FLOOD04236

• Designation Number: 421
• County: Arapahoe
• County: Adams
• Community: Aurora
• Stream Name: Coyote Run, Upper Box Elder Creek
• Basin: South Platte
• Title: FHAD - Coyote Run and Upper Box Elder Creek
• Date: 12/1/1995
• Prepared For: Aurora / Arapahoe County / Adams County
• Prepared By: UDFCD
• Floodplain - Doc Type: Floodplain Report/Masterplan

Section 1.0
Introduction

1.4 Mapping

The UDFCD provided I-inch to 200 feet, 2-foot contour interval mapping of the FHAD
study areas, This mapping was produced by Landmark Mapping under separate
agreement with UDFCD, Mapping for the remainder of the study area consisted of
United States Geological Survey (USGS) quadrangles.

1.1 Authorization

This study was authorized by the Urban Drainage and Flood Control District (UDFCD),
the City of Aurora, Arapahoe County, and Adams County under UDFCD Agreement
No, 92-11.06 dated October 7, 1993. CH2M HilL was retained to complete the scope of
work summarized in subsection 1.3, This Flood Hazard Area Delineation Report (FHAD)
comprises one of the final report deliverables for the overall study. The other is the
Preliminary Design Report showing the selected Outfall Systems Plan for the study area.

1.5 Background Information

Background information provided by the sponsors and others was used to develop the
hydrology and alternative analyses, Information provided is identified below and is listed
in Section 5, References,

1.2 Purpose

The purpose of the study is to provide local jurisdictions with regulatory floodplain maps
and floodway data for dealing with land development activities, Land development
pressure is increasing in the area because of the construction of Denver International
Airport.

1.3 Scope of Work

The scope of work includes a hydrologic and alternative analysis of the study area shown
in Figure 1-1. The original scope included a FHAD for the Coyote Run Tributary.

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Urban Drainage and Flood Control District (CCWCD, 1987) (CaE, 1989)
City of Aurora (Aurora, 1989) (Adams County, et al" 1990) (Aurora,
1993)
Arapahoe County (FEMA, 1993)
Adams County (FEMA, 1989)
Colorado Water Conservation Board (WRC, 1979)

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1.6 Project Advisory Committee

A project advisory committee was formed at the outset of the study to obtain input from
as many interested organizations as possible, In addition to the project sponsors, the
following organizations were notified of the project, invited to project meetings, and
received meeting minutes:

Following is a summary of the scope of work:

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Meet periodically with the project sponsors to exchange information and
discuss project progress and direction,

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Complete a review of all relevant data,

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Complete a field reconnaissance.

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Estimate existing and future development condition peak discharges and
volumes for the 2-, 5-, 10-, 50-, 100-, and 500-year storm events,

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Conduct hydraulic analysis to determine 10-year and 100-year water surface
elevations and delineate floodplain boundaries,

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Analyze floodways based on encroachments yielding maximum increases in
energy gradeline of 0,5 feet and 1,0 feet.

Of these, staff from the first six organizations attended project meetings and provided
input during the hydrologic and alternative evaluation phase of the study,

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Colorado Water Conservation Board
Federal Emergency Management Agency
Colorado State Land Board
Central Colorado Water Conservancy District
Colorado Department of Transportation
Henrylyn Irrigation District
North Front Range Water Quality Planning Association
Soil Conservation Service
Colorado Division of Wildlife
U.S, Army Corps of Engineers
Colorado Water Quality Control Division
U.S, Environmental Protection Agency

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Seventeen project meetings were held between October 26, 1993 and June 20, 1995 to
discuss results and solicit input from the advisory committee,

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