U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 8667783 PUBLICATION DATE: 05/16/2003
Name: OTTER ISLAND, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670)
USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000)
To reach the tidal bench marks from U.S. Highway 17 in Jacksonboro, proceed
south on U.S. Highway 17 for 13 km (8 mi), crossing Ashepoo River, to a rest
area and the intersection of State Road S-15-26, turn left on State Road S-15-26
and go 25.1 km (15.6 mi) to the end of the pavement, turn right onto the dirt
road and continue 0.3 km (0.2 mi) to the boat ramps at Bennetts Point, continue
by boat for about 12.4 km (6.7 nautical mi) down the Ashepoo River to Otter
Island. The bench marks are behind the berm line and west of the dense brush on
the beach of Otter Island. The tide gage and staff were on a platform
constructed offshore of the west side of the island at the mouth of Ashepoo
River at St. Helena Sound.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 7783 A 1978
DESIGNATION: 866 7783 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 4395
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID:
LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000)
The primary bench mark is a disk crimped to a galvanized steel rod, located
41.85 m (137.3 ft) NNW of Bench Mark 7783 B 1978, and 1.25 m (4.1 ft) WSW of a
metal witness post. The bench mark is 0.09 m (0.3 ft) above the ground, crimped
to a galvanized steel rod driven 12 m (38 ft) 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
Station ID: 8667783 PUBLICATION DATE: 05/16/2003
Name: OTTER ISLAND, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670)
USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 7783 B 1978
DESIGNATION: 866 7783 B TIDAL
MONUMENTATION: Tidal Station disk VM#: 4396
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000)
The bench mark is a disk set in the top of a concrete monument, 46 m (151 ft)
north of Bench Mark 7783 C 1978, 1.13 m (3.7 ft) west of a metal witness post,
and 0.09 m (0.3 ft) above the ground.
BENCH MARK STAMPING: 7783 C 1978
DESIGNATION: 866 7783 C TIDAL
MONUMENTATION: Tidal Station disk VM#: 4397
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID:
LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000)
The bench mark is a disk crimped to a galvanized steel rod, located 50.38 m
(165.3 ft) feet NNE of Bench Mark 7783 D 1978, and 1.22 m (4.0 ft) west of a
metal witness post. The bench mark is 0.09 m (0.3 ft) above the ground, crimped
to a galvanized steel rod driven 7 m (22 ft) 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 3 of 5
Station ID: 8667783 PUBLICATION DATE: 05/16/2003
Name: OTTER ISLAND, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670)
USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 7783 D 1978
DESIGNATION: 866 7783 D TIDAL
MONUMENTATION: Tidal Station disk VM#: 4398
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete momument OPUS PID:
LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000)
The bench mark is a disk set in the top of a concrete monument, 44.17 m (144.9
ft) north of Bench Mark 7783 E 1978, 0.85 m (2.8 ft) west of a metal witness
post, and 0.03 m (0.1 ft) above the ground.
BENCH MARK STAMPING: 7783 E 1978
DESIGNATION: 866 7783 E TIDAL
MONUMENTATION: Tidal Station disk VM#: 4399
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Galvinized steel rod OPUS PID:
LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000)
The bench mark is a disk crimped to a galvanized steel rod, located 13.41 m
(44.0 ft) west of a 0.15 m (0.5 ft) diameter twin cedar tree, and 1.04 m (3.4
ft) west of a metal witness post. The bench mark is 0.09 m (0.3 ft) above the
ground, crimped to a galvanized steel rod driven 6.71 m (22.0 ft) 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 4 of 5
Station ID: 8667783 PUBLICATION DATE: 05/16/2003
Name: OTTER ISLAND, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670)
USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000)
T I D A L D A T U M S
Tidal datums at OTTER ISLAND, ST. HELENA SOUND based on:
LENGTH OF SERIES: 8 MONTHS
TIME PERIOD: April 1978 - November 1978
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8667999 BEAUFORT
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 2.004
MEAN HIGH WATER MHW = 1.895
MEAN SEA LEVEL MSL = 1.023
MEAN TIDE LEVEL MTL = 0.979
MEAN LOW WATER MLW = 0.064
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
7783 A 1978 2.536 0.641
7783 B 1978 2.542 0.647
7783 C 1978 2.638 0.743
7783 D 1978 2.513 0.618
7783 E 1978 2.621 0.726
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 8667783 PUBLICATION DATE: 05/16/2003
Name: OTTER ISLAND, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670)
USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000)
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.