Figure 1. Stream-gaging station at Ashuelot River in West Swanzey, N.H.

USGS Fact Sheet 050-03

June 2003

NEW HAMPSHIRE’S STREAM-GAGING NETWORK: 

STATUS AND FUTURE NEEDS

U.S. Geological Survey

U.S. Department of Interior

INTRODUCTION

The U.S. Geological Survey 

(USGS), in cooperation with local, 

State, and Federal agencies, operates a 

network of 50 continuously recording 

stream-gaging stations in New Hampshire (fig. 1). Accurate and unbiased 

information provided by these USGS 

stations on the amount of water in rivers, streams, lakes, and reservoirs in 

New Hampshire is essential to safeguarding lives and property, monitoring and managing water resources, and 

understanding the effects of climate 

and land-use change on hydrology.

What is a Stream-gaging Station?

A stream-gaging station is a 

device (fig. 2) along a river or stream 

that measures the stage or watersurface elevation of the river. Equipment at the stream-gaging station automatically measures and records the 

stage every 15 minutes. The stage then 

is converted to streamflow (defined 

here as the volume of the water in cubic 

feet passing the site every second) 

based on the relation between stage and 

streamflow. This relation is developed 

and maintained for accuracy by USGS 

personnel by measuring the flow of a 

river directly at each station with a flow 

meter at various stages throughout the 

year. Because of ice cover and changes 

in riverbed form, roughness, and vegetation, the relation between stage and 

streamflow is changing continually and 

direct measurements are made frequently.

At some stations—called partialrecord stream-gaging stations—continuous streamflow data are not collected, 

only streamflow information, such as 

peak- or low-flow data, are collected.

History of Measuring Streamflow 

in New Hampshire

The earliest known systematic 

collection of surface-water data in 

New Hampshire began in 1886 on the 

Pemigewasset River at Plymouth, by 

the Proprietors of Locks and Canals at 

Lowell, Mass. In August of 1900, the 

USGS began collecting flow data on 

the Connecticut River at Orford. By 

1903, surface-water data collection had 

begun on the Merrimack River at Franklin Junction, and on the Contoocook 

River at West Hopkinton. Flooding in 

1927, 1936, and 1938, along with interest in the development of reservoirs, 

led to the expansion of the streamgaging network to 32 stations by 1939. 

Through the years, the network has 

evolved as Federal and State interests 

in surface-water resources and funds 

for operating the network have 

increased.

Currently (2002), the streamgaging network consists of 50 continuously recording stream-gaging stations 

(1 is a lake station) and 5 partial-record 

stations. Stage data from New Hampshire stations are sent by satellite to 

USGS computers once every 4 hours, 

and more frequently at times of flooding. Many Federal, State, and local 

agencies and industries rely on these 

satellite-transmitted real-time data for 

disaster response and daily operations. 

These data are available on the World 

Wide Web at http://nh.water.usgs.gov

and are accessed regularly by many 
data users. Approximately 13,000 

pages of New Hampshire real-time 

streamflow data are requested through 

the Web site each month. Historical 

data from active and discontinued stations also are available on the Web site 

and daily mean streamflow data are 

published annually in printed reports.

Stream-gaging stations are distributed across New Hampshire (fig. 1) 

providing sufficient spatial coverage of 

the State’s waterways. Various stream 

types are represented by the network−

from steep, mountainous streams to 

low gradient, meandering streams; 

from free-flowing streams to streams 

with sufficient reservoir storage to 

moderate the effects of flooding; and 

from small brooks to large rivers. The 

drainage-basin size upstream from stations varies from 3.6 to 5,493 square 

miles. 

There are some gaps in the basin 

characteristics represented by the 

stream-gaging network as shown in 

figure 3. For example, few sites have a 

drainage area of 15-35 square miles 

and most are greater than 35 square 

miles (fig. 3a). There are few stations 

with drainage basins in an urban setting 

(fig. 3b). Mean basin elevation and 

mean basin stream slope data appear to 

be adequately represented considering 

the ranges applicable to New Hampshire (figs. 3c and d). There also are 

few sites representing mean annual 

basin precipitation greater than 

50 inches (fig. 3e). 

The USGS has operated most of 

the stream-gaging network in New 

Hampshire, in cooperation with multiple organizations, to ensure uniform 

costs, consistency of data collection 

and analysis, quality control, and wide 

availability of resultant databases. 

Funding for a stream-gaging station 

typically is shared between the USGS 

and a cooperator(s) in proportion to the 

extent of Federal interests relative to 

those of the cooperating agencies, and 

may range from full USGS funding to 

full funding by the cooperator. In particular, the U.S. Army Corps of 

Engineers (USACE) and the New 

Hampshire Department of Environmental Services (NHDES) have been 

major cooperators in the operation of 

the network (fig. 4).

In 2002, the annual operating 

cost of a full-time, continuously 

recording stream-gaging station with 

satellite telemetry was $11,300. The 

entire New Hampshire network cost 

was approximately $570,000 in 2002, 

which includes operating the stations, 

maintaining the data systems, and disseminating the data.

Individual stations in the network have been installed and funded 

for specific purposes such as flood 

forecasting and warnings, flood-control 

operations, operation of lakes and reservoirs, water allocation, monitoring of 

streamflow withdrawals, and waterquality management, including the 

maintenance of instream flows. The 

collection of flow records for more 

than 10 or 20 years also is necessary to 

assess water resources, the flowfrequency characteristics of streams, 

and trends in basin yield.

The streamflow data-collection 

network in New Hampshire has 

evolved in response to a diverse range 

of needs during the past 100 years; 

therefore, the effectiveness of the 

network in meeting current and anticipated future data needs must be 

Base from U.S. Geological Survey

Digital line graphs, 1:24,000 or

1:25,000 scale, 1983

72 ̊

71 ̊ 45 ̊

44 ̊

43 ̊

MAINE

VERMONT

CANADA

NEW HAMPSHIRE

EXPLANATION

 Stream-gaging

 station 

MASSACHUSETTS

0 30 MILES

0 30 KILOMETERS

Contoocook R

Merrimack R.

Lake

C

Winnipesaukee onnecticut R.

Pemigewasset R.

Nubanusit Brk.

Keene

Salem

Rochester

Orford

Franklin 

Plymouth

Peterborough

Figure 2. Distribution of active, continuousrecording stream-gaging stations in New 

Hampshire.

EXPLANATION

 One stream-gaging station

36 38 42 46 50 52 58 60

MEAN ANNUAL BASIN PRECIPITATION, IN INCHES

40 44 48 54 56

0 10 20 30 40 50 60 70 80 90 100

PERCENTAGE OF BASIN AREA IN URBAN LAND USE

1 10 100 1,000 10,000

DRAINAGE AREA, IN SQUARE MILES

10-3.000 10-2.000 10-1.000

MEAN BASIN STREAM SLOPE, IN FEET PER FOOT

2 3 4 5 67 2 3 4 5 67 2 3 4 5

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000

MEAN BASIN ELEVATION, IN FEET [NATIONAL GEODETIC VERTICAL DATUM 1929]

a.

b.

c.

d.

e.

Figure 3. Distribution of stream-gaging station basin characteristics in New Hampshire.
N.H. Department of

 Environmental Services

 (28.3 percent) 

U.S. Army Corps

 of Engineers

 (19.7 percent)

U.S. Geological Survey

 (47 percent)

Rochester (2 percent)

Keene (1 percent)

Salem (2 percent)

Figure 4. New Hampshire stream-gaging network funding sources with 

percentages of total network cost.

Figure 5. Stream-gaging stations providing 

data used for flood forecasting and flood 

control in New Hampshire.

Base from U.S. Geological Survey

Digital line graphs, 1:24,000 or

1:25,000 scale, 1983

72 ̊

71 ̊ 45 ̊

44 ̊

43 ̊

MAINE

VERMONT

CANADA

NEW HAMPSHIRE

MASSACHUSETTS

0 30 MILES

0 30 KILOMETERS

Contoocook R

Merrimack R.

Lake

Winnipesaukee

Pemigewasset R.

Connecticut River

Stream-gaging station 

 used for flood forecasting

Stream-gaging station 

 used for flood control

Stream-gaging station

 used for both flood 

 forecasting and control

EXPLANATION

evaluated. These needs include the protection of lives and property, monitoring and managing water resources, and 

understanding the effects of climate 

and land-use change on hydrology.

Safeguarding Lives and Property

Flooding is the most costly natural hazards that is experienced in New 

Hampshire. Streamflow data provide 

critical information that is used to forecast floods, issue warnings, and operate 

flood-control structures. The National 

Weather Service Northeast River Forecast Center (NERFC) is responsible for 

issuing river forecasts and warnings in 

New Hampshire. In the Merrimack, 

Contoocook, and Connecticut River 

Basins, there are 19 stations (fig. 5) that 

are used by the NERFC to forecast 

river flooding.

Real-time streamflow data from 

28 stations are used by the USACE 

Reservoir Regulation Team for managing their reservoirs in the Connecticut, 

Merrimack, and Contoocook River 

Basins for flood-control operations 

(fig. 5). Data from two other stations 

assist local officials in the Town of 

Salem, N.H., in mitigating, or lessening 

the effects of, flooding. The availability 

of near real-time streamflow data has 

improved the response time to floods of 

the NERFC, the USACE, and other 

agencies.

Historical streamflow data also 

are used to mitigate flood hazards. 

Long-term record (greater than 

10 years) is required for computing 

flood-flow characteristics, such as the 

100-year flood flow or the flow rate 

that is exceeded once, on the average, 

in 100 years. Flow statistics such as 

these provide the design criteria for 

building culverts, bridges, dams, and 

other infrastructure in and near water to 

ensure that these structures perform 

safely even during floods. These statistics also are used for floodplain mapping and management and by the 

Federal Emergency Management 

Agency to set flood-insurance rates.

Often, flow characteristics are 

needed at a stream site where no data 

have been collected. In this situation, 

statistical techniques that relate flow 

characteristics at stream-gaging stations to basin characteristics, such as 

drainage area or channel slope, can be 

used to estimate the desired flow characteristic at an ungaged site. Accurate 

flow estimates require a statewide 

stream-gaging network that spatially 

covers New Hampshire with an adequate period of record that represents a 

complete range of basin and streamflow characteristics (fig. 3). Olson 

(2002) reports that the error in estimating streamflow using statistical techniques would be reduced by adding 

stations with drainage areas smaller 

than 45 square miles.

As the population of New 

Hampshire continues to grow, enhancements to the stream-gaging network 

will be critical for comprehensive flood 

forecasting, control, and warning. 

Basins undergoing extensive development or prone to flooding are potential 

locations for new stations. In particular, 

ungaged streams in southern New 

Hampshire and in areas with recreational development encroaching on 

streams in mountainous regions are 

candidates for new stations.

Managing and Optimizing New 

Hampshire’s Water Resources

Data from the New Hampshire 

stream-gaging network are used on a 

daily basis to monitor and manage 

water resources. For example, the 

NHDES funds a large portion of the 
network to provide information for the 

management of lakes and reservoirs. 

Under the Rivers Management and 

Protection Act, NHDES has the authority and responsibility of protecting designated stream reaches and maintaining 

streamflows for public uses. To do so 

requires data from the stream-gaging 

network.

Streamflow data also are used 

for drought forecasting and drought 

management. The streamflow data, 

along with precipitation data, provide 

officials at the National Oceanic and 

Atmospheric Administration and 

NHDES with the information needed 

to make decisions regarding issuing 

drought statements, warnings, and classification levels. The data then are used 

by the NHDES Drought Management 

Team to decide on a course of action to 

mitigate drought conditions. Streamflow data are used for determining the 

amount of effluent wastewater-treatment facilities can discharge while 

maintaining stream water-quality standards to ensure public health. 

As water resources become 

more stressed with a growing population, water managers will rely more 

heavily on data from the New Hampshire stream-gaging network for allocating water resources; monitoring 

municipal, industrial, agricultural, and 

recreational stream withdrawals; optimizing hydropower generation; and 

maintaining riverine habitat. Various 

network improvements can be considered to support these emerging needs. 

Stream-gaging stations on ungaged 

river reaches designated to be protected 

under the Rivers Management and Protection Act could be established. To 

evaluate basin yield and water-resource 

sustainability as demands for water 

increase, additional stations could be 

established on ungaged streams in rapidly developing drainage basins. Additional stations on streams flowing into 

lakes, particularly Lake Winnipesaukee 

(fig. 1), could improve lake level and 

streamflow management for multiple 

users.

Monitoring Effects of Climate and 

Land-use Change

The New Hampshire streamgaging network provides unique data 

for evaluating the effects of climate and 

land-use change on water resources. 

Long-term stations are essential for 

evaluating trends in streamflow that 

can be linked to changes in climate, 

land use, or water use. For example, 

population growth and sprawl can 

decrease streamflow because of the 

increased demands on aquifers that 

supply some of the flow. Increases in 

population also may result in increased 

runoff, and peak-flood flows, and a 

decrease in ground-water recharge 

because of the increased amount of 

developed or impervious land surface. 

These trends are of particular importance in southern New Hampshire 

where the population has increased.

To better monitor the effects of 

changes in land use on hydrology, stations are required in regions undergoing land-use changes such as southern 

New Hampshire. The collection of data 

over a long time period also is important because long streamflow records 

provide more confidence in identifying 

trends in water resources.

SUMMARY

Accurate streamflow data have 

many uses and are essential to safeguarding lives and property, monitoring 

and managing water resources, and 

understanding the effects of climate 

and land-use change on water 

resources. To meet the demands of a 

growing population in New Hampshire, 

many water-resource issues need to be 

addressed such as public water-supply 

sustainability, wastewater treatment, 

flood forecasting and control, industrial 

water use, water-quality protection, and 

riverine habitat. To address these 

issues, an increase in the statewide coverage to include stream-gaging stations in ungaged basins is important.

Enhancements to the streamgaging network could include additional stations (1) for flood forecasting 

and warning in areas where development is encroaching on waterways, 

such as recreational development along 

mountainous streams that react quickly 

to rainfall; (2) on or near ungaged 

reaches designated as protected under 

the Rivers Management and Protection 

Act to assist NHDES in monitoring 

instream flow requirements; and (3) for 

lake and reservoir management.

Finally, continued operation of 

the present stream-gaging network is 

important. Long-term data and continuity in the network are important for 

evaluating trends in streamflow. Longterm data also are effective in minimizing the error in computed peak-flood 

and low-flow frequency characteristics 

used as criteria for bridge design, 

flood-insurance rates, and wastewatertreatment-plant discharge permits.

—By Scott A. Olson

References Cited

Olson, Scott A., 2003, Effectiveness of 

the stream-gaging network in providing regional streamflow information: U.S. Geological Survey 

Water-Resources Investigations 

Report 03-4041, 64 p., accessed 

May 28, 2003, at 

http://pubs.water.usgs.gov/wri/

wrir03-4041

For more information on the streamgaging network in New Hampshire, 

please contact:

Kenneth W. Toppin

U.S. Geological Survey

361 Commerce Way

Pembroke, NH 03275

(603) 226-7808 Phone

E-mail: ktoppin@usgs.gov

OR

Visit USGS Web sites at:

http://www.usgs.gov or

http://nh.water.usgs.gov