Flood Insurance Study, revised March 16, 2016

Federal Emergency Management Agency · from FEMA · 91 pages · 2.1 MB
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Federal Emergency Management Agency 
FLOOD INSURANCE STUDY NUMBER
25025CV000B 
SUFFOLK COUNTY,
MASSACHUSETTS
(ALL JURISDICTIONS)
COMMUNITY NAME COMMUNITY NUMBER 
BOSTON, CITY OF 250286
CHELSEA, CITY OF 250287
REVERE, CITY OF 250288
WINTHROP, TOWN OF 250289
SUFFOLK COUNTY

NOTICE TO 
FLOOD INSURANCE STUDY USERS 
Communities participating in the National Flood Insurance Program have established repositories of flood
hazard data for floodplain management and flood insurance purposes. This Flood Insurance Study (FIS) may
not contain all data available within the repository. It is advisable to contact the community repository for any
additional data. 
The Federal Emergency Management Agency (FEMA) may revise and republish part or all of this
Preliminary FIS report at any time. In addition, FEMA may revise part of this FIS report by the Letter of
Map Revision (LOMR) process, which does not involve republication or redistribution of the FIS report.
Therefore, users should consult community officials and check the Community Map Repository to obtain
the most current FIS components. 
Initial Countywide FIS Effective Date: September 25, 2009 
Revised Countywide FIS Date: March 16. 2016

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TABLE OF CONTENTS 
Page 
1.0 INTRODUCTION ........................................................................................................................... 1 
1.1 Purpose of Study ................................................................................................................. 1 
1.2 Authority and Acknowledgments ....................................................................................... 1 
1.3 Coordination ....................................................................................................................... 3 
2.0 AREA STUDIED ............................................................................................................................ 4 
2.1 Scope of Study .................................................................................................................... 4 
2.2 Community Description ...................................................................................................... 6 
2.3 Principal Flood Problems .................................................................................................... 8 
2.4 Flood Protection Measures ............................................................................................... 11 
3.0 ENGINEERING METHODS ........................................................................................................ 12 
3.1 Riverine Hydrologic Analyses .......................................................................................... 12 
3.2 Riverine Hydraulic Analyses ............................................................................................ 14 
3.3 Coastal Hydrologic Analyses ............................................................................................ 16 
3.4 Coastal Hydraulic Analyses .............................................................................................. 19 
3.5 Vertical Datum .................................................................................................................. 38 
4.0 FLOODPLAIN MANAGEMENT APPLICATIONS ................................................................... 39 
4.1 Floodplain Boundaries ...................................................................................................... 39 
4.2 Floodways ......................................................................................................................... 40 
5.0 INSURANCE APPLICATIONS ................................................................................................... 45 
6.0 FLOOD INSURANCE RATE MAP ............................................................................................. 46 
7.0 OTHER STUDIES ......................................................................................................................... 48 
8.0 LOCATION OF DATA ................................................................................................................. 48 
9.0 BIBLIOGRAPHY AND REFERENCES ...................................................................................... 49

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TABLE OF CONTENTS - continued 
Page 
FIGURES 
Figure 1 – Transect Schematic .................................................................................................................... 25 
Figure 2 – Transect Location Map .............................................................................................................. 34 
Figure 3 – Floodway Schematic ................................................................................................................. 42 
TABLES 
Table 1 – Initial, Intermediate, and Final CCO Meetings............................................................... 3 
Table 2 – Flooding Sources Studied by Detailed Methods............................................................. 4 
Table 3 – Flooding Sources Studied by Approximate Methods ..................................................... 5 
Table 4 – Letters of Map Change ................................................................................................... 5 
Table 5 – Summary of Discharges ................................................................................................ 14 
Table 6 – Manning’s “n” Values .................................................................................................. 16 
Table 7 – Summary of Pre-Countywide Stillwater Elevations ..................................................... 17 
Table 8 – Summary of Coastal Stillwater Elevations ................................................................... 18 
Table 9 – Summary of Revised Coastal Stillwater Elevations ..................................................... 18 
Table 10 – Summary of Transect Methodology ........................................................................... 19 
Table 11 – Transect Descriptions ................................................................................................ .27 
Table 12 – Transect Data .............................................................................................................. 35 
Table 13 – Floodway Data ............................................................................................................ 43 
Table 14 – Community Map History ............................................................................................ 47

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TABLE OF CONTENTS - continued 
EXHIBITS 
Exhibit 1 - Flood Profiles 
Charles River Panels 01P-05P 
Mill Creek Panel 06P 
Mother Brook Panels 07P-09P 
Muddy River Panels 10P-16P 
Neponset River Panels 17P-28P 
Stony Brook Panels 29P-34P 
Exhibit 2 - Flood Insurance Rate Map Index 
Flood Insurance Rate Map

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FLOOD INSURANCE STUDY 
SUFFOLK COUNTY (ALL JURISDICTIONS) 
1.0 INTRODUCTION 
1.1 Purpose of Study 
This Flood Insurance Study (FIS) revises and updates information on the existence and
severity of flood hazards in the geographic area of Suffolk County, including the Cities of
Boston, Chelsea, Revere and the Town of Winthrop; (referred to collectively herein as
Suffolk County), and aids in the administration of the National Flood Insurance Act of
1968 and the Flood Disaster Protection Act of 1973. This study has developed flood-risk
data for various areas of the community that will be used to establish actuarial flood
insurance rates and to assist the community in its efforts to promote sound floodplain
management. Minimum floodplain management requirements for participation in the
National Flood Insurance Program (NFIP) are set forth in the Code of Federal Regulations
at 44 CFR, 60.3. 
In some states or communities, floodplain management criteria or regulations may exist
that are more restrictive or comprehensive than the minimum Federal requirements. These
criteria take precedence over the minimum federal criteria for purposes of regulating
development in the floodplain, as set forth in the Code of Federal Regulations at 44 CFR,
60.3. In such cases, the more restrictive criteria take precedence and the state (or other
jurisdictional agency) will be able to explain them. 
1.2 Authority and Acknowledgments 
The sources of authority for this FIS report are the National Flood Insurance Act of 1968
and the Flood Disaster Protection Act of 1973. 
The September 25, 2009 FIS (Reference 1) was prepared to include the incorporated
communities within Suffolk County in a countywide format. Information on the authority
and acknowledgments for each jurisdiction included in the 2009 countywide FIS, as compiled
from their previously printed FIS reports, is shown below. 
Boston, City of: The hydrologic and hydraulic analyses for the November 2,
1990 study represent a revision of the original October 1, 1983
analyses prepared by Harris-Toups Associates for the Federal
Emergency Management Agency (FEMA) under Contract No.
H-4024. The work for the original 1983 study was completed
in November 1979. The hydrologic and hydraulic analyses for
this updated 1990 study were prepared by Dewberry & Davis
for FEMA under Contract No. EMW-85-C-2044. This work
was completed in December 1987. 
Chelsea, City of: The hydrologic and hydraulic analyses for the original
February 2, 1982 study were prepared by Anderson Nichols &
Co., Inc. for FEMA under Contract No. H-4524. This work
was completed in May 1980.

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Revere, City of: The hydrologic and hydraulic analyses for the original April
16, 1984, FIS report and the October 16, 1984, Revere FIRM
(hereinafter referred to as the 1984 Revere FIS), were prepared
by Stone & Webster Engineering Corporation for FEMA under
Contract No. H-4772 Modification No. 5. That work was
completed in April 1983. 
The hydrologic and hydraulic analyses for the August 20, 2002
revision were prepared by Roald Haestad, Inc. for FEMA
under Contract No. EMB-1999-CO-0564. This work was
completed in November 2000. 
Winthrop, Town of: The hydrologic and hydraulic analyses for the original and
revised February 15, 1984 FIS were prepared by Stone &
Webster Engineering Corporation for FEMA under Contract
No. H-4772. This work was completed in January 1983. 
For the 2009 countywide study, the 1- and 0.2-percent-annual-chance floodplain
boundaries for the Atlantic coastline in Suffolk County were redelineated using more up to
date topographic information, including MassGIS and LiDAR data, which meets the
accuracy standards for flood hazard mapping (https://www.mass.gov/mgis/ and
https://maps.csc.noaa.gov.TMC/). That work was performed by CDM for FEMA, under
Contract No. EME-2003-CO-0340, and by Ocean and Coastal Consultants, Inc. for CDM,
under Contract No. 2809-999-003-CS. No new detailed or approximate studies were
performed. 
The coastal wave height analysis for this coastal study was prepared by the Strategic
Alliance for Risk Reduction (STARR) for FEMA under Contract No. HSFEHQ-09-D-0370
and completed September 13, 2013. This new analysis resulted in revisions to the coastal
Special Flood Hazards Areas (SFHA) for all communities in Suffolk County. The far outer
islands in Boston Harbor (City of Boston) were not included in this analysis. 
STARR mapped the results of the September 13, 2013 analysis under Contract No.
HSFEHQ-09-D-0370 up to the November 13, 2013 Preliminary release of the Suffolk
County FIS. 
FEMA funded the Post Preliminary Processing of coastal analyses based on appeal under
Contract No. HSFEHQ-09-D-0370 and Task Order No.s HSFEHQ-10-J-0004 and
HSFE01-14-J-0015 . Under this contract, the hydrologic and hydraulic analyses in the
November 13, 2013 Preliminary FIS report were updated by STARR for FEMA for the
Belle Island Inlet, Boston Harbor, Dorchester Bay and the Pines, Chelsea, Charles, and
Neponset River flooding sources affecting the communities of Boston, Chelsea, Revere,
and Winthrop. That work was completed May 30, 2015. 
For the 2009 countywide study FIRM panels, base map information shown was derived
from digital orthophotography. Base map files were provided in digital form by
Massachusetts Geographic Information System (MassGIS). Ortho imagery was produced
at a scale of 1:5,000. Aerial photography is dated April 2005. The projection used in the
preparation of this map was Massachusetts State Plane mainland zone (FIPSZONE2001).
The horizontal datum was NAD 83, GRS80 spheroid (Reference 2).

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Base map information shown on the FIRM panels produced for this 2013 revision and post
preliminary appeal were derived from USGS High Resolution orthophotography dated
April 10 and April 18, 2008 produced at six inch and one foot resolution cells. The
horizontal datum used was North American Datum of 1983 (NAD 83) (Reference 3). 
Differences in datum, spheroid, projection or State Plane zones used in the production of
FIRMs for adjacent jurisdictions may result in slight positional differences in map features
across jurisdiction boundaries. These differences do not affect the accuracy of this FIRM. 
1.3 Coordination 
Consultation Coordination Officer’s (CCO) meetings may be held for each jurisdiction in this
countywide FIS. An initial CCO meeting is held typically with representatives of FEMA, the
community, and the study contractor to explain the nature and purpose of a FIS and to
identify the streams to be studied by detailed methods. An intermediate CCO meeting is held
typically with representatives of FEMA, the community, and the study contractor to discuss
interim concerns of the study. A final CCO meeting is held typically with representatives of
FEMA, the community, and the study contractor to review the results of the study. 
Prior to the initial 2009 countywide FIS, the dates of the initial, intermediate, and final
CCO meetings held for the incorporated communities within Suffolk County are shown in
Table 1, "Initial, Intermediate, and Final CCO Meetings." 
TABLE 1 – INITIAL, INTERMEDIATE, AND FINAL CCO MEETINGS 
Community Name Initial CCO Date 
Intermediate
CCO Date Final CCO Date 
City of Boston April 13, 1987 * April 11, 1989 
City of Chelsea May 13, 1977 July 27, 1980 July 22, 1981 
City of Revere January 4, 2000 * August 28, 2001 
Town of Winthrop April 13, 1978 December 13, 1979 September 26, 1983 
* Data not Available 
For the 2009 countywide FIS, no initial CCO meeting was held. The results of the study
were reviewed at the final CCO meetings held on December 17 th , 2008 and January 14 th ,
2009, and were attended by representatives of FEMA, Massachusetts Department of
Conservation and Recreation (DCR), CDM, Ocean & Coastal Consultants Inc. (OCC), and
Suffolk County communities. All problems raised at that meeting have been addressed in
this study. 
For the 2013 coastal study revision, outreach meetings were held on March 28 and 29,
2011. Letters were sent to inform the communities of the scope of the FIS, and to solicit
pertinent local information. Work map discussion meetings were held with the
communities on August 1 and 12, 2013, to discuss the initial results of the new coastal
flood hazard analysis. 
For this revised preliminary based on appeal, CCO meetings were held on January 21, 2014
and January 29, 2014 and were attended by representatives of FEMA Region I, STARR,

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and the Massachusetts NFIP Coordinator. 
2.0 AREA STUDIED 
2.1 Scope of Study 
This FIS report covers the geographic area of Suffolk County, MA including the
incorporated communities listed in Section 1.1. The areas studied by detailed methods were
selected with priority given to all known flood hazards and areas of projected development
or proposed construction. 
2009 Countywide Study: 
All or portions of the flooding sources listed in Table 2, “Flooding Sources Studied by
Detailed Methods,” were studied by detailed methods in the pre-countywide FISs. Limits
of detailed study are indicated on the Flood Profiles (Exhibit 1) and on the FIRM. 
TABLE 2 – FLOODING SOURCES STUDIED BY DETAILED METHODS 
Flooding Source Description 
Atlantic Ocean For the entire coastline within the Town of Winthrop 
Charles River From upstream of the Route 28 bridge in the City of Boston to the
City of Boston-Town of Dedham corporate limits 
Mill Creek From its confluence with the Chelsea River to approximately
5,400 feet upstream. 
Mother Brook From its confluence with Neponset River to the City of Boston-
Town of Dedham corporate limits. 
Muddy River From its confluence with Charles River to Willow Pond 
Neponset River From upstream of the dam at Lower Mills to the Boston-Dedham
corporate limits 
Stony Brook From upstream of the entrance to the Stony Brook culvert to
Turtle Pond in the City of Boston. 
Portions of the Muddy River within the detailed study limits are referred to locally as the
Back Bay Fens. Wherever referenced in this report, the name Muddy River shall be
assumed to include the area known as the Back Bay Fens. 
All or portions of numerous flooding sources in the county were studied by approximate
methods. Approximate analyses were used to study those areas having a low development
potential or minimal flood hazards. The scope and methods of study were proposed to, and
agreed upon, by FEMA and the individual communities within Suffolk County.

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All or portions of the flooding sources listed in Table 3, “Flooding Sources Studied by
Approximate Methods,” were studied by approximate methods in the pre-countywide FISs. 
TABLE 3 – FLOODING SOURCES STUDIED BY APPROXIMATE METHODS 
Flooding Source Community 
Chandler's Pond Boston 
Jamaica Pond Boston 
Chestnut Hill Reservoir Boston 
Muddy River including Back Bay Fens Boston 
Neponset River Boston 
Sawmill Brook Boston 
Stony Brook Boston 
Unnamed Ponding Area near Genoa Street Revere 
This FIS also incorporates the determinations of letters issued by FEMA resulting in map
changes (Letter of Map Revision [LOMR], Letter of Map Revision – based on Fill
[LOMR-F], and Letter of Map Amendment [LOMA]), as shown in Table 4, “Letters of
Map Change.” 
TABLE 4 – LETTERS OF MAP CHANGE 
Community Flooding Source(s)/Project Identifier Effective Date Type Case Number 
Boston, City of Massachusetts Bay/Boston Harbor 07/09/2004 LOMR 04-01-013P 
Boston, City of Dorchester Bay 12/05/2008 LOMR 08-01-1020P 
Revere, City of Broad Sound 09/20/2007 LOMR 07-01-0489P 
Detail studied streams that were not restudied as part of this revision may include a profile
baseline on the FIRM. The profile baselines for these streams were based on the best
available data at the time of their study and are depicted as they were on the previous
FIRMs. In some cases the transferred profile baseline may deviate significantly from the
channel or may be outside of the floodplain. 
2013 Coastal Study 
The coastal wave height analysis for this countywide coastal study and Post Preliminary
Processing of coastal analyses based on appeal, was prepared by STARR. This new
analysis resulted in revisions to the FIRM for the Cities of Boston, Chelsea, and Revere and
the Town of Winthrop. Based on the new updated analysis, the results of LOMR cases 05-
01-0110A, 10-01-0596P, 10-01-0786A, 10-01-1204A, and 10-01-1783A were superseded.

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2.2 Community Description 
Suffolk County is located on the seacoast of the Atlantic Ocean in eastern Massachusetts.
In Suffolk County there are four (4) incorporated communities. The Cities of Boston,
Chelsea, and Revere and the Town Winthrop. 
Suffolk County is bordered by the Atlantic Ocean on the east; by Essex County, including
the towns of Lynn and Saugus, to the north; by Middlesex County, including the towns of
Melrose, Malden, Everett, Somerville, Cambridge, Watertown and Newton, to the west;
and by Norfolk County, including the towns of Needham, Dedham, Canton, Milton and
Quincy, to the South. It is 44 miles from Providence, Rhode Island, 106 miles from
Portland, Maine, and 93 miles from Hartford, Connecticut. 
According to the U.S. Census, the population of Suffolk County was 722,023 in 2010,
689,807 in 2000 and 663,906 in 1990. The land area of Suffolk County consists of 120.19
square miles (Reference 4). 
Suffolk County is the hub of a larger metropolitan area, serving some 3.25 million people;
the sixth largest population center in the United States. 
The climate of Suffolk County is moderate and can be described as a continental climate.
Summers are warm and humid, while winters are cold, windy and snowy. The hottest
month is July, with an average high of 82 degrees Fahrenheit (ºF) and an average low of
66ºF. The coldest month is January, with an average high of 36F and an average low of
22ºF. The mean annual temperature is 50 degrees Fahrenheit (ºF). The temperature ranges
from an average of 29°F in January to an average of 72°F in July (Reference 5). The
average annual rainfall is 42 inches. The average annual snowfall is approximately 40.9
inches (Reference 6). There is no dry season and, on the average, no dry spell lasts more
than two weeks. From June to September, rainfall usually occurs in the form of showers or
thunderstorms, which produce heavy, sometimes excessive, amounts of rain. Throughout
the year, the heaviest gales are usually from the northeast or east and are more common and
severe during the winter. Though the coastal location on the North Atlantic moderates
temperatures in Suffolk County, it also makes the County very prone to Northeaster
weather systems, which can result in an abundance of snow and rain (Reference 7). 
Boston was originally a peninsula with great areas of salt marsh to the north, along the
banks of the Charles and Mystic Rivers, and at the mouth of the Neponset River to the
south. Large areas of filled land occur in the Back Bay, the West End, South Boston,
Dorchester, Charlestown and East Boston. In 1910, a dam on the Charles River at Leverett
Street was constructed to prevent tidal flooding of the lowlands, to cover unsightly tidal
flats at the mouth of the river, and to create an aesthetically pleasing recreational pool –
now known as the Charles River Basin. 
However, the creation of the basin accelerated growth along its banks, which in turn
resulted in the conversion of many former open spaces to developed and paved areas. This
change increased the speed and amount of runoff above the existing dam, making it
inadequate to carry the discharges predicted. The U.S. Army Corps of Engineers (USACE)
constructed a new dam at Warren Avenue to replace the 1910 dam at Leverett Street in
order to accommodate the increased run-off. The Warren Avenue bridge was removed
preconstruction of the Charles River Dam Local Protection Project that was initiated back

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in November, 1972. The project was completed in May 1978 and it situated the new dam
approximately 2,250 feet downstream of the old Charles River Dam. 
The land throughout the City of Boston is densely settled, except for limited areas in the
west. 
The City of Revere is also densely developed and attracts both permanent and transient
populations. Coastal development in Revere is a mixture of residential, commercial,
industrial, and recreational. Located along the eastern shore, from Point of Pines to Elliott
Circle, is Revere Beach, a popular Metropolitan District Commission recreational facility.
The beach experiences severe erosion problems. A breakwater is located at the southern
end of Revere Beach at Cherry Island Bar. 
Of the Town of Winthrop’s total land area, the majority of the land is classified as urban
land, Within urban land space, high density residential areas comprises more than half of
that land classification (Reference 8). The recreational lands consist primarily of the
beaches along the eastern shore of the town. Exposure of the beaches to the open coast has
caused severe erosion. To retard erosion, a 0.4-mile long breakwater was constructed 0.2
mile off of and parallel to Winthrop Beach. Coastal development is primarily residential
and recreational. Because Winthrop is long and narrow in shape, the entire town is within
the Massachusetts Coastal Zone. 
The coastline of the City of Chelsea is heavily developed with commercial and industrial
properties, predominately related to petroleum products and storage. The Mill Creek
watershed is heavily developed with commercial and residential properties. 
The topography of the County is generally level, with elevations ranging from sea level to
180 feet. Occasional hills composed of glacial till, rise as high as 300 feet. The tidal
shoreline along the Atlantic Ocean is 87.7 miles in length. Most of the county was formed
by glacial till; its coastline includes scattered coves, beaches, and rocky shoals. Located at
the northwest boundary of Winthrop is Belle Isle Marsh, a 250-acre salt marsh that is one
of the last remaining salt marshes in the Boston Harbor region. 
The Charles River has its headwaters in Echo Lake in Hopkinton. It flows generally
northeast, finally becoming the northern boundary of the City of Boston, before discharging
into Boston Harbor. It has a drainage area of approximately 300 square miles. Mother
Brook, beginning as a partial diversion of the Charles River in the Town of Dedham, flows
east through the Hyde Park section of Boston, discharging into the Neponset River. Flows
in Mother Brook are limited to approximately one-third that of the Charles River. Muddy
River rises out of Jamaica Pond and flows north, passing through highly-developed areas of
Boston and Brookline before discharging into the Back Bay Fens. The Fens then empty
into the Charles River Basin. The Neponset River originates in the Neponset Reservoir in
Foxborough. It flows generally northeast, becoming the southern boundary for the City of
Boston before discharging into Dorchester Bay. Stony Brook originates in Turtle Pond and
flows south through Stony Brook Reservation before entering the Stony Brook culvert. 
Boston Harbor is bordered by the Atlantic Ocean to the east and is protected on the north
by Winthrop Peninsula and to the south by Hull Peninsula. From north to south, Boston
Harbor is bounded by the Logan International Airport, East Boston, Charlestown, the
Mystic and Charles Rivers, the downtown area, South Boston, Dorchester, and the

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Neponset River. The harbor has a number of islands including Deer, Spectacle, Thompson,
Long and Gallops Islands. The entire coastline is densely developed, and much of the
waterfront is under redevelopment pressure. Much of the recent construction has involved
the downtown waterfront area, including condominiums, offices, parks and commercial
establishments. 
2.3 Principal Flood Problems 
Suffolk County is most vulnerable to riverine and coastal flooding from severe storms that
produce heavy rain, such as hurricanes, tropical storms and northeasters; and winter events
that can produce significant snowfall and heavy rain. Snowmelt and ice jams can also
create flood hazards. The Suffolk County coastline is heavily populated and susceptible to
coastal storms with high winds, causing coastal erosion and storm surge. 
Investigations into flooding within the corporate limits of Boston have revealed that there
has been severe flooding resulting in extensive damage, especially to the Charles River
Basin and the surrounding lowlands. The problem is caused primarily by the difference
between the established normal water level in the basin and the high tide in the harbor. In
the flood of August 1955, 12.5 inches of rain coupled with a peak high tide of 8.2 feet
resulted in raising the basin elevation to a record high of 6.90 feet. Over 1,750 acres,
mostly highly-developed Cambridge and Boston, lying along the 8.6-mile long basin were
subject to serious flooding. The 1955 hurricane, equivalent to a 1-percent-annual-chance
storm, resulted in flood damage along the lower Charles River amounting to 5.5 million
dollars. The same flood level in 1980 would have resulted in an estimated damage of 20
million dollars. In March 1968, 7.7 inches of rain combined with the spring thaw produced
the second highest basin levels of 4.5 feet, inundating many areas along Storrow Drive.
Although the peak discharge upstream was the same as the 1955 flood, the river peak did
not coincide with the tidal peaks as in the 1955 flood, and resulting damage was less
extensive. Flooding problems from the 1955 and 1968 storms also occurred along the
Neponset River in the Hyde Park area. Numerous private properties, automobiles and
roadways were damaged as a result of the storm. 
Flooding also occurs along the coastline of Boston and Chelsea and in the low-lying coastal
areas of Revere and Winthrop, greatly influenced by storm surge elevations of Boston
Harbor that result from severe storms. The most recent example of severe flooding was
during the northeaster of February 1978, which was comparable to a 1-percent-annual-
chance flood event. Elevations of flooding ranged from 8.6 to 10.1 feet, which caused one
to three feet of flooding in areas such as Rowes, India, Long, Commercial and Battery
Wharves. Low-level flooding occurred at a number of East Boston locations such as East
Boston Pier, the airport access road, and several parking lots on commercial piers. More
serious damage occurred as a result of wave action. The recorded flood elevation was 9.8
feet at the New Charles River Dam, 9.5 feet at the U.S.S. Constitution, and 9.5 feet at the
Commonwealth Pier gage. The 1978 northeaster caused significant damage in excess of
$15 million in the City of Revere. Other significant storms to cause flooding in Revere
include the storms of December 1909 and 1959 (a flood event that had approximately 0.6-
and 6.7-percent-annual-chance of occurring or being exceeded, respectively) and February
1972 (approximate recurrence of 4-percent-annual-chance). 
In Chelsea, severe flooding due to poor drainage frequently occurs near Mill Creek
upstream of U.S. Route 1. This area was not studied in detail because of its small drainage

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area. Minor flooding has been reported from residents near Mill Creek adjacent to Forbes
Park (formerly Forbes Industrial Park), though no structural damage or injuries have been
reported. 
The heavily developed areas of Point of Pines and Oak Island, in Revere, have suffered
severe damage from storms annually. The Point of Pines area is subject to coastal and
riverine flooding. The encroachment of development into the Saugus River - Pines River
Marsh has reduced storage capacity of the marsh and increased the flooding potential in the
area. The Beachmont area, which faces the ocean and backs up to Belle Isle Marsh,
experiences flooding as a result of storms and high tides. 
In Winthrop, the majority of storms cause damage only to low coastal roads, boats,
beaches, and seawalls. Occasionally, a major storm accompanied by strong onshore winds
results in high tides and wave activity that cause extensive property damage and erosion.
Some of the more significant storms in the Winthrop area include those of December 1909,
December 1959, February 1972, and February 1978. The storms had approximate
recurrence of 0.6-, 6.7-, 4-, and 1.1-percent annual chance, respectively. Harbors, marinas,
and residential and commercial developments were damaged by the storms. 
More than ten major flooding events have occurred in Massachusetts over the last 50 years.
Many of these have caused minimal-to-moderate damage to Suffolk County. Hurricane
Gloria in September 1985 arrived at low tide and resulted in storm surges less than 5 feet
above normal, minimizing damage to the coastline. Hurricane Bob in August 1991 passed
south of Suffolk County primarily affecting southeastern Massachusetts, Cape Cod and the
Islands. An unnamed coastal storm in October 1991 joined up with the remains of
Hurricane Grace and produced the third highest tide recording at the Boston gage. This
storm was labeled as the Perfect Storm by the National Weather Service. Winds measured
over 80 MPH and waves were over 30 feet in some parts of the Massachusetts coastline,
causing flooding and wind damage to several counties, including Suffolk (References 9 and
10). 
A coastal storm in December 1992 caused more than $12.6 million in damages to the
Massachusetts public infrastructure such as; roads, bridges, public facilities, and public
utilities. Suffolk County also saw flooding from severe storms in October 1996, June 1998,
March 2001, April 2004 and May 2006. The June 1998 storm was slow moving and
produced rainfall of 6 to 12 inches over much of eastern Massachusetts (Reference 10). 
In August 2011, Hurricane Irene, weakened to a tropical storm, flooded numerous roads in
the Greater Boston area, including Storrow Drive and Memorial Drive. More than 150
fallen trees blocked MBTA tracks, shutting down service temporarily. Boston’s strongest
wind gusts were 63 mph at 11:10 am (Reference 11). 
In March 2010, heavy rainfall of 6 to 10 inches fell over much of Southern New England
resulting in major flooding across eastern Massachusetts and Rhode Island, including the
Boston area (Reference 12). 
From December 2010 through February 2011, Southern New England, including Suffolk
County, saw a series of winter storms that led to record snowfall for the season. Boston
snowfall total was over 70 inches, more than 45 inches above average for the time of year.

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Heavy snow, combined with rain led to numerous flooding problems across the county,
roof collapses, and downed trees and utility lines (Reference 13). 
On October 29 and October 30, 2012, Hurricane Sandy, a hybrid storm with both tropical
and extra-tropical characteristics, brought high winds and coastal flooding to southern New
England, including Suffolk County. Sandy reached hurricane status over the southwest
Caribbean and headed north through the Bahamas where it interacted with a vigorous
weather system loving west to east across the United States, making landfall near Atlantic
City, NJ on October 29, 2012 as a category 1 hurricane based on the Saffir-Simpson
Hurricane Wind Scale. Sustained wind speeds of 41 mph and gusts to 62 mph were
reported by the Automated Surface Observing System at Logan International Airport in
East Boston. Seas built to between 20 and 25 feet just off the east coast with a storm surge
generally about 2.5 feet to 4.5 feet, peaking in between high tide cycles. Moderate coastal
flooding occurred within Suffolk County. In Revere, eighteen inches of water flooded Bell
Circle. In Boston, the intersection of Columbia Road and Quincy Street flooded and the
ramp for Morissey Boulevard was closed due to flooding. In Winthrop, rocks from the
seawall were pushed with the morning high tide onto Winthrop Shore Drive. Several other
coastal locations were flooded due to water coming over seawalls and numerous roads were
closed countywide due to flooding and down trees (Reference 12). 
The Blizzard of 2013 occurred on February 8th and 9th of that year, and produced
moderate to major coastal flooding, most notably during the time of the high tide Saturday
morning along the Massachusetts east coast. At the storm's height near the early morning
low tide, the storm surge reached 3 to 4 feet along much of the Massachusetts east coast
from Boston south. At the time of the mid-morning high tide, the winds had shifted from
northeast to north and the surge had dropped to 1.5 to 2.5 feet for most Massachusetts east
coast locations. However, this was an astronomically high tide given the nearness to the
time of the new moon, and waves to 30 feet had built just 15 miles off the coast. In Revere,
Pines Road was inundated by ocean water. Winthrop Parkway experienced splashover with
ocean debris in the road. In Winthrop, Shirley Street, Tafts Avenue, and Winthrop Shore
Drive were flooded with up to two feet of water. Yirrell Beach at Mugford Street was
flooded with water flowing around and under buildings (Reference 12). 
On March 7th and 8th of 2013, a storm brought heavy snow and significant coastal
flooding to the area. The Massachusetts east coast was hit by widespread moderate and
pockets of major coastal flooding for two high tide cycles and beach erosion for at least 5
high tide cycles. In Boston, Morrissey Boulevard was closed in both directions from the
University of Massachusetts Boston campus to Freeport Street. Exit 14 from Interstate 93
northbound was closed due to the flooding on Morrissey Boulevard. In Winthrop, six roads
were flooded up to the curbs with splashover reaching the front steps of houses. Winthrop
Shore Drive was flooded with water and overwash material. In Revere, Winthrop Parkway
was flooded with water and debris (Reference 12). 
Hurricanes Irene and Sandy, and the snowstorms of early 2013 that impacted the Suffolk
County shoreline, occurred while the coastal flood hazard study completed in 2013 was in
progress. Consequently, those events were not included in this study.

11 
2.4 Flood Protection Measures 
The primary flood problem within the City of Boston is in the area along the Charles River
Basin. In 1910, a dam on the Charles River at Leverett Street was constructed, but with
newly developed and paved areas, the dam became inadequate to carry the discharge
predicted. The USACE replaced the Leverett Street dam with the new and improved
Warren Avenue Dam to accommodate the growth of metropolitan Boston. 
In the early 1970’s the Charles River Dam Local Protection Project was initiated, thus
removing the Warren Avenue Dam and replacing it with the current Charles River Dam,
which provides flood protection to 2,440 acres of urban property along the banks of the
Charles River. The project consisted of the construction of an earthfill and concrete dam
with stone slope protection stretching between Boston and Charlestown. The dam is 400
feet long with an elevation of 12.5 feet above mean sea level. The connecting pumping
station is 190 feet long and 122 feet high and contains six pumps. There are three
navigation locks for commercial and recreational vessels. Two of the locks, for small
recreational craft, each measure 200 feet long, 22 feet wide, and eight feet deep. The third
lock, 40 feet wide, 300 feet long, and 17 feet deep, accommodates commercial vessels,
large recreational boats, and the overflow of small craft during peak days. 
The Baker Dam is located within the boundaries of the Dorchester/Milton Lower Mills
Industrial Complex along the Neponset River and was originally built in the mid-1960’s for
the purpose of privately owned industrial mills. In the wake of hurricane Diane, the MDC
took over the Lower Neponset, including its dams. In 1962, the MDC flood control project
began, covering a stretch of the Neponset River from the freshwater limit to upstream of
the Neponset Valley Parkway and CONRAIL crossing. The Baker dam was rebuilt in the
same general style as the original, except the top of the dam was lowered by three or more
feet to improve its discharge capacity during storm events. The average water level at
Baker was also reduced by about three feet, thus providing better flood protection. This
project also included channel straightening and channel and bridge modifications. These
measures, in conjunction with proper operation of the floodgates on the dams, will
effectively contain the 1- and 0.2-percent-annual-chance floods within the channel banks.
Much of the land bordering riverine areas has been designated as parkland, thereby limiting
development in floodplain areas. Flood control measures along the harbor are scattered, but
include such measures as seawalls and rip-rapping. 
At the time of this study, the USACE was conducting a feasibility study regarding the
removal of the Baker Dam for Neponset River restoration purposes
(http://www.neponset.org/projects.htm). It was recommended by the Massachusetts
Riverways Program’s Technical Advisory Committee to remove this dam, as it is no longer
serving the purpose for which it was built. 
In Chelsea, a tide gate exists on Mill Creek at the culvert under the east ramp of the U.S.
Route 1 interchange with State Route 16. In 1979, the state locked the gate in an open
position to help alleviate the occasional flooding problems upstream. There are no other
flood protection structures or measures in Chelsea. 
In Revere and Winthrop, the MDC provides concrete seawalls and stone revetments to
protect coastal highways. Other protective structures are generally built and maintained by
the local municipality and private property owners to satisfy individual requirements within

12 
their financial capabilities. These structures include such backshore protection as timber
and steel sheet piles, bulkheads, stone revetments, concrete seawalls, and pre-cast concrete
units (Reference 14). Limited financial resources sometimes result in less than adequate
protection. 
3.0 ENGINEERING METHODS 
For the flooding sources studied by detailed methods in the community, standard hydrologic and
hydraulic study methods were used to determine the flood-hazard data required for this study.
Flood events of a magnitude that is expected to be equaled or exceeded once on the average during
any 10-, 50-, 100-, or 500-year period (recurrence interval) have been selected as having special
significance for floodplain management and for flood insurance rates. These events, commonly
termed the 10-, 50-, 100-, and 500-year floods, have a 10-, 2-, 1-, and 0.2-percent chance,
respectively, of being equaled or exceeded during any year. Although the recurrence interval
represents the long-term, average period between floods of a specific magnitude, rare floods could
occur at short intervals or even within the same year. The risk of experiencing a rare flood
increases when periods greater than 1 year are considered. For example, the risk of having a flood
that equals or exceeds the 1-percent-annual-chance flood in any 50-year period is approximately
40 percent (4 in 10); for any 90-year period, the risk increases to approximately 60 percent
(6 in 10). The analyses reported herein reflect flooding potentials based on conditions existing in
the community at the time of completion of this study. Maps and flood elevations will be amended
periodically to reflect future changes. 
3.1 Riverine Hydrologic Analyses 
Hydrologic analyses were carried out to establish peak discharge-frequency relationships
for floods of the selected recurrence intervals for each flooding source studied by detailed
methods affecting the county 
For the 2009 countywide FIS, no new Hydrologic Analyses were conducted. For each
community within Suffolk County, the hydrologic analyses described in their previous FIS
reports have been compiled and summarized below. 
Peak discharge estimates for the upper reach of the Charles River for the 10-, 2-, 1-, and
0.2-percent-annual-chance floods were based on a log-Pearson Type III analysis of the
USGS gage data from the gages (no. 01104500 and no. 01103500) located at Waltham and
Charles River Village, respectively (Reference 15). 
As a result of the 8,400 cfs pumping capacity of the New Charles River Dam, peak
discharge estimates for the Charles River Basin for floods of the selected recurrence
intervals were not determined. Peak inflow hydrographs developed by the USACE were
used to determine pumping curves so as to maintain basin levels near the normal elevation
of 2.5 feet during the 10-, 2-, and 1-percent-annual-chance floods (Reference 16). Damage
resulting from floodwaters along the Charles River Basin begins at an elevation of 3.8 feet.
During a 1-percent-annual-chance event, the pumping station will control basin levels to an
elevation of 3.5 feet, which is below the level at which damage will occur. For the 0.2-
percent-annual-chance event, basin levels will be held to an elevation of 5.2 feet and
minimal damage will result. This assumes, however, that the basin will not be drawn down
and that sluicing will not be possible.

13 
Mother Brook acts as a diversion channel from the Charles River to the Neponset River.
The discharges for Mother Brook are limited by law to approximately one-third of the peak
discharge for the Charles River (Reference 17). 
Peak discharge estimates for the Muddy River and Back Bay Fens for floods of the selected
recurrence intervals were not calculated, as the Muddy River and Back Bay Fens act as a
reservoir during periods of great runoff. For this reason, hydrologic analyses were
conducted to establish peak volume rather than peak discharge-frequency data. Flood
volume data was developed by the USACE using unit hydrographs and rainfall-frequency
analyses (References 16 and 18). This data was checked for reasonableness and
incorporated into this study. 
Peak discharge-frequency estimates of the Neponset River for the 10-, 2-, 1-, and 0.2-
percent-annual-chance floods were determined for the FIS for the Town of Milton in
Norfolk County and were incorporated into this study (Reference 19). 
Peak discharge-frequency estimates for Stony Brook for the 10-, 2-, and 1-percent-annual-
chance floods were computed using the SCS peak discharge determination methods for
small watersheds (Reference 17). The 0.2-percent-annual-chance peak discharge estimate
was determined by linear extrapolation of a log-Pearson Type III probability curve on the
other floods. 
Two high-water marks in Chelsea were obtained from the USGS. The elevation on Mill
Creek upstream of Broadway Avenue in Chelsea is 8.8, and the elevation on the Chelsea
River at the MDC Sewerage Division Maintenance Yard is 9.5 (Reference 20). 
The Mill Creek discharges in Chelsea and Revere were obtained from a drainage study of
Mill Creek prepared for the Massachusetts Department of Public Works in 1975 (Reference
21). The analysis incorporated rainfall simulation modeling, simulation of runoff, and the
drainage system response to rainfall through the use of a computerized catchments model.
The 0.2-percent-annual-chance discharge was extrapolated from the three calculated flow
values. 
Peak discharge-drainage area relationships for the flooding sources studied by detailed
methods are shown in Table 5, “Summary of Discharges.”

14 
TABLE 5 – SUMMARY OF DISCHARGES 
PEAK DISCHARGES (CUBIC FEET PER SECOND) 
FLOODING SOURCE
AND LOCATION 
DRAINAGE AREA
(SQUARE MILES) 
10-PERCENT
ANNUAL
CHANCE 
2-PERCENT
ANNUAL
CHANCE 
1-PERCENT
ANNUAL
CHANCE 
0.2-PERCENT
ANNUAL
CHANCE 
CHARLES RIVER 
At upstream Boston-
Dedham corporate
limits 227 2,125 3,102 3,578 4,850 
MILL CREEK 
At confluence with
Chelsea River 1.3 600 1,690 2,300 4,790 
MOTHER BROOK 
At City of Boston
corporate limits 2.4 740 1,210 1,470 2,250 
NEPONSET RIVER 
At dam at Lower Mills
in the City of Boston 98 2,450 3,410 3,730 4,750 
STONY BROOK 
At Stony Brook culvert
in the City of Boston 13 90 150 200 286 
3.2 Riverine Hydraulic Analyses 
Analyses of the hydraulic characteristics of flooding from the sources studied were carried
out to provide estimates of the elevations of floods of the selected recurrence intervals.
Users should be aware that flood elevations shown on the FIRM [Flood Insurance Rate
Map (FIRM)] represent rounded whole-foot elevations and may not exactly reflect the
elevations shown on the Flood Profiles or in the Floodway Data tables in the FIS report.
Flood elevations shown on the FIRM are primarily intended for flood insurance rating
purposes. For construction and/or floodplain management purposes, users are cautioned to
use the flood elevation data presented in this FIS in conjunction with the data shown on the
FIRM. 
Cross sections were field surveyed and located at close intervals above and below bridges
and culverts in order to compute the significant backwater effects of these structures. All
bridges, dams, and culverts in the county were field surveyed to obtain elevation data and
structural geometry. In long reaches between structures, appropriate valley sections were
also surveyed.

15 
Locations of selected cross sections used in the hydraulic analyses are shown on the Flood
Profiles (Exhibit 1). For stream segments for which a floodway was computed
(Section 4.2), selected cross-section locations are also shown on the FIRM. 
The hydraulic analyses for this study were based on unobstructed flow. The flood
elevations shown on the Flood Profiles (Exhibit 1) are thus considered valid only if
hydraulic structures remain unobstructed, operate properly, and do not fail. 
For the 2009 countywide FIS, no new hydraulic analyses were conducted. For each
community within Suffolk County that has a previously printed FIS report, the hydraulic
analyses described in those reports have been compiled and are summarized below. 
In Boston, overbank extensions of field-surveyed channel cross sections, and additional
sections needed for hydraulic continuity were taken from topographic maps at a scale of
1:1,200 with a 5 foot contour interval (Reference 22). Present culvert conditions were used
and recent modifications were taken into consideration in the use of flood marks. 
The overbank portions of the cross-section data for Mill Creek were obtained from
topographic maps prepared by photogrammetric methods (Reference 23). The below-water
sections were obtained by field measurement. All bridges and culverts were field surveyed
to obtain elevation data and structural geometry. 
Water-surface elevations for Stony Brook, Mill Creek, Mother Brook, Neponset River, and
the upper reach of the Charles River were developed using the HEC-2 computer program
developed by the USACE (Reference 24). Starting water-surface elevations for Mill Creek
were based on mean high-water elevations. The storm surge elevations from the coastline
were superimposed on the profile to the location on Mill Creek where backwater flooding
from the coast no longer exists. Starting water-surface elevations for Stony Brook were
taken from a rating curve developed at the entrance to the Stony Brook culvert. 
At one location on Mill Creek, the analysis indicates that the flow would be supercritical.
Because of the inherent instability of supercritical flow, critical depth was assumed at this
location when establishing the profile elevations for this study. 
Water-surface elevations for floods of the selected recurrence intervals along the Neponset
River were obtained from a previously published report by Anderson-Nichols Co. and the
FIS for the Town of Milton in Norfolk County (References 19 and 25). They were checked
for reasonableness and incorporated into this study. 
For the Charles River Basin, elevations were developed using inflow hydrographs in
respect to the pumping capacity of the New Charles River Dam (References 16 and 26).
Elevations along the Muddy River were developed using the "modified puls" method of
reservoir routing in conjunction with the discharge capacity of the Charles River Basin
(References 16, 18, 26 and 27). Elevations for the floods for the Back Bay Fens, the Muddy
River and the Charles River Basin were developed by the USACE in their detailed analysis
of the Charles River Basin (References 16 and 18). 
In some locations, such as the Boston Harbor shoreline within Winthrop, water levels were
computed by correlating synthetically-produced water levels with elevations obtained
during historic floods (Reference 28). Historic flood damage information was also used to

16 
ensure reasonable delineation of flood-prone areas along the Revere and Winthrop
shoreline (Reference 29). 
The City of Revere has no qualifying bench marks within its corporate limits. 
Roughness factors (Manning's "n") used in the hydraulic computations were estimated
based on field inspection of flood plain areas. The channel "n" and overbank "n” values for
the streams studied by detailed methods are shown in Table 6, “Manning’s “n” Values”: 
TABLE 6 – MANNING’S “n” VALUES 
FLOODING SOURCE CHANNEL ”n” OVERBANK “n” 
Charles River 0.025-0.035 0.065 
Mill Creek 0.040 0.060-0.085 
Mother River 0.015-0.100 0.100 
Neponset River 0.035 0.060 
Stony Brook 0.020-0.050 0.100 
3.3 Coastal Hydrologic Analyses 
In Suffolk County, for the coastal areas within the limits of tidal inundation, water level
fluctuations above astronomical tide levels are caused primarily by the passage of
hurricanes and winter storms known as northeasters. Of these, the northeasters produce the
more frequent and severe storm tides. 
Extreme water levels along the shoreline are caused by the combination of storm surges
and high astronomical tides. Astronomical tide levels are extremely important in the
determination of total water levels as they have a mean range of 8.7 feet and a spring range
of more than 11.2 feet (Reference 1). These ranges are considerably larger than the
expected storm surges, thus making the phasing of the astronomical tide critical to the
determination of total water levels. 
Storm surges in the Boston area are caused mainly by onshore winds, wave setup and low
barometric pressures that cause a rise in the water-surface elevation. As discussed above,
these water level fluctuations are due primarily to the passage of hurricanes and
northeasters through the area. The dominant surge-producing storm in the Boston area, as
in most of the New England regions, is the northeaster. These storms are typically less
intense than hurricanes, but they occur more frequently and are larger and slower-moving.
Thus, they have a significantly greater probability of combining with a high astronomical
tide causing an extreme high-water level. Hurricanes in the New England region are
considerably weaker than the very destructive storms found in the Gulf of Mexico and off
the southeastern coast of the United States. These factors, along with the relatively narrow
continental shelf off Boston, combine to reduce the effect of the hurricanes on the tide
levels at the coast.

17 
Revised coastal analyses were performed for the open water flooding sources for Belle
Island Inlet, Boston Harbor, Dorchester Bay and the Pines, Chelsea, Charles, and Neponset
River flooding sources affecting the communities of Boston, Chelsea, Revere, and
Winthrop. A description of these revised analyses is presented in the countywide coastal
analyses sections below. 
Coastal Stillwater elevations presented in the pre-countywide FISs that have not been
superseded by this coastal study update have been compiled and are summarized below. 
Pre-countywide Analyses 
Stillwater elevations for the Charles River Basin upstream of the New Charles River Dam
were obtained from a 1979 USACE report (Reference 30). The 2013 coastal study extends
only as far as the Route 28 bridge over the Charles River between Boston and Cambridge,
therefore the pre-countywide analysis of the Charles River remains in effect upstream of
that point. 
The pre-countywide stillwater elevations have been determined for the 10-, 2-, 1-, and 0.2-
percent-annual-chance floods for the flooding sources studied by detailed methods and are
summarized in Table 7, “Summary of Pre-countywide Stillwater Elevations.” 
TABLE 7 – SUMMARY OF PRE-COUNTYWIDE STILLWATER ELEVATIONS 
ELEVATION (NAVD 88) 1 
FLOODING SOURCE
AND LOCATION 
10-PERCENT-
ANNUAL-
CHANCE 
2-PERCENT-
ANNUAL-
CHANCE 
1-PERCENT-
ANNUAL-
CHANCE 
0.2-PERCENT-
ANNUAL-
CHANCE 
CHARLES RIVER BASIN 
Immediately upstream of
Route 28 Bridge 3.0 3.2 3.5 5.2 
1 North American Vertical Datum of 1988 (NAVD 88) 
2013 Coastal Study 
The stillwater elevation is the elevation of the water due to the effects of the astronomic
tides and storm surge on the water surface. Hydrologic analyses carried out to establish the
peak discharge-frequency relationships for the Belle Island Inlet, Boston Harbor,
Dorchester Bay and the Pines, Chelsea, Charles, and Neponset River flooding sources
affecting the communities of Boston, Chelsea, Revere, and Winthrop serve as a basis of
coastal hydraulic analyses using detailed methods in accordance with Appendix D of the
“Guidance for Coastal Flooding Analyses and Mapping,” of the April 2003 FEMA
“Guidelines and Specifications for Flood Hazard Mapping Partners” (Reference 31). 
For this study, the 10-, 2-, 1-, and 0.2-percent-annual-chance floods for the nearest gages to
Suffolk County on the Belle Island Inlet, Boston Harbor, Dorchester Bay and the Pines,
Chelsea, Charles, and Neponset River were obtained from the “Regional Frequency
Analyses using L-Moments” memorandum developed by STARR (Reference 32) for areas
subject to coastal flooding. There is one gage located within Suffolk County. Stillwater

18 
elevations at the nearest two gages (USACE-NED gage at New Bedford; and NOAA gage
8419870 at Seavey Island) were linearly interpolated to all coastal transects throughout the
county for use in the coastal hydraulic analyses. Table 8, “Summary of Countywide
Stillwater Elevations” contains the stillwater elevations determined at the Boston tide gage
station within Suffolk County. 
TABLE 8 – SUMMARY OF COASTAL STILLWATER ELEVATIONS 
ELEVATION (NAVD 88) 1 
FLOODING SOURCE 
AND LOCATION 
10-
PERCENT-
ANNUAL-
CHANCE 
2- 
PERCENT-
ANNUAL-
CHANCE 
1- 
PERCENT-
ANNUAL-
CHANCE 
0.2- 
PERCENT-
ANNUAL-
CHANCE 
Boston, MA tide gage station 8443970
(42˚21.2’ N, 71˚3.2’ W) 8.45 9.51 10.04 11.46 
11 North American Vertical Datum of 1988 (NAVD 88) 
During the Appeal period for Suffolk County, the stillwater elevations were revised using
an independent frequency analysis performed on the Boston Harbor tide gage data recorded
from 1921 to 2007. Annual maxima were identified, corrected to current MSL using the
most recent sea level trend, and fit to a Pearson Type III distribution. A summary of the
stillwater elevations developed for the appeal are provided in Table 9, “Summary of
Revised Coastal Stillwater Elevations.” 
TABLE 9 – SUMMARY OF REVISED COASTAL STILLWATER ELEVATIONS 
ELEVATION (NAVD 88) 1 
FLOODING SOURCE 
AND LOCATION 
10-
PERCENT-
ANNUAL-
CHANCE 
2- 
PERCENT-
ANNUAL-
CHANCE 
1- 
PERCENT-
ANNUAL-
CHANCE 
0.2- 
PERCENT-
ANNUAL-
CHANCE 
Atlantic Ocean 
Entire Shoreline within the
City of Revere * * 9.2 10.0 
At Broad Sound in the Town
of Winthrop * * 9.1 9.9 
Belle Isle Inlet 
Entire Shoreline * * 8.8 9.6 
Boston Harbor 
East of Logan Airport * * 8.8 9.6 
East of Governor’s Island * * 9.1 9.6 
Northeast of Spectacle Island * * 9.2 10.1 
Southeast of Castle Island * * 9.3 10.1 
At Long Island * * 9.3 10.2 
East of Thompson Island * * 9.4 10.3 
1 North American Vertical Datum of 1988 (NAVD 88) 
*Data not available

19 
TABLE 9 – SUMMARY OF REVISED COASTAL STILLWATER ELEVATIONS - continued 
ELEVATION (NAVD 88) 1 
FLOODING SOURCE 
AND LOCATION 
10-
PERCENT-
ANNUAL-
CHANCE 
2- 
PERCENT-
ANNUAL-
CHANCE 
1- 
PERCENT-
ANNUAL-
CHANCE 
0.2- 
PERCENT-
ANNUAL-
CHANCE 
Boston Inner Harbor 
Entire shoreline in the City of
Boston * * 9.4 10.2 
Dorchester Bay 
At Old Harbor * * 9.7 10.5 
West of Thompson Island * * 9.9 10.7 
At Neponset River * * 10.6 11.4 
Massachusetts Bay 
At Deer and Lovell Islands * * 9.2 10.1 
Mystic River 
Immediately upstream of
Mystic River Bridge * * 9.5 * 
1 North American Vertical Datum of 1988 (NAVD 88) 
*Data not available 
3.4 Coastal Hydraulic Analyses 
The hydraulic methods described in this section are those used for the 2013 coastal study. 
As a result of incorporating appeals received during the study, there are different coastal
hydraulic methods used based upon the source of the studied transect. Table 10, “Summary
of Transect Methodology” contains the wave climatology and wave setup information used
on each transect along with the study source. 
TABLE 10 – SUMMARY OF TRANSECT METHODOLOGY 
TRANSECT 
1- 
PERCENT-
ANNUAL-
CHANCE
STILLWATER 1 
SIGNIFICANT
WAVE
HEIGHT 1 
PEAK
PERIOD 
HOW
DETERMINED 
WAVE
SETUP 
HOW
DETERMINED 
1 9.2 2.3 12.5 SWAN 2D 0.46 SWAN 1D 
2 9.2 5.8 12.5 SWAN 2D 0.94 SWAN 1D 
3 9.2 21.22 12.5 SWAN 2D 1.76 SWAN 1D 
4 9.2 21.22 12.5 SWAN 2D 1.76 SWAN 1D 
5 9.2 21.22 12.5 SWAN 2D 1.86 SWAN 1D 
6 9.2 21.22 12.5 SWAN 2D 1.9 SWAN 1D 
7 9.8 21.22 12.5 STWAVE 3.12 DIM 
1 North American Vertical Datum of 1988 (NAVD 88)

20 
TABLE 10 – SUMMARY OF TRANSECT METHODOLOGY - continued 
TRANSECT 
1- 
PERCENT-
ANNUAL-
CHANCE
STILLWATER 1 
SIGNIFICANT
WAVE
HEIGHT 1 
PEAK
PERIOD 
HOW
DETERMINED 
WAVE
SETUP 
HOW
DETERMINED 
8 9.2 21.22 12.5 SWAN 2D 2 SWAN 1D 
9 9.1 23.09 12.5 SWAN 2D 2.67 SWAN 1D 
10 9.7 23.09 12.5 STWAVE 4.44 DIM 
11 9.7 23.09 12.5 STWAVE 4.5 DIM 
12 9.1 23.09 12.5 SWAN 2D 2.3 SWAN 1D 
13 9.1 23.09 12.5 SWAN 2D 2.45 SWAN 1D 
14 9.7 23.09 12.5 STWAVE 3.96 DIM 
15 9.1 23.09 12.5 SWAN 2D 2.4 SWAN 1D 
16 9.8 23.09 12.5 STWAVE 3.62 DIM 
17 8.8 2.3 5.6 SWAN 2D 0.03 SWAN 1D 
18 9.7 2.83 12.5 STWAVE 1.17 DIM 
19 9.4 2.58 5.17 SWAN 2D 0.04 SWAN 1D 
20 9.4 1.3 2.1 ACES 0.04 SWAN 1D 
21 8.8 0.93 1.77 ACES 0.32 SWAN 1D 
22 9.5 1.53 2.22 ACES 0.07 SWAN 1D 
23 9.4 0.85 5.17 SWAN 2D 0.18 SWAN 1D 
24 9.4 2.58 5.17 SWAN 2D 0.04 SWAN 1D 
25 9.4 2.58 5.17 SWAN 2D 0.08 SWAN 1D 
26 9.4 5.47 5.17 SWAN 2D 0.72 SWAN 1D 
27 9.9 15.62 12.5 STWAVE 3.48 DIM 
28 9.7 3.85 4.15 SWAN 2D 0.41 SWAN 1D 
29 9.7 3.85 4.15 SWAN 2D 0.37 SWAN 1D 
30 9.9 3.85 4.15 SWAN 2D 0.59 SWAN 1D 
31 9.9 3.7 3.72 SWAN 2D 0.36 SWAN 1D 
32 10.6 3.7 3.72 SWAN 2D 0.19 SWAN 1D 
33 10 15.62 12.5 STWAVE 1.93 DIM 
34 9.8 15.62 12.5 STWAVE 3.8 DIM 
35 9.9 15.62 12.5 STWAVE 3.83 DIM 
36 9.8 21.73 12.5 STWAVE 2.93 DIM 
37 9.8 21.73 12.5 STWAVE 4.62 DIM 
1 North American Vertical Datum of 1988 (NAVD 88) 
Wave Climatology 
STWAVE 
The energy-based significant wave height (Hmo) and peak wave period (Tp) are used as
inputs to wave setup and wave runup calculations and were calculated using the Steady-
State Spectral Wave Model (STWAVE). STWAVE is a phased-averaged spectral wave

21 
model that simulates depth-induced wave refraction and shoaling, depth-and steepness-
induced wave breaking, diffraction, wind-wave growth, and wave-wave interaction and
white capping that redistribute and dissipate energy in a growing wave field. The model
accepts a spectral form of the wave as an input condition and provides Hmo and Tp results
over the gridded model domain. 
STARR team developed STWAVE models for the entire coastline of Suffolk County, and
the results were obtained from the model for the coastal flooding analysis in the Cities of
Boston, Chelsea, Revere, and the Town of Winthrop. 
Offshore (deepwater) wave heights, wave setup, and wave runup for each transect were
calculated using Mathcad sheets developed by STARR to apply methodologies from the
USACE’s Coastal Engineering Manual (Reference 33) and FEMA Guidelines and
Specifications (Reference 34). Methodologies for each type of calculation are discussed in
more detail below. Results from the Mathcad calculations performed for each transect were
compiled in a summary spreadsheet. 
SWAN 
SWAN is a third-generation wave model, approved by FEMA, for obtaining realistic
estimates of wave parameters in coastal areas from given wind, bottom, and current
conditions. SWAN includes wave generation, dissipation, non-linear interactions, and
transformations. It also includes bottom friction, currents, shoaling, refraction, diffraction,
depth induced breaking, and wave setup. SWAN represents a model based approach that
accounts for the physics of the waves, including the process of wave setup. 
The SWAN 2D simulations were run using the same model domains, bathymetric grids,
wind, and input deepwater wave conditions that were utilized during the STWAVE
modeling for Suffolk County. Data available from the US Army Corps of Engineers
(USACE) Wave Information Studies (WIS) were used to confirm the deepwater wave
conditions used to drive the STWAVE model. The WIS database contains 20 years of
wave hindcast data from 1979 to 1999 at locations along the Atlantic, Gulf of Mexico, and
Pacific US coastlines. The closest WIS station to Boston Harbor is Sta. 63053, located near
the southeast corner of the coarse grid model domain. Extremal analyses published by the
USACE on data from Sta. 63053 indicate a 100-year wave height of 9.35 meters (30.66 ft). 
Results from the SWAN 2D simulation of 100-year wave conditions were used to generate
significant wave conditions required for input at each transect in FEMA’s CHAMP
program. FEMA followed the same steps in using results from their STWAVE model to
generate significant wave conditions needed for CHAMP. However, FEMA’s criteria used
to select representative wave conditions from the model output (as described above) varied
from those used for transects evaluated in the appeals. The SWAN model also provides a
more robust approach for producing wind-generated waves, in addition to the wave
transformations. This is particularly important for complex shorelines and sheltered
regions like Boston Harbor where the ocean swell waves may eventually have less energy
than the local wind generated waves. As such, SWAN generally produces higher wave
heights in areas where the wind-generated components of the wave field become more
dominant.

22 
ACES 
For the more sheltered transects added during the appeal period at SF-20, SF-21, and SF-
22; the Automated Coastal Engineering System (ACES) software available through the
Coastal Engineering and Design Analysis System (CEDAS, Version 4.0) was utilized to
generate the wave conditions needed for CHAMP and the SWAN 1-D modeling of wave
setup. At these locations, it is expected that the wave conditions will be solely wind
generated waves from storm winds. The geometry of the shoreline and landforms that
surround the transects were defined by establishing a series of radial fetches at 10 degree
intervals. The fetch bands were used in the Wave Prediction – Wind Adjustment and Wave
Growth (restricted fetch) module of ACES to define the distance and depth over water that
storm winds can generate local waves. A wind speed of 25.7 meters/sec (50 knots) taken
from the FEMA FIS for Suffolk County was used to simulate the 100-year storm condition. 
Overland Wave Propagation 
Overland wave heights were calculated for restricted and unrestricted fetch settings using
the Wave Height Analysis for Flood Insurance Studies (WHAFIS), Version 4.0 (Reference
35), within the Coastal Hazard Analysis for Mapping Program (CHAMP) (Reference 36),
following the methodology described in the FEMA Guidelines and Specifications for each
coastal transect. 
The fundamental analysis of overland wave effects for an FIS is provided by FEMA’s
Wave Height Analysis For Flood Insurance Studies computer program, WHAFIS 4.0, a
computer program that uses representative transects to compute wave crest elevations in a
given study area. Topographic, vegetative, and cultural features are identified along each
specified transect landward of the shoreline. WHAFIS uses this and other input information
to calculate wave heights, wave crest elevations, flood insurance risk zone designations,
and flood zone boundaries along the transects. 
The original basis for the WHAFIS model was the 1977 National Academy of Sciences
(NAS) report “Methodology for Calculating Wave Action Effects Associated with Storm
Surges” (Reference 39). The NAS methodology accounted for varying fetch lengths,
barriers to wave transmission, and the regeneration of waves over flooded land areas. Since
the incorporation of the NAS methodology into the initial version of WHAFIS, periodic
upgrades have been made to WHAFIS to incorporate improved or additional wave
considerations. 
WHAFIS 4.0 was applied using CHAMP to calculate overland wave height propagation
and establish base flood elevations. For profiles with vertical structures or revetments, a
failed structure analysis was performed and a new profile of the failed structure was
generated and analyzed. 
The general working procedure for the transects included eight steps: 1) laying out
transects; 2) determining off-shore significant wave heights and corresponding wave
periods from STWAVE outputs; 3) performing the off-shore engineering analysis; 4)
preparing WHAFIS input data and populating the CHAMP database; 5) performing erosion
analysis for erodible transects without a coastal structure; 6) performing WHAFIS
modeling runs on eroded transects and transects with both intact and failed structures, as
applicable; 7) performing wave runup analysis on intact and failed structures; and 8)
identifying primary frontal dunes.

23 
Coastal engineering analysis was performed for each coastal transect using wave condition
extracted from the wave climatology model output and stillwater elevation (SWEL) data to
generate wave setup and wave runup values for open coast transects and transects with
vertical structures or revetments, and to generate input used in developing CHAMP and
WHAFIS input data. Mathcad sheets were developed and applied by STARR for the
calculations to help ensure consistency and accuracy. The input data and results of the
analysis were compiled for each transect in a summary spreadsheet. The Mathcad sheets
and summary spreadsheet are included in the digital data files compiled for the coastal
submittal. This STWAVE model was developed for the entire coastline of Suffolk County,
and the results were obtained from the model for the coastal flooding analysis in the Cities
of Boston, Chelsea, and Revere; and the Town of Winthrop. 
CHAMP is a Microsoft (MS) Windows-interfaced Visual Basic language program that
allows the user to enter data, perform coastal engineering analyses, view and tabulate
results, and chart summary information for each representative transect along a coastline
within a user-friendly graphical interface. With CHAMP, the user can import digital
elevation data, perform storm-induced erosion treatments, wave height and wave runup
analyses, plot summary graphics of the results, and create summary tables and reports in a
single environment. CHAMP version 2.0 (Reference 36) was used to perform erosion
analysis, run WHAFIS, and apply RUNUP 2.0 to transects without coastal structures.
Application of CHAMP followed the instructions in the FEMA Guidelines and
Specifications (Reference 34) and the Coastal Hazard Analysis Modeling Program user’s
guide found in the software documentation (Reference 37). 
Wave Setup 
Direct Integration Method 
Wave setup can be a significant contributor to the total water level at the shoreline and was
included in the determination of coastal base flood elevations. Wave setup is defined as the
increase in total stillwater elevation against a barrier caused by the attenuation of waves in
shallow water. Wave setup is based upon wave breaking characteristics and profile slope.
Wave setup values were calculated for each coastal transect using the Direct Integration
Method (DIM),developed by Goda (2000) (Reference 38), as described in the FEMA
Guidelines and Specifications, Equation D.2.6-1. For those coastal transects where a
structure was located, documentation was gathered on the structure, and the wave setup
against the coastal structure was also calculated. 
SWAN 
For the appeal submitted engineering, the wave setup values were revised using the SWAN
1D model. Results from the SWAN 2D simulation of 100-year wave conditions were used
as input to drive SWAN 1D simulations at each of the transects evaluated as part of the
appeal. The purpose of the SWAN 1D simulations was to develop wave setup at each site
specific transect location. 
Bathymetric and topographic conditions were taken directly from the 2013 Preliminary FIS
FEMA CHAMP database. Transects where FEMA modeled structure failure and erosion
were utilized in place of the intact conditions. The FEMA CHAMP transect data were
interpolated to an evenly-spaced 1 meter resolution for input to SWAN 1D. Water levels
were set to reflect the revised 100-year SWELs shown in Table 10. Incident wave

24 
conditions were obtained from the SWAN 2D model simulation and summarized in Table
10. For the transects SF-20, SF-21, and SF-22, the incident wave conditions were obtained
from the ACES modeling. Waves were assumed to conservatively approach normal to the
shoreline (along the axis of the transects) and spectral spreading was turned off in the
model (to ensure that the peak energy was not muted). This represents a conservative
assumption where the model computed wave setup using peak wave conditions, rather than
a spectral spread of the waves. Results from the SWAN 1D simulations were reviewed and
the maximum wave setup along each transect was identified. 
Wave Runup 
Wave runup is the uprush of water caused by the interaction of waves with the area of
shoreline where the stillwater hits the land or other barrier intercepting the stillwater level.
The wave runup elevation is the vertical height above the stillwater level ultimately
attained by the extremity of the uprushing water. Wave runup at a shore barrier can provide
flood hazards above and beyond those from stillwater inundation. Guidance in the FEMA
Guidelines and Specifications (Reference 34) suggests using the 2-percent wave runup
value, the value exceeded by 2 percent of the runup events. The 2-percent wave runup
value is particularly important for steep slopes and vertical structures. 
Wave runup was calculated for each coastal transect using methods described in the FEMA
Guidelines and Specifications (Reference 34). Runup estimates were developed for vertical
walls using the guidance in Figure D.2.8-3 of the FEMA Guidelines and Specifications
(Reference 34), taken from the Shore Protection Manual (Reference 40). Technical
Advisory Committee for Water Retaining Structures (TAW) method was applied for sloped
structures with a slope steeper than 1:8. For slopes milder than 1:8, the FEMA Wave
Runup Model RUNUP 2.0 was used. Both the SPM and RUNUP 2.0 provide mean wave
runup. The mean wave runup was multiplied by 2.2 to obtain the 2percent runup height.
Wave runup elevation was added to the stillwater elevation and does not include wave
setup. 
Limit of Moderate Wave Action 
Areas of coastline subject to significant wave attack are referred to as coastal high hazard
zones. The USACE (Reference 41) has established the 3-foot breaking wave as the
criterion for identifying the limit of coastal high hazard zones. The 3-foot wave has been
established as the minimum size wave capable of causing major damage to conventional
wood frame and brick veneer structures. WHAFIS results show where the waves are
greater than 3 feet (VE zone) and less than 3 feet (AE zone). 
The LiMWA is determined and defined as the location of the 1.5-foot wave. Typical
constructions in areas of wave heights less than 3-feet high have experienced damage,
suggesting that construction requirements within some areas of the AE zone should be
more like those requirements for the VE zone. Testing and investigations have confirmed
that a wave height greater than 1.5 feet can cause structure failure. The LiMWA was
determined for all areas subject to significant wave attack in accordance with “Procedure
Memorandum No. 50 – Policy and Procedures for Identifying and Mapping Areas Subject
to Wave Heights Greater than 1.5 feet as an Informational Layer on Flood Insurance Rate
Maps (FIRMs)” (Reference 42). The effects of wave hazards in the Zone AE areas (or
shoreline in areas where VE Zones are not identified) and the limit of the LiMWA

25 
boundary are similar to, but less severe than, those in Zone VE where 3-foot breaking
waves are projected during a 1-percent-annual-chance flooding event. 
The effects of wave hazards in the Zone AE areas (or shoreline in areas where VE Zones
are not identified) and the limit of the LiMWA boundary are similar to, but less severe
than, those in Zone VE where 3-foot breaking waves are projected during a 1-percent-
annual-chance flooding event. 
Primary Frontal Dune 
Primary frontal dune (PFD) evaluations were performed for all communities in Suffolk
County and mapped where sufficient data was available to support the delineation. PDFs
were identified in the City of Revere. Provided below is a summary of the analyses
performed. All revised coastal analyses were performed in accordance with the FEMA
Guidelines and Specifications (Reference 34). 
In accordance with 44 CFR Section 59.1 of the National Flood Insurance Program (NFIP),
the effect of the PFD on coastal high hazard area (V Zone) mapping was evaluated for the
communities in Suffolk County. Identification of the PFD was based upon a FEMA-
approved numerical approach for analyzing the dune’s dimensional characteristics. Using
this methodology, the landward toe of the PFD is delineated based on knowledge of local
geological processes and remote sensing/GIS technologies utilizing LiDAR data. The PFD
defined the landward limit of the V Zone along the northeastern shoreline of the Point of
Pines in Revere. 
Figure 1 is a profile for a typical transect illustrating the effects of energy dissipation and
regeneration on a wave as it moves inland. This figure shows the wave crest elevations
being decreased by obstructions, such as buildings, vegetation, and rising ground
elevations, and being increased by open, unobstructed wind fetches. Actual wave
conditions in the community may not include all the situations illustrated in Figure 1. 
FIGURE 1 – TRANSECT SCHEMATIC

26 
Transects (profiles) were located for coastal hydrologic and hydraulic analyses
perpendicular to the average shoreline along areas subject to coastal flooding; transects
extend off-shore to areas representative of deep water conditions and extend inland to a
point where wave action ceases, in accordance with the “User’s Manual for Wave Height
Analysis” (Reference 43). Transects were placed with consideration of topographic and
structural changes of the land surface, as well as the cultural characteristics of the land, so
that they would closely represent local conditions. Transects were spaced close together in
areas of complex topography and dense development. In areas having more uniform
characteristics, transects were spaced at larger intervals. It was also necessary to locate
transects in areas where unique flooding existed and in areas where computed wave heights
varied significantly between adjacent transects. 
Coastal transect topography data was obtained from Light Detection and Ranging (LiDAR)
data collected in 2011 by STARR, accurate to 2-foot contours (Reference 44).
Additionally, portions of fifteen (15) coastal transects were surveyed by Green
International Affiliates in May 2011 to supplement the contour data for the study area.
Coastal field inspection were also conducted in February 2011. Georeferenced global
positioning system (GPS) points and tracks, as well as photographs, were collected and
attributed with various descriptive information, such as upland type, coastal formations,
including dunes and bluffs, coastal vegetation, coastal structures, and shore type. As
appropriate, coastal protection structure details and 0.0 ft NAVD88 elevation were included
and noted in the transect field surveys. Bathymetric data was obtained from the NOAA
National Ocean Service (NOS) Hydrographic Data Base (NOSHDB) and Hydrographic
Survey Meta Data Base (HSMDB) (NOAA, May 27, 2010) (Reference 45). The sounding
datum of mean low low water (MLLW) was converted to vertical datum NAVD 88. 
Transects were spaced close together in areas of complex topography and dense
development. In areas having more uniform characteristics, transects were spaced at larger
intervals. It was also necessary to locate transects in areas where unique flooding existed
and in areas where computed wave heights varied significantly between adjacent transects. 
Table 11 provides a description of the transect locations, the 1-percent-annual-chance
stillwater elevations, and the maximum 1-percent-annual-chance wave crest elevations.
Figure 2, "Transect Location Map," illustrates the location of the transects for the county.

27 
TABLE 11 – TRANSECT DESCRIPTIONS 
ELEVATION (feet NAVD 88 2 ) 
TRANSECT LOCATION 
1-PERCENT-
ANNUAL-CHANCE
STILLWATER 
MAXIMUM 1-
PERCENT ANNUAL
CHANCE
WAVE CREST 1 
1 The transect extends over Point of Pines
barrier spit in Revere. It intersects
grassy vegetated dunes, a retaining wall
at Rice Ave, and down Bateman Ave.
The shoreline is sandy, upland
development is dense single-family
residential homes. 
9.2 12.3 
2 The transect crosses a sandy beach,
five-foot concrete seawall, then
intersects Rice Ave. Upland vegetation
is limited to turf and ornamental trees
and shrubs on residential properties.
Development is dense single-family
residential homes. 
9.2 15.6 
3 The transect extends over sandy beach,
a 2.5 ft concrete seawall, and Revere
Beach Blvd. Upland vegetation is
generally open with few ornamental
shrubs and trees. Development is
limited to one row of single family
residential houses. 
9.2 16.8 
4 The transect crosses sandy beach and a
small 2.5 foot concrete seawall at
Revere Beach Blvd. Upland vegetation
is very sparse. The transect then extends
over low lying residential area and
across the tidal flats of Pine River. 
9.2 16.8 
5 The transect crosses sandy beach and a
2.5 ft concrete seawall-boardwalk at
Revere Beach Blvd. Upland
development is mostly open parking
lots. The transect crosses a low marshy
area before terminating in a dense
residential area. 
9.2 17.0 
1 Because of map scale limitations, the maximum wave elevation may not be shown on the FIRM. 
2 North American Vertical Datum of 1988

28 
TABLE 11 – TRANSECT DESCRIPTIONS - continued 
ELEVATION (feet NAVD 88 2 ) 
TRANSECT LOCATION 
1-PERCENT-
ANNUAL-CHANCE
STILLWATER 
MAXIMUM 1-
PERCENT ANNUAL
CHANCE
WAVE CREST 1 
6 The transect crosses sandy beach
separated from the upland area by a
small 2.5 foot concrete seawall at
Revere Beach Blvd. Upland
development consists of mostly
parking lots and some high rise
residential structures. 
9.2 17.0 
7 This transect extends over a gabion
revetment and 15 foot concrete seawall
into the residential area of Roughan's
Point Revere. The shoreline is heavily
engineered with a gabion revetment
approximately 20 feet wide and 6 feet
high. 
9.8 19.8 
8 The transect crosses a mixed sand and
gravel beach and 7 foot concrete
seawall with some large gabions at the
base of Winthrop Parkway (State
Highway 145) near Beachmont in
Revere. Upland development consists
of single and multi-family residential
units. 
9.2 17.2 
9 The transect crosses a cobble shoreline
with both stable and eroding sections
of 12 ft gabion revetment. Upland
development is medium density single-
family residential. Elevations increase
sharply moving inland. 
9.1 18.1 
10 The transect crosses a cobble beach
with a double concrete revetment built
into the steep hillside at Seal Point in
Winthrop. Upland development
consists of large high-rise apartment
buildings. 
9.7 22.3 
1 Because of map scale limitations, the maximum wave elevation may not be shown on the FIRM. 
2 North American Vertical Datum of 1988

29 
TABLE 11 – TRANSECT DESCRIPTIONS - continued 
ELEVATION (feet NAVD 88 2 ) 
TRANSECT LOCATION 
1-PERCENT-
ANNUAL-CHANCE
STILLWATER 
MAXIMUM 1-
PERCENT ANNUAL
CHANCE
WAVE CREST 1 
11 The transect crosses a mixed sand,
gravel, and cobble beach with a small
revetment below a 10 foot concrete
seawall. Upland development is
medium density single-family
residential. Topography is steep and
elevations rise quickly moving inland. 
9.7 21.8 
12 The transect crosses a sandy beach at
Winthrop Beach and is separated from
the upland area by a 10-foot concrete
seawall with two groins to the North
and South. Upland development is
medium density single-family
residential. 
9.1 17.5 
13 The transect crosses a mostly sand
beach with some mixed cobble/gravel
substrate extending towards the
offshore breakwaters. A four foot
concrete seawall separates the beach
from Winthrop Shore Dr. Upland
development is medium density
residential. 
9.7 22.1 
14 The transect crosses a mixed sand,
gravel, and cobble beach and a small 3
foot concrete seawall at the base of a
large gabion reinforced bluff. Upland
development is single family
residential. Topography rises quickly
to the top of Cottage Hill. 
9.7 21.0 
15 The transect crosses sandy beach at
Point Shirley extends over a small 2-
foot concrete seawall running parallel
to Brewster Ave. Upland development
is medium to high density residential
homes. 
9.1 17.6 
1 Because of map scale limitations, the maximum wave elevation may not be shown on the FIRM. 
2 North American Vertical Datum of 1988

30 
TABLE 11 – TRANSECT DESCRIPTIONS - continued 
ELEVATION (feet NAVD 88 2 ) 
TRANSECT LOCATION 
1-PERCENT-
ANNUAL-CHANCE
STILLWATER 
MAXIMUM 1-
PERCENT ANNUAL
CHANCE
WAVE CREST 1 
16 The transect crosses over the Deer
Island wastewater treatment plant.
The shoreline is heavily reinforced
with a large concrete seawall
approximately 15ft high. Upland
development is almost solely
impervious surface and treatment plant
buildings. 
9.8 20.6 
17 The transect crosses a gravel shore and
seawall built into a steep bluff at
Bartlett Pkwy at Cottage Park in
Winthrop. Development is medium
density residential homes. 
8.8 11.4 
18 The transect crosses over a section of
Logan Airport at Governors Island.
The shoreline is reinforced with a
gabion revetment approximately 15
feet high. Upland development and
vegetation is open grass, with some
impervious surfaces. 
9.7 14.0 
19 The transect crosses a 3 foot concrete
seawall with a 5 foot gabion revetment
in front, then extends into parkland
and a residential area of East Boston. 
9.4 12.3 
20 The transect extends from Boston
Inner Harbor over an undeveloped
piece of property and then into a
residential area of East Boston. 
9.4 10.9 
21 The transect extends from Belle Island
Inlet over the parkland of Constitution
Beach and then in a residential area of
East Boston. 
8.8 9.9 
1 Because of map scale limitations, the maximum wave elevation may not be shown on the FIRM. 
2 North American Vertical Datum of 1988

31 
TABLE 11 – TRANSECT DESCRIPTIONS - continued 
ELEVATION (feet NAVD 88 2 ) 
TRANSECT LOCATION 
1-PERCENT-
ANNUAL-CHANCE
STILLWATER 
MAXIMUM 1-
PERCENT ANNUAL
CHANCE
WAVE CREST 1 
22 The transect extends from the Mystic
River over a rock revetment backed by
a 3 foot seawall. This transect is in
Charlestown and extends back to the
county boundary. 
9.5 11.2 
23 The transect extends over one of the
main steel seawall piers at
Charlestown Navy Yard, then
terminates in vegetated parkland. 
9.4 10.5 
24 This transect crosses a seawall
approximately 10 feet high at Lewis
Wharf in downtown Boston. Upland
development is high density mixed use
commercial and residential with
parking lots. 
9.4 12.3 
25 The transect crosses a seawall at the
South Boston Waterfront, extending
over parking lot areas and over Seaport
Blvd. 
9.4 12.3 
26 The transect crosses a 15 foot timber
seawall at the South Boston waterfront
around the Black Falcon area. Upland
development is mostly large industrial
buildings and impervious surface. 
9.4 15.0 
27 The transect crosses a gabion
breakwater at Pleasure Bay in South
Boston, extends into Pleasure Bay,
then runs up a sandy beach and small
seawall before ending in parkland. 
9.9 20.5 
1 Because of map scale limitations, the maximum wave elevation may not be shown on the FIRM. 
2 North American Vertical Datum of 1988

32 
TABLE 11 – TRANSECT DESCRIPTIONS - continued 
ELEVATION (feet NAVD 88 2 ) 
TRANSECT LOCATION 
1-PERCENT-
ANNUAL-CHANCE
STILLWATER 
MAXIMUM 1-
PERCENT ANNUAL
CHANCE
WAVE CREST 1 
28 The transect crosses a sandy beach
immediately adjacent to Day Blvd in
South Boston, and rises in elevation to
parkland and dense multi-family
residential. 
9.7 14.4 
29 The transect crosses a sandy beach
approximately 150 ft wide at Carson
Beach in South Boston, intersects both
Day Blvd and Columbia Rd, enters
parkland, then terminates at a large
housing development complex. 
9.7 14.3 
30 The transect crosses a gabion
revetment and through open space at
UMASS Boston Campus. Topography
rises gradually and is mostly open
parkland with some rigid vegetation.
Upland development is institutional
buildings and parking lots. 
9.9 14.8 
31 The transect crosses a mixed sand and
cobble beach at Morrissey Blvd,
crosses over parkland, then extends
through Dorchester Bay, and over
Interstate 93 to Dorchester Ave. 
9.9 14.3 
32 The transect crosses a mixed timber
seawall at a marina on the mouth of
the Neponset River, extends south
down Lawley Street, then terminates at
Redfield St. 
10.6 14.9 
33 The transect crosses a sand-gravel
beach at Thompson Island within
Boston Harbor. Upland vegetation is
composed of manicured turf. No
development exists along the transect. 
10.0 18.4 
1 Because of map scale limitations, the maximum wave elevation may not be shown on the FIRM. 
2 North American Vertical Datum of 1988

33 
TABLE 11 – TRANSECT DESCRIPTIONS - continued 
ELEVATION (feet NAVD 88 2 ) 
TRANSECT LOCATION 
1-PERCENT-
ANNUAL-CHANCE
STILLWATER 
MAXIMUM 1-
PERCENT ANNUAL
CHANCE
WAVE CREST 1 
34 The transect crosses a 15 foot gabion
revetment at the shoreline of Spectacle
Island. Upland vegetation is open turf
parkland with some small stature trees.
There is no private development on the
island and no structures along the
transect. 
9.8 23.5 
35 This transect represents Long Island
within Boston Harbor. The transect
crosses an 8 foot masonry seawall,
with a small gabion revetment at the
base. Upland of the shoreline,
elevations rise sharply and with dense
medium stature trees and shrubs. 
9.9 21.1 
36 This transect runs across Lovells
Island in Boston Harbor. The
shoreline is a mixed substrate beach
with remnants of old gabion
revetment. Vegetation upland of the
shoreline is composed of dense small
stature trees and shrubs. 
9.8 19.6 
37 This transect crosses George's Island
and Fort Warren. The shoreline is 6
foot masonry seawall with a small
gabion revetment below. Elevations
increase sharply moving inland.
Upland vegetation is limited to turf
and small shrubs. 
9.8 22.4 
1 Because of map scale limitations, the maximum wave elevation may not be shown on the FIRM. 
2 North American Vertical Datum of 1988

¬ « 21 
¬ « 23 
¬ « 22 
¬ « 26 
¬ « 04 
¬ « 05 
¬ « 25 
¬ « 27 
¬ « 31 
¬ « 13 
¬ « 12 
¬ « 29 
¬ « 06 
¬ « 02 
¬ « 07 
¬ « 32 
¬ « 01 
¬ « 14 
¬ « 18 
¬ « 35 
¬ « 16 
¬ « 03 
¬ « 15 
¬ « 17 ¬ « 20 
¬ « 28 
¬ « 24 
¬ « 30 
¬ « 09 
¬ « 10 
¬ « 19 
¬ « 36 
¬ « 08 
¬ « 37 ¬ « 34 
¬ « 33 
¬ « 11 
FIGURE 2
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
(ALL JURISDICTIONS) TRANSECT LOCATION MAP
0 2 4 6 8 10
Miles
APPROXIMATE SCALE 
Atlantic Ocean 
§ ¨ ¦ 90 
§ ¨ ¦ 93 
§ ¨ ¦ 93 
£ ¤ 1 
City of Boston
City of Boston
City of Boston
City of Boston
City of Revere
Town of
Winthrop
City of
Chelsea 
Boston Harbor

35
The results of the coastal analysis using detailed methods are summarized in Table 12,
"Transect Data," which provides the flood hazard zone and base flood elevations for each
coastal transect, along with the 10-, 2-, 1- and 0.2-percent-annual-chance flood stillwater
elevations from the Belle Island Inlet, Boston Harbor, Dorchester Bay and the Pines,
Chelsea, Charles, and Neponset River flooding sources, including effects of wave setup
where applicable.
TABLE 12 – TRANSECT DATA
STILLWATER ELEVATIONS (FEET NAVD88 3 )
TOTAL
WATER
LEVEL 1 
1-PERCENT-
ANNUAL-
CHANCE ZONE
BASE
FLOOD
ELEVATION 2 
(FEET
NAVD 88 3 ) TRANSECT
10-
PERCENT-
ANNUAL
CHANCE
2-
PERCENT-
ANNUAL-
CHANCE
1-
PERCENT-
ANNUAL-
CHANCE
0.2-
PERCENT-
ANNUAL-
CHANCE
1 * * 9.2 10.0 9.7 VE 12, 13 
AE 10,11
2 * * 9.2 10.0 10.1 VE 13, 15 
AE 10,11 
3 * * 9.2 10.0 11.0 VE 15 
AE 10, 11, 12, 14 
4 * * 9.2 10.0 11.0 VE 10, 15, 16 
AE 8, 9, 10, 11,
12 
5 * * 9.2 10.0 11.1 VE 14, 16 
AE 11, 12 
6 * * 9.2 10.0 11.1 VE 14, 16, 17 
AE 11, 12 
7 * * 9.8 11.2 12.9 VE 22 
AH 6 
8 * * 9.2 10.0 11.2 VE 15 
AE 11, 12
*Data not available. 
1 Including stillwater elevation and effects of wave setup. 
2 Due to map scale limitations, base flood elevations shown on the FIRM represent average elevations for the zones
depicted. 
3 North American Vertical Datum of 1988

36
TABLE 12 – TRANSECT DATA - continued
STILLWATER ELEVATIONS (FEET NAVD88 3 )
TOTAL
WATER
LEVEL 1 
1-PERCENT-
ANNUAL-
CHANCE ZONE
BASE
FLOOD
ELEVATION 2 
(FEET
NAVD 88 3 ) TRANSECT
10-
PERCENT-
ANNUAL
CHANCE
2-
PERCENT-
ANNUAL-
CHANCE
1-
PERCENT-
ANNUAL-
CHANCE
0.2-
PERCENT-
ANNUAL-
CHANCE
9 * * 9.1 9.9 11.8 VE 16 
AE 12 
10 * * 9.7 11.1 14.6 VE 17 
11 * * 9.7 11.1 14.2 VE 17 
12 * * 9.1 9.9 11.4 VE 16 
AE 11 
AO 1 
13 * * 9.1 9.9 11.6 VE 17 
AE 11, 15, 16 
14 * * 9.7 11.1 13.7 VE 19 
AE 15 
15 * * 9.1 9.9 11.5 VE 12, 13, 15 
AE 11, 12 
16 * * 9.8 11.4 13.4 VE 29
17 * * 8.8 9.6 8.8 VE 15 
18 * * 9.7 11.1 10.9 VE 13 
19 * * 9.4 10.2 9.4 VE 13 
20 * * 9.4 10.2 9.4 AE 11, 10 
*Data not available. 
1 Including stillwater elevation and effects of wave setup. 
2 Due to map scale limitations, base flood elevations shown on the FIRM represent average elevations for the zones
depicted. 
3 North American Vertical Datum of 1988

37
TABLE 12 – TRANSECT DATA - continued
STILLWATER ELEVATIONS (FEET NAVD88 3 )
TOTAL
WATER
LEVEL 1 
1-PERCENT-
ANNUAL-
CHANCE ZONE
BASE
FLOOD
ELEVATION 2 
(FEET
NAVD 88 3 ) TRANSECT
10-
PERCENT-
ANNUAL
CHANCE
2-
PERCENT-
ANNUAL-
CHANCE
1-
PERCENT-
ANNUAL-
CHANCE
0.2-
PERCENT-
ANNUAL-
CHANCE
21 * * 8.8 10.2 8.8 AE 10 
22 * * 9.5 10.2 9.5 AE 10, 11 
AO 2 
23 * * 9.4 10.2 9.5 VE 11 
AE 10 
24 * * 9.4 10.2 9.4 VE 13 
AE 10 
25 * * 9.4 10.2 9.4 VE 13 
AE 10, 11 
26 * * 9.4 10.2 10.1 VE 15 
AE 12, 10 
27 * * 9.9 11.4 13.4 VE 16 
AE 15, 16 
28 * * 9.7 10.5 10.0 VE 13 
AE 11 
29 * * 9.7 10.5 10.0 VE 13 
AE 10, 11, 12 
30 * * 9.9 10.7 10.4 VE 13, 14
31 * * 9.9 10.7 10.2 VE 12, 13, 14 
AE 11, 12 
*Data not available. 
1 Including stillwater elevation and effects of wave setup. 
2 Due to map scale limitations, base flood elevations shown on the FIRM represent average elevations for the zones
depicted. 
3 North American Vertical Datum of 1988

38
TABLE 12 – TRANSECT DATA - continued
STILLWATER ELEVATIONS (FEET NAVD88 3 )
TOTAL
WATER
LEVEL 1 
1-PERCENT-
ANNUAL-
CHANCE ZONE
BASE
FLOOD
ELEVATION 2 
(FEET
NAVD 88 3 ) TRANSECT
10-
PERCENT-
ANNUAL
CHANCE
2-
PERCENT-
ANNUAL-
CHANCE
1-
PERCENT-
ANNUAL-
CHANCE
0.2-
PERCENT-
ANNUAL-
CHANCE
32 * * 10.6 11.4 10.7 VE 14 
AE 11, 13 
33 * * 10.0 11.6 12.0 VE 14 
AE 12 
34 * * 9.8 11.4 14.0 VE 19 
35 * * 9.9 11.5 13.8 VE 33 
AE 15 
36 * * 9.8 11.4 12.8 VE 15 
37 * * 9.8 11.4 14.7 VE 17 
*Data not available. 
1 Including stillwater elevation and effects of wave setup. 
2 Due to map scale limitations, base flood elevations shown on the FIRM represent average elevations for the zones
depicted. 
3 North American Vertical Datum of 1988 
3.5 Vertical Datum
All FIS reports and FIRMs are referenced to a specific vertical datum. The vertical datum
provides a starting point against which flood, ground, and structure elevations can be
referenced and compared. Until recently, the standard vertical datum used for newly
created or revised FIS reports and FIRMs was the National Geodetic Vertical Datum of
1929 (NGVD). With the completion of the North American Vertical Datum of 1988
(NAVD), many FIS reports and FIRMs are now prepared using NAVD as the referenced
vertical datum.
All flood elevations shown in this FIS report and on the FIRM are referenced to the NAVD
88. These flood elevations must be compared to structure and ground elevations referenced
to the same vertical datum. Ground, structure, and flood elevations may be compared
and/or referenced to NGVD 29 by applying a standard conversion factor. The conversion
factor from NGVD 29 to NAVD 88 is -0.8, and from NAVD 88 to NGVD 29 is +0.8.

39 
For information regarding conversion between the NGVD and NAVD, visit the National
Geodetic Survey website at www.ngs.noaa.gov , or contact the National Geodetic Survey at
the following address: 
Vertical Network Branch, N/CG13 
National Geodetic Survey, NOAA 
Silver Spring Metro Center 3 
1315 East-West Highway 
Silver Spring, Maryland 20910 
(301) 713-3191 
Temporary vertical monuments are often established during the preparation of a flood
hazard analysis for the purpose of establishing local vertical control. Although these
monuments are not shown on the FIRM, they may be found in the Technical Support Data
Notebook associated with the FIS report and FIRM for this county. Interested individuals
may contact FEMA to access these data. 
The BFEs shown on the FIRM represent whole-foot rounded values. For example, a BFE
of 102.4 will appear as 102 on the FIRM and 102.6 will appear as 103. Therefore, users
that wish to convert the elevations in this FIS to NGVD 29 should apply the stated
conversion factor to elevations shown on the Flood Profiles and supporting data tables in
the FIS report, which are shown at a minimum to the nearest 0.1 foot. 
To obtain current elevation, description, and/or location information for benchmarks shown
on this map, please contact the Information Services Branch of the NGS at (301) 713-3242,
or visit their website at www.ngs.noaa.gov. 
4.0 FLOODPLAIN MANAGEMENT APPLICATIONS 
The National Flood Insurance Program encourages State and local governments to adopt sound
floodplain management programs. To assist in this endeavor, each FIS report provides
1-percent-annual-chance floodplain data, which may include a combination of the following: 10-,
2-, 1-, and 0.2-percent-annual-chance flood elevations; delineations of the 1- and
0.2-percent-annual-chance floodplains; and a 1-percent-annual-chance floodway. This information
is presented on the FIRM and in many components of the FIS report, including Flood Profiles,
Floodway Data tables, and Summary of Stillwater Elevation tables. Users should reference the data
presented in the FIS report as well as additional information that may be available at the local
community map repository before making flood elevation and/or floodplain boundary
determinations. 
4.1 Floodplain Boundaries 
To provide a national standard without regional discrimination, the
1-percent-annual-chance flood has been adopted by FEMA as the base flood for floodplain
management purposes. The 0.2-percent-annual-chance flood is employed to indicate
additional areas of flood risk in the community. For each stream studied by detailed
methods, the 1- and 0.2-percent-annual-chance floodplain boundaries have been delineated
using topographic maps (Reference 15, 21, 46, 47, 49, 50).

40 
In the pre-countywide, City of Boston FIS, floodplain boundaries were interpolated
between cross-sections using topographic maps at a scale of 1"=400’ with a contour
interval of 5 feet (Reference 15). 
In the 1984 Winthrop FIS, the boundaries were interpolated between cross-sections, using
topographic maps at a scale of 1:4,800 with a contour interval of 5 feet (Reference 47). 
Flood boundaries for areas in Boston studied by approximate methods were obtained from
the previous October 1, 1983 FIS for the City of Boston (Reference 48). For areas in
Chelsea studied by approximate methods, the boundary of the 1-percent-annual-chance
flood was delineated using USGS topographic maps and a drainage study prepared for the
Massachusetts Department of Public Works (References 21 and 49). In the 1984 Revere
FIS, for areas of flooding studied by approximate methods, the 1-percent-annual-chance
flood boundary was delineated using the topographic maps referenced above. In the
Revere August 2, 2002 revision, an area of approximate flooding in the northeast comer of
Revere was delineated in order to match the approximate flooding in the contiguous
community of the City of Malden in Middlesex County. The delineation involved the use
of topographic maps at a scale of 1:25,000 and a contour interval of 10 feet (Reference 50) 
For the 2009 countywide study, the 1- and 0.2-percent-annual-chance floodplain
boundaries for detailed study flooding sources in Suffolk County were redelineated using
more up to date topographic information, including MassGIS and LiDAR data, which
meets the accuracy standards for flood hazard mapping (https://www.mass.gov/mgis/ and
https://maps.csc.noaa.gov.TMC/). 
For the 2013 coastal study and post preliminary processing of coastal analyses based on
appeal, the 1-, and 0.2-percent-annual-chance coastal floodplains have been delineated
using the flood elevations determined at each transect and LiDAR data with a 2-foot
contour interval accuracy equivalency (Reference 44). 
The 1- and 0.2-percent-annual-chance floodplain boundaries are shown on the FIRM. On
this map, the 1-percent-annual-chance floodplain boundary corresponds to the boundary of
the areas of special flood hazards (Zones A, AE, AH, AO and VE), and the
0.2-percent-annual-chance floodplain boundary corresponds to the boundary of areas of
moderate flood hazards. In cases where the 1- and 0.2-percent-annual-chance floodplain
boundaries are close together, only the 1-percent-annual-chance floodplain boundary has
been shown. Small areas within the floodplain boundaries may lie above the flood
elevations, but cannot be shown due to limitations of the map scale and/or lack of detailed
topographic data. 
For the streams studied by approximate methods, only the 1-percent-annual-chance
floodplain boundary is shown on the FIRM. 
4.2 Floodways 
Encroachment on floodplains, such as structures and fill, reduces flood-carrying capacity,
increases flood heights and velocities, and increases flood hazards in areas beyond the
encroachment itself. One aspect of floodplain management involves balancing the
economic gain from floodplain development against the resulting increase in flood hazard.
For purposes of the NFIP, a floodway is used as a tool to assist local communities in this

41 
aspect of floodplain management. Under this concept, the area of the
1-percent-annual-chance floodplain is divided into a floodway and a floodway fringe. The
floodway is the channel of a stream, plus any adjacent floodplain areas, that must be kept
free of encroachment so that the base flood can be carried without substantial increases in
flood heights. Minimum Federal standards limit such increases to 1 foot, provided that
hazardous velocities are not produced. The floodways in this study are presented to local
agencies as minimum standards that can be adopted directly or that can be used as a basis
for additional floodway studies. 
The floodway presented in this study was computed on the basis of equal conveyance
reduction from each side of the floodplain. Floodway widths were computed at cross
sections. Between cross sections, the boundaries were interpolated. In cases where the
floodway and 1-percent-annual-chance floodplain boundaries are either close together or
collinear, only the floodway boundary has been shown. Portions of the floodway widths of
Chelsea and Revere’s Mill Creek extend beyond the corporate limits. The results of the
floodway computations are tabulated at selected cross sections for each stream segment for
which a floodway is computed (See Table 11). 
Encroachment into areas subject to inundation by floodwaters having hazardous velocities
aggravates the risk of flood damage, and heightens potential flood hazards by further
increasing velocities. A listing of stream velocities at selected cross sections is provided in
Table 11, "Floodway Data". To reduce the risk of property damage in areas where the
stream velocities are high, the community may wish to restrict development in areas
outside the floodway. 
Floodway encroachments were not determined for the Neponset River. This river is located
entirely within the Neponset River Reservations. In analyzing this portion of the river using
the HEC-2 program, the selected effective flow areas of the river were well inside the
boundaries of the reservation. The computer was programmed not to recognize the areas of
slack water beyond the effective flow limits. Therefore any encroachment up to the
reservation boundary will have no appreciable effect on the river velocity or water-surface
elevation. However, almost the entire land area from the banks of the Neponset River up to
the 1-percent-annual-chance flood boundary has been subjected to an Order of Restriction
in accordance with Chapter 131, Section 40A, of the General Laws of the Commonwealth
of Massachusetts. Under this law, any permanent wetland so designated by the state cannot
be built upon in any way. 
The identical situation exists along the Charles River. The restricted wetlands almost
completely occupy the areas inundated by the 1-percent-annual-chance flood. The areas not
covered are so small that the delineation of a floodway would be useless as a functional
tool to be used by the community for its floodplain management program. Therefore, no
floodway has been defined for both the Neponset and Charles Rivers. Additionally,
floodways were not computed for Muddy River and Stony Brook. 
The area between the floodway and 1-percent-annual-chance floodplain boundaries is
termed the floodway fringe. The floodway fringe encompasses the portion of the floodplain
that could be completely obstructed without increasing the water-surface elevation of the
1-percent-annual-chance flood by more than 1.0 foot at any point. Typical relationships
between the floodway and the floodway fringe and their significance to floodplain
development are shown in Figure 3, “Floodway Schematic”.

42 
In Chelsea and Revere, near the mouths of streams studied in detail, floodway
computations were made without regard to flood elevations on the receiving water body.
Therefore, "Without Floodway" elevations presented in Table 11 for certain downstream
cross sections of Mill Creek are lower than the regulatory flood elevations in that area,
which must take into account the 1-percent-annual-chance flooding due to backwater from
other sources. 
Additionally, no floodways were computed for the Town of Winthrop. 
FIGURE 3 – FLOODWAY SCHEMATIC

A 502 310 / 210 2 2561 0.9 9.8 4.1 3 5.1 1.0
B 1447 140 / 40 2 753 3.1 9.8 4.1 3 5.1 1.0
C 2777 120 / 100 2 951 2.4 12.5 12.5 12.5 0.0
D 3305 80 / 60 2 897 2.6 12.6 12.6 12.6 0.0
E 4572 90 / 20 2 786 2.9 13.0 13.0 13.5 0.5
1
2
3 
TABLE 13 MILL CREEK
BASE FLOOD
WATER SURFACE ELEVATION
(FEET NAVD) 
FLOODWAY DATA 
FLOODWAY
FEDERAL EMERGENCY MANAGEMENT AGENCY
SECTION
AREA
(SQUARE FEET)
FLOODING SOURCE
DISTANCE 1 
SUFFOLK COUNTY, MA 
WITHOUT
FLOODWAY
WITH
FLOODWAY INCREASE REGULATORY 
WIDTH/WIDTH WITHIN SUFFOLK COUNTY
ELEVATION COMPUTED WITHOUT CONSIDERATION OF TIDAL FLOODING FROM CHELSEA RIVER 
CROSS
SECTION
ALL JURISDICTIONS
WIDTH
(FEET)
MEAN
VELOCITY
(FEET PER SECOND) 
FEET ABOVE CONFLUENCE WITH CHELSEA RIVER

A 300 45 187 7.8 43.1 43.1 43.1 0.0
B 750 52 324 4.5 43.4 43.4 43.4 0.0
C 950 50 322 4.6 43.6 43.6 43.6 0.0
D 1,100 64 414 3.6 43.8 43.8 43.8 0.0
E 1,233 64 415 3.5 43.8 43.8 43.8 0.0
F 1,600 60 321 4.6 43.9 43.9 43.9 0.0
G 2,050 60 379 3.9 44.6 44.6 44.8 0.2
H 2,725 153 646 2.3 45.6 45.6 45.8 0.2
I 4,095 84 186 7.9 48.5 48.5 48.5 0.0
J 5,000 200 1445 1.0 49.9 49.9 49.9 0.0
K 6,000 147 1036 1.4 49.9 49.9 49.9 0.0
L 7,130 102 728 2.0 50.1 50.1 50.2 0.1
1 
FLOODWAY DATA 
FLOODWAY
FEDERAL EMERGENCY MANAGEMENT AGENCY
SECTION
AREA
(SQUARE FEET)
FLOODING SOURCE
DISTANCE 1 WITHOUT
FLOODWAY
WITH
FLOODWAY INCREASE 
TABLE 13 MOTHER BROOK
BASE FLOOD
WATER SURFACE ELEVATION
(FEET NAVD)
REGULATORY
CROSS
SECTION
ALL JURISDICTIONS
WIDTH
(FEET)
MEAN
VELOCITY
(FEET PER SECOND) 
FEET ABOVE CONFLUENCE WITH NEPONSET RIVER 
SUFFOLK COUNTY, MA

45 
5.0 INSURANCE APPLICATIONS 
For flood insurance rating purposes, flood insurance zone designations are assigned to a community
based on the results of the engineering analyses. The zones are as follows: 
Zone A 
Zone A is the flood insurance rate zone that corresponds to the 1-percent annual chance
floodplains that are determined in the FIS by approximate methods. Because detailed
hydraulic analyses are not performed for such areas, no base (1-percent-annual-chance)
flood elevations (BFEs) or depths are shown within this zone. 
Zone AE 
Zone AE is the flood insurance rate zone that corresponds to the 1-percent annual chance
floodplains that are determined in the FIS by detailed methods. In most instances,
whole-foot BFEs derived from the detailed hydraulic analyses are shown at selected
intervals within this zone. 
Zone AH 
Zone AH is the flood insurance rate zone that corresponds to areas of
1-percent-annual-chance shallow flooding (usually areas of ponding) where average depths
are between 1 and 3 feet. Whole-foot BFEs derived from the detailed hydraulic analyses
are shown at selected intervals within this zone. 
Zone AO 
Special Flood Hazard Areas inundated by types of 1-percent-annual-chance flood shallow
flooding, where depths are between 1 and 3 feet. Depths are shown within this zone 
Zone D 
Zone D is the flood insurance rate zone that corresponds to unstudied areas where flood
hazards are undetermined, but possible. 
Zone VE 
Zone VE is the flood insurance rate zone that corresponds to the 1-percent annual chance
coastal floodplains that have additional hazards associated with storm waves. Whole-foot
BFEs derived from the detailed hydraulic analyses are shown at selected intervals within
this zone. 
Zone X 
Zone X is the flood insurance rate zone that corresponds to areas outside the 500-year
floodplain, areas within the 0.2-percent annual chance floodplain, and areas of 1-percent
annual chance flooding where average depths are less than 1 foot, areas of 1-percent annual
chance flooding where the contributing drainage area is less than 1 square mile, and areas

46 
protected from the 1-percent annual chance flood by levees. No BFEs or depths are shown
within this zone. 
6.0 FLOOD INSURANCE RATE MAP 
The FIRM is designed for flood insurance and floodplain management applications. 
For flood insurance applications, the map designates flood insurance rate zones as described in
Section 5.0 and, in the 1-percent-annual-chance floodplains that were studied by detailed methods,
shows selected whole-foot BFEs or average depths. Insurance agents use zones and BFEs in
conjunction with information on structures and their contents to assign premium rates for flood
insurance policies. 
For floodplain management applications, the map shows by tints, screens, and symbols, the 1- and
0.2-percent-annual-chance floodplains, floodways, and the locations of selected cross sections used
in the hydraulic analyses and floodway computations. 
The countywide FIRM presents flooding information for the entire geographic area of Suffolk
County. Previously, FIRMs were prepared for each incorporated community and the
unincorporated areas of the County identified as flood-prone. This countywide FIRM also includes
flood-hazard information that was presented separately on Flood Boundary and Floodway Maps
(FBFMs), where applicable. Historical data relating to the maps prepared for each community are
presented in Table 14, “Community Map History.”

COMMUNITY NAME INITIAL IDENTIFICATION
FLOOD HAZARD
BOUNDARY MAP
REVISION DATE(S)
FLOOD INSURANCE
RATE MAP
EFFECTIVE DATE
FLOOD INSURANCE
RATE MAP
REVISION DATE(S) 
Boston, City of
Chelsea, City of
Revere, City of
Winthrop, Town of
November 22, 1974
June 7, 1974
June 28, 1974
June 28, 1974
February 11, 1977
June 7, 1977
December 27, 1974
February 18, 1977
None
April 1, 1982
August 2, 1982
October 16, 1984
October 8, 1976
October 1, 1983
November 2, 1990
July 2, 1992
N/A
August 20, 2002
August 15, 1984
July 2, 1992
T
A
B
L
E
14 
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
(ALL JURISDICTIONS)
COMMUNITY MAP HISTORY

48 
7.0 OTHER STUDIES 
Information pertaining to revised and unrevised flood hazards for each jurisdiction within Suffolk
County has been compiled in this FIS. Therefore, this FIS supersedes all previously printed FIS
reports, FIRMs, and/or FHBMs for all of the incorporated jurisdictions within Suffolk County. 
Suffolk County is bordered by Essex County, MA to the north, Norfolk County, MA to the south,
and Middlesex County, MA to the west. The results of the 2013 coastal analysis of the Suffolk
County coast indicate that coastal flooding will affect communities in Middlesex County. However,
at the time of this revision, no revision to the Middlesex County FIS has been initiated and
therefore the results of the Suffolk County coastal analysis have not been incorporated into the
Middlesex County FIS. 
Due to its highly developed state, the City of Boston has been subject to numerous flood-related
studies as a result of construction proposals, waterway improvements, water quality assessments
and flood plain management studies. 
The Charles River and the lower Charles River Basin have been extensively studied by the USACE,
SCS, and C. E. Maguire, Inc., as a result of its serious flood problems (References 16, 18 and 26).
Elevations for the floods of the selected recurrence intervals, discharge data, inflow hydrographs
and other pertinent hydrologic and hydraulic data were adopted into this countywide FIS, as were
flood elevations for the Muddy River. 
Flood elevations for the Neponset River and Mother Brook were coordinated with detailed studies
done in 1971 and 1973 (References 25 and 51). Elevations were coordinated with the FISs of the
surrounding Cities of Quincy and Newton, and Towns of Milton, Dedham, Needham, Brookline,
and Winthrop (References 17, 19, and 52-56). 
Flood elevations for Mother Brook at the Boston-Dedham corporate limits are slightly higher in this
study than those shown calculated in the Dedham FIS (Middlesex County) because of more up-to-
date hydraulic analyses. 
In Chelsea, a drainage study of Mill Creek was performed for the Massachusetts Department of
Public Works in 1975 (Reference 21). The purpose of the study was to analyze the causes of
frequent flooding at the housing project near Mill Creek upstream of U. S. Route 1. Discharges
related to the drainage study were compared to discharges developed by a Massachusetts regional
equation (Reference 57). The differences between the values determined by the two methods were
so great that a third method was applied. A SCS method derived for small watersheds was
incorporated to develop additional flow values (Reference 58). The 1-percent-annual-chance
discharge determined by the SCS method was very similar to that developed for the drainage study.
As the SCS method may not be appropriate for such extensively urbanized watersheds, the values
from the drainage study were adopted for the hydraulic analysis in this countywide study. 
8.0 LOCATION OF DATA 
Information concerning the pertinent data used in the preparation of this study can be obtained by
contacting FEMA Region I, 99 High Street, 6th Floor, Boston, MA 02110.

49 
9.0 BIBLIOGRAPHY AND REFERENCES 
1. Federal Emergency Management Agency, Flood Insurance Study, Suffolk County, Suffolk County,
Massachusetts, Washington, D.C., September 25, 2009. 
2. MassGIS, 2005 1:5,000 Color Orthoimagery, http://www.massgis.gov/mgis, April 2005. 
3. MassGIS, 2008 USGS High Resolution Color Orthoimagery, http://www.massgis.gov/mgis, April
2008 
4. U.S. Census Bureau (2010): Retrieved June 13, 2012.
http://quickfacts.census.gov/qfd/states/09/09007.html 
5. National Weather Service, Taunton. Boston Daily Normals. 2006. 
6. Weatherbase. Historical Weather for Boston, Massachusetts, United States of America. 2008. 
7. City of Boston Film Bureau. Weather. 2007. 
8. Massachusetts Agricultural Experiment Station, Remote Sensing 20 Years of Change in Suffolk and
Norfolk Counties, Massachusetts, 1951-1971 by William P. McConnell, August 1974. 
9. NOAA Satellite and Information Service, National Climatic Data Center, US Department of
Commerce, retrieved July 2012 from
http://www.ncdc.noaa.gov/oa/satellite/satelliteseye/cyclones/pfctstorm91/pfctstorm.html 
10. Massachusetts Emergency Management Agency, Department of Conservation and Recreation,
Commonwealth of Massachusetts, State Hazard Mitigation Plan, October 2010. 
11. Boston Globe, Tired Irene slaps N.E., retrieved July 2012 from http://articles.boston.com/2011-08-
29/news/29941847_1_flood-waters-hurricane-irene-vermont-town/ 
12. NOAA Satellite and Information Service, National Climatic Data Center, US Department of
Commerce, retrieved November 2013 from http://www.ncdc.noaa.gov/stormevents 
13. Boston Globe, Strain on roofs, roads, spirits, retreived July 2012 from,
http://www.boston.com/news/local/massachusetts/articles/2011/02/03/slush_collapses_roofs_floods
_roads 
14. U.S. Army Corps of Engineers, North Atlantic Division. National Shoreline Study. Regional
Inventory Report, North Atlantic Region, Volume I. New York, 1971. 
15. Water Resources Council, A Uniform Technique for Determining Flood Flow Frequency, Bulletin
15, Washington, D. C., December 1967.

50 
16. U.S. Army Corps of Engineers, New England District, Interim Report on the Charles River for
Flood Control and Navigation; Lower Charles River, Waltham, Massachusetts, May 1968. 
17. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood
Insurance Study, Town of Dedham, Norfolk County, Massachusetts, Washington, D.C., May 1977. 
18. U.S. Army Corps of Engineers, New England District, Charles River Study, Appendices D and H,
Waltham, Massachusetts, May 1972. 
19. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood
Insurance Study, Town of Milton, Norfolk County, Massachusetts, Washington, D.C., March 1977. 
20. U.S. Department of the Interior, Geological Survey, Coastal Flood of February 7, 1978, in Maine,
Massachusetts, and New Hampshire, No. 79-61, Boston, Massachusetts, 1979. 
21. Congdon, Gurney and Towle, Inc., prepared for the Massachusetts Department of Public Works,
Mill Creek Drainage Study, Boston, Massachusetts, 1975. 
22. Stone & Webster Engineering Corporation, Development and Verification of a Synthetic
Northeaster Model for Coastal Flood Analysis, Boston, Massachusetts, October 1979 
23. Moore Survey and Mapping Corporation of Shrewsbury, Massachusetts, Topographic Maps
compiled by photogrammetric methods, Scale 1"=400’, Contour Interval 5 Feet: Chelsea,
Massachusetts, 1977. 
24. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-2 Water Surface Profiles,
Generalized Computer Program, Davis, California, October 1973. 
25. Anderson-Nichols Co., Neponset River Basin Flood Plain and Wetland Encroachment Study,
Boston, Massachusetts, April 1971. 
26. C.E. Maguire, Inc., The Proposed Charles River Project, Waltham, Massachusetts, October 1974. 
27. U.S. Army Corps of Engineers, New England District, Charles River Locks and Dam (Design
Memorandum No. 1) Hydrology and Tidal Hydraulics, Waltham, Massachusetts, May 1971. 
28. U.S. Department of the Interior, Geological Survey, Water Resources Investigations 79-61, Coastal
Flood of February 7, 1978, Maine, Massachusetts, and New Hampshire, Boston, Massachusetts,
1979. 
29. Federal Disaster Assistance Administration, Damage Survey Reports & the Town of Winthrop,
Massachusetts, Washington, D.C., February 1978. 
30. U.S. Army Corps of Engineers, New England District, Frequency of Tidal Flooding at Boston
Harbor, Waltham, Massachusetts, April 1979. 
31. Federal Emergency Management Agency, Guidelines and Specifications for Flood Hazard Mapping
Partners. Appendix D, Guidance for Coastal Flooding Analyses and Mapping, April 2003.

51 
32. STARR, prepared for the Federal Emergency Management Agency, Regional Frequency Analyses
using L Moments, November 3, 2010. 
33. U.S. Army Corps of Engineers. 2002, updated through 2011. Coastal Engineering Manual. Engineer
Manual 1110-2-1100, U.S. Army Corps of Engineers, Washington, D.C. (in 6 volumes). 
34. Federal Emergency Management Agency, Atlantic Ocean and Gulf of Mexico Coastal Guidelines
Update, Final Draft, Washington, D.C., February 2007. 
35. Divoky, D., Supplementary WHAFIS Documentation, WHAFIS 4.0, A Revision of FEMA’s
WHAFIS 3.0 Program, August 10, 2007. 
36. Federal Emergency Management Agency, Coastal Hazard Analysis Modeling Program (CHAMP),
Version 2.0, Washington, D.C., August 2007. 
37. Federal Emergency Management Agency, Coastal Hazard Analysis Modeling Program (CHAMP),
Users Guide, Version 2.0, Washington, D.C., August 2007. 
38. Yoshimi Goda, Random Seas and Design of Maritime Structures, 2nd Edition, World Scientific,
2000. 
39. National Academy of Sciences, Methodology for Calculating Wave Action Effects Associated with
Storm Surges, Washington, D.C., 1977. 
40. U.S. Army Corps of Engineers, Coastal Engineering Research Center, Shore Protection Manual,
(Volumes I and II, 4th Edition), Washington, D.C., 1984. 
41. U.S. Army Corps of Engineers, Galveston District, Guidelines for Identifying Coastal High Hazard
Zones, Galveston, Texas, June 1975. 
42. Federal Emergency Management Agency, Procedure Memorandum No. 50 – Policy and Procedure
for Identifying and Mapping Areas Subject to Wave Heights Greater than 1.5 feet as an Information
Layer on Flood Insurance Rate Maps (FIRMs), Washington, D.C., December 3, 2008. 
43. Federal Emergency Management Agency, Users Manual for Wave Height Analysis, Washington,
D.C., Revised February 1981. 
44. STARR, Light Detecting and Ranging (LiDAR) data. 5-foot floating point digital elevation model
(DEM), North American Vertical Datum of 1988 (NAVD 88). 2-foot contours were created from
the terrain deliverable. 
45. National Oceanographic and Atmospheric Administration (NOAA) National Ocean Service (NOS)
Hydrographic Data Base (NOSHDB) and Hydrographic Survey Meta Data Base (HSMDB)
(NOAA), Bathymetry, May 27, 2010. 
46. Boston Redevelopment Authority, Topographic Mapping, City of Boston, Scale 1:1,200, Contour
Interval 5 Feet, Boston, Massachusetts, 1967.

52 
47. James W. Sewall Co., of Old Town, Maine, Topographic Maps, Scale 1: 2,400, Contour Interval 5
Feet: Winthrop, Massachusetts, December 1978. 
48. Federal Emergency Management Agency, Flood Insurance Study, City of Boston, Suffolk County,
Massachusetts, Washington, D. C., October 1, 1983. 
49. U.S. Department of the Interior, Geological Survey, 7.5-Minute Series Topographic Maps, Scale
1:24,000, Contour Interval 10 Feet: Boston North, Massachusetts, 1971. 
50. U.S. Department of Interior, USGS. Topographic Maps. Scale 1:25,000, Contour Interval 10 feet.
Lynn, 1970; Boston North, 1979. 
51. Anderson-Nichols Co., Mother Brook, Flood Control Feasibility Study, Boston, Massachusetts,
February 1973. 
52. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood
Insurance Study, City of Quincy, Norfolk County, Massachusetts, Washington, D.C., March 1973. 
53. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood
Insurance Study, City of Newton, Middlesex County, Massachusetts, Washington, D.C., December
1977. 
54. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood
Insurance Study, Town of Needham, Norfolk County, Massachusetts, Washington, D.C., November
1972. 
55. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood
Insurance Study, Town of Brookline, Norfolk County, Massachusetts, Washington, D.C., November
1976. 
56. U.S. Department of Housing and Urban Development, Federal Insurance Administration, Flood
Insurance Study, Town of Winthrop, Suffolk County, Massachusetts, Washington, D.C., September
1975. 
57. U.S. Department of the Interior, Geological Survey, Water Resources Investigations 77-39,
Estimating the Magnitude and Frequency of Floods Natural-Flow Streams in Massachusetts by S.W.
Wandle, Jr., Washington, D.C. 1977. 
58. U.S. Department of Agriculture, Soil Conservation Service, Technical Paper 149, A Method for
Estimating Volume and Rate of Runoff in Small Watersheds, Washington, D.C., April 1973.

65
70
75 75
80 80
85 85
90 90
95 95
100 100
105 105
110 110
124400 124600 124800 125000 125200 125400 125600 125800 126000 126200 126400 126600 126800 127000
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE MOUTH
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA 
ALL JURISDICTIONS
FLOOD PROFILES
CHARLES RIVER
01P
LIMIT OF FLOODING AFFECTING COMMUNITIES
CITY OF NEWTON
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
MIDDLESEX COUNTY
SUFFOLK COUNTY
CITY OF BOSTON

65
70
75 75
80 80
85 85
90 90
95 95
100 100
105 105
110 110
127000 127200 127400 127600 127800 128000 128200 128400 128600 128800 129000 129200 129400 129600
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE MOUTH
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
CHARLES RIVER
02P
A B C
RAILROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

65
70
75 75
80 80
85 85
90 90
95 95
100 100
105 105
110 110
129600 129800 130000 130200 130400 130600 130800 131000 131200 131400 131600 131800 132000 132200
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE MOUTH
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
CHARLES RIVER
03P
D
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

60
65
70 70
75 75
80 80
85 85
90 90
95 95
100 100
105 105
132200 132400 132600 132800 133000 133200 133400 133600 133800 134000 134200 134400 134600 134800
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE MOUTH
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
CHARLES RIVER
04P
E F G
SPRING STREET
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

65
70
75 75
80 80
85 85
90 90
95 95
100 100
105 105
110 110
134800 135000 135200 135400 135600 135800 136000 136200 136400 136600 136800
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE MOUTH
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
CHARLES RIVER
05P
CITY OF BOSTON
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
SUFFOLK COUNTY
NORFOLK COUNTY
TOWN OF DEDHAM
LIMIT OF FLOODING AFFECTING COMMUNITY

-15
-10
-5 -5
0 0
5 5
10 10
15 15
20 20
25 25
30 30
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH CHELSEA RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MILL CREEK
06P
A B C D E
CONFLUENCE WITH CHELSEA RIVER
LIMIT OF DETAILED STUDY
BOSTON AND MAINE RAILROAD
BROADWAY
ACCESS ROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
1% BACKWATER EFFECT FROM CHELSEA RIVER

20
25
30 30
35 35
40 40
45 45
50 50
55 55
60 60
65 65
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH NEPONSET RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MOTHER BROOK
07P
A B C D E F
G
CONFLUENCE WITH NEPONSET RIVER
HYDE PARK AVENUE
RAILROAD
RESERVATION ROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

25
30
35 35
40 40
45 45
50 50
55 55
60 60
65 65
70 70
2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600 4800 5000 5200
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH NEPONSET RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MOTHER BROOK
08P
H I
J
KNIGHT STREET
RIVER STREET
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

30
35
40 40
45 45
50 50
55 55
60 60
65 65
70 70
75 75
5200 5400 5600 5800 6000 6200 6400 6600 6800 7000 7200 7400 7600
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH NEPONSET RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MOTHER BROOK
09P
K L
CITY OF BOSTON
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
NORFOLK COUNTY
SUFFOLK COUNTY
TOWN OF DEDHAM
LIMIT OF DETAILED STUDY

-15
-10
-5 -5
0 0
5 5
10 10
15 15
20 20
25 25
30 30
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH CHARLES RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MUDDY RIVER
10P
A B C D
CONFLUENCE WITH CHARLES RIVER
STORROW MEMORIAL DRIVE
COMMONWEALTH AVENUE
SERVICE ROAD
MASSACHUSETTS TURNPIKE
RAILROAD
FENWAY
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
INTERSTATE 90
IPSWICH STREET
BEACON STREET
CULVERT

-15
-10
-5 -5
0 0
5 5
10 10
15 15
20 20
25 25
30 30
2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600 4800 5000 5200
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH CHARLES RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MUDDY RIVER
11P
E
F
AGASSIZ BRIDGE
FOOTBRIDGE
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

-15
-10
-5 -5
0 0
5 5
10 10
15 15
20 20
25 25
30 30
5200 5400 5600 5800 6000 6200 6400 6600 6800 7000 7200 7400 7600 7800
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH CHARLES RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MUDDY RIVER
12P
G
H FOOTBRIDGE
LOUIS PASTEUR BRIDGE
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
CULVERT

-15
-10
-5 -5
0 0
5 5
10 10
15 15
20 20
25 25
30 30
7800 8000 8200 8400 8600 8800 9000 9200 9400 9600 9800 10000 10200 10400
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH CHARLES RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MUDDY RIVER
13P
I
PILGRIM ROAD
BROOKLINE AVE
RIVERWAY
RIVERWAY
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
CULVERT

-15
-10
-5 -5
0 0
5 5
10 10
15 15
20 20
25 25
30 30
10400 10600 10800 11000 11200 11400 11600 11800 12000 12200 12400 12600 12800
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH CHARLES RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MUDDY RIVER
14P
J
K
LONGWOOD AVENUE
NETHERLANDS ROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

-15
-10
-5 -5
0 0
5 5
10 10
15 15
20 20
25 25
30 30
12800 13000 13200 13400 13600 13800 14000 14200 14400 14600 14800 15000 15200 15400
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH CHARLES RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MUDDY RIVER
15P
L M N
O
BROOKLINE AVENUE
RIVER ROAD
WASHINGTON STREET
ACCESS ROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
CULVERT
LEVERETT POND

-15
-10
-5 -5
0 0
5 5
10 10
15 15
20 20
25 25
30 30
15400 15600 15800 16000 16200 16400 16600 16800 17000 17200 17400 17600 17800 18000
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH CHARLES RIVER
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
MUDDY RIVER
16P
P
LIMIT OF DETAILED STUDY
WILLOW POND ROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
CULVERT
LEVERETT POND WILLOW POND

-5
0
5 5
10 10
15 15
20 20
25 25
30 30
35 35
40 40
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
17P
A B C D E F G
DAM AT LOWER MILLS
AUTHORITY RAILROAD
CENTRAL AVENUE
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
MASSACHUSETTS BAY TRANSPORTATION

-5
0
5 5
10 10
15 15
20 20
25 25
30 30
35 35
40 40
2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600 4800 5000 5200
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
18P
H I
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

0
5
10 10
15 15
20 20
25 25
30 30
35 35
40 40
45 45
5200 5400 5600 5800 6000 6200 6400 6600 6800 7000 7200 7400 7600 7800
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
19P
J K L
M
TRANSPORTATION AUTHORITY
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
MASSACHUSETTS BAY

5
10
15 15
20 20
25 25
30 30
35 35
40 40
45 45
50 50
7800 8000 8200 8400 8600 8800 9000 9200 9400 9600 9800 10000 10200 10400
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
20P
N O P
Q
BLUEHILL PARKWAY
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

10
15
20 20
25 25
30 30
35 35
40 40
45 45
50 50
55 55
10400 10600 10800 11000 11200 11400 11600 11800 12000 12200 12400 12600 12800 13000
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
21P
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

10
15
20 20
25 25
30 30
35 35
40 40
45 45
50 50
55 55
13000 13200 13400 13600 13800 14000 14200 14400 14600 14800 15000 15200 15400 15600
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
22P
R S T U
RAILROAD
TILESTON AND HOLLINGSWORTH DAM
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

15
20
25 25
30 30
35 35
40 40
45 45
50 50
55 55
60 60
15600 15800 16000 16200 16400 16600 16800 17000 17200 17400 17600 17800 18000 18200
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
23P
V
RAILROAD BRIDGE
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

15
20
25 25
30 30
35 35
40 40
45 45
50 50
55 55
60 60
18200 18400 18600 18800 19000 19200 19400 19600 19800 20000 20200 20400 20600 20800
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
24P
W X Y Z
AA
CONFLUENCE OF MOTHER BROOK
FAIRMONT AVENUE
RAILROAD
DANA AVENUE
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
STRUCTURE IS NOT SHOWN
WITHIN THIS PANEL
(BOTTOM OF ROAD 53.2)

15
20
25 25
30 30
35 35
40 40
45 45
50 50
55 55
60 60
20800 21000 21200 21400 21600 21800 22000 22200 22400 22600 22800 23000 23200 23400
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
25P
AB AC
GLENWOOD AVENUE FOOTBRIDGE
RAILROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

15
20
25 25
30 30
35 35
40 40
45 45
50 50
55 55
60 60
23400 23600 23800 24000 24200 24400 24600 24800 25000 25200 25400 25600 25800 26000
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
26P
AD
TRUMAN HIGHWAY
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

20
25
30 30
35 35
40 40
45 45
50 50
55 55
60 60
65 65
26000 26200 26400 26600 26800 27000 27200 27400 27600 27800 28000 28200 28400 28600
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
27P
AE
NEPONSET VALLEY PARKWAY
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

20
25
30 30
35 35
40 40
45 45
50 50
55 55
60 60
65 65
28600 28800 29000 29200 29400 29600 29800 30000 30200 30400 30600 30800 31000 31200
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE DAM AT LOWER MILLS
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNTY, MA
ALL JURISDICTIONS
FLOOD PROFILES
NEPONSET RIVER
28P
SUFFOLK COUNTY / CITY OF BOSTON
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
NORFOLK COUNTY / TOWN OF DEDHAM LIMIT OF DETAILED STUDY

35
40
45 45
50 50
55 55
60 60
65 65
70 70
75 75
80 80
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CULVERT ENTRANCE
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNT, MA
ALL JURISDICTIONS
FLOOD PROFILES
STONY BROOK
29P
ENNEKING PARKWAY
ENNEKING PARKWAY
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
CULVERT ENTRANCE LIMIT OF DETAILED STUDY

35
40
45 45
50 50
55 55
60 60
65 65
70 70
75 75
80 80
1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CULVERT ENTRANCE
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNT, MA
ALL JURISDICTIONS
FLOOD PROFILES
STONY BROOK
30P
A B C
D
ACCESS ROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

70
75
80 80
85 85
90 90
95 95
100 100
105 105
110 110
115 115
2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700 3800 3900
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CULVERT ENTRANCE
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNT, MA
ALL JURISDICTIONS
FLOOD PROFILES
STONY BROOK
31P
E
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

95
100
105 105
110 110
115 115
120 120
125 125
130 130
135 135
140 140
3900 4000 4100 4200 4300 4400 4500 4600 4700 4800 4900 5000 5100 5200
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CULVERT ENTRANCE
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNT, MA
ALL JURISDICTIONS
FLOOD PROFILES
STONY BROOK
32P
F
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION

105
110
115 115
120 120
125 125
130 130
135 135
140 140
145 145
150 150
5200 5300 5400 5500 5600 5700 5800 5900 6000 6100 6200 6300 6400 6500
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CULVERT ENTRANCE
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNT, MA
ALL JURISDICTIONS
FLOOD PROFILES
STONY BROOK
33P
G H
TURTLE POND ACCESS ROAD
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
TURTLE POND

110
115
120 120
125 125
130 130
135 135
140 140
145 145
150 150
155 155
6500 6600 6700 6800 6900 7000
ELEVATION IN FEET (NAVD 88)
STREAM DISTANCE IN FEET ABOVE CULVERT ENTRANCE
FEDERAL EMERGENCY MANAGEMENT AGENCY
SUFFOLK COUNT, MA
ALL JURISDICTIONS
FLOOD PROFILES
STONY BROOK
34P
LIMIT OF DETAILED STUDY
LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION LOCATION
TURTLE POND