U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 7
Station ID: 8724527 PUBLICATION DATE: 10/30/2003
Name: COW KEY CHANNEL
FL
NOAA Chart: 11441 Latitude: 24° 34.2' N ( 24.57000)
USGS Quad: BOCA CHICA KEY Longitude: 81° 45.0' W ( -81.75000)
To reach the tidal bench marks from the junction of U.S. Highway 1 and State
Highway A1A, proceed east on U.S. Highway 1 for 0.40 km (0.25 mi) to the U.S.
Highway 1 bridge over Cow Key Channel. The bench marks are on the bridge and in
the vicinity of the bridge. The tide gage and staff were at the east end of the
south side of the bridge.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: G 121 RESET 1977
DESIGNATION: G 121 RESET
MONUMENTATION: Bench Mark disk VM#: 10991
AGENCY: National Geodetic Survey (NGS) IDB PID#: AA0670
SETTING CLASSIFICATION: Concrete guardrail OPUS PID:
LATITUDE: 24° 34.3' N ( 24.57170) LONGITUDE: 81° 44.9' W ( -81.74830)
The primary bench mark is a disk set in top of the north concrete guardrail at
the west end of the northbound bridge, 1 m (3 ft) above the level of the road.
BENCH MARK STAMPING: 4527 D 1982
DESIGNATION: 872 4527 D TIDAL
MONUMENTATION: Tidal Station disk VM#: 10992
AGENCY: National Ocean Survey (NOS) IDB PID#: AA1016
SETTING CLASSIFICATION: Concrete manhole foundation OPUS PID:
LATITUDE: 24° 34.2' N ( 24.57000) LONGITUDE: 81° 44.9' W ( -81.74830)
The bench mark is a disk set in a concrete manhole foundation located on the
hospital grounds at the west end of the U.S. Highway 1 bridge over Cow Key
Channel, 36.94 m (121.2 ft) north of the centerline of the west bound lane of
U.S. Highway 1, 9.94 m (32.6 ft) NE of power pole A-1-3, 8.23 m (27.0 ft) west
of the centerline of Junior College Road, and 0.03 m (0.1 ft) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 7
Station ID: 8724527 PUBLICATION DATE: 10/30/2003
Name: COW KEY CHANNEL
FL
NOAA Chart: 11441 Latitude: 24° 34.2' N ( 24.57000)
USGS Quad: BOCA CHICA KEY Longitude: 81° 45.0' W ( -81.75000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4527 F 1986
DESIGNATION: 872 4527 F
MONUMENTATION: Tidal Station disk VM#: 10993
AGENCY: National Ocean Service (NOS) IDB PID#: AA1629
SETTING CLASSIFICATION: Concrete manhole foundation OPUS PID:
LATITUDE: 24° 34.2' N ( 24.57000) LONGITUDE: 81° 45.0' W ( -81.75000)
The bench mark is a disk set in the top of a concrete manhole foundation, 10.36
m (34.0 ft) NNW of the centerline of the northbound lane of the highway, 10.15 m
(33.3 ft) east of the SE corner of the southbound bridge, 7.77 m (25.5 ft) SSE
of the centerline of the southbound lane of the highway, and 2.01 m (6.6 ft) SSE
of a metal guardrail.
BENCH MARK STAMPING: 4527 G 1986
DESIGNATION: 872 4527 G
MONUMENTATION: Tidal Station disk VM#: 10994
AGENCY: National Ocean Service (NOS) IDB PID#: AA1630
SETTING CLASSIFICATION: Concrete bridge abutment OPUS PID:
LATITUDE: 24° 34.2' N ( 24.57000) LONGITUDE: 81° 44.9' W ( -81.74830)
The bench mark is a disk set in the west abutment of the southbound bridge lane,
11.19 m (36.7 ft) NNW of the centerline of the southbound lane of the highway,
6.10 m (20.0 ft) east of the NW corner of a metal guardrail, 0.27 m (0.9 ft) NNW
of the north side of the bridge, and 0.15 m (0.5 ft) SSE of a 0.46 m (1.5 ft)
diameter water main pipe.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 7
Station ID: 8724527 PUBLICATION DATE: 10/30/2003
Name: COW KEY CHANNEL
FL
NOAA Chart: 11441 Latitude: 24° 34.2' N ( 24.57000)
USGS Quad: BOCA CHICA KEY Longitude: 81° 45.0' W ( -81.75000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4527 E
DESIGNATION: 872 4527 E TIDAL
MONUMENTATION: Bench Mark disk VM#: 10995
AGENCY: Florida Department of Transportation
(FDLT) IDB PID#: AA1628
SETTING CLASSIFICATION: Concrete guardrail OPUS PID:
LATITUDE: 24° 34.2' N ( 24.57000) LONGITUDE: 81° 45.0' W ( -81.75000)
The bench mark is a disk set in the north concrete guardrail located at the east
end of the southbound bridge, 7.19 m (23.6 ft) NNW of the centerline of the
southbound lane of the highway, and 5.85 m (19.2 ft) WSW of the east end of the
guardrail.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 7
Station ID: 8724527 PUBLICATION DATE: 10/30/2003
Name: COW KEY CHANNEL
FL
NOAA Chart: 11441 Latitude: 24° 34.2' N ( 24.57000)
USGS Quad: BOCA CHICA KEY Longitude: 81° 45.0' W ( -81.75000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: A271
DESIGNATION: A 271 FLHD
MONUMENTATION: Survey disk VM#: 17088
AGENCY: Florida Department of Transportation
(FLDT) IDB PID#: AA0055
SETTING CLASSIFICATION: Concrete bridge abutment OPUS PID:
LATITUDE: 24° 34.3' N ( 24.57170) LONGITUDE: 81° 44.9' W ( -81.74830)
The bench mark is a disk set on the top of the south end of the east concrete
abutment of the westbound lane of the highway over Cow Key Channel, 1m (4 ft)
south of the south curb of the bridge, and 0.3 m (1 ft) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 7
Station ID: 8724527 PUBLICATION DATE: 10/30/2003
Name: COW KEY CHANNEL
FL
NOAA Chart: 11441 Latitude: 24° 34.2' N ( 24.57000)
USGS Quad: BOCA CHICA KEY Longitude: 81° 45.0' W ( -81.75000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: Z 267
DESIGNATION: Z 267 FLHD
MONUMENTATION: Survey disk VM#: 17136
AGENCY: Florida Highway Department (FHD) IDB PID#: AA0053
SETTING CLASSIFICATION: Concree bridge abutment OPUS PID:
LATITUDE: 24° 34.3' N ( 24.57170) LONGITUDE: 81° 45.0' W ( -81.75000)
The bench mark is a disk set on the top of the north end of the west abutment of
the westbound lane of the highway for Cow Key Channel, 2.38 m (7.8 ft) north of
the north bridge curb, and 0.3 m (1 ft) above the level of the highway.
BENCH MARK STAMPING: NO 1 1975
DESIGNATION: 872 4527 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 17137
AGENCY: National Ocean Survey (NOS) IDB PID#: AA1015
SETTING CLASSIFICATION: Concrete pipe support OPUS PID:
LATITUDE: 24° 34.2' N ( 24.57000) LONGITUDE: 81° 45.0' W ( -81.75000)
The bench mark is a disk set in the top of a concrete support for an Aquaduct
pipe, 24 m (79 ft) west of Bell System manhole cover , 12 m (39 ft) north of the
north edge of the westbound lane of the road, and 2 m (7 ft) below the highway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 7
Station ID: 8724527 PUBLICATION DATE: 10/30/2003
Name: COW KEY CHANNEL
FL
NOAA Chart: 11441 Latitude: 24° 34.2' N ( 24.57000)
USGS Quad: BOCA CHICA KEY Longitude: 81° 45.0' W ( -81.75000)
T I D A L D A T U M S
Tidal datums at COW KEY CHANNEL based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: February 1975 - February 1975
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8724580 KEY WEST
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
North American Vertical Datum NAVD88 = 0.395
MEAN HIGHER HIGH WATER MHHW = 0.388
MEAN HIGH WATER MHW = 0.303
MEAN SEA LEVEL MSL = 0.181
MEAN TIDE LEVEL MTL = 0.178
MEAN LOW WATER MLW = 0.053
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
G 121 RESET 1977 3.969 3.666
4527 D 1982 1.411 1.108
4527 F 1986 3.050 2.747
4527 G 1986 2.464 2.161
4527 E 3.806 3.503
A271 3.184 2.881
Z 267 3.078 2.775
NO 1 1975 1.884 1.581
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 7
Station ID: 8724527 PUBLICATION DATE: 10/30/2003
Name: COW KEY CHANNEL
FL
NOAA Chart: 11441 Latitude: 24° 34.2' N ( 24.57000)
USGS Quad: BOCA CHICA KEY Longitude: 81° 45.0' W ( -81.75000)
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.