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National Ocean Service
Datums Page Page 1 of 5
Station ID: 9462705 PUBLICATION DATE: 11/07/2013
Name: GREEN BIGHT
AK
NOAA Chart: 16531 Latitude: 54° 6.6' N ( 54.11028)
USGS Quad: UNIMAK A - 6 Longitude: 165° 39.7' W (-165.66139)
To reach the tidal bench marks from the Unalaska (Dutch Harbor) City Dock,
proceed NNE 14.0 km (7.6 nm) to Priest Rock, then proceed east for 47.5 km (25.7
nm) through Akutan Pass and past Battery Point to the north, then proceed north
for 8.3 km (4.5 nm) making for the west side of Akun Strait. The tide station
is located at the northern end of Green Bight on the far eastern peninsula of
Akutan Island, and the tidal bench marks are south along the shore of Green
Bight.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 2705 E 2013
DESIGNATION: 946 2705 E
MONUMENTATION: Tidal Station disk VM#: 20827
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: Stainless Steel rod with sleeve OPUS PID#: BBDC39
LATITUDE: 54° 6.9' N ( 54.11453) LONGITUDE: 165° 40.2' W (-165.67022)
The bench mark is a stainless steel rod set in grass above cobble beach and
below grass bluff, 20.40 m (66.9 ft) NNW of seaward extent of vegetation at top
of cobble beach, 6.01 m (19.7 ft) SSE of base of bluff, and 1.01 m (3.3 ft) SW
of 1.8 m (6 ft) long drift wood log set in ground sticking up 0.90 m (3 ft). The
datum point is the top of a stainless steel rod with greased sleeve driven 4.03
m (13.2 ft) to refusal, and encased in a 5-inch NOS logo cover.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9462705 PUBLICATION DATE: 11/07/2013
Name: GREEN BIGHT
AK
NOAA Chart: 16531 Latitude: 54° 6.6' N ( 54.11028)
USGS Quad: UNIMAK A - 6 Longitude: 165° 39.7' W (-165.66139)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 2705 A 2013
DESIGNATION: 946 2705 A
MONUMENTATION: Tidal Station disk VM#: 20823
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 54° 7.0' N ( 54.11742) LONGITUDE: 165° 39.7' W (-165.66194)
The primary bench mark is a disk set in the east end of a house size
conglomerate rock on a cobble beach at the NE end of Green Bight, 27.50 m (90.2
ft) SW of an undercut rock cliff at NE end of beach, 5.28 m (17.3 ft) SW of the
seaward end of a separate garage size rock, 2.42 m (7.9 ft) NNW of seaward
extent of rock, and 1.18 m (3.9 ft) above the beach.
BENCH MARK STAMPING: 2705 B 2013
DESIGNATION: 946 2705 B
MONUMENTATION: Tidal Station disk VM#: 20824
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 54° 7.0' N ( 54.11711) LONGITUDE: 165° 39.8' W (-165.66272)
The bench mark is a disk set in a conglomerate rock outcrop near the north end
of the beach and surrounded by cobbles, 41.45 m (136.0 ft) SW of westernmost of
3 large rocks near cliff at north end of beach, 19.50 m (64.0 ft) NE of 12 m
(40.0 ft) high rock outcrop that projects from cliff onto beach, 5.24 m (17.2
ft) SE of vegetation line, and 0.50 m (1.6 ft) above the cobble beach.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9462705 PUBLICATION DATE: 11/07/2013
Name: GREEN BIGHT
AK
NOAA Chart: 16531 Latitude: 54° 6.6' N ( 54.11028)
USGS Quad: UNIMAK A - 6 Longitude: 165° 39.7' W (-165.66139)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 2705 C 2013
DESIGNATION: 946 2705 C
MONUMENTATION: Tidal Station disk VM#: 20825
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 54° 7.0' N ( 54.11672) LONGITUDE: 165° 39.8' W (-165.66367)
The bench mark is a disk set in a rock outcrop below cliffs and at the top of
the cobble beach, 39.90 m (131.0 ft) WSW of 12 m (40.0 ft) high rock outcrop
that projects from cliff onto beach, 8.70 m (28.5 ft) WSW of seaward point of
next rock outcrop to north measuring 2.5 m (8 ft) high by 4 m (13 ft) wide and 6
m (20 ft) long, 1.95 m (6.4 ft) NW of seaward edge of rock, and 0.70 m (2.0 ft)
above the beach.
BENCH MARK STAMPING: 2705 D 2013
DESIGNATION: 946 2705 D
MONUMENTATION: Tidal Station disk VM#: 20826
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: Bouler OPUS PID:
LATITUDE: 54° 7.0' N ( 54.11625) LONGITUDE: 165° 39.9' W (-165.66550)
The bench mark is a disk set in a 1.5 m (5 ft) high by 1 m (3 ft) wide rock,
30.90 m (101.4 ft) slope distance SSE of base of rock cliff, 14.40 m (47.2 ft)
NNW of edge of vegetation, 0.77m (2.5 ft) NW of seaward edge of boulder, and
0.90 m (3.0 ft) above the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9462705 PUBLICATION DATE: 11/07/2013
Name: GREEN BIGHT
AK
NOAA Chart: 16531 Latitude: 54° 6.6' N ( 54.11028)
USGS Quad: UNIMAK A - 6 Longitude: 165° 39.7' W (-165.66139)
T I D A L D A T U M S
Tidal datums at GREEN BIGHT based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: July 2013 - July 2013
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9459881 KING COVE, DEER PASSAGE, PACIFIC OCEAN
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 1.528
MEAN HIGH WATER MHW = 1.370
MEAN TIDE LEVEL MTL = 0.887
MEAN SEA LEVEL MSL = 0.873
MEAN LOW WATER MLW = 0.404
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
2705 E 2013 9.171 7.801
2705 A 2013 3.208 1.838
2705 B 2013 4.365 2.995
2705 C 2013 6.755 5.385
2705 D 2013 9.640 8.270
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9462705 PUBLICATION DATE: 11/07/2013
Name: GREEN BIGHT
AK
NOAA Chart: 16531 Latitude: 54° 6.6' N ( 54.11028)
USGS Quad: UNIMAK A - 6 Longitude: 165° 39.7' W (-165.66139)
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.