Superseded Bench Mark Sheet for 8724307, CONTENT KEY,GULF OF MEXICO FL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:  11/09/1987
Station ID: 8724307                                SUPERCEDED DATE:   04/21/2003
Name:       CONTENT KEYS, CONTENT PASSAGE                     
            FLORIDA
NOAA Chart: 11448                                  Latitude:         24° 47.4' N
USGS Quad:  CONTENT KEYS                           Longitude:        81° 29.0' W


To reach the tidal bench marks from the west end of the U.S. Highway 1 bridge
over Niles Channel on the east side of Summerland Key, proceed by boat north and
then NW on Niles Channel for 5.5 miles (8.9 km) to Channel Marker #64, then head
north across the shallows for 4.5 miles (7.2 km) to the NE tip of the
easternmost key on the west side of Content Passage.  The bench marks are
located on the NE tip of the key.  The tide gage and staff were located on a
platform offshore.


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


                 PRIMARY BENCH MARK STAMPING:  NO 2 1970

MONUMENTATION:           Survey Disk                               VM#:    11328
AGENCY:                                                            PID#:  AA0338
SETTING CLASSIFICATION:  Shallow-set Pipe


The bench mark is in a small clearing near the east shoreline of the key, 16
feet (5 m) west of the east shoreline, and 1 foot (0.3 m) east of a metal
witness post.  The bench mark is 1 foot (0.3 m) above ground level, set on top
of a 3-inch pipe driven 10 feet (3 m) to refusal.



                         BENCH MARK STAMPING:  NO 3 1970

MONUMENTATION:           Survey Disk                               VM#:    11329
AGENCY:                                                            PID#:  AA0339
SETTING CLASSIFICATION:  Shallow-set Pipe


The bench mark is in a small clearing near the east shoreline of the key, 50.0
feet (15.2 m) west of the east shoreline, 39.3 feet (12.0 m) west of Bench Mark
NO 2 1970, and 1 foot (0.3 m) east of a metal witness post.  The bench marks is
1.2 feet (0.4 m) above ground level, set on top of a 3-inch pipe driven 10 feet
(3 m) to refusal.

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

                                                   PUBLICATION DATE:  11/09/1987
Station ID: 8724307                                SUPERCEDED DATE:   04/21/2003
Name:       CONTENT KEYS, CONTENT PASSAGE                     
            FLORIDA
NOAA Chart: 11448                                  Latitude:         24° 47.4' N
USGS Quad:  CONTENT KEYS                           Longitude:        81° 29.0' W


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


                         BENCH MARK STAMPING:  NO 5 1970

MONUMENTATION:           Survey Disk                               VM#:    11330
AGENCY:                                                            PID#:  AA0341
SETTING CLASSIFICATION:  Shallow-set Pipe


The bench mark is in a small clearing near the east shoreline of the key, 33
feet (10 m) NE of Bench Mark NO 4A 1973, 12 feet (4 m) west of the shoreline,
and 1.5 feet (0.5 m) SE of a metal witness post.  The bench mark is 2.6 feet
(0.8 m) above ground level, set on top of a 3-inch pipe driven 10 feet (3 m) to
refusal.



                         BENCH MARK STAMPING:  NO 1A 1973

MONUMENTATION:           Survey Disk                               VM#:    11331
AGENCY:                                                            PID#:  AA1632
SETTING CLASSIFICATION:  Shallow-set Pipe


The bench mark is set in concrete inside a 4-inch metal pipe, in a small
clearing near the east shoreline of the key, 49.4 feet (15.1 m) south of Bench
Mark NO 2 1970, 20 feet (6 m) west of the shoreline, 2 feet (1 m) SE of a metal
witness post, and 0.2 foot (0.1 m) above ground level.



                         BENCH MARK STAMPING:  NO 4A 1973

MONUMENTATION:           Survey Disk                               VM#:    11332
AGENCY:                                                            PID#:  AA1631
SETTING CLASSIFICATION:  Shallow-set Pipe


The bench mark is in a small clearing near the east shoreline of the key, 36
feet (11 m) north of Bench Mark NO 3 1970, 28 feet (9 m) SW of the shoreline,
and 1 foot (0.3 m)  west of a metal witness post.  The bench mark is 1 foot (0.3
m) above ground level, set in concrete on top of a 3-inch pipe driven 10 feet (3
m) to refusal.

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

                                                   PUBLICATION DATE:  11/09/1987
Station ID: 8724307                                SUPERCEDED DATE:   04/21/2003
Name:       CONTENT KEYS, CONTENT PASSAGE                     
            FLORIDA
NOAA Chart: 11448                                  Latitude:         24° 47.4' N
USGS Quad:  CONTENT KEYS                           Longitude:        81° 29.0' W


                            T I D A L   D A T U M S 


Tidal datums at CONTENT KEYS, CONTENT PASSAGE based on:

     LENGTH OF SERIES:      12 MONTHS
     TIME PERIOD:           MARCH 1974-FEBRUARY 1975
     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 (10/23/1973)         =   4.95
     MEAN HIGHER HIGH WATER                     MHHW   =   3.54
     MEAN HIGH WATER                            MHW    =   3.30
     MEAN TIDE LEVEL                            MTL    =   1.87
   * NATIONAL GEODETIC VERTICAL DATUM           NGVD29 =   1.64
     MEAN LOW WATER                             MLW    =   0.44
     MEAN LOWER LOW WATER                       MLLW   =   0.00
     LOWEST  OBSERVED WATER LEVEL (06/21/1971)         =  -0.87

   * 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

     NO 2 1970                                   6.02      2.72
     NO 3 1970                                   5.82      2.52
     NO 5 1970                                   6.32      3.02
     NO 1A 1973                                  4.78      1.48
     NO 4A 1973                                  6.27      2.97


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

                                                   PUBLICATION DATE:  11/09/1987
Station ID: 8724307                                SUPERCEDED DATE:   04/21/2003
Name:       CONTENT KEYS, CONTENT PASSAGE                     
            FLORIDA
NOAA Chart: 11448                                  Latitude:         24° 47.4' N
USGS Quad:  CONTENT KEYS                           Longitude:        81° 29.0' 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.

Return to Top
Products available at 8724307 CONTENT KEY,GULF OF MEXICO, FL