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SWToolbox Software Information

March 4, 2019

Note to Users of the Surface-Water and Groundwater Toolboxes

The Surface-Water and Groundwater Toolboxes have been superseded by the Hydrologic Toolbox as of May 2022. The Hydrologic Toolbox combines the analytical and statistical functionality of the Surface-Water and Groundwater Toolboxes and provides several enhancements to these programs. The Hydrologic Toolbox is available at will be no further updates to the Surface-Water or Groundwater Toolboxes


Error in Adjusted Harmonic Mean calculation

The adjusted harmonic mean is incorrectly computed in SWToolbox when a time series contains both 1) zero values and 2) gaps in the record. Gaps in the record are treated as zeroes for this particular calculation in the software, resulting in an over-adjusted (lower) value.  The adjusted harmonic mean should not be computed using the SWToolbox for records which meet these two criteria.


Overview and Help

The primary functions of SWToolbox are conduct a n-day frequency analysis (most commonly used for computation of 7Q10) and to computer biologically-based design flows.  Flow duration curves can also be computed. The software is designed to facilitate easy import of USGS NWIS streamflow data as well as user-defined text files.

SWToolbox is built on the EPA BASINS system. The SW Toolbox Documentation found under the Help menu provides information on the functionality of the software. Most of the information on use of the software is general and applies to all applications built on the BASINS platform.


Download Software

The latest software release, USGS SWToolbox 1.0.5, is available for download in the link below. Version 1.0.5 corrects known bugs in the previous version and includes some enhancements:

  • Frequency statistics (e.g., 7Q10) for sites with zero flows are now being computed correctly with the Conditional Probability adjustment (CPA) in all routines (Design flow, DFLOW, n-day Frequency grid and report, interactive, and batch mode).
  • "Custom dates" option is applied correctly in"N-day, trend, and frequency" and "Design Flow" routines.
  • SWToolbox 1.0.5 is now compatible with the latest version of R 3.6. It will still run with older versions of R.
  • Descriptive statistics and variables associated with the n-day frequency analysis (e.g., K-values) have been added to the batch mode output. Previously these values were only available from the exported frequency grid in interactive mode.

The executable file will install the software on Windows machines. Note that R, both 32- and 64-bit, must be installed on a user's system in order to access some functionality under the "Integrated Design Flow" workflow. 


Software and Manual Release

The user manual describes the functionality of the software and walks the user through an example session. It is available for viewing and download through the USGS publications warehouse:

The installation file below will install the software on Windows machines. Note that R must be installed on a user's system in order to access some functionality under the "Integrated Design Flow" workflow. The integration with R has been seamless on Windows 7 and 8 computers, but we have encountered problems with Windows 10 that we are still trying to resolve.


Updates and Feedback

We are always looking for feedback on the SWToolbox software. If you encounter any problems, please let us know by sending an email to

Publication Year 2019
Title SWToolbox Software Information
DOI 10.3133/ofr83433B
Product Type Software Release
Record Source USGS Digital Object Identifier Catalog