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*

# WYOMING

## STATEWIDE RURAL

### Summary

Wyoming is divided into three 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 500 years. The explanatory basin variables
used in the equations are contributing drainage area (A), in
square miles; mean basin elevation (ELEV) in feet; mean annual
precipitation (PR), in inches (fig. 2); and basin slope (Sb), in
feet per mile. In the Plains and High Desert regions, a
geographic factor (Gf) (fig. 3) is used. The constants of ELEV is
divided by 1000 in the computer application of the equations. The
user should enter the actual value for ELEV. The variables A, E,
and Sb can be measured from topographic maps; the variables PR
and Gf are shown in figures 2 and 3, respectively. The regression
equations were developed from peak-discharge records available as
of December 1986 at 361 stations. The equations are applicable
only to natural-flow streams, and the regional average standard
errors of estimate of the regression equations range from 50 to
75 percent. The report by Lowham (1988) includes procedures for
estimating flood characteristics from channel geometry as well as
ones for estimating mean annual and mean monthly flows by various
methods. Also included in the report are flood-frequency
characteristics, basin characteristics, and channel widths at
stations used in the analysis.

### Procedure

Topographic maps, the hydrologic regions map (fig. 1), the
mean annual precipitation map (fig. 2), the geographic factors
map (fig. 3), and the following equations are used to estimate
the needed peak discharges QT, in cubic feet per second, having
selected recurrence intervals T.

### Mountainous Regions

### Plains Region

### High Desert Region

### Reference

Lowham, H.W., 1988, Streamflows in Wyoming: U.S.
Geological Survey Water-Resources Investigations Report 88-4045,
78 p.

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

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

Figure 3. Geographic factors in Wyoming. (PostScript file of Figure 3.)