U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 Station ID: 8667783 PUBLICATION DATE: 05/16/2003 Name: OTTER ISLAND, ST. HELENA SOUND SC NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670) USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000) To reach the tidal bench marks from U.S. Highway 17 in Jacksonboro, proceed south on U.S. Highway 17 for 13 km (8 mi), crossing Ashepoo River, to a rest area and the intersection of State Road S-15-26, turn left on State Road S-15-26 and go 25.1 km (15.6 mi) to the end of the pavement, turn right onto the dirt road and continue 0.3 km (0.2 mi) to the boat ramps at Bennetts Point, continue by boat for about 12.4 km (6.7 nautical mi) down the Ashepoo River to Otter Island. The bench marks are behind the berm line and west of the dense brush on the beach of Otter Island. The tide gage and staff were on a platform constructed offshore of the west side of the island at the mouth of Ashepoo River at St. Helena Sound. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: 7783 A 1978 DESIGNATION: 866 7783 A TIDAL MONUMENTATION: Tidal Station disk VM#: 4395 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Galvanized steel rod OPUS PID: LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000) The primary bench mark is a disk crimped to a galvanized steel rod, located 41.85 m (137.3 ft) NNW of Bench Mark 7783 B 1978, and 1.25 m (4.1 ft) WSW of a metal witness post. The bench mark is 0.09 m (0.3 ft) above the ground, crimped to a galvanized steel rod driven 12 m (38 ft) to refusal, and encased in a 4-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 Station ID: 8667783 PUBLICATION DATE: 05/16/2003 Name: OTTER ISLAND, ST. HELENA SOUND SC NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670) USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 7783 B 1978 DESIGNATION: 866 7783 B TIDAL MONUMENTATION: Tidal Station disk VM#: 4396 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Concrete monument OPUS PID: LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000) The bench mark is a disk set in the top of a concrete monument, 46 m (151 ft) north of Bench Mark 7783 C 1978, 1.13 m (3.7 ft) west of a metal witness post, and 0.09 m (0.3 ft) above the ground. BENCH MARK STAMPING: 7783 C 1978 DESIGNATION: 866 7783 C TIDAL MONUMENTATION: Tidal Station disk VM#: 4397 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Galvanized steel rod OPUS PID: LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000) The bench mark is a disk crimped to a galvanized steel rod, located 50.38 m (165.3 ft) feet NNE of Bench Mark 7783 D 1978, and 1.22 m (4.0 ft) west of a metal witness post. The bench mark is 0.09 m (0.3 ft) above the ground, crimped to a galvanized steel rod driven 7 m (22 ft) to refusal, and encased in a 4-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 Station ID: 8667783 PUBLICATION DATE: 05/16/2003 Name: OTTER ISLAND, ST. HELENA SOUND SC NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670) USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 7783 D 1978 DESIGNATION: 866 7783 D TIDAL MONUMENTATION: Tidal Station disk VM#: 4398 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Concrete momument OPUS PID: LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000) The bench mark is a disk set in the top of a concrete monument, 44.17 m (144.9 ft) north of Bench Mark 7783 E 1978, 0.85 m (2.8 ft) west of a metal witness post, and 0.03 m (0.1 ft) above the ground. BENCH MARK STAMPING: 7783 E 1978 DESIGNATION: 866 7783 E TIDAL MONUMENTATION: Tidal Station disk VM#: 4399 AGENCY: National Ocean Survey (NOS) IDB PID#: SETTING CLASSIFICATION: Galvinized steel rod OPUS PID: LATITUDE: 32° 28.6' N ( 32.47670) LONGITUDE: 80° 25.2' W ( -80.42000) The bench mark is a disk crimped to a galvanized steel rod, located 13.41 m (44.0 ft) west of a 0.15 m (0.5 ft) diameter twin cedar tree, and 1.04 m (3.4 ft) west of a metal witness post. The bench mark is 0.09 m (0.3 ft) above the ground, crimped to a galvanized steel rod driven 6.71 m (22.0 ft) to refusal, and encased in a 4-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 Station ID: 8667783 PUBLICATION DATE: 05/16/2003 Name: OTTER ISLAND, ST. HELENA SOUND SC NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670) USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000) T I D A L D A T U M S Tidal datums at OTTER ISLAND, ST. HELENA SOUND based on: LENGTH OF SERIES: 8 MONTHS TIME PERIOD: April 1978 - November 1978 TIDAL EPOCH: 1983-2001 CONTROL TIDE STATION: 8667999 BEAUFORT Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: MEAN HIGHER HIGH WATER MHHW = 2.004 MEAN HIGH WATER MHW = 1.895 MEAN SEA LEVEL MSL = 1.023 MEAN TIDE LEVEL MTL = 0.979 MEAN LOW WATER MLW = 0.064 MEAN LOWER LOW WATER MLLW = 0.000 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW 7783 A 1978 2.536 0.641 7783 B 1978 2.542 0.647 7783 C 1978 2.638 0.743 7783 D 1978 2.513 0.618 7783 E 1978 2.621 0.726
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 Station ID: 8667783 PUBLICATION DATE: 05/16/2003 Name: OTTER ISLAND, ST. HELENA SOUND SC NOAA Chart: 11517 Latitude: 32° 28.6' N ( 32.47670) USGS Quad: ST HELENA SOUND Longitude: 80° 25.2' W ( -80.42000) 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.