Superseded Bench Mark Sheet for 8724441, OHARA KEY, NORTH POINT FL

Present Epoch

Printable version

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
Datums Page                                                        Page  1 of  4

                                                   PUBLICATION DATE:  09/14/1987
Station ID: 8724441                                SUPERCEDED DATE:   04/21/2003
Name:       OHARA KEY, NORTH POINT, WALTZ KEY BASIN           
            FLORIDA
NOAA Chart: 11445                                  Latitude:         24° 37.0' N
USGS Quad:  BOCA CHICA KEY                         Longitude:        81° 38.7' W


To reach the tidal bench marks from the bridge between Big Coppitt Key and
Saddlebunch Keys, proceed north by boat for approximately 1 statute mile (2 km)
to the northernmost tip of OHara 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

MONUMENTATION:           Survey Disk                               VM#:     9613
AGENCY:                                                            PID:         
SETTING CLASSIFICATION:  Concrete/Rod Monument


The bench mark is set in concrete atop a copper-clad steel rod driven to refusal
on the northernmost point of the Key, 33 feet (10 m) south of the outer northern
edge of mangroves, 1 foot (0.3 m) NW of a witness post, and 0.3 foot (0.1 m)
above the ground.



                         BENCH MARK STAMPING:  OHARA 1934

MONUMENTATION:           Survey Disk                               VM#:     9612
AGENCY:                                                            PID#:  AA1081
SETTING CLASSIFICATION:  Concrete Monument


The bench mark is set in a concrete monument on a pile in the northernmost point
of the Key, 164 feet (50 m) east of the west edge of mangroves, 134 feet (41 m)
west of the east edge of mangroves, 121 feet (37 m) south of the north edge of
mangroves, 0.5 foot (0.2 m) NNW 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:  09/14/1987
Station ID: 8724441                                SUPERCEDED DATE:   04/21/2003
Name:       OHARA KEY, NORTH POINT, WALTZ KEY BASIN           
            FLORIDA
NOAA Chart: 11445                                  Latitude:         24° 37.0' N
USGS Quad:  BOCA CHICA KEY                         Longitude:        81° 38.7' W


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


                         BENCH MARK STAMPING:  NO 2 1974

MONUMENTATION:           Survey Disk                               VM#:     9614
AGENCY:                                                            PID:         
SETTING CLASSIFICATION:  Concrete/Rod Monument


The bench mark is set in concrete atop a copper-clad steel rod driven to refusal
on the northernmost point of the Key, 52.6 feet (16.0 m) WSW of Bench Mark NO 1
1974, 51 feet (16 m) east of the outer western edge of mangroves, 0.7 foot (0.2
m) NW of a witness post, and 0.3 foot (0.1 m) above the ground.



                         BENCH MARK STAMPING:  NO 3 1974

MONUMENTATION:           Survey Disk                               VM#:     9615
AGENCY:                                                            PID:         
SETTING CLASSIFICATION:  Concrete/Rod Monument


The bench mark is set in concrete atop a copper-clad steel rod driven to refusal
on the northernmost point of the Key, 51 feet (16 m) SW of Bench Mark NO 2 1974,
38.5 feet (11.7 m) WNW of Bench Mark OHARA 1934, 0.6 foot (0.2 m) NW of a
witness post, and 0.5 foot (0.2 m) above the ground.



                         BENCH MARK STAMPING:  NO 4 1974

MONUMENTATION:           Survey Disk                               VM#:     9616
AGENCY:                                                            PID:         
SETTING CLASSIFICATION:  Concrete/Rod Monument


The bench mark is set in concrete atop a copper-clad steel rod driven to refusal
on the northernmost point of the Key, 50 feet (15 m) SSW of Bench Mark NO 3
1974, 46.3 feet (14.1 m) WSW of Bench Mark OHARA 1934, 1.1 feet (0.3 m) SW of a
witness post, and 0.3 foot (0.1 m) above the ground.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  3 of  4

                                                   PUBLICATION DATE:  09/14/1987
Station ID: 8724441                                SUPERCEDED DATE:   04/21/2003
Name:       OHARA KEY, NORTH POINT, WALTZ KEY BASIN           
            FLORIDA
NOAA Chart: 11445                                  Latitude:         24° 37.0' N
USGS Quad:  BOCA CHICA KEY                         Longitude:        81° 38.7' W


                            T I D A L   D A T U M S 


Tidal datums at OHARA KEY, NORTH POINT, WALTZ KEY BASIN based on:

     LENGTH OF SERIES:      1 MONTH
     TIME PERIOD:           JANUARY 1975
     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 (12/13/1974)         =   2.54
     MEAN HIGHER HIGH WATER                     MHHW   =   1.86
     MEAN HIGH WATER                            MHW    =   1.60
     MEAN TIDE LEVEL                            MTL    =   0.90
     MEAN LOW WATER                             MLW    =   0.20
     MEAN LOWER LOW WATER                       MLLW   =   0.00
     LOWEST  OBSERVED WATER LEVEL (01/23/1975)         =  -0.53

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In FEET above:

     Stamping or Designation                    MLLW        MHW

     NO 1 1974                                   1.86      0.26
     OHARA 1934                                  2.36      0.76
     NO 2 1974                                   1.64      0.04
     NO 3 1974                                   1.75      0.15
     NO 4 1974                                   1.86      0.26


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

                                                   PUBLICATION DATE:  09/14/1987
Station ID: 8724441                                SUPERCEDED DATE:   04/21/2003
Name:       OHARA KEY, NORTH POINT, WALTZ KEY BASIN           
            FLORIDA
NOAA Chart: 11445                                  Latitude:         24° 37.0' N
USGS Quad:  BOCA CHICA KEY                         Longitude:        81° 38.7' 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.

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