U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 8666767 PUBLICATION DATE: 02/05/2004
Name: SNAKE ISLAND, STONO RIVER
SC
NOAA Chart: 11522 Latitude: 32° 38.4' N ( 32.64000)
USGS Quad: LEGARVILLE Longitude: 80° 0.9' W ( -80.01500)
To reach the tidal bench marks from the State Highway 171 bridge over Wappo
Creek (Intracoastal Waterway), proceed south on State Highway 171 (Folly Road)
for 9.5 km (5.9 mi) to State Highway 632 (Sol Leagre Road), turn right onto
State Highway 632 and go west for 4.2 km (2.6 mi) to a public boat landing at
the end of the road, then travel by boat south on Stono River for 3.7 km (2.0
nm) to Day Marker #2. The bench marks are north of the marker along the primary
and secondary dune lines on Snake Island. The tide gauge and staff were located
on a four-pile platform just inshore of Day Marker #2.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 6767 A 1978
DESIGNATION: 866 6767 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 6645
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID#: DM3224
LATITUDE: 32° 38.4' N ( 32.64000) LONGITUDE: 80° 0.9' W ( -80.01500)
The primary bench mark is a disk located on the beach of Snake Island between
the shore and the first set of dunes, north of Day Marker #2, 10 m (33 ft) SW of
the base of the dune, 5 m (17 ft) NE of the approximate high water line, and
1.77 m (5.8 ft) SE of a metal witness post. The bench mark is set at ground
level, crimped to the top of a galvanized steel rod driven 10.7 m (35 ft) 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 2 of 5
Station ID: 8666767 PUBLICATION DATE: 02/05/2004
Name: SNAKE ISLAND, STONO RIVER
SC
NOAA Chart: 11522 Latitude: 32° 38.4' N ( 32.64000)
USGS Quad: LEGARVILLE Longitude: 80° 0.9' W ( -80.01500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 6767 B 1978
DESIGNATION: 866 6767 B TIDAL
MONUMENTATION: Tidal Station disk VM#: 6646
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 32° 38.4' N ( 32.64000) LONGITUDE: 80° 0.9' W ( -80.01500)
The bench mark is a disk set in a concrete monument at the base of the dunes NE
of the Day Marker #2, 32 m (104 ft) east of bench mark 6767 A 1978, 14.20 m
(46.6 ft) south of a 1m (2 ft) diameter scrub oak tree, 8 m (27 ft) north of the
approximate high water line, and 0.91 m (3.0 ft) west of a witness post.
BENCH MARK STAMPING: 6767 C 1978
DESIGNATION: 866 6767 C TIDAL
MONUMENTATION: Tidal Station disk VM#: 6647
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID:
LATITUDE: 32° 38.4' N ( 32.64000) LONGITUDE: 80° 0.9' W ( -80.01500)
The bench mark is a disk located behind the front dune line near a small tidal
pool, 22.04 m (72.3 ft) north of bench mark 6767 B 1978, 7.83 m (25.7 ft) NNE of
a large scrub oak behind the front dunes, and 2.01 m (6.6 ft) NE of a metal
witness post. The bench mark is set at ground level, crimped to the top of a
galvanized steel rod driven 10.7 m (35 ft) 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 3 of 5
Station ID: 8666767 PUBLICATION DATE: 02/05/2004
Name: SNAKE ISLAND, STONO RIVER
SC
NOAA Chart: 11522 Latitude: 32° 38.4' N ( 32.64000)
USGS Quad: LEGARVILLE Longitude: 80° 0.9' W ( -80.01500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 6767 D 1978
DESIGNATION: 866 6767 D TIDAL
MONUMENTATION: Tidal Station disk VM#: 6648
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 32° 38.4' N ( 32.64000) LONGITUDE: 80° 0.9' W ( -80.01500)
The bench mark is a disk set in a concrete monument located on top of the
secondary dune line at the center of the island, 25.39 m (83.3 ft) NW of bench
mark 6767 C 1978, 7.22 m (23.7 ft) south of the palmetto tree in line with bench
mark 6767 E 1978, 3.20 m (10.5 ft) SE of the center of a twin oak tree, 1.95 m
(6.4 ft) SSE of a metal witness post.
BENCH MARK STAMPING: 6767 E 1978
DESIGNATION: 866 6767 E TIDAL
MONUMENTATION: Tidal Station disk VM#: 6649
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID:
LATITUDE: 32° 38.4' N ( 32.64000) LONGITUDE: 80° 0.9' W ( -80.01500)
The bench mark is a disk located in the center of a small clearing surrounded by
palmetto trees, 24.29 m (79.7 ft) north of bench mark 6767 D 1978, 17.37 m (57.0
ft) north of the palmetto tree in line with bench mark 6767 D 1978, 15.91 m
(52.2 ft) SW of the easternmost of two 0.09 m x 0.15 m (0.3 ft x 0.5 ft)
treated posts (part of an old sign), and 0.98 m (3.2 ft) SE of a metal witness
post. The bench is crimped to the top of a galvanized steel rod driven 10.7 m
(35 ft) 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
Station ID: 8666767 PUBLICATION DATE: 02/05/2004
Name: SNAKE ISLAND, STONO RIVER
SC
NOAA Chart: 11522 Latitude: 32° 38.4' N ( 32.64000)
USGS Quad: LEGARVILLE Longitude: 80° 0.9' W ( -80.01500)
T I D A L D A T U M S
Tidal datums at SNAKE ISLAND, STONO RIVER based on:
LENGTH OF SERIES: 3 MONTHS
TIME PERIOD: February 1978 - April 1978
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8665530 CHARLESTON, COOPER RIVER ENTRANCE
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 1.780
MEAN HIGH WATER MHW = 1.666
MEAN SEA LEVEL MSL = 0.885
MEAN TIDE LEVEL MTL = 0.863
MEAN LOW WATER MLW = 0.059
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
6767 A 1978 2.503 0.837
6767 B 1978 3.095 1.429
6767 C 1978 2.709 1.043
6767 D 1978 3.328 1.662
6767 E 1978 3.533 1.867
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 8666767 PUBLICATION DATE: 02/05/2004
Name: SNAKE ISLAND, STONO RIVER
SC
NOAA Chart: 11522 Latitude: 32° 38.4' N ( 32.64000)
USGS Quad: LEGARVILLE Longitude: 80° 0.9' W ( -80.01500)
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 NGS's Integrated Data Base (IDB PID)
provides geodetic datum based on traditionally leveled and bluebooked ties to
the National Spatial Reference System(NSRS) https://www.ngs.noaa.gov/datasheets/.
The NGS Online Positioning User Service (OPUS PID) provides geodetic datum based
on GPS position & tie it to the NSRS https://www.ngs.noaa.gov/OPUS/.
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.