U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
Station ID: 8668227 PUBLICATION DATE: 02/05/2004
Name: JOHNSON'S CREEK, HARBOR ISLAND
SC
NOAA Chart: 11516 Latitude: 32° 23.5' N ( 32.39170)
USGS Quad: ST. HELENA SOUND Longitude: 80° 26.3' W ( -80.43830)
To reach the tidal bench marks from Frogmore Post Office in Beaufort County,
proceed 15.1 km (9.4 mi) east on U.S. Highway 21 to Johnson Creek. The bench
marks are located at the bridge and along the highway. The tide gage and staff
were located on the NW side of the bridge over Johnson Creek.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: JCB NO 1 1974
DESIGNATION: 866 8227 TIDAL JCB 1
MONUMENTATION: Tidal Station disk VM#: 4479
AGENCY: National Ocean Survey (NOS) IDB PID#: CK2340
SETTING CLASSIFICATION: Bridge curb OPUS PID:
LATITUDE: 32° 23.5' N ( 32.39170) LONGITUDE: 80° 26.4' W ( -80.44000)
The primary bench mark is a disk set flush in the top of the west curb of the NW
end of the bridge, 3.51 m (11.5 ft) west of the centerline of the highway, and
0.3 m (1.0 ft) above highway level.
BENCH MARK STAMPING: JCB NO 2 1974
DESIGNATION: 866 8227 TIDAL JCB 2
MONUMENTATION: Tidal Station disk VM#: 4480
AGENCY: National Ocean Survey (NOS) IDB PID#: CK2341
SETTING CLASSIFICATION: Bridge curb OPUS PID:
LATITUDE: 32° 23.4' N ( 32.39000) LONGITUDE: 80° 26.3' W ( -80.43830)
The bench mark is a disk set flush in the top of the east curb of the SE end of
the bridge, 3.51 m (11.5 ft) east of the centerline of the highway, and 0.3 m (1
ft) above highway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 8668227 PUBLICATION DATE: 02/05/2004
Name: JOHNSON'S CREEK, HARBOR ISLAND
SC
NOAA Chart: 11516 Latitude: 32° 23.5' N ( 32.39170)
USGS Quad: ST. HELENA SOUND Longitude: 80° 26.3' W ( -80.43830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: JCB NO 3 1974
DESIGNATION: 866 8227 TIDAL JCB 3
MONUMENTATION: Tidal Station disk VM#: 4481
AGENCY: National Ocean Survey (NOS) IDB PID#: CK2342
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 32° 23.4' N ( 32.39000) LONGITUDE: 80° 26.3' W ( -80.43830)
The bench mark is a disk located near a lone palmetto tree, 91 m (300 ft) SE of
the SE end of the Johnson Creek bridge, 15.24 m (50.0 ft) NE of the easternmost
of two posts for a sign reading "Park Entrance Public Beach - 1.4 miles", 10.15
m (33.3 ft) west of utility pole #130225, 8.38 m (27.5 ft) ENE of the centerline
of the highway 21, 4.57 m (15.0 ft) NNW of a lone 0.76 m (2.5 ft) palmetto
tree, and 0.58 m (1.9 ft) NW of a witness post. The bench mark is set 6 cm (0.2
ft) above ground level, crimped to a copper-clad steel rod driven 25.6 m (84
ft), and surrounded by concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 8668227 PUBLICATION DATE: 02/05/2004
Name: JOHNSON'S CREEK, HARBOR ISLAND
SC
NOAA Chart: 11516 Latitude: 32° 23.5' N ( 32.39170)
USGS Quad: ST. HELENA SOUND Longitude: 80° 26.3' W ( -80.43830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: JCB NO 5 1974
DESIGNATION: 866 8227 TIDAL JCB 5
MONUMENTATION: Tidal Station disk VM#: 4482
AGENCY: National Ocean Survey (NOS) IDB PID#: CK2344
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 32° 23.2' N ( 32.38670) LONGITUDE: 80° 26.3' W ( -80.43830)
The bench mark is a disk located in the SE angle of the intersection of county
road S-7-348, 10.21 m (33.5 ft) south of the centerline of the road leading to
the state park campground, 9.14 m (30.0 ft) ESE of the centerline of the highway
21, 7.47 m (24.5 ft) SW of the SE gate post to the campground, 5.39 m (17.7 ft)
NNE of utility pole #40-206986, 3 m (10 ft) SSE of the easternmost post for a
sign reading Campground Campers Only - Trading Post, and 0.50 m (1.6 ft) NW of a
witness post. The bench mark is set 0.91 m (3.0 ft) below highway level,
crimped to a copper-clad steel rod driven 21.3 m (69.88 ft), and surrounded by
concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 8668227 PUBLICATION DATE: 02/05/2004
Name: JOHNSON'S CREEK, HARBOR ISLAND
SC
NOAA Chart: 11516 Latitude: 32° 23.5' N ( 32.39170)
USGS Quad: ST. HELENA SOUND Longitude: 80° 26.3' W ( -80.43830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 8227 F 1982
DESIGNATION: 866 8227 F TIDAL
MONUMENTATION: Tidal Station disk VM#: 4483
AGENCY: National Ocean Survey (NOS) IDB PID#: CK2343
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 32° 23.3' N ( 32.38830) LONGITUDE: 80° 26.3' W ( -80.43830)
The bench mark is a disk located near the sign reading Hunting Island State
Park, 19.81 m (65.0 ft) west of utility pole #111401, 8.90 m (29.2 ft) SSE of a
phone junction box, 8.84 m (29.0 ft) NW of the centerline of the highway, 3.29 m
(10.8 ft) NE of a lone 0.67 m (2.2 ft) diameter palmetto tree, 1.19 m (3.9 ft)
north of the westernmost post supporting the sign, and 0.30 m (1.0 ft) SSW of a
witness post. The bench mark is set 0.6 m (2 ft) below ground level, crimped to
the top of a copper-clad steel rod driven 14.6 m (48 ft), encased in a PVC pipe
and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 8668227 PUBLICATION DATE: 02/05/2004
Name: JOHNSON'S CREEK, HARBOR ISLAND
SC
NOAA Chart: 11516 Latitude: 32° 23.5' N ( 32.39170)
USGS Quad: ST. HELENA SOUND Longitude: 80° 26.3' W ( -80.43830)
T I D A L D A T U M S
Tidal datums at JOHNSON'S CREEK, HARBOR ISLAND based on:
LENGTH OF SERIES: 1 YEAR
TIME PERIOD: March 1975 - February 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) = 2.497
MEAN HIGHER HIGH WATER MHHW = 1.970
MEAN HIGH WATER MHW = 1.851
North American Vertical Datum NAVD88 = 1.091
MEAN SEA LEVEL MSL = 0.994
MEAN TIDE LEVEL MTL = 0.955
MEAN LOW WATER MLW = 0.059
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (02/19/1976) = -0.676
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
JCB NO 1 1974 4.612 2.761
JCB NO 2 1974 4.585 2.734
JCB NO 3 1974 3.125 1.274
JCB NO 5 1974 3.008 1.157
8227 F 1982 2.770 0.919
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 8668227 PUBLICATION DATE: 02/05/2004
Name: JOHNSON'S CREEK, HARBOR ISLAND
SC
NOAA Chart: 11516 Latitude: 32° 23.5' N ( 32.39170)
USGS Quad: ST. HELENA SOUND Longitude: 80° 26.3' W ( -80.43830)
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.