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National Ocean Service
Datums Page Page 1 of 5
Station ID: 8573903 PUBLICATION DATE: 04/30/2003
Name: TOWN POINT WHARF
MD
NOAA Chart: 12277 Latitude: 39° 30.2' N ( 39.50330)
USGS Quad: NORTH EAST Longitude: 75° 55.0' W ( -75.91670)
To reach the tidal bench marks from South Chesapeake City, proceed 5 km (3 mi)
south on U.S. Highway 213 to Town Point Road, then 5.1 km (3.2 mi) west on Town
Road to Hollywood Beach Road, turn right and go 1.5 km (0.9 mi) NW on a black
top road to its end, bear left at the Y onto Gour Road. The bench marks are
located along Gour Road. The tide gage and staff were located on Town Point
Wharf.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 5 1972
DESIGNATION: 857 3903 TIDAL 5
MONUMENTATION: Tidal Station disk VM#: 5896
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete slab OPUS PID:
LATITUDE: 39° 30.2' N ( 39.50330) LONGITUDE: 75° 55.0' W ( -75.91670)
The primary bench mark is a disk set flush in the SW corner of a concrete slab
at the base of a 18 m (60 ft) tower in the center of the wharf, 8.69 m (28.5 ft)
east of the west end of the wharf, and 7.47 m (24.5 ft) south of the north wall
of the wharf.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 8573903 PUBLICATION DATE: 04/30/2003
Name: TOWN POINT WHARF
MD
NOAA Chart: 12277 Latitude: 39° 30.2' N ( 39.50330)
USGS Quad: NORTH EAST Longitude: 75° 55.0' W ( -75.91670)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: M 130 1971
DESIGNATION: M 130
MONUMENTATION: Bench Mark disk VM#: 5895
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU1847
SETTING CLASSIFICATION: Copper-clad steel rod with baseplate OPUS PID:
LATITUDE: 39° 30.1' N ( 39.50170) LONGITUDE: 75° 54.9' W ( -75.91500)
The bench mark is a disk located 58.80 m (192.9 ft) NW of the centerline of the
road leading SW to the North Bluff (this road is perpendicular to Gour Road),
8.90 m (29.2 ft) SW of the center of a large concrete street drain near the NE
gate post, 6.77 m (22.2 m) south of the SW gate post for the gate across the
road, 5.09 m (16.7 ft) SW of the centerline of Gour Road, 5.45 m (17.8 ft) SE of
the twin trunk 5-feet diameter tree, and 5.58 m (18.3 ft) NW of the most
southern of two 6x6-feet gate posts. The bench mark is set 6 cm (0.2 ft) below
ground level, crimped to the top of a 1.22 m (4 ft) copper-clad steel rod
attached to a metal base plate, and encased in a 4-inch steel pipe.
BENCH MARK STAMPING: NO 2 1975
DESIGNATION: 857 3903 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 5898
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Retaining walls OPUS PID:
LATITUDE: 39° 30.2' N ( 39.50330) LONGITUDE: 75° 55.0' W ( -75.91670)
The bench mark is a disk set flush in a concrete bulkhead in front of a private
residence, 5.58 m (18.3 ft) west of the centerline of the road leading to the
wharf, and 0.88 m (2.9 ft) west of the east end of the bulkhead.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 8573903 PUBLICATION DATE: 04/30/2003
Name: TOWN POINT WHARF
MD
NOAA Chart: 12277 Latitude: 39° 30.2' N ( 39.50330)
USGS Quad: NORTH EAST Longitude: 75° 55.0' W ( -75.91670)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 3903 A 1986
DESIGNATION: 857 3903 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 5899
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 39° 30.2' N ( 39.50330) LONGITUDE: 75° 55.0' W ( -75.91670)
The bench mark is a disk located near Town Point Wharf at the end of Gour Road,
20.21 m (66.3 ft) SE of a telephone pole with a light on the north side of North
Bluff Road, 9.75 m (32.0 ft) SE of the centerline of North Bluff Road, 7.74 m
(25.4 ft) SW of the centerline of Gour Road, and 3.63 m (11.9 ft) SW of the most
northerly mailbox post of eleven mailboxes. The bench mark is set 15 cm (0.5 ft)
below ground level, crimped to the top of a stainless steel rod driven 9.1 m (30
ft) and encased in a 6-inch PVC pipe with a cap.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 8573903 PUBLICATION DATE: 04/30/2003
Name: TOWN POINT WHARF
MD
NOAA Chart: 12277 Latitude: 39° 30.2' N ( 39.50330)
USGS Quad: NORTH EAST Longitude: 75° 55.0' W ( -75.91670)
T I D A L D A T U M S
Tidal datums at TOWN POINT WHARF based on:
LENGTH OF SERIES: 7 YEARS
TIME PERIOD: January 1987 - December 1993
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8574680 BALTIMORE, FORT MCHENRY, PATAPSCO RIVER
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (09/06/1979) = 2.024
MEAN HIGHER HIGH WATER MHHW = 0.817
MEAN HIGH WATER MHW = 0.721
MEAN TIDE LEVEL MTL = 0.390
MEAN SEA LEVEL MSL = 0.383
MEAN LOW WATER MLW = 0.059
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (04/05/1975) = -1.128
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
NO 5 1972 2.209 1.488
M 130 1971 3.232 2.511
NO 2 1975 2.600 1.879
3903 A 1986 4.632 3.911
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 8573903 PUBLICATION DATE: 04/30/2003
Name: TOWN POINT WHARF
MD
NOAA Chart: 12277 Latitude: 39° 30.2' N ( 39.50330)
USGS Quad: NORTH EAST Longitude: 75° 55.0' W ( -75.91670)
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.