U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 07/15/1986
Station ID: 8723971 SUPERCEDED DATE: 04/21/2003
Name: BOOT KEY HARBOR
FLORIDA
NOAA Chart: 11449 Latitude: 24° 42.2' N
USGS Quad: MARATHON Longitude: 81° 6.3' W
To reach the tidal bench marks from the east end of the Seven Mile bridge,
proceed east on U.S. Highway 1 for 1.5 miles (2.4 km) to County Road C931,
proceed south on County Road C931 for 0.25 mile (0.40 km) to the bridge over
Boot Key Harbor. The bench marks are located along the bridge. The tide gage
and staff were located on the SE end of the bridge.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1 1975
MONUMENTATION: Survey Disk VM#: 6295
AGENCY: PID#: AA0890
SETTING CLASSIFICATION: Concrete Bridge Sidewalk
The bench mark is set flush in the concrete bridge sidewalk at the NE corner of
the bridge, 16.8 feet (5.1 m) east of the centerline of County Road C931, 11
feet (3 m) south of the north end of the bridge, and 0.5 foot (0.2 m) above road
level.
BENCH MARK STAMPING: NO 2 1975
MONUMENTATION: Survey Disk VM#: 6296
AGENCY: PID#: AA0889
SETTING CLASSIFICATION: Concrete Pad
The bench mark is set flush in a concrete pad for a bridge caution light, 85
feet (26 m) NW of Bench Mark NO 1 1975, 68 feet (21 m) north of the NW corner of
the bridge, and 20 feet (6 m) west of the centerline of County Road C931.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 07/15/1986
Station ID: 8723971 SUPERCEDED DATE: 04/21/2003
Name: BOOT KEY HARBOR
FLORIDA
NOAA Chart: 11449 Latitude: 24° 42.2' N
USGS Quad: MARATHON Longitude: 81° 6.3' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 3971 C
MONUMENTATION: Survey Disk VM#: 6297
AGENCY: PID#: AA0891
SETTING CLASSIFICATION: Concrete Bridge Guardrail
The bench mark is set flush in a concrete bridge guardrail at the NW corner of
the bridge, 75 feet (23 m) south of Bench Mark NO 2 1975, 35 feet (11 m) west of
Bench Mark NO 1 1975, 18.5 feet (5.6 m) west of the centerline of County Road
C931, 8 feet (2 m) south of the north end of the guardrail, and 3 feet (1 m)
above road level.
BENCH MARK STAMPING: 3971 D 1982
MONUMENTATION: Survey Disk VM#: 6298
AGENCY: PID#: AA0892
SETTING CLASSIFICATION: Concrete Bridge Foundation
The bench mark is set flush in a concrete bridge foundation, 188.5 feet (57.5 m)
south of the NE corner of the bridge, 37.1 feet (11.3 m) east of the NE corner
of the bridge tenders building, 18.2 feet (5.5 m) east of the centerline of
County Road C931, and at road level.
BENCH MARK STAMPING: 3971 E 1982
MONUMENTATION: Survey Disk VM#: 6299
AGENCY: PID#: AA0893
SETTING CLASSIFICATION: Concrete Bridge Guardrail
The bench mark is set flush in the top of the concrete guardrail at the SE
corner of the bridge, 17.5 feet (5.3 m) east of the centerline of County Road
C931, 7.9 feet (2.4 m) north of the south end of the guardrail, 0.5 foot (0.2 m)
south of the bridge abutment, and 3 feet (1 m) above road level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 07/15/1986
Station ID: 8723971 SUPERCEDED DATE: 04/21/2003
Name: BOOT KEY HARBOR
FLORIDA
NOAA Chart: 11449 Latitude: 24° 42.2' N
USGS Quad: MARATHON Longitude: 81° 6.3' W
T I D A L D A T U M S
Tidal datums at BOOT KEY HARBOR based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: APRIL-MAY 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 (05/14/1975) = 2.66
MEAN HIGHER HIGH WATER MHHW = 1.98
MEAN HIGH WATER MHW = 1.75
MEAN TIDE LEVEL MTL = 0.96
MEAN LOW WATER MLW = 0.18
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (03/27/1975) = -0.80
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
NO 1 1975 27.80 26.05
NO 2 1975 24.57 22.82
3971 C 30.62 28.87
3971 D 1982 33.49 31.74
3971 E 1982 13.29 11.54
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 07/15/1986
Station ID: 8723971 SUPERCEDED DATE: 04/21/2003
Name: BOOT KEY HARBOR
FLORIDA
NOAA Chart: 11449 Latitude: 24° 42.2' N
USGS Quad: MARATHON Longitude: 81° 6.3' 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.