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National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
Station ID: 8660854 PUBLICATION DATE: 05/28/2004
Name: COMBINATION BRIDGE
SC
NOAA Chart: 11535 Latitude: 33° 42.8' N ( 33.71330)
USGS Quad: MYRTLE BEACH Longitude: 78° 55.3' W ( -78.92170)
To reach the tidal bench marks from the intersection of U.S. Highway 17 and
State Highway 501 in Myrtle Beach, proceed NW along State Highway 501 for 1.0 km
(0.6 mi) to the bridge over the Intracoastal Waterway. The bench marks are
located along the State Highway 501 bridge, on the old railroad highway
combination drawbridge adjacent to the highway bridge, and along the approaches
to the bridges. The tide gage and staff were located on a wooden fender on the
SE side of the combination bridge.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 0854 A 1976
DESIGNATION: 866 0854 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 3731
AGENCY: National Ocean Survey (NOS) IDB PID#: DD0822
SETTING CLASSIFICATION: Curb OPUS PID#: DD0822
LATITUDE: 33° 42.9' N ( 33.71500) LONGITUDE: 78° 55.3' W ( -78.92170)
The primary bench mark is a disk set in the NE corner of the combination bridge
curb, 16.15 m (53.0 ft) north of the center of the road, 11.06 m (36.3 ft) ENE
of power pole #20864 with three guy wires and transformers, 3.44 m (11.3 ft) ENE
of the center of the ramp, 0.37 m (1.2 ft) WNW of a witness post, and 0.21 m
(0.3 ft) west of the south corner of the NE guardrail.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 8660854 PUBLICATION DATE: 05/28/2004
Name: COMBINATION BRIDGE
SC
NOAA Chart: 11535 Latitude: 33° 42.8' N ( 33.71330)
USGS Quad: MYRTLE BEACH Longitude: 78° 55.3' W ( -78.92170)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0854 B 1976
DESIGNATION: 866 0854 B TIDAL
MONUMENTATION: Tidal Station disk VM#: 3732
AGENCY: National Ocean Survey (NOS) IDB PID#: DD0823
SETTING CLASSIFICATION: Pile cap OPUS PID:
LATITUDE: 33° 42.8' N ( 33.71330) LONGITUDE: 78° 55.3' W ( -78.92170)
The bench mark is a disk set in a pile cap near the center pier of the bridge
over the intracoastal waterway, 7.01 m (23.0 ft) SSE of the centerline of the
paved road under the bridge, 5.49 m (18.0 ft) SW of the west corner of the NE
bridge pier, 1.86 m (6.1 ft) ENE of the north corner of the center bridge pier,
0.49 m (1.6 ft) SSE of a witness post at the NW edge of the pile cap, and 0.61 m
(2.0 ft) above the road.
BENCH MARK STAMPING: 0854 D 1976
DESIGNATION: 866 0854 D TIDAL
MONUMENTATION: Tidal Station disk VM#: 3733
AGENCY: National Ocean Survey (NOS) IDB PID#: DD0825
SETTING CLASSIFICATION: Copper clad steel rod OPUS PID:
LATITUDE: 33° 42.8' N ( 33.71330) LONGITUDE: 78° 55.2' W ( -78.92000)
The bench mark is a disk located on the west side of the approach road to the
combination bridge, 0.2 km (0.1 mi) SE of the combination drawbridge, 40.75 m
(133.7 ft) SW of a fire hydrant, 33.86 m (111.1 ft) west of a sign post for
Bridgeport Subdivision in the median of a paved road right, 20.21 m (66.3 ft) SW
of the SW most railroad tracks, 11.09 m (36.4 ft) SW of the centerline of the
road, and 1.19 m (3.9 ft) NNW of power pole #29862. The bench mark is set level
with the ground, crimped to the top of a copper-clad steel rod driven 4.6 m (15
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 6
Station ID: 8660854 PUBLICATION DATE: 05/28/2004
Name: COMBINATION BRIDGE
SC
NOAA Chart: 11535 Latitude: 33° 42.8' N ( 33.71330)
USGS Quad: MYRTLE BEACH Longitude: 78° 55.3' W ( -78.92170)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0854 F 1982
DESIGNATION: 866 0854 F TIDAL
MONUMENTATION: Tidal Station disk VM#: 3734
AGENCY: National Ocean Survey (NOS) IDB PID#: DD1578
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 33° 42.7' N ( 33.71170) LONGITUDE: 78° 55.1' W ( -78.91830)
The bench mark is a disk located on the east side of the railroad tracks leading
to the combination bridge, 33.28 m (109.2 ft) ENE of the centerline of the road
leading to the combination bridge, 30.69 m (100.7 ft) NW of a fire hydrant,
12.98 m (42.6 ft) NE of the NE most rail of the railroad tracks, 11.16 m (36.6
ft) NNW of the center of the gravel road, 6.19 m (20.3 ft) WSW of a witness
post, 4.82 m (15.8 ft) NE of power pole #51990, and 0.21 m (0.7 ft) west of a
witness post. The bench mark is set level with the ground, crimped to the top
of a stainless steel rod driven 14.6 m (48 ft) to refusal, and encased in a
5-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 8660854 PUBLICATION DATE: 05/28/2004
Name: COMBINATION BRIDGE
SC
NOAA Chart: 11535 Latitude: 33° 42.8' N ( 33.71330)
USGS Quad: MYRTLE BEACH Longitude: 78° 55.3' W ( -78.92170)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0854 G 1982
DESIGNATION: 866 0854 G TIDAL
MONUMENTATION: Tidal Station disk VM#: 3735
AGENCY: National Ocean Survey (NOS) IDB PID#: DD1576
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 33° 42.7' N ( 33.71170) LONGITUDE: 78° 55.1' W ( -78.91830)
The bench mark is a disk located on the west side of U.S. Highway 501 in the
vicinity of a large cinder block sign WELCOME TO MYRTLE BEACH, 0.5 km (0.3 mi)
SE of the south side of the bridge over the Intracoastal Waterway, 17.98 m (59.0
ft) SW of the center of the road, 16.70 m (54.8 ft) south of the west end of a
0.46 m (1.5 ft) concrete pipe culvert beneath the frontage road, 5.21 m (17.1
ft) WNW of a meter pole, 2.01 m (6.6 ft) SW of the west corner of a concrete
block planter bed for the Welcome to Myrtle Beach sign, and 1.31 m (4.3 ft) SE
of a witness post. The bench mark is set level with the ground, crimped to a
stainless steel rod driven 11.0 m (36 ft), encased in a 5-inch PVC pipe and
concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 8660854 PUBLICATION DATE: 05/28/2004
Name: COMBINATION BRIDGE
SC
NOAA Chart: 11535 Latitude: 33° 42.8' N ( 33.71330)
USGS Quad: MYRTLE BEACH Longitude: 78° 55.3' W ( -78.92170)
T I D A L D A T U M S
Tidal datums at COMBINATION BRIDGE based on:
LENGTH OF SERIES: 10 MONTHS
TIME PERIOD: March 1977 - December 1977
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8661139 BUCKSPORT, WACCAMAW RIVER
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 0.620
MEAN HIGH WATER MHW = 0.573
MEAN TIDE LEVEL MTL = 0.313
MEAN SEA LEVEL MSL = 0.312
North American Vertical Datum NAVD88 = 0.077
MEAN LOW WATER MLW = 0.052
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
0854 A 1976 6.761 6.188
0854 B 1976 6.883 6.310
0854 D 1976 6.499 5.926
0854 F 1982 6.103 5.530
0854 G 1982 6.437 5.864
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 8660854 PUBLICATION DATE: 05/28/2004
Name: COMBINATION BRIDGE
SC
NOAA Chart: 11535 Latitude: 33° 42.8' N ( 33.71330)
USGS Quad: MYRTLE BEACH Longitude: 78° 55.3' W ( -78.92170)
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.
Station Location
Published bench mark
Unpublished bench mark
