U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
Station ID: 8762419 PUBLICATION DATE: 03/09/2004
Name: U.S. HIGHWAY 51, PASS MANCHAC
LOUISIANA
NOAA Chart: 11369 Latitude: 30° 17.1' N
USGS Quad: MANCHAC Longitude: 90° 24.1' W
To reach the tidal bench marks proceed to Galva at the south end of the U.S.
Highway 51 bridge over Pass Manchac. The bench marks are along old U.S. Highway
51 south of the bridge. The tide gage and staff are at the north end of the
abandoned roadbed of the old U.S. Highway 51 bridge on the south side of Pass
Manchac.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 2419 A 1982
DESIGNATION: 876 2419 A TIDAL
MONUMENTATION: Tidal Station disk VM#: 11368
AGENCY: National Ocean Survey (NOS) PID#: BJ3732
SETTING CLASSIFICATION: Stainless steel rod
The primary bench mark is a disk located at the south end of the old U.S.
Highway 51 bridge, 50 m (163 ft) north of utility pole #5 40, 15 m (48 ft) NNW
of the NW corner of a shed east of old U.S. Highway 51, 10 m (32 ft) SE of the
SE corner of the old U.S. Highway bridge, 5 m (15 ft) ENE of the centerline of
old U.S. Highway 51, and 1 m (3 ft) SW of utility pole #67. The bench mark is
set 9 cm (0.3 ft) below ground level, crimped to the top of a stainless steel
rod driven 15.8 m (52 ft) to substantial resistance, and encased in a 4-inch PVC
pipe and concrete kickblock.
BENCH MARK STAMPING: 2419 B 1982
DESIGNATION: 876 2419 B
MONUMENTATION: Tidal Station disk VM#: 11369
AGENCY: National Ocean Survey (NOS) PID:
SETTING CLASSIFICATION: Stainless steel rod
The bench mark is a disk located 67 m (219 ft) south of bench mark 2419 A 1982,
32 m (106 ft) NNW of a utility pole located between U.S. Highway 51 and old U.S.
Highway 51 SW of the Sportsmans Lodge building, 12 m (41 ft) WSW of the
centerline of old Highway 51, and 12 m (38 ft) ENE of the centerline of U.S.
Highway 51. The bench mark is set 9 cm (0.3 ft) below ground level, crimped to
the top of a stainless steel rod driven 17.1 m (56 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 2 of 6
Station ID: 8762419 PUBLICATION DATE: 03/09/2004
Name: U.S. HIGHWAY 51, PASS MANCHAC
LOUISIANA
NOAA Chart: 11369 Latitude: 30° 17.1' N
USGS Quad: MANCHAC Longitude: 90° 24.1' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 2419 C 1982
DESIGNATION: 876 2419 C
MONUMENTATION: Tidal Station disk VM#: 11370
AGENCY: National Ocean Survey (NOS) PID:
SETTING CLASSIFICATION: Stainless steel rod
The bench mark is a disk located 69 m (227 ft) SSE of bench mark 2419 B 1982, 67
m (220 ft) SSE of a utility pole located between U.S. Highway 51 and old U.S.
Highway 51 SW of the Sportsmans Lodge building, 23 m (75 ft) north of a utility
pole south of the previously described utility pole, 20 m (65 ft) ENE of the
centerline of U.S. Highway 51, and 6 m (20 ft) WSW of the centerline of old U.S.
Highway 51. The bench mark is set 9 cm (0.3 ft) below ground level, crimped to
the top of a stainless steel rod driven 17.1 m (56 ft) to substantial
resistance, and encased in a 4-inch PVC pipe and concrete kickblock.
BENCH MARK STAMPING: GALVA 2 1955
DESIGNATION: GALVA 2
MONUMENTATION: Triangulation Station disk VM#: 11372
AGENCY: US Coast and Geodetic Survey (USC&GS) PID#: BJ1522
SETTING CLASSIFICATION: Concrete monument
The bench mark is a disk set in a concrete monument, 0.24 km (0.15 mi) south of
the south end of the U.S. Highway 51 bridge over Pass Manchac, on old U.S.
Highway 51, 8.38 m (27.5 ft) SW of the SW corner of a 1-story frame house, 7.16
m (23.5 ft) east of the centerline of old U.S. Highway 51, 4.72 m (15.5 ft) NW
of the NW corner of a 1-story frame house with 2 doors on the west side, and 3
cm (0.1 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 8762419 PUBLICATION DATE: 03/09/2004
Name: U.S. HIGHWAY 51, PASS MANCHAC
LOUISIANA
NOAA Chart: 11369 Latitude: 30° 17.1' N
USGS Quad: MANCHAC Longitude: 90° 24.1' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: GALVA 2 NO 3 1955
DESIGNATION: GALVA 2 RM 3
MONUMENTATION: Reference Mark disk VM#: 11373
AGENCY: US Coast and Geodetic Survey (USC&GS) PID#: BJ1523
SETTING CLASSIFICATION: Concrete post
The bench mark is a disk set in a concrete post 0.24 km (0.15 mi) south of the
south end of the U.S. Highway 51 bridge over Pass Manchac, 17.43 m (57.2 ft)
north of bench mark GALVA 2 1955, 7.16 m (23.5 ft) east of the centerline of old
U.S. Highway 51, 3.14 m (10.3 ft) NW of the NW corner of a 1-story frame house,
2.29 m (7.5 ft) SW of a power line pole with transformer, and about level with
the highway.
BENCH MARK STAMPING: GALVA 2 NO 5 1973
DESIGNATION: GALVA 2 RM 5
MONUMENTATION: Reference Mark disk VM#: 11374
AGENCY: US Coast and Geodetic Survey (USC&GS) PID#: AE6861
SETTING CLASSIFICATION: Concrete post
The bench mark is a disk set in a concrete post 0.24 km (0.15 mi) south of the
south end of the U.S. Highway 51 bridge over Pass Manchac, SW of and across old
U.S. Highway 51 from bench mark GALVA 2 NO 3 1955, 9.17 m (30.1 ft) west of
bench mark GALVA 2 1955, 4.57 m (15 ft) west of the centerline of old U.S.
Highway 51, and at ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 8762419 PUBLICATION DATE: 03/09/2004
Name: U.S. HIGHWAY 51, PASS MANCHAC
LOUISIANA
NOAA Chart: 11369 Latitude: 30° 17.1' N
USGS Quad: MANCHAC Longitude: 90° 24.1' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: C 275 1969
DESIGNATION: C 275
MONUMENTATION: Bench Mark disk VM#: 11375
AGENCY: US Coast and Geodetic Survey (USC&GS) PID#: BJ1524
SETTING CLASSIFICATION: Concrete abutment
The bench mark is a disk set on top of the east end of the south concrete
abutment of the U.S. Highway 51 bridge over Pass Manchac, 5.91 m (19.4 ft) east
of the centerline of the highway, 0.73 m (2.4 ft) west of the east end of the
abutment, and about level with the highway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 8762419 PUBLICATION DATE: 03/09/2004
Name: U.S. HIGHWAY 51, PASS MANCHAC
LOUISIANA
NOAA Chart: 11369 Latitude: 30° 17.1' N
USGS Quad: MANCHAC Longitude: 90° 24.1' W
T I D A L D A T U M S
Tidal datums at U.S. HIGHWAY 51, PASS MANCHAC based on:
LENGTH OF SERIES: 8 YEARS
TIME PERIOD: January 1983 - December 1990
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8761927 USCG NEW CANAL STA., LAKE PONT.
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (10/29/1985) = 1.460
MEAN HIGHER HIGH WATER (MHHW) = 0.126
MEAN HIGH WATER (MHW) = 0.125
MEAN SEA LEVEL (MSL) = 0.068
MEAN TIDE LEVEL (MTL) = 0.063
MEAN LOW WATER (MLW) = 0.000
MEAN LOWER LOW WATER (MLLW) = 0.000
NORTH AMERICAN VERTICAL DATUM-1988 (NAVD) = -0.179
LOWEST OBSERVED WATER LEVEL (04/12/1988) = -0.668
National Geodetic Vertical Datum (NGVD 29)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
2419 A 1982 1.152 1.027
2419 B 1982 0.888 0.763
2419 C 1982 1.029 0.904
GALVA 2 1955 1.413 1.288
GALVA 2 NO 3 1955 1.448 1.323
GALVA 2 NO 5 1973 1.478 1.353
C 275 1969 1.601 1.476
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 8762419 PUBLICATION DATE: 03/09/2004
Name: U.S. HIGHWAY 51, PASS MANCHAC
LOUISIANA
NOAA Chart: 11369 Latitude: 30° 17.1' N
USGS Quad: MANCHAC Longitude: 90° 24.1' 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 (NAVD 88).
NGVD 29 is a fixed datum adopted as a national standard geodetic reference for
heights but is now considered superseded. NGVD 29 is sometimes referred to as
Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological
Survey Topographic Quads. NGVD 29 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 NGVD 29 are available from the National
Geodetic Survey (NGS) data base via the World Wide Web at
National Geodetic Survey.
NAVD 88 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. NAVD 88 replaces NGVD 29 as the national
standard geodetic reference for heights. Bench mark elevations relative to
NAVD 88 are available from NGS through the World Wide Web at
National Geodetic Survey.
NGVD 29 and NAVD 88 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 NAVD 88 elevation is shown on the Elevations of Tidal Datums Table Referred
to MLLW only when two or more of the bench marks listed have NAVD 88 elevations.
The NAVD 88 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, NAVD 88 bench mark elevations computed indirectly from the tidal
datums elevation table may differ slightly from NAVD 88 elevations listed for
each bench mark in the NGS database.