Lab Assignment
Part B - Recurrence Intervals
Data from the chart below was collected at the USGS site andincludes the 20 largest discharge events for Sweetwater Creek atstation 02337000 from January 1, 2008 through May 1, 2015,excluding the dramatic 2009 flood (we will learn more about thatlater). In order to create a flood-frequency graph, you must firstcalculate the recurrence interval (one is calculated below as anexample). A recurrence interval refers to theaverage time period within which a given flood event will beequaled or exceeded once. To calculate it, first evaluate the rankof the flood, with a “1” going to the highest discharge event and a“20” going to the lowest discharge event. Calculate the recurrenceinterval using the following equation:
RI = (n+1) ÷ m
where, RI = Recurrence Interval (years)
n = number of years of records (in this case, 8)
m = rank of flood. Peak Discharge Date | Discharge (cubic ft/sec = cfs) | Rank | Recurrence Interval (years) |
08/27/2008 | 5,140 |
03/02/2009 | 2,360 |
10/13/2009 | 3,290 |
11/12/2009 | 6,120 | 1 | 9 |
12/03/2009 | 2,860 |
12/10/2009 | 2,170 |
12/19/2009 | 3,830 |
12/26/2009 | 2,650 |
01/25/2010 | 2,500 |
02/06/2010 | 3,680 |
03/12/2010 | 3,600 |
03/10/2011 | 2,350 |
04/17/2011 | 3,100 |
02/24/2013 | 2,060 |
02/27/2013 | 2,190 |
05/06/2013 | 3,610 |
12/23/2013 | 3,790 |
04/08/2014 | 4,170 |
01/05/2015 | 3,970 |
04/20/2015 | 2,940 |
