U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 07/30/1985
Station ID: 8417911 SUPERCEDED DATE: 04/21/2003
Name: VAILL ISLAND, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 40.6' N
USGS Quad: PORTLAND EAST Longitude: 70° 9.3' W
To reach the tidal bench marks proceed by boat to Vaill Island located in the
southwest section of Casco Bay, southeast of Long Island. The bench marks are
located on the west side of Vaill Island, set around the shoreline of a small
cove. The tide gage was located on the beach and the orifice and tubing
extended offshore. The tide staff was free standing offshore.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 841 7911 A 1979
MONUMENTATION: Survey Disk VM#: 1899
AGENCY: PID:
SETTING CLASSIFICATION: Rock Outcrop
The bench mark is set flush in a rock outcrop on the NW side of Vaill Island,
bears ENE from the northernmost tower on Cushing Island, SSE from the tower on
Long Island, and west from the west point on the NW corner of Vaill Island.
BENCH MARK STAMPING: 841 7911 B 1979
MONUMENTATION: Survey Disk VM#: 1900
AGENCY: PID:
SETTING CLASSIFICATION: Rock Outcrop
The bench mark is set flush in a rock outcrop on the NW side of Vaill Island,
43.9 feet (13.4 m) NE of Bench Mark 841 7911 A 1979, and bears ENE from the
northernmost tower on Cushing Island, SSE from the tower on Long Island and SSE
from the west point of land from the NW corner on Vaill Island.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 07/30/1985
Station ID: 8417911 SUPERCEDED DATE: 04/21/2003
Name: VAILL ISLAND, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 40.6' N
USGS Quad: PORTLAND EAST Longitude: 70° 9.3' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 841 7911 C 1979
MONUMENTATION: Survey Disk VM#: 1901
AGENCY: PID:
SETTING CLASSIFICATION: Rock Outcrop
The bench mark is set flush in a rock outcrop on a ledge that forms the NW side
of Vaill Island, 625 feet (190 m) NNW of Bench Mark 841 7911 B 1979, 25 feet
(7.6 m) north of the shore line on the south side of the ledge, bears NE from
the northernmost tower on Cushing Island, NNE from Ram Island Ledge Light and
SSE from the tower on Long Island.
BENCH MARK STAMPING: 841 7911 D 1979
MONUMENTATION: Survey Disk VM#: 1902
AGENCY: PID:
SETTING CLASSIFICATION: Rock Ledge
The bench mark is set flush in a rock ledge that forms the NW side of Vaill
Island, 97.5 feet (29.7 m) NE of Bench Mark 841 7911 C 1979, bears NNE from Ram
Island Ledge Light and south of the tower on Long Island.
BENCH MARK STAMPING: 841 7911 E 1979
MONUMENTATION: Survey Disk VM#: 1903
AGENCY: PID:
SETTING CLASSIFICATION: Rock Ledge
The bench mark is set flush in the top of a rock ledge that forms the NW side of
Vaill Island, 103 feet (31.4 m) NNE of Bench Mark 841 7911 D 1979, bears NNE
from the Ram Island Ledge Light and south of the tower on Long Island.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 07/30/1985
Station ID: 8417911 SUPERCEDED DATE: 04/21/2003
Name: VAILL ISLAND, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 40.6' N
USGS Quad: PORTLAND EAST Longitude: 70° 9.3' W
T I D A L D A T U M S
Tidal datums at VAILL ISLAND, CASCO BAY based on:
LENGTH OF SERIES: 41 HW & 40 LW
TIME PERIOD: OCTOBER 12-NOVEMBER 1,1979
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8418150 PORTLAND
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (10/24/1979) = 10.33
MEAN HIGHER HIGH WATER MHHW = 9.75
MEAN HIGH WATER MHW = 9.30
MEAN TIDE LEVEL MTL = 4.83
MEAN LOW WATER MLW = 0.35
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (11/01/1979) = -0.57
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
841 7911 A 1979 12.37 3.07
841 7911 B 1979 12.76 3.46
841 7911 C 1979 17.26 7.96
841 7911 D 1979 17.17 7.87
841 7911 E 1979 19.30 10.00
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 07/30/1985
Station ID: 8417911 SUPERCEDED DATE: 04/21/2003
Name: VAILL ISLAND, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 40.6' N
USGS Quad: PORTLAND EAST Longitude: 70° 9.3' W
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 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.