Bench Mark Sheet for 8724441, OHARA KEY, NORTH POINT FL

Superseded Epoch

Large map location marker Station Location
Small red map location marker Published bench mark
Small blue map location marker Unpublished bench mark

Bench mark positions only appear on the map if their coordinates in the CO-OPS database are at the precision of degrees/minutes/seconds/and tenths of seconds. If the coordinates are less precise, the mark will not appear.

Printable version

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
Datums Page                                                        Page  1 of  5

                                                                                
Station ID: 8724441                         PUBLICATION DATE:  02/05/2004
Name:       O'HARA KEY, NORTH POINT                           
            FL
NOAA Chart: 11445                           Latitude:   24° 37.0' N (  24.61670)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 38.7' W ( -81.64500)


To reach the tidal bench marks from the bridge between Big Coppitt Key and
Saddlebunch Keys via boat, proceed north for 2 km (1 statute mi) to the
northernmost tip of O'Hara Key.  The bench marks are located at the northern end
of the Key.  The tide gage and staff were located just north of the north tip of
the Key.


                         T I D A L   B E N C H   M A R K S


                 PRIMARY BENCH MARK STAMPING:  NO 1 1974
                         DESIGNATION:          872 4441 TIDAL 1

MONUMENTATION:           Tidal Station disk                    VM#:         9613
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 37.0' N (  24.61670)          LONGITUDE:  81° 38.7' W ( -81.64500)


The primary bench mark is a disk located on the northernmost point of the Key,
10 m (33 ft) south of the outer northern edge of mangroves, and 0.30 m (1.0 ft)
NW of a witness post. The bench mark is set 9 cm (0.3 ft) above ground level,
crimped to the top of a copper-clad steel rod driven to refusal.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of  5

                                                                                
Station ID: 8724441                         PUBLICATION DATE:  02/05/2004
Name:       O'HARA KEY, NORTH POINT                           
            FL
NOAA Chart: 11445                           Latitude:   24° 37.0' N (  24.61670)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 38.7' W ( -81.64500)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  OHARA 1934
                         DESIGNATION:          OHARA 1934

MONUMENTATION:           Survey disk                           VM#:         9612
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  AA1081
SETTING CLASSIFICATION:  Concrete monument                     OPUS PID:        
LATITUDE:   24° 37.0' N (  24.61670)          LONGITUDE:  81° 38.7' W ( -81.64500)


The bench mark is a disk set in a concrete monument on a pile in the
northernmost point of the Key, 50 m (164 ft) east of the west edge of mangroves,
41 m (134 ft) west of the east edge of mangroves, 37 m (121 ft) south of the
north edge of mangroves, 0.15 m (0.5 ft) NNW of a witness post, and 0.21 m (0.7
ft) above the ground.  NOTE:  A 15 m pole signal with target was erected over
the mark.  The entire area is covered by a heavy growth of mangrove, and
extensive clearing will be necessary for its recovery.



                         BENCH MARK STAMPING:  NO 2 1974
                         DESIGNATION:          872 4441 TIDAL 2

MONUMENTATION:           Tidal Station disk                    VM#:         9614
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 37.0' N (  24.61670)          LONGITUDE:  81° 38.7' W ( -81.64500)


The bench mark is a disk located on the northernmost point of the Key, 16.03 m
(52.6 ft) WSW of bench mark NO 1 1974, 16 m (51 ft) east of the outer western
edge of mangroves, and 0.21 m (0.7 ft) NW of a witness post. The bench mark is
set 9 cm (0.3 ft) above ground level, crimped to the top of a copper-clad steel
rod driven to refusal.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  3 of  5

                                                                                
Station ID: 8724441                         PUBLICATION DATE:  02/05/2004
Name:       O'HARA KEY, NORTH POINT                           
            FL
NOAA Chart: 11445                           Latitude:   24° 37.0' N (  24.61670)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 38.7' W ( -81.64500)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  NO 3 1974
                         DESIGNATION:          872 4441 TIDAL 3

MONUMENTATION:           Tidal Station disk                    VM#:         9615
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 37.0' N (  24.61670)          LONGITUDE:  81° 38.7' W ( -81.64500)


The bench mark is a disk located on the northernmost point of the Key, 16 m (51
ft) SW of bench mark NO 2 1974, 11.73 m (38.5 ft) WNW of bench mark OHARA 1934,
and 0.18 m (0.6 ft) NW of a witness post. The bench mark is set 15 cm (0.5 ft)
above ground level, crimped to the top of a copper-clad steel rod driven to
refusal.



                         BENCH MARK STAMPING:  NO 4 1974
                         DESIGNATION:          872 4441 TIDAL 4

MONUMENTATION:           Tidal Station disk                    VM#:         9616
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 37.0' N (  24.61670)          LONGITUDE:  81° 38.7' W ( -81.64500)


The bench mark is a disk located on the northernmost point of the Key, 15 m (50
ft) SSW of bench mark NO 3 1974, 14.11 m (46.3 ft) WSW of bench mark OHARA 1934,
and 0.34 m (1.1 ft) SW of a witness post. The bench mark is set 9 cm (0.3 ft)
above ground level, crimped to a copper-clad steel rod driven to refusal.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  4 of  5

                                                                                
Station ID: 8724441                         PUBLICATION DATE:  02/05/2004
Name:       O'HARA KEY, NORTH POINT                           
            FL
NOAA Chart: 11445                           Latitude:   24° 37.0' N (  24.61670)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 38.7' W ( -81.64500)


                            T I D A L   D A T U M S 


Tidal datums at O'HARA KEY, NORTH POINT 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   =  0.554
     MEAN HIGH WATER                            MHW    =  0.475
     MEAN TIDE LEVEL                            MTL    =  0.267
     MEAN SEA LEVEL                             MSL    =  0.246
     MEAN LOW WATER                             MLW    =  0.059
     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                                   0.494    0.019
     OHARA 1934                                  0.645    0.170
     NO 2 1974                                   0.427   -0.048
     NO 3 1974                                   0.462   -0.013
     NO 4 1974                                   0.493    0.018


                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  5 of  5

                                                                                
Station ID: 8724441                         PUBLICATION DATE:  02/05/2004
Name:       O'HARA KEY, NORTH POINT                           
            FL
NOAA Chart: 11445                           Latitude:   24° 37.0' N (  24.61670)
USGS Quad:  BOCA CHICA KEY                  Longitude:  81° 38.7' W ( -81.64500)


                             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.

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