U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 9462808 PUBLICATION DATE: 04/19/2010
Name: SCOTCH CAP, UNIMAK ISLAND
AK
NOAA Chart: 16520 Latitude: 54° 23.6' N ( 54.39364)
USGS Quad: UNIMAK (A-5) Longitude: 164° 44.7' W (-164.74572)
To reach the bench marks from the Dutch Harbor Spit Dock, proceed NNE 14.0 km
(7.6 nm) to Priest Rock, then NE for 39.8 km (21.5 nm) to the entrance to Akutan
Pass, then east for 75.7 km (40.9 nm) to Scotch Cap. The bench marks are along
the rock outcrops at either end of the bight below the lighthouse. The tide
gauge was located in the destroyed lighthouse and the sensors were located
offshore to the ESE.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 2 1937
DESIGNATION: 946 2808 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 19215
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Bedrock outcrop OPUS PID:
LATITUDE: 54° 23.6' N ( 54.39411) LONGITUDE: 164° 44.4' W (-164.73978)
The primary bench mark is set flush in the top of one of many ridges composed of
volcanic rock that extend into the ocean, 78.50 m (257.5 ft) ESE of the mouth of
a creek where it flows from the grass line to a cobble beach, 19 m (62.3 ft) NW
of the grass line, 12.90 m (42.3 ft) SSE of bench mark 946 2808 TIDAL 4, and
2.30 m (7.5 ft) above the grass line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9462808 PUBLICATION DATE: 04/19/2010
Name: SCOTCH CAP, UNIMAK ISLAND
AK
NOAA Chart: 16520 Latitude: 54° 23.6' N ( 54.39364)
USGS Quad: UNIMAK (A-5) Longitude: 164° 44.7' W (-164.74572)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4 1938
DESIGNATION: 946 2808 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 19216
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Bedrock outcrop OPUS PID#: BBBH99
LATITUDE: 54° 23.7' N ( 54.39422) LONGITUDE: 164° 44.4' W (-164.73981)
The bench mark is set flush in the top of one of many ridges composed of
volcanic rock that extend into the ocean, 68.49 m (224.7 ft) ESE of the mouth of
a creek where it flows from the grass line to a cobble beach, 12.89 m (42.3 ft)
NNW of bench mark 946 2719 TIDAL 2, 6.58 m (21.6 ft) SE of the grass line, and
1.49 m (4.9 ft) above the grass line.
BENCH MARK STAMPING: 2808 A 2009
DESIGNATION: 946 2808 A
MONUMENTATION: Tidal Station disk VM#: 19217
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock outcrop OPUS PID:
LATITUDE: 54° 23.6' N ( 54.39364) LONGITUDE: 164° 44.7' W (-164.74572)
The bench mark is set flush in the top of a 0.80 m (2.6 ft) tall by 0.40 m (1.3
ft) projection of bedrock, 141.98 m (465.8 ft) SW of the orange and white Coast
Guard Warning light at the top of the bluff, 67.00 m (219.8 ft) SW of the NW
corner of the lighthouse ruins, 38.98 m (127.9 ft) SE of the SE corner of a
concrete pad half way up the bluff, and 0.80 m (2.6 ft) above the surrounding
bedrock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9462808 PUBLICATION DATE: 04/19/2010
Name: SCOTCH CAP, UNIMAK ISLAND
AK
NOAA Chart: 16520 Latitude: 54° 23.6' N ( 54.39364)
USGS Quad: UNIMAK (A-5) Longitude: 164° 44.7' W (-164.74572)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 2808 B 2009
DESIGNATION: 946 2808 B
MONUMENTATION: Tidal Station disk VM#: 19218
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock outcrop OPUS PID:
LATITUDE: 54° 23.6' N ( 54.39386) LONGITUDE: 164° 44.6' W (-164.74397)
The bench mark is set flush in bedrock at the base of the cliff below the ruins
of the lighthouse, 29.20 m (95.8 ft) ENE of the west corner of the western most
concrete retaining wall, 8.90 m (29.2 ft) WSW of the west corner of a 17.19 m
(56.4 ft) concrete retaining wall, 1.19 m (3.9 ft) south of the face of the
cliff, 3.51 m (11.5 ft) below the top of the cliff and 0.75 m (2.5 ft) above
surrounding rock.
BENCH MARK STAMPING: 2808 C 2009
DESIGNATION: 946 2808 C
MONUMENTATION: Tidal Station disk VM#: 19219
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock outcrop OPUS PID:
LATITUDE: 54° 23.7' N ( 54.39475) LONGITUDE: 164° 44.3' W (-164.73861)
The bench mark is set flush in the top of a bedrock outcrop near a cobble beach,
97.08 m (318.5 ft) NE of bench mark 946 2719 TIDAL 4, 11.61 m (38.1 ft) SE of
the grass line, and 5.70 m (18.7 ft) south of a 12 cm (0.39 ft) rusty iron
eyebolt.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9462808 PUBLICATION DATE: 04/19/2010
Name: SCOTCH CAP, UNIMAK ISLAND
AK
NOAA Chart: 16520 Latitude: 54° 23.6' N ( 54.39364)
USGS Quad: UNIMAK (A-5) Longitude: 164° 44.7' W (-164.74572)
T I D A L D A T U M S
Tidal datums at SCOTCH CAP, UNIMAK ISLAND based on:
LENGTH OF SERIES: 4 MONTHS
TIME PERIOD: May 2009 - August 2009
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9459881 KING COVE, DEER PASSAGE, PACIFIC OCEAN
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 1.883
MEAN HIGH WATER MHW = 1.715
MEAN TIDE LEVEL MTL = 1.104
MEAN SEA LEVEL MSL = 1.103
MEAN LOW WATER MLW = 0.494
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
2 1937 4.904 3.189
4 1938 5.717 4.002
2808 A 2009 5.822 4.107
2808 B 2009 4.455 2.740
2808 C 2009 4.826 3.111
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9462808 PUBLICATION DATE: 04/19/2010
Name: SCOTCH CAP, UNIMAK ISLAND
AK
NOAA Chart: 16520 Latitude: 54° 23.6' N ( 54.39364)
USGS Quad: UNIMAK (A-5) Longitude: 164° 44.7' W (-164.74572)
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.