U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 Station ID: 8724698 PUBLICATION DATE: 10/14/2011 Name: LOGGERHEAD KEY, DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.9' N ( 24.63170) USGS Quad: DRY TORTUGAS Longitude: 82° 55.2' W ( -82.92000) To reach the tidal bench marks, proceed west by boat from Key West for 70 nautical miles to Loggerhead Key. The bench marks are in the vicinity of the lighthouse and the tide gauge was located on the north side of the pier. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: NO 1 1952 DESIGNATION: 872 4698 TIDAL 1 MONUMENTATION: Tidal Station disk VM#: 11240 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: SETTING CLASSIFICATION: Concrete slab OPUS PID: LATITUDE: 24° 37.9' N ( 24.63170) LONGITUDE: 82° 55.2' W ( -82.92000) The primary bench mark is a disk set in the center of a 1.07 m (3.5 ft) square concrete slab, approximately 100.58 m (330.0 ft) SSE of Dry Tortugas Lighthouse, 10.06 m (33.0 ft) west of inshore end of boat pier, 4.42 m (14.5 ft) south of SE end of a concrete sidewalk and 1.22 m (4.0 ft) SE of flagpole.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 Station ID: 8724698 PUBLICATION DATE: 10/14/2011 Name: LOGGERHEAD KEY, DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.9' N ( 24.63170) USGS Quad: DRY TORTUGAS Longitude: 82° 55.2' W ( -82.92000) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 2 1952 DESIGNATION: 872 4698 TIDAL 2 MONUMENTATION: Tidal Station disk VM#: 11241 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: SETTING CLASSIFICATION: Concrete porch OPUS PID: LATITUDE: 24° 37.9' N ( 24.63170) LONGITUDE: 82° 55.2' W ( -82.92000) The bench mark is a disk set in a concrete porch of a two-story brick building, 54.86 m (180.0 ft) south of Dry Tortugas Lighthouse, 2.90 m (9.5 ft) west of the west edge of the sidewalk leading north to the lighthouse, 2.59 m (8.5 ft) south of the center of the front doorway of the building, 0.30 m (1.0 ft) north of the south edge of the porch, and 0.30 m (1.0 ft) east of the east face of the building, BENCH MARK STAMPING: NO 3 1952 DESIGNATION: 872 4698 TIDAL 3 MONUMENTATION: Tidal Station disk VM#: 11242 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: SETTING CLASSIFICATION: Brick foundation OPUS PID: LATITUDE: 24° 37.9' N ( 24.63170) LONGITUDE: 82° 55.2' W ( -82.92000) The bench mark is a disk set in a brick foundation of lighthouse, 0.30 m (1.0 ft) east of the center line of a concrete sidewalk leading directly to lighthouse and 0.15 m (0.5 ft) south of base of tower.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 Station ID: 8724698 PUBLICATION DATE: 10/14/2011 Name: LOGGERHEAD KEY, DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.9' N ( 24.63170) USGS Quad: DRY TORTUGAS Longitude: 82° 55.2' W ( -82.92000) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 4 1960 DESIGNATION: 872 4698 TIDAL 4 MONUMENTATION: Tidal Station disk VM#: 11243 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: SETTING CLASSIFICATION: Concrete footing OPUS PID: LATITUDE: 24° 37.9' N ( 24.63170) LONGITUDE: 82° 55.2' W ( -82.92000) The bench mark is a disk set in a concrete footing, 16.76 m (55.0 ft) SSW of the most southerly part of the lighthouse, 8.84 m (29.0 ft) west of centerline of sidewalk, 7.62 m (25.0 ft) south of the SW corner of power house, and 0.15 m (0.5 ft) NW of NW edge of an angle plate in the NW base of a water tower. BENCH MARK STAMPING: NO 5 1961 DESIGNATION: 872 4698 TIDAL 5 MONUMENTATION: Tidal Station disk VM#: 11244 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: SETTING CLASSIFICATION: Concrete sidewalk OPUS PID: LATITUDE: 24° 37.9' N ( 24.63170) LONGITUDE: 82° 55.2' W ( -82.92000) The bench mark is a disk set in a drill hole in a concrete sidewalk leading to steps, located at the NE end of steps leading to the SE entrance to the Coast Guard personnel living quarters, a building most northerly on island and is of brick construction, approximately 69 m (225 ft) NNE of Lighthouse Tower.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 Station ID: 8724698 PUBLICATION DATE: 10/14/2011 Name: LOGGERHEAD KEY, DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.9' N ( 24.63170) USGS Quad: DRY TORTUGAS Longitude: 82° 55.2' W ( -82.92000) T I D A L D A T U M S Tidal datums at LOGGERHEAD KEY, DRY TORTUGAS based on: LENGTH OF SERIES: 1 YEAR TIME PERIOD: June 2000 - May 2001 TIDAL EPOCH: 1983-2001 CONTROL TIDE STATION: 8724580 KEY WEST Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: HIGHEST OBSERVED WATER LEVEL (02/09/2005) = 0.880 MEAN HIGHER HIGH WATER MHHW = 0.509 MEAN HIGH WATER MHW = 0.423 MEAN TIDE LEVEL MTL = 0.253 MEAN SEA LEVEL MSL = 0.252 MEAN LOW WATER MLW = 0.083 MEAN LOWER LOW WATER MLLW = 0.000 LOWEST OBSERVED WATER LEVEL (02/08/2001) = -0.365 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW NO 1 1952 2.619 2.196 NO 2 1952 2.442 2.019 NO 3 1952 2.175 1.752 NO 4 1960 2.173 1.750 NO 5 1961 1.769 1.346
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 Station ID: 8724698 PUBLICATION DATE: 10/14/2011 Name: LOGGERHEAD KEY, DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.9' N ( 24.63170) USGS Quad: DRY TORTUGAS Longitude: 82° 55.2' W ( -82.92000) 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.