This document summarizes a study projecting future coastal flood risk for Massachusetts Bay using available data and numerical modeling. It presents the methodology, which includes using published hydrodynamic modeling data from the US Army Corps of Engineers and developing a high-resolution coupled ADCIRC and SWAN model. The model is validated against historical hurricanes and used to simulate storm surge and waves from a synthetic hurricane under present and future sea level rise scenarios. The results are analyzed to identify flood risk and how risk may increase with sea level rise.

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Proactive By Design.
Our Company Commitment
COASTAL DATA
APPLICATION
Projecting Future Coastal Flood
Risk for Massachusetts Bay
Bin Wang, Tianyi Liu,
Daniel Stapleton & Michael Mobile
2015 Coastal GeoTools

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 Overview of available data sources for coastal and
water resource engineers
 Overview of numerical hydrodynamic modeling
Outline
Objective: to present method and steps for site-specific
coastal flood hazard analysis
• Small budget
• Relatively short project schedule
• Use of published data by USACE NACCS and
other government agencies

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Background
Coastal Flooding
Erosion
Flood Damage Structural Damage

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Background
Need to identify/quantify flood hazards:
 stillwater elevations
 wave action
 environmental loads
 shoreline and nearshore response
To achieve coastal resiliency:
 critical infrastructure
 communities
 biohabitats
 natural resources
Coastal Resiliency

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Massachusetts Bay &
Cape Cod Bay
• Total Number of Cities/Towns = 53
• Population = 1.90 M (2010 Census)
• Historical Coastal Towns
Background

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Massachusetts Bay
Coastal Flood
Hazard
Background
“Nor-Easters”

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Hurricanes
Background
Massachusetts Bay
Coastal Flood
Hazard

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Available Data
South Shore Coastal Geomorphology: Beaches, Estuaries, Marsh,
Structures
GZA Coastal Engineering GeoTool

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Available Data
South Shore Coastal Geomorphology: Shoreline Change

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Available Data
North Shore Coastal Geomorphology: Beaches, Estuaries, Rocky
Shore, Scarps, Structures

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NOAA SLOSH Model • Hydrodynamic Model
• Develops hurricane
windfield
• NOAA developed DEMs
Available Data

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Available Data

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NOAA/NOS/CO-OPS Tide Gages
• Observed water levels, e.g., time series
for model validation/verification; extreme
value analysis; empirical simulation
technique (EST);
• Predicted tides and tidal constituents;
• Datum conversions (w/ Vdatum);
• Sea level trend
Available Data

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NOAA/NOS/CO-OPS 8443970: Boston Harbor
5
6
7
8
9
10
11
12
1 10 100 1,000
StillwaterElevation(feet,NAVD88)
Return Period (Years)
Observed Annual Maximum - Original Tide Data (ft, NAVD88) Observed Annual Maximum Adjusted w/ Sea Level Rise
Calculated Stage-Frequency Curve w/ Original Tide Data Calculated Stage-Frequency Curve w/ Sea Level Rise-Adjusted Tide Data
Hingham Harbor (FEMA 2012)
Generalized
Extreme
Value (GEV)
Available Data

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Available Data
FEMA Flood Insurance Study and Rate Maps

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Available Data
FEMA Flood Insurance Study and Rate Maps

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Wave Information Studies (WIS)
• Frequency analysis
• Time series
Available Data

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Wave Information Studies (WIS)
100-year return
period
significant deep water
wave height: +/- 35 ft
Available Data

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USACE North Atlantic Coast Comprehensive Study
(NACCS) Numerical Hydrodynamic Storm Surge and
Wave Models
USACE NACCS

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Site-Specific High Resolution Storm Surge, Wave and
Flood Modeling
Coupled ADCIRC + SWAN Models
Numerical
Hydrodynamic Modeling

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• NOAA or State GIS topographic &
hydrographic data layers (DEM)
• National or state land cover database
• NOAA COOPS tide gages – water levels
and other data;
• USACE Wave Information System (WIS)
– wave & wind gages
• National Climate Data Center - ground
climate/weather stations
• NHC Hurricane Re-analysis project – best
track data
• Other (e.g., USGS stream gage data)
Model inputs
and calibration
Model construction
Data Sources

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U.S. Coastal Relief Model (30-m)LiDAR Terrain Data (2009 Boston @ 1-m)
Note: datum conversions & units
Data Sources

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Land Use – building nodal attributes, Manning’s friction
values, surface roughness coefficients …
Data Sources
State: MassGIS LU2005 National: NLCD 2011 (v.2014)

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Tropical Cyclones:
• HURDAT / HURDAT 2
• Historical Tracks
• IBtrACS - Int. Best
Track Archive
• Others (e.g., RAMMB)
Data Sources
Time Series
Verification
Statistical analysis

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Extratropical Cyclones
Data Sources
Book: New England Weather, New England Climate (Zielinski & Keim, 2003)
February 7, 1978

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USACE NACCS ADCIRC+SWAN Coupled Grid
Numerical Model
FEMA Model Grids Refined for New England

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GZA High Resolution, Locally-Refined ADCIRC+SWAN
Coupled Grid
GZA High
Resolution Local Model
FEMA Region II Refined for Southern New England

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Model Validation
Hurricane Bob 1991
August 16 - 28
Landfall: 41.4N, 71.4W

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Validation – Hurricane Bob 1991
Model Validation
0
5
10
15
20
25
30
35
40
45
18 19 20 21
SignificantWaveHeight(ft)
Days in August, 1991
NDBC Buoy Station 44008
Observed Simulated
-3
-2
-1
0
1
2
3
4
5
6
18 19 20 21
WaterSurfaceElevation(ft,
NAVD88)
Days in August, 1991
Hurricane Bob Storm Surge Newport, RI
Observed Simulated

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Bearing 10 °
Rmax 35 nm
Vf 20 kt
Vmax 105 kt
DP 68 mb
Modeling Extreme (Very
Low Probability) Hurricane
Synthetic Hurricane

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Typical track
direction, similar to
historical events
Synthetic Hurricane

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Sea Level Rise
Note: The Commonwealth of Massachusetts has not officially adopted any SLC scenario.

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Synthetic Hurricane
Present Sea Level

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Synthetic Hurricane
2100 USACE High SLR

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Synthetic Hurricane
Present Sea Level 2100 USACE High SLR

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North Shore at
greater risk for
waves
Synthetic Hurricane

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1
2
3
4
5 -10
-5
0
5
10
15
0 1 2 3 4
ADCIRC+SWANCalculated
WL(ft,NAVD88)
Simulation Time (days)
Station 1 - Salem
Station 3 - Boston
Station 5 - Scituate
Peak storm tide
• varies in space
• synchronized
• Boston at greater risk
Synthetic Hurricane

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Impact of
Sea Level Rise
Peak Storm Tides for Selected Sea Level Scenarios
0
2
4
6
8
10
12
14
16
18
Salem Revere Boston Quincy Scituate
CalculatedStillwaterLevel(ft,
NAVD88)
Present
SLR Int.
SLR High
North South

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- Slightly nonlinear storm tide response to sea level rise;
- For non-extreme cases, approximation by linear superposition;
- For more extreme cases, numerical modeling needed
1.5
1.6
1.7
1.8
Salem Revere Boston Quincy Scituate
CalculatedStillwaterLevel
Increase(ft)
SLR Int. - Present
Input SLR Int.
4.8
4.9
5.0
5.1
Salem Revere Boston Quincy Scituate
CalculatedStillwaterLevel
Increase(ft)
SLR High - Present
Input SLR High
Impact of
Sea Level Rise

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USACE NACCS Data Output “Save” Points
Comparison with
USACE NACCS

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3
6
9
12
15
1 10 100 1,000 10,000
StillwaterElevation(feet,
NAVD88)
Return Period (Years)
Observed Annual Maximum Adjusted w/ Sea Level Rise Calculated Stage-Frequency Curve w/ Sea Level Rise-Adjusted Tide Data
Hingham Harbor (FEMA 2012) NACCS Boston Harbor MT
NACCS Boston Harbor HT
NOAA/NOS/CO-OPS 8443970: Boston Harbor; NACCS-
predicted flood-frequency curve
Comparison with
USACE NACCS
MT ~ HT

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Overland Wave Inundation:
CEDAS: ACES Module
Applying Model
Output

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Flood Inundation Models
Hydrodynamic Loads on
Protective Barrier
Maximum Flow Depth
(ft)
1.9
MaximumVelocity (ft/s) 1.7
Impact Force (pounds)
per linear feet
7.7
Applying Model
Output

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Estuary Circulation; sediment
transport
Applying Model
Output
Shoreline Processes
Beach Erosion

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Applying Model
Output
Resiliency Design

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Take-away
• Massachusetts Bay has significant flood
risk:
 Tropical cyclones and nor’easters
 Sea level rise
 Large population
 Critical infrastructure
• USACE NACCS: provides updated flood
projections
• NACCS can be coupled with local, high resolution
surge and wave models

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Bin Wang, P.E.
Technical Specialist
Norwood, MA
781-278-5809
Bin.Wang@gza.com
Daniel C. Stapleton, P.E.
Principal
Norwood, MA 02062
781-278-5743
Daniel.Stapleton@gza.com
Tianyi Liu, Ph.D.
Coastal Engineer Specialist
Norwood, MA
781-278-3819
Tianyi.Liu@gza.com
Michael A. Mobile, Ph.D.
Technical Specialist
Bedford, NH
603-232-8738
Michael.Mobile@gza.com
Thank You!

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Synthetic Hurricane