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Superseded Bench Mark Sheet for 8724138, BAHIA HONDA KEY

Present Epoch

Printable version

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
Datums Page                                                        Page  1 of  4

                                                   PUBLICATION DATE:  03/10/1986
Station ID: 8724138                                SUPERCEDED DATE:   04/21/2003
Name:       BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F
            FLORIDA
NOAA Chart: 11449                                  Latitude:         24° 39.3' N
USGS Quad:  BIG PINE KEY                           Longitude:        81° 16.9' W


To reach the tidal bench marks from the Post Office at Marathon, proceed 13.4
miles (21.6 km) SW on U.S Highway 1 to the east end of the Bahia Honda Bridge
over Big Spanish Channel, 0.2 mile (0.3 km) south of the new bridge.  The bench
marks are located on the old highway bridge which is above an abandoned railroad
bridge at the state recreation area, and near the tackle shop.  The tide gage
and staff were located on the NE concrete wingwall of the railroad bridge.


                         T I D A L   B E N C H   M A R K S


                 PRIMARY BENCH MARK STAMPING:  W BAHIA RM 2 1935

MONUMENTATION:           Survey Disk                               VM#:     6369
AGENCY:                                                            PID#:  AA0269
SETTING CLASSIFICATION:  Concrete Wingwall


The bench mark is set in the top of the south concrete wingwall of the old
bridge, 315 feet (96 m) west of the east end of the bridge, 33 feet (10 m) south
of the centerline of the highway, 17.2 feet (5.2 m) SE of Bench Mark NO 4 1936,
and 35 feet (11 m) below highway level.



                         BENCH MARK STAMPING:  4138 F 1982

MONUMENTATION:           Survey Disk                               VM#:     6365
AGENCY:                                                            PID#:  AA0898
SETTING CLASSIFICATION:  Concrete Walkway


The bench mark is near the tackle shop, set in a concrete walkway, 35.4 feet
(10.8 m) NW of the south corner of the dive shop, 16.5 feet (5.0 m) east of the
NE edge of the parking lot, 4.4 feet (1.3 m) SSW of the west corner of the
tackle shop, and 0.5 foot (0.2 m) SW of the stairs behind the tackle shop.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of  4

                                                   PUBLICATION DATE:  03/10/1986
Station ID: 8724138                                SUPERCEDED DATE:   04/21/2003
Name:       BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F
            FLORIDA
NOAA Chart: 11449                                  Latitude:         24° 39.3' N
USGS Quad:  BIG PINE KEY                           Longitude:        81° 16.9' W


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  D 70 RESET 1936 TIDAL NO 2

MONUMENTATION:           Survey Disk                               VM#:     6366
AGENCY:                                                            PID#:  AA0267
SETTING CLASSIFICATION:  Concrete Wingwall


The bench mark is set in the top of the north concrete wingwall of the old
bridge, 315 feet (96 m) west of the east end of the bridge, 16 feet (5 m) north
of the centerline of the highway, and 30 feet (9 m) below highway level.



                         BENCH MARK STAMPING:  G 329 1970

MONUMENTATION:           Survey Disk                               VM#:     6367
AGENCY:                                                            PID#:  AA0271
SETTING CLASSIFICATION:  Concrete Wingwall


The bench mark is near the old bridge, set in the top of the NW corner of the
6th concrete step from the bottom of the landing, 150 feet (46 m) north of the
north edge of the bridge, 142.1 feet (43.3 m) east of the east face of the
concrete wingwall of the railroad bridge and the NE corner of the highway
bridge, 58 feet (18 m) south of the shoreline, and 10 feet (3 m) above  water
level.



                         BENCH MARK STAMPING:  NO 4 1936

MONUMENTATION:           Survey Disk                               VM#:     6368
AGENCY:                                                            PID#:  AA0268
SETTING CLASSIFICATION:  Concrete Wingwall


The bench mark is set in the top of the south concrete wingwall of the old
bridge, 315 feet (96 m) west of the east end of the bridge, 16 feet (5 m) south
of the centerline of the highway, and 30 feet (9 m) below highway level.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  3 of  4

                                                   PUBLICATION DATE:  03/10/1986
Station ID: 8724138                                SUPERCEDED DATE:   04/21/2003
Name:       BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F
            FLORIDA
NOAA Chart: 11449                                  Latitude:         24° 39.3' N
USGS Quad:  BIG PINE KEY                           Longitude:        81° 16.9' W


                            T I D A L   D A T U M S 


Tidal datums at BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F based on:

     LENGTH OF SERIES:      12 MONTHS
     TIME PERIOD:           FEBRUARY 1971-JANUARY 1972
     TIDAL EPOCH:           1960-1978
     CONTROL TIDE STATION:  8724580 KEY WEST


Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:

     HIGHEST OBSERVED WATER LEVEL (11/05/1971)         =   2.76
     MEAN HIGHER HIGH WATER                     MHHW   =   1.57
     MEAN HIGH WATER                            MHW    =   1.34
     MEAN TIDE LEVEL                            MTL    =   0.74
   * NATIONAL GEODETIC VERTICAL DATUM           NGVD29 =   0.53
     MEAN LOW WATER                             MLW    =   0.15
     MEAN LOWER LOW WATER                       MLLW   =   0.00
     LOWEST  OBSERVED WATER LEVEL (04/26/1971)         =  -0.75

   * NGVD reference based on elevations published in Quad 240811, 1972, and NOS
     leveling of 1975. 
North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In FEET above:

     Stamping or Designation                    MLLW        MHW

     W BAHIA RM 2 1935                          22.88     21.54
     4138 F 1982                                 5.71      4.37
     D 70 RESET 1936 TIDAL NO 2                 25.83     24.49
     G 329 1970                                 12.95     11.61
     NO 4 1936                                  26.02     24.68


                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  4 of  4

                                                   PUBLICATION DATE:  03/10/1986
Station ID: 8724138                                SUPERCEDED DATE:   04/21/2003
Name:       BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F
            FLORIDA
NOAA Chart: 11449                                  Latitude:         24° 39.3' N
USGS Quad:  BIG PINE KEY                           Longitude:        81° 16.9' W


                             D E F I N I T I O N S


Mean Sea Level (MSL) is a tidal datum determined over a 19-year National Tidal
Datum Epoch.  It pertains to local mean sea level and should not be confused
with the fixed datums of North American Vertical Datum of 1988 (NAVD88).

NAVD88 is a fixed datum derived from a simultaneous, least squares, minimum
constraint adjustment of Canadian/Mexican/United States leveling observations.
Local mean sea level observed at Father Point/Rimouski, Canada was held fixed as
the single initial constraint.  NAVD88 replaces NGVD29 as the national
standard geodetic reference for heights.  Bench mark elevations relative to
NAVD88 are available from NGS through the World Wide Web at 
National Geodetic Survey.

NGVD29 is a fixed datum adopted as a national standard geodetic reference for
heights but is now considered superseded.  NGVD29 is sometimes referred to as
Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological
Survey Topographic Quads.  NGVD29 was originally derived from a general
adjustment of the first-order leveling networks of the U.S. and Canada after
holding mean sea level observed at 26 long term tide stations as fixed.
Numerous local and wide-spread adjustments have been made since establishment in
1929.  Bench mark elevations relative to NGVD29 are available from the National
Geodetic Survey (NGS) data base via the World Wide Web at 
National Geodetic Survey.

NAVD88 and NGVD29 are fixed geodetic datums whose elevation relationships to
local MSL and other tidal datums may not be consistent from one location to
another.

The Vertical Mark Number (VM#) and PID# shown on the bench mark sheet are unique
identifiers for bench marks in the tidal and geodetic databases, respectively.
Each bench mark in either database has a single, unique VM# and/or PID# assigned.
Where both VM# and PID# are indicated, both tidal and geodetic elevations are
available for the bench mark listed.

The NAVD88 elevation is shown on the Elevations of Tidal Datums Table Referred
to MLLW only when two or more of the bench marks listed have NAVD88 elevations.
The NAVD88 elevation relationship shown in the table is derived from an average
of several bench mark elevations relative to tide station datum.  As a result of
this averaging, NAVD88 bench mark elevations computed indirectly from the tidal
datums elevation table may differ slightly from NAVD88 elevations listed for
each bench mark in the NGS database.

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Revised: 08/08/2018
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