FLOOD03877

• County: Fremont
• Community: Florence
• Basin: Arkansas
• Title: FIS - Florence
• Date: 3/17/2002
• Prepared For: Fremont County
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

each overflow flow path (east and west) using the U.S. Army
Corps of Engineers HEC-2 computer program (Reference 6).
Blockage of flow from buildings and other unnatural
obstructions were simulated in the overbank calculations to
predict the impacts these features have on flood elevations.

The flooded areas determined for the East and West Overflows
of Coal Creek can be characterized as shallow flooding, with
depths ranging from 1 to 3 feet. This flooding occurs with
flows in excess of the la-year frequency on Coal Creek, due
primarily because of the constriction of Coal Creek at the
Denver and Rio Grande Western Railroad. Overflows moving east
and west from the main Coal Creek channel were determined
upstream of the Denver and Rio Grande Western Railroad and
analyzed using a uniform depth analysis (Manning's equation)
up to the point where flow was determined to move northward
through the City of Florence, via the east and west overflow
paths. The shallow flooding depths along the overflow path
were computed using the U. S. Army Corps of Engineers HEC-2
Water Surface Profile Program (Reference 6).

Flood profiles were drawn showing computed water-surface
elevations to an accuracy of 0.5 foot for floods of the
selected recurrence intervals. The flood profiles presented
in this study are based on the effects of flow through
unobstructed hydraulic structures and are, thus, considered
valid only if these structures do not fail and remain
unobstructed. The hydraulic analyses were conducted by COM,
the study contractor.

All elevations are referenced to the National Geodetic and
Vertical Datum of 1929 (NGVD) Elevation Reference Marks
(ERMs) used in this study are shown on the maps. ERMs shown
on the FIRM represent those used during the preparation of
this and previous Flood Insurance Studies. The elevations
associated with each ERM were obtained and/or developed during
FIS production to establish vertical control for determination
of flood elevations and flood plain boundaries shown on the
FIRM. Users should be aware that these ERM elevations may
have changed since the publication of this Frs. To obtain
up-to-date elevation information on National Geodetic Survey
(NGS) ERMs shown on this map, please contact the Information
Services Branch of the NGS at [phone], or visit their
website at www.nqS.noaa.qov. Map users should seek
verification of non-NGS ERM monument elevations when using
these elevations for construction or flood plain management
purposes.

Generally, the distances on the flood profiles correspond to
distances measured along the centerline of the designated
watercourses. For the Coal Creek East Overflow and Coal Creek
West Overflow, however, the lack of any well-defined
watercourse necessitated use of distances measured along the
centerline of the 100-year flow paths. On the maps these

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