U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 09/01/1987
Station ID: 9439069 SUPERCEDED DATE: 04/21/2003
Name: KNAPPA, KNAPPA SLOUGH
OREGON
NOAA Chart: 18523 Latitude: 46° 11.2' N
USGS Quad: SVENSEN Longitude: 123° 35.4' W
To reach the tidal bench marks from Astoria, proceed east on U.S. Highway 30 for
10.5 miles (16.9 km) to Knappa Road, turn north onto Knappa Road for 0.2 mile
(0.3 km) around bend in road, then turn right onto Blind Slough Road and go
north for 1.2 miles (1.9 km) to a wooden bridge over railroad tracks; cross the
bridge and continue north for 0.2 mile (0.3 km) to the end of the road at Knappa
Dock. The bench marks are located along Knappa Dock Road, Waterhouse Road, and
Knappa Plat Road. The tide gage and staff were located about 500 feet (152 m)
SW of Knappa Dock Road on the pilings of a floating pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: J 31 1920
MONUMENTATION: Survey Disk VM#: 8885
AGENCY: PID#: SC0447
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in the top of a concrete monument in the vicinity of the
railroad crossing at Waterhouse Road, 97.5 feet (29.7 m) west of Bench Mark NO 3
1950, 45 feet (14 m) east of the centerline of Waterhouse Road, and 15 feet (5
m) south of the centerline of the railroad tracks.
BENCH MARK STAMPING: NO 3 1950
MONUMENTATION: Survey Disk VM#: 8886
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Footing
The bench mark is set vertically in the south face of the NW concrete footing
for the wooden bridge over railroad tracks, about 10 feet (3 m) north of the
centerline of the tracks, and 1 foot (0.3 m) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 09/01/1987
Station ID: 9439069 SUPERCEDED DATE: 04/21/2003
Name: KNAPPA, KNAPPA SLOUGH
OREGON
NOAA Chart: 18523 Latitude: 46° 11.2' N
USGS Quad: SVENSEN Longitude: 123° 35.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 9069 A 1981
MONUMENTATION: Survey Disk VM#: 8887
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Vault
The bench mark is set vertically in the SW corner of an abandoned concrete vault
that is approximately 7 feet (2 m) wide and 16 feet (5 m) high, about 190 feet
(58 m) north of the centerline of the railroad tracks, 150 feet (46 m) NW of
the NW corner of the wooden bridge over railroad tracks, 60 feet (18 m) NW of
the center of the intersection of Knappa Dock Road and Waterhouse Road, and 6
feet (2 m) above the ground.
BENCH MARK STAMPING: 9069 B 1981
MONUMENTATION: Survey Disk VM#: 8888
AGENCY: PID:
SETTING CLASSIFICATION: Unknown
The bench mark is set on the west side of Knappa Plat Road, about 300 feet (91
m) south of the SW corner of the wooden bridge over railroad tracks on Knappa
Dock Road, 55.5 feet (16.9 m) SE of a red brick foundation of a residence, 6
feet (2 m) east of the centerline of a driveway to a private residence, 2.5 feet
(0.8 m) west of utility pole #PPL 0807 170905, and 0.8 foot (0.2 m) below the
ground encased in a 4-inch PVC pipe.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
PUBLICATION DATE: 09/01/1987
Station ID: 9439069 SUPERCEDED DATE: 04/21/2003
Name: KNAPPA, KNAPPA SLOUGH
OREGON
NOAA Chart: 18523 Latitude: 46° 11.2' N
USGS Quad: SVENSEN Longitude: 123° 35.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 9069 C 1981
MONUMENTATION: Survey Disk VM#: 8889
AGENCY: PID:
SETTING CLASSIFICATION: Unknown
The bench mark is set on the west side of Knappa Plat Road, about 485 feet (148
m) south of the SW corner of the wooden bridge over railroad tracks on Knappa
Dock Road, 70 feet (21 m) NE of the NE corner of a private residence at #525
Knappa Plot Road, 21.5 feet (6.6 m) west of the centerline of Knappa Plot Road,
10.7 feet (3.3 m) NE of the NE corner of a concrete water meter box, 10 feet (3
m) east of utility pole #PPL 0807 170901, and 0.8 foot (0.2 m) below the ground
encased in a 4-inch PVC pipe.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
PUBLICATION DATE: 09/01/1987
Station ID: 9439069 SUPERCEDED DATE: 04/21/2003
Name: KNAPPA, KNAPPA SLOUGH
OREGON
NOAA Chart: 18523 Latitude: 46° 11.2' N
USGS Quad: SVENSEN Longitude: 123° 35.4' W
T I D A L D A T U M S
Tidal datums at KNAPPA, KNAPPA SLOUGH based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: OCTOBER-NOVEMBER 1981
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 (11/14/1981) = 11.97
MEAN HIGHER HIGH WATER MHHW = 8.16
MEAN HIGH WATER MHW = 7.49
MEAN TIDE LEVEL MTL = 4.23
MEAN LOW WATER MLW = 0.96
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (10/18/1981) = -1.26
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
J 31 1920 15.12 7.63
NO 3 1950 13.36 5.87
9069 A 1981 22.17 14.68
9069 B 1981 75.73 68.24
9069 C 1981 81.94 74.45
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 09/01/1987
Station ID: 9439069 SUPERCEDED DATE: 04/21/2003
Name: KNAPPA, KNAPPA SLOUGH
OREGON
NOAA Chart: 18523 Latitude: 46° 11.2' N
USGS Quad: SVENSEN Longitude: 123° 35.4' 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.