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National Ocean Service
Datums Page Page 1 of 6
Station ID: 8724306 PUBLICATION DATE: 05/28/2004
Name: GOPHER KEY
FL
NOAA Chart: 11445 Latitude: 24° 38.5' N ( 24.64170)
USGS Quad: SUMMERLAND KEY Longitude: 81° 29.1' W ( -81.48500)
To reach the tidal bench marks from the Bow Channel Landing on Sugarloaf Key,
proceed by boat SE for 3.0 km (2.0 nm) to the south shore of Gopher Key, 0.8 km
(0.5 mi) SW of the south end of Cudjoe Bay. The bench marks are located on the
eastern half of Gopher Key. The tide gage and staff were located offshore on
the south side of the Key.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: GOP 1935
DESIGNATION: GOP 1935
MONUMENTATION: Triangulation Station disk VM#: 6924
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AA1561
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 38.5' N ( 24.64170) LONGITUDE: 81° 29.0' W ( -81.48330)
The primary bench mark is a disk set in a square concrete monument located in
the center of the narrow neck which forms the east section of the Key, 65 m (213
ft) west of the east end of the Key, 2.04 m (6.7 ft) SW of a witness sign nailed
to a tree, 0.18 m (0.6 ft) south of a witness post, and 0.06 m (0.2 ft) above
ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 8724306 PUBLICATION DATE: 05/28/2004
Name: GOPHER KEY
FL
NOAA Chart: 11445 Latitude: 24° 38.5' N ( 24.64170)
USGS Quad: SUMMERLAND KEY Longitude: 81° 29.1' W ( -81.48500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: GOP NO 1 1935
DESIGNATION: GOP RM 1
MONUMENTATION: Reference Mark disk VM#: 6925
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 38.5' N ( 24.64170) LONGITUDE: 81° 29.1' W ( -81.48500)
The bench mark is a disk set in a square concrete monument, 18.07 m (59.3 ft)
west of bench mark GOP NO 2 1935, 10 m (33 ft) NW of bench mark GOP 1935, 5.03 m
(16.5 ft) south of the edge of the mangroves, 0.30 m (1.0 ft) east of a witness
post, and 0.09 m (0.3 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 8724306 PUBLICATION DATE: 05/28/2004
Name: GOPHER KEY
FL
NOAA Chart: 11445 Latitude: 24° 38.5' N ( 24.64170)
USGS Quad: SUMMERLAND KEY Longitude: 81° 29.1' W ( -81.48500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: GOP NO 2 1935
DESIGNATION: GOP RM 2
MONUMENTATION: Reference Mark disk VM#: 6926
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 24° 38.5' N ( 24.64170) LONGITUDE: 81° 29.1' W ( -81.48500)
The bench mark is a disk set in a square concrete monument, 11.31 m (37.1 ft) NE
of bench mark GOP 1935, 5.03 m (16.5 ft) south of the edge of the mangroves,
0.91 m (3.0 ft) SSW of a witness sign nailed to a tree, 0.21 m (0.7 ft) SW of a
witness post, and 0.12 m (0.4 ft) above ground level.
BENCH MARK STAMPING: NO 4 1974
DESIGNATION: 872 4306 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 6927
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID:
LATITUDE: 24° 38.5' N ( 24.64170) LONGITUDE: 81° 29.1' W ( -81.48500)
The bench mark is a disk located in a cut in the mangroves, 55 m (180 ft) west
from the east tip of the Key, 12.19 m (40.0 ft) SSE of bench mark GOP 1935, 10 m
(33 ft) north of the outer edge of the mangroves, and 0.15 m (0.5 ft) SW of a
witness post. The bench mark is set 0.46 m (1.5 ft) above ground level, and
crimped to a 4-inch diameter steel pipe atop a copper-clad rod driven to
refusal.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 8724306 PUBLICATION DATE: 05/28/2004
Name: GOPHER KEY
FL
NOAA Chart: 11445 Latitude: 24° 38.5' N ( 24.64170)
USGS Quad: SUMMERLAND KEY Longitude: 81° 29.1' W ( -81.48500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4306 E 1984
DESIGNATION: 872 4306 E 1984
MONUMENTATION: Tidal Station disk VM#: 6928
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 24° 38.5' N ( 24.64170) LONGITUDE: 81° 29.1' W ( -81.48500)
The bench mark is a disk near the south shoreline of Gopher Key, 7.32 m (24.0
ft) south of bench mark NO 4 1974, and 3 m (9 ft) north of the outer edge of the
mangroves. The bench mark is crimped to the top of a stainless steel rod driven
1.2 m (4 ft) to refusal, and encased in a 6-inch diameter PVC pipe projecting
0.5 m (1.5 ft) .
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 8724306 PUBLICATION DATE: 05/28/2004
Name: GOPHER KEY
FL
NOAA Chart: 11445 Latitude: 24° 38.5' N ( 24.64170)
USGS Quad: SUMMERLAND KEY Longitude: 81° 29.1' W ( -81.48500)
T I D A L D A T U M S
Tidal datums at GOPHER KEY based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: October 1974 - October 1974
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 = 0.496
MEAN HIGH WATER MHW = 0.413
MEAN TIDE LEVEL MTL = 0.231
MEAN SEA LEVEL MSL = 0.227
MEAN LOW WATER MLW = 0.049
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
GOP 1935 0.442 0.029
GOP NO 1 1935 0.466 0.053
GOP NO 2 1935 0.442 0.029
NO 4 1974 0.685 0.272
4306 E 1984 0.515 0.102
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 8724306 PUBLICATION DATE: 05/28/2004
Name: GOPHER KEY
FL
NOAA Chart: 11445 Latitude: 24° 38.5' N ( 24.64170)
USGS Quad: SUMMERLAND KEY Longitude: 81° 29.1' W ( -81.48500)
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.