U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 4 PUBLICATION DATE: 03/24/1988 Station ID: 8724971 SUPERCEDED DATE: 04/21/2003 Name: DAVID KEY, BARFIELD BAY FLORIDA NOAA Chart: 11429 Latitude: 25° 55.0' N USGS Quad: MARCO ISLAND Longitude: 81° 41.2' W To reach the tidal bench marks from Marco Island, proceed by boat south in Roberts Bay to Caxambas Bay, then east through Caxambas Bay to marker 18, then north into Barfield Bay to David Key. The bench marks are located in the vicinity of the easternmost point of David Key. The tide gage and staff were on a small offshore platform 50 feet (15 m) east of the easternmost point of David Key. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: 4971 A 1978 MONUMENTATION: Survey Disk VM#: 9743 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is on the east point of the key, at the outer mangrove edge, and 1.3 feet (0.4 m) north of a witness post. The bench mark is 1.0 foot (0.3 m) above ground level, crimped to a galvanized steel rod driven 34 feet (10 m) to refusal, and encased in a 4-inch steel pipe. BENCH MARK STAMPING: 4971 B 1978 MONUMENTATION: Survey Disk VM#: 9744 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is 75.3 feet (23.0 m) west of Bench Mark 4971 A 1978, 14 feet (4 m) south of the outer mangrove edge, and 1.2 feet (0.4 m) north of a witness post. The bench mark is 1.3 feet (0.4 m) above ground level, crimped to a galvanized steel rod driven 32 feet (10 m) to refusal, and encased in a 4-inch steel pipe.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 4 PUBLICATION DATE: 03/24/1988 Station ID: 8724971 SUPERCEDED DATE: 04/21/2003 Name: DAVID KEY, BARFIELD BAY FLORIDA NOAA Chart: 11429 Latitude: 25° 55.0' N USGS Quad: MARCO ISLAND Longitude: 81° 41.2' W T I D A L B E N C H M A R K S BENCH MARK STAMPING: 4971 C 1978 MONUMENTATION: Survey Disk VM#: 9745 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is 102.6 feet (31.3 m) WSW of Bench Mark 4971 B 1978, 15 feet (5 m) SSE of the outer mangrove edge, and 1.3 foot (0.4 m) NW of a witness post. The bench mark is 1.4 feet (0.4 m) above ground level, crimped to a galvanized steel rod driven 35 feet (11 m) to refusal, and encased in a 4-inch steel pipe. BENCH MARK STAMPING: 4971 D 1978 MONUMENTATION: Survey Disk VM#: 9746 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is at the outer mangrove edge, 137.1 feet (41.8 m) east of Bench Mark 4971 C 1978, 0.8 foot (0.2 m) north of a witness post. The bench mark is 1.2 feet (0.4 m) above ground level, crimped to a galvanized steel rod driven 34 feet (10 m) to refusal, and encased in a 4-inch steel pipe. BENCH MARK STAMPING: 4971 E 1978 MONUMENTATION: Survey Disk VM#: 9747 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is 63.7 feet (19.4 m) WSW of Bench Mark 4971 D 1978, 9 feet (3 m) SSE of the outer mangrove edge, and 1.3 feet (0.4 m) south of a witness post. The bench mark is 1.5 feet (0.5 m) above ground level, crimped to a galvanized steel rod driven 33 feet (10 m) to refusal, and encased in a 4-inch steel pipe.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 4 PUBLICATION DATE: 03/24/1988 Station ID: 8724971 SUPERCEDED DATE: 04/21/2003 Name: DAVID KEY, BARFIELD BAY FLORIDA NOAA Chart: 11429 Latitude: 25° 55.0' N USGS Quad: MARCO ISLAND Longitude: 81° 41.2' W T I D A L D A T U M S Tidal datums at DAVID KEY, BARFIELD BAY based on: LENGTH OF SERIES: 5 MONTHS TIME PERIOD: APRIL-AUGUST 1978 TIDAL EPOCH: 1960-1978 CONTROL TIDE STATION: 8724967 MARCO ISLAND Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET: HIGHEST OBSERVED WATER LEVEL (05/04/1978) = 4.27 MEAN HIGHER HIGH WATER MHHW = 3.25 MEAN HIGH WATER MHW = 3.02 MEAN TIDE LEVEL MTL = 1.77 MEAN LOW WATER MLW = 0.53 MEAN LOWER LOW WATER MLLW = 0.00 LOWEST OBSERVED WATER LEVEL (03/29/1978) = -0.72 Bench Mark Elevation Information In FEET above: Stamping or Designation MLLW MHW 4971 A 1978 2.66 -0.36 4971 B 1978 3.09 0.07 4971 C 1978 4.04 1.02 4971 D 1978 2.63 -0.39 4971 E 1978 3.45 0.43
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 4 PUBLICATION DATE: 03/24/1988 Station ID: 8724971 SUPERCEDED DATE: 04/21/2003 Name: DAVID KEY, BARFIELD BAY FLORIDA NOAA Chart: 11429 Latitude: 25° 55.0' N USGS Quad: MARCO ISLAND Longitude: 81° 41.2' 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.