U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 7
Station ID: 1619910 PUBLICATION DATE: 04/21/2003
Name: SAND ISLAND, MIDWAY ISLANDS
NOAA Chart: 19481 Latitude: 28° 12.7' N
USGS Quad: NOT APPLICABLE Longitude: 177° 21.6' W
To reach the tidal bench marks from the Midway Air Terminal proceed east on
Peters Avenue, turn right (SE) onto Nimitz Avenue at Midway Mall, proceed then
turn left (ENE) onto Cannon Avenue and follow Cannon Avenue as it winds north to
Hennessy Avenue. Go east (right) on Hennessy until the small boat basin seawall
terminates. The tidal bench marks are located along the roads leading from the
air terminal to Pier 6 and around the boat basin. The tide house is located at
the NE corner of the small boat basin.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 21 1959
DESIGNATION: 161 9910 TIDAL 21
MONUMENTATION: Tidal Station disk VM#: 83
AGENCY: US Coast and Geodetic Survey (USC&GS) PID:
SETTING CLASSIFICATION: Concrete manhole
The primary bench mark is a disk set flush in a concrete manhole structure at NE
corner of the Inner Harbor Boat Basin, 15 m (48.0 ft) west of the east seawall
projected, 20.27 m (66.5 ft) north of the north seawall face, and 0.46 m (1.5
ft) south of cover of the manhole.
BENCH MARK STAMPING: NO 2 1941
DESIGNATION: 161 9910 TIDAL 2
MONUMENTATION: Tidal Station disk VM#: 73
AGENCY: US Coast and Geodetic Survey (USC&GS) PID#: TW0155
SETTING CLASSIFICATION: Sea wall
The bench mark is a disk set on top of an old sea wall, now filled with land on
both sides, on the south side of and parallel to a taxi way to an old seaplane
hanger and on the south side of an antenna farm, 47.24 m (155.0 ft) west of a
manhole in an octogonal concrete base, 0.61 m (2.0 ft) south of the north edge
of the seawall, 0.37 m (1.2 ft) north of an orange witness post, 0.15 m (0.5 ft)
north of the south edge of the sea wall, and flush with ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 7
Station ID: 1619910 PUBLICATION DATE: 04/21/2003
Name: SAND ISLAND, MIDWAY ISLANDS
NOAA Chart: 19481 Latitude: 28° 12.7' N
USGS Quad: NOT APPLICABLE Longitude: 177° 21.6' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 18 1950
DESIGNATION: 161 9910 TIDAL 18
MONUMENTATION: Tidal Station disk VM#: 75
AGENCY: US Coast and Geodetic Survey (USC&GS) PID:
SETTING CLASSIFICATION: Concrete manhole
The bench mark is a disk set in the NE corner of a 2 m x 3 m (7 ft x 9 ft)
concrete manhole at NW corner of Nimitz Avenue and Halsey Drive, 10 m (33 ft)
west of centerline of Nimitz Avenue, 17 m (56 ft) north of the centerline of
Halsey Drive, 0.46 m (1.5 ft) south of north edge of manhole foundation, and
about 0.46 m (1.5 ft) west of east edge of manhole foundation.
BENCH MARK STAMPING: 19 1959
DESIGNATION: 161 9910 TIDAL 19
MONUMENTATION: Tidal Station disk VM#: 76
AGENCY: US Coast and Geodetic Survey (USC&GS) PID:
SETTING CLASSIFICATION: Sea wall
The bench mark is a disk set flush in top of a seawall near the NE corner of the
Inner Harbor Boat Basin, 5 m (15 ft) south of the corner projected, and about
0.3 m (1 ft) east of the edge of the wall.
BENCH MARK STAMPING: 20 1959
DESIGNATION: 161 9910 TIDAL 20
MONUMENTATION: Tidal Station disk VM#: 77
AGENCY: US Coast and Geodetic Survey (USC&GS) PID:
SETTING CLASSIFICATION: Steel bollard
The bench mark is a disk set flush in top of 1 m (3 ft) high steel bollard, near
NE corner of Inner Harbor Boat Basin, 4.69 m (15.4 ft) west of west corner of
the tide house, and 2.29 m (7.5 ft) north of seawall.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 7
Station ID: 1619910 PUBLICATION DATE: 04/21/2003
Name: SAND ISLAND, MIDWAY ISLANDS
NOAA Chart: 19481 Latitude: 28° 12.7' N
USGS Quad: NOT APPLICABLE Longitude: 177° 21.6' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO 22 1965
DESIGNATION: 161 9910 TIDAL 22
MONUMENTATION: Tidal Station disk VM#: 79
AGENCY: US Coast and Geodetic Survey (USC&GS) PID:
SETTING CLASSIFICATION: Sea wall
The bench mark is a disk set in concrete cap of the north seawall at the Inner
Harbor Boat Basin, 20 m (65 ft) SW of bench mark 21 1959, 18.44 m (60.5 ft) west
of bench mark 20 1959, 1.16 m (3.8 ft) north of the seawall face, and 1.04 m
(3.4 ft) SE of orange witness post.
BENCH MARK STAMPING: NO 25 1969
DESIGNATION: 161 9910 TIDAL 25
MONUMENTATION: Tidal Station disk VM#: 81
AGENCY: US Coast and Geodetic Survey (USC&GS) PID:
SETTING CLASSIFICATION: Concrete manhole
The bench mark is a disk set in the SW corner of a 2 m x 2 m (7 ft x 7 ft)
concrete manhole structure under a large ironwood tree, 55 m (180 ft) SW of the
NW corner of the Inner Harbor Boat Basin, 5.03 m (16.5 ft) east of the
centerline of a dirt road, 4.42 m (14.5 ft) NW of the west seawall face of the
Boat Basin, 1.37 m (4.5 ft) NW of a large ironwood tree, 0.91 m (3.0 ft) west of
the center of the manhole cover, 0.61 m (2.0 ft) north of treated 1 m x 1 m (4
ft x 4 ft) post painted orange, and flush with ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 7
Station ID: 1619910 PUBLICATION DATE: 04/21/2003
Name: SAND ISLAND, MIDWAY ISLANDS
NOAA Chart: 19481 Latitude: 28° 12.7' N
USGS Quad: NOT APPLICABLE Longitude: 177° 21.6' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 9910 A 1982
DESIGNATION: 161 9910 A
MONUMENTATION: Tidal Station disk VM#: 82
AGENCY: National Ocean Service (NOS) PID:
SETTING CLASSIFICATION: Concrete deck
The bench mark is a disk set in concrete deck at the inshore end of Pier 6 in
the Inner Harbor Boat Basin, 15.70 m (51.5 ft) south of centerline of road, 8.66
(28.4 ft) SE of light pole, 0.58 m (1.9 ft) NE of NW inshore end of pier, and
0.15 m (0.5 ft) east of concrete curb of pier.
BENCH MARK STAMPING: 9910 B 1988
DESIGNATION: 161 9910 B
MONUMENTATION: Tidal Station disk VM#: 113
AGENCY: National Ocean Service (NOS) PID:
SETTING CLASSIFICATION: Concrete slab
The bench mark is a disk set in the SE corner of a 2 m x 3 m (5 ft x 9 ft)
concrete slab behind the boat house, 19 m (63 ft) NW of the west seawall of the
inner harbor, 6.74 m (22.1 ft) NE of the NE corner of the boat house (building
3522), 1.43 m (4.7 ft) SE of a concrete wall, and 1.07 m (3.5 ft) SE of an
orange witness post.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 7
Station ID: 1619910 PUBLICATION DATE: 04/21/2003
Name: SAND ISLAND, MIDWAY ISLANDS
NOAA Chart: 19481 Latitude: 28° 12.7' N
USGS Quad: NOT APPLICABLE Longitude: 177° 21.6' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 9910 C 1988
DESIGNATION: 161 9910 C
MONUMENTATION: Tidal Station disk VM#: 114
AGENCY: National Ocean Service (NOS) PID:
SETTING CLASSIFICATION: Concrete manhole foundation
The bench mark is a disk set in the north corner of a 2 m x 2 m (5 ft x 7 ft)
concrete manhole in the Midway Memorial Park along the east side of Nimitz
Avenue between Peters and Cannon Avenues, 25.15 m (82.5 ft) north of an aluminum
light standard, 14 m (45 ft) south of the southern-most World War II gun mount,
and 6 m (20 ft) east of the east edge of Nimitz Avenue, and 0.37 m (1.2 ft)
above grade.
BENCH MARK STAMPING: MIDWAY SECOR ARMY MAP SVC 1966
DESIGNATION: 161 9910 MIDWAY
MONUMENTATION: Bench Mark disk VM#: 115
AGENCY: US Army Corps of Engineers (USE) PID:
SETTING CLASSIFICATION: Concrete apron
The bench mark is a disk set in the concrete parking apron along the west
seawall of the inner harbor, 55 m (180 ft) SW of the south side of the boat
house (building 3522), 40 m (131 ft) west of the SW inshore corner of a small
boat ramp, and 26 m (86 ft) NW of the seawall on the west side of the inner
harbor.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 7
Station ID: 1619910 PUBLICATION DATE: 04/21/2003
Name: SAND ISLAND, MIDWAY ISLANDS
NOAA Chart: 19481 Latitude: 28° 12.7' N
USGS Quad: NOT APPLICABLE Longitude: 177° 21.6' W
T I D A L D A T U M S
Tidal datums at SAND ISLAND, MIDWAY ISLANDS based on:
LENGTH OF SERIES: 19 Years
TIME PERIOD: January 1983 - December 2001
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION:
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (01/11/1958) = 1.249
MEAN HIGHER HIGH WATER (MHHW) = 0.382
MEAN HIGH WATER (MHW) = 0.328
MEAN TIDE LEVEL (MTL) = 0.197
MEAN SEA LEVEL (MSL) = 0.196
MEAN LOW WATER (MLW) = 0.065
MEAN LOWER LOW WATER (MLLW) = 0.000
LOWEST OBSERVED WATER LEVEL (02/01/1975) = -0.458
National Geodetic Vertical Datum (NGVD 29)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
21 1959 2.419 2.091
NO 2 1941 1.847 1.519
NO 18 1950 2.050 1.722
19 1959 2.250 1.922
20 1959 3.237 2.909
NO 22 1965 2.255 1.927
NO 25 1969 2.731 2.403
9910 A 1982 2.359 2.031
9910 B 1988 2.013 1.685
9910 C 1988 2.513 2.185
MIDWAY SECOR ARMY MAP SVC 1966 1.969 1.641
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 7
Station ID: 1619910 PUBLICATION DATE: 04/21/2003
Name: SAND ISLAND, MIDWAY ISLANDS
NOAA Chart: 19481 Latitude: 28° 12.7' N
USGS Quad: NOT APPLICABLE Longitude: 177° 21.6' 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 (NAVD 88).
NGVD 29 is a fixed datum adopted as a national standard geodetic reference for
heights but is now considered superseded. NGVD 29 is sometimes referred to as
Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological
Survey Topographic Quads. NGVD 29 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 NGVD 29 are available from the National
Geodetic Survey (NGS) data base via the World Wide Web at
National Geodetic Survey.
NAVD 88 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. NAVD 88 replaces NGVD 29 as the national
standard geodetic reference for heights. Bench mark elevations relative to
NAVD 88 are available from NGS through the World Wide Web at
National Geodetic Survey.
NGVD 29 and NAVD 88 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 NAVD 88 elevation is shown on the Elevations of Tidal Datums Table Referred
to MLLW only when two or more of the bench marks listed have NAVD 88 elevations.
The NAVD 88 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, NAVD 88 bench mark elevations computed indirectly from the tidal
datums elevation table may differ slightly from NAVD 88 elevations listed for
each bench mark in the NGS database.