U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
Station ID: 9450973 PUBLICATION DATE: 12/02/2010
Name: BLASHKE ISALND, CLARENCE STRAIT
AK
NOAA Chart: 17401 Latitude: 56° 7.6' N ( 56.12670)
USGS Quad: PETERSBURG (A-3) Longitude: 132° 53.7' W (-132.89500)
To reach the bench marks from the village of Coffman Cove via boat, proceed 0.9
km (0.5 nm) NNW from the small harbor in Coffman Cove, then 2 km (1 nm) NNE into
Kashevarof Passage, then 11 km (6 nm) NNW to the west entrance into Blashke
Island. Then proceed 1 km (0.5 nm) along the NW side of a narrow channel to
where two channels diverge, then 0.4 km (0.2 nm) SE through the right most
channel, then 0.4 km (0.2 nm) north throgh a narrow channel past the end of the
island to the east and past a point of land on the west, then 0.2 km (0.1 nm)
ENE through a narrow opening which is a rapids at low tide, and then 1 km (0.5
nm) NNE to the SE side of an island. The tidal bench marks are along the SE
side of the island in the exposed rock along the water. The zoning gauge was
located on the beach.
T I D A L B E N C H M A R K S
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 9450973 PUBLICATION DATE: 12/02/2010
Name: BLASHKE ISALND, CLARENCE STRAIT
AK
NOAA Chart: 17401 Latitude: 56° 7.6' N ( 56.12670)
USGS Quad: PETERSBURG (A-3) Longitude: 132° 53.7' W (-132.89500)
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: A
DESIGNATION: 945 0973 A
ALIAS: 0973 A 2002
MONUMENTATION: Bolt VM#: 16885
AGENCY: LCMF, Inc. IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 0° 0.0' N ( 0.00000) LONGITUDE: 0° 0.0' W ( 0.00000)
The primary bench mark is a 1/2" diameter expansion bolt set in bedrock and
secured with nut, washer, and concrete, 40 m (131 ft) SW of bench mark 945 0973
B, 15 m (48 ft) north of a rock point on the water's edge at the entrance to a
tidal slough which wraps around behind the tide station, 10 m (34 ft) south from
the ceder trees inland of the bench mark, 7 m (23 ft) west from the closest edge
of a vertical rock face along the water's edge, and 0.03 m (0.1 ft) above
ground. Note: The side of the nut is stamped "A".
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 9450973 PUBLICATION DATE: 12/02/2010
Name: BLASHKE ISALND, CLARENCE STRAIT
AK
NOAA Chart: 17401 Latitude: 56° 7.6' N ( 56.12670)
USGS Quad: PETERSBURG (A-3) Longitude: 132° 53.7' W (-132.89500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING:
DESIGNATION: 945 0973 B
ALIAS: 0973 B 2002
MONUMENTATION: See descriptive text VM#: 16886
AGENCY: LCMF, Inc. IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 0° 0.0' N ( 0.00000) LONGITUDE: 0° 0.0' W ( 0.00000)
The bench mark is a tip of an orange painted triangular point of bedrock in a
broken rock draw leading up from the water's edge, 40 m (131 ft) NE from bench
mark 945 0973 A, 12 m (39 ft) from a high rock point and angle point in the
shoreline, and 4 m (13 ft) SE from the top of the rock draw and the edge of the
vegetation. Note: The rock has "B" chiseled on the face with a chiseled line
leading to the point of the rock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 9450973 PUBLICATION DATE: 12/02/2010
Name: BLASHKE ISALND, CLARENCE STRAIT
AK
NOAA Chart: 17401 Latitude: 56° 7.6' N ( 56.12670)
USGS Quad: PETERSBURG (A-3) Longitude: 132° 53.7' W (-132.89500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING:
DESIGNATION: 945 0973 C
ALIAS: 0973 C 2002
MONUMENTATION: Bolt VM#: 16887
AGENCY: LCMF, Inc IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 0° 0.0' N ( 0.00000) LONGITUDE: 0° 0.0' W ( 0.00000)
The bench mark is a 1/2" diameter expansion bolt set in bedrock on top of a rock
face along the water's edge and secured with nut, washer, and concrete, 55 m
(180 ft) SSE from the south edge of a grass covered entrance to a tidal slough,
17 m (56 ft) north from a high rock point and angle point in the shoreline, 11 m
(35 ft) NE from a 0.15 m (0.5 ft) diameter pine tree with a plywood sign nailed
to the trunk about 1 m (4 ft) above the ground, and 0.04 m (0.1 ft) above
ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 9450973 PUBLICATION DATE: 12/02/2010
Name: BLASHKE ISALND, CLARENCE STRAIT
AK
NOAA Chart: 17401 Latitude: 56° 7.6' N ( 56.12670)
USGS Quad: PETERSBURG (A-3) Longitude: 132° 53.7' W (-132.89500)
T I D A L D A T U M S
Tidal datums at BLASHKE ISALND, CLARENCE STRAIT based on:
LENGTH OF SERIES: 22 DAYS
TIME PERIOD: August 26 2002 - September 16 2002
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9450460 KETCHIKAN, TONGASS NARROWS
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 4.822
MEAN HIGH WATER MHW = 4.548
MEAN TIDE LEVEL MTL = 2.498
MEAN SEA LEVEL MSL = 2.471
MEAN LOW WATER MLW = 0.447
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
A 6.441 1.893
945 0973 B 4.099 -0.449
945 0973 C 5.792 1.244
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 9450973 PUBLICATION DATE: 12/02/2010
Name: BLASHKE ISALND, CLARENCE STRAIT
AK
NOAA Chart: 17401 Latitude: 56° 7.6' N ( 56.12670)
USGS Quad: PETERSBURG (A-3) Longitude: 132° 53.7' W (-132.89500)
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.