U.S. DEPARTMENT OF COMMERCE
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National Ocean Service
Datums Page Page 1 of 5
Station ID: 9451376 PUBLICATION DATE: 12/08/2007
Name: DOROTHY COVE, NECKER BAY
AK
NOAA Chart: 17328 Latitude: 56° 43.3' N ( 56.72170)
USGS Quad: PORT ALEXANDR (D-4) Longitude: 135° 4.5' W (-135.07500)
To reach the bench marks from Sitka, AK, via boat, go approximately 25 km (13
NM) SSW through Sitka Sound, at Biorka Island, continue SE for 33 km (18 NM),
at the Guibert Islets, continue NE for 11.5 km (6.2 NM) through Necker Bay, to
Dorothy Cove. The area is at the southern end of Dorothy Cove, and consists of
an island, approximately 300m wide, at the mouth of Toy Harbor. The island is
approximately 200 m ENE from the islet at the mouth of Toy Harbor. The tide
gauge was installed on the beach and the bench marks are located in the vicinity
on the beach.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 1376 A 2007
DESIGNATION: 945 1376 A
MONUMENTATION: Tidal Station disk VM#: 18453
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Boulder outcrop OPUS PID:
LATITUDE: 56° 43.3' N ( 56.72170) LONGITUDE: 135° 4.7' W (-135.07800)
The primary bench mark set in a 1.50 m x 1.50 m (4.9 ft x 4.9 ft) boulder
outcropping on the west shore of the large island NE of Toy Harbor, 209.0 m
(685.7 ft) from the island west of the entrance to Toy Harbor, 84.00 m (275.6
ft) from the south point of the larger island, 71.00 m (232.9 ft) from bench
mark 945 1376 B, and 1.50 m (4.9 ft) above the approximate high water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9451376 PUBLICATION DATE: 12/08/2007
Name: DOROTHY COVE, NECKER BAY
AK
NOAA Chart: 17328 Latitude: 56° 43.3' N ( 56.72170)
USGS Quad: PORT ALEXANDR (D-4) Longitude: 135° 4.5' W (-135.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1376 B 2007
DESIGNATION: 945 1376 B
MONUMENTATION: Tidal Station disk VM#: 18454
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 56° 43.3' N ( 56.72170) LONGITUDE: 135° 4.7' W (-135.07800)
The bench mark is set in a 1.00 m x 1.00 m (3.3 ft x 3.3 ft) granite boulder on
the north shore of the SW bight on the large island east of Toy Harbor, 240.0 m
(787.4 ft) from the island west of the entrance to Toy Harbor, 72.30 m (237.2
ft) from bench mark 945 1376 A, 60.00 m (196.9 ft) from the south point of the
NW bight of the island, 45.00 m (147.6 ft) from the west point of the SW bight
of the island, and 1.00 m (3.3 ft) above the approximate high water line.
BENCH MARK STAMPING: 1376 C 2007
DESIGNATION: 945 1376 C
MONUMENTATION: Tidal Station disk VM#: 18455
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 56° 43.2' N ( 56.72000) LONGITUDE: 135° 4.7' W (-135.07800)
The bench mark is set in a 1.00 m x 1.00 m (3.3 x3.3 ft) boulder on the west
point of the SW bight on the of the large island east of Toy Harbor, 224.0 m
(734.9 ft) from the small island west of the entrance to Toy Harbor, 84.00 m
(275.6 ft) from bench mark 945 1376 A, 60.00 m (196.9 ft) from the SW point of
the NW bight of the island, and 0.50 m (1.6 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: 9451376 PUBLICATION DATE: 12/08/2007
Name: DOROTHY COVE, NECKER BAY
AK
NOAA Chart: 17328 Latitude: 56° 43.3' N ( 56.72170)
USGS Quad: PORT ALEXANDR (D-4) Longitude: 135° 4.5' W (-135.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 3 1924
DESIGNATION: 945 1376 TIDAL 3
MONUMENTATION: Tidal Station disk VM#: 18456
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock OPUS PID:
LATITUDE: 56° 43.3' N ( 56.72170) LONGITUDE: 135° 4.7' W (-135.07800)
The bench mark is cemented atop a 3.00 m x 3.00 m (9.8 ft x 9.8 ft) rounded mass
of broken bedrock east of the mainland gravel beach and SSE of the large island,
on which the tide gauge and staff reside, 385.0 m (1,263.1 ft) from the south
point of the small island west of the entrance to Toy Harbor, 152.0 m (498.7 ft)
from bench mark 945 1376 C, 145.0 m (475.7 ft) from the SW point of the SW bight
on the large island, 110.0 m (360.9 ft) from the unstamped bench mark 945 1376
TIDAL 1, and 0.25 m (0.8 ft) above the approximate high water line.
BENCH MARK STAMPING: 1 1924
DESIGNATION: 945 1376 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 18457
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 43.3' N ( 56.72170) LONGITUDE: 135° 4.6' W (-135.07700)
The bench mark is cemented atop a rounded 3.00 m x 3.00 m (9.8 ft x 9.8 ft) knob
of broken bedrock on the protected south side of the large island, on which the
tide gauge and staff reside, 213.90 m (701.7 ft) bearing from the small island
to the east, 116.0 m (380.6 ft) 945 1376 TIDAL 3, 60.00 m (196.8 ft) from the
tip of the small mainland peninsula ESE, NNE from the peak of the 605.0 m (1,970
ft) mountain to the south, and 1.00 m (3.3 ft) above the approximate high water
line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9451376 PUBLICATION DATE: 12/08/2007
Name: DOROTHY COVE, NECKER BAY
AK
NOAA Chart: 17328 Latitude: 56° 43.3' N ( 56.72170)
USGS Quad: PORT ALEXANDR (D-4) Longitude: 135° 4.5' W (-135.07500)
T I D A L D A T U M S
Tidal datums at DOROTHY COVE, NECKER BAY based on:
LENGTH OF SERIES: 4 MONTHS
TIME PERIOD: April 2007 - July 2007
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9451600 SITKA, BARONOF ISLAND, SITKA SOUND
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 2.928
MEAN HIGH WATER MHW = 2.699
MEAN TIDE LEVEL MTL = 1.559
MEAN SEA LEVEL MSL = 1.553
MEAN LOW WATER MLW = 0.419
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
1376 A 2007 3.923 1.224
1376 B 2007 3.833 1.134
1376 C 2007 3.267 0.567
3 1924 3.869 1.170
1 1924 3.102 0.402
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9451376 PUBLICATION DATE: 12/08/2007
Name: DOROTHY COVE, NECKER BAY
AK
NOAA Chart: 17328 Latitude: 56° 43.3' N ( 56.72170)
USGS Quad: PORT ALEXANDR (D-4) Longitude: 135° 4.5' W (-135.07500)
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.