The document summarizes the methodology and results of a request for a Letter of Map Revision (LOMR) along the coast of Hingham, Massachusetts. The original 2012 FEMA flood maps were found to have issues with storm surge modeling. An independent re-analysis was performed using updated tide gauge data, wind statistics, additional transect locations, and numerical modeling. This generally resulted in a reduction of around 2 feet for the 100-year stillwater elevation and Special Flood Hazard Area boundaries. A multi-year process involved analyses, public review, and an approved LOMR from FEMA that updated five flood insurance rate panels. Key factors in a successful LOMR included detailed site-specific analyses and interpretation of results.

1. Page | 1
Sharing Valuable Experience
on Request for Letter of Map
Revision (LOMR)
Bin Wang, P.E.
Peter Williams, P.E.
Tianyi Liu, Ph.D.
Daniel Stapleton, P.E.
David Leone, P.E.
October 15, 2015

2. Page | 2
Background
Acronyms:
• Federal Emergency Management Agency (FEMA)
• National Flood Insurance Program (NFIP)
• Flood Insurance Study (FIS)
• Flood Insurance Rate Map (FIRM)
• Base Flood Elevation (BFE)
• Special Flood Hazard Area (SFHA)
• Letter of Map Amendment (LOMA)
• Letter of Map Revision (LOMR)

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Background
• Three integral
parts of NFIP:
o Mapping
o Insurance
o Regulations
FIS/FIRMs:
• Floodplain boundaries
• Projected flood elevations
• Flood velocities
• Floodway dimensions
• Insurance rating zones

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Background
• FIS and FIRMs updated by FEMA;
• Latest FIRMs - significant increase in water levels in
coastal areas;
• Potential impacts on local communities;
Map Revisions:
• Map updates - new effective maps;
• LOMA – excluding property from floodplain
(elevation certificate);
• LOMR – partial map revision (new analysis)

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Background
NFIP
FIS & FIRMs
Coastal studies:
• Storm surge & waves
• Transects
• Hydraulics
Riverine studies:
• Hydrology
• Cross sections
• Hydraulics
FIS report and FIRMs
 Base flood elevation
 Coastal high hazard area
 Coastal floodplain map
 Flood profiles
 Floodplain map
 Floodway analysis

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Methodology
Technical Review
Effective FIS/FIRM &
Technical support data
Coastal:
• Transects
• Flood zone
delineation
Riverine:
• River flood
• Flood profiles
Narrative, analysis results & maps
Stillwater, wind,
wave setup and
runup calculation
Detailed
numerical
modeling
Stream gage
statistics
Detailed
riverine H&H
analyses
Optional
Required

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Case Study
"HinghamMainStreet" by Timothy Valentine

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Quincy Bay
Hingham Bay
Dorchester
Bay

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Background

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Background
Significant changes
along coastal areas
(100- & 500-yr)
Detailed
analysis not
performed 3
1
4
2
0
2
4
6
8
10
12
14
16
Pt-1 Pt-2 Pt-3 Pt-4
El(ft,NAVD88)
1986
2012

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Analyses
Review of Supporting
Calculations
• Issues identified:
o Stillwater elevation;
o 100-year wind speed;
o Fetch length;
o Transects;
o Change with no supporting
documentation
GZA’s Independent Re-
analyses
• Analyses performed
o Tide gage analysis;
o Statistical analysis on
directional wind speed;
o Wave calculations;
o Additional transects;
o Hydraulic analysis

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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)
Boston Tide Gage 8443970 - Generalized Extreme Value (GEV) Distribution
Stillwater

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Stillwater
Annual
Exceedance
Probability
(%)
Return
Period
(yr.)
Previous
Annual
Maxima
Method
1988
USACE
Tidal
Flood
Profile
2012
FEMA
FIS
GZA
2013
Annual
Maxima
Method
10 10 8.0 8.4 8.4 8.4
2 50 8.9 9.3 9.3 9.2
1 100 9.2 9.5 9.7 9.5
0.2 500 10.0 - 10.6 10.2
Summary of Calculated Stillwater Elevation (feet, NAVD88)

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Stillwater
Annual
Exceedance
Probability
(%)
Return
Period
(yr.)
Previous
Annual
Maxima
Method
1988
USACE
Tidal
Flood
Profile
2012
FEMA
FIS
GZA
2013
Annual
Maxima
Method
10 10 8.0 8.4 8.4 8.4
2 50 8.9 9.3 9.3 9.2
1 100 9.2 9.5 9.7 9.5
0.2 500 10.0 - 10.6 10.2
Summary of Calculated Stillwater Elevation (feet, NAVD88)

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0 to 22.5
22.5 to 45
45 to 67.5
67.5 to 90
90 to 112.5
112.5 to 135
135 to 157.5
157.5 to 180
180 to 202.5
202.5 to 225
225 to 247.5
247.5 to 270
270 to 292.5
292.5 to 315
315 to 337.5
337.5 to 360
<11 mph
11 - 22 mph
22 - 34 mph
34 - 45 mph
45 - 56 mph
56 - 67 mph
67 - 78 mph
Boston Logan Airport AWS 725090 (10-meter, 2-minute Wind) – 1936 through 2013
Wind

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Wind
Boston Logan Airport AWS 725090 – 1936 through 2013
-80
-40
0
40
80
-80 -40 0 40 80
Top 20 Annual Maximum Wind Speed (mph)
Carol 1954
(86 mph)
Nor’easters
Hurricanes

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0
25
50
75
100
West Northwest North Northeast East Southeast
100-yr10-m,2-minWindSpeed(mph)
Wind Direction
GEV Distr
Max Obs.
Wind
Boston Logan Airport AWS 725090 – 1936 through 2013
-30%

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Transects
Original transects in 2012 FIRMs

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Transects
Additional transects for re-analysis

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LiDAR & DEM

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Wave Fetches
Fan Graphs

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• Wave characteristics – ACES (CEDAS)
• Wave setup – DIM method
• Wave overland propagation – WHAFIS (CHAMP)
• Wave runup – RUNUP (CHAMP) & ACES (CEDAS)
Waves

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Transects
Additional transects for re-analysisSUMMARY OF CEDAS INPUT DATA & RESULT FOR DIRECTIONAL WINDS
1 HOUR WIND DURATION
Transect Fetch (miles)
Fetch
Direction
Wind Speed
(mph)
Wave Height
(H) (Ft.)
Wave Period (sec.)
HI-1 5.31 NW 53.6 4.15 3.98
HI-2 5.76 NW 53.6 3.23 3.55
HI-3 1.02 W 42.1 1.45 2.25
HI-4 1.76 N 49.8 2.39 2.90
HI-5 1.17 NE 51.7 1.89 2.55
HI-6 1.35 NE 51.7 2.16 2.73
HI-7 1.02 SE 57.4 2.20 2.70
HI-8 3.02 NW 53.6 3.50 3.54
HI-9 3.89 N 49.8 2.95 3.40
HI-10 2.1 NW 53.6 2.90 3.19
HI-11 2.47 N 49.8 2.83 3.18
HI-12 0.8 NE 51.7 1.71 2.39
HI-13 0.94 NE 51.7 1.82 2.48
HI-14 0.87 NE 51.7 1.79 2.45
HI-15 1.17 NE 51.7 2.07 2.66
HI-16 1.87 NW 53.6 2.17 2.79
HI-17 0.34 N 49.8 0.88 1.69

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Results
5
10
15
20
HI-1 HI-2 HI-3 HI-4 HI-5 HI-6 HI-7 HI-8 HI-9 HI-10 HI-11 HI-12
DesignationatShoreline-VE(ft,NAVD88)
Transect
Previous Revised

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 Most transects revised;
 Average reduction of AE/VE elevation by 2’;
 Changes in AE/VE boundaries;
 Minimal changes in landward extend of BFE
 Five FIRM panels updated
Mapping

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TimelineOct2013
Dec2013
Feb2014
May2014
Proposal &
contract
Analyses
completed
Request
for LOMR
Submitted
FEMA
approves
LOMR
Broad
Cove Info
request
(FEMA)
Info
request
(FEMA)
Jul2014
Dec2014
Public
Comment
Period
Apr-Jul2015
LOMR
becomes
Effective
Aug2015

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Summary
Key to a successful request for LOMR:
 Site-specific information
 Best-available data
 Refined analyses
 Local knowledge
 Proper interpretation of results

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Questions
“White Mountain October 2015" by Bin Wang

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Thank you
Bin Wang, P.E.
Technical Specialist
781-278-5809
Bin.Wang@gza.com
Tianyi Liu, Ph.D.
Coastal Engineer
781-278-3819
Tianyi.Liu@gza.com
Peter J. Williams, P.E.
Senior Project Manager
781-278-4821
Peter.Williams@gza.com
Daniel C. Stapleton, P.E.
Principal
781-278-5743
Daniel.Stapleton@gza.com
David M. Leone, P.E.
Associate Principal
781-278-5788
Davidm.Leone@gza.com