Data Filtering, Extracting an n-Day Duration Time Series

This example demonstrates how to extract an n-day duration time series from another time series. The original data for this example consists of daily average streamflow at the Sinnemahoning Creek at Sinnemahoning, PA stream gage. This stream gage is operated by the USGS. The period of record used for this example is from 1938 to 2016. To view the data from HEC-SSP, right-click on the data record labeled "Sinnemahoning Creek-Daily" in the study explorer and then select Plot. A plot of the data will appear as shown in Figure 1.

To begin extracting an n-day duration time series, right click on the Sinnemahoning Creek-Daily data record and select Filter Data. Within the Filter editor, click on the Duration tab. For this example, a 5-day duration time series will be extracted.  Within the Duration panel, click the Average Data over Duration check box and enter a Duration of 5 days, as shown in Figure 2.

After clicking the Save Filtered Data Set As button, enter a Name of "Sinnemahoning Creek-Daily-5DAY", ensure the E-part is set to 1DAY, and the F-Part is defined as "USGS – 5DAY", as shown in Figure 3.

After clicking the OK button, a new data set will be added to the study.  The original data as well as the filtered data is shown in Figure 4.

A sample of the computations for the first ten days are shown in Table 1.  As shown within this table, the filtered data set contains four fewer values than the original data set.  This was necessary in order to compute a 5-day average for the first 5 days of the time series.  The 5-day average is computed on day 5 using the following formula:

$//<![CDATA[ \begin{array}{l}35.8=\frac{(41 + 38 + 35 + 33 + 32)}{5}\end{array} //]]>$

Similarly, the 5-day average is computed on day 7 using the following formula:

$//<![CDATA[ \begin{array}{l}36.4=\frac{(38 + 35 + 33 + 32 + 44)}{5}\end{array} //]]>$

Table 1. First Ten Days of Original and Filtered Data

A detailed view of the original data as well as the filtered data for the June 1972 time period is shown in Figure 5.  The filtered data set constitutes a moving 5-day daily average streamflow time series.