U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 4
PUBLICATION DATE: 06/10/1985
Station ID: 8725916 SUPERCEDED DATE: 04/21/2003
Name: CASEY KEY, BLACKBURN BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 9.2' N
USGS Quad: LAUREL Longitude: 82° 29.0' W
To reach the tidal bench marks from the intersection of U.S. Highway 41 and
state road 72 in Sarasota proceed 6.1 miles (9.8 km) south to a road leading to
Blackburn Point and Casey Key, proceed 1 mile (2 km) west on the road to Casey
Key turn left and go south for 2 miles (3 km) to Jeff Mathers resident. The
bench marks are located along the seawall. The tide gage and staff were located
on the private dock.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 5916 A 1977
MONUMENTATION: Survey Disk VM#: 6102
AGENCY: PID#: AG7747
SETTING CLASSIFICATION: Concrete Seawall
The bench mark is set in the top of a concrete seawall, 46.4 feet (14.1 m) north
of a wooden boat dock, 46.0 feet (14.0 m) east of the centerline of the blacktop
road, and 1.5 feet (0.5 m) south of the north end of the seawall.
BENCH MARK STAMPING: 5916 B 1977
MONUMENTATION: Survey Disk VM#: 6103
AGENCY: PID#: AG7748
SETTING CLASSIFICATION: Concrete Seawall
The bench mark is set in the top of the seawall, 80.0 feet (24.4 m) south of
Bench Mark 5916 A 1977, 34.0 feet (10.4 m) east of the centerline of a blacktop
rod, and 28.4 feet (8.7 m) south of the west end of the boat dock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
PUBLICATION DATE: 06/10/1985
Station ID: 8725916 SUPERCEDED DATE: 04/21/2003
Name: CASEY KEY, BLACKBURN BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 9.2' N
USGS Quad: LAUREL Longitude: 82° 29.0' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5916 C 1977
MONUMENTATION: Survey Disk VM#: 6104
AGENCY: PID#: AG7749
SETTING CLASSIFICATION: Concrete Seawall
The bench mark is set in the top of the concrete seawall, 73.0 feet (22.3 m)
south of Bench Mark 5916 B 1977, and 37.0 feet (11.3 m) east of the centerline
of a blacktop road.
BENCH MARK STAMPING: 5916 D 1977
MONUMENTATION: Survey Disk VM#: 6105
AGENCY: PID#: AG7750
SETTING CLASSIFICATION: Concrete Seawall
The bench mark is set in the top of the concrete seawall, 111.0 feet (33.8 m)
south of Bench Mark 5916 C 1977, 37.0 feet (11.3 m) east of the centerline of a
blacktop road.
BENCH MARK STAMPING: 5916 E 1977
MONUMENTATION: Survey Disk VM#: 6106
AGENCY: PID#: AG7751
SETTING CLASSIFICATION: Concrete Seawall
The bench mark is set in the top of a concrete seawall, 156.0 feet (47.5 m)
south of Bench Mark 5916 D 1977, and 41.0 feet (12.5 m) east of the centerline
of a blacktop road.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
PUBLICATION DATE: 06/10/1985
Station ID: 8725916 SUPERCEDED DATE: 04/21/2003
Name: CASEY KEY, BLACKBURN BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 9.2' N
USGS Quad: LAUREL Longitude: 82° 29.0' W
T I D A L D A T U M S
Tidal datums at CASEY KEY, BLACKBURN BAY based on:
LENGTH OF SERIES: 3 MONTHS
TIME PERIOD: OCTOBER-DECEMBER 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 (01/09/1978) = 3.15
MEAN HIGHER HIGH WATER MHHW = 1.82
MEAN HIGH WATER MHW = 1.52
MEAN TIDE LEVEL MTL = 0.89
MEAN LOW WATER MLW = 0.27
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (12/11/1977) = -0.79
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
5916 A 1977 4.93 3.41
5916 B 1977 5.05 3.53
5916 C 1977 5.06 3.54
5916 D 1977 5.09 3.57
5916 E 1977 5.17 3.65
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
PUBLICATION DATE: 06/10/1985
Station ID: 8725916 SUPERCEDED DATE: 04/21/2003
Name: CASEY KEY, BLACKBURN BAY
FLORIDA
NOAA Chart: 11424 Latitude: 27° 9.2' N
USGS Quad: LAUREL Longitude: 82° 29.0' 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.