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National Ocean Service
Datums Page Page 1 of 5
Station ID: 9451853 PUBLICATION DATE: 03/04/2009
Name: SERGIUS NARROWS
AK
NOAA Chart: 17323 Latitude: 57° 24.6' N ( 57.41000)
USGS Quad: SITKA (B-5) Longitude: 135° 37.6' W (-135.62700)
To reach the tidal bench marks from Sitka, AK, proceed about 34 km (21 mi) north
through Sitka Sound to Salisbury Sound, then proceed NE though the Sound to
Kakul Narrows and then continue north towards Suloia Point. Proceed to a small
cove on the north shore of Sergius Narrows 275 m (900 ft) beyond Sergius Point
Light between Sergius Point and Shoal Point, due north of Pinta Head and across
from Buoy 10 (approximate location 57 degrees 24.58 N latitude and 135 degrees
37.53 W longitude). The bench marks are located along the shore in rock outcrop
and the gauge was located on the beach.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: SHOAL 2 NO 2 1950
DESIGNATION: 945 1853 SHOAL 2 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 14457
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AH7509
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 57° 24.6' N ( 57.41000) LONGITUDE: 135° 37.6' W (-135.62700)
The primary bench mark is a disk set in an outcropping rock on Shoal Point, on
the western side of Sergius Narrows, on the first point of the land east of
Sergius Narrows Light, and about 1 m (4 ft) above apparent high water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9451853 PUBLICATION DATE: 03/04/2009
Name: SERGIUS NARROWS
AK
NOAA Chart: 17323 Latitude: 57° 24.6' N ( 57.41000)
USGS Quad: SITKA (B-5) Longitude: 135° 37.6' W (-135.62700)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: SHOAL 2 1950
DESIGNATION: 945 1853 SHOAL 2
MONUMENTATION: Triangulation Station disk VM#: 14456
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: UV0768
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 57° 24.6' N ( 57.41000) LONGITUDE: 135° 37.6' W (-135.62700)
The bench mark is a disk set in an outcropping bedrock on the tip of Shoal
Point, on the western side of Sergius Narrows, on the first point of the land
east of Sergius Narrows Light, at the edge of the tree line, about 0.91 m (3.0
ft) south and about 0.3 m (1 ft) below the apparent high water line.
BENCH MARK STAMPING: SHOAL 2 NO 1 1950
DESIGNATION: 945 1853 SHOAL 2 TIDAL 1
MONUMENTATION: Reference Mark disk VM#: 14458
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AH7511
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 57° 24.6' N ( 57.41000) LONGITUDE: 135° 37.6' W (-135.62700)
The bench mark is a disk set in a large boulder on Shoal Point, on the western
side of Sergius Narrows, on the first point of the land east of Sergius Narrows
Light, and about 1 m (3 ft) above apparent high water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9451853 PUBLICATION DATE: 03/04/2009
Name: SERGIUS NARROWS
AK
NOAA Chart: 17323 Latitude: 57° 24.6' N ( 57.41000)
USGS Quad: SITKA (B-5) Longitude: 135° 37.6' W (-135.62700)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1853 A 2002
DESIGNATION: 945 1853 A
MONUMENTATION: Tidal Station disk VM#: 16670
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Granite boulder OPUS PID:
LATITUDE: 57° 24.6' N ( 57.41000) LONGITUDE: 135° 37.6' W (-135.62700)
The bench mark is a disk set in a large granite boulder of size 1.5 m x 1.2 m (5
ft x 4 ft), 56 m (183 ft) SW from bench mark 1853 B 2002, 7.70 m (25.3 ft) from
vegetation line, and 1 m (3 ft) above the apparent high water line.
BENCH MARK STAMPING: 1853 B 2002
DESIGNATION: 945 1853 B
MONUMENTATION: Tidal Station disk VM#: 16671
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Granite boulder OPUS PID:
LATITUDE: 57° 24.6' N ( 57.41000) LONGITUDE: 135° 37.6' W (-135.62700)
The bench mark is a disk set in a large prominate square granite boulder of size
3 m x 2.7 m (10 ft x 9 ft), 56 m (184 ft) NE along the high water line from
bench mark 1853 A 2002, 23.1 m (75.8 ft) south from bench mark SHOAL 2 NO 2
1950, 12 m (40 ft) SW (220 degrees magnetic) from a large sloping, flat faced,
granite outcrop, 7.50 m (24.6 ft) from the vegetation line, and 1 m (3 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: 9451853 PUBLICATION DATE: 03/04/2009
Name: SERGIUS NARROWS
AK
NOAA Chart: 17323 Latitude: 57° 24.6' N ( 57.41000)
USGS Quad: SITKA (B-5) Longitude: 135° 37.6' W (-135.62700)
T I D A L D A T U M S
Tidal datums at SERGIUS NARROWS based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: April 2002 - May 2002
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 = 3.973
MEAN HIGH WATER MHW = 3.709
MEAN SEA LEVEL MSL = 2.122
MEAN TIDE LEVEL MTL = 2.090
MEAN LOW WATER MLW = 0.471
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
SHOAL 2 NO 2 1950 4.389 0.680
SHOAL 2 1950 3.064 -0.644
SHOAL 2 NO 1 1950 4.302 0.593
1853 A 2002 4.349 0.640
1853 B 2002 4.019 0.311
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9451853 PUBLICATION DATE: 03/04/2009
Name: SERGIUS NARROWS
AK
NOAA Chart: 17323 Latitude: 57° 24.6' N ( 57.41000)
USGS Quad: SITKA (B-5) Longitude: 135° 37.6' W (-135.62700)
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.