U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 Station ID: 8723861 PUBLICATION DATE: 12/27/2005 Name: ALLIGATOR REEF LIGHTHOUSE FL NOAA Chart: 11449 Latitude: 24° 51.0' N ( 24.85000) USGS Quad: UPPER MATECUMBE KEY Longitude: 80° 37.1' W ( -80.61830) To reach the tidal bench marks from the east end of the bridge between Lower Matecumbe Key and Upper Matecumbe Key, proceed by boat SE for 6.4 km (4.0 statute mi) to Alligator Reef Lighthouse. The lighthouse is an octagonal steel skeleton tower on the pile foundation. The bench marks are located on the lighthouse structure. The tide gage and staff were located on the lighthouse structure. Each of the vertical members (legs) has a painted number on it. The numbers increase in a counter-clockwise direction. Leg No. 8 is the first leg west of the landing platform. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: NO 1 DESIGNATION: 872 3861 TIDAL 1 MONUMENTATION: See descriptive text VM#: 10923 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Lighthouse structure OPUS PID: LATITUDE: 24° 51.0' N ( 24.85000) LONGITUDE: 80° 37.1' W ( -80.61830) The primary bench mark is the high point of the most southerly nut on the NE stud of three at the leg No. 8 joint, 8.38 m (27.5 ft) NNW of bench mark NO 3, and 0.46 (1.5 ft) above the landing platform.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 Station ID: 8723861 PUBLICATION DATE: 12/27/2005 Name: ALLIGATOR REEF LIGHTHOUSE FL NOAA Chart: 11449 Latitude: 24° 51.0' N ( 24.85000) USGS Quad: UPPER MATECUMBE KEY Longitude: 80° 37.1' W ( -80.61830) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 2 DESIGNATION: 872 3861 TIDAL 2 MONUMENTATION: See descriptive text VM#: 10924 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Lighthouse structure OPUS PID: LATITUDE: 24° 51.0' N ( 24.85000) LONGITUDE: 80° 37.1' W ( -80.61830) The bench mark is the high point of the most northerly nut on the most westerly stud of three at the leg No. 7 joint, 5.97 m (19.6 ft) east of bench mark NO 1, and 0.46 (1.5 ft) above the landing platform. BENCH MARK STAMPING: NO 3 DESIGNATION: 872 3861 TIDAL 3 MONUMENTATION: See descriptive text VM#: 10925 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Lighthouse structure OPUS PID: LATITUDE: 24° 51.0' N ( 24.85000) LONGITUDE: 80° 37.1' W ( -80.61830) The bench mark is the high point of the northernmost bolt at the center leg joint joining leg No. 7 with the center leg, 8.38 m (27.5 ft) SSW of bench mark NO 2, 0.64 m (2.1 ft) above the horizontal spoke, and 0.46 (1.5 ft) above the landing platform.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 Station ID: 8723861 PUBLICATION DATE: 12/27/2005 Name: ALLIGATOR REEF LIGHTHOUSE FL NOAA Chart: 11449 Latitude: 24° 51.0' N ( 24.85000) USGS Quad: UPPER MATECUMBE KEY Longitude: 80° 37.1' W ( -80.61830) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 4 DESIGNATION: 872 3861 TIDAL 4 MONUMENTATION: See descriptive text VM#: 10926 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Lighthouse structure OPUS PID: LATITUDE: 24° 51.0' N ( 24.85000) LONGITUDE: 80° 37.1' W ( -80.61830) The bench mark is the high point of the eastern nut of the most northerly stud of three at the leg No. 5 joint, 8.69 m (28.5 ft) ESE of bench mark NO 3, and 0.46 (1.5 ft) above the landing platform. BENCH MARK STAMPING: NO 5 DESIGNATION: 872 3861 TIDAL 5 MONUMENTATION: See descriptive text VM#: 10927 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Lighthouse structure OPUS PID: LATITUDE: 24° 51.0' N ( 24.85000) LONGITUDE: 80° 37.1' W ( -80.61830) The bench mark is the high point of the southern nut on the southeasterly stud of three at the leg No. 3 joint, 8.78 m (28.8 ft) SSW of bench mark NO 3, and 0.64 m (2.1 ft) above the horizontal spoke connecting the center leg with leg No. 3.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 Station ID: 8723861 PUBLICATION DATE: 12/27/2005 Name: ALLIGATOR REEF LIGHTHOUSE FL NOAA Chart: 11449 Latitude: 24° 51.0' N ( 24.85000) USGS Quad: UPPER MATECUMBE KEY Longitude: 80° 37.1' W ( -80.61830) T I D A L D A T U M S Tidal datums at ALLIGATOR REEF LIGHTHOUSE based on: LENGTH OF SERIES: 7 MONTHS TIME PERIOD: May 1971 - November 1971 TIDAL EPOCH: 1983-2001 CONTROL TIDE STATION: 8723747 TAVERNIER HAWK CHANNEL Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: MEAN HIGHER HIGH WATER MHHW = 0.679 MEAN HIGH WATER MHW = 0.636 MEAN SEA LEVEL MSL = 0.352 MEAN TIDE LEVEL MTL = 0.348 MEAN LOW WATER MLW = 0.060 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 3.876 3.240 NO 2 3.868 3.232 NO 3 3.922 3.286 NO 4 3.882 3.246 NO 5 3.897 3.261
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 Station ID: 8723861 PUBLICATION DATE: 12/27/2005 Name: ALLIGATOR REEF LIGHTHOUSE FL NOAA Chart: 11449 Latitude: 24° 51.0' N ( 24.85000) USGS Quad: UPPER MATECUMBE KEY Longitude: 80° 37.1' W ( -80.61830) 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.