U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 03/16/1982
Station ID: 8667508 SUPERCEDED DATE: 04/21/2003
Name: HALL ISLAND, R.R.BRIDGE, BROAD RIVER
SOUTH CAROLINA
NOAA Chart: 0 Latitude: 32° 31.3' N
USGS Quad: YAMASSEE Longitude: 80° 50.3' W
To reach the tidal bench marks from the intersection of US Route 21 and SC
Highway S-7-71 in Gray's Hill proceed west on S-7-71, 0.5 mile (0.8 km) to the
railroad tracks then 2.2 miles (3.54 km) to the county boat ramp on Whale
Branch, then proceed by boat south and southwest for approximately 1.8 miles
(2.90 km) on Whale Branch to Broad River, then 2.1 miles (3.38 km) northwest on
Broad River to the Hall Island railroad bridge. The gage and staff were located
on the center turn gear trestle.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 7508 A 1978
MONUMENTATION: Survey Disk VM#: 4355
AGENCY: PID:
SETTING CLASSIFICATION: Turn Gear Support of Bridge
The bench mark is set in the concrete that supports the center turn gear of the
bridge, 5.6 feet (1.71 m) east of the center of the trestle and 9.4 feet (2.87
m) beneath the trestle deck.
BENCH MARK STAMPING: 7508 B 1978
MONUMENTATION: Survey Disk VM#: 4356
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Bridge Footing
The bench mark is set in a concrete bridge footing, 74.2 feet (22.62 m)
southwest of the center turn gear, 5.6 feet (1.71 m) northeast of the center of
the trestle, and 9.4 feet (2.87 m) beneath the trestle deck.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 03/16/1982
Station ID: 8667508 SUPERCEDED DATE: 04/21/2003
Name: HALL ISLAND, R.R.BRIDGE, BROAD RIVER
SOUTH CAROLINA
NOAA Chart: 0 Latitude: 32° 31.3' N
USGS Quad: YAMASSEE Longitude: 80° 50.3' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 7508 C 1978
MONUMENTATION: Survey Disk VM#: 4357
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Bridge Footing
The bench mark is set in a concrete bridge footing, 76.4 feet (23.29 m)
northeast of the center turn gear, 5.6 feet (1.71 m) northeast of the center of
the trestle and 9.4 feet (2.87 m) below the trestle deck.
BENCH MARK STAMPING: 7508 D 1979
MONUMENTATION: Survey Disk VM#: 4358
AGENCY: PID:
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is 23.7 feet (7.22 m) north northeast of the north corner of the
north side of the railroad trestle, 9.4 feet (2.87 m) northwest of the
centerline of the rock trestle, and 1.4 feet (0.43 m) southeast of a steel
witness post. The bench mark is crimped to the top of a stainless steel rod
driven 15 feet (4.6 m) to refusal, 0.1 foot (0.03 m) above ground level and
surrounded by a PVC pipe in concrete.
BENCH MARK STAMPING: 7508 E 1979
MONUMENTATION: Survey Disk VM#: 4359
AGENCY: PID:
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is 183 feet (55.8 m) northeast of Bench Mark 7508 D 1979, 7.3
feet (2.2 m) northwest of the centerline of the rock causeway, 3.3 feet (1.01 m)
southeast of the northwest edge of the causeway, and 1.4 feet (0.43 m) southeast
of a steel witness post. The bench mark is crimped to the top of a stainless
steel rod driven 27 feet (8.23 m) to refusal and 0.1 foot (0.03 m) above ground
level and surrounded by a PVC pipe in concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
PUBLICATION DATE: 03/16/1982
Station ID: 8667508 SUPERCEDED DATE: 04/21/2003
Name: HALL ISLAND, R.R.BRIDGE, BROAD RIVER
SOUTH CAROLINA
NOAA Chart: 0 Latitude: 32° 31.3' N
USGS Quad: YAMASSEE Longitude: 80° 50.3' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 7508 F 1979
MONUMENTATION: Survey Disk VM#: 4360
AGENCY: PID:
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is 175 feet (53 m) northeast of Bench Mark 7508 E 1979, 8.5 feet
(2.59 m) southeast of the centerline of the causeway, 4.2 feet (1.28 m)
northwest of a steel witness post and 4.1 feet (1.25 m) northwest of the
southeast edge of the causeway. The bench mark is crimped to the top of a
stainless steel rod driven 24 feet (7.3 m) to refusal, 0.1 foot (0.03 m) above
ground level and surrounded by a PVC pipe in concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
PUBLICATION DATE: 03/16/1982
Station ID: 8667508 SUPERCEDED DATE: 04/21/2003
Name: HALL ISLAND, R.R.BRIDGE, BROAD RIVER
SOUTH CAROLINA
NOAA Chart: 0 Latitude: 32° 31.3' N
USGS Quad: YAMASSEE Longitude: 80° 50.3' W
T I D A L D A T U M S
Tidal datums at HALL ISLAND, R.R.BRIDGE, BROAD RIVER based on:
LENGTH OF SERIES: 21 MONTHS
TIME PERIOD: SEPTEMBER 1978 -DECEMBER 1980
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8665530 CHARLESTON, SC
Elevations of tidal datums referred to Mean Low Water (MLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (05/16/1980) = 10.49
MEAN HIGH WATER (MHW) = 8.08
MEAN TIDE LEVEL (MTL) = 4.04
MEAN LOW WATER (MLW) = 0.00
LOWEST OBSERVED WATER LEVEL (01/25/1979) = -2.74
National Geodetic Vertical Datum (NGVD 29)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLW MHW
7508 A 1978 13.27 5.19
7508 B 1978 13.24 5.16
7508 C 1978 13.27 5.19
7508 D 1979 20.36 12.28
7508 E 1979 20.45 12.37
7508 F 1979 19.51 11.43
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 03/16/1982
Station ID: 8667508 SUPERCEDED DATE: 04/21/2003
Name: HALL ISLAND, R.R.BRIDGE, BROAD RIVER
SOUTH CAROLINA
NOAA Chart: 0 Latitude: 32° 31.3' N
USGS Quad: YAMASSEE Longitude: 80° 50.3' 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.