Superseded Bench Mark Sheet for 9454662, Snug Harbor AK

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:  09/11/2000
Station ID: 9454662                                SUPERCEDED DATE:   04/21/2003
Name:       SNUG HARBOR, KNIGHT ISLAND                        
            ALASKA
NOAA Chart: 16700                                  Latitude:         60° 15.0' N
USGS Quad:  Seward B-2                             Longitude:       147° 43.0' W


To reach the tidal bench marks, from Cordova head north out of Orca Inlet to
Orca Bay, continue west through Orca Bay to Prince William Sound, north of Green
Island head SW to Snug Harbor.  The tide station is located 1.3 km (0.7 nm) SW
of Discovery Point.  The bench marks were located in the vicinity along the
shore.


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


                 PRIMARY BENCH MARK STAMPING:  4662 B 1998
                         DESIGNATION:          945 4662 B

MONUMENTATION:           Tidal Station disk                        VM#:    15194
AGENCY:                  National Ocean Service (NOS)              PID:         
SETTING CLASSIFICATION:  Rock outcrop


The primary bench mark is a disk located on a low wide rock area at the base of
a steep 7 m (23 ft) high rock cliff,  47 m (155 ft) NW (360 degrees magnetic) of
bench mark 4662 C 1998, and 38 m (125 ft) SW (190 degrees magnetic) of bench
mark 4662 A 1998.



                         BENCH MARK STAMPING:  4662 A 1998
                         DESIGNATION:          945 4662 A

MONUMENTATION:           Tidal Station disk                        VM#:    15193
AGENCY:                  National Ocean Service (NOS)              PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set on top of a tall rock, 38 m (125 ft) NE (010
degrees magnetic) of bench mark 4662 B 1998, and approximatly 2 m (7 ft) above
the apparent high water line.

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

                                                   PUBLICATION DATE:  09/11/2000
Station ID: 9454662                                SUPERCEDED DATE:   04/21/2003
Name:       SNUG HARBOR, KNIGHT ISLAND                        
            ALASKA
NOAA Chart: 16700                                  Latitude:         60° 15.0' N
USGS Quad:  Seward B-2                             Longitude:       147° 43.0' W


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


                         BENCH MARK STAMPING:  4662 C 1998
                         DESIGNATION:          945 4662 C

MONUMENTATION:           Tidal Station disk                        VM#:    15195
AGENCY:                  National Ocean Service (NOS)              PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set on a flat outcrop area close to the treeline, 47 m
(155 ft) south (180 degrees magnetic) of bench mark 4662 B 1998, and 29 m (95
ft) NE (020 degrees magnetic) of bench mark 4662 D 1998.



                         BENCH MARK STAMPING:  4662 D 1998
                         DESIGNATION:          945 4662 D

MONUMENTATION:           Tidal Station disk                        VM#:    15196
AGENCY:                  National Ocean Service (NOS)              PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set on top of a rock outcrop, 36 m (118 ft) NE (050
degrees magnetic) of bench mark 4662 E 1998, 29 m (95 ft) SW (200 degrees
magnetic) of bench mark 4662 C 1998, and approximately 3 m (10 ft) high relative
to the gravel beach to its south.



                         BENCH MARK STAMPING:  4662 E 1998
                         DESIGNATION:          945 4662 E

MONUMENTATION:           Tidal Station disk                        VM#:    15197
AGENCY:                  National Ocean Service (NOS)              PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set on a flat surface on top of a 1 m x 1 m x 2 m (3 ft
x 4 ft x 7 ft) rock, just south of a prominent rocky outcrop next to a gravel
beach, and 36 m (118 ft) SW (330 degrees magnetic) of bench mark 4662 D 1998.

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

                                                   PUBLICATION DATE:  09/11/2000
Station ID: 9454662                                SUPERCEDED DATE:   04/21/2003
Name:       SNUG HARBOR, KNIGHT ISLAND                        
            ALASKA
NOAA Chart: 16700                                  Latitude:         60° 15.0' N
USGS Quad:  Seward B-2                             Longitude:       147° 43.0' W


                            T I D A L   D A T U M S 


Tidal datums at SNUG HARBOR, KNIGHT ISLAND based on:

     LENGTH OF SERIES:      1 MONTH
     TIME PERIOD:           SEPTEMBER 1999
     TIDAL EPOCH:           1960-1978
     CONTROL TIDE STATION:  9454050 CORDOVA, ORCA INLET, PRINCE WILLIAM SD


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

     MEAN HIGHER HIGH WATER                     MHHW   =  3.487
     MEAN HIGH WATER                            MHW    =  3.218
     MEAN SEA LEVEL                             MSL    =  1.866
     MEAN TIDE LEVEL                            MTL    =  1.828
     MEAN LOW WATER                             MLW    =  0.439
     MEAN LOWER LOW WATER                       MLLW   =  0.000



Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     4662 B 1998                                 4.096    0.878
     4662 A 1998                                 5.201    1.983
     4662 C 1998                                 5.130    1.912
     4662 D 1998                                 5.724    2.506
     4662 E 1998                                 4.310    1.092


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

                                                   PUBLICATION DATE:  09/11/2000
Station ID: 9454662                                SUPERCEDED DATE:   04/21/2003
Name:       SNUG HARBOR, KNIGHT ISLAND                        
            ALASKA
NOAA Chart: 16700                                  Latitude:         60° 15.0' N
USGS Quad:  Seward B-2                             Longitude:       147° 43.0' 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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