U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 8
Station ID: 8724093 PUBLICATION DATE: 01/23/2004
Name: LITTLE DUCK KEY
FL
NOAA Chart: 11449 Latitude: 24° 40.9' N ( 24.68170)
USGS Quad: SEVENMILE BRIDGE Longitude: 81° 13.7' W ( -81.22830)
To reach the tidal bench marks from the post office at Marathon, proceed 15.4 km
(9.6 mi) SW along U.S. Highway 1 to the west end of Sevenmile Bridge. The bench
marks are located at the east end of Little Duck Key on the concrete wing wall
of the bridge, and in the vicinity of a boat ramp. The tide gage and staff were
located at the south end of the south concrete wing wall.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1
DESIGNATION: 872 4093 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 6331
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AA0279
SETTING CLASSIFICATION: Concrete wing wall OPUS PID:
LATITUDE: 24° 41.0' N ( 24.68330) LONGITUDE: 81° 13.7' W ( -81.22830)
The primary bench mark is a disk set in the top of the south concrete wingwall
of the west abutment, 5 m (15 ft) south of the centerline of the highway, and 1
m (2 ft) below highway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 8
Station ID: 8724093 PUBLICATION DATE: 01/23/2004
Name: LITTLE DUCK KEY
FL
NOAA Chart: 11449 Latitude: 24° 40.9' N ( 24.68170)
USGS Quad: SEVENMILE BRIDGE Longitude: 81° 13.7' W ( -81.22830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4093 E 1982
DESIGNATION: 872 4093 E TIDAL
MONUMENTATION: Tidal Station disk VM#: 6325
AGENCY: National Ocean Survey (NOS) IDB PID#: AA0959
SETTING CLASSIFICATION: Concrete bulkhead OPUS PID:
LATITUDE: 24° 40.9' N ( 24.68170) LONGITUDE: 81° 13.7' W ( -81.22830)
The bench mark is a disk set flush in the top of a concrete bulkhead for a boat
ramp located on the north side of the highway, 73 m (240 ft) west of the west
end of the bridge, 15.45 m (50.7 ft) south of the north end of a small pier,
8.90 m (29.2 ft) north of the south end of the bulkhead, and 4.21 m (13.8 ft)
west of the centerline of the boat ramp.
BENCH MARK STAMPING: 4093 F 1982
DESIGNATION: 872 4093 F TIDAL
MONUMENTATION: Tidal Station disk VM#: 6326
AGENCY: National Ocean Survey (NOS) IDB PID#: AA0960
SETTING CLASSIFICATION: Concrete sea wall OPUS PID:
LATITUDE: 24° 40.9' N ( 24.68170) LONGITUDE: 81° 13.7' W ( -81.22830)
The bench mark is a disk set flush in the top of a concrete seawall located on
the north side of the highway, 55 m (180 ft) west of the west end of the bridge,
38.71 m (127.0 ft) west of the end of the seawall, 20.67 m (67.8 ft) east of
bench mark 4093 E 1982, 16.46 m (54.0 ft) east of the centerline of the boat
ramp, and 0.34 m (1.1 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 8
Station ID: 8724093 PUBLICATION DATE: 01/23/2004
Name: LITTLE DUCK KEY
FL
NOAA Chart: 11449 Latitude: 24° 40.9' N ( 24.68170)
USGS Quad: SEVENMILE BRIDGE Longitude: 81° 13.7' W ( -81.22830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4093 G
DESIGNATION: 872 4093 G TIDAL
MONUMENTATION: Bench Mark disk VM#: 6327
AGENCY: Florida Department of Transportation
(FLDT) IDB PID#: AA0958
SETTING CLASSIFICATION: Concrete guardrail OPUS PID:
LATITUDE: 24° 40.9' N ( 24.68170) LONGITUDE: 81° 13.7' W ( -81.22830)
The bench mark is a disk set in the top of the SW concrete guardrail of the
bridge, 6.00 m (19.7 ft) south of the centerline of the bridge, 2 m (7 ft) east
of the SW corner of the guardrail, and 0.85 m (2.8 ft) above highway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 8
Station ID: 8724093 PUBLICATION DATE: 01/23/2004
Name: LITTLE DUCK KEY
FL
NOAA Chart: 11449 Latitude: 24° 40.9' N ( 24.68170)
USGS Quad: SEVENMILE BRIDGE Longitude: 81° 13.7' W ( -81.22830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: B 70 RESET 1936
DESIGNATION: B 70 RESET
MONUMENTATION: Bench Mark disk VM#: 6328
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AA0281
SETTING CLASSIFICATION: Concrete wing wall OPUS PID:
LATITUDE: 24° 41.0' N ( 24.68330) LONGITUDE: 81° 13.7' W ( -81.22830)
The bench mark is a disk set in the top of the north concrete wing wall, 4 m (12
ft) north of the centerline of the highway, 0.24 m (0.8 ft) SE of triangulation
station DUCK 2 1937, and 1 m (2 ft) below highway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 8
Station ID: 8724093 PUBLICATION DATE: 01/23/2004
Name: LITTLE DUCK KEY
FL
NOAA Chart: 11449 Latitude: 24° 40.9' N ( 24.68170)
USGS Quad: SEVENMILE BRIDGE Longitude: 81° 13.7' W ( -81.22830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: DUCK 2 1937
DESIGNATION: DUCK 2
MONUMENTATION: Triangulation Station disk VM#: 6329
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AA0282
SETTING CLASSIFICATION: Concrete wing wall OPUS PID:
LATITUDE: 24° 40.9' N ( 24.68170) LONGITUDE: 81° 13.7' W ( -81.22830)
The bench mark is a disk set in the top of the north concrete wing wall, 4 m (12
ft) north of the centerline of the highway, and 1 m (2 ft) below highway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 8
Station ID: 8724093 PUBLICATION DATE: 01/23/2004
Name: LITTLE DUCK KEY
FL
NOAA Chart: 11449 Latitude: 24° 40.9' N ( 24.68170)
USGS Quad: SEVENMILE BRIDGE Longitude: 81° 13.7' W ( -81.22830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: DUCK 2 NO 1 1937 TIDAL 3
DESIGNATION: DUCK 2 RM 1
MONUMENTATION: Reference Mark disk VM#: 6330
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AA0280
SETTING CLASSIFICATION: Concrete wing wall OPUS PID:
LATITUDE: 24° 41.0' N ( 24.68330) LONGITUDE: 81° 13.7' W ( -81.22830)
The bench mark is a disk set in the top of the north concrete wing wall, 25.54 m
(83.8 ft) north of the centerline of the highway, and 3 m (10 ft) below highway
level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 8
Station ID: 8724093 PUBLICATION DATE: 01/23/2004
Name: LITTLE DUCK KEY
FL
NOAA Chart: 11449 Latitude: 24° 40.9' N ( 24.68170)
USGS Quad: SEVENMILE BRIDGE Longitude: 81° 13.7' W ( -81.22830)
T I D A L D A T U M S
Tidal datums at LITTLE DUCK KEY based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: June 1974 - June 1974
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8724211 BIG PINE KEY VIADUCT
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
North American Vertical Datum NAVD88 = 0.455
MEAN HIGHER HIGH WATER MHHW = 0.378
MEAN HIGH WATER MHW = 0.307
MEAN TIDE LEVEL MTL = 0.177
MEAN SEA LEVEL MSL = 0.176
MEAN LOW WATER MLW = 0.047
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
NO 1 5.105 4.798
4093 E 1982 1.091 0.784
4093 F 1982 0.865 0.558
4093 G 6.548 6.241
B 70 RESET 1936 5.279 4.972
DUCK 2 1937 5.236 4.929
DUCK 2 NO 1 1937 TIDAL 3 1.578 1.271
Foot Notes:
Bench Marks 4093 E 1982, 4093 F 1982, and 4093 G are based on one differential
leveling connection and do not meet the quality control standards of the NOS.
Therefore, caution should be used when deriving elelvations for these marks.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 8 of 8
Station ID: 8724093 PUBLICATION DATE: 01/23/2004
Name: LITTLE DUCK KEY
FL
NOAA Chart: 11449 Latitude: 24° 40.9' N ( 24.68170)
USGS Quad: SEVENMILE BRIDGE Longitude: 81° 13.7' W ( -81.22830)
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.