Superseded Bench Mark Sheet for 8458694, WATCH HILL POINT RI

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:  08/06/1987
Station ID: 8458694                                SUPERCEDED DATE:   04/21/2003
Name:       WATCH HILL POINT, BLOCK ISLAND SOUND              
            RHODE ISLAND
NOAA Chart: 13214                                  Latitude:         41° 18.3' N
USGS Quad:  WATCH HILL                             Longitude:        71° 51.6' W


To reach the tidal bench marks from the city of Watch Hill proceed south 0.5
mile (0.8 km) to the abandoned U.S. Coast Guard Watch Hill Station at Watch Hill
Point.  The bench marks are located in the area around the Coast Guard Station
and Watch Hill Point Lighthouse.  The gage and staff were located on a piling in
a small cove NW of the Coast Guard Station.  NOTE:  These bench mark
descriptions are based on September 10, 1962 recovery information.


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


                 PRIMARY BENCH MARK STAMPING:  BM NO 2 1939

MONUMENTATION:           Survey Disk                               VM#:     2219
AGENCY:                                                            PID#:  LW0809
SETTING CLASSIFICATION:  Concrete Foundation


The bench mark is set in the concrete base of the wooden steps at the NW
entrance door to the main Coast Guard Station Building, 17.4 feet (5.3 m) NNE of
the west corner of the building, and 0.4 foot (0.1 m) NE of the NE edge of the
bottom step.



                         BENCH MARK STAMPING:  BM NO 1 1939

MONUMENTATION:           Survey Disk                               VM#:     2218
AGENCY:                                                            PID#:  LW0810
SETTING CLASSIFICATION:  Concrete Foundation


The bench mark is set in the concrete apron in the south corner of the Coast
Guard station garage at the gate entrance, 2 feet (1 m) SW of the SW edge of the
SW door of the garage, and 0.4 foot (0.1 m) NE of the SW edge of the apron.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of  4

                                                   PUBLICATION DATE:  08/06/1987
Station ID: 8458694                                SUPERCEDED DATE:   04/21/2003
Name:       WATCH HILL POINT, BLOCK ISLAND SOUND              
            RHODE ISLAND
NOAA Chart: 13214                                  Latitude:         41° 18.3' N
USGS Quad:  WATCH HILL                             Longitude:        71° 51.6' W


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


                         BENCH MARK STAMPING:  BM NO 3 1939

MONUMENTATION:           Survey Disk                               VM#:     2220
AGENCY:                                                            PID#:  LW0808
SETTING CLASSIFICATION:  Concrete Seawall


The bench mark is set in the top of a concrete seawall, 35.8 feet (10.9 m) NW of
the north corner of the main building for the Watch Hill Point lighthouse, 14.7
feet (4.5 m) SW of the top of the seawall where the wall goes down to a lower
level.



                         BENCH MARK STAMPING:  BM NO 4 1961

MONUMENTATION:           Survey Disk                               VM#:     2221
AGENCY:                                                            PID:         
SETTING CLASSIFICATION:  Concrete Seawall


The bench mark is set in the western breakwater at the Coast Guard Station,
291.3 feet (88.8 m) north of Bench Mark BM NO 3 1939, 248.4 feet (75.7 m) SW of
Bench Mark BM NO 2 1939, about 35 feet (11 m) east of the approximate high water
mark, and 8.6 feet (2.6 m) south of the north end of the breakwater.

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

                                                   PUBLICATION DATE:  08/06/1987
Station ID: 8458694                                SUPERCEDED DATE:   04/21/2003
Name:       WATCH HILL POINT, BLOCK ISLAND SOUND              
            RHODE ISLAND
NOAA Chart: 13214                                  Latitude:         41° 18.3' N
USGS Quad:  WATCH HILL                             Longitude:        71° 51.6' W


                            T I D A L   D A T U M S 


Tidal datums at WATCH HILL POINT, BLOCK ISLAND SOUND based on:

     LENGTH OF SERIES:      1 MONTH
     TIME PERIOD:           AUGUST 1962
     TIDAL EPOCH:           1960-1978
     CONTROL TIDE STATION:  8461490 NEW LONDON, CT


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

     HIGHEST OBSERVED WATER LEVEL (09/21/1938)         =  11.40
     MEAN HIGHER HIGH WATER                     MHHW   =   3.02
     MEAN HIGH WATER                            MHW    =   2.75
     MEAN TIDE LEVEL                            MTL    =   1.45
   * NATIONAL GEODETIC VERTICAL DATUM           NGVD29 =   1.04
     MEAN LOW WATER                             MLW    =   0.15
     MEAN LOWER LOW WATER                       MLLW   =   0.00
     LOWEST  OBSERVED WATER LEVEL (05/31/1962)         =  -0.78

   * NGVD reference based on elevations published in Quad 410713, 1970, and NOS
     leveling of 1962. 
North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In FEET above:

     Stamping or Designation                    MLLW        MHW

     BM NO 2 1939                               20.75     18.00
     BM NO 1 1939                               10.88      8.13
     BM NO 3 1939                               14.77     12.02
     BM NO 4 1961                               12.85     10.10


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

                                                   PUBLICATION DATE:  08/06/1987
Station ID: 8458694                                SUPERCEDED DATE:   04/21/2003
Name:       WATCH HILL POINT, BLOCK ISLAND SOUND              
            RHODE ISLAND
NOAA Chart: 13214                                  Latitude:         41° 18.3' N
USGS Quad:  WATCH HILL                             Longitude:        71° 51.6' 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.

Return to Top
Products available at 8458694 WATCH HILL POINT, RI