U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 4 PUBLICATION DATE: 09/14/1987 Station ID: 8724507 SUPERCEDED DATE: 04/21/2003 Name: CHANNEL KEY, FLORIDA BAY FLORIDA NOAA Chart: 11441 Latitude: 24° 36.2' N USGS Quad: BOCA CHICA KEY Longitude: 81° 43.5' W To reach the tidal bench marks from the west end of the bridge between Stock Island and Boca Chica Key, proceed NNW by boat for approximately 1.9 statute miles (3.1 km) to the west entrance of a small channel, locally known as Channel Grassy, dividing Channel Key. The bench marks are located in the NW section of the southern portion of the key. The tide gage and staff were located at the western entrance to Channel Grassy. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: CHANNEL KEY 2 1934 MONUMENTATION: Survey Disk VM#: 11306 AGENCY: PID#: AA1096 SETTING CLASSIFICATION: Concrete Monument The bench mark is set in a 1-foot (0.3 m) square concrete monument on a pile on the west side of the key, about 246 feet (75 m) SE of the entrance to Channel Grassy, about 82 feet (25 m) NE of the SW side of the key, 0.5 foot (0.2 m) west of a witness post, and 1 foot (0.3 m) above the ground. BENCH MARK STAMPING: BM NO 2 1973 MONUMENTATION: Survey Disk VM#: 11020 AGENCY: PID: SETTING CLASSIFICATION: Concrete Monument The bench mark is set on top of a 0.5-foot (0.2 m) square concrete monument on the west side of the key, about 225 feet (69 m) SSE of the entrance to Channel Grassy, 55.2 feet (16.8 m) WSW of Bench Mark CHANNEL KEY 2 RM 2 1934, 36.0 feet (11.0 m) NNW of Bench Mark CHANNEL KEY 2 RM 1 1934, and 0.5 foot (0.2 m) NW of a witness post.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 4 PUBLICATION DATE: 09/14/1987 Station ID: 8724507 SUPERCEDED DATE: 04/21/2003 Name: CHANNEL KEY, FLORIDA BAY FLORIDA NOAA Chart: 11441 Latitude: 24° 36.2' N USGS Quad: BOCA CHICA KEY Longitude: 81° 43.5' W T I D A L B E N C H M A R K S BENCH MARK STAMPING: CHANNEL KEY 2 RM 1 1934 MONUMENTATION: Survey Disk VM#: 11307 AGENCY: PID#: AE4421 SETTING CLASSIFICATION: Concrete Monument The bench mark is set in a 1-foot (0.3 m) square concrete monument on a pile on the west side of the key, about 295 feet (90 m) SE of the entrance to Channel Grassy, about 92 feet (28 m) NE of the SW side of the key, 46.7 feet (14.2 m) ESE of Bench Mark CHANNEL KEY 2 1934, 0.8 foot (0.2 m) NW of a witness post, and about 1 foot (0.3 m) above the ground. BENCH MARK STAMPING: CHANNEL KEY 2 RM 2 1934 MONUMENTATION: Survey Disk VM#: 11308 AGENCY: PID#: AE4422 SETTING CLASSIFICATION: Concrete Monument The bench mark is set in a 1-foot (0.3 m) square concrete monument on a pile on the west side of the key, about 295 feet (90 m) SSE of the entrance to Channel Grassy, 57.6 feet (17.6 m) SW of Bench Mark CHANNEL KEY 2 1934, 13 feet (4 m) east of the west side of the key, 0.5 foot (0.2 m) NNW of a witness post, and about 1 foot (0.3 m) above the ground. BENCH MARK STAMPING: NO 1 1973 MONUMENTATION: Survey Disk VM#: 11309 AGENCY: PID: SETTING CLASSIFICATION: Concrete/Rod Monument The bench mark is set in concrete atop a rod driven 8 feet (2 m) to refusal on the west side of the key, 94 feet (29 m) south of Channel Grassy, 55.7 feet (17.0 m) WNW of Bench Mark CHANNEL KEY 2 1934, 0.6 foot (0.2 m) NNW of a witness post, and 0.5 foot (0.2 m) above the ground.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 4 PUBLICATION DATE: 09/14/1987 Station ID: 8724507 SUPERCEDED DATE: 04/21/2003 Name: CHANNEL KEY, FLORIDA BAY FLORIDA NOAA Chart: 11441 Latitude: 24° 36.2' N USGS Quad: BOCA CHICA KEY Longitude: 81° 43.5' W T I D A L D A T U M S Tidal datums at CHANNEL KEY, FLORIDA BAY based on: LENGTH OF SERIES: 4 MONTHS TIME PERIOD: JANUARY-APRIL 1974 TIDAL EPOCH: 1960-1978 CONTROL TIDE STATION: 8724211 BIG PINE KEY VIADUCT Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET: HIGHEST OBSERVED WATER LEVEL (12/16/1973) = 2.56 MEAN HIGHER HIGH WATER MHHW = 1.37 MEAN HIGH WATER MHW = 1.08 MEAN TIDE LEVEL MTL = 0.62 MEAN LOW WATER MLW = 0.17 MEAN LOWER LOW WATER MLLW = 0.00 LOWEST OBSERVED WATER LEVEL (12/23/1973) = -0.55 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In FEET above: Stamping or Designation MLLW MHW CHANNEL KEY 2 1934 1.70 0.62 BM NO 2 1973 1.55 0.47 CHANNEL KEY 2 RM 1 1934 1.65 0.57 CHANNEL KEY 2 RM 2 1934 1.85 0.77 NO 1 1973 1.13 0.05
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 4 PUBLICATION DATE: 09/14/1987 Station ID: 8724507 SUPERCEDED DATE: 04/21/2003 Name: CHANNEL KEY, FLORIDA BAY FLORIDA NOAA Chart: 11441 Latitude: 24° 36.2' N USGS Quad: BOCA CHICA KEY Longitude: 81° 43.5' 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.