U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 9450938 PUBLICATION DATE: 02/15/2011
Name: THORNE ISLAND, WHALE PASSAGE
AK
NOAA Chart: 17400 Latitude: 56° 3.5' N ( 56.05830)
USGS Quad: PETERSBURG A-3 Longitude: 132° 58.1' W (-132.96800)
To reach the tidal bench marks from Wrangell via boat, proceed 12.5 km (6.8 nm)
west to Stikine Strait, then continue south through the Strait to the Triplets,
Deichman Rock, and Kashevarof Passage for approximately 50 km (27 nm). Then
proceed NW through Kashevarof Passage for 13 km (7 nm) to Thorne Island. Then
head SW between Thorne Island and Stevenson Island for approximately 4 km (2 nm)
to a small islet at the entrance to Whale Passage, 40 m (131 ft) south from the
SE corner of Thorne Island. Two bench marks are located on south tip of Thorne
Island and three bench marks are located on this small islaet. The tide gauge
was located on the small islet.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: BM 1 1967
DESIGNATION: 945 0938 TIDAL 1
MONUMENTATION: Topographic Station disk VM#: 16481
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 56° 3.5' N ( 56.05830) LONGITUDE: 132° 59.1' W (-132.98500)
The primary bench mark is a disk set in a flat rock which slopes lightly seward,
on a small wooded islet connected to the SE corner of Thorne Island at low water
and located at the entrance to Whale Passage, and 8.99 m (29.5 ft) SE from the
highest point on the islet.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9450938 PUBLICATION DATE: 02/15/2011
Name: THORNE ISLAND, WHALE PASSAGE
AK
NOAA Chart: 17400 Latitude: 56° 3.5' N ( 56.05830)
USGS Quad: PETERSBURG A-3 Longitude: 132° 58.1' W (-132.96800)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: BM 2 1967
DESIGNATION: 945 0938 TIDAL 2
MONUMENTATION: Topographic Station disk VM#: 16482
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 56° 3.5' N ( 56.05830) LONGITUDE: 132° 59.1' W (-132.98500)
The bench mark is a disk set in a rock outcrop on the SE corner of Thorne
Island, 95 m (312 ft) NW of the highest point on a small wooded island which is
connected to the SE corner of Thorne Island at low water, 53.28 m (174.8 ft) NW
(270 degrees magnetic) from bench mark 0938 B 2001, 7.71 m (25.3 ft) seaward of
the treeline, and at the apparent high waterline .
BENCH MARK STAMPING: BM 3 1967
DESIGNATION: 945 0938 TIDAL 3
MONUMENTATION: Topographic Station disk VM#: 16483
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 56° 3.5' N ( 56.05830) LONGITUDE: 132° 59.1' W (-132.98500)
The bench mark is a disk set in a rock outcrop on a small islet, 20 m (66 ft) NW
from the highest point of a small islet which is connected to the SE corner of
Thorne Island at low water, 13.3 m (44.3 ft) north (355 degrees magnetic) from
bench mark 0938 A 2001, 6.5 m (21.6 ft) north of a large fallen tree trunk, and
2 m (6 ft) above the apparent high waterline.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9450938 PUBLICATION DATE: 02/15/2011
Name: THORNE ISLAND, WHALE PASSAGE
AK
NOAA Chart: 17400 Latitude: 56° 3.5' N ( 56.05830)
USGS Quad: PETERSBURG A-3 Longitude: 132° 58.1' W (-132.96800)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0938 A 2001
DESIGNATION: 945 0938 A
MONUMENTATION: Tidal Station disk VM#: 16484
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 3.5' N ( 56.05830) LONGITUDE: 132° 59.1' W (-132.98500)
The bench mark is a disk set in a flat bedrock face on a small wooded islet
located 40 m (133 ft) south of the SE corner of Thorne Island, 21.12 m (69.3
ft) west (250 degrees magnetic ) from bench mark BM 1 1967, 13.50 m (44.3 ft)
south (175 degrees magnetic) from bench mark BM 3 1967, 5 m (17 ft) from the
apparent high water line, and at the edge of the vegetation line,.
BENCH MARK STAMPING: 0938 B 2001
DESIGNATION: 945 0938 B
MONUMENTATION: Tidal Station disk VM#: 16485
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock ledge OPUS PID:
LATITUDE: 56° 3.5' N ( 56.05830) LONGITUDE: 132° 59.1' W (-132.98500)
The bench mark is a disk set in a bedrock ledge that is connected to a small
islet at low water and that extends SE off the southern corner of Thorne Island,
55.84 m (183.2 ft) north of the high point of the small islet, 53.28 m (174.8
ft) east (090 degrees magnetic) from bench mark BM 2 1967, 35.54 m (116.6 ft)
north (350 degrees magnetic) from bench mark BM 3 1967, 11.37 m (37.3 ft) inland
from the seaward extent of the ledge, and 5 m (16 ft) above the apparent high
water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9450938 PUBLICATION DATE: 02/15/2011
Name: THORNE ISLAND, WHALE PASSAGE
AK
NOAA Chart: 17400 Latitude: 56° 3.5' N ( 56.05830)
USGS Quad: PETERSBURG A-3 Longitude: 132° 58.1' W (-132.96800)
T I D A L D A T U M S
Tidal datums at THORNE ISLAND, WHALE PASSAGE based on:
LENGTH OF SERIES: 26 Days
TIME PERIOD: April 19 2001 - May 14 2001
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9450460 KETCHIKAN, TONGASS NARROWS
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 4.861
MEAN HIGH WATER MHW = 4.599
MEAN TIDE LEVEL MTL = 2.534
MEAN SEA LEVEL MSL = 2.519
MEAN LOW WATER MLW = 0.469
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
BM 1 1967 6.093 1.494
BM 2 1967 5.435 0.836
BM 3 1967 6.591 1.993
0938 A 2001 5.672 1.073
0938 B 2001 4.802 0.203
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9450938 PUBLICATION DATE: 02/15/2011
Name: THORNE ISLAND, WHALE PASSAGE
AK
NOAA Chart: 17400 Latitude: 56° 3.5' N ( 56.05830)
USGS Quad: PETERSBURG A-3 Longitude: 132° 58.1' W (-132.96800)
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.