Peak-Flow Frequency Estimates for

U.S. Geological Survey Streamflow-Gaging 

Stations in Connecticut

Prepared in cooperation with the

CONNECTICUT DEPARTMENT OF TRANSPORTATION and the

CONNECTICUT DEPARTMENT OF ENVIRONMENTAL PROTECTION

U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 03-4196
Peak-Flow Frequency Estimates for 

U.S. Geological Survey Streamflow-Gaging 

Stations in Connecticut

By Elizabeth A. Ahearn

East Hartford, Connecticut

2003

Water-Resources Investigations Report 03-4196

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

CONNECTICUT DEPARTMENT OF TRANSPORTATION and the

CONNECTICUT DEPARTMENT OF ENVIRONMENTAL PROTECTION
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

For additional information write to:

District Chief

U.S. Geological Survey

101 Pitkin Street

East Hartford, CT 06108

http://ct.water.usgs.gov

Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286
Contents iii

CONTENTS

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

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

Annual Peak-Flow Data ...................................................................................................................................... 2

Peak-Flow Frequency Analysis at Streamflow-Gaging Stations ........................................................................ 2

Assumptions of Frequency Analysis .......................................................................................................... 4

Generalized Skew Coefficient .................................................................................................................... 4

Peak-Flow Magnitude and Frequency of Floods from Log-Pearson Type III Distribution ...................... 5

Flows Altered by Flood-Control Dams and Reservoirs .................................................................... 8

Multiple-Site Station Records ........................................................................................................... 8

Accuracy of Peak-Flow Frequency Estimates ........................................................................................... 8

Mixed-Population Analysis ........................................................................................................................ 9

Maximum Known Peak Flows ............................................................................................................................ 11

Summary and Conclusions .................................................................................................................................. 12

References Cited ................................................................................................................................................. 13

Appendix 1. Description of U.S. Geological Survey Streamflow-Gaging Station Locations, Connecticut ....... 22
iv Figures

FIGURES

Figure 1. Map showing U.S. Geological Survey streamflow-gaging stations with at least 10 years of

annual peak streamflow data, Connecticut ....................................................................................... 3

Figure 2. Map showing station skews plotted at the centroid of each basin for geographic and

topographic patterns, Connecticut .................................................................................................... 6

Figure 3. Graph showing frequency curves for mixed-population analysis, Pomperaug River at Southbury, 

Connecticut ....................................................................................................................................... 10

Figure 4. Graph showing relation of maximum known peak flow to drainage area for streamflow-gaging

stations in Connecticut....................................................................................................................... 11

Figure 5. Graph showing relation of discharge for 100-year recurrence interval to drainage area for

streamflow-gaging stations in Connecticut........................................................................................ 12
Tables v

TABLES

Table 1. Peak-flow frequency estimates for streams in Connecticut for selected recurrence intervals .......... 16

Table 2. Arithmetic mean and standard error of prediction for 36 U.S. Geological Survey streamflowgaging stations used to develop a generalized station skew for Connecticut ................................... 7

Table 3. Length of record needed to be within 25 percent of the correct peak-flow frequency value

95 and 80 percent of the time ............................................................................................................ 9
vi Conversion Factors 

CONVERSION FACTORS

CONVERSION FACTORS

Multiply By To obtain

mile (mi) 1.609 kilometer

square mile (mi2) 2.590 square kilometer

cubic foot per second (ft3/s) 0.02832 cubic meter per second
Abstract 1

Peak-Flow Frequency Estimates for U.S. Geological 

Survey Streamflow-Gaging Stations in Connecticut

by Elizabeth A. Ahearn

ABSTRACT

Annual peak-flow data from 128 U.S. 

Geological Survey streamflow-gaging stations in 

Connecticut with at least 10 consecutive years of 

record were used to estimate peak-flow 

magnitudes for 1.5-, 2-, 10-, 25-, 50-, 100- and 

500-year recurrence intervals (exceedance 

probabilities of 0.67, 0.50, 0.10, 0.04, 0.02, 0.01, 

and 0.002, respectively). Peak-flow frequency 

analyses of annual peak flows through the 2001 

water year were performed using the procedures in 

the publication “Guidelines for Determining 

Flood-Flow Frequency,” commonly referred to as 

Bulletin 17B, by the Interagency Advisory 

Committee on Water Data (1982). A generalized 

skew coefficient of 0.34, with a standard error of 

prediction of 0.51, was developed to improve 

peak-flow frequency estimates in the state; this 

replaces the generalized skew coefficients for 

Connecticut shown in Bulletin 17B. 

INTRODUCTION

The magnitude and frequency of peak flows are 

needed to design hydraulic structures, delineate floodhazard zones, minimize property damage, and reduce 

the loss of life caused by floods. In an effort to provide 

updated information for regulatory, planning, and 

design activities in Connecticut, the U.S. Geological 

Survey (USGS) performed a cooperative study with the 

Connecticut Department of Transportation and the 

Connecticut Department of Environmental Protection 

to provide peak-flow frequency estimates at 

streamflow-gaging stations. 

This report presents the peak-flow frequency 

estimates for 1.5-, 2-, 10-, 25-, 50-, 100-, and 500-year 

recurrence intervals for selected streamflow-gaging 

stations in Connecticut. Information about the annual 

peak-flow data and computational procedures for peakflow frequency analysis is included in the report. 

Graphs are presented that illustrate the magnitude of 

floods by drainage area. 

This report updates and supersedes previously 

published peak-flow frequency estimates for 

streamflow-gaging stations in Connecticut (Weiss, 

1983; see also the section “Floods” in the series of 

reports, Water Resources Inventory of Connecticut, 

Parts 1 to 10) by incorporating 20 additional years of 

streamflow data and updated methods of peak-flow 

frequency analysis. The additional data and 

development of a generalized skew for Connecticut 

provide more accurate peak-flow frequency estimates 

for streamflow-gaging stations than peak-flow 

frequency estimates from earlier reports.

The author gratefully acknowledges the 

following USGS personnel: Toby Feaster and Andral 

Caldwell, for their assistance in providing quality 

control and quality assurance of the annual peak-flow 

data and in the application of several computer 

programs used in a review of the peak-flow data; 

William H. Kirby, for his technical help in analyzing 

and reviewing the mixed-population data; Glenn 

Hodgkins, for his assistance in developing the 

generalized skew; and Claudia Tamayo, for her 

valuable help in reviewing peak-flow data and in 

compiling results.
2 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

ANNUAL PEAK-FLOW DATA

The USGS streamflow-gaging network provides 

valuable information on high flows and historical 

floods that is important to the understanding of 

hydrologic events. The basis for characterizing the 

frequency of floods is the annual peak-flow data. The 

annual peak flow is defined as the maximum 

instantaneous flow occurring in a water year (October 1 

to September 30). Annual peak flows range from flows 

that barely exceed the natural stream banks and have 

minimal effects to flows that inundate the floodplain 

and cause extensive damage. 

Annual peak-flow data through water year 2001 

from 128 streamflow-gaging stations in Connecticut 

with at least 10 consecutive years of flow data were 

used to characterize floods. A minimum of 10 years of 

record is the recommended criterion for developing 

peak-flow frequency estimates (Interagency Advisory 

Committee on Water Data, 1982, p. 2). Locations of the 

USGS streamflow-gaging stations are shown in figure 

1, and detailed descriptions of the stations, including 

geographic coordinates, are provided in appendix 1.

Annual peak-flow data, along with the 

corresponding flow dates, gage heights, and 

information pertaining to the basin (for example, 

urbanization or regulation) or to the cause of the annual 

peak (for example, dam failure or ice jam) are stored in 

the USGS National Water Information System (NWIS) 

database and can be accessed at 

http://waterdata.usgs.gov/nwis/peak. The NWIS 

database contains two types of peak-flow record: the 

systematic record (gaged period) where the annual 

peak is observed for each water year, and the historic 

record (ungaged period) where the annual peak for a 

flow of an unusually large magnitude is determined 

from flood marks. Prior to the establishment of a 

streamflow-gaging station, notable peak flows are 

considered to be “historic.” Typically, the magnitude of 

historic peak flows are determined by indirect 

measurements that involve determining the watersurface elevation from flood marks and computing the 

discharge using hydraulic equations. Historic peakflow magnitudes determined by indirect methods, 

though less accurate than those determined by direct 

measurement, can improve the accuracy of the peakflow frequency estimates. Peak-flow records for 

Connecticut range from a few years to more than 100 

years in length. Flow data extend back to 1901 

(Housatonic River at Gaylordsville), and historic flood 

records extend back to 1683 (Connecticut River at 

Hartford). Historical information on the floods used in 

this analysis, such as the date of occurrence and height 

of the water surface, can be obtained from USGS files 

available at the District Office in East Hartford, 

Connecticut, and in Thomson and others (1964).

A comprehensive review of the NWIS peak-flow 

database was an essential element of the study. Several 

computer programs (C.L. Sanders, Jr., U.S. Geological 

Survey, written commun., 1999) were used to perform 

the QA/QC review of the peak-flow data. The QA/QC 

review and computational steps performed by these 

computer programs are described by Feaster and 

Tasker (2002, p. 5-11). Several discrepancies between 

the values in the published record and the peak-flow 

file were discovered and revisions to the published 

record and (or) peak-flow database were made. 

PEAK-FLOW FREQUENCY ANALYSIS AT 

STREAMFLOW-GAGING STATIONS

 Peak-flow frequency analysis is a statistical 

technique used to estimate exceedance probabilities 

associated with floods. Through analysis of past floods, 

a relation between peak-flow magnitude and frequency 

can be established. The peak-flow frequency analysis 

for this study is based on guidelines published by the 

Interagency Advisory Committee on Water Data 

(1982), commonly referred to as Bulletin 17B. These 

guidelines promote a uniform technique to estimate 

peak-flow frequencies for gaged stream sites. 

The frequency of a flood (annual peak flow) is 

described in terms of exceedance probabilities or 

recurrence intervals. Exceedance probability is the 

percent chance or likelihood that a given flow will be 

exceeded in any 1-year period. Recurrence interval is 

the average time interval (in years) during which a 

given flow is expected to be exceeded one time. 

Recurrence interval is the reciprocal of exceedance 

probability multiplied by 100. Exceedance 

probabilities define the average length of time that 

separates peak flows of a given magnitude, but it is 

possible that such flows could occur during consecutive 

years. Floods with the smallest exceedance 

probabilities are potentially catastrophic. Because the 

recurrence interval is most commonly used by federal 

and state agencies, the peak-flow frequencies for this 

report are presented as recurrence intervals in table 1

(at back of report).
Peak-Flow Frequency Analysis at Streamflow-Gaging Stations 3 41

 

 

01190500

01190100

01190200

01191500

01196600

01191900

01212100

01209500

01208850

01209600

01206500

01204800

01203600

01203510

01203000

01202500

01201500

01120000

01199200

01195200 01195000

01194500

01194000

01193800

01192700

01192600

01189500

01189200

01187800

01187850

01187400

01184500

01184300

01

01211700 01209770

01208900

01208700

01208400

01208100

01203700

01203100

01202700

01199150

01196700

01193300

01193250

01193120

01192800

01192650

01190050

01188100

01184260

01127800

011

01119450

01119360

01119300

01196620

01196500

01192883

01188000

01199050

01193500

01195100

01205500

01204000

01208950

01208925

01208990

01209700

01121000

0

01184490

01184100

01189000

01199000

01200500

01192500

01187300

01208873

01208500

01208420

01208013

01206900

01206000

01205700

01205600

01201930

01201890

01201190

01198860

01198500

01196580

01195490

01191000

01190600

01190300 01190070

01190000

01189995

01189390

01188090

01187980

01187000

01186500

01186100

01186000

01184000

01183990

01127760

01127700

01122500

01122000

01121300

01119820

01119600

01119500

01119255

73 ̊ 

 ̊

42 ̊

EXPLANATION

Streamflow-gaging 

01195000

River

Housatonic

Connecticut

River

0 10 20 MILES

0 10 20 KILOMETERS

Figure 1. U.S. Geological Survey streamflow-gaging stations with at least 10 years of annual peak streamflow data, Connecticut.
4 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

Assumptions of Frequency Analysis

Several assumptions are implicit in peak-flow 

frequency analysis: (1) the annual peak flows are 

independent of each other and random, (2) the 

processes affecting the flows are stationary with 

respect to time (homogeneity), and (3) the statistical 

characteristics of the sample (annual peak-flow series) 

represent those of the population (all annual peak 

flows—past, present and future). The validity of these 

assumptions must be verified periodically to ensure 

useful and accurate statistical results. Substantial 

changes to the basin (for example, increased 

urbanization or construction of flood-control dams) 

that affect peak-flow magnitudes invalidate the 

assumptions of frequency analysis. Because past flood 

records are used to predict future peak-flow 

probabilities, changes in land cover and (or) extent of 

regulation of peak flow in a basin can invalidate the 

assumptions of stationarity in the hydrologic time 

series. The sample statistics (mean, standard deviation 

and skew) must be a reasonable representation of the 

population statistics to yield reasonable estimates of 

flood characteristics. Statistically, if the sample is 

different from the population, large errors are 

introduced in the peak-flow frequency estimates. Peakflow frequency estimates should be recalculated if any 

of these assumptions are proven to be invalid. 

To verify that the assumptions of frequency 

analysis are valid, statistical tests and graphical 

methods were performed on data from streamflowgaging stations. Time-series plots of the annual peak 

flows were visually inspected and used to make 

preliminary inferences concerning possible changes in 

the magnitude of the annual peak flow over time. In 

addition to visual inspection of time-series plots, the 

Mann-Kendall trend test was performed to test for 

changes in the distribution of annual peak flows at 

stations with at least 30 years of record. The MannKendall test is a nonparametric trend test (Helsel and 

Hirsch, 1992) and uses a rank-based procedure that 

tests for one-directional (monotonic) changes over 

time. 

Trend test results indicated annual peak-flow 

data from 11 streamflow-gaging stations are not 

homogeneous at a 0.05-significance level: 

USGS 01122000 Natchaug River at Willimantic,

USGS 01126000 Fivemile River at Killingly,

USGS 01184100 Stony Brook near West Suffield,

USGS 01184500 Scantic River at Broad Brook,

USGS 01187300 Hubbard River near West Hartland,

USGS 01189000 Pequabuck River at Forestville,

USGS 01192500 Hockanum River near East Hartford,

USGS 01194000 Eightmile River at North Plain,

USGS 01196500 Quinnipiac River at Wallingford,

USGS 01202500 Shepaug River at Woodville, and

USGS 01209500 Saugatuck River near Westport.

The trend test is sensitive to extreme climatic 

anomalies near the beginning and the end of the record. 

These 11 streamflow-gaging stations with detected 

trends were established during one of three statewide 

droughts (from July 1929 to December 1932, from 

September 1940 to April 1945, and from August 1961 

to November 1971) (Weiss, 1991). Because the 

streamflow-gaging stations started during drought 

periods, it is possible the trends were caused by the 

extreme climatic anomalies at the beginning of the 

record and may not necessarily be caused by a change 

in the magnitude of the peak flows over time. The 

drought period at the beginning of the record probably 

influences the trend results. Also, there is a 5-percent 

chance that a detected trend could have arisen by 

chance rather than from an actual change in the 

magnitude of the peak flows over time. In other words, 

trends could be detected at 6 to 7 sites by chance rather 

than from an actual change in magnitude of the peak 

flows over time. Although peak-flow frequency 

estimates were made for these (11) stations, a further 

assessment of the watershed history would be needed 

to ensure that no major changes have taken place in the 

watershed during the period of record before using the 

peak-flow frequency estimates with certainty. 

Generalized Skew Coefficient

The coefficient of skew calculated from the 

station data affects the shape of the peak-flow 

frequency curve. Steep basin and channel slopes, low 

infiltration rates, fast conveyance through systems, and 

(or) one or more extremely high peak flows (high 

outliers) can cause large positive skew values. 

Conversely, low mean-basin slopes, high infiltration 

rates, high channel losses, a substantial percentage of a 

basin controlled by lakes or swamps, and (or) one or 

more very low peak flows (low outliers) can cause 

large negative skew values. 
Peak-Flow Frequency Analysis at Streamflow-Gaging Stations 5

Three methods for developing a generalized 

skew coefficient are described in Bulletin 17B: (1) plot 

computed station skews on a map and construct skew 

isolines on the map, (2) develop a skew prediction 

equation relating basin characteristics to station skews, 

and (3) compute the arithmetic mean of station skew 

coefficients from regional gaging stations with 25 or 

more years of record. Guidelines in Bulletin 17B 

recommend using a weighted skew coefficient to 

reduce the uncertainty in peak-flow frequency 

estimates. The weighted skew coefficient is calculated 

by mathematically weighting the station skew 

coefficient and generalized skew coefficient. The 

generalized skew coefficient can provide some regional 

geographic continuity by combining the statistical 

parameter, coefficient of skew, from many nearby 

stations. 

The three methods were compared using data 

from 36 streamflow-gaging stations in Connecticut 

with 25 or more years of streamflow record to derive 

the most accurate generalized skew coefficient. For 

method 1, the computed station skews were plotted at 

the centroid of each basin and evaluated for any 

geographic or topographic trends (fig. 2). No definable 

pattern is evident. For method 2, a statistically 

significant prediction equation that relates the 

computed skew coefficients to basin characteristics 

(drainage area, stream length, or channel slope) could 

not be derived. For method 3, the arithmetic mean and 

standard error of prediction of the skews were 

computed using data from 36 stations with 25 or more 

years of streamflow record. 

The arithmetic mean (method 3) provided a skew 

coefficient estimate of 0.34. This replaces the skew 

coefficient from Bulletin 17B (plate 1), which was used 

for previous peak-flow frequency studies in 

Connecticut. The arithmetic mean of the 36 stations 

was computed after the station skew was adjusted for 

bias (Tasker and Stedinger, 1986). The generalized 

skew coefficient from Bulletin 17B was derived from 

fewer stations with less peak-flow record than were 

used for this study and was not adjusted to account for 

high outliers or historic floods. The new generalized 

skew coefficient, 0.34, has the same standard error of 

prediction (0.50) as the coefficient in Bulletin 17B for 

the same stations (table 2). 

Peak-Flow Magnitude and Frequency of Floods 

from Log-Pearson Type III Distribution

Peak-flow frequency relations are defined by 

fitting the annual peak-flow series to a theoretical 

probability distribution. Guidelines in Bulletin 17B 

recommend the Pearson Type III distribution with log 

transformation of the annual peak flows as the 

theoretical distribution for determining peak-flow 

frequency estimates for streamflow-gaging stations. 

The log-Pearson Type III distribution is described by 

the three statistical parameters: mean—grouping of 

observations about a central value; standard 

deviation—dispersion of the observations; and 

coefficient of skew— degree of asymmetry of the 

distribution. The equation for fitting a log-Pearson 

Type III distribution to the annual peak-flow series, and 

ultimately determining the peak-flow magnitudes for 

given exceedance probabilities, is

, (1)

where

The USGS computer program PEAKFQ 

(Thomas & others, written commun., 1998), which is 

based on Bulletin 17B guidelines, provides estimates of 

the magnitude of annual peak flows having recurrence 

intervals of 1.5, 2, 10, 25, 50, 100, and 500 years 

(exceedance probabilities of 0.67, 0.50, 0.10, 0.04, 

0.02, 0.01, and 0.002, respectively). PEAKFQ ranks 

the annual peak flows from highest to lowest and then 

fits them to a log-Pearson type III distribution using 

equation 2. The frequency curves generated from 

PEAKFQ for this study were reviewed to determine 

how well the annual peak flows fit the theoretical (logPearson type III) distribution; and were adjusted for 

outliers using historic flood information when 

appropriate. The computer program and user manual 

for PEAKFQ are available at http://water.usgs.gov/

software/peakfq.html (accessed on August 21, 2003).

Q = the flow for a given recurrence interval, in 

cubic feet per second;

 = the mean of the logarithms of annual peak 

flows at the streamflow-gaging station;

K = a factor dependent on the skew coefficient 

and exceedance probability; and

S = the standard deviation about the mean of 

the logarithms of annual peak flows.

LogQ X KS = +

X
6 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

MASSACHUSETTS

CONNECTICUT MASS.

RI.

CONNECTICUT

RHODE ISLAND

CONNECTICUT

NEW YORK

NEW YORK

MASSACHUSETTS

0.42

0.65

0.76

0.80

0.52

 0.04

0.41

0.21

0.16

0.53

0.31

0.14

0.36

0.30

0.57

0.10

0.22

0.72

0.61

 0.34 0.60

0.57

0.80

0.05

1.59 0.29

 0.33

 0.12

 0.19

0.82

0.36

0.82

0.29

0.01

0.31

 0.05

73 ̊ 72 ̊

41 ̊30

42 ̊30

EXPLANATION

0 - 500

500 - 1,000

1,000 - 1,500

 

Above 1,500

10 MILES 20

10 KILOMETERS 20

0

0

Housatonic River

Connecticut River

Nauagatuck River

Thames River

Quinnebaug

River

0.7

0.5

Streamflow-gaging 

station

Altitude, in feet

0.7

Generalized skew 

coefficient from

Bulletin 17B

National map

Figure 2. Station skews plotted at the centroid of each basin for geographic and topographic patterns, Connecticut.
Peak-Flow Frequency Analysis at Streamflow-Gaging Stations 7

Table 2. Arithmetic mean and standard error of prediction for 36 U.S. Geological Survey streamflow-gaging stations used to develop a generalized 

station skew for Connecticut

[USGS, U.S. Geological Survey]

USGS 

streamflowgaging station 

number

USGS streamflow-gaging 

station name

Station 

skew

Systematic 

peak

Bias 

correction1

1Bias correction=>[1+(6/systematic peaks)].

Unbiased 

skew2

2Unbiased skew=>station skew * bias correction.

Generalized 

skew 

(Bulletin 17B)

01118300 Pendleton Hill Bk nr Clarks Falls -0.049 43 1.140 -0.056 0.700

01120000 Hop R nr Columbia 0.307 52 1.115 0.342 0.678

01120500 Safford Bk nr Woodstock Valley 0.289 31 1.194 0.345 0.694

01121000 Mount Hope R nr Warrenville 0.613 61 1.098 0.673 0.686

01123000 Little R nr. Hanover 0.103 50 1.120 0.115 0.696

01126000 Fivemile R at Killingly 0.302 47 1.128 0.341 0.700

01126500 Moosup R at Moosup 0.210 52 1.115 0.234 0.700

01127500 Yantic R at Yantic 0.415 71 1.085 0.450 0.693

01184100 Stony Bk nr West Suffield 0.362 42 1.143 0.414 0.631

01184300 Gillette Bk at Somers 0.009 25 1.240 0.011 0.657

01184490 Broad Bk at Broad Brook -0.186 35 1.171 -0.218 0.650

01184500 Scantic R at Broad Brook 0.523 55 1.109 0.580 0.649

01187300 Hubbard River nr West Hartland -0.119 45 1.133 -0.135 0.599

01187800 Nepaug R nr Nepaug 0.052 26 1.231 0.064 0.620

01188000 Burlington Bk nr Burlington -0.314 70 1.086 -0.341 0.624

01189000 Pequabuck R at Forestville 0.568 60 1.100 0.625 0.639

01192500 Hockanum R nr East Hartford 0.138 75 1.080 0.149 0.654

01192883 Coginchaug River at Middlefield -0.341 40 1.150 -0.392 0.663

01193500 Salmon R nr East Hampton 0.801 73 1.082 0.867 0.675

01194000 Eightmile R at North Plain 0.245 47 1.128 0.276 0.685

01194500 East Branch Eightmile R nr North Lyme 1.588 44 1.136 1.805 0.685

01195000 Menunketesuck R nr Clinton 0.817 26 1.231 1.006 0.684

01196500 Quinnipiac R at Wallingford -0.038 71 1.085 -0.041 0.662

01196620 Mill R nr Hamden 0.601 25 1.240 0.745 0.662

01199000 Housatonic R at Falls Village 0.653 89 1.067 0.697 0.562

01199050 Salmon Ck at Lime Rock 0.724 40 1.150 0.833 0.561

01200500 Housatonic R at Gaylordsville 0.421 88 1.068 0.450 0.596

01201500 Still R nr Lanesville 0.358 53 1.113 0.399 0.622

01203000 Shepaug R nr Roxbury 0.763 54 1.111 0.848 0.623

01204000 Pomperaug R at Southbury 0.528 69 1.087 0.574 0.639

01206500 Leadmine Bk nr Thomaston 0.572 53 1.113 0.637 0.625

01208925 Mill R nr Fairfield -0.798 29 1.207 -0.963 0.678

01208950 Sasco Bk nr Southport 0.822 42 1.143 0.939 0.679

01208990 Saugatuck R nr Redding -0.332 40 1.150 -0.382 0.657

01209500 Saugatuck R nr Westport 0.160 35 1.171 0.187 0.675

01209700 Norwalk R at South Wilton 0.220 39 1.154 0.254 0.675
8 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

For this study, annual peak-flow data from 

128 streamflow-gaging stations in Connecticut were 

used to define the magnitude and frequency of floods. 

Stations used in this frequency analysis have 10 

consecutive years or more of peak-flow data and are 

not substantially altered by regulation. Peak-flow 

frequency estimates for the 1.5-, 2-, 10-, 25-, 50-, 100-, 

and 500-year recurrence intervals for the 128 gaging 

stations are listed in table 1 (at back of report). The 

peak-flow frequency estimates are based on station 

skews weighted with the new generalized skew value. 

Frequency curves were adjusted for historical flood 

information and for high outliers following Bulletin 

17B guidelines. The maximum known peak flow, date 

of the maximum known peak flow, and the period of 

record (historic and systematic record) for each 

streamflow-gaging station are included in table 1 (at 

back of report). 

Flows Altered by Flood-Control Dams and Reservoirs

The procedures described in Bulletin 17B for 

peak-flow frequency analysis do not apply to basins 

where the flood flows are substantially modified by 

flood-control dams or reservoir operations. Types of 

analyses (for example, simulation models that include 

reservoir-routing procedures) other than statistical 

methods are more appropriately used to evaluate the 

effect of detention storage on flood flows. For the 

purpose of this peak-flow frequency analysis, annual 

peak flows were considered to be affected by regulation 

if the upstream drainage area at the streamflow-gaging 

station has more than 4.5 million cubic feet of usable 

storage per square mile (Benson, 1962). Using this 

criterion, the annual peak flows at 22 streamflowgaging stations in Connecticut are affected by 

regulation (table 1). Nineteen of 22 streamflow-gaging 

stations are downstream of U.S. Army Corps of 

Engineers (USACOE) flood-control dams. Three other 

stations where the annual peak flows are substantially 

affected by flood-control regulation are: 01190800, 

Trout Brook at West Hartford; 01191000, North 

Branch Park River at Hartford; and 01198500, 

Blackberry River at Canaan. Some regulated sites have 

pre-flood control peak-flow data of sufficient length 

(10 or more years) to perform frequency analysis. 

Flood-frequency estimates were made at 12 of the 22 

regulated stations using annual peaks from the 

unregulated period of record (pre-flood control or 

natural flow conditions).

Multiple-Site Station Records

Peak-flow frequency estimates from nearby 

stations are compared, and when appropriate, records 

from nearby stations (on the same river) can be 

combined into one record to provide better estimates of 

peak flows, particularly when the period of record is 

short. Four streamflow-gaging stations used in this 

study had been moved to another location on the same 

river, resulting in two records for each river. The 

changes in drainage area for the four streamflowgaging stations ranged from 3 to 19 percent. Peak-flow 

frequency estimates were made on the individual 

records (old and new sites) on the Mattabessett River, 

Coginchaug River, Still River, and Leadmine River. 

Split-flow records were combined into one record, and 

peak-flow frequency estimates were made on each 

combined record. Peak-flow data were transferred from 

the shorter record site to the longer record site. The 

following equation in the Connecticut Department of 

Transportation drainage manual for transferring 

streamflow data was used to increase or decrease the 

annual peak flows for the change in drainage area 

(Connecticut Department of Transportation, 

Preliminary Drainage Manual (eq. 6.12), written 

commun., 2000) prior to the frequency analysis:

(2)

where

Accuracy of Peak-Flow Frequency Estimates

The accuracy of peak-flow frequency estimates 

depends on the frequency distribution selected to 

estimate peak-flow magnitudes and how well the 

population parameters (mean, standard deviation, and 

skew) are estimated from the sample data. Because the 

sample is an estimate of the underlying population, 

Q1 = flow at the ungaged point of interest, in 

cubic feet per second, 

A1 = basin area at the ungaged point of interest, 

in square miles,

Q2 = flow at the streamflow-gaging station, in 

cubic feet per second,

A2 = basin area at the streamflow-gaging 

station, in square miles. 

Q1

Q2A1

A2

------------

A1

0.894/A1

0.048 [ ] ( ) – 1

A2

0.894/A2

0.048 [ ] ( ) – 1

= × --------------------------------------------
Peak-Flow Frequency Analysis at Streamflow-Gaging Stations 9

large errors in the estimates can occur when the period 

of record is short. Generally, the longer the period of 

record (observed peak flows) at a station, the more 

reliably peak-flow frequencies can be estimated. 

The accuracy of peak-flow frequency estimates 

was studied by Benson (1960), and the results are 

shown in table 3. Benson determined the years of 

record needed for peak-flow frequency estimates from 

a sample to be comparable to peak-flow frequency 

estimates from a population. The results indicated that 

the 10-, 25-, 50-, or 100-year floods can be computed 

from 18-, 31-, 39-, or 48-year records, respectively, 

with some degree of accuracy (within 25 percent of the 

correct value 95 percent of the time). Estimates of peak 

flows determined using a shorter than recommended 

period of record (as shown in table 3) should be 

interpreted conservatively. 

Confidence limits about the annual exceedance 

probabilities can be used to evaluate the uncertainties 

inherent in the estimates. The 95-percent confidence 

limits for the peak-flow frequency estimates are 

generated as part of PEAKFQ output and are available 

at the USGS District Office in East Hartford, 

Connecticut.

Mixed-Population Analysis

Some of the largest floods in Connecticut are 

associated with tropical cyclonic storms. In the summer 

and early fall, tropical cyclones can produce extremely 

intense precipitation and substantial runoff because of 

warm temperatures and atmospheric moisture. Tropical 

cyclonic storms can be an important weather system in 

Connecticut from June to November (Weiss, 1991). 

From 1936 to 1997, about 40 tropical cyclones affected 

southern New England (Vallee and Dion, 1998). The 

most notable tropical cyclonic storms (hurricanes) 

occurred in September 1938 and August 1955, causing 

124 and 87 deaths, respectively. Information on the 

dates and locations of the tropical cyclone events for 

Connecticut was obtained from the National Weather 

Service (data accessed on the World Wide Web on 

10/18/00 at http://www.nhc.noaa.gov/pastall.shtml). 

Annual peak flows associated with different 

climatic processes or flood-producing events (such as 

hurricanes and periods of intense snowmelt) often will 

fit different frequency distributions. If the distributions 

are very different, their composite frequency 

distribution may have a sharp curvature or “dog-leg” 

that cannot be fit by a log-Pearson Type III distribution. 

In such cases, a mixed-population analysis, which takes 

into account the different frequency distributions and 

frequencies of occurrence of the different floodcausing events, may produce an estimated frequency 

curve that fits the observed peak flows better than a 

log-Pearson Type III frequency curve. 

The single-population (standard Bulletin 17B 

log-Pearson Type III) frequency curve results were 

examined for an inadequate fit that may be improved 

by a mixed-population analysis. In all cases, the logPearson Type III frequency curves from the singlepopulation analysis produced an adequate fit of the 

observed peak flows to the frequency distribution. The 

fit of the tropical cyclone peaks was consistent with the 

non-tropical cyclone peaks. Although there was no 

reason to expect that a mixed-population analysis 

would improve the results, several stations were 

selected for mixed-population analysis to quantitatively 

evaluate the potential improvement. Each selected 

station had more than 50 years of record and had one or 

more peak flows that departed substantially from the 

theoretical (log-Pearson Type III) frequency curve and 

resulted from hurricanes and tropical cyclones. 

 Annual peak flows caused by tropical cyclones 

were separated from those caused by nontropical 

cyclones. Peak-flow frequency curves were computed 

separately on the two data sets. The Bulletin 17B 

limitation to records of at least 10 annual peaks was 

relaxed in the case of the tropical cyclone data sets 

because only 5 to 9 tropical cyclone peaks were 

available at each station. Results of the separate 

analyses were combined to form the composite mixedpopulation frequency curve using the following 

formula (W.H. Kirby, USGS, written commun., 1999):

(3)

Table 3. Length of record needed to be within 25 percent of the correct 

peak-flow frequency value 95 and 80 percent of the time

[ND, not determined]

Magnitude of flood

Length of record, in years

95 percent of the time 80 percent of the time

10 years 18 8

25 years 31 12

50 years 39 15

100 years 48 ND

P x( ) = PH x( )*ph PN x + ( )*pn
10 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

where

The probabilities ph and pn were computed as the 

corresponding fractions of the number of annual peaks. 

Three sites were studied for mixed-population 

analysis: Pomperaug River at Southbury, USGS 

streamflow-gaging station 01204000; Housatonic River 

at Falls Village, USGS streamflow-gaging station 

0119000; and Quinnipiac River at Wallingford, USGS 

streamflow-gaging station 01196500. The results of the 

analysis indicate a marginal improvement of the fit of 

the frequency estimates to the observed data. The 

mixed-population curves at the Pomperaug River 

station and the Housatonic River station had slightly 

sharper curvature and slightly steeper slopes at the 

upper end than the log-Pearson Type III curves. The 

mixed-population curve at the Quinnipiac River had a 

flatter slope than the log-Pearson Type-III curve.

The case where the mixed-population analysis 

had the greatest effect is illustrated in figure 3. In this 

case, the peak of record is a hurricane (August 1955) 

that stands well above the trend of the fitted-frequency

P = the probability of the annual peak flow in 

any year exceeding a given value, x;

PH = the conditional probability of the annual 

peak flow in any year exceeding a given 

value, x, given that the annual peak results 

from a tropical cyclone;

ph = the probability that the annual peak result 

from a tropical cyclone;

PN = the conditional probability of the annual 

peak flow in any year exceeding a given 

value, x, given that the annual peak does 

not result from a tropical cyclone; and

pn = the probability that the annual peak does 

not result from a tropical cyclone.

99.5 99.0 98.0 95.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 5.0 2.0 1.0 0.5 0.2

ANNUAL EXCEEDANCE PROBABILITY, IN PERCENT

100

1,000

10,000

100,000

1,000,000

ANNUAL PEAK FLOW, IN CUBIC FEET PER SECOND 

1.00 1.01 1.11 2 5 10 20 50 100 200 500

RECURRENCE INTERVAL, IN YEARS

Tropical cyclone frequency curve

Nontropical cyclone frequency curve

Single-population analysis

Mixed-population analysis 

Nontropical cyclone peaks based on single-population analysis

Tropical cyclone peaks based on single-population analysis

Figure 3. Frequency curves for mixed-population analysis, Pomperaug River at Southbury, Connecticut (USGS station 01204000).
Maximum Known Peak Flows 11

curve and slightly above the trend of the conditional 

tropical-cyclone frequency curve. In both data sets, the 

peak of record could be considered a high outlier, and it 

could be argued that the peak of record improperly 

distorts the shape of the mixed-population curve. In 

figure 3, the single-population curve is the standard 

Bulletin 17B (log-Pearson Type-III) curve based on all 

69 peaks in the record and including a high-outlier 

adjustment. The gaged record is 69 years (1931-2001), 

and the historic record (1852-2001) is 149 years.

The single-population analysis was used to 

compute the final peak-flow frequency estimates 

because (1) only marginal improvements to the fit of 

the frequency estimates to the observed data were 

noted with mixed-population analysis, (2) the number 

of tropical cyclones was too small to reliably determine 

the conditional probability frequency curve of tropical 

cyclones, and (3) the observed tropical cyclone events 

were consistent with the single-population frequency 

curve.

MAXIMUM KNOWN PEAK FLOWS

Extreme floods, referred to in table 1 as 

“maximum known peak flow,” are plotted by drainage 

area in figures 4 and 5. Curves are drawn over the range 

of data (maximum known peak flow and 100-year peak 

flow estimates) based on visual inspection of the data. 

In figure 4, the curve defines the upper boundary of the 

peak flows in the state since about 1900 for a range of 

drainage areas. In figure 5, the curve defines the upper 

boundary of the 100-year peak-flow estimates based on 

this frequency analysis for a range of drainage areas. 

Peak flows caused by ice jams or dam failures are 

excluded from figures 4 and 5. Figure 4 serves as a

1 10 100 1,000

DRAINAGE AREA, IN SQUARE MILES

100

1,000

10,000

100,000 DISCHARGE, IN CUBIC FEET PER SECOND

Figure 4. Relation of maximum known peak flow to drainage area for streamflow-gaging stations in Connecticut. (Curve defines upper 

boundary of peak flows in the State since about 1900.)
12 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

general guide for making estimates of the potential 

flood magnitudes in Connecticut without reference to 

their frequency. Some of the most notable “maximum 

known peak flows” occurred in March 1936, 

September 1938, August 1955, October 1955, and June 

1982. These peak flows are associated with recurrence 

intervals greater than 100 years. 

SUMMARY AND CONCLUSIONS

Records of annual peak flows and annual 

exceedance probabilities are used extensively in 

hydraulics, hydrology, and in engineering studies 

related to the design and operation of hydraulic 

structures (bridges, culverts, dams, erosion-control 

structures). In response to the ever-increasing need for 

flood information for zoning, planning, and designing, 

the U.S. Geological Survey (USGS), in cooperation 

with the Connecticut Department of Transportation 

(DOT) and the Connecticut Department of 

Environmental Protection (DEP), began a study in 

2000 to estimate the frequency and magnitude of peak 

flows in Connecticut. Peak flows for recurrence 

intervals of 1.5, 2, 10, 25, 50, 100, and 500 years 

(exceedance probabilities of 0.67, 0.50, 0.10, 0.04, 

0.02, 0.01, and 0.002, respectively) were determined 

for 128 streamflow-gaging stations in Connecticut 

using the USGS computer program PEAKFQ. Peakflow frequency estimates were derived from data 

through water year 2001 by fitting the annual series of 

peak-flow data to a log-Pearson type III frequency 

distribution. Frequency estimates were adjusted for 

historical flood information and for high outliers. The 

1 10 100 1,000 10,000

DRAINAGE AREA, IN SQUARE MILES

100

1,000

10,000

100,000

1,000,000

DISCHARGE, IN CUBIC FEET PER SECOND

Figure 5. Relation of discharge for 100-year recurrence interval to drainage area for streamflow-gaging stations in Connecticut. (Curve defines the 

upper boundary of the 100-year peak-flow estimates.)
References Cited 13

frequencies of peak flows over a range of magnitudes 

were computed following the guidelines recommended 

in Bulletin 17B by the Interagency Advisory 

Committee on Water Data (1982). An average 

generalized skew coefficient of 0.34, with a standard 

error of prediction of 0.51, was computed for 

streamflow-gaging sites in Connecticut, replacing the 

skew values for Connecticut shown in Bulletin 17B that 

were used in previous peak-flow frequency studies. 

A mixed-population analysis of tropical cyclonic 

and nontropical cyclonic storms was conducted at three 

stations to quantitatively evaluate the potential 

improvement of the fit of the observed peak flows to 

the frequency distribution. The single-population 

analysis (not separated by event type) was used to 

compute the final peak-flow frequency estimates 

because only marginal improvements to the fit of the 

frequency estimates to the observed data were noted 

with mixed-population analysis, the number of tropical 

cyclones was too small to reliably determine the 

conditional probability frequency curve of tropical 

cyclones, and the observed tropical cyclone events 

were consistent with the single-population frequency 

curve.

REFERENCES CITED

Benson, M.A. 1960, Characteristics of frequency curves 

based on a theoretical 1,000-year record, in Dalrymple, 

Tate, 1960, Peak-flow frequency analyses, Manual of 

hydrology, part 3, Flood-flow techniques: U.S. 

Geological Survey Water-Supply Paper 1543-A, p. 51–

74. 

Benson, M.A., 1962, Factors influencing the occurrence of 

floods in a humid region of diverse terrain: U.S. 

Geological Survey Water-Supply Paper 1580-B, 64 p.

Feaster, T.D., and Tasker, G.D., 2002, Techniques for 

estimating the magnitude and frequency of floods in 

rural basins of South Carolina, 1999: U.S. Geological 

Survey Water-Resources Investigations Report 02-

4140, p. 5–11. 

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: New York, Elsevier, 522 p.

Interagency Advisory Committee on Water Data, 1982, 

Guidelines for determining flood flow frequency—

Bulletin 17B of the Hydrology Subcommittee: U.S. 

Geological Survey, Office of Water-Data Collection, 

183 p.

Tasker, G.D. and Stedinger, J.R., 1986, Regional skew with 

weighted LS regression: Journal of Water Resources 

Planning and Management, v. 112, no. 2, p. 225–237. 

Thomson, M.T., Gannon, W.B., Thomas, M.P., Hayes, G.S., 

and others, 1964, Historical floods in New England: 

U.S. Geological Survey Water-Supply Paper 1779-M, 

105 p. 

Vallee, D.R. and Dion, M.R., 1998, Southern New England 

tropical storms and hurricanes, a 98-year summary, 

summary 1909-1997: Taunton, Mass., National 

Weather Service.

Weiss, L.A., 1983, Evaluation and design of a streamflowdata network for Connecticut: Connecticut Water 

Resources Bulletin 36, 30 p. 

Weiss, L.A., 1991, Connecticut floods and droughts, with a 

section on “water management” by C.J. Hughes, in

Paulson, R.W., Chase, E.B., Roberts, R.S., and Moody, 

D.W. (compilers), National Water Summary 1988-89-

Hydrologic events and floods and droughts: U.S. 

Geological Survey Water-Supply Paper 2375, p. 215–

222.

Water Resource Inventory Reports:

Part 1: Randall, A.D., Thomas, M.P., Thomas, C. E., Jr., and 

Baker, J.A., 1966, Water resources inventory of 

Connecticut, part 1, Quinebaug River basin: 

Connecticut Water Resources Bulletin 8, 102 p. 

Part 2: Thomas, M.P., Bednar, G.A., Thomas, C.E., Jr., and 

Wilson, W.E., 1967, Water resources inventory of 

Connecticut, part 2, Shetucket River basin: Connecticut 

Water Resources Bulletin 11, 96 p. 

Part 3: Thomas, C.E., Jr., Cervione, M.A., Jr., and Grossman, 

I.G., 1968, Water resources inventory of Connecticut, 

part 3, lower Thames and southeastern coastal river 

basins: Connecticut Water Resources Bulletin 15,

105 p. 

Part 4: Ryder, R.B., Cervione, M.A., Jr., Thomas, C.E., Jr., 

and Thomas, M.P., 1970, Water resources inventory of 

Connecticut, part 4, southwestern coastal river basins: 

Connecticut Water Resources Bulletin 17, 54 p. 

Part 5: Wilson, W.E., Burke, E.L., and Thomas, C.E., Jr., 

1974, Water resources inventory of Connecticut, part 5, 

lower Housatonic River basin: Connecticut Water 

Resources Bulletin 19, 79 p.

Part 6: Cervione, M.A., Jr., Mazzaferro, D.L., and Melvin, 

R.L., 1972, Water resources inventory of Connecticut, 

part 6, upper Housatonic River basin: Connecticut 

Water Resources Bulletin 21, 84 p.

Part 7: Ryder, R.B., Thomas, M.P., and Weiss, L.A., 1981, 

Water resources inventory of Connecticut, part 7, upper 

Connecticut River basin: Connecticut Water Resources 

Bulletin 24, 78 p. 
14 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

Part 8: Mazzaferro, D.L., Handman, E.H., and Thomas, 

M.P., 1979, Water resources inventory of Connecticut, 

part 8, Quinnipiac River basin: Connecticut Water 

Resources Bulletin 27, 88 p. 

Part 9: Handman, E.H., Haeni, F.P., and Thomas, M.P., 1986, 

Water resources inventory of Connecticut, part 9, 

Farmington River basin: Connecticut Water Resources 

Bulletin 29, 91 p. 

Part 10: Weiss, L.A., Bingham, J.W., and Thomas, M.P., 

1982, Water resources inventory of Connecticut, part 

10, lower Connecticut River basin: Connecticut Water

Resources Bulletin 31, 85 p.
Table 1 15

Table 1. Peak-Flow Frequency Estimates for Streams in

Connecticut for Selected Recurrence Intervals
16 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut Table 1. Peak-flow frequency estimates for streams in Connecticut for selected recurrence intervals [Peak-flow frequency estimates are based on 10 or more years of unregulated flow record. Period of record includes historical information outside the period of syste

station. Period of record in italics represents the period when flows were affected by flood-control regulation. regulated, flood-control reservoir affects flow (regulated 

from the gaging station has more than 4.5 million cubic feet of usable storage per mile (Benson, 1962)); mi2, square miles; ft3/s, cubic feet per second; nr, near; rev, r

U.S. Geological Survey streamflow-gaging station Drainage area (mi2) Period of record (water years) Peak-flow frequency estimates for given recurrence 

(ft3/s) 

Number Name 1.5 years 2 years 10 years 25 years 50 years 100 year

PAWCATUCK RIVER BASIN 01118300 Pendleton Hill Brook nr Clarks Falls 4.02 1959-2001 108 132 242 303 351 402 

SOUTHEAST COASTAL BASINS 01118750 Haleys Brook nr Old Mystic 4.37 1962-1984 75 96 234 346 453 585 

01127800 Fourmile River nr E Lyme 4.30 1961-1984 80 96 194 267 334 415 

THAMES RIVER BASIN 01119255 Delphi Brook nr Staffordville 2.59 1964-1976 62 88 260 394 517 664 

01119300 Roaring Brook nr Staffordville 5.61 1960-1984 198 258 559 736 877 1,030 01119360 Conat Brook at W Willington 2.40 1964-1983 46 59 129 174 212 254 01119450 Eagleville Brook at Storrs 0.36 1953-1969 74 84 123 141 153 165 01119500 Willimantic River nr Coventry 121 1932-2001 1,680 2,160 5,170 7,520 9,730 12,400 01119600 Ash Brook nr N Coventry 2.79 1960-1970 134 151 224 261 289 317 01119820 Skungamaug River at N Coventry 24.7 1963-1975 420 556 1,400 2,050 2,640 3,330 01120000 Hop River nr Columbia 74.8 1933-1984 1,610 2,040 4,450 6,070 7,470 9,050 01120500 Safford Brook nr Woodstock Valley 4.15 1951-1981 275 338 659 860 1,030 1,210 01121000 Mount Hope River nr Warrenville 28.6 1938, 1941-2001 816 1,030 2,280 3,180 4,000 4,950 01121300 Fenton River at E Willington 11.4 1964-1976 272 349 720 933 1,100 1,280 01122000 Natchaug River at Willimantic (regulated) 170 1931-1951, 1952-2001 2,540 3,110 6,820 9,770 12,600 16,100 01122500 Shetucket River nr Willimantic (regulated) 404 1904-1906, 1920-1921, 1929- 1951, 1952-2001 6,000 6,120 12,300 16,900 21,100 26,100 01122680 Merrick Brook nr Scotland 5.21 1960-1984 211 274 639 894 1,120 1,380 01123000 Little River nr Hanover 30.0 1936, 1938, 1952-2001 698 881 1,820 2,410 2,900 3,430 01124000 Quinebaug River at Quinebaug (regulated) 155 1932-1959, 1960-2001 1,520 1,900 4,510 6,700 8,880 11,600 01124151 Quinebaug River at W. Thompson (regulated) 172 1967-2001, 1920-1940 Entire period of record regulated for flood contr01125300 English Neighborhood Brook at N Woodstock 4.66 1962-1984 130 187 547 805 1,030 1,290 01125490 Little River at Harrisville 35.8 1936, 1938, 1962-1976 548 682 1,350 1,760 2,090 2,440 01125500 Quinebaug River at Putnam (regulated) 328 1930-1959, 1960-2001 3,030 3,800 8,300 11,600 14,500 18,000 01125600 Mashamoquet Brook at Abington 11.1 1963-1976 350 434 815 1,020 1,180 1,340 01125650 Wappoquia Brook nr Pomfret 4.20 1964-1984 167 203 389 508 609 721 01125900 Cady Brook at E Putnam 8.29 1964-1984 231 309 721 979 1,190 1,420 01126000 Fivemile River at Killingly 57.8 1936, 1938-1984 542 669 1,330 1,750 2,100 2,490 01126500 Moosup River at Moosup 83.6 1933-1984 1,210 1,480 2,810 3,610 4,260 4,970 01126600 Blackwell Brook nr Brooklyn 17.0 1962-1976 384 515 1,260 1,760 2,180 2,660 
Table 1 17

01126700 Kitt Brook nr Canterbury 11.1 1964-1976 176 206 344 421 481 544 01126950 Pachaug River at Pachaug 53.0 1936, 1938, 1961-1973 502 596 1,010 1,230 1,400 1,570 01127000 Quinebaug River at Jewett City (regulated) 713 1919-1964, 1965-2001 6,270 7,640 15,600 21,300 26,400 32,300 01127100 Broad Brook nr Preston City 12.5 1961-1976 292 341 556 672 762 855 01127400 Susquetonscut Brook at Yantic 15.7 1962-1976 378 434 655 761 838 914 01127500 Yantic River at Yantic 89.3 1931-2001 2,100 2,640 5,740 7,860 9,730 11,800 01127700 Trading Cove Brook nr Thamesville 8.46 1961-1974 286 361 758 1,010 1,220 1,450 01127760 Hunts Brook at Old Norwich Rd. at Quaker Hill 11.5 1964-1976 195 244 512 686 835 1,000 

CONNECTICUT RIVER BASIN

01183990 Jawbuck Brook nr Hazardville 2.16 1967-1976 42 50 89 111 129 147 01184000 Connecticut River at Thompsonville 9,660 1929-2001 Peak-flow frequency estimates available upon req01184100 Stony Brook nr W Suffield 10.4 1955, 1960-2001 303 405 1,060 1,560 2,030 2,580 01184260 Namerick Brook nr Warehouse Point 2.70 1964-1984 176 229 505 677 819 972 01184300 Gillette Brook at Somers 3.60 1960-1984 98 126 273 367 446 533 01184490 Broad Brook at Broad Brook 15.5 1938, 1962-1976, 1982-2001 329 417 848 1,100 1,300 1,520 01184500 Scantic River at Broad Brook 98.2 1929-1984 859 1,070 2,260 3,080 3,800 4,640 01186000 W Branch Farmington River at Riverton

(regulated)

131 1955-1968, 1969-2001 1,560 2,030 5,660 9,050 12,600 17,300 

01186100 Mad River at Winsted (regulated) 18.5 1955, 1957-1961, 1962-1969 Less than 10 years of unregulated flow 01186500 Still River at Robertsville (regulated) 85.0 1936, 1938, 1949-1961, 1962-

2001

2,200 2,880 7,110 10,300 13,200 16,700 

01187000 W Branch Farmington River at Riverton 217 1930-1956 5,010 6,590 18,100 28,100 38,200 51,100 01187300 Hubbard River nr W Hartland 19.9 1938-19541, 1955, 1957-2001 971 1,270 2,820 3,750 4,510 5,320 01187400 Valley Brook nr W Hartland 7.03 1940-19541, 1955-1972 245 350 1,060 1,610 2,130 2,740 01187800 Nepaug River nr Nepaug 23.5 1922-19541, 1955, 1958-1984 637 843 1,990 2,750 3,390 4,110 01187850 Clear Brook nr Collinsville 0.59 1922-19541, 1955-1973 10 14 35 50 64 81 01187980 Farmington River at Collinsville (regulated) 360 1928, 1936, 1938, 1955, 1963-

1968, 1969-1977

Less than 10 years of unregulated flow 

01188000 Burlington Brook at Burlington 4.10 1932-2001 217 294 702 953 1,160 1,370 01188090 Farmington River at Unionville (regulated) 378 1978-2001, 1920-1940 Entire period of record regulated for flood contr01188100 Roaring Brook at Unionville 7.60 1962-1984 142 194 518 755 967 1,210 01189000 Pequabuck River at Forestville 45.8 1938, 1942-2001 1,290 1,650 3,840 5,470 6,960 8,740 01189200 Stratton Brook nr Simsbury 5.13 1964-1984 100 134 316 432 528 633 01189390 E Branch Salmon Book at Granby 39.5 1955-1956, 1964-1976 555 764 2,450 4,080 5,810 8,130 

Table 1. Peak-flow frequency estimates for streams in Connecticut for selected recurrence intervals--Continued[Peak-flow frequency estimates are based on 10 or more years of unregulated flow record. Period of record includes historical information outside the period of syste

station. Period of record in italics represents the period when flows were affected by flood-control regulation. regulated, flood-control reservoir affects flow (regulated 

from the gaging station has more than 4.5 million cubic feet of usable storage per mile (Benson, 1962)); mi2, square miles; ft3/s, cubic feet per second; nr, near; rev, r

U.S. Geological Survey

streamflow-gaging station Drainage 

area 

(mi2)

Period of record

 (water years)

Peak-flow frequency estimates for given recurrence 

(ft3/s)

Number Name 1.5

years

2 

years

10 

years

25

years

50 

years

100 

year
18 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut 01189500 Salmon Brook nr Granby2 67.4 1947-1963 1,440 1,930 5,780 9,500 13,400 18,800 

01189995 Farmington River at Tariffville (regulated) 577 1913-1939, 1971-2001 Peak-flow frequency estimates not determined at th01190000 Farmington River at Rainbow (regulated) 590 1928, 1936-1968, 1969-1986 5,540 7,120 18,100 27,300 36,500 48,000 01190050 Podunk River at Wapping 4.34 1962-1976 77 93 184 247 303 368 01190070 Connecticut River at Hartford 10,493 1905-2001 Peak-flow frequency estimates available upon req01190100 Piper Brook at Newington Junction3 14.6 1955, 1958-1984 571 745 1,630 2,160 2,590 3,050 01190200 Mill Brook at Newington3 2.65 1955, 1958-1984 159 217 489 636 745 854 01190300 Trout Brook at W Hartford (regulated) 14.6 1955, 1958-1963, 1964-1972, 1975, 1980 Less than 10 years of unregulated flow 01190500 S Branch Park River at Hartford3 39.9 1936-1972, 1974-1981 1,130 1,500 3,660 5,160 6,480 7,980 01190600 Wash Brook at Bloomfield 5.54 1955, 1959-1971 156 198 476 702 921 1,190 01191000 N Branch Park River at Hartford (regulated) 26.8 1936-1962, 1963-1996 943 1,150 2,460 3,430 4,330 5,400 01191500 Park River at Hartford3 72.5 1936-1962 1,770 2,150 4,590 6,460 8,220 10,400 01191900 Charter Brook nr Crystal Lake 8.51 1965-1984 203 275 647 869 1,050 1,230 01192500 Hockanum River nr E Hartford 73.4 1920-1921, 1929-2001 826 1,050 2,200 2,940 3,550 4,220 01192600 S Branch Salmon Brook at Buckingham 0.94 1961-1976 18 24 66 99 130 167 01192650 Roaring Brook at Hopewell 24.3 1962-1976 439 507 852 1,060 1,240 1,430 01192700 Mattabesset River at E Berlin 46.5 1962-1979, 1995-19984 1,310 1,590 2,780 3,400 3,880 4,360 01192800 Parmalee Brook nr Durham 2.79 1960-84 174 215 397 494 569 645 01192883 Coginchaug River at Middlefield 29.8 1962-1980; 1981-20015 581 747 1,550 2,010 2,370 2,750 01193120 Ponset Brook nr Higganum 5.72 1962-1977, 1982 188 246 598 855 1,090 1,360 01193250 Judd Brook nr Colchester 3.93 1962-1979 116 157 403 578 732 908 01193300 Blackledge River nr Gilead 6.75 1960-1984 161 198 366 459 532 608 01193500 Salmon River nr E Hampton 100 1929-2001 2,140 2,730 6,460 9,390 12,200 15,500 01193800 Hemlock Valley Brook at Hadlyme 2.62 1961-1976 97 123 245 314 368 424 01194000 Eightmile River at N Plain 20.1 1938-1984 679 861 1,850 2,500 3,060 3,680 01194500 E Branch Eightmile River nr N Lyme 22.3 1938-1982 536 645 1,350 1,900 2,430 3,070 

SOUTH CENTRAL COASTAL BASINS

01195000 Menunketesuck River nr Clinton 11.2 1938, 1942-1967, 1982 448 410 873 1,210 1,520 1,890 01195100 Indian River nr Clinton 5.68 1982-2001 140 176 405 578 738 930 01195200 Neck River nr Madison 6.55 1962-1982 144 183 401 548 675 818 01195490 Quinnipiac River at Southington3 17.4 1988-2001 384 461 785 949 1,070 1,200 

Table 1. Peak-flow frequency estimates for streams in Connecticut for selected recurrence intervals--Continued[Peak-flow frequency estimates are based on 10 or more years of unregulated flow record. Period of record includes historical information outside the period of syste

station. Period of record in italics represents the period when flows were affected by flood-control regulation. regulated, flood-control reservoir affects flow (regulated 

from the gaging station has more than 4.5 million cubic feet of usable storage per mile (Benson, 1962)); mi2, square miles; ft3/s, cubic feet per second; nr, near; rev, r

U.S. Geological Survey

streamflow-gaging station Drainage 

area 

(mi2

)

Period of record

 (water years)

Peak-flow frequency estimates for given recurrence 

(ft3/s)

Number Name 1.5

years

2 

years

10 

years

25

years

50 

years

100 

year
Table 1 19

01196500 Quinnipiac River at Wallingford 110 1931-2001 1,690 2,100 4,100 5,260 6,180 7,140 01196580 Muddy River nr N Haven 18.0 1963-1976 626 712 1,080 1,280 1,440 1,590 01196600 Willow Brook nr Cheshire 9.34 1960-1983 210 278 780 1,230 1,690 2,290 01196620 Mill River nr Hamden 24.5 1969-1970, 1979-2001 718 946 2,420 3,580 4,670 5,980 01196700 Wepawaug River at Milford 18.4 1962-1984 520 667 1,580 2,280 2,930 3,700 

HOUSATONIC RIVER BASIN

01198500 Blackberry River at Canaan (regulated) 45.9 1949-1961, 1962-1981 1,400 1,830 4,190 5,740 7,070 8,550 01198860 Deming Brook nr Huntsville 1.08 1971-1984 62 91 309 495 676 900 01199000 Housatonic River at Falls Village 634 1913-2001 5,250 6,260 11,600 15,100 18,100 21,400 01199050 Salmon Creek at Lime Rock 29.4 1949, 1955, 1962-2001 450 588 1,510 2,250 2,970 3,850 01199150 Furnace Brook at Cornwall Bridge 13.3 1945, 1949, 1955, 1962-1976 229 312 921 1,460 1,990 2,680 01199200 Guinea Brook at W Woods Rd at Ellsworth 3.50 1960-1981 76 96 199 262 314 369 01200500 Housatonic River at Gaylordsville 996 1901-1914, 1924, 1928-2001 8,660 10,600 21,200 28,100 33,900 40,500 01201190 W Aspetuck River at Sand Rd nr New Milford 23.8 1963-1972 276 360 842 1,180 1,480 1,820 01201500 Still River nr Lanesville 67.5 1932-1966, 1967-19847 938 1,220 2,940 4,190 5,320 6,630 01201890 Pond Brook nr Hawleyville 11.9 1963-1976 316 425 1,100 1,600 2,050 2,580 01201930 Marshepaug River nr Milton 9.24 1968-19818 182 224 392 472 530 588 01202500 Shepaug River at Woodville 38.0 1936-1988 956 1,280 3,120 4,320 5,340 6,460 01202700 Butternut Brook nr Litchfield 2.42 1960-1984 176 229 506 677 817 968 01203000 Shepaug River nr Roxbury 132 1931-1984 2,320 2,960 7,210 10,600 14,000 18,100 01203100 Jacks Brook nr Roxbury Falls 7.90 1961-1984 410 542 1,230 1,650 2,000 2,370 01203510 Pootatuck River at Sandy Hook 24.8 1966-84 1,040 1,290 2,390 2,970 3,410 3,860 01203600 Nonnewaug River at Minortown 17.7 1955, 1963-1979, 2001 1,070 1,460 3,740 5,320 6,680 8,220 01203700 Wood Creek nr Bethlehem 3.39 1962-1984 154 197 458 649 824 1,030 01204000 Pomperaug River at Southbury 75.1 1933-2001 2,210 2,810 6,490 9,190 11,600 14,600 01204800 Copper Mill Brook nr Monroe 2.45 1959-1976 122 148 257 312 352 391 01205500 Housatonic River at Stevenson 1,544 1924-1925, 1928-2001 15,400 20,000 45,200 61,700 75,700 91,200 01205600 W Branch Naugatuck River at Torrington

(regulated)

33.8 1955, 1957-1961, 1962-1996 Less than 10 years of unregulated flow 

01205700 E Branch Naugatuck River at Torrington

(regulated)

13.6 1955, 1957-1963, 1964-1996 Less than 10 years of unregulated flow 

01206000 Naugatuck River nr Thomaston 71.0 1931-1959 2,630 3,260 7,120 10,000 12,600 15,800 01206500 Leadmine Brook nr Thomaston 24.3 1931-59, 1960-19849 938 1,240 3,320 5,010 6,640 8,640 

Table 1. Peak-flow frequency estimates for streams in Connecticut for selected recurrence intervals--Continued[Peak-flow frequency estimates are based on 10 or more years of unregulated flow record. Period of record includes historical information outside the period of syste

station. Period of record in italics represents the period when flows were affected by flood-control regulation. regulated, flood-control reservoir affects flow (regulated 

from the gaging station has more than 4.5 million cubic feet of usable storage per mile (Benson, 1962)); mi2, square miles; ft3/s, cubic feet per second; nr, near; rev, r

U.S. Geological Survey

streamflow-gaging station Drainage 

area 

(mi2)

Period of record

 (water years)

Peak-flow frequency estimates for given recurrence 

(ft3/s)

Number Name 1.5

years

2 

years

10 

years

25

years

50 

years

100 

year
20 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut 01206900 Naugatuck River at Thomaston (regulated) 99.8 1955, 1960-2001 Less than 10 years of unregulated flow 

01208013 Branch Brook nr Thomaston (regulated) 20.8 1971-2001, 1920-1940 Entire period of record regulated for flood contr01208100 Hancock Brook nr Terryville 1.18 1960-1981 95 118 219 274 315 357 01208400 Hop Brook nr Middlebury 9.43 1955, 1962-1975 333 436 1,050 1,480 1,870 2,310 01208420 Hop Brook nr Naugatuck (regulated) 16.3 1955, 1970-2001 Less than 10 years of unregulated flow 01208500 Naugatuck River at Beacon Falls (regulated) 260 1920-1959, 1960-2001 6,700 8,620 20,700 29,900 38,400 48,500 01208700 Little River at Oxford 4.54 1960-1984 186 243 600 870 1,120 1,420 

SOUTHWEST COASTAL BASINS 01208850 Pequonnock River at Trumbull 15.6 1955, 1962-1984 555 732 1,720 2,380 2,950 3,580 

01208873 Rooster River at Fairfield3 10.6 1978-2001 959 1,140 1,800 2,070 2,250 2,410 01208900 Patterson Brook nr Easton 1.21 1960-1984 61 72 116 139 156 173 01208925 Mill River nr Fairfield 28.6 1973-2001 507 679 1,530 2,020 2,390 2,780 01208950 Sasco Brook nr Southport 7.38 1960-2001 205 270 728 1,120 1,500 1,970 01208990 Saugatuck River nr Redding 21.0 1962-2001 456 586 1,220 1,580 1,860 2,160 01209500 Saugatuck River nr Westport 79.8 1933-1967 1,140 1,540 3,950 5,680 7,220 8,990 01209600 Comstock Brook at N Wilton 3.50 1960-1975 116 137 251 325 388 459 01209700 Norwalk River at S Wilton 30.0 1956, 1963-2001 778 1,010 2,320 3,220 4,000 4,880 01209770 Fivemile River nr Norwalk 8.96 1956, 1962-1984 431 536 1,130 1,540 1,890 2,300 01211700 E Branch Byram River at Round Hill 1.69 1960-1975 78 100 225 306 376 452 01212100 E Branch Byram River at Riversville 11.1 1963-1984 409 567 1,450 2,020 2,490 3,000 

1Peak flow for these water years is a maximum daily average. 2Gaging station formerly published under the name West Branch Salmon Brook at Granby, Connecticut. 3Discharge is affected by urbanization or channelization. 41995–98 streamflow data collected at station 01192704, Mattabesset River at Rt. 372 at East Berlin adjusted to site (data transferred using transfer equation 6.1

Transportation, January 2000). 51962–80 streamflow data collected at station 01192890, Coginchaug River at Rockfall adjusted to site (data transferred using transfer equation 6.12, Drainage 

Transportation, January 2000). 6Peak flow affected by dam break.

71967–84 streamflow data collected at station 01201510, Still River at Lanesville adjusted to site (data transferred using transfer equation 6.12, Drainage Manu

January 2000). 8Peak-flow frequency estimates based on water years 1972–81.

91960–84 streamflow data collected at station 01206400, Leadmine Brook near Harwinton adjusted to site (data transferred using transfer equation 6.12, Drain

Transportation, January 2000).

10Peak flow augmented by release of storage from dam failure.11Peak flow affected by dam failures.

Table 1. Peak-flow frequency estimates for streams in Connecticut for selected recurrence intervals--Continued[Peak-flow frequency estimates are based on 10 or more years of unregulated flow record. Period of record includes historical information outside the period of syste

station. Period of record in italics represents the period when flows were affected by flood-control regulation. regulated, flood-control reservoir affects flow (regulated 

from the gaging station has more than 4.5 million cubic feet of usable storage per mile (Benson, 1962)); mi2, square miles; ft3/s, cubic feet per second; nr, near; rev, r

U.S. Geological Survey

streamflow-gaging station Drainage 

area 

(mi2

)

Period of record

 (water years)

Peak-flow frequency estimates for given recurrence 

(ft3/s)

Number Name 1.5

years

2 

years

10 

years

25

years

50 

years

100 

year
Appendix 1 21

Appendix 1. Description of U.S. Geological Survey StreamFlow-Gaging Station Locations, Connecticut
22 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

Appendix 1. Description of U.S. Geological Survey streamflow-gaging station locations, Connecticut

[lat, latitude; long, longitude; mi, miles; ft, feet; right and left bank are referenced facing downstream]

Station 

number Station name Station location

01118300 Pendleton Hill Brook near 

Clarks Falls, CT

Lat 41°28’30”, long 71°50’03”, New London County, Hydrologic Unit 01090005, on left bank just 

upstream from twin culverts on Grindstone Hill Road, 0.1 mi west of State Route 49 in the 

township of North Stonington, 1.6 mi northwest of Clarks Falls, and 3.4 mi northeast of village 

of North Stonington.

01118750 Haleys Brook near

Old Mystic, CT

Lat 41°23’21”, long 71°59’09”, New London County, Hydrologic Unit 01100003, at bridge on 

Colonel Ledyard Highway, 1.25 mi west of Old Mystic.

01119255 Delphi Brook near 

Staffordville, CT

Lat 42°01’23”, long 72°14’53”, Tolland County, Hydrologic Unit 01100002, at bridge on 

State Highway 19, 2.1 mi northeast of Staffordville.

01119300 Roaring Brook near 

Staffordville, CT

Lat 41°59’05”, long 72°13’45”, Tolland County, Hydrologic Unit 01100002, at abandoned bridge 

beside Bradway Road, 1.7 mi east of Staffordville.

01119360 Conat Brook at 

West Willington, CT

Lat 41°52’18”, long 72°17’30”, Tolland County, Hydrologic Unit 01100002, at bridge on Sharps 

Hill Road, 0.5 mi southeast of West Willington.

01119450 Eagleville Brook at

Storrs, CT

Lat 41°48’32”, long 72°15’42”, Tolland County, Hydrologic Unit 01100002, at South side of 

Eagleville Road, at Storrs.

01119500 Willimantic River near 

Coventry, CT

Lat 41°45’02”, long 72°15’56”, Tolland County, Hydrologic Unit 01100002, on left bank 700 ft 

upstream from bridge on State Rt. 31, 1 mi downstream from Mill Brook, 2.4 mi southeast of 

South Coventry, 2.8 mi upstream from Hop River and 6.3 mi upstream from mouth.

01119600 Ash Brook near 

North Coventry, CT

Lat 41°46’47”, long 72°23’58”, Tolland County, Hydrologic Unit 01100002, at bridge on Brewster 

Street, 2 mi southwest of North Coventry, and 2 mi northwest of Bolton.

01119820 Skungamaug River at 

North Coventry, CT

Lat 41°47’32”, long 72°21’20”, Tolland County, Hydrologic Unit 01100002, at bridge on State 

Highway 31, 1.0 mi southeast of North Coventry.

01120000 Hop River near 

Columbia, CT

Lat 41°43’39”, long 72°18’09”, Tolland County, Hydrologic Unit 01100002, 1,500 ft downstream 

from Hop River Village near Columbia.

01120500 Safford Brook near 

Woodstock Valley, CT

Lat 41°55’35”, long 72°03’35”, Windham County, Hydrologic Unit 01100002, on right bank at 

downstream side of bridge on Hopkins Road, 0.3 mi downstream from Bradford Brook, 0.3 mi 

upstream from mouth, and 2 mi southwest of West Woodstock.

01121000 Mount Hope River near 

Warrenville, CT

Lat 41°50’37”, long 72°10’08”, Windham County, Hydrologic Unit 01100002, on left bank 250 ft 

downstream from Knowlton Brook, 700 ft upstream from bridge on State Route 89, 1.8 mi south 

of Warrenville, and 3.2 mi southwest of Ashford.

01121300 Fenton River at 

East Willington, CT

Lat 41°52’20”, long 72°14’31”, Tolland County, Hydrologic Unit 01100002, at bridge on 

U.S. Highway 44, at East Willington.

01122000 Natchaug River at 

Willimantic, CT

Lat 41°43’11”, long 72°11’46”, Windham County, Hydrologic Unit 01100002, on left bank at 

upstream side of bridge on State Route 66, 1 mi northeast of Willimantic, 1.6 mi upstream from 

mouth, and 3.7 mi downstream from Mansfield Hollow Dam.

01122500 Shetucket River near 

Willimantic, CT

Lat 41°42’01”, long 72°10’57”, Windham County, Hydrologic Unit 01100002, on right bank at 

downstream side of Bingham Bridge on Plains Road, 500 ft upstream from Penn. Central Co. 

railroad bridge, 500 ft downstream from Potash Brook, 1.3 mi downstream from confluence of 

Willimantic and Natchaug Rivers, 1.5 mi southeast of Willimantic, and 17 mi upstream from 

mouth.

01122680 Merrick Brook near

Scotland, CT

Lat 41°43’43”, long 72°05’07”, Windham County, Hydrologic Unit 01100002, by Brook Road, 2.1 

mi north of Scotland.

01123000 Little River near

Hanover, CT

Lat 41°40’16”, long 72°03’11”, Windham County, Hydrologic Unit 01100002, on left bank 800 ft 

upstream from bridge on Hanover Road, 0.7 mi downstream from Peck Brook, 2.3 mi northeast 

of Hanover, and 6.5 mi upstream from mouth.

01124000 Quinebaug River at 

Quinebaug, CT

Lat 42°01’20”, long 71°57’22”, Windham County, Hydrologic Unit 01100001, on right bank at 

Quinebaug, 500 ft upstream from bridge on State Route 197, 0.2 mi downstream from 

Massachusetts-Connecticut State line, 7.8 mi upstream from French River, and at mile 46.
Appendix 1 23

01124151 Quinebaug River at 

West Thompson, CT

Lat 41°56’36”, long 71°54’03”, Windham County, Hydrologic Unit 01100001, on left bank near 

downstream end of tailrace, upstream from concrete V-notch weir at flood control dam at West 

Thompson.

01125300 English Neighborhood 

Brook at 

N. Woodstock, CT

Lat 41°59’27”, long 71°59’50”, Windham County, Hydrologic Unit 01100001, at bridge on State 

Highway 93, at North Woodstock.

01125490 Little River at 

Harrisville, CT

Lat 41°55’40”, long 71°55’49”, Windham County, Hydrologic Unit 01100001, at bridge on Tripp 

Road, 0.5 mi east of Harrisville.

01125500 Quinebaug River at 

Putnam, CT

Lat 41°54’33”, long 71°54’48”, Windham County, Hydrologic Unit 01100001, on right bank at 

Putnam, 0.15 mi downstream from Little River, 0.3 mi upstream from New York, New Haven 

and Hartford Railroad bridge, 2.8 mi downstream from French River, 3.0 mi downstream from 

West Thompson Dam, and 36 mi upstream from mouth.

01125600 Mashamoquet Brook at 

Abington, CT

Lat 41°52’27”, long 72°00’34”, Windham County, Hydrologic Unit 01100001, at bridge on Taft 

Pond Road, 1 mi north of Abington.

01125650 Wappoquia Brook near 

Pomfret, CT

Lat 41°51’57”, long 71°57’29”, Windham County, Hydrologic Unit 01100001, at bridge on Day 

Road, 2 mi south of Pomfret.

01125900 Cady Brook at 

East Putnam, CT

Lat 41°54’32”, long 71°49’09”, Windham County, Hydrologic Unit 01100001, at bridge on 

E. Putnam Rd., 1/3 mi south of E. Putnam.

01126000 Fivemile River at 

Killingly, CT

Lat 41°50’14”, long 71°53’08”, Windham County, Hydrologic Unit 01100001, at Penn. 

Central Railroad Co. bridge, 0.6 mi south of Killingly.

01126500 Moosup River at

Moosup, CT

Lat 41°42’38”, long 71°53’10”, Windham County, Hydrologic Unit 01100001, at Kaman 

Aircraft Corp. at Moosup.

01126600 Blackwell Brook near 

Brooklyn, CT

Lat 41°45’55”, long 71°57’24”, Windham County, Hydrologic Unit 01100001, on left bank 75 ft 

upstream from bridge on State Highway 169, 1.5 mi south of Brooklyn.

01126700 Kitt Brook near 

Canterbury, CT

Lat 41°40’50”, long 71°58’42”, Windham County, Hydrologic Unit 01100001, at bridge on 

Mudhole (Elmdale) Road, 1.25 mi south of Canterbury.

01126950 Pachaug River at

Pachaug, CT

Lat 41°35’05”, long 71°56’03”, New London County, Hydrologic Unit 01100001, at right bank 300 

ft from bridge on State Highway 138 at Pachaug, and 0.3 mi downstream from Pachaug Pond.

01127000 Quinebaug River at 

Jewett City, CT

Lat 41°35’52”, long 71°59’05”, New London County, Hydrologic Unit 01100001, on left bank 

behind high school on Slater Avenue at Jewett City, 570 ft downstream from outlet of canal from 

Wedgewood Mills at mouth of Pachaug River, 1,000 ft downstream from railroad bridge and at 

mile 6.1.

01127100 Broad Brook near 

Preston City, CT

Lat 41°33’14”, long 71°58’13”, New London County, Hydrologic Unit 01100001, at bridge on 

State Highway 164, 1.8 mi north of Preston City.

01127400 Susquetonscut Brook at 

Yantic, CT

Lat 41°34’16”, long 72°08’00”, New London County, Hydrologic Unit 01100003, at bridge on 

State Highway 87, 1 mi northeast of Yantic.

01127500 Yantic River at 

Yantic, CT

Lat 41°33’32”, long 72°07’18”, New London County, Hydrologic Unit 01100003, on left bank at 

Yantic, 700 ft downstream from stone-arch highway bridge, 1 mi downstream from 

Susquetonscut Brook, and 4.8 mi upstream from mouth.

01127700 Trading Cove Brook near 

Thamesville, CT

Lat 41°30’03”, long 72°06’59”, New London County, Hydrologic Unit 01100003, at culvert on 

Conn. Turnpike, 1.5 mi west of Thamesville and 3 mi southwest of Norwich.

01127760 Hunts Brook at Old 

Norwich Road at 

Quaker Hill, CT

Lat 41°24’04”, long 72°07’16”, New London County, Hydrologic Unit 01100003, at bridge on Old 

Norwich Road, at Quaker Hill.

01127800 Fourmile River near 

East Lyme, CT

Lat 41°21’26”, long 72°15’39”, New London County, Hydrologic Unit 01100003, at bridge on 

Stones Ranch Road, 2.5 mi west of East Lyme.

01183990 Jawbuck Brook near 

Hazardville, CT

Lat 42°00’25”, long 72°33’14”, Hartford County, Hydrologic Unit 01080205, at bridge on North 

Maple Street, 1.5 mi north of Hazardville.

Appendix 1. Description of U.S. Geological Survey streamflow-gaging station locations, Connecticut--Continued

[lat, latitude; long, longitude; mi, miles; ft, feet; right and left bank are referenced facing downstream]

Station 

number Station name Station location
24 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

01184000 Connecticut River at 

Thompsonville, CT

Lat 41°59’12”, long 72°36’20”, Hartford County, Hydrologic Unit 01080205, on right bank just 

upstream from Enfield Dam, 1.0 mi downstream from Thompsonville, 3.0 mi downstream from 

Massachusetts-Connecticut State line, and at mile 63.6.

01184100 Stony Brook near 

West Suffield, CT

Lat 41°57’39”, long 72°42’38”, Hartford County, Hydrologic Unit 01080205, at bridge on South 

Grand Street, 2.1 mi south of West Suffield.

01184260 Namerick Brook near 

Warehouse Point, CT

Lat 41°54’13”, long 72°36’45”, Hartford County, Hydrologic Unit 01080205, at bridge on U.S. 

Highway 5, 1.7 mi south of Warehouse Point.

01184300 Gillette Brook at 

Somers, CT

Lat 41°59’31”, long 72°26’04”, Tolland County, Hydrologic Unit 01080205, at twin culverts on 

Battle Street, 0.7 mi northeast of Somers.

01184490 Broad Brook at 

Broad Brook, CT

Lat 41°54’50”, long 72°32’58”, Hartford County, Hydrologic Unit 01080205, on left bank just 

upstream from bridge on State Route 191 (Mill Street) at Broad Brook, 0.5 mi upstream from 

mouth.

01184500 Scantic River at 

Broad Brook, CT

Lat 41°54’42”, long 72°33’46”, Hartford County, Hydrologic Unit 01080205, upstream from 

bridge on State Highway 191, at Broad Brook.

01186000 West Branch Farmington 

River at Riverton, CT

Lat 41°57’47”, long 73°01’05”, Litchfield County, Hydrologic Unit 01080207, on right bank at 

downstream side of bridge on State Route 20 at Riverton, 0.3 mi upstream from Still River, 2.0 

mi downstream from Goodwin Dam of West Branch Reservoir, and at mile 55.

01186100 Mad River at 

Winsted, CT

Lat 41°55’51”, long 73°04’53”, Litchfield County, Hydrologic Unit 01080207, on left bank by U.S. 

Highway 44 at Winsted, 0.2 mi upstream from Indian Meadow Brook, 0.2 mi downstream from 

Winsted City line, 0.5 mi downstream from Mad River Dam, and 1.8 mi upstream from mouth.

01186500 Still River at 

Robertsville, CT

Lat 41°58’01”, long 73°02’02”, Litchfield County, Hydrologic Unit 01080207, on left bank 1,500 

ft downstream from Sandy Brook, 1 mi southeast of Robertsville, 1 mi northwest of Riverton, 

and 1 mi upstream from mouth.

01187000 West Branch Farmington 

River at Riverton, CT 

Lat 41°57’14”, long 73°00’50”, Litchfield County, Hydrologic Unit 01080207, on right bank 0.4 

mi downstream from Still River, 0.6 mi south of Riverton.

01187300 Hubbard River near 

West Hartland, CT

Lat 42°02’15”, long 72°56’22”, Hartford County, Hydrologic Unit 01080207, on left bank at 

Massachusetts-Connecticut Stateline, 800 ft upstream from bridge on State Route 20, 0.5 mi 

upstream from confluence with Valley Brook, and 2.6 mi northeast of West Hartland.

01187400 Valley Brook near 

West Hartland, CT

Lat 42°02’04”, long 72°55’48”, Hartford County, Hydrologic Unit 01080207, on right bank just 

upstream from bridge on State Highway 20, 0.25 mi south of Connecticut-Connecticut State 

Line, 0.3 mi upstream from confluence with Hubbard River, and 2.25 mi northeast of West 

Hartland.

01187800 Nepaug River near 

Nepaug, CT

Lat 41°49’15”, long 72°58’13”, Litchfield County, Hydrologic Unit 01080207, beside U.S. 

Highway 202, 0.2 mi upstream from Nepaug Reservoir.

01187850 Clear Brook near 

Collinsville, CT

Lat 41°47’44”, long 72°57’05”, Hartford County, Hydrologic Unit 01080207, on right bank 200 ft 

upstream from Nepaug Reservoir beside Clear Brook Road, 1.75 mi southwest of Collinsville.

01187980 Farmington River at 

Collinsville, CT

Lat 41°47’56”, long 72°55’34”, Hartford County, Hydrologic Unit 01080207, on left bank at 

abandoned hydroelectric plant 0.8 mi south of Collinsville, and at mile 39.8.

01188000 Burlington Brook near 

Burlington, CT

Lat 41°47’10”, long 72°57’54”, Hartford County, Hydrologic Unit 01080207, on left bank 1.2 mi 

north of Burlington, 3 mi upstream from mouth, 2,000 ft east of the intersection of Covey Road 

and Hotchkiss Road, and 3 mi southwest of Collinsville.

01188090 Farmington River at 

Unionville, CT

Lat 41°45’22”, long 72°53’13”, Hartford County, Hydrologic Unit 01080207, at right bank 

upstream from steel truss highway bridge on State Route 177 at Unionville, 4.1 mi downstream 

from Burlington Brook and 3.0 mi upstream from Pequabuck River.

01188100 Roaring Brook at 

Unionville, CT

Lat 41°45’24”, long 72°52’56”, Hartford County, Hydrologic Unit 01080207, at bridge on State 

Highway 4, at Unionville.

01189000 Pequabuck River at 

Forestville, CT

Lat 41°40’24”, long 72°53’59”, Hartford County, Hydrologic Unit 01080207, on left bank 500 ft 

upstream from bridge on Central Street, 0.2 mi downstream from Copper Mine Brook, and 6.5 

mi upstream from mouth.

Appendix 1. Description of U.S. Geological Survey streamflow-gaging station locations, Connecticut--Continued

[lat, latitude; long, longitude; mi, miles; ft, feet; right and left bank are referenced facing downstream]

Station 

number Station name Station location
Appendix 1 25

01189200 Stratton Brook near 

Simsbury, CT

Lat 41°52’12”, long 72°49’27”, Hartford County, Hydrologic Unit 01080207, at bridge on Farms 

Village Road, 400 ft upstream from mouth, and 1.0 mi west of Simsbury.

01189390 East Branch Salmon 

Brook at Granby, CT

Lat 41°57’15”, long 72°46’46”, Hartford County, Hydrologic Unit 01080207, on right bank at 

downstream side of bridge on State Highway 20, 0.5 mi upstream from West Branch Salmon 

Brook, and 1.8 mi downstream from Manitook Lake.

01189500 Salmon Brook near 

Granby, CT

Lat 41°56’15”, long 72°46’34”, Hartford County, Hydrologic Unit 01080207, on left bank 50 ft 

upstream from New York, New Haven and Hartford Railroad bridge, 0.5 mi downstream from 

confluence of East Branch and West Branch.

01189995 Farmington River at 

Tariffville, CT

Lat 41°54’29”, long 72°45’40”, Hartford County, Hydrologic Unit 01080207, on right bank at 

Tariffville, behind house at 20 Tunxis Road, 0.3 mi downstream from bridge on State Route 189 

and 5.5 mi upstream from gage at Rainbow.

01190000 Farmington River at 

Rainbow, CT

Lat 41°54’40”, long 72°41’17”, Hartford County, Hydrologic Unit 01080207, on left bank at 

Rainbow, 300 ft from Stevens Paper Mill, 0.4 mi downstream from Farmington River Power Co. 

dam, 1.3 mi upstream from Poquonock, 6.4 mi downstream from Salmon Brook, and at mile 8.2.

01190050 Podunk River at 

Wapping, CT

Lat 41°49’37”, long 72°33’51”, Hartford County, Hydrologic Unit 01080205, at bridge on 

Ellington Road, 0.5 mi west of Wapping.

01190070 Connecticut River at 

Hartford, CT

Lat 41°46’08”, long 72°40’01”, Hartford County, Hydrologic Unit 01080205, at Bulkley Memorial 

Bridge on U.S. Highway 84, at Hartford, 1.5 mi downstream from Podunk River and 1.2 mi 

upstream from Hockanum River.

01190100 Piper Brook at Newington 

Junction, CT

Lat 41°42’45”, long 72°44’13”, Hartford County, Hydrologic Unit 01080205, at bridge on Willard 

Avenue at Newington Junction.

01190200 Mill Brook at 

Newington, CT

Lat 41°42’17”, long 72°43’33”, Hartford County, Hydrologic Unit 01080205, at bridge on Dowd 

Street. 0.5 mi north of Newington.

01190300 Trout Brook at 

West Hartford CT

Lat 41°46’12”, long 72°44’13”, Hartford County, Hydrologic Unit 01080205, on left bank 250 ft 

upstream from Fern Street Bridge in West Hartford.

01190500 South Branch Park River 

at Hartford, CT

Lat 41°44’03”, long 72°42’49”, Hartford County, Hydrologic Unit 01080205, on left bank 100 ft 

downstream from bridge on Newfield Avenue in Hartford, 0.7 mi downstream from confluence 

of Trout Brook and Piper Brook, and 3.3 Mi upstream from confluence with North Branch.

01190600 Wash Brook at 

Bloomfield, CT

Lat 41°49’33”, long 72°44’21”, Hartford County, Hydrologic Unit 01080205, on right bank just 

upstream from bridge on Gabb Road, 0.4 mi south of Bloomfield.

01191000 North Branch Park River 

at Hartford, CT

Lat 41°47’02”, long 72°42’32”, Hartford County, Hydrologic Unit 01080205, on right bank 60 ft 

downstream from stone-arch bridge on Albany Avenue in Hartford, and 3 mi upstream from 

confluence with South Branch.

01191500 Park River at 

Hartford, CT

Lat 41°45’36”, long 72°41’40”, Hartford County, Hydrologic Unit 01080205, at bridge at Broad 

Street at Hartford, 1 mi upstream from Connecticut River and 1 mi downstream from confluence 

of North Branch Park River and South Branch Park R.

01191900 Charter Brook near 

Crystal Lake, CT

Lat 41°54’23”, long 72°24’12”, Tolland County, Hydrologic Unit 01080205, at bridge on Browns 

Bridge Road, 2 mi southwest of Crystal Lake.

01192500 Hockanum River near

East Hartford, CT

Lat 41°46’60”, long 72°35’13”, Hartford County, Hydrologic Unit 01080205, on left bank at end of 

Preston Street, 0.2 mi upstream from bridge on Walnut Street, 1.5 mi downstream from Hop 

Brook, and 2.8 mi east of East Hartford.

01192600 South Branch Salmon 

Brook at

Buckingham, CT

Lat 41°43’04”, long 72°32’23”, Hartford County, Hydrologic Unit 01080205, on left bank 

upstream from culvert on Keeney Street at Buckingham.

01192650 Roaring Brook at 

Hopewell, CT

Lat 41°39’49”, long 72°34’54”, Hartford County, Hydrologic Unit 01080205, at bridge on Matson 

Hill Road at Hopewell.

01192700 Mattabasset River at 

East Berlin, CT

Lat 41°37’08”, long 72°42’46”, Hartford County, Hydrologic Unit 01080205, at bridge on Berlin 

Street, at East Berlin.

Appendix 1. Description of U.S. Geological Survey streamflow-gaging station locations, Connecticut--Continued

[lat, latitude; long, longitude; mi, miles; ft, feet; right and left bank are referenced facing downstream]

Station 

number Station name Station location
26 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

01192800 Parmalee Brook near 

Durham, CT

Lat 41°27’09”, long 72°42’06”, Middlesex County, Hydrologic Unit 01080205, at bridge on Saw 

Mill Road, 2 mi southwest of Durham.

01192883 Coginchaug River at 

Middlefield, CT

Lat 41°31’12”, long 72°42’22”, Middlesex County, Hydrologic Unit 01080205, on right bank just 

upstream from Cider Mill Road, 0.5 mi northeast of Middlefield, and 0.75 mi upstream from 

Wadsworth Falls.

01193120 Ponset Brook near 

Higganum, CT

Lat 41°28’45”, long 72°33’26”, Middlesex County, Hydrologic Unit 01080205, at bridge on 

Skinner Road, 1.25 mi upstream from mouth, at Higganum.

01193250 Judd Brook near 

Colchester, CT

Lat 41°35’56”, long 72°21’11”, Tolland County, Hydrologic Unit 01080205, at bridge on 

Colchester Road, 2 mi northwest of Colchester.

01193300 Blackledge River near 

Gilead, CT

Lat 41°41’47”, long 72°27’20”, Hartford County, Hydrologic Unit 01080205, at box culverts on 

State Highway 94, 3 mi west of Gilead, and 4 mi east of Buckingham.

01193500 Salmon River near 

East Hampton, CT

Lat 41°33’08”, long 72°26’56”, Middlesex County, Hydrologic Unit 01080205, on left bank at 

Route 16 Bridge, 450 ft downstream from New London-Middlesex County line, 300 ft 

downstream from Comstock Bridge, 0.7 mi downstream from Dickinson Creek, and 3.5 mi 

southeast of East Hampton.

01193800 Hemlock Valley Brook at 

Hadlyme, CT

Lat 41°25’43”, long 72°25’23”, Middlesex County, Hydrologic Unit 01080205, on right bank just 

upstream from culvert on Bone Mill Road at Hadlyme, 0.5 mi upstream from mouth.

01194000 Eightmile River at 

North Plain, CT

Lat 41°26’29”, long 72°19’58”, Middlesex County, Hydrologic Unit 01080205, at bridge on State 

Highway 82, at North Plain.

01194500 East Branch Eightmile 

River near

North Lyme, CT

Lat 41°25’39”, long 72°20’06”, New London County, Hydrologic Unit 01080205, on left bank at 

State Rt. 156 bridge, 0.7 mi south of intersection of State Rt. 82, 0.4 mi upstream from 

confluence of Eightmile River, and 5.5 mi above mouth.

01195000 Menunketesuck River near 

Clinton, CT

Lat 41°18’07”, long 72°30’55”, Middlesex County, Hydrologic Unit 01100004, on right bank at 

Fairy Dell, 100 ft downstream from Cobb's Bridge, 1.7 mi north of Clinton, 2.4 mi downstream 

from Kelseytown Reservoir, and 4.9 mi upstream from mouth.

01195100 Indian River near 

Clinton, CT

Lat 41°18’21”, long 72°31’52”, Middlesex County, Hydrologic Unit 01100004, on right 

downstream side of bridge at Hurd Bridge Road, 2.0 mi north of Clinton.

01195200 Neck River near 

Madison, CT

Lat 41°16’58”, long 72°37’08”, New Haven County, Hydrologic Unit 01100004, on left bank just 

upstream from culvert on Fort Path Road, 1.2 mi west of Madison, and 3.5 mi upstream from 

mouth.

01195490 Quinnipiac River at 

Southington, CT

Lat 41°36’13”, long 72°52’59”, Hartford County, Hydrologic Unit 01100004, on west bank, 400 ft 

downstream from bridge on Mill Street, and 500 ft upstream from bridge on Center Street in 

Southington.

01196500 Quinnipiac River at 

Wallingford, CT

Lat 41°26’60”, long 72°50’28”, New Haven County, Hydrologic Unit 01100004, on right bank on 

Wilbur Cross Highway, 0.8 mi downstream from bridge on Quinnipiac Street in Wallingford, and 

2 mi upstream from Wharton Brook.

01196580 Muddy River near

North Haven, CT

Lat 41°22’07”, long 72°50’30”, New Haven County, Hydrologic Unit 01100004, at bridge on 

Velvet Street, 2 mi southeast of North Haven.

01196600 Willow Brook near 

Cheshire, CT

Lat 41°27’35”, long 72°55’02”, New Haven County, Hydrologic Unit 01100004, at bridge on 

Mount Sanford Road, at corner of Harrison Avenue, 2.5 mi south of Cheshire.

01196620 Mill River near 

Hamden, CT

Lat 41°25’14”, long 72°54’10”, New Haven County, Hydrologic Unit 01100004, 150 ft 

downstream from bridge on Mount Carmel Avenue, 0.4 mi downstream from Eaton's Brook, and 

2.5 mi north of Hamden.

01196700 Wepawaug River at 

Milford

Lat 41°14’10”, long 73°03’28”, New Haven County, Hydrologic Unit 01100004, by bridge on 

Walnut Street, at Milford.

01198500 Blackberry River at 

Canaan, CT

Lat 42°01’26”, long 73°20’31”, Litchfield County, Hydrologic Unit 01100005, at bridge on U.S. 

Highway 44, at Canaan.

01198860 Deming Brook near 

Huntsville, CT

Lat 41°57’51”, long 73°18’05”, Litchfield County, Hydrologic Unit 01100005, 20 ft downstream 

from Under Mountain Road, 1.5 mi northeast of Huntsville.

Appendix 1. Description of U.S. Geological Survey streamflow-gaging station locations, Connecticut--Continued

[lat, latitude; long, longitude; mi, miles; ft, feet; right and left bank are referenced facing downstream]

Station 

number Station name Station location
Appendix 1 27

01199000 Housatonic River at 

Falls Village, CT

Lat 41°57’26”, long 73°22’09”, Litchfield County, Hydrologic Unit 01100005, on left bank at 

hydroelectric plant of Connecticut Light and Power Company at Falls Village, 1.4 mi 

downstream from Hollenbeck River, and at mile 75.9.

01199050 Salmon Creek at 

Lime Rock, CT

Lat 41°56’32”, long 73°23’28”, Litchfield County, Hydrologic Unit 01100005, on left bank 300 ft 

upstream from bridge on Uptown Salisbury Road, 0.6 mi north of Lime Rock, and 3.0 mi 

upstream from mouth.

01199150 Furnace Brook at 

Cornwall Bridge, CT

Lat 41°49’07”, long 73°22’08”, Litchfield County, Hydrologic Unit 01100005, at bridge on State 

Highway 4, 0.2 mi from mouth.

01199200 Guinea Brook at West 

Woods Road at 

Ellsworth, CT

Lat 41°49’28”, long 73°25’48”, Litchfield County, Hydrologic Unit 01100005, on left bank just 

upstream from culvert on West Woods Road, 0.4 mi southwest of Ellsworth, 3 mi west of 

Cornwall Bridge, and 4.5 mi southeast of Sharon.

01200500 Housatonic River at 

Gaylordsville, CT

Lat 41°39’12”, long 73°29’24”, Litchfield County, Hydrologic Unit 01100005, on left bank 0.4 mi 

downstream from hydroelectric plant of Connecticut Light and Power Co., 0.5 mi upstream from 

bridge on U.S. Route 7 at Gaylordsville, 1.5 mi downstream from Tenmile River, and at mile 

50.6.

01201190 West Aspetuck River at 

Sand Road near New 

Milford, CT

Lat 41°36’29”, long 73°25’29”, Litchfield County, Hydrologic Unit 01100005, at downstream side 

of bridge on Sand Road, off Long Mountain Road, 1000 ft west of State Highway 129, 1 mi 

northwest of Wellsville, and 2 mi north of New Milford.

01201500 Still River near 

Lanesville, CT

Lat 41°31’12”, long 73°25’06”, Litchfield County, Hydrologic Unit 01100005, on left bank on 

upstream side of Highway bridge, 0.25 mi east of U.S. Highway 7, 1.1 mi south of Lanesville, 3 

mi upstream from mouth, and 4 mi south of New Milford.

01201890 Pond Brook near 

Hawleyville, CT

Lat 41°27’22”, long 73°20’06”, Fairfield County, Hydrologic Unit 01100005, at bridge on Pond 

Brook Road, 2 mi northeast of Hawleyville.

01201930 Marshepaug River near 

Milton, CT

Lat 41°47’21”, long 73°15’32”, Litchfield County, Hydrologic Unit 01100005, on left bank 

downstream from bridge on Maple Street, 0.7mi downstream from Woodridge Lake, and 1.5 mi 

northeast of Milton.

01202500 Shepaug River at 

Woodville, CT

Lat 41°43’24”, long 73°17’38”, Litchfield County, Hydrologic Unit 01100005, at left end of dam at 

outlet of Shepaug Reservoir, 1 mi North of Woodville, and 3.5 mi upstream from Bantam River.

01202700 Butternut Brook near 

Litchfield, CT

Lat 41°44’35”, long 73°13’12”, Litchfield County, Hydrologic Unit 01100005, at bridge on Ripley 

Road, 1.5 mi west of Litchfield.

01203000 Shepaug River near 

Roxbury, CT

Lat 41°32’59”, long 73°19’47”, Litchfield County, Hydrologic Unit 01100005, at Wellers Bridge, 

1.2 mi southwest of Roxbury.

01203100 Jacks Brook near 

Roxbury Falls, CT

Lat 41°31’42”, long 73°18’31”, Litchfield County, Hydrologic Unit 01100005, at bridge on River 

Road, 1.2 mi north of Roxbury Falls.

01203510 Pootatuck River at 

Sandy Hook, CT

Lat 41°25’12”, long 73°16’56”, Fairfield County, Hydrologic Unit 01100005, at bridge on Church 

Hill Road, at Sandy Hook.

01203600 Nonewaug River at 

Minortown, CT

Lat 41°34’33”, long 73°10’43”, Litchfield County, Hydrologic Unit 01100005, on right bank 1,000 

ft downstream from bridge by State Routes. 6 and 202 at Minortown, and 2.5 mi northeast of 

Woodbury.

01203700 Wood Creek near 

Bethlehem, CT

Lat 41°37’38”, long 73°13’32”, Litchfield County, Hydrologic Unit 01100005, a bridge on State 

Highway 132, 1.25 mi southwest of Bethlehem.

01204000 Pomperaug River at 

Southbury, CT

Lat 41°28’54”, long 73°13’29”, New Haven County, Hydrologic Unit 01100005, on right bank 200 

ft upstream from bridge on Poverty Road, 800 ft downstream from Bullet Hill Brook, 0.6 mi west 

of Southbury, and 5.8 mi upstream from mouth.

01204800 Copper Mill Brook near 

Monroe, CT

Lat 41°21’46”, long 73°13’06”, Fairfield County, Hydrologic Unit 01100005, on right bank just 

upstream from Twin culverts on Hammertown Road, 700 ft upstream from mouth, 1.2 mi west of 

State Highway 111, 2.2 mi northwest of Monroe, and 2.2 mi east of Botsford.

Appendix 1. Description of U.S. Geological Survey streamflow-gaging station locations, Connecticut--Continued

[lat, latitude; long, longitude; mi, miles; ft, feet; right and left bank are referenced facing downstream]

Station 

number Station name Station location
28 Peak-Flow Frequency Estimates for U.S. Geological Survey Streamflow-Gaging Stations in Connecticut

01205500 Housatonic River at 

Stevenson, CT

Lat 41°23’02”, long 73°10’02”, New Haven County, Hydrologic Unit 01100005, on left bank, 0.2 

mi downstream from dam of Connecticut Light and Power Company at Stevenson, Fairfield 

County, 0.2 mi upstream from Eightmile Brook, and at mile 19.2.

01205600 West Branch Naugatuck 

River at Torrington, CT

Lat 41°48’04”, long 73°07’26”, Litchfield County, Hydrologic Unit 01100005, on right bank just 

downstream from bridge on Prospect Street in Torrington, 0.5 mi upstream from confluence with 

East Branch, and 3.0 mi upstream from Stillwater Pond.

01205700 East Branch Naugatuck 

River at Torrington, CT

Lat 41°48’11”, long 73°07’05”, Litchfield County, Hydrologic Unit 01100005, on upstream side of 

Wall Street bridge in Torrington, 0.3 mi downstream from Troy Brook, and 0.6 mi upstream from 

confluence with West Branch.

01206000 Naugatuck River near 

Thomaston, CT

Lat 41°42’14”, long 73°03’54”, Litchfield County, Hydrologic Unit 01100005, on right bank near 

downstream side of Twomile Bridge, 250 ft downstream from New York, New Haven, and 

Hartford Railroad bridge, 0.4 mi upstream from Leadmine Brook.

01206500 Leadmine Brook near 

Thomaston, CT

Lat 41°42’07”, long 73°03’27”, Litchfield County, Hydrologic Unit 01100005, on left bank 10 ft 

downstream from Highway bridge, 0.4 mi upstream from mouth.

01206900 Naugatuck River at 

Thomaston, CT

Lat 41°40’26”, long 73°04’12”, Litchfield County, Hydrologic Unit 01100005, on left bank at 

downstream side of bridge on U.S. Routes 6 and 202 at Thomaston, 1.5 mi downstream from 

Thomaston Reservoir, 2.5 mi upstream from Branch Brook, and at mile 29.5.

01208013 Branch Brook near 

Thomaston, CT

Lat 41°39’14”, long 73°05’42”, Litchfield County, Hydrologic Unit 01100005, on right bank 140 ft 

upstream from State Highway 6, and 1.7 mi southwest of Thomaston.

01208100 Hancock Brook near 

Terryville, CT

Lat 41°39’41”, long 73°00’11”, Litchfield County, Hydrologic Unit 01100005, at bridge on 

Waterbury Road, at corner of South Main Street, 1.1 mi south of Terryville.

01208400 Hop Brook near 

Middlebury, CT

Lat 41°31’26”, long 73°05’36”, New Haven County, Hydrologic Unit 01100005, at bridge on 

Shaddock Road, 1.5 mi east of Middlebury

01208420 Hop Brook near 

Naugatuck, CT

Lat 41°30’22”, long 73°03’32”, New Haven County, Hydrologic Unit 01100005, on left bank 30 ft 

downstream from Porter Avenue bridge at the borough of Naugatuck golf course, 400 ft east of 

State Highway 63, 0.8 mi downstream from Hop Brook Lake, 1.4 mi north of Naugatuck, and 0.6 

mi upstream from mouth.

01208500 Naugatuck River at 

Beacon Falls, CT

Lat 41°26’31”, long 73°03’47”, New Haven County, Hydrologic Unit 01100005, on left bank at 

downstream side of bridge on Bridge Street at Beacon Falls, 0.4 mi upstream from Bronson 

Brook, and at mile 10.1.

01208700 Little River at 

Oxford, CT

Lat 41°26’03”, long 73°07’02”, New Haven County, Hydrologic Unit 01100005, at bridge on 

Governor Hill Road, at Oxford.

01208850 Pequonnock River at 

Trumbull, CT

Lat 41°14’48”, long 73°11’51”, Fairfield County, Hydrologic Unit 01100006, at bridge on Daniels 

Farm Road at Trumbull.

01208873 Rooster River at 

Fairfield, CT

Lat 41°10’48”, long 73°13’09”, Fairfield County, Hydrologic Unit 01100006, on left bank, on 

floodwall, at corner of Renwick Drive and Renwick Place, Bridgeport.

01208900 Patterson Brook near 

Easton, CT

Lat 41°17’17”, long 73°17’32”, Fairfield County, Hydrologic Unit 01100006, at culvert on State 

Highway 59, 2.5 mi north of Easton.

01208925 Mill River near 

Fairfield, CT

Lat 41°09’55”, long 73°16’13”, Fairfield County, Hydrologic Unit 01100006, on right bank just 

downstream from bridge on Duck Farm Road, 1.5 mi north of Fairfield, 14.0 mi downstream 

from headwater of Mill River.

01208950 Sasco Brook near

Southport, CT

Lat 41°09’10”, long 73°18’21”, Fairfield County, Hydrologic Unit 01100006, on left downstream 

abutment of bridge on Hulls Farm Road, 1.5 mi northwest of Southport.

01208990 Saugatuck River near 

Redding, CT

Lat 41°17’40”, long 73°23’42”, Fairfield County, Hydrologic Unit 01100006, on right downstream 

side of bridge on State Route 53, 100 ft south of intersection of State Routes 53 and 107, 0.8 mi 

upstream from Saugatuck Reservoir, and 1.0 mi southwest of Redding.

01209500 Saugatuck River near 

Westport, CT

Lat 41°10’15”, long 73°21’53”, Fairfield County, Hydrologic Unit 01100006, on left bank on Old 

Ford Road (Clinton Avenue), 400 ft downstream from West Branch, 600 ft downstream from 

Aspetuck River, 2 mi north of Westport, and 5.5 mi upstream from mouth.

Appendix 1. Description of U.S. Geological Survey streamflow-gaging station locations, Connecticut--Continued

[lat, latitude; long, longitude; mi, miles; ft, feet; right and left bank are referenced facing downstream]

Station 

number Station name Station location
Appendix 1 29

01209600 Comstock Brook at

North Wilton, CT

Lat 41°12’46”, long 73°27’30”, Fairfield County, Hydrologic Unit 01100006, at bridge on Nod Hill 

Road, at North Wilton.

01209700 Norwalk River at 

South Wilton, CT

Lat 41°09’50”, long 73°25’11”, Fairfield County, Hydrologic Unit 01100006, on right bank at 

upstream side of bridge on Kent Road at South Wilton, 2.5 mi north of Norwalk.

01209770 Fivemile River near 

Norwalk, CT

Lat 41°06’02”, long 73°27’16”, Fairfield County, Hydrologic Unit 01100006, at bridge on West 

Cedar Street, 1.75 mi west of Norwalk.

01211700 East Branch Byram River 

at Round Hill, CT

Lat 41°05’57”, long 73°40’59”, Fairfield County, Hydrologic Unit 01100006, at bridge on John 

Street, 0.8 mi west of Round Hill.

01212100 East Branch Byram River 

at Riversville, CT

Lat 41°03’39”, long 73°40’29”, Fairfield County, Hydrologic Unit 01100006, at bridge on 

Riversville Road just downstream from Merritt Parkway, 0.2 mi upstream from mouth.

Appendix 1. Description of U.S. Geological Survey streamflow-gaging station locations, Connecticut--Continued

[lat, latitude; long, longitude; mi, miles; ft, feet; right and left bank are referenced facing downstream]

Station 

number Station name Station location