Mapping Storm Tide Pathways in Cape Cod Bay, Massachusetts

A report prepared for the Cape Cod Cooperative Extension Funded through the Massachusetts Seaport Economic Council

by The Coastal Processes and Ecosystems Lab at the Center for Coastal Studies, Provincetown, Massachusetts and the School for the Environment at the University of Massachusetts, Boston Mark Borrelli, Stephen T. Mague, Bryan Legare, Bryan McCormack, Samantha J. McFarland, Daniel Solazzo Publication: 21-CL-05 Acknowledgements: Funding for this project was provided by Massachusetts Seaport Economic Council. We thank Michael Maguire and Shannon Hulst from the Cape Cod Cooperative Extension, and Sean O’Brien, the Director of the Barnstable County Department of Health and Environment.

Suggested citation: Borrelli, M., Mague S.T., Legare, B.J., McCormack, B., McFarland, S.J., Solazzo, D., 2021. Mapping Storm Tide Pathways in Cape Cod Bay. Tech. Rep. presented to the Cape Cod Cooperative Extension: 21-CL-05. p. 73.

TABLE OF CONTENTS

EXECUTIVE SUMMARY ...... 1 PROJECT BACKGROUND AND OVERVIEW ...... 2 METHODS ...... 5 Composite Storm Tide Profile for Mapping Cape Cod Bay STPs ...... 5 Overview ...... 5 Characterizing Coastal Inundation ...... 6 A Word about Datums ...... 7 The Mapping of Storm Tide Pathways ...... 8 Desktop Analysis...... 9 Field Work...... 11 RESULTS AND DISCUSSION ...... 14 Creating a Composite Storm Tidal Profile for Mapping Cape Cod Bay STPs ...... 14 Developing the Cape Cod Bay Composite Storm Tide Profile ...... 18 Storm Tide Pathways and National Weather Service Storm Surge Predictions ...... 20 Storm Tide Pathways Across Cape Cod Bay ...... 22 Storm Tide Pathways by Town ...... 28 Town of Barnstable ...... 30 Town of Brewster ...... 32 Town of Dennis ...... 34 Town of Eastham ...... 36 Town of Orleans ...... 38 Town of Provincetown ...... 40 Town of Sandwich ...... 42 Town of Truro ...... 44 Town of Wellfleet ...... 46 Town of Yarmouth ...... 48 Coastal Flood Threat and Inundation Mapping webpage ...... 50 Stormtides.org: A new Website ...... 51 References: ...... 53

iii

Flood Insurance Studies used for analysis in this study: ...... 55 APPENDIX A: Water Level Measurements and Tidal datums ...... 56 Results ...... 57 Appendix References ...... 69

iv

EXECUTIVE SUMMARY 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

1 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.

PROJECT BACKGROUND AND OVERVIEW Cape Cod has many low-lying coastal communities that have historically been vulnerable to inundation associated with coastal storms and flooding. These threats are further exacerbated by rising sea levels as flooding events, superimposed onto sea level rise, increase in frequency and magnitude. Recent local storms such as the Nor’easters of 2015 and 2018, as well as the Halloween Storm of 1991 and Sandy in 2012, highlight management challenges that 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.

Consensus among scientists indicates that sea levels are rising at an increasing rate. Therefore, much attention has been focused on efforts that enhance adaptation and increase resiliency related to climate change in coastal settings. As shown in Figure 1, projections vary from a low of 1.5 feet to a high of over 10.0 ft (0.45 m - >3.0 m) by the end of this century. However, such a broad range of projected sea level rise creates significant uncertainty 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 despite the unavoidable uncertainties inherent in century-scale sea level rise projection scenarios. Annual or even decadal planning horizons are not easily defined or addressed within the context of sea level rise. Further, 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 to address sea level rise, the ability of coastal managers to identify potential vulnerabilities effectively and efficiently and to educate residents and community leaders about the threats associated with coastal inundation has been severely limited by the lack of accurate elevation data at a scale that is usable at the community level. For example, Flood Insurance Rate Maps (FIRMS) produced by the Federal Emergency Management Agency (FEMA) have long been standard planning resources for coastal

2 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 efforts at regional scales and not appropriate for identifying the increasing threats associated with coastal storms over timeframes that meet the needs 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. Further, vertical uncertainties associated with some of these models can be too coarsely scaled to inform area-specific decisions expected of local coastal managers.

Figure 1. Relative sea level rise scenario estimates (in feet NAVD88) for Boston, MA. Taken from https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?id=8443970. Approximate range of relative sea level rise for the Boston area, which is nearly identical to Cape Cod Bay, is 1.50 (0.45 m) to more than 10 ft (>3.0 m).

Based on the long-range projections of sea level rise, and the catastrophic damages associated with large coastal storms, much attention is focused 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 emissions, to promote green energy, and to 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. Often 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 municipalities.

3

Recognizing the limited financial and technical resources of coastal communities and their unique geography, local responses and strategies to sea level rise and climate change need to operate effectively in the context of short-term planning horizons and frequently changing leadership. Specifically, short term planning efforts should identify actions or responses that are:

• Achievable within an appropriate time frame (e.g., 30 years) • Implementable with current technology • Financially feasible • Politically viable (i.e., not extreme – e.g., wholesale retreat) • Adaptable to changing future scenarios • 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 past and present storm tide elevations provide another effective means of characterizing local coastal hazard vulnerabilities for community level planning actions. Figure 2 depicts estimates from various sources of 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.

In recent history the “Blizzard of ‘78” had been the storm of record for Boston and areas to the north of Cape Cod. However, the January 4th, 2018 storm, approximately 9.8 ft NAVD88 (or 15.3 ft local MLLW) surpassed the total water level for the 1978 storm for much of the same area and is now the new storm of record for Provincetown Harbor. The USGS tide gauge for Sesuit Harbor recorded a maximum water level of approximately 10.6 feet NAVD88 (or ~16.4 feet local MLLW) for the January 27th, 2015 Nor’easter. Slightly higher in elevation in absolute terms than the 2018 storm, this contemporary elevation was used as the mapping reference for Cape Cod Bay. Interestingly, the 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, illustrating the point that municipalities appear to be more susceptible to storm- related flooding now, and that preparing for these storm events can help communities prepare for future sea level rise. The plot further reveals that earlier estimates of storm tide heights have probably equaled or exceeded the 2018 maximum numerous times since the 17th century.

Identifying potential future storm tide heights, coastal flooding extents, and areas of potential vulnerability using historical data provides several benefits to coastal communities. First, using actual historical storm tide data to identify coastal hazard vulnerabilities helps communicate a higher level of certainty by removing sea level rise and the disparity of projections (Figure 1) from the discussion of the most appropriate sea level rise elevation upon which to base short term planning strategies. Sea level rise notwithstanding, storm tides of significant magnitude have been

4 experienced in the past and will continue to be experienced again in the future. Second, contemporary storms of record provide an accurate, actual (i.e., indisputable) reference elevation that towns can plan for when history repeats or surpasses itself. Finally, as discussed below, using emerging data gathering technologies to identify inundation pathways yields valuable information that can be used by coastal communities to plan and implement ground level strategy in response to sea level rise.

Figure 2. Historical Storm tides and sea level rise.

METHODS Composite Storm Tide Profile for Mapping Cape Cod Bay STPs

Overview The use of the historical record to supplement predicted storm and spring tide elevation data can provide valuable baseline information to Emergency Managers, Public Works Departments, Harbormasters, Planners, and Coastal Resource Managers. Independent of long-term sea level rise projections, storm surge projections considered in the context of contemporary storms of record and accurate ground elevation data can be used to map the location of storm tide pathways with a high degree of certainty. As demonstrated in previous storm tide pathway mapping projects in Provincetown (Borrelli, et al., 2016b), Nantucket (Borrelli, et al., 2016b), Truro (Borrelli et al., 2017), Scituate and Cohasset (Borrelli, et al., 2020), funded via the Massachusetts Office of Coastal Zone Management Management’s Coastal Resiliency Grant Program and the Municipal Vulnerability Preparedness (MVP) Program, when referenced to a common vertical datum that spans the land-sea interface, these data can be used by towns as the basis for short-term community

5 planning decisions and real-time decisions necessary to respond to approaching coastal storms and related storm surge.

Characterizing Coastal Inundation As relative sea level continues to rise, many coastal communities are beginning to experience minor flooding with the higher tides of the month (e.g., spring tides). Often referred to as nuisance flooding since it is rarely associated with dramatic building or property damage, this type of flooding is becoming more frequent, resulting in chronic impacts that include overwhelmed drainage systems, frequent road closures, and the general deterioration of infrastructure not designed to withstand saltwater immersion (Sweet, et. al., 2014).

In addition to minor monthly inundation, relatively short duration, high intensity storms (e.g., hurricanes), many coastal communities are also experiencing severe flooding associated with low intensity but longer duration coastal storms (e.g., northeasters). 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) or mean low water (MLW)). Storm surge refers to the increase in water level associated with the presence of a coastal storm. As the arithmetic difference between the actual level of the storm tide and the predicted tide height, storm surges are not referenced to a datum.

Storm surge magnitude and the time at which the maximum surge occurs relative to the stage of the astronomical tide are critical components of the maximum storm tide elevation experienced during any storm. The significance of this relationship is illustrated by the following example.

Prior to January 4, 2018, the storm of record for the Boston Tide Gauge (#8443970) occurred on February 7, 1978 (the Blizzard of ’78) with a maximum storm tide elevation of 9.59 ft referenced to the North American Vertical Datum of 1988 (NAVD88) (15.1 ft, MLLW). 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 8.16 ft, NAVD88 (13.67 ft, MLLW). Occurring well after the astronomical high tide, this total water level elevation represented the combination of an astronomical tide height of 4.79’ 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 low water, the corresponding storm tide elevation was only -1.1’ NAVD88. Had the maximum storm surge associated with the 2015 storm occurred during the 2018 storm water level would have been approximately one foot above the 2018 storm and done considerably more damage.

6

Recognizing the significance of not only the magnitude of the predicted storm surge but when it will occur relative to the stage of the tide, the National Weather Service (NWS) in Norton, MA maintains an informative website that estimates storm surge and total water level at various Massachusetts locations (http://www.weather.gov/box/coastal)1 as coastal storms approach New England. This project supplements information developed in previous CZM Resiliency projects for Provincetown and Truro to provide the NWS Norton office with an additional data set of accurately mapped storm tide pathways that can be incorporated into its coastal storm surge website to reduce the uncertainty and improve the utility of storm tide inundation forecasts for the Cape Cod Bay area.

A Word about Datums 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 to which a point’s position on the earth’s surface can be referenced (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).2 It is important to note that as local phenomena, the heights of tidal datums can vary significantly from one area 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).3

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.4 Although comparable in height, generally one daily tide is slightly higher than the other and, correspondingly, one low tide is lower than the other. 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.)

1 At the time of writing the NWS website was down for redesign. The web address may change after the redesign is completed. 2 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. 3 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. 4 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. 7

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 an even 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, and 1924-1942 (NOAA, 2000a).

Table 1. Common Tidal Datums (*Source: NOAA, 2000b). Tidal Datum Definition Average of the highest high water (or single high water) of each tidal day Mean Higher High Water (MHHW) observed at a specific location over the NTDE* Average of all high-water heights observed at a specific location over the Mean High Water (MHW) NTDE* Arithmetic mean of hourly tidal heights for a specific location observed Mean Sea Level (MSL) over the NTDE* Arithmetic mean of mean high and mean low water calculated for a Mean Tide Level (MTL) specific location Average of all low water heights observed at a specific location over the Mean Low Water (MLW) NTDE* Average of the lowest low water (or single low water) of each tidal day Mean Lower Low Water (MLLW) observed at a specific location of the NTDE*

The Mapping of Storm Tide Pathways Initial mapping of storm tide pathways begins with a computer-based analysis of the most representative lidar data. Importantly, this analysis is then supplemented with field verification of the lidar data and conditions on the ground at the time of mapping. Metadata for the 2013-14 lidar accuracy reported that data was compiled to meet a horizontal accuracy of 0.30 - 0.36 meters (~1.0 – 1.2 feet) at 95% confidence level while Consolidated Vertical Accuracy (CVA) tested 0.189 meters (0.6 feet) consolidated vertical accuracy at the 95th percentile level. The metadata cautions, however, that users should be aware temporal changes may have occurred since the dataset was collected and that some parts of these data may no longer represent actual surface conditions. This can be particularly significant for coastal datasets where the latest available lidar data sets often do not represent current field conditions due to the dynamic and constantly evolving nature of coastal landforms. Therefore, the rigorous and time-consuming fieldwork of verifying the lidar and real-world conditions are important components of the mapping process.

8

Desktop Analysis The ability to conduct accurate fieldwork is an important component of the STP verification process. First, though lidar data is the most accurate and cost-effective spatial data collected over broad areas, it only characterizes the topography of the mapped area for the actual; date/time of the data acquisition. Due to the dynamic nature of the coast and its relationship to coastal flooding patterns, the location of many natural storm tide pathways is ephemeral with new pathways emerging in areas that have never flooded in the past. Second, the use of an RTK-GPS instrument provides the accuracy necessary for acquiring and verifying 3-dimensional positional data. In this way field data collected with the Center’s GPS are used to corroborate or eliminate the presence of STPs identified in the desktop lidar analysis. Third, due to the dynamic nature of coastal environments, visual assessment of STPs in their geographic setting, often reveals changes in the landscape that are not revealed in a desktop analysis of lidar data. Lastly, as noted above and also related to the ephemeral characteristics of the areas proximate to the shoreline, even the most current lidar is frequently out of date in these dynamic areas. Consequently, the GPS survey, coupled with field observation of each STP, provides the most current information regarding STPs that may have been modified due to changes in landform.

LIght-Detection And Ranging, or lidar, is similar to radar and sonar but rather than using radio or sound waves it uses light to collect elevation data. The lidar used for this study was collected via aerial surveys in 2013-2014 by the United States Geological Survey (USGS) along the coast of Cape Cod as part of a post-Hurricane Sandy study. A small portion of inland areas were not covered by this lidar data and a USGS 2011 Lidar dataset was used to expand landward coverage. The post-processing of lidar collected via aerial surveys can introduce uncertainties that exaggerate or diminish features in three-dimensional data and, as a result, can obscure or conflate the presence and scale of an inundation 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 (Figure 3) or “pulled down” in areas where bridges and roads cross streams or valleys, further emphasizing the value of field verification.

All lidar data are downloaded in a raster format, brought into ESRI’s ArcGIS software, and divided into smaller tiles to facilitate data analysis and archiving. These lidar tiles are then brought into QPS’s Fledermaus data visualization software for initial screening. 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 storm tide pathways where the accuracy of the initial analysis is limited primarily by the uncertainty and resolution of the lidar itself.

9

Figure 3. Example of ‘pull up’ near a water tower in Provincetown. Dotted red 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), image taken from Borrelli, et al. 2017.

The power of Fledermaus lies in its ability to work quickly with large data files. Although individual files can be multiple gigabytes in size, Fledermaus moves rapidly through the data facilitating visual inspection, ‘fly-throughs’, and similar functions. Using the Fledermaus software, horizontal planes representing incrementally higher flood levels are created and used to identify corresponding potential pathway elevations. These planes are added to a Fledermaus project or ‘scene’ and form the basis for the initial pathway identification. (Figure 4).

Another valuable feature of this data visualization software is the ability to drape 2-dimensional data, such as an aerial photograph, over a 3D dataset (lidar). This allows the analyst to better document the STP location and to acquire information about the landscape setting of the STP and the substrate on which it is located. For example, an STP found on or near an ephemeral coastal feature such as a sandy beach or dune is characterized differently than one atop a concrete wall or other relatively static feature. In addition to providing managers with information on how to address an individual STP, these characterizations also inform the field team to more closely examine areas that are naturally evolving and to inspect the area for other to potential STPs that might not have appeared in the now dated lidar. The ability to drape aerial photographs proved extremely helpful for conducting the GPS field work, serving as a quick means of orientation, and placing the potential STP in its broader geographic context.

10

Figure 4. Draped aerial photograph over Lidar surface in North Truro. Blue areas are horizontal plane created in Fledermaus at increasing elevation. Lower right is example of a storm-tide pathway with accompanying profile. These images were generated before field work to identify potential STPs (image taken from Borrelli, et al. 2017).

Field Work Once a preliminary inventory of potential Cape Cod Bay STPs was compiled in the desktop analysis and reviewed in a group setting by the project team, an extensive fieldwork assessment program was conducted to verify the presence or absence of the STP. When the presence of an STP was confirmed, the accurate horizontal and vertical location was obtained with the Center’s Trimble® R10 GNSS receiver utilizing Real-Time-Kinematic GPS (RTK-GPS). The Center subscribes to a proprietary Virtual Reference Station (VRS) network (KeyNetGPS) that provides virtual base stations via cellphone from Southern Maine to Virginia, including a station located on the roof of the Center’s laboratory building. This allows the Center to collect RTK-GPS without the need for a terrestrial base station or to post-process the GPS data, streamlining the field effort and increasing field work efficiency.

The Center performed a rigorous analysis of this system to quantify the accuracy of this network (Borrelli, et al, in press). 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.

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

11 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 used to assess and quantify uncertainty. Significantly, there was little difference between the values 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) yielded a National Standard for Spatial Data Accuracy (95%) of 0.0484 m (H) and 0.0483 m (V).

At the completion of the desktop analysis, all potential STPs were compiled into a spatial 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 STP location, and the adjacent area, is inspected by a 2-3-person team and occupied with the GPS mobile unit. This served four purposes, first to map the real-world location of the STP identified during the desktop analysis; second to increase the positional accuracy of the verified STP itself; third, to verify consistency with the current landscape setting; and lastly to confirm the positional accuracy of the lidar data.

Significantly, using the GPS instrument to navigate to the location of a potential STP also afforded the field crew the opportunity to investigate potential alternative or additional STPs based on visual inspection of the area. Many coastal sites are characterized by low relief (i.e., relatively flat) and verifying the presence of an STP, its exact location, and the direction of water flow required professional judgment and experience in the principles and practices of topographic mapping as well as a thorough knowledge of coastal processes.

After the field work was completed, the team returned to the laboratory to remove those points from the database determined not be STPs, incorporate newly identified STPs documented in the field, and provide all STPs with horizontal and vertical position information, substrate and geographic context labels, photograph links, and other pertinent information for inclusion into a comprehensive database. Once the information was quality controlled, the database was brought into the project GIS for use as an interactive archive of final STP 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 documented by the GPS observations and professional judgment to accurately represent the final STP location.

With the final compilation of the STP spatial database, the file was brought into ESRI’s ArcGIS to provide a working or living archive for local managers: 1) to proactively identify and prioritize which STPs to address prior to storm events; 2) to prepare for approaching storms; and 3) to plan for longer-term improvements to mitigate other STPs.

12

To increase the utility of the STP data inundation planes were created to make visualizations more user friendly for local managers. Recognizing that floodplain mapping is not a goal of the project, the use of planes to visualize STPs was determined to be the clearest way of presenting the data in a useful manner while recognizing the uncertainty associated with the lidar. After reviewing the various scenarios, the lowest plane was begun at the approximate elevation of a composite mean high water spring tide (MHWS) for Cape Cod Bay. Planes were developed in 6-inch intervals and extracted for each range to a maximum elevation represented by the project storm of record plus four feet. In addition to providing an upper limit to project elevations, the project storm of record plus 4 feet provides a useful representation of potential future sea level rise scenarios that would have practical implications for local managers.

During the field work portion of the project, data was not collected on private property. If a point was inaccessible to the field team, it was labeled as an unverified STP, meaning the STP was identified as a potential STP in the desktop analysis, but due to circumstances it was inadvisable (e.g., assumed to be private property) or impossible (e.g., beneath substantial tree cover and, therefore no GPS signal coverage)) for the field team to ‘occupy’ the potential STP. Due to the rapidly changing coastal landscape, STPs located on dynamic landforms such as coastal dunes were also labeled as unverified to not convey a sense of permanency to these locations. For this reason, unverified STPs located on rapidly changing natural landforms such as dunes or barrier beaches or in areas experiencing erosion should be viewed as a guide requiring periodic updating or verification.

Unverified STPs are not indicative of a lack of hazard, rather because it was chosen as a potential STP it warrants further investigation by the towns. The field team adjusts the STP location based on the real-world conditions if needed by selecting the lowest elevation point if the STP identified in the desktop analysis does not reflect the on-the-ground topography.

Mapping storm tide pathways, as with any mapping effort, is a balance between reflecting on the ground conditions and providing clear and useful information. To assist the user with STP interpretation, planes showing the extent of potential flooding at half-foot intervals have been provided with the GIS data. Based solely on lidar, the range planes are not intended to be used as an accurate source of floodplain boundaries but as a way to visualize how storm tides of increasing heights can make their way inland. For this reason, it is important to view STPs with the planes to help evaluate the level of threat posed by an approaching coastal storm and to develop potential mitigation strategies, particularly in flat areas where inundation is not controlled by discrete STPs but exhibits sheet flow across broad areas with no easily identifiable points that can be used to halt or control the inland flow of water.

13

For example, along flat sections of road where there are multiple, closely spaced low spots, identifying multiple STPs provides little value to the user. In these situations, typically information on the lowest STP has been provided to characterize the level at which the road will begin to experience inundation. Areas with STPs potentially triggered by an approaching storm should then be viewed in the context of the appropriate range plane to assess appropriate responses.

Similarly, in areas of parallel roads, the use of multiple STPs on each road to try visualize the inland progression of potential flooding associated with an approaching coastal storm typically yields an overwhelming amount of data that are redundant and do not contribute to the development of mitigation strategies. This is particularly true in areas where the inland progression of storm related flooding occurs more as sheet flow rather than along definable pathways. For this reason, in areas characterized by multiple parallel roads, an STP has been provided at the most seaward road to indicate an inundation point. As always, the STP should be viewed in conjunction with the range planes to assess potential inland response measures related to estimated storm surge heights.

In many areas, culverts, bridges, etc. provide a continuous connection that could carry tide water inland. Since hydraulic analyses of these types of structures is not part of this project, coastal flooding is assumed to be able to be carried inland unrestricted and STP information, therefore, is provided on the more inland parallel roads to help guide potential mitigation efforts.

RESULTS AND DISCUSSION Creating a Composite Storm Tidal Profile for Mapping Cape Cod Bay STPs

The impacts of storm tides on coastal communities are dependent on many factors. These include: • The landscape setting of the community (e.g., east facing v. south facing shores). • The elevations of astronomical tides (e.g., the elevation of mean high water (MHW) in Boston Harbor is 4.31 feet NAVD88 v. an elevation of 0.56’ NAVD88 for the mean high water in Woods Hole). • General characteristics of astronomical tides (e.g., the average range (MHW minus MLW) of Boston Harbor tides is 9.49 feet while that of Woods Hole tides is only 1.79 feet). • The topography (e.g., the elevation of the land relative to the community tidal profile) and 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 community development and adjacent water levels (e.g., development in Boston began in the early 17th century with the water levels at that time

14

influencing the elevation of not only individual wharves but large-scale land-making projects).

As discussed in the Methods section of this report, with such variation in physical characteristics, the initial step in the identification of storm tide pathways is the development of a datum- referenced tidal profile that characterizes average tidal heights, nuisance flooding, and storm tides for the area of interest. 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 considers the high-water lines of datum referenced historical storm tides including the elevation of the maximum contemporary storm tide experienced (i.e., the project storm of record) by the area. As sea levels continue to rise, an estimate of potential future storm tides is provided by adding four feet to this localized storm of record (Zervas, 2009).

In previous storm tide pathway mapping efforts, working storm tide profiles were developed based on data from one tide station that covered a limited geographic area of one or two towns. Since tidal datums vary locally and the Cape Cod Bay mapping project consists of ten towns along approximately 63 miles of shoreline, a composite storm tide profile was developed using information available from two real-time tide stations located in Sesuit (Dennis) and Provincetown Harbors and from a series of month-log tide observations conducted between April and June of 2019 by CCS at six Cape Cod Bay tidally influenced locations. Initial data was collected at Pamet, Wellfleet, Rock (Eastham/Orleans), and Barnstable Harbors. This tide data was supplemented with additional month-long tidal observations in Sandwich at the Boardwalk and at the railroad bridge behind the former Route 6A police station. The locations of these tide data observations are shown in Figure 5.

The Provincetown Harbor tide station (#420259070105600) was installed by the United States Geological Survey (USGS) in December of 2014. The Sesuit Harbor tide station (#414507070091400) was installed by the USGS in the following January. Both stations are referenced to NAVD88. CCS tide observations were obtained during the spring and early summer of 2019 using HOBO™ Water Level Titanium U20-TI pressure sensors from ONSET® affixed to stationary structures, such as pilings on piers, at various locations. This data was also referenced to NAVD88 based on benchmark surveys using CCS’s Trimble® R8 GNSS receiver utilizing Real-Time-Kinematic GPS (RTK-GPS) connected to a proprietary Virtual Reference Station (VRS) network (KeyNetGPS). A detailed report describing CCS tidal observations for Cape Cod Bay is included in the Appendix.

15

Figure 5. Cape Cod Bay Tide Stations.

Based on this data, CCS developed tidal datum values for each station, referenced to NAVD88, for the 1983-2001 National Tidal Datum Epoch (NTDE) (Cole, 1997; NOAA, 2003). The NTDE is a specific 19-year period adopted by the National Ocean Service as the official time segment over which tide observations are taken and reduced to obtain mean values (e.g., mean lower low water, etc.) for tidal datums (NOAA, 2003). It is necessary for standardization because of periodic and apparent secular trends in sea level associated with meteorological (seasonal and storms) and astronomical (the non-coincident orbital paths of the earth and moon about the sun) effects and to provide closure on a calendar year (Marmer, 1951). NTDEs are typically revisited every 20-25 years and updated, as necessary with the present NTDE is for the period 1983-2001 published in April 2003.

Table 2 summarizes contemporary tidal datums (NTDE 1983-2001) for Cape Cod Bay. Contemporary datums published by NOAA for tide stations in the area (Boston Harbor, Plymouth Harbor, Sandwich Marina in the Canal, and the East Canal Breakwater) have also been provided

16

Contemporary Cape Cod Bay Tidal Datums Table 2. Contemporary CapeNTDE: Cod 1983Bay Tidal- 2001 Datums (NTDE: 1983-2001) Units: FEET FEET Boston Harbor Plymouth Harbor Sandwich Marina Sandwich Sandwich Boardwalk Sandwich Police Sta. 8443970 8446493 8447180 Canal East Brkwater (Elevated LW) (Elevated LW) DATUM NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW MHHW 4.77 10.28 4.76 10.53 4.08 9.45 4.79 10.58 4.52 --- 4.50 --- MHW 4.33 9.84 4.32 10.09 3.59 8.96 4.34 10.13 4.14 --- 4.13 --- MSL -0.30 5.21 -0.39 5.38 -0.67 4.70 -0.42 5.37 ------MTL -0.42 5.09 -0.56 5.21 -0.78 4.59 -0.57 5.22 0.85 --- 2.22 --- MLW -5.16 0.35 -5.43 0.34 -5.15 0.22 -5.48 0.31 -2.44 --- 0.31 --- MLLW -5.51 0.00 -5.77 0.00 -5.37 0.00 -5.79 0.00 ------

GT 10.28 10.28 10.53 10.53 9.45 9.45 10.58 10.58 ------MN 9.49 9.49 9.75 9.75 8.74 8.74 9.82 9.82 6.58 --- 3.82 ---

Highest Obs. Tide Elevation 9.66 15.17 6.93 12.70 7.68 13.05 9.40 15.19 ------Date 1/4/2018 1/4/2018 6/23/1990 6/23/1990 3/17/2018 3/17/2018 2/7/1978 2/7/1978 ------Time 17:42 17:42 ------

FEET Barnstable Harbor Sesuit Harbor Rock Harbor Wellfleet Harbor Pamet Harbor Provincetown Harbor --- 8447241 (Elevated LW) ------8446121 DATUM NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW MHHW 4.95 10.56 4.69 10.46 4.74 --- 5.04 10.96 4.66 10.10 4.62 10.08 MHW 4.52 10.13 4.24 10.01 4.28 --- 4.54 10.46 4.19 9.63 4.16 9.62 MSL ------0.54 5.23 ------0.41 5.03 -0.43 5.03 MTL -0.40 5.21 -0.62 5.15 0.58 --- -0.63 5.29 -0.46 4.98 -0.48 4.98 MLW -5.32 0.29 -5.49 0.28 -3.13 --- -5.80 0.12 -5.10 0.34 -5.13 0.33 MLLW -5.61 0.00 -5.77 0.00 ------5.92 0.00 -5.44 0.00 -5.46 0.00

GT 10.56 10.56 10.46 10.46 ------10.96 10.96 10.10 10.10 10.08 10.08 MN 9.84 9.84 9.73 9.73 7.41 --- 10.34 10.34 9.29 9.29 9.29 9.29

Highest Obs. Tide Elevation ------10.61 16.38 ------8.6 14.52 9.79 15.23 9.77 15.23 Date ------1/27/2015 1/27/2015 ------12/29/1959 12/29/1959 1/4/2015 1/4/2015 1/4/2018 1/4/2018 Time ------12:45 12:45

METERS Boston Harbor Plymouth Harbor Sandwich Marina Sandwich Sandwich Boardwalk Sandwich Police Sta. 8443970 8446493 8447180 Canal East Brkwater (Elevated LW) (Elevated LW) DATUM NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW MHHW 1.45 3.13 1.45 3.21 1.24 2.88 1.46 3.23 1.38 --- 1.37 --- MHW 1.32 3.00 1.32 3.08 1.09 2.73 1.32 3.09 1.26 --- 1.26 --- MSL -0.09 1.59 -0.12 1.64 -0.20 1.43 -0.13 1.64 ------MTL -0.13 1.55 -0.17 1.59 -0.24 1.40 -0.17 1.59 0.26 --- 0.68 --- MLW -1.57 0.11 -1.66 0.10 -1.57 0.07 -1.67 0.09 -0.74 --- 0.09 --- MLLW -1.68 0.00 -1.76 0.00 -1.64 0.00 -1.77 0.00 ------

GT 3.13 3.13 3.21 3.21 2.88 2.88 3.23 3.23 ------MN 2.89 2.89 2.97 2.97 2.66 2.66 2.99 2.99 2.01 --- 1.16 ---

Highest Obs. Tide Elevation 2.95 4.63 2.11 3.87 2.34 3.98 2.87 4.63 ------Date 1/4/2018 1/4/2018 6/23/1990 6/23/1990 3/17/2018 3/17/2018 2/7/1978 2/7/1978 ------Time 17:42 17:42 ------

METERS Barnstable Harbor Sesuit Harbor Rock Harbor Wellfleet Harbor Pamet Harbor Provincetown Harbor --- 8447241 (Elevated LW) ------8446121 DATUM NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW MHHW 1.51 3.22 1.43 3.19 1.45 --- 1.54 3.34 1.42 3.08 1.41 3.07 MHW 1.38 3.09 1.29 3.05 1.30 --- 1.38 3.19 1.28 2.94 1.27 2.93 MSL ------0.16 1.59 ------0.13 1.53 -0.13 1.53 MTL -0.12 1.59 -0.19 1.57 0.18 --- -0.19 1.61 -0.14 1.52 -0.15 1.52 MLW -1.62 0.09 -1.67 0.09 -0.95 --- -1.77 0.04 -1.55 0.10 -1.56 0.10 MLLW -1.71 0.00 -1.76 0.00 ------1.80 0.00 -1.66 0.00 -1.66 0.00

GT 3.22 3.22 3.19 3.19 ------3.34 3.34 3.08 3.08 3.07 3.07 MN 3.00 3.00 2.97 2.97 2.26 --- 3.15 3.15 2.83 2.83 2.83 2.83

Highest Obs. Tide Elevation ------3.23 4.99 ------2.62 4.43 2.98 4.64 2.98 4.64 Date ------1/27/2015 1/27/2015 ------12/29/1959 12/29/1959 1/4/2015 1/4/2015 1/4/2018 1/4/2018 Time ------12:45 12:45

17

NOAA COOPS NOAA Tide Station USGS USGS Real Time Tide Gauge CCS Based on 1 Month CCS Tide Readings Sandwich Historical Record for informational purposes. Values are provided in feet and meters and are referenced to NAVD88, a common geodetic datum, for comparison around Cape Cod Bay. Values are also referenced to mean lower low water (MLLW), a local tidal datum used by the National Weather Service and the chart datum for Cape Cod Bay. NAVD88 values demonstrate that, while the elevations are similar, MLLW elevations vary from a low in Wellfleet Harbor of approximately -5.92 ft NAVD88 to a high of -5.44 in Pamet Harbor. While of little significance to boaters, as the plane of reference for NWS estimates of total water level, differences in relative MLLW elevation for the Bay did have to be considered to visualize storm tide pathways and inundation planes around Cape Cod Bay seamlessly.

Developing the Cape Cod Bay Composite Storm Tide Profile As shown by Table 2, comparisons of contemporary Cape Cod Bay tidal datums referenced to NAVD88 vary as one moves along the shoreline from the Cape Cod Canal in Sandwich to Provincetown Harbor, with the greatest variations encountered around Wellfleet Harbor. While these variations must be considered when integrating final storm tide pathway data with NWS total water level estimates, initial identification and mapping of individual storm tide pathways is conducted with all data referenced to NAVD88, a vertical, geodetic reference system allowing direct comparisons within the study area.

For analysis purposes, therefore, a composite storm tide profile was developed based on an average of tidal datum heights for seven tidal stations: Plymouth Harbor (Sta 8446493), Sandwich Canal E. Breakwater, Barnstable Harbor, Sesuit Harbor (Sta 8447241), Wellfleet Harbor, Pamet Harbor, and Provincetown Harbor (Sta 8446121). As with previous CCS projects conducted north of Cape Cod where historical high water levels are largely associated with northeasters, the upper elevation limit of the storm pathway project was established by developing a historical record and identifying contemporary record storms for the Cape Cod Bay area, referencing associated high water levels to NAVD88 to the extent possible, and adding four feet to the maximum identified high water level.

Table 3 summarizes the results of research conducted to identify reliable historical high water elevations within Cape Cod Bay. Due to its proximity to Cape Cod Bay, similar tidal characteristics, susceptibilities to northeast storms, and a robust historical tidal record, historical high water elevations for Boston Harbor were included for comparative purposes. Source material considered during the research can be found in the references contained at the end of this report.

18

Table 3. Cape Cod Bay Historical High Water Elevations. Orleans/ Dennis Truro CC Canal Barnstable Eastham Wellfleet P'town Named Storm Date Boston Sandwich Yarmouth Sesuit Brewster Pamet East End Harbor Rock Harbor Harbor Harbor Harbor Harbor

2018-03-17 4.91 7.68 5.33 5.33 2018-01-04 9.66 10.35 9.92 2015-01-27 8.1 10.61 8.65 Christmas Nor'easter 1992-12-12 8.6 Halloween Nor'easter 1991-10-30 8.6 1987-02-01 8.7 1979-01-25 8.5 Blizzard of '78 1978-02-07 9.57 9.2 9.3 9.3 9.25 9.25 9.25 9.2 9.2 9.36 1972-02-19 8.3 7.3 1967-03-26 8.1 6.4 1961-01-20 8.0 7.9 1959-12-29 8.5 8.1 8.0 9.1 8.6 7.6 8.2 1956-03-17 7.6 8.0 1954-08-31 7.42 7.9 1947-11-12 7.3 7.1 1944-12-30 8.0 Nor'easter 1940-04-21 8.1 8.0 8.0 Hurricane of '38 1938-09-21 5.23 8.7 1931-03-04 8.0 Christmas Gale 1909-12-26 9.1-9.8 8.7 Portland Gale 1898-11-27 8.4-9.3 8.0 1861-11-03 7.9 1854-12-03 8.0 1853-12-29 8.1 Minots Light Gale 1851-04-16 9.1-9.4 8.9 Triple Hurricanes 1839-12-15 8.4-9.4 Triple Hurricanes 1839-12-27 8.4-9.4 1830-03-26 8.2 December Gale 1786-12-04 8.1-9.4 1723-02-24 8.3-9.9 1722-02-24 8.9 Great Colonial Hurricane 1635-08-25 4.4 High Water Observations (NAVD88 Feet) (Italics denote estimated NAVD88)

As shown by Table 3, until recently (at least for the post-World War II era) the Blizzard of ’78 (February 7, 1978) was recognized as the storm of record for the area north of Cape Cod. The maximum high-water elevations for this storm were recorded as 9.57 feet NAVD88 on the Boston Harbor tide gauge and 9.36 feet NAVD88 for Provincetown Harbor. Lacking a tide gauge, the maximum high-water elevation for Provincetown Harbor was documented by Dr. Graham Giese of the Center for Coastal Studies, who measured water levels on MacMillan Wharf throughout the storm. Based on this and other data, water levels of more than 9 feet NAVD88 for Cape Cod Bay have been documented by the Corps of Engineers in its 1988 Tidal Flood Profiles New England Coastline technical report.

The high-water levels associated with the Blizzard of ’78 retained the title of Cape Cod Bay contemporary storm of record for almost a half century when they were eclipsed by several northeast storms occurring in 2015 and 2018. As shown in Table 2, new records were established for Boston Harbor (9.66 feet NAVD88) and Provincetown Harbor (9.92 feet NAVD88) in 2018 with a January 4th northeaster. Significantly, these high-water levels did not eclipse the high-water level recorded on the Sesuit Harbor, Dennis tide gauge for a northeast storm occurring on January

19

27, 2015. As the highest reliable water level identified for the Cape Cod Bay area over the last century, the elevation of 10.61 feet NAVD88 in Sesuit Harbor was used as the base line (or project storm of record) for the Cape Cod Bay STP analysis. Adding approximately four feet to this elevation establishes an upper limit for the analysis of 14.61 feet NAVD88. Table 4 summarizes the Composite Storm Tide Profile used to analyze Cape Cod Bay STPs (As shown in the table the upper limit of the analysis was increased to 14.76 ft NAVD88 to correspond to an even 4.5 meters NAVD88 since lidar data used in the analysis is provided in meters). Four feet above the storm of record was chosen as a reasonable compromise between current needs and future planning for sea level rise.

Table 4 Composite Storm Tide Profile used for Mapping Cape Cod Bay STPs. Std Std MLLW NAVD88 NAVD88 Events and Datums Dev Dev (ft) Comments (FT) (FT) (FT) (FT) Approx. January 27, 2015 Upper Limit of Storm Tide Nor’easter plus 4.15 ft 14.76 -- 4.50 -- 20.44 Pathway Analysis (Rounded (1.27 m) to 4.5 m NAVD 88) Sesuit Harbor Tide Gauge January 27, 2015 Nor’easter 10.61 -- 3.23 -- 16.29 East Dennis (Contemporary Maximum) Average: Plymouth Hbr (Sta 8446493), Sandwich Canal E. Breakwater, Barnstable Hbr, MHWS 5.48 0.04 1.67 0.01 11.16 Sesuit Hbr (Sta 8447241), Wellfleet Hbr, Pamet Hbr, Provincetown Hbr (Sta 8446121) MHHW 4.79 0.16 1.46 0.05 10.47 “

MHW 4.33 0.15 1.32 0.05 10.01 “

MSL -0.44 0.07 -0.13 0.02 5.24 “

MTL -0.53 0.09 -0.16 0.03 5.15 “

MLW -5.39 0.24 -1.64 0.07 0.29 “

MLLW -5.68 0.18 -1.73 0.06 000 “

GT 10.5 -- 3.19 -- 10.5 “

MN 9.7 -- 2.96 -- 9.7 “

Storm Tide Pathways and National Weather Service Storm Surge Predictions For certain areas, the NWS provides a qualitative description of the impacts likely to be associated with its estimates for potential total water levels associated with approaching storm tides. Related directly to the physical characteristics of a threatened area, the descriptions are characterized by

20 the following general categories and suggest action levels or stages for coastal communities threatened by approaching coastal storms. The action levels are summarized below. • Action Stage: The water level at which some mitigation action should be considered in preparation for an approaching coastal storm tide. • Minor Flooding Stage: The water level at which some public threat, such as minor flooding of low-lying roads and infrastructure, may be anticipated although minimal or no property damage is expected. • Moderate Flooding Stage: The water level at which some inundation of structures and roads and possibly some evacuation of people and/or transfer of property to higher elevations can be anticipated. • Major Flooding Stage: The water level at which extensive inundation of structures, properties, and roads and significant evacuation of people to higher elevations is anticipated.

As an elevation-based system for describing the location and level at which storm tides begin to flow inland, storm tide pathways can be associated with the NWS descriptive flood stages. For this reason, STPs comprising the final data set relate directly to MLLW and have been color coded to correspond to NWS’s characterization of action levels. Over time, these descriptions can be expanded, modified, and supplemented with more detailed information corresponding to individual STPs based on the observations of municipal emergency managers and responders. Similarly, descriptions of Action Levels for areas not covered by NWS descriptions could be developed by archiving observations that correlate water levels with actual flooding events, elevations, and locations. As an example, Table 5 summarizes the current NWS description of Action Levels for Provincetown. (Source: https://water.weather.gov/ahps2/hydrograph.php?wfo=box&gage=pvhm3).

Elevation Action Level (MLLW FT.) Major life threatening flooding occurs in Provincetown and Truro. Provincetown becomes isolated, with inundation along Routes 6 and 6A. Significant inundation occurs in the greater vicinity of Commercial Street and many adjacent side streets. Truro could 17 become bisected with flooding along Route 6 and streets in the greater vicinity of the Pamet River and Little Pamet River marshes. Heed the advice of local officials and evacuate if asked to do so. Major coastal flooding occurs in Provincetown and Truro, with Provincetown becoming isolated due to inundation of Routes 6 and 6A. Numerous roads in Provincetown are flooded, including but not limited to large stretches of Commercial Street, Routes 6 and 16 6A, as well as connecting side streets. Provincetown Airport is completely flooded. In Truro major flooding occurs in the greater vicinity of the Pamet River and Little Pamet River and associated marshland, with inundation along numerous nearby roads. Major coastal flooding occurs in Provincetown and Truro. This includes flooding of 15 Provincetown Airport, and inundation along stretches of numerous roads including Routes 6 and 6A, stretches of Commercial Street and nearby side streets. Provincetown

21

may become isolated. In Truro portions of Route 6 and 6A are also flooded, with flooding of roadways including Dechampes Way, Great Hills and Salt Marsh Lanes, and Fisher, Old County, Castle, Great Hills, and Old Pamet Roads. Expect moderate coastal flooding in the vicinity of Provincetown and Truro. In Provincetown, flooding occurs at Provincetown Municipal Airport, Race Point Road, Provincelands Road, and portions of Commercial Street and Route 6A. In Truro flooding 14 occurs in the vicinity of the Pamet River and Parker Marsh, with flooding on several roads including Castle Road, Eagle Neck Road, Phats Valley Road and Mill Pond Road. Heed the advice of local officials, and evacuate if asked to do so Expect minor coastal flooding of some low-lying roadways. Minor coastal flooding 13 occurs in Provincetown, in the vicinity of Race Point Road and Provincetown Airport. In Truro backwater flooding occurs along the Pamet River. Table 5. Provincetown NWS Action Levels.

Table 6 illustrates the relationship between NWS Action Levels and contemporary Cape Cod Bay tidal datums for Sandwich, Sesuit, and Provincetown. Action levels for Boston and Scituate have been provided for a comparison of various action levels based on geographic location.

Boston Harbor Scituate Harbor Sesuit Harbor Provincetown Harbor Sandwich 8443970 8445138 8447241 8446121 NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW STP Mapping Elevations Upper Limit (Meters) ------4.5 --- 4.5 --- 4.5 --- 4.5 --- Upper Limit (FT) ------14.75 20.00 14.75 20.00 14.75 20.00 14.75 20.00 Base ------9.66 14.90 10.61 16.38 10.61 16.38 10.61 16.38

NWS Action Levels Major 10.5 16.0 10.0 15.5 9.2 15.0 10.2 16.0 9.5 15.0 Moderate 9.0 14.5 8.0 13.5 8.2 14.0 8.7 14.5 8.5 14.0 Minor 7.0 12.5 6.0 11.5 6.2 12.0 7.2 13.0 7.5 13.0 Action 6.0 11.5 5.5 11.0 5.7 11.5 6.2 12.0 6.5 12.0

Tidal Datums MHHW 4.77 10.28 4.28 9.74 4.79 10.58 4.69 10.46 4.62 10.08 MHW 4.33 9.84 3.84 9.30 4.34 10.13 4.24 10.01 4.16 9.62 MSL -0.30 5.21 -0.57 4.89 -0.42 5.37 -0.54 5.23 -0.43 5.03 MTL -0.42 5.09 -0.64 4.83 -0.57 5.22 -0.62 5.15 -0.48 4.98 MLW -5.16 0.35 -5.11 0.35 -5.48 0.31 -5.49 0.28 -5.13 0.33 MLLW -5.51 0.00 -5.46 0.00 -5.79 0.00 -5.77 0.00 -5.46 0.00

GT 10.28 10.28 9.74 9.74 10.58 10.58 10.46 10.46 10.08 10.08 MN 9.49 9.49 8.95 8.95 9.82 9.82 9.73 9.73 9.29 9.29

Highest Obs. Tide Elevation 9.66 15.17 9.49 14.95 9.40 15.19 10.61 16.38 9.77 15.23 Date 1/4/2018 1/4/2018 2/8/1978 2/8/2019 2/7/1978 2/7/1978 1/27/2015 1/27/2015 1/4/2018 1/4/2018 Time 17:42 17:42 12:45 12:45 Table 6. National Weather Service Action Levels Cape Cod Bay Units: Feet

Storm Tide Pathways Across Cape Cod Bay The desktop analysis of the 2013-2014 lidar data yielded 1,646 potential STPs throughout 8 towns, Barnstable, Brewster, Dennis, Eastham, Orleans, Sandwich, Wellfleet, and Yarmouth. Additional

22 fieldwork was not conducted in Provincetown and Truro as the 2013-2014 lidar was used in the previous studies for those towns (Borrelli et al., 2016, Borrelli et al., 2017). The fieldwork took place over 19 days from March 13th to July 3rd, 2019, and October 24th - 29th of 2019.

Each potential STP identified in the desktop analysis was inspected by the field team and the location was moved when observations by the field team determined that the lidar no longer reflected the 2019 terrain. Interestingly, the team started field work at the Sandwich East Boat Basin along the east side of the Cape Cod Canal. where the initial STPs to be mapped were clearly incorrect. After checking survey control, comparing 2013-14 and 2008 orthophotos, and conversations with the Sandwich Harbormaster, it was determined that the Basin and the surrounding municipal buildings had undergone significant construction activity between the time of the lidar data collection and March of 2019. Consequently, the team reassessed the area in the field, identified and collected new (and former if still relevant) STP data for incorporation into the final map products and database - a reminder of the value and need for field verification.

Where possible, the field team occupied all original 1,646 STPs identified in the desktop analysis. As discussed above, however, where STPs were found to be located on private property, dynamic natural landforms, or otherwise inaccessible STPs were logged in the database attribute table as unverified for labeling in map documents, Of the 1,646 STPs identified in the desktop analysis, 415 were eliminated during the field verification process and removed from the final database. Conversely, the field team located and evaluated potential STPs in low-lying areas that were not captured by the lidar data during desktop analysis and, where warranted, added them as part of the fieldwork to better reflect the present-day topography and/or vulnerability, once again highlighting the need for field-based verification of each potential STP.

A total of 164 additional STPs were added to the final database as a result of the fieldwork, yielding a final set of 1,395 STPs throughout the 8 towns. During the field work 710 pathways (50.8% of the total) were moved more than a meter horizontally from their original position determined in the desktop analysis to better reflect current, real-world conditions. The 1,395 STPs were added to the existing storm tide pathway database from Provincetown and Truro for a final total of 1,505 pathways along the 10 towns from the Cape Cod Canal to Race Point in Provincetown (Figure 6).

Several types of STPs are included in this dataset: standard storm tide pathways (STPs) as discussed above; ‘spillways’ (STP-S); ‘roadways’ (STP-R); and unverified (STP-U) (Table 7). These sub-types were developed to reflect different on-the-ground morphologies and techniques needed to identify and/or describe the geographic setting of the STPs at these locations. It should be noted that 371 of the final 1,505 STPs were tidally restricted (i.e., subject to potentially restricted flow conditions due to the presence of culverts and other limiting conditions) and cross over multiple types of STPs and therefore were not identified by the tidally restricted designation alone.

23

Figure 6. Location of the mapped storm tide pathways for the study area. STPs are color-coded by elevation.

Table 7. Storm Tide Pathways for Cape Cod Bay by type. Storm Tide Standard Spillway Roadway Unverified Pathways (STP) (STP-S) (STP-R) (STP-U) 1505 845 269 184 207

The ‘standard’ STP can be described as a relatively narrow low-lying area or pathway that could convey coastal flood waters inland. (Figure 4). Stopping flow at such an STP would prevent inundation up to a given elevation defined as a Pathway Activation Level (PAL), or the level at which water will begin to flow. For example, the PAL for the STP in Figure 4 is 3.41 m (NAVD 88). Therefore, when the water level reaches 3.41 m regardless of the driver (i.e., storm surge, waves, sea level rise) it will begin to flow inland. The PALs can be used by town staff to prioritize the most vulnerable STPs as efficiently and effectively as possible. The data are grouped in 0.5 ft increments in Table 8 for the study entire area and for each town below.

The term ‘spillway’ was developed as a way to reflect STPs located on areas of broad, low relief. The STP-S are situated in very flat areas and are representative of long broad weir-like formations

24 as opposed to the discrete point-like nature of the conventional STPs (Figure 7). Actions planned to mitigate spillway STPs generally require detailed topographic surveys and design solutions for broad areas in order to minimize associated flooding during future events. While difficult to visualize, these areas are of concern because of the lack of well-defined pathways that can be used to control flood waters. Due to this lack of definition, relocation may be more appropriate than efforts to control or redirect floodwaters. Roadway STPs are simply those that only flow over a roadway. No other resource is at risk.

Figure 7. Example of topography consistent with a spillway STP. Almost 20% of the STPs mapped in the study were spillways. These areas will require a more extensive and concerted efforts to address.

Finally, an unverified STP (STP-U) was defined to be an STP that was identified during the lidar analysis but was unable to be located or occupied by the field team for several reasons. The lidar used for this study is a ‘bare earth’ lidar data set, which is typical for these types of analyses. As discussed above, vegetation (e.g., trees, bushes, beach grass, salt marsh, etc.) and structures (e.g., houses, buildings, etc.) are removed from the data during processing, hence the ‘bare earth’ name. Where this occurs, areas such as low spots found in the lidar analysis are not always physically accessible, often located on private property, or merely artifacts of the bare-earth process. 207 STP-Us found in this study were located in low areas that will experience water flow, however, actual STP locations could not be determined solely by the desktop analysis. These situations were encountered typically in areas of natural topographic change (e.g., coastal dune migration) or human alteration (construction, development) since the date of lidar collection. For the former, new surveys could be conducted by field teams using drones or when new lidar becomes available. For the latter, further field work will require permission to enter private property. All these STP- U’s are included in the final database as towns may want to pursue permission to locate critical STPs on private property or to monitor the changing positions of those located on dynamic landforms (e.g., with periodic and localized drone surveys).

25

Plane Total Acres by STPs Range (ft) (ft) Acres TWL 11.5 34 11.01-11.50 930.2 12.0 16 11.51-12.00 1,416.4 486.2 12.5 32 12.01-12.50 1,835.2 418.8 13.0 48 12.51-13.00 2,269.2 434.0 13.5 64 13.01-13.50 2,697.5 428.3 14.0 84 13.51-14.00 3,183.9 486.4 14.5 177 14.01-14.50 4,850.9 1,666.9 15.0 176 14.51-15.00 5,985.3 1,134.4 15.5 133 15.01-15.50 6,477.7 492.5 16.0 112 15.51-16.00 6,935.6 457.9 16.5 63 16.01-16.50 8,303.3 1,367.7 17.0 130 16.51-17.00 9,291.8 988.5 17.5 67 17.01-17.50 9,919.3 627.6 18.0 41 17.51-18.00 10,176.4 257.1 18.5 96 18.01-18.50 10,822.9 646.4 19.0 70 18.51-19.00 11,244.7 421.8 19.5 64 19.01-19.50 11,687.3 442.6 20.0 58 19.51-20.00 12,360.8 673.6 20.5 40 20.01-20.50 12,829.2 468.4 1,505 11,899.0 Table 8. Total storm tide pathways and areas inundated and by Total Water Level (TWL). ‘Acres by TWL’ are the acres that become inundated with a 6-inch increase of TWL.

Many low-lying coastal areas are experiencing inundation associated with nuisance, or sunny day flooding, storm surge and sea level rise. Based on data developed in this study, on average approximately 660 acres of land are inundated for every 6 inches of rise in total water level from 11.5 – 20.5 ft (MLLW) (Figure 8). For the ten Cape Cod Bay towns, this increase ranges from a low of 257 acres between 17.5 – 18.0 ft, to a high of 1,667 acres between 14.0 - 14.5 ft.

Using the GIS data, these and other types of STP summary data can be developed by towns to focus long-term planning and design efforts on threshold or priority elevations that highlight areas subject to inundation associated with sea level rise or with an increasing frequency of nuisance, or sunny day flooding. In addition, summary information can be generated to guide and develop short-term, storm preparation and proactive mitigation measures and strategies. The initial 2016 and 2017 STP pilot mapping projects have been used by Provincetown and Truro to prepare for approaching storms. For certain storms, town staff have monitored NWS real-time total water level predictions and implemented pre-storm mitigation measures successfully for affected STPs using sandbags, portable flood walls, and cordoning off potential hazardous roads for vehicles or pedestrians.

26

Cape Cod Bay Municipalities

Total Acres Acres by TWL 14,000 2,000 12,000 10,000 1,500 8,000 1,000 6,000 4,000 500 2,000 TWL by Acres

0 0 Cumulative Acres Inundated Acres Cumulative Total Water Level (MLLW, ft)

Figure 8. Acres of Inundation. Red line represents the approximate total cumulative area inundated with each 6-inch increase in total water level. Green line represents the approximate area inundated for each individual 6-inch increase in total water level. The average is approximately 660 acres per 6-inch increase in total water level.

It should be noted that for the following town summaries, the total water level of the January 4th, 2018 nor’easter (9.9 ft NAVD 88 or 15.2 ft MLLW) was used as the ‘storm of record’ for the Provincetown, Truro, Wellfleet, Eastham, and Orleans statistics. For the rest of the towns (Brewster, Dennis, Yarmouth, Barnstable and Sandwich) the higher total water level of the January 27th, 2015 nor’easter (10.6 ft NAVD 88 or 16.4 ft MLLW) was used.

Although the greatest increase in inundation area for a 0.5-foot increase in total water level falls within the historical range of past flooding (1,428 acres between 14.0 - 14.5 ft), the second largest increase in area flooded, approximately 1,050 acres, occurs between 16.0 – 16.5 ft, an elevation that is less than a foot above the project storm of record for Provincetown, Truro, Wellfleet, Eastham, and Orleans. In fact, if the storm surge of the Blizzard of January 2018 occurred closer to high tide and mirrored the magnitude of the Blizzard of 2015, 4.5 feet vs 3.7 feet, an additional 1,244 acres may have been inundated. The 2015 storm demonstrates that storms surges of this magnitude are not uncommon. For these reasons, the upper limit of the storm tide pathways maps was extended to an elevation above that of the identified project storm of record to allow municipalities the time to prepare and respond to more powerful storms in the future.

As illustrated by the final database, many of the mapped STPs are located just above the water elevation of the project storm of record used as the baseline for mapping STPs (10.61 feet NAVD88). Based on the completed mapping, 237 STPs were found to be less than 12 inches above the project storm of record (Figure 9). In other words, included in the STP mapping data are 237 locations throughout the study area that have never been flooded before, but would likely be

27 inundated with another 12 inches of water. A total of 108 of those 237 STPs would likely flood with only an increase in 6 inches to the total water level.

Figure 9. Storm Tide pathways throughout the study area that are <12 inches above the storm of record denoted by white circles (n = 237). These areas were not flooded due to storm tides (storm surge, high tides, waves, etc.) associated with the 2014 project storm of record used as the baseline for this analysis.

STORM TIDE PATHWAYS BY TOWN

The Center for Coastal Studies and the Cape Cod Cooperative Extension met with each of the following towns individually at the beginning of the project: Barnstable, Brewster, Dennis, Eastham, Orleans, Sandwich, Wellfleet, and Yarmouth. These meetings were held with staff from Police, Fire and Public Works Departments as well as Resource Managers and other town staff for the purpose of presenting town staff with preliminary maps of their town showing initial STP locations to get feedback on mapped areas and any potential STPs that may have been missed. This feedback was a useful way of confirming the observations of the field surveys and, where necessary, adjusting final data to reflect the observations of those most familiar with the vulnerable areas of each town. At the end of the project, in the spring of 2021, three meetings were held with

28 regional groupings of town staff to present findings and demonstrate the stormtides.org website. (See discussion below for more details about the website).

The sections below provide a brief summary for each town of some of the STP that can be developed from the GIS data. As executive summaries for each town the entire report should be read to understand the methodology, terminology, and findings of the mapping work. The sections are formatted to provide summary data for each town and to facilitate comparisons between towns including general reference for identifying STPs that may potentially impact more than one town.

All elevations presented the town tables are referenced to MLLW. As the plane of reference for soundings on NOAA navigation charts and tide tables, MLLW is often referred to as “chart datum” and used for many local coastal management applications. As discussed above, MLLW is used by the National Weather Service (NWS) for its estimates of total water level (TWL) (astronomical tide height plus storm surge) associated with approaching coastal storms. For this reason, all TWL are presented in MLLW. Recognizing that MLLW varies locally, elevation referenced to NAVD88 are included within the GIS database developed for this project to facilitate regional comparisons.

29

Town of Barnstable Field work to verify and locate storm tide pathways in the town of Barnstable was conducted in April and May of 2019. Based on the desktop analysis and the field verification, a total of 135 storm tide pathways were identified in the Barnstable study area (Table 9, Figure 10). Of that total 17 STPs were identified as potentially tidally restricted (i.e., subject to potentially restricted flow Figure 10. All 135 Storm Tide Pathways in Barnstable. Sandwich (red) to the west and Yarmouth (green) to the east are included as flooding through conditions due to the presence of these STPs may affect Barnstable. Due to the rapidly evolving nature of culverts and other flow limiting Sandy Neck, no STPs were mapped there. structures or conditions). These STPs should be monitored and may warrant further analysis by a professional engineer as associated water levels are likely to be affected by the Table 9. Barnstable STPs by Elevation. hydraulics of the restrictions. MLLW Total ∆ (ft) STPs Acres Acres Analysis of the storm tide pathways throughout the study area 11.50 1 324.0 illustrate the nature of the future threat faced by low-lying 12.00 1 422.1 98.1 areas. The project storm of record used for Barnstable is the 12.50 2 503.9 81.8 January 27th, 2015 storm. This study has identified 12 13.00 2 645.1 141.2 pathways in Barnstable that are 12 inches above the water 13.50 2 762.5 117.4 level recorded by the USGS Sesuit Harbor tide gauge (16.4 ft 14.00 8 862.6 100.1 14.50 7 960.4 97.9 MLLW). Such a 1-foot increase in total water level is likely to 15.00 20 1,054.2 93.8 flood approximately 152 acres of land (Figure 11). For 15.50 21 1,142.8 88.6 example, from 16.5 to 17.0 ft (MLLW) approximately 66 16.00 8 1,257.6 114.8 additional acres are flooded, while from 17.0 to 17.5 ft 16.50 4 1,414.1 156.5 (MLLW) an additional 85 acres are flooded. These represent 17.00 8 1,480.9 66.8 new areas of flooding that town staff may not be aware of but 17.50 11 1,566.0 85.1 might want to consider for future planning efforts. 18.00 2 1,590.7 24.7 18.50 16 1,725.6 134.9 19.00 7 1,789.7 64.0 For the reasons presented above, the final location of 41 19.50 4 1,856.4 66.7 pathways (30%) were moved from their initial position 20.00 9 1,926.8 70.4 identified in the desktop analysis more than 1 m horizontally 20.50 2 2,001.2 74.4 during field surveys. In addition, it should be noted that 39 of the STPs were not field verified either due to their location on private property in a dynamic setting subject to natural change such

30

Barnstable 2500

2000

1500

1000 Acres Inundated Acres 500

0 11 12 13 14 15 16 17 18 19 20 Total Water Level in MLLW (ft)

Figure 11. Town of Barnstable. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline. as a coastal dune, or physically inaccessible to the field survey team. For example, it was determined that no STPs were to be mapped on Sandy Neck for this reason. Overall, these STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

31

Town of Brewster

Field work to verify and locate storm tide pathways found in the town of Brewster was conducted in June of 2019. Based on the desktop analysis and the field verification, a total of 74 storm tide pathways were identified in the Brewster study area (Table 10, Figure 12). Of that total 20

Figure 12. All 71 Storm Tide Pathways in Brewster. Dennis (green) to the were identified as potentially west and Orleans (blue) to the east are included as flooding through these tidally restricted (i.e., subject to STPs may affect Brewster. potentially restricted flow conditions due to the presence of culverts and other flow limiting structures or conditions). These STPs should be monitored and may warrant further analysis by a professional engineer as associated water levels are likely to be affected by the hydraulics of the restrictions. Table 10. Brewster STPs by Elevation. Analysis of the storm tide pathways throughout the MLLW Total study area illustrate the nature of the future threat faced (ft) STPs Acres ∆ Acres by low-lying areas. The project storm of record used for 11.50 0 39.2 th Brewster is the January 27 , 2015 storm. This study has 12.00 0 73.5 34.3 identified 12 pathways in Brewster that are 12 inches 12.50 2 102.4 28.9 above the water level recorded by the USGS Sesuit 13.00 1 123.1 20.6 Harbor tide gauge (16.4 ft MLLW). Such a 1-foot 13.50 3 141.8 18.7 increase in total water level is likely to flood 14.00 1 163.8 22.0 approximately 49 acres of land (Figure 13). For 14.50 3 185.1 21.3 example, from 16.5 to 17.0 ft (MLLW) approximately 15.00 3 202.9 17.8 27 acres are flooded, while from 17.0 to 17.5 ft 15.50 218.3 15.3 (MLLW) 22 acres are flooded. These represent new 16.00 4 232.8 14.5 areas of flooding that town staff may not be aware of 16.50 1 248.8 16.0 but might want to consider for future planning efforts. 17.00 11 275.6 26.8 17.50 1 298.2 22.6 18.00 2 309.1 10.8 For the reasons presented above, the final location of 50 18.50 6 343.2 34.1 pathways (67%) were moved from their initial position 19.00 7 397.0 53.9 identified in the desktop analysis more than 1 m 19.50 11 417.7 20.6 horizontally during field surveys. In addition, it should 20.00 13 469.4 51.7 be noted that 12 of the STPs were not field verified due 20.50 5 492.4 23.1 to their location on private property, in a dynamic setting subject to natural change, such as a coastal dune, or physically inaccessible to the field

32

Brewster 600

500

400

300

200 Acres Inundated Acres 100

0 11 12 13 14 15 16 17 18 19 20 Total Water Level in MLLW (ft)

Figure 13. Town of Brewster. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline. survey team. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

33

Town of Dennis

Field work to verify and locate storm tide pathways found in the town of Dennis was conducted in June of 2019. Based on the desktop analysis and the field verification, a total of 187 storm tide pathways were identified were identified in the Dennis study area (Table 11, Figure 14). Of that final total 62 were identified as potentially tidally restricted (i.e., subject to Figure 14. All 238 Storm Tide Pathways in Dennis. STPs in Barnstable potentially restricted flow (green) to the west and Yarmouth (blue) to the east are included as conditions due to the presence of flooding through these STPs may affect Dennis. culverts and other flow limiting structures or conditions). These STPs should be monitored and may warrant further analysis by a professional engineer as associated water levels are Table 11. Dennis STPs by Elevation. likely to be affected by the hydraulics of the restrictions. MLLW Total (ft) STPs Acres ∆ Acres Analysis of the storm tide pathways throughout the 11.50 1 51.8 study area illustrate the nature of the future threat faced 12.00 3 95.5 43.7 by low-lying areas. The project storm of record used for 12.50 3 130.5 35.0 Dennis is the January 27th, 2015 storm. This study has 13.00 0 162.3 31.7 identified 41 pathways in Dennis that are 12 inches 13.50 5 191.4 29.1 above the water level recorded by the USGS Sesuit 14.00 9 220.1 28.7 14.50 15 253.9 33.8 Harbor tide gauge (16.4 ft MLLW). Such a 1-foot 15.00 18 288.1 34.2 increase in total water level is likely to flood 15.50 11 333.2 45.1 approximately 66 acres of land (Figure 15). For 16.00 24 372.1 38.8 example, from 16.5 to 17.0 ft (MLLW) approximately 16.50 2 410.9 38.9 34 acres are flooded, while from 17.0 to 17.5 ft 17.00 28 445.1 34.2 (MLLW) another 32 acres are flooded. These represent 17.50 13 476.8 31.7 new areas of flooding that town staff may not be aware 18.00 7 494.0 17.2 18.50 15 555.7 61.7 of but might want to consider for future planning 19.00 9 585.8 30.1 efforts. 19.50 10 646.1 60.3 20.00 8 687.2 41.0 For the reasons presented above, the final location of 78 20.50 6 739.0 51.9 pathways were moved from their initial position identified in the desktop analysis more than 1 m horizontally during field surveys (42%). In addition, it should be noted that 12 STPs were not field

34

Dennis 800 700 600 500 400 300

Acres Inundated Acres 200 100 0 11 12 13 14 15 16 17 18 19 20 Total Water Level in MLLW (ft)

Figure 15. Town of Dennis. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline. verified either due to their location on private property, in a dynamic setting subject to natural change, such as a coastal dune, or physically inaccessible to the survey team. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

35

Town of Eastham

Field work to verify and locate storm tide pathways found in the town of Eastham was conducted in July and October of 2019. Based on the desktop analysis and the field verification, a total of 195 storm tide pathways were identified in the Eastham study area (Table 12, Figure 16). Of that final total 49 were identified as potentially tidally restricted (i.e., subject to potentially restricted flow conditions due to Figure 16. All 178 Storm Tide Pathways in Eastham. Orleans (blue) to the south and Wellfleet (green) to the east are included as flooding through the presence of culverts and other these STPs may affect Eastham. flow limiting structures or conditions). These STPs should be monitored and may warrant further analysis by a professional engineer as associated water levels are likely to be Table 12. Eastham STPs by Elevation. affected by the hydraulics of the restrictions. MLLW Total (ft) STPs Acres ∆ Acres Analysis of the storm tide pathways throughout the 11.50 1 74.0 study area illustrate the nature of the future threat faced 12.00 3 112.3 38.3 by low-lying areas. The project storm of record used for 12.50 4 151.9 39.6 Eastham is the January 4th, 2018 storm. This study has 13.00 14 175.7 23.8 identified 21 pathways in Eastham that are 12 inches 13.50 16 203.9 28.2 above the water level recorded by the USGS 14.00 12 235.4 31.6 14.50 14 260.0 24.6 Provincetown Harbor tide gauge (15.3 ft MLLW). Such 15.00 14 289.8 29.8 a 1-foot increase in total water level is likely to flood 15.50 16 317.2 27.4 approximately 53.3 acres of land (Figure 17). For 16.00 13 342.4 25.2 example, from 15.5 to 16.0 ft (MLLW) approximately 16.50 8 370.6 28.1 25 acres are flooded, from 16.0 to 16.5 ft (MLLW) 28 17.00 25 565.9 195.4 acres are flooded. These represent new areas of flooding 17.50 8 592.5 26.5 that town staff may not be aware of but might want to 18.00 14 624.3 31.8 18.50 16 720.1 95.8 consider for future planning efforts. 19.00 6 760.8 40.7 19.50 6 807.1 46.4 For the reasons presented above, the final location of 20.00 1 1009.2 202.0 108 pathways were moved from their initial position 20.50 4 1059.7 50.6 identified in the desktop analysis more than 1 m horizontally during field surveys (55%). In addition, it should be noted that 24 STPs were not field verified due to their location on private

36

Eastham 1200

1000

800

600

400 Acres Inundated Acres 200

0 11 12 13 14 15 16 17 18 19 20 Total Water Level in MLLW (ft)

Figure 17. Town of Eastham. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline. property, in a dynamic setting subject to natural change such as a coastal dune, or physically inaccessible to the field survey team. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

37

Town of Orleans

Field work to verify and locate storm tide pathways found in the town of Orleans was conducted in June and July of 2019. Based on the desktop analysis and the field verification, a total of 104 storm tide pathways were identified in the Orleans study area (Table 13, Figure 18). Of that final total 17 were identified as potentially tidally restricted (i.e., subject to potentially restricted flow conditions due to Figure 18. All 135 Storm Tide Pathways in Orleans. Brewster (green) to the south and Eastham (pink) to the north are included as flooding through the presence of culverts and other these STPs may affect Orleans. flow limiting structures or conditions). These STPs should be monitored and may Table 13. Orleans STPs by Elevation. warrant further analysis by a professional engineer as MLLW Total associated water levels are likely to be affected by the (ft) STPs Acres ∆ Acres hydraulics of the restrictions. 11.50 0 28.2 12.00 0 50.6 22.4 Analysis of the storm tide pathways throughout the 12.50 0 67.6 16.9 study area illustrate the nature of the future threat faced 13.00 0 81.6 14.0 by low-lying areas. The project storm of record used for 13.50 1 100.1 18.5 Orleans is the January 4th, 2018 storm. This study has 14.00 3 146.9 46.7 identified 17 pathways in Orleans that are 12 inches 14.50 8 172.2 25.4 above the water level recorded by the USGS 15.00 6 188.9 16.6 Provincetown Harbor tide gauge (15.3 ft MLLW). Such 15.50 12 207.0 18.1 a 1-foot increase in total water level is likely to flood 16.00 15 225.6 18.6 approximately 66 acres of land (Figure 19). For 16.50 2 273.1 47.5 17.00 12 288.4 15.2 example, from 15.5 to 16.0 ft (MLLW) approximately 17.50 6 305.2 16.8 19 acres are flooded while from 16.0 to 16.5 ft (MLLW) 18.00 1 315.2 10.0 47 acres are flooded. These represent new areas of 18.50 11 339.7 24.5 flooding that town staff may not be aware of but might 19.00 8 361.1 21.4 want to consider for future planning efforts. 19.50 6 382.8 21.7 20.00 6 399.3 16.6 For the reasons presented above, the final location of 51 20.50 7 419.2 19.9 pathways were moved from their initial position identified in the desktop analysis more than 1 m horizontally during field surveys (49%). In

38

Orleans 500 450 400 350 300 250 Acres 200 150 100 50 0 11 12 13 14 15 16 17 18 19 20 Elevation (MLLW FT)

Figure 19. Town of Orleans. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline. addition, it should be noted that 23 of the STPs were not field verified due to their location on private property, in a dynamic setting subject to natural change such as a coastal dune, or physically inaccessible to the project team. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

39

Town of Provincetown

Field work to verify and locate storm tide pathways found in the town of Provincetown was conducted for a previous study (Borrelli, et al., 2016) STPs were integrated with the present work. Since the NWS references total water level estimates to local MLLW, after meeting with NWS staff, the planes for both Truro and Provincetown were updated, as necessary, for Figure 20. All 135 Storm Tide Pathways in Provincetown. Truro (blue) to seamless visualization on the the east is included as flooding through these STPs may affect NWS Storm Surge website and Provincetown. in the CCS app.

Based on the desktop analysis and the field verification, Table 14. Provincetown STPs by Elevation. a total of 72 storm tide pathways were identified in the Provincetown study area (Table 14, Figure 20). Of that MLLW Total (ft) STPs Acres ∆ Acres final total 6 were identified as potentially tidally 11.50 0 128.6 restricted (i.e., subject to potentially restricted flow 12.00 0 219.1 90.5 conditions due to the presence of culverts and other 12.50 2 292.8 73.7 flow limiting structures or conditions). These STPs 13.00 1 372.2 79.4 should be monitored and may warrant further analysis 13.50 7 459.3 87.2 by a professional engineer as associated water levels are 14.00 7 582.6 123.2 14.50 12 659.8 77.3 likely to be affected by the hydraulics of the restrictions. 15.00 10 788.5 128.6 15.50 11 917.2 128.7 16.00 1 986.1 68.9 Analysis of the storm tide pathways throughout the 16.50 3 1276.6 290.6 study area illustrate the nature of the future threat faced 17.00 1 1767.9 491.3 by low-lying areas. The project storm of record used for 17.50 1 1959.6 191.6 the Provincetown and Truro analyses was the Blizzard 18.00 2008.8 49.2 th 18.50 2074.4 65.6 of ’78 (15.1 ft MLLW) that occurred on February 7 , 19.00 2121.6 47.2 th 1978. On January 4 , 2018, this historical water level 19.50 2206.3 84.7 was exceeded by 0.2 feet with water levels recorded at 20.00 2283.0 76.7 15.3 ft MLLW on the USGS Provincetown Harbor Tide 20.50 2324.2 41.1 Gauge. Unlike other areas along the southerly shore of Cape Cod Bay where the January storm of 2015 serves as the project storm of record, the 2018 storm remains the contemporary storm of

40 record for Provincetown Harbor and Pamet Harbor in Truro. With total water levels for the contemporary storm of record for Provincetown and Pamet Harbors less than a foot lower than along the southerly shoreline of Cape Cod Bay, original STP values for these two areas were integrated into the present analysis.

This study has identified 4 pathways in Provincetown that are approximately 12 inches above the project storm used as the baseline for the 2016 study. Such a 1-foot increase in total water level is likely to flood approximately 359 acres of land (Figure 21). For example, from 15.5 to 16.0 ft (MLLW) approximately 69 acres are flooded while from 16.0 to 16.5 ft (MLLW) 291 acres are flooded. These represent new areas of flooding that town staff may not be aware of but might want to consider for future planning efforts. Provincetown 3000

2500

2000

1500

1000 Acres Inundated Acres 500

0 11 12 13 14 15 16 17 18 19 20 Total Water Level in MLLW (ft)

Figure 21. Town of Provincetown. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline.

For the reasons presented above, the final location of 22 pathways were moved from their initial position identified in the desktop analysis more than 1 m horizontally during field surveys (30%). In addition, it should be noted that 5 of the STPs were not field verified due to their location on private property, in a dynamic setting subject to natural change such as a coastal dune, or physically inaccessible to the survey team. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways. 41

Town of Sandwich

Field work to verify and locate storm tide pathways found in the town of Sandwich was conducted in March and April of 2019. A total of 396 pathways were identified in the initial desktop analysis. Based on the desktop analysis and the field verification, a total of 325 storm tide pathways were identified in the Sandwich study area (Table 15, Figure 22). Of that final total Figure 12. All 135 Storm Tide Pathways in Sandwich. Bourne (green) to 87 were identified as potentially the left and Barnstable (yellow) to the right are included as flooding tidally restricted (i.e., subject to through these STPs may affect Sandwich. potentially restricted flow conditions due to the presence of culverts and other flow limiting structures or conditions). These STPs should be monitored and may warrant further Table 15. Sandwich STPs by Elevation. analysis by a professional engineer as associated water levels are likely to be affected by the hydraulics of the MLLW Total (ft) STPs Acres ∆ Acres restrictions. 11.50 12 86.6 12.00 2 148.8 62.3 Analysis of the Sandwich storm tide pathways 12.50 13 213.3 64.5 illustrates the nature of the future threat faced by low- 13.00 25 270.8 57.5 lying areas. The project storm of record used for 13.50 22 337.8 67.0 Sandwich is the January 27th, 2015 storm. This study 14.00 22 401.8 64.0 14.50 23 466.5 64.7 has identified 32 pathways in Sandwich that are 12 15.00 34 528.1 61.6 inches above the water level recorded by the USGS 15.50 22 590.7 62.6 Sesuit Harbor tide gauge (16.4 ft MLLW). Such a 1- 16.00 16 646.5 55.8 foot increase in total water level is likely to flood 16.50 20 728.8 82.4 approximately 213 acres of land (Figure 23). For 17.00 17 792.3 63.4 example, from 16.5 to 17.0 ft (MLLW) approximately 17.50 15 941.9 149.7 63 acres are flooded, from 17.0 to 17.5 ft (MLLW) 18.00 7 993.5 51.6 18.50 10 1098.0 104.5 150 acres are flooded. These represent new areas of 19.00 20 1165.0 67.1 flooding that town staff may not be aware of but might 19.50 19 1224.4 59.3 want to consider for future planning efforts. 20.00 13 1300.5 76.2 20.50 13 1384.9 84.4 For the reasons presented above, the final location of 128 pathways were moved from their initial position identified in the desktop analysis more than 1 m horizontally during field surveys

42

Sandwich 1600 1400 1200 1000 800 600

Acres Inundated Acres 400 200 0 11 12 13 14 15 16 17 18 19 20 Total Water Level in MLLW (ft)

Figure 23. Town of Sandwich. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline.

(39%). In addition, it should be noted that 66 STPs were not field verified due to their location on private property, in a dynamic setting subject to natural change such as a coastal dune, or physically inaccessible to the survey team. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

43

Town of Truro

Field work to verify and locate storm tide pathways found in the town of Truro was conducted in for a previous study (Borrelli, et al., 2017) STPs were integrated with the present work. Since the NWS references total water level estimates to local MLLW, after meeting with NWS staff, the planes for both Truro and Provincetown were updated, as necessary, for seamless visualization on the NWS Storm Figure 24. All 135 Storm Tide Pathways in Truro. Provincetown (green) to the north and Wellfleet (green) to the south are included as flooding Surge website and in the CCS through these STPs may affect Truro. app. Table 16. Truro STPs by Elevation. Based on the desktop analysis and the field verification, MLLW Total a total of 38 storm tide pathways were identified in the (ft) STPs Acres ∆ Acres Truro study area (Table 16, Figure 24). Of that final 11.50 2 22.2 total 12 were identified as potentially tidally restricted 12.00 1 32.8 10.6 (i.e., subject to potentially restricted flow conditions 12.50 1 41.7 8.9 due to the presence of culverts and other flow limiting 13.00 1 56.8 15.1 13.50 1 68.0 11.2 structures or conditions). These STPs should be 14.00 4 87.6 19.6 monitored and may warrant further analysis by a 14.50 17 292.4 204.7 professional engineer as associated water levels are 15.00 15 928.9 636.5 likely to be affected by the hydraulics of the restrictions. 15.50 1 962.1 33.2 16.00 1 985.8 23.8 Analysis of the storm tide pathways throughout the 16.50 3 1420.9 435.1 17.00 4 1450.5 29.6 study area illustrate the nature of the future threat faced 17.50 2 1484.5 34.0 by low-lying areas. The project storm of record used for 18.00 1 1508.5 23.9 the Provincetown and Truro analyses was the Blizzard 18.50 1547.7 39.2 of ’78 (15.1 ft MLLW) that occurred on February 7th, 19.00 1572.5 24.8 1978. On January 4th, 2018, this historical water level 19.50 1600.4 27.9 was exceeded by 0.2 feet with water levels recorded at 20.00 1667.4 67.0 15.3 ft MLLW on the USGS Provincetown Harbor Tide 20.50 1708.1 40.7 Gauge. Unlike other areas along the southerly shore of Cape Cod Bay where the January storm of 2015 serves as the project storm of record, the 2018 storm remains the project storm of record for Provincetown Harbor and Pamet Harbor in Truro. With total water levels for the project storm of

44 record for Provincetown and Pamet Harbors less than a foot lower than along the southerly shoreline of Cape Cod Bay, original STP values for these two areas were integrated into the present analysis.

This study has identified 4 pathways in Truro that are 12 inches above the 2018 storm. Such a 1- foot increase in total water level is likely to flood approximately 459 acres of land (Figure 25). For example, from 15.5 to 16.0 ft (MLLW) approximately 23 acres are flooded, while from 16.0 to 16.5 ft (MLLW) 435 acres are flooded. The large number of acres flooded at this interval largely reflects upper Pamet Harbor becoming inundated. These represent new areas of flooding that town staff may not be aware of but might want to consider for future planning efforts.

Truro 2500

2000

1500

1000 Acres Inundated Acres 500

0 11 12 13 14 15 16 17 18 19 20 Total Water Level in MLLW (ft)

Figure 25. Town of Truro. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline.

For the reasons presented above, the final location of 26 pathways were moved from their initial position identified in the desktop analysis more than 1 m horizontally during field surveys (68%). In addition, it should be noted that 8 of the STPs were not field verified due to their location on private property in a dynamic setting subject to natural change, such as a coastal dune, or physically inaccessible to the survey crew. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

45

Town of Wellfleet

Field work to verify and locate storm tide pathways found in the town of Wellfleet was conducted in October of 2019. Based on the desktop analysis and the field verification, a pathways total of 278 storm tide pathways were identified in the Wellfleet study area (Table 17, Figure 26). Of that final total 100 were identified as potentially tidally restricted (i.e., subject to potentially restricted flow Figure 36. All 135 Storm Tide Pathways in Wellfleet. Truro (blue) to the north and Eastham (purple) to the south are included as flooding through conditions due to the presence of these STPs may affect Wellfleet. culverts and other flow limiting structures or conditions). These STPs should be monitored and may warrant further analysis by a professional engineer as associated water levels are Table 17. Wellfleet STPs by Elevation. likely to be affected by the hydraulics of the restrictions. MLLW Total (ft) STPs Acres ∆ Acres Analysis of the storm tide pathways throughout the 11.50 17 138.7 study area illustrate the nature of the future threat faced 12.00 6 194.6 55.9 by low-lying areas. The project storm of record used for 12.50 5 235.6 41.0 Wellfleet analysis is the January 4th, 2018 storm. This 13.00 4 264.1 28.6 study has identified 39 pathways in Wellfleet that are 13.50 6 296.0 31.9 12 inches above the water level recorded by the USGS 14.00 14 328.4 32.3 14.50 72 1424.6 1096.3 Provincetown Harbor tide gauge (15.3 ft MLLW). Such 15.00 42 1471.2 46.5 a 1-foot increase in total water level is likely to flood 15.50 27 1524.4 53.2 approximately 307 acres of land (Figure 27). For 16.00 27 1581.9 57.5 example, from 15.5 to 16.0 ft (MLLW) approximately 16.50 12 1831.2 249.3 58 acres are flooded, from 16.0 to 16.5 ft (MLLW) 249 17.00 10 1873.8 42.6 acres are flooded. The large number of acres getting 17.50 9 1920.0 46.2 flooded at this interval largely reflects Herring River 18.00 6 1953.7 33.6 18.50 9 2002.9 49.3 above the Chequessett Neck Dike becoming inundated. 19.00 5 2051.7 48.8 These represent new areas of flooding that town staff 19.50 3 2086.6 34.9 may not be aware of but might want to consider for 20.00 3 2137.2 50.6 future planning efforts. 20.50 1 2196.3 59.2

For the reasons presented above, the final location of 218 pathways were moved from their initial

46

Wellfleet 3000

2500

2000

1500 Acres 1000

500

0 11 12 13 14 15 16 17 18 19 20 Elevation (MLLW FT)

Figure 27. Town of Wellfleet. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline. The two large jumps between 14.0 – 14.5 (1,096 acres) and 16.0 - 16.5 (249 acres) reflect inundation above the Chequessett Neck Dike. position identified in the desktop analysis more than 1 m horizontally during field surveys (78%). In addition, it should be noted that 99 of the STPs were not field verified due to their location on private property, in a dynamic setting subject to natural change such as a coastal dune, or physically inaccessible to the survey crew. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

47

Town of Yarmouth

Field work to verify and locate storm tide pathways found in the town of Yarmouth was conducted in May of 2019. Based on the desktop analysis and the field verification, a total of 97 storm tide pathways were identified in the Yarmouth study area (Table 18, Figure 28). Of that final total 7 were identified as potentially tidally restricted (i.e., subject to potentially restricted flow conditions due to Figure 48. All 135 Storm Tide Pathways in Yarmouth. Barnstable (yellow) to the west and Dennis (blue) to the east are included as flooding through the presence of culverts and other these STPs may affect Yarmouth. flow limiting structures or conditions). These STPs should be monitored and may warrant further analysis by a professional engineer as associated water levels are likely to be Table 18. Yarmouth STPs by Elevation. affected by the hydraulics of the restrictions. MLLW Total (ft) STPs Acres ∆ Acres

11.50 0 36.8 Analysis of the storm tide pathways throughout the 12.00 0 67.0 30.2 study area illustrate the nature of the future threat faced 12.50 0 95.6 28.5 by low-lying areas. The project storm of record used for 13.00 0 117.5 22.0 Yarmouth is the January 27th, 2015 storm. This study 13.50 1 136.6 19.1 has identified 16 pathways in Yarmouth that are 12 14.00 4 154.8 18.2 14.50 6 175.8 21.0 inches above the water level recorded by the USGS 15.00 14 244.7 68.9 Sesuit Harbor tide gauge (16.4 ft MLLW). Such a 1-foot 15.50 12 264.9 20.2 increase in total water level is likely to flood 16.00 3 304.8 39.9 approximately 46 acres of land (Figure 29). For 16.50 8 328.2 23.4 example, from 16.5 to 17.0 ft (MLLW) approximately 17.00 14 351.3 23.1 23 acres are flooded, from 17.0 to 17.5 ft (MLLW) 23 17.50 1 374.6 23.3 acres are flooded. These represent new areas of flooding 18.00 1 378.8 4.2 18.50 13 415.7 36.9 that town staff may not be aware of but might want to 19.00 8 439.5 23.9 consider for future planning efforts. 19.50 5 459.6 20.1 20.00 5 480.9 21.3 For the reasons presented above, the final location of 36 20.50 2 504.1 23.2 pathways were moved from their initial position identified in the desktop analysis more than 1 m horizontally during field surveys (37%). In addition, it should be noted that 14 of the STPs were

48

Yarmouth 600

500

400

300 Acres 200

100

0 11 12 13 14 15 16 17 18 19 20 Elevation (MLLW FT)

Figure 29. Town of Yarmouth. Total area inundated with ½ ft increases in total water level. Dotted red line is trendline. not field verified due to their location on private property, in a dynamic setting subject to natural change such as a coastal dune, or physically inaccessible to the survey team. These STPs and adjacent areas should be examined further (and perhaps periodically within dynamic settings) on a case-by-case basis to monitor the risk associated with them. Field verification and positional adjustments of the STP identification of unverified STPs in the final database reflect the importance of fieldwork when mapping storm tide pathways.

49

Coastal Flood Threat and Inundation Mapping webpage

SNEWFO-NWS maintains a webpage (https://www.weather.gov/box/coastal) with tide and storm surge forecasts for numerous stations throughout southern New England. As coastal storms approach, viewers can manipulate the webpage to depict the areas and approximate extents and depths of flooding based on the predicted tide stage and forecasted storm surge. As noted on the webpage these layers are based on ‘static water surface elevations’ and are shown in 0.5 ft increments. Although predicted wave heights are provided with Coastal Flood Statements, wave modeling is not incorporated into these storm-related forecasts. Using a DEM with 5-meter grid cell, location-specific water level data, and the results of storm surge forecasting, the webpage provides users with forecasts of total water level (astronomical predicted tide height and the estimated storm surge) referenced to local MLLW and estimates of the extent of potential inundation as a coastal storm approaches a given coastal area (e.g., Provincetown Harbor, Sesuit Harbor, etc.). The data from this project was delivered to the SNEWFO-NWS and will be displayed on their website after internal review is completed. Figure 30 provides an example of the website and how it visualizes potential threats to Provincetown associated with an approaching storm.

Figure 30. Example of NWS website showing STPs and extents of inundation in downtown Provincetown. A similar map package will be available for the towns of throughout the study area. It should be noted that at the time of writing the NWS was redeveloping their webpage and these data were available intermittently.

50

The range planes provided to SNEWFO-NWS by the Center for Coastal Studies are referenced to local MLLW and begin at the highest high tide of the year and increase to an elevation equal to the project storm of record plus 4 feet in 0.5-foot increments. The additional 4 ft of STPs was included to account for the potential effects of sea level rise on nuisance and storm flood conditions. As discussed above, these data are grouped into four flooding categories used by SNEWFO-NWS in its coastal forecasts: Action, Minor, Moderate, and Major. National Weather Service Action Levels for Cape Cod Bay are shown in Table 6.

Stormtides.org: A new Website The Center for Coastal Studies, with Hansen & Dopchev Web Development, built a stand-alone webpage to host the publicly available storm tide pathways data (Figure 31). The website is very similar to the NWS page with storm tide pathways, inundation extents, depths, and real-time NWS total water level predictions displayed for the study area. The stormtides.org webpage is hosted by the Center and can be easily updated by Center staff. At the conclusion of this project, CCS conducted a training seminar to familiarize town staff with website features and functionality of the webpage and worked through various practical uses and scenarios.

Figure 31. Screenshot of stormtides.org.

As discussed at these demonstrations, the webpage can also be used as a teaching tool for students and the public. Immediately prior to an approaching storm those interested can go to the website and raise the water level to the projected NWS total water level elevations to view threatened coastal areas. Although not designed for this purpose, the website can also be used, with caution, to view potential sea level rise scenarios at the local level. Additional applications are being explored and will be developed by Center staff, who hope to have the webpage evolve to maximize its use by first-responders, public works professional, managers, planners, and the public.

51

The mapping of storm tide pathways in the manner developed by the Center for Coastal Studies has a diverse set of applications, ranging from short term preparation for and response to approaching storms to medium term planning for tourism and resource protection to long-term municipal planning and economic growth considerations with regards to rising sea level and development pressure. These maps can be used by first-responders, planners, managers, and the general public to better understand the dynamic nature of the coast and the role storms and sea level rise will play in the future.

52

REFERENCES: Alomassor, L., et al. 2016. January 2016 Nor’easter. NOAA Water Level and Meteorological Data Report. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service, and Center for Operational Oceanographic Products and Services. June 2016. 55 pages. Bodnar, A.N. 1981. Estimating Accuracies of Tidal Datums From Short Term Observations. Technical Report NOS CO-OPS 0074. 40 pages. Borrelli, M., Mague, S.T., Smith, T.L., Legare, B., 2016a. A New Method for Mapping Inundation Pathways to Increase Coastal Resiliency, Provincetown Massachusetts. A report prepared for the Town of Provincetown, Massachusetts. Borrelli, M., Mague, S.T., Smith, T.L., Legare, B., 2016b. Empowering Coastal Communities to Prepare for and Respond to Sea Level Rise and Storm-related Inundation: A Pilot Project for Nantucket Island. Tech. Report. p. 32. Borrelli, M., Mague, S.T., Smith, T.L., Legare, B, 2017. Mapping Inundation Pathways to Provide Communities with Real-time Coastal Flood Forecasts: A Pilot Project with the National Weather Service. Center for Coastal Studies. p. 32 Borrelli, M., McCormack, B., Mague, S.T., 2020. Mapping Storm Tide Pathways in Scituate and Cohasset: Assessing Coastal Vulnerability to Storms and Sea Level Rise. Borrelli, M., Smith, T.L., Mague, S.T., in press. Vessel-Based, Shallow Water Mapping with A Phase-Measuring Sidescan Sonar. Estuaries and Coasts. Cole, G. M. 1997. Water Boundaries. John Wiley & Sons. New York, NY. 193 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. Massachusetts Water resources Commission. Charles I. Sterling, Director. December 1962. 63 pages. 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 Blizzard 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. Legare, B. 2017. Tidal Water Level Monitoring Update 7/21/17. A report for the Cape Cod National Seashore prepared by the Center for Coastal Studies, 5 Holway Avenue, Provincetown, MA 02657 Legare, B., Giese, G.S., Borrelli, M., 2018. Analysis of short term and long term tidal water levels within the Cape Cod National Seashore: A Vulnerability Study, Center for Coastal Studies, Provincetown MA, Tech Rep. pp 88. Marmer, H.A. 1927, revised, 1951. Tidal Datum Planes. Special Publication No. 135, U.S. Dept. of Commerce, U.S. Coast and Geodetic Survey. Marmer, H. A. (1951). Changes in sea level determined from tide observations. Coastal Engineering Proceedings, 1(2), 6. 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, 100 Nashua 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 Affairs. 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. 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.

53

NOAA, 2003. Computational Techniques for Tidal Datums Handbook. NOAA Special Publication NOS CO-OPS 2. National Oceanic and Atmospheric Administration, National Ocean Service, Center for Operational Oceanographic Products and Services. Silver Spring, Maryland. September 2003. 113 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 Project, 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 Tide Climatology for Boston, Massachusetts. NOAA technical Memorandum NWS TDL 71. Techniques Development Laboratory, Silver Springs, MD. November 1982. 67 pages. Rosen, P.S., and D.B. Vine. Evolution of seawall construction methods in Boston Harbor, Massachusetts. 1995. Proc. Instn. Civ. Engrs Structs Bldgs, 1995, 110, Aug. 239 – 249. Structural and Building Board Structural Panel Paper 10539. August 1995. 10 pages. Swanson, R. L. (1974). Variability of tidal datums and accuracy in determining datums from short series of observations (No. 64). National Ocean Survey. Sweet, W., Park, J., Marra, J., Zervas, C., Gill, S. 2014. Sea level Rise and Nuisance Flood Frequency Changes around 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 report 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, 2009. Sea Level Variations of the United States 1854-2006. NOAA Technical Report NOS CO-OPS 053. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Serve, Center for Operational Oceanographic Products and Services. December 2009. 194 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.

54

Flood Insurance Studies used for analysis in this study:

2014. Flood Insurance Study, Barnstable County, Massachusetts (All Jurisdictions). Effective July 16, 2014. Federal Emergency Management Agency. Flood Insurance Study Number 25001CV000A. 110 pages. 1984. Flood Insurance Study, Town of Provincetown, Barnstable County. December 19, 1984. Federal Emergency Management Agency. Community Number 255218. 27 pages. 1985. Flood Insurance Study, Town of Truro, Barnstable County. January 3, 1985. Federal Emergency Management Agency. Community Number 255222. 29 pages. 1984. Flood Insurance Study, Town of Wellfleet, Barnstable County. December 19, 1984. Federal Emergency Management Agency. Community Number 250014. 43 pages. 1986. Flood Insurance Study, Town of Eastham, Barnstable County. July 3, 1985. Federal Emergency Management Agency. Community Number 250006. 44 pages. 1986. Flood Insurance Study, Town of Orleans, Barnstable County. September 4, 1986. Federal Emergency Management Agency. Community Number 250010. 43 pages. 1991. Flood Insurance Study, Town of Orleans, Barnstable County. Revised December 3, 1991. Federal Emergency Management Agency. Community Number 250010. 24 pages. 1985. Flood Insurance Study, Town of Brewster, Barnstable County. December 19, 1985. Federal Emergency Management Agency. Community Number 250003. 27 pages. 1976. Flood Insurance Study, Town of Dennis, Barnstable County, Massachusetts. May 1976. Federal Insurance Administration. U.S. Department of Housing and Urban Development. 21 pages. 1986. Flood Insurance Study, Town of Dennis, Barnstable County. July 3, 1986. Federal Emergency Management Agency. Community Number 250005. 32 pages. 1976. Flood Insurance Study, Town of Yarmouth, Barnstable County, Massachusetts. November 1976. Federal Insurance Administration. U.S. Department of Housing and Urban Development. 27 pages. 1986. Flood Insurance Study, Town of Yarmouth, Barnstable County. June 17, 1986. Federal Emergency Management Agency. Community Number 250015. 33 pages. 1977. Flood Insurance Study, Town of Barnstable, Barnstable County, Massachusetts. August 1977. Federal Insurance Administration. U.S. Department of Housing and Urban Development. 25 pages. 1985. Flood Insurance Study, Town of Barnstable, Barnstable County. February 19, 1985. Federal Emergency Management Agency. Community Number 250001. 45 pages. 1979. Flood Insurance Study, Town of Sandwich, Barnstable County, Massachusetts. December 1979. Federal Insurance Administration. U.S. Department of Housing and Urban Development. 19 pages. 1985. Flood Insurance Study, Town of Sandwich, Barnstable County. January 3, 1985. Federal Emergency Management Agency. Community Number 250012. 25 pages. 1991. Flood Insurance Study, Town of Sandwich, Barnstable County. August 5, 1991. Federal Emergency Management Agency. Community Number 250012. 26 pages.

55

APPENDIX A: WATER LEVEL MEASUREMENTS AND TIDAL DATUMS Water level data for this project were collected during April, May, and June of 2019 and were recorded by Onset HOBO pressure recorders installed in the towns of Sandwich, Barnstable, Eastham, and Wellfleet (Figure A1). It was collected to develop a first approximation of local tidal datums relative to NAVD88 for the Cape Cod Bay area. In addition, water level data was incorporated from previous CCS work in Provincetown and Truro (Borrelli et al. 2017, Legare et al. 2017) and from United States Geological Survey (USGS) real-time tide gauges located in Provincetown Harbor (https:\\waterdata.usgs.gov\\ma\\nwis\\uv\\?site_no=420259070105600) and Sesuit Harbor in Dennis (https://waterdata.usgs.gov/nwis/uv?site_no=414507070091400) (Figure A1).

Installation of Onset HOBO pressure recorders followed instructions laid out in Legare et al. (2017). In locations where hard structures were not available to attach loggers, a 30-inch earth anchor was deployed (Figure A2). A stainless-steel screw was set as a benchmark to confirm that the anchor had not shifted during deployment. Where hard structures were available, the logger was inserted into a perforated PVC pipe for protection and fixed to the structure (often dock piling). A stainless-steel screw was utilized as a benchmark to confirm that the logger had not shifted in location between deployment and retrieval (Figure A3).

56

Figure A1. Locations of Cape Cod Bay tide data. Circles represent locations of pressure loggers where data was collected during this project. Triangles represent the locations of tide data collected during previous projects or by the USGS.

Figure A2. Earth anchor deployment for pressure loggers to obtained tide readings.

Figure A3. PVC deployment for pressure loggers to obtained tide readings.

Results A total of 5 stations were deployed during from April to June 2019 (Table A1) for the creation of monthly tidal statistics. GPS surveys indicated that the maximum any stations shifted during deployment is +/- 0.01 m (Table A2).

57

Table A1 Station deployment and GPS survey summary data for each station. Deplo Retrie Referenc Referen Referen Distance to Sensor Station yed ved e X ce Y ce Z Sensor Elevation 4/30/2 6/6/20 4642495 415056. Wellfleet 019 19 .104 149 -1.72 -0.13 -1.845 Sandwich 4/10/2 6/4/20 4624707 376519. Boardwalk 019 19 .154 978 -0.87 -0.13 -0.996 Sandwich 4/10/2 6/4/20 4624484 375679. Police 019 19 .016 693 -0.23 -0.13 -0.357 4/10/2 6/4/20 4628210 416454. Rock Harbor 019 19 .278 739 -0.02 -1.76 -1.773 Barnstable 4/30/2 6/4/20 4617892 391892. Harbor 019 19 .573 864 -0.89 -1.19 -2.076

Table A2 Change in vertical position (m) between deployment and retrieval. Station Deployment Z (m) Retrieval Z (m) Delta (m) Wellfleet -1.72 -1.73 -0.01 Sandwich Boardwalk -0.87 -0.86 0.01 Sandwich Police -0.23 -0.24 -0.01 Rock Harbor -0.02 -0.02 0.00 Barnstable Harbor -0.89 -0.89 0.00

Tidal data was downloaded from each station and corrected for the effects of atmospheric pressure using data from a HOBO atmospheric pressure recorder established at the Barnstable Harbor and at Wellfleet Harbor stations to remove error due to the distance between the tidal and atmospheric pressure-recording instruments. Sea level data were adjusted to the vertical geodetic datum, NAVD88 by means of precision GPS surveys. 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 to create a data set of monthly averages.

Where the full tidal range was present, local tidal datums were calculated using the standard method (Wellfleet, Barnstable, Dennis, Provincetown, and Truro). A combination of the standard method (Marmer 1951) or the height difference method (Swanson 1974) was used where low water was not reached (Rock Harbor and Sandwich).

58

Table A3 Monthly averages derived from deployed water level loggers or the USGS tidal station in Dennis. Note Dennis is based on 15-minute tidal readings whereas the others are from 6-minute tidal readings. All elevations are in NAVD88 meters. Time Period Station MSL MHW MLW Range Boston 0.08 1.50 -1.39 2.89 Barnstable 0.08 1.55 -1.43 2.99 Eastham (Rock Harbor) 0.11 1.48 -0.95 2.44 May - 2019 Sandwich (Boardwalk) 0.21 1.43 -0.74 2.17 Sandwich (Police Station) 0.52 1.42 0.10 1.33 Wellfleet 0.07 1.57 -1.55 3.12 Dennis 0.01 1.61 -1.64 3.25 Pamet River (Truro) 0.00 1.46 -1.47 2.93 Jun - 2016 Provincetown -0.01 1.45 -1.51 2.96

Table A4 Local datums previously reported in Legare et al., (2017) and from the USGS water level gauge in Sesuit Harbor (Dennis). Elevations in meters. (1983-2001 NTDE)

Provincetown Harbor Sesuit Harbor Pamet Harbor NOAA Station 8446121 NOAA Station 8447241 CCS Tide Readings DATUM NAVD88 MLLW NAVD88 MLLW NAVD88 MLLW MHHW 1.41 3.07 1.43 3.19 1.42 3.08 MHW 1.27 2.93 1.29 3.05 1.28 2.94 MSL -0.13 1.53 -0.16 1.59 -0.12 1.53 MTL -0.15 1.52 -0.19 1.57 -0.14 1.52 MLW -1.56 0.10 -1.67 0.09 -1.55 0.10 MLLW -1.66 0.00 -1.76 0.00 -1.66 0.00

GT 3.07 3.07 3.19 3.19 3.08 3.08 MN 2.83 2.83 2.97 2.97 2.83 2.83

Highest Obs. Tide Elevation 2.98 4.64 3.33 5.09 2.98 4.64 Date 1/4/2018 1/4/2018 1/27/2015 1/27/2015 1/4/2015 1/4/2015

59

Figure A4. Location of Sandwich stations behind the Police station on Route 6A (left) and at the boardwalk (Right).

Table A5. Local tidal datums for Sandwich stations. Collected during May 2019.

Sandwich Police Station Sandwich Boardwalk Tidal Datums (NAVD88) Tidal Datums (NAVD88) Meters Feet Meters Feet MHHW 1.37 4.5 MHHW 1.38 4.52 MHW 1.26 4.13 MHW 1.26 4.14 MTL 0.68 2.22 MTL 0.11 0.37 MSL 0.52 1.71 MSL 0.21 0.68 DTL 0.64 2.09 DTL 0.22 0.86 MLW 0.10 0.31 MLW -0.74 -2.44 MLLW 0.10 0.31 MLLW -0.74 -2.44 GT 1.27 4.18 GT 2.12 6.96 MN 1.16 3.82 MN 2.01 6.59

60

Figure A5. May 2019 tide readings from the Sandwich Police station.

Figure A6. Location of tide station behind Sandwich Police Station.

61

Figure A7. May 2019 tide readings from the Sandwich Boardwalk station

62

Figure A8. Location of Barnstable tide station.

Table A6 Local tidal datums for Barnstable harbor station. Collected during May 2019. NTDE:1983-2001

Barnstable Tidal Datums (NAVD88) Meters Feet MHHW 1.51 4.95 MHW 1.38 4.52 MTL -0.12 -0.40 MSL 0.08 0.26 DTL -0.10 -0.33 MLW -1.62 -5.32 MLLW -1.71 -5.61 GT 3.22 10.56 MN 3.00 9.85

63

Figure A9. May 2019 tide readings from the Barnstable Harbor station

Figure A10. Tide station installed in Barnstable Harbor.

64

Figure A11. Location of Rock Harbor (Eastham) tide station.

Table A7 Local tidal datums for Rock Harbor (Eastham) station. Collected during May 2019. LW Restricted NTDE:1983-2001

Rock Harbor Datum Planes (NAVD88) Meters Feet MHHW 1.44 4.74 MHW 1.30 4.28 MTL 0.18 0.58 MSL 0.11 0.38 DTL 0.15 0.49 MLW -0.95 -3.13 MLLW -0.95 -3.13 GT 2.40 8.47 MN 2.26 7.41

65

Figure A12. May 2019 tide readings from the Rock Harbor (Eastham) station.

Figure A13. Tide station installed in Rock Harbor.

66

Figure A14. Location of Wellfleet tide station.

Table A8 Local tidal datums for the Wellfleet station. Collected during May 2019. NTDE:1983-2001

Wellfleet Harbor Datum Planes (NAVD88) Meters Feet MHHW 1.54 5.04 MHW 1.38 4.54 MTL -0.19 -0.63 MSL 0.07 0.22 DTL -0.13 -0.44 MLW -1.77 -5.80 MLLW -1.80 -5.92 GT 3.34 10.96 MN 3.15 10.34

67

Figure A15. May 2019 tide readings from the Wellfleet station.

Figure A16. Tide station installed in Wellfleet Harbor.

68

Figure A17. Mean Low Lower Water in NAV88 (ft) for each section of Cape Cod Bay based on contemporary analysis. Each color represents the extent of each section’s local tidal datum. It should be noted that the delineations are somewhat arbitrary, but for the purposes of this study the authors felt that they best represented the relatively small tidal variability throughout Cape Cod Bay.

APPENDIX REFERENCES Borrelli, M., Mague, S.T., Smith, T.L., Legare, B, 2017. Mapping Inundation Pathways to Provide Communities with Real- time Coastal Flood Forecasts: A Pilot Project with the National Weather Service. Center for Coastal Studies. p. 32 Legare, B. 2017. Tidal Water Level Monitoring Update 7/21/17. A report for the Cape Cod National Seashore prepared by the Center for Coastal Studies, 5 Holway Avenue, Provincetown, MA 02657 Marmer, H. A. (1951). Changes in sea level determined from tide observations. Coastal Engineering Proceedings, 1(2), 6. Swanson, R. L. (1974). Variability of tidal datums and accuracy in determining datums from short series of observations (No. 64). National Ocean Survey.

69