U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 Station ID: 8724697 PUBLICATION DATE: 11/13/2003 Name: GARDEN KEY,DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.6' N ( 24.62670) USGS Quad: DRY TORTUGAS Longitude: 82° 52.3' W ( -82.87170) To reach the tidal bench marks from Key West, proceed west by boat for about 109 km (68 statute mi) to Garden Key in Dry Tortugas, and then to the SE side of the Key. The bench marks are located in the vicinity of the main dock. The tide gage and staff were located at the SW end of the main dock at Fort Jefferson Park. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: NO 1 1974 DESIGNATION: 872 4697 TIDAL 1 MONUMENTATION: Survey disk VM#: 9690 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Concrete dock OPUS PID: LATITUDE: 24° 37.6' N ( 24.62670) LONGITUDE: 82° 52.3' W ( -82.87170) The primary bench mark is a disk set flush in the south corner of the concrete dock, near the entrance to Fort Jefferson, 3.41 m (11.2 ft) east of the east corner of a wooden building, 1.86 m (6.1 ft) NW of the south corner of the concrete dock, and 0.30 m (1.0 ft) NE of the SW side of the dock. BENCH MARK STAMPING: E DESIGNATION: 872 4697 E TIDAL MONUMENTATION: Survey disk VM#: 9691 AGENCY: Department of Interior IDB PID#: SETTING CLASSIFICATION: Moat wall OPUS PID: LATITUDE: 24° 37.6' N ( 24.62670) LONGITUDE: 82° 52.3' W ( -82.87170) The bench mark is a disk set flush in the top of the moat wall near the entrance to Fort Jefferson, 61.42 m (201.5 ft) SW of Bench Mark F, 59.28 m (194.5 ft) SW of the centerline of the bridge, and 0.70 m (2.3 ft) SE of the NW edge of the moat wall.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 Station ID: 8724697 PUBLICATION DATE: 11/13/2003 Name: GARDEN KEY,DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.6' N ( 24.62670) USGS Quad: DRY TORTUGAS Longitude: 82° 52.3' W ( -82.87170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: F DESIGNATION: 872 4697 F TIDAL MONUMENTATION: Survey disk VM#: 9692 AGENCY: Department of Interior IDB PID#: SETTING CLASSIFICATION: Moat wall OPUS PID: LATITUDE: 24° 37.6' N ( 24.62670) LONGITUDE: 82° 52.3' W ( -82.87170) The bench mark is a disk set flush in the top of the moat wall near the entrance to Fort Jefferson, 2.13 m (7.0 ft) NE of the centerline of the bridge across the moat, and 0.79 m (2.6 ft) SE of the NW edge of the moat wall. BENCH MARK STAMPING: H DESIGNATION: 872 4697 H TIDAL MONUMENTATION: Survey disk VM#: 9693 AGENCY: Department of Interior IDB PID#: SETTING CLASSIFICATION: Moat wall OPUS PID: LATITUDE: 24° 37.6' N ( 24.62670) LONGITUDE: 82° 52.3' W ( -82.87170) The bench mark is set flush in the top of the moat wall near the entrance to Fort Jefferson, 11.37 m (37.3 ft) NE of the centerline of the bridge across the moat, 9.24 m (30.3 ft) NE of Bench Mark F, and 0.73 m (2.4 ft) SE of the NW edge of the moat wall.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 Station ID: 8724697 PUBLICATION DATE: 11/13/2003 Name: GARDEN KEY,DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.6' N ( 24.62670) USGS Quad: DRY TORTUGAS Longitude: 82° 52.3' W ( -82.87170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: M DESIGNATION: 872 4697 M TIDAL MONUMENTATION: Survey disk VM#: 9694 AGENCY: Department of Interior IDB PID#: SETTING CLASSIFICATION: Moat wall OPUS PID: LATITUDE: 24° 37.6' N ( 24.62670) LONGITUDE: 82° 52.3' W ( -82.87170) The bench mark is a disk set flush in the top of the moat wall near the entrance to Fort Jefferson, 60.44 m (198.3 ft) NE of the centerline of the bridge across the moat, and 49 m (161 ft) NE of Bench Mark H.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 Station ID: 8724697 PUBLICATION DATE: 11/13/2003 Name: GARDEN KEY,DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.6' N ( 24.62670) USGS Quad: DRY TORTUGAS Longitude: 82° 52.3' W ( -82.87170) T I D A L D A T U M S Tidal datums at GARDEN KEY,DRY TORTUGAS based on: LENGTH OF SERIES: 2 MONTHS TIME PERIOD: March 1974 - April 1974 TIDAL EPOCH: 1983-2001 CONTROL TIDE STATION: 8724580 KEY WEST Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: MEAN HIGHER HIGH WATER MHHW = 0.534 MEAN HIGH WATER MHW = 0.437 MEAN TIDE LEVEL MTL = 0.266 MEAN SEA LEVEL MSL = 0.266 MEAN LOW WATER MLW = 0.095 MEAN LOWER LOW WATER MLLW = 0.000 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW NO 1 1974 1.964 1.527 E 1.406 0.969 F 1.449 1.012 H 1.447 1.010 M 1.361 0.923
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 Station ID: 8724697 PUBLICATION DATE: 11/13/2003 Name: GARDEN KEY,DRY TORTUGAS FL NOAA Chart: 11438 Latitude: 24° 37.6' N ( 24.62670) USGS Quad: DRY TORTUGAS Longitude: 82° 52.3' W ( -82.87170) 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.