U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 12/23/1985
Station ID: 8668255 SUPERCEDED DATE: 04/21/2003
Name: ST. HELENA ISLAND, CAPERS CREEK
SOUTH CAROLINA
NOAA Chart: 11513 Latitude: 32° 22.3' N
USGS Quad: ST. PHILLIPS ISLAND Longitude: 80° 36.3' W
To reach the tidal bench marks from the intersection of U.S. Highway 21 and
State Road S-7-45 in Frogmore, proceed south on State Road S-7-45 for 2.3 miles
(3.7 km) to State Road S-7-164, then NW on State Road S-7-164 for 0.7 mile (1.1
km) to State Road S-7-113, then SW on State Road S-7-113 for 0.3 mile (0.5 km)
to the entrance to Orange Grove Plantation, and west along the drive for 0.2
mile (0.3 km) to the Trask house. The bench marks are located on the Trask
property. The tide gage and staff were located on a dock 200 feet (61 m) west
of the house.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 8255 B 1980
MONUMENTATION: Survey Disk VM#: 12101
AGENCY: PID:
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is near the dock, 250.2 feet (76.3 m) NE of Bench Mark 8255 H
1981, 83.0 feet (25.3 m) SW of Bench Mark 8255 G 1981, 49.5 feet (15.1 m) east
of the center of a grove of seven oak trees, 33.2 feet (10.1 m) SSE of a 4.0-
foot (1.2 m) diameter twin oak tree, and 1.7 feet (0.5 m) SW of the inside
corner of a small tabby ruin (consisting only of one corner). The bench mark is
level with the ground, crimped to a stainless steel rod driven 30 feet (9 m) to
refusal, and encased in a 5-inch PVC pipe and concrete kickblock.
BENCH MARK STAMPING: 8255 D 1980
MONUMENTATION: Survey Disk VM#: 12102
AGENCY: PID:
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is near the creek north of the dock, 156.0 feet (47.5 m) NW of
Bench Mark 8255 F 1981, 50.0 feet (15.2 m) WNW of a pair of 2.0-foot (0.6 m)
diameter leaning oak trees, 40.5 feet (12.3 m) north of the base of a very large
pittosporium bush (wax leaf), 30.0 feet (9.1 m) ESE of the bank of the creek,
and 9.7 feet (3.0 m) SSW of a 2.0-foot (0.6 m) diameter live oak. The bench
mark is level with the ground, crimped to a stainless steel rod driven 28 feet
(9 m) to refusal, and encased in a 4-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 12/23/1985
Station ID: 8668255 SUPERCEDED DATE: 04/21/2003
Name: ST. HELENA ISLAND, CAPERS CREEK
SOUTH CAROLINA
NOAA Chart: 11513 Latitude: 32° 22.3' N
USGS Quad: ST. PHILLIPS ISLAND Longitude: 80° 36.3' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 8255 F 1981
MONUMENTATION: Survey Disk VM#: 12103
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is near the duck pond and sheds north of the house, 156.0 feet
(47.5 m) SE of Bench Mark 8255 D 1980, 86.6 feet (26.4 m) NE of the NE corner of
a brick generator building, 37.8 feet (11.5 m) WSW of the SW corner of a wooden
tool shed, and 4.0 feet (1.2 m) east of utility pole #232780. The bench mark is
level with the ground.
BENCH MARK STAMPING: 8255 G 1981
MONUMENTATION: Survey Disk VM#: 12104
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is near an old graveyard north of the house, 83.0 feet (25.3 m)
NE of Bench Mark 8255 B 1980, 22.0 feet (6.7 m) west of the center of top of
grave marker for Ann P. Fripp, 7.5 feet (2.3 m) NE of a 3.5-foot (1.1 m)
diameter oak tree, 5.2 feet (1.6 m) south of the center of the grave marker for
Peter Perry, and 1.7 feet (0.5 m) NE of the inside SW corner of the tabby wall
surrounding the graveyard. The bench mark is level with the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
PUBLICATION DATE: 12/23/1985
Station ID: 8668255 SUPERCEDED DATE: 04/21/2003
Name: ST. HELENA ISLAND, CAPERS CREEK
SOUTH CAROLINA
NOAA Chart: 11513 Latitude: 32° 22.3' N
USGS Quad: ST. PHILLIPS ISLAND Longitude: 80° 36.3' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 8255 H 1981
MONUMENTATION: Survey Disk VM#: 12105
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is near the creek south of the dock, 250.2 feet (76.3 m) SW of
Bench Mark 8255 B 1980, 173.0 feet (52.7 m) WNW of the center of the front steps
of the Trask residence, 29.0 feet (8.8 m) SSE of the south face of a 3.5-foot
(1.1 m) diameter twin oak tree, and 10.7 feet (3.3 m) NW of the center of three
palmetto trees. The bench mark is level with the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
PUBLICATION DATE: 12/23/1985
Station ID: 8668255 SUPERCEDED DATE: 04/21/2003
Name: ST. HELENA ISLAND, CAPERS CREEK
SOUTH CAROLINA
NOAA Chart: 11513 Latitude: 32° 22.3' N
USGS Quad: ST. PHILLIPS ISLAND Longitude: 80° 36.3' W
T I D A L D A T U M S
Tidal datums at ST. HELENA ISLAND, CAPERS CREEK based on:
LENGTH OF SERIES: 7 MONTHS
TIME PERIOD: FEBRUARY-NOVEMBER 1981
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8667999 Beaufort
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (05/04/1981) = 9.93
MEAN HIGHER HIGH WATER MHHW = 8.02
MEAN HIGH WATER MHW = 7.65
MEAN TIDE LEVEL MTL = 3.93
MEAN LOW WATER MLW = 0.21
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (04/06/1981) = -1.83
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
8255 B 1980 15.88 8.23
8255 D 1980 13.72 6.07
8255 F 1981 12.03 4.38
8255 G 1981 15.55 7.90
8255 H 1981 13.24 5.59
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 12/23/1985
Station ID: 8668255 SUPERCEDED DATE: 04/21/2003
Name: ST. HELENA ISLAND, CAPERS CREEK
SOUTH CAROLINA
NOAA Chart: 11513 Latitude: 32° 22.3' N
USGS Quad: ST. PHILLIPS ISLAND Longitude: 80° 36.3' 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.