U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
Station ID: 8668146 PUBLICATION DATE: 02/05/2004
Name: HARBOR RIVER BRIDGE, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 24.2' N ( 32.40330)
USGS Quad: ST. HELENA SOUND Longitude: 80° 27.2' W ( -80.45330)
To reach the tidal bench marks from the post office in Frogmore, proceed east on
U.S. Highway 21 for 12.9 km (8.0 mi) to the steel swing bridge over the north
entrance to Harbor River. The bench marks are on the bridge and along the
highway north of the bridge. The tide gauge and staff were on the bridge
fender.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1 1956
DESIGNATION: 866 8146 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 4461
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: CK0845
SETTING CLASSIFICATION: Concrete abutment OPUS PID#: CK0845
LATITUDE: 32° 24.2' N ( 32.40330) LONGITUDE: 80° 27.0' W ( -80.45000)
The primary bench mark is a disk set in the NE concrete abutment at the SE end
of the bridge, 305 m (1000 ft) east if the midpoint of the steel swing span of
the bridge, 3.81 m (12.5 ft) north of the centerline of the highway, and 0.3 m
(1 ft) above the highway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 8668146 PUBLICATION DATE: 02/05/2004
Name: HARBOR RIVER BRIDGE, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 24.2' N ( 32.40330)
USGS Quad: ST. HELENA SOUND Longitude: 80° 27.2' W ( -80.45330)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 2 1956
DESIGNATION: 866 8146 TIDAL 2
MONUMENTATION: Bench Mark disk VM#: 4462
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: CK0844
SETTING CLASSIFICATION: Concrete abutment OPUS PID:
LATITUDE: 32° 24.4' N ( 32.40670) LONGITUDE: 80° 27.5' W ( -80.45830)
The bench mark is a disk set in the NE concrete abutment at the NW end of the
bridge, 610 m (2000 ft) west of the midpoint of the steel swing span of the
bridge, 3.78 m (12.4 ft) north of the centerline of the highway, and 0.3 m (1
ft) above the highway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 8668146 PUBLICATION DATE: 02/05/2004
Name: HARBOR RIVER BRIDGE, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 24.2' N ( 32.40330)
USGS Quad: ST. HELENA SOUND Longitude: 80° 27.2' W ( -80.45330)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: SWING NO 1 1963
DESIGNATION: SWING RM 1
MONUMENTATION: Reference Mark disk VM#: 4463
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: CK2337
SETTING CLASSIFICATION: Bridge curb OPUS PID:
LATITUDE: 32° 24.4' N ( 32.40670) LONGITUDE: 80° 27.5' W ( -80.45830)
The bench mark is a disk set in the SW curbing at the NW corner of the bridge,
8.38 m (27.5 ft) ESE of the NW end of the bridge, and 0.3 m (1 ft) above the
highway.
BENCH MARK STAMPING: NO 4 1974
DESIGNATION: 866 8146 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 17112
AGENCY: National Ocean Survey (NOS) IDB PID#: CK2335
SETTING CLASSIFICATION: Concrete post OPUS PID:
LATITUDE: 32° 24.5' N ( 32.40830) LONGITUDE: 80° 28.0' W ( -80.46670)
The bench mark is a disk set in the top of a concrete post along the SW side of
U.S. Route 21, 0.8 km (0.5 mi) NW along Highway 21 from the NW end of the bridge
over Harbor River, 8.69 m (28.5 ft) south of the center line of Highway 21, 0.88
m (2.9 ft) NNW of a first metal witness post with sign, 0.40 m (1.3 ft) NE of a
second witness post with sign, 0.46 m (1.5 ft) below the highway, and 6 cm (0.2
ft) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 8668146 PUBLICATION DATE: 02/05/2004
Name: HARBOR RIVER BRIDGE, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 24.2' N ( 32.40330)
USGS Quad: ST. HELENA SOUND Longitude: 80° 27.2' W ( -80.45330)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 5 1974
DESIGNATION: 866 8146 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 17113
AGENCY: National Ocean Survey (NOS) IDB PID#: CK2336
SETTING CLASSIFICATION: Concrete post OPUS PID:
LATITUDE: 32° 24.5' N ( 32.40830) LONGITUDE: 80° 27.8' W ( -80.46330)
The bench mark is a disk set in the top of a concrete post along the SW side of
U.S. Route 21, 0.5 km (0.3 mi) NW along Highway 21 from the NW end of the bridge
over Harbor River, 14.11 m (46.3 ft) NNE of telephone junction box RP-90, 9.85 m
(32.3 ft) north of the center line of Highway 21, 1.98 m (6.5 ft) north of
telephone pole #RP68, 0.64 m (2.1 ft) NNE of metal witness post with sign, 0.76
m (2.5 ft) below the highway, and 6 cm (0.2 ft) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 8668146 PUBLICATION DATE: 02/05/2004
Name: HARBOR RIVER BRIDGE, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 24.2' N ( 32.40330)
USGS Quad: ST. HELENA SOUND Longitude: 80° 27.2' W ( -80.45330)
T I D A L D A T U M S
Tidal datums at HARBOR RIVER BRIDGE, ST. HELENA SOUND based on:
LENGTH OF SERIES: 1 YEAR
TIME PERIOD: February 1975 - January 1976
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8665530 CHARLESTON, COOPER RIVER ENTRANCE
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (11/02/1975) = 2.542
MEAN HIGHER HIGH WATER MHHW = 2.038
MEAN HIGH WATER MHW = 1.920
North American Vertical Datum NAVD88 = 1.133
MEAN SEA LEVEL MSL = 1.039
MEAN TIDE LEVEL MTL = 0.992
MEAN LOW WATER MLW = 0.064
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (11/13/1974) = -1.061
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
NO 1 1956 4.584 2.664
NO 2 1956 4.621 2.701
SWING NO 1 1963 4.905 2.985
NO 4 1974 3.741 1.821
NO 5 1974 3.421 1.501
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 8668146 PUBLICATION DATE: 02/05/2004
Name: HARBOR RIVER BRIDGE, ST. HELENA SOUND
SC
NOAA Chart: 11517 Latitude: 32° 24.2' N ( 32.40330)
USGS Quad: ST. HELENA SOUND Longitude: 80° 27.2' W ( -80.45330)
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.