U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 01/13/1992
Station ID: 8666775 SUPERCEDED DATE: 04/21/2003
Name: LEADENWAH CREEK, NORTH EDISTO RIVER
SOUTH CAROLINA
NOAA Chart: 11522 Latitude: 32° 38.2' N
USGS Quad: WADMALAW ISLAND Longitude: 80° 12.1' W
To reach the tidal bench marks from the intersection of U.S. Highway 17 and
State Highway 20 west of Charleston, proceed south on State Highway 20 for 6.4
miles (10.3 km) to State Highway 700, turn right and go SW on State Highway 700
for 8.6 miles (13.8 km) to Edith L. Frierson Elementary School, turn right onto
a dirt road and go 1 mile (2 km) to a three-way split in the road, bear left and
go 0.3 mile (0.5 km) to another intersection, bear left and go 0.1 mile (0.2 km)
to the driveway of Johnson's residence, turn right and go another 0.1 mile (0.2
km) to the main house. The bench marks are along to driveway and at Johnson's
pier. The tide gauge and staff were on Johnson's pier and on Dr. Pratt and
Thomas' pier to the north after 11/18/77.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 6775 A 1977
MONUMENTATION: Survey Disk VM#: 6655
AGENCY: PID:
SETTING CLASSIFICATION: Copper-clad Steel Rod
The primary bench mark is between Johnson's residence and the pier, 50.3 feet
(15.3 m) west of the SW corner of the house, 41 feet (12 m) south of a lone oak
tree at the bluff, and 35.8 feet (10.9 m) ESE of the centerline of the south end
of the wooden catwalk leading to the pier. The bench mark is level with the
ground, crimped to a copper-clad steel rod driven 40 feet (12 m) to
refusal, and encased in a PVC pipe and concrete kickblock.
BENCH MARK STAMPING: 6775 B 1977
MONUMENTATION: Survey Disk VM#: 6656
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a concrete monument along the driveway leading to
Johnson's residence, 77.3 feet (23.6 m) SSE of the east corner of the brick
porch at the shed, 12 feet (4 m) NNE of the centerline of the driveway, 2.5 feet
(0.8 m) ESE of power pole #33 SE 88D, and level with the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 01/13/1992
Station ID: 8666775 SUPERCEDED DATE: 04/21/2003
Name: LEADENWAH CREEK, NORTH EDISTO RIVER
SOUTH CAROLINA
NOAA Chart: 11522 Latitude: 32° 38.2' N
USGS Quad: WADMALAW ISLAND Longitude: 80° 12.1' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 6775 C 1977
MONUMENTATION: Survey Disk VM#: 6700
AGENCY: PID:
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is along the driveway near the tennis court, 60.4 feet (18.4 m)
NE of the center of the tennis court, 59.6 feet (18.2 m) south of the centerline
of the driveway, 32.5 feet (9.9 m) south of NW corner of the shed, and 1.5 feet
(0.5 m) ENE of the NE corner of the chainlink backstop fence. 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 PVC pipe and concrete kickblock.
BENCH MARK STAMPING: 6775 D 1977
MONUMENTATION: Survey Disk VM#: 6701
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is on the south side of the driveway between the entrance and the
tennis court, 177.4 feet (54.1 m) SSE of the SE corner of the backstop, 26.7
feet (8.1 m) west of the centerline of the driveway, 7.7 feet (2.3 m) SSE of a
three forked oak tree, and level with the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
PUBLICATION DATE: 01/13/1992
Station ID: 8666775 SUPERCEDED DATE: 04/21/2003
Name: LEADENWAH CREEK, NORTH EDISTO RIVER
SOUTH CAROLINA
NOAA Chart: 11522 Latitude: 32° 38.2' N
USGS Quad: WADMALAW ISLAND Longitude: 80° 12.1' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 6775 E 1977
MONUMENTATION: Survey Disk VM#: 6702
AGENCY: PID:
SETTING CLASSIFICATION: Copper-clad Steel Rod
The bench mark is at the entrance of the driveway leading to Johnson's
residence, 48 feet (15 m) SSW of a 4.5-foot (1.4 m) diameter oak tree, 25.3 feet
(7.7 m) NNW of the centerline of the main road, 16.8 feet (5.1 m) WSW of the
centerline of the driveway, and 3.5 feet (1.1 m) NW of a mailbox. The bench
mark is level with the ground, crimped to a copper-clad steel rod driven 36 feet
(11 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 4 of 5
PUBLICATION DATE: 01/13/1992
Station ID: 8666775 SUPERCEDED DATE: 04/21/2003
Name: LEADENWAH CREEK, NORTH EDISTO RIVER
SOUTH CAROLINA
NOAA Chart: 11522 Latitude: 32° 38.2' N
USGS Quad: WADMALAW ISLAND Longitude: 80° 12.1' W
T I D A L D A T U M S
Tidal datums at LEADENWAH CREEK, NORTH EDISTO RIVER based on:
LENGTH OF SERIES: 10 MONTHS
TIME PERIOD: DECEMBER 1977 - OCTOBER 1978
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 (06/01/1977) = 9.10
MEAN HIGHER HIGH WATER MHHW = 6.61
MEAN HIGH WATER MHW = 6.27
MEAN TIDE LEVEL MTL = 3.24
MEAN LOW WATER MLW = 0.22
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (01/09/1978) = -2.87
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
6775 A 1977 15.83 9.56
6775 B 1977 16.99 10.72
6775 C 1977 18.20 11.93
6775 D 1977 20.46 14.19
6775 E 1977 20.24 13.97
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 01/13/1992
Station ID: 8666775 SUPERCEDED DATE: 04/21/2003
Name: LEADENWAH CREEK, NORTH EDISTO RIVER
SOUTH CAROLINA
NOAA Chart: 11522 Latitude: 32° 38.2' N
USGS Quad: WADMALAW ISLAND Longitude: 80° 12.1' 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.