U.S. DEPARTMENT OF COMMERCE
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National Ocean Service
Datums Page Page 1 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
To reach the tidal bench marks from the toll booths on the west end of the Walt
Whitman Bridge proceed 0.2 km (0.1 mi) west to exit 47 (to I-95) but keep right
and follow signs to Front Street, turn left and proceed 0.5 km (0.3 mi) north on
Front Street to Oregon Avenue, turn right and proceed 1.1 km (0.7 mi) east to
Christopher Columbus Avenue, turn left and proceed 4.8 km (3.0 mi) north on
Christopher Columbus Avenue to Municipal Pier No. 11 North (Marine Police and
Fire Boat Pier) underneath the Benjamin Franklin Bridge. The bench marks are
located in the vicinity of the pier and west along Arch Street. The tide house
was located on the SE end of the pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 35 1931
DESIGNATION: 854 5530 TIDAL 35
MONUMENTATION: Tidal Station disk VM#: 362
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU2225
SETTING CLASSIFICATION: Granite doorsill OPUS PID:
LATITUDE: 39° 57.2' N ( 39.95330) LONGITUDE: 75° 8.4' W ( -75.14000)
The primary bench mark is a disk set in top of the north end of a granite sill
of the most southerly of three doorways on the west side of Christopher Columbus
Avenue just north of Race Street near the Benjamin Franklin Bridge foundations,
44.80 m (147.0 ft) south of the centerline of a closed I-95 ramp, 38.19 m (125.3
ft) north of the centerline of Race Street, and 12.10 m (39.7 ft) west of the
centerline of southbound Christopher Columbus Avenue.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5530 A 1989
DESIGNATION: 854 5240 A
MONUMENTATION: Tidal Station disk VM#: 361
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 39° 57.2' N ( 39.95330) LONGITUDE: 75° 8.4' W ( -75.14000)
The bench mark is a disk located along the south edge of the USCG property on
the east side of Christopher Columbus Avenue, 33.10 m (108.6 ft) SE of the SW
corner of the main building, 25.79 m (84.6 ft) west of the fiberglass gage
house, 19.87 m (65.2 ft) south of the south face of the main building, 1.22 m
(4.0 ft) north of the chain link fence, and 1.22 m (4.0 ft) east of a light
post. The bench mark is crimped to a stainless steel rod driven 13.4 m (44 ft)
to refusal, encased in a 5 inch PVC pipe with concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 23 1922 ELEV. 7.894 FT.
DESIGNATION: 854 5530 TIDAL 23
ALIAS: TIDAL 23 STA 1
MONUMENTATION: Tidal Station disk VM#: 363
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU0721
SETTING CLASSIFICATION: Granite step OPUS PID:
LATITUDE: 39° 57.2' N ( 39.95330) LONGITUDE: 75° 8.4' W ( -75.14000)
The bench mark is a disk set in top of a granite step at the main entrance to
the city pumping station at the SW corner of Race Street and Christopher
Columbus Avenue, 30.48 m (100.0 ft) SSW of the centerline of Race Street, 11.61
m (38.1 ft) WNW of the centerline of Christopher Columbus Avenue, 6.31 m (20.7
ft) NNE of the SE corner of the building, 5.79 m (19.0 ft) SW of a fire hydrant,
and 0.21 m (0.7 ft) above ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 21 1922 ELEV. 10.755 FT.
DESIGNATION: 854 5530 TIDAL 21
ALIAS: TIDAL 21 STA 1
MONUMENTATION: Tidal Station disk VM#: 364
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU0730
SETTING CLASSIFICATION: Concrete step OPUS PID:
LATITUDE: 39° 57.2' N ( 39.95330) LONGITUDE: 75° 8.3' W ( -75.13830)
The bench mark is a disk set in the south coping of the concrete steps behind
the building on the east side of Christopher Columbus Avenue between Arch and
Race Streets near Pier 9, 7.41 m (24.3 ft) north of the northern most bollard on
the north-south bulkhead, 5.00 m (16.4 ft) west of the western most bollard on
the south side of Pier 9, 1.19 m (3.9 ft) south of the south wall of Pier 9, and
1.01 m (3.3 ft) above the pier.
BENCH MARK STAMPING: TIDAL 1
DESIGNATION: 854 5530 TIDAL 1
MONUMENTATION: Tidal Station disk VM#: 365
AGENCY: National Ocean Survey (NOS) IDB PID#:
SETTING CLASSIFICATION: Concrete footing OPUS PID:
LATITUDE: 39° 57.2' N ( 39.95330) LONGITUDE: 75° 8.3' W ( -75.13830)
The bench mark is a disk set in top of a concrete footing for the building at
the east end of Municipal Pier 11 North (Marine Police and Fire Boat Pier),
14.60 m (47.9 ft) north of the south face of pier, 9.81 m (32.2 ft) south of the
north face of pier, 6.49 m (21.3 ft) west of the east end of pier, and 0.3 m (1
ft) south of the north end of the steel door opening.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 24 1922 ELEV. 28.819 FT.
DESIGNATION: 854 5530 TIDAL 24
ALIAS: TIDAL 24 STA 1
MONUMENTATION: Tidal Station disk VM#: 367
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU0724
SETTING CLASSIFICATION: Granite sill OPUS PID:
LATITUDE: 39° 57.1' N ( 39.95170) LONGITUDE: 75° 8.5' W ( -75.14170)
The bench mark is a disk set in the granite door sill at the west end of the
entrance to the building at 109 Arch Street, 34.29 m (112.5 ft) west of the
centerline of Front Street, 10.70 m (35.1 ft) ENE of a light pole, 9.30 m (30.5
ft) NNE of the centerline of Arch Street, 0.40 m (1.3 ft) SSW from the face of
the building, and 0.40 m (1.3 ft) above ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 25 1922 ELEV. 39.678 FT.
DESIGNATION: 854 5530 TIDAL 25
ALIAS: TIDAL 25 STA 1
MONUMENTATION: Tidal Station disk VM#: 368
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU0725
SETTING CLASSIFICATION: Granite step OPUS PID:
LATITUDE: 39° 57.1' N ( 39.95170) LONGITUDE: 75° 8.6' W ( -75.14330)
The bench mark is a disk set in the east end of the top granite step of the main
entrance to the Merchants Seamans Center at the NE corner of the intersection of
Third Street and Arch Street, 19.20 m (63.0 ft) west of the centerline of the
entrance to the Betsy Ross House, 18.11 m (59.4 ft) ENE of the centerline of
Third Street, 9.69 m (31.8 ft) north of the centerline of Arch Street, 0.18 m
(0.6 ft) south of the face of the building, and 0.15 m (0.5 ft) above ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 7 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 27 1922 ELEV. 44.439 FT.
DESIGNATION: 854 5530 TIDAL 27
ALIAS: TIDAL 27 STA 1
MONUMENTATION: Tidal Station disk VM#: 369
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU0726
SETTING CLASSIFICATION: Granite step OPUS PID:
LATITUDE: 39° 57.2' N ( 39.95330) LONGITUDE: 75° 9.4' W ( -75.15670)
The bench mark is a disk set in a granite step at the main entrance to the
Winston Building at 1010 Arch Street, 48.19 m (158.1 ft) west of the centerline
of 10th Street, 20.51 m (67.3 ft) ESE of a fire hydrant, 10.00 m (32.8 ft) SSW
of the centerline of Arch Street, 0.18 m (0.6 ft) north of the face of the
building, and 0.18 m (0.6 ft) above ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 8 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 29 1922 ELEV. 46.775 FT.
DESIGNATION: 854 5530 TIDAL 29
ALIAS: TIDAL 29 STA 1
MONUMENTATION: Tidal Station disk VM#: 370
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU0727
SETTING CLASSIFICATION: Granite slab OPUS PID:
LATITUDE: 39° 57.2' N ( 39.95330) LONGITUDE: 75° 9.8' W ( -75.16330)
The bench mark is a disk set near the NE corner of a large granite slab under
the north Broad Street entrance archway of the City Hall Building, 8.29 m (27.2
ft) SSW of the first step to the entrance of City Hall, 5.88 m (19.3 ft) NE of
the NW corner of the vaulted ceiling support, 2.29 m (7.5 ft) ESE of the
centerline of the entrance to City Hall, and 0.21 m (0.7 ft) WNW of the face of
the entrance archway.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 9 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: U 237 1959
DESIGNATION: U 237
MONUMENTATION: Bench Mark disk VM#: 371
AGENCY: US Coast and Geodetic Survey
(USC&GS) IDB PID#: JU0722
SETTING CLASSIFICATION: Concrete bulkhead OPUS PID:
LATITUDE: 39° 57.2' N ( 39.95330) LONGITUDE: 75° 8.4' W ( -75.14000)
The bench mark is a disk set in the concrete bulkhead between Pier 11 and Pier 9
on the east side of Christopher Columbus Avenue, 36.27 m (119.0 ft) north of the
NW corner of Pier 9, 19.60 m (64.3 ft) east of the centerline of northbound
Christopher Columbus Avenue, 8.81 m (28.9 ft) south of the SW corner of the
building on Pier 11, and 3.99 m (13.1 ft) SSE of the center of a large water
pump intake valve.
BENCH MARK STAMPING: 5530 B 1989
DESIGNATION: 854 5240 B
MONUMENTATION: Tidal Station disk VM#: 372
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 39° 56.0' N ( 39.93330) LONGITUDE: 75° 8.5' W ( -75.14170)
The bench mark is a disk located near the NW corner of the USCG property, 31.88
m (104.6 ft) west of the NE corner of the fence post, 12.62 m (41.4 ft) NW of
the curved concrete curb of the USCG personnel parking lot, 8.35 m (27.4 ft)
south of the traffic signal post at the SE corner of Christopher Columbus Avenue
and Christian Street, 7.16 m (23.5 ft) SE of the eastern curb of Christopher
Columbus Avenue, and 3.20 m (10.5 ft) south of the NW corner fence post. The
bench mark is crimped to a stainless steel rod driven 11 m (36 ft) to refusal,
encased in a 5 inch PVC pipe with concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 10 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5530 C 1989
DESIGNATION: 854 5240 C
MONUMENTATION: Tidal Station disk VM#: 373
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 39° 57.1' N ( 39.95170) LONGITUDE: 75° 8.6' W ( -75.14330)
The bench mark is a disk located near the front lawn of the USCG property, 45.90
m (150.6 ft) NW of the flagpole at the entrance of the main building, 24.69 m
(81.0 ft) south of the light pole on the east side of Christopher Columbus
Avenue, 9.21 m (30.2 ft) NNE of the north curb of Washington Avenue, 8.50 m
(27.9 ft) SE of the eastern curb of Christopher Columbus Avenue, and 8.20 m
(26.9 ft) east of the traffic signal post at the NE corner of Washington and
Christopher Columbus Avenues. The bench mark is set 0.18 m (0.6 ft) below
ground, crimped to a stainless steel rod driven 11.9 m (39 ft) to refusal,
encased in a 5 inch PVC pipe with concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 11 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 5530 D 1989
DESIGNATION: 854 5240 D
MONUMENTATION: Tidal Station disk VM#: 374
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 39° 57.1' N ( 39.95170) LONGITUDE: 75° 8.7' W ( -75.14500)
The bench mark is a disk located in the NW corner of the U.S. Park Service's
Gloria Dei - Old Swedes Church property, 19.51 m (64.0 ft) west of the
centerline of the church driveway at Christian Street, 19.29 m (63.3 ft) SW of
the SW corner of the brick garage at the church entrance gate, 16.61 m (54.5 ft)
east of the brick wall along Water Street, and 16.49 m (54.1 ft) south of the
brick wall along Christian Avenue. The bench mark is crimped to a stainless
steel rod driven 14.9 m (49 ft) to refusal, encased in a 5 inch PVC pipe with
concrete kickblock.
BENCH MARK STAMPING: 5530 E 1989
DESIGNATION: 854 5240 E
MONUMENTATION: Tidal Station disk VM#: 375
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod OPUS PID:
LATITUDE: 39° 57.1' N ( 39.95170) LONGITUDE: 75° 8.7' W ( -75.14500)
The bench mark is a disk located on the west side of Christopher Columbus Avenue
near the intersection of Christopher Columbus Avenue and Queen Street, 14.29 m
(46.9 ft) south of the south curb of Queen Street, 8.90 m (29.2 ft) SW of a fire
hydrant, 6.61 m (21.7 ft) west of the western curb of Christopher Columbus
Avenue, and 1.80 m (5.9 ft) east of the east face of a brick wall surrounding
townhouses. The bench mark is crimped to a stainless steel rod driven 3.35 m
(11.0 ft) to refusal, encased in a 5 inch PVC pipe with concrete kickblock.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 12 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
T I D A L D A T U M S
Tidal datums at PHILADELPHIA (PIER 11 NORTH), DEL. RIVER based on:
LENGTH OF SERIES: 10 Years
TIME PERIOD: January 1979 - December 1988
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8557380 LEWES, FT. MILES
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (11/25/1950) = 3.226
MEAN HIGHER HIGH WATER MHHW = 2.080
MEAN HIGH WATER MHW = 1.962
MEAN SEA LEVEL MSL = 1.069
MEAN TIDE LEVEL MTL = 1.011
North American Vertical Datum NAVD88 = 0.987
MEAN LOW WATER MLW = 0.059
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (12/31/1962) = -2.047
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
35 1931 2.668 0.706
5530 A 1989 3.554 1.592
23 1922 ELEV. 7.894 FT. 3.004 1.042
21 1922 ELEV. 10.755 FT. 3.899 1.937
TIDAL 1 3.262 1.300
24 1922 ELEV. 28.819 FT. 9.420 7.458
25 1922 ELEV. 39.678 FT. 10.890 8.928
27 1922 ELEV. 44.439 FT. 14.182 12.220
29 1922 ELEV. 46.775 FT. 14.876 12.914
U 237 1959 2.995 1.033
5530 B 1989 3.580 1.618
5530 C 1989 4.263 2.301
5530 D 1989 5.282 3.320
5530 E 1989 2.998 1.036
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 13 of 13
Station ID: 8545530 PUBLICATION DATE: 04/21/2003
Name: PHILADELPHIA (PIER 11 NORTH), DEL. RIVER
PA
NOAA Chart: 12313 Latitude: 39° 57.2' N ( 39.95330)
USGS Quad: PHILADELPHIA Longitude: 75° 8.3' W ( -75.13830)
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.