U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 8724153 PUBLICATION DATE: 12/12/2003
Name: JOHNSON KEYS SOUTH
FL
NOAA Chart: 11448 Latitude: 24° 44.6' N ( 24.74330)
USGS Quad: BIG PINE KEY Longitude: 81° 18.0' W ( -81.30000)
To reach the tidal bench marks by boat proceed 5.6 km (3.5 statute mi) NNW from
the west end of the bridge between Bahia Honda Key and West Summerland Keys to
channel marker R 28 of Big Spanish Channel, then travel 6.0 km (3.7 statute mi)
to the SE end of the central and largest of the Johnson Keys group. The bench
marks are located around the southern tip of the key. The tide gage and staff
were located on the small temporary offshore structure.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1 1974
DESIGNATION: 872 4153 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 6375
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 24° 44.6' N ( 24.74330) LONGITUDE: 81° 18.0' W ( -81.30000)
The primary bench mark is a disk located 29 m (96 ft) from the outer mangrove
edge, 22.62 m (74.2 ft) SSE of bench mark NO 2 1974, 2.96 m (9.7 ft) SW of a
witness sign nailed to a tree, and 0.30 m (1.0 ft) south of a witness post. The
bench mark is set atop a copper-clad steel rod driven an unspecified depth to
refusal, and encased in concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 8724153 PUBLICATION DATE: 12/12/2003
Name: JOHNSON KEYS SOUTH
FL
NOAA Chart: 11448 Latitude: 24° 44.6' N ( 24.74330)
USGS Quad: BIG PINE KEY Longitude: 81° 18.0' W ( -81.30000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 2 1974
DESIGNATION: 872 4153 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 6376
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 24° 44.6' N ( 24.74330) LONGITUDE: 81° 18.0' W ( -81.30000)
The bench mark is a disk located in a large grassy clearing, 22.62 m (74.2 ft)
NNW of bench mark NO 1 1974, 19.48 m (63.9 ft) west of bench mark NO 5 1974, and
0.34 m (1.1 ft) SW of a witness post. The bench mark is set atop a copper-clad
steel rod driven an unspecified depth to refusal, and encased in concrete.
BENCH MARK STAMPING: NO 3 1974
DESIGNATION: 872 4153 TIDAL 3
MONUMENTATION: Tidal Station disk VM#: 6377
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 24° 44.6' N ( 24.74330) LONGITUDE: 81° 18.0' W ( -81.30000)
The bench mark is a disk located in a clearing, 38.92 m (127.7 ft) north of
bench mark NO 1 1974, 23.16 m (76.0 ft) NW of bench mark NO 5 1974, 20.06 m
(65.8 ft) NNE of bench mark NO 2 1974, 0.24 m (0.8 ft) SSW of the witness post.
The bench mark is set atop a copper-clad steel rod driven an unspecified depth
to refusal, and encased in a concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 8724153 PUBLICATION DATE: 12/12/2003
Name: JOHNSON KEYS SOUTH
FL
NOAA Chart: 11448 Latitude: 24° 44.6' N ( 24.74330)
USGS Quad: BIG PINE KEY Longitude: 81° 18.0' W ( -81.30000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 4 1974
DESIGNATION: 872 4153 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 6378
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 24° 44.6' N ( 24.74330) LONGITUDE: 81° 18.0' W ( -81.30000)
The bench mark is a disk located in a clearing, 26.52 m (87.0 ft) ENE of bench
mark NO 2 1974, 18.53 m (60.8 ft) ESE of bench mark NO 3 1974, 12.80 m (42.0 ft)
north of bench mark NO 5 1974, 6 m (19 ft) north of a 0.30 m (1 ft) diameter
dead tree with a witness sign attached, and 0.39 m (1.3 ft) south of a witness
post. The bench mark is set atop a copper-clad steel rod driven an unspecified
depth to refusal, and encased in concrete.
BENCH MARK STAMPING: NO 5 1974
DESIGNATION: 872 4153 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 6379
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 24° 44.6' N ( 24.74330) LONGITUDE: 81° 18.0' W ( -81.30000)
The bench mark is a disk located on the east side of a large clearing, 23.16 m
(76.0 ft) SE of bench mark NO 3 1974, 19.48 m (63.9 ft) east of bench mark NO 2
1974, 12.80 m (42.0 ft) SSW of bench mark NO 4 1974, 7 m (23 ft) east of the
dead tree with a witness sign attached, 0.30 m (1.0 ft) SW of a witness post.
The bench mark is set atop a copper-clad steel rod driven an unspecified depth
to refusal, and encased in concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 8724153 PUBLICATION DATE: 12/12/2003
Name: JOHNSON KEYS SOUTH
FL
NOAA Chart: 11448 Latitude: 24° 44.6' N ( 24.74330)
USGS Quad: BIG PINE KEY Longitude: 81° 18.0' W ( -81.30000)
T I D A L D A T U M S
Tidal datums at JOHNSON KEYS SOUTH based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: August 1974 - August 1974
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8724211 BIG PINE KEY VIADUCT
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 0.398
MEAN HIGH WATER MHW = 0.330
MEAN SEA LEVEL MSL = 0.205
MEAN TIDE LEVEL MTL = 0.200
MEAN LOW WATER MLW = 0.070
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 1974 0.735 0.405
NO 2 1974 0.494 0.164
NO 3 1974 0.425 0.095
NO 4 1974 0.514 0.184
NO 5 1974 0.477 0.147
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 8724153 PUBLICATION DATE: 12/12/2003
Name: JOHNSON KEYS SOUTH
FL
NOAA Chart: 11448 Latitude: 24° 44.6' N ( 24.74330)
USGS Quad: BIG PINE KEY Longitude: 81° 18.0' W ( -81.30000)
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.