NOAA Start here:
May 30 2006 15:10 ELEVATIONS ON STATION DATUM
National Ocean Service (NOAA)
T.M.: 0 W
Units: Feet
Epoch:1983-2001
Elevation Relative to Station DatumDatum / 8444525
NUT ISLAND / 8444162
BOSTON LIGHT / 8443970
BOSTON HARBOR
Mean Higher-High Water / MHHW / 25.15 ft / 17.20 ft. / 13.80
Mean High Water / MHW / 24.70 / 16.76 / 13.36
Mean Diurnal Tide Level / DTL / 20.04 / 12.29 / 8.66
Mean Tide Level / MTL / 19.99 / 12.24 / 8.61
Mean Sea Level / MSL / 20.10 / 12.30 / 8.73
Mean Low Water / MLW / 15.28 / 7.71 / 3.86
Mean Lower-Low Water / MLLW / 14.93 / 7.39 / 3.52
Great Diurnal Range / GT / 10.21 / 9.82 / 10.27
Mean Range of Tide / MN / 9.42 / 9.05 / 9.49
Mean Diurnal High Water Inequality / DHQ / 0.45 / 0.44 / 0.44
Mean Diurnal LowWater Inequality / DLQ / 0.34 / 0.33 / 0.34
Greenwich High Water Interval (hr) / HWI / 3.75 / 3.72 / 3.74
Greenwich LowWater Interval (hr) / LWI / 9.95 / 9.90 / 9.93
North American Vertical Datum / NAVD / ?! / ?! / 9.03
Highest Water Level on Station Datum / Maximum / 27.97 / 19.11 / 18.62
Date Of Highest Water Level / Max Date / 20010306 / 20010110 / 19780207
Time Of Highest Water Level / Max Time / 12:42 / 16:00 / 10:36
LowestWater Level on Station Datum / Minimum / 11.80 / 4.54 / -0.20
Date Of Lowest Water Level / Min Date / 20010211 / 20010212 / 19400324
Time Of Lowest Water Level / Min Time / 00:06 / 00:54 / 00:00
MHHW referred to MLLW / 10.2 / 9.8 / 10.3
MSL referred to MLLW / 5.1 / 4.9 / 5.2
MLLW referred to Tidal Benchmark meters / 7.749 / 3.1
MLLW referred to Tidal Benchmark feet / 25.0 / -5.5
Tidal Benchmark referred to NAVD feet
MLLW referred to NAVD feet
MSL referred to NAVD feet / 0.3
Station ID: 8444162 PUBLICATION DATE: 02/05/2004
Name: BOSTON LIGHT, BOSTON HARBOR
MASSACHUSETTS
NOAA Chart: 13270 Latitude: 42° 19.7' N
USGS Quad: HULL Longitude: 70° 53.5' W
Tidal datums at BOSTON LIGHT, BOSTON HARBOR based on:
LENGTH OF SERIES: 1 YEAR
TIME PERIOD: July 2001 - June 2002
TIDAL EPOCH: 1983-2001
CONTROL TIDE STATION: 8443970 BOSTON, BOSTON HARBOR
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (01/10/2001) = 3.573
MEAN HIGHER HIGH WATER (MHHW) = 2.992
MEAN HIGH WATER (MHW) = 2.858
MEAN SEA LEVEL (MSL) = 1.498
MEAN TIDE LEVEL (MTL) = 1.479
MEAN LOW WATER (MLW) = 0.100
MEAN LOWER LOW WATER (MLLW) = 0.000
LOWEST OBSERVED WATER LEVEL (02/12/2001) = -0.867
National Geodetic Vertical Datum (NGVD 29)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
844 4162 NO 8 7.749 4.891
USE 1885 7.608 4.750
10 1926 4.819 1.961
9 1926 7.014 4.156
LITTLE BREWSTER 1981 8.368 5.510
Station ID: 8444525 PUBLICATION DATE: 04/21/2003
Name: NUT ISLAND, QUINCY BAY
MASSACHUSETTS
NOAA Chart: 13270 Latitude: 42° 16.8' N
USGS Quad: HULL Longitude: 70° 57.2' W
Tidal datums at NUT ISLAND, QUINCY BAY based on:
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (03/06/2001) = 3.973
MEAN HIGHER HIGH WATER (MHHW) = 3.113
MEAN HIGH WATER (MHW) = 2.976
MEAN SEA LEVEL (MSL) = 1.574
MEAN TIDE LEVEL (MTL) = 1.540
MEAN LOW WATER (MLW) = 0.104
MEAN LOWER LOW WATER (MLLW) = 0.000
LOWEST OBSERVED WATER LEVEL (02/11/2001) = -0.954
National Geodetic Vertical Datum (NGVD 29)
Bench Mark Elevation Information In METERS above:
Stamping or Designation MLLW MHW
NI 8 5.448 2.472
4525 A 2000 5.450 2.474
4525 B 2000 10.843 7.867
4525 C 2000 9.122 6.146
4525 D 2000 10.408 7.432
DATABASE = Sybase ,PROGRAM = datasheet, VERSION = 7.36
1 National Geodetic Survey, Retrieval Date = MAY 31, 2006
MY2474 ***********************************************************************
MY2474 DESIGNATION - WOLLASTON
MY2474 PID - MY2474
MY2474 STATE/COUNTY- MA/SUFFOLK
MY2474 USGS QUAD -
MY2474
MY2474 *CURRENT SURVEY CONTROL
MY2474 ______
MY2474* NAD 83(1996)- 42 16 19.61194(N) 070 59 55.26084(W) ADJUSTED
MY2474* NAVD 88 - 3.6 (meters) 12. (feet) VERTCON
MY2474 ______
MY2474 LAPLACE CORR- 3.55 (seconds) DEFLEC99
MY2474 GEOID HEIGHT- -27.90 (meters) GEOID03
MY2474
MY2474 HORZ ORDER - SECOND
MY2474
MY2474.The horizontal coordinates were established by classical geodetic methods
MY2474.and adjusted by the National Geodetic Survey in June 1998..
MY2474
MY2474.The NAVD 88 height was computed by applying the VERTCON shift value to
MY2474.the NGVD 29 height (displayed under SUPERSEDED SURVEY CONTROL.)
MY2474
MY2474.The Laplace correction was computed from DEFLEC99 derived deflections.
MY2474
MY2474.The geoid height was determined by GEOID03.
MY2474
MY2474; North East Units Scale Factor Converg.
MY2474;SPC MA M - 891,415.152 241,355.352 MT 0.99996533 +0 20 12.3
MY2474;SPC MA M - 2,924,584.54 791,846.68 sFT 0.99996533 +0 20 12.3
MY2474;UTM 19 - 4,681,923.651 335,177.627 MT 0.99993427 -1 20 41.0
MY2474
MY2474! - Elev Factor x Scale Factor = Combined Factor
MY2474!SPC MA M - 1.00000382 x 0.99996533 = 0.99996915
MY2474!UTM 19 - 1.00000382 x 0.99993427 = 0.99993809
MY2474
MY2474 SUPERSEDED SURVEY CONTROL
MY2474
MY2474 NAD 83(1996)- 42 16 19.61061(N) 070 59 55.26026(W) AD( ) 2
MY2474 NAD 83(1992)- 42 16 19.61058(N) 070 59 55.26024(W) AD( ) 2
MY2474 NAD 83(1992)- 42 16 19.61461(N) 070 59 55.25852(W) AD( ) 2
MY2474 NAD 83(1986)- 42 16 19.61399(N) 070 59 55.25928(W) AD( ) 2
MY2474 NGVD 29 (05/01/88) 3.8 (m) 12. (f) VERT ANG
MY2474
MY2474.Superseded values are not recommended for survey control.
MY2474.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums.
MY2474.See file dsdata.txt to determine how the superseded data were derived.
MY2474
MY2474_U.S. NATIONAL GRID SPATIAL ADDRESS: 19TCG3517881924(NAD 83)
MY2474_MARKER: DE = TRAVERSE STATION DISK
MY2474_SETTING: 7 = SET IN TOP OF CONCRETE MONUMENT
MY2474_SP_SET: TOP OF SQUARE CONCRETE MONUMENT
MY2474_MAGNETIC: O = OTHER; SEE DESCRIPTION
MY2474_STABILITY: C = MAY HOLD, BUT OF TYPE COMMONLY SUBJECT TO
MY2474+STABILITY: SURFACE MOTION
MY2474
MY2474 HISTORY - Date Condition Report By
MY2474 HISTORY - 1978 MONUMENTED MAGS
MY2474
MY2474 STATION DESCRIPTION
DESCRIBED BY MASSACHUSETTS GEODETIC SURVEY 1978 (WJK)
THE STATION IS ABOUT 6.8 KM (4.2 MI) EAST-NORTHEAST OF MILTON TOWN
HALL AND ABOUT 2.3 KM (1.4 MI) NORTH-NORTHEAST OF QUINCY CITY HALL.
OWNERSHIP--STATE HIGHWAY RIGHT OF WAY.
TO REACH THE STATION FROM THE INTERSECTION OF SQUANTUM STREET AND
MORRISSEY BOULEVARD (QUINCY SHORE DRIVE) AT THE NORTH END OF
WOLLASTON BEACH, GO SOUTH ON MORRISSEY BOULEVARD ABOUT 2.6 KM
(1.6 MI) TO A PARKING AREA AND REST AREA ON THE RIGHT AND THE
STATION AT THE SOUTH END OF THE AREA.
THE STATION IS MARKED BY A MAGS DISK STAMPED---WOLLASTON---,
IS SET IN THE TOP OF A SQUARE CONCRETE MONUMENT 13 CM ON A SIDE,
THE TOP OF WHICH IS ABOUT 15 CM BELOW GRADE. IT IS
- 86.6 FT WEST OF A CROSS CUT IN A CATCH BASIN FRAME
- 55.61 FT EAST OF A BRASS PIN IN LEAD ON TOP OF THEWEST MOST BOULDER&
- 31.3 FT SOUTH OF POINT OF CURBING ON NORTH SIDE OF REST AREA
- 23.6 FT NORTH OF THECENTER LINE OF THE BICYCLE PATH.
31.3 FT SOUTH OF POINT OF CURBING ON NORTH SIDE OF REST AREA
(ie QSD side, not marsh side, one of 2 ‘points’ at egress area)
55.61 FT EAST OF A BRASS PIN IN LEAD ON TOP OF THE WEST MOST BOULDER.
(possibly moved by construction) / THE STATION IS MARKED BY A MAGS DISK STAMPED---WOLLASTON---, &
IS SET IN THE TOP OF A SQUARE CONCRETE MONUMENT 13 CM ON A SIDE,
THE TOP OF WHICH IS ABOUT 15 CM BELOW GRADE. / 86.6 FT WEST OF A CROSS CUT IN A CATCH BASIN FRAM
(QSD Southbound, RHS, just after parking lot egress curbing)
23.6 FT NORTH OF THE CENTER LINE OF THE BICYCLE PATH.
(Not a ‘single point’!)
MY2474'
MY2474'HEIGHT OF LIGHT SHOWN WAS 1.5 METERS ABOVE THE MARK.
MY2474'
MY2474'DESCRIBED BY W.J.KENNEDY, MAGS.
*** retrieval complete.
Elapsed Time = 00:00:00
Links Between Tides and Maps:
- Mean High Water (MHW)
- Typically marked as the shoreline on most maps and charts
- Mean Lower Low Water (MLLW)
- Zero point of the tidal datum
- Zero point of all nautical charts
- Mean Sea Level (MSL)
- Zero point of the National Geodetic Vertical Datum of 1929 (NGVD29)
- Zero point of USGS DEMs
(Shalowitz, 1962)
NGVD29 based on MSL from tide gauges.
NAVD88 to NGVD29 is not easily converted.
3.2 Other Vertical Datums and Their Relationship to Tidal Datums
In addition to tidal datums, other vertical datums are determined and employed for various
applications. Examples are fixed datums of the National Geodetic Reference System, or the
National Geodetic Vertical Datum (NGVD 1929) (previously referred to as the Sea Level Datum
of 1929), or the North American Vertical Datum of 1988 (NAVD 88). NGVD 1929 is a fixed datum
adopted as a standard geodetic reference for heights and was derived from a general adjustment of
the first order leveling nets of the US and Canada, in which MSL was held fixed as observed at 26
stations in the US and Canada. Numerous adjustments have been made to these leveling networks
since originally established in 1929. The North American Vertical Datum of 1988 (NAVD 88)
involved a simultaneous least-squares, minimum constraint adjustment of the Canadian-Mexican-US
leveling observations. Local MSL was held fixed at Father Point/Rimouski, Quebec, Canada, as the
single constraint. The North American Vertical Datum of 1988 (NAVD 88) and International Great
Lakes Datum of 1985 (IGLD 85) are both based upon this simultaneous, least-squares, minimum
constraint adjustment of Canada, Mexico, and U.S. leveling observations. These fixed geodetic
datums (e.g., NGVD 1929 and NAVD 88) do not reflect the changes in sea level and because they
represent a “best” fit over a broad area, their relationship to local mean sea level differs from one
location to another. MSL is a tidal datum often confused with NGVD 1929 and they are not
equivalent. NGVD 1929 was replaced by NAVD 88 and the National Geodetic Survey no longer
supports the NGVD 1929 system.
Figure 12 shows the datums related to Station Datum (STND) at San Francisco Bay, CA. The
elevation of the primary bench mark (PBM 180 1936), is 5.794 m above STND. The Highest Water
Level (HWL) recorded at San Francisco is 4.462 m above station datum, and the Lowest Water
Level (LWL) is 0.945 m . HWL and LWL are not tidal datums, but are the extreme values of the
maximum and minimum water levels recorded at the station. For San Francisco Bay, the value of
NGVD 29 is below Mean Sea Level (MSL), and NAVD88 is lower still. MSL pertains to local
mean sea level and should not be confused with NAVD 88, the ellipsoid or the superseded NGVD
29. Figures 13a and 13b show why the direct transfer of tidal datum relationships through NAVD
88, NGVD 29 or the ellipsoidal differences, even within the same bay, estuary or river, may not be
accurate. The graph illustrates that tidal datums are local datums relative to the land and great care
must be taken to extrapolate tidal datum differences and relationships to geodetic datums. In some
instances, linear interpolation can be used to estimate datum relationships between two known points
along a stretch of shoreline that is not very complicated in a topographic and bathymetric sense.
When in doubt of the relationship of a tidal datum to a geodetic datum, establishment of a tide
station and connection to geodetic datum using differential levels or GPS is recommended for most
applications. NOS establishes geodetic connections at the NWLON stations through differential
levels between tidal bench marks and geodetic bench marks. Use of GPS survey equipment to
occupy tidal bench marks is the emerging state-of-the-art method for making the connections. See
the NOS Web-sites at and for further
information on geodetic and tidal datum elevations on bench marks.
22
Figure 12. A tidal datum stick diagram for San Francisco, CA showing the
relationships of the various tidal and geodetic datums.
23
3.3 Steps Required to Compute Tidal Datums at Short-Term Stations
Due to time and resource constraints, primary determinations of tidal datums ( i.e. using 19 years
of data) are not practical at every location along the entire coast where tidal datums are required. At
intermediate locations, a secondary determination of tidal datums can usually be made using
observations covering much shorter periods than 19 years. Results are corrected to an equivalent
mean value by comparison with a suitable control tide station (Marmer, 1951).
Conceptually, the following steps need to be completed in order to compute equivalent NTDE
tidal datums listed in section 3.1 at short term stations using the method of comparison of
simultaneous observations:
1) Select the time period over which the simultaneous comparison will be made.
2) Select the appropriate control tide station for the subordinate station of interest based on
location, tidal characteristics, and availability of data.
. 3) Obtain the simultaneous data from subordinate and control stations and obtain or tabulate
the tides and compute monthly means, as appropriate.
4) Obtain the accepted NTDE values of the tidal datums at the control station from NOS via
the CO-OPS Website (
5) Compute the mean differences and/or ratios (as appropriate) in the tidal parameters between
the subordinate and control station over the period of comparison.
6) Apply the mean differences and ratios computed in step 5, above, to the accepted values at
the control station to obtain equivalent or corrected NTDE values for the subordinate
station. The computations use slightly different formulas depending on the type of tide.
These differences are explained in section 3.4 and in Chapter 4.
3.4 Datum Computation Methods
There are some key datum computation methods used by NOS (in step 6, above) that differ
slightly depending upon the tidal characteristics and the type of tide.
Standard Method. This method is generally used for the West Coast and Pacific Island stations
and is also called the Range Ratio Method. First, equivalent NTDE values for MTL, Mn, DHQ and
DLQ are determined by comparison with an appropriate control. From these, the following are then
computed:
MLW = MTL - (0.5 x Mn)
MHW = MLW + Mn
MLLW= MLW - DLQ
MHHW = MHW + DHQ
26
Modified-Range Ratio Method. This method is generally used for the East Coast, Gulf Coast
and Caribbean Island stations. First, equivalent NTDE values for MTL, DTL, Mn and Gt as
determined by comparison with an appropriate control. The difference from the Standard Method
is that ratios of the DHQ and DLQ values are not used to compute MHHW and MLLW because
numerically the values are very small for semidiurnal tide areas. A Gt ratio about DTL is used
instead. From these, the following are computed:
MLW = MTL - (0.5 x Mn)
MHW = MLW + Mn
MLLW= DTL - (0.5 x Gt)
MHHW = MLLW + Gt
Direct Method. This method is usually used only when a full range of tidal values are not
available. For example, direct MHW can be computed for situations when low waters are not
recorded, such as in the upper reaches of a marsh. Since MTL, DTL, and Mn and Gt cannot be
determined if low waters are cut-off, equivalent NTDE values for MHW and MHHW datums are
determined directly by comparison of high tides with an appropriate control using the available part
of the tidal cycle.
3.5 Accuracy
Generalized accuracies for datums computed at secondary or tertiary stations in terms of the
standard deviation error for the length of the record are summarized in Table 1 (see Swanson, 1974).
These values were calculated using accepted datums for control station pairs in the NWLON. The
values in Table 1 are the confidence intervals for the tidal datums based on the standard deviation.
Table 1. Generalized accuracy of tidal datums for East, Gulf, and West Coasts when determined
from short series of record and based on the standard deviation( one-sigma). From Swanson (1974).
Series Length
(months)
East Coast
(cm) (ft.)
Gulf Coast
(cm) (ft.)
West Coast
(cm) (ft.)
1 3.96 0.13 5.48 0.18 3.96 0.13
3 3.05 0.10 4.57 0.15 3.35 0.11
6 2.13 0.07 3.65 0.12 2.43 0.08
12 1.52 0.05 2.74 0.09 1.82 0.06
It is helpful to view the data in Table 1 graphically (Figure 14). The Swanson error curves are
similarly shaped for each coast. Ranked by coast, the errors are smallest for the East and West
coasts, with the largest errors on the Gulf coast. The largest errors coincide with the least data, and
decrease asymptotically to a finite value with increasing data. This handbook contains examples
which apply datum computation techniques to water level data with series lengths of about 1 week,
and also for twelve months. Examples containing a week of data or less should be interpreted as
having generalized errors greater than or equal to those for a 1-month data series shown on the first
27
Estimated Error in Tidal Datums vs. Length of Series
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0
2
4
6
8
10
12
14
TIME (months)
One-Standard Deviation
(meters)
East Coast
Gulf Coast
West Coast
Figure 14. Estimated Error in Tidal Datums from Swanson (1974)
row of Table 1. Examples containing a year of data have generalized errors that correspond to the
fourth row.
Th
e uncertainty in the value of the tidal datum translates into a horizontal uncertainty of the location
of a marine boundary when the tidal datum line is surveyed to the land (Demarcating and Mapping
Tidal Boundaries, 1970). Table 2 expresses the uncertainty in the marine boundary as a function
of the slope of the land. A slope of 1% means that the land rises 1 meter for every 100 meters of
horizontal distance. This is illustrated in Figure 15.
Benchmark Stations
8444162Boston Light, MA / 8443970Boston, MA8444788Weymouth Fore River, MA / 8444525Nut Island, MA
8419399Cape Neddick, ME / 8419528Fort Point, York Harbor, ME
8419870Seavey Island, ME / 8420411Dover, Cocheco River, NH
8423898Fort Point, NH / 8440273Salisbury Point, Merrimack Riv
8440369Merrimacport, Merrimack River, / 8440452Plum Island, Merrimack River
8440466Newburyport, Merrimack River, / 8440889Riverside, Merrimack River, MA
8441551Rockport Harbor, MA / 8441571Lobster Cove, Annisquam River
8441771Essex, Essex River, MA / 8441841Gloucester Harbor, MA
8442417Beverly, Beverly Harbor, MA / 8442645Salem, Salem Harbor, MA
8443187Lynn, Lynn Harbor, MA / 8443662Amelia Earhart Dam, Mystic Riv
8443725Chelsea, MA / 8443970Boston, MA
8444162Boston Light, MA / 8444525Nut Island, MA
8444788Weymouth Fore River, MA / 8445138Scituate, Scituate Harbor, MA
8446009Brant Rock, Green Harbor River / 8446166Duxbury, Duxbury Harbor, MA
8446493Plymouth, Plymouth Harbor, MA / 8447173Station 115, Cape Cod Canal, M
8447180Sandwich, MA / 8447191Station 200, Cape Cod Canal, M
8447241Sesuit Harbor, East Dennis, MA / 8447270Buzzards Bay, MA
8447277Onset Beach T-12, MA / 8447281Steepbrook, MA
8447295Gray Gables, MA / 8447355Monument Beach T-8, MA
8447368Great Hill, MA / 8447386Fall River, MA
8447416Piney Point, MA / 8447435Chatham, Lydia Cove, MA
8447495Saquatucket Harbor, MA / 8447505Chatham, Stage Harbor, MA
8447685Chappaquoit Point, MA / 8447712New Bedford, Clarks Point, MA
8447842Round Hill Point, MA / 8447930Woods Hole, MA
8448376Cuttyhunk, MA / 8449130Nantucket Island, MA
MEAN SEA LEVEL DIFFERENCE
Units: Feet
Station Name 1983-2001 1960-1978 Residual
------
8443970 BOSTON, BOSTON HARBOR, MA 8.73 8.60 0.13
8444162
BOSTON LIGHT, BOSTON HARBOR, MA 12.30 12.21 0.09
8444525 NUT ISLAND, QUINCY BAY, MA 20.10 19.98 0.11