In this example, known inflow to Sayers Dam is available for 68 years in 1936 and from 1955 - 2021.  Nearby gages with more years of data can be used to extend the record and improve estimates of inflow.  Several gages were screened within a Correlation Analysis.  The Penns Creek at Penns Creek, PA gage was selected to extend the Sayers Dam inflow record.

Create a New Record Extension Analysis

  • Click Analysis | New | Record Extension to create a new Record Extension analysis.
  • Name the new analysis "SayersDam_3day_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.
  • Within the Locations panel, select the Penns Creek dataset as the Primary (Long Record) and the Sayers Dam dataset as the Secondary (Short Record).
  • 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 as if the record were being extended for all years. The MOVE.3 (Bulletin 17C) method 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.

SayersDam_3day_MOVE3 Data Tab

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 regression techniques 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 12 years.
    • Also, the most recent 12 years have been automatically selected for you.
  • The Record Extension tab should resemble the following figure.

SayersDam_3day_MOVE3 Record Extension Tab

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 the Save Extended Record to New Data Set button, as shown in the following figure.

  • Name the new data set "SayersDam_3day_MOVE3".
  • Change the Short ID to match the name.
  • 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 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.
  • Select the original Sayers Dam (i.e. unextended) and Sayers Dam MOVE3 data sets by holding the ctrl key and left-clicking.
  • Select Data | Plot. A plot containing both data sets should be presented that resembles the following figure.  Notice the additional years of record contained within the extended data set.

Additional Data

Continue to Task 4. Create Bulletin 17 Analyses for the 3-day Duration Inflow and Compute LPIII Parameters using Bulletin 17C Methodology.