U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 4 PUBLICATION DATE: 03/10/1986 Station ID: 8724138 SUPERCEDED DATE: 04/21/2003 Name: BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F FLORIDA NOAA Chart: 11449 Latitude: 24° 39.3' N USGS Quad: BIG PINE KEY Longitude: 81° 16.9' W To reach the tidal bench marks from the Post Office at Marathon, proceed 13.4 miles (21.6 km) SW on U.S Highway 1 to the east end of the Bahia Honda Bridge over Big Spanish Channel, 0.2 mile (0.3 km) south of the new bridge. The bench marks are located on the old highway bridge which is above an abandoned railroad bridge at the state recreation area, and near the tackle shop. The tide gage and staff were located on the NE concrete wingwall of the railroad bridge. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: W BAHIA RM 2 1935 MONUMENTATION: Survey Disk VM#: 6369 AGENCY: PID#: AA0269 SETTING CLASSIFICATION: Concrete Wingwall The bench mark is set in the top of the south concrete wingwall of the old bridge, 315 feet (96 m) west of the east end of the bridge, 33 feet (10 m) south of the centerline of the highway, 17.2 feet (5.2 m) SE of Bench Mark NO 4 1936, and 35 feet (11 m) below highway level. BENCH MARK STAMPING: 4138 F 1982 MONUMENTATION: Survey Disk VM#: 6365 AGENCY: PID#: AA0898 SETTING CLASSIFICATION: Concrete Walkway The bench mark is near the tackle shop, set in a concrete walkway, 35.4 feet (10.8 m) NW of the south corner of the dive shop, 16.5 feet (5.0 m) east of the NE edge of the parking lot, 4.4 feet (1.3 m) SSW of the west corner of the tackle shop, and 0.5 foot (0.2 m) SW of the stairs behind the tackle shop.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 4 PUBLICATION DATE: 03/10/1986 Station ID: 8724138 SUPERCEDED DATE: 04/21/2003 Name: BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F FLORIDA NOAA Chart: 11449 Latitude: 24° 39.3' N USGS Quad: BIG PINE KEY Longitude: 81° 16.9' W T I D A L B E N C H M A R K S BENCH MARK STAMPING: D 70 RESET 1936 TIDAL NO 2 MONUMENTATION: Survey Disk VM#: 6366 AGENCY: PID#: AA0267 SETTING CLASSIFICATION: Concrete Wingwall The bench mark is set in the top of the north concrete wingwall of the old bridge, 315 feet (96 m) west of the east end of the bridge, 16 feet (5 m) north of the centerline of the highway, and 30 feet (9 m) below highway level. BENCH MARK STAMPING: G 329 1970 MONUMENTATION: Survey Disk VM#: 6367 AGENCY: PID#: AA0271 SETTING CLASSIFICATION: Concrete Wingwall The bench mark is near the old bridge, set in the top of the NW corner of the 6th concrete step from the bottom of the landing, 150 feet (46 m) north of the north edge of the bridge, 142.1 feet (43.3 m) east of the east face of the concrete wingwall of the railroad bridge and the NE corner of the highway bridge, 58 feet (18 m) south of the shoreline, and 10 feet (3 m) above water level. BENCH MARK STAMPING: NO 4 1936 MONUMENTATION: Survey Disk VM#: 6368 AGENCY: PID#: AA0268 SETTING CLASSIFICATION: Concrete Wingwall The bench mark is set in the top of the south concrete wingwall of the old bridge, 315 feet (96 m) west of the east end of the bridge, 16 feet (5 m) south of the centerline of the highway, and 30 feet (9 m) below highway level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 4 PUBLICATION DATE: 03/10/1986 Station ID: 8724138 SUPERCEDED DATE: 04/21/2003 Name: BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F FLORIDA NOAA Chart: 11449 Latitude: 24° 39.3' N USGS Quad: BIG PINE KEY Longitude: 81° 16.9' W T I D A L D A T U M S Tidal datums at BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F based on: LENGTH OF SERIES: 12 MONTHS TIME PERIOD: FEBRUARY 1971-JANUARY 1972 TIDAL EPOCH: 1960-1978 CONTROL TIDE STATION: 8724580 KEY WEST Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET: HIGHEST OBSERVED WATER LEVEL (11/05/1971) = 2.76 MEAN HIGHER HIGH WATER MHHW = 1.57 MEAN HIGH WATER MHW = 1.34 MEAN TIDE LEVEL MTL = 0.74 * NATIONAL GEODETIC VERTICAL DATUM NGVD29 = 0.53 MEAN LOW WATER MLW = 0.15 MEAN LOWER LOW WATER MLLW = 0.00 LOWEST OBSERVED WATER LEVEL (04/26/1971) = -0.75 * NGVD reference based on elevations published in Quad 240811, 1972, and NOS leveling of 1975. North American Vertical Datum (NAVD88) Bench Mark Elevation Information In FEET above: Stamping or Designation MLLW MHW W BAHIA RM 2 1935 22.88 21.54 4138 F 1982 5.71 4.37 D 70 RESET 1936 TIDAL NO 2 25.83 24.49 G 329 1970 12.95 11.61 NO 4 1936 26.02 24.68
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 4 PUBLICATION DATE: 03/10/1986 Station ID: 8724138 SUPERCEDED DATE: 04/21/2003 Name: BAHIA HONDA KEY, BIG SPANISH CHANNEL, STRAITS OF F FLORIDA NOAA Chart: 11449 Latitude: 24° 39.3' N USGS Quad: BIG PINE KEY Longitude: 81° 16.9' 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.