U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
Station ID: 8720093 PUBLICATION DATE: 01/26/2010
Name: HALFMOON ISLAND
FL
NOAA Chart: 11488 Latitude: 30° 34.6' N ( 30.57670)
USGS Quad: HEDGES Longitude: 81° 36.5' W ( -81.60830)
To reach the tidal bench marks from the intersection of State Road A1A and U.S.
Highway 17 at Yulee, proceed south on U.S. Highway 17 for 6.75 km (4.2 mi) to
the south side of the highway bridge over the Nassau River. The bench marks are
on the bridge, in the vicinity, and north of it. The tide gage and staff were
west of the bridge on the north side of the river at Charley's Fishing Camp.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: HALFMOON NO 3 1934
MONUMENTATION: Tidal Station disk VM#: 5012
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: BC0115
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 30° 34.4' N ( 30.57330) LONGITUDE: 81° 36.6' W ( -81.61000)
The primary bench mark is a disk set in the top of a concrete monument south of
the bridge, 58.5 m (192.0 ft) NW of the centerline of U.S. Highway 17, as
measured from a point 49.2 m (161.5 ft) south of the south end of the bridge
span over the Nassau River, 34.8 m (114.0 ft) NW of a 17-inch pine tree (the
easternmost tree of a 3-pine cluster), 9.8 m (32.0 ft) NE of a 17-inch Chinese
Tallow tree, 9.1 m (30.0 ft) north of a 4-inch x 4-inch wood post, 6.1 m (20.0
ft) north of an 8-inch oak tree, 0.3 m (1.0 ft) east of a carsonite witness
post, and projecting 0.1 m (4.0 in) above ground level. NOTE; A magnet was
buried at the south side of the mark.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 8720093 PUBLICATION DATE: 01/26/2010
Name: HALFMOON ISLAND
FL
NOAA Chart: 11488 Latitude: 30° 34.6' N ( 30.57670)
USGS Quad: HEDGES Longitude: 81° 36.5' W ( -81.60830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: HALFMOON NO 2 1934
MONUMENTATION: Tidal Station disk VM#: 19190
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: BC0116
SETTING CLASSIFICATION: Concrete filled sewer tile OPUS PID#: BC0116
LATITUDE: 30° 34.4' N ( 30.57330) LONGITUDE: 81° 36.6' W ( -81.61000)
The bench mark is a disk set flush in the top of a concrete filled sewer tile
flush with the ground, 34.1 m (112.0 ft) WNW of the NW corner of the south
abutment of the U.S. Highway 17 bridge over the Nassau River, 27.1 m (89.0 ft)
NW of an 18-inch pine tree (tree is 25.1 m (82.5 ft) NW of the NW corner of the
south bridge abutment), 23.6 m (77.5 ft) NNW of a 28-inch pine tree, 19.8 m
(65.0 ft) SW of the SW side of the open water of the Nassau River, 15.5 m (51
ft) NW of a 10-inch cypress tree, and 0.3 m (1.0 ft) SE of a carsonite witness
post. NOTE: A magnet was buried at the south side of the mark.
BENCH MARK STAMPING: N 331 1975
MONUMENTATION: Vertical Control disk VM#: 19194
AGENCY: National Geodetic Survey (NGS) IDB PID#: BC0119
SETTING CLASSIFICATION: Concrete abutment OPUS PID:
LATITUDE: 30° 34.4' N ( 30.57330) LONGITUDE: 81° 36.6' W ( -81.61000)
The bench mark is a disk located 9.0 km (5.6 mi) southerly along U.S. Highway 17
from the junction of State Highway A1A in Yulee, 31.7 m (104.0 ft) west of and
level with the highway centerline, in top of and 1.6 m (5.2 ft) east of the west
end of the north concrete abutment of the CSX transportation railroad bridge
spanning Inconstantion Creek, and 1.6 m (5.2 ft) east of the near rail. NOTE:
The disk has been mutilated and the stamping is dim, but legible.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 8720093 PUBLICATION DATE: 01/26/2010
Name: HALFMOON ISLAND
FL
NOAA Chart: 11488 Latitude: 30° 34.6' N ( 30.57670)
USGS Quad: HEDGES Longitude: 81° 36.5' W ( -81.60830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: T 143 1954
MONUMENTATION: Bench Mark disk VM#: 19195
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: BC0118
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 30° 34.4' N ( 30.57330) LONGITUDE: 81° 36.6' W ( -81.61000)
The bench mark is a disk located 8.1 km (5.0 mi) southerly along U.S. Highway 17
from the junction of State Highway A1A in Yulee, 64.0 m (210.0 ft) NE of a
utility pole, 46.2 m (151.6 ft) SW of a utility pole, 38.2 m (125.3 ft) SW of an
underground cable warning sign, 16.3 m (53.5 ft) NW of the highway centerline,
0.6 m (2.0 ft) below the level of the highway, 0.4 m (1.3 ft) SE of a witness
post, and the monument is flush with the ground surface. NOTES: The monument
has been hit and the southeast side is missing, but is solid in place. A magnet
was buried at the south side of the mark.
BENCH MARK STAMPING: 0093 F 2004
MONUMENTATION: Tidal Station disk VM#: 19197
AGENCY: Florida Dept. of Environmental
Protection (FLDEP) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 30° 34.4' N ( 30.57330) LONGITUDE: 81° 36.6' W ( -81.61000)
The bench mark is a disk set in the top of a round concrete monument flush with
the ground, 161.1 m (528.4 ft) NE of the NE concrete hand rail of the highway
bridge over the Nassau River, 107 m (351.0 ft) NE of the north end of the steel
guard rail at the NE end of the bridge, 13.78 m (45.2 ft) SE of the centerline
of U.S. Highway 17, 2.68 m (8.8 ft) west of the second wooden power pole NE of
the Nassau River, and 0.3 m (1.0 ft) NW of a carsonite witness post. NOTE: A
magnet was buried at the south side of the mark.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 8720093 PUBLICATION DATE: 01/26/2010
Name: HALFMOON ISLAND
FL
NOAA Chart: 11488 Latitude: 30° 34.6' N ( 30.57670)
USGS Quad: HEDGES Longitude: 81° 36.5' W ( -81.60830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0093 G 2004
MONUMENTATION: Flange-encased Rod VM#: 19198
AGENCY: Florida Dept. of Environmental
Protection (FLDEP) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 30° 34.4' N ( 30.57330) LONGITUDE: 81° 36.6' W ( -81.61000)
The benchmark is a flange-encased rod located 81.9 m (268.8 ft) NE of wooden
power pole number 18281, about 45.7 m (150.0 ft) SW of the SW bank of the Nassau
River, 37.1 m (121.8 ft) SE of the centerline of U.S. Highway 17, 32.5 m (106.7
ft) SSE of the south end of the concrete handrail of the highway bridge over the
Nassau River and 0.3 m (1.0 ft) west of a carsonite witness post. The datum
point is accessed through a 5-inch NGS logo cap flush with the ground and about
1.5 m (5.0 ft) below the level of U.S. Highway 17, recessed 0.1 m (0.3 ft) below
the level of the NGS logo cap, being the top of a stainless steel rod, driven to
refusal at a depth of 11.9 m (39.1 ft). NOTE: A magnet was buried at the south
side of the mark.
BENCH MARK STAMPING: 0093 H 2004
MONUMENTATION: Tidal Station disk VM#: 19199
AGENCY: Florida Dept. of Environmental
Protection (FLDEP) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 30° 34.4' N ( 30.57330) LONGITUDE: 81° 36.6' W ( -81.61000)
The bench mark is a disk set in the top of a round concrete monument flush with
the ground, 176.2 m (578.0 ft) SW of the south end of the SE concrete handrail
of the U.S. Highway 17 bridge over the Nassau River, 85.8 m (281.5 ft) SW of
wooden power pole number 18281, 13.08 m (42.9 ft) SE of the centerline of U.S.
Highway 17, 1.829 m (6.0 ft) SW of wooden power pole number 18241, and 0.3 m
(1.0 ft) NW of a carsonite witness post.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 8720093 PUBLICATION DATE: 01/26/2010
Name: HALFMOON ISLAND
FL
NOAA Chart: 11488 Latitude: 30° 34.6' N ( 30.57670)
USGS Quad: HEDGES Longitude: 81° 36.5' W ( -81.60830)
D A T U M S
Datums at HALFMOON ISLAND based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: July 1978 - August 1978
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8720098 NASSAUVILLE, NASSAU RIVER EAST
Elevations of datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 1.386
MEAN HIGH WATER MHW = 1.330
North American Vertical Datum NAVD88 = 0.795
MEAN SEA LEVEL MSL = 0.779
MEAN TIDE LEVEL MTL = 0.696
MEAN LOW WATER MLW = 0.061
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
HALFMOON NO 3 1934 1.803 0.473
HALFMOON NO 2 1934 1.506 0.176
N 331 1975 3.172 1.842
T 143 1954 3.170 1.840
0093 F 2004 2.122 0.792
0093 G 2004 1.972 0.642
0093 H 2004 2.323 0.993
Foot Notes:
Geodetic heights of the bench marks meet all NOAA/NOS/NGS quality Geodetic
heights of the bench marks meet all NOAA/NOS/NGS quality control standards for
Second Order, Class 1 leveling. It is advised that a confirmation set of levels
be established for bench marks 0093 F 2004, 0093 G 2004, 0093 H 2004, Halfmoon
NO 2 1934, N 331 1975, and T 143 1954 to verify height differences before using
tidal bench mark elevation information.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 8720093 PUBLICATION DATE: 01/26/2010
Name: HALFMOON ISLAND
FL
NOAA Chart: 11488 Latitude: 30° 34.6' N ( 30.57670)
USGS Quad: HEDGES Longitude: 81° 36.5' W ( -81.60830)
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.