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Bench Mark Sheet for 8724397, JOHNSTON 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Superseded Epoch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Small blue map location marker Unpublished bench mark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: 8724397                         PUBLICATION DATE:  11/13/2003
Name:       JOHNSTON KEY                                      
            FL
NOAA Chart: 11448                           Latitude:   24° 42.6' N (  24.71000)
USGS Quad:  SUGARLOAF KEY                   Longitude:  81° 35.6' W ( -81.59330)


To reach the tidal bench marks from the bridge between Cudjoe Key and Sugarloaf
Key, proceed NWW by boat for 9.7 km (6.0 statute mi) to the SW tip of Johnston
Key.  The bench marks are located on the SW tip of the key.  The tide gage and
staff were located just west of the SW tip of the key.


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


                 PRIMARY BENCH MARK STAMPING:  JOHNSTON KEY 2 RM 1 1934-35
                         DESIGNATION:          JOHNSTON  RM 1

MONUMENTATION:           Reference Mark disk                   VM#:         7059
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AE4416
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   24° 42.6' N (  24.71000)          LONGITUDE:  81° 35.6' W ( -81.59330)


The primary bench mark is a disk set in the top of a 0.18 m (0.6 ft) square
concrete monument, 43 m (141 ft) SE of the approximate high water line, 24.25 m
(79.6 ft) east of Bench Mark JOHNSTON KEY 2 1934-35, and 0.06 m (0.2 ft) above
the ground.

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

                                                                                
Station ID: 8724397                         PUBLICATION DATE:  11/13/2003
Name:       JOHNSTON KEY                                      
            FL
NOAA Chart: 11448                           Latitude:   24° 42.6' N (  24.71000)
USGS Quad:  SUGARLOAF KEY                   Longitude:  81° 35.6' W ( -81.59330)


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


                         BENCH MARK STAMPING:  JOHNSTON KEY 2 1934-35
                         DESIGNATION:          JOHNSTON KEY 2

MONUMENTATION:           Triangulation Station disk            VM#:         7058
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AA1037
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   24° 42.7' N (  24.71170)          LONGITUDE:  81° 35.6' W ( -81.59330)


The bench mark is a disk set in the top of a 0.21 m x 0.21 m ( 0.7 ft x 7 ft)
concrete monument, about 136 m (446 ft) NE of the most SW tip of the key, 50 m
(164 ft) NW of the mangroves on the SE shore, 30 m (98 ft) east of the mangroves
on the west shore, 1.07 m (3.5 ft) NNW of a witness post, and 0.06 m (0.2 ft)
above the ground.

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

                                                                                
Station ID: 8724397                         PUBLICATION DATE:  11/13/2003
Name:       JOHNSTON KEY                                      
            FL
NOAA Chart: 11448                           Latitude:   24° 42.6' N (  24.71000)
USGS Quad:  SUGARLOAF KEY                   Longitude:  81° 35.6' W ( -81.59330)


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


                         BENCH MARK STAMPING:  JOHNSTON KEY 2 RM 2 1934-35
                         DESIGNATION:          JOHNSTON  RM 2

MONUMENTATION:           Reference Mark disk                   VM#:         7060
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AE4417
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   24° 42.6' N (  24.71000)          LONGITUDE:  81° 35.6' W ( -81.59330)


The bench mark is a disk set in the top of a 0.18 m (0.6 ft) square concrete
monument, 30 m (98 ft) NE of the outer edge of mangroves, 20.70 m (67.91 ft) SSW
of Bench Mark JOHNSTON KEY 1934-35, and 0.06 m (0.2 ft) above the ground.



                         BENCH MARK STAMPING:  NO 1 1973
                         DESIGNATION:          872 4397 TIDAL 1

MONUMENTATION:           Tidal Station disk                    VM#:         7061
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Rock outcrop                          OPUS PID:        
LATITUDE:   24° 42.6' N (  24.71000)          LONGITUDE:  81° 35.6' W ( -81.59330)


The bench mark is a disk set in rock outcrop, 110 m (361 ft) NE of the most SW
tip of the key, 36.58 m (120.0 ft) west of Bench Mark JOHNSTON KEY 2 RM 2
1934-35, 12 m (41 ft) SSW of Bench Mark NO 2 1973, 6 m (20 ft) ESE of the outer
edge of mangroves on the west side of the key, 0.40 m (1.3 ft) SE of an 0.46 m
(1.5 ft) high copper-clad rod driven into the ground.

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

                                                                                
Station ID: 8724397                         PUBLICATION DATE:  11/13/2003
Name:       JOHNSTON KEY                                      
            FL
NOAA Chart: 11448                           Latitude:   24° 42.6' N (  24.71000)
USGS Quad:  SUGARLOAF KEY                   Longitude:  81° 35.6' W ( -81.59330)


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


                         BENCH MARK STAMPING:  NO 2 1973
                         DESIGNATION:          872 4397 TIDAL 2

MONUMENTATION:           Tidal Station disk                    VM#:         7062
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Rock outcrop                          OPUS PID:        
LATITUDE:   24° 42.6' N (  24.71000)          LONGITUDE:  81° 35.6' W ( -81.59330)


The bench mark is a disk set in rock outcrop, 122 m (400 ft) NE of the most SW
tip of the key, 36.73 m (120.5 ft) WNW of Bench Mark JOHNSTON KEY 2 RM 2
1934-35, 12.50 m (41.0 ft) NE of Bench Mark NO 1 1973, 3.35 m (11.0 ft) ESE of
the outer edge of mangroves on the west side of the key.

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

                                                                                
Station ID: 8724397                         PUBLICATION DATE:  11/13/2003
Name:       JOHNSTON KEY                                      
            FL
NOAA Chart: 11448                           Latitude:   24° 42.6' N (  24.71000)
USGS Quad:  SUGARLOAF KEY                   Longitude:  81° 35.6' W ( -81.59330)


                            T I D A L   D A T U M S 


Tidal datums at JOHNSTON KEY based on:

     LENGTH OF SERIES:      3 MONTHS
     TIME PERIOD:           December 1973 - February 1974
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  8724580 KEY WEST


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

     MEAN HIGHER HIGH WATER                     MHHW   =  0.604
     MEAN HIGH WATER                            MHW    =  0.513
     MEAN TIDE LEVEL                            MTL    =  0.275
     MEAN SEA LEVEL                             MSL    =  0.244
     MEAN LOW WATER                             MLW    =  0.038
     MEAN LOWER LOW WATER                       MLLW   =  0.000

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     JOHNSTON KEY 2 RM 1 1934-35                 0.502   -0.011
     JOHNSTON KEY 2 1934-35                      0.532    0.019
     JOHNSTON KEY 2 RM 2 1934-35                 0.476   -0.037
     NO 1 1973                                   0.222   -0.291
     NO 2 1973                                   0.190   -0.323


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

                                                                                
Station ID: 8724397                         PUBLICATION DATE:  11/13/2003
Name:       JOHNSTON KEY                                      
            FL
NOAA Chart: 11448                           Latitude:   24° 42.6' N (  24.71000)
USGS Quad:  SUGARLOAF KEY                   Longitude:  81° 35.6' W ( -81.59330)


                             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 8724397 JOHNSTON KEY, FL

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