U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 4 PUBLICATION DATE: 09/14/1987 Station ID: 8724441 SUPERCEDED DATE: 04/21/2003 Name: OHARA KEY, NORTH POINT, WALTZ KEY BASIN FLORIDA NOAA Chart: 11445 Latitude: 24° 37.0' N USGS Quad: BOCA CHICA KEY Longitude: 81° 38.7' W To reach the tidal bench marks from the bridge between Big Coppitt Key and Saddlebunch Keys, proceed north by boat for approximately 1 statute mile (2 km) to the northernmost tip of OHara Key. The bench marks are located at the northern end of the Key. The tide gage and staff were located just north of the north tip of the Key. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: NO 1 1974 MONUMENTATION: Survey Disk VM#: 9613 AGENCY: PID: SETTING CLASSIFICATION: Concrete/Rod Monument The bench mark is set in concrete atop a copper-clad steel rod driven to refusal on the northernmost point of the Key, 33 feet (10 m) south of the outer northern edge of mangroves, 1 foot (0.3 m) NW of a witness post, and 0.3 foot (0.1 m) above the ground. BENCH MARK STAMPING: OHARA 1934 MONUMENTATION: Survey Disk VM#: 9612 AGENCY: PID#: AA1081 SETTING CLASSIFICATION: Concrete Monument The bench mark is set in a concrete monument on a pile in the northernmost point of the Key, 164 feet (50 m) east of the west edge of mangroves, 134 feet (41 m) west of the east edge of mangroves, 121 feet (37 m) south of the north edge of mangroves, 0.5 foot (0.2 m) NNW of a witness post, and 0.7 foot (0.2 m) above the ground.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 4 PUBLICATION DATE: 09/14/1987 Station ID: 8724441 SUPERCEDED DATE: 04/21/2003 Name: OHARA KEY, NORTH POINT, WALTZ KEY BASIN FLORIDA NOAA Chart: 11445 Latitude: 24° 37.0' N USGS Quad: BOCA CHICA KEY Longitude: 81° 38.7' W T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 2 1974 MONUMENTATION: Survey Disk VM#: 9614 AGENCY: PID: SETTING CLASSIFICATION: Concrete/Rod Monument The bench mark is set in concrete atop a copper-clad steel rod driven to refusal on the northernmost point of the Key, 52.6 feet (16.0 m) WSW of Bench Mark NO 1 1974, 51 feet (16 m) east of the outer western edge of mangroves, 0.7 foot (0.2 m) NW of a witness post, and 0.3 foot (0.1 m) above the ground. BENCH MARK STAMPING: NO 3 1974 MONUMENTATION: Survey Disk VM#: 9615 AGENCY: PID: SETTING CLASSIFICATION: Concrete/Rod Monument The bench mark is set in concrete atop a copper-clad steel rod driven to refusal on the northernmost point of the Key, 51 feet (16 m) SW of Bench Mark NO 2 1974, 38.5 feet (11.7 m) WNW of Bench Mark OHARA 1934, 0.6 foot (0.2 m) NW of a witness post, and 0.5 foot (0.2 m) above the ground. BENCH MARK STAMPING: NO 4 1974 MONUMENTATION: Survey Disk VM#: 9616 AGENCY: PID: SETTING CLASSIFICATION: Concrete/Rod Monument The bench mark is set in concrete atop a copper-clad steel rod driven to refusal on the northernmost point of the Key, 50 feet (15 m) SSW of Bench Mark NO 3 1974, 46.3 feet (14.1 m) WSW of Bench Mark OHARA 1934, 1.1 feet (0.3 m) SW of a witness post, and 0.3 foot (0.1 m) above the ground.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 4 PUBLICATION DATE: 09/14/1987 Station ID: 8724441 SUPERCEDED DATE: 04/21/2003 Name: OHARA KEY, NORTH POINT, WALTZ KEY BASIN FLORIDA NOAA Chart: 11445 Latitude: 24° 37.0' N USGS Quad: BOCA CHICA KEY Longitude: 81° 38.7' W T I D A L D A T U M S Tidal datums at OHARA KEY, NORTH POINT, WALTZ KEY BASIN based on: LENGTH OF SERIES: 1 MONTH TIME PERIOD: JANUARY 1975 TIDAL EPOCH: 1960-1978 CONTROL TIDE STATION: 8724580 KEY WEST Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET: HIGHEST OBSERVED WATER LEVEL (12/13/1974) = 2.54 MEAN HIGHER HIGH WATER MHHW = 1.86 MEAN HIGH WATER MHW = 1.60 MEAN TIDE LEVEL MTL = 0.90 MEAN LOW WATER MLW = 0.20 MEAN LOWER LOW WATER MLLW = 0.00 LOWEST OBSERVED WATER LEVEL (01/23/1975) = -0.53 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In FEET above: Stamping or Designation MLLW MHW NO 1 1974 1.86 0.26 OHARA 1934 2.36 0.76 NO 2 1974 1.64 0.04 NO 3 1974 1.75 0.15 NO 4 1974 1.86 0.26
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 4 PUBLICATION DATE: 09/14/1987 Station ID: 8724441 SUPERCEDED DATE: 04/21/2003 Name: OHARA KEY, NORTH POINT, WALTZ KEY BASIN FLORIDA NOAA Chart: 11445 Latitude: 24° 37.0' N USGS Quad: BOCA CHICA KEY Longitude: 81° 38.7' W 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 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.