U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 6 Station ID: 8724397 PUBLICATION DATE: 11/13/2003 Name: JOHNSTON KEY FL NOAA Chart: 11448 Latitude: 24° 42.6' N ( 24.71000) USGS Quad: SUGARLOAF KEY Longitude: 81° 35.6' W ( -81.59330) To reach the tidal bench marks from the bridge between Cudjoe Key and Sugarloaf Key, proceed NWW by boat for 9.7 km (6.0 statute mi) to the SW tip of Johnston Key. The bench marks are located on the SW tip of the key. The tide gage and staff were located just west of the SW tip of the key. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: JOHNSTON KEY 2 RM 1 1934-35 DESIGNATION: JOHNSTON RM 1 MONUMENTATION: Reference Mark disk VM#: 7059 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: AE4416 SETTING CLASSIFICATION: Concrete monument OPUS PID: LATITUDE: 24° 42.6' N ( 24.71000) LONGITUDE: 81° 35.6' W ( -81.59330) The primary bench mark is a disk set in the top of a 0.18 m (0.6 ft) square concrete monument, 43 m (141 ft) SE of the approximate high water line, 24.25 m (79.6 ft) east of Bench Mark JOHNSTON KEY 2 1934-35, and 0.06 m (0.2 ft) above the ground.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 6 Station ID: 8724397 PUBLICATION DATE: 11/13/2003 Name: JOHNSTON KEY FL NOAA Chart: 11448 Latitude: 24° 42.6' N ( 24.71000) USGS Quad: SUGARLOAF KEY Longitude: 81° 35.6' W ( -81.59330) T I D A L B E N C H M A R K S BENCH MARK STAMPING: JOHNSTON KEY 2 1934-35 DESIGNATION: JOHNSTON KEY 2 MONUMENTATION: Triangulation Station disk VM#: 7058 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: AA1037 SETTING CLASSIFICATION: Concrete monument OPUS PID: LATITUDE: 24° 42.7' N ( 24.71170) LONGITUDE: 81° 35.6' W ( -81.59330) The bench mark is a disk set in the top of a 0.21 m x 0.21 m ( 0.7 ft x 7 ft) concrete monument, about 136 m (446 ft) NE of the most SW tip of the key, 50 m (164 ft) NW of the mangroves on the SE shore, 30 m (98 ft) east of the mangroves on the west shore, 1.07 m (3.5 ft) NNW of a witness post, and 0.06 m (0.2 ft) above the ground.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 6 Station ID: 8724397 PUBLICATION DATE: 11/13/2003 Name: JOHNSTON KEY FL NOAA Chart: 11448 Latitude: 24° 42.6' N ( 24.71000) USGS Quad: SUGARLOAF KEY Longitude: 81° 35.6' W ( -81.59330) T I D A L B E N C H M A R K S BENCH MARK STAMPING: JOHNSTON KEY 2 RM 2 1934-35 DESIGNATION: JOHNSTON RM 2 MONUMENTATION: Reference Mark disk VM#: 7060 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: AE4417 SETTING CLASSIFICATION: Concrete monument OPUS PID: LATITUDE: 24° 42.6' N ( 24.71000) LONGITUDE: 81° 35.6' W ( -81.59330) The bench mark is a disk set in the top of a 0.18 m (0.6 ft) square concrete monument, 30 m (98 ft) NE of the outer edge of mangroves, 20.70 m (67.91 ft) SSW of Bench Mark JOHNSTON KEY 1934-35, and 0.06 m (0.2 ft) above the ground. BENCH MARK STAMPING: NO 1 1973 DESIGNATION: 872 4397 TIDAL 1 MONUMENTATION: Tidal Station disk VM#: 7061 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Rock outcrop OPUS PID: LATITUDE: 24° 42.6' N ( 24.71000) LONGITUDE: 81° 35.6' W ( -81.59330) The bench mark is a disk set in rock outcrop, 110 m (361 ft) NE of the most SW tip of the key, 36.58 m (120.0 ft) west of Bench Mark JOHNSTON KEY 2 RM 2 1934-35, 12 m (41 ft) SSW of Bench Mark NO 2 1973, 6 m (20 ft) ESE of the outer edge of mangroves on the west side of the key, 0.40 m (1.3 ft) SE of an 0.46 m (1.5 ft) high copper-clad rod driven into the ground.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 6 Station ID: 8724397 PUBLICATION DATE: 11/13/2003 Name: JOHNSTON KEY FL NOAA Chart: 11448 Latitude: 24° 42.6' N ( 24.71000) USGS Quad: SUGARLOAF KEY Longitude: 81° 35.6' W ( -81.59330) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 2 1973 DESIGNATION: 872 4397 TIDAL 2 MONUMENTATION: Tidal Station disk VM#: 7062 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Rock outcrop OPUS PID: LATITUDE: 24° 42.6' N ( 24.71000) LONGITUDE: 81° 35.6' W ( -81.59330) The bench mark is a disk set in rock outcrop, 122 m (400 ft) NE of the most SW tip of the key, 36.73 m (120.5 ft) WNW of Bench Mark JOHNSTON KEY 2 RM 2 1934-35, 12.50 m (41.0 ft) NE of Bench Mark NO 1 1973, 3.35 m (11.0 ft) ESE of the outer edge of mangroves on the west side of the key.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 6 Station ID: 8724397 PUBLICATION DATE: 11/13/2003 Name: JOHNSTON KEY FL NOAA Chart: 11448 Latitude: 24° 42.6' N ( 24.71000) USGS Quad: SUGARLOAF KEY Longitude: 81° 35.6' W ( -81.59330) T I D A L D A T U M S Tidal datums at JOHNSTON KEY based on: LENGTH OF SERIES: 3 MONTHS TIME PERIOD: December 1973 - February 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 = 0.604 MEAN HIGH WATER MHW = 0.513 MEAN TIDE LEVEL MTL = 0.275 MEAN SEA LEVEL MSL = 0.244 MEAN LOW WATER MLW = 0.038 MEAN LOWER LOW WATER MLLW = 0.000 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW JOHNSTON KEY 2 RM 1 1934-35 0.502 -0.011 JOHNSTON KEY 2 1934-35 0.532 0.019 JOHNSTON KEY 2 RM 2 1934-35 0.476 -0.037 NO 1 1973 0.222 -0.291 NO 2 1973 0.190 -0.323
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 6 of 6 Station ID: 8724397 PUBLICATION DATE: 11/13/2003 Name: JOHNSTON KEY FL NOAA Chart: 11448 Latitude: 24° 42.6' N ( 24.71000) USGS Quad: SUGARLOAF KEY Longitude: 81° 35.6' W ( -81.59330) 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.