U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 06/25/1987
Station ID: 8726089 SUPERCEDED DATE: 04/21/2003
Name: LONGBOAT KEY, SARASOTA BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 20.4' N
USGS Quad: SARASOTA Longitude: 82° 35.4' W
To reach the tidal bench marks from the NW end of the State Highway 789 Bridge
over New Pass at Longboat Key proceed NW on State Highway 789 for 0.7 mile (1.1
km) to the Longboat Key Marina. The bench marks are located on the bridge,
along State Highway 789, and at the marina. The tide gage and staff were
located on the marinas pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1 1973
MONUMENTATION: Survey Disk VM#: 6131
AGENCY: PID#: AG7398
SETTING CLASSIFICATION: Concrete Seawall
The bench mark is set flush in the concrete seawall at the NW corner of the
small boat basin at the Longboat Key Marina, about 45 feet (14 m) SE of the
office buidling about 30 feet (9 m) SW of the bay front seawall, about 20 feet
(6 m) NW of the north side of the basin water entrance, and level with the
ground.
BENCH MARK STAMPING: W 92 1942
MONUMENTATION: Survey Disk VM#: 6127
AGENCY: PID#: AG5037
SETTING CLASSIFICATION: Concrete Seawall
The bench mark is set horizontally in the sloping seawall abutment in the NE
corner of the bridge and sidewalk, 27.3 feet (8.3 m) NE of the centerline of the
highway, 2.6 feet (0.8 m) north of the NW end of the NE wall of the bridge, and
level with the highway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 06/25/1987
Station ID: 8726089 SUPERCEDED DATE: 04/21/2003
Name: LONGBOAT KEY, SARASOTA BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 20.4' N
USGS Quad: SARASOTA Longitude: 82° 35.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1 WSA 56 1963
MONUMENTATION: Survey Disk VM#: 6128
AGENCY: PID#: AG7394
SETTING CLASSIFICATION: Concrete Sidewalk
The bench mark is set flush in the center of the concrete sidewalk on the
bridge, 6 feet (2 m) SE of the drawbridge section and open observation platform,
3 feet (1 m) NE of a concrete guardrail, and 3 feet (1 m) SW of the SW curb.
BENCH MARK STAMPING: DOT BM26 EL-2.817
MONUMENTATION: Survey Disk VM#: 6129
AGENCY: PID#: AG7395
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in the top of a concrete monument along State Highway 789,
about 0.4 mile (0.6 km) NW of the bridge, about 264 feet (80 m) SE of Bench Mark
NO3 1973, 52.0 feet (15.8 m) east of the centerline of the highway, 25.0 feet
(7.6 m) south of concrete power pole, 1 foot (0.3 m) west of a witness post, and
level with the ground.
BENCH MARK STAMPING: DOT BM27 EL-4.980
MONUMENTATION: Survey Disk VM#: 6130
AGENCY: PID#: AG7397
SETTING CLASSIFICATION: Concrete Monument
The bench mark is set in the top of a concrete monument at Longboat Marina,
about 250 feet (76 m) north of the centerline of the entrance to the marina 68.4
feet (20.8 m) north of a power pole with two transformers, 51.6 feet (15.7 m)
east of the centerline of State Highway 789, and level with the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
PUBLICATION DATE: 06/25/1987
Station ID: 8726089 SUPERCEDED DATE: 04/21/2003
Name: LONGBOAT KEY, SARASOTA BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 20.4' N
USGS Quad: SARASOTA Longitude: 82° 35.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 2 1973
MONUMENTATION: Survey Disk VM#: 6132
AGENCY: PID#: AG7399
SETTING CLASSIFICATION: Concrete Retainer Wall
The bench mark is set in the top of the intersection of a seawall and a retainer
wall at the Longboat Key Marina, about 20 feet (6 m) north of the NW corner of
the office building, 3 feet (1 m) SE of a slight bend in the seawall, and about
level with the ground.
BENCH MARK STAMPING: NO 3 1973
MONUMENTATION: Survey Disk VM#: 6133
AGENCY: PID#: AG7396
SETTING CLASSIFICATION: Concrete Culvert
The bench mark is set flush in the top of a 12 foot (4 m) long concrete culvert
abutment, about 422 feet (129 m) SE of the entrance road to Longboat Key Marina,
about 400 feet (122 m) NW of the entrance to Longboat Key Club and Golf Course,
about 75 feet (23 m) SW and across the highway from concrete powerline pole NO.
45G68, 40 feet (12 m) SW of a similar culvert abutment on the other side of the
highway, and 18 feet (5 m) SW of the centerline of State Highway 789.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
PUBLICATION DATE: 06/25/1987
Station ID: 8726089 SUPERCEDED DATE: 04/21/2003
Name: LONGBOAT KEY, SARASOTA BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 20.4' N
USGS Quad: SARASOTA Longitude: 82° 35.4' W
T I D A L D A T U M S
Tidal datums at LONGBOAT KEY, SARASOTA BAY based on:
LENGTH OF SERIES: 2 YEARS
TIME PERIOD: AUG 1973-JULY 1974 & OCT 1976 -SEPT 1977
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8726520 ST. PETERSBURG
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (06/25/1974) = 4.59
MEAN HIGHER HIGH WATER MHHW = 2.07
MEAN HIGH WATER MHW = 1.75
MEAN TIDE LEVEL MTL = 1.05
MEAN LOW WATER MLW = 0.35
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (04/05/1977) = -1.53
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
NO 1 1973 2.93 1.18
W 92 1942 12.32 10.57
1 WSA 56 1963 19.36 17.61
DOT BM26 EL-2.817 3.45 1.70
DOT BM27 EL-4.980 5.60 3.85
NO 2 1973 4.00 2.25
NO 3 1973 3.93 2.18
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 06/25/1987
Station ID: 8726089 SUPERCEDED DATE: 04/21/2003
Name: LONGBOAT KEY, SARASOTA BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 20.4' N
USGS Quad: SARASOTA Longitude: 82° 35.4' 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.