U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 11/04/1995
Station ID: 8418031 SUPERCEDED DATE: 04/21/2003
Name: PORTLAND HEAD LIGHT, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 37.4' N
USGS Quad: CAPE ELIZABETH Longitude: 70° 12.4' W
To reach the tidal bench marks from the South Portland south 2 miles (3.2 km)
along Shore Road to the Coast Guard Light Station at Portland Head. The bench
marks are located in the vicinity of the Light Station. Tide tide gage and
staff were located along the vertical cliff, east of the Light Station.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 841 8031 A 1979
MONUMENTATION: Survey Disk VM#: 1934
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Support
The bench mark is located within the confines of the Portland Head Coast Guard
Light Station set flush in the SE corner support of the Coast Guard fog horn
compressor shed, 34.1 feet (10.4 m) ESE of the Portland Head Lighthouse, bears
WSW from the Ram Island Ledge Light, and set 1.4 feet (0.4 m) above ground level
in the NE corner of the support.
BENCH MARK STAMPING: 841 8031 B 1979
MONUMENTATION: SURVEY DISK VM#: 1935
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Support
The bench mark is located within the confines of the Portland Head Coast Guard
Light Station, set flush in a rock ledge outcrop on the northern side of the
Light Station, 105 feet (32.0 m) WNW of Bench Mark 841 8031 A 1979, 49.5 feet
(15.1 m) NW of the intersection of the lighthouse and museum portion of the
station, 12.5 feet (3.8 m) NNE of the NE corner of the Coast Guard living
quarters and bears SW from the Ram Island Ledge Light.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 11/04/1995
Station ID: 8418031 SUPERCEDED DATE: 04/21/2003
Name: PORTLAND HEAD LIGHT, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 37.4' N
USGS Quad: CAPE ELIZABETH Longitude: 70° 12.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 841 8031 C 1979
MONUMENTATION: Survey Disk VM#: 1936
AGENCY: PID:
SETTING CLASSIFICATION: Rock Outcrop
The bench mark is located within the confines of the Portland Head Coast Guard
Light Station, set in a rock ledge outcrop west of the stations automobile
garage, 85 feet (25.9 m) NW of Bench Mark 841 8031 B 1979, 44.5 feet (13.6 m) NW
of the NW corner of the Coast Guard living quarters, 26.5 feet (8.1 m) west of
the SW corner of the garage, and 24.5 feet (7.5 m) north of the centerline of
the driveway leading to the station.
BENCH MARK STAMPING: 841 8031 D 1979
MONUMENTATION: Survey Disk VM#: 1937
AGENCY: PID:
SETTING CLASSIFICATION: Rock Outcrop
The bench mark is located within the confines of the Portland Head Coast Guard
Light Station, set in a rock outcrop on the south side of the Light Station,
98.5 feet (30.0 m) SSW of Bench Mark 841 8031 C 1979, 95 feet (28.9 m) NW of the
intersection of the south side of the station Museum building and the
lighthouse, 23.8 feet (7.3 m) SSW of the SW corner of the Coast Guard living
quarters and is 10.0 feet (3.0 m) north of the vertical cliff on the south side
of the station.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
PUBLICATION DATE: 11/04/1995
Station ID: 8418031 SUPERCEDED DATE: 04/21/2003
Name: PORTLAND HEAD LIGHT, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 37.4' N
USGS Quad: CAPE ELIZABETH Longitude: 70° 12.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 841 8031 E 1979
MONUMENTATION: Survey Disk VM#: 1938
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Pad
The bench mark is located within the confines of the Portland Head Light
Station, set in the SE corner of the concrete foundation of a permament bicycle
rack NE of the driveway leading to the Light Station, 60.5 feet (18.4 m) NW of
Bench Mark 841 8031 C 1979, 24.5 feet (7.5 m) NE of the centerline of the
driveway leading to the station, and 11.8 feet ((3.6 m) NW of the rock ledge
where Bench Mark 841 8031 C 1979 is set.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
PUBLICATION DATE: 11/04/1995
Station ID: 8418031 SUPERCEDED DATE: 04/21/2003
Name: PORTLAND HEAD LIGHT, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 37.4' N
USGS Quad: CAPE ELIZABETH Longitude: 70° 12.4' W
T I D A L D A T U M S
Tidal datums at PORTLAND HEAD LIGHT, CASCO BAY based on:
LENGTH OF SERIES: 114 HW & 114 LW
TIME PERIOD: SEPTEMBER 12-NOVEMBER 9, 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 (10/07/1979) = 11.96
MEAN HIGHER HIGH WATER MHHW = 9.65
MEAN HIGH WATER MHW = 9.21
MEAN TIDE LEVEL MTL = 4.77
MEAN LOW WATER MLW = 0.33
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (11/04/1979) = -1.86
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
841 8031 A 1979 35.66 26.45
841 8031 B 1979 40.25 31.04
841 8031 C 1979 40.50 31.29
841 8031 D 1979 42.22 33.01
841 8031 E 1979 40.60 31.39
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 11/04/1995
Station ID: 8418031 SUPERCEDED DATE: 04/21/2003
Name: PORTLAND HEAD LIGHT, CASCO BAY
MAINE
NOAA Chart: 13290 Latitude: 43° 37.4' N
USGS Quad: CAPE ELIZABETH Longitude: 70° 12.4' 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.