A flow frequency analysis can be started in two ways within the software, either by right clicking on the Bulletin 17 folder in the study explorer and selecting New, or by going to the Analysis menu and selecting New and then Bulletin 17 Analysis. When a new Bulletin 17 Analysis is selected, the user is required to first enter a Name for the analysis, enter an optional Description, and select an annual peak flow data set from the available data sets stored in the current study DSS file (see chapter 4 for importing data into the study). The Bulletin 17 Analysis editor will not allow further edits by the user until the name is defined and the data set is selected. The list of data that can be selected for a Bulletin 17 Analysis will only include those data that have an irregular interval, like IR-CENTURY and IR-YEAR (E-part pathname). Also, only one value per water year may exist within the selected data set. Within the Bulletin 17 Analysis, the water year is assumed to be 01Oct – 30Sep.

If the user attempts to compute a Bulletin 17 Analysis using a data set that contains more than one value per water year, an error message will be shown. The General Frequency Analysis described within Chapter 6 can be used to demarcate a different water year (i.e. 01Jan – 31Dec, etc).

Once a name is entered and a flow data set is selected, the DSS File Name and Report File will automatically be populated. The DSS filename is by default a DSS file with the same name as the analysis. The report file is given the same name as the analysis with the extension ".rpt". The Bulletin 17 Editor is shown in the figure below.

Bulletin 17 Analysis Editor