U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 07/12/1989
Station ID: 8459338 SUPERCEDED DATE: 04/21/2003
Name: OLD HARBOR, BLOCK ISLAND SOUND
RHODE ISLAND
NOAA Chart: 13217 Latitude: 41° 10.4' N
USGS Quad: BLOCK ISLAND Longitude: 71° 33.4' W
To reach the tidal bench marks from Point Judith or New London, CT, proceed by
ferry to the ferry terminal at Old Harbor on Block Island. The bench marks are
in the harbor area and along Water Street. The tide gage and staff were on the
NW side of the large pier of the ferry landing.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 4 1938
MONUMENTATION: Survey Disk VM#: 2222
AGENCY: PID#: LW0927
SETTING CLASSIFICATION: Stone Base
The bench mark is set in top of the east side of the stone base of the Womens
Christian Temperance Union statue in the center of the intersection of Front,
High, and Water Streets, near the SE corner of the base, 72.2 feet (22.0 m) SW
of the SW porch corner of Chapel Cottage on Front Street, 57.1 feet (17.4 m)
south of the south corner of a 3-story blue and white building at the
intersection of Front and Water Streets, and 44.2 feet (13.5 m) east of an
unnumbered power pole at the intersection of Water and High Streets, and at
ground level.
BENCH MARK STAMPING: 9338 A 1987
MONUMENTATION: Survey Disk VM#: 2223
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is set in the NE corner of the Block Island Post Office loading
platform, 95.5 feet (29.1 m) SW of the centerline of Corn Neck Road, 33.2 feet
(10.1 m) west of the NE corner of the post office, 2.7 feet (0.8 m) east of the
southernmost of two loading platform columns, and 2.1 feet (0.6 m) above ground
level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 07/12/1989
Station ID: 8459338 SUPERCEDED DATE: 04/21/2003
Name: OLD HARBOR, BLOCK ISLAND SOUND
RHODE ISLAND
NOAA Chart: 13217 Latitude: 41° 10.4' N
USGS Quad: BLOCK ISLAND Longitude: 71° 33.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 9338 B 1987
MONUMENTATION: Survey Disk VM#: 2224
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Retaining Wall
The bench mark is set in top of the north corner of the concrete retaining wall
in front of the National Hotel, 85.4 feet (26.0 m) north of the center railing
of the steps for the main entrance to the hotel, 54.5 feet (16.6 m) SE of the
bottom step of the entrance to the Surf Hotel, 21.0 feet (6.4 m) SW of the
centerline of the bend in Water Street, 0.5 foot (0.2 m) west of a white picket
fence, and at sidewalk level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 07/12/1989
Station ID: 8459338 SUPERCEDED DATE: 04/21/2003
Name: OLD HARBOR, BLOCK ISLAND SOUND
RHODE ISLAND
NOAA Chart: 13217 Latitude: 41° 10.4' N
USGS Quad: BLOCK ISLAND Longitude: 71° 33.4' W
T I D A L D A T U M S
Tidal datums at OLD HARBOR, BLOCK ISLAND SOUND based on:
LENGTH OF SERIES: 12 MONTHS
TIME PERIOD: APRIL 1988-MARCH 1989
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8452660 NEWPORT
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (10/22/1988) = 5.38
MEAN HIGHER HIGH WATER MHHW = 3.28
MEAN HIGH WATER MHW = 3.02
MEAN TIDE LEVEL MTL = 1.57
MEAN LOW WATER MLW = 0.12
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (02/09/1989) = -1.96
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
4 1938 25.68 22.66
9338 A 1987 11.06 8.04
9338 B 1987 20.36 17.34
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 07/12/1989
Station ID: 8459338 SUPERCEDED DATE: 04/21/2003
Name: OLD HARBOR, BLOCK ISLAND SOUND
RHODE ISLAND
NOAA Chart: 13217 Latitude: 41° 10.4' N
USGS Quad: BLOCK ISLAND Longitude: 71° 33.4' 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.