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 AND URBAN

### Summary

New Jersey is treated as a single 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; storage area in basin (St), which is the
percentage of the basin occupied by lakes and swamps; and
impervious cover (I), in percent, which is a function of
population density. The constant 1 is added to St and I in the
computer application of the regression equations. The user should
enter the actual values of St and I. The variables A, S, and St
can be measured from topographic maps; the latter variable I
requires data from census reports. The regression equations were
developed from peak-discharge records through 1972 for 103 gaging
stations where record lengths ranged from 6 to 74 years. The
equations are applicable to non-tidal streams whose flow is not
significantly affected by regulation or diversion and whose
drainage areas are between 1 and 1,000 square miles. The
regression equations do apply to urbanized areas. The standard
errors of estimate of the regression equations range from 48 to
54 percent. The report by Stankowski (1974) includes the basin
characteristics for the stations used in developing the
relations, and a discussion of the effects of urbanization.

### Procedure

Topographic maps, census data, and the following equations are
used to estimate the needed peak discharges QT, in cubic feet per
second, having selected recurrence intervals T. Census data are
available from regional, State, and local planning
agencies.

where D = basin population density in persons per square
mile.

### Reference

Stankowski, S.J., 1974, Magnitude and
frequency of floods in New Jersey with affects of urbanization:
New Jersey Department of Environmental Protection, Division of
Water Resources, Special Report 38, 46 p.