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Tybee Island
Adaptation Plan
Sea Level Rise
FINAL REPORT APRIL 2016
Funded by the National Sea Grant Program
Administered by the National Oceanic and Atmospheric
Administration (NOAA), Sea Grant conducts research,
outreach and education in 33 coastal and Great Lakes states.
The University of Georgia Marine Extension Service
The University of Georgia Marine Extension Service
Publication supported in part by an
Institutional Grant (NA10OAR4170098)
to the Georgia Sea Grant College
Program from the National Sea
Grant Oce, National Oceanic and
Atmospheric Administration, U.S.
Department of Commerce. All views,
opinions, ndings, conclusions, and
recommendations expressed in this
material are those of the author(s) and
do not necessarily reect the opinions
of the Georgia Sea Grant College
Program or the National Oceanic
and Atmospheric Administration.
The University of Georgia Marine Extension Service
Publication supported in part by an
Institutional Grant (NA10OAR4170098)
to the Georgia Sea Grant College
Program from the National Sea
Grant Oce, National Oceanic and
Atmospheric Administration, U.S.
Department of Commerce. All views,
opinions, ndings, conclusions, and
recommendations expressed in this
material are those of the author(s) and
do not necessarily reect the opinions
of the Georgia Sea Grant College
Program or the National Oceanic
and Atmospheric Administration.
Publication supported in part by an
Institutional Grant (NA10OAR4170098)
to the Georgia Sea Grant College
Program from the National Sea
Grant Oce, National Oceanic and
Atmospheric Administration, U.S.
Department of Commerce. All views,
opinions, ndings, conclusions, and
recommendations expressed in this
material are those of the author(s) and
do not necessarily reect the opinions
of the Georgia Sea Grant College
Program or the National Oceanic
and Atmospheric Administration.
INTRODUCTION
|
1
FINAL REPORT
April 2016
Authors:
Jason M. Evans, Jill Gambill, Robin J. McDowell,
P. Warwick Prichard, and Charles S. Hopkinson
funded by the national
sea grant college program
Administered by the National Oceanic and Atmospheric
Administration (), Sea Grant conducts research,
outreach and education in coastal and Great Lakes states.
TYBEE
ISLAND ADAPTATION PLAN
Sea Level Rise
2 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Through an award provided by the National Oceanographic and Atmospheric
Administration’s (noaa) National Sea Grant College Program, the City of Tybee Island
partnered with researchers and outreach professionals from Georgia Sea Grant, the
University of Georgia, and Stetson University to develop this sea-level rise adaptation
plan. Using a participatory approach, this project assessed how coastal flooding risks
in the City of Tybee Island are being exacerbated by sea-level rise and also explored
potential adaptation actions for making the City more resilient over time.
Sea Level Rise Impacts
Long-term data from the National Oceanographic and Atmospheric Administration
() tide gauge at Fort Pulaski, located within a few miles of Tybee Island, document
inches of local sea-level rise since . is study summarizes and documents several
ways in which the City of Tybee Island is already being impacted by rising seas. e most
visible of these impacts include:
More frequent closures of US Highway , the sole road access
connecting the City of Tybee Island to mainland Chatham County,
due to periodic tidal ooding.
Tidal backup of stormwater drainage systems in low-lying
areas of Tybee Island, resulting in periodic saltwater ooding
of neighborhood roads and yards.
Increased coastal erosion, particularly on Tybee Island’s
Atlantic beaches.
Adaptation Options
Project researchers worked with citizens and public ocials to identify a series of ve
adaptation actions for their potential to make the City of Tybee Island more resilient to
sea-level rise and coastal ooding. While it is acknowledged that other kinds of sea-level
rise adaptation approaches may be required in the future, identication and consideration
of these ve actions is regarded as an initial step for long-term sea-level rise planning.
Elevating Well Pump Houses
e City of Tybee Island utilizes three well pump houses for public water supply from the
Upper Floridan Aquifer. Two of these well pump houses, one located on Butler Ave. and
one located on th St., show high risk of damages from coastal ooding. A third well
pump house, located at Van Horne Ave., is located on relatively high ground with less
coastal ooding risk.
Executive Summary
EXECUTIVE SUMMARY
|
3
Benet-cost analyses indicate very high justication for near-term elevation and
ood-proong of the Butler Ave. and th St. well pump house facilities. Further technical
evaluation of the Van Horne Ave. pump house facility is also recommended to ensure the
highest level of protection for this public water supply source.
Elevating US Highway 80
Tidal ooding of US Highway , the sole road access to Tybee Island, occurs on a low-
lying causeway located between the Lazaretto Creek and Bull River bridges. Local tide
gauge data suggest that this corridor of US Highway experienced approximately tidal
ooding events in , which is signicantly more than in any year since the tide gauge
was installed in . e full tide gauge record at Fort Pulaski indicates that long-term
sea-level rise is largely responsible for the increased number of tidal ood events on US
Highway .
is highway ooding is known to restrict accessibility to Tybee Island and poses clear
risks to public safety, particularly through loss of emergency vehicle access and blockage
of the City’s sole evacuation route. Due to these public safety concerns, it is recommended
that current plans to modernize US Highway , including the replacement of the Lazaretto
Creek and Bull River bridges, consider the ood risk impacts from future sea-level rise as
a primary design criterion.
Stormwater Retrofits
e City of Tybee Island has recently undertaken signicant eorts to retrot stormwater
systems in low-lying areas known to experience tidal ooding. Investments undertaken by
the City include construction of larger underground pipe conveyances and installation of
tidal backow preventers on low-lying stormwater discharge points. Benet-cost analysis
indicates that these stormwater system investments are highly justied as an approach for
avoiding damage to property and economic activity under any sea-level rise scenario over
a -year time frame.
It is recommended
that current plans
to modernize US
Highway 80 consider
the flood risk impacts
from future sea-level
rise as a primary
design criterion.
Image: ‘The Tybee Island Pier’, http://flic.kr/m01229/16613725822_37d18ab4c1_o. License at http://creativecommons.org/licenses/by/2.0.
4 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Enhanced Sea Wall
Due to concerns about future ood risk, the project team was asked to evaluate poten-
tial benets and costs for construction of an enhanced sea wall along a low-lying section
of Tybee Island. Technical analyses indicated that the enhanced sea wall would provide
little tidal ood protection benet for several decades and, due to high construction costs,
would only provide net benets under a very high sea-level rise scenario. Follow-up dis-
cussions with City of Tybee Island ocials and stakeholders indicated that pursuit of an
enhanced sea wall for sea-level rise adaptation should not be recommended at this time.
Beach Renourishment
e Atlantic beaches of Tybee Island, which provide signicant ood protection to the
City and are a primary driver for the local tourism economy, are subject to high rates of
erosion. Much of this coastal erosion is directly attributable to federal construction of
the Savannah Harbor channel, which is located directly north of Tybee Island. However,
sea-level rise is also increasing long-term beach erosion at Tybee Island and many other
coastal communities.
Periodic sand renourishment projects by the U.S. Army Corps of Engineers, as autho-
rized through a federal agreement called the Tybee Island Shoreline Protection Plan, have
proven critical to the maintenance of Tybee Island’s beaches over the past several decades.
Large-scale beach dune restoration activities by the City of Tybee Island and the Georgia
Department of Natural Resources have also produced substantial shoreline protection
benets.
e current Tybee Island Shoreline Protection Plan is scheduled to expire in . Early
discussions to re-authorize and renew the Tybee Island Shoreline Protection Plan provide
an opportunity to include future sea-level rise scenarios and enhanced dune-eld con-
struction in the design of future beach renourishment projects implemented within the
City of Tybee Island.
A Regional and National Model
In recognition of the wide-reaching impacts of this project, the Tybee Island Sea-Level
Rise Plan received Sea Grant’s highest national outreach award in . e
project has also been included as a case study for sea-level rise adaptation by the U.S.
Climate Resilience Toolkit, the Union for Concerned Scientists, and U.S. Senator Sheldon
Whitehouse of Rhode Island. Methodologies and approaches for sea-level rise planning
originally developed in cooperation with the City of Tybee Island are currently being
utilized in several other U.S. southeast communities, including St. Marys, Georgia; Hyde
County, North Carolina; and Monroe County, Florida.
The Tybee Island
Sea-Level Rise Plan
received noaa Sea
Grant’s 2014 highest
national outreach award
and was included
as a case study for
sea-level rise
adaptation by the
U.S. Climate
Resilience Toolkit.
INTRODUCTION
|
5
Sea-level rise is one of the most pressing long-term concerns for
coastal communities throughout the world. Whether through more
frequent and widespread flooding or devastating destruction due to
intensified storm surges, sea-level rise has the potential to dramati-
cally affect the economic, infrastructural, and environmental bases
of communities within the coastal zone.
Introduction
Local observations and scientic knowledge have conrmed that rising seas are already
aecting communities in the United States. Diverse impacts that include loss of road
access during high-tides, increased ood damage to low-lying buildings, and documented
shis in coastal ecosystems necessitate new kinds of planning and resource mobilization.
To meet this challenge, private citizens, businesses, non-governmental organizations, and
governments at the local, state, and federal level are engaging in innovative partnerships
that mark critical initial steps toward long-term sea-level rise adaptation.
Tybee Island is one of the rst communities in Georgia to formally plan for sea-level
rise. As a low-lying barrier island and beach community, Tybee Island is particularly vul-
nerable. e island has already experienced approximately inches of sea-level rise since
, and this trend is expected to accelerate in the future. A major tourism hub of the
Georgia coast, Tybee Island also is a signicant driver of the state’s coastal economy. Both
in leadership and risk, the island is at the front lines of sea-level rise adaptation.
rough an innovative partnership with Georgia Sea Grant and the University of Ge orgia,
with funding from the National Oceanographic and Atmospheric Administration’s ()
National Sea Grant College Program, Tybee Island has taken its rst steps in planning for
and adapting to sea-level rise. Pairing local knowledge with academic expertise, this eort
has analyzed how the island might be aected by sea-level rise over the next years. e
study documents how the island is being impacted and discusses how infrastructure such
as roads, water supply wells, and stormwater drainage might be made less vulnerable to
sea-level rise and more resilient to sea-level rise. rough a community-driven process,
an interdisciplinary team assisted the City of Tybee Island in identifying and prioritizing
vulnerable areas and assets, as well as analyzing the costs and benets of potential adap-
tation options.
is project has been held up as a model for other coastal governments throughout
the country, via the U.S. Climate Resilience Toolkit and on the U.S. Senate Floor, and
has inspired similar planning eorts in communities throughout the southeastern United
States. Recipient of Sea Grant’s National Superior Outreach Programming Award,
the project has reached over , citizens, students, government ocials, and scientists
in its development.
CHAPTER 1:
6 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
AN INNOVATIVE PARTNERSHIP
In November , ocials from the City of Tybee Island began discussing local concerns
about sea-level rise with faculty and sta from Georgia Sea Grant and the University
of Georgia’s Carl Vinson Institute of Government. Citizens were reporting an increase
in ooding during large spring tide events and expressed particular concern about the
ooding of U.S. Highway , the sole road on and o the island. is regular tidal ooding
was occurring independently of rain or storm events, and community members worried
that rising sea-levels were increasing the frequency and severity of ooding over time.
Implications of sea-level rise on evacuation and emergency management plans, public
health, property values, and the overall economic vitality of the community were also
discussed.
In February , Georgia Sea Grant and the Institute of Government were awarded
a Community Climate Adaptation Initiative () grant from the National Sea
Grant College Program to work with the City of Tybee Island on a sea-level rise adap-
tation plan. e explicit intent of the program was to enhance planning in coastal
communities, such as Tybee Island, being impacted by sea-level rise and other climate
stressors. Partners in this grant application included the Georgia Department of Natural
Resources Coastal Resources Division (-), the Chatham-Savannah Metropolitan
Planning Commission () and Catalysis Adaptation Partners, (). Other
entities that provided data and technical assistance with the planning process included
the Georgia Coastal Regional Commission (), Georgia Department of Transportation
(), Skidaway Institute of Oceanography (), the United States Army Corps of
Engineers (), and the Ecological Planning Group.
e purpose of the project was to lay a foundation for climate adaptation on
Tybee Island by:
Identifying impacts due to current and future tidal ooding;
Educating community members about their vulnerability
to ooding and sea-level rise
Assessing the nancial feasibility of potential adaptation
responses
Informing decisions about how to avoid or mitigate impacts,
and thus minimize expected vulnerabilities and economic
losses over time
US80 DURING A KING TIDE
EVENT, OCTOBER 2015
INTRODUCTION
|
7
is report is the capstone of the Tybee Island Coastal Communities Climate Adaptation
Initiative project. It provides a synthesis of the public engagement processes, technical
research, and sea-level rise adaptation strategies identied in partnership with the City of
Tybee Island. An overall philosophy behind the report is that thorough consideration of
future sea-level rise scenarios is critical for developing appropriate public policies and ini-
tiating sound infrastructural investments. ere is also recognition that reduction of ood
risks should be balanced by costs of adaptation action and the sustainable maintenance of
a community’s character, supporting ecosystems, and economic vitality.
It is important to note that this plan does not provide a complete accounting of all
future risks on Tybee Island due to sea-level rise, or contain an exhaustive list of potential
actions that may be taken in response to these risks. Instead, the plan is an initial eort
to characterize vulnerabilities, explore potential adaptation actions, and, as appropriate,
recommend implementation of those identied actions that show clear benet. Ideally,
these initial steps can become a foundation for future planning iterations informed by
greater experience, better knowledge, and improved technologies. Such a continuous and
adaptive process that actively incorporates new information into future decision-making
is the essence of resilience planning.
ADAPTATION FOCUS AREAS
In a series of facilitated public input sessions, Tybee Island residents and government
ocials worked with the project team to characterize risks and vulnerabilities, identify
potential adaptation actions, and explore policy measures. It was recognized that one of
the earliest impacts of rising sea-levels on Tybee Island is decreased stormwater drainage
as higher tides push into swales, ditches, and underground pipe conveyances. Back-up
of stormwater systems during high tides was identied as a source of increased ooding
within the local community during major rainfall events.¹ During very high tides, some
stormwater systems had been observed to ow backwards on days without rainfall, poten-
tially resulting in the conveyance of saltwater onto roads, yards, and low-lying struc-
tures. Increased occurrence of such tidal ooding events, sometimes called “sunny day
ooding,” was identied as a primary concern from sea-level rise.² ere was also recog-
nition that rising seas can result in the replacement of upland ecosystems with intertidal
marsh and estuarine mudats systems, while also increasing saltwater contamination risks
for drinking water wells and underground aquifers.³
1 Parkinson, R.W. and T. McCue. 2011. Assessing municipal vulnerability to predicted sea-level rise: City of Satellite Beach, Florida.
2 Davenport, C. 2014. Miami finds itself ankle-deep in climate change debate. The New York Times, May 7.
http://www.nytimes.com/2014/05/08/us/florida-finds-itself-in-the-eye-of-the-storm-on-climate-change.html?_r=0.
Accessed December 29, 2015.
3 Passeri, D.L., S.C. Hagen, S.C. Medeiros, M.V. Bilskie, K. Alizad, and D. Wang. 2015. The dynamic effects of
sea-level rise on low-gradient coastal landscapes: A review. Earth’s Future 3:159–181.
Image top left:“View South from the Tybee Island (GA) Pier & Pavilion July 2012” by Ron Cogswell, http:// flic.kr/22711505@
N05/7808031678. License at http://creativecommons.org/licenses/by/2.0.
PAUL WOLFF, DR. ROBIN
MCDOWELL AND DR. JASON EVANS
OUTSIDE TYBEE ISLAND CITY HALL
8 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
rough this engagement process, the following “Focus Areas” emerged as the basis for
framing and evaluating the community’s sea-level rise adaptation options.
A. MUNICIPAL INFRASTRUCTURE: Since Tybee Island is a low-lying barrier island,
much of the City’s infrastructure and private property is vulnerable to ooding.
Sea-level rise can be expected to exacerbate these vulnerabilities over time.
Identifying these vulnerabilities, evaluating the relative costs and benets of infra-
structure improvement options, and recommending specic adaptation actions for
municipal implementation were dened as key goals for sea-level rise planning.
B. ACCESS AND CONNECTIVITY: Tybee Island’s sole road to the mainland, linking
it with the Savannah Metropolitan area, is US Highway . Sections of this
highway are very low lying and currently ood during large spring tide events.
Sea-level rise can be expected to increase the frequency and severity of these
ood events over the next several decades. Development of data and analyses
that characterize future sea-level rise impacts on US and contribute to evalu-
ation of improvement projects for the highway was identied as a key goal of the
planning eort.
C. COASTAL DYNAMICS: Barrier islands like Tybee Island are the visible portion
of a much larger and highly dynamic coastal sediment system. Coastal erosion
problems on Tybee Island can be expected to worsen with sea-level rise and
dredging impacts from the Savannah Harbor deepening, and therefore will need
to be managed through a variety of management interventions. Some approaches
include beach renourishment, dune restoration, living shorelines, coastal
armoring, and relocation of vulnerable infrastructure.
D. MANAGEMENT AND STEWARDSHIP: Preservation of Tybee Island’s rich history
and proactive management promoting future sustainability are core values of
the community. Careful planning, coordination across jurisdictional boundaries,
and adaptation to unanticipated changes will all be required for Tybee Island
to maintain its heritage and remain a thriving community over the next
several decades.
INTRODUCTION
|
9
PLAN OVERVIEW
Following this introduction, the remainder of the plan is organized into four chapters.
Chapter provides a general overview of coastal hazards on Tybee Island and how these
hazards are exacerbated by sea-level rise. Chapter , Community Outreach and Engagement,
provides a specic history of the public participation processes used to inform the planning
eort on Tybee Island. Key to this public participation process was identication of specic
actions that could be evaluated using future ood risk calculations and associated bene-
t-cost analyses. Chapter , Analysis, describes the ood risk calculations and benet-cost
modeling results for the adaptation actions chosen through the public participation
process. ese results provide an important starting point for further discussion of the
suitability of the specic actions evaluated, and provide a basis for exploring other sets of
adaptation actions that may emerge in continued planning. e report concludes with
Chapter , Project Impacts, which discusses the broader impacts of this project to the City
of Tybee Island, other coastal communities, higher education, and national discussions
about climate change adaptation.
Image: ‘Tybee Island’ by Grant Dawson, http://flic.kr/grantdaws/17476748923. License at http://creativecommons.org/licenses/by/2.0.
10 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
FIGURE 2.1: TYBEE ISLAND, GEORGIA
00.5 10.25
MILES
Source: Esri, DigitalGlobe,
GeoEye, i-cubed, Earthstar
Geographics, CNES/Airbus DS,
USDA, USGS, AEX, Getmapping,
Aerogrid, IGN, IGP, swisstopo
PRIMARY MAP EXTENT
TYBEE ISLAND, GA
N
Sources: Esri, HERE, DeLorme, Intermap, increment P Corp, GEBCO, USGS,
FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri
Japan, METI, Esri China (Hong Kong), swisstopo, MapmyIndia, ©
OpenStreetMap contributors, and the GIS User Community
COASTAL HAZARDS AT TYBEE ISLAND
|
11
Coastal Hazards at Tybee Island
CHAPTER 2:
Although the most densely developed of Georgia’s barrier islands, Tybee Island maintains
a quaint “beach town” character that features many historic sites, thriving local businesses,
and productive coastal ecosystems. ese unique attributes contribute to Tybee Island’s
increasing popularity with visitors from around the state, nation, and world. During the
summer season, the resident population of Tybee Island approximately doubles due to an
inux of seasonal residents and long-term vacationers. In addition, a signicant number
of daily visitors come to the island from surrounding coastal communities. Some reports
indicate that, on busy summer weekends, the number of visitors to Tybee Island can
exceed ,, resulting in signicant benets to the local and state economy.
e City of Tybee Island has an average upland elevation of approximately . feet, as
referenced to the North American Vertical Datum of (). e island’s highest
elevations, which in a few isolated locations exceed feet above , occur on
vegetated beach dunes adjacent to the Atlantic Ocean coastline (Figure .). e western
shoreline of the island is bordered by extensive saltmarshes dominated by Spartina alterni-
ora and other salt tolerant vegetation.
FORT PULASKI TIDE GAUGE
A long-term tide gauge station, originally installed in , is located within several
miles of the City of Tybee Island at the Fort Pulaski National Monument. Records from the
Fort Pulaski tide gauge shows that waters in and around Tybee Island experience a daily
tide range of . feet. e daily tide range on Tybee Island can exceed nine feet during
bi-monthly “spring tides” that occur during full and new moon phases.
Flooding of streets and yards has long been a concern in Tybee Island, particularly
during heavy rainfall events that occur at high tide. In addition to such stormwater
ooding, Tybee Island also has historically experienced occasional saltwater ooding
Tybee Island is the northernmost barrier island on the Georgia
coastline (FIGURE 2.1). Located in Chatham County about 15 miles
due east of Savannah, the incorporated City of Tybee Island
covers an area of about 2.7 square miles (~1,712 acres) and
is home to approximately 3,000 permanent residents
4 Senate Research Office. 2007. Final Report of the Senate Tybee Island Beach Renourishment Study Committee. Atlanta:
Georgia State Senate. http://www.senate.ga.gov/sro/Documents/StudyCommRpts/07TybeeIslandRpt.pdf. Accessed January 5, 2016.
5 NOAA. 2016. Datums for 8670870, Fort Pulaski, GA. http://tidesandcurrents.noaa.gov/datums.html?id=8670870.
Accessed January 5, 2016.
6 Allred, K. 2011. Flash flood warning continues: Chatham & Jasper Counties. June 29. http://www.wsav.com/story/20697103/
flash-flood-warning-continues-chatham-jasper-counties. Accessed June 12, 2015.
12 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Historical data
from the Ft. Pulaski
tide gauge indicates
that the frequency
of nuisance flooding
events is steadily
increasing over time.
during “king tide” events (Figure .), which are colloquially dened as the highest spring
tides that naturally occur each year. Although strong onshore winds can aperiodically
raise the height of any tide, large king tides are highly predictable occurrences caused by
the position of the moon and sun in relation to the earth.
A king tide that causes minor saltwater ooding of roads and yards is oen referred to
as a source of “nuisance” tidal ooding. For the Savannah and Tybee Island region,
denes a nuisance tidal ood as water that reaches at least . feet above at the
00.5 10.25
MILES
JONES
6TH
TYBRISSA
HORSEPEN POINT
JONES
14TH
CHATHAM
6TH
SOLOMON
VAN HORNE
LEWIS
CAMPBELL
80
80
N
LIDAR Elevation
Feet above NAVD88
< 0
0 – 2.6
2.6 – 5.2
5.2 – 7.8
7.8 – 10.4
10.4 – 13.0
13.0 – 15.6
15.6 – 18.2
18.2 – 20.8
20.8 – 28.0
FIGURE 2.2: ELEVATION MAP FOR TYBEE ISLAND, GEORGIA, AND VICINITY. ELEVATION DATA ORIGINATED FROM
THE 2009 CHATHAM COUNTY GEORGIA LIDAR PROJECT (HTTP://WWW.NGDC.NOAA.GOV/DOCUCOMP/PAGE?XM-
L=NOAA/NESDIS/NGDC/MGG/LIDAR/ISO/XML/2009_CHATHAM_LIDAR_M1121.XML&VIEW=GETDATAVIEW&HEAD-
ER=NONE). LIDAR POINT CLOUD WAS PROCESSED INTO 5’ RESOLUTION DIGITAL ELEVATION MODEL (DEM) TILES
THROUGH NOAA DIGITAL COAST (HTTPS://COAST.NOAA.GOV/DIGITALCOAST/ABOUT).
Elevation map
for Tybee
Island, Georgia,
and vicinity.
INTRODUCTION
|
13
Ft. Pulaski tide gauge. e Ft. Pulaski tide gauge record indicates that the frequency of
nuisance ood events has steadily increased at Tybee Island over the past several decades
(Figure .). A total of separate nuisance ood events were recorded at Ft. Pulaski in
alone, which is the most of any year within the -year tide gauge record. Although
the frequency of nuisance tidal oods uctuates each year due to variations in weather
and astronomical tide cycles, the long-term trend of increased nuisance ooding on Tybee
Island is a clear consequence of rising sea-level.
7 NOAA. 2015. Fort Pulaski Tide Gage. National Weather Service, Advanced Hydrologic Prediction Service. http://water.weather.gov/
ahps2/hydrograph.php?gage=fpkg1&wfo=chs. Accessed June 12, 2015.
FIGURE 2.3: LOCAL TIDAL FLOODING DURING A KING TIDE EVENT NOVEMBER 14, 2012 (Photos by Jason Evans)
FIGURE 2.4:
NUISANCE FLOODING AT TYBEE
ISLAND, GEORGIA FROM 1980–2015.
VALUES REPRESENT THE ANNUALIZED
AVERAGE OF TIDE EVENTS THAT EXCEED
9.2 FEET ABOVE MEAN LOWER-LOW
WATER (MLLW), OR 1.7 FEET ABOVE
MEAN HIGHER-HIGH WATER (MHHW),
OVER A ROLLING FIVE-YEAR PERIOD
AT NOAA’S FORT PULASKI TIDE GAUGE.
LISTED YEARS REPRESENT THE
MID-POINT OF A GIVEN FIVE-YEAR
PERIOD. FOR EXAMPLE, 1982 COVERS
THE 5-YEAR PERIOD FROM 1980–1984,
WHILE 2013 COVERS THE FIVE-YEAR
PERIOD FROM 2011–2015.
ANNUAL NUISANCE FLOODS (5-Year Average)
15
12
9
6
3
0
y = 0.2533x – 500.31x
R² = 0.6568
1982
—
1984
—
1986
—
1988
—
1990
—
1992
—
1994
—
1996
—
1998
—
2000
—
2003
—
2005
—
2007
—
2009
—
2011
—
2013
Nuisance Flooding at
Tybee Island, Georgia
14 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Recent sea level
rise is likely the
highest that has
been experienced
on earth for several
thousand years.
SEA-LEVELS AND GLOBAL CLIMATE CHANGE
Global sea-level is controlled by two primary factors: ) the average temperature of the
oceans; and ) the amount of water held within the earth’s continental ice sheets. Ocean
temperature aects sea-level due to the basic physical property of warmer water having
more volume than cooler water. In other words, because warmer water takes up more
space than cooler water, warming of the oceans causes a rise in sea-level. Continental ice
sheets are another important control on sea-level because they store large amounts of the
earth’s water outside of the ocean basin. Much like adding ice cubes will raise the level
of water in a cup, melting ice sheets have the eect of raising global sea-level due to the
increased amount of water being put into the ocean system.
It is well-known that major changes in sea level have occurred throughout earth’s
geologic ages. For example, global sea level during the warmest portion of earth’s last
major interglacial period, or approximately , years before present, reached approx-
imately feet higher than today. Most of the landmasses that make up Georgia’s current
barrier islands (Figure .), including what is now Tybee Island, were either submerged or
not yet formed during this ancient stand of higher sea-level (Figure .). By contrast, sea
8 USGS. 2016. Ice, Snow, and Glaciers: The Water Cycle. http://water.usgs.gov/edu/watercycleice.html. Accessed January 5, 2016.
9 Markewich, H.W. and W. Markewich. 1991. An Overview of Pleistocene and Holocene Island Dunes in Georgia and the Carolinas —
Morphology, Distribution, Age, and Paleoclimate. U.S. Geological Survey Bulletin 2069. Washington: United States Government
Printing Office. http://pubs.usgs.gov/bul/2069/report.pdf. Accessed January 6, 2016.
SUBMERSED AT HIGH STAND
2015 COUNTRY BOUNDARY
Little Cumberland Island
Cumberland Island
Jekyll Island
St. Simons Island
Sea Island
Wolf Island
Sapelo Island
Blackbeard Island
St. Catherines Island
Ossabaw Island
Wassaw Island
Little Tybee Island
Tybee Island
Little St. Simons Island
Atlantic Ocean
Richmond
Hill
Hinesville
Savannah
Pembroke
Ludowici
Darien
Brunswick
Woodbine
St. Marys
South Carolina
Florida MILES
010205
Richmond
Hill
Little Cumberland Island
Cumberland Island
Jekyll Island
St. Simons Island
Sea Island
Wolf Island
Sapelo Island
Blackbeard Island
St. Catherines Island
Ossabaw Island
Wassaw Island
Little Tybee Island
Tybee Island
Hinesville
Savannah
Pembroke
Ludowici
Darien
Brunswick
Woodbine
St. Marys
South Carolina
GEORGIA COUNTRIES (2015)
Little St. Simons Island
Atlantic Ocean
Florida MILES
010205
FIGURE 2.5: OVERVIEW MAP OF
GEORGIA’S COASTAL REGION
FIGURE 2.6: VISUALIZATION OF GEORGIA’S COASTAL REGION AT PLEISTOCENE
HIGH STAND SEA-LEVEL (~118,000 BP)
INTRODUCTION
|
15
level during the height of the last ice age, or approximately , years before present, was
about feet lower than today. is low sea-level was caused by the very large volumes of
water being held in continental ice sheets across the northern hemisphere, as well as lower
global ocean temperatures that were present during the glaciation. During this lower sea-
level stand, the Atlantic coastline of Georgia was located approximately miles eastward
of today’s coastal barrier islands (Figure .).
Beginning about , years ago, rapid melting of ice sheets in North American and
northern Europe brought about several thousand years of very rapid sea-level rise, which
at times may have exceeded over feet of rise per years. Aer several melt cycles,
ice sheets then stabilized at about , years before present. e ice sheet stabilization
brought about a long period of time, notably encompassing all of written human history,
in which sea level has remained relatively constant.
A large body of tide gauge and, since , satellite measurements indicates that global
sea-level rose by about seven to eight inches over the th century. While this rate of
recent sea-level rise is low compared to the rise at the end of the last ice age, it is likely the
10 Gornitz, V. 2012. The great ice meltdown and rising seas: Lessons for tomorrow. NASA, Goddard Institute for Space Studies.
http://www.giss.nasa.gov/research/briefs/gornitz_10. Accessed January 6, 2016.
N
South
Carolina
Florida
Tybee Island
Amelia Island
Cumberland Island
Jekyll Island
Little St. Simons Island
St. Simons Island
Sapelo Island
St. Catherines Island
Ossabaw Island
Wassaw Island
Hilton Head Island
Pritchards Island
Hunting Island
Edisto Island
Kiawah Island
Georgia
Richmond Hill
Darien
Brunswick
St. Marys
Savannah
Atlantic Ocean
MILES
02550
Land Mass At Pleistocene Glacial Maximum
(~21 ,0 00 Years Be fore Pres ent)
FIGURE 2.7: VISUALIZATION OF
THE GEORGIA BIGHT REGION AT
PLEISTOCENE LOW STAND
SEA-LEVEL (~21,000 BP)
16 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
highest rise in sea-level that has been experienced on earth for several thousand years.
e documented local sea-level rise at Fort Pulaski is approximately inches since ,
or about inches if averaged over a -year period (Figure .). Geologists have identi-
ed regional land subsidence, or local sinking of the land surface, as the most likely cause
for the higher rate of sea-level rise observed at Fort Pulaski as compared to the recent
global average.
ere is wide agreement among scientists that the increased sea-level rise observed
over the past century is a consequence of rising ocean temperatures and glacial melting
associated with anthropogenic global warming. For this reason, scientists are concerned
that sea-levels have the potential to rise at a much faster pace over the st century due to
the high likelihood of accelerated climate change. A recent report by suggests that
global sea-levels in the year will almost certainly be at least eight inches higher than
present, but could potentially rise by up to . feet (Figure .). e most recent report
from the Intergovernmental Panel on Climate Change () suggests that sea-level
rise is most likely to be between about one to three feet, although the possibility of higher
sea-level rise is not ruled out.
11 Hay, C.C., E. Morrow, R.E. Kopp, and J.X. Mitrovica. 2015. Probabilistic reanalysis of twentieth-century sea-level rise.
Nature 517:481-484.
12 Davis, G.H. 1987. Land subsidence and sea level rise on the Atlantic coastal plain of the United States. Environmental Geology and
Water Sciences 10:67–80.
13 Parris, A., P. Bromirski, V. Burkett, D. Cayan, M. Culver, J. Hall, R. Horton, K. Knuuti, R. Moss, J. Obeysekera, A. Sallenger, and
J. Weiss. 2012. Global sea level rise scenarios for the National Climate Assessment. NOAA Tech Memo OAR CPO. http://scenarios.
globalchange.gov/sites/default/files/NOAA_SLR_r3_0.pdf.
14 IPCC. 2014. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report
of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. Geneva: IPCC.
2012
1992
1992
MEASURED BY
TIDAL GAUGES
+7 INCHES
Low
+1.6 FEET
Int. Low
+3.9 FEET
Int. High
+6.6 FEET
High
00
2 FT
5 FT
PREDICTED
SCENARIOS
1992 MEAN SEA LEVEL
THE MIDPOINT OF THE
NATIONAL TIDAL DATUM EPOCH
NTDE CALCULATED FROM
19832001 OBSERVATIONS
1900
1950
2000
2050
210 0
FIGURE 2.9: NOAA PROJECTIONS FOR GLOBAL
SEA-LEVEL RISE TO 2100. THE LOWEST
SCENARIO ASSUMES VERY MODERATE GLOBAL
CLIMATE CHANGE AND A GENERAL CON-
TINUATION OF THE SEA-LEVEL RISE TREND
OBSERVED IN THE 20TH CENTURY TIDE GAUGE
RECORD. THE HIGHEST SCENARIO ASSUMES
SIGNIFICANT GLOBAL CLIMATE CHANGE THAT
INDUCES LARGE-SCALE MELTING OF THE
GREENLAND AND ANTARCTIC ICE SHEETS.
NOAA Projections
for Global
Sea-Level Rise
to 2100
INTRODUCTION
|
17
HURRICANES AND STORM SURGES
Like most other barrier islands in Georgia and the US Atlantic coast, Tybee Island is at
signicant risk of tidal surge ooding from hurricanes and other large storms. Reecting
this storm surge risk, all of Tybee Island has been designated as a Special Flood Hazard
Area () by the Federal Emergency Management Agency ().
e most recent direct landfall from a hurricane-strength storm in Georgia was
Hurricane David in September . David was a massive storm that le tremendous
destruction and thousands dead in the Caribbean, but weakened signicantly before
reaching the Georgia coast as a minimal Category storm. Fortunately, the largest portion
of Hurricane David’s storm surge in Tybee Island occurred near low tide, and therefore
local tidal ooding was relatively minor. More recently, Hurricane Floyd was projected to
strike the Georgia coast at major hurricane strength, prompting large-scale evacuations
in September . However, the hurricane changed course and instead made a highly
destructive landfall in coastal North Carolina. Georgia’s coastal communities experienced
almost no damage from the near miss of Hurricane Floyd.
Because Georgia has not experienced a direct landfall from a major hurricane in over
a century, there is some public perception that hurricanes are unlikely to strike Georgia’s
coast, or that Georgia’s coast is somehow immune to hurricanes altogether. It is very
important to stress that such perceptions are quite mistaken. In fact, the geologic record
FIGURE 2.8: THE NOAA TIDE GAUGE
AT FORT PULASKI HAS RECORDED
APPROXIMATELY 10 INCHES OF
SEA-LEVEL RISE SINCE 1935.
15 http://www.cityoftybee.org/EmergencyMgmt.aspx?CNID=139. Accessed June 15, 2015.
16 The National Hurricane Center (http://www.nhc.noaa.gov/aboutsshws.php, accessed January 5, 2016) defines a major hurricane
as having winds of at least 111 miles per hour, or a Category 3 storm or higher on the Saffir-Simpson hurricane wind scale.
17 Pavey, R. 2010. Georgia rarely gets hit by hurricanes: here’s why. The Augusta Chronicle. September 1. http://chronicle.augusta.com/
content/blog-post/rob-pavey/2010-09-01/georgia-rarely-gets-hit-hurricanes-here-s-why.
FEMA has
designated
the entirety of
Tybee Island a
Special Flood
Hazard Area
(SFHA).
1940 1950 1960 1970 1980 1990 2000 2010
23.1
23
22.9
22.8
22.7
22.6
22.5
22.4
22.3
22.2
Fort Pulaski
Tide Gauge Data
1935 –2010
LOCAL TREND:
APPROX.
1 FT. RISE OVER 100 YEARS
18 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
shows that the Georgia coast has been frequently impacted by large hurricanes over
the past millennia. is indicates that future hurricanes, including very powerful and
destructive storms, can and should be expected to aect the region.
During the th century alone, six major hurricanes made direct landfalls on the
Georgia coast, including the years of , , , , and . e most severe
of these was the Sea Islands Hurricane, estimated to have been at Category strength
when it made landfall on August near Tybee Island. Approximately , U.S. fatalities
were caused by this hurricane, leading the Savannah Morning News to dub it the “Cyclone
of Death”. Many of the fatalities were associated with a massive storm surge, estimated at
feet above predicted tidal conditions at Tybee Island. Records from the time indicate
that almost all structures on Tybee Island were destroyed by the powerful storm surge and
erce winds associated with this hurricane.
e City of Tybee Island is well-recognized for its extensive eorts to promote storm
surge awareness and hurricane preparedness among its citizens and visitors. For example,
the City has installed several storm surge displays that show the potential ood heights
associated with hurricanes of variable intensity, including a prominent display at the
entrance of City Hall. e City also has a one-foot freeboard requirement, which mandates
the elevation of rst oors for new or substantially improved homes at one foot above the
designated -year oodplain height. Further examples of hurricane and storm surge
ood protection activities undertaken by the City of Tybee Island can be found at the City’s
Emergency Management website (http://www.cityoybee.org/emergencymgmt.aspx).
In a planning eort, hazard planners in the City of Tybee Island, Chatham County,
and other local governments identied the need to better understand how sea-level rise is
changing ood risks from storm surges and potential impacts to the built environment.
18 Kiage, L.M., D. Deocampo, T.A. McCloskey, T.A. Bianchette, and M. Hursey. 2011. A 1900-year Paleohurricane Record from Wassaw
Island, Georgia, USA. Journal of Quarternary Science 26:714–722.
19 Fraser, W.J. 2006. Lowcountry Hurricanes: Three Centuries of Storms at Sea and Ashore. Athens: University of Georgia Press.
20 Ciucevitch, R.A. 2005. Tybee Island: The Long Branch of the South. Charleston: Arcadia Publishing.
21 Chatham Emergency Management Agency. 2010. Chatham County Multi-Jurisdictional Pre-Disaster Hazard Mitigation Plan.
Developed in cooperation with the governments of: Chatham County, City of Bloomingdale, City of Garden City, City of Pooler, City
of Port Wentworth, Town of Thunderbolt, City of Savannah, City of Tybee Island. http://www.chathamemergency.org/!Chatham%20
Base%20HMP_CFA_102110.pdf. Accessed June 15, 2015.
Perceptions that
Georgia’s coast is
somehow immune
to hurricanes are
quite mistaken.
US80 DURING A KING TIDE EVENT, OCTOBER 2015 Credit: Tybee Island Police Department
INTRODUCTION
|
19
e large-scale ooding associated with Superstorm Sandy, which devastated portions
of the northeast US Atlantic coast in October , raised broader national attention to
the problem of sea-level rise resulting in larger storm surge events that overwhelm the
capacity of existing coastal defense infrastructure. Although the magnitude of recent
sea-level rise on Tybee Island (~ inches since , or ~ inches over the past years) is
relatively small compared to a major hurricane storm surge, it is well-understood that a higher
base sea-level inexorably increases the potential damages from a given storm surge event.
BEACH EROSION AND SHORELINE PROTECTION
e beaches and shorelines of Tybee Island are subject to the natural forces of erosion
(removal of sediments that leads to loss of land) and accretion (deposit of sediments that
leads to the building of land). e beaches of Tybee Island, like most barrier islands of
the southeast US Atlantic coast, tend to erode sands from the island’s northern end, while
sands tend to deposit and accrete on the southern end of the island. Much of this natural
sand movement process, known as the longshore dri, is driven by prevailing winds and
associated wave angles. Hurricanes and other large storms can also have very large, and
sometimes quite dierent, impacts on the local erosion and accretion of beach sediments.
Natural beach erosion and accretion processes on Tybee Island have been substantially
altered by human activities for well over a century. For example, a technical report
by the US Army Corps of Engineers found that historic dredging of the Savannah Harbor
channel, which connects from the Savannah River to the Atlantic Ocean just north of
Tybee Island, is responsible for between .–. percent of the net beach erosion that
has occurred on Tybee Island since . is impact is caused by the deepened channel
signicantly reducing the velocity of the longshore dri current, which then results in
22 Miller, K.G., R.E. Kopp, B.P. Horton, J.V. Browning, and A.C. Kemp. 2013. A geological perspective on sea-level rise and its impacts
along the U.S. mid-Atlantic coast. Earth’s Future 1:3–18.
23 Neumann, J.E., K. Emanuel, S. Ravela, L. Ludwig, P. Kirshen, K. Bosma, and J. Martinich. 2015. Joint effects of storm surge and
sea-level rise on US coasts: New economic impacts, adaptation, and benefits of mitigation policy. Climatic Change 129:337–349.
24 Tebaldi, C., B.H. Strauss, and C.E. Zervas. 2012. Modelling sea level rise impacts on storm surges along US coasts. Environmental
Research Letters 7:021001.
25 Griffin, M.M. and V.J. Henry. 1984. Historical Changes in the Mean High Water Shoreline of Georgia. Bulletin 98. Atlanta: Georgia
Geologic Survey. https://epd.georgia.gov/sites/epd.georgia.gov/files/related_files/site_page/B-98.pdf. Accessed January 5, 2016.
26 McKee Smith, J. D.K. Stauble, B.P. Williams, and M.J. Wutkowski. 2008. Impact of Savannah Harbor Deep Draft Navigation Project
on Tybee Island Shelf and Shoreline. ERDC/CHL TR-08-5. Savannah: U.S. Army Corps of Engineers.
A GEORGIA SEA GRANT MARINE EDUCATION INTERN COLLECTING FLOOD DATA ON TYBEE ISLAND, OCTOBER 5, 2015
20 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
beach sediments falling out of suspension into the channel bottom. Consequently, beach
sediments that would have reached Tybee Island under natural conditions instead become
trapped in the Savannah Harbor channel.
Increased shoreline erosion was apparent on Tybee Island soon aer the Savannah
Harbor channel project was initiated in the th century. ese erosion issues then
prompted a long history of additional coastal engineering interventions that have
attempted to abate and reverse beach erosion eects on Tybee Island. Perhaps the most
notable early (circa –) project was construction of a large concrete sea wall, with
a top height approximately feet above mean low water, on the Atlantic beach side of
Tybee Island. is sea wall, constructed largely by the federal government through the
Depression-era Works Project Administration (), successfully halted most westward
erosion on Tybee Island. However, wave scour erosion was signicantly worsened on the
east (beach) side of the sea wall. As a result, many high tides from the s to early s
directly submerged much of Tybee Island’s Atlantic beach, allowing waves to crash directly
onto the sea wall. is then progressively eroded the beach even further over time.
In a decades-long series of attempts to reverse this erosion cycle, coastal engineers at
the federal, state, and local level designed and installed a variety of beach groins and sand
berm structures east of the sea wall on Tybee Island. ese structural interventions
largely failed, however, and rapid beach erosion continued almost unabated on Tybee
27 The City of Tybee Island. 2014. Tybee Island Beach Management Plan. http://weblink.cityoftybee.org/weblink/0/edoc/15641/070_050_
Tybee%20Island%20Beach%20Management%20plan%20October%2027%202014.pdf.
Accessed January 6, 2016.
TYBEE ISLAND BEACH RENOURISH-
MENT, NOVEMBER 4, 2014
(U.S. Army Corps of Engineers
photo by Billy Birdwell)
INTRODUCTION
|
21
Island through the early s. A comprehensive report by the US Army Corps of
Engineers identied loss of beach sediment supply due to the Savannah Harbor channel,
continued wave scouring due to the sea wall, and long-term sea-level rise—as docu-
mented locally at the Fort Pulaski tide gauge—as the primary contributing causes of this
chronic beach erosion problem at Tybee Island.
Since the mid-s the beaches of Tybee Island, like many eroding US beaches, have
been maintained through large-scale sand renourishment projects. Sand renourishment
involves the use of mechanical dredges to capture suitable sediments from oshore areas
and subsequent deposit of these sediments onto the beach and nearshore coastal waters.
e agreement between local, state, and federal authorities that covers the renourishment
of Tybee Island’s beaches, called the “Tybee Island Shore Protection Project,” is autho-
rized by the Federal Shore Protection provisions of the Water Resources Development
Act of . e provisions of the Tybee Island Shore Protection Project make the beaches
of Tybee Island eligible for federally assisted renourishment every seven years through
.
Large-scale sand renourishment under the Tybee Island Shore Protection Project began
in –. Other renourishment projects were completed on Tybee Island in -
, –, , and –. Over time, these renourishment projects have
almost completely covered the sea wall with beach sands, thus eectively removing
the enhanced wave scour and accelerated beach erosion eects once associated with this
structure. e renourishment projects are generally regarded as essential to the creation
and maintenance of large areas of recreational beach on Tybee Island, which has served as a
primary driver in the growth of the City’s tourist economy over the past several decades.
ese signicant economic benets provide a primary justication for the local, state, and
federal expenditures required to complete the renourishment projects on Tybee Island.
Another fundamental goal of the Tybee Island Shore Protection project is to manage
and renourish the City’s beaches in a way that provides “ood control protection from
hurricanes and storm damage”. Consistent with this goal, a long-term partnership between
the City of Tybee Island and the Georgia Department of Natural Resources has resulted
in the restoration of large expanses of vegetated sand dunes along most of Tybee Island’s
beaches. ese dune restoration activities have provided signicant ood protection
benets for Tybee Island residents, while also further reducing the impacts of beach
erosion and improving habitat conditions for several shore-dependent wildlife species.
In recognition of these important ecosystem services, the most recent Tybee Island Beach
Management Plan, developed by the City of Tybee Island, calls for increasing eort to
expand and strengthen dune-building activities across all of the City’s beaches.
28 Oertel, G.F., J.E. Fowler, and J. Pope. 1985. History of Erosion and Erosion Control Efforts at Tybee Island, Georgia. AD–A156 163.
Vicksburg: U.S. Army Corps of Engineers.
29 US Army Corps of Engineers. 2014. Final Environmental Assessment and Finding of No Significant Impact: Tybee Island, Georgia
Shore Protection Project 2014-2015 Renourishment. Savannah: US Army Corps of Engineers. http://www.sas.usace.army.mil/
Portals/61/docs/Planning/Plansandreports/TybeeFinalEA/FinalEA.pdf. Accessed January 6, 2016.
30 Toma, M. and A. Brewer. 2007. The Economic Impact of Tybee Island Beach Renourishment on Georgia’s Economy.
Savannah: Center for Regional Analysis, Armstrong Atlantic University. http://www.cityoftybee.org/Assets/Files/BeachTaskForce/
BeachEconomicImpact.pdf.
31 The City of Tybee Island. 2014. Tybee Island Beach Management Plan. http://weblink.cityoftybee.org/weblink/0/
edoc/15641/070_050_Tybee%20Island%20Beach%20Management%20plan%20October%2027%202014.pdf.
Accessed January 6, 2016.
Restoration of
vegetated sand
dunes along Tybee
Island’s beaches
has provided
significant flood
protection benefits.
22 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
US80 DURING A KING TIDE EVENT, NOVEMBER 2012
COMMUNITY OUTREACH AND ENGAGEMENT
|
23
is eort entailed:
n Analyzing local vulnerability to sea-level rise;
n Identifying possible solutions to problems associated with ooding; and
n Weighing the cost and benets of adaptation actions.
e project was developed and implemented using a trans-disciplinary approach that inte-
grated expert knowledge, stakeholder engagement, and a participatory decision-making
process. is promoted a planning process that was more consistent with existing local
infrastructure, relevant laws and ordinances, and cultural preferences.
A series of three town hall meetings, all open to the public and held at the Tybee Island
City Hall, were a central component of the project. Press releases, local media coverage,
yers, email announcements, social media and advertisements on the City of Tybee Island
website, a local access television station, and the electric marquee outside of the City Hall
Building were used to inform stakeholders about the meetings and invite their participation.
An in-depth log of the town hall meeting content is provided in Appendix I.
Making Data Accessible
e rst town hall meeting, held in May , featured a series of expert presentations
on sea-level rise science and adaptation, and also solicited input from public ocials and
local citizens about unique issues faced by Tybee Island. In discussing future projections
of sea-level rise, the project team worked with the community to explain and compare
CHAPTER 3:
Community Outreach and Engagement
Recent research documents the extent to which rising sea-levels
are already impacting property, infrastructure, and ecosystems
in many US coastal communities, including Tybee Island.
Focusing on a 50-year time frame, the Tybee Island Sea-level
Rise Adaptation Plan was developed through a multi-tiered
community-driven planning approach.
32 Sweet, W., J. Park, J. Marra, C. Zervas, and C. Gill. 2014. Sea Level Rise and Nuisance Flood Frequency Changes around the United
States. NOAA Technical Report NOS CO-OPS 073. http://tidesandcurrents.noaa.gov/publications/NOAA_Technical_Report_NOS_
COOPS_073.pdf. Accessed September 17, 2015
33 Angelstam, P. K. Anderson. M. Annerstedt, R. Axelsson, M. Elbadidze, P. Garrido, I. Stjernquist, et al. 2013. Solving problems
in socio-ecological systems: Definition, practice and barriers of transdisciplinary research. Ambio – A Journal of the Human
Environment 42:254–265.
34 Thompson Klein, J. 2013. The transdisciplinary moment(um). Integral Review: A Transdisciplinary & Transcultural Journal for
New Thought, Research, and Praxis 9:189–199.
24 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
dierent models and scenarios. Particular eort was made to acknowledge uncertainties
in future projections and communicate hazards on a human time-scale.
e project team employed a variety of visualization and facilitation tools in support
of this objective. For example, the Sea-level Rise and Coastal Flooding Impacts Viewer
(https://coast.noaa.gov/digitalcoast/tools/slr), launched in by ’s Oce for
Coastal Management, allows website visitors to simulate dierent rates of sea-level rise
in locations around the country. It uses a modied “bathtub” approach to sea-level rise,
taking into account elevation, tidal variability, and hydro-connectivity to map coastal
inundation under dierent sea-level rise scenarios. By using the Viewer to display Tybee
Island with three-feet of sea-level rise (Figure .), the project team showed Tybee Island’s
vulnerability in a way that was concrete, relatable, and accessible to stakeholders.
Identifying Vulnerabilities
A second series of town hall meetings, held in August , worked with local ocials
and citizens to identify local assets at-risk from sea-level rise, review sea-level rise adaptation
strategies, and choose the rates of sea-level rise to be used in the adaptation planning process.
Utilizing a modied version of the Vulnerability, Consequences, and Adaptation
Planning Scenarios () facilitation process, meeting participants were encouraged
inundated
inundated
Rt. 80 to mainland
FLOODING DURING TODAY’S HIGHEST TIDESFLOODING WITH WATER LEAV ES THREE FEET HIGHER
Current
MHHW
3 Feet above
MHHW
FIGURE 3.1. SEA-LEVEL RISE AND
COASTAL FLOODING IMPACTS
VIEWER MAPS OF TYBEE ISLAND
TODAY (LEFT) AND WITH THREE
FEET OF SEA-LEVEL RISE (RIGHT).39
35 NOAA. 2015. Frequent Questions: Digital Coast Sea Level Rise and Coastal Flooding Impacts Viewer. http://coast.noaa.gov/digitalcoast/_/
pdf/SLRViewerFAQ.pdf. Accessed January 5, 2016.
39 Greenhalgh, E. 2014. On Georgia seashore, visualizing sea level rise to set planning priorities. https://www.climate.gov/news-features/
climate-case-studies/georgia-seashore-visualizing-sea-level-rise-set-planning. Accessed January 5, 2016
39 Greenhalgh, E. 2014. On Georgia seashore, visualizing sea level rise to set planning priorities. https://www.climate.gov/news-features/
climate-case-studies/georgia-seashore-visualizing-sea-level-rise-set-planning. Accessed January 5, 2016
COMMUNITY OUTREACH AND ENGAGEMENT
|
25
to oer their institutional knowledge on vulnerable areas and anecdotal information on
historic ooding events. rough this process, the project team gathered critical feedback
and on-the-ground insights from local residents and community leaders. As summarized
in Figure ., meeting participants identied the following concerns related to sea-level rise:
n FAILURES OF THE LOCAL STORMWATER MANAGEMENT SYSTEM
n FLOODING OF ROADS, PARTICULARLY US HIGHWAY 80
n INCREASED BEACH EROSION
n SALTWATER INTRUSION
n HIGHER AND STRONGER STORM SURGES
Choosing Sea-Level Rise Scenarios
Meeting participants also worked with the project team to
decide upon the projected height of sea-level rise to use in
planning for the future. A wide range of published sea-level
rise scenarios were discussed through facilitated discussion,
with present members of the Tybee Island City Council pro-
viding nal determination of model parameters through
majority votes. rough this process, it was decided that
widely cited sea-level rise curves published by climate scien-
tists Martin Vermeer and Stefan Ramhstorf would be used
for the High and Intermediate sea-level rise scenarios in the
City’s adaptation planning through the year . e Low
sea-level rise value would be based on linear extrapolation of
the Ft. Pulaski tide gauge record. A summary of these sea-
level rise scenarios is provided in Table .
SCENARIO PROJECTED SEALEVEL
RISE BY 2060*
High 31 inches
Intermediate 14 inches
Low 6 inches
TABLE 3.1: 2060 SEA-LEVEL RISE SCENARIOS FOR
THE TYBEE ISLAND SEA-LEVEL RISE ADAPTATION PLAN.
THE ASSUMED BASE YEAR FOR SEA-LEVEL IS 2010.38
36 Vermeer, M. and S. Rahmstorf. 2009. Global sea level linked to global temperature. Proceedings of the National Academy of Sciences
of the United States of America.106:21527-21532.
38 Technical description of the methods to derive sea-level rise scenarios is provided in Appendix II.
Image: U.S. Army Corps of Engineers Savannah District by Billy Birdwell, http://flic.kr/savannahcorps/15534084458.
License at http://creativecommons.org/licenses/by/2.0.
26 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
FIGURE 3.2. DIAGRAM OF DISCUSSIONS
ON SEA-LEVEL RISE VULNERABILITIES AND
ADAPTATION OPTIONS FROM TYBEE TOWN
HALL MEETING ON MAY 7, 2012.
Tybee Town
Hall Meeting
May 7, 2012.
Hazards
Preparedness Storm severity/
frequency
Dune building
Renourishment
Groins
Armoring
Beach erosion
Shoreline encroachment
Existing dunes
Harbor deepening
Availability of state/
federal funds
Permits
Higher high tides
Height regulations
Warning system
for road ooding
Decreased surge buer Property damage
Lost property value
Potential loss of life
Current structures
Lost tourism Less tax revenue
Increased insurance
rates
Increased
maintenance costs
Accidents
Potential for standing Property damage
Lost property value
Potential loss of life
Raise causeway
Flooded roads
(e.g., US 80 causeway)
Availability of
state/federal funds
Permits
Sea level rise Compaction
Subsidence
OUTCOMEMANAGEMENT
CONCERN
STRESSOR CONTEXTCONSEQUENCE MANAGEMENT
ACTION
COMMUNITY OUTREACH AND ENGAGEMENT
|
27
Choosing Adaptation Options
e project team presented a wide range of adaptation options and examples of
sea-level rise planning practices from other communities. Some of these options and prac-
tices included infrastructure elevation, wet ood-proong, dry ood-proong, rolling
easements, fee simple acquisition of vulnerable property, beach renourishment, and shore-
line armoring. Based upon the specic sea-level rise vulnerabilities facing Tybee Island,
ve potential local adaptation actions were selected by the community for more detailed
consideration:
ACTION 1: ELEVATION OF MUNICIPAL WELL PUMPS:
Elevating the rst oor of the City’s well houses
and electronic components to three feet above
the -year oodplain.
ACTION 2: ELEVATION OF US 80:
Elevating the US causeway between
Wilmington Island and Tybee Island to
three feet above current grade.
ACTION 3: STORMWATER RETROFITS:
Retrots of low-lying stormwater infrastructure
to prevent ooding from tidewater backow.
ACTION 4: BUILDING A SEAWALL:
Construction of a back-island seawall, at a height of
three feet over the current nuisance tidal ooding level,
to prevent bank overow in low-lying areas.
ACTION 5: ENHANCED BEACH NOURISHMENT:
Increased frequency of beach renourishment relative
to increased sea-level rise out to .
28 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Choosing Benefit-Cost Criteria
e nal component of the August town hall meetings was determination of the
technical criteria that would be used to develop dollar-based inputs for adaptation
modeling. e two criteria chosen through participant consensus were the tax-assessed
values of buildings and the annual economic activity generated by the City’s hotel-motel
tax receipts. Assessed values of buildings were to be obtained from Chatham County’s
property parcel database, while the spatial component of economic activity was to be
developed by linking hotel-motel tax receipts to property addresses. e revenues would
then be adjusted by a standard multiplier to account for economic activity from tourism.
An annualized discount rate of percent was chosen for modeling future ooding damage
to both buildings and economic activity.
Weighing Results and Refining the Approach
A series of two town hall meetings, held in March , presented a suite of technical eval-
uations and benet-cost analyses for selected adaptation actions identied in the August
meetings. Upon reviewing the results, members of the Tybee Island City Council
directed the project team to further rene project analyses and recommendations in
conjunction with the City of Tybee Island’s Community Resources Committee and the
Beach Task Force Committee.
Follow-up meetings with the Community Resources Committee provided feedback on
-based maps showing predicted extents of local king tides and oered guidance into
additional areas where regular tidal ooding has been observed. Following these discus-
sions, members of the Community Resources Committee initiated the Tybee Island King
Tide Project, which provides an online repository of photographs that document local
tidal ooding events.
Meetings with the Beach Task Force Committee provided clear direction that formal
benet-cost modeling of sea-level rise and enhanced beach renourishment was beyond the
resources available for this project. While current Congressional authorizations and sched-
ules being followed by the US Army Corps of Engineers did not allow for additional dune
elevation to be included as a design parameter in the – renourishment cycle, the
Committee expressed interest in pursuing other avenues for promoting enhanced dune
development as a storm buer, sea-level rise adaptation, and overall oo d mitigation strategy.
Additional Input and Outreach
is planning process involved extensive public outreach to Tybee Island residents, business
leaders, elected ocials, and government sta in making decisions about the scope and
focus of the plan. In addition to public town hall-style meetings, regular communication
took place with government sta, city committees, and other stakeholders. ese conver-
sations and collaborations provided additional data and insights that were included in the
planning process. Additional technical and logistical support was provided by personnel
from the Department of Natural Resources Coastal Resources Division (-), the
Chatham County Metropolitan Planning Commission (), and Catalysis Adaptation
Partners (). Other entities that provided data and technical assistance through this
process included the Georgia Coastal Regional Commission (), Georgia Department
of Transportation (), Skidaway Institute of Oceanography (), and the United
States Army Corps of Engineers ().
37 Tybee Island King Tide Project. 2015. https://www.flickr.com/groups/tybeekingtide. Accessed January 5, 2016.
ASSESSMENT OF ADAPTATION ACTIONS
|
29
To facilitate local decision-making, the project team developed
a series of analyses to assess the relative benefits and costs
of four selected adaptation options. This chapter summarizes
the technical approaches used to develop these benefit-cost
analyses and discusses the results.
Assessment of Adaptation Actions
ACTION 1: ELEVATION OF MUNICIPAL WELL PUMPS
Safe and sustainable sources of drinking water are a clear requirement for the health and
welfare of any community. Tybee Island currently relies on three groundwater wells, all
located within the City, to obtain its drinking water. During town hall meetings and fol-
low-up discussions, City ocials expressed a high degree of concern about the potential
ooding of these wells as a result of a major storm surge or other high water event.
City sta reported on a recent visit to nearby Hilton Head,
SC, where pump houses had been retrotted such that elec-
tronic components were elevated above the -year base ood
elevation, and preliminary cost estimates had been obtained for
conducting a similar project at Tybee Island’s three well houses.
For these reasons, City ocials and stakeholders requested
assistance in characterizing benets of elevating well pumps
as a component of the sea-level rise adaptation plan. Elevating
the pump houses to a height above the projected probability
ood area (-year oodplain) was selected as an adaptation
option to address this identied vulnerability.
CHAPTER 4:
30 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Current Well House Elevations
Floor elevation for each of the well pump houses was measured using two approaches:
) ground level elevations extracted from the well-pump locations; and ) onsite
ground elevations of the pump house sites, as obtained from a precision three-dimen-
sional Online Position User Service () unit. Table . provides a comparison
of the estimated ground elevations at each of the City’s well pump houses. e
measurements were presumed to provide a higher point elevation accuracy and were used
for all subsequent calculations.
Table . also provides a summary of the ood height probabilities heights, as based on
a oodplain study completed by . ese ood heights include the percent annual
ood probability area (oen referred to as the -year oodplain), percent annual ood
probability area (-year oodplain), percent annual ood probability area (-year
oodplain), and the . percent annual ood probability area (-year oodplain). e
percent probability area, or the -year oodplain, is the regulatory oodplain for which
the “base ood elevation” () is calculated (Figure .).
THE 100-YEAR FLOODPLAIN
EXPLAINED.
The term “100-year floodplain” is an often mis-
understood term of art in floodplain management
that leads many people to misconceive the level
of threat that building in the 100-year floodplain
presents. The 100-year floodplain refers to the
area that computer models show has a 1 percent
chance of flooding in any given year. This means
that theoretically, the return interval for such an
event happening is 100 years. This leads many
people to believe that these types of floods only
happen once every century. In reality, there is a
1 percent chance of that level of flooding every
year regardless of when the last flood occurred.
This means that over 30 years, there is a 26
percent chance that a structure located in the
100-year floodplain (also known as the 1 percent
annual flood probability area) will flood.42
40 The device used was an iGage X90-OPUS L1L2 Precision Static Occupation GPS. Results were processed through rapid static
algorithms provided by the NOAA Online Position User Service (OPUS) (http://www.ngs.noaa.gov/OPUS/about.jsp#accuracy).
41 FEMA. 2009. Digital Flood Insurance Rate Map (DFIRM) Database (Chatham). Georgia GIS Clearinghouse. Retrieved from
https://data.georgiaspatial.org/index.asp?body=preview&dataId=43928
42 Graphic adapted from, Frost-Tift, S., A. Mahadevia, D. Mills, A. Reeder, A. Sheldon, and J. Squerciati. 2014. Homeowner’s
Guide to Retrofitting: Six Ways to Protect Your Home From Flooding. FEMA P-312. http://www.fema.gov/media-li-
brary-data/1404148604102-f210b5e43aba0fb393443fe7ae9cd953/FEMA_P-312.pdf. Accessed January 6, 2016.
26%
6%
45%
96%
71%
10 50 100 500 (-Year)
Percent Chance for
One or More Floods
of a Given Magnitude
Being Equalled
or Exceeded in
30-Year Period
25
FLOOD MAGNITUDE
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0
FIGURE 4.1: THE 100-YEAR FLOODPLAIN EXPLAINED
The 100-Ye ar
Floodplain
ASSESSMENT OF ADAPTATION ACTIONS
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31
Capital Damage Assessment
Capital damages to these three pumps from potential ood damage were calculated on the
assumption of a , value and depth-damage relationships for municipal wells. e
depth-damage equations used for this analysis are provided as Appendix . Importantly,
these damage assessments assume no permanent contamination of wells from oodwa-
ters, but instead only estimate damages to well equipment associated with ood waters.
Damages are also maximized at percent of value for ood depths of six feet and higher.
To account for sea-level rise in these calculations, the ood heights all ood eventswere
adjusted upwards on an annual basis using the selected
Low, Intermediate, and High sea-level rise scenarios.
ese adjusted ood depths were factored into the damage
estimates for the years following . Details of this
calculation, including an assumed percent annualized
discount rate, are presented as Appendix IV. e results
of the cumulative -year damage assessment for the City
of Tybee Island’s municipal well pump houses under each
sea-level rise scenario are shown in Table ..
43 Ground elevations are subject to the limitations of the techniques used, and should not be regarded as survey quality.
Further site investigations by a licensed surveyor would provide the basis for more robust assessment.
44 FEMA. 2013. Multi-hazard loss estimation methodology, HAZUS-MH, Flood Model. Technical Manual.
http://www.fema.gov/media-library-data/20130726-1820-25045-8292/hzmh2_1_fl_tm.pdf. Accessed June 15, 2015.
PUMP HOUSE LIDAR
ELEVATION
OPUS
ELEVATION
10%
PROBABILITY
FLOOD
2%
PROBABILITY
FLOOD
1%
PROBABILITY
FLOOD BFE
0.2%
PROBABILITY
FLOOD
Van Horne
Ave. 11.3 ft. 12.2 ft. 8.3 ft. 10.5 ft. 12 ft. 13.2 ft.
Butler Ave. 8.0 ft. 8.5 ft. 10.5 ft. 12.4 ft. 13 ft. 14.7 ft.
14th St. 9.3 ft. 9.2 ft. 8.3 ft. 10.5 ft. 12 ft. 13.2 ft.
TABLE 4.1: ESTIMATED
GROUND ELEVATIONS FOR
CITY OF TYBEE ISLAND
WELL PUMP HOUSES43
PUMP HOUSE LOW INTERMEDIATE HIGH
Van Horne
Ave. $129 $197 $498
Butler Ave. $37,091 $38,264 $71,464
14th St. $7,738 $8,936 $13,548
TABLE 4.2: CUMULATIVE 50-YEAR CAPITAL DAMAGE ASSESSMENT
FOR CITY OF TYBEE ISLAND WELL PUMP HOUSES BY SEA-LEVEL
RISE SCENARIO
32 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Economic Loss Assessment
Capital damage assessments were appended with a cumulative economic loss assessment
to account for the economic losses that would result from a reduced water supply due to
the shortages or rationing in the aermath of a ood event. It was assumed that six feet of
ooding in the pump house structure would cause loss of operation for two weeks, while
lower ood level damages were reduced proportionately to ood height from six feet.
A loss of per capita per day was used as a conservative estimate of the economic
impact of the loss of the water. e economic losses were then divided by three to appor-
tion the losses between the three wells. ese single event losses were then extrapolated
out to a cumulative -year damage assessment and discounted to present value. Full
equations for this method are provided as Appendix V. e modeled economic loss results
for each well pump are shown in Table ..
Combined Loss Assessment and Benefit-Cost Ratio
Combining the capital damage and economic loss impacts, the total cumulative modeled
ood risk cost for each of the City of Tybee Island’s well pump facilities is shown in Table ..
e estimated price of elevating the pump-house structures was , per struc-
ture. Using this estimate, the benet-cost ratio for elevating each of the pump-houses was
calculated as:
R = D/E
R = benet-cost ratio;
D = cumulative -Year Damage Assessment;
E = estimated cost to elevate(,).
Results of these benet-cost estimates over a -year period are summarized in Table ..
45 FEMA. 2009. BCA Reference Guide. June 2009. https://www.fema.gov/media-library/assets/documents/18870.
Accessed January 5, 2016.
46 Aubuchon, C.P. and K.M. Morley. 2013. The economic value of water: Providing confidence and context to
FEMA’s methodology. Journal of Homeland Security and Emergency Management 10:245-25.
TABLE 4.5: TABLE 4.4: 50-YEAR BENEFIT COST RATIO FOR PUMP
HOUSE ELEVATION TO 3 FEET ABOVE BASE FLOOD ELEVATION
PUMP HOUSE LO W INTERMEDIATE HIGH
Van Horne Ave. 0.11 0.2 0.44
Butler Ave. 14.17 15.53 19.83
14th St. 3.06 3.56 5.52
TABLE 4.3: CUMULATIVE 50-YEAR ECONOMIC LOSS DAMAGE
ASSESSMENT FOR CITY OF TYBEE ISLAND WELL PUMP HOUSES
BY SEA-LEVEL RISE SCENARIO
PUMP HOUSE LOW INTERMEDIATE HIGH
Van Horne
Ave. $16,905 $29,516 $65,053
Butler Ave. $2,088,646 $2,291,663 $2,903,376
14th St. $451,002 $525,118 $814,633
PUMP HOUSE LOW INTERMEDIATE HIGH
Van Horne
Ave. $17,034 $29,713 $65,551
Butler Ave. $2,125,737 $2,329,927 $2,974,840
14th St. $458,740 $534,054 $828,181
TABLE 4.4: CUMULATIVE 50-YEAR TOTAL LOSS DAMAGE
ASSESSMENT FOR CITY OF TYBEE ISLAND WELL PUMP HOUSES
BY SEA-LEVEL RISE SCENARIO
ASSESSMENT OF ADAPTATION ACTIONS
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33
Discussion and Recommendations
e benet-cost ratios from this analysis indicate that the Butler Avenue pump house is at
high risk of ooding and should be elevated as soon as is practical. is conclusion can be
derived completely independent of the sea-level rise scenario due to the very high bene-
t-cost ratios (. –.). e St. pump house also shows a benet-cost signicantly
greater than one under all scenarios, which suggests that near-term elevation of this pump
house is also justied.
e Van Horne pump house, by contrast, is located at a somewhat higher elevation
with signicantly lower identied ood risk. For this reason, the benet-cost results do
not indicate a need for immediate adaptation action under any sea-level rise scenario.
However, we do note that these arguably are conservative estimates of water supply
disruption following a catastrophic ood event, as the results do not account for possible
contamination of the water source associated with storm surge ooding. Further assess-
ments are likely justied to determine the suitability of the Van Horne pump house for
future elevation or other improvements to improve ooding resilience.
ACTION 2: ELEVATION OF US HIGHWAY 80
e sole road access to Tybee Island is a . mile section of US Highway that connects
the island to the City of Savannah and the mainland. is portion of US begins at a
bridge from Wilmington Island that crosses the Bull River, runs along several miles of an
earthen causeway surrounded by tidal marsh, and leads into the City of Tybee Island over
a bridge crossing Lazaretto Creek (Figure .).
e public input for this project raised several well-known issues with the current
conguration of this stretch of US :
e highway lacks emergency lanes across both the Lazaretto
Creek and Bull River bridges. Trac accidents and other
obstructions have resulted in a complete loss of ground trans-
portation access to and from Tybee Island for hours at a time.
Low grade at several sections along the earthen causeway
allows for periodic ooding in high tide situations. is
ooding results in highway closures that prevent trac ow on
and o of Tybee Island. is situation could also signicantly
restrict evacuation times during the approach of a hurricane or
other large coastal storm event.
Narrow right of way shoulders present general safety concerns
for motorists, bicyclists, and pedestrians, while also constrict-
ing trac ow options following accident events and in emer-
gency evacuation situations.
The sole road access
to Tybee Island is
a 5.5 mile section
of US Highway 80
that connects
the island to the
City of Savannah
and the mainland.
FLOODING ON US 80
34 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
At the time of this project, the Georgia Department of Transportation (), the
Coastal Region Metropolitan Planning Organization ( ), and the Chatham-
Savannah Metropolitan Planning Commission (), had long been considering options
to redesign and reconstruct US to address many of these issues. Plans developed by
in the early to mid-s involved widening the entire road section and the Bull
River bridge to four lanes, replacing the Lazaretto Creek bridge with a four-lane structure,
creating a -foot raised grass median, and constructing two -foot outside shoulders
with . foot wide bike paths. e plan also called for raising the entire road grade
by three feet over the tidal ood stage to provide a margin of safety for pre-hurricane evac-
uations. is plan, however, was not implemented by , largely due to its expense,
environmental impacts, and concerns expressed by local and state stakeholders regarding
potential for increased congestion within the City of Tybee Island.
In December , the released a comprehensive study outlining options for
replacing the Bull River and Lazaretto Creek bridges, as well making other improvements
to the US corridor. is study describes several new design options for improving the
US corridor into Tybee Island and outlines a participatory process used to select a
preferred alternative. e recommended alternative calls for replacement of the Bull River
and Lazaretto Creek bridges, maintenance of two-lane trac but with addition of -foot
shoulders suitable for biking, and improved access to the existing McQueen’s Island pedes-
trian trail. Tidal ooding problems would be addressed by elevating the low-lying areas
of the road to an elevation above minimal ood stage and uniform with the remainder of
the road bed. e local ood elevation is minimally dened by as . feet above
.
47 Lewis and Zimmerman Associates. 2003. SR 26/US 80 Widening from Bull River to the Lazaretto Creek, Chatham County,
Georgia, Value Engineering Study Report. Atlanta: Georgia Department of Transportation.
48 CDM Smith. 2012. US 80 Bridges Replacement Study: GDOT P.I. No. 0009379. CORE Coastal Region MPO. Savannah, GA.
http://www.thempc.org/documents/Transportation/US 80 Bridges Study/US 80 Final Report/US 80 Final Report_
NoAppendices.pdf. Accessed June 15, 2015.
49 NOAA. 2014. National Weather Service Advanced Hydrologic Prediction Service, Fort Pulaski Tide Gage.
http://water.weather.gov/ahps2/hydrograph.php?gage=fpkg1&wfo=chs. Accessed January 5, 2016.
80
MILES
N
0 0.25 0.5 1 1.5 2
US80
The recommended
alternative plan
for US 80 calls
for replacement
of the Bull River
and Lazaretto
Creek bridges and
10-foot shoulders
suitable for biking.
FIGURE 4.2: US HIGHWAY 80 TO TYBEE ISLAND. HIGHLIGHTED RED PORTION SHOWS STRETCH FROM
BULL RIVER TO LAZARETTO CREEK BRIDGES.
ASSESSMENT OF ADAPTATION ACTIONS
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35
Future Flood Analysis for US 80
Using the minimum tidal ooding threshold of . (~. above )
for the Savannah and Tybee Island region, we performed a ood threshold exceedance
analysis using , high tide readings covering the four-year period from January ,
– December , at the Fort Pulaski tide gauge. A total of tide height values in
excess of . feet above were recorded over the – period, giving an initial
average of eight ood events per year. We note that this is a conservative initial estimate,
as more recent tide records indicate an increase in nuisance ood events recorded at Fort
Pulaski subsequent to our analysis period (as shown in Figure .).
A comparison of annual tide events projected to exceed the ood stage at Ft. Pulaski
through under dierent sea-level rise scenarios is provided in Figure .. e Low
sea-level rise is expected to result in at least annual tidal ooding events by , which
is well over a three-fold increase over the average number of annual tidal ooding events
observed from –. Flood events from the Intermediate sea-level rise scenario (
inches) would be well approximately per year, while the High sea-level rise scenario (
inches) would result in ood events per year. Because Fort Pulaski typically has two
separate high tide peaks per day, the occurrence of more than one ood per day indicates
that on many days the road would ood on both high tides.
It is important to note that sea-level rise will not only increase the frequency of tidal
ooding events, but will also increase both the height of high tides and the duration of
time in which tidal ooding conditions are likely
to result in road closures of US . Using a sinu-
soidal analysis described in Appendix VI, the tide
gauge at Fort Pulaski showed an annual average
of about . annual hours in excess of ood
stage from –. As shown in Figure ., a
scenario of Low sea-level rise would be expected
to result in almost annual hours ooding on
US by , or approximately . times more
hours of closure per year as compared to –
. e Intermediate sea-level rise projection
would result in approximately hours per year
of tidal ooding on US at , while High
sea-level rise would result in approximately ,
hours of tidal ooding per year.
FLOOD EVENTS
High Sea Level Rise
Intermediate Sea Level Rise
Low Sea Level Rise
600
500
400
300
200
100
0
FIGURE 4.3: ANNUAL US 80 TIDAL FLOODING EVENTS WITH
SEA LEVEL RISE SCENARIOS
2010
|
2020
|
2030
|
2040
|
2050
|
2060
36 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Benefit-Cost Modeling Exercise
rough the auspices of the public engagement process, a preliminary benet-cost
exercise for adaptation of US was performed for the City of Tybee Island. Using facili-
tated participatory and stakeholder input, the dollar loss value (i.e., cost) of US ooding
was pegged to the loss of economic activity on the City of Tybee Island due to loss of
accessibility.
e at-risk economic activity was further derived through analysis of hotel/motel tax
receipts collected by the City of Tybee Island in -. ese tax receipts totaled .
million, which approximated . in private hotel revenue. A multiplier of . was then
used to transform hotel/motel tax revenue into a total estimate of . million in tour-
ism-based economic activity for the City of Tybee Island. is amounts to ,/hour of
economic activity in the City of Tybee Island presumed to be at risk from tidal ooding
of US . e analysis then assumed a one-to-one correspondence between hours of tidal
ooding of US and lost economic activity in the City of Tybee Island, with a percent
discount function applied annually for each year through .
51 Toma, M. and A. Brewer. 2007. The Economic Impact of Tybee Island Beach Renourishment on Georgia’s Economy. Savannah: Center
for Regional Analysis, Armstrong Atlantic University. http://www.cityoftybee.org/Assets/Files/BeachTaskForce/BeachEconomicImpact.pdf.
HOURS FLOODED
High Sea Level Rise
Intermediate Sea Level Rise
Low Sea Level Rise
1400
1200
1000
800
600
400
200
0
FIGURE 4.4: ANNUAL
US 80 TIDAL FLOODING
HOURS WITH SEA LEVEL
RISE SCENARIOS
2010
|
2020
|
2030
|
2040
|
2050
|
2060
ASSESSMENT OF ADAPTATION ACTIONS
|
37
Results of this preliminary benet-cost analysis were presented in public forums and
included in a review copy of this report. While the analysis was a useful exercise for con-
ceptualizing risk from road ooding, comments by technical reviewers convincingly
indicate that the assumptions are too simplifying and the results do not provide a sucient
assessment of benets and costs associated with road elevation. For example, the analysis
and results explicitly did not include numerous other damage and risk factors associated
with tidal ooding of a major road. Such other factors include:
Overwash and groundwater damages to the roadbed
and road surface
Public safety and emergency management hazards associated
with loss of road access
Potential for increased vehicle accidents when the road is ooded
xPotential for increased under-carriage corrosion to cars that
travel through saltwater
yVulnerability to major storm surges and the potential for
premature loss of US before landfall of a hurricane.
Due to concerns about publication of a limited benet-cost analysis, and with explicit
acknowledgment that the present project lacked the resources and scope to perform
such an engineering scale benet-cost assessment of a major highway corridor, we have
removed the results of this benet-cost analysis from the nal report. Instead, we rec-
ommend that our methodology for assessing the extent and duration of future tidal road
ooding risks under dierent sea-level rise scenarios be incorporated into an alternative
designs framework for roadway elevation within the ongoing US bridge replacement
and road bed improvement project. e substantial tidal ooding of US in clearly
underscores the substantial vulnerabilities of the existing roadway elevation and provides
renewed impetus for ensuring that signicant concerns about long-term public safety,
infrastructure maintenance, and disaster resilience are incorporating into the nal US
bridge replacement and road bed improvement project.
38 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
ACTIONS 3 & 4:
STORMWATER RETROFITS AND BUILDING A SEA WALL
Discussions at townhall meetings indicated that tidal ooding during king tide condi-
tions is regularly observed within several areas of the City of Tybee Island. However, the
most extensive issues were described to occur within the southwest quadrant of the island
(Figures .–.). City ocial reported that much of the property in the southwest corner
of Tybee Island is composed of lands created during the early century by the depo-
sition of dredge and ll material onto low-lying marshlands. e likely combination of
low native topography and accelerated soil subsidence has subsequently resulted in a low
elevation prole for the built environment now located on these former marshland areas.
Flooding concerns associated with this low elevation prole are illustrated by observa-
tions of saltwater discharge from several stormwater drains onto adjacent streets and yards
during extreme spring tide events (Figures .–.), particularly along the St. corridor.
Such tidal penetration into the stormwater system is of high concern not only because
of the direct ood risks from saltwater overow into
the built environment, but also because the inux of
tidewaters into stormwater pipes is associated with a
signicant loss of drainage capacity. Heavy rainfall
events that occur concurrently with high tides, there-
fore, have the potential to create signicant ooding
due to the lack of stormwater drainage potential
within pipes ooded by tidewater.
ese existing ood concerns have already
prompted signicant action by the City of Tybee
Island, including a major upgrade of stormwater pipes
and installation of backow preventers at the storm-
water discharge point near the intersection of St.
and Venetian Dr. (Figure .). Due to the additional
concerns associated with sea-level rise, public ocials
and local stakeholders expressed interest in further
evaluation of two adaptation actions: ) installation of
tidal backow preventers on additional stormwater
discharge points throughout the low-lying southwest
island; and ) construction of an engineered sea wall
at three feet above the current tidal ooding stage
(top of wall height at . feet ) to protect low-ly-
ing properties. Figure . provides a map visualiza-
tion overview of these suggested adaptation actions.
LIDAR Elevation
Feet above NAVD88
<0
0 – 2.6
2.6 – 5.2
5.2 – 7.8
7.8 – 10.4
10.4 – 13.0
13.0 – 15.6
15.6 – 18.2
18.2 – 20.8
20.8 – 28.0
Sources: Esri, HERE, DeLorme, Intermap, increment P Corp., NRCAN, Esri
Japan, METI, Esri China (Hong Kong), Esri(Thailand), TomTom, MapmyIndia,
© OpenStreetMap contributors, and the GIS User Community
00.05 0.1 0.2 MILES
TIDAL FLOODING AREA
(Figure 4.8)
TIDAL FLOODING AREA
(Figure 4.6 – 4.7)
N
FIGURE 4.5: LIDAR ELEVATION PROFILE FOR CITY
OF TYBEE ISLAND, SOUTHWEST QUADRANT
ASSESSMENT OF ADAPTATION ACTIONS
|
39
FIGURE 4.6: STORMWATER DRAIN WITH SALTWATER DISCHARGE DURING KING TIDE, NOVEMBER 14, 2012
FIGURE 4.7: SALTWATER FLOODING OF YARDS AND STREETS FROM STORMWATER DRAIN DISCHARGE DURING KING TIDE, NOVEMBER 14, 2012
40 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
FIGURE 4.8: SALTWATER FLOODING OF YARDS AND STREETS FROM BANK OVERFLOW DURING KING TIDE, NOVEMBER 14, 2012
FIGURE 4.9: STORMWATER TIDAL BACKFLOW PREVENTERS, NEAR INTERSECTION OF 14TH ST. AND VENETIAN DR.
ASSESSMENT OF ADAPTATION ACTIONS
|
41
FIGURE 4.10: VISUALIZATION OF
STORMWATER BACKFLOW AND SEA
WALL ACTIONS FOR CITY OF TYBEE
ISLAND, SOUTHWEST QUADRANT. RED
CIRCLES INDICATE DISCHARGE POINTS
THAT SHOW CONNECTIVITY TO LOW-
LYING AREAS VULNERABLE TO TIDAL
BACKFLOW FLOODING.
D
D
D
D
D
DDD
D
DD
Sources: Esri, HERE, DeLorme, Intermap, increment P Corp., NRCAN, Esri
Japan, METI, Esri China (Hong Kong), Esri(Thailand), TomTom, MapmyIndia,
© OpenStreetMap contributors, and the GIS User Community
00.05 0.1 0.2 MILES
N
D
Stormwater Discharge
Proposed Sea Wall Extent
Stormwater Conveyance
Stormwater Inlets
Discharge Pipe with Backflow Control
42 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Approach
A building-based assessment, using values obtained through the property tax assess-
ment dataset from Chatham County and hotel-motel tax receipts collected by the City
of Tybee Island, was utilized as the basis for analyzing the stormwater retrot and sea
wall actions. return elevation points processed to a ve-square-foot cell size digital
elevation model () were used as the basis for determining ood vulnerability in each
building. A four-year tidal record (–) from the Fort Pulaski tide gauge was
used to develop decadal tidal event exceedance predictions for each sea-level rise scenario.
ese methods are dened in Appendix .
Avoided loss functions were determined by each sea-level rise scenario and adaptation
action. A hydrologic connectivity analysis indicated that signicant oodwater penetra-
tion would be prevented for tides up to . feet above through use of backow
preventers alone, as existing bank elevation and bulkhead structures are sucient to block
overland tide ows under . feet tides. Avoided damage functions were therefore allo-
cated solely to stormwater backow preventers for all tides below . feet.
Bank overow would, however, presumably cause overland ooding into low-lying
areas beyond . feet tidal elevations, rendering the backow preventers ineective as a
standalone ood prevention strategy. Avoided damages for tides above . feet were there-
fore allocated solely to the sea wall. However, it is important to note that sea wall eec-
tiveness assumes that pipe ow stormwater penetration and groundwater are also averted
through backow preventers or other means. Cost of stormwater backow preventers
and additional upgrades to the stormwater system, including the recent expansion of pipe
capacity along the St. corridor, were assumed as million. e cost of an engineered
concrete sea wall at a height of . feet above was estimated at million.
Avoided damages for tides above
6.2 feet were allocated solely to the
sea wall; however, it is important
to note that sea wall effectiveness
assumes that pipe flow stormwater
penetration and groundwater is
also averted through backflow
preventers or other means.
SEALEVEL RISE
SCENARIO
DAMAGE AVOIDED
BY TIDE GATE
NET PRESENT VALUE
BENEFITCOST
RATIO
Low $15,400,000 5.13
Intermediate $36,200,000 12.07
High $39,200,000 13.07
TABLE 4.6: AVOIDED DAMAGE AND BENEFIT COST
CALCULATIONS FOR STORMWATER BACKFLOW
PRE-VENTERS, SOUTHWEST TYBEE ISLAND
TABLE 4.7: AVOIDED DAMAGE CALCULATIONS FOR SEA WALL
8.2 FT. ABOVE NAVD88, SOUTHWEST TYBEE ISLAND
SEALEVEL RISE
SCENARIO
DAMAGE AVOIDED
BY SEA WALL
NET PRESENT VALUE
BENEFITCOST
RATIO
Low $700,000 0.02
Intermediate $3,600,000 0.10
High $60,800,000 1.74
ASSESSMENT OF ADAPTATION ACTIONS
|
43
RESULTS
A summary table of avoided damages for stormwater backow preventers is provided in
Table .. ese results indicate that stormwater retrots with backow preventers repre-
sent a good investment under all sea-level rise scenarios and likely are a “no-regret” action.
However, it is also notable that stormwater retrots, even if maintained in perfect working
condition, would begin to fail as a standalone investment under the high sea-level rise
scenario well before . is assumed failure is due to the occurrence of bank overow
ooding that bypasses the stormwater system as tides begin to exceed the . feet bank
height on a regular basis.
Avoided damages for the sea wall are provided in Table .. ese results indicate that
the sea wall is a poor investment under the Low and Intermediate sea-level rise scenarios,
but shows marginal benet (.) under High sea-level rise. is latter result reects the
accrual of ood reduction benets from the sea-wall aer tides begin to exceed . feet
on a regular basis. However, the High sea-level rise scenario ultimately leads to tides that
exceed . feet before , thus presumably overtopping the sea wall and causing exten-
sive ood damage. Discussions with Tybee Island ocials indicate that the additional
stressors associated with a high rate of sea-level rise, poor benet-cost results for other
sea-level rise scenarios, and high ancillary environmental costs associated with construc-
tion of such a project all argue against further pursuit of the sea wall adaptation option at
this time.
44 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
ACTIONS 5: ENHANCED BEACH RENOURISHMENT
As noted in Chapter , the resources and scope of this project prevented formal analysis of
enhanced beach renourishment action (Action ) as a strategy for sea-level rise adaptation
and storm surge protection on Tybee Island. However, the importance of beach renour-
ishment for the local tourism economy and ood protection at Tybee Island is well-docu-
mented in other studies, as summarized in Chapter .
Even with the reduced beach erosion impacts at Tybee Island due to burial of the
sea wall and intensive dune-eld revegetation eorts, it is widely assumed that
maintenance of Tybee Island’s existing beach prole — and associated ood protection
benets — is completely dependent on the continuation of periodic renourishment activ-
ities. Deepening of the Savannah
Harbor channel to accommodate
larger “Post-Panamax” cargo ships
and ongoing sea-level rise only
strengthen this assumption, as both
processes can be expected to increase
the long-term beach erosion forces
on Tybee Island. With the current
Tybee Island Shore Protection
Project scheduled to expire in ,
the early stages of the re-authoriza-
tion process provide an opportunity
for local, state, and federal ocials to
incorporate sea-level rise as a central
design and management parameter
within a revised renourishment and
shoreline protection plan.
52 See, for example, Leatherman, S.P. 1989. National Assessment of Beach Renourishment Requirements Associated
with Accelerated Sea Level Rise. College Park, MD: U.S. EPA Office of Policy, Planning, and Evaluation.
http://www.papers.risingsea.net/federal_reports/rtc_leatherman_nourishment.pdf.
Deepening of the Savannah
Harbor channel to accommodate
larger ‘Post-Panamax’ cargo ships
along with ongoing sea-level rise
can be expected to increase
the long-term beach erosion
forces on Tybee Island.
SUMMARY & CONCLUSION
|
45
The City of Tybee Island is one of the first communities in Georgia
to formally address sea-level rise. Throughout the span of this
planning project, city officials and the general public engaged with
the project team to confront challenges and evaluate actions for
helping the community adapt and thrive over the coming decades.
Summary and Conclusion
ELEVATING CITY WELL HOUSES
e City of Tybee Island operates three well pump houses that are the sole source of public
water supply for the community. If these well houses are disabled by a ood, drinking
water and waste disposal could be limited for several days or even weeks. Technical
analyses indicate that the City’s Butler Ave. well house is at very high risk of ooding
and that action should likely be taken to elevate or otherwise oodproof this facility as
soon as possible. e th St. well house also shows high risk of ooding and benet-cost
analyses indicate that elevation or other oodproong of this facility is immediately jus-
tied. e Van Horne Ave. well house shows lower ood risk and benet-cost analysis
does not indicate the need for immediate action for elevating or oodproong this facility.
However, future study and assessments are warranted to ensure the long-term safety of the
Van Horne Ave. facility.
ADAPTING U.S. 80
US Highway , the sole road access to Tybee Island, currently oods several times a
year during high tide conditions. In , Tybee Island experienced a total of tides that
were high enough to cause minor to moderate ooding conditions on US , by far the
largest number that has been observed in any year on record. ese ooding conditions
cut Tybee Island o from the mainland for hours at a time, causing signicant safety and
evacuation concerns, as well as economic impacts. Sea-level rise will worsen these road
ooding and accessibility issues unless US is elevated signicantly above its current
grade. Cooperation between the City of Tybee Island, the Coastal Region Metropolitan
Planning Organization, the Georgia Department of Transportation, and other agencies is
needed to ensure that sea-level rise is factored into ongoing engineering plans to replace
two bridges and otherwise modernize the US corridor.
CHAPTER 5:
46 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
STORMWATER RETROFITS AND SEA WALL PROTECTION
Several areas in the southwest section of Tybee Island have low-lying stormwater drainage
systems that become inundated and can even ow backwards during exceptionally high
tides. is backow causes saltwater ooding of streets and yards, while also increasing
ood risks during rainfall events.
If no action is taken, sea-level rise can only be expected to worsen these conditions
over time. e City of Tybee Island has already installed three tidal backow preventers
on stormwater pipe outfalls that drain the most vulnerable areas. Benet-cost modeling
indicates that these and other retrots that prevent tidal backow into southwest Tybee
Island would be expected to accrue – million in avoided economic damages over a
-year period. Continuation of such stormwater retrots therefore appears to be a highly
cost-eective, no-regrets adaptation strategy.
Additional modeling suggested that construction of a large engineered sea wall on the
southwest portion of the island is likely not an appropriate adaptation strategy to pursue
at this time. e benet-cost ratio for the sea wall is positive only under the High sea-level
rise scenario, and most ood protection benets from the structure would not accrue until
at least – years into the future.
BEACH RENOURISHMENT
Beginning in , the US Army Corps of Engineers added approximately . million
cubic yards of sand onto Tybee Island beaches. is eort marks one of the nal renour-
ishments of Tybee Island through the US Army Corps of Engineer’s current authorization
from Congress, which expires in . A priority for future beach renourishment projects
and negotiation of a new authorization should be maintenance of ood protection under
a condition of accelerating sea-level rise. Additionally, inspired by communities in the
Northeast that suered comparatively low damages during Superstorm Sandy, the City of
Tybee is investigating the possibility of augmenting their sand dune system to help protect
the island from storm surge during hurricanes.
COMMUNITY RATING SYSTEM
e City of Tybee Island recently underwent a review for ’s Community Rating
System (). A federal incentive program designed to incentivize ood resiliency,
rewards communities for adopting oodplain management ordinances, adhering to
minimum standards for new construction and educating citizens about their ood risk.
Due to the extensive public investments, outreach, and regulation that the City of Tybee
has pursued over recent years, the City improved its rating to a score of ve. is
rating translated into a percent discount in ood insurance for each resident in the
Special Flood Hazard Area.
53 Savannah Morning News. 2014. Tybee beach renourishment kicks off. http://savannahnow.com/news/2014-10-22/tybee-beach-renour-
ishment-kicks. Accessed January 5, 2016.
The new
CRS rating will
translate into a
25 percent discount
in flood insurance
for each resident in
the Special Flood
Hazard Area.
SUMMARY & CONCLUSION
|
47
A NATIONAL LEADER
Due to the hard work and vision of Tybee Island’s City Council, government sta, and
community members, the City has emerged as national leader in climate adaptation
planning and coastal resilience. In addition to planning for sea-level rise, Tybee Island has
focused on decreasing its carbon footprint through renewable energy production.
e City is also widely recognized for its successful eorts to reduce stormwater pol-
lution and improve local water quality through innovative ltration techniques. With
funding from National Fish and Wildlife Foundation’s Five Star Urban Waters Restoration
Grant Program, Tybee Island has recently partnered with Marine Extension, Georgia
Sea Grant, ’s Carl Vinson Institute of Government, and other partners to construct a
living shoreline along a tidal creek at the Burton -H Center. is living shoreline project,
which is being constructed out of oyster shells and marsh vegetation, is expected to
enhance sheries habitat and improve local water quality.
In recognition of the outreach and educational eorts undertaken through this project,
in the Tybee Island Sea-Level Rise Plan received Sea Grant’s highest national
outreach award. e project has also been featured as a case study in the U.S. Climate
Resiliency Toolkit and in a report by the Union of Concerned Scientists. Senator
Sheldon Whitehouse from Rhode Island visited Tybee Island during his Southeast
Climate Road Trip and praised the island’s climate adaptation eorts on the oor of the
U.S. Senate. Technical methodologies originally developed in Tybee Island have been
subsequently utilized for resilience planning projects in several other coastal communi-
ties, including St. Marys, Georgia; Hyde County, North Carolina; the City of Islamorada,
Florida and Monroe County, Florida.
54 Landers, M. 2015. As Solarize Tybee gains popularity, price drops. Savannah Morning News. http://savannahnow.com/news/2015-02-
25/solarize-tybee-gains-popularity-price-drops. Accessed January 6, 2016.
55 Landers, M. 2011. Tybee gets good grades for beach water quality. Savannah Morning News. http://savannahnow.com/news/2011-
07-02/tybee-gets-good-grades-beach-water-quality. Accessed January 6, 2016.
56 U.S. Climate Resilience Toolkit. 2015. Show Don't Tell: Visualizing Sea Level Rise to Set Planning Priorities,” Taking Action: Case
Studies of Resilience in Action. https://toolkit.climate.gov/taking-action/show-dont-tell-visualizing-sea-level-rise-set-planning-priori-
ties. Accessed January 6, 2016.
57 Spanger-Siegfried, E., M. Fitzpatrick, and K. Dahl. 2014. Encroaching tides: How sea level rise and tidal flooding threaten US east
and gulf coast communities over the next 30 years. Cambridge: Union of Concerned Scientists.
58 Landers, M. 2014. Update: Senator posts video of tour of Ga. climate change hot spots. Savannah Morning News. http://savan-
nahnow.com/news/2014-04-24/senator-tours-ga-hot-spots-climate-change. Accessed January 6, 2016.
48 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
CLOSING THOUGHTS
is nal report is intended as an initial step that will assist
the City of Tybee Island with its eorts to include sea-level rise
within local ood preparedness policies and environmental
sustainability initiatives. For this reason, this report is intended
to serve as a living document that can be freely appended and
updated by City ocials over time as new information and
conditions may merit.
One of the biggest lessons learned through this project is that
sea-level rise and climate adaptation is a complex endeavor with
many challenges and uncertainties. e project team sincerely
thanks Tybee Island’s elected ocials, municipal sta, and local
residents for their partnership and patience in working through
this planning process.
The project team sincerely
thanks Tybee Island’s
elected officials, municipal
staff, and local residents
for their partnership
and patience in working
through this planning process.
APPENDIX
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49
Appendix
I: PUBLIC ENGAGEMENT AND OUTREACH LOG
Town Hall Meetings
A series of formal town hall meetings, all open to the public and held at the Tybee Island
City Hall, were a central component of the project. ese meetings featured expert presen-
tations on sea-level rise science and adaptation, as well as solicited public input for con-
sidering adaptation options appropriate to the unique conditions faced by Tybee Island.
Public Meeting I
introduction to the project and connections with existing
hazard programs // may 7, 2012
Tybee Island is a complex, multifaceted environment, with a host of overlapping issues
and challenges. To kick o the public outreach process, the project’s rst public meeting
focused on presenting the threats of sea-level rise to the island, as well as adaptation options
for Tybee Island to consider. Speakers:
n Dr. Charles S. Hopkinson, Georgia Sea Grant Director.
Project Introduction.
n Dr. Robin J. McDowell, Environmental Policy Program Director,
Carl Vinson Institute of Government. Meeting Overview and
Facilitation Ground Rules.
n Dr. Jason M. Evans, Environmental Sustainability Analyst,
Carl Vinson Institute of Government. City of Tybee Island Climate
Adaptation Planning: Project Timeline and Technical Overview.
n Jennifer Kline, Coastal Hazards Specialist, Coastal Resources
Division, Georgia Department of Natural Resources.
Georgia Coastal Hazards Program Eorts.
n Jackie Jackson Teel, Director of Comprehensive Planning,
Chatham County—Savannah Metropolitan Planning Commission.
e Next Steps aer Chatham County’s Coastal Risk Workshop.
Facilitated session: Perceived and known vulnerabilities to ooding and
sea-level rise in the City of Tybee Island.
50 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
McDowell and Evans led an open discussion with meeting attendees to gather detailed
information about perceived current and future impacts of sea-level rise for the City of
Tybee Island. As shown in Figure , a owchart summary of this discussion was developed
using diagram protocols from the Vulnerability, Consequences, and Adaptation Planning
Scenarios () methodology and as implemented through the Open Source Visual
Understanding Environment () soware. Key issues identied through this discus-
sion included:
Periodic over wash ooding of US Highway , the sole road
access route to Tybee Island, during high tide events. Identied
consequences of this ooding include road closings that cause severe
trac backups, cuto from emergency services, and loss of evacu-
ation route during storm events; hazards to drivers when ooding
occurs with little warning and no associated road closure; and long-
term damage to the road bed from repeated over wash events.
Periodic yard and street ooding within the City of Tybee Island
during extreme high tide events. Consequences of this ooding
include damage to landscaping from saltwater intrusion; potential
threats to low-lying structures, particularly if high tides are accompa-
nied by rainfall events; and potential loss of property values in areas
impacted by repetitive ooding.
Increased beachfront and marsh front erosion due to the force
of higher tides, as well as loss of near shore sediment transport
due to the dredged shipping channel in the Savannah River.
Consequences of erosion include loss of private property, physical
threats to waterfront structures, increased need for beach renourish-
ment, reduced recreational values as beaches retreat, and higher risk
from storm surge events if dune elds are compromised.
59 Tufts University. 2013. Visual Understanding Environment. http://vue.tufts.edu/. Accessed January 5, 2016.
APPENDIX
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51
Public Meeting II
vulnerability assessment and definition of adaptation options
–,
A key element of the plan’s strategy was to test a wide range of adaptation options and
explore their tradeos over a long time period. Dr. Sam Merrill, Director of the New
England Environmental Finance Center, walked participants through sea-level rise
adaptation options for Tybee Island. Dr. Merrill also presented examples of sea-level rise
planning currently being practiced in other communities.
Sea-level rise adaptation options depend heavily on a projected height of sea-level
rise. rough facilitated discussion and straw poll votes, meeting participants decided to
consider a range of sea-level rise scenarios for Tybee Island. ese included a low scenario
of inches, an intermediate scenario of . feet and a high scenario of . feet by the year
. ese scenarios closely match recommendations made by and other federal
agencies for sea-level rise adaptation planning.
Local adaptation options identied for further evaluation included raising the city's
well pump houses, making local storm water improvements, marsh-side armoring of the
shoreline, increasing the height of future beach renourishment to accommodate sea-level
rise and elevating US four feet above current grade. Speakers:
nDr. Chuck Hopkinson, Georgia Sea Grant Director. Meeting
Introduction.
n Dr. Robin J. McDowell, Environmental Policy Program Director,
Carl Vinson Institute of Government. Meeting Overview and
Facilitation Ground Rules.
nDr. Jason M. Evans, Environmental Sustainability Analyst, Carl
Vinson Institute of Government. Review and Recap of Meeting
Vulnerability Discussions.
nDr. Sam Merrill, New England Environmental Finance Center and
Catalysis Adaptation Partners, . Benet-Cost Modeling through
the Coastal Adaptation to Sea level rise Tool ().
Facilitated session 1: Discuss and dene sea-level rise scenarios and vulnerable assets
to be used for the adaptation planning exercise
52 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Sea-level rise scenarios
Merrill and Evans led an open discussion with meeting attendees to dene the sea-level
rise scenarios to be used for the City’s planning exercise, as well as to dene the at-risk
assets of concern that would be modeled for dollar values out to the year . e sce-
narios were discussed in an open public forum, with present members of the Tybee Island
City Council providing nal determination of model parameters through majority votes.
rough this process it was decided that the High and Intermediate sea-level rise values
used for the City’s adaptation planning would be based upon semi-empirical sea-
level rise curves published by Martin Vermeer and Stefan Ramhstorf. e Low sea-level
rise value would be based upon linear extrapolation of the Ft. Pulaski tide gauge record.
e Ft. Pulaski tide gauge has maintained an almost continual record of tide heights
since its original installation in . e slope of the straight line regression for sea-level
over this record provides an average rise of approximately . inches per year. Simple
extrapolation of this linear trend through was used as the basis for the City of Tybee
Island’s Low sea-level rise scenario. By the year , the tide gauge linear trend amounts
to approximately inches of sea-level rise over a baseline at Tybee Island.
e Interme diate sea-level rise curve, as dened by the work of Vermeer and Rahmstorf,
is based upon lowered greenhouse emissions that minimize future warming of oceans and
polar ice sheet melt, but nevertheless still result in an acceleration of sea-level rise over
that observed during the th century. By the year , this results in a sea-level rise of
approximately inches ( cm) over a baseline.
e High sea-level rise curve, as dened by the work of Vermeer and Rahmstorf, is
based upon a scenario of high greenhouse gas emissions and accelerated climate change
that induces rapid thermal expansion of oceans and enhanced polar ice sheet melt. By the
year , this results in a sea-level rise of approximately inches ( cm) over a
baseline.
Benefit-cost inputs
Merrill led a discussion with meeting attendees to decide upon the assets that would be
used to develop dollar-based inputs for benet-cost modeling. e following two assets
were chosen: ) tax assessed values of buildings; and ) annual economic activity, as
extrapolated from the City’s hotel-motel tax receipts. Assessed values of buildings were
to be obtained from Chatham County’s property parcel database, while the spatial
component of economic activity would be developed by linking hotel-motel tax receipts
to parcels on an annualized basis. An annualized discount rate of percent was chosen for
modeling future ooding damage to both buildings and economic activity.
Facilitated session 2: Discuss and dene adaptation actions for benet-cost modeling
Merrill and Evans led a technical discussion with meeting attendees to dene several
adaptation actions that would be assessed in detail through the auspices of this project.
A series of general adaptation action types were presented and discussed. ese included
infrastructural elevation, wet ood-proong, dry ood-proong, rolling easements, fee
simple acquisition, beach renourishment, and shoreline armoring.
60 Vermeer, M. and S. Rahmstorf. 2009. Global sea level linked to global temperature. Proceedings of the National Academy of Sciences
of the United States of America. 106:21527-21532.
APPENDIX
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53
rough these discussions, the following ve locally specic adaptation options
were chosen for more detailed analyses.
Retrot elevation of the rst oor of city well houses and electronic
components to heights above the year oodplain.
Elevation of the US causeway between Wilmington Island
and Tybee Island to feet above current minimum grade.
Increased rates of beach renourishment relative to increased
sea-level rise out to .
xRetrots of stormwater infrastructure to prevent ooding from
tidewater backow, particularly within low-lying areas of the
southwest island.
yConstruction of a back island seawall at feet over mean higher high
water () to prevent ooding from bank overow, particularly
within low-lying areas of the southwest island.
Public Meeting III
presentation of benefit-cost modeling results
march 4–5, 2013
Dr. Jason Evans presented a series of benet-cost evaluations for identied adaptation
actions. Several actions, such as beach renourishment, elevation of well pumps and con-
struction of tide valve gates on stormwater outlets that drain low-lying areas of the island,
showed clear net economic benets for all scenarios. Elevation of US requires further
analysis, but was judged to have high benets with consideration of increased evacuation
times before hurricanes and continuous access to the island during future high tide events.
Speakers:
n Dr. Robin J. McDowell, Environmental Policy Program Director,
Carl Vinson Institute of Government. Meeting Introduction and
Facilitation Ground Rules.
n Dr. Jason M. Evans, Environmental Sustainability Analyst, Carl
Vinson Institute of Government. Tybee Island Sea-level Rise Planning:
Benet-Cost Evaluation Results for Adaptation Action Scenarios.
Facilitated session (March ): Feedback from City Department Heads on modeling results
and identication of other critical priorities
Evans and McDowell presented a suite of technical evaluations and benet-cost analyses
for adaptation actions dened in the August and , townhall meetings. In summary,
the evaluations indicated a very likelihood of signicant economic benet from use of
backow preventers on stormwater discharge pipes. Although not easily quantiable
through economic analyses tied to property and economic activity, very high ood resil-
ience benets were identied for the well pump and road elevation actions. Back island
sea wall construction, however, was found to be a poor investment for ood protection at
current dollar values.
54 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
FLOOD
HEIGHT FT.
DEPTH DAMAGE
FUNCTION EQUATION
0 – 2 D = 0.01F*V
2 – 3 D = (0.03F – 0.04)*V
3 – 4 D = (0.15F – 0.40)*V
4 – 6 D = (0.05F)*V
> 6 D = 0.3*V
TABLE III.1: SINGLE EVENT DEPTH
DAMAGE EQUATIONS
FOR MUNICIPAL WELL,
CAPITAL COST (ADAPTED
FROM FEMA 2013)
II: SEA-LEVEL RISE EQUATIONS
Deterministic sea-level rise curves based on the Low, Intermediate, and High sea-level
rise scenarios provide the baseline for the technical assessment of adaptation action pre-
sented in Chapter . As adapted from methods recommended by , sea-level rise
projections were calculated through the following quadratic equation:
E(t) = at + bt; where
E(t) = eustatic sea-level rise (inches)
t = years since baseline
a = annual local linear trend sea-level rise (inches)
b = sea-level rise acceleration coecient (inches).
e Fort Pulaski tide gauge the record provides a local value (i.e., integrating local sub-
sidence and global sea-level rise) of a = . for all scenarios. Values for b are as follows:
bHigh= .
bIntermediate = .
bLow =.
e curves dened by Vermeer and Rahmstorf begin at a sea-level. For this
reason, a correction factor unique to each scenario was required to maintain a consis-
tent baseline among all scenarios for the City of Tybee Island. is correction factor
involves subtracting the amount of rise suggested by each respective scenario from –
for the projected sea-level rise in all years from –. For the Low scenario, the
correction factor is . inches (. feet). For the Intermediate scenario, the correction
factor is . inches (. feet). For the High scenario, the correction factor is . inches
(. feet).
61 Eastern Research Group. 2013. What Will Adaptation Cost? An Economic Framework for Coastal Community Infrastructure.
Charleston: NOAA Coastal Services Center. http://seagrant.noaa.gov/Portals/0/Documents/what_we_do/climate/NOAA_
What_Will_Adaptation_Cost_Report.pdf. Accessed January 5, 2016.
62 NOAA. 2014. Mean Sea Level Trend, 8670870 Ft. Pulaski, Georgia. http://tidesandcurrents.noaa.gov/sltrends/
sltrends_station.shtml?stnid=8670870. Accessed January 5, 2016.
63 Vermeer, M. and S. Rahmstorf. 2009. Global sea level linked to global temperature. Proceedings of the National Academy
of Sciences of the United States of America. 106:21527-21532.
APPENDIX
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55
III: SINGLE-EVENT DEPTH DAMAGE EQUATIONS
FOR MUNICIPAL WELL (CAPITAL COST)
e basis for single event losses to the capital infrastructure was depth damage thresh-
olds for municipal wells developed by (), which were converted into continuous
depth damage functions (Table .).
IV: SEA-LEVEL RISE ADJUSTMENT TO DEPTH-DAMAGE FUNCTION
Beginning from a baseline of sea-level, the ood heights (F) for year, year,
year, and year storm surges were adjusted upwards on an annual basis using
low, intermediate, and high sea-level rise scenarios. erefore,
F(t)SLRS = F + E(t)SLRS ; where
F(t)SLRS = Adjusted ood height at time period t (i.e., years since )
under given sea-level rise scenario
F = Flood height at baseline
E(t) = eustatic sea-level rise at t under given sea-level rise scenario.
Using these adjustments, a cumulative damage estimate for each well covering all years
and associated sea-level rise scenario adjustments from (t = ) to (t = ) was
then calculated as:
CSLRS = ∑ ((D(t) * P + D(t) * P + D(t) * P +D(t) * P ) / ( + i)); where
CSLRS = Cumulative damage estimate () to well pump for given sea-level rise scenario
D(t) = depth damage from Table . under F(t) as adjusted to year ood height
at year t
D(t) = depth damage from Table . under F(t) as adjusted to year
ood height at year t
D(t) = depth damage from Table . under F(t) as adjusted to year
ood height at year t
D(t) = depth damage from Table . under F(t) as adjusted to year
ood height at year t
P = . (Probability of year ood event)
P = . (Probability of year ood event)
P = . (Probability of year ood event)
P = . (Probability of year ood event)
i = . (Discount rate)
56 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
V: CUMULATIVE ECONOMIC LOSS
DAMAGE ASSESSMENT OF MUNICIPAL WELLS
Equation for well pump time down:
T (Time down) = [Max (F / (feet), )] * (Days), Where F = Flood height
Rationale: Any ood above feet will cause a maximum loss of days. Flood depths
below feet are adjusted to cause less time out proportional to the ood height.
Single event economic ood loss equation:
L = (T * (per person per day) * , (people on Tybee)) / (Well pumps).
L = Economic loss per ood event
Cumulative -year projected economic loss from loss of well pumps, with ood heights
adjusted by sea-level rise scenario as dened in Appendix IV.
LSLRS ∑ ((L(t)*P+ L(t) *P + L(t) *P + L(t) *P) / (+i));
VI: SINUSOIDAL TIDAL FLOODING EXCEEDANCE
FOR US HIGHWAY 80
e ood exceedance time-period analysis is based upon the assumption of sinusoidal
tide with a set period (p) of minutes, which is the approximate average period between
peak high tides (Ht) observed at the Fort Pulaski tide gauge. e initial sinusoidal equation
form is:
yt= A sin (π xt/p), where
yt = height of tide at minute xt
Ht = peak high tide during the given tidal cycle
At = elevation of the high tide peak above mean sea-level, which was assumed as Ht/
xt = minutes since beginning of tidal cycle
p = period ( minutes)
All minutes (m) where yt > . feet above navd were tracked across the full set of tide
records (n=,) for –, and then normalized to an annual value of exceedance
minutes using the following function:
∑m/
APPENDIX
|
57
Estimates of future event and time exceedances were developed through decadal cal-
culations of eustatic sea-level rise, dened as E(t) in Appendix II, at the years , ,
, , and for each sea-level rise scenario. All initial tide heights (n=,) were
adjusted for each decadal increment under each sea-level rise scenario as:
ytSLR = E(t)I + yt, where
ytSLR = Revised tide height (at minute xt) under the given sea-level rise scenario
E(t) = Eustatic sea-level rise at given year (t), as dened in Appendix II
yt = Original tide height
All minutes (mSLR) where yt > . feet above were again tracked across the full set
of tide records (n=,) for –, and then annualized as:
∑ mSLR/
VII: DAMAGE AVOIDANCE ASSESSMENT FOR STORMWATER
RETROFIT AND SEA WALL ACTIONS
A building-based sea-level rise vulnerability assessment for stormwater and sea wall actions
was performed using a multi-step analytic process. First, ground elevation return
points were processed to a cell size digital elevation model () through the
Digital Coast (http://coast.noaa.gov/digitalcoast/) website. Original raster tile datasets
provided through Digital Coast were then mosaicked using Arc . into a seamless
digital elevation model dataset covering the City of Tybee Island. Because the original
contained null values for cells dominated by non-ground (e.g., building rooops)
returns, an inverse distance weighting () procedure was then utilized in Arc . to
interpolate elevation values such that estimated ground elevations were dened within the
for all areas of the City of Tybee Island. A Zonal Statistics procedure was then used in
Arc . to solve for minimum, mean, and maximum values within the boundaries
of building footprint polygons. ese interpolated ground elevations underneath building
footprints were used as the basis for ood risk analyses on a structure by structure basis.
A spatial join procedure in Arc . was used to place tax
assessed values for buildings from the property tax assessment
dataset into each dened building footprint. On parcels containing
numerous buildings in the footprint layer, the total assessed values
at the parcel value were divided according to relative polygon area
among the individual buildings.
64 Chatham County, GA. 2012. 2009 Chatham County, Georgia Lidar. Charleston: NOAA Coastal Services Center. http://www.csc.noaa.gov/
dataviewer/index.html?action=advsearch&qType=in&qFld=ID&qVal=1121. Accessed January 5, 2016.
YEAR 5.2' 5.7'
NAVD
5.7' 6.2'
NAVD
6.2' 7.2'
NAVD
2010 7.00 1.00
2020 8.25 1.50
2030 9.50 2.50 0.25
2040 11.50 3.50 0.50
2050 15.75 4.50 1.00
2060 20.25 6.75 1.25
TABLE VII.1: DECADAL FT. PULASKI
PROJECTED TIDAL EVENT OCCURENCES
WITH LOW SEA-LEVEL RISE
58 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
Tide gauge data: All daily high tides from the – Ft. Pulaski tide gauge record
were additively adjusted at decadal increments (, , , , and ) to
simulate each scenario of sea-level rise (Low, Medium, and High) using the equations
in Appendix II. Annualized tide events for high tides corresponding from . .–. .,
.–. ., .– . ., and ..–. . above were then recorded for each decadal
interval from - and as based upon each sea-level rise scenario. ese values are
summarized in Tables VI.–VI.. A generic depth-damage relationship adapted from the
United States Army Corps of Engineers (Table .) was then applied for each building in
southwest Tybee Island at decadal increments for each sea-level rise scenario. To be con-
servative with damage assessment, the lower range of each tidal ooding increment was
used as the basis for calculating ood depths at each structure. For example, in the range
.–. feet, the tidal depth was set to . feet for all analyses.
Decadal point estimates of damage losses (LB) by building value (VB) were calculated
across each sea-level rise scenario through a relationship with exceedance frequencies in
Tables .–. and depth damage relationships in Table .:
LB = Tide * FTide * VB, as constrained to LB = Min(Tide * FTide * VB, VB)
A discounted damage function across all buildings (B) by decadal period (, ,
, , , and ) and sea-level rise scenario (Low, Intermediate, and High) was
then calculated as:
Lt = ∑ (LB/(.), where t = years since
ese decadal estimates were then used to t discounted damage curves over time.
Cumulative damage values for taking no action under each scenario were then calculated
through denite integrals to solve for area under damage curves across years –
(Figures VI.–VI.).
TABLE VII.2: DECADAL FT. PULASKI PROJECTED
TIDAL EVENT OCCURRENCES
WITH INTERMEDIATE SEA-LEVEL RISE
YEAR 5.2' 5.7'
NAVD
5.7' 6.2'
NAVD
6.2' 7.2'
NAVD
2010 7.00 1.00
2020 8.25 2.75
2030 15.00 4.25 1.25
2040 29.50 7.75 2.00
2050 55.25 15.00 5.25
2060 79.25 36.75 11.25
TABLE VII.3: DECADAL FT. PULASKI PROJECTED
TIDAL EVENT OCCURRENCES WITH HIGH SEA-LEVEL RISE
YEAR 5.2' 5.7'
NAVD
5.7' 6.2'
NAVD
6.2' 7.2'
NAVD
7.2' 8.2'
NAVD
> 8.2'
NAVD
2010 7.00 1.00
2020 13.75 3.50 0.50
2030 48.00 11.25 3.25
2040 83.00 48.50 14.75 0.50
2050 154.50 96.25 70.50 5.50
2060 143.50 166.00 190.75 35.25 1.50
APPENDIX
|
59
FIGURE VII.1: AVOIDED
DAMAGES FOR PIPE
BACKFLOW PREVENTERS,
LOW SEA-LEVEL RISE
FIGURE VII.2: AVOIDED
DAMAGES FOR PIPE BACKFLOW
PREVENTERS, INTERMEDIATE
SEA-LEVEL RISE
65 United States Army Corps of Engineers. 2000. Economic Guidance Memorandum (EGM) 01-03, Generic Depth-Damage Relationships.
http://planning.usace.army.mil/toolbox/library/EGMs/egm01-03.pdf. Accessed June 15, 2015.
TABLE VII.4: TIDAL FLOODING DEPTH-DAMAGE
RELATIONSHIP USED FOR CITY
OF TYBEE ISLAND STRUCTURES, AS
ADOPTED FROM THE UNITED STATES
ARMY CORPS OF ENGINEERS65
FLOOD DEPTH DAMAGE*
00%
12.5%
213.4%
323.3%
432.1%
YEARS (SINCE 2010)
$450,000
$350,000
$250,000
$150,000
$50,000
∫ (–364.4x² + 24097x + 10252)dx = 1.542 x 10
∫ (57.999x² + 26999x + 10252)dx = 3.62794 x 10
$1,600,000
$1,200,000
$800,000
$400,000
$0
10 | 20 | 30 | 40 | 50
YEARS (SINCE 2010)
10 | 20 | 30 | 40 | 50
DDF = -0.008d3 + 0.0567d2 – 0.0182d – 0.0013;
Where DDF = Percent damage
d = depth of ood, calculated as T – E,
where T = tide increment; E = Maximum
Lidar ground elevation within building footprint
*The original depth damage curves were
adjusted upward by 2 feet to approximate
actual building oor elevations, which are
unknown at a building level, above interpolated
Lidar ground elevation.
60 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
FIGURE VII.3: AVOIDED DAMAGES
FOR PIPE BACKFLOW PREVENTERS,
HIGH SEA-LEVEL RISE ∫ (–8715.9x² + 261144x + 10252)dx = 3.92413 x 10
$2,500,000
$2,000,000
$1,500,000
$1,000,000
$500,000
$0
FIGURE VII.4: AVOIDED DAMAGES WITH
SEA WALL, LOW SEA-LEVEL RISE
YEARS (SINCE 2010)
10 | 20 | 30 | 40 | 50
∫ (–7.474x² + 807.36x)dx = 697382
$25,000
$20,000
$15,000
$10,000
$5,000
$0
YEARS (SINCE 2010)
10 | 20 | 30 | 40 | 50
APPENDIX
|
61
FIGURE VII.5: AVOIDED DAMAGE
WITH SEA WALL, INTERMEDIATE
SEA-LEVEL RISE
FIGURE VII.6: AVOIDED DAMAGES WITH
SEA WALL, HIGH SEA-LEVEL RISE
∫ (93.399x² – 2946.7x + 30127x)dx = 6.08014 x 10
$6,000,000
$5,000,000
$4,000,000
$3,000,000
$2,000,000
$1,000,000
$0
YEARS (SINCE 2010)
10 | 20 | 30 | 40 | 50
∫ (3.128x² + 2568.9x)dx = 3.34017 x 10
$1,600,000
$1,200,000
$800,000
$400,000
$0
YEARS (SINCE 2010)
10 | 20 | 30 | 40 | 50
62 TYBEE ISLAND SEA LEVEL RIS E ADAPTATION PLAN // APRIL 2016
GRAPHIC & PUBLICATION DESIGN: JULIE SPIVEY, ASSOCIATE PROFESSOR,
LAMAR DODD SCHOOL OF ART, UNIVERSITY OF GEORGIA; WITH ASSISTANCE
FROM UNDERGRADUATE STUDENTS KYLIE WAGNER,‘13 AND NICOLE KIM, ‘17.
Publication supported in part by an Institutional
Grant () to the Georgia Sea Grant
College Program from the National Sea Grant Oce,
National Oceanic and Atmospheric Administration,
US Department of Commerce. All views, opinions,
ndings, conclusions, and recommen dations
expressed in this material are those of the authors and
do not necessarily reect the opinions of the Georgia
Sea Grant College Program or the National Oceanic
and Atmospheric Administration.
Many people and institutions made invaluable con-
tributions to the educational outreach and research
components of this project. While we note that any
list of acknowledgments is incomplete (and apologize
in advance for unintended omissions), we give great
thanks to all of the following for their critical support
to this project. We also note that acknowledged indi-
viduals bear no responsibility for the contents of the
document.
We thank the sta, elected ocials, and engaged
local citizens in the City of Tybee Island for their
support. We especially acknowledge each of the
following City ocials for their high level of engage-
ment and support: Diane Schleicher (City Manager)
for her local leadership over the project period and
her enthusiasm for the partnership with educational
institutions on sea-level rise adaptation; Joe Wilson
(Director of Public Works) for detailed, entertain-
ing tours and explanations of the City’s stormwater
and dune-eld infrastructure; George Reese (Water
Department Manager) for tours of the sewage treat-
ment plant and access to well-houses for
measurements; Sharon Shaver (Assistant to the
City Manager) for handling organizational logistics
and providing delicious refreshments for all public
meetings; and Michael Bodine (IT Support) for
seamlessly handling all of our audio-visual requests
with patience and expertise. e members of the
Community Resources Committee and Beach Task
Force also provided the project team with a tremen-
dous amount of institutional knowledge and insights
that greatly informed our understanding and the evo-
lution of the nal report. Altogether, the people of
Tybee Island were exceptionally generous with their
time and gracious hosts for the project team.
Faculty, students, and sta across numerous
departments at the University of Georgia supported
this project through a wide variety of formal presenta-
tion venues and informal discussions. We give special
thanks to Laurie Fowler, J.D., of the University of
Georgia’s River Basin Center, as well as her graduate
and law students from the Environmental Practicum
course in the fall semester. e policy background
research conducted by Laurie and her students was
especially helpful in understanding the permitting
and costing issues associated with sea wall construc-
tion. We also give special thanks to Dr. Elizabeth King
and Dr. Meredith Welch-Devine of the University
of Georgia’s Center for Integrative Conservation, as
well as their graduate students from the Spring
course in integrative conservation. ese professors
and students engaged deeply with the issue of sea-
level rise at Tybee Island, and brought critical per-
spectives that strengthened the focus and outcomes
of the overall project. J. Scott Pippin of the University
of Georgia’s Carl Vinson Institute of Government also
made signicant research and outreach contributions
that greatly improved the nal report. David Bryant,
formerly the Assistant Director of the Georgia Sea
Grant College Program, provided signicant admin-
istrative support and outreach assistance through the
beginning portions of the project period.
Other individuals who provided outreach support
and/or information critical to the nal project
include: Jackie Jackson Teel (Chatham-Savannah
Metropolitan Planning Commission); Jennifer Kline
(Coastal Resources Division, Georgia Department
of Natural Resources); Kelly Spratt (Georgia Sea
Grant), Dr. Clark R. Alexander (Skidaway Institute
of Oceanography); Darrell Richardson (Georgia
Department of Transportation); and Dr. Sam Merrill
(Catalysis Adaptation Partners, ). We especially
recognize Courtney Reich and Ed DiTommaso, both
of the Ecological Planning Group, , for technical
comments and feedback that greatly improved the
overall project.
Acknowledgments
The University of Georgia Marine Extension Service
The University of Georgia Marine Extension Service
Publication supported in part by an
Institutional Grant (NA10OAR4170098)
to the Georgia Sea Grant College
Program from the National Sea
Grant Oce, National Oceanic and
Atmospheric Administration, U.S.
Department of Commerce. All views,
opinions, ndings, conclusions, and
recommendations expressed in this
material are those of the author(s) and
do not necessarily reect the opinions
of the Georgia Sea Grant College
Program or the National Oceanic
and Atmospheric Administration.
The University of Georgia Marine Extension Service
Publication supported in part by an
Institutional Grant (NA10OAR4170098)
to the Georgia Sea Grant College
Program from the National Sea
Grant Oce, National Oceanic and
Atmospheric Administration, U.S.
Department of Commerce. All views,
opinions, ndings, conclusions, and
recommendations expressed in this
material are those of the author(s) and
do not necessarily reect the opinions
of the Georgia Sea Grant College
Program or the National Oceanic
and Atmospheric Administration.
Publication supported in part by an
Institutional Grant (NA10OAR4170098)
to the Georgia Sea Grant College
Program from the National Sea
Grant Oce, National Oceanic and
Atmospheric Administration, U.S.
Department of Commerce. All views,
opinions, ndings, conclusions, and
recommendations expressed in this
material are those of the author(s) and
do not necessarily reect the opinions
of the Georgia Sea Grant College
Program or the National Oceanic
and Atmospheric Administration.
Tybee Island
Adaptation Plan
Sea Level Rise
FINAL REPORT APRIL 2016
Funded by the National Sea Grant Program
Administered by the National Oceanic and Atmospheric
Administration (NOAA), Sea Grant conducts research,
outreach and education in 33 coastal and Great Lakes states.
