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National Ocean Service
Datums Page Page 1 of 5
Station ID: 9451421 PUBLICATION DATE: 06/16/2004
Name: GOLF ISLAND, NECKER ISLANDS
AK
NOAA Chart: 17320 Latitude: 56° 47.2' N ( 56.78670)
USGS Quad: PORT ALEXANDER (D-5) Longitude: 135° 23.6' W (-135.39300)
To reach the tidal bench marks via boat from Sitka, Alaska, turn left after the
Sitka Breakwater. Proceed until passing Batterly Island by about 0.46 km (0.25
nm). Then come left to a course of about 197 T (171 magnetic). Continue on
course for about 18.5 km (10 nm) until Peisar Island is abeam to port. Then
change course as needed to transit Biorka Channel located between Biorka Island
ad Ataku Island. Ease left around Necker Islands passing Golovni, and Urilof
Islands. Continue left until John Rock is abeam to port. The southern edge of
Golf Island bears about 078 T (052 magnetic) at a range of 4.6 km (2.5 nm) from
the southern edge of John Rock. The bench marks are located in a small cove SE
of the Jackknife Islands on the western side of Golf Island, Alaska, at
approximately 56 47' 10.46" N, 135 23' 40.29" W. The tide gauge was installed
on the beach.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 2
DESIGNATION: 945 1421 TIDAL 2
ALIAS: 1942
MONUMENTATION: Tidal Station disk VM#: 17134
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 47.2' N ( 56.78670) LONGITUDE: 135° 23.6' W (-135.39300)
The primary bench mark is a disk set in the highest of mass rough bedrock,
boulders of lower elevation surrounding bedrock, sitting in a slight depression
at the top end and on the west side of Golf Island, about midway from the
deepest part of rock cove to its southern entrance, 7 m (22 ft) from the
vegetation line, 5 m (18 ft) above apparent mean lower low water, and 4 m (13
ft) from and about 2 m (6 ft) above the high water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9451421 PUBLICATION DATE: 06/16/2004
Name: GOLF ISLAND, NECKER ISLANDS
AK
NOAA Chart: 17320 Latitude: 56° 47.2' N ( 56.78670)
USGS Quad: PORT ALEXANDER (D-5) Longitude: 135° 23.6' W (-135.39300)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1421 A 2003
DESIGNATION: 945 1421 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 17131
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock shelf OPUS PID:
LATITUDE: 56° 47.2' N ( 56.78670) LONGITUDE: 135° 23.6' W (-135.39300)
The bench mark disk is a disk set flush into a large bedrock shelf, the
northern-most bench mark at the site on the western side of Golf Island located
730 m (2,395 ft) NE of the Beehive, 111 m (364 ft) north of bench mark 1421 B
2003, 8 m (27 ft) from the tree line, and 9 m (31 ft) horizontally from and 1 m
(4 ft) vertically above the apparent mean high water line.
BENCH MARK STAMPING: 1421 B 2003
DESIGNATION: 945 1421 B TIDAL
MONUMENTATION: Tidal Station disk VM#: 17132
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock outcropping OPUS PID:
LATITUDE: 56° 47.2' N ( 56.78670) LONGITUDE: 135° 23.6' W (-135.39300)
The bench mark disk is a disk set flush on top of a large irregular shaped gray
rock part of a bedrock outcropping, located at about the mid point of the small
cove on the western side of Golf Island, flush with the vegetation line, 111 m
(364 ft) south of bench mark 1421 A, 55 m (180 ft) NE of bench mark NO 3, and 16
m (54 ft) horizontally and 2 m (8 ft) vertically above the apparent mean high
water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9451421 PUBLICATION DATE: 06/16/2004
Name: GOLF ISLAND, NECKER ISLANDS
AK
NOAA Chart: 17320 Latitude: 56° 47.2' N ( 56.78670)
USGS Quad: PORT ALEXANDER (D-5) Longitude: 135° 23.6' W (-135.39300)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 1
DESIGNATION: 945 1421 TIDAL 1
ALIAS: 1942
MONUMENTATION: Tidal Station disk VM#: 17133
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 47.2' N ( 56.78670) LONGITUDE: 135° 23.6' W (-135.39300)
The bench mark is a disk set in bedrock on rounded ledge overlooking rocky cove,
0.8 km (0.5 mi) from southern end and on the west side of Golf Island, on smooth
gray rock marking southern etrance to rocky cove, 9 m (30 ft) from tree line, 2
m (6 ft) below the highest part of rock, and 5 m (15 ft) above apparent mean low
water.
BENCH MARK STAMPING: NO 3
DESIGNATION: 945 1421 TIDAL 3
ALIAS: 1942
MONUMENTATION: Tidal Station disk VM#: 17135
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 47.2' N ( 56.78670) LONGITUDE: 135° 23.6' W (-135.39300)
The bench mark is a disk set in the top of a large gray portion of bedrock which
slopes gently towards the water and is consideraly cracked, 0.8 km (0.5 mi) from
the southern end and on the west side of Golf Island and just SW of the deepest
point of rocky cove, 7 m (22 ft) from the vegetation line, 6 m (19 ft) above the
apparent mean lower low water line, and 3 m (11 ft) from and 3 m (11 ft) above
the high water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9451421 PUBLICATION DATE: 06/16/2004
Name: GOLF ISLAND, NECKER ISLANDS
AK
NOAA Chart: 17320 Latitude: 56° 47.2' N ( 56.78670)
USGS Quad: PORT ALEXANDER (D-5) Longitude: 135° 23.6' W (-135.39300)
T I D A L D A T U M S
Tidal datums at GOLF ISLAND, NECKER ISLANDS based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: May 9 2003 - June 26 2003
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 = 2.958
MEAN HIGH WATER MHW = 2.726
MEAN TIDE LEVEL MTL = 1.578
MEAN SEA LEVEL MSL = 1.572
MEAN LOW WATER MLW = 0.431
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 2 5.030 2.304
1421 A 2003 4.303 1.577
1421 B 2003 5.452 2.726
NO 1 4.644 1.918
NO 3 5.200 2.475
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9451421 PUBLICATION DATE: 06/16/2004
Name: GOLF ISLAND, NECKER ISLANDS
AK
NOAA Chart: 17320 Latitude: 56° 47.2' N ( 56.78670)
USGS Quad: PORT ALEXANDER (D-5) Longitude: 135° 23.6' W (-135.39300)
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.