus 

limited by the vertical conductivity of either 

fine-grained interbeds or the basalt flow centers.

Simulated water-level rises, relative to future 

equilibrium conditions, resulting from the proposed 

CBIP irrigation expansion, Phases 1 and 2, are 

typical of those for the Wanapum unit (fig. 20). 

Comparing figures 19 and 20 indicates that the 

conclusions regarding the simulated effects of Phase 

1 only are also applicable to the effects of Phases 1 

and 2: where there is new irrigation, water levels 

rose within a few feet of land surface and the largest

48
122° 120° 118° 116°

48° -

47° -

46° -

45° -

EXPLANATION 20 40 60 80 100 KILOMETERS

f I 

(~|

Extent of ground-water model layer 3

Area of thin or absent unit not included in 

ground-water model

Columbia Plateau aquifer system 

study area boundary

State boundary

Line of equal simulated water-level rise, 

1963-85 pumpage. Interval, in feet, is variable

 «> Line of equal simulated water-level rise,

reduced pumpage. Interval, in feet, is variable

« Cell simulated as unsaturated, 

both simulations

 Cell simulated as unsaturated,

1983-85 equilibrium simulation only

Figure 19. Simulated water-level rises in the Wanapum unit under future equilibrium conditions resulting from the 

proposed expansion of the Columbia Basin Irrigation Project, Phasel.

49
EXPLANATION

i i i r

0 20 40 60 80 100 KILOMETERS

I | Extent of ground-water model layer 3

[~| Area of thin or absent unit not included in 

ground-water model

 Columbia Plateau aquifer system 

study area boundary

 State boundary

 <o Line of equal simulated water-level rise,

1963-85 pumpage. Interval, in feet, is variable

-'<> Line of equal simulated water-level rise,

reduced pumpage. Interval, in feet, is variable

 Cell simulated as unsaturated, 

both simulations

* Cell simulated as unsaturated,

1983-85 equilibrium simulation only

Figure 20. Simulated water-level rises in the Wanapum unit under future equilibrium conditions resulting from the 

proposed expansion of the Columbia Basin Irrigation Project, Phases 1 and 2.

50
effects were in the Wanapum unit. Water-level rises 

in the overburden aquifer were nearly identical to 

those for Phase 1 because additional irrigation under 

Phase 2 is only in areas east of the Quincy Basin 

where the overburden aquifer is absent.

Water-level rises of more than 110 ft were simulated at the easternmost part of the Saddle Mountains 

unit. Moreover, 32 model cells in the Saddle Mountains unit became saturated. Maximum water-level 

rises of about 600 ft were simulated in the Wanapum 

unit (fig. 20). These maximum rises occurred in 

about the center of the main part of the new irrigation 

area that is east of the East Low Canal; this was the 

area with the large simulated water-level declines 

under future-equilibrium conditions (fig. 17). Waterlevel rises of more than 50 ft in the Wanapum unit 

extended from this main part as much as 20 mi 

upgradient to the northeast and as much as 17 mi 

downgradient to the southwest. Westward and northward extension of water-level rises in the Wanapum 

unit were limited for the same reasons given for 

Phase 1 only.

Water-level rises in both the upper and lower 

Grande Ronde were more widespread and of greater 

magnitude than those simulated under Phase 1 for 

both pumping scenarios. For example, for the 

reduced pumping scenario, water-level rises of more 

than 50 ft in the upper Grande Ronde covered a 

roughly circular area of about 65 mi in diameter 

(about three times as great as for Phase 1), and maximum rises were about 300 ft (compared with 100 ft 

for Phase 1 only). For the 1983-85 pumping 

scenario, water-level rises in the upper Grande Ronde 

of more than 50 ft covered a roughly circular area of 

about 40 mi in diameter, whereas Phase 1 had almost 

no areas with rises of greater than 50 ft. For both 

pumping scenarios, water-level rises in the lower 

Grande Ronde of more than 50 ft covered an area 

almost identical to that for the upper Grande Ronde. 

The area of water-level rises was more than three 

times that of the reduced pumping scenario and more 

than two times that of the 1983-85 pumping scenario 

of Phase 1. Thus, for the Grande Ronde unit, both 

the area served by new irrigation and the quantity of 

future pumpage were critical to the configuration of 

future water levels. Moreover, for any particular 

scenario, the upper and lower Grande Ronde layers 

are affected to about the same magnitude and extent.

Both phases of the CBIP simulations show that 

most changes to the ground-water flow system would 

be within the proposed expansion areas. In the 

reduced pumping scenario, the increased discharge to 

drains would be 114 percent and 109 percent of the 

increased recharge for Phase 1 and Phases 1 and 2, 

respectively. The simulations show that most of the 

new recharge would follow short flow paths to 

nearby drains; also, discharge from drains would 

increase where water levels rise because of reduced 

pumping rates. Where pumpage is reduced in the 

units underlying the uppermost unit, water levels 

would rise. This rise would increase the upward flow 

to the upper units, for eventual discharge to drains. 

In the 1983-85 pumping rate scenario, the increased 

discharge to drains would be 82 and 88 percent of the 

increase in recharge for Phase 1 and Phases 1 and 2, 

respectively.

Quantities of recharge and discharge simulated 

for Phase 1 and Phases 1 and 2 for each pumping 

scenario are shown in table 3. The simulated 

changes in the water budget from future equilibrium 

conditions resulting from the proposed CBIP irrigation expansion for Phase 1 and Phases 1 and 2 

(reduced pumping scenario) are shown in diagrammatic sections in figures 21 and 22, respectively. The 

greatest changes for both phases were in the 

Wanapum unit, because it directly underlies a veneer 

of loess over most of the CBIP expansion areas. For 

the reduced pumping scenario, 78 percent of the 

additional recharge to the Wanapum unit would 

discharge locally to drains for Phase 1 and 99 percent 

for Phases 1 and 2. For the overburden aquifer, drain 

discharge exceeded the increased recharge for both 

phases and both pumping scenarios.

For the reduced pumping scenario, the amount 

of change in the vertical flow between layers is much 

smaller than the increased recharge. For Phase 1, 

recharge to the Wanapum unit increased by 227 ft3/s; 

downward flow from the Wanapum unit increased by 

only 8 ft3/s, and upward flow from the Grande Ronde 

unit by only 14 ft /s. For Phases 1 and 2, the increase

o

in recharge to the Wanapum unit was 750 ft /s; 

downward flow from the Wanapum unit decreased by 

1 ft3/s, and upward flow from the Grande Ronde unit 

increased by 55 ft3/s.

51
86.6

-0.1 ^

^

12.7 <^ 

-0.2 ^

4.1 <

-3.8 ^

19.8 ^

14.9 <^^s

R

R

R

R

-49.1

r

T J L J

CO

!"'

il r.

^f-

$2|

I ^

L

3

0.0

O

1

d

!

L

^ 

1

_ .

G > -0.1

\171.5 

D ' T 1.9

f G > 0.0 

q

CO m

CO

1 r 

2 -33.8

O

r i

U D>10.5

f

o 

d

I °°

r X 

f -37.5 T

O I CO

1 ^i

sl t

86.6

^F Recharge

EXPLANATION

(Units are cubic feet per second)

226.7

G > 3.7

_ \1785 D >l/0-^ 

V16.9

G ^> 

D ^> 

<r

Downward Upward -49.1

^ " ^

-0.1 ^ R Leakage from rivers ^ ^

12.7 <CJ R Leakage to rivers

CD CO

_ r\ . Leakage to general- ^ cd G .x-0.1 '

^ head boundaries

D r> 171.5 Leakage to drains v

() P

Figure 21. Diagrammatic section showing simulated water-budget changes from future equilibrium con

from the proposed expansion of the Columbia Basin Irrigation Project, Phase 1.
94.4

-0.5^

30.1 <^ 

-0.9^

17.1 <

10.0^

26.5^

34.9 <^

R

R

R

R

49- 1 G > 0.0

4±\

iU

fCO ' ^j

-tsi

v_>/ CM n ^!^2;£ 

^ T V 113.3

°A »J °>o.o 

w ?

I °^ D ^ 95.5

j L I

i r X 

2 -81 .2 o

T X-N O

O

V 750.5

 ir v ^

T T -121.6 T

o

G

D

>5.5

\745.8

1 1?

si t

EXPLANATION

^15.0

G

D

>0.2

^> 20.8

(Units are cubic feet per second)

94.4

^^ Recharge Downward Upward

-0.5 ^^ Leakage from rivers t

30.1 <J Leakage to rivers

G f^> 0.0 Leakage to general- o ^

head boundaries ^~

D r> 1 98.2 Leakage to drains ^ r

-49.1

o Pumpage

Figure 22. Diagrammatic section showing simulated water-budget changes from future equilibrium con

expansion of the Columbia Basin Irrigation Project, Phases 1 and 2.
SUMMARY AND CONCLUSIONS

A study of the aquifers in both basalt rocks and 

overlying unconsolidated sediments of the Columbia 

Plateau was undertaken as part of the U.S. Geological Survey's Regional Aquifer-System Analysis 

program. In order to obtain a better understanding of 

-the area's water budget, to provide capabilities for 

assessment of management alternatives, and to 

improve the understanding of the regional groundwater flow system, a three-dimensional finitedifference numerical model of ground-water flow 

was constructed and used. The model was used to 

quantify both the components of the ground-water 

flow system and the effects of current and potential 

future stresses on the aquifer system.

Regional ground-water flow in the study area 

generally is from upland peripheral areas, where 

recharge from precipitation ranges from about 4 to 

more than 10 in/yr, toward the Columbia and Snake 

Rivers where they cut through the low-lying central 

part of the study area. Most ground water originating 

in the uplands discharges locally to small streams. 

Natural recharge from precipitation in the low-lying 

areas is generally less than 1 in/yr, but where there is 

extensive surface-water-supplied irrigation, recharge 

has increased to more than 10 in/yr. Water levels are 

only a few feet below land surface in these areas. 

Ground-water pumping for irrigation from the basalt 

aquifers has caused declines of more than 200 ft.

The aquifer system was discretized into five 

layers for modeling purposes; one for the overlying 

unconsolidated sediments representing the overburden aquifer, one for the Saddle Mountains Basalt 

plus minor amounts of intercalated and immediately 

underlying sedimentary interbeds, one for the 

Wanapum Basalt including immediately underlying 

sedimentary interbeds, and two for the Grande Ronde 

Basalt. The Grande Ronde Basalt, which is generally 

much thicker than any of the overlying units, was 

divided into two layers to better simulate vertical 

variation of head. The aquifer system within the 

modeled area underlies 32,688 square miles and was 

discretized into 17,899 cells, each of which covers 

2.5 minutes of latitude and 2.0 minutes of longitude 

with an average area of about 4.67 mi .

Boundary conditions for the model consisted 

of no-flow boundaries, where the Columbia River 

Basalt Group pinches out against older rock of low

permeability, and head-dependent flux boundaries at 

rivers, streams, canyon walls, farm drains, and wasteways. Hydraulic characteristics were initially 

estimated from specific-capacity data, published 

reports, and ongoing investigations. Long-term average ground-water recharge for both predevelopment 

(1850's) and current (1980's) land-use conditions was 

independently estimated for 53 drainage basins and 

subareas within the study area using a soil moisture 

budgeting model. For the remainder of the area, 

recharge was estimated using a regression equation 

relating long-term average annual precipitation to 

long-term average annual recharge on the basis of the 

results of the soil moisture model for the 53 areas. 

Total recharge to the aquifer system was estimated to 

be 10,205 ft*/s during 1983-85. Ground-water 

pumping was independently estimated for 1983 and 

1984 and the average during 1983-85 was about 

I,135ft3/s.

The ground-water flow model was calibrated to 

the observed water levels for the period spring 1983 

to spring 1985. These water levels were not yet at 

equilibrium but were simulated as such by using the 

average of the 1983-85 conditions and by incorporating changes in ground-water storage during this 

period into a source term of the numerical model.

Calibration of the model resulted in distributions of lateral and vertical hydraulic conductivities 

that were not evident in the specific-capacity data. In 

order to reasonably simulate water levels in the basalt 

units, much smaller lateral and vertical hydraulic 

conductivities were required in uplifted anticlinal and 

monoclinal areas, whereas, much larger values were 

required in discharge areas. Smaller hydraulic 

conductivities in the uplands are possibly due to the 

numerous faulted offsets of the more permeable but 

thin interflow zones. Large, apparent vertical 

hydraulic conductivities beneath major rivers may, in 

part, be due to unmapped deeply incised channels 

that have been back-filled with coarse material.

Calibrated lateral hydraulic conductivities for 

the basalts ranged from about 10"6 to 10"4 ft/s and 

have a median of about 1.7xlO~5 ft/s. This median is 

about the 30th percentile of the values computed 

from specific-capacity data. Calibrated lateral 

hydraulic conductivities for the overburden aquifer 

ranged from about 5x10~7 to 1.3x10 ft/s and have a 

median of about 5x10~4 ft/s. The median of values 

computed from the specific-capacity data is about

54
"5

2.8x10 ft/s. Median values for the calibrated vertical conductances between layers are, from top to 

bottom, 2.6xlO-8 s' 1 , 2xl(Tlf s-1 , 6xlO' 12 s' 1 , and 

5x10 s . The unconfined storage coefficient for 

the basalts, where water-level changes were 

observed, was calibrated at 0.04. A storage coefficient for the overburden aquifer was not determined 

because this unit was at approximate equilibrium for 

the time-averaged simulation.

The model reasonably simulates the observed 

and estimated water levels. Accuracy is diminished 

in the steep-terrain areas where lateral head changes 

can approach 600 ft over a model cell. However, 

calculated heads in the steep terrain areas may be 

more representative of the vertically averaged head 

over a unit's thickness than are the observed water 

levels that are mostly from shallow wells. Root mean 

square residuals for cells with observation wells, 

from layer 1 to layer 4, were 58, 91, 142, and 253 ft, 

respectively.

The model was used to estimate the regional 

ground-water budget for 1983-85 conditions using 

the independent estimates of recharge (10,205 ft3/s) 

and pumpage (1,135 ft3/s). Leakage to drains, which 

generally were used to represent small perennial and 

intermittent streams, was the largest discharge 

component at 5,596 ft3/s. Leakage to rivers was 

3,804 ft3/s and is the next largest discharge component. Leakage to general head boundaries, which 

represent seepage faces where a unit is completely 

truncated, was only 423 ft3/s. The rate of change in 

storage based on water-level declines from 1983 to 

1985 was about 187 ft3/s. Of the total recharge, 

4,161 ft3/s recharged the upper Grande Ronde; this 

layer mainly crops out in the upland and peripheral 

areas of the plateau. Discharge to drains in the upper 

Grande Ronde unit was about 2,888 ft3/s. Thus, 

most of the recharge in upland and peripheral areas 

follows short flow paths and discharges to nearby 

streams and canyons.

After the time-averaged steady-state model was 

calibrated, six other simulations were completed: 

(1) predevelopment (1850's) conditions, (2) future 

equilibrium conditions with 1983-85 stresses, 

(3) Phase 1 expansion of the CBIP retaining 1983-85 

pumpage, (4) Phase 1 expansion of the CBIP with 

reduced 1983-85 pumpage, (5) Phases 1 and 2 expansion of the CBIP retaining 1983-85 pumpage, and 

(6) Phases 1 and 2 expansion of the CBIP with 

reduced 1983-85 pumpage.

The most pronounced change in the regional 

ground-water flow system from predevelopment to 

1983-85 conditions is a rise in water levels in areas 

irrigated by surface water. In the overburden aquifer, 

the average of the simulated water-level rises is about 

40 ft, with a maximum of more than 200 ft in northern Quincy Basin, Wash. For the Saddle Mountains 

unit, simulated water-level rises average about 65 ft, 

with a maximum of more than 200 ft in the southern 

CBIP, north of Pasco, Wash. An additional 23 mi3 of 

the Saddle Mountains unit has been saturated in the 

areas of water-level rises. Only small, localized 

water-level declines due to pumpage were simulated 

for either of these units. For the Wanapum unit, 

however, about twice as much area had water-level 

declines as had rises. Generally, areas of rises in the 

Wanapum unit correspond with those of the overburden aquifer and the Saddle Mountains unit. 

Water-level rises in the Wanapum unit averaged 

about 55 ft, with maximum rises of as much as 300 ft 

in the northwestern part of the Quincy Basin. Areas 

of water-level declines occur in the Odessa-Lind, 

Wash., area, within some of the valleys in the Yakima 

Fold Belt, on the south slope of Horse Heaven Hills, 

Wash., in the Walla Walla River Basin, and along the 

lower Umatilla River, Oreg. Declines in the 

Wanapum unit average about 60 ft, but were more 

than 200 ft in some areas.

Water levels in the upper Grande Ronde have 

risen and declined over approximately equal areas. 

Rises in the upper Grande Ronde occurred in the 

surface-water irrigated areas and along narrow strips 

under and adjacent to the dammed parts of the major 

rivers. Rises averaged about 30 ft and declines 

averaged about 35 ft. Maximum simulated rises and 

declines both exceeded 200 ft. Rises and declines for 

the lower Grande Ronde are similar to those of the 

upper Grande Ronde, but the maximums are attenuated by about 80 to 100 ft.

From predevelopment time to 1983-85, estimated average recharge increased from 6,566 to 

10,205 ft3/s, while pumpage increased to 1,135 ft3/s. 

One hundred eighty-seven cubic feet per second of 

pumpage was taken from storage, and an extra 

2,698 ft3/s of water was being discharged to rivers, 

drains, and seepage faces during 1983-85. Most of 

the simulated 1,651 ft3/s increase in discharge to 

drains is to the farm drains and wasteways; this 

indicates that most recharge in the intensively 

surface-water-irrigated areas follows short flow paths

55
to discharge locations. Net discharge to rivers 

increased by 1,048 ft3/s while discharge to seepage 

faces decreased by 3 ft3/s. Discharge quantities in 

the peripheral and upland areas generally were not 

changed from predevelopment conditions; this indicates that the large amounts of recharge in these areas 

generally are not available for movement to the existing areas of concentrated pumpage. The simulated 

effects of water development on the regional aquifer 

system presented above generally agree with available historic data and are believed to be a reasonable 

representation of actual effects that have not been 

historically monitored.

The ground-water flow model was used to simulate the long-term future (equilibrium) conditions of 

the aquifer system under the 1983-85 recharge and 

pumpage stresses. Simulation results indicate significant water-level declines in all four basalt layers but 

none in the overburden aquifer. The greatest 

declines, more than 400 ft in the Wanapum unit, are 

indicated for the pumping areas of Horse Heaven 

Hills because of the small amount of recharge and 

contributing area and relatively poor hydraulic 

connection to the aquifers in other areas. Water-level 

declines of similar magnitude in the Saddle Mountains and Wanapum units are simulated about 8 mi 

northeast of Yakima in a ground-water-irrigated 

valley that is bounded by anticlines. Water-level 

declines in the Odessa-Lind area are simulated to be 

as much as 200 ft in the Wanapum unit and 50 ft in 

the Grande Ronde unit. Simulated ground-water 

discharge to rivers, drains, and seepage faces 

decreased by 127 ft3/s. Ground-water pumpage 

decreased by 40 ft3/s because of desaturation of some 

cells with pumping.

The CBIP was originally authorized to develop 

1,095,000 acres for irrigated agricultural crops using 

Columbia River water; about 556,000 acres are currently developed, and 539,000 acres are available for 

potential future expansion. Under a proposed plan to 

develop the remaining acreage, the expansion would 

proceed in two phases-Phase 1 (160,000 acres) and 

Phase 2 (379,000 acres). Four model simulations 

were made to estimate the effects of increased 

recharge due to the additional surface-water irrigation. The increased recharge was made on the basis 

of average current CBIP application rates. Two 

simulations (Phase 1 and Phases 1 and 2) retained the 

current (1983-85) ground-water pumping rate, and in 

the remaining two simulations pumping was eliminated in areas to be served by the CBIP expansion.

For any particular expansion phase, water-level 

rises in the overburden aquifer, Saddle Mountains 

unit, and Wanapum unit, where they outcrop, were 

identical for the two pumping scenarios. All four 

simulations showed water levels rising up to land 

surface in those parts of the uppermost unit directly 

underlying the irrigated areas. This is because the 

amount of increased recharge to these units exceeds 

their capacity to laterally and vertically transmit this 

water; as a result, ground water rises to just below 

land surface, where it discharges to drains. The 

amount of ground water removed by pumping was 

too small to prevent such water-level rises. Compared with the Wanapum and Grande Ronde units, 

only small parts of the overburden aquifer and Saddle 

Mountains unit were simulated to have water-level 

rises (only a small part of each underlies the expansion areas).

The largest simulated rises occur in the 

Wanapum unit; about 400 ft for Phase 1 and about 

600 ft for Phases 1 and 2. For Phase 1, water-level 

rises of more than 50 ft in the Wanapum unit extend 

as far as about 15 mi beyond the southeastern part of 

the expansion area and about 7 mi beyond the northeastern part. For Phases 1 and 2, water-level rises of 

more than 50 ft in the Wanapum unit extend about 

20 mi beyond the northeastern part of the expansion 

area and about 17 mi beyond the southwestern part. 

Water-level rises in the Wanapum unit do not extend 

appreciably to the north because the unit is cut on the 

north by Crab Creek.

Water-level rises in the underlying upper and 

lower Grande Ronde units were much smaller but 

more widespread than the overlying Wanapum unit. 

For both pumping scenarios of Phase 1, water-level 

rises of more than 10 ft covered about twice the area 

as they did for the Wanapum unit. For the reduced 

pumping scenario of Phase 1, water-level rises in the 

Grande Ronde of more than 50 ft covered only about 

half the area as for the Wanapum unit. Maximum 

water-level rises in the upper and lower Grande 

Ronde were about 100 ft and 50 ft, respectively. For 

the 1983-85 pumping scenario of Phase 1, there were 

almost no areas of water-level rises of more than 

50 ft in the upper Grande Ronde and 35 ft in the 

lower Grande Ronde.

Simulated water-level rises for Phases 1 and 2 in 

the upper and lower Grande Ronde were more widespread and of greater magnitude than for Phase 1 

only. For the reduced pumping scenario, water-level 

rises of more than 50 ft in the upper Grande Ronde

56
covered a roughly circular area about 65 mi in diameter (about three times as great as for Phase 1), and 

maximum rises were about 300 ft (compared with 

100 ft for Phase 1 only). For the 1983-85 pumping 

scenario, water-level rises in the upper Grande Ronde 

of more than 50 ft covered a roughly circular area of 

about 40 mi in diameter, whereas, Phase 1 had almost 

no areas with rises of greater than 50 ft. In the lower 

Grande Ronde, for both pumping scenarios, waterlevel rises of greater than 50 ft covered an almost 

identical area as for the upper Grande Ronde. This 

area is more than twice that as for the reduced pumping Phase 1 in the Grande Ronde unit. Thus, for the 

upper and lower Grande Ronde, both the area served 

by new irrigation and the amount of future pumpage 

probably are important controls on the potential 

configuration of water levels. Moreover, for any 

particular scenario, the upper and lower Grande 

Ronde are affected to about the same magnitude 

and extent.

The CBIP simulations show that most changes 

to the budget components of the ground-water flow 

system would be within the proposed expansion 

areas. For the reduced pumping rate scenario, the 

increased discharge to drains would be 114 percent 

and 109 percent of the increased recharge for Phase 1 

and Phases 1 and 2, respectively. The simulations 

showed that most of the new recharge would follow 

short flow paths to drains nearby. Reduced pumping 

in the units underlying the uppermost unit causes 

water levels there to rise, causing increased upward 

flow to, and decreased downward flow from, the 

upper units. For the 1983-85 pumping rate scenario, 

the increased discharge to drains would be 82 and 88 

percent of the increase in recharge for Phase 1 and 

Phases 1 and 2, respectively.

SELECTED REFERENCES

Barker, R.A., 1979, Computer simulation and geohydrology of a basalt aquifer system in the 

Pullman-Moscow basin, Washington and Idaho: 

Washington State Department of Ecology, 

Water-Supply Bulletin 45, 119 p.

Barker, R.A., and MacNish, R.D., 1976, Digital 

model of the gravel aquifer, Walla Walla River 

basin, Washington and Oregon: Washington 

Department of Ecology Water-Supply Bulletin 

45, 49 p.

Bauer, H.H., and Vaccaro, J.J., 1987, Documentation 

of a deep percolation model for estimating 

ground-water recharge: U.S. Geological Survey 

Open-File Report 86-536,180 p.

__1990, Estimates of ground-water recharge to the 

Columbia Plateau regional aquifer system, 

Washington, Oregon, and Idaho, for predevelopment and current land-use conditions: U.S. 

Geological Survey Water-Resources Investigations Report 88-4108, 37 p., 2 plates.

Bauer, H.H., Vaccaro, J.J., and Lane, R.C., 1985, 

Maps showing ground-water levels in the 

Columbia River Basalt and overlying material, 

spring 1983, southeastern Washington: U.S. 

Geological Survey Water-Resources Investigations Report 84-4360,4 sheets.

Bear, Jacob, 1979, Hydraulics of ground water, 

McGraw-Hill Inc., 569 p.

Bennett, G.D., Kontis, A.L., and Larson, S.P, 1982, 

Representation of multiaquifer well effects in 

three-dimensional ground-water flow simulation: Ground Water, v. 20, no. 3, p. 334-341.

Bierschenk, W.H., 1959, Aquifer characteristics and 

ground-water movement at Hanford: unclassified AEC Research and Development report, 

p. 33.

Bolke, E.L., and Skrivan, J.A., 1981, Digital-model 

simulation of the Toppenish alluvial aquifer, 

Yakima Indian Reservation, Washington: U.S. 

Geological Survey Water-Resources Investigations, Open-File Report 81-425, 34 p.

Bolke, E.L., and Vaccaro, J.J., 1981, Digital-model 

simulation of the hydrologic flow system, with 

emphasis on ground water in Spokane Valley, 

Washington and Idaho: U.S. Geological Survey 

Water-Resources Investigations, Open-File 

Report 80-1300, 43 p.

Bush, P.W., and Johnston, R.H., 1988, Ground-water 

hydraulics, regional flow, and ground-water 

development of the Floridan aquifer system in 

Florida and in parts of Georgia, South Carolina, 

and Alabama: U.S. Geological Survey Professional Paper 1403-C, 80 p.

57
Camp, V.E., Hooper, P.R., Swanson, D.A., and 

Wright, T.L., 1982, Columbia River Basalt in 

Idaho: physical and chemical characteristics, 

flow distribution, and tectonic implications, in 

B. Bonnichsen and R. M. Breckenridge, eds., 

Cenozoic Geology of Idaho: Idaho Bureau of 

Mines and Geology, Bulletin 26, p. 55-75.

Cline, D.R., 1984, Ground-water levels and pumpage 

in east-central Washington, including the 

Odessa-Lind area, 1967 to 1981: Washington 

State Department of Ecology, Water-Supply 

Bulletin no. 55, 34 p.

Cline, D.R., and Collins, C.A., 1992, Ground-water 

pumpage in the Columbia Plateau, Washington 

and Oregon, 1945 to 1984: U.S. Geological 

Survey Water-Resources Investigations Report 

90-4085, 31 p., 5 plates.

Cline, D.R., and Knadle, M.E., 1990, Ground-water 

pumpage from the Columbia Plateau regional 

aquifer system, Washington, 1984: U.S. Geological Survey Water-Resources Investigations 

Report 87-4135, 32 p., 1 sheet.

Collins, C.A., 1987, Ground-water pumpage from 

the Columbia Plateau regional aquifer system, 

Oregon, 1984: U.S. Geological Survey WaterResources Investigations Report 86-4211, 21 p.

Davies-Smith, A., Bolke, E.L., and Collins, C.A., 

1988, Geohydrology and digital simulation of 

the ground-water flow system in the Umatilla 

Plateau and Horse Heaven Hills area, Oregon 

and Washington: U.S. Geological Survey 

Water-Resources Investigations Report 

87-4268, 70 p.

Downey, J.S., 1986, Geohydrology of bedrock aquifers in the northern Great Plains in parts of 

Montana, North Dakota, South Dakota, and 

Wyoming: U.S. Geological Survey Professional 

Paper 1402-E, 87 p.

Drost, B.W., and Whiteman, K.J., 1986, Surficial 

geology, structure, and thickness of selected 

geohydrologic units in the Columbia Plateau, 

Washington: U.S. Geological Survey WaterResources Investigations Report 84-4326, 

10 sheets.

Drost, B.W., Whiteman, K.J., and Gonthier, J.B., 

1990, Geologic framework for the Columbia 

Plateau regional aquifer system, Washington, 

Oregon, and Idaho: U.S. Geological Survey 

Water-Resources Investigations Report 

87-4238,10 p., 10 sheets.

Eddy, P.A., 1976, Description, preliminary results, 

and pumping tests-observation well 13 near 

George, Washington: Washington Department 

of Ecology Water-Resources Information 

Series, Technical Bulletin 19, 43 p.

Elassal, A.A., and Caruso, V.M., 1983, U.S. Geological Survey digital cartographic data schedules: 

Digital elevation models: U.S. Geological 

Survey Circular 895-B, 40 p.

Farooqui, S.M., Beaulieu, J.B., Bunker, R.C.,

Stensland, D.E., and Thorns, R.E., 1981, Dalles 

Group: Neogene formations overlying the 

Columbia River Basalt Group in north-central 

Oregon: Oregon Department of Geology and 

Mineral Industries, Oregon Geology, v. 43, 

no. 10, p. 131-140.

Ferris, J.G., Knowles, D.B., Brown, R.H., and 

Stallman, R.W., 1962, Theory of aquifer test: 

U.S. Geological Survey Water-Supply Paper 

1536-E, 174 p.

Flint, R.F., 1938, Origin of the Cheney-Palouse 

scabland tract: Geological Society of America 

Bulletin, v. 49, 461 p.

Freeman, O.W., Forrester, J.O., and Lupher, R.L., 

1945, Physiographic divisions of the Columbia 

Intermontane Province: Annual Association 

American Geographer, v. 35, no. 2, p. 50-75.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater, 

Prentice-Hall, Inc., Englewood Cliffs, New 

Jersey, 604 p.

Gonthier, J.B., 1990, Geology, structure, and thickness of hydrogeologic units in part of the 

Columbia Plateau, Oregon: U.S. Geological 

Survey Water-Resources Investigations Report 

86-4001, 6 sheets.

Hansen, A.J., 1993, Modifications to the modular 

three-dimensional, finite-difference, groundwater flow model used for the Columbia Plateau 

Regional Aquifer-System Analysis, Washington, Oregon, and Idaho: U.S. Geological Survey 

Open-File Report 91-532,162 p.

Hansen, A.J., Vaccaro, J.J., and Bauer, H.H., 1994, 

Ground-water flow simulation of the Columbia 

Plateau regional aquifer system, Washington, 

Oregon, and Idaho: U.S. Geological Survey 

Water-Resources Investigations Report 

91-4178, 81 p., 15 sheets.

Hooper, PR., 1982, The Columbia River Basalts: 

Science, v. 215, no. 4539, p. 1,463-1,468.

58
IMSL, 1982, Interpolation, chapter I, in International 

mathematics and science library reference 

manual, v. 2: Houston, Texas, IMSL, Inc.

Jacob, C.E., 1940, On the flow of water in an elastic 

artesian aquifer: Transactions of the American 

Geophysical Union, v. 21, pt. 2, p. 574-586.

Lane, R.C., and Whiteman, K.J., 1989, Ground-water 

levels, spring 1985, and ground-water level 

changes, spring 1983 to spring 1985, in three 

basalt units underlying the Columbia Plateau, 

Washington and Oregon: U.S. Geological 

Survey Water-Resources Investigations Report 

88-4018, 4 sheets.

LaSala, A.M., Jr., and Doty, G.C., 1971, Preliminary 

evaluation of hydrologic factors related to radioactive waste storage in basaltic rocks at the 

Hanford Reservation, Washington: U.S. 

Geological Survey Open-File Report, 68 p.

Lohman, S.W., and others, 1972, Definitions of 

selected ground-water terms revisions and 

conceptual refinements: U.S. Geological 

Survey Water-Supply Paper 1988, 21 p.

Luckey, R.R., Gutentag, E.D., Heimes, F.J., and

Weeks, J.B., 1986, Digital simulation of groundwater flow in the High Plains Aquifer in parts of 

Colorado, Kansas, Nebraska, New Mexico, 

Oklahoma, South Dakota, Texas, and Wyoming: 

U.S. Geological Survey Professional Paper 

1400-D, 57 p.

Lum, W.E., Smoot, J.L., and Ralston, D.R., 1990, 

Geohydrology and numerical model analysis of 

ground-water flow in the Pullman-Moscow area, 

Washington and Idaho: U.S. Geological Survey 

Water-Resources Investigations Report 

89-4103, 73 p.

Luzier, J.E., and Burt, R.J., 1974, Hydrology of 

basalt aquifers and depletion of groundwater in 

east-central Washington: Washington State 

Department of Ecology Water-Supply Bulletin 

no. 33, 53 p.

Luzier, J.E., and Skrivan, J.A., 1973, Digital simulation and projection of water-level declines in 

basalt aquifers of the Odessa-Lind area, eastcentral Washington: U.S. Geological Survey 

Open-File Report, 56 p.

Mackin, J.H., 1955, Geology of the Priest Rapids 

hydroelectric development, in Grant County 

Public Utility District No. 2, Priest Rapids 

hydroelectric development, Columbia River, 

Washington, v. 3 - appendices to v. 2, sec. A - 

Geology and Construction Materials, 38 p.

MacNish, R.D., and Barker, R.A., 1976, Digital 

simulation of a basalt aquifer system, Walla 

Walla River basin, Washington and Oregon: 

Washington Department of Ecology WaterSupply Bulletin no. 44, 51 p.

McDonald, M.G., and Harbaugh, R.A., 1988, A 

modular three-dimensional finite-difference 

ground-water flow model: U.S. Geological 

Survey Techniques of Water-Resources Investigations, Book 6, chap. 41, 11 chaps.

Myers, C.W., and Price, S.M., 1979, Geologic

studies of the Columbia Plateau, a status report: 

Rockwell International, Rockwell Hanford 

Operations RHO-BWI-ST-4, 520 p.

__1981, Subsurface geology of the Cold Creek 

Syncline: Rockwell International, Rockwell 

Hanford Operations, RHO-BWI-ST-14.

Nelson, L.M., 1991, Surface-water resources for the 

Columbia Plateau, Washington, Oregon, and 

Idaho: U.S. Geological Survey WaterResources Investigations Report 88-4105, 

4 sheets.

Neuzil, C.E., 1986, Ground-water flow in lowpermeability environments: Water-Resources 

Research, v. 22, no. 8, p. 1,163-1,195.

Newcomb, R.C., 1958, Ringold Formation for 

Pleistocene age in type locality, the White 

Bluffs, Washington: American Journal of 

Science, v. 259, p. 328.

__1961, Storage of ground water behind subsurface dams in Columbia River Basalt, Washington, Oregon, and Idaho: U.S. Geological Survey 

Professional Paper 383-A, 15 p.

__1965, Geology and ground-water resources of 

the Walla Walla River basin, WashingtonOregon: Washington State Division of Water 

Resources, Water-Supply Bulletin 21, 151 p.

__1969, Effect of tectonic structure on the occurrence of ground water in the basalt of the 

Columbia River Group of The Dalles area, 

Oregon and Washington: U.S. Geological 

Survey Professional Paper 383-C, 33 p. 

Newcomb, R.C., Strand, J.R., and Frank, F.J., 1972, 

Geology and ground-water characteristics of the 

Hanford Reservation of the U.S. Atomic Energy 

Commission, Washington: U.S. Geological 

Survey Professional Paper 717, 78 p.

59
Packard, F.A., Hansen, A.J., Jr., and Bauer, H.H., 

1996, Hydrology and simulation of flow and the 

effects of development alternatives on the basalt 

aquifers of the Horse Heaven Hills, southcentral Washington: U.S. Geological Survey 

Water-Resources Investigations Report 

94-4068.

Price, C.E., 1960, Artificial recharge of a well 

tapping basalt aquifers, Walla Walla area, 

Washington: Washington Division of Water 

Resources, Water-Supply Bulletin 7, 50 p.

Prych, E.A., 1983, Numerical simulation of groundwater flow in lower Satus Creek basin, Yakima 

Indian Reservation, Washington: U.S. Geological Survey Water-Resources Investigations 

Report 82-4065, 78 p.

Raymond, J.R., and Tillson, D.D., 1968, Evaluation 

of a thick basalt sequence in south-central 

Washington: Pacific Northwest Laboratory, 

Battelle Memorial Institute, BNWL-776, 120 p.

Reidel, S.P., 1982, Stratigraphy of the Grande Ronde 

Basalt, Columbia River Basalt Group, from the 

lower Salmon River and northern Hells Canyon 

area, Idaho, Oregon, and Washington; in Bill 

Bonnichsen and R.M. Breckenridge, eds., 

Cenozoic geology of Idaho: Idaho Bureau of 

Mines and Geology Bulletin 26, p. 77-101.

Skrivan, J.A., 1987, Ground-water hydrology of the 

Toppenish Creek basin, Yakima Indian Reservation, Washington: U.S. Geological Survey 

Water-Resources Investigations Report 

82-4010,47 p.

Steinkampf, W.C., 1989, Water-quality characteristics of the Columbia Plateau regional aquifer 

system in parts of Washington, Oregon, and 

Idaho: U.S. Geological Survey WaterResources Investigations Report 85-4242, 37 p.

Swanson, D.A., Anderson, J.L., Bentley, R.D., 

Byerly, G.R., Camp, V.E., Gardner, J.N., and 

Wright, T.L., 1979a, Reconnaissance geologic 

map of the Columbia River Basalt Group in 

eastern Washington and northern Idaho: U.S. 

Geological Survey Open-File Report 79-1363, 

26 p., scale 1:250,000, 12 sheets.

Swanson, D.A., Anderson, J.L., Camp, V.E., Hooper, 

P.R., Taubeneck, W.H., and Wright, T.L., 1981, 

Reconnaissance geologic map of the Columbia 

River Basalt Group, northern Oregon and western Idaho: U.S. Geological Survey Open-File 

Report 81-797, 35 p.

Swanson, D.A., Brown, J.C., Anderson, J.L.,

Bentley, R.D., Byerly, G.R., Gardner, J.N., and 

Wright, T.L., 1979b, Preliminary structure contour maps on the top of the Grande Ronde and 

Wanapum Basalts, eastern Washington and 

northern Idaho: U.S. Geological Survey OpenFile Report 79-1364, scale 1:500,000, 2 sheets.

Swanson, D.A., and Wright, T.L., 1978, Bedrock 

geology of the southern Columbia Plateau and 

adjacent areas, chapter 3, in V.R. Baker and 

D. Nummedal, eds., The channeled scabland: 

Planetary Geology Program, National Aeronautical and Space Administration, Washington, 

D.C., p. 37-57.

Swanson, D.A., Wright, T.L., and Helz, R.T., 1975, 

Linear vent systems and estimated rates of 

magma production and eruption for the Yakima 

Basalt on the Columbia Plateau: American 

Journal of Science, v. 275, Oct. 1975, 

p. 877-905.

Swanson, D.A., Wright, T.L., Hooper, PR., and

Bentley, R.D., 1979c, Revisions in stratigraphic 

nomenclature of the Columbia River Basalt 

Group: U.S. Geological Survey Bulletin 

1457-G, 59 p.

Swanson, D.A., Wright, T.L., and Zeitz, L, 1979d, 

Aeromagnetic map and geologic interpretation 

of the west-central Columbia Plateau, Washington and adjacent Oregon: U.S. Geological 

Survey Map GP-917, scale 1:250,000.

Tanaka, H.H., Barrett, G.T., and Wildrick, L., 1979, 

Regional basalt hydrology of the Columbia 

Plateau in Washington: RHO-BWI-C-60, 

Rockwell Hanford Operations, Richland, 

Washington, 303 p.

Tanaka, H.H., Hansen, A.J., and Skrivan, J.A., 1974, 

Digital-model study of ground-water hydrology, 

Columbia Basin Irrigation Project area, Washington: Washington State Department of 

Ecology, Water-Supply Bulletin 40, 60 p.

Theis, C.V., 1963, Estimating the transmissibility of 

a water-table aquifer from the specific capacity 

of a well, in Bentall, Ray, compiler, Methods of 

determining permeability, transmissibility, and 

drawdown: U.S. Geological Survey WaterSupply Paper 1536-1, p. 332-336.

60
Tolan, T.L., and Reidel, S.R, 1989, Structure map 

of a portion of the Columbia River floodbasalt province, plate: in S.R Reidel and 

P.R. Hooper, eds., Volcanism and Tectonism in 

the Columbia River Flood-Basalt Province, 

Geological Society of America, Special Paper 

239, 386 p.

Tolan, T.L., Reidel, S.P., Beeson, M.H., Anderson, 

J.L., Fecht, K.R., and Swanson, D.A., 1989, 

Revisions to the areal extent and volume of the 

Columbia River Basalt Group, in S.P. Reidel 

and P.R. Hooper, eds., Volcanism and Tectonism 

in the Columbia River Flood-Basalt Province, 

Geological Society of America, Special paper 

239, 386 p.

Tolan, T.L., Reidel, S.R, Beeson, M.H., Anderson, 

J.L., Fecht, K.R., and Swanson, D.A., 1987, 

Revisions to the areal extent and volume of 

the Columbia River Basalt Group: Geological 

Society of America, Abstracts with Programs, 

v. 19, no. 6, p. 458.

U.S. Geological Survey, 1974, The channeled

scablands of eastern Washington, the geologic 

study of the Spokane flood, 25 p.

Washington State Department of Ecology, 1974, 

Inventory and reconnaissance of irrigation 

districts in the State of Washington: URS/Hill, 

Ingman, Chase and Co., 3 volumes.

Water Conservation Steering Committee, 1987, 

Executive summary: Columbia Basin Project 

EIS Water Conservation Steering Committee 

report, draft September 24, 1987, 6 pages plus 

appendices and attachments.

Weiss, E., 1982, A computer program for calculating 

relative-transmissivity input arrays to aid model 

calibration: U.S. Geological Survey Open-File 

Report 82-447,18 p.

Whiteman, K.J., 1986, Ground-water levels in three 

basalt hydrologic units underlying the Columbia 

Plateau in Washington and Oregon, spring 1984: 

U.S. Geological Survey Water-Resources Investigations Report 86-4046,4 sheets.

Whiteman, K.J., Vaccaro, J.J., Gonthier, J.B., and 

Bauer, H.H., 1994, The hydrogeologic framework and geochemistry of the Columbia Plateau 

aquifer system, Washington, Oregon, and Idaho: 

U.S. Geological Survey Professional Paper 

1413-B, 73 p.

Williams, J.R., and Pearson, H.E., 1985, Streamflow 

statistics and drainage-basin characteristics for 

southwestern and eastern regions, Washington, 

Volume II, Eastern Washington: U.S. Geological Survey Open-File Report 84-145-B, 662 p.

Wukelic, G.E., Foote, H.P., Blair, S.C., and Begej, 

C.D., 1981, Monitoring land- and water-use 

dynamics in the Columbia Plateau using 

remote-sensing computer analysis and integration techniques: Rockwell International, 

RHO-BW-CR-122P/PNL-4047, 50 p.

61

 if U.S. GOVERNMENT PRINTING OFFICE: 2000 589-121 / 03017 Region No. 10