|
<br />000245
<br />
<br />ungaged and on whether the drainage area upstream
<br />from a site crossed a hydrologic region boundary.
<br />This study differs from most of the previous flood-
<br />frequency studies in areal coverage. number of gaging
<br />stalions used. and lengths of streamflow records used.
<br />Data used in the study were from previous flood-
<br />frequency studies. about 2,700 additional years of
<br />gaging-station record through waler year 1993, and
<br />64 additional gaging stations. Only one gaging station
<br />per stream was used unless the drainage area of a
<br />downstream gaging station was greater than about
<br />2.5 times the drainage area of the upstream gaging
<br />station.
<br />Flood-frequency curves were detennined for
<br />328 gaging stations on unregulaled streams having
<br />at least 10 years of record based on a Log-Pearson
<br />Type III probability distribution. Historical adjust-
<br />ments to the recorded gaging-station data were used
<br />where applicable. and low outliers were deleted using
<br />the low-outlier lest recommended by the lACWD
<br />(1982). The regional regression equations discussed in
<br />this report relate flood magnitude to easily measured
<br />drainage-basin and climatic characteristics. The study
<br />area was divided into five distinct hydrologic regions
<br />because basin physiography and climale differ greatly
<br />throughout the area: the mountain. Rio Grande, south-
<br />west. northwest, and the plains regions. Separate
<br />regression equations for estimating peak discharges
<br />were developed for each of these five regions for
<br />recurrence intervals of 2, 5, 10, 25. 50, 100, 200, and
<br />500 years.
<br />An OLS regression was used for preliminary
<br />delineation of flood regions and selection of statisti-
<br />cally significant explanatory drainage-basin and
<br />climatic characteristics. GLS regression analysis
<br />was used to compute the final regression equations.
<br />Drainage area was the most statistically significant
<br />variable in all of the regression equations. Other statis-
<br />tically significant variables were mean annual precipi-
<br />tation and mean drainage-basin slope. Application of
<br />the regression equations to sites having drainage-basin
<br />characteristics outside the range of those used in the
<br />study may provide unreliable results.
<br />Methods are presented for determining the
<br />magnitude of peak discharges for sites located at
<br />gaging stations, for sites located near gaging stalions
<br />on the same stream when the ratio of drainage-basin
<br />areas is between about 0.5 and 1,5, and for sites where
<br />the drainage basin crosses a flood-region boundary or
<br />a State boundary,
<br />
<br />12 Analysis of the Magnitude and Frequency of Floods in Colorado
<br />
<br />.,
<br />
<br />REFERENCES CITED
<br />
<br />(;,-:
<br />(;,.\
<br />C
<br />c:
<br />C
<br />C
<br />C:I
<br />C
<br />C ~I
<br />c'
<br />c,
<br />C"
<br />,
<br />Ct
<br />C[I
<br />C-r
<br />C1
<br />e:1
<br />e,
<br />,
<br />ef
<br />e[
<br />et
<br />e[
<br />e.
<br />I
<br />e'
<br />~
<br />e
<br />e
<br />e
<br />e
<br />e
<br />e-:
<br />e
<br />e
<br />e
<br />~
<br />~
<br />~.
<br />~
<br />~
<br />~
<br />~.
<br />~
<br />i..'
<br />
<br />Asquith. W.H.. and Slade. R.M.. Jr.. 1997, Regional equa-
<br />tions for estimation of peak-streamflow frequency for
<br />natural basins in Texas: U.S. Geological Survey Waler-
<br />Resources Investigations Report 96-4307, 68 p.
<br />Clement, R.W., 1987. Floods in Kansas and techniques for
<br />estimating their magnitude nnd frequency on unregu-
<br />lated streams: U.S. Geological Survey Water-
<br />Resources Investigations Report 87--4008. 50 p.
<br />Flynn. K.M.. Hummel. P.R.. Lumb. A.M.. and Kittle. J.L.. Jr.,
<br />1995, User's manual for ANNIE, version 2. a computer
<br />program for interactive hydrologic data management:
<br />U.S. Geological Survey Waler-Resources Investigations
<br />Report 95--4085, 211 p.
<br />Hedman, E.R., Moore, D.O., and Livingston, R.K.. 1972.
<br />Selected streamflow characteristics as related to
<br />channel geometry of perennial streams in Colorado:
<br />U.S. Geological Survey Open-File Report 72-160.
<br />24p.
<br />Interagency Advisory Committee on Water Data. 1982,
<br />Guidelines for detennining flood flow frequency:
<br />Hydrology Subcommittee Bulletin 17B. 183 p.
<br />Jarrett. R.D.. and Costa, J.E.. 1988, Evaluation of the flood
<br />hydrology in the Colorado Front Range using precipi-
<br />tation. streamflow. and paleoflood data [or the Big
<br />Thompson River Basin: U.S. Geological Survey
<br />Water-Resources Investigations Report 87--4117, 37 p.
<br />Kircher, J.E.. Choquette. A.F.. and Richter, B.D.. 1985, Esti-
<br />mation of natural streamflow characteristics in westem
<br />Colorado: U.S. Geological Survey Water-Resources
<br />Investigations Report 85--4086. 28 p.
<br />Livingston. R.K., 1970, Evaluation of the streamflow-data
<br />program in Colorado: U.S. Geological Survey Open-
<br />File Report 71-182, 72 p.
<br />Livingston, R.K., and Minges. D.R., 1987, Techniques
<br />for estimating regional flood characteristics of small
<br />rural watersheds in the plains of eastern Colorado:
<br />U.S. Geological Survey Water-Resources Investiga-
<br />tions Report 87--4094.72 p.
<br />Lowham. H.W.. 1988, Streamflow in Wyoming: U.S.
<br />Geological Survey Water-Resources Investigations
<br />Report 88--4045. 84 p.
<br />Matthai. H.E. 1968. Magnitude and frequency of floods in
<br />the United States-Part 6-B, Missouri River Basin
<br />below Sioux City, Iowa: U.S. Geological Survey
<br />Water-Supply Paper 1680,491 p.
<br />McCain, J.F.. and Jarrett. RD.. 1976, Manual for estimating
<br />flood characteristics of natural-flow streams in Colo-
<br />rado: Colorado Water Conservation Board Technical
<br />Manual I, 68 p.
<br />
|