2018-12-26_REVISION - M2008078 ‎(28)‎

• Permit No: M2008078
• IBM Index Class Name: Revision
• Doc Date: 12/26/2018
• Doc Name Note: Preliminary - Part 4 of 4
• Doc Name: Adequacy Review Response
• From: J&T Consulting
• To: DRMS
• Type & Sequence: AM1
• Email Name: AME
• Media Type: D
• Archive: No

Elevation reference marks (ERMs) and their descriptions 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 floodplain boundaries shown on the FIRM. Users should be
aware that these ERM elevations may have changed since the publication of this
FIS. 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.ngs.noaa.gov. Map
users should seek verification of non-NGS ERM monument elevations when
using these elevations for construction or floodplain management purposes.
Qualifying bench marks within a given jurisdiction that are cataloged by the
National Geodetic Survey (NGS) and entered into the National Spatial Reference
System (NSRS) as First or Second Order Vertical and have a vertical stability
classification of A, B, or C are shown and labeled on the FIRM with their 6-
character NSRS Permanent Identifier.
Bench marks catalogued by the NGS and entered into the NSRS vary widely in
vertical stability classification. NSRS vertical stability classifications are as
follows:
Stability A: Monuments of the most reliable nature, expected to hold position/
elevation well (e.g., mounted in bedrock)
Stability B: Monuments which generally hold their position/elevation well (e.g.,
concrete bridge abutments)
Stability C: Monuments which may be affected by surface ground movements
(e.g., concrete monument below frost line)
Stability D: Mark of questionable or unknown vertical stability (e.g., concrete
monument above frost line or steel witness post)
To obtain up-to-date elevation information on NGS bench marks shown on the
FIRM, please contact the Information Services Branch of the NGS at (301) 713-
3242, or visit their website at www.ngs.noaa.gov. Map users should seek
verification of non-NGS monument elevations when using these elevations for
construction or floodplain management purposes.
Temporary vertical monuments are often established during the preparation of a
flood hazard analysis for the purpose of establishing local vertical control.
Although these monuments are not shown on the FIRM, they may be found in the
Technical Support Data Notebook associated with this FIS report and FIRM for
this community. Interested individuals may contact FEMA to access this data.
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