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Last modified
1/25/2010 7:13:26 PM
Creation date
10/5/2006 3:22:46 AM
Metadata
Fields
Template:
Floodplain Documents
County
Statewide
Basin
Statewide
Title
Techniques for Estimating the Magnitude and Frequency of Floods in Minnesota
Date
1/1/1988
Prepared For
USDOT
Prepared By
USGS
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />The length of the main channel is measured to be 1.49 miles to the end of <br />the watershed divide. <br /> <br />Elevation at mile 0.15 (10% of channel length) is 1,212 ft <br /> <br />Elevation at mile 1.27 (85% of channel length) is 1,235 ft <br /> <br />Main channel slope is (1235-121Z)/1.12 - ZO.5 ft/mi. <br /> <br />7. Region D equation for 25-year flood (table 1): <br />QZ5 19.5AO.723(St+l)-0.409S0.347RO.801 <br /> <br />Q25 19.5(1.28)0.723(2.6)-0.409(20.5)0.347(3.0)0.801 <br /> <br />QZ5 19.5xl.195x.6765x2.852x2.411 <br />Q25 108 ft3/s (3.06 m3/s) <br /> <br />Although the discharge is reported to three significant digits, the <br />accuracy of the estimating technique does NOT warrant confiden~e to this <br />de~ree of accuracy. The 95-percent confidence limits are 40 ft /s to 290 <br />ft /s. <br /> <br />Transfer of Flood-Flow Information from a Ga2ed Site <br /> <br />The flood characteristics defined by frequency analyses of gaging-station <br />records listed in tables 2 through 5 (tables 2 - 5 are at end of the report) <br />provide estimates for ungaged locations near a station, particularly '.here <br />10ng- term records are available. Transfer of defined flow- frequency infor- <br />mation to upstream or downstream sites on the same stream should be accom. <br />plished by an adjustment factor that is a function of the basin character- <br />istics showing significant intrabasin variation. The transfer equation may be <br />a function of several characteristics; however, the equation always includes <br />drainage area. Consequently, frequency data are transferred most often using <br />the following equation: <br /> <br />QT,u - QT,g(~/Ag)B <br /> <br />where: <br /> <br />QT u is the T-year flood-magnitude estimate for the ungaged site, <br />, <br />QT,g is the computed T-year flood-frequency value for the gaged <br /> site (from tables Z to 8), <br />~ is the drainage area for the ungaged site, <br />Ag is the drainage area for the gaged site (from tables 2 to 8), <br /> and <br /> <br />B is the exponent for drainage area for the T-year flood obtained <br />from the regression equation for the region in which the site <br />is located. <br /> <br />13 <br />
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