U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5052

Prepared in cooperation with the 

Connecticut Department of Environmental Protection

Regional Regression Equations to Estimate

Flow-Duration Statistics at Ungaged 

Stream Sites in Connecticut
Cover. Photograph showing Sasco Brook (U.S. Geological Survey station 01208950) from bridge on Hulls Farm Road in Fairfield, CT 

taken on October 23, 2008. Photograph courtesy of Jason Pollender.
Regional Regression Equations to Estimate 

Flow-Duration Statistics at Ungaged 

Stream Sites in Connecticut

By Elizabeth A. Ahearn

In cooperation with the Connecticut Department of Environmental Protection 

Scientific Investigations Report 2010–5052

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Ahearn, E.A., 2010, Regional regression equations to estimate flow-duration statistics at ungaged stream sites in 

Connecticut: U.S. Geological Survey Scientific Investigations Report 2010–5052, 45 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................2

Physical Setting.....................................................................................................................................2

Previous Studies ...................................................................................................................................3

Data-Set Development..................................................................................................................................3

Calculation of Flow-Duration Statistics at Streamgages...............................................................7

Drainage-Basin Characteristics of the Streamgages ....................................................................7

Regional Regression Analysis .....................................................................................................................8

Development of Regression Equations .............................................................................................8

Assessment of Regression Equations.............................................................................................12

Final Regression Equations...............................................................................................................12

Limitation of the Regression Equations...........................................................................................17

Summary........................................................................................................................................................19

Acknowledgments.......................................................................................................................................19

References Cited..........................................................................................................................................19

Appendix 1. Basin characteristics considered for use in regression analysis .............................40

Appendix 2. Predictor and explanatory variable names used in StreamStats ..............................44

Figures

1. Map showing locations of continuous-record streamgages considered for

regionalizing flow durations in Connecticut.............................................................................6

2. Map showing locations of streamgages and short-term continuous-record and

partial-record sites in Connecticut and surrounding states considered for use in

developing a regression equation to estimate the non-bioperiod 99-percent flow 

exceedance (Q99).........................................................................................................................13

3. Map showing residuals of the regression equation for the non-bioperiod

99-percent flow exceedance (Q99) for the study area...........................................................18
iv

Conversion Factors and Datum

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second per square

mile [(ft3

/s)/mi2]

0.01093 cubic meter per second per square

kilometer [(m3/s)/km2]

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Tables

1. Bioperiods for which flow-duration statistics and regression equations were

developed.......................................................................................................................................2

2. Descriptions of streamgages with 10 or more years of record considered for

regionalizing flow durations in Connecticut.............................................................................4

3. Flow-duration statistics for streamgages with at least 10 years of continuous

record in Connecticut and neighboring states considered for regression analysis: 

A, Actual streamflow; B, Normalized streamflow.................................................................22

4. Characteristics of the drainage basins tested for statistical significance in

developing regression equations to estimate flow-duration statistics in Connecticut....9

5. Characteristics of the drainage basins used for regionalizing flow-duration

statistics in Connecticut: A, Continuous streamgages; B, Short-term or

partial-record streamgages......................................................................................................30

6. Climate characteristics used for regionalizing flow-duration statistics in

Connecticut..................................................................................................................................38

7. Pearson’s correlation coefficients of basin characteristic and climate

characteristics in Connecticut.................................................................................................10

8. Descriptions of short-term streamgages and partial-record sites considered for

regionalizing flow-duration statistics in Connecticut...........................................................14

9. Summary of regression equations for estimating flow-duration statistics at 

ungaged stream sties in Connecticut and performance metrics .......................................16
Abstract

Multiple linear regression equations for determining 

flow-duration statistics were developed to estimate select flow 

exceedances ranging from 25- to 99-percent for six “bioperiods”—Salmonid Spawning (November), Overwinter (December–February), Habitat Forming (March–April), Clupeid 

Spawning (May), Resident Spawning (June), and Rearing and 

Growth (July–October)—in Connecticut. Regression equations also were developed to estimate the 25- and 99-percent 

flow exceedances without reference to a bioperiod. In total, 

32 equations were developed. The predictive equations were 

based on regression analyses relating flow statistics from 

streamgages to GIS-determined basin and climatic characteristics for the drainage areas of those streamgages. Thirty-nine 

streamgages (and an additional 6 short-term streamgages 

and 28 partial-record sites for the non-bioperiod 99-percent 

exceedance) in Connecticut and adjacent areas of neighboring States were used in the regression analysis. Weighted 

least squares regression analysis was used to determine the 

predictive equations; weights were assigned based on record 

length. The basin characteristics—drainage area, percentage 

of area with coarse-grained stratified deposits, percentage of 

area with wetlands, mean monthly precipitation (November), 

mean seasonal precipitation (December, January, and February), and mean basin elevation—are used as explanatory 

variables in the equations.

Standard errors of estimate of the 32 equations ranged 

from 10.7 to 156 percent with medians of 19.2 and 55.4 percent to predict the 25- and 99-percent exceedances, respectively. Regression equations to estimate high and median 

flows (25- to 75-percent exceedances) are better predictors 

(smaller variability of the residual values around the regression line) than the equations to estimate low flows (less than 

75-percent exceedance). The Habitat Forming (March–April) 

bioperiod had the smallest standard errors of estimate, ranging 

from 10.7 to 20.9 percent. In contrast, the Rearing and Growth 

(July–October) bioperiod had the largest standard errors, ranging from 30.9 to 156 percent. The adjusted coefficient of determination of the equations ranged from 77.5 to 99.4 percent 

with medians of 98.5 and 90.6 percent to predict the 25- and 

99-percent exceedances, respectively.

Descriptive information on the streamgages used 

in the regression, measured basin and climatic characteristics, and estimated flow-duration statistics are provided in this report. Flow-duration statistics and the 

32 regression equations for estimating flow-duration 

statistics in Connecticut are stored on the U.S. Geological Survey World Wide Web application “StreamStats” 

(http://water.usgs.gov/osw/streamstats/index.html). The regression equations developed in this report can be used to produce 

unbiased estimates of select flow exceedances statewide.

Introduction

The concept that a river has a natural flow regime 

upon which its ecological integrity depends has been firmly 

established (Poff and others, 1997). Historically, streamflow 

standards have been based on a minimum flow regime with no 

or little natural variability. “In 2005 the Connecticut legislature passed an act expanding existing environmental flow 

protection to all streams in the state (previously they covered 

only stocked streams) and required DEP1

 to establish flow 

regulations to “preserve and protect the natural aquatic life” 

(State of Connecticut, 2009) and be based, to the maximum 

extent practicable, on natural variation of flows and water 

levels while providing for the needs and requirements of public 

health, flood control, industry, public utilities, water supply, public safety, agriculture, and other lawful uses of such 

waters.” (Smith, 2009).

In early 2010, the State proposed new streamflow standards to safeguard rivers that support a natural flow regime 

on which the ecological integrity of the riverine ecosystems 

depends. These streamflow standards and regulations require 

the quantification of flow exceedances that are based on 

biological processes or “bioperiods.” Bioperiods are defined 

by the State of Connecticut as the time of year during which 

certain biological processes that are dependent on flow occur 

or are likely to occur (State of Connecticut, 2009). In an effort 

to provide water managers with the ability to determine flow 

exceedances that are based on bioperiods at ungaged stream 

1

Connecticut Department of Environmental Protection.

Regional Regression Equations to Estimate Flow-Duration 

Statistics at Ungaged Stream Sites in Connecticut

By Elizabeth A. Ahearn
2 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

sites in Connecticut, this study was conducted by the U.S. 

Geological Survey (USGS) in cooperation with the Connecticut Department of Environmental Protection (DEP) and the 

New England Interstate Water Pollution Control Commission.

To meet future challenges, improved web-based tools are 

needed to easily obtain streamflow statistics, characteristics 

of a drainage basin, and other information for planning and 

management of the water resources. The regression equations developed from this study are included in the USGS 

StreamStats web-based Geographic Information System (GIS) 

(Ahearn and others, 2006) to provide users with access to 

analytical tools and streamflow statistics. StreamStats can be 

accessed at http://water.usgs.gov/osw/streamstats/index.html 

and allows users to obtain flow statistics, characteristics of a 

drainage basin, and other information for user-selected sites on 

a stream. Using a GIS-based interactive map of Connecticut, 

the user can ‘point and click’ on a location and StreamStats 

will delineate the basin upstream from the selected location 

and provide flow-duration statistics for the selected location. 

The user can also ‘point and click’ on USGS streamgages and 

receive flow statistics and information about those locations.

Purpose and Scope

This report presents 32 regression equations for predicting flow-duration statistics for select exceedances from 25- to 

99-percent. Thirty of these equations are for particular months 

or seasons, called bioperiods (table 1), and two equations 

are not associated with any bioperiod. To differentiate the 

25- and 99-percent flow exceedances (Q25 and Q99) associated 

with bioperiods from the Q25 and Q99 that are not based on 

a particular bioperiod (but on all the data in the streamgage 

record), the latter are referred to herein as the “non-bioperiod” 

exceedances. The regression equations were developed using 

streamflow data collected through September 2007. This 

report (1) presents estimates of flow-duration statistics for 

the six bioperiods and the Q25 and Q99 for non-bioperiods at 

41 streamgages; (2) describes methods used to develop the 

regression equations; and (3) describes the accuracy and limitations of the equations.

Physical Setting

Connecticut encompasses an area of 5,009 mi2 and can 

be divided into four physiographic regions: western uplands 

(northwestern part of the state), eastern uplands (northeastern 

part of the state), central valley (central part of the state), and 

coastal lowlands. The western uplands generally have the 

steepest topography; land-surface elevations range from about 

500 to 2,300 ft above NAVD 88 with average slopes of about 

11 percent. Land-surface elevations in the eastern uplands 

range from about 500 to 1,300 ft above NAVD 88 with average slopes of about 8 percent. Topographic relief along the 

coastal lowlands and central valley generally is low with 

land-surface elevations ranging from 0 to about 500 ft above 

NAVD 88 (U.S. Geological Survey, 2006). Average slopes 

along the coastal lowlands and central valley are less than 

7 percent.

The surficial geologic materials of Connecticut, described 

by Stone and others (1992), are primarily glacial deposits. 

Unconsolidated glacial deposits of varying thickness blanket 

the bedrock surface across most of the state. Glacial till is 

the most widespread surficial deposit and is generally thin 

(less than 15 ft thick). Till was deposited directly by glacial 

ice, is a nonsorted material ranging in grain size from clay to 

large boulders, and covers much of the slopes in the State and 

upland areas. Stratified deposits occur primarily in valleys and 

lower, flatter areas both inland and along the coast of Connecticut. These materials were laid down by glacial meltwater 

in streams and lakes and consist of layers of gravel, sand, silt, 

and clay. These materials are most widespread in the broad 

central Connecticut Valley and along the coast. Till, bedrock, 

and fine-grained stratified deposits (very fine sand, silt, and 

clay) generally have lower permeability than the coarsegrained stratified deposits (gravel and sand), which generally 

have high permeability.

Table 1. Bioperiods for which flow-duration statistics and regression equations were developed.

Bioperiod Months Typical flow Significance

Salmonid Spawning November Medium Increased flows needed for spawning migrations and spawning by salmonids (e.g., Atlantic salmon, brook trout).

Overwinter December–February Low Necessary flows for aquatic species, including incubating salmonid eggs, 

to survive freezing conditions and scour by ice.

Habitat Forming March–April High Maintain natural habitat and connectivity with flood plain, channel formation, and flushing and transport of fine-grained sediment.

Clupeid Spawning May Medium Increased flows needed for spawning migrations and spawning by anadromous clupeids, primarily herring and shad.

Resident Spawning June Medium Flows needed for spawning migrations and spawning by resident fishes 

(e.g., fallfish, white sucker).

Rearing and Growth July–October Low Flows needed to sustain and grow aquatic life, including resident and 

anadromous fishes, during metabolically active (i.e., warmer) seasons.
Data-Set Development 3

The climate in Connecticut generally is temperate and 

humid with four distinct seasons. Prevailing westerly winds 

alternately transport cool, dry, continental-polar, and warm, 

moist, maritime-tropical air masses into the region, resulting 

in frequent weather changes. Precipitation is distributed fairly 

evenly throughout the year and averages about 45 in. annually 

(based on long-term data from 1920 to 1996 (Miller and others, 2002)). The climate is moderated by maritime influences 

along coastal regions. Regional differences in topography, 

elevation, and proximity to the ocean can result in a substantial areal variation in snowfall amounts. Mean snowfall ranges 

from 30 in. along coastal areas, to 40 in. inland, to 60 in. in the 

northwestern part of the state (Miller and others, 2002). Average annual temperatures range from 51.7°F in coastal areas 

(Bridgeport) to 49.9°F in the central valley (Hartford) (Northeast Region Climate Center, 2009).

Land cover in Connecticut is highly mixed, with forests 

dominating the north, and densely populated urban areas are 

prominent along the southwestern-coastal and central-valley 

regions. Most of the land cover in Connecticut can be classified as forested with little urban development or low population density. The National Land Cover Data (NLCD) for 

the early 1990s, at a 30-m resolution grid for Connecticut, 

indicates the following categorization of land cover (MultiResolution Land Characteristics Consortium, 1992):

• 59 percent is forest (deciduous, evergreen, and mixed 

forest),

• 12 percent is open space developed and low intensity 

developed (suburban),

• 5.0 percent is high intensity developed (commercial, 

industrial, and high population density), and

• 24 percent is one of the following—open water, barren 

land, shrub, grassland, pasture, wetlands, agriculture, 

and medium intensity developed.

Previous Studies

Several studies by the USGS that provide estimates of 

flow-duration statistics in Connecticut have been published, 

including a series of basin studies (Cervione and others, 1972; 

Handman and others, 1986; Mazzaferro and others, 1979; 

Randall and others, 1966; Ryder and others, 1970; Ryder and 

others, 1981; Thomas and others, 1968; Thomas and others, 1967; Weiss and others, 1982; Wilson and others, 1974). 

Ahearn (2007) published estimates of flow durations, low-flow 

frequencies, and monthly median flows for selected streams in 

Connecticut using data through 2005. That report updated and 

superseded previously published flow durations, low-flow frequencies, and monthly median flow estimates in Connecticut 

and was a precursor to the development of regression equations to estimate the flow-duration statistics described in this 

report. Regional regression techniques to estimate low-flow 

and flood-flow statistics at ungaged stream sites have been 

applied in Connecticut (Thomas and Benson, 1970; Cervione 

and others, 1982; Weiss, 1983; Ahearn, 2004). Studies published by USGS within the last 20 years that regionalized 

flow-duration statistics in Massachusetts include Archfield and 

others (2010) and Ries and Friesz (2000).

Data-Set Development

Data from about 100 streamgages with 10 or 

more years of daily mean flows in Connecticut and 

in the neighboring states of Rhode Island, Massachusetts, and New York were retrieved from the USGS 

National Water Inventory System (NWIS) database at 

http://nwis.waterdata.usgs.gov/usa/nwis/discharge and 

considered for the regression study (Ahearn, 2007). Subsequently, Connecticut DEP and USGS made a rigorous effort 

to identify and eliminate any of the streamgages that were 

impacted by anthropogenic activities (such as flow augmentation, diversions, or water-supply/industrial withdrawals in the 

upstream drainage basin). After evaluating all available 100 

flow records, 41 continuous-record streamgages, 6 short-term 

streamgages and 28 partial-record sites2

 met the criterion of a 

natural or near-natural flow regime (table 2 and fig. 1). Of the 

41 continuous-record streamgages, 27 are in Connecticut; 10 

of these were active in 2007. The 6 short-term streamgages 

and 28 partial-record sites are located in Connecticut and 

were available for regionalization of the Q99 without reference to a bioperiod. In a companion study that preceded the 

regression analysis presented in this report, several low-flow 

statistics, including the Q99, were estimated for the short-term 

streamgages and partial-record sites (Ahearn, 2007).

Streamgages outside Connecticut were included in the 

regionalization of flow-duration statistics because of the sparse 

coverage of long-term streamgages with natural flow conditions within the State. These streamgages are within 15 mi 

of the State line. Inclusion of more streamgages may provide 

a more representative sample of the range of physiographic 

characteristics of Connecticut.

The flow records for the 41 continuous-record 

streamgages ranged from 10 to 95.2 years with an average of 

36.2 years. The flow records for the short-term streamgages 

and partial-record sites ranged from 3.5 to 19.6 years with 

an average of 13.1 years. Fourteen continuous-record 

streamgages had flow records less than 20 years. Twenty 

or 30 years of flow record would have provided a broader 

representation of flow variability in the region and would 

have minimized the influence of unusually wet or dry periods. However, using a longer minimum record length would 

have decreased the number of available streamgages in the 

region of the study that already had limited data coverage. 

The additional streamgages in the regression analysis can 

2

A short-term streamgage has continuous-stage recording equipment with 

less than 10 years of record. A partial-record site has periodic streamflow 

measurements and does not have continuous stage-recording equipment.
4 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut Table 2. Descriptions of streamgages with 10 or more years of record considered for regionalizing flow durations in Connecticut.—Continued [USGS, U.S. Geological Survey; no., number; mi2, square miles] USGS streamgage no. Streamgage name State Latitude (decimal degrees) Longitude (decimal degrees) Drainage area (mi2

)

Years of 

record Period of record

01111300 Nipmuc River near Harrisville Rhode Island 41.981 -71.686 16.0 41.6 Mar 1964–Sep 1991,

Oct 1993–Sep 2007

01111500 Branch River at Forestdale Rhode Island 41.996 -71.563 91.2 67.7 1Jan 1940–Sep 2007

01115098 Peeptoad Brook at Elmdale Road near Westerly Rhode Island 41.853 -71.606 4.83 13.3 Jun 1994–Sep 2007

01115187 Ponaganset River at South Foster Rhode Island 41.819 -71.705 14.4 13.5 Mar 1994–Sep 2007

01117468 Beaver River near Usquepaug Rhode Island 41.493 -71.628 8.87 32.8 Dec 1974–Sep 2007

01117500 Pawcatuck River at Wood River Junction Rhode Island 41.445 -71.681 100 66.9 2Dec 1940–Sep 2007

01117800 Wood River near Arcadia Rhode Island 41.574 -71.721 35.2 42.7 Jan 1964–Sep 1981,

Oct 1982–Sep 2007

01118000 Wood River at Hope Valley Rhode Island 41.498 -71.716 72.4 66.6 Mar 1941–Sep 2007

01118300 Pendleton Hill Brook near Clarks Falls Connecticut 41.475 -71.834 4.02 49.0 Oct 1958–Sep 2007

01120500 Safford Brook near Woodstock Valley Connecticut 41.926 -72.057 4.15 32.0 Oct 1950–Oct 1981

01121000 Mount Hope River near Warrenville Connecticut 41.844 -72.169 28.6 67.0 Oct 1940–Sep 2007

01123000 Little River near Hanover Connecticut 41.672 -72.052 30.0 56.0 Oct 1951–Sep 2007

01125490 Little River at Harrisville Connecticut 41.928 -71.930 35.8 10.1 Aug 1961–Sep 1971

01126600 Blackwell Brook near Brooklyn Connecticut 41.765 -71.956 17.0 13.0 Oct 1963–Oct 1976

01126950 Pachaug River at Pachaug Connecticut 41.585 -71.933 53.0 12.2 Aug 1961–Oct 1973

01176000 Quaboag River at West Brimfield Massachusetts 42.182 -72.264 150 95.2 Aug 1912–Sep 2007

01187300 Hubbard Brook near West Hartland Connecticut 42.037 -72.939 19.9 68.0 Oct 1938–Sep 1955,

Oct 1956–Sep 2007

01187400 Valley Brook near West Hartland Connecticut 42.034 -72.930 7.03 32.0 Oct 1940–Sep 1972

01187800 Nepaug River near Nepaug Connecticut 41.821 -72.970 23.5 52.0 Oct 1921–Sep 1955,

Oct 1957–Sep 1972,Oct 1998–Sep 2001

01187850 Clear Brook near Collinsville Connecticut 41.796 -72.951 0.59 55.0 Oct 1921–Oct 1973,

Oct 1998–Sep 2001
Data-Set Development

5

Table 2. Descriptions of streamgages with 10 or more years of record considered for regionalizing flow durations in Connecticut.—Continued[USGS, U.S. Geological Survey; no., number; mi2, square miles]

USGS

streamgage 

no.

Streamgage name State

Latitude

(decimal

degrees)

Longitude

(decimal

degrees)

Drainage

area

(mi2)

Years of 

record Period of record

01188000 Bunnell Brook near Burlington Connecticut 41.786 -72.965 4.10 76.0 Oct 1931–Sep 2007

01192600 South Branch Salmon Brook at Buckingham Connecticut 41.718 -72.540 0.94 16.0 Oct 1960–Sep 1976

01193500 Salmon River near East Hampton Connecticut 41.552 -72.449 100 79.0 Oct 1928–Sep 2007

01193800 Hemlock Valley Brook at Hadlyme Connecticut 41.428 -72.423 2.62 16.3 Jul 1960–Oct 1976

01194000 Eightmile River at North Lyme Connecticut 41.442 -72.333 20.1 29.0 Oct 1937–Sep 1966

01194500 East Branch Eightmile River near North Lyme Connecticut 41.428 -72.334 22.3 50.0 Oct 1937–Sep 1981,

Oct 2001–Sep 2007

01195100 Indian River near Clinton Connecticut 41.306 -72.531 5.68 25.9 Nov 1981–Sep 2007

01195200 Neck River near Madison Connecticut 41.283 -72.619 6.55 20.2 Sep 1961–Nov 1981

01198000 Green River near Great Barrington Massachusetts 42.192 -73.391 51.0 22.5 Oct 1951–Sep 1971,

Mar 1994–Sep 1996

01199200 Guinea Brook at West Woods Road at Ellsworth Connecticut 41.824 -73.430 3.50 21.2 Aug 1960–Oct 1981

01201190 West Aspectuck River at Sand Road near New 

Milford

Connecticut 41.608 -73.425 23.8 10.0 Oct 1962–Sep 1972

01201930 Marshepaug River near Milton Connecticut 41.790 -73.259 9.24 14.1 Oct 1967–Oct 1981

01204800 Copper Mill Brook near Monroe Connecticut 41.363 -73.218 2.45 18.0 Oct 1958–Oct 1976

01206400 Leadmine Brook near Harwinton Connecticut 41.730 -73.053 19.6 13.0 Oct 1960–Oct 1973

01206500 Leadmine Brook near Thomaston Connecticut 41.702 -73.057 24.3 29.0 Oct 1930–Sep 1959

01208950 Sasco Brook near Southport Connecticut 41.153 -73.306 7.38 43.0 Oct 1964–Sep 2007

01208990 Saugatuck River near Redding Connecticut 41.295 -73.395 21.0 43.0 Oct 1964–Sep 2007

01372200 Wappinger Creek near Clinton Corners New York 41.815 -73.763 92.4 20.0 Jan 1956–Dec 1975

01372800 Fishkill Creek at Hopewell Junction New York 41.573 -73.807 57.3 28.3 Oct 1957–Dec 1985

01374598 Horse Pound Brook near Lake Carmel New York 41.476 -73.689 3.94 11.1 Aug 1996–Sep 2007

01374890 Cross River near Cross River New York 41.260 -73.602 17.1 11.8 Dec 1995–Sep 2007

1Flow durations based on data from Oct 1956 through Sep 2007.2Flow durations based on data from Oct 1969 through Sep 2007.
6 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Figure 1. Locations of continuous-record streamgages considered for regionalizing flow durations in Connecticut.

01187800

01115098

CONNECTICUT

MASSACHUSETTS

RHODE ISLAND

NEW YORK

Long Island NEW YORK

CONNECTICUT

01208990

01208950

01206500

01206400

01204800

01201930

01201190

01199200

01195200 01195100

01194000 01194500

01193800

01193500

01192600 01188000

01187850

01187300 01187400

01126950

01126600

01125490

01123000

01121000

01120500

01118300

01374890

01374598

01372800

01372200

01198000 01176000

01118000

01117800

01117500

01117468

01115187

01111500 01111300

73°30' 72° 71°30'

42°30'

42°

41°30'

41°

73° 72°30'

01117500

Hartford 

New London

New Haven

Long Island Sound

Base from U.S. Geological Survey digital data 1:100,000

2000, Connecticut State Plane projection

EXPLANATION

U.S. Geological Survey

streamgage and number 

0 15 30 MILES

0 25 50 KILOMETERS
Data-Set Development 7

result in a set of equations that are more robust. Although an 

effort was made by Connecticut DEP and USGS to eliminate 

streamgages with flow records that have been impacted by 

anthropogenic activities, the possibility exists that some of the 

flow records, particularly those in neighboring states, were 

affected by anthropogenic impacts.

Plots of the data revealed some streamgages are outliers; 

that is, data values from them depart substantially from the 

rest of the data. For example, Clear Brook (station 01187850), 

with a drainage area of only 0.59 mi2

, is an outlier. The 

groundwater drainage area and surface-water drainage area in 

this basin are not coincident. Also, Marshepaug River (station 

01201930), with a drainage area of 9.24 mi2, is an outlier. The 

stage-discharge relation is not well defined at this streamgage 

and consequently is considered less reliable than at the other 

streamgages. These two outlier streamgages were dropped 

from the regression analysis, leaving 39 streamgages.

Calculation of Flow-Duration Statistics at 

Streamgages

Flow durations represent the percentage of time that a 

given flow, measured over a specified time interval, has been 

equaled or exceeded during that time interval. For example, a 

99-percent flow exceedance (Q99) represents a streamflow that 

is equaled or exceeded 99 percent of the time. Flow values at 

or below the Q99 indicate extremely low flows. Conversely, 

a 25-percent flow exceedance (Q25) represents a daily-mean 

streamflow that is equaled or exceeded 25 percent of the time. 

Flow values at or above the Q25 represent high-flow conditions 

because 75 percent of all daily mean streamflows in the record 

are smaller than that flow. Typically, flow durations characterize the range of flows for the period over which data were collected. The streamflow data from the streamgages used in this 

study are based on periods of record with varying starting and 

ending years (table 2) with the earliest starting in 1912 and the 

most recent ending in September 2007.

Flow-duration statistics are computed by sorting 

the daily mean streamflows for the period of record from 

the largest value to the smallest value and assigning each 

streamflow value a rank, starting with 1 for the largest value. 

The exceedance probabilities are then computed using the 

Weibull formula for computing plotting position (Helsel 

and Hirsch, 1992):

P = 100 * [M / (n + 1)], (1)

where

P = the probability that a given flow will be 

equaled or exceeded (percentage of time),

M = the ranked position (dimensionless), and

n = the number of events for the period of 

record (dimensionless).

Flow-duration statistics, in units of cubic feet per second, 

were derived from historical data through September 2007 

(table 3A, at back of this report). The flow exceedances were 

computed from daily mean flows for the period of record. 

Seasonal and monthly flow exceedances, representative of 

the bioperiods, were computed from daily mean flows for the 

period of record during each of the six bioperiods. For example, the Q99 in the Salmonid Spawning bioperiod is calculated 

using just daily mean flows for every November in the period 

of record. Similarly, the Q99 for the Overwinter bioperiod is 

calculated using all the daily mean flows for every December, 

January, and February in the period of record. Flow-duration 

statistics were computed using a commercial statistics and 

data-management software package called Spotfire S+®

(TIBCO Software Inc., 2008).

To compare flow-duration statistics across basins, 

the flows were divided by their respective drainage areas 

(table 3B, at back of this report). The normalized nonbioperiod Q99 ranged from 0.0 to 0.90 ft3

/s/mi2; the average 

value was 0.09 ft3

/s/mi2. For the Rearing and Growth bioperiod (low-flow conditions), the normalized Q99 ranged from 

0.0 to 0.90 ft3

/s/mi2, the average value was 0.08 ft3/s/mi2. 

With the exclusion of Clear Brook, which is a low-flow 

outlier, the normalized non-bioperiod Q99 ranged from 0.0 to 

0.33 ft3

/s/mi2, the average value was 0.07 ft3/s/mi2. For the 

Rearing and Growth bioperiod, the normalized Q99 ranged 

from 0.0 to 0.30 ft3

/s/mi2, the average value was 0.05 ft3/s/mi2. 

During high-flow conditions, the normalized non-bioperiod 

Q25 ranged from 1.56 to 3.56 ft3

/s/mi2; the average value 

was 2.41 ft3

/s/mi2. For the Habitat Forming bioperiod (highflow conditions), the normalized Q25 ranged from 3.19 to 

5.69 ft3

/s/mi2; the average value was 4.26 ft3/s/mi2. A common 

time period was not used to derive the normalized flow values, 

and the differences in flows per square mile between the 

streamgages are partly attributed to the varying record lengths.

Previously derived flow-duration statistics for the 

Q99 from short-term streamgages and partial-record sites 

were used in conjunction with the 39 continuous-record 

streamgages in the regression analysis of the non-bioperiod 

Q99. In a previous study (Ahearn, 2007), the Q99 was derived 

using the MOVE3 method (Vogel and Stedinger, 1985) for 

7 short-term continuous-record and 31 partial-record sites in 

Connecticut; flow-duration statistics were not computed for 

the bioperiods. The flow-duration statistics at the short-term 

continuous-record streamgages and partial-record sites were 

calculated based on the relation between same-day flows at the 

short-term streamgages and partial-record sites and concurrent 

daily mean flows at a nearby continuous-record streamgage 

with natural flow conditions.

Drainage-Basin Characteristics of the 

Streamgages

Flow characteristics of streams are directly related to 

the physical, land-cover, geologic, and climatic features of 
8 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

the basin. Characteristics of the drainage basin were selected 

for use as potential explanatory variables in the regression 

analysis based on their theoretical relation to flows, results of 

previous studies in similar hydrologic regions, and the ability 

to measure the basin characteristics using digital data sets and 

GIS technology. Measuring the basin characteristics with GIS 

technology facilitates automation of the process and solving 

the regional regression equations in StreamStats.

A GIS database was set up to store the characteristics 

of the drainage basins measured for the streamgages used in 

the regression analysis. The name, units of measure, method 

of measurement, and source of data for each measured basin 

characteristic are listed in appendix 1. The drainage-basin 

characteristics considered for use in the Connecticut regression analysis are listed in table 4, and the measured values are 

in tables 5 (physical, land-cover, and geologic characteristics) 

and 6 (climate characteristics) (at the back of this report).

Regional Regression Analysis

Multiple linear regression (MLR) analysis was used 

to develop equations to predict flow-duration statistics at 

ungaged stream sites in Connecticut. MLR analysis provides a 

mathematical equation of the relation between a response variable (flow exceedance) and one or more explanatory variables 

(basin characteristics). After developing such equations, if the 

explanatory variables are known (can be measured or quantified) at the ungaged locations, the fitted equations can be used 

to make predictions of the response variables.

Development of Regression Equations

Basic plots and initial regression runs using all the data 

were used to decide if variable transformations were needed. 

The plots indicated that a log transformation was needed in 

order to meet the assumptions of linear regression. Logarithmic (base-10) transformations were made of the flow 

exceedances (response variable) and basin characteristics 

(explanatory variables) to linearize the relation between the 

explanatory variables and the response variables, to stabilize 

the variance by obtaining equal variance about the regression 

line, and to improve the spread of the data.

Plots of transformed and untransformed explanatory 

variables also were examined to eliminate redundant (correlated) explanatory variables in the variable selection process 

of the regression analysis. The explanatory variables were 

selected based on their relation to flow and correlation to 

other basin characteristics using Pearson’s correlation coefficient (R). If a moderate correlation (R less than 0.6) existed 

between two explanatory variables, the two variables were 

evaluated individually in the variable selection process. 

Pearson’s correlation coefficients were computed for each 

explanatory variable. If an explanatory variable showed low 

correlation to flow and high correlation to another explanatory 

variable with high correlation to flow, it was eliminated from 

consideration in the study. Several explanatory variables were 

found to be moderately or highly correlated to other explanatory variables (table 7).

Two automated statistical methods for selecting 

explanatory variables were used in the regression analysis, 

“all-possible subsets” and “stepwise selection.” Both selection methods determined the statistical contribution of the 

explanatory variable that was entered into the equation and 

variables were retained or deleted based on their statistical importance. In “all-possible subsets,” all the equations 

created from all possible combinations of explanatory variables were examined and the coefficient of determination (R2

) 

was used to check for the best combination of explanatory 

variables. With this method, each explanatory variable can be 

included or excluded independently of the other explanatory 

variables. Efroymson’s stepwise-selection method (Efroymson, 1960) is similar to forward selection, which involves testing variables one by one and including them in the equation 

if they are statistically significant, except that when each new 

variable is added to the subset, partial correlations are considered to see if any of the variables in the subset should be 

dropped. When basin characteristics were found to be highly 

correlated, only one basin characteristic at a time was used in 

the selection process.

To identify the best combination of explanatory 

variables, different equations from the regression analysis 

were compared based on the adj-R2

, Mallow’s Cp, PRESS 

statistics, and SEr.

• Adjusted-R-squared (adj-R2), also called the adjusted 

coefficient of determination, is a measure of the 

percentage of the variation explained by the explanatory variables of the equation and is adjusted for the 

number of parameters in the equation;

• Mallow’s Cp statistic is an estimate of the standardized 

mean square error of prediction. Cp statistic is a compromise between maximizing the explained variance 

by including all relevant variables and minimizing the 

standard error by keeping the number of variables as 

small as possible (Helsel and Hirsch, 1992);

• Predicted Residual Sum of Squares (PRESS) statistic is a validation-type estimator of error (Helsel 

and Hirsch, 1992). PRESS uses n-1 observations to 

develop the equation, then estimates the value of the 

observation that was left out. The process is repeated 

for each observation and the prediction errors are 

squared and summed;

• Standard error of estimate (SEr, in percent), also 

referred to as the root-mean-squared error of the 

residuals, is the standard deviation of observed values 

about the regression line. It is computed by dividing 

the unexplained variation or the error sum of squares 

by its degrees of freedom. In this study, the SEr is 

based on one standard deviation.
Regional Regression Analysis 9

Table 4. Characteristics of the drainage basins tested for statistical significance in developing 

regression equations to estimate flow-duration statistics in Connecticut.

[NAVD, North American Vertical Datum of 1988; NLCD, National Land Cover Dataset; NWI, National Wetlands Dataset; PRISM, Parameter-elevation Regressions on Independent Slopes Model (Prism Group, Oregon Climatic Service of 

Oregon State University); SSURGO, Soil Survey Geographic Database (Natural Resources Conservation Service, 2007)]

Physical characteristics

Drainage area (square miles)

Basin perimeter (miles)

Total river miles (miles)

Maximum basin elevation (feet, NAVD 88)

Mean basin elevation (feet, NAVD 88)

Basin relief (feet)

Mean basin slope (percent)

Latitude of basin centroid (feet)

Longitude of basin centroid (feet)

Gage latitude (decimal degrees)

Gage longitude (decimal degrees)

Total streams in contact with coarse stratified deposits (miles)

Land-cover characteristics (NLCD and NWI)

Deciduous forest (percent)

Evergreen forest (percent)

Mixed forest (percent)

Deciduous and mixed forest (percent)

Developed, open space (percent)

Developed, low intensity (percent)

Developed, open space and low intensity (percent)

Open water (percent)

Impervious area (percent)

Wetlands (percent)

Soil characteristics SSURGO

Soil hydrologic groups A, B, C, and D (dimensionless)

Surficial Geology (Connecticut Surficial Geology Map (Stone and others, 1992))

Percent till and thick till (percent)

Percent coarse stratified deposits (percent)

Percent alluvium deposits (percent)

Precipitation, drainage basin average (PRISM)

Precipitation 1971–2000, Mean annual (inches)

Precipitation 1971–2000, Maximum annual (inches)

Precipitation 1971–2000, Mean monthly salmonid spawning, November (inches)

Precipitation 1971–2000, Mean seasonal overwinter, December–February (inches)

Precipitation 1971–2000, Mean seasonal habitat forming, March–April (inches)

Precipitation 1971–2000, Mean monthly clupeid spawning, May (inches)

Precipitation 1971–2000, Mean monthly resident spawning, June (inches)

Precipitation 1971–2000, Mean seasonal rearing and growth, July–October (inches)

Temperature, drainage basin average (PRISM)

Temperature 1971–2000, Mean annual minimum (degrees Fahrenheit)

Temperature 1971–2000, Mean annual maximum (degrees Fahrenheit)

Temperature 1971–2000, Mean monthly salmonid spawning, November (degrees Fahrenheit)

Temperature 1971–2000, Mean seasonal overwinter, December–February (degrees Fahrenheit)

Temperature 1971–2000, Mean seasonal habitat forming, March–April (degrees Fahrenheit)

Temperature 1971–2000, Mean monthly clupeid spawning, May (degrees Fahrenheit)

Temperature 1971–2000, Mean monthly resident spawning, June (degrees Fahrenheit)

Temperature 1971–2000, Mean seasonal rearing and growth, July–October (degrees Fahrenheit)
10 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 7. Pearson’s correlation coefficients of basin characteristic and climate characteristics in Connecticut.

[Red italics, basin characteristics used in regression equations; shaded, bold figures are correlations equal to or greater than 0.6] Drainage area Basin perimeter Total river miles Maximum basin elevation Mean basin elevation Basin relief Mean basin slope Latitude of basin centroid Longitude of basin centroid Gage latitude Gage longitude Total streams in contact with coarse stratified deposits Deciduous forest Evergreen forest

Mixed forestDeciduous and mixed forestDeveloped, open spaceDeveloped, low intensityDeveloped, open space and low intensity

Drainage area 1.0

Basin perimeter 0.9 1.0

Total river miles 1.0 0.9 1.0

Maximum basin elevation 0.2 0.2 0.1 1.0

Mean basin elevation -0.1 -0.0 -0.1 0.9 1.0

Basin relief 0.4 0.6 0.3 0.8 0.5 1.0

Mean basin slope -0.0 0.1 -0.1 0.7 0.6 0.7 1.0

Latitude of basin centroid 0.2 0.1 0.2 -0.6 -0.5 -0.4 -0.7 1.0

Longitude of basin centroid 0.3 0.3 0.3 0.6 0.6 0.5 0.2 0.2 1.0

Gage latitude 0.3 0.2 0.2 0.6 0.7 0.4 0.2 0.1 1.0 1.0

Gage longitude 0.1 0.0 0.2 -0.6 -0.5 -0.5 -0.7 1.0 0.2 0.2 1.0

Total streams in contact with coarse-stratified deposits 0.8 0.6 0.9 -0.1 -0.2 0.1 -0.3 0.4 0.2 0.1 0.3 1.0

Deciduous forest -0.5 -0.5 -0.5 -0.0 0.1 -0.2 0.3 -0.1 -0.2 -0.2 -0.1 -0.5 1.0

Evergreen forest 0.3 0.2 0.3 0.1 0.1 0.1 -0.0 0.3 0.4 0.4 0.3 0.4 -0.6 1.0

Mixed forest 0.1 0.1 0.1 0.5 0.5 0.4 0.2 0.0 0.6 0.6 0.0 -0.0 -0.4 0.3 1.0

Deciduous and mixed forest -0.5 -0.5 -0.5 0.3 0.4 0.1 0.4 -0.1 0.1 0.1 -0.1 -0.5 0.8 -0.4 0.2 1.0

Developed, open space -0.2 -0.3 -0.2 -0.4 -0.3 -0.3 -0.1 -0.3 -0.6 -0.6 -0.3 -0.2 -0.2 -0.1 -0.3 -0.3 1.0

Developed, low intensity -0.0 -0.2 -0.0 -0.4 -0.3 -0.3 -0.3 -0.0 -0.3 -0.2 -0.0 0.1 -0.4 0.1 -0.2 -0.5 0.6 1.0

Developed, open space and low intensity -0.2 -0.3 -0.2 -0.4 -0.4 -0.4 -0.2 -0.3 -0.5 -0.5 -0.3 -0.1 -0.3 -0.0 -0.3 -0.4 0.9 0.8 1.0

Open water 0.5 0.4 0.5 0.1 -0.0 0.2 0.0 0.1 0.0 0.0 0.1 0.5 -0.2 0.2 0.0 -0.2 -0.2 -0.2 -0.2

Impervious area 0.0 -0.1 0.1 -0.4 -0.4 -0.3 -0.4 -0.1 -0.3 -0.3 -0.1 0.1 -0.4 0.0 -0.2 -0.5 0.7 0.9 0.9

Wetlands 0.4 0.3 0.4 -0.2 -0.2 -0.1 -0.4 0.6 0.1 0.1 0.6 0.7 -0.2 0.4 -0.1 -0.2 -0.3 -0.1 -0.3

Hydrologic soil type A 0.4 0.3 0.4 0.0 -0.1 0.1 -0.1 0.2 0.2 0.2 0.2 0.5 -0.1 0.3 -0.2 -0.3 -0.2 -0.0 -0.2

Hydrologic soil type B -0.1 -0.0 -0.1 0.2 0.3 0.1 0.1 -0.1 0.3 0.3 -0.1 -0.2 -0.2 0.2 0.2 -0.1 -0.0 0.2 0.0

Hydrologic soil type C -0.1 0.0 -0.1 0.5 0.5 0.3 0.1 -0.1 0.5 0.5 -0.0 -0.2 -0.3 0.1 0.8 0.2 -0.3 -0.3 -0.3

Hydrologic soil type D -0.4 -0.3 -0.4 -0.5 -0.4 -0.4 -0.1 -0.1 -0.7 -0.7 -0.1 -0.3 0.4 -0.5 -0.4 0.2 0.4 0.1 0.3

Hydrologic soil type D and A/D and C/D -0.4 -0.4 -0.4 -0.4 -0.3 -0.3 -0.0 -0.2 -0.6 -0.6 -0.2 -0.4 0.4 -0.5 -0.3 0.3 0.4 0.1 0.3

Percent till and thick till -0.4 -0.4 -0.4 0.1 0.3 -0.1 0.2 -0.2 -0.0 -0.1 -0.1 -0.5 0.4 -0.5 0.3 0.6 0.1 -0.3 -0.0

Percent coarse stratified deposits 0.3 0.2 0.3 -0.3 -0.4 -0.2 -0.4 0.5 0.1 0.1 0.5 0.5 -0.4 0.6 -0.2 -0.5 -0.1 0.4 0.1

Percent alluvium deposits -0.1 0.1 -0.1 0.2 0.2 0.1 0.2 -0.2 -0.0 -0.0 -0.2 -0.3 0.1 -0.2 -0.1 0.1 -0.2 -0.2 -0.2

Mean annual precipitation -0.4 -0.4 -0.4 -0.1 0.1 -0.3 -0.1 -0.0 -0.2 -0.2 -0.0 -0.3 0.2 -0.2 0.2 0.3 0.1 0.1 0.1

Maximum annual precipitation -0.3 -0.3 -0.3 0.0 0.2 -0.1 0.1 -0.2 -0.2 -0.1 -0.2 -0.3 0.1 -0.2 0.3 0.3 0.1 0.1 0.1

Mean monthly precipitation, salmonid spawning (Nov) -0.2 -0.3 -0.2 -0.6 -0.4 -0.6 -0.5 0.6 -0.2 -0.2 0.7 -0.0 0.1 -0.0 0.1 0.2 -0.1 0.1 -0.0

Mean seasonal precipitation, overwinter (Dec–Feb) -0.2 -0.3 -0.1 -0.6 -0.4 -0.6 -0.6 0.7 -0.2 -0.2 0.7 0.0 0.1 -0.0 0.1 0.2 -0.2 0.0 -0.1

Mean seasonal precipitation, habitat forming (Mar–Apr) -0.4 -0.4 -0.3 -0.6 -0.4 -0.6 -0.5 0.4 -0.4 -0.4 0.4 -0.1 0.2 -0.2 -0.0 0.2 0.1 0.2 0.2

Mean monthly precipitation, clupeid spawning (May) -0.2 -0.2 -0.3 0.5 0.6 0.4 0.6 -0.9 -0.1 -0.1 -0.9 -0.3 0.1 -0.2 0.2 0.2 0.3 0.1 0.3

Mean monthly precipitation, resident spawning (Jun) -0.2 -0.2 -0.3 0.6 0.7 0.3 0.5 -0.8 0.1 0.1 -0.8 -0.4 0.1 -0.2 0.3 0.3 0.2 0.0 0.1

Mean seasonal precipitation, rearing and growth (Jul–Oct) -0.3 -0.2 -0.3 0.5 0.6 0.2 0.5 -0.6 0.0 0.1 -0.6 -0.5 0.1 -0.1 0.2 0.2 0.1 -0.0 0.1

Mean annual minimum temperature -0.1 -0.2 -0.1 -0.8 -0.8 -0.6 -0.4 0.1 -0.8 -0.8 0.1 0.1 0.1 -0.2 -0.6 -0.3 0.6 0.4 0.5

Mean annual maximum temperature -0.0 -0.0 -0.0 -0.7 -0.8 -0.4 -0.3 0.1 -0.8 -0.8 0.1 0.0 0.1 -0.2 -0.7 -0.4 0.5 0.3 0.5

Mean monthly temperature, salmonid spawning (Nov) -0.0 -0.1 -0.0 -0.9 -0.9 -0.5 -0.5 0.3 -0.8 -0.8 0.3 0.1 0.1 -0.1 -0.7 -0.4 0.4 0.3 0.5

Mean seasonal temperature, overwinter (Dec–Feb) -0.1 -0.1 -0.1 -0.5 -0.6 -0.3 -0.1 -0.2 -0.8 -0.8 -0.3 -0.1 -0.0 -0.3 -0.5 -0.3 0.7 0.4 0.7

Mean seasonal temperature, habitat forming (Mar–Apr) -0.1 -0.0 -0.1 -0.6 -0.7 -0.4 -0.2 -0.0 -0.8 -0.8 -0.0 -0.0 0.1 -0.2 -0.7 -0.3 0.5 0.3 0.5

Mean monthly temperature, clupeid spawning (May) -0.0 0.1 -0.1 -0.2 -0.4 -0.0 0.1 -0.3 -0.5 -0.4 -0.3 -0.2 0.0 -0.1 -0.5 -0.3 0.4 0.2 0.4

Mean monthly temperature, resident spawning (Jun) 0.0 0.1 -0.0 -0.3 -0.5 -0.1 0.0 -0.3 -0.6 -0.6 -0.3 -0.1 -0.1 -0.1 -0.6 -0.4 0.5 0.3 0.5

Mean seasonal temperature, rearing and growth (Jul–Oct) -0.0 0.0 -0.0 -0.7 -0.8 -0.3 -0.2 -0.0 -0.8 -0.8 -0.0 -0.0 0.0 -0.2 -0.7 -0.4 0.5 0.3 0.5
Regional Regression Analysis 11

Table 7. Pearson’s correlation coefficients of basin characteristics and climate characteristics in Connecticut.—Continued

[Red italics, basin characteristics used in regression equations; shaded, bold figures are correlations equal to or greater than 0.6] Open water Impervious area Wetlands Hydrologic soil type A Hydrologic soil type B Hydrologic soil type C Hydrologic soil type D Hydrologic soil type D and A/D and C/D Percent till and thick till Percent coarse stratified deposits Percent alluvium deposits Mean annual precipitation Maximum annual precipitation Mean monthly precipitation, salmonid spawning (Nov) Mean seasonal precipitation, overwinter (Dec-Feb) Mean seasonal precipitation, habitat forming (Mar-Apr) Mean monthly precipitation, clupeid spawning (May) Mean monthy precipitation, resident spawning (Jun) Mean seasonal precipitation, rearing and growth (Jul-Oct) Mean annual minimum temperature Mean annual maximum temperature Mean monthly temperature, salmonid spawing (Nov) Mean seasonal temperature, overwinter (Dec-Feb) Mean seasonal temperature, habitat forming (Mar-Apr)

Mean monthly temperature, clupeid spawing (May)Mean monthly temperature, resident spawning (Jun)Mean seasonal temperature, rearing and growth, (Jul-Oct)

1.0

-0.1 1.0

0.5 -0.1 1.0

0.4 -0.0 0.7 1.0

-0.2 0.0 -0.3 -0.5 1.0

-0.1 -0.3 -0.2 -0.4 0.4 1.0

-0.3 0.2 -0.5 -0.6 -0.2 -0.3 1.0

-0.3 0.1 -0.5 -0.7 -0.2 -0.2 1.0 1.0

-0.2 -0.2 -0.4 -0.6 0.1 0.4 0.4 0.5 1.0

0.1 0.3 0.5 0.5 0.0 -0.3 -0.4 -0.4 -0.9 1.0

-0.2 -0.2 -0.4 -0.6 0.4 0.2 0.3 0.3 0.1 -0.3 1.0

-0.1 0.1 -0.2 -0.4 0.1 0.3 0.3 0.3 0.5 -0.3 0.2 1.0

-0.0 0.1 -0.3 -0.4 0.1 0.4 0.2 0.3 0.5 -0.3 0.2 0.9 1.0

0.0 0.0 0.2 -0.2 -0.1 0.1 0.3 0.3 0.3 0.1 -0.1 0.7 0.5 1.0

0.0 -0.0 0.3 -0.1 -0.1 0.1 0.2 0.2 0.2 0.1 -0.1 0.6 0.5 1.0 1.0

-0.1 0.2 0.1 -0.3 -0.1 0.0 0.4 0.4 0.4 -0.0 -0.0 0.8 0.7 0.9 0.9 1.0

-0.1 0.1 -0.5 -0.3 0.1 0.2 0.2 0.2 0.3 -0.5 0.2 0.3 0.5 -0.3 -0.4 -0.1 1.0

-0.2 0.0 -0.5 -0.3 0.2 0.4 0.0 0.1 0.4 -0.5 0.2 0.5 0.6 -0.2 -0.3 0.0 0.8 1.0

-0.0 -0.0 -0.6 -0.4 0.4 0.4 0.0 0.1 0.4 -0.5 0.4 0.6 0.7 -0.1 -0.2 0.1 0.7 0.8 1.0

0.1 0.4 0.1 0.1 -0.4 -0.6 0.5 0.4 -0.1 0.1 -0.2 0.1 -0.0 0.3 0.2 0.4 -0.1 -0.3 -0.3 1.0

0.1 0.4 0.1 0.2 -0.4 -0.6 0.4 0.3 -0.3 0.2 -0.1 -0.1 -0.1 0.2 0.2 0.3 -0.2 -0.4 -0.3 0.9 1.0

0.1 0.4 0.2 0.1 -0.4 -0.6 0.5 0.4 -0.2 0.3 -0.2 -0.0 -0.1 0.4 0.3 0.4 -0.4 -0.5 -0.4 0.9 1.0 1.0

0.0 0.5 -0.1 0.0 -0.4 -0.5 0.5 0.4 -0.0 -0.1 -0.1 0.1 0.1 0.0 -0.0 0.2 0.2 0.0 -0.1 0.8 0.8 0.8 1.0

0.2 0.4 0.1 0.2 -0.4 -0.6 0.4 0.3 -0.2 0.1 -0.1 -0.0 -0.0 0.1 0.1 0.2 -0.1 -0.3 -0.2 0.9 1.0 0.9 0.8 1.0

0.2 0.3 -0.1 0.2 -0.2 -0.4 0.1 0.1 -0.2 -0.0 -0.0 -0.0 -0.0 -0.2 -0.2 -0.1 0.1 0.0 0.2 0.5 0.7 0.6 0.7 0.8 1.0

0.1 0.4 -0.2 0.1 -0.2 -0.4 0.3 0.2 -0.2 -0.0 0.0 -0.1 -0.1 -0.1 -0.2 -0.0 0.1 -0.0 0.1 0.6 0.8 0.7 0.8 0.9 1.0 1.0

0.1 0.4 -0.0 0.1 -0.4 -0.6 0.5 0.4 -0.3 0.1 -0.1 -0.1 -0.1 0.1 0.1 0.2 -0.1 -0.3 -0.3 0.9 1.0 0.9 0.8 1.0 0.8 0.9 1.0
12 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

The equations with a smaller SEr, Mallow’s Cp, and 

PRESS statistic and higher adj-R2

 were preferred. In addition, 

the explanatory variables were selected based on (1) statistical 

significance at the 95-percent confidence level, (2) an analysis 

of the residuals, and (3) how the explanatory variables might 

affect flows. Explanatory variables that had a 95-percent probability of effectiveness (probably a good predictor of flow and 

not due to chance) were classified as significant. If an explanatory variable was significant but had only a small effect on 

the standard error (arbitrarily chosen as less than a 2-percent 

change), it was left out of the equation.

An additional criterion in selecting explanatory variables for the final regression equations was to have no more 

than three variables (basin characteristics). This was done 

to minimize overfitting the regression equation and to avoid 

multicollinearity among variables, which makes it difficult to 

evaluate the relative importance of the individual explanatory 

variable in the regression equation. Multicollinearity occurs 

when two (or more) explanatory variables are more highly 

correlated with each other than they are correlated with the 

predictor variable. The statistic used to measure the amount of 

multicollinearity is the variance-inflation factor (VIF) (Montgomery and others, 2001). VIF values express the ratio of the 

actual variance of the coefficient of the explanatory variable to 

its variance if it were independent of the explanatory variables 

(Cavalieri and others, 2000). A VIF value greater than 5–10 

generally indicates that multicollinearity is a serious problem 

in the regression model. The basin characteristics with a VIF 

value less than five were chosen as the final set of explanatory 

variables to form the regression equations.

Ordinary least squares (OLS) and weighted least squares 

(WLS) regression were used for developing the equations 

and deriving the final coefficients in the equations (Helsel 

and Hirsch, 1992). In OLS regression, equal weight is given 

to all streamgages in the analysis regardless of record length. 

However, the records are not equally reliable; records from 

a streamgage with 10 years of flow data are not as reliable as 

records from a streamgage with 50 years of data. The WLS 

method assigns more weight in the regression to sites with 

longer records than shorter records, and thus, presumably, the 

equations are more accurate. In WLS regression, the userdefined weights were computed as the years of record at the 

streamgage divided by the average number of years (34.6) 

of record of all of the streamgages. For example, Pendleton Brook (USGS streamgage 01118300) with 49 years of 

record was assigned a weight of 1.42 (49/34.6), while Indian 

River (USGS streamgage 01195100) with 26 years of record 

(23 years less than Pendleton Brook) was assigned a weight 

of 0.75 (26/34.6).

Short-term and partial-record sites were used in conjunction with continuous-record streamgages in developing the 

regression equation to estimate the non-bioperiod Q99 (table 8, 

fig. 2). Short-term and partial-record sites are considered less 

reliable than continuous-record streamgages but were used to 

increase the number of sites in the analysis. For WLS weighting, short-term and partial-record sites were assigned 0.5 year 

for each year in which measurements were made. The userdefined weights were based on the assumption that 1 year at 

a partial-record site is equal to 2 years at a continuous-record 

site. WLS regression was used to compute the final coefficients in all 32 regression equations.

Assessment of Regression Equations

Methods of assessing the adequacy of the equations 

included testing each one carefully for violations of the 

regression assumptions and problems with outliers. The basic 

assumptions for a regression equation include: (1) the equation adequately describes the relation between the response 

and explanatory variables, (2) the mean of the residual error is 

zero, (3) the variance of the residual error is constant, (4) the 

residual errors are normally distributed, and (5) the residual 

errors are independent of one another (Helsel and Hirsch, 

1992). Examination of the residuals plots indicated no unusual 

patterns. Overall, the equations appeared to fit the data reasonably well and adequately described the relation between the 

response and explanatory variables. The p-values from the 

WLS regression were checked for significance and found to be 

less than or equal to 0.05, which indicates the probability that 

the regression coefficient is significant.

Diagnostic checks on the equations included evaluating 

outliers and influential observations. The presence of outliers 

is a subtle form of non-normality and influential observations 

are data that substantially change the fit of the regression line. 

The influence of an individual observation on the regressions 

is measured with Cook’s D statistic (Helsel and Hirsch, 1992). 

Cook’s D statistic is a measure of the change in the parameter 

estimates when an observation is deleted from the regression 

analysis. No influential observations were found with Cook’s 

D statistic; therefore, no individual observation appreciably 

altered the slope of the regression line.

Final Regression Equations

Final regression equations are listed in table 9, along 

with the number of stations used in the regression analysis 

and several performance metrics. The StreamStats variable 

name and the explanatory variable name used in the final 

regression equations, along with a definition of the variable 

and the units of measure, are listed in appendix 2. Six basin 

characteristics—drainage area, percentage of area with coarse 

stratified deposits, percentage of the area with wetlands, mean 

monthly precipitation (November), mean seasonal precipitation (December, January, and February), and mean basin 

elevation—are used as explanatory variables in the equations. 

The explanatory variables in the equations were statistically 

significant at the 95-percent confidence level or better, were 

not correlated with other explanatory variables, and improved 

the standard errors by more than 2 percent. The performance 

metrics used to report the adequacy of the final regression 

equations included the adj-R2

 in percent and the SEr in percent 

(described in “Development of Regression Equations”). The 
Regional Regression Analysis 13

Figure 2. Locations of streamgages and short-term continuous-record and partial-record sites in Connecticut and surrounding 

states considered for use in developing a regression equation to estimate the non-bioperiod 99-percent flow exceedance (Q99).

CONNECTICUT

MASSACHUSETTS

NEW YORK

CONNECTICUT

Long Island NEW YORK

73°30' 73° 72°30' 72° 71°30'

42°30'

42°

41°30'

41°

01187800

01115098

01193800

01194000

01117468

01125490 01120500

01119360

01119255

01127100

01208999

01203700

01203100

01201890

01198800

01198700

01196600

01195146

01193300

01193210

01193130

01192800 01193120

01187680 01191900

01186400 01184300

01183990

01127800

01127700

01127400

01126700

01125900

01125600

01125300

01121300

01120920

01120200

01119320

01118750

01118350

01208990

01208950

01206500

01206400

01204800

01201930

01201190

01199200

01195200

01195100

01194500

01193500

01192600

01188000

01187400

01187300

01126950

01126600

01123000

01121000

01118300

01374890

01374598

01372800

01372200

01198000 01176000

01118000

01117800

01117500

01115187

01111500

01111300

01187850

RHODE ISLAND

Long Island Sound

Base from U.S. Geological Survey digital data 1:100,000

2000, Connecticut State Plane projection

EXPLANATION

0 15 30 MILES

0 25 50 KILOMETERS

01117500

01118750

01195146

Continuous record

Partial record

Short-term record

Streamgage station type and number

Hartford 

New London

New Haven
14 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut Table 8. Descriptions of short-term streamgages and partial-record sites considered for regionalizing flow-duration statistics in Connecticut..—Continued [USGS, U.S. Geological Survey; no., number; mi2, square miles; SHT, short-term record; P, partial record; ft3/s, cubic feet per second] USGS streamgage no. Streamgage name Latitude (decimal degrees) Longitude (decimal degrees) Drainage area (mi2

)

Years of 

record Period of record Type

99-percent

flow duration 

(ft3/s)

01118350 Green Fall River at Clarks Falls 41.455 -71.814 19.8 12.9 Oct 1960–Sep 1973

P 0.92

01118750 Haleys Brook near Old Mystic 41.389 -71.986 4.37 16.5 Feb 1962–Aug 1978

P 0.07

01119255 Delphi Brook near Staffordville 42.023 -72.248 2.59 13.0 Aug 1962–Aug 1975

P 0.08

01119320 Roaring Brook near Stafford Springs 41.934 -72.261 14.6 5.1 Aug 1961–Sep 1966 SHT 0.47

01119360 Conat Brook at West Willington 41.871 -72.291 2.40 15.3 Jun 1963–Sep 1978

P 0.45

01120200 Tenmile River near Willimantic 41.707 -72.247 16.3 11.3 Jun 1962–Sep 1973

P 0.35

01120920 Mount Hope River at Westford 41.920 -72.179 3.16 11.1 Jul 1962–Aug 1973

P 0.11

01121300 Fenton River at East Willington 41.872 -72.241 11.4 14.8 Oct 1960–Jul 1975

P 0.88

01125300 English Neighborhood Brook at North Woodstock 41.991 -71.997 4.66 17.1 Jul 1961–Aug 1978

P 0.01

01125600 Mashamoquet Brook at Abington 41.874 -72.009 11.1 14.0 Jul 1961–Jul 1975

P 0.30

01125900 Cady Brook at East Putnam 41.909 -71.819 8.29 18.0 July 1961–July 1979

P 0.40

01126700 Kitt Brook near Canterbury 41.681 -71.978 11.1 14.1 Jul 1961–Aug 1975

P 0.34

01127100 Broad Brook near Preston City 41.554 -71.970 12.5 12.9 Oct 1960–Jun 1965,

Jun 1967–Aug 1975

P 0.51

01127400 Susquetonscut Brook at Yantic 41.571 -72.133 15.7 14.8 Oct 1960–Aug 1975

P 0.56

01127700 Trading Cove Brook near Thamesville 41.501 -72.116 8.46 12.7 Oct 1960–Jun 1973

P 0.41

01127800 Fourmile River near East Lyme 41.357 -72.261 4.30 18.3 Oct 1960–Jan 1979

P 0.10

01183990 Jawbuck Brook near Hazardville 42.007 -72.553 2.16 13.3 Mar 1963–Jun 1976

P 0.35

01184300 Gillette Brook at Somers 41.992 -72.434 3.64 19.6 Sep 1960–Apr 1980

P 0.01

01186400 Sandy Brook at State Highway 8 at Robertsville 41.978 -73.045 34.9 9.0 Oct 1967–Oct 1976 SHT 2.99

01187680 Cherry Brook near Canton Center 41.872 -72.906 8.23 4.9 Oct 1966–Sep 1971 SHT 0.03

01191900 Charter Brook near Crystal Lake 41.906 -72.404 8.51 17.9 Oct 1960–Sep 1978

P 0.40

01192800 Parmalee Brook near Durham 41.452 -72.702 2.79 17.9 Oct 1960–Sep 1978

P 0.25

01193120 Ponset Brook near Higganum 41.479 -72.557 5.72 15.5 Jan 1962–Jul 1977

P 0.20

01193130 Candlewood Hill Brook near Higganum 41.474 -72.596 3.84 12.9 Oct 1960–Sep 1973

P 0.13
Regional Regression Analysis

15

Table 8. Descriptions of short-term streamgages and partial-record sites considered for regionalizing flow-duration statistics in Connecticut..—Continued[USGS, U.S. Geological Survey; no., number; mi2, square miles; SHT, short-term record; P, partial record; ft3/s, cubic feet per second]

USGS 

streamgage 

no.

Streamgage name

Latitude

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Drainage 

area

(mi2)

Years of 

record Period of record Type

99-percent

flow duration 

(ft3/s)

01193210 Raymond Brook near Amston 41.640 -72.343 3.52 9.9 Oct 1960–Jul 1964,

Aug 1967–Sep 1973

P 0.02

01193300 Blackledge River near Gilead 41.696 -72.456 6.75 15.0 Sep 1960–Aug 1975,

Sep 1978

P 0.17

01195146 Pond Meadow Brook near Killingworth 41.383 -72.589 5.92 8.9 Sep 1984–Aug 1993 SHT 0.02

01196600 Willow Brook near Cheshire 41.460 -72.918 9.34 18.6 Sep 1986–Apr 2005 P 1.97

01198700 Brown Brook at Lower City 41.926 -73.280 5.56 7.9 Sep 1960–Aug 1968 P 0.12

01198800 Hollenbeck River at Huntsville 41.949 -73.321 18.1 3.9 Oct 1970–Sep 1974 SHT 1.21

01201890 Pond Brook near Hawleyville 41.456 -73.335 11.9 12.9 Oct 1962–Sep 1975 P 0.42

01203100 Jacks Brook near Roxbury Falls 41.528 -73.308 7.90 15.0 Sep 1960–Aug 1975,

Aug 1978

P 0.33

01203700 Wood Creek near Bethlehem 41.627 -73.226 3.39 17.1 Oct 1960–Nov 1966,

Jul 1968–Jul 1979

P 0.12

01208999 Little River at Sanfordtown 41.293 -73.368 5.50 3.5 Mar 1965–Sep 1968 SHT 0.04
16 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 9. Summary of regression equations for estimating flow-duration statistics at ungaged stream sites in Connecticut and 

performance metrics.

[adj-R2, adjusted coefficient of determination; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow exceedance; Q80, 80-percent exceedance; Q90, 90-percent flow exceedance; Q95, 95-percent flow exceedance; Q99, 99-percent flow exceedance; DRNAREA, Drainage area, in square 

miles; PPTnov, mean monthly precipitation for November, in inches; CRSDFT, percentage of drainage area underlain with coarse stratified deposits; PPTow, 

mean seasonal precipitation for Dec-Feb, in inches; WETLAND, percentage of drainage area with wetlands; ELEV, mean basin elevation, in feet]

Regression equation

Number

of

stations 

used in 

analysis

adj-R2

(percent)

Average percent 

standard error

of estimate

(range)

Salmonid Spawning 

(November)

Q25 = (10 -0.3513) (DRNAREA0.9813) (PPTnov 1.0465) 39 98.5 20.9 (23.0 to -18.7)

Q50 = (10 -0.8383) (DRNAREA0.9761) (PPTnov 1.3863) 39 98.2 21.1 (23.2 to -18.8)

Q75 = (10 -1.7042) (DRNAREA1.0175) (PPTnov 2.1755) 39 96.4 27.4 (30.9 to -23.6)

Q90 = (10 -3.0117) (DRNAREA1.0418) (PPTnov 3.5009) (CRSDFT0.1240) 39 95.8 36.0 (41.8 to -29.5)

Q99 = (10 -4.7478) (DRNAREA1.1056) (PPTnov 5.2826) (CRSDFT0.2370) 39 90.6 55.4 (67.8 to -40.4)

Overwinter

(December–

February)

Q25 = (10 -0.5449) (DRNAREA1.0092) (PPTow 1.6126) 39 97.9 19.2 (21.0 to -17.4)

Q50 = (10 -0.9813) (DRNAREA1.0204) (PPTow 1.9523) 39 97.4 21.4 (23.6 to -19.1)

Q75 = (10 -1.4090) (DRNAREA1.0328) (PPTow 2.2826) 39 97.4 20.7 (22.7 to -18.5)

Q95 = (10 -2.0997) (DRNAREA1.0425) (PPTow 2.8578) 39 96.4 24.9 (27.8 to -21.7)

Q99 = (10 -3.3438) (DRNAREA1.0733) (PPTow 4.4479) 39 96.0 28.4 (32.1 to -24.3)

Habitat Forming 

(March–April)

Q25 = (10 0.6225) (DRNAREA1.0043) 39 99.4 11.1 (11.7 to -10.5)

Q50 = (10 0.4185) (DRNAREA1.0142) 39 99.4 10.7 (11.2 to -10.1)

Q75 = (10 0.1998) (DRNAREA1.0074) (CRSDFT0.0641) 39 99.3 12.9 (13.7 to -12.0)

Q95 = (10 -0.0583) (DRNAREA0.9998) (CRSDFT0.1007) 39 98.4 19.3 (21.1 to -17.4)

Q99 = (10 -0.2160) (DRNAREA0.9979) (CRSDFT0.1138) 39 98.0 20.9 (22.9 to -18.6)

Clupeid Spawning 

(May)

Q25 = (10 0.4126) (DRNAREA0.9859) (CRSDFT0.0376) 39 99.0 15.1 (16.2 to -14.0)

Q50 = (10 0.1782) (DRNAREA0.9932) (CRSDFT0.0867) 39 98.8 17.2 (18.6 to -15.7)

Q75 = (10 -0.0217) (DRNAREA0.9959) (CRSDFT0.1207) 39 98.4 19.1 (20.8 to -17.2)

Q95 = (10 -0.3712) (DRNAREA1.0109) (CRSDFT0.1999) 39 96.9 28.1 (31.7 to -24.1)

Q99 = (10 -0.6137) (DRNAREA1.0322) (CRSDFT0.2525) 39 95.8 36.5 (42.4 to -29.8)

Resident Spawning 

(June)

Q25 = (10 0.1626) (DRNAREA0.9296) (CRSDFT0.0629) (WETLAND 0.1276) 39 98.1 21.9 (24.2 to -19.5)

Q50 = (10 -0.1910) (DRNAREA0.9454) (CRSDFT0.1302) (WETLAND 0.1242) 39 97.8 24.9 (27.7 to -21.7)

Q75 = (10 -0.5148) (DRNAREA0.9561) (CRSDFT0.1971) (WETLAND 0.1518) 39 96.7 31.9 (36.5 to -26.7)

Q90 = (10 -0.8412) (DRNAREA1.0469) (CRSDFT0.2837) 39 94.5 40.5 (47.7 to -32.3)

Q99 = (10 -1.3044) (DRNAREA1.1021) (CRSDFT0.3671) 39 90.1 67.3 (84.3 to -45.7)

Rearing and Growth 

(July–October)

Q25 = (10 -0.2991) (DRNAREA1.0311) (CRSDFT0.0962) 38 96.6 30.9 (35.2 to -26.0)

Q50 = (10 -0.7849) (DRNAREA1.0784) (CRSDFT0.1958) 38 94.5 40.7 (47.9 to -32.4)

Q75 = (10 -1.2209) (DRNAREA1.1328) (CRSDFT0.2765) 38 91.9 54.2 (66.1 to -39.8)

Q80 = (10 -1.3276) (DRNAREA1.1531) (CRSDFT0.2915) 38 90.9 59.2 (72.9 to -42.2)

Q99 = (10 -2.4534) (DRNAREA1.3776) (CRSDFT0.4798) 36 77.5 156 (203 to -67.0)

Nonbioperiod

Q25 = (10 -0.6903) (DRNAREA0.9976) (ELEV-0.1146) 39 99.2 14.5 (15.5 to -13.4)

Q99 = (10 -2.0567) (DRNAREA1.2141) (CRSDFT0.5037) 72 81.8 111 (145 to -59.1)
Regional Regression Analysis 17

metrics indicate how well the equations perform on the sites 

used in the regression analysis. Theoretically, the equations 

should perform equally well for ungaged sites as long as the 

basin characteristics are within the same range as those used 

to develop the equation. The SEr

 measures the difference 

between the observed value (flow derived from the streamgage 

record) and the predicted value (flow derived from the 

regression equation).

In general, the physical processes controlling high flows 

are related to drainage area and precipitation; the physical processes controlling low flows are related to geologic 

characteristics as well as drainage area. “Drainage area” was 

the predominant predictor in all the equations. “Precipitation” was an important predictor in two high-flow bioperiods: Salmonid Spawning (mean monthly precipitation for 

November) and Overwinter (mean seasonal precipitation for 

December through February). The inclusion of the precipitation characteristics in the regression models explained an 

additional 4.2 and 4.9 percent of the variability and improved 

the standard errors of estimate by 10.3 and 13.8 percent in the 

Q99 for the Salmonid Spawning and Overwinter bioperiods, 

respectively. The explanatory variable “percentage of area 

with coarse, stratified deposits” was an important predictor in 

all the bioperiods, with the exception of Overwinter (December–February); typically, this characteristic was important at 

the exceedances higher than Q75 (low-flow conditions). Drainage basins underlain with a large percent of coarse stratified 

deposits have larger base flows than drainage basins underlain 

with glacial till and bedrock (Thomas, 1966). The inclusion of the variable “percentage of area with coarse stratified 

deposits” in the equations explained an additional 4.7, 7.4, 

and 6.6 percent of the variability and improved the standard 

errors of estimate by 11.0, 15.6, and 19.0 percent in the Q99

for the Clupeid Spawning, Resident Spawning, and Rearing 

and Growth bioperiods, respectively. The explanatory variable “percentage of the area with wetlands” was a predictor of 

flows in the Resident Spawning bioperiod for the Q25-Q75 (June 

high and median flows). This explanatory variable, which 

showed a positive correlation to flow, may serve as an indicator for other factors such as soil-moisture content and surface 

storage that cause variation between basins but are difficult to 

evaluate. During wetter periods (spring), soils are saturated, 

and infiltration and surface storage are reduced. The explanatory variable “percentage of the area with wetlands” explained 

an additional 1 percent of the variability and improved the 

standard error of estimate by 4.4, 2.6, and 2.5 percent in the 

Q25, Q50, and Q75, respectively.

Where possible, the same explanatory variables were 

used for all flow exceedances in a bioperiod to ensure that the 

flow estimates decrease with an increase in the exceedance 

probability. For example, the Q99 is less than the Q90, and the 

Q90 is less than the Q75. In several bioperiods, an additional 

explanatory variable was added to the set of explanatory 

variables when it improved the standard error of estimate by 

more than 2 percent. The regression equations were checked to 

ensure that the flow estimates decrease with an increase in the 

exceedance probability in cases where an additional explanatory variable was added to the bioperiod.

The proportion of the variability in the flow statistic 

explained by the explanatory variable (adj-R2

) was greater 

than 90 percent for all exceedances with two exceptions: 

equations explained only 77.5 percent of the variability in the 

Q99 for the Rearing and Growth bioperiod and 81.3 percent 

of the variability in the non-bioperiod Q99 . The adj-R2

 of the 

32 regression equations ranged from 77.5 to 99.4 percent; 

the medians were 98.5 and 90.6 percent for the Q25 and Q99, 

respectively. Regression equations for high and median flows 

(Q25, Q50, and Q75) generally had higher predictive power 

than regression equations for low flows (Q90, Q95, and Q99). 

The standard errors of estimate to predict the Q25 and Q99 had 

medians of 19.2 and 55.4 percent, respectively. The Habitat 

Forming (March–April) bioperiod had the smallest standard 

errors of estimate, ranging from 10.7 to 20.9 percent for 

the Q50 and Q99, respectively. In contrast, the Rearing and 

Growth (July–Oct) bioperiod had the largest standard errors, 

ranging from 30.9 to 156 percent for the Q25 and Q99, respectively. Table 9 lists the range of standard errors, as well as 

the average, for each regression equation. In this study, the 

range is important when the average standard error is large. 

For example, for the Q99 in the Rearing and Growth bioperiod, 

the average standard error of estimate is 156 percent. If the 

regression equation resulted in a flow of 10 ft3

/s, the range of 

flows could be between 3.3 and 30.3 ft3

/s based on the range 

of the standard error of estimate. Using the average of the 

standard error of estimate would give a range of flows between 

-5.6 and 25.6 ft3

/s, which is not possible.

It is difficult to characterize low flows from information 

available in existing data sets. Subsequently, low flows typically have a large standard error of estimate. High evaporation 

rates, along with increased use of water by riparian vegetation, 

are processes that cause low flow but are difficult to capture as 

explanatory variables. The number of streamgages in the analysis, the number of years of record, the degree of the relation 

between the explanatory variable and the flow statistic, and the 

accuracy of the actual measurements all affect the accuracy of 

the estimates. Increasing any of these factors will improve the 

estimates. Future improvements in the regression equations 

for estimating flow durations, particularly low flows, may be 

made by evaluating different groupings of subsurface geologic 

characteristics and by incorporating higher spatial-resolution 

data as they become available.

Limitation of the Regression Equations

Statewide equations were developed because of the 

limited number of sites available for use in the regression 

analysis. An analysis of the residuals of the 32 regression 

equations indicated that no strong regional biases were 

evident. The residuals for each of the equations were plotted 

on a map. Several plots that include the variable “percentage of area with coarse stratified deposits” may show a slight 

regional bias. For example, figure 3 shows that the Q99 flows 
18 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Figure 3. Residuals of the regression equation for the non-bioperiod 99-percent flow exceedance (Q99) for the study area. 

Several stations considered as outliers or having a Q99 value of zero were dropped from the non-bioperiod Q99 regression 

analysis including Clear Brook (01187850), Marshepaug River (01201930), and Guinea Brook (01199200).

CONNECTICUT

MASSACHUSETTS

RHODE ISLAND

NEW YORK

CONNECTICUT

Long Island NEW YORK

73°30' 73° 72°30' 72° 71°30'

42°30'

42°

41°30'

41°

Long Island Sound

Base from U.S. Geological Survey digital data 1:100,000

2000, Connecticut State Plane projection

EXPLANATION

0 15 30 MILES

0 25 50 KILOMETERS

Regression residuals

0.25 to 0.75

0.00 to less than 0.25

-0.25 to less than 0.00

-0.87 to less than -0.25

Hartford 

New London

New Haven
References Cited 19

in the eastern half of the State tend to be over-predicted and 

flows in the western half tend to be under-predicted. Regionalization of streamflow characteristics may be improved if 

there is an increased number of streamgages thus allowing for 

smaller subregions. The smaller subregions may provide a set 

of parameters with stronger predictive power. The regression 

equations developed in this study are not intended to be used 

at ungaged sites in which the basin characteristics are outside 

of the range of those used to create the regression equations 

(tables 5 and 6, at the back of this report). Flow statistics 

predicted by the equations represent natural flow conditions in 

Connecticut; effects of dams or other flow alterations are not 

included in the equations.

Summary

This report documents the development of regression 

equations with statewide application that can be used for 

determining flow-duration statistics at ungaged stream sites 

in Connecticut. Multiple linear regression equations using 

a weighted least squares (WLS) technique for determining 

flow-duration statistics were developed to estimate the 25-, 

50-, 75- and 99-percent flow exceedances (Q25, Q50, Q75, and 

Q99) for six bioperiods—Salmonid Spawning (November), 

Overwinter (December–February), Habitat Forming (March–

April), Clupeid Spawning (May), Resident Spawning (June), 

and Rearing and Growth (July–October)—and one additional 

low-flow-duration statistic for each bioperiod—the 80-percent 

exceedance (Q80) for the Rearing and Growth bioperiod; the 

90-percent exceedance (Q90) for the Resident Spawning and 

Salmonid Spawning bioperiods; and the 95-percent exceedance (Q95) for the Overwinter, Habitat Forming, and Clupeid 

Spawning bioperiods. Regression equations also were developed to estimate the 25- and 99-percent exceedances (Q25 and 

Q99) without reference to a bioperiod.

Streamflow data and GIS-derived basin characteristics 

from 39 streamgages having 10 or more years of continuous 

record were used to develop the final equations. The equations 

were developed using WLS regression analyses with userdefined weights based on the years of streamflow record so 

that more weight was given in the regression models to sites 

with longer periods of record. Presumably, this would result 

in flow statistics that are more accurate. Flow exceedances 

computed from streamflow data through 2007 were statistically related to the basin characteristics upstream from the 

streamgages in the regression analysis. The basin characteristics—drainage area, percentage of area with coarse stratified deposits, percentage of the area with wetlands, monthly 

mean precipitation (November), mean seasonal precipitation 

(December–February), and mean basin elevation—were used 

as explanatory variables in the equations. These variables 

show a positive correlation to the flow for all exceedances.

The regression equations explain greater than 90 percent of the variability in the flow-duration statistics for all 

exceedances with two exceptions: 77.5 percent of the variability in the Q99 for the Rearing and Growth bioperiod and 

81.3 percent of the variability in the Q99 for the long-term 

flow conditions. The standard errors of estimates for the 32 

regression equations ranged from 10.7 to 156 percent. The 

Habitat Forming (March–April) bioperiod had the smallest 

standard errors of estimate, ranging from 10.7 to 20.9 percent 

for the Q50 and Q99, respectively. In contrast, the Rearing and 

Growth (July–October) bioperiod had the largest standard 

errors of estimate, ranging from 30.9 to 156 percent for the Q25

and Q99, respectively. 

Acknowledgments

The author is most grateful for help from a number of 

colleagues. Christopher Bellucci and Mary Becker of DEP 

provided assistance with identifying study basins with natural 

flows. Julie Kiang from the USGS Office of Surface Water 

provided invaluable assistance with many parts of the regionalization study, particularly in the selection of the best models 

and performing the weighted least squares regression. David 

Lorenz from the USGS wrote scripts for calculating bioperiod 

statistics and provided invaluable assistance with interpreting 

the output of the regression models. Thomas Trombley and 

Lance Ostiguy (USGS) provided assistance with assembling 

the GIS data and compiling the drainage-basin characteristics. 

CT DEP and USGS colleague reviewers—Peter Aarrestad, 

Mary Becker, Christopher Bellucci, Corinne Fitting (all from 

DEP), and Julie Kiang, Scott Olson, and Marla Stuckey (all 

from USGS)—graciously provided thorough and timely 

reviews of the report. Finally, the author is also very grateful 

to Kim Otto and Virginia de Lima and for their exceptional 

editorial skills.

References Cited

Ahearn, E.A., 2004, Regression equations for estimating flood 

flows for the 2-, 10-, 25-, 50-, 100-, and 500-year recurrence 

intervals in Connecticut: U.S. Geological Survey Scientific 

Investigations Report 2004–5160, 62 p.

Ahearn, E.A., 2007, Flow durations, low-flow frequencies, and 

monthly median flows for selected streams in Connecticut 

through 2005: U.S. Geological Survey Scientific Investigations Report 2007–5270, 33 p.

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22 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 3. Flow-duration statistics for streamgages with at least 10 years of continuous record in Connecticut and neighboring states 

considered for regression analysis: A, Actual streamflow; B, Normalized streamflow.

[USGS, U.S. Geological Survey; no. number; mi2, square miles; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow 

exceedance; Q90, 90-percent flow exceedance; Q99, 99-percent flow exceedance]

A. Actual streamflow, in cubic feet per second

USGS 

streamgage no. Streamgage name State Drainage area (mi2

)

Non-bioperiod

Q25 Q99

01111300 Nipmuc River near Harrisville Rhode Island 16.0 39.0 0.34

01111500 Branch River at Forestdale Rhode Island 91.2 228 13.0

01115098 Peeptoad Brook at Elmdale Road near Westerly Rhode Island 4.83 14.0 0.09

01115187 Ponaganset River at South Foster Rhode Island 14.4 35.0 0.11

01117468 Beaver River near Usquepaug Rhode Island 8.87 30.0 2.09

01117500 Pawcatuck River at Wood River Junction Rhode Island 100 266 28.0

01117800 Wood River near Arcadia Rhode Island 35.2 103 7.70

01118000 Wood River at Hope Valley Rhode Island 72.4 210 19.0

01118300 Pendleton Hill Brook near Clarks Falls Connecticut 4.02 11.0 0.06

01120500 Safford Brook near Woodstock Valley Connecticut 4.15 8.50 0.02

01121000 Mount Hope River near Warrenville Connecticut 28.6 66.0 1.00

01123000 Little River near Hanover Connecticut 30.0 69.0 4.90

01125490 Little River at Harrisville Connecticut 35.8 56.0 0.60

01126600 Blackwell Brook near Brooklyn Connecticut 17.0 38.0 0.70

01126950 Pachaug River at Pachaug Connecticut 53.0 130 0.76

01176000 Quaboag River at West Brimfield Massachusetts 150 344 16.0

01187300 Hubbard Brook near West Hartland Connecticut 19.9 43.0 0.56

01187400 Valley Brook near West Hartland Connecticut 7.03 16.0 0.30

01187800 Nepaug River near Nepaug Connecticut 23.5 46.0 1.50

01187850 Clear Brook near Collinsville1 Connecticut 0.59 2.1 0.53

01188000 Bunnell Brook near Burlington Connecticut 4.10 9.30 0.65

01192600 South Branch Salmon Brook at Buckingham Connecticut 0.94 2.00 0.31

01193500 Salmon River near East Hampton Connecticut 100 238 6.40

01193800 Hemlock Valley Brook at Hadlyme Connecticut 2.62 6.90 0.20

01194000 Eightmile River at North Plain Connecticut 20.1 50.0 0.60

01194500 East Branch Eightmile River near North Lyme Connecticut 22.3 58.0 0.63

01195100 Indian River near Clinton Connecticut 5.68 13.0 0.08

01195200 Neck River near Madison Connecticut 6.55 15.0 0.06

01198000 Green River near Great Barrington Massachusetts 51.0 102 3.30

01199200 Guinea Brook at West Woods Road at Ellsworth Connecticut 3.50 9.20 2

0.00

01201190 West Aspectuck River at Sand Road near New Milford Connecticut 23.8 44.0 0.95

01201930 Marshepaug River near Milton1 Connecticut 9.24 27.0 0.45

01204800 Copper Mill Brook near Monroe Connecticut 2.45 5.70 0.10

01206400 Leadmine Brook near Harwinton Connecticut 19.6 45.0 0.60

01206500 Leadmine Brook near Thomaston Connecticut 24.3 56.0 0.60

01208950 Sasco Brook near Southport Connecticut 7.38 16.0 0.09

01208990 Saugatuck River near Redding Connecticut 21.0 51.0 0.35

01372200 Wappinger Creek near Clinton Corners New York 92.4 160 4.10

01372800 Fishkill Creek at Hopewell Junction New York 57.2 105 2.00

01374598 Horse Pound Brook near Lake Carmel New York 3.94 10.0 0.04

01374890 Cross River near Cross River New York 17.1 44.0 0.46

1

Site not used in regression.

2

Zero value not used in regression. 
Table 3 23

Table 3. Flow-duration statistics for streamgages with at least 10 years of continuous record in Connecticut and neighboring states 

considered for regression analysis: A, Actual streamflow; B, Normalized streamflow.—Continued

[USGS, U.S. Geological Survey; no. number; mi2, square miles; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow 

exceedance; Q90, 90-percent flow exceedance; Q99, 99-percent flow exceedance]

A Actual streamflow, in cubic feet per second 

USGS 

streamgage no.

Salmonid Spawning USGS 

streamgage no.

Overwinter

Q25 Q50 Q75 Q90 Q99 Q25 Q50 Q75 Q95 Q99

01111300 33.0 17.0 7.90 4.10 0.89 01111300 48.0 30.0 18.0 8.50 4.70

01111500 202 120 75.0 45.0 21.0 01111500 280 176 113 60.0 36.0

01115098 11.0 7.00 2.80 1.04 0.54 01115098 18.0 11.0 6.20 2.30 0.99

01115187 29.0 17.0 8.40 4.20 2.20 01115187 46.0 27.0 16.0 8.40 3.70

01117468 24.0 13.0 7.10 4.40 3.30 01117468 35.0 24.0 15.0 6.90 3.40

01117500 209 118 76.0 55.0 39.0 01117500 344 223 151 79.0 52.0

01117800 81.0 50.0 31.0 17.0 9.50 01117800 128 86.0 55.0 28.0 15.0

01118000 168 94.5 60.0 39.0 22.0 01118000 250 171 114 60.0 35.0

01118300 10.0 5.40 2.90 1.40 0.53 01118300 15.0 9.00 5.40 2.50 1.50

01120500 9.60 4.50 1.70 0.94 0.25 01120500 11.0 5.60 3.20 1.50 0.90

01121000 60.0 29.0 15.0 8.60 2.80 01121000 78.0 46.0 27.0 13.0 8.00

01123000 62.5 34.0 18.0 12.0 5.90 01123000 84.0 52.0 32.0 17.0 11.0

01125490 52.0 25.0 12.5 5.40 2.80 01125490 65.0 36.0 24.0 12.0 9.20

01126600 33.0 15.0 7.80 3.05 0.78 01126600 50.0 29.0 15.0 7.80 5.10

01126950 110 54.5 34.0 10.5 6.00 01126950 156 96.0 67.0 22.0 12.0

01176000 274 142 81.0 46.0 21.0 01176000 360 220 132 60.0 39.0

01187300 47.0 26.0 12.0 6.00 2.60 01187300 44.5 25.0 16.0 7.10 4.20

01187400 14.0 7.10 2.80 1.20 0.55 01187400 14.0 8.60 5.80 2.60 1.70

01187800 38.0 20.0 9.90 5.80 3.10 01187800 45.0 27.0 16.0 7.30 5.00

01187850 1.50 1.10 0.97 0.77 0.61 01187850 1.60 1.20 0.88 0.53 0.40

01188000 9.05 5.30 2.90 1.70 1.00 01188000 9.50 6.00 3.90 2.10 1.30

01192600 1.30 0.88 0.62 0.40 0.31 01192600 1.90 1.20 0.75 0.41 0.31

01193500 200 106 56.0 29.0 16.0 01193500 288 170 103 46.0 26.0

01193800 4.90 2.60 1.70 0.70 0.43 01193800 8.55 5.20 3.10 1.60 1.00

01194000 41.0 21.0 8.20 5.00 2.40 01194000 60.0 37.0 24.0 11.0 5.70

01194500 52.0 28.0 14.0 8.00 4.30 01194500 75.0 44.0 26.0 12.0 7.50

01195100 12.0 6.30 3.10 1.50 0.68 01195100 16.0 9.80 5.90 2.90 1.40

01195200 10.0 5.05 2.30 1.20 0.44 01195200 19.0 11.0 6.10 2.50 1.40

01198000 106 43.5 17.0 7.30 3.20 01198000 100 56.0 37.0 21.0 6.10

01199200 9.00 4.20 1.80 0.48 0.07 01199200 9.70 5.20 2.80 1.20 0.45

01201190 28.0 18.0 8.60 4.20 2.50 01201190 45.0 30.0 19.0 11.0 6.00

01201930 33.0 21.0 7.95 4.85 0.80 01201930 30.0 18.0 6.60 1.90 0.26

01204800 4.40 2.70 1.50 0.85 0.21 01204800 7.10 4.20 2.50 1.20 0.70

01206400 44.0 28.0 15.0 4.00 1.20 01206400 47.0 28.0 21.0 9.90 6.40

01206500 50.0 23.5 10.0 5.90 1.80 01206500 59.0 34.0 19.0 8.00 4.30

01208950 15.0 8.30 3.90 1.60 0.32 01208950 20.0 12.0 7.20 2.70 0.88

01208990 47.0 26.0 14.0 5.40 1.00 01208990 67.0 40.0 23.0 9.70 5.00

01372200 114 62.0 28.0 12.0 5.80 01372200 180 100 60.0 21.0 10.0

01372800 71.0 41.0 15.0 6.70 4.30 01372800 124 76.0 43.0 14.0 6.90

01374598 12.0 6.00 2.40 0.76 0.17 01374598 12.0 7.50 3.95 1.20 0.63

01374890 46.0 25.0 9.90 1.95 1.10 01374890 57.0 33.0 16.5 5.10 2.50
24 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 3. Flow-duration statistics for streamgages with at least 10 years of continuous record in Connecticut and neighboring states 

considered for regression analysis: A, Actual streamflow; B, Normalized streamflow.—Continued

[USGS, U.S. Geological Survey; no. number; mi2, square miles; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow 

exceedance; Q90, 90-percent flow exceedance; Q99, 99-percent flow exceedance]

A Actual streamflow, in cubic feet per second 

USGS 

streamgage no.

Habitat Forming USGS 

streamgage no.

Clupeid Spawning

Q25 Q50 Q75 Q95 Q99 Q25 Q50 Q75 Q95 Q99

01111300 69.0 44.0 30.0 17.0 12.0 01111300 43.0 29.0 20.0 11.0 8.00

01111500 395 254 173 101 69.0 01111500 240 162 116 66.0 51.0

01115098 24.0 16.0 11.0 6.80 4.00 01115098 15.0 10.0 6.90 4.40 2.70

01115187 60.0 37.0 24.0 16.0 11.0 01115187 36.0 23.0 15.0 9.60 5.40

01117468 44.0 31.0 23.0 16.0 11.0 01117468 33.0 25.0 19.0 13.0 11.0

01117500 429 307 224 149 114 01117500 319 234 183 133 99.0

01117800 158 112 83.0 55.0 40.0 01117800 110 84.0 62.0 43.0 36.0

01118000 324 234 176 118 87.0 01118000 228 172 132 91.0 72.0

01118300 18.0 12.0 8.30 5.20 3.60 01118300 13.0 8.30 5.70 3.10 2.10

01120500 18.0 10.0 6.10 3.20 2.00 01120500 8.10 4.90 3.20 1.50 0.88

01121000 113 73.0 52.0 30.0 22.0 01121000 72.0 48.0 31.0 16.0 11.0

01123000 113 77.0 55.0 33.0 22.0 01123000 75.0 53.0 38.0 23.0 19.0

01125490 148 90.0 54.0 25.0 20.0 01125490 64.0 41.5 30.0 14.0 7.80

01126600 64.0 43.0 30.0 17.0 12.0 01126600 39.0 28.0 20.0 11.0 5.40

01126950 215 153 106 62.0 46.0 01126950 154 104 77.5 48.0 26.0

01176000 660 445 300 160 110 01176000 412 286 192 114 83.0

01187300 103 55.0 31.0 16.0 10.0 01187300 55.0 30.0 19.0 8.60 5.00

01187400 40.0 23.0 14.0 7.10 5.00 01187400 22.0 14.0 9.30 4.90 2.80

01187800 99.0 60.0 40.0 22.0 16.0 01187800 56.5 37.0 25.0 13.0 9.30

01187850 2.60 2.00 1.40 0.88 0.61 01187850 2.70 2.20 1.70 1.10 0.97

01188000 17.0 11.0 7.40 4.30 3.10 01188000 11.0 7.40 5.30 3.10 2.20

01192600 3.00 2.40 1.70 0.98 0.71 01192600 2.60 2.00 1.40 0.92 0.74

01193500 408 270 189 118 88.0 01193500 272 180 124 73.0 51.0

01193800 11.0 7.60 5.60 3.60 2.80 01193800 9.10 5.80 4.00 2.40 1.60

01194000 86.0 57.0 41.0 26.0 20.0 01194000 54.0 36.0 24.0 15.0 10.0

01194500 100 65.0 45.0 27.0 19.0 01194500 66.0 44.0 29.0 18.0 12.0

01195100 20.0 13.0 8.20 5.40 4.10 01195100 13.0 8.00 5.30 2.60 1.60

01195200 27.0 17.0 12.0 7.15 5.40 01195200 18.0 11.5 7.70 4.30 3.00

01198000 237 140 86.0 44.0 30.0 01198000 128 91.0 65.0 33.0 22.0

01199200 17.0 11.0 6.60 2.80 2.10 01199200 11.0 6.70 4.30 1.70 0.96

01201190 88.0 58.0 39.0 23.0 18.0 01201190 56.0 35.0 24.0 12.0 8.50

01201930 44.0 26.0 12.0 4.00 1.30 01201930 25.0 14.0 8.20 1.90 0.90

01204800 10.0 6.50 4.50 2.90 2.20 01204800 6.30 4.00 2.80 1.40 0.73

01206400 93.0 57.0 39.0 22.0 19.0 01206400 48.0 32.0 24.0 9.80 6.30

01206500 118 68.0 45.0 27.0 16.0 01206500 68.0 41.0 26.0 12.0 9.00

01208950 26.0 16.0 11.0 6.60 4.90 01208950 18.0 11.0 6.60 2.90 1.80

01208990 87.0 52.0 36.0 22.0 15.0 01208990 55.0 34.0 22.0 11.0 6.30

01372200 348 208 136 67.0 52.0 01372200 172 109 74.0 37.0 25.0

01372800 206 136 91.0 45.0 35.0 01372800 113 77.0 53.0 28.0 21.0

01374598 15.0 9.90 6.70 3.50 2.80 01374598 8.90 5.30 3.40 1.70 1.20

01374890 65.0 42.0 30.0 14.0 11.0 01374890 41.0 26.0 16.0 7.30 3.70
Table 3 25

Table 3. Flow-duration statistics for streamgages with at least 10 years of continuous record in Connecticut and neighboring states 

considered for regression analysis: A, Actual streamflow; B, Normalized streamflow.—Continued

[USGS, U.S. Geological Survey; no. number; mi2, square miles; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow 

exceedance; Q90, 90-percent flow exceedance; Q99, 99-percent flow exceedance]

A Actual streamflow, in cubic feet per second 

USGS 

streamgage no.

Resident Spawning USGS 

streamgage no.

Rearing and Growth

Q25 Q50 Q75 Q90 Q99 Q25 Q50 Q75 Q95 Q99

01111300 26.0 12.0 6.90 3.80 1.50 01111300 8.70 3.60 1.60 1.30 0.13

01111500 144 81.5 53.0 37.0 24.0 01111500 75.0 43.0 27.0 24.0 9.10

01115098 10.0 4.65 2.50 1.50 0.70 01115098 2.40 0.99 0.53 0.45 0.03

01115187 23.0 10.0 4.75 2.90 1.10 01115187 7.20 2.50 0.98 0.77 0.04

01117468 26.0 16.0 11.0 8.80 5.90 01117468 10.0 6.60 4.30 3.80 1.80

01117500 236 150 110 86.0 63.0 01117500 113 75.0 52.0 48.0 24.0

01117800 77.0 47.0 33.0 25.0 16.0 01117800 36.0 22.0 14.0 13.0 6.00

01118000 153 100 72.0 55.0 36.0 01118000 75.0 49.0 34.0 31.0 16.0

01118300 7.30 3.80 2.00 1.10 0.50 01118300 2.90 1.20 0.50 0.41 0.03

01120500 3.40 1.90 1.10 0.60 0.15 01120500 1.90 0.70 0.28 0.20 0.01

01121000 40.0 20.0 11.0 6.50 2.90 01121000 17.0 7.90 3.70 3.10 0.67

01123000 45.0 27.0 18.0 13.0 8.30 01123000 22.0 13.0 8.50 7.90 4.40

01125490 37.0 21.0 11.0 6.80 2.35 01125490 12.0 5.90 2.70 2.20 0.50

01126600 25.0 11.0 6.30 3.40 1.40 01126600 8.50 3.80 1.90 1.50 0.60

01126950 106 63.0 37.0 22.0 18.0 01126950 49.0 19.0 11.0 11.0 20.00

01176000 228 132 85.0 58.0 30.0 01176000 122 67.0 40.0 36.0 11.0

01187300 27.0 12.0 6.00 3.40 1.60 01187300 12.0 4.60 2.10 1.90 0.40

01187400 12.0 6.00 3.50 1.80 0.70 01187400 3.50 1.40 0.70 0.60 0.20

01187800 33.0 18.0 10.0 6.95 3.50 01187800 14.0 6.90 3.90 3.30 0.70

01187850 2.40 1.90 1.60 1.20 0.88 01187850 1.70 1.30 1.00 0.97 0.53

01188000 6.60 3.90 2.60 1.80 0.97 01188000 3.70 2.10 1.30 1.20 0.50

01192600 2.10 1.50 1.10 0.74 0.51 01192600 1.20 0.84 0.60 0.55 0.28

01193500 148 82.0 48.0 31.0 16.0 01193500 66.0 31.0 17.0 15.0 4.80

01193800 4.25 2.40 1.30 0.80 0.38 01193800 1.60 0.73 0.38 0.33 0.15

01194000 24.0 14.0 8.00 4.80 2.00 01194000 10.0 4.50 2.30 2.00 0.40

01194500 33.0 18.0 10.0 6.15 2.45 01194500 15.0 6.10 2.90 2.40 0.35

01195100 7.70 3.30 1.30 0.78 0.34 01195100 2.70 1.00 0.45 0.38 0.02

01195200 8.10 4.10 2.50 1.50 0.68 01195200 3.00 1.30 0.50 0.39 0.02

01198000 52.0 32.5 20.0 14.0 9.10 01198000 21.0 11.0 6.10 5.60 2.90

01199200 5.60 2.30 1.10 0.55 0.11 01199200 1.90 0.49 0.16 0.11 20.00

01201190 37.5 16.5 7.50 5.30 3.30 01201190 11.0 4.70 2.60 2.30 0.80

01201930 14.5 7.25 4.60 2.45 1.20 01201930 12.0 4.65 2.80 2.30 0.36

01204800 2.70 1.60 0.85 0.55 0.24 01204800 1.50 0.63 0.31 0.27 0.09

01206400 30.0 16.0 7.80 3.80 1.60 01206400 14.0 4.80 2.00 1.70 0.50

01206500 34.0 16.0 8.20 4.50 2.20 01206500 14.0 5.00 2.00 1.70 0.30

01208950 11.0 4.75 2.30 1.20 0.46 01208950 4.80 1.90 0.72 0.57 0.04

01208990 33.0 15.0 8.30 4.95 2.20 01208990 16.0 6.00 2.30 1.80 0.20

01372200 103 57.0 33.0 22.0 8.80 01372200 50.0 22.0 12.0 10.0 2.80

01372800 78.0 39.0 26.0 16.0 4.40 01372800 36.0 17.0 8.10 6.90 1.20

01374598 8.20 3.40 1.50 0.77 0.48 01374598 2.80 1.00 0.45 0.36 0.01

01374890 34.0 14.0 6.80 3.90 2.00 01374890 16.0 5.10 2.00 1.70 0.29
26 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 3. Flow-duration statistics for streamgages with at least 10 years of continuous record in Connecticut and neighboring states 

considered for regression analysis: A, Actual streamflow; B, Normalized streamflow.—Continued

[USGS, U.S. Geological Survey; no. number; mi2, square miles; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow 

exceedance; Q90, 90-percent flow exceedance; Q99, 99-percent flow exceedance]

B Normalized streamflow, in cubic feet per second per square mile

USGS 

streamgage no. Streamgage name State Drainage area(mi2

)

Non-bioperiod

Q25 Q99

01111300 Nipmuc River near Harrisville Rhode Island 16.0 2.44 0.02

01111500 Branch River at Forestdale Rhode Island 91.2 2.50 0.14

01115098 Peeptoad Brook at Elmdale Road near Westerly Rhode Island 4.83 2.90 0.02

01115187 Ponaganset River at South Foster Rhode Island 14.4 2.43 0.01

01117468 Beaver River near Usquepaug Rhode Island 8.87 3.38 0.24

01117500 Pawcatuck River at Wood River Junction Rhode Island 100 2.66 0.28

01117800 Wood River near Arcadia Rhode Island 35.2 2.93 0.22

01118000 Wood River at Hope Valley Rhode Island 72.4 2.90 0.26

01118300 Pendleton Hill Brook near Clarks Falls Connecticut 4.02 2.74 0.01

01120500 Safford Brook near Woodstock Valley Connecticut 4.15 2.05 0.00

01121000 Mount Hope River near Warrenville Connecticut 28.6 2.31 0.03

01123000 Little River near Hanover Connecticut 30.0 2.30 0.16

01125490 Little River at Harrisville Connecticut 35.8 1.56 0.02

01126600 Blackwell Brook near Brooklyn Connecticut 17.0 2.24 0.04

01126950 Pachaug River at Pachaug Connecticut 53.0 2.45 0.01

01176000 Quaboag River at West Brimfield Massachusetts 150 2.29 0.11

01187300 Hubbard Brook near West Hartland Connecticut 19.9 2.16 0.03

01187400 Valley Brook near West Hartland Connecticut 7.03 2.28 0.04

01187800 Nepaug River near Nepaug Connecticut 23.5 1.96 0.06

01187850 Clear Brook near Collinsville1 Connecticut 0.59 3.56 0.90

01188000 Bunnell Brook near Burlington Connecticut 4.10 2.27 0.16

01192600 South Branch Salmon Brook at Buckingham Connecticut 0.94 2.13 0.33

01193500 Salmon River near East Hampton Connecticut 100 2.38 0.06

01193800 Hemlock Valley Brook at Hadlyme Connecticut 2.62 2.63 0.08

01194000 Eightmile River at North Plain Connecticut 20.1 2.49 0.03

01194500 East Branch Eightmile River near North Lyme Connecticut 22.3 2.60 0.03

01195100 Indian River near Clinton Connecticut 5.68 2.29 0.01

01195200 Neck River near Madison Connecticut 6.55 2.29 0.01

01198000 Green River near Great Barrington Massachusetts 51.0 2.00 0.06

01199200 Guinea Brook at West Woods Road at Ellsworth Connecticut 3.50 2.63 0.00

01201190 West Aspectuck River at Sand Road near New Milford Connecticut 23.8 1.85 0.04

01201930 Marshepaug River near Milton1 Connecticut 9.24 2.92 0.05

01204800 Copper Mill Brook near Monroe Connecticut 2.45 2.33 0.04

01206400 Leadmine Brook near Harwinton Connecticut 19.6 2.30 0.03

01206500 Leadmine Brook near Thomaston Connecticut 24.3 2.30 0.02

01208950 Sasco Brook near Southport Connecticut 7.38 2.17 0.01

01208990 Saugatuck River near Redding Connecticut 21.0 2.43 0.02

01372200 Wappinger Creek near Clinton Corners New York 92.4 1.73 0.04

01372800 Fishkill Creek at Hopewell Junction New York 57.2 1.84 0.03

01374598 Horse Pound Brook near Lake Carmel New York 3.94 2.54 0.01

01374890 Cross River near Cross River New York 17.1 2.57 0.03

Minimum 1.56 0.00

Maximum 3.56 0.90

Average 2.41 0.09
Table 3 27

Table 3. Flow-duration statistics for streamgages with at least 10 years of continuous record in Connecticut and neighboring states 

considered for regression analysis: A, Actual streamflow; B, Normalized streamflow.—Continued

[USGS, U.S. Geological Survey; no. number; mi2, square miles; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow 

exceedance; Q90, 90-percent flow exceedance; Q99, 99-percent flow exceedance]

B Normalized streamflow, in cubic feet per second per square mile

USGS 

streamgage no.

Salmonid Spawning USGS 

streamgage no.

Overwinter

Q25 Q50 Q75 Q90 Q99 Q25 Q50 Q75 Q95 Q99

01111300 2.06 1.06 0.49 0.26 0.06 01111300 3.00 1.88 1.13 0.53 0.29

01111500 2.21 1.32 0.82 0.49 0.23 01111500 3.07 1.93 1.24 0.66 0.39

01115098 2.28 1.45 0.58 0.22 0.11 01115098 3.73 2.28 1.28 0.48 0.20

01115187 2.01 1.18 0.58 0.29 0.15 01115187 3.19 1.88 1.11 0.58 0.26

01117468 2.71 1.47 0.80 0.50 0.37 01117468 3.95 2.71 1.69 0.78 0.38

01117500 2.09 1.18 0.76 0.55 0.39 01117500 3.44 2.23 1.51 0.79 0.52

01117800 2.30 1.42 0.88 0.48 0.27 01117800 3.64 2.44 1.56 0.80 0.43

01118000 2.32 1.31 0.83 0.54 0.30 01118000 3.45 2.36 1.57 0.83 0.48

01118300 2.49 1.34 0.72 0.35 0.13 01118300 3.73 2.24 1.34 0.62 0.37

01120500 2.31 1.08 0.41 0.23 0.06 01120500 2.65 1.35 0.77 0.36 0.22

01121000 2.10 1.01 0.52 0.30 0.10 01121000 2.73 1.61 0.94 0.45 0.28

01123000 2.08 1.13 0.60 0.40 0.20 01123000 2.80 1.73 1.07 0.57 0.37

01125490 1.45 0.70 0.35 0.15 0.08 01125490 1.82 1.01 0.67 0.34 0.26

01126600 1.94 0.88 0.46 0.18 0.05 01126600 2.94 1.71 0.88 0.46 0.30

01126950 2.08 1.03 0.64 0.20 0.11 01126950 2.94 1.81 1.26 0.42 0.23

01176000 1.83 0.95 0.54 0.31 0.14 01176000 2.40 1.47 0.88 0.40 0.26

01187300 2.36 1.31 0.60 0.30 0.13 01187300 2.24 1.26 0.80 0.36 0.21

01187400 1.99 1.01 0.40 0.17 0.08 01187400 1.99 1.22 0.83 0.37 0.24

01187800 1.62 0.85 0.42 0.25 0.13 01187800 1.91 1.15 0.68 0.31 0.21

01187850 2.54 1.86 1.64 1.31 1.03 01187850 2.71 2.03 1.49 0.90 0.68

01188000 2.21 1.29 0.71 0.41 0.24 01188000 2.32 1.46 0.95 0.51 0.32

01192600 1.38 0.94 0.66 0.43 0.33 01192600 2.02 1.28 0.80 0.44 0.33

01193500 2.00 1.06 0.56 0.29 0.16 01193500 2.88 1.70 1.03 0.46 0.26

01193800 1.87 0.99 0.65 0.27 0.16 01193800 3.26 1.98 1.18 0.61 0.38

01194000 2.04 1.04 0.41 0.25 0.12 01194000 2.99 1.84 1.19 0.55 0.28

01194500 2.33 1.26 0.63 0.36 0.19 01194500 3.36 1.97 1.17 0.54 0.34

01195100 2.11 1.11 0.55 0.26 0.12 01195100 2.82 1.73 1.04 0.51 0.25

01195200 1.53 0.77 0.35 0.18 0.07 01195200 2.90 1.68 0.93 0.38 0.21

01198000 2.08 0.85 0.33 0.14 0.06 01198000 1.96 1.10 0.73 0.41 0.12

01199200 2.57 1.20 0.51 0.14 0.02 01199200 2.77 1.49 0.80 0.34 0.13

01201190 1.18 0.76 0.36 0.18 0.11 01201190 1.89 1.26 0.80 0.46 0.25

01201930 3.57 2.27 0.86 0.52 0.09 01201930 3.25 1.95 0.71 0.21 0.03

01204800 1.80 1.10 0.61 0.35 0.09 01204800 2.90 1.71 1.02 0.49 0.29

01206400 2.24 1.43 0.77 0.20 0.06 01206400 2.40 1.43 1.07 0.51 0.33

01206500 2.06 0.97 0.41 0.24 0.07 01206500 2.43 1.40 0.78 0.33 0.18

01208950 2.03 1.12 0.53 0.22 0.04 01208950 2.71 1.63 0.98 0.37 0.12

01208990 2.24 1.24 0.67 0.26 0.05 01208990 3.19 1.90 1.10 0.46 0.24

01372200 1.23 0.67 0.30 0.13 0.06 01372200 1.95 1.08 0.65 0.23 0.11

01372800 1.24 0.72 0.26 0.12 0.08 01372800 2.17 1.33 0.75 0.24 0.12

01374598 3.05 1.52 0.61 0.19 0.04 01374598 3.05 1.90 1.00 0.30 0.16

01374890 2.69 1.46 0.58 0.11 0.06 01374890 3.33 1.93 0.96 0.30 0.15

Minimum 1.18 0.67 0.26 0.11 0.02 1.82 1.01 0.65 0.21 0.03

Maximum 3.57 2.27 1.64 1.31 1.03 3.95 2.71 1.69 0.90 0.68

Average 2.10 1.15 0.59 0.31 0.15 2.80 1.71 1.03 0.48 0.27
28 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 3. Flow-duration statistics for streamgages with at least 10 years of continuous record in Connecticut and neighboring states 

considered for regression analysis: A, Actual streamflow; B, Normalized streamflow.—Continued

[USGS, U.S. Geological Survey; no. number; mi2, square miles; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow 

exceedance; Q90, 90-percent flow exceedance; Q99, 99-percent flow exceedance]

B Normalized streamflow, in cubic feet per second per square mile

USGS 

streamgage no.

Habitat Forming USGS 

streamgage no.

Clupeid Spawning

Q25 Q50 Q75 Q95 Q99 Q25 Q50 Q75 Q95 Q99

01111300 4.31 2.75 1.88 1.06 0.75 01111300 2.69 1.81 1.25 0.69 0.50

01111500 4.33 2.79 1.90 1.11 0.76 01111500 2.63 1.78 1.27 0.72 0.56

01115098 4.97 3.31 2.28 1.41 0.83 01115098 3.11 2.07 1.43 0.91 0.56

01115187 4.17 2.57 1.67 1.11 0.76 01115187 2.50 1.60 1.04 0.67 0.38

01117468 4.96 3.49 2.59 1.80 1.24 01117468 3.72 2.82 2.14 1.47 1.24

01117500 4.29 3.07 2.24 1.49 1.14 01117500 3.19 2.34 1.83 1.33 0.99

01117800 4.49 3.18 2.36 1.56 1.14 01117800 3.13 2.39 1.76 1.22 1.02

01118000 4.48 3.23 2.43 1.63 1.20 01118000 3.15 2.38 1.82 1.26 0.99

01118300 4.48 2.99 2.06 1.29 0.90 01118300 3.23 2.06 1.42 0.77 0.52

01120500 4.34 2.41 1.47 0.77 0.48 01120500 1.95 1.18 0.77 0.36 0.21

01121000 3.95 2.55 1.82 1.05 0.77 01121000 2.52 1.68 1.08 0.56 0.38

01123000 3.77 2.57 1.83 1.10 0.73 01123000 2.50 1.77 1.27 0.77 0.63

01125490 4.13 2.51 1.51 0.70 0.56 01125490 1.79 1.16 0.84 0.39 0.22

01126600 3.76 2.53 1.76 1.00 0.71 01126600 2.29 1.65 1.18 0.65 0.32

01126950 4.06 2.89 2.00 1.17 0.87 01126950 2.91 1.96 1.46 0.91 0.49

01176000 4.40 2.97 2.00 1.07 0.73 01176000 2.75 1.91 1.28 0.76 0.55

01187300 5.18 2.76 1.56 0.80 0.50 01187300 2.76 1.51 0.95 0.43 0.25

01187400 5.69 3.27 1.99 1.01 0.71 01187400 3.13 1.99 1.32 0.70 0.40

01187800 4.21 2.55 1.70 0.94 0.68 01187800 2.40 1.57 1.06 0.55 0.40

01187850 4.41 3.39 2.37 1.49 1.03 01187850 4.58 3.73 2.88 1.86 1.64

01188000 4.15 2.68 1.80 1.05 0.76 01188000 2.68 1.80 1.29 0.76 0.54

01192600 3.19 2.55 1.81 1.04 0.76 01192600 2.77 2.13 1.49 0.98 0.79

01193500 4.08 2.70 1.89 1.18 0.88 01193500 2.72 1.80 1.24 0.73 0.51

01193800 4.20 2.90 2.14 1.37 1.07 01193800 3.47 2.21 1.53 0.92 0.61

01194000 4.28 2.84 2.04 1.29 1.00 01194000 2.69 1.79 1.19 0.75 0.50

01194500 4.48 2.91 2.02 1.21 0.85 01194500 2.96 1.97 1.30 0.81 0.54

01195100 3.52 2.29 1.44 0.95 0.72 01195100 2.29 1.41 0.93 0.46 0.28

01195200 4.12 2.60 1.83 1.09 0.82 01195200 2.75 1.76 1.18 0.66 0.46

01198000 4.65 2.75 1.69 0.86 0.59 01198000 2.51 1.78 1.27 0.65 0.43

01199200 4.86 3.14 1.89 0.80 0.60 01199200 3.14 1.91 1.23 0.49 0.27

01201190 3.70 2.44 1.64 0.97 0.76 01201190 2.35 1.47 1.01 0.50 0.36

01201930 4.76 2.81 1.30 0.43 0.14 01201930 2.71 1.52 0.89 0.21 0.10

01204800 4.08 2.65 1.84 1.18 0.90 01204800 2.57 1.63 1.14 0.57 0.30

01206400 4.74 2.91 1.99 1.12 0.97 01206400 2.45 1.63 1.22 0.50 0.32

01206500 4.86 2.80 1.85 1.11 0.66 01206500 2.80 1.69 1.07 0.49 0.37

01208950 3.52 2.17 1.49 0.89 0.66 01208950 2.44 1.49 0.89 0.39 0.24

01208990 4.14 2.48 1.71 1.05 0.71 01208990 2.62 1.62 1.05 0.52 0.30

01372200 3.77 2.25 1.47 0.73 0.56 01372200 1.86 1.18 0.80 0.40 0.27

01372800 3.60 2.38 1.59 0.79 0.61 01372800 1.98 1.35 0.93 0.49 0.37

01374598 3.81 2.51 1.70 0.89 0.71 01374598 2.26 1.35 0.86 0.43 0.30

01374890 3.80 2.46 1.75 0.82 0.64 01374890 2.40 1.52 0.94 0.43 0.22

Minimum 3.19 2.17 1.30 0.43 0.14 1.79 1.16 0.77 0.21 0.10

Maximum 5.69 3.49 2.59 1.80 1.24 4.58 3.73 2.88 1.86 1.64

Average 4.26 2.76 1.86 1.08 0.78 2.72 1.81 1.26 0.71 0.50
Table 3 29

Table 3. Flow-duration statistics for streamgages with at least 10 years of continuous record in Connecticut and neighboring states 

considered for regression analysis: A, Actual streamflow; B, Normalized streamflow.—Continued

[USGS, U.S. Geological Survey; no. number; mi2, square miles; Q25, 25-percent flow exceedance; Q50, 50-percent flow exceedance; Q75, 75-percent flow 

exceedance; Q90, 90-percent flow exceedance; Q99, 99-percent flow exceedance]

B Normalized streamflow, in cubic feet per second per square mile

USGS 

streamgage no.

Resident Spawning USGS 

streamgage no.

Rearing and Growth

Q25 Q50 Q75 Q90 Q99 Q25 Q50 Q75 Q80 Q99

01111300 1.63 0.75 0.43 0.24 0.09 01111300 0.54 0.23 0.10 0.08 0.01

01111500 1.58 0.89 0.58 0.41 0.26 01111500 0.82 0.47 0.30 0.26 0.10

01115098 2.07 0.96 0.52 0.31 0.14 01115098 0.50 0.20 0.11 0.09 0.01

01115187 1.60 0.69 0.33 0.20 0.08 01115187 0.50 0.17 0.07 0.05 0.00

01117468 2.93 1.80 1.24 0.99 0.67 01117468 1.13 0.74 0.48 0.43 0.20

01117500 2.36 1.50 1.10 0.86 0.63 01117500 1.13 0.75 0.52 0.48 0.24

01117800 2.19 1.34 0.94 0.71 0.45 01117800 1.02 0.63 0.40 0.37 0.17

01118000 2.11 1.38 0.99 0.76 0.50 01118000 1.04 0.68 0.47 0.43 0.22

01118300 1.82 0.95 0.50 0.27 0.12 01118300 0.72 0.30 0.12 0.10 0.01

01120500 0.82 0.46 0.27 0.14 0.04 01120500 0.46 0.17 0.07 0.05 0.00

01121000 1.40 0.70 0.38 0.23 0.10 01121000 0.59 0.28 0.13 0.11 0.02

01123000 1.50 0.90 0.60 0.43 0.28 01123000 0.73 0.43 0.28 0.26 0.15

01125490 1.03 0.59 0.31 0.19 0.07 01125490 0.34 0.16 0.08 0.06 0.01

01126600 1.47 0.65 0.37 0.20 0.08 01126600 0.50 0.22 0.11 0.09 0.04

01126950 2.00 1.19 0.70 0.42 0.34 01126950 0.92 0.36 0.21 0.21 0.00

01176000 1.52 0.88 0.57 0.39 0.20 01176000 0.81 0.45 0.27 0.24 0.07

01187300 1.36 0.60 0.30 0.17 0.08 01187300 0.60 0.23 0.11 0.10 0.02

01187400 1.71 0.85 0.50 0.26 0.10 01187400 0.50 0.20 0.10 0.09 0.03

01187800 1.40 0.77 0.43 0.30 0.15 01187800 0.60 0.29 0.17 0.14 0.03

01187850 4.07 3.22 2.71 2.03 1.49 01187850 2.88 2.20 1.69 1.64 0.90

01188000 1.61 0.95 0.63 0.44 0.24 01188000 0.90 0.51 0.32 0.29 0.12

01192600 2.23 1.60 1.17 0.79 0.54 01192600 1.28 0.89 0.64 0.59 0.30

01193500 1.48 0.82 0.48 0.31 0.16 01193500 0.66 0.31 0.17 0.15 0.05

01193800 1.62 0.92 0.50 0.31 0.15 01193800 0.61 0.28 0.15 0.13 0.06

01194000 1.19 0.70 0.40 0.24 0.10 01194000 0.50 0.22 0.11 0.10 0.02

01194500 1.48 0.81 0.45 0.28 0.11 01194500 0.67 0.27 0.13 0.11 0.02

01195100 1.36 0.58 0.23 0.14 0.06 01195100 0.48 0.18 0.08 0.07 0.00

01195200 1.24 0.63 0.38 0.23 0.10 01195200 0.46 0.20 0.08 0.06 0.00

01198000 1.02 0.64 0.39 0.27 0.18 01198000 0.41 0.22 0.12 0.11 0.06

01199200 1.60 0.66 0.31 0.16 0.03 01199200 0.54 0.14 0.05 0.03 0.00

01201190 1.58 0.69 0.32 0.22 0.14 01201190 0.46 0.20 0.11 0.10 0.03

01201930 1.57 0.78 0.50 0.27 0.13 01201930 1.30 0.50 0.30 0.25 0.04

01204800 1.10 0.65 0.35 0.22 0.10 01204800 0.61 0.26 0.13 0.11 0.04

01206400 1.53 0.82 0.40 0.19 0.08 01206400 0.71 0.24 0.10 0.09 0.03

01206500 1.40 0.66 0.34 0.19 0.09 01206500 0.58 0.21 0.08 0.07 0.01

01208950 1.49 0.64 0.31 0.16 0.06 01208950 0.65 0.26 0.10 0.08 0.01

01208990 1.57 0.71 0.40 0.24 0.10 01208990 0.76 0.29 0.11 0.09 0.01

01372200 1.11 0.62 0.36 0.24 0.10 01372200 0.54 0.24 0.13 0.11 0.03

01372800 1.36 0.68 0.45 0.28 0.08 01372800 0.63 0.30 0.14 0.12 0.02

01374598 2.08 0.86 0.38 0.20 0.12 01374598 0.71 0.25 0.11 0.09 0.00

01374890 1.99 0.82 0.40 0.23 0.12 01374890 0.94 0.30 0.12 0.10 0.02

Minimum 0.82 0.46 0.23 0.14 0.03 0.34 0.14 0.05 0.03 0.00

Maximum 4.07 3.22 2.71 2.03 1.49 2.88 2.20 1.69 1.64 0.90

Average 1.66 0.91 0.56 0.37 0.21 0.75 0.38 0.22 0.20 0.08
30 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 5. Characteristics of the drainage basins used for regionalizing flow-duration statistics in Connecticut: A, Continuous 

streamgages; B, Short-term or partial-record streamgages.—Continued

[Geographic Information System used to derive all basin characteristics (table 4); USGS, U.S. Geological Survey; no., number; mi2, square miles; mi, miles;

ft, feet; --, not determined; Q99, 99-percent flow exceedence]

A Continuous streamgages used for all flow durations

USGS 

continuous 

streamgage 

no.

Drainage 

area

(mi2

)

Basin 

perimeter 

(mi)

Total river 

miles

(mi)

Maximum 

basin

elevation 

(ft)

Mean

basin

elevation 

(ft)

Basin relief 

(ft)

Mean basin 

slope

(percent)

Latitude of 

basin

centroid

(CT state 

plane ft)

Longitude 

of basin 

centroid

(CT state 

plane ft)

01111300 16.32 27.44 38.63 769.69 532.20 425.59 5.44 1,282,922 932,738

01111500 91.22 62.39 201.66 813.25 497.08 615.26 6.41 1,290,774 912,635

01115098 4.83 13.48 11.67 707.78 463.05 394.65 7.00 1,306,577 883,974

01115187 14.36 19.94 35.11 841.96 612.73 490.58 5.15 1,275,302 872,818

01117468 9.50 23.34 27.80 562.01 388.47 383.53 4.21 1,302,743 758,712

01117500 100.13 59.25 290.45 563.19 196.90 514.34 4.14 1,318,057 747,689

01117800 35.31 44.48 95.79 682.78 389.68 559.88 6.10 1,273,313 791,046

01118000 74.53 53.53 215.21 682.78 333.67 615.88 5.77 1,276,820 776,075

01118300 4.00 12.81 12.98 529.92 339.22 373.72 6.79 1,248,957 742,323

01120500 4.17 12.93 11.21 936.06 748.02 400.85 7.66 1,191,997 905,667

01121000 29.00 43.97 99.49 1,257.15 652.28 936.78 7.50 1,157,147 884,863

01123000 30.06 46.83 104.59 792.95 508.21 557.41 7.05 1,190,714 837,547

01125490 36.11 46.63 93.59 938.62 546.00 669.06 7.34 1,207,681 916,057

01126600 17.11 32.35 43.23 771.33 477.75 630.74 7.19 1,206,176 855,508

01126950 52.92 59.10 103.14 656.20 343.66 505.35 5.57 1,243,813 770,826

01176000 149.48 84.71 439.39 1,223.43 810.35 839.76 8.13 1,181,949 1,019,052

01187300 20.66 33.69 39.18 1,643.86 1,286.82 1,048.85 8.70 938,756 954,443

01187400 7.39 19.40 15.58 1,490.12 1,099.08 945.77 14.50 955,253 950,908

01187800 23.77 41.54 57.59 1,186.68 843.48 677.23 10.22 925,452 866,592

01187850 0.56 4.14 0.80 929.86 731.52 410.73 11.71 942,782 849,379

01188000 3.99 12.82 11.20 1,170.01 924.27 435.24 5.93 934,055 843,189

01192600 0.92 5.73 1.78 753.05 466.57 511.61 7.81 1,061,848 823,114

01193500 101.64 81.62 232.70 897.31 488.72 836.09 7.47 1,092,884 789,620

01193800 2.79 12.88 8.18 627.99 354.60 555.41 8.30 1,090,559 726,676

01194000 20.20 29.95 53.38 637.80 406.95 599.84 7.51 1,111,696 740,573

01194500 22.45 41.27 60.79 644.29 365.45 573.33 6.82 1,127,472 735,634

01195100 5.73 19.60 19.98 494.78 236.93 447.47 7.54 1,055,303 681,705

01195200 6.59 25.10 17.15 421.29 167.74 416.70 5.15 1,032,139 677,963

01198000 51.06 53.55 82.86 2,058.04 1,181.24 1,368.96 14.14 812,825 1,020,715

01199200 3.48 12.48 10.58 1,550.07 1,292.07 408.83 9.32 811,218 861,346

01201190 23.85 36.34 52.92 1,421.06 786.92 1,153.48 14.48 818,125 807,974

01201930 9.50 29.87 21.68 1,635.60 1,337.36 550.98 6.96 862,620 868,700

01204800 2.45 8.76 8.25 663.58 490.12 327.82 6.87 872,857 688,797

01206400 19.76 29.70 55.72 1,187.17 900.63 648.79 7.69 916,528 844,459

01206500 24.44 35.88 69.50 1,187.17 873.97 695.47 8.13 916,393 840,680

01208950 7.43 16.90 23.92 397.74 230.11 338.02 5.28 846,137 629,043

01208990 20.67 42.49 53.77 1,001.57 574.21 703.41 11.82 809,886 679,749

01372200 91.05 82.45 193.81 1,398.88 621.61 1,162.17 10.18 741,627 875,346

01372800 57.40 65.74 139.78 1,397.67 656.65 1,174.08 11.41 741,723 787,015

01374598 3.90 14.24 8.06 1,159.35 806.46 586.61 11.37 740,555 742,154

01374890 15.70 28.32 34.49 994.49 592.49 656.50 11.46 776,104 662,551

Range of basin characteristics for continuous-record streamgages only

Minimum 0.56 4.14 0.80 398 168 328 4.14 -- --

Maximum 149.48 84.71 439.39 2,058 1,337 1,369 14.50 -- --

Average 29.67 34.82 75.55 968 623 638 8.10 -- --
Table 5 31

Table 5. Characteristics of the drainage basins used for regionalizing flow-duration statistics in Connecticut: A, Continuous 

streamgages; B, Short-term or partial-record streamgages.—Continued

[Geographic Information System used to derive all basin characteristics (table 4); USGS, U.S. Geological Survey; no., number; mi2, square miles; mi, miles;

ft, feet; --, not determined; Q99, 99-percent flow exceedence]

A Continuous streamgages used for all flow durations

USGS 

continuous 

streamgage 

no.

Latitude of 

streamgage

(decimal 

degrees)

Longitude of 

streamgage

(decimal 

degrees)

River miles 

in contact 

with sand 

and gravel 

(mi)

Deciduous

forest

(percent)

Evergreen 

forest

(percent)

Mixed

forest

(percent)

Deciduous 

and mixed 

forest

(percent)

Developed, 

open space 

(percent)

Developed,

low 

intensity 

(percent)

01111300 41.981 -71.686 18.19 66.3 6.9 4.8 71.1 5.3 1.5

01111500 41.996 -71.563 69.51 59.1 6.4 4.0 63.1 5.2 4.4

01115098 41.853 -71.606 5.81 71.5 1.8 0.9 72.4 4.5 3.3

01115187 41.819 -71.705 10.46 70.5 2.7 0.9 71.5 4.6 1.5

01117468 41.493 -71.628 17.63 66.0 4.3 2.1 68.2 5.9 2.0

01117500 41.445 -71.681 178.76 43.0 7.3 4.7 47.7 5.3 3.6

01117800 41.574 -71.721 43.87 56.9 11.3 4.7 61.7 4.8 1.0

01118000 41.498 -71.716 86.53 55.6 10.6 4.2 59.8 4.9 2.5

01118300 41.475 -71.834 1.24 73.9 0.5 0.1 73.9 4.3 0.4

01120500 41.926 -72.057 0.39 54.8 8.0 10.5 65.3 5.8 0.5

01121000 41.844 -72.169 5.62 60.3 1.9 12.0 72.3 6.0 0.8

01123000 41.672 -72.052 22.33 57.2 2.6 7.1 64.3 5.2 0.7

01125490 41.928 -71.930 11.42 43.9 5.8 8.1 52.0 5.8 1.4

01126600 41.765 -71.956 5.17 59.8 1.6 7.0 66.8 5.5 0.8

01126950 41.585 -71.933 28.26 48.4 10.4 3.4 51.7 3.6 2.1

01176000 42.182 -72.264 133.93 46.1 7.2 6.8 52.9 6.6 2.2

01187300 42.037 -72.939 0.75 51.4 5.7 31.7 83.2 2.6 0.2

01187400 42.034 -72.930 1.37 70.5 7.4 13.7 84.2 2.3 0.1

01187800 41.821 -72.970 4.50 59.5 9.3 7.6 67.1 6.2 1.3

01187850 41.796 -72.951 0.36 61.1 22.9 5.7 66.8 8.7 0.0

01188000 41.786 -72.965 1.87 59.9 2.7 1.9 61.8 7.0 1.8

01192600 41.718 -72.540 0.99 49.1 12.9 5.8 55.0 14.7 11.4

01193500 41.552 -72.449 20.37 56.0 1.6 5.0 61.1 7.8 2.9

01193800 41.428 -72.423 0.94 77.0 0.6 0.3 77.4 7.5 0.3

01194000 41.442 -72.333 6.12 71.4 1.1 4.4 75.8 5.8 0.4

01194500 41.428 -72.334 7.62 68.2 0.4 1.3 69.5 5.6 2.0

01195100 41.306 -72.531 1.70 74.3 0.4 0.3 74.7 9.1 2.2

01195200 41.283 -72.619 2.60 64.3 0.9 0.5 64.8 14.2 4.9

01198000 42.192 -73.391 18.54 57.5 7.9 11.9 69.5 3.5 0.4

01199200 41.824 -73.430 0.11 77.8 0.3 0.3 78.1 4.5 0.1

01201190 41.608 -73.425 4.33 71.9 1.4 0.9 72.8 5.2 0.6

01201930 41.790 -73.259 0.53 51.5 4.0 5.5 57.0 7.3 1.4

01204800 41.363 -73.218 1.76 59.7 1.8 1.8 61.5 9.6 9.9

01206400 41.730 -73.053 5.09 55.6 2.6 8.2 63.8 9.0 5.0

01206500 41.702 -73.057 5.57 57.1 3.0 9.3 66.4 8.2 4.2

01208950 41.153 -73.306 0.31 46.7 2.2 1.5 48.2 30.3 7.2

01208990 41.295 -73.395 9.08 72.7 1.9 0.6 73.3 11.9 0.9

01372200 41.815 -73.763 44.75 50.5 3.3 1.3 51.8 4.3 1.3

01372800 41.573 -73.807 22.74 55.4 3.0 1.7 57.1 6.2 2.6

01374598 41.476 -73.689 0.00 76.5 1.0 0.4 77.0 10.5 1.1

01374890 41.260 -73.602 0.53 61.2 6.3 1.0 62.1 13.1 0.4

Range of basin characteristics for continuous-record streamgages only

Minimum -- -- 0.00 43.0 0.3 0.1 47.7 2.3 0.0

Maximum -- -- 178.76 77.8 22.9 31.7 84.2 30.3 11.4

Average -- -- 19.55 60.7 4.7 5.0 65.7 7.3 2.2
32 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 5. Characteristics of the drainage basins used for regionalizing flow-duration statistics in Connecticut: A, Continuous 

streamgages; B, Short-term or partial-record streamgages.—Continued

[Geographic Information System used to derive all basin characteristics (table 4); USGS, U.S. Geological Survey; no., number; mi2, square miles; mi, miles;

ft, feet; --, not determined; Q99, 99-percent flow exceedence]

A Continuous streamgages used for all flow durations

USGS 

continuous 

streamgage 

no.

Developed, 

open space 

and low 

intensity

(ft)

Open water 

(percent)

Impervious

surface

(percent)

Wetlands 

(percent)

Soil type A 

(percent)

Soil type B 

(percent)

Soil type C 

(percent)

Soil type D 

(percent)

01111300 6.9 0.2 0.13 9.08 100.0 0.0 0.0 0.0

01111500 9.5 2.6 0.35 9.16 100.0 0.0 0.0 0.0

01115098 7.8 0.5 0.21 10.69 100.0 0.0 0.0 0.0

01115187 6.2 2.8 0.13 15.99 100.0 0.0 0.0 0.0

01117468 7.9 0.5 0.08 12.46 100.0 0.0 0.0 0.0

01117500 9.0 2.9 0.27 18.14 100.0 0.0 0.0 0.0

01117800 5.8 0.9 0.09 13.83 77.4 9.3 7.1 6.2

01118000 7.4 1.9 0.20 16.76 86.7 4.8 3.7 4.7

01118300 4.7 0.0 0.06 4.45 0.0 0.0 0.0 100.0

01120500 6.3 0.1 0.07 1.46 0.0 33.3 41.7 25.0

01121000 6.8 1.5 0.08 1.43 5.0 36.5 34.0 24.5

01123000 6.0 0.4 0.06 3.05 10.8 30.1 39.2 19.9

01125490 7.2 1.2 0.10 3.89 14.2 39.7 28.9 17.2

01126600 6.3 0.4 0.08 2.84 6.4 40.4 30.9 22.3

01126950 5.7 4.7 0.15 7.21 9.2 37.6 12.9 40.3

01176000 8.9 3.2 0.20 9.02 98.3 0.8 0.4 0.5

01187300 2.8 2.1 0.02 5.35 4.2 1.7 79.2 5.0

01187400 2.4 0.1 0.02 2.16 4.7 25.6 11.6 2.3

01187800 7.5 0.1 0.10 1.84 6.9 50.8 21.5 20.8

01187850 8.7 0.0 0.03 0.00 66.7 33.3 0.0 0.0

01188000 8.8 0.3 0.18 1.10 26.1 13.0 34.8 26.1

01192600 26.1 0.0 0.47 0.69 20.0 80.0 0.0 0.0

01193500 10.7 0.9 0.20 1.50 4.2 50.4 20.2 25.3

01193800 7.8 1.3 0.05 0.55 0.0 0.0 0.0 100.0

01194000 6.3 1.4 0.05 1.17 0.0 1.8 0.9 97.3

01194500 7.6 0.5 0.12 1.39 0.0 4.0 2.4 93.7

01195100 11.3 0.2 0.18 0.67 0.0 0.0 0.0 100.0

01195200 19.1 0.2 0.39 1.17 0.0 0.0 0.0 100.0

01198000 3.9 0.7 0.04 2.98 51.1 11.7 27.0 0.0

01199200 4.6 0.6 0.02 3.72 0.0 52.6 5.3 42.1

01201190 5.8 1.9 0.05 2.60 4.6 40.0 20.0 35.4

01201930 8.7 10.6 0.12 2.52 11.3 41.5 35.8 11.3

01204800 19.6 0.4 0.47 0.27 0.0 0.0 0.0 100.0

01206400 14.0 0.8 0.40 1.43 3.2 47.2 33.0 16.7

01206500 12.3 0.7 0.33 1.32 2.2 53.7 30.9 13.2

01208950 37.6 0.0 0.61 0.48 0.0 0.0 0.0 100.0

01208990 12.8 1.3 0.14 1.72 0.0 0.0 0.0 100.0

01372200 5.6 0.8 0.11 3.38 100.0 0.0 0.0 0.0

01372800 8.8 1.9 0.18 3.86 100.0 0.0 0.0 0.0

01374598 11.5 2.0 0.12 2.81 100.0 0.0 0.0 0.0

01374890 13.5 3.6 0.08 5.03 80.7 0.0 0.0 19.3

Range of basin characteristics for continuous-record streamgages only

Minimum 2.4 0.0 0.02 0.00 0.0 0.0 0.0 0.0

Maximum 37.6 10.6 0.61 18.14 100.0 80.0 79.2 100.0

Average 9.5 1.4 0.16 4.61 36.4 18.0 12.7 31.0
Table 5 33

Table 5. Characteristics of the drainage basins used for regionalizing flow-duration statistics in Connecticut: A, Continuous 

streamgages; B, Short-term or partial-record streamgages.—Continued

[Geographic Information System used to derive all basin characteristics (table 4); USGS, U.S. Geological Survey; no., number; mi2, square miles; mi, miles;

ft, feet; --, not determined; Q99, 99-percent flow exceedence]

A Continuous streamgages used for all flow durations

USGS 

continuous 

streamgage 

no.

Soil type D, 

A_D, and C_D

Till

(percent)

Coarse

stratified 

deposits 

(percent)

Alluvium 

deposits 

(percent)

01111300 0.0 71.6 26.9 1.3

01111500 0.0 66.7 30.0 0.2

01115098 0.0 76.1 22.9 0.0

01115187 0.0 82.5 14.5 0.0

01117468 0.0 74.0 25.2 0.0

01117500 0.0 48.7 43.8 0.0

01117800 6.2 68.6 26.9 3.0

01118000 4.7 71.1 25.2 1.4

01118300 100.0 85.7 9.0 5.1

01120500 25.0 98.8 0.9 0.3

01121000 24.5 92.0 4.2 2.2

01123000 19.9 78.1 15.3 5.2

01125490 17.2 82.0 11.4 3.5

01126600 22.3 87.5 5.0 3.7

01126950 40.3 63.6 23.2 4.8

01176000 0.5 78.5 20.1 1.3

01187300 15.0 99.7 0.3 0.0

01187400 58.1 90.8 6.3 2.9

01187800 20.8 84.5 8.1 7.2

01187850 0.0 55.1 44.9 0.0

01188000 26.1 68.8 25.4 5.8

01192600 0.0 44.9 55.1 0.0

01193500 25.3 84.8 8.2 4.4

01193800 100.0 93.0 4.7 2.3

01194000 97.3 89.2 6.6 2.5

01194500 93.7 88.3 8.3 2.9

01195100 100.0 90.9 7.3 1.9

01195200 100.0 79.3 14.3 4.0

01198000 10.3 78.9 11.3 3.4

01199200 42.1 93.5 1.6 4.8

01201190 35.4 88.2 2.7 4.1

01201930 11.3 84.1 1.3 4.5

01204800 100.0 87.4 9.8 2.6

01206400 16.7 91.3 4.1 3.7

01206500 13.2 91.8 3.9 3.4

01208950 100.0 97.6 1.7 0.7

01208990 100.0 84.7 9.8 4.5

01372200 0.0 47.5 17.7 2.2

01372800 0.0 53.8 14.8 2.4

01374598 0.0 85.7 0.0 0.0

01374890 19.3 83.9 1.9 0.9

Range of basin characteristics for continuous-record streamgages only

Minimum 0.0 44.9 0.0 0.0

Maximum 100.0 99.7 55.1 7.2

Average 32.8 79.6 14.0 2.5
34 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 5. Characteristics of the drainage basins used for regionalizing flow-duration statistics in Connecticut: A, Continuous 

streamgages; B, Short-term or partial-record streamgages.—Continued

[Geographic Information System used to derive all basin characteristics (table 4); USGS, U.S. Geological Survey; no., number; mi2, square miles; mi, miles;

ft, feet; --, not determined; Q99, 99-percent flow exceedence]

B Short-term or partial-record streamgages; used with continuous-record streamgages only for Q99

USGS 

short-term 

or partialrecord 

streamgage 

no.

Drainage 

area

(mi2

)

Basin 

perimeter 

(mi)

Total river 

miles

(mi)

Maximum 

basin

elevation

(ft)

Mean

basin

elevation

(ft)

Basin

relief

(ft)

Mean basin 

slope

(percent)

Latitude of 

basin

centroid

(CT state 

plane ft)

Longitude 

of basin 

centroid

(CT state 

plane ft)

01118350 19.25 34.00 71.33 530 285 461 7.0 1,251,142 740,216

01118750 4.41 15.42 12.04 350 239 253 5.1 1,204,274 709,388

01119255 2.57 9.58 7.90 1,204 1,006 434 10.9 1,140,243 937,992

01119320 15.13 28.94 43.92 1,304 909 708 8.7 1,140,846 916,506

01119360 2.13 9.80 8.64 960 653 450 7.0 1,128,898 884,213

01120200 16.29 29.24 32.24 726 492 484 6.2 1,127,838 809,059

01120920 3.44 13.28 10.48 1,257 914 588 8.8 1,153,136 905,198

01121300 10.93 24.06 34.32 1,204 768 763 8.5 1,143,424 894,975

01125300 4.46 14.11 11.42 876 673 492 7.7 1,197,966 924,512

01125600 11.02 28.41 26.20 890 685 407 7.3 1,197,595 887,264

01125900 8.29 21.83 24.05 836 648 417 6.5 1,262,431 885,894

01126700 10.66 26.45 36.05 662 388 491 6.1 1,203,871 825,347

01127100 12.30 29.31 33.77 535 290 419 6.4 1,223,431 753,552

01127400 15.27 35.10 44.62 671 368 558 7.9 1,153,856 791,794

01127700 8.91 25.22 27.09 518 294 468 8.4 1,162,583 749,714

01127800 4.38 17.75 10.53 427 216 348 8.0 1,133,911 702,460

01183990 2.04 12.77 5.74 239 194 102 3.7 1,058,147 936,493

01184300 3.66 12.08 8.68 1,114 677 835 12.9 1,091,888 927,606

01186400 35.56 52.07 74.11 1,812 1,360 1,243 10.4 896,972 936,358

01187680 8.14 20.98 23.64 1,215 897 774 11.4 959,039 893,427

01191900 8.47 16.83 21.07 1,050 723 507 7.8 1,094,204 900,328

01192800 2.90 12.15 7.81 733 396 524 10.3 1,009,014 720,159

01193120 5.63 16.89 14.79 681 489 539 8.2 1,048,948 725,974

01193130 3.71 11.97 12.71 727 479 523 9.4 1,038,605 729,826

01193210 3.66 12.64 8.19 784 583 395 6.3 1,109,630 801,910

01193300 6.78 18.24 16.66 897 657 421 7.0 1,081,517 827,909

01195146 6.24 19.25 16.97 662 491 354 5.5 1,047,945 709,447

01196600 9.40 24.28 21.19 873 346 760 8.9 949,946 735,484

01198700 5.55 16.00 15.06 1,747 1,414 975 13.0 864,070 901,264

01198800 19.02 38.60 51.18 1,747 1,254 1,089 14.4 858,794 892,784

01201890 11.86 22.00 37.40 825 513 577 8.4 834,407 717,297

01203100 7.82 18.30 13.43 1,044 687 752 9.8 853,226 761,022

01203700 3.40 12.05 7.31 1,138 904 578 11.0 864,778 797,037

01208999 5.52 15.71 14.67 851 633 476 8.6 829,355 678,368

Range of basin characteristics for all streamgages

Minimum 0.56 4.14 0.80 239 168 102 3.7 -- --

Maximum 149.48 84.71 439.39 2,058 1,414 1,369 14.5 -- --

Average 20.20 28.57 52.04 944 628 604 8.3 -- --
Table 5 35

Table 5. Characteristics of the drainage basins used for regionalizing flow-duration statistics in Connecticut: A, Continuous 

streamgages; B, Short-term or partial-record streamgages.—Continued

[Geographic Information System used to derive all basin characteristics (table 4); USGS, U.S. Geological Survey; no., number; mi2, square miles; mi, miles;

ft, feet; --, not determined; Q99, 99-percent flow exceedence]

B Short-term or partial-record streamgages; used with continuous-record streamgages only for Q99

USGS 

short-term 

or partialrecord 

streamgage 

no.

Latitude of 

streamgage

(decimal 

degrees)

Longitude of 

streamgage

(decimal 

degrees)

River miles 

in contact 

with sand 

and gravel 

(mi)

Deciduous

forest

(percent)

Evergreen 

forest

(percent)

Mixed

forest

(percent)

Deciduous 

and mixed 

forest

(percent)

Developed, 

open space 

(percent)

Developed,

low 

intensity 

(percent)

01118350 41.455 -71.814 14.88 73.0 1.5 0.2 73.2 3.4 0.6

01118750 41.389 -71.986 1.52 64.7 0.6 0.0 64.7 5.8 2.5

01119255 42.023 -72.248 0.47 73.6 1.8 10.3 83.9 6.3 0.6

01119320 41.934 -72.261 0.83 56.3 7.8 18.9 75.2 4.6 0.2

01119360 41.871 -72.291 0.80 44.5 1.9 21.2 65.7 7.2 0.8

01120200 41.707 -72.247 1.89 64.2 0.5 2.9 67.1 4.4 1.3

01120920 41.920 -72.179 0.34 62.9 2.5 6.1 68.9 10.1 0.9

01121300 41.872 -72.241 2.44 70.7 1.5 10.3 80.9 5.0 0.8

01125300 41.991 -71.997 0.36 56.5 4.2 10.7 67.3 5.9 0.4

01125600 41.874 -72.009 3.41 66.7 1.6 5.7 72.4 4.9 0.3

01125900 41.909 -71.819 9.41 58.8 9.4 10.2 68.9 3.2 1.4

01126700 41.681 -71.978 14.00 56.2 0.6 5.0 61.2 4.5 0.8

01127100 41.554 -71.970 9.93 52.9 0.7 0.2 53.2 2.8 0.9

01127400 41.571 -72.133 8.17 50.6 0.7 3.2 53.8 4.3 1.5

01127700 41.501 -72.116 4.89 75.1 0.5 1.1 76.2 5.2 3.2

01127800 41.357 -72.261 1.11 78.3 0.2 0.1 78.4 2.6 1.0

01183990 42.007 -72.553 1.59 25.2 5.5 1.2 26.4 15.4 14.8

01184300 41.992 -72.434 0.77 73.0 3.6 4.6 77.6 6.4 1.3

01186400 41.978 -73.045 5.92 54.6 5.8 23.7 78.3 4.2 0.2

01187680 41.872 -72.906 0.00 76.4 3.1 4.0 80.4 5.5 0.6

01191900 41.906 -72.404 0.96 57.9 4.3 7.3 65.2 6.2 1.5

01192800 41.452 -72.702 0.62 58.3 1.2 1.7 60.0 6.7 7.1

01193120 41.479 -72.557 4.74 77.6 0.8 1.9 79.5 6.7 1.8

01193130 41.474 -72.596 2.24 81.7 0.8 5.0 86.8 5.8 0.6

01193210 41.640 -72.343 0.20 58.2 0.2 0.6 58.8 6.5 2.8

01193300 41.696 -72.456 0.63 65.5 0.4 2.9 68.4 5.6 2.6

01195146 41.383 -72.589 2.47 72.3 0.4 0.6 72.9 8.0 0.8

01196600 41.460 -72.918 8.48 54.1 1.0 0.6 54.7 15.4 15.3

01198700 41.926 -73.280 0.04 70.3 7.3 12.7 83.1 1.0 0.0

01198800 41.949 -73.321 2.87 68.8 8.4 10.1 78.9 2.9 0.2

01201890 41.456 -73.335 3.65 59.2 1.1 1.0 60.2 10.5 7.3

01203100 41.528 -73.308 0.54 67.0 0.7 1.5 68.5 7.4 0.7

01203700 41.627 -73.226 0.08 76.0 0.7 0.2 76.2 5.9 0.2

01208999 41.293 -73.368 0.77 76.7 1.2 0.2 76.9 8.0 0.9

Range of basin characteristics for all streamgages

Minimum -- -- 0.00 25.2 0.2 0.0 26.4 1.0 0.0

Maximum -- -- 178.76 81.7 22.9 31.7 86.8 30.3 15.3

Average -- -- 12.17 62.2 3.7 5.2 67.4 6.8 2.2
36 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 5. Characteristics of the drainage basins used for regionalizing flow-duration statistics in Connecticut: A, Continuous 

streamgages; B, Short-term or partial-record streamgages.—Continued

[Geographic Information System used to derive all basin characteristics (table 4); USGS, U.S. Geological Survey; no., number; mi2, square miles; mi, miles;

ft, feet; --, not determined; Q99, 99-percent flow exceedence]

B Short-term or partial-record streamgages; used with continuous-record streamgages only for Q99

USGS shortterm

or partialrecord 

streamgage 

no.

Developed, 

open space 

and low 

intensity

(ft)

Open water 

(percent)

Impervious

surface

(percent)

Wetlands 

(percent)

Soil Type A 

(percent)

Soil type B 

(percent)

Soil type C 

(percent)

Soil type D 

(percent)

01118350 4.0 1.3 0.06 6.7 0.0 0.4 0.0 99.6

01118750 8.3 0.0 0.25 1.2 0.0 0.0 0.0 100.0

01119255 6.9 0.3 0.06 2.7 0.0 18.8 43.7 31.3

01119320 4.8 1.4 0.03 1.3 2.5 49.4 11.1 37.0

01119360 8.0 0.9 0.08 2.8 0.0 63.6 0.0 36.4

01120200 5.7 0.8 0.09 1.3 3.3 35.6 37.8 23.3

01120920 11.0 4.5 0.15 1.4 14.9 25.5 40.4 19.1

01121300 5.8 1.3 0.09 1.7 3.2 37.0 40.3 19.5

01125300 6.2 0.0 0.05 3.2 0.0 50.0 28.1 21.9

01125600 5.2 1.2 0.04 4.5 6.3 27.0 46.0 20.6

01125900 4.6 1.0 0.10 16.7 75.0 22.7 2.3 0.0

01126700 5.3 0.4 0.07 4.3 10.3 46.6 25.9 17.2

01127100 3.7 0.0 0.07 2.3 1.4 15.7 7.1 75.7

01127400 5.8 0.1 0.12 0.8 2.3 32.6 50.0 15.1

01127700 8.3 0.5 0.25 0.4 0.0 6.0 6.0 88.0

01127800 3.6 1.2 0.06 1.9 0.0 0.0 0.0 100.0

01183990 30.3 2.1 1.53 4.1 36.4 36.4 0.0 27.3

01184300 7.7 1.1 0.09 0.5 0.0 38.1 19.0 42.9

01186400 4.5 2.0 0.04 5.3 1.0 29.2 33.2 31.7

01187680 6.1 0.4 0.06 0.4 0.0 71.1 20.0 8.9

01191900 7.7 0.1 0.10 0.8 4.3 61.7 10.6 23.4

01192800 13.8 0.2 0.28 0.2 0.0 0.0 0.0 100.0

01193120 8.5 0.0 0.15 0.7 0.0 0.0 0.0 100.0

01193130 6.4 0.0 0.06 0.2 0.0 0.0 0.0 100.0

01193210 9.3 0.9 0.23 1.2 0.0 25.5 56.9 17.6

01193300 8.2 0.5 0.13 2.5 2.1 43.6 24.5 29.8

01195146 8.7 1.2 0.09 3.1 0.0 0.0 0.0 100.0

01196600 30.7 0.1 0.99 0.6 0.0 0.0 0.0 100.0

01198700 1.0 1.0 0.00 2.4 1.2 53.7 1.2 43.9

01198800 3.1 0.4 0.03 1.5 2.8 54.2 14.0 29.0

01201890 17.9 1.9 0.52 0.7 0.0 0.0 0.0 100.0

01203100 8.2 0.1 0.09 0.5 0.0 25.0 11.4 63.6

01203700 6.1 0.6 0.05 0.5 0.0 59.6 25.5 14.9

01208999 8.9 0.4 0.10 0.2 0.0 0.0 0.0 100.0

Range of basin characteristics for all streamgages

Minimum 1.0 0.0 0.00 0.0 0.0 0.0 0.0 0.0

Maximum 37.6 10.6 1.53 18.1 100 80.0 79.2 100.0

Average 9.0 1.1 0.08 3.6 23.0 22.6 15.0 40.2
Table 5 37

Table 5. Characteristics of the drainage basins used for regionalizing flow-duration statistics in Connecticut: A, Continuous 

streamgages; B, Short-term or partial-record streamgages.—Continued

[Geographic Information System used to derive all basin characteristics (table 4); USGS, U.S. Geological Survey; no., number; mi2, square miles; mi, miles;

ft, feet; --, not determined; Q99, 99-percent flow exceedence]

B Short-term or partial-record streamgages; used with continuous-record streamgages only for Q99

USGS shortterm

or partialrecord 

streamgage 

no.

Soil type D, 

A_D, and C_D

Till

(percent)

Coarse

stratified 

deposits 

(percent)

Alluvium 

deposits 

(percent)

01118350 99.6 83.2 10.6 3.7

01118750 100.0 82.8 9.6 5.3

01119255 37.5 94.9 1.5 3.7

01119320 37.0 93.5 1.5 3.5

01119360 36.4 78.2 19.5 1.5

01120200 23.3 91.3 2.6 4.4

01120920 19.1 89.6 4.3 1.5

01121300 19.5 92.3 3.9 2.5

01125300 21.9 93.3 0.8 5.4

01125600 20.6 87.5 7.4 4.2

01125900 0.0 74.4 23.6 1.2

01126700 17.2 74.6 22.1 2.9

01127100 75.7 81.7 15.8 2.3

01127400 15.1 79.6 13.2 7.1

01127700 88.0 84.2 8.8 4.1

01127800 100.0 87.5 6.3 2.1

01183990 27.3 0.8 46.0 2.4

01184300 42.9 90.8 6.2 1.9

01186400 36.6 92.7 2.5 3.2

01187680 8.9 97.4 0.0 2.6

01191900 23.4 90.1 5.9 4.0

01192800 100.0 86.0 8.9 5.1

01193120 100.0 79.3 13.3 0.6

01193130 100.0 94.9 5.1 0.0

01193210 17.6 98.2 0.7 0.5

01193300 29.8 91.7 3.9 3.9

01195146 100.0 90.4 5.3 2.4

01196600 100.0 56.1 39.2 4.6

01198700 43.9 92.6 2.6 3.7

01198800 29.0 89.4 4.7 5.5

01201890 100.0 85.8 8.0 4.4

01203100 63.6 93.0 3.9 2.9

01203700 14.9 93.3 1.6 4.5

01208999 100.0 97.5 1.3 0.6

Range of basin characteristics for all streamgages

Minimum 0.0 1.8 0.0 0.0

Maximum 100.0 99.7 55.1 7.2

Average 41.4 81.7 12.2 2.8
38 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut

Table 6. Climate characteristics used for regionalizing flow-duration statistics in Connecticut.

[Climate characteristics are basinwide averages for the streamgages. USGS, U.S. Geological Survey; no., number; Precip, precipitation, in inches; Temp, 

temperature, in degrees Fahrenheit]

USGS 

streamgage 

no.1

Precipitation Temperature Salmonid Spawning Overwinter

Mean annual Maximum 

annual

Mean annual 

minmum

Mean annual 

maxmum Precip Temp Precip Temp

01111300 49.4 50.2 37.23 58.42 4.58 50.2 4.04 36.4

01111500 50.2 52.2 37.99 58.77 4.68 50.6 4.14 37.0

01115098 50.5 50.9 38.76 58.93 4.73 50.8 4.20 37.6

01115187 52.0 52.2 38.36 58.51 4.88 50.4 4.40 37.1

01117468 50.1 50.5 38.97 58.57 4.85 51.0 4.25 37.8

01117500 50.4 51.2 40.31 58.87 4.90 51.6 4.27 38.6

01117800 49.6 49.9 38.06 59.23 4.61 51.1 4.09 37.7

01118000 49.7 50.3 38.45 59.26 4.65 51.2 4.12 37.8

01118300 50.1 50.2 39.57 59.09 4.67 51.2 4.16 37.6

01120500 50.8 51.0 36.85 57.18 4.63 48.5 4.05 34.6

01121000 50.5 51.1 36.91 57.61 4.56 49.0 3.99 35.2

01123000 51.0 51.5 37.31 58.40 4.73 49.9 4.14 36.0

01125490 50.9 51.3 36.75 58.10 4.67 49.6 4.08 35.7

01126600 50.8 51.0 37.14 58.47 4.76 50.0 4.16 36.1

01126950 49.6 50.6 38.44 59.53 4.58 51.4 4.06 37.9

01176000 48.4 49.6 35.70 56.79 4.26 47.8 3.70 33.9

01187300 53.1 54.3 33.80 55.07 4.71 46.0 4.12 32.0

01187400 52.3 53.4 34.03 55.94 4.63 46.9 4.08 32.9

01187800 53.7 54.0 35.64 57.23 4.57 48.6 4.06 34.4

01188000 53.3 53.6 35.44 56.97 4.55 48.5 4.00 34.4

01192600 49.2 50.1 37.55 58.60 4.39 49.8 3.78 35.9

01193500 51.5 52.4 37.81 58.72 4.66 50.3 4.04 36.5

01193800 52.4 52.7 38.28 58.80 4.93 50.5 4.28 36.8

01194000 51.7 52.1 37.79 58.68 4.81 50.5 4.17 36.7

01194500 51.6 51.8 37.90 58.97 4.84 50.8 4.19 37.1

01195100 50.3 51.5 39.69 59.61 4.68 51.9 4.04 38.3

01195200 49.8 51.1 40.53 59.86 4.55 52.1 3.97 52.6

01198000 47.7 49.6 34.07 55.63 3.97 46.3 3.31 26.5

01199200 48.4 49.2 36.20 55.92 3.96 46.8 3.47 29.7

01201190 49.9 51.2 37.06 58.18 4.22 49.3 3.57 38.8

01204800 53.9 54.1 41.10 60.14 4.83 51.7 4.11 50.1

01206400 52.9 53.9 35.51 57.11 4.53 48.4 4.00 34.2

01206500 52.8 53.9 35.62 57.27 4.53 48.5 3.98 34.8

01208950 50.2 51.1 41.98 60.58 4.38 52.5 3.76 53.7

01208990 52.7 53.1 40.81 60.22 4.57 51.5 3.90 48.3

01372200 44.8 47.4 36.02 59.01 3.48 49.7 3.19 40.7

01372800 48.7 51.2 37.69 59.34 4.01 50.1 3.54 42.4

01374598 50.7 50.9 37.99 59.04 4.21 49.8 3.78 41.6

01374890 52.2 53.0 41.30 60.47 4.57 51.5 3.83 48.8

Minimum 44.8 47.4 33.80 55.07 3.48 46.0 3.19 26.5

Maximum 53.9 54.3 41.98 60.58 4.93 52.5 4.40 53.7

Average 50.7 51.5 37.71 58.39 4.55 49.9 3.98 38.1 1

Clear Brook (01187850) and Marshepaug River (01201930) are not included in this data set.
Table 6 39

Table 6. Climate characteristics used for regionalizing flow-duration statistics in Connecticut.—Continued

[Climate characteristics are basinwide averages for the streamgages. USGS, U.S. Geological Survey; no., number; Precip, precipitation, in inches; Temp, 

temperature, in degrees Fahrenheit]

USGS 

streamgage 

no.1

Habitat Forming Clupeid Spawning Resident Spawning Rearing and Growth

Precip Temp Precip Temp Precip Temp Precip Temp

01111300 4.33 51.0 3.75 68.6 3.80 76.7 4.12 73.8

01111500 4.44 51.7 3.78 68.8 3.82 76.7 4.14 73.8

01115098 4.50 52.0 3.80 68.8 3.79 76.4 4.12 73.5

01115187 4.70 51.8 3.83 68.7 3.92 76.1 4.19 73.2

01117468 4.59 51.2 3.96 67.0 3.79 75.5 3.95 73.7

01117500 4.64 51.1 3.99 66.6 3.82 75.2 3.91 73.8

01117800 4.31 52.2 3.79 68.9 3.65 76.7 4.16 74.0

01118000 4.37 52.1 3.83 68.6 3.68 76.6 4.11 74.2

01118300 4.43 51.6 3.90 67.9 3.71 76.4 4.11 74.4

01120500 4.39 49.5 3.96 67.7 4.08 75.9 4.31 72.4

01121000 4.34 50.1 3.98 68.0 4.05 76.1 4.33 73.0

01123000 4.45 50.9 3.96 68.5 3.89 76.8 4.27 73.8

01125490 4.41 50.7 3.92 68.6 3.99 76.8 4.31 73.6

01126600 4.47 51.0 3.91 68.8 3.87 76.9 4.20 74.0

01126950 4.24 52.3 3.79 68.9 3.61 77.1 4.23 74.6

01176000 4.06 49.2 4.07 67.4 3.99 75.8 4.22 72.4

01187300 4.44 47.8 4.85 66.1 4.47 74.0 4.46 70.7

01187400 4.36 48.6 4.74 67.0 4.41 74.9 4.39 71.6

01187800 4.54 50.3 4.66 68.1 4.42 76.1 4.69 72.6

01188000 4.51 50.2 4.65 68.0 4.39 76.0 4.68 72.5

01192600 4.20 51.0 4.21 68.6 3.93 76.9 4.29 73.8

01193500 4.46 51.4 4.18 68.6 4.05 77.0 4.39 74.0

01193800 4.63 51.5 4.24 67.8 3.91 76.0 4.30 73.9

01194000 4.54 51.5 4.19 67.9 3.96 76.2 4.29 74.0

01194500 4.55 51.7 4.17 68.1 3.95 76.5 4.25 74.3

01195100 4.49 52.1 4.12 68.2 3.96 76.6 4.12 74.8

01195200 4.45 52.2 4.15 68.2 3.93 76.8 4.11 75.0

01198000 3.91 48.3 4.81 66.9 4.01 75.1 4.29 71.4

01199200 3.95 49.0 4.53 66.7 4.21 74.6 4.35 71.3

01201190 4.21 51.4 4.56 68.8 4.10 76.6 4.50 73.5

01204800 4.91 53.3 4.86 69.7 4.39 78.2 4.43 75.3

01206400 4.49 50.1 4.63 67.9 4.32 75.9 4.64 72.3

01206500 4.48 50.2 4.62 68.0 4.31 76.0 4.63 72.5

01208950 4.44 53.3 4.69 69.4 4.06 78.2 4.23 75.7

01208990 4.52 53.4 4.86 70.3 4.30 78.6 4.56 75.3

01372200 3.56 51.9 4.36 69.7 3.99 78.0 4.04 74.7

01372800 3.98 52.5 4.46 70.1 4.25 77.9 4.35 74.9

01374598 4.12 52.4 4.45 69.8 4.39 77.3 4.52 74.6

01374890 4.46 53.7 4.96 70.9 4.20 78.9 4.55 75.5

Minimum 3.56 47.8 3.75 66.1 3.61 74.0 3.91 70.7

Maximum 4.91 53.7 4.96 70.9 4.47 78.9 4.69 75.7

Average 4.38 51.2 4.26 68.4 4.04 76.5 4.30 73.7
40 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut Appendix 1. Basin characteristics considered for use in regression analysis (includes units, method or procedure, and source data).—Continued [Red italics, basin characteristics used in regression equations] Variable name Units Method Source data Drainage area square miles StreamStats and ArcGIS 9.3 ArcToolbox - calculate field U.S. Geological Survey, 2006, National Elevation Dataset: accessed on June 25, 2009, at http://ned.usgs.gov. Watershed Boundary Dataset drainage boundaries (http://www.ncgc.nrcs. usda.gov/products/datasets/watershed/, accessed June 25, 2009) Basin perimeter miles ArcGIS 9.3 ArcToolbox - calculate field Total river miles miles ArcGIS 9.3 ArcToolbox - calculate field U.S. Geological Survey, 2009, National Hydrography Dataset: accessed on June 25, 2009, at http://nhd.usgs.gov. Maximum basin elevation; Mean basin elevation feet ArcGIS 9.3 ArcToolbox - spatial analyst tools U.S. Geological Survey, 2006, National Elevation Dataset: accessed on June 25, 2009, at http://ned.usgs.gov. Basin relief feet Maximum basin elevation minus minimum basin elevation (“Minimum basin elevation” from same method and source data as maxi- mum and mean basin elevation) U.S. Geological Survey, 2006, National Elevation Dataset: accessed on June 25, 2009, at http://ned.usgs.gov. Mean basin slope percent ArcGIS 9.3 ArcToolbox - spatial analyst tools U.S. Geological Survey, 2009, National Hydrography Dataset: accessed on June 25, 2009, at http://nhd.usgs.gov. National Elevation slope grid, 30-meter resolution (http://ned.usgs.gov/), accessed June 25, 2009 Latitude of basin centroid; Longitude of basin centroid feet divide by 100,000; ArcGIS 9.3 ArcToolbox - zonal geometry tool Gage latitude; Gage longitude decimal degrees USGS NWIS database, accessed June 25, 2009 Total streams in contact with coarse stratified deposits miles ArcGIS 9.3 ArcToolbox - spatial analyst tools Deciduous forest; Evergreen forest; and Mixed forest percent (Sum of area of the land cover classifica- tion/drainage area)*100; land cover classifications (41-deciduous, 42-ev- ergreen, and 43-mixed) are defined at http://www.mrlc.gov/nlcd_definitions.asp Multi-Resolution Land Characteristics Consortium, 1992, Na- tional Land-Cover Dataset 1992: accessed on June 25, 2009, at http://www.mrlc.gov/mric2k_nlcd.asp. Multi-Resolution Land Characteristics Consortium, 2001, Na- tional Land-Cover Dataset 2001: accessed on June 25, 2009, at http://www.mrlc.gov/mric2k_nlcd.asp. Deciduous and mixed forest percent (Sum of areas of two land cover clas- sification/drainage area)*100; land cover classifications (41-deciduous for- est, 43-mixed forest) are defined at http://www.mrlc.gov/nlcd_definitions.asp Multi-Resolution Land Characteristics Consortium, 1992, Na- tional Land-Cover Dataset 1992: accessed on June 25, 2009, at http://www.mrlc.gov/mric2k_nlcd.asp. Multi-Resolution Land Characteristics Consortium, 2001, Na- tional Land-Cover Dataset 2001: accessed on June 25, 2009, at 

http://www.mrlc.gov/mric2k_nlcd.asp.
Appendixes

41

Appendix 1. Basin characteristics considered for use in regression analysis (includes units, method or procedure, and source data).—Continued[Red italics, basin characteristics used in regression equations]

Variable name Units Method Source data

Developed, open space;Developed, low intensity

percent (Sum of area of land cover classification/

drainage area)*100; land cover classifications (21-developed, open space; 22-developed-low intensity) are defined at http://www.mrlc.gov/nlcd_definitions.asp

Multi-Resolution Land Characteristics Consortium, 1992, National Land-Cover Dataset 1992: accessed on June 25, 2009, at 

http://www.mrlc.gov/mric2k_nlcd.asp.

Multi-Resolution Land Characteristics Consortium, 2001, National Land-Cover Dataset 2001: accessed on June 25, 2009, at 

http://www.mrlc.gov/mric2k_nlcd.asp.

Developed, open space and low 

intensity

percent (Sum of areas of land cover classifications 

21 and 22/drainage area)*100; land cover classifications (21-developed, open space; 22-developed, low intensity) are defined at http://www.mrlc.gov/nlcd_definitions.asp

Multi-Resolution Land Characteristics Consortium, 1992, National Land-Cover Dataset 1992: accessed on June 25, 2009, at 

http://www.mrlc.gov/mric2k_nlcd.asp.

Multi-Resolution Land Characteristics Consortium, 2001, National Land-Cover Dataset 2001: accessed on June 25, 2009, at 

http://www.mrlc.gov/mric2k_nlcd.asp.

Open water;Impervious area

percent (Sum of area of land cover classification/drainage area)*100; land cover classifications 

(11-open water, impervious) are defined at http://www.mrlc.gov/nlcd_definitions.asp

Multi-Resolution Land Characteristics Consortium, 1992, National Land-Cover Dataset 1992: accessed on June 25, 2009, at 

http://www.mrlc.gov/mric2k_nlcd.asp.

Multi-Resolution Land Characteristics Consortium, 2001, National Land-Cover Dataset 2001: accessed on June 25, 2009, at 

http://www.mrlc.gov/mric2k_nlcd.asp.

Wetlands percent (Sum of area /drainage area)*100 U.S. Fish and Wildlife Service, 2009, National Wetlands Inventory: Branch 

of Resource and Mapping Support, accessed on August 5, 2009, at http://www.fws.gov/wetlands/.

Soil hydrologic group A, B, C, 

and D1

percent (Area of type soil/drainage area)*100, type A 

is high infiltration rate soils, type D is low infiltration rate soils

Natural Resources Conservation Service, 2009a, Soil Data Mart: 

U.S. Department of Agriculture, accessed on April 20, 2009, at http://soildatamart.nrcs.usda.gov.

Percent till and thick till percent (Area of till and thick till/drainage area)*100 Connecticut: Stone, J.R., Schafer, J.P., London, E.H., and Thompson, 

W.B., Compilation sheets at 1:24,000 scale for Stone, J.R., Schafer, J.P., London, E.H., and Thompson, W.B., 1992, Surficial materials map of Connecticut: U.S. Geological Survey Special Map, 2 sheets, scale 1:125,000, accessed on April 20, 2009, at http://www.ct.gov/dep/cwp/view.asp?a=2698&q=322898&depNav_GID=1707#Geology.New York: New York State Geological Survey, Surficial Geology, New York State Museum Technology Center, http://www.nysm.nysed.gov/gis.html, accessed on April 20, 2009

Rhode Island: Glacial Deposits, Rhode Island Geographic Information System,http://www.edc.uri.edu/rigis/data/data.aspx?ISO=geoscientificInformation, accessed on April 20, 2009.Massachusetts: MassGIS, Surficial Geology (1:24,000), accessed on April 20, 2009.
42 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut Appendix 1. Basin characteristics considered for use in regression analysis (includes units, method or procedure, and source data).—Continued [Red italics, basin characteristics used in regression equations] Variable name Units Method Source data Percent coarse stratified depos- its (percent) percent (Area of coarse stratified deposits /drainage area)*100; glacial meltwater deposits (strati- fied) consists of coarse deposits and stacked coarse deposits Connecticut: Stone, J.R., Schafer, J.P., London, E.H., and Thompson, W.B., Compilation sheets at 1:24,000 scale for Stone, J.R., Schafer, J.P., London, E.H., and Thompson, W.B., 1992, Surficial materials map of Connecticut: U.S. Geological Survey Special Map, 2 sheets, scale 1:125,000, accessed on April 20, 2009, at http://www.ct.gov/dep/cwp/view. asp?a=2698&q=322898&depNav_GID=1707#Geology. New York: New York State Geological Survey, Surficial Geology, New York State Museum Technology Center, http://www.nysm.nysed.gov/gis.html, accessed on April 20, 2009 Rhode Island: Glacial Deposits, Rhode Island Geographic Information System, http://www.edc.uri.edu/rigis/data/data.aspx?ISO=geoscientificInformation, accessed on April 20, 2009. Massachusetts: MassGIS, Surficial Geology (1:24,000), accessed on April 20, 2009. Percent alluvium deposits percent (Area of postglacial deposits/drainage area)*100; postglacial deposits consists of floodplain alluvium and swamp deposits Connecticut: Stone, J.R., Schafer, J.P., London, E.H., and Thompson, W.B., Compilation sheets at 1:24,000 scale for Stone, J.R., Schafer, J.P., London, E.H., and Thompson, W.B., 1992, Surficial materials map of Connecticut: U.S. Geological Survey Special Map, 2 sheets, scale 1:125,000, accessed on April 20, 2009, at http://www.ct.gov/dep/cwp/view. asp?a=2698&q=322898&depNav_GID=1707#Geology. New York: New York State Geological Survey, Surficial Geology, New York State Museum Technology Center, http://www.nysm.nysed.gov/gis. html, accessed on April 20, 2009 Rhode Island: Glacial Deposits, Rhode Island Geographic Information System, http://www.edc.uri.edu/rigis/data/data.aspx?ISO=geoscientificInformation, accessed on April 20, 2009. Massachusetts: MassGIS, Surficial Geology (1:24,000), accessed on April 20, 2009. Precipitation 1971–2000, Mean annual inches Averaged over the basin surface area minus 40 estimated using ArcInfo Grid Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/. Precipitation 1971–2000, Maxi- mum annual inches Averaged over the basin surface area minus 40 estimated using ArcInfo Grid Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/.

Precipitation 1971–2000, November, Mean monthly inches Averaged over the basin surface area estimated using ArcInfo Grid Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon State University, accessed on August 5, 2009, at 

http://www.prism.oregonstate.edu/.
Appendixes

43

Appendix 1. Basin characteristics considered for use in regression analysis (includes units, method or procedure, and source data).—Continued[Red italics, basin characteristics used in regression equations]

Variable name Units Method Source data

Precipitation 1971–2000, 

December–February, Mean seasonal

inches Averaged over the basin surface area estimated 

using ArcInfo Grid as sum of monthly averages of December, January, and February divided by 3

Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon

State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/.

Precipitation 1971–2000, 

March–April, Mean seasonal

inches Averaged over the basin surface area estimated 

using ArcInfo Grid as sum of monthly averages of March and April divided by 2

Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon

State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/.

Precipitation 1971–2000, June, 

Mean monthly

inches Averaged over the basin surface area estimated 

using ArcInfo Grid

Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon

State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/.

Precipitation 1971–2000, July–

Oct, Mean seasonal

inches Averaged over the basin surface area estimated 

using ArcInfo Grid as sum of monthly averages of July, August, September, and October divided by 4

Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon

State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/.

Temperature 1971–2000, Mean 

annual

degrees Fahrenheit Averaged over the basin surface area minus 50 estimated using ArcInfo Grid Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon State University, accessed on August 5, 2009, at 

http://www.prism.oregonstate.edu/.

Temperature 1971–2000, Maximum annual degrees Fahren- heit Averaged over the basin surface area minus 50 estimated using ArcInfo Grid Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon State University, accessed on August 5, 2009, at 

http://www.prism.oregonstate.edu/.

Temperature 1971–2000, November, Mean monthly degrees Fahren- heit Averaged over the basin surface area estimated using ArcInfo Grid Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon State University, accessed on August 5, 2009, at 

http://www.prism.oregonstate.edu/.

Temperature 1971–2000, 

December–February, Mean seasonal

degrees Fahrenheit Averaged over the basin surface area estimated using ArcInfo Grid as sum of monthly averages of December, January, and February 

divided by 3

Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon

State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/.

Temperature 1971–2000, 

March–April, Mean seasonal

degrees Fahrenheit Averaged over the basin surface area estimated using ArcInfo Grid as sum of monthly averages of March and April divided by 2 Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/.

Temperature 1971–2000, June, 

Mean monthly

degrees Fahrenheit Averaged over the basin surface area estimated using ArcInfo Grid Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon State University, accessed on August 5, 2009, at 

http://www.prism.oregonstate.edu/.

Temperature 1971–2000, July–

Oct, Mean seasonal

degrees Fahrenheit Averaged over the basin surface area estimated using ArcInfo Grid as sum of monthly averages of July, August, September, and October 

divided by 4

Prism Climate Group, 2009, Precipitation: Corvallis, Oreg., Oregon

State University, accessed on August 5, 2009, at http://www.prism.oregonstate.edu/.

1Massachusetts, New York, and Rhode Island geology and soils data from abutting states.
44 Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut Appendix 2. Predictor and explanatory variable names used in StreamStats (includes units, method, and source data). [Method and source of data are in Appendix 1] Predictor variable Variable name shown in equation in Table 9 StreamStats/National Streamflow Statistic name Definition Units Salmonid Spawning (November) 25-percent flow duration Q25 NOVD25 November streamflow exceeded 25 percent of the time cubic feet per second 50-percent flow duration Q50 NOVD50 November streamflow exceeded 50 percent of the time cubic feet per second 75-percent flow duration Q75 NOVD75 November streamflow exceeded 75 percent of the time cubic feet per second 90-percent flow duration Q90 NOVD90 November streamflow exceeded 90 percent of the time cubic feet per second 99-percent flow duration Q99 NOVD99 November streamflow exceeded 99 percent of the time cubic feet per second Overwinter (December, January, and February) 25-percent flow duration Q25 D25_12_02 December through February streamflow exceeded 25 percent of time cubic feet per second 50-percent flow duration Q50 D50_12_02 December through February streamflow exceeded 50 percent of time cubic feet per second 75-percent flow duration Q75 D75_12_02 December through February streamflow exceeded 75 percent of time cubic feet per second 95-percent flow duration Q95 D95_12_02 December through February streamflow exceeded 95 percent of time cubic feet per second 99-percent flow duration Q99 D99_12_02 December through February streamflow exceeded 99 percent of time cubic feet per second Habitat Forming (March–April) 25-percent flow duration Q25 D25_03_04 March through April streamflow exceeded 25 percent of time cubic feet per second 50-percent flow duration Q50 D50_03_04 March through April streamflow exceeded 50 percent of time cubic feet per second 75-percent flow duration Q75 D75_03_04 March through April streamflow exceeded 75 percent of time cubic feet per second 95-percent flow duration Q95 D95_03_04 March through April streamflow exceeded 95 percent of time cubic feet per second 99-percent flow duration Q99 D99_03_04 March through April streamflow exceeded 99 percent of time cubic feet per second Clupeid Spawning (May) 25-percent flow duration Q25 MAYD25 November streamflow exceeded 25 percent of the time cubic feet per second 50-percent flow duration Q50 MAYD50 November streamflow exceeded 50 percent of the time cubic feet per second 75-percent flow duration Q75 MAYD75 November streamflow exceeded 75 percent of the time cubic feet per second 95-percent flow duration Q95 MAYD95 November streamflow exceeded 90 percent of the time cubic feet per second 99-percent flow duration Q99 MAYD99 November streamflow exceeded 99 percent of the time cubic feet per second Resident Spawning (June) 25-percent flow duration Q25 JUND25 June streamflow exceeded 25 percent of the time cubic feet per second 50-percent flow duration Q50 JUND50 June streamflow exceeded 50 percent of the time cubic feet per second 75-percent flow duration Q75 JUND75 June streamflow exceeded 75 percent of the time cubic feet per second 90-percent flow duration Q90 JUND90 June streamflow exceeded 90 percent of the time cubic feet per second 99-percent flow duration Q99 JUND99 June streamflow exceeded 99 percent of the time cubic feet per second Rearing through Growth (July, August, September, through October) 25-percent flow duration Q25 D25_07_10 July through October streamflow exceeded 25 percent of time cubic feet per second 50-percent flow duration Q50 D50_07_10 July through October streamflow exceeded 50 percent of time cubic feet per second

75-percent flow duration Q75 D75_07_10 July through October streamflow exceeded 25 percent of time cubic feet per second

80-percent flow duration Q80 D80_07_10 July through October streamflow exceeded 25 percent of time cubic feet per second

99-percent flow duration Q99 D99_07_10 July through October streamflow exceeded 25 percent of time cubic feet per second

Non-bioperiod25-percent flow duration Q25 D25 Streamflow exceeded 25 percent of time cubic feet per second

99-percent flow duration Q99 D99 Streamflow exceeded 99 percent of time cubic feet per second
Appendixes

45

Appendix 2. Predictor and explanatory variable names used in StreamStats (includes units, method, and source data). —Continued[Method and source of data are in Appendix 1]

Explanatory variable

Variable name 

shown in equation in 

Table 9

StreamStats/National 

Streamflow Statistic 

name

Definition Units

Drainage area DRNAREA DNRAREA Area that drains to a point on a steram square miles

Mean basin elevation ELEV ELEV Mean basin elevation feet

Wetlands WETLAND WETLAND Percentage of wetlands percent

Percent coarse stratified deposits CRSDFT CRSDFT Percentage of area of coarse stratified deposits percent

Precipitation 1971–2000, November, 

mean monthly 

PPTnov NOVAVPRE Average monthly precipitation for November for the climatological period 

1971–2000 

inches

Precipitation 1971–2000, December–

February, mean seasonal 

PPTow PRCWINTER Average of the three 30-year average monthly precipitation values (December, 

January, and February) for the climatological period 1971–2000 

inches
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Prepared by the West Trenton and Pembroke Publishing Service Centers.

For more information concerning this report, contact:

Director

U.S. Geological Survey

Connecticut Water Science Center

101 Pitkin Street

East Hartford, CT 06108

dc_ct@usgs.gov

(860) 291-6741

or visit our web site at:

http://ct.water.usgs.gov
Ahearn—Regional Regression Equations to Estimate Flow-Duration Statistics at Ungaged Stream Sites in Connecticut—SIR 2010–5052