Kentucky is divided into seven hydrologic regions (fig. 1). The regression equations developed for these regions are for estimating peak discharges (QT) having recurrence intervals T that range from 2 to 100 years. The explanatory basin variables used in the equations are contributing drainage area (Ac), in square miles; main-channel slope (Sc), in feet per mile; basin shape index (Bs), which is the ratio of basin length, in miles, squared to total drainage area, in square miles; and main channel sinuosity (Ss), which is the ratio of main channel length to basin length. All of these basin variables can be measured from topographic maps. The regression equations were developed from peak-discharge records through water year 1985 at 266 continuous and partial-record stations. The regression equations are applicable only to natural-flow streams draining less than 1,000 square miles. Standard errors of the regression equations range from 21 to 52 percent. The report by Choquette (1987) includes a list of gaging stations used in the analysis, the periods of record, maximum observed discharges and values of selected basin variables for each station.
Topographic maps, the hydrologic regions map (fig. 1), and the following equations are used to estimate the needed peak discharges QT, in cubic feet per second, having selected recurrence intervals T.
Figure 1. Flood-frequency region map for Kentucky. (PostScript file of Figure 1.)
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U.S. Department of the Interior, U.S. Geological Survey
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