U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 Station ID: 8723921 PUBLICATION DATE: 04/01/2004 Name: GRASSY KEY NORTH SIDE, FLORIDA BAY FL NOAA Chart: 11449 Latitude: 24° 46.3' N ( 24.77170) USGS Quad: GRASSY KEY Longitude: 80° 56.4' W ( -80.94000) To reach the tidal bench marks from the post office at Layton, proceed 14.0 km (8.7 mi) SW along U.S. Highway 1 to a paved private drive on the right, continue 0.24 km (0.15 mi) north on the private drive to an abandoned ferry landing on the Dorset Estate. The bench marks are along the driveway and near the old ferry landing, on the gulf side of Grassy Key. The tide gage and staff were located on the pier at the boat basin west of the old ferry landing. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: BM NO 2 1935 DESIGNATION: 872 3921 TIDAL 2 MONUMENTATION: Tidal Station disk VM#: 6266 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: AA0354 SETTING CLASSIFICATION: Coral outcrop OPUS PID: LATITUDE: 24° 46.4' N ( 24.77330) LONGITUDE: 80° 56.4' W ( -80.94000) The primary bench mark is a disk set in a large coral outcrop, 20 m (67 ft) SW of the extended centerline of the road, 9 m (30 ft) NE of the north corner of an old 4 m (12 ft) square concrete block building, 3 m (9 ft) SE of the shoreline, and at road level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 Station ID: 8723921 PUBLICATION DATE: 04/01/2004 Name: GRASSY KEY NORTH SIDE, FLORIDA BAY FL NOAA Chart: 11449 Latitude: 24° 46.3' N ( 24.77170) USGS Quad: GRASSY KEY Longitude: 80° 56.4' W ( -80.94000) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 5 1964 DESIGNATION: 872 3921 NO 5 MONUMENTATION: Bench Mark disk VM#: 6267 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: AA0356 SETTING CLASSIFICATION: Coral outcrop OPUS PID: LATITUDE: 24° 46.4' N ( 24.77330) LONGITUDE: 80° 56.4' W ( -80.94000) The bench mark is a disk set in the top of a coral outcrop, 36 m (117 ft) NE of the extended centerline of the road near the old ferry landing, 4.11 m (13.5 ft) west of a small button-wood tree with a triangle blaze cut on its west side, 4 m (13 ft) NW of the NW side of a 1 m (4 ft) boulder which projects 1 m (2 ft), 3 m (10 ft) SE of the shoreline, and at ground level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 Station ID: 8723921 PUBLICATION DATE: 04/01/2004 Name: GRASSY KEY NORTH SIDE, FLORIDA BAY FL NOAA Chart: 11449 Latitude: 24° 46.3' N ( 24.77170) USGS Quad: GRASSY KEY Longitude: 80° 56.4' W ( -80.94000) T I D A L B E N C H M A R K S BENCH MARK STAMPING: H 328 1970 DESIGNATION: H 328 MONUMENTATION: Bench Mark disk VM#: 6269 AGENCY: National Geodetic Survey (NGS) IDB PID#: AA0352 SETTING CLASSIFICATION: Coral outcrop OPUS PID: LATITUDE: 24° 46.4' N ( 24.77330) LONGITUDE: 80° 56.4' W ( -80.94000) The bench mark is a disk set in top of a coral outcrop west of the boat basin, 71 m (234 ft) SW of the extended centerline of the paved drive near the old ferry landing, 29.05 m (95.3 ft) west of the NW corner of a house, 9 m (31 ft) west of the centerline of a driveway, 4.11 m (13.5 ft) SW of the centerline of the boat ramp, 3.35 m (11.0 ft) east of the east side of a 1 m (3 ft) high wall at the shoreline, and 0.30 m (1.0 ft) below driveway level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 Station ID: 8723921 PUBLICATION DATE: 04/01/2004 Name: GRASSY KEY NORTH SIDE, FLORIDA BAY FL NOAA Chart: 11449 Latitude: 24° 46.3' N ( 24.77170) USGS Quad: GRASSY KEY Longitude: 80° 56.4' W ( -80.94000) T I D A L D A T U M S Tidal datums at GRASSY KEY NORTH SIDE, FLORIDA BAY based on: LENGTH OF SERIES: 1 YEAR TIME PERIOD: January 1971 - December 1971 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 (02/19/1972) = 0.702 North American Vertical Datum NAVD88 = 0.422 MEAN HIGHER HIGH WATER MHHW = 0.388 MEAN HIGH WATER MHW = 0.337 MEAN TIDE LEVEL MTL = 0.207 MEAN SEA LEVEL MSL = 0.185 MEAN LOW WATER MLW = 0.076 MEAN LOWER LOW WATER MLLW = 0.000 LOWEST OBSERVED WATER LEVEL (02/04/1971) = -0.355 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW BM NO 2 1935 0.644 0.307 NO 5 1964 0.695 0.358 H 328 1970 1.275 0.938
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 Station ID: 8723921 PUBLICATION DATE: 04/01/2004 Name: GRASSY KEY NORTH SIDE, FLORIDA BAY FL NOAA Chart: 11449 Latitude: 24° 46.3' N ( 24.77170) USGS Quad: GRASSY KEY Longitude: 80° 56.4' W ( -80.94000) 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.