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#:  DF6541
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



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 any other fixed island datum.

This tide station location has a local island datum.  Island datums
are specific fixed geodetic datums whose elevation relationship 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.