U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 10/11/1988
Station ID: 9446025 SUPERCEDED DATE: 04/21/2003
Name: POINT VASHON, VASHON ISLAND, PUGET SOUND
WASHINGTON
NOAA Chart: 18448 Latitude: 47° 30.7' N
USGS Quad: DUWAMISH HEAD Longitude: 122° 27.8' W
To reach the tidal bench marks from Fauntleroy, take the ferry across Puget
Sound to Vashon Island. The bench marks are in the sea wall and along the ferry
pier. The tide gage and staff were located on the east side of the ferry pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 6025 A 1977
MONUMENTATION: Survey Disk VM#: 9108
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is set flush in the concrete foundation of the Point Vashon Ferry
Terminal at the NW end of the pier, at the south corner of the ferry office, and
0.7 foot (0.2 m) east of te NE corner of a telephone booth.
BENCH MARK STAMPING: 6025 D 1977
MONUMENTATION: Survey Disk VM#: 9109
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Retaining Wall
The bench mark is set flush on top of the north end of the north-south retaining
wall, 70 feet (21 m) south of a restaurant, and 30 feet (9 m) east of the
centerline of the roadway that leads to Cover, Burton (Vashon Isle Highway).
BENCH MARK STAMPING: 6025 E 1977
MONUMENTATION: Survey Disk VM#: 9110
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is set flush in a 3 x 3 foot (1 x 1 m) concrete slab at the base
of a sign, and 51 feet (16 m) NW of the centerline of the SW end of the pier.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 10/11/1988
Station ID: 9446025 SUPERCEDED DATE: 04/21/2003
Name: POINT VASHON, VASHON ISLAND, PUGET SOUND
WASHINGTON
NOAA Chart: 18448 Latitude: 47° 30.7' N
USGS Quad: DUWAMISH HEAD Longitude: 122° 27.8' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 944 6025 F 1981
MONUMENTATION: Survey Disk VM#: 9111
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is located in the top of a 1.3 foot (0.4 m) square concrete
monument that supports a concrete sea wall, 157 feet (48 m) NW of the inshore
centerline end of the Vashon Ferry Pier at the NW end of a concrete sea wall,
and is 1.3 feet (0.4 m) below the top of the sea wall.
BENCH MARK STAMPING: 944 6025 G 1981
MONUMENTATION: Survey Disk VM#: 9112
AGENCY: PID:
SETTING CLASSIFICATION: Rock
The bench mark is set in the top of a large 3 feet (1 m) high grey boulder that
is split (on the offshore side of a wooden bulkhead), 170 feet (52 m) NW of the
Vashon Ferry Pier, and 1.3 feet (0.4 m) SE of the highest point of the boulder.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 10/11/1988
Station ID: 9446025 SUPERCEDED DATE: 04/21/2003
Name: POINT VASHON, VASHON ISLAND, PUGET SOUND
WASHINGTON
NOAA Chart: 18448 Latitude: 47° 30.7' N
USGS Quad: DUWAMISH HEAD Longitude: 122° 27.8' W
T I D A L D A T U M S
Tidal datums at POINT VASHON, VASHON ISLAND, PUGET SOUND based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: OCTOBER 1977
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 9447130 SEATTLE
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (11/15/1977) = 13.57
MEAN HIGHER HIGH WATER MHHW = 11.53
MEAN HIGH WATER MHW = 10.66
MEAN TIDE LEVEL MTL = 6.76
MEAN LOW WATER MLW = 2.86
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (11/11/1977) = -2.23
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
6025 A 1977 18.83 8.17
6025 D 1977 25.05 14.39
6025 E 1977 19.75 9.09
944 6025 F 1981 14.75 4.09
944 6025 G 1981 13.19 2.53
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 10/11/1988
Station ID: 9446025 SUPERCEDED DATE: 04/21/2003
Name: POINT VASHON, VASHON ISLAND, PUGET SOUND
WASHINGTON
NOAA Chart: 18448 Latitude: 47° 30.7' N
USGS Quad: DUWAMISH HEAD Longitude: 122° 27.8' 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.