FLOOD07371

• County: Jefferson
• Community: Arvada
• Basin: South Platte
• Title: Ralston/ Leyden Creeks Hydrology Report
• Date: 8/1/2002
• Prepared For: UDFDC
• Prepared By: Boyle Engineering Corporation
• Floodplain - Doc Type: Floodplain Report/Masterplan

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BO~LE

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215 Union Blvd" Suile 500
Lakewood, CO 80228
TEL: [phone]
FAX: [phone]
www.boyleengineering.com

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August 2 I, 2002

Mr. David Lloyd, P,E,
Chief, Capital Construction Program
URBAN DRAINAGE AND FLOOD CONTROL D1STRlCT
2480 W. 26th Ave" Suite IS6B
Denver, CO 80211

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Ralston/Leyden Creeks Hydrology Update and Flood Hazard Area Delineation
UDFCD Agreement No. 01.10.04
Boyle Project No, DN.U02.770.01

Dear Dave:

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Boyle Engineering Corporation is pleased to submit the attached hydrology report, which updates the
hydrology model for the Ralston Creek watershed, including Leyden and Van Bibber Creeks, This model
has been prepared using CUHP and SWMM, and is intended to replace the previous model, which used
MITCAT,

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This report summarizes the hydrologic evaluation for the watershed, As directed, we have prepared two
models for the watershed, The first model represents future conditions without Leyden Lake or the
Arvada/Blunn Reservoir; this model can be used for calibration purposes for comparison to the previous
study, The second model adds effects from Leyden Lake, which was recently upgraded, and the
Arvada/Blunn Reservoir. These reservoirs were not included in the previous study, but the effects of the
lakes can be used for reduction of the floodplain extents, The peak flows are reported for the 10-, 50-,
100-, and 500.year storm events for each model. The hydrologic results will be used to prepare a Flood
Hazard Area Delineation in the next phase of this project.

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We have enjoyed working with the project sponsors throughout the preparation of this report,

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Sincerely,

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Boyle Engineering Corporation

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Kevin Houck, P,E,
Proj ect Engineer

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