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Bench Mark Sheet for 8723861, ALLIGATOR REEF LIGHTHOUSE 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Superseded Epoch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Small blue map location marker Unpublished bench mark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: 8723861                         PUBLICATION DATE:  12/27/2005
Name:       ALLIGATOR REEF LIGHTHOUSE                         
            FL
NOAA Chart: 11449                           Latitude:   24° 51.0' N (  24.85000)
USGS Quad:  UPPER MATECUMBE KEY             Longitude:  80° 37.1' W ( -80.61830)


To reach the tidal bench marks from the east end of the bridge between Lower
Matecumbe Key and Upper Matecumbe Key, proceed by boat SE for 6.4 km (4.0
statute mi) to Alligator Reef Lighthouse.  The lighthouse is an octagonal steel
skeleton tower on the pile foundation.  The bench marks are located on the
lighthouse structure.  The tide gage and staff were located on the lighthouse
structure.  Each of the vertical members (legs) has a painted number on it.  The
numbers increase in a counter-clockwise direction.  Leg No. 8 is the first leg
west of the landing platform.


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


                 PRIMARY BENCH MARK STAMPING:  NO 1
                         DESIGNATION:          872 3861 TIDAL 1

MONUMENTATION:           See descriptive text                  VM#:        10923
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Lighthouse structure                  OPUS PID:        
LATITUDE:   24° 51.0' N (  24.85000)          LONGITUDE:  80° 37.1' W ( -80.61830)


The primary bench mark is the high point of the most southerly nut on the NE
stud of three at the leg No. 8 joint, 8.38 m (27.5 ft) NNW of bench mark NO 3,
and 0.46 (1.5 ft) above the landing platform.

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

                                                                                
Station ID: 8723861                         PUBLICATION DATE:  12/27/2005
Name:       ALLIGATOR REEF LIGHTHOUSE                         
            FL
NOAA Chart: 11449                           Latitude:   24° 51.0' N (  24.85000)
USGS Quad:  UPPER MATECUMBE KEY             Longitude:  80° 37.1' W ( -80.61830)


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


                         BENCH MARK STAMPING:  NO 2
                         DESIGNATION:          872 3861 TIDAL 2

MONUMENTATION:           See descriptive text                  VM#:        10924
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Lighthouse structure                  OPUS PID:        
LATITUDE:   24° 51.0' N (  24.85000)          LONGITUDE:  80° 37.1' W ( -80.61830)


The bench mark is the high point of the most northerly nut on the most westerly
stud of three at the leg No. 7 joint, 5.97 m (19.6 ft) east of bench mark NO 1,
and 0.46 (1.5 ft) above the landing platform.



                         BENCH MARK STAMPING:  NO 3
                         DESIGNATION:          872 3861 TIDAL 3

MONUMENTATION:           See descriptive text                  VM#:        10925
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Lighthouse structure                  OPUS PID:        
LATITUDE:   24° 51.0' N (  24.85000)          LONGITUDE:  80° 37.1' W ( -80.61830)


The bench mark is the high point of the northernmost bolt at the center leg
joint joining leg No. 7 with the center leg, 8.38 m (27.5 ft) SSW of bench mark
NO 2, 0.64 m (2.1 ft) above the horizontal spoke, and 0.46 (1.5 ft) above the
landing platform.

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

                                                                                
Station ID: 8723861                         PUBLICATION DATE:  12/27/2005
Name:       ALLIGATOR REEF LIGHTHOUSE                         
            FL
NOAA Chart: 11449                           Latitude:   24° 51.0' N (  24.85000)
USGS Quad:  UPPER MATECUMBE KEY             Longitude:  80° 37.1' W ( -80.61830)


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


                         BENCH MARK STAMPING:  NO 4
                         DESIGNATION:          872 3861 TIDAL 4

MONUMENTATION:           See descriptive text                  VM#:        10926
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Lighthouse structure                  OPUS PID:        
LATITUDE:   24° 51.0' N (  24.85000)          LONGITUDE:  80° 37.1' W ( -80.61830)


The bench mark is the high point of the eastern nut of the most northerly stud
of three at the leg No. 5 joint, 8.69 m (28.5 ft) ESE of bench mark NO 3, and
0.46 (1.5 ft) above the landing platform.



                         BENCH MARK STAMPING:  NO 5
                         DESIGNATION:          872 3861 TIDAL 5

MONUMENTATION:           See descriptive text                  VM#:        10927
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Lighthouse structure                  OPUS PID:        
LATITUDE:   24° 51.0' N (  24.85000)          LONGITUDE:  80° 37.1' W ( -80.61830)


The bench mark is the high point of the southern nut on the southeasterly stud
of three at the leg No. 3 joint, 8.78 m (28.8 ft) SSW of bench mark NO 3, and
0.64 m (2.1 ft) above the horizontal spoke connecting the center leg with leg
No. 3.

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

                                                                                
Station ID: 8723861                         PUBLICATION DATE:  12/27/2005
Name:       ALLIGATOR REEF LIGHTHOUSE                         
            FL
NOAA Chart: 11449                           Latitude:   24° 51.0' N (  24.85000)
USGS Quad:  UPPER MATECUMBE KEY             Longitude:  80° 37.1' W ( -80.61830)


                            T I D A L   D A T U M S 


Tidal datums at ALLIGATOR REEF LIGHTHOUSE based on:

     LENGTH OF SERIES:      7 MONTHS
     TIME PERIOD:           May 1971 - November 1971
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  8723747 TAVERNIER HAWK CHANNEL


Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:

     MEAN HIGHER HIGH WATER                     MHHW   =  0.679
     MEAN HIGH WATER                            MHW    =  0.636
     MEAN SEA LEVEL                             MSL    =  0.352
     MEAN TIDE LEVEL                            MTL    =  0.348
     MEAN LOW WATER                             MLW    =  0.060
     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                                        3.876    3.240
     NO 2                                        3.868    3.232
     NO 3                                        3.922    3.286
     NO 4                                        3.882    3.246
     NO 5                                        3.897    3.261


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

                                                                                
Station ID: 8723861                         PUBLICATION DATE:  12/27/2005
Name:       ALLIGATOR REEF LIGHTHOUSE                         
            FL
NOAA Chart: 11449                           Latitude:   24° 51.0' N (  24.85000)
USGS Quad:  UPPER MATECUMBE KEY             Longitude:  80° 37.1' W ( -80.61830)


                             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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Products available at 8723861 ALLIGATOR REEF LIGHTHOUSE, FL

Revised: 10/15/2013
NOAA / National Ocean Service
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