U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 Station ID: 9451785 PUBLICATION DATE: 08/09/2004 Name: THE BROTHERS, STEPHENS PASSAGE AK NOAA Chart: 17362 Latitude: 57° 17.7' N ( 57.29500) USGS Quad: SUMDUM (B-6) Longitude: 133° 47.8' W (-133.79700) To reach the tidal bench marks from Petersburg, Alaska, navigate 73.2 km (39.5 nm) (317 degrees true) to the western side of the small island to the east of East Brothers Island to latitude 57 degrees 17.7' N, longitude 133 degrees 47.8' W. The bench marks are located on the SW side of the island on a ledge extending from the southern side of a small bight. The ledge lies north-south along the island. The gage was located towards the southern end of the island. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: 1785 A 1993 DESIGNATION: 945 1785 A MONUMENTATION: Tidal Station disk VM#: 13119 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Granitic rock outcrop OPUS PID: LATITUDE: 57° 17.7' N ( 57.29500) LONGITUDE: 133° 47.8' W (-133.79700) The primary bench mark is a disk set in weathered outcrop of granitic rock, 3 m (10 ft) from a vertical cliff face that dominates the entire island, NE (030 degrees magnetic) from a rock awash, just south of the southern point of East Brothers Island, SE (130 degrees magnetic) from a tangent to the northern point of East Brothers Island, NE (080 degrees magnetic) from the southernmost cove on the east side of East Brothers Island, and 1 m (3 ft) above the apparent high water line.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 Station ID: 9451785 PUBLICATION DATE: 08/09/2004 Name: THE BROTHERS, STEPHENS PASSAGE AK NOAA Chart: 17362 Latitude: 57° 17.7' N ( 57.29500) USGS Quad: SUMDUM (B-6) Longitude: 133° 47.8' W (-133.79700) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 1785 B 1993 DESIGNATION: 945 1785 B MONUMENTATION: Tidal Station disk VM#: 13120 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Granitic rock outcrop OPUS PID: LATITUDE: 57° 17.7' N ( 57.29500) LONGITUDE: 133° 47.8' W (-133.79700) The bench mark is a disk set in weathered, green granitic rock, located directly across from the southernmost cove on the east side of East Brothers Island, on the seaward side of a large pile of boulders at the base of the cliff, and 10 m (33 ft) north of a 30 m (99 ft) vertical cliff face. BENCH MARK STAMPING: 1785 C 1993 DESIGNATION: 945 1785 C MONUMENTATION: Tidal Station disk VM#: 13121 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Granitic rock outcrop OPUS PID: LATITUDE: 57° 17.7' N ( 57.29500) LONGITUDE: 133° 47.8' W (-133.79700) The bench mark is a disk set in weathered outcrop of granitic rock, 15 m (49 ft) south of a large crevasse in the vertical rock face, NE (030 degrees magnetic) from the rock at the south end of East Brothers Island, NE (066 degrees magnetic) from the southernmost cove of the island, the tangent to the northern end of East Brothers is NW (320 degrees magnetic), and 1 m (3 ft) above the apparent high water line.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 Station ID: 9451785 PUBLICATION DATE: 08/09/2004 Name: THE BROTHERS, STEPHENS PASSAGE AK NOAA Chart: 17362 Latitude: 57° 17.7' N ( 57.29500) USGS Quad: SUMDUM (B-6) Longitude: 133° 47.8' W (-133.79700) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 1785 D 1993 DESIGNATION: 945 1785 D MONUMENTATION: Tidal Station disk VM#: 13122 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Rock ledge OPUS PID: LATITUDE: 57° 17.7' N ( 57.29500) LONGITUDE: 133° 47.8' W (-133.79700) The bench mark is a disk set on a 3 m x 5 m (10 ft x 16 ft) ledge 6 m (20 ft) below the high point of the feature, 80 m (262 ft) south of bench mark 1785 E 1993, NE (066 degrees magnetic) from the southernmost cove on the east side of East Brothers Island, and NW (294 degrees magnetic) on a tangent to the north point of East Brothers Island. BENCH MARK STAMPING: 1785 E 1993 DESIGNATION: 945 1785 E MONUMENTATION: Tidal Station disk VM#: 13123 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Granitic rock outcrop OPUS PID: LATITUDE: 57° 17.7' N ( 57.29500) LONGITUDE: 133° 47.8' W (-133.79700) The bench mark is a disk set in weathered outcrop of granitic rock, 2 m (7 ft) below the highest point of the outcrop, 0.5 m (1.7 ft) from the edge of a sharp 5 m (16 ft) drop to the next ledge level, NE (028 degrees magnetic) from the rock at the south end of East Brothers Island, NE (060 degrees magnetic) from the southernmost cove, the tangent to the northern end of East Brothers is SE (150 degrees magnetic), and 2 m (7 ft) above the apparent high water line.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 Station ID: 9451785 PUBLICATION DATE: 08/09/2004 Name: THE BROTHERS, STEPHENS PASSAGE AK NOAA Chart: 17362 Latitude: 57° 17.7' N ( 57.29500) USGS Quad: SUMDUM (B-6) Longitude: 133° 47.8' W (-133.79700) T I D A L D A T U M S Tidal datums at THE BROTHERS, STEPHENS PASSAGE based on: LENGTH OF SERIES: 1 MONTH TIME PERIOD: April 1995 - May 1995 TIDAL EPOCH: 1983-2001 CONTROL TIDE STATION: 9450460 KETCHIKAN, TONGASS NARROWS Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: MEAN HIGHER HIGH WATER MHHW = 4.522 MEAN HIGH WATER MHW = 4.238 MEAN SEA LEVEL MSL = 2.374 MEAN TIDE LEVEL MTL = 2.357 MEAN LOW WATER MLW = 0.475 MEAN LOWER LOW WATER MLLW = 0.000 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW 1785 A 1993 5.021 0.783 1785 B 1993 5.377 1.139 1785 C 1993 5.057 0.819 1785 D 1993 4.265 0.027 1785 E 1993 5.468 1.230
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 Station ID: 9451785 PUBLICATION DATE: 08/09/2004 Name: THE BROTHERS, STEPHENS PASSAGE AK NOAA Chart: 17362 Latitude: 57° 17.7' N ( 57.29500) USGS Quad: SUMDUM (B-6) Longitude: 133° 47.8' W (-133.79700) 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.