FLOOD04442

• County: Boulder
• Community: Longmont
• Stream Name: Lefthand Creek
• Basin: South Platte
• Title: LOMR - Affected Panel 08013C 0269 F - Case No. 97-08-394P
• Date: 5/14/1999
• Prepared For: Longmont
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

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CHANGES ARE MADE IN DETERMINATIONS OF BASE FLOOD ELEVATIONS FOR THE CITY
OF LONGMONT, BOULDER COUNTY, COLORADO, UNDER THE NATIONAL FLOOD
INSURANCE PROGRAM

On June 2, 1995, the Federal Emergency Management Agency identified Special Flood Hazard Areas
(SFHAs) in the City of Longmont, Boulder County, Colorado, through issuance of a Flood Insurance Rate
Map (FIRM). The Mitigation Directorate has determined that modification of the elevations of the flood
having a I-percent chance of being equaled or exceeded in any given year (base flood) for certain locations
in this community is appropriate, The modified base flood elevations (BFEs) revise the FIRM for the
community.

The changes are being made pursuant to Section 206 of the Flood Disaster Protection Act of 1973 (Public
Law 93-234) and are in accordance with the National Flood Insurance Act of 1968, as amended (Title XIII
of the Housing and Urban Development Act of 1968, Public Law 90-448), 42 U.S.C. 4001-4128, and
44 CFR Part 65.

A hydraulic analysis was performed along Lefthand Creek to incorporate updated topographic information
and revised bridge modeling at the State Highway 119 and Burlington Northern Railroad bridges. The
revised analysis defined two channels along the overflow area shown on the effective FIRM. Lefthand
Creek North Overflow Channel is created by floodwater that leaves the main channel just upstream of the
southbound lane of State Highway 119 and Burlington Northern Railroad. Lefthand Creek South Overflow
Channel is created by floodwater that leaves the main channel between the northbound lane of State
Highway 119 and Burlington Northern Railroad. Both overflow channels rejoin the main channel just
upstream of South Hover Road. The revised hydraulic analysis has resulted in a decrease in SFHA width
and increased and decreased BFEs for Lefthand Creek North Overflow Channel from just upstream of
South Hover Road to just downstream of Burlington Northern Railroad and a portion of the ponding area
just upstream of State Highway 119 southbound. The table below indicates existing and modified BFEs
for selected locations along the affected lengths of the flooding source(s) cited above.

Location

Existing BFE
(feet)*

Modified BFE
(feet)*

Approximately 750 feet upstream
of South Hover Road
Just upstream of State Highway 119 southbound

4,996
5,008

4,993
5,010

*National Geodetic Vertical Datum, rounded to nearest whole foot

Under the above-mentioned Acts of 1968 and 1973, the Mitigation Directorate must develop criteria for
floodplain management. To participate in the National Flood Insurance Program (NFIP), the community
must use the modified BFEs to administer the floodplain management measures of the NFIP. These
modified BFEs will also be used to calculate the appropriate flood insurance premium rates for new
buildings and their contents and for the second layer of insurance on existing buildings and contents,

Upon the second publication of notice of these changes in this newspaper, any person has 90 days in which
he or she can request, through the Chief Executive Officer of the community, that the Mitigation
Directorate reconsider the determination. Any request for reconsideration must be based on knowledge
of changed conditions or new scientific or technical data. All interested parties are on notice that until the
90-day period elapses, the Mitigation Directorate's determination to modify the BFEs may itself be
changed.