U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
Station ID: 9454642 PUBLICATION DATE: 03/29/2011
Name: LOUIS BAY
AK
NOAA Chart: 16700 Latitude: 60° 27.7' N ( 60.46170)
USGS Quad: Seward B-2 Longitude: 147° 40.3' W (-147.67200)
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 4642 A 1978
DESIGNATION: 945 4642 A
MONUMENTATION: Bench Mark disk VM#: 15174
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Drill Hole in a Rock Outcrop OPUS PID:
LATITUDE: 60° 27.7' N ( 60.46170) LONGITUDE: 147° 40.3' W (-147.67200)
The bench mark is a disk set in a drill hole on top of a northern most point of
a rock outcropping south of a large offshore rock in the southern end of the
eastern arm of Louis Bay, Knight Island, 14.17 m (46.5 ft ) north of bench mark
4642 B 1978, 12.19 m (40.0 ft) west of bench mark 4642 C 1978, and approximately
1.22 m (4.0 ft) above apparent high water line.
BENCH MARK STAMPING: 4642 B 1978
DESIGNATION: 945 4642 B
MONUMENTATION: Bench Mark disk VM#: 15175
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Drill Hole in a Rock Outcrop OPUS PID:
LATITUDE: 60° 27.7' N ( 60.46170) LONGITUDE: 147° 40.3' W (-147.67200)
The bench mark is a disk set in a drill hole on the western side on top of a
projecting rock point on the south of a large offshore rock in the southern end
of the eastern arm of Louis Bay, 14.48 m (47.5 ft) north of bench mark NO 1,
14.17 m (46.5 ft) south of bench mark 4642 A 1978, 1.22 m (4.0 ft) SE of the NW
face of the rock point, and approximately 3.28 m (10 ft) above the apparent high
water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
Station ID: 9454642 PUBLICATION DATE: 03/29/2011
Name: LOUIS BAY
AK
NOAA Chart: 16700 Latitude: 60° 27.7' N ( 60.46170)
USGS Quad: Seward B-2 Longitude: 147° 40.3' W (-147.67200)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4642 C 1978
DESIGNATION: 945 4642 C
MONUMENTATION: Bench Mark disk VM#: 15178
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Drill Hole in a Rock Outcrop OPUS PID:
LATITUDE: 60° 27.7' N ( 60.46170) LONGITUDE: 147° 40.3' W (-147.67200)
The bench mark is a disk set in a drill hole in the top of the eastern side of a
projecting rock point south of a large offshore rock in the southern end of the
eastern arm of Louis Bay, 12.22 m (40.1 ft) west of bench mark 4642 A 1978, 10 m
(34 ft) NE of a 5 m (15 ft) high stump, 3 m (10 ft) south of the north edge of
the rock, 1.2 m (4 ft) west of the east edge of the rock, and approximately 1 m
(3 ft) above the apparent high water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
Station ID: 9454642 PUBLICATION DATE: 03/29/2011
Name: LOUIS BAY
AK
NOAA Chart: 16700 Latitude: 60° 27.7' N ( 60.46170)
USGS Quad: Seward B-2 Longitude: 147° 40.3' W (-147.67200)
T I D A L D A T U M S
Tidal datums at LOUIS BAY based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: August 1998 - September 1998
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9454240 VALDEZ, PRINCE WILLIAM SOUND
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 3.674
MEAN HIGH WATER MHW = 3.404
MEAN SEA LEVEL MSL = 1.975
MEAN TIDE LEVEL MTL = 1.940
MEAN LOW WATER MLW = 0.477
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
4642 A 1978 4.160 0.756
4642 B 1978 6.047 2.643
4642 C 1978 3.874 0.470
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
Station ID: 9454642 PUBLICATION DATE: 03/29/2011
Name: LOUIS BAY
AK
NOAA Chart: 16700 Latitude: 60° 27.7' N ( 60.46170)
USGS Quad: Seward B-2 Longitude: 147° 40.3' W (-147.67200)
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.