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Datums Page Page 1 of 5
Station ID: 9450998 PUBLICATION DATE: 07/14/2014
Name: DRY PASS, EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-5 Longitude: 133° 24.8' W (-133.41300)
To reach the tidal bench marks by boat from Wrangell, AK head W 85 km (53 mi) to
Point Baker, turn left and proceed S 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 W entrance to Dry Pass, and proceed E through Dry
Pass for 4 km (2 mi) to Day Marker Green 7. The benchmarks are located along
the shoreline S and W of the day marker. The tide gauges were bolted to rock at
the point 200 m (656 ft) WSW of the day marker.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: TIDAL 1
DESIGNATION: 945 0998 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 20877
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 9.8' N ( 56.16267) LONGITUDE: 133° 24.9' W (-133.41531)
The primary bench mark is a disk set in a rock outcrop point SW of the west
entrance to Dry Pass, 49.0 m (160.8 ft) WSW of the center of the prominent rock
outcrop orientated to the NE, 1.10 m (3.61 ft) NNW of the tree line, and 1.00 m
(3.3 ft) above grade.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9450998 PUBLICATION DATE: 07/14/2014
Name: DRY PASS, EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-5 Longitude: 133° 24.8' W (-133.41300)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: TIDAL 3
DESIGNATION: 945 0998 TIDAL 3
MONUMENTATION: Tidal Station disk VM#: 20878
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID#: BBCV62
LATITUDE: 56° 9.8' N ( 56.16264) LONGITUDE: 133° 24.9' W (-133.41569)
The bench mark is a disk set in a rock outcrop point SW of the west entrance to
Dry Pass, 2.62 m (8.6 ft) west of a 1.80 m high x 5.00 m wide (5.9 ft ft high by
x 16.4 ft wide) rocky knob.
BENCH MARK STAMPING: 0998 A 2012
DESIGNATION: 945 0998 A
MONUMENTATION: Tidal Station disk VM#: 20879
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 9.7' N ( 56.16133) LONGITUDE: 133° 24.9' W (-133.41575)
The bench mark is a disk set in a rock outcrop along the east side of a bight of
tidal-flat lands SW of the west entrance to Dry Pass, 2.80 m (9.2 ft) WSW of the
vegetation line at the base of the trees, and 0.40 m (1.3 ft) above grade.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9450998 PUBLICATION DATE: 07/14/2014
Name: DRY PASS, EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-5 Longitude: 133° 24.8' W (-133.41300)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 0998 B 2012
DESIGNATION: 945 0998 B
MONUMENTATION: Tidal Station disk VM#: 20880
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 9.6' N ( 56.16039) LONGITUDE: 133° 24.9' W (-133.41447)
The bench mark is a disk set in a 1.70 m (5.6 ft) wide exposed portion of
bedrock along the east side of a bight of tidal-flat lands SW of the west
entrance to Dry Pass, 15.0 m (49.2 ft) NE of a grass and bolder high water line
boundary, 4.30 m (14.1 ft) SW of the tree line, and 0.40 m (1.3 ft) above grade.
BENCH MARK STAMPING: 0998 C 2012
DESIGNATION: 945 0998 C
MONUMENTATION: Tidal Station disk VM#: 20881
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 56° 9.8' N ( 56.16264) LONGITUDE: 133° 24.8' W (-133.41328)
The bench mark is a disk set in a rock outcrop of the west entrance to Dry Pass,
87.30 m (286.4 ft) south of Day Marker Green 7 , 75 m (246 ft) east of a
prominent rock outcrop, and 2.7 m (8.9 ft) SE of the high water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9450998 PUBLICATION DATE: 07/14/2014
Name: DRY PASS, EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-5 Longitude: 133° 24.8' W (-133.41300)
T I D A L D A T U M S
Tidal datums at DRY PASS, 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 = 3.580
MEAN HIGH WATER MHW = 3.329
MEAN TIDE LEVEL MTL = 1.877
MEAN SEA LEVEL MSL = 1.872
MEAN LOW WATER MLW = 0.425
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
TIDAL 1 3.964 0.635
TIDAL 3 4.132 0.803
0998 A 2012 3.008 -0.321
0998 B 2012 3.961 0.632
0998 C 2012 3.495 0.166
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9450998 PUBLICATION DATE: 07/14/2014
Name: DRY PASS, EL CAPITAN PASSAGE
AK
NOAA Chart: 17387 Latitude: 56° 9.8' N ( 56.16330)
USGS Quad: PETERSBURG A-5 Longitude: 133° 24.8' W (-133.41300)
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.