Water Resources Applications Software

Geochemical || Ground Water || Surface Water || Water Quality || General

Summary of HYSEP

       hysep - Hydrograph separation program

       HYSEP performs hydrograph separation, estimating the ground-water,
       or base flow, component of streamflow.  The program provides an
       automated and consistent method for estimating base flow.  Any of
       the three hydrograph-separation techniques of Pettyjohn and Henning
       (1979) can be used:  fixed interval, sliding interval, or local

       See Pettyjohn and Henning (1979).

       Version 2.2 1997/06/10 - Includes implementation of a seasonal-
          distribution table and bar graph of base flow and surface runoff.
          Problems with the fixed-interval separation method were
          corrected: (1) the accuracy of computed base flow was improved
          for the first year in the period to be analyzed by including the
          final days of the immediately previous year in the analysis, when
          available (using data from adjacent years in this way was
          previously done with all years except the first year in the
          period to be analyzed); and (2) fixed-interval separation is now
          correctly performed for the final days of the final year in the
          period to be analyzed when that year coincides with the end of
          the available input data. Previously, if the number of days in
          the final year was not evenly divisible by the interval length,
          fixed-interval separation was not correctly handled for the final
          days in the year, with the result of those days being treated as
          missing values.

       Version 2.1 1996/03/01 - General release.

       The original version was written by Ronald Sloto in 1982.  That
       version was enhanced to read input from Watershed Data Management
       (WDM) files (see below) in addition to files in the conventional
       format from the U.S. Geological Survey Water Data Storage and
       Retrieval System (WATSTORE) and Automated Data Processing System
       (ADAPS) data bases.  A character-based user interface was also added
       to the program.  See HASS-CUI for details on the interface.

       Some additional changes were made to Sloto's original program:

       - Base-flow separation is performed using a period of data beginning
         and ending in any month specified by the user, i.e., input is no
         longer restricted to complete water or calendar years.  The user
         can also specify summary output to be in water, calendar, or any
         other user-defined years.  Output in both calendar year and water
         year in a single run was dropped, however.  The program must be
         run twice in order to get both calendar and water year output for
         the same input data.

       - Periods of missing streamflow data of any length, falling anywhere
         within the period of record specified by the user, are handled by
         the program.  Formerly, only complete missing years within the
         period of record could be handled gracefully.

       - Accuracy of base-flow separation was improved at the year
         boundaries, i.e., base-flow values computed for the days at the
         beginning and end of each 12-month period within a period of
         record are more exact and consistent by using, when available,
         data from adjacent years.

       Daily mean stream discharge in daily values card-image format or as
       stored in WDM files is used as input to HYSEP.  WDM files are
       binary, direct-access files that allow for efficient storage and
       fast retrieval of data.  Stream discharge in the daily values card-
       image format also can be reformatted to a WDM file using the program

       Tables of statistical output are produced by HYSEP, namely
       frequency, flow-duration, and seasonal-distribution tables as well
       as monthly and annual summaries of the hydrograph separation.  A
       program option allows for storage of the estimated daily base flow
       and (or) surface runoff on the user's WDM file, making the base-flow
       data available for further processing, such as the performance of
       flow-duration analysis using the program SWSTAT.  The estimated
       daily base flow and (or) surface runoff can also be output in card-
       image format.

       HYSEP can direct graphical output to any of the devices allowed in
       your system's implementation of the Graphical Kernel System (GKS).
       Alternate output devices are specified in a local file called
       "TERM.DAT".  See HASS-CUI and your system's GKS documentation for

       HYSEP is written in Fortran 77 with the following extension: use of
       include files. The ANN, WAIDE, GRAPH, STATS, AIDE, WDM, ADWDM, and
       UTIL libraries from LIB are required to recompile. For more
       information, see System Requirements in LIB.

       Sloto, R.A., and Crouse, M.Y., 1996, HYSEP: A computer program for
          streamflow hydrograph separation and analysis: U.S. Geological
          Survey Water-Resources Investigations Report 96-4040, 46 p.

       Pettyjohn, W.A., and Henning, Roger, 1979, Preliminary estimate of
          ground-water recharge rates, related streamflow and water quality
          in Ohio:  Ohio State University Water Resources Center Project
          Completion Report Number 552, 323 p.

       Sloto, R.A., 1988, A computer method for estimating ground-water
          contribution to streamflow using hydrograph-separation
          techniques:  National Computer Technology Meeting, Phoenix, Ariz.

       There is no regularly scheduled class for HYSEP.  Base-flow
       separation techniques are included in Ground-water/Surface-water
       Relationships (ID2015TC), offered annually at the USGS National
       Training Center.

       Operation and Distribution:
          U.S. Geological Survey
          Hydrologic Analysis Software Support Program
          437 National Center
          Reston, VA 20192

       Official versions of U.S. Geological Survey water-resources analysis
       software are available for electronic retrieval via the World Wide
       Web (WWW) at:


       and via anonymous File Transfer Protocol (FTP) from:

         (path: /pub/software).

       The WWW page and anonymous FTP directory from which the HYSEP
       software can be retrieved are, respectively:


       hass-cui - Character-based user interface
       iowdm(1) - Program to store time-series data in a WDM file
       swstat(1) - Surface-water statistics
       wdm(1) - Watershed Data Management system

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