U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 7
Station ID: 9440569 PUBLICATION DATE: 05/03/2023
Name: SKAMOKAWA, COLUMBIA RIVER
WA
NOAA Chart: 18523 Latitude: 46° 16.0' N ( 46.26670)
USGS Quad: SKAMOKAWA Longitude: 123° 27.1' W (-123.45200)
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, turn left
after the Skamokawa Creek bridge and continue to the public boat ramp. The bench
marks are along State Highway 4 and Steamboat Slough Road. The tide station is
located on the north side of the boat ramp.
T I D A L B E N C H M A R K S
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 7
Station ID: 9440569 PUBLICATION DATE: 05/03/2023
Name: SKAMOKAWA, COLUMBIA RIVER
WA
NOAA Chart: 18523 Latitude: 46° 16.0' N ( 46.26670)
USGS Quad: SKAMOKAWA Longitude: 123° 27.1' W (-123.45200)
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: N 317 21 1939
DESIGNATION: N 317
MONUMENTATION: Triangulation Station disk VM#: 8908
AGENCY: US Army Corps of Engineers (USE) IDB PID#:
SETTING CLASSIFICATION: Bridge sidewalk OPUS PID:
LATITUDE: 46° 16.2' N ( 46.27019) LONGITUDE: 123° 27.4' W (-123.45592)
The primary bench mark is a disk set in the sidewalk at the SE end of the State
Highway 4 bridge over Skamokawa Creek, 2.55 m (8.37 ft) north of fire hydrant
#4, 0.40 m (1.4 ft) west of the east end of the bridge sidewalk, and 0.20 m (0.5
ft) north of the inside of the south guard-rail.
BENCH MARK STAMPING: 944 0569 B 1981
DESIGNATION: 944 0569 B
MONUMENTATION: Tidal Station disk VM#: 8911
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete bridge curb OPUS PID:
LATITUDE: 46° 16.2' N ( 46.26944) LONGITUDE: 123° 27.3' W (-123.45456)
The bench mark is a disk set flush in the NE corner of a concrete bridge curb on
the Highway 4 (Steamboat Slough) bridge that spans Brooks Slough, 41.45 m (136.0
ft) SSE of the NE corner of Skamokawa Inn Bed & Breakfast Suites, 3.81 m (12.5
ft) east of the centerline of Steamboat Slough Road, and 0.06 m (0.2 ft) west of
a concrete pillar on the bridge.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 7
Station ID: 9440569 PUBLICATION DATE: 05/03/2023
Name: SKAMOKAWA, COLUMBIA RIVER
WA
NOAA Chart: 18523 Latitude: 46° 16.0' N ( 46.26670)
USGS Quad: SKAMOKAWA Longitude: 123° 27.1' W (-123.45200)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0569 C 2010
DESIGNATION: 944 0569 C
ALIAS: BBCB47
MONUMENTATION: Flange-encased Rod VM#: 19823
AGENCY: National Geodetic Survey (NGS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID#: BBCB47
LATITUDE: 46° 16.2' N ( 46.27003) LONGITUDE: 123° 27.3' W (-123.45578)
The bench mark is a stainless steel rod located along the east side of Skamokawa
Creek, 35.80 m (117.5 ft) NE of the SW corner of the former Skamokawa Bed and
Breakfast 4-plex building, 21.40 m (70.2 ft) south of power pole number 172860,
and 7.50 m (24.6 ft) SW of the southern most of three septic tank inspection
covers. The datum point is set 12 cm (0.4 ft) below the ground, being the top
of a stainless steel rod driven 5.6 m (18.3 ft) to refusal, encased in a 6-inch
PVC pipe with concrete kick block, and a 6-inch NGS logo cap.
BENCH MARK STAMPING: 0569 D 2011
DESIGNATION: 944 0569 D
MONUMENTATION: Survey disk VM#: 20225
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Massive retaining wall OPUS PID#: BBCV74
LATITUDE: 46° 16.2' N ( 46.26997) LONGITUDE: 123° 27.3' W (-123.45514)
The bench mark is a disk set in a large retaining wall along the parking lot in
front of the General Store Hotel, 6.90 m (22.6 ft) SE of the mile marker number
29 sign, 23.60 m (77.4 ft) NW of the centerline of the front entrance to the
General Store Hotel, 11.90 m (39.0 ft) south of the centerline of State Highway
4, and 0.80 m (2.6 ft) above grade.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 7
Station ID: 9440569 PUBLICATION DATE: 05/03/2023
Name: SKAMOKAWA, COLUMBIA RIVER
WA
NOAA Chart: 18523 Latitude: 46° 16.0' N ( 46.26670)
USGS Quad: SKAMOKAWA Longitude: 123° 27.1' W (-123.45200)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0569 E 2011
DESIGNATION: 944 0569 E
MONUMENTATION: Survey disk VM#: 20226
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete bridge curb OPUS PID:
LATITUDE: 46° 16.1' N ( 46.26906) LONGITUDE: 123° 27.3' W (-123.45450)
The bench mark is a disk set in the SE corner of the Steam Boat Slough Road
bridge abutment, 41.20 m (135.2 ft) SSE of bench mark 944 0569 B, 4.30 m (14.1
ft) east of the centerline of Steamboat Slough Road, 10.70 m (35.1 ft) NNE of a
power pole number 10 labeled on the transformer, 1.25 m (4.1 ft) north of a
green 24 in. diameter sewer vent, 1.00 m (3.3 ft) NNE of an orange witness post,
and 0.20 m (0.7 ft) above grade.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 7
Station ID: 9440569 PUBLICATION DATE: 05/03/2023
Name: SKAMOKAWA, COLUMBIA RIVER
WA
NOAA Chart: 18523 Latitude: 46° 16.0' N ( 46.26670)
USGS Quad: SKAMOKAWA Longitude: 123° 27.1' W (-123.45200)
T I D A L D A T U M S
Tidal datums at SKAMOKAWA, COLUMBIA RIVER based on:
LENGTH OF SERIES: 13 Years
TIME PERIOD: 8/02-10/02 & 7/04-9/15 Low Water Months Only
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9439040 ASTORIA, TONGUE POINT, COLUMBIA RIVER
Elevations of tidal datums referred to Columbia River Datum (CRD), in METERS:
MEAN HIGHER HIGH WATER MHHW = 2.389
MEAN HIGH WATER MHW = 2.199
MEAN TIDE LEVEL MTL = 1.289
MEAN SEA LEVEL MSL = 1.265
MEAN LOW WATER MLW = 0.380
MEAN LOWER LOW WATER MLLW = 0.148
COLUMBIA RIVER DATUM CRD = 0.000
North American Vertical Datum NAVD88 = -0.380
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MHW CRD
N 317 21 1939 5.051 7.250
944 0569 B 1981 4.449 6.648
0569 C 2010 1.156 3.355
0569 D 2011 2.989 5.188
0569 E 2011 4.839 7.038
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 7
Station ID: 9440569 PUBLICATION DATE: 05/03/2023
Name: SKAMOKAWA, COLUMBIA RIVER
WA
NOAA Chart: 18523 Latitude: 46° 16.0' N ( 46.26670)
USGS Quad: SKAMOKAWA Longitude: 123° 27.1' W (-123.45200)
Foot Notes:
Columbia River Datum (CRD) is the adopted fixed low water reference plane for
this area. CRD is a U.S. Army Corps of Engineers non-tidal datum defined at
distinct river miles relative to NAVD88, and is used as chart datum above river
mile 23 on the Columbia River. Datums are computed using observations from the
low river stages of the year, generally August through October due to the
masking of the tidal signal from strong seasonal river runoff during other
portions of the year. Depending on river flow, water levels can be significantly
higher than Columbia River Datum. As of 2014, the U.S. Army Corps of Engineers
provided updated offsets for CRD that have been applied to this station. Station
Datum (STND) is no longer set equal to CRD.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 7
Station ID: 9440569 PUBLICATION DATE: 05/03/2023
Name: SKAMOKAWA, COLUMBIA RIVER
WA
NOAA Chart: 18523 Latitude: 46° 16.0' N ( 46.26670)
USGS Quad: SKAMOKAWA Longitude: 123° 27.1' W (-123.45200)
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 NGS's Integrated Data Base (IDB PID)
provides geodetic datum based on traditionally leveled and bluebooked ties to
the National Spatial Reference System(NSRS) https://www.ngs.noaa.gov/datasheets/.
The NGS Online Positioning User Service (OPUS PID) provides geodetic datum based
on GPS position & tie it to the NSRS https://www.ngs.noaa.gov/OPUS/.
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.