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FLOOD06253
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FLOOD06253
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Last modified
1/25/2010 7:08:23 PM
Creation date
10/5/2006 2:07:37 AM
Metadata
Fields
Template:
Floodplain Documents
County
Boulder
Community
Longmont
Stream Name
St. Vrain/Lefthand Creeks
Basin
South Platte
Title
Floods on St. Vrain and Lefthand Creeks at Longmont, CO
Date
11/30/1962
Prepared For
County of Boulder
Prepared By
USGS
Floodplain - Doc Type
Flood Documentation Report
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<br /> <br />; <br /> <br />A similar procedure can be used to estimate depths of flow of <br /> <br /> <br />the 50-year flood in the main channel and in parts of the flood plain; <br /> <br /> <br />but because of the comprex cross flow and the effects of local <br /> <br /> <br />vagaries of topography, water-surface elevations of the 50-year flood <br />in most of the flood plain will have little or no relation to ele- <br />vations at the thalweg, and further, cannot be predicted with acceptablE <br />accuracy, except to say that depths will be generally less than 2 feet. <br />However, elevations and depths of flow over the highway embankments <br /> <br />and immediately upstream from them can be estimated. The values at <br /> <br /> <br />points shown by the capital letters on plate 2 for the. 50-year flood <br /> <br /> <br />are tabulated in table 3, p. 25. Depths over embankments are measured <br /> <br /> <br />from the low point of the centerline of the road; depths upstream <br /> <br /> <br />from the embankment are measured from the general elevation of the <br /> <br /> <br />ground. <br /> <br />Velocities of Flow <br />Point velocities of flow Will range from less than 1 fps (foot <br />per second) in the flood plain above some of the embankments to <br />more than 20 fps in the main channel for the 50-year flood at the <br />downstream side of the bridge at Hover Road. Velocities on the <br />flood plain for both floods generally will be low, except where <br />the geometry of constrictions has appreciable effect on the flow <br /> <br />pattern. <br /> <br />Effects of Alterations <br />The natural flow pattern of St. Vrain Creek in the study area <br /> <br />24 <br /> <br />
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