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Bench Mark Sheet for 8728255, ALLIGATOR HARBOR 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Superseded Epoch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Small blue map location marker Unpublished bench mark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: 8728255                         PUBLICATION DATE:  05/12/2004
Name:       ALLIGATOR HARBOR                                  
            FL
NOAA Chart: 11405                           Latitude:   29° 54.7' N (  29.91170)
USGS Quad:  LIGHTHOUSE POINT                Longitude:  84° 21.9' W ( -84.36500)


To reach the tidal bench marks from the intersection of State Road 370
(Alligator Drive) and U.S. Highway 98 south of Ochlockonee Bay, proceed east on
State Road 370 for 4.2 km (2.6 mi) to a shell road, then turn and proceed south
on the shell road for 45.72 m (150.0 ft) to a stilt house on the left.  The
bench marks are located along State Road 370.  The tide gage and staff were
located at the end of a catwalk behind the stilt house.


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


                 PRIMARY BENCH MARK STAMPING:  8255 A 1976
                         DESIGNATION:          872 8255 A TIDAL FLDNR

MONUMENTATION:           Tidal Station disk                    VM#:         9773
AGENCY:                  Florida Department of Natural Resources
                         (FLDNR)                               IDB PID#:  AS0457
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   29° 54.8' N (  29.91330)          LONGITUDE:  84° 22.1' W ( -84.36830)


The primary bench mark is a disk located 26.76 m (87.8 ft) SW of the SW corner
of the stilt house, 26.12 m (85.7 ft) WNW of the dock, 14.08 m (46.2 ft) west of
a 0.46 m (1.5 ft) diameter oak tree, 1.92 m (6.3 ft) south of a fence corner of
the SW corner of a private property, and 0.30 m (1.0 ft) north of a witness
post.  The bench mark is crimped to the top of a copper-coated steel rod driven
9.8 m (32 ft) to refusal, and encased in a 4-inch diameter PVC pipe and concrete
kickblock.

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

                                                                                
Station ID: 8728255                         PUBLICATION DATE:  05/12/2004
Name:       ALLIGATOR HARBOR                                  
            FL
NOAA Chart: 11405                           Latitude:   29° 54.7' N (  29.91170)
USGS Quad:  LIGHTHOUSE POINT                Longitude:  84° 21.9' W ( -84.36500)


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


                         BENCH MARK STAMPING:  8255 B 1976
                         DESIGNATION:          872 8255 B TIDAL FLDNR

MONUMENTATION:           Tidal Station disk                    VM#:         9774
AGENCY:                  Florida Department of Natural Resources
                         (FLDNR)                               IDB PID#:  AS0456
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   29° 54.9' N (  29.91500)          LONGITUDE:  84° 22.1' W ( -84.36830)


The bench mark is a disk located near the intersection of the shell road and
State Road 370 (Alligator Drive), 24.44 m (80.2 ft) WNW of the centerline of the
shell road, 12 m (39 ft) SW of the centerline of State Road 370, 5.94 m (19.5
ft) NE of a 0.37 m (1.2 ft) diameter oak tree, 1.77 m (5.8 ft) ENE of a power
pole, and 0.30 m (1.0 ft) south of a witness post.  The bench mark is crimped to
the top of a copper-coated steel rod driven 17.1 m (56 ft) to refusal, and
encased in a 4-inch diameter PVC pipe and concrete kickblock.  NOTE: Mark not
found by US Power Squadron in 1998.



                         BENCH MARK STAMPING:  8255 C 1976
                         DESIGNATION:          872 8255 C TIDAL FLDNR

MONUMENTATION:           Tidal Station disk                    VM#:         9775
AGENCY:                  Florida Department of Natural Resources
                         (FLDNR)                               IDB PID#:  AS0455
SETTING CLASSIFICATION:  Concrete post                         OPUS PID:        
LATITUDE:   29° 54.9' N (  29.91500)          LONGITUDE:  84° 22.1' W ( -84.36830)


The bench mark is a disk set in the top of a concrete post at the edge of the
road right-of-way on the north side of State Road 370 (Alligator Drive), 15.15 m
(49.7 ft) NE of the centerline of the road, 13.59 m (44.6 ft) east of a lone
palm tree on the road right-of-way, 0.30 m (1.0 ft) west of a metal witness
post, and set in a concrete post projecting 0.09 m (0.3 ft) above ground level.

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

                                                                                
Station ID: 8728255                         PUBLICATION DATE:  05/12/2004
Name:       ALLIGATOR HARBOR                                  
            FL
NOAA Chart: 11405                           Latitude:   29° 54.7' N (  29.91170)
USGS Quad:  LIGHTHOUSE POINT                Longitude:  84° 21.9' W ( -84.36500)


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


                         BENCH MARK STAMPING:  8255 D 1976
                         DESIGNATION:          872 8255 D TIDAL FLDNR

MONUMENTATION:           Tidal Station disk                    VM#:         9776
AGENCY:                  Florida Department of Natural Resources
                         (FLDNR)                               IDB PID#:  AS0454
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   29° 54.9' N (  29.91500)          LONGITUDE:  84° 22.1' W ( -84.36830)


The bench mark is a disk located west of bench mark 8255 C 1976, 17.53 m (57.5
ft) SW of the centerline of State Road 370 (Alligator Drive), 12.74 m (41.8 ft)
west of the centerline of a road perpendicular to State Road 370, 3.84 m (12.6
ft) SW of a telephone cable terminal box, and 3.35 m (11.0 ft) west of a 0.37 m
(1.2 ft) diameter pine tree.  The bench mark is crimped to the top of a
copper-coated steel rod driven 12.2 m (40 ft) to refusal, and encased in a
4-inch diameter PVC pipe and concrete kickblock.



                         BENCH MARK STAMPING:  21 M 1943 15
                         DESIGNATION:          21 M USGS

MONUMENTATION:           Bench Mark disk                       VM#:         9777
AGENCY:                  US Geological Survey (USGS)           IDB PID#:  AS0453
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   29° 55.0' N (  29.91670)          LONGITUDE:  84° 22.1' W ( -84.36830)


The bench mark is a disk set in the top of a concrete monument, 88.39 m (290.0
ft) NE of a microwave tower, 19 m (62 ft) NE of the centerline of State Road
370, 4.85 m (15.9 ft) NE of a power pole, 0.34 m (1.1 ft) NW of a metal witness
post, and 0.06 m (0.2 ft) above ground level.

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

                                                                                
Station ID: 8728255                         PUBLICATION DATE:  05/12/2004
Name:       ALLIGATOR HARBOR                                  
            FL
NOAA Chart: 11405                           Latitude:   29° 54.7' N (  29.91170)
USGS Quad:  LIGHTHOUSE POINT                Longitude:  84° 21.9' W ( -84.36500)


                            T I D A L   D A T U M S 


Tidal datums at ALLIGATOR HARBOR based on:

     LENGTH OF SERIES:      2 MONTHS
     TIME PERIOD:           June 1976 - July 1976
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  8728360 TURKEY POINT


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

     MEAN HIGHER HIGH WATER                     MHHW   =  0.890
     MEAN HIGH WATER                            MHW    =  0.820
     North American Vertical Datum              NAVD88 =  0.523
     MEAN TIDE LEVEL                            MTL    =  0.501
     MEAN SEA LEVEL                             MSL    =  0.486
     MEAN LOW WATER                             MLW    =  0.181
     MEAN LOWER LOW WATER                       MLLW   =  0.000

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     8255 A 1976                                 1.801    0.981
     8255 B 1976                                 4.036    3.216
     8255 C 1976                                 3.905    3.085
     8255 D 1976                                 4.816    3.996
     21 M 1943 15                                4.884    4.064


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

                                                                                
Station ID: 8728255                         PUBLICATION DATE:  05/12/2004
Name:       ALLIGATOR HARBOR                                  
            FL
NOAA Chart: 11405                           Latitude:   29° 54.7' N (  29.91170)
USGS Quad:  LIGHTHOUSE POINT                Longitude:  84° 21.9' W ( -84.36500)


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