U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 Station ID: 8417881 PUBLICATION DATE: 06/09/2021 Name: GREAT CHEBEAGUE ISLAND ME NOAA Chart: 13290 Latitude: 43° 43.3' N ( 43.72170) USGS Quad: PORTLAND EAST Longitude: 70° 8.5' W ( -70.14170) To reach the tidal bench marks proceed by boat to Indian Point, located on Great Chebeague Island, which is in the SW section of Casco Bay. The bench marks are located in the vicinity of the pier at Indian Point, and extend east towards the dirt road leading to the pier. The staff was located on the NW side of the pier. The tide gage was mounted in a shed east of the pier. The orifice and tubing extended offshore (west of the pier). T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: DESIGNATION: 841 7881 S TIDAL MONUMENTATION: Triangulation Station disk VM#: 1894 AGENCY: US Army Corps of Engineers (USE) IDB PID: SETTING CLASSIFICATION: Rock outcropping OPUS PID: LATITUDE: 43° 43.3' N ( 43.72170) LONGITUDE: 70° 8.5' W ( -70.14170) The primary bench mark is a disk set flush in a rock outcropping, east of the pier, 44.5 m (146 ft) NW of a 15.2 m (50 ft) tall oak tree, the only tree on Indian Point, 13.6 m (44.5 ft) east of the NE concrete leg of the pier, and 11.4 m (37.5 ft) north of the NE corner of a shed, the only building on Indian Point.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 Station ID: 8417881 PUBLICATION DATE: 06/09/2021 Name: GREAT CHEBEAGUE ISLAND ME NOAA Chart: 13290 Latitude: 43° 43.3' N ( 43.72170) USGS Quad: PORTLAND EAST Longitude: 70° 8.5' W ( -70.14170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 841 7881 B 1979 DESIGNATION: 841 7881 B TIDAL MONUMENTATION: Tidal Station disk VM#: 1895 AGENCY: National Ocean Survey (NOS) IDB PID: SETTING CLASSIFICATION: Rock outcrop OPUS PID: LATITUDE: 43° 43.3' N ( 43.72170) LONGITUDE: 70° 8.5' W ( -70.14170) The bench mark is a disk set flush in a rock outcrop, south of the pier, 48.5 m (159 ft) west of a 15.2 m (50 ft) tall oak tree, the only tree on Indian Point, 27.0 m (88.5 ft) south of the SE corner of the SE concrete leg of the pier, and 14.5 m (47.5 ft) SW of the SW corner of a shed, the only building on Indian Point. BENCH MARK STAMPING: 841 7881 C 1979 DESIGNATION: 841 7881 C TIDAL MONUMENTATION: Tidal Station disk VM#: 1896 AGENCY: National Ocean Survey (NOS) IDB PID: SETTING CLASSIFICATION: Rock outcrop OPUS PID: LATITUDE: 43° 43.3' N ( 43.72170) LONGITUDE: 70° 8.5' W ( -70.14170) The bench mark is a disk set flush in a rock crop NE of the pier, 42.7 m (140 ft) NNE of a 15.2 m (50 ft) tall oak tree, the only tree on Indian Point, 31.9 m (104.5 ft) NE of the NE corner of a shed, the only building on Indian Point, and 21.5 m (70.5 ft) NE of bench mark 841 7881 S.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 Station ID: 8417881 PUBLICATION DATE: 06/09/2021 Name: GREAT CHEBEAGUE ISLAND ME NOAA Chart: 13290 Latitude: 43° 43.3' N ( 43.72170) USGS Quad: PORTLAND EAST Longitude: 70° 8.5' W ( -70.14170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 841 7881 D 1979 DESIGNATION: 841 7881 D TIDAL MONUMENTATION: Tidal Station disk VM#: 1897 AGENCY: National Ocean Survey (NOS) IDB PID: SETTING CLASSIFICATION: Rock outcrop OPUS PID: LATITUDE: 43° 43.3' N ( 43.72170) LONGITUDE: 70° 8.5' W ( -70.14170) The bench mark is a disk set flush in a rock outcrop NE of the pier, 73.2 m (240 ft) NNW of a 15.2 m (50 ft) tall oak tree, the only tree on Indian Point, 61.0 m (200 ft) NNE of the NE corner of a shed, the only building on Indian Point, and 31.1 m (102 ft) north of bench mark 841 7881 C 1979. BENCH MARK STAMPING: 841 7881 E 1979 DESIGNATION: 841 7881 E TIDAL MONUMENTATION: Tidal Station disk VM#: 1898 AGENCY: National Ocean Survey (NOS) IDB PID: SETTING CLASSIFICATION: Rock outcrop OPUS PID: LATITUDE: 43° 43.3' N ( 43.72170) LONGITUDE: 70° 8.5' W ( -70.14170) The bench mark is a disk set flush in a rock outcrop NE of the pier, 58.8 m (193 ft) NE of the NE corner of a small shed, the only building on Indian Point, 51.2 m (168 ft) north of a 15.2 m (50 ft) tall oak tree, the only tree on Indian Point, 29.2 m (96 ft) east of bench mark 841 7881 C 1979, and 1.5 m (5.0 ft) south of a small pier on Indian Point.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 Station ID: 8417881 PUBLICATION DATE: 06/09/2021 Name: GREAT CHEBEAGUE ISLAND ME NOAA Chart: 13290 Latitude: 43° 43.3' N ( 43.72170) USGS Quad: PORTLAND EAST Longitude: 70° 8.5' W ( -70.14170) T I D A L D A T U M S Tidal datums at GREAT CHEBEAGUE ISLAND based on: LENGTH OF SERIES: 1 MONTH TIME PERIOD: October 1979 - October 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 = 3.020 MEAN HIGH WATER MHW = 2.884 MEAN SEA LEVEL MSL = 1.503 MEAN TIDE LEVEL MTL = 1.495 MEAN LOW WATER MLW = 0.106 MEAN LOWER LOW WATER MLLW = 0.000 Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW 841 7881 S TIDAL 4.619 1.735 841 7881 B 1979 3.718 0.834 841 7881 C 1979 3.603 0.719 841 7881 D 1979 4.069 1.185 841 7881 E 1979 3.623 0.739
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 Station ID: 8417881 PUBLICATION DATE: 06/09/2021 Name: GREAT CHEBEAGUE ISLAND ME NOAA Chart: 13290 Latitude: 43° 43.3' N ( 43.72170) USGS Quad: PORTLAND EAST Longitude: 70° 8.5' W ( -70.14170) 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.