U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 7
Station ID: 8726089 PUBLICATION DATE: 02/05/2004
Name: LONGBOAT KEY
FL
NOAA Chart: 11424 Latitude: 27° 20.4' N ( 27.34000)
USGS Quad: SARASOTA Longitude: 82° 35.4' W ( -82.59000)
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 0.8 km (0.5
mi) 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 marina's pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: NO 1 1973
DESIGNATION: 872 6089 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 6131
AGENCY: National Ocean Survey (NOS) IDB PID#: AG7398
SETTING CLASSIFICATION: Concrete sea wall OPUS PID:
LATITUDE: 27° 20.3' N ( 27.33830) LONGITUDE: 82° 35.4' W ( -82.59000)
The primary bench mark is a disk set flush in the concrete seawall at the NW
corner of the small boat basin at the Longboat Key Marina, about 14 m (45 ft) SE
of the office buidling, 9 m (30 ft) SW of the bay front seawall, 6 m (20 ft) NW
of the north side of the basin's water entrance.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 7
Station ID: 8726089 PUBLICATION DATE: 02/05/2004
Name: LONGBOAT KEY
FL
NOAA Chart: 11424 Latitude: 27° 20.4' N ( 27.34000)
USGS Quad: SARASOTA Longitude: 82° 35.4' W ( -82.59000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: W 92 1942
DESIGNATION: W 92
MONUMENTATION: Bench Mark disk VM#: 6127
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: AG5037
SETTING CLASSIFICATION: Bridge abutment OPUS PID:
LATITUDE: 27° 20.0' N ( 27.33330) LONGITUDE: 82° 35.0' W ( -82.58330)
The bench mark is a disk set horizontally in the sloping seawall abutment in the
NE corner of the bridge and sidewalk, 8.32 m (27.3 ft) NE of the centerline of
the highway, 0.79 m (2.6 ft) north of the NW end of the NE wall of the bridge.
Note: The bench mark has been disturbed on one side and should be used with
caution.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 7
Station ID: 8726089 PUBLICATION DATE: 02/05/2004
Name: LONGBOAT KEY
FL
NOAA Chart: 11424 Latitude: 27° 20.4' N ( 27.34000)
USGS Quad: SARASOTA Longitude: 82° 35.4' W ( -82.59000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: IWSA 56 1963
DESIGNATION: IWSA 56 USE
MONUMENTATION: Bench Mark disk VM#: 6128
AGENCY: US Army Corp of Engineers (USE) IDB PID#: AG7394
SETTING CLASSIFICATION: Concrete sidewalk OPUS PID:
LATITUDE: 27° 19.9' N ( 27.33170) LONGITUDE: 82° 34.9' W ( -82.58170)
The bench mark is a disk set flush in the center of the concrete sidewalk on the
bridge, 2 m (6 ft) SE of the drawbridge section and open observation platform, 1
m (3 ft) NE of a concrete guardrail, and 1 m (3 ft) SW of the SW curb.
BENCH MARK STAMPING: DOT BM26 EL-2.817
DESIGNATION: 26 FLDT
MONUMENTATION: Bench Mark disk VM#: 6129
AGENCY: Florida Department of Transportation
(FLDT) IDB PID#: AG7395
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 27° 20.2' N ( 27.33670) LONGITUDE: 82° 35.3' W ( -82.58830)
The bench mark is a disk set in the top of a concrete monument along State
Highway 789, 0.6 km (0.4 mi) NW of the bridge, about 80 m (264 ft) SE of bench
mark NO 3 1973, 15.85 m (52.0 ft) east of the centerline of the highway, 7.62 m
(25.0 ft) south of concrete power pole, 1.3 m (4.3 ft) NE of the NE edge of the
sidewalk, and 0.3 m (1 ft) west of a witness post.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 7
Station ID: 8726089 PUBLICATION DATE: 02/05/2004
Name: LONGBOAT KEY
FL
NOAA Chart: 11424 Latitude: 27° 20.4' N ( 27.34000)
USGS Quad: SARASOTA Longitude: 82° 35.4' W ( -82.59000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: DOT BM27 EL-4.980
DESIGNATION: 27 FLDT
MONUMENTATION: Bench Mark disk VM#: 6130
AGENCY: Florida Department of Transportation
(FLDT) IDB PID#: AG7397
SETTING CLASSIFICATION: Concrete monument OPUS PID:
LATITUDE: 27° 20.3' N ( 27.33830) LONGITUDE: 82° 35.4' W ( -82.59000)
The bench mark is a disk set in the top of a concrete monument located at
Longboat Marina, 76 m (250 ft) north of the centerline of the entrance to the
marina, 20.85 m (68.4 ft) north of a power pole with two transformers, and 15.73
m (51.6 ft) east of the centerline of State Highway 789.
BENCH MARK STAMPING: NO 2 1973
DESIGNATION: 872 6089 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 6132
AGENCY: National Ocean Survey (NOS) IDB PID#: AG7399
SETTING CLASSIFICATION: Concrete retaining wall OPUS PID#: AG7399
LATITUDE: 27° 20.3' N ( 27.33830) LONGITUDE: 82° 35.4' W ( -82.59000)
The bench mark is a disk set in the top of the intersection of a seawall and a
retainer wall located at the Longboat Key Marina, 6 m (20 ft) north of the NW
corner of the office building, 1 m (3 ft) SE of a slight bend in the seawall.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 7
Station ID: 8726089 PUBLICATION DATE: 02/05/2004
Name: LONGBOAT KEY
FL
NOAA Chart: 11424 Latitude: 27° 20.4' N ( 27.34000)
USGS Quad: SARASOTA Longitude: 82° 35.4' W ( -82.59000)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 3 1973
DESIGNATION: 872 6089 TIDAL 3
MONUMENTATION: Tidal Station disk VM#: 6133
AGENCY: National Ocean Survey (NOS) IDB PID#: AG7396
SETTING CLASSIFICATION: Concrete culvert abutment OPUS PID:
LATITUDE: 27° 20.2' N ( 27.33670) LONGITUDE: 82° 35.3' W ( -82.58830)
The bench mark is a disk set flush in the top of a 4 m (12 ft) long concrete
culvert abutment, 129 m (422 ft) SE of the entrance road to Longboat Key Marina,
122 m (400 ft) NW of the entrance to Longboat Key Club and Golf Course, 23 m (75
ft) SW and across the highway from concrete powerline pole NO. 45G68, 12 m (40
ft) SW of a similar culvert abutment on the other side of the highway, and 5 m
(18 ft) SW of the centerline of State Highway 789.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 7
Station ID: 8726089 PUBLICATION DATE: 02/05/2004
Name: LONGBOAT KEY
FL
NOAA Chart: 11424 Latitude: 27° 20.4' N ( 27.34000)
USGS Quad: SARASOTA Longitude: 82° 35.4' W ( -82.59000)
T I D A L D A T U M S
Tidal datums at LONGBOAT KEY based on:
LENGTH OF SERIES: 1 YEAR
TIME PERIOD: August 1973 - July 1974
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8726520 ST. PETERSBURG, TAMPA BAY
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (06/25/1974) = 1.335
MEAN HIGHER HIGH WATER MHHW = 0.630
MEAN HIGH WATER MHW = 0.516
North American Vertical Datum NAVD88 = 0.456
MEAN SEA LEVEL MSL = 0.323
MEAN TIDE LEVEL MTL = 0.322
MEAN LOW WATER MLW = 0.128
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (04/05/1977) = -0.530
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
NO 1 1973 0.829 0.313
W 92 1942 3.692 3.176
IWSA 56 1963 5.837 5.321
DOT BM26 EL-2.817 0.990 0.474
DOT BM27 EL-4.980 1.642 1.126
NO 2 1973 1.155 0.639
NO 3 1973 1.131 0.615
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 7
Station ID: 8726089 PUBLICATION DATE: 02/05/2004
Name: LONGBOAT KEY
FL
NOAA Chart: 11424 Latitude: 27° 20.4' N ( 27.34000)
USGS Quad: SARASOTA Longitude: 82° 35.4' W ( -82.59000)
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.