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National Ocean Service
Datums Page Page 1 of 5
Station ID: 9450997 PUBLICATION DATE: 07/14/2014
Name: EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-4 Longitude: 133° 19.8' W (-133.33000)
To reach the tidal bench marks by boat from Wrangell, AK head west 85 km (53 mi)
to Point Baker, turn left and proceed south through Sumner Strait for 19 km (12
mi) to the Shakan Bay, proceed SE 9 km (6 mi) to Shakan Strait, continue through
Shakan Strait for 9 km (6 mi) to the western entrance to Dry Pass, and proceed
east through Dry Pass for 10 km (6 mi) to the Forest Service Dock for El Capitan
Caves on Prince of Wales Island. The benchmarks are located along the shoreline
between the Forest Service Dock and Bear Valley Lodge. The tide gauges and staff
were located on the metal dock pilings.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 1957 NO 5
DESIGNATION: 945 0997 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 20872
AGENCY: U.S. Geological Survey (USGS) IDB PID#:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 56° 9.8' N ( 56.16408) LONGITUDE: 133° 19.9' W (-133.33189)
The primary bench mark is a disk set in a boulder under a tree, 42.47 m (139.3
ft) NW of tidal bench mark 945 0997 TIDAL 6, 18.61 (61.1 ft) NW of the west
corner of the riprap pad for the Bear Valley Lodge floating dock, 12.13 m (39.8
ft) SW of the west most piling for the Bear Valley Lodge deck (sloped distance),
and 0.35 m (1.1 ft) above ground.
BENCH MARK STAMPING: 1957 NO 6
DESIGNATION: 945 0997 TIDAL 6
ALIAS:
MONUMENTATION: Tidal Station disk VM#: 20873
AGENCY: U.S. Geological Survey (USGS) IDB PID#:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 56° 9.8' N ( 56.16386) LONGITUDE: 133° 19.9' W (-133.33133)
The bench mark is a disk set in a boulder near the HW line, 61.95 m (203.2 ft)
WNW of tidal bench mark 945 0997 LYN, 42.47 m (139.3 ft) SE of tidal bench mark
945 0997 TIDAL 5, 25.88 m (84.9 ft) ESE of the west corner of the riprap pad for
the Bear Valley Lodge floating dock, 10.25 m (33.6 ft) SSE of a 1.3 m (4.3 ft)
diameter evergreen, and 0.30 m (1.0 ft) above ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9450997 PUBLICATION DATE: 07/14/2014
Name: EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-4 Longitude: 133° 19.8' W (-133.33000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0997 A 2012
DESIGNATION: 946 0997 A
MONUMENTATION: Tidal Station disk VM#: 20874
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 9.8' N ( 56.16375) LONGITUDE: 133° 19.6' W (-133.32742)
The bench mark is a disk set in bedrock near the HW line, 192.78 m (632.5 mi)
east of tidal bench mark 945 0997 LYN, 170.93 m (560.8 ft) west of tidal bench
mark 945 0997 B, and 1 m (5 ft) S of the vegetation root line.
BENCH MARK STAMPING: 0997 B 2012
DESIGNATION: 945 0997 B
MONUMENTATION: Tidal Station disk VM#: 20875
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 56° 9.8' N ( 56.16353) LONGITUDE: 133° 19.5' W (-133.32469)
The bench mark is a disk set in a boulder near the HW line, 30 m (98 ft) west of
the location where a small creek exits the forest, and 4 m (13 ft) SSE of the
edge of the tree canopy.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9450997 PUBLICATION DATE: 07/14/2014
Name: EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-4 Longitude: 133° 19.8' W (-133.33000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: LYN
DESIGNATION: 945 0997 LYN
MONUMENTATION: Tidal Station disk VM#: 20876
AGENCY: US Army Corps of Engineers (USACE) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID#: BBCV41
LATITUDE: 56° 9.8' N ( 56.16356) LONGITUDE: 133° 19.8' W (-133.33050)
The bench mark is disk set in a sloping limestone bedrock outcropping, 17.25 m
(56.6 ft) WSW of a 0.2 m (0.7 ft) high metal eyebolt set in the limestone
outcropping, and 9 m (30 ft) SSW of the edge of the tree canopy.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9450997 PUBLICATION DATE: 07/14/2014
Name: EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-4 Longitude: 133° 19.8' W (-133.33000)
T I D A L D A T U M S
Tidal datums at EL CAPITAN PASSAGE based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: July 2012 - July 2012
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9451054 PORT ALEXANDER, BARANOF ISLAND
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 3.402
MEAN HIGH WATER MHW = 3.151
MEAN TIDE LEVEL MTL = 1.787
MEAN SEA LEVEL MSL = 1.786
MEAN LOW WATER MLW = 0.423
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
1957 NO 5 3.834 0.683
1957 NO 6 3.169 0.018
0997 A 2012 3.781 0.630
0997 B 2012 3.737 0.586
LYN 3.227 0.076
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9450997 PUBLICATION DATE: 07/14/2014
Name: EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-4 Longitude: 133° 19.8' W (-133.33000)
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.