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Bench Mark Sheet for 8724697, GARDEN KEY, DRY TORTUGAS 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Superseded Epoch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Small blue map location marker Unpublished bench mark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: 8724697                         PUBLICATION DATE:  11/13/2003
Name:       GARDEN KEY,DRY TORTUGAS                           
            FL
NOAA Chart: 11438                           Latitude:   24° 37.6' N (  24.62670)
USGS Quad:  DRY TORTUGAS                    Longitude:  82° 52.3' W ( -82.87170)


To reach the tidal bench marks from Key West, proceed west by boat for about 109
km (68 statute mi) to Garden Key in Dry Tortugas, and then to the SE side of the
Key.  The bench marks are located in the vicinity of the main dock.  The tide
gage and staff were located at the SW end of the main dock at Fort Jefferson
Park.


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


                 PRIMARY BENCH MARK STAMPING:  NO 1 1974
                         DESIGNATION:          872 4697 TIDAL 1

MONUMENTATION:           Survey disk                           VM#:         9690
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Concrete dock                         OPUS PID:        
LATITUDE:   24° 37.6' N (  24.62670)          LONGITUDE:  82° 52.3' W ( -82.87170)


The primary bench mark is a disk set flush in the south corner of the concrete
dock, near the entrance to Fort Jefferson, 3.41 m (11.2 ft) east of the east
corner of a wooden building, 1.86 m (6.1 ft) NW of the south corner of the
concrete dock, and 0.30 m (1.0 ft) NE of the SW side of the dock.



                         BENCH MARK STAMPING:  E
                         DESIGNATION:          872 4697 E TIDAL

MONUMENTATION:           Survey disk                           VM#:         9691
AGENCY:                  Department of Interior                IDB PID#:        
SETTING CLASSIFICATION:  Moat wall                             OPUS PID:        
LATITUDE:   24° 37.6' N (  24.62670)          LONGITUDE:  82° 52.3' W ( -82.87170)


The bench mark is a disk set flush in the top of the moat wall near the entrance
to Fort Jefferson, 61.42 m (201.5 ft) SW of Bench Mark F, 59.28 m (194.5 ft) SW
of the centerline of the bridge, and 0.70 m (2.3 ft) SE of the NW edge of the
moat wall.

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

                                                                                
Station ID: 8724697                         PUBLICATION DATE:  11/13/2003
Name:       GARDEN KEY,DRY TORTUGAS                           
            FL
NOAA Chart: 11438                           Latitude:   24° 37.6' N (  24.62670)
USGS Quad:  DRY TORTUGAS                    Longitude:  82° 52.3' W ( -82.87170)


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


                         BENCH MARK STAMPING:  F
                         DESIGNATION:          872 4697 F TIDAL

MONUMENTATION:           Survey disk                           VM#:         9692
AGENCY:                  Department of Interior                IDB PID#:        
SETTING CLASSIFICATION:  Moat wall                             OPUS PID:        
LATITUDE:   24° 37.6' N (  24.62670)          LONGITUDE:  82° 52.3' W ( -82.87170)


The bench mark is a disk set flush in the top of the moat wall near the entrance
to Fort Jefferson, 2.13 m (7.0 ft) NE of the centerline of the bridge across the
moat, and 0.79 m (2.6 ft) SE of the NW edge of the moat wall.



                         BENCH MARK STAMPING:  H
                         DESIGNATION:          872 4697 H TIDAL

MONUMENTATION:           Survey disk                           VM#:         9693
AGENCY:                  Department of Interior                IDB PID#:        
SETTING CLASSIFICATION:  Moat wall                             OPUS PID:        
LATITUDE:   24° 37.6' N (  24.62670)          LONGITUDE:  82° 52.3' W ( -82.87170)


The bench mark is set flush in the top of the moat wall near the entrance to
Fort Jefferson, 11.37 m (37.3 ft) NE of the centerline of the bridge across the
moat, 9.24 m (30.3 ft) NE of Bench Mark F, and 0.73 m (2.4 ft) SE of the NW edge
of the moat wall.

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

                                                                                
Station ID: 8724697                         PUBLICATION DATE:  11/13/2003
Name:       GARDEN KEY,DRY TORTUGAS                           
            FL
NOAA Chart: 11438                           Latitude:   24° 37.6' N (  24.62670)
USGS Quad:  DRY TORTUGAS                    Longitude:  82° 52.3' W ( -82.87170)


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


                         BENCH MARK STAMPING:  M
                         DESIGNATION:          872 4697 M TIDAL

MONUMENTATION:           Survey disk                           VM#:         9694
AGENCY:                  Department of Interior                IDB PID#:        
SETTING CLASSIFICATION:  Moat wall                             OPUS PID:        
LATITUDE:   24° 37.6' N (  24.62670)          LONGITUDE:  82° 52.3' W ( -82.87170)


The bench mark is a disk set flush in the top of the moat wall near the entrance
to Fort Jefferson, 60.44 m (198.3 ft) NE of the centerline of the bridge across
the moat, and 49 m (161 ft) NE of Bench Mark H.

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

                                                                                
Station ID: 8724697                         PUBLICATION DATE:  11/13/2003
Name:       GARDEN KEY,DRY TORTUGAS                           
            FL
NOAA Chart: 11438                           Latitude:   24° 37.6' N (  24.62670)
USGS Quad:  DRY TORTUGAS                    Longitude:  82° 52.3' W ( -82.87170)


                            T I D A L   D A T U M S 


Tidal datums at GARDEN KEY,DRY TORTUGAS based on:

     LENGTH OF SERIES:      2 MONTHS
     TIME PERIOD:           March 1974 - April 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   =  0.534
     MEAN HIGH WATER                            MHW    =  0.437
     MEAN TIDE LEVEL                            MTL    =  0.266
     MEAN SEA LEVEL                             MSL    =  0.266
     MEAN LOW WATER                             MLW    =  0.095
     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                                   1.964    1.527
     E                                           1.406    0.969
     F                                           1.449    1.012
     H                                           1.447    1.010
     M                                           1.361    0.923


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

                                                                                
Station ID: 8724697                         PUBLICATION DATE:  11/13/2003
Name:       GARDEN KEY,DRY TORTUGAS                           
            FL
NOAA Chart: 11438                           Latitude:   24° 37.6' N (  24.62670)
USGS Quad:  DRY TORTUGAS                    Longitude:  82° 52.3' W ( -82.87170)


                             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 8724697 GARDEN KEY, DRY TORTUGAS, FL

Revised: 10/15/2013
NOAA / National Ocean Service
Web site owner: Center for Operational Oceanographic Products and Services