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Bench Mark Sheet for 9454721, PERRY ISLAND (SOUTH BAY) AK

Superseded Epoch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Small blue map location marker Unpublished bench mark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: 9454721                         PUBLICATION DATE:  06/16/2011
Name:       PERRY ISLAND (SOUTH BAY)                          
            AK
NOAA Chart: 16705                           Latitude:   60° 40.3' N (  60.67170)
USGS Quad:  Seward C-3                      Longitude: 147° 55.9' W (-147.93200)


To reach the tidal bench marks follow along the western shore of South Bay which
is located on the south shore of Perry Island.  The site is located in a cove
which is off the NW corner of South Bay.  Once inside the cove there are several
buildings (a house and barns) on the western shore and two islets in
approximately the middle of the cove.  At the head of the cove is a narrow
passage that leads to a small hidden bay.  The site is located on and around the
larger of the two islets.


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


                 PRIMARY BENCH MARK STAMPING:  No. 4 1966
                         DESIGNATION:          945 4721 TIDAL 4

MONUMENTATION:           Survey disk                           VM#:        14664
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:        
SETTING CLASSIFICATION:  In bedrock in prominent rock ledge    OPUS PID:        
LATITUDE:   60° 40.3' N (  60.67170)          LONGITUDE: 147° 55.9' W (-147.93200)


The bench mark is a disk set in bedrock in a prominent rock ledge point on the
eastern shore of the entrance to the narrow passage at the north head of the
South Bay, 9.14 m (30.0 ft) west of an 2.44 m (8.0 ft) rock-faced bluff and
19.51 m (64.0 ft) SW of bench mark No. 5 1966.  To the west is an islet about
18.29 m (60.0 ft) long (north to south) and 9.14 m (30.0 ft) high which forms
the western part of the passage.

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

                                                                                
Station ID: 9454721                         PUBLICATION DATE:  06/16/2011
Name:       PERRY ISLAND (SOUTH BAY)                          
            AK
NOAA Chart: 16705                           Latitude:   60° 40.3' N (  60.67170)
USGS Quad:  Seward C-3                      Longitude: 147° 55.9' W (-147.93200)


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


                         BENCH MARK STAMPING:  No. 5 1966
                         DESIGNATION:          945 4721 TIDAL 5

MONUMENTATION:           Survey disk                           VM#:        14665
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:        
SETTING CLASSIFICATION:  Bedrock                               OPUS PID:        
LATITUDE:   60° 40.3' N (  60.67170)          LONGITUDE: 147° 55.9' W (-147.93200)


The bench mark is a disk set in bedrock at the base of an 2.44 m (8.0 ft)
rock-faced bluff ,19.51 m (64.0 ft) NE of bench mark No. 4 1966, and about 2.44
m (8.0 ft) north of the north face of a bluff ledge that extends to within 9.14
m (30.0 ft) of bench mark No. 4 1966.



                         BENCH MARK STAMPING:  4721 A 1994
                         DESIGNATION:          945 4721 A 1994

MONUMENTATION:           Survey disk                           VM#:        14666
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:                                        OPUS PID:        
LATITUDE:   60° 40.3' N (  60.67170)          LONGITUDE: 147° 55.9' W (-147.93200)


The bench mark is a disk located on the south end of the larger islet, 14.50 m
(47.6 ft) NW (330  magnetic) from bench mark 4721 B 1994, 90.0 m (295.3 ft) NE
(070  magnetic) from bench mark No. 4 1966 and NE (060  magnetic) from bench
mark No. 5 1966, and about 1.40 m (4.6 ft) above the approximate high water
line.

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

                                                                                
Station ID: 9454721                         PUBLICATION DATE:  06/16/2011
Name:       PERRY ISLAND (SOUTH BAY)                          
            AK
NOAA Chart: 16705                           Latitude:   60° 40.3' N (  60.67170)
USGS Quad:  Seward C-3                      Longitude: 147° 55.9' W (-147.93200)


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


                         BENCH MARK STAMPING:  4721 B 1994
                         DESIGNATION:          945 4721 B 1994

MONUMENTATION:           Survey disk                           VM#:        14667
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:                                        OPUS PID:        
LATITUDE:   60° 40.3' N (  60.67170)          LONGITUDE: 147° 55.9' W (-147.93200)


The bench mark is a disk located on the north end of the larger islet, 14.50 m
(47.6 ft) SE (150  magnetic) from bench mark 4721 A 1994, 90.0 m (295.3 ft) NW
(350  magnetic) from bench mark 4721 C 1994, and about 1.60 m (5.25 ft) above
the approximate high water line.



                         BENCH MARK STAMPING:  4721 C 1994
                         DESIGNATION:          945 4721 C 1994

MONUMENTATION:           Survey disk                           VM#:        14668
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Rock ledge                            OPUS PID:        
LATITUDE:   60° 40.3' N (  60.67170)          LONGITUDE: 147° 55.9' W (-147.93200)


The bench mark is a disk which is set on the high point of the ledge
approximately 1.80 m (5.9 ft) above the approximate high water line where there
is a rock ledge which sits at the approximate high water line on the gravel
beach, located on the western shore of the cove, 90.0 m (295.3 ft) SE (170 
magnetic) from bench mark 4721 B 1994.  The smaller islet bears SE (110 
magnetic). 

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

                                                                                
Station ID: 9454721                         PUBLICATION DATE:  06/16/2011
Name:       PERRY ISLAND (SOUTH BAY)                          
            AK
NOAA Chart: 16705                           Latitude:   60° 40.3' N (  60.67170)
USGS Quad:  Seward C-3                      Longitude: 147° 55.9' W (-147.93200)


                            T I D A L   D A T U M S 


Tidal datums at PERRY ISLAND (SOUTH BAY) based on:

     LENGTH OF SERIES:      2 MONTHS
     TIME PERIOD:           September 1995 - October 1995
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  9454240 VALDEZ, PRINCE WILLIAM SOUND


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

     MEAN HIGHER HIGH WATER                     MHHW   =  3.643
     MEAN HIGH WATER                            MHW    =  3.353
     MEAN SEA LEVEL                             MSL    =  1.938
     MEAN TIDE LEVEL                            MTL    =  1.902
     MEAN LOW WATER                             MLW    =  0.450
     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. 4 1966                                  3.875    0.522
     No. 5 1966                                  3.343   -0.010
     4721 A 1994                                 4.691    1.337
     4721 B 1994                                 4.765    1.412
     4721 C 1994                                 4.974    1.621


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

                                                                                
Station ID: 9454721                         PUBLICATION DATE:  06/16/2011
Name:       PERRY ISLAND (SOUTH BAY)                          
            AK
NOAA Chart: 16705                           Latitude:   60° 40.3' N (  60.67170)
USGS Quad:  Seward C-3                      Longitude: 147° 55.9' W (-147.93200)


                             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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