PUBLICATION DATE: 10/01/1991 Page 1
LOUISIANA 876 1207
U.S. DEPARTMENT OF COMMERCE
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
NATIONAL OCEAN SERVICE
TIDAL BENCH MARKS
EMPIRE, DOULLUT CANAL
LATITUDE: 29ø 22.5' N LONGITUDE: 89ø 36.1' W
NOAA CHART: 11364 USGS QUAD: EMPIRE
To reach the tidal bench marks from the north end of the State Highway 23
hi-rise bridge over Doullut Canal at Empire, proceed south on State Highway 23
for 1.2 miles (1.9 km) to a service road on the right, turn onto the service
road and go 0.1 mile (0.2 km) west to a locked gate on the left, go through the
gate and follow a shell road west along the levee to the Corps of Engineers
floodgate. The bench marks are near the floodgate and southeasterly along a
power line running parallel to and on the north side of a flood protection
levee. The tide gage and staff were at the SW corner of the concrete structure
of the floodgate on the east side of Doullut Canal.
................................................................................
BENCH MARK STAMPING: 1207 B 1985
MONUMENTATION: Survey Disk VM#: 7140
AGENCY: PID#: AT1391
SETTING CLASSIFICATION: Stainless Steel Rod
The primary bench mark is 365.0 feet (111.3 m) NE of Bench Mark 1207 A 1985,
19.8 feet (6.0 m) SSW of the top bracket of a guy wire anchor assembly on the
NE side of the first utility pole east of the floodgate structure, 12.8 feet
(3.9 m) SE of a railroad spike driven 2.6 feet (0.8 m) above ground level on
the south side of the pole, and 1.7 feet (0.5 m) SW of a witness post. The
bench mark is 0.3 foot (0.1 m) below ground level, crimped to a stainless steel
rod driven 60 feet (18 m) to substantial resistance, and encased in a 5-inch
PVC pipe and concrete kickblock.
BENCH MARK STAMPING: 1207 C 1985
MONUMENTATION: Survey Disk VM#: 7141
AGENCY: PID#:
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is 298.0 feet (90.8 m) ESE of Bench Mark 1207 B 1985, 20.0 feet
(6.1 m) SSE of the second utility pole east of the floodgate, and 2.0 feet (0.6
m) south of a witness post. The bench mark is 0.2 foot (0.1 m) below ground
level, crimped to a stainless steel rod driven 54 feet (16 m) to refusal, and
encased in a 5-inch PVC pipe and concrete kickblock.
PUBLICATION DATE: 10/01/1991 Page 2
LOUISIANA 876 1207
EMPIRE, DOULLUT CANAL
BENCH MARK STAMPING: 1207 D 1985
MONUMENTATION: Survey Disk VM#: 7142
AGENCY: PID#:
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is 302.0 feet (92.0 m) east of Bench Mark 1207 C 1985, 12.7 feet
(3.9 m) ESE of a railroad spike driven 2.7 feet (0.8 m) above ground level on
the south side of the third utility pole east of the floodgate, and 1.8 feet
(0.5 m) south of a witness post. The bench mark is 0.3 foot (0.1 m) below
ground level, crimped to a stainless steel rod driven 48 feet (15 m) to
refusal, and encased in a 5-inch PVC pipe and concrete kickblock.
BENCH MARK STAMPING: 1207 E 1985
MONUMENTATION: Survey Disk VM#: 7143
AGENCY: PID#:
SETTING CLASSIFICATION: Stainless Steel Rod
The bench mark is 301.0 feet (91.7 m) ESE of Bench Mark 1207 D 1985, 20.0 feet
(6.1 m) SSE of the fourth utility pole east of the floodgate, and 1.2 feet (0.4
m) south of a witness post. The bench mark is 0.3 foot (0.1 m) below ground
level, crimped to a stainless steel rod driven 60 feet (18 m) to substantial
resistance, and encased in a 5-inch PVC pipe and concrete kickblock.
PUBLICATION DATE: 10/01/1991 Page 3
LOUISIANA 876 1207
EMPIRE, DOULLUT CANAL
Tidal datums at EMPIRE, DOULLUT CANAL are based on the following:
LENGTH OF SERIES = 51 MONTHS
TIME PERIOD = 1986-1990
TIDAL EPOCH = 1960-1978
CONTROL TIDE STATION = GRAND ISLE (876 1724)
Elevations of tidal datums referred to mean lower low water (MLLW) are as follows:
HIGHEST OBSERVED WATER LEVEL (08/15/1985) = 3.14 FEET
MEAN HIGHER HIGH WATER (MHHW) = 0.97 FEET
MEAN HIGH WATER (MHW) = 0.95 FEET
MEAN TIDE LEVEL (MTL) = 0.48 FEET
MEAN LOW WATER (MLW) = 0.01 FEET
MEAN LOWER LOW WATER (MLLW) = 0.00 FEET
*NATIONAL GEODETIC VERTICAL DATUM-1929 (NGVD) = -0.25 FEET
LOWEST OBSERVED WATER LEVEL (12/23/1989) = -2.06 FEET
*NGVD reference based on elevations published in Quad L24836, 1984, and NOS
leveling of 1991.
Bench mark elevation information:
ELEVATION IN FEET ABOVE:
BENCH MARK STAMP/DESIGNATION MLLW MHW
1207 B 1985 1.64 0.69
1207 C 1985 1.68 0.73
1207 D 1985 2.49 1.54
1207 E 1985 2.26 1.31
The reliability of the elevations at this station may be reduced due to bench
mark instability and subsidence in the general area.
PUBLICATION DATE: 10/01/1991 Page 4
LOUISIANA 876 1207
EMPIRE, DOULLUT CANAL
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
www.ngs.noaa.gov.
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
www.ngs.noaa.gov
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.