Superseded Bench Mark Sheet for 8724033, PIGEON KEY (INSIDE) FL

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:  05/14/1986
Station ID: 8724033                                SUPERCEDED DATE:   04/21/2003
Name:       PIGEON KEY INSIDE, ATLANTIC SIDE                  
            FLORIDA
NOAA Chart: 11449                                  Latitude:         24° 42.3' N
USGS Quad:  SEVENMILE BRIDGE                       Longitude:        81°  9.4' W


To reach the tidal bench marks from the post office at Marathon, proceed 4.8
miles (7.7 km) SW along U.S. Highway 1 to the ramp leading down from Seven Mile
Bridge to Pigeon Key.  The bench marks are located on the concrete bases of the
bridge piers of the old bridge and near the pool on the south end of the Key. 
The tide gage and staff were located on the dock at the north end of the Key. 
This bench mark network was also used for tide station 872 4032 which was
located on the south end of the Key.


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


                 PRIMARY BENCH MARK STAMPING:  NO 1 1935

MONUMENTATION:           Survey Disk                               VM#:     6315
AGENCY:                                                            PID#:  AA0292
SETTING CLASSIFICATION:  Concrete Base for Bridge Pier


The bench mark is located on Pigeon Key under the old Savannah Bridge, set in
the top of the north corner of the concrete base to the third pier NE of the
bridge pier at the edge of the water on the west side of the Key, 32 feet (10 m)
west of the extended centerline of the dock on the north side of the Key, 9 feet
(3 m) SW of the center of a sideway, 0.5 foot (0.2 m) north of the north corner
of the bridge pier, and 1.5 foot (0.5 m) above ground level.



                         BENCH MARK STAMPING:  NO 3 1935

MONUMENTATION:           Survey Disk                               VM#:     6316
AGENCY:                                                            PID#:  AA0291
SETTING CLASSIFICATION:  Concrete Base for Bridge Pier


The bench mark is located on Pigeon Key under the old Savannah Bridge, set in
the top of the north corner of the concrete base of a bridge pier at the edge of
the water on the west side of the Key, 6 feet (2 m) NE of the extended
centerline of the ramp leading to the Key, and 2 feet (1 m) above ground level.

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

                                                   PUBLICATION DATE:  05/14/1986
Station ID: 8724033                                SUPERCEDED DATE:   04/21/2003
Name:       PIGEON KEY INSIDE, ATLANTIC SIDE                  
            FLORIDA
NOAA Chart: 11449                                  Latitude:         24° 42.3' N
USGS Quad:  SEVENMILE BRIDGE                       Longitude:        81°  9.4' W


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


                         BENCH MARK STAMPING:  MOSER 1935 NO 4 1976

MONUMENTATION:           Survey Disk                               VM#:     6317
AGENCY:                                                            PID#:  AA0924
SETTING CLASSIFICATION:  Concrete Floor


The bench mark is located on Pigeon Key near the shark pool, set in the top of
the SE corner of the concrete floor of the picnic area, 79.7 feet (24.3 m) north
of Bench Mark 90 70 C17, 68.9 feet (21.0 m) SSE of the corner of a fence at the
entrance to Pigeon Key, and 0.1 foot (0.03 m) above ground level.



                         BENCH MARK STAMPING:  V 278 1966

MONUMENTATION:           Survey Disk                               VM#:     6318
AGENCY:                                                            PID#:  AA0289
SETTING CLASSIFICATION:  Concrete Curb


The bench mark is located near the junction of U.S. Highway 1 and the road
leading down the ramp to Pigeon Key, set in the top of the north curb at the old
Seven Mile Bridge, 10 feet (3 m) north of the centerline of the highway, and 0.5
foot (0.2 m) above highway level.



                         BENCH MARK STAMPING:  90 70 C17

MONUMENTATION:           Survey Disk                               VM#:     6319
AGENCY:                                                            PID#:  AA0923
SETTING CLASSIFICATION:  Concrete Monument


The bench mark is located on the south side of Pigeon Key near the pool, set in
the top of a concrete post, 369 feet (112 m) south of the bridge abutment, 85.4
feet (26 m) SW of the NW end of the shark pool, 18.4 feet (5.6 m) NW of the SW
end of the pool, 9.3 feet (2.8 m) west of the west end of the pool, 1.8 feet
(0.5 m) east of a witness post, and at ground level.

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

                                                   PUBLICATION DATE:  05/14/1986
Station ID: 8724033                                SUPERCEDED DATE:   04/21/2003
Name:       PIGEON KEY INSIDE, ATLANTIC SIDE                  
            FLORIDA
NOAA Chart: 11449                                  Latitude:         24° 42.3' N
USGS Quad:  SEVENMILE BRIDGE                       Longitude:        81°  9.4' W


                            T I D A L   D A T U M S 


Tidal datums at PIGEON KEY INSIDE, ATLANTIC SIDE based on:

     LENGTH OF SERIES:      2 MONTHS
     TIME PERIOD:           NOVEMBER-DECEMBER 1973
     TIDAL EPOCH:           1960-1978
     CONTROL TIDE STATION:  8724211 BIG PINE KEY VIADUCT


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

     HIGHEST OBSERVED WATER LEVEL (10/25/1973)         =   2.26
     MEAN HIGHER HIGH WATER                     MHHW   =   0.99
     MEAN HIGH WATER                            MHW    =   0.74
     MEAN TIDE LEVEL                            MTL    =   0.44
     MEAN LOW WATER                             MLW    =   0.14
   * NATIONAL GEODETIC VERTICAL DATUM           NGVD29 =   0.13
     MEAN LOWER LOW WATER                       MLLW   =   0.00
     LOWEST  OBSERVED WATER LEVEL (12/23/1973)         =  -0.53

   * NGVD reference based on elevations published in Quad 240811, 1982, and NOS
     leveling of 1982. 
North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In FEET above:

     Stamping or Designation                    MLLW        MHW

     NO 1 1935                                   4.04      3.30
     NO 3 1935                                   4.01      3.27
     MOSER 1935 NO 4 1976                        2.83      2.09
     V 278 1966                                 27.76     27.02
     90 70 C17                                   3.07      2.33


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

                                                   PUBLICATION DATE:  05/14/1986
Station ID: 8724033                                SUPERCEDED DATE:   04/21/2003
Name:       PIGEON KEY INSIDE, ATLANTIC SIDE                  
            FLORIDA
NOAA Chart: 11449                                  Latitude:         24° 42.3' N
USGS Quad:  SEVENMILE BRIDGE                       Longitude:        81°  9.4' 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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