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<br />Northwest Region
<br />
<br />Q2 = 0.795 A 0,820 p100
<br />Q5 = 1.86 AO,794 pO,871
<br />QIO = 2,86 AO,78! pO,802
<br />Q25 = 4.45 AO,768 pO.732
<br />Q50 = 5.90 A 0,759 pO.686
<br />QIOO= 7.54 AO,752 pO.646
<br />Q200= 9.49 AO,745 pO,609
<br />Q500 = 12.4 A 0.737 pO.565
<br />
<br />Reference
<br />
<br />Kircher, ],E., Choquette, A,F., and Richter, B.D" 1985, Esti-
<br />mation of natural streamflow characteristics in western
<br />Colorado: U,S. Geological Survey Water-Resources
<br />Investigations Repon 85-4086, 28 p,
<br />
<br />Additional Reference
<br />
<br />U,S. Weather Bureau, 1967, Normal annual precipitation.
<br />normal May,September precipitation 1931-60,
<br />Colorado: U,S, Weather Bureau map (Available from
<br />the Colorado Water Conservation Board),
<br />
<br />EASTERN COLORADO, PLAINS REGION
<br />(DRAINAGE AREAS LESS THAN 20 M12)
<br />
<br />Summary
<br />
<br />Eastern Colorado is treated as a single (Plains)
<br />hydrologic region for drainage areas less than 20 mi2;
<br />the sand-hill areas are excluded (fig. I). The regression
<br />equations developed for this hydrologic region are for
<br />estimating peak discharges (QT) having recurrence
<br />intervals T that range from 5 to 100 years, The basin
<br />explanatory variables used in the equations are effec-
<br />tive drainage area (AE), in square miles, which is the
<br />total drainage area minus the area upstream from all
<br />erosion-control or flood-retention structures; relief fac-
<br />tor (RF), in feet, computed as the altitude difference
<br />between that for the highest point within the effective
<br />drainage area and that of the study site minus 18; and
<br />(124-] (0) which is the 100-year 24-hour rainfall, in
<br />inches, The constant 18 is suhtracted from RF in the
<br />equations, The user should enter the actual value of RF
<br />The variables AE and RF can be measured from topo-
<br />graphic maps, and 124-100 can be determined from fig-
<br />
<br />ure 2. The regression equations were developed from
<br />rainfall-runoff data collected at 35 gaging stations
<br />operated in Colorado from ] 969 through ] 979, on
<br />peak-discharge data available for] 7 gaging stations in
<br />adjoining States, and on long-term climatological
<br />records.
<br />The regression equations are applicable to
<br />streams with effective drainage areas ranging from 0.3
<br />to 20 square miles, Standard errors of estimate of the
<br />regression equations range from 36 to 47 percent using
<br />the three basin variables. Standard errors range from 39
<br />to 5] percent when only effective drainage area is
<br />included in the regression equations, Both sets of
<br />regression equations are provided in the following sec-
<br />tions.
<br />The report includes a relation for estimating
<br />flood volume from peak discharge, Also included is a
<br />dimensionless-hydrograph technique that produces
<br />synthetic flood hydrographs very similar in shape to
<br />recorded flood hydrographs. Some information on
<br />rainfall-runoff data in the Plateau Region of western
<br />Colorado is also included.
<br />
<br />Procedure
<br />
<br />Topographic maps, the lOO-year 24-hour rainfall
<br />map (fig, 2) and the following equations are used to
<br />estimate the needed peak discharges QT, in cubic feet
<br />per second, having selected recurrence intervals T,
<br />
<br />Log Q5 = 2.56 + 0,57 (Log RF)(Log 124-1 (0) -
<br /> 1.09 AE,O,25
<br />Log QIO = 3,05 + 0.53 (Log RF)(Log 124-1(0)-
<br /> 1.29 AE,o,25
<br />Log Q25 = 3.64 + 0.45 (Log RF)(Log 124-](0)-
<br /> 1.53 AE"O,25
<br />Log Q50 = 4,03 + 0.39 (Log RF)(Log 124- I (0) -
<br /> 1.70 AE-Q,25
<br />Log QlOO = 4.41 + 0.33 (Log RF)(Log 124-] (0) -
<br /> 1.85 AE"O,25
<br />
<br />Reference
<br />
<br />Livingston, R. K" and Minges, D. R" 1987, Techniques for
<br />estimating regional flood characteristics of small rural
<br />watersheds in the plains region of eastern Colorado:
<br />U,S. Geological Survey Water-Resources Investiga,
<br />tions Repon 874094, 70 p.
<br />
<br />42 Nationwide Summary of U.S. Geological Survey Regional Regression Equations for Estimating Magnitude and Frequency ot
<br />Floodolor Ungogod Siteo, 1993
<br />
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