• Open HEC-SSP and select Help | Install Example Data.... 
  • Create a folder for the examples and save the file. Once the installation is complete, open the SSP_Examples.ssp study.
  • In the Data section, click the Potomac River-Flow-Annual Peak dataset and select Data | Tabulate as shown in the figure below.

Tabulate Point of Rocks discharge data

  • Select the last column and copy the data as shown in the figure below.

Copy Point of Rocks discharge data

  • Open Excel and paste the data. 
  • Name the sheet Data. You will use this sheet as a starting point for the distribution fitting tests.
  • Select the column containing the data and select Data | Sort. Sort the column from smallest to largest as shown in the figure below.

Sort discharge data in Excel

  • TItle the column Q for discharge.
  • Add a column to the left of the discharge data titled i and number the elements in increasing order. The smallest discharge value should have an i value of 1.
  • Add a column to the right of the discharge data titled Y = log10(Q). The log10-normal distribution is sometimes used for describing annual peak streamflow since the distribution's support is (0, \infty) and streamflow values are always non-negative. The log10-normal distribution describes a random variable whose base 10 logarithm is normally distributed. Therefore, to evaluate the goodness of fit of this distribution, the base 10 logarithm of the discharge values must be used.
  • Calculate the distribution parameters using the base 10 logarithm of discharge. Use Excel functions AVERAGE and STDEV.S to compute the sample mean and standard deviation. 

The Excel sheet should look similar to the figure below. In HEC-SSP, double click on Distribution Fitting Test 20. Select the Analysis tab and click the Distribution Summary Statistics button on the bottom. Navigate to the Standard Product Moments tab.

Take note of the summary statistics for the log10-normal distribution (Log10-Normal in HEC-SSP). Notice that the computed mean and standard deviation below are the same as the values from HEC-SSP.

The Excel functions AVERAGE and STDEV.S estimate the unbiased sample distribution parameters using the Method of Moments (or Standard Product Moments).

Sample distribution statistics

Continue to Task 2. Kolmogorov-Smirnov Test.