U.S. DEPARTMENT OF COMMERCE
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National Ocean Service
Datums Page Page 1 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
To reach the tidal bench marks from the Dauphin Island Post Office, proceed 0.3
km (0.2 mi) south on Lockland Street to its intersection with Bienville
Boulevard, then 4.0 km (2.5 mi) east on Bienville Boulevard to Fort Gaines at
the east end of the island. The bench marks are located near Fort Gaines and
the Dauphin Island Sea Lab complex. The tide gage is located atop a 7.6 m (25
ft) 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
DESIGNATION: 873 5180 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 787
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: BH1756
SETTING CLASSIFICATION: Gun mount on wall of fort OPUS PID#: BH1756
LATITUDE: 30° 15.0' N ( 30.24958) LONGITUDE: 88° 4.5' W ( -88.07553)
The primary bench mark is a disk set in the top of the NE corner of the concrete
gun mount located outside the main fort wall near the NW corner of the main
fort, 6.98 m (22.90 ft) west of the east edge of the gun emplacement, 3.85 m
(12.63 ft) north of the south edge of the gun emplacement, 0.41m (1.35 ft) south
of the north edge of the gun emplacement, and 0.39 m (1.28 ft) east of the west
edge of gun emplacement.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 2 1960
DESIGNATION: 873 5180 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 788
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: BH1757
SETTING CLASSIFICATION: Wall OPUS PID:
LATITUDE: 30° 15.0' N ( 30.24922) LONGITUDE: 88° 4.5' W ( -88.07572)
The bench mark is a disk set in a concrete gun mount on top of the main wall,
7.62 m (25.00 ft) SE of the extreme NW corner of the fort, 3.25 m (10.66 ft) NE
of an iron cannon, 3.03 m (9.94 ft) SW of the NE edge of the fort wall, and 0.64
m (2.10 ft) NW of the SE edge of the fort wall.
BENCH MARK STAMPING: NO 3 1960
DESIGNATION: 873 5180 TIDAL 3
MONUMENTATION: Tidal Station disk VM#: 789
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: BH1758
SETTING CLASSIFICATION: Wall gun mount OPUS PID:
LATITUDE: 30° 14.9' N ( 30.24878) LONGITUDE: 88° 4.5' W ( -88.07489)
The bench mark is a disk set in a concrete gun mount on top of the main wall at
the NE corner of the fort, 6.45 m (21.16 ft) SW of the NE edge of the gun
emplacement, 5.08 m (16.67 ft) south of the north edge of the fort wall, and
1.00 m (3.28 ft) NW of an iron cannon.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 4 1966
DESIGNATION: 873 5180 TIDAL 4
MONUMENTATION: Tidal Station disk VM#: 790
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: BH1760
SETTING CLASSIFICATION: Fort wall gun mount OPUS PID:
LATITUDE: 30° 14.9' N ( 30.24792) LONGITUDE: 88° 4.5' W ( -88.07531)
The bench mark is a disk set in a concrete coping near a gun mount on the SE
side of the fort, 38.10 m (125.00 ft) SE of bench mark tidal steel pipe, 13.30 m
(43.64 ft) east of the west edge of concrete coping, 1.60 m (5.25 ft) west of
the east edge, and 0.52 m (1.71 ft) NW of the SE edge of the fort wall.
BENCH MARK STAMPING: 5180 A 1976
DESIGNATION: 873 5180 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 791
AGENCY: National Ocean Survey (NOS) IDB PID#: BH1761
SETTING CLASSIFICATION: Retaining wall OPUS PID:
LATITUDE: 30° 14.9' N ( 30.24806) LONGITUDE: 88° 4.6' W ( -88.07633)
The bench mark is a disk set on top of the NE end of the SE retaining wall of
the SW bastion of the fort, 10.00 m (32.81 ft) SE of the NE end of the NW
retaining wall of the SW bastion, 7.62 m (25.00 ft) NE of the south corner of a
concrete building, and 2.77 m (9.09 ft) east of the east corner of the concrete
building.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5180 B 1976
DESIGNATION: 873 5180 B TIDAL
MONUMENTATION: Tidal Station disk VM#: 792
AGENCY: National Ocean Survey (NOS) IDB PID#: BH1755
SETTING CLASSIFICATION: Concrete post OPUS PID#: BH1755
LATITUDE: 30° 15.0' N ( 30.24969) LONGITUDE: 88° 4.6' W ( -88.07600)
The bench mark is a disk set in a concrete monument at the NE corner of a
U-drive entrance to the parking area of Fort Gaines, 48.91m (160.466 ft) east of
the west driveway entrance, 16.39 m (53.77 ft) south of the centerline of the
boulevard, 4.67 m (15.32 ft) west of the approximate center of the east drive to
the fort, and 2.60 m (8.53 ft) north of the wood fence at front of parking lot.
BENCH MARK STAMPING: 5180 C 1976
DESIGNATION: 873 5180 C TIDAL
MONUMENTATION: Tidal Station disk VM#: 793
AGENCY: National Ocean Survey (NOS) IDB PID#: BH1752
SETTING CLASSIFICATION: Concrete slab OPUS PID#: BH1752
LATITUDE: 30° 15.0' N ( 30.24947) LONGITUDE: 88° 4.6' W ( -88.07681)
The bench mark is a disk set in the top concrete slab 5.0 m x 6 m (16.4 ft x
19.7 ft) near the north edge, 18.50 m (60.70 ft) SSW of the SE corner of the
east wing of the Administration Building, 14.60 m (47.90 ft) SSE of the north
guy anchor of a tower, 14.20 m (46.59 ft) NNW of the SE guy wire anchor, 3.67 m
(12.04 ft) north of the south edge of slab, 3.11 m (10.20 ft) west of the east
edge of slab, 3.04 m (9.97 ft) east of the west edge of slab, and 0.79 m (2.592
ft) south of the north edge of slab.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5180 E 1976
DESIGNATION: 873 5180 E
MONUMENTATION: Tidal Station disk VM#: 795
AGENCY: National Ocean Survey (NOS) IDB PID#: BH1754
SETTING CLASSIFICATION: Foundation pad OPUS PID:
LATITUDE: 30° 15.0' N ( 30.24933) LONGITUDE: 88° 4.6' W ( -88.07700)
The bench mark is a disk set on top of a concrete foundation at the NE corner of
a very long aluminum storage shed behind the Administration Building/Library,
38.95 m (127.79 ft) east of the centerline of the driveway on the west side of
the Administration Building/Library, 30.85 NNW of the NE corner of the tech
support shop, 28.12 m (92.26 ft) SW of bench mark C, 20.55 m (67.42 ft) SE of
the SW corner of the Dauphin Island Sea Lab Library, 14.44 m (47.38 ft) SSE of
the SE corner of the Library/Administration Building, and 6.10 m (20.01 ft) west
of the center door to shed. Note - the storage shed covers the southern half of
the mark.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING:
DESIGNATION: 873 5180 TIDAL STEEL PIPE
ALIAS: NO STAMPING 1
MONUMENTATION: Chiseled Triangle VM#: 796
AGENCY: Unknown IDB PID#: BH1759
SETTING CLASSIFICATION: Wall OPUS PID:
LATITUDE: 30° 14.9' N ( 30.24806) LONGITUDE: 88° 4.5' W ( -88.07483)
The bench mark is a chiseled triangle set in the top of a 2-inch diameter steel
rod on the east side of the fort, 38.10 m (125.00 ft) NE of bench mark NO 4
1966, 5.35 m (17.55 ft) ESE of the front of the cannon mount, 2.00 m (6.56 ft)
WNW of the extreme east corner of the fort wall, and 0.45 m (1.48 ft) above wall
level.
BENCH MARK STAMPING: 21D 2E
DESIGNATION: 21D 2E
MONUMENTATION: Survey disk VM#: 13671
AGENCY: US Army Corps of Engineers (USE) IDB PID#: BH1751
SETTING CLASSIFICATION: Unspecified OPUS PID#: BH1751
LATITUDE: 30° 15.0' N ( 30.24969) LONGITUDE: 88° 4.6' W ( -88.07667)
The bench mark is a disk located 17.20 m (56.43 ft) ENE of the NE corner of the
Dauphin Island Sea Lab Building, 10.51 m (34.48 ft) west of the western-most
entrance to historic Fort Gaines parking lot, and 10.51 m (34.48 ft) west of the
western-most entrance to historic Fort Gaines parking lot.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 21D - 2C 17.82
DESIGNATION: 873 5180 21D - 2C
MONUMENTATION: Survey disk VM#: 16581
AGENCY: US Army Corps of Engineers (USE) IDB PID:
SETTING CLASSIFICATION: Gun mount OPUS PID:
LATITUDE: 30° 15.0' N ( 30.24967) LONGITUDE: 88° 4.5' W ( -88.07542)
The bench mark is a disk set in top of the NE corner of a concrete gun mount,
outside the main fort wall near the NW corner of the Fort Gaines, 3.54 m (11.61
ft) north of bench mark NO 1 1960, 1.78 m (5.84 ft) NE of the SW face of the gun
mount, 1.56 m (5.12 ft) south of the north face of the mount, 1.24 m (4.07 ft)
NW of the SE face of the mount, 1.00 m (3.28 ft) north of the south edge of fort
wall, 0.91 m (2.99 ft) east of the west edge of the fort wall, and 0.85 m (2.79
ft) south of the north edge of fort wall.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 8 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: CGS DI 2
DESIGNATION: CGS DI 2
MONUMENTATION: Bench Mark disk VM#: 22847
AGENCY: US Army Corps of Engineers (USACE) IDB PID:
SETTING CLASSIFICATION: Curb OPUS PID:
LATITUDE: 30° 15.0' N ( 30.25075) LONGITUDE: 88° 4.8' W ( -88.07942)
The bench mark is a brass disk set in the curb to the left of the main entry
gate for USCG Station Dauphin Island, 9.936 m (32.6 ft) NE of light pole #42691,
9.631 m (31.6 ft) east of the west fence line of the USCG property, 3.901 m
(12.8 ft) north of the south fence line of the USCG property, and set in a curb
12.7 cm (5 in) above the road surface.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 9 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
T I D A L D A T U M S
Tidal datums at DAUPHIN ISLAND, MOBILE BAY based on:
LENGTH OF SERIES: 29 YEARS
TIME PERIOD: 01/83-12/97, 10/01-09/03, 02/05-01/12, 09/13-08/18
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8729840 PENSACOLA, PENSACOLA BAY
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (09/16/2004) = 2.178
MEAN HIGHER HIGH WATER MHHW = 0.371
MEAN HIGH WATER MHW = 0.365
MEAN TIDE LEVEL MTL = 0.184
MEAN SEA LEVEL MSL = 0.174
North American Vertical Datum NAVD88 = 0.158
MEAN LOW WATER MLW = 0.004
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (01/19/1977) = -0.632
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
NO 1 1960 5.412 5.047
NO 2 1960 6.896 6.531
NO 3 1960 6.398 6.033
NO 4 1966 6.547 6.182
5180 A 1976 6.859 6.494
5180 B 1976 2.672 2.307
5180 C 1976 2.667 2.302
5180 E 1976 2.612 2.247
873 5180 TIDAL STEEL PIPE 6.388 6.023
21D 2E 2.144 1.779
21D - 2C 17.82 5.277 4.912
CGS DI 2 2.231 1.866
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 10 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
Foot Notes:
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 11 of 11
Station ID: 8735180 PUBLICATION DATE: 02/01/2021
Name: DAUPHIN ISLAND, MOBILE BAY
AL
NOAA Chart: 11376 Latitude: 30° 15.0' N ( 30.25000)
USGS Quad: LITTLE DAUPHIN ISLAND Longitude: 88° 4.5' W ( -88.07500)
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.