U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 6 Station ID: 8571117 PUBLICATION DATE: 03/18/2011 Name: EWELL, SMITH ISLAND MD NOAA Chart: 12261 Latitude: 37° 59.7' N ( 37.99500) USGS Quad: EWELL Longitude: 76° 1.9' W ( -76.03170) To reach the tidal bench marks from the city dock in Crisfield, proceed by charter boat (Captain Jason) west to Smith Island and Ewell at the north end of the island. The bench marks are located in the vicinity of the Bayside Inn, the Methodist Church, and Caleb Jones Road. The tide gauge was located at the dock NW of the Bayside Inn. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: NO 2 1997 DESIGNATION: 857 1117 TIDAL 2 MONUMENTATION: Survey disk VM#: 13882 AGENCY: US Army Corps of Engineers (USE) IDB PID#: SETTING CLASSIFICATION: Aluminum alloy rod OPUS PID#: BBBZ40 LATITUDE: 37° 59.8' N ( 37.99608) LONGITUDE: 76° 2.0' W ( -76.03300) The primary bench mark is a disk located near the county dock, 5.81 m (19.1 ft) NW of the W corner of a refreshment stand, 5.24 m (17.2 ft) W of the N corner of a refreshment stand, 3.45 m (11.3 ft) NE of the end of the county dock, 0.90 m (3.0 ft) SW of the end of a wooden boardwalk, and 0.55 m (1.8 ft) SE of a witness post. The bench mark is set 21 cm (0.7 ft) below ground level, crimped to the top of an aluminum rod driven 12.8 m (42.0 ft), 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 6 Station ID: 8571117 PUBLICATION DATE: 03/18/2011 Name: EWELL, SMITH ISLAND MD NOAA Chart: 12261 Latitude: 37° 59.7' N ( 37.99500) USGS Quad: EWELL Longitude: 76° 1.9' W ( -76.03170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: DESIGNATION: 857 1117 USE 1 ALIAS: NO STAMPING 1 MONUMENTATION: Survey disk VM#: 13881 AGENCY: US Army Corps of Engineers (USE) IDB PID#: SETTING CLASSIFICATION: Concrete sidewalk OPUS PID: LATITUDE: 37° 59.7' N ( 37.99500) LONGITUDE: 76° 1.9' W ( -76.03170) The primary bench mark is a disk set in a concrete sidewalk on the NW side of the front entrance to the Methodist Church on Caleb Jones Road in Ewell, about 15 m (50 ft) east of the intersection of Caleb Jones Road and Smith Island Road. BENCH MARK STAMPING: NO 3 1997 DESIGNATION: 857 1117 TIDAL 3 MONUMENTATION: Survey disk VM#: 13883 AGENCY: US Army Corps of Engineers (USE) IDB PID#: SETTING CLASSIFICATION: Aluminum alloy rod OPUS PID#: BBDN51 LATITUDE: 37° 59.7' N ( 37.99567) LONGITUDE: 76° 2.0' W ( -76.03289) The bench mark is a disk located just east of the Smith Island Town Center, 25.42 m (83.4 ft) SW of the SE corner of the Bayside Inn, 22.20 m (72.8 ft) SE of the SE corner of the Bayside Gift Shop, 4.72 m (15.5 ft) north of the SE property corner of the Bayside Inn, and 0.52 m (1.7 ft) NE of a USACE witness post. The bench mark is 12 cm (0.4 ft) below ground level, crimped to the top of an aluminum rod driven 11.9 m (39.0 ft), 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 6 Station ID: 8571117 PUBLICATION DATE: 03/18/2011 Name: EWELL, SMITH ISLAND MD NOAA Chart: 12261 Latitude: 37° 59.7' N ( 37.99500) USGS Quad: EWELL Longitude: 76° 1.9' W ( -76.03170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: NO 4 1997 DESIGNATION: 857 1117 TIDAL 4 MONUMENTATION: Survey disk VM#: 13884 AGENCY: US Army Corps of Engineers (USE) IDB PID#: SETTING CLASSIFICATION: Aluminum alloy rod OPUS PID#: BBDN62 LATITUDE: 37° 59.7' N ( 37.99503) LONGITUDE: 76° 1.9' W ( -76.03233) The bench mark is a disk, located near the ball field, 12.80 m (42.0 ft) SE of the centerline of Campground Road, 11.35 m (37.2 ft) SW of the centerline of Somers Road, 3.52 m (11.5 ft) S of the SW corner of a small wooden building, and 0.34 m (1.1 ft) west of a USACE witness post at the west side of a baseball field backstop. The bench mark is 12 cm (0.4 ft) below ground level, crimped to the top of an aluminum rod driven 12.8 m (42 ft), and encased in a 4-inch PVC pipe and concrete kickblock. BENCH MARK STAMPING: NO 5 1997 DESIGNATION: 857 1117 TIDAL 5 MONUMENTATION: Survey disk VM#: 13885 AGENCY: US Army Corps of Engineers (USE) IDB PID#: SETTING CLASSIFICATION: Concrete step OPUS PID: LATITUDE: 37° 59.7' N ( 37.99578) LONGITUDE: 76° 1.9' W ( -76.03214) The bench mark is an aluminum survey disk set flush in the concrete step in front of the Verizon Telephone building at 20884 Caleb Jones Road, 7.25 m (23.8 ft) NE of the SE corner of a concrete walk, 4.27 m (14.0 ft) SE of the NW corner of the building, and 2.87 m (9.4 ft) WNW of the east corner of the building.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 6 Station ID: 8571117 PUBLICATION DATE: 03/18/2011 Name: EWELL, SMITH ISLAND MD NOAA Chart: 12261 Latitude: 37° 59.7' N ( 37.99500) USGS Quad: EWELL Longitude: 76° 1.9' W ( -76.03170) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 1117 A 2010 DESIGNATION: 857 1117 A MONUMENTATION: Survey disk VM#: 19713 AGENCY: National Ocean Service IDB PID#: SETTING CLASSIFICATION: in concrete OPUS PID: LATITUDE: 37° 59.7' N ( 37.99517) LONGITUDE: 76° 2.0' W ( -76.03331) The bench mark is disk set flush in a concrete sidewalk located on the NE side of the front entrance to the United Methodist Church on Caleb Jones Road, 13.10 m (43.0 ft) south of SW corner of the Town Center Building, 7.12 m (23.4 ft) SSW of the centerline of Caleb Jones Road, 2.10 m (6.9 ft) NW of the NE corner of the church, and 0.42 m (1.4 ft) NNE of the north wall of the church.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 6 Station ID: 8571117 PUBLICATION DATE: 03/18/2011 Name: EWELL, SMITH ISLAND MD NOAA Chart: 12261 Latitude: 37° 59.7' N ( 37.99500) USGS Quad: EWELL Longitude: 76° 1.9' W ( -76.03170) T I D A L D A T U M S Tidal datums at EWELL, SMITH ISLAND based on: LENGTH OF SERIES: 4 MONTHS TIME PERIOD: July 2010 - October 2010 TIDAL EPOCH: 1983-2001 CONTROL TIDE STATION: 8635750 LEWISETTA, POTOMAC RIVER Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: MEAN HIGHER HIGH WATER MHHW = 0.563 MEAN HIGH WATER MHW = 0.510 MEAN SEA LEVEL MSL = 0.286 MEAN TIDE LEVEL MTL = 0.278 MEAN LOW WATER MLW = 0.046 MEAN LOWER LOW WATER MLLW = 0.000 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW NO 2 1997 0.982 0.472 857 1117 USE 1 1.216 0.706 NO 3 1997 0.809 0.299 NO 4 1997 0.868 0.358 NO 5 1997 1.772 1.262 1117 A 2010 1.224 0.714
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 6 of 6 Station ID: 8571117 PUBLICATION DATE: 03/18/2011 Name: EWELL, SMITH ISLAND MD NOAA Chart: 12261 Latitude: 37° 59.7' N ( 37.99500) USGS Quad: EWELL Longitude: 76° 1.9' W ( -76.03170) 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.