Superseded Bench Mark Sheet for 9451074, BUSHY ISLAND, SNOW PASSAGE AK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:  08/22/2000
Station ID: 9451074                                SUPERCEDED DATE:   04/21/2003
Name:       BUSHY ISLAND, SNOW PASSAGE                        
            ALASKA
NOAA Chart: 17382                                  Latitude:         56° 16.6' N
USGS Quad:  Petersburg (B-3)                       Longitude:       132° 59.1' W


To reach the tidal bench marks from Wrangell, navigate west out of Wrangell
Harbor to Stikine Starit, continue south to Clarence Strait.  Upon reaching
Nesbitt Reef, head NW through Clarence Strait to Snow Passage, then 1.7 km (0.9
nm) west of the Fl 4s 22 ft 6M light to Bushy island.  The tidal bench marks and
tide station were located on the NW tip of the Bushy Island.


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


                 PRIMARY BENCH MARK STAMPING:   
                         DESIGNATION:          945 1074 BM 2
                         ALIAS:                2  1916

MONUMENTATION:           Tidal Station disk                        VM#:    16165
AGENCY:                  U.S. Coast & Geodetic Survey
                         (USC&GS)                                     PID:         
SETTING CLASSIFICATION:  Bedrock


The primary bench mark is a disk set in a bedrock on the NW lobe of Bushy
Island, in the middle of a small point, NE of the mouth of a creek, 7.40 m (24.3
ft) north of the tree line, 5.40 m (17.7 ft) south of the apparent high water
line, and approximately 1 m (3 ft) above the apparent high water line.



                         BENCH MARK STAMPING:   
                         DESIGNATION:          945 1074 BM 3
                         ALIAS:                3  1916

MONUMENTATION:           Tidal Station disk                        VM#:    16166
AGENCY:                  U.S. Coast & Geodetic Survey
                         (USC&GS)                                     PID:         
SETTING CLASSIFICATION:  Granite boulder


The bench mark is a disk set flush on a grey/white granite boulder of
approximate size 2 m x 2 m (7 ft x 5 ft) which is the only light colored boulder
in the area, positioned west of a creek located on the NW lobe of Bushy Island,
6.50 m (21.3 ft) from the tree line, and 0.21 m (0.7 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:  08/22/2000
Station ID: 9451074                                SUPERCEDED DATE:   04/21/2003
Name:       BUSHY ISLAND, SNOW PASSAGE                        
            ALASKA
NOAA Chart: 17382                                  Latitude:         56° 16.6' N
USGS Quad:  Petersburg (B-3)                       Longitude:       132° 59.1' W


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


                         BENCH MARK STAMPING:  1074 B 2000
                         DESIGNATION:          945 1074 B

MONUMENTATION:           Tidal Station disk                        VM#:    16167
AGENCY:                  National Ocean Service (NOS)              PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set flush in a rock outcrop, located west of a creek on
the NW lobe of Bushy Island, 18 (59 ft) north of the tree line, 0.50 m (1.6 ft)
south of the apparent high water line, and 0.40 m (1.3 ft) above the apparent
high water line.



                         BENCH MARK STAMPING:  1074 C 2000
                         DESIGNATION:          945 1074 C

MONUMENTATION:           Tidal Station disk                        VM#:    16168
AGENCY:                  National Ocean Service (NOS)              PID:         
SETTING CLASSIFICATION:  Bedrock


The bench mark is a disk set in a bedrock, located west of a creek on the NW
lobe of Bushy Island, 6.40 m (21.0 ft) from the tree line, 1.30 m (4.3 ft) from
the apparent high water line, and 0.20 m (0.7 ft) above the apparent high water
line.

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

                                                   PUBLICATION DATE:  08/22/2000
Station ID: 9451074                                SUPERCEDED DATE:   04/21/2003
Name:       BUSHY ISLAND, SNOW PASSAGE                        
            ALASKA
NOAA Chart: 17382                                  Latitude:         56° 16.6' N
USGS Quad:  Petersburg (B-3)                       Longitude:       132° 59.1' W


                            T I D A L   D A T U M S 


Tidal datums at BUSHY ISLAND, SNOW PASSAGE based on:

     LENGTH OF SERIES:      1 MONTHS
     TIME PERIOD:           April 2000 - April 2000
     TIDAL EPOCH:           1960-1978
     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   =  4.480
     MEAN HIGH WATER                            MHW    =  4.219
     MEAN TIDE LEVEL                            MTL    =  2.331
     MEAN SEA LEVEL                             MSL    =  2.302
     MEAN LOW WATER                             MLW    =  0.444
     MEAN LOWER LOW WATER                       MLLW   =  0.000



Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     945 1074 BM 2                               5.710    1.491
     945 1074 BM 3                               4.999    0.780
     1074 B 2000                                 5.037    0.818
     1074 C 2000                                 5.265    1.046


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

                                                   PUBLICATION DATE:  08/22/2000
Station ID: 9451074                                SUPERCEDED DATE:   04/21/2003
Name:       BUSHY ISLAND, SNOW PASSAGE                        
            ALASKA
NOAA Chart: 17382                                  Latitude:         56° 16.6' N
USGS Quad:  Petersburg (B-3)                       Longitude:       132° 59.1' 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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