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SELECT BOARD MEETING 03/06/2023

COASTALVULNERABILITY ACTION

MANCHESTER-BY-THE-SEA |

PLAN

ABOUT THE PLAN

 Manchester-by-the-Sea experiences frequent flooding in the downtown and inner harbor area

 Critical infrastructure is at lower elevations

 Plan will provide a roadmap to reduce coastal flood risks and increase coastal resilience

 Build upon past studies

 Develop a phased approach to establishing action-oriented mitigation measures

PLANNING APPROACH & ANTICIPATED TIMELINE

(JUN 2023)

(APR – JUN 2023)

(MAR – APR 2023)

(NOV 2022 – FEB 2023)

(JAN – MAR 2023)

EXISTING CONDITIONS ASSESSMENT

 Compiling mapping information and collecting data on past flood elevations

 Performing site assessments and collecting critical elevations

VULNERABILITY ASSESSMENT

 Build upon the 2016 Town-wide Vulnerability and Risk Assessment

 Assess current and future flooding conditions, water surface elevations, and projected habitat change

 Develop inundation maps and a detailed, asset-specific assessment for buildings and infrastructure

EXISTING CONDITIONS

WETLANDS DELINEATION CONFIRMATION/EXTENSION

(Rimmer, 2015) (Woods Hole Group 1/17/23)

SEA LEVEL RISE

HISTORICAL SEA LEVEL RISE |

BOSTONTIDE GAUGE,STATION 8443970

The relative sea level trend is 2.89 millimeters/year with a 95% confidence interval of +/- 0.15 mm/yr based on monthly mean sea level data from 1921 to 2021 which is equivalent to a change of 0.95 feet in 100 years.

SEA LEVEL RISE PROJECTIONS

MASSACHUSETTS COASTAL FLOOD RISK MODEL (MC-FRM) NORTH (DECONTO & KOPP, 2017)

Relative Mean Sea Level (feet NAVD88)

Note: MA selected the High Scenario for planning

Observed Monthly Average

Scenarios (High)

2008 Baseline (1999-2017)

NOAA Epoch (19832001)

NOTES: (1) Projections from Resilient MA Labels in flags are relative sea level rise from baseline year of 2008 (1999-2017) in MC-FRM & (2) Boston Tide Gauge (Station 8443970) Local Tidal Datums: MHHW is 5.1 FT. above MSL

-2 0 2 4 6 8 10 12 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

× ×

Extreme High Intermediate-High Intermediate MC-FRM

Intermediate Scenarios × × × × × × up to +1.3 ft up to +2.5 ft up to +4.3 ft up to +7.7 ft × × × +0.8 ft × +1.5 ft +2.4 ft +4.1 ft

LOCAL TIDE GAUGE DEPLOYMENT

2 1

Projected Tidal Benchmarks (elevation in ft. NAVD88)

2030 2050 2070 2030 2050 2070 MHHW 6.2 7.5 9.4 6.2 7.5 9.4 MHW 5.8 7.1 9.0 5.6 6.9 8.8 MLW -3.3 -2.1 -0.5 -3.1 -1.9 -0.3 MLLW -3.5 -2.4 -0.7 -3.5 -2.4 -0.7 

Outer Harbor Inner Harbor MC-FRM Tidal Benchmarks Adjusted for Attenuation

Tide gauge used to refine MCFRM tidal benchmarks  Little attenuation between inner and outer harbor

PROJECTED MEAN HIGHER HIGH WATER

Mean Higher High Water (MHHW) is the avg of the higher high water heights of each tidal day observed over a 19-year period

HIGH TIDE FLOODING 1/23/23

HIGH TIDE FLOODING 1/23/23

HIGH TIDE FLOODING 1/23/23

STORMS

EXTREMEWATER LEVELS IN BOSTON (STATION 8443970 )

1/4/18: NEW STORM OF RECORD

*Note: Historic water levels recorded at the Boston tide gauge may not be representative of actual storm surge elevations in Manchester Harbor; comparisons are an approximation only and should only be used to put future water levels into a local context.

Note: 12/23/22 storm produced the 8th highest water level recorded in Boston, and the specific water level for MBTS according to our tide gauge was: 8.3 ft NAVD88.

12/23/22 STORM

Note: 12/23/22 storm produced the 8th highest water level recorded in Boston, and the specific water level for MBTS according to our tide gauge was: 8.3 ft NAVD88.

12/23/22 STORM

MASSACHUSETTS COAST FLOOD RISK MODEL (MC-FRM)

INPUTS

SEA LEVEL RISE

PROBABILISTIC /

HYDRODYNAMIC MODEL

TROPICAL / EXTRATROPICAL STORMS

LANDSCAPE ELEVATION

CHANGING CLIMATE

Includes relevant physical processes: sea level rise, tides, storm surge, wind, wave setup / run-up / overtopping, future climate scenarios

Future version to incorporate coastal erosion

FLOOD PROBABILITY

FLOOD DEPTH

FLOOD

DURATION

FLOOD VOLUMES

FLOOD

PATHWAYS

WINDS

WAVES

CURRENTS OUTPUTS

MASSACHUSETTS COAST FLOOD RISK MODEL (MC-FRM)

MC-FRM WATER SURFACE ELEVATIONS (WSE)* FOR MANCHESTER STUDY AREA

Historic Water Levels

Boston Harbor (NOAATide Gauge)*

#1 9.65 ft NAVD88 Winter Storm Grayson (1/4/18)

#2 9.59 ft NAVD88 Blizzard of ’78 (2/7/78)

Warren B., M. Reilly and G. Belfit (2018) Town of Manchester-by-the-Sea Community Resilience Building Workshop Summary of Findings. Salem Sound Coastwatch,Tighe & Bond,Town of Manchester-by-the-Sea, Massachusetts.

Annual Coastal Flood Exceedance Probability (%) Manchester Harbor Maximum MC-FRM WSE (ft NAVD88) 2030 2050 2070 0.1 10.7 12.4 14.2 0.2 10.4 12.0 13.9 0.5 10.0 11.6 13.4 1 9.7 11.2 13.1 2 9.4 10.9 12.7 5 9.0 10.4 12.2 10 8.6 10.0 11.8 25 8.2 9.5 11.3 50 7.9 9.1 10.9

MC-FRM WATER SURFACE ELEVATIONS (WSE)* FOR MANCHESTER STUDY AREA

Historic Water Levels

Boston Harbor (NOAATide Gauge)*

#5 8.63 ft NAVD88 Perfect Storm (10/30/91)

MC-FRM

WATER SURFACE ELEVATIONS (WSE)* FOR MANCHESTER STUDY AREA

Historic Water Levels

Boston Harbor (NOAATide Gauge)

#8 8.46 ft NAVD88 Christmas Storm (12/23/22)

Woods Hole Group’s tide gauge was in the water for the 12/23/22 storm and recorded a maximum water level of 8.33 ft

NAVD88 locally in Manchester Harbor

photo courtesy of Town of Manchester by the Sea

VULNERABILITY ASSESSMENT

VULNERABILITY ASSESSMENT METHODS

0.1% 0.2% 0.5% 1% 2% 5% 10% 20% 25% 30% 50% 100%

FLOOD EXCEEDANCE

2030

COASTAL

PROBABILITY

VULNERABILITY ASSESSMENT METHODS

0.1% 0.2% 0.5% 1% 2% 5% 10% 20% 25% 30% 50% 100%

2050

COASTAL FLOOD EXCEEDANCE PROBABILITY

VULNERABILITY ASSESSMENT METHODS

0.1% 0.2% 0.5% 1% 2% 5% 10% 20% 25% 30% 50% 100% COASTAL FLOOD EXCEEDANCE PROBABILITY 2070

CRITICAL ELEVATION (CE) SURVEY (1/19/23 & 1/23/23)

CRITICAL ELEVATION (CE) SURVEY (1/19/23 & 1/23/23)

CRITICAL ELEVATION (CE) SURVEY (1/19/23 & 1/23/23)

BUILDING FLOOD PROBABILITY 2030

*CEs from surveyed lower-level entry points where available or from minimum LiDAR elevation within building footprint

BUILDING FLOOD PROBABILITY 2050

*CEs from surveyed lower-level entry points where available or from minimum LiDAR elevation within building footprint

BUILDING FLOOD PROBABILITY 2070

*CEs from surveyed lower-level entry points where available or from minimum LiDAR elevation within building footprint

SUMMARY OF BUILDING VULNERABILITY ASSESSMENT (BUILDING COUNTS)

REVIEW OF NEXT STEPS

NEXT STEPS

(NOV 2022 – FEB 2023) (JAN – MAR 2023)

– APR 2023)

– JUN 2023)

2023)

(MAR

(APR

(JUN

ALTERNATIVES ANALYSIS

Identify potential neighborhood-scale and sitescale alternatives

Maximize the potential of nature-based and hybrid design approaches

Propose phasing of improvements



ALTERNATIVES: SITE SCALE

Building Form +

Access

Building

Adaptation

Building Systems Site

(Credit: Modified from Boston Planning & Development Agency, Coastal Flood Resilience Design Guidelines)

ALTERNATIVES: NEIGHBORHOOD SCALE

Protect (hardened infrastructure)

Protect (natural or nature-based infrastructure)

Protect (hybrid infrastructure)

Relocate/Retreat

(Credit: Modified from NYCPlanning, Coastal Climate Resilience Urban Waterfront Adaptive Strategies)

 Public meetings  Project website  https://tinyurl.com/yck5dm9n  Email sign-up form

PUBLIC ENGAGEMENT

THANK YOU

Thank you for your time and we look forward to engaging with you as the project moves forward

Contact:

 Alex Maxwell, Resilience Planner | Project Manager, Fuss & O’Neill: amaxwell@fando.com  Joseph Famely, Climate & Sustainability Team Lead | Woods Hole Group: jfamely@woodsholegroup.com

