U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
PUBLICATION DATE: 07/25/1989
Station ID: 8735180 SUPERCEDED DATE: 04/21/2003
Name: DAUPHIN ISLAND (FORT GAINES), MOBILE BAY
ALABAMA
NOAA Chart: 11378 Latitude: 30° 15.0' N
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W
To reach the tidal bench marks from the Dauphin Island Post Office, proceed 0.2
mile (0.3 km) south on Lockland Street to its intersection with Bienville
Boulevard, then 2.5 miles (4.0 km) east on Bienville Boulevard to Fort Gaines at
the east end of the island. The bench marks are near Fort Gaines and the
Dauphin Island Sea Lab complex. The tide gage and electric tape gage are atop a
25-foot (8 m) high tower on the SE side of a large fishing pier north of the
fort.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1 1960
MONUMENTATION: Survey Disk VM#: 787
AGENCY: PID#: BH1756
SETTING CLASSIFICATION: Gun Mount
The bench mark is set in the NE corner of a concrete gun mount outside the main
wall at the NW corner of the fort, 50 feet (15 m) east of a radio tower.
BENCH MARK STAMPING: NO 2 1960
MONUMENTATION: Survey Disk VM#: 788
AGENCY: PID#: BH1757
SETTING CLASSIFICATION: Gun Mount
The bench mark is set in a concrete gun mount on top of the main wall, 25.0 feet
(7.6 m) SE of the extreme NW corner of the fort, and 12.0 feet (3.7 m) NE of an
iron cannon.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
PUBLICATION DATE: 07/25/1989
Station ID: 8735180 SUPERCEDED DATE: 04/21/2003
Name: DAUPHIN ISLAND (FORT GAINES), MOBILE BAY
ALABAMA
NOAA Chart: 11378 Latitude: 30° 15.0' N
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 3 1960
MONUMENTATION: Survey Disk VM#: 789
AGENCY: PID#: BH1758
SETTING CLASSIFICATION: Gun Mount
The bench mark is set in a concrete gun mount on top of the main wall at the NE
corner of the fort, and 3.0 feet (0.9 m) NW of an iron cannon.
BENCH MARK STAMPING: NO 4 1966
MONUMENTATION: Survey Disk VM#: 790
AGENCY: PID#: BH1760
SETTING CLASSIFICATION: Gun Mount
The bench mark is set in a concrete coping of a gun mount on the SE side of the
fort, and 5.0 feet (1.5 m) NW of the SE edge of the fort wall.
BENCH MARK STAMPING: 5180 A 1976
MONUMENTATION: Survey Disk VM#: 791
AGENCY: PID#: BH1761
SETTING CLASSIFICATION: Retaining Wall
The bench mark is set on top of the NE end of the SE retaining wall of the SW
bastion of the fort, 33.8 feet (10.3 m) SE of the NE end of the NW retaining
wall of the SW bastion, 25.3 feet (7.7 m) NE of the south corner of a concrete
building, and 9.1 feet (2.8 m) east of the east corner of the concrete building.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
PUBLICATION DATE: 07/25/1989
Station ID: 8735180 SUPERCEDED DATE: 04/21/2003
Name: DAUPHIN ISLAND (FORT GAINES), MOBILE BAY
ALABAMA
NOAA Chart: 11378 Latitude: 30° 15.0' N
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5180 B 1976
MONUMENTATION: Survey Disk VM#: 792
AGENCY: PID#: BH1755
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in a concrete monument at the NE corner of the yard of a
U-drive entrance to the parking area at Fort Gaines, 55.0 feet (16.8 m) south of
the centerline of Bienville Boulevard, 15.0 feet (4.6 m) west of the centerline
of the east drive to the fort, and at ground level.
BENCH MARK STAMPING: 5180 C 1976
MONUMENTATION: Survey Disk VM#: 793
AGENCY: PID#: BH1752
SETTING CLASSIFICATION: Concrete Slab
The bench mark is set on a 15x20-foot (5x6 m) concrete slab in the NE corner of
the Dauphin Island Sea Lab complex, 65.1 feet (19.8 m) SSW of the SE corner of
the east wing of the administration building, 47.5 feet (14.5 m) SSE of the
north guy wire anchor, 46.6 feet (14.2 m) NNW of the SE guy wire anchor, and 0.5
foot (0.2 m) above ground level.
BENCH MARK STAMPING: 5180 D 1976
MONUMENTATION: Survey Disk VM#: 794
AGENCY: PID#: BH1753
SETTING CLASSIFICATION: Concrete Fuel Tank Cradle
The bench mark is set on top of the south end of the east concrete cradle
supporting a fuel tank, 66.6 feet (20.3 m) WNW of the SE guy wire anchor, 58.8
feet (17.9 m) WSW of Bench Mark 5180 C 1976, 29.1 feet (8.9 m) east of the SE
corner of the Dauphin Island Sea Lab Library, and 2.5 feet (0.8 m) above ground
level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
PUBLICATION DATE: 07/25/1989
Station ID: 8735180 SUPERCEDED DATE: 04/21/2003
Name: DAUPHIN ISLAND (FORT GAINES), MOBILE BAY
ALABAMA
NOAA Chart: 11378 Latitude: 30° 15.0' N
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5180 E 1976
MONUMENTATION: Survey Disk VM#: 795
AGENCY: PID#: BH1754
SETTING CLASSIFICATION: Foundation
The bench mark is set on top at the NE corner of a concrete foundation of a
storage shed, 101.2 feet (30.8 m) NNW of the NE corner of the Tech Support Shop,
68.0 feet (20.7 m) SE of the SW corner of the Dauphin Island Sea Lab Library,
and 47.9 feet (14.6 m) SSE of the SE corner of the library.
BENCH MARK STAMPING: NO STAMPING 1
MONUMENTATION: Metal Rod VM#: 796
AGENCY: PID#: BH1759
SETTING CLASSIFICATION: Wall
The bench mark is the top of a 2-inch diameter steel rod with a triangle
chiseled in the top on the east side of the fort, 125.0 feet (38.1 m) NE of
Bench Mark No 4 1966, 5.0 feet (1.5 m) WNW of the extreme east corner of the
fort wall, and 1.5 feet (0.5 m) above wall level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
PUBLICATION DATE: 07/25/1989
Station ID: 8735180 SUPERCEDED DATE: 04/21/2003
Name: DAUPHIN ISLAND (FORT GAINES), MOBILE BAY
ALABAMA
NOAA Chart: 11378 Latitude: 30° 15.0' N
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W
T I D A L D A T U M S
Tidal datums at DAUPHIN ISLAND (FORT GAINES), MOBILE BAY based on:
LENGTH OF SERIES: 17 YEARS
TIME PERIOD: 1967-1987
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8729840 PENSACOLA, FL
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (09/02/1985) = 4.76
MEAN HIGHER HIGH WATER MHHW = 1.22
MEAN HIGH WATER MHW = 1.21
MEAN TIDE LEVEL MTL = 0.62
MEAN LOW WATER MLW = 0.04
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (01/19/1977) = -1.88
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
NO 1 1960 17.95 16.74
NO 2 1960 22.81 21.60
NO 3 1960 21.18 19.97
NO 4 1966 21.70 20.49
5180 A 1976 22.70 21.49
5180 B 1976 8.97 7.76
5180 C 1976 8.95 7.74
5180 D 1976 10.33 9.12
5180 E 1976 8.77 7.56
NO STAMPING 1 21.15 19.94
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
PUBLICATION DATE: 07/25/1989
Station ID: 8735180 SUPERCEDED DATE: 04/21/2003
Name: DAUPHIN ISLAND (FORT GAINES), MOBILE BAY
ALABAMA
NOAA Chart: 11378 Latitude: 30° 15.0' N
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' 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.