Lab Assignment

Part B - Recurrence Intervals

Data from the chart below was collected at the USGS site and includes the 20 largest discharge events for Sweetwater Creek at station 02337000 from January 1, 2008 through May 1, 2015, excluding the dramatic 2009 flood (we will learn more about that later). In order to create a flood-frequency graph, you must first calculate the recurrence interval (one is calculated below as an example). A recurrence interval refers to the average time period within which a given flood event will be equaled or exceeded once. To calculate it, first evaluate the rank of the flood, with a 1 going to the highest discharge event and a 20 going to the lowest discharge event. Calculate the recurrence interval 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