U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 08/04/1986
Station ID: 9447827 SUPERCEDED DATE: 04/21/2003
Name: DOUBLE BLUFF, WHIDBEY ISLAND
WASHINGTON
NOAA Chart: 18441 Latitude: 47° 58.7' N
USGS Quad: HANSVILLE Longitude: 122° 33.0' W
To reach the tidal bench marks on Whidbey Island and SE end of Mutiny Bay,
proceed 1.4 miles (2.25 km) south of Austin, 0.25 mile (0.40 km) north of the
western bluff of Double Bluff. The bench marks are in the same area. The tide
gage was located in the area of the Double Bluff Island Company and the CO-OP
boat house.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 1977 #7827 A
MONUMENTATION: Survey Disk VM#: 9217
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Slab
The bench mark is on the SW corner of a concrete slab on the water side of the
aluminum boat house and east of eight distinct lone pilings which are mostly in
tidal range, set flush into the concrete.
BENCH MARK STAMPING: 1977 #7827 B
MONUMENTATION: Survey Disk VM#: 9218
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is N 30 W (magnetic) and one house north of Bench Mark 1977 #7827
A and in the NW corner of the foundation footing of the house immediately north
of the aluminum boat house.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 08/04/1986
Station ID: 9447827 SUPERCEDED DATE: 04/21/2003
Name: DOUBLE BLUFF, WHIDBEY ISLAND
WASHINGTON
NOAA Chart: 18441 Latitude: 47° 58.7' N
USGS Quad: HANSVILLE Longitude: 122° 33.0' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1977 #7827 C
MONUMENTATION: Survey Disk VM#: 9219
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Slab
The bench mark is N 20 W, 159.0 feet (48.5 m) and 6 houses northerly of Bench
Mark 1977 #7827 B and in the SW corner of the slab in front of a private home,
set into the concrete.
BENCH MARK STAMPING: 1977 #7827 D
MONUMENTATION: Survey Disk VM#: 9220
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Slab
The bench mark is N 20 W, 230.0 feet (70.1 m) and 7 houses northerly from Bench
Mark 1977 #7827 C, 10.0 feet (3.0 m) east of the HWL and in the SW corner of the
slab in front of a private home, set flush into the concrete.
BENCH MARK STAMPING: 1977 #7827 E
MONUMENTATION: Survey Disk VM#: 9221
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Slab
The bench mark is N 20 W, 200.0 feet (61.0 m) and 6 houses northerly from Bench
Mark 1977 #7827 D, 30.0 feet (9.1 m) east of the HWL and in the center of the
western face of the raised portion of the concrete in front of a private home,
set flush into the concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 08/04/1986
Station ID: 9447827 SUPERCEDED DATE: 04/21/2003
Name: DOUBLE BLUFF, WHIDBEY ISLAND
WASHINGTON
NOAA Chart: 18441 Latitude: 47° 58.7' N
USGS Quad: HANSVILLE Longitude: 122° 33.0' W
T I D A L D A T U M S
Tidal datums at DOUBLE BLUFF, WHIDBEY ISLAND based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: MARCH 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 (03/16/1977) = 11.36
MEAN HIGHER HIGH WATER MHHW = 10.08
MEAN HIGH WATER MHW = 9.00
MEAN TIDE LEVEL MTL = 5.88
MEAN LOW WATER MLW = 2.77
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (02/16/1977) = -3.14
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
1977 #7827 A 12.38 3.38
1977 #7827 B 12.69 3.69
1977 #7827 C 13.88 4.88
1977 #7827 D 13.05 4.05
1977 #7827 E 14.86 5.86
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 08/04/1986
Station ID: 9447827 SUPERCEDED DATE: 04/21/2003
Name: DOUBLE BLUFF, WHIDBEY ISLAND
WASHINGTON
NOAA Chart: 18441 Latitude: 47° 58.7' N
USGS Quad: HANSVILLE Longitude: 122° 33.0' 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.