Annual Peak Record Extension - MF Eel River

The MFEelRiver_RecordExtension example demonstrates the usage of the Record Extension Analysis in order to extend a shorter annual maximum flow time series using a site with a longer period of record.

Input Data

In this example, time series representing annual maximum flow at two locations within the Eel River watershed in California are analyzed.  The primary (i.e. long record) time series is from the Eel River at Scotia, CA stream gage, which has a drainage area of approximately 3113 square miles (sq mi) and a period of record from 1911 - 2021.  The secondary (i.e. short record) time series is from the Middle Fork Eel River near Dos Rios, CA stream gage, which has a drainage area of approximately 745 sq mi and a period of record from 1966 - 2021.  The location of these stream gages is shown in Figure 1.  The time series are plotted within Figure 2 and tabulated within Table 1.

Table 1. Input Time Series for MFEelRiver_RecordExtension Example

Inspecting the 56 years of overlapping data, it is evident that some of the annual peaks are not "truly" concurrent (i.e. the annual peak for a given water year at the long term site occurred during a different runoff event when compared to the short term site), as shown in Figure 4. Per Bulletin 17C: "For the purposes of record extension, concurrent flood peaks are those that occurred in the same water year, not on the same flood event."  As such, the entire overlapping record was considered concurrent within this example.

The Correlation Analysis within HEC-SSP can be used to identify any peak flow data points that are many days apart. For an example of how to create a Correlation Analysis for this purpose, see Using a Correlation Analysis to Select a Suitable Nearby Gage for Record Extension.

General Tab

A Record Extension Analysis has been developed for this example. To open the analysis, either double-click on the analysis labeled MFEelRiver_RecordExtension from the study explorer or from the Analysis menu select open, then select MFEelRiver_RecordExtension from the list of available analyses. When MFEelRiver_RecordExtension is opened, the General tab within the Record Extension Analysis editor will appear as shown in Figure 4. For this analysis, the MOVE.3 (Bulletin 17C) computational method and the Annual Maximum (One Per Year) data type was selected.  The Scotia time series was selected as the Primary (Long Record) while the Dos Rios time series was selected as the Secondary (Short Record).  The default Year Specification (Water Year) was left unchanged. No modifications were made to the time window or the output labeling.

Data Tab

The Data tab contains several tables detailing the complete, concurrent (i.e. overlapping), and non-concurrent (i.e. non-overlapping) records.  Additionally, a plot showing the concurrent record is included.  The  primary record (Scotia) is shown on the x-axis while the secondary record (Dos Rios) is shown on the y-axis.  Prior to a successful compute, the plot will only contain the concurrent record (blue circles), as shown in Figure 5.  Following a successful compute, the extended record (red circles) will be added to the plot, as shown in Figure 6.

Computing the Analysis

Once all of the General information has been selected and the data reviewed on the Data tab, the user can press the Compute button to perform the analysis.  Once the computations have been completed, a message window will open stating Compute Complete.

The Record Extension Analysis will use all values within the concurrent time period when computing correlation coefficients, estimators for augmentation, and the extended record.  No values will be removed from consideration even though they may not have resulted from the same runoff event, as was mentioned above.

Record Extension Tab

The Record Extension tab contains several tables detailing the Matalas-Jacobs Estimators (MJ-Mean and MJ-Variance), the Estimators for Augmentation, and statistics of the extended record.  Additionally, a plot showing the input time series is included.  Prior to a successful compute, the plot will only contain the primary record (Scotia; green circles) and the secondary record (Dos Rios; blue circles), as shown in Figure 7.  Following a successful compute, the extended record (red circles) will be added to the plot, as shown in Figure 8.

Since this example made use of the MOVE.3 (Bulletin 17C) computational method and the Annual Maximum (One Per Year) data type, following a successful compute, the effective record length (n_e) of the variance will be used to select data for extension.  Specifically, the most recent n_e years will be selected and the Save Extended Record to New Data Set button will become enabled.

The user may select a different portion of the extended record to save to a new data set.  However, the Estimators for Augmentation were computed using the most recent n_e years.  As such, choosing a different portion of the extended record will not result in the Matalas-Jacobs estimators being reproduced within the extended record.  It is recommended that the user selects the default extended record when saving to a new data set.

The Save Extended Record to New Data Set button will only be active following a successful compute.  

When the Save Extended Record to New Data Set is clicked, a dialog will be presented allowing for the definition of a Name, Description, Short ID, and DSS Pathname Parts for the new data set, as shown within Figure 9.

Upon clicking the Next button, a Save As New Data Set Summary dialog will be shown allowing the user to review the metadata of the new data set as well as a tabulation and plot of the data that is about to be imported, as shown in Figure 10.

Once the extended record is saved to a new data set, it can be used to compute updated flow-frequency information.  An example of this type of application is shown here.

Report File

In addition to the tabular and graphical results, there is a report file that echoes the input data, selected computational options, and results. To review the report file, press the View Report button at the bottom of the analysis window. When this button is selected a text viewer will open the report file and display it on the screen, as shown in Figure 11. 

Different types and amounts of information will show up in the report file depending on the data and the options that have been selected for the analysis.