U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 9451805 PUBLICATION DATE: 04/13/2005
Name: SCRAGGY ISLAND
AK
NOAA Chart: 17323 Latitude: 57° 20.4' N ( 57.34000)
USGS Quad: SITKA (B-5) Longitude: 135° 42.4' W (-135.70700)
To reach the tidal bench marks from Sitka, Alaska, proceed north through Sitka
Sound to Scraggy Island in Salisbury Sound for 34 km (21 mi), then proceed to SW
region of island, approximate location of the tide gauge is at 57 20.46' N; 135
42.42' W. The bench marks are located along the beach on bedrock outcrop.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 1805 A 2002
DESIGNATION: 945 1805 A
MONUMENTATION: Tidal Station disk VM#: 16665
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 57° 20.4' N ( 57.34000) LONGITUDE: 135° 42.4' W (-135.70700)
The primary bench mark is a disk set flush in bedrock, in a prominent flat
topped rock 2 m x 1.30 m x 1.40 m (6.6 ft x 4.3 ft x 4.6 ft) which runs
north/south on seaward side of crevasse, west of a white shell beach, 5 m (15
ft) south of a large rock, and 1 m (3 ft) above high water line.
BENCH MARK STAMPING: 1805 B 2002
DESIGNATION: 945 1805 B
MONUMENTATION: Tidal Station disk VM#: 16666
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 57° 20.4' N ( 57.34000) LONGITUDE: 135° 42.4' W (-135.70700)
The bench mark is a disk set flush in bedrock, east of and at the base of a 3 m
(11 ft) high rock outcropping, 17 m (55 ft) NE from bench mark 1805 A 2002, 10 m
(33 ft) north of the apparent high water line, and 4 m (12 ft) to the vegetation
line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 9451805 PUBLICATION DATE: 04/13/2005
Name: SCRAGGY ISLAND
AK
NOAA Chart: 17323 Latitude: 57° 20.4' N ( 57.34000)
USGS Quad: SITKA (B-5) Longitude: 135° 42.4' W (-135.70700)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1805 C 2002
DESIGNATION: 945 1805 C
MONUMENTATION: Tidal Station disk VM#: 16667
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 57° 20.4' N ( 57.34000) LONGITUDE: 135° 42.4' W (-135.70700)
The bench mark is a disk set flush in bedrock at the SW base of a prominent 5 m
(16 ft) jagged rock face, located on the west side of Scraggy Island, 30 m (98
ft) north of bench mark 1805 B 2002, 4 m (13 ft) NE of a prominent jagged
boulder of size 3 m x 3 m x 0.5 m (10 ft x 9 ft x 1.6 ft) which has a flat
eastern face, 4 m (13 ft) from the apparent high water line and 2.01 m (6.6 ft)
above it.
BENCH MARK STAMPING: 1805 D 2002
DESIGNATION: 945 1805 D
MONUMENTATION: Tidal Station disk VM#: 16668
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 57° 20.4' N ( 57.34000) LONGITUDE: 135° 42.4' W (-135.70700)
The bench mark is a disk set flush in a non-prominent bedrock, 41 m (135 ft)
from bench mark 1805 C 2002, 10 m (33 ft) NW of a 15 m (49 ft) high jagged
vertical rock set behind the tree line, 6 m (20 ft) from the apparent high water
line, 2 m (7 ft) from the vegetation line, and 2 m (7 ft) above the apparent
high water line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 9451805 PUBLICATION DATE: 04/13/2005
Name: SCRAGGY ISLAND
AK
NOAA Chart: 17323 Latitude: 57° 20.4' N ( 57.34000)
USGS Quad: SITKA (B-5) Longitude: 135° 42.4' W (-135.70700)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1805 E 2002
DESIGNATION: 945 1805 E
MONUMENTATION: Tidal Station disk VM#: 16669
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 57° 20.4' N ( 57.34000) LONGITUDE: 135° 42.4' W (-135.70700)
The bench mark is a disk set flush in a large 2 m x 12 m x 3 m (7 ft x 39 ft x
10 ft) bedrock extension, 120 m (394 ft) south of the northern extent of the
island, 35 m (115 ft) NE of bench mark 1805 D 2002, and 8 m (26 ft) from the
vegetation line.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 9451805 PUBLICATION DATE: 04/13/2005
Name: SCRAGGY ISLAND
AK
NOAA Chart: 17323 Latitude: 57° 20.4' N ( 57.34000)
USGS Quad: SITKA (B-5) Longitude: 135° 42.4' W (-135.70700)
T I D A L D A T U M S
Tidal datums at SCRAGGY ISLAND based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: May 2004 - May 2004
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9451600 SITKA, BARONOF ISLAND, SITKA SOUND
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 3.037
MEAN HIGH WATER MHW = 2.779
MEAN TIDE LEVEL MTL = 1.618
MEAN SEA LEVEL MSL = 1.609
MEAN LOW WATER MLW = 0.457
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
1805 A 2002 3.140 0.361
1805 B 2002 3.364 0.585
1805 C 2002 3.838 1.059
1805 D 2002 3.393 0.614
1805 E 2002 4.296 1.517
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 9451805 PUBLICATION DATE: 04/13/2005
Name: SCRAGGY ISLAND
AK
NOAA Chart: 17323 Latitude: 57° 20.4' N ( 57.34000)
USGS Quad: SITKA (B-5) Longitude: 135° 42.4' W (-135.70700)
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.