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Bench Mark Sheet for 9451785, THE BROTHERS, STEPHENS PASSAGE 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Superseded Epoch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Small blue map location marker Unpublished bench mark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: 9451785                         PUBLICATION DATE:  08/09/2004
Name:       THE BROTHERS, STEPHENS PASSAGE                    
            AK
NOAA Chart: 17362                           Latitude:   57° 17.7' N (  57.29500)
USGS Quad:  SUMDUM (B-6)                    Longitude: 133° 47.8' W (-133.79700)


To reach the tidal bench marks from Petersburg, Alaska, navigate 73.2 km (39.5
nm) (317 degrees true) to the western side of the small island to the east of
East Brothers Island to latitude 57 degrees 17.7' N, longitude 133 degrees 47.8'
W.  The bench marks are located on the SW side of the island on a ledge
extending from the southern side of a small bight.  The ledge lies north-south
along the island. The gage was located towards the southern end of the island.


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


                 PRIMARY BENCH MARK STAMPING:  1785 A 1993
                         DESIGNATION:          945 1785 A

MONUMENTATION:           Tidal Station disk                    VM#:        13119
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Granitic rock outcrop                 OPUS PID:        
LATITUDE:   57° 17.7' N (  57.29500)          LONGITUDE: 133° 47.8' W (-133.79700)


The primary bench mark is a disk set in weathered outcrop of granitic rock, 3 m
(10 ft) from a vertical cliff face that dominates the entire island, NE (030
degrees magnetic) from a rock awash, just south of the southern point of East
Brothers Island, SE (130 degrees magnetic) from a tangent to the northern point
of East Brothers Island, NE (080 degrees magnetic) from the southernmost cove on
the east side of East Brothers Island, and 1 m (3 ft) above the apparent high
water line.

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

                                                                                
Station ID: 9451785                         PUBLICATION DATE:  08/09/2004
Name:       THE BROTHERS, STEPHENS PASSAGE                    
            AK
NOAA Chart: 17362                           Latitude:   57° 17.7' N (  57.29500)
USGS Quad:  SUMDUM (B-6)                    Longitude: 133° 47.8' W (-133.79700)


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


                         BENCH MARK STAMPING:  1785 B 1993
                         DESIGNATION:          945 1785 B

MONUMENTATION:           Tidal Station disk                    VM#:        13120
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Granitic rock outcrop                 OPUS PID:        
LATITUDE:   57° 17.7' N (  57.29500)          LONGITUDE: 133° 47.8' W (-133.79700)


The bench mark is a disk set in weathered, green granitic rock, located directly
across from the southernmost cove on the east side of East Brothers Island, on
the seaward side of a large pile of boulders at the base of the cliff, and 10 m
(33 ft) north of a 30 m (99 ft) vertical cliff face. 



                         BENCH MARK STAMPING:  1785 C 1993
                         DESIGNATION:          945 1785 C

MONUMENTATION:           Tidal Station disk                    VM#:        13121
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Granitic rock outcrop                 OPUS PID:        
LATITUDE:   57° 17.7' N (  57.29500)          LONGITUDE: 133° 47.8' W (-133.79700)


The bench mark is a disk set in weathered outcrop of granitic rock, 15 m (49 ft)
south of a large crevasse in the vertical rock face, NE (030 degrees magnetic)
from the rock at the south end of East Brothers Island, NE (066 degrees
magnetic) from the southernmost cove of the island, the tangent to the northern
end of East Brothers is NW (320 degrees magnetic), and 1 m (3 ft) above the
apparent high water line.

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

                                                                                
Station ID: 9451785                         PUBLICATION DATE:  08/09/2004
Name:       THE BROTHERS, STEPHENS PASSAGE                    
            AK
NOAA Chart: 17362                           Latitude:   57° 17.7' N (  57.29500)
USGS Quad:  SUMDUM (B-6)                    Longitude: 133° 47.8' W (-133.79700)


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


                         BENCH MARK STAMPING:  1785 D 1993
                         DESIGNATION:          945 1785 D

MONUMENTATION:           Tidal Station disk                    VM#:        13122
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Rock ledge                            OPUS PID:        
LATITUDE:   57° 17.7' N (  57.29500)          LONGITUDE: 133° 47.8' W (-133.79700)


The bench mark is a disk set on a 3 m x 5 m (10 ft x 16 ft) ledge 6 m (20 ft)
below the high point of the feature, 80 m (262 ft) south of bench mark 1785 E
1993, NE (066 degrees magnetic) from the southernmost cove on the east side of
East Brothers Island, and NW (294 degrees magnetic) on a tangent to the north
point of East Brothers Island.



                         BENCH MARK STAMPING:  1785 E 1993
                         DESIGNATION:          945 1785 E

MONUMENTATION:           Tidal Station disk                    VM#:        13123
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Granitic rock outcrop                 OPUS PID:        
LATITUDE:   57° 17.7' N (  57.29500)          LONGITUDE: 133° 47.8' W (-133.79700)


The bench mark is a disk set in weathered outcrop of granitic rock, 2 m (7 ft)
below the highest point of the outcrop, 0.5 m (1.7 ft) from the edge of a sharp
5 m (16 ft) drop to the next ledge level, NE (028 degrees magnetic) from the
rock at the south end of East Brothers Island, NE (060 degrees magnetic) from
the southernmost cove, the tangent to the northern end of East Brothers is SE
(150 degrees magnetic), and 2 m (7 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: 9451785                         PUBLICATION DATE:  08/09/2004
Name:       THE BROTHERS, STEPHENS PASSAGE                    
            AK
NOAA Chart: 17362                           Latitude:   57° 17.7' N (  57.29500)
USGS Quad:  SUMDUM (B-6)                    Longitude: 133° 47.8' W (-133.79700)


                            T I D A L   D A T U M S 


Tidal datums at THE BROTHERS, STEPHENS PASSAGE based on:

     LENGTH OF SERIES:      1 MONTH
     TIME PERIOD:           April 1995 - May 1995
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  9450460 KETCHIKAN, TONGASS NARROWS


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

     MEAN HIGHER HIGH WATER                     MHHW   =  4.522
     MEAN HIGH WATER                            MHW    =  4.238
     MEAN SEA LEVEL                             MSL    =  2.374
     MEAN TIDE LEVEL                            MTL    =  2.357
     MEAN LOW WATER                             MLW    =  0.475
     MEAN LOWER LOW WATER                       MLLW   =  0.000

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     1785 A 1993                                 5.021    0.783
     1785 B 1993                                 5.377    1.139
     1785 C 1993                                 5.057    0.819
     1785 D 1993                                 4.265    0.027
     1785 E 1993                                 5.468    1.230


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

                                                                                
Station ID: 9451785                         PUBLICATION DATE:  08/09/2004
Name:       THE BROTHERS, STEPHENS PASSAGE                    
            AK
NOAA Chart: 17362                           Latitude:   57° 17.7' N (  57.29500)
USGS Quad:  SUMDUM (B-6)                    Longitude: 133° 47.8' W (-133.79700)


                             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 9451785 THE BROTHERS, STEPHENS PASSAGE, AK

Revised: 10/15/2013
NOAA / National Ocean Service
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