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Bench Mark Sheet for 8723921, GRASSY KEY NORTH SIDE, FLORIDA BAY 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Superseded Epoch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Small blue map location marker Unpublished bench mark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: 8723921                         PUBLICATION DATE:  04/01/2004
Name:       GRASSY KEY NORTH SIDE, FLORIDA BAY                
            FL
NOAA Chart: 11449                           Latitude:   24° 46.3' N (  24.77170)
USGS Quad:  GRASSY KEY                      Longitude:  80° 56.4' W ( -80.94000)


To reach the tidal bench marks from the post office at Layton, proceed 14.0 km
(8.7 mi) SW along U.S. Highway 1 to a paved private drive on the right, continue
0.24 km (0.15 mi) north on the private drive to an abandoned ferry landing on
the Dorset Estate.  The bench marks are along the driveway and near the old
ferry landing, on the gulf side of Grassy Key.  The tide gage and staff were
located on the pier at the boat basin west of the old ferry landing.


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


                 PRIMARY BENCH MARK STAMPING:  BM NO 2 1935
                         DESIGNATION:          872 3921 TIDAL 2

MONUMENTATION:           Tidal Station disk                    VM#:         6266
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AA0354
SETTING CLASSIFICATION:  Coral outcrop                         OPUS PID:        
LATITUDE:   24° 46.4' N (  24.77330)          LONGITUDE:  80° 56.4' W ( -80.94000)


The primary bench mark is a disk set in a large coral outcrop, 20 m (67 ft) SW
of the extended centerline of the road, 9 m (30 ft) NE of the north corner of an
old 4 m (12 ft) square concrete block building, 3 m (9 ft) SE of the shoreline,
and at road level.

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

                                                                                
Station ID: 8723921                         PUBLICATION DATE:  04/01/2004
Name:       GRASSY KEY NORTH SIDE, FLORIDA BAY                
            FL
NOAA Chart: 11449                           Latitude:   24° 46.3' N (  24.77170)
USGS Quad:  GRASSY KEY                      Longitude:  80° 56.4' W ( -80.94000)


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


                         BENCH MARK STAMPING:  NO 5 1964
                         DESIGNATION:          872 3921 NO 5

MONUMENTATION:           Bench Mark disk                       VM#:         6267
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AA0356
SETTING CLASSIFICATION:  Coral outcrop                         OPUS PID:        
LATITUDE:   24° 46.4' N (  24.77330)          LONGITUDE:  80° 56.4' W ( -80.94000)


The bench mark is a disk set in the top of a coral outcrop, 36 m (117 ft) NE of
the extended centerline of the road near the old ferry landing, 4.11 m (13.5 ft)
west of a small button-wood tree with a triangle blaze cut on its west side, 4 m
(13 ft) NW of the NW side of a 1 m (4 ft) boulder which projects 1 m (2 ft), 3 m
(10 ft) SE of the shoreline, and at ground level.

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

                                                                                
Station ID: 8723921                         PUBLICATION DATE:  04/01/2004
Name:       GRASSY KEY NORTH SIDE, FLORIDA BAY                
            FL
NOAA Chart: 11449                           Latitude:   24° 46.3' N (  24.77170)
USGS Quad:  GRASSY KEY                      Longitude:  80° 56.4' W ( -80.94000)


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


                         BENCH MARK STAMPING:  H 328 1970
                         DESIGNATION:          H 328

MONUMENTATION:           Bench Mark disk                       VM#:         6269
AGENCY:                  National Geodetic Survey (NGS)        IDB PID#:  AA0352
SETTING CLASSIFICATION:  Coral outcrop                         OPUS PID:        
LATITUDE:   24° 46.4' N (  24.77330)          LONGITUDE:  80° 56.4' W ( -80.94000)


The bench mark is a disk set in top of a coral outcrop west of the boat basin,
71 m (234 ft) SW of the extended centerline of the paved drive near the old
ferry landing, 29.05 m (95.3 ft) west of the NW corner of a house, 9 m (31 ft)
west of the centerline of a driveway, 4.11 m (13.5 ft) SW of the centerline of
the boat ramp, 3.35 m (11.0 ft) east of the east side of a 1 m (3 ft) high wall
at the shoreline, and 0.30 m (1.0 ft) below driveway level.

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

                                                                                
Station ID: 8723921                         PUBLICATION DATE:  04/01/2004
Name:       GRASSY KEY NORTH SIDE, FLORIDA BAY                
            FL
NOAA Chart: 11449                           Latitude:   24° 46.3' N (  24.77170)
USGS Quad:  GRASSY KEY                      Longitude:  80° 56.4' W ( -80.94000)


                            T I D A L   D A T U M S 


Tidal datums at GRASSY KEY NORTH SIDE, FLORIDA BAY based on:

     LENGTH OF SERIES:      1 YEAR
     TIME PERIOD:           January 1971 - December 1971
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  8724580 KEY WEST


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

     HIGHEST OBSERVED WATER LEVEL (02/19/1972)         =  0.702
     North American Vertical Datum              NAVD88 =  0.422
     MEAN HIGHER HIGH WATER                     MHHW   =  0.388
     MEAN HIGH WATER                            MHW    =  0.337
     MEAN TIDE LEVEL                            MTL    =  0.207
     MEAN SEA LEVEL                             MSL    =  0.185
     MEAN LOW WATER                             MLW    =  0.076
     MEAN LOWER LOW WATER                       MLLW   =  0.000
     LOWEST  OBSERVED WATER LEVEL (02/04/1971)         = -0.355

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     BM NO 2 1935                                0.644    0.307
     NO 5 1964                                   0.695    0.358
     H 328 1970                                  1.275    0.938


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

                                                                                
Station ID: 8723921                         PUBLICATION DATE:  04/01/2004
Name:       GRASSY KEY NORTH SIDE, FLORIDA BAY                
            FL
NOAA Chart: 11449                           Latitude:   24° 46.3' N (  24.77170)
USGS Quad:  GRASSY KEY                      Longitude:  80° 56.4' W ( -80.94000)


                             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 8723921 GRASSY KEY NORTH SIDE, FLORIDA BAY, FL

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