U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 8417941 PUBLICATION DATE: 05/20/2004
Name: LONG ISLAND, CASCO BAY
ME
NOAA Chart: 13290 Latitude: 43° 41.4' N ( 43.69000)
USGS Quad: PORTLAND EAST Longitude: 70° 10.2' W ( -70.17000)
To reach the tidal bench marks from Portland, Maine, proceed by boat to the Long
Island Ferry Pier at Ponce Landing, on the west side of Long Island located in
the SW section of Casco Bay. The bench marks are located in the vicinity of the
Post Office. The tide gage and staff were located on the Ferry Pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: LONG ISLAND BM 3 10.22
DESIGNATION: 3 USE
MONUMENTATION: Tidal Station disk VM#: 1904
AGENCY: US Army Corps of Engineers (USE) IDB PID#: OC0186
SETTING CLASSIFICATION: Bedrock OPUS PID#: OC0186
LATITUDE: 43° 41.4' N ( 43.69000) LONGITUDE: 70° 10.1' W ( -70.16830)
The primary bench mark is a disk set flush in a bedrock outcrop at Ponce
Landing, 122 m (400 ft) north of the Post Office, 63 m (206 ft) north of the NE
corner of Cushmans Bakery, 41 m (133 ft) SE of the SE corner of the dock house
on wharf, 4 m (12 ft) NW of the shoreline, and 2.0 m (6.6 ft) SW of the SW
corner of the pier. The bench mark is submerged at high water.
BENCH MARK STAMPING: LONG ISLAND BM 4 23.06
DESIGNATION: 4 USE
MONUMENTATION: Tidal Station disk VM#: 1905
AGENCY: US Army Corps of Engineers (USE) IDB PID#: OC0187
SETTING CLASSIFICATION: Bedrock OPUS PID:
LATITUDE: 43° 41.4' N ( 43.69000) LONGITUDE: 70° 10.1' W ( -70.16830)
The bench mark is a disk set flush in bedrock at Ponce Landing on the west side
of Long Island, 20 m (67 ft) SW of the SE corner of the pier, 16 m (54 ft) NW of
the north corner of a building called The Spar, and 8.7 m (28.6 ft) SW of the
centerline of the road leading to the pier.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 8417941 PUBLICATION DATE: 05/20/2004
Name: LONG ISLAND, CASCO BAY
ME
NOAA Chart: 13290 Latitude: 43° 41.4' N ( 43.69000)
USGS Quad: PORTLAND EAST Longitude: 70° 10.2' W ( -70.17000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 5 1948
DESIGNATION: 841 7941 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 1906
AGENCY: US Coast & Geodetic Survey
(USC&GS) IDB PID#:
SETTING CLASSIFICATION: Rock ledge OPUS PID:
LATITUDE: 43° 41.4' N ( 43.69000) LONGITUDE: 70° 10.1' W ( -70.16830)
The bench mark is a disk set flush in the top of a rock ledge, 13 m (42 ft)
south of bench mark Long Island BM 4 23.06, 9 m (30 ft) SW of the SW corner of a
white painted building call The Spar, and 4 m (12 ft) NW of a small flagpole.
BENCH MARK STAMPING: 841 7941 D 1979
DESIGNATION: 841 7941 D TIDAL
MONUMENTATION: Tidal Station disk VM#: 1907
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 43° 41.4' N ( 43.69000) LONGITUDE: 70° 10.1' W ( -70.16830)
The bench mark is a disk set flush in a rock ledge outcrop on the west side of
the road leading to the ferry pier, 12.5 m (41.0 ft) NE of bench mark N0 5 1948,
4.2 m (13.9 ft) NE of the NE corner of the Spar house, which is the first
building on the west side of the road directly up from the ferry pier, and 1.3 m
(4.2 ft) west of the centerline of the road leading to the pier.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 8417941 PUBLICATION DATE: 05/20/2004
Name: LONG ISLAND, CASCO BAY
ME
NOAA Chart: 13290 Latitude: 43° 41.4' N ( 43.69000)
USGS Quad: PORTLAND EAST Longitude: 70° 10.2' W ( -70.17000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 841 7941 E 1979
DESIGNATION: 841 7941 E TIDAL
MONUMENTATION: Tidal Station disk VM#: 1908
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 43° 41.4' N ( 43.69000) LONGITUDE: 70° 10.1' W ( -70.16830)
The bench mark is a disk set flush in a rock ledge outcrop directly behind the
War Memorial and Flagpole, underneath some heavy brush, 27.4 m (90.0 ft) SE of
Long Island Post Office, which is connected to the Spar building, and 6.6 m
(21.5 ft) SE of the base of the flagpole.
BENCH MARK STAMPING: 841 7941 F 1979
DESIGNATION: 841 7941 F TIDAL
MONUMENTATION: Tidal Station disk VM#: 1909
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 43° 41.4' N ( 43.69000) LONGITUDE: 70° 10.1' W ( -70.16830)
The bench mark is a disk set flush in a rock ledge outcrop in the front yard of
an old wooden church which is directly across the street from the General Store,
14.0 m (46.0 ft) east of the centerline of the paved road which runs to the west
of the church, 3.8 m (12.3 ft) SW of the NW corner of the concrete landing of
the church stairs, and 2.5 m (8.3 ft) north of the SW corner of the church.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 8417941 PUBLICATION DATE: 05/20/2004
Name: LONG ISLAND, CASCO BAY
ME
NOAA Chart: 13290 Latitude: 43° 41.4' N ( 43.69000)
USGS Quad: PORTLAND EAST Longitude: 70° 10.2' W ( -70.17000)
T I D A L D A T U M S
Tidal datums at LONG ISLAND, CASCO BAY based on:
LENGTH OF SERIES: 1 MONTH
TIME PERIOD: September 1979 - September 1979
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8418150 PORTLAND, CASCO BAY
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 3.006
MEAN HIGH WATER MHW = 2.874
MEAN SEA LEVEL MSL = 1.502
MEAN TIDE LEVEL MTL = 1.489
MEAN LOW WATER MLW = 0.104
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
LONG ISLAND BM 3 10.22 3.144 0.270
LONG ISLAND BM 4 23.06 7.060 4.186
NO 5 1948 8.184 5.310
841 7941 D 1979 8.048 5.174
841 7941 E 1979 13.101 10.227
841 7941 F 1979 13.941 11.067
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 8417941 PUBLICATION DATE: 05/20/2004
Name: LONG ISLAND, CASCO BAY
ME
NOAA Chart: 13290 Latitude: 43° 41.4' N ( 43.69000)
USGS Quad: PORTLAND EAST Longitude: 70° 10.2' W ( -70.17000)
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.