U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Datums Page Page 1 of 6
Station ID: 9418637 PUBLICATION DATE: 03/07/2018
Name: COCKROBIN ISLAND BRIDGE, EEL RIVER
CA
NOAA Chart: 18620 Latitude: 40° 38.2' N ( 40.63722)
USGS Quad: CANNIBL ISLAND Longitude: 124° 16.9' W (-124.28222)
To reach the tidal bench marks from the US Post Office at 338 Main Street in
Loleta, proceed 0.4 km (0.2 mi) north and then west on Main Street to the
intersection with Eel River Drive, continue straight at the intersection on
Cannibal Island Road and proceed west 4.7 km (2.9 mi) to the intersection with
Cockrobin Island Road, turn left and proceed south 0.6 km (0.4 mi) on Cockrobin
Island Road to the bridge leading to Cockrobin Island. The bench marks are
located along Cockrobin Island Road. The tide gauge is located 35 m (114.8 ft)
from the north end of the Cockrobin Island bridge.
T I D A L B E N C H M A R K S
PRIMARY BENCH MARK STAMPING: 8637 C 2017
DESIGNATION: 941 8637 C
MONUMENTATION: Flange-encased Rod VM#: 22268
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: OPUS PID#: BBFP93
LATITUDE: 40° 38.3' N ( 40.63853) LONGITUDE: 124° 17.0' W (-124.28264)
The primary bench mark is a flange encased rod set 0.13 km (0.08 mi) north of
the bridge to Cockrobin Island, 17.58 m (57.7 ft) south of a one lane bridge
sign, 4.58 m (15.0 ft) NE of the wooden fence post corner, 1.75 m (5.7 ft) west
of the edge of pavement, and 0.64 m (2.1 ft) east of a witness post. The bench
mark is set 6 cm (2 inches) below grade, being the top of a stainless steel rod
driven 16.5 m (54.0 ft) to refusal, in a sleeve extending to 0.9 m (3.0 ft) and
encased in a 7 inch national ocean service logo cover containing magnets with
concrete kick block.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 2 of 6
Station ID: 9418637 PUBLICATION DATE: 03/07/2018
Name: COCKROBIN ISLAND BRIDGE, EEL RIVER
CA
NOAA Chart: 18620 Latitude: 40° 38.2' N ( 40.63722)
USGS Quad: CANNIBL ISLAND Longitude: 124° 16.9' W (-124.28222)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 8637 A 2017
DESIGNATION: 941 8637 A
MONUMENTATION: Bench Mark disk VM#: 22269
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: Bridge Parapet OPUS PID:
LATITUDE: 40° 38.1' N ( 40.63542) LONGITUDE: 124° 16.9' W (-124.28147)
The bench mark is a disk set in the parapet near the SW end of the bridge, it is
16.70 m (54.8 ft) SSE of the center of the southernmost metal grate on the
bridge decking, 4.70 m (15.4 ft) west of SE most post of the bridge railing,
3.42 m (11.2 ft) NNW of the south end of the west parapet, 0.60 m (2.0 ft) NNW
of the end of the bridge concrete decking, 0.12 m (0.4 ft) ENE of west edge of
the parapet and about 0.30 above the bridge deck.
BENCH MARK STAMPING: 8637 B 2017
DESIGNATION: 941 8637 B
MONUMENTATION: Bench Mark disk VM#: 22270
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: Bridge parapet OPUS PID:
LATITUDE: 40° 38.2' N ( 40.63744) LONGITUDE: 124° 16.9' W (-124.28231)
The bench mark is a disk set in the NW parapet wall of the bridge leading to
Cockrobin Island, it is 17.35 m (56.9 ft) NNW of the center of the northern most
grate on bridge, 4.51 m (14.8 ft) SSW of the NE most post of bridge railing,
2.72 m (8.9 ft) SSE of the north end of the west parapet wall, 1.24 m (4.1 ft)
west of the end of the concrete bridge decking, 0.12 m (0.4 ft) ENE of the west
edge of the parapet wall and 0.30 above the bridge decking.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 3 of 6
Station ID: 9418637 PUBLICATION DATE: 03/07/2018
Name: COCKROBIN ISLAND BRIDGE, EEL RIVER
CA
NOAA Chart: 18620 Latitude: 40° 38.2' N ( 40.63722)
USGS Quad: CANNIBL ISLAND Longitude: 124° 16.9' W (-124.28222)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 8637 E 2017
DESIGNATION: 941 8637 E
MONUMENTATION: Flange-encased Rod VM#: 22271
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: OPUS PID:
LATITUDE: 40° 38.4' N ( 40.64031) LONGITUDE: 124° 17.0' W (-124.28261)
The bench mark is a flange encased rod located in the right of way on the west
side of the Cockrobin Island road, it is 39.45 m (129.4 ft) NNE of a utility
pole located in a pasture, 1.14 m (3.7 ft) west of the west edge of the
pavement, and 0.23 m (0.8 ft) east of a witness post. The bench mark is set 7 cm
(3 inches) below grade, being the top of a stainless steel rod driven 17.1 m
(56.0 ft) to refusal, in a sleeve extending to 0.9 m (3.0 ft) and encased in a 7
inch national ocean service logo cover containing magnets with concrete kick
block.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 4 of 6
Station ID: 9418637 PUBLICATION DATE: 03/07/2018
Name: COCKROBIN ISLAND BRIDGE, EEL RIVER
CA
NOAA Chart: 18620 Latitude: 40° 38.2' N ( 40.63722)
USGS Quad: CANNIBL ISLAND Longitude: 124° 16.9' W (-124.28222)
T I D A L B E N C H M A R K S
BENCH MARK STAMPING: 8637 D 2017
DESIGNATION: 941 8637 D
MONUMENTATION: Flange-encased Rod VM#: 22297
AGENCY: National Ocean Service IDB PID#:
SETTING CLASSIFICATION: OPUS PID:
LATITUDE: 40° 38.4' N ( 40.63947) LONGITUDE: 124° 17.0' W (-124.28256)
The bench mark is a flange encased rod located in the right of way on the west
side of the road, it is 85.85 m (281.7 ft) north of a one lane bridge sign,
53.15 m (174.4 ft) south-southeast of a utility pole in a pasture, 0.55 m (1.8
ft) west of the edge of pavement, and 0.30 m (1.0 ft) east of a witness post.
The bench mark is set 3 cm (1 inch) below grade, being the top of a stainless
steel rod driven 24.7 m (81.0 ft) to refusal, in a sleeve extending to 0.9 m
(3.0 ft) and encased in a 7 inch national ocean service logo cover containing
magnets with concrete kick block.
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 5 of 6
Station ID: 9418637 PUBLICATION DATE: 03/07/2018
Name: COCKROBIN ISLAND BRIDGE, EEL RIVER
CA
NOAA Chart: 18620 Latitude: 40° 38.2' N ( 40.63722)
USGS Quad: CANNIBL ISLAND Longitude: 124° 16.9' W (-124.28222)
T I D A L D A T U M S
Tidal datums at COCKROBIN ISLAND BRIDGE, EEL RIVER based on:
LENGTH OF SERIES: 5 MONTHS
TIME PERIOD: May 2017 - September 2017
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 9418767 NORTH SPIT, HUMBOLDT BAY
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
MEAN HIGHER HIGH WATER MHHW = 1.897
MEAN HIGH WATER MHW = 1.686
MEAN SEA LEVEL MSL = 1.028
MEAN TIDE LEVEL MTL = 1.016
MEAN LOW WATER MLW = 0.346
MEAN LOWER LOW WATER MLLW = 0.000
North American Vertical Datum (NAVD88)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
8637 C 2017 3.901 2.215
8637 A 2017 8.089 6.403
8637 B 2017 8.117 6.431
8637 E 2017 3.434 1.748
8637 D 2017 4.032 2.346
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Ocean Service
Page 6 of 6
Station ID: 9418637 PUBLICATION DATE: 03/07/2018
Name: COCKROBIN ISLAND BRIDGE, EEL RIVER
CA
NOAA Chart: 18620 Latitude: 40° 38.2' N ( 40.63722)
USGS Quad: CANNIBL ISLAND Longitude: 124° 16.9' W (-124.28222)
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.