STREAM-GAGING PROGRAM

OF THE 

U.S. GEOLOGICAL SURVEY

U.S. GEOLOGICAL SURVEY CIRCULAR 1 123
Front cover Stilling well and shelter for measuring the stage

of a river 

Cable car, current meter, and weight used for measuring the

discharge of a river from a cableway 

Photography by David F. Usher
THE STREAM-GAGING PROGRAM OF THE 

U.S. GEOLOGICAL SURVEY

By Kenneth L. Wahl, Wilbert O. Thomas, Jr., and Robert M. Hirsch 

U.S. GEOLOGICAL SURVEY CIRCULAR 1123

Reston, Virginia 

1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

GORDON P. EATON, Director

Any use of trade, product, or firm names in this

publication is for descriptive purposes only and does

not imply endorsement by the U.S. Government

UNITED STATES GOVERNMENT PRINTING OFFICE: 1995

Free on application to the 

U.S. Geological Survey

Information Services

Box 25286, Federal Center

Denver, CO 80225
CONTENTS

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

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

Overview of the Stream-Gaging Program............................................................................................................. 2

Funding the Program...................................................................................................................................... 3

Uses of Streamflow Data................................................................................................................................ 4

Data for Current Needs............................................................................................................................ 5

Data for Future or Long-Term Needs...................................................................................................... 6

Specific Categories of Use....................................................................................................................... 7

History and Growth of the Stream-Gaging Program...................................................................................... 11

Data-Collection Process......................................................................................................................................... 13

Measuring Stage............................................................................................................................................. 13

Measuring Discharge...................................................................................................................................... 14

Determining a Continuous Record of Discharge............................................................................................ 15

Data Collected by Other Agencies.................................................................................................................. 17

Dissemination of Data ................................................................................................................................... 17

Evaluating the Program.......................................................................................................................................... 18

Challenges for the Future....................................................................................................................................... 20

References............................................................................................................._^ 22

FIGURES

1. Cumulative reservoir storage in the United States.......................................................................................... 2

2. Number of stations operated by the U.S. Geological Survey in 1994, by State or possession...................... 3

3. Number of stations and sources of funds, 1994 fiscal year........................................................................... 3

4. Relation between standard error of estimate and record length for Minnesota.............................................. 7

5. Relation between drainage area and 50-year flood for small rural streams in eastern Massachusetts........... 7

6. Number of stations and record lengths with acceptable data for studying climate fluctuations..................... 8

7. Percentage distribution of funds for U.S. Geological Survey hydrologic data collection, 1994 fiscal year.. 9

8. Map showing areal distribution of stations for Kansas by funding source..................................................... 12

9. Number of stations in the U.S. Geological Survey data base, 1900-90........................................................ 12

10. Schematic of a stilling well and shelter.......................................................................................................... 13

11. Discharge measurements made in 1993, by State or possession.................................................................... 16

12. Sections of stage-discharge relations for the Colorado River at the Colorado Utah State line................... 16

13. Schematic of the data flow for realtime operations ........................................................................................ 18

14. Percentages of stations by category of use..................................................................................................... 19

15. Distribution of stations as a function of the number of data-use categories.................................................. 19

16. Number of stations in a given year with acceptable data for studying climate fluctuations........................... 20

Contents III
CONVERSION FACTORS

Multiply By To obtain

foot (ft)

mile (mi)

square mile (mi2) 

cubic foot per second (ft3/s)

acre-foot (acre-ft)

0.3048

1.609

2.590 

0.02832

0.001233

meter

kilometer

square kilometer 

cubic meter per second

cubic hectometer

IV Stream-Gaging Program of the U.S. Geological Survey
Stream-Gaging Program of the U.S. Geological Survey

By Kenneth L. Wahl, Wilbert O. Thomas, Jr., and Robert M. Hirsch

Abstract

The U.S. Geological Survey (USGS) streamgaging program provides streamflow data for a 

variety of purposes that range from current needs, 

such as flood forecasting, to future or long-term 

needs, such as detection of changes in streamflow 

due to human activities or global warming. The 

development of data on the flow of the Nation's 

rivers mirrors the development of the country. 

From the establishment of the first stream-gaging 

station operated by the USGS in 1889, this program has grown to include 7,292 stations in operation as of 1994. Data from the active stations, as 

well as from discontinued stations, are stored in a 

computer data base that currently holds mean 

daily-discharge data for about 18,500 locations 

and more than 400,000 station-years of record. 

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

design, hydrologic research, and operation of 

water-resources projects.

More than 600 State, Federal, and local 

agencies provide funding for the stream-gaging 

program. More than 50 percent of the 7,292 

stations operated by the USGS are funded through 

the Federal-State Cooperative Program whereby 

the USGS provides up to 50 percent of the funds 

and the State or local agency provides the rest. 

The USGS provides full support for fewer than 10 

percent of the stations that it operates.

The uses of streamflow data are described, and 

the growth of the stream-gaging program is 

related to legislation and the need to manage the 

Nation's water resources better. The dynamic 

nature of the stream-gaging program is illustrated

by noting the changes in the program from 1981 

through 1986 and from 1985 through 1994.

A brief description is provided of techniques 

for measuring stage and discharge, computing 

streamflow records, and disseminating the data 

through published reports and electronic media. A 

brief history is provided of the nationwide evaluations of the stream-gaging program that were 

undertaken to ensure that the program was keeping abreast of changes in objectives and technology and meeting the needs of the data users. 

Finally, challenges for the future are identified. 

These challenges includemaintaining a long-term 

and consistent data base, upgrading the streamgaging structures and equipment, providing ready 

access of streamflow data to users, and training 

and maintaining a skilled staff to operate the stations in the stream-gaging program.

INTRODUCTION

The growth and development of the United States 

has been dependent on the availability of water 

resources. In colonial times, springs, shallow wells, 

streams, and rainwater collected in cisterns provided 

water for domestic and livestock uses. These supplies 

were subject to the uncertainties of droughts and were 

vulnerable to contamination. Major population centers 

developed along rivers and streams that provided 

water for public supply and transportation. Urban 

growth in the Eastern United States, particularly after 

1800, caused the quality of many city water supplies to 

deteriorate noticeably. Shallow ground-water supplies 

often were contaminated by household privies that 

commonly were located near family wells. Rainwater 

stored in cisterns was subject to contamination by 

accumulations of soot, dust, and street debris that

Introduction 1
collected on roofs and in gutters. The use of water for 

washing streets increased because it was believed that 

the epidemics of yellow fever, typhoid fever, cholera, 

and smallpox were related to the filthy conditions of 

the streets. As a result, early in the 19th century, such 

cities as Boston, New York, and Philadelphia began 

looking for ways to ensure reliable water supplies. 

Development of such supplies required the use of storage reservoirs, aqueducts, and distribution systems.

As the population grew during the 1880's, people 

moved west and away from perennial water supplies. 

The westward expansion also moved population into 

more arid regions of the country where the flow of rivers and streams was much less dependable than in the 

humid East. Dependence on water storage and transmission increased as the distances from reliable water 

sources increased.

During the first two-thirds of the 20th century, 

water planners and managers sought to develop the 

Nation's water resources to meet the growing needs of 

the country. Large reservoirs and aqueducts were constructed to provide water for public supply, industry, 

irrigation, and hydropower; to provide flood control; 

and to foster regional economic development. By the 

1960's and the 1970's, concerns about the environmental effects of large reservoirs, as well as increasing 

construction costs and the scarcity of suitable storage 

sites, curtailed the construction of significant additional reservoir capacity (fig. 1).

The development of data on the flow of the 

Nation's rivers mirrored the development of the country. Increasing need for reliable water supplies quickly 

led to the need for streamflow data with which to

500

400

300

±. 200

100

An acre-foot of water 

covers 1 acre of land 

to a depth of 1 foot

1900 1930 

YEAR

1960 1990

Figure 1. Cumulative reservoir storage in the United States 

(from U.S. Geological Survey, 1990).

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 stream-gaging program of the 

USGS has grown to include (as of 1994) 7,292 continuous-record stream-gaging stations (herein referred to 

as "stations") in the United States, Puerto Rico, and 

the Trust Territories of the Pacific Islands (fig. 2). 

More than 90 percent of these stations are operated 

with at least partial support from other Federal, State, 

and local agencies. This report briefly describes the 

evolution and current status of the stream-gaging program of the USGS, the uses of streamflow data, the 

data-collection process, evaluations of the stream-gaging program, and challenges for the future.

OVERVIEW OF THE STREAM-GAGING 

PROGRAM

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 originally were established for various 

purposes. Because the data from about 4,200 of the 

7,292 stations are telemetered by an earth-satellitebased communications system, those data are available in realtime for many agencies to conduct waterresources projects and for the National Weather Service (NWS) to forecast floods. Data from the active 

stations, as well as from discontinued stations, are 

stored in a computer data base that currently 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. Increasing the length of individual station records is valuable for at least two 

reasons. Additional years of record provide everimproving accuracy of estimates of streamflow characteristics, such as the magnitude of extreme infrequent floods or low flows, and an opportunity 

to determine how streamflow characteristics are

2 Stream-Gaging Program of the U.S. Geological Survey
W 600 

O

W

fc 40° 

DC 

g

i 200

0

-

-

III. 1. Inlllili, .,,!.. ihl.illlnllli Mill

-

-

.din

^ ° ^ ^

STATE OR OTHER POSSESSION

Figure 2. Number of stations operated by the U.S. Geological Survey in 1994, by State or possession.

changing over time due to such causes as agricultural 

practices, urbanization, ground-water development, or 

climate change.

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 (Condes, 1994). Federal funds used for hydrologic data-collection activities of the USGS come from the following primary 

sources: funds made available by Congress to the 

USGS for matching State or local agency offerings 

under the USGS Federal-State Cooperative Program 

(herein referred to as the "Cooperative Program"), 

transfer of funds from other Federal agencies to meet 

their water-resources-data needs, and funds appropriated by Congress and designated specifically for use 

by the USGS for collection of streamflow and waterquality data.

More than 50 percent of the 7,292 stations operated 

by the USGS are funded through the Cooperative Program (fig. 3). Under that program, the USGS provides 

up to 50 percent of the funds, and the State or local 

agency provides the remainder. Currently, more than 

600 State and local agencies participate in the streamgaging 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 water-resources 

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 funded primarily by State or local 

funds are critically important to USGS-funded programs, such as the National Water Quality Assessment 

(NAWQA) Program (Leahy and Thompson, 1994). As

COOP 

4,092

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 3. Number of stations and sources of funds, 1994 

fiscal year.

Overview of the Stream-Gaging Program 3
discussed below, continuous streamflow data are 

essential to water-quality studies. The NAWQA Program could not be conducted without the stations 

funded by the Cooperative Program or other Federal 

agencies.

Because many of the stations are funded from 

multiple sources (Federal, State, and local agencies), 

each agency that participates in funding the streamgaging program has a proprietary interest in the 

activity. State agencies, for example, view the datacollection activities in the Cooperative Program as a 

shared governmental responsibility in which they 

have a large, long-term financial investment and 

vested interest. The investment and the vested interest are carefully guarded, and changes in data-collection activities must be negotiated to mutual satisfaction. As a result of the strong vested interest, changes 

in the way the program is carried out require sensitivity to user reactions, thereby inhibiting unilateral 

action by the USGS.

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.

Data analyses as well as research and 

development of new predictive techniques 

can be accomplished by innumerable public 

or private water-resource agencies, as the 

need arise, if the long-term basic data exists. 

If the data is lacking, no one, including the 

U.S.G.S., can manufacture it. Accordingly, 

this activity must be one of U.S.G.S.'s highest 

priorities [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].

Because interests in and the need for hydrologic 

data varies in time and space, stream-gaging networks are continually changing with time. The 

USGS attempts to balance availability of funding 

support with the needs of all interested parties to 

ensure that essential information is provided to all 

users. Budget constraints at State and Federal levels 

have forced many cooperators to reduce funding support for hydrologic data-collection activities. In some

instances, monitoring activities at a particular site are 

discontinued because the needs of the supporting 

agency have been met. When funding support for a 

monitoring site is withdrawn, the USGS attempts to 

notify all potentially interested agencies of the 

impending changes to allow users of the data an 

opportunity to make alternative arrangements for 

funding the collection of data that are critical to their 

needs.

In the summer of 1994 the USGS learned 

that the California Department of Water 

Resources would be unable to fund their share 

of support for 85 cooperatively-funded stations 

in California. This situation raised considerable 

concern among Federal, State, and local agencies in California. In a letter to the USGS, U.S. 

Senator Barbara Boxer said she understood 

"that a number of California state and county 

agencies, including the Department of Fish and 

Game and the Division of Water Rights are 

dependent upon this long-term, uninterrupted 

data for interpreting and satisfying water 

resource demands....". Senator Boxer went on 

to say that she was "concerned that the loss of 

these stream gaging stations would deal a serious blow to the reliable, science-based management of our water resources.....". Despite 

tight budgetary times throughout the State of 

California, State and local agencies offered 

cooperative funds sufficient to continue streamflow data collection at 73 of the original 85 stations scheduled for closure [James Mullen, 

U.S. Geological Survey, oral commun., January 

1995].

Uses of Streamflow Data

The USGS stream-gaging program provides hydrologic information needed to help define, use, and manage the Nation's water 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 the following:

 Enhancing the public safety by providing data for 

forecasting and managing floods

 Characterizing current water-quality conditions

 Determining input rates of various pollutants into 

lakes, reservoirs, or estuaries

4 Stream-Gaging Program of the U.S. Geological Survey
 Computing the loads of sediment and chemical constituents

 Understanding the biological effects of contamination

 Delineating and managing flood plains

 Operating and designing multipurpose reservoirs

 Setting permit requirements for discharge of treated 

wastewater

 Designing highway bridges and culverts

 Setting minimum flow requirements for meeting 

aquatic life goals

 Monitoring compliance with minimum flow requirements

 Developing or operating recreation facilities

 Scheduling power production

 Designing, operating, and maintaining navigation 

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

 Evaluating surface- and ground-water interaction

 Undertaking scientific studies of long-term 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 or to develop estimates of flow 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, but currently 

unplanned, bridge or reservoir or development of basinwide pollution control plans, are referred to as "data 

for future or long-term needs." Some data, of course, 

fit into both classifications; for example, a station that 

supplies data for flood forecasting and also provides 

data to define long-term trends.

Data for Current Needs

Streamflow data are needed at many sites on a daily 

basis for forecasting flow extremes, making watermanagement 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. 

These needs generally are best satisfied by operating a 

station to produce a continuous record of flow. The 

locations of the stations and the periods of operation 

are dictated by the uses to be made of the data.

More than one-half of the USGS stations provide 

current information (mostly by way of satellite telemetry) to agencies that operate water-resource systems 

and forecast floods. The NWS is charged by law with 

the responsibility of issuing forecasts and warnings of 

floods to the Nation to help save lives and to help mitigate property damage. The NWS uses data from 

USGS stations to forecast river stages and flow conditions on large rivers and their associated tributaries. 

Flood forecasts are issued at about 4,000 locations 

strategically located throughout the Nation. Th? reliability of flood forecasts depends on having reliable 

current data for precipitation and streamflow. The 

USGS collects the streamflow data, and the NVS collects the precipitation data and combines both t; fpes of 

data when making the flood forecasts. The NWS does 

not fund stations, but relies on the data from stations 

operated by the USGS for other agencies.

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 flood" 

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 floods, USGS 

field personnel made more than 2,000 visits to stations 

in the flood-affected 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 and the COE and formed the 

basis for flood forecasts that allowed people to be 

evacuated from areas about to be inundated. Tl e COE 

and local agencies used the streamflow information to 

protect lives and property and to focus flood-fighting 

activities where they were most needed. As a national 

organization, the USGS was able to move staff from 

other offices into the disaster areas. Because th^se 

hydrologists and technicians were already familiar 

with the equipment and procedures, they could begin 

to work immediately upon arrival in the area. This 

same experience with the realtime use of USGS

Overview of the Stream-Gaging Program 5
streamflow data is repeated several times each year as 

catastrophic floods strike various sections of the 

Nation.

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 gaging 

points on the same stream on the basis of drainagearea 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 (mathematical models) 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. An example of a regional relation 

for estimating flood discharges for central Ohio is as 

follows (Koltun and Roberts, 1989):

where

£?50 is the 50-year flood discharge, in cubic feet per

second, that has 1 chance in 50 (0.02 probability)

of being exceeded in any given year; 

A is the drainage area (or size of the watershed), in

square miles;

S is the main-channel slope, in feet per mile; and 

St is the percentage of the watershed occupied by

lakes, ponds, and swamps.

The above equation was computed by using values 

of £5o, A, 5, and St at 180 stations in central Ohio. The 

streamflow characteristic, Q$Q, was computed at each

station by using streamflow records, and tH basin 

characteristics A, 5, and St were measured from topographic maps. To estimate £?50 at an ungaged site, the 

user determines the values of A, 5 and St fcr a specific 

site of interest from a topographic map and1 substitutes 

the values in the above equation. A compilation of 

regional relations for estimating flood discharges (like 

£?5o) for rural and urban streams throughout the United 

States was given by Jennings and others (1994).

Studies of the uncertainties of these regional relations have been used to guide the USGS ard its cooperators in determining how to change the s'ream-gaging program to reduce the uncertainty in estimates of 

streamflow characteristics. These studies permit the 

analyst to evaluate ways of reducing the uncertainty in 

the regional relations by adding new stations with certain ranges of basin characteristics, continuing operation of existing stations, or some combinat: on of both 

approaches (Medina, 1987).

Regardless of the methods used to transfer information, actual streamflow data are required. The stations 

that supply these data must be representative of the 

streams in the region. The data provided serve as the 

basis for defining and calibrating the equations (models) that serve as the transfer mechanism.

A modeling approach does not decrease 

the amount of data required; in fact, it increases 

it. Modeling is not a replacement for observation 

[National Research Council, 1992, p. 14].

Some applications of data require long-tmi records 

to achieve a specified accuracy. The nature1 variation 

that is inherent in the flow of rivers produces uncertainty in estimates of the characteristics of those flows. 

The uncertainty is dependent on the variab; lity of 

streamflow in the region and the length of streamflow 

record; uncertainty decreases as the record length 

increases. This is true no matter what is be;ng discussed; for example, flood characteristics or the longterm average flow of the river. The relation between 

the standard error of estimate (a measure of uncertainty) and the record length for the mean-annual flow 

and the 50-year flood for Minnesota is shovn in figure 

4. If errors are normally distributed, then tH standard 

error of estimate is the error to be expected1 for about 

two-thirds of the streamflow estimates.

The relation in figure 4 shows that given a 20-year 

record at a station, the 50-year flood can be estimated 

for that site with a standard error of about 35 percent. 

As the record length increases, the standard error or 

uncertainty in the 50-year-flood estimate decreases.

6 Stream-Gaging Program of the U.S. Geological Survey
80

60

cc

2 40

20

-i i i i i-

 Mean annual discharge

 50-year flood discharge

10 20 30 40 

LENGTH OF RECORD, IN YEARS

50

Figure 4. Relation between standard error of estimate and 

record length for Minnesota (from Benson and Carter, 

1973).

When streamflow characteristics from stations are 

used to define a regional relation for use at ungaged 

sites, the error in the streamflow characteristics is a 

part of the total error in the regional relation. For 

example, note the scatter around the regional (regression) relation between the 50-year flood and the drainage area for rural streams in eastern Massachusetts 

(Wandle, 1983) (fig. 5). The scatter about the regional 

relation includes the error that results when drainage 

area alone is used to estimate the 50-year flood, as 

well as the error in estimates of the 50-year flood at 

the individual stations. Thus, it is imperative that the 

data used in defining the equations be as accurate as 

possible, and that can be achieved only with long

10,000 c

Q

8i

io 

a:

>- cc

10

1,000

100

10

oo

The data points are the estimated 

50-year floods at the stations. The 

line is from the regression analysis

0.1 1 10 100 

DRAINAGE AREA, IN SQUARE MILES

1,000

Figure 5. Relation between drainage area and 50-year 

flood for small rural streams in eastern Massachusetts (from 

Wandle, 1983).

records. Note in figure 5 that a tenfold increase in 

drainage area results in about a fivefold increase in 

flood size. This is typical for flood characteristics, 

although the specific relation varies with hydrologic 

region.

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 wanning. 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 record^ that 

reflected natural conditions and could be useful in 

trend analysis. They identified 1,659 stations that 

could be used for this purpose in the United States and 

its possessions. The distribution of record lengths for 

these stations is shown in figure 6. More than 500 stations identified by Slack and Landwehr (1992) have 

record lengths in excess of 50 years.

Detection of hydrologic change requires a 

committed, international, long-term effort and 

requires also that the data meet rigorous standards for accuracy [National Research Council, 

1991, p. 220].

Specific Categories of Use

A recent nationwide evaluation of the USGS 

stream-gaging program identified uses of the data for 

individual stations in the program (Thomas and Wahl, 

1993). Between 1983 and 1988, uses of data were 

defined for 6,238 of the approximately 7,000 stations 

then operated by the USGS. Individual stations were 

identified as belonging to one or more of nine categories on the basis of the principal uses made of the data. 

The uses of data were determined through a survey of 

cooperators and other known users of the data. These 

users were recognized as representing only a limited 

sampling of all users of streamflow data. Many other 

organizations and individuals use data from the 

stream-gaging program, but these uses cannot be easily documented. Many times those users (and uses) 

become known only when a station is discontinued.

Overview of the Stream-Gaging Program
70

60

50

40

O

ffi 30

20

10

Note: 1,659 stations 

judged as suitable

III.Illl. .

20 40 60 80 

LENGTH OF RECORD WITH ACCEPTABLE DATA, IN YEARS

100 120

Figure 6. Number of stations and record lengths with acceptable data for studying climate fluctuations (from Slack and Landwehr, 1992).

The station on the Green River at Warren 

Bridge, near Daniel, Wyoming, was started in 

1932. It was funded under the Cooperative Program with the Wyoming State Engineer, but 

because of funding cuts by the Wyoming legislature, it was discontinued, along with several 

other key stations, in 1992. That station, however, was also used by numerous other agencies: Bureau of Reclamation for planning 

reservoir operations downstream, both the 

National Weather Service and the Natural 

Resources Conservation Service in flood and 

water-supply forecasting, several researchers 

for trend studies, and it was identified as part of 

the USGS Hydro-Climatic Data Network by 

Slack and Landwehr (1992). The station was 

restarted in 1994 and is presently funded by the 

Bureau of Reclamation [Joel Schuetz, U.S. Geological Survey, oral commun., January 1995].

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. 

Development of water resources has so altered 

the hydrology of some streams that station data 

at a given point primarily reflects the human 

manipulations. Data from about 4,200 stations 

operated by the USGS are used to understand 

and evaluate the resource, diversions, and return 

flows (water that has been used for some application and is being returned to the stream) that 

must be accounted for. Data from these stations 

also are useful in estimating hydraulic characteristics of aquifers, ground-water recharge, and 

evapotranspiration and in calibrating groundwater models. At State and interstate levels, 

many of the stations serve a key role in the process of allocating and regulating wate^ rights. 

These stations provide data to satisfy current and 

future needs.

I am writing you on behalf of the Misrouri 

River Basin Association, a coalition of eight 

states and twenty-eight Indian Tribes in th? 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 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. Edwarc1 

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. Because they provide 

data that reflect natural conditions, these stations 

serve as the basis for defining the characteristics 

of streamflow and for developing the regional 

relations described in a previous section of this 

report. Data from about 3,800 stations operated 

by the USGS can be used for this punose. 

Designers and planners of water-cont"ol and 

water-related facilities increasingly use the statistical characteristics of streamflow rather than 

the flow for specific periods in the pa~t. For 

example, many highway bridges are designed on

8 Stream-Gaging Program of the U.S. Geological Survey
the basis of the flood that will be exceeded on the 

average of once in 50 or 100 years. Determining 

the appropriate design flood for a highway 

bridge is critical to balancing construction costs 

against risks to human safety and potential damage to property. Using too small a design flood 

can lead to a bridge design that causes water to 

back up and inundate the road itself or property 

along the flood plain upstream from the bridge. 

Too large a design flood can lead to a design that 

is wasteful and requires an unnecessarily wide 

opening, an unnecessarily high roadway, or both. 

By using long-term streamflow records, storage 

reservoirs can be designed on the basis of the 

probability of deficiency of storage to meet given 

discharge rates from storage. The water available 

for dilution of treated wastewater releases or 

other similar purposes may be stated in terms of 

the mean flow or probability of nonexceedance 

of flow magnitudes for periods of a year, season, 

month, week, or day. For example, if estimated 

low flows are understated, then there would be a 

requirement for additional costly wastewater 

treatment to meet water-quality standards. However, if low flows are overstated, then the treatment requirements would lead to unacceptable 

water quality when low flows occur.

Project operation. Data from stations in this classification are used on an ongoing basis to assist 

water managers in making daily operational 

decisions. These decisions include managing 

daily and hourly flows through gates and hydropower penstocks, pumping water into diversion 

systems or hydroelectric reservoirs. They also 

include extensive balancing of uses among multiple sources of water in regional systems, 

including many reservoirs and ground water supplies. Such decisions are a daily reality when 

dealing with water requirements for municipal, 

industrial, and agricultural uses; hydroelectric 

power generation; and space for flood control in 

reservoirs. For example, data from about 2,900 

stations operated by the USGS are used by the 

COE, the BOR, and others to operate more than 

2,000 flood control, navigation, and water-supply reservoirs. Data from stations in this category 

satisfy a current need.

Hydrologic forecasting. Data from stations so classified provide information for flood and watersupply forecasting. These stations play a key role 

in efforts by Federal, State, and local agencies to

protect the lives and welfare of the general public 

through the evacuation of people from areas 

about to be inundated. More than 3,000 of the 

stations operated by the USGS are used in the 

NWS's flood-forecasting system. These data supply an immediate and high-priority current need. 

Because these stations are located at critical 

points on streams, they also generally provide 

valuable information on the statistics of flows 

that will be quite useful for meeting future needs.

Water-quality monitoring. The stations discussed 

in this paper are only a part, albeit the largest 

part, of the USGS hydrologic data-collection 

program. Other program components provide 

data on the chemical quality of water resources, 

sediment in streams and lakes, surface- and 

ground-water resources, and water use (fig. 7). 

Although the various program components are 

funded separately, they are highly interdependent 

and complementary. The programs on water 

quality and sediment provide information on the 

concentrations of chemical constituents in the 

water. The sediment and chemical quality of a 

river is intimately linked to the streamflow. 

Rapid variations in streamflow due to rainfall or 

snowmelt typically are associated with rapid 

variations in sediment or chemical concentrations. Consequently, understanding the movement of sediment and chemicals in a river 

depends on the availability of water samples at 

these times of rapid flow variation. One of the 

ways this is accomplished is to equip the station

Water quality 

17.6

Sediment

3.1 \;

Total 1994 funds for

collection of all types

of data is $128,200,000

Surface water 

62.3

Figure 7. Percentage distribution of funds for U.S. Geological Survey hydrologic data collection, 1994 fiscal year.

Overview of the Stream-Gaging Program
with an automatic pump sampler that is activated 

by a microcomputer programmed to call for samples based on stage, changes in stage, concentrations of chemical constituents, time since the last 

sample, or some combination of the above. 

These automatic sampling systems are vital to 

the study water-quality impacts of urban or agricultural land uses in small watersheds. The stations in this category also provide the flow data 

required to convert concentrations to loads (the 

total amount of the material transported by the 

water). The load transported by the flow is 

needed to understand fully and monitor the 

movement and fate of the material in flowing 

water. The approximately 2,700 stations operated by the USGS that provide discharge data for 

water-quality monitoring are fulfilling a current 

need. However, these data also may fulfill a 

future need if they are used to examine long-term 

trends in water quality or to determine the relative importance of various sources of pollution to 

a water body such as a reservoir, lake or estuary.

The USGS operated a gaging station on the 

Garcia River from 1962 to 1983 as part of their 

cooperative program with the State. A stream 

gaging station on the Garcia River would provide 

essential hydrologic data to properly manage instream gravel mining operations on the Garcia 

River. Significant bedload transport oc-curs only 

during larger runoff events. Prudent management of in-stream mining calls for limiting or curtailing mining during drought years. A stream 

gage operated by the USGS would provide an 

objective record of the yearly flood events. Mining operations would be requested to suspend 

operations in years when the annual flood was 

less than a specified size. Therefore, it is imperative that the data be collected by an impartial 

and respected agency such as the USGS 

[Excerpt from a letter to Senator Barbara Boxer, 

California, from Dennis Jackson, Mendocino 

County Water Agency, Ukiah, California, October 29, 1993, requesting assistance in getting 

the USGS to reestablish a stream-gaging station 

on the Garcia River in Mendocino County].

Planning and design. Data from about 1,100 stations operated by the USGS in this category are 

needed to plan and design a specific project, such 

as a reservoir, levee, water-treatment facility, or 

hydroelectric powerplant. Because these data 

relate to a specific project, they generally are filling a current need.

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 Carswell, 

Jr., Delaware River Master, U.S. Geological 

Survey, oral commun., January 1995].

Research. Data from about 700 stations operated 

by USGS are collected for a particular research 

or water-investigation study. 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 longterm, 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. These stations supply data for uses that do 

not fit into any of the eight categories above. 

These include, for example, recreational purposes, such as providing data for canoeists, 

rafters, and fishermen. Data from about 700 stations operated by the USGS supply a current 

need for water-resource information.

The USGS in New Mexico instituted a directdial telephone number and recording for current 

streamflow information. The "Streamflow Hotline" was established to provide river rafters, fisherman, ranchers and farmers, and other interested parties with a telephone number that they 

could call 24 hours a day to obtain current 

streamflow information on major rivers in New 

Mexico. The hotline is updated daily during the 

spring runoff period, and depending on river 

releases, at least two to three times a week the 

remainder of the year. Calls to the hotline during 

the spring runoff period of April through June 

average about 1,000 per month and about 100 

per month during November through February. 

The number of stations included on the hotline 

has increased to 18 due to requests from individual users and other agencies [John Borland, 

U.S. Geological Survey, oral commun., January 

1995].

10 Stream-Gaging Program of the U.S. Geological Survey
A growing number of stations are used for purposes 

that do not fit readily into one of the above nine categories. Data needed to define instream uses are good 

examples. Instream use refers to water that is used, but 

not withdrawn, from a surface-water source. Instream 

uses can be broadly characterized as streamflows 

required to meet human, ecological, or environmental 

needs. Human needs include recreation, hydroelectric 

power generation, transportation, waste assimilation, 

aesthetics, and cultural-resource preservation. Ecological or environmental needs include fish and wildlife 

habitat, wetlands preservation, freshwater dilution of 

saline estuaries, and maintenance of the riparian zone. 

Thus, these uses cut across most of the nine categories 

discussed above.

Quantitative estimates for most instream uses are 

difficult to compile. However, because such uses compete with offstream uses and affect the quantity and 

quality of water resources for all uses, effective waterresources management requires that methods, definitions, and procedures be devised to enable instream 

uses to be assessed quantitatively. The need to maintain some flow in streams has long been recognized as 

an important requirement for healthy stream ecosystems. In recent years, many court and compact decisions also have recognized the importance of instream 

flows and often have mandated an increase in instream 

flows to meet various environmental, recreational, and 

water-quality needs. Data from stations are critical to 

determine whether mandated instream flows are being 

maintained.

In New Jersey, the USGS operates 25 stations downstream from water-supply reservoirs 

and pumping stations. These station monitor 

whether the streamflow rates are being maintained at or above a permitted minimum flow. 

This minimum passing flow is selected by the 

State in order to protect the ecology of the 

streams and also the water rights of downstream users [Robert Schopp, U.S. Geological 

Survey, oral commun., January 1995].

History and Growth of the Stream-Gaging 

Program

The USGS, which was created in 1879, was authorized in 1894 to survey irrigable lands in arid areas and 

to measure the flow of rivers and streams. As noted in 

an earlier section, the first USGS station was established on the Rio Grande in 1889. In 1895, the first 

Cooperative Program in the Nation began in Kansas

through an agreement with the newly established Kansas Board of Irrigation Survey and Experiment (now 

known as the Division of Water Resources of the Kansas Department of Agriculture). This agreement provided for measurement of streamflow at seven sites to 

ascertain water-supply potential. In 1995, 100 years 

after the inception of the Cooperative Program, the 

USGS operates 166 stations in Kansas, 84 of which 

are operated in cooperation with 10 State, city, or local 

agencies (fig. 8). The other stations are supported by 

either Federal agencies or funds appropriated to the 

USGS.

Virtually every business day in this country 

consulting engineers in the private sector, in 

addition to engineers working at all levels of 

government, rely on the unbiased and objective 

scientific information and data provided... One 

could even argue persuasively that certain 

aspects of the USGS should be strengthened 

and expanded. For instance, in the Federal/ 

State Cooperative Program for Water Data Collection Analysis the critical backbone of the 

nation's essential surface water data gathering 

network....[Excerpt from a letter from Stafford 

E. Thornton, President, American Society of 

Civil Engineers, January 26,1995].

The initial growth of the stream-gaging program 

was slow. At the turn of the century, only 163 stations 

were in operation. Most of the stations were in the 

West and were used to satisfy needs for irrigation. 

Growth of the program after 1900 was more dramatic, 

as shown by the number of active stations in each 

decade from 1900 to 1990 (fig. 9).

The growth and evolution of the USGS stream-gaging program was related to increased concern about 

floods and droughts, the increased use of water for irrigation and hydroelectric power, and specific legislative acts. The Federal Power Act was passed in 1920; 

during the next 20 to 30 years, planning for hydroelectric power development caused increased need for 

data. Congress passed legislation in 1929 that officially recognized the Cooperative Program in which 

costs are shared with State and local agencies, and in 

the ensuing years, cooperative stream-gaging programs were established with many State and local 

agencies. Also, the severe midcontinent drought in the 

early 1930's and the floods in 1936-37 in the Ohio 

and the Potomac River Basins increased the awareness 

among Federal, State, and local agencies that management of the water resources requires comprehensive, 

reliable streamflow data.

Overview of the Stream-Gaging Program 11
ft=^*£h^te^

Base from U.S. Environmental Protection Agency digital data,1:500,000,1982,

and Kansas Geological Survey digital data, 1:24,000,1992 

Lambert Conformal Conic projection 

Standard parallels 33° and 45°

0 20 40 60 MILES 

0 20 40 60 KILOMETERS

EXPLANATION

Complete-record station 

and funding source

Cooperative

Other Federal agencies

Federal

More than one of 

the above sources

> Boundary of drainage basin

Figure 8. Areal distribution of stations for Kansas, by funding source.

10,000

8,000

6,000

O 

rr

m 4,000

2,000

LENGTH OF RECORD

Greater than or equal to 50 years 

I Greater than 20 and less than 50 years 

Less than or equal to 20 years

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 

YEAR

Figure 9. Number of stations in the U.S. Geological Survey 

database, 1900-90.

Passage of the Watershed Protection and Flood Prevention Act of 1954 and construction of the interstate 

highway system in the 1960's increased the need for 

streamflow data for small watersheds. Some of this 

need was provided by partial-record stations that 

recorded data only for flood peaks, but the numbers of 

continuous-record stations also increased. The need 

for data at the thousands of points where the highway 

systems crossed streams created an immediate need 

for methods to estimate flood magnitudes at ungaged 

sites. This need was satisfied by streamflow data to 

calibrate the regional equations used to make those 

estimates. The National Flood Insurance Act of 1968 

increased emphasis on flood-plain mapping and 

emphasized the need for reliable flood-frequency data.

The Surface Mining and Control and Reclamation 

Act of 1977 also increased the need for data on 

streams affected by surface mining and other energy 

development. However, the additional stations

12 Stream-Gaging Program of the U.S. Geological Survey
constructed in the 1970's generally were offset by 

reductions in other areas of the network. Reevaluation 

of the program in the early 1970's (Benson and Carter, 

1973), the beginning of stringent financial constraints 

on the parties to the program, and the completion of 

many water-development projects were factors in limiting expansion of the program.

The major factors that have affected trends in the 

network since the late 1970's appear to be related to 

economic concerns and energy programs. In the 

1970's, the oil crises gave impetus to a large expansion of research in coal and oil shale as sources of 

energy. Definition of the effects of such energy development on streamflow and water quality required 

streamflow data. Numerous stations were installed to 

provide those data. As concern for energy sources 

waned in the early 1980's, many of those stations were 

discontinued.

In 1987, a poll was made of USGS offices to identify stations discontinued or started from 1981 to 1986. 

This poll was taken in response to NWS concerns that 

the number of stations in the USGS stream-gaging 

program was declining. Between 1981 and 1986, 873 

stations were added, but 1,744 stations were discontinued; thus, there was a net loss of 871 stations from the 

program. This illustrates the complexity of change; 

stations that were added and then deleted during the 

period (125) were not counted in this poll.

A more recent poll of USGS offices in Delaware, 

Georgia, Iowa, Idaho, Maryland, Michigan, Oklahoma, and South Dakota showed little net change in 

numbers of stations between 1985 and 1994. These 

States, which were selected as a representative sample, 

had 832 stations at the beginning of the period. During 

the period, 189 stations were added, and 170 were 

dropped; this represents about a 20-percent turnover 

rate in 10 years. An additional 29 stations were started 

and dropped. Of the stations that were dropped, record 

lengths were more than 20 years at 97 stations and 

more than 40 years at 30 stations.

DATA-COLLECTION PROCESS

The basic piece of data obtained at a station is the 

stage, which is the height of the water surface above a 

reference elevation. If the stage of the streambed is 

known and is subtracted from the water-surface stage, 

then the result is the depth of water in the stream. 

Although stage of a stream is useful in itself in planning uses of flood plains, most users of streamflow

data need to know the discharge of the stream. Discharge is defined as the volume of flow passing a 

specified point in a given interval of time and includes 

the volume of the water and any sediment or other solids that may be dissolved or mixed with the water. The 

units of discharge usually are measured in cubic feet 

per second (or cubic meters per second, if metric units 

are used). Discharge is derived from the stage data 

through the use of a relation between stage and discharge. The stage-discharge relation for a specific 

stream location is defined from periodic discharge 

measurements made at known stages.

Standard methods of data collection are used as 

described by Rantz and others (1982) and in the publication series Techniques of Water-Resources Investigations of the U.S. Geological Survey. Those methods 

are briefly described in the following sections.

Measuring Stage

Perhaps the most common method of measuring the 

stage of a river is through the use of a stilling well. 

Stilling wells are located on the bank of a stream or on 

a bridge pier and are topped by a shelter that holds 

recorders and other instruments associated with the 

station. The well is connected to the stream by several 

intakes such that when the water level changes in the 

stream, the level simultaneously changes in the well 

(fig. 10). Thus, the water surface in the well is mainFigure 10. Schematic of a stilling well and shelter.

Data-Collection Process 13
tained at the same level (stage) as the water surface in 

the stream. The well damps out the momentary fluctuations in the water surface in the stream due to waves 

and surging action that may be present in the river. An 

outside reference gage, typically a graduated staff 

gage, is read periodically to verify that the water level 

in the well is indeed the same as the water level in the 

stream and that the intakes are not plugged. As the 

water level in the well rises or falls, a float in the well 

also rises or falls. A graduated tape or beaded cable 

attached to the float and with a counterweight on the 

other end is hung over a pulley. This pulley drives a 

recording device. Historically, the recording device 

would have used a pen that recorded a graph of the 

river stage as it changed with time. Graphic recorders 

are still in use; today, however, the stage is more commonly recorded on a punched paper tape or an electronic recorder or is transmitted to the office by means 

of satellite.

In many cases, stilling wells are impractical 

because of difficulties either in installation or operation. Stations that use a bubbler system are an alternative because the shelter and recorders can be located 

hundreds of feet from the stream. In a bubbler system, 

an orifice is attached securely below the water surface 

and connected to the instrumentation by a length of 

tubing. Pressurized gas (usually nitrogen or air) is 

forced through the tubing and out the orifice. Because 

the pressure in the tubing is a function of the depth of 

water over the orifice, a change in the stage of the river 

produces a corresponding change in pressure in the 

tubing. Changes in the pressure in the tubing are 

recorded and are converted to a record of the river 

stage.

Measuring Discharge

The most practical method of measuring the discharge of a stream is through the velocity-area 

method. This method requires the physical measurement of the cross-sectional area and the velocity of the 

flowing water. Discharge is determined as the product 

of the area times the velocity. Velocity is measured by 

using a current meter. The meter consists of a propeller that is rotated by the action of flowing water. The 

rotation depends on the velocity of the water passing 

by the propeller. With each complete rotation, an electrical circuit is completed and recorded in some fashion. Given the number of revolutions in a given time

interval, velocity can be determined for the location of 

the current meter.

Measuring the average velocity of an entire cross 

section is impractical, so the method uses an incremental method. The width of the stream is divided into 

a number of increments; the size of the increments 

depends on the depth and velocity of the stream. The 

purpose is to divide the section into about 25 increments with approximately equal discharges. For each 

incremental width, the stream depth and average 

velocity of flow are measured. For each incremental 

width, the meter is placed at a depth where average 

velocity is expected to occur. That depth has been 

determined to be about 0.6 of the distance from the 

water surface to the streambed when depths are shallow. When depths are large, the average velocity is 

best represented by averaging velocity readings at 0.2

Current meter and weight suspended from a bridge crane.

14 Stream-Gaging Program of the U.S. Geological Survey
Wading rod and current meter used for measuring the discharge of a river.

Crane, current meter, and weight used for measuring the 

discharge of a river from a bridge.

way, the reel is mounted in a cable car suspended from 

the cableway that crosses the river. The basic procedure of measuring width and velocity is the same, 

however, whether the measurement is made by wading 

or from a cableway or bridge. The USGS makes more 

than 60,000 discharge measurements each year. The 

distribution of measurements made in 1993 is shown 

in figure 11.

and 0.8 of the distance from the water surface to the 

streambed. The product of the width, depth, and velocity of the section is the discharge through that increment of the cross section. The total of the incremental 

section discharges equals the discharge of the river.

When the stage is low and the stream can be waded, 

the measurements are made by wading with the current meter mounted on a wading rod. The meter is 

positioned at the appropriate depth on the wading rod, 

which also is used to measure the water depth. If the 

water is too deep for wading, then the measurement is 

made either from a bridge or cableway across the 

stream. If the measurement is made from a bridge or 

cableway, then the meter is suspended on a thin cable 

wound on a reel. A torpedo-shaped weight is attached 

below the meter to permit it to be lowered into the 

water and to hold it in position once submerged. If 

measuring from a bridge, then the reel is mounted on a 

wheeled frame (or crane) that permits the lowering of 

the meter assembly over the bridge rail; from a cableDetermining a Continuous Record of 

Discharge

Measurements made over the range in stage of the 

stream are plotted against the corresponding stages to 

define the stage-discharge relation that is used in conjunction with the recorded stage record to determine 

the discharges throughout the year. The procedure 

would be fairly straightforward were it not for all the 

natural processes that occur in streams. Flowing water 

moves sediment and other material that if eroded from 

or deposited on the streambed or banks, can alter the 

cross-sectional area of the stream at a given stage. 

Growth of vegetation along the banks and aquatic 

growth in the channel itself can impede the velocity, as 

can deposition of downed trees in the channel. Processes like these will alter the stage-discharge relations and are characteristic of most streams. In addition, ice and snow can produce large changes in stageData-Collection Process 15
5,000

4,000

3,000

2,000

1,000 ill illLlllll.ll.il

Figure

STATE OR OTHER POSSESSION

11. Discharge measurements made in 1993, by State or possession.

discharge realtions, and the degree of change can vary 

dramatically with time.

The stage-discharge relation will be stable if the 

hydraulic characteristics of the general reach of stream 

are unchanging and the bed material does not move 

appreciably. On a stable stream, periodic measurements are made every 6 to 8 weeks to verify that the 

relation has not undergone some unrecognized change. 

The stage-discharge relation will be unstable, changing with time and with the flow conditions, if the streambed or the hydraulic roughness is changing (as 

might occur with a sand-bed stream). In such cases, 

frequent measurements (about weekly) are needed to 

define how the rating is changing and to define its 

present condition (fig. 12).

Sometimes, current-meter measurements are not 

possible during large floods. However, the stage and 

discharge of those floods are essential in defining the

10

O Measurements since October 1,1993

+ Measurements before October 1,1993

 Present relation

' Prior relation

1

1,000

Note: Present relation

began October 1,1993

10,000 

DISCHARGE, IN CUBIC FEET PER SECOND

20,000

Figure 12. Sections of stage-discharge relations for the 

Colorado River at the Colorado-Utah State line.

rating for the range of flow. Therefore, the discharge is 

determined indirectly by surveying the high-water 

marks left by the flood and by using hydraulic formulas to calculate the discharge for the peak stage.

Because the relation between stage and discharge 

may vary with time, the discharge is known only with 

certainty at the time of discharge measurements. If the 

relation is changing, then judgement must be used to 

determine the most probable status of the stage-discharge relation for times between discharge measurements. In fact, changes in the stage-discharge relation 

may not be evident until a whole series of measurements are available for analysis. Therefore, the computational process usually goes through the following 

steps:

1. Following a measurement, a preliminary evaluation 

is made of the degree to which the stage-discharge relation has changed on the basis of measurements made up to that time. Provisional 

discharges are determined, assuming that the 

most recent measurements define the channel 

condition.

2. This process is repeated following each measurement. However, with each measurement, more 

measurements are available to evaluate the stagedischarge relation. This may lead to changes in 

the provisional discharges that had been computed for previous months.

3. At the end of the year, all measurements are available for review. The entire set of measurements 

are used to reevaluate the rating conditions for 

the year. Final decisions are made about the 

stage-discharge relation that were in effect

16 Stream-Gaging Program of the U.S. Geological Survey
during the year and the record is refined or 

recomputed as necessary. This record is then 

passed through a rigorous review process and, 

once approved, the data are considered final and 

are placed in the archives and published.

Data Collected by Other Agencies

Other agencies, most notably State agencies, collect 

some streamflow data, as do a number of cities, local 

governments, and other Federal agencies. The primary 

differences between the USGS networks and those of 

the other agencies are the purposes for which the data 

are collected. Other agencies, whether they are Federal, State, or local, often collect only those parts of 

the data needed for a specific mission or task. For 

example, data collected by other agencies to fulfill 

permitting requirements associated with wastewater or 

treated water commonly do not include the full range 

of flows. These data, while vital for that specific mission, generally have little transfer value and are, therefore, of limited value in addressing issues of national 

and regional scope (Hren and others, 1987; Childress 

and others, 1989). Consequently, these data are not 

usually placed in accessible archives and made readily 

available to others.

Some data collected by other agencies, however, 

have value beyond the specific purpose for which the 

data were collected. Data from stations operated by 

other agencies are reviewed by the USGS, published 

in the annual State Water Data Reports series compiled by the USGS and entered in the USGS data base 

(see fig. 9). In 1990, data from about 400 stations were 

provided to the USGS by other agencies.

Dissemination of Data

Currently, daily-discharge data are published on a 

water-year basis for each State in the USGS report 

series Water Resources Data [State Name]. A water 

year is the 12-month period from 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. The present report series, in which the data 

are released on a state-boundary basis, began with the 

1971 water year.

Before the introduction of the present publ; nation 

series, water-resources data were published ir USGS 

Water-Supply Papers. Before September 1960, data 

for each major river basin were published in annual 

Water-Supply Papers. From 1961 through 1970, the 

data for the major river basins were published in 5- 

year summaries.

Many streamflow-data users must make operational 

decisions daily. For these users, streamflow records 

are computed and made available on a provisional 

basis. Today, more than one-half of the currently operating stations have equipment that permits immediate 

transmission of data by means of satellite from the 

data-collection site. By using the telemetry, d^ta are 

transmitted around the clock by means of twc geostationary operations environmental satellites (GOES) 

that are positioned above the Earth at an altitude 

22,300 miles above the Equator over the eastern 

Pacific Ocean and Brazil. The satellites are operated 

by the National Oceanic and Atmospheric Ad ministration. These data then are retransmitted by means of a 

domestic satellite, and the resulting signal is received 

by the USGS and other users (fig. 13). The transmission and receipt of the signals are automated, as are the 

provisional discharge computations that are available 

for meeting current data needs.

Automated telemetry provides the water-data users 

with provisional stage and discharge information in a 

timeframe that meets water-management needs. This 

technology permits the USGS field offices to monitor 

the operation of the hydrologic stations contir'iously, 

time visits to stations to coincide with times cf maximum need for data (such as during floods), ard to service equipment at the stations.

In northeastern New Jersey, the USGS 

operates 18 satellite data transmitters at stations as a part of the Passaic Flood Warning 

System. The Passaic River Basin is one of tM 

most flood-prone basins in the United States 

with an estimated annual average flood damage of 84 million dollars [Robert Schopp, U.r 

Geological Survey, oral commun., January 

1995].

In addition to the published record, the data collected by the USGS are archived in the National Water 

Data Storage and Retrieval System, which is a computerized data base widely known by the acronym 

WATSTORE (Hutchinson, 1975). The WATSTORE 

system contains the data and a number of programs 

that can be used to analyze and produce statistical 

summaries of the data contained therein.

Data-Collection Process 17
GOES DOMSAT

Hydrologic Stations

User operations

Wallops, Virginia,

Command and

Data Acquisition Center

Figure 13. Schematic of the data flow for realtime operations.

Beginning with the 1990 water year, Water Data 

Reports also are available on Compact Disk-Read 

Only Memory (CD-ROM). The Water-Supply Papers, 

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. The USGS 

currently is 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. The USGS 

"Home Page" on the World Wide Web is

http://www.usgs.gov.

EVALUATING THE PROGRAM

The stream-gaging program of the USGS is continually changing because the needs for data and the abilities of the many entities to fund their components of 

the program are changing. Any activity of long standing needs to be reexamined periodically to verify that 

the program is keeping abreast of changes in objectives, technology, and (or) external constraints. This is 

especially true for the national stream-gaging program 

because it also is an aggregation of many local or 

regional programs that have a variety of primary 

objectives.

The USGS has a long history of analyzing and evaluating the stream-gaging program. The first known 

nationwide review of the stream-gaging program was 

conducted between 1953 and 1958. The purpose of the 

review was to design a hydrologic network of stations 

in accordance with principles described by Langbein 

(1954). During this review, stations were classified 

according to the primary uses of the data as either 

water management or hydrologic network (regional 

hydrology). Within the hydrologic network, the concept of primary and secondary stations was developed. 

The primary stations were used for long-tern sampling of streamflow, and the secondary stations, which 

were operated for 5 to 10 years, were used to obtain 

geographic coverage of streamflow characteristics. 

Estimation of long-term statistics at the secondary stations was based on the correlation of monthly flows 

with the long-term primary stations. Recommendations were made for improving the stream-gaging program.

The second national study of the streamf ow datacollection program was conducted in 1969-70. The 

stations were classified on the basis of the principal 

uses of data as providing data for current us~. (water 

management), planning and design (regional hydrology), and defining long-term trends and the stream 

environment. The goals of the program for planning 

and design data were to provide informatior that is

18 Stream-Gaging Program of the U.S. Geological Survey
equivalent to 25 years of record for principal streams 

(which drain 500 square miles or more) and 10 years 

for minor streams (which drain less than 500 square 

miles) (Carter and Benson, 1969). These data were to 

be provided by either a gaged record or equations that 

relate streamflow characteristics to basin characteristics. In general, these goals were met only in the 

humid Eastern United States. The results are described 

in a series of statewide reports entitled "A Proposed 

Streamflow Program for [State Name]." A summary of 

the nationwide study, including recommendations for 

improving the program, is provided by Benson and 

Carter (1973).

The most recent nationwide evaluation was conducted during the mid-1980's to define the cost effectiveness of the operation of the stream-gaging program 

(Thomas and Wahl, 1993). The objective of the 

nationwide study was to define and document the most 

cost-effective methods of furnishing streamflow information. The study involved the following phases: an 

analysis of the data uses and availability and documentation of the sources of funding for each station; 

an evaluation of the utility of using less costly alternative methods, such as hydrologic-flowrouting models 

and statistical methods, to provide the needed streamflow information; and an analysis of the cost-effective 

operation of the stream-gaging program that relates 

the accuracy of the streamflow records to various 

operating budgets. A prototype study for the nationwide analysis was described by Fontaine and others 

(1984). Statewide analyses were performed by hydrologists in the USGS State Offices. The reports that 

described the analyses for the individual States were 

summarized and referenced in Thomas and Wahl 

(1993).

The results of the poll on data uses are summarized 

in figures 14 and 15. The categories were described 

earlier in this report in the section on "Uses of Streamflow Data." The percentages in figure 14 total more 

than 100 percent because data uses for a given station 

may be included in more than one category.

Although stations usually are established for a specific reason, the data collected are useful for many 

purposes. On average, there are more than two categories of data use per station. The uses of data from only 

about 20 percent of the stations fall into a single datause category. The greatest number of the stations in 

only a single data-use category are in regional hydrology (34.4 percent) and hydrologic systems (30.2 percent). More than 1,500 stations (25 percent) have four 

or more data-use categories.

Other

Research

Legal obligations

< Planning and design

Data from most

stations are used

in 2 or more categorier

Water quality

Forecasting

Project operation

Regional hydrology

Hydrologic systems

10 20 30 40 50 

PERCENTAGE OF STATIONS

60

Figure 14. Percentages of stations by category of use 

(from Thomas and Wahl, 1993).

The nationwide analysis documented that multiple 

uses were being made of data collected at stations in 

the stream-gaging program, simulated flows from 

hydrologic -flow-routing models and statistical methods generally were not of sufficient accuracy for most 

uses, and the program was being operated in an efficient and cost-effective manner (Thomas and Wahl, 

1993). Network analyses and program evaluation will 

continue to play a prominent role in the management 

of the program. Future directions will likely involve 

the development of techniques for a more coordinated 

analysis of water-quality, ground- water, and streamflow networks.

Data from 80 percent of stations are 

used in 2 or more categories

40

30

20

10

012345678 

NUMBER OF CATEGORIES IN WHICH DATA ARE USED

Figure 15. Distribution of stations as a function of the number of data-use categories (from Thomas and Wah1 .1993).

Evaluating the Prog-am 19
The existing data networks should be 

viewed by hydrologic scientists as opportunities 

upon which they can build. To optimize these 

opportunities, it is first necessary to define the 

characteristics of the data sets that hydrologic 

scientists need. These characteristics include 

the variables to be measured and the locations, 

frequencies, durations, and accuracies of the 

measurements. They should be derived from 

knowledge about the hydrologic phenomena to 

be explored and from the hypotheses to be 

tested [National Research Council, 1991, 

p. 221].

CHALLENGES FOR THE FUTURE

As we approach the 21st century, the limited water 

supply and established water storage and distribution 

systems must be managed effectively to meet increasing demands. Evidence abounds, however, that the era 

of building large dams and conveyance systems has 

ended. Thus, "new" future supplies likely will come 

from conservation, reuse, and improved water-use 

efficiency rather than from ambitious water-supply 

projects. The Governors of the Western States issued a 

policy statement that called for sharply enhanced efficiency in water use; and the President signed into law 

the Energy Policy Act of 1992 (Public Law 102^86), 

which calls for government agencies to take the lead in 

water-use efficiency measures and sets new standards 

for water-conserving plumbing fixtures. A supply that 

has ecological and economic limits cannot be continuously expanded to try to meet insatiable demands. 

Comprehensive streamflow data are needed to account 

for the water in the Nation's hydrologic systems and to 

quantify the stress on existing supplies. Just as managers needed supply information during the dam-building era, they now need more comprehensive streamflow data to assess the effectiveness of various 

management options and to monitor mandated 

instream flows.

Water management will be increasingly 

looking for flexible policies which can quickly 

adapt to a variable climate. Such policies 

require comprehensive monitoring of changing 

drought conditions to provide lead-time to water 

managers [National Science Foundation, 

1990].

Perhaps the biggest challenge that confronts the 

stream-gaging program, and indeed of the hydrologic 

community, is that of maintaining long-term and consistent nationwide data sets. Agreement is widespread

about the need for such data sets. Because of the manner in which the data program is funded, th Q- networks 

of stations are dynamic. Interest in and the need for 

hydrologic information vary in time and space. This 

variation of interest, coupled with the budget limitations, means that all needs simply cannot b*. met. In 

some instances, monitoring activities at a particular 

site are discontinued because the needs of the supporting agencies have been met. In other cases, even 

though the needs have not yet been met, bu-iget allocations dictate reductions for hydrologic data-collection 

activities. Since the late 1960's, reductions have been 

sharp in the number of stations that provide data that 

are appropriate for studies of climate variability (fig. 

16). This is but one striking example of how budget 

constraints have caused a reduction in the availability 

of the streamflow data needed to address an important 

current issue.

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. Of particular concern is the need to 

maintain the length and continuity of the h/drologic data record, because interruptions in data 

collection can cause extreme hydrologica1 

events to go unrecorded" [From American Society of Civil Engineers Policy Statement on Surface-Water Data Collection, October 24,1993].

550 -

350 -

150 -

1870 1990

Figure 16. Number of stations in a given year Hth acceptable data for studying climate fluctuations (from Slack and 

Landwehr, 1992).

20 Stream-Gaging Program of the U.S. Geological Survey
Despite the increasingly recognized importance of data records of long duration, only a 

few dedicated research organizations have successfully maintained high-quality data collection 

efforts over periods of 50 to 200 years. Furthermore, these organizations have experienced difficulty in committing limited research monies 

year after year to an activity that is frequently 

termed "monitoring," often with pejorative overtones [National Research Council, 1991, p. 222].

Maintaining the stations and equipment needed to 

gage the Nation's streams also will pose a large challenge for the future. Of the 7,292 stations in operation 

in 1994, many have been inplace for more than 20 

years. Because of the streamside locations, the stations 

and cableways, as well as the associated recorders and 

equipment, require significant amounts of upkeep. In 

addition, the changes in technology related to waterlevel sensors and data recorders in recent years have 

been phenomenal. Replacing existing sensors and 

recorders with equipment based on the newer technology will not only be costly, but will require fundamental changes in modes of operation. Past improvements 

in sensors and recorders have increased the reliability 

of the streamflow records (Thomas and Wahl, 1993) 

and decreased the frequency of visits to the station for 

equipment repair. Further improvements in technology 

should result in savings in labor required to operate the 

stream-gaging program and improved accuracy of 

streamflow records. For example, the use of satellite 

telemetry or cellular phone technology provides 

USGS staff with knowledge of equipment failure and 

unusual flow conditions so that costly field visits can 

be scheduled when they are most needed, thereby 

reducing the average number of visits to the station.

One of the most pressing and immediate challenges 

relates to the mechanisms for releasing interim data. 

Traditionally, the stream-gaging program has been oriented towards producing data to be placed in the 

archives for use in future analyses. Those persons or 

agencies with an immediate need for data generally 

participated in the collection of the data and, therefore, 

had ready access to the interim data. With the advent 

of data transmission by means of satellites, the needs 

for and uses of realtime data have significantly 

increased. Forecasters and managers now rely on 

interim data received in near realtime to make operational decisions. The data upon which those decisions 

are based must be the best that can possibly be produced in a short timeframe.

A related problem is that of access to the archived 

data. Historically, data have been archived in the 

WATSTORE data base. It evolved from the computer

technology of 20 to 30 years ago and was designed initially for experienced users of the data base. Irferest in 

and need for access to that data base is much broader 

than is possible through the WATSTORE sys*a,m and 

technology. As noted earlier, the USGS will soon 

make the data accessible by means of Internet. When 

that is accomplished, many potential users woMld have 

ready access to the archived data.

The immediate, unrefined products of 

observation and experimentation are scientif'c 

data. These are obviously available to those 

who collect them, but their primary value is 

often realized by others at a later date and in a 

quite different scientific context. For hydrolodc 

science to move forward it is essential that d^ta 

sets, once acquired, be properly identified and 

described...be catalogued and archived (including archival maintenance), and be made ava:|- 

able to the scientific community at reasonable 

cost and effort [National Research Council, 

1991, p. 310].

Finally, operation of the stream-gaging program is 

dependent on a committed and talented staff of 

hydrologic technicians who maintain and sendee the 

gages, make the measurements that define the rating 

curves, and compute the discharges that compose the 

data base. Maintaining and training the skilled staff 

necessary to do these tasks will be one of the largest 

challenges

In the history of the hydrologic sciences as 

in other sciences, most of the significant 

advances have resulted from new measurements. Yet today there is schism between dr*a 

collectors and analysts. The pioneers of modern hydrology were active observers and measurers, yet now designing and executing data 

programs, as distinct from experiments carried 

out in a field setting with a specific research 

question in mind, are too often viewed as mundane or routine. It is therefore difficult for agencies and individuals to be doggedly persisted 

about the continuity of high-quality hydrologic 

data sets. In the excitement about glamorous 

scientific and social issues, the scientific community tends to allow data-collection programs 

to erode [National Research Council, 1991, p. 

214].

The USGS continues to be committed to 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.

Challenges for the FiT'ire 21
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Carter, R.W., and Benson, M.A., 1969, Concepts for the 

design of stream-flow data programs: U.S. Geological Survey open-file report, 20 p.

Childress, C.J.O., Chancy, T.H., Myers, D.N., Norris,

J.M., and Hren, Janet, 1989, Evaluation of 1984 field 

and laboratory quality assurance practices, Phase 2 

of Water-quality data-collection activities in Colorado and Ohio: U.S. Geological Survey WaterSupply Paper 2295-B, 49 p.

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22 Stream-Gaging Program of the U.S. Geological Survey *U.S. G.P.O.:1995-387-030:75