Technical ReportPDF Available

A New Method for Mapping Inundation Pathways to Increase Coastal Resiliency, Provincetown Massachusetts

Authors:
  • Center for Coastal Studies, Provincetown
A New Method for Mapping Inundation Pathways to Increase
Coastal Resiliency, Provincetown Massachusetts
A report prepared for the Town of Provincetown, Massachusetts
Funded through the Massachusetts Office of Coastal Zone Management’s
Coastal Resiliency Grant program | FY 2015 RFR ENV 15 CZM 03
Prepared by
Mark Borrelli, PhD
Steve T. Mague
Theresa L. Smith
Bryan Legare
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PROJECT BACKGROUND AND OVERVIEW
The impacts of coastal inundation have historically confronted coastal managers dealing with
vulnerabilities to existing infrastructure and planning for future infrastructure improvements.
Occurring on multiple temporal and spatial scales, impacts range from chronic encroachment of
tides to the episodic destruction associated with coastal storms and flooding. As evidenced by
recent storms such as Katrina and Sandy, management challenges are becoming more acute as
current climate conditions appear to be producing higher intensity or longer duration storms
accompanied by large storm surges that result in significant coastal flooding events.
Within this context, much attention has been focused on the subjects of climate change and sea
level rise. With regard to the latter, many scientists have concluded that sea levels are not only
rising, but at an increasing rate. As shown in Figure 1, projections vary from a low of 0.15
meters (0.5 feet) to a high of 2 meters (>6 feet) by the end of this century. Such a broad range
creates significant issues for coastal managers faced with identifying potential hazards to, and
vulnerabilities of property and infrastructure, prioritizing response actions, and demonstrating to
local governments the need to undertake actions in spite of the unavoidable uncertainties
inherent in century-scale sea level rise projection scenarios. Traditionally (and necessarily)
shorter planning horizons are not easily defined within the context of sea level rise discussions
and effective response actions, implementable at the local level are difficult to identify.
In addition to the issue of defining a suitable planning horizon, the ability of coastal managers to
effectively and efficiently recognize potential vulnerabilities and to educate residents and
community leaders about the threats associated with coastal inundation has been severely limited
by the lack of regional-scale, accurate elevation data. For example, Flood Insurance Rate Maps
(FIRMS), produced by the Federal Emergency Management Agency (FEMA), have long been
standard resources for coastal communities, however, these maps were intended to facilitate the
determination of flood insurance rates and historically have lacked the topographic detail
necessary for focused planning efforts. Until recently the accuracy of relatively low cost
elevation data has been appropriate only for general planning at regional scales and not
appropriate for identifying inundation and flooding impacts over timeframes that meet the needs
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and budgets of most municipalities. Numerical modeling of storm surge, sea level rise, waves, or
sediment transport (coastal erosion) can be effective for regional efforts to understand coastal
evolution, but can also be cost prohibitive. Furthermore, these models are typically too coarsely-
scaled to inform local decisions, appropriately-scaled studies are critical for coastal managers
and municipalities.
Figure 1. Relative sea level rise scenario estimates (in feet NAVD88) for Boston, MA. Modifed after Figure 5 in,
Sea Level Rise: Understanding and Applying Trends and Future Scenarios for Analysis and Planning. Massachusetts
Office of Coastal Zone Management, December 2013. Available at:
http://www.mass.gov/eea/docs/czm/stormsmart/slr-guidance-2013.pdf.)
Based on the long range projections of sea level rise and the catastrophic damages associated
with large coastal storms much attention has been placed on long term strategies to reverse
current climate trends and slow the rate of, or reverse sea level rise. Strategies to reduce Green
House Gas (GHG) emissions, promote green energy, and deal with rising temperatures, glacial
ice melt, and thermal expansion of sea water over the next hundreds of years are being discussed
and debated at the international, national, and state levels. Clearly the planning and costs to
confront these issues are long term, and capital intensive. Lost in these discussions are viable
hazard planning strategies that can be adopted and implemented at the local level within the
shorter planning horizons and financial means of local municipalities.
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Reflective of the limited financial and technical resources of coastal communities and their
unique geography, local responses and strategies to sea level rise and climate change will be
more successful particularly in the context of short-term planning horizons and frequently
changing leadership. Specifically, the short term planning should identify actions or responses
that are:
1) Achievable within an appropriate time frame (e.g., 30 years)
2) Implementable with current technology
3) Financially feasible
4) Politically viable (i.e., not extreme – e.g., wholesale retreat)
5) Adaptable to future scenarios
6) Focused on both infrastructure and natural resources
While sea level rise projections are clearly critical for longer term planning considerations,
particularly for large scale efforts, actual storm tide elevations may provide a more effective
means of characterizing coastal hazard vulnerability for local planning actions. Figure 2 depicts
estimates of various historical storm tide elevations for the Boston area (an easterly facing shore)
for various storms for the 17th - 21st centuries. The current projections for the highest sea level
rise scenario and the NOAA regression rate scenario based on current tide gauge data obtained
from the Boston tide gauge are shown through the year 2100.
Not surprisingly, the graph illustrates that in recent history the storm of record for Boston and
areas to the north of Cape Cod was the “Blizzard of ‘78”. Significantly, this plot indicates that
the storm tides and associated flooding for Boston reached an elevation of approximately 1 meter
(~3 feet) above that of the highest sea level rise projection for the year 2100. The plot further
reveals that earlier estimates of storm tide heights have probably equaled or exceeded the 1978
maximum numerous times since the 17th century.
Using historical data to identify potential storm tide heights, coastal flooding extents, and areas
of potential vulnerability provides important, high certainty planning information to local
communities with several benefits. First, using historical storm tides to identify coastal hazard
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vulnerabilities removes sea level rise and the disparity of projections (Figure 1) from the
discussion of the most appropriate sea level rise elevation to use to develop short term planning
responses. Sea level rise notwithstanding, storm tides of these magnitudes
Figure 2. Historical Storm tides and sea level rise.
have been experienced in the past and are very likely to be experienced again in the future.
Second, storms of record provide an accurate, actual (i.e., indisputable) reference elevation that
towns can plan for when history repeats itself. Finally, as discussed below, using emerging data
gathering technologies to identify inundation impacts, will yield valuable information that can be
used by coastal communities to plan and implement ground level strategy in response to sea level
rise.
Accurate Elevation Data, Record Inundations and Potential Pathways
Over the past ten years, light detection and ranging (lidar) surveys have emerged as a cost-
effective source of coastal elevation data. Covering broad geographic areas with horizontal
accuracies on the order of 3 meters (~10 feet) and vertical accuracies on the order of 15-30 cm
(0.5-1.0 feet), this relatively high resolution topographic information is a valuable initial resource
for coastal managers developing inundation scenarios that can be used to begin to visualize
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threats associated with coastal storms. Despite improvements in vertical accuracy, the use of
lidar alone to map areas of storm vulnerability and to develop community response strategies has
historically been limited. Recognizing data limitations, current guidelines for inundation
modeling using lidar elevation data sets with vertical accuracies of 15 cm (0.5 feet) recommend
analyses be performed at increments of 58.8 cm (~2.0 feet), a resolution clearly too coarse for the
development of local action items. This base level information, however, when supplemented
with area-specific high resolution elevation data to reduce uncertainties, can be used to identify
and prioritize potential coastal hazards at the local level in a cost effective manner.
In 2011, the Natural Resource Conservation Service, United States Department of Agriculture
(NRCS) completed terrestrial lidar surveys of Barnstable County, Massachusetts. The horizontal
and vertical accuracies [can we say what the reported values are?] of this publically available
contemporary elevation data provide a reliable base map and can be used as the foundation for
local action planning.
A primary goal of this Provincetown pilot project is to, using lidar as a base level guide,
accurately map pathways or areas through which storm tides might pass, threatening vulnerable
areas of the town with inundation of varying depths. For purposes of this project, these locations
have been termed ‘storm tide pathways’ or ‘inundation pathways’.
The term ‘storm tide’ refers to the rise in water level experienced during a storm event resulting
from the combination of storm surge and the astronomical (predicted) tide level. Storm tides are
referenced to datums, either to geodetic datums (e.g., NAVD88 or NGVD29) or to local tidal
datums (e.g., mean lower low water (MLLW)). Storm surge refers to the increase in water level
associated with the presence of a coastal storm. As the difference between the actual level of the
storm tide and the predicted tide height, storm surges are not referenced to a datum.
Generally, inundation pathways, by virtue of their elevation relative to the elevation of the storm
tide, provide a direct connection between coastal waters and low lying inland areas. Examples of
pathways that may serve as direct hydraulic connections include: low spots in built environment
(e.g., roads, walkways, dikes, seawalls, etc.); and low spots in natural topography (e.g. low lying
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earthen berms, barrier beaches, and dune systems susceptible to erosion and breaching). Low-
lying infrastructure can also serve as unintended conduits (e.g., storm water system, sanitary
sewers, electrical/utility conduits), however, analysis of potential conduit hydraulics should be
evaluated by a qualified engineer to accurately assess potential vulnerabilities.
As discussed above, to minimize the uncertainties associated with sea level rise projections and
to provide information that is reliable within a 30 year planning horizon, the study used recorded
flood elevations associated with actual coastal storm tides. As discussed below, research of
available records and studies indicates that, as for Boston, the best approximation of the storm of
record for Provincetown would appear to be storm tide elevation of the Blizzard of ’78. This
storm tide was recorded by Dr. Graham S. Giese of the Center for Coastal Studies in
Provincetown to be 9.36 feet (2.85 meters) NAVD88. This elevation represents an actual storm
tide elevation that is approximately 5 feet above contemporary mean higher high water (MHHW)
and approximately 11 feet above contemporary mean sea level (MSL).
METHODS
Datums: Definition and Uses
A datum is a reference point, line, or plane from which linear measurements are made.
Horizontal datums (e.g., the North American Datum of 1983 (NAD83)) provide a common
reference system in the x, y-dimension from which a point’s position on the earth’s surface can
be reported (e.g., latitude and longitude). Similarly, vertical datums provide a common reference
system in the z-direction from which heights (elevation) and depths (soundings) can be
measured. For many marine and coastal applications, the vertical datum is the height of a
specified sea or water surface, mathematically defined by averaging the observed values of a
particular stage or phase of the tide, and is known as a tidal datum (Hicks, 1985).1 It is important
to note that as local phenomena, the heights of tidal datums can vary significantly from one area
1 The definition of a tidal datum, a method definition, generally specifies the mean of a particular tidal phase(s)
calculated from a series of tide readings observed over a specified length of time (Hicks, 1985). Tidal phase or stage
refers to those recurring aspects of the tide (a periodic phenomenon) such as high and low water.
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to another in response to local topographic and hydrographic characteristics such as the geometry
of the landmass, the depth of nearshore waters, and the distance of a location from the open
ocean (Cole, 1997).2
As almost every coastal resident knows, tides are a daily occurrence along the Massachusetts
coast. Produced largely in response to the gravitational attraction between the earth, moon and
sun, the tides of Massachusetts are semi-diurnal - i.e., two high tides and two low tides each tidal
day.3 Although comparable in height, generally one daily tide is slightly higher than the other
and, correspondingly, one low tide is lower than the other (Table 1). Tidal heights vary
throughout the month with the phases of the moon with the highest and lowest tides (referred to
as spring tides) occurring at the new and full moons. Neap tides occur approximately halfway
between the times of the new and full moons exhibiting tidal ranges 10 to 30 percent less than
the mean tidal range (NOAA, 2000a.)
Tidal heights also vary over longer periods of time due to the non-coincident orbital paths of the
earth and moon about the sun. This variation in the path of the moon about the sun introduces
significant variation into the amplitude of the annual mean tide range and has a period of
approximately 18.6 years (a Metonic cycle), which forms the basis for the definition of a tidal
epoch (NOAA, 2000a). In addition to the long-term astronomical effects related to the Metonic
cycle, the heights of tides also vary in response to relatively short-term seasonal and
meteorological effects. To account for both meteorological and astronomical effects and to
provide closure on a calendar year, tidal datums are typically computed by taking the average of
the height of a specific tidal phase over a 19-year period referred to as a National Tidal Datum
Epoch (NTDE) (Marmer, 1951). The present NTDE, published in April 2003, is for the period
1983-2001 superseding previous NTDEs for the years 1960-1978, 1941-1959, 1924-1942 and
1960-1978 (NOAA, 2000a).
2 For example, the relative elevation of MHW in Massachusetts Bay is on the order of 2.8 feet higher than that
encountered on Nantucket Sound and 3.75 feet higher than that of Buzzards Bay.
3 A tidal day is the time or rotation of the earth with respect to the moon, and is approximately equal to 24.84 hours
(NOAA, 2000a). Consequently, the times of high and low tides increase by approximately 50 minutes from calendar
day to calendar day.
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Table 1. Common Tidal Datums (Source: NOAA, 2000b).
Identifying existing Inundation pathways (IP) in a dynamic coastal environment is a multi-step
process. First, a datum referenced tidal profile is established for the local area. For Provincetown
Harbor, existing benchmarks for NOAA CO-OPS tidal station # 8446121 were recovered,
occupied by the Center’s Real-Time-Kinematic Global Positioning System (RTK GPS) and
referenced vertically to the North American Vertical Datum of 1988 (NAVD88). Tidal station #
8446121 was established in Provincetown Harbor on March 5, 2010 and tidal datums referenced
to the station datum and reported on the NOAA CO-OPS website [tidesandcurrents.noaa.gov],
were then converted to NAVD88 for reference throughout the project. Figure 3 shows the
contemporary tidal datums for Provincetown Tidal Station # 8446121 referenced to NAVD88
and Mean Lower Low Water (MLLW). As shown in Figure 3, this tidal profile is compares
closely with resemble that for Boston Harbor.
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Figure 3. Tidal datum profiles for Boston and Provincetown.
Having established a datum referenced tidal profile, historical coastal storms were then
researched to determine significant storm tide (storm surge + astronomical tide) events that have
occurred since 1921, the beginning of the continuous tidal record for Boston Harbor. As noted
above, the storm of record for this study was identified to be 9.36 feet NAVD88.
In addition to the major inundation that often accompanies coastal storms, many coastal
communities are also beginning to experience occasional minor flooding during spring tides as
relative sea level continues to rise. Often referred to as nuisance flooding since it is rarely
associated with dramatic building and property damage, this type of minor flooding is becoming
more common with chronic impacts that include overwhelmed drainage systems, frequent road
closures, and the general deterioration of infrastructure not designed to withstand saltwater
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immersion (NOAA, 2014). A complete discussion of the results of this research is presented
below in the Results and Discussion section.
Spatial Analysis
Based on the Provincetown Harbor tidal characterization discussed below, analysis begins in the
laboratory. Here, using state-of-the-art software and powerful computers to examine the existing
elevation (lidar) data using varying water levels to identify potential IPs.
A list of potential IPs begins with the desktop analysis of the best available synoptic elevation
data for the study area. The latest lidar data were downloaded from the NOAA website
(https://coast.noaa.gov/digitalcoast/). The website has default settings for horizontal and vertical
reference datums, spheroid and projection as well as units (metric vs standard). Metadata for
these data indicate horizontal and vertical accuracies of +/- 1.0 m and +/- 0.15 m respectively.
Recognizing that previous lidar data sets produced for the area possessed double the vertical
uncertainty. it is important to note that use of the most accurate and most recent lidar for the
desktop analysis greatly facilitates filed verification of IPs
For the purposes of this study, Center staff altered the default download parameters for ease of
use within several software packages. Regardless of the spatial parameters, the positional
information within the lidar are not altered. The final data products at the conclusion of the
project are reported in feet referenced to the MLLW datum for Provincetown Harbor to simplify
use at the local level.
All data are downloaded in a raster format and brought into ESRI’s ArcGIS software and the
raster is divided into smaller tiles to facilitate data analysis and archiving. These lidar tiles are
then brought into QPS’s Fledermaus data visualization software. While acquired by CCS as an
integral component of its Seafloor Mapping Program, the Fledermaus software package has
proven to be an ideal platform for the initial desktop identification of IPs in which the accuracy
of the initial analysis is limited primarily by the uncertainty and resolution of the lidar itself.
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The power of Fledermaus lies in its ability to work with very large data files quickly. Individual
files can be multiple GBs in size, yet Fledermaus rapidly moves through the data for visual
inspection, ‘fly-throughs’ and similar functions. Horizontal planes, representing an identified
potential IP elevations can be added to a Fledermaus project or ‘scene’ and these planes can be
increased or decreased to simulate changes in water levels, IP elevations, or storm tide conditions
(Figure 4).
Figure 4. Downtown Provincetown, draped aerial photograph over Lidar surface. Blue areas are horizontal plane
created in Fledermaus at increasing elevation. Lower left is example of a storm-tide pathway with accompanying
profile. These images were generated before field work to identify potential IPs.
Another invaluable feature of this data visualization software is the ability to drape a 2
dimensional data set such a vertical aerial photograph over a 3D dataset (lidar). This allows the
analyst to better document the IP and also to gain valuable information as to the substrate the IP
is located in and its landscape setting. For example, an IP found on or near a naturally evolving
coastal feature such as a beach or dune would be characterized differently than one atop a
concrete wall or other relatively static feature. This is important not only for a final assessment
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of the most appropriate way to address an IP in a critical area but also serves to inform the field
team to more closely examine areas that are naturally evolving and to be vigilant for other to
potential IPs in close proximity to the identified point but not present in the lidar. Although as
discussed below the GPS was critical for the location of individual IPs, the ability to drape aerial
photographs also proved extremely helpful, serving as a quick means of field orientation while
placing the potential IP in its broader geographic context. The terrestrial lidar collected in the
Spring of 2011 by the NRCS for all of Barnstable county used as the base mapping for the
desktop or phase one analysis provided an accurate and extremely useful synoptic elevation
dataset that facilitated fieldwork discussed below.
Field Work
Once an inventory of possible IPs was compiled in the desktop exercise, an extensive fieldwork
assessment program was conducted to verify the presence or absence of the IP. Further, where
the suspected presence of an IP was confirmed, an accurate horizontal and vertical location was
obtained.
A Trimble® R8 GNSS receiver utilizing Real-Time-Kinematic GPS (RTK-GPS) was used for all
positioning and tide correction fieldwork. The Center subscribes to a proprietary Virtual
Reference Station (VRS) network (KeyNetGPS) that provides virtual base stations via cellphone
from Southern Maine to Virginia. This allows the Center to collect RTK-GPS without the need
to setup a terrestrial base station or post-process the GPS data in any way, reducing mobilization
and demobilization costs, streamlining the field effort, and maximizing vessel-based survey time.
The Center undertook a rigorous analysis of this system to quantify the accuracy of this network
(Mague and Borrelli, in prep). Over 25 National Geodetic Survey (NGS) and Massachusetts
Department of Transportation (DOT) survey control points, with published state plane coordinate
values relating to the Massachusetts Coordinate System, Mainland Zone (horizontal: NAD83;
vertical NAVD88), were occupied. Control points were distributed over a wide geographic area
of the Cape and Islands.
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Multiple observation sessions, or occupations, were conducted at each control point with
occupations of 1 second, 90 seconds, and 15 minutes. To minimize potential initialization error,
the unit was shut down at the end of each session and re-initialized prior to the beginning of the
next session. The results of each session (i.e., 1 second, 90 second, and 15 minute occupations)
were averaged to obtain final x, y, and z values to further evaluate the accuracy of short-term
occupation. Survey results from each station for each respective time period were then compared
with published NGS and DOT values and the differences (error) used to assess and quantify
uncertainty. Significantly, there was little difference between the error obtained for the 1 second,
90 second, and 15 minute occupations. The overall uncertainty analysis for these data yielded an
average error of 0.008 m in the horizontal (H) and 0.006 m in the vertical (V). An RMSE of
0.0280 m (H) and 0.0247 m (V) and a National Standard for Spatial Data Accuracy (95%) of
0.0484 m (H) and 0.0483 m (V).
The ability to conduct accurate fieldwork was a critical component of the IP verification process
for several reasons. First, lidar collected via aerial surveys and the post-processing involved can
introduce uncertainties that exaggerate or diminish features in three dimensional data and, as a
result, obscure or conflate the presence and scale of a storm-tide pathway. These effects have
been shown to be associated with ‘bare earth’ models where elevations tend to be “pulled up”
adjacent to areas where buildings have been removed and “pulled down” in areas where bridges
and roads cross streams or valleys.
Figure 5. Example of ‘pull up’ near water tower in Provincetown. Dotted line is more representative of elevations at
the water tower. Blue line in image is location in profile. Profile units = meters (Vert. NAVD88, Hor. NAD83).
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Second, the use of an RTK-GPS instrument affords the high accuracy necessary for acquiring
and verifying 3-dimensional positional data. In this way. GPS data is used to corroborate or
eliminate the presence of IPs identified from the desktop lidar analysis. Third, due to the
dynamic nature of coastal environments, visual assessment conducted as part of the field work
sometimes reveals IPs that are not visible in a desktop analysis of lidar data. Lastly, and also
related to the ephemeral characteristics of the areas proximate to the shoreline, even the most
current lidar may rapidly out of date in certain dynamic areas. Consequently, the GPS survey
provides real time information to eliminate IPs that may have appeared in the lidar but no longer
exist due to changes in landform.
At the completion of the desktop analysis, all potential IPs were compiled into a database with x,
y, z coordinates and uploaded into the Center’s GPS. Using the “stakeout” function and aerial
photographs to navigate to the precise location identified with the lidar, each potential IP
location was inspected by a 3-person team and occupied with the GPS mobile unit. The field
team inspected? the lidar data via a laptop in the field in real-time while RTK-GPS data were
collected at each location. This served three purposes, first to map the real-world location of the
IP identified during the desktop analysis of the lidar data; the second to increase the positional
accuracy of the verified IP itself; and lastly to confirm the positional accuracy of the lidar data.
Significantly, using the GPS instrument to navigate to the location of a potential IP also afforded
the field crew the opportunity to investigate alternative or additional IPs based on visual
inspection of the area. Many coastal sites have very low relief (relatively flat) and verifying
whether an IP existed, its exact location, and the direction of water flow required professional
judgment facilitated with experience in the principles and practices of land surveying as well as a
thorough knowledge of coastal processes.
After the field work was completed, the team returned to the laboratory to cull those points
determined not be IPs, incorporate newly identified IPs documented in the field, and provide all
IPs with horizontal and vertical position information, substrate and geographic context labels,
and other pertinent information for inclusion into a comprehensive database. Once quality
controlled, the database was brought into the project GIS for use as an archive of important IP
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information. Importantly, the database was annotated to note those areas where the lidar was
found to correlate poorly with current conditions or real-world position as determined by the
GPS observations and professional judgment was necessary to accurately represent the IP.
With the compilation of the comprehensive IP database, the file was brought into ESRI’s ArcGIS
to visualize IP locations to provide a working or living archive for local managers to: 1)
proactively address IPs prior to storm events; 2) prepare for approaching storms; and 3) to plan
for longer-term improvements to mitigate other IPs.
Although field delineation of inundation extents for each IP is beyond the scope of the project,
the lidar data was used in 2 interactive ways to visualize IP inundation levels and hopefully
maximize the utility of the final product. The first depiction is referred to as the Pathway
Activation Level (PAL). The PAL represents the elevation at which water begins to flow over an
IP. To visualize the PAL its extent was delineated as a continuous contour derived from the lidar
elevation data. For example, based on the GPS fieldwork, an IP with a PAL of 13.6 feet MLLW
indicates that the moment the water level reaches 13.6 feet MLLW water will begin to flow
inland via the IP. Using the data visualization software, a water elevation of 13.6 feet MLLW
was then used to trace the area that would hypothetically be inundated (assuming storm tide
water levels are maintained long enough for the entire area to become flooded). If a storm tide
recedes after reaching the PAL, then this depiction can be viewed perhaps as a “best” case
scenario for impacts associated with a specific storm tide. If water levels were to continue to rise
above the PAL, higher than 13.6 feet MLLW, however, obviously more area would be inundated
leading to the need for a second means of visualizing IPs.
For this reason and to increase the utility of the IP data and make visualizations more user
friendly for local mangers, Inundation Ranges (IRs) were developed for the entire study area
rather than creating PALs for every IP and all potential flood elevations. After several attempts at
visualizing IPs and recognizing that floodplain mapping was not a goal of the project, it was felt
that the use of IRs would be the clearest way of making the data useful while addressing the
associated with the lidar. The IR visualizations were based on a series of iterations of potential
inundation scenarios, including nuisance flooding. After reviewing the various scenarios, the
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lower end of the IR range was begun at the highest Spring tide of the year. Inundation ranges
were developed in 1 foot intervals to maximum elevation of the Storm of Record plus three feet
and inundation planes extracted for each range. In addition to providing an upper limit to project
elevations, it was felt that using the Storm of Record +1ft; the Storm of Record +2ft; and the
Storm of Record +3ft. also provides a useful representation of future sea level rise scenarios that
would have practical implications for local managers.
RESULTS AND DISCUSSION
Provincetown Harbor Tidal Profile
As noted above in the Methods section, to document IPs an elevation profile for the community
was developed to characterize both storm tides and nuisance flooding within its landscape and
landform setting. In addition to the more common tidal datums of mean high water springs
(MHWS), mean higher high water (MHHW), mean high water (MHW), and mean sea level
(MSL) this tidal profile also includes datum referenced storm tides of the past, including the
elevation of the maximum storm tide experienced (i.e., the storm of record), and an estimate of
potential future storm tides reflected by adding three feet to the storm of record.
The storm of record for the Boston Tide Gauge (#8443970) occurred on February 7, 1978 with a
maximum storm tide elevation of 9.59ft NAVD88. Occurring at approximately the time of the
predicted or astronomical high tide, the storm surge was approximately 3.5 feet. By comparison,
the maximum storm tide elevation experienced during the blizzard of January 27, 2015 was
8.16ft NAVD88. Occurring shortly after the astronomical high tide, this elevation resulted from
the combination of an astronomical tide height of 4.79ft NAVD88 and a storm surge of 3.37 feet.
Significantly the maximum storm surge for this event was observed to be 4.5 feet, however,
because it occurred close to the time of the astronomical low water the corresponding storm tide
elevation was only -1.1ft NAVD88. Had the maximum storm surge occurred approximately 6
hours earlier at the time of the astronomical high tide, the resulting storm tide elevation would
have been 9.2ft NAVD88, approximately 5 inches below the elevation of Boston’s storm of
record and 2 inches below the maximum recorded elevation for the same storm in Provincetown.
Recognizing the significance of not only the magnitude of the predicted storm but the time it will
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occur relative to the stage of the tide, the National Weather Service in Boston, MA maintains an
informative website that estimates storm surge and total water level at various stations
(http://www.weather.gov/box/coastal) as coastal storms approach New England. Used in
conjunction with IPs, this information has the potential to provide valuable short-term response
information to emergency managers.
The effects of storm tides on coastal communities are dependent on many factors. These include
coastal orientation (e.g., east facing v. south facing shores); the elevations of astronomical tides
(e.g., the elevation of mean high water in Boston Harbor is 4.31ft NAVD88 v. the elevation of
mean high water for Woods Hole is 0.56ft NAVD88); general characteristics of astronomical
tides (e.g., the average range – MHW minus MLW – of Boston tides is 9.49 feet while that of
Woods Hole tides is only 1.79 feet); topography (e.g., the elevation of the land relative to the
community tidal profile); nearshore bathymetry (e.g., the deeper the water relative to shore, the
greater the potential wave energy); topographic relief (i.e., a measure of the flatness or steepness
of the land with flatter areas more sensitive to small changes in water levels); the nature of
coastal landforms (e.g., the rock shorelines of the North shore v. the dynamic sandy shorelines of
Cape Cod); and the vertical relationship between historical community development and
adjacent water levels (e.g., development in Boston began in the early 17th century with the water
levels at that time influencing the elevation of not only pile supported structures but large scale
land-making – filling – projects). With such variation in physical and cultural characteristics, the
initial step in the identification of storm tide pathways for a community is the development of a
datum-referenced tidal profile.
Based on conversations with Center staff, on December 31, 2014, the U.S. Geological Survey
(USGS) Water Resources installed a datum-referenced (NAVD88, feet) station in Provincetown
Harbor. This station now provides a real-time source of 15-minute datum-referenced, water level
observations for north Cape Cod Bay. The gage is accessible at the following website:
http://waterdata.usgs.gov/ma/nwis/uv/?site_no=420259070105600&PARAmeter_cd=00065,000
60.
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Prior to 2015, tidal and water level information for Provincetown Harbor was established based
on a secondary NOAA tide station (#8446121) established within the Harbor on March 5, 2010
and water level observations recorded for a period of four months from April to July, 2010. The
gage was referenced to a station datum memorialized with four benchmarks established around
the harbor. Tide station #8443970, the primary tide station located in Boston Harbor and the
longest continuously operating station in Massachusetts (since 1921) was used as the control
station to publish local tidal datum elevations. These datums represent mean tidal elevations for
the 1983 to 2001 National Tidal Datum Epoch (NTDE). Information on the NOAA tide station
#8446121 can be found at http://tidesandcurrents.noaa.gov/datums.html?id=8446121.
Recognizing that tidal heights vary with location, the published tidal datums were converted to
NAVD88 for reference throughout the project area and for direct comparison with the tidal
profiles of other areas. To accurately convert elevations from the Station Datum to NAVD88, the
four benchmarks for tidal station # 8446121 were recovered and occupied for 15 minutes each by
the Center’s RTK GPS to obtain benchmark elevations referenced vertically to NAVD88. Since
each benchmark is also referenced to the station datum the published tidal information for #
8446121 was converted to NAVD88. Figure 3 depicts contemporary tidal datums for
Provincetown Harbor referenced to NAVD88 and mean lower low water (MLLW), the local
tidal or chart datum.
As noted above, NOAA tide station #8443970 located in Boston Harbor is a primary tide station
and has been used historically as the control station for published tide information in Cape Cod
Bay. Figure 3 depicts the tidal profile for Boston Harbor referenced to NAVD88 and MLLW.
Referencing tidal heights to NAVD88 allows for Provincetown and Boston Harbors to be
compared directly and as shown in Figure 3 the tidal profiles for the two harbors are very close.
The Provincetown tidal profile was completed with historical research of significant coastal
storms to determine, where possible, the elevation of the associated storm tide (astronomical tide
+ storm surge). APPENDIX A includes a list of references summarizing major coastal storm
events and associated storm tide elevations.
- 20 -
With similar tidal profiles, Boston Harbor was used as a proxy for Provincetown Harbor. Table
2 summarizes the highest water levels for Boston Harbor since May 3, 1921 when tidal station
#8443970 was installed. Since this time, the maximum water level for Boston Harbor was
observed to be 9.59ft NAVD88 on February 7, 1978 during the “Blizzard of ‘78”.
While no tide station was available at this time in Provincetown Harbor, Dr. Graham S. Giese,
co-founder of the Center for Coastal Studies, was on scene at MacMillan Wharf to record
observations of water height during the Blizzard. Significantly, Dr. Giese referenced the water
readings to a 1933 NOAA tidal benchmark, which was recovered as part of this project and
occupied with the Center’s RTK GPS instrument to convert water level readings to NAVD88.
Based on this work, the elevation of the Blizzard of ’78 storm tide for Provincetown Harbor was
determined to be 9.36ft NAVD88. Interestingly, this was found to be 0.71 feet above the
maximum water level of 8.65ft NAVD88 measured by CCS during the January 27, 2015
blizzard.
Table 2. Significant historical storm-tides recorded at the Boston Harbor Tide Station. (#8443970)
Boston&Harbor&(Station&#8443970)
Highest&Recorded&Water&Lev els
Rank Date NAVD88&(Ft.) MLLW&(Ft.)
1 2/7/1978 9.59 15.11
2 1/2/1987 8.69 14.21
3 10/30/1991 8.66 14.18
4 1/25/1979 8.53 14.05
5 12/12/1992 8.52 14.04
6 12/29/1959 8.49 14.01
7 4/18/2007 8.29 13.81
8 5/25/2005 8.27 13.79
9 2/19/1972 8.19 13.71
10 12/27/2010 8.19 13.71
11 5/26/2005 8.16 13.68
12 1/27/2015 8.13 13.65
13 5/26/1967 8.11 13.63
14 6/5/2012 8.07 13.59
15 3/4/1931 7.97 13.49
16 11/30/1944 7.87 13.39
17 1/20/1961 7.85 13.37
18 4/21/1940 7.83 13.35
- 21 -
Table 3 represents the resulting Provincetown Harbor tidal profile constructed for use in
screening potential IPs. As shown by the table, the maximum water level elevation considered in
this analysis was the storm tide of record plus 3 feet (12.36ft NAVD88). To evaluate potential
nuisance flooding associated with more frequent non-storm tidal events, the lowest elevation
considered in the IP analysis was that of the maximum predicted high tide for 2015 (6.44ft
NAVD88). A review of the NOAA tide charts for Provincetown Harbor indicated that the
maximum astronomical high water predicted for 2015 was 6.44ft NAVD88.
Table 3. Provincetown Harbor Tidal Profile
Provincetown+Harbor+Tidal+Profile
Station:+8446121
NAVD88+(FT) MLLW+(FT) Comments
Storm+of+Record+++++++++++++++++++++++++
plus+3+Feet
12.36 17.82
Upper+Limit+of+Storm+++++++++++++++++++++++++++
Tide+Pathway+Analysis
Blizzard(of('15(if(max(storm(surge(
occurred(at(((((((((((((((((((((((((((((((((((((
Max(Predicted(High(For(Year
10.74 16.20
Max.(Storm(Surge(=(4.30'((((((((((((((((((
occurred(at(approx.(low(tide
Blizzard+of+1978+++++++++++++++++++++++++++
Maximum+Storm+Tide
9.36 14.82
Storm+of+Record+++++++++++++++++++++++++++++++++++++++
Based+on+CCS+Observations
Blizzard(of('15((if(max(storm(surge(
had(occurred(at(Predicted(High
9.19 14.65
Max.(Storm(Surge(=(4.30'((((((((((((((((((
occurred(at(approx.(low(tide
Blizzard(of(2015(((((((((((((((
Maximum(Storm(Tide
8.65 14.11
Based(on(CCS(Observations(((((((((((((((
Storm(Surge(=(3.65',(Predicted((High(
Tide(El.(=(5.00'(NAVD88(at(0430(hrs
Maximum((2015(((((((((((((((((((
Predicted(High
6.44 11.90
From(2015(NOAA(Tide(Predictions
MHWS 5.54 11.00
NOAA(Tide(Station(#8446121
MHHW 4.62 10.08
NOAA(Tide(Station(#8446121
MHW 4.16 9.62
NOAA(Tide(Station(#8446121
MSL -0.43 5.03
NOAA(Tide(Station(#8446121
MTL -0.48 4.98
NOAA(Tide(Station(#8446121
MLW -5.13 0.33
NOAA(Tide(Station(#8446121
MLLW -5.46 0.00
NOAA(Tide(Station(#8446121
- 22 -
Inundation Pathways
Desktop analysis of the lidar data in phase one yielded 81 potential IPs throughout the study
area. Each location was inspected by the 3-person field team. The team incorporated the lidar
data via a laptop in the field in real-time while RTK-GPS data were collected at each location.
Where necessary, IPs were moved based on field observations when the team determined the
2011 lidar was not representative of the real-world terrain in 2015.
The final IP dataset developed for this project contains 72 storm-tide pathways. There are several
types of IPs included in this dataset: standard Storm Tide Pathways (IPs) as discussed above;
‘spillways’ (IP-S); ‘roadways’ (IP-R); and unverified (IP-U) (Table 4). These sub-types, while
not initially anticipated, were developed to reflect different on-the-ground morphologies and
techniques needed to identify and/or describe potential inundation at these locations.
Pathways
Standard (IP)
Spillway (IP-S)
Roadway (IP-R)
Unverified (IP-U)
72
43
15
9
5
Table 4. Summary of Storm Tide Pathways
The ‘standard’ IP can be described as a relatively narrow low-lying area where flowing water
would be directed inland by the natural topography (Figure 6). The term ‘spillway’ was
developed as a way to reflect to reflect the low relief of the area. The IP-S are situated in very
flat areas and are representative of long broad weir-like formations as opposed to the discrete
point-like nature of the standard IPs. Actions planned to mitigate spillway IPs generally require
action along a broad area and detailed topographic surveys in order to minimize associated
flooding during future events. While difficult to visualize these areas may be of great concern
precisely because of the characteristic that makes them a spillway, a broad flat area of inundation
with no clear, narrow pathway for flood waters to enter.
- 23 -
Figure 6. Top: Location of initial locations for IPs based on desktop analysis of lidar. Middle: final location of IPs
based on field work. Bottom: pre- and post-fieldwork IPs, several IPs were found based on the fieldwork that were
evident in the lidar data.
- 24 -
The roadways IP (IP-R) were delineated as they are associated with those inundation pathways
that generally only impact roadways. All nine IP-Rs found in this study were located along Route
6, near East Harbor (Pilgrim Lake). Although relatively low lying (12.2 – 14.2 ft MLLW) the
path water would need to take through the IP-Rs would be circuitous and likely occur only when
storm surge and wind conditions prevented tidewater from draining over several tidal cycles. As
mentioned above, the focus of this study is on identifying and locating storm tide pathways and it
does not attempt to quantify the probability of flooding events., Recognizing this, it is likely that,
under the right storm conditions, these IP-Rs could receive tidewater flowing from Cape Cod
Bay, flooding the gully directly
south of Route 6 and then
flowing over the road and into
East Harbor. While this gully is
deep it appears possible that it
could fill under certain storm
conditions and if deemed critical
further analysis could be
performed by a qualified coastal
engineer.
Finally, an unverified IP (IP-U)
was defined to be an IP that was
identified during the lidar analysis, but was unable to be located and occupied by the field team.
The lidar used for this study is a ‘bare earth’ lidar data set, which is typical for these types of
analyses. As discussed above, during the processing of these data the vegetation, (tress, bushes,
beach grass, salt marsh, etc.) and structures (houses, buildings, etc.) are removed from the data,
hence the ‘bare earth’ name. Therefore, certain low spots found in the lidar analysis could not be
accessed or were otherwise inaccessible (private property) (IP-U figure) or may in fact have been
artifacts of the bare-earth process.
The 5 IP-Us found in this study are in low areas that will experience water flowage but the
Figure 7. Example of an IP-U. This was an unverified IP as the field team could
not lawfully gain access to the exact location of the IP.
- 25 -
precise location of the IP is unknown.
With further analysis the precise location
of the IP may be ascertained, but remains
beyond the scope of this study.
A tide staff was installed in the harbor at
the direction of the Harbormaster. This is a
custom-made fiberglass tide staff built to
be visible at a distance (Figure 8). This
will serve several purposes: first, it will
link the elevation of the inundation
pathways to a visual water level for the
Harbormaster’s office. During storm
events the actual level of the water will be
easily noted from the safety of the
Harbormaster’s office. Then action items
can be developed based on present water
levels, peak of upcoming high tide and
other considerations. For example, an
elevation of 11.7 ft (MLLW) is seen at the
tide staff, but high tide is still 1 hour away
and is known to raise ~2 feet in that one
hour. Town managers can prepare for a
13.7 ft (MLLW) flood event. The storm
surge may lessen, winds may change direction, but the town now has reliable data, as it happens,
upon which to base storm preparations and response.
The tide staff will also provide the critical, real-time connection between the water levels in the
harbor with the map of inundation pathways. Following the example above, if the harbormaster
anticipates a 13.7 ft (MLLW) inundation event then all of the IPs that are at or near that level
will have to be addressed in some way (Figure 8).
Figure 8. Top section of tide staff prior to installation.
Pictured, R. McKinsey-Provincetown Harbormaster.
- 26 -
Finally, the tide staff will also provide the public with a more substantial and tangible
understanding of coastal inundation and how it relates to their preconceived notions of water
levels. For example, the general public typically is not aware that the difference between a 10-
year storm and a 100-year storm can be as little as 12-18 inches (FEMA, 2014). By reinforcing
that relatively minor changes in water level can dramatically alter the impact of coastal storms
have can be useful not only in improving the understanding of storms, but the vulnerability of
low-lying coastal areas to small changes in water levels. This will also be useful for putting sea
level rise projections of, for example, 1 foot over a given time period into its proper context. A 1-
foot rise in sea level, or storm surge can have profound impacts on the vulnerability of coastal
areas not only from storms or sea level rise but also from the increasing frequency of nuisance
flooding and the extent of the associated flooding.
Figure 9. Example of colored coded inundation pathways that match the tide staff elevations in MLLW ft.
This study is deterministic rather than probabilistic, the focus was on creating a high-resolution
map of where inundation would occur and when, or at what water level inundation would begin.
- 27 -
The uncertainties associated with quantifying the how and why of coastal flooding, the modelling
of storm surge, sea level rise, waves, etc. are prohibitive when dealing with inundation events at
the local level by coastal managers. These uncertainties and others are largely removed by the
‘where and when’ of mapping inundation pathways.
- 28 -
Appendix A
A Summary of References Concerning Major Coastal Storm Events, Associated Storm
Tide Elevations ,and Tidal Datums
Bodnar, A.N. 1981. Estimating Accuracies of Tidal Datums from Short term Observations.
Technical Report CO-OPS 0074. U.S. Department of Commerce, National Oceanic and
Atmospheric Administration, National Ocean Serve, Center for Operational Oceanographic
Products and Services. March 1981. 32 pages.
Cole, L.A. 1929. Tidal Bench Marks State of Massachusetts. Special Publication No. 155.
Department of Commerce,. U.S. Coast and Geodetic Survey. Washington. 1929. 39 pages.
Crane, D.A. 1962. Coastal Flooding in Barnstable County, Cape Cod Mass. Massahcuetts Water
resources Commission. Charles I. Sterling, Director. December 1962. 63 pages.
FEMA, 2014. Flood Insurance Study, Barnstable County, Massachusetts (All Jurisdictions).
Federal Emergency Management Agency, p. 110.
Flick, R. Murray, J. and Ewing, L 2003.. Trends in United States Tidal Datum Statistics and Tide
Range. Journal Of Waterway, Port, Coastal And Ocean Engineering. ASCE. July/August 2003.
Pages 155–164.
Giese, G.S. 1978. Effects of the Blizzard of 1978 on the Coastline of Cape Cod. Provincetown
Center for Coastal Studies. Chapter in “The Bizzard of 1978”, Effects of the Coastal
Environments of Southeastern New England. Boston State College. 1978.
Gill S. K. and Schultz J. R. Tidal Datums and Their Applications. NOAA Special Publication,
NOS CO-OPS 1. February, 2001. 111 pp.
Kedzierski, J. 1992. High Water Marks of the Halloween Coastal Storm, October 1991. U.S.
Army Corps of Engineers, Waltham MA. October 1992. 445 pages.
Massachusetts Geodetic Survey. 1939. Storm Tide Hurricane of September 1938 in
Massachusetts. Supplemented by High Water Data Floods of March 1936 and September 1938
in a separate volume herewith. Mass. WPA Project No. 16565, 100Nashua Street, Boston, MA.
Sponsored by: Massachusetts Department of Public Works. 1939. 22 pages plus maps and tables.
Massachusetts Office of Coastal Zone Management. 2013. Sea Level Rise: Understanding and
Applying Trends and Future Scenarios for Analysis and Planning. Executive Office of Energy
and environmental Afairs. December 2013. 22 pages.
McCallum, B.E., et. al. 2013. Monitoring Storm Tide and Flooding from Hurricane Sandy along
the Atlantic Coast of the United States, October 2012. Open-File Report 2013-1043. U.S.
Department of the Interior. U.S. Geological Survey. 42 pages.
- 29 -
Natural Disaster Survey Report. 1992. The Halloween Nor’easter of 1991. East Coast of the
United states…Maine to Florida and Puerto Rico. October 28 to November 1, 1991. U.S.
Department of Commerce. National Oceanic and Atmospheric Administration. National Weather
Service. June 1992. 101 pages.
Peterson, K.R. and Goodyear, H.V. 1964. Criteria for a standard Project Northeaster for New
England North of Cape Cod. National Hurricane Research Porject, Report No. 68. U.S.
Department of Commerce, Weather Bureau. Washington D.C. March 1964. 66 pages.
Richardson, W.S., Pore, N.A., and Feit, D.M. 1982. A Tiude Climatology for Boston,
Massachusetts. NOAA technical Memorandum NWS TDL 71. Techniques Development
Laboratory, Silver Springs, MD. November 1982. 67 pages.
Sweet, W., Park, J., Marra, J., Zervas, C., Gill, S. 2014. Sea level Rise and Nuisance Flood
Frequency Changesaround the United States. NOAA Technical Report NOS CO-OPS 073. U.S.
Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean
Serve, Center for Operational Oceanographic Products and Services. June 2014. 58 pages.
U.S. Army Corps of Engineers. 1988. Tidal Flood Profiles New England Coastline. Prepared by
the Hydraulics and Water Quality Section New England Division. September 1988. 29 pages.
Weber, K.M., List, J.H., and Morgan, K.L.M. 2004. An Operational Mean High Water datum
for Determination of Shoreline Position from Topographic Lidar Data. Open-File freport 2004-
xxx. U.S. Department of the Interior. U.S. Geological Survey. June, 2004. 124 pages.
Zervas, C. 2013. Extreme Water Levels of the United States1893-2010. NOAA Technical Report
NOS CO-OPS 067. U.S. Department of Commerce, National Oceanic and Atmospheric
Administration, National Ocean Serve, Center for Operational Oceanographic Products and
Services. September 2013. 200 pages.
Zervas, C. 2005. Response of Extreme Storm Tide Levels to Long-term Sea Level Change.
NOAA/National+Ocean+Service+Center+for+Operational+Oceanographic+Products+and+Services.+
2005+IEEE.++6+pages.+
Technical Report
Full-text available
Coastal tourism, recreational use and enjoyment of natural, coastal resources, and the ecosystem services these resources provide are large contributors to the State’s economy. To sustain activities such as these, managers, first-responders, and public works professionals in low-lying coastal communities need information in real-time, and for future planning purposes, that is responsive to the threats posed by coastal hazards such coastal storms and related flooding on a scale commensurate with their responsibilities. The mapping of storm tide pathways provides town staff and the public with contemporary information on the location of the potential pathways that can, depending on the magnitude of a storm, convey coastal flood waters inland enabling communities to respond to real time events and address future inundation. Storm tide pathways describe spatially how coastal waters will flow inland during a flooding event associated with storm surge, extreme high tides, or sea level rise. Storm tide pathways mapped along Cape Cod Bay shores are visualized in ½ foot increments starting at the elevation of the highest annual high tide up to the project storm of record plus ~4 feet to account for future sea level rise. Field work to verify and locate pathways accurately was conducted over 19 days starting in March through July and in October of 2019 in Barnstable, Brewster, Dennis, Eastham, Orleans, Sandwich, Wellfleet, and Yarmouth along the Cape Cod Bay shoreline. A total of 1,646 pathways were identified in the initial desktop analysis. Field verification work resulted in final database total of 1,505 pathways along the 10 towns from the Cape Cod Canal to Race Point in Provincetown. Presently, many low-lying coastal areas flood regularly during high water storm events with some beginning to flood during monthly spring tides. To illustrate the nature of the future threat faced by low-lying communities this study has identified 260 pathways between 16.5 – 17.5 ft (MLLW), approximately a foot above the project storm of record, that have not flooded historically to account for of sea level rise or a larger storm. While not the focus of this project, preliminary calculations indicate that these water levels could result in an additional 1,600+ acres of inundation throughout the study area. Municipalities should be aware of the pathways that are just above the project storm of record, what resources might be affected by flooding in these areas, and what steps could be taken to prevent or minimize potential threats. There are three ways to view and use these data. The first are digital, GIS-based data layers that can be used to generate hardcopy maps for training purposes, field use, or to have on hand in the event of power loss. Second, in collaboration with the Southern New England Weather Forecast Office of the National Weather Service (SNEWFO-NWS), the incorporation of these data into the NWS Coastal Flood Threat and Inundation Mapping webpage (weather.gov/box/coastal) provides real-time total water level predictions for coming storm events to town staff and the public. The GIS data generated from this project were reformatted to conform to NWS standards to display the data relative to NWS forecasts of ‘Action Level’, ‘Minor’, ‘Moderate’ and ‘Major’ flooding. These real-time NWS forecasts can be used with the webpage to aid in visualizing how an approaching storm and related flooding could impact an area. Finally, the Center for Coastal Studies has developed an application to view these data that combines the real-time water level forecasts of the NWS with the maps of storm tide pathways by building a standalone website (stormtides.org) that is easily updateable and maintained by the Center. A stand-alone data set can also be used offline by management entities and others. The mapping of storm tide pathways provides town staff and the public with critical information on the precise location of potential flooding that enables communities to address each individual pathway and prevent future inundation. These improved, accessible data will help communities to avoid, mitigate and prepare for increasingly severe flooding events.
Article
Full-text available
Yearly tidal datum statistics and tide ranges for the National Oceanic and Atmospheric Administration/National Ocean Service long-term stations in the United States tide gauge network were compiled and used to calculate their trends and statistical significance. At many stations, significant changes in the tide range were found, either in the diurnal tide range mean higher high water MHHWmean lower low water MLLW, or mean tide range mean high water MHWmean low water MLW. For example, at San Francisco, the diurnal tide range increased by 64 mm from 1900 to 1998, while at Wilmington, N.C., the mean tide range increased at a rate of 542 mm per century from 1935 to 1999. This analysis suggests that any studies concerned with present or future water levels should take into account more tidal datum statistics than just mean sea level MSL. For example, coastal flooding and storm damage studies should consider trends in high water levels, since it is the peak values that cause flooding and determine the design of coastal structures. For habitat restoration planning, mean low water and tide range changes should be considered.
Conference Paper
The occurrence of dangerously high or low water levels at coastal locations is an important public concern and is a significant factor in coastal hazard assessment, navigational safety, and ecosystem management. The monthly highest and lowest water levels at 117 NOAA/National Ocean Service water level stations show a clear response to local mean sea level trends. The extreme levels reached by hurricanes and extra-tropical storms of the past can be adjusted for sea level trend, so that unbiased comparisons can be made. A data set of the annual highest and lowest water levels is derived from the monthly data and used to determine the expected frequency of future storm tides rising above or falling below any given level. The same analysis is also applied to the data for each individual month in order to estimate the varying likelihood of extreme high or low levels by season. The results are a set of annual and monthly exceedance probability levels relative to the tidal datums for each station. This information should prove useful for identifying, in real time, when a rare event threshold has been crossed. The exceedance probability levels can be adjusted in the future to reflect newly-updated tidal datums.
Department of Commerce, National Oceanic and Atmospheric Administration
  • A N Bodnar
Bodnar, A.N. 1981. Estimating Accuracies of Tidal Datums from Short term Observations. Technical Report CO-OPS 0074. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Serve, Center for Operational Oceanographic Products and Services. March 1981. 32 pages.
Tidal Bench Marks State of Massachusetts. Special Publication No. 155. Department of Commerce
  • L A Cole
Cole, L.A. 1929. Tidal Bench Marks State of Massachusetts. Special Publication No. 155. Department of Commerce,. U.S. Coast and Geodetic Survey. Washington. 1929. 39 pages.
Coastal Flooding in Barnstable County, Cape Cod Mass. Massahcuetts Water resources Commission. Charles I. Sterling, Director
  • D A Crane
Crane, D.A. 1962. Coastal Flooding in Barnstable County, Cape Cod Mass. Massahcuetts Water resources Commission. Charles I. Sterling, Director. December 1962. 63 pages.
Massachusetts (All Jurisdictions). Federal Emergency Management Agency
FEMA, 2014. Flood Insurance Study, Barnstable County, Massachusetts (All Jurisdictions). Federal Emergency Management Agency, p. 110.
Effects of the Blizzard of 1978 on the Coastline of Cape Cod
  • G S Giese
Giese, G.S. 1978. Effects of the Blizzard of 1978 on the Coastline of Cape Cod. Provincetown Center for Coastal Studies. Chapter in "The Bizzard of 1978", Effects of the Coastal Environments of Southeastern New England. Boston State College. 1978.
Tidal Datums and Their Applications
  • S K Gill
  • J R Schultz
Gill S. K. and Schultz J. R. Tidal Datums and Their Applications. NOAA Special Publication, NOS CO-OPS 1. February, 2001. 111 pp.