U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 8
PUBLICATION DATE: 09/29/2000
Station ID: 8761724 SUPERCEDED DATE: 04/21/2003
Name: GRAND ISLE, EAST POINT
LOUISIANA
NOAA Chart: 11358 Latitude: 29° 15.8' N
USGS Quad: FORT LIVINGSTON Longitude: 89° 57.4' W
To reach the tidal bench marks from the Post Office in Grand Isle, proceed
northeasterly along State Highway 1 for 3.9 km (2.4 mi), thence 1.3 km (0.8 mi)
northeasterly along a paved road, thence 0.2 km (0.1 mi) northwesterly along
Semper Road leading to the U.S. Coast Guard Station. The bench marks are
located within the U.S. Coast Guard compound. The tide gage is located next to
the boat house.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 10
DESIGNATION: 10
MONUMENTATION: Survey disk VM#: 817
AGENCY: US Coast Guard (USCG) PID#: AT0687
SETTING CLASSIFICATION: Concrete bulkhead
The primary bench mark is a disk set in top of a concrete sea wall at the Coast
Guard Station, 7.92 m (26.0 ft) SSW of the north end of the concrete boat ramp,
6.61 m (21.7 ft) NNW of the NW corner of the boat house, and 1.60 m (5.2 ft) SE
of the east side of the small boat ramp.
BENCH MARK STAMPING: 13 1975
DESIGNATION: 876 1724 TIDAL 13
MONUMENTATION: Tidal Station disk VM#: 821
AGENCY: National Ocean Survey (NOS) PID#: AT0688
SETTING CLASSIFICATION: Concrete bulkhead
The bench mark is a disk set in top of a concrete bulkhead at the Coast Guard
Station, 44.99 m (147.6 ft) NW of the NW face of a boat house, 29.70 m (97.4 ft)
SW of the extended center of the road, 9.90 m (32.5 ft) SE of the NW end of the
concrete bulkhead, and 0.30 m (1.0 ft) above the level of the road.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 8
PUBLICATION DATE: 09/29/2000
Station ID: 8761724 SUPERCEDED DATE: 04/21/2003
Name: GRAND ISLE, EAST POINT
LOUISIANA
NOAA Chart: 11358 Latitude: 29° 15.8' N
USGS Quad: FORT LIVINGSTON Longitude: 89° 57.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1724 A 1980
DESIGNATION: 876 1724 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 822
AGENCY: National Ocean Survey (NOS) PID#: AT0683
SETTING CLASSIFICATION: Stainless steel rod
The bench mark is a disk located 64.10 m (210.3 ft) NW of bench mark 1724 B
1980, 51.80 m (169.9 ft) SW of the center of Semper Road, 12.01 m (39.4 ft) SE
of the south corner of the foundation of a building, 3.50 m (11.5 ft) NW of the
west corner of a chain-link fence, 3.10 m (10.2 ft) west of the fence, and 0.30
m (1.0 ft) below the level of the road. The bench mark is recessed 21 cm (0.7
ft) below ground level, crimped to a stainless steel rod driven 18.3 m (60 ft)
to substantial resistance, and encased in a 4-inch PVC pipe and concrete
kickblock.
BENCH MARK STAMPING: 1724 B 1980
DESIGNATION: 876 1724 B TIDAL
MONUMENTATION: Tidal Station disk VM#: 823
AGENCY: National Ocean Survey (NOS) PID#: AT0682
SETTING CLASSIFICATION: Stainless steel rod
The bench mark is a disk located 64.40 m (211.3 ft) NW of bench mark 1724 C
1980, 64.10 m (210.3 ft) SE of bench mark 1724 A 1980, 32.30 m (106.0 ft) SW of
the center of Semper Road, 15.10 m (49.5 ft) SSW of the east corner of a
chain-link fence corner, 5.70 m (18.7 ft) ENE of the south corner of a
chain-link fence, 5.60 m (18.4 ft) east of the fence, and 0.30 m (1.0 ft) below
the level of the road. The bench mark is recessed 30 cm (1.0 ft) below ground
level, crimped to a stainless steel rod driven 19.8 m (65 ft) to substantial
resistance, and encased in a 4-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 8
PUBLICATION DATE: 09/29/2000
Station ID: 8761724 SUPERCEDED DATE: 04/21/2003
Name: GRAND ISLE, EAST POINT
LOUISIANA
NOAA Chart: 11358 Latitude: 29° 15.8' N
USGS Quad: FORT LIVINGSTON Longitude: 89° 57.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1724 C 1980
DESIGNATION: 876 1724 C TIDAL
MONUMENTATION: Tidal Station disk VM#: 824
AGENCY: National Ocean Survey (NOS) PID#: AT0681
SETTING CLASSIFICATION: Stainless steel rod
The bench mark is a disk located 64.40 m (211.3 ft) SE of bench mark 1724 B
1980, 61.00 m (200.1 ft) NW of the center of a paved road, 20.90 m (68.6 ft) SW
of the center of Semper Road leading to the Coast Guard Station, 20.70 m (67.9
ft) SW of the south corner of a foundation for 2 fuel tanks, 3.80 m (12.5 ft)
WNW of a fence corner and gate post, 0.40 m (1.3 ft) north of a witness post,
and 0.30 m (1.0 ft) below the level of Semper Road. The bench mark is recessed
30 cm (1.0 ft) below ground level, crimped to a stainless steel rod driven 18.3
m (60 ft) to substantial resistance, and encased in a 4-inch PVC pipe and
concrete kickblock.
BENCH MARK STAMPING: 1724 D 1980
DESIGNATION: 876 1724 D TIDAL
MONUMENTATION: Tidal Station disk VM#: 825
AGENCY: National Ocean Survey (NOS) PID#: AT0689
SETTING CLASSIFICATION: Stainless steel rod
The bench mark is a disk located 17.70 m (58.1 ft) NE of bench mark T 358 1982,
13.40 m (44.0 ft) NW of and level with the center of the road, 11.30 m (37.1 ft)
east of the SE corner of a house, 1.30 m (4.3 ft) SW of a chain-link fence
corner, and 0.30 m (1.0 ft) NW of a chain-link fence. The bench mark is
recessed 20 cm (0.7 ft) below ground level, crimped to a stainless steel rod
driven 18.3 m (60 ft) to substantial resistance, and encased in a 4-inch PVC
pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 8
PUBLICATION DATE: 09/29/2000
Station ID: 8761724 SUPERCEDED DATE: 04/21/2003
Name: GRAND ISLE, EAST POINT
LOUISIANA
NOAA Chart: 11358 Latitude: 29° 15.8' N
USGS Quad: FORT LIVINGSTON Longitude: 89° 57.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: T 358 1982
DESIGNATION: T 358
MONUMENTATION: Flange-encased Rod VM#: 827
AGENCY: National Geodetic Survey (NGS) PID#: AT0680
SETTING CLASSIFICATION: Stainless steel rod in sleeve
The bench mark is a flange-encased rod, 17.70 m (58.1 ft) SW of bench mark 1724
D 1980, 13.40 m (44.0 ft) NW of and level with the center of the road, 7.90 m
(25.9 ft) NE of the center of Semper Road leading to the Coast Guard Station,
3.70 m (12.1 ft) north of a utility light pole, 1.90 m (6.2 ft) ENE of the SE
leg of a sign (U.S. Coast Guard), and 0.70 m (2.3 ft) NW of a chain-link fence.
The datum point is the top of a stainless steel rod driven 24.4 m (80 ft),
encased in a sleeve extending to a depth of 6 m (20 ft), and set in a standard
NGS logo cap.
BENCH MARK STAMPING: 11
DESIGNATION: 11
MONUMENTATION: Survey disk VM#: 828
AGENCY: US Coast Guard (USCG) PID#: AT0685
SETTING CLASSIFICATION: Concrete bulkhead
The bench mark is a disk set flush in top of a concrete bulkhead next to the
small boat house, 46.63 m (153.0 ft) west of the entrance doors to the Coast
Guard administration building, 18.50 m (60.7 ft) south of the NE corner of the
concrete bulkhead, and 7.38 m (24.2 ft) north of the NE pile of the NOAA tide
station platform.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 8
PUBLICATION DATE: 09/29/2000
Station ID: 8761724 SUPERCEDED DATE: 04/21/2003
Name: GRAND ISLE, EAST POINT
LOUISIANA
NOAA Chart: 11358 Latitude: 29° 15.8' N
USGS Quad: FORT LIVINGSTON Longitude: 89° 57.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1724 F 1992
DESIGNATION: 876 1724 F
MONUMENTATION: Tidal Station disk VM#: 13752
AGENCY: National Ocean Service (NOS) PID:
SETTING CLASSIFICATION: Concrete foundation
The bench mark is a disk set flush in the concrete footing at the east end of
the garage door at the entrance of Coast Guard Maintenance Building, 93.27 m
(306.0 ft) NE of the center of the driveway, 26.60 m (87.3 ft) NW of a light
pole with concrete base, 19.30 m (63.3 ft) west of the SE corner of the Coast
Guard Maintenance Building, and 3.30 m (10.8 ft) east of the SW corner of the
maintenance building.
BENCH MARK STAMPING: 1724 G 1992
DESIGNATION: 876 1724 G
MONUMENTATION: Tidal Station disk VM#: 13753
AGENCY: National Ocean Service (NOS) PID:
SETTING CLASSIFICATION: Concrete foundation
The bench mark is a disk set flush in the foundation at the SW corner of
Hazardous Material Storage Garage, 32.80 m (107.6 ft) NNW of the NW corner of
the building, 7 m (23 ft) west of the SE corner of the building, 0.30 m (1.0 ft)
east of SW corner of the building, and 0.21 m (0.7 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 8
PUBLICATION DATE: 09/29/2000
Station ID: 8761724 SUPERCEDED DATE: 04/21/2003
Name: GRAND ISLE, EAST POINT
LOUISIANA
NOAA Chart: 11358 Latitude: 29° 15.8' N
USGS Quad: FORT LIVINGSTON Longitude: 89° 57.4' W
T I D A L D A T U M S
Tidal datums at GRAND ISLE, EAST POINT based on:
LENGTH OF SERIES: 5 YEARS
TIME PERIOD: January 1990 - December 1994
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION:
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (10/27/1985) = 1.365
MEAN HIGHER HIGH WATER MHHW = 0.338
MEAN HIGH WATER MHW = 0.330
MEAN SEA LEVEL MSL = 0.171
MEAN TIDE LEVEL MTL = 0.169
MEAN LOW WATER MLW = 0.007
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum NAVD88 = -0.138
LOWEST OBSERVED WATER LEVEL (02/03/1951) = -0.842
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
10 1.054 0.724
13 1975 1.074 0.744
1724 A 1980 0.920 0.590
1724 B 1980 0.858 0.528
1724 C 1980 0.885 0.555
1724 D 1980 0.793 0.463
T 358 1982 0.834 0.504
11 1.079 0.749
1724 F 1992 1.226 0.896
1724 G 1992 1.271 0.941
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 8
PUBLICATION DATE: 09/29/2000
Station ID: 8761724 SUPERCEDED DATE: 04/21/2003
Name: GRAND ISLE, EAST POINT
LOUISIANA
NOAA Chart: 11358 Latitude: 29° 15.8' N
USGS Quad: FORT LIVINGSTON Longitude: 89° 57.4' W
Foot Notes:
The Louisiana coast has anomalous relative sea level trends compared to most
other geographic regions in the United States. This is do to a general
subsidence of land in this area, which has been occurring at a rapid rate.
Because of the magnitude of the sea level trends in these areas, NOAA has
adopted a procedure for computing accepted tidal datums for the National Water
Level Observation Network (NWLON) using the last several years of sea level data
rather than the 19- year tidal epoch. The tide ranges are still based on the
1960-1978 National Tidal Datum Epoch (NTDE) and are applied to the 5 year
(1990-1994) mean tidal level (MTL) to compute other tidal datums. The adoption
of this procedure was necessary to ensure that these tidal datums accurately
represent the existing stand of sea level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 8 of 8
PUBLICATION DATE: 09/29/2000
Station ID: 8761724 SUPERCEDED DATE: 04/21/2003
Name: GRAND ISLE, EAST POINT
LOUISIANA
NOAA Chart: 11358 Latitude: 29° 15.8' N
USGS Quad: FORT LIVINGSTON Longitude: 89° 57.4' 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.