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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I. INTRODUCTION

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Methods of Analysis

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The
lOa-year
reaches,

hydrologic analysis was performed to establish the 5-, 10-, 50-, and
frequency flood discharges at a number of points along the study
This analysis is based on anticipated future development conditions

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in the town. Town zoning maps and eva1uationof existing development densities

were used to establish the future runoff potential.

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The Soil Conservation Service (SCS) procedure described in "Urban Hydrolo-

gy for Small Watersheds" - Technical Release No. 55 was used to predict flood

magnitudes. This method was developed specifically to analyze'the effects of

urbanization on rainfall-runoff relationships.

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Continued urbanization of open space in the watershed increases the imper-

vious area and thereby increases peak rates of runoff, The volume of runoff

is determined by the amount of rainfall and by infiltration rates related to

soil type, type of vegetal cover, impervious surfaces, and surface retention.

The travel time of the peak flow from a given location to a downstream point

is controlled by slope, flow length, depth of flow, and the channel surface

roughness. Peak rates of flow are based on the relationship of the above

parameters as well as the drainage area.

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Procedures outlined 1.n the SCS National Engineering Handbook, Section 4,

Hydrology were also used to derive hydrographs of runoff where necessary.

Runoff hydrographs were developed to evaluate the effects of the on-stream

detention reservoir on peak flows, Each hydrograph was routed through the

reservoir and added to hydrographs developed at a number of downstream loca-

tions to determine peak flows,

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