Hydrosphere's Duration Frequency for Windows program is a Winx application that calculates exceedence/non-exceedence probabilities for streamflow or other data. Duration Frequency for Windows operates directly against any Hydrodata USGS Daily Values or NCDC Summary of the Day disc, or against a user-supplied text file of data values. The software fits the data to the Log-Pearson Type III distribution in order to calculate the probabilities of extreme events.
The Windows interface allows specification of the station, parameter and period of record for analysis, among others.
The results include exceedence/non-exceedence probabilities with recurrence intervals and the associated value of streamflow or other variable. When non-positive values are present in the data set, adjusted probabilities are calculated according to USGS Bulletin 17B. Other outputs include the annual values used in the computation and a count of missing values.
The results can be saved to a file, copied via the clipboard to other programs, or graphed directly within the program.
The program can be run interactively, entering stations from the application, or in a batch mode where numerous runs may be specified in a file that is read into the application.
Duration Frequency for Windows operates as follows: it begins with the first day of the analysis period and calculates the average of the values starting with the first day and extending over the duration you have specified. It then moves to the second day and repeats the process, moves to the third day and repeats the process, and so on until an average value has been calculated for every sequential duration of the first year. It then selects the maximum or minimum value for that year (depending on the user specifications) and moves on to the second year. When it has selected maximum or minimum values for each year in the analysis period, it fits the data to the Log-Pearson Type III probability distribution and calculates values for the range of recurrence intervals.
Download the User's Manual as a Help File (165,409 bytes)
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