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Report on Collection and Analysis of Tidal Data from Boston Harbor,
Meetinghouse Pond, Chatham Fish Pier and Outermost Harbor:
June, 2016 – September, 2018
by
Graham S. Giese and Bryan Legare
for
The Pleasant Bay Resource Management Alliance
January 8, 2019
Report prepared by the Coastal Processes and Ecosystems Laboratory
At the Center for Coastal Studies
Publication: 19-CL01
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INTRODUCTION
The continuous change of channels, inlets and landforms of the barrier beach
complex separating the Pleasant Bay/Chatham Harbor estuarine system from the
greater Atlantic Ocean in turn produces changes in tidal and wave patterns within
the estuary. The breaching of Nauset Beach during a severe northeasterly storm on
January 2, 1987, ended a long period of growth of the barrier beach - a century of
incremental southward extension. New channels were formed as well as shoals,
and a second breaching in 2007 produced another tidal inlet north of that formed in
1987 (e.g., Giese, Mague and Rogers, 2009). On April 1, 2017, the breaching of
northernmost South Beach produced a channel (“Fools Inlet”) adjacent to the 1987
inlet, thereby providing tidal flow and navigation between Chatham Harbor and
previously separated systems to its south and west.
The altered tide and wave patterns within this dynamic system are affecting its
ecology, human use and management. Since tidal monitoring can assist
understanding of the changing system and enable improved management, we have
compiled and analyzed tidal data from the following locations: Meetinghouse
Pond, at the extreme head of the Chatham Harbor/Pleasant Bay system; Chatham
Fish Pier, which lies between the two tidal inlets at the mouth of the system; and,
at Outermost Harbor Marina since March, 2017, (added in anticipation of the
breaching of South Beach which occurred on April 1, 2017). During the course of
the study it was determined that some pronounced changes of the local Pleasant
Bay/Chatham Harbor tides relate directly to regional tidal characteristics. To help
delineate these regional influences, limited tidal data from Boston Harbor have
been included in this report.
In summary, we report here results of our study of tidal data recorded between
June, 2016, and September, 2018, at four stations: two within the Chatham
Harbor/Pleasant Bay estuary system, one adjacent to the new “Fools Inlet”, and a
one in Boston Harbor. The original tide readings at all four stations were recorded
at 6-minute intervals, except for occasional periods of instrument malfunction.
Details of the ongoing tidal study that includes this time period are presented in an
earlier and more extensive report (Giese, 2012). The present report includes
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discussion of the new results in context of our previous reports in this ongoing
study, and plots of station data extend back in time to 2012.
METHODS
The objective of the analysis was to focus attention on patterns of sea level, high
and low tide levels, and tidal range change within the Pleasant Bay/Chatham
Harbor estuary at annual and inter-annual time scales.
Meetinghouse Pond, Chatham Fish Pier and Outermost Harbor
Tidal data collected during this reporting period (June, 2016 – September, 2018)
were recorded by Onset HOBO pressure recorders installed at Nauset-East Marina
on Meetinghouse Pond in Orleans, and at Chatham Fish Pier in Chatham (Fig. 1).
We also report tidal data recorded from March, 2017, through September, 2018, by
Onset HOBO pressure recorders installed at the Outermost Harbor Marine Marina
in Chatham (Fig. 2).
Boston Harbor
The Boston Harbor data were recorded on a NOAA tide recorder and made
available on the NOAA tides and water levels website
(www.tidesandcurrents.noaa.gov).
Analysis
Initial tidal data from stations within the estuary were corrected for effects of
atmospheric pressure using data from HOBO atmospheric pressure recorders
established at both Chatham Fish Pier and Meetinghouse Pond to reduce error due
to the distance between the tidal and atmospheric pressure-recording instruments.
The sea level data were then adjusted to the vertical geodetic datum, NAVD88, by
means of precision GPS surveys. The instrument-provided tide levels were
periodically checked against visual readings of a nearby tide staff and compared to
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the now repaired NOAA tide gauge at Chatham Fish Pier. Times are reported as
local standard time.
Statistics for each data set were calculated using MATLAB software. Using the
six-minute data as input, mean sea level (MSL), mean high and low water (MHW
and MLW), and mean tidal range (MTR) were derived for the individual time
series.
Table 1. Abbreviations used in the report
CCNS
Cape Cod National Seashore
CCS
Center for Coastal Studies
GPS
Global Positioning System
MHW
Mean High Water
MLW
Mean Low Water
MSL
Mean Sea Level
MTR
Mean Tidal Range
NAVD88
North American Vertical Datum of 1988
NOAA
National Oceanic and Atmospheric Administration
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Figure 1. Location of tide recorders at Meetinghouse Pond and Chatham Fish Pier.
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Figure 2. Location of tide recorders at Chatham Fish Pier and Outermost Harbor.
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Figure 3. Summary data from Boston Harbor NOAA tide recorder from January
2012 to September 2018. Mean Sea Level (Green), Mean High Water (Red), and
Mean Low Water (Blue) are given in NAVD88 (meters). Tide Range (Black) is
also given in meters.
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Table 2. Summary data from Chatham Fish Pier tide recorder from June 2016 to
September 2018. Mean Sea Level (MSL), Mean High Water (MHW), and Mean
Low Water (MLW) are given in NAVD88 (meters). Tide Range (Range) is also
given in meters.
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Figure 4. Summary data from Chatham Fish Pier tide recorder from January 2012
to September 2018. Mean Sea Level (Green), Mean High Water (Red), and Mean
Low Water (Blue) are given in meters (NAVD88). Tide Range (Black) is also
given in meters. Dashed line: June 2017.
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Table 3. Summary data from Meetinghouse Pond tide recorder from June 2016 to
September 2018. Mean Sea Level (MSL), Mean High Water (MHW), and Mean
Low Water (MLW) are given in NAVD88 (meters). Tide Range (Range) is also
given in meters.
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Figure 5. Summary data from Meetinghouse Pond tide recorder from January 2012
to September 2018. Mean Sea Level (Green), Mean High Water (Red), and Mean
Low Water (Blue) are given in NAVD88 (meters). Tide Range (Black) is also
given in meters. Dashed line indicates June 2017.
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Table 4. Summary data from Outermost Harbor tide recorder from March 2017 to
September 2018. Mean Sea Level (MSL), Mean High Water (MHW), and Mean
Low Water (MLW) are given in NAVD88 (meters). Tide Range (Range) is also
given in meters.
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Figure 6. Summary data from Outermost Harbor tide recorder from March 2017 to
September 2018. Mean Sea Level (Green), Mean High Water (Red), and Mean
Low Water (Blue) are given in NAVD88 (meters). Tide Range (Black) is also
given in meters. Dashed line indicates June 2017.
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Figure 7. Mean Low Water from Meetinghouse Pond (Red) and Chatham Fish Pier
(Blue) from tide recordings from January 2012 to September 2018. Values are
given in NAVD88 (meters). Dashed line indicates June 2017.
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Figure 8. Summary data from Outermost Harbor (X) and Chatham Fish Pier (O)
tide recorders from January 2017 through September 2018. Mean Sea Level
(Green), Mean High Water (Red), and Mean Low Water (Blue) are given in meters
(NAVD88). Tide Range (Black) is in meters. Dashed line indicates June 2017.
DISCUSSION
The tidal results presented above, together with those presented and discussed in
previous reports, bear a significant relationship to trends of geomorphic change of
the Pleasant Bay-Nauset Beach system, and they point to additional changes that
may occur in the decade ahead.
Boston Tides and Anomalous Regional Sea Levels. The single most striking event
recorded in our time series of monthly tide data is the abrupt, short-lived regional
sea level rise that occurred in March, 2018 (e.g., Fig. 3). With that event, Boston
monthly mean sea level reached its highest level in the almost 100-year history of
official tide recording, slightly exceeding the previous maximum reached in
March, 2010 (Fig. 9).
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Figure 9. Historic monthly sea levels for Boston adjusted by removal of seasonal
trends (NOAA, 2018). The maximum, the mean monthly sea level for March 2018,
is indicated by the red circle.
This sea level anomaly occurred throughout the U.S. northeast coast. Tidal stations
from Portland, Maine, to New York City recorded increases ranging from 0.2 to
0.3 meters between February and March, 2018. In that regard, if not in its
longevity, this event is reminiscent of the multiyear regional sea level anomaly
discussed in our August, 2012, report as well as those reported by others (e.g.,
Sweet, et al., 2014). Local impacts of the 2018 sea level regional anomaly are
treated in the following discussion.
Chatham Fish Pier Tides and Reversal of Decreasing Tide Range. Previous reports
(e.g., Legare and Giese, 2016) discussed the multi-year trend of increasing low
water levels and decreasing tide range at Chatham Fish Pier that became
pronounced in 2013. The new data reveal that this trend abruptly reversed between
June and July, 2017, particularly with respect to tide range (Fig. 4). By September,
2018, the range at Chatham Fish Pier had increased 0.3 m (1 ft.) above that of
June, 2017. This change was concurrent with a major geomorphic reconfiguration
of the northern terminus of North Beach Island and the North Inlet complex of
shoals and channels (T. Keon, personal communication and Fig. 10).
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Figure 10. Aerial photographs showing changes in configuration of North Inlet
between June and October, 2017. The breakup of the NW-trending spit on northern
North Beach Island made way for a more efficient ebb tidal channel along the
southern margin of the North Inlet complex of shoals and channels (courtesy of T.
Keon).
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Ebb Channel Reconfiguration. Summarizing previous discussions, for several
years following the 2007 breaching of Nauset Beach seaward of Ministers Point
(i.e., the opening of North Inlet), tidal flows through the new inlet were primarily
incoming flood tides, and the main ebb channel connecting Pleasant Bay and Little
Pleasant Bay to the open sea continued southward through Chatham Harbor to the
system’s major (1987) tidal inlet, South Inlet. Ebb flow in the channel was
enhanced by increasing tidal range at Meetinghouse Pond which reached a
maximum in 2012, having increased approximately 0.3 m (1 ft.) following the
2007 breaching due to a combination of the increased flood tides and a regional sea
level anomaly (Giese, 2012).
As a result of scouring by increased ebb flows through South Inlet, Chatham Fish
Pier experienced decreased low tide levels until 2012 (Legare and Giese, 2016);
however beginning then and continuing into 2017, Chatham Fish Pier low tides
began a steady 5-year rise, ending only in mid-2017 (Figs. 4 and 7). Initially
Meetinghouse Pond low tides rose also, but the rising ended in 2013 and that
change marked the beginning a three-year sustained drop in the elevation
difference between Meetinghouse Pond and Chatham Fish Pier low water levels.
As discussed in our previous two reports, we suggest that until 2013, six years
following initiation of North Inlet, South Inlet dominated the system’s tidal
hydraulics. However, we suggest that a turning point occurred in 2013 initiating a
decrease in the relative dominance of South Inlet. Decreasing low water elevation
differences between Meetinghouse Pond and Chatham Fish Pier following 2013
and continuing into mid-2017 indicate a continuing decrease of flow in the ebb
channel through Chatham Harbor south to South Inlet, and a corresponding
increase in ebb flow through North Inlet. It seems likely that the breaching of
South Beach at “Fools Inlet” in April, 2017, and much more importantly, the
breakup of northern North Beach Island in June, 2017, resulted in further
decoupling the two inlets from a hydrodynamical point-of-view.
However, we suggest that it was not until the anomalous sea level rise event of
March, 2018, (see p. 15-16) that the system’s ebb channel reconfiguration was
completed. The much-discussed unusually swift ebb flows in the vicinity of
Ministers Point that occurred in March, 2018 - those associated with extreme
coastal erosion there - completed the connection of the system’s major ebb channel
with North Inlet (Fig. 11), the final major element of the inlet development phase
of the century-and-a-half long geomorphic/hydrographic cycle that was initiated in
1987.
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Figure 11. August 7, 2018, photograph showing established connection of the ebb
tidal channel with North Inlet. Part of Ministers Point can be seen at extreme upper
right and Chatham Fish Pier facilities at center upper left.
Looking forward, considerations of morphodynamic/hydrodynamic stability
(Giese, Mague and Smith, 2009) suggest that only the final stages of the system’s
inlet development phase of remain to play out. During the coming decade, North
Beach Island will likely follow the path already taken by South Beach in becoming
a relic landform. It will become more frequently overwashed by storm tides, and its
sediment will episodically be shifted to produce more stable landforms to its south
and west, making way for initiation of the inlet migration phase to follow. Likely
socio-economic effects of these changes include navigational impacts in the region
around South Inlet, including Outermost Harbor and Morris Island Cut, and
episodic coastal erosion of the mainland shore presently protected by North Beach
Island.
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ACKNOWLEDGEMENTS
Our sincere thanks to the many individuals and organizations whose support
contributed to the success of this study. The tide recorder at Chatham Fish Pier was
donated by the Orleans Pond Coalition. Nauset Marine East marina made available
facilities for mounting the Meetinghouse Pond tide recorder, while Oharra
Deschamps provided visual readings of a nearby tide staff. The National
Oceanographic and Atmospheric Administration provided the processed tide data
for Boston Harbor and the initial data for Chatham Fish Pier. Mark Adams (CCNS)
provided the surveying required to adjust the Chatham Fish Pier data to the
contemporary national vertical datum. Outermost Harbor Marina allowed the
installation of tide recorder at their facility, allowing for further analysis.
This study was supported by the Pleasant Bay Resource Management Alliance, and
benefitted greatly from the guidance of its director, Carole Ridley, and the
members of its Coastal Resource Work Group. We acknowledge with special
thanks the contributions of Ted Keon, Director of Coastal Resources for the Town
of Chatham, who kindly reviewed of an early draft of this report and provided
comments and aerial imagery revealing the significant tidal impacts associated
with the break-up of North Beach Island’s northern terminus that began in June
2017 (Fig. 10).
Suggested citation:
Giese, G.S., Legare, B., 2019. Report on Collection and Analysis of Tidal Data
from Boston Harbor, Meetinghouse Pond, Chatham Fish Pier and Outermost
Harbor: June, 2016 – September, 2018. Technical Report: 19-CL01. Center for
Coastal Studies, Provincetown, MA, 21p
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REFERENCES
Giese, G.S., S.T. Mague and S.S. Rogers, 2009. A geomorphological analysis of
Nauset Beach/Pleasant Bay/Chatham Harbor for the purpose of estimating future
configurations and conditions. Technical Report to the Pleasant Bay Resource
Management Alliance. Center for Coastal Studies, Provincetown, MA, 31p.
Giese, G.S., 2012. Analysis of tidal data from Meetinghouse Pond, Chatham Fish
Pier and Boston: with application to management. Technical Report to the Pleasant
Bay Resource Management Alliance, Center for Coastal Studies, Provincetown,
MA, 17p.
Legare, B., Giese, G.S., 2016. Analysis of Tidal Data from Meetinghouse Pond,
Chatham Fish Pier and Boston: July 2015 – July 2016. Technical Report to the
Pleasant Bay Resource Management Alliance. Center for Coastal Studies,
Provincetown, MA, 10p
Sweet, W.V., J. Park, J. J. Marra, C. Zervas, S. Gill (2014), Sea level rise and
nuisance flood frequency changes around the United States, in NOAA
Technical Report NOS COOPS 73, 53 pp.
