Superseded Bench Mark Sheet for 9440569, Skamokawa WA

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:  04/02/1991
Station ID: 9440569                                SUPERCEDED DATE:   04/21/2003
Name:       SKAMOKAWA, SKAMOKAWA CREEK, COLUMBIA RIVER        
            WASHINGTON
NOAA Chart: 18523                                  Latitude:         46° 16.2' N
USGS Quad:  SKAMOKAWA                              Longitude:       123° 27.1' W


To reach the tidal bench marks from the U.S. Post Office on State Highway 4 in
Skamokawa, proceed west on State Highway 4 to Skamokawa Vista Park, veer left
just inside the park and go to the public boat ramp.  The bench marks are along
State Highway 4 and Steamboat Slough Road.  The tide gage and staff are on the
group of four pilings NE of the boat ramp.


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


                 PRIMARY BENCH MARK STAMPING:  5 1940

MONUMENTATION:           Survey Disk                               VM#:     8910
AGENCY:                                                            PID#:  SC0340
SETTING CLASSIFICATION:  Concrete Retaining Wall


The primary bench mark is set flush in a concrete retaining wall along State
Highway 4, 56.5 feet (17.2 m) south of the centerline of the highway, 53.2 feet
(16.2 m) NE of the NE corner of Hobys Store, 50 feet (15 m) west of the
centerline of Steamboat Slough Road, and 17 feet (5 m) south of a utility pole.



                         BENCH MARK STAMPING:  N 317 21 1939

MONUMENTATION:           Survey Disk                               VM#:     8908
AGENCY:                                                            PID#:  SC0338
SETTING CLASSIFICATION:  Concrete Sidewalk


The bench mark is set in the sidewalk at the SE end of the State Highway 4
bridge over Skamokawa Creek, 1.4 feet (0.4 m) west of the east end of the bridge
sidewalk, and 0.5 foot (0.2 m) north of the inside of the south guard- rail.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of  4

                                                   PUBLICATION DATE:  04/02/1991
Station ID: 9440569                                SUPERCEDED DATE:   04/21/2003
Name:       SKAMOKAWA, SKAMOKAWA CREEK, COLUMBIA RIVER        
            WASHINGTON
NOAA Chart: 18523                                  Latitude:         46° 16.2' N
USGS Quad:  SKAMOKAWA                              Longitude:       123° 27.1' W


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


                         BENCH MARK STAMPING:  3 1940

MONUMENTATION:           Survey Disk                               VM#:     8909
AGENCY:                                                            PID#:  SC0339
SETTING CLASSIFICATION:  Concrete Retaining Wall


The bench mark is set flush in a concrete retaining wall south of State Highway
4, 96 feet (29 m) NW of the NW corner of Hobys Store, 62.5 feet (19.0 m) NE of
the NE corner of Skamokawa Post Office, 30.5 feet (9.3 m) south of the
centerline of the highway, and 1 foot (0.3 m) south of a witness post.



                         BENCH MARK STAMPING:  944 0569 B 1981

MONUMENTATION:           Survey Disk                               VM#:     8911
AGENCY:                                                            PID:         
SETTING CLASSIFICATION:  Concrete Bridge Curb


The bench mark is set flush in the concrete curb on the Steamboat Slough Road
bridge over Brooks Slough, 136 feet (41 m) WSW of the NE corner of Hobys Store,
12.5 feet (3.8 m) east of the centerline of Steamboat Slough Road, and 0.2 foot
(0.1 m) west of a concrete pillar on the bridge.

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

                                                   PUBLICATION DATE:  04/02/1991
Station ID: 9440569                                SUPERCEDED DATE:   04/21/2003
Name:       SKAMOKAWA, SKAMOKAWA CREEK, COLUMBIA RIVER        
            WASHINGTON
NOAA Chart: 18523                                  Latitude:         46° 16.2' N
USGS Quad:  SKAMOKAWA                              Longitude:       123° 27.1' W


                            T I D A L   D A T U M S 


Tidal datums at SKAMOKAWA, SKAMOKAWA CREEK, COLUMBIA RIVER based on:

     LENGTH OF SERIES:      12 MONTHS
     TIME PERIOD:           SEPTEMBER 1985-AUGUST 1986
     TIDAL EPOCH:           1960-1978
     CONTROL TIDE STATION:  9439040 ASTORIA


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

     HIGHEST OBSERVED WATER LEVEL (02/24/1986)         =   9.49
     MEAN HIGHER HIGH WATER                     MHHW   =   7.13
     MEAN HIGH WATER                            MHW    =   6.51
     MEAN TIDE LEVEL                            MTL    =   3.63
   * NATIONAL GEODETIC VERTICAL DATUM           NGVD29 =   1.43
     MEAN LOW WATER                             MLW    =   0.75
     MEAN LOWER LOW WATER                       MLLW   =   0.00
     LOWEST  OBSERVED WATER LEVEL (11/13/1985)         =  -1.80

   * NGVD reference based on elevations published in Quad 23 Wash, 1956, and NOS
     leveling of 1990. 
North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In FEET above:

     Stamping or Designation                    MLLW        MHW

     5 1940                                     17.34     10.83
     N 317 21 1939                              23.02     16.51
     3 1940                                     19.58     13.07
     944 0569 B 1981                            21.04     14.53


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

                                                   PUBLICATION DATE:  04/02/1991
Station ID: 9440569                                SUPERCEDED DATE:   04/21/2003
Name:       SKAMOKAWA, SKAMOKAWA CREEK, COLUMBIA RIVER        
            WASHINGTON
NOAA Chart: 18523                                  Latitude:         46° 16.2' N
USGS Quad:  SKAMOKAWA                              Longitude:       123° 27.1' 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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