Report to Congress—

Progress Toward Establishing a National Assessment 

of Water Availability and Use

Circular 1384

U.S. Department of the Interior

U.S. Geological Survey
Cover. Big Lazer Creek, Talbot County, Georgia. (Photo by Alan Cressler, U.S. Geological Survey)
Report to Congress—

Progress Toward Establishing a National 

Assessment of Water Availability and Use

By William M. Alley, Eric J. Evenson, Nancy L. Barber, Breton W. Bruce, 

Kevin F. Dennehy, Mary C. Freeman, Ward O. Freeman, Jeffrey M. Fischer, 

William B. Hughes, Jonathan G. Kennen, Julie E. Kiang, Kelly O. Maloney, 

MaryLynn Musgrove, Barbara Ralston, Steven Tessler, and James P. Verdin

Circular 1384

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Alley, W.M., Evenson, E.J., Barber, N.L., Bruce, B.W., Dennehy, K.F., Freeman, M.C., Freeman, W.O., Fischer, J.M., 

Hughes, W.B., Kennen, J.G., Kiang, J.E., Maloney, K.O., Musgrove, MaryLynn, Ralston, Barbara, Tessler, Steven, and 

Verdin, J.P., 2013, Progress toward establishing a national assessment of water availability and use: U.S. Geological 

Survey Circular 1384, 34 p.
iii

About This Report

Many reports have recognized the need for a National Water Census (Water Census) for 

the United States, and have called upon the U.S. Geological Survey (USGS) to undertake this 

challenge. The United States Congress, in Subtitle F of the Omnibus Public Land Management 

Act of 2009 (Public Law (P.L.) 111-11), established a “blueprint” for a national assessment 

of water availability and use that outlines the information needed from a Water Census. This 

report, “Progress Toward Establishing a National Assessment of Water Availability and Use,” 

describes the initial steps taken by the USGS to institute a Water Census and the progress the 

USGS has made toward establishing such a Census. It explains, for both Congress and the 

public, the steps the USGS will take to fulfill the requirements of Subtitle F of P.L. 111-11, and 

describes plans for the future of the Water Census.

This report presents the history and background of and the need for a Water Census. It 

describes the initial steps taken toward accomplishing the Water Census, which is designed 

to systematically provide information that will allow resource managers to assess the water 

availability of the Nation. The report explains how the Water Census is being organized around 

the unifying theme of a water budget, and explains why water budgets are critical for assessing 

water availability for the Nation. The report describes the importance of understanding, 

assessing, and delivering information about the uncertainty of water-availability information, 

as well as the collaboration and coordination with other agencies and organizations that is 

essential for the Water Census to succeed. The report explains the planned regional framework 

for presenting water-availability data through a set of geographic focus area studies and the 

planned national framework for providing uniform information on water-budget components 

across the country through topical area studies. The report also explains how the USGS will 

incorporate water-quality information into the water-availability analysis. Finally, the report 

describes the information management and delivery activities that are necessary for the goals of 

the Water Census to be achieved. 
iv

Contents

About This Report .........................................................................................................................................iii

Executive Summary.......................................................................................................................................1

1.0 Introduction...........................................................................................................................................2

2.0 National Water Census .......................................................................................................................3

2.1 Water Budgets as a Unifying Theme .......................................................................................4

2.2 Characterizing Uncertainty........................................................................................................7

2.3 Coordination and Collaboration ................................................................................................7

2.4 Progress Toward Goals ..............................................................................................................8

3.0 Geographic Focus Area Studies........................................................................................................9

3.1 Apalachicola-Chattahoochee-Flint River Basin.....................................................................9

3.2 Colorado River Basin ...............................................................................................................12

3.3 Delaware River Basin...............................................................................................................12

4.0 Topical Areas ......................................................................................................................................16

4.1 Surface Water............................................................................................................................16

4.2 Groundwater..............................................................................................................................17

4.3 Evapotranspiration....................................................................................................................19

4.4 Water Use...................................................................................................................................20

4.5 Ecological Water Science .......................................................................................................23

5.0 Water Availability and Water Quality..............................................................................................28

6.0 Delivering the Data.............................................................................................................................28

6.1 Data Integration and Mapping................................................................................................28

6.2 The National Data Platform .....................................................................................................30

7.0 Planning for the Future......................................................................................................................30

8.0 Acknowledgments..............................................................................................................................31

9.0 References Cited................................................................................................................................32
v

Figures

1. Diagram showing components of a simple water budget for part of a watershed...........5

2. Map showing location of Apalachicola-Chattahoochee-Flint (ACF) River Basin............10

3. Map showing location of discharge measurements made in the lower 

Apalachicola–Chattahoochee–Flint River Basin and western and central parts 

of the Aucilla–Suwanee–Ochlockonee River Basin, Georgia and Florida, showing 

gaining, losing, and dry stream reaches during July 2011...................................................11

4. Map showing location of Colorado River Basin....................................................................13

5. Graph showing water supply and water use in the Colorado River Basin, 

1923–2008 .....................................................................................................................................14

6. Map showing location of Delaware River Basin...................................................................15

7. Screen capture of estimated annual runoff for the period October 1, 2010, through 

September 30, 2011, for each of the 8-digit hydrologic unit code cataloging units 

in the United States ....................................................................................................................16

8. Map showing U.S. Geological Survey Groundwater Resources Program regionalscale groundwater study areas ...............................................................................................19

9. Map showing estimated total annual evapotranspiration in the Colorado River 

Basin for 2010 determined by using Moderate Resolution Imaging Spectroradiometer 

(MODIS) land-surface temperature imagery and the Simplified Surface Energy 

Balance (SSEB) method ............................................................................................................21

10. Graph showing 2005 water withdrawals in the United States by water-use 

category .......................................................................................................................................22

11. Map showing freshwater irrigation withdrawals in the United States 

by county, 2005 ............................................................................................................................23

12. Maps showing example findings from the U.S. Geological Survey National 

Water-Quality Assessment Program.......................................................................................29
vi

Boxes

A. Report Requested in SECURE Water Act (P.L. 111-11)............................................................3

B. Hydrologic Units............................................................................................................................6

C. Coordination of the Water Census with the Bureau of Reclamation...................................7

D. Groundwater Availability Study of the California Central Valley ........................................18

E. Ecological Water Science—Apalachicola-Chattahoochee-Flint (ACF) River Basin......25

F. Ecological Water Science—Colorado River Basin ..............................................................26

G. Ecological Water Science—Delaware River Basin .............................................................27
Progress Toward Establishing a National Assessment 

of Water Availability and Use

By William M. Alley, Eric J. Evenson, Nancy L. Barber, Breton W. Bruce, Kevin F. Dennehy, Mary C. Freeman, 

Ward O. Freeman, Jeffrey M. Fischer, William B. Hughes, Jonathan G. Kennen, Julie E. Kiang, 

Kelly O. Maloney, MaryLynn Musgrove, Barbara Ralston, Steven Tessler, and James P. Verdin

Executive Summary

The Omnibus Public Land Management Act of 2009 (Public Law 111-11) was passed into law on March 30, 2009. Subtitle F, also known as the SECURE Water Act, calls for the establishment of a “national water availability and use assessment 

program” within the U.S. Geological Survey (USGS). A major driver for this recommendation was that national water availability and use have not been comprehensively assessed since 1978. 

This report fulfills a requirement to report to Congress on progress in implementing the national water availability and use 

assessment program, also referred to as the National Water Census. The SECURE Water Act authorized $20 million for each of 

fiscal years (FY) 2009 through 2023 for assessment of national water availability and use. The first appropriation for this effort 

was $4 million in FY 2011, followed by an appropriation of $6 million in FY 2012. 

The National Water Census synthesizes and reports information at the regional and national scales, with an emphasis on 

compiling and reporting the information in a way that is useful to states and others responsible for water management and 

natural-resource issues. The USGS works with Federal and non-Federal agencies, universities, and other organizations to ensure 

that the information can be aggregated with other types of water-availability and socioeconomic information, such as data on 

food and energy production. To maximize the utility of the information, the USGS coordinates the design and development of 

the effort through the Federal Advisory Committee on Water Information.

A National Water Census is a complex undertaking, particularly because there are major gaps in the information needed to 

conduct such an assessment. To maximize progress, the USGS engaged stakeholders in a discussion of priorities and leveraged 

existing studies and program activities to enhance efforts toward the development of a National Water Census. 

Photo by Tim Merrick, 

U.S. Geological Survey
2 Progress Toward Establishing a National Assessment of Water Availability and Use

1.0 Introduction

Water is a key ingredient for healthy communities, 

economies, and natural environments. The Nation faces an 

increasingly large set of water-resource challenges as water 

shortages and water-use conflicts become more commonplace. 

As competition for water grows—for irrigation of crops, for 

use by cities and communities, for use in energy production, 

and for the environment—the need for information and tools 

to aid water-resource managers also grows, yet no comprehensive assessment or census of information currently exists that 

summarizes the availability of the Nation’s freshwater, with 

respect to both quantity and quality, for human and environmental needs.

Subtitle F of the Omnibus Public Land Management Act 

of 2009 (Public Law (P.L.) 111-11), which was passed into law 

on March 30, 2009, helps address this need. Also known as the 

SECURE Water Act, it contains substantive mandates for both 

the U.S. Geological Survey (USGS) and the U.S. Bureau of 

Reclamation (USBR). 

Section 9508 of the SECURE Water Act calls for the 

establishment of a “national water availability and use assessment program” within the USGS to:

• provide a more accurate assessment of the status of the 

water resources of the United States;

• assist in the determination of the quantity of water that 

is available for beneficial uses;

• assist in the determination of the quality of the water 

resources of the United States;

• identify long-term trends in water availability;

• use each long-term trend to provide a more accurate 

assessment of the change in the availability of water in 

the United States; and

• develop the basis for an improved ability to forecast 

the availability of water for future economic, energyproduction, and environmental uses.

The national water availability and use assessment program called for by the SECURE Water Act also is referred to 

as a National Water Census (or simply the Water Census). It is 

one of six major science directions identified by the USGS in 

2007 in its Science Plan for the next decade (U.S. Geological 

Survey, 2007). 

The Water Census is part of an overarching Department 

of the Interior initiative known as WaterSMART (Sustain 

and Manage America’s Resources for Tomorrow). Through 

WaterSMART, the Department is working to achieve a sustainable water strategy to help meet the Nation’s water needs, 

and the Water Census will help inform that strategy (U.S. 

Department of the Interior, 2012). 

Included in the SECURE Water Act is a requirement 

to report to Congress on progress made in implementing 

the national water availability and use assessment program 

(see Box A). This report fulfills that requirement as of 

December 31, 2012.

Strategically, the planning of the Water Census 

is encouraged to look towards developing an 

on-going, effective tool on a par with the social 

and economic censuses that supports national 

decision making.

National Research Council (2009)—Toward a 

Sustainable and Secure Water Future 

Photo by Alan Cressler, 

U.S. Geological Survey
2.0 National Water Census 3

Box A. Report Requested in SECURE Water Act (P.L. 111-11)

Not later than December 31, 2012, and every 5 years thereafter, the Secretary shall submit to the appropriate committees of 

Congress a report that provides a detailed assessment of—

(1) the current availability of water resources in the United States, including—

(A) historic trends and annual updates of river basin inflows and outflows;

 (B) surface water storage;

 (C) groundwater reserves; and

 (D) estimates of undeveloped potential resources (including saline and brackish water and wastewater);

(2) significant trends affecting water availability, including each documented or projected impact to the availability 

 of water as a result of global climate change;

(3) the withdrawal and use of surface water and groundwater by various sectors, including—

 (A) the agricultural sector;

 (B) municipalities;

 (C) the industrial sector;

 (D) thermoelectric power generators; and

 (E) hydroelectric power generators;

(4) significant trends relating to each water use sector, including significant changes in water use due to the 

 development of new energy supplies;

(5) significant water use conflicts or shortages that have occurred or are occurring; and

(6) each factor that has caused, or is causing, a conflict or shortage described in paragraph (5).

2.0 National Water Census

National water availability and use have not been comprehensively assessed in more than 30 years (U.S. General 

Accounting Office, 2003). A rudimentary national assessment 

published by the U.S. Water Resources Council in 1968 was 

followed by a more comprehensive Second National Water 

Assessment in 1978 (U.S. Water Resources Council, 1968, 

1978). Efforts were made to update components of the Second 

National Water Assessment to reflect conditions for the year 

1995 as part of the National Assessment of the Potential 

Consequences of Climate Variability and Change (Frederick and Schwarz, 1999). Recently, the National Science and 

Technology Council, Committee on Environment and Natural 

Resources Sustainability, through the Subcommittee on Water 

Availability and Quality (SWAQ), has issued several reports 

calling attention to the need for an up-to-date, comprehensive 

assessment of the Nation’s water availability (National Science and Technology Council, 2004, 2007). 

National water availability and use has not been 

comprehensively assessed in more than 30 years.

U.S. General Accounting Office (2003) 

Initial concepts for a Water Census were developed 

in 2002 when, as part of the report on the Fiscal Year 2002 

Appropriations for Interior and Related Agencies, the House 

Committee on Appropriations directed the 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.” To 

prepare that report, the USGS solicited input from many individuals and organizations involved in issues of water availability and use (U.S. Geological Survey, 2002). We asked what 

types of decisions and policy issues would benefit from the 

availability of 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 collaborative opportunities could most 

effectively be expanded. 

Several clear messages emerged from the responses. 

Many individuals emphasized the potential for improved 

methodologies and standards for consistency of nationwide 

data, the importance of ecological flows as a component of 

water use and availability, and the connections between water 

quantity and water quality. National organizations noted the 

need for consistent indicators of water availability across the 

Nation. Individuals representing state and local governments 

emphasized that many states have done extensive planning 

to quantify water availability now and in the future, and that 

the availability of water is inherently a local issue in most 

respects. The design of the Water Census builds upon these 

comments and recommendations. 

At the request of Congress, a pilot assessment was initiated in 2005 to quantify the source, movement, and dynamics of water resources in the U.S. portion of the Great Lakes 

Basin. New methods of hydrologic analysis and improved 
4 Progress Toward Establishing a National Assessment of Water Availability and Use

strategies for delivering water-related information were developed and tested in the process of assessing the availability of 

water in the region (Reeves, 2011). A second small pilot study 

focused on groundwater depletion in Arizona’s Southwest 

Alluvial Basins (Tillman and others, 2011). 

In a broad sense, water availability is viewed in terms 

of both human and environmental/ecological uses. The Water 

Census will synthesize and report information at the regional 

and national scales, with an emphasis on compiling and reporting this information in a way that is useful to states and others 

responsible for water management and natural-resource issues. 

The focus is on the scientific aspects of water availability, and 

the program reports on the physical, chemical, and biological characteristics that are important as indicators of water 

availability. The USGS works with Federal and non-Federal 

agencies, universities, and other organizations to ensure that 

the information can be aggregated with other types of wateravailability and socioeconomic information. To maximize the 

utility of the information, the USGS coordinates the design 

and development of the effort through the Federal Advisory 

Committee on Water Information (ACWI). 

A national assessment of water availability and use is 

a complex undertaking. At the time of the previous national 

assessments, water availability was viewed in comparatively 

simple terms. These early assessments focused largely on 

basic statistics about the quantities of water available for various human uses. Since then, competition for water resources 

has increased greatly and considerably more importance is 

attached to the availability of water for environmental and 

ecosystem needs, in addition to human use. Likewise, concerns have grown about groundwater depletion, streamflow 

alteration, climate change and variability, and water-quality 

impairment. Moreover, awareness of the connectivity of 

surface water and groundwater and the linkages between 

water availability and use of other natural resources has 

greatly increased. 

The Water Census program provides broad coverage 

across jurisdictional boundaries and in a consistent manner 

from year to year. The information it provides is designed to 

be useful to policymakers addressing a wide range of naturalresource issues. The limitations of the data and information 

also must be recognized, however. Although the data are useful for national water assessments and general statewide and 

regional overviews, they cannot be used to address specific, 

localized issues. 

As the primary Federal agency responsible for scientific evaluation of the natural resources of the United States, 

including its water and biological resources, the USGS has a 

key role in the national assessment of water availability and 

use. The agency employs a diverse cadre of scientists and 

technicians who evaluate the status and trends of freshwater 

quality and quantity for human and environmental needs at 

the local, state, regional, and national levels. The USGS has 

an existing infrastructure that allows it to conduct a regular 

inventory of natural resources and water use, including water 

quantity, water quality, and environmental water needs, in 

partnership with local, state, and regional water and environmental agencies. The USGS also has the biological capabilities 

needed to relate the presence of individual species, groups of 

species, and ecosystem function to the quantity, quality, and 

timing of water movement, as well as to the environmental 

habitat requirements of those organisms.

2.1 Water Budgets as a Unifying Theme

Much of the information that makes up a national assessment of water availability and use is essentially the components of water budgets for watersheds and aquifers. Water 

budgets account for the inputs to, outputs from, and changes 

in the amount of water in the various components of the water 

cycle. They are the hydrologic equivalent of the deposits to, 

withdrawals from, and changes in the balance in a checking 

account and provide the hydrologic foundation for analysis 

of water availability. Basic components of water budgets are 

precipitation, evapotranspiration, surface-water and groundwater flow into and out of the watershed, change in surface-water 

and groundwater storage, change in snow and ice storage, and 

human withdrawals and interbasin transfers (fig. 1). As with a 

monetary budget or checking account, knowing where, when, 

and how much water (or money) is “flowing” into or out of a 

water budget (or checking account) can illuminate how much is 

left for other uses (water availability) and reveal where stresses 

to the budget (the unpaid bills or water shortages) exist or 

are developing.

Water budgets account for the inputs to, outputs 

from, and changes in the amount of water in the 

various components of the water cycle. They 

are the hydrologic equivalent of the deposits to, 

withdrawals from, and changes in the balance in 

a checking account and provide the hydrologic 

foundation for analysis of water availability.

Unfortunately, information about most water-budget 

components is not available in a consistent form across the 

Nation. Therefore, a major undertaking of the Water Census is 

to provide estimates of selected water-budget components at 

consistent spatial and temporal scales. The Water Census will 

provide information about the following water-budget components through a series of topical area studies, which address 

surface water, groundwater, evapotranspiration, and water use. 

These topical area studies will provide quantitative information 

about the amount of water that resides in, or is moving through, 

each of these water-budget components. This information will 

be developed through direct field measurements obtained from 

data-collection networks and through the use of models that 

extend measured data into spatial areas and temporal periods 

for which measurements are not available. An additional topical area study will advance the science of ecological water, 

which quantitatively examines the relations between water 
2.0 National Water Census 5

Precipitation

Surface-water inflow,

imported water

(pipelines, canals)

Groundwater inflow

Surface-water outflow,

exported water

(pipelines, canals)

Groundwater outflow

Aquifer

Evapotranspiration

Bedrock

Water table

Unsaturated zone

Figure 1. Components of a simple water budget for part of a watershed. (From Healy and others, 2007)

availability and healthy ecosystems. In addition to providing 

a basis for national indicators of water flow and storage for 

the Water Census, these studies will support analyses of water 

availability by local and regional agencies and will contribute 

to research quantifying the national and global water cycle. 

Some water-budget components, such as evapotranspiration, 

have proven difficult to estimate accurately with existing 

measurement techniques. Therefore, the program supports 

development of improved methods for quantifying this and 

other selected water-budget components. In the future, if sufficient resources are available, the Water Census may expand 

the study of topical areas beyond the five indicated above.

The size of the watershed area for which a water budget 

is calculated determines, in part, the water-resource questions 

that can be addressed. Calculating a water budget for a watershed area that is too large can mask water-availability problems that become apparent at a smaller scale. In contrast, calculating a water budget for a small watershed may not provide 

the regional or national context that the user desires. A longterm objective of the Water Census is to provide measured or 

estimated information for all water-budget components at the 

12-digit hydrologic unit code (HUC-12) scale (see Box B)—

that is, for drainage basins (watersheds) across the Nation with 

an average size of 37 square miles. This information can then 

be aggregated for larger watersheds. Although the HUC-12 

scale is established as a long-term goal for the Water Census, 

many types of data currently (2012) can be determined only at 

coarser scales. This point is discussed farther on in this report.
6 Progress Toward Establishing a National Assessment of Water Availability and Use

Box B. Hydrologic Units

4-Digit HUC 6-Digit HUC 8-Digit HUC 10-Digit HUC

2-Digit HUC

01

02

03

04

05

06

07

08

09

10A

10B

11

12

13

14 

15

16

17

18

19

20 21

8,098 Units

Mean area 34 square miles (mi2)

Mean area 164,300 mi2

The United States is divided and subdivided into successively smaller 

watersheds. (A watershed is an area of land from which all of the water 

drains to the same place.) These watersheds are represented as hydrologic 

units, which are classified into six levels. Each hydrologic unit is identified 

by a unique hydrologic unit code (HUC) consisting of 2 to 12 digits based on 

the six levels of classification—the smaller the watershed, the more digits 

in the code to capture the “nesting” within larger watersheds. This coding 

system provides an orderly way to classify watersheds for the purpose of 

water-availability analysis.

50° 120° 100° 80°

40°

30°

Density of hydrologic unit codes (HUCs) at different levels illustrated by using the 2-digit HUC Region 03 

(South Atlantic-Gulf). 

Mean area 8,655 mi Mean area 15,387 mi2 2

17 Units 31 Units 199 Units 1,549 Units

Mean area 182 mi Mean area 1,392 mi2 2

12-Digit HUC
2.0 National Water Census 7

Groundwater presents a particular challenge with respect 

to developing a complete water budget for a watershed. Aquifer systems are complex, three-dimensional geologic features. 

They can cover large areas, commonly do not conform to 

surface-water divides, and may obtain most of their recharge 

from locations that are far from those where the groundwater is pumped from a well or flows to a surface-water body. 

Because of these and other complexities, groundwater systems 

are incorporated into the Water Census in two ways. A major 

element of the Water Census focuses on regional analyses of 

groundwater availability in 30 to 40 principal aquifers that collectively account for more than 90 percent of the Nation’s total 

groundwater withdrawals. In addition, to the extent possible, 

estimates of groundwater recharge, storage, and discharge at 

the watershed scale will be made by using a combination of 

information from the large-scale studies, data from observation-well networks, analysis of streamflow records, and other 

available information. 

The temporal scale of a water budget, the time period 

for which the water budget is calculated, is also of primary 

importance. The long-term objective of the Water Census 

is to provide information about water-budget components 

on a monthly basis in order to capture seasonal variations. 

Data for some components, such as water use, currently are 

available largely on an annual or less frequent basis. The 

USGS is working with states and other agencies to increase 

the frequency of data collection and to develop methods for 

disaggregating historical annual data to monthly estimates. 

In addition to monthly data for water-budget analysis, data 

at other time steps, such as continuous or daily streamflow 

records for ecological flow analysis, will be included in other 

aspects of the Water Census.

2.2 Characterizing Uncertainty

All water-resource decisions are made in the face of 

uncertainty. Uncertainty is an inherent factor in hydrologic 

data collection, estimation techniques, and simulation (modeling). Errors associated with measurement techniques arise 

from the inability to accurately measure specific aspects of 

the hydrologic system, such as streamflow, the water level 

in a well, or soil properties that control evapotranspiration 

and runoff. Uncertainty arises from the inability of our datacollection networks to fully characterize the natural spatial 

and temporal variability associated with hydrology, geology, 

climate, and land use. Uncertainty also is present in hydrologic models because it is impossible to reproduce a natural 

hydrologic system in a model with complete accuracy.

To the extent possible, the USGS will strive to quantify 

or estimate the uncertainty associated with Water Census 

information products. The USGS also will address uncertainty in the highest priority water data and information by 

improving spatial and temporal coverage for key hydrologic 

variables, improving estimation techniques through advanced 

incorporation of key data layers into statistical and physical 

models, and providing quantitative (or qualitative, where 

quantitative estimates are unavailable) guidance about data 

and model uncertainties to information-product users. 

2.3 Coordination and Collaboration

The USGS is developing plans for the Water Census in 

coordination and collaboration with Federal and non-Federal 

agencies, universities, and other organizations. Collaboration 

across agency boundaries ensures that information produced 

by the USGS can be aggregated with data on other types of 

physical, social, economic, and environmental factors that 

affect water availability. Data that are germane to issues of 

water availability include population statistics, land use, 

water costs and pricing, climate data, and instream-flow 

requirements for aquatic species and 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 (USDA), the 

Both the USGS and the U.S. Bureau of Reclamation (USBR) have substantive responsibilities under the Department of the 

Interior WaterSMART initiative. The primary USGS WaterSMART activity is the Water Census. WaterSMART activities in the 

USBR include the River Basin Supply and Demand Studies; the WaterSMART Grants Program, which concentrates on water 

conservation and sustainability grants; and the Title XVI Program, which concentrates on water recycling and reuse projects. 

WaterSMART activities require close coordination between the two agencies. There is a natural synergy between the USBR 

River Basin Supply and Demand Studies and the USGS Geographic Focus Area Studies, which are described farther on in this 

report. To achieve this coordination, the USGS and USBR have established routine biweekly communications to stay apprised 

of activities of shared interest. In addition, the USGS and USBR have been active participants in the planning and execution of 

the studies that have joint interest. This joint interest is directly apparent in the Colorado River Basin studies—the USGS Geographic Focus Area Study of the Colorado River Basin was designed to fulfill a data need identified during the execution of the 

USBR River Basin Supply and Demand Study of the Colorado River.

Box C. Coordination of the Water Census with the Bureau of Reclamation
8 Progress Toward Establishing a National Assessment of Water Availability and Use

Department of Energy, the National Oceanic and Atmospheric 

Administration (NOAA), the U.S. Army Corps of Engineers, 

the USBR, and the U.S. Environmental Protection Agency. 

The USGS receives guidance on the Water Census 

through the 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 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 (2012) has several subgroups examining 

water-quality monitoring, data methods and comparability, 

spatial water data, hydrology, streamgaging, cooperative water 

programs, and science issues. The USGS has worked with the 

Sustainable Water Resources Roundtable in ACWI to convene 

a multi-organization ad hoc committee of stakeholders in 

water availability to make recommendations on the priorities, 

design, and methods of presentation of the Water Census.

2.4 Progress Toward Goals

The SECURE Water Act authorized $20 million per 

year for the Water Census for FY 2009 through 2023. The 

first appropriation for this effort was $4 million in FY 2011, 

followed by an appropriation of $6 million in FY 2012, for a 

total of $10 million of the $80 million authorized during this 

period. This funding provided for the startup of three Geographic Focus Area Studies described in the next section, as 

well as initial efforts to build capability and address gaps in 

our ability to conduct a complete Water Census. The USGS 

also leveraged existing studies and activities from ongoing 

USGS programs to enhance efforts toward a Water Census. 

The USGS engaged stakeholders to establish priorities for 

work in surface water, groundwater, evapotranspiration, water 

use, and ecological water science—all key areas for the Water 

Census. The studies of surface water and groundwater are fundamental to addressing items (1) and (2) in the periodic reports 

requested by the SECURE Water Act (see Box A), whereas 

evapotranspiration estimates, water use, and ecological water 

science are fundamental to items (3) to (6). Below, we first 

discuss the Geographic Focus Area Studies and then describe 

the five topical areas.

Photo by Alan Cressler, 

U.S. Geological Survey
3.0 Geographic Focus Area Studies 9

3.0 Geographic Focus Area Studies

Competition for water resources has reached a level of 

national attention and concern in a number of areas throughout 

the United States. The competing interests may arise from 

multiple human needs (demands for potable water, irrigation, 

energy, industrial processes, etc.), from competition between 

human and aquatic ecosystem needs, or both. These types of 

competition are noted in the SECURE Water Act as areas of 

“significant water use conflicts or shortages that have occurred 

or are occurring” (see Box A). The Water Census includes 

studies focused on these areas. These Geographic Focus Area 

Studies serve several purposes. They (1) contribute to ongoing assessments of water availability in large watersheds with 

potential water-use conflicts, (2) provide opportunities to test 

and improve approaches to water-availability assessment, and 

(3) inform and “ground truth” the Water Census with local 

information. Watershed stakeholders in each Geographic 

Focus Area are seeking a comprehensive technical assessment of water availability using the best available tools. The 

Apalachicola-Chattahoochee-Flint, Colorado, and Delaware 

River Basins were selected for the initial Geographic Focus 

Area Studies. 

3.1 Apalachicola-Chattahoochee-Flint River

Basin

The Apalachicola-Chattahoochee-Flint (ACF) River 

Basin (fig. 2) covers 19,800 square miles in Georgia, southeastern Alabama, and northwestern Florida. The basin includes 

the drainages of the Chattahoochee River and the Flint River, 

which join to form the Apalachicola River. The Apalachicola 

River flows into the Gulf of Mexico at Apalachicola Bay. 

Conflict over water resources in the ACF River Basin 

(fig. 2) among Alabama, Florida, and Georgia has resulted 

from increases in water use for public supply, industry, power 

generation, and agriculture as the region has grown and 

developed over the past 50 years. Conflicts over water are not 

limited to interstate issues; during drought conditions, competition among all water users can become pronounced.

A primary example of this conflict is the legal action 

regarding the numerous uses of Lake Lanier near Atlanta, 

Georgia. These uses include water supply, power generation, 

maintenance of water quality, supply for downstream reservoirs, and maintenance of minimum flows to support aquatic 

species. The debate over water availability has focused on the 

management of water in reservoirs that are operated by the 

U.S. Army Corps of Engineers. These reservoirs typically have 

sufficient storage capacity for human uses and to maintain 

streamflows. Information needed for reservoir management to 

maintain flows in the ACF mainstem rivers is largely available. However, information on the many water-availability 

influences that are distributed across the basin—specifically, 

water withdrawals and wastewater returns, groundwater 

pumping for irrigation, interbasin transfers, storage in unmanaged reservoirs, and effects of increases in impervious surface 

and climate variability—have received less detailed study. 

These less examined factors are the primary target of the ACF 

Geographic Focus Area Study and will provide much needed 

data to the various Federal, state, and local groups involved in 

interstate water-supply negotiations and the overall management of the ACF River Basin.

“Our ability to understand and respond to 

problems and issues in every Alabama watershed 

including those with interstate implications 

such as the ACF Basin depends on accurate 

information. A fundamental tool such as the 

USGS Water Census that provides us with a 

uniform baseline of hydrologic information of both 

current water conditions and historical trends is 

invaluable in developing a technical consensus 

among government agencies, non-government 

organizations (NGOs), and stakeholders. Information 

from the Water Census can serve as a foundation 

for resolving more contentious aspects of how 

best to plan and prepare for the future of these 

watersheds.” 

J. Brian Atkins, Director, Alabama Office of Water 

Resources

The Geographic Focus Area Study of the ACF River 

Basin has three major components that build on ongoing 

USGS data collection and modeling capabilities: (1) estimating water use, (2) simulating surface-water and groundwater flow, and (3) establishing ecological flow relations. The 

water-use component is developing a site-specific database 

of water use for the ACF River Basin, developing improved 

methods for estimating agricultural withdrawals, and compiling available water-use projections. Calculations of net water 

use will be improved by obtaining information on interbasin 

transfers, determining irrigation and septic-tank return flows, 

and estimating consumptive use by thermoelectric power 

plants. The hydrologic simulation component will consist 

of a surface-water model of the entire ACF River Basin and 

a groundwater model of the lower ACF River Basin. These 

models will be linked where agricultural pumpage of groundwater is greatest to improve the simulation of groundwater/

surface-water interactions. The study included coordinated 

monitoring of streamflow (discharge measurement locations 

shown in figure 3), groundwater levels, and water-quality measurements of surface water during drought conditions in July 

2011 to support the hydrologic simulation component. As part 

of the ecological water science component (see section 4.5), 

ecological models will be used to predict changes in fish and 

mussel species occupancy due to variations in flow conditions 

associated with climate change, land-use change, and changes 

in water withdrawals or discharges. Together, these databases 

and models can be used to inform and improve decision making regarding the effects of future growth and water use on the 

availability of water for diverse uses.
10 Progress Toward Establishing a National Assessment of Water Availability and Use

G U L F O F M E X I C O

GEORGIA

ALABAMA

FLORIDA

SOUTH

CAROLINA

Chattahoochee River

Chipola River

Apalachicola River

New River

Flint River

Lake Lanier

West Point Lake

Walter F. George

Reservoir

Lake

Seminole

Lake Harding

Athens

Atlanta

Columbus

Auburn

Tallahassee

86° 85° 84° 83°

34°

33°

32°

31°

30°

Base modified from U.S. Geological Survey

1:100,000-scale digital data

FL

AL GA

TN NC

MS

KY VA

SC

IL MO WV

LA

AR

IN

0 25 50 MILES

0 25 50 KILOMETERS

Figure 2. Location of Apalachicola-Chattahoochee-Flint (ACF) River Basin.
3.0 Geographic Focus Area Studies 11

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19.19

LEON

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EARLY

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TIFT

IRWIN

CALHOUN

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SUMTER

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MITCHELL

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WILCOX

CRISP

MILLER COOK

TERRELL TURNER

CALHOUN

DOUGHERTY

BEN HILL

GULF

SEMINOLE

COFFEE

9110

9160 8980 5.26

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8040

8460 8110

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7990

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2010

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1.42 19

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220

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26.7

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8.02

0.594

–0.37

0.316

0.038

0.585

0.442 0.051

0.084

14.77

18.79

19.19

EXPLANATION

Discharge location and amount, in 

 cubic feet per second, July 2011

 

 

Stream reach

Measurement site—No gage

Spring

USGS streamgaging station

Gaining 

Losing 

Dry

03120002 Subbasin hydrologic unit code

100

2,630

03130008

03130011

03120002

03110203

03110204

03130006

03130007

03130009

03130010

03130012

03130004

03110202

03130005

GA

FL

AL

FL

7.73

03110103

03120003

03120001

03130013

03130003

GULF OF MEXICO

River

Flint River

Lake

Seminole

Lake 

Blackshear

Walter F 

George

Reservoir

Chattahoochee

Apalachicola River

Ochlockonee River

Aucilla River

85° 84° 83°

32°

31°

30°

0 10 20 40 MILES

Base modifed from U.S. Geological Survey 

1:100,000-scale digital data

0 20

30

10 30 40 KILOMETERS

Figure 3. Location of discharge measurements made in the lower Apalachicola–Chattahoochee–Flint River Basin and western and 

central parts of the Aucilla–Suwanee–Ochlockonee River Basin, Georgia and Florida, showing gaining, losing, and dry stream reaches 

during July 2011. (Modified from Gordon and others, 2012)
12 Progress Toward Establishing a National Assessment of Water Availability and Use

3.2 Colorado River Basin

The Colorado River Basin (fig. 4) covers about 

246,000 square miles, including parts of Arizona, California, 

Colorado, Nevada, New Mexico, Utah, and Wyoming, before 

the river flows into Mexico. The river supplies water to more 

than 30 million people, irrigates nearly 4 million acres of 

cropland in the U.S. and Mexico, and supplies hydropower 

plants that generate more than 10 billion kilowatt-hours annually. The river provides both recreational opportunities and 

an array of environmental benefits, supports a wide diversity 

of fish and wildlife and their habitats, and preserves flow 

and water-dependent ecological systems. Increasing population, decreasing streamflows, and the uncertain effects of a 

changing climate indicate the need for an improved understanding of water use and water availability in the Colorado 

River Basin.

The USGS coordinates the Colorado River Basin Focus 

Area Study with the USBR WaterSMART Basin Study Program. The purpose of the USBR study is to define the extent 

of water supply and demand imbalances in the Colorado 

River Basin through 2060 (fig. 5). The USBR study also will 

develop and analyze strategies to resolve those imbalances 

under a range of conditions that could occur during the next 

50 years. 

The USGS study complements the USBR study by 

focusing on the components of the water budget that are the 

least well understood. Through stakeholder consultation, the 

USGS has identified the following major components of the 

basin water budget for investigation: (1) estimation of current 

water use–particularly consumptive water use–and historical 

trends in water use; (2) regional and field-scale assessments 

of evapotranspiration and the dynamic variation in snowpack 

water content; and (3) estimation of groundwater discharge to 

streams and rivers. More accurate quantification of these components of the basin water budget will provide water managers with increased knowledge of water sources and movement 

and enhance their ability to make informed resource-management decisions to maximize water availability for human and 

ecological needs (see section 4.5). The water-use component 

of the study will expand the collection of water-use data to 

include information on some uses not currently estimated (for 

example, self-supplied commercial use). Existing water-use 

data also will be re-aggregated from a county distribution to 

an 8-digit hydrologic unit code (HUC-8) distribution to facilitate water-management applications. 

Evapotranspiration and variations in the water content 

of the mountain snowpack (including volume and timing of 

snow-water releases) are important components of the water 

budget in the Colorado River Basin. These budget components 

are difficult to measure, especially over such a large area. 

This study will couple several recently developed remotesensing techniques with both new and existing ground-based 

measurements to extrapolate evapotranspiration across the 

entire Colorado River Basin (see section 4.3). Recently developed snow-water models also will be applied and calibrated. 

Evapotranspiration data and water content of the mountain 

snowpack will aid in identifying water supply and consumptive use in irrigated agricultural areas—one of the largest 

water-use categories in the Colorado River Basin.

The groundwater contribution to streams in the Colorado 

River Basin is one of the least well understood components of 

the regional water budget. Preliminary studies by the USGS 

indicate that between 20 and 60 percent of the surface-water 

flow in the upper basin is derived from groundwater discharge. 

Future development of groundwater in the basin could have 

significant effects on surface-water flows. Identification of 

stream reaches that receive large amounts of groundwater 

discharge will be a major effort in the upper Colorado River 

Basin during the study. Information about the geologic controls on groundwater flow will be refined and stream reaches 

likely to receive significant groundwater discharge will be 

identified. Natural and anthropogenic chemical tracers will 

be measured to confirm that groundwater discharge is occurring and to estimate its relative contribution. This effort will 

culminate in a map indicating the location and amount of the 

groundwater contribution to the surface-water flow system.

Preliminary USGS studies estimate that 20 to 60 

percent of surface-water flow in the upper Colorado 

River Basin is derived from groundwater discharge.

3.3 Delaware River Basin

The Delaware River Basin (fig. 6) covers 13,500 square 

miles in parts of four states—New York, New Jersey, Pennsylvania, and Delaware. The population within the basin is 

approximately 7.3 million. 

The basin has the largest interbasin withdrawal of water 

east of the Mississippi River and provides water to more than 

15 million people. Two Supreme Court decrees and coordination by an interstate river basin commission are just part of the 

history of allocating water resources in the basin. Concerns 

about the effects of new natural-gas development and the 

freshwater requirements for a recently discovered endangered 

mussel species have added new complexities to water management in the upper part of the basin. 

With input from more than 60 stakeholder groups, including Federal, state, and local governments, NGOs, academia, 

and others, the following issues were identified as priorities in 

the Delaware River Basin:

• acquisition, management, and integration of improved 

water-use and water-supply data;
3.0 Geographic Focus Area Studies 13

Base modified from U.S. Geological Survey

1:100,000-scale digital data

115° 110° 105°

40°

35°

Lake

Powell

Great

Salt Lake

Lake

Mead

Utah Lake

Colorado

River

Little Colorado R iver

Virgin River

San Pedro River Salt River

Gila

River

Green River

Yampa River

Green River

San Juan River

White River

Provo

Denver

Tucson

Phoenix

El Paso

Las Vegas

Boise

Albuquerque

Fort Collins

Salt Lake City

UTAH

ARIZONA

NEVADA

WYOMING

IDAHO

NEW MEXICO

COLORADO

CALIFORNIA

TEXAS

CA

MT

AZ

ID

NV

NM

CO

OR

UT

WY

WA

TX

ND

SD

NE

0 100 200 KILOMETERS

0 100 200 MILES

Figure 4. Location of Colorado River Basin.
14 Progress Toward Establishing a National Assessment of Water Availability and Use 1923 1930 1940 1950 1960 1970 1980

199020002008

25

20

15

10

5

0

Millions of acre-feet

Calendar year

Water supply

Water use

Historical 10-year running average,

Colorado River Basin

EXPLANATION

Figure 5. Water supply and water use in the Colorado River Basin, 1923–2008. (From U.S. 

Bureau of Reclamation, 2011)

• development of ecological water science that includes 

enhancement of the existing Decision Support System 

for parts of the Delaware River, definition of relations 

between streamflow processes and aquatic-assemblage 

responses in tributaries, and development of a streamflow-estimation tool for ungaged sites (Archfield and 

others, 2010); and

• development of a hydrologic watershed model to 

evaluate the effects of water stressors, such as growth 

of population centers, land-use change, and climate 

variability and change, on water resources in the basin.

Products of this study will include (1) a database of 

water-withdrawal, water-use, and return-flow information for 

watersheds that will be accessible to water-resource managers 

in the basin; (2) a Web-based tool developed by using index 

streamgages to estimate baseline daily streamflow at ungaged 

streams in the basin from 1960 to 2010; (3) an evaluation of 

water needs for aquatic ecological systems within the basin, 

including an updated decision support system for sections 

of the river, and development of flow/aquatic-assemblage 

response relations for tributaries; and (4) a hydrologic model 

of the nontidal portions of the watershed tributaries with an 

easy-to-use interface that will allow water-resource managers 

to evaluate potential effects of future population, land-use, or 

water-demand scenarios.

The Delaware River Basin Commission (DRBC) has 

developed a “Strategy for Sustainable Water Resources–2060.” 

The information, databases, and products developed as part 

of this study will contribute substantially to the information 

needs of the DRBC strategy. Additional information on the 

characteristics of the basin can be found at the DRBC Web site 

at http://www.state.nj.us/drbc/.

“The Water Census is a great example of leveraging 

resources for both the benefit of regional water 

management and the national water use and 

availability initiative. The Delaware River Basin 

Commission is getting invaluable assistance in the 

form of customized work products that advance 

our long-term Strategy for Sustainable Water 

Resources–2060, and the USGS is getting very 

specific integrated water resource management 

feedback from a data rich basin that will inform and 

ground truth the Water Census–to ensure that it is a 

value added to water managers across the nation.” 

Robert Tudor, Deputy Executive Director, Delaware 

River Basin Commission
3.0 Geographic Focus Area Studies 15

NEW YORK

PENNSYLVANIA

NEW JERSEY

MARYLAND

DELAWARE

Allentown

Trenton

Dover

Baltimore

Philadelphia

Neversink River

Lehigh River

Schuylkill River

Delaware

River

Musconetcong River

Maurice River

Pepacton

Reservoir

Cannonsville

Reservoir

Lake

Wallenpaupack

Lake Hopatcong

Delaware

Bay

ATLANTIC

OCEAN

Chesapeake Bay

0 25 50 MILES

0 25 50 KILOMETERS

76° 75° 74°

42°

41°

40°

39°

NY

PA

ME

VT

VA

NH

MA

CT

MD NJ

WV

DE

RI

Base modified from U.S. Geological Survey

1:100,000-scale digital data

Figure 6. Location of Delaware River Basin.
16 Progress Toward Establishing a National Assessment of Water Availability and Use

4.0 Topical Areas

Five topical areas key to the Water Census are discussed 

below. For each topical area, we explain the information needs 

and past and ongoing efforts to fill them. Then, we describe 

the information that the Water Census will add to this existing body of work. We also discuss the use of the Geographic 

Focus Area Studies to provide opportunities to test and 

improve approaches to water-availability assessment.

4.1 Surface Water

The SECURE Water Act calls for annual updates of 

river-basin flows and analysis of historical trends. The USGS 

National Streamflow Information Program (NSIP) provides 

a strong and essential foundation for this type of streamflow information. The USGS operates approximately 7,800 

streamgages to provide information on floods, droughts, and 

current water availability across the U.S. This network of 

streamgages provides real-time information and historical context for water-resources planning and assessment. For studies 

of trends in streamflow and water availability, long historical 

records are critical.

Because the streamgage network cannot provide direct 

observations of streamflow at every location of interest, information about streamflow at ungaged locations is needed. To 

meet this need, the USGS has conducted statistical analyses of 

streamgage records and has developed hydrologic models for 

specific basins. For example, WaterWatch (http://waterwatch.

usgs.gov) is a national application that provides estimates 

of runoff (in flow per unit area) for HUC-8 watersheds in 

the continental U.S. These estimates are calculated by using 

runoff measurements made at nearby gages and are available 

at monthly and annual time steps (see figure 7). Estimates of 

streamflow statistics describing peak flows or low flows are 

often needed at specific ungaged locations. The USGS StreamStats (http://streamstats.usgs.gov) Web application has been 

implemented for many states to provide estimates of these 

statistics. These estimates are derived by using mathematical 

regression techniques that have been developed for use with 

streamflow statistics. The “point-and-click” StreamStats interface allows users to choose a location of interest and calculate 

streamflow statistics “on the fly.” 

The Water Census aims to improve upon the information 

that is currently available for ungaged locations by providing 

estimates of daily streamflow for subwatersheds nationally 

through a “point-and-click” Web application. Estimates will 

EXPLANATION

Runoff, in millimeters

0–49

50–99

100–199

200–299

300–399

400–749

750–999

Greater than 999

Figure 7. Screen capture of estimated annual runoff for the period October 1, 2010, through September 30, 2011, for each of 

the 8-digit hydrologic unit code cataloging units in the United States. (From http://waterwatch.usgs.gov/; no data shown for 

Alaska, Hawaii, or Puerto Rico)
4.0 Topical Areas 17

be provided for the most recent 30-year historical period. 

Although uncertainty will be greater for estimated time series 

than for time series measured at a streamgage, these estimates can provide information needed by water managers 

to make decisions and by ecologists to evaluate ecological 

water requirements.

Many existing modeling techniques could be employed 

to develop these streamflow estimates. To make the most 

efficient use of limited resources, a national plan is being 

developed by comparing the accuracy, ease of implementation, 

and value-added capabilities of several different streamflowestimation models. Because model performance varies with 

location, different models may perform better or worse in different parts of the country. 

A second major activity is to evaluate trends in streamflow over time. Changes in surface-water hydrology can 

result from a wide variety of causes, including changes in 

water-management strategies, land-use changes, and climate 

variability or change. Changes in hydrology can impact water 

availability for public supply, industry, power generation, or 

agricultural use, and can affect water quality and aquatic ecosystems. Characterizing trends in streamflow and developing 

a greater understanding of the causes of trends are therefore 

critical to understanding future water availability. 

Climate variability and change is the least well understood driver of streamflow change. The USGS has conducted 

a number of studies to characterize trends in streamflow at 

gages that are relatively free of direct human influences. Most 

studies are based on gages included in the HydroClimatic Data 

Network (HCDN) (Slack and Landwehr, 1992). Gages in the 

HCDN were recently updated and the dataset now includes 

information from 743 streamgages (Lins, 2012). Continued 

maintenance of a national network of such gages is necessary 

to allow scientists to detect and understand streamflow change.

Analyses of streamflow records have revealed temporal changes in some aspects of flow. For example, many 

regions that are snow-dominated in winter have shown a shift 

toward earlier spring runoff peaks associated with snowmelt. Studies analyzing annual flow or peak flows have been 

less conclusive.

Because streamflow is naturally highly variable, analyzing trends in streamflow records is difficult. Moreover, 

changes in many different characteristics of flow may be 

important to water managers or to local ecology. For example, 

changes in seasonality of flow or day-to-day variability in flow 

may be just as important as shifts in annual mean streamflow. 

Still other flow characteristics may be important for other, 

specific purposes or concerns. Future studies will need to 

consider these factors and their effects on water management 

and water availability.

4.2 Groundwater

A national assessment of water availability requires an 

assessment of the Nation’s groundwater reserves. The Water 

Census will leverage a long history of groundwater studies and 

accelerate ongoing regional studies to achieve this goal. These 

groundwater assessments provide consistent and integrated 

information that enables the resource to be viewed and understood on aquifer-wide scales that cross political boundaries. 

The USGS began a program of regional groundwater 

availability studies in 2004 (Dennehy, 2005) to provide the 

public and water managers with a better understanding of the 

status of and trends in the Nation’s groundwater availability. 

These studies cover a variety of hydrogeologic terrains and 

include aquifer systems that account for much of the Nation’s 

groundwater use. Additionally, the USGS has outlined an 

approach for developing an understanding of future groundwater availability aggregated from these regional-scale studies 

and has summarized current knowledge of groundwater availability at the national scale (Reilly and others, 2008). 

One of the first regional studies completed was that for 

California’s Central Valley (see Box D). As part of this assessment, the USGS developed a three-dimensional hydrologic 

modeling tool that can be used to simulate water-management 

scenarios, providing managers with an improved ability to 

plan water supplies that accounts for anticipated conversion 

of farmland to urban use as well as potential future effects 

of climate variability and change. Several additional studies 

have been completed or are underway across the United States 

(see figure 8). 

Current plans call for studies of 30 to 40 regional aquifer 

systems that, once completed, will collectively lead to a 

national assessment of groundwater availability. The Water 

Census funding in FY 2011 provided an opportunity to accelerate this program with assessment of the glacial aquifer system that extends across all or parts of 25 northern states from 

Maine to Washington and Alaska. The glacial deposits are the 

source of the largest withdrawals for public and domestic supply in the United States, and an estimated 22.5 million people 

rely on the glacial aquifer system for their drinking water. 

“Our present and future water management 

challenges must be based on sound science and the 

best data available. It is an old, but true, adage that 

you can’t manage what you don’t measure. Often, 

we lack sufficient data on existing water uses 

and supplies to make informed decisions. Better 

water resources management and decisionmaking 

requires more and better data, and especially more 

real-time data, as well as an indication of the level 

of confidence in the data.”

Tony Willardson, Executive Director, Western States 

Water Council
18 Progress Toward Establishing a National Assessment of Water Availability and Use

Box D. Groundwater Availability Study of the California Central Valley (From Faunt, 2009)

Figure D1. Central Valley agriculture along 

the California Aqueduct.

California’s continued population increase has heightened 

competition for water within the Central Valley. As water 

resources become more valuable, a number of issues have 

gained prominence, including how to conserve agricultural 

land; the conjunctive use of surface and groundwater supplies; 

changing land-surface elevation in response to groundwater 

pumping; aquifer storage and recovery; the effect of land-use 

changes on water supplies; and climate change. USGS scientists 

developed a regional three-dimensional hydrologic modeling 

tool to help resource agencies understand and address many 

issues affecting the joint use of surface- and groundwater 

supplies in the Central Valley.

Pacific Ocean

A

A'

Detail of model grid

Central

Valley California

Sacramento Valley

San Joaquin 

Basin

Tulare Basin

Delta and 

Eastside Streams

Land surface

Layer 10

Layer 9

Layer 8 Layer 7

Layer 3 Layer 2 Layer 1

Corcoran Clay 

(layers 4, 5)

Cross section 

Not in model

A A'

0 57 DISTANCE ALONG SECTION, IN MILES

ALTITUDE, IN FEET

-2,500

Sea 

level

1,000

Layer 6

Central Valley Hydrologic Model 

(CVHM)

The CVHM was built by using 

data and modeling techniques from 

the U.S. Geological Survey and 

information from other Federal, 

State, and local studies. The CVHM 

was constrained by simulated and 

historically observed groundwater 

levels, streamflows, and 

subsidence. The detail and 

breadth of this hydrologic 

modeling tool provides a better 

understanding of valley-wide 

hydrologic processes and a way 

to forecast system responses to 

future development and climate 

variability and change.

"Variable"

to Dry

"Variable"

to Dry

"Variable"

to Wet Dry Wet Dry Wet

Water year

Change in groundwater storage,

in millions of acre-feet

0

-20

-60

-40

-80

20

1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002

Entire Central Valley

By region

Sacramento Valley

Delta and Eastside Streams

San Joaquin Basin

Tulare Basin

EXPLANATION

Figure D2. Simulated cumulative annual 

change in aquifer-system storage from 

water year 1962 through 2003 for the 

Central Valley, California. During wet 

and dry periods, the aquifer storage 

responds as expected; however, the 

Central Valley Hydrologic Modeling 

tool enables definition of the spatial 

and temporal implications of changing 

climatic conditions and the resulting 

storage response. The cumulative change 

in storage reached a maximum loss of 

62.7 million acre-feet in the mid 1990s.
4.0 Topical Areas 19

120° 110° 100° 90° 80° 70° 60°

110° 100° 90° 80° 70°

30°

30°

0

0

500 MILES

500 KILOMETERS

EXPLANATION

Completed

FY09–FY12

FY10–FY11

(Suspended)

FY11–FY14

FY11–FY16

FY12–FY15

FY13–FY16

Columbia

Plateau

Great Basin 

Carbonate

Central

Valley Denver

Basin High

Plains

Glacial

Lake

Michigan

Basin

Southeast

Coastal Plain

Floridan

Mississippi

Embayment

Hawaiian

Volcanics Glacial

deposits

Columbia

Plateau

Great Basin 

Carbonate

Central

Valley Denver

Basin High

Plains

Glacial

Williston and Powder

River Basins Lake

Michigan

Basin

Northern Atlantic

Coastal Plain

Southeast

Coastal Plain

Floridan

Mississippi

Embayment

Hawaiian

Volcanics Glacial

deposits

Base modified from U.S. Geological Survey

1:2,000,000-scale digital data

Figure 8. U.S. Geological Survey Groundwater Resources Program regional-scale groundwater study areas. (Modified 

from http://water.usgs.gov/ogw/gwrp/activities/regional.html; explanation indicates the fiscal years during which the 

studies are plannned to occur)

4.3 Evapotranspiration

Evapotranspiration (ET) is the upward flux of water 

from the land surface to the atmosphere, a combination of 

evaporation from the soil and transpiration by plants. An 

essential component of water-budget determinations for water 

availability, ET is also a fundamental variable of water use, 

especially for irrigation, and has important implications for 

administration of water rights and river-basin compacts. Historically, reliable estimation of ET has required site-specific 

field measurements made by using specialized instruments. 

However, because these sites represent conditions only in their 

immediate vicinity, quantifying ET over broad areas such as 

irrigation districts, river basins, or states is a difficult task. In 

the past 15 years, substantial progress has been made in meeting this challenge by using satellite imagery to make estimates 

of ET across the landscape. State agencies and consultants 

have embraced this approach, and a variety of methods have 

come into common use, though all rely on the same underlying physical principles. The USGS also has adopted this 

practice, and is applying its satellite remote-sensing resources 

and expertise to quantify ET for the Water Census.

The Geographic Focus Area Study of the Colorado River 

Basin provides the context for testing ET remote-sensing 

methods for eventual application across the western United 

States and the country as a whole. In order to construct water 

budgets to determine water availability, ET is being estimated 

across the entire landscape by using 1-kilometer-resolution 

National Aeronautics and Space Administration (NASA) 

Moderate Resolution Imaging Spectroradiometer (MODIS) 

land-surface temperature imagery from the archive at the 

USGS Earth Resources Observation Science (EROS) Data 

Center. Although such images are collected daily, energybudget calculations are made on 8-day composites that greatly 

reduce problems of cloud cover. These results, in turn, are 

accumulated into monthly, seasonal, and annual summaries 

at the spatial scale of 8-digit HUCs. In FY 2012, this task is 

being accomplished for data covering the period from 2000 to 

2011. Results are being compared with site-specific data from 

stations in the Colorado River Basin to provide uncertainty 
20 Progress Toward Establishing a National Assessment of Water Availability and Use

estimates for the MODIS satellite approach. Initial results for 

estimated annual ET in the Colorado River Basin in 2010 are 

shown in figure 9.

Water-use reporting requires estimates of ET at the scale 

of agricultural fields. USGS Landsat thermal infrared imagery, with a resolution of 60 to 120 meters, is being used for 

this purpose in the Colorado River Basin. The Cropland Data 

Layer from the USDA National Agricultural Statistics Service is used as a reference to identify the relevant subset of 

the landscape for which estimates are required. In FY 2012, 

this task is being conducted for a single calendar year over all 

the croplands in the basin, with as much cloud-free imagery 

as possible. (Landsat image acquisitions occur only every 

16 days. Joint use of Landsat and MODIS images is being 

tested to fill temporal gaps.) Monthly, seasonal, and annual 

totals are being compiled for 8-digit HUC areas and measurements from ET stations are being used to verify results. The 

successful launch of Landsat 8 in February 2013 will benefit 

the Water Census by ensuring an uninterrupted flow of essential field-scale thermal infrared imagery. 

An established ET remote-sensing community with a 

history of estimating crop water use with Landsat imagery 

already exists in the western United States. Universities, 

consultants, state agencies, and the USBR all have contributed 

to the development and application of techniques of this kind. 

The Western States Water Council gave voice to the concern of 

this community for inclusion of a thermal infrared imager on 

Landsat 8. The USGS acknowledges the experience and expertise of this community, and at the same time recognizes the 

potential for duplication of effort and disputes over differing 

methods and results. In anticipation of both possibilities and 

of eventual contributions to the Water Census by non-USGS 

organizations, the USGS has entered into a partnership with 

Utah State University to develop specifications and guidelines 

for estimating crop ET in the West by using remote sensing. 

The vision is for a prescribed framework for inputs, techniques, and proven model performance, within which a state, 

Tribe, consultant, university, or Federal agency could employ 

the model of its choosing, and publish crop water-use figures 

that would be recognized and accepted by the broad community of western water stakeholders. In this way, important 

economies would be realized while simultaneously meeting 

Water Census standards for accuracy and precision. FY 2012 

marked the beginning of this 3-year effort, which will involve 

detailed technical evaluations and stakeholder interactions.

The quantification of water use for supplemental irrigation in the eastern United States is also being addressed with 

ET remote sensing. The Geographic Focus Area Studies of the 

Delaware and Apalachicola-Chattahoochee-Flint (ACF) River 

Basins provide a context for testing an approach in which 

satellite imagery is used. 

ET remote-sensing methods are also being tested in the 

Central Valley of California, where ongoing USGS research 

on water productivity is being leveraged and the need for 

improved quantification of fallowed-land extent is being 

addressed (Thenkabail and Wu, 2012). In the first case, both 

yields and water use are being mapped, field by field, to reveal 

variations in the amount of “crop per drop,” a valuable refinement to water-use reporting. In the second case, the objective is to better characterize the impacts of water shortages 

on irrigated agricultural land, a significant information gap 

identified by the California Department of Water Resources 

and other stakeholders participating in the National Integrated 

Drought Information System (NIDIS) California pilot study 

led by NOAA.

Although initial applications in the three Geographic 

Focus Area Studies are targeting monthly summaries of ET 

at the HUC-8 level, these efforts are designed so that they 

can ultimately be “scaled up” to daily summaries at the finer 

HUC-12 scale.

4.4 Water Use

The SECURE Water Act places considerable emphasis 

on assessment of the use of surface water and groundwater for 

understanding the demand side of water availability; however, 

information on the Nation’s water use is relatively limited. 

Better information is needed on withdrawal, conveyance, consumptive use, and return flow by sector of use as well as on 

the factors that influence these components of water use. Such 

information will allow water managers and planners to make 

more effective decisions for the future. Water-use data are 

vital to water-availability studies such as those that simulate 

watershed and groundwater processes. Regular assessments 

of water use provide trend information, which is critical to 

decision making for future water needs. As an indication of its 

importance, activities are underway to improve the quality and 

availability of water-use information in all three Geographic 

Focus Areas.

Every 5 years since 1950, the USGS has produced a 

report on the “Estimated Use of Water in the United States.” 

These reports are a substantial undertaking, requiring coordination and assemblage of information from multiple Federal 

sources, as well as from all 50 states. The 2010 report is 

planned to be released in calendar year 2014. The most comprehensive of these reports, for 1995, provided estimates of 

withdrawals, public-supply deliveries, wastewater returns, and 

consumptive use for 11 sectors of water use: public supply, 

domestic, commercial, irrigation, livestock, animal specialties, 

industrial, mining, thermoelectric power, hydroelectric power, 

and wastewater treatment. The scope of the report was reduced 

for 2000 and 2005, with the 2005 report covering public 

supply, domestic, irrigation, livestock, aquaculture (replacing animal specialties), industrial, mining, and thermoelectric 

power use. Public-supply deliveries were estimated only for 

domestic use, no estimates were prepared for commercial and 

hydroelectric water use or for wastewater returns, and, most 

critically, consumptive use was not estimated. In addition, in 

the 1985, 1990, and 1995 reports, water use was estimated 

for counties and for watersheds (at the HUC-8 level); in the 

2000 and 2005 reports, only county water use was estimated. 
4.0 Topical Areas 21

UTAH

ARIZONA

NEVADA

WYOMING

IDAHO

NEW MEXICO

COLORADO

CALIFORNIA

TEXAS

0 100 200 KILOMETERS

0 100 200 MILES

Estimated 2010 evapotranspiration 

in the Colorado River Basin, 

in millimeters

1,000

0

EXPLANATION

115° 110° 105°

40°

35°

Figure 9. Estimated total annual evapotranspiration in the Colorado River Basin for 2010 determined by using Moderate 

Resolution Imaging Spectroradiometer (MODIS) land-surface temperature imagery and the Simplified Surface Energy Balance 

(SSEB) method. (From Senay and others, 2011)
22 Progress Toward Establishing a National Assessment of Water Availability and Use

The omitted components reduce the usefulness of this periodic 

assessment of the Nation’s water use. As part of the Water 

Census, the USGS plans to return to the full assessment as 

represented by the 1995 report.

Efforts also are underway to improve estimation methods for the two largest sectors of the Nation’s water use: 

thermoelectric power and irrigation. Thermoelectric power 

represented 49 percent of U.S. withdrawals in 2005 (Kenny 

and others, 2009), although substantial amounts of the water 

withdrawn are returned to a surface-water body and are readily available for other uses. The geographic distribution of 

five different categories of water withdrawals are shown in 

figure 10. Thermoelectric withdrawals are predominant in the 

eastern and coastal states, whereas irrigation withdrawals are 

predominant in the arid western states. The USGS is developing improved estimation techniques for power plants utilizing 

data reported to the U.S. Energy Information Administration 

(EIA). The two agencies are working together to improve the 

quality and usefulness of the reported data. In the USGS study, 

power plants are divided into several classes on the basis of 

the level of data available for them, and estimation methods 

will incorporate information on plant characteristics, power 

generation, and fuel use to estimate a range of reasonable 

water demand. The results will help quality assure information on thermoelectric power water demands from various 

sources. The thermoelectric power study also will develop 

techniques for estimating consumptive use for power plants by 

using heat-budget data. A retrospective study of estimates for 

the period from 1975 to 1985 is examining factors that affect 

thermoelectric power water demand, such as cooling-system 

type, fuel type, and weather conditions, to better understand 

future changes in demand. An additional planned study will 

attempt to quantify consumptive use outside the power-plant 

property, specifically the evaporation caused by the increase in 

temperature of the water used for cooling after it is returned to 

a stream or reservoir.

Water withdrawals for irrigation made up 31 percent of 

withdrawals in 2005. The geographic distribution of irrigation 

withdrawals is shown in figure 11. Compared to thermoelectric 

power water use, the proportion of the water withdrawn for 

irrigation that is consumed through ET or incorporated into 

the crop is larger, leaving less available for immediate reuse. 

The USGS has initiated several studies to analyze and improve 

estimation methods for irrigation water use. An analysis of 

the data and methods used for the 2000 and 2005 national 

estimates of irrigation water use (Dickens and others, 2011) 

compared data sources for irrigated crop acreage and water 

use and the methods used. Recommendations were made for 

improving future USGS estimates of irrigation water use. 

USGS irrigated-acreage estimates were compared to acreage 

reported by the USDA for similar years to assess the differences in magnitude and trends. The study also calculated 

0 

5,000 

10,000 

15,000 

20,000 

25,000 

30,000 

35,000 

40,000 

45,000 

50,000 

Hawaii

Alaska

Oregon

Washington

California Nevada

Idaho

Arizona

Utah

Montana

Wyoming

New Mexico

Colorado

North Dakota

South Dakota

Nebraska

Texas

Kansas

Oklahoma

Minnesota

Iowa

Missouri

Louisiana

Arkansas

Wisconsin

Mississippi

Illinois

Alabama

Tennessee Indiana

Kentucky

Michigan

Georgia

Ohio

Florida

South Carolina

West Virginia

North Carolina

Virginia

Pennsylvania

MarylandD.C.

New YorkDelaware

New Jersey

Connecticut

Vermont Massachusetts

Rhode Island

New Hampshire

Maine

Puerto Rico

U.S. Virgin Islands

Total withdrawals, in million gallons per day

WEST EAST

Public supply

Other

Irrigation

Industrial

Thermoelectric power 

EXPLANATION

Water-use category 

States and other geographic jurisdictions

Figure 10. Graph showing 2005 water withdrawals in the United States by water-use category. (States and other geographic 

jurisdictions are arranged from west to east.) (From Barber, 2010)
4.0 Topical Areas 23

70° 180° 160° 140°

60°

160° 155°

20°

130° 50° 120° 110° 100° 90° 80° 70°

40°

30°

0 250 500 MILES

0 250 500 KILOMETERS

0 500 1,000 2,500 5,000 10,000 >10,000

Freshwater irrigation withdrawals,

in gallons per day per square mile, 2005

EXPLANATION

Base modified from U.S. Geological Survey

1:2,000,000-scale digital data

Figure 11. Freshwater irrigation withdrawals in the United States by county, 2005.

a state irrigation withdrawal estimate by using an indirect 

method involving irrigated acreage, consumptive water 

requirement by crop, and potential water losses while irrigating. Estimates made by using the indirect method were compared to the published 2005 estimates for selected states as a 

means of evaluating both the indirect method and a potential 

benchmark to quality assure future state irrigation estimates. 

Another effort is underway to develop improved irrigation 

estimates for the New England, Mid-Atlantic, and a few southern states. Deriving estimates for these regions is difficult as a 

result of a lack of observed irrigation water use, smaller crop 

sizes, and humid climate conditions that mask typical irrigation water-use practices and preempt estimation methods that 

are used in the West. 

A major goal with respect to water use is to refine the 

scale of water-use information from the county level, as given 

in the current USGS national reports, to the finer watershed 

scale. Efforts are underway to develop a national site-specific 

water-use database as part of the USGS National Water Information System (NWIS) that will contain withdrawal, conveyance, use, and discharge information. Withdrawal locations, 

conveyances, and water-system information are initially being 

entered for the public-supply sector. Thermoelectric power 

plant locations and withdrawals will be added to the database, 

followed by other sectors for which site-specific information can be developed. Detailed, long-term information on 

withdrawals, conveyances, consumptive use, and return flows 

will provide the critical demand component for studies of the 

interactions between human water use and the natural hydrologic system.

4.5 Ecological Water Science

Ecological water science is the study of the quantity, 

timing, and quality of water flow and storage required to 

sustain freshwater and estuarine ecosystems and the human 

well-being and livelihoods that depend on them. Water flow 

and storage include stream and river flows as well as variations in water levels in lakes, rivers, streams, springs, wetlands, and aquifers. Ecological water science has advanced 

greatly over the past two decades, driven largely by a need to 

better understand the relation between ecological water uses 

and the streamflows required to maintain those uses, prevent 
24 Progress Toward Establishing a National Assessment of Water Availability and Use

degradation of freshwater ecosystems, and improve the balance between human and ecological water needs. 

As part of the Water Census, the USGS will develop 

innovative tools and Web-available resources that provide 

stakeholders and ecological water science practitioners with 

the hydrologic and biological information necessary for comparing natural and altered hydrologic regimes and determining 

the effects of streamflow alteration and water withdrawals on 

aquatic ecosystems. This approach is being applied nationally 

as well as to large river basins as part of the Geographic Focus 

Area Studies. 

In support of ecological water science at the national 

scale, the Water Census is developing and comparing flowsimulation modeling tools for building a national foundation 

of baseline hydrographs that will ultimately provide hydrologic statistics for all ungaged streams in the U.S. A baseline 

hydrograph is a graph that reflects the natural fluctuations in 

the duration, magnitude, timing, frequency, and rate of change 

in streamflow. This information will be served directly to 

stakeholders by means of a map-based National Data Platform 

that will enable connections to other large data compilations, 

including those collected by other Federal, state, and Tribal 

organizations. Estimates of daily streamflow as well as a suite 

of ecologically relevant hydrologic measurements will be 

integrated with biological observations in the platform through 

a common spatial framework. In addition, a national streamflow classification structure and set of flexible tools are being 

developed that will allow stakeholders to evaluate a region of 

interest at the scale necessary for sound management. These 

tools are being designed to serve a predetermined set of stream 

classes derived from a subset of existing baseline hydrographs 

and, alternatively, to provide users with the option of deriving 

a set of stream classes based on user-specified input. 

In addition to the national-scale efforts, ecological water 

science is part of each of the Geographic Focus Area Studies 

at the large-river-basin scale. These efforts are as follows.

Apalachicola-Chattahoochee-Flint (ACF) River 

Basin—The physical and biological diversity of this basin 

and its importance to the many water users provide an ideal 

context for developing tools that will allow stakeholders to 

improve estimation of streamflow requirements for ecological purposes. Ecological water science activities in the ACF 

River Basin combine basinwide streamflow models with 

on-the-ground measurements of changes in the occurrence 

or abundance of various kinds of fish and mussel species. 

These biological measurements (conducted seasonally in six 

ACF subbasins) will allow scientists to calibrate simulation 

models that project changes in species occurrences in relation 

to changes in streamflow patterns. It is envisioned that the 

findings of this study will have broad transferability to other 

river basins and regions throughout the U.S. Extension to 

other systems may be achieved by expressing models in terms 

that describes the characteristics of those fishes or mussels that 

respond most strongly to various changes in streamflow (such 

as lower or more variable flow during warm months). For 

example, models relating daily water withdrawal to changes 

in number of fluvial specialists (species that rely on flowing 

water for survival) provide a basis for estimating effects of 

increasing water demand on the persistence or abundance of 

valued imperiled and recreational fish species (see Box E). 

Colorado River Basin—This basin is experiencing 

rapid population growth and water demands by many sectors, 

including energy, agriculture, and municipal water supplies. 

Resource managers are concerned with finding the most 

effective means of supporting diverse riparian and aquatic 

ecosystems in this highly regulated basin. Given the large 

size of the river basin, a subregional basin- and subbasinscale perspective will inform questions about the appropriate 

scale for management decisions. The upper Verde River (see 

Box F) is the first subbasin in the Colorado River Basin to be 

the subject of ecological water analysis. The analysis includes 

determining the hydrologic record, the magnitude of departure 

of the seasonal hydrology from the historic record, the amount 

of habitat needed to support different types of aquatic species under different flow volumes and groundwater levels, the 

status of the native and nonnative species, and a water budget 

that includes groundwater and helps identify reaches that are 

vulnerable to drying. 

Delaware River Basin—Competing water needs in the 

drainage basin of the Delaware River, the longest undammed 

river east of the Mississippi, make it an ideal case study for 

developing tools for sustainable management and waterconflict resolution. Ecological water science activities in the 

Delaware River Basin are being implemented to broaden the 

capabilities of an integrated Decision Support System to better 

understand and simulate the effects of alternative water-management scenarios on habitat availability for key native species (for example, trout, American shad, and dwarf wedgemussel; see Box G). Detailed field and laboratory experiments are 

underway to develop habitat suitability criteria that simulate 

the relation between the physiological response of key species 

and changes in temperature and hydrology. Simulation estimates of habitat characteristics are also being developed for 

large mainstem reaches of the Delaware River Basin across a 

range of discharge conditions. Planned work with the Decision 

Support System will help identify data gaps, support evaluation of the feasibility of extending the modeled area farther 

down the mainstem, and provide options for several alternative water-management scenarios. 

Research findings and modeling tools developed as part 

of the ecological water science effort will be useful to state 

and Federal natural-resource agencies and other stakeholders charged with ensuring that water-management actions are 

consistent with (1) meeting human needs and protecting biological integrity as mandated by the Clean Water Act, and (2) 

conserving imperiled and (or) recreationally valued species. 

Developing modeling tools with a high degree of transferability is an important element of the Water Census, and the 

research, tools, and applications being developed as part of the 

ecological water science efforts are expected to have applicability well beyond the borders of the study areas for which 

they were developed. 
4.0 Topical Areas 25

Box E. Ecological Water Science—Apalachicola-Chattahoochee-Flint (ACF) River Basin

Local colonization and extinction of fishes and 

mussels (referred to as metapopulation dynamics) are being 

tracked in six ACF subbasins representing Blue Ridge, 

Piedmont, and Coastal Plain streams. Field data will be 

combined with fine-scale hydrologic data and models 

within each subbasin to investigate changes in species 

distributions in response to streamflow variation, including 

drought, flood, and intermediate flow conditions.

0 25 50 KILOMETERS

0 25 50 MILES

30°

31°

32°

33°

34°

85°

84°

EXPLANATION

0 125 250 MILES

0 125 250 KILOMETERS

35°

30°

90° 85° 80°

Physiographic province

Coarse network hydrologic

 response unit

Ecological flow study 

subbasin

Coarse-resolution stream 

network

Boundary of ApalachicolaChattahoochee-Flint 

River Basin

Coastal Plain

Piedmont

Blue Ridge

Valley and Ridge

Appalachian Plateaus

Interior Low Plateaus

Ozark Plateaus

Figure E1. Ecological flow study subbasins in the ApalachicolaChattahoochee-Flint River Basin.

Hydrologic models Geomorphic context

Metapopulation dynamics

Simulation: 

Water availability -> Biological change

Field data

Figure E2. Fish assemblage sampling in the upper ACF 

River Basin. Field data will inform models that can be used to 

simulate biological responses to changes in water availability. 

(Photo by M. Freeman, U.S. Geological Survey)

0 1 2 3 4 5

0

-2

-4

-6

-8

-10

-12

-14

-16

-18

Daily water withdrawal, in million gallons per day

Change in number of species, in percent

Fluvial-specialist species

Generalist species

All species

Figure E3. An example ecological water science product 

showing relations between simulated daily water withdrawals 

and the predicted change in the richness of fish species in 

Potato Creek, Georgia (From Freeman and others, 2012). This 

example shows how changes in water withdrawals from 0.5 

to 4.0 million gallons per day may result in a 16-percent loss 

in the richness of fluvial-specialist species (pink line). Such 

relations can provide water managers, stakeholders, and 

policy makers with insight into how best to meet ongoing 

human water demand while minimizing the proportional loss of 

important recreational fish species that depend on streamflow 

for survival and reproduction.
26 Progress Toward Establishing a National Assessment of Water Availability and Use

Box F. Ecological Water Science—Colorado River Basin

Two to three subbasins within the Colorado River Basin will be used to examine in detail the Ecological Limits of Hydrologic Alteration (ELOHA) framework (a scientific framework that evaluates ecological water needs at multiple spatial scales) as 

a basis for understanding the relations between streamflow characteristics and aquatic-species response. The upper Verde River 

was initially selected because a collaborative ecological water study was underway in the basin. The study began in 2010 and the 

transferability of the approach to other subbasins is being evaluated.

A

Ve r d e

R i

v

e

r

112°30' 112° 111°30'

35°

34°30'

0 5 MILES

0 5 KILOMETERS

Base from U.S. Geological Survey digital datasets

North American Datum 1983

Universal Transverse Mercator zone 12

LOCATION OF

STUDY AREA

Phoenix

Tucson

Yuma

Flagstaff

NV Page

CA NM

UT

AZ

CO B

Figure F1. A, Ecological flow study area and, B, aquatic-invertebrate assemblage sampling in the upper Verde River, Colorado River 

Basin. (Map by Nicholas Paretti, U.S. Geological Survey; photo by A. Brasher, U.S. Geological Survey) 

100,000

10,000

1,000

100

10

Discharge, in cubic feet per second

Water year

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

EXPLANATION

Extreme low flow

Base flow

Small flood

High-flow pulse

Extreme high flow

Figure F2. Streamflow 

characteristics for the Verde River 

near Clarkdale, AZ (U.S. Geological 

Survey station number 09504000). 

Hydrologic data-collection efforts 

support the development of 

habitat availability models across 

a range of water volumes and 

provide information on seasonal 

flow characteristics that may 

be limiting the abundance and 

distribution of aquatic fauna in 

the upper Verde River (Nicholas 

Paretti, U.S. Geological Survey, 

written commun., 2013).
4.0 Topical Areas 27

Box G. Ecological Water Science—Delaware River Basin

Prior and ongoing research efforts have illustrated a highly variable flow regime in the Delaware River as a result of 

stormflow and water-management operations. It is not uncommon for extensive areas of the riverbed, submersed under median 

flow, to be exposed during low-flow events. In a relatively short time period, these same areas can experience highly turbulent 

conditions during high-flow events. These rapid changes (that is, rises and falls) in the hydrograph may negatively affect the 

abundance and distribution of riverine fauna and flora.

A B C

Figure G1. Delaware River near Callicoon, NY (U.S. Geological Survey station number 01427510): A, median flow conditions in late 

August 2010 (1,430 cubic feet per second), facing upstream from the Callicoon bridge; B, low flow in late September 2010 (653 cubic feet 

per second), facing downstream; and C, high flow during October 2010 (63,814 cubic feet per second), facing upstream. (Photos A, B, 

and C by Kelly Maloney, U.S. Geological Survey)

To provide better management solutions, several USGS Science Centers are working collaboratively to broaden the capabilities of a decision support system (DSS). The DSS is an integrative tool with a user-friendly Graphical User Interface (GUI) 

that combines habitat suitability criteria (HSC) with modeled estimates of habitat for large reaches of the Delaware River Basin. 

DSS users can modify the HSC, visualize alternative flow scenarios, examine available habitat over the entire range of the hydrograph, and identify areas with the greatest capacity to support key species of concern (for example, trout, American shad, and 

dwarf wedgemussel).

Equation for

displayed habitat

suitability maps

Display of hydrograph

for all scenarios

Hydroperiod

of interest

Amount of available habitat

by scenario by date

Map of site

location

Daily average

amount of

available habitat

over period

of interest

Geographic information Color-coded habitat maps for each scenario

system functionality

Selection of

key species

Habitat

suitability

criteria can

be modified

Figure G2. Graphical User Interface for the Decision Support System tool that is being developed as part of the Delaware River Basin 

Focus Area Study. Example shows three alternative flow-management scenarios (Rev1, Rev7, and ffmp) for the spawning stage of the 

American shad.
28 Progress Toward Establishing a National Assessment of Water Availability and Use

5.0 Water Availability and Water 

Quality

Determining the relation between water availability and 

water quality is critical to the maintenance of water availability for human uses and aquatic ecosystems. Even plentiful 

water supplies might not be suitable for use if water quality 

is impaired. The connections between water availability and 

water quality manifest in various ways. The most obvious 

water-quality constraint on water availability results from the 

release of anthropogenic contaminants to the environment, but 

naturally occurring contaminants, such as arsenic, radium, and 

uranium, also can affect water quality and its availability for 

particular uses. Salinity and sediment also commonly affect 

water availability. Moreover, water- and land-use practices, 

such as groundwater pumping and urban development, 

can modify groundwater flow and chemistry in ways that 

mobilize contaminants. 

Since 1991, the USGS has evaluated the quality of the 

Nation’s streams and groundwater through the National WaterQuality Assessment (NAWQA) Program. During 1991–2000 

(Cycle 1), the NAWQA Program focused on interdisciplinary, 

baseline assessments of the quality of streams, groundwater, 

and aquatic ecosystems in 51 of the Nation’s largest and most 

important river basins and aquifers (see http://water.usgs.

gov/nawqa/nawqa_sumr.html). During 2001–12 (Cycle 2), 

the NAWQA Program built upon the baseline assessments 

completed in the previous decade through (1) increased 

emphasis on assessment of long-term trends, (2) assessments 

of water quality in major river basins that discharge into 

some of the Nation’s key estuaries (see http://water.usgs.gov/

nawqa/studies/mrb), (3) regional assessments of water quality 

in 19 of the Nation’s 62 principal aquifers (see http://water.

usgs.gov/nawqa/studies/praq/), and (4) an initial assessment 

of contaminants in currently used sources of drinking water. 

Results of studies conducted by the NAWQA Program relating 

the distribution of contaminants in domestic wells, of nitrate 

contamination in deep groundwater, and of the pesticide atrazine in streams draining agricultural areas in the United States 

are shown in figure 12. These studies demonstrate the effect of 

water quality on water availability.

The Cycle 1 and 2 studies conducted as part of the 

NAWQA Program provide a foundation for examining the 

relations between water quality and water availability as part 

of the upcoming Cycle 3 studies. In a recent review of the 

NAWQA Program, the National Research Council (NRC) 

noted that the “NAWQA program can be particularly effective in contributing to forecasts of water availability through 

the program’s ability to relate its assessment of water quality 

and ecosystem health to changes in land use and land cover, 

natural and engineered infrastructure, water use, and climate 

change” (National Research Council, 2012). 

Of particular importance will be the development and 

application of water-quality models that integrate information 

on water quality, chemical use, land use, and environmental 

factors to explain how water-quality conditions vary regionally 

and nationally (see http://water.usgs.gov/nawqa/modeling). 

The integration of modeling with monitoring helps to extend 

water-quality understanding to unmonitored areas under 

a range of possible circumstances. The models are essential tools for cost-effective management of water resources 

because managing contaminants requires far more information 

than we can afford to measure directly for all important places, 

times, and contaminants. In addition, many management decisions—including how much to spend on implementing a management strategy, monitoring priorities, and registering pesticides—inherently depend on predicting the potential effects on 

water quality for locations that have little to no monitoring. 

6.0 Delivering the Data

To meet the objectives of the Water Census, data from 

multiple disciplines and sources need to be assembled and 

integrated. Some of these data will be obtained from existing 

sources within the USGS and partner agencies, whereas other 

data are being developed directly as part of the Water Census 

activities. Many of the “data” developed by the Water Census are derived from models, statistical estimation, and other 

transformation processes. 

A data-management plan is being developed to provide 

a framework that will guide and document these activities 

across the entire Water Census effort. Data-management planning spans the entire data life cycle to include data acquisition, 

documentation, processing, analysis, preservation, and delivery. The data-management plan will emphasize adoption of 

existing international and Federal standards for data elements, 

processing, preservation, and delivery to serve as unifying and 

integrating criteria to facilitate interoperability with partners. 

Coordination of data activities with partners, data providers, 

and Federal advisory organizations such as ACWI will ensure 

that the Water Census data are useful to a wide range of users 

and purposes.

6.1 Data Integration and Mapping

Conceptually, the data resources made available by the 

Water Census can be seen as a nationally consistent base 

layer of well-documented data covering the five topical areas 

(ET, groundwater, surface water, water use, and ecological 

water) and water quality. These data represent a collection 

of values associated with points, lines, areas, and grids, and 

are derived from a range of activities as diverse as collecting 

of fish in individual stream reaches and the interpretation of 

satellite imagery. 

A map view is a convenient model for organizing and 

coordinating the Water Census data, and a map interface is 

one of the most useful means of presenting raw data and 

analytic products to users. For the Water Census, a map of 

HUC-12 watersheds will be the base layer used to integrate 
6.0 Delivering the Data 29

EXPLANATION

!

Predicted nitrate concentration, 

in milligrams per liter as N

<1 >1–5

EXPLANATION

Missing data

Atrazine concentrations Atrazine use

(in micrograms per liter, μg/L) Very low

Low

Medium

High

Low (<0.05)

Medium (0.05 – 0.5)

High (>0.05)

EXPLANATION

At least one contaminant concentration 

greater than a human-health benchmark

No contaminant concentration greater 

than a human-health benchmark

>5–10

>10

Alaska

Hawaii

Alaska

Hawaii

Alaska

Hawaii

More than 20 percent of private domestic wells 

sampled nationwide (more than 2,100 wells in 25 

principal aquifers, shown by background colors) 

contained at least one contaminant at levels of 

potential health concern. About 43 million 

people—or 15 percent of the Nation’s 

population—use drinking water from private wells. 

These results are prior to any on-site treatment by 

homeowners. Community water systems using 

groundwater from these aquifers test and treat the 

water supply to meet drinking-water standards. 

(From DeSimone and others, 2009)

Results from a national statistical model for deep 

groundwater used as drinking water suggest 

moderate (shown in yellow and orange) to severe 

(shown in red) nitrate contamination in relatively 

deep groundwater (greater than 164 feet or 50 

meters below land surface). These areas typically 

are associated with large nitrogen input; natural 

soil, landscape, and geologic features that promote 

rapid transport of groundwater; and a lack of 

biogeochemical processes that convert nitrate to 

other forms of nitrogen. (From Dubrovsky and 

others, 2010)

The concentrations of atrazine measured in

agricultural streams correlated with the distribution

of its use on crops—primarily corn. Some of the 

highest concentrations occurred in the corn-growing 

areas of Illinois, Indiana, Iowa, Nebraska, and Ohio. 

(From Gilliom and others, 2006)

Figure 12. Example findings from the U.S. Geological Survey National Water-Quality Assessment Program (From DeSimone and 

others, 2009; Dubrovsky and others, 2010; and Gilliom and others, 2006).
30 Progress Toward Establishing a National Assessment of Water Availability and Use

water-budget components and will serve as the exploratory 

framework for the representation of data to users. Other data 

that can be included in the map are various natural and geopolitical boundaries, descriptive layers such as soil and landcover characteristics, and the National Hydrography Dataset 

of streamlines and associated features. Although many data 

layers of various scales can be useful to data exploration, the 

analytic and reporting scale of the Water Census is targeted at 

monthly HUC-12 values.

6.2 The National Data Platform

The USGS has a long history of building national-level, 

Web-accessible data stores that can serve various types of 

users simultaneously while providing them with tools for 

evaluating the data, including mapping, graphing, and other 

forms of data exploration and visualization (examples include 

the NAWQA Program, WaterWatch, StreamStats, the National 

Map, NWIS Web, and the Water Quality Portal). A National 

Data Platform will enable stakeholders and other interested 

parties to explore and focus their data activities on areas and 

times of interest, offer appropriate filters to narrow their data 

retrieval, and make available other tools to fit their specific needs. The platform will follow the President’s Digital 

Government Strategy by using a rich set of Web services to 

provide underlying data. This strategy will allow any data system or interactive Web-based analytical service to leverage the 

Water Census data by making automated queries and retrievals 

from the data store. The National Data Platform will use Web 

services to create a comprehensive and nationally consistent 

interactive map interface and a set of trend-analysis and other 

tools that work directly with the data.

Data products from individual components of the water 

budget will be made available as stand-alone datasets to 

serve the specific needs of users who need information from 

particular portions of the data store. In addition, value-added 

and integrated data will be provided, removing the integration effort from the user and promoting a uniform approach to 

combining datasets that may have originated in mixed scales 

and standards. It is critical that the sources and transformations of the data being served by the Water Census are fully 

documented and available with the data. 

Serving Water Census data to users will involve the 

technology needed to mediate language and format issues that 

would otherwise make a Web-based delivery system inconsistent and nonintuitive. The approach planned for the National 

Data Platform will incorporate current technologies and best 

practices–such as searchable metadata catalogs, semantic 

services that facilitate the conceptual relation of data to other 

data, and format mediation to handle data translation and provide user-selected output types–allowing users to focus on the 

discovery, exploration, and retrieval of the data rather than on 

reconciling inconsistencies in the data served by the system.

7.0 Planning for the Future

Many effective programs are underway to measure 

aspects of our water resources. However, simply 

stated, quantitative knowledge of U.S. water supply 

is currently inadequate.

Report of the National Science and Technology 

Council, Committee on Environment and Natural 

Resources, Subcommittee on Water Availability and 

Quality (2007)

Progress toward a Water Census has been made by 

integrating information from a number of programs, including new funding targeted toward the Water Census; ongoing 

national-scale efforts such as those undertaken by the USGS 

National Water-Quality Assessment (NAWQA) and Groundwater Resources Programs; and the legacy provided by longterm monitoring and assessment programs such as the USGS 

Cooperative Water Program and the National Streamflow 

Information Program (NSIP). Over the next few years, progress will continue with existing efforts and expand as funding 

allows. In addition to completing the ongoing work described 

in this report, priorities for future work (not in priority order) 

are as follows.

Expand Geographic Focus Area Studies 

Geographic Focus Area Studies provide an opportunity to 

test new approaches and leverage and support ongoing wateravailability studies. As the three current Geographic Focus 

Area Studies are completed, future Geographic Focus Areas 

will be identified by using criteria being developed as part of 

future implementation planning for the Water Census.

Evaluate impaired surface water and groundwater that may be 

important future sources of water supply

The national water availability and use assessment, 

described in the SECURE Water Act, includes assessment of 

“impaired surface water and groundwater supplies that are 

known, accessible, and used to meet ongoing water demands.” 

Likewise, the Act calls for an assessment of brackish groundwater. Since the SECURE Water Act was passed, the USGS 

Groundwater Resources Program has undertaken preliminary 

work to develop approaches for assessing brackish water in 

three areas. This work will be expanded and enhanced.
8.0 Acknowledgments 31

Continue to develop ways to bring information together from 

multiple sources

It is critical that the Water Census use information available from multiple sources to the maximum possible extent. 

The Water Census program will continue to work through 

the Federal Advisory Committee on Water Information to 

enhance this capability, including investigating possibilities 

for data portals that provide ready access to data from multiple 

agencies, similar to the one proposed by the advisory group’s 

Subcommittee on Ground Water.

Work with Federal, state, and other agencies to enhance 

water-use datasets 

Studies summarizing water use highlight limitations and 

inconsistencies in water-use-data collection and reporting 

across the United States (National Research Council, 2002; 

U.S. Government Accountability Office, 2009). Reported 

water use relies heavily on estimates by state agencies, and 

estimation procedures vary from state to state. The Water 

Census provides an opportunity to establish agreed-upon 

standards for estimating, reporting, and storing water-use data 

for various use categories and sources. In addition, the USGS 

has increased efforts to work with other Federal agencies such 

as the Department of Energy’s Energy Information Administration (EIA) and the Department of Agriculture, particularly 

with respect to water-use data related to thermoelectric power 

generation and irrigation water use. These efforts need to be 

expanded to leverage the capacity, knowledge, and data available from other organizations. 

Identify areas of greatest uncertainty in various types of data

The Water Census must focus efforts on the most critical 

gaps and needs rather than spread its effort equally across 

the resources and geographic areas. One factor to consider 

in focusing efforts is where the uncertainty in different types 

of data is greatest. The Water Census is assessing the use of 

uncertainty analysis from models to help address this issue. 

Expand links to water availability in Cycle 3 of the NAWQA 

Program 

The NAWQA Program in Cycle 3 will place an emphasis 

on its national water-quality monitoring networks for streams 

and groundwater, which have gradually eroded over the past 

15 years as inflation has reduced the number of monitoring 

sites that could be supported. These monitoring networks provide the only nationally consistent and long-term water-quality 

monitoring of its kind. These data, along with the continued 

use of models to boost understanding of undersampled areas 

(National Research Council, 2012), will provide key information needed to integrate water-quality and water-availability 

information by the Water Census. 

In summary, the USGS is working with partners to build 

the capabilities necessary to provide policymakers, citizens, 

and natural-resource managers with fundamental information about the Nation’s water availability through a National 

Water Census. To complete this effort, the Water Census must 

address surface-water flows and storage, groundwater flows 

and storage, reservoirs, lakes, springs, storage in snow pack 

and ice fields, soil moisture, evapotranspiration, and all facets 

of water use, including withdrawals, water reuse, consumptive 

use, interbasin transfers, and return flows. The Water Census must additionally address how water quality influences 

water availability. The information presented will be current and up to date, and will include trends in historical data. 

The USGS envisions the Water Census to be an ongoing and 

continuous activity. 

The resources available to support the Water Census are 

finite and necessitate the use of an incremental process. The 

USGS envisions that estimates of flow at ungaged locations 

and estimates of evapotranspiration will be among the earliest products. Providing complete water-use information and 

adequately assessing the Nation’s groundwater resources with 

respect to water availability will require additional time. Providing the public with ecological water science that addresses 

a classification system for streams and provides access to 

biological and streamflow databases that can be analyzed with 

statistical tools needed by biological managers will take most 

of the next decade to accomplish. 

Although the existing data are limited and much work 

remains to be done, funding over the past 2 years has allowed 

substantial progress to be made toward a Water Census. The 

effort is well matched to the USGS’s capabilities and mission. 

The USGS will continue to work with partner agencies and 

organizations to maximize the utility of the information for a 

broad range of uses.

8.0 Acknowledgments

The following individuals provided helpful reviews 

of the draft report: Kara Capelli and Sonja Jones, USGS; 

Christopher Carlson, U.S. Department of Agriculture–Forest 

Service; Adam Carpenter, Grace Chan, and Roland Steiner, 

representing the American Water Resources Association; Donald Cline, National Weather Service; Peter Evans and Robert 

Tudor, representing the Interstate Commission on Water 

Policy; Richard Juricich, representing the Sustainable Water 

Resources Roundtable; Eloise Kendy, The Nature Conservancy; David Kreamer, National Ground Water Association; 

and Michael Muse, U.S. Environmental Protection Agency. 

In addition, the USGS thanks the organizations and agencies 

listed below who participated in the Water Census Ad Hoc 

Advisory Committee organized under the Sustainable Water 

Resources Roundtable:
32 Progress Toward Establishing a National Assessment of Water Availability and Use

Non-Federal Agencies and Organizations

• Association of American State Geologists (AASG)

• Association of Fish and Wildlife Agencies (AFWA)

• Association of State Drinking Water Administrators 

(ASDWA)

• American Water Resources Association (AWRA)

• American Water Works Association (AWWA)

• Interstate Council on Water Policy (ICWP)

• National Ground Water Association (NGWA)

• National Tribal Water Council (NTWC)

• The Nature Conservancy (TNC)

• Water Systems Council (WSC)

• Western States Water Council (WSWC)

Federal Agencies

• National Aeronautic and Space Administration (NASA)

• National Oceanic and Atmospheric Administration—

National Weather Service (NOAA—NWS)

• U.S. Army Corps of Engineers (USACE)

• U.S. Department of Agriculture—Economic Research 

Service (USDA—ERS)

• U.S. Department of Agriculture—Forest Service 

(USDA—FS)

• U.S. Department of Agriculture—National Agricultural 

Statistics Service (USDA—NASS)

• U.S. Department of Agriculture—Natural Resources 

Conservation Service (USDA—NRCS)

• U.S. Department of Energy (USDOE)

• U.S. Department of the Interior—Bureau of Reclamation (USBR)

• U.S. Environmental Protection Agency (USEPA)

• U.S. Fish and Wildlife Service (USFWS)

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available online at http://pubs.usgs.gov/circ/2007/1309/.

U.S. Government Accountability Office, 2009, Energy-water 

nexus: Improvements to federal water use data would 

increase understanding of trends in power plant water 

use—U.S. Government Accountability Office GAO-10-23, 

72 p., also available online at http://www.gao.gov/new.items/

d1023.pdf.

U.S. Water Resources Council, 1968, The Nation’s water 

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Photo by Judy Denver, 

U.S. Geological Survey
For more information concerning this publication contact:

Eric J. Evenson

Coordinator—National Water Census

U.S. Geological Survey

810 Bear Tavern Road, Suite 206

West Trenton, New Jersey 08628

Or visit the USGS National Water Census Web site:

http://water.usgs.gov/watercensus/

Publishing support provided by West Trenton Publishing Service Center
Alley and others—Progress Toward Establishing a National Assessment of Water Availability and Use—Circular 1384