Published Bench Mark Sheet for 8723933 GRASSY KEY, ATLANTIC SIDE FLORIDA
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 05/15/1986
Station ID: 8723933 SUPERCEDED DATE: 04/21/2003
Name: GRASSY KEY, ATLANTIC SIDE
FLORIDA
NOAA Chart: 11449 Latitude: 24° 45.3' N
USGS Quad: GRASSY KEY Longitude: 80° 57.5' W
To reach the tidal bench marks from the post office in Marathon, Florida,
proceed 7.9 miles (12.7 km) NE on U.S. Highway 1 to the Rainbow Bend Resort. The
bench marks are in the area around the resort. The tide gage and staff were
located on the resorts pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 4 1975
MONUMENTATION: Survey Disk VM#: 6284
AGENCY: PID#: AA0861
SETTING CLASSIFICATION: Concrete Pad
The bench mark is set in the south corner of a concrete pad, 74.5 feet (22.7 m)
SE of the centerline of U.S. Highway 1, 42.6 feet (12.9 m) south of the north
corner of a concrete wall at the north property corner, 33 feet (10 m) NE of
Bench Mark NO 3 1975, 20.5 feet (6.2 m) NE of the centerline of the NE entrance
drive to the resort, and 0.5 foot (0.2 m) above ground level.
BENCH MARK STAMPING: NO 1 1975
MONUMENTATION: Survey Disk VM#: 6281
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Seawall
The bench mark is set flush in a concrete seawall at the Rainbow Bend Resort,
50.0 feet (15.2 m) east of the SE corner of a multi-unit apartment building.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 05/15/1986
Station ID: 8723933 SUPERCEDED DATE: 04/21/2003
Name: GRASSY KEY, ATLANTIC SIDE
FLORIDA
NOAA Chart: 11449 Latitude: 24° 45.3' N
USGS Quad: GRASSY KEY Longitude: 80° 57.5' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 2 1975
MONUMENTATION: Survey Disk VM#: 6282
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is set flush in a concrete foundation at the NE corner of a
multi-unit apartment building south of U.S. Highway 1, 63.5 feet (19.4 m) NW of
Bench Mark NO 1 1975, and NW of a wooden pier.
BENCH MARK STAMPING: NO 3 1975
MONUMENTATION: Survey Disk VM#: 6283
AGENCY: PID#: AA0862
SETTING CLASSIFICATION: Concrete Walkway
The bench mark is set in a concrete walkway near the NW entrance to the
apartment building near the north corner of the property, 134 feet (41 m) north
of Bench Mark NO 2 1975, 5 feet (2 m) west of the NW corner of the building.
BENCH MARK STAMPING: NO 5 1975
MONUMENTATION: Survey Disk VM#: 6285
AGENCY: PID#: AA0863
SETTING CLASSIFICATION: Concrete Walkway
The bench mark is set in the walk near the NE entrance to the apartment building
at the west corner of the property, 113.5 feet (34.6 m) west of Bench Mark NO 4
1975, and 11.5 feet (3.5 m) NW of the north corner of the building.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
PUBLICATION DATE: 05/15/1986
Station ID: 8723933 SUPERCEDED DATE: 04/21/2003
Name: GRASSY KEY, ATLANTIC SIDE
FLORIDA
NOAA Chart: 11449 Latitude: 24° 45.3' N
USGS Quad: GRASSY KEY Longitude: 80° 57.5' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 3933 F 1982
MONUMENTATION: Survey Disk VM#: 6286
AGENCY: PID#: AA0865
SETTING CLASSIFICATION: Concrete Step
The bench mark is set in the steps leading from the beach to the pool, 34.1 feet
(10.4 m) SW of the east corner of the pools patio, 12.1 feet (3.7 m) SE of the
south corner of the pool, and 10.7 feet (3.3 m) NE of the south corner of the
pools patio, and 2 feet (1 m) above ground.
BENCH MARK STAMPING: 3933 G 1982
MONUMENTATION: Survey Disk VM#: 6287
AGENCY: PID#: AA0864
SETTING CLASSIFICATION: Concrete Walkway
The bench mark is 43.0 feet (13.1 m) NW of a stairway, 8.0 feet (2.4 m) NE of
the center of a path between the two-story apartment building, and 4.7 feet (1.4
m) west of the west corner of the northeasternmost two-story apartment building.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
PUBLICATION DATE: 05/15/1986
Station ID: 8723933 SUPERCEDED DATE: 04/21/2003
Name: GRASSY KEY, ATLANTIC SIDE
FLORIDA
NOAA Chart: 11449 Latitude: 24° 45.3' N
USGS Quad: GRASSY KEY Longitude: 80° 57.5' W
T I D A L D A T U M S
Tidal datums at GRASSY KEY, ATLANTIC SIDE based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: JUNE 1975
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8723747 TAVERNIER, HAWK CHANNEL
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (06/12/1975) = 2.82
MEAN HIGHER HIGH WATER (MHHW) = 2.06
MEAN HIGH WATER (MHW) = 1.89
MEAN TIDE LEVEL (MTL) = 1.03
MEAN LOW WATER (MLW) = 0.17
MEAN LOWER LOW WATER (MLLW) = 0.00
LOWEST OBSERVED WATER LEVEL (06/22/1975) = -0.46
National Geodetic Vertical Datum (NGVD 29)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
NO 4 1975 6.18 4.29
NO 1 1975 4.94 3.05
NO 2 1975 5.33 3.44
NO 3 1975 6.14 4.25
NO 5 1975 6.09 4.20
3933 F 1982 6.58 4.69
3933 G 1982 6.30 4.41
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 05/15/1986
Station ID: 8723933 SUPERCEDED DATE: 04/21/2003
Name: GRASSY KEY, ATLANTIC SIDE
FLORIDA
NOAA Chart: 11449 Latitude: 24° 45.3' N
USGS Quad: GRASSY KEY Longitude: 80° 57.5' 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 (NAVD 88).
NGVD 29 is a fixed datum adopted as a national standard geodetic reference for
heights but is now considered superseded. NGVD 29 is sometimes referred to as
Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological
Survey Topographic Quads. NGVD 29 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 NGVD 29 are available from the National
Geodetic Survey (NGS) data base via the World Wide Web at
National Geodetic Survey.
NAVD 88 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. NAVD 88 replaces NGVD 29 as the national
standard geodetic reference for heights. Bench mark elevations relative to
NAVD 88 are available from NGS through the World Wide Web at
National Geodetic Survey.
NGVD 29 and NAVD 88 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 NAVD 88 elevation is shown on the Elevations of Tidal Datums Table Referred
to MLLW only when two or more of the bench marks listed have NAVD 88 elevations.
The NAVD 88 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, NAVD 88 bench mark elevations computed indirectly from the tidal
datums elevation table may differ slightly from NAVD 88 elevations listed for
each bench mark in the NGS database.
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