U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 Station ID: 8724246 PUBLICATION DATE: 03/09/2004 Name: BIG SPANISH KEY FL NOAA Chart: 11448 Latitude: 24° 47.3' N ( 24.78830) USGS Quad: CONTENT KEYS Longitude: 81° 24.7' W ( -81.41170) To reach the tidal bench marks from the U.S. Highway 1 bridge over Bahia Honda, proceed by boat NW on Bahia Honda and Big Spanish Channel for 19 km (12 statute mi) to channel marker 36 and the SW shore of Big Spanish Key. The bench marks are located on the SW side of the Key. The tide gage and staff were located offshore. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: NO 1 1973 DESIGNATION: 872 4246 TIDAL 1 MONUMENTATION: Tidal Station disk VM#: 6855 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID: LATITUDE: 24° 47.3' N ( 24.78830) LONGITUDE: 81° 24.7' W ( -81.41170) The primary bench mark is a disk located near the center of the stretch constituting the SW shore of Big Spanish Key, 10.76 m (35.3 ft) NW of bench mark NO 3 1973, 7 m (24 ft) NE of the SW side of the key, 0.30 m (1.0 ft) west of an old witness post, and 0.30 m (1.0 ft) SW of a new witness post. The bench mark is set at ground level, crimped to the top of a copper-clad steel rod driven an unspecified depth to refusal.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 Station ID: 8724246 PUBLICATION DATE: 03/09/2004 Name: BIG SPANISH KEY FL NOAA Chart: 11448 Latitude: 24° 47.3' N ( 24.78830) USGS Quad: CONTENT KEYS Longitude: 81° 24.7' W ( -81.41170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 2 1973 DESIGNATION: 872 4246 TIDAL 2 MONUMENTATION: Tidal Station disk VM#: 6856 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID: LATITUDE: 24° 47.3' N ( 24.78830) LONGITUDE: 81° 24.7' W ( -81.41170) The bench mark is a disk located 20 m (67 ft) NE of the SW side of the Key, 14.78 m (48.5 ft) ESE of bench mark NO 1 1973, 1.98 m (6.5 ft) NNW of a witness sign nailed to a tree, and 0.30 m (1.0 ft) SW of a witness post. The bench mark is set at ground level, crimped to the top of a copper-clad steel rod driven an unspecified depth to refusal. BENCH MARK STAMPING: NO 3 1973 DESIGNATION: 872 4246 TIDAL 3 MONUMENTATION: Tidal Station disk VM#: 6857 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Copper-clad steel rod OPUS PID: LATITUDE: 24° 47.3' N ( 24.78830) LONGITUDE: 81° 24.7' W ( -81.41170) The bench mark is a disk located near the center of the stretch constituting the SW shore of Big Spanish Key, 11.28 m (37.0 ft) SW of bench mark NO 2 1973, 9 m (30 ft) NE of the SW side of the Key, 1.92 m (6.3 ft) north of a witness sign nailed to a tree, and 0.30 m (1.0 ft) SW of a witness post. The bench mark is set at ground level, crimped to the top of a copper-clad steel rod driven an unspecified depth to refusal.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 Station ID: 8724246 PUBLICATION DATE: 03/09/2004 Name: BIG SPANISH KEY FL NOAA Chart: 11448 Latitude: 24° 47.3' N ( 24.78830) USGS Quad: CONTENT KEYS Longitude: 81° 24.7' W ( -81.41170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 4246 D 1984 DESIGNATION: 872 4246 D MONUMENTATION: Tidal Station disk VM#: 6858 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Stainless steel rod OPUS PID: LATITUDE: 24° 47.3' N ( 24.78830) LONGITUDE: 81° 24.7' W ( -81.41170) The bench mark is a disk located near the center of the SW shore of the Key, 13.87 m (45.5 ft) NW of bench mark NO 1 1973, 7 m (24 ft) NE of the outer edge of the mangroves, and 0.30 m (1.0 ft) SW of a witness post. The bench mark is set 0.73 m (2.4 ft) above ground level, crimped to a stainless steel rod driven an unspecified depth to refusal, and encased in a 6-inch PVC pipe which projects 0.85 m (2.8 ft) above ground level. BENCH MARK STAMPING: 4246 E 1984 DESIGNATION: 872 4246 E MONUMENTATION: Tidal Station disk VM#: 6859 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Stainless steel rod OPUS PID: LATITUDE: 24° 47.3' N ( 24.78830) LONGITUDE: 81° 24.7' W ( -81.41170) The bench mark is a disk located near the center of the SW shore of the Key, 16.00 m (52.5 ft) NW of bench mark NO 3 1973, 8.72 m (28.6 ft) SSE of bench mark 4246 D 1984, 6.49 m (21.3 ft) WNW of bench mark NO 1 1973, 5 m (15 ft) NE of the outer edge of the mangroves, and 0.30 m (1.0 ft) SW of a witness post. The bench mark is set 0.76 m (2.5 ft) above ground level, crimped to a stainless steel rod driven an unspecified depth to refusal, and encased in a 6-inch PVC pipe which projects 0.82 m (2.7 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 Station ID: 8724246 PUBLICATION DATE: 03/09/2004 Name: BIG SPANISH KEY FL NOAA Chart: 11448 Latitude: 24° 47.3' N ( 24.78830) USGS Quad: CONTENT KEYS Longitude: 81° 24.7' W ( -81.41170) T I D A L D A T U M S Tidal datums at BIG SPANISH KEY based on: LENGTH OF SERIES: 1 MONTH TIME PERIOD: January 1974 - January 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 = 0.980 MEAN HIGH WATER MHW = 0.901 MEAN TIDE LEVEL MTL = 0.502 MEAN SEA LEVEL MSL = 0.482 MEAN LOW WATER MLW = 0.103 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 1973 0.426 -0.475 NO 2 1973 0.520 -0.381 NO 3 1973 0.562 -0.339 4246 D 1984 1.045 0.144 4246 E 1984 1.074 0.173
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 Station ID: 8724246 PUBLICATION DATE: 03/09/2004 Name: BIG SPANISH KEY FL NOAA Chart: 11448 Latitude: 24° 47.3' N ( 24.78830) USGS Quad: CONTENT KEYS Longitude: 81° 24.7' W ( -81.41170) 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.