U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
Station ID: 8633532 PUBLICATION DATE: 05/29/2009
Name: TANGIER ISLAND, CHESAPEAKE BAY
VA
NOAA Chart: 12228 Latitude: 37° 49.7' N ( 37.82830)
USGS Quad: TANGIER ISLAND Longitude: 75° 59.6' W ( -75.99330)
To reach the tidal bench marks proceed by boat from Crisfield, MD, or private
plane to Tangier Island. The bench marks are located along Main Street (East
Ridge Road) south of the county dock, West Ridge Road, and at the north and
south ends of the airport runway. The tide gage and staff were located at the
inside corner of the elbow in the county dock.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 3532 D
DESIGNATION: 863 3532 D
MONUMENTATION: Tidal Station disk VM#: 3399
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID:
LATITUDE: ' °deg (0) LONGITUDE: ' °deg (0)
The primary bench mark is a disk located south of the county dock along the east
ridge road (Main Street), near the intersection of a road leading east to Canton
Ridge, in the NE corner of the yard of the Landon residence, 11.00 m (36.1 ft)
SE of the SE corner of the 2-story Wheatley residence, 5.30 m (17.4 ft) NE of
the NE corner of the 2-story Landon residence, and 0.67 m (2.2 ft) north of a
power pole. The bench mark is crimped to the top of a galvanized steel rod
driven 17.1 m (56 ft) to refusal.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
Station ID: 8633532 PUBLICATION DATE: 05/29/2009
Name: TANGIER ISLAND, CHESAPEAKE BAY
VA
NOAA Chart: 12228 Latitude: 37° 49.7' N ( 37.82830)
USGS Quad: TANGIER ISLAND Longitude: 75° 59.6' W ( -75.99330)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 3532 B
DESIGNATION: 863 3532 B
MONUMENTATION: Tidal Station disk VM#: 3397
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete footing OPUS PID:
LATITUDE: ' °deg (0) LONGITUDE: ' °deg (0)
The bench mark is a disk set in the SE concrete footing of a tower north of the
telephone company building, south of the county dock along Main Street, across
from the Methodist Church, 9.33 m (30.6 ft) SE of the NW corner of a fence
around the tower, 6.98 m (22.9 ft) NE of a T intersection in the fence, and 5.03
m (16.5 ft) NE of a corner of the telephone company building.
BENCH MARK STAMPING: 3532 F
DESIGNATION: 863 3532 F
MONUMENTATION: Tidal Station disk VM#: 3401
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Galvanized steel rod OPUS PID:
LATITUDE: ' °deg (0) LONGITUDE: ' °deg (0)
The bench mark is a disk located south of the county dock on East Ridge Road
near its southern end, then west on a black top road over two bridges to the
intersection of West Ridge Road, 23.16 m (76.0 ft) NE of a 1-story frame house,
21.34 m (70.0 ft) NW of the intersection, 15.54 m (51.0 ft) SE of the SE corner
of the Parks residence, and 1.19 m (3.9 ft) west of power pole #4-2-22. The
bench mark is crimped to the top of a galvanized steel rod driven 17.1 m (56 ft)
to refusal.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
Station ID: 8633532 PUBLICATION DATE: 05/29/2009
Name: TANGIER ISLAND, CHESAPEAKE BAY
VA
NOAA Chart: 12228 Latitude: 37° 49.7' N ( 37.82830)
USGS Quad: TANGIER ISLAND Longitude: 75° 59.6' W ( -75.99330)
T I D A L D A T U M S
Tidal datums at TANGIER ISLAND, CHESAPEAKE BAY based on:
LENGTH OF SERIES: 2 MONTHS
TIME PERIOD: April 2005 - May 2005
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8635750 LEWISETTA, POTOMAC RIVER
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 0.536
MEAN HIGH WATER MHW = 0.487
MEAN SEA LEVEL MSL = 0.260
MEAN TIDE LEVEL MTL = 0.258
MEAN LOW WATER MLW = 0.028
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
3532 D 0.972 0.485
3532 B 1.337 0.850
3532 F 0.919 0.432
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
Station ID: 8633532 PUBLICATION DATE: 05/29/2009
Name: TANGIER ISLAND, CHESAPEAKE BAY
VA
NOAA Chart: 12228 Latitude: 37° 49.7' N ( 37.82830)
USGS Quad: TANGIER ISLAND Longitude: 75° 59.6' W ( -75.99330)
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.