U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
PUBLICATION DATE: 10/16/1986
Station ID: 8551702 SUPERCEDED DATE: 04/21/2003
Name: FORT DELAWARE, PEA PATCH ISLAND, DELAWARE RIVER
DELAWARE
NOAA Chart: 12311 Latitude: 39° 35.0' N
USGS Quad: DELAWARE CITY Longitude: 75° 34.4' W
To reach the tidal bench marks, proceed to the Parks and Recreation Facility
located in Delaware City, Delaware from the recreation facility proceed on tour
boat to the wooden dock on Pea Patch Island. The tidal bench marks are located
on Fort Delaware State Park. The tide gage and staff were located on the base
of the docking pier.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 1702 A 1983
MONUMENTATION: Survey Disk VM#: 2976
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is located directly below and in the front center of the Fort
Delaware State Park sign, 80.9 feet (24.7 m) north of the NW corner of the
concrete sidewalk, 78.5 feet (23.9 m) NW of the north corner of the same
concrete sidewalk skirting the gravel roadway, 34.7 feet (10.6 m) north of the
center of the gravel roadway, and 5.0 feet (1.5 m) in from the gravel/grassline.
The bench mark is set flush in a 1-foot (0.3 m) diameter by 3.0-foot (0.9 m)
deep concrete plug at ground level.
BENCH MARK STAMPING: 1702 B 1983
MONUMENTATION: Survey Disk VM#: 2977
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is located on SE of the road that runs from the wooden dock to
Fort Delaware, 194.5 feet (59.3 m) NE of the NW corner of the concrete sidewalk
skirting the gravel roadway, 9.6 feet (2.9 m) SE of the center of the gravel
roadway, and 3.0 feet (0.9 m) from the edge of the roadway. The bench mark is
set flush in a 1.0-foot (0.3 m) diameter by 3.0-foot (0.9 m) deep concrete plug
at ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
PUBLICATION DATE: 10/16/1986
Station ID: 8551702 SUPERCEDED DATE: 04/21/2003
Name: FORT DELAWARE, PEA PATCH ISLAND, DELAWARE RIVER
DELAWARE
NOAA Chart: 12311 Latitude: 39° 35.0' N
USGS Quad: DELAWARE CITY Longitude: 75° 34.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1702 C 1983
MONUMENTATION: Survey Disk VM#: 2978
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is located on the SE side of the road that runs from the wooden
dock to Fort Delaware, 352.2 feet (107.4 m) NE of the NW corner of the concrete
sidewalk skirting the gravel road, 157.7 feet (48.1 m) NE of Bench Mark 1702 B
1983, and 7.0 feet (2.1 m) SE of the center of the gravel roadway. The bench
mark is set flush in a 1.0-foot (0.3 m) diameter by 3.0-foot (0.9 m) deep
concrete plug.
BENCH MARK STAMPING: 1702 D 1983
MONUMENTATION: Survey Disk VM#: 2979
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is located on the SE side of the road that runs from the wooden
dock to Fort Delaware across from an old concrete guardhouse on stilts, 695.2
feet (211.9 m) NE of the NW corner of the concrete sidewalk skirting the gravel
roadway, 500.7 feet (152.6 m) NE of Bench Mark 1702 B 1983, 343.0 feet (104.5 m)
NE of Bench Mark 1702 C 1983, 14.1 feet (4.3 m) SE of the south corner of the
derelict concrete guard house located across the roadway and 7.2 feet (2.2 m) SE
of the center of the gravel roadway. The bench mark is set flush in a 1-foot
(0.3 m) diameter by 3.0-foot (0.9 m) deep concrete plug at ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
PUBLICATION DATE: 10/16/1986
Station ID: 8551702 SUPERCEDED DATE: 04/21/2003
Name: FORT DELAWARE, PEA PATCH ISLAND, DELAWARE RIVER
DELAWARE
NOAA Chart: 12311 Latitude: 39° 35.0' N
USGS Quad: DELAWARE CITY Longitude: 75° 34.4' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1702 E 1983
MONUMENTATION: Survey Disk VM#: 2980
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Foundation
The bench mark is located on the SE side of the road that runs from the wooden
dock to Fort Delaware, 399.0 feet (121.6 m) NE of the NE face of the derelict
guardhouse which is across from the roadway from Bench Mark 1702 D 1983, 8.2
feet (2.5 m) NW of the center of the gravel roadway, 8.2 feet (2.5 m) SE of a
0.4-foot (0.1 m) diameter ailanthus tree, and 2.0 feet (0.6 m) east of a small
wooden sign warning tourists of the hazards of picking the reeds. The bench
mark is set flush in a 1.0-foot (0.3 m) diameter by 3.0-foot (0.9 m) deep
concrete plug at ground level.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
PUBLICATION DATE: 10/16/1986
Station ID: 8551702 SUPERCEDED DATE: 04/21/2003
Name: FORT DELAWARE, PEA PATCH ISLAND, DELAWARE RIVER
DELAWARE
NOAA Chart: 12311 Latitude: 39° 35.0' N
USGS Quad: DELAWARE CITY Longitude: 75° 34.4' W
T I D A L D A T U M S
Tidal datums at FORT DELAWARE, PEA PATCH ISLAND, DELAWARE RIVER based on:
LENGTH OF SERIES: 4 MONTHS
TIME PERIOD: JULY - OCTOBER 1983
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8557380 LEWES
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (10/25/1983) = 7.63
MEAN HIGHER HIGH WATER MHHW = 6.18
MEAN HIGH WATER MHW = 5.80
MEAN TIDE LEVEL MTL = 2.99
MEAN LOW WATER MLW = 0.18
MEAN LOWER LOW WATER MLLW = 0.00
LOWEST OBSERVED WATER LEVEL (10/29/1983) = -0.81
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
1702 A 1983 8.40 2.60
1702 B 1983 7.71 1.91
1702 C 1983 8.21 2.41
1702 D 1983 8.79 2.99
1702 E 1983 9.31 3.51
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
PUBLICATION DATE: 10/16/1986
Station ID: 8551702 SUPERCEDED DATE: 04/21/2003
Name: FORT DELAWARE, PEA PATCH ISLAND, DELAWARE RIVER
DELAWARE
NOAA Chart: 12311 Latitude: 39° 35.0' N
USGS Quad: DELAWARE CITY Longitude: 75° 34.4' 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 (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 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.