U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 05/19/1986
Station ID: 8724474 SUPERCEDED DATE: 04/21/2003
Name: DUCK KEY POINT, WALTZ KEY BASIN
FLORIDA
NOAA Chart: 11445 Latitude: 24° 37.4' N
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W
To reach the tidal bench marks from the public boat ramp at the Boca Chica
Channel Bridge, proceed NNE by boat for approximately 4 statute miles (6 km) to
the NE tip of Duck Key Point, a small island just north of Duck Key. The bench
marks are located in a large grassy clearing in the middle and the northern end
of the island. The tide gage and staff were located off the NE tip of the Key.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: SNAKE 1934
MONUMENTATION: Survey Disk VM#: 11073
AGENCY: PID#: AA1086
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a 0.4x0.4-foot (0.1x0.1 m) concrete monument in a
grassy clearing on Duck Key Point, 98 feet (30 m) north of the north edge of
mangrove swamp which covers the southern end of the Point, 49 feet (15 m) east
and west of the edges of mangroves surrounding the clearing, 0.5 foot (0.2 m)
north of a witness post, and 0.7 foot (0.2 m) above the ground.
BENCH MARK STAMPING: RM 1 1935 SNAKE
MONUMENTATION: Survey Disk VM#: 11074
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a 1x1-foot (0.3x0.3 m) concrete monument in a grassy
clearing on Duck Key Point, 68.9 feet (21.0 m) SSE of Bench Mark SNAKE 1934, 0.8
foot (0.2 m) north of a witness post, and 0.7 foot (0.2 m) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 05/19/1986
Station ID: 8724474 SUPERCEDED DATE: 04/21/2003
Name: DUCK KEY POINT, WALTZ KEY BASIN
FLORIDA
NOAA Chart: 11445 Latitude: 24° 37.4' N
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: RM 2 1935 SNAKE
MONUMENTATION: Survey Disk VM#: 11075
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a 1x1-foot (0.3x0.3 m) concrete monument in a grassy
clearing on Duck Key Point, 63.4 feet (19.3 m) NW of Bench Mark SNAKE 1934, and
0.6 foot (0.2 m) west of a witness post.
BENCH MARK STAMPING: NO 4 1974
MONUMENTATION: Survey Disk VM#: 11076
AGENCY: PID:
SETTING CLASSIFICATION: Concrete/Rod Monument
The bench mark is set in concrete atop a cooper-clad steel rod driven to refusal
on the edge of a grassy clearing in Duck Key Point, 111.0 feet (33.8 m) north of
Bench Mark SNAKE 1934, 63 feet (19.2 m) west of the outer mangrove edge on the
east shore, 57.0 feet (17.4 m) NNE of Bench Mark RM 2 1935 SNAKE, and 1.0 foot
(0.3 m) west of a witness post.
BENCH MARK STAMPING: NO 5 1974
MONUMENTATION: Survey Disk VM#: 11077
AGENCY: PID:
SETTING CLASSIFICATION: Concrete/Rod Monument
The bench mark is set in concrete atop a cooper-clad steel rod driven to refusal
on the edge of a grassy clearing in Duck Key Point, 69.0 feet (21.0 m) NW of
Bench Mark NO 4 1974, 63 feet (19 m) west of the outer mangrove edge on the east
shore, and 0.9 foot (0.3 m) east of a witness post.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 05/19/1986
Station ID: 8724474 SUPERCEDED DATE: 04/21/2003
Name: DUCK KEY POINT, WALTZ KEY BASIN
FLORIDA
NOAA Chart: 11445 Latitude: 24° 37.4' N
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' W
T I D A L D A T U M S
Tidal datums at DUCK KEY POINT, WALTZ KEY BASIN based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: SEPTEMBER-OCTOBER 1974
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 (10/15/1974) = 3.39
MEAN HIGHER HIGH WATER MHHW = 2.09
MEAN HIGH WATER MHW = 1.84
MEAN TIDE LEVEL MTL = 1.03
MEAN LOW WATER MLW = 0.23
MEAN LOWER LOW WATER MLLW = 0.00
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
SNAKE 1934 2.78 0.94
RM 1 1935 SNAKE 2.80 0.96
RM 2 1935 SNAKE 3.04 1.20
NO 4 1974 2.50 0.66
NO 5 1974 2.60 0.76
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 05/19/1986
Station ID: 8724474 SUPERCEDED DATE: 04/21/2003
Name: DUCK KEY POINT, WALTZ KEY BASIN
FLORIDA
NOAA Chart: 11445 Latitude: 24° 37.4' N
USGS Quad: BOCA CHICA KEY Longitude: 81° 41.1' 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.