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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

OHIO

STATEWIDE RURAL

Summary

Ohio is divided into three 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 100 years. The explanatory basin characteristics used in the equations are drainage area (A), in square miles; main channel slope (S), in feet per mile; and the percentage of the basin occupied by lakes, ponds, and swamps (St). The constant 1 is added to St in the computer application of the regression equations. The user should enter the actual value of St. These variables can be measured from topographic maps. The regression equations were developed from peak-discharge records for 275 gaging stations and are applicable to rural, unregulated streams having less than 30 percent of the drainage basin strip mined. The standard errors of prediction for the regression equations range from 33 to 41 percent.

Procedure

Topographic maps, the hydrologic regions 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.

where

RC is the regression constant for a region from the following matrix:

Reference

Koltun, G.F., and Roberts, J.W., 1989, Techniques for estimating flood-peak discharges of rural, unregulated streams in Ohio: U.S. Geological Survey Water-Resources Investigations Report 89-4126, 68 p.

STATEWIDE URBAN

Summary

The regression equations were developed for estimating urban peak discharges (UQT) 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; mean annual precipitation minus 30 (P-30), in inches; and a basin development factor (BDF). The constant 30 is subtracted from P in the computer application of the regression equations. The user should enter the actual value of P. The first variable A can be measured from topographic maps, P can be determined from figure 2 and the method of estimating BDF is defined earlier in this report in the section entitled Urban Flood-Frequency Techniques. The equations are based on peak-discharge records of 5-8 years in length at 30 stations in urban areas of Ohio. Record lengths were extended to 66-87 years by use of a rainfall-runoff model. The equations are applicable only to urban streams draining less than 4.09 square miles. The standard errors of prediction range from 34 to 40 percent. The report by Sherwood (1993) also includes procedures for estimating flood volumes and hydrographs.

Procedure

Topographic maps, the precipitation map (fig. 2), and the following equations are used to estimate the needed urban peak discharges UQT, in cubic feet per second, having selected recurrence intervals T.

Reference

Sherwood, J.M., 1993, Estimation of peak-frequency relations, flood hydrographs, and volume-duration-frequency relations of ungaged small urban streams in Ohio: U.S. Geological Survey Open-File Report 93135, 53 p.

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

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