U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 03/24/1988
Station ID: 8724971 SUPERCEDED DATE: 04/21/2003
Name: DAVID KEY, BARFIELD BAY
FLORIDA
NOAA Chart: 11429 Latitude: 25° 55.0' N
USGS Quad: MARCO ISLAND Longitude: 81° 41.2' W
To reach the tidal bench marks from Marco Island, proceed by boat south in
Roberts Bay to Caxambas Bay, then east through Caxambas Bay to marker 18, then
north into Barfield Bay to David Key. The bench marks are located in the
vicinity of the easternmost point of David Key. The tide gage and staff were on
a small offshore platform 50 feet (15 m) east of the easternmost point of David
Key.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 4971 A 1978
MONUMENTATION: Survey Disk VM#: 9743
AGENCY: PID:
SETTING CLASSIFICATION: Galvanized Steel Rod
The bench mark is on the east point of the key, at the outer mangrove edge, and
1.3 feet (0.4 m) north of a witness post. The bench mark is 1.0 foot (0.3 m)
above ground level, crimped to a galvanized steel rod driven 34 feet (10 m) to
refusal, and encased in a 4-inch steel pipe.
BENCH MARK STAMPING: 4971 B 1978
MONUMENTATION: Survey Disk VM#: 9744
AGENCY: PID:
SETTING CLASSIFICATION: Galvanized Steel Rod
The bench mark is 75.3 feet (23.0 m) west of Bench Mark 4971 A 1978, 14 feet (4
m) south of the outer mangrove edge, and 1.2 feet (0.4 m) north of a witness
post. The bench mark is 1.3 feet (0.4 m) above ground level, crimped to a
galvanized steel rod driven 32 feet (10 m) to refusal, and encased in a 4-inch
steel pipe.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 03/24/1988
Station ID: 8724971 SUPERCEDED DATE: 04/21/2003
Name: DAVID KEY, BARFIELD BAY
FLORIDA
NOAA Chart: 11429 Latitude: 25° 55.0' N
USGS Quad: MARCO ISLAND Longitude: 81° 41.2' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4971 C 1978
MONUMENTATION: Survey Disk VM#: 9745
AGENCY: PID:
SETTING CLASSIFICATION: Galvanized Steel Rod
The bench mark is 102.6 feet (31.3 m) WSW of Bench Mark 4971 B 1978, 15 feet (5
m) SSE of the outer mangrove edge, and 1.3 foot (0.4 m) NW of a witness post.
The bench mark is 1.4 feet (0.4 m) above ground level, crimped to a galvanized
steel rod driven 35 feet (11 m) to refusal, and encased in a 4-inch steel pipe.
BENCH MARK STAMPING: 4971 D 1978
MONUMENTATION: Survey Disk VM#: 9746
AGENCY: PID:
SETTING CLASSIFICATION: Galvanized Steel Rod
The bench mark is at the outer mangrove edge, 137.1 feet (41.8 m) east of Bench
Mark 4971 C 1978, 0.8 foot (0.2 m) north of a witness post. The bench mark is
1.2 feet (0.4 m) above ground level, crimped to a galvanized steel rod driven 34
feet (10 m) to refusal, and encased in a 4-inch steel pipe.
BENCH MARK STAMPING: 4971 E 1978
MONUMENTATION: Survey Disk VM#: 9747
AGENCY: PID:
SETTING CLASSIFICATION: Galvanized Steel Rod
The bench mark is 63.7 feet (19.4 m) WSW of Bench Mark 4971 D 1978, 9 feet (3 m)
SSE of the outer mangrove edge, and 1.3 feet (0.4 m) south of a witness post.
The bench mark is 1.5 feet (0.5 m) above ground level, crimped to a galvanized
steel rod driven 33 feet (10 m) to refusal, and encased in a 4-inch steel pipe.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 03/24/1988
Station ID: 8724971 SUPERCEDED DATE: 04/21/2003
Name: DAVID KEY, BARFIELD BAY
FLORIDA
NOAA Chart: 11429 Latitude: 25° 55.0' N
USGS Quad: MARCO ISLAND Longitude: 81° 41.2' W
T I D A L D A T U M S
Tidal datums at DAVID KEY, BARFIELD BAY based on:
LENGTH OF SERIES: 5 MONTHS
TIME PERIOD: APRIL-AUGUST 1978
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8724967 MARCO ISLAND
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (05/04/1978) = 4.27
MEAN HIGHER HIGH WATER MHHW = 3.25
MEAN HIGH WATER MHW = 3.02
MEAN TIDE LEVEL MTL = 1.77
MEAN LOW WATER MLW = 0.53
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (03/29/1978) = -0.72
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
4971 A 1978 2.66 -0.36
4971 B 1978 3.09 0.07
4971 C 1978 4.04 1.02
4971 D 1978 2.63 -0.39
4971 E 1978 3.45 0.43
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 03/24/1988
Station ID: 8724971 SUPERCEDED DATE: 04/21/2003
Name: DAVID KEY, BARFIELD BAY
FLORIDA
NOAA Chart: 11429 Latitude: 25° 55.0' N
USGS Quad: MARCO ISLAND Longitude: 81° 41.2' 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.