Superseded Bench Mark Sheet for 9452067, HOLKHAM BAY, STEPHENS PASSAGE AK

Present Epoch

Printable version

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
Datums Page                                                        Page  1 of  5

                                                   PUBLICATION DATE:  11/08/2000
Station ID: 9452067                                SUPERCEDED DATE:   04/21/2003
Name:       HOLKHAM BAY, STEPHENS PASSAGE                     
            ALASKA
NOAA Chart: 17300                                  Latitude:         57° 45.6' N
USGS Quad:  SUMDUM (D-5)                           Longitude:       133° 36.2' W


To reach tidal bench marks from SE Alaska, go to Holkam Bay at the entrance of
Tracy and Endicott Arms, then 0.4 km (0.3 mi) east of Harbor Island, and then go
0.6 km (0.4 mi) north of Rond Inlet.  The bench marks and tide gage were located
on the easterly point of the small unnamed island.


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


                 PRIMARY BENCH MARK STAMPING:  TIDAL 1 1973
                         DESIGNATION:          945 2067 TIDAL 1

MONUMENTATION:           Tidal Station disk                        VM#:    13682
AGENCY:                  National Ocean Survey (NOS)               PID:         
SETTING CLASSIFICATION:  Rock outcrop


The primary bench mark is a disk set in rock outcrop, 0.76 m (2.5 ft) north of
bench mark Tidal 2 1973, about 1 m (2 ft) west of the apparent high water line,
and 1 m (2 ft) above the apparent high water line.



                         BENCH MARK STAMPING:  TIDAL 2 1973
                         DESIGNATION:          945 2067 TIDAL 2

MONUMENTATION:           Tidal Station disk                        VM#:    13683
AGENCY:                  National Ocean Survey (NOS)               PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set in rock outcrop, 12 m (41 ft) north of bench mark
Tidal 3 1973, about 3 m (10 ft) west of the apparent high water line, and 1 m (2
ft) above the apparent high water line.

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

                                                   PUBLICATION DATE:  11/08/2000
Station ID: 9452067                                SUPERCEDED DATE:   04/21/2003
Name:       HOLKHAM BAY, STEPHENS PASSAGE                     
            ALASKA
NOAA Chart: 17300                                  Latitude:         57° 45.6' N
USGS Quad:  SUMDUM (D-5)                           Longitude:       133° 36.2' W


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


                         BENCH MARK STAMPING:  TIDAL 3 1973
                         DESIGNATION:          945 2067 TIDAL 3

MONUMENTATION:           Tidal Station disk                        VM#:    13684
AGENCY:                  National Ocean Survey (NOS)               PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set in rock outcrop, 12 m (40 ft) NE of bench mark
Tidal 4 1973, 1 m (3 ft) west of the apparent high water line, and 1 m (4 ft)
above the apparent high water line.



                         BENCH MARK STAMPING:  TIDAL 4 1973
                         DESIGNATION:          945 2067 TIDAL 4

MONUMENTATION:           Tidal Station disk                        VM#:    13685
AGENCY:                  National Ocean Survey (NOS)               PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set in rock outcrop, 9 m (28 ft) east of bench mark
Tidal 5 1973, 1 m (4 ft) north of the apparent high water line, and 1 m (3 ft)
above the apparent high water line.



                         BENCH MARK STAMPING:  TIDAL 5 1973
                         DESIGNATION:          945 2067 TIDAL 5

MONUMENTATION:           Tidal Station disk                        VM#:    13686
AGENCY:                  National Ocean Survey (NOS)               PID:         
SETTING CLASSIFICATION:  Rock outcrop


The bench mark is a disk set in rock outcrop, 1 m (2 ft) north of the apparent
high water line, and 0.46 m (1.5 ft) above the apparent high water line.

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

                                                   PUBLICATION DATE:  11/08/2000
Station ID: 9452067                                SUPERCEDED DATE:   04/21/2003
Name:       HOLKHAM BAY, STEPHENS PASSAGE                     
            ALASKA
NOAA Chart: 17300                                  Latitude:         57° 45.6' N
USGS Quad:  SUMDUM (D-5)                           Longitude:       133° 36.2' W


                            T I D A L   D A T U M S 


Tidal datums at HOLKHAM BAY, STEPHENS PASSAGE based on:

     LENGTH OF SERIES:      81 hws and 81 lws
     TIME PERIOD:           May 14,1997 - June 25,1997
     TIDAL EPOCH:           1960-1978
     CONTROL TIDE STATION:  9452210 JUNEAU, GASTINEAU CHANNEL, STEPHENS PASS


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

     MEAN HIGHER HIGH WATER                     MHHW   =  4.749
     MEAN HIGH WATER                            MHW    =  4.474
     MEAN SEA LEVEL                             MSL    =  2.513
     MEAN TIDE LEVEL                            MTL    =  2.470
     MEAN LOW WATER                             MLW    =  0.467
     MEAN LOWER LOW WATER                       MLLW   =  0.000



Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     TIDAL 1 1973                                5.386    0.912
     TIDAL 2 1973                                6.181    1.707
     TIDAL 3 1973                                5.422    0.949
     TIDAL 4 1973                                5.531    1.057
     TIDAL 5 1973                                5.378    0.904


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

                                                   PUBLICATION DATE:  11/08/2000
Station ID: 9452067                                SUPERCEDED DATE:   04/21/2003
Name:       HOLKHAM BAY, STEPHENS PASSAGE                     
            ALASKA
NOAA Chart: 17300                                  Latitude:         57° 45.6' N
USGS Quad:  SUMDUM (D-5)                           Longitude:       133° 36.2' W


Foot Notes:

Portions of SE Alaska in the area of Lynn Canal and Stephens Passage have
anomalous relative sea level trends compared to most other geographic regions in
the United States. This is due to a general uplift of the land in this area,
which has been occurring at a rapid rate. Because of the magnitude of the sea
level trends in these areas, NOAA has adopted a procedure for computing accepted
tidal datums for the National Water Level Observation Network (NWLON) using the
last several years of sea level data rather than the 19-year tidal epoch. The
tide ranges are still based on the 1960 - 1978 National Tidal Datum Epoch (NTDE)
and are applied to the five year (1994 - 1998) Mean Tide Level (MTL) to compute
other tidal datums. The adoption of this procedure was necessary to ensure that
these tidal datums accurately represent the existing stand of sea level.

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

                                                   PUBLICATION DATE:  11/08/2000
Station ID: 9452067                                SUPERCEDED DATE:   04/21/2003
Name:       HOLKHAM BAY, STEPHENS PASSAGE                     
            ALASKA
NOAA Chart: 17300                                  Latitude:         57° 45.6' N
USGS Quad:  SUMDUM (D-5)                           Longitude:       133° 36.2' 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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