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Bench Mark Sheet for 8724209, LITTLE SPANISH KEY ISLAND 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Superseded Epoch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Small blue map location marker Unpublished bench mark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: 8724209                         PUBLICATION DATE:  04/29/2004
Name:       LITTLE SPANISH KEY ISLAND                         
            FL
NOAA Chart: 11448                           Latitude:   24° 46.4' N (  24.77330)
USGS Quad:  HORSESHOE KEYS                  Longitude:  81° 22.1' W ( -81.36830)


To reach the tidal bench marks from Bogie Channel Bridge linking Big Pine Key
and No Name Key, proceed by boat NNW for 6.7 km (4.8 nm) to the middle of the NE
shore of Little Spanish Key.  The bench marks are located in a small grassy
clearing SW of the mangrove fringe.  The tide gage and staff were located
offshore NE of the NE shoreline.


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


                 PRIMARY BENCH MARK STAMPING:  NO 1 1974
                         DESIGNATION:          872 4209 TIDAL 1

MONUMENTATION:           Tidal Station disk                    VM#:         6441
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 46.4' N (  24.77330)          LONGITUDE:  81° 22.1' W ( -81.36830)


The primary bench mark is a disk located 0.5 km (0.3 mi) SE of the northern tip
of the key, 16 m (53 ft) WSW of the eastern shore outer mangrove fringe, 13 m
(44 ft) SW of a witness sign nailed to a tree at the waters edge, 4 m (12 ft)
west of the inner mangrove fringe, and 0.21 m (0.7 ft) south 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 rod driven to an unspecified depth to refusal.

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

                                                                                
Station ID: 8724209                         PUBLICATION DATE:  04/29/2004
Name:       LITTLE SPANISH KEY ISLAND                         
            FL
NOAA Chart: 11448                           Latitude:   24° 46.4' N (  24.77330)
USGS Quad:  HORSESHOE KEYS                  Longitude:  81° 22.1' W ( -81.36830)


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


                         BENCH MARK STAMPING:  NO 2 1974
                         DESIGNATION:          872 4209 TIDAL 2

MONUMENTATION:           Tidal Station disk                    VM#:         8877
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 46.4' N (  24.77330)          LONGITUDE:  81° 22.1' W ( -81.36830)


The bench mark is a disk located at the edge of the inner mangrove fringe, 25 m
(83 ft) SW of the outer mangrove fringe, 24.29 m (79.7 ft) west of bench mark NO
1 1974, 1.49 m (4.9 ft) from a witness sign nailed to a tree, and 0.3 m (1 ft)
east of a witness post.  The bench mark is set 12 cm (0.4 ft) above ground
level, crimped to the top of a copper-clad rod driven an unspecified depth to
refusal.



                         BENCH MARK STAMPING:  NO 3 1974
                         DESIGNATION:          872 4209 TIDAL 3

MONUMENTATION:           Tidal Station disk                    VM#:        15988
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 46.4' N (  24.77330)          LONGITUDE:  81° 22.1' W ( -81.36830)


The bench mark is a disk located in a small grassy clearing, 23.65 m (77.6 ft)
SW of bench mark NO 2 1974,  12.37 m (40.6 ft) ESE of bench mark NO 5 1974, and
0.52 m (1.7 ft) north 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 rod driven an
unspecified depth to refusal.

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

                                                                                
Station ID: 8724209                         PUBLICATION DATE:  04/29/2004
Name:       LITTLE SPANISH KEY ISLAND                         
            FL
NOAA Chart: 11448                           Latitude:   24° 46.4' N (  24.77330)
USGS Quad:  HORSESHOE KEYS                  Longitude:  81° 22.1' W ( -81.36830)


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


                         BENCH MARK STAMPING:  NO 4 1974
                         DESIGNATION:          872 4209 TIDAL 4

MONUMENTATION:           Tidal Station disk                    VM#:        15989
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 46.4' N (  24.77330)          LONGITUDE:  81° 22.1' W ( -81.36830)


The bench mark is a disk located in a small clearing, 16 m (52 ft) SW of bench
mark NO 3 1974, 13 m (42 ft) south of bench mark NO 5 1974, and 0.55 m (1.8 ft)
south of a witness post.  The bench mark is set 6 cm (0.2 ft) above ground
level, crimped to the top of a copper-clad rod driven an unspecified depth to
refusal.



                         BENCH MARK STAMPING:  NO 5 1974
                         DESIGNATION:          872 4209 TIDAL 5

MONUMENTATION:           Tidal Station disk                    VM#:        15990
AGENCY:                  National Ocean Survey (NOS)           IDB PID#:        
SETTING CLASSIFICATION:  Copper-clad steel rod                 OPUS PID:        
LATITUDE:   24° 46.4' N (  24.77330)          LONGITUDE:  81° 22.1' W ( -81.36830)


The bench mark is a disk located in a small clearing, 33 m (107 ft) WSW of bench
mark NO 2 1974, 12.80 m (42.0 ft) north of bench mark NO 4 1974, 13 m (41 ft)
west of NO 3 1974, and 0.3 m (1 ft) south of the old witness post.  The bench
mark is set 6 cm (0.2 ft) above ground level, crimped to the top of a
copper-clad rod driven an unspecified depth to refusal.

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

                                                                                
Station ID: 8724209                         PUBLICATION DATE:  04/29/2004
Name:       LITTLE SPANISH KEY ISLAND                         
            FL
NOAA Chart: 11448                           Latitude:   24° 46.4' N (  24.77330)
USGS Quad:  HORSESHOE KEYS                  Longitude:  81° 22.1' W ( -81.36830)


                            T I D A L   D A T U M S 


Tidal datums at LITTLE SPANISH KEY ISLAND based on:

     LENGTH OF SERIES:      1 MONTH
     TIME PERIOD:           August 1974 - August 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   =  0.878
     MEAN HIGH WATER                            MHW    =  0.805
     MEAN TIDE LEVEL                            MTL    =  0.462
     MEAN SEA LEVEL                             MSL    =  0.448
     MEAN LOW WATER                             MLW    =  0.119
     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                                   1.060    0.255
     NO 2 1974                                   0.918    0.113
     NO 3 1974                                   0.940    0.135
     NO 4 1974                                   0.885    0.080
     NO 5 1974                                   0.894    0.089


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

                                                                                
Station ID: 8724209                         PUBLICATION DATE:  04/29/2004
Name:       LITTLE SPANISH KEY ISLAND                         
            FL
NOAA Chart: 11448                           Latitude:   24° 46.4' N (  24.77330)
USGS Quad:  HORSESHOE KEYS                  Longitude:  81° 22.1' W ( -81.36830)


                             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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Revised: 08/08/2018
NOAA / National Ocean Service
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