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Bench Mark Sheet for 8724507, CHANNEL KEY FL

Superseded Epoch

Large map location marker Station Location
Small red map location marker Published bench mark
Small blue map location marker Unpublished bench mark

Bench mark positions only appear on the map if their coordinates in the CO-OPS database are at the precision of degrees/minutes/seconds/and tenths of seconds. If the coordinates are less precise, the mark will not appear.

Printable version

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
Datums Page                                                        Page  1 of  6

                                                                                
Station ID: 8724507                         PUBLICATION DATE:  03/09/2004
Name:       CHANNEL KEY                                       
            FL
NOAA Chart: 11441                           Latitude:   24° 36.2' N (  24.60330)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 43.5' W ( -81.72500)


To reach the tidal bench marks from the west end of the bridge between Stock
Island and Boca Chica Key, proceed by boat NNW for 3.1 km (1.9 statute mi) to
the west entrance of a small channel, locally known as Channel Grassy, dividing
Channel Key.  The bench marks are located in the NW section of the southern
portion of the key.  The tide gage and staff were located at the western
entrance to Channel Grassy.


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


                 PRIMARY BENCH MARK STAMPING:  CHANNEL KEY 2 1934
                         DESIGNATION:          CHANNEL KEY 2
                         ALIAS:                1

MONUMENTATION:           Triangulation Station disk            VM#:        11306
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AA1096
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   24° 36.2' N (  24.60330)          LONGITUDE:  81° 43.4' W ( -81.72330)


The primary bench mark is a disk set in a 0.3 m (1.0 ft) square concrete
monument on a pile on the west side of the key, 75 m (246 ft) SE of the entrance
to Channel Grassy, 25 m (82 ft) NE of the SW side of the key, 0.15 m (0.5 ft)
west of a witness post, and 0.30 m (1.0 ft) above the ground.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of  6

                                                                                
Station ID: 8724507                         PUBLICATION DATE:  03/09/2004
Name:       CHANNEL KEY                                       
            FL
NOAA Chart: 11441                           Latitude:   24° 36.2' N (  24.60330)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 43.5' W ( -81.72500)


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


                         BENCH MARK STAMPING:  NO 2 1973
                         DESIGNATION:          872 4507 TIDAL 2

MONUMENTATION:           Tidal Station disk                    VM#:        11020
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   24° 36.2' N (  24.60330)          LONGITUDE:  81° 43.5' W ( -81.72500)


The bench mark is a disk set on top of a 0.15 m (0.5 ft) square concrete
monument on the west side of the key, 69 m (225 ft) SSE of the entrance to
Channel Grassy, 16.82 m (55.2 ft) WSW of bench mark CHANNEL KEY 2 NO 2 1934, 11
m (36 ft) NNW of bench mark CHANNEL KEY 2 NO 1 1934, and 0.15 m (0.5 ft) NW of a
witness post.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  3 of  6

                                                                                
Station ID: 8724507                         PUBLICATION DATE:  03/09/2004
Name:       CHANNEL KEY                                       
            FL
NOAA Chart: 11441                           Latitude:   24° 36.2' N (  24.60330)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 43.5' W ( -81.72500)


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


                         BENCH MARK STAMPING:  CHANNEL KEY 2 NO 1 1934
                         DESIGNATION:          CHANNEL KEY 2 RM 1
                         ALIAS:                2

MONUMENTATION:           Reference Mark disk                   VM#:        11307
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AE4421
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   24° 36.2' N (  24.60330)          LONGITUDE:  81° 43.5' W ( -81.72500)


The bench mark is a disk set in a 0.30 m (1.0 ft) square concrete monument on a
pile on the west side of the key, 90 m (295 ft) SE of the entrance to Channel
Grassy, 28 m (92 ft) NE of the SW side of the key, 14.23 m (46.7 ft) ESE of
bench mark CHANNEL KEY 2 1934, 0.24 m (0.8 ft) NW of a witness post, and 0.30 m
(1.0 ft) above ground level.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  4 of  6

                                                                                
Station ID: 8724507                         PUBLICATION DATE:  03/09/2004
Name:       CHANNEL KEY                                       
            FL
NOAA Chart: 11441                           Latitude:   24° 36.2' N (  24.60330)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 43.5' W ( -81.72500)


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


                         BENCH MARK STAMPING:  CHANNEL KEY 2 NO 2 1934
                         DESIGNATION:          CHANNEL KEY 2 RM 2
                         ALIAS:                3

MONUMENTATION:           Reference Mark disk                   VM#:        11308
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AE4422
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   24° 36.2' N (  24.60330)          LONGITUDE:  81° 43.5' W ( -81.72500)


The bench mark is a disk set in a 0.30 m (1.0 ft) square concrete monument on a
pile on the west side of the key, 90 m (295 ft) SSE of the entrance to Channel
Grassy, 17.56 m (57.6 ft) SW of bench mark CHANNEL KEY 2 1934, 4 m (13 ft) east
of the west side of the key, 0.15 m (0.5 ft) NNW of a witness post, and 0.30 m
(1.0 ft) above the ground.



                         BENCH MARK STAMPING:  NO 1 1973
                         DESIGNATION:          872 4507 TIDAL 1

MONUMENTATION:           Tidal Station disk                    VM#:        11309
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 36.2' N (  24.60330)          LONGITUDE:  81° 43.5' W ( -81.72500)


The bench mark is a disk located on the west side of the key, 29 m (94 ft) south
of Channel Grassy, 16.98 m (55.7 ft) WNW of bench mark CHANNEL KEY 2 1934, 0.18
m (0.6 ft) NNW of a witness post, and 0.15 m (0.5 ft) above the ground. The
bench mark is crimped to a  copper-clad steel rod driven 2.4 m (8 ft) to
refusal.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  5 of  6

                                                                                
Station ID: 8724507                         PUBLICATION DATE:  03/09/2004
Name:       CHANNEL KEY                                       
            FL
NOAA Chart: 11441                           Latitude:   24° 36.2' N (  24.60330)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 43.5' W ( -81.72500)


                            T I D A L   D A T U M S 


Tidal datums at CHANNEL KEY based on:

     LENGTH OF SERIES:      4 MONTHS
     TIME PERIOD:           January 1974 - April 1974
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  8724211 BIG PINE KEY VIADUCT


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

     MEAN HIGHER HIGH WATER                     MHHW   =  0.411
     MEAN HIGH WATER                            MHW    =  0.319
     MEAN TIDE LEVEL                            MTL    =  0.184
     MEAN SEA LEVEL                             MSL    =  0.184
     MEAN LOW WATER                             MLW    =  0.049
     MEAN LOWER LOW WATER                       MLLW   =  0.000

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     CHANNEL KEY 2 1934                          0.449    0.130
     NO 2 1973                                   0.404    0.085
     CHANNEL KEY 2 NO 1 1934                     0.434    0.115
     CHANNEL KEY 2 NO 2 1934                     0.494    0.175
     NO 1 1973                                   0.274   -0.045


                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  6 of  6

                                                                                
Station ID: 8724507                         PUBLICATION DATE:  03/09/2004
Name:       CHANNEL KEY                                       
            FL
NOAA Chart: 11441                           Latitude:   24° 36.2' N (  24.60330)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 43.5' W ( -81.72500)


                             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 NGS's Integrated Data Base (IDB PID)
provides geodetic datum based on traditionally leveled and bluebooked ties to
the National Spatial Reference System(NSRS) https://www.ngs.noaa.gov/datasheets/.
The NGS Online Positioning User Service (OPUS PID) provides geodetic datum based
on GPS position & tie it to the NSRS https://www.ngs.noaa.gov/OPUS/.

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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Products available at 8724507 CHANNEL KEY, FL

Revised: 08/08/2018
NOAA / National Ocean Service
Web site owner: Center for Operational Oceanographic Products and Services