U.S. DEPARTMENT OF COMMERCE
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National Ocean Service
Datums Page Page 1 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
To reach the tidal bench marks from Interstate 95 heading north, take Exit 1
(State Highway 103) which is 1.0 km (0.6 mi) north of the Maine state line, and
continue on State Highway 103 for 2.3 km (1.4 mi) to the main gate of Portsmouth
Naval Shipyard. The bench marks are located on the shipyard compound. The tide
gage and staff are located at Berth 3. Access to Portsmouth Naval Shipyard is
restricted to authorized personnel only.
T I D A L B E N C H M A R K S
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 5 1928
DESIGNATION: TIDAL 5 STA 92
MONUMENTATION: Tidal Station disk VM#: 1974
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: OC0514
SETTING CLASSIFICATION: Water table OPUS PID:
LATITUDE: 43° 4.9' N ( 43.08086) LONGITUDE: 70° 44.4' W ( -70.74072)
The primary bench mark is a brass disk set in the top horizontal ledge of the
water table, 5.9 m (19.4 ft) north of the northern rail track leading to the
warehouse, 5.4 m (17.7 ft) NE of the NE edge of the steps leading to the door on
the south face of the building, and 1.5 m (4.9 ft) SW of the SE corner of the
building. The mark is 0.7 m (2.3 ft) above the ground surface
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 7 1940
DESIGNATION: TIDAL 7 STA 92
MONUMENTATION: Tidal Station disk VM#: 1976
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: OC0516
SETTING CLASSIFICATION: Concrete monolith OPUS PID:
LATITUDE: 43° 4.9' N ( 43.08169) LONGITUDE: 70° 44.5' W ( -70.74111)
The bench mark is 12.2 m (40.0 ft) east of the triangulation bench mark with
stamping 177, 7.9 m (25.9 ft) south of the northern rail track for the large
loading crane #37, 14 cm (6 inches) north of the south face of the shipfitters
shop wall, at the corner of the building where it meets the loading dock and in
the top face of a concrete monolith.
BENCH MARK STAMPING: 9870 A 2020
DESIGNATION: 841 9870 A
MONUMENTATION: Tidal Station disk VM#: 23453
AGENCY: National Ocean Survey/Service
(NOS)ZZZZZZZz IDB PID:
SETTING CLASSIFICATION: Seawall OPUS PID:
LATITUDE: 43° 4.8' N ( 43.07964) LONGITUDE: 70° 44.5' W ( -70.74111)
The bench mark is a brass disk located at berth 3 near the security boat house,
14.2 m (46.6 ft) south of the SE corner of the security boat house, 0.9 m (3.0
ft) east of the western edge of the seawall, and 0.11 m (0.4 ft) west of the
eastern edge of the seawall, set flush with the concrete surface.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: H-135
DESIGNATION: H-135
MONUMENTATION: Tidal Station disk VM#: 23454
AGENCY: U.S. Navy IDB PID:
SETTING CLASSIFICATION: Seawall OPUS PID:
LATITUDE: 43° 4.8' N ( 43.08039) LONGITUDE: 70° 44.5' W ( -70.74146)
The bench mark is a brass disk set flush with the concrete surface located 29.9
m (98.1 ft) south of the southern rail track along bailey avenue, 2.8 m (9.2 ft)
north of the southern edge of the seawall at berth 2a, and 0.8 m (2.6 ft) west
of the eastern edge of the seawall at berth 2a.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: H-131
DESIGNATION: H-131
MONUMENTATION: Tidal Station disk VM#: 23455
AGENCY: U.S. Navy IDB PID:
SETTING CLASSIFICATION: Concrete Foundation OPUS PID:
LATITUDE: 43° 4.9' N ( 43.08142) LONGITUDE: 70° 44.5' W ( -70.74214)
The bench mark is a disk set flush with the concrete surface, located 48.4 m
(158.8 ft) east of the western edge of the seawall, 11.4 m (37.4 ft) south of
the SE corner of office building r-dd1-e, 2.3 m (7.5 ft) NE of the northern rail
track.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: D-605 1975
DESIGNATION: D 605 MEDT
MONUMENTATION: Survey disk VM#: 23456
AGENCY: Maine Department of Transportation IDB PID#: OC1233
SETTING CLASSIFICATION: Foundation OPUS PID:
LATITUDE: 43° 5.1' N ( 43.08567) LONGITUDE: 70° 44.6' W ( -70.74408)
The mark is a disk set vertically in the foundation 22.3 m (73.2 ft) west of the
telephone pole #35, 17.7 m (58.1 ft) south of the loading dock for the post
office, 16.2 m (53.1 ft) north of the centerline of government street, and 0.3 m
(1.0 ft) north of the SE corner of the building, set vertically 27 cm (11
inches) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: S 99 1943
DESIGNATION: S 99
MONUMENTATION: Bench Mark disk VM#: 23457
AGENCY: CGS IDB PID#: OC0512
SETTING CLASSIFICATION: Abutment OPUS PID:
LATITUDE: 43° 5.3' N ( 43.08875) LONGITUDE: 70° 44.3' W ( -70.73808)
The bench mark is a disk set flush with the ground on top of a 1.23 m (4.0 ft)
wide concrete headwall for a 30 cm (12 inch) pipe culvert running under the
highway located 21.3 m (69.9 ft) NE of telephone pole #8, 18.47 m (60.6 ft) west
of the centerline of the driveway for the house at 37 whipple road, and 8.2 m
(26.9 ft) north of the centerline of whipple road.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 8 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
T I D A L D A T U M S
Tidal datums at SEAVEY ISLAND, PORTSMOUTH HARBOR based on:
LENGTH OF SERIES: 1 YEAR
TIME PERIOD: July 2020 - June 2021
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8418150 PORTLAND,CASCO BAY
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (02/07/1978) = 3.841
MEAN HIGHER HIGH WATER MHHW = 2.712
MEAN HIGH WATER MHW = 2.583
North American Vertical Datum NAVD88 = 1.436
MEAN SEA LEVEL MSL = 1.359
MEAN TIDE LEVEL MTL = 1.340
MEAN LOW WATER MLW = 0.097
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (11/30/1955) = -0.996
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
5 1928 7.316 4.733
7 1940 5.250 2.667
9870 A 2020 4.029 1.446
H-135 4.363 1.780
H-131 4.389 1.806
D-605 1975 11.376 8.793
S 99 1943 7.969 5.386
Foot Notes:
Bench marks D-605 1975 and S 99 1943 are based on one differential leveling
connection and do not meet the quality control standards of the NOS. Therefore,
caution should be used when deriving elevations for these marks.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 9 of 9
Station ID: 8419870 PUBLICATION DATE: 12/06/2021
Name: SEAVEY ISLAND, PORTSMOUTH HARBOR
ME
NOAA Chart: 13283 Latitude: 43° 4.8' N ( 43.07972)
USGS Quad: KITTERY Longitude: 70° 44.5' W ( -70.74111)
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.