StreamStats is an integrated GIS application developed through a cooperative effort of the USGS and ESRI, Inc1. StreamStats makes the process of computing streamflow statistics for ungaged sites much faster, more accurate, and more consistent than previously used manual methods. It also makes streamflow statistics for gaged sites available without the need to locate, obtain, and read the publications in which they were originally provided. Examples of streamflow statistics that can be provided by StreamStats 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.
StreamStats uses ArcIMS, ArcSDE, ArcGIS, and 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 basins and measures basin characteristics; and a GIS database that contains land elevation models, historic weather data, and other data needed for delineations, for measuring drainage-basin characteristics, and for locating sites of interest in the user interface.
The user interface can be used to zoom in by various methods to select locations where information is desired. When a USGS data-collection station is selected, information for the station appears in a pop-up Web browser window. When an ungaged site is selected, StreamStats computes the drainage-basin boundary for the site and presents it to the user in the map frame. The user can then check the validity of the boundary and use the EditBasin tool to make any necessary corrections. After the user indicates that the boundary is correct, StreamStats measures the drainage-basin characteristics for the site. The values are then input to a separate program named the USGS National Flood Frequency Program (NFF), which is a Microsoft Windows program that contains all of the USGS-developed equations for estimating flood-frequency statistics in the nation. NFF has been modified for StreamStats to contain equations for estimating other types of streamflow statistics. NFF estimates the streamflow statistics for the ungaged site and then StreamStats presents the statistics and the basin characteristics for the site in a pop-up Web-browser window. All of the equations in NFF are documented through links to each individual state from the NFF Web site.
The equations used to estimate streamflow statistics for ungaged sites were developed through a process known as regionalization. This process involves use of regression analysis to relate streamflow statistics computed for a group of selected streamgaging stations (usually within a state) to 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. Users should note that estimates provided assume natural flow conditions at the site. Learn about additional limitations of the equations and StreamStats in the Limitations section.
Each state is implemented in StreamStats as a separate application that can be accessed from the State Applications page. For states that have not yet been implemented, information for USGS data-collection stations can be accessed through the USGS Station Statistics page.
1The use of trade or product names is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.