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National Ocean Service
Datums Page Page 1 of 5
Station ID: 9454851 PUBLICATION DATE: 06/16/2011
Name: COCHRANE BAY, PR. WILLIAM SOUND
AK
NOAA Chart: 16705 Latitude: 60° 39.8' N ( 60.66330)
USGS Quad: Seward D-4 Longitude: 148° 21.4' W (-148.35700)
To reach the tidal bench marks, follow the eastern shore of Cochrane Bay south
approximately 13 km (7 nm) until the bay narrows. The cove in which the station
is located is the only one with two islands. The station lies on the north
shore and on a rock outcrop which extends to the south. At approximate high
water the outcrop appears as an islet that is 30.0 m (98.4 ft) in the
north-south direction and 15.0 m (49.2 ft) in the east-west direction.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 4851 B 1995
DESIGNATION: 945 4851 B 1995
MONUMENTATION: Survey disk VM#: 14705
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 60° 39.8' N ( 60.66330) LONGITUDE: 148° 21.4' W (-148.35700)
The primary bench mark is a disk located on the rocky outcrop, bearing SE (184
magnetic) from the east tip of the western island, 16.50 m (54.1 ft) SE (149
magnetic) from bench mark 4851 A 1995, and just west of the vegetation line
approximately 1.6 m (5.25 ft) above the approximate high water line. The
eastern island and bench mark 4851 A 1995 are not visible from bench mark 4851 B
1995.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9454851 PUBLICATION DATE: 06/16/2011
Name: COCHRANE BAY, PR. WILLIAM SOUND
AK
NOAA Chart: 16705 Latitude: 60° 39.8' N ( 60.66330)
USGS Quad: Seward D-4 Longitude: 148° 21.4' W (-148.35700)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4851 A 1995
DESIGNATION: 945 4851 A 1995
MONUMENTATION: Survey disk VM#: 14704
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 60° 39.8' N ( 60.66330) LONGITUDE: 148° 21.4' W (-148.35700)
The bench mark is a disk located on the seaward extent of the ledge, bearing SE
(141 magnetic) from the east tip of the eastern island and south (180
magnetic) from the east tip of the western island, and just south of the
vegetation line approximately 2.0 m (6.6 ft) above the approximate high water
line.
BENCH MARK STAMPING: 4851 C 1995
DESIGNATION: 945 4851 C 1995
MONUMENTATION: Survey disk VM#: 14706
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 60° 39.8' N ( 60.66330) LONGITUDE: 148° 21.4' W (-148.35700)
The bench mark is a disk located on a ledge approximately 12.0 m (39.4 ft)
seaward of the north shore which is west of the large rock outcrop and east of a
large boulder 3.0 m x 3.0 m (9.8 ft x 9.8 ft) with a unique right angle on the
SW corner, bearing SE (144 magnetic) from the west tip of the eastern island
and SE (160 magnetic) from the east tip of the western island, 32 m (105 ft) SE
(140 magnetic) from bench mark 4851 B 1995, and just south of a small tuft of
grass and approximately 1.0 m (3.3 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: 9454851 PUBLICATION DATE: 06/16/2011
Name: COCHRANE BAY, PR. WILLIAM SOUND
AK
NOAA Chart: 16705 Latitude: 60° 39.8' N ( 60.66330)
USGS Quad: Seward D-4 Longitude: 148° 21.4' W (-148.35700)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4851 D 1995
DESIGNATION: 945 4851 D 1995
MONUMENTATION: Survey disk VM#: 14707
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 60° 39.8' N ( 60.66330) LONGITUDE: 148° 21.4' W (-148.35700)
The bench mark is a disk located on a rocky ledge on the north shore,
approximately 1.0 m (3.3 ft) seaward of treeline, bearing SE (156 magnetic)
from the west tip of the eastern island and SW (182 magnetic) from the east tip
of the western island, and 40.0 m (131.2 ft) SE (150 magnetic) from bench mark
4851 C 1995.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9454851 PUBLICATION DATE: 06/16/2011
Name: COCHRANE BAY, PR. WILLIAM SOUND
AK
NOAA Chart: 16705 Latitude: 60° 39.8' N ( 60.66330)
USGS Quad: Seward D-4 Longitude: 148° 21.4' W (-148.35700)
T I D A L D A T U M S
Tidal datums at COCHRANE BAY, PR. WILLIAM SOUND based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: September 1995 - September 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 = 3.731
MEAN HIGH WATER MHW = 3.457
MEAN SEA LEVEL MSL = 2.002
MEAN TIDE LEVEL MTL = 1.958
MEAN LOW WATER MLW = 0.460
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
4851 B 1995 4.133 0.676
4851 A 1995 4.692 1.235
4851 C 1995 4.091 0.634
4851 D 1995 4.353 0.896
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9454851 PUBLICATION DATE: 06/16/2011
Name: COCHRANE BAY, PR. WILLIAM SOUND
AK
NOAA Chart: 16705 Latitude: 60° 39.8' N ( 60.66330)
USGS Quad: Seward D-4 Longitude: 148° 21.4' W (-148.35700)
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.