U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 7 Station ID: 8723918 PUBLICATION DATE: 01/23/2004 Name: TOM'S HARBOR CHANNEL FL NOAA Chart: 11449 Latitude: 24° 46.6' N ( 24.77670) USGS Quad: GRASSY KEY Longitude: 80° 55.4' W ( -80.92330) To reach the tidal bench marks from the Post Office in Layton, proceed 12.2 km (7.6 mi) SW on U.S. Highway 1 to the SW end of the bridge over Toms Harbor Channel, at the NE end of Grassy Key. The bench marks are located near the west end of the old highway bridge, now used as a fishing pier, and at the east and west end of the new bridge, which is north of the old bridge. The tide gage and staff were located on the SW concrete wing wall of the old bridge. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: 1 1935 DESIGNATION: 872 3918 TIDAL 1 1935 MONUMENTATION: Tidal Station disk VM#: 6260 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: AA0361 SETTING CLASSIFICATION: Concrete sea wall OPUS PID: LATITUDE: 24° 46.6' N ( 24.77670) LONGITUDE: 80° 55.4' W ( -80.92330) The primary bench mark is a disk set in the top of a short concrete sea wall at the SW end of the SW concrete wing wall of the old bridge, 6 m (21 ft) SE of the centerline of the old highway, 0.61 m (2.0 ft) NE of the SW end of the sea wall, and 5 m (15 ft) below highway level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 7 Station ID: 8723918 PUBLICATION DATE: 01/23/2004 Name: TOM'S HARBOR CHANNEL FL NOAA Chart: 11449 Latitude: 24° 46.6' N ( 24.77670) USGS Quad: GRASSY KEY Longitude: 80° 55.4' W ( -80.92330) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 3918 D DESIGNATION: 872 3918 D TIDAL MONUMENTATION: Bench Mark disk VM#: 6261 AGENCY: Florida Department of Transportation (FLDT) IDB PID#: AA0860 SETTING CLASSIFICATION: Concrete bridge guardrail OPUS PID: LATITUDE: 24° 46.6' N ( 24.77670) LONGITUDE: 80° 55.4' W ( -80.92330) The bench mark is a disk set in the top of the SW end of the guardrail at the SW end of the new bridge, 5.82 m (19.1 ft) SE of the centerline of U.S. Highway 1, 3.17 m (10.4 ft) NE of the SW end of the guardrail, 0.21 m (0.7 ft) SW of the bridge abutment, and 1 m (3 ft) above highway level. BENCH MARK STAMPING: 3918 E DESIGNATION: 872 3918 E TIDAL MONUMENTATION: Bench Mark disk VM#: 6262 AGENCY: Florida Department of Transportation (FLDT) IDB PID#: AA0859 SETTING CLASSIFICATION: Concrete bridge guardrail OPUS PID: LATITUDE: 24° 46.7' N ( 24.77830) LONGITUDE: 80° 55.2' W ( -80.92000) The bench mark is a disk set in the top of the NE end of the guardrail at the NE end of the new bridge, 6.04 m (19.8 ft) NW of the centerline of U.S. Highway 1, 3 m (10 ft) SW of the NE end of the guardrail, 0.3 m (1 ft) NE of the bridge abutment, and 1 m (3 ft) above highway level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 7 Station ID: 8723918 PUBLICATION DATE: 01/23/2004 Name: TOM'S HARBOR CHANNEL FL NOAA Chart: 11449 Latitude: 24° 46.6' N ( 24.77670) USGS Quad: GRASSY KEY Longitude: 80° 55.4' W ( -80.92330) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 1 1975 DESIGNATION: 872 3918 TIDAL 1 1975 MONUMENTATION: Tidal Station disk VM#: 6263 AGENCY: National Ocean Survey (NOS) IDB PID#: AA0661 SETTING CLASSIFICATION: Concrete wing wall OPUS PID: LATITUDE: 24° 46.6' N ( 24.77670) LONGITUDE: 80° 55.4' W ( -80.92330) The bench mark is a disk set flush in the top of the SW concrete wing wall of the old bridge, 16 m (54 ft) east of bench mark 1 1935, 9.60 m (31.5 ft) SE of the centerline of the old highway, and 3 feet (1 m) below highway level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 7 Station ID: 8723918 PUBLICATION DATE: 01/23/2004 Name: TOM'S HARBOR CHANNEL FL NOAA Chart: 11449 Latitude: 24° 46.6' N ( 24.77670) USGS Quad: GRASSY KEY Longitude: 80° 55.4' W ( -80.92330) T I D A L B E N C H M A R K S BENCH MARK STAMPING: Q 278 1966 DESIGNATION: Q 278 MONUMENTATION: Bench Mark disk VM#: 6264 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: AA0360 SETTING CLASSIFICATION: Concrete wing wall OPUS PID: LATITUDE: 24° 46.6' N ( 24.77670) LONGITUDE: 80° 55.4' W ( -80.92330) The bench mark is a disk set in the top of the NW concrete wing wall at the SW end of the old bridge, 5.49 m (18.0 ft) NW of the centerline of the old highway, 5 m (15 ft) north of the SW end of the NW guardrail, and 1 m (3 ft) below highway level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 7 Station ID: 8723918 PUBLICATION DATE: 01/23/2004 Name: TOM'S HARBOR CHANNEL FL NOAA Chart: 11449 Latitude: 24° 46.6' N ( 24.77670) USGS Quad: GRASSY KEY Longitude: 80° 55.4' W ( -80.92330) T I D A L B E N C H M A R K S BENCH MARK STAMPING: R 278 1966 DESIGNATION: R 278 MONUMENTATION: Bench Mark disk VM#: 6265 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: AA0359 SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID: LATITUDE: 24° 46.6' N ( 24.77670) LONGITUDE: 80° 55.5' W ( -80.92500) The bench mark is a disk located 0.2 km (0.1 mi) SW of the SW end of the new bridge, 14.17 m (46.5 ft) SE of the centerline of U.S. Highway 1, 6 m (20 ft) NE of a concrete marker post for a water line, 1.07 m (3.5 ft) SW of utility pole #B421, and 0.3 m (1 ft) NE of a metal witness post. The bench mark is crimped to the top of a copper-clad steel rod driven 3.7 m (12 ft) to refusal, encased in a 5-inch iron pipe projecting 0.3 m (1 ft), and 2 m (8 ft) below highway level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 6 of 7 Station ID: 8723918 PUBLICATION DATE: 01/23/2004 Name: TOM'S HARBOR CHANNEL FL NOAA Chart: 11449 Latitude: 24° 46.6' N ( 24.77670) USGS Quad: GRASSY KEY Longitude: 80° 55.4' W ( -80.92330) T I D A L D A T U M S Tidal datums at TOM'S HARBOR CHANNEL based on: LENGTH OF SERIES: 1 MONTH TIME PERIOD: February 1975 - February 1975 TIDAL EPOCH: 1983-2001 CONTROL TIDE STATION: 8724211 BIG PINE KEY VIADUCT Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: North American Vertical Datum NAVD88 = 0.388 MEAN HIGHER HIGH WATER MHHW = 0.244 MEAN HIGH WATER MHW = 0.205 MEAN SEA LEVEL MSL = 0.133 MEAN TIDE LEVEL MTL = 0.131 MEAN LOW WATER MLW = 0.057 MEAN LOWER LOW WATER MLLW = 0.000 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW 1 1935 0.833 0.628 3918 D 5.524 5.319 3918 E 5.533 5.328 NO 1 1975 2.796 2.591 Q 278 1966 3.611 3.406 R 278 1966 1.621 1.416 Foot Notes: Bench marks 3918 D, 3918 E, and R 278 1966 are based on one differential leveling connection and do not meet the quality control standards of the NOS. Therefore, caution should be used when deriving elevations for these marks.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 7 of 7 Station ID: 8723918 PUBLICATION DATE: 01/23/2004 Name: TOM'S HARBOR CHANNEL FL NOAA Chart: 11449 Latitude: 24° 46.6' N ( 24.77670) USGS Quad: GRASSY KEY Longitude: 80° 55.4' W ( -80.92330) 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.