Task 1. Create a new HEC-SSP Study and Import Data

Download the data file here: InputData.dss

Create a New HEC-SSP Study

The first step in performing a frequency analysis within HEC-SSP is to establish which directory you wish to work in and to enter a title for the new study.

• Create a new HEC-SSP study.
• Name this project “Annual_Peak_Record_Extension”.
• Leave the Unit System and Coordinate System set to their default values of English and Geographic, respectively.

Import Data

In this example, the gage location of primary interest is USGS 14211010, Clackamas River near Oregon City.  At this location, annual maxima are only available for about 20 years from 2001-2020, but nearby gages with more years of data will be used to extend the record. A previous tutorial Using a Correlation Analysis to Select a Suitable Nearby Gage for Record Extension used a correlation analysis to decide which gages are best suited for record extension. The Clackamas River at Estacada gage is the primary long-term site for this analysis.  These gages are shown and detailed below.

The Clackamas River at Clackamas gage, USGS ID 14211000, has streamflow records from 1963-1983. This site is very close to the Oregon City site, with a difference in drainage area of less than 1%. For the sake of this example, this site is assumed not to exist for simplicity. If this dataset were used, the best process would be to first extend the record at Oregon City using the Clackamas gage data. A simple drainage area ratio would be applied, since the difference in area is so small. Then, the Estacada gage would be correlated with the Oregon City data from 1963-1983 and 2002-2020 to perform the record extension. This would boost confidence in the record extension and likely allow for a longer data extension.

Now you need to import the annual maximum series for the Clackamas River near Oregon City (14211010) and Clackamas River at Estacada (14210000) gages.  These data sets will be used to perform the subsequent analyses.  You will import a data set from an existing DSS file.

• Click Data | New | Using Import Wizard to open the new Data Importer Wizard.
• Click Next.
• Leave the Source as HEC-DSS and click Next.
• Click the ellipsis button within the Selected DSS File entry field.
• Within the pop up window, navigate to the “InputData.dss” file.  Click Open to select this file.  This will cause the contents of the selected DSS file to populate within the table listing selectable data sets.
• Double click on the FLOW-ANNUAL PEAK and CODE time series (four total) to add them to the window at the bottom of the Data Importer.
• Click Next and review your data one last time.
• When ready, click Import to to import the data sets and return to the main HEC-SSP desktop.
• Click the Save button () to save the study.
• You should notice that four new records (flows and codes for both Oregon City and Estacada) were added to the Study Explorer window under Data.

Continue to Task 2. Inspect the Data.