Superseded Bench Mark Sheet for 9418802, EUREKA SLOUGH, HUMBOLDT BAY CA

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:  11/04/1995
Station ID: 9418802                                SUPERCEDED DATE:   04/21/2003
Name:       EUREKA SLOUGH BRIDGE, HUMBOLDT BAY                
            CALIFORNIA
NOAA Chart: 18622                                  Latitude:         40° 48.4' N
USGS Quad:  EUREKA                                 Longitude:       124°  8.5' W


To reach the tidal bench marks from Eureka exit U.S. Highway 101 south at Fourth
Street, proceed westerly on Fourth Street, right at intersection of X and First
Streets, east to fork in road, left at fork and cross over the Northwest Pacific
railroad tracks.  The bench marks are located between First through Fourth
Streets.  The tide gage and staff were located on the south side of Northwest
Pacific railroad bridge over the slough.


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


                 PRIMARY BENCH MARK STAMPING:  8802 B 1978

MONUMENTATION:           Survey Disk                               VM#:     8739
AGENCY:                                                            PID#:  LV0639
SETTING CLASSIFICATION:  Galvanized Steel Rod


The bench mark is on a galvanized steel rod 85.3 feet (26.0 m) SW of SW corner
of Northwest Pacific railroad bridge over the slough, 50.9 feet (15.5 m) SSW of
south rail, 16.4 feet (5.0 m) SSW of Northwest Pacific railroad excess road
centerline, and 9.8 feet (3.0 m) NNW of a utility pole.  The mark is driven to
38 feet 11.6 m) and encased in PVC pipe and concrete.



                         BENCH MARK STAMPING:  8802 A 1978

MONUMENTATION:           Survey Disk                               VM#:     8738
AGENCY:                                                            PID#:  LV0640
SETTING CLASSIFICATION:  Concrete Pier


The bench mark is in top of concrete pier at west end of the Northwest Pacific
railroad left span over the slough, in the SW corner of the pier, and 7 feet
(2.1 m) below the rails.

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

                                                   PUBLICATION DATE:  11/04/1995
Station ID: 9418802                                SUPERCEDED DATE:   04/21/2003
Name:       EUREKA SLOUGH BRIDGE, HUMBOLDT BAY                
            CALIFORNIA
NOAA Chart: 18622                                  Latitude:         40° 48.4' N
USGS Quad:  EUREKA                                 Longitude:       124°  8.5' W


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


                         BENCH MARK STAMPING:  8802 C 1978

MONUMENTATION:           Survey Disk                               VM#:     8740
AGENCY:                                                            PID:         
SETTING CLASSIFICATION:  Galvanized Steel Rod


The bench mark is on a galvanized steel rod 101.7 feet (31.0 m) NW of NW corner
of Pepsi bottling plant (NW corner of Second and Y Streets), 36.1 feet (11.0 m) 
SSW of south rail, 8.2 feet (2.5 m) SSW of centerline of Northwest Pacific
railroad access road, and 3.2 feet (1.0 m) east of a witness post.  The rod is
driven to 41 feet (12.5 m) and encased in PVC pipe and concrete.



                         BENCH MARK STAMPING:  8802 D 1978

MONUMENTATION:           Survey Disk                               VM#:     8741
AGENCY:                                                            PID:         
SETTING CLASSIFICATION:  Galvanized Steel Rod


The bench mark is on a galvanized steel rod 75.5 feet (23.0 m) ESE of center of
intersection of X and First Streets, and 1.6 feet (0.8 m) south of a steel gate
post.  The rod is driven to 46 feet (14.0 m) and encased in PVC pipe and
concrete.



                         BENCH MARK STAMPING:  J 75 1931 RESET 1942

MONUMENTATION:           Survey Disk                               VM#:     8742
AGENCY:                                                            PID#:  LV0287
SETTING CLASSIFICATION:  Concrete Curb


The bench mark is in top of SE end of concrete curb of bridge 4-22 over the
slough , 1.1 miles (1.8 km) east along U.S. Highway 101 from the post office at
Highway Marker 79.78, 14.0 feet (4.3 m) SE of centerline of SE lanes of highway,
5.0 feet (1.5 m) NE of SW end of curb, and 0.5 foot (0.2 m) above the highway.

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

                                                   PUBLICATION DATE:  11/04/1995
Station ID: 9418802                                SUPERCEDED DATE:   04/21/2003
Name:       EUREKA SLOUGH BRIDGE, HUMBOLDT BAY                
            CALIFORNIA
NOAA Chart: 18622                                  Latitude:         40° 48.4' N
USGS Quad:  EUREKA                                 Longitude:       124°  8.5' W


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


                         BENCH MARK STAMPING:  W 108 1967 RESET 1969

MONUMENTATION:           Survey Disk                               VM#:     8743
AGENCY:                                                            PID#:  LV0289
SETTING CLASSIFICATION:  Culvert Headwall


The bench mark is in top of a culvert headwall, 0.7 mile (1.1 km) north of
highway bridge over the slough at milepost 80.57 and 43 feet (13.1 m) east of
the white strip for the northbound lanes.

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

                                                   PUBLICATION DATE:  11/04/1995
Station ID: 9418802                                SUPERCEDED DATE:   04/21/2003
Name:       EUREKA SLOUGH BRIDGE, HUMBOLDT BAY                
            CALIFORNIA
NOAA Chart: 18622                                  Latitude:         40° 48.4' N
USGS Quad:  EUREKA                                 Longitude:       124°  8.5' W


                            T I D A L   D A T U M S 


Tidal datums at EUREKA SLOUGH BRIDGE, HUMBOLDT BAY based on:

     LENGTH OF SERIES:      7 MONTHS
     TIME PERIOD:           APRIL-OCTOBER 1978
     TIDAL EPOCH:           1960-1978
     CONTROL TIDE STATION:  9419750 CRESCENT CITY


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

     MEAN HIGHER HIGH WATER                     MHHW   =   7.48
     MEAN HIGH WATER                            MHW    =   6.76
   * NATIONAL GEODETIC VERTICAL DATUM           NGVD29 =   4.04
     MEAN TIDE LEVEL                            MTL    =   4.01
     MEAN LOW WATER                             MLW    =   1.27
     MEAN LOWER LOW WATER                       MLLW   =   0.00

   * NGVD reference based on adjustment of 1968 and NOS levels of 1978. 
North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In FEET above:

     Stamping or Designation                    MLLW        MHW

     8802 B 1978                                13.42      6.66
     8802 A 1978                                10.17      3.41
     8802 C 1978                                10.72      3.96
     8802 D 1978                                11.38      4.62
     J 75 1931 RESET 1942                       26.07     19.31
     W 108 1967 RESET 1969                       6.75     -0.01


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

                                                   PUBLICATION DATE:  11/04/1995
Station ID: 9418802                                SUPERCEDED DATE:   04/21/2003
Name:       EUREKA SLOUGH BRIDGE, HUMBOLDT BAY                
            CALIFORNIA
NOAA Chart: 18622                                  Latitude:         40° 48.4' N
USGS Quad:  EUREKA                                 Longitude:       124°  8.5' 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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