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Bench Mark Sheet for 8724153, JOHNSON KEYS SOUTH 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Superseded Epoch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Small blue map location marker Unpublished bench mark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  5

                                                                                
Station ID: 8724153                         PUBLICATION DATE:  12/12/2003
Name:       JOHNSON KEYS SOUTH                                
            FL
NOAA Chart: 11448                           Latitude:   24° 44.6' N (  24.74330)
USGS Quad:  BIG PINE KEY                    Longitude:  81° 18.0' W ( -81.30000)


To reach the tidal bench marks by boat proceed 5.6 km (3.5 statute mi) NNW from
the west end of the bridge between Bahia Honda Key and West Summerland Keys to
channel marker R 28 of Big Spanish Channel, then travel 6.0 km (3.7 statute mi)
to the SE end of the central and largest of the Johnson Keys group.  The bench
marks are located around the southern tip of the key.  The tide gage and staff
were located on the small temporary offshore structure.


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


                 PRIMARY BENCH MARK STAMPING:  NO 1 1974
                         DESIGNATION:          872 4153 TIDAL 1

MONUMENTATION:           Tidal Station disk                    VM#:         6375
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 44.6' N (  24.74330)          LONGITUDE:  81° 18.0' W ( -81.30000)


The primary bench mark is a disk located 29 m (96 ft) from the outer mangrove
edge, 22.62 m (74.2 ft) SSE of bench mark NO 2 1974, 2.96 m (9.7 ft) SW of a
witness sign nailed to a tree, and 0.30 m (1.0 ft) south of a witness post.  The
bench mark is set atop a copper-clad steel rod driven an unspecified depth to
refusal, and encased in concrete.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of  5

                                                                                
Station ID: 8724153                         PUBLICATION DATE:  12/12/2003
Name:       JOHNSON KEYS SOUTH                                
            FL
NOAA Chart: 11448                           Latitude:   24° 44.6' N (  24.74330)
USGS Quad:  BIG PINE KEY                    Longitude:  81° 18.0' W ( -81.30000)


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


                         BENCH MARK STAMPING:  NO 2 1974
                         DESIGNATION:          872 4153 TIDAL 2

MONUMENTATION:           Tidal Station disk                    VM#:         6376
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 44.6' N (  24.74330)          LONGITUDE:  81° 18.0' W ( -81.30000)


The bench mark is a disk located in a large grassy clearing, 22.62 m (74.2 ft)
NNW of bench mark NO 1 1974, 19.48 m (63.9 ft) west of bench mark NO 5 1974, and
0.34 m (1.1 ft) SW of a witness post.  The bench mark is set atop a copper-clad
steel rod driven an unspecified depth to refusal, and encased in concrete.



                         BENCH MARK STAMPING:  NO 3 1974
                         DESIGNATION:          872 4153 TIDAL 3

MONUMENTATION:           Tidal Station disk                    VM#:         6377
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 44.6' N (  24.74330)          LONGITUDE:  81° 18.0' W ( -81.30000)


The bench mark is a disk located in a clearing, 38.92 m (127.7 ft) north of
bench mark NO 1 1974, 23.16 m (76.0 ft) NW of bench mark NO 5 1974, 20.06 m
(65.8 ft) NNE of bench mark NO 2 1974, 0.24 m (0.8 ft) SSW of the witness post. 
The bench mark is set atop a copper-clad steel rod driven an unspecified depth
to refusal, and encased in a concrete.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  3 of  5

                                                                                
Station ID: 8724153                         PUBLICATION DATE:  12/12/2003
Name:       JOHNSON KEYS SOUTH                                
            FL
NOAA Chart: 11448                           Latitude:   24° 44.6' N (  24.74330)
USGS Quad:  BIG PINE KEY                    Longitude:  81° 18.0' W ( -81.30000)


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


                         BENCH MARK STAMPING:  NO 4 1974
                         DESIGNATION:          872 4153 TIDAL 4

MONUMENTATION:           Tidal Station disk                    VM#:         6378
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 44.6' N (  24.74330)          LONGITUDE:  81° 18.0' W ( -81.30000)


The bench mark is a disk located in a clearing, 26.52 m (87.0 ft) ENE of bench
mark NO 2 1974, 18.53 m (60.8 ft) ESE of bench mark NO 3 1974, 12.80 m (42.0 ft)
north of bench mark NO 5 1974, 6 m (19 ft) north of a 0.30 m (1 ft) diameter
dead tree with a witness sign attached, and 0.39 m (1.3 ft) south of a witness
post.  The bench mark is set atop a copper-clad steel rod driven an unspecified
depth to refusal, and encased in concrete.



                         BENCH MARK STAMPING:  NO 5 1974
                         DESIGNATION:          872 4153 TIDAL 5

MONUMENTATION:           Tidal Station disk                    VM#:         6379
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 44.6' N (  24.74330)          LONGITUDE:  81° 18.0' W ( -81.30000)


The bench mark is a disk located on the east side of a large clearing, 23.16 m
(76.0 ft) SE of bench mark NO 3 1974, 19.48 m (63.9 ft) east of bench mark NO 2
1974, 12.80 m (42.0 ft) SSW of bench mark NO 4 1974, 7 m (23 ft) east of the
dead tree with a witness sign attached, 0.30 m (1.0 ft) SW of a witness post. 
The bench mark is set atop a copper-clad steel rod driven an unspecified depth
to refusal, and encased in concrete.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  4 of  5

                                                                                
Station ID: 8724153                         PUBLICATION DATE:  12/12/2003
Name:       JOHNSON KEYS SOUTH                                
            FL
NOAA Chart: 11448                           Latitude:   24° 44.6' N (  24.74330)
USGS Quad:  BIG PINE KEY                    Longitude:  81° 18.0' W ( -81.30000)


                            T I D A L   D A T U M S 


Tidal datums at JOHNSON KEYS SOUTH based on:

     LENGTH OF SERIES:      1 MONTH
     TIME PERIOD:           August 1974 - August 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   =  0.398
     MEAN HIGH WATER                            MHW    =  0.330
     MEAN SEA LEVEL                             MSL    =  0.205
     MEAN TIDE LEVEL                            MTL    =  0.200
     MEAN LOW WATER                             MLW    =  0.070
     MEAN LOWER LOW WATER                       MLLW   =  0.000

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     NO 1 1974                                   0.735    0.405
     NO 2 1974                                   0.494    0.164
     NO 3 1974                                   0.425    0.095
     NO 4 1974                                   0.514    0.184
     NO 5 1974                                   0.477    0.147


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

                                                                                
Station ID: 8724153                         PUBLICATION DATE:  12/12/2003
Name:       JOHNSON KEYS SOUTH                                
            FL
NOAA Chart: 11448                           Latitude:   24° 44.6' N (  24.74330)
USGS Quad:  BIG PINE KEY                    Longitude:  81° 18.0' W ( -81.30000)


                             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 8724153 JOHNSON KEYS SOUTH, FL

Revised: 08/08/2018
NOAA / National Ocean Service
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