Estimate Bankfull Return Interval Exercise

Exercise Objective

Exercise Process

You can either view the graph on this FGM Module page, or use Excel to view the relationship. In Excel, if you downloaded the completed workbook, the graph is already plotted. If you would like to create the graph, the Excel column to use in the Watstore worksheet is discharge, and then rank, probability, and recurrence interval are populated using the procedure described in FGM Module Section 7 slide 12.

With the Bankfull Discharge estimated earlier, find the associated return interval. To get return interval, read the nearest graphical data point, as no equation is given for this curvilinear fit.

1. Recall the Bankfull Discharge value found earlier in this FGM Module Section.
2. Find the Bankfull Discharge (y axis) on the peak discharge graph to locate the associated Bankfull return interval, yrs, (x axis) point.
3. Consider the scatter of the data, and consider how a regression line would plot between these points, and choose the most representative for your estimate. If you are using Excel, view the data table of discharge and return interval and consider interpolating a point.
4. Record the return interval in years from the log plot.