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National Ocean Service
Datums Page Page 1 of 5
Station ID: 9462782 PUBLICATION DATE: 04/07/2011
Name: TIGALDA BAY, TIGALDA ISLAND
AK
NOAA Chart: 16531 Latitude: 54° 7.2' N ( 54.12000)
USGS Quad: UNIMAK A-3 Longitude: 164° 58.6' W (-164.97700)
To reach the station from the Unalaska (Dutch Harbor) City Dock, proceed NNE by
boat 18 km (10 nm) past the north end of Unalaska Island, proceed east 48 km (26
nm) through Akutan Pass, then proceed 44 km (24 nm) NE through Avatanak Strait,
turn SE and proceed 7 km (4 nm) to the southeast end of Tigalda Bay. The
station is located on a rock outcrop just west of a creek and mooring area.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: No 1
DESIGNATION: 946 2782 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 19830
AGENCY: USC&GS (United States Coast &
Geodetic Survey) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 54° 7.1' N ( 54.11817) LONGITUDE: 164° 58.6' W (-164.97636)
The bench mark is set in bedrock located near the seaward west end of a rock
point, 10.69 m (35.1 ft) west of 946 2782 TIDAL 2, 7.37 m (24.2 ft) north of 946
2782 TIDAL 3, and 3.85 m (12.6 ft) north of the north edge of a 1.5 m wide slot
in the rock point.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9462782 PUBLICATION DATE: 04/07/2011
Name: TIGALDA BAY, TIGALDA ISLAND
AK
NOAA Chart: 16531 Latitude: 54° 7.2' N ( 54.12000)
USGS Quad: UNIMAK A-3 Longitude: 164° 58.6' W (-164.97700)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: No 2
DESIGNATION: 946 2782 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 19831
AGENCY: USC&GS (United States Coast &
Geodetic Survey) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 54° 7.1' N ( 54.11817) LONGITUDE: 164° 58.6' W (-164.97622)
The bench mark is set in bedrock located on the north side of an east/west rock
point, 21.05 m (69.1 ft) west of 946 2782 TIDAL 4, 12.28 m (40.3 ft) NE of 946
2782 TIDAL 3, 5.06 m (16.6 ft) north of the highest rock ( 1.4 m x 1.3 m x 0.7 m
high) on this point, and 2.25 m (7.4 ft) SSE of the north side of the rock
point.
BENCH MARK STAMPING: No 3
DESIGNATION: 946 2782 TIDAL 3
MONUMENTATION: Tidal Station disk VM#: 19832
AGENCY: USC&GS (United States Coast &
Geodetic Survey) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID#: BBCD10
LATITUDE: 54° 7.1' N ( 54.11811) LONGITUDE: 164° 58.6' W (-164.97636)
The bench mark is set in bedrock located near the seaward west end of a rock
point, 18.46 m (60.6 ft) NW of 946 2782 TIDAL 5, 12.28 m (40.3 ft) SW of 946
2782 TIDAL 2, 10.55 m (34.6 ft) west of the highest rock ( 1.4 m x 1.3 m x 0.7 m
high) on this point, 7.37 m (24.2 ft) south of 946 2782 TIDAL 1, 2.95 m (9.7 ft)
east of the west edge of the rock, and 1.98 m (6.5 ft) north of the south edge
of the rock point and a small inlet separating the rock point to the south.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9462782 PUBLICATION DATE: 04/07/2011
Name: TIGALDA BAY, TIGALDA ISLAND
AK
NOAA Chart: 16531 Latitude: 54° 7.2' N ( 54.12000)
USGS Quad: UNIMAK A-3 Longitude: 164° 58.6' W (-164.97700)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4 1935
DESIGNATION: 946 2782 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 19833
AGENCY: USC&GS (United States Coast &
Geodetic Survey) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 54° 7.1' N ( 54.11808) LONGITUDE: 164° 58.6' W (-164.97589)
The bench mark is set in bedrock located on the north side of an east/west
grassy rock point, 21.10 m (69.2 ft) east of the highest rock ( 1.4 m x 1.3 m x
0.7 m high) on this point, 21.05 m (69.1 ft) east of 946 2782 TIDAL 2, and 2.85
m (9.3 ft) south of the north side of the grassy rock point.
BENCH MARK STAMPING: 5 1935
DESIGNATION: 946 2782 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 19834
AGENCY: USC&GS (United States Coast &
Geodetic Survey) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 54° 7.1' N ( 54.11797) LONGITUDE: 164° 58.6' W (-164.97619)
The bench mark is set in rock midway along an east/west grassy rock point ;
south of the rock point on which all of the other tidal bench marks are located,
21.00 m (68.9 ft) east of the seaward edge of the rock point, 18.46 m (60.6 ft)
SE of 946 2782 TIDAL 3, 12.78 m (41.9 ft) SSE of the highest rock ( 1.4 m x 1.3
m x 0.7 m high) on the separate rock point to the north, 4.52 m (14.8 ft) north
of the south side of the rock point, and 2.53 m (8.2 ft) south of the north side
of the rock point.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9462782 PUBLICATION DATE: 04/07/2011
Name: TIGALDA BAY, TIGALDA ISLAND
AK
NOAA Chart: 16531 Latitude: 54° 7.2' N ( 54.12000)
USGS Quad: UNIMAK A-3 Longitude: 164° 58.6' W (-164.97700)
T I D A L D A T U M S
Tidal datums at TIGALDA BAY, TIGALDA ISLAND based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: June 2010 - June 2010
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9462620 UNALASKA, DUTCH HARBOR
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 0.954
MEAN HIGH WATER MHW = 0.918
MEAN SEA LEVEL MSL = 0.492
MEAN TIDE LEVEL MTL = 0.480
MEAN LOW WATER MLW = 0.042
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
No 1 4.122 3.204
No 2 6.377 5.459
No 3 5.949 5.031
4 1935 6.006 5.088
5 1935 6.927 6.009
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9462782 PUBLICATION DATE: 04/07/2011
Name: TIGALDA BAY, TIGALDA ISLAND
AK
NOAA Chart: 16531 Latitude: 54° 7.2' N ( 54.12000)
USGS Quad: UNIMAK A-3 Longitude: 164° 58.6' W (-164.97700)
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.