U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 5
Station ID: 8571702 PUBLICATION DATE: 10/19/2011
Name: SMITHVILLE ROAD BRIDGE, BEAVERDAM CREEK
MD
NOAA Chart: 12261 Latitude: 38° 25.7' N ( 38.42833)
USGS Quad: SELBYVILLE Longitude: 76° 14.2' W ( -76.23667)
To reach the tidal bench marks from the intersection of MD-16 and MD-341 in
Cambridge, proceed east on MD-16 21.4 KM (13.3 miles), then turn left onto
Smithville Road and continue south for 7.40 KM (4.6 miles) to the boat ramp at
Beaverdam Creek. The bench marks are located south of the ramp along Smithville
Road and the tide gauge is located on the bulkhead adjacent to the ramp.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 1702 E 2005
DESIGNATION: 857 1702 E
MONUMENTATION: Flange-encased Rod VM#: 17846
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod in sleeve OPUS PID:
LATITUDE: 38° 25.5' N ( 38.42500) LONGITUDE: 76° 14.4' W ( -76.24000)
The primary bench mark is a flange-encased rod located on the west side of
Smithville Road, 14.0 m (45.9 ft) SW of power pole T693, 13.6 m (44.6 ft) east
of a "National Wildlife Refuge" sign, and 4.08 m (13.39 ft) NNW of the
centerline of the road. The datum point is set flush with the ground, being the
top of a stainless steel rod driven 18.3 m (60 ft) to refusal, in a sleeve
extending to a depth of 0.61 m (2.0 ft) and encased in a 5-inch NOS logo cap.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 5
Station ID: 8571702 PUBLICATION DATE: 10/19/2011
Name: SMITHVILLE ROAD BRIDGE, BEAVERDAM CREEK
MD
NOAA Chart: 12261 Latitude: 38° 25.7' N ( 38.42833)
USGS Quad: SELBYVILLE Longitude: 76° 14.2' W ( -76.23667)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1702 D 2005
DESIGNATION: 857 1702 D
MONUMENTATION: Flange-encased Rod VM#: 17847
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod in sleeve OPUS PID:
LATITUDE: 38° 25.6' N ( 38.42670) LONGITUDE: 76° 14.4' W ( -76.24000)
The bench mark is a flange-encased rod located on the east side of Smithville
Road, 11.56 m (37.9 ft) SSE of power pole "T691," and 4.15 m (13.6 ft) SSE of
the center of the road. The datum point is set flush with the ground, being the
top of a stainless steel rod driven 18.3 m (60 ft) to refusal, in a sleeve
extending to a depth of 0.61 m (2.0 ft) and encased in a 5-inch NOS logo cap.
BENCH MARK STAMPING: 1702 C 2005
DESIGNATION: 857 1702 C
MONUMENTATION: Flange-encased Rod VM#: 17848
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod in sleeve OPUS PID:
LATITUDE: 38° 25.6' N ( 38.42670) LONGITUDE: 76° 14.3' W ( -76.23830)
The bench mark is a flange-encased rod located on the east side of Smithville
Road, 9.02 m (29.6 ft) SE of power pole "689," 3.75 m (12.3 ft) of power pole
"51456", and 3.60 m (11.81 ft) SE of the centerline of the road. The datum
point is set flush with the ground, being the top of a stainless steel rod
driven 21.9 m (72 ft) to refusal, in a sleeve extending to a depth of 0.6 m (2.0
ft) and encased in a 5-inch NOS logo cap.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 5
Station ID: 8571702 PUBLICATION DATE: 10/19/2011
Name: SMITHVILLE ROAD BRIDGE, BEAVERDAM CREEK
MD
NOAA Chart: 12261 Latitude: 38° 25.7' N ( 38.42833)
USGS Quad: SELBYVILLE Longitude: 76° 14.2' W ( -76.23667)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 1702 B 2005
DESIGNATION: 857 1702 B
MONUMENTATION: Flange-encased Rod VM#: 17849
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod in sleeve OPUS PID:
LATITUDE: 38° 25.6' N ( 38.42670) LONGITUDE: 76° 14.3' W ( -76.23830)
The bench mark is a flange-encased rod located on the west side of Smithville
Road, 27.89 m (91.5 ft) south of power pole "687," 10.00 m, (32.8 ft) west of an
unstamped power pole on the east side of the road, 3.66 m (12.0 ft) west of the
center of the road, and 0.58 m (1.9 ft) from a witness post. The datum point is
set flush with the ground, being the top of a stainless steel rod driven 23.8 m
(78 ft) to refusal, in a sleeve extending to a depth of 0.61 m (2.0 ft), and
encased in a 5-inch NOS logo cap.
BENCH MARK STAMPING: 1702 A 2005
DESIGNATION: 857 1702 A
MONUMENTATION: Flange-encased Rod VM#: 17850
AGENCY: National Ocean Service (NOS) IDB PID#:
SETTING CLASSIFICATION: Stainless steel rod in sleeve OPUS PID:
LATITUDE: 38° 25.7' N ( 38.42830) LONGITUDE: 76° 14.3' W ( -76.23830)
The bench mark is a flange-encased rod located on the west side of Smithville
Road, 39.68 m (130.2 ft) WSW of power pole "51459," 38.89 m (127.6 ft) SW of
power pole "684", 4.11 m (13.5 ft) NW of the centerline of the road, and 0.70 m
(2.3 ft) from an orange witness post. The datum point is set flush with the
ground, being the top of a stainless steel rod driven 57.4 m (188 ft) to
refusal, in a sleeve extending to a depth of 0.6 m (2.0 ft) and encased in a
5-inch NOS logo cap.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 5
Station ID: 8571702 PUBLICATION DATE: 10/19/2011
Name: SMITHVILLE ROAD BRIDGE, BEAVERDAM CREEK
MD
NOAA Chart: 12261 Latitude: 38° 25.7' N ( 38.42833)
USGS Quad: SELBYVILLE Longitude: 76° 14.2' W ( -76.23667)
T I D A L D A T U M S
Tidal datums at SMITHVILLE ROAD BRIDGE, BEAVERDAM CREEK based on:
LENGTH OF SERIES: 2 YEARS
TIME PERIOD: February 2006 - January 2008
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8577330 SOLOMONS ISLAND, PATUXENT RIVER
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (11/17/2006) = 1.002
MEAN HIGHER HIGH WATER MHHW = 0.487
MEAN HIGH WATER MHW = 0.438
MEAN SEA LEVEL MSL = 0.257
MEAN TIDE LEVEL MTL = 0.245
MEAN LOW WATER MLW = 0.052
MEAN LOWER LOW WATER MLLW = 0.000
LOWEST OBSERVED WATER LEVEL (01/03/2008) = -0.427
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
1702 E 2005 1.001 0.563
1702 D 2005 0.861 0.423
1702 C 2005 1.208 0.770
1702 B 2005 1.152 0.714
1702 A 2005 1.336 0.898
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 5
Station ID: 8571702 PUBLICATION DATE: 10/19/2011
Name: SMITHVILLE ROAD BRIDGE, BEAVERDAM CREEK
MD
NOAA Chart: 12261 Latitude: 38° 25.7' N ( 38.42833)
USGS Quad: SELBYVILLE Longitude: 76° 14.2' W ( -76.23667)
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.