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Datums Page Page 1 of 5
Station ID: 8761529 PUBLICATION DATE: 09/12/2008
Name: MARTELLO CASTLE, LAKE BORGNE
LA
NOAA Chart: 11369 Latitude: 29° 56.7' N ( 29.94500)
USGS Quad: MARTELLO CASTLE Longitude: 89° 50.1' W ( -89.83500)
By boat from the boat launch on Marina Road north of the town of Chalmette,
proceed 1.8 km (1.1 mi) NNE to a more well defined canal, continue 2.4 km (1.5
mi) NE through the locks into the Mississippi River-Gulf Outlet canal (MRGO),
turn right and proceed 9.5 km (5.9 mi) SE to the entrance to Lake Borgne, then
turn left and proceed 0.6 km (0.4 mi) to the remains of Martello Castle in Lake
Borgne. The tide house was located on a wooden platform on the east side of the
castle remains. The bench marks are located on the castle remains, the marsh arm
south of the castle, and on the hurricane protection levee on the SW bank of the
MRGO.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 1529 F 2006
DESIGNATION: 876 1529 F
MONUMENTATION: Tidal Station disk VM#: 18493
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 29° 56.7' N ( 29.94500) LONGITUDE: 89° 50.1' W ( -89.83500)
The primary bench mark is a disk set in massive rough poured concrete on the
west side of the remains of Martello Castle, 23.88 m (78.3 ft) east of tidal
bench mark 8761529 E, 3.0 m (10 ft) SE of the top of the brick rubble, 2.4 m (8
ft) NW of the outside edge of Martello Castle concrete footing, and flush with
the concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 8761529 PUBLICATION DATE: 09/12/2008
Name: MARTELLO CASTLE, LAKE BORGNE
LA
NOAA Chart: 11369 Latitude: 29° 56.7' N ( 29.94500)
USGS Quad: MARTELLO CASTLE Longitude: 89° 50.1' W ( -89.83500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1529 E 2006
DESIGNATION: 876 1529 E
MONUMENTATION: Tidal Station disk VM#: 18494
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 29° 56.7' N ( 29.94500) LONGITUDE: 89° 50.1' W ( -89.83500)
The bench mark is a disk set in a concrete footing on the east side of the
remains of Martello Castle, 23.88 m (78.3 ft) west of tidal bench mark 8761529
F, 2.1 m (7 ft) south of the north end of the concrete footing, 0.76 m (2.5 ft)
west of the ESE edge of the footing, 0.6 m (2 ft) east of the WNW edge of the
concrete footing and flush with the concrete.
BENCH MARK STAMPING: 1529 G 2006
DESIGNATION: 876 1529 G
MONUMENTATION: Flange-encased Rod VM#: 18495
AGENCY: National Geodetic Survey IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod in sleeve OPUS PID:
LATITUDE: 29° 56.5' N ( 29.94170) LONGITUDE: 89° 50.2' W ( -89.83670)
The bench mark is a sleeve encased rod located in the top centerline of a small
containment berm used for disposal of dredging spoil from the Mississippi River
Gulf Outlet (MRGO) canal, approximately 120 m (400 ft) NNE of the NE bank of the
MRGO, 64.23 m (210.7 ft) east of tidal bench mark 8761529 H, and approximately
18 m (60 ft) south of the marsh vegetation line with Lake Borgne. The datum
point is set flush with the ground, being the top of a stainless steel roddriven
18.90 m (62.0 ft) to refusal, in a sleeve extending to a depth of 0.9 m (3 ft),
and encased in a 8 inch NGS logo cap set in concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 8761529 PUBLICATION DATE: 09/12/2008
Name: MARTELLO CASTLE, LAKE BORGNE
LA
NOAA Chart: 11369 Latitude: 29° 56.7' N ( 29.94500)
USGS Quad: MARTELLO CASTLE Longitude: 89° 50.1' W ( -89.83500)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1529 H 2006
DESIGNATION: 876 1529 H
MONUMENTATION: Flange-encased Rod VM#: 18496
AGENCY: National Geodetic Survey IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod in sleeve OPUS PID:
LATITUDE: 29° 56.5' N ( 29.94170) LONGITUDE: 89° 50.2' W ( -89.83670)
The bench mark is a sleeve encased rod located in the top centerline of a small
containment berm used for disposal of dredging spoil from the Mississippi River
Gulf Outlet (MRGO) canal, approximately 107 m (350 ft) NNE of the NE bank of the
MRGO, 64.23 m (210.7 ft) west of tidal bench mark 8761529 G, approximately 30 m
(100 ft) south of the marsh vegetation line with Lake Borgne, and approximately
15 m (50 ft) SE of the marsh vegetation line at a washed out cut between the
channel and Lake Borgne. The datum point is set flush with the ground, being the
top of a stainless steel rod driven 19.51 m (64.0 ft) to refusal, in a sleeve
extending to a depth of 0.9 m (3 ft), and encased in a 8 inch NGS logo cap set
in concrete.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 8761529 PUBLICATION DATE: 09/12/2008
Name: MARTELLO CASTLE, LAKE BORGNE
LA
NOAA Chart: 11369 Latitude: 29° 56.7' N ( 29.94500)
USGS Quad: MARTELLO CASTLE Longitude: 89° 50.1' W ( -89.83500)
T I D A L D A T U M S
Tidal datums at MARTELLO CASTLE, LAKE BORGNE based on:
LENGTH OF SERIES: 5 MONTHS
TIME PERIOD: January 2007 - May 2007
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8747437 BAY WAVELAND YC, BAY ST. LOUIS
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 0.419
MEAN HIGH WATER MHW = 0.382
MEAN SEA LEVEL MSL = 0.207
MEAN TIDE LEVEL MTL = 0.198
MEAN LOW WATER MLW = 0.015
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
1529 F 2006 0.724 0.342
1529 E 2006 0.821 0.439
1529 G 2006 1.437 1.055
1529 H 2006 1.121 0.739
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 8761529 PUBLICATION DATE: 09/12/2008
Name: MARTELLO CASTLE, LAKE BORGNE
LA
NOAA Chart: 11369 Latitude: 29° 56.7' N ( 29.94500)
USGS Quad: MARTELLO CASTLE Longitude: 89° 50.1' W ( -89.83500)
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.