Create a new HEC-SSP Project

  • Open the build of HEC-SSP provided on the previous page.
  • From the top ribbon, select File | New Study....
  • Enter "SanLorenzo_POT" as the Study Name and enter an appropriate Description.
  • Select a Directory to save the project.
  • Leave the Unit System and Coordinate System as the defaults (English and Geographic).
  • Click the OK button to create the project.

Import Mean Daily Flow Data from HEC-DSS

  • Download the SanLorenzoStreamflow.dss file from Peaks Over Threshold Analysis: Flood Separation and Threshold Choice.
  • Select Data | New | Using Import Wizard from the top ribbon or right click on the Data folder and select New | Using Import Wizard.
  • Select the Next button to accept the defaults on the first screen of the wizard.
  • Make sure the Source is set to HEC-DSS and click Next.
  • Use the ellipses () to select the SanLorenzoStreamflow.dss file
  • You should see a single record in the middle portion of the dialog, as shown below:
  • Double left click on the DSS record to select it. You should see the pathname in the lower portion of the dialog once the record is selected.
  • Click Next.
  • Review your inputs on the Review Data screen.
  • Click Import.

Extract the Annual Maximum Series

  • Select the SAN LORENZO R-BIG TREES CA-FLOW dataset under the Data folder in the Study Explorer.
  • Right click and select Filter Data or from the top ribbon, select Data | Filter Data.
  • On the Peaks tab, select the Filter to Annual Maxima checkbox in the Annual Maxima panel.
  • Change the Start of Year to 01Oct.

    The Peaks tab should look like this:


  • Click the Save Filtered Data Set As button.
  • Edit the Name and F-part fields to include "AMS" as shown below.

QUESTION 1: How many events are in the annual maximum series? What are the magnitudes of the minimum and maximum annual peak? How do you feel about calling the minimum annual peak flow an extreme event?

There are 88 annual peaks in the 88 years of record. The minimum and maximum annual peaks are 128 and 17,000 cfs, respectively.

Looking at the streamflow time series, an annual peak flow of 128 cfs does not appear extreme. This peak. and several others. can be considered opportunistic peaks, meaning they are the largest flows observed in otherwise dry years rather than truly extreme events.

Create a Peaks Over Threshold Analysis

  • Create a new Peaks Over Threshold Analysis by selecting Analysis | New | Peaks Over Threshold Analysis from the top ribbon or by right clicking on the Peaks Over Threshold folder in the tree and selecting New....
  • Enter "SanLorenzo_Low" as the Name.
  • Enter an appropriate description, such as "Investigation of low threshold".
  • In the Data Set drop down, select the continuous daily flow datatset, named "SAN LORENZO R-BIG TREES CA-FLOW".
  • The analysis editor should appear as in the image below:
  • Leave the default selections on the General tab.
  • Move to the Filtering tab. 

Continue to Task 2. Investigate Threshold Sensitivity.