U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 1 of 4
Station ID: 8674623 PUBLICATION DATE: 01/17/1985
Name: DOG HAMMOCK, SAPELO RIVER
GEORGIA
NOAA Chart: 11509 Latitude: 31ø 31.9' N
USGS Quad: SHELLMAN BLUFF Longitude: 81ø 16.2' W
To reach the tidal bench marks, proceed by boat on the Sapelo River, Sapelo
Sound to 1.0 NM (1.8 km) west of the entrance to the Mud River and the
northwestern end of Dog Hammock. The bench marks are located in the marshy
area of Dog Hammock, SE of Day Mark 149. The tide gage and staff were located
on Day Mark 149.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 4623 A 1980
MONUMENTATION: Survey Disk VM#: 4807
AGENCY: PID:
SETTING CLASSIFICATION: Unspecified Rod
The bench mark is located in a marshy area in Dog Hammock in Sapelo River NW and
immediately adjacent to Day Mark 149, 110 feet (33.5 m) south of the shore-
line, 89.0 feet (27.1 m) east of Bench Mark NO 2 1964. The bench mark is at
ground level crimped to a rod driven 65 feet (19.8 m) to refusal, encased in a
4-inch PVC pipe and concrete kickblock.
BENCH MARK STAMPING: NO. 1 1964
MONUMENTATION: Survey Disk VM#: 4805
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is located on the shell bank SE of Day Mark 149, 84.5 feet (25.8
m) east of Bench Mark NO STAMPING 2 and next to a steel witness post. The
bench mark is set in 4-inch orangeburg pipe filled with concrete, 4-inches
above ground and 3.0 feet (1.0 m) in the ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 4
Station ID: 8674623 PUBLICATION DATE: 01/17/1985
Name: DOG HAMMOCK, SAPELO RIVER
GEORGIA
NOAA Chart: 11509 Latitude: 31ø 31.9' N
USGS Quad: SHELLMAN BLUFF Longitude: 81ø 16.2' W
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: NO. 2 1964
MONUMENTATION: Survey Disk VM#: 4806
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Monument
The bench mark is located on the shell bank SE of Day Mark 149, 232.7 feet (70.9
m) SE of Bench Mark NO 1 1964 with steel witness post and C&GS sign next to the
mark. The bench mark is set in 4-inch orangeburg pipe 4-inches above ground
and 3.0 feet (1.0 m) in the ground.
BENCH MARK STAMPING: NO STAMPING 1
MONUMENTATION: Survey Disk VM#: 4808
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Post
The bench mark is located on the shell bank SE of Day Mark 149, 175.0 feet (53.3
m) SE of Day Mark 149, in line with small rock jetty next to a C&GS sign and a
steel witness post. The bench mark is set in a 10 x 10 concrete post 0.5 foot
(0.2 m) above ground.
BENCH MARK STAMPING: NO STAMPING 2
MONUMENTATION: Brass Plug VM#: 4809
AGENCY: PID:
SETTING CLASSIFICATION: Concrete Post
The bench mark is located on the shell bank SE of Day Mark 149, 66.9 feet (20.4
m) SE of the Bench Mark NO STAMPING 1 and next to a steel witness post and C&GS
sign. The bench mark is set in a 10 x 10 square concrete post 0.5 foot (0.2 m)
above ground.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 4
Station ID: 8674623 PUBLICATION DATE: 01/17/1985
Name: DOG HAMMOCK, SAPELO RIVER
GEORGIA
NOAA Chart: 11509 Latitude: 31ø 31.9' N
USGS Quad: SHELLMAN BLUFF Longitude: 81ø 16.2' W
T I D A L D A T U M S
Tidal datums at DOG HAMMOCK, SAPELO RIVER based on:
LENGTH OF SERIES: 87 HW & 87 LW
TIME PERIOD: MARCH 15 - APRIL 28, 1980
TIDAL EPOCH: 1960-1978
CONTROL TIDE STATION: 8670870 FT. PULASKI
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET:
HIGHEST OBSERVED WATER LEVEL (04/17/1980) = 9.34
MEAN HIGHER HIGH WATER (MHHW) = 7.77
MEAN HIGH WATER (MHW) = 7.40
MEAN TIDE LEVEL (MTL) = 3.80
MEAN LOW WATER (MLW) = 0.20
MEAN LOWER LOW WATER (MLLW) = 0.00
LOWEST OBSERVED WATER LEVEL (04/15/1980) = -3.16
Bench Mark Elevation Information In FEET above:
Stamping or Designation MLLW MHW
4623 A 1980 8.74 1.34
NO. 1 1964 9.92 2.52
NO. 2 1964 8.96 1.56
NO STAMPING 1 7.55 0.15
NO STAMPING 2 8.22 0.82
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 4
Station ID: 8674623 PUBLICATION DATE: 01/17/1985
Name: DOG HAMMOCK, SAPELO RIVER
GEORGIA
NOAA Chart: 11509 Latitude: 31ø 31.9' N
USGS Quad: SHELLMAN BLUFF Longitude: 81ø 16.2' 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.