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<br />EASTERN COLORADO, PLAINS REGION
<br />(DRAINAGE AREAS MORE THAN 20 M,2)
<br />
<br />Summary
<br />
<br />A second Plains Region is for streams with drain-
<br />age areas greater than 20 mi2 (fig. I), The regression
<br />equations developed for this region are for estimating
<br />peak discharges (QT) having recurrence intervals T of
<br />10-, 50-, 100- and 500 years, The explanatory basin
<br />variables used in the equations are drainage area (A), in
<br />square miles; and streambed (channel) slope (Sb), in
<br />feet per mile, The regression equations are applicable
<br />for unregulated streams draining areas greater than 20
<br />mi2. The standard errors of estimate for the regression
<br />equations range from 24 to 45 percent.
<br />
<br />Procedure
<br />
<br />Topographic maps and the following equations
<br />are used to estimate the needed peak discharges QT, in
<br />cubic feet per second, having selected recurrence inter-
<br />vals T.
<br />
<br />QIO = 144 A 0.528 SbOJ36
<br />Q50 = 891 AO,482 SbO,l54
<br />Qloo = 1,770 A 0,463 SbO,086
<br />Q500 = 5,770 A 0,432
<br />
<br />Reference
<br />
<br />McCain, J.E, and Jarrett, R.D., 1976, Manual for estimating
<br />flood characteristics of natural-flow streams in
<br />Colorado: Colorado Department of Natural Resources
<br />Technical Manual No, I, 68 p,
<br />
<br />COLORADO FRONT RANGE
<br />
<br />Summary
<br />
<br />A multidisciplinary study of precipitation, and
<br />streamflow data, and paleoflood studies of channel fea-
<br />tures was made to analyze the flood hydrology of foot-
<br />hill and mountain streams in the Front Range of
<br />Colorado (South Platte River basin above the conflu-
<br />ence of Cache La Poudre, fig. 2). The regression equa-
<br />tions were developed for estimating peak discharges
<br />(QT) having recurrence intervals T that range from 2 to
<br />500 years, The only explanatory basin variable used is
<br />the drainage area (AB8), in square miles, below 8,000
<br />feet. The area above 8,000 feet is shown in figure 2 as
<br />a guide in determining AB8. The standard errors of
<br />estimates of the regression equations range from 42 to
<br />100 percent.
<br />
<br />Procedure
<br />
<br />For the South Platte River basin above the con-
<br />fluence of Cache La Poudre with South Platte River,
<br />use topographic maps and the following equations to
<br />estimate the needed peak discharges QT, in cubic feet
<br />per second, having selected recurrence intervals T,
<br />
<br />Q2 = 36.9 (AB8)O,61
<br />QIO = III (AB8)O,75
<br />Q50 = 231 (AB8)O,83
<br />Qloo = 302 (AB8)O,86
<br />Q500 = 533 (AB8)O,92
<br />
<br />Reference
<br />
<br />Jarrett, R.D"and Costa, J.E" 1988, Evaluation of the flood
<br />hydrology in the Colorado Front Range using
<br />precipitation, streamflow, and paleoflood data for the
<br />Big Thompson River basin: V.S, Geological Survey
<br />Water,Resources Investigations Repon 87-4117, 37 p.
<br />
<br />COLORADO 43
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