Water Resources of the United States

The following documentation was taken from:

U.S. Geological Survey Water-Resources Investigations Report 94-4002:*
Nationwide summary of U.S. Geological Survey regional regression equations for
estimating magnitude and frequency of floods for ungaged sites, 1993*

## STATEWIDE RURAL

### Summary

Indiana is divided into seven hydrologic areas (fig. 1). The
regression equations developed for these areas 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 (DA), in square miles;
storage (STOR), which is the percentage of the contributing
drainage area covered by lakes, ponds, and wetlands; mean annual
precipitation (PREC), in inches; runoff coefficient (RC), which
relates storm runoff to soil permeability; main-channel slope
(SL), in feet per mile; precipitation (I24,2), in inches, the
2-year 24-hour precipitation; and main-channel length (L), in
miles. The constants of 1, -30, and -2.5 are added to STOR, PREC,
and I24,2 in the computer application of the regression
equations. The user should enter the actual values of STOR, PREC,
and I24,2. The variables DA, STOR, SL, and L can be measured from
topographic maps. Variable PREC can be determined from figure 2;
I24,2 can be determined from figure 3; and RC can be determined
from figure 4. The regression equations were developed from
peak-discharge records for 242 stations in Indiana, Ohio, and
Illinois. The equations should be used only for unregulated,
nonurbanized streams. Standard errors of estimate of the
regression equations range from 24 to 45 percent. The report by
Glatfelter (1984) includes flood-frequency data based on observed
peaks for 270 gaged locations.

### Procedure

Topographic maps, the hydrologic area map (fig. 1), the mean
annual precipitation map (fig. 2), the 2-year 24-hour
precipitation map (fig. 3), the map showing major soil groups and
runoff coefficients (fig. 4), and the following equations are
used to estimate the needed peak discharges QT, in cubic feet per
second, having selected recurrence intervals T.

### Area 1

### Area 2

### Area 3

### Area 4

### Area 5

### Area 6

### Area 7

### Reference

Glatfelter, D.R., 1984, Techniques for
estimating magnitude and frequency of floods on streams in
Indiana: U.S. Geological Survey Water-Resources Investigations
Report 84-4134, 110 p.

Figure 1. Flood-frequency region map for Indiana. (PostScript file of Figure 1.)

Figure 2. Mean annual precipitation in Indiana. (PostScript file of Figure 2.)

Figure 3. The 2-year 24-hour precipitation in Indiana.
(PostScript file of Figure 3.)

Figure 4. Hydrologic soil-groups map for Indiana. (PostScript file of Figure 4.)