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National Ocean Service
Datums Page Page 1 of 5
Station ID: 9454721 PUBLICATION DATE: 06/16/2011
Name: PERRY ISLAND (SOUTH BAY)
AK
NOAA Chart: 16705 Latitude: 60° 40.3' N ( 60.67170)
USGS Quad: Seward C-3 Longitude: 147° 55.9' W (-147.93200)
To reach the tidal bench marks follow along the western shore of South Bay which
is located on the south shore of Perry Island. The site is located in a cove
which is off the NW corner of South Bay. Once inside the cove there are several
buildings (a house and barns) on the western shore and two islets in
approximately the middle of the cove. At the head of the cove is a narrow
passage that leads to a small hidden bay. The site is located on and around the
larger of the two islets.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: No. 4 1966
DESIGNATION: 945 4721 TIDAL 4
MONUMENTATION: Survey disk VM#: 14664
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: In bedrock in prominent rock ledge OPUS PID:
LATITUDE: 60° 40.3' N ( 60.67170) LONGITUDE: 147° 55.9' W (-147.93200)
The bench mark is a disk set in bedrock in a prominent rock ledge point on the
eastern shore of the entrance to the narrow passage at the north head of the
South Bay, 9.14 m (30.0 ft) west of an 2.44 m (8.0 ft) rock-faced bluff and
19.51 m (64.0 ft) SW of bench mark No. 5 1966. To the west is an islet about
18.29 m (60.0 ft) long (north to south) and 9.14 m (30.0 ft) high which forms
the western part of the passage.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9454721 PUBLICATION DATE: 06/16/2011
Name: PERRY ISLAND (SOUTH BAY)
AK
NOAA Chart: 16705 Latitude: 60° 40.3' N ( 60.67170)
USGS Quad: Seward C-3 Longitude: 147° 55.9' W (-147.93200)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: No. 5 1966
DESIGNATION: 945 4721 TIDAL 5
MONUMENTATION: Survey disk VM#: 14665
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 60° 40.3' N ( 60.67170) LONGITUDE: 147° 55.9' W (-147.93200)
The bench mark is a disk set in bedrock at the base of an 2.44 m (8.0 ft)
rock-faced bluff ,19.51 m (64.0 ft) NE of bench mark No. 4 1966, and about 2.44
m (8.0 ft) north of the north face of a bluff ledge that extends to within 9.14
m (30.0 ft) of bench mark No. 4 1966.
BENCH MARK STAMPING: 4721 A 1994
DESIGNATION: 945 4721 A 1994
MONUMENTATION: Survey disk VM#: 14666
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: OPUS PID:
LATITUDE: 60° 40.3' N ( 60.67170) LONGITUDE: 147° 55.9' W (-147.93200)
The bench mark is a disk located on the south end of the larger islet, 14.50 m
(47.6 ft) NW (330 magnetic) from bench mark 4721 B 1994, 90.0 m (295.3 ft) NE
(070 magnetic) from bench mark No. 4 1966 and NE (060 magnetic) from bench
mark No. 5 1966, and about 1.40 m (4.6 ft) above the approximate high water
line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9454721 PUBLICATION DATE: 06/16/2011
Name: PERRY ISLAND (SOUTH BAY)
AK
NOAA Chart: 16705 Latitude: 60° 40.3' N ( 60.67170)
USGS Quad: Seward C-3 Longitude: 147° 55.9' W (-147.93200)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4721 B 1994
DESIGNATION: 945 4721 B 1994
MONUMENTATION: Survey disk VM#: 14667
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: OPUS PID:
LATITUDE: 60° 40.3' N ( 60.67170) LONGITUDE: 147° 55.9' W (-147.93200)
The bench mark is a disk located on the north end of the larger islet, 14.50 m
(47.6 ft) SE (150 magnetic) from bench mark 4721 A 1994, 90.0 m (295.3 ft) NW
(350 magnetic) from bench mark 4721 C 1994, and about 1.60 m (5.25 ft) above
the approximate high water line.
BENCH MARK STAMPING: 4721 C 1994
DESIGNATION: 945 4721 C 1994
MONUMENTATION: Survey disk VM#: 14668
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock ledge OPUS PID:
LATITUDE: 60° 40.3' N ( 60.67170) LONGITUDE: 147° 55.9' W (-147.93200)
The bench mark is a disk which is set on the high point of the ledge
approximately 1.80 m (5.9 ft) above the approximate high water line where there
is a rock ledge which sits at the approximate high water line on the gravel
beach, located on the western shore of the cove, 90.0 m (295.3 ft) SE (170
magnetic) from bench mark 4721 B 1994. The smaller islet bears SE (110
magnetic).
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9454721 PUBLICATION DATE: 06/16/2011
Name: PERRY ISLAND (SOUTH BAY)
AK
NOAA Chart: 16705 Latitude: 60° 40.3' N ( 60.67170)
USGS Quad: Seward C-3 Longitude: 147° 55.9' W (-147.93200)
T I D A L D A T U M S
Tidal datums at PERRY ISLAND (SOUTH BAY) based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: September 1995 - October 1995
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9454240 VALDEZ, PRINCE WILLIAM SOUND
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 3.643
MEAN HIGH WATER MHW = 3.353
MEAN SEA LEVEL MSL = 1.938
MEAN TIDE LEVEL MTL = 1.902
MEAN LOW WATER MLW = 0.450
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. 4 1966 3.875 0.522
No. 5 1966 3.343 -0.010
4721 A 1994 4.691 1.337
4721 B 1994 4.765 1.412
4721 C 1994 4.974 1.621
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9454721 PUBLICATION DATE: 06/16/2011
Name: PERRY ISLAND (SOUTH BAY)
AK
NOAA Chart: 16705 Latitude: 60° 40.3' N ( 60.67170)
USGS Quad: Seward C-3 Longitude: 147° 55.9' W (-147.93200)
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.