U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 6 Station ID: 9452368 PUBLICATION DATE: 07/12/2018 Name: SWANSON HARBOR AK NOAA Chart: 17316 Latitude: 58° 12.9' N ( 58.21500) USGS Quad: JUNEAU A-4 Longitude: 135° 7.6' W (-135.12700) To reach the tidal bench marks from the town of Gustavus, Icy Passage, proceed by boat SE along Icy Strait for about 43 km (23 nm) to the junction of Icy Strait and Lynn Canal, then north to the entrance to Swanson Harbor. The bench marks are on Ansley Island, mostly on the east coast. The tide gage and staff were on the SE coast of the island. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: 4 1959 DESIGNATION: 945 2368 TIDAL 4 MONUMENTATION: Tidal Station disk VM#: 9430 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: SETTING CLASSIFICATION: Rock outcrop OPUS PID: LATITUDE: 58° 12.0' N ( 58.20000) LONGITUDE: 135° 6.5' W (-135.10800) The primary bench mark is a disk set in a large granite outcrop on the east side of the island, north of the rocky point of the beach, about 366 m (1200 ft) north of the cliff that bench mark 945 2368 BOLT is set in, and near the apparent high water line.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 6 Station ID: 9452368 PUBLICATION DATE: 07/12/2018 Name: SWANSON HARBOR AK NOAA Chart: 17316 Latitude: 58° 12.9' N ( 58.21500) USGS Quad: JUNEAU A-4 Longitude: 135° 7.6' W (-135.12700) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 3 1959 DESIGNATION: 945 2368 TIDAL 3 MONUMENTATION: Tidal Station disk VM#: 9429 AGENCY: US Coast and Geodetic Survey (USC&GS) IDB PID#: SETTING CLASSIFICATION: Bedrock OPUS PID: LATITUDE: 58° 12.3' N ( 58.20500) LONGITUDE: 135° 6.5' W (-135.10800) The bench mark is a disk set in a slightly sloping surface formed at the bottom of a chain-shaped rock, on the east side of the first rocky point south of the north end of the island, and near the apparent high water line. BENCH MARK STAMPING: 2368 A 1986 DESIGNATION: 945 2368 A MONUMENTATION: Tidal Station disk VM#: 9431 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Bedrock OPUS PID: LATITUDE: 58° 12.0' N ( 58.20000) LONGITUDE: 135° 6.5' W (-135.10800) The bench mark is a disk set in bedrock on the east side of the island, at the base of the south edge of a large crack in the third rocky bluff, 290 m (950 ft) SE of bench mark 945 2368 BOLT, and near the apparent high water line.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 6 Station ID: 9452368 PUBLICATION DATE: 07/12/2018 Name: SWANSON HARBOR AK NOAA Chart: 17316 Latitude: 58° 12.9' N ( 58.21500) USGS Quad: JUNEAU A-4 Longitude: 135° 7.6' W (-135.12700) T I D A L B E N C H M A R K S BENCH MARK STAMPING: SWANSON 1987 DESIGNATION: SWANSON MONUMENTATION: Tidal Station disk VM#: 9433 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Rock boulder OPUS PID: LATITUDE: 58° 12.0' N ( 58.20000) LONGITUDE: 135° 6.5' W (-135.10800) The bench mark is a disk set between bench marks 2368 A 1986 and 2368 B 1986 in a large flat-topped boulder among a group of the largest boulders on a foul shoreline covered with sharp jagged boulders.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 6 Station ID: 9452368 PUBLICATION DATE: 07/12/2018 Name: SWANSON HARBOR AK NOAA Chart: 17316 Latitude: 58° 12.9' N ( 58.21500) USGS Quad: JUNEAU A-4 Longitude: 135° 7.6' W (-135.12700) T I D A L B E N C H M A R K S BENCH MARK STAMPING: DESIGNATION: 945 2368 BOLT ALIAS: NO STAMPING 1 MONUMENTATION: Bolt VM#: 9434 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Bedrock OPUS PID: LATITUDE: 58° 12.0' N ( 58.20000) LONGITUDE: 135° 6.5' W (-135.10800) The bench mark is a cross cut in a copper bolt set in the face of a bluff on the east side of the island, about halfway between the northern and southern tips, and 6 m (20 ft) SE of a recess in the bluff resembling a cave.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 6 Station ID: 9452368 PUBLICATION DATE: 07/12/2018 Name: SWANSON HARBOR AK NOAA Chart: 17316 Latitude: 58° 12.9' N ( 58.21500) USGS Quad: JUNEAU A-4 Longitude: 135° 7.6' W (-135.12700) T I D A L D A T U M S Tidal datums at SWANSON HARBOR based on: LENGTH OF SERIES: 1 MONTH TIME PERIOD: October 1986 TIDAL EPOCH: 2012-2016 CONTROL TIDE STATION: 9452210 JUNEAU, GASTINEAU CHANNEL, STEPHENS PASS Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: MEAN HIGHER HIGH WATER MHHW = 4.662 MEAN HIGH WATER MHW = 4.352 MEAN SEA LEVEL MSL = 2.451 MEAN TIDE LEVEL MTL = 2.417 MEAN LOW WATER MLW = 0.482 MEAN LOWER LOW WATER MLLW = 0.000 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW 4 1959 7.434 3.082 3 1959 5.264 0.912 2368 A 1986 6.060 1.708 SWANSON 1987 7.200 2.848 945 2368 BOLT 7.613 3.261
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 6 of 6 Station ID: 9452368 PUBLICATION DATE: 07/12/2018 Name: SWANSON HARBOR AK NOAA Chart: 17316 Latitude: 58° 12.9' N ( 58.21500) USGS Quad: JUNEAU A-4 Longitude: 135° 7.6' W (-135.12700) 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.