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.