In reply, refer to
Mail Stop 415

Office of Surface Water Technical Memorandum No. 2009.03

Subject: Selection of basin characteristic and streamflow statistic labels for regionalization studies

U.S. Geological Survey Water Science Centers actively engage in regionalization projects that have the goal of estimating streamflow statistics for ungaged sites. Regionalization is the process of using regression analysis to relate streamflow statistics (peak flow, low flow, and flow duration) computed for a group of selected streamgaging stations (usually within a state) to basin characteristics measured for the stations. The end products of regionalization projects are reports that contain regression equations that allow estimation of various streamflow statistics for an ungaged basin so long as that basin’s characteristics are known. The regression equations presented in these reports are entered into the National Streamflow Statistics (NSS) program (/osw/programs/nss/index.html) to make solving them easy for users. While NSS is a stand-alone program, NSS is also used to solve the flow equations for use in the StreamStats program (

Until now, report authors have been allowed to use whatever names they chose for basin characteristics and flow statistics in their reports. The resulting basin characteristic and flow statistic names were reproduced in the NSS program to maintain consistency between NSS and the reports. This practice, however, has led to confusion when different reports use different names for the same basin characteristics and streamflow statistics. In addition, StreamStats serves previously published regionalization project information nationally and it is essential to use consistent names for the basin characteristics and streamflow statistics so that the information can be compared between stations and between states. In order to avoid confusing inconsistencies, from this point forward, the Office of Surface Water (OSW) requires the use of consistent naming conventions for basin characteristics and streamflow statistics that are published in reports that contain regional regression equations. This new practice will eliminate conflicts between the names and definitions of basin characteristics and streamflow statistics in different regionalization project reports.

To avoid conflicts between basin characteristic and streamflow statistic labels submitted for entry into NSS and StreamStats, the regionalization study project chiefs are required to consult the tables of existing labels, variable names, and definitions maintained by OSW. These tables are regularly updated and can be found at /osw/streamstats/def.html. The project chief must refer to these official listings during the planning and execution of a regionalization project and must use existing variable names and definitions if they already exist in the official list. This website contains two tables, one for basin characteristics and one for the streamflow statistics. Each table contains the label (StatLabel), name (Statistic Name), and the definition of the label (Definition). The names and labels conform to an established protocol that facilitates development and maintenance of NSS and StreamStats. The StatLabel, which is a name of 10 characters or less, is shown in the output from NSS. The Statistic Name is displayed in the input portion of NSS where the user is asked to input the independent variables. The definitions are not displayed to the user in NSS, but there are plans to display the definitions soon through hyperlinks in StreamStats outputs.

If the study project chief is unable to find an existing label from the official list that fits the variables used in their study, they must contact the NSS project manager, Robert Holmes, ( to discuss label naming for the study.

Steve Blanchard 703-648-5629
Chief, Office of Surface Water 703-648-6693 (FAX)
Delaware River Master 571-216-1423 (Cell)
U.S. Geological Survey
National Center, MS415
12201 Sunrise Valley Drive
Reston, VA 20192