U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
PUBLICATION DATE: 04/07/1988
Station ID: 8665726 SUPERCEDED DATE: 04/21/2003
Name: FORT JOHNSON, CHARLESTON HARBOR
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 45.1' N
USGS Quad: CHARLESTON Longitude: 79° 53.9' W
To reach the tidal bench marks from the intersection of U.S. Highway 17 and
State Highway 171 (Folly Road) in Charleston, proceed south on State Highway 171
for 1.7 miles (2.7 km), turn left on Harbor View Road and go 3.8 miles (6.1 km)
to a stop sign, bear left onto Fort Johnson Road for 0.7 mile (1.1 km) to the
gates of Fort Johnson Marine Resource Center, then 0.5 mile (0.8 km) along the
paved road to the boat slip. The bench marks are located on the Marine Resource
Center grounds. The tide gage and staff were located on the south bulkhead of
the boat slip.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: JOHNSON USE 1933
MONUMENTATION: Survey Disk VM#: 4219
AGENCY: PID#: CJ0146
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a 1.3-foot (0.4 m) diameter concrete monument on the
east side of the Fort Johnson grounds, 98.2 feet (29.9 m) WSW of large granite
boulders on the harbor side protecting the land, 81.5 feet (24.8 m) NE of the NE
corner of a brick magazine, 29.0 feet (8.8 m) WSW of a medium size cedar tree,
29.0 feet (8.8 m) NNE of a north-south line of oak trees, and 1.4 feet (0.4 m)
above ground level.
BENCH MARK STAMPING: NO 1 JOHNSON USE 1933
MONUMENTATION: Survey Disk VM#: 4220
AGENCY: PID#: CJ0145
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a 1.1-foot (0.3 m) diameter concrete monument on the
east side of the Fort Johnson grounds, 84.5 feet (25.8 m) north of a 6.0-foot
(1.8 m) tall Civil War monument to the first shot fired on Fort Sumter, 76.0
feet (23.2 m) SW of Bench Mark JOHNSON USE 1933, 46.7 feet (14.2 m) ENE of the
center of a double oak tree, 41.8 feet (12.7 m) NE of the NE corner of a brick
magazine, 28.2 feet (8.6 m) east of the SE corner of a brick magazine, 11.7 feet
(3.6 m) west of a north-south line of oak trees, and 0.5 foot (0.2 m) above
ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
PUBLICATION DATE: 04/07/1988
Station ID: 8665726 SUPERCEDED DATE: 04/21/2003
Name: FORT JOHNSON, CHARLESTON HARBOR
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 45.1' N
USGS Quad: CHARLESTON Longitude: 79° 53.9' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 2 JOHNSON USE 1933 1983
MONUMENTATION: Survey Disk VM#: 4221
AGENCY: PID#: CJ0650
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a concrete monument, 80 feet (24 m) north of Bench Mark
NO 1 JOHNSON USE 1933, 74.5 feet (22.7 m) north of the NW corner of an old brick
building (former powder magazine), 46.5 feet (14.2 m) WNW of Bench Mark JOHNSON
USE 1933, and at ground level. NOTE: This mark was reconditioned and restamped
in 1983 by NGS.
BENCH MARK STAMPING: JOHNSON USE 1934 1983
MONUMENTATION: Survey Disk VM#: 4222
AGENCY: PID#: CJ0398
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a concrete monument between the marine biology lab and
an old mortar building (former powder magazine), 74.4 feet (22.7 m) SSE of the
SE corner of the white lab building, 55.8 feet (17.0 m) SSW of Bench Mark NO 2
JOHNSON USE 1933 1983, 55.2 feet (16.8 m) NW of Bench Mark NO 1 JOHNSON USE
1933, 22.4 feet (6.8 m) north of the NE corner of the white mortar building, and
at ground level. NOTE: This mark was reconditioned and restamped in 1983 by
NGS.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
PUBLICATION DATE: 04/07/1988
Station ID: 8665726 SUPERCEDED DATE: 04/21/2003
Name: FORT JOHNSON, CHARLESTON HARBOR
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 45.1' N
USGS Quad: CHARLESTON Longitude: 79° 53.9' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: FT JOHNSON NO 8 1971
MONUMENTATION: Survey Disk VM#: 4223
AGENCY: PID#: CJ0400
SETTING CLASSIFICATION: Concrete Sea Wall
The bench mark is set flush in the surface of the east sea wall at Fort Johnson,
163.3 feet (49.8 m) west of the NW corner of the South Carolina Sea Grant
Consortium building, 144.4 feet (44.0 m) NNW of Bench Mark 5726 D 1982, 49.0
feet (14.9 m) SSW of the north edge of the east sea wall, 37.1 feet (11.3 m)
SW of the SW corner of the concrete access cover to underground waste water
pipes, and 1.3 feet (0.4 m) east of the west edge of the sea wall.
BENCH MARK STAMPING: 5726 D 1982
MONUMENTATION: Survey Disk VM#: 4224
AGENCY: PID#: CJ0399
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a 1.1-foot (0.3 m) diameter concrete monument at the
north end of the Fort Johnson grounds, 70.0 feet (21.3 m) ESE of the east side
of the east sea wall of the boat slip, 50.3 feet (15.3 m) WSW of the center of
the north steps of the Sea Grant Consortium building, 48.1 feet (14.7 m) WNW of
the center of the south steps of the building, 3.6 feet (1.1 m) SE of a metal
flag pole, and at ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
PUBLICATION DATE: 04/07/1988
Station ID: 8665726 SUPERCEDED DATE: 04/21/2003
Name: FORT JOHNSON, CHARLESTON HARBOR
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 45.1' N
USGS Quad: CHARLESTON Longitude: 79° 53.9' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5726 E 1982
MONUMENTATION: Survey Disk VM#: 4225
AGENCY: PID#: CJ0397
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is on the south side of the marine biology lab, 18.6 feet (5.7
m) SSW of a utility pole with electric meter, 8.0 feet (2.4 m) SSE of the SE
corner of the chain link fence surrounding the waste treatment plant, 5.5 feet
(1.7 m) WNW of a guy wire anchor, and 5.5 feet (1.7 m) north of an 0.8-foot (0.2
m) diameter oak tree. The bench mark is 0.4 foot (0.1 m) below ground level,
crimped to the top of a stainless steel rod driven 48 feet (15 m) to refusal,
and 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
PUBLICATION DATE: 04/07/1988
Station ID: 8665726 SUPERCEDED DATE: 04/21/2003
Name: FORT JOHNSON, CHARLESTON HARBOR
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 45.1' N
USGS Quad: CHARLESTON Longitude: 79° 53.9' W
T I D A L D A T U M S
Tidal datums at FORT JOHNSON, CHARLESTON HARBOR based on:
LENGTH OF SERIES: 4 MONTHS
TIME PERIOD: NOVEMBER 1982-FEBRUARY 1983
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8665530 CHARLESTON
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (02/28/1983) = 7.75
MEAN HIGHER HIGH WATER (MHHW) = 5.63
MEAN HIGH WATER (MHW) = 5.28
MEAN TIDE LEVEL (MTL) = 2.74
* NATIONAL GEODETIC VERTICAL DATUM-1929 (NGVD) = 2.32
MEAN LOW WATER (MLW) = 0.19
MEAN LOWER LOW WATER (MLLW) = 0.00
LOWEST OBSERVED WATER LEVEL (12/30/1982) = -1.52
* NGVD reference based on elevations published in Quad 320794, 1971, and NOS
leveling of 1983.
National Geodetic Vertical Datum (NGVD 29)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
JOHNSON USE 1933 11.34 6.06
NO 1 JOHNSON USE 1933 10.94 5.66
NO 2 JOHNSON USE 1933 1983 10.97 5.69
JOHNSON USE 1934 1983 10.15 4.87
FT JOHNSON NO 8 1971 9.37 4.09
5726 D 1982 13.50 8.22
5726 E 1982 8.88 3.60
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
PUBLICATION DATE: 04/07/1988
Station ID: 8665726 SUPERCEDED DATE: 04/21/2003
Name: FORT JOHNSON, CHARLESTON HARBOR
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 45.1' N
USGS Quad: CHARLESTON Longitude: 79° 53.9' 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 (NAVD 88).
NGVD 29 is a fixed datum adopted as a national standard geodetic reference for
heights but is now considered superseded. NGVD 29 is sometimes referred to as
Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological
Survey Topographic Quads. NGVD 29 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 NGVD 29 are available from the National
Geodetic Survey (NGS) data base via the World Wide Web at
National Geodetic Survey.
NAVD 88 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. NAVD 88 replaces NGVD 29 as the national
standard geodetic reference for heights. Bench mark elevations relative to
NAVD 88 are available from NGS through the World Wide Web at
National Geodetic Survey.
NGVD 29 and NAVD 88 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 NAVD 88 elevation is shown on the Elevations of Tidal Datums Table Referred
to MLLW only when two or more of the bench marks listed have NAVD 88 elevations.
The NAVD 88 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, NAVD 88 bench mark elevations computed indirectly from the tidal
datums elevation table may differ slightly from NAVD 88 elevations listed for
each bench mark in the NGS database.