U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
Station ID: 8773037 PUBLICATION DATE: 09/28/2020
Name: SEADRIFT, SAN ANTONIO BAY
TX
NOAA Chart: 11315 Latitude: 28° 24.4' N ( 28.40690)
USGS Quad: SEADRIFT, TX Longitude: 96° 42.7' W ( -96.71240)
To reach the station from the town of Seadrift, proceed South on Main St. at the
intersection of HWY 185 and Main St, and proceed for .5miles (.8km) to the boat
ramp basin at the end of Main st. The tide station is about 30 meters (98.4 ft)
from the shore on a platform installed by the Conrad Blucher Institute. A boat
is needed to access the station. The station bench marks can be found on the
south side of Bay Ave in the grass between the boat ramp and the public park.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 90031 A 1992
DESIGNATION: 877 3037 A
ALIAS: 3037 A 1992
MONUMENTATION: Bench Mark disk VM#: 17545
AGENCY: Conrad Blucher Institute (CBI) IDB PID#: DR3183
SETTING CLASSIFICATION: Stainless steel rod OPUS PID#: BBFJ07
LATITUDE: 28° 24.4' N ( 28.40739) LONGITUDE: 96° 42.7' W ( -96.71239)
The primary bench mark is a brass disk located approximately 55.0 m (180.4 ft)
NNE of the platform, 17.2 m (56.4 ft) SSE of a wooden utility pole with two
transformers mounted on it, 17.1 m (56.1 ft) SW of a post in the SW corner of a
wooden bulkhead around some boat slips on the west side of the boat ramp, 13.7 m
(44.9 ft) WSW of a wooden utility pole nearest the SW corner of a wooden
bulkhead, crimped to a stainless steel rod driven to an unspecified refusal and
encased in a 6 inch PVC pipe with concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 8773037 PUBLICATION DATE: 09/28/2020
Name: SEADRIFT, SAN ANTONIO BAY
TX
NOAA Chart: 11315 Latitude: 28° 24.4' N ( 28.40690)
USGS Quad: SEADRIFT, TX Longitude: 96° 42.7' W ( -96.71240)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 90031 B 1992
DESIGNATION: 877 3037 B
ALIAS: B 1992
MONUMENTATION: Bench Mark disk VM#: 17546
AGENCY: Conrad Blucher Institute (CBI) IDB PID:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 28° 24.5' N ( 28.40822) LONGITUDE: 96° 42.7' W ( -96.71219)
The bench mark is a brass disk located on the south side of Bay Street, 91.4 m
(299.9 ft) north of bench mark 90031 A 1992, 8.6 m (28.2 ft) south of the south
edge of the pavement of Bay Street, 3.6 m (11.8 ft) NW of the northern most
wooden R/V utility hookup post in a north-south line of five such posts, 2.1 m
(6.9 ft) east of a power pole, 1.5 m (4.9 ft) south of an electric power line,
crimped to a stainless steel rod driven to unspecified depth and encased in a 6
inch PVC pipe with concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 8773037 PUBLICATION DATE: 09/28/2020
Name: SEADRIFT, SAN ANTONIO BAY
TX
NOAA Chart: 11315 Latitude: 28° 24.4' N ( 28.40690)
USGS Quad: SEADRIFT, TX Longitude: 96° 42.7' W ( -96.71240)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 90031 D RESET
DESIGNATION: 877 3037 D RESET
ALIAS: D 1992
MONUMENTATION: Metal Rod VM#: 17548
AGENCY: Conrad Blucher Institute (CBI) IDB PID:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 28° 24.5' N ( 28.40839) LONGITUDE: 96° 42.9' W ( -96.71419)
The benck mark is a brass disk located on the south side of Bay Street, 1.5 m (5
ft) south of the centerline of an electric power line, crimped to a stainless
steel rod driven to refusal to an unspecified depth and encased in a 6 inch PVC
pipe with concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 8773037 PUBLICATION DATE: 09/28/2020
Name: SEADRIFT, SAN ANTONIO BAY
TX
NOAA Chart: 11315 Latitude: 28° 24.4' N ( 28.40690)
USGS Quad: SEADRIFT, TX Longitude: 96° 42.7' W ( -96.71240)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 90031 E 1992
DESIGNATION: 877 3037 E
ALIAS: E 1992
MONUMENTATION: Bench Mark disk VM#: 17549
AGENCY: Conrad Blucher Institute (CBI) IDB PID:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID#: BBGD75
LATITUDE: 28° 24.5' N ( 28.40850) LONGITUDE: 96° 42.9' W ( -96.71519)
The bench mark is a brass disk located on the south side of Bay Street, 5.6 m
(18.4 ft) NNE of the SE corner of the top step of a set of five concrete steps
leading down a slope towards the Lions' Club Pavilion, 4.7 m (15.4 ft) south of
the south edge of the pavement of Bay Street, 4.2 m (13.8 ft) WNW of an upright
cross constructed of 8-inch steel pipe, 1.5 m (4.9 ft) south of the centerline
of an electric power line, crimped to a stainless steel rod driven to refusal to
an unspecified depth encased in a 6 inch PVC pipe with concrete kickblock.
BENCH MARK STAMPING: 3037 F 2012
DESIGNATION: 877 3037 F 2012
MONUMENTATION: Tidal Station disk VM#: 22134
AGENCY: Conrad Blucher Institute (CBI) IDB PID:
SETTING CLASSIFICATION: Concrete bulkhead OPUS PID#: BBGD76
LATITUDE: 28° 24.4' N ( 28.40747) LONGITUDE: 96° 42.7' W ( -96.71222)
The bench mark is a disk set in concrete bulkhead of the southern most boat
slip, 71.6 m (235.14 ft) NNE of the tide station, 32.1 m (105.5 ft) SSW of the
NNW corner of northern most boat slip, 18.3 m (60.1 ft) ENE of benchmark 90031 A
1992.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 8773037 PUBLICATION DATE: 09/28/2020
Name: SEADRIFT, SAN ANTONIO BAY
TX
NOAA Chart: 11315 Latitude: 28° 24.4' N ( 28.40690)
USGS Quad: SEADRIFT, TX Longitude: 96° 42.7' W ( -96.71240)
T I D A L D A T U M S
Tidal datums at SEADRIFT, SAN ANTONIO BAY based on:
LENGTH OF SERIES: 1 YEAR
TIME PERIOD: September 2017 - August 2018
TIDAL EPOCH: 2002-2006
CONTROL TIDE STATION: 8775792 PACKERY CHANNEL
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (08/26/2017) = 1.805
MEAN HIGHER HIGH WATER MHHW = 0.106
MEAN HIGH WATER MHW = 0.106
MEAN SEA LEVEL MSL = 0.057
MEAN TIDE LEVEL MTL = 0.056
MEAN LOW WATER MLW = 0.007
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum NAVD88 = -0.302
LOWEST OBSERVED WATER LEVEL (01/16/2018) = -0.516
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
90031 A 1992 0.735 0.629
90031 B 1992 0.949 0.843
90031 D RESET 2.329 2.223
90031 E 1992 2.791 2.685
3037 F 2012 1.053 0.947
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 8773037 PUBLICATION DATE: 09/28/2020
Name: SEADRIFT, SAN ANTONIO BAY
TX
NOAA Chart: 11315 Latitude: 28° 24.4' N ( 28.40690)
USGS Quad: SEADRIFT, TX Longitude: 96° 42.7' W ( -96.71240)
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.