U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
Station ID: 8724503 PUBLICATION DATE: 01/23/2004
Name: STOCK ISLAND
FL
NOAA Chart: 11445 Latitude: 24° 34.6' N ( 24.57670)
USGS Quad: BOCA CHICA KEY Longitude: 81° 43.3' W ( -81.72170)
To reach the tidal bench marks from the Catholic Church in Key West, proceed NE
on U.S. Highway 1 for 8.5 km (5.3 mi) to the west end of the Boca Chica - Stock
Island bridge. The bench marks are located on the bulkheads and guard rails of
the east and westbound bridge lanes. The tide gage and staff were located on
the NW concrete bulkhead.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1 1973
DESIGNATION: 872 4503 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 11023
AGENCY: National Ocean Survey (NOS) IDB PID#: AA1024
SETTING CLASSIFICATION: Concrete bulkhead OPUS PID:
LATITUDE: 24° 34.6' N ( 24.57670) LONGITUDE: 81° 43.3' W ( -81.72170)
The primary bench mark is a disk set flush in a concrete bulkhead, 21.67 m (71.1
ft) north of the south end of the north-south bulkhead below the bridge, 7.80 m
(25.6 ft) north of the north side of the west end of the westbound lane, and 4 m
(12 ft) below highway level.
BENCH MARK STAMPING: NO 2 1973
DESIGNATION: 872 4503 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 11024
AGENCY: National Ocean Survey (NOS) IDB PID#: AA1023
SETTING CLASSIFICATION: Concrete bridge guardrail OPUS PID:
LATITUDE: 24° 34.6' N ( 24.57670) LONGITUDE: 81° 43.3' W ( -81.72170)
The bench mark is a disk set flush in a concrete guardrail at the NW end of the
westbound lane of the bridge, 6.80 m (22.3 ft) north of the centerline of the
westbound lane of the highway, 0.88 m (2.9 ft) east of the west end of the guard
rail, and 1 m (3 ft) above highway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
Station ID: 8724503 PUBLICATION DATE: 01/23/2004
Name: STOCK ISLAND
FL
NOAA Chart: 11445 Latitude: 24° 34.6' N ( 24.57670)
USGS Quad: BOCA CHICA KEY Longitude: 81° 43.3' W ( -81.72170)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4503 F
DESIGNATION: 872 4503 F TIDAL
MONUMENTATION: Bench Mark disk VM#: 11025
AGENCY: Florida Department of Transportation
(FLDT) IDB PID#: AA1022
SETTING CLASSIFICATION: Concrete bridge guardrail OPUS PID:
LATITUDE: 24° 34.6' N ( 24.57670) LONGITUDE: 81° 43.3' W ( -81.72170)
The bench mark is a disk set flush in a concrete guardrail, 5.91 m (19.4 ft)
north of the centerline of the eastbound lane, 1.55 m (5.1 ft) east of the west
end of the guard rail, 0.37 m (1.2 ft) west of the bridge abutment, and 1 m (3
ft) above highway level.
BENCH MARK STAMPING: 4503 G 1982
DESIGNATION: 872 4503 G TIDAL
MONUMENTATION: Tidal Station disk VM#: 11026
AGENCY: National Ocean Survey (NOS) IDB PID#: AA1025
SETTING CLASSIFICATION: Concrete bulkhead OPUS PID:
LATITUDE: 24° 34.6' N ( 24.57670) LONGITUDE: 81° 43.3' W ( -81.72170)
The bench mark is a disk set flush in a concrete bulkhead, 2.59 m (8.5 ft) north
of the north edge of the eastbound lane, 2.29 m (7.5 ft) south of the south edge
of the westbound lane, and 4 m (12 ft) below highway level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
Station ID: 8724503 PUBLICATION DATE: 01/23/2004
Name: STOCK ISLAND
FL
NOAA Chart: 11445 Latitude: 24° 34.6' N ( 24.57670)
USGS Quad: BOCA CHICA KEY Longitude: 81° 43.3' W ( -81.72170)
T I D A L D A T U M S
Tidal datums at STOCK ISLAND based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: April 1974 - April 1974
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 = 0.394
MEAN HIGHER HIGH WATER MHHW = 0.344
MEAN HIGH WATER MHW = 0.259
MEAN TIDE LEVEL MTL = 0.153
MEAN SEA LEVEL MSL = 0.148
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 1973 1.484 1.225
NO 2 1973 5.935 5.676
4503 F 6.118 5.859
4503 G 1982 1.452 1.193
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
Station ID: 8724503 PUBLICATION DATE: 01/23/2004
Name: STOCK ISLAND
FL
NOAA Chart: 11445 Latitude: 24° 34.6' N ( 24.57670)
USGS Quad: BOCA CHICA KEY Longitude: 81° 43.3' W ( -81.72170)
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.