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