HomeMy Public PortalAboutFlood Insurance Study_2008FLOOD
INSURANCE
STUDY
CHATHAM COUNTY,
GEORGIA
AND
INCORPORATED AREAS
Community
Name
BLOOMINGDALE, CITY OF
CHATHAM COUNTY
(UNINCORPORATED AREAS)
GARDEN CITY, CITY OF
POOLER, CITY OF
PORT WENTWORTH, CITY OF
SAVANNAH, CITY OF
THUNDERBOLT, TOWN OF
TYBEE ISLAND, CITY OF
VERNONBURG, TOWN OF
Community
Number
130452
130030
135161
130261
135162
135163
130460
135164
135165
CHATHAM COUNTY
Effective: September 26, 2008
Federal Emergency Management Agency
FLOOD INSURANCE STUDY NUMBER
13051 CV000A
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) report may not
contain all data available within the Community Map Repository. Please contact
the Community Map Repository for any additional data.
The Federal Emergency Management Agency (FEMA) may revise and republish
part or all of this FIS report at any time. In addition, FEMA may revise part of
this FIS report by the Letter of Map Revision process, which does not involve
republication or redistribution of the FIS report. Therefore, users should consult
with community officials and check the Community Map Repository to obtain
the most current FIS report components.
Selected Flood Insurance Rate Map (FIRM) panels for this community contain
information that was previously shown separately on the corresponding Flood
Boundary and Floodway Map panels (e.g., floodways, cross sections). In
addition, former flood hazard zone designations have been changed as follows:
Old Zone(s) New Zone
Al through A30 AE
VI through V30 VE
B X
C X
Initial Countywide FIS Effective Date: September 26, 2008
TABLE OF CONTENTS
1.0 INTRODUCTION 1
1.1 Purpose of Study 1
1.2 Authority and Acknowledgments 1
1.3 Coordination 5
2.0 AREA STUDIED 6
2.1 Scope of Study 6
2.2 Community Description 10
2.3 Principle Flood Problems 11
2.4 Flood Protection Measures 15
3.0 ENGINEERING METHODS 15
3.1 Hydrologic Analyses 15
3.2 Hydraulic Analyses 22
3.3 Wave Height Analysis 28
3.4 Vertical Datum 32
4.0 FLOODPLAIN MANAGEMENT APPLICATIONS 38
4.1 Floodplain Boundaries 38
4.2 Floodways 39
4.3 Base Flood Elevations 44
4.4 Velocity Zones 44
5.0 INSURANCE APPLICATIONS 44
6.0 FLOOD INSURANCE RATE MAP 46
7.0 OTHER STUDIES 47
8.0 LOCATION OF DATA 47
9.0 BIBLIOGRAPHY AND REFERENCES 47
i
TABLE OF CONTENTS (CONTINUED)
FIGURES
Figure 1 - Transect Location Map 29
Figure 2 - Transect Schematic 32
Figure 3 - Floodway Schematic 40
TABLES
Table 1 - Parameter Values for Surge Elevation Computations 16
Table 2 - Summary of Discharges 19
Table 3 - Summary of Stillwater Elevations 22
Table 4 - Transect Locations, Stillwater Starting Elevations, and Initial Wave Crests 30
Table 5 - Transect Data 33
Table 6 - Vertical Datum Conversion 37
Table 7 - Floodway Data 41
Table 8 - Community Map History 48
EXHIBITS
Exhibit 1 - Flood Profiles
Black Creek
Black Creek Tributary No. 2
Casey Canal
Chippewa Canal
Colonial Oaks Canal
Colonial Oaks Canal Tributary No. 1
Colonial Oaks Canal Tributary No. 1.1
Hardin Canal
Harmon Canal
Kingsway Canal
Little Ogeechee River
Little Ogeechee River Tributary
Louis Mills Branch
Ogeechee River
Pipe Makers Canal
Pipe Makers Canal Tributary No. 2
Salt Creek Tributary
Savannah River
Springfield Canal
Springfield Canal Tributary A
St. Augustine Creek
St. Augustine Creek Tributary
Tributary to Little Ogeechee River Tributary
ii
Panels 01P -04P
Panels 05P -06P
Panels 07P -09P
Panel 10P
Panels 11P -12P
Panel 13P
Panel 14P
Panels 15P -17P
Panels 18P -19P
Panel 20P
Panels 21P -22P
Panels 23P -26P
Panels 27P -28P
Panel 29P
Panels 30P -32P
Panels 33P -34P
Panels 35P -36P
Panels 37P -38P
Panel 39P
Panels 40P-41P
Panel 42P
Panels 43P -44P
Panels 45P -46P
TABLE OF CONTENTS (CONTINUED)
EXHIBITS (CONTINUED)
Exhibit 1 - Flood Profiles (Continued)
Wilshire Canal
Wilshire Canal Tributary A
Wilshire Canal Tributary A -1
Windsor Forest Canal East
Windsor Forest Canal Tributary
Windsor Forest Canal Tributary No. 2
Windsor Forest Canal Tributary No. 3
Windsor Forest Canal West
Exhibit 2 - Flood Insurance Rate Map Index
Flood Insurance Rate Map
iii
Panel 47P
Panel 48P
Panel 49P
Panels 50P -51P
Panel 52P
Panel 53P
Panel 54P
Panel 55P
FLOOD INSURANCE STUDY
CHATHAM COUNTY, GEORGIA AND INCORPORATED AREAS
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 Chatham
County, including the Cities of Bloomingdale, Garden City, Pooler, Port
Wentworth, Savannah, and Tybee Island; the Towns of Thunderbolt and
Vernonburg; and the unincorporated areas of Chatham County (referred to
collectively herein as Chatham 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. In such cases, the more restrictive criteria take precedence and the
State (or other jurisdictional agency) will be able to explain them.
The Digital Flood- Insurance Rate Map (DFIRM) and FIS report for this
countywide study have been produced in digital format. Flood hazard
information was converted to meet the Federal Emergency Management Agency
(FEMA) DFIRM database specifications and Geographic Information System
(GIS) format requirements. The flood hazard information was created and is
provided in a digital format so that it can be incorporated into a local GIS and be
accessed more easily by the community.
1.2 Authority and Acknowledgments
The sources of authority for this FIS are the National Flood Insurance Act of
1968 and the Flood Disaster Protection Act of 1973.
Precountywide Analyses
Information on the authority and acknowledgements for each jurisdiction
included in this countywide FIS, as compiled from their previously printed FIS
reports, is shown below in the following tabulation:
1
Bloomingdale, City of:
Chatham County
(Unincorporated Areas):
For the initial January 2, 1981, FIS report and
the July 2, 1981 Flood Insurance Rate Map
(FIRM) (FIA, 1981a), the hydrologic and
hydraulic analyses were prepared by Post,
Buckley, Schuh & Jernigan, Inc. (PBS &J), for
the Federal Insurance Administration (FIA),
under Contract No. H -4778. The work was
completed in July 1979.
For the May 7, 2001, revision (FEMA, 2001),
the hydrologic and hydraulic analyses for Pipe
Makers Canal Tributary No. 2 were prepared
by Braswell Engineering, Inc., for FEMA,
under Contract No. EMW -96 -CO -0021. The
work was completed in May 1999.
For the May 19, 1987, FIS report (FEMA,
1987a), the hydrologic and hydraulic analyses
for the coastal flooding from the Atlantic
Ocean were performed by PBS &J for FEMA,
under Contract No. EMW -C -0947. The work
was completed in February 1984.
All remaining flooding information was taken
from the previous Type 10 (FIA, 1971) and
Type 15 (FEMA, 1983) FIS reports.
Garden City, City of: For the May 19, 1987, FIS report (FEMA,
1987b), the hydrologic and hydraulic analyses
were obtained from the FIS report for Chatham
County, Georgia (Unincorporated Areas)
(FEMA, 1987a).
Pooler, City of: For the March 30, 1981, FIS report (FIA,
1981b), the hydrologic and hydraulic analyses
were performed by PBS &J, for the FIA, under
Contract No. H -4778. The work was
completed in August 1979.
Port Wentworth, City of: For the May 19, 1987 FIS report (FEMA,
1987c), the hydrologic and hydraulic analyses
were obtained from the Type 19 (FEMA,
1987a) and Type 15 (FEMA, 1983) FIS
reports for Chatham County, Georgia
(Unincorporated Areas).
Savannah, City of:
Thunderbolt, Town of:
Tybee Island, City of:
Vernonburg, Town of:
This Countywide FIS Report
For the September 4, 1987 (FEMA, 1987d) FIS
report, the hydrologic and hydraulic analyses
for the storm surge were obtained from the
Type 19 (FEMA, 1987a) FIS report for
Chatham County, Georgia (Unincorporated
Areas).
The riverine hydrologic and hydraulic analyses
were obtained from the previous Type 19 FIS
report for the City of Savannah, Chatham
County, Georgia and Flood Plain Information
Reports for Pipe Makers Canal, Dundee Canal
and Salt Creek, Casey Canal -North, Casey
Canal - South, Springfield Canal, Harmon
Canal, and Wilshire Canal and Tributaries
(USACE, 1968a; USACE, 1968b; USACE,
1972; USACE, 1969; USACE, 1974; USACE,
1970; USACE, 1971).
The hydrologic and hydraulic analyses for the
July 2, 1987, FIS report (FEMA, 1987e), were
obtained from the Type 19 FIS report for
Chatham County, Georgia (Unincorporated
Areas) (FEMA, 1987a).
The hydrologic and hydraulic analyses for the
June 17, 1986, FIS report (FEMA, 1986), were
obtained from the FIS report for Chatham
County, Georgia (Unincorporated Areas)
(FEMA, 1987a).
The hydrologic and hydraulic analyses for the
July 2, 1987, FIS report (FEMA, 19870, were
obtained from the FIS report for Chatham
County, Georgia (Unincorporated Areas)
(FEMA, 1987a).
For this initial countywide FIS, PBS &J was contracted by Chatham County to
complete the Mapping Services to Update Flood Hazard Maps in Chatham
County, Contract No. QBS- 06 -8 -4. Under this contract, PBS &J upgraded
previously completed engineering reports for inclusion into the FEMA DFIRM
and FIS for Chatham County. The previously completed engineering reports
contained detailed hydrology and hydraulic modeling for various flooding
sources within Chatham County which were submitted to and approved by
Chatham County. The flooding sources and previously completed engineering
reports upgraded by PBS &J under this contract are presented in the following
table:
Flooding Source
Hardin Canal
Kingsway Canal
Louis Mills Branch
Pipe Makers
Canal
Placentia Canal
Quacco Canal
Rahn Dairy Canal
Engineering Report Company
Hardin Canal Re- Analysis Using
ATLM Data
Kingsway Canal Design Study
Report
Louis Mills Branch /Redgate
Canal Engineering Analysis
Pipe Makers Canal Drainage
Study, Supplemental Report
Placentia Canal Concept Design
Shell Road to Tide Gate
Quacco /Regency Park Drainage
Improvements Alternatives
Report
Redgate /Rahn Dairy Canal
Design Study Report
Thomas & Hutton
Engineering Company
Thomas & Hutton
Engineering Company
Thomas & Hutton
Engineering Company
EMC Engineering
Hussey, Gay, Bell, &
DeYoung, Inc.
Thomas & Hutton
Engineering Company
Date of Study
January 7, 2000
July 2004
March 27, 1998
April 1999
May 1996
November 2005
Thomas & Hutton July 2004
Engineering Company
The hydrologic and hydraulic analyses for Black Creek and Black Creek
Tributary No. 2 were reviewed and incorporated by PBS &J, for the Georgia
Department of Natural Resources (DNR), under Contract No. EMA- 2005 -CA-
5211, with FEMA. The work was completed in July 2007.
The flooding sources incorporated by PBS &J under Contract No. DR912 with
the City of Savannah are listed in the following table:
Flooding Source
Casey Canal
Chippewa Canal
Coffee Bluff Basin
Colonial Oaks Canal
Colonial Oaks Canal Tributary No. 1
Colonial Oaks Canal Tributary No. 1.1
Evergreen Cemetery Tributary
Fell Street Basin
Harmon Canal
Little Ogeechee River Tributary
Springfield Canal
Springfield Canal Tributary A
Tributary to Little Ogeechee River Tributary
Wilshire Canal
Wilshire Canal Tributary A
Wilshire Canal Tributary A -1
Windsor Forest Canal East
Windsor Forest Canal Tributary
4
Study Contractor
EMC Engineering
USACE
Hussey, Gay, Bell, & DeYoung, Inc.
EMC Engineering
EMC Engineering
EMC Engineering
USACE
EMC Engineering
USACE
Kimley - Horn
Thomas & Hutton Engineering Company and
PBS &J
Thomas & Hutton Engineering Company
Kimley - Horn
Thomas & Hutton Engineering Company
Thomas & Hutton Engineering Company
Thomas & Hutton Engineering Company
EMC Engineering
EMC Engineering
Flooding Source Study Contractor
Windsor Forest Canal Tributary No. 2
Windsor Forest Canal Tributary No. 3
Windsor Forest Canal West
EMC Engineering
EMC Engineering
EMC Engineering
Base map information shown on the Flood Insurance Rate Map (FIRM) was
provided for Chatham County and captured at a resolution of 1 foot per pixel.
The projection used in the preparation of this map is Georgia State Plane East
(FIPS zone 1001). The horizontal datum is North American Datum 1983.
1.3 Coordination
An initial meeting is held with representatives from FEMA, the community, and
the study contractor to explain the nature and purpose of a FIS, and to identify
the streams to be studied or restudied.
Precountywide Analyses
The initial and final meeting dates for previous FIS reports for Chatham County
and its communities are listed in the following tabulation:
Communit
Bloomingdale, City of
Chatham County
(Unincorporated Areas)
Garden City, City of
Pooler, City of
Port Wentworth, City of
Savannah, City of
Thunderbolt, Town of
Tybee Island, City of
Vernonburg, Town of
FIS Date
January 2, 1981
May 7, 2001
May 19, 1987
May 19, 1987
March 30, 1981
May 19, 1987
September 4, 1987
July 2, 1987
June 17, 1986
July 2, 1987
*Notified by a letter ** Data not available
This Countywide FIS Report
Initial Meeting
May 1978
July 1, 1999*
June 22, 1982
Final Meeting
August 27, 1980
November 21, 1985
November 19, 1985
August 27, 1980
November 19, 1985
November 21, 1985
November 19, 1985
November 20, 1985
November 22, 1985
For this initial countywide FIS, the initial meeting was held on
September 29, 2004, and attended by representatives of FEMA, the Georgia
DNR, PBS &J, and the communities. The final meeting was held on November 7,
2007, and attended by representatives of FEMA, the Georgia DNR, PBS &J, and
all the communities except for the Town of Vernonburg. All problems raised at
the meeting have been addressed.
5
2.0 AREA STUDIED
2.1 Scope of Study
This FIS covers the geographic area of Chatham County, Georgia, 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.
Precountywide Analyses
The following streams were studied by detailed methods in Chatham County:
Atlantic Ocean
Black Creek
Black Creek Tributary No. 2
Casey Canal
Chippewa Canal
Colonial Oaks Canal
Colonial Oaks Canal Tributary No. 1
Colonial Oaks Canal Tributary No. 1.1
Hardin Canal
Harmon Canal
Kingsway Canal
Little Ogeechee River
Little Ogeechee River Tributary
Louis Mills Branch
Ogeechee River
Pipe Makers Canal
Pipe Makers Canal Tributary No. 2
Salt Creek Tributary
Savannah River
Springfield Canal
Springfield Canal Tributary A
St. Augustine Creek
St. Augustine Creek Tributary
Tributary to Little Ogeechee River Tributary
Wilshire Canal
Wilshire Canal Tributary A
Wilshire Canal Tributary A -1
Windsor Forest Canal East
Windsor Forest Canal Tributary
Windsor Forest Canal Tributary No. 2
Windsor Forest Canal Tributary No. 3
Windsor Forest Canal West
The limits of detailed study are indicated on the Flood Profiles (Exhibit 1) and
on the FIRM (Exhibit 2).
For the May 19, 1987, FIS report for Chatham County, Georgia (Unincorporated
Areas), the areas studied by detailed methods were selected based on the extent
and validity of available existing hydrologic and hydraulic data. A detailed
coastal flooding analysis of the Atlantic Ocean was performed on the complete
coastline of Chatham County.
This Countywide Analyses
For this initial countywide FIS, the areas studied by detailed methods were
selected based on the extent and validity of available existing hydrologic and
hydraulic data.
The following streams were studied by detailed methods as part of this
countywide revision:
6
Stream Reach Limits
Black Creek
Black Creek Tributary No. 2
Chippewa Canal
Colonial Oaks Canal
Colonial Oaks Canal Tributary No. 1
Colonial Oaks Canal Tributary No. 1.1
Hardin Canal
Harmon Canal
Kingsway Canal
Little Ogeechee River Tributary
Louis Mills Branch
Pipe Makers Canal
Placentia Canal*
From its confluence with Savannah River to approximately
11,540 feet upstream of Augusta Road / State Highway 30 / 21
From its confluence with Black Creek to approximately 2,980 feet
upstream of Saussy Road
From its confluence with Harmon Canal to approximately 1,060
feet upstream of Mall Boulevard
From 420 feet downstream of Coffee Bluff Road to Briarcliff
Circle
From its confluence with Colonial Oaks Canal to approximately
660 feet upstream of Rockingham Road
From its confluence with Colonial Oaks Canal Tributary No. 1 to
approximately 310 feet upstream of Stillwood Drive
From U.S. Highway 17 / Atlantic Coastal Highway / Ogeechee
Road to approximately 1,180 feet upstream of Osteen Road
From the confluence with Vernon River to approximately 600 feet
upstream of West Montgomery Cross Road / State Highway 204
From its confluence with Vernon River to approximately 1,180
feet upstream of Kings Way
From Little Neck Road to approximately 3,120 feet upstream of
Middle Landing Road
From its confluence with South Springfield Canal to
approximately 1,980 feet upstream of Marshall Avenue
From its confluence with Savannah River to U.S. Highway 80 /
State Highway 17 / 26
From its confluence with Wilmington River to Bona Bella Avenue
Quacco Canal* From the Atlantic Coastal Highway / State Highway 25 / U.S.
Highway 17 to Quacco Road
Rahn Dairy Canal* From its confluence with Salt Creek to Buckhalter Avenue
Tributary to Little Ogeechee River Tributary From its confluence with Little Ogeechee River Tributary to
approximately 3,300 feet upstream of Middle Landing Road
Windsor Forest Canal East From its confluence with Windsor Forest Canal West to
approximately 710 feet upstream of Deerfield Road
* Flooding controlled entirely by the
Atlantic Ocean
7
Stream
Windsor Forest Canal Tributary
Reach Limits
From its confluence with Windsor Forest Canal West to
approximately 2,980 feet upstream of the confluence
Windsor Forest Canal Tributary No. 2 From its confluence with Windsor Forest Canal East to
approximately 390 feet upstream of Winwood Place
Windsor Forest Canal Tributary No. 3 From its confluence with Windsor Forest Canal East and Colonial
Oaks Canal to approximately 410 feet upstream of Windsor Road
Windsor Forest Canal West From Thorny Bush Road to approximately 3,410 feet upstream of
Roger Warlick Drive
For this countywide revision, reaches of streams that have been studied by
detailed methods were selected for redelineation based on more recent
topography. Chatham County provided PBS &J with countywide digital GIS
topographic data dated August 2001 (Thomas & Hutton, 2001). The
topographic data was provided as a Digital Elevation Model (DEM) in raster
grid format and the elevation data in the North American Vertical Datum of
1988 (NAVD). The DEM was created from 1 -foot contour data, with a vertical
accuracy of 6 inches, generated from a countywide airborne LIDAR survey
completed in 1999. The following streams were redelineated as part of this
countywide revision:
Stream Reach Limits
Casey Canal
Coffee Bluff Basin*
Evergreen Cemetery Basin
Fell Street Basin
Springfield Canal
Springfield Canal Tributary A
*A. stillwater elevation was also developed
in the basin model for Coffee Bluff
Ponding Area.
From approximately 2,600 feet downsream of East
Montgomery Cross Road to East Victory Drive / U.S.
Highway 80 / State Highway 26
From its confluence with Vernon River to approximately
1,080 feet upstream of Bordeaux Lane
From Mitchell Street to approximately 1,600 feet upstream of
Mitchell Street
From approximately 2,050 feet upstream of its confluence
with Savannah River to approximately 500 feet upstream of
Tuten Avenue
From Louisville Road to approximately 2,700 feet upstream
of Derenne Avenue / Highway 516
From its confluence with Springfield Canal to Ogeechee
Road / State Highway 25 / U.S. Highway 17
8
Stream Reach Limits
Wilshire Canal From approximately 1,220 feet downstream of White Bluff
Road to just upstream of Wilshire Boulevard
For this countywide FIS, the FIS report and FIRM were converted to countywide
format, and the flooding information for the entire county, including both
incorporated and unincorporated areas, is shown. Also, the vertical datum was
converted from the National Geodetic Vertical Datum of 1929 (NGVD) to
NAVD. In addition, the Transverse Mercator, State Plane coordinates,
previously referenced to the North American Datum of 1927, are now referenced
to the North American Datum of 1983.
Approximate analyses were used to study those areas having low development
potential or minimal flood hazards. The scope and methods of study were
proposed to and agreed upon by FEMA and the communities.
The following tabulation presents Letters of Map Change (LOMCs) incorporated
into this countywide study:
LOMC Case Number
Date Issued Project Identifier
LOMR 914074 June 11, 1991 Site - specific wave height analysis, in
the vicinity of Navajo Road and
Apache Street, just south of
Abercorn Extension
LOMR 92- 04 -070P June 17, 1992 Kemira Plant site south of Barnwell
Island and the Savannah River,
north of the Wilmington River, and
west of Elba Island in the vicinity of
Habersham Creek
LOMR 95- 04 -325P April 3, 1996 Restudy of the Ogeechee River
LOMR 00- 04 -045P June 18, 2000 Pipe Makers Canal Tributary No. 2,
from its confluence with Pipe Makers
Canal to approximately 5,175 feet
upstream of its confluence
LOMR 00- 04 -047P June 18, 2000 Pipe Makers Canal Tributary No. 2,
from its confluence with Pipe Makers
Canal to approximately 2,798 feet
upstream of its confluence
LOMR 00-04-051P February 16, 2001 Little Ogeechee River
LOMR 03- 04 -063P May 15, 2003 Site - specific wave height analysis,
approximately 1,000 feet southwest
of the intersection of Apache Avenue
and Fulton Road
9
LOMC Case Number Date Issued
LOMR 03- 04 -587P
LOMR 04- 04 -205P
Project Identifier
March 30, 2004 Site- specific wave height analysis,
approximately 1,700 feet southwest
of the intersection of State Route
359 and Rio Road
June 3, 2004
Site - specific wave height analysis on
six areas just west of the intersection
of State Route 359 and Rio Road
The following tabulation lists streams that have names in this countywide FIS
other than those used in the previously printed FIS reports for the communities
in which they are located.
Community
Garden City, City of
Bloomingdale, City of
Chatham County
(Unincorporated Areas)
Pooler, City of
Chatham County
(Unincorporated Areas)
2.2 Community Description
Old Name New Name
Savannah and Ogeechee Canal
Tributary No. 2
Dundee Canal
Pipe Makers Canal Tributary
No. 2
Lower Springfield Canal Tributary Louis Mills Branch
Chatham County, approximately 438 square miles in area, is located in the
southeastern portion of Georgia, bordering the Atlantic Ocean. The county is
bordered by Bryan County to the southwest across the Ogeechee River; Liberty
County to the south across St. Catherine's Sound; Effingham County to the
northwest; Jasper County, South Carolina, to the northeast across the Savannah
River; and, the Atlantic Ocean to the southeast. The Atlantic Ocean coastline
accounts for approximately 30 miles of the county's border.
The 2000 population of Chatham County was reported to be 232,048 (U.S.
Census Bureau, 2000). Savannah, the county seat and the largest city in the
county, had a population of 131,510 in 2000. The county is served by several
primary highways and by one major airport.
The climate in southeast Georgia is warm and temperate to subtropical. The
average temperature in January is 63 degrees Fahrenheit ( °F), and is 92 °F in
July. The average annual precipitation is 49.6 inches, with the maximum
average monthly precipitation occurring in August (The Weather Channel,
2007).
The county is situated on a low coastal plain with much of its area consisting of
tidal marshes and swamps. Elevations range from sea level at the coast to
approximately 50 feet in the northwestern portion of the county.
10
The Savannah River (northern boundary) and the Ogeechee River (southern
boundary) have drainage areas extending far beyond the limits of Chatham
County. Other streams have chiefly tidal estuaries within the county and include
the Little Ogeechee River, Vernon River, Bear River, Wilmington River, Bull
River, and numerous tributaries to these. Main openings to the Atlantic Ocean
are Ossabaw Sound and Wassaw Sound, both of which are wide and deep.
Much of the land situated in the floodplain is undeveloped marshland, with some
residential, commercial, and industrial development.
2.3 Principal Flood Problems
Chatham County is subject to flooding caused by hurricanes and tropical storms.
Major storms and hurricanes caused flooding in 1871, 1881, 1885, 1893, 1896,
1898, 1911, 1940, 1944, 1947, 1952, 1959, and 1979 (Dunn and Miller, 1964;
National Climatic Center, 1979; Tannehill, 1956). The highest surges occurred
during the hurricanes of 1881 and 1893, which caused flood heights up to 15 and
18 feet NAVD, respectively, in Savannah Beach (Dunn and Miller, 1964;
Tannehill, 1956).
Georgia hasn't been hit by a major hurricane in 108 years, but hurricanes do not
have to be fully developed or even make landfall in Georgia to wreak havoc.
More recently, according to the Georgia Emergency Management Agency
(GEMA), major storms and hurricanes caused flooding in 1989, 1994, 1996,
1999, and 2005 (GEMA, 2006).
The primary factors contributing to flooding in Chatham County are its openness
to Atlantic Ocean surges and unfavorable bathymetry extending offshore. Many
of the large streams near the coast have wide mouths and are bordered by
extensive areas of low marsh. In addition, the terrain at the coast is generally too
low to provide an effective barrier. The offshore ocean depths are shallow for
great distances, generating a high Atlantic Ocean surge.
A storm history of Chatham County and its vicinity during the past 140 years is
summarized below. Damage figures are determined in dollar values at the time of
the storm. No attempt has been made to adjust these figures to current dollar
values.
August 16 - 19, 1871
A tropical cyclone moved overland from Florida and caused damage along the
Florida, Georgia, and South Carolina coasts. At Savannah, Georgia, the wind
speed was 72 miles per hour (mph) from the north.
August 21 - 29, 1881
This storm reached hurricane intensity northeast of Puerto Rico on August 22.
The lowest barometric pressure reading was 29.08 inches. The storm center
11
entered the coast south of Savannah on August 27. Damage in Savannah was
estimated at $1.5 million. Approximately 335 people were killed in and near the
city. Nearly 100 vessels were wrecked along the Atlantic coast. Damage was
very heavy on Tybee Island and other coastal islands near Savannah. The highest
tide observed was estimated to reach an elevation of 15.6 feet NAVD at Savannah
Beach, approximating a flood of at least 1- percent - annual- chance magnitude.
August 21 - 26, 1885
This storm moved inland north of Savannah on August 25. It caused heavy
damage in the Carolinas. Total damage was estimated at about $1.7 million.
Damage inflicted by this storm in Georgia was relatively light.
August 15 - September 2, 1893
This major hurricane, which originated near the Cape Verde Islands, reached the
Georgia coast on August 27. It was accompanied by a tremendous storm wave
that submerged the islands along the Georgia and South Carolina coasts. Between
2,000 and 2,500 people lost their lives on the coastal islands and in the lowland
between Tybee Island and Charleston. Property damage along the Atlantic coast
was estimated at $10 million. Nearly every building on Tybee Island was
damaged and the railroad to the island was wrecked. The highest tide known to
have occurred in the county was estimated to have a range of 16.1 to 18.6 feet
NAVD at Savannah Beach.
September 22 - 29, 1896
This hurricane entered the northwestern Florida coast near St. Mark. Its center
passed through southeastern Georgia and South Carolina on September 28 and 29.
Hurricane winds persisted when the hurricane moved inland. Savannah recorded
maximum winds of 75 mph. Damage in Savannah was estimated at $1 million.
Damage was also heavy on Tybee Island and over much of southeastern Georgia.
Because the damaging hurricane wind was of a short duration near Chatham
County and occurred during a low tide period, destruction caused by storm surge
was relatively light compared with the hurricanes of 1881 and 1893.
August 30 - September 1, 1898
This hurricane entered the Georgia -South Carolina coast on August 30. Its center
passed over Tybee Island. Winds on Tybee Island were estimated at 100 mph.
The storm surges were not high enough to cause extensive damage; however, the
hurricane was accompanied by very heavy rain, and the countryside was flooded
for 100 miles around Savannah. Most roads and railroads were impassable
because of high water.
August 23 - 30, 1911
The center of this hurricane entered the coast between Savannah and Charleston
on August 28. A maximum wind of 88 mph from the northwest was recorded at
Savannah. Damage in the Savannah area was remarkably low; however, property
on Tybee Island was heavily damaged. Excessive rains accompanied the storm
and caused considerable damage to roads, crops, and other property throughout
southern Georgia.
August 5 - 15, 1940
This was the first hurricane to affect Georgia since August 1911. Its center
entered the South Carolina coast to the north of Savannah on August 11. The
wind at Savannah reached 73 mph, and damage in the Savannah area was
estimated at $850,000. The highest tide observed at Beaufort, South Carolina,
was estimated to be 11.5 feet NAVD. High tides of 6.5 and 5.5 feet NAVD were
recorded at Fort Pulaski, Georgia, and at Fort Jackson, Savannah Harbor, Georgia,
respectively.
October 12 - 23, 1944
This hurricane entered the gulf coast of Florida and moved northeastward across
the peninsula. Its center crossed the east coast near Jacksonville, Florida, in a
north- northeast direction and moved inland again near Savannah. The hurricane
was downgraded to a tropical storm by the time it reached Georgia. The highest
tide, 5.0 feet NAVD along the Georgia coast, was observed at Fort Pulaski, near
the mouth of the Savannah River. The estimated damage in Georgia was
$500,000.
October 9 - 16, 1947
The center of this hurricane entered the Georgia coast just south of Savannah on
October 15. At Savannah, the maximum wind speed was 77 mph, and the lowest
barometric pressure was 28.77 inches. Heavy losses were sustained at Savannah
and Savannah Beach, where more than 1,500 buildings were substantially
damaged. Total damage in the coastal area was estimated at more than $2 million.
The highest tide, 7.0 feet NAVD, was recorded at Fort Jackson.
August 18 - September 2, 1952 (Hurricane Able)
Hurricane Able moved inland on August 30. Its center passed near Beaufort with
maximum winds of approximately 100 mph. Damage from this storm was
estimated at about $2.8 million.
September 20 - October 2, 1959 (Hurricane Gracie)
Hurricane Gracie moved inland on September 29. Its center passed over the
South Carolina coast near Beaufort. Wind gusts of hurricane force were felt in
the Savannah area, and damage was inflicted over the upper Georgia coastal area.
The total damage inflicted by the storm was estimated at $14 million with damage
in Georgia estimated at more than $500,000. Highwater marks, which were
reported near Edisto Beach, South Carolina, ranged from 6.4 to 11.0 feet NAVD.
August 25 - September 7, 1979 (Hurricane David)
Hurricane David was the most intense storm of the century to affect the islands of
the eastern Caribbean. However, the storm was not a major hurricane when it
struck the United States. David struck just north of Palm Beach, Florida, on
September 3 and made a second landfall about 24 hours later near Savannah
Beach, Georgia. In the United States, David was responsible for five deaths and
about $300 million in damages. The death toll and damage were much greater in
Dominica, Cuba, and the Dominican Republic (NCC, 1979).
September 9 - September 25, 1989 (Hurricane Hugo)
Hurricane Hugo was a destructive Category 5 hurricane that killed 82 people, left
56,000 homeless and caused $16.3 billion in damages, making it the most
destructive hurricane ever recorded up to that time. Hugo was originally forecast
to move toward Savannah, but instead turned north toward Charleston, South
Carolina. Savannah was evacuated in anticipation of Hugo but saw no effects
other than isolated showers (GEMA, 2006).
June 30 - July 10, 1994 (Tropical Storm Alberto)
Tropical Storm Alberto made landfall in the Florida Panhandle on July 4, 1994,
then moved into western Georgia, where it made a loop July 5 -6, dumping 27.61
inches of rain in Americus (21 inches within 24 hours). Alberto's winds and tides
did only minor damage to the Florida coast, but the excessive rains that fell in
Georgia caused catastrophic flooding from Clayton County through central and
southwest Georgia to the Florida border, resulting in 33 deaths, $500 billion in
damage and a major disaster declaration for 55 counties (GEMA, 2006).
September 27 - October 6, 1995 (Hurricane Opal)
After coming ashore in the Florida Panhandle on October 4, 1995, Opal swept
through Georgia with high winds, heavy rain and tornadoes, killing 14 people and
resulting in a major disaster declaration for 50 counties (GEMA, 2006).
September 7 - September 19, 1999 (Hurricane Floyd)
Hurricane Floyd triggered the second largest evacuation in U.S. history when 2.6
million coastal residents of five states including around 350,000 people in
Georgia, were ordered from their homes as Hurricane Floyd approached. Floyd
struck the Bahamas at peak strength, causing heavy damage. It then paralleled the
east coast of the U.S., causing massive evacuations and costly preparations. In
total, Floyd was responsible for 57 fatalities and $5.7 billion in damage, mostly in
North Carolina (GEMA, 2006).
August 23 - August 31, 2005 (Hurricane Katrina)
Hurricane Katrina was the costliest and one of the deadliest hurricanes in the
history of the U.S. Katrina formed on August 23, 2005, and caused devastation
along much of the north- central Gulf Coast. At least 1,836 people lost their lives
in Hurricane Katrina and in the subsequent floods. It is estimated to have been
responsible for $81.2 billion in damages (GEMA, 2006).
2.4 Flood Protection Measures
Some inland drainage has been improved. The seawall at Savannah Beech
provides some protection from waves and flooding.
Levees exist in the study area that provide the community with some degree of
protection against flooding. However, it has been ascertained that some of these
levees may not protect the community from rare events such as the 1- percent-
annual- chance flood. The criteria used to evaluate protection against the 1-
percent- annual- chance flood are 1) adequate design, including freeboard, 2)
structural stability, and 3) proper operation and maintenance. Levees that do not
protect against the 1- percent - annual- chance flood are not considered in the
hydraulic analysis of the 1- percent - annual- chance floodplain.
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 are 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 (100 -year) 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 Hydrologic Analyses
Hydrologic analyses were carried out to establish peak discharge- frequency
relationships for each flooding source studied by detailed methods affecting the
community.
Precountywide Analyses
Probability estimates for the 1- percent - annual- chance flood for Casey Canal,
Salt Creek Tributary, Wilshire Canal, Wilshire Canal Tributary A, and Wilshire
Canal Tributary A -1 are partially based on a statistical analysis of storm rainfall,
runoff, and tide characteristics. In order to determine the 1- percent - annual-
chance flood, statistical studies on storm rainfall made by the Weather Bureau
15
and storm tide records were used. On Casey Canal, flood heights were
computed from the ponding that would result, assuming that the storm tide
would keep the tide gate at Montgomery Cross Road closed.
Frequency curves of peak flows were constructed at selected locations along Salt
Creek Tributary. These curves reflect the judgment of engineers who have
studied the area and are familiar with the region.
Flood discharges for the Little Ogeechee River and the Ogeechee River were
determined utilizing the regression equations developed by the U.S. Geological
Survey (USGS) (USGS, 1993).
Peak discharge rates for Pipe Makers Canal Tributary No. 2 were calculated
using the USGS urban regression equations (USGS, 1994).
Elevations for the Savannah River were obtained from a map provided by the
USACE which showed 1- percent - annual- chance elevations (USACE, 1976).
Flood discharges for Springfield Canal, Springfield Canal Tributary A, St.
Augustine Creek, and St. Augustine Creek Tributary were determined using a
regional flood - frequency analysis (FIA, 1971).
Inundation from the Atlantic Ocean caused by passage of storms (storm surge)
was determined by the Environmental Sciences Services Administration's
(ESSA) joint probability method (ESSA, 1970). The storm populations were
described by probability distributions of 5 parameters that influence surge
heights. These parameters were central pressure depression (which measures the
intensity of the storm), radius to maximum winds, forward speed of the storm,
shoreline crossing point, and crossing angle. These characteristics were
described statistically based on an analysis of observed storms in the vicinity of
Chatham County. The National Oceanic and Atmospheric Administration
(NOAA) is the primary source of hurricane data (NOAA, 1973; NOAA, 1981;
NOAA, 1965; and NOAA, 1975). A summary of the parameters used for the
area is presented in Table 1.
Table 1 - Parameter Values for Surge Elevation Computations
P PP F PF R PR A PA FN
83 0.03 7 0.45 12 0.24 65 ` / 0.00107
67 0.08
53 0.11 327 0.51 20' / 0.0012
Entering 42 0.13 11 0.30 20 0.26
Storms 33 0.16 301 0.49 252 / 0.00124
23 0.29
9 0.20 15 0.25 28 0.50 702/ 0.00131
16
Table 1 - Parameter Values for Surge Elevation Computations (Continued)
P PP
F
PF
R
PR
A PA FN
Parallel
Storms
83 0.03 7 0.32 12 0.24
67 0.08
53 0.11
42 0.13 11 0.30 20 0.26 35 1.0
33 0.16
23 0.29
9 0.20 15 0.38 28 0.50
651 / 0.00393 /
0.00424
201 / 0.00453 /
0.00484
252/0.00513/
0.00544
702 / 0.00583 /
0.00614
83 0.03 7 0.45 12 0.24
67 0.08
Exiting 53 0.11
Storms 42 0.13 20 0.26
33 0.16
23 0.29
9 0.20 13 0.55 28 0.50
651 / 0.0026
54 0.75 201 / 0.0013
94 0.25 252 / 0.00069
702 / 0.00056
P = Central Pressure (in millibars)
PP = Probability of storm with P Value
F = Forward velocity of storm (KTS)
PF = Probability of storm with F Value
R = Radius to maximum winds (NM)
PR = Probability of storm with R Value
A = Direction of storm (Degrees from true North)
PA = Probability of storm with A Value
D = Distance from shore (NM)
FN = Frequency of storm occurrence (Nautical Mile / Year)
1 Nautical miles south of Georgia / South Carolina Boundary
2 Nautical miles north of Georgia / South Carolina Boundary
3 15 Nautical miles offshore
4 45 Nautical miles offshore
This Countywide Revision
For Black Creek and Black Creek Tributary No. 2, the USACE Hydrologic
Engineering Center's (HEC) HEC -HMS Version 2.1.2 (HEC, 2001a) was used
to generate flood hydrographs.
A calibrated XP -SWMM (XP Software, Inc., 2006) model for Coffee Bluff
Ponding Area, Colonial Oaks Canal, Colonial Oaks Canal Tributary No. 1,
Colonial Oaks Canal Tributary No. 1.1, Windsor Forest Canal East, Windsor
Forest Canal Tributary, Windsor Forest Canal Tributary No. 2, Windsor Forest
Canal Tributary No. 3, and Windsor Forest Canal West representing as- built,
17
existing conditions was provided by the City of Savannah. The model applied
the Soil Conservation Service (SCS) unit - hydrograph methodology with a Type
III rainfall distribution (SCS, 1986). The unit - hydrograph peak rate factor
applied in the model ranged between 200 and 300.
The hydrology for Harmon Canal and Chippewa Canal was revised by the
USACE, Savannah District. The USACE study applied the HEC -HMS, Version
1.0 (HEC, 1998), computer software for the existing conditions watershed,
segmenting the watershed into 11 sub - watersheds. The HEC -HMS model
applied the SCS hydrology methodology (SCS, 1986) to estimate peak runoff.
The model was calibrated to the July 15, 1996, flood, adjusting the unit-
hydrograph parameters to match the peak and volume of the observed flood.
The modified Puls flood hydrograph routing procedure was used to model the
flood peak attenuation for ponds, reservoirs, and storage features throughout the
watershed. The Muskingum -Cunge method was applied to translate the flood
hydrographs through stream reaches between watershed model nodes. The flood
discharges computed by the model were compared to the discharges estimated
by the USGS regional flood discharge- frequency relationships (USGS, 1993).
The hydrology for Hardin Canal, Kingsway Canal, Louis Mills Branch, Quacco
Canal, and Rahn Dairy Canal was adapted from studies prepared by Thomas &
Hutton Engineering in the period between 1998 and 2004 (Thomas & Hutton,
1998, 2000, 2004a, 2004b, and 2005). The hydrology for Pipe Makers Canal
was adapted from a study prepared by EMC Engineering dated April 1999
(EMC, 1999). The hydrology for Placentia Canal was adapted from a study
prepared by Hussey, Gay, Bell, & DeYoung dated May 1996 (Hussey, Gay,
Bell, & DeYoung, 1996). The studies applied either the XP -SWMM or
Interconnected Channel and Pond Routing (ICPR) dynamic routing computer
software (Streamline Technologies, Inc., 2002) and the SCS dimensional unit-
hydrology methodology (SCS, 1986) applying a peak rate factor of 323. The
National Weather Service Technical Paper 40 rainfall- depth- duration - frequency
relationships (NWS, 1961) were used in the runoff modeling with an SCS Type
III distribution. The peak runoff rates computed in the models were compared to
estimates of peak discharge computed by the USGS regional regression
relationships for Georgia (USGS, 1993).
The report provided by Kimley -Horn and Associates for the Little Ogeechee
River Tributary and the Tributary to Little Ogeechee River Tributary describes
the methodology used to delineate the drainage sub - basins using a combination
of ESRI ArcMap 9.1 (ESRI, 2005), USGS topographic contours, survey data,
and field investigations. The watershed was divided into 16 sub - basins, ranging
in size from 47 acres to 1,166 acres. The USGS rural regression equations
(USGS, 1993) were used to determine peak discharges.
Peak discharge- drainage area relationships for 10 -, 2 -, 1 -, and 0.2- percent-
annual- chance floods for each of the flooding sources studied in detail in the
county are presented in Table 2.
Table 2 - Summary of Discharges
Peak Discharges (cubic feet per second)
10- Percent-
Drainage Area Annual- 2- Percent- 1- Percent- 0.2- Percent-
Floodinq Source and Location (square miles) Chance Annual- Chance Annual- Chance Annual- Chance
BLACK CREEK
At confluence with 26.55 1,039 1,553 2,084 2,713
Savannah River
Just upstream of Interstate 22.50 1,056 1,344 1,841 2,329
Highway 95 / State
Highway 405
At confluence of Black 20.49 1,059 1,347 1,845 2,333
Creek Tributary No. 2
At Augusta Road / State 19.52 794 1,039 1,287 1,619
Highway 30 / 21
At confluence of Black 18.54 1,018 1,345 1,799 2,249
Creek Tributary No. 1
At CSX 16.63 802 1,102 1,579 1,928
At Norfolk Southern Railway 13.44 807 1,116 1,639 1,992
BLACK CREEK TRIBUTARY
NO. 2
At confluence with Black 0.97 246 303 536 675
Creek
CASEY CANAL * * * *
CHIPPEWA CANAL
At confluence with Harmon
Canal
COLONIAL OAKS CANAL
Outfall at Atlantic Ocean
At divergence from Windsor
Forest Canal East
COLONIAL OAKS CANAL
TRIBUTARY NO. 1
Just above confluence with
Colonial Oaks Canal
COLONIAL OAKS CANAL
TRIBUTARY NO. 1.1
Just above confluence with
Colonial Oaks Canal
Tributary No. 1
*Data not available
* *Flow split; contributing
drainage area not determined
1.15 1,116 1,463
1,633 2,000
359 448 492 558
9 9 9 9
0.19 139 159 171 193
0.06 47 52 54 58
19
Table 2 - Summary of Discharges (Continued)
Peak Discharges (cubic feet per second)
10- Percent-
Drainage Area Annual- 2- Percent- 1- Percent- 0.2-Percent-
Flooding Source and Location (square miles) Chance Annual- Chance Annual- Chance Annual- Chance
HARDIN CANAL
At Atlantic Coastal Highway 18.20 * * 547
/ U.S. Highway 17 /
Ogeechee Road
At Interstate Highway 16 / 14.40 * * 1,224
State Highway 404
At Interstate Highway 95 / 13.10 * * 1,094
State Highway 405
At Bloomingdale Road / 1.50 * * 186
State Highway 17
At Osteen Road 0.90 * 78
HARMON CANAL
At confluence with Vernon
River
Just downstream of the
confluence of Chippewa
Canal
3.13 2,442 3,213 3,585
2.94 2,415 3,160 3,523
KINGSWAY CANAL
At confluence with Vernon 0.40 * * 355
River
At Harry Truman Parkway 0.30 * * 187
LITTLE OGEECHEE RIVER
Just upstream of Interstate 32.6 1,530 2,530 3,020
Highway 16 / State
Highway 404
*
4,402
4,321
4,280
LITTLE OGEECHEE RIVER
TRIBUTARY
At Little Neck Road 7.31 605 995 1,183 1,666
At New Hampstead 2.86 338 553 657 921
Parkway
At Highgate Boulevard 0.55 122 199 235 327
LOUIS MILLS BRANCH
At confluence with South 2.85 * 577
Springfield Canal
At Louis Mills Boulevard /
Chatham Parkway 0.30 281
OGEECHEE RIVER
*
PIPE MAKERS CANAL
At Augusta Road 44.10 976 1,148 1,314 1,565
At Interstate Highway 95 / 19.70 860 1,117 1,374 1,698
State Highway 405
PIPE MAKERS CANAL
TRIBUTARY NO. 2
At confluence with Pipe
Makers Canal
*Data not available
1.43 268 456 556 803
20
Table 2 - Summary of Discharges (Continued)
Peak Discharges (cubic feet per second)
10- Percent-
Drainage Area Annual- 2- Percent- 1- Percent- 0.2- Percent-
Flooding Source and Location (square miles) Chance Annual- Chance Annual- Chance Annual- Chance
PIPE MAKERS CANAL
TRIBUTARY NO. 2
(Continued)
Just downstream of U.S.
Highway 80 / State
Highway 26
0.65 166 277 336 481
SALT CREEK TRIBUTARY
At confluence with Salt 7.40 * 810
Creek
At Interstate Highway 16 / 6.40 * * 720
State Highway 404
SAVANNAH RIVER
SPRINGFIELD CANAL
SPRINGFIELD CANAL
TRIBUTARY A
ST. AUGUSTINE CREEK
ST. AUGUSTINE CREEK
TRIBUTARY
TRIBUTARY TO LITTLE
OGEECHEE RIVER
TRIBUTARY
*
At the confluence with Little 0.71 143 232 275 383
Ogeechee River
Tributary
At Highgate Boulevard 0.19 62 101 119 165
WILSHIRE CANAL
WILSHIRE CANAL *
TRIBUTARY A
WILSHIRE CANAL * * *
TRIBUTARY A -1
WINDSOR FOREST CANAL
EAST
At confluence with Windsor
Forest Canal West
Just below divergence of
Colonial Oaks Canal /
confluence of Windsor
Forest Canal Tributary No.
3
*Data not available
* *Flow split; contributing
drainage area not determined
**
436 558 615 718
0.05 129 144 157 185
21
Table 2 - Summary of Discharges (Continued)
Peak Discharges (cubic feet per second)
10- Percent-
Drainage Area Annual- 2- Percent- 1- Percent- 0.2- Percent-
Floodinq Source and Location (square miles) Chance Annual- Chance Annual- Chance Annual- Chance
WINDSOR FOREST CANAL
EAST (CONTINUED)
Just above divergence of ** 39 52 58 66
Colonial Oaks Canal /
confluence of Windsor
Forest Canal Tributary No.
3
WINDSOR FOREST CANAL
TRIBUTARY
Just above confluence with
Windsor Forest Canal
West
1.04 182 239 261 304
WINDSOR FOREST CANAL
TRIBUTARY NO. 2
Just above Windsor Road 0.03 36 46 51 69
WINDSOR FOREST CANAL
TRIBUTARY NO. 3
Just above Windsor Road 0.09 100 116 121 128
WINDSOR FOREST CANAL
WEST
Outfall at Atlantic Ocean
* *Flow split; contributing
drainage area not determined
1.40 519 702 777 948
Stillwater elevations for lakes studied in detail are shown in Table 3.
Table 3 - Summary of Stillwater Elevations
Water Surface Elevations (Feet NAVD1)
10- Percent- 2- Percent- 1- Percent- 0.2- Percent-
Floodinq Source Annual- Chance Annual- Chance Annual- Chance Annual- Chance
Coffee Bluff Ponding Area
11.6 13.2
North American Vertical Datum of 1988
3.2 Hydraulic Analyses
13.8 14.4
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 represent rounded whole -foot elevations and may not exactly reflect the
elevations shown on the Flood Profiles or in the Floodway Data Table in the
22
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 report in conjunction with the data shown on the FIRM.
Users of the FIRM should also be aware that coastal flood elevations are
provided in the Transect Data table in this report. If the elevation on the FIRM
is higher than the elevation shown in this table, a wave height, wave run -up
and/or wave setup component likely exists, in which case, the higher elevation
should be used for construction and/or floodplain management purposes.
Precountywide Analyses
Hydraulic analyses of the shoreline characteristics of the flooding sources
studied in detail were carried out to provide estimates of the elevations of floods
of the selected recurrence intervals along each of the shorelines.
Cross section data for Pipe Makers Canal Tributary No. 2 were obtained from
field surveys. All bridges, dams, and culverts were field surveyed to obtain
elevation data and structural geometry.
Flood profiles for Casey Canal were computed using stream characteristics for
the selected reaches as determined from observed flood profiles, topographic
maps, and valley cross sections which were surveyed in 1967 (USACE, 1968b).
Elevations for the Savannah River were obtained from a map provided by the
USACE which showed 1- percent - annual- chance elevations (USACE, 1976).
Water surface profiles for St. Augustine Creek, St. Augustine Creek Tributary,
Springfield Canal, Springfield Canal Tributary A, were taken from the Type 10
FIS (FIA, 1971) report performed by the SCS for Chatham County. All data are
on file with the SCS.
Water surface elevations ( WSELs) of floods of the selected recurrence intervals
on the Ogeechee River were computed using the USACE's HEC -2 step -
backwater computer program (HEC, 1984).
WSELs of floods of the selected recurrence intervals on the Little Ogeechee
River and Pipe Makers Canal Tributary No. 2 were computed using the
USACE's HEC -2 step - backwater computer program (HEC, 1991).
Water surface profiles for Wilshire Canal, Wilshire Canal Tributary A, and
Wilshire Canal Tributary A -1 were computed using stream characteristics for the
selected reaches as determined from observed conditions, topographic maps, and
valley cross sections obtained in 1970.
Starting WSELs for Pipe Makers Canal Tributary No. 2 were based on the slope
- area method.
Hydraulic analyses, considering storm characteristics and the shoreline and
bathymetric characteristics of the flooding sources studied, were carried out to
provide estimates of the elevations of floods of the selected recurrence intervals
along each of the shorelines.
For areas subject to flooding directly from the Atlantic Ocean, the FEMA
standard storm surge model was used to simulate the coastal surge generated by
any chosen storm (that is, any combination of the 5 storm parameters defined
previously). By performing such simulations for a large number of storms, each
of known total probability, the frequency distribution of surge height can be
established as a function of coastal location. These distributions incorporate the
large -scale surge behavior, but do not include an analysis of the added effects
associated with much fine scale wave phenomena, such as wave height or runup.
As the final step in the calculations, the astronomic tide for the region is then
statistically combined with the computed storm surge to yield recurrence
intervals of total water level (TetraTech, Inc., 1981).
The storm -surge elevations for the 10 -, 2 -, 1 -, and 0.2- percent - annual- chance
floods have been determined for Chatham County and are shown in Table 4,
Transect Data. The analyses reported herein reflect the stillwater elevations due
to tidal and wind setup effects and include the contributions from wave action
effects.
All dunes and structures were assumed to remain intact for purposes of this
analysis. The FEMA storm surge model was utilized to simulate the
hydrodynamic behavior of the surge generated by the various synthetic storms.
This model utilizes a grid pattern approximating the geographical features of the
study area and the adjoining areas. Surges were computed utilizing grids of 8 by
5 nautical miles and 6,000 feet by 6,000 feet, depending on the resolution
required.
Underwater depths and land heights for the model grid systems were obtained
from NOAA nautical charts, USGS topographic maps, and aerial
photogrammetry and field surveys conducted as part of this study (NOAA, 1977;
NOAA, 1979; USGS, various dates; Woolpert Consultants, 1982 and 1983).
This Countywide Revision
A calibrated XP -SWMM model (XP Software, Inc., 2006) for Coffee Bluff
Basin, Colonial Oaks Canal, Colonial Oaks Canal Tributary No. 1, Colonial
Oaks Tributary No. 1.1, Windsor Forest Canal East, Windsor Forest Canal
Tributary, Windsor Forest Canal Tributary No. 2, Windsor Forest Canal
Tributary No. 3, and Windsor Forest Canal West representing as- built, existing
conditions was provided by the City of Savannah. Top of roadway elevations
were estimated from the topographic data from the countywide Digital Elevation
Model (DEM). A cross section was drawn perpendicular to the flow -path at
each node in the XP -SWMM model. The cross sections were transferred to the
DEM in the ArcGIS (ESRI, 2005) platform. The WSEL was integrated with the
bare earth DEM to create a flood depth grid which was transferred to the flood
delineation polygon.
Flood water elevations for Louis Mills Branch were estimated using the ICPR
model which uses the node -link concept to describe the connectivity between
subbasins. The node -link network provides the computational framework for the
ICPR model. For Louis Mills Branch, the node locations were compared to the
topographic map and aerial photographs. The original node locations in the work
map were digitized into ArcGIS (ESRI, 2005).
The flow hydrographs for Black Creek and Black Creek Tributary No. 2 were
imported into HEC -RAS, Version 3.0.1 (HEC, 2001b), to use for an unsteady
flow analysis.
The estimated WSELs for Pipe Makers Canal were based on a XP-SW MM
model study prepared by EMC Engineering (EMC, 1999). Airborne Laser
Terrain Mapping (ALTM) was used to estimate channel and floodplain
geometry, supplemented by field surveys of culvert and bridge crossings of the
canal.
The estimated WSELs for Hardin Canal, Kingsway Canal, Louis Mills Branch,
Quacco Canal, and Rahn Dairy Canal were based on ICPR model studies
prepared by Thomas & Hutton (Thomas & Hutton, 1998, 2000, 2004a, and
2004b). ALTM was used to estimate channel and floodplain geometry.
The estimated WSELs for Placentia Canal were based on a XP -SWMM model
prepared by Hussey, Gay, Bell & DeYoung (Hussey, Gay, Bell & DeYoung,
1996).
A calibrated HEC -RAS, Version 3.1.1 (HEC, 2003), computer model prepared
by the USACE, Savannah District, was used to estimate the flood elevation
profiles for Harmon Canal and Chippewa Canal.
The hydraulics for Little Ogeechee River Tributary and Tributary to Little
Ogeechee River Tributary were developed using HEC - GeoRAS (HEC, 2002)
within ArcMap 9.1 (ESRI, 2005) to import channel and overbank geometries
into a HEC -RAS, Version 3.1.3 (HEC, 2005), model. The City of Savannah's 2-
foot contour interval topographic mapping data were used as the source for the
digital terrain model, supplemented with survey data for the existing and newly
built structures (Little Neck Road and Highgate Boulevard, respectively). The
structure at New Hampstead Parkway was not included in the final existing
model since it was not complete at the time of the report submission. Other
structures seen in aerial photographs were old logging road crossings that
currently have remains of rusted, flattened CMP culverts. The culverts are in the
process of being removed as part of the site development and, in some cases, as
mandated by the USACE.
The estimated WSELs for Coffee Bluff Basin were based on an XP -SWMM
model provided by the City of Savannah. The model used a fixed backwater
elevation of 3.59 feet NAVD, mean high tide.
The starting WSELs applied in the ICPR model for Hardin Canal, Kingsway
Canal, and Rahn Dairy Canal was 4.4 feet NAVD. The 1- percent - annual- chance
flooding for Hardin Canal is controlled by the flooding effects from the Atlantic
Ocean in the stream reach from the confluence with Salt Creek to Interstate
Highway 16. The 1- percent - annual- chance flooding for Kingsway Canal is
controlled by the flooding effects from the Atlantic Ocean upstream of the
confluence with the Vernon River.
The starting WSELs for Black Creek, Black Creek Tributary No. 2, Chippewa
Canal, Harmon Canal, Little Ogeechee River Tributary, and Tributary to Little
Ogeechee River Tributary were based on normal depth.
The starting WSELs for Colonial Oaks Canal, Colonial Oaks Canal Tributary
No. 1, Colonial Oaks Canal Tributary 1.1, Windsor Forest Canal East, Windsor
Forest Canal Tributary, Windsor Forest Canal Tributary No. 2, Windsor Forest
Canal Tributary No. 3, and Windsor Forest Canal West were based on mean high
tide.
Initial stage, representing the starting WSEL for Louis Mills Branch, was
specified at each node.
The starting WSELs applied in the XP -SWMM model for Pipe Makers Canal
was 2.66 feet NAVD.
The starting WSELs applied in the XP -SWMM model for Placentia Canal was
4.4 feet NAVD.
The starting WSELs applied in the ICPR model for Quacco Canal was 5.13 feet
NAVD.
The 1- percent - annual- chance flooding for Placentia Canal, Quacco Canal, Rahn
Dairy Canal is controlled by the flooding effects from the Atlantic Ocean for the
entire stream reaches. The 1- percent - annual- chance flood elevation from the
Atlantic Ocean is 11.1 feet NAVD.
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 (Exhibit 2).
The Manning's "n" values for all detailed studied streams are listed in the
following table:
FLOODING SOURCE
CHANNEL "n" OVERBANK "n"
Black Creek 0.060 -0.100 0.100
Black Creek Tributary No. 2 0.040 0.100
Casey Canal * *
Chippewa Canal 0.033 -0.050 0.030 -0.110
Coffee Bluff Basin 0.015 -0.025 0.200 -0.300
Colonial Oaks Canal 0.025 -0.150 0.020 -0.030
Colonial Oaks Canal Tributary No. 1 0.025 -0.150 0.020 -0.030
Colonial Oaks Canal Tributary No. 1.1 0.025 -0.150 0.200 -0.300
Hardin Canal 0.040 -0.050 0.100 -0.150
Harmon Canal 0.033 to 0.05 0.030 -0.110
Kingsway Canal 0.030 -0.040 *
Little Ogeechee River * *
Little Ogeechee River Tributary 0.040 -0.040 0.030 -0.100
Louis Mills Branch 0.035 -0.070 0.080 -0.120
Ogeechee River *
Pipe Makers Canal 0.070 -0.300 0.150 -0.250
Pipe Makers Canal Tributary No. 2 0.030 0.040 -0.085
Placentia Canal *
Quacco Canal 0.030 -0.040 0.050 -0.120
Rahn Dairy Canal 0.030 0.040 -0.050
Salt Creek Tributary * *
Savannah River * *
Springfield Canal * *
Springfield Canal Tributary A * *
St. Augustine Creek * *
St. Augustine Creek Tributary * *
Tributary to Little Ogeechee River Tributary 0.040 -0.040 0.030 -0.100
Wilshire Canal * *
Wilshire Canal Tributary A * *
Wilshire Canal Tributary A -1 * *
Windsor Forest Canal East 0.025 -0.150 0.020 -0.030
Windsor Forest Canal Tributary 0.025 -0.150 0.020 -0.030
Windsor Forest Canal Tributary No. 2 0.025 -0.150 0.200 -0.300
Windsor Forest Canal Tributary No. 3 0.025 -0.150 0.020 -0.030
Windsor Forest Canal West 0.025 -0.150 0.020 -0.030
* Data not available
The profile baselines depicted on the FIRM represent the hydraulic modeling
baselines that match the flood profiles on this FIS report. As a result of
improved topographic data, the profile baseline, in some cases, may deviate
significantly from the channel centerline or appear outside the Special Flood
Hazard Area.
27
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.
3.3 Wave Height Analysis
The methodology for analyzing the effects of wave heights associated with
coastal storm surge flooding was developed by the National Academy of
Sciences (NAS) (NAS, 1977). This method is based on the following three major
concepts. First, depth - limited waves in shallow water reach a maximum breaking
height that is equal to 0.78 times the stillwater depth. The wave crest elevation is
70- percent of the total wave height plus the stillwater elevation. The second
major concept is that wave height may be diminished by dissipation of energy
due to the presence of obstructions such as sand dunes, dikes and seawalls,
buildings, and vegetation. The amount of energy dissipation is a function of the
physical characteristics of the obstruction and is determined by procedures
described in the NAS report. The third major concept is that wave height can be
regenerated in open fetch areas due to the transfer of wind energy to the water.
This added energy is related to the fetch length and depth.
As described in Procedures for Applying Marsh Grass Methodology (FEMA,
1984), a modification to the NAS Methodology (NAS, 1977) has been
developed to analyze in detail the attenuating effect of marsh grass on waves.
The rate of wave energy dissipation is dependent on the wave characteristics
(e.g. height and period), and the species of marsh grass. Two conditions result
from this modification depending on the initial wave height at the beginning of
the marsh segment: 1) if the initial wave is relatively small, wave growth will
occur but at a significantly lower rate as compared to the NAS methodology, and
2) if the initial wave is sufficiently large, a wave height reduction will occur over
the marsh.
Wave heights were computed along transects (cross section lines) that were
located along the coastal areas, as illustrated in the Transect Location Map
(Figure 1), in accordance with the Users Manual for Wave Height Analysis
(FEMA, 1981c). These transects are also shown on the FIRM. The transects
were located with consideration given to the physical and cultural characteristics
28
m
G)
c
x
m
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
TRANSECT LOCATION MAP
ATLANTIC OCEAN
of the land so that they would closely represent conditions in their locality.
Transects were spaced close together in areas of complex topography and dense
development. In areas having more uniform characteristics, they 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.
The transects were continued inland until the wave was dissipated or until
flooding from another source with equal or greater elevation was reached.
Along each transect, wave heights and elevations were computed considering the
combined effects of changes in ground elevation, vegetation, and physical
features. The stillwater elevations for the 1- percent - annual- chance flood were
used as the starting elevations for these computations. Wave heights were
calculated to the nearest 0.1 foot, and wave elevations were determined at
whole -foot increments along the transects. Areas with a wave height component
3 -feet or greater were designated as velocity zones (VE). Other areas subject to
wave action were designated as AE Zones with Base Flood Elevations (BFEs)
adjusted to include wave crest elevations. Table 4 provides a listing of the
transect locations and stillwater starting elevations, as well as the initial wave
crest elevations
Table 4 - Transect Locations, Stillwater Starting Elevations, and Initial Wave Crest Elevations
Transect
1
2
3
4
5
6
7
8
9
10
Across Ossabaw
intersection betw
line
Across Ossabaw
of Bear River
Across Ossabaw
of Bear River
Across Ossabaw
Point
Across Ossabaw
Pelican Point
Across Ossabaw
Point
Across Ossabaw
Point
Across Ossabaw
Point
Across Ossabaw
Bradley Point
Across Raccoon
of CSX Railroad
Stillwater Wave Crest
Location (feet NAVD) (feet NAVD)
Island approximately 1 mile northeast of the
een Bryan, Chatham, and Liberty Counties boundary
Island approximately 1 mile east of the confluence
Island approximately 2 miles east of the confluence
Island approximately 1 mile southwest of Pelican
Island approximately 1,000 feet southwest of
Island approximately 1 mile northeast of Pelican
Island approximately 2 miles northeast of Pelican
Island approximately 2 miles southwest of Bradley
Island approximately 1,000 feet southwest of
Key and continues up to approximately 1 mile south
30
12.1
12.1
12.1
12.1
12.1
12.1
12.1
12.1
12.1
12.1
19.2
19.2
19.2
19.2
19.2
19.2
19.2
19.2
19.2
19.2
Table 4 - Transect Locations, Stillwater Starting Elevations, and Initial Wave Crest Elevations
(Continued)
Stillwater Wave Crest
Transect Location (feet NAVD) (feet NAVD)
Across the western side of Wassaw Island, continuing through the
11 western portion of Skidaway Island 12.1 19.2
Across Wassaw Island approximately 0.5 mile southeast of the
12 confluence of the Odingsell River, continuing through Skidaway 12.1 19.2
Island
Across Wassaw Island approximately 1.5 miles southeast of the
13 confluence of the Odingsell River, continuing through Skidaway 12.1 19.2
Island
Across Wassaw Island approximately 2.5 miles southeast of the
14 confluence of the Odingsell River, continuing through Skidaway 12.1 19.2
Island
Across Wassaw Island approximately 3 miles south of the confluence
15 of the Wilmington River, continuing through Skidaway Island 12.1 19.2
Across the eastern portion of Wassaw Island approximately 3 miles
16 southeast of the confluence of the Wilmington River 12.1 19.2
Across Cabbage Island approximately 1 mile east of the confluence
17 of the Wilmington River 12.1 19.2
Across the western portion of Petit Chou Island approximately 1 miles
18 southeast of the confluence of the Tybee River 12.1 19.2
Across Tybee Island approximately 2 miles southeast of the
19 confluence of the Bull River 12.1 19.2
Across Tybee Island approximately 2.3 miles southeast of the
20 confluence of the Bull River 12.1 19.2
Across Tybee Island approximately 2 miles southwest of the
21 confluence of Tybee Creek 12.1 19.2
Across Tybee Island approximately 0.8 mile southwest of the
22 confluence of Tybee Creek 12.1 19.2
23 Across Tybee Island approximately 0.5 mile east of the confluence of 12.1 19.2
Tybee Creek
Across the eastern portion of Tybee Island approximately 1 mile
24 southeast of the Tybee Island Lighthouse 12.1 19.2
After analyzing wave heights along each transect, wave elevations were
interpolated between transects. Various source data were used in the
interpolation, including topographic maps (USGS, various dates), aerial
photographs (Woolpert Consultants, 1983), and engineering judgment.
Controlling features affecting the elevations were identified and considered in
relation to their positions at a particular transect and their variation between
transects.
Figure 2 is a profile for a hypothetical transect showing the effects of energy
dissipation on a wave as it moves inland. This figure shows the wave elevations
being decreased by obstructions, such as buildings, vegetation, and rising ground
elevations and being increased by open, unobstructed wind fetches. Actual wave
conditions may not necessarily include all of the situations shown in Figure 2.
31
V Zone
Wave Height Greater Than 3 Ft.
Base Flood Elevation
Including Wave Effects
100 -Year
Stilwater Elevation
NAVD-\
•
Sho eline Sand Beach
Buidings
A Zone
Wave Height Less Than 3 Ft.
•
•
1
Overland Vegetated Region Limit of Flooding
Wind Fetch and Waves
Figure 2 - Transect Schematic
Results from the wave height analysis are incorporated into the information
presented on the FIRM and summarized in Table 5. Computed wave elevations
were based on existing topography, vegetation, and development patterns.
3.4 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 in use for newly created or revised FIS reports and
FIRMs was the NGVD. With the finalization of the NAVD, many FIS reports
and FIRMs are being prepared using NAVD as the referenced vertical datum.
All flood elevations shown in this FIS report and on the FIRM are referenced to
NAVD. Structure and ground elevations in the community must, therefore, be
referenced to NAVD. It is important to note that adjacent communities may be
referenced to NGVD. This may result in differences in BFEs across the corporate
limits between the communities. The average conversion factor that was used to
convert the data in this FIS report to NAVD was calculated using the National
Geodetic Survey's VERTCON online utility (NGS, 2007). The data points used
to determine the conversion are listed in Table 6.
32
FLOODING SOURCE
TRANSECTS
STILLWATER ELEVATION (FEET NAVD)
ZONE'
BASE FLOOD
ELEVATION
(FEET NAVD)2
10- PERCENT-
ANNUAL - CHANCE
2- PERCENT-
ANNUAL - CHANCE
1- PERCENT-
ANNUAL - CHANCE
0.2- PERCENT-
ANNUAL - CHANCE
ATLANTIC OCEAN
1 -10
8.7
10.7
12.1
13.3
VE
14 -19
*
*
*
*
AE
12 -14
9.3
11.0
11.1
13.5
VE
13 -16
*
*
*
*
AE
11 -13
1 -8
9.6
11.6
12.1
14.5
VE
14 -19
*
*
*
*
AE
12 -14
9.3
11.0
11.1
13.5
VE
13 -16
*
*
*
*
AE
11 -13
1 -9
9.5
11.3
12.1
14.0
VE
14 -19
*
*
*
*
AE
12 -14
9.3
11.0
11.1
13.5
VE
13 -16
*
*
*
*
AE
11 -13
8 -10
9.5
11.3
12.1
14.0
VE
14 -19
*
*
*
*
AE
12 -14
9.7
11.8
13.1
14.5
VE
15 -17
9.3
11.0
11.1
13.5
VE
13 -16
*
*
*
*
AE
11 -13
'Includes the effects of wave action, where applicable
2Due to map scale limitations, BFEs shown on the FIRM may represent average elevation for the zone depicted
*Data not available
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
TRANSECT DATA
ATLANTIC OCEAN
FLOODING SOURCE
TRANSECTS
STILLWATER ELEVATION (FEET NAVD)
ZONE'
BASE FLOOD
ELEVATION
(FEET NAVD)2
10- PERCENT-
ANNUAL - CHANCE
2- PERCENT-
ANNUAL - CHANCE
1- PERCENT-
ANNUAL - CHANCE
0.2- PERCENT-
ANNUAL - CHANCE
ATLANTIC OCEAN
6 -10
9.5
11.3
12.1
14.0
VE
14 -19
(CONTINUED)
9.7
11.8
13.1
14.5
VE
15 -17
9.3
11.0
11.1
13.5
VE
13
*
*
*
*
AE
11 -13
8 -13
9.5
11.3
12.1
14.0
VE
14 -19
*
*
*
*
AE
14
9.7
11.8
13.1
14.5
VE
15 -17
9.4
10.9
11.1
12.7
VE
13
*
*
*
*
AE
11 -13
11 -16
8.8
10.8
12.1
13.6
VE
14 -19
*
*
*
*
AE
12 -14
9.4
10.9
11.1
12.7
VE
13
*
*
*
*
AE
11 -13
14 -17
9.2
11.3
12.1
13.9
VE
14 -19
*
*
*
*
AE
12 -14
10.2
12.4
13.1
15.2
VE
15 -17
Co
rn
tri
'Includes the effects of wave action, where applicable
2Due to map scale limitations, BFEs shown on the FIRM may represent average elevation for the zone depicted
*Data not available
FEDERAL EMERGENCY MANAGEMENT AGENCY
TRANSECT DATA
CHATHAM COUNTY, GA
AND INCORPORATED AREAS ATLANTIC OCEAN
FLOODING SOURCE
TRANSECTS
STILLWATER ELEVATION (FEET NAVD)
ZONE'
BASE FLOOD
ELEVATION
(FEET NAVD)2
10- PERCENT-
ANNUAL - CHANCE
2- PERCENT-
ANNUAL - CHANCE
1- PERCENT-
ANNUAL - CHANCE
0.2- PERCENT-
ANNUAL - CHANCE
ATLANTIC OCEAN
14 -17
8.3
10.2
11.1
13.2
VE
13 -14
(CONTINUED)
(CONTINUED)
*
*
*
*
AE
11 -13
13 -16
9.2
11.3
12.1
13.9
VE
14 -19
*
*
*
*
AE
12 -14
10.2
12.4
13.1
15.2
VE
15 -17
8.3
10.2
11.1
13.2
VE
13 -14
*
*
*
*
AE
11 -13
17 -20
9.2
11.3
12.1
13.9
VE
14 -19
*
*
*
*
AE
12 -14
10.5
12.4
13.1
14.7
VE
15 -17
*
*
*
*
AE
13 -15
8.3
10.2
11.1
13.2
VE
14 -16
*
*
*
*
AE
11 -13
17 -24
9.2
11.3
12.1
13.9
VE
14 -19
*
*
*
AE
12 -14
10.5
12.4
13.1
14.7
VE
15 -17
'Includes the effects of wave action, where applicable
2Due to map scale limitations, BFEs shown on the FIRM may represent average elevation for the zone depicted
*Data not available
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
TRANSECT DATA
ATLANTIC OCEAN
FLOODING SOURCE
TRANSECTS
STILLWATER ELEVATION (FEET NAVD)
ZONE'
BASE FLOOD
ELEVATION
(FEET NAVD)2
10- PERCENT-
ANNUAL - CHANCE
2- PERCENT-
ANNUAL - CHANCE
1- PERCENT-
ANNUAL - CHANCE
0.2- PERCENT-
ANNUAL - CHANCE
ATLANTIC OCEAN
17 -24
*
*
*
*
AE
13 -15
(CONTINUED)
(CONTINUED)
8.3
10.2
11.1
13.2
VE
14 -16
*
*
*
*
AE
11 -13
19 -24
9.4
11.6
12.1
14.6
VE
14 -19
*
*
*
*
AE
13 -14
10.5
12.4
13.1
14.7
VE
16 -48
8.3
10.2
11.1
13.2
VE
13 -15
*
*
*
*
AE
13
21 -24
9.4
11.6
12.1
14.6
VE
14 -19
*
*
*
*
AE
13 -14
10.5
12.4
13.1
14.7
VE
16 -48
8.3
10.2
11.1
13.2
VE
13 -15
*
*
*
*
AE
13
N/A
9.1
10.4
11.1
12.6
AE
11
N/A
8.0
9.4
9.9
11.4
AE
10
N/A
9.4
10.9
11.5
12.7
AE
11
'Includes the effects of wave action, where applicable
2Due to map scale limitations, BFEs shown on the FIRM may represent average elevation for the zone depicted
*Data not available
FEDERAL EMERGENCY MANAGEMENT AGENCY
Co
CHATHAM COUNTY, GA
m AND INCORPORATED AREAS
TRANSECT DATA
ATLANTIC OCEAN
Table 6 - Vertical Datum Conversion
Quad Name Corner Latitude Longitude Conversion from
NGVD to NAVD
Meldrim SW 81.37 32.13 -0.856
Meldrim NE 81.25 32.25 -0.915
Meldrim SE 81.25 32.12 -0.902
`a t
Port Wentworth NE 81.20 32.25 -0.922 j J O �,,es
Port Wentworth SE 81.13 32.13 -0.928 C12- a' da+
Limehouse SE 81.00 32.13 -0.919 I q ii
Mildrem SE SE 81.25 32.00 -0.892 ,
Garden City SE 81.13 32.00 -0.919 f C
Savannah SE 81.00 32.00 -0.932
Fort Pulaski SE 80.88 32.00 - 0.932.) i
Tybee Island North SE 80.75 32.00 -0.958 r/'
Richmond Hill SE 81.25 31.87 -0.928
Burroughs SE 81.13 31.87 -0.928
Isle of Hope SE 81.00 31.87 -0.942
Wassaw Sound SE 80.88 31.87 -0.958
Oak Level SE 81.12 31.75 -0.955
Racoon Key SE 81.00 31.75 -0.965
Meldrim SW 81.37 32.13 -0.856
Average: -0.927
For additional information regarding conversion between 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 community. Interested individuals may contact FEMA to access these data.
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 NFIP encourages State and local governments to adopt sound floodplain
management programs. Therefore, each FIS provides 1- percent - annual- chance (100 -
year) flood elevations and delineations of the 1- and 0.2- percent - annual- chance (500 -
year) floodplain boundaries and 1- percent - annual- chance floodway to assist
communities in developing floodplain management measures. This information is
presented on the FIRM and in many components of the FIS report, including Flood
Profiles, Floodway Data Table, and Summary of Stillwater Elevations Table. Users
should reference the data presented in the FIS report as well as additional information
that may be available at the local 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 the flood elevations
determined at each cross section.
For the Atlantic Ocean and the coastally influenced flooding sources; Ogeechee
River, Salt Creek Tributary, Savannah River, St. Augustine Creek, St.
Augustine Creek Tributary, Wilshire Canal, from the confluence of Wilshire
Canal Tributary A to just downstream of Mercy Road, Wilshire Canal
Tributary A, and Wilshire Canal Tributary A -1, the boundaries were
interpolated between transects using topographic maps at a scale of 1:24,000,
with a contour interval of 5 feet (USGS, various dates).
The boundaries on Pipe Makers Canal Tributary No. 2 were interpolated
between cross sections, using site mapping at a scale of 1:4,800, with a contour
interval of 1 foot (Braswell Engineering, 1999), based on February 1997 aerial
photography.
The boundaries on the Little Ogeechee River were interpolated between cross
sections using a certified topographic survey map at a scale of 1:6,000, with a
contour interval of 1 foot (Hussey, Gay, Bell & DeYoung, 2000).
For Black Creek, Black Creek Tributary No. 2, Casey Canal, Chippewa Canal,
Coffee Bluff Basin, Colonial Oaks Canal, Colonial Oaks Canal Tributary No. 1,
Colonial Oaks Canal Tributary No. 1.1, Evergreen Cemetery Basin, Fell Street
Basin, Hardin Canal, Harmon Canal, Kingsway Canal, Little Ogeechee River
Tributary, Louis Mills Branch, Pipe Makers Canal, Placentia Canal, Quacco
38
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10/22/2010 3:42 PM
Canal, Rahn Dairy Canal, Springfield Canal, Springfield Canal Tributary A,
Tributary to Little Ogeechee River Tributary, Wilshire Canal, from
approximately 1,285 feet downstream of White Bluff Road to the confluence of
Wilshire Canal Tributary A, Windsor Forest Canal East, Windsor Forest Canal
Tributary, Windsor Forest Canal Tributary No. 2, Windsor Forest Canal
Tributary No. 3, and Windsor Forest Canal West, the boundaries were
interpolated using 1 -foot contours derived from LiDAR data (Thomas &
Hutton, 2001).
For the streams studied by approximate methods, only the 1- percent - annual-
chance floodplain boundary was delineated using the Type 15 FIS for Chatham
County and Flood Hazard Boundary Map for Chatham County (FEMA, 1983
and FIA, 1976).
The 1- and 0.2- percent - annual- chance floodplain boundaries are shown on the
FIRM (Exhibit 2). On this map, the 1- percent - annual- chance floodplain
boundary corresponds to the boundary of the areas of special flood hazards
(Zones A, AE, 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.
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 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 1- percent - annual- chance 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 floodways presented in this FIS report and on the FIRM were computed for
certain stream segments on the basis of equal- conveyance reduction from each
39
side of the floodplain. Floodway widths were computed at cross sections.
Between cross sections, the floodway boundaries were interpolated. The
results of the floodway computations have been tabulated for selected cross
sections (Table 7). 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.
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 WSEL of the 1- percent - annual- chance flood more than 1 foot at any point.
Typical relationships between the floodway and the floodway fringe and their
significance to floodplain development are shown in Figure 3.
GROUND SURFACE
FILL
LIMIT OF FLOODPLAIN FOR UNENCROACHED 1% ANNUAL CHANCE FLOOD
FLOODWAY
FRINGE
4 FLOODWAY r�FL RINGS �
FRINGE
STREAM
CHANNEL
FLOOD ELEVATION WHEN
CONFINED WITHIN FLOODWAY
ENCROACHMENT
FILL
ENCROACHMENT
FILL
SURCHARGE'
AREA OF ALLOWABLE
ENCROACHMENT; RAISING
GROUND SURFACE WILL
NOT CAUSE A SURCHARGE
THAT EXCEEDS THE
INDICATED STANDARDS
FLOOD ELEVATION
BEFORE ENCROACHMENT
ON FLOODPLAIN
LINE A - B IS THE FLOOD ELEVATION BEFORE ENCROACHMENT
LINE C - D IS THE FLOOD ELEVATION AFTER ENCROACHMENT
*SURCHARGE NOT TO EXCEED 1.0 FOOT (FEMA REQUIREMENT) OR LESSER HEIGHT IF SPECIFIED BY STATE OR COMMUNITY.
Figure 3 - Floodway Schematic
No floodways were computed for Black Creek, Black Creek Tributary No. 2,
Casey Canal, Chippewa Canal, Colonial Oaks Canal, Colonial Oaks Canal
Tributary No. 1, Colonial Oaks Canal Tributary No. 1.1, Hardin Canal, Harmon
Canal, Kingsway Canal, Little Ogeechee River, Little Ogeechee River Tributary,
Louis Mills Branch, Ogeechee River, Salt Creek Tributary, Savannah River,
40
FLOODING SOURCE
FLOODWAY'
1- PERCENT - ANNUAL - CHANCE FLOOD
WATER SURFACE ELEVATION
2
WIDTH
PEAK
VELOCITY
REGULATORY
WITHOUT
WITH
INCREASE
NODES
LINKS
DISTANCE
(FEET)
FLOW
(CFS)
(FEET PER
SECOND)
(FEET NAVD)
FLOODWAY
(FEET NAVD)
FLOODWAY
(FEET NAVD)
(FEET)
PIPE MAKERS CANAL
A
15,025
11.3
11.3
12.1
0.8
A -B
1,430
1,672
0.2
B
15,628
11.3
11.3
12.1
0.8
C
20,903
11.4
11.4
12.2
0.8
C -D
1,523
1,888
0.2
D
21,596
11.4
11.4
12.2
0.8
E
25,805
12.1
12.1
13.1
1.0
E -F
2733
2345
0.4
F
26,405
12.1
12.1
13.1
1.0
G
30,004
12.7
12.7
13.5
0.8
G -H
998
2645
0.7
H
30,603
12.8
12.8
13.6
0.8
I
35,153
15.9
15.9
16.6
0.7
I -J
1725
2609
1.3
J
36,291
15.9
15.9
16.6
0.7
K
42,582
17.3
17.3
18.1
0.8
K -L
1463
1620
1.2
L
43,579
17.4
17.4
18.2
0.8
M
50,600
19.0
19.0
19.8
0.8
M -N
1056
1331
0.8
N
51,602
19.2
19.2
20.0
0.8
I-
m
'Values represent maximum along link
2Feet above confluence with Savannah River
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
FLOODWAY DATA
PIPE MAKERS CANAL
FLOODING SOURCE
FLOODWAY'
WATER SURFACE ELEVATION
NODES
LINKS
2
DISTANCE
WIDTH3
(FEET)
PEAK
FLOW
(CFS)
VELOCITY
(FEET PER
SECOND)
REGULATORY
(FEET NAVD)
WITHOUT
FLOODWAY
(FEET NAVD)
WITH
FLOODWAY
(FEET NAVD)
INCREASE
(FEET)
PIPE MAKERS
(CONTINUED)
O
P
Q
R
CANAL
0-P
Q -R
60,626
61,626
65,121
65,823
729
665
451
570
1.8
0.7
19.9
20.0
20.6
20.7
19.9
20.0
20.6
20.7
20.7
20.8
21.2
21.3
0.8
0.8
0.6
0.6
'Values represent maximum along link
2Feet above confluence with Savannah River
I TABLE 7
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
FLOODWAY DATA
PIPE MAKERS CANAL
FLOODING SOURCE
FLOODWAY
1- PERCENT - ANNUAL - CHANCE -FLOOD
WATER SURFACE ELEVATION
SECTION
MEAN
WITHOUT
WITH
CROSS SECTION
DISTANCE'
WIDTH
(FEET)
AREA
(SQUARE
VELOCITY
(FEET
SECOND)
REGULATORY
(FEET NAVD)
FLOODWAY
(FEET NAVD)
FLOODWAY
(FEET NAVD)
INCREASE
(FEET)
PIPE MAKERS
TRIBUTARY NO. 2
A
1,870
130
385
1.4
19.6
18.82
19.8
1.0
B
2,778
150
465
1.2
19.6
19.22
20.2
1.0
C
5,368
240
649
0.9
19.6
19.52
20.5
1.0
D
6,597
285
798
0.7
19.7
19.7
20.7
1.0
E
7,962
195
478
1.2
19.9
19.9
20.8
0.9
F
8,554
195
443
0.8
20.0
20.0
21.0
1.0
G
9,481
165
428
0.8
21.1
21.1
21.7
0.6
H
10,055
676
1,613
0.2
21.2
21.2
21.8
0.6
I-
m
'Feet above confluence with Pipe Makers Canal
2Elevation computed without consideration of backwater effects from Pipe Makers Canal
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
FLOODWAY DATA
PIPE MAKERS TRIBUTARY NO. 2
Springfield Canal, Springfield Canal Tributary A, St. Augustine Creek, St.
Augustine Creek Tributary, Tributary to Little Ogeechee River Tributary,
Wilshire Canal, Wilshire Canal Tributary A, Wilshire Canal Tributary A -1,
Windsor Forest Canal East, Windsor Forest Canal Tributary, Windsor Forest
Canal Tributary No. 2, Windsor Forest Canal Tributary No. 3, and Windsor Forest
Canal West.
4.3 Base Flood Elevations
Areas within the community studied by detailed engineering methods have
BFEs established in AE and VE Zones. These are the elevations of the 1-
percent- annual- chance (base flood) relative to NAVD. In coastal areas affected
by wave action, BFEs are generally maximum at the normal open shoreline.
These elevations generally decrease in a landward direction at a rate dependent
on the presence of obstructions capable of dissipating the wave energy. Where
possible, changes in BFEs have been shown in 1 -foot increments on the FIRM.
However, where the scale did not permit, 2- or 3 -foot increments were
sometimes used. BFEs shown in the wave action areas represent the average
elevation within the zone. Current program regulations generally require that all
new construction be elevated such that the first floor, including basement, is
elevated to or above the BFE in AE and VE Zones.
4.4 Velocity Zones
The USACE has established the 3 -foot wave height as the criterion for
identifying coastal high hazard zones (USACE, 1975). This was based on a
study of wave action effects on structures. This criterion has been adopted by
FEMA for the determination of VE zones. Because of the additional hazards
associated with high- energy waves, the NFIP regulations require much more
stringent floodplain management measures in these areas, such as elevating
structures on piles or piers. In addition, insurance rates in VE zones are higher
than those in AE zones.
The location of the VE zone is determined by the 3 -foot wave as discussed
previously. The detailed analysis of wave heights performed in this study
allowed a much more accurate location of the VE zone to be established. The
VE zone generally extends inland to the point where the 1- percent - annual-
chance stillwater flood depth is insufficient to support a 3 -foot wave.
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. These zones are as follows:
44
Zone A
Zone A is the flood insurance risk 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 BFEs or base flood depths are
shown within this zone.
Zone AE
Zone AE is the flood insurance risk 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 VE
Zone VE is the flood insurance risk 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 risk zone that corresponds to areas outside the 0.2- percent-
annual- chance floodplain, areas within the 0.2- percent - annual- chance floodplain, 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 protected from the 1- percent - annual- chance flood by levees. No BFEs or
base flood depths are shown within this zone.
The FIRM for Chatham County includes areas designated by Congress as units of the
Coastal Barrier Resources System (CBRS), where federally backed flood insurance is not
available.
The Coastal Barrier Resources Act of 1982 and the Coastal Barrier Improvement Act of
1990 define and establish a system of protected coastal areas (including the Great Lakes)
known as the CBRS. The Acts define areas within the CBRS as depositional geologic
features consisting of unconsolidated sedimentary materials; subject to wave, tidal, and
wind energies; and protecting landward aquatic habitats from direct wave attack. The
Acts further define coastal barriers as "all associated aquatic habitats, including the
adjacent wetlands, marshes, estuaries, inlets and nearshore waters, but only if such
features and associated habitats contain few manmade structures and these structures and
man's activities on such features, and within such habitats do not significantly impede
geomorphic and ecological processes." The Acts provide protection to CBRS areas by
prohibiting most expenditures of Federal funds within them. These prohibitions refer to
45
"any form of loan, grant, guarantee, insurance, payment, rebate, subsidy or any other
form of direct or indirect Federal assistance," with specific and limited exceptions. The
CBRS boundaries depicted on the FIRM for Chatham County were adopted into public
law by Acts of Congress and are, therefore, considered final and not subject to appeal.
In addition to the CBRS, the Coastal Barrier Improvement Act of 1990 established
Otherwise Protected Areas (OPAs). OPAs are undeveloped coastal barriers within the
boundaries of an area established under Federal, State, or local law, or held by a
qualifying organization, primarily for wildlife refuge, sanctuary, recreational, or natural
resource conservation purposes.
Congress designated the initial CBRS areas in 1982. Subsequent modifications of the
CBRS are introduced as legislation to be acted on by Congress, and originate from State
and local requests, as well as recommendations made by the U.S. Fish and Wildlife
Service. After Congress approves additions to the CBRS, the new areas are assigned a
unique effective date, after which Federal assistance prohibitions apply. In cooperation
with the U.S. Department of the Interior, FEMA transfers CBRS boundaries to FIRMs
using Congressionally adopted source maps titled Coastal Barrier Resources System.
FIRMs clearly depict the different CBRS areas and their effective dates with special map
notes and symbols. It should be noted that although FEMA shows CBRS areas on
FIRMs, only Congress may authorize a revision of CBRS boundaries.
Within CBRS boundaries, Federal flood insurance is not available for structures built or
substantially improved on or after the date that the subject area was added to the CBRS.
To assist map users in determining the correct insurance prohibition date in CBRS areas,
each separate CBRS unit is clearly identified on the FIRM. It is important to note that
insurance for structures in OPAs may be obtained if written documentation is provided,
which certifies that the structures are used in a manner consistent with the purpose for
which the area is protected.
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 risk 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 the 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.
46
The countywide FIRM presents flooding information for the entire geographic area of
Chatham 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, where applicable. Historical data relating to the maps
prepared for each community are presented in Table 8.
7.0 OTHER STUDIES
This report either supersedes or is compatible with all previous studies on streams studied
in this report and should be considered authoritative for purposes of the NFIP.
8.0 LOCATION OF DATA
Information concerning the pertinent data used in the preparation of this study can be
obtained by contacting FEMA, Federal Insurance and Mitigation Division, Koger
Center - Rutgers Building, 3003 Chamblee Tucker Road, Atlanta, Georgia 30341.
9.0 BIBLIOGRAPHY AND REFERENCES
Braswell Engineering, Inc., Flood Insurance Study Work Map, Scale 1"=400', City of
Bloomingdale, Georgia, 1999.
Dunn, G.E. and B.I. Miller, Atlantic Hurricanes, Louisiana State University, 1964.
EMC Engineering, Pipe Makers Canal Drainage Study, Supplemental Report, April
1999.
Environmental Sciences Services Administration, Joint Probability Method of Tide
Frequency Analysis, Technical Memorandum WBTM, Hydro 11, V.A. Myers, U.S.
Department of Commerce, April 1970.
ESRI, ArcView GIS Version 9.1 for Windows, Redlands, California, May 18, 2005.
Federal Emergency Management Agency, Type 15 Flood Insurance Study, Chatham
County, Unincorporated Areas, Georgia, August 1980, revised October 1983.
Federal Emergency Management Agency, Users Manual for Wave Height Analysis,
Revised February 1981.
Federal Emergency Management Agency, Procedures for Applying Marsh Grass
Methodology, July 1984.
47
COMMUNITY
NAME
INITIAL
IDENTIFICATION
FLOOD HAZARD
BOUNDARY MAP
REVISION DATE
FIRM
EFFECTIVE DATE
FIRM
REVISION DATE
Bloomingdale, City of
October 15, 1976
None
July 2, 1981
September 26, 2008
May 7, 2001
Chatham County
March 5, 1976
None
August 1, 1980
September26, 2008
(Unincorporated Areas)
September 20, 1995
September 3, 1992
May 19, 1987
October 1, 1983
Garden City, City of
March 16, 1973
None
March 16, 1973
September 26, 2008
May 19, 1987
November 21, 1980
March 19, 1976
July 1, 1974
Pooler, City of
July 25, 1975
None
September 30, 1981
September 26, 2008
Port Wentworth, City of
March 16, 1973
None
March 16, 1973
September 26, 2008
May 19, 1987
December 26, 1975
July 1, 1974
Savannah, City of
September 18, 1970
None
May 21, 1971
September 26, 2008
September 4, 1987
November 21, 1980
July 1, 1974
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
COMMUNITY MAP HISTORY
COMMUNITY
NAME
INITIAL
IDENTIFICATION
FLOOD HAZARD
BOUNDARY MAP
REVISION DATE
FIRM
EFFECTIVE DATE
FIRM
REVISION DATE
Thunderbolt, Town of
Tybee Island, City of
Vernonburg, Town of
December 23, 1977
January 14, 1972
July 27, 1973
None
None
None
July 2, 1987
January 14, 1972
July 27, 1973
September 26, 2008
September 26, 2008
June 17, 1986
September 5, 1975
July 1, 1974
September 26, 2008
July 2, 1987
October 31, 1975
July 1, 1974
1 TABLE 8
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
COMMUNITY MAP HISTORY
Federal Emergency Management Agency, Flood Insurance Study, City of Tybee
Island, Chatham County, Georgia, June 17, 1986.
Federal Emergency Management Agency, Flood Insurance Study, Chatham County
(Unincorporated Areas), Georgia, May 19, 1987a.
Federal Emergency Management Agency, Flood Insurance Study, City of Garden City,
Chatham County, Georgia, May 19, 1987b.
Federal Emergency Management Agency, Flood Insurance Study, City of Port
Wentworth, Chatham County, Georgia, May 19, 1987c.
Federal Emergency Management Agency, Flood Insurance Study, City of Savannah,
Chatham County, Georgia, September 4, 1987d.
Federal Emergency Management Agency, Flood Insurance Study, Town of
Thunderbolt, Chatham County, Georgia, July 2, 1987e.
Federal Emergency Management Agency, Flood Insurance Study, Town of
Vernonburg, Chatham County, Georgia, July 2, 1987f.
Federal Emergency Management Agency, Flood Insurance Study, City of
Bloomingdale, Chatham County, Georgia, May 7, 2001.
Federal Insurance Administration, Type 10 Flood Insurance Study, Chatham County,
Unincorporated Areas, Georgia, June 1971.
Federal Insurance Administration, Flood Hazard Boundary Map, Chatham County
Georgia (Unincorporated Areas), March 1976.
Federal Insurance Administration, Flood Insurance Study, City of Bloomingdale,
Chatham County, Georgia, Flood Insurance Study Report, January 2, 1981a; Flood
Insurance Rate Map, July 2, 1981a.
Federal Insurance Administration, Flood Insurance Study, Town of Pooler, Chatham
County, Georgia, Flood Insurance Study Report, March 30, 1981b; Flood Insurance
Rate Map, September 30, 198 lb.
Georgia Emergency Management Agency, Preparedness Bulletin #2, April 14, 2006.
Hussey, Gay, Bell, & DeYoung, Inc., Certified Topographic Survey Map, Scale 1" =500',
Contour Interval 1 foot, January 31, 2000.
Hussey, Gay, Bell, & DeYoung, Inc., Placentia Canal Concept Design Shell Road to Tide
Gate, May 1996.
50
Hydrologic Engineering Center, HEC -2 Water Surface Profiles, U.S. Army Corps of
Engineers, Davis, California, April 1984.
Hydrologic Engineering Center, HEC -2 Water Surface Profiles, U.S. Army Corps of
Engineers, Davis, California, May 1991.
Hydrologic Engineering Center, HEC -HMS Hydrologic Modeling System, Version
1.0, U.S. Army Corps of Engineers, Davis, California, March 1998.
Hydrologic Engineering Center, HEC -HMS Hydrologic Modeling System, Version
2.1.2, U.S. Army Corps of Engineers, Davis, California, June 2001a.
Hydrologic Engineering Center, HEC -RAS River Analysis System, Version 3.0.1, U.S.
Army Corps of Engineers, Davis, California, March 2001b.
Hydrologic Engineering Center, HEC - GeoRAS, Version 3.1.1, U.S. Army Corps of
Engineers, Davis, California, October 2002.
Hydrologic Engineering Center, HEC -RAS River Analysis System, Version 3.1.1, U.S.
Army Corps of Engineers, Davis, California, May 2003.
Hydrologic Engineering Center, HEC -RAS River Analysis System, Version 3.1.3, U.S.
Army Corps of Engineers, Davis, California, May 2005.
National Academy of Sciences, Methodology for Calculating Wave Action Effects
Associated With Storm Surges, 1977.
National Climatic Center, North Atlantic Tropical Cyclones, P.C. Herbert, U.S.
Department of Commerce, Asheville, North Carolina, 1979.
National Geodetic Survey, VERTCON -North American Vertical Datum Conversion
Utility. Retrieved March 13, 2007, from http: / /www.ngs.noaa.gov /.
National Oceanic and Atmospheric Administration, Technical Paper No. 55, Tropical
Cyclones of the North Atlantic Ocean, G.W. Cry, U.S. Department of Commerce,
Washington, D.C., 1965.
National Oceanic and Atmospheric Administration, Environmental Data Service,
National Climatic Center, Tropical Cyclone Card Deck 993, U.S. Department of
Commerce, Asheville, North Carolina, 1973.
National Oceanic and Atmospheric Administration, Technical Report NWS 15, Some
Climatological Characteristics of Hurricanes and Tropical Storms, Gulf and East
Coasts of the United States, F.P. Ho, R.W. Schwerdt, and H.V. Goodyear, U.S.
Department of Commerce, May 1975.
51
National Oceanic and Atmospheric Administration, National Ocean Survey, Nautical
Charts, Charleston Light to Cape Canaveral, Scale 1:449,659, Chart 11480, U.S.
Department of Commerce, December 1977.
National Oceanic and Atmospheric Administration, National Ocean Survey, Nautical
Charts, Cape Hatteras to Charleston, Scale 1:449,659, Chart 11520, U.S. Department
of Commerce, April 1979.
National Oceanic and Atmospheric Administration, Tropical Cyclones of the North
Atlantic Ocean, 1871 -1980, C.J. Neuman, G.W. Cry, E.L. Caso, and B.R. Jarvinen,
Asheville, North Carolina, U.S. Department of Commerce, July 1981.
National Weather Service, Rainfall Frequency Atlas of the United States, 30- Minute to
24 -Hour Durations, 1- to 100 -year Return Periods, Technical Paper No. 40, U.S.
Department of Commerce, 1961.
Soil Conservation Service, Urban Hydrology for Small Watersheds, Technical Release
No. 55, U.S. Department of Agriculture, 1986.
Streamline Technologies, Inc., Interconnected Channel and Pond Routing (ICPR)
Model, Version 3.02, 2002.
Tannehill, Ray I., Hurricanes — Their Nature and History, Princeton, New Jersey, 1956.
TetraTech, Inc., Coastal Flooding Storm Surge Model, Parts 1 and 2, prepared for the
Federal Emergency Management Agency, 1981.
Thomas & Hutton Engineering Company, Louis Mills Branch/Redgate Canal
Engineering Analysis, March 27, 1998.
Thomas & Hutton Engineering Company, Hardin Canal Re- Analysis Using ALTM Data,
January 7, 2000.
Thomas & Hutton Engineering Company, LiDAR Data, Contour Interval 1 foot:
Chatham County, Georgia, August 2001.
Thomas & Hutton Engineering Company, Kingsway Canal Design Study Report, July
2004a.
Thomas & Hutton Engineering Company, Redgate/Rahn Dairy Canal Design Study
Report, July 2004b.
Thomas & Hutton Engineering Company, Quacco /Regency Park Drainage Improvements
Alternatives Report, November 2005.
52
U.S. Army Corps of Engineers, Savannah District, Flood Plain Information Report,
Casey Canal -North, August 1968a.
U.S. Army Corps of Engineers, Savannah District, Flood Plain Information Report,
Casey Canal - South, June 1968b.
U.S. Army Corps of Engineers, Savannah District, Flood Plain Information Report,
Harmon Canal, July 1969.
U.S. Army Corps of Engineers, Savannah District, Flood Plain Information Report,
Springfield Canal, January 1970.
U.S. Army Corps of Engineers, Savannah District, Flood Plain Information Report,
Wilshire Canal and Tributaries, July 1971.
U.S. Army Corps of Engineers, Savannah District, Flood Plain Information Report,
Dundee Canal and Salt Creek, September 1972.
U.S. Army Corps of Engineers, Savannah District, Flood Plain Information Report,
Pipe Makers Canal, June 1974.
U.S. Army Corps of Engineers, Guidelines for Identifying Coastal High Hazard Zones,
Galveston District, Galveston, Texas, June 1975.
U.S. Army Corps of Engineers, 100 -Year Tidal Flood Elevations for Chatham County,
Georgia, Scale 1:48,000, December 1976.
U.S. Census Bureau, American Fact Finder, Chatham County, Georgia, 2000.
Retrieved July 23, 2007, from http: / /factfinder.census.gov.
U.S. Geological Survey, 7.5 Minute Series Topographic Maps, Scale 1:24,000,
Contour Interval 5 feet: Tybee Island South, Georgia, 1979; Tybee Island North,
Georgia -South Carolina, 1978; Raccoon Key, Georgia, 1979; Isle of Hope, Georgia,
1979; Savannah, Georgia -South Carolina, 1979; Lime House, South Carolina- Georgia,
1980; St. Catherines Sound, Georgia, 1979; Oak Level, Georgia, 1979; Burroughs,
Georgia, 1979; Garden City, Georgia, 1980; Meldrim, SE, Georgia, 1958; Limerick,
SE, Georgia, 1979; Richmond Hill, Georgia, 1980, U.S. Department of the Interior,
various dates.
U.S. Geological Survey, Techniques For Estimating Magnitude and Frequency of
Floods in Rural Basins of Georgia, Water - Resources Investigations Report 93 -4016,
U.S. Department of the Interior, 1993.
53
U.S. Geological Survey, Flood Frequency Relations for Urban Streams in Georgia —
1994 Update, Water Resources Investigations Report 95 -4017, U.S. Department of the
Interior, 1994.
The Weather Channel, Monthly Averages for City of Savannah, Georgia. Retrieved
July 23, 2007, from http: / /www.weather.com.
Woolpert Consultants Aerial Photographs, Mobile, Alabama, December 1982 and
January 1983.
XP Software Inc., XP -SWMM Storm and Wastewater Management Model, Version
10.00, Portland, Oregon, February 2006.
54
ELEVATION IN FEET (NAVD)
15
10
5
0
- 5
- 10
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ELEVATION IN FEET (NAVD)
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15
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LEGEND
0.2% ANNUAL CHANCE FLOOD
1% ANNUAL CHANCE FLOOD
2% ANNUAL CHANCE FLOOD
10% ANNUAL CHANCE FLOOD
STREAM BED
CROSS SECTION
LOCATION
13,000 14,000 15,000
16,000 17,000 18,000
19,000 20,000 21,000 22,000
STREAM DISTANCE IN FEET ABOVE CONFLUENCE WITH SAVANNAH RIVER
23,000
24,000
25,000
25
20
15
10
26,000
FLOOD PROFILES
BLACK CREEK
FEDERAL EMERGENCY MANAGEMENT AGENCY
CHATHAM COUNTY, GA
AND INCORPORATED AREAS
02P
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