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Basic Information
DFLOW 3.0 is a Windows-based revision of the DFLOW computer code developed by EPA to estimate design stream flows for use in water quality standards and TMDL waste load allocations. DFLOW 3.0 uses the same algorithms as the original program, but provides an improved graphical-user interface and additional functionality. The earliest version of DFLOW was used on an EPA mainframe computer in the 1980's; the latest version can by any user in a PC Windows environment.
Installing DFLOW 3.0
- Download DFLOW 3.1 (zip file) (4.7 Mb, about Zip files)
- Run DFlow_Install.exe to launch the set up wizard to install DFLOW 3.1
- Run USGSFlow1.8.exe to launch the set up wizard to install a flow download tool
DFLOW Functions
DFLOW can be used by anyone interested in calculating and analyzing low flow statistics. The uses of DFLOW include:
- Calculating the 4B3 and 7Q10 for one or more streams. These results can then be used to compare the relationship between the biologically-based 4B3 with the hydrologically-based 7Q10.
- Calculating any alternative design flow in the form of xQy or xBy (where x is the averaging period and y is the frequency of excursion). These results can be readily used to compare various design flow statistics.
- Calculating seasonal design flow statistics.
- Determining the return period for the hydrologically-based design flow numerically closest to a user-specified biologically-based design flow.
- Calculating the harmonic mean flow for each gage in the specified period.
- Providing results in a form that can easily be copied into a spreadsheet for further analysis.
How to use DFLOW
- Before using DFLOW, the user must obtain daily stream flow data for the gauge(s) of interest. These data are typically available in text files generated from stream data repositories such as USGS Daily Streamflow for the Nation.
- DFLOW 3.0 prompts the user with a dialogue box to select flow input file(s) from any location on the computer or network.
- The user specifies the dates of the calculation period and selects to perform the calculation on either a full-year or seasonal basis.
- The final step in using DFLOW is to specify the biological and/or hydrological design parameters.
After the user selects the "Calculate Design Flows" button, the results are displayed in a scrollable table, where each gauging station is a separate row. The columns are the gauge, period of record, days in the record, number of days with zero flow or missing data, the user-specified biologically-based design flow (i.e., xBy), the xBy percentile, the number of xBy excursions every three years, the user-specified hydrologically-based design flow (i.e., xQy), the xQy percentile, the number of xQy excursions in the entire record, number of xQy excursions every three years, the return period, value, and percentile of the hydrologically-based design flow that best represents the xBy, the harmonic mean flow, and the percentile of the harmonic mean flow.
The "Copy to clipboard" button in DFLOW 3.0 places all results on the clipboard in a format suitable for pasting into Microsoft Excel or a similar spreadsheet program.
