U.S. DEPARTMENT OF COMMERCE
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National Ocean Service
Datums Page Page 1 of 7
Station ID: 8724474 PUBLICATION DATE: 02/05/2004
Name: DUCK KEY POINT
FL
NOAA Chart: 11445 Latitude: 24° 37.4' N ( 24.62330)
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W ( -81.68500)
To reach the tidal bench marks from the public boat ramp at the Boca Chica
Channel Bridge, proceed by boat NNE for 6 km (4 statute mi) to the NE tip of
Duck Key Point, a small island just north of Duck Key. The bench marks are
located in a large grassy clearing in the middle and the northern end of the
island. The tide gage and staff were located off the NE tip of the Key.
T I D A L B E N C H M A R K S
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 7
Station ID: 8724474 PUBLICATION DATE: 02/05/2004
Name: DUCK KEY POINT
FL
NOAA Chart: 11445 Latitude: 24° 37.4' N ( 24.62330)
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W ( -81.68500)
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: SNAKE 1934
DESIGNATION: SNAKE 1934 MONROE CO SW
MONUMENTATION: Survey disk VM#: 11073
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AA1086
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 37.3' N ( 24.62170) LONGITUDE: 81° 41.0' W ( -81.68330)
The primary bench mark is a disk set in a 0.12 m (0.4 ft) square concrete
monument in a grassy clearing on Duck Key Point, 30 m (98 ft) north of the north
edge of mangrove swamp which covers the southern end of the Point, 15 m (49 ft)
east and west of the edges of mangroves surrounding the clearing, 0.15 m (0.5
ft) north of a witness post, and 0.21 m (0.7 ft) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 7
Station ID: 8724474 PUBLICATION DATE: 02/05/2004
Name: DUCK KEY POINT
FL
NOAA Chart: 11445 Latitude: 24° 37.4' N ( 24.62330)
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W ( -81.68500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: RM 1 1935 SNAKE
DESIGNATION: SNAKE RM 1
MONUMENTATION: Reference Mark disk VM#: 11074
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 37.4' N ( 24.62330) LONGITUDE: 81° 41.1' W ( -81.68500)
The bench mark is a disk set in a 0.30 m (1.0 ftt) square concrete monument in a
grassy clearing on Duck Key Point, 21 m (69 ft) SSE of bench mark SNAKE 1934,
0.24 m (0.8 ft) north of a witness post, and 0.21 m (0.7 ft) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 7
Station ID: 8724474 PUBLICATION DATE: 02/05/2004
Name: DUCK KEY POINT
FL
NOAA Chart: 11445 Latitude: 24° 37.4' N ( 24.62330)
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W ( -81.68500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: RM 2 1935 SNAKE
DESIGNATION: SNAKE RM 2
MONUMENTATION: Reference Mark disk VM#: 11075
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 37.4' N ( 24.62330) LONGITUDE: 81° 41.1' W ( -81.68500)
The bench mark is a disk set in a 0.30 m (1.0 ft) square concrete monument in a
grassy clearing on Duck Key Point, 19.32 m (63.4 ft) NW of bench mark SNAKE
1934, and 0.2 m (0.6 ft) west of a witness post.
BENCH MARK STAMPING: NO 4 1974
DESIGNATION: 872 4474 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 11076
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 24° 37.4' N ( 24.62330) LONGITUDE: 81° 41.1' W ( -81.68500)
The bench mark is a disk located on the edge of a grassy clearing in Duck Key
Point, 33.83 m (111.0 ft) north of bench mark SNAKE 1934, 19.20 m (63.0 ft) west
of the outer mangrove edge on the east shore, 17.37 m (57.0 ft) NNE of bench
mark RM 2 1935 SNAKE, and 0.30 m (1.0 ft) west of a witness post. The bench mark
is crimped to a copper-clad steel rod driven to refusal.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 7
Station ID: 8724474 PUBLICATION DATE: 02/05/2004
Name: DUCK KEY POINT
FL
NOAA Chart: 11445 Latitude: 24° 37.4' N ( 24.62330)
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W ( -81.68500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 5 1974
DESIGNATION: 872 4474 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 11077
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 24° 37.4' N ( 24.62330) LONGITUDE: 81° 41.1' W ( -81.68500)
The bench mark is a disk located on the edge of a grassy clearing in Duck Key
Point, 21 m (69 ft) NW of bench mark NO 4 1974, 19 m (63 ft) west of the outer
mangrove edge on the east shore, and 0.27 m (0.9 ft) east of a witness post. The
bench mark is crimped to a copper-clad steel rod driven to refusal.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 7
Station ID: 8724474 PUBLICATION DATE: 02/05/2004
Name: DUCK KEY POINT
FL
NOAA Chart: 11445 Latitude: 24° 37.4' N ( 24.62330)
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W ( -81.68500)
T I D A L D A T U M S
Tidal datums at DUCK KEY POINT based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: September 1974 - October 1974
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8724580 KEY WEST
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 0.626
MEAN HIGH WATER MHW = 0.548
MEAN TIDE LEVEL MTL = 0.309
MEAN SEA LEVEL MSL = 0.289
MEAN LOW WATER MLW = 0.069
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
SNAKE 1934 0.777 0.229
RM 1 1935 SNAKE 0.783 0.235
RM 2 1935 SNAKE 0.856 0.308
NO 4 1974 0.692 0.144
NO 5 1974 0.721 0.173
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 7
Station ID: 8724474 PUBLICATION DATE: 02/05/2004
Name: DUCK KEY POINT
FL
NOAA Chart: 11445 Latitude: 24° 37.4' N ( 24.62330)
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W ( -81.68500)
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.