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TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
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DRAFT
TOWN OF COHASSET
HAZARD MITIGATION PLAN
2020 UPDATE
Draft Plan Update
May 15, 2020
DRAFT
TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
II
ACKNOWLEDGEMENTS & CREDITS
This plan was prepared for the Town of Cohasset by the Metropolitan Area Planning Council
(MAPC) under the direction of the Massachusetts Emergency Management Agency (MEMA) and
the Massachusetts Department of Conservation and Recreation (DCR). The plan was funded by the
Town of Cohasset.
MAPC Officers
President, Erin Wortman, Town of Stoneham
Vice President, Adam Chapdelaine, Town of Arlington
Secretary, Sandra Hackman, Town of Bedford
Treasurer, Sam Seidel, Gubernatorial
Executive Director, Marc Draisen, MAPC
Credits
Project Manager: Martin Pillsbury
Lead Project Planner: Anne Herbst
Mapping/GIS Services: Caitlin Spence
Massachusetts Emergency Management Agency
Director: Samantha Phillips
Department of Conservation and Recreation
Commissioner: Jim Montgomery
Cohasset Local Hazard Mitigation Planning Team
Lauren Lind Planning Director, Project Manager
Glenn Pratt Director, Emergency Management
William Quigley Police Chief
Michelle Leary Procurement and Contracts Manager
Brian Joyce Director, Public Works
Jason Federico Engineer, Public Works
Chris Senior Town Manager
Lorri Gibbons Harbormaster
Jeff Summers Conservation Agent
Gregory Lennon Police Lieutenant
Bob Egan Building Commissioner
Robert Silvia Fire Chief
Jennifer Oram Assistant Director Planning
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TABLE OF CONTENTS
ACKNOWLEDGEMENTS & CREDITS .................................................................................... II
TABLE OF CONTENTS ............................................................................................................ III
LIST OF TABLES & FIGURES ................................................................................................. IV
SECTION 1: EXECUTIVE SUMMARY .................................................................................... 6
SECTION 2: INTRODUCTION ............................................................................................. 10
SECTION 3: PLANNING PROCESS & PUBLIC PARTICIPATION .................................... 14
SECTION 4: RISK ASSESSMENT ......................................................................................... 20
SECTION 5: HAZARD MITIGATION GOALS .................................................................... 70
SECTION 6: EXISTING MITIGATION MEASURES ............................................................ 71
SECTION 7: MITIGATION MEASURES FROM PREVIOUS PLAN ................................... 78
SECTION 8: HAZARD MITIGATION STRATEGY .............................................................. 80
SECTION 9: PLAN ADOPTION & MAINTENANCE .......................................................... 90
SECTION 10: LIST OF REFERENCES ................................................................................... 92
APPENDIX A: MEETING AGENDAS ................................................................................... 93
APPENDIX B: HAZARD MAPPING ...................................................................................... 97
APPENDIX C: PUBLIC MEETINGS .................................................................................... 108
APPENDIX D: PLAN ADOPTION...................................................................................... 115
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LIST OF TABLES & FIGURES
TABLES
Table 1: Plan Review and Update Process ................................................................................................. 7
Table 2: Presidentially Declared Disasters, 1991-2018 ........................................................................ 10
Table 3: FEMA-Funded Mitigation Projects ............................................................................................... 12
Table 4: Cohasset Characteristics ................................................................................................................ 13
Table 5: Cohasset Public Meetings .............................................................................................................. 18
Table 6: Climate Change and Natural Hazards ..................................................................................... 26
Table 7: Hazards Risk Summary .................................................................................................................. 27
Table 8: Norfolk County Flood Events, 2010 through 2019 .................................................................. 29
Table 9: Status of Dams in Cohasset ........................................................................................................... 32
Table 10: Locally Identified Areas of Flooding ........................................................................................ 33
Table 11: Summary of Repetitive Losses and Claims .............................................................................. 34
Table 12: Frequency of Massachusetts Drought Levels ........................................................................... 35
Table 13: Eastern Norfolk County Coastal Floods, 2010 through 2019 ............................................. 37
Table 14: Norfolk County Extreme Cold and Wind Chill Occurrences 2010 through 2019 ........... 40
Table 15: Norfolk County Excessive Heat Occurrences 2010-2019 ................................................... 41
Table 16: Hurricane Records for Massachusetts, 1938 to 2020 ........................................................... 45
Table 17: Saffir/Simpson Scale .................................................................................................................. 45
Table 18: NESIS Categories ......................................................................................................................... 47
Table 19: Severe Weather Major Disaster Declarations in Eastern MA ............................................. 47
Table 20: Heavy Snow Events and Impacts in Eastern Norfolk County, 2010 through 2019 ......... 48
Table 21: Enhanced Fujita Scale ................................................................................................................. 49
Table 22: Tornado Records for Norfolk County ....................................................................................... 50
Table 23: Norfolk County Thunderstorm Events, 2010 through 2019 ................................................. 51
Table 24: Hail Size Comparisons ................................................................................................................ 52
Table 25: Norfolk County Hail Events, 2010 through 2019 .................................................................. 53
Table 26: Richter Scale and Effects ............................................................................................................ 54
Table 27: Historical Earthquakes in Massachusetts or Surrounding Area ............................................ 54
Table 28: Town of Cohasset, MA 2016 Land Use ................................................................................... 57
Table 29: Summary of Cohasset Developments, 2012-2018 ............................................................... 58
Table 30: Relationship of Potential Development to Hazard Areas .................................................... 59
Table 31: Critical Facilities and Relationship to Hazard Areas............................................................. 61
Table 32: Estimated Damages from Hurricanes ....................................................................................... 65
Table 33: Estimated Damages from Earthquakes .................................................................................... 66
Table 34: Estimated Damages from Flooding .......................................................................................... 66
Table 35: Existing Natural Hazard Mitigation Measures in Cohasset.................................................. 75
Table 36: Mitigation Measures from the 2012 Plan ............................................................................... 78
Table 37: Mitigation Measures Prioritization ............................................................................................ 83
Table 38: Potential Hazard Mitigation Measures .................................................................................... 87
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FIGURES
Figure 1: Six-Step Planning Process ............................................................................................................ 14
Figure 2: Observed Increase in Temperature ........................................................................................... 21
Figure 3: Projected Increase in Annual Days Over 90 Degrees F ........................................................ 22
Figure 4: Observed Change in Total Annual Precipitation Falling ........................................................ 23
Figure 5: Projected Change in Total Annual Precipitation Falling ......................................................... 24
Figure 6: Observed Increase in Sea Level Rise ........................................................................................ 24
Figure 7: Recent and Projected Increase in Sea Level Rise .................................................................... 25
Figure 8: March 2010 USGS Old Swamp River Gage .......................................................................... 29
Figure 9: Weeks of Severe Drought (2001-2017) .................................................................................. 36
Figure 10: Shoreline Change 1970--2014 ............................................................................................... 39
Figure 11: Wind Chill Temperature Index and Frostbit Risk .................................................................. 40
Figure 12: Heat Index Chart ........................................................................................................................ 41
Figure 13: Wildfire Risk Areas .................................................................................................................... 44
Figure 14: State of Massachusetts Earthquake Probability Map .......................................................... 56
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SECTION 1: EXECUTIVE SUMMARY
Hazard Mitigation planning is a proactive effort to identify actions that can be taken to reduce
the dangers to life and property from natural hazard events. In the communities of the Boston
region of Massachusetts, hazard mitigation planning tends to focus most on flooding, the most
likely natural hazard to impact these communities. The Federal Disaster Mitigation Act of 2000
requires all municipalities that wish to be eligible to receive FEMA funding for hazard mitigation
grants, to adopt a local multi-hazard mitigation plan and update this plan in five year intervals.
PLANNING PROCESS
Planning for the Hazard Mitigation Plan update was led by the Cohasset Local Hazard Mitigation
Planning Team, composed of staff from a number of different town departments. This team met on
July 23, 2019, October 8, 2019, and January 21, 2020 and discussed where the impacts of
natural hazards most affect the town, the effects of climate change, goals for addressing these
impacts, updates to the Town’s existing mitigation measures, and new or revised hazard mitigation
measures that would benefit the town.
Public participation in this planning process is important for improving awareness of the potential
impacts of natural hazards and to build support for the actions the Town takes to mitigate them.
The Town’s Local Hazard Mitigation Planning Team hosted two public meetings, the first on
November 20, 2019 and the second on June 3, 2020 and the draft plan update was posted on
the Town’s website for public review. Key town stakeholders and neighboring communities were
notified and invited to review the draft plan and submit comments. See Public Meetings for
comments.
RISK ASSESSMENT
The Cohasset Hazard Mitigation Plan assesses the potential impacts to the town from flooding,
high winds, winter storms, brush fire, geologic hazards, extreme temperatures, drought and,
invasive species. . For each risk, the assessment identifies the projected impacts of a warming
climate. These are shown in the map series in Appendix B. The Cohasset Local Hazard Mitigation
Planning Team identified 85 critical facilities. These are also shown on the map series and listed in
Table 31, identifying which facilities are located within the mapped hazard zones.
Hazards U.S. – Multihazards (HAZUS-MH) is a standardized methodology developed by FEMA
that utilizes Geographic Information Systems (GIS) to estimate physical, economic, and social
impacts of disasters. The HAZUS-MH analysis for Cohasset estimates property damages from
Hurricanes of category 2 and 4 ($14 million to $53 million), earthquakes of magnitudes 5 and 7
($159 million to $1.2 billion), and the 1% and .2% chance of flooding ($51 to $64 million).
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HAZARD MITIGATION GOALS
The Cohasset Local Multiple Hazard Community Planning Team endorsed the following eleven
hazard mitigation goals at the October 8, 2019 team meeting. The team added the eleventh
goal focused on incorporating future climate change projections.
1. Ensure that critical infrastructure sites are protected from natural hazards.
2. Protect existing residential and business areas from flooding.
3. Maintain existing mitigation infrastructure in good condition.
4. Continue to enforce existing zoning and building regulations.
5. Educate the public about zoning and building regulations.
6. Work with surrounding communities to ensure regional cooperation and solutions for
hazards affecting multiple communities.
7. Encourage future development and redevelopment in areas that are not prone to
natural hazards.
8. Educate the public about natural hazards and mitigation measures.
9. Make efficient use of public funds for hazard mitigation.
10. Pursue land acquisition strategies.
11. Consider the potential impacts of future climate change. Incorporate climate
sustainability and resiliency in hazard mitigation planning.
HAZARD MITIGATION STRATEGY
The Cohasset Local Hazard Mitigation Planning Team identified a number of mitigation measures
that would serve to reduce the Town’s vulnerability to natural hazard events. Overall, the hazard
mitigation strategy recognizes that mitigating hazards for Cohasset will be an ongoing process as
our understanding of natural hazards and the steps that can be taken to mitigate their damages
changes over time. Global climate change and a variety of other factors impact the Town’s
vulnerability in the future, and local officials will need to work together across municipal lines and
with state and federal agencies in order to understand and address these changes. The Hazard
Mitigation Strategy will be incorporated into the Town’s other related plans and policies.
PLAN REVIEW & UPDATE PROCESS
The process for developing Cohasset’s Hazard Mitigation Plan 2020 Update is summarized in
Table 1.
Table 1: Plan Review and Update Process
Section Reviews and Updates
Section 3: Public
Participation
The Local Hazard Mitigation Planning Team placed an emphasis on
public participation for the update of the Hazard Mitigation Plan,
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discussing strategies to enhance participation opportunities at the first
local committee meeting. During plan development, the plan was
discussed at two public meetings hosted by the Planning Board and the
Board of Selectmen. The plan was also available on the Town’s website
for public comment. See Public Meetings for comments.
Section 4: Risk
Assessment
MAPC gathered the most recently available hazard and land use data
and met with town staff to identify changes in local hazard areas and
development trends. Town staff reviewed critical infrastructure with
MAPC staff in order to create an up-to-date list. MAPC also used the
most recently available version of HAZUS and assessed the potential
impacts of flooding using the latest data.
Section 5: Goals The Hazard Mitigation Goals were reviewed and endorsed by the
Cohasset Local Hazard Mitigation Planning Team.
Section 6: Existing
Mitigation
Measures
The list of existing mitigation measures was updated to reflect current
mitigation activities in the town.
Sections 7 and 8:
Hazard Mitigation
Strategy
Mitigation measures from the 2012 plan were reviewed and assessed as
to whether they were completed, in progress, or deferred. The Local
Hazard Mitigation Planning Team determined whether to carry forward
measures into the 2020 Plan Update or modify or delete them. The Plan
Update's hazard mitigation strategy reflects both new measures and
measures carried forward from the 2012 plan. The Local Hazard
Mitigation Team prioritized all of these measures based on current
conditions.
Section 9: Plan
Adoption &
Maintenance
This section of the plan was updated with a new on-going plan
implementation review and five year update process that will assist the
Town in incorporating hazard mitigation issues into other Town planning
and regulatory review processes and better prepare the Town for the
next comprehensive plan update.
As indicated in Table 36, Cohasset made good progress implementing mitigation measures
identified in the 2012 Hazard Mitigation Plan. Work on Bound Brook Dam and the culvert at
Jerusalem Road was completed. The Town completed mapping the drainage system with GIS.
An automatic tidegate was installed at Jacob’s Meadow, a management plan implemented, and
generator installed. A contract for backup generators addressed the need for coverage. In
addition, Police and Fire now have a tank for their generator. The Cohasset Conservation Trust
purchased the Remick Salt Marsh, a 2-acre marsh and upland property that connects with town
land to provide flood protection.
Some projects were partially completed, and/or will be continued to the next plan for on-going
maintenance. These include tree removal from the Sanctuary Pond earthen dam, repairs to the
Margin Street seawall, generator upgrades, gas line replacements, and GIS maintenance.
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Moving forward into the next five-year plan implementation period there will be many more
opportunities to incorporate hazard mitigation into the Town’s decision-making processes. As in
the past, the Town will document any actions taken within this iteration of the Hazard Mitigation
Plan on challenges met and actions successfully adopted as part of the ongoing plan maintenance
to be conducted by the Cohasset Hazard Mitigation Implementation Team, as described in Section
9 Plan Adoption and Maintenance.
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SECTION 2: INTRODUCTION
PLANNING REQUIREMENTS UNDER THE FEDERAL DISASTER MITIGATION ACT
The Federal Disaster Mitigation Act, passed in 2000, requires that after November 1, 2004, all
municipalities that wish to continue to be eligible to receive FEMA funding for hazard mitigation
grants, must adopt a local multi-hazard mitigation plan and update this plan in five year
intervals. This planning requirement does not affect disaster assistance funding.
Federal hazard mitigation planning and grant programs are administered by the Federal
Emergency Management Agency (FEMA) in collaboration with the states. These programs are
administered in Massachusetts by the Massachusetts Emergency Management Agency (MEMA) in
partnership with the Department of Conservation and Recreation (DCR).
The Town of Cohasset contracted with the Metropolitan Area Planning Council (MAPC), to assist
the Town in updating its local Hazard Mitigation Plan, which was first adopted in 2007 as a
multijurisdictional plan.
WHAT IS A HAZARD MITIGATION PLAN?
Natural hazard mitigation planning is the process of determining how to systematically reduce or
eliminate the loss of life and property damage resulting from natural hazards such as floods,
earthquakes, and hurricanes. Hazard mitigation means to permanently reduce or alleviate the
losses of life, injuries, and property resulting from natural hazards through long-term strategies.
These long-term strategies include planning, policy changes, programs, projects, and other
activities. This plan incorporates consideration of future risks due to projections for the increased
frequency and severity of extreme weather fueled by a warming planet.
PREVIOUS FEDERAL/STATE DISASTERS
Since 1991, there have been 24 natural hazard events that triggered federal or state disaster
declarations that included Norfolk County. These are listed in Table 2 below. The majority of the
events involved flooding, while others were due to hurricanes or nor’easters, and severe winter
weather.
Table 2: Presidentially Declared Disasters, 1991-2018
Disaster Name Date of Event Declared Areas
Hurricane Bob August 1991 Counties of Barnstable, Bristol, Dukes, Essex, Hampden,
Middlesex, Plymouth, Nantucket, Norfolk, Suffolk
Severe Coastal Storm
No Name Storm October 1991 Counties of Barnstable, Bristol, Dukes, Essex, Middlesex,
Plymouth, Nantucket, Norfolk, Suffolk
Blizzard March 1993 Statewide
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Disaster Name Date of Event Declared Areas
Blizzard January 1996 Statewide
Severe Storms, Flood October 1996 Counties of Essex, Middlesex, Norfolk, Plymouth, Suffolk
Heavy Rain, Flood June 1998 Counties of Bristol, Essex, Middlesex, Norfolk, Suffolk,
Plymouth, Worcester
Severe Storms, Flood March 2001 Counties of Bristol, Essex, Middlesex, Norfolk, Suffolk,
Plymouth, Worcester
Snowstorm March 2001 Berkshire, Essex, Franklin, Hampshire, Middlesex, Norfolk,
Worcester
Snowstorm February 2003 Statewide
Snowstorm December 2003
Barnstable, Berkshire, Bristol, Essex, Franklin, Hampden,
Hampshire, Middlesex, Norfolk, Plymouth, Suffolk,
Worcester
Flooding April 2004 Essex, Middlesex, Norfolk, Suffolk, Worcester
Snow January 2005 Statewide
Hurricane Katrina August 2005 Statewide
Severe Storms,
Flooding October 2005 Statewide
Severe Storms, Flooding May 2006 Statewide
Severe Storm, Inland,
Coastal Flooding April 2007 Statewide
Severe Storms, Flooding December 2008 Statewide
Severe Storms, Flooding March/April
2010
Bristol, Essex, Middlesex, Suffolk, Norfolk, Plymouth,
Worcester
Severe Winter Storm,
Snowstorm
January 2011 Berkshire, Essex, Hampden, Hampshire, Middlesex, Norfolk,
Suffolk
Tropical Storm Irene August 2011 Barnstable, Berkshire, Bristol, Dukes, Franklin, Hampden,
Hampshire, Norfolk, Plymouth
Severe Winter Storm,
Snowstorm and
Flooding
February, 2013 Statewide
Severe winter storm,
snowstorm and flooding April 2015 Barnstable, Bristol, Dukes, Essex, Middlesex, Nantucket,
Norfolk, Plymouth, Suffolk, Worcester
Severe winter storm
and flooding March 2018 Barnstable, Bristol, Essex, Nantucket, Norfolk, Plymouth
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Disaster Name Date of Event Declared Areas
Severe winter storm
and Snowstorm March 2018 Essex, Middlesex, Norfolk, Suffolk, Worcester
Source: MA Hazard Mitigation and Climate Adaptation Plan, 2018
FEMA FUNDED MITIGATION PROJECTS
The Town of Cohasset has received funding from FEMA for three mitigation projects under FEMA’s
grant programs. These projects totaled $1,338,000, with $978,434 covered by FEMA grants
and $334,500 by local funding. The projects are summarized in Table 3 below.
Table 3: FEMA-Funded Mitigation Projects
Project Title Scope of Work Total Cost Federal
Funding
Local
Funding
Jacob's
Meadow
Drainage
Improvements
Placement of pipe with new tide
valve; replace box culvert;
widen existing channelized
section of James Brook. New
Self-Regulating tide gate
$595,000 $445,786 $148,750
Town wide
Drainage
Improvements
Replace concrete pipe on
conduit and replace culvert
pipe; channel improvements;
install diversion pipe and outlet
structure.
$585,000 $414,148 $146,250
Jerusalem
Road Culvert
Project
Culvert improvements. $158,000 $118,500 $39,500
Source: MEMA Database
COMMUNITY PROFILE
Cohasset covers a nine square mile area in a setting of colonial homes and ocean vistas of
spectacular beauty. The town is predominantly residential; many of its residents making the daily
commute to Boston by car, train, or commuter boat. Cohasset's central village lies around a
spacious common with a small pond, and includes specialty shops, the colonial First Parish Meeting
House and St. Stephen's Church. The town has active Community and Arts Centers, three historical
museums and the renowned South Shore Music Circus. Along the shores of Cohasset Harbor are
facilities for dining, sailing and a replica of the famous Minot's light.
Cohasset is bordered by Hingham on the west, Hull on the northwest, the Atlantic Ocean on the
north, and Scituate on the south and east. Cohasset is about 20 miles southeast of Boston. The
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total area of the town, including water bodies, is 31.47 square miles; the total land area is 9.89
square miles. The town maintains a website at www.cohassetma.org. The website below from the
Chamber of Commerce is also quite informative and helpful: www.cohassetchamber.org.
Table 4: Cohasset Characteristics
Population = 8,393 people
• 7.3% are under age 5
• 26.5% are under age 18
• 17.3% are over age 65
• .5% of households are limited English-speaking
• 1.7% of households have no vehicle available
• Over 98% of the population is White
Number of Housing Units = 3,473
• 22.6% are renter-occupied housing units
• 29.8% of housing units were built before 1940
Source: 2017 American Community Survey
The Town of Cohasset has several unique characteristics to keep in mind while planning for natural
hazards:
• Cohasset has been proactive in addressing the impact of climate on natural hazards.
Cohasset is certified by the state as a Municipal Vulnerability Preparedness community. The
results of that effort have been incorporated in this plan.
• As a coastal community, Cohasset is vulnerable to future sea level rise and coastal storms.
However, Cohasset is fortunate that significant segments of its waterfront consist of elevated
ledge bluffs.
• While Cohasset has ample water supply, invasive species are a threat to drinking water
quality.
• The businesses and infrastructure of Cohasset Harbor are vulnerable to coastal storms and
future sea level rise.
• Cohasset has the benefits of significant forest and tree cover. However, power outages and
damage from falling trees are important concerns.
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SECTION 3: PLANNING PROCESS & PUBLIC PARTICIPATION
MAPC employs a six-step planning process based on FEMA’s hazard mitigation planning
guidance focusing on local needs and priorities but maintaining a regional perspective matched to
the scale and nature of natural hazard events and regional climate change. Public participation is
a central component of this process, providing critical information about the local occurrence of
hazards while also serving to build a base of support for hazard mitigation activities. MAPC
supports participation by the general public and other plan stakeholders through two public
meetings hosted by the local Hazard Mitigation Team, posting of the plan to the Town’s website,
and invitations sent to neighboring communities, town boards and commissions, and other local or
regional entities to review the plan and provide comment.
PLANNING PROCESS SUMMARY
The six-step planning process outlined below is based on the guidance provided by FEMA in the
Local Multi-Hazard Mitigation Planning Guidance. Public participation is a central element of this
process, which attempts to focus on local problem areas and identify needed mitigation measures
based on where gaps occur in the existing mitigation efforts of the municipality. By working on
municipal hazard mitigation plans in groups of neighboring cities and towns, MAPC can identify
regional opportunities for collaboration and facilitate communication between communities. In
plan updates, the process described below allows staff to bring the most recent hazard
information into the plan, including new hazard occurrence data, changes to a municipality’s
existing mitigation measures, and progress made on actions identified in previous plans.
Figure 1: Six-Step Planning Process
1. Map the Hazards – MAPC relies on data from a number of different federal, state, and
local sources in order to map the areas with the potential to experience natural hazards.
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This mapping represents a multi-hazard assessment of the municipality and is used as a set
of base maps for the remainder of the planning process. A particularly important source
of information is the knowledge drawn from local municipal staff on where natural hazard
impacts have occurred. These maps can be found in Appendix B.
2. Assess the Risks & Potential Damages – Working with local staff, critical facilities,
infrastructure, vulnerable populations, and other features are mapped and contrasted
with the hazard data from the first step to identify those that might represent particular
vulnerabilities to these hazards. Land use data and development trends are also
incorporated into this analysis. In addition, MAPC develops estimates of the potential
impacts of certain hazard events on the community. MAPC drew on the following resources
to complete the plan:
• General Bylaws for the Town of Cohasset
• Zoning Bylaw for the Town of Cohasset
• Cohasset 2019 Master Plan
• Town of Cohasset Community Resilience Building Workshop Summary of Findings
June 2018
• Town of Cohasset Open Space and Recreation Plans 2018-2024 and 2010-2017
• Blue Hill Observatory
• FEMA, Flood Insurance Rate Maps for Norfolk County, MA, 2012
• FEMA, Hazards U.S. Multi-Hazard
• FEMA, Local Mitigation Plan Review Guide, October 2011
• Fourth National Climate Assessment, 2018
• Massachusetts Flood Hazard Management Program
• Massachusetts Office of Coastal Zone Management Shoreline Change Data
• Massachusetts Office of Dam Safety, Inventory of Massachusetts Dams 2018
• Massachusetts State Hazard Mitigation Plan, 2013
• Massachusetts State Hazard Mitigation and Climate Adaptation Plan, 2018
• Metropolitan Area Planning Council, GIS Lab, Regional Plans and Data
• National Weather Service
• Nevada Seismological Library
• New England Seismic Network, Boston College Weston Observatory,
http://aki.bc.edu/index.htm
• NOAA National Climatic Data Center, http://www.ncdc.noaa.gov/
• Northeast Climate Adaptation Science Center
• Northeast States Emergency Consortium, http://www.nesec.org/
• Tornado History Project
• US Census, 2010 and American Community Survey 2017 5-Year Estimates
• USGS, National Water Information System,
http://nwis.waterdata.usgs.gov/usa/nwis
3. Review Existing Mitigation – Municipalities in the Boston Metropolitan Region have an
active history in hazard mitigation as most have adopted flood plain zoning districts,
wetlands protection programs, and other measures as well as enforcing the State building
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code, which has strong provisions related to hazard resistant building requirements. All
current municipal mitigation measures must be documented.
4. Develop Mitigation Strategies – MAPC works with the local municipal staff to identify
new mitigation measures, utilizing information gathered from the hazard identification,
vulnerability assessments, and the community’s existing mitigation efforts to determine
where additional work is necessary to reduce the potential damages from hazard events.
Additional information on the development of hazard mitigation strategies can be found
in Section 7.
5. Plan Approval & Adoption – Once a final draft of the plan is complete it is sent to
MEMA for the state level review and, following that, to FEMA for approval. Typically,
once FEMA has approved the plan the agency issues a conditional approval (Approval
Pending Adoption), with the condition being adoption of the plan by the municipality.
More information on plan adoption can be found in Section 9 and documentation of plan
adoption can be found in Appendix D.
6. Implement & Update the Plan – Implementation is the final and most important part of
any planning process. Hazard Mitigation Plans must also be updated on a five-year basis
making preparation for the next plan update an important on-going activity. Section 9
includes more detailed information on plan implementation.
2012 PLAN IMPLEMENTATION & MAINTENANCE
The 2012 Town of Cohasset Hazard Mitigation Plan contained a risk assessment of identified
hazards for the town and mitigation measures to address the risk and vulnerability from these
hazards. Since approval of the plan by FEMA and local adoption, progress has been made on
implementation of the measures. The Town has advanced a number of projects for
implementation, including tidegate, drainage, and culvert improvements, as well as GIS mapping,
and land preservation.
THE LOCAL MULTIPLE HAZARD COMMUNITY PLANNING TEAM
MAPC worked with the local community representatives to organize a Local Hazard Mitigation
Planning Team for Cohasset. MAPC briefed the local representatives as to the desired
composition of that team as well as the need for public participation in the local planning process.
The Local Hazard Mitigation Planning Team is central to the planning process as it is the primary
body tasked with developing a mitigation strategy for the community. The local team was tasked
with working with MAPC to set plan goals, provide information on the hazards that impact the
town, existing mitigation measures, and helping to develop new mitigation measures for this plan
update. The Local Hazard Mitigation Planning Team membership is listed below.
Name Representing
Lauren Lind Planning Director, Project Manager
Glenn Pratt Director, Emergency Management
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William Quigley Police Chief
Michelle Leary Procurement and Contracts Manager
Brian Joyce Director, Public Works
Jason Federico Engineer, Public Works
Chris Senior Town Manager
Lorri Gibbons Harbormaster
Jeff Summers Conservation Agent
Gregory Lennon Police Lieutenant
Bob Egan Building Commissioner
Robert Silvia Fire Chief
Jennifer Oram Assistant Director, Planning
The Cohasset Planning Board and Conservation Commission are the primary entities responsible
for regulating development in town. Feedback was assured through the participation of the
Conservation Agent, the Director of Planning, and the Town Manager. In addition, MAPC, the
State-designated regional planning authority for Cohasset, works with all agencies that that
regulate development in the region, including the listed municipal entities and state agencies, such
as the MassDOT and the MBTA.
The Local Hazard Mitigation Planning Team met on the following dates: July 23, 2019; October
8, 2019; and January 21, 2020. The purpose of the meetings was to introduce the Hazard
Mitigation planning program, review and update hazard mitigation goals, and to gather
information on local hazard mitigation issues and sites or areas related to these. Later meetings
focused on verifying information gathered by MAPC staff and discussion of existing mitigation
practices, the status of mitigation measures identified in the 2012 hazard mitigation plan, and
potential new or revised mitigation measures. The agendas for these meetings are included in
Appendix A.
PUBLIC MEETINGS
Public participation in the hazard mitigation planning process is important, both for plan
development and for later implementation of the plan. Residents, business owners, and other
community members are an excellent source for information on the historic and potential impacts
of natural hazard events and particular vulnerabilities the community may face from these
hazards. Their participation in this planning process also builds understanding of the concept of
hazard mitigation and climate impacts, potentially creating support for mitigation actions taken in
the future to implement the plan. To gather this information and educate residents on hazard
mitigation, the Town hosted two public meetings, one during the planning process and one after a
complete draft plan was available for review.
Natural hazard mitigation plans unfortunately rarely attract much public involvement in the Boston
region, unless there has been a recent hazard event. One of the best strategies for overcoming
this challenge is to include discussion of the hazard mitigation plan on the agenda of an existing
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board or commission. With this strategy, the meeting receives widespread advertising and a
guaranteed audience of the board or commission members plus those members of the public who
attend the meeting. These board and commission members represent an engaged audience that is
informed and up to date on many of the issues that relate to hazard mitigation planning and
climate change resilience in the locality and will likely be involved in plan implementation, making
them an important audience with which to build support for hazard mitigation and climate
resilience measures. In addition, these meetings frequently receive press coverage, expanding the
audience that has the opportunity to hear the presentation and provide comment.
The public had an opportunity to provide input to the Cohasset hazard mitigation planning
process during a meeting of the Planning Board held on November 20, 2019 at Cohasset Town
Hall. The draft plan update was presented at a Board of Selectmen meeting on June 3, 2020 at
Cohasset Town Hall. The Board of Selectmen meeting was broadcast on local cable television
and Facebook live. Both meetings were publicized in accordance with the Massachusetts Public
Meeting Law. The attendance list for each meeting can be found in Table 5. See public meeting
notices in Appendix C.
Table 5: Cohasset Public Meetings
Meeting #1 November 20, 2019
Total Attendance: 13
Name Representing
Lauren Lind Director of Planning
Jennifer Oram Assistant Director of Planning
5 members of the Planning Board and 6 members of the public.
Meeting #2 June 3, 2020
Total Attendance:
Name Representing
LOCAL STAKEHOLDER INVOLVEMENT
The local Hazard Mitigation Planning Team was encouraged to reach out to local stakeholders
that might have an interest in the Hazard Mitigation Plan including neighboring communities,
agencies, businesses, nonprofits, and other interested parties. Notice was sent to the following
organizations and neighboring municipalities inviting them to review the Hazard Mitigation Plan
and submit comments to the Town:
• Cohasset Chamber of Commerce
• Cohasset Land Trust
• South Shore Hospital
• Straits Pond Watershed Association
• Town of Norwell
• Town of Hull
• Town of Hingham
• Town of Scituate
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See Appendix C for public meeting notices. The draft Cohasset Hazard Mitigation Plan 2020
Update was posted on the Town’s website for the second public meeting. Members of the public
could access the draft document and submit comments or questions to the Town. See public
comments .
CONTINUING PUBLIC PARTICIPATION
Following the adoption of the plan update, the planning team will continue to provide residents,
businesses, and other stakeholders the opportunity to learn about the hazard mitigation planning
process and to contribute information that will update the town’s understanding of local hazards.
As updates and a review of the plan are conducted by the Hazard Mitigation Implementation
Team, these will be placed on the Town’s web site, and any meetings of the Hazard Mitigation
Implementation Team will be publicly noticed in accordance with town and state open meeting
laws.
PLANNING TIMELINE
July 23, 2019 Meeting of the Cohasset Local Hazard Mitigation Planning Team
October 8, 2019 Meeting of the Cohasset Local Hazard Mitigation Planning Team
November 20, 2019 First Public Meeting with the Cohasset Planning Board
January 21, 2010 Meeting of the Cohasset Local Hazard Mitigation Planning Team
June 3, 2020 Second Public Meeting with the Cohasset Board of Selectmen
Draft Plan Update submitted to MEMA
Draft Plan Update submitted to FEMA
Notice of Approvable Pending Adoption sent by FEMA
Plan Adopted by the Cohasset Board of Selectmen
FEMA final approval of the plan for 5 years, until xxxxxxxx
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SECTION 4: RISK ASSESSMENT
The risk assessment analyzes the potential natural hazards that could occur within the Town of
Cohasset as well as the relationship between those hazards and current land uses, potential future
development, and critical infrastructure. This section also includes a vulnerability assessment that
estimates the potential damages that could result from certain large-scale natural hazard events.
In order to update Cohasset’s risk assessment, MAPC gathered the most recently available hazard
and land use data and met with Town staff to identify changes in local hazard areas and
development trends. MAPC also used FEMA’s damage estimation software, HAZUS.
With the adoption of the Hazard Mitigation and Climate Adaptation Plan 2018 (SHMCAP),
Massachusetts became the first state to integrate climate projections in a state hazard mitigation
plan. Following the state model, the projected impacts of our warming climate on natural hazards
are integrated throughout the risk assessment. Key impacts include rising temperatures, which in
turn affect precipitation patterns, sea level, and extreme weather.
CLIMATE CHANGE OBSERVATIONS AND PROJECTIONS
Climate change observations come from a variety of sources that have measured and recorded
changes in recent decades and centuries. Climate change projections, however, predict future
climate impacts and by their nature cannot be observed or measured. As a result of the inherent
uncertainty in predicting future conditions, climate projections are generally expressed as a range
of possible impacts.
Temperature
Our climate has always been regulated by gases including carbon dioxide, methane, and nitrous
oxide, that blanket the earth. These gases trap heat that would otherwise be reflected out to
space; without them our planet would be too cold to support life. We refer to these gases as
“greenhouse gases” (GHGs) for their heat trapping capacity. The combustion of fossil fuels, our
primary energy source in the age of industrialization, releases GHGs into the atmosphere. In the
past century, human activity associated with industrialization has contributed to a growing
concentration of GHGs in our atmosphere.
Records from the Blue Hill Observatory in Milton, MA show that average temperatures (30-year
mean) have risen approximately 3 degrees (F) in the almost 200 years since record keeping
began in 1831.
“Global climate is changing rapidly compared to the pace of natural variations in climate that
have occurred throughout Earth’s history. Global average temperature has increased by about
1.8°F from 1901 to 2016, and observational evidence does not support any credible natural
explanations for this amount of warming; instead, the evidence consistently points to human
activities, especially emissions of greenhouse or heat-trapping gases, as the dominant cause.”
Fourth National Climate Assessment, 2018 (Chapter 2-1)
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Figure 2: Observed Increase in Temperature
Climate projections include an increase in average temperature and in the number of extreme
heat days. Extreme cold day are projected to decrease in number. The Northeast Climate
Adaptation Science Center (NECASC) projects average temperatures in Massachusetts will
increase by 5 degrees F by mid-century and nearly 7 degrees F by the end of the century. These
increases may be slightly less in coastal communities like Cohasset. Table 3 shows the NECASC
range of projections for increases in the number of days over 90 degrees annually.
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Figure 3: Projected Increase in Annual Days Over 90 Degrees F
Source: Northeast Climate Adaptation Science Center
Precipitation Patterns
Annual precipitation in Massachusetts has increased by approximately 10% in the fifty-year
period from 1960 to 2010 (MA Climate Adaptation Report, 2011). Moreover, there has been a
significant increase in the frequency and intensity of large rain events. For the Northeast US,
according to the Fourth National Climate Assessment 2018, in the past sixty years there has been
a 55% increase in the amount of annual precipitation that falls in the top 1% of storm events
(Figure 4). Changes in precipitation are fueled by warming temperatures which increase
evaporation and the amount of water vapor the air can hold.
Total annual precipitation in Massachusetts is projected to increase by 1 to 6 inches by mid-
century, and by 1.2 to 7.3 inches by the end of this century (SHMCAP p. 2-22). The Fourth
National Climate Assessment predicts that the pattern of increasing frequency and intensity of
extreme rain events will continue. By 2070 to 2099, (relative to 1986 to 2015) they project a
30-40% increase in total annual precipitation falling in the heaviest 1% of rain events (Figure 5).
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Figure 4: Observed Change in Total Annual Precipitation Falling
in the Heaviest 1% of Events
Source: Fourth National Climate Assessment, 2018
Numbers circled in black indicate % change.
Despite overall increasing precipitation, more frequent and significant summer droughts are also
a projected consequence of climate change. This is due to projections that precipitation will
increase in winter and spring and decrease slightly in the summer and fall, and a result of earlier
snow melt, and higher temperatures that will reduce soil moisture.
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Figure 5: Projected Change in Total Annual Precipitation Falling
in the Heaviest of 1% of Events for 2070-2099
Source: Fourth National Climate Assessment, 2018
Sea Level Rise
Records from the Boston Tide Station show nearly one foot of sea level rise in the past century
(Figure 6). Warming temperatures contribute to sea level rise in two ways. First, warm water
expands to take up more space. Second, rising temperatures are melting land-based ice which
enters the oceans as melt water. A third, quite minor, contributor to sea level rise in New England
is not related to climate change. New England is still experiencing a small amount of land
subsidence in response to the last glacial period.
Figure 6: Observed Increase in Sea Level Rise
Source: NOAA
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Projections of sea level rise through 2100 vary significantly depending on future greenhouse gas
emissions and melting of land-based glaciers. Currently sea level is rising at an increasing rate.
Figure 7 shows the recent rate of sea level rise, and a range of sea level rise scenarios.
Projections for 2100 range from 4 feet to 10 feet. With ten feet representing the most extreme
scenario. For 2050, the projections range approximately 1.5 to 3 feet.
Figure 7: Recent and Projected Increase in Sea Level Rise
Source: SHMCAP
Following the outline of the Massachusetts State Hazard Mitigation and Climate Adaptation Plan
(SHMCAP), this local hazard mitigation plan organizes consideration of natural hazards based on
their relationship to projected climate changes. The one exception is that as coastal and inland
flooding are interrelated they are considered together. Table 6 below, from the SHMCAP,
summarizes the natural hazards reviewed in this plan, climate interactions, and expected impacts.
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Table 6: Climate Change and Natural Hazards
Primary Climate
Change Interaction
Natural Hazard Other Climate Change
Interactions
Representative Climate Change Impacts
Changes in
Precipitation
Inland Flooding
Extreme Weather
Flash flooding, urban flooding, drainage
system impacts (natural and human-made),
lack of groundwater recharge, impacts to
drinking water supply, public health impacts
from mold and worsened indoor air quality,
vector-borne diseases from stagnant water,
episodic drought, changes in snow-rain
ratios, changes in extent and duration of
snow cover, degradation of stream channels
and wetland
Drought
Rising Temperatures,
Extreme Weather
Landslide
Rising Temperatures,
Extreme Weather
Sea Level Rise
Coastal Flooding Extreme Weather
Increase in tidal and coastal floods, storm
surge, coastal erosion, marsh migration,
inundation of coastal and marine
ecosystems, loss and subsidence of wetlands
Coastal Erosion
Changes in Precipitation,
Extreme Precipitation
Tsunami Rising Temperatures
Rising
Temperatures
Average/Extreme
Temperatures
N/A
Shifting in seasons (longer summer, early
spring, including earlier timing of spring peak
flow), increase in length of growing season,
increase of invasive species, ecosystem
stress, energy brownouts from higher
energy demands, more intense heat waves,
public health impacts from high heat
exposure and poor outdoor air quality,
drying of streams and wetlands,
eutrophication of lakes and ponds
Wildfires
Changes in Precipitation
Invasive Species
Changes in Precipitation,
Extreme Weather
Extreme Weather
Hurricanes/Tropical Storms Rising Temperatures,
Changes in Precipitation
Increase in frequency and intensity of
extreme weather events, resulting in greater
damage to natural resources, property, and
infrastructure, as well as increased potential
for loss of life
Severe Winter Storm /
Nor’easter
Rising Temperatures,
Changes in Precipitation
Tornadoes Rising Temperatures,
Changes in Precipitation
Other Severe Weather
(Including Strong Wind and
Extreme Precipitation)
Rising Temperatures,
Changes in Precipitation
Non-Climate-
Influenced
Hazards
Earthquake
Not Applicable
There is no established correlation between
climate change and this hazard
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OVERVIEW OF HAZARDS AND IMPACTS
Table 7 summarizes the frequency and severity of hazard risks for Massachusetts and Cohasset.
The Massachusetts frequency assessment is based on data in the SHMCAP. The Cohasset
frequency assessment reflects data from the National Climatic Data Center (NOAA) for Norfolk
County*, from the SHMCAP** and, from the local Hazard Mitigation Team***.
Table 7: Hazards Risk Summary
Hazard Frequency Severity
Massachusetts Cohasset Massachusetts Cohasset
Inland Flooding Substantial every 3rd
year 3.2 per year* Serious Minor
Drought 1% any given month 1% any given month*** Minor Minor
Landslides Every other year None recorded** Minor Minor
Coastal Flooding 6 events per year 2 per year* Serious Serious
Coastal Erosion Frequency can’t be
measured Stable**** Serious Minor
Tsunami 1in every 39 years 1 in every 39 years*** Extensive Extensive
Extreme
Temperatures
2 heat events and 1
cold event event/year
4 heat events in 10
8years/2 cold events in
10 years*
Minor Minor
Brush Fires One notable event
per year
No significant event in
40 years*** Minor Minor
Hurricane/Tropical
Storm One every two years 3 recorded events Serious Extensive
Severe Winter
Storms/Nor’easters
One notable event
per year 1.8 per year* Extensive Extensive
Tornadoes 1.7 per year None recorded Serious Serious
Other Severe
Weather
(Thunderstorms/High
Winds)
20-30 thunderstorms
annually; 43.5 high
wind events annually
3 per year* Minor Minor
Earthquake
10 - 15% chance of
Mag 5 in 10-year
period
10 - 15% chance of
Mag 5 in 10-year
period***
Extensive Extensive
Severity
• Minor: Limited and scattered property damage; limited damage to public infrastructure and essential
services not interrupted; limited injuries or fatalities.
• Serious: Scattered major property damage; some minor infrastructure damage; essential services are
briefly interrupted; some injuries and/or fatalities.
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• Extensive: Widespread major property damage; major public infrastructure damage (up to several
days for repairs); essential services are interrupted from several hours to several days; many injuries
and/or fatalities.
• Catastrophic: Property and public infrastructure destroyed; essential services stopped; numerous
injuries and fatalities.
CHANGING PRECIPITATION PATTERNS
INLAND FLOODING
Inland flooding can be associated with overflowing rivers and streams, stormwater flooding due
to impervious surfaces and inadequate stormwater infrastructure, and in more rare cases ice jams,
ground failures (erosion), and in some communities beaver dams. Inland flooding is generally
caused by hurricanes, nor’easters, severe rainstorms, and thunderstorms. Climate change is
projected to exacerbate these issues due to increasing frequency of extreme rainfall events.
Increases in average annual rainfall may also lead to more incidents of basement flooding and
impacts on septic systems caused by high seasonal groundwater levels.
Flooding was the most prevalent serious natural hazard identified by local officials in Cohasset.
The Town of Cohasset is subject to two kinds of flooding; coastal flooding (discussed further under
Sea Level Rise) where wind and tide leads to flooding along the shore and tidal waterways and
inland flooding where the rate of precipitation or amount of water overwhelms the capacity of
natural and structured drainage systems to convey water causing it to overflow the system. These
two types of flooding are often combined as inland flooding is prevented from draining by the
push of wind and tide driven water
Cohasset’s relatively high geography offers it some degree of protection from flooding of all
types. Inland flooding has historically only been an issue in the James Brook watershed and
around the Post Office area. In both cases, flooding is more the result of high tides blocking the
ability of storm water to drain. Other areas where inland flooding can occur are near the
reservoir, but this area is wooded with only a few homes.
The March 2010 rainstorms fit the profile of a type of event expected to increase in frequency as
the climate warms. That is, significant precipitation, falling in late winter as rain rather than snow,
on frozen ground, and while vegetation is still dormant. The Blue Hill Observatory in Milton
recorded 17.7 inches of rain from three storms in the 19 days from March 13 to 31. As shown at
the USGS gage nearest to Cohasset, the Old Swamp River in South Weymouth, river levels
surged with each storm (Figure 8). The March 2010 storms were a federally declared disaster
making federal assistance available to property owners who did not carry flood insurance.
Based on the claims, Cohasset experienced less flood damage than many towns, with no flood
insurance claims and ten disaster claims, none of which were located in FEMA Special Flood
Hazard Areas. This highlights the challenge of managing stormwater flooding and the reality that
much of our flooding occurs outside of FEMA special flood hazard areas. See Map 3 in Appendix
B for claim locations.
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Figure 8: March 2010 USGS Old Swamp River Gage
Local data for previous flooding occurrences are not collected by the Town of Cohasset. The best
available local data is for Norfolk County through the National Climatic Data Center. Norfolk
County, which includes the Town of Cohasset, experienced 32 flood events from 2010 through
2019. No deaths or injuries were reported and the total reported property damage in the county
was $25 million dollars. Nearly all of the damage is attributed to the events in March 2010. This
is an average of 3.2 flood events each year.
Table 8: Norfolk County Flood Events, 2010 through 2019
Date Deaths Injuries Property Damage
03/14/2010 0 0 16.64M
03/29/2010 0 0 8.320M
04/01/2010 0 0 0.00K
07/24/2010 0 0 20.00K
08/05/2010 0 0 0.00K
08/25/2010 0 0 8.00K
08/28/2011 0 0 0.00K
08/15/2012 0 0 0.00K
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Date Deaths Injuries Property Damage
10/29/2012 0 0 0.00K
06/07/2013 0 0 0.00K
07/29/2013 0 0 0.00K
08/09/2013 0 0 15.00K
10/22/2014 0 0 0.00K
10/23/2014 0 0 0.00K
8/15/2015 0 0 0.00K
8/18/2015 0 0 0.00K
6/07/2016 0 0 5.00K
8/14/2016 0 0 5.00K
4/1/2017 0 0 5.00K
7/12/2017 0 0 0.00K
7/18/2017 0 0 1.00K
8/2/2017 0 0 0.00K
9/30/2017 0 0 10.00K
10/25/2017 0 0 0.00K
10/29/2017 0 0 0.00K
01/12/2018 0 0 0.00K
01/13/2018 0 0 0.00K
04/16/2018 0 0 0.00K
07/06/2018 0 0 10.00K
10/29/2018 0 0 0.00K
11/03/2018 0 0 0.00K
4/15/2019 0 0 0.00K
Total 0 0 25 M
Source: NOAA, National Climatic Data Center
ICE JAMS
Ice jams occur in cold weather when normally flowing water begins to freeze effectively damming
the waterway and causing localized flooding. Flooding may also occur when ice jams break up
and ice may pile up at culverts or around bridges. There is no recent history of ice jams leading to
flooding in Cohasset and town staff did not identify this hazard as an issue for the town. As
coastal Massachusetts experiences somewhat warmer winters than the western part of the state
and salt water is less subject to freezing, this hazard is unlikely to be an issue in Cohasset
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DAM FAILURE OR OVERTOPPING
Dams can fail because of structural problems or age, independent of any storm event. Dam
failure can follow an earthquake by causing structural damage. Dams can also fail structurally
because of flooding arising from a storm or they can overspill due to flooding. In the event of a
dam failure, the energy of the water stored behind even a small dam can cause loss of life and
property damage if there are people or buildings downstream. The number of fatalities from a
dam failure depends on the amount of warning provided to the population and the number of
people in the path of the dam’s floodwaters.
A concern for dams in Massachusetts is that many were built in the 19th century without the
benefits of modern engineering or construction oversight. In addition, some dams have not been
properly maintained. The increasing intensity of precipitation is the primary climate concern
related to dams, as they were most likely designed based on historic weather patterns. The
SHMCAP indicates that changing precipitation patterns may increase the likelihood of overflow
events. Dam failure is a highly infrequent occurrence, but a severe incident could result in loss of
lives and significant property damage. According to the Association of State Dam Safety
Officials, three dams have failed in Massachusetts since 1984, one of which resulted in a death.
Dams in Cohasset are listed below:
Aaron River Dam – The Aaron River Dam impounds water to create the Aaron River Reservoir,
which is Cohasset’s primary source for drinking. This is a town-owned dam and it is inspected and
monitored frequently. It is a high hazard dam.
Bound Brook Control Dam – This town-owned structure is used to control water flow and flooding
for the southwestern corner of the Town, which is the water supply area. This structure is actively
managed and monitored frequently. Failure of this structure could lead to significant flooding
downstream, most especially in North Scituate. It is listed as a significant hazard dam.
Heron Pond Dam- This DCR owned dam in Wompatuck State Park is listed as a low hazard dam.
Nichols Road Dam – This dam is owned by the Town of Cohasset. DCR lists it as a significant
hazard dam.
Sanctuary Pond Dam - The Sanctuary Pond Dam near the headwaters of James Brook is owned
by the Trustees of Reservations. The DPW worked with the Trustees to assure needed tree
removal and maintenance on the impoundment was performed. It is currently in adequate
condition. The structure does not meet the DCR definition of a dam as it does not meet the acre-
foot volume or height requirements. Establishment of downstream detention measures should be
considered to improve flood control capacity.
Straits Pond Tide Gate –The tide gate is located on the Hull/Cohasset border and is managed to
control the water level and salinity of Straits Pond. The tide gate is managed by the Town of Hull
Department of Public Works. It has automated controls and an alarm system. The Town of Hull
reduces the water level when significant nor’easters are forecast, as ocean overwash across
Atlantic Avenue has raised the pond level as much as two feet in one tide cycle. Low-lying
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properties along Straits Pond could be subject to flooding in extreme storm events. DCR lists it as
a significant hazard dam.
Table 9: Status of Dams in Cohasset
Dam Name River Owner Hazard
Classification
Nichols Road Dam Richardson Brook Town of Cohasset, Board of
Selectmen Significant
Aaron River Dam Aaron River Town of Cohasset, Board of
Selectmen High
Bound Brook Dam Bound Brook Town of Cohasset, Board of
Selectmen Significant
Heron Pond Dam Tributary of Bound Brook MA Department of
Conservation and Recreation Low
Straits Pond Dam
(tide gate) Tributary of Weir River Town of Hull, Board of
Selectmen Significant
Source: DCR Office of Dam Safety, August 2018
LOCALLY IDENTIFIED AREAS OF INLAND AND COASTAL FLOODING
Information on potential flood hazard areas was taken from two sources. The first is the National
Flood Insurance Rate Maps (FIRM). The FIRM flood zones are shown on Map 3 in Appendix B. The
“Locally Identified Areas of Flooding” described below were identified by town staff as areas
where flooding is known to occur. These areas do not necessarily coincide with the flood zones on
the FIRM maps. Flood sources include inadequate drainage systems, high groundwater, coastal
storms, or other local conditions that may not be within a Special Flood Hazard Area. The
numbers correspond to the numbers on Map 8, “Local Hazard Areas.”
DCR Dam Hazard Classification
High: Dams located where failure or mis-operation will likely cause loss of life and serious damage to
homes(s), industrial or commercial facilities, important public utilities, main highways(s) or railroad(s).
Significant: Dams located where failure or mis-operation may cause loss of life and damage home(s),
industrial or commercial facilities, secondary highway(s) or railroad(s)
Low: Dams located where failure or mis-operation may cause minimal property damage to others. Loss of
life is not expected.
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Table 10: Locally Identified Areas of Flooding
Map
ID Name Description
1
Treats
Pond /
Atlantic
Avenue
Flooding in this area is largely caused by the outflow pipe being
buried under up to six feet of sand. Update: Design and permitting is
complete for a project to extend the outflow pipe 450 feet. This will
place the end of the pipe beyond the area where the beach accretes
sand. Easements from abutters are required to commence the project.
2 Jacob’s
Meadow
As the downstream end of the James Brook system, this area is
impacted by storm surges and heavy rainfall. Flooding is aggravated
within the James Brook watershed due to the tidal restrictions which
hinder stormwater release when Cohasset Harbor water levels
exceed that of Jacobs Meadow at the mouth of the brook. At such
times Jacob's Meadow becomes the storage pond for all flows coming
from the watershed. This makes volumetric restrictions of runoff from
all development within this watershed essential to help mitigate
flooding. Under extreme storm surge conditions, sea water may
overtop the seawall at Border Street and flow into Jacobs Meadow
and the adjoining neighborhood. Automatic operation of a tide gate
relieves flooding in most circumstances. The Town draws down water
levels to the degree possible in advance of storms. A flapper valve
installed at Elm Street addresses tidal inflow to the stormwater
system. Flooding still occurs when the seawall at Border Street is
overtopped, and when there are extreme rains that can’t be released
by the tide gate until the tide recedes.
3
South
Main, 100
Block
A culvert that used to cause flooding has been repaired, however this
location is subject to flooding under the same circumstances as Jacob’s
Meadow.
4 Post Office This location is subject to flooding under the same circumstances as
Jacob’s Meadow.
5
Peppermint
Brook at
3A
Litter and debris, much of it from the highway, results in a blocked
culvert and flooding. A new grate has been fabricated which should
reduce flooding issues. This area is partly under state jurisdiction.
8 Rocky
Beach
Flooding from tidal surges combined with limited drainage in this area
results in road closures.
9 Route 3A Heavy rain in the vicinity of Forest Street causes closure of the
southbound lane.
REPETITIVE LOSS STRUCTURES
As defined by FEMA, a repetitive loss property is a NFIP-insured structure that has had two or
more paid flood losses of $1,000 or more in any given 10-year period since 1978. There are 11
repetitive loss properties in Cohasset. The properties are shown on the maps in Appendix A.
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These repetitive loss properties had a total of 35 losses between 1978 and 2018, with $501,975
in damages. For more information on repetitive losses see
https://www.fema.gov/txt/rebuild/repetitive_loss_faqs.txt and
https://www.fema.gov/repetitive-flood-claims-grant-program-fact-sheet.
Table 11 summarizes the number and location of loss structures located in Cohasset and the
number of losses and claims associated with them.
Table 11: Summary of Repetitive Losses and Claims
A, AE, AO,
AH Zones
VE Zone B, C, X
Zones Total
Number of Properties 8 1 2 11
Number of Losses 22 4 9 35
Total Claims $252,655 $136,377 $112,944 $501,975
Source: Department of Conservation and Recreation, FEMA Repetitive Loss data
DROUGHT
Drought is a temporary irregularity in precipitation and differs from aridity since the latter is
restricted to low rainfall regions and is a permanent feature of climate. Drought is a period
characterized by long durations of below normal precipitation. Drought conditions occur in
virtually all climatic zones, yet its characteristics vary significantly from one region to another since
it is relative to the normal precipitation in that region. Drought can affect agriculture, water
supply, aquatic ecology, wildlife, and plant life.
Droughts are projected to increase in frequency and intensity in the summer and fall as weather
patterns change. Drought impacts can include reduced groundwater and surface water levels,
affecting water quality and quantity, and the organisms that rely on aquatic resources. Drought
also increases stress on plant communities and the likelihood of forest and brush fires.
Communities may be affected by water use restrictions, affecting drinking water supply and
outdoor water use. Economic sectors impacted could include recreation, agriculture, and forestry.
Five levels of drought have been developed to characterize drought severity: Normal, Advisory,
Watch, Warning, and Emergency. These drought levels are based on the conditions of natural
resources and are intended to provide information on the current status of water resources. The
levels provide a basic framework from which to take actions to assess, communicate, and respond
to drought conditions.
Cohasset does not collect data relative to drought events. Because drought tends to be a regional
natural hazard, this plan references state data as the best available data for drought. The
SHMCAP using data collected since 1850, calculates that statewide there is a 1% chance of
being in a drought emergency in any given month. For drought warning and watch levels, the
chance is 2% and 8% respectively in any given month (Table 12).
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Table 12: Frequency of Massachusetts Drought Levels
Drought Level
Frequency Since 1850 Probability of Occurrence in a
Given Month
Drought Emergency 5 occurrences 1% chance
Drought Warning 5 occurrences 2% chance
Drought Watch 46 occurrences 8% chance
Source: SHMCAP
Drought emergencies have been reached infrequently, with five events occurring between 1850
and 2012: 1883, 1911, 1941, 1957, and 1965 to 1966. Due to its long duration, the drought
from 1965 to 1966 is viewed as the most severe drought to have occurred in Massachusetts in
modern times. The drought that extended from July 2016 to April 2017 reached the Drought
Warning level. Determinations regarding the end of a drought or reduction of the drought level
focus on two key drought indicators: precipitation and groundwater levels. These two factors have
the greatest long-term impact on stream flow, water supply, reservoir levels, soil moisture, and the
potential for forest fires.
The U.S. Drought Monitor characterizes droughts as moderate, severe, extreme, or exceptional.
Severe drought is characterized by likely crop and pasture losses, water shortages, and water
restrictions. As shown in Figure 9 below, Cohasset experienced 13-25 weeks of severe drought
between 2001 and 2017. Cohasset was under a drought warning from July to November 2016.
During that time, mandatory water restrictions were implemented and the water level in Lily Pond
was so low that no flow was entering Bound Brook.
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Figure 9: Weeks of Severe Drought (2001-2017)
Source: SHMCAP
LANDSLIDES
According to the U.S. Geological Survey, “The term landslide includes a wide range of ground
movement, such as rock falls, deep failure of slopes, and shallow debris flows. Although gravity
acting on an over steepened slope is the primary reason for a landslide, there are other
contributing factors.” Among the contributing factors are: erosion by rivers or ocean waves over
steepened slopes; rock and soil slopes weakened through saturation by snowmelt or heavy rains;
earthquake created stresses that make weak slopes fail; excess weight from accumulation of rain
or snow; and stockpiling of rock or ore from waste piles or man-made structures. In Massachusetts,
according to the SHMCAP, the most common cause of landslides are geologic conditions combined
with steep slopes and/or heavy rains. Landslides associated with heavy rains typically occur on
steep slopes with permeable soils underlain by till or bedrock.
Landslides can result from human activities that destabilize an area or can occur as a secondary
impact from another natural hazard, such as flooding. In addition to structural damage to
buildings and the blockage of transportation corridors, landslides can lead to sedimentation of
water bodies. Typically, a landslide occurs when the condition of a slope changes from stable to
unstable. Natural precipitation such as heavy snow accumulation, torrential rain, and run-off may
saturate soil, creating instability enough to contribute to a landslide. More frequent extreme rain
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events may increase the chance of landslides as saturated soils are conducive to landslides.
Drought may also increase the likelihood of landslides if loss of vegetation decreases soil stability.
The SHMCAP, utilizing data from the MA Department of Transportation from 1986 to 2006
estimates that, on average, roughly one to three known landslides have occurred each year. A
slope stability map published by the MA Geological Survey and UMass-Amherst indicates that the
most significant risk of landslide is in western Massachusetts.
Cohasset is classified as having a moderate susceptibility and low incidence of landslides (see
Map 4, Appendix B). Should a landslide occur in the future, the type and degree of impacts
would be highly localized. The town’s vulnerabilities could include damage to structures, damage
to transportation and other infrastructure, and localized road closures. Injuries and casualties,
while possible, would be unlikely given the low extent and impact of landslides in Cohasset.
There are no recorded instances of landslides having occurred in the Town of Cohasset.
SEA LEVEL RISE
COASTAL FLOODING
Coastal flooding is most often associated with severe coastal storms that, through the combination
of winds and tides, drive tidal waters to higher levels than normally experienced, leading to the
inundation of low-lying land areas and the overtopping of sea walls. In low-lying areas coastal
flooding can also be associated with routine tidal flooding or higher astronomic tides. Fueled by
the warming climate, coastal flooding will become more frequent and severe due to the
combination of sea level rise and more frequent and intense storms.
While the rocky elevated section of Cohasset’s more northerly coast is less vulnerable to coastal
flooding, Cohasset Harbor and Rocky Beach as well are two locations the town has identified as
flooding areas of key concern. At Jacob’s Meadow, high tides and storm surge also cause
upstream flooding as they limit the ability of stormwater to drain from inland waterways.
Local data for previous coastal flooding occurrences are not collected by the Town of Cohasset.
The best available local data is for Norfolk County through the National Climatic Data Center.
Eastern Norfolk County, which includes the Town of Cohasset, experienced 20 coastal flood events
from 2010 through 2019 (see Table 13). No deaths or injuries were reported and the total
reported property damage in the county was $1.1 million dollars. This is an average of 2 coastal
floods each year.
Table 13: Eastern Norfolk County Coastal Floods, 2010 through 2019
DATE DEATHS INJURIES PROPERTY DAMAGE
1/2/2010 0 0 0
3/1/2010 0 0 20,000
12/27/2010 0 0 100,000
6/3/2012 0 0 0
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6/4/2012 0 0 0
6/4/2012 0 0 450,000
10/29/2012 0 0 0
12/27/2012 0 0 0
2/9/2013 0 0 500,000
3/7/2013 0 0 75,000
12/15/2013 0 0 0
1/2/2014 0 0 0
1/3/2014 0 0 0
10/23/2014 0 0 0
11/2/2014 0 0 0
1/27/2015 0 0 0
2/8/2016 0 0 0
1/4/2018 0 0 0
1/30/2018 0 0 0
3/2/2018 0 0 0
TOTAL 0 0 1,145,000
Source: NOAA, National Climatic Data Center
COASTAL EROSION
Coastal shorelines change constantly in response to storms, seasons, sea level, and human
alterations. Coastal erosion is measured as a rate of change over time. According to the
SHMCAP frequency of erosion cannot be measured. Risings seas and more frequent and intense
storms will tend to increase erosion, although some areas may actually accrete material. Erosion
may be exacerbated by efforts to protect shorelines as when engineered hard structures reduce
sediment sources to downdrift areas or increase erosion seaward of structures due to interaction
with waves.
Massachusetts Coastal Zone Management in cooperation with the U. S. Geological Survey (USGS)
provides shoreline change data for the Massachusetts coast. They provide long-term (1800’s –
2014) and short-term (1970-2014) data. Coastal erosion rates for Cohasset are shown below
(see Figure 10). For the most part, the Cohasset coast has been stable, showing no statistical
change. There are pockets, including Sandy Cove, where the coast has accreted.
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Figure 10: Shoreline Change 1970--2014
Source: CZM Shoreline Change
TSUNAMI
A tsunami is a surge of water typically caused by an offshore earthquake. Tsunamis can cause
wave heights of 100 feet or more. According to the SHMCAP, Massachusetts has never
experienced a significant tsunami, although two tsunamis have occurred with no deaths or
damages recorded. Damage from a tsunami could be very significant, but it is a low likelihood
event, having occurred approximately once every 39 years along the entire east coast. No
tsunami has impacted Massachusetts since 1950. The portions of Cohasset’s shoreline that are
elevated on ledge would with withstand a tsunami better than low-lying beachfront areas.
RISING TEMPERATURES
AVERAGE AND EXTREME TEMPERATURES
Extreme temperatures occur when either high temperature or low temperatures relative to
average local temperatures occur. These can occur for brief periods of time and be acute, or they
can occur over long periods of time where there is a long stretch of excessively hot or cold
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weather. Cohasset has four well-defined seasons. The seasons have several defining factors, with
temperature one of the most significant. Extreme temperatures can be defined as those that are
far outside of the normal seasonal ranges for Massachusetts
EXTREME COLD
Extreme cold temperature is typically measured using the Wind Chill Temperature Index, which is
provided by the National Weather Service (NWS). The wind chill is the apparent temperature
felt on exposed skin due to the combination of air temperature and wind speed. The index is
provided in Figure 11 below. Extreme cold is a dangerous situation that can result in health
emergencies for susceptible people, such as those without shelter, those who are stranded, or
those who live in homes that are poorly insulated or without heat.
Figure 11: Wind Chill Temperature Index and Frostbit Risk
Source: National Weather Service
The Town of Cohasset does not collect data for previous occurrences of extreme cold. The best
available local data are for Norfolk County, through the National Climatic Data Center (NCDC).
There have been two extreme cold events in the past ten years, which caused no deaths, no
injuries, or property damage. This is an average of one event every 5 years.
Table 14: Norfolk County Extreme Cold and Wind Chill Occurrences 2010 through 2019
Date Deaths Injuries Damage ($)
2/13/2016 0 0 0
1/6/2018 0 0 0
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Total 0 0 0
Source: NOAA, National Climatic Data Center
EXTREME HEAT
A heat wave in Massachusetts is defined as three or more consecutive days above 90°F. Another
measure used for identifying extreme heat events relies on the Heat Index. According to the
National Weather Service (NWS), the Heat Index is a measure of how hot it really feels relative
humidity is factored in with the actual air temperature. The NWS issues an advisory when the
heat index (Figure 12) is forecast to exceed 100°F for two or more hours; an excessive heat
advisory is issued if the forecast predicts the temperature will rise above 105°F.
Figure 12: Heat Index Chart
Source: National Weather Service
The Town of Cohasset does not collect data on excessive heat occurrences. The best available
local data are for Norfolk County, through the National Climatic Data Center. In the past ten
years there have been four excessive heat days and no deaths, injuries, or property damage (see
Table 15). This is an average of one heat occurrences every 2.5 years.
Table 15: Norfolk County Excessive Heat Occurrences 2010-2019
Date Deaths Injuries Damage ($)
7/22/2011 0 0 0
7/1/2018 0 0 0
7/3/2018 0 0 0
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8/28/2018 0 0 0
Total 0 0 0
Source: NOAA, National Climatic Data Center
Extreme cold events are predicted to decrease in the future, while extreme heat days, as well as
average temperatures are projected to increase. The projected increase in extreme heat and
heat waves is the source of one of the key health concerns related to climate change. Prolonged
exposure to high temperatures can cause heat-related illnesses, such as heat cramps, heat
exhaustion, heat stroke, and death. Heat exhaustion is the most common heat-related illness and if
untreated, it may progress to heat stroke. People who perform manual labor, particularly those
who work outdoors, are at increased risk for heat-related illnesses. Prolonged heat exposure and
the poor air quality and high humidity that often accompany heat waves can also exacerbate
pre-existing conditions, including respiratory illnesses, cardiovascular disease, and mental
illnesses.
Older adults are often at elevated risk due to a high prevalence of pre-existing and chronic
conditions. People who live in older housing stock and in housing without air conditioning have
increased vulnerability to heat-related illnesses. Power failures are more likely to occur during
heat waves, affecting the ability of residents to remain cool during extreme heat. Individuals with
pre-existing conditions and those who require electric medical equipment may be at increased
risk during a power outage.
Due to what is termed the “heat island effect”, areas with less shade and more dark surfaces
(pavement and roofs) will experience even hotter temperatures; these surfaces absorb heat
during the day and release it in the evening, keeping nighttime temperatures warmer as well.
Map 10 in Appendix B displays areas that are among the hottest 5% of land in the MAPC region
based on land surface temperature derived from satellite imagery on July 13, 2016, when the
high temperature at Logan Airport was 92°F. While Cohasset is generally not as hot as more
urban locations, the hot spots in Cohasset include Cohasset Middle-High School, Deer Hill School,
and the commercial area that includes Walgreen’s and Shaw’s.
WILDFIRE
A wildfire is a non-structure fire occurring in a forested, shrub or grassland area. In the Boston
metropolitan region these fires rarely grow to the size of wildfires seen more typically in the
western U.S. A more likely occurrence is brush fires that typically burn no more than the
underbrush of a forested area. There are three different classes of wildfires:
• Surface fires are the most common type and burn along the floor of a forest, moving
slowly and killing or damaging trees
• Ground fires are usually started by lightning and burn on or below the forest floor
• Crown fires spread rapidly by wind, jumping along the tops of trees
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A wildfire differs greatly from other fires by its extensive size, the speed at which it can spread
out from its original source, its potential to unexpectedly change direction, and its ability to jump
gaps such as roads, rivers, and fire breaks. Wildfire season can begin in March and usually ends
in late November. The majority of wildfires typically occur in April and May, when most
vegetation is void of any appreciable moisture, making them highly flammable. Once "green-up"
takes place in late May to early June, the fire danger is usually reduced somewhat. As the
climate warms, drought and warmer temperatures may increase the risk of wildfire as vegetation
dries out and becomes more flammable.
Fire can present a hazard where there is the potential to spread into developed or inhabited
areas, particularly residential areas where sufficient fuel materials might exist to allow the fire
the spread into homes. Protecting structures from fire poses special problems and can stretch
firefighting resources to the limit. If heavy rains follow a fire, other natural disasters can occur,
including landslides, mudflows, and floods. If the wildfire destroys the ground cover, then erosion
becomes one of several potential problems.
POTENTIAL BRUSHFIRE HAZARD AREAS
The SCHMCAP includes a graphic that depicts statewide fire risk incorporating three risk
components: fuel, wildland-urban interface, and topography (Figure 13). The wildland-urban
interface reflects communities where housing and vegetation intermingle, and fire can spread
from structures to vegetated areas. The most susceptible fuels are pitch pine, scrub oak and oak
forests. Topography can affect the behavior of fires, as fire spreads more easily uphill. Cohasset
is in a high-risk zone. However, the Fire Chief reports that brush fires have been an infrequent
occurrence, with only one major brushfire in the past forty years. Based on this information brush
fires in Cohasset are an infrequent occurrence. Nevertheless, access to some of Cohasset’s large
wooded areas would be a challenge in the event of a fire. The most common cause of wildfires is
the careless disposal of smoking materials and untended campfires.
The following areas of town were identified as having the highest potential for brush fires. The
numbers correspond to the numbers on Map 8, “Hazard Areas”:
6) West Cohasset
7) Wheelwright Park
10) Scituate Town Forest
11) Ingram Park
12) Wooded wetland area (west of the Cohasset Golf Course)
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Figure 13: Wildfire Risk Areas
Source: SHMCAP
INVASIVE SPECIES
The 2018 SHMCAP includes invasive species as a natural hazard for the first time. They are
defined as “non-native species that cause or are likely to cause harm to ecosystems, economies,
and/or public health”. The Cohasset team identified two invasive species of particular concern.
Phragmites were identified for their susceptibility to brush fire; milfoil was identified due to its
presence in the Cohasset water supply. Town officials are investigating the impacts of, and
potential treatment for, milfoil.
EXTREME WEATHER
HURRICANES AND TROPICAL STORMS
A hurricane is a violent wind and rainstorm with wind speeds of 74 to 200 miles per hour. A
hurricane is strongest as it travels over the ocean and is particularly destructive to coastal
property as the storm hits land. A tropical storm has similar characteristics, but wind speeds are
below 74 miles per hour. Climate models suggest that hurricanes and tropical storms will become
more intense as warmer ocean waters provide more fuel for the storms. In addition, rainfall
amounts associated with hurricanes are predicted to increase because warmer air can hold more
water vapor. Since 1900, 39 tropical storms have impacted New England (NESEC).
Massachusetts has experienced approximately 32 tropical storms, nine Category 1 hurricanes,
five Category 2 hurricanes and one Category 3 hurricane.
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Given its location at the coast, the Town of Cohasset’s entire area is vulnerable to hurricanes,
which occur between June and November. As shown in the hazard mapping in Appendix B,
tropical storms tracked through Cohasset in 1888 and 1916. Category 2 Hurricane Bob tracked
through Cohasset in 1991. A hurricane or storm track is the line that delineates the path of the
eye of a hurricane or tropical storm. The town also experiences the impacts of the wind and rain
from hurricanes and tropical storms regardless of whether the storm track passed through the
town. The hazard mapping indicates that the 100-year wind speed in Cohasset is 110 miles per
hour.
Table 16: Hurricane Records for Massachusetts, 1938 to 2020
Hurricane Event Date
Great New England Hurricane* September 21, 1938
Great Atlantic Hurricane* September 14-15, 1944
Hurricane Doug September 11-12, 1950
Hurricane Carol* August 31, 1954
Hurricane Edna* September 11, 1954
Hurricane Diane August 17-19, 1955
Hurricane Donna September 12, 1960
Hurricane Gloria September 27, 1985
Hurricane Bob August 19, 1991
Hurricane Earl September 4, 2010
Tropical Storm Irene August 28, 2011
Hurricane Sandy October 29-30, 2012
Source: National Oceanic and Atmospheric Administration
*Category 3
Hurricane intensity is measured according to the Saffir/Simpson scale, which categorizes hurricane
intensity linearly based upon maximum sustained winds, barometric pressure, and storm surge
potential. These are combined to estimate potential damage. The following gives an overview of
the wind speeds, surges, and range of damage caused by different hurricane categories:
Table 17: Saffir/Simpson Scale
Scale No. (Category) Winds (mph) Surge (ft) Potential Damage
1 74 – 95 4 - 5 Minimal
2 96 – 110 6 - 8 Moderate
3 111 – 130 9 - 12 Extensive
4 131 – 155 13 - 18 Extreme
5 > 155 >18 Catastrophic
Source: NOAA
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Hurricanes typically have regional impacts beyond their immediate tracks. Falling trees and
branches are a significant problem because they can result in power outages when they fall on
power lines or block traffic and emergency routes. Hurricanes are a town-wide hazard in
Cohasset. Potential hurricane damages to Cohasset have been estimated using HAZUS-MH. Total
damages are estimated at $24 million for a Category 2 hurricane and $130 million for a
Category 4 hurricane.
SEVERE WINTER STORM/NOR’EASTER
A northeast storm, known as a nor’easter, is typically a large counterclockwise wind circulation
around a low-pressure center. Featuring strong northeasterly winds blowing in from the ocean
over coastal areas, nor’easters are relatively common in the winter months in New England
occurring one to two times a year. The storm radius of a nor’easter can be as much as 1,000 miles
and these storms feature sustained winds of 10 to 40 mph with gusts of up to 70 mph. These
storms are accompanied by heavy rain or snow, depending on temperatures. Many of the historic
flood events identified in the previous section were precipitated by nor’easters, including the
“Perfect Storm” event in 1991. More recently, blizzards in February 2013, January 2015, and in
March 2018 were large nor’easters that caused significant snowfall amounts.
Cohasset is vulnerable to both the wind and precipitation that accompany nor’easters. High winds
can cause damage to structures, fallen trees, and downed power lines leading to power outages.
Intense rainfall can overwhelm drainage systems causing localized flooding of rivers and streams
as well as urban stormwater ponding and localized flooding. Fallen tree limbs as well as heavy
snow accumulation and intense rainfall can impede local transportation corridors, and block
access for emergency vehicles. Nor’easters are also a cause of coastal flooding.
A blizzard is a winter snowstorm with sustained or frequent wind gusts to 35 mph or more,
accompanied by falling or blowing snow which reduces visibility to or below ¼ mile. These
conditions must be the predominant condition over a three-hour period. Extremely cold
temperatures are often associated with blizzard conditions but are not a formal part of the
definition. The hazard related to the combination of snow, wind, and low visibility significantly
increases when temperatures drop below 20 degrees.
The National Weather Service defines “heavy snow fall” as an event generating at least four
inches of snowfall within a 12-hour period. The Northeast Snowfall Impact Scale (NESIS),
developed by Paul Kocin of The Weather Channel and Louis Uccellini of the National Weather
Service (Kocin and Uccellini, 2004), characterizes and ranks high impact northeast snowstorms.
These storms have large areas of 10-inch snowfall accumulations and greater. NESIS has five
categories: Extreme, Crippling, Major, Significant, and Notable. NESIS scores are a function of the
area affected by the snowstorm, the amount of snow, and the number of people living in the path
of the storm. The largest NESIS values result from storms producing heavy snowfall over large
areas that include major metropolitan centers. The NESIS categories are summarized below:
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Table 18: NESIS Categories
Category NESIS Value Description
1 1 – 2.499 Notable
2 2.5 – 3.99 Significant
3 4 – 5.99 Major
4 6 – 9.99 Crippling
5 10+ Extreme
Source: Massachusetts State Hazard Mitigation Plan, 2013
The most significant winter storm in recent history was the “Blizzard of 1978,” which resulted in
over three feet of snowfall and multiple day closures of roadways, businesses, and schools. In
Cohasset, blizzards and severe winter storms have occurred in the following years:
Table 19: Severe Weather Major Disaster Declarations in Eastern MA
Storm Event Date
Severe Winter Storm and Snowstorm March 2018
Severe Winter Storm, Snowstorm, and Flooding January 2015
Severe Winter Storm, Snowstorm, and Flooding February 2013
Hurricane Sandy October/November 2012
Severe Storm and Snowstorm October 2011
Tropical Storm Irene August 2011
Severe Winter Storm and Snowstorm January 2011
Severe Winter Storm and Flooding December 2008
Severe Storms and Inland and Coastal Flooding April 2007
Severe Storm and Flooding October 2005
Severe Storms & Flooding March 2001
Blizzard January 1966
Winter Coastal Storm December 1992
Severe Coastal Storm October 1991
Hurricane Bob August 1991
Hurricane Gloria September 1985
Coastal Storm, Flood, Ice, Snow February 1978
Hurricane, floods August 1955
Hurricanes September 1954
Source: FEMA
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As with hurricanes, warmer ocean water and air will provide more fuel for storms. According to
the SHMCAP it appears that Atlantic coast nor’easters are increasing in frequency and intensity.
Winter storms, including heavy snow, blizzards, and ice storms, are the most common and most
familiar of the region’s hazards that affect large geographic areas. The majority of blizzards
and ice storms in the region cause more inconvenience than they do serious property damage,
injuries, or deaths. However, periodically, a storm will occur which is a true disaster, and
necessitates intense large-scale emergency response. The impacts of winter storms are often
related to the weight of snow and ice, which can cause roof collapses and also causes tree limbs
to fall. This in turn can cause property damage and potential injuries. Power outages may also
result from fallen trees and utility lines.
Winter storms are a potential town-wide hazard in Cohasset. Map 6 in Appendix A indicates that
the average annual average snowfall in most of Cohasset is between 36 and 48 inches. A
number of public safety issues can arise during snowstorms. Impassible streets are a challenge for
emergency vehicles and affect residents and employers. Snow-covered sidewalks force people to
walk in streets, which are already less safe due to snow, slush, puddles, and ice. Large piles of
snow can also block sight lines for drivers, particularly at intersections. Refreezing of melting snow
can cause dangerous roadway conditions. In addition, transit operations may be impacted, as
they were in the 2015 blizzards which caused the closure of the MBTA system for one day and
limited services on the commuter rail for several weeks.
The Town of Cohasset does not keep local records of winter storms. Data for Norfolk County is the
best available data to help understand previous occurrences and impacts of heavy snow events.
According to National Climate Data Center (NCDC) records, from 2010 through 2019, Norfolk
County experienced 18 heavy snowfall events, resulting in no injuries, deaths, or property
damage (Table 20).
Table 20: Heavy Snow Events and Impacts in Eastern Norfolk County, 2010 through 2019
Date Deaths Injuries Property Damage ($)
2/16/2010 0 0 0
1/12/2011 0 0 0
1/26/2011 0 0 0
2/8/2013 0 0 0
3/7/2013 0 0 0
3/18/2013 0 0 0
12/14/2013 0 0 0
1/2/2014 0 0 0
1/21/2014 0 0 0
2/5/2014 0 0 0
2/2/2015 0 0 0
2/8/2015 0 0 0
2/14/2015 0 0 0
2/5/2016 2 0 0
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Date Deaths Injuries Property Damage ($)
2/8/2016 0 0 0
4/4/2016 0 0 0
3/14/2017 0 0 0
11/15/2018 0 0 0
Total 2 0 0
Source: NOAA, National Climatic Data Center
Heavy snow is considered to be high frequency events based on past occurrences, as there have
been 18 events in the past ten years, for an average of almost 2 events each winter. As with
nor’easters, warmer ocean water and air will provide more fuel for storms. According to the
SHMCAP changing atmospheric patterns favor the development of winter storms.
TORNADO
A tornado is a violent windstorm characterized by a twisting, funnel-shaped cloud. These events
are spawned by thunderstorms and occasionally by hurricanes and may occur singularly or in
multiples. They develop when cool air overrides a layer of warm air, causing the warm air to rise
rapidly. Most vortices remain suspended in the atmosphere. Should they touch down, they become
a force of destruction. Some ingredients for tornado formation include:
• Very strong winds in the mid and upper levels of the atmosphere
• Clockwise turning of the wind with height (from southeast at the surface to west aloft)
• Increasing wind speed with altitude in the lowest 10,000 feet of the atmosphere (i.e., 20
mph at the surface and 50 mph at 7,000 feet)
• Very warm, moist air near the ground with unusually cooler air aloft
• A forcing mechanism such as a cold front or leftover weather boundary from previous
shower or thunderstorm activity
Tornado damage severity is measured by the Fujita Tornado Scale, in which wind speed is not
measured directly but rather estimated from the amount of damage. As of February 1, 2007, the
National Weather Service began rating tornados using the Enhanced Fujita-scale (EF-scale), which
allows surveyors to create more precise assessments of tornado severity. The EF-scale is
summarized below:
Table 21: Enhanced Fujita Scale
Fujita Scale Derived Operational EF Scale
F Number Fastest ¼
mile (mph)
3-second
gust (mph) EF Number 3-second
gust (mph) EF Number 3-second
gust (mph)
0 40 – 72 45 – 78 0 65 – 85 0 65 – 85
1 73 – 112 79 – 117 1 86 – 109 1 86 – 110
2 113 – 157 118 – 161 2 110 – 137 2 111 – 135
3 158 – 207 162 – 209 3 138 – 167 3 136 – 165
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4 208 – 260 210 – 261 4 168 – 199 4 166 – 200
5 261– 318 262 – 317 5 200 – 234 5 Over 200
Source: Massachusetts State Hazard Mitigation Plan, 2013
The frequency of tornadoes in eastern Massachusetts is low; on average, there are six tornadoes
that touchdown somewhere in the Northeast region every year. The strongest tornado in
Massachusetts history was the Worcester Tornado in 1953 (NESEC). Recent tornado events in
Massachusetts were in Springfield in 2011 and in Revere in 2014. The Springfield tornado
caused significant damage and resulted in four deaths in June of 2011. The Revere tornado
touched down in Chelsea just south of Route 16, moved north into Revere’s business district along
Broadway, and ended near the intersection of Routes 1 and 60. The path was approximately two
miles long and 3/8 mile wide, with wind speeds up to 120 miles per hour. Approximately 65
homes had substantial damages and 13 homes and businesses were rendered uninhabitable.
Since 1950, there have been eleven tornadoes in Norfolk County recorded by the Tornado
History Project. There have been one F3 and one F2, and three FI tornados. These eleven
tornadoes resulted in a total of one fatality and 23 injuries and $4.1 million in damages, as
summarized in Table 22. This an average of one tornado every 6 years.
Table 22: Tornado Records for Norfolk County
Date Fujita Fatalities Injuries Width Length Damage
6/9/1953 3 0 17 667 28 $500K – 5M
11/21/1956 2 0 0 17 0.1 $500-$5000
8/9/1972 1 1 6 30 4.9 $5K-$50K
9/6/1973 1 0 0 10 1.1 $5K-$50K
7/10/1989 0 0 0 23 0.1 $500-$5000
5/18/1990 0 0 0 10 0.2 $500-$5000
5/18/1990 0 0 0 10 0.2 $500-$5000
6/30/2001 0 0 0 80 0.1 -
8/21/2004 1 0 0 40 6 $1,500,000
5/9/2013 0 0 0 50 0.38 $20,000
6/23/2015 0 0 0 200 0.48 -
Source: The Tornado History Project
Buildings constructed prior to current building codes may be more vulnerable to damages caused
by tornadoes. Evacuation of impacted areas may be required on short notice. Sheltering and
mass feeding efforts may be required along with debris clearance, search and rescue, and
emergency fire and medical services. Key routes may be blocked by downed trees and other
debris, and widespread power outages are also typically associated with tornadoes.
Although tornadoes are a potential town-wide hazard in Cohasset, tornado impacts are relatively
localized compared to severe storms and hurricanes. Damages from any tornado in Cohasset
would greatly depend on the track of the tornado. Based on the record of previous occurrences
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since 1956, tornado events in Cohasset are a low frequency event as there is no record of
tornado activity in Cohasset. According to the SHMCAP, it is possible that severe thunderstorms
which can include tornadoes may increase in frequency and intensity. However, scientists have
less confidence in the models that seek to project future changes in tornado activity.
OTHER SEVERE WEATHER
SEVERE THUNDERSTORMS
While less severe than the other types of storms discussed, thunderstorms can lead to localized
damage and represent a hazard risk for communities. A thunderstorm typically features lightning,
strong winds, rain, and/or hail. Thunderstorms sometime give rise to tornados. On average, these
storms are only around 15 miles in diameter and last for about 30 minutes. A severe thunderstorm
can include winds of close to 60 mph and rain sufficient to produce flooding.
The best available data on previous occurrences of thunderstorms in Cohasset is for Norfolk
County through the National Climatic Data Center (NCDC). For the years 2010 through 2019,
NCDC records show 30 thunderstorm events in Norfolk County (Table 21). These storms resulted in
a total of $307,500 in property damage. There were no injuries or deaths reported. This is an
average of 3 events per year.
Table 23: Norfolk County Thunderstorm Events, 2010 through 2019
DATE MAGNITUDE DEATHS INJURIES_DIRECT PROPERTY DAMAGE
6/6/2010 53 0 0 0
6/20/2010 50 0 0 5,000
6/24/2010 50 0 0 0
8/19/2011 50 0 0 1,000
6/23/2012 50 0 0 25,000
8/10/2012 50 0 0 5,000
8/15/2012 40 0 0 500
6/17/2013 50 0 0 3,000
7/29/2013 50 0 0 20,000
7/3/2014 50 0 0 20,000
7/28/2014 60 0 0 50,000
6/23/2015 50 0 0 5,000
8/4/2015 50 0 0 10,000
8/15/2015 50 0 0 10,000
2/25/2016 50 0 0 15,000
6/7/2016 50 0 0 10,000
7/18/2016 50 0 0 50,000
7/22/2016 50 0 0 50,000
7/23/2016 40 0 0 5,000
8/14/2016 50 0 0 5,000
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6/9/2017 45 0 0 1,000
6/13/2017 48 0 0 1,000
6/23/2017 50 0 0 1,000
8/2/2017 50 0 0 2,500
9/6/2017 50 0 0 1,000
7/17/2018 45 0 0 3,000
9/6/2018 50 0 0 1,000
11/3/2018 50 0 0 500
7/17/2019 50 0 0 2,000
7/31/2019 50 0 0 5,000
TOTAL 0 0 307,500
Source: NOAA, National Climatic Data Center
*Magnitude refers to maximum wind speed
Severe thunderstorms are a town-wide hazard for Cohasset. The town's vulnerability to severe
thunderstorms is similar to that of nor'easters. High winds can cause falling trees and power
outages, as well as obstruction of key routes and emergency access. Records from NOAA
indicate that numerous trees were downed during a thunderstorm on June 20, 2010. Heavy
precipitation may also cause localized flooding, both riverine and urban drainage related.
Based on the record of previous occurrences, severe thunderstorms in Cohasset are high frequency
events as this hazard has occurred an average of three times per year in the past ten years. As
noted previously, the intensity of rainfall events has increased significantly, and those trends are
expected to continue. The SHMCAP does not specifically address whether climate will affect the
intensity or frequency of thunderstorms.
ICE STORMS
The ice storm category covers a range of different weather phenomena that collectively involve
rain or snow being converted to ice in the lower atmosphere leading to potentially hazardous
conditions on the ground. Hail size typically refers to the diameter of the hailstones. Warnings
and reports may report hail size through comparisons with real-world objects that correspond to
certain diameters:
Table 24: Hail Size Comparisons
Description Diameter (inches)
Pea 0.25
Marble or mothball 0.50
Penny or dime 0.75
Nickel 0.88
Quarter 1.00
Half dollar 1.25
Walnut or ping pong ball 1.50
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Golf ball 1.75
Hen's egg 2.00
Tennis ball 2.50
Baseball 2.75
Teacup 3.00
Grapefruit 4.00
Softball 4.50
While ice pellets and sleet are examples of these, the greatest hazard is created by freezing
rain conditions, which is rain that freezes on contact with hard surfaces leading to a layer of ice
on roads, walkways, trees, and other surfaces. The conditions created by freezing rain can make
driving particularly dangerous and emergency response more difficult. The weight of ice on tree
branches can also lead to falling branches damaging electric lines.
Town-specific data for previous ice storm occurrences are not collected by the Town of Cohasset.
The best available local data is for Norfolk County through the National Climatic Data Center.
Norfolk County experienced twelve events from 2010 through 2019. That is an average of 1.2
events each year. There is some indication that if winters warm, temperatures may be more likely
to produce icing conditions.
Table 25: Norfolk County Hail Events, 2010 through 2019
DATE MAGNITUDE DEATHS INJURIES PROPERTY DAMAGE
6/5/2010 1.5 0 0 0
6/20/2010 1 0 0 0
6/1/2011 0.75 0 0 0
6/23/2012 0.88 0 0 0
7/18/2012 0.75 0 0 0
5/21/2013 0.75 0 0 0
9/1/2013 0.75 0 0 0
8/7/2014 0.75 0 0 0
5/12/2015 0.75 0 0 0
6/23/2015 1 0 0 0
8/4/2015 1 0 0 0
6/30/2019 0.75 0 0 0
TOTAL 0 0 0
Source: NOAA, National Climatic Data Center
*Magnitude refers to diameter of hail stones in inches
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NON-CLIMATE INFLUENCED HAZARDS
EARTHQUAKES
Earthquakes are the sole natural hazard for which there is no established correlation with climate
impacts. Damage in an earthquake stems from ground motion, surface faulting, and ground
failure in which weak or unstable soils, such as those composed primarily of saturated sand or silts,
liquefy. The effects of an earthquake are mitigated by distance and ground materials between
the epicenter and a given location. An earthquake in New England affects a much wider area
than a similar earthquake in California due to New England’s solid bedrock geology (NESEC).
Seismologists use a magnitude scale known as the Richter scale to express the seismic energy
released by each earthquake. The typical effects of earthquakes in various ranges are
summarized below:
Table 26: Richter Scale and Effects
Richter Magnitudes Earthquake Effects
Less than 3.5 Generally not felt, but recorded
3.5- 5.4 Often felt, but rarely causes damage
Under 6.0 At most slight damage to well-designed buildings. Can cause major
damage to poorly constructed buildings over small regions.
6.1-6.9 Can be destructive in areas up to about 100 km. across where people
live.
7.0- 7.9 Major earthquake. Can cause serious damage over larger areas.
8 or greater Great earthquake. Can cause serious damage in areas several hundred
meters across.
Source: Nevada Seismological Library (NSL), 2005
According to the State Hazard Mitigation Plan, New England experiences an average of five
earthquakes per year. From 1668 to 2007, 355 earthquakes were recorded in Massachusetts
(NESEC). Most have originated from the La Malbaie fault in Quebec or from the Cape Anne fault
located off the coast of Rockport. The region has experienced larger earthquakes in the distant
past, including a magnitude 5.0 earthquake in 1727 and a 6.0 earthquake that struck in 1755
off the coast of Cape Anne. More recently, a pair of damaging earthquakes occurred near
Ossipee, NH in 1940. A 4.0 earthquake centered in Hollis, Maine in October 2012 was felt in the
Boston area. Historic records of some of the more significant earthquakes in the region are shown
in Table 27.
Table 27: Historical Earthquakes in Massachusetts or Surrounding Area
Location Date Magnitude
MA - Cape Ann 11/10/1727 5
MA - Cape Ann 12/29/1727 NA
MA - Cape Ann 2/10/1728 NA
MA - Cape Ann 3/30/1729 NA
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Location Date Magnitude
MA - Cape Ann 12/9/1729 NA
MA - Cape Ann 2/20/1730 NA
MA - Cape Ann 3/9/1730 NA
MA - Boston 6/24/1741 NA
MA - Cape Ann 6/14/1744 4.7
MA - Salem 7/1/1744 NA
MA - Off Cape Ann 11/18/1755 6
MA - Off Cape Cod 11/23/1755 NA
MA - Boston 3/12/1761 4.6
MA - Off Cape Cod 2/2/1766 NA
MA - Offshore 1/2/1785 5.4
MA - Wareham/Taunton 12/25/1800 NA
MA - Woburn 10/5/1817 4.3
MA - Marblehead 8/25/1846 4.3
MA - Brewster 8/8/1847 4.2
MA - Boxford 5/12/1880 NA
MA - Newbury 11/7/1907 NA
MA - Wareham 4/25/1924 NA
MA - Cape Ann 1/7/1925 4
MA - Nantucket 10/25/1965 NA
MA - Boston 12/27/74 2.3
MA - Nantucket 4/12/12 4.5
ME - Hollis 10/17/12 4.0
Source: Boston HIRA
One measure of earthquake risk is ground motion, which is measured as maximum peak horizontal
acceleration, expressed as a percentage of gravity (%g). The range of peak ground acceleration
in Massachusetts is from 10 %g to 20 %g, with a 2% probability of exceedance in 50 years.
Cohasset is in the middle part of the range for Massachusetts, at 14 %g to 16 %g, making it a
relatively moderate area of earthquake risk within the state, although the state as a whole is
considered to have a low risk of earthquakes compared to the rest of the country. There have
been no recorded earthquake epicenters within Cohasset.
Although New England has not experienced a damaging earthquake since 1755, seismologists
state that a serious earthquake occurrence is possible. There are five seismological faults in
Massachusetts, but there is no discernible pattern of previous earthquakes along these fault lines.
Earthquakes occur without warning and may be followed by aftershocks. The majority of older
buildings and infrastructure were constructed without specific earthquake resistant design
features.
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Figure 14: State of Massachusetts Earthquake Probability Map
Earthquakes are a hazard with multiple impacts beyond the obvious building collapse. Buildings
may suffer structural damage which may or may not be readily apparent. Earthquakes can cause
major damage to roadways, making emergency response difficult. Water lines and gas lines can
break, causing flooding and fires. Another potential vulnerability is equipment within structures.
For example, a hospital may be structurally engineered to withstand an earthquake, but if the
equipment inside the building is not properly secured, the operations at the hospital could be
severely impacted during an earthquake. Earthquakes can also trigger landslides.
According the SHMCAP there is a 10-15% chance of a magnitude 5 earthquake in a given ten-
year period. Earthquakes are a potential town-wide hazard in Cohasset. Although new
construction under the most recent building codes generally will be built to seismic standards, much
of the development in the town pre-dates the most recent building code. Potential earthquake
damages to Cohasset have been estimated using HAZUS-MH. Total building damages are
estimated at $145.5 million for a 5.0 magnitude earthquake and $795 million for a 7.0
magnitude earthquake. Other potential impacts are detailed in Table 33.
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LAND USE AND DEVELOPMENT TRENDS
Existing Land Use
The most recent land use statistics available from the state are from aerial imagery completed in
2016. Table 28 shows the acreage and percentage of land in 15 categories. If the primary
residential categories are aggregated, residential uses make up 38% of the area of the town.
Commercial and industrial uses combined make up 4% of the town. Agriculture, Forest, Water,
Open Land, and Recreation total a little over 12% of the land. However, the tax-exempt
category represents more than a third of Cohasset’s land. Most of this land is additional open
space.
Table 28: Town of Cohasset, MA 2016 Land Use
Land Use Type Acres Percentage
Residential - single family 2114 32.8
Residential - multi-family 331 5.1
Mixed use, primarily residential 15 0.2
Mixed use, primarily commercial 121 1.9
Commercial 133 2.1
Mixed use, other 15 0.2
Industrial 74 1.1
Agriculture 8 0.1
Forest 21 0.3
Water 64 1.0
Open land 530 8.2
Recreation 205 3.2
Unknown 144 2.2
Right-of-way 305 4.7
Tax exempt 2356 36.6
Total 6437 100.0
For more information on how the land use and land cover data were developed and the
definitions of the categories, please go to https://docs.digital.mass.gov/dataset/massgis-data-
2016-land-coverland-use
Economic Elements
Cohasset is a suburban bedroom community. Ninety percent of residents work outside of town
and residential taxes account for 93% of Cohasset’s tax base. Retail commercial establishments
make up most of the business tax base, with a relatively small industrial sector. Employment and
commerce are concentrated along Route 3A, South Main Street, and Cohasset Harbor. Cohasset
Harbor is subject to coastal flooding and future impacts of sea level rise. Flood waters reach
South Main Street when heavy precipitation coincides with high tides.
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NATURAL, CULTURAL, AND HISTORICAL RESOURCE AREAS
The two historic centers of settlement in Cohasset are the village and harbor area, focusing on
maritime pursuits, and the Beechwood area, which was once the center of the town’s agricultural
life. The Town Common and Government Island are listed on the National Register of Historic
Places as Historic Districts and the Caleb Lothrup House (1821) is a National Register Individual
Site. The Town Common and surrounding historic churches and residences also comprise a local
historic district. The Joshua Bates house, dating from 1695, and a number of 18th century houses
are valuable historic resources. In addition to the colonial and early national period buildings
and sites in Cohasset, the Victorian mansions built along Jerusalem Road and Atlantic Avenue
represent examples of later, significant historic architectural styles. The drive along Jerusalem
Road became famous in the late 19th century not only for the picturesque views of the rocky
shore and ocean, but also for the substantial homes perched on the rocks. Also listed as a
National Register Individual Site is the Hagerty House, located near Sandy Beach. Built in 1938,
the Hagerty House was designed in the international style by Walter Gropius in association with
Marcel Breuer. (This section is excerpted from the Cohasset Open Space and Recreation Plan
2010-2017)
DEVELOPMENT TRENDS
Development trends throughout the metropolitan region are tracked by MassBuilds, MAPC’s
Development Database, which provides an inventory of new development over the last decade.
The database tracks both completed developments and those currently under construction. The
database includes six completed projects in the Town of Cohasset since 2012.
The database also includes several attributes of the new development, including housing units, and
commercial space. The six developments in Cohasset include a total of 258 housing units and
222,448 square feet of commercial space.
Table 29: Summary of Cohasset Developments, 2012-2018
Name Status Year Housing
Units
Commercial
Square Feet Project Type
Scituate Racquet and Fitness Club Completed 2013 0 147,533 Commercial
South Shore Auto Wash Completed 2013 0 54,786 Commercial
Cohasset Village Town Homes Completed 2015 11 Residential
Stop and Shop Gas Facility Completed 2013 0 20, 129 Commercial
The Cook Estate Completed 2013 27 Residential
Avalon Completed 2012 220 Residential
POTENTIAL FUTURE DEVELOPMENT
MAPC consulted with the Local Hazard Mitigation Planning Team to determine areas that may be
developed in the future, based on the Town’s comprehensive planning efforts and current trends
and projects. These areas are listed below with their flood risk, heat and sea level rise risk,
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outlined in Table 30. In order to characterize any change in the town’s vulnerability associated
with new developments, a GIS mapping analysis was conducted which overlaid the development
sites with the FEMA Flood Insurance Rate Map. Potential future development projects:
A) Curtis Estate: Development is expected here although there is currently no specific proposal
B) 55 Main Street: a 10-15 unit mixed use development is anticipated
C) 2 Smith Place: 20-30 condominiums are expected
D) Harborview Nursing Home: redevelopment will likely occur here
E) 380-400 Chief Justice Cushing Highway: a 20-unit mixed use development is proposed
F) Pine Ridge Farm, 280 Beechwood Street: this is a 10+ acre site. Redevelopment will
probably consider a combination of cottage-style affordable, market, and/or senior housing.
G) Cohasset Harbor Inn, 124 Elm Street, condominium redevelopment is anticipated
H) 34 Crocker Lane: This site is a capped landfill. Ground-mounted solar site is proposed.
I) Scituate Hill Subdivision, Lots 2A-4A: An Assisted Living Facility is proposed.
FUTURE DEVELOPMENT IN HAZARD AREAS
Table 30 shows the relationship between potential future development areas and the applicable
mapped hazard areas (flood zones, sea level rise and heat). This information is provided so that
planners can ensure that development proposals comply with floodplain zoning and that careful
attention is paid to drainage and other issues.
Table 30: Relationship of Potential Development to Hazard Areas
Map ID Potential Future Project Flood Zones Sea Level Rise (3 feet MHW) High Heat
A Curtis Estate NA NA NA
B 55 Main Street NA NA NA
C 2 Smith Place NA NA NA
D Harborview Nursing
Home NA NA NA
E 380-400 Chief Justice
Cushing Highway NA NA NA
F Pine Ridge Farm NA NA 15%
G Cohasset Harbor Inn 97% in AE zone 71% inundated NA
H 34 Crocker Lane NA NA NA
I Scituate Hill Subdivision NA NA NA
CRITICAL FACILITIES & INFRASTRUCTURE IN HAZARD AREAS
Critical facilities and infrastructure includes facilities that are important for disaster response and
evacuation (such as emergency operations centers, fire stations, water pump stations,
communications, and electricity) and facilities where additional assistance might be needed during
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an emergency (such as nursing homes, elderly housing, day care centers, etc.). There are 88
facilities identified in Cohasset. These are listed in Table 31 and are shown on the maps in
Appendix B.
Explanation of Columns in Table 31
• Column 1: ID #: The first column in Table 31 is an ID number which appears on the maps that are
part of this plan. See Appendix B.
• Column 2: Name: The second column is the name of the site.
• Column 3: Type: The third column indicates what type of site it is.
• Column 4: FEMA Flood Zone: The fourth column addresses the risk of flooding. A “No” entry in this
column means that the site is not within any of the mapped risk zones on the Flood Insurance Rate
Maps (FIRM maps). If there is an entry in this column, it indicates the type of flood zone. as follows:
Zone A (1% annual chance) -Areas subject to inundation by the 1-percent-annual-chance flood
event generally determined using approximate methodologies. Because detailed hydraulic
analyses have not been performed, no Base Flood Elevations (BFEs) or flood depths are shown.
Mandatory flood insurance purchase requirements and floodplain management standards apply.
Zone AE (1% annual chance) - Areas subject to inundation by the 1-percent-annual-chance flood
event determined by detailed methods. Base Flood Elevations (BFEs) are shown. Mandatory flood
insurance purchase requirements and floodplain management standards apply.
Zone VE (1% annual chance) - Areas subject to inundation by the 1-percent-annual-chance flood
event with additional hazards due to storm-induced velocity wave action. Base Flood Elevations
(BFEs) derived from detailed hydraulic analyses are shown. Mandatory flood insurance purchase
requirements and floodplain management standards apply.
Zone X (.2% annual chance) - Zones X is the flood zone that corresponds to the 500-year
floodplain.
• Column 5: Locally Identified Area of Flooding: The fifth column indicates the risk of flooding in local
hazard areas. A “No” entry in this column means that the site is not within any of the mapped flood
hazard zones. If there is an entry in this column, it indicates the local hazard area.
• Column 6: Brush Fire Area: The sixth column indicates the risk of brush fire in local hazard areas. A
“No” entry in this column means that the site is not within any of the mapped brush fire hazard
zones. If there is an entry in this column, it indicates the local hazard area.
• Column 7: Hot spots indicates areas that are within the 5% of hottest areas in the MAPC region
based on satellite data from 2016 year.
• Colum 8: Includes infrastructure that is within the projected new MHHW line with 3 feet of sea level
rise.
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Table 31: Critical Facilities and Relationship to Hazard Areas
ID NAME TYPE FEMA
Flood
Zone
Local ID Flood
Zone
Local ID
Brush
Fire
Hot
Spot
3 FT Sea
Level
Rise
1 Milliken Field/Landing Zone Municipal No No No No No
2 Joseph Osgood School School - Special Needs No No No No No
4 Cohasset Police Station Municipal No No No No No
5 Town Hall Municipal No No No No No
6 United States Post Office Post Office X Post Office No No No
7 Second Congregational Church of Cohasset Church No No No No No
8 CVS Pharmacy Medical Facility No No No No No
9 Human Service Options Special Needs Housing No No No No No
11 Human Service Options Special Needs Housing No No No No No
12 Harborview Housing Housing Authority No No No No No
14 Cohasset Town Of Fire Dept Municipal No No No No No
15 Sohier Street Well Well No No No No No
16 Deer Hill School No No No No No
17 Stop & Shop Grocery Store No No No No No
18 Sunrise Assisted Living Medical Facility No No No No No
19 Cohasset Middle-High School School No No No Yes No
20 Walgreen's Medical Facility No No No Yes No
21 Water Treatment Plant Drinking Water Treatment No No No No No
22 Water Storage Tank Water Storage Tank No No No No No
23 Emergency Communications Tower
(Secondary)
Communication Tower No No No No No
24 Library/Rec Center Municipal No No No No No
28 Water Storage Tank Water Storage Tank No No No No No
29 Sand Castle Child Care Child Care No No No No No
30 South Shore Community Ctr School No No No No No
31 First Parish Church/Hall Place of Assembly No No No No No
32 First Parish Church Church No No No No No
33 St Stephens Episc. Church Church No No No No No
34 St Anthony's Parish House Place of Assembly X South Main, 100
Block
No No No
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ID NAME TYPE FEMA
Flood
Zone
Local ID Flood
Zone
Local ID
Brush
Fire
Hot
Spot
3 FT Sea
Level
Rise
35 St Anthony's Church Church X South Main, 100
Block
No No No
36 Aaron River Dam Dam No No No No No
37 Aaron River Reservoir Water Supply A No No No No
38 Beechwood St Bridge & Bound Brook
Control Structure
Dam A No No No No
39 Meeting House and Museum Museum No No No No No
40 Sanctuary Pond Dam Dam X No No No No
41 Cell Tower Communication Tower No No West
Cohasset
No No
42 Shaw's Supermarket Grocery Store No No No No No
43 Vedanta Centre Church No No No No No
44 Greek Orthodox Church Church AE No No No No
45 Edward Maree Landing Boat Ramp AE No No No Yes
46 Cohasset Harbor Marina Marina AE No No No Yes
47 Harbor Master Building Municipal AE No No No No
48 Cohasset Sailing Club Marina AE No No No Yes
49 Cohasset Yacht Club Marina AE No No No Yes
50 Brass Kettle Medical Building Medical Facility No Route 3A No No No
51 Cohasset Harbor Inn Hotel AE Jacob's Meadow No No Yes
52 Red Lion Inn Hotel No No No No No
53 Breakwater VE No No No Yes
54 Border St. Pump Station Waste Water Pump Station AE No No No Yes
55 Holly Lane Pump Station Waste Water Pump Station No No No No No
56 Smith Place Pump Station Waste Water Pump Station AE No No No No
57 Veterans (Tupelo Road) Pump Station Waste Water Pump Station AE Peppermint Brook
at 3A
No No No
58 Parker Ave. Pump Station Waste Water Pump Station AE No No No No
59 Woodland Drive Pump Station Waste Water Pump Station No No No No No
60 Cohasset Middle-High School Pump Station Waste Water Pump Station No No No No No
61 Deer Hill School Pump Station Waste Water Pump Station No No No No No
62 Waste Water Treatment Plant Municipal AE Jacob's Meadow No No No
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ID NAME TYPE FEMA
Flood
Zone
Local ID Flood
Zone
Local ID
Brush
Fire
Hot
Spot
3 FT Sea
Level
Rise
63 Influent Pump Station Waste Water Pump Station AE Jacob's Meadow No No No
64 Mill Bridge Bridge AE No No No Yes
65 Cunningham Bridge Bridge VE No No No Yes
66 Beechwood Cemetery Cemetery No No No No No
67 Woodside Cemetery Cemetery No No No No No
68 Cohasset Central Cemetery Cemetery No No No No No
69 North Cohasset Cemetery Cemetery No No No No No
70 Cedar Street Cemetery Cemetery No No No No No
71 Ellms Meadow Wells Drinking Water Well No No No No No
72 South Shore Music Circus Place of Assembly No No No No No
73 Water Department Pump Station Drinking Water Pump
Station
No No No No No
74 Greenbush Line Railroad Station Transportation Facility No No No No No
75 Atlantic Avenue Causeway Causeway AO No No No No
77 Sandy Beach Beach VE No No No No
78 Mass Highway Transportation Facility No No No No No
79 Aaron River Reservoir Emergency Spillway Dam No No No No No
80 Cell Tower Communication Tower No No West
Cohasset
No No
81 Cell Tower Communication Tower No No No No No
82 DPW Facility Municipal No No Wooded
wetland
area
No No
83 Cell Tower Communication Tower No No No No No
84 Senior Center Municipal A No No No No
85 Nichols Road Dam Dam AE No No No No
86 Straits Pond Dam (tide gate) Dam AE No No No Yes
87 Emergency Communications Tower (Primary) Communication Tower No No No No No
88 Cell Tower Communication Tower No No No No No
89 Cohasset Kennel Animal Shelter No No No No No
90 Crazy Paws Veterinarian No No No No No
91 Lily Pond Reservoir Water Supply No No No No No
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ID NAME TYPE FEMA
Flood
Zone
Local ID Flood
Zone
Local ID
Brush
Fire
Hot
Spot
3 FT Sea
Level
Rise
92 Food Pantry Food Pantry AE South Main, 100
Block
No No No
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VULNERABILITY ASSESSMENT
The purpose of the vulnerability assessment is to estimate the extent of potential damages from
natural hazards of varying types and intensities. A vulnerability assessment and estimation of
damages was performed for hurricanes, earthquakes, and flooding through the HAZUS-MH
software.
Introduction to HAZUS-MH
HAZUS-MH (multiple-hazards) is a computer program developed by FEMA to estimate losses due
to a variety of natural hazards. The following overview of HAZUS-MH is taken from the FEMA
website. For more information on the HAZUS-MH software, go to https://www.fema.gov/hazus/
“HAZUS-MH is a nationally applicable standardized methodology and software program
that contains models for estimating potential losses from earthquakes, floods, and
hurricane winds. HAZUS-MH was developed by the Federal Emergency Management
Agency (FEMA) under contract with the National Institute of Building Sciences (NIBS). Loss
estimates produced by HAZUS-MH are based on current scientific and engineering
knowledge of the effects of hurricane winds, floods and earthquakes. Estimating losses is
essential to decision-making at all levels of government, providing a basis for developing
and evaluating mitigation plans and policies as well as emergency preparedness,
response and recovery planning.
HAZUS-MH uses state-of-the-art geographic information system (GIS) software to map
and display hazard data and the results of damage and economic loss estimates for
buildings and infrastructure. It also allows users to estimate the impacts of hurricane winds,
floods and earthquakes on populations.”
There are three modules included with the HAZUS-MH software: hurricane wind, flooding, and
earthquakes. There are also three levels at which HAZUS-MH can be run. Level 1 uses national
baseline data and is the quickest way to begin the risk assessment process. The analysis that
follows was completed using Level 1 data. Level 1 relies upon default data on building types,
utilities, transportation, etc. from national databases as well as census data. While the databases
include a wealth of information on the Town of Cohasset, it does not capture all relevant
information. In fact, the HAZUS training manual notes that the default data is “subject to a great
deal of uncertainty.”
However, for the purposes of this plan, the analysis is useful. This plan is attempting to generally
indicate the possible extent of damages due to certain types of natural disasters and to allow for
a comparison between different types of disasters. Therefore, this analysis should be considered
to be a starting point for understanding potential damages from the hazards.
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ESTIMATED DAMAGES FROM HURRICANES
The HAZUS software was used to model potential damages to the community from a 100-year
and 500-year hurricane event; storms that are 1% and 0.2% likely to happen in a given year,
and roughly equivalent to a Category 2 and Category 4 hurricane. The damages caused by
these hypothetical storms were modeled as if the storm track passed directly through the town,
bringing the strongest winds and greatest damage potential.
Though there are no recorded instances of a hurricane equivalent to a 500-year storm passing
through Massachusetts, this model was included in order to present a reasonable “worst case
scenario” that would help planners and emergency personnel evaluate the impacts of storms that
might be more likely in the future, as we enter into a period of more intense and frequent storms.
Table 32: Estimated Damages from Hurricanes
Category 2 Category 4
Building Characteristics
Estimated total number of buildings 3,097
Estimated total building replacement value (2014 $) $1,552,000,000
Building Damages
# of buildings sustaining minor damage 193 716
# of buildings sustaining moderate damage 15 138
# of buildings sustaining severe damage 0 12
# of buildings destroyed 0 8
Population Needs
# of households displaced 0 2
# of people seeking public shelter 0 1
Debris
Building debris generated (tons) 509 2,257
Tree debris generated (tons) 4,472 10,643
# of truckloads to clear building debris 20 97
Value of Damages
Total property damage (buildings and content) $14,419,000 $53,441,000
Total losses due to business interruption $415,550 $3,611,790
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ESTIMATED DAMAGES FROM EARTHQUAKES
The HAZUS earthquake module allows users to define an earthquake magnitude and model the
potential damages caused by that earthquake as if its epicenter had been at the geographic
center of the study area. For the purposes of this plan, two earthquakes were selected:
magnitude 5.0 and a magnitude 7.0. Historically, major earthquakes are rare in New England,
though a magnitude 5 event occurred in 1963.
Table 33: Estimated Damages from Earthquakes
Magnitude 5.0 Magnitude 7.0
Building Characteristics
Estimated total number of buildings 3,097
Estimated total building replacement value (2014 $) $1,552,000,000
Building Damages
# of buildings sustaining slight damage 902 138
# of buildings sustaining moderate damage 471 762
# of buildings sustaining extensive damage 125 917
# of buildings completely damaged 41 1,269
Population Needs
# of households displaced 54 54
# of people seeking public shelter 28 28
Debris
Building debris generated (tons) 24,000 24,000
# of truckloads to clear debris (@ 25 tons/truck) 960 960
Value of Damages
Total property damage $158,717,300 $1,219,795,300
Total losses due to business interruption $28,906,300 $163,592,300
ESTIMATED DAMAGES FROM FLOODING
The HAZUS flooding module allows users model the potential damages caused by a 100-year
flood event and a 500-year flood event.
Table 34: Estimated Damages from Flooding
100-Year Flood 500-Year Flood
Building Characteristics
Estimated total number of buildings 3,097
Estimated total building replacement value (2014 $) $1,552,000,000
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Building Damages
# of buildings sustaining limited damage 10 12
# of buildings sustaining moderate damage 44 58
# of buildings sustaining extensive damage 9 14
# of buildings substantially damaged 3 3
Population Needs
# of households displaced 9 13
# of people seeking public shelter 593 715
Value of Damages
Total property damage $50,770,000 $63,620,000
Total losses due to business interruption $31,700,000 $38,610,000
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RISK ASSESSMENT SUMMARY
CLIMATE
CHANGE
NATURAL
HAZARD PRIORITY KEY CONCERNS
SOCIETY
KEY CONCERNS
BUILT ENVIRONMENT
KEY CONCERNS
NATURAL
RESOURCES
Changes in
Precipitation
Inland
Flooding
High Occurs regularly Damage to property/financial
loss
Downtown business
district, Jacob’s
Meadow
Pollutants
washed into
waterways
Drought
Medium Drought is not
frequent, but effects can be
significant.
Drinking water supply is ample.
Loss of landscaping.
NA Low river flow,
plant, aquatic
life. Fires.
Landslide
Low There is no record of
landslides in Cohasset.
Not a big risk, no identified
concerns.
Not a big risk, no
identified concerns.
Not a big risk,
no identified
concerns.
Sea Level
Rise
Coastal
Flooding
High Occurs often. Much of
Cohasset is elevated on ledge,
harbor is vulnerable.
Property damage and public
safety.
Inflow and Infiltration
(I/ I) in sewers, road
closures.
Harbor/Jacob’s
Meadow.
Damage to sea
grass and salt
marsh. I/I
sewage release.
Coastal
Erosion
Low As much of the Cohasset
coastline is ledge, areas of risk
are limited.
Possible loss of beach resource.
The town has two
causeways that could
be vulnerable to
erosion
Erosion has not
been significant;
beaches should
be monitored.
Tsunami
Low Localized impacts could
be significant, but occurrence is
rare.
NA NA NA
Rising
Temperatures
Average and
Extreme
Temperatures
Medium There are few high
heat areas, but susceptible
residents will be impacted.
Heat risks for elderly, young,
those with chronic illnesses.
Aquaculture (e.g. lobstering)
impacted.
Power outages in times
of extreme heat.
Increasing
invasives, ocean
heat and acidity
Wildfires
Medium This is a concern for
heavily wooded areas, not so
much for the residential
interface.
NA NA Damage to
forested areas.
Phragmites are
a fire risk.
Invasive
species
Low Milfoil and phragmites are
two invasive species of concern.
The town is investigating milfoil
impacts to quality of drinking
water.
NA Phragmites are
a fire risk.
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Extreme
Weather
Hurricanes /
Tropical
Storms
Medium As warm weather
events, these have lesser life
safety impact than winter
storms.
Power outages, damage to
property.
Power outages,
flooding.
Tree damage
and loss.
Severe Winter
Storms
High These are frequent events. Power outages – risk to health
and safety.
Power outages,
keeping roads open.
Tree damage
and loss.
Tornadoes Low There is no record of
tornadoes in Cohasset.
Property damage, power
outages.
Power outages,
damage to facilities
Tree damage
and loss
Other (Wind/
Thunderstorms)
Medium As warm weather
events, these have lesser life
safety impact than winter
storms.
Property damage, power
outages
Power outages Tree damage
and loss
Non-Climate
Hazard
Earthquake Low Localized impacts could
be significant, but occurrence is
rare.
Property damage Damage to facilities
and roadways
Unknown
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SECTION 5: HAZARD MITIGATION GOALS
The Cohasset Local Hazard Mitigation Planning Team reviewed and discussed the goals from the
2012 Hazard Mitigation Plan for the Town of Cohasset. All of the goals are considered critical
for the Town and they are not listed in order of importance. Prior to the Hazard Mitigation Plan
update process, the Town of Cohasset completed a climate vulnerability assessment. The local
team chose to incorporate climate considerations as noted in Goal 11.
GOAL 1: Ensure that critical infrastructure sites are protected from natural hazards.
GOAL 2: Protect existing residential and business areas from flooding
GOAL 3: Maintain existing mitigation infrastructure in good condition.
GOAL 4: Continue to enforce existing zoning and building regulations.
GOAL 5: Educate the public about zoning and building regulations.
GOAL 6: Work with surrounding communities to ensure regional cooperation and solutions
for hazards affecting multiple communities.
GOAL 7: Encourage future development and redevelopment in areas that are not prone to
natural hazards.
GOAL 8: Educate the public about natural hazards and mitigation measures.
GOAL 9: Make efficient use of public funds for hazard mitigation.
GOAL 10: Pursue land acquisition strategies.
GOAL 11: Consider the potential impacts of future climate change. Incorporate climate
sustainability and resiliency in hazard mitigation planning.
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SECTION 6: EXISTING MITIGATION MEASURES
The existing protections in the Town of Cohasset are a combination of zoning, land use, and
environmental regulations, infrastructure maintenance, and drainage infrastructure improvement
projects. Infrastructure maintenance generally addresses localized drainage clogging problems,
while large scale capacity problems may require pipe replacement or invert elevation
modifications. These more expensive projects are subject to the capital budget process and lack
of funding is one of the biggest obstacles to completion of some of these. Cohasset’s adoption of
a stormwater utility will contribute significantly to efforts to address stormwater flooding.
The Town's existing mitigation measures, which were in place prior to the original 2005 Plan, are
listed by hazard type here and are summarized in Table 35 below. Many upgrades to existing
measures are noted in the following sections.
EXISTING MULTI-HAZARD MITIGATION MEASURES
Comprehensive Emergency Management Plan (CEMP) – Every community in Massachusetts is
required to have a Comprehensive Emergency Management Plan. These plans address mitigation,
preparedness, response and recovery from a variety of natural and man-made emergencies.
These plans contain important information regarding flooding, hurricanes, tornadoes, dam
failures, earthquakes, and winter storms. Therefore, the CEMP is a mitigation measure that is
relevant to all of the hazards discussed in this plan.
Communications Equipment – Cohasset has full coverage of the Town with emergency services
radio. Incident command units are available through Plymouth County and MEMA. Cohasset is
now part of the South Shore Regional Emergency Communications center serving Cohasset,
Hingham, Hull, and Norwell.
Massachusetts State Building Code – The Massachusetts State Building Code contains many
detailed regulations regarding wind loads, earthquake resistant design, flood-proofing, and snow
loads.
Emergency Power Generators – Emergency power generators can be found in the High School,
elementary school, the Fire/Police Station, and the DPW. In addition, the Town has three
portable generators. The Town has upgraded generators and generator availability.
Local Emergency Management Planning Committee (LEPC) – The LEPC is meets as necessary and is
composed of Town Department heads.
EXISTING TOWN-WIDE MITIGATION FOR FLOOD-RELATED HAZARDS
Cohasset employs a number of practices to help minimize potential flooding and impacts from
flooding, and to maintain existing drainage infrastructure. Existing town-wide mitigation measures
include the following:
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National Flood Insurance Program (NFIP) – Cohasset participates in the NFIP with 149 policies in
force as of the August 30, 2019. FEMA maintains a database on flood insurance policies and
claims. This database can be found on the FEMA website at https://www.fema.gov/policy-claim-
statistics-flood-insurance.
The following information is provided for the Town of Cohasset:
Flood insurance policies in force 149
Coverage amount of flood insurance policies $44,782,100
Premiums paid $296,268
Closed losses (losses that have been paid) 102
Substantial Damage Claims since 1978 7
Total payments (total amount paid on losses) $1,363,146
The Town complies with the NFIP by enforcing floodplain regulations, maintaining up-to-date
floodplain maps, and providing information to property owners and builders regarding
floodplains and building requirements.
Public Works Operations/Maintenance Activities – The Public Works Department actively maintains
the Town’s storm drain system. The following specific activities serve to maintain the capability of
the drainage system through the reduction of sediment and litter build up and proper
maintenance and repair.
o o Street sweeping – Street sweeping is conducted annually.
o Catch basin cleaning – There are approximately 1200 catch basins, which are cleaned
annually.
o Roadway treatments – Sand/salt mix is used for snow/ice treatment.
o Other – Continued repair and rehabilitation of drainage systems
Flood Control Master Plan – The Town engaged a consultant to study flooding in two areas of the
City, the Atlantic Avenue and James Brook Watershed areas. The results of this work have led to
an increased understanding of the causes of flooding within these systems and implementation of
a number of recommended mitigation measures.
Town of Cohasset Master Plan – An updated Master Plan has just been adopted.
Open Space and Recreation Plan – The latest update to the Open Space and Recreation Plan is
underway. The current plan identifies a number of open space parcels and actions to improve
environmental quality, which could also benefit hazard mitigation efforts.
Weir River Estuary Land Protection Plan – The 2006 Weir River Estuary Land Protection Plan,
covering an area that includes portions of Hull, Hingham, and Cohasset includes land protection
goals for shoreline lands and wetlands that could also serve as flood and storm damage
mitigation. The efforts to date have protected 368 acres of estuary land and there are
approximately 150 acres of key parcels that have been identified as a priority for protection.
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Floodplain Zoning District – Zoning is intended to protect the public health and safety through the
regulation of land use. The Cohasset Zoning Bylaw includes a Special Flood Plain and Watershed
Protection District (Section 9). The purposes of this district are:
1. To protect persons and property from the hazards of flood and pollution.
2. To protect, preserve, and maintain the water table and water recharge areas within the
town so as to preserve and protect the water supplies of the town and adjacent towns.
3. To assure the continuation of the natural flow patterns of the watercourses within the town
in order to provide adequate and safe water storage and runoff capacity.
The Floodplain District is an overlay district, defined by the 100-year floodplain as designated
by FEMA and shown on the FIRM maps. Within the District, the following requirements must be
met:
• In any area outside of the flood plain as shown on the flood plain and watershed
protection map within Zone A, where the 100 year flood elevation is not provided on the
FIRM, the applicant for a special permit shall obtain any existing flood elevation data
and it shall be reviewed by the conservation commission and the building inspector. If the
data is sufficiently detailed and accurate in the opinion of the conservation commission
and the building inspector, it shall be relied upon to require compliance with this bylaw
and the state building code.
• All development, including structural and nonstructural activities, whether permitted by
right or by special permit must be in compliance with Massachusetts General Laws,
Chapter 131, Section 40, and with the requirements of the Massachusetts State Building
Code pertaining to construction in a flood plain.
• All encroachments in floodways, including fill, new construction, substantial improvements to
existing structures, and other development are prohibited unless certification by a
registered professional engineer is provided by the applicant for a special permit
demonstrating that such encroachment shall not result in any increase of flood levels during
the occurrence of the 100 year flood.
• Within the areas designated as coastal high hazard areas (Zone V) within the flood plain
district, all new construction shall be located landward of the reach of the mean high tide.
No development or land alteration is allowed within the district without a special permit and the
permitting body is able to attach a range of conditions intended to safeguard the property,
health, and safety of occupants of the premises and of other land, and to insure conformity with
the purposes of this section and this bylaw.
Stormwater Bylaw – The purpose of the Cohasset Stormwater Management Bylaw is to prevent
and reduce flooding, protect water quality, increase groundwater recharge, reduce erosion and
sedimentation, promote environmentally sensitive site design practices, ensure long-term
maintenance of stormwater controls, and help the Town meet Federal requirements under Phase II
of the National Pollutant Discharge Elimination System (Clean Water Act). Flood prevention is
emphasized in this bylaw. The Bylaw and the associated Stormwater Management Rules &
Regulations (the Regulations) establish minimum requirements and procedures to control the
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adverse effects of increased stormwater runoff, decreased groundwater recharge, and nonpoint
source pollution associated with new development and redevelopment.
Wetlands Protection Bylaw – The purpose of the Wetlands Protection Bylaw is to further protect
the Town’s wetlands, related water resources, and adjoining land areas for, among other reasons,
flood control, erosion and sedimentation control, storm damage prevention, and water pollution
control. The by-law regulates development activity within 100 feet of wetlands and water
resources and within 25 feet of any isolated land subject to flooding.
DCR dam safety regulations – The state has enacted dam safety regulations mandating inspections
and emergency action plans. All new dams are subject to state permitting.
Seawalls, Jetties, and Dikes – Cohasset has a limited number of seawalls and jetties, which are
generally in good condition. These include seawalls where public roads run directly along the
coastline and jetties at the entrance to the harbor. The Margin Street seawall is beginning to
show signs of deterioration.
EXISTING TOWN-WIDE MITIGATION FOR WIND-RELATED HAZARDS
Massachusetts State Building Code – The town enforces the Massachusetts State Building Code
whose provisions are generally adequate to protect against most wind damage. The code’s
provisions are the most cost-effective mitigation measure against tornados given the extremely
low probability of occurrence. If a tornado were to occur, the potential for severe damages
would be extremely high.
Tree-trimming program – The electric utility company conducts tree trimming and maintenance
around power lines.
EXISTING TOWN-WIDE MITIGATION FOR WINTER-RELATED HAZARDS
Snow disposal –The town conducts general snow removal operations with its own equipment and
has adequate snow storage/disposal space.
EXISTING TOWN-WIDE MITIGATION FOR GEOLOGIC HAZARDS
Massachusetts State Building Code – The State Building Code contains a section on designing for
earthquake loads (780 CMR 1612.0). Section 1612.1 states that the purpose of these provisions
is “to minimize the hazard to life to occupants of all buildings and non-building structures, to
increase the expected performance of higher occupancy structures as compared to ordinary
structures, and to improve the capability of essential facilities to function during and after an
earthquake”. This section goes on to state that due to the complexity of seismic design, the
criteria presented are the minimum considered to be “prudent and economically justified” for the
protection of life safety. The code also states that absolute safety and prevention of damage,
even in an earthquake event with a reasonable probability of occurrence, cannot be achieved
economically for most buildings.
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Section 1612.2.5 sets up seismic hazard exposure groups and assigns all buildings to one of these
groups according to a Table 1612.2.5. Group II includes buildings which have a substantial
public hazard due to occupancy or use and Group III are those buildings having essential facilities
which are required for post-earthquake recovery, including fire, rescue and police stations,
emergency rooms, power-generating facilities, and communications facilities.
EXISTING TOWN-WIDE MITIGATION FOR FIRE HAZARDS
Burn Permits – The Town fire department requires a written permit for outdoor burning, which
includes explanation of the related regulations and precautions for the permit-holder to take. The
permit-holder must call the fire department on the proposed burn day to confirm weather
conditions are suitable for outdoor burning. Outdoor burning is only allowed from January to
May.
Subdivision/Development Review – The Fire Department participates in the review of new
subdivisions and development projects.
COMPILATION OF EXISTING MITIGATION
Table 35 summarizes the many existing natural hazard mitigation measures already in place in
Cohasset when the first Hazard Mitigation Plan was adopted in 2005. Because of the number of
entities, public and private, involved in natural hazard mitigation, it is likely that this list is a
starting point for a more comprehensive inventory of all measures.
Table 35: Existing Natural Hazard Mitigation Measures in Cohasset
Table 14- Cohasset Existing Mitigation Measures
Type of Existing
Mitigation Measures
Area
Covered
Effectiveness/
Enforcement
Improvements/
Changes Needed
MULTIPLE HAZARDS
Comprehensive
Emergency
Management Plan
Town-wide. Emphasis is on emergency
response.
Communications
Equipment
Town-wide. Effective
Massachusetts State
Building Code
Town-wide. Effective for new construction
Emergency Power
Generators
Town-wide. Effective. Have added back-up
generators and tide gate
generator
Public Safety
generator is old
Participation in the Local
Emergency Planning
Committee (LEPC)
Town-wide. A forum for inter-departmental
cooperation on natural and
manmade disasters.
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Table 14- Cohasset Existing Mitigation Measures
Type of Existing
Mitigation Measures
Area
Covered
Effectiveness/
Enforcement
Improvements/
Changes Needed
FLOOD HAZARDS
Participation in the
National Flood Insurance
Program (NFIP)
Town-wide There are 149 policies in force Encourage eligible
homeowners to
obtain insurance
Public Works
Operations/Maintenance
Activities
Town-wide Effective
Flood Control Master
Plan
Town-wide Many suggestions were
implemented
Somewhat dated
at this point
Cohasset Master Plan Town-wide Effective A new plan has
been adopted.
Open Space and
Recreation Plan
Town-wide Effective Updated plan is
underway
Weir River Estuary Land
Protection Plan
Estuary Effective - tri-town project Needs to be
updated
Zoning – Floodplain
District
1% flood
plain
Effective for new construction
Stormwater Bylaw Town-wide Effective
Wetlands Protection
Bylaw
Resource
Areas
Effective Update rainfall
standard to NOAA
14
DCR Dam Safety
Regulations
Dams Effective
Seawalls, Jetties, and
Dikes
Portions of
the
coastline
Somewhat effective. Repairs
have been done.
Regular
maintenance and
upgrades needed.
WIND HAZARDS
The Massachusetts State
Building Code
Town-wide Effective for most situations
except severe storms
Tree trimming program Town-wide Satisfactory
WINTER HAZARDS
Snow Disposal Site Town-wide Sufficient
GEOLOGIC HAZARDS
The Massachusetts State
Building Code
Town-wide Effective
FIRE HAZARDS
Burn Permit Town-wide Effective
Development Review Town-wide Effective
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MITIGATION CAPABILITIES AND LOCAL CAPACITY FOR IMPLEMENTATION
Under the Massachusetts system of “Home Rule,” the Town of Cohasset is authorized to adopt and
from time to time amend local bylaws and regulations that support the town’s capabilities to
mitigate natural hazards. These include Zoning Bylaws, Subdivision and Site Plan Review
Regulations, Wetlands Bylaws, Health Regulations, Public Works regulations, and local
enforcement of the State Building Code. Local Bylaws may be amended at Town Meeting to
improve the town’s capabilities, and changes to most regulations simply require a public hearing
and a vote of the authorized board or commission. Several departments including Public Works,
Water, and Sewer will address the many planned infrastructure projects.
SECTION 7: MITIGATION MEASURES FROM PREVIOUS PLAN
IMPLEMENTATION PROGRESS ON THE PREVIOUS PLAN
At a meeting of the Cohasset Hazard Mitigation Planning Committee, Town staff reviewed the
mitigation measures identified in the 2012 Cohasset Hazard Mitigation Plan and determined
whether each measure had been implemented or deferred. Of those measures that had been
deferred, the committee evaluated whether the measure should be deleted or carried forward
into this Hazard Mitigation Plan 2020 Update. The decision on whether to delete or retain a
particular measure was based on the committee’s assessment of the continued relevance or
effectiveness of the measure and whether the deferral of action on the measure was due to the
inability of the Town to take action on the measure. Table 36 summarizes the status of mitigation
measures from the 2012 plan.
Table 36: Mitigation Measures from the 2012 Plan
Mitigation Action Priority in
2012 plan Current Status
Include in
2020
Plan?
Rebuild Bound Brook
Dam High Complete No
Rebuild Culvert at
Jerusalem Road High Complete No
Upgrade Sanctuary
Pond Dam High
Owned by Trustees of Reservations. It is an
earthen dam. The most important work, which
was removing trees on the dam, is complete.
Yes
Repair Margin Street
Seawall High It has been shored up and repaired several
times. This is an ongoing issue. Yes
Jacobs Meadow Salt
Marsh Restoration &
Flood Control
High
The Town installed a new tidegate that
operates automatically and installed a
generator. No work was done on the marsh.
No
James Brook Tide gate
Management Plan High The tide gate was installed and a management
plan implemented. No
James Brook Drainage
Improvements High Not complete Yes
Join Community Rating
System Program (CRS) Medium Investigation determined this would not be a
cost-effective project. No
Upgrade GIS
Capabilities &
Drainage Maps
Medium
The Town has completed implementation of
GIS, but maintenance and improvements will be
ongoing.
Yes
Upgrade Area Utilities Low National Grid has replaced several miles of
gas pipes, this is an on-going project. Yes
Floodplain
Management High Enforcement of floodplain zoning and FEMA
map updates is on-going. Yes
Floodplain Mapping High This is handled with GIS and part of floodplain
management. No
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Mitigation Action Priority in
2012 plan Current Status
Include in
2020
Plan?
Acquisition of Vacant
Flood Prone Lands High
Cohasset Land Trust has purchased some land.
The Town is working on identifying properties
as part of the Open Space Plan update
Yes
Municipal Building
Earthquake Assessment Low Not complete; the new bridge is earthquake
resistant Yes
Replace Generator at
Fire/Police Station High Not done Yes
Emergency Power
Generators High
A contract for backup service covers this. The
Police and Fire have their own tank for the
generator. There are still on-going needs.
Yes
As indicated in Table 36, Cohasset made good progress implementing mitigation measures
identified in the 2012 Hazard Mitigation Plan. Infrastructure projects include dam upgrades at
Bound Brook and Sanctuary Pond; culvert work at Jerusalem Road; tide gate management for the
James Brook Area; and seawall repairs. Other achievements include land purchases; GIS
development and stormwater mapping; and provisions for generators. In addition, Cohasset
recently completed a climate vulnerability planning process and received grant to investigate
ocean flooding pathways.
Projects that were not completed and will be continued into this plan update. Include repairs to
Sanctuary Pond Dam, drainage improvements in the James Brook watershed, municipal building
assessment and generator for the public safety buildings. Projects where significant work was
done, but that continue as on-going priorities include seawall repairs, GIS upgrades, gas pipeline
replacements, and emergency generator management. Other on-going priorities include land
purchases and floodplain management.
Overall, ten mitigation measures from the 2012 plan will be continued in the plan update. Most
retain the same priority in this 2020 Update. Moving forward into the next five-year plan
implementation period there will be many more opportunities to incorporate hazard mitigation
into the Town’s decision-making processes. The challenges the Town faces in implementing these
measures are primarily due to limited funding and available staff time. This plan should help the
Town prioritize the best use of its limited resources for enhanced mitigation of natural hazards.
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_ f _faf
SECTION 8: HAZARD MITIGATION STRATEGY
WHAT IS HAZARD MITIGATION?
Hazard mitigation means to permanently reduce or alleviate the losses of life, injuries and
property resulting from natural hazards through long-term strategies. These long-term strategies
include planning, policy changes, education programs, infrastructure projects and other activities.
FEMA currently has three mitigation grant programs: the Hazards Mitigation Grant Program
(HGMP), the Pre-Disaster Mitigation program (PDM), and the Flood Mitigation Assistance (FMA)
program. The three links below provide additional information on these programs.
https://www.fema.gov/hazard-mitigation-grant-program
https://www.fema.gov/pre-disaster-mitigation-grant-program
https://www.fema.gov/flood-mitigation-assistance-grant-program
Hazard Mitigation Measures can generally be sorted into the following groups:
• Prevention: Government administrative or regulatory actions or processes that influence
the way land and buildings are developed and built. These actions also include public
activities to reduce hazard losses. Examples include planning and zoning, building codes,
capital improvement programs, open space preservation, and stormwater management
regulations.
• Property Protection: Actions that involve the modification of existing buildings or
infrastructure to protect them from a hazard or removal from the hazard area. Examples
include acquisition, elevation, relocation, structural retrofits, flood proofing, storm shutters,
and shatter resistant glass.
• Public Education & Awareness: Actions to inform and educate citizens, elected officials,
and property owners about the potential risks from hazards and potential ways to
mitigate them. Such actions include outreach projects, real estate disclosure, hazard
information centers, and school-age and adult education programs.
• Natural Resource Protection: Actions that, in addition to minimizing hazard losses also
preserve or restore the functions of natural systems. These actions include sediment and
erosion control, stream corridor restoration, watershed management, forest and
vegetation management, and wetland restoration and preservation.
• Structural Projects: Actions that involve the construction of structures to reduce the impact
of a hazard. Such structures include storm water controls (e.g., culverts), floodwalls,
seawalls, retaining walls, and safe rooms.
• Emergency Services Protection: Actions that will protect emergency services before,
during, and immediately after an occurrence. Examples of these actions include protection
of warning system capability, protection of critical facilities, and protection of emergency
response infrastructure.
(Source: FEMA Local Multi-Hazard Mitigation Planning Guidance)
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REGIONAL AND INTER-COMMUNITY CONSIDERATIONS
Some hazard mitigation issues are strictly local. The problem originates primarily within the
municipality and can be solved at the municipal level. Other issues are inter-community and
require cooperation between two or more municipalities. There is a third level of mitigation which
is regional and may involve a state, regional or federal agency or three or more municipalities.
REGIONAL PARTNERS
In developed urban and suburban communities such as the metropolitan Boston area, mitigating
natural hazards, particularly flooding, is more than a local issue. The drainage systems that serve
these communities are complex systems of storm drains, roadway drainage structures, pump
stations and other facilities owned and operated by a wide array of agencies including the Town,
the Department of Conservation and Recreation (DCR), the Massachusetts Department of
Transportation (MassDOT) and the Massachusetts Bay Transportation Authority (MBTA). The
planning, construction, operation and maintenance of these structures are integral to the flood
hazard mitigation efforts of communities. These agencies must be considered the communities’
regional partners in hazard mitigation. These agencies also operate under the same constraints as
communities do including budgetary and staffing constraints and they must make decisions about
numerous competing priorities.
Following, is a brief overview of regional facilities found in Cohasset and a discussion of inter-
municipal issues.
OVERVIEW OF REGIONAL FACILITIES WITHIN COHASSET
Major facilities owned, operated and maintained by state or regional entities include:
• Straits Pond Tidegate (Hingham/Hull/Cohasset)
• State Routes 3A and 228 (MassDOT)
• MBTA Greenbush Commuter Rail Line (MBTA)
• Cohasset water partially supplied by the Town of Hingham
• Wompatuck State Park (Mass DCR)
• Cohasset, Hull, Hingham, and Norwell jointly operate emergency communications response
at a site located in Hingham
INTER-COMMUNITY CONSIDERATIONS
Mitigation measures for the following regional issues should be taken into account as Cohasset
develops its own local plan:
A) Coordinate and Review Developments on a Regional Basis
As Cohasset and the surrounding communities are undergoing development, it is vital that
these communities communicate and provide input during the review processes. When
addressing housing, transportation, and economic development projects, the impacts to
neighbors must be addressed.
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B) Weir River Watershed
Part of Cohasset is within the Weir River watershed. The watershed provides drinking water
for part of Cohasset and floodplain management is a shared concern that crosses town lines.
C) Straits Pond
Cohasset and Hull share the shoreline of Straits Pond. The Town of Hull Department of Public
Works take primary responsibility for managing the tide gate to prevent flooding.
NEW DEVELOPMENT AND INFRASTRUCTURE
As part of the process of developing recommendations for new mitigation measures for this plan
update, the Town considered the issues related to new development, redevelopment, and
infrastructure needs in order limit future risks. One of the mitigation measures adopted in this
plan is to update the local wetlands bylaw for improved stormwater management. Taking into
consideration the ongoing Open Space Plan update, the recently completed Master Plan, the
Wetlands Act and bylaw enforced by the Conservation Commission, the town determined that
existing regulatory measures are taking good advantage of local Home Rule land use regulatory
authority to minimize natural hazard impacts of development.
PROCESS FOR SETTING PRIORITIES FOR MITIGATION MEASURES
The last step in developing the Town’s mitigation strategy is to assign a level of priority to each
mitigation measure so as to guide the focus of the Town’s limited resources towards those actions
with the greatest potential benefit. At this stage in the process, the Local Hazard Mitigation
Planning Team had limited access to detailed analyses of the cost and benefits of any given
mitigation measure, so prioritization is based on the local team members’ understanding of
existing and potential hazard impacts and an approximate sense of the costs associated with
pursuing any given mitigation measure.
Priority setting was based on local knowledge of the hazard areas, including impacts of hazard
events, the extent of the area impacted, and the relation of a given mitigation measure to the
Town’s goals. In addition, the local Hazard Mitigation Planning Team also took into consideration
factors such as the number of homes and businesses affected, whether or not road closures
occurred and what impact closures had on delivery of emergency services and the local economy,
anticipated project costs, whether any environmental constraints existed, and whether the Town
would be able to justify the costs relative to the anticipated benefits.
Table 37 below demonstrates the prioritization of the Town’s potential hazard mitigation
measures. For each mitigation measure, the geographic extent of the potential benefiting area is
identified as is an estimate of the overall benefit and cost of the measures. The benefits, costs,
and overall priority were evaluated in terms of:
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HAZARD MITIGATION STRATEGY
Estimated Benefits
High Action will result in a significant reduction of hazard risk to people and/or property from a
hazard event
Medium Action will likely result in a moderate reduction of hazard risk to people and/or property
from a hazard event
Low Action will result in a low reduction of hazard risk to people and/or property from a hazard
event
Estimated Costs
High Estimated costs greater than $100,000
Medium Estimated costs between $10,000 to $100,000
Low Estimated costs less than $10,000 and/or staff time
Priority
High Action very likely to have political and public support and necessary maintenance can occur
following the project, and the costs seem reasonable considering likely benefits from the
measure
Medium Action may have political and public support and necessary maintenance has potential to
occur following the project
Low Not clear if action has political and public support and not certain that necessary
maintenance can occur following the project
Table 37: Mitigation Measures Prioritization
CLIMATE
CHANGE ACTION GEOGRAPHIC
COVERAGE
ESTIMATED
BENEFIT
ESTIMATED
COST PRIORITY
Changes in
Precipitation
Inland Flooding
Upgrades to Sanctuary Pond Dam Site specific Medium Low Low
Upgrade drainage system GIS Town-wide High Medium High
Acquire vacant flood prone land Flood Zones Variable High Low
Purchase a street sweeper Town-wide High High High
Update rainfall standards in
wetland and stormwater bylaws Town-wide High Low High
Reduce sewer infiltration and
inflow
Flood-prone
areas High High High
Install sewer at South Main Street Site specific High High High
Improve James Brook watershed
drainage Site specific High Medium Medium
Improve Bound Brook Watershed
drainage Site specific High Medium Medium
Drought
Increase capacity of Lily Pond and
Aaron River Reservoir Site specific High High High
Landslide
Assess landslide susceptibility Town-wide Low Low Low
Coastal Flooding (and Tsunamis)
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DESCRIPTION OF MITIGATION MEASURES
Changes in Precipitation
Inland Flooding
Upgrades to Sanctuary Pond Dam: The dam is privately owned by the Trustees of Reservations.
Trees were removed from the dam since the last Hazard Mitigation Plan. Additional measures
Sea Level
Rise
Repairs to Margin Street Seawall Site Specific High Low High
Elevate seawalls four feet Harbor High High High
Investigate options to elevate the
breakwater Site specific Medium High High
Coastal Erosion
Monitor causeways and beaches Site Specific Low Low Low
Rising
Temperatures
Extreme Heat and Heat Waves
Develop microgrid capacity Critical
facilities High High Medium
Wildfires
Purchase a brush truck and water
tanker Forested areas High High High
Open access roads in forested
areas Forested Areas High Low High
Invasive species
Investigate phragmites
management strategies Site specific Medium Low Medium
Remove milfoil from water supply
Lily Pond
Aaron Pond
Reservoir
Medium Medium High
Extreme
Weather
Hurricanes and Tropical storms (see Multihazards)
Severe Winter Storm/Nor’easter
Build a new salt shed Town-wide High High High
Tornadoes (see Multihazards)
Other Severe weather (wind, thunderstorms) (see Multihazards)
Multihazards
Multihazards
Assess the health of town trees
(Hurricane, Winter, Tornado, other
Severe weather)
Town-wide High Medium High
Upgrade generators (Hurricane,
Winter, Tornado, other Severe
weather)
Multi-site High High High
Work with National Grid to harden
electric infrastructure, replace gas
lines (all Extreme Weather,
Earthquakes)
Town-wide High Medium Medium
Non-Climate
Hazard Earthquake (see Multihazards)
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could be taken to upgrade the dam. The Town will work with the owner to encourage additional
flood mitigation measures. The Town will also consider downstream detention options.
Upgrade GIS mapping of the stormwater drainage system: The Town made significant strides in
developing a GIS program and mapping the drainage system. This will be an ongoing project in
order to maintain compliance with the Town’s stormwater (MS4) permit.
Acquire Vacant Flood Prone Land: The Town does not currently have target properties, but this
remains an ongoing priority. Priorities will be developed as the Open Space and Recreation plan
is currently being updated. Community Preservation Act funds are a potential source of purchases
for open space and stormwater retention.
Purchase a street sweeper: The current street sweeper is over twenty years old and in need of
replacement. Street sweeping is critical to maintaining stormwater drainage and removing
pollutants from the water supply.
Update stormwater rainfall standards: Revise the Wetlands and Stormwater regulations to
reflect current rainfall rates from NOAA 2014 or the Northeast Regional Climate Center. The
10-year, 24-hour rainfall rates for Cohasset have increased from the currently used standard of
4.5 inches in (NOAA 1961) to 5.23 inches (NOAA 2014).
Reduce sewer infiltration and inflow (I/I): Complete project to tighten and elevate manhole
covers above the floodplain.
Extend sewer lines to South Main Street area: Replacing septic systems with sewer service will
improve water quality.
Improve James Brook watershed drainage: Develop additional stormwater detention and
infiltration facilities within the watershed, upgrade of existing stormwater detention facilities such
as Sanctuary Pond and better regulation and control of stormwater flows to better prevent
flooding of low lying areas when tidal restriction prevent draining of the watershed; repair and
restore stream bed.
Improve Bounds Brook watershed drainage: Develop additional stormwater detention and
infiltration facilities within the watershed, upgrade of existing stormwater detention facilities and
better regulation and control of stormwater flows to better prevent flooding of low lying areas
Drought
Increase capacity of Lily Pond and Aron River Reservoir: Consider options to remove siltation
and address organics (stumps) in the pond.
Landslide
Assess landslide susceptibility: Do a town-wide survey to identify any areas that may be
susceptible to landslides.
Sea Level Rise
Coastal Flooding (and Tsunamis)
Repairs to Margin Street Seawall: The seawall needs regular and ongoing maintenance. The
Town has approved funds to patch and repoint the wall.
Elevate seawalls four feet: This reflects a need to address the reality of ongoing sea level rise.
The walls can already be overtopped during significant coastal storms. This is a very high cost
item that will require future planning and funding.
Investigate options to raise the breakwater: This is also a very high cost item. A further
complication is the breakwater is not owned by the town and it is located in Scitu ate. The Town
wishes to investigate the options for work to increase the size of the breakwater.
Coastal Erosion
Monitor causeways and beaches: Data shows that, for the most part, Cohasset is not susceptible
to coastal erosion. The town does have two causeways and two sandy beaches where erosion
could be a concern, and where future monitoring is appropriate.
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Rising Temperatures
Extreme Heat and Heatwaves
Develop microgrid capacity: As power outages are one of Cohasset’s key concerns, investigate
opportunities to establish microgrids for energy resilience.
Wildfires
Purchase a brush truck and water tanker: Acquire brushfire truck for difficult to access wooded
areas subject to fire hazards. Acquire a water tanker to ensure access to water supply when
fighting fires in wooded areas. The Town will consider the feasibility of shared purchase with
neighboring towns.
Open access roads in forested areas: Maintain or create access pathways for firefighting
equipment. The access way may also be beneficial for public access.
Invasive species
Investigate phragmites management strategies: Investigate management and/or eradication
strategies to reduce fire risk.
Remove milfoil from water supply: Rake or vacuum milfoil from Lily Pond and the Aron River
Reservoir.
Severe winter storms/nor’easter
Acquire a new salt shed: The town needs to replace the salt shed which is in failing condition.
Multihazards
Assess the health of town trees: Hire a consultant to do an assessment of the health of town
trees to identify those at risk of damage during storms. This addresses all of the Extreme
Weather hazards.
Upgrade Emergency Power Generators: Upgrade all generators as needed. This addresses all
Extreme Weather hazards and Earthquakes.
Work with National Grid to harden electric and gas utilities: This work is ongoing. The Town will
work with the utility to ensure timely replacement of gas lines and, hardening of electric lin es. This
addresses all Extreme Weather, Earthquakes, and Flooding.
INTRODUCTION TO POTENTIAL MITIGATION MEASURES TABLE
Description of the Mitigation Measure – The description of each mitigation measure is brief and
cost information is given only if cost data were already available from the community. The cost
data represent a point in time and would need to be adjusted for inflation and for any changes
or refinements in the design of a particular mitigation measure.
Priority – As described above and summarized in Table 38, the designation of high, medium, or
low priority was done considering potential benefits and estimated project costs, as well as other
factors in the STAPLEE (Social, Technical, Administrative, Legal, Economic, and Environmental)
analysis.
Implementation Responsibility – The designation of implementation responsibility was done based
on a general knowledge of what each municipal department is responsible for. It is likely that
most mitigation measures will require that several departments work together and assigning staff
is the sole responsibility of the governing body of each community.
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Time Frame – The time frame was based on a combination of the priority for that measure, the
complexity of the measure and whether or not the measure is conceptual, in design, or already
designed and awaiting funding. Because the time frame for this plan is five years, the timing for
all mitigation measures has been kept within this framework. The identification of a likely time
frame is not meant to constrain a community from taking advantage of funding opportunities as
they arise.
Potential Funding Sources – This column attempts to identify the most likely sources of funding for
a specific measure. The information on potential funding sources in this table is preliminary and
varies depending on a number of factors. These factors include whether or not a mitigation
measure has been studied, evaluated or designed, or if it is still in the conceptual stages. MEMA
and DCR assisted MAPC in reviewing the potential eligibility for hazard mitigation funding. Each
grant program and agency has specific eligibility requirements that would need to be taken into
consideration. In most instances, the measure will require a number of different funding sources.
Identification of a potential funding source in this table does not guarantee that a project will be
eligible for or selected for funding. Upon adoption of this plan, the local team responsible for its
implementation should begin to explore the funding sources in more detail.
Additional information on funding sources – The best way to determine eligibility for a particular
funding source is to review the project with a staff person at the funding agency. The following
websites provide an overview of programs and funding sources.
Army Corps of Engineers (ACOE) – The website for the North Atlantic district office is
http://www.nae.usace.army.mil/. The ACOE provides assistance in a number of types of
projects including shoreline/streambank protection, flood damage reduction, flood plain
management services and planning services.
Massachusetts Emergency Management Agency (MEMA) – The grants page
https://www.mass.gov/hazard-mitigation-assistance-grant-programs describes the various
Hazard Mitigation Assistance Program.
Table 38: Potential Hazard Mitigation Measures
CLIMATE
CHANGE ACTION PRIORITY LEAD TIME
FRAME COST FUNDING
SOURCE
Changes in
Precipitation
INLAND FLOODING
Upgrades to Sanctuary
Pond Dam Low Conservation On-
going Low Private
Upgrade drainage system
GIS High Public Works On-
going Medium Town
funding
Acquire vacant flood prone
land Low Planning On-
going High CPA funds
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Purchase a street sweeper High Public Works 2024 High Capital
budget
Update rainfall standards
in wetland and stormwater
regulations
High Conservation 2020 Low NA
Reduce sewer infiltration
and inflow High Sewer 2021 High Enterprise
Fund
Install sewer at South Main
Street High Sewer 2023 High
State
Revolving
Fund/Ec.
Dev.
Funds
Improve James Brook
watershed drainage Medium Public Works 2021 High unknown
Improve Bound Brook
watershed drainage Medium Public Works 2021 High unknown
DROUGHT
Increase capacity of Lily
Pond and Aaron River
Reservoir
High Water 2025 High bond
LANDSLIDE
Assess landslide
susceptibility Low Building 2025 Low Town
funds
Sea Level
Rise
Coastal Flooding (and Tsunamis)
Repairs to Margin Street
Seawall High Public Works 2021 Low Town
Meeting
Elevate seawalls four feet High Public Works 2025 High Grants
Bonds
Investigate options to raise
breakwater High Public Works 2025 High unknown
Coastal Erosion
Monitor causeways and
beaches Low Public Works
Conservation 2025 Low town
Rising
Temperatures
Extreme Heat and Heat Waves
Develop microgrid capacity Medium Public Works 2025 High grants
Wildfires
Purchase a brush truck and
water tanker High Fire 2025 High
Grants,
regional
sharing
Open access roads in
forested areas High Fire On-
going Low Town
funds
Invasives
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Investigate phragmites
management Medium Fire On-
going Low Town
funds
Remove milfoil from water
supply High Water On-
going Medium Dept.
funds
Extreme
Weather
Multihazards
Hurricanes and Tropical storms (see Multihazards)
Extreme Cold and Severe Winter Storms
Build a new salt shed High Public Works 2025 High
Chapter
91, Town
Meeting
Tornadoes (see Multihazards)
Other Severe weather (wind, thunderstorms) (see Multihazards)
Multihazards
Do a third-party
assessment of town trees
(Hurricane, Winter,
Tornado, other Severe
weather)
High Public Works On-
going Medium Town,
grants
Upgrade generators
(Hurricane, Winter,
Tornado, other Severe
weather)
High Facilities
Public Works 2022 High
Town
Meeting,
grants
Work with National Grid to
harden electric
infrastructure, replace gas
lines (all Extreme Weather,
Earthquakes)
Medium Public Works On-
going Medium
Private
funds,
grants
Non Climate
Hazard Earthquake (see Multihazards)
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SECTION 9: PLAN ADOPTION & MAINTENANCE
PLAN ADOPTION
The Cohasset Hazard Mitigation Plan 2020 Update was adopted by the Board of Selectmen on
[ADD DATE]. See Appendix D for documentation. The plan was approved by FEMA on [ADD
DATE] for a five-year period that will expire on [ADD DATE].
PLAN MAINTENANCE
MAPC worked with the Cohasset Hazard Mitigation Planning Team to prepare this plan. After
approval of the plan by FEMA, this group will meet to function as the Hazard Mitigation
Implementation Team, with the LEPC and CRS Coordinators jointly designated as coordinators.
Additional members could be added to the local implementation team from businesses, non-profits
and institutions. The Town will encourage public participation during the next 5-year planning
cycle. As annual updates and a review of the plan are conducted by the Hazard Mitigation
Implementation Team, these will be placed on the Town’s web site, and any meetings of the
Hazard Mitigation Implementation Team will be publicly noticed in accordance with town and
state open meeting laws.
IMPLEMENTATION AND EVALUATION SCHEDULE
Annual Review – The coordinator of the Hazard Mitigation Implementation Team will convene the
team annually to consider changes or revisions to the plan that may be needed, progress and
accomplishments, and any new hazards or problem areas that have been identified.
This information will be used to prepare a report or addendum to the local hazard mitigation
plan in order to evaluate its effectiveness in meeting the plan’s goals and identify areas that
need to be updated in the next plan. The Hazard Mitigation Implementation Team, coordinated
by the CRS and LEPC Coordinators, will have primary responsibility for tracking progress,
evaluating, and updating the plan.
Begin to Prepare for the next Plan Update – FEMA’s approval of this plan is valid for five years,
by which time an updated plan must be approved by FEMA in order to maintain the town’s
approved plan status and its eligibility for FEMA mitigation grants. Given the lead time needed
to secure funding and conduct the planning process, the Hazard Mitigation Implementation Team
will begin to prepare for an update of the plan in year three. This will help the Town avoid a
lapse in its approved plan status and grant eligibility when the current plan expires.
The Hazard Mitigation Implementation Team will use the information from the annual review to
identify the needs and priorities for the plan update and seek funding for the plan update
process. Potential sources of funding may include FEMA Pre-Disaster Mitigation grants and the
Hazard Mitigation Grant Program. Both grant programs can pay for 75% of a planning project,
with a 25% local cost share required.
Prepare and Adopt an Updated Local Hazard Mitigation Plan – Once the resources have been
secured to update the plan, the Hazard Mitigation Implementation Team may decide to
undertake the update themselves, contract with the Metropolitan Area Planning Council to update
the plan or to hire another consultant. However, the Hazard Mitigation Implementation Team
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decides to update the plan, the group will need to review the current FEMA hazard mitigation
plan guidelines for any changes. The Cohasset Hazard Mitigation Plan Update will be forwarded
to MEMA and DCR for review and to FEMA for approval.
INTEGRATION OF THE PLANS WITH OTHER PLANNING INITIATIVES
Upon approval of the Cohasset Hazard Mitigation Plan 2020 Update by FEMA, the Local
Hazard Mitigation Team will provide all interested parties and implementing departments with a
copy of the plan and will initiate a discussion regarding how the plan can be integrated into that
department’s ongoing work. At a minimum, the plan will be reviewed and discussed with the
following departments:
• Fire
• Police
• Public Works
• Planning
• Harbormaster
• Conservation
• Building Department
Other groups that will be coordinated with include large institutions, Chambers of Commerce, land
conservation organizations and watershed groups. The plan will also be posted on the Town’s
website with the caveat that a local team coordinator will review the plan for sensitive
information that would be inappropriate for public posting. The posting of the plan on the website
will include a mechanism for citizen feedback such as an e-mail address to send comments.
The Hazard Mitigation Plan will be integrated into other town plans and policies as they are
updated and renewed, including the Open Space and Recreation Plan, Comprehensive
Emergency Management Plan, Master Plan, and Capital Plan.
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SECTION 10: LIST OF REFERENCES
General Bylaws for the Town of Cohasset
Zoning Bylaw for the Town of Cohasset
Cohasset 2019 Master Plan
Town of Cohasset Community Resilience Building Workshop Summary of Findings June 2018
Town of Cohasset Open Space and Recreation Plans 2018-2024 and 2010-2017
Blue Hill Observatory
FEMA, Flood Insurance Rate Maps for Norfolk County, MA, 2012
FEMA, Hazards U.S. Multi-Hazard
FEMA, Local Mitigation Plan Review Guide, October 2011
Fourth National Climate Assessment, 2018
Massachusetts Flood Hazard Management Program
Massachusetts Office of Coastal Zone Management Shoreline Change Data
Massachusetts Office of Dam Safety, Inventory of Massachusetts Dams 2018
Massachusetts State Hazard Mitigation Plan, 2013
Massachusetts State Hazard Mitigation and Climate Adaptation Plan, 2018
Metropolitan Area Planning Council, GIS Lab, Regional Plans and Data
National Weather Service
Nevada Seismological Library
New England Seismic Network, Boston College Weston Observatory, http://aki.bc.edu/index.htm
NOAA National Climatic Data Center, http://www.ncdc.noaa.gov/
Northeast Climate Adaptation Science Center
Northeast States Emergency Consortium, http://www.nesec.org/
Tornado History Project
US Census, 2010 and American Community Survey 2017 5-Year Estimates
USGS, National Water Information System, http://nwis.waterdata.usgs.gov/usa/nwis
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APPENDIX A: MEETING AGENDAS
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Cohasset Hazard Mitigation Plan Update
LOCAL HAZARD MITIGATION PLANNING TEAM
Meeting #1
Tuesday, July 23, 2019
Cohasset Town Hall
AGENDA
1. Welcome and Introductions
2. Overview of the Planning Process
3. Identify/update local hazard areas
a) Flood Hazard Areas
b) Fire Hazard Areas (brushfires/ wildfires)
c) Other hazards
4. Identify and Map Potential New Development Sites
5. Review Critical Infrastructure
6. Update Hazard Mitigation Goals
7. Next Meeting
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Cohasset Hazard Mitigation Plan 2020 Update
October 8, 2019
1:00 – 2:30 pm
Meeting #2
AGENDA
1. Review climate projections and MVP Workshop results
2. Review original existing mitigation measures from 2012 plan
• confirm effectiveness
• note any needed changes
3. Review recommended mitigation measures from 2012 plan
• current status
• decide which to carry forward into 2020 plan
• evaluate priority
4. Next Steps – plan for first public meeting
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Cohasset Hazard Mitigation Plan 2020 Update
January 21, 2020
1:00 – 2:30 pm
Meeting #3
AGENDA
5. Update Hazard Mitigation Goals
6. Propose new mitigation measures for the 2020 plan
• Review carried over items
• Review MVP workshop results
• Consider new items
7. Fill out climate summary sheet
• Any new items as a result
8. Next steps
• Complete plan
• Schedule final public meeting
• Submit to MEMA and FEMA for review
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APPENDIX B: HAZARD MAPPING
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APPENDIX C: PUBLIC MEETINGS
TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
LIST OF REFERENCES 110 of 117
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CALENDAR LISTING / MEDIA ADVISORY
COHASSET’S DRAFT HAZARD MITIGATION PLAN TO BE
PRESENTED AT NOVEMBER 20 PUBLIC MEETING
Meeting to present Cohasset’s Hazard Mitigation Plan and solicit public comments
Who: Cohasset residents, business owners, representatives of non-profit organizations
and institutions, and others who are interested in preventing and reducing damage
from natural hazards.
What: At the Cohasset Planning Board meeting on Wednesday, November 20 at 6:30
PM, a presentation will be made by the Metropolitan Area Planning Council
(MAPC), which is assisting the Town on the development of its Hazard Mitigation
Plan update.
The plan identifies natural hazards affecting Cohasset such as floods, hurricanes,
winter storms, and earthquakes, as well as actions that the Town can take to
reduce its vulnerability to these hazards. Upon approval of the plan by the Town
and by FEMA, Cohasset will be eligible for hazard mitigation grants.
When: Wednesday, November 20 at 6:30 PM
Where: Cohasset Town Hall
Lower Level Meeting Room
41 Highland Avenue
Cohasset, MA
MAPC is the regional planning agency for 101 communities in the metropolitan
Boston area, promoting smart growth and regional collaboration. More
information about MAPC is available at www.mapc.org.
##
TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
LIST OF REFERENCES 111 of 117
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TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
LIST OF REFERENCES 112 of 117
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TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
LIST OF REFERENCES 113 of 117
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Amanda Linehan, Communications Manager, Metropolitan Area Planning Council
617-933-0705, alinehan@mapc.org
CALENDAR LISTING / MEDIA ADVISORY
COHASSET’S DRAFT HAZARD MITIGATION PLAN TO BE
PRESENTED AT JUNE 3 PUBLIC MEETING
Meeting to present Cohasset’s Hazard Mitigation Plan and solicit public comments
Who: Cohasset residents, business owners, representatives of non-profit organizations
and institutions, and others who are interested in preventing and reducing damage
from natural hazards.
What: At the Cohasset Board of Selectmen meeting on Wednesday, June 3 at 7:00 PM,
a presentation will be made by the Metropolitan Area Planning Council (MAPC),
which is assisting the Town on the development of its Hazard Mitigation Plan
update.
The plan identifies natural hazards affecting Cohasset such as floods, hurricanes,
winter storms, and earthquakes, as well as actions that the Town can take to
reduce its vulnerability to these hazards. Upon approval of the plan by the Town
and by FEMA, Cohasset will be eligible for hazard mitigation grants.
When: Wednesday, June 3 at 7:00 PM
Where: The meeting is available in the following locations:
Zoom link attached to agenda can be downloaded at:
http://www.cohassetma.org/AgendaCenter/Board-of-Selectmen-12
Broadcast on Local Cable 143TV
Broadcast on Town of Cohasset Facebook page
MAPC is the regional planning agency for 101 communities in the metropolitan
Boston area, promoting smart growth and regional collaboration. More
information about MAPC is available at www.mapc.org.
##
TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
LIST OF REFERENCES 114 of 117
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TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
LIST OF REFERENCES 115 of 117
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June 3rd Board of Selectmen agenda to be inserted here
TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
LIST OF REFERENCES 116 of 117
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APPENDIX D: PLAN ADOPTION
TOWN OF COHASSET – HAZARD MITIGATION PLAN – 2020 UPDATE
LIST OF REFERENCES 117 of 117
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<TOWN LETTERHEAD>
CERTIFICATE OF ADOPTION
BOARD OF SELECTMEN
TOWN OF COHASSET, MASSACHUSETTS
A RESOLUTION ADOPTING THE
TOWN OF COHASSET HAZARD MITIGATION PLAN 2020 UPDATE
WHEREAS, the Town of Cohasset established a Committee to prepare the Town of Cohasset
Hazard Mitigation Plan 2020 Update; and
WHEREAS, the Town of Cohasset Hazard Mitigation Plan 2020 Update contains several potential
future projects to mitigate potential impacts from natural hazards in the Town of Cohasset, and
WHEREAS, duly noticed public meetings were held by the LOCAL HAZARD MITIGATION
PLANNING TEAM on November 20, 2019 and June 3, 2020 and
WHEREAS, the Town of Cohasset authorizes responsible departments and/or agencies to execute
their responsibilities demonstrated in the plan, and
NOW, THEREFORE BE IT RESOLVED that the Town of Cohasset Board of Selectmen adopts
the Town of Cohasset Hazard Mitigation Plan 2020 Update, in accordance with M.G.L. 40 §4
or the charter and bylaws of the Town of Cohasset.
ADOPTED AND SIGNED this Date. _____________________________
Name(s)
Title(s)
Signature(s)