U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 12/19/1991
Station ID: 8724527 SUPERCEDED DATE: 04/21/2003
Name: STOCK ISLAND, COW KEY CHANNEL
FLORIDA
NOAA Chart: 11441 Latitude: 24° 34.2' N
USGS Quad: KEY WEST Longitude: 81° 45.0' W
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 0.25 mile (0.40 km) 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
MONUMENTATION: Survey Disk VM#: 10991
AGENCY: PID#: AA0670
SETTING CLASSIFICATION: Concrete Guardrail
The primary bench mark is set in top of the north concrete guardrail at the west
end of the northbound bridge, 3 feet (1 m) above the level of the road.
BENCH MARK STAMPING: 4527 D 1982
MONUMENTATION: Survey Disk VM#: 10992
AGENCY: PID#: AA1016
SETTING CLASSIFICATION: Concrete Manhole Box
The bench mark is set in a concrete manhole in the hospital grounds at the west
end of the U.S. Highway 1 bridge over Cow Key Channel, 121.2 feet (36.9 m) north
of the centerline of the west bound lane of U.S. Highway 1, 32.6 feet (9.9 m) NE
of power pole A-1-3, 27.0 feet (8.2 m) west of the centerline of the hospital
road, and 0.1 foot (0.03 m) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 12/19/1991
Station ID: 8724527 SUPERCEDED DATE: 04/21/2003
Name: STOCK ISLAND, COW KEY CHANNEL
FLORIDA
NOAA Chart: 11441 Latitude: 24° 34.2' N
USGS Quad: KEY WEST Longitude: 81° 45.0' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4527 F 1986
MONUMENTATION: Survey Disk VM#: 10993
AGENCY: PID#: AA1629
SETTING CLASSIFICATION: Concrete Manhole Box
The bench mark is set in the top of a concrete box with a manhole, 34.0 feet
(10.4 m) NNW of the centerline of the northbound lane of the highway, 33.3 feet
(10.1 m) east of the SE corner of the southbound bridge, 25.5 feet (7.8 m) SSE
of the centerline of the southbound lane of the highway, and 6.6 feet (2.0 m)
SSE of a metal guardrail.
BENCH MARK STAMPING: 4527 G 1986
MONUMENTATION: Survey Disk VM#: 10994
AGENCY: PID#: AA1630
SETTING CLASSIFICATION: Concrete Bridge Abutment
The bench mark is set in the west abutment of the southbound bridge, 36.7 feet
(11.2 m) NNW of the centerline of the southbound lane of the highway, 20.0 feet
(6.1 m) east of the NW corner of a metal guardrail, 0.9 foot (0.3 m) NNW of the
north side of the bridge, and 0.5 foot (0.2 m) SSE of a 1.5-foot (0.5 m)
diameter water main pipe.
BENCH MARK STAMPING: 4527 E
MONUMENTATION: Survey Disk VM#: 10995
AGENCY: PID#: AA1628
SETTING CLASSIFICATION: Concrete Guardrail
The bench mark is set in the north concrete guardrail at the east end of the
southbound bridge, 23.6 feet (7.2 m) NNW of the centerline of the southbound
lane of the highway, and 19.2 feet (5.9 m) WSW of the east end of the guardrail.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 12/19/1991
Station ID: 8724527 SUPERCEDED DATE: 04/21/2003
Name: STOCK ISLAND, COW KEY CHANNEL
FLORIDA
NOAA Chart: 11441 Latitude: 24° 34.2' N
USGS Quad: KEY WEST Longitude: 81° 45.0' W
T I D A L D A T U M S
Tidal datums at STOCK ISLAND, COW KEY CHANNEL based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: FEBRUARY 1975
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8724580 KEY WEST
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (02/23/1975) = 1.72
MEAN HIGHER HIGH WATER MHHW = 1.30
MEAN HIGH WATER MHW = 1.02
MEAN TIDE LEVEL MTL = 0.60
* NATIONAL GEODETIC VERTICAL DATUM NGVD29 = 0.21
MEAN LOW WATER MLW = 0.18
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (01/23/1975) = -0.52
* NGVD reference based on elevations published in Quad 240814, 1971, and NOS
leveling of 1982.
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
G 121 RESET 1977 13.28 12.26
4527 D 1982 4.88 3.86
4527 F 1986 10.27 9.25
4527 G 1986 8.34 7.32
4527 E 12.75 11.73
Foot Notes:
The reliability of the elevations at this station may be reduced
due to staff movement of 0.035 foot.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 12/19/1991
Station ID: 8724527 SUPERCEDED DATE: 04/21/2003
Name: STOCK ISLAND, COW KEY CHANNEL
FLORIDA
NOAA Chart: 11441 Latitude: 24° 34.2' N
USGS Quad: KEY WEST Longitude: 81° 45.0' W
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 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.