U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 06/19/1989
Station ID: 8665426 SUPERCEDED DATE: 04/21/2003
Name: SHEM CREEK
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 47.6' N
USGS Quad: CHARLESTON Longitude: 79° 52.9' W
To reach the tidal bench marks from the east end of the Silas Pearman Bridge
over Charleston Harbor, proceed 1.5 miles (2.4 km) east along Old U.S. Route 17
to the concrete road bridge over Shem Creek. The bench marks are along Old U.S.
Route 17 and near the Trawler Restaurant. The tide gage and staff were on a
dock directly behind the Trawler Restaurant adjacent to the bridge.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 5426 A 1977
MONUMENTATION: Survey Disk VM#: 4168
AGENCY: PID#: CJ0288
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is behind the Trawler Restaurant, 47.6 feet (14.5 m) SE of the
centerline of the wood dock ramp, 35.6 feet (10.9 m) south of a silver LP gas
tank, 6.0 feet (1.8 m) NNE of the centerline of the bottom of the metal stairs
leading into the restaurant, and 2.5 feet (0.8 m) NNE of the edge of the Trawler
Restaurant hot water heating shed. The bench mark is level with the ground,
crimped to a copper-clad steel rod driven 32 feet (10 m) to refusal, and encased
in a 4-inch PVC pipe and concrete kickblock.
BENCH MARK STAMPING: S 123 1962
MONUMENTATION: Survey Disk VM#: 4167
AGENCY: PID#: CJ0071
SETTING CLASSIFICATION: Concrete Bridge Abutment
The bench mark is set flush in the NE end of the bridge, 12.4 feet (3.8 m) SSW
of power pole #46804, 6.8 feet (2.1 m) west of the curb of the bridge, 1.3 feet
(0.4 m) east of the guardrail on the NE corner of the bridge, and 0.4 foot (0.1
m) south of the NE corner of the bridge.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 06/19/1989
Station ID: 8665426 SUPERCEDED DATE: 04/21/2003
Name: SHEM CREEK
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 47.6' N
USGS Quad: CHARLESTON Longitude: 79° 52.9' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5426 B 1977
MONUMENTATION: Survey Disk VM#: 4169
AGENCY: PID#: CJ0290
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is at the south end of the bridge, 34.8 feet (10.6 m) WSW of the
centerline of Old U.S. Highway 17, 19.7 feet (6.0 m) SSE of telephone pole
#C-42169, 14.0 feet (4.3 m) SSE of the SW end of the bridge, and 6.4 feet
(2.0 m) WSW of the highway curb. The bench mark is crimped to a copper-clad
steel rod driven 24 feet (7 m) to refusal, and encased in a 4-inch PVC pipe and
concrete kickblock.
BENCH MARK STAMPING: 5426 C 1977
MONUMENTATION: Survey Disk VM#: 4170
AGENCY: PID#: CJ0292
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is near the NW end of the bridge, 82.3 feet (25.1 m) east of
utility pole #221797, 76.8 feet (23.4 m) SSE of the curb at the entrance to the
OK Tire Store, 9.5 feet (2.9 m) WSW of the curb of Old U.S. Highway 17, and 4.2
feet (1.3 m) SSE of utility pole #92. The bench mark is at ground level,
crimped to a copper-clad steel rod driven 24 feet (7 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 3 of 5
PUBLICATION DATE: 06/19/1989
Station ID: 8665426 SUPERCEDED DATE: 04/21/2003
Name: SHEM CREEK
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 47.6' N
USGS Quad: CHARLESTON Longitude: 79° 52.9' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: MOUNT
MONUMENTATION: Survey Disk VM#: 4171
AGENCY: PID#: CJ0291
SETTING CLASSIFICATION: Concrete Bridge Abutment
The bench mark is set flush in the concrete bridge abutment at the NW end of the
bridge, 26.2 feet (8.0 m) NNW of an unnumbered vine covered power pole, 3.5 feet
(1.1 m) SE of the NW end of the bridge, 3.0 feet (0.9 m) ENE of the guardrail
along the bridge, and 2.9 feet (0.9 m) SW of the curb of the bridge.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
PUBLICATION DATE: 06/19/1989
Station ID: 8665426 SUPERCEDED DATE: 04/21/2003
Name: SHEM CREEK
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 47.6' N
USGS Quad: CHARLESTON Longitude: 79° 52.9' W
T I D A L D A T U M S
Tidal datums at SHEM CREEK based on:
LENGTH OF SERIES: 4 MONTHS
TIME PERIOD: APRIL-JULY 1977
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8665330 CHARLESTON
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (06/01/1977) = 7.77
MEAN HIGHER HIGH WATER MHHW = 5.74
MEAN HIGH WATER MHW = 5.39
MEAN TIDE LEVEL MTL = 2.79
MEAN LOW WATER MLW = 0.19
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (04/06/1977) = -2.33
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
5426 A 1977 7.57 2.18
S 123 1962 19.65 14.26
5426 B 1977 18.44 13.05
5426 C 1977 13.75 8.36
MOUNT 19.63 14.24
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 06/19/1989
Station ID: 8665426 SUPERCEDED DATE: 04/21/2003
Name: SHEM CREEK
SOUTH CAROLINA
NOAA Chart: 11524 Latitude: 32° 47.6' N
USGS Quad: CHARLESTON Longitude: 79° 52.9' 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 (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.