Application Description
StreamStats is a Web-based Geographic Information Systems (GIS) application for use in water resources planning and mangement, and in engineering design, that was 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 functionality is based primarily on the ArcHydro Data Model and Tools and is implemented using ArcGIS Server technology. 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 digital representations of the land surface (digital elevation models and derivative products), historic climate data, and other data needed for locating sites of interest in the user interface, delineating drainage basin, measuring drainage-basin characteristics, and searching upstream and downstream along streams from selected sites to identify activities that may affect streamflow or water quality at the sites.
StreamStats applications are developed separately for each state, generally through cost-sharing agreements between the USGS and state agencies. The State Applications link to the left provides a map to indicate where StreamStats has been implemented and where work is in progress. The page also provides links to introductory pages for each application that describe the available functionality, provide links to related reports, and identify cooperating agencies. The information contained on the User Instructions page should be read before attempting to use StreamStats. For states that have not yet been implemented, information for USGS data-collection stations can be accessed through the USGS Station Statistics page.
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.
StreamStats determines drainage-basin boundaries by use of digital elevation data. These data usually are derived from digital elevation data from the National Elevation Dataset (NED) that have been specially processed so that the elevation data conforms to the digital stream channels depicted in the high-resolution version of the National Hydrography Dataset (NHD) and to the drainage-basin boundaries of the Watershed Boundary Dataset WBD. This processing results in drainage-basin boundary delineations that generally are superior to delineations that can be obtained directly from the NED. Still, users should be aware that use of any digital elevation data to delineate drainage boundaries can lead to errors; especially in flat areas. Users should check delineations carefully and use the EditBasin basin boundary editing tool that is provided in StreamStats to correct any errors, if necessary.
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 Streamflow Statistics Program (NSS), which is a desktop program that contains all of the USGS-developed equations for estimating flood-frequency statistics in the nation, plus equations for estimating other streamflow statistics in many states. NSS 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 NSS are documented in reports that can be accessed through links to each individual state from the NSS Web site. The StreamStats Web site also has links to these reports on introductory pages for each state application. The introductory pages can be accessed from the State Applications link.
The equations used to estimate streamflow statistics for ungaged sites were developed through a process know 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. The StreamStats Limitations page describes additional limitations for use of the equations and StreamStats, in general.
In addition to use of regression equations to estimate streamflow statistics for ungaged sites, StreamStats is able to estimate the statistics based on the flow per unit area of statistics for an upstream or downstream gaging station. This method is documented on page 9 of a report by Ries (2006). Application of this method is limited to ungaged sites with drainage areas that are within 0.5 and 1.5 times the drainage area for an upstream or downstream gaging station.
StreamStats also has the ability to search upstream or downstream or both along the stream channel from a user-selected point to identify the associated stream reaches and activities along the stream that may affect the quantity or quality of streamflow at the selected location. This ability, known as network navigation, is described in more detail on the Network Navigation page.
