BOARD01784

• Board Meeting Date: 11/16/2004
• Description: Flood Section - Floodplain Information to be Designated
• Board Meetings - Doc Type: Memo

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Technical Issues: This report was authorized by the Urban Drainage and Flood Control District
(UD&FCD) and Douglas County to update flood hazard data for the subject stream reaches and to
produce new plan and profile information for the 100-year floodplains. The total study area includes just .
over II square miles of drainage area in the southern portion of the Denver Metro region. The CUHP
program was used to develop rainfall-runoff hydrographs with flow routing done using UDSWM.
Hydraulic analyses were carried out using HEC-RAS prepared 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 Douglas County Digital Flood Insurance Rate Map that is now
in progress.
Community response: The UD&FCP transmitted a letter to the CWCB dated July 21, 2004 and
Douglas County transmitted a letter dated June 8, 2004 requesting CWCB designation and approval of the
subject report. 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 methods and results. CWCB staff concurs with the
UDFCD request for designation and approval of the study.
Staff findings: CWCB staffhas determined that the subject IOO-year detailed floodplain information for
the studied stream reaches is conformance with the CWCB' s rules and regulations for floodplain
designation and approval. The CWCB staffhas relied on the technical competence ofWRC Engineering
that produced the study and the technical review by the UD&FCD and local sponsors, and therefore
endorses this study as containing the most current floodplain mapping available and urges the affected
communities to adopt said study for land use regulation purposes pursuant to statutory authority.
Staff recommendation: Staff recommends that the Board: I) designate and approve the IOO-year detailed
floodplain information contained in said report within Douglas County and 2) authorize staff to prepare a
floodplain resolution to be signed by the Director and transmitted to the UD&FCD, Douglas County, and
to FEMA. This action is recommended in order to meet statutory requirements. .

STAFF RECOMMENDATION SUMMARY
Resolution Number 04-579:
Staff recommends that the Board: I) designate and approve the 100-year detailed floodplain information
contained in said report within Gunnison County and the Town of Marble, and 2) authorize staff to
prepare a floodplain resolution to be signed by the Director and transmitted to the affected communities
and to FEMA. This action is recommended in order to meet statutory requirements.

Resolution Number 04-580:
Staff recommends that the Board; I) designate and approve the IOO-year floodplain information contained
in said report within Hinsdale County, and 2) authorize staff to prepare a floodplain resolution to be
signed by the Director and transmitted to the affected communities and to FEMA. This action is
recommended in order to meet statutory requirements.

Resolution Number 04-581:
Staff recommends that the Board: I) designate and approve the IOO-year detailed floodplain information
contained in said report within Douglas County and 2) authorize staff to prepare a floodplain resolution to
be signed by the Director and transmitted to the UD&FCD, Douglas County, and to FEMA. This action is
recommended in order to meet statutory requirements

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

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