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

New Hampshire is considered to be one hydrologic region. The
regression equations developed for the State 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 drainage area (A), in square miles; channel slope
(S), in feet per mile; and the 2-year 24-hour precipitation
(I2,24), in inches. The variables A and S can be measured from
topographic maps, and I2,24 taken from the U.S. Weather Bureau
Technical Paper (TP) 29 is shown (fig. 1).

The regression equations were developed from peak-discharge
records for 59 stations. The equations are applicable to streams
whose flows are not significantly affected by regulation,
diversion or urbanization, and whose drainage areas are between
0.27 and 622 square miles. The standard errors of estimate of the
regression equations range from 35 to 58 percent. The report by
LeBlanc (1978) also includes selected basin and flood
characteristics for gaging stations.

### Procedure

Topographic maps, the 2-year 24-hour precipitation 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.

### Reference

LeBlanc, D.R., 1978, Progress report on
hydrologic investigations of small drainage areas in New
Hampshire-Preliminary relations for estimating peak discharges on
rural, unregulated streams: U.S. Geological Survey
Water-Resources Investigations Report 78-47, 10 p.

Figure 1. The 2-year 24-hour precipitation in New Hampshire.
(PostScript file of Figure 1.)