FLOOD05101

• County: Elbert
• Community: Elizabeth
• Stream Name: Elizabeth Drainage
• Basin: Arkansas
• Title: Elizabeth Drainage Study Hydrologic Analysis
• Date: 7/1/1979
• Prepared For: State of Colorado
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Hydrologic Procedures

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The first step in the hydrologic analysis is to establish the amount and

pattern of rainfall to be expected for the 5-, 10-, 50-, and 100-year frequency

storms. The National Weather Service has published rainfall data for the area

which relates rainfall depth, duration, and frequency. This data was analyzed

to produce realistic rainstorms for each rainstorm frequency.

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The soils in the watershed have been catalogued by the SCS in a draft report
for the western part of Elbert County according to their hydrologic properties.
This information was used to estimate infiltration rates for the various soils
in Elizabeth, Infiltration rates in combination with vegetal cover and the
percentage of impervious area establishes a rainfall-runoff relationship for
each drainage sub-has in. The various frequency rainstorms are then applied and
the resulting runoff is computed.

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Storm hydrographs were computed for all design points affected by the deten-

tion reservoir, The hydrographs provide a continuous reading of discharge at

any time during a storm, Thus, the lagging of peak flows due to the effect of

the reservoir is accurately reflected in the peak flow computat~ons downstream,

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