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National Ocean Service
Datums Page Page 1 of 7
Station ID: 8423898 PUBLICATION DATE: 12/19/2018
Name: FORT POINT, NEWCASTLE ISLAND
NH
NOAA Chart: 13283 Latitude: 43° 4.3' N ( 43.07139)
USGS Quad: KITTERY Longitude: 70° 42.6' W ( -70.71056)
To reach the benchmarks from the Portsmouth traffic circle (Junction of I-95 and
US-1 Bypass) proceed south on US 1 Bypass for 2.6 km (1.6 mi) where US 1 Bypass
joins US 1, continue south on US 1 for 0.8 km (0.5 mi) and turn east (left) onto
Elwin Road, go 2.3 km (1.4 mi) on Elwin Road to the intersection of route 1-A
(Sagemore Road) and turn NW (left), proceed on route 1-A for 0.7 km (0.4 mi) to
the intersection of route 1-A and Route 1-B (Wentworth Road), turn NE (right)
and proceed 4.2 km (2.6 mi) to where Route 1-B turns sharp left onto Main
Street, (there is a sign for the Coast Guard and Fort Constitution) stay on
Wentworth Road (straight), continue 0.5 km (0.3 mi) to the access road for the
Coast Guard Base and the pier, turn right and proceed 0.24 km (0.1 mi) to the
gate, after passing through the gate, follow the parking lot NE for .08 km (0.05
mi), turn left between two buildings to the boathouse. The tide gage is located
on the SW corner of the boathouse and the benchmarks are in the immediate area.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 2 1919
DESIGNATION: 842 3898 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 17345
AGENCY: US Coast & Geodetic Survey
(USC&GS) IDB PID#: OC0427
SETTING CLASSIFICATION: Boulder OPUS PID:
LATITUDE: 43° 4.2' N ( 43.07083) LONGITUDE: 70° 42.7' W ( -70.71114)
The primary benchmark is a standard disk set into a rocky ledge south of the
entrance gate to the Coast Guard Base, just west of the pavement and on a small
plateau on the hill leading to Battery Farnsworth, 64.4 m (211.3 ft) SSW of
benchmark "1 1919", 58.5 m (191.9 ft) N of benchmark "1941 NO 1 143, 4.5 m (14.8
ft) SSE of a fire hydrant near a light pole, and is about 3.35 m (11.0 ft)
upslope from the edge of the pavement to the northwest of the helicopter landing
pad.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 7
Station ID: 8423898 PUBLICATION DATE: 12/19/2018
Name: FORT POINT, NEWCASTLE ISLAND
NH
NOAA Chart: 13283 Latitude: 43° 4.3' N ( 43.07139)
USGS Quad: KITTERY Longitude: 70° 42.6' W ( -70.71056)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 1 1919
DESIGNATION: 842 3898 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 17346
AGENCY: US Coast & Geodetic Survey
(USC&GS) IDB PID:
SETTING CLASSIFICATION: Sea wall OPUS PID:
LATITUDE: 43° 4.3' N ( 43.07136) LONGITUDE: 70° 42.4' W ( -70.70664)
The benchmark is a standard disk set into a granite block that makes up a
portion of the seawall on the northwestern side (Piscataqua River) of the
peninsula at Fort Point located directly seaward of a metal building
constructeed in 2003 and is slighly under a chainlink fence and a PVC conduit,
which are easily moved for placing a rod for leveling, 64.4 m (211.3 ft) NNW of
bench mark NO. 2 1919, 40.0 m (131.2 ft) WSW of bench mark NO 6 1944, 20.0 m
(65.6 ft) WSW of the tide gage, across the water from the Coast Guard boat
house, 2.0 m (6.6 ft) NW of a concrete and steel electrical service box, and
0.3 m (1.0 ft) from the edge of the bulkhead.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 7
Station ID: 8423898 PUBLICATION DATE: 12/19/2018
Name: FORT POINT, NEWCASTLE ISLAND
NH
NOAA Chart: 13283 Latitude: 43° 4.3' N ( 43.07139)
USGS Quad: KITTERY Longitude: 70° 42.6' W ( -70.71056)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING:
DESIGNATION: 842 3898 TIDAL US
ALIAS: BM 4
MONUMENTATION: Bolt VM#: 17347
AGENCY: National Ocean Survey (NOS) IDB PID:
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 43° 4.3' N ( 43.07089) LONGITUDE: 70° 42.7' W ( -70.71217)
The benchmark is an iron bolt set into a rock outcropping in the SE side of the
cove between the Fort Point penisula and point leading to the large pier,
located north of a guard rail and downslope, and between the first two power
poles on the SE side of the cove, 120 m (393.7 ft) WSW of bench mark NO. 1 1919,
and 110 m (360.9 ft) ESE of bench mark Portsmouth USCG 1994.
BENCH MARK STAMPING: NO 6 1944
DESIGNATION: 842 3898 TIDAL 6
MONUMENTATION: Survey disk VM#: 17348
AGENCY: US Coast & Geodetic Survey
(USC&GS) IDB PID:
SETTING CLASSIFICATION: Sea wall OPUS PID:
LATITUDE: 43° 4.3' N ( 43.07158) LONGITUDE: 70° 42.6' W ( -70.71042)
The benchmark is a disk set into a granite block that makes up a portion of the
seawall on the northwestern side (Piscataqua River) of the peninsula at Fort
Point located adjacent to the catwalk leading to a floating dock, adjacent to
the northeastern side of the Coast Guard boathouse, directly behind the
northeastern most corner of the Coast Guard "Ready Room" building, 40 m (131.2
ft) ENE of bench mark NO 1 1919, 20.2 m (66.3 ft) ENE of the tide gage, and 0.25
m (0.8 ft) from the edge of the bulkhead.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 7
Station ID: 8423898 PUBLICATION DATE: 12/19/2018
Name: FORT POINT, NEWCASTLE ISLAND
NH
NOAA Chart: 13283 Latitude: 43° 4.3' N ( 43.07139)
USGS Quad: KITTERY Longitude: 70° 42.6' W ( -70.71056)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: PORTSMOUTH USCG 1994
DESIGNATION: PORTSMOUTH USCG
MONUMENTATION: Horizontal Station disk VM#: 17349
AGENCY: National Geodetic Survey (NGS) IDB PID#: AB2631
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 43° 4.3' N ( 43.07088) LONGITUDE: 70° 42.8' W ( -70.71349)
The bench mark is a disk set into a rock ledge on the SW side of the road
leading to Fort Point located between two parking lots, a small one near the
head of the road leading to Fort Point and a larger one adjacent to "Battery
Farnsworth", 230 m (754.5 ft) WSW of the tide gage, and 110 m (360.9 ft) WNW of
bench mark US.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 7
Station ID: 8423898 PUBLICATION DATE: 12/19/2018
Name: FORT POINT, NEWCASTLE ISLAND
NH
NOAA Chart: 13283 Latitude: 43° 4.3' N ( 43.07139)
USGS Quad: KITTERY Longitude: 70° 42.6' W ( -70.71056)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: CONSTITUTION 147 NO 1 1941
DESIGNATION: CONSTITUTION 147 RM 1
MONUMENTATION: Reference Mark disk VM#: 17350
AGENCY: US Coast & Geodetic Survey
(USC&GS) IDB PID#: OC0429
SETTING CLASSIFICATION: Rock outcrop OPUS PID:
LATITUDE: 43° 4.2' N ( 43.07031) LONGITUDE: 70° 42.7' W ( -70.71087)
The bench mark is a CGS reference mark disk cemented in a drill hole in the rock
ledge bank of Portsmouth Harbor located 53.65 m (176.02 ft) west of the west
end of the concrete seawall in front of the coast guard station building, 16.3 m
(53.5 ft) southwest of the southwest corner of the asphalt enclosing the
helicopter landing pad, 7.62 m (25.00 ft) southeast of an iron bar in the west
end of a horse shoe pit, 5.4 m (17.7 ft) north of a small metal anchor bolt in
the rock ledge, and 1.83 m (6.00 ft) south of the south edge of the grassy lawn
of the Coast Guard recreation area. The mark is 0.3 m (1.0 ft) below the level
of the lawn.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 7
Station ID: 8423898 PUBLICATION DATE: 12/19/2018
Name: FORT POINT, NEWCASTLE ISLAND
NH
NOAA Chart: 13283 Latitude: 43° 4.3' N ( 43.07139)
USGS Quad: KITTERY Longitude: 70° 42.6' W ( -70.71056)
T I D A L D A T U M S
Tidal datums at FORT POINT, NEWCASTLE ISLAND based on:
LENGTH OF SERIES: 8 YEARS
TIME PERIOD: 10/03-9/05, 1/08-12/10, 8/11-7/14
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 (01/02/2010) = 3.742
MEAN HIGHER HIGH WATER MHHW = 2.863
MEAN HIGH WATER MHW = 2.733
North American Vertical Datum NAVD88 = 1.524
MEAN SEA LEVEL MSL = 1.429
MEAN TIDE LEVEL MTL = 1.418
MEAN LOW WATER MLW = 0.103
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (02/02/2018) = -0.827
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
2 1919 6.684 3.951
NO 1 1919 4.434 1.701
842 3898 TIDAL US 2.908 0.175
NO 6 1944 4.488 1.755
PORTSMOUTH USCG 1994 8.870 6.137
CONSTITUTION 147 NO 1 1941 6.003 3.270
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 7
Station ID: 8423898 PUBLICATION DATE: 12/19/2018
Name: FORT POINT, NEWCASTLE ISLAND
NH
NOAA Chart: 13283 Latitude: 43° 4.3' N ( 43.07139)
USGS Quad: KITTERY Longitude: 70° 42.6' W ( -70.71056)
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.