U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
Datums Page                                                        Page  1 of  4

                                                                                
Station ID: 9466298                         PUBLICATION DATE:  01/14/2011
Name:       NELSON IS (BLUFF S.E. OF TUNUNAK)                 
            AK
NOAA Chart: 16006                           Latitude:   60° 31.0' N (  60.51670)
USGS Quad:  NUNIVAK ISLAND C-1              Longitude: 165°  8.0' W (-165.13300)


To reach the bench marks from the Toksook Bay runway, proceed 0.4 mi (0.6 km) NW
on Airport Road to where the road curves to the left, continue 0.7 mi (1.1 km)
WSW on Airport Road to where the road turns left, continue 0.8 mi (1.3 km) SSE
on Airport Road along the west side of the fuel tank farm to the beach in front
of the village of Toksook Bay. Continue by skiff 1.5 mi (2.4 km) WSW following
the shoreline to the second prominent rock point, with 12 m (40 ft) high
overhanging cliffs.  The bench marks are on top of the bluff, between the
seaward point and the first small stream 0.1 mi (0.2 km) to the east. The tide
gauges were housed on top of the point and the orifices were offshore of the
point.


                         T I D A L   B E N C H   M A R K S


                 PRIMARY BENCH MARK STAMPING:  6298 C 2010
                         DESIGNATION:          946 6298 C

MONUMENTATION:           Metal Rod                             VM#:        19707
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod in sleeve         OPUS PID#: BBBZ36
LATITUDE:   60° 31.1' N (  60.51858)          LONGITUDE: 165°  8.5' W (-165.14233)


The primary bench mark is a disk set in the tundra 77.49 m (254.2 ft) NNE of
bench mark 946 6298 B, 66.0 m (217 ft) west of a small stream where it flows SE
over the bluff to the beach below, 58.0 m (190 ft) west of the 7 m (23 ft) high
bluff, and 17.1 m (56 ft) NW of the centerline of a dirt track all terrain
vehicle trail.  The datum point is set 7 cm (0.2 ft) below grade, being the top
of a stainless steel rod driven 3.7 m (12.3 ft) to refusal, in a sleeve
extending to a depth of 0.9 m (3 ft), and encased in a 6-inch PVC pipe with
7-inch diameter National Geodetic Survey logo cap.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of  4

                                                                                
Station ID: 9466298                         PUBLICATION DATE:  01/14/2011
Name:       NELSON IS (BLUFF S.E. OF TUNUNAK)                 
            AK
NOAA Chart: 16006                           Latitude:   60° 31.0' N (  60.51670)
USGS Quad:  NUNIVAK ISLAND C-1              Longitude: 165°  8.0' W (-165.13300)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  6298 B 2010
                         DESIGNATION:          946 6298 B

MONUMENTATION:           Metal Rod                             VM#:        19708
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod in sleeve         OPUS PID:        
LATITUDE:   60° 31.1' N (  60.51794)          LONGITUDE: 165°  8.6' W (-165.14264)


The bench mark is set in the tundra 77.50 m (254.3 ft) north of bench mark 946
6298 A, 77.49 m (254.2 ft) SSW of bench mark 946 6298 C, and 56.0 m (184 ft)
west of the bluff.  The datum point is set 11 cm (0.4 ft) below grade, being the
top of a stainless steel rod driven 3.0 m (9.8 ft) to refusal, in a sleeve
extending to a depth of 0.9 m (3 ft), and encased in a 6-inch PVC pipe with
7-inch diameter National Ocean Service logo cap.



                         BENCH MARK STAMPING:  6298 A 2010
                         DESIGNATION:          946 6298 A

MONUMENTATION:           Metal Rod                             VM#:        19709
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod in sleeve         OPUS PID:        
LATITUDE:   60° 31.0' N (  60.51725)          LONGITUDE: 165°  8.5' W (-165.14233)


The bench mark is set in the tundra 77.50 m (254.3 ft) south of bench mark 946
6298 B, 77.30 m (253.6 ft) NW of bench mark 946 6298 TIDAL 2, 65.16 m (213.8 ft)
NW of bench mark 946 6298 TIDAL 4, and 51 m (167 ft) west of the bluff.  The
datum point is set 14 cm (0.5 ft) below grade, being the top of a stainless
steel rod driven 1.7 m (5.7 ft) to refusal, in a sleeve extending to a depth of
0.9 m (3 ft), and encased in a 6-inch PVC pipe with 7-inch diameter National
Ocean Service logo cap.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  3 of  4

                                                                                
Station ID: 9466298                         PUBLICATION DATE:  01/14/2011
Name:       NELSON IS (BLUFF S.E. OF TUNUNAK)                 
            AK
NOAA Chart: 16006                           Latitude:   60° 31.0' N (  60.51670)
USGS Quad:  NUNIVAK ISLAND C-1              Longitude: 165°  8.0' W (-165.13300)


                            T I D A L   D A T U M S 


Tidal datums at NELSON IS (BLUFF S.E. OF TUNUNAK) based on:

     LENGTH OF SERIES:      3 MONTHS
     TIME PERIOD:           July 2010 - September 2010
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:   


Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:

     MEAN HIGHER HIGH WATER                     MHHW   =  2.805
     MEAN HIGH WATER                            MHW    =  2.682
     MEAN SEA LEVEL                             MSL    =  1.503
     MEAN TIDE LEVEL                            MTL    =  1.500
     MEAN LOW WATER                             MLW    =  0.317
     MEAN LOWER LOW WATER                       MLLW   =  0.000

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     6298 C 2010                                11.730    9.048
     6298 B 2010                                13.872   11.190
     6298 A 2010                                14.862   12.180


                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  4 of  4

                                                                                
Station ID: 9466298                         PUBLICATION DATE:  01/14/2011
Name:       NELSON IS (BLUFF S.E. OF TUNUNAK)                 
            AK
NOAA Chart: 16006                           Latitude:   60° 31.0' N (  60.51670)
USGS Quad:  NUNIVAK ISLAND C-1              Longitude: 165°  8.0' W (-165.13300)


                             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.