TR 84-2
.. -
NATURAL RESOURCES
OF COlliER COUNTY
FlOR IDA
,//
PART 2
COASTAL BARRIER RESOURCES
\~B~"'Z-
1984
Research supported in part by the
Florida Department of Environmental Regulation and the
Coastal Zone Management Act of 1972, as amended. Administered by the
Office of Coastal Zone Management, National Oceanic and Atmospheric Administration
SOt>
TECHNICAL REPORTS
NATURAL RESOURCES OF COLLIER COUNTY
84-l.
84-2.
84-3.
84-4.
NATURAL RESOURCES MANAGEMENT PLAN
COASTAL BARRIER RESOURCES
COASTAL ESTUA~INE RESOURCES
COASTAL ZONE MANAGEMENT UNITS:
Data Inventory and Analysis
COASTAL ZONE MANAGEMENT UNITS: Atlas
DRAFT ORDINANCES FOR PROTECTION OF
COASTAL ECOSYSTEMS
84-5.
84-6.
Technical Report No.84-2
JUDSON WI HARVEY
PRINCIPAL AUTHOR
MARK A. BENEDICT, PH.D.
Director
ROBERT H. GORE, PH.D.
Coastal Zone Management
Specialist
JUDSON w. HARVEY
Coastal Zone Management
Associate
MAURA E. CURRAN
Coastal Zone Management
Technician
(f)
NATURAL RESOURCES MANAGEMENT DEPARTMENT
COLLIER COUNTY GOVERNMENT COMPLEX
3301 TAMIAMI TRAIL EAST
NAPLES. FLORlDA 33942-4977
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TABLE OF CONTENTS
Pref ace .................................................................................................. v
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SECTION 1
Synopsis.......................................................................................................... .1
SECTION 2
In trod u c t 10 n .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 11
SECTION 3
Background: Physical Setting
Location
Definition
Geomorphic Classification
Physiographic Zonation
1. Nearshore Zone
2. Active Beach Zone
3. Dune/Washover Zone
4. Stabilized Back-Barrier Zone
5. Wetlands Zone ...............
A.
B.
C.
D.
. .13
..13
..........16
..18
. . . 18
..19
..19
..............21
. .21
SECTION 4
Background: Climatic-Hydrographic
Seasonal Wind Distribution
Hurricanes and Tropical Storms
Tides .......
Wave Climate
Setting
A.
B.
C.
D.
.22
.25
...27
...27
SECTION 5
Littoral Drift
A. Introduction
B. Methods
C. Results and Discussion
D. Summ.ary. . . . . . . . . . . . . . .
..30
. .30
.. 32
.. 34
Sand
A.
B.
C.
D.
SECTION 6
Supply
Introduction
Methods
Results and Discussion
S UITllD.a ry ................
. . . 35
. .35
. . . 36
.....39
SECTION 7
Tidal Pass Dynamics
A. Introduction
B. Methods ......
C. Results and Discussion
. . . .41
...42
.. .42
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TABLE OF CONTENTS (Continued)
D . Summa ry .................................................. 56
SECTION 8
Trends of Shoreline Change
A. Introduction ..............
B . Me t hod s .............
C. Results and Discussion
D. Summary. . . . . . . . . . . . . . . . . .
1. Future Shoreline Change Predictions
. . . . . .60
.......
. . . .60
....62
.....67
. . . . .69
SECTION 9
Beach and Dune Zone Characteristics
A. Introduction
B. Methods
C. Results and Discussion
D. Summary. . . . . . . . . . . . . . .
.......72
. . . . . . .72
......74
......78
SECTION 10
Cone lus ion .................................................... 81
LITERATURE CITED AND APPENDICES
Literature Cited
Appendices ......
1. Annotated Bibliography of Previous Studies
2. Beach Erosion Rate Measurements: 1885 to 1981
3. Nearshore Changes in Sand Volume: 1885 to 1970
4. Active Beach and DunejWashover Zone Measurements
5. Data Summation: Beach segment maps and tables
.84
.87
.87
........91
.......97
.100
.103
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FIGURE
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20
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LIST OF FIGURES
Collier County Barrier Coastline:
An Overview of Resources, Land Use,
Dynamics and Erosion Hazards .............................
Location Map: Collier County Barrier Coastline ..........
Barrier Beaches and Tidal Passes of Collier County.......
Physiographic Descriptions and Barrier Beach Profiles ....
Seasonal Wind Roses For Coastal Collier County...........
Annual Wind Rose For the Collier Barrier Coastline .......
Theoretical Net Littoral Drift Rates .....................
Nearshore Volumetric Changes in Sand Supply..............
Sand Budget Summary ......................................
Wiggins Pass: 1927 to 1981 ...............................
Clam Pass: 1952 to 1981..................................
Doctors Pass: 1927 to 1981 ...............................
Gordon Pass: 1927 to 1981 ................................
Hurricane Pass and Vicinity:
Big Marco Pass: 1927 to 1981
1927 to 1981 ................
...... ..... ..................
Caxambas Pass: 1927 to 1981 ..............................
Blind Pass to Cape Romano: 1927 to 1981 ..................
Net Shoreline Changes Along North Collier
County: 1885 to 1981 .....................................
Net Shoreline Changes Along South Collier
County: 1885 to 1981..................................... 65
Potential Rates of Shoreline Change: Collier
County, 1885 to 1981 ..................................... 66
Trends in Shoreline Migration: Collier
County, 1885 to 1981 ..................................... 68
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31
37
38
43
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57
63
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TABLE
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4
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LIST OF TABLES
Hurricanes Affecting the Collier
County Barrier Coastline ................................. 26
Wind Frequency Percent vs. Sea Height:
Southwest Florida........................................ 29
Dune/Washover Zone Character:
Breakdown of Vegetation Types ............................ 77
Comparison of Beach and Dune Widths With Setback
of Land Development Activities ........................... 79
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PREFACE
Overview
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Collier County's coastal zone. defined for administrative purposes as
that area of the County on the Gulf side of U.S. 41 (the Tamiami Trail),
encompasses 328 square miles of coastal barrier, bay, wetland, and
maritime upland habitats. The coastal zone stretches 57 miles from the
northwest to southeast and varies in width from 2 miles at the north
county line. to 12 miles in the vicinity of Marco Island and 8 miles near
the southern county border. Collier County's coastal zone, which makes
up 16 percent of the County's total land area, is inhabited by 38,800
people (1980 census). 45 percent of the County's population. An addi-
tional 29,300 people live within 5 miles east of U.S. 41. In total, 79
percent of the county's population is found within 10 miles of the Gulf
of Mexico.
The County's coastal zone is characterized by both developed and undevel-
oped areas. Of the 328 square miles in the coastal zone 67 square miles
(21 percent) are developed. Of the remaining 261 square miles 123 square
miles (37 percent) are undeveloped and preserved as Federal (Everglades
National Park. Rookery Bay National Estuarine Sanctuary). State (Faka-
hatchee Strand. Collier-Seminole. and Delnor-Wiggins State Parks and
Barefoot Beach State Preserve). and County (Tigertail and Clam Pass Beach
Parks) resource management and protection areas. The remaining 138
square miles (42 percent) are undeveloped and in private ownership.
Unlike most of the rapidly developing counties in South Florida. Collier
County is unique in that the great majority of its coastal zone is still
in its natural state. Hundreds of thousands of acres of coastal barriers,
wetlands. bays. and marine grassbeds are still relatively undisturbed.
much as they have been for thousands of years. It is these areas that
have made Collier County so aesthetically attractive. If properly
managed they will continue to function in this respect.
Of equal importance, however, are the natural resources of these
undeveloped regions of the coastline areas which are ecologically vital
to both the County and southwest Florida. The coastal barriers, if they
remain unal tered, serve as a first line of defense against the sea.
Storm surge damage, coastal flooding, and erosion of the mainland can be
alleviated or slowed by a functioning, natural system of coastal
barriers. The we tlands, shallow bays, and marine grassbeds are other
important parts of the coastal ecosystem. The mangrove forests (those in
Collier County being some of the largest, undisturbed systems in the
United States and one of the best developed in the world) and associated
marshes provide the organic materials and detritus that form the basis of
the coastal food chain and support the abundant shellfish and finfish
resources of southwest Florida. The unaltered coastal ecosystem not only
functions as a haven for birds, fish, and other wildlife, but may also
provide necessary refuge for those species that have been driven from
adjacent. heavily altered or extirpated coastal systems. The undisturbed
natural systems of Collier County form the keystone for the south Florida
ecosystem. The coastal zone links the estuarine systems of Lee and
Monroe County while the vast, unspoiled eastern area of the County
connects the coastal and interior wetland systems with those of Dade and
Broward Counties.
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Almost half of the unaltered coastal zone in Collier County is under the
ownership and/or management of Federal. State. or Local agencies for the
sole purpose of protecting the natural systems. Although this is
gratifying. it is important to remember that the other half of the
undisturbed coastal area is in private ownership. In addition, both the
private and the managed coastal areas are bounded by uplands that are
either developed or projected for future urban or agricultural dev-
elopment. Activities undertaken in the private areas of the coastal zone
or on adjacent upland property, if not properly planned, could result in
the degradation of our remaining undisturbed coastal areas in only a few
decades and the loss of their resources. In a recent position paper R.
A. Livingston wrote that "if history is our guide, one basic problem lies
in public acceptance of almost any level of environmental deterioration
as long as it occurs gradually enough". To safeguard the coastal zone
resources of Collier County from gradual deterioration and to ensure
their continuing function as a vital part of the southwest Florida
ecosystem. positive and direct steps must be taken. Predominant among
these must be the implementation of a program to ensure that all future
land use activities proposed for the coastal zone are designed to be
totally compatible with. or at least not inimical to. the natural
resources and the associated recreation values of the County's un-
disturbed coastal areas.
Collier County Coastal Zone Management Program
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The coastal zone is one of Collier County's major assets. Abundant.
natural resources, ample recreation opportunities. and popularity as a
homesite for many seasonal and full time residents are factors of the
coastal zone well recognized by the Board of County Commissioners, the
County staff. and many local conservation and business groups. For these
reasons the community as a whole has supported past and present coastal
zone management activities in Collier County.
With the support of the Board of County Commissioners and grants from
the Office of Coastal Management. Florida Department of Environmental
Regulation. and the Erosion Control Program. Florida Department of
Natural Resources. the Collier County Natural Resources Management
Department is developing a County Coastal Zone Management Program. A
major goal of this program is the protection of the natural resources of
Collier County's coastal barriers. bays. and wetlands and the management
of coastal development in order to ensure that future land-use activities
will not degrade these resources. The Program is a continuous. multi-
year project involving. research. implementation. and environmental
protection activities. Progress to date includes data incorporated into
the following Technical Reports:
Technical Reports 83-1. 83-2. 83-3
Beach Management Planning and
Implementation Strategies at
the Local Level
The Beach in Collier County: A
Model in Southwest Florida
Drafts plans for beach and
coastal barrier management
in Collier County; describes
major components and imple-
men~ation of Collier County
Coastal Zone Management Pro-
gram; identifies Collier
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A Resource Management Program for
the Coastal Barriers of Collier
County. Florida
Technical Report 84-1
Natural Resources Management Plan
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Technical Reports 84-2, 84-3
Coastal Barrier Resources
Coastal Estuarine Resources
Technical Report 84-4, 84-5
Coastal Zone Management Units:
Data Inventory and Analysis
Coastal Zone Management Units:
Atlas
Technical Report 84-6
Draft Ordinances for Protection
of Coastal Ecosystems
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County as a model for beach
management in Florida; pro-
vides background data on
beach resources, dynamics,
and past management activi-
ties;
Sets natural resource goals
and policies for county and
describes how they will
be implemented; highlights
coastal barriers, bays. and
wetlands as areas of special
management ,concern; delin-
eates the currently undevel-
oped portions of the coastal
zone as a distinct land-use
type requiring careful re-
view prior to any land de-
velopmental or alterational
activities;
Evaluates and analyzes the
current resources and en-
vironmental features of the
county's coas tal barriers
and coastal estuarine areas;
presents data on shoreline
migration. beach and inlet
dynamics. and estuarine eco-
systems; describes man's
presence in the coastal zone
and his current and poten-
tial impacts;
Delineates the coastal zone
of Collier County into dis-
crete management units and
beach segments; compiles
site-specific data on re-
sources and management for
each unit;
Reviews the existing codes
and environmental ordinances
for Collier County in CODl-
parison to those from other
Floridan counties; drafts
model ordinances covering
resource review. vegetation
standards. coastal construc-
tion activities, and perfor-
mance bonds.
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Upcoming Program activities include: (1) The design and implementation
of a development review procedure that closely ties the permitting of a
land-use activity. proposed in or adjacent to the currently undeveloped
regions of the coastal zone, to a specific ecological community, its
resource values. and its limiting biological and physical factors. The
procedure will be designed to ensure that only those activities
compatible with habitat values and functions, or designed to minimize
adverse impacts on those values. will be allowed (project funded by
D.E.R. Office of Coastal Management); and (2) The continuation of dune
restoration and protection activities at all County beach parks and
access points. The latter project involves the removal of exotic plant
species, the reconstruction and revegetation of dunes damaged by storm
activity or visitor use, the construction of back dune feeder walkways
and dune crossovers, and the placement of signs and low profile fences to
maintain the restored dunes (project funded by the D.N.R. Erosion Control
Program). The results of these and other projects conducted under the
County Coastal Zone Management Program will be the subject of future
Technical Reports prepared by the Natural Resources Management Dep-
artment.
Acknowledgements
The Natural Resources Management Department thanks the staff of the
D.E.R. Coastal Management Office and the D.N.R. Erosion Control Program
for the assistance they have given in the development of the Collier
County Coastal Zone Management Program. The Department also acknowledges
the staff of other County agencies and Departments that have provided
technical support to this Program. Special appreciation and gratitude is
expressed to Diane Brubaker, Linda Greenfield, and Margaret Tinney of the
Community Development Division. whose assistance materially aided in the
preparation of these Technical Reports.
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SECTION 1
SYNOPSIS
1.
From the north County line, the Collier barrier coastline extends
south 36 miles to Cape Romano. Ten major coastal barrier units are
recognized; they are separated by twelve tidal passes. The coastal
barriers are generally low in elevation (3.5 to 8 ft.) and narrow in
width (200 to 1,000 ft.).
2.
The coastal barriers of Collier County comprise a variety of geo-
morphic types including a coastal headland with attached barrier
spits (14%), numerous beach ridge barrier islands (61%), and several
actively migrating washover barriers (25%). The oldest and most
fully developed coastal barriers in Collier County are beach ridge
barriers that occur in the vicinity of Barefoot Beach and Marco
Island. In contrast, relatively recent washover terraces comprise
the barrier features along much of the Vanderbilt Beach unit, north
Keewaydin Island and Coconut, Kice and Morgan Islands. The barriers
can be divided into five basic physiographic zones: nearshore,
active beach, dune/washover, stabilized back-barrier and wetlands.
Each zone differs in its physical and ecological character and is
subject to different controlling processes such as tides, littoral
drift, storm overwash and hurricane surge.
3. The predominant offshore and alongshore winds that occur in Collier
County reduce wave activity along its beaches. The north-northwest
to south-southeast orientation of the County's coastal barriers
shields the Gulf sides of these islands from waves generated by
winds blowing from the north and east. Waves that affect the
coastline are generated by winds from the west and south on only one
third of the days of the year. Wave-generating winds are more
frequent in the summer (averaging 40% of the time) than the winter
(28%).
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4. The waves striking Collier County beaches are small because of the
predominance of offshore winds, short wave producing fetches, and
the presence of a broad and shallow continental shelf. The mean
wave height in Collier County is estimated to be 20 to 25 cm.
Winter cold fronts and summer tropical storms or hurricanes create
large but infrequent seas that have a major affect on the beaches.
Approximately 15 to 30 cold fronts pass through Collier County each
winter yet only a small number of those generate waves or littoral
currents of sufficient magnitude to cause significant shoreline
change. Hurricances have passed within 100 miles of Collier County
on the average of 4 times per decade. It is during these brief
periods when tidal surge and high waves overtop coastal barriers
that the most change occurs on the beaches of Collier County.
Hurricanes affected Collier County with greatest frequency between
1920 and 1950. During that period, a hurricane passed within 100
miles of the coastline every 1.5 years. The past 30 years has been
a quiet storm period for Collier County. Since 1950 only 6 hurri-
canes passed in the vicinity. Since this storm frequency is far
below historical averages, it is likely that such storms will affect
Collier County more frequently in the future.
5. In a typical year waves from the northwest and south exert rela-
tively equal yet opposing forces along the Collier County coastline.
Consequently, the net littoral drift is weak, averaging less than
80,000 cubic yards per year transported in a southerly direction. A
major change in the orientation of the Collier coastline at Gordon
Pass drastically affects the rate and direction of littoral transport.
In the north County a drift divide is located along the southern
portion of the Vanderbilt Beach unit. North of the divide the net
annual littoral transport is to the north while south of the divide
it is to the south. Compared to the north County the shoreline in
the south County faces approximately 20 degrees further southwest.
The south County shoreline is highly irregular because of the
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numerous tidal passes that segment the coast and compartmentalize
the sand supply in the nearshore zone. The net transport of sand is
generally to the south except at points where localized reversals in
the direction of littoral drift occur as a result of wave refraction
around ebb tidal deltas. In general, Collier County possesses a
small scale, compartmentalized littoral drift system in comparison
with most Atlantic coastal barrier systems.
6.
The nearshore zone where active sand transport occurs extends 0.5 to
0.75 miles offshore in the north County and 0.75 to 1.5 miles
offshore in the south County. The slope of the nearshore zone
varies but is steepest along the north central barrier coast (1:40
slope) and gentlest along the southern extreme of the coast (1:80 to
1:100 slope). In the north County pervasive erosion and steepening
of the nearshore zone has occurred over the past 100 years. Sand
was transported in the littoral drift to the north and south and
offshore onto the continental shelf. Over 40 million cubic yards of
sand were lost to the nearshore system of the north County. Since
1885 erosion in the south County has been localized, and related to
ebb tidal delta dynamics. A large volume of sand was deposited in
the central sector of the south County, in an accreting spit at
south Keewaydin Island and in the nearshore zone of Marco Island.
Sand present in the nearshore zone 100 years ago has remained.
During the past century 90 million cubic yards of additional sand
has been transported into the nearshore zone of the south County.
7. Neither a large tidal range nor sustained high level of wave energy
exists to dominate the morphology or control the dynamics of the
tidal passes in Collier County. Consequently, the passes range in
classification from the wave-dominated variety, where the exchange
of water through the pass is small and the pass subject to rapid
migration along the shore, to the tide-dominated variety, where
larger tidal prism increases flushing through the pass causing
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greater stability of the pass opening and increased interruption of
the littoral drift. The majority of the County's passes are tide-
dominated. These include Wiggins, Gordon, Hurricane, Capri. Big
Marco and Caxambas passes. The ebb tidal deltas at these passes
dissipate and refract oncoming waves. For this reason accretion
often occurs on the sheltered beaches behind the deltas. However,
minor readjustments in the shape and position of the ebb tidal
deltas can cause the newly accreted beaches to be eroded quickly.
Features indicative of wave-dominated passes are present at Clam
Pass, Doctors Pass, Little Marco Pass, Blind Pass and Morgan Pass.
Morgan Pass and Little Marco Pass (before it functionally became a
part of Hurricane Pass) migrated south during this century at rates
ranging from 150 to 200 feet per year. Newly accreted spits associ-
ated with wave-dominated passes can be wide or narrow depending on
sand supply but are always low in elevation and subject to storm
flooding or breaching by new tidal passes. In Collier County tidal
pass morphology and dynamics are the major factor determining the
character and stability of adjacent beaches.
8.
The magnitude of shoreline changes averaged 2 to 10 times larger in
south Collier County than in the north County. Forty-four percent
of the Collier barrier coastline receded at a rate between 1 and
8 feet per year. The receding shorelines were concentrated along
the Vanderbilt Beach, Park Shore, Coconut Island and Kice Island
barrier units. Receding shorelines are found along relatively
straight and uninterrupted stretches of the coast where the supply
of sand in the nearshore zone is diminishing. All the County's
receding beaches are expected to continue receding in the future.
Approximately 22% of the coastline experienced severe fluctuations
both landward and seaward during the past hundred years. Those
areas are concentrated in the South County. Frequently changing
periods of erosion and accretion and exceptional shoreline migration
rates in the range of +15 to -15 feet per year were the trends in
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those areas. Fluctuating beaches are found in close proximity to
the major tidal passes which control the cycles of erosion and
deposition. Along most of the remaining 34% of the coastline little
shoreline change has occurred. In some areas minor short term
accretion was the trend. Shoreline changes ranging from -1 to +8
feet per year occurred in those areas. Favorable combinations of
wave energy, nearshore slope and sand supply have created a stable
sand budget or a sand surplus at Barefoot Beach, south Naples,
central Keewaydin Island and south central Marco Island. These
stable conditions could, however, change in the future because (1)
sea level is rising, (2) the sand supply in the nearshore zone is
being depleted, particularly in the north County, and (3) the storm
frequency is expected to increase.
9. The rate of shoreline recession can be expected to accelerate both
along previously receding shorelines and previously stable or
accreting shorelines in Collier County. This effect will be most
pronounced in the north County where the sand supply is being
diminished most quickly. Increased storm activity in the future
will be the catalyst for a transition to a period of accelerated
recession or decreased stability along the beaches in the north
County. Greater storm activity will also increase rates of reces-
sion in the south County.
In the absence of major storms the shoreline of the Barefoot Beach
barrier unit will be relatively stable over the next 10 to 30 years.
Net shoreline change data indicated that there has been a long term
trend of accretion in the vicinity of the County line unrelated to
temporary fluctuations adjacent to a tidal pass. Nearshore sand
budget data were unavailable for the area but the extrapolation of
data from the south suggests that the supply will be stable or
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depleted at a slow rate. Several major storms could breach this
barrier at the previous site of Little Hickory Pass. Such an
occurrence would reduce the sand supply available to the beaches and
cause fluctuations of the adjacent beaches.
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Shoreline recession along the southern two thirds of the Vanderbilt
Beach unit is expected to continue or increase in the near future.
The Park Shore unit, which has in the past received sand eroded
along the Vanderbilt unit, will also begin to recede although the
effect of a diminishing sand supply may be delayed for 10 years or
more if the incidence of severe storms does not increase.
Shoreline stability and accretion along portions of the City of
Naples beaches have been largely due to shoreline hardening caused
by the construction of groins. This stable trend is not expected to
continue because of the loss of sand occurring in the nearshore zone
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immediately seaward. In the south County decreased stability is
expected along south central Keewaydin Island. The trend of erosion
present along north Keewaydin Island in the past will very likely
spread to the south in the future. Storm breaching is also probable
along both north central and south central Keewaydin Island.
Formation of a new pass would induce drastic fluctuations of the
adjacent beaches.
North and south Coconut Islands will continue to erode. South
Coconut Island could eventually be eliminated by erosion. In this
case sand would become available to promote aggradation of new
islands in the area. If formed, these islands will be temporary in
nature and unsuitable for land development.
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The north shoreline of Marco Island, adjacent to Big Marco Pass,
will continue to erode at about 3 feet per year as a result of the
southward shifting of the main channel. Along northwest and north
central Marco severe erosion is occurring at present. In the future
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the trend of erosion there may slow or reverse itself in accordance
with the changing shape of the ebb tidal delta at Big Marco Pass.
Continued hardening of the shoreline with seawalls and revetments
along north central Marco Island will. however. prevent the natural
processes of sand bar welding. overwash accumulation and dune
formation from occurring. South central Marco Island may well
experience continued stability given its gentle seaward slope and
growing sand supply. Extreme southern Marco Island will continue to
recede as long as sand depletion continues in the nearshore zone
immediately seaward.
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Kice and north Morgan Islands will continue to migrate landward. To
the south. Morgan Spit will very likely disappear during a major
storm and then slowly reform from sand eroded from Kice and north
Morgan Islands. Cape Romano Island will probably be stable in the
future because of its orientation.
10. Man's impact on shoreline changes in Collier County was determined
from measurements of shoreline position and sequential mapping of
shorelines adjacent to tidal passes. Although it is difficult to
quantify. the construction of seawalls. revetments. groins and
jetties have played a role in shoreline change. The consequences of
shoreline hardening have been pronounced in several areas of the
County. The following examples specify instances in which man's
interference drastically altered natural shoreline processes in
Collier County. (1) Land clearing and seawall construction in the
1950's along the one mile Vanderbilt Beach subdivision accelerated
erosion in that area. Recession of the shoreline and vegetation
line occurred between 1952 and 1962 at about twice the rate of
adjacent undisturbed areas. (2) Jetties were constructed at
Doctors Pass about 1960. These jetties interrupted longshore
currents to the south and resulted in a 30 to 40 feet recession of
the downdrift shoreline soon after their installation. (3) Groin
and jetty construction at Gordon Pass have caused the partial loss of
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the protective ebb tidal delta. Maintenance dredging of a naviga-
tional channel in Gordon Pass has removed approximately 1 million
cubic yards of sand from the nearshore system in south Naples. (4)
North central Marco Island has eroded an average of 12 feet per year
since 1962. Over 700 feet of seawall was constructed at the beach/
dune interface during the early 1970's. During the mid 1970's
coastal strand vegetation on either side of the seawall was cleared
for development as the seawall became progressively exposed to the
daily swash of waves. The seawall caused increased wave power and
turbulence during storm tides and consequently increased shoreline
recession. The seawall currently extends into the nearshore zone
and is thus exposed to wave swash during even the lowest tides. It
acts as a wave reflector inhibiting longshore bar formation and as a
groin restricting the longshore transport of sand. During the
passage of the "no name" storm in June 1982, approximately 40 feet
of recession occurred north of the seawall in a matter of hours.
(5) A seawalled "compound" was constructed adjacent to and on the
north side of Caxambas Pass in 1952. Increased wave power in the
vicinity of the compound upset the delicate balance of sand trans-
port and wave sheltering provided by the ebb tidal delta. During
the 1950's and 60's the ebb tidal delta was redistributed to the
south which opened up south Marco Island to the unshielded approach
of oncoming waves. From 1952 to 1981 south Marco Island eroded over
400 feet.
r
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11. The active beach and dune/washover zones in Collier County are
subject to periodic overwash and rapid fluctuations of the shore-
line. Together, a wide beach and vegetated dune field form a
resilient but flexible storm buffer that affords a partial barrier
to storm wave overtopping yet allows some overwash and dissipation
of wave energy across the zones. This system is self healing in
that storm washover deposits build up the elevation of the dune zone
and are quickly colonized by native dune grasses that stabilize the
sand and cause further dune growth. There will usually be a net
loss of sand after a storm; however, some sand lost offshore will
8
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be returned to the beach by the onshore migration of sandbars. A
naturally vegetated dune/washover zone maximizes protection of the
stabilized back-barrier from the effects of storm waves.
The widths of the beach and dune zones average 99 feet and 147 feet
respectively in Collier County. Narrow dune zones (less than
100 feet) are found in the vicinity of receding beaches where sand
supply is limited. Wide dune zones (greater than 200 feet) are
found along fluctuating or accreting beaches where sand surpluses
occur. Land development has occurred in the beach and dune zones
along 36% of Collier County's coastline. Coastal land development
has reduced the total width of the two zones by over 50% and in
some cases by as much as 90%. Current practices of shorefront
development have caused (1) increased shoreline recession. (2)
reduction in the width of the recreational beach. (3) loss of sand
stored in the dune zone. (4) prevention of overwash - a natural
process of sand replenishment, and (5) increased potential for
habitable and accessory structures to be damaged by storm waves.
12.
Beach conditions and the intensity of land development vary tremen-
dously along Collier's coastline. Since it is difficult to be
familiar with site-specific beach characteristics. large scale
maps (1" = 200') and data summary tables were prepared to provide
detailed first hand data to property owners. County officials.
scientists and engineers. The beach segment maps locate coastal
vegetation types. seawalls. groins. and public accesses. The
accompanying tables contain detailed information on coastal barrier
type. shoreline migration history. recreational value and potential
management conflicts. The maps and tables are included in Appendix 5.
13.
This study addressed coastal barrier resources. dynamics. land use.
and erosion hazards. A County-wide overview of the results is
presented in Figure 1.
9
:z: z W Ul
e
~ :z: 0 ! W
Q ~ j: ~ cr:
~ Q e W e
i (J ~
:z: i&: Q
ii cr:
(J W Ul e
e z N
W ;:) e z e
III .. Q ~ -W :z:
!~ :0 (J QO
.
;:::::i ! Q ZZ :z:
~ . Z We 52
.. e cr::Z:
~ ~ ~ ~(J :z:
County KEY
line
BAREFOOT 3
BEACH BEACH I DUNE WIDTH
Wi ins 2 P;.~~l.e.ch
PISS
1 r.d Dune
VANDERBIL T . Land development
BEACH 3 _u_ CCCL
Clam 2
Pass
PARK LAND CLASSIFICATION
SHORE 1 Developed
Doclors 2 Public owned
Pass
3 Undeveloped I
C unprotected
NAPLES
HEADLAND SHORELINE
D TREND IN
CHANGE
Gordon A MaSSive
Pass A fluctuations
B a Moderate
recession
KEEWAYDIN 3 C a'
Slow recession
ISLAND C Stable
D
0 Accreting
A
Hurricane
Pass 3 HIGH HAZARD AREAS
COCONUT B ~ Existing
.....::-...
B,q Marco :~:::::~::::::
Pass Potential
MARCO
ISLAND
Caxamllas
Pass KICE ('~'\ B
\ :>/ No CCCl 2 ~ c",
ISLAN D ~\ ~ ROMA....O
Blind ISLA....O
( ,:::::::::::::::::: ~ ' II]
Pass MORGAN ):~-\
'0......... I
3 A ,...................~
Gu1l1van ISLAND . . .....:: :'" No CCCl I~<)))\ j Miles
Pass 1__ -- ..
0 1 2 3 4 5
Figure 1.
Collier County barrier coastline: an overview of resources,
land use, dynamics, and erosion hazards.
10
SECTION 2
INTRODUCT ION
(
!
Coastal barriers are unique landforms in that one can witness minor
alterations in the shape of their beaches over the period of a day, and
major changes in their size and position over the period of a lifetime.
Shorelines on coastal barriers are in constant flux with the rise and
fall of the tides and the swash of waves. The active, unvegetated beach
is the interface for the exchange of sand between submerged sand storage
areas such as longshore bars, and upland sand storage areas such as dunes
and washover fans. The study of shoreline changes is useful in judging
trends of beach erosion or migration; however, those studies are only one
indication that sand exchange has taken place. The submerged and upland
portions of coastal barriers must be studied together as an interdependent
sand sharing system to fully understand the implications of shoreline
changes and to develop scientifically based management programs for the
protection of coastal barrier resources.
(
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,
I
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I
i
This report describes shoreline changes and the migration of coastal
barriers in Collier County and relates those changes to the sand supply
in the nearshore zone and to the width and condition of the beach and
dune zones. The loss and gain of sand in different sectors of the County
was measured and compared using data collected as early as 1885. This
report includes data on the physical and climatic settings of coastal
Collier County (Sections 3 and 4), littoral drift (Section 5), sand
supply in the nearshore zone (Section 6), tidal pass dynamics (Section
7), shoreline migration (Section 8), and beach and dune zone characteris-
tics (Section 9).
Overall trends in shoreline migration were summarized by relating the
long term rate and direction of shoreline changes to expected changes
in sand supply and the width and condition of the beach and dune zones.
These trends were categorized and applied to the prediction of future
11
migration along coastal barriers of Collier County. A synopsis of the
coastal barrier research is found at the beginning of this report and a
conclusion section (Section 1) is placed at the reports's end.
Site-specific research on coastal barrier resources and land-use are
summarized for management purposes in Technical Report Number 34-4.
12
SECTION 3
BACKGROUND: PHYSICAL SETTING
Location
The barrier coastline of Collier County forms the southern terminus of
the Southwest Florida coastal barrier chain that begins at Anclote Key in
Pasco County. 175 miles to the north (Figure 2). In Collier County an
uninterrupted barrier coastline extends 36 miles from the north County
line to Cape Romano. Ten major barrier units are recognized in the
County; they are separated by twelve major tidal passes (Figure 3).
Definition
Coastal barriers were recently the subject of Federal legislation
(Coastal Barrier Resources Act. 1982). For the purpose of this study a
"coastal barrier" is defined as a depositional geologic feature that
currently fronts the Gulf of Mexico or can be shown. using aerial photo-
graphs and historic charts, to have fronted the Gulf of Mexico in the
past. A coastal barrier also (1) is subject to regular or predictable
wave, tidal and wind energies, and (2) protects inland, wetland or
coastal bay habitats from direct attack by waves. The coastal barriers
of Collier County are composed almost entirely of unconsolidated sand and
shell and are, with a major exception, classifiable under the stricter
definition of barrier islands (shore parallel islands composed primarily
of sand and shell and separated from the mainland by coastal bays or
saltwater wetlands). The exception is in the vicinity of the City of
Naples where the coastal barrier is a part of the mainland. In this
situation the landward limit of the coastal barrier is the inland
boundary of the velocity zone (as identified on National Flood Insurance
rate maps) or the Coastal Construction Control Line. whichever is further
inland.
13
Figure 2.
~
/ton
eYf1loo
Ca laa II hil,
oSI
BeaCh ISI.
1",
C/h
..r",
Iller
SIIIId
I(ey
TreaSure Isl.
Long Key
MUllet Key
Egmont Key
Anna Maria ISland
Longboat Ke~
Lido Key
SieSla Key
Casey Key
PAanasofa Key
Knight. Don Pedro and
Little G a spa ri II a islands
Gasparilla '51,
Cayo Cost a Isl,
North Captiva
Captiva Isl.
Sanibel 151.
fstero 151.
Lovers Key
Big Hickory Isl.
little HiCkory 151.
Barefoot Beach
Vanderbilt Beach
Park Shore Beach
Naples Headland
Keewaydin Island
Coconut Island Group
Marco Island
Kice Island
Morgan Island Group
Cape Romano Islend
iIIf/CI
ole
key,
~()
(Q~
(Q'~
-?-~
. ..c.:
t....
Location map: Collier County barrier coastline.
14
TIDAL
PASSES
COASTAL
BARRIERS
BAREFOOT
BEACH
Wiggins Pass
VANDERBILT
BEACH
Clam Pass
MORGAN
ISLAND GROUP
PARK
SHORE
Doctors Pass
NAPLES
HEADLAND
Gordon Pass
Miles
1____...
o 1 2 3 4 5
/
KE EWAYDIN
ISLAND
Hurricane Pass
Capri Pass
Big Marco Pass
COCONUT
ISLAND GROU P
MARCO
ISLAND
Caxambas Pass
~
KICE
ISLAND
Blind Pass
North Morgan Pass
South Morgan Pass
Gullivan Pass
CAPE ROMANO
iSLAND
Figure 3. Coastal barriers and tidal passes of Collier County.
The asterisks locate recent or ephemeral tidal passes.
15
This study is limited to the barrier coastline in the northwest part of
Collier County. Numerous isolated coastal barriers south of Cape Romano
have been excluded because of their poorly integrated sand supply and the
low level of land development acitivity in the area.
Geomorphic Classification
The coastal barriers of Collier County comprise a variety of geomorphic
types including a coastal plain remnant barrier (9%), numerous beach
ridge barriers (69%), and several actively migrating washover barriers
(22%). The distinctiveness of each barrier type is related to the
pre-existing topography, the mode of formation of the present barriers,
and the local sand supply. Each barrier type possesses a characteristic
topography as shown in Figure 4 which compares the width and elevation of
Collier's barriers. They are generally low in elevation (3.5 to 8 ft.)
and narrow in width (200 to 1,000 ft.).
Two separate chains of barrier islands can be distinguished in Figure 4.
They are connected to a coastal plain remnant barrier (Godfrey and
Reinhardt, 1983) in the vicinity of the City of Naples. The coastal
plain remnant is an exposure of older, Pleistocene sands to the Gulf of
Mexico that have been eroded and reworked over the centuries to nourish
the barrier islands to the north and south. A barrier of this type is
also frequently referred to as a coastal headland. Today the headland at
Naples is relatively stable and the sand supply is no longer as well
integrated among the barrier islands in different parts of the County.
The most fully developed barriers in Collier County are multiple beach
ridge barriers (Godfrey and Reinhardt. 1983). These occur at south
Keewaydin Island. Marco Island, and Barefoot Beach. Beach ridges were
formed by the deposition of coarse sand and shell in the intertidal zone
with the level of maximum wave run-up corresponding to the top of the
ridge. Each beach ridge was deposited in sequence with the present berm
crest representing the most recent ridge. The linear patters of beach
16
A. Multiple beach ridge
barrier island
10
Ul~
MHW -=
o (ft) 1000 ...
B.
Single beach ridge barrier
backed by ma ngrove
swamp
MHW~ 1l1OO~'
C. Coastal headland
1500
D. Migrating washover barrier in an
area of former tidal passes
)
I
MHW~~
o 50
E. Arcuate progradi n g spit
with low, multiple beach
ridges
,j
MHW~
o 1000
F.
Fully developed
barrie r with
multiple beach
ridges
r
MH:~~
o 1000
G. Gulf-exposed mangrove
is land with attached
washover barrier
,/
MHW~
o
~
1000
_:~
Figure 4. Physiographic descriptions and coastal
barrier profiles: Collier County.
17
0.-
D.
Mil..
,-----
o 1 2 3 4 5
ridges which are clearly visible on aerial photographs attest to a long
and complex history of growth and migration. The earliest beach ridges
are perhaps 3,000 years old. Today the islands range between 5 and 10
feet in elevation and are generally wider than 500 feet.
Single beach ridge and washover barriers (Godfrey and Reinhardt, 1983)
are widely distributed along the County's coastline, especially where the
sand supply has historically been depleted. The entire barrier features
along north central Keewaydin Island. Coconut Island and Kice and Morgan
Islands are comprised of recent washover deposits. These islands migrate
landward by the spreading of sand across them by storm overwash. In this
manner the beach sand is recycled and the island's landforms are maintained
(Godfrey and Godfrey, 1974). Lagoonal muds and peat exposed in the surf
zone are evidence that the islands have been migrating in a periodic
washover sequence. Other islands in Collier County are composites of
both types of barriers exhibiting evidence of beach ridge formation and
washover deposition. The Vanderbilt Beach and Park Shore units are
barriers of this type.
Physiographic Zonation
The coastal barriers of Collier County were divided into five physiographic
zones that are roughly parallel to the shoreline. The characteristics
of each zone are described below:
Nearshore Zone: The broad and gently sloping continental shelf west of
Collier County is composed of a mixture of quartz sand and shell, as
well as silt and mud at some locations. Sloping upwards at a rate of 2
to 3 feet per mile, the continental shelf joins the barrier coastline at
the nearshore zone. The nearshore zone (Davis, 1978) is a submerged zone
of sediment transport subject to the effects of waves and littoral and
tidal currents. It is located immediately seaward of the beach and
extends as a steep wedge of sand from the mean low water shoreline to the
seaward limit of the effects of waves. In Collier County the nearshore
18
zone levels off and joins the continental shelf at approximately -21 feet
M.S.L. The slope of the nearshore zone ranges from 1:30 along the
steepest areas to 1:100 along the gentler gradients depending on the
local wave climate, thickness and supply of sand in the immediate area,
and the proximity to a tidal pass. The seaward edge of the nearshore
zone is located between 0.5 and 1.5 miles seaward of the shoreline. Sand
and shell deposits in the nearshore zone of southwest Florida barriers
range from 0 to 18 feet in thickness and average about 6 feet (Davis,
Hine and Belknap, 1982). The thickest deposits of sediment are generally
those on the seaward side of the tidal passes called ebb tidal deltas.
The nearshore zone overlays muddy or limestone strata below.
Active Beach Zone: The nearshore zone is the seaward, submarine expres-
sion of a coastal barrier that stores and occasionally exchanges sand
with the upland feature. The avenue of sand exchange is the active beach
zone. A beach (Davis, 1978) is a partially submerged zone of unconsolidated
sediment which extends from the mean low water shoreline landward to a
boundary of abrupt change in the elevation or composition of the environment.
In southwest Florida and most other coastal barrier environments the
landward limit of the beach is typically the line of contiguous vegetation.
Dune/Washover Zone: The vegetated dune/washover zone begins at the
boundary to the active beach zone and extends landward to the limit of
the "coastal strand" plant community. These plants and the associated
habitat have been thoroughly described for the barrier islands of Lee
County (Cooley, 1955; Herwitz, 1977; Morrill and Harvey, 1980) but not
for Collier County. The plants of the coastal strand community are
adapted to, and in fact dependent on, frequent disturbance by storms to
maintain the characteristic assemblage of species.
The presence and condition of the coastal strand is an excellent indicator
of recent shoreline changes and storm tide penetration of the coastal
I'
19
barrier. Several times each season super-elevated storm tides and waves
flood the entire active beach zone. If the swash of a wave reaches above
the elevation of the berm crest or vegetated foredune it will travel
landward rather than return seaward. This process is called overwash.
As a part of the process a relatively thin and flat layer of sand called
a washover will be deposited well above the normal level of the tides.
Narrow delta-like deposits are called washover fans whereas expansive
deposits are called washover terraces (Pierce, 1970; Cleary and Hosier,
1979). Washovers may become vegetated by the upward growth of specially
adapted plants, such as Spartina patens, through the deposits (Godfrey
and Godfrey, 1973 and 1974) or they may be colonized by dune grasses such
as Uniola paniculata that will begin a new cycle of dune growth before
the overwash process repeats itself (Hosier and Cleary, 1977).
In southwest Florida recent washovers first become vegetated by hardy
grass species such as Sporobolus domingensis and Cenchrus tribuloides.
Sea Oats (Uniola paniculata) colonize the area by seed germination and
vegetative propagation from the high tide lines that are subsequently
deposited on the washover. As the sea oats spread they stimulate the
growth of low dunes on the washover (Morrill and Harvey, 1980).
Geomorphic sequences of overwash and dune formation are extremely
important in the maintenance of an elevated storm buffer on Collier
County's coastal barriers. It was stated earlier that on 22% of Collier's
barriers recent washovers make up the entire upland feature. On all of
the barriers it is the washovers and dunes that are often the highest
point of the barrier and the storage place for sand that is used to
nourish the beaches during erosional phases. The plants of this zone are
adapted to the harsh conditions of salt spray, blowing sand and inunda-
tion by salt water and sand. Many of them also have a fine network of
roots that stabilize the dune and washover features against the effects
of wind and moderate storm tides.
20
Stabilized Back-Barrier Zone: Landward of the dune/washover zone is the
stabilized back-barrier zone. This zone extends to the mangrove swamps
and saltwater wetlands on the landward side of the coastal barriers. The
back-barriers are geologically older areas and are subject to less
frequent disturbance by erosion and overwash. The characteristic ridge
and swale topography throughout this zone is indicative of historic beach
and dune/washover zone environments. However, because of the protection
afforded these environments by the present beach and dune/washover zones,
abundant dune grasses and salt tolerant shrubs will gradually be replaced
with open grassland communities dominated by purple muhly, Muhlenbergia
capillaris and by cabbage palm forests or tropical hardwood hammocks
(Morrill and Harvey, 1980).
Wetlands Zone: The wetlands zone is characterized by moist or saturated
soils and assemblages of plants that can survive under those conditions.
Saltwater wetlands occur on the fringe of coastal bays or estuaries on
the landward side of coastal barriers and generally below 2.5 feet M.S.L.
Freshwater wetlands occur away from the influence of salt water intrusion
and wherever the elevation of the barrier drops below the seasonal water
table.
. .
21
SECTION 4
BACKGROUND: CLIMATIC-HYDROGRAPHIC SETTING
Seasonal Wind Distribution
,
,
I
The climate of southwest Florida is influenced by two major weather
systems (Jordan, 1973). The "Bermuda High" is a high pressure cell
centered over Florida in the summer that generates light winds from the
south, east and western quadrants. In the winter the "Bermuda High"
shifts away from Florida as cold, continental air masses create a pre-
vailing air flow from the north and east. These weather systems have
winds with higher average velocities than those of the summer (Figure 5).
During spring and fall southwest Florida is influenced by a mixture of
the two climatic systems.
,
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The predominant offshore and alongshore winds that occur in Collier
County reduce wave activity along its beaches. The NNW-SSE orientation
of the County's barrier coastline shields the Gulf beaches from waves
generated by winds blowing from the north and east. Waves are generated
by winds from the west and south which blow consistently on only one
third of the days of the year. Wave-generating winds (west of NNW and
SSE) are more frequent in the summer (averaging 40% of the time) than the
winter (28%).
In Collier County the northerly and southerly components of wave-generating
winds are well balanced. During the year the wind blows onshore with a
southerly component 60% of the time; 40% of the time there is a northerly
component to the onshore winds. The strongest regular winds affecting
the beaches blow from the northwest and south. Such winds are nearly
parallel to the orientation of the coastline. Onshore wind speeds are in
general higher during the winter and spring. Occasional, locally intense,
summer winds are associated with summertime thunderstorms and tropical
storms (Riggs, 1975). Winds over 20 knots blow most frequently from the
northwest during the passage of cold fronts (Figure 6).
22
f
r
frequency percent
OCTOBER TO FEBRUARY
APRIL TO AUGUST
Figure 5. Seasonal wind roses (percent frequency of different
wind directions) for coastal Collier County. The
raw data were collected in Ft. Myers, Florida by NOAA
from 1948 to 1953. Ft. Myers is located approximately
40 miles north of the study area.
. .
23
I.i'
~
'11'.
s
5 knots
orientation of coastline
s
~
:;.,l
'II'.
Figure 6. Annual wind roses for the Collier County coastline:
frequency'percent vs. wind speed from wave generating
directions. The data were collected offshore from
southwest Florida (data square 0024) by the Naval
Weather Service Command from 1951 to 1970. Adapted
from Harvey (1982).
notes: 1 degree equals 0.5 frequency percent
0-3 knots totaled 9.8% for all coastal
directed seas
24
Hurricanes and Tropical Storms
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Tropical storms occur during the summer and early fall in the southeastern
United States. Tropical storms with sustained winds above 74 mph are
called hurricanes. During the hurricane season (June to November) storms
will occasionally sweep northwest into the Gulf of Mexico. Such storms
produce a tidal surge that can reach 13 to 18 feet above sea level, high
enough to completely overtop the coastal barriers. The height of the
storm surge is controlled by numerous factors including wind velocity and
direction. barometric pressure, forward speed of the storm, wave fetch,
and slope of the inner continental shelf (Davis, 1982).
r
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,
In Collier County hurricanes generate a storm surge and large waves that
generally approach the coast from the south or southwest. The wave
energy associated with hurricanes may exceed that of winter cold fronts
by two to three orders of magnitude (Stephen, 1981). Although hurricanes
are short-lived phenomena they play an extremely important role in the
transfer of sand from the nearshore zone to the beach and dune zone, as
well as from the dunes and nearshore zone seaward. This transfer is
accomplished by the deposition of washover fans. A direct strike by a
hurricane such as Fredrick. which affected Dauphin Island, Alabama. in
1979, could completely alter the shape of Collier County's barrier
coastline. Most geologic change on coastal barriers in Collier County
occurs during brief hurricane passages.
In the past hundred years at least 40 hurricanes have passed within 100
miles of Collier County's barrier coastline. This is an average of 3 to
4 per decade. Table 1 is a checklist of the storms that have affected
Collier County. Hurricane passages were most frequent during the 1920's
(6 hurricanes) and 1940's (8 hurricanes). Severe storms affected Collier
County in 1873, 1910, 1921, 1926, 1944. and 1960.
,
J
,
,
25
TABLE 1. HURRICANES AFFECTING THE COLLIER COUNTY BARRIER COASTLINE:
1873 TO 1983.
YEAR
*
1873
1876
1878
1878
1881
1885
1888
1891
1894
1896
1903
1906
1906
1910
1911
1916
1919
1921
1924
1925
1926
1926
1929
1932
1935
1935
1936
1941
1944
1945
1946
1947
1947
1948
1948
1950
1950
1960
1964
1965
1966
1966
r
r
I
f
*
*
*
*
*
MONTH
HIT
September
October
July
September
August
October
August
July
September
October
August
June
October
October
August
November
September
October
October
November
September
October
September
August
September
October
August
October
October
September
October
September
October
September
October
September
October
September
September
September
June
September
North
Di rect
Direct
Direct
Direct
North
Direct
Direct
Direct
North
North
East
East
Direct
West
South
South
North
Direct
Direct
Direct
Direct
North
Direct
South
Direct
Direct
West
East
West
Direct
South
South
South
West
East
Direct
East
South
West
South
No local hurricanes since 1966.
COMMENT
Surge reported 14 ft. + at
Punta Rassa (Lee County)
Surge reported 10.3 ft. at
Everglades City (Collier
County)
Surge reported 11.1 ft. at
Punta Rassa
Surge reported 11.3 ft.
Surge reported 11.0 ft. at
Naples
Surge reported 11.7 ft. at
Naples
* Effects of storms known to have exceeded category 2 hazards in
Collier County (winds 110 mph, storm surge 9 to 12 ft.,
Saffir/Simpson scale).
26
Over the period of record the average interval between hurricane passages
was 3 years. From 1920 to 1950. 22 hurricanes affected Collier County
averaging 1 storm every 1.5 years. Hurricanes have been infrequent since
1950. averaging 1 storm every 5 years. From 1950 to 1980 only 6 hurricanes
passed within 100 miles of Collier County with Hurricane Donna making the
last recorded direct hit in 1960. The past 30 years have been a relatively
quiet period in the history of coastal storms in the region. In the
future it is likely that hurricanes will affect Collier County with
greater frequency (than that of last 30 years).
Tides
Astronomical tides in Collier County are a mixture of semi-diurnal and
diurnal types. Diurnal tides have one high and one low in a 24-hour
period. Along the Gulf shore of Collier County the mean tidal range is
2.3 feet (70 cm). The phase and declination of the moon control monthly
cycles of tidal range. Spring tides and Neap tides occur twice each
month. Astronomical and meteorological variations combine to influence
the seasonal level of the tides in southwest Florida. The mean level of
the tide fluctuates over a year's time with the highest tides occurring
between May and October. Monthly mean high water levels are approxi-
mately 0.6 feet higher in the midsummer than in the midwinter in Collier
County. Superimposed on the monthly and yearly fluctuations of tide
level is a long term trend of sea level rise. In southwest Florida the
rise has averaged 0.7 feet per 100 years (Provost, 1970).
Wave Climate
The waves striking southwest Florida beaches are small as a result of the
predominance of offshore winds, short wave producing fetches, and the
presence of a broad and shallow continental shelf. The mean wave height
is estimated to be 20 to 25 cm (Tanner, 1960; Hayes, 1979). Thompson
(1971) shows average significant wave heights (average of highest 1/3 of
waves) to be 25 to 35 cm. Waves approach the Collier barrier coastline
predominately from the northwest and south. Brief but intense northwest
winds in the winter create the largest waves that regularly affect the
27
, ,
.
I
beaches during the course of the year. South winds blow regularly all
year long and consequently create seas a greater percentage of the time.
The percentage of time that waves greater than 3 feet approach the
coastline with a northerly component (24.1) nearly balances the per-
centage that waves approach with a southerly component (27.4). As a
result, in a typical year waves from the northwest and south exert
relatively equal and opposing forces in both directions along the
coastline (Table 2). Consequently, the net annual littoral drift of sand
is relatively small. The net transport of sand during anyone year might
be determined by the direction of approach of several storms or even a
single major storm.
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[
28
l
TABLE 2. Offshore Wind Frequency Percent vs. Sea Height: Southwest
Florida. Data from square 0024, S.S.M.O. Naval Weather Service
Command; 1951-1970.
FREQUENCY PERCENT
r
I
FREQ. % VS.
SEA HEIGHTS
SEA HEIGHT (Ft.) NW W SW S ALL DIRECTIONS
1 2.9 2.5 2.9 5.3 13.6%
1-2 6.3 5.3 6.7 13.0 31. 3%
3-4 5.8 3.8 4.8 12.5 26.9%
5-6 4.8 1.9 2.4 3.3 14.4%
7 2.9 1.0 1.0 2.4 7.3%
8-9 1.4 0.5 0.5 0.5 2.9%
10-11 1.0 1.0%
12 0.5 0.5%
1 3- 16 0.5 0.5%
Freq. % vs.
Direction for
All Coastal
Directed Seas
24.1
15.0
18.3
39.0
Seas 3 Ft.
16.9
7.2
8.7
18.7
northerly
component
southerly
component
24. 1 %
27.4%
Adapted from Harvey (1982).
29
the beaches in the past. In addition to the above passes, an approximately
equal number of short-lived or temporary tidal passes have opened and
closed in the recorded history of the area as a result of storm activity
and changes in littoral drift.
Methods
f
r
f
[
Historical aerial photography dating back as far as 1927 was collected
for each of the eleven major tidal passes. Using a slide projector for
scaling purposes, sequential changes in the position of the shoreline and
in the orientation of the ebb tidal delta and major tidal channels were
mapped for each inlet. Comparisons of shoreline erosion and accretion
were made between each photographic interval.
Results and Discussion
.....
I
Wiggins Pass: Wiggins Pass separates the Barefoot Beach unit to the
north from Vanderbilt Beach unit to the south (Figure 10). Water from a
relatively large interior area of mangrove swamps and shallow coastal
bays along with the freshwater discharge of the Cocohatchee River traverses
Wiggins Pass. Like most tidal passes in southwest Florida Wiggins Pass
exhibits both wave-dominated and tide-dominated characteristics. Aerial
photographs indicate the presence of a well developed ebb tidal delta,
evidence of a flood tidal delta which aggraded and became attached to the
Vanderbilt Beach unit, and a history of rapid shifting of the adjacent
shorelines in response to the changing configuration of the ebb tidal
delta.
Substantial accretion occurred on the beaches adjacent to the pass
between 1927 and 1952. Accretion was the general trend in extreme north
Collier County during that period, however, the accretion adjacent to
the Pass was not related specifically to pass dynamics. After 1952 the
.,.....,.------....
(42 )
SECTION 5
LITTORAL DRIFT
Introduction
r
r
J
!
,
J
Sand in the nearshore zone moves onshore, offshore and parallel to the
shore. This movement is driven by the oblique approach of waves.
Predominant winds from the northwest and south insure that waves rarely
strike the beach head-on and consequently there is always a lateral
component of motion in the breaker zone. An offset in the uprush and
backwash of water carries sand along the shore away from the approaching
waves and is responsible for a net transport of sand along the coastline.
This process is referred to as littoral drift. The quantity of sand
transported over a year's time results in an annual littoral drift.
Methods
Theoretical littoral drift rates were calculated for the coast of Florida
by Walton (1976). These data are based on relationships between wave
size and direction, littoral current velocity and littoral sand transport.
Shipboard wave observations between 1951 and 1970 were used as the data
base. The derived littoral drift rates include corrections for the local
wave climate and for variations in the orientation, of the coastline.
Walton's estimates of littoral drift are the most comprehensive ones
available for the County.
Figure 7 is a graphic representation of Walton's littoral drift rates for
the Collier barrier coastline. The annual net rate of transport as well
as the net rate in January and June are depicted. Following the methods
outlined in Walton (1976) data were plotted along the shore to correlate
with the orientation of each segment of the coastline. In the vicinity of
passes, tidal currents and the sheltering of waves by ebb tidal deltas
affects the rate and direction of littoral transport. It was assumed that
I
L
30
~
II
r II
II
CL
f
PI ....
f PI
-
\ ~
&
lit
~ 4
~
-
{ ?:
~
! 2
;-~
( ~CI)
>< 0
t") _
,,~
f >&
~li)
c: 2
III
~
-
~
( ~
!
-
~
0
z
KEY
Net Littoral Drift Rate
(
\ Annual - - - Hypothesized Annual Drift
r I. . . . . . : ~ ~ : : : I January Miles
, .......... ..
. 0 1 2 3 4 5
I I June
.,
Figure 7. Theoretical net littoral drift rates: Collier County. The
graphed values represent thousands of cubic yards of sand
in transport. Also represented are tidal pass influenced
zones (PI), substantiated littoral drift divides (*) I and a
hypothesized net annual drift divide (X). Note the varia-
tion in littoral drift rates between the north and south
County.
31
[
in geomorphologically determined "Pass Zones II littoral transport is
toward the pass with increasing proximity to the pass opening. This
assumption is based on theoretical and empirical data that describe the
effects of wave refraction and tidal currents on the littoral drift in
the vicinity of tidal passes (Hayes. Goldsmith and Hobbs, 1970; Dean and
Walton, 1973). Pass influenced zones in Collier County are shown in
Figure 7.
Results and Discussion
The Collier barrier coastline can be divided into two major provinces
of littoral transport; (1) north County and (2) south County (Figure 7).
A major change in the orientation of the coastline at Gordon Pass defines
the boundary between the north and south County provinces. The north
County coastline possesses a north-northwest to south-southeast orienta-
tion. A 20 to 25 degree eastward rotation of the coastline at Gordon
Pass creates a northwest to southeast orientation. The difference in
orientation of the two coastal provinces, as well as variations in tidal
pass morphology, drastically affects the rate and character of littoral
sand transport.
Based on Walton's data, littoral drift in the north County is unidirec-
tional and relatively uniform in rate. The net annual transport of sand
is predicted to be southerly averaging 100,000 cubic yards per year; net
transport in January is predicted to occur at approximately three times
that rate. In June littoral transport is inferred to be northerly,
averaging 15,000 cubic yards per year. The actual rate of littoral
transport is probably overestimated by Walton's data because of the
effect of Sanibel Island. Sanibel is located 40 miles to the north
and projects far westward into the Gulf of Mexico. This situation
modifies the wave climate in north Collier County in a way not taken
into account by Walton's data. We hypothesize that Sanibel Island
reduces the actual net transport rate in north Collier County.
32
Geomorphic evidence suggests the presence of a major. net annual drift
divide along the central part of the Vanderbilt Beach unit. The morph-
ology of the nearby tidal passes (Wiggins Pass, Clam Pass, Doctors Pass)
implies that net transport is to the north towards Lee County on the
north side of the divide and to the south towards Gordon Pass on the
south side. In addition, the nearshore zone is narrowest and beach
erosion rates are highest in the central sector of the Vanderbilt unit.
The presence of Sanibel Island to the north causes refraction and reduc-
tion in the power of waves from the northwest. This could explain the
discrepancy between this geomorphic interpretation and Walton's data.
The hypothesized net annual drift divide is shown in Figure 7 as a dashed
line on the left half of the graph.
In the south County the predicted rate of littoral drift varies widely.
It ranges from 100.000 cubic yards per year in a northerly direction to
300,000 cubic yards per year in a southerly direction. Many factors
account for this variation. As stated earlier, the coastline in the
south County faces 20 degrees further south than the north County coast-
line. The shoreline is also much more irregular. As a result the
littoral power of waves is emphasized in some portions of the south
County and de-emphasized in others. For this reason the predicted rates
of transport in the south County are probably overestimates. Trans-
port in multiple directions also means that the volume of sand available
for transport is probably much less than is needed to supply sand at the
predicted rates.
The predicted rate of sand transport in the south County is generally to
the south except at three "drift divides" where localized reversals in
the direction of transport occur. The drift divides along the south
Collier barrier coastline are located adjacent to, and are a result of
the morphology of Gordon Pass, Big Marco Pass and Caxambas Pass (Figure
7). The actual point of divide occurs in a zone on the south side of
each pass where the net littoral transport rate is zero. On the north
side of each drift divide, sand is transported north towards the pass and
33
vice versa on the south side. Shorelines adjacent to drift divides are
normally sites of massive erosion since sand is supplied both to the
north and to the south from the null zone.
Summary
Tidal passes affects littoral transport to only a small degree in north
Collier County. While littoral drift is controlled by tidal pass dynamics
along 36% of the south County coastline only 9% of the north County
coastline was judged to be pass influenced. Rather, it is a drift divide
along the central Vanderbilt Beach unit that controls littoral transport
in the north County. There sand tends to be transported to the north out
of the County and to the south across Gordon Pass.
r
Tidal passes exert a greater effect on the rate and direction of littoral
transport of sand in the south County because of their larger cross
sectional areas, greater volume of tidal flushing, and increased volume
of sand stored in their ebb tidal deltas. In general, the littoral drift
regime in the south County tends to transport sand to the pass areas from
the north and then retain it on the south side of the passes. The rate
of sand transport across the passes of the south County is probably much
lower than in the north County. In this sense the sand supply in the
south County is more fragmented and poorly integrated than that in the
north County.
34
SECTION 6
SAND SUPPLY
Introduction
r
!
On barrier coastlines the submerged portion of the sandy beach is known
as the nearshore zone. This zone can be divided into two sub-categories:
(1) the surf zone - or area where breaking waves create a longshore
current that transports sand along the coast; (2) the shoreface - or
steep wedge of sand extending below the surf zone to the seaward boundary
of the effects of waves and currents. The area of the newshore zone
where the interaction between littoral currents and tidal currents
dominates sand movement is known as the pass influenced zone.
In Collier County the nearshore zone extends from the shoreline down to
the 24 foot submarine contour where the effect of waves and littoral
drift diminishes considerably and where the slope levels off to 2 or 3
feet per mile. This zone where active sand transport occurs extends
approximately 0.5 to 0.75 miles offshore in the north County and 0.75 to
1.5 miles offshore in the south County. The slope of the nearshore zone
varies and is steepest along the north central barrier coast (1:40 slope)
and gentlest along the southern most part of the coast (1:80 to 1:100
slope).
Methods
The United States Coast and Geodetic Survey mapped the County's nearshore
zone in 1885. In 1970 the U.S. Army Corps of Engineers resurveyed the
nearshore zone along 46 profiles and plotted the data in comparison with
those made in 1885. Using the comparative profiles supplied by the Corps
of Engineers, areas of erosion and deposition were measured by planimeter
at each profile location. The areas of erosion and deposition were
grouped into 6 foot intervals for measurement (+3 to -3, -3 to -9, -9 to
~
35
-15, and -15 to -21 MSL). The results ~ere plotted on a graph depicting
profile changes from 1885 to 1970 along the barrier coastline (Figure 8).
The raw data are presented in Appendix 3. These data were then inter-
polated between profiles to add the third dimension for the calculation
of absolute volumes of erosion and deposition in different parts of the
County. The result is a "sand budget" that compares volumes of erosion
and deposition in the nearshore zone between 1885 and 1970. The sand
budget is summarized in Figure 9.
Results and Discussions
In all. 42 million cubic yards of sand were eroded and transported out of
the nearshore zone in north Collier County. This sand could have been
transported along numerous pathways including (1) along the shore in the
littoral drift. (2) offshore as a result of the erosion and steepening of
the nearshore zone. (3) onto or over the islands by the process of
overwash. or (4) into the tidal passes as a result of tidal currents.
Sand movements along these routes have been shown to be important paths of
transport along other barrier coastlines (Stapor. 1971; Dean and Walton.
1973; Entsminger. 1975; Fisher and Simpson. 1979).
The nearshore volumetric data suggested a separation of two major coastal
provinces in Collier County. The coastal provinces correlated closely
with those established using littoral drift data. Gordon Pass marks the
separation of the two provinces. In the north County pervasive erosion
and steepening of the nearshore zone occurred from 1885 to 1970. Steepen-
ing and landward translation of the nearshore slope were the trends in
the Naples. Park Shore and south Vanderbilt Beach barrier units. Over
the 85 year study period these areas lost 22.1. 14.7 and 12.7 million
cubic yards respectively from their nearshore zones. An exception to the
general trend occurred along the north Vanderbilt Beach unit where a
general flattening of the nearshore slope resulted from deposition in the
lower nearshore zone. In this area, directly south of Wiggins Pass. 7.5
million cubic yards of sand was deposited in the ebb tidal delta. swash
36
~
r
\
\
\
\ .~
I \
',\ J ..., " 'rl:
'1 '\ '. I
\', J \ ", J
\. ..'/ --'_ ~'J
\ I
~ J
\ I
\ I
Y
....
..
>-
C'), 400
].
c:
o.
'jij 200
o
..
w
.0
(
,I . .
: I ,",.:
;/ '.
".'
~
,....
...
>-
f"t' 200
j.
I
c:
o
-= 400
M
o
CL
<<>
o
KEY
Net Volumetric Change: 1885 to 1970
I I +3 to -21 ft MSL
~--1 -3 to -9 ft
1........1 -15 to -21 ft
o
c:
.
E
o
,gJ@j
t
I
I
I
Miles
1 2 3 4 5
Figure 8. Nearshore volumetric changes in sand supply,Collier
County: 1885 to 1970.
37
t
I
I 1
- -- - -
limit of study r 7.5
2.6 @
9.9 ~
~---
'\
Miles
1____...
o 1 2 3 4 5
+- - - -
22.1
15.8
KEY
SAND BUDGET
5.0 Erosion x 106yd3
5.0 Deposition x 106yd3
C Onshore I Oil shore transport
) littoral transport
~ Inferred transport
~mit~sl~
\ 13.5
\ 3~6
2.7
t
\
\
\
~ Cape Romano
Figure 9. Sand budget summarYr Collier County: 1885 to 1970. The
bounderies of the study area extended from +3 to -21 MSL.
38
platform, and accreting shoreline. In addition, deposition occurred in
the nearshore zone directly adjacent to and on the south side of the
other passes in the north County.
In the south County erosion in the nearshore zone tended to be localized
and related directly to fluctuations in the size and position of the ebb
tidal deltas. Notable sites of erosion were seaward of north Keewaydin
Island (4.4 x 106 yd3) , Coconut Island (7.1 x 106 yd3), and south Marco
6 3
Island (2.7 x 10 yd). Erosion occurred primarily in the upper nearshore
zone with little disturbance taking place below the 15 foot submarine
contour. A significant volume of sand was deposited in the central
sector of the south County's nearshore zone. The major areas of deposi-
tion were seaward of south Keewaydin Island (36.8 x 106 yd3), and north
and central Marco Island (49.1 x 106 yd3). Spit growth since 1885 at
south Keewaydin Island extended the southern tip 1.6 miles. During the
past 100 years Marco Island was a major site of shoreline accretion and
nearshore sand deposition as a result of the funneling of sand from the
north and south into the central Marco nearshore zone.
Summary
Since 1885, north Collier County experienced a net loss of sand (42 x
106 yd3 deficit) while the south County gained sand (91 x 106 yd3 surplus)
in its nearshore zone. The north County lost sand along all possible
transport routes. Sand was carried in the littoral drift out of the
County at its northern boundary and across Gordon Pass to the south. In
addition sand was transported offshore onto the continental shelf and
inshore through tidal passes or by overwash.
The south County gained sand in its nearshore zone. This sand came from
the north County by the littoral drift. Once sand entered the south
County's nearshore zone it was retained there, particularly in the
vicinity of the ebb tidal deltas. Data indicate that little erosion
occurred in the lower nearshore zone, except where the ebb tidal deltas
L .
39
shifted or migrated. It is probable that little sand was lost farther
offshore on the deep subtidal continental shelf.
L
40
SECTION 7
TIDAL PASS DYNAMICS
Introduction
An inlet is a tidally maintained interruption in a barrier coastline
that allows exchange between oceanic water and enclosed coastal bays or
estuaries (Fisher. 1982). The morphology of these features is controlled
by the interaction of littoral and tidal currents. which combined can
cause the formation of large sub tidal and inter tidal sand bodies called
tidal deltas. Ebb tidal deltas are present directly seaward of the inlet
and flood tidal deltas appear landward or just inside the enclosed
embayment. Generally. ebb deltas are best developed on tide dominated
barrier coastlines (large tidal range. small mean wave height) and flood
deltas are more prominent on wave dominated coastlines (Hayes. 1973).
Tidal inlets are called passes in southwest Florida. The morphology of
the approximately 30 tidal passes is highly diverse owing to the fact
that neither a large tidal range nor sustained high level of wave energy
exists to dominate tidal pass dynamics. Consequently. the morphology of
tidal passes in Collier County ranges from the wave dominated variety. in
which the exchange of water through the pass is small and the pass is
subject to rapid migration along the shore. to the tide-dominated variety.
where a greater tidal prism increases flushing through the pass causing
increased interruption of the littoral drift and greater stability of the
pass opening.
In 1981 Collier County's barrier coastline was segmented by eleven major
tidal passes. Listed from north to south they were: Wiggins Pass. Clam
Pass. Doctors Pass. Gordon Pass. Hurricane Pass. Capri Pass. Big Marco
Pass. Caxambas Pass. Blind Pass. Morgan Pass and Gullivan Pass. These
passes are relatively persistent features of Collier County's barrier.
having influenced changes in the nearshore sand supply and stability of
41
1927 -1952
1952 -1962
'" I"': .~.,::.:;;.-
'\ lV..j ('f:;>
\ t"'? I::;
\ '':;:\ 1/
'-"':.,." (.:;:.::;:~_/
~ ~'::'!::/i/
1962-1973
o 1000
- -
FEET
2000
I
.C' .IJ
-- "., ~',J(
-- '"' ~:::....
t.;..{::::., )
-,;.:.j ...,...."'
\~ '- f?"
1973-1979
::\
- -- ~~;0.>~<&@\
"'<tl:2.~ /1
1979-1981
WIGGINS PASS
A
\3
~
~
o
'd
Vegetated
<:::::::::::::: 0 =::::::::::.
Dave loped
Sparsely vegetated beach
(f/jj) Submerged delta; approx. -3 ft MSL
o Submerged delta; approx. -6 ft MSL
. Erosion
~ Accretion
Wiggins Pass: 1927 to 1981. Note the
ebb channel and channel margin bars to alternately
north and south. Massive shoreline changes on the adjacent
beaches are correlated with ebb tidal delta dynamics.
43
Figure lO.
tendency of the main
shift
shoreline adjacent to the pass experienced cyclic periods of erosion and
accretion that were related specifically to pass dynamics. As the ebb
tidal delta shifted north from 1962 to 1969 in front of Barefoot Beach,
the beach accreted almost 300 feet behind it. Yet, during the next 12
years nearly 200 feet of the new beach eroded as the ebb tidal delta
shifted back in front of Del Nor Wiggins State Park on the south side of
the Pass. As indicated by the sequence of changes observed at Wiggins
Pass, accretion typically occurs where the presence of an ebb tidal
delta shelters landward beaches from direct attack by waves. Erosion
typically occurs on the side of the pass not directly sheltered by the
ebb tidal delta.
Clam Pass: Clam Pass separates the Vanderbilt Beach unit to the north
from the Park Shore unit to the south (Figure 11). It flushes a small
but elongated system of shallow bays and mangrove swamps behind the
narrow barrier ridge along that section of the coast. Clam Pass is a
wave-dominated pass that is subject to periodic closure by littoral
drift (e.g. Clam Pass closed at least three time during the 1960's and
70's).
Clam Pass migrated north during the past 50 years. Earlier passes
visible to the south on historic aerial photographs were closed by spit
growth and storm overwash. The sites of these former tidal passes were
heavily invaded by Australian Pines ( Casuarina equisetifolia) during the
1960's and 1970's. The dense Australian pine canopy and heavy litterfall
has restricted the formation of dunes in this area. The opening of nearby
accessory channels during storms is common at Clam Pass. The "no name"
storm of June 18, 1982 breached the spit 500 feet to the south of Clam
pass. The accessory channel was closed quickly by northward littoral
drift and overwash.
During the 30 year period of aerial photographic record the submerged
flood tidal delta inside Clam Pass was colonized by mangroves, forming a
small island that has continued to grow. Colonization of flood tidal
1
~
44
1952
r-
r '
1
1952 - 1973
Figure 11. Clam Pass: 1952 to 1981.
Sparsely vegetated beach areas
were invaded by Australian 9ine,
Casuarina equisetifolia, during
the 1960's and 1970's. The flood
tidal delta inside Clam Pass was
colonized and vegetated by man-
groves during the same period.
45
...... """. ."'.....'"
1973 - 1981
~@~
o
... -
1000
FEET
CLAM PASS
~.'~. ,-', \legetated
\j!j}l VI
:..
2000
1
@ Developed
@ Sparsely vegetated beach
CD Submerged delta; approx.-3 ft MSL
o Submerged delta approx-6ft MSL
. Erosion
~ Accretion
. Australian pine
deltas and overwash fans by wetland species is an important process in
maintaining biological productivity along wave dominated barrier coast-
lines. Studies in North Carolina indicate that over 50% of barrier
coastlines may have been the site of a tidal pass or the site of an
extensive overwash fan in recent history (Cleary and Hosier, 1979).
Doctors Pass: Prior to 1960 Doctors Pass was a small, wave-dominated
tidal pass similar to Clam Pass in size and the volume of water exchanged
(Figure 12). The morphology of Doctors Pass suggests that it migrated
several thousand feet to the south over the past several hundred years.
Prior to stabilization about 1960, the location of the Pass had always
been temporary and subject to closure if the elongated spit to the north
were breached.
Between 1927 and 1952 the shoreline on either side of Doctors Pass eroded
an average of 300 feet. The stability of the beaches between 1952 and
1962 indicates that erosion slowed during that period. In 1960 two 500
foot jetties were constructed to stabilize the position of the Pass.
The jetties were designed by Per Bruun to allow natural bypassing of
sand to the south. Narrow channels through the mangrove swamps behind
Doctors Pass were widened and deepened for navigation and development.
In the two years following jetty construction, the beach on the south
side of the Pass receded 150 feet. The erosion was due to the inter-
ruption of the littoral drift by the jetties. During the 1960's sub-
division construction widened the narrow barrier ridge north of Doctor's
Pass from 200 feet to 1,000 feet by dredging and filling. Nearly
contiguous seawalls and groins were constructed on both sides of the
Pass. Between 1962 and 1973, 150 to 200 feet of erosion occurred on both
sides of the Pass.
Since 1973, accretion has occurred on the north side of the Pass. This
is a result of the trapping of southerly moving sand by the north jetty.
However, the interruption of this southerly littoral drift further
exacerbated recreational beach conditions on the south side of the pass.
By the early 1970's the wide sandy beach that had existed in the 1950's
and 1960's had mostly disappeared.
46
@ Developed
o Sparsely vegetated beach
CD Submerged delta; approx. -3 ft MSL.
o Submerged delta; approx. -6 ft MSl
~ Erosion
~ Accretion
Doctors Pass: 1927:to 1981. Prior to dredging and filling in
the 1960's Doctors Pass was similar in cross section and vol-
ume of flushing to Clam Pass to the north. Two 1,000 foot
jetties were constructed to stabilize the Pass about 1960.
47
1927 - 1952
c:.:~~.;~}
1952 - 1962
~ 0 ===<:::::::;:>
o
I::. r-.
1000
2000
3000
J
-
FEET
Figure 12.
,.....
'\. ......_-....
.....---_J
1962 - 1973
1973 - 1981
DOCTORS PASS
(3 Vegetated
Gordon Pass: Gordon Pass separates the Naples headland to the north from
Keewaydin Island to the south (Figure 13). Gordon Pass was dredged in
1958 and 1967. It flushes two moderate size embayments (Naples Bay and
Dollar Bay) and also receives the freshwater discharge of the Gordon
River and Golden Gate Canal.
Like Wiggins Pass. Gordon Pass exhibits a mixture of wave-dominated and
tide-dominated features including evidence of recurved spit formation and
pass migration as well as a well developed ebb tidal delta. Between 1927
and 1952 the throat of Gordon Pass shifted several hundred feet to the
south. During this 25-year interval accretion occurred on both sides of
the Pass with north Keewaydin Island building seaward 500 feet. Erosion
and the widening of the throat of the Pass occurred during the 1950's as
a result of channel dredging and the construction of a 1.400 foot jetty
on the south side of the Pass. The dredged sand was pumped onto the
beach at north Keewaydin Island. widening the beach an average of 350
feet. Four groins constructed north of the Pass during the 1950's
promoted limited accretion soon thereafter. During the 1960's four more
groins were installed. Two additional groins were added in the 1970's.
Although groins tend to cause localized accretion in the nearshore
zone and thus stabilize the shoreline that is immediately adjacent, they
also tend to create a deep trough immediately seaward that can inhibit
longshore bar formation and migration. The groins north of Gordon Pass
appear to have caused the formation of a trough that separated the ebb
tidal delta from the beach to the north side of the Pass. This deep.
artifically created. trough became more pronounced between 1973 and 1979.
By 1979 the trough had become a major conduit by which sand was transported
into the Pass and removed from the littoral drift.
Hurricane Pass and Vicinity: A myriad of short, overlapping coastal
barriers enclose an area of extensive shallow bays and tidal creeks along
the south central sector of the Collier barrier coastline. At present,
three tidal passes exist in this vicinity: Hurricane. Capri and Big Marco
Passes. These passes separate Keewaydin. North Coconut, South Coconut
48
."IIi";~~:~~~~t.th~~(iiB~IT
'\......... '\, )
"..:..:.;,-:;.,
"(::~ /
,,-::~ /
"".~./
1927-1952
~. .:::.>y
t.......J...
r/':\".i
I ~.,,;
I
\-... /'
I
I
I
/
"
(
/
,.../
- -'
I
195 2 -1 962
,
/':l
.... (.'.":,:.1 1
'\ \'::'.::.~ I
\ Y....'! I
\ (") I
\ I
.....
"-
\
\
/
/
/
/
/
"
.....-
1962 -1973
Figure 13.
....
'\,
l I
....-""'" -, ,..--"
-
'"
-_/
/'
1973-1979
_/'
1979-1981
GORDON PASS
(f;':j Vegetated
~
'=-f'N\
v-'-~
-
N."
\:Y
8',
"",'' .-..,
,'"''
m....
.' ",
,0
o
.
~
Developed
Sparsely vegetated beach
Submerged
delta; approx. -3 ft
Su bmerged
delta; approx. -6 ft
Erosion
o
1000
2000
3000
I
Accret ion
FEET
Gordon Pass: 1927 to 1981. The throat of Gordon Pass
widened after extensive dredging occurred inside the
Pass during the 1950's. A 1,400 foot groin was con-
structed on the south side of the Pass about 1962.
I ~
and Marco Island (Figure 14). Big Marco Pass has the largest cross
sectional area and therefore dominates tidal flushing in the area. The
geomorphic history of Big Marco Pass will be discussed in the next
section.
Massive shoreline changes have occurred in the vicinity of Hurricane Pass
since 1927. Coconut Island was 3.75 miles long in 1927; during the next
forty years it was breached in two places by the formation of Hurricane
and Capri Passes. The volume of tidal flooding is a function of the
tidal prism or surface area of enclosed enbayments times the mean tidal
range. By increasing the total cross-section area of tidal passes in the
vicinity, the new passes reduced the current speeds and volumes of water
exchanged by the former tidal passes, Big Marco and Little Marco Passes.
Little Marco Pass migrated south after 1927 as a result of the reduced
tidal forces and the release of hydraulic controls on its position.
Coincident with the migration of Little Marco Pass, the southern tip of
Keewaydin Island grew over 0.5 miles in length. From 1952 to 1981
Keewaydin Island continued to grow south. adding an additional one mile
of beach. The southerly growth of this spit slowed at the point where
Little Marco Pass became an accessory channel to Hurricane Pass during
the late 1970's.
Since 1927 the majority of the sand transported south along Keewaydin
Island in the littoral drift system became tied up in the accreting spit
and ebb tidal delta of Hurricane Pass. The capture of sand in the
vicinity of Hurricane Pass caused massive downdrift erosion on Coconut
Island. From 1927 to 1981 Coconut Island eroded approximately 1,200
feet. By 1973 south central Coconut Island had been narrowed to the
point where it was easily breached during a storm creating Capri Pass.
Some of the sand eroded from Coconut Island was transported a short
distance to the north in the form of an accreting spit that by 1979 had
joined Cannon Island and closed a major channel in Hurricane Pass.
Overall, large fluctuations in the shorelines and continual reorganiza-
tion of tidal flushing routes were the trends in the Hurricane Pass area.
These trends can be expected to continue in the future.
l .
50
r
, " .., .' "
~~ 0
~~
2 3
4
1927
1000 FEET
f
i~i~\~~~~~!{'~
~~:~~'::- \.
. . :..:-:(
. .'. <-;<:::::::::::::\
........., ",\.......)
'" ". ...............~..~..:..:....:-.:..:-:.. "/<::::::::::::
........ .. . .. . . .. .:0\ A.. .. . . .
"-''''.................................... ,\... .......)
".......,........, :t;>
- '<~\1~0 ..-7~
'\:.:::.:.:::., /Y" \.\.
"-...;. ,/' J')
<..:.:. ..:::::1 ;v.
C'~
/)fi'
,0
~U'
U'
1927 - 1952
::.....:)/!FFfJ;-2s.
'. '.' . .'. "i;' \
% =i2J!iG2/)je
I:J
~8
8
l;:'
r' ((
I:}: 1 ~ I"
V' :-:'l--,
fl' .c... (:0
10 ..~
'9>
III
III
1952 -1981
Figure
14.
Hurricane Pass
storm breaching
rier islands in
and Vicinity:
caused
the locale.
1927 to 1981. Spit growth
massive reorganization of the
See Figure 10 for key.
and
bar-
51
Big Marco Pass: Big Marco Pass separates south Coconut Island from Marco
Island to the south (Figure 15). It is a major pass that contributes to
the flushing of over 27 miles of coastal bays, tidal creeks and wetlands.
The pronounced ebb tidal delta and the characteristic seaward offset of
the island on the downdrift side indicate that the Pass is tide-dominated.
The ebb tidal delta of Big Marco Pass is one of the largest in southwest
Florida, containing over 25 million cubic yards of sand.
Between 1927 and 1962 the main ebb channel of Big Marco Pass shifted
about 300 feet to the south. This resulted in severe erosion along the
inlet shoreline of Marco Island. During the same period, the onshore
migration and attachment of swash bars from the ebb tidal delta caused
600 feet of accretion on the northwest tip of Marco Island. The new land
was extremely low in elevation. As the ebb tidal shifted in position
between 1962 and 1969 the protection afforded by the shallow water was
removed. As a result approximately 300 feet of beach eroded adjacent to
the pass at the northwest tip. Over the same period 100 to 250 feet of
accretion occurred in new areas protected by the migrating swash bars of
the ebb tidal delta.
By 1969 the main ebb channel of Big Marco Pass had recut a new pathway
directly offshore. This natural shift in position released a pulse of
sand in the form of swash bars that migrated to the southeast towards
Marco Island. The natural bypassing of sand benefited beach areas south
of the opening to Clam Bayou. In the meantime the northwest tip of Marco
Island continued to erode. From 1973 to 1981 an average of 300 feet
eroded, which realigned the shoreline in the position it occupied in
1927. Massive and frequently changing cycles of erosion and accretion
on north Marco Island have occurred throughout the period of record.
This cyclical trend is expected to continue in the future.
52
.:.
<'
.,,--/-""',
c......./ ().
......" ~/.:::':'.:.\
" ~.:.::-:::.::-:::::.::-::
\, \::::'::'~::)
I \........1
I t:.::::.:/::.::..
\ l:. .:..f
\ r:::::':::::'{
\ f:/.:::::.:t
I V':::::::/
I {:/::.::-J
\ (:/::::1
J (/.:::'$
\ r::/ (.~
~'" QZU5UiS/
,.
1927 -1962
~
';',' . " ./-',"\
f(.'. .:. '.'j \
1'-;....../
-\"j \
I .<?\
\ 1.':....1
.,\ ~::::::::::)
\ <;:.:..:......,
)JJfj;/
1/,:::::3
( (/:::}/
J .... ":'J
\ ~:::::'JI
~:':':':{:,
\\)r
\ l """
\ \
" \
" '-
'- "-
__.J
1962 - 1969
Figure 15.
'-
"
'-
'\
\
I
)
J
(
\
\
~11
1)(
f::) I
\:>~)
\~
\ \
\-:=\ \ ~.-:;..":,,> ,....
\::10,." /' ~..:..;;:.;;..:..~.z..::.;;......'\1
'\::;~ "..J "-
, '<.;:~BQt?)_ -----/
0'--....
1969 - 1973 ~
/",
,J
--
.....'"
/
I
{
(
\
\
1
/
I
I
I
(
\
...........
;-_./ \
I I
I \
\ )
\ 0'K
\ V'.V
\. h>
'\ .(J
I l::i
I ",,';
I ) ;-
) / ~ - - ---
/ . ::::'~',~. -;-,,:r-:'.~r ."
/ /I.'. ................"'=":~.........;.- --
/ . " '.~- --:"'''':-:0--_ _
I I "..... _ _--- ---
If 1,....-- ---
,J ../
o
2
3
"
I
1973 -1981
1000 FEET
Big Marco Pass: 1927 to 1981. Massive erosion and accretion
occurred on Marco Island in response to the changing shape
of the ebb tidal delta. See Figure lO for key.
53
(
I
f
r
Caxambas Pass: Caxambas Pass separates Marco Island to the north from
Kice Island to the south (Figure 16). The Pass flushes several shallow
bays and numerous dredged canals to the east. Prior to 1952 a well
developed ebb tidal delta existed seaward of the Pass. The delta pro-
moted natural bypassing of sand from Marco Island to Kice Island and also
allowed the transport of sand from the shallow nearshore zone on the
south side of the Pass back to Marco Island. In the early 1950's a
seawalled missile tracking station now known as the "compound" was
constructed on the southwest tip of Marco Island. The seawall quickly
became exposed to daily tidal action and attack by waves.
Historical patterns of deposition in the nearshore zone have resulted in
the gulf shore of Marco Island being offset seaward compared to the
barrier islands to the north and south. This offset creates a delicate
balance between sand stored in the nearshore zone and on the beach. The
recent history of Caxambas Pass attests to this.
Stephen (1981) related morphological and functional changes that occurred
at Caxambas Pass in the past 30 years to man induced alterations of the
south Marco shoreline. Fed from the eroding beach in front of the
seawall compound, the ebb tidal delta shifted to the south between 1952
to 1962. Between 1962 and 1969 the connection of the ebb tidal delta to
south Marco Island was breached. causing the delta to migrate to the
southeast toward Kice Island. The consequent effect on the beach of
south Marco Island was severe. Over 400 feet of erosion occurred on
south Marco Island from 1951 to 1981. Stephen's (1981) study of Caxambas
Pass showed that construction of the "compound" on south Marco Island in
the early 1950's probably increased wave energy in the immediate vicinity
and very likely caused the massive redistribution of the ebb tidal delta
depicted in Figure 16. His conclusion, based on available evidence, was
that the construction of the vertical seawall "compound" adjacent to the
Pass indirectly caused the recession of the shoreline of south Marco
Island.
54
~,oI;""
.-..-:
;' -~~
/ ~r\
..... \'.:.;~
1927 - 1952
\:::::::::::::-~
\...... .":.\
i:);'~ _:.;.
I .........J
";"';"f
{ f,;-:?'>
I '(=I
\ l:,;..
\ 4':')
{.-:.~
\. ~(}J
~ "'< ThCillilltS'z:;:-?
1952 - 1962
1962 - 1969
Figure 16.
1969 -1973
1973 - 1981
-' .~~~-=....
",. '.~.
~ /..~
~"... .,...<(:/:::/
/. .. /.'..............,;1
10.:.... ., .:-:.::::::::';';"-'':''''
\. '. . "J,,'''
~t:l:); ;;.
''\ -,
\a~
0<' \ $ -::-:::>
" " c e /'f.1
~ .../
r.:\ /~:.;
C':':':\. __ /..:./:i
,..~.- r.-.....
- ,~:::.~'\ ...............
...... ..,.,.,.... ....../
":{4iji:j'}
CAXAMBAS PASS
~@
~
@ Vegetated
~ Developed
(] Sparsely vegetated beach
CD S ubmerged d~lta ; approx. -3 ft. MSL
o Submerged delta; approx. -6ft. MSL
. Erosion
~ Accretion
o
2
4
6
I
1000 FEET
Caxambas Pass: 1927 to 1981. Seawall construction on south
Marco Island and the separation and southeasterly migration
of the ebb tidal delta caused erosion on south Marco Island
after 1952.
55
Blind Pass to Cape Romano: Figure 17 depicts the southwest portion of
the Cape Romano complex. In 1927 the Morgan Island area looked much the
same as it did in 1981. Without the aid of a sequence of aerial photo-
graphy there would appear to have been only minor changes in the position
of the shoreline since the area was mapped in 1927. An aerial photo-
graphic sequence however showed that Morgan Island eroded completely
between 1927 and 1952 and then was subsequently reformed. In addition,
the tip of Cape Romano fluctuated over 1,500 feet during that period.
Between 1927 and 1952 approximately 400 feet of beach eroded from Morgan
Island. Erosion and landward migration of the barrier ridge on Morgan
Island during that time was probably related to the passage of numerous
tropical storms in the 1940's. After 1952 the erosion and southerly
transport of sand from Kice Island fed a growing spit near the 1927
position of the original Morgan Spit. The presence of a spit feature at
the south tip of Morgan Island is a cyclical phenomenom related to storm
frequency and transport of sand into the Cape Romano shoals. Aerial
photographic evidence suggests a high probability that the present Morgan
Spit will erode in the near future and be redistributed as subtidal
shoals in the nearshore zone.
Cape Romano shoals lie at the terminus of the Collier barrier coastline.
The shoals are a wide and shallow sand deposit that extends due south
approximately 5 miles from Cape Romano. Much of the sand in the shoals
was deposited over centuries of transport and reworking of sand from the
barrier islands to the north. Sand in the nearshore zone of Kice and
Morgan Island will continue to be transported into the Cape Romano shoals
in the future.
Summary
The major tidal passes of Collier County can be categorized by their
physical characteristics and history of morphological change as wave-
dominated or tide-dominated. Wave-dominated passes (e.g. south Morgan
I
I
\
56
1927
C~8:~:::~""
':. ~.:~~~~.). . ~ .~~ :.~~ .a~':~:' ~:~ ~..\:.~~,;'\.,.1.,-\'~)\ ~ :..,~:~:'I
.~, ~i~:..... .....~ ...~::. ; ... ~"l'-~ ~i:*t ;~':~';~'..'A:} ~:~) ~:"~ ,__'';'1.'
~~'~ ~~~~. ..~ ~.~.;~-) '~'.~:,~:;.; ~ '~~ ~..: -...~ :--:. ~~; ....~ ~ ~
"""'-,':-"",\' ~ "'\'-~~;' :.... ..~..."y.,"'). '..~~.,-"","\~," ",'0
...~~.'.....~'...;.1'_ .~it, ~''''''.. r,;"1\:-"~ ~).....~, ...\....'.........y.., -l""
1 ,r, .~:".),,\)....f\...:\;;-~..~I\~\..'...,....~~~..,.... ~~...
-~.~*\.~j~.~, '-,.' ~"'... ""'\')~. ""\,..
-, .. '., - - - ~.~"'\...... 'L ~ -\:=~..-~ ",\, .;~:,..... ::.......... ....:.-.. .......
~ .....'"\ "'i .:".)"",
~3~~~
-.. .,,\', ""\"" ""\
-.".;......,...
~._.:....-r. -,
~,.)"-\. <to
""'
'J . ' . . , ". l' 'y) ~ "1'\' . ')., "..,
,. ~~;~-:;...\.:..._".. ." l "\" ",'"
1927 - 1952
'b
1952 - 1981
Figure
17.
Blind Pass
Sequences of
and erosion
portions of
ardous for land
10 for key.
to Cape
spit growth,
have made the
Romano: 1927 to 1981.
storm breaching
narrow upland
Morgan Island extremely haz-
development. See Figure
,@
~
3
I
o
57
1000 FEET
Pass and Little Marco Pass) have been subject to rapid migration along
the coastline. The rate of migration is in the range of 150 to 200 feet
per year. The newly accreted spits on the updrift sides of the passes
can be wide or narrow depending on sand supply. Regardless of width
they are always low in elevation and subject to storm flooding. Under
storm conditions the passes are subject to closure with the potential
existing for a storm to breach the island and form a new pass in the
vicinity. Clam Pass and Blind Pass are the other examples of wave-
dominated passes in Collier County.
At tide-dominated passes a larger tidal prism and stronger ebb tidal
currents promote the growth of shallow sand deltas on their seaward side
(ebb tidal deltas). Periodic adjustments in the size and shape of the
deltas control cycles of erosion and accretion on the adjacent beaches.
Big Marco Pass. Caxambas Pass and Wiggins Pass are tide dominated passes.
At tide-dominated passes the ebb tidal delta dissipates the energy of
approaching waves by causing them to shoal and refract around the delta.
A cycle of channel migration and then recutting in its former position
releases large "pulses" of sand to the nearshore zone that. contained in
swash bars, can migrate shoreward and become attached to the beach. For
this reason accretion often occurs on the sheltered beaches behind the
delta. As sequential mapping of pass dynamics showed. minor hydraulic
readjustments of the passes can. however, cause the new beaches to be
eroded quickly with the sand being reclaimed by the submerged ebb tidal
delta.
Several passes in Collier County are difficult to categorize because of
man's alteration of their natural processes by the construction of groins
and jetties. Jetties were constructed at Doctors Pass in 1960. Longshore
currents to the south were subsequently interrupted, causing erosion on
the south side of the Pass. Groin and jetty construction at Gordon Pass
caused partial dissipation of the ebb tidal delta and decreased stability
of the adjacent beaches. Artificial sand bypassing by periodic dredging and
58
disposal on the south side of the Gordon Pass is currently accelerating
the loss of sand available to beaches of south Naples. A seawalled
"compound" constructed at Caxambas Pass in 1952 caused the redistribution
of the ebb tidal delta to the south and also caused massive erosion on
south Marco Island.
59
SECTION 8
TRENDS OF SHORELINE CHANGE
Introduction
When sand is transported away from a stretch of beach in greater quanti-
ties than other sand is transported to the beach, the shoreline recedes
and erosion is said to have occurred. Under the converse circumstance
the shoreline builds seaward and the beach is said to have accreted.
Erosion and accretion are parts of a cumulative process that operates over
a long period of time. This process, however, is immediately responsive
to daily alterations in wave activity, tide level, and the shape of the
beach. It is possible to measure significant changes in the position of
the shoreline on daily, seasonal, yearly and decennial time scales. This
section describes shoreline changes in Collier County on the yearly and
decennial time scales.
Methods
In order to evaluate long term trends of shoreline change, historical
aerial photographic coverage was obtained for the Collier barrier coastline
for the years 1952, 1962, 1973 and 1981. U.S. Coast and Geodetic Survey
"smooth sheets" delimiting hydrographic and topographic contours and
dating back to 1885 were also utilized in the shoreline change analysis.
Seventy-three distinct reference transects were established on each set
of photographic imagery. The reference transects were drawn perpendicular
to the shoreline and were spaced at approximately 3,000 foot intervals.
Horizontal control was obtained by using easily definable and consistent
points (e.g. the centers of tree canopies and the intersection of road
centerlines that were identified on each set of aerial photographs).
Hydrographic and topographic charts were corrected to a common scale
with the aerial photographs (111 = 1,000') using the overlay projection
method. Distances were measured from the reference points to the high
60
water line for each set of imagery. The high water line is approximated
by mapping the wet sand mark on the aerial photographs. Other researchers
have found that the wet sand mark is identifiable as a distinct change in
the grey tone on the aerial photographs and that it does not differ
significantly in horizontal position from the mean high water line when
used to calculate shoreline changes (Dolan, ~ al, 1980). The resulting
comparisons of shoreline position were plotted on graphs that exhibit
shoreline change as a function of position along the barrier coastline.
The raw data are reported in Appendix 2. Techniques of reference
transect location, measurement, analysis and interpretation generally
followed those of Stafford (1971), Dolan ~ al, (1977 and 1980) and
Hayden ~ al, (1979a and 1979b).
Rates of shoreline change were calculated from the raw data at each
photographic reference transect for the following intervals: 1885 to
1981, 1927 to 1981, 1962 to 1981, and 1973 to 1981. These data were
termed net rates of change. At each reference transect the mean of the
net rates of change (M) was calculated. Although this mean is an average
of both short and long term photographic intervals it is heavily weighted
towards the more recent intervals. The resulting value can therefore be
considered to be a short-term weighted mean of the rate of change. The
mean (M) is graphed for the Collier barrier coastline in Figure 20.
In addition to calculating net rates of change, rates were also calcu-
lated for the following intervals: 1885 to 1927, 1927 to 1952, 1952 to
1962. 1962 to 1973, and 1973 to 1981. These data were termed cumulative
rates of change (m) and are considered to be a better estimate of the
magnitude of change in anyone year since the intervals are shorter than
those used to calculate the net rates of change. Shoreline changes
should tend to be more uni-directional over shorter intervals; therefore,
the rates of change would tend to be higher in magnitude. For this
reason cumulative rates of change were used to calculate the standard
deviation of the rate of shoreline change (SD).
61
In order to express the potential rates of shoreline change at each
reference transect. the mean net rate of change (M) and the standard
deviation (SD) were added together. The result expresses the potential
for shoreline change at any given transect during anyone year. This
value (M & SD) is graphed in Figure 20. The technique of analysis and
interpretation of potential rates of shoreline change was adapted from
Dolan et al. (1977).
r'
In addition to aerial photographic analysis. recent beach changes were
evaluated using ground survey techniques. Beach profiles were surveyed
in the field at 17 locations along the Collier County barrier coastline
during October 1982. The profiles extended from approximately mean low
water across the intertidal and backshore portion of the beach into the
dunes or developed upland area. The profile stations were established at
sites surveyed by the Florida Department of Natural Resources in March
1973. Nine of the profiles were chosen as representative of beach
changes along the altered or developed coastline of Collier County over
the past ten years. Beach changes following the "no name" storm of June
18-19. 1982 created difficulties in the interpretation of the comparative
profiles. The beach had not fully re-equilibrated with the typical fall
beach when the profiling was conducted. Ridge and runnel features
associated specifically with the "no name" storm were present at many of
the 1982 profile locations.
Results and Discussion
Since 1885 the position of the shoreline along the sixteen miles of
barrier coastline between the north County line and Gordon Pass fluctuated
landward and seaward of its present position over a range of 25 to 300
feet (Figure 18). The north central sector of this shoreline (Vanderbilt
Beach unit) receded 50 to 200 feet while the northern and southern
extremes of this shoreline (Barefoot Beach and Naples) experienced
stability or small fluctuations between erosion and accretion. Moderate
shoreline fluctuations (200 to 300 ft.) occurred adjacent to all of the
tidal passes.
62
.,
...,
~
Miles
1____...
o 1 2 3 4 5
'"
'"
..
A.
c:
o
'V
...
o
Cl
,~
II:
...,8
.....
I
I
400 I
c I
0 I
en I
0 I
~
W 200 I
I
I
I
0
(ft)
C 200
.Q
.....
~ ~\~
()
()
<{ 400
KEY
Erosion
Net Shoreline Changes
n
l:..:J
0,
'"
o
.
Long term
Moderate term
Short term
Recent
4-
A
.
o
1885 - 1981
1927 -1981
1962 - 1981
1973 - 1981
Figure 18. Net shoreline changes along north Collier County:
1885 to 1981.
63
The position of the shore along the south Collier County barrier coast-
line (Gordon Pass to Cape Romano) fluctuated landward and seaward over a
range of 200 to 1.200 feet, exceeding shoreline changes in the north
County by approximately one order of magnitude (Figure 19). In the south
County recession occurred along central Keewaydin Island, Coconut Island
and Kice Island. Massive fluctuations (ranging from 800 to 1,200 feet)
occurred along extreme north and south Keewaydin Island, north Marco
Island and Morgan Island. These changes were associated with the dynamics
of the adjacent tidal passes.
The potential for shoreline recession averaged 2 to 10 times higher in
south Collier County than in the north County (Figure 20). The highest
potential for shoreline erosion was measured at north Marco Island (-53
ft./yr.). South Marco Island, the Coconut Island group and north Keewaydin
Island exhibited erosion potentials of over -25 feet per year. The
erosion potential at Kice and Morgan Island ranges between -15 and -26
ft./yr. In the north County the highest potentials for shoreline erosion
were measured in the immediate vicinity of the passes. and ranged between
-13 and -15 feet per year. Along the Barefoot Beach and Vanderbilt Beach
units. potential rates of shoreline recession ranged from -3 to -8 feet
per year. Along the beach of north Naples, erosional fluctuations ranged
from 0 to -3 feet per year. The southern three quarters of the Naples
headland possessed the lowest potential for shoreline recession along the
entire Collier barrier coastline. Shoreline changes in each of the
individual barrier units of the Collier County coastline are discussed in
detail in Technical Report 84-4.
64
.
:.
,
600
.... 0\
...~
1 ......,
1 ......,
......,
......,
."".,
... 1
<:'1
.j!~
.
c
o
.-
(J)
o
"-
UJ
200
(ft) 0
C 200
o
I' ,
I '
I I I
\IJl ~\ /
1 ~
\
, \
. '~ I
\ Ii !
\ I \ I:
,. \~II
\ I \ II
, I' \ r
I I i
\ I fi
II II
'\: ...
.
r
i
~
i I
! I
\: I
i I
i I
~
I
I
I
I
I
..
I
I
I
.
1"-'
.......
Q)
"-
()
() 400
<(
60
Erosion
CJ Long term
D Moderate term
[] SharI term
. Ree ent
~
,
.
t
Miles
1____...
o 1 2 3 4 5
:.
o
~J
.... .1
..
u
...
" A
. . . .
. " I
.. .. l
: :: .. J
i
\
\
I
1
I
.
Net Shoreline Changes
4 1885 - 1981
A 1927 - 1981
. 1962 - 1981
o 1973 - 1981
Figure 19. Net shoreline changes along south Collier County:
1885 to 1981. 65
~
c:
.2
i)
...
u
u
~
o
c
.
E
o
II:
a~A
. . .
.
KEY
.
o
Potential Rate of Shoreline Change
Mean rate of change ( M)
o 1
Mean rate of change + Standard deviation (M+SD)
Miles
- ...
2 3 4 5
Figure 20. Potential rates of shoreline change, Collier County:
1885 to 1981. Note the difference in the range of
values between the north and south County.
~~
00
Summary
A graph was prepared to summarize trends in shoreline migration along
Collier County's barrier coastline (Figure 21). Fourty-four percent (17
miles) of the coastline has experienced a trend of gradual recession over
the past hundred years. Since 1885 these areas. which are concentrated
along the Vanderbilt Beach. Park Shore and Kice Island barrier units.
have experienced a steady landward movement of the shoreline on the order
of -1 ft./yr. to -8 ft./yr. About 6.5 miles of Collier County's coast-
line receded in the past at rates averaging less than -3 ft./yr. and
about 8.0 miles receded at rates greater than -3 ft./yr. Receding
shorelines are found along the relatively straight and uninterrupted
stretches of the coast where the supply of sand is limited and where
shoreline changes are dominated by the effects of waves. Future rates of
recession will be influenced by sea level rise. littoral drift and the
frequency of overwash. If storm and hurricane activity increases in the
eastern Gulf higher rates of recession along these beaches would be
expected.
In the vicinity of the major tide-dominated passes in Collier County,
cycles of beach erosion and accretion are controlled by the effects of
tidal currents and ebb tidal deltas that influence the wave energy regime
and the direction of littoral sand transport. Wave refraction around ebb
tidal deltas can control shoreline changes as far as 1.5 miles away.
Approximately 34% of the County's barrier beaches are characterized by
fluctuating shorelines. Exceptional rates of shoreline migration and
frequently changing periods of erosion and accretion have occurred along
these beaches. The rates of shoreline change typically range from +15
ft./yr. to -18 ft./yr. Fluctuating shorelines occur adjacent to the
major tide-dominated passes along the coastline yet are concentrated in
the south County where passes are larger and play a more important role
in controlling shoreline changes on adjacent beaches. Massive shoreline
fluctuation in these areas is expected to continue in the future.
67
~
,
DCA B
.
.
.
0..
o
Ie
.
E
o
II:
,~
I~
U
#I; I 0'
"0#(.1
'~ ==---
J
.
a~~
B
,
B
DAB AB D B
A
Miles
- ......
o 1 2 3 4 5
KEY
TREND IN SHORELINE MIGRATION
A
Fluctuating
-18 to +15 ft/yr
B
Receding
-3 to -8 ft/yr,
B' -1 to - 3 ft/yr
c
Stable
-1 to.1 ft/yr
D
Accretiona I
.1 to +8 ft/yr
Figure 21. Trends in shoreline migration, Collier County: l885 to 1981.
The categorization is heavily weighted towards recent shore-
line changes. The breakdown of categories by percentages is
as follows: A - 22%, B - 44%, C - l8%, D - 16%.
68
seaward slope and growing sand supply. Extreme southern Marco Island
will continue to recede as long as sand depletion continues in the
nearshore zone immediately seaward.
Kice and north Morgan Islands will continue to migrate landward. To
the south, Morgan Spit will very likely disappear during a major storm
and then slowly reform from sand eroded from Kice and north Morgan
Islands. Cape Romano Island will probably be stable in the future
because of its orientation.
71
SECTION 9
BEACH AND DUNE ZONE CHARACTERISTICS
Introduction
Beaches and dunes make up two of the most dynamic physiographic zones of
coastal barriers. The active beach zone is the coast's first line of
defense against attack by storm waves. The vegetated, dune/washover
zone is a resilient but flexible storm buffer that builds in elevation
as a result of storm overwash and dune growth yet releases stored sand to
the active beach when needed to dissipate the energy of storm waves. The
zones act together in an interdependent, sand sharing system that protects
both natural habitats and man-made structures located in the stabilized
back-barrier zone.
r
Natural vegetation plays an important role in coastal processes. The
plant communities of three large and relatively undisturbed barrier
islands in Lee County have previously been described (Cooley, 1955;
Herwitz, 1977; Morrill and Harvey, 1980). The coastal strand plant
community is an assemblage primarily composed of grasses and shrubs that
are subject to harsh environmental conditions and regular disturbance by
storm overwash. The dominant plant species are adapted to cope with the
stresses associated with salt spray, saltwater inundation and washover
deposition. Coastal strand plants playa major role in the stabilization
of this everchanging environment. The dense shoots and leaves, and fine
net-like root structures of Uniola paniculata and Panicum amarulum induce
sand deposition rather than scouring during overwash. In addition these
dune grasses trap blowing sand and promote dune growth between storm
events.
Methods
Aerial photography was used to obtain data on the characteristics of the
beach and dune zones. The widths of the active beach and dune/washover
l.
72
zones were measured at 73 photographic reference transects spaced approx-
imately 3.000 feet apart along Collier County's shoreline. The reference
transects were the same as those used to measure the shoreline changes
described in Section 6. The wet sand mark. which is clearly visible on
aerial photographs, was used to approximate the position of the mean
high water line. The width of the active beach zone was measured for the
years 1952, 1962, 1973 and 1981. In order to reduce variations due to
daily and seasonal trends in wave climate and sand supply at the time of
each photographic overflight, measurements taken along each transect were
averaged. Averaging beach widths over the time series also took into
account the effects of seawall and groin construction on beach width. If
"upland protection structures" increase local wave energy and cause a
narrowing of the beach where they are exposed to the swash of waves. then
an average of beach widths including earlier instances in which seawalls
were not present would be a better approximation of the width of the
beach on a particular transect.
The dune/washover zone was delineated based on vegetation and evidence of
storm overwash. Measurements of the width of the dune/washover zone were
made on April 1979 photographic prints at a scale of 1 inch = 100 feet.
Where that coverage was not available the most recent available aerial
photography was used. The width of the coastal strand plant community
was chosen as a measure of the width of the dune/washover zone. The
transition from the dynamic dune/washover zone to the stabilized back-
barrier was marked by the seaward limit of cabbage palms. The cabbage
palm. Sabal palmetto. is abundant in every major upland plant community
of local coastal barriers except for the coastal strand where it is
infrequent or absent (Cooley. 1955; Herwitz, 1977; Morrill and Harvey,
1980). It is a slow growing tree requiring 15 to 30 years to grow on
newly accreted land to heights and densities that are conspicuous on
aerial photographs. The cabbage palm is relatively intolerant of over-
wash, being able to withstand occasional but not repeated events (per-
sonalobservation). For these reasons the seaward limit of cabbage palms
was chosen to delineate the transition from the dune/washover zone to
73
the stabilized back-barrier zone. Where native plant communities were
not present, the penetration distance of historic storm washovers was
chosen as an alternate measurement. Although this measurement tended to
vary more along short segments of the coastline. it was considered to be
a good second choice.
In addition to measuring the width of the beach and dune zones. aerial
photography was used to identify and map the coastal vegetation of
Collier County's dune/washover zone. Plant associations were delineated
on the basis of plant dominance. The percentage of coastline vegetated
by each association was calculated. In areas where the dune/washover
zone has been disturbed by development. the percentage reduction in the
width of the active beach and dune/washover zone was also calculated.
Results and Discussion
The active beach occupies the zone between the mean low water shoreline
and the vegetation line. Where the vegetation line is absent any other
marked change in character of the environment (i.e. seawall, scarp) is
used to identify this zone. The active beach defines the zone that is
affected by waves and littoral drift at its seaward boundary and scour by
storm waves at its landward limit. The dune/washover zone extends from
the vegetation line to the landward limit of the coastal strand plant
community. Where delineation of the active beach zone is a relatively
simple procedure, identifying the landward boundary of the the dune/
washover zone requires a more detailed analysis of physical factors and
plant cover.
The results of the active beach and dune/washover zone measurements are
reported in Appendix 4. The active beach zone in Collier County averaged
99 feet wide between 1952 and 1981. Very little difference exists
between the average widths of the south and north County beaches (101
!
I
t.
74
feet vs 96 feet). Landward of the beach the mean width of the dune/
washover zone was 147 feet in 1979; this zone was, however, on the
average, wider in the south County (173 feet vs. 120 feet). The active
beach and the dune/was~over zones tended to be wider adjacent to Wiggins,
Gordon, Hurricane, Big Marco and Morgan passes. Along those shorelines
the average widths were 140 feet for the active beach zone and 255 feet
for the dune/washover zone.
The width of the active beach and dune/washover zones in Collier County
is primarily related to the local sand supply and to trends of shoreline
change in the vicinity. The zones tend to be narrowest along shorelines
categorized as receding (Figure 23). Elevations are low or moderate (4
to 7 feet) and the barriers are usually less than 200 feet wide. The
zones are widest along fluctuating shorelines (Figure 23) where the
sand supply in the nearshore zone is the greatest. The expanded width
is a result of rapid and frequently changing periods of erosion and
accretion. Wide, newly accreted areas quickly become vegetated with
coastal strand plants. A cycle of erosion, however, will usually cause
erosion of the newly accreted area as quickly as it formed (Section 9).
The elevation and width of the dune/washover zone is extremely important
in determining the frequency of disturbance by overwash. Suboceanic
Consultants (1980) determined a storm surge return period of 8.5 to 12
years for a still water level of 6 feet. Based on topographic maps. this
would mean nearly complete inundation of the dune/washover zone in the
south County and scattered occurrences of submergence along the coast of
the north County. Aerial photographic inspection indicates that overwash
occurs most frequently across narrow barriers less than 6 feet in eleva-
tion, such as Coconut and Kice Islands. Overwash may recur in these
areas every 1 to 2 years. The rate of recession of these shorelines is
controlled by the frequency of overwash. For this reason the lowest and
narrowest coastal barriers in Collier County are also the most rapidly
receding (Coconut Island -17 ft/yr. and Kice Island -13 ft/yr.).
75
Local variations in native plant cover are also an important determinant
of the condition of the dune/washover zone. Five vegegation types were
identified in Collier County's dune/washover zone (Table 3). Two were
sub-associations of the coastal strand plant community, and three were
anomalies produced by the naturalization of an exotic tree, rapid erosion.
and land development. Vegetation type 1 is a coastal strand sub-
association dominated by dune grasses and shrubs. Approximately 15% of
the length of Collier's barrier coastline is vegetated by the type 1
association. Another 13% of the coast has become invaded by monotypic
stands of Australian pine, Casuarina equisetifolia (type 3 association).
Casuarina quickly colonizes washovers and outcompetes herbaceous dune
plants to form dense stands with little or no understory. Along 24% of
the coastline a transition is taking place from vegetation type 1 to type
3. In these areas various stages of co-dominance between Casuarina and
herbaceous dune plants exist (type 2 association). These data indicate
that Casuarina has shaded and crowded out almost 5 miles of native
coastal strand vegetation since the early 1950's when it became a notice-
able element of the coastal strand habitat. Because of its wide range of
physiological and ecological tolerance and terrific growth rate, Casuarina
may become dominant along another 9 miles of coastline within this
decade.
Rapid erosion along several isolated shoreline segments (13%) in the
south County has exposed several plant communities more characteristic
of bays ide or central barrier locations. These communities make up
vegetation type 4. The primary plant community of this type is mangrove
forest. The largest part of Collier's barrier coastline (36%) has been
altered by man's land development activities including construction of
habitable and accessory structures, construction of seawalls and revet-
ments, clearing of native coastal strand vegetation and installation of
sod and ornamental landscapes. The plant assemblages in those areas were
classified as type 5.
I
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76
TABLE 3. DUNE/WASH OVER ZONE CHARACTER: BREAKDOWN OF
VEGETATION TYPES.
DUNE/WASHOVER ZONE CHARACTER (%)
TYPE TYPE TYPE TYPE TYPE
BARRIER UNIT 1 2 3 4 5 MILES
BAREFOOT BEACH 10 51 14 25 3.0
VANDERBILT BEACH 11 55 6 28 4.6
PARK SHORE 2 17 12 69 2.3
NAPLES 100 5.6
KEEWAYDIN ISLAND 16 28 46 10 7.9
COCONUT ISLAND 38 62 2.0
MARCO ISLAND 9 22 4 64 5.2
KICE ISLAND 11 89 2.4
MORGAN ISLAND 40 60 2. 1
CAPE ROMANO ISLAND 45 55 2.3
TOTAL MILES 5.5 9.0 4.8 4.7 13.4 37.4
% TOTAL 14.7 23.9 12.8 12.6 36.0
KEY
TYPE 5
Coastal Strand. Dominated by native grasses and shrubs.
Coastal Strand. Casuarina in various stages of community
invasion and dominance.
Casuarina Forest. Casuarina in near monotype condition.
Mangrove Forest. Understory of grasses and succulent
herbs.
Ornamental Landscape. Typically sod and ornamental
plants.
TYPE 1
TYPE 2
TYPE 3
TYPE 4
77
The comparison of the width of pre-development beach and dune/washover
zones with the setback of land development activities revealed that, in
general, coastal land development has reduced the total width of the two
zones by over 50% and in some cases by as much as 90% (Table 4). Coastal
land development limits natural functions of the beach and dune/washover
zones. For example the construction of a vertical seawall on the active
beach interferes with coastal dynamics by increasing the power and
turbulence of waves and decreasing the effectiveness of the beach to
dissipate that energy. In addition, seawalls prohibit overwash which is
necessary for the maintenance of a functional storm barrier. Seawalls
were identified as a cause of enhanced erosion at Vanderbilt Beach,
North Marco Island and South Marco Island (Sections 8 and 9).
Where man has altered the active beach zone, accelerated shoreline
recession and reduction of the recreational beaches have already occurred.
The potential for storm damage to structures on the beach is extremely
high. Where the dune/washover zone has been altered, its function of
sand storage and storm protection has been reduced. Increased loss of
sand from the dune/washover zone and higher potentials for damage to
structures can be anticipated in the future. Structures located behind
the active beach and dune/washover zones will not interfere with these
zones natural function. Only these structures can be assured of even a
moderate level of protection from damage by tropical storms.
Summary
The active beach and dune/washover zones in Collier County are subject
to periodic overwash and rapid fluctuations in the shoreline. Together.
a wide beach and vegetated dune field form a resilient but flexible storm
buffer that affords a partial barrier to storm waves but allows some
overwash and dissipation of wave energy across the zones. A naturally
vegetated dune/washover zone maximizes storm protection of the stabilized
back-barrier.
78
TABLE 4. COMPARISON OF BEACH AND DUNE WIDTHS WITH SETBACK OF LAND
DEVELOPMENT ACTIVITIES.
AVERAGE
SETBACK AVERAGE % OF
OF LAND REDUCTION IN
WIDTH OF DEVELOPMENT WIDTH OF
BEACH & ACTIVITIES BEACH AND
DUNE ZONE FROM MHW DUNE ZONE
f BEACH SEGMENT (FEET) (FEET) (%)
f LEL Y BEACH 360 90 68
VANDERBILT BEACH 202 40 80
NORTH PARK SHORE 199 200 0
SOUTH PARK SHORE 164 100 39
f THE MOORINGS 168 75 55
NORTH NAPLES 154 35 77
CENTRAL NAPLES 152 75 50
OLDE NAPLES 145 40 72
NORTH PORT ROYAL 165 85 48
SOUTH PORT ROYAL 144 40 72
SOUTH KEEWAYDIN ISLAND 371 350 6
NORTH MARCO SPIT 251 20 92
CENTRAL MARCO BEACH 180 150 17
1
i
79
By definition the active beach zone is affected by the swash of waves
on a daily or seasonal basis. The dune/washover zone is overwashed
periodically depending on the topography and peak elevation of the zone.
Overwash may occur as frequently as every 1 to 2 years or as infrequenly
as once every 30 years. Narrow dune/washover zones (less than 100 feet)
are found in the vicinity of receding beaches where the sand supply is
limited. Wide dune/washover zones (greater than 200 feet) are found
along fluctuating or accreting beaches where sand surpluses occur. In
those areas shifting tidal deltas can cause rapid erosion on adjacent
beaches.
Five vegetation types were identified in the dune/washover zone of
Collier County. These included two variants of the coastal strand plant
community (vegetation types 1 and 2), monotypic stands of a naturalized
exotic tree (type 3), several back-barrier plant communities exposed to
the Gulf of Mexico by erosion (type 4), and ornamental landscapes planted
by man (type 5).
The width of the pre-development active beach and dune/washover zones was
compared with the setback of land development activities. In general,
coastal land development has reduced the total width of the two zones by
over 50% and in some cases by as much as 90%. Those alterations have
caused (1) increased shoreline recession, (2) reduction in the width of
the recreational beach, (3) loss of sand stored in the dune/washover
zone and (4) increased damage potential to habitable and accessory
structures. Only structures located behind both zones will not interfere
with their natural function and can be assured of even a moderate level
of protection from damage by tropical storms.
~
80