Ml 

l 

( p,>;. VN Otl 

t ' 

KY 'r 

PROFESSIONAL PAPER 1425 
Availability of Publications of the U.S. Geological Survey 

Order U.S. Geological Survey (USGS) publications from the 

offices listed below. Detailed ordering instructions, along with 

prices of the last offerings, are given in the current-year issues 

of the catalog "New Publications of the U.S. Geological 

Survey." 

Books, Maps, and Other Publications 

By Mail 

Books, maps, and other publications are available by mail 

fro inUSGS Information Services 

Box 25286, Federal Center 

Denver, CO 80225 

Publications include Professional Papers, Bulletins, WaterSupply Papers, Techniques of Water-Resources Investigations, 

Circulars, Fact Sheets, publications of general interest, single 

copies of permanent USGS catalogs, and topographic and 

thematic maps. 

Over the Counter 

Books, maps, and other publications of the U.S. Geological 

Survey are available over the counter at the following USGS 

Earth Science Information Centers (ESIC's), all of which are 

authorized agents of the Superintendent of Documents: 

• Anchorage, Alaska-Rm. 101,4230 University Dr. 

• Denver, Colorado-Bldg. 810, Federal Center 

• Menlo Park, California-Rm. 3128, Bldg. 3, 

345 Middlefield Rd. 

• Reston, Virginia-Rm. 1C402, USGS National Center, 

12201 Sunrise Valley Dr. 

• Salt Lake City, Utah-2222 West, 2300 South (books and 

maps available for inspection only) 

• Spokane, Washington-Rm. 135, U.S. Post Office 

Building, 904 West Riverside Ave. 

• Washington, D.C.-Rm. 2650, Main Interior Bldg., 

18th and C Sts., NW. 

Maps only may be purchased over the counter at the following 

USGS office: 

• Rolla, Missouri-1400 Independence Rd. 

Electronically 

Some USGS publications, including the catalog "New Publications of the U.S. Geological Survey" are .also available electronically on the USGS's World Wide Web home page at 

http://www.usgs.gov 

Preliminary Determination of Epicenters 

Subscriptions to the periodical "Preliminary Determination of 

Epicenters" can be obtained only from the Superintendent of 

Documents. Check or money order must be payable to the 

Superintendent of Documents. Order by mail fromSuperintendent of Documents 

Government Printing Office · 

Washington, DC 20402 

Information Periodicals 

Many Information Periodicals products are available through 

the systems or formats listed below: 

Printed Products 

Printed copies of the Minerals Yearbook and the Mineral Commodity Summaries can be ordered from the Superintendent of 

Documents, Government Printing Office (address above). 

Printed copies of Metal Industry Indicators and Mineral Industry Surveys can be ordered from the Center for Disease Control 

and Prevention, National Institute for Occupational Safety and 

Health, Pittsburgh Research Center, P.O. Box 18070, Pittsburgh, PA 15236-0070. 

Mines FaxBack: Return fax service 

1. Use the touch-tone handset attached to your fax machine's 

telephone jack. (ISDN [digital] telephones cannot be used with 

fax machines.) 

2. Dial (703) 648-4999. · 

3. Listen to the menu options and punch in the number of your 

selection, using the touch-tone telephone. 

4. After completing your selection, press the start button on 

your fax machine. 

CD-ROM 

A disc containing chapters of the Minerals Yearbook (1993-

95), the Mineral Commodity Summaries (1995-97), a statistical compendium (1970-90), and other publications is updated 

three times a year and sold by the Superintendent of Documents, Government Printing Office (address above). 

World Wide Web 

Minerals information is available electronically at 

http://minerals.er.usgs.gov/minerals/ 

Subscription to the catalog "New Publications of the U.S. 

Geological Survey" 

Those wishing to be placed on a free subscription list for the 

catalog "New Publications of the U.S. Geological Survey" 

should write toU.S. Geological Survey 

903 National Center 

Reston, VA 20192 
Hydrologic Budgets of Regional Aquifer 

Systems of the United States for 

Predevelopment and Development 

Conditions 

By RICHARD H. JOHNSTON 

REGIONAL AQUIFER-SYSTEM ANALYSIS 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1425 
Revised 1999 

Reston, Virginia 1999 

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 in this publication is for 

descriptive purposes only and does not imply endorsement by the 

U.S. Government. 

Library of Congress Cataloging in Publication Data 

Johnston, Richard H. 

Hydrologic budgets of regional aquifer systems of the United States for predevlopment and development conditions/ by Richard H. Johnston. 

p. cm.-(Regional aquifer-system analysis) (U.S. Geological Survey professional paper: 1425) 

Includes bibliographical references. 

Supt. ofDocs. no.: I 19. 16: 1425 

1. Aquifers-United States. 2. Water balance (Hydrology)-United States. I. Title. II. Series. III. Series: U.S. Geolo~cal Survey professional paper; 1425. 

GB1199.2.J64 1997 

553.7'9'0973-dc21 97-6177 

CIP 

ISBN 0-607-90427-5 

For sale by U.S. Geological Survey, Branch of Information Services, Box 25286, 

Federal Center, Denver, CO 80225 
FOREWORD 

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM 

The Regional Aquifer-System Analysis (RASA) Program represents a 

systematic effort to study a number of the Nation's most important aquifer 

systems, which, in aggregate, underlie much of the country and which represent an important component of the Nation's total water supply. In general, 

the boundaries of these studies are identified by the hydrologic extent of each 

system and, accordingly, transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for 

each study is to assemble geologic, hydrologic, and geochemical information; 

to analyze and develop an understanding of the system; and to develop predictive capabilities that will contribute to the effective management of the 

system. The use of computer simulation is an important element of the RASA 

studies to develop an understanding of the natural, undisturbed hydrologic 

system and the changes brought about in it by human activities, and to provide a means of predicting the regional effects of future pumping or other 

stresses. 

The final interpretive results of the RASA Program are presented in a 

series of U.S. Geological Survey Professional Papers that describe the geology, 

hydrology, and geochemistry of each regional aquifer system. Each study 

within the RASA Program is assigned a single Professional Paper number 

beginning with Professional Paper 1400. 

Charles G. Groat 

Director 

CONTENTS 

Page Page 

Forward ............................................................................................ III Floridan aquifer system .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 18 

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

Introduction .. . . . . .. . .. ... .. . .. . .. .. . .. . .. . .. .. . .. . .. ... ... . .. . .. ... ... . . . . .. . .. . .. . .. . ... ... .. . . 1 

Edwards-Trinity aquifer system ......................................... 18 

Ozark Plateaus aquifer system ........................................... 19 

Regional aquifer systems........................................................... 2 

Simulation of flow in regional aquifer systems........................ 3 

Regional, intermediate, and local ground-water flow 

Madison aquifer of the Northern Great Plains .................. 19 

Carbonate-rock province of the Great Basin ...................... 20 

Clastic-rock aquifer systems of the central and the western 

regimes............................................................................ 3 United States........................................................................ 20 

Simulated regional ground-water budgets from coarsemesh models-The scale problem.................................. 4 

Regional ground-water budgets...................................................... 8 

Great Plains aquifer system (Dakota Sandstone and 

associated units).............................................................. 21 

High Plains aquifer.............................................................. 22 

Clastic-rock aquifer systems of the Atlantic and the Gulf California Central Valley aquifer system ........................... 22 

Coastal Plains....................................................................... 10 Basaltic-rock aquifer systems of the Pacific Northwest.. ........ 24 

Gulf Coastal Plain aquifer systems .. ...... .. .... .. .... .. ...... .... .. .. 10 Snake River Plain aquifer system .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 24 

Northern Atlantic Coastal Plain aquifer system ............... 13 Columbia Plateau aquifer system .... .. .. .. .. .. .................. ...... 25 

Southeastern Coastal Plain aquifer system ....................... 15 Sources of water supplying pumpage from regional aquifer 

Carbonate-rock aquifer systems ...... ...... .. .... ...... ...... ...... .. .. .. ..... 15 systems ........................................................................................ 26 

Cambrian-Ordovician aquifer system of the Northern Summary and conclusions ............................................................... 31 

Midwest ........................................................................... 16 References ......................................... ~ .............................................. 32 

FIGURE 1. 

2.-4. 

5.-6. 

7. 

8.-12. 

ILLUSTRATIONS 

Page 

Map showing location of regional aquifers and aquifer systems with hydrologic budgets described in this report............... 2 

Generalized hydrogeologic sections showing: 

2. Flow systems in: A, Basalt aquifer units of the Columbia Plateau aquifer system; B, The Floridan aquifer 

system in the north-central Florida Springs area..................................................................................................... 4 

3. Relation of local and regional scale ground-water flow to discretization in computer flow models....................... 8 

4. Aquifers and confining units and designation of layers in the regional flow model of the Gulf Coast aquifer 

systems ........................................................................................................................................................................ 11 

Diagrams showing: 

5. Vertical structure of regional flow model of the Gulf Coastal Plain aquifer systems and simulated 1985 

rates of recharge, discharge, and pumpage... ... . ... ... ... .. . ... . .. ... ... ... . .. ... ... . . . ... .. . .. . .. . .. ... .. . .. . .. .. .. . .. ... .. .. . .. .. ... .. .. .. . .. .. . .. .. .. 12 

6. Ground-water budgets before and after development of clastic-rock aquifer systems in the Atlantic and 

the Gulf Coastal Plains............................................................................................................................................... 13 

Graph showing change in simulated regional ground-water budget of the Gulf Coastal Plain aquifer systems from 

predevelopment to 1985................................................................................................................................................................ 14 

Diagrams showing: 

8. Ground-water budgets before and after development of carbonate-rock aquifer systems in the Midwestern 

and the Southern United States................................................................................................................................ 16 

9. Predevelopment ground-water budgets of carbonate-rock aquifer systems in the Ozark Plateaus, the 

Northern Great Plains, and the Great Basin ............................................................................................................ 17 

10. Ground-water budgets before and after development of clastic-rock aquifer systems in the Central and 

the Western United States ......................................................................................................................................... 21 

11. Ground-water budgets before and after development of basaltic-rock aquifer systems in the Pacific 

Northwest .................................................................................................................................................................... 25 

12. Sources of water that supply pumpage from regional aquifer systems ................................................................... 29 

13. Graph showing change of recharge-leakage rates to regional aquifer systems, predevelopment to recent pumping 

conditions ...................................................................................................................................................................................... 30 

v 
VI 

CONTENTS 

TABLES 

Page 

TABLE 1. Computer models used for simulation ofpredevelopment and development flow conditions in regional aquifer systems......... 6 

2. Rates and characteristics of predevelopment recharge and discharge of regional aquifer systems............................................. 9 

3. Sources of water that supply pumpage from regional aquifer systems .......................................................................................... 28 

CONVERSION FACTORS AND VERTICAL DATUM 

Multiply 

inch (in) 

foot (ft) 

mile (mi) 

acre 

square mile (mi 2 ) 

acre-foot (acre-ft) 

billion gallons per day (Ggal/d) 

million gallons per day (Mgal!d) 

cubic feet per second (ft3

/s) 

gallon per minute (gal/min) 

foot squared per day (ft2

/d) 

inch per year (in/yr) 

acre-foot per year (acre-ft/yr) 

By 

Length 

25.4 

0.3048 

1.609 

Area 

0.4047 

2.590 

Volume 

1,233 

Flow 

43.81 

0.04381 

0.02832 

0.06308 

0.09290 

25.4 

0.00123 

To obtain 

millimeter 

meter 

kilometer 

hectare 

square kilometer 

cubic meter 

cubic meter per second 

cubic meter per second 

cubic meter per second 

liter per second 

meter squared per day 

millimeter per year 

cubic hectometer per year 

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 ofboth the United States and 

Canada, formerly called "Sea Level Datum of 1929". 
REGIONAL AQUIFER-SYSTEM ANALYSIS 

HYDROLOGIC BUDGETS OF 

REGIONAL AQUIFER SYSTEMS OF THE UNITED STATES FOR 

PREDEVELOPMENT AND DEVELOPMENT CONDITIONS 

BY RICHARD H. JOHNSTON 

ABSTRACT 

Ground-water budgets are presented in this report for 14 regionally extensive aquifer systems; pumpage from 11 of these systems provided from 40 to 50 percent of the ground water withdrawn in the 

United States during the 1970's and 1980's. The budgets are based on 

simulation results from computer-based models developed as part of 

the Regional Aquifer-System Analysis Program of the U.S. Geological 

Survey. Most of the models cover large areas (30,000-300,000 square 

miles) and generally are constructed with coarse-mesh finite-difference 

grids designed to simulate regional ground-water flow. The groundwater budgets derived from these models generally do not include 

local flow that enters and exits regional aquifers after traveling only a 

few miles or flow in overlying surficial aquifers. Budgets are presented 

for predevelopment and recent pumping conditions for most of the 

aquifer systems. 

Before development, many of the regional aquifer systems in 

humid areas were brim full; that is, most of the potential recharge was 

rejected from areas of outcrop. Climate, topography, and hydrogeologic setting (especially the occurrence of confined and unconfined 

conditions and the hydraulic properties of aquifers and confining 

units) were the major controls on rates of recharge and discharge. Predevelopment regional flow tended to be sluggish in the deep confined 

parts of the aquifer systems. The inability of clastic aquifers in the 

extensive Gulf Coastal Plain aquifer systems (underlying 290,000 

square miles) to transmit water away from recharge areas limited predevelopment regional recharge to 4,500 cubic feet per second. In contrast, the Floridan aquifer system (underlying 100,000 square miles), 

which occurs in a similar humid climate but is characterized by a different hydrogeologic setting (very permeable carbonate rocks that 

occur at shallow depth throughout a large area), had a predevelopment 

recharge rate of 21,500 cubic feet per second. In the drier parts of the 

Central and the Western United States, recharge to and flow through 

most regional aquifer systems were small before development. For 

example, predevelopment recharge to the southern part of the unconfined High Plains aquifer (underlying 29,000 square miles in Texas and 

New Mexico) was only 270 cubic feet per second. Predevelopment 

recharge to the Great Plains aquifer system (the Dakota Sandstone and 

associated units), which is deeply buried throughout most of its areal 

extent of 170,000 square miles in the central Great Plains, was about 340 

cubic feet per second. 

The effect of ground-water withdrawals on water budgets is evident for the 11 regional aquifer systems with significant pumpage. A 

major consequence of development is a large increase in regional flow 

through the deeper parts of the systems. In nine of the aquifer systems, 

more than 50 percent of the ground water pumped is supplied by 

increased recharge that occurs by means of one or more of the following mechanisms: an increase in the percolation rate from outcrop and 

(or) subcrop recharge areas into the deeper and generally confined 

parts of aquifer systems, induced leakage from overlying or underlying aquifers, and return flow of excess irrigation water that is supplied 

by imported surface water or pumped ground water. The largest 

increases in regional recharge have occurred in the three most heavily 

pumped aquifer systems-the Gulf Coast, the High Plains, and the 

California Central Valley. Return flow from irrigation has been the 

principal source of increased inflow to the High Plains and the California Central Valley aquifer systems; increased downward percolation 

and induced leakage have been the principal sources of inflow to the 

Gulf Coastal Plain aquifer systems. Pumpage from two aquifer systems-the Edwards-Trinity of Texas and the Southeastern Coastal 

Plain-is supplied mostly by interception of ground water that otherwise would discharge either to streams and springs or as diffuse 

upward leakage. 

Ground-water withdrawals have caused moderate to large losses 

of storage in three regional aquifer systems. A large decrease in confined aquifer storage owing to inelastic compaction of fine-grained sediments accompanied by extensive land subsidence has occurred in the 

southern part of the California Central Valley aquifer system (the San 

Joaquin Valley) and, to a much lesser extent, in two localities of the 

Gulf Coastal Plain aquifer systems. Long-term water-table declines 

with significant decreases in saturated aquifer thickness have occurred 

in a large area of the southern High Plains aquifer and, to a lesser 

degree, in the Mississippi River Valley alluvial aquifer, which is a major 

unit of the Gulf Coastal Plain aquifer systems. 

INTRODUCTION 

The hydrologic budgets of the regional aquifer systems described in this report were developed during 

the Regional Aquifer-System Analysis (RASA) Program 

of the U.S. Geological Survey (USGS). The RASA Program has provided quantitative appraisals of the major 

ground-water systems of the United States. A summary 

of the RASA Program, which includes brief descriptions 

of the hydrology of the 25 regional aquifer systems 

investigated, is presented in Sun and Johnston (1994). 
2 REGIONAL AQUIFER-SYSTEM ANALYSIS 

The final reports of each RASA study are a series of 

USGS Professional Papers numbered from 1400 to 1424. 

Generally, one· chapter in each numbered professional 

paper is devoted to a quantitative description of the 

regional ground-water flow system. Many of these 

flow-system descriptions provide for the first time 

ground-water budgets for predevelopment and recent 

pumping conditions. These budgets are based on computer simulations of predevelopment and development 

conditions and use the regional hydrologic data bases, 

information on boundary conditions, and pumpage 

data compiled during the RASA studies. The publications that give detailed descriptions of the groundwater budgets and characteristics of the regional 

ground-water flow systems can be found in the "References" section at the end of this report. 

The purposes of this report are to provide summary 

descriptions of the ground-water budgets of 14 regional 

aquifer systems, which provided nearly one-half of the 

ground water pumped in the United States during the 

1970's and 1980's; to describe the hydraulic and geologic factors that control flow through regional aquifer 

systems under natural conditions; and to describe the 

sources of water withdrawn from the regional aquifer 

systems on the basis of differences between predevelopment and development ground-water budgets. 

REGIONAL AQUIFER SYSTEMS 

Aquifer systems investigated under the RASA program were classified by Sun (1986) as being of two general types-an aquifer system that comprises an 

extensive set of associated aquifers and confining units 

that may be discontinuous locally but which act hydrologically as a single aquifer system on a regional scale, 

or a system that consists of a set of independent aquifers that share many common hydrologic characteristics. 

Aquifer systems of the first type may contain several 

geologic formations and chronostratigraphic units, as 

well as several regional aquifers and confining units. 

Examples include the California Central Valley aquifer 

system, which contains numerous beds of gravel, sand, 

silt, and clay, and the Floridan aquifer system, which 

consists of several carbonate-rock formations that 

underlie Florida and parts of three other States. 

Hydraulic continuity exists to the extent that a flow system can be defined for the entire aquifer system. Given 

sufficient water-level data, potentiometric surfaces can 

be mapped for the aquifer system or its component 

aquifers. The 14 aquifer systems for which groundwater budgets are presented in this report are of the 

first general type. Locations of these aquifer systems are 

shown on figure 1. 

FIGURE 1.-Location of regional aquifers and aquifer systems with hydrologic budgets described in this report. 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 3 

Examples of the second type of aquifer system 

include those found in the alluvial basins of Arizona 

and New Mexico and in the glacial outwash valleys of 

the Northeastern United States. These aquifer systems 

contain numerous isolated flow systems and cannot be 

simulated as a single hydrologic unit. Hydrologic 

changes in one aquifer have virtually no effect on other 

aquifers. The RASA approach was to investigate a few 

of these isolated aquifers to establish common principles and hydrogeologic characteristics that control the 

occurrence, movement, and quality of ground water. 

SIMUlATION OF FLOW IN REGIONAL AQUIFER 

SYSTEMS 

REGIONAL, INTERMEDIATE, AND LOCAL GROUND-WATER 

FLOW REGIMES 

Natural ground-water flow can be subdivided into 

local, intermediate, and regional flow regimes, as 

described by Toth (1963). Local flow generally is controlled by topography. Recharge to local flow regimes 

occurs in topographically high areas, and discharge 

occurs in nearby low areas, such as stream valleys. 

Local flow paths are characteristically short and occur 

at relatively shallow depth, as shown in figure 2A. Intermediate flow paths are longer and deeper than local 

flow paths and underlie several local flow regimes. 

Regional flow regimes extend from regional recharge 

areas to distant discharge areas, such as major rivers or 

other surface-water bodies, or at the downgradient terminus of an aquifer system. In general, regional flow 

moves slowly through deep, confined parts of an aquifer system and constitutes a small percentage of the 

total flow through the aquifer system. However, under 

development conditions that involve large groundwater withdrawals from deep confined aquifers, significant quantities of local and intermediate flow can be 

diverted into the regional flow regime. 

Toth's (1963) concept of three ground-water flow 

regimes assumed that aquifers are homogenous and 

isotropic. Consequently, any geologic feature or condition that introduces heterogeneity on a moderately 

large scale can distort or modify this concept. Some 

examples of geologic conditions that cause aquifer heterogeneity and anisotropy are as follows: 

• Karstic features in carbonate rocks, such as large cavernous openings, can distort short local flow paths 

and concentrate flow along highly preferential, 

longer (intermediate to regional) flow paths. 

• Major faults, if sealed along fault planes, can restrict 

flow or, if open, can enhance flow in preferred directions. 

• Abrupt facies changes from fine- to coarse-grained 

sediments can disrupt ground-water flow and create 

preferential flow paths along highly permeable, 

coarse-grained beds. 

The effects of geology (specifically heterogeneity 

and anisotropy) on ground-water flow patterns were 

demonstrated by Freeze and Witherspoon (1967) by 

using numerically simulated flow nets. These investigations illustrate the influence of permeability variations 

in combination with topography on flow patterns. 

Despite the wide variety of flow patterns that result 

from differences in geology and topography, Toth's 

(1963) concept is very useful for describing flow in the 

regional aquifer systems described in this report. Figure 

2 shows Toth's three flow regimes in two regional aquifer systems for which ground-water budgets are discussed in this report. 

In the Columbia Plateau (basaltic-rock) aquifer system of the Pacific Northwest, Hansen and others (1994) 

defined local flow systems with flow paths that extend 

up to about 10 mi in length, intermediate flow systems 

with flow paths from about 10 to 30 mi in length, and 

regional flow paths of more than 30 mi in length. Most 

local flow occurs in upland areas with water that moves 

along the short flow paths to discharge at small streams 

or seeps and springs along canyon walls (fig. 2A). 

Much of the water that moves along the longer intermediate flow paths also occurs in the uplands, and 

some of it mixes with local flow to become part of the 

local flow-system discharge (Hansen and others, 1994). 

Some of the intermediate flow also merges with the 

regional flow paths that ultimately terminate in the 

regional discharge area located in the lowest part of 

the Columbia Plateau along major streams, such as the 

Columbia and the Snake Rivers. Simulated discharge 

to major streams from the combined intermediate and 

regional flow systems accounts for more than onethird of the total simulated flow through the aquifer 

system. 

Ground-water flow in the Floridan aquifer system 

that underlies the karstic springs area of north-central 

and northwestern peninsular Florida differs markedly 

from that in the basaltic rock aquifer system just 

described. Small streams are almost nonexistent in the 

karst area, and ground-water discharge occurs at large 

springs or major streams that are incised into the upper 

part of the Floridan aquifer system (fig. 2B). The local 

ground-water flow system of Toth (1963) generally does 

not exist; flow paths are longer, and intermediate flow 

systems are dominant. Deep regional flow in the lower 

part of the Floridan aquifer system comprises only a 

small percentage of the total ground water that is 

recharged and discharged within the karstic springs 

area. The dominance of intermediate flow in the karst 

area is indicated by flow simulations (Bush and 

Johnston, 1988, p. 44) and ground-water chemistry 

(Faulkner, 1973, p. 75). However, in the hilly outcrop 
4 

w 

Basement confining unit 

NOT TO SCALE 

A 

w 

Gu lf of Mexico 

REGIONAL AQUIFER-SYSTEM ANALYSIS 

Grande Ronde unit 

EXPLANATION 

Generalized ground-water 

flow systems 

---- ~ 

-

Local 

Intermediate 

Regional 

Floridan aquifer system 

E 

From Hanson and others, 1994 

Land surface 

E 

-------------------1 NOT TO SCALE From Bush and Johnston, 1988 

8 

FIGURE 2.-Flow systems in: A, Basalt aquifer units of the Columbia Plateau aquifer system; B, The Floridan aquifer system in the 

north-central Florida Springs area. 

area of the Floridan aquifer system in Georgia, surface 

drainage is better developed, and local flow probably 

accounts for most of the total ground-water flow. 

According to Bush and Johnston (1988), flow patterns in 

other unconfined and semiconfined areas of the Floridan aquifer system "are some combination of these 

extremes" but are more like those of the karstic springs 

area than the Georgia outcrop area. 

SIMULATED REGIONAL GROUND-WATER BUDGETS FROM 

COARSE-MESH MODELS-THE SCALE PROBLEM 

Most of the regional flow models developed during 

the RASA Program were used to simulate predevelopment and recent pumping conditions. Because the 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 5 

regional RASA models were developed to simulate 

aquifer systems of tens of thousands of square miles 

(for example, those underlying the Atlantic arid the 

Gulf Coastal Plains, the High Plains, the Great Plains, 

the central and northern Midwest, and the California 

Central Valley), the discretization of most of the systems 

is relatively coarse. The grid spacing and other features 

of the regional models discussed in this report are summarized in table 1. Note that the area of the grid blocks 

in 12 of the 14 coarse-mesh models ranges from 16 to 

256 mi2. However, in two of the models (those used for 

simulation of the Columbia Plateau aquifer system and 

the Edwards-Trinity aquifer system), finer meshes were 

used. 

In most terranes where a modeled system includes 

near-surface aquifers, the fraction of the total groundwater flow that the model simulates becomes smaller as 

the size of model grid cells becomes larger. In the 

approximated flow system of the model, gradients in 

head exist ~nly between blocks. Thus, wate.t; that enters 

and leaves the aquifer system within the area represented by the faces of a single block cannot be simulated 

except by superimposing sources or sinks, a mechanism 

that cannot be practically used to account for all inflows 

and outflows. In areas of hills and valleys with numerous small streams (fig. 2A), much of the recharge travels 

as local flow only short distances before it discharges to 

the streams. Consequently, local flow is not simulated 

by many coarse-grid regional models, as indicated in 

figure 3. In contrast, in areas of little topographic relief 

and few streams, such as the karst areas of the Floridan 

aquifer system (fig. 2B), a much smaller fraction of the 

recharge discharges locally, and proportionately more 

of the total ground-water flow is simulated by a 

regional model. 

Although other factors are involved, the most 

important factors that control the fraction of total 

ground-water flow simulated by a regional model that 

includes near-surface units are topography and drainage density. These characteristics are typically variable 

across large regional aquifer systems. Accordingly, the 

fraction of total ground-water flow that is simulated by 

a coarse-grid model varies spatially, thus making the 

differentiation of flow regimes difficult to quantify for 

the model as a whole. Although most RASA modelers 

have confronted this problem by describing the effect of 

these variations on their simulations, rigorous quantitative analysis of the effect is lacking. 

Simulation of development conditions that involves 

pumping from deep confined aquifers generally 

requires some diversion of local flow from shallow 

aquifers into the regional flow regime. A mechanism is 

thus required that permits vertical flow into the deep 

aquifers. Some RASA models used specified heads in 

model layers that represented shallow aquifers as a 

method of supplying vertical flow to deep aquifers. 

[See, for example, the discussion of boundary and initial conditions in the Cambrian-Ordovician aquifer system of the northern Midwest by Mandie and Kontis 

(1992, p. 31)]. This approach assumes that heads in the 

shallow aquifer are unaffected by pumping from the 

deep aquifer. A drawback of this method is that an 

unrealistically large volume of vertical flow into deep 

aquifers can be computed unless the volume is limited 

to a probable maximum amount. A different approach 

was used to simulate pumping conditions in the unconfined and confined aquifers of the Northern Atlantic 

Coastal Plain aquifer system. The coarse-grid model 

used a top boundary condition termed "modified specified-flux boundary condition" to simulate withdrawals 

in the unconfined aquifers (Leahy and Martin, 1993). 

This boundary condition "which included stream-stage 

elevations, deep percolation, and discharge to streams 

allowed heads in the unconfined system to change with 

time in response to changing withdrawals" (Leahy and 

Martin, 1993, p. 21). As a result, the model simulated 

local flow in the unconfined part of the aquifer system 

in addition to deep (regional) flow in the confined aquifers and allowed for variable rates of vertical flow from 

and to the confined aquifers. 

Most of the ground-water budgets presented in this 

report are derived from coarse-grid computer models 

designed to simulate "regional flow." Such budgets 

generally do not include local flow that enters and exits 

regional aquifers after traveling only a few miles or 

flow in overlying surficial aquifers (fig. 3). The percentage of the total ground-water flow system represented 

by "regional flow" is partly dependent on the mesh size 

of the model. During predevelopment conditions, the 

amount of local flow was commonly much greater than 

regional flow, especially in humid areas. A common 

characteristic of humid and semiarid areas is that rates 

of regional flow are increased by development. In the 

humid East, especially, much "local" flow is diverted 

into the regional flow system as withdrawals from deep 

confined aquifers increase. For example, in the Cambrian-Ordovician aquifer system of the northern Midwest, simulated recharge to the regional flow system 

was small (570 ft3 /s) before development. However, 

simulated recharge to the regional flow system for 

recent pumping conditions (mostly induced vertical 

leakage) was about 1,400 ft3 /s (Mandie and Kontis, 

1992, fig. 37). 

Total recharge to a regional aquifer system does not 

necessarily increase under pumping conditions; only 

the part of the total recharge that percolates to zones of 

pumping within the intermediate or regional, flow 

regimes increases. Where local flow systems do not 
6 REGIONAL AQUIFER-SYSTEM ANALYSIS 

TABLE I.-Computer models used for simulation of predevelopment and development flow conditions in regional aquifer systems 

(mi, mile; ft, foot; 3-0, three dimensional; 2-D, two dimensional; RASA, Regional Aquifer-System Analysis] 

Regional aquifer system Problem Characteristics of model used Computer program RASA report references references 

California Central Simulation of flow in 3-D finite-difference Trescott (1975), Williamson and others 

Valley aquifer sand-silt-clay aquifer model; four active Trescott and (1989). 

system. system that involves layers and 6-mile Larson (1976), 

very large ground- grid spacing. Meyer and Carr 

water withdrawals, (1979), Torak 

land subsidence, and (1982). 

recharge by imported 

surface water. 

Cambrian-Ordovician Simulation of flow in 3-D finite difference Trescott (1975), Mandie and Kontis 

aquifer system of sandstone and model; five active Kontis and (1992). 

the northern carbonate-rock layers and 16-mi Mandie (1988). 

Midwest. aquifers that involves grid spacing. 

pumping from multiaquifer wells and 

variable density flow. 

Carbonate-rock Simulation of shallow 3-D finite difference McDonald and Prudic and others 

province of the flow in basin-fill model; two active Harbaugh (1988). (1995). 

Great Basin. deposits super- layers and 5- by 7.5-

imposed over deeper mile grid blocks. 

flow through 

fractured carbonate 

rocks. 

Columbia Plateau Simulation of flow in 3-D finite-difference McDonald and Hansen and others 

aquifer system. basaltic and sedi- model; five active Harbaugh (1988). (1994). 

mentary aquifers that layers and 8,500-

involve pumpage and by 15,000-foot grid 

recharge from applied blocks. 

irrigation water and 

canal leakage. 

Edwards-Trinity Simulation of flow in 2-D finite-element Kuniansky (1990). Kuniansky and 

aquifer system. carbonate aquifers model; single layer Halligan (1994). 

of complex geometry and variable size 

owing to fracturing elements. 

and faulting. 

Floridan aquifer Simulation of flow in 3-D finite-difference Trescott (1975), Bush and Johnston 

system. carbonate aquifers model; two active Trescott and (1988). 

characterized by layers and 8-mi Larson (1976). 

large areal variations grid spacing. 

of transmissivity, 

flow activity, and 

pumpage. 

Great Plains aquifer Simulation of flow in 3-D finite-difference McDonald and Helgesen and others 

system. Dakota Sandstone and model; four active Harbaugh (1993). 

associated units that layers and 14-mi (1988). 

involves withdrawal grid spacing. 

of ground water and 

petroleum. 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 7 

TABLE I.-Computer models used for simulation of predevelopment and development flow conditions in regional aquifer systems-Continued 

Regional aquifer system Problem Characteristics of model used Computer program RASA report references references 

Gulf Coastal Plain Simulation of variable 3-D finite-difference Kuiper (1983, Williamson (in press) 

aquifer systems. density flow in very model; 10 active 1985). 

thick sand-silt-clay layers and 10-mile 

aquifer systems with grid spacing. 

faulting, salt domes, 

geopressured zones 

at depth, and large 

ground-water 

withdrawals. 

Southern High Plains Simulation of flow in 2-D finite-difference Trescott and Larson Luckey and others 

aquifer. unconfined aquifer model; single layer (1976), Larson (1986). 

with very large ground- and 10-mile grid (1978). 

water withdrawals and spacing. 

large reductions of 

saturated thickness 

locally. 

Northern Atlantic Simulation of flow in 3-D finite difference Trescott (1975), Leahy and Martin 

Coastal Plain heterogeneous clastic model; 10 active Leahy (1982). (1993). 

aquifer system. aquifers with localized layers and 7-mile 

pumping centers. grid spacing. 

Ozark Plateaus Simulation of pre- 3-D finite-difference McDonald and Imes and Emmett 

aquifer system. development flow in model; four active Harbaugh (1988). (1994). 

predominantly layers and 14-mile 

carbonate-rock grid spacing. 

aquifers of Paleozoic 

age. 

Madison aquifer of Simulation of variable Two 3-D finite difference Trescott (1975), Downey (1984, 1986). 

the Northern density flow in models; two to five Weiss (1982). 

Great Plains. Paleozoic and active layers and 

Mesozoic bedrock variable grid spacing. 

aquifers before 

development of 

ground water and 

petroleum. 

Snake River Plain Simulation of flow in 2-D parameter estima- Garabedian (1986), Garabedian (1992), 

aquifer system. basalt aquifers of tion model and 3-D McDonald and Lindholm (1996). 

eastern plain that finite difference Harbaugh (1988). 

involves large model; four active 

withdrawals and layers and 4-mi 

recharge by imported grid spacing. 

surface water. 

Southeastern Coastal Simulation of deep flow 3-D finite-difference McDonald and Miller (1992), Barker 

Plain aquifer in clastic coastal plain model; three active Harbaugh (1988). and Pernik (1994). 

system. aquifers with locally layers and 8-mile 

heavy pumping. grid spacing. 
·s REGIONAL AQUIFER-SYSTEM ANALYSIS 

Regional model 

grid spacing 

Local model 

grid spacing 

~~:·~.:~,,.,, .. ~~,,.,, .. ~~,,.,, .. ~~,,.,, .. ~ 

NOT TO SCALE 

EXPLANATION 

CJ Aquifer 

CJ Confining unit 

----.- Regional scale ground-water flow-Simulated in regional flow model 

---- ~ Local scale ground-water flow-Simulated only in local scale models 

FIGURE 3.-Relation of local and regional scale ground-water flow to discretization in computer flow models. 

exist, as in some karst areas, pumping causes virtually 

no increase in percolation to intermediate or regional 

flow regimes. This condition occurs in the Suwanee 

River drainage area of northern Florida, which is an 

internally drained karst area underlain by the Floridan 

aquifer system (fig. 2B). Simulated recharge to the intermediate-regional flow regimes in this karst area was 

about 5,800 ft3 /s for predevelopment and recent pumping conditions (Bush and Johnston, 1988, p. 45, figs. 22, 

32, and 33). The pumpage in the Suwanee River drainage area is supplied by a decrease in springflow and 

discharge to surface-water bodies. 

REGIONAL GROUND-WATER BUDGETS 

Regional aquifer systems are grouped into four categories for presentation of regional ground-water budgets. The first category is the clastic-rock aquifer 

systems of the Atlantic and the Gulf Coastal Plains. The 

second category is the carbonate-rock aquifer systems 

in several physiographic provinces from the Atlantic 

Coastal Plain of Florida to the Great Basin of Nevada. 

The third category is the clastic-rock aquifer systems of 

the Central and the Western United States. The fourth 

category is the basaltic-rock aquifer systems of the 

Pacific Northwest. Of the 14 aquifer systems, 11 are 

extensively developed, and budgets are presented for 

predevelopment and development conditions for those 

systems. As of the early 1980's, three carbonate-rock 

aquifer systems had little ground-water development; 

only predevelopment budgets are presented for those 

systems. A summary of predevelopment recharge and 

discharge rates for the 14 regional aquifer systems is 

given in table 2. 

The ground-water budgets for development conditions are dependent on the time period that was simulated. Each budget is a snapshot of a recent year or 

period of years and is not an average of long-term 

development conditions. In particular, the amount of 

water that comes from storage depends on the history 

of ground-water withdrawals and how close the system 

is to a new equilibrium. As an example of how groundwater budgets have changed since ground-water development began, the following discussions of the Gulf 

Coastal Plain aquifer systems describe budgets for several periods from predevelopment to 1985. For the other 

aquifer systems, one budget is described for a recent 

development period. 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 9 

TAHLE 2.-Rates and characteristics of predevelopment recharge and discharge of regional aquifer systems 

[mi2

, square mile; in/yr, inch per year; ft 3

/s, cubic feet per second; RASA, Regional Aquifer-System Analysis] 

Predevelopment recharge Predevelopment discharge 

Areal Percolation and Discharge 

Regional aquifer system extent Precipitation leakage rate Area rate Nature of discharge RASA report references 

(mi 2 ) (in/yr) [ft% and (in/yr)] (mi 2 ) (ft 3

/s} 

California Central 20,000 5-26 1280 10,900 280 Evapotransporation Williamson and others 

Valley aquifer (0.35) and upward (1989). 

system. 2

2,760 

leakage to streams. 

2,350 Evapotranspiration. 

(3.4) 410 To streams. 

Cambrian-Ordovician 161,000 30 570 () 570 To streams or as Mandie and 

aquifer system of diffuse leakage. Kontis (1992). 

the northern 

Midwest. 

Carbonate-rock 100,000 3-60 1

2,210 (3) 1,658 Evapotranspiration. Prudic and others 

province of the 274 To springs. (1995). 

Great Basin. 192 To lakes and rivers. 

83 Other discharge. 

Columbia Plateau 4

50,600 6-45 2

7,120 32,700 2,750 To rivers. Hansen and others 

aquifer system. (3.0) 3,945 To small streams. (1994). 

425 To seepage faces. 

Edwards-Trinity 455,700 10-32 13,870 51,900 3,870 To springs and Kuniansky and 

aquifer system. (1.01) rivers. Holligan (1994). 

Floridan aquifer 594,000 53 221,500 67,000 12,500 To springs. Bush and Johnston 

system. (4.4) 6,500 To streams and (1988). 

lakes. 

2,500 Diffuse drainage. 

Great Plains aquifer 4

170,000 12-28 1

340 () 290 Diffuse leakage. Helgesen and others 

system. 50 To streams. (1993). 

Gulf Coastal Plain 5230,000 24-60 14,500 127,000 4,500 To streams and Williamson (in press). 

aquifer systems. (0.48) Gulf of Mexico 

or as diffuse 

leakage. 

Southern High Plains 29,000 16-20 1

270 29,000 270 To streams, springs, Luckey and others 

aquifer. (0.13) and seeps along (1986); Gutentag 

eastern escarpment. and others (1984). 

Northern Atlantic 5

55,000 47 1

920 25,000 920 Diffuse, upward Leahy and Martin 

Coastal Plain (0.5) leakage. (1993). 

aquifer system. 

Ozark Plateaus aquifer 65,000 36-50 1

7,091 40,000 4,035 To streams·and lakes. Imes and Emmett 

system. (2.4) 3,056 To major rivers and (1994). 

adjoining aquifer 

systems. 
10 REGIONAL AQUIFER-SYSTEM ANALYSIS 

TABLE 2.-Rates and characteristics of predevelopment recharge and discharge of regional aquifer systems-Continued 

Predevelopment recharge Predevelopment discharge 

Region~l aquifer system 

Madison aquifer of 

the northern 

Great Plains. 

Areal 

extent Precipitation 

(mi2) (in/yr) 

4 210,000 10-20 

Percolation and 

leakage rate 

[ft% and (in/yr)] 

Discharge 

rate Nature of discharge 

(ft%) 

RASA report references 

47 Diffuse leakage to Downey (1984). 

adjoining aquifer 

systems. 

Snake River Plain 

aquifer system 

(eastern part). 

10,800 68-10 

7

20-60 

10,800 86,100 Seepage and spring Garabedian (1992). 

flow to Snake 

River. 

Southeastern Coastal 

Plain aquifer 

system. 

210,000 51 12,165 

(0.6) 

46,500 1,720 

445 

To streams. Barker and Pernik 

(1994); Miller 

(1992). 

1 Deep regional flow regime only. 

2 Deep regional flow plus some local intermediate-scale flow. 

3 Size of recharge area is uncertain. 

4 Areal extent of RASA investigation; full extent of aquifer system is larger. 

5 Excludes offshore areas. 

6 On the plain. 

7 In tributary basins. 

Diffuse leakage and 

outflow to 

adjoining aquifer 

systems. 

8 Rates for the Snake River Plain aquifer system are for 1891 through 1895, before development of ground water. Some recharge was supplied by percolation of excess irrigation water from 

surface-water sources. Accretion of ground-water storage was about 1,360. 

The details of the digital models used to simulate 

ground-water flow and to calculate ground-water budgets for aquifer systems are not described in this report. 

The interested reader is referred to the references listed 

in table 1 for those details. However, as an example, the 

following discussion of a regional ground-water budget 

(for the Gulf Coastal Plain aquifer systems) briefly 

describes how three large regional aquifer systems with 

complex boundary conditions are represented in a 

coarse-grid digital model. 

CLASTIC-ROCK AQUIFER SYSTEMS OF THE 

ATLANTIC AND THE GULF COASTAL PLAINS 

Several major aquifer systems that consist of unconsolidated to semiconsolidated clastic rocks underlie the 

Atlantic and the Gulf Coastal Plains of the Eastern and 

the Southern United States. These rocks are mostly of 

Cretaceous through Quaternary age and contain many 

prolific sand aquifers. The subdivision of this thick 

sequence of sands and fine-grained sediments into 

aquifer systems for investigation during the RASA Program was somewhat arbitrary. The sediments of the 

western Gulf Coast and the Mississippi Embayment 

were subdivided into three aquifer systems that are collectively referred to as the "Gulf Coastal Plain aquifer 

systems" (fig. 1). The laterally equivalent clastic sediments to the east were named the Southeastern Coastal 

Plain aquifer system, and those further northeast were 

named the Northern Atlantic Coastal Plain aquifer system (fig. 1); the Cape Fear Arch, which is located in the 

vicinity·of the North Carolina-South Carolina State line, 

is a natural hydrogeologic boundary that separates 

those two aquifer systems. 

GULF COASTAL PLAIN AQUIFER SYSTEMS 

The Gulf Coastal Plain aquifer systems consist 

mostly of sediments of Cenozoic age that underlie 

about 290,000 mi2

; the aquifer systems extend from 

Texas to Florida and include the Mississippi Embayment, the Gulf Coastal Plain of Texas, and offshore areas 

beneath the Gulf of Mexico (fig. 1). These sediments are 

an interbedded sequence of sand, silt, and clay with 

some gravel, lignite, and limestone. The thickness of the 

sediments increases toward the Gulf of Mexico in a general wedge shape; maximum thickness of more than 

30,000 ft occurs in southern Louisiana. 

According to Williamson (in press), recharge to the 

Gulf Coastal Plain aquifer systems is not related to the 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS II 

average rainfall, but rather to the capacity of the aquifer 

systems to transmit water away from the recharge 

areas.:_"where the flow capacity is limited by the small 

hydraulic gradient or by resistance to flow of the aquifer system, most of the rainfall which potentially would 

recharge the regional aquifer systems is discharged to 

local surface-water bodies." Pumpage from the Gulf 

Coastal Plain aquifer systems increased from about 870 

ft3 Is in 1930 to 13,500 ft3 Is (8.7 Ggall d) in 1985. The 

development of ground water has caused land subsidence, a lowering of hydraulic heads, and changes in 

aquifer storage, rates and locations of recharge and discharge, direction and magnitude of flow, and water 

quality (Williamson, in press). 

Areally, the following aquifer systems were delineated on the basis of regional ground-water flow and 

sediment characteristics: the Mississippi Embayment, 

the Texas coastal uplands, and the coastal lowlands. For 

simulation in a regional flow model, these aquifer systems were divided into 11 regional aquifers and permeable zones and 6 regional confining units by Hosman 

and Weiss (1991) and Weiss (1992); most of these units 

are shown in the north-south section of figure 4. The 

resulting 17 model layers do not necessarily correspond 

to previously named geologic or geohydrologic units. 

For example, layer 11 in figure 4 represents the Missis5,000 

SEA 

LEVEL 

5,000 

10,000 

N MISSISSIPPI EMBAYMENT 

AQUIFER SYSTEM 

sippi River Valley alluvial aquifer in the northern part 

of the section and permeable zones in Holocene-upper 

Pleistocene-age deposits in the south part of the section. 

The two parts of layer 11 shown in figure 4 are actually 

connected hydraulically in central Louisiana (Williamson, in press). 

Regional flow within the Gulf Coastal Plain aquifer 

systems was simulated with a finite-difference, variable-density flow model that was developed by Williamson (in press) and that used a computer solver code 

by Kuiper (1983, 1985). The density of ground water, 

although variable in space, was assumed to be constant 

in time. Figure 5 shows the representation of aquifers 

and confining units and boundary conditions in the 

model. A constant-head boundary was simulated in a 

shallow recharge-discharge layer above the top aquifer 

in figure 5. Heads in this layer do not vary with time. 

The base of the flow system is specified as a no-flow 

boundary at the top of either the Midway confining unit 

or the geopressured zone where it is above the Midway 

confining unit (figs. 4, 5). Most of the lateral aquifer system boundaries are specified as no flow except that estimated data may be used in some areas to extend the noflow boundaries for some distance beyond the area of 

interest. Because of the very large study area, Williamson (in press) used a very coarse grid model to simulate 

COASTAL LOWLANDS 

AQUIFER SYSTEM 

s 

15,000 __,_ ________________________ _,.____;L. _______________ L_ 

SCALE IS APPROXIMATE 

EXPLANATION 

~ Aquifer and model layer number-

~ Patterned area contains saline water 

Confining unit and model layer 

number 

+ + + + Unit truncated at edge of Continental 

Shelf 

0 50 100 MILES 

0 50 100 KILOMETERS 

FIGURE 4.-Aquifers and confining units and designation of layers in the regional flow model of the Gulf Coastal Plain aquifer systems 

(from Williamson, in press, fig. lOA). 
12 REGIONAL AQUIFER-SYSTEM ANALYSIS 

N s 

MISSISSIPPI EMBAYMENT 

AQUIFER SYSTEM 

COASTAL LOWLANDS 

AQUIFER SYSTEM 

Coast ~ 

Midway confining unit 

Ocean 

EXPLANATION 

Constant head 

Aquifer and model layer number 

Confining unit and model layer number 

Direct flow between layers 

No flow 

jP = 991 Pumpage, in cubic feet per second 

Recharge and discharge rates, 

in cubic feet per second 

FIGURE 5.-Vertical structure of the regional flow model of the Gulf Coastal Plain aquifer systems and simulated 1985 rates ofrecharge, 

discharge, and pumpage (modified from Williamson, in press, fig. lOB). 

regional ground-water flow. However, he stated that 

even with the 10-mi horizontal grid spacing, "the 

regional features affecting flow in the aquifer systems 

are generally preserved." 

The model was used to simulate ground-water flow 

for predevelopment conditions (about 1900) and transient pumping conditions from 1930 through 1985. Simulated total recharge and discharge and pumpage from 

the principal aquifers for the 1985 pumping simulation 

are shown in figure 5. After using this model to simulate 

variable-density flow in the deeper saline parts of the 

aquifer systems, Williamson (in press) concluded that 

the density of the saline water probably has a significant 

effect on flow in the saline and freshwater parts of the 

aquifer systems. 

Ground-water budgets for the Gulf Coastal Plain 

aquifer systems during predevelopment and for 1985 

pumping conditions are shown in figure 6. Note that the 

rates of regional recharge and discharge have been substantially changed by ground-water pumping. The 1985 

pumpage is about three times the predevelopment 

recharge rate. About two-thirds of the 1985 pumpage 

was supplied by increased percolation to regional aquifers in their outcrop and subcrop areas and by increased 

vertical flow to confined parts of regional aquifers (Williamson, in press). The remaining one-third was supplied by a decrease in discharge to surface-water bodies 

and evapotranspiration and, to a lesser extent, by loss of 

aquifer storage. Most of the loss from storage was 

accounted for by water-table declines in the Mississippi 

River Valley alluvial aquifer (model layer 11, fig. 5). 

Some loss of artesian storage has occurred in the Houston, Texas, and the Baton Rouge, Louisiana, areas, 

which has resulted in the inelastic compaction of finegrained beds and land subsidence. Williamson (in 

press) noted that some aquifers are "self-supporting"; 

that is, most of their pumpage was supplied by 

increased recharge (in outcrop or subcrop areas) or by 

decreased discharge from the aquifer itself (model layers 5, 8-11, fig. 5). However, one major aquifer with a 

narrow outcrop and subcrop band (model layer 2) had 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 

NORTHERN ATLANTIC 

COASTAL PLAIN 

AQUIFER SYSTEM 

Predevelopment 

Natural recharge 

61,900 

· ... .Unconfined 

aq1.,1ifers 

. 92.0 

Confined . 

Discharge to 

streams 

61,000 

aquif~rs . ~-

Diffuse 

upward 

leakage 

920 

Development conditions 

(1980) 

Natural 

recharge 

61,900 

Decrease 

in storage 

30 

Pumpage 

1,870 

Discharge to 

streams 

59,700 

Diffuse 

upward 

leakage 

390 

Source: Leahy and Martin (1993) 

SOUTHEASTERN 

COASTAL PLAIN 

AQUIFER SYSTEM 

Predevelopment 

Outcrop Downward leakage 

recharge and lateral inflow 175 

1,990 

.. Aquitei · 

· · systetrr· · 

.. ....-.,...;....·, .. . . .·· . . . ., 

: ; ~:: 

Upward 

leakage and 

lateral outflow 

445 

Discharge 

to streams 

1,720 

Development conditions 

(1981-85) 

Downward 

leakage and 

lateral 

inflow 260 Pumpage 765 

·-:·:· ..... ·-·- ~· .. 

Upward 

·. : · ·. · · . : : leakage and 

· . ~ :I: lateral outflow . :-: . . : : 345 

·.· • .·. : ·: : ·. . Discharge 

· ·. ·:. to streams '-'----r- '--~~-'--' 1 ,375 

Decrease 

in storage 

235 

Source: Barker and Pernik (1994) 

GULF 

COASTAL PLAIN 

AQUIFER SYSTEMS 

Predevelopment 

Natural recharge 4,500 

.-..........-: .. · 

· 

: Aquifer 

sy~lem 

· ·:':·.·:: :._.~::·· 

Discharge to 

surface-water 

bodies and 

evapotranspiration 4,500 

Development conditions 

(1985) 

Natural and 

induced recharge 

13,400 Pumpage 13,500 

Decrease 

in storage 

1,700 

-~: 

·· .. · .. ···•··•·· ... · .•. : ... -.......;.,... . 

Discharge to 

surface-water 

bodies and 

evapotranspiration 1,600 

Source: Williamson (in press) 

13 

FIGU RE 6.-Ground-water budgets before and after development of clastic-rock aquifer systems in the Atlantic and Gulf Coastal Plains. 

Values in cubic feet per second. Sum of outflows may not exactly equal sum of inflows as a result of independent rounding. 

80 percent of its pumpage supplied by downward leakage from an overlying aquifer. 

Changes to the regional ground-water budget during the development era (1930-85) are shown in greater 

detail in figure 7. Pumpage steadily increased from 870 

ft3/s in 1930 to 14,700 ft3/s (9.5 Ggal/d) in 1980 with a 

small decrease in 1985. Pumpage throughout the development period has been supplied mostly by steadily 

increasing recharge to the regional aquifers and, to a 

lesser extent, by decrease in natural discharge and loss 

of aquifer storage. For much of the period, the percentage of pumpage supplied from aquifer storage ranged 

from 8 to 16 percent. An exception occurred in 1950 

when the storage contribution increased to 27 percent 

(fig. 7) as a result of primarily a large increase in pumpage from the Mississippi River Valley alluvial aquifer. 

Williamson (in press) stated that, although only a small 

part of the 1985 pumpage was supplied from aquifer 

storage, the system was far from equilibrium with 1985 

pumping conditions. 

NORTHERN ATlANTIC COASTAL PlAIN AQUIFER SYSTEM 

The Northern Atlantic Coastal Plain aquifer system 

extends from Long Island, New York, to the North 

Carolina-South Carolina State boundary and underlies 

about 55,000 mi2 (fig. 1). The aquifer system consists of 

consolidated and unconsolidated gravel, sand, silt, and 

clay of Jurassic to Holocene age (Trapp, 1993). These 

sediments form an eastward-thickening wedge that 

contains aquifers that are the major source of fresh 

ground water in the area. The sediments have been subdivided into 11 regional aquifers and 9 confining units 

on the basis of continuity of permeability (Trapp, 1993). 

Recharge to the aquifers is from infiltration of precipitation at rates that range from 10 to 25 in/ yr. Most of this 

recharge flows through shallow aquifers and discharges 

to nearby streams; a small amount (about 0.5 in / yr) per-
14 REGIONAL AQUIFER-SYSTEM ANALYSIS 

18,000 

1"5,000 

12,000 

0 

z 

<( 

ui 9,000 

(.!)0 

<(Z 

CLQ 

:::!:U 

15: ~ 6,000 .a: 

ww 

l:)CL 

~t;:j i5 ~ 3,000 

(f)U oiii 

w' G 

~z o <( -_ 

IW 

Ul:J 

W<( 

~ ~ -3,000 

01-

(f)(f) 

wz 

t--

~ ~ - 6,000 

oz 

w<t: 

I-I 

<(U :5 -9,000 

::2: 

(f) 

- 12,000 

- 15,000 

-18,000 

// ~ 

4,500 ,,790 

v // 

' 

4,500 4,040 

' 1- --'-- 870 '--

I I 

PREDEVELOPMENT 1930 

570 

920 ~ 

150 r. 

p ~ 

'7.~ 0 

s,s2'o O / 

/ ... /, , / / 

3,12o 2,590 

3,610 

~ 

~ 

t---

1,800 3,310 - 5,830 

~ 

-

I I I 

1940 1950 1960 

~ 1,710 ' .... : .. ~ 0 Loss 

~ ·.···. of storage ~ 

.. · .. :. • .··. · · /, ~ 

± ~ , 

~ + ~ / // 

;%" ... "/, 

~ ,, · / 

/ v 3, 45~ - Recharge / 14,000 

1),500 

:;;so / 8,500 // 

/; / 0' ~/ i:· v / ~ , 

0" , ~ '/ / 

1,850 \660 1,640 2,390 2, 180 - Discharge 

f----'- _:,._____ - ~ r---

6,880 8, 480 

11 ,240 - Pumpage 

'---'- 14,700 13,480 

~ 

-

'--

'--

I I I 

1970 1980 1990 

FJGL"RE 7.-Change in simulated regional ground-water budget of the Gulf Coastal Plain aquifer systems from predevelopment to 1985 

(modified from Williamson, in press, fig. 45). 

colates into the deeper confined aquifers. Ground-water 

pumpage (excluding irrigation and rural withdrawals) 

has increased from about 155 ft3 / s in 1900 to about 

1,870 ft3 / s (1.2 Ggal / d) in 1980. As a result of pumpage 

for industrial and public supply, extensive cones of 

depression occur in New Jersey, the Delmarva Peninsula, and southern Virginia and adjacent North Carolina. 

Simulations of steady-state flow in the aquifer system were made for predevelopment conditions, and 

simulations of transient pumping conditions were 

made for 10 pumping periods of varying duration from 

1900 to 1980 by using a 10-layer finite-difference model 

(Leahy and Martin, 1993). For simulation of transient 

pumping conditions, the top boundary of the model in 

the onshore area was treated as a flux and a specifiedhead boundary. This boundary condition enabled the 

model to simulate transient heads in and near outcrop 

areas and allowed for variable rates of vertical flow to 

and from confined aquifers (Leahy and Martin, 1993, p. 

18-21). 

Ground-water budgets for the Northern Atlantic 

Coastal Plain aquifer system for predevelopment and 

1980 conditions are shown in figure 6. Because these 

budgets represent the total ground-water flow system, 

the areal recharge rate is the same for predevelopment 

and 1980 conditions-about 62,000 ft3 / s. Note that 

pumpage in 1980 (1,870 ft3 / s) represents only about 3 

percent of the recharge that entered the ground-water 

flow system. Pumpage, which is primarily from the 

confined aquifers, is supplied, for the most part, by an 

increase in downward percolation to the confined aqui-
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 15 

fers and a decrease in diffuse upward leakage and eventual discharge to surface-water bodies. At the end of the 

1978 through 1980 pumping period, less than 2 percent 

of the pumpage was supplied by water derived from 

aquifer storage. However, Leahy and Martin (1993) 

emphasized that because withdrawals are not distributed evenly (spatially) over the system, the local effects 

of water released from storage can be significant. As in 

predevelopment time, shallow ground-water flow 

accounts for most of the flow through the aquifer system. However, by 1980, pumpage caused the rate of 

deep percolation into confined aquifers to more than 

double compared with predevelopment and the 

upward leakage from confined aquifers to occur at less 

than one-half the predevelopment rate. Because only a 

small volume of water was being released from storage 

at the end of each pumping period, Leahy and Martin 

(1993) concluded that the system adjusts rapidly (less 

than 3 years) to changes in withdrawal rates. Their simulations also suggested that the total volume of vertical 

flow (downward leakage) is much greater than lateral 

flow through aquifers from outcrop areas. This occurs 

because of the very large areal extent of the cones of 

depression in comparison with the much smaller crosssectional areas of the aquifers through which lateral 

flow occurs. In general, vertical flow from overlying 

aquifers is the dominant source of pumpage from confined aquifers (Leahy and Martin, 1993). 

SOUTHEASTERN COASTAL PLAIN AQUIFER SYSTEM 

The Southeastern Coastal Plain aquifer system comprises a thick sequence of mostly poorly consolidated 

clastic rocks of Cretaceous to late Tertiary age (Miller, 

1992). The aquifer system underlies an area of about 

120,000 mi2 of the Coastal Plains of Alabama, Georgia, 

Mississippi, and South Carolina (fig. 1) and contains 

numerous aquifers and confining units. However, for 

the purpose of simulating regional flow by using a 

coarse-mesh computer model, Renken (1996) grouped 

the rocks into four regional aquifers separated by three 

regional confining units. 

Most of the recharge that occurred in aquifer outcrop areas (about 7 inlyr) infiltrates to shallow depths 

and discharges to nearby streams; only about 0.6 inlyr 

percolates to the deep confined parts of the aquifer system. A coarse-mesh finite-difference model (8-mi grid 

spacing) was used by Barker and Pernik (1994) to simulate deep regional ground-water flow. Simulation of 

predevelopment (steady-state) conditions indicated that 

deep regional flow was about 2,165 ft3 Is, of which 

about 80 percent discharged to large rivers and about 20 

percent discharged upward as diffuse leakage to overlying aquifers or adjacent aquifer systems (fig. 6). 

A more detailed ground-water budget, which was 

based on cross-sectional flow models and analysis of 

stream base flows, was presented by· Faye and Mayer 

(1990) for part of the aquifer system in Georgia and the 

adjacent areas of Alabama and South Carolina. They 

concluded that total ground-water recharge in that area 

was about 9,000 £t3 Is, which ultimately discharged as 

follows: 5,150 ft3 Is (58 percent) to streams close to 

points of recharge (local flow), 1,950 ft3 Is (22 percent) to 

tributaries of major rivers (intermediate flow), 780 ft3 Is 

(9 percent) to major rivers (regional flow), 660 ft3 Is (8 

percent) as riparian evapotranspiration, and 310 ft3 Is (3 

percent) as leakage to overlying aquifers (regional 

flow). This analysis and the regional model results indicate about a 10 to 1 ratio of shallow (local to intermediate) recharge to regional recharge. This ratio 

"emphasizes the sharp contrast between the relatively 

large amount of water that circulates within the 

dynamic, shallow flow regime and the relatively small 

amount circulating within the less vigorous, deeper 

parts of the confined flow regime" (Barker and Pernik, 

1994, p. C32). 

By 1985, pumpage from the entire aquifer system 

was about 765 £t3 Is (495 Mgal/d) and water-level 

declines, which exceeded 100ft, had locally developed 

in the downdip confined parts of the pumped aquifers. 

Except in a few places, water levels i.n outcrop areas 

were not affected by pumping in the confined parts of 

the aquifers. For this reason, according to Barker and 

Pernik (1994), recharge to outcro2 areas was applied at 

the predevelopment rate (1,990 ft3 Is) for transient simulations of 1900 through 1985 development conditions. 

Where water levels have declined in or near outcrop 

areas, the percolation rate to the deep confined aquifers 

undoubtedly has increased; however, they further 

explain that with the large grid-cell size (8 x 8 mi), it is 

impossible to simulate head changes in very small 

areas. The greatest change from predevelopment to 

1985 conditions is a simulated reduction of about 345 

ft3 Is in the base flow of streams and a decrease of about 

235 ft3 Is in aquifer storage. The decrease in storage is 

documented by long-term head declines in wells 

located in the principal pumping centers in the deep 

regional aquifers (Barker and Pernik, 1994, plates 6 and 

7). A lesser amount of pumpage is supplied by induced 

leakage from overlying aquifers and reduced diffuse 

upward leakage to them (fig. 6). 

CARBONATE-ROCK AQUIFER SYSTEMS 

There are 27 major carbonate-rock terranes in North 

America (Brahana and others, 1988). Some of the carbonate-rock units are highly permeable and productive 
16 REGIONAL AQUIFER-SYSTEM ANALYSIS 

aquifers, whereas other units are characterized by low 

permeability and function, for the most part, as confining units. This wide variation in hydrogeologic characteristics results from the many geologic and hydrologic 

processes that affect the porosity and permeability of 

carbonate rocks (Brahana and others, 1988, table 1). 

. Non.Darcian (conduit) flow occurs in many carbonate-rock terranes, especially through large cavernous 

openings. However, the volume of rock affected by nonDarcian flow is usually small compared with the total 

volume of a regional carbonate-aquifer system. A major 

assumption in applying numerical models to simulate 

flow in carbonate-rocks is that the flow can be treated as 

flow through porous media. At the scale of a coarsemesh regional model (grid-block spacing of a few miles 

or more), this assumption is considered to be reasonable 

(Bush and Johnston, 1988, p. 27). 

Ground-water budgets are presented in this section 

for six regional carbonate-aquifer systems. Three of 

these systems-the Floridan, the Cambrian-Ordovician 

of the northern Midwest, and the Edwards-Trinity of 

Texas-are extensively developed and provide public 

water supplies to major cities. Budgets for predevelopment and recent development conditions are presented 

for these aquifer systems in figure 8. The other three 

systems-the Madison aquifer, the Ozark Plateaus aquifer system, and the carbonate-rock province of the Great 

Basin-were minimally developed (as of the 1980's) and 

only predevelopment water budgets could be defined 

during the RASA Program investigations, as shown in 

figure 9. 

CAMBRIAN-ORDOVICIAN AQUIFER SYSTEM OF THE 

NORTHERN MIDWEST 

The Cambrian-Ordovician aquifer system comprises mainly marine sandstone and carbonate rocks 

that underlie an area of about 161,000 mi2 in Illinois, 

CAMBRIAN-ORDOVICIAN 

AQUIFER SYSTEM IN 

THE NORTHERN MIDWEST 

FLORIDAN 

AQUIFER SYSTEM 

EDWARDS-TRINITY 

AQUIFER SYSTEM 

Predevelopment 

Natural recharge 

570 

Natural 

discharge 

570 

Development conditions 

(1976-80) 

Natural and 

+. 

Decrease in storage 

220 

Source: Mandie and Kontis (1992) 

Predevelopment 

Natural recharge 

21,500 Discharge to 

fr- ..J.......-'-.-'--r....l...:l.... springs and 

streams 

19,000 

Upward 

leakage 

2,500 

Development conditions 

(1980) 

Natural and 

induced recharge 

24,000 Pumpage 4,100 

+ ~ I I I I 

Almost no change 

in storage 

~ 

~ 

Discharge to 

springs and 

streams 

18,100 

Upward 

leakage 

1,800 

Source: Bush and Johnston (1988) 

Predevelopment 

Mountains Recharge: 

and High From 

Plains aquifer Areal streams 

300 2,540 1,030 

Discharge to 

-'--r-'--r-"1? springs and 

f-l-.-'-.-:.......,~.,...-Jc...,...l-..j streams 

3,870 

Development conditions 

(1974-75) 

Recharge: 

Mountains 

and High From 

Plains aquifer Areal streams 

400 2,540 1,150 

1f 

t-

• 

No change in storage 

Pumpage 

1,160 

Discharge to 

springs and 

streams 

2,930 

Source: Kuniansky and Halligan (1994) 

FIGL'RE 8.-Ground-water budgets before and after development of carbonate-rock aquifer systems in the Midwestern and Southern 

United States. Values in cubic feet per second. Sum of outflows may not exactly equal sum of inflows as a result of independent rounding. 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 17 

Indiana, Iowa, Wisconsin, Minnesota, and Missouri (fig. 

1). The aquifer system was divided into an upper shale 

confining unit, three major aquifers (sandstone and 

dolomite), and two internal confining units (shale, siltstone, and dense dolomite) by Young (1992). Generally, 

the aquifer system is directly overlain by and hydraulically connected to a Silurian-Devonian aquifer (limestone· and dolomite). In much of the area, rocks of 

Paleozoic-age are covered by a veneer of glacial drift. 

Most recharge and discharge in the northern Midwest occurs in local flow systems within the glacial 

drift. Some water enters the Devonian-Silurian aquifer 

and the Cambrian-Ordovician aquifer system and 

moves along intermediate or regional flow paths away 

from high areas in the north to low areas in the south 

and east. Principal discharge areas for regional flow are 

the Mississippi and the Missouri Rivers, the Illinois and 

the Michigan structural basins, and Lake Michigan. 

Simulations indicate that the Cambrian and Ordovician 

rocks constitute a regionally continuous aquifer system 

because of the similarity of the flow patterns within the 

aquifers and locations of their recharge and discharge 

areas (Mandie and Kontis, 1992, p. 95). 

Development of the aquifer system began in the 

1860's near Lake Michigan in eastern Wisconsin and 

northeastern Illinois and along the valleys of the Mississippi River and its nearby tributaries. Wells flowed initially with hydraulic heads that were more than 100 ft 

above the water level of Lake Michigan at Chicago, Illinois, and Milwaukee, Wisconsin. By 1980, large-scale 

pumping had caused the hydraulic heads to decline as 

much as 375 ft at Milwaukee and 900 ft at Chicago 

(Young, 1992). 

A steady-state simulation of predevelopment conditions and transient simulations of pumping conditions 

(1861-1980) in the Cambrian-Ordovician aquifer system were made by using a coarse-grid (16-mi grid spacing) finite-difference model (Mandie and Kontis, 1992). 

The model incorporated an additional computer code to 

calculate withdrawal rates from individual aquifers 

tapped by a multiaquifer well. 

The predevelopment ground-water budget (fig. 8) 

indicates that flow through this bedrock aquifer system 

was comparatively small (570 ft3 /s) considering the 

large areal extent of the system. The 1976 through 1980 

pumpage of 1,210 ft3 /s (782 Mgal/d) is more than double the predevelopment recharge rate. This pumpage 

was supplied, for the most part, by an increase in 

recharge into the confined Cambrian-Ordovician aquifer system (830 ft3 /s) from overlying glacial drift and 

rocks of Cretaceous age and, to a lesser extent, by a 

decrease in natural discharge to streams (160 ft3 /s) and 

a release of water from aquifer storage (220 ft3 /s). A 

detailed simulation of flow in the Cambrian-Ordovician aquifer system in the Chicago-Milwaukee area 

indicates that recharge to the aquifer system occurs 

most readily where it subcrops beneath glacial drift 

(Young, 1992). 

OZARK PLATEAUS 

AQUIFER SYSTEM 

MADISON AQUIFER 

OF THE NORTHERN 

GREAT PLAINS 

CARBONATE-ROCK 

PROVINCE OF THE 

GREAT BASIN 

Recharge 

7,091 

Discharge 

f-r..l.r....,-.l.......r-'-...--'-,--9""" + to streams 

Aquifer 

. · system · 

77TTT>'7 

?zzz)zz 

and lakes 

4,035 

Discharge to 

+ Mississippi, 

Missouri, 

Neosho, and 

Arkansas Rivers 

and adjacent 

aquifer systems 

3,056 

Source: lmes and Emmett (1994) 

Recharge in highland areas 

of Montana and Wyoming 

47 

Discharge to 

f-r~.-L.-,-C..,...J.._,..C['" Cretacea us-age 

rocks 

27 

Discharge to 

1-'-....-'---.,---'---,r--'---.-L--.=~ rocks of 

Source: Downey (1984) 

Cambrian and 

Ordovician 

age 

20 

Evapotranspiration 

1,658 

Discharge 

to springs 

274 

Seepage 

1-r-...J.....,r--'-..,-'-r...J.._..-"'~ to I a kes 

and rivers 

192 

6..!.."""""'==--'-~~'=="'rr Other 

discharge 

83 

Source: Prudic and others (1995) 

FIGU RE 9.-Predevelopment ground-water budgets of carbonate-rock aquifer systems in the Ozark Plateaus, 

the Northern Great Plains, and the Great Basin. Values in cubic feet per second. Sum of outflows may not 

exactly equal sum of inflows as a result of independent rounding. 
18 REGIONAL AQUIFER-SYSTEM ANALYSIS 

FLORIDAN AQUIFER SYSTEM 

The Floridan aquifer system is a thick sequence of 

hydraulically connected carbonate rocks (limestone and 

dolomite) that range in age from late Paleocene to early 

Miocene (Miller, 1986). This highly productive a~uifer 

system underlies an area of about 100,000 mi and 

includes Florida, most of southern Georgia, and smaller 

areas of Alabama and South Carolina (fig. 1). The aquifer system generally consists of an upper aquifer and a 

lower aquifer that are separated by a less permeable 

confining unit. Transmissivity of the upper aquifer in 

the Floridan aquifer system ranges from more than 

1,000,000 ft2 I d in the unconfined karst areas of central 

and northern Florida to less than 50,000 ft2 I d in areas 

where the aquifer is confined by thick clay sections 

(Bush and Johnston, 1988). Large average rainfall (about 

53 inlyr) in conjunction with topography characterized 

by plains and low hills provides abundant recharge to 

the Floridan aquifer system. 

The distribution of natural recharge, discharge, and 

flow is strongly influenced by the degree of confinement of the Floridan aquifer system by overlying finegrained clastic sediments. In the unconfined and semiconfined karst areas of central and northwestern peninsular Florida and southwestern Georgia, recharge rates 

are large (10-20 inlyr), surface drainage is sparse, and 

ground water moves along flow paths of intermediate 

length (generally a few tens of miles) to discharge at 

large springs or streams (fig. 2B). In contrast, in the hilly 

outcrop areas of central Georgia, where surface drainage is well developed, ground water moves primarily 

within the sandy hills that overlie the Floridan aqifer 

system for short distances to streams; only a small fraction of the recharge enters the Floridan aquifer system 

and moves into the deep confined parts of the aquifer 

system (Bush and Johnston, 1988). Thus, the simulated 

ground-water budgets for the Floridan aquifer system 

(fig. 8) represent virtually 100 percent of the total 

ground-water flow in the karst areas, but only a small 

percentage of the total flow in the hilly outcrop areas. 

Steady-state simulations of flow in the Floridan 

aquifer system for predevelopment and 1980 conditions 

were made by using a coarse-grid finite-difference computer model (table 1). A transient simulation of development conditions was not feasible because the time 

required for the system to reach a new steady-state condition following a change in pumpage can range from 

days in highly transmissive semiconfined areas to years 

in less transmissive, tightly confined areas (Bush and 

Johnston, 1988, p. 22-25). 

The first wells were constructed into the Floridan 

aquifer system during the late 1880's, and withdrawals, 

which have increased steadily since then, totaled about 

3 Ggall d by the early 1980's. Pumping caused longterm water-level declines of more than 50 ft in three 

large areas-coastal Georgia and nearby Florida and 

South Carolina, west-central Florida, and the western 

panhandle of Florida. Ancillary effects of pumping 

include saltwater intrusion in ·a few coastal areas, 

induced collapse of sinkholes in karst areas, and a 

minor amount of land subsidence in one area as a result 

of the inelastic compaction of fine-grained sediments 

that overlie the Floridan aquifer system. 

Before development, total discharge from the Floridan aqifer system was about 21,500 £t3 Is, of which 

about 19,000 ft3 Is (88 percent) was discharge to springs 

and streams, which are mainly in the unconfined and 

semiconfined areas (fig. 8). Diffuse upward leakage, 

which occurred mostly in the confined areas, accounted 

for 2,500 ft3 Is (12 percent) of the predevelopment discharge. Although pumpage had reached 4,100 ft3 Is by 

1980, ground-water development has not greatly 

affected the ground-water budget of the Floridan aquifer system. Simulation of 1980 pumpage indicated that 

the recharge and discharge rates have increased by only 

about 2,500 ft3 Is to about 24,000 ft3 Is. Recharge to the 

Floridan system increased as a result of expansion of 

the recharge area from about 67,000 mi2 before development to about 76,000 mi2 by 1980. About 75 percent of 

the 1980 Floridan aquifer system discharge was to 

springs and streams; the remaining 25 percent consisted 

of pumpage (17 percent) and diffuse upward leakage (8 

percent). Pumpage was supplied almost entirely by 

diversion of natural discharge and induced recharge 

with almost no loss of water from aquifer storage (Bush 

and Johnston, 1988). 

EDWARDS-TRINITY AQUIFER SYSTEM 

The Edwards-Trinit~ aquifer system underlies an 

area of about 80,000 mi in central Texas, southeastern 

Oklahoma, and southwestern Arkansas (fig. 1). However, the area investigated under the RASA Program 

was limited to about 55,000 mi2 in west-central Texas, 

which includes the most productive parts of the aquifer 

system. The aquifer system comprises three carbonaterock aquifers of Cretaceous age-the Edwards, the Trinity, and the Edwards-Trinity. The Edwards aquifer comprises mostly fractured and dissolutioned limestone, 

and regional flow is controlled by a complex pattern of 

faults. The Edwards aquifer is characterized by large 

transmissivity (200,000-2,000,000 ft2 I d) and the capacity to accept large quantities of recharge during wet 

periods (Maclay and Small, 1986). Because of these factors, no long-term loss of water from storage as a result 

of ground-water withdrawals has occurred in the 

Edwards aquifer. In contrast, the Trinity and the 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 19 

Edwards-Trinity aquifers comprise less permeable carbonate and clastic rocks, and transmissivities generally 

are less than 10,000 ft2 I d. 

During the late 1980's, an estimated 1,650 ft3 Is was 

withdrawn from the Edwards-Trinity aquifer system 

for all uses. Almost one-half of this pumpage, which 

was primarily for municipal and industrial uses in the 

San Antonio metropolitan area (which is about 3 percent of the aquifer system area), was from the Edwards 

aquifer. 

Simulation of regional flow in the Edwards-Trinity 

aquifer system is complicated by the large areal variation of fracturing and dissolution of the carbonate rocks 

and the areal distribution of pumping. The finite-ele-· 

ment method was chosen for the flow simulations 

because of the ability to vary areally the direction of 

anisotropy and because of the flexibility in designing an 

irregularly spaced mesh of elements (Kuniansky and 

Halligan, 1994). Steady-state simulations were completed for predevelopment conditions and for pumping 

conditions during winter 1974-75 (selected because of 

the availability of an accurate regional potentiometric 

surface map). 

Simulations indicate that total flow through the 

aquifer system is similar for predevelopment and 1974-

75 development conditions-about 4,000 ft3 Is. However, the distribution of discharge has changed (fig. 8). 

Most of the pumpage (1,160 ft3 Is) is now supplied by a 

reduction of natural discharge to streams and springs 

rather than by induced recharge. Discharge to streams 

after development has been 20 percent less than the predevelopment discharge; springflow following development has been 30 percent less than the predevelopment 

spring discharge (Kuniansky and Halligan, 1994). The 

discharges of several major springs that discharge from 

the aquifer have been reduced or eliminated as a result 

of ground-water pumpage. 

OZARK PLATEAUS AQUIFER SYSTEM 

The Ozark Plateaus aquifer system comprises carbonate and clastic rocks of Paleozoic age that contain 

mostly freshwater and are surrounded by rocks that 

contain mostly saline water. The areal extent of the 

aquifer system is about 65,000 mi2

; it underlies most of 

northwestern Arkansas and southern Missouri and 

adjacent areas of Kansas and Oklahoma (fig. 1). The 

aquifer system has been subdivided into three regional 

aquifers and two confining units (Imes and Emmett, 

1994). Locally, a well-developed, near-surface karst terrane has developed where the carbonate rocks crop out, 

and discharge to springs is substantial within the karst 

areas. 

Although about 25 percent of the precipitation (36-

50 inlyr) infiltrates to the water table, only about 6 percent of the precipitation (about 7,000 ft3 Is) is inflow to 

the regional ground-water flow regime. Most groundwater recharge discharges as local flow to nearby 

streams and springs. Differentiation between local and 

regional flows was made on the basis of stream base 

flows and topography (Imes and Emmett, 1994). Withdrawals of ground water are small (!3-bout 320 ft3 Is from 

1970 through 1979) compared with the rates of natural 

recharge and discharge. Although water levels have 

declined at several pumping centers, regional decline of 

heads is not apparent in the aquifer system. 

A very coarse mesh (14-mi grid spacing) finite-difference model was used for steady-state simulations of 

regional flow in the Ozark Plateaus aquifer system 

before development (table 1). Because recent withdrawal rates are small compared with the large rates of 

natural recharge and discharge, Imes and Emmett 

(1994, p. 116) concluded, "the predevelopment regional 

ground-water budget of the Ozark Plateaus aquifer system is probably similar to the present-day regional budget." Simulation indicates that predevelopment 

recharge was about 7,000 ft3 Is. About 4,000 ft3 Is discharged to streams and springs; about 3,000 ft3 Is discharged to major rivers located along the boundary of 

the aquifer system and to adjacent aquifer systems (fig. 

9). Simulated flow from the Ozark Plateau aquifer system into the Mississippi Embayment aquifer system 

(located to the southeast) is substantial (about 880 ft3 I 

s), according to Imes and Emmett (1994, p. 116). 

MADISON AQUIFER OF THE NORTHERN GREAT PLAINS 

The northern Great Plains of Montana, Wyoming, 

and North and South Dakota are underlain by a thick 

sequence of Paleozoic and Mesozoic sedimentary rocks 

that contain five regionally extensive, deep, confined 

aquifers (Downey, 1986). One of these aquifers-the 

Madison-was the subject of a 5-year intensive investigation to evaluate the water-supply potential for possible development of coal reserves. The brief discussion 

of the Madison aquifer presented in this report is 

included as an example of a deep confined aquifer characterized by limited recharge, little development (as of 

the late 1970's), and generally sluggish regional flow. 

The Madison aquifer comprises Mississippian 

marine carbonate rocks (limestone and dolomite) and 

evaporites. The aquifer underlies an area of about 

210,000 mi2 in parts of Montana, Wyoming, and North 

and South Dakota (fig. 1); in addition, it underlies a considerable area in the Canadian Provinces of Manitoba 

and Saskatchewan. The Madison aquifer crops out only 

in the western recharge areas (the highlands of Montana 
20 REGIONAL AQUIFER-SYSTEM ANALYSIS 

and Wyoming and the Black Hills of South Dakota). The 

outcrop areas are characterized by development of karst 

features that include enlarged joints, caves, and sinkholes. The general pattern of predevelopment flow in 

the Madison aquifer is recharge from precipitation in 

the highland areas of Montana, Wyoming, and South 

Dakota; regional flow to the northeast and east; and discharge by leakage to Cretaceous rocks in eastern South 

Dakota and by leakage to Cambrian and Ordovician 

rocks in Manitoba (Downey, 1984; p. 28-35, figs. 39, 41). 

A large part of the recharge water is discharged from 

springs and seeps within the highland areas after moving only a short distance in the aquifer. The remaining 

fraction of the recharge water enters the regional flow 

system and moves along flow paths that extend up to 

600 mi in length. 

Steady-state simulations of regional predevelopment (before 1950) flow were completed for the Madison aquifer by using two very large finite-difference 

flow models with variable grid spacing. The initial 

model simulated flow in the Madison aquifer and an 

underlying Cambrian-Ordovician aquifer (Downey, 

1984); a later expanded model simulated flow in the full 

sequence of Paleozoic and Mesozoic rocks, which 

include the Madison aquifer and four other regional 

aquifers in the Northern Great Plains (Downey, 1986). 

Flow of water of variable density was simulated by 

using a computer code by Weiss (1982) and estimates of 

fluid density calculated from field measurements of 

fluid temperature, pressure, and dissolved solids content. Both flow models indicated that re§ional flow 

through the Madison aquifer is only 47 ft Is (fig. 9). 

Discharge was about 27 ft3 Is to rocks of Early Cretaceous age in the Dakotas and about 20 ft3 Is to rocks of 

Cambrian and Ordovician age in Manitoba, Canada. 

Regional flow velocities generally are small-less than 

20 ft/yr in most of the area underlain by the Madison 

aquifer and less than 2 ft/yr in much of Wyoming and 

in the deep Williston Basin of North Dakota (Downey, 

1984). A body of brine occurs in the Williston Basin that 

impedes regional flow, and much of the freshwater flow 

through the basin is apparently deflected around the 

brine or leaks into overlying aquifers. 

CARBONATE-ROCK PROVINCE OF THE GREAT BASIN 

The carbonate-rock province of the Great Basin is an 

area of about 100,000 mi2 that encompasses eastern 

Nevada, western Utah, and adjacent areas in Arizona, 

California, and Idaho (fig. 1). The climate of the province generally is arid to semiarid; however, the precipitation is highly variable and ranges from less than 3 in/ 

yr in some desert valleys to more than 60 in/ yr in the 

higher mountain ranges. The province is characterized 

by a complex ground-water system made up of shallow 

basin-fill deposits underlain by permeable Paleozoic 

carbonate rocks (Prudic and others, 1995). Evidence for 

deep widespread interbasin flow through carbonaterock aquifers has been presented by many workers (see, 

for example, Winograd and Thordarson, 1975). 

Prudic and others (1995) conceptualized groundwater flow in the province as consisting of "relatively 

shallow flow primarily through basin-fill deposits and 

adjacent mountain ranges superimposed over deeper 

flow through primarily carbonate rocks." Regional 

ground-water flow in the province was simulated by 

using a coarse-grid, two-layer, finite-difference model 

(table 1). The upper model layer was used to simulate 

flow through the basin fill, and the lower layer, to simulate deep flow through the underlying carbonate rocks 

(beneath mountain ranges and basin fill). All simulations were for steady-state predevelopment conditions. 

Simulations suggested that flow in the carbonate rocks 

could be subdivided into five deep-flow regions and 

that flow in the basin fill occurs in 17 shallow-flow 

regions that generally coincide with shallow-flow systems, which were defined on the basis of topography, 

water levels, discharge areas, and water budgets (Prudic and others, 1995). Simulated predevelopment 

recharge to and discharge from the five deep-flow 

regions total about 2,200 ft3 Is (fig. 9). Recharge that 

ultimately reaches the deep-flow system occurred primarily in the mountain ranges and was about 3 percent 

of the total precipitation. About 75 percent of the discharge from the five deep-flow regions occurred as 

evapotranspiration before reaching terminal sinks. The 

simulated values of recharge and discharge given in figure 9 should be considered highly approximate, as 

noted by Prudic and others (1995), because amounts of 

recharge and discharge are only approximately known, 

water-level data are not available for many parts of the 

modeled area, and several simplifying assumptions 

were made in designing the simulation model. 

CLASTIC-ROCK AQUIFER SYSTEMS OF THE 

CENTRAL AND THE WESTERN UNITED STATES 

The clastic-rock aquifer systems of the Central and 

the Western United States include the two most 

intensely pumped ground-water systems in the 

Nation-the High Plains aquifer and the California 

Central Valley aquifer system. The combination of very 

large ground-water withdrawals and large return flows 

from irrigation (which is supplied by ground-water 

pumpage in the High Plains aquifer and largely by 

imported surface water in the California Central Valley 

aquifer system) has altered regional flow and dramati-
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 21 

cally changed the water budgets of both aquifer systems. Although withdrawals from the Great Plains 

aquifer system have been small, the water budget also 

has changed considerably as a result of development. 

GREAT PLAINS AQUIFER SYSTEM (DAKOTA SANDSTONE AND 

ASSOCIATED UNITS) 

equivalents), and the Maha aquifer (Dakota Sandstone 

and equivalents). The aquifer system was recognized by 

Darton (1905) as being a major artesian reservoir characterized by a regional flow system that extends several 

hundred miles from west to east in the "Dakota water 

horizons." 

The Great Plains aquifer system comprises mostly 

sandstone and shale of early Cretaceous age (Helgeson 

and others, 1993). These clastic rocks occur throughout 

the Great Plains of North America. However, the hydrologic investigation of the aquifer system conducted 

under the RASA Program was limited to an area of 

about 170,000 mi2 in the central Great Plains (fig. 1). 

Helgeson and others (1993) defined the aquifer system 

as comprising three regional geohydrologic units-the 

Apishapa aquifer (Cheyenne Sandstone and equivalents), the Apishapa confining unit (Kiowa Shale and 

Confined conditions occur throughout most of the 

aquifer system, and much of the ground water is brackish. Regional flow is generally from west to east. Water 

is transmitted very slowly through the aquifer system; 

water in the deeply buried parts of the system is virtually stagnant except in terms of geologic time (Helgeson 

and others, 1993). 

Regional flow was simulated by using a very coarse 

mesh (14-mi grid spacing), four-layer, finite-difference 

flow model (table 1). Simulation of steady-state conditions before development indicate that the natural 

recharge to and discharge from this very large aquifer 

system was only 340 ft3 Is, as shown in figure 10. 

GREAT PLAINS AQUIFER 

SYSTEM (DAKOTA SANDSTONE 

AND ASSOCIATED STRATA) 

Predevelopment 

Outcrop 

recharge 

40 

. 

Leakage 

300 

· -· - · .+ · Outcrop 

· · i+ streams 

· Aquifer 50 system . 

i+ Leakage 

L...:.-'-~----' 290 

Developm'ent conditions 

(1970-79) 

Outcrop 

recharge 

40 

Natural 

and induced 

leakage 

880 Pumpage 

r--+-.-__.__,.-~-,----=-1 .. ----,-J 800 

Outcrop 

.· + streams 

. 50 

. ·. :=?-" · · - + Leakage / ... . . 300 

Decrease in storage 

230 

Source: Helgesen and others (1993); J.O. Helgesen, U.S. Geological Survey, written 

commun., July 1994 

HIGH PLAINS AQUIFER 

(SOUTHERN PART) 

Predevelopment 

Natural 

recharge 

270 

. .. .. ·. C!9 .o'o' <7> c:> · o. 

. Natural 

. ·Aquifer . ~ discharge . . . 270 

~~ .o..aQC> 

Development conditions 

(1960-80 average) 

Irrigation 

Recharge return flow 

1,830 4, 50 Pumpage 

(

: !Q .<!> · · ·. . J ,640 

· : · . · · · Natural 

.· . · · .. · . :: ....:.f+ discharge 

·c: ~. " ':"' - <;:> 0 · 120 

Decrease in storage 

3,870 

Source: Luckey and others (1986) 

CALIFORNIA CENTRAL VALLEY 

AQUIFER SYSTEM 

Predevelopment 

Areal Streamflow 

recharge loss Evapotranspiration 

2,070 690 2,350 

· · Aquife; . · · 

·system ~ 

. _....:.. _--....._... ·.- ~ -. 

Discharge 

to streams 

410 

Development conditions 

(1961-77 average) 

Irrigation 

Areal return Streamflow 

recharge flow loss 

2,070 12,980 690 Discharge 

Decrease in storage 

1,110 

to streams 

410 

Pumpage 

16,440 

Source: Williamson and others (1989) 

· FIGURE 10.-Ground-water budgets before and after development of clastic-rock aquifer systems in the Central and the Western United 

States. Values in cubic feet per second. Sum of outflows may not exactly equal sum of inflows as a result of independent rounding. 
22 REGIONAL AQUIFER-SYSTEM ANALYSIS 

Recharge occurred mostly as vertical leakage from overlying units rather than directly in the outcrop areas of 

the aquifer system. The low rate of outcrop recharge (40 

ft3 /s) is due to the small extent of the outcrop areas (less 

than 5 percent of the aquifer system areally), the small 

hydraulic conductivity of the aquifer system in outcrop 

areas, and faulting, which offsets the aquifer system in 

outcrop areas and cuts off recharge and lateral flow 

downgradient (Helgeson and others, 1993). Predevelopment discharge occurred mostly as vertical leakage to 

rock units that underlie and overlie the aquifer system 

and, to a lesser extent, as discharge to streams or as 

evapotranspiration or spring flow in outcrop areas. 

Fresh ground water is withdrawn from the upper 

1,000 ft of the system, and oil and gas is withdrawn 

from the system below 3,000 ft. Transient simulations of 

development conditions were completed for four 10-

year periods from 1940 through 1979. For simulation of 

1970 through 1979 conditions, an average withdrawal 

rate of 800 ft3 is was specified in the model; this is more 

than twice the predevelopment recharge rate. As shown 

in figure 10, about 70 percent of the pumpage is supplied by an increase in leakage, primarily from overlying units. Helgeson and others (1993) stated that the 

rate of adjustment to pumpage was extremely slow and 

that storage depletion was probably substantial. They 

further explained that leakage is readily induced where 

the aquifer system is in direct contact with the overlying 

High Plains aquifer and that storage loss is minimized if 

leakage continues. However, where pumping has lowered heads in the High Plains aquifer (described in the 

following section), upward leakage from the Great 

Plains aquifer system has increased. For this reason, 

leakage out of the Great Plains aquifer system is slightly 

greater for 1970 through 1979 conditions than for predevelopment conditions (fig. 10). 

IDGH PlAINS AQUIFER 

The High Plains aquifer is a regionally extensive 

water-table aquifer that comprises mostly near-surface 

sand and gravel deposits of late Tertiary and Quaternary age (Gutentag and others, 1984). The aquifer 

underlies 174,000 mi2 of the Central United States, (fig. 

1). Rainfall is moderate in this area (16-28 in/yr), and 

estimated recharge rates vary from 0.02 in/yr in Texas 

to 6 in/yr in south-central Kansas. Regional groundwater flow is generally from west to east at a rate of 

about 1ft/ d. 

The High Plains aquifer is the most intensely 

pumped ground-water system in the United States. 

Pumpage is principally for irrigation; during 1980, 

about 170,000 wells pumped about 25,000 ft3 /s. This 

pumpage has resulted in widespread ground-waterlevel declines, particularly in the southern High Plains. 

The saturated thickness of the High Plains aquifer has 

decreased by more than 25 percent in an area of 14,000 

mi2, which is mostly in the High Plains of Texas and 

western Kansas. As a result, declining well yields have 

caused a decrease in the average number of acres irrigated per well (Weeks and others, 1988). 

Simulations of steady-state conditions before development and transient simulations of the 1940 through 

1980 pumping conditions in the High Plains aquifer 

were made by using three coarse-mesh (10-mi grid 

spacing) finite-difference models, as described by 

Luckey and others (1986). Two-dimensional models 

were used because on a regional scale, vertical flow 

components were considered to be small enough to be 

neglected. The three models simulated flow in the aquifer in the southern High Plains (area south of about latitude 35°N), the central High Plains (area between 

latitude 35°N and 39°N), and the northern High Plains 

(area north of latitude 39°N). Only the simulated 

ground-water budgets for the southern High Plains 

(where the impacts of development have been greatest) 

will be discussed here. 

Under natural conditions, evapotranspiration 

demand is much greater than precipitation, and there is 

little or no recharge to the High Plains aquifer except in 

sandy soils with large infiltration rates, high permeability, and low field capacity (Weeks and others, 1988). 

Simulation indicates that the total recharge before 

development in the southern High Plains was only 270 

ft3 Is (fig. 10). 

Withdrawals from the aquifer in the southern High 

Plains, which includes 29,000 mi2 in eastern New Mexico and the western Panhandle of Texas (fig. 1), totaled 

about 140 million acre-ft (9,600 ft3 /s) from 1960 through 

1980. As a result of this large withdrawal, the water 

budgets for the aquifer in the southern High Plains are 

radically different for predevelopment and 1960 

through 1980 conditions (fig. 10). The contrast between 

the predevelopment and the development groundwater budgets for the southern High Plains aquifer is 

probably greater than any other major aquifer in the 

United States. Note that the 1960 through 1980 average 

pumpage exceeds natural recharge by more than 35 

times, and depletion of aquifer storage occurs at a rate 

that is about 14 times greater than that of natural 

recharge. Most inflow to the aquifer from 1960 through 

1980 was return flow from irrigation (Luckey and others, 1986). 

CALIFORNIA CENTRAL VALLEY AQUIFER SYSTEM 

The Calfornia Central Valley aquifer system comprises mostly continental deposits (lenses of gravel, 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 23 

sand, silt, clay) of post-Eocene age (Bertoldi and others, 

1991). The aquifer system is in a long, narrow, structural 

trough that occupies about 20,000 mi2 of flatland 

between the Sierra Nevada and the coast ranges of California (fig. 1). Before the RASA study, investigators generally described the deposits in the northern part-the 

Sacramento Valley-as a water-table aquifer and those 

in the southern part-San Joaquin Valley-as consisting 

of two aquifers separated by a regional clay confining 

unit. However, Williamson and others (1989) suggested 

a new concept in which all continental deposits constitute one aquifer system characterized by varying vertical leakance and confinement that depend on the 

proportion of fine-grained sediments. 

The climate in the Central Valley is a Mediterranean 

type with precipitation that ranges from 13 to 26 in/yr 

in the Sacramento Valley and from 5 to 16 in/yr in the 

San Joaquin Valley. Recharge is from rainfall on the valley floor and infiltration of streamflow that enters the 

Central Valley from the Sierra Nevada and the Klamath 

Mountains. 

Ground-water pumpage for irrigation, which began 

about 1880, increased dramatically during the 1940's 

and 1950's. During the 1960's and 1970's, withdrawals 

from wells averaged about 16,440 ft3 /s (11.5 million 

acre-ft/yr) and provided about one-half of the water for 

irrigation (Williamson and others, 1989). The large 

withdrawals caused water levels to decline more than 

400 ft in the southern and western parts of the San 

Joaquin Valley. Since the drought of 1976-77, surfacewater imports have increased, ground-water pumpage 

has decreased, and local ground-water levels have 

recovered (Bertoldi and others, 1991). 

Computer simulations of regional flow in the Central Valley aquifer system before and after development 

used a coarse-mesh (6-mi grid spacing), multilayer, 

finite-difference model, as described by Williamson and 

others (1989). Initially, the model was calibrated for 

transient conditions with hydrologic data observed 

from 1961 through 1975; later, steady-state simulations 

of predevelopment conditions and transient simulations of pumping conditions from 1961 through 1977 

were completed. The computer program of Trescott 

(1975) was modified to simulate the effects of land subsidence as a result of inelastic compaction of clays by 

using a procedure described by Meyer and Carr (1979). 

Simulation of predevelopment conditions indicated 

that areal recharge from precipitation provided about 75 

percent of predevelopment recharge (fig. 10). Seepage 

from stream channels (mostly along the upper reaches 

of large streams that enter the valley from surrounding 

mountains) provided about 25 percent of the predevelopment recharge. Simulated percolation to the deep 

regional ground-water flow regime was slightly more 

than 10 percent of total recharge (Williamson and others, 1989). 

Development of ground water involved the construction of about 100,000 irrigation wells in the Central 

Valley; many of these wells have long intervals of perforated casing that provide hydraulic connection between 

permeable zones within the aquifer system. Simulations 

described by Williamson and others (1989) suggest that 

the average vertical leakage of the aquifer system was 

effectively increased by an order of magnitude as a 

result of to the hydraulic connection provided by the 

multizone wells. Consequently, the comparisons of predevelopment and development conditions presented 

here, are for the entire ground-water flow regime, not 

simply the deep regional flow regime. 

The combination of large ground-water withdrawals 

and large imports of surface water for irrigation has 

completely changed the ground-water budget of the 

Central Valley aquifer system. Figure 10 shows that the 

average recharge rate for the 1961 through 1977 development period is nearly six times larger than the predevelopment recharge rate. Of the total recharge (15,740 

ft3 /s), most (12,980 ft3 /s) is irrigation return flow; the 

recharge rates from precipitation and streamflow have 

not changed. Nearly all ground-water discharge is from 

pumping wells under development conditions. During 

the 1961 through 1977 period, depletion of storage in 

the aquifer system occurred at a rate equivalent to 

about 40 percent of the rate of natural recharge, and 

about 7 percent of the pumpage was being supplied 

from water in storage. The decrease in aquifer system 

storage during the 1961 through 1977 period (about 

1,100 ft3 /s) was due to water released from inelastic 

compaction of fine-grained sediments (57 percent) and 

decline of the water table (43 percent). However, during 

the early 1980's, ground-water pumpage decreased, 

water-levels rose in many areas, and depletion of 

ground water in storage virtually stopped (Bertoldi and 

others, 1991). The principal effects of development on 

the ground-water flow system, as described by Williamson and others (1989), can be summarized as follows: 

• Before development, ground water flowed toward the 

axial part of the Central Valley and discharged as 

evapotranspiration from marshes that formerly 

existed there. By the 1970's, ground-water flow was 

mostly from areas recharged by imported surface 

water toward areas of wells pumped for irrigation. 

• After development, most ground-water discharge is 

from pumping wells rather than from evapotranspiration or discharge to streams. 

• From the start of development until1977, an estimated 60 million acre-ft of aquifer storage had been 

lost. 

• In the western and southern parts of the San Joaquin 
24 REGIONAL AQUIFER-SYSTEM ANALYSIS 

Valley, the large decline of hydraulic head caused 

inelastic compaction of fine-grained sediments, 

which resulted in land subsidence that is unequaled 

anywhere else in the world. About 5,000 mi2 of the 

Valley has undergone subsidence of more than 1 ft, 

and, at one location, subsidence is nearly 30ft. 

BASALTIC-ROCK AQUIFER SYSTEMS OF THE 

PACIFIC NORTHWEST 

A thick sequence of Tertiary and Quaternary volcanic rocks underlies an area of about 140,000 mi2 in parts 

of Washington, Oregon, Idaho, California, and Nevada. 

The name "Columbia Lava Plateau" was applied to this 

area by Heath (1984) in his classification of the groundwater regions of the United States. Two extensive basalt 

units, the Columbia River Basalt Group and the Snake 

River Group, occur throughout nearly one-half of the 

Columbia Lava Plateau. For investigation under the 

RASA Program, the two basalt units and associated 

Quaternary and Tertiary sedimentary rocks were designated as the "Columbia Plateau aquifer system" and the 

"Snake River Plain aquifer system" (fig. 1). These two 

basaltic-rock aquifer systems are characterized by very 

high transmissivity and yield large quantities of goodquality water (Lindholm and Vaccaro, 1988). Water 

development has been primarily for irrigation in both 

aquifer systems, and development has proceeded in 

similar manner-surface-water diversions first and 

ground-water withdrawals later. 

SNAKE RIVER PLAIN AQUIFER SYSTEM 

The Snake River Plain occupies an area of about 

15,600 mi2 in southern Idaho and easternmost Oregon 

(fig. 1). For study purposes under the RASA Program, 

the Snake River Plain was divided into eastern and 

western parts on the basis of geology and hydrology. 

The eastern plain (10,800 mi2) is a downwarp filled 

mostly with Quaternary basalt; the western plain (4,800 

mi2) is a graben filled predominantly with fine-grained 

Tertiary and Quaternary sedimentary rocks (Lindholm, 

1996). The discussion here is limited to the aquifer system that underlies the eastern plain. 

The thickness of the basaltic-rock aquifer system in 

the eastern,plain is largely unknown; however, it is estimated to be as much as 5,000 ft; a maximum of 3,500 ft 

may be saturated (Lindholm, 1996). Individual lava 

flows average about 20 ft in thickness. The fractured, 

rubbly tops of individual flows typically are very 

porous and permeable. Simulation and pumping tests 

suggest that the transmissivity of the Quaternary basatlic-rock a~uifer system ranges from about 4,000 to 

10,000,000 ft I d (Garabedian, 1992). 

The regional ground-water flow system in the eastern plain was simulated in two steps-initially, a twodimensional steady-state model that included a nonlinear least-squares regression technique was used to estimate aquifer properties, and later, a three-dimensional 

model was developed for simulating steady-state and 

transient conditions. Calibration consisted of comparing measured changes in water-levels and groundwater discharges with simulated values (Garabedian, 

1992). This model was designed with four active layers 

and a moderately coarse mesh (4-mi grid spacing). The 

model was used to simulate transient development conditions from 1891 through 1980 (involving eighteen 5-

year stress periods). The predevelopment budget 

described here is for 1891 through 1895, which is before 

the development of ground water but after the diversion of surface water for irrigation had begun. 

Use of surface water for irrigation began in the 

Snake River Plain during the 1880's and initially caused 

an increase in ground-water recharge as a result of percolation of excess applied water (Lindholm, 1996). The 

period from the 1890's to the early 1950's was characterized by accretion of ground-water storage. Since 1950, 

the use of ground water for irrigation has increased 

greatly, and the rate of depletion has generally been 

higher than that of accretion of storage (Garabedian, 

1992). The recent loss of storage has been attributed to 

several factors, which include decreased use of surface 

water for irrigation, increased pumpage of ground 

water, conversion from flood to sprinkler irrigation, and 

the occurrence of dry years during which ground-water 

pumpage increased and recharge from surface water 

decreased. 

The ground-water budget for the aquifer system in 

the eastern Snake River Plain has changed markedly 

since the late 1800's as a result of imports of surface 

water for irrigation and increased pumpage from wells 

as shown in figure 11. During the early 1890's, most 

recharge was supplied by losses from the Snake River 

and by losses of streamflow and ground-water underflow from tributary basins to the Snake River Plain, 

Most of the northern tributary streams lost their flow to 

basalt aquifers within a short distance after entering the 

plain (Lindholm and Vaccaro, 1988). The remainder of 

the recharge was derived from precipitation on the 

plain and by percolation of excess irrigation water from 

surface-water sources (fig. 11). All natural discharge 

from the aquifer system primarily as spring flow, was to 

the Snake River. Along a 90-mi reach of the Snake River, 

11 springs have discharges of more than 100 ft3 Is (Lindholm and Vaccaro, 1988). 

As a result of irrigation practices, recharge to the 

aquifer system in the Eastern Snake River Plain 

increased about 50 percent by 1980 (fig. 11). All the 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 25 

EASTERN SNAKE RIVER PLAIN 

AQUIFER SYSTEM 

Before ground water development (1891-95) 

Irrigation Tributary Snake 

return basins River 

flow under flow 

.1.010 2,300 

losses 

3,180 

Precipitation 

970 

--\ .... t t _; < < < 1\ '7 Aquifer system v 

> --\ £- --\ 

'7 < 

Increase in storage 1,350 

Development conditions 

(1980) 

Underflow Stream 

Irrigation from Snake and 

return tributary River canal 

Discharge to 

Snake River 

6,100 

flow basins losses losses Precipitation 

6,685 1,990 950 540 970 

;--- --t,~~ Pumpage 

' " 1,575 

< v < ':- ':-

v 

Decrease in storage 220 

Source: Garabedian (1992) 

1\ 

Discharge to 

Snake River 

9,780 

> 

Natural 

recharge 

6,565 

< 

COLUMBIA PLATEAU 

AQUIFER SYSTEM 

Predevelopment 

Leakage 

from rivers 

555 

v Aquifer system 

--\ 

Rivers 

< ... 2,750 

Small 

+ streams 

3,945 

< 

Development conditions 

(1983-85 average) 

+ Seepage 

faces 

425 

Recharge from Leakage 

precipitation 

and irrigation 

10,205 

+ v '7 

< 

< 

from 

rivers 

560 

t --\ 

':- > 

Pumpage 

1,135 

+ Rivers 

.. 3,805 

.. Small streams 

v > and drains 

5,595 --\ '7 

£- ~ " £- 1\ + Seepage L__ ___ +--------' faces 

Decrease in storage 190 420 

Source: Hansen and others (1994) 

FIGURE 11.-Ground-water budgets before and after development of basaltic-rock aquifer systems in the Pacific Northwest. 

Values in cubic feet per second. Sum of outflows may not exactly equal sum of inflows as a result of independent rounding. 

additional recharge was derived from percolation of 

excess irrigation water. Net ground-water pumpage in 

1980 was 1,570 ft3 /s (1.1 million acre-ft/yr), or about 14 

percent of the total ground-water discharge. The 

decrease in aquifer storage (220 ft3 /s) represents about 

2 percent of the total1980 ground-water budget. 

COLUMBIA PLATEAU AQUIFER SYSTEM 

The Columbia Plateau aquifer system underlies an 

area of about 50,600 mi2 in Washington and Oregon and 

adjacent areas of Idaho (fig. 1). The aquifer system comprises mostly Miocene basalt flows of the Columbia 

River Basalt Group, which has a maximum thickness of 

16,000 ft near the center of the plateau (Hansen and others, 1994). The basalts and interbedded sediments were 

divided into several units for regional analysis-three 

basalt aquifers (Saddle Mountains, Wanapum, Grande 

Ronde) and two confining units. Overlying the basalt 

flows in the central and western parts of the Plateau are 

unconsolidated sedimentary rocks of Miocene to Quaternary age, that are known as the Overburden aquifer, 

and that also are part of the aquifer system (fig. 2). 

Mean annual precipitation varies throughout the plateau according to the land-surface altitude and ranges 

from 6 in. in the central lowlands to more than 45 in. in 

the surrounding mountains. 

In 1984, ground-water withdrawals which exclude 

domestic and stock uses, were about 1,140 ft3 /s from an 

estimated 3,500 large capacity wells. Of the total pumpage, 75 percent was from the three basalt aquifers (fig. 

2), and 25 percent was from the Overburden aquifer 

(Hansen and others, 1994). Nearly 90 percent of the 

pumpage was used to irrigate about 500,000 acres of 

cropland. Irrigation with surface water is practiced in a 

larger area, and return flow from excess applied irrigation water has significantly increased ground-water 

recharge (Hansen and others, 1994). 
26 REGIONAL AQUIFER-SYSTEM ANALYSIS 

Ground-water flow was simulated throughout a 

32,700-mi2 area of the Columbia Plateau by using a 

finite-difference model with five active layers and 8,500-

by 15,000-ft grid cells. Because of the small cell size 

(compared with other regional flow models listed in 

table 1), local flow, as well as regional and intermediate 

flows, could be simulated in this model. Most of the 

local flow occurs in the upland areas and the Overburden aquifer (fig. 2). Simulations of steady-state flow in 

the aquifer system were made for predevelopment and 

recent pumping conditions. The model was calibrated 

to average hydrologic conditions for the period from 

spring 1983 to spring 1985; after accounting for the 

change in storage (190 ft3 Is) during this period, the 

model was considered to approximate steady-state conditions (Hansen and others, 1994). 

Before development, recharge to and discharge from 

the aquifer system totaled about 7,120 ft3 Is (fig. 11). 

Water development, which included pumping from 

wells beneath irrigated areas and irrigation with surface 

water withdrawn from dammed rivers, has caused flow 

through the aquifer system to increase more than 50 

percent-from about 7,120 ft3 Is to nearlj 10,800 ft3 Is. 

The increase in recharge (about 3,640 ft Is) is mostly 

return flow from surface-water-supplied irrigation. 

Rises of ground-water levels have been more widespread than declines because the area irrigated with 

surface water is larger than that irrigated with ground 

water (Hansen and others, 1994). Vertical flow through 

the basalt units in the aquifer system has been enhanced 

because most of the wells are uncased below the top of 

the basalt and, thus, are open to all units penetrated 

(Hansen and others, 1994). 

SOURCES OF WATER SUPPLYING PUMPAGE FROM REGIONAL AQUIFER SYSTEMS 

The response of an aquifer to withdrawals from 

wells was succinctly explained by Theis (1940). He 

noted that the following essential factors control aquifer 

response: the character of the recharge and its distance 

from pumping wells, the distance to the localities of 

natural discharge, and the character of the cones of 

depression, which are dependent on the rate and length 

of pumping and hydraulic properties of the aquifer and 

its confining units, surrounding the pumped wells. 

Theis further e·xplained that all water withdrawn from 

wells is balanced by a loss of water somewhere. To 

some extent, this loss is from storage in the aquifer and 

also can include an increase in recharge (if recharge was 

previously rejected) and a decrease in natural discharge. 

Theis' concepts were presented in the following 

equation (Lohman, 1972, p. 63): 

~h R + ~R = D + ~D + q + S .1t 

where R =recharge rate per unit area, 

~R =change in recharge rate per unit area, 

D =natural discharge rate per unit area, 

~D =change in discharge rate per unit area, 

q = rate of withdrawal from wells per unit 

~h area, and 

S~ =rate of change in storage per unit area 

t (equal to 0 under steady-state conditions). 

The mechanisms by which a change in recharge is 

caused by pumping from wells require some explanation. Total ground-water recharge in a region js rarely, if 

ever, increased except by artificial means, such as 

importation of water for irrigation, removal of native 

vegetation, or removal of low-permeability soils that 

impede recharge. However, flow of water into the 

deeper confined parts of aquifers can be increased d uring development by the following mechanisms: 

• Capture of local ground-water flow that would naturally discharge in the outcrop or shallow subcrop 

areas of a regional aquifer and diversion of that flow 

into the deeper parts of the aquifer. This can occur 

when cones of depression that are created by pumping from wells completed in a confined aquifer 

extend into its outcrop or subcrop area. The resulting transfer of ground water from local to intermediate or regional flow systems has occurred to some 

extent in the aquifer systems in humid areas that are 

discussed in this report. 

• Vertical leakage across confining units that overlie or 

underlie a pumped confined aquifer. This mechanism is potentially a major source of water where 

the size of outcrop or subcrop areas is small compared with areal extent of a confined aquifer. The 

importance of this mechanism was demonstrated by 

simulations of flow in the Gulf Coastal Plain aquifer 

systems [see previous discussion of this aquifer system; Williamson (in press)]. 

• Infiltration of excess water applied on irrigated lands 

and percolation into the deeper parts of an aquifer. 

Where the irrigation source is imported surface 

water, this process is a major source of new 

recharge. Where ground water is used for irrigation, 

the process is simply recirculation. Percolation of 

excess applied irrigation water is a major component of the ground-water budgets of the heavily 

pumped California Central Valley aquifer system 

(surface and ground water) and the High Plains 

aquifer (mostly ground water) (fig. 10). 

The decrease in natural discharge as a result of 

ground-water withdrawals has been documented for a 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 27 

few aquifer systems by long-term records of springflow 

or stream discharge (see, for example, the discussion of 

the Edwards-Trinity aquifer system and fig. 8). However, if the decrease in natural discharge consists mostly 

of diffuse upward leakage from confined aquifers, then 

it cannot be confirmed by field measurements-it can be 

only estimated from simulation results. Note that the 

capture of "local flow" and diversion into deep confined aquifers could be considered to be either an 

increase in recharge or a decrease in natural discharge. 

Where the flow of small streams in aquifer outcrop 

areas decreases, many hydrologists would refer to this 

as an increase in recharge owing to capture of previously rejected recharge [following the principles of 

Theis (1940)]. Where simulation indicates a reduction in 

diffuse upward leakage, most hydrologists would probably call this a decrease in discharge. 

Pumping from wells always results in some loss of 

water from storage in the aquifer system, as noted by 

Theis (1940). The largest decreases in storage owing to 

pumping have occurred in the southern High Plains 

aquifer and the California Central Valley aquifer system, both of which are located in arid to semiarid areas 

of the Western United States (fig. 10). In the High Plains 

aquifer, water-table declines caused by pumping have 

decreased the saturated thickness of the aquifer by 

more than 25 percent in more than one quarter of the 

High Plains of New Mexico and Texas (Weeks and others, 1988). The total volume of storage loss in the aquifer 

was estimated to be 160 million acre-ft as of 1980. In the 

California Central Valley, large head declines that 

resulted from pumping have caused inelastic compaction of fine-grained sediments and the largest volume of 

land subsidence in the world. Long term field measurements indicate that loss of storage in the Central Valley 

aquifer system was an estimated 60 million acre-ft by 

the late 1970's (Williamson and others, 1989). 

The sources of water that supply pumpage from 11 

of the 14 regional aquifer systems discussed in this 

report are summarized in table 3. The amount of water 

supplied by each source (induced downward percolation and leakage, infiltration of excess irrigation water, 

reduction of natural discharge, loss of aquifer storage) 

is based on differences between flow rates in the predevelopment and development hydrologic budgets of the 

aquifer systems (figs. 6, 8-11). 

Figure 12 shows the sources of water as percentages 

withdrawn from the aquifer systems after development. 

The percentages from each source are for the times, 

pumping rates, and locations of pumping from the most 

recent simulation described in the references given in 

table 3. If pumping were to continue indefinitely at the 

rates and location used in the most recent simulations, 

then the quantity of water supplied from storage would 

approach zero. The source of water pumped would then 

be a combination of recharge and (or) leakage and a 

decrease in natural discharge that is different from the 

proportions shown in figure 12. 

Several factors affect the percentage contributed by 

the three sources indicated on figure 12 as follows: 

• Most of the 11 aqu~fer systems have been characterized by steadily increasing withdrawals during 

recent years. In tum, this has caused the percentage 

contribution from the sources to change, which 

depends on the timing and locations of the pumpage increase. As an example, figure 7 shows changes 

in simulated ground-water budget components as 

pumpage from the Gulf Coastal Plain aquifer system increased from 1930 through 1985. 

• The time required for the aquifer systems in figure 12 

to reach a new steady-state condition after a change 

in pumpage varies greatly. The Floridan aquifer system and the Edwards-Trinity aquifer systems equilibrate rapidly after pumping changes and are in a 

quasi-steady-state condition much of the time. Because only steady-state simulations could be accomplished for these systems, therefore, no change in 

storage is indicated in figure 12 or table 3. However, 

locally and for short periods of time (days or weeks) 

after changes in pumpage, the quantity of water 

supplied from storage may not be negligible. The 

North Atlantic Coastal Plain aquifer system equilibrates within a few years, and only 2 percent of the 

1980 pumpage was supplied from storage (table 3). 

In contrast, the deeply buried Great Plains aquifer 

system, where storage supplied about 30 percent of 

the 1970 through 1979 pumpage, may require hundreds or thousands of years for a new equilibrium to 

be reached (Helgeson and others, 1993). 

• The sources of pumped ground water from the four 

aquifer systems where irrigation return flow provided significant recharge can vary greatly from 

year to year. Dry years generally lead to increased 

pumpage from wells, reduced recharge from irrigation return flow supplied by imported surface water, 

and increased storage contribution to ground-water 

pumpage. Wet years cause the opposite effects. 

Quantitative comparisons of the "snapshot values" 

in figure 12 are not appropriate because the values represent different stages of ground-water development. 

All but two of the aquifer systems, however, are located 

within the quarter of the diagram where more than 50 

percent of pumpage is supplied by "increased 

recharge"; that is, by some combination of induced 

downward percolation, increased leakage, and (or) irrigation return flow. 

Most of the ground-water budgets described in this 

report were derived from coarse-mesh digital models 
28 REGIONAL AQUIFER-SYSTEM ANALYSIS 

TABLE 3.-Sources of water that supply pumpage from regional aquifer systems 

[Vaules in cubic feet per second; percentage(%) of purnpage from individual sources in parenthesis;--, not applicable; RASA, Regional Aquifer-System Analysis] 

Regional aquifer system 

Period of 

pumping 

California Central 1961-77 

Valley aquifer 

system. 

Cambrian-Ordovician 1976-80 

aquifer system of the 

northern Midwest. 

Columbia Plateau 

aquifer system. 

Edwards-Trinity 

aquifer system. 

Floridan aquifer 

system. 

Great Plains aquifer 

system (Dakota 

Sandstone and 

associated units). 

Gulf Coastal Plain 

aquifer systems. 

Southern High Plains 

aquifer. 

Northern Atlantic 

Coastal Plain 

aquifer system 

(confined aquifers). 

Eastern Snake River 

Plain aquifer system. 

1983-85 

1974-75 

1980 

1970-79 

1985 

1960-80 

1980 

1980 

Southeastern Coastal 1981-85 

Plain aquifer system. 

1 Includes some infiltration of irrigation water. 

Pump age 

16,440 

1,210 

1,140 

1,160 

4,100 

800 

13,500 

9,640 

1,570 

765 

Induced 

downward 

percolation 

and leakage 

830 

(69%) 

1

950 

(83%) 

220 

(19%) 

2,500 

(61%) 

570 

(71%) 

8,900 

(66%) 

1,560 

(16%) 

1,140 

(67%) 

85 

(11%) 

Infiltration 

of irrigation 

water 

12,980 

(79%) 

4,050 

(42%) 

1,350 

(86%) 

Reduction in 

natural 

discharge 

2,350 

(14%) 

160 

(13%) 

940 

(81%) 

1,600 

(39%) 

2,900 

(21%) 

150 

(2%) 

530 

(31%) 

445 

(58%) 

Decrease in 

storage 

1,110 

(7%) 

220 

(18%) 

190 

(17%) 

230 

(29%) 

1,700 

(13%) 

3,870 

(40%) 

30 

(2%) 

220 

(14%) 

235 

(31%) 

RASA report references 

Williamson and others 

(1989). 

Mandie and Kontis 

(1992). 

Hansen and others 

(1994). 

Kuniansky and 

Holligan (1994). 

Bush and Johnston 

(1988). 

Helgesen and 

others (1993). 

Williamson (in press). 

Luckey and others 

(1986). 

Leahy and Martin 

(1993). 

Garabedian (1992); 

Lindholm (1996). 

Barker and Pernik 

(1994); Miller 

(1992). 

2 Sources of water that supply purnpage on the basis of simulation of steady-state conditions; no change in storage is, therefore, indicated. 

3 Purnpage is from confined aquifers only. 

designed to simulate regional flow, and thus, small local 

flow systems were not simulated. Even under these 

conditions, however, the model-derived budgets indicate diversion of local flow into regional flow regimes 

and increased downward leakage into deep aquifers. 

Circulation in the regional flow regimes that may have 

been sluggish under natural conditions becomes more 

vigorous as pumping increases. Figure 13 shows the 

increase in simulated recharge-leakage rates for the 

r~gional aquifer systems as withdrawals have 

increased. 

Development has resulted in large increases in 

recharge-leakage rates for the three most heavily 

pumped aquifer systems. From predevelopment to 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 29 

~L_----~----~~----~------~----~~----~L---~L-----~----~~----~~ 100 50 0 

PERCENTAGE OF PUMPAGE SUPPLIED BY DECREASE IN NATURAL DISCHARGE 

EXPLANATION 

7 Pumpage supplied by induced recharge 3 Columbia Plateau aquifer system (1983-85) • and leakage, decreased natura l discharge, 

and loss of storage. Number indicates 4 Edwards-Trinity aquifer system (1974-75) 

aquifer system 

5 Floridan aquifer system (1980) 

40 Pumpage supplied by induced recharge 

and leakage, decreased natural discharge. 6 Great Plains aquifer system (1970-79) 

No change in storage. Number indicates 

aquifer system 7 Gulf Coastal Plain aquifer systems (1985) 

1. Pumpage supplied partly by irrigation 8 High Plains aquifer (southern part) (1960-80) 

return flow. Number indicates 

aquifer system 9 Northern Atlantic Coastal aquifer 

system (1980) 

AQUIFER SYSTEMS 

California Central Valley aquifer 10 Eastern Snake River Plain aquifer 

system ( 1961-77) system (1980) 

2 Cambrian-Ordovician aquifer system 11 Southeastern Coastal Plain 

of the northern Midwest (1976-80) aquifer system (1981-85) 

FIGURE 12.-Sources of water that supply pumpage from regional aquifer systems. 

recent years, the simulated recharge-leakage rate has 

increased 22 times for the southern High Plains aquifer, 

6 times for the California Central Valley aquifer system, 

and 3 times for the Gulf Coastal Plain aquifer systems. 

About 70 percent of the increase for the High Plains 

aquifer is return flow from irrigation, and 30 percent is 

mostly increased recharge from precipitation on croplands (Luckey and others, 1986). In the California Cen-
30 

18,000 

16,000 

0 

z 14,000 0 

u 

LU 

(f) 

a: 12,000 LU 

a... 

fLU 

LU 10,000 u.. 

S2 

cc 

::J 8,000 u 

z 

LU• 

6,000 t:J 

<l: 

a... 

2: 

::J 4,000 a... 

2,000 

Predevelopment 

conditions 

100 

REGIONAL AQUIFER-SYSTEM ANALYSIS 

1,000 10,000 

RECHARGE/LEAKAGE RATE, IN CUBIC FEET PER SECOND 

EXPLANATION 

Regional aquifer systems 

1 California Central Valley aquifer system 

2 Cambrian-Ordovician aquifer system of 

the Northern Midwest 

3 Columbia Plateau aquifer system 

4 Edwards-Trinity aquifer system 

5 Floridan aquifer system 

6 Great Plains aquifer system 

7 Gulf Coastal Plain aquifer systems 

8 Southern High Plains aquifer 

5 

9 Northern Atlantic Coastal Plain aquifer system 

10 Snake River Plain aquifer sytem 

11 Southeastern Coastal Plain aquifer system 

100,000 

FIGURE 13.-Change of recharge-leakage rates to regional aquifer systems, predevelopment to recent pumping conditions. 

tral Valley aquifer system, most of the increase is due to 

irrigation return flow supplied by imported surface 

wa ter (Williamson and others, 1989). In the Gulf Coastal 

Plain aquifer systems, downward vertical flow 

increased substantially in all aquifers as a result of 

ground-water pumpage and the consequent reversal of 

vertical hydraulic gradients (Williamson, in press). A 

large part of the increased regional recharge is captured 

local discharge. 

ern Coastal Plain aquifer systems (fig. 13). Regional 

recharge rates to the Floridan aquifer system are naturally large as a result of high average rainfall, flat to 

gently rolling topography, and the dominance of intermediate to regional flow systems in the karst areas 

where the aquifer system crops out or is thinly covered 

(fig. 2). Although 60 percent of the pumpage from the 

Floridan aquifer system is derived from increased 

regional recharge and leakage, this represents only a 12 

percent increase over the predevelopment rechargeleakage rate. The small increase in the recharge-leakage 

rate in the Southeastern Coastal Plain aquifer system is 

The smallest percentage increases in regional 

recharge-leakage rates have occurred in the Floridan 

aquifer system, the Edwards-Trinity, and the Southeast-
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 31 

probably due to the location of the largest head declines 

in middip confined areas. According to Barker and 

Pernik (1994), "most of the induced downward leakage 

is simulated to have occurred updip, while the reduced 

upward leakage occurs in middip and downdip areas." 

The capacity of the Edwards-Trinity aquifer system to 

accept almost all of the available recharge into its 

regional flow system before development and lack of 

change since indicates that development can never 

cause a significant increase in the recharge-leakage rate. 

Before development, rates of recharge to the regional 

flow regimes of the Great Plains aquifer system and the 

Cambrian-Ordovician aquifer system of the northern 

Midwest were small, and both flow systems were sluggish. The rate of recharge into deep confined aquifers of 

the Cambrian-Ordovician system has more than doubled as a result of development; likewise, the rate of 

downward leakage into the Great Plains aquifer system 

also has more than doubled. Induced recharge or leakage provides more than 70 percent of the pumped water 

from both aquifer systems. 

SUMMARY AND CONCLUSIONS 

The predevelopment hydrologic budgets of the 14 

regional aquifer systems in the United States indicate a 

wide variation in regional flow activity. Recharge to and 

discharge from these systems range from 47 ft3 Is for the 

Madison aquifer to 21,500 ft3 Is for the Floridan aquifer 

system (table 2). Climate, topography, and the hydrogeologic setting (especially the nature and extent of 

unconfined and confined areas and the hydraulic properties of aquifers and confining units) are the principal 

natural controls on rates of recharge and discharge. A 

generalized classification of the 14 aquifer systems, 

which is based on regional flow activity before development, is as follows: 

1. 

2. 

Flow activity 

Vigorous regional flow 

systems. 

Restricted regional flow 

systems (humid climates). 

Aquifer systems 

Edwards-Trinity 

Floridan 

Ozark Plateaus 

Columbia Plateau 

Snake River Plain 

North Atlantic 

Coastal Plain 

Gulf Coastal Plain 

Southeastern Coastal 

Plain 

Cambrian-Ordovician 

(of the northern Midwest) 

3. 

4. 

Flow activity 

Restricted regional flow 

systems (arid to semiarid climates). 

Sluggish to virtually stagnant regional flow 

systems. 

Aquifer systems 

Southern High 

Plains 

California Central 

Valley 

Carbonate-rock province 

of the Great Basin 

Great Plains 

Madison aquifer 

The occurrence of fractured and dissolutioned carbonate rock in outcrop/recharge areas and generally 

high transmissivity enable the Edwards-Trinity, the 

Floridan, and the Ozark Plateaus aquifer systems to 

accept large amounts of recharge during wet periods 

and transmit much water, thus resulting in vigorous 

flow systems. Similarly, the Columbia Plateau and the 

Snake River Plain aquifer systems are characterized by 

high transmissivity and the ability to accept and transmit large quantities of water. These two basaltic-rock 

aquifer systems are located in arid to semiarid areas; 

however, they receive most recharge from the surrounding highlands, which receive much more precipitation. 

The ability of these five carbonate- and basaltic-rock 

aquifer systems to transmit large quantities of ground 

water is attested by the fact that 66 of the 78 first-magnitude springs (discharge greater than 100 ft3 /s) in the 

United States discharge from these five systems. [References on first-magnitude springs are listed in Rosenau 

and others (1977).] 

In contrast, the clastic-rock aquifer systems of the 

North Atlantic, the Southeastern, and the Gulf Coastal 

Plains and the Cambrian-Ordovician (carbonate-rock) 

of the northern Midwest, which are located in humid 

areas, have "restricted" regional flow systems. Under 

natural conditions, the combination of topography, 

size and patterns of outcrop I subcrop recharge areas, 

and small hydraulic gradients restrict flow into and 

through the deep confined aquifers that constitute the 

regional flow systems .. Most of the recharge is rejected; 

that is, it flows through shallow aquifers and discharges at nearby streams. Therefore, 9nly a small fraction of total ground-water flow occurs within the deep 

confined aquifers. Much recharge is available for "capture" when heads decline as a result of pumping from 

deep confined aquifers in these four systems. 

Under predevelopment conditions, three extensive 

aquifer systems in the Central and the Western United 

States-the Southern High Plains, the California Central Valley, and the carbonate-rock province of the Great 

Basin-had limited recharge and regional flow. The 

"restricted" flow systems occur primarily because of the 
32 REGIONAL AQUIFER-SYSTEM ANALYSIS 

arid to semiarid climates with high evapotranspiration 

rates that exceed precipitation. The Madison aquifer 

and the Great Plains aquifer system (principally the 

Dakota Sandstone and associated units) have vast 

regional flow systems that extend several hundred 

miles from west to east. Water is transmitted very 

slowly through these mostly confined aquifer systems; 

water in the deeply buried parts of these two systems is 

virtually stagnant and is highly saline. 

Water development has dramatically altered the 

regional flow systems and hydrologic budgets of the 

three most heavily pumped aquifer systems in the 

United States-the High Plains, the California Central 

Valley, and the Gulf Coastal Plain aquifer systems. 

Pumpage from the Central Valley aquifer system from 

1961 through 1977 was about 6 times the prepumping 

recharge rate; pumpage from the southern High Plains 

aquifer from 1960 through 1980 was about 35 times the 

prepumping recharge rate; and pumpage from the Gulf 

Coastal Plain aquifer systems during 1985 was about 3 

times the prepumping recharge rate (figs. 7, 10). Inflow 

to the three regional flow systems increased markedly 

as a result of development. The increased inflow to the 

High Plains and the Califorina Central Valley aquifer 

systems was derived mostly from irrigation return flow 

(supplied either by imported surface water or pumped 

ground water). Increased inflow to the regional flow 

system in the Gulf Coastal Plain aquifer systems was 

supplied largely by increased percolation to regional 

aquifers in their outcrop I subcrop areas (that is, by capture of shallow ground water that would have naturally 

discharged to nearby streams) and by increased vertical 

leakage to confined aquifers. Pumpage also has resulted 

in depletion of confined aquifer storage in the California Central Valley aquifer system as a result of inelastic 

compaction of fine-grained sediments. This has been 

accompanied by the largest volume of land subsidence 

observed anywhere in the world. Long-term decline of 

- the water table in the southern High Plains aquifer has 

resulted in more than 25 percent decrease in saturated 

thickness of the aquifer in more than one quarter of the 

High Plains of New Mexico and Texas. Loss of storage 

was much less in the Gulf Coastal Plain aquifer systems, 

and most of the loss was due to decline of the water 

table in the Mississippi River Valley alluvial aquifer. 

Eight of the regional aquifer systems with less intensive ground-water development (withdrawals ranged 

from about 800 to 4,100 ft3 Is) were characterized by 

smaller changes in regional ground-water budgets as a 

result of pumping. In six aquifer systems (CambrianOrdovician, Columbia Plateau, Floridan, Great Plains, 

North Atlantic Coastal Plain, and Snake River Plain), 

the most significant budget change was increased 

inflow to the regional flow system by some combination 

of increased percolation from outcrop I subcrop areas 

into deeper and generally confined aquifers in the system, induced vertical leakage from overlying or underlying aquifers, or· irrigation return flow (only in the 

Columbia Plateau and the Snake River aquifer systems). 

In two aquifer systems (the Edwards-Trinity and the 

Southeastern Coastal Plain), the major budget change 

was a decrease in aquifer discharge either to streams 

and springs or as diffuse upward leakage. 

REFERENCES 

Ackerman, D.J., 1996, Hydrology of the Mississippi River Valley alluvial aquifer, south-central United States: U.S. Geological Survey 

Professional Paper 1416-D, 56 p. 

Back, William, Rosenshein, J.S., and Seaber, P.R., eds., 1988, Hydrogeology: Boulder, Colorado, Geological Society of America, The 

Geology of North America, v. 0-2, 524 p. 

Barker, R.A., and Pernik, Maribeth, 1994, Regional hydrology and 

simulation of deep ground-water flow in the Southeastern 

Coastal Plain aquifer system in Mississippi, Alabama, Georgia, 

and South Carolina: U.S. Geological Survey Professional Paper 

1410-C, 87 p. 

Bertoldi, G.L., Johnston, R.H., and Evenson, K.D., 1991, Ground water 

in the Central Valley, California-A summary report: U.S. Geological Survey Professional Paper 1401-A, 44 p. 

Brahana, J.V., Thraikill, J., Freeman, T., and Ward, W.C., 1988, Carbonate rocks, in Back, William, Rosenshein, J.S., and Seaber, P.R., 

eds., Hydrogeology: Boulder, Colorado, Geological Society of 

America, The Geology of North America, v. 0-2, p. 333-352. 

Bredehoeft, J.D., Papadopulos, S.S., and Cooper, H.H., 1982, Groundwater-The water-budget myth, in Studies in geophysics- Scientific basis of water resources management: Washington, D.C., 

National Academy Press, p. 51-57. 

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. 

Chamberlin, T.C., 1885, Requisite and qualifying conditions of artesian wells, in 5th Annual Report to the Secretary of the Interior, 

1883-84: U.S. Geological Survey, p. 131-173. 

Darton, N.H., 1905, Geology and underground water resources of the 

central Great Plains: U.S. Geological Survey Professional Paper 

32,433 p. 

Downey, J.S., 1984, Geohydrology of the Madison and associated 

aquifers in parts of Montana, North Dakota, South Dakota, and 

Wyoming: U.S. Geological Survey Professional Paper 1273-G, 

47p. 

--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, 

87p. 

Faulkner, G.L., 1973, Geohydrology of the Cross-Florida Barge Canal 

area with special reference to the Ocala vicinity: U.S. Geological 

Survey Water-Resources Investigations Report 73-1, 117 p. 

Faye, R.E., and Mayer, G.C., 1990, Ground-water flow and streamaquifer relations in the northern Coastal Plain of Georgia and 

adjacent parts of Alabama and South Carolina: U.S. Geological 

Survey Water-Resources Investigations Report 88-4143,83 p. 
HYDROLOGIC BUDGETS OF REGIONAL AQUIFER SYSTEMS 33 

Freeze, R.A., and Witherspoon, P.A., 1967, Effect of water-table configuration and subsurface permeability variation, chap. 2 of Theoretical analysis of regional ground-water flow: Water Resources 

Research, v. 3, no. 2, p. 623-634. 

Garabedian, S.P., 1986, Application of a parameter-estimation technique to modeling the regional aquifer underlying the eastern 

Snake River Plain, Idaho: U.S. Geological Survey Water-Supply 

Paper 2278, 60 p. 

---1992, Hydrology and digital simulation of the regional aquifer 

system-Eastern Snake River Plain, Idaho: U.S. Geological Survey Professional Paper 1408-F, 102 p. 

Gutentag, E.D., Heimes, F.J., Krothe, N.C., Luckey, R.C., and Weeks, 

J.B., 1984, Geohydrology of 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-B, 63 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 91-4187, 81 p. 

Heath, R.C., 1984, Ground-water regions of the United States: U.S. 

Geological Survey Water-Supply Paper 2242, 78 p. 

Helgesen, J.O., Leonard, R.B., and Wolf, R.J., 1993, Hydrology of the 

Great Plains aquifer system in Nebraska, Colorado, Kansas, and 

adjacent areas: U.S. Geological Survey Professional Paper 

1414-E, 80 p. 

Hosman, R.L., and Weiss, J.S., 1991, Geohydrologic units of the Mississippi embayment and Texas coastal uplands aquifer system-South-central United States: U.S. Geological Survey 

Professional Paper 1416-B, 19 p. 

Imes, J.L., and Emmett, L.F., 1994, Geohydrology of the Ozark Plateaus aquifer system in parts of Missouri, Arkansas, Oklahoma, 

and Kansas: U.S. Geological Survey Professional Paper 1414-D, 

127 p. 

Johnston, R.H., 1989, The hydrologic responses to development in 

regional sedimentary aquifers: Ground Water, v. 27, no. 3, 

p. 316-322. 

Kontis, A.L., and Mandie, R.J., 1988, Modifications of the three-dimensional ground-water flow model to account for variable water 

density and effects of multiaquifer wells: U.S. Geological Survey 

Water-Resources Investigations Report 87-4276, 78 p. 

Kuiper, L.K., 1983, A numerical procedure for the solution of the 

steady-state variable-density groundwater flow equation: Water 

Resources Research, v. 19, no. 1, p. 234-240. 

---1985, Documentation of a numerical code for the simulation of 

variable density ground-water flow in three dimensions: u.s. 

Geological Survey Water-Resources Investigations Report 84-

4032, 90 p. 

Kuniansky, E.L., 1990, A finite-element model for simulation of twodimensional steady-state flow in confined aquifers: U.S. Geological Survey Open-File Report 90-187, 77 p. 

Kuniansky, E.L., and Holligan, K.Q., 1994, Simulations of flow in the 

Edwards-Trinity aquifer system and contiguous hydraulically 

connected units-West-central Texas: U.S. Geological Survey 

Water-Resources Investigations Report 93-4039,40 p. 

Laney, R.L., and Davidson, C.B., 1986, Aquifer nomenclature guidelines: U.S. Geological Survey Open-File Report 86-534, 46 p. 

Larson, S.P., 1978, Direct solution algorithm for the two-dimensional 

ground-water flow model: U.S. Geological Survey Open-File 

Report 79-202, 25 p. 

Leahy, P.P., 1982, A three-dimensional ground-water flow model modified to reduce computer memory requirements and better simulate confining-bed and aquifer pinchouts: U.S. Geological 

Survey Water-Resources Investigations Report 82-4023, 60 p. 

Leahy, P.P., and Martin, Mary, 1993, Geohydrology and simulation of 

ground-water flow in the Northern Atlantic Coastal Plain aquifer system: U.S. Geological Survey Professional Paper 1404-K, 

81 p. 

Lindholm, G.F., 1996, Summary of the Snake River Plain aquifer-system analysis: U.S. Geological Survey Professional Paper 1408-A. 

Lindholm, G.F., and Vaccaro, J.J., 1988, Region 2-Columbia River 

Plateau, in Back, William, Rosenshein, J.S., and Seaber, P.R., eds., 

Hydrogeology: Boulder, Colorado, Geological Society of America, The Geology of North America, v. 0-2, p. 37-50. 

Lohman, S.W., 1972, Ground-water hydraulics: U.S. Geological Survey Professional Paper 708, 70 p. 

Luckey, R.R., Gutentag, E.D., Heimes, F.J., and Weeks, J.B., 1986, Digital simulation of ground-water 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. 

Maclay, R.W., and Small, T.A., 1986, Carbonate geology and hydrology of the Edwards aquifer in the San Antonio area, Texas: Texas 

Water Development Board Report 296,90 p. 

Mandie, R.J., and Kontis, A.L., 1992, Simulation of regional groundwater flow in the Cambrian-Ordovician aquifer system in the 

Northern Midwest, United States: U.S. Geological Survey Professional Paper 1405-C, 97 p. 

McDonald, M.G., and Harbaugh, A.W., 1988, A modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Techniques of Water-Resources Investigations, book 

6, chap. A1, 578 p. 

Meyer, W.R., and Carr, J.E., 1979, A digital model for simulation of 

ground-water hydrology in the Houston area, Texas: Texas 

Department of Water Resources Report LP-103, 131 p. 

Miller, J.A., 1986, Hydrogeologic framework of the Floridan aquifer 

system in Florida and in parts of Georgia, Alabama, and South 

Carolina: U.S. Geological Survey Professional Paper 1403-B, 

91 p. 

--1992, Summary of the hydrology of the Southeastern Coastal 

Plain aquifer system in Mississippi, Alabama, Georgia, and 

South Carolina: U.S. Geological Survey Professional Paper 

1410-A, 38 p. 

Prudic, D.E., Harrill, J.E., and Burbey, T.J., 1995, Conceptual evaluation of regional ground-water flow in the carbonate-rock province of the Great Basin, Nevada, Utah, and adjacent States: U.S. 

Geological Survey Professional Paper 1409-D, 102 p. 

Renken, R.A., 1996, Geology and hydrogeology of the Southeastern 

Coastal Plain aquifer system in Mississippi, Alabama, Georgia, 

and South Carolina: U.S. Geological Survey Professional Paper 

1410-B. 

Rosenau, J.C., Faulkner, G.L., Hendry, C.W., and Hull, R.W., 1977, 

Springs of Florida (2d ed.): Florida Division of Geology Bulletin 

31, revised, 461 p. 

Sun, R.J., ed., 1986, Regional Aquifer-System Analysis Program of the 

U.S. Geological Survey-Summary of projects, 1978-84: U.S. 

Geological Survey Circular 1002, 264 p. 

Sun, R.J., and Johnston, R.H., 1994, Regional Aquifer-System Analysis 

Program of the U.S. Geological Survey, 1978-1992: U.S. Geological Survey Circular 1099, 126 p. 

Theis, C.V., 1940, The source of water derived from wells: Civil Engineering, v. 10, no. 5, p. 277-280. 

Torak, L.J., 1982, Modification and corrections to the finite-difference 

model for simulation of three-dimensional ground-water flow: 

U.S. Geological Survey Water-Resources Investigations Report 

82-4025, 67 p. 

Toth, J., 1963, A theoretical analysis of ground-water flow in small 

drainage basins: Journal of Geophysical Research, v. 68, no. 16, 

p. 4795-4812. 
34 REGIONAL AQUIFER-SYSTEM ANALYSIS 

Trapp, Henry, Jr., 1993, Hydrogeologic framework of the northern 

Atlantic Coastal Plain in parts of North Carolina, Virginia, 

Maryland, Delaware, New Jersey, and New York: U.S. Geological Survey Professional Paper 1404-G, 59 p. 

Trescott, P.C., 1975, Documentation of finite-difference model for simulation of three-dimensional ground-water flow: U.S. Geological 

Survey Open-File Report 75-438, 104 p. 

Trescott, P.C., and Larson, S.P., 1976, Supplement to Open-File Report 

75-438-Documentation of finite-difference model for simulation of three-dimensional ground-water flow: U.S. Geological 

Survey Open-File Report 76-591, 21 p. 

Weeks, J.B., Gutentag, E.D., Heimes, F.J., and Luckey, R.R., 1988, Summary of the High Plains regional aquifer-system analysis in 

parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, 

South Dakota, Texas, and Wyoming: U.S. Geological Survey Professional Paper 1400-A, 30 p. 

Weiss, Emanuel, 1982, A model for the simulation of flow of variable 

density ground water in three-dimensions under steady-state 

conditions: U.S. Geological Survey Open-File Report 82-352, 

66p. 

Weiss, J.S., 1992, Geohydrologic units of the coastal lowlands aquifer 

system-South-central United States: U.S. Geological Survey 

Professional Paper 1416-C, 32 p. 

Williamson, A.K., in press, Ground-water flow in the Gulf Coastal 

Plain aquifer systems-South-central United States: U.S. Geological Survey Professional Paper 1416-F. 

Williamson, A.K., Prudic, D.E., and Swain, L.A., 1989, Ground-water 

flow in the Central Valley, California: U.S. Geological Survey 

Professional Paper 1401-D, 127 p. 

Winograd, I.J., and Thordarson, William, 1975, Hydrogeologic and 

hydrochemical framework-Southeastern Great Basin, with special reference to the Nevada Test Site: U.S. Geological Survey 

Professional Paper 712-C, 126 p. 

Young, H.L., 1992, Summary of ground-water hydrology of the Cambrian-Ordovician aquifer system in the Northern Midwest: U.S. 

Geological Survey Professional Paper 1405-A, 55 p. 
Selected Series of U.S. Geological Survey Publications 

Books and Other Publications 

Professional Papers report scientific data and interpretations 

of lasting scientific interest that cover all facets of USGS investigations and research. 

Bulletins contain significant data and interpretations that are of 

lasting scientific interest but are generally more limited in 

scope or geographic coverage than Professional Papers. 

Water-Supply Papers are comprehensive reports that present 

significant interpretive results of hydrologic investigations of 

wide interest to professional geologists, hydrologists, and engineers. The series covers investigatiO!tS in all phases of hydrology, including hydrogeology, availability of water, quality of 

water, and use of water. 

Circulars are reports of programmatic or scientific information 

of an ephemeral nature; many present important scientific 

information of wide popular interest. Circulars are distributed 

at no cost to the public. 

Fact Sheets communicate a wide variety of timely information 

on USGS programs, projects, aud research. They commonly 

address issues of public interest. Fact Sheets generally are two 

or four pages long and are distributed at no cost to the public. 

Reports in the Digital Data Series (DDS) distribute large· 

amounts of data through digital media, including compact discread-only memory (CD-ROM). They are high-quality, interpre-· 

tive publications designed as self-contained packages for viewing and interpreting data and typically contain data sets, 

software to view the data, and explanatory text. 

Water-Resources Investigations Reports are papers of an 

interpretive nature made available to the public outside the formal USGS publications series. Copies are produced on request 

(unlike formal USGS publications) and are also available for 

public. inspection at depositories indicated in USGS catalogs. 

Open-File Reports can consist of basi~ data, preliminary 

reports, and a wide range of scientific documents on USGS 

investigations. Open-File Reports are designed for fast release 

and are available for public consultation at depositories. 

Maps 

Geologic Quadrangle Maps (GQ's) are multicolor geologic 

maps on topographic bases in 7.5- or 15-minute quadrangle 

formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, 

surficial, or engineering geology. Maps generally include brief 

texts; some maps include structure and columnar sections only. 

Geophysical Investigations Maps (GP's) are on topographic 

or planimetric bases at various scales. They show results of 

geophysical investigations using gravity, magnetic, seismic, or 

radioactivity surveys, which provide data on subsurface structures that are of economic or geologic significance. 

Miscellaneous Investigations Series Maps or Geologic 

Investigations Series (l's) are on planimetric or topographic 

bases at various scales; they present a wide variety of format 

and subject matter. The series also incudes 7 .5-minute quadrangle photogeologic maps on planimetric bases and planetary 

maps. 

Information Periodicals 

Metal Industry Indicators (Mil's) is a free monthly newsletter that analyzes and forecasts the economic health of five 

metal industries with composite leading and coincident 

indexes: primary metals, steel, copper, primary and secondary 

aluminum, and aluminum mill products. 

Mineral Industry Surveys (MIS's) are free periodic statistical 

and economic reports designed to provide timely statistical data 

on production, distribution, stocks, and consumption of significant mineral commodities. The surveys are issued monthly, 

quarterly, annually, or at other regular intervals, depending on 

the need for current data. The MIS's ar~ published by commodity as well as by State. A series of international MIS 's is also 

available. 

Published on an annual basis, Mineral Commodity Summaries is the earliest Government publication to furnish estimates 

covering nonfuel mineral industry data. Data sheets contain 

information on the domestic industry structure, Government 

programs, tariffs, and 5-year salient statistics for more than 90 

individual minerals and materials. 

The Minerals Yearbook discusses the performance of the 

worldwide minerals and materials industry during a calendar 

year, and it provides background information to assist in· interpreting that performance. The Minerals Yearbook consists of 

three volumes. Volume I, Metals and Minerals, contains chapters about virtually all metallic and industrial mineral commodities important to the U.S. economy. Volume II, Area Reports: 

Domestic, contains a chapter on the minerals industry of each 

of the 50 States and Puerto Rico.and the Administered Islands. 

Volume III, Area Reports: International, is published as four 

separate reports. These reports collectively contain the latest 

available mineral data on more than 190 foreign countries and 

discuss the importance of minerals to the economies of these 

nations and the United States. · 

Permanent Catalogs 

"Publications of the U.S. Geological Survey, 1879-1961" 

and "Publications of the U.S. Geological Survey, 1962-

1970" are available in paperback book form and as a set of 

microfiche. 

"Publications of the U.S. Geological Survey, 1971-1981" is 

available in paperback book form (two volumes, publications 

·listing and index) and as a' set of microfiche. 

Annual supplements for 1982, 1983, 1984, 1985, 1986, and 

subsequent years are available in paperback book form.