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UFL/COEL-86\017
INLET EBB SHOAL VOLUMES RELATED TO COASTAL
PHYSICAL PARAMETERS
by
James N. Marino
Thesis
1986
INLET EBB SHOAL VOLUMES RELATED
TO COASTAL PHYSICAL PARAMETERS
By
JAMES N. MARINO
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF MASTER OF ENGINEERING
UNIVERSITY OF FLORIDA
1986
To my wife,
whom I love for her support
through yet another phase of my career.
To my parents,
for giving me the opportunity to develop my own character.
ACKNOWLEDGEMENTS
Many people have contributed to this work, giving of
themselves and their time. Above all, the author expresses
his gratitude to Dr. A. J. Mehta, chairman of the
supervisory committee, and to the other members of the
committee: Dr. H. Wang and Dr. R. G. Dean. Particular
thanks go to Mr. C. P. Jones for his much needed help and
sharing his insight.
Others have helped by providing information necessary
for the completion of this thesis, including Administration
Inc., Jupiter--Mr. C. Christian and Ms. L. R. MacDonald;
Coastal Planning and Engineering, Boca Raton--Mr. N.
H. Beumel; Department of Environmental Resources Management,
Miami--Mr. D. Ettman; Florida Oceanographic Society, Inc.,
Stuart--Mr. M. D. Perry; Ft. Pierce Port and Airport
Authority--Mr. M. Baggett; Gee and Jenson, West Palm Beach
--Mr. J. S. Yeend; Ponce de Leon Port Authority--Mr. D. M.
O'Brien; Port-Everglades Port Authority--Mr. R. T. Clapp;
Sebastian Inlet Tax District Commission--Mr. T. W. Smith and
Ms. J. Farrington; U.S. Army Corps of Engineers,
Jacksonville District--Mr. J. Lillycrop, Ms. B. Lancaster,
Mr. C. Stevens, Mr. R. Murphy, and Mr. Wm. Ivey.
iii
Special thanks go to Ms. Lillean Pieter for her
graphics, to Ms. Cynthia Vey for her technical typing
advice, and to Ms. Lucille Lehman and Ms. Helen Twedell for
their unending support in the Coastal Engineering Archives.
Gratitude is due to the United States Army and the
State of Florida Department of Natural Resources for their
financial support. Much of this research was funded under
DNR contract C3470.
My sincere thanks go to my peers who have helped me
with so much, particularly Mr. D. Mann and Mr. E. Cervantes
with whom I began this study.
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ................................. iii
LIST OF TABLES ................................... vii
LIST OF FIGURES.................................. viii
LIST OF SYMBOLS......................... ......... x
ABSTRACT............ ............ .. ................ xiii
CHAPTERS
I. INTRODUCTION.. ................ .... .......... 1
Rationale.................................. 1
Objectives................................. 3
Coastal Physical Parameters................ 3
General Physical Environment .............. 6
II. EVOLUTION OF EBB TIDAL SHOALS.............. 12
Introductory Note.......................... 12
St. Augustine Inlet........................ 14
St. Lucie Inlet............................ 16
Boca Raton Inlet...................... ... 19
Conclusion................................ 21
III. METHODOLOGY .... .......................... 23
Dimensional Analysis................... 23
Ebb Shoal Volume.......................... 29
Tidal Prism .............. ......... .... 32
Cross-Sectional Area, Width, and Depth..... 34
Wave Energy ......................********. 34
Volume vs. Prism Relationship............. 36
IV. RESULTS AND ANALYSIS............ 0......... 38
Physical Parameters....................*.. 38
Comparison of Volumes........... .......... 39
Regression Analysis ........... ............ 56
Results of Dimensional Analysis............ 58
Discussion..........................************.. 63
V. CONCLUSIONS AND RECOMMENDATIONS............. 67
Conclusions........... ...... ........... 67
Recommendations............................ 68
APPENDICES
A. INFLUENCE OF WAVE ENERGY................... 70
B. FLORIDA'S EAST COAST INLETS................ 73
St. Marys Entrance ....................... 75
Nassau Sound.................................. 77
Ft. George/St. Johns Inlet................. 79
St. Augustine Inlet..................... 81
Matanzas Inlet............................ 83
Ponce de Leon Inlet....................... 85
Port Canaveral Entrance.................. 87
Sebastian Inlet .............. ............. 89
Ft. Pierce Inlet.. ................... ...... 91
St. Lucie Inlet............................. 93
Jupiter Inlet.............................. 95
Lake Worth Inlet........................... 97
South Lake Worth Inlet...................... 99
Boca Raton Inlet........................... 101
Hillsboro Inlet............................ 103
Port Everglades Inlet...................... 105
Bakers Haulover Inlet...................... 107
Government Cut...... ....................... 109
REFERENCES......................... ...... ...... 111
BIOGRAPHICAL SKETCH .............................. 115
LIST OF TABLES
Page
TABLE
I-1 Origin of Florida's East Coast Inlets..... 4
IV-1 St. Marys Entrance........................ 40
IV-2 Nassau Sound.............. ................ 41
IV-3 Ft. George/St. Johns Inlet................ 42
IV-4 St. Augustine Inlet....................... 43
IV-5 Matanzas Inlet.......................... 44
IV-6 Ponce de Leon Inlet....................... 45
IV-7 Port Canaveral Entrance.................. 46
IV-8 Sebastian Inlet........................... 47
IV-9 Ft. Pierce Inlet ......................... 48
IV-10 St. Lucie Inlet........................... 49
IV-11 Jupiter Inlet............................ 50
IV-12 Lake Worth Inlet...................... ... 41
IV-13 South Lake Worth Inlet..................... 52
IV-14 Boca Raton Inlet.......................... 53
IV-15 Bakers Haulover Inlet.................... 54
IV-16 Dimensionless Parameters.................. 59
IV-17 W/D versus V Comparison.................. 63
IV-18 Shear Stress Comparison.................. 65
vii
LIST OF FIGURES
FIGURE
I-1 COASTLINE DISTANCE VS. WAVE ENERGY........ 8
1-2 COASTLINE DISTANCE VS. SHELF WIDTH........ 9
I-3 COASTLINE DISTANCE VS. TIDE RANGE......... 10
I-4 COASTLINE DISTANCE VS. NET SOUTHERLY
LITTORAL DRIFT RATE ..................... 11
II-1 ST. AUGUSTINE SHORELINE AND SHOAL
COMPARISON, 1937, 1975.................. 15
11-2 ST. LUCIE SHORELINE AND SHOAL COMPARISON,
1883, 1948, 1970.... ....... ......... ...... 17
II-3 BOCA RATON SHORELINE AND SHOAL COMPARISON,
1883, 1929, 1979............. ............. 20
IV-1 COMPARISON OF VOLUME ESTIMATES............ 55
IV-2 COMPARISON OF LINEAR REGRESSION ANALYSIS
RESULTS.......... ....... ............. ...... 57
IV-3 PLOT OF V/P VS. W/D WITH RESPECT TO Ac/ao2 61
A-I PLOT OF V/P VS. Hs2Tw2/ao2T2 WITH RESPECT
TO W/D................................... 72
B-1 ST. MARYS ENTRANCE, 1975.................. 76
B-2 NASSAU SOUND, 1954......................... 78
B-3 FT. GEORGE/ST. JOHNS INLET, 1978.......... 80
B-4 ST. AUGUSTINE INLET, 1979................ 82
B-5 MATANZAS INLET, 1978..................... 84
viii
Paae
FIGURE
B-6 PONCE DE LEON INLET, 1974................. 86
B-7 PORT CANAVERAL ENTRANCE, 1979............. 88
B-8 SEBASTIAN INLET, 1974.................. 90
B-9 FT. PIERCE INLET, 1975.................... 92
B-10 ST. LUCIE INLET, 1964.................... 94
B-11 JUPITER INLET, 1978............. ... 96
B-12 LAKE WORTH INLET, 1967................... 98
B-13 SOUTH LAKE WORTH INLET, 1979.............. 100
B-14 BOCA RATON INLET, 1981.................... 102
B-15 HILLSBORO INLET, 1961.................... 104
B-16 PORT EVERGLADES INLET, 1978............... 106
B-17 BAKERS HAULOVER INLET, 1969............... 108
B-18 GOVERNMENT CUT, 1978...................... 110
LIST OF SYMBOLS
a: Equal to log b
ab: Bay spring tidal amplitude
ao: Ocean spring tidal amplitude
Ab: Bay surface area; Maximum water particle displacement
Ac: Inlet cross-sectional area
b: Linear regression coefficient
CK: Prism correction coefficient defined by Keulegan
d: Water depth
ds: Bed roughness
D: Inlet depth at throat
Et: Tidal energy
E,: Wave energy
fc: Friction factor due to current
fw: Friction factor due to waves
ft: Feet
F: Force
g: Acceleration due to gravity
Hs: Significant wave height
L: Length; Wave length
Lo: Deep-water wave length
m: Meter; Number of fundamental dimensions; Linear
regression coefficient
x
I
mm: Millimeter
M: Littoral drift rate
n: Number of selected, governing physical quantities
N: Newton
Nij: Number of occurences in both the i- and j-domain
P: Spring tidal prism
PH: Hydraulic prism
PV: Volumetric prism
s: Offshore bottom slope
sec: second
SUM: Summation
T: Tidal period; Time
Tj: Wave period in the j-domain
T,: Weighted mean wave period
Ua: Alongshore current
uc: Water velocity due to currents
uw: Water velocity due to waves
V: Ebb shoal volume
Vmax:Cross-sectional inlet average maximum velocity
ws: Sediment settling velocity
W: Inlet width at throat
x: Equal to log P
R: Mean value of x
y: Equal to log V
7: Mean value of y
xi
yr: Year
p: Density of seawater
T : Shear stress due to currents
T : Shear stress due to waves
xii
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering
INLET EBB SHOAL VOLUMES RELATED
TO COASTAL PHYSICAL PARAMETERS
By
JAMES NICHOLAS MARINO
DECEMBER 1986
Chairman: Dr. A. J. Mehta
Major Department: Coastal and Oceanographic Engineering
Tidal inlets impact significantly on the local coastal
sedimentary budget. The general nature of inlet ebb shoal
development was examined through three case studies on the
east coast of Florida. Next, the ebb shoal volumes of the
eighteen inlet systems on the east coast of Florida were
estimated. Finally, the degree to which various coastal
physical parameters influence the ebb shoal volume was
investigated.
The case studies were those of St. Augustine,
St. Lucie and Boca Raton Inlets. It was found that ebb
shoals at these inlets evolved in quite different manners.
There is a general trend of decreasing ebb shoal volume from
north to south. A total of 420 million cubic meters of
sediment are found to reside in the ebb shoals of
xiii
------"
the eighteen inlet systems. Of that total, 83% resides in
four northernmost inlet systems. The ebb shoal volume, V, is
found to depend on the spring tidal prism, P, the inlet
width/depth ratio, W/D, the flow cross-sectional area, Ac,
and the tidal amplitude, ao. The effect of the width/depth
ratio on the ebb shoal volume signifies the role of both
inlet current and waves in influencing ebb shoal
development, as observed previously by Walton and Adams.
'Cairman
xiv
CHAPTER I
INTRODUCTION
Rationale
Tidal inlets impact significantly on the local coastal
environment. The inlet provides access to sheltered harbors
from strong ocean currents and waves, to both the commercial
and recreational user. The ebb tidal shoal is one of the
most dominant features of a coastal inlet.
The ebb shoal occurs at an inlet when sediment is
trapped offshore of the mouth due to various coastal
physical processes. The sediment is removed from the
littoral drift and deposited typically in a crescent- or
kidney-shaped formation. Once the shoal has developedit
can serve as a bridge of sorts, transporting material from
the updrift beach to the downdrift side, when conditions
permit. Since the shoal is typically a much shallower area
than its surrounding region, it also serves as an energy
dissipator. As ocean waves approach the shore, they break
and dissipate their energies in the shallow water regions.
If the shoal causes these waves to break offshore, then the
local beach or coastline is in effect sheltered from the
erosional impact of these waves.
If the shoal is significantly large, it is a possible
source of sediment for beach nourishment. Several factors
impact on the feasibility of using this material in beach
renourishment projects. One must consider the relative
amounts of material needed and that which is available.
Ideally, the material used for the fill should be of the
same or greater coarseness than that of the native material.
After the factors have been considered, the accessibility of
the area needs to be taken into account. Whereas, flood or
bay shoals may have been ruled out because of possible
detrimental environmental effects and distant offshore
troughs ruled out because of the lack of quantity or quality
of material and transport problems, the ebb shoals can pose
a different kind of problem. The dredge or device used to
collect the material from the shoal may very likely be
subject to extreme breaking wave conditions. An additional
consideration before determining whether or not the ebb
shoal should be used for renourishment is the effect that
its removal will have on the local wave climate. If the
shoal had been sheltering the coast, how will its removal
change the erosional patterns? Should only part of the shoal
be removed? How will its removal impact on navigation? These
are some of the questions which must be considered in the
determining the best course of action to be taken with
regard to ebb shoals.
Objectives
The objectives of this study were three-fold. First,
the general nature of ebb shoal development was examined
with reference to three inlet systems on the east coast of
Florida. Next, the ebb shoal volumes at eighteen coastal
inlet systems, also along Florida's east coast, were
estimated. Finally, the degree to which significant coastal
physical parameters are related to ebb shoal volumes was
investigated.
Each of the eighteen inlet systems is unique in its own
way. Although an "ideal" ebb shoal can be drawn graphically
or developed in a laboratory, rarely can one be found in
nature. This holds true for the east coast of Florida. The
origins of all eighteen systems are summarized in Table I-1.
This table details the origin of each inlet, whether natural
or man-made, the year in which it was opened and.when
jetties were constructed, if any.
Coastal Physical Parameters
This study will investigate the following parameters
and their relationship to ebb shoal volume, V, spring tidal
prism, P, inlet cross-sectional area, Ac, inlet width, W,
inlet depth, D, spring tide amplitude, ao. Several other
physical parameters characterize the ebb shoal; however,
only these more significant ones are examined in this study.
Table I-1. Origin of Florida's East Coast Inlets
Inlet Origin Remarks
St. Marys natural jettied 1881-1904
Nassau Sound natural
Ft. George/St. Johns natural
St. Augustine man-made
Matanzas
Ponce de Leon
Port Canaveral
Sebastian
Ft. Pierce
St. Lucie
Jupiter
Lake Worth
South Lake Worth
Boca Raton
Hillsboro
Port Everglades
natural
natural
man-made
man-made
man-made
man-made
natural
man-made
man-made
man-made
natural
man-made
jettied 1881
opened in 1940, 4 km
north of natural
inlet; jettied 1941,
1957
jettied 1968-1971
opened in 1950;
jettied 1953-1954
opened in 1948;
jettied 1952,1955
opened in 1921;
jettied 1921
opened in 1892;
jettied 1926-1929,
1982
jettied 1922
opened in 1917;
jettied 1918-1925
opened in 1927;
jettied 1927
opened in 1925;
jettied 1930-1931
jettied 1952,1966
opened in 1926;
jettied 1926-1928;
replaced two nearby
inlets
Table I-1--continued
Inlet
Bakers Haulover
Government Cut
Origin
man-made
man-made
Remarks
opened in 1925;
jettied 1925,1975,
1986
opened in 1902;
jettied 1902,1907
Source: Marino and Mehta (1986)
Each of the parameters has been studied at one time or
another by other investigators, but never collectively.
Relevant previous work is utilized and presented in this
study. A dimensional analysis approach is used to determine
which parameters best explain trends and relationships that
are found with respect to the inlet ebb shoals on Florida's
east coast.
General Physical Environment
The general physical environmental condition along the
east coast of Florida would serve as useful background
information prior to examining the possible relationships
between the various selected parameters and the ebb shoal
volumes. Figures I-1 through I-4 depict the following
coastal environmental parameters versus coastline distance
along the east coast of Florida, from St. Marys.Entrance to
Government Cut: wave energy, shelf width, tide range, and
net littoral drift rate. The derivation of the wave energy
data is covered in Chapter III. The shelf width data are
obtained from National Ocean Survey (NOS) nautical charts.
The tide range data are the spring tide values taken from
the National Ocean Survey (NOS) Tide Tables. The littoral
drift rate data are taken from the U.S. Army Corps of
Engineers (1967).
Figure I-1 shows a somewhat higher wave energy defined
as HsTw2, where Hs is the significant wave height and Tw
is the wave period in the northern eleven inlet systems. The
wave energy parameter, Hs2T2 decreases most noticeably
between Jupiter Inlet and Lake Worth Inlet. The shadow
effect caused by the Bahama Islands may be the most
significant factor in that respect.
Figure I-2 depicts the constant narrowing of the shelf
width from north to south. The shelf width remains nearly
constant from Lake Worth Inlet to the south. Figure I-3
shows that the spring tide range in the northern inlets is
somewhat higher than in those from Sebastian Inlet to the
south. Figure I-4 depicts the general, although not uniform,
decrease in the net littoral drift rate from north to south.
The data presented subsequently in this study are
derived primarily from charts and survey maps of the
National Ocean Survey, the U.S. Army Corps of Engineers and
from reports of the University of Florida. Aerial
photographs supplemented the information from these sources.
No field measurements or observations were made as a part of
this study. Personal visits were made to each of the inlets
and their respective controlling agencies, in an effort to
gain the most recent information.
o Hindcost Data
A CDN Dato
N.4
01 0
""a a-0 <
I-
20 oc
20 0
X" 0
mo LI o
o" o a.
S9A o? LAI r .
' fl rl 3 ...0
w w No +" '4
L It II
=r C
>w CI L 3 A cu
SI I I I I I
C0 100 200 300 400 500
DISTANCE (km)
FIGURE I-1. COASTLINE DISTANCE VS. WAVE ENERGY
0
o
r VtA C+
U' 1
I L I I
ZC 0 C K
' c O C H
I I
200
'U
D
0*
-*. 0
r+
Ft
C1 3 v
3 3 3 3
"1 :y a
i I T
300 400 500
DISTANCE (km)
FIGURE 1-2. COASTLINE DISTANCE VS. SHELF WIDTH
w
0
o
nr
nj i
w o
G'3
r+n
Ft W" 2
crn
M
m
to'
ro(
w
I I
I
r
C)
o0
2. -
0 0 <-
w g 3
o 0
0 0, 0 0 0
0 0
o 0o" C o 0
-u A o o o ao0
SI I I I
) 100 200 300 400 500
DISTANCE (km)
OC -0 a# m I D
100 200 300 400 500
DISTANCE (kmn)
FIGURE 1-3. COASTLINE DISTANCE VS. TIDE RANGE
S400
0 -U
pq I
b II a lb l. -
oo
2 0 0 cc
S0; IIk
200- o
DISTANCE (ki()
FIGURE -4. COASTLINE DISTANCE VS. NET SOUTHERLY LITTORAL DRIFT RATE
oo 100 c CC, Ir < -2. =r \
&+ 0 I i r-
z Q L W a no
-0 100 200 300 400 500
CHAPTER II
EVOLUTION OF EBB TIDAL SHOALS
Introductory Note
To trace the evolution of an inlet ebb shoal, a time
history of the inlet must be studied. Man-made or artificial
inlets were chosen that have been opened in relatively
modern times. The inlets of St. Augustine, St. Lucie and
Boca Raton were selected as case studies. Each has a unique
history and helps in explaining differences in evolutionary
trends as well as difficulties which are typically
encountered in precisely determining the shoal volume at any
particular point in time.
Much work has been done in the laboratory concerning
the development of ebb tidal shoals. This work includes, but
is not limited to, that done by Mayor-Mora (1977), Ozsoy
(1986), and Sill, Fisher. and Whiteside (1981). The Mayor-
Mora study conducted a series of idealized movable-bed tidal
inlet model tests. A significant conclusion found in that
study shows that as the tidal prism increases the inlet area
also increases, as was found by O'Brien (1969) and Jarrett
(1976). Ozsoy studied the mass transport by turbulent jets
issuing from tidal inlets through a mathematical model.
Important conclusions from this study are that the sediments
supplied by littoral processes are then entrained into the
tidal residual circulation and finally deposited in the
shoals and that the pattern of deposition depends on bottom
friction, slope, inlet current intensity, and the size of
sediment. The Sill, Fisher and Whiteside study was designed
to evaluate the appropriateness of the ebb jet hypothesis in
a laboratory model. Primary conclusions drawn from this
study state that the equilibrium shoal length and width
increase in direct proportion to the average inlet velocity
at the point of initiation of ebb jet, and that inlet width
and "critical" sediment velocity are appropriate scale
factors for laboratory shoals. Each of these represent
controlled environments and the variables are limited.
Unfortunately, that is not the case in nature.
The three inlets chosen differ from each other not so
much as in the way they were opened, but in how each local
coastline reacted to its opening. The effects of jetties,
dredging and longshore sediment transport become evident in
the investigation. St. Augustine Inlet was cut 4 kilometers
north of an existing inlet in 1941. St. Lucie Inlet was
created by local residents in 1892, to serve as a connecting
channel between the Indian River and the Atlantic Ocean.
Boca Raton Inlet is considered a man-made inlet although it
existed as a natural inlet from time to time prior to its
stabilization in 1925, according to Strock and Associates
(1983a).
St. Augustine Inlet
Figure II-i depicts both the previously (1937) existing
shoreline and shoal patterns with that of the present (1975)
for St. Augustine Inlet (U.S. Army Corps of Engineers,
1977). Locations A and B on the figure represent the areas
through which the old, natural inlet meandered, prior to the
new inlet opening at location C, in 1940. The shoal contour
lines delineate significant levels of sediment deposition
above the ideal beach profile, in feet (lft=0.305m). The
ideal profile is defined as the the natural beach profile
in that local area, as if the inlet were not present. For
example, any area outside the 5 ft (1.5 m) contour line
would have a deposition above the assumed ideal profile of
less than 5 ft (1.5 m). The area within the 5 ft (1.5 m)
contour would have deposition of greater than 5 ft (1.5 m)
above the ideal profile, up to the 10 ft (3.1 m) contour and
so forth. The exact volumes and methods used in determining
those volumes are covered in Chapters III and IV. It can be
seen in Figure II-1 that as a result of the opening of a new
inlet, the previously existing ebb shoal was caused to
migrate. The old shoal formation moved both westward, to
form what is now known as Conch Island, and northward to the
new inlet. The old inlet, which was located at location B in
S---- 1975 Shoreline
B ---- 1937Shoreline
5' / 1975 Shoal Contours
"/ / -- -- 1937 Shoal Contours
I \ / Shcol Contour Conversion
/ I It. 0.305 m
10'
\ /. / 5" /
:' : ^ .
S?
5 -. .- Scale -elr
FIGURE II-1. ST. AUGUSTINE SHORELINE AND SHOAL
COMPARISON, 1937, 1975
1937, was completely closed by 1957. The present shoal is
rather elongated as opposed to crescent-shaped. This is
believed to be due to the presence of a predominant
longshore current to the south. The narrowest part of the
shoal seen directly east of the inlet is evidence of the
dredging done by sidecast dredges through the shoal area
since 1940. The large bulge adjacent to the south jetty is a
direct result of the jetty being constructed in 1957. The
shoreline since construction has moved eastward
approximately 750 meters adjacent to the jetty. This is
evidence of jetty sand-trapping during periodic seasonal
reversals of the littoral drift.
St. Lucie Inlet
St. Lucie Inlet is depicted in Figure 11-2. Walton
(1974a) presents several individual charts which have been
overlayed here to show the dramatic effect of the opening of
a new inlet on the coastline. The figure shows the
approximately 1000 meter retreat of the shoreline at the
south side of the inlet. The majority of this retreat
occurred prior to 1948, as is seen in the figure.
No shoal existed prior to the inlet being opened in
1892. It is seen that the shoal is divided into two lobes
rather than a single elongated shoal. The southern lobe is
situated directly over the location of the pre-construction
shoreline. It is believed that much of the material present
197OShoreline "
-- -1948Shoreline
----- 1883Shoreline
Shoal Contours
Shoal Contour Corwersion
0 500 1000
Scale meters
FIGURE 11-2. ST. LUCIE SHORELINE AND SHOAL
COMPARISON, 1883, 1949, 1970
in this shoal was once a part of the shoreline prior to its
erosion and migration westward. The division of the two
lobes is maintained by periodic dredging of a channel
through the shoal. In the last 20 years approximately
382,000 cubic meters of dredge material has been deposited
in the vicinity of the south lobe (Florida Oceanographic
Society, 1982).
There is strong evidence that, although the shoreline
has retreated significantly, not all of the sand has eroded
and lost to the downdrift beaches. A close examination of
the land area suggests that the northern part of Jupiter
Island (south of the inlet) has migrated westward as sand
has washed through the inlet and deposited in the lagoon
area behind the island. The land areas presented in Figure
II-1 were planimetered to determine the approximate areas
involved. The land area present in 1883 was 2.2 million
square meters, while it is found to be 2.7 million square
meters in 1970. While this computation of areas does not
necessarily correspond to representative volumes, it does
give some idea as to where a significant amount of the sand
seems to have gone.
Further compounding the shoal development issue is the
existence of a reef which runs parallel to the coastline
approximately 1000 meters offshore. The reef had caused a
natural tidal current to form that ran from the inlet to the
south according to the Florida Oceanographic Society (1982).
This fact lends further credibility to the observation
regarding sand being washed into the inlet during flood tide
and being deposited on the lagoonal side of Jupiter Island.
The construction of a south jetty in 1980-1982 has since
diverted this tidal current eastward.
Boca Raton Inlet
Boca Raton Inlet, depicted in Figure II-3, is unique in
that it was closed during a storm as recently as 1967.
Again, an examination of this inlet shows clearly the effect
of jetties and the longshore current on shoal formation. The
shoreline has not eroded nor retreated with the same
severity as seen at St. Lucie. The elongated shape of the
shoal in the southerly direction depicts the influence of
the predominant littoral drift. The net longshore transport
rate in the southerly direction is reported to be between
90,000 and 170,000 m3/yr according to the U.S. Army Corps of
Engineers (1967).
The inlet was opened by dredging in 1925 and jetties
were emplaced in 1930. The inlet has had a history of
continual shoaling. The jetties were relatively short and
acted as little more than retaining walls, particularly on
the north side. In 1975 the north jetty was extended 55
meters to the east. In. 1980, a 20 meter weir section was
constructed. The south jetty was reinforced and extended
N
5'
19
1979 Shoreline
1929 Shoreline
1883 Shoreline
1979 Shoal Contours
Shoal Contour Conversion
I ft = 0.305 m
600
900
FIGURE 11-3.
Scale meters
BOCA RATON SHORELINE AND SHOAL
COMPARISON, 1883, 1929, 1979
0 300
~~~~~~~
landward to prevent flanking. In an examination of aerial
photographs from Strock and Associates (1983a), it can be
seen how the lengthening of the north jetty has forced the
shoal to form approximately 250 meters away from the inlet
mouth. With the help of a dredge which by-passes material
from within the inlet, the inlet has not shoaled since 1967.
Further examination of aerial photographs reveals that the
ebb shoal serves as a moderately efficient sand by-passing
bridge, since no channel is dredged through it.
Conclusion
These three inlets are mere examples of how ebb shoals
form and how the coastline reacts and adjusts due to the
formation of an inlet. It can be seen that by constructing
jetties of sufficient length to stabilize an inlet, as was
done at St. Augustine and Boca Raton, the shoals are
maintained a significant distance away from the inlet. It
can also be observed that dredging significantly affects the
shape of the shoal. At St. Lucie and St. Augustine the
shoals are divided into two distinct lobes, where there are
channels dredged, rather than one large mass as is the case
with the Boca Raton, where there is no dredged channel. In
all three cases, the great majority of the shoal area is
located to the southeast of the inlet mouth. This is
apparently due to the effect of the predominant longshore
current along the coast (see Figure 1-4).
22
Each of the eighteen inlet systems identified have
their own unique features. The remainder of this study deals
with estimating the ebb shoal volumes associated with those
inlets and in explaining how the various physical parameters
are related to those volumes.
CHAPTER III
METHODOLOGY
Dimensional Analysis
One approach to determine which parameters are
important in characterizing the ebb shoal volume is through
appropriate non-dimensional governing variables, using the
procedure of dimensional analysis. The basic objective in
dimensional analysis is to reduce the number of separate
governing variables involved to a smaller number of
independent dimensionless parameters. This procedure was
originally presented in 1915 by Buckingham and summarized in
Roberson and Crowe (1975). The Buckingham Pi Theorem shows
that the number of independent dimensionless parameters
needed to correlate the variables in a given process is
equal to n m, where n is the number of selected, governing
physical quantities and m is the number of fundamental
dimensions.
The process is started by identifying those variables
that are significant to the problem. In the most general
sense, the following variables may be selected as having a
bearing upon the ebb shoal volume: the (maximum) inlet
current velocity, Vmax, inlet width, W, inlet depth, D,tidal
range or amplitude, ao, tidal period, T, wave height, Hs,
wave period, Tw, alongshore current, ua, offshore bottom
slope, s, acceleration due to gravity, g, density of
saltwater,p and sediment settling velocity, ws. Some of
these parameters have been previously noted by other
researchers including Dean and Walton (1973), Walton and
Adams (1976), Sill, Fisher and Whiteside (1981), and Ozsoy
(1986). Considering, however, the Florida east coast
environment (as described in Chapter I) and practical limits
imposed by the availability and accuracy of data used, only
the more significant of these variables could be considered;
these may be combined to form a functional relationship
which can be written as
f(V,P,W,D,Ew,Et,ao2,s) = 0 (1)
where V is the ebb shoal volume, P is the spring tidal
prism, W is the inlet width at the throat, D is the inlet
depth, Ew is the wave energy, Et is the tidal energy, ao is
the spring tide amplitude, and s is the offshore bottom
slope. The slope, s, may be excluded in the derivation of
dimensionless parameters. The slope, s, was obtained by
measuring the perpendicular distance offshore to the 10
meter depth contour and dividing that distance by the depth.
This was done in all but the northern three inlets, where
the 6 meter contour was used due the complex nature of the
offshore bathymetry in the area. NOS charts 11467, 11472,
11476, 11485, 11488, and 11489 were used to obtain this
information. The slope was eliminated from further
discussion since all the values (presented in Tables IV-1
through IV-15) lie in a very narrow range, between 0.3 and
1.0 degrees. Furthermore, the ratio of the standard
deviation to the mean was found to be significantly small
(0.34).
Thus, the functional relationship is reduced to
f(V,P,W,D,Ew,Et,ao2) = 0 (2)
with seven physical quantities. Of the three possible
fundamental dimensions, force, F, length, L, and time, T, F
and L are present. Therefore, there are n m = 5
dimensionless parameters or Pi-terms. Choosing Ew and W as
the repeating variables, which include F and L, the first
Pi-term can be expressed as a product of the repeating
variables to unknown exponents and any one other variable to
the first power:
Pil = (Ewx) (WY) (V) (3)
Since Pil is now dimensionless, the requirement of
dimensional homogeneity yields
FOL0 = (FxL-x) (LY) (L3) (4)
Equating exponents yields
F: 0 = x (5)
and
L: 0 = -x + y + 3
or y = -3. Therefore,
Pi1 = V/W3
This procedure is repeated for the next four Pi-terms:
Pi2 = (EX) (WY) (P)
FOLO = (FXL-X) (LY) (L3)
(9)
yielding
F: 0 = x
L: 0 = -x + y + 3
(10)
(11)
or y = -3. Therefore,
Pi2 = P/W3
Pi3 = (EX) (WY) (D)
and
FOL0 = (FXL-X) (LY) (L)
(12)
(13)
(14)
yielding
F: 0 = x
L: 0 = -x + y +
(15)
(16)
or y = -1. Therefore,
Pi3 = D/W
Pi4 = (EX) (WY) (ao2)
and
FOLO = (FXL-x) (LY) (L2)
(17)
(18)
(19)
yielding
and
and
and
F: 0 = x (20)
and
L: 0 = -x + y + 2 (21)
or y = -2. Therefore,
Pi4 = ao /W2 142)
Pi5 = (EwX) (wY) (Et) (23)
and
FO0L = (FXL-x) (LY) (FL-1) (24)
yielding
F: 0 = x + 1 (25)
and
L: 0 = -x + y 1 (26)
or x = -1 and y = 0. Therefore,
Pi5 = Et/Ew (27)
According to the rules of dimensional analysis some re-
arranging is authorized. The Pi3-term is raised to the -1 to
yield
Pi3 = W/D (28)
The Pi3-term is divided by the Pi4-term to yield
Pi4 = Ac/ao2 (29)
Finally, the Pi5-term is raised to the -1 to yield
Pi5 = Ew/Et (30)
These, along with the original Pil- and Pi2-terms yield the
following functional relationship:
f(V/W3,p/W3,W/D,Ac/ao2,Ew/Et) = 0 (31)
The fifth Pi-term can be eliminated from further
consideration for the reason that follows. The wave energy,
Ew, values lie in the same range as defined by Walton and
Adams (1976). Walton and Adams state that if the values of
the wave energy parameter Hs2T 2 are between approximately 3
and 30 m2sec2, then the wave energy climate is considered to
be "moderate" (as opposed to "high" for values greater than
30 m2sec2 and "low" for values less than 3 m2sec2). The wave
energy values as presented in Tables IV-1 through IV-15 for
the east coast of Florida all fall within that range. This
study compares the ebb shoal volume to prism relationship
with that presented by Walton and Adams (1976). Since Walton
and Adams related that V/P ratio to the Ew parameter solely,
and not the Ew/Et ratio, it is essential that this study
rely on the same criteria for comparison. The Ew-term can be
considered as being predominant in this ratio, because it is
more widely varying. Since the wave energies all lie within
the moderate range, the energy parameter, Ew/Et, is
eliminated from further consideration. An alternate
explanation of the elimination of the energy parameter is
given in Appendix A. There it is shown that within the
"moderate" energy band, Florida's east coast inlet shoal
volumes showed no identifiable relationship to the ratio of
wave energy to tidal energy.
This leaves the following functional relationship to be
further examined for significant trends:
V/W3 = f(p/w3,W/D,Ac/ao2) (32)
These parameters are related to the kinematic aspects of the
tidal inlets. A dynamic analysis involves the consideration
of forces acting on the fluid particles in motion with
respect to one another. Shearing forces are important in the
analysis (Yuan, 1967). The shear stresses involved and their
effects are examined in detail, in Chapter IV. Additional
dynamic aspects are considered in Appendix A, when comparing
the energy parameter, Ew/Et, relative to V, P and W/D. Thus
the ebb shoal volume V, is seen to be dependent on the
spring tidal prism, P, the inlet aspect ratio (width to
depth), W/D, and the ratio Ac/ao2. This last parameter has
been used by O'Brien and Clark (1973) for characterizing
inlet-bay hydraulics, particularly as it relates to the size
of the inlet-bay system, and the manner in which bay filling
through tide occurs. The next step is to determine the
actual values of the parameters involved.
Ebb Shoal Volume
The ebb shoals include most of the stored sediment at
an inlet. The inlets under consideration presented several
different problems in the details of analysis, but in every
case, the basic technique applied for ebb shoal volume
estimation was that developed by Dean and Walton (1973), for
differentiating between the sands making up the ebb shoal
and those of the coast proper. The technique is explained in
detail in that reference and is summarized in this report.
NOS nautical charts and hydrographic sheets were used for
each of the eighteen inlet systems. The steps taken to
estimate the volumes of sand residing in the ebb shoal are
as follows:
1. Construct idealized, no-inlet contour lines.
2. Impose a 305 meter (1000 foot) square grid system on
the chart and calculate differences between actual
depth and idealized no-inlet depth at grid line
intersections.
3. Average depth differences at intersections and
record in center of block.
4. Compute volume of sand in outer shoal by summing
averaged block depth differences and multiply by
9.29x104 meters2 (106 feet2).
This technique worked well in most instances; however
some adjustments had to be made in cases where conditions
were less than "ideal". Two significant problems were the
existence of offshore reefs in southern Florida and the the
existence of large, natural offshore shoals between St.
Marys Entrance and St. Johns River Inlet. In their simplest
description, the offshore contour lines updrift and
downdrift of the inlet would be shore-parallel, and
represent the idealized no-inlet condition. In the case of
Nassau Sound, there were no parallel contour lines which
appeared to fit the idealized description. Hence, the value
of the ebb shoal volume used was taken from Dean and Walton
(1973). In the case of the southern inlets, from Ft. Pierce
to Government Cut, consideration had to be given to reef
formations. As an example, the contour lines at Ft. Pierce
updrift and downdrift of the inlet were not at the same
distances from the shoreline. The idealized contours were
therefore drawn by interpolation between the updrift and
downdrift sides. In the case of three inlets, Hillsboro, Pt.
Everglades, and Government Cut, the presence of offshore
reefs and associated shoals made the estimation of the ebb
shoal volumes too complex. These inlets were, therefore,
eliminated from further consideration. Chronological
development at these inlets is presented in Appendix B.
Another problem to be worked out was in determining how
inlets, which were very wide or had significant offsets,
were to be dealt with. Where the updrift and downdrift sides
of the inlet were offset (or imbalanced) with respect to
each other, special consideration had to be given in
determining which grid pattern would be used. The best
solution was to reduce the size of the grid overlay from 305
meter square to 152 or 76 meter square. By using a smaller
grid less detail was lost in the vicinity of the inlet.
.'e
Once the idealized contours and the appropriate grid
size were selected, they were superimposed on the charts.
The depth differences between the actual and idealized no-
inlet contours were calculated to the nearest 0.3 meters (1
foot) at the intersection of grid lines. Depth differences
were then averaged for each grid square. These values were
added to give the total volume difference between the actual
and the idealized condition. The results are presented in
Tables IV-1 through IV-15.
Tidal Prism
The values selected for prism on the spring range of
tide were taken from published sources with the exception of
two inlets, South Lake Worth and Boca Raton. Three
techniques were found to have been used in literature for
the estimation of tidal prism. The techniques are the
Hydraulic Prism Method presented by Keulegan (1967), the
Cubature Method presented by Jarrett (1976), and the
Volumetric Prism Method.
The hydraulic prism is defined as
PH = (Vmax Ac T) / ( WCK) (33)
where Vmax is the cross-sectional average maximum velocity
of the tidal current through the inlet,.Ac is the inlet
cross-sectional area, T is the tide period (taken as 44,640
seconds for a semi-diurnal tide), and CK is a coefficient
developed by Keulegan (understood as 0.86 for this study).
This equation was used in estimating the prism values for
South Lake Worth and Boca Raton Inlets.
The Cubature Method for calculating tidal prisms takes
into account the time required for a tidal wave to propagate
through an inlet and into a bay (Jarrett, 1976). The method
divides the bay into areas which have approximately the same
phase range of tide, rather than assuming that the tide
rises and falls uniformly. The average surface area of each
sub-area is measured and multiplied by the phase range to
obtain the volume of water entering or leaving the sub-area
between succeeding periods of slack water. All of the sub-
area values are then summed to yield the tidal prism.
The volumetric method is simply stated by the
following
PV = 2 Ab ab (34)
where Ab is the area of the bay and ab is the bay tide
amplitude. The particular problem in using this relationship
arises from the difficulty in accurately estimating the bay
area. If the bay is of an irregular shape or is ill-defined,
it is difficult to correctly compute the area.
If data cannot be physically measured for use in these
prism formulas, then the NOS Tide Tables, Current Tables and
Navigation Charts can be used to obtain the velocity, inlet
cross-sectional area, bay area, and tidal amplitude data.
Cross-Sectional Area, Width and Depth
The cross-sectional area, width and depth values were
obtained from previous studies. The sources for these sets
of data are enumerated within Tables IV-1 through IV-15. It
should be noted that cross-sectional area was measured at
the inlet throat or the narrowest point. The width and depth
values were taken from previous studies for each inlet.
Where more than one source is noted, the values have been
combined by averaging to yield one value for the purpose of
this study.
Wave Energy
Wave energy is defined by Walton and Adams (1976) in
terms of the parameter, Hs 2T, where Hs is the wave height
and Tw is the wave period. This parameter is derived from
fundamental Airy Wave Theory. The wave energy per unit width
is represented by the expression
Ew = pgHs2L/8 (35)
where p is the density of seawater, g is the acceleration
due to gravity, Hs is the significant wave height, and L is
the wave length. Further, the deep-water wave length, Lo, is
related to the wave period, Tw, by the expression
Lo = gTw2/2n (36)
Lo is related to L through Table C-l, Coastal Engineering
Research Center, Shore Protection Manual (1984), as they are
both a function of water depth. Thus, the wave energy can be
conveniently represented as a function of Hs2Tw2. The tidal
energy parameter, ao2T2, can be derived in a similar
fashion. Here, ao is the tidal amplitude and T the period.
Jensen (1983) presents hindcast, shallow-water,
significant wave information covering a 20-year period. The
data are available for each of the East Coast inlets. The
average significant wave height, Hs, is given for each
location. However, the wave period is given in ten frequency
bands for each of ten wave height bands. These values were
combined to obtain a weighted mean period, Tw, using the
following expression
Tw = ((SUM Tj)(SUM Nij)] / (SUMij Nij) (37)
where SUM Tj is the summation of the values in each
frequency range, SUM Nij is the summation of the number of
occurrences of each frequency range and SUMij Nij is the
summation of the total number of occurrences for that
location. These data are plotted in Figure I-1 and the
values are presented in Tables IV-1 through IV-15.
University of Florida Coastal Data Network (CDN) values for
1984 are also given in Figure I-1. Even though these values
are only for a single year, they are useful for comparison
purposes. The values of Hs and Tw from these data were
derived in the same manner as previously described for T,,
however only five locations are available for use.
The values derived from the hindcast data are then
analyzed to determine which energy range they fit into, as
defined by Walton and Adams (1976). The ranges chosen to
describe mildly exposed, moderately exposed, and highly
exposed were 0.0-3.0, 3.0-30.0, and >30.0, respectively (in
m2sec2). The results are provided in Tables IV-1 through IV-
15.
Volume vs. Prism Relationship
The ebb shoal volume versus spring tidal prism
relationship presented by Walton and Adams (1976) was used
as the focus of this study's analysis. That study concluded
that there is a strong correlation between the volume of
sand stored in the ebb shoals of inlets with their
respective tidal prisms (and cross-sectional areas). The
wave energy parameter was used to explain the differences in
the correlation of these parameters. Of the three ranges of
energy, previously described, the mildly exposed coast
contained the largest volumes, while the highly exposed
coasts had the smallest volumes. Walton and Adams (1976)
found the volume/prism ratio to be a function of inlet
cross-sectional area and wave energy. A linear regression
analysis is conducted to determine a comparable volume/prism
relationship based on this study's data. The volume/prism
relationship derived from this analysis is then compared to
that presented by Walton and Adams (1976). The correlation
coefficient for each set of data is determined and compared
for relative accuracy (scatter).
This study takes that conclusion one step further to
determine which parameters explain the scatter of data
within the same relative wave energy range. The dimensional
analysis, previously discussed, revealed that the volume is
likely to be dependent upon the prism, the cross-sectional
area/tidal amplitude (squared) ratio and the width/depth
ratio when the wave energy is invariant, as shown in
equation (32). These parameters are used to determine what
physical trends exist and their degree of correlation.
CHAPTER IV
RESULTS AND ANALYSIS
Physical Parameters
Estimated and compiled values of each of the
parameters, V, P, A,, W, D, ao, s, Hs, Tw, and Hs2Tw2, are
presented in Tables IV-1 through IV-15. Each of these tables
represents the fifteen individual inlets under
consideration. The tables include the various sources from
which the data were derived. Where more than one source is
listed, the corresponding average value is presented in the
table. The volume estimates (with the exception of Nassau
Sound, as previously noted) list the source used and date.
The data are selected based on their appropriateness in
time, relative to the volume estimates. For example, at St.
Augustine Inlet, Walton and Adams (1976) present prism and
cross-sectional area data from 1954-1957, which is the
period when the inlet was undergoing migration from its old
southern location to the present northern location. More
recent data are available from Florida Coastal Engineers
(1976), which more closely meet with the 1979 chart used for
volume estimation. Although no sediment-related data are
listed specifically for each inlet, it may be noted here
that the sediment grain sizes range from 0.12mm to 0.52mm
along the coast. Thus the sediment is in the range of fine-
to medium-sized sand.
It should be noted that the dates corresponding to the
various parameters, in most cases, do not exactly coincide.
Effort was made in obtaining data based on dates as close to
each other as feasible, as explained in the case of St.
Augustine Inlet.
Comparison of Volumes
The ebb shoal volume estimates obtained in this study
and those values from the corresponding inlets in Walton and
Adams (1976) are plotted against one another in Figure IV-1.
This plot was made to ascertain whether the values for each
inlet obtained from two different sources were close enough
to permit further comparison of related parameters. An
inspection of the figure reveals that the values are
relatively close to each other. All of the values have a
relative error of 11% or less, except for the two smallest
values, i.e. those for Jupiter and Bakers Haulover inlets.
These values have relative errors exceeding 30%. This is
explained by the fact that these volumes are so small (less
than 500,000 cubic meters) that even a relatively small
deviation yields a large percentage error.
Table IV-1. St. Marys Entrance
Parameter Value Sources
V 95.1x106m3 NOS charts 11488,11502; 1975
P 154.0x106m3 Parchure (1982)
A, 12.4x103m2 Parchure (1982)
W 12.7x102m Parchure (1982)
D 9.5m Parchure (1982)
ao 2.1m NOS Tide Tables (1986)
s 0.30 NOS chart 11489; 1981
Hs 0.55m Jensen (1983)
Tw 6.0sec Jensen (1983)
Hs2Tw2 10.9m2sec2
Remark: Data from Parchure (1982) are compiled from O'Brien
and Clark (1974), Bruun (1958), Environmental Science and
Engineering (1980), Walton and Adams (1976), Hou (1974) and
Olsen (1977).
Table IV-2.
Parameter
V
P
Ac
W
D
ao
s
Hs
sTw
Hs2Tw2
Nassau Sound
Value
40.5x106m3
62.3x106m3
67.4x106m2
14.7x102m
4.6m
1.9m
0.70
0.56m
5.9sec
10.9m2sec2
Sources
Dean and Walton (1973)
Walton and Adams (1976;,
Jarrett (1976)
Walton and Adam (1376),
Jarrett (Q976)
Jarrett (1976)
Jarrett (1976)
NOS Tide Tables (1986)
NOS chart 11489; 1981
Jensen (1983)
Jensen (1983)
42
Table IV-3. Ft. George/St. Johns Inlet
Parameter
V
P
Ac
W
w
D
ao
S
s
Hs
Value
131.3x106m3
60.2x106m3
50.6x102m2
8.4x102m
13.7m
1.7m
0.80
0.69m
Sources
NOS chart 11488; 1978
Jarrett (1976),
Kojima and Hunt (1980)
Jarrett (1976),
Kojima and Hunt (1980)
Jarrett (1976),
Kojima and Hunt (1980)
Jarrett (1976),
Kojima and Hunt (1980)
NOS Tide Tables (1986)
NOS Chart 11489; 1981
Jensen (1983)
T, 6.2sec
Hs2Tw2 18.3m2sec2
Jensen (1983)
Remarks: The prism, cross-sectional area, width and depth
values for each individual inlet have been combined for the
two inlets to coincide with the combined volume calculation.
This is recognized as a potential source of error and is
considered in the analysis of these data. It is felt that
less error would occur in combining these values then in
attempting to divide the ebb shoal between the two inlets.
Table IV-4. St. Augustine
Parameter Value
V 83.3x106m3
P 81.6x106m3
Ac 46.1x102m2
W 3.4x102m
D 13.7m
ao 1.6m
s 0.80
Hs 0.72m
Tw 6.0sec
Hs2T 2 18.7m2sec2
43
Inlet
Sources
NOS charts 11486; 1979,
11488; 1978
Florida Coastal Engineers
(1976)
Florida Coastal Engineers
(1976)
Florida Coastal Engineers
(1976)
Florida Coastal Engineers
(1976)
NOS Tide Tables (1986)
NOS chart 11488; 1978
Jensen (1983)
Jensen (1983)
Table IV-5.
Parameter
V
P
Ac
w
W
D
ao
s
Hs
Tw
Hs 2 Tw2
Matanzas Inlet
Value
4.8x106m3
14.2x106m3
9.1x102m2
3.3x102m
2.7m
1.5m
0.80
0.72m
6.3sec
20.6m2sec2
Sources
NOS chart 11486; 1978
Mehta and Jones (1977)
Mehta and Jones (1977)
Mehta and Jones (1977)
Mehta and Jones (1977)
NOS Tide Tables (1986)
NOS chart 11485; 1974
Jensen (1983)
Jensen (1983)
Table IV-6. Ponce de Leon Inle
Parameter Value
V 17.0x106m3
P 16.3x106m3
Ac 11.7x102m2
3.1x102m
4.1m
0.8m
0.90
0.82m
6.3sec
26.7m2sec2
et
Sources
NOS chart 11485; 1974
Jones and Mehta (1978)
Jones and Mehta (1978),
Walton and Adams (1976)
Jones and Mehta (1978)
Jones and Mehta (1978)
NOS Tide Tables (1986)
NOS chart 11485; 1974
Jensen (1983)
Jensen (1983)
W
D
ao
s
Hs
Tw
Hs2w2
Table IV-7. Port Canaveral Entrance
Parameter Value
V 4.3x106m3 NOS cl
P 2.5x106m3 Hunt
Ac 22.3x102m2 Hunt
W 2.0xl02m Hunt
D 10.7m Hunt
ao 1.2m NOS T:
s 0.50 NOS cl
Hs 0.71m Jensez
T, 6.9sec Jensei
Hs2Tw2 24.0m2sec2
Sources
hart 11476; 1979
(1980)
(1980)
(1980)
(1980)
ide Tables (1986)
hart 11476; 1979
1 (1983)
1 (1983)
Table IV-8. Sebastian Inlet
Parameter Value Sources
V O.1x106m3 NOS chart 11472; 1981
P 8.5x106m3 Mehta, Adams and Jones (1976)
Ac 3.6x102m2 Mehta, Adams and Jones (1976)
W 1.4x102m Mehta, Adams and Jones (1976)
D 2.6m Mehta, Adams and Jones (1976)
ao 0.8m NOS Tide Tables (1986)
s 1.00 NOS chart 11472; 1981
Hs 0.80m Jensen (1983)
T, 6.7sec Jensen (1983)
HS2T2 28.7m2sec2
Remark: Prism data presented in Mehta, Adams and Jones
(1976) were taken from Bruun (1966).
Table IV-9.
Parameter
V
P
Ac
w
D
ao
Hs
Tws
Hs 2Tw 2
Ft. Pierce Inlet
Value
22.2x106m3
17.3x106m3
9.8x102m2
2.7x102m
4.2m
0.9m
0.60
0.78m
6.6sec
26.5m2sec2
Sources
NOS chart 11474; 1975
O'Brien and Clark (1973),
Jarrett (1976)
O'Brien and Clark (1973),
Jarrett (1976)
Jarrett (1976)
Jarrett (1976)
NOS Tide Tables (1986)
NOS chart 11472; 1981
Jensen (1983)
Jensen (1983)
49
Table IV-10. St. Lucie Inlet
Parameter
. ,
Value
16.4x106m3
16.4x106m3
13.9x102m2
5.5x102m
2.6m
Sources
NOS chart 11472; 1981,
USACE (1965)
Jarrett (1976)
Jarrett (1976), Walton (1974a)
Jarrett (1976), Walton (1974a)
Jarrett (1976), Walton (1974a)
l.lm
0.50
0.83m
NOS Tide Tables (1986)
NOS chart 11472; 1981
Jensen (1983)
T, 6.5sec Jensen (1983)
Hs2T2 29.1m2sec2
Remarks: Volume is calculated using the survey chart
presented by the U.S. Army Corps of Engineers, Jacksonville
District (1965) due to its smaller scale and greater detail.
Prism data from Jarrett are derived from the cubature method
and taken from the U.S. Army Corps of Engineers,
Jacksonville District (undated).
I /-
Table IV-11.
Parameter
V
P
Ac
Jupiter Inlet
Value
0.3x106m3
3.0x106m3
4.2x102m2
Sources
NOS chart 11472; 1981
Jarrett (1976)
Jarrett (1976),
Dean and Walton (1973)
W 1.0x102m Jarrett (1976)
D 2.8m Jarrett (1976)
ao 0.9m NOS Tide Tables (1986)
s 0.50 NOS chart 11472; 1981
Hs 0.82m Jensen (1983)
T, 6.4sec Jensen (1983)
H2T 2 27.5m2sec2
Remark: Prism data presented in Jarrett (1976) are derived
from the cubature method and taken from U.S. Army Corps of
Engineers, Jacksonville District (undated).
Table IV-12. Lake Worth Inlet
Parameter
V
P
Ac
W
D
ao
s
Hs
Value
2.9x106m3
28.4x106m3
13.5x102m2
2.9x102m
4.0m
0.8m
0.80
0.72m
Sources
NOS chart 11472; 1981,
COED, University of Florida
(1967)
Jarrett (1976),
O'Brien and Clark (1973)
Jarrett (1976),
O'Brien and Clark (1973)
Jarrett (1976)
Jarrett (1976)
NOS Tide Tables (1986)
NOS chart 11472; 1981
Jensen (1983)
5.3sec
Jensen (1983)
Hs2T2 14.6m2sec2
Remarks: Volume is calculated using a survey chart presented
by the Coastal and Oceanographic Engineering Department
University of Florida (1967), rather than NOS chart 11472
due to the smaller scale used, yielding greater detail and
therefore, less error. The prism data from Jarrett (1976)
include values reported by Bruun (1958) and the U.S. Army
Corps of Engineers, Jacksonville District (undated), along
with that from the cubature method.
Table IV-13. South Lake Worth
Parameter
V
P
Ac
W
D
ao
s
Value
1.lx106m3
3.1x106m3
1.0x102m2
0.3x102m
3.1m
0.9m
0.90
Sources
NOS chart 11467; 1978
Mock (1962)
CEL, University of Florida
(1964)
CEL, University of Florida
(1964)
CEL, University of Florida
(1964)
NOS Tide Tables (1986)
NOS chart 11467; 1978
0.68m
5.7sec
Jensen (1983)
Jensen (1983)
15.0m2sec2
Remark: The prism value is calculated using the mean maximum
velocity presented in Mock (1962) and the cross-sectional
area presented in Coastal Engineering Laboratory, University
of Florida (1964) with the hydraulic prism equation (24)
presented in Chapter III.
Hs2Tw2
Table IV-14. Boca Raton Inlet
Parameter
V
Value
0.8x106m3
5.5x106m3
1.8x102m2
0.5x102m
3.4m
0.8m
1.00
0.69m
Sources
NOS chart 11467; 1978,
Strock (1983a)
Strock (1983a)
Strock (1983a)
Strock (1983a)
Strock (1983a)
NOS Tide Tables (1986)
NOS chart 11467; 1978
Jensen (1983)
5.8sec
Jensen (1983)
H 2T 2 16.0m2sec2
sw
Remarks: The volume is calculated using the survey chart
presented by Strock (1983a) due to its smaller scale and
greater detail rather than the NOS chart 11467. The prism is
calculated using the mean maximum velocity and cross-
sectional area presented by Strock (1983a) with the
hydraulic prism equation (24) presented in Chapter III.
I
Table IV-15.
Parameter
V
Bakers Haulover
Value
0.5x106m3
Inlet
Sources
NOS chart 11467; 1978,
COED, University of Florida
(1969)
P 10.2x106m3 Jarrett (1976)
Ac 4.1x102m2 Jarrett (1976)
W 1.1xl02m Jarrett (1976)
D 3.6m Jarrett (1976)
ao 0.9m NOS Tide Tables (1986)
s 0.30 NOS chart 11467; 1978
Hs 0.53m Jensen (1983)
T, 4.3sec Jensen (1983)
Hs2Tw2 5.2m2sec2
Remark: The volume is calculated using the survey chart
presented by the Coastal and Oceanographic Engineering
Department, University of Florida (1969) due to its smaller
scale and greater detail than NOS chart 11467 (1978).
I i I I I I
E
10 St. Marys
100- x
Q 80- x St.Augustin
z
60-
tJ
5 40- Nassau Sound
y20- Ponce De Leon
Jupiter
0 Bakers Hulover ,
0O 20 40 60 80 100
VOLUME ESTIMATE- PRESENT
STUDY (x lOm3)
FIGURE IV-1. COMPARISON OF VOLUME ESTIMATES
Regression Analysis
Correlations were made of the inlets examined in this
study with the equation
V = bPm (38)
where V is the ebb shoal volume in cubic meters, P is the
spring tidal prism in cubic meters, and b and m are
coefficients to be determined through linear regression. The
equation can be written as
Y = a + mR (39)
where y = log V x = log P and a = log b.
Solve for m, using the expression:
m = SUM [(x x) (y y)] / SUM (x )2 (40)
yielding
m = 1.39 (41)
Then solve for a, using the expression:
a = y mx (42)
yielding
a = -3.25 or b = 5.59x10-4 (43)
Thus regression analysis yields the following
V = 5.59x10-4 p1.39 (44)
This equation is plotted on Figure IV-2, along with the
equation from Walton and Adams (1976) for moderate energy
environment. The indicated data points are those from this
study. Correlation coefficients for both sets of data were
computed to determine the relative accuracy.
100 I I I 1 1 1
50- V 559 x 104 P39 (Present Study)
V=6.08x 10t3 P '(Walton and Adams)
St. Marys/
E 10 y /
10 x St.Auqustine
0 7 NsNossu x Ft.George/
S/ Sound St. Johns
Lake Worth x '
L 4x Ft. Pierce
cr Bakers Houlover Ponce De Leon
1a. 10 an Matanzas
J 1. ebostion x
o 0.5- x
/1 Jupiter
x x South Lake Worth
7 x Pt. Canaveral
0.11,, --- .. I I I I----
I 0.5 1.0 5 10 50 100 500 000
EBB SHOAL VOLUMES (x Knrr1)
FIGURE IV-2. COMPARISON OF LINEAR REGRESSION
ANALYSIS RESULTS
An examination of Figure IV-2 reveals a considerable
spread of values. Although the data from Walton and Adams
(1976) are not plotted on this figure, a similar spread of
data exists. For prism values which are approximately equal
there is considerable scatter, even within the same wave
energy environment range as is presented here.
The correlation coefficient for data from this study is
0.75 and for Walton and Adams (1976) it is 0.80. These
values may be considered to be rather low, indicating
unsatisfactory correlation between the values. These
somewhat poor correlations suggest the possibility of
examining the influence of other parameters as expressed in
equation (23).
Results of Dimensional Analysis
The dimensional analysis, presented in Chapter III
yielded the following relationship to be examined for
trends:
V/W3f( P/W3, W/D, Ac/a02) (32)
Since V and P are both a function of W3, they will be
combined to form the ratio V/P for the discussion (although
it is noted that V and P are not linearly related). The
values of the three dimensionless parameters are contained
in Table IV-16.
The variability of each of these parameters may be
demonstrated by calculating the standard deviation of each
Table IV-16. Dimensionless
Inlet V/P
St. Marys 0.62
Nassau Sound 0.65
Ft. George/ 2.18
St. Johns
St. Augustine 1.02
Matanzas 0.34
Ponce de Leon 1.04
Port Canaveral 1.72
Sebastian 0.01
Ft. Pierce 1.28
St. Lucie 1.00
Jupiter 0.10
Lake Worth 0.10
South Lake Worth 0.35
Boca Raton 0.15
Bakers Haulover 0.05
set and dividing
are as follows
Parameters
W/D
133
320
61
25
123
*75
19
55
64
211
35
74
11
16
31
by their respective mean values. The values
V/P: Std Dev/Mean = 0.93 (45)
W/D: Std Dev/Mean = 1.01 (46)
Ac/ao2: Std Dev/Mean = 0.66 (47)
These relatively large values of the normalized
standard deviation are indicative of the fairly wide
Aao2(xl0-3)
2.8
1.9
1.7
1.8
0.4
2.0
1.6
0.6
1.2
1.2
0.5
2.3
0.1
0.2
0.5
variation of the three parameters. While such a variability
does not, by itself, imply correlation, the possibility of
correlation is suggested. It should be noted that since the
cross-sectional area is not directly related to the W/D
ratio, two inlets with identical areas can have widely
different aspect ratios. This situation is portrayed by
comparing St. Lucie and Lake Worth Inlets. In this case,
their cross-sectional areas are relatively equal, 13,900
square meters and 13,500 square meters, respectively.
However, their W/D ratios are 211 and 74, respectively.
The parameters are plotted in Figure IV-3. An
examination of Figure IV-3 reveals a somewhat significant
trend with respect to the aspect ratio, W/D. Two zones can
be determined as is depicted by the dashed line. This line
is represented by the equation:
V/P = 0.0033 W/D + 1 (48)
This line, although clearly somewhat arbitrarily chosen,
divides the domain into two distinct zones with respect to
the values of Ac/ao2. V/P ratios will be greater than
predicted by equation (48) when Ac/ao2 is greater than 1000.
Likewise, V/P will be less than predicted by equation (48)
when Ac/ao2 is less than 1000. This relationship holds in 14
of 15 cases presented. In the case of Lake Worth Inlet, for
which the relationship does not hold, the V/P ratio is a low
Note: Numbers in Parentheses ( )
Represent Ac Volues xl0"3
ao
x (I.e
(20)
K
- 0.0033- +1
x(2.4 )
x (0.4)
x (0.2)
x (0.5) x(23)
(o. 5), tosl
100
150
W/D
x(1.2)
x (1.9)
A ( I.0)
o I
200
250
300
FIGURE IV-3. PLOT OF V/P VS. W/D WITH RESPECT TO Ac/a 2
I1 I -
2.0
x(1.7)
x(1.6)
1.5h
x(. 2)
1.0K
0.5
x (0.1)
I
1-j
350
I
0.10. From equation (44), a value of not less than 0.75
should be expected for the V/P ratio.
Equation (44) should be used mainly as an expedient
means of estimating the maximum or minimum volume stored in
the ebb shoals. The width and depth can be easily measured
in most field environments. The cross-sectional area can be
estimated from the width and depth. The tide range can be
found locally or derived from Tide Tables. The prism can be
estimated from the Prism Area Relationship, as presented
for example by O'Brien (1969)
Ac = 2.0x10-5 P (49)
With these parameters now known, the maximum or minimum
volume of sand stored in the shoals can be estimated within
the bounds of the two zones defined. For example, assume the
width of the inlet is 500 meters and the depth is 10 meters.
The cross-sectional area is then 5000 square meters. Assume
the tide range squared is 3.0 square meters. The Ac/ao2
value is 1666 which is greater than 1000. The prism is
estimated, using equation (49), to be 2.5x108 cubic meters.
From equation (48), we know that the V/P value must be
greater than 0.84. Therefore, the minimum volume estimated
to be stored in the ebb shoal is 2.1x108 cubic meters.
Results of Figure IV-3 imply that if the wave energy
and prism (and therefore cross-sectional area via O'Brien,
1969) are kept constant, then a greater W/D ratio will yield
a smaller volume and vice versa. This can be seen on a
relative basis by using Matanzas, Ponce de Leon and Ft.
Pierce as examples. These inlets have prism values of
14.2x106m3, 16.3x106m3, and 17.3x106m3, respectively. Their
cross-sectional areas are 910m2, 1170m2, and 980m2
respectively. These values may be considered as being
essentially constant for the present purpose. It can be
seen from Table IV-17 that as the W/D ratio decreases from
Matanzas to Ft. Pierce, the volume increases, lending
credibility to the hypothesis that volume is in fact a
function of not only prism (or cross-sectional area), but
also the aspect ratio, W/D.
Table IV-17. W/D versus V Comparison
Inlet W/D V(m3)
Matanzas 123 4.8x106
Ponce de Leon 75 17.0x106
Fort Pierce 64 22.2x106
Discussion
It would be difficult to find an ideal case in nature
where the wave energy, prism, area and tide are all
constant. However, this requirement may be further examined
through mathematical or physical modeling. Using a
relatively simple approach, the effect of varying W/D ratios
on the ebb shoal volume may be best realized by examining
the influence of the bed shear stress. The critical shear
stress is that value of the bed shear stress that is exerted
at the point of incipient motion. When the actual bed shear
stress exceeds the critical shear stress, the bed material
is put into motion.
Jonsson (1966) finds that the wave friction factor, fw,
is significantly larger than the current friction factor,
fc. The equations representing the shear stress due current,
Tc, and waves, Tw are
Tc = 0.5 p fc uc2 (50)
and
Tw = 0.5 p fw uw2 (51)
respectively, where p is the density of seawater, uc is the
water velocity due to current and uw is the water velocity
due to waves near the bed.
For the problem at hand, it is sufficient to consider
two inlets of the same cross-section, Ac, but having
different aspect ratios, W/D. Let inlet #1 be 3 meters deep
by 400 meters wide, and inlet #2 be 6 meters deep by 200
meters wide. Thus both inlets have a cross-sectional area of
1200 m2, but the corresponding aspect ratios are 133 and 33,
respectively. It can be shown that by virtue of equations
(33) and (49), the maximum ebb velocity through both the
inlets will be the same. Let us assume that the velocity,
uc, over the ebb shoal will as well be the same in both
cases, in spite of the differences in the flow depth over
the bar. Let uc be 0.3 m/sec, a representative value. Select
further, a representative wave height of 1 m and a wave
period of 7 sec applicable to ebb shoals at both inlets. For
current, a typical value of 4.1x10-3 may be selected for fc.
The magnitude of fw depends on the relative bottom
roughness, i.e. the maximum water particle displacement near
the bed, Ab, divided by the bed roughness, ds. fw was
estimated by using calculated Reynolds Numbers of 2.85x106
and 1.33x106 and corresponding Ab/ds values of 2264 and 1586
for inlets #1 and #2, respectively. The fw values are
estimated to be 8.0x10-3 and 9.0xl0-3 for inlets #1 and #2,
respectively.
Table IV-18. Shear Stress Comparison
D(m) c(/m2 (N/m2)
Inlet #1 3 0.18 3.23
Inlet #2 6 0.18 1.62
In Table IV-18, the current shear stress, Tc, and wave
shear stress, Tw, are given for the two inlets. It is
observed that in the case of both inlets, the wave shear
stress is dominant. Hence the precise selection of the
magnitude of uc for the inlets is not a matter of critical
importance, so long as reasonable values are selected. Since
the shear stress is greater in the shallower inlet, it is
more likely that the critical shear stress will be exceeded
there more often than in the deeper inlet. As the sand is
put into motion, it is moved by the longshore current and
wave forces back towards the shore. This movement of sand,
therefore, occurs more significantly in shallower inlets
than in deeper inlets, allowing the shoals of deeper inlets
to grow to greater volumes than those of shallow inlets.
This reasoning is in agreement with the conclusion of Walton
and Adams (1976). They state that more material is stored in
the shoals of low wave energy coasts than in high wave
energy coasts. This is because there is more energy
available to drive the sand back to shore in high energy
environment after being deposited as a shoal. In the present
study, the same relative wave energy environment was
considered, and the local effect of the shear stress caused
by incoming waves has been examined. The role of the aspect
ratio in determining the ebb shoal volume is thus shown to
be significant, along with the tidal prism and cross-
sectional area.
CHAPTER V
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
A few important conclusions with respect to Florida's
east coast inlets are in order.
1. There is a general (but not uniform) trend of
decreasing ebb shoal volume from St. Marys Entrance
(95x106 cubic meters) south to Bakers Haulover Inlet
(0.5x106 cubic meters).
2. The total amount of material stored in the ebb shoals
of all eighteen inlet systems is 420x106 cubic meters.
Of that amount, approximately 83% resides in the ebb
shoals of the four northernmost inlet systems-- St.
Marys, Nassau Sound, Ft. George/St. Johns and St.
Augustine. None of the other inlets account for more
than 5% of the total volume, individually.
3. The east coast inlets of Florida all reside within the
moderate wave energy range as defined in Walton and
Adams (1976).
4. The volume of material found in the ebb shoals appears
to be a function of spring tidal prism, P, inlet area,
Ac, amplitude of tide, ao, and the inlet width to depth
ratio, W/D.
5. The influence of the W/D ratio appears to arise as a
result of the differing effect of wave-induced sand
transport at different depths over the ebb shoal.
6. Two distinct regions are defined by relating V/P to W/D
and Ac/ao2. For values of Ac/ao2 greater than 1000, the
V/P value will be greater than that predicted by the
equation V/P = 0.0033 W/D + 1, in most instances.
For values of Ac/ao2 less than 1000, the V/P value will
be less than that predicted by equation (48).
Recommendations
Throughout this investigation, many ideas came to mind
or were brought to the author's attention that could be used
to improve upon what has been presented within this text, in
the future. Some general comments should be made at this
time.
Ideally, the parameter values used for each inlet
should be compiled from identical periods of time. This
would eliminate problems arising from relating the ebb shoal
volume from one period with the prism or cross-sectional
area from another, and would add a significant degree of
confidence to the results. This, however, will not be an
easy task to perform.
The next logical step would be to collect these same
parameters from inlets of the Atlantic, Pacific and Gulf
Coasts of the United States and to analyze them in the same
69
manner as performed here. That analysis may prove to
reinforce those trends discovered in this study, or those
trends may prove to be unique to the east coast of Florida.
The use of an electronic digitizer to perform volume
calculations will save enormous amounts of time and add to
the accuracy of volume estimates. The data can then be more
easily stored, retrieved and updated.
APPENDIX A
INFLUENCE OF WAVE ENERGY
The wave energy parameter, Hs2Tw2, used by Walton and
Adams (1976), is useful in defining ranges of approximately
equivalent wave environments. It was concluded, through data
and arguments presented in Chapters III and IV, that the
wave energy environment for each of the inlets on the east
coast of Florida is of the moderate range. The wave energy
parameter, therefore, was eliminated from further
consideration as a determining factor of ebb shoal volumes
in the analysis. Had the wave energy of each inlet not been
found to lie in the same range, the parameter would have had
to be considered in the analysis. It is felt that such an
analysis may be beneficial in locating any similar trends to
those found in Chapter IV, regardless of wave environment.
A dimensional analysis similar to that performed in
2 2
Chapter III can be conducted using Hs2 T2. This analysis can
be shown to yield a characteristic nondimensional parameter
Hs2T 2 / a 2T2, where T is the tidal period. The
significance of this parameter is that it represents the
ratio of wave energy to tidal energy. If no waves are
present, the magnitude of this parameter would be zero.
Consequently, the magnitude of this parameter is an
indicator of the importance of waves relative to tide. The
functional relationship of interest is thus
V/W3 = f(P/W3, W/D, Hs2T2/ao2T2) (52)
This relationship is plotted in Figure A-i. An examination
of this figure does not yield any clear trends with respect
to the three parameters. The data points tend to group
together without regard to parameter value. A possible
reason for this lack of correlation is the variable nature
of the energy parameter itself. The values of Hs T2 and
ao2T2 are averages of relatively widely varying (with time)
values, whereas the other parameters reflect averages of
comparatively less variable values. For a more definitive
conclusion concerning the influence of wave energy, it will
be essential to evaluate trends in Figure A-i using a much
larger data base involving wider variations in wave energy,
as was done by Walton and Adams (1976), although in a
different manner.
I I I
Note:Numbers in Parentheses( )
Represent W/D Values
x (19)
X(64)
x(211)
X(123)
X(31) ,
PA --
x (I)
X(35)
X) 150
-t-'(2 x 1O
ao2T2
0
FIGURE A-i. PLOT OF V/P VS. H2 Tw2/ao2T
RESPECT TO W/D
250
x(61)
2001-
150t-
x(25)
x (75)
200
250
WITH
I -----~- -T-
I (55),
, (320)
x(7 16)
x( !)
APPENDIX B
FLORIDA'S EAST COAST INLETS
A chronological development of Florida's east coast
inlets is presented to aid in the understanding of coastline
evolution. A brief description of the sections that follow
is appropriate at this time. There are nineteen inlets on
the east coast of Florida. However, as noted before, Ft.
George and St. Johns are considered together because these
two closely spaced inlets are characterized by a single
large ebb shoal, leaving eighteen inlet systems to be
examined. Each section is comprised of a brief history of
the inlet, including a summary of works and a figure
delineating ebb shoal volumes.
The figures depict the area of ebb shoal calculations
which are portrayed by rather straight, rectangular lines.
Within these areas, significant levels of deposition are
delineated. These levels are enclosed by contour lines
ranging from 5 to 20 ft (1.5 to 6.1 m), in increments of 5
ft (1.5 m). For example, any area outside the 5 ft (1.5 m)
contour line would have deposition above the assumed ideal
profile of less than 5 ft (1.5 m). The area within the 5 ft
(1.5 m) contour would imply deposition of greater than 5 ft
(1.5 m) above the ideal profile, up to the 10 ft (3.1 m)
contour, and so forth.
In all but the Ft. George/St. Johns Inlet system, the
contour lines are contained within the rectangular box. In
this case, the shoal system to the north of the inlet is
complicated by factors beyond the influence of the inlet
itself. The effect of those other factors are not addressed
in this study. Engineering judgement must be applied in
determining how much of this shoal is due to the inlet
processes and how much is due to other factors.
In all but three cases, the rectangular boxes which
contain the ebb shoal volumes are displayed. These three
cases are Nassau Sound, Port Everglades, and Government Cut.
Nassau Sound has a complex system of shoals which tend to
merge, to a varying degree, with the shoal systems to the
north and to the south. It was determined that Port
Everglades and Government Cut had shoals which could not be
accurately determined. This determination is complicated by
the presence of an extensive network of offshore reefs and
dredging of the channels, which makes total volume
calculations difficult, at best. At Hillsboro Inlet, a scour
hole or depression was found, giving rise to a negative
volume being recorded. Since Port Everglades, Hillsboro and
Government Cut did not have identifiable shoals, they were
not considered in the analysis portion of this study.
1. St Marys Entrance
An extensive history of this inlet is presented by
Parchure (1982) and is summarized here. Prior to the
stabilization of the channel by the construction of jetties,
St. Marys Entrance was fronted on its seaward side by a very
large bar formation which was cut by two relatively stable
channels. The deepest section of the inlet was believed to
be 20 meters, in the vicinity of Ft. Clinch. The bar was
located seaward of Amelia Island at a distance of 3.2
kilometers. The controlling depth was 2 meters below mean
low water (mlw).
In 1881, construction was begun on the jetties. Five
spur groins were installed along the westernmost shoreline
of Ft. Clinch to halt rapid recession at that point. Jetty
construction was completed in 1904. The two natural channels
had disappeared, leaving only a single entrance through the
inlet.
During the period 1905-1937, maintenance dredging and
jetty repair work was conducted on an as needed basis. In
1957, the entrance channel was realigned and deepened to 10
m, in connection with the King's Bay Army Terminal. In 1978-
79 the project depth for the navigation channel was
increased to 11-12 meters. The channel is presently 125
meters wide. The north jetty and south jetties are 5840
meters and 3415 meters in length, respectively.
Note I To'oi Vo!ume of Ebb Shool
Above !deal Profile= 95.1 x 106 Cu r
Note2 Isolirne Indncote Depth of Shoal
Above Ideal Profile
0 2000 4000
Scale : meters
FIGURE B-1. ST. MARYS ENTRANCE, 1975
2. Nassau Sound
Nassau Sound is a natural inlet that connects the
Nassau River and Amelia River to the Atlantic Ocean. It has
not been altered by dredging or the construction of jetties.
Over the last hundred years, major changes have been the
recession of Amelia Island to the north, the accretion of
Little Talbot Island to the south and the emergence of Bird
Island near Little Talbot Island. Nassau Sound is presently
1700 meters wide with variable depth. The maximum depth is 7
meters. There are many tidal flats in the inlet mouth.
Note I. Total Volume of Ebb Shoal
Above Ideal Profile =40.5 x 106cu.m.
(Dean and Walton, 1973)
Note 2. Limits of Study Area could not be
Set due to Complicated Shoaling
Patterns
1000
2000
FIGURE B-2. NASSAU SOUND, 1954
Scole: meters
4
3. Ft. George/St. Johns Inlet
Ft. George and St. Johns are natural inlets. Ft. George
has not been stabilized except by the presence of the north
jetty of the St. Johns River. In 1881, two jetties were
constructed at the St. Johns River inlet. The north jetty
was 2900 meters long and the south jetty was 2075 meters in
length. These jetties were submerged at the seaward end. In
1895, the jetties were lengthened to 3360 meters and 3230
meters, respectively.
In the early 1900's, the channel was dredged to 7
meters. This was completed in 1910 when authorization was
granted for deepening to 9 meters. In 1934, the north jetty
was capped with concrete and holes were plugged to make the
jetty less permeable. In 1937, the jetties were extended to
4360 meters and 3410 meters, respectively. The channel was
deepened to 13 meters, in 1965, in conjunction with the
Mayport Naval Air Station.
Ft. George Inlet has a variable bathymetry due to
shifting shoals. The main channel is approximately 2 meters
deep. Kojima and Hunt (1980) present a detailed history of
this inlet.
Note I Totol Volume of Lbt Shool
Above Ideal Protle 131.3 x 106Cu m
Note 2 Isolines Indcote Deoth of Shoal
Above Ideal Profile
Note3. Isolines of the North End of the Study
Area are left Open due to the
Complicated Shoal System which
Merges with that of Nassau Sound
( I ft.= 0305 m)
N
"-Limits of Study Area
0 2000 4000
Scole: meters
FIGURE B-3. FT. GEORGE/ST. JOHNS INLET, 1978
4. St. Augustine Inlet
St, Augustine existed as a natural inlet prior to its
stabilization in 1940. The inlet had meandered naturally
between two well-defined locations. The inlet was first
studied by the U.S. Army Corps of Engineers in 1887. In
1940, a new inlet was cut approximately 600 meters north of
North Point. In 1941, the north jetty was constructed. By
1946, the old inlet to the south showed signs of
deterioration and shoaling. The old ebb shoal bar had begun
to move shoreward to form Conch Island. In 1957, a south
jetty was constructed and the old inlet had almost
completely closed. In addition, the old inlet shoals and
bars had moved landward to form Conch Island as it is today.
A detailed study shows that accretion has occurred in all
regions, with no significant erosion until a point
approximately 6.5 kilometers south of the inlet in the
vicinity of St. Augustine Beach. A more detailed history of
the inlet can be found in Florida Coastal Engineers (1976).
The entrance channel is 60 meters wide and 5 meters deep.
The north and south jetties are 480 meters and 1130 meters
long, respectively.
Note I TotlG Volume of Ebb Shool
Above Ideal Profile-- 83 106 Luu
Note2. Isolines Indicole Deoth of Shoal
Above Ideal Profile
(lft.= 305m)
N
-s '
/ Limits of Study Area
0 :ODO 2000
Scowe meteri
FIGURE B-4. ST. AUGUSTINE INLET, 1979
5. Matanzas Inlet
Matanzas Inlet is a natural inlet located approximately
21 kilometers south of St. Augustine and 64 kilometers north
of Daytona.Beach. Much of the historical information which
follows is summarized from Mehta and Jones (1977).
A by-pass channel 2880 meters long through the marsh
west of the inlet was constructed to link the inlet with the
intracoastal waterway in 1932. In 1964, Hurricane Dora
struck the St. Johns County coastline on September 9th
causing widespread erosion, as well as the undermining of
the coast and structures. This hurricane was responsible for
the breakthrough at Rattlesnake Island which caused
significant changes in the area. The breakthrough had
widened to 75 meters by 1972. Erosion along both sides of
the inlet had taken place, although it was more significant
at Summer Haven. The breakthrough was closed, in 1976, with
the construction of a steel, sheet pile dike. A channel was
dredged through the shoal, in 1977, and 1000 meters of the
south beach was nourished. The inlet is approximately 290
meters wide with a maximum depth of 5-6 meters.
Total Volume of Ebb Shoal
Above Ideal Profile 4.8 x 106 cum
Ebb Shoal Depth Less Than 5ft.
Above Ideal Profile Throughout
Study Area
(I ft.=0305 m.)
N
Limits of Study Area
0 1000 2000
Scale: meter
FIGURE B-5. MATANZAS INLET, 1978
6. Ponce de Leon Inlet
The history of Ponce de Leon inlet goes back as far as
recorded documents by early Spanish settlers in the 1500's.
Much of the historical information which follows comes from
Jones arv Mehta (1978).
The early Spanish settlers sailed through the inlet as
early as 1513. It was named Mosquito Inlet at that time. The
first recorded depths were made in 1573. The reported depth
was between 1-2 meters. In 1765, the British surveyed the
inlet and reported depths of 2-3 meters. In 1883,
construction was begun on a lighthouse. In 1926, the inlet
was renamed Ponce de Leon. Construction of jetties was begun
in 1968. Each jetty was approximately 1200 meters in length.
The north jetty had a 550 meter weir section to produce an
impoundment basin. Jetty construction was completed in 1971.
A northeast storm breached a channel through the north side
shoal in 1973. This breach was closed by dredging in 1974.
In 1984, the north jetty weir section was closed. The inlet
is 490 meters wide at the jetty entrance and as narrow as
300 meters.inside the inlet shoals. The channel is 5 meters
deep and 60 meters wide.
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