Introduction

S

treamflow statistics, such 

as the 1-percent flood, 

the mean flow, and the 

7-day 10-year low flow, are used by 

engineers, land managers, biologists, 

and many others to help guide 

decisions in their everyday work. For 

example, estimates of the 1-percent 

flood (the flow that is exceeded, on 

average, once in 100 years and has a 

1-percent chance of being exceeded 

in any year, sometimes referred to as 

the 100-year flood) are used to create 

flood-plain maps that form the basis 

for setting insurance rates and land-use 

zoning. This and other streamflow 

statistics also are used for 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 the setting 

of minimum required streamflows 

to protect freshwater ecosystems. 

In addition, researchers, planners, 

regulators, and others often need 

to know the physical and climatic 

characteristics of the drainage basins 

(basin characteristics) and the influence 

of human activities, such as dams and 

water withdrawals, on streamflow 

upstream from locations of interest 

to understand the mechanisms that 

control water availability and quality 

at those locations. Knowledge of the 

streamflow network and downstream 

human activities also is necessary to 

adequately determine whether an 

upstream activity, such as a water 

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS 2008–3067

2008

Figure 1. View of the StreamStats user interface for Massachusetts.
withdrawal, can be allowed without 

adversely affecting downstream 

activities.

Streamflow statistics could be 

needed at any location along a 

stream. Most often, streamflow 

statistics are needed at ungaged 

sites, where no streamflow data are 

available to compute the statistics. 

At U.S. Geological Survey (USGS) 

streamflow data-collection stations, 

which include streamgaging stations, 

partial-record stations, and 

miscellaneous-measurement stations, 

streamflow statistics can be computed 

from available data for the stations. 

Streamflow data are collected 

continuously at streamgaging stations. 

Streamflow measurements are 

collected systematically over a period 

of years at partial-record stations 

to estimate peak-flow or low-flow 

statistics. Streamflow measurements 

usually are collected at miscellaneousmeasurement stations for specific 

hydrologic studies with various 

objectives.

StreamStats is a Web-based 

Geographic Information System (GIS) 

application (fig. 1) that was created 

by the USGS, in cooperation with 

Environmental Systems Research 

Institute, Inc. (ESRI)1, to provide users 

with access to an assortment of 

analytical tools that are useful for waterresources planning and management. 

StreamStats functionality is based on 

ESRI’s ArcHydro Data Model and 

Tools, described on the Web at 

http://support.esri.com/index.

cfm?fa=downloads.dataModels.

filteredGateway&dmid=15. 

StreamStats allows users to easily 

obtain streamflow statistics, basin 

characteristics, and descriptive 

information for USGS data-collection 

stations and user-selected ungaged 

sites. It also allows users to identify 

stream reaches that are upstream 

and downstream from user-selected 

sites, and to identify and obtain 

information for locations along the 

streams where activities that may affect 

streamflow conditions are occurring. 

This functionality can be accessed 

through a map-based user interface 

that appears in the user’s Web browser 

(fig. 1), or individual functions can be 

requested remotely as Web services 

by other Web or desktop computer 

applications. StreamStats can perform 

these analyses much faster than 

historically used manual techniques.

StreamStats was designed so that 

each state would be implemented as a 

separate application, with a reliance on 

local partnerships to fund the individual 

applications, and a goal of eventual 

full national implementation. Idaho 

became the first state to implement 

StreamStats in 2003. By mid-2008, 14 

states had applications available to the 

public, and 18 other states were in 

various stages of implementation.

Functionality

A previous Fact Sheet (Ries 

and others, 2004) described the 

development, functionality, and 

limitations of the initial version of 

StreamStats. In 2008, StreamStats 

was enhanced to provide additional 

functionality and access to some 

functionality through Web services. 

Additional enhancements are planned 

for the future. Current functionality 

(2008) for all state applications includes 

the ability to:

• View a range of base-map 

features, such as roads, streams, 

political boundaries, and USGS 

topographic maps in the user 

interface map frame for navigation 

purposes;

• Re-center the map on a userspecified point;

• Zoom in or out to a different 

map scale based on input of (1) a 

user-drawn rectangle, (2) a place 

name, (3) coordinates of longitude 

and latitude, (4) a specified scale, 

(5) a National Hydrography 

Dataset (NHD) reach address, or 

(6) the full extent of the state;

• Get information on the various 

map layers shown in the interface;

• Get previously published 

streamflow statistics, basin 

characteristics, and descriptive 

information for USGS 

data-collection stations, and link 

to the USGS National Water 

Information System (NWIS) Web 

site that provides access to the 

data collected at the selected 

stations;

• Delineate the drainage-basin 

boundary for a user-selected 

ungaged site;

• Edit the basin boundary;

• Measure basin characteristics, 

such as drainage area and stream 

slope, and determine the NHD 

reach address for the selected site;

• Estimate streamflow statistics and 

provide indicators of the accuracy 

of the estimates for the site;

• Search upstream or downstream 

along the stream from a selected 

2 StreamStats: A Water Resources Web Application

Figure 2. The StreamStats link frame that 

appears on each Web page.

1

 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.
site to identify connected stream 

reaches and to locate and 

provide information on natural or 

manmade features, such as dams 

and wastewater discharges, that 

may affect the quantity or quality 

of the flow in the stream;

• Download the basin boundary for 

use in other applications, along 

with any basin characteristics and 

streamflow statistics that have 

been computed for the site; and

• Print whatever is showing in the 

user interface map frame.

In addition to the standard 

functionalities listed above, some 

state applications also have custom 

functionalities. 

Web Site

The StreamStats home page is at 

http://streamstats.usgs.gov. This page 

provides a brief description of the 

application. A gray box to the left of 

the page (fig. 2) provides links to other 

pages that document and provide 

access to the application. This gray box 

is duplicated on all other StreamStats 

Web pages for easy navigation.

The State Applications link is 

used to access the individual state 

applications. It presents a map of the 

United States with individual states 

shown in different colors depending 

on their implementation status. Users 

can access an introductory page for an 

individual state by selecting the state 

from a scroll list at the top of the page, 

or by selecting an implemented state 

shown as green or purple on the map.

Each state introductory page (1) 

identifies the area in which StreamStats 

is implemented, if the entire state is not 

available, (2) identifies the streamflow 

statistics for which there are regression 

equations available for estimating 

those statistics for ungaged sites, (3) 

identifies and provides links to the 

reports that describe the development 

of the equations, (4) provides a link to 

the state application, (5) describes any 

special functionality or limitations for 

use of the application, and (6) identifies 

the other agencies that cooperated 

with the USGS in implementing the 

application. Clicking on the Interactive 

Map link causes a new Web browser 

window to appear on the user’s 

computer desktop that contains the 

application user interface for the state.

It is highly recommended that 

users read the information on the 

StreamStats Description, User 

Instructions, and Limitations pages 

before attempting to use the 

application. Users who plan to use 

StreamStats to estimate streamflow 

statistics for ungaged sites should also 

review the reports listed on the state 

introductory pages to understand 

how the regression equations were 

developed, how they should be 

applied, and to view any special 

instructions for estimating streamflow 

statistics for ungaged sites in the state.

StreamStats User Interface

The StreamStats user interface 

(fig. 1) allows users to locate, select, 

and obtain information for gaged and 

ungaged sites of interest. The largest 

part of the interface consists of the 

Map Frame, which displays default 

and selected digital map layers. The 

Console, to the left of the map, allows 

control of the display of map layers 

and map navigation, and provides 

information about the map. The 

Toolbar above the map frame contains 

a series of buttons (tools) that are used 

to change the scale (zooming in and 

out) and the center (panning) of the 

map, and that allow users to initiate the 

various StreamStats functions.

This Fact Sheet does not fully 

describe all of the available functions. 

The Help button, located at the far 

right of the Toolbar, gives access to 

brief directions for use of each of the 

buttons. Complete documentation can 

be accessed through the links provided 

on the main and other StreamStats 

Web pages.

Streamflow Statistics for 

Data-Collection Stations

StreamStats provides convenient 

access to descriptive information, 

basin characteristics, and streamflow 

statistics for USGS data-collection 

stations. Users can zoom in to the 

location of a data-collection station 

in the user interface, click on the 

Gaging Station Information button, and 

then click on the station symbol to 

obtain a report that contains available 

information for the station. A national 

application that is accessible through 

the USGS Station Statistics Web page 

provides access to this functionality 

for data-collection stations in all states. 

Similar functionality also is available in 

the applications for each implemented 

state.

Descriptive information provided 

in the StreamStats output for the 

data-collection stations includes: the 

USGS station identification number, 

station name, station type, period of 

record, latitude, longitude, hydrologic 

unit code (HUC), major drainage 

basin name, county, U.S. Census 

Bureau Minor Civil Division (MCD) 

name, directions to locate the station, 

and remarks indicating any effects 

of human impacts or other pertinent 

information about the stations. 

Only previously published basin 

characteristics and streamflow statistics 

are available from StreamStats. Content 

varies among stations depending on 

station type and the interests of local 

cooperators who may have shared in 

the cost of computing the statistics. 

The outputs contain citations to the 

original source reports that explain 

the methods used to determine the 

information. The Definitions links from 

the StreamStats homepage define 

the Streamflow Statistics and Basin 

Characteristics provided in the output.

Streamflow Statistics for 

Ungaged Sites

StreamStats can estimate 

streamflow statistics for ungaged 

sites either on the basis of regional 

regression equations or on the basis 

of the known flows for nearby streamgaging stations. Both methods are 

discussed below.

The USGS has developed 

numerous regression equations that can 

be used to estimate various streamflow 

statistics for locations on ungaged 

streams throughout the Nation. 

Regression equations are developed 

by statistically relating the streamflow 

statistics to the basin characteristics 

for a group of data-collection stations 

within a region. Estimates of streamflow 

statistics for ungaged sites can then 

3 StreamStats: A Water Resources Web Application
be obtained by measuring the basin 

characteristics for the ungaged site 

and inserting them into the regression 

equations. (See inset above.)

StreamStats automates the process 

of measuring the basin characteristics 

and solving the applicable regression 

equations for ungaged sites. 

Depending on the size of the basin 

and the types of basin characteristics 

measured, this automated process can 

save an hour to a few days of the labor 

that would be needed to do the work 

manually. Users need to (1) locate their 

ungaged site of interest on the map, (2) 

use the Point Delineation tool to obtain 

the drainage basin for the site, and then 

(3) use the Generate Flow Statistics

tool to obtain the estimates. When the 

process is complete, a Web browser 

window will appear that reports the 

time of the analysis, the location of 

the site, the basin characteristics, the 

estimated streamflow statistics, and 

indicators of the errors associated with 

the estimates for the site.

StreamStats determines the 

drainage-basin boundary for a selected 

site by use of a Digital Elevation Model 

(DEM), which is a regularly spaced 

grid of elevation points, and a digital 

representation of the stream network. 

When a user selects 

a site along the digital 

stream network, the site 

location is transferred 

to a point in the DEM, 

and the DEM is then 

used to determine the 

drainage boundary. The 

DEM for most states 

has been enhanced by 

a process that ensures 

conformity with the 

stream network and a 

dataset of pre-existing 

drainage boundaries. 

As a result, delineations 

obtained from 

StreamStats usually are 

of greater accuracy than 

delineations obtained 

from a standard DEM.

The process for 

obtaining estimates of 

flow statistics for an 

ungaged site based on 

the known flows for 

nearby streamgaging 

stations is similar to that 

for obtaining estimates from regression 

equations. Users still need to locate 

sites of interest and delineate the 

drainage boundaries. The Generate 

Flows Based on Similar Gages tool is 

then used to obtain the flow estimates. 

When this tool is used, StreamStats 

searches upstream and downstream 

along the stream network to locate 

nearby streamgaging stations. Usually, 

streamgaging stations will be used as 

the basis for estimating streamflow 

statistics for the ungaged site if the 

drainage area for the ungaged site is 

within 0.5 and 1.5 times the drainage 

area for the streamgaging station. This 

range of drainage-area ratios can vary 

by state. The streamflow statistics and 

the drainage area for the station with 

the drainage-area ratio closest to one 

will be retrieved from a database and 

the flow per unit area will be computed 

for each statistic. These flows per unit 

area will then be multiplied by the 

drainage area for the ungaged site to 

obtain the estimates. If another station 

in the opposite direction along the 

stream network also has a drainagearea ratio within the specified limits, 

then it also will be used to estimate 

streamflow statistics for the ungaged 

site. If both an upstream and a 

downstream station were used for 

estimation, then final estimates will be 

determined by weighting the upstream 

and downstream estimates by a 

process explained in Ries and Dillow 

(2006).

Limitations for Ungaged Site 

Estimates

Estimates of streamflow statistics 

that are obtained from regression 

equations are based on the assumption 

of natural flow conditions at the 

ungaged site. If human activities 

such as dam regulation and water 

withdrawals substantially affect the 

timing, magnitude, or duration of 

flows at a selected site, the regressionequation estimates provided by 

StreamStats should be adjusted by the 

user to account for those activities.

StreamStats can be used to 

obtain regression-equation estimates 

of streamflow statistics for USGS 

data-collection stations. Users should 

understand that there are errors 

associated with estimates determined 

from available data for the stations 

as well as estimates determined from 

regression equations, and some 

disagreement between the two sets 

of estimates is expected. If the flows 

at the stations are affected by human 

activities, then users should not 

assume that the differences between 

the data-based estimates and the 

regression-equation estimates are 

equivalent to the effects of human 

activities on streamflow at the stations.

When StreamStats is used to 

obtain regression-equation estimates 

for sites with basin characteristics 

outside the ranges of those for the 

sites used to develop the regression 

equations, the estimates are extrapolated. Errors associated with these 

estimates are unknown and may be 

very large. StreamStats provides a 

warning when extrapolation occurs.

When the Generate Flows Based 

on Similar Gages tool is used to 

obtain estimates for ungaged sites, 

StreamStats users can specify whether 

to include only stations with natural 

flow conditions in the analysis or to 

also include stations that are affected 

by flow regulations. This decision must 

be made carefully. If users choose 

4 StreamStats: A Water Resources Web Application
information for other points of interest 

that are located along the network. 

An explanation of stream networks, 

focusing on the NHD, is needed 

before this functionality can be fully 

understood and utilized.

A stream network is a digital 

representation of streams and 

constructed channels for a given 

area as would be seen on an aerial 

photograph or on a topographic map. 

As with photographs and maps, stream 

networks can be shown at various 

scales, with smaller scales having less 

detail than larger scales. In a digital 

stream network, connecting lines are 

drawn through lakes, wetlands, bridges, 

culverts, and any other features where 

the stream channel is not visible from 

maps or photographs, thus eliminating 

any breaks in the network.

In a stream network, reaches are 

segments of surface water with similar 

hydrologic characteristics. Reaches 

are commonly defined by a length of 

stream between two confluences, or 

a lake or pond. Each reach is assigned 

a unique reach code, flow direction, 

reach length, reach type, and other 

characteristics that are stored as reach 

attributes. In addition, points of interest 

to allow use of regulated stations, 

then they should consider how the 

effects of regulation could change 

between the streamgaging station and 

the ungaged site. For example, if a 

regulated station is downstream from 

the ungaged site, it is possible that the 

stream is not affected by regulation 

at the ungaged site, and therefore the 

streamflow statistics estimated on the 

basis of the flow per unit area at the 

station will not be representative of 

the flow conditions at the ungaged 

site. Conversely, if the regulated station 

is upstream from the ungaged site, 

streamflow from tributaries entering 

between the station and the ungaged 

site may dampen the effects of the 

regulation at the station and cause the 

estimated streamflow statistics to be 

unrepresentative of conditions at the 

ungaged site.

Stream Network Navigation

StreamStats has the ability, known 

as “stream network navigation,” to 

analyze the stream network upstream 

and downstream from a user-selected 

point and to identify and obtain 

5 StreamStats: A Water Resources Web Application

along a network, such as the locations 

of dams, streamgaging stations, and 

effluent discharges, can be assigned 

a reach address, which consists of 

a reach code and the percentage 

distance along the reach from the 

downstream end. These points of 

interest are called point events. 

This stream network data structure 

allows users to navigate upstream 

or downstream from a user-selected 

point on a stream to locate and obtain 

information for the associated reaches 

and point events.

The NHD was developed 

cooperatively by the USGS and the 

U.S. Environmental Protection Agency 

(USEPA). A medium-resolution version 

of the NHD is available nationally at a 

scale of 1:100,000. A high-resolution 

version of the NHD is also available 

for nearly the entire Nation at a scale 

of 1:24,000. In addition, some State 

and local agencies are creating localresolution versions of the NHD at 

various scales with finer resolution 

than the high-resolution NHD. Detailed 

information on the NHD and access 

to available data can be found on the 

Web at http://nhd.usgs.gov.

The StreamStats Toolbar contains 

three tools for network navigation. 

The network may be a version of the 

NHD or any other stream network 

that is available in StreamStats. The 

Config tool is used to specify the 

network upon which tracing (searching 

upstream or downstream) will be 

done, the direction of the trace, and 

the map layers of point events that will 

participate in the trace. Tracing can 

be done either by first delineating a 

drainage basin for a selected site and 

then using the Config tool and the 

Trace from Outlet tool in sequence, 

or by first using the Config tool and 

then using the Perform and Ad Hoc 

Trace tool and selecting any point on 

a stream to begin the trace. When the 

process is complete, a window will 

appear that contains a table that lists 

the reaches and point events found 

from the trace. Items in the table 

usually will contain links from the items 

to additional information about them. 

In addition, the map frame will redraw, 

with the stream reaches identified in 

the trace highlighted.

A view of the StreamStats Map 

Frame that illustrates the results of an 

Figure 3. View of the StreamStats map frame showing an upstream network trace for a 

user-selected point on a stream in Massachusetts where the upstream stream network is 

light blue, the selected point is a dark blue circle with a red cross behind it, the drainage 

area is shaded magenta, dams are dark blue pentagons, and streamgaging stations are red 

diamonds.
upstream trace for a user-selected point 

on a stream in Massachusetts is shown 

in figure 3. A user has selected a point 

(dark blue dot with a red cross behind 

it) and used the Point Delineation

tool to delineate the drainage basin 

(shaded magenta area) for the point. 

The Config button was then used to 

select the NHD Flowline data layer and 

the upstream direction for tracing. As a 

result, StreamStats has highlighted the 

reaches (in light blue) that were found 

in the trace. These reaches include the 

reach on which the selected point is 

located and all upstream reaches. A 

streamgaging station, represented as 

a red diamond, and three dams, 

represented as dark blue pentagons, 

were also found in the trace. The report 

produced as a result of the trace (not 

shown) provides information for each 

of the reaches and the point events 

identified in the trace.

The primary benefit of the trace 

functionality is to understand how the 

flow at a particular site may be 

affected by upstream activities or 

how downstream flow may be affected 

by existing or proposed activities at the 

selected site. The USEPA and many 

State and local agencies have worked 

to associate their water-related data 

to the NHD, and many similar efforts 

are underway. Dams and USGS 

streamgaging stations have also been 

associated to the NHD. The layers that 

are associated to stream networks in 

StreamStats will vary by state and with 

time.

Web Services

Some StreamStats functionality 

is available through Web services, 

meaning that other remote computer 

applications or Web sites can initiate 

a request for a particular function 

over the Internet, and StreamStats can 

perform that function and deliver the 

result back to the remote application. 

As an example, a user may be using 

a desktop mapping application to 

identify a location for which the 

drainage-basin boundary is needed. If 

the desktop application does not have 

the ability to delineate boundaries, the 

user may request the boundary from 

the StreamStats Web service.

A Web-based form has been 

created to aid developers in building 

StreamStats Web Services (fig. 4). The 

user first selects the type of query 

from the top scroll list in the form. The 

display then changes depending on 

the requested service. In this example, 

a basin delineation is requested. The 

user selects the desired state, output 

format, and map coordinate system 

from the scroll lists, and then enters 

the coordinates (in this case, latitude 

and longitude) for the site of interest 

and submits the information. The query 

builder will then output a Web address 

that can be submitted through the 

user’s application, causing StreamStats 

to return the basin boundary in the 

format that was requested in the form.

Web services that are available 

include drainage area delineation, use 

of regression equations to estimate 

streamflow statistics, and determination of NHD reach and measure; 

and for Kentucky, estimation of daily 

precipitation time series for selected 

basins. Additional Web services are 

planned for the future. Readers who 

are interested in making use of any 

of these services or in having more 

services added should contact GS-W_

StreamStats_help@usgs.gov.

References

Ries III, K.G., Steeves, P.A., Coles, 

J.D., Rea, A.H., and 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.

Ries III, K.G., and Dillow, J.J.A., 2006, 

Magnitude and frequency of floods 

on nontidal streams in Delaware: 

U.S. Geological Survey Scientific 

Investigations Report 2006–5146, 

p. 31.

Figure 4. The Web Service Query Builder form set to provide a drainage area delineation 

in Kentucky.

USGS Fact Sheet

FS 2008-3067

Prepared by USGS West Trenton Publishing 

Service Center.

Edited by Valerie M. Gaine.

Graphics and design by Timothy W. Auer.

For additional information, contact:

Kernell G. Ries III

USGS MD-DE-DC Water Science Center

5522 Research Park Drive

Baltimore, MD 21228

kries@usgs.gov

443-498-5617

or visit the StreamStats homepage at:

http://streamstats.usgs.gov