Frequently Asked Questions
Below is a list of common questions from StreamStats users. If you have any further question, please contact us.
How is the information from StreamStats used?
The primary products delivered by StreamStats are streamflow statistics and basin characteristics. Examples of streamflow statistics include the 100-year flood, the mean annual flow, and the 7-day, 10-year low flow. Examples of basin characteristics include the drainage area, stream slope, mean annual precipitation and percentage of forested area. Basin characteristics are the physical factors that control delivery of water to a point on a stream. This information is used to protect people and property from floods and droughts, and to manage land, water, and biological resources. StreamStats also provides descriptive information for data-collection stations, such as station name, identification number, latitude, longitude, and station type.
Engineers, land managers, biologists, and many others use streamflow statistics to help guide decisions in their everyday work. For example, engineers use streamflow statistics to map flood plains for cities and towns, and to design roads, bridges, and culverts. Scientists use streamflow statistics and basin characteristics to model the effects of changes in land use on streamflow; information that is valuable for planning purposes. Land and water-resource managers use streamflow statistics for design and management of water supplies, and for waste-water discharge permitting. Biologists use the information to determine flows needed to protect endangered aquatic animals and their habitat. Corporations use streamflow statistics to design and operate hydroelectric facilities and factories that use water or discharge waste into streams or water bodies.
How do I use StreamStats?
StreamStats has an easy-to-use interface that operates through your Web browser window. You do not need to download anything to use it. The User Instructions page provides detailed instructions on use of the application and example outputs, which you should read before attempting to use StreamStats. Also, the StreamStats user interface contains a Help button in the upper right corner that gives access to additional information.
How are streamflow statistics determined?
The USGS currently operates a nation-wide network of about 7,300 streamgaging stations, where streamflow is monitored continuously. Historically, the USGS also has operated more than 12,000 streamgaging stations that are not currently operated. In addition, the USGS operates thousands of partial-record stations where streamflow is measured periodically. Data collected at the continuous streamgaging stations and partial-record stations are used to calculate the streamflow statistics for the stations. These data may be accessed through the NWIS-Web database. The statistics are calculated by following standard procedures prescribed by the USGS Office of Surface Water.
A process known as regionalization is used to develop equations that can be used to estimate streamflow statistics for ungaged sites. Regionalization involves use of regression analysis to relate streamflow statistics computed for a group of selected streamgaging stations (usually within a State) and basin characteristics measured for the stations. Basin characteristics measured for ungaged sites can be entered into the resulting equations to obtain estimates of the streamflow statistics.
Citations for reports that contain regression equations for each state are provided in a Web page that you will view when you select a state from the menu on the StreamStats State Applications page. The state pages also contain a link to the application for the state. You should read the cited reports to understand how StreamStats provides estimates of flows for data-collection stations and ungaged sites in the state.
How does StreamStats work?
StreamStats was developed through a cooperative effort of the USGS and ESRI, Inc.sup>1 It is an integrated GIS application that is based on ArcGIS Server technology and the ArcHydro Tools. It incorporates a map-based user interface for site selection; a Microsoft Access database that contains information for data-collection stations; a GIS program that delineates drainage-basin boundaries and measures physical and climatic characteristics of the drainage basins; and a GIS database that contains land elevation models, historic weather data, and other data needed for measuring drainage-basin characteristics and for locating sites of interest in the user interface. After StreamStats measures the drainage-basin characteristics, the values are input to a separate program named the USGS National Streamflow Statistics (NSS) program, which is a Microsoft Windows program that contains all of the USGS-developed equations for estimating flood-frequency statistics in the Nation. NSS has been modified for StreamStats so that it can also contain equations for estimating other types of streamflow statistics. All of the equations in NSS are documented through links to each individual State from the NSS Web site. Output from NSS and from the Access database is presented to StreamStats users in a pop-up window on their computer desktop.
What streamflow statistics and basin characteristics does StreamStats provide?
The information provided varies by State, as programming for each State is separate in StreamStats. This allows the application to be customized for the needs of individual States. All streamflow statistics and basin characteristics provided for USGS data-collection stations were published previously in reports or on the Web, and a reference is provided for each piece of information. The database contains nearly 500 different streamflow statistics, but only a small number of them will commonly be available for individual stations. Go to the Definitions page to view a table showing the types of streamflow statistics that may be available and their definitions. The basin characteristics that are provided for ungaged sites will include all characteristics that are used in the regression equations that are applicable to the location and may include some additional basin charactertics.
What if StreamStats is not operational for my State?
The State Application link provides a map and explanation indicating implementation progress. If your State is not highlighted on the map and you are interested in making StreamStats operational there, contact the USGS Water Science Center Director for your State.
In a series of estimated flow statistics for an ungaged site, such as peak-flows at various recurrence intervals or flow-duration statistics, why do I sometimes get estimates for lower flows that are higher than the estimates for higher flows?
The regression equations that are used to estimate flow statistics for ungaged sites were developed using computed streamflow statistics and measured basin characteristics for a selected group of streamgaging stations. The regression equations have errors associated with them that can result in reversals of magnitude in a series of flow estimates. These errors occur because the stations that are used in the regression analysis are only a sample of the streams within the region, and the sample does not capture all of the variability in the streamflow statistics and basin characteristics that would be obtained if all streams within the region were gaged. In addition, flow statistics and basin characteristics can’t be measured with 100 percent accuracy, and it is not possible to include in the regression equations all possible basin characteristics or other factors that cause flows to vary from site to site within the region. StreamStats provides one or more indicators of the accuracy of the estimates produced from regression equations. Often, differences in the magnitudes of flow estimates within a series may be small (for example, the difference between the 85- and 90-percent flow), and the errors associated with the estimates may be relatively large. As a result, it is possible that an equation for the 90-percent flow will give an estimate that is larger than the estimate from an equation for the 85-percent flow, even though the 85-percent flow is a larger flow than the 90-percent flow. Usually in these cases, if prediction intervals are available for the estimates, the prediction intervals for the estimates will overlap each other.
