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Bench Mark Sheet for 9454561, Perch Point 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Superseded Epoch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Small blue map location marker Unpublished bench mark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: 9454561                         PUBLICATION DATE:  06/23/2003
Name:       PERCH POINT                                       
            AK
NOAA Chart: 16701                           Latitude:   60°  7.5' N (  60.12500)
USGS Quad:  SEWARD (A-3)                    Longitude: 147° 24.0' W (-147.40000)


To reach the tidal marks from Chenega Bay, head 3.0 km (1.6 nm) ESE from Sawmill
Bay to Latouche Passage.  Turn NW and head 7.8 km (4.2 nm) through Latouche
Passage until abeam of Point Grace, then transit WNW for 25.4 km (13.7 nm)
across Montague Strait to Perch Point on Montague Island just south of a black
shale beach.  The bench marks are located along the shore in the vicinity and
the tide gauge was located behind the vegetation line.


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


                 PRIMARY BENCH MARK STAMPING:  4561 A 2000
                         DESIGNATION:          945 4561 A

MONUMENTATION:           Tidal Station disk                    VM#:        16324
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Bedrock                               OPUS PID:        
LATITUDE:   60°  7.5' N (  60.12500)          LONGITUDE: 147° 24.0' W (-147.40000)


The primary bench mark is a disk set in bedrock located SW of the black shale
beach, 132 m (433 ft) NE from bench mark 4561 C 2000, 54.50 m (178.8 ft) ENE (74
degrees magnetic) of bench mark 4561 B 2000, 22.80 m (74.8 ft) south from the
high point of the ledge at the north tip of Perch Point, 3.60 m (11.8 ft)
seaward of the vegetation line, and 3 m (10 ft) inshore of the apparent high
water line.

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

                                                                                
Station ID: 9454561                         PUBLICATION DATE:  06/23/2003
Name:       PERCH POINT                                       
            AK
NOAA Chart: 16701                           Latitude:   60°  7.5' N (  60.12500)
USGS Quad:  SEWARD (A-3)                    Longitude: 147° 24.0' W (-147.40000)


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


                         BENCH MARK STAMPING:  4561 B 2000
                         DESIGNATION:          945 4561 B

MONUMENTATION:           Tidal Station disk                    VM#:        16325
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Bedrock                               OPUS PID:        
LATITUDE:   60°  7.5' N (  60.12500)          LONGITUDE: 147° 24.0' W (-147.40000)


The bench mark is a disk set in bedrock on the high point of a 4 m x 4 m (13 ft
X 13 ft) bedrock outcrop which is 2 m (7 ft) above the surrounding bedrock, SW
of the black shale beach, 77 m (253 ft) NE (55 degrees magnetic) from bench mark
4561 C 2000, 60 m (197 ft) SW from the high point of the ledge at the north tip
of Perch Point, 54.50 m (178.8 ft) WSW (243 degrees magnetic) of bench mark 4561
A 2000, 6 m (20 ft) seaward of the vegetation line, and 1 m (3 ft) inshore of
the apparent high water line.          



                         BENCH MARK STAMPING:  4561 C 2000
                         DESIGNATION:          945 4561 C

MONUMENTATION:           Tidal Station disk                    VM#:        16326
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Bedrock                               OPUS PID:        
LATITUDE:   60°  7.5' N (  60.12500)          LONGITUDE: 147° 24.0' W (-147.40000)


The bench mark is a disk set in bedrock on a 2 m x 2 m (6 ft x 7 ft) raised
outcrop located 132 m (433 ft) SW of bench mark 4561 A 2000, 130 m (427 ft) SW
from the high point of the ledge at the north tip of Perch Point, 77 m (253 ft)
SW (235 degrees magnetic) of bench mark 4561 B 2000, 32 m (105 ft) NE (40
degrees magnetic) of bench mark 4561 D 2000, 14 m (46 ft) inshore of the
apparent high water line, 7.50 m (24.6 ft) east of a large tree stump, and 2 m
(8 ft) seaward of the vegetation line.            

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

                                                                                
Station ID: 9454561                         PUBLICATION DATE:  06/23/2003
Name:       PERCH POINT                                       
            AK
NOAA Chart: 16701                           Latitude:   60°  7.5' N (  60.12500)
USGS Quad:  SEWARD (A-3)                    Longitude: 147° 24.0' W (-147.40000)


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


                         BENCH MARK STAMPING:  4561 D 2000
                         DESIGNATION:          945 4561 D

MONUMENTATION:           Tidal Station disk                    VM#:        16327
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Bedrock                               OPUS PID:        
LATITUDE:   60°  7.5' N (  60.12500)          LONGITUDE: 147° 24.0' W (-147.40000)


The bench mark is a disk set in a 2 m (7 ft) high bedrock outcrop located 32 m
(105 ft) SW (220 degrees magnetic) of bench mark 4561 C 2000, 30 m (98 ft) NE
(40 degrees magnetic) of bench mark 4561 E 2000, 6 m (20 ft) inshore of the
apparent high water line, 5 m (16 ft) seaward of the vegetation line, and 2 m (5
ft) seaward of a large bedrock boulder located just beyond the vegetation line. 
      



                         BENCH MARK STAMPING:  4561 E 2000
                         DESIGNATION:          945 4561 E

MONUMENTATION:           Tidal Station disk                    VM#:        16328
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Bedrock                               OPUS PID:        
LATITUDE:   60°  7.5' N (  60.12500)          LONGITUDE: 147° 24.0' W (-147.40000)


The bench mark is a disk set in bedrock located 50m (164 ft) NE of the most
southern tip of the bedrock ledge at Perch Point, 30 m (98 ft) SW (220 degrees
magnetic) of bench mark 4561 D 2000, 9 m (29 ft)  inshore of the apparent high
water line, 5 m (16 ft) seaward of the vegetation line, and 3 m (10 ft) above
the apparent high water line.                

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

                                                                                
Station ID: 9454561                         PUBLICATION DATE:  06/23/2003
Name:       PERCH POINT                                       
            AK
NOAA Chart: 16701                           Latitude:   60°  7.5' N (  60.12500)
USGS Quad:  SEWARD (A-3)                    Longitude: 147° 24.0' W (-147.40000)


                            T I D A L   D A T U M S 


Tidal datums at PERCH POINT based on:

     LENGTH OF SERIES:      2 MONTHS
     TIME PERIOD:           September 2000 - October 2000
     TIDAL EPOCH:           1983-2001
     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   =  3.571
     MEAN HIGH WATER                            MHW    =  3.270
     MEAN SEA LEVEL                             MSL    =  1.876
     MEAN TIDE LEVEL                            MTL    =  1.852
     MEAN LOW WATER                             MLW    =  0.434
     MEAN LOWER LOW WATER                       MLLW   =  0.000

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     4561 A 2000                                 4.705    1.434
     4561 B 2000                                 4.719    1.448
     4561 C 2000                                 4.745    1.474
     4561 D 2000                                 5.222    1.951
     4561 E 2000                                 5.411    2.140


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

                                                                                
Station ID: 9454561                         PUBLICATION DATE:  06/23/2003
Name:       PERCH POINT                                       
            AK
NOAA Chart: 16701                           Latitude:   60°  7.5' N (  60.12500)
USGS Quad:  SEWARD (A-3)                    Longitude: 147° 24.0' W (-147.40000)


                             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 9454561 Perch Point, AK

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