U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 09/15/1988
Station ID: 8661419 SUPERCEDED DATE: 04/21/2003
Name: GARDEN CITY BRIDGE, MAIN CREEK
SOUTH CAROLINA
NOAA Chart: 11535 Latitude: 33° 34.7' N
USGS Quad: BROOKGREEN Longitude: 79° 0.2' W
To reach the tidal bench marks from the intersection of U.S. Highway 17 and a
state road 3 miles (5 km) NE of Murrells Inlet, proceed 0.6 mile (1.0 km) SE on
the state road towards Garden City Beach and the bridge over Main Creek. The
bench marks are along the road NW of the bridge. The tide gage and staff were
on the SW side of the bridge near the NW end.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: GCB NO 1 1975
MONUMENTATION: Survey Disk VM#: 3766
AGENCY: PID#: DD1494
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is about 300 feet (91 m) NW of the NW end of the bridge over Main
Creek, 31.5 feet (9.6 m) NE of the centerline of the highway, 17.4 feet (5.3 m)
SE of the center of the last driveway before reaching the bridge on the NE side
of the highway, 3.6 feet (1.1 m) east of utility pole #1C-17-1-D, and 2.7 feet
(0.8 m) west of a steel witness post. The bench mark is 0.1 foot (0.03 m) below
ground level, crimped to a copper-clad steel rod driven 48 feet (15 m) to
refusal, and encased in a 5-inch PVC pipe and concrete kickblock.
BENCH MARK STAMPING: GCB NO 2 1975
MONUMENTATION: Survey Disk VM#: 3767
AGENCY: PID#: DD1493
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is about 345 feet (105 m) NW of Bench Mark GCB NO 1 1975, 26.9
feet (8.2 m) NE of the centerline of the highway, 6.8 feet (2.1 m) west of a
0.8-foot (0.2 m) diameter pine tree, 3.5 feet (1.1 m) north of utility pole
#1C-17-1-C, and 2.3 feet (0.7 m) NE of a steel witness post. The bench mark is
0.1 foot (0.03 m) below ground level, crimped to a copper-clad steel rod driven
48 feet (15 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 2 of 5
PUBLICATION DATE: 09/15/1988
Station ID: 8661419 SUPERCEDED DATE: 04/21/2003
Name: GARDEN CITY BRIDGE, MAIN CREEK
SOUTH CAROLINA
NOAA Chart: 11535 Latitude: 33° 34.7' N
USGS Quad: BROOKGREEN Longitude: 79° 0.2' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: GCB NO 3 1975
MONUMENTATION: Survey Disk VM#: 3768
AGENCY: PID#: DD1492
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is about 540 feet (165 m) NW of Bench Mark GCB NO 2 1975, 82.5
feet (25.1 m) NW of the centerline of West Canal Drive, 27.7 feet (8.4 m) SW of
the centerline of the highway, 16.8 feet (5.1 m) NE of underground telephone
cable junction box #1C-5, and 4.8 feet (1.5 m) SE of utility pole #6 1/4 B. The
bench mark is 0.1 foot (0.03 m) below ground level, crimped to a copper-clad
steel rod driven 45 feet (14 m) to refusal, and encased in a 4-inch PVC pipe and
concrete kickblock.
BENCH MARK STAMPING: GCB NO 4 1975
MONUMENTATION: Survey Disk VM#: 3769
AGENCY: PID#: DD1491
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is about 375 feet (114 m) NW of Bench Mark GCB NO 3 1975, 31.7
feet (9.7 m) SW of the centerline of the highway, 30.9 feet (9.4 m) NW of the
centerline of East Bank Road, 20.0 feet (6.1 m) north of a lighted brick fence
post on the north side of East Bank Road, and 3.2 feet (1.0 m) west of utility
pole #B 5 1/2. The bench mark is 0.1 foot (0.03 m) below ground level, crimped
to a copper-clad steel rod driven 48 feet (15 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: 09/15/1988
Station ID: 8661419 SUPERCEDED DATE: 04/21/2003
Name: GARDEN CITY BRIDGE, MAIN CREEK
SOUTH CAROLINA
NOAA Chart: 11535 Latitude: 33° 34.7' N
USGS Quad: BROOKGREEN Longitude: 79° 0.2' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: GCB NO 5 1975
MONUMENTATION: Survey Disk VM#: 3770
AGENCY: PID#: DD1490
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is about 330 feet (101 m) NW of Bench Mark GCB NO 4 1975, 31.1
feet (9.5 m) NW of the centerline of Clubhouse Road, 29.5 feet (9.0 m) SW of the
centerline of the highway, 10.9 feet (3.3 m) NW of a 4-foot (1 m) high lighted
brick fence post on the north side of Clubhouse Road, and 1.7 feet (0.5 m) from
the first brick fence post north of the lighted post. The bench mark is 0.1
foot (0.03 m) below ground level, crimped to a copper-clad steel rod driven 48
feet (15 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 4 of 5
PUBLICATION DATE: 09/15/1988
Station ID: 8661419 SUPERCEDED DATE: 04/21/2003
Name: GARDEN CITY BRIDGE, MAIN CREEK
SOUTH CAROLINA
NOAA Chart: 11535 Latitude: 33° 34.7' N
USGS Quad: BROOKGREEN Longitude: 79° 0.2' W
T I D A L D A T U M S
Tidal datums at GARDEN CITY BRIDGE, MAIN CREEK based on:
LENGTH OF SERIES: 12 MONTHS
TIME PERIOD: DECEMBER 1974 - NOVEMBER1975
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 (06/10/1975) = 6.89
MEAN HIGHER HIGH WATER MHHW = 4.81
MEAN HIGH WATER MHW = 4.44
MEAN TIDE LEVEL MTL = 2.29
MEAN LOW WATER MLW = 0.14
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (11/22/1975) = -0.35
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
GCB NO 1 1975 9.05 4.61
GCB NO 2 1975 10.13 5.69
GCB NO 3 1975 13.62 9.18
GCB NO 4 1975 14.52 10.08
GCB NO 5 1975 17.25 12.81
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 09/15/1988
Station ID: 8661419 SUPERCEDED DATE: 04/21/2003
Name: GARDEN CITY BRIDGE, MAIN CREEK
SOUTH CAROLINA
NOAA Chart: 11535 Latitude: 33° 34.7' N
USGS Quad: BROOKGREEN Longitude: 79° 0.2' 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.