U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 03/06/1985
Station ID: 8728255 SUPERCEDED DATE: 04/21/2003
Name: ST. JAMES ISLAND, ALLIGATOR HARBOR
FLORIDA
NOAA Chart: 11405 Latitude: 29° 54.7' N
USGS Quad: LIGHTHOUSE POINT Longitude: 84° 21.9' W
To reach the tidal bench marks from the intersection of State Road 370 and U.S.
Highway 98, proceed east on State Road 370 2.6 miles (4.2 km) to a shell road,
go south on the shell road 150 feet (45.7 m) to a stilt house on the left. The
bench marks are located along State Road 370 and 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
MONUMENTATION: Survey Disk VM#: 9773
AGENCY: PID#: AS0457
SETTING CLASSIFICATION: Copper-coated Steel Rod
The bench mark is 87.8 feet (26.8 m) SW of the SW corner of the stilt house,
85.7 feet (26.1 m) WNW of the dock, 46.2 feet (14.1 m) west of a 1.5 foot (0.5
m) diameter oak tree, 6.3 feet (1.9 m) south of a fence corner of the SW corner
of a private property, and 1 foot (0.3 m) north of a witness post. The bench
mark is crimped to a copper-coated steel rod driven 32 feet (10 m) to refusal,
and encased in a 4-inch diameter PVC pipe and concrete kickblock.
BENCH MARK STAMPING: 8255 B 1976
MONUMENTATION: Survey Disk VM#: 9774
AGENCY: PID#: AS0456
SETTING CLASSIFICATION: Copper-coated Steel Rod
The bench mark is near the intersection of the shell road and State Road 370,
80.2 feet (24.4 m) WNW of the centerline of the shell road, 39.0 feet (11.9 m)
SW of the centerline of State Road 370, 19.5 feet (5.9 m) NE of a 1.2 foot (0.4
m) diameter oak tree, 5.8 feet (1.8 m) ENE of a power pole, and 1 foot (0.3 m)
south of a witness post. The bench mark is crimped to a copper-coated steel rod
driven 56 feet (17 m) 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 4
PUBLICATION DATE: 03/06/1985
Station ID: 8728255 SUPERCEDED DATE: 04/21/2003
Name: ST. JAMES ISLAND, ALLIGATOR HARBOR
FLORIDA
NOAA Chart: 11405 Latitude: 29° 54.7' N
USGS Quad: LIGHTHOUSE POINT Longitude: 84° 21.9' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 8255 C 1976
MONUMENTATION: Survey Disk VM#: 9775
AGENCY: PID#: AS0455
SETTING CLASSIFICATION: Concrete Post
The bench mark is at the edge of the road right-of-way on the north side of
State Road 370, 49.7 feet (15.1 m) NE of the centerline of the road, 44.6 feet
(13.6 m) east of a lone palm tree on the road right-of-way, 1.0 foot (0.3 m)
west of a metal witness post, and set in a concrete post projecting 0.3 foot
(0.1 m) above ground level.
BENCH MARK STAMPING: 8255 D 1976
MONUMENTATION: Survey Disk VM#: 9776
AGENCY: PID#: AS0454
SETTING CLASSIFICATION: Copper-coated Steel Rod
The bench mark is west of Bench Mark 8255 C 1976, 57.5 feet (17.5 m) SW of the
centerline of State Road 370, 41.8 feet (12.7 m) west of the centerline of a
road perpendicular to State Road 370, 12.6 feet (3.8 m) SW of a telephone cable
terminal box, and 11.0 feet (3.4 m) west of a 1.2 foot (0.4 m) diameter pine
tree. The bench mark is crimped to a copper-coated steel rod driven 40 feet (12
m) to refusal, and encased in a 4-inch diameter PVC pipe and concrete kickblock.
BENCH MARK STAMPING: 21 M 1943 15
MONUMENTATION: Survey Disk VM#: 9777
AGENCY: PID#: AS0453
SETTING CLASSIFICATION: Concrete Post
The bench mark is 290 feet (88 m) NE of a microwave tower, 62.0 feet (18.9 m) NE
of the centerline of State Road 370, 15.9 feet (4.8 m) NE of a power pole, and
1.1 feet (0.3 m) NW of a metal witness post, and set in a concrete post
projecting 0.2 foot (0.1 m) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 03/06/1985
Station ID: 8728255 SUPERCEDED DATE: 04/21/2003
Name: ST. JAMES ISLAND, ALLIGATOR HARBOR
FLORIDA
NOAA Chart: 11405 Latitude: 29° 54.7' N
USGS Quad: LIGHTHOUSE POINT Longitude: 84° 21.9' W
T I D A L D A T U M S
Tidal datums at ST. JAMES ISLAND, ALLIGATOR HARBOR based on:
LENGTH OF SERIES: 3 MONTHS
TIME PERIOD: APRIL-JULY 1976
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8728360 TURKEY POINT
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (05/15/1976) = 4.18
MEAN HIGHER HIGH WATER MHHW = 2.96
MEAN HIGH WATER MHW = 2.69
MEAN TIDE LEVEL MTL = 1.65
MEAN LOW WATER MLW = 0.61
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (05/05/1976) = -0.91
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
8255 A 1976 5.96 3.27
8255 B 1976 13.29 10.60
8255 C 1976 12.86 10.17
8255 D 1976 15.85 13.16
21 M 1943 15 16.08 13.39
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 03/06/1985
Station ID: 8728255 SUPERCEDED DATE: 04/21/2003
Name: ST. JAMES ISLAND, ALLIGATOR HARBOR
FLORIDA
NOAA Chart: 11405 Latitude: 29° 54.7' N
USGS Quad: LIGHTHOUSE POINT Longitude: 84° 21.9' W
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 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.