FLOOD01635

• Designation Number: 558
• County: Douglas
• Community: Douglas County Unincorporated
• Title: Flood Hazard Area Delineation - Plum Creek Watershed
• Date: 11/1/2001
• Designation Date: 1/2/2002
• Prepared By: UDFCD, WRC Engineering
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Mr. Bill DeGroot, PE
WRC File: 2048/21
September 28, 2001
Page 2

November 9, 2001

floodplain limits delineated herein, except Plum Creek itself, are based upon future flood hydrology and current channel
conditions, The floodplain limits for Plum Creek utilize the current effective FEMA flood hydrology as presented in the
effective FIS.

Mr, Bill DeGroot, PE
Urban Drainage & Flood Control District
2480 West 26th Avenue, Suite 156-B
Denver, Colorado 80211

WRC File: 2048/21

The floodplain and floodway information provided herein should assist Douglas County in administration of
floodprone areas to maintain and improve channel capacity for the I DO-year flood event,

RE: Plum Creek Watershed
Flood Hazard Area Delineation Report

Dear Mr. DeGroot: '

We appreciate the opportunity to prepare this floodplain and floodway delineation for the Plum Creek Watershed,

Enclosed herein is the Flood Hazard Area Delineation report for the Plum Creek Watershed. This report
docunients the Flood Hazard Area Delineation process from initiation through fmal floodplain and floodway delineations.
This report was prepared in conjunction with Outfall Systems Planning of the Plum Creek Watershed. This report
presents a synopsis of the project history, description of the study area and field inventory, summary of hydrology and
hydraulics analysis, evaluation of capacities of existing facilities (i.e., bridges, culverts, detention ponds), HECRAS water
surface profile computer modeling for the 10-,50-,100- and'500-year storm events, and determination of 0.5 foot and
1.0 foot rise floodways,

Respectfully Submitted,

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WRC ENGINEERING, INC.

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Alan J. Leak, P.E.
Principal-In-Charge

The Plum Creek Watershed consists generally of open prairie and large lot development. The exception to this
is along Plum Creek itself where industrial and commercial development occurs along U.S. Highway 85 and at the Towns
of Louviers and Sedalia. The major drainageways are almost exclusively open natural or grass-lined channels with
culverts or bridges at street and railroad crossings. The 1 DO-year floodplain is contained within the main channel and
large overbank areas for a majority of the drainageways. A notable exception to this occurs north of Titan Road on Plum
Creek. At this location, a significant amount of private property and/or buildings (homes) are encompassed in the 100-
year floodplain,

The 1 DO-year floodplains for portions of the Plum Creek Watershed were delineated as part of a Flood Insurance
Study (FIS) prepared for the Federal Emergency Management Agency (FEMA) in 1973, Channel aggregation and
increases in drainageway vegetation have resulted in changes in the I DO-year floodplain limits, The 1 DO-year

AlL/ell

CONSULTING ENGINEERS

950 SOUTH CHERRY STREET. SUITE 404 . OENVER. COLORADO 80246 . [phone] . FAX [phone] 'wrce@wrcen9,com