U.S. DEPARTMENT OF COMMERCE
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National Ocean Service
Datums Page Page 1 of 6
Station ID: 8724427 PUBLICATION DATE: 02/05/2004
Name: MIDDLE NARROWS
FL
NOAA Chart: 11445 Latitude: 24° 40.0' N ( 24.66670)
USGS Quad: SNIPE KEYS Longitude: 81° 37.8' W ( -81.63000)
To reach the tidal bench marks from the U.S. Highway 1 bridge between Coppitt
Key and Saddlebunch Keys, proceed NNE by boat for approximately 7.2 km (4.5
statute mi) to the Middle Narrows, between Snipe Keys. The bench marks are
located on the SE point of the middle or the largest key of the Snipe Keys
group. The tide gage and staff were located south of the SE point of the
largest key in the group.
T I D A L B E N C H M A R K S
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 8724427 PUBLICATION DATE: 02/05/2004
Name: MIDDLE NARROWS
FL
NOAA Chart: 11445 Latitude: 24° 40.0' N ( 24.66670)
USGS Quad: SNIPE KEYS Longitude: 81° 37.8' W ( -81.63000)
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: PEK 1934
DESIGNATION: PEK 1934
MONUMENTATION: Survey disk VM#: 9602
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AA1112
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 40.1' N ( 24.66830) LONGITUDE: 81° 37.8' W ( -81.63000)
The primary bench mark is a disk set in a concrete monument on a pile in the SE
point of the largest key in the Snipe Keys group, 60 m (197 ft) NW of the point,
48 m (157 ft) inshore of the SW shoreline, 20 m (66 ft) inshore of the NE
shoreline (or line of mangroves), 0.15 m (0.5 ft) NNW of a witness post, and
0.24 m (0.8 ft) above the ground.
BENCH MARK STAMPING: NO 1 1974
DESIGNATION: 872 4427 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 9603
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 40.0' N ( 24.66670) LONGITUDE: 81° 37.8' W ( -81.63000)
The bench mark is a disk set in concrete atop a copper-clad steel rod driven to
refusal, located in the SE corner of the largest key in the Snipe Keys group,
SSW of a witness sign nailed to a tree at the water's edge, 12 m (41 ft) south
of the outer edge of the mangroves, 0.40 m (1.3 ft) NNE of a witness post, and
0.15 m (0.5 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 8724427 PUBLICATION DATE: 02/05/2004
Name: MIDDLE NARROWS
FL
NOAA Chart: 11445 Latitude: 24° 40.0' N ( 24.66670)
USGS Quad: SNIPE KEYS Longitude: 81° 37.8' W ( -81.63000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 2 1974
DESIGNATION: 872 4427 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 9604
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 40.0' N ( 24.66670) LONGITUDE: 81° 37.8' W ( -81.63000)
The bench mark is a disk set in concrete atop a copper-clad steel rod driven to
refusal, located in the SE corner of the largest key in the Snipe Keys group, 8
m (26 ft) SSW of bench mark NO 1 1974, 0.27 m (0.9 ft) NNW of a witness post,
and 0.15 m (0.5 ft) above ground level.
BENCH MARK STAMPING: NO 3 1974
DESIGNATION: 872 4427 TIDAL 3
MONUMENTATION: Tidal Station disk VM#: 9605
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 40.0' N ( 24.66670) LONGITUDE: 81° 37.8' W ( -81.63000)
The bench mark is a disk set in concrete atop a copper-clad steel rod driven to
refusal, located in the SE corner of the largest key in the Snipe Keys group, 7
m (23 ft) NW of bench mark PEK 1934, 5 m (17 ft) SSW of bench mark NO 2 1974,
0.27 m (0.9 ft) NNW of a witness post, and 0.15 m (0.5 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 8724427 PUBLICATION DATE: 02/05/2004
Name: MIDDLE NARROWS
FL
NOAA Chart: 11445 Latitude: 24° 40.0' N ( 24.66670)
USGS Quad: SNIPE KEYS Longitude: 81° 37.8' W ( -81.63000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 4 1974
DESIGNATION: 872 4427 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 9606
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 40.0' N ( 24.66670) LONGITUDE: 81° 37.8' W ( -81.63000)
The bench mark is a disk set in concrete atop a copper-clad steel rod driven to
refusal, located in the SE corner of the largest key in the Snipe Keys group, 9
m (31 ft) SSW of bench mark PEK 1934, 0.30 m (1.0 ft) north of a witness post,
and 0.15 m (0.5 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 8724427 PUBLICATION DATE: 02/05/2004
Name: MIDDLE NARROWS
FL
NOAA Chart: 11445 Latitude: 24° 40.0' N ( 24.66670)
USGS Quad: SNIPE KEYS Longitude: 81° 37.8' W ( -81.63000)
T I D A L D A T U M S
Tidal datums at MIDDLE NARROWS based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: January 1975 - January 1975
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8724580 KEY WEST
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 0.551
MEAN HIGH WATER MHW = 0.469
MEAN SEA LEVEL MSL = 0.262
MEAN TIDE LEVEL MTL = 0.258
MEAN LOW WATER MLW = 0.047
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
PEK 1934 0.684 0.215
NO 1 1974 0.455 -0.014
NO 2 1974 0.542 0.073
NO 3 1974 0.516 0.047
NO 4 1974 0.522 0.053
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 8724427 PUBLICATION DATE: 02/05/2004
Name: MIDDLE NARROWS
FL
NOAA Chart: 11445 Latitude: 24° 40.0' N ( 24.66670)
USGS Quad: SNIPE KEYS Longitude: 81° 37.8' W ( -81.63000)
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.