Fact Sheet

United States Geological Survey

An Overview of the Stream-Gaging Program

The USGS provides maps, reports, and information to help others meet their needs to manage, 

develop, and protect America's water, energy, mineral, and land resources. We help find 

natural resources needed to build tomorrow, and supply scientific understanding needed to 

help minimize or mitigate the effects of natural hazards and environmental damage caused 

by human activities. The results of our efforts touch the daily lives of almost every American.

Introduction

The growth and development of the 

United States has been dependent on the 

availability of water resources. As the 

population grew during the late 1800's, 

people moved west into more arid regions 

of the country where the flow of rivers 

and streams was much less dependable 

than in the humid East. The necessity of 

reliable water supplies led to the need for 

streamflow data with which to design 

storage and distribution facilities. In 

1889, the first stream-gaging station operated in the United States by the U.S. Geological Survey (USGS) was established 

on the Rio Grande near Embudo, New 

Mexico. The establishment of this early 

station was an outgrowth of efforts to 

train individuals to measure the flow of 

rivers and streams and to define standard 

stream-gaging procedures. As the need 

for streamflow data increased, the streamgaging program operated by the USGS 

has grown to include, in 1994, 7,292 continuous-record stream-gaging stations 

(herein referred to as "stations") in the 

United States, Puerto Rico, and the Trust 

Territory of the Pacific Islands (fig. 1). 

More than 90 percent of these stations are 

operated with at least partial support from 

other Federal, State, and local agencies.

The stream-gaging program of the 

USGS does not represent a single "network" 

of stations, but is an aggregation of networks and individual streamflow stations 

that had been established for various purposes. Data from the 7,292 active stations, 

as well as from discontinued stations, are 

available through the USGS's National 

Water Data Storage and Retrieval System 

(WATSTORE) that holds mean daily-discharge data for about 18,500 locations and 

more than 400,000 station-years of record, 

or more than 146 million individual mean 

daily-discharge values. Additional data are 

added to the data base each year. The 

stream-discharge data base is an ever-growing resource for water-resources planning 

and design, hydrologic research, and operation of water-resources projects.

Funding the Program

Just as the network of stations represents an aggregation, so does the program 

funding. Operating funds for individual 

stations in the program may come from a 

blend of Federal funds appropriated to the 

USGS, funds from State and local agencies, and funds appropriated to other Federal agencies. More than 50 percent of the 

7,292 stations operated in 1994 by the 

USGS are funded through the USGS Fed600

400

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5 *" '

i > 2^ D.U.OW 5

STATE OR OTHER POSSESSION

Figure 1 . Number of stations operated by the U.S. Geological Survey in 1994, by State or possession.

eral-State Cooperative Program (fig. 2). 

Under that program, the USGS provides 

up to 50 percent of the funds, and the State 

or local agency provides the remainder. 

Presently, more than 600 State and local 

agencies provide funds for the stream-gaging program. Other stations in the program 

are operated by the USGS and funded by 

other Federal agencies, such as the U.S. 

Army Corps of Engineers (COE) and the 

Bureau of Reclamation (BOR), to provide 

those agencies with the hydrologic data 

needed for planning and operating waterresources projects. Additionally, some of 

the stations are funded by the USGS to 

support national programs of waterresources investigations; to collect data 

required by court decree, treaty, or compact; and to conduct hydrologic research. 

The USGS provides full support for fewer 

than 10 percent of the stations that it operates. Many of the stations supported primarily by State, local, or other Federal agency 

funds are critically important to USGSfunded programs such as the National 

Water Quality Assessment Program.

Uses of Streamflow Data

The USGS stream-gaging program provides hydrologic information needed to help 

define, use, and manage the Nation's water

SOURCES OF FUNDS

COOP Combination of USGS and non-Federal agency

OFA Other Federal agencies

USGS USGS appropriations

COMBINED A combination of any two or more from

OFA, USGS, and COOP 

Total stations in 1994 is 7,292

Figure 2. Number of stations and sources of 

funds, 1994 fiscal year.
resources. The program provides a continuous, well-documented, well-archived, unbiased, and broad-based source of reliable and 

consistent water data. Because of the 

nationally consistent, prescribed standards 

by which the data are collected and processed, the data from individual stations are 

commonly used for purposes beyond the 

original purpose for an individual station. 

Those possible uses include, but are not 

limited to, the following:

 Providing data for forecasting and 

managing floods

 Characterizing current water-quality 

conditions

 Delineating and managing flood plains

 Operating and designing multipurpose 

reservoirs

 Setting permit requirements for discharge of treated wastewater

 Designing highway bridges and 

culverts

 Monitoring compliance with minimum 

flow requirements

 Scheduling power production

 Designing, operating, and maintaining 

navigation and recreational facilities

 Allocating water for municipal, industrial, and irrigation uses

 Administering compacts or resolving 

conflicts on interstate rivers

 Defining and apportioning the water 

resources at our international borders

 Undertaking scientific studies of longterm changes in the hydrologic cycle

Data for one or more of these purposes 

are needed at some point in time on virtually every stream in the country, and a 

data-collection system must be in place to 

provide the required information. The 

general objective of the stream-gaging 

program is to provide information on 

streamflow characteristics at any point on 

any stream. Streamflow data are needed 

for immediate decisionmaking and future 

planning and project design. Data, such as 

that needed to issue and update flood forecasts, are referred to as "data for current 

needs." Other data, such as that needed 

for the design of a future bridge or reservoir, are referred to as "data for future or 

long-term needs." Some data, of course, 

fit into both classifications; a station that 

supplies data for flood forecasting and 

also provides data to define long-term 

trends clearly fits both classifications.

Data for Current Needs

Streamflow data are needed at many 

sites on a daily basis for forecasting flow

extremes, water-management decisions, 

assessing current water availability, managing water quality, and meeting legal 

requirements. These activities require 

streamflow information at a given location for a specified time or period. These 

needs generally are best satisfied by operating a station to produce a continuous (or 

daily) record of flow.

Data from about 4,200 of the 7,292 

stations are telemetered by an earth-satellite-based communications system that 

enables the data to be available in realtime for the operation of water-resources 

projects by many agencies and for flood 

forecasting by the National Weather Service (NWS). The NWS uses data from 

USGS stations in concert with its own 

precipitation data to forecast river stages 

and flow conditions on large rivers and 

their associated tributaries.

The U.S. Geological Survey stream 

gaging network is vital to the National 

Weather Service's river forecast and 

warning program and the goal to 

reduce flood damages and loss of 

life. Without data from this network, 

this nation would experience increased 

losses from floods of both life and 

property [Elbert W. Friday, Jr., Assistant Administrator for Weather Services, National Weather Service, 

written commun., January 19,1995].

During the 1993 Mississippi River 

flood, USGS field personnel made more 

than 2,000 visits to stations in the floodaffected areas to verify that the instruments were working properly, to make 

repairs as needed, and to make direct 

measurements of the streamflow. Data 

from these stations were provided continuously to the NWS, the COE, and local 

agencies and formed the basis for flood 

forecasts that allowed people to be evacuated from areas about to be inundated. 

The COE and local agencies used the 

streamflow information to protect lives 

and property and to focus flood-fighting 

activities where they were most needed.

Data for Future or 

Long-Term Needs

The collection of data to meet future 

needs often represents a larger challenge 

than does collection of data for current 

needs because the future needs are seldom 

known precisely and, in fact, may be 

impossible to anticipate. Because operating stations at all points on all streams is

physically and economically impossible, 

mechanisms must be available to transfer 

streamflow information from stations to 

points where there are no streamflow data 

(ungaged sites).

Transfer of streamflow information for 

unregulated streams may be accomplished in many ways, ranging from the 

simple to the complex. Simple methods 

are interpolation between or extrapolation 

from stations on the same stream on the 

basis of drainage-area size. More complex methods may involve transferring 

information from basins with similar 

hydrologic characteristics, mapping station data to define approximate lines of 

equal runoff values, or correlating short 

records with long records. A statistical 

technique known as multiple-regression 

analysis has proven to be effective for 

defining equations that relate streamflow 

characteristics to the basin and climatic 

characteristics that affect streamflow. The 

resulting equations usually are referred to 

as "regional relations" because they can 

be applied to ungaged streams within a 

defined hydrologic area or region (Jennings and others, 1994).

Trend analysis is another application 

that requires long records. Concern is 

widespread that increased greenhouse-gas 

concentrations in the atmosphere are 

affecting the climate and the hydrology of 

the Earth. Analysts have used actual 

streamflow records to determine whether 

streamflows are beginning to change as a 

result of human activities or global warming. Natural climatic episodes of wetter or 

dryer than normal and lasting longer than a 

decade have been observed. Given the 

occurrence of such episodes and the inherent variability of streamflow, record 

lengths of more than 50 years are essential 

if real trends are to be detected. Slack and 

Landwehr (1992) reviewed the USGS data 

base to identify streamflow records that 

reflected natural conditions and could be 

useful in trend analysis. They identified 

1,659 stations in the United States and its 

possessions. Over 500 of these stations 

have record lengths in excess of 50 years.

Specific Categories of Use

The USGS has a long history of analyzing and evaluating its stream-gaging 

program. As part of the most recent 

nationwide evaluation from 1983 to 1988, 

uses of the data for individual stations 

were defined for 6,238 of the approxi-
mately 7,000 stations then operated by 

USGS (Thomas and Wahl, 1993). Individual stations were identified as belonging to one or more of nine categories, 

which are based on the principal uses 

made of the data.

Hydrologic systems. One of the 

more common uses of streamflow data is 

to account for and monitor the flow 

through a river basin or to define the general hydrologic conditions in the basin. 

Data from about 4,200 active stations are 

used to understand and evaluate the interactions of ground- and surface-water 

resources and to monitor diversions and 

return flows. At the State and interstate 

level, many of the stations serve a key 

role in the process of allocating and regulating water rights.

I am writing you on behalf of the Missouri River Basin Association, a coalition of eight states and twenty-eight 

Indian Tribes in the Missouri basin. For 

years, we have been working closely 

with the federal agencies that have 

jurisdiction in the basin to improve 

management of the basin's water 

resources. As you know from your 

years with the USGS, good water management depends upon good data. An 

important source of good data has 

been USGS's Coop Program [Excerpt 

of letter from J. Edward Brown, President, Missouri River Basin Association 

to Gordon P. Eaton, Director, U.S. Geological Survey, February 14,1994].

Regional hydrology. Stations supplying 

data that are largely unaffected by manmade 

storage or diversion furnish much of the 

data needed for future or long-term needs. 

Data from about 3,800 active stations can be 

used to develop regional relations for estimating streamflow characteristics at 

ungaged sites or sites where only small 

amounts of streamflow data are available.

Project operation. Data from stations 

in this classification are used by water 

managers in maki rig daily operational 

decisions. For example, data from about 

2,900 active stations are used by the COE, 

the BOR, and others to operate more than 

2,000 flood control, navigation, and watersupply reservoirs.

Hydrologic forecasting. Data from stations so classified provide information for 

flood and water-supply forecasting. These 

stations play a key role in efforts by Federal, 

State, and local agencies to protect the lives 

and welfare of the public. More than 3,000

of the stations operated by the USGS are 

used in the NWS's flood-forecasting system.

Water-quality monitoring. The evaluation of water quality in rivers, lakes, reserand estuaries depends on having data

; chemistry of the water and the

voirs 

onth

streamflow. Other program components 

provide data on the chemical quality of 

surface- and ground-water resources, sediment in streams and lakes, and water use 

(fig. 3). To compare the relative amounts of 

contaminants coming from different 

sources (various tributaries or wastewater 

treatment plants), one must know the flux 

of the contaminants computed as the concentration times the rate of streamflow. 

Data from about 2,700 active stations in 

this category provide the streamflow data 

needed to evaluate the quality of the 

Nation's surface-water resources.

Planning and design. Data from about 

1,100 active stations in this category are 

used to plan and design a specific project, 

such as a reservoir, levee, water-treatment 

facility, or hydroelectric powerplant.

The U.S.G.S. basic water data collection program is of vital importance to 

water resource planning, design, and 

operation in the United States. Reductions in surface water data collection 

will have long-term adverse effects on 

the efficiency and certainty of planning, 

design, construction, and operation of 

projects. Civil engineers rely on surface 

water data for numerous projects, 

including flood control, pollution control, transportation, and navigation 

[Excerpt from American Society of Civil 

Engineers Policy Statement on Surface-Water Data Collection, October 

24,1993].

Water quality.__ 

17.6

Total 1994 funds for

collection of all types

of data is $128,200,000

Figure 3. Percentage distribution of funds for 

U.S. Geological Survey hydrologic data collection, 1994 fiscal year.

Legal obligations. Data from these 

stations satisfy a legal responsibility of 

the USGS or of signatories of treaties, 

compacts, and decrees. The USGS operates about 250 stations in support of 17 

interstate compacts, 2 Supreme Court 

decrees, and 1 international treaty.

The U.S. Supreme Court in a 1954 

decree required that the USGS monitor 

flows in the Delaware River at Montague, New Jersey and the diversions 

out of the Delaware River Basin through 

the Delaware and Raritan Canal. The 

decree settled a water-rights suit in 

which four States were involved. The 

USGS operates two stations to monitor 

the flows as identified in the U.S. 

Supreme Court decree [William J. 

Carswell, Jr., Delaware River Master, 

U.S. Geological Survey, oral commun., 

January 1995].

Research. Data from about 700 active 

stations are collected for particular 

research or water-investigation studies. As 

such, the data supply a current need. The 

length of time that the data will be needed 

is dictated by the particular project. Some 

research needs, such as detection of hydrologic trends, can be met only by long-term, 

high-quality streamflow records.

Detection of hydrologic change 

requires long-term data sets of 

greater quality and reliability than are 

normally needed in the investigations 

of processes [National Research 

Council, 1991, p. 223].

Other uses. These stations supply 

data for uses that do not fit into any of the 

other categories. These include, for 

example, recreational purposes, such as 

providing data for canoeists, rafters, and 

fishermen. Data from about 700 active 

stations supply a current need for 

recreational-type information.

The nationwide analysis (Thomas and 

Wahl, 1993) documented that multiple 

uses were being made of data collected at 

stations in the USGS stream-gaging program with about 80 percent of the stations 

having data uses in two or more of the 

above categories and about 25 percent having data uses in four or more categories.

Dissemination Of Data

Currently (1995), daily-discharge data 

are published annually for each State in a 

USGS report series entitled "Water 

Resources Data [State Name]." The data 

are published on a water-year basis. A
water year is the 12-month period of October 1 through September 30 and is designated by the calendar year in which it ends. 

Thus, the 1994 water year ends September 

30, 1994. Because of the need for review 

of the completed computations, these 

reports generally are published from 6 

months to 1 year after the end of the water 

year. Many streamflow data users must 

make operational decisions daily. For these 

users, streamflow records are computed 

and made available on a provisional basis.

Automated telemetry provides the data 

users with provisional stage and discharge 

data in a timeframe that meets water-management needs. This technology also permits the USGS field offices to continuously 

monitor the operation of the hydrologic 

stations, time visits to stations to coincide 

with times of maximum need for data 

(such as during floods) and to service 

equipment at the stations. Currently, more 

than half of the 7,292 USGS stations are 

equipped with automated telemetry.

In addition to the published record, the 

data collected by the USGS are archived 

in the nationwide WATSTORE data base. 

The number of active stations in the 

WATSTORE data base with associated 

record lengths is given in figure 4 for each 

decade from 1900 to 1990. The data in 

figure 4 also include stations operated by 

other agencies (primarily State agencies) 

for which the data are reviewed, archived, 

and published by USGS. In 1990, data 

from about 400 stations were provided to 

the USGS by other agencies.

Beginning with the 1990 water year, 

Water Data Reports are also available on 

Compact Disk-Read Only Memory 

(CD-ROM). The Water Data Reports and 

the CD-ROM's are distributed to participating agencies and libraries; they also 

are available for sale by the USGS Earth 

Science Information Center, Denver, Colorado. Currently (1995), the USGS is

10,000

5,000

||

1900 10 20 30 40 50 60 70 801990 

YEAR

EXPLANATION

LENGTH OF RECORD 

I Greater than or equal to 50 years 

g Greater than 20 and less than 50 years 

0 Less than or equal to 20 years

Figure 4. Number of stations in the U.S. Geological Survey data base, 1900-90.

developing procedures to allow access to 

streamflow data by means of Internet. 

Historical mean daily-discharge data for 

about 18,500 stations will soon be available through this source.

Final Comments

The USGS stream-gaging program 

provides data to many agencies and organizations involved in water-resources 

projects. USGS goals and objectives for 

ensuring the continued relevance of this 

vital program include the following:

 Maintain a long-term and consistent 

nationwide data base

 Maintain state-of-the-art recorders, 

sensors, and equipment for data collection

 Provide easy access to archived and 

realtime data

 Maintain a skilled staff of hydrologists 

and hydrologic technicians for collecting and computing the streamflow records

The USGS continues to be committed 

to the collection and dissemination of 

high-quality streamflow data as a critical 

part of its overall mission of providing 

earth science information for the wise

management of the Nation's natural 

resources. The maintenance of a viable 

stream-gaging program is an integral part 

of managing these natural resources.

We believe that the U.S.G.S. basic 

water quantity data collection activities 

are: 1) essential, because the value of 

hydrologic data increases with both 

the length and continuity of the record; 

2) the logical responsibility of the Federal Government because the States 

cannot possibly assume the support 

and leadership role of U.S.G.S. for 

interstate water systems; 3) cost-effective, because coordinated water data 

collection eliminates overlapping and 

duplicative efforts [Statements of William J. Carroll, President-elect, American Society of Civil Engineers, before 

the Subcommittee on Interior and 

Related Agencies, Committee on 

Appropriations, U.S. House of Representatives, March 10,1988].

References

Jennings, M.E., Thomas, W.O., Jr., and Riggs, 

H.C., 1994, Nationwide summary of U.S. 

Geological Survey regional regression equations for estimating magnitude and frequency 

of floods for ungaged sites, 1993: U.S. Geological Survey Water-Resources Investigations Report 94-4002,196 p.

National Research Council, 1991. Opportunities in the hydrologic sciences: Washington, D.C., National Academy Press, 348 p.

Slack, J.R., and Landwehr, J. M., 1992, HydroClimatic Data Network (HCDN) A U.S. 

Geological Survey streamflow data set for 

the United States for the study of climate 

fluctuations, 1874-1988: U.S. Geological 

Survey Open-File Report 92-129,193 p.

Thomas, W.O., Jr., and Wahl, K.L, 1993, Summary of the nationwide analysis of the cost 

effectiveness of the U.S. Geological Survey stream-gaging program (1983-88): 

U.S. Geological Survey Water Resources 

Investigations Report 93^168, 27 p.

Kenneth L. Wahl, Wilbert O. Thomas, 

Jr., and Robert M. Hirsch

For more information contact any of the following:

Chief Hydrologist 

409 National Center 

Reston, Virginia 22092 

(703) 648-5215

Office of Surface Water 

415 National Center 

Reston, Virginia 22092 

(703) 648-5301

Additional earth science information 

can be found by accessing the USGS 

"Home Page" on the World Wide Web at 

"http://www.usgs.gov", or by calling 1-800- 

H20-9000 (1-800-426-9000).

For more information on all USGS reports 

and products (including maps, images, and 

computerized data), call 1-800-USA-MAPS.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet FS-066-95