Water Resources of Tallahassee Florida

Duration Plots Based on Mean Daily Flow in the Florida Panhandle

02315500 Suwanne River at White Springs, FL

02319000 Withlacoochee River near Pinetta, FL

02319500 Suwannee River at Ellaville, FL

02320500 Suwannee River at Branford, FL

02321500 Santa Fe River at Worthington Springs, FL

02322500 Santa Fe River at Fort White, FL

02323500 Suwannee River near Wilcox, FL

02324000 Steinhatchee River near Cross City, FL

02326000 Econfina River near Perry, FL

02326900 St. Marks River near Newport, FL

02327100 Sopchoppy River near Sopchoppy, FL

02329000 Ochlockonee River near Havana, FL

02359000 Chipola River near Altha, FL

02365500 Choctawhatchee River at Caryville, FL

02366500 Choctawhatchee River near Bruce, FL

02368000 Yellow River at Milligan, FL

02369000 Shoal River near Crestview, FL

02370000 Blackwater River near Baker, FL

02375500 Escambia River near Century, FL

Explanation of Duration Graphs

Duration graphs charaterize the state of the hydrology of a stream with respect to time. The plotted percentiles are best explained by an example. Suppose 40 years of daily value flow data exist for a station and the 5-percentile flow is 25 cubic feet per second (cfs) for a single day of the year, say January 3. This means that 5 percent of all flows that occurred on the day January 3 of each of the 40 years of data were equal to or less than 25 cfs. To quantify the state of the hydrology for the current year, the current daily mean flows are compared to these percentiles.

In the duration graphs, the percentiles are smoothed to minimize considerable day-to-day variation. However, the daily minimums and maximums for the period of record are not smoothed.

To interpret the graphs, please consider the following:

1. Although not completely correct in a statistical sense, the non-exceedance of the 5-percentile and the exceedance of the 95-percentile flows may be considered to have a recurrence interval of approximately 20 years.

Likewise, the 10- and 90-percentile flows may be considered to have a recurrence interval of approximately 10 years, and the 25- and 75-percentile flows may be considered to have recurrence intervals of approximately 4 years.

2. In the graphs, it is assumed that "normal flows" lie between the 25- and 75-percentiles, based on the assumption that agriculture, industry, and municipalities can operate normally under high and low flows having a recurrence interval of 4 years.

3. The 7-day minimum flow with a recurrence interval of 10 years is represented on the graph as the 7Q10 line.