FOLD

LINE

Report to Congress

Concepts for National Assessment

of Water Availability and Use

Circular 1223

U.S. Department of the Interior

U.S. Geological Survey
Report to Congress

Concepts for

National Assessment of 

Water Availability and Use

U.S. Geological Survey Circular 1223

Reston, Virginia

2002
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the 

U.S. Government

Library of Congress Cataloging-in-Publications Data

Concepts for national assessment of water availability and use / by

Paul M. Barlow... [et al.].

p. cm. -- (U.S. Geological Survey circular ; 1223)

Includes bibliographical references.

ISBN 0-607-98593-3

 1. Water-supply--United States. 2. Water use--United States. I.

Title. II. Series.

TD223 .B37 2002

363.6'1'0973--dc21

2002023650

Reston, Virginia 2002

Free on application to the

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225-0286
III

PREFACE

will there be sufficient freshwater resources in the future to sustain economic growth 

and the quality of life? In many parts of the country, competition for water to meet the needs 

of homes, cities, farms, and industries is increasing. At the same time, requirements to leave 

water in the streams and rivers for environmental and recreational uses are expanding. Waterresources information is needed at many levels to help shed light on overall changing conditions of water scarcity, use, and competition and to help inform discussions about potential 

changes in water-resource policies and investment plans.

This report responds to a directive from Congress to the U.S. Geological Survey 

(USGS) to “prepare a report describing the scope and magnitude of the efforts needed 

to provide periodic assessments of the status and trends in the availability and use of freshwater resources.” In response to this directive, the USGS describes in this report efforts 

needed to develop and report on indicators of the status and trends in storage volumes, flow 

rates, and uses of water nationwide. This would be analogous to the task of other Federal 

statistical programs that produce and regularly update indicator variables that describe 

economic, demographic, and health conditions of the Nation. The assessment also would 

provide regional estimates of recharge, evapotranspiration, interbasin transfers, and other 

components of the water cycle. These regional estimates would support analyses of water 

availability that are undertaken by many agencies and would benefit research quantifying 

variability and changes in the national and global water cycle. 

The effort described would require coordination among many organizations, Federal 

and non-Federal agencies, and universities to ensure that the information produced can

be aggregated with other types of water-availability and socioeconomic information. The 

efforts identified concerning flows, storages, and uses of water would be used with waterquality information from existing programs to provide a more complete national picture of 

the quantity and quality aspects of water availability. To maximize the utility of the information, the design and development of these efforts should be coordinated through the Federal 

Advisory Committee on Water Information.

The assessment would use existing data collected by the USGS and by others to 

create the indicator variables. Data gaps identified by the program would be coordinated 

with improvements in data-collection networks for surface water and ground water defined 

by USGS plans for the National Streamflow Information Program and the Ground-Water 

Resources Program, and as part of the Cooperative Water Program. Water-use estimation 

by the program would be strengthened from existing efforts along the lines suggested by the 

National Research Council.
IV

CONTENTS

Preface III

Introduction 1

National Assessment of Water Availability and Use 3

Coordination and Collaboration 5

Indicators of Water Availability 6

Surface Water 8

Streamflow 8

Surface-Water Storage 14

Ground Water 15

Ground-Water Levels 15

Ground-Water Storage 17

Water Use 19

Water-Cycle Characterization 22

Summary 26

Acknowledgments 27

References Cited 28

Appendix A—List of Individuals Providing Input to this Report 31
V

BOXES

Box A -- Quantity and Quality of Water Define Availability: An Example from South Florida 4

Box B -- Water-Level Monitoring and Ground-Water Depletion in the High Plains Aquifer 18

Box C -- A Plan to Enhance the National Water-Use Information Program 21

Box D -- Water Supply and Dry Rivers in the Humid East—Modeling the Effects of 

Water Withdrawals on Streamflow in the Ipswich River Basin, Massachusetts 24

Box E -- Cooperative Science Helps Determine Water Availability in Southern California 25
1

Water-resources information useful for 

regional and national assessments of freshwater 

availability and use requires a continuing process of 

coordination and collaboration with representatives 

of the water-users community. During preparation 

of this report, the USGS solicited input from many 

individuals and organizations involved in issues of 

water availability and use (Appendix A). We asked 

them what types of decisions and policy issues need 

improved water facts today and in the future, 

what variables or indicators would be useful, what 

spatial and temporal scales would be appropriate, 

how to build on existing efforts, and where to 

expand collaborative opportunities. In response 

to our request, we heard from nearly 100 water 

users, managers, researchers, and advocates 

through mail and e-mail, phone conversations, 

and face-to-face meetings.

Concepts for National Assessment 

of Water Availability and Use

INTRODUCTION

This report responds to the following directive from Congress to the U.S. Geological Survey (USGS) 

as part of the report on the Fiscal Year 2002 Appropriations for Interior and Related Agencies (House 

Committee on Appropriations).

“The Committee is concerned about the future of water availability for the Nation. 

Water is vital to the needs of growing communities, agriculture, energy production, 

and critical ecosystems. Unfortunately, a nationwide assessment of water availability 

for the United States does not exist, or, at best, is several decades old. The Committee 

directs that by January 31, 2002, the Survey prepare a report describing the scope 

and magnitude of the efforts needed to provide periodic assessments of the status and 

trends in the availability and use of freshwater resources.”

In this new century, the United States will be challenged to provide sufficient 

quantities of high-quality water to its growing population. Water is a limiting 

resource for human well-being and social development, and projections of population growth as well as changing social values suggest that demands for this 

resource will increase significantly. These projections have fueled concerns among 

the public and water resources professionals alike about the adequacy of future 

water supplies, the sustainability and restoration of aquatic ecosystems, and the 

viability of our current water resource research programs and our institutional 

and physical water resource infrastructures.

National Research Council, 2001, 

Preface to “Envisioning the Agenda for Water Resources Research 

in the Twenty-First Century”
2

There were several clear messages from those 

with whom we met or corresponded. First, there 

was consensus that a better set of facts is needed to 

inform decisions related to water availability. Many 

individuals emphasized the potential for improved 

methodologies and standards for consistency of 

nationwide data, the importance of leaving water in 

the stream (instream flow) as a component of water 

use, and the connections between water quantity 

and water quality. National organizations, in particular, noted the need for consistent indicators of 

water availability across the Nation. Individuals 

representing State and local governments reminded 

us that many States have done extensive planning 

to quantify water availability now and in the future, 

and that the availability of water is largely a local 

issue. Concerns also were expressed that any efforts 

proposed should not detract from USGS basic data 

collection nor from USGS partnerships with States 

and others on local assessments of water availability 

and use.

There have been several efforts over the 

past few decades to compile national assessments 

of water availability. Perhaps the most notable originated from the Water Resources Planning Act of 

1965 (Public Law 89–80) that created and empowered the U.S. Water Resources Council to oversee 

an ongoing study of the Nation’s water resources. 

A rudimentary national assessment was published 

by the Council in 1968 (U.S. Water Resources 

Council, 1968), followed by a comprehensive 

Second National Water Assessment in 1978 

(U.S. Water Resources Council, 1978). It has 

been argued that the primary value of these 

national assessments was their contribution to 

the general debate over the definition of national 

water problems and the direction for national 

water policy (Osborn and Shabman, 1988).

The U.S. Water Resources Council ceased 

operations in the early 1980’s. In the years that 

followed, the USGS issued a series of reports 

under the general title of “National Water 

Summary” that focused on particular aspects 

of water resources and provided State-by-State 

summaries. The first National Water Summary, 

published in 1984 and referencing 1980 as a 

base year, documented water-resources issues in 

each of the 50 States and principal Territories 

(U.S. Geological Survey, 1984). More recently, 

as part of the water-sector contributions to the 

National Assessment of the Potential Consequences 

of Climate Variability and Change, efforts were 

made to update components of the Second National 

Water Assessment to reflect water-availability conditions for the year 1995 (Frederick and Schwarz, 

1999).
3

NATIONAL ASSESSMENT OF WATER 

AVAILABILITY AND USE

Water availability and use are a function of 

the total flow of water through a basin, its quality, 

and the structures, laws, regulations, and economic 

factors that control its use. Because water availability and water use are closely linked, “water 

availability” will be used for brevity in the following 

sections to include both water availability and water 

use.

It is evident that a national water-availability 

assessment means different things to different 

people. Many different types of assessments and 

assessment products were envisioned by those 

whose advice was solicited. Recommendations 

for products included forecasts of water availability, 

calculations of constructed flow regimes in the 

absence of human management, calculations 

of water demands for protection or restoration 

of wildlife, and an assessment that would include 

policy-related data linking the institutional and physical environments. The scope and magnitude of an 

effort to meet all of the recommendations that were 

received would be an immense undertaking.

A national assessment of water availability 

is proposed that would report on indicators of the 

status and trends in storage volumes, flow rates, 

and uses of water nationwide. Currently, this information is not available in an up-to-date, nationally 

comprehensive and integrated form. The assessment also would provide regional information on 

recharge, evapotranspiration, interbasin transfers, 

and other components of the water cycle across 

the country. This regional information would 

support analyses of water availability that are 

undertaken by many agencies nationwide and 

would benefit research quantifying variability and 

changes in the national and global water cycle.

An assessment would require basic hydrologic 

data collected by the USGS and by others to create 

the indicator variables. This process of computing 

indicators from the basic data would help to elucidate uncertainties in our knowledge of the Nation’s 

hydrologic conditions and would provide useful 

feedback to the design of data-collection networks. 

Improved networks for the collection of surfacewater and ground-water data are defined by USGS 

plans for the National Streamflow Information 

Program (U.S. Geological Survey, 1998a and 

1999) and the Ground-Water Resources Program 

(U.S. Geological Survey, 1998b), and as part of the 

Cooperative Water Program. Water-use information 

developed by the assessment would expand upon 

and strengthen existing water-use efforts along the 

lines suggested by the National Research Council 

(2002).

There are numerous examples from across 

the Nation where water quality is the limiting 

factor to water availability (Box A). Considerable 

information is currently synthesized about the 

Nation’s water quality at regional and national 

scales through a number of State and Federal 

water-quality programs. The USGS National 

Water-Quality Assessment (NAWQA) program, for 

example, collects and analyzes water-quality data in 

many of the Nation’s major river basins and aquifers 

covering nearly all 50 States. Rather than duplicate 

existing water-quality information, the indicators of 

the flows, storages, and uses of water developed as 

part of a national assessment should be used with 

water-quality information from existing programs 

to provide a more complete national picture of the 

quantity and quality aspects of water availability.
4

A

Quantity and Quality of Water Define Availability:

An Example from South Florida

Big Cypress

National Preserve Miami

Tampa

Everglades

National Park

Lake

Okeechobee

Florida Bay

Historically, availability of water could be viewed simply 

as an issue of quantity, and water management could focus 

largely on controlling or alleviating impacts of droughts and 

floods. With escalating population growth and increasing 

demands for multiple water uses, it is now clear that quality 

is equally critical to the long-term sustainability of the Nation’s 

human communities and ecosystems.

Resolution of water issues at the local and regional 

scale commonly requires a framework that links both the 

quantity and quality needs. This framework is perhaps 

nowhere more evident than for the water-rich South Florida 

region with its competing uses of water for agriculture, 

urban growth, and natural-resource protection. An abundant 

and uncontaminated supply of freshwater was a primary 

characteristic of southern Florida in predevelopment times. 

Increased human population and activity, however, have 

brought not only an increased need for water but also 

a decrease in water supply and deterioration in water quality 

(McPherson and Halley, 1996; McPherson and others, 2000). 

Before the construction of more than 1,400 miles 

of primary canals and more than 100 water-control structures, 

water moved from Lake Okeechobee in a large sheet passing 

through the Everglades National Park and Big Cypress 

National Preserve into Florida Bay. Numerous small streams 

and rivers near the coast drained into mangrove forests and 

tidal waters and provided the freshwater that sustained the 

highly productive and abundant coastal fisheries around 

the southern end of the peninsula. 

Approximately 40 percent of that water is now 

diverted, much of which is used to support heavily irrigated 

agriculture and urban development along the coast. Such 

drainage and development have adversely affected water 

quality and ecology throughout southern Florida. For example, 

average phosphorus concentrations in Lake Okeechobee 

have increased two and one-half times over the past 15 years, 

and massive algal blooms have become more frequent and 

persistent. In addition, urban uses of water have affected 

water quality. Stormwater runoff commonly carries heavy 

metals, nutrients, bacteria, viruses, and pesticides.

Many integrated and collaborative efforts are ongoing 

to study the Everglades and address some of these conflicting 

needs for water. For example, recent decisions have been 

made to set land aside south of the agricultural area to 

help remove nutrients before the water moves farther southward. Additionally, water is being recycled from agricultural 

lands back to the fields, instead of moving south toward 

Florida Bay, thus holding back nutrients and reducing water 

demand. Water conservation in the urban areas may well 

stabilize, or even decrease, the population demands for water. 

Water issues in South Florida demonstrate that water availability challenges every region of the Nation where sufficient 

quantity and quality of water are needed to sustain the many 

competing demands for the resource.

Figure A–1. Competition for water to meet the needs of cities, farms, industries, and critical ecosystems challenges every 

region of the Nation, including south Florida where urbanization and agricultural activities have altered the hydrologic environment. Left, irrigation of crops in southern Everglades C–111 agricultural basin; upper right, northern Everglades; lower right,

aerial view of Miami. Photographs by Benjamin F. McPherson.
5

Coordination and Collaboration

The goals of a national assessment are 

consistent with the mission of the USGS to provide 

scientific information to support decision-making 

on issues of resources, environmental quality, and 

natural hazards. An effort to develop the national 

indicators of water availability and the water-cycle 

information should be done in coordination and 

collaboration with other organizations, Federal and 

non-Federal agencies, and universities. Collaboration across agency boundaries would ensure that 

information produced could be aggregated with 

other types of physical, social, economic, and environmental data that affect water availability. Data 

that are germane to issues of water availability 

include water-quality conditions, population statistics, land uses, water costs and pricing, climate 

data, and instream-flow requirements for aquatic 

habitats. These data are compiled by State and local 

agencies, by universities and water-resource organizations, and by several Federal agencies including 

the Department of Agriculture, the National 

Oceanic and Atmospheric Administration, the 

U.S. Army Corps of Engineers, the Bureau 

of Reclamation, and the U.S. Environmental 

Protection Agency. Such an assessment could 

include external research grants and contracts 

that would be used to improve the methodology 

and understanding of water availability and to 

gather, analyze, and disseminate program results.

The assessment should coordinate the design 

and development of water-availability indicators 

and water-cycle information through the Federal 

Advisory Committee on Water Information (ACWI). 

ACWI members represent 35 organizations from 

all levels of government (Federal, State, Tribal, and 

local), public interest groups, academia, private 

industry, and nonprofit and professional organizations. ACWI is chaired by the Deputy Assistant 

Secretary of the Interior for Water and Science 

and is staffed and supported by the USGS under a 

charter established pursuant to the Federal Advisory 

Committee Act by Office of Management and 

Budget Memorandum 92–01. ACWI currently has 

several subgroups examining water-quality monitoring, data methods and comparability, spatial 

water data, hydrology, stream gaging, cooperative 

water programs, and science issues. An additional 

subgroup should be established to make recommendations on the design and methods of presentation 

of the proposed indicators of flows, storages, and 

uses of water and the integration of these indicators 

with water-quality information and other measures 

of water availability.

Glen Canyon Dam 

impounds the Colorado 

River and Lake Powell near 

the Arizona-Utah border. 

The reservoir storage 

content of Lake Powell is 

monitored by the Bureau 

of Reclamation. Photograph by Michael Collier.
6

Indicators of Water Availability

An assessment should develop and report 

up-to-date, nationally consistent indicators that 

would reflect the status and trends in water availability nationwide. Indicators would be developed 

for surface-water flows and storage, ground-water 

levels and storage, and water use (table 1). Data 

sets and analyses produced by the proposed 

assessment would be posted on the Internet and 

published in reports and scientific journals. Efforts 

to develop indicators should comply with the Office 

of Management and Budget Information Quality 

Guidelines.

There are several spatial scales at which the 

indicators of water availability could be reported. 

Past assessments have focused on the individual 

States and the 21 major water-resources regions 

of the United States (fig. 1). Because of technological 

advances for managing, presenting, and sharing 

spatial data, it is now possible to provide information 

at a more refined scale needed by decision-makers.

An assessment should use the 352 river-basin 

hydrologic accounting units (fig. 2) as the basis for 

reporting the national indicators. These accounting 

units are watersheds that are typically from 5,000 

to 20,000 square miles and are used by the USGS 

for designing and managing the National Water 

Data Network (Seaber and others, 1987). In 

most cases, however, boundaries of the hydrologic 

accounting units do not coincide with those of major 

aquifer systems. Ground-water variables, therefore, 

should be reported primarily by major aquifer 

system.

Table 1. Summary of proposed indicators of water availability

Surface-water indicators

Streamflow: annual and periodic (5- to 10-year) summaries; assessments 

of long-term trends

Reservoir storage, construction, sedimentation, and removal

Storage in large lakes, perennial snowfields, and glaciers

Ground-water indicators

Ground-water-level indices for a range of hydrogeologic environments 

and land-use settings

Changes in ground-water storage due to withdrawals, saltwater intrusion, 

mine dewatering, and land drainage

Number and capacity of supply wells and artificial recharge facilities

Water-use indicators

Total withdrawals by source (surface water and ground water) and sector 

(public supply, domestic, commercial, irrigation, livestock, industrial, 

mining, thermoelectric power, and hydropower)

Reclaimed wastewater

Conveyance losses

Consumptive uses
7

In testimony before the Environment and Public Works Committee, Subcommittee on Fisheries, Wildlife and Water, on November 14, 2001, Ane D. Deister, 

Co-Chair of the Interim National Drought Council, identified the following areas 

as needing coordinated data collection, analysis, and evaluation:

• Ground-water supplies and recharge and extraction rates of aquifers

• Water-use consumption, demand forecasting, and accurate estimates of 

water supply and demand balance

• Conservation measures in urban, agricultural, commercial, institutional 

and industrial sectors

• Stream gages and other watershed monitoring

• Weather prediction and long-term patterns and trends

Figure 1. Water-resources regions of the United States (U.S. Geological Survey, 

1982).

0 500 MILES

0 500 KILOMETERS

PACIFIC

NORTHWEST

MISSOURI

UPPER

MISSISSIPPI

TEXAS–GULF

LOWER MISSISSIPPI

LOWER

COLORADO

RIO GRANDE

UPPER

COLORADO

GREAT BASIN CALIFORNIA

GREAT

LAKES

NEW

ENGLAND

MID–

ATLANTIC

OHIO

SOUTH

ATLANTIC–

GULF

ARKANSAS–

WHITE–RED

SOURIS–RED–

RAINY

TENNESSEE

ALASKA

HAWAII CARIBBEAN
8

SURFACE WATER

Indicators of surface-water availability 

would include measures of both streamflow and 

surface-water storage, each of which change 

continuously in response to natural and humaninduced processes (table 2).

Streamflow

Currently, the USGS provides a number 

of assessment-type streamflow products at daily, 

weekly, and monthly time scales. These products, 

such as the online Water Watch Internet site of 

maps and graphs (fig. 3), are useful to emergency 

managers, public officials, and others tracking 

floods and droughts and to private citizens 

planning recreational activities. The USGS will 

continue to produce these types of information 

on daily to monthly conditions through our 

existing programs.

Streamflow indicators that support longer 

term water-availability decisions require more interpretive, value-added information at annual and 

longer time scales than is currently obtainable. To 

fulfill these longer term requirements, the following 

three specific types of streamflow indicators would 

need to be produced:

Knowledge about hydrologic fluctuations with durations of decades to 

centuries is important because the lifetimes of man-made water resource 

systems and of the consequences of resource management decisions are often 

of comparable duration.

Water Cycle Study Group, U.S. Global Change Research Program, May 2001

(Hornberger and others, 2001, p. 11)

Water availability varies seasonally and 

from year to year in response to changing weather 

conditions and water-use demands. A meaningful 

national assessment must remove seasonal and 

short-term variability to isolate trends and patterns 

that have regional and national significance. Hence, 

the status and trends of most indicators should be 

reported and evaluated every 5 to 10 years. To 

place these periodic evaluations into long-term 

perspective, an initial retrospective assessment 

of the past 100 years should be undertaken to 

reveal, to the extent possible, changes in water 

availability during the 20th century. In addition, 

annual reporting of some indicators, such as 

surface-water flow, should be done to provide an 

indication of year-to-year variability of water availability. Monitoring networks for surface-water flow 

are sufficiently developed to allow for annual 

reporting and evaluation.
9

• Annual summaries (graphical and tabular) of 

surface-water discharge for each of the 352 

hydrologic accounting units of the United 

States: Annual summaries would provide simple 

and concise representations of the net effects of 

climatic events, water management, and water 

withdrawals on surface-water supply during a 

year, as well as from one year to the next.

• Periodic summaries of changes in surfacewater discharge for each hydrologic accounting 

unit over periods of 5 to 10 years: Historically, 

some regions of the United States are predisposed to persistent periods of wetness or 

dryness. These periods can last a decade or 

more. To evaluate such persistent patterns 

and to gage their overall severity, periodic 

summaries of interannual change in surfacewater supply are needed.

• Periodic assessments of long-term trends in 

surface-water discharge in each hydrologic 

accounting unit: The ability to determine 

systematic long-term changes in surfacewater supplies is an important capability of 

the national stream-gaging network. Recent 

questions associated with global climate and 

related environmental change increase the 

imperative for periodic assessments of trends 

in the Nation's water supply at regional and 

national scales.

EXPLANATION

Hydrologic accounting

 unit

Water-resources region

PACIFIC

NORTHWEST

MISSOURI UPPER

MISSISSIPPI

TEXAS–GULF LOWER MISSISSIPPI

LOWER

COLORADO RIO GRANDE

UPPER

COLORADO

GREAT BASIN

CALIFORNIA

GREAT

LAKES

NEW

ENGLAND

MID–

ATLANTIC

OHIO

SOUTH

ATLANTIC–

GULF

ARKANSAS–

WHITE–RED

SOURIS–RED–

RAINY

TENNESSEE

ALASKA HAWAII

CARIBBEAN

0 500 MILES

0 500 KILOMETERS

Figure 2. Hydrologic accounting units of the United States (U.S. Geological Survey, 1982).
10

An example of the kind of information that 

can be discerned by analysis of long-term (multidecadal) streamflow records across the Nation is 

given in figure 4, which depicts changes in the 

annual 7-day low flow for selected unregulated 

(fig. 4A) and regulated (fig. 4B) rivers. The annual 

7-day low flow can be used as an indicator of hydrologic drought. The graphs in figure 4A indicate 

long-term low-flow changes on rivers that are minimally affected by surface-water diversions and reservoirs and are, therefore, more reflective of climatic 

variations. They provide a means of determining 

how annual dryness (including drought) has changed 

through time; for example, have droughts become 

more or less frequent or severe? In contrast, the 

graphs in figure 4B indicate changes on rivers 

where human activities have altered the natural 

flow, such as by dams and diversions. As such, 

they not only reflect the influence of climate but 

also provide information on how and where human 

activities have affected low streamflow and drought. 

In combination, the two sets of graphs give resource 

managers and policy makers important information 

on how and where low-flow conditions are changing 

around the Nation.

As part of the streamflow indicators, the 

assessment would provide an accounting of the 

status and trends in the availability of water for 

instream uses in various parts of the country by 

defining the amount of water remaining in a stream 

after offstream uses. Because instream-flow requirements can be estimated only by detailed analysis of 

local situations, an assessment would not estimate 

them.

Table 2. Mechanisms that cause changes in streamflow and surface-water storage

Natural mechanisms Human-induced mechanisms

Runoff from rainfall and snowmelt

Evaporation from soil and surface-water bodies

Transpiration by vegetation

Ground-water discharge from aquifers

Ground-water recharge from surface-water bodies

Sedimentation of lakes and wetlands

Formation or dissipation of glaciers, snowfields, 

and permafrost

Surface-water withdrawals and transbasin 

diversions

River-flow regulation for hydropower and 

navigation

Construction, removal, and sedimentation of 

reservoirs and stormwater detention ponds

Stream channelization and levee construction

Drainage or restoration of wetlands

Land-use changes such as urbanization that alter 

rates of erosion, infiltration, overland flow, or 

evapotranspiration

Wastewater outfalls

Irrigation wastewater return flow
11

Figure 3. Near-realtime streamflow map of the United States, December 5, 2001 (U.S. Geological 

Survey, 2001). Streamflow conditions across the country are reported daily by maps and graphs on 

the U.S. Geological Survey Water Watch Internet site (http://water.usgs.gov/waterwatch/).
12

Black River at Kingstree, SC

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

1,000

1,200

1,400

800

600

400

200

0

DISCHARGE, IN CUBIC

FEET PER SECOND

YEAR

Rappahannock River near Fredericksburg, VA

1930 1940 1950 1960 1970 1980 1990 2000

3,000

4,000

2,000

1,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

St. John River below Fish River at Fort Kent, ME

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

10,000

15,000

5,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

Gila River near Gila, NM

1930 1940 1950 1960 1970 1980 1990 2000

200

300

400

100

0

DISCHARGE, IN CUBIC

FEET PER SECOND

YEAR

Hatchie River at Bolivar, TN

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

2,000

3,000

1,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

Clarks Fork Yellowstone River near Belfry, MT

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

1,500

2,000

1,000

500

0

DISCHARGE, IN CUBIC

FEET PER SECOND

Little Fork River at Littlefork, MN

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

1,500

1,000

500

0

DISCHARGE, IN CUBIC

FEET PER SECOND

Pecatonica River at Freeport, IL

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

6,000

5,000

4,000

3,000

2,000

1,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

Eel River at Scotia, CA

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

0

200

400

600

800

1,000

DISCHARGE, IN CUBIC

FEET PER SECOND

John Day River at Service Creek, OR

1930 1940 1950 1960YEAR1970 1980 1990 2000

0

500

1,000

1,500

2,000

2,500

DISCHARGE, IN CUBIC

FEET PER SECOND

A

Figure 4. The ability to determine systematic long-term changes in surface-water availability is an 

important capability of the national stream-gaging network maintained by the USGS. These graphs 

show annual 7-day low flow for the 70-year period from 1930 to 1999 on selected unregulated (A) 

and regulated (B) rivers. The annual 7-day low flow is a streamflow statistic that is often used as an 

indicator of hydrologic drought. Years when the annual 7-day low flow is relatively low typically 

correspond with drought or abnormally dry periods. The plots in figure 4A depict long-term changes 

in low flow on rivers that are not significantly affected by surface-water diversions and reservoirs, 

whereas those in figure 4B depict long-term changes in low flow on rivers where human activities 

have altered the natural flow, such as by dams and diversions. By assessing both situations, it is 

possible to determine how, where, and why hydrologic drought is changing in the United States.
13

Schuylkill River at Pottstown, PA

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

0

1,000

2,000

3,000

4,000

5,000

DISCHARGE, IN CUBIC

FEET PER SECOND

Androscoggin River near Gorham, NH

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

0

2,000

4,000

6,000

8,000

12,000

10,000

14,000

DISCHARGE, IN CUBIC

FEET PER SECOND

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

Saluda River near Columbia, SC

10,000

8,000

6,000

4,000

2,000

12,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

Coyote Creek near Golondrinas, NM 50

40

30

20

10

0

DISCHARGE, IN CUBIC

FEET PER SECOND

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

Snoqualmie River near Carnation, WA

10,000

8,000

6,000

4,000

2,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

Sacramento River at Verona, CA

80,000

60,000

40,000

20,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

Snake River near Blackfoot, ID

20,000

15,000

10,000

5,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

Mississippi River near Royalton, MN

25,000

20,000

15,000

10,000

5,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

Suwannee River at Ellaville, FL

25,000

20,000

15,000

10,000

5,000

0

DISCHARGE, IN CUBIC

FEET PER SECOND

1930 1940 1950 1960

YEAR

1970 1980 1990 2000

Republican River at Clay Center, KS

2,000

1,500

1,000

500

0

DISCHARGE, IN CUBIC

FEET PER SECOND

B

Figure 4.—Continued.
14

Surface-Water Storage

Indicators of the status and trends in surfacewater storage would consist of annual summaries 

of storage conditions within each of the hydrologic 

accounting units; periodic summaries of changes 

in surface-water storage for each hydrologic 

accounting unit over periods of 5 to 10 years; and 

periodic assessments of long-term trends in surfacewater storage in each hydrologic accounting unit. 

The indicators would account for storage changes 

in surface reservoirs and in selected natural freshwater bodies, including large lakes such as the Great 

Lakes and Lake Champlain, perennial snowfields, 

and glaciers.

The primary changes in surface-water 

storage in most basins arise from changes in the 

total capacity of, and conditions within, surface 

reservoirs. Reservoir construction in the United 

States and Puerto Rico peaked during the 

1960’s and has slowed markedly since then (fig. 5). 

Presently, there are nearly 77,000 dams higher 

than 6 feet in the United States and Puerto Rico 

(U.S. Army Corps of Engineers, 2001). Because 

some reservoirs have multiple dams, this corresponds to about 68,000 reservoirs nationwide. 

Omitting dams that are control structures on large 

natural lakes, such as Superior or Okeechobee, 

the total volume of water stored in these reservoirs 

under typical conditions is about 422 million 

acre-feet (520 cubic kilometers) (Stallard, 1998).

Total reservoir storage conditions change 

in response to hydrologic and water-use variability, 

reservoir sedimentation, and reservoir construction 

and removal. An assessment would regularly 

update reservoir storage conditions and account 

for construction of new reservoirs, decreases in 

reservoir storage capacity due to sedimentation, 

and any removal of dams. The RESIS (Steffen, 

1996) and RESIS-II (Stallard and others, 2001) 

databases of sediment deposition in U.S. reservoirs 

would serve as the basis for evaluating changes in 

reservoir sedimentation. These databases track 

losses in reservoir storage capacity throughout 

the United States and are the master databases 

for regional erosion studies (Stallard, 1998).

Development of indicators of surfacewater storage would require close coordination 

with many agencies and groups because most reservoir data are collected and maintained primarily by 

agencies other than the USGS. A primary source of 

information on dams and reservoirs is the National 

Inventory of Dams, which is maintained by the 

U.S. Army Corps of Engineers in cooperation with 

the 50 States, Puerto Rico, the Association of State 

Dam Safety Officials, and 16 other Federal agencies. Additional data are available from city and 

State agencies and water districts that oversee or 

operate dams and reservoirs. Moreover, a large 

number of Federal and other governmental agencies presently monitor surface-water levels and 

reservoir storage on a continuing basis.

Before

1920

1920

to

1929

1930

to

1939

1940

to

1949

1950

to

1959

1960

to

1969

1970

to

1979

Number

Capacity

1980

to

1988

0

100

0

30

60

90

120

150

200

300

400

500

600

NUMBER OF RESERVOIRS

TOTAL NORMAL CAPACITY, IN MILLION ACRE-FEET

Figure 5. Reservoirs are important 

indicators of water availability. The 

graph shows the number and total 

normal capacity of large reservoirs 

in the United States and Puerto Rico 

completed before 1920, during each 

decade from 1920 to 1979, and from 

1980 to 1988. Normal capacity is the 

total volume in a reservoir below the 

normal retention level (figure from 

Ruddy and Hitt, 1990).
15

GROUND WATER

Long-term, systematic measurements of 

ground-water levels provide essential data needed 

to evaluate changes in ground-water storage over 

time. Using these data, the assessment would 

include two types of indicators to describe the 

nationwide status and trends of ground-water 

availability: ground-water-level indices and periodic 

assessments of changes in ground-water storage.

No nationwide, systematic ground-water-level 

monitoring program exists. At present there are 

approximately 42,000 long-term observation wells 

in the United States that have 5 or more years of 

water-level records (Taylor and Alley, 2002). The 

density of existing monitoring wells, however, varies 

considerably from State to State (fig. 6). The extent 

of water-level monitoring varies even more among 

major aquifers, with very limited monitoring in 

many aquifers. Thus, an inventory of existing 

water-level networks for major aquifer systems 

would be made early in the assessment to identify 

data gaps and opportunities for collaboration across 

the Nation.

Ground-Water Levels

The assessment should develop several 

indices of ground-water-level changes; some would 

represent composite indices for the Nation, whereas 

others would be analogous to “sector” indices in the 

stock market and would reflect specific geographic 

regions or specific types of aquifers, terrains, environments, or land-use settings. The various indices 

would provide water managers, major water users, 

and the public with quick summaries of the magnitudes and significance of trends in water-level 

changes.

WA

MT ND

MN

WI

IL IN

MI

NY

VT

NH

MA

RI

CT

NJ

DE

MD

ME

PA

WV VA

NC

SC

MS AL GA

FL

KY

TN

OH

IA

MO

AR

LA

SD

NE

KS

OK

TX

WY

CO

UT

AZ

AK

HI PR

NM

ID

NV

OR

CA

1 well or fewer

2 to 5 wells

6 to 10 wells

11 to 15 wells

16 to 21 wells

22 to 30 wells

More than 30 wells

Number of long-term

 water-level observation

 wells per 1,000-square-

 mile area

EXPLANATION

Figure 6. Number of ground-water-level observation wells having at least 5 years 

of water-level record per 1,000-square-mile area in each State and in Puerto Rico 

(modified from Taylor and Alley, 2002).
16

To have national or even regional significance, 

indices of ground-water levels have to be based on 

repeated observations at relatively large numbers of 

observation wells located in a wide range of representative hydrogeological environments. Ground-water 

systems are dynamic and adjust continually to shortterm and long-term changes in climate, groundwater withdrawals, and land uses. Water levels in wells 

change in response to a number of types of local and 

regional stresses, some of which are natural and some 

of which are human induced (table 3). Because subsurface hydraulic properties are highly variable, waterlevel responses to stresses vary considerably with 

location and depth. Stresses take time to propagate 

through ground-water systems, so water-level changes 

are transient phenomena that are strongly affected by 

distances from the monitoring wells to imposed 

stresses.

Ground-water-level monitoring networks 

should include wells open to water-table aquifers 

and deep artesian aquifers, wells tapping a 

variety of rock types, wells located both near and 

distant from pumping centers, wells located in 

typical land-use settings, and wells that are widely 

distributed geographically. Because the magnitude 

of water-level fluctuations in wells depends on many 

factors, water levels in some wells may fluctuate 

by tens of feet within a day, but in other wells, 

water levels may change by only tenths of a foot 

over a year. Therefore, some wells may need 

to be monitored continuously, whereas others 

may only need to be measured once per year. 

Among the several indices that would be derived 

for this assessment, some might be updated daily, 

others might be updated monthly, and still others 

annually.

Table 3. Mechanisms that cause changes in ground-water levels and storage (modified from 

Freeze and Cherry, 1979)

Natural mechanisms Human-induced mechanisms

Recharge

Evaporation from the water table

Transpiration by vegetation

Discharge to streams, springs, and seeps

Surface-water-level fluctuations in hydraulically 

connected streams, ponds, or lakes

Ground-water withdrawals

Deep-well injection

Agricultural irrigation

Drainage of agricultural lands, swamps, and 

wetlands

Artificial recharge of water

Wastewater recharge through lagoons, landfills, 

and septic systems

Dewatering of mines, tunnels, or other structures

Leakage from surface-water reservoirs

Urbanization impacts such as leaky water and 

sewer lines, lawn irrigation, and impervious 

surfaces (paved roads, parking lots, and so 

forth)
17

Ground-Water Storage

The amount of ground water in storage in 

the United States is changing (mostly decreasing) 

in response to ground-water withdrawals and other 

mechanisms shown in table 3. Data from several 

ground-water basins and aquifers already show 

significant depletions in freshwater availability over 

several decades. An example showing the greatest 

depletion (or ground-water mining) is the High 

Plains aquifer of the central United States, where 

ground-water withdrawals—primarily for irrigation—have caused large-scale, regional declines 

of the water table and accompanying reductions 

in ground-water storage (Box B).

Periodic national assessments of changes in 

aquifer storage due to ground-water withdrawals, 

saltwater intrusion, mine dewatering, land drainage, 

and other mechanisms that affect ground-water 

availability should be undertaken. These assessments would be based on nationwide summaries 

of observed water-level changes and ancillary data 

describing the aquifers and their changing storage 

conditions. These assessments would require a 

greater level of effort than that required for development of the ground-water-level indices because estimates of changes in ground-water storage require 

knowledge of aquifer storage properties and spatial 

interpolation of ground-water-level measurements. 

The assessment also could provide measures of the 

nationwide status of ground-water-supply infrastructure, such as changes in the number and capacity 

of water-supply wells and artificial recharge facilities; these measures would be analogous to those 

reported for surface-water reservoirs.

Changes in ground-water use and the effects 

of ground-water development are not usually as variable year to year as are those for surface water and, 

therefore, the periodic assessments of ground-water 

storage could be made at 5- to 10-year intervals. 

Ground-water-storage changes should be evaluated 

by major aquifer and then aggregated into regional 

and national assessments. A retrospective analysis 

of changes in ground-water storage during the 

20th century would be made at the beginning of 

the assessment. In some cases, historical changes 

in ground-water storage may need to be estimated 

by use of ground-water simulation models that 

account for all ground-water storage processes, 

including storage changes in confining units. This 

modeling would build, in part, on work from the 

USGS Regional Aquifer-System Analysis (RASA) 

Program, which studied and modeled the Nation’s 

regional aquifers from 1978 to 1995.

Changes in ground-water storage over 

the past 100 years may be large enough to have 

global implications. If the volume of ground water 

stored on the continents has decreased significantly 

over the past century, then it might represent and 

account for a measurable fraction of the sea-level 

rise observed during that time period. This would 

have implications for global climate modeling and 

predictions of future sea-level rise. The impact of 

ground-water declines could be offset by increases 

in water stored in reservoirs, so global impacts 

must be assessed in light of both components 

of water storage. An assessment of changes in 

ground-water storage in the United States perhaps 

could be integrated into a global perspective in 

collaboration with other countries and international 

organizations.

By pumping the vast reserves of ground water, 

farmers have developed the San Joaquin 

Valley of California into a major agricultural 

region. Photograph courtesy of the California 

Department of Water Resources.
18

B

Water-Level Monitoring and Ground-Water 

Depletion in the High Plains Aquifer

NEW MEXICO

COLORADO

TEXAS

NEBRASKA

KANSAS

WYOMING SOUTH DAKOTA

OKLAHOMA

Water-level change,

 in feet

EXPLANATION

More than 150

100 to 150

50 to 100

10 to 50

Boundary of the

 High Plains aquifer

Declines

More than 10

Rises

Less than 10-foot

 change

0

0 150 KILOMETERS

150 MILES

105°

40°

35°

100°

RIVER

RIVER

South

River

North 

Platte

River

PLATTE

RIVER

RIVER

C ANADIAN

ARKANSAS

REPUBLICAN

Platte

40

20

0

–20

–40

–60

1987 1989 1991 1993 1995 1997 1999

YEAR

CUMULATIVE CHANGE IN GROUND-WATER

STORAGE SINCE 1987, IN MILLIONS OF ACRE-FEET

Storage accretion

Storage depletion

Ongoing water-level monitoring in the High Plains 

aquifer documents the long-term ground-water depletion of a 

national resource and provides a good example of the type of 

water-level network required to assess ground-water availability in the Nation’s major aquifer systems. The High Plains 

aquifer is a 174,000-square-mile area underlying parts of eight 

States from South Dakota to Texas. Irrigation water pumped 

from the aquifer has made the High Plains one of the Nation’s 

most important agricultural areas.

The intense use of ground water has caused major 

water-level declines and reduced the saturated thickness of 

the aquifer (the ground water remaining in storage) in some 

areas to a level at which it is no longer economical to use 

the aquifer as a water supply. The changes are particularly 

evident in the central and southern High Plains (fig. B–1), 

where more than 50 percent of the predevelopment saturated 

thickness has been dewatered in some areas. 

Water-level declines increase pumping lift, decrease 

well yields, and limit development of the ground-water 

resource. The net amount of water removed from storage 

in the aquifer is estimated to have been 220 million acre-feet 

(270 cubic kilometers) through 1999. This is a very large 

volume of freshwater—equal to more than half the volume 

of water in Lake Erie. If the total volume depleted from this 

single, multi-State aquifer was spread over the surface of 

the oceans, it would raise sea level about 0.75 millimeter, 

or about 0.5 percent of the sea-level rise observed during 

the entire 20th century.

In response to declines in water levels and groundwater storage (fig. B–2), a monitoring program was begun 

across the High Plains in 1988 to assess annual groundwater-level changes in the aquifer. Water-level measurements 

have been made each year in more than 7,000 wells. This 

substantial effort requires collaboration among numerous 

Federal, State, and local water-resource agencies. Water 

levels continue to decline in many areas of the aquifer, but the 

monitoring program indicates overall reductions in the rate of 

decline during the past two decades in some areas (McGuire 

and Sharpe, 1997). This change is attributed to decreases in 

irrigated acreage, reduced water needs because of improved 

irrigation and cultivation practices, and above-normal precipitation and recharge during this period.

Figure B–1. Changes in ground-water levels in the High 

Plains aquifer from before ground-water development to 

1997 (V.L. McGuire, U.S. Geological Survey, written 

commun., 1998).

Figure B–2. Cumulative changes in ground-water 

storage in the High Plains aquifer system since 1987.
19

WATER USE

Existing water-use estimation efforts need 

improved coordination and analysis of program 

effectiveness to reflect the increased importance of, 

and demands for, national water-use data and analyses. The USGS has compiled and disseminated estimates of water use for the Nation at 5-year intervals 

since 1950 (Solley and others, 1998). Water-use 

information is compiled in collaboration with the 

States through the USGS Cooperative Water 

Program. Differences among the States in the types 

of water uses, in funding priorities, and in regulations 

that require reporting of water-use information have 

resulted in an unevenness in the breadth and 

depth of water-use data collected for each State.

A goal of this element of an assessment 

is to strengthen and enhance future studies of the 

Nation’s water use along the lines recommended 

by the National Research Council (NRC) in a recent 

review of the USGS water-use program (Box C). A 

key recommendation of the NRC review was to use 

sampling strategies and mathematical (regression) 

modeling to develop statistically derived water-use 

estimates. This statistical approach, which could 

be undertaken as part of the assessment, would 

identify demographic, economic, geologic, hydrologic, and climatic indicators that are correlated 

with water use and that can be used to supplement 

existing water-use data. Statistical correlations developed between water use and these related indicators 

might allow improved understanding of past trends 

in water use and better prediction of future changes 

in water demands and water uses. Estimates of 

irrigation water use, for example, are well suited 

to statistical applications because irrigation withdrawals are closely related to indicators such as 

climate, farming and irrigation techniques, and 

irrigated acreage (fig. 7). Reshaping the national 

water-use data-collection strategies by using statistical techniques also would help to develop consistent methods for estimating water use across State 

and regional boundaries.

Under such an assessment, water-use estimates would be provided at 5-year intervals by 

county, State, and major water-resources regions 

of the Nation. As statistical techniques are developed, the assessment would move toward annual 

accounting of high-priority water-use sectors such 

as public supply and irrigation. In addition, efforts 

would be made to develop water-use estimates for 

each of the 352 hydrologic accounting units and for 

the Nation’s major aquifer systems. As in previous 

water-use assessments, State agencies would be a 

major partner in the collection and reporting of 

water-use indicators.

An enhanced national water-use database 

would be developed and maintained to provide 

ready access to water-withdrawal, conveyance, 

and return-flow information. The database also 

would store ancillary data sets on the related 

water-use indicators. Some of the data sets for these 

related indicators are available from State agencies 

and other Federal agencies, such as the Department 

of Agriculture, Department of Energy, Bureau 

of Economic Analysis, and Bureau of the Census. 

Consistent and accessible water-use data made 

available through a national water-use database 

would be the foundation for integrating wateruse data with water-flow and water-quality data to 

generate policy-relevant information about human 

impacts on water and ecological resources.

Center pivot irrigation system, Kansas. Photograph 

by Kevin F. Dennehy.
20

1960 1965 1970 1975 1980 1985 1990 1995

0

10,000

20,000

30,000

40,000

50,000

60,000

Total

Irrigated acreage in the United States, 1960–1995

Western United States

Eastern United States

IRRIGATED ACREAGE, IN THOUSANDS OF ACRES

Figure 7. Nationally, withdrawals for irrigation are a large percentage of total water 

use, accounting for 40 percent of total withdrawals and 80 percent of consumptive 

uses in 1995 (Solley, 1998). Total irrigation withdrawals and irrigated acreage in the 

United States steadily increased between 1960 and 1980, but then declined in 1985 and 

has remained fairly steady since. The decrease in irrigated acreage in the West is a result of 

expanding urban areas and an increase in dryland farming. In contrast, irrigated acreage in 

the East increased steadily over the same 35-year period, especially in areas with favorable 

climate, topography, and available water. (Data compiled from U.S. Geological Survey 

Circulars titled “Estimated use of water in the United States” published in 5-year intervals 

between 1960 and 1995.)
21

C

A Plan to Enhance the 

National Water-Use Information Program

• The NWUIP is the Nation’s only comprehensive source of information on the status and trends of 

water use. The USGS is uniquely suited to provide this essential national information, working 

with its State-level cooperative partners and with other Federal agencies.

• The NWUIP should be viewed as much more than a data-collection and database management 

program. The NWUIP should be elevated to a water-use science program, emphasizing applied 

research and techniques development in both the statistical estimation of water use, as well 

as the determinants and impacts of water using behaviors.

• To better support water-use science, the USGS should build on existing data-collection efforts to 

systematically integrate data sets, including those maintained by other Federal and State agencies, 

within the data-collection and water-use estimation activities of the NWUIP.

• The USGS should systematically compare water-use estimation methods to identify the techniques 

best suited to the requirements and limitations of the NWUIP. One goal of this comparison 

should be to determine the standard error for every water-use estimate.

• The USGS should focus on the scientific integration of water use, water flow, and water quality, to 

expand knowledge and generate policy-relevant information about human impacts on both water 

and ecological resources.

The National Research Council Committee on USGS Water Resources Research recently conducted 

a review of the National Water-Use Information Program (NWUIP) to determine the best approach for future 

studies of water use by the USGS (National Research Council, 2002). The following are some of the findings 

and recommendations of the Committee to the USGS:
22

Many of those who provided input regarding 

a national assessment of water availability indicated 

a need for improved regional-scale estimates of 

recharge, evapotranspiration, interbasin transfers, 

and other components of the water cycle. Elements 

of the water cycle typically are organized and interpreted in terms of water budgets (fig. 8). State, 

local, and Federal water managers often rely on the 

USGS for quantitative information on water-cycle 

components to better understand water budgets and 

to support water-management decisions. Information on water-cycle components for regional water 

budgets, however, is not always available in a consistent form across the Nation. To meet these information needs, the assessment should provide regional 

estimates of selected water-cycle components across 

the Nation. These estimates would support analyses 

of water availability that are undertaken by many 

local and regional agencies, would benefit research 

quantifying variability and changes in the national 

and global water cycle, and would aid in the interpretation of trends identified in the national indicators of water storage, flow, and use. Some of the 

water-cycle components, such as evapotranspiration, have proven difficult to estimate accurately 

using existing measurement techniques. Therefore, 

the assessment should support development of 

improved methods for quantifying water-cycle 

components.

The effort for improved characterization 

of water-cycle components outlined here would 

complement, build upon, and extend the gains 

made through the existing USGS Cooperative 

Water Program. The Cooperative Water 

Program is a cost-sharing partnership between 

the USGS and water-resource agencies at the 

State, local, and Tribal levels. As part of the 

cooperative program, the USGS conducts analyses 

of water availability in support of water-resource 

management decisions from local to statewide 

levels. These analyses often are done to estimate 

specific components of the water cycle or to quantify interactions among multiple components of the 

water cycle.

Two examples from the USGS Cooperative 

Water Program illustrate the value of water-cycle 

information for water-resource management, as 

well as the level of effort that is required for watercycle studies. In the Eastern United States, the 

USGS is studying interactions among water withdrawals, streamflow reductions, and streamflow 

requirements for aquatic-habitat protection 

(Box D). In the Southwest, the USGS developed 

improved methods for estimating evapotranspiration by native vegetation to better understand 

the water budget of Owens Valley (Box E). It 

has been difficult, however, to synthesize local 

analyses into regional and national pictures. 

Regional and national analyses of water-cycle 

components could be accomplished more effectively 

through a coordinated national initiative such as the 

assessment described in this report.

Water-Cycle Characterization
23

What is a water budget?

Precipitation

Drainage-basin

boundary

Evapotranspiration

Surface-water inflow,

imported water

(pipelines, canals)

Ground-water inflow

Surface-water outflow,

exported water

(pipelines, canals)

Ground-water outflow

Aquifer

Evaporation

Hydrologists use water budgets to 

account for flow and storage changes in 

natural systems that contain water. Systems 

of interest can be features such as rivers, lakes, 

drainage basins, the land surface, or aquifers. Water 

budgets for each of these systems use the relation:

 (WATER INFLOW)–(WATER OUTFLOW)=(CHANGE IN WATER STORAGE)

WATER INFLOW

 —Precipitation

 —Surface-water flow into basin

 — Imported water

 —Ground-water inflow

WATER OUTFLOW

 —Evaporation

 —Transpiration by vegetation

 (evapotranspiration)

 —Surface-water outflow

 —Exported water

 —Ground-water outflow

CHANGE IN WATER STORAGE, 

 increased/decreased water in:

 —Snowpack

 —Unsaturated soil zone

 —Streams, rivers, reservoirs

 —Aquifers

Typical water budget components

Bedrock

Water table

Figure 8. Water-cycle components and simplified water budget of a drainage basin.
24

D

Water Supply and Dry Rivers in 

the Humid East—Modeling the Effects of 

Water Withdrawals on Streamflow in the 

Ipswich River Basin, Massachusetts

ATLANTIC OCEAN

Ipswich River Basin

Boston

MASSACHUSETTS

South Middleton

Ipswich River

Water shortages, dry riverbeds, and impaired stream 

habitats are most often associated with the arid West. Yet 

with increasing regularity, these water-resource issues are 

making headlines in the humid East. Water withdrawals for 

domestic, commercial, and other uses in the Ipswich River 

Basin in northeastern Massachusetts (fig. D–1), for example, 

frequently cause streamflows in the upper one-third of the 

basin to become very low or to cease completely during the 

summer, which results in sections of dry riverbed. Reduced 

streamflows stress aquatic communities, cause fish and 

mussel kills during dry years, and limit the value of the 

river as a biological, recreational, and scenic resource.

Recognizing that solutions to the basin’s waterresource problems require cooperation among the many 

stakeholders, the Ipswich River Task Force was formed in 

1996 to address water-resource issues in the basin. The 

Task Force determined that a watershed model was needed 

to serve as a basis for water-resources-management decisions in the basin. The following year, the USGS, in cooperation with the Massachusetts Departments of Environmental 

Management and Environmental Protection, began development and testing of such a model to determine the effects 

of water-use and land-use patterns on streamflow in the basin 

(Zarriello and Ries, 2000). Results of the model indicate that 

ground-water withdrawals substantially decrease streamflows 

during periods of low flow. For example, the model estimated 

that because of ground-water withdrawals, the Ipswich River 

ceases to flow at the site shown in the photographs below 

during some low-flow periods; without such withdrawals, 

the river would maintain a minimum flow of about 2.5 million 

gallons per day.

The model is a dynamic tool that continues to be 

applied to water-related issues in the basin. Most recently, 

the model was used to determine streamflows at sites along 

the main stem of the Ipswich River that were identified in 

a related study to be critical for fish passage during low 

flows (Armstrong and others, 2001). Model simulations 

were required because natural (unregulated) flow conditions 

are unknown at these sites. Results of the modeling and 

stream-habitat studies are currently being used by the 

Massachusetts Department of Environmental Protection to 

help establish withdrawal limits for water-supply wells, and are 

the cornerstone of a comprehensive watershed management 

plan being developed for the basin.

Figure D–1. View of the Ipswich River near South Middleton, Massachusetts, during normal streamflow (left) and during 

the summer drought of 1999 (right). Figures modified from Zarriello and Ries, 2000. Photographs by David Armstrong and 

Timothy Driskell.
25

E

Cooperative Science Helps Determine 

Water Availability in Southern California

Owens Valley, a long narrow valley along the eastern 

flank of the Sierra Nevada in east-central California, is the 

main source of water for the City of Los Angeles. Diversion 

of streamflow for irrigation in the early 1900’s and to the 

Owens River–Los Angeles Aqueduct after 1913 greatly 

altered the water budget of the valley. In 1970, a second 

pipeline to Los Angeles was completed, thereby increasing 

the capacity for exporting water. The additional water for 

Los Angeles was obtained by increasing surface-water diversions, by reducing irrigation, and by pumping ground water. As 

a result, ground-water levels were lowered, and native plants 

dependent on shallow ground water declined over large 

areas of the valley. The concern of residents that the additional export of water was degrading the environment of 

Owens Valley prompted lawsuits against Los Angeles. 

A clear, authoritative, and unbiased assessment of water 

availability in the valley was needed to settle the developing 

controversy.

Consequently, the USGS was approached by Inyo 

County and the City of Los Angeles and in the early 1980’s 

began cooperative studies with them to evaluate the geology, 

water resources, and native vegetation of the valley. Hydrologic field investigations included innovative measurements 

of evapotranspiration, and simulations with a new valley-wide 

ground-water-flow model examined historical, current, and 

future water budgets for Owens Valley (Danskin, 1998). These 

USGS studies documented large decreases in evapotranspiration and springflows in response to water management in 

the 1970’s and 1980’s (fig. E–1) and projected even larger 

possible decreases in the future. As described in the settlement documents to pending lawsuits, the USGS studies 

“became the technical foundation for the joint long-term 

ground-water management plan” between Los Angeles and 

Inyo County, an operational plan designed to avoid long-term 

ground-water mining and the resultant adverse effects on 

native vegetation.

Los Angel

Pacific Ocean

Ground-Water Outflow

Water Years 1963–69

Water Years 1970–84

Evapotranspiration 53%

Lower

Owens

River

9%

Riveraqueduct

channel

9%

Pumped and

flowing wells

11%

Springs and

seeps

11%

Underflow

5%

Evapotranspiration 34%

Lower

Owens

River

7%

Riveraqueduct

channel

3%

Pumped and

flowing wells

50%

Springs

and

seeps

1%

Underflow

5%

CALIFORNIA

Owens Valley

Inyo

County

Los Angeles

Figure E–1. Simulated outflow components of the groundwater budget for Owens Valley for water years 1963–69 

(prior to completion of the second Los Angeles aqueduct) 

and water years 1970–84 (during the initial operation of that 

aqueduct), showing large declines in evapotranspiration 

and springflow in response to large increases in groundwater pumpage (figure modified from Danskin, 1998).
26

In response to a directive from Congress, this 

report describes concepts for a national assessment 

of freshwater availability and use. The assessment 

would develop and report on indicators of the status 

and trends in storage volumes, flow rates, and uses 

of water nationwide. Currently, this information is 

not available in an up-to-date, nationally comprehensive and integrated form. The development 

and reporting of national indicators of water availability and use would be analogous to the task of 

other Federal statistical programs that produce 

and regularly update indicator variables that 

describe economic, demographic, and health conditions of the Nation. The effort to develop indicators 

should comply with the Office of Management and 

Budget Information Quality Guidelines. The assessment also would provide regional information on 

recharge, evapotranspiration, interbasin transfers, 

and other components of the water cycle across the 

country. This regional information would support 

analyses of water availability that are undertaken 

by many agencies nationwide and would benefit 

research quantifying variability and changes in 

the national and global water cycle.

The assessment would use basic hydrologic 

data collected by the USGS and by others to create 

the indicator variables. This process of computing 

indicators from the basic data would help to elucidate uncertainties in our knowledge of the Nation’s 

hydrologic conditions. Data gaps identified by the 

program would provide useful feedback to the 

design of the data-collection networks. Thus, the 

assessment should influence basic-data programs 

by showing where uncertainty is greatest. Improved 

networks for the collection of surface-water and 

ground-water data are defined by USGS plans for 

the National Streamflow Information Program 

(U.S. Geological Survey, 1998a and 1999) and the 

Ground-Water Resources Program (U.S. Geological 

Survey, 1998b), and as part of the Cooperative 

Water Program. Water-use information developed 

by the program would expand upon and strengthen 

existing water-use efforts along the lines suggested 

by the National Research Council (2002).

The timeframe over which the indicators 

could become available would vary with the 

type of indicator. Surface-water indicators could 

be developed in a preliminary way over about a 

year’s time. A year or more would be required to 

inventory existing data relevant to ground-water 

indicators and to determine appropriate ways to 

synthesize these data prior to development of the 

indicators. Several years would be required to 

develop improved approaches for estimating the 

water-use indicators prior to their implementation. 

The estimation of water-cycle components could 

be done in a stepwise basis over multiple years, 

depending on the scale of the effort.

The assessment should be highly collaborative, involving many Federal and State agencies, 

universities, and non-governmental interests. 

Collaboration across agency boundaries would 

ensure that information produced by the assessment 

could be aggregated with other types of physical, 

social, economic, and environmental data that affect 

water availability. These data include water-quality 

conditions, population statistics, land uses, water 

costs and pricing, climate data, and instream-flow 

requirements for aquatic habitats. To maximize 

the utility of the information, the design and development of the assessment should be coordinated 

through the Federal Advisory Committee on 

Water Information.

SUMMARY
27

ACKNOWLEDGMENTS

U.S. Geological Survey contributors to this report included 

Robert M. Hirsch, William M. Alley, Paul M. Barlow, Michael D. 

Dettinger, W. Scott Gain, Pixie A. Hamilton, Susan S. Hutson, 

William H. Kirby, Leonard F. Konikow, Stanley A. Leake, Harry F. 

Lins, Molly A. Maupin, John E. Schefter, Gregory E. Schwarz, 

James R. Slack, and Gregg J. Wiche. Joy Monson and Margo 

VanAlstine prepared the final manuscript and illustrations.
28

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2001, Assessment of habitat, fish communities, 

and streamflow requirements for habitat protection, 

Ipswich River, Massachusetts, 1998–99: U.S. 

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Report 01–4161, 72 p.

Danskin, W.R., 1998, Evaluation of the hydrologic 

system and selected water-management 

alternatives in the Owens Valley, California: 

U.S. Geological Survey Water-Supply Paper 2370, 

175 p.

Frederick, K.D., and Schwarz, G.E., 1999, 

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Beven, K., Foufoula-Georgiou, E., Katul, G., 

Kinter, J.L., III, Koster, R.D., Lettenmaier, D.P., 

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new science initiative on the global water cycle: 

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Program, 118 p.

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Florida environment—A region under stress: U.S. 

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Anne, 2000, Water quality in southern Florida, 

1996–1998: U.S. Geological Survey Circular 1207, 

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APPENDIX A
33

We thank individuals and organizations listed below who responded to our solicitation for input on a 

plan for a national assessment of water availability and use.

State Agencies and Organizations

Barney Austin, Texas Water Development Board, Austin, TX

William Turner, New Mexico Office of Natural Resources Trustee, Albuquerque, NM

Rhea Graham, New Mexico Interstate Stream Commission, Albuquerque, NM

Larry Anderson, Utah Department of Natural Resources, Division of Water Resources, Salt Lake City, UT

Don Ostler, Utah Department of Environmental Quality, Division of Water Quality, Salt Lake City, UT

Karl Muessig, Office of the State Geologist, New Jersey Geological Survey, Trenton, NJ

Marcia Willhite, Bureau of Water, Illinois Environmental Protection Agency, Springfield, IL

Richard Cobb, Bureau of Water, Illinois Environmental Protection Agency, Springfield, IL

William Compton, Illinois Governor’s Groundwater Advisory Council, Springfield, IL

Derek Winstanley, Illinois State Water Survey, Champaign, IL

David Hamilton, Surface Water Quality Division, Michigan Department of Environmental Quality, 

Lansing, MI

Mimi Garstang, Geological Survey and Resource Assessment Division, Missouri Department of Natural 

Resources, Rolla, MO

Rodney DeHan, Florida Geological Survey, Tallahassee, FL

Federal Agencies and Organizations

Henry Diaz, Climate Diagnostics Center, National Oceanic and Atmospheric Administration, Boulder, CO

Robert Webb, Climate Diagnostics Center, National Oceanic and Atmospheric Administration, Boulder, CO

Donald Scavia, National Ocean Service and National Centers for Coastal Ocean Science, National Oceanic 

and Atmospheric Administration, Silver Spring, MD

Kathy Jacobs, Office of Global Programs, National Oceanic and Atmospheric Administration, Silver 

Spring, MD

Richard Lawford, Office of Global Programs, National Oceanic and Atmospheric Administration, Silver 

Spring, MD

Robert Kripowicz, Office of Fossil Energy, U.S. Department of Energy, Washington, DC

Thomas Feeley III, National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, PA

Terry Ackman, National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, PA

David Beecy, Office of Fossil Energy, U.S. Department of Energy, Washington, DC

Randy Pennington, Office of Fossil Energy, U.S. Department of Energy, Germantown, MD

Reid Goforth, Office of Research Coordination, U.S. Fish and Wildlife Service, Arlington, VA

Theodore Heintz, Office of Policy Analysis, U.S. Department of the Interior, Washington, DC

Sidney Eugene Gibson, Tennessee Valley Authority, Knoxville, TN

Janet Herrin, Tennessee Valley Authority, Knoxville, TN

Katherine Smith, Economic Research Service, U.S. Department of Agriculture, Washington, DC

Tim Smith, U.S. Interagency Working Group on Sustainable Development Indicators, Washington, DC

David Berry, U.S. Interagency Working Group on Sustainable Development Indicators, Washington, DC

Kevin Whalen, Bureau of Land Management, Washington, DC 

Shannon Cunniff, Bureau of Reclamation, Washington, DC

Donald Ralston, Bureau of Reclamation, Washington, DC

David Wingerd, U.S. Army Corps of Engineers, Washington, DC

Dan Kimball, National Park Service, Fort Collins, CO

Sharon Kliwinski, National Park Service, Washington, DC

List Of Individuals Providing Input To This Report
34

Universities

David Maidment, Department of Civil Engineering, The University of Texas, Austin, TX

Roger Bales, Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ

Richard Luthy, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA

Dara Entekhabi, Department of Civil and Environmental Engineering, Massachusetts Institute of 

Technology, Cambridge, MA

Richard Vogel, Department of Civil and Environmental Engineering, Tufts University, Medford, MA

Paul Kirshen, Department of Civil and Environmental Engineering, Tufts University, Medford, MA

Donald Siegel, Department of Earth Sciences, Syracuse University, Syracuse, NY

Leonard Shabman, Virginia Water Resources Research Center, Virginia Polytechnic Institute and State 

University, Blacksburg, VA

Robert Ward, Colorado Water Resources Research Institute, Colorado State University, Fort Collins, CO

Gary Johnson, Department of Geological Sciences, University of Idaho, Idaho Falls, ID

Thomas Harter, Department of Land, Air and Water Resources and Kearney Agricultural Center, University 

of California, Davis, CA

Neil Grigg, Department of Civil Engineering, Colorado State University, Fort Collins, CO

Richard Sparks, Illinois Water Resources Center, University of Illinois, Urbana, IL

William McDowell, New Hampshire Water Resources Research Center, Department of Natural Resources, 

University of New Hampshire, Durham, NH

Kenneth Steele, Department of Geosciences, University of Arkansas, Fayetteville, AR

Henry Vaux, University of California, Division of Agriculture and Natural Resources, Oakland, CA

Charles Turner, Department of Civil Engineering, University of Texas, El Paso, TX

Jeffery Ballweber, Water Resources Research Institute, Mississippi State University, Mississippi State, MS

Charles Howe, Institute of Behavioral Science, University of Colorado, Boulder, CO

S. Lawrence Dingman, Earth Sciences Department, University of New Hampshire, Durham, NH

Other Individuals and Organizations

Gerald Galloway, International Joint Commission, Washington, DC

William Nuttle, Consultant and Member of National Research Council Committee on Hydrological Sciences, 

Ontario, Canada

Robert Goldstein, Electric Power Research Institute, Palo Alto, CA

National Research Council Committee on Hydrologic Science, Washington, DC

National Research Council Committee on Water Resources, Washington, DC

Western States Water Council, Midvale, UT

William Horvath, National Association of Conservation Districts, Stevens Point, WI

Susan Seacrest, The Groundwater Foundation, Lincoln, NE

Thomas Curtis, American Water Works Association, Washington, DC

Stephen Ragone, National Ground Water Association, Reston, VA

Susan Gilson, Interstate Council on Water Policy, Washington, DC

Robert Hughes, American Fisheries Society, Corvallis, OR

Ghassan Rassam, American Fisheries Society, Bethesda, MD

Robin O’Malley, The H. John Heinz III Center for Science, Economics and the Environment, 

Washington, DC

Barry Norris, Association of Western State Engineers, Salem, OR

S. Elizabeth Birnbaum, American Rivers, Washington, DC

Linda Mather Walker, League of Women Voters, New Orleans, LA

Betsy Cody, Congressional Research Service, Washington, DC

Claudia Copeland, Congressional Research Service, Washington, DC 

Mary Tiemann, Congressional Research Service, Washington, DC 

Jeff Zinn, Congressional Research Service, Washington, DC
Concepts for National Assessment of Water Availability and Use Circular 1223

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