FLOOD07750

• Designation Number: 448
• County: Arapahoe
• Community: Unincorporated Arapahoe County
• Stream Name: Big Dry Creek
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Big Dry Creek & Tributaries
• Date: 11/1/1996
• Designation Date: 3/1/1997
• Floodplain - Doc Type: Floodplain Report/Masterplan

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w~c C'N6INC'C'~ING, I~c.

Mr. Bill DeGroot. P.E.
November 19, 1996
WRC File: 1913/46
Page 2

November 19, 1996

The Big Dry Creek and Tributaries 100-year floodplain was first delineated in 1975. Significant
changes in development patterns, construction of regional detention facilities, and increases in drainageway
vegetation have resulted in changes in the 100-year floodplain limits. The 100-year floodplain limits
delineated herein are based upon the most probable flood hydrology and Current channel conditions.

Mr. Bill DeGroot, P.E.
Urban Drainage & Flood Control District
2480 West 26'" Avenue, Suite 156-B
Denver, Colorado 80211

The floodplain and flood way information provided herein should assist the various local communities
in administration of floodprone areas to maintain and improve cbannel capacity for the 100-year flood event.

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WRC File: 1913/46

RE: Big Dry Creek (ARAPCO) and Tributaries
Flood Hazard Area Delineation Report

We appreciate the opportunity to prepare this floodplain and floodway delineation for Big Dry Creek
and Tributaries.

Dear Mr. DeGroot:

Respectfully Submitted,

Enclosed herein is the Flood Hazard Area Delineation report for Big Dry Creek (ARAPCO) and
Tributaries. This report documents the Flood Hazard Area Delineation process from initiation through final
floodplain and floodway delineations. This report was prepared in conjunction with Major Drainageway
Planning of Big Dry Creek and Tributaries. This report presents a synopsis of the project history, description
of the srody area and drainageway field inventory, summary of project bydrology and hydraulics, evaluation
of capacities of existing facilities (i.e. bridges, culverts, detention ponds), HEC-2 water surface profi!e
computer modelling for the 10-, 50-, and 100-year storm events, and determination of 0.5 foot and 1.0 foot
rise floodways.

WRC ENGINEERING, INC.

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The Big Dry Creek watershed consists generally of existing urban development north of South
University Boulevard (in Highlands Ranch) and rapidly urbanizing areas south of South University Boulevard.
The major drainageway is almost exclusively open naroral or grass-lined channels with culverts at street
crossings. The 100-year floodplain is contained within the main channel and large overbank arc... for a
majority of the drainageway. Notable exceptions to this occur from the South Platte River to upstream of
South Windermere Street, from Orchard Road to upstream of South Franklin Street, and from the Julia
DeKovend Park to Arapahoe Road. At these locations, a significant amount of private property and/or
buildings (homes) are encompassed in the 100-year floodplain.

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Bruce J. Buttner, P.E.
Principal-In-Charge

1I119/q6

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Alan J. Leak, P.E.
Project Manager

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CONSULTING ENGINEERS

950 SOUTH CHERRY STREET. SUITE 404. DENVER, COLORADO 80222. [phone]. FAX [phone]