U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 09/21/2000
Station ID: 9449932 SUPERCEDED DATE: 04/21/2003
Name: ARMITAGE ISLAND
WASHINGTON
NOAA Chart: 18430 Latitude: 48° 32.1' N
USGS Quad: BLAKELY ISLAND Longitude: 122° 47.8' W
To reach the tidal bench marks which are accessible only by boat, from the
nearest boat launch facilities in Anacortes, Washington, proceed through town on
the Highway 20 Spur to the light at Sunset Avenue. Go straight on Sunset Avenue
to its terminus in Washington Park. From the boat launch, Armitage Island is
approximately 8.5 km (5.3 mi) to the NW across Rosario Strait along the
southeastern side of Blakely Island. The bench marks are located along the
shore on the southwestern side of the Island. The tide gauge is on a private
pier on the west side of the Island.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1 1972
DESIGNATION: 944 9932 NO 1
MONUMENTATION: Tidal Station disk VM#: 13728
AGENCY: National Ocean Survey (NOS) PID:
SETTING CLASSIFICATION: Rock ledge
The primary bench mark is a disk set in a rock ledge, approximately 11 m (36 ft)
SE (163 degrees magnetic) from a shore end of a small dock located on the
western shore, and approximately 1 m (4 ft) above the apparent high water mark.
BENCH MARK STAMPING: NO 3 1972
DESIGNATION: 944 9932 NO 3
MONUMENTATION: Tidal Station disk VM#: 13729
AGENCY: National Ocean Survey (NOS) PID:
SETTING CLASSIFICATION: Rock ledge
The bench mark is a disk set in a rock ledge, located approximately 24 m (78 ft)
SW (191 degrees magnetic) from bench mark NO 2 1972, and 0.61 m (2.0 ft) above
the apparent high tide mark.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 09/21/2000
Station ID: 9449932 SUPERCEDED DATE: 04/21/2003
Name: ARMITAGE ISLAND
WASHINGTON
NOAA Chart: 18430 Latitude: 48° 32.1' N
USGS Quad: BLAKELY ISLAND Longitude: 122° 47.8' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 2 1972
DESIGNATION: 944 9932 NO 2
MONUMENTATION: Tidal Station disk VM#: 13730
AGENCY: National Ocean Survey (NOS) PID:
SETTING CLASSIFICATION: Rock ledge
The bench mark is a disk set in a rock ledge, located approximately 15 m (48 ft)
SE (177 degrees magnetic) from bench mark NO 1 1972, and 1 m (4 ft) above the
apparent high tide mark.
BENCH MARK STAMPING: NO 4 1972
DESIGNATION: 944 9932 NO 4
MONUMENTATION: Tidal Station disk VM#: 13731
AGENCY: National Ocean Survey (NOS) PID:
SETTING CLASSIFICATION: Rock ledge
The bench mark is a disk set in a rock ledge, located approximately 16 m (53 ft)
SW (201 degrees magnetic) from bench mark NO 3 1972, and 0.91 m (3.0 ft) above
the apparent high tide mark.
BENCH MARK STAMPING: NO 5 1972
DESIGNATION: 944 9932 NO 5
MONUMENTATION: Tidal Station disk VM#: 13732
AGENCY: National Ocean Survey (NOS) PID:
SETTING CLASSIFICATION: Rock ledge
The bench mark is a disk set in a rock ledge, located approximately 20 m (64 ft)
SE (177 degrees magnetic) from bench mark NO 4 1972, and 0.91 m (3 ft) above the
apparent high tide mark.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 09/21/2000
Station ID: 9449932 SUPERCEDED DATE: 04/21/2003
Name: ARMITAGE ISLAND
WASHINGTON
NOAA Chart: 18430 Latitude: 48° 32.1' N
USGS Quad: BLAKELY ISLAND Longitude: 122° 47.8' W
T I D A L D A T U M S
Tidal datums at ARMITAGE ISLAND based on:
LENGTH OF SERIES: 33 MONTHS
TIME PERIOD: August 1997 - April 2000
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 9449880 FRIDAY HARBOR, SAN JUAN CHANNEL
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (12/16/1997) = 3.223
MEAN HIGHER HIGH WATER MHHW = 2.387
MEAN HIGH WATER MHW = 2.189
MEAN TIDE LEVEL MTL = 1.467
MEAN SEA LEVEL MSL = 1.422
MEAN LOW WATER MLW = 0.745
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (12/25/1999) = -1.076
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
NO 1 1972 3.873 1.684
NO 3 1972 3.259 1.070
NO 2 1972 3.874 1.685
NO 4 1972 3.592 1.403
NO 5 1972 3.590 1.401
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 09/21/2000
Station ID: 9449932 SUPERCEDED DATE: 04/21/2003
Name: ARMITAGE ISLAND
WASHINGTON
NOAA Chart: 18430 Latitude: 48° 32.1' N
USGS Quad: BLAKELY ISLAND Longitude: 122° 47.8' 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.