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Datums Page Page 1 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
To reach the tidal bench marks from the seaplane base at Juneau, Alaska, proceed
110 km (59 nm) west to the community of Elfin Cove. From the seaplane float
located in the outer cove, proceed 250 m (820 ft) SE along the community board
walk to the north shore of the inner cove. The bench marks are located along
the NE shoreline of the inner cove.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 2634 F 2005
DESIGNATION: 945 2634 F TIDAL
MONUMENTATION: Tidal Station disk VM#: 17943
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: In rock outcrop OPUS PID#: BBBB67
LATITUDE: 58° 11.7' N ( 58.19472) LONGITUDE: 136° 20.8' W (-136.34694)
The primary bench mark is a disk set flush in a rock outcropping north of the
dock leading to the fuel dock, 11.31 m (37.1 ft) SSW of a white sign that says
This is not a dump no metal glass or food , and 5.79 m (19.0 ft) north of Toner
& Nordland survey disk.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 4 1959
DESIGNATION: 945 2634 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 14511
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID:
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 58° 11.6' N ( 58.19403) LONGITUDE: 136° 20.7' W (-136.34458)
The bench mark is a disk set in top of a 1 m (3 ft) high boulder located on the
N side of the walk, 8.41 m (27.6 ft) NW of the NE corner of the yellow building
on the S side (shore side) of the boardwalk, 1.58 m (5.2 ft) N of the N edge of
the boardwalk, and 0.70 m (2.3 ft) E of the yellow shed attached to the E side
of the yellow shingled house.
BENCH MARK STAMPING: 1952
DESIGNATION: 945 2634 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 14512
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID:
SETTING CLASSIFICATION: Steel pipe OPUS PID:
LATITUDE: 58° 11.6' N ( 58.19353) LONGITUDE: 136° 20.6' W (-136.34392)
The bench mark is a disk set flush with natural grade in the top of a 2-1/2-inch
steel pipe projecting from a cairn of rocks just E of a small creek, 4.51 m
(14.8 ft) ESE of the center of a stream, 3.41 m (11.2 ft) NNW of the NW center
of a wooden shed, and 0.79 m (2.6 ft) N of the boardwalk.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 2634 A 1991
DESIGNATION: 945 2634 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 14513
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 58° 11.6' N ( 58.19392) LONGITUDE: 136° 20.6' W (-136.34406)
The bench mark is a disk set flush in a rock outcropping on the water side of
the boardwalk betwen the large yellow shingled house called The Gift and Gab
Shop and the gray shed next to the small creek running under the boardwalk,
10.50 m (34.4 ft) SE of the center of a root on the large tree N of the
boardwalk used as brace for stairway up the hill, 1.0 m (3.3 ft) S of the
boardwalk, and 0.91 m (3.0 ft) below the boardwalk.
BENCH MARK STAMPING: 2634 B 1991
DESIGNATION: 945 2634 B TIDAL
MONUMENTATION: Tidal Station disk VM#: 14514
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 58° 11.6' N ( 58.19378) LONGITUDE: 136° 20.6' W (-136.34389)
The bench mark is a disk set flush in a rock outcropping on the landward side of
the boardwalk between the large yellow shingled house called The Gift and Gab
Shop and the gray shed next to the small creek running under the boardwalk,
14.39 m (47.2 ft) WNW of the NW corner of wooden shed, 7.99 m (26.2 ft) W of the
center of the creek, 0.3 m (1 ft) N of the boardwalk, and 0.61 m (2.0 ft) above
the boardwalk.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 2634 G 2005
DESIGNATION: 945 2634 G
MONUMENTATION: Tidal Station disk VM#: 17942
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: In rock outcrop OPUS PID:
LATITUDE: 58° 11.7' N ( 58.19422) LONGITUDE: 136° 20.8' W (-136.34744)
The bench mark is a disk set flush in an outcropping of rock near the waters
edge S of the fuel dock, 43.89 m (144.0 ft) N of the N corner of the green
generator shed which is N of the general store, 24.29 m (79.7 ft) SE of 2.01 m
(6.6 ft) high x 1.49 m (4.9 ft) wide x 3.99 m (13.1 ft) long rock point exposed
at mean high water which projects 1 m (3.3 ft) above the barnacle line. 1 m (3.3
ft) W of a witness sign that is visible only from the boardwalk approach to the
mark.
BENCH MARK STAMPING: 2634 E 2005
DESIGNATION: 945 2634 E
MONUMENTATION: Tidal Station disk VM#: 17944
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: In rock outcrop OPUS PID:
LATITUDE: 58° 11.7' N ( 58.19503) LONGITUDE: 136° 20.8' W (-136.34711)
The bench mark is a disk set flush in a rock outcropping at the waters edge
between the fuel dock and transient dock, 25.70 m (84.3 ft) NNW of a white This
is not a dump sign, 4.11 m (13.5 ft) N of a 0.40 m (1.3 ft) high anchor bolt
securing a cable that supports a dolphin near the fuel dock, and recessed 0.04 m
(0.1 ft) into outcrop.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 2634 D 2005
DESIGNATION: 945 2634 D TIDAL
MONUMENTATION: Tidal Station disk VM#: 17945
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: In rock outcrop OPUS PID:
LATITUDE: 58° 11.7' N ( 58.19508) LONGITUDE: 136° 20.8' W (-136.34589)
The bench mark is a disk set flush in a 6.0 m (19.7 ft) long x 2.5 m (8.2 ft)
wide x 0.9 m (3.0 ft) high rock outcropping in front of the Elfin Cove Lodge,
36.52 m (119.8 ft) ENE of the 8th pair of pilings from the end of the boardwalk
leading to the main boat dock, 19.29 m (63.3 ft) WSW of a 0.1 m (0.3 ft) square
metal post that supports the sign for the Fishmasters Inn set in a 0.79 m (2.6
ft) square concrete foundation straddling the boardwalk to boat dock, and 7.89 m
(25.9 ft) NW of the bottom stair leading from the deck of the Elfin Cove Lodge
to the bench on the shore side of lodge.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: TERRA SURVEYS TIDAL BM YAGER
USACE 2003
DESIGNATION: YAGER
MONUMENTATION: Tidal Station disk VM#: 17947
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: Retaining walls OPUS PID:
LATITUDE: 58° 11.7' N ( 58.19500) LONGITUDE: 136° 20.8' W (-136.34667)
The bench mark is a disk set vertically in the grey retaining wall of the fuel
tank farm, 7.10 m (23.3 ft) SW from the NW corner of the grey retaining wall,
4.69 m (15.4 ft) ESE from the SE corner of a white utility building, 2.50 m (8.2
ft) NE of the corner of wooden foot bridge, 1.19 m (3.9 ft) ESE from the
centerline of the 1.0 m (3.3 ft) wide trail, and 0.4 m (1.3 ft) above ground.
BENCH MARK STAMPING: 2634 J 2011
DESIGNATION: 945 2634 J
MONUMENTATION: Tidal Station disk VM#: 20193
AGENCY: National Ocean Service (NOS) IDB PID:
SETTING CLASSIFICATION: Concrete foundation OPUS PID:
LATITUDE: 58° 11.6' N ( 58.19414) LONGITUDE: 136° 20.7' W (-136.34550)
The bench mark is a disk set flush in the western edge of the concrete
foundation for an electrical transformer on the west side of the Jim Lewis Elfin
Cove Power Generating Facility on the east side of the boardwalk, 34.20 m (112.2
ft) NW of a white flagpole at the SW corner of the Elfin Cove Post Office, 11.90
m (39.0 ft) SE of the bottom of a ramp leading to the entrance of COHO's Bar and
Grill, 8.50 m (27.9 ft) SSE of the bottom stair of the deck leading to the gift
shop, 0.70 m (2.3 ft) west of a green electrical utility box, and 0.13 m (0.4
ft) above natural grade.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 2634 K 2016
DESIGNATION: 945 2634 K
MONUMENTATION: Bench Mark disk VM#: 21959
AGENCY: National Ocean Service IDB PID:
SETTING CLASSIFICATION: OPUS PID:
LATITUDE: 58° 11.6' N ( 58.19369) LONGITUDE: 136° 20.8' W (-136.34725)
The bench mark disk set in bedrock ledge 24 m (78.7 ft) NW of the W corner of
tank farm dam wall 15 m (49.2 ft) SE of N point of rock ledge 4 m (13.1 ft) E of
forest line 2 m (6.6 ft) W of MHW line.
BENCH MARK STAMPING: 2634 L 2016
DESIGNATION: 945 2634 L
MONUMENTATION: Bench Mark disk VM#: 21960
AGENCY: National Ocean Service IDB PID:
SETTING CLASSIFICATION: OPUS PID:
LATITUDE: 58° 11.7' N ( 58.19439) LONGITUDE: 136° 20.8' W (-136.34728)
The bench mark disk set in bedrock ledge 15 m (49.2 ft) N of the NW corner of
Elfin Cove General Store building, 6.1 m (20.0 ft) W of the NW corner of
generator building, 2.6 m (8.5 ft) W of boardwalk, 0.6 m (2.0 ft) E of ledge
face and MHW line
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 8 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
T I D A L D A T U M S
Tidal datums at ELFIN COVE, PORT ALTHORP based on:
LENGTH OF SERIES: 12 YEARS
TIME PERIOD: May 2006 - April 2018
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9451600 SITKA, BARANOF ISLAND, SITKA SOUND
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (12/31/2005) = 4.580
MEAN HIGHER HIGH WATER MHHW = 3.354
MEAN HIGH WATER MHW = 3.084
MEAN TIDE LEVEL MTL = 1.765
MEAN SEA LEVEL MSL = 1.747
MEAN LOW WATER MLW = 0.445
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (12/14/2008) = -1.406
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
2634 F 2005 5.384 2.300
4 1959 6.510 3.426
1952 6.408 3.324
2634 A 1991 4.986 1.902
2634 B 1991 6.608 3.524
2634 G 2005 4.890 1.806
2634 E 2005 3.644 0.560
2634 D 2005 3.888 0.804
TERRA SURVEYS TIDAL BM YAGER USACE
2003 6.051 2.967
2634 J 2011 7.401 4.317
2634 K 2016 3.682 0.598
2634 L 2016 4.322 1.238
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 9 of 9
Station ID: 9452634 PUBLICATION DATE: 10/13/2020
Name: ELFIN COVE, PORT ALTHORP
NOAA Chart: 17302 Latitude: 58° 11.7' N ( 58.19472)
USGS Quad: MT. FAIRWEATHER (A-1) Longitude: 136° 20.8' W (-136.34694)
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.