If you have already imported the Big Sandy River at Bruceton, TN annual maximum series, you may continue using that project. However, you may also start with this project:
Now you will create a Bulletin 17 analysis to fit Log Pearson Type III analytical distributions to the peak inflow data set using Bulletin 17B (B17B) methodology for the systematic record. The B17B guidance guided the development of peak flow frequency analyses within the United States for over 30 years (early 1980s until the adoption of B17C guidance in the late 2010s). This guidance recommended the use of the Log Pearson Type III probability distribution for annual peak flows on unregulated streams fit by the Method of Moments (Interagency Advisory Committee on Water Data, 1982). Using the B17B methodology, distribution parameters are estimated from the moments of the sample data (i.e. mean, standard deviation and skew). B17B also includes adjustments to those parameters for non-standard data (missing years, flows below gage base, or estimated flows), low outliers, and historical events. Adjustments can be made with a series of specified procedures including the conditional probability adjustment and the historical adjustment (weighted moments) procedure. The B17B methodology characterizes the peak flow in each year as either (1) part of the systematic (observed) record, for which a point estimate of flow exists or (2) an historical event from a time before a gage was present but for which an estimate of flow can be made.
Create a New Bulletin 17 Analysis
To begin, select Analysis | New | Bulletin 17 Analysis.
Name the new analysis “BigSandyRiver_Systematic_B17B” and add an adequate description.
Select the “BigSandyRiver” data set.
Select “17B Methods” within the Method for Computing Statistics and Confidence Limits panel.
Utilize the default selections of Use Station Skew, Single Grubbs-Beck low outlier test, and Median plotting position.
The General tab should look similar to the following figure.
No modifications are needed on the Options tab.
Click Compute.
Analyze Results
Click Plot Curve. This will result in the computed curve, 5- and 95-percent confidence limits, and observed events being plotted.
Close the computed curve window.
Move to the Tabular Results Note the computed curve, 5-, and 95-percent confidence limits for all of the desired frequency ordinates, the moments/parameters of the Log Pearson Type III fit to the data, and other data related to the analysis.
