Next, use the Estacada data set to extend the shorter Oregon City data set.

Create a New Record Extension Analysis

  • Click Analysis | New | Record Extension to create a new Record Extension analysis.
  • Name the new analysis "OregonCity_MOVE3".
  • Under the Computational Method panel, ensure the MOVE.3 (Bulletin 17C) method is selected. This method will perform the record extension for annual maximum peak flows in accordance with the modified MOVE.3 procedure, as laid out in Appendix 8 of Bulletin 17C. Select the "Use Most-Recent Years" method for this example.
  • Within the Locations panel, select the Estacada dataset as the Primary (Long Record) and the Oregon City dataset as the Secondary (Short Record).

Make sure you do not select the codes!

  • The General tab should resemble the following figure.

Compute and Visualize the Results

  • Click Compute and move to the Data tab.
    • You should notice that statistics for the complete records, concurrent periods, and non-concurrent periods have been computed and are tabulated.
    • Also, a plot showing the long-term peak flows against the short-term peak flows (blue circles) is provided.

    • Additionally, since the analysis was computed, the extended record is also shown for the years where the short-term gage does not exist (red circles).

      The red circles are shown only for the years that an extended record was produced (not all years). The MOVE.3 method Bulletin 17C limits the number of years allowed for extending the data. The Record Extension tab shows this in more detail.  

  • The Data tab should resemble the following figure.

Question: Why does the extended record plot along a straight line (in log space)?

The MOVE.3 (Bulletin 17C) record extension method relies upon linear techniques (adaptation of linear regression) to predict the extended record.  As such, the resultant predicted flows are perfectly linear (in log space).


  • Move to the Record Extension tab.
    • Note that the allowable years of record extension per Bulletin 17C procedures is 26 years.
    • Also, the most recent 26 years have been automatically selected for you.
  • The Record Extension tab should resemble the following figure.

Question: What is the mean (of logs) and variance (of logs) of the extended record from water year 1976 - 2020?

The mean (of logs) and variance (of logs) of the extended record is approximately 4.518 and 0.054, respectively.  This can be confirmed by copying the 1976 - 2020 time series to Excel, computing the log10 transform of each peak flow, and calculating the average and variance of the log10 values.  This matches the computed Matalas-Jacobs estimators.

Create an Extended Record Data Set

Now that you've computed the extended record, save it to a new data set so it can be used in other analyses.

  • Click Save Extended Record to New Data Set.
  • Name the new data set "OregonCity_MOVE3".
  • Change the F-Part to "USGS-MOVE3", and change the Name and ShortID to OregonCity_MOVE3.
  • The Save as New Data Set dialog should resemble the following figure.
    Saving the Extended Data Set
  • Click Next and review the extended data.
  • When ready, click Import to import the extended record and return to the main HEC-SSP desktop.
  • Click the Save button () to save the study.
  • You should notice that the extended record was added to the Study Explorer window under Data.

Continue to Task 5. Fit an LPIII Distribution to the Extended Data and Compare the Results.