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)
*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.
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)
*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.
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)
#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
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
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