U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 11/12/1990
Station ID: 8665552 SUPERCEDED DATE: 04/21/2003
Name: BREACH INLET
SOUTH CAROLINA
NOAA Chart: 11523 Latitude: 32° 46.6' N
USGS Quad: FORT MOULTRIE Longitude: 79° 48.7' W
To reach the tidal bench marks from Sullivans Island, proceed north on State
Highway 703 to William Thompson Memorial Bridge over Breach Inlet. The bench
marks are at both ends of the bridge. The tide gage and staff were on the north
side of the bridge near the Isle of Palms end.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: BREACH NO 1 1963
MONUMENTATION: Survey Disk VM#: 4190
AGENCY: PID#: CJ0605
SETTING CLASSIFICATION: Concrete Bridge Sidewalk
The bench mark is set in the south sidewalk near the SW end of the bridge over
Breach Inlet, 45.7 feet (13.9 m) NNE of the William Thompson Memorial Monument,
43.5 feet (13.3 m) NE of the SW end of the bridge, 15.0 feet (4.6 m) SE of the
centerline of the highway, and 2.1 feet (0.6 m) NW of the guard rail.
BENCH MARK STAMPING: BREACH NO 2 1963
MONUMENTATION: Survey Disk VM#: 4191
AGENCY: PID#: CJ0606
SETTING CLASSIFICATION: Concrete Bridge Sidewalk
The bench mark is set in the north sidewalk of the SW end of the bridge over
Breach Inlet, 14.0 feet (4.3 m) NW of the centerline of the highway, 3.0 feet
(0.9 m) SE of the NW corner of the bridge, and 2.5 feet (0.8 m) NW of the curb.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 11/12/1990
Station ID: 8665552 SUPERCEDED DATE: 04/21/2003
Name: BREACH INLET
SOUTH CAROLINA
NOAA Chart: 11523 Latitude: 32° 46.6' N
USGS Quad: FORT MOULTRIE Longitude: 79° 48.7' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: BI NO 3 1975
MONUMENTATION: Survey Disk VM#: 4192
AGENCY: PID#: CJ0607
SETTING CLASSIFICATION: Concrete Abutment
The bench mark is set in the north concrete abutment on the NE end of the bridge
over Breach Inlet, 31.3 feet (9.5 m) NE of a metal light pole, 20.1 feet (6.1 m)
NW of the centerline of the highway, and 4.0 feet (1.2 m) SW of the Willian
Thompson Memorial Bridge concrete sign.
BENCH MARK STAMPING: BI NO 4 1975
MONUMENTATION: Survey Disk VM#: 4193
AGENCY: PID#: CJ0608
SETTING CLASSIFICATION: Concrete Abutment
The bench mark is set in the south concrete abutment on the NE end of the bridge
over Breach Inlet, 81.0 feet (24.7 m) west of power pole #71478, and 19.6 feet
(6.0 m) SE of the centerline of the highway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 11/12/1990
Station ID: 8665552 SUPERCEDED DATE: 04/21/2003
Name: BREACH INLET
SOUTH CAROLINA
NOAA Chart: 11523 Latitude: 32° 46.6' N
USGS Quad: FORT MOULTRIE Longitude: 79° 48.7' W
T I D A L D A T U M S
Tidal datums at BREACH INLET based on:
LENGTH OF SERIES: 12 MONTHS
TIME PERIOD: JUNE 1975-MAY 1976
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) = 7.36
MEAN HIGHER HIGH WATER MHHW = 5.55
MEAN HIGH WATER MHW = 5.19
MEAN TIDE LEVEL MTL = 2.70
MEAN LOW WATER MLW = 0.21
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (12/21/1976) = -3.03
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
BREACH NO 1 1963 15.07 9.88
BREACH NO 2 1963 15.12 9.93
BI NO 3 1975 15.12 9.93
BI NO 4 1975 15.11 9.92
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 11/12/1990
Station ID: 8665552 SUPERCEDED DATE: 04/21/2003
Name: BREACH INLET
SOUTH CAROLINA
NOAA Chart: 11523 Latitude: 32° 46.6' N
USGS Quad: FORT MOULTRIE Longitude: 79° 48.7' 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.