BOARD01402

• Board Meeting Date: 5/16/2006
• Description: Flood Section - Consent Agenda 2A2B - Flood Area Delineation, Massey Draw, SJCD, for UDFCD, Jefferson County, City of Littleton, Clear Creek, Adams County,CDOT
• Board Meetings - Doc Type: Memo

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profiles. CWCB staff performs technical reviews on the following types of reports and maps for
approval and designation by the Board:

. "Flood Insurance Study" (FIS), which is produced by the Federal Emergency Management Agency
(FEMA) and used for floodplain management, regulation, and insurance purposes.
. "Flood Insurance Rate Map" (FIRM), which is produced by FEMA and used for floodplain
management, regulation, and insurance purposes, A FIRM may be published with or without an
associated hydrologic and hydraulic report,
. "Flood Hazard Boundary Map" (FHBM), which was produced by the Federal Insurance
Administration and are used for floodplain management, regulation, and insurance purposes. An
FHBM usually depicts approximate floodplain boundaries only, and does not have an
accompanying report. Note: For all FHBM designations, the CWCB staffwill perform (in-house or
by contract with a consultant) hydrologic analyses.
. "Floodplain Information Report", which is produced by local governments, state and federal
agencies, special districts, or the private sector, and are used for floodplain management purposes
and sometimes adopted by FEMA for use in Flood Insurance Rate Map revisions.
. Various hydrology studies and related floodplain studies (community-wide or site specific) that
depict 100-year floodplain information that is useful for floodplain management purposes.
. "Floodplain Information" is a generic term used to describe any ofthe above types of reports and/or
maps in the CWCB's "rules and regulations..."
. "Floodplain Resolution" is a formal document prepared by CWCB staff describing the Floodplain
Information that is to be designated and approved by the Board.

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1) Consent Al!enda Item 2.a
Floodplain resolution number: FPR 06-588
Affected communities: Jefferson County, City of Littleton
Name of study to be formally acted on: "Flood Hazard Area Delineation, Massey Draw and SJCD
(South)" dated December 2005.
Studied streams: Massey Draw and SJCD (South)
Technical Issues: This report was authorized by the Urban Drainage and Flood Control District
(UD&FCD), Jefferson County, and the City of Littleton to update flood hazard data for the subject stream
reaches, to produce new plan and profile information for the 100-year floodplains, and to define
floodways for the subject stream reaches. The total study area includes 12.4 square miles of drainage area
in the southwest portion of the Denver Metro region. The Colorado Urban Hydrograph Procedure
(CUHP) program was used to develop rainfall-runoff hydrographs with flow routing done using the
Urban Drainage Stormwater Management Model (UDSWM), Hydraulic analyses were carried out using
the U.S. Army Corps of Engineers River Analysis System (HEC-RAS) based on steady flow conditions.
Floodways were computed assuming both 0.5' and 1.0' rise criteria. The CWCB and the UD&FCD plans
to include this new information within the Jefferson and Arapahoe County Digital Flood Insurance Rate
Maps that are now in progress.
Community response: The UD&FCD transmitted a letter to the CWCB dated February 8, 2006 and
Jefferson County transmitted a letter dated February 21, 2006 requesting CWCB designation and approval
of the subject report. No letter has been received from the City of Littleton, but they have indicated in
verbal conversations that they also desire designation and approval. The UD&FCD also sent follow-up
emails to staff regarding the proposed designation action. The UD&FCD staff worked directly with the
affected communities during the course of the study and received input and endorsement for the study

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Flood Protection. Water Project Planning and Financing. Stream and Lake Protection
Water Supply Protection. Conservation Planning

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