U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 8665424 PUBLICATION DATE: 02/05/2004
Name: CROSBY'S DOCK, FOLLY RIVER
SC
NOAA Chart: 11521 Latitude: 32° 40.5' N ( 32.67500)
USGS Quad: JAMES ISLAND Longitude: 79° 57.1' W ( -79.95170)
To reach the tidal bench marks from the intersection of State Highways 171
(Folly Road) and 700 (Maybank Highway) on James Island, proceed 10.6 km (6.6 mi)
south on Folley Road to the highway bridge that crosses Folly Creek. The bench
marks are located in the bridge abutments and extend SE of the bridge. The tide
gage and staff were located on the SW side of the dock behind Crosbys Bait and
Tackle Shop.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: CD NO 1 1975
DESIGNATION: 866 5424 TIDAL CD 1
MONUMENTATION: Tidal Station disk VM#: 4162
AGENCY: National Ocean Survey (NOS) IDB PID#: CJ0437
SETTING CLASSIFICATION: Concrete sidewalk OPUS PID#: CJ0437
LATITUDE: 32° 40.5' N ( 32.67500) LONGITUDE: 79° 57.0' W ( -79.95000)
The primary bench mark is a disk set flush in the concrete sidewalk at the SW
end of the Folly Creek bridge, 5.18 m (17.0 ft) SW of the centerline of State
Highway 171, 4.72 m (15.5 ft) north of power pole #134598, 0.12 m (0.4 ft) NW of
the end of the bridge, and 0.30 m (1.0 ft) above the highway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 8665424 PUBLICATION DATE: 02/05/2004
Name: CROSBY'S DOCK, FOLLY RIVER
SC
NOAA Chart: 11521 Latitude: 32° 40.5' N ( 32.67500)
USGS Quad: JAMES ISLAND Longitude: 79° 57.1' W ( -79.95170)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: CD NO 2 1975
DESIGNATION: 866 5424 TIDAL CD 2
MONUMENTATION: Tidal Station disk VM#: 4163
AGENCY: National Ocean Survey (NOS) IDB PID#: CJ0436
SETTING CLASSIFICATION: Concrete sidewalk OPUS PID:
LATITUDE: 32° 40.5' N ( 32.67500) LONGITUDE: 79° 57.0' W ( -79.95000)
The bench mark is a disk set flush in the concrete sidewalk at the SE end of the
Folly Creek bridge, 7.16 m (23.5 ft) WNW of power pole #162502, 4.88 m (16.0 ft)
NE of the centerline of State Highway 171, 0.18 m (0.6 ft) NW of the end of the
bridge, and 0.3 m (1 ft) above the highway.
BENCH MARK STAMPING: CD NO 3 1975
DESIGNATION: 866 5424 TIDAL CD 3
MONUMENTATION: Tidal Station disk VM#: 4164
AGENCY: National Ocean Survey (NOS) IDB PID#: CJ0435
SETTING CLASSIFICATION: Concrete sidewalk OPUS PID#: CJ0435
LATITUDE: 32° 40.6' N ( 32.67670) LONGITUDE: 79° 57.1' W ( -79.95170)
The bench mark is a disk set flush in the concrete sidewalk at the NW end of the
Folly Creek bridge, 238 m (780 ft) NW of bench mark CD No 1 1975, 4.75 m (15.6
ft) SW of the centerline of State Highway 171, 0.21 m (0.7 ft) SE of the end of
the bridge, and 0.3 m (1.0 ft) above the highway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 8665424 PUBLICATION DATE: 02/05/2004
Name: CROSBY'S DOCK, FOLLY RIVER
SC
NOAA Chart: 11521 Latitude: 32° 40.5' N ( 32.67500)
USGS Quad: JAMES ISLAND Longitude: 79° 57.1' W ( -79.95170)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: C-5 1974
DESIGNATION: C 5
MONUMENTATION: Survey disk VM#: 4166
AGENCY: BCD Regional Planning Council IDB PID#: CJ0434
SETTING CLASSIFICATION: Concrete wing wall OPUS PID:
LATITUDE: 32° 40.6' N ( 32.67670) LONGITUDE: 79° 57.1' W ( -79.95170)
The bench mark is a disk set in the in the top of the NE concrete wing wall of
the bridge over Folly Creek, 6.61 m (21.7 ft) NE of the centerline of State
Highway 171, 0.3 m (1.0 ft) SW of the NE end of of the wing wall, and 0.3 m (1.0
ft) above highway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 8665424 PUBLICATION DATE: 02/05/2004
Name: CROSBY'S DOCK, FOLLY RIVER
SC
NOAA Chart: 11521 Latitude: 32° 40.5' N ( 32.67500)
USGS Quad: JAMES ISLAND Longitude: 79° 57.1' W ( -79.95170)
T I D A L D A T U M S
Tidal datums at CROSBY'S DOCK, FOLLY RIVER based on:
LENGTH OF SERIES: 1 YEAR
TIME PERIOD: October 1975 - September 1976
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:
HIGHEST OBSERVED WATER LEVEL (10/05/1975) = 2.306
MEAN HIGHER HIGH WATER MHHW = 1.824
MEAN HIGH WATER MHW = 1.707
North American Vertical Datum NAVD88 = 1.018
MEAN SEA LEVEL MSL = 0.921
MEAN TIDE LEVEL MTL = 0.882
MEAN LOW WATER MLW = 0.057
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (01/01/1976) = -0.644
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
CD NO 1 1975 4.206 2.499
CD NO 2 1975 4.201 2.494
CD NO 3 1975 4.218 2.511
C-5 1974 4.225 2.518
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 8665424 PUBLICATION DATE: 02/05/2004
Name: CROSBY'S DOCK, FOLLY RIVER
SC
NOAA Chart: 11521 Latitude: 32° 40.5' N ( 32.67500)
USGS Quad: JAMES ISLAND Longitude: 79° 57.1' W ( -79.95170)
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.