FLOOD08569

• Designation Number: 574
• County: Jefferson
• Community: Arvada
• Stream Name: Ralston Creek and Leyden Creek
• Basin: South Platte
• Title: FHAD - Ralston Creek and Leyden Creek
• Date: 6/1/2004
• Prepared For: Douglas County, Arvada
• Prepared By: UDFCD
• Floodplain - Doc Type: Floodplain Report/Masterplan

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BOIrILE

215 Union Blvd., Suite 500
Lakewood. CO 80228
TEL: [phone]
FAX: 13031987-3908
www.boyleengineering.com

June 28. 2QO..1

~1r. David Lloyd. P.E.
Chief, Capital Construction Program
URBAN DRAINAGE AI'D FLOOD CONTROL DISTRICT
2-1.80 W. 26th Ave., Suite 1568
Denver. CO 80211

J{alstnnlLl'~'dt'n Cn'eks Flood lIaz.ud Area ()l'lint:'ation
UnFeD Agn.'t'nu'nl i\"o. 01-10.04
Bo~'le Prujl'"Ct :-\0. I>!','-C02-770-01

Dear Dave:

Boyle Engineering CO'l1oration is pleased to suhmlt the aHachcd Flood Hazard Area Delineation
(fHAD) report. whkh update~ Iloodplain infomlalion of Ralston Creek from the Ar\'uda/Blunn
reservOIr 10 Its conllucncc with Clear Creek and Leyden Creek from Leyden Lake to Its conllucncc with
Ralston Creek. This report utilizes the revised hydrology based on the conversion from ~nTCAT to
CUHP and SW:-'11\1. and the hydraulics of the Slreams for "future basin conditions:" Hydrologic data
were developed under the "RalstonfLeydl:n Hydrology Report" dated April 2003 (Updated).

This report provides updated hydraulic information for Ralston and Leyden creeks based on the
inclusion of the ArvadalBlunn reservOir and Leyden Lake. Leyden Lake was recently upgraded from a
water storJge facility to J flood control facility. but the Arvada/Blunn reservoir remains a ""ater storage
facility With flood attenuation benefits. It is proposed to raise the ArvadaIBlunn reservoir by 5 feet
using a Labyrinth Weir. II is assumed. based on preliminary studies. that this improvement will not
impact the FHAD. These reservoirs were not previously included in FE:-'lA flood studies. but can now
utilize the attenuating affects to reduce lhe floodplain extents downstream.

We wish to express our appreciatIon to Mr. Dave Lloyd and ~lr. Bill DeGroot of the District staff,:V1r.
Patrick Dougherty and Ms. Georgia Simpson of the Cil)' of Arvada. and ~ls. Paula Lundquist of
Jefferson County for their assistance and attention during the preparation of this report.

Sincerely.

Boyle Engineering Corporation
I( ) C . ,L.
_[vyrtU- r 0-'- LLit i';

Douglas P. Stewart. P.E.
Project ~1anagcr

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BOYLE ENGINEERING CORPORATION

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