Introduction

An important mission of the U. S. Geological Survey (USGS) is to provide information on streamflow in the Nation's rivers. Streamflow statistics are used by 

water managers, engineers, scientists, and 

others to protect people and property 

during floods and droughts, and to 

manage land, water, and biological 

resources. Common uses for streamflow 

statistics include dam, bridge, and culvert 

design; water-supply planning and management; water-use appropriations and 

permitting; wastewater and industrial discharge permitting; hydropower-facility 

design and regulation; and flood-plain 

mapping for establishing flood-insurance 

rates and land-use zones. 

In an effort to improve access to published streamflow statistics, and to make 

the process of computing streamflow statistics for ungaged stream sites easier, 

more accurate, and more consistent, the 

USGS and the Environmental Systems 

Research Institute, Inc. (ESRI) developed 

StreamStats (Ries and others, 2004). 

StreamStats is a Geographic Information 

System (GIS)-based Web application for 

serving previously published streamflow 

statistics and basin characteristics for 

USGS data-collection stations, and computing streamflow statistics and basin 

characteristics for ungaged stream sites. 

The USGS, in cooperation with the Connecticut Department of Environmental 

Protection and the Connecticut Department of Transportation, has implemented 

StreamStats for Connecticut. 

StreamStats User Interface

StreamStats consists of (1) a user interface (fig. 1) that displays maps and allows 

users to select stream locations for which 

they want streamflow statistics, (2) a database (StreamStatsDB) that contains previously published streamflow statistics and 

Prepared in cooperation with the Connecticut Department of Environmental Protection and the Connecticut Department of Transportation

Streamstats: U.S. Geological Survey Web Application for 

Streamflow Statistics for Connecticut

By Elizabeth A. Ahearn, Kernell G. Ries III, and Peter A. Steeves 

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–2006–3129

Printed on recycled paper October 2006

StreamStats is a GIS-based Web application for serving previously published streamflow 

statistics and basin characteristics for USGS data-collection stations, and for computing 

streamflow statistics and basin characteristics for ungaged stream sites. 

The StreamStats website provides 

detailed documentation, definitions 

of the streamflow statistics and 

basin characteristics, and instructions for using the application for 

Connecticut at (http://

water.usgs.gov/osw/streamstats/

connecticut.html

Figure 1. View of the StreamStats user interface zoomed into Connecticut.
descriptive information for USGS datacollection stations, (3) an automated GIS 

process that determines drainage boundaries and basin characteristics for userselected ungaged stream sites, (4) a geographic database (geodatabase) that stores 

base-map data, and (5) an automated process that uses the computed basin characteristics to solve regression equations for 

estimating selected streamflow statistics. 

The StreamStats user interface lets 

users choose locations of interest from an 

interactive map and obtain information for 

these locations. If a USGS data-collection 

station is selected, StreamStats will provide published streamflow statistics and 

basin characteristics for that station from 

the StreamStats database. If an ungaged 

stream site is selected, a GIS-based process determines the boundary of the drainage basin above the site, computes basin 

characteristics, and solves regression 

equations for estimating streamflow statistics. The computed basin characteristics, streamflow statistics, and a map of 

the basin boundary with the basin characteristics embedded as attributes are provided in the StreamStats output. Citations 

for reports containing the published statistics, basin characteristics, and regression 

equations, if applicable, also are provided 

in the output. 

The StreamStats Map Frame displays 

default and user-selected map layers. The 

Map Layers Frame, located to the right of 

the Map Frame, shows the content layers 

that can be displayed on the Map Frame. 

Content layers can be turned on or off as 

desired. A “Zoom To” pull-down menu 

above the Map Layers Frame facilitates 

zooming to a user-specified town or city, 

water feature, or a specified latitude and 

longitude. A series of buttons above the 

Map Frame allow navigation within the 

map by zooming in and out, panning, or 

returning to a previous or original map 

extent. Other buttons above the Map 

Frame provide additional options, such as 

allowing the user to delineate or clear 

drainage boundaries, print the views 

shown in the Map Frame, or retrieve information from the National Water Information System Web (NWISWeb) database 

(http://waterdata.usgs.gov), a national 

USGS database that contains information 

for all data-collection stations.

Streamflow Statistics and 

Basin Characteristics at 

USGS Data-Collection Stations

Currently (2006), StreamStats can be 

used to obtain previously published 

streamflow statistics and (or) basin characteristics for about 210 USGS data-collection stations in Connecticut. These stations may be streamflow-gaging stations, 

where streamflow data are collected continuously; partial-record stations, where 

streamflow measurements are collected 

intermittently (usually to estimate peakor low-flow statistics); or miscellaneousrecord sites, where streamflow measurements are collected for hydrologic studies 

with specific objectives. The output from 

StreamStats contains descriptive information, and published streamflow statistics 

and basin characteristics for these stations 

(fig. 2). 

Descriptive information for a data-collection station includes station identification number, station name, station type, 

period of record, latitude and longitude, 

hydrologic unit code, major drainage 

basin name, county name, directions to 

the station, and remarks 

indicating any significant effects of human 

activities on streamflow 

in the basin. 

The StreamStats 

database currently 

(2006) contains data for 

44 streamflow statistics 

and 13 basin characteristics for stations in 

Connecticut. Values for 

all streamflow statistics 

and basin characteristics 

may not be available for 

each station. Published 

streamflow statistics in 

the database are

(1) annual and monthly 

mean flow statistics; 

(2) general flow statistics (minimum, maximum, and average daily 

flow); (3) flow-duration 

statistics for the 1- to 99-

percent flow duration; 

(4) base-flow statistics;

and (5) peak-flow statistics for recurrence 

intervals of 1.5- to 500-years (annualexceedance probabilities of 0.67 to 0.002, 

respectively). Peak-flow statistics are 

available for stations with 10 of more 

years of record (as of 2001) that had no 

substantial effects of flood control or 

urbanization (Ahearn, 2004).

All USGS data-collection stations in 

the StreamStats database have information on one basin characteristic: drainage 

area. For selected stations, the database 

contains values for as many as 13 additional basin characteristics: mean basin 

elevation and the 24-hour duration rainfall 

for the 2-, 10-, 25-, 50-, and 100-year 

recurrence interval, main-channel length; 

main-channel slope; maximum basin elevation; minimum basin elevation; relief 

(difference between maximum and minimum basin elevation); mean annual precipitation (1961-1990); percent area of 

wetland; storage (percent area of lakes, 

ponds, reservoirs, and wetlands in a 

basin); total length of streams; and a basin 

shape factor (main channel length squared 

divided by the drainage area).

StreamStats Data-Collection Station Report 

USGS Station 

Number

01121000

Station Name MOUNT HOPE RIVER NEAR WARRENVILLE, CT.

 Click here to link to available data on NWIS-Web for this site.

Descriptive Information

Station Type Gaging Station, continuous record

Regulated? False

Period of Record 1938, 1941-2001

Remarks No or minimal impacts to peak flows by flood regulation.

Latitude (degrees 

NAD83)

41.84371

Longitude (degrees 

NAD83)

-72.16897

Hydrologic unit code 01100002

Local Basin -

County -

MCD -

Directions to station on left bank 250 ft downstream from Knowlton Brook, 700 ft 

upstream from bridge on State Route 89

 

Physical Characteristics

Characteristic Name Value Units Citation Number

24_Hour_2_Year_Precipitation 3.23 inches 55

24_Hour_10_Year_Precipitation 4.5 inches 55

24_Hour_25_Year_Precipitation 5.43 inches 55

24_Hour_50_Year_Precipitation 6.27 inches 55

List of basin characteristics and streamflow statistics continues

Figure 2. Streamflow statistics report for a data-collection station.
Streamflow Statistics and 

Basin Characteristics at 

Ungaged Stream Sites

Currently (2006), StreamStats can be 

used to compute only the peak-flow statistics for ungaged stream sites in Connecticut. The peak-flow equations in StreamStats were derived by regression analysis 

(fig. 3), which statistically relates the 

streamflow statistics for a group of datacollection stations to the basin characteristics (Ahearn, 2004). The computed 

streamflow statistics (2-, 10-, 25-, 50-, 

100-, and 500-year peak flows), basin 

characteristics, and prediction errors associated with the computed streamflow statistics are displayed in a pop-up Webbrowser window (fig. 4) for printing.

Determination of drainage area (fig. 5) 

is a critical step in solving the peak-flow 

equations. StreamStats uses an automated 

GIS process to determine drainage basin 

boundaries from a digital representation 

of the stream network, a geospatial data 

set of predetermined drainage boundaries, 

and a (30-meter) Digital Elevation Model 

(DEM), which is a regularly spaced grid 

of elevation values. The drainage boundary for a stream site is determined by 

using the DEM to define the boundary up 

to the point at which the new boundary 

intersects with previously determined 

boundaries (Connecticut Dept. of 

Environmental Protection, 1995). The 

new boundary and 

the predetermined 

boundaries are then 

merged to form the 

drainage boundary 

for the ungaged 

stream site. The 

basin boundaries 

determined by 

StreamStats can be 

downloaded as a 

shape file and 

imported into other 

GIS applications. 

In the future, if 

regression equations 

to estimate low-flow 

frequency or other 

commonly used 

streamflow statistics 

become available, 

the equations can be 

incorporated into 

StreamStats. Also, 

other geospatial datasets that can used to 

determine additional basin characteristics 

can be incorporated into StreamStats.

Applicability and Limitations 

of Regression Equations in 

StreamStats

The regression equations in StreamStats that are used to compute peak flow at 

ungaged stream sites are subject to the 

same applications and limitations as those 

described in the original peak-flow report 

(Ahearn, 2004). The equations should not 

be used for basins in which flood-control 

and other manmade structures may substantially reduce peak flows. This is 

because the equations do not account for 

detention storage, which is used to reduce 

peak flows, or for reservoirs, where flow 

is controlled. 

For basins with characteristics that are 

outside the range of values used to 

develop the regression equations and for 

basins that extend outside the state boundaries, peak flows are extrapolated, and 

warning messages are provided with the 

StreamStats output. The ranges of basin 

characteristics used in the original regression study are provided in the StreamStats 

output, and the user is warned if a variable 

value exceeds the range. Users are further 

cautioned that the standard errors in the 

peak-flow statistics can be larger than the 

Q2 = 0.329 (DA)0.769 (P2)2.947 (EL)0.262

Q10 = 0.510 (DA)0.776 (P10)2.485(EL)0.260

Q25 = 0.947 (DA)0.784(P25)2.064 (EL)0.243

Q50 = 1.37 (DA)0.790(P50)1.826 (EL)0.235

Q100 = 1.86 (DA)0.799 (P100)1.628 (EL)0.231

Q500 = 107 (DA)0.790 (El)0.204

where

Qx is the peak flow for selected recurrence intervals,

in cubic feet per second;

DA is the drainage area, in square miles;

Px is the x-year, 24-hour rainfall, in inches; and

EL is the mean basin elevation, in feet.

Figure 3. Regression equations for computing peak flows for the 2-, 10-, 25-, 50-, 100-, 

and 500-year recurrence intervals at ungaged stream sites in Connecticut. 

(From Ahearn, 2004, table 4.) 

Figure 4. Streamflow statistics 

Figure 4. Streamflow statistics report for an ungaged stream site.
reported errors. Also, when computing 

peak-flow statistics for basins in two 

states, users must manually weight the 

peak-flow statistics based on the percentage of drainage area in each state (Jennings and others, 1994). In addition, 

StreamStats does not allow the computation of peak-flow statistics for ungaged 

stream sites on the main stem of the Housatonic and Connecticut Rivers, where the 

geospatial data for the computing the 

basin characteristics are incomplete. 

It should not be assumed that StreamStats will provide appropriate warnings in 

all cases (flood-control structures), or that 

differences between the streamflow statistics reported for a USGS data-collection 

station and those derived by the regression 

equations fully and accurately represent 

the effects of human activity in the basin. 

References

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

estimating flood flows for the 2-, 10-, 25-, 

50-, 100-, and 500-year recurrence intervals 

in Connecticut: U.S. Geological Survey Scientific Investigations Report 2004-5160, 

62 p. 

Connecticut Department of Environmental 

Protection, 1995, Drainage basins digital 

dataset.

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

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

Geological Survey regional regression 

equations for estimating magnitude and frequency of floods for ungaged sites, 1993: 

U.S. Geological Survey Water-Resources 

Investigations Report 94-4002, 196 p. 

Ries, K.G. III, Steeves, P.A., Coles, J.D., Rea, 

A.H., Stewart, D.W., 2004, StreamStats: A 

U.S. Geological Survey web application for 

stream information: U.S. Geological Survey 

Fact Sheet 2004-3115, 4 p. 

Additional Information

For further information, please contact:

Director

USGS Connecticut Water Science Center

101 Pitkin St.

East Hartford, CT 06108

http://ct.water.usgs.gov

(860) 291-6740

or visit the USGS Office of Surface 

Water StreamStats Program homepage at:

http://water.usgs.gov/osw/programs/

streamstats.html

The use of trade, product, or firm names 

in this report is for descriptive purposes 

only and does not imply endorsement by 

the U.S. Government.

Figure 5. Delineation of a drainage basin for an ungaged stream site.