• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Introduction
 Sediment bypassing
 Sediment volumes near an inlet
 Evolution of ebb and flood...
 Sand trapping
 Ebb shoals
 References






Group Title: UFL/COEL (University of Florida. Coastal and Oceanographic Engineering Laboratory) ; 89/002
Title: Short course on principles and applications of beach nourishment, February 21, 1989
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 Material Information
Title: Short course on principles and applications of beach nourishment, February 21, 1989
Series Title: UFLCOEL
Physical Description: 1 v. in various pagings : ill. ; 28 cm.
Language: English
Creator: Florida Shore & Beach Preservation Association
University of Florida -- Coastal and Oceanographic Engineering Dept
Publisher: Coastal and Oceanographic Engineering Laboratory, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1989
 Subjects
Subject: Beach erosion   ( lcsh )
Shore protection   ( lcsh )
Coastal and Oceanogrpahic Engineering thesis M.S
Coastal and Oceanographic Engineering -- Dissertations, Academic -- UF
Genre: non-fiction   ( marcgt )
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Bibliography: Includes bibliographical references.
Statement of Responsibility: organized by Florida Shore and Beach Preservation Association and the Dept. of Coastal and Oceanographic Engineering, University of Florida.
Funding: This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.
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Resource Identifier: oclc - 20302011

Table of Contents
    Front Cover
        Front Cover
    Title Page
        Title Page
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
    Sediment bypassing
        Page 5
        Page 6
        Page 4
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Sediment volumes near an inlet
        Page 15
        Page 14
    Evolution of ebb and flood shoals
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
    Sand trapping
        Page 20
        Page 21
        Page 22
        Page 19
        Page 23
        Page 24
    Ebb shoals
        Page 25
        Page 26
        Page 27
        Page 28
        Page 24
        Page 29
        Page 30
    References
        Page 31
        Page 32
Full Text


UFL/COEL 89/002


SHORT COURSE

ON

PRINCIPLES AND APPLICATIONS

OF


BEACH NOURISHMENT


February 21, 1989


* Instructors *
Thomas Campbell
Robert G. Dean
Ashish J. Mehta
Hsiang Wang




* Organized by *
FLORIDA SHORE AND BEACH PRESERVATION ASSOCIATION
DEPARTMENT OF COASTAL AND OCEANOGRAPHIC ENGINEERING.
UNIVERSITY OF FLORIDA











Short Course


on

Principles and Applications

of

Beach Nourishment


February 21, 1989




Organized by

Florida Shore and Beach Preservation Association
Department of Coastal and Oceanographic
Engineering, University of Forida


Instructors
Thomas Campbell
Robert G. Dean
Ashish J. Mehta
Hsiang Wang











Chapter 4

SEDIMENT STORAGE AT TIDAL INLETS
Ashish J. Mehta
Coastal and Oceanographic Engineering Department
University of Florida, Gainesville



INTRODUCTION

Accumulation of sediment around tidal inlets has become a matter of

renewed interest mainly for three reasons. The first of these is the need to

estimate the shoal volumes, particularly in the ebb shoal, as a potential

source of sediment for beach nourishment. Portions of the ebb shoal can be

transferred to the beach provided there are no measurable adverse effects on

navigation, or on the stability of the shoreline near the inlet. Such an

operation, for example, has been carried out successfully at Redfish Pass, on

the Gulf of Mexico coast of Florida (Olsen, 1979). A schematic example of a

potential site for ebb shoal excavation and sand transfer to the downdrift

beach is shown in Fig. 4.1.

The second reason is the need to assess the role of the inlet in

influencing the rate of erosion of downdrift shoreline, as a result of

interruption or deflection of the littoral drift. For example, the effect of

construction of Port Canaveral Entrance channel, Florida, on the downdrift

beach is shown in Fig. 4.2 (Dean, 1987). The beach shoreline eroded at a

comparatively rapid rate over a ~ 5 km stretch immediately south of the inlet,

and a beach nourishment project was consequently carried out in 1974.

Finally, an evaluation of inlet sediment accumulation is essential to

account for the long term sedimentary budget of shorelines interrupted by

inlets, as schematized in Fig. 4.3. The budget in this case is for the "box"

volume enclosed by shore-parallel and shore-normal boundaries. Q1 through Q8


































Figure 4.1.




5




w


z
LU
z
=


w
n:
0 -5
=
Cl)



Figure 4.2.


A Schematic Example of a Potential Site (Area Enclosed by Dashed
Lines) for Ebb Shoal Excavation and Sand Transfer. Depth Contours
are Hypothetical.


20 40 60
DISTANCE SOUTH FROM PORT CANAVERAL
ENTRANCE (km)

Effect of Construction of Port Canaveral Entrance, on the Atlantic
Coast of Florida, on Downdrift (Southward) Shoreline (After Dean 1987).


I


























. \ ea
Q3. ."


Bay




Q Q7





Q.


Figure 4.3. Box Volume Approach for Sediment Budget near a Tidal Inlet.










are volumetric rates of sediment transport across these boundaries. The

algebraic sum of all the Q's equals the time-rate of change of sediment volume

within the box. For an illustrative example see Jones and Mehta (1978).

In reference to these issues, quantities of particular interest are the

volume of sediment presently stored in the ebb shoal, and the volume of

material trapped, either as a result of training works such as jetties, or as

a consequence of the opening of an artificial inlet and the growth of

associated shoals. There is also the related question of volumetric erosion

of the downdrift shoreline. These issues will be examined with specific

reference to major inlets on the east coast of Florida together with

additional examples from Georgia inlets, following some comments concerning

natural and artificial sediment bypassing at sandy inlets.



SEDIMENT BYPASSING

Natural Bypassing

It has been well established that waves striking obliquely along the

coastline cause a significant transport of sediment along the coastline in

what has been called "the littoral drift system." An inlet located along such

a coastline represents a discontinuity to the littoral drift system, and

although the exact processes of the interaction between the inlet and the

littoral drift system are not fully understood, the gross effects are; namely,

accumulation of sediment in the ebb and flood shoals and a considerable

sediment exchange between the inlet channel and the shoal complexes (Dean and

Walton, 1975, Byrne et al., 1974, and FitzGerald, et al., 1976).

A schematic representation of the sediment transport processes at an

inlet has been given by Bruun et al., (1978) and is shown in Fig. 4.4 (Winton

and Mehta, 1981). Sediment moving down the coast in the littoral drift system























iFLOODOR' \ EBB
\BAY SHOAL : MAIN EBB CHANNEL ,SHOAL
S :.(BED AND SUSPENDED LOAD)
-- MARGINAL FLOOD CHANNEL .
; (BED AND SUSPENDED LOAD)'--

BARRIER :" DRIFT


Schematic Diagram Showing Inlet Ebb/Flood
Transport (After Winton and Mehta, 1981).


Sho


SEA










als and Sediment


^-.> ^- BARRIER ISLAND




FLOOD SHOALS/ :: THROATiii
:. L i // -BAR BYPASSING
::::::: ::: p -


TIDAL
BYPASSING



BARI.iER I.SLAND-.. \ / EB H A
SEBB SHOAL







Figure 4.5a. Bar Bypassing and Tidal Flow Bypassing at an Inlet.


B


Figure 4.4.










enters the inlet mouth mainly through the swash or marginal flood channels,

and to a lesser extent over the ebb shoals. When the flow through the inlet

is in the flood stage, some of the littoral drift will be carried through the

inlet to the bay or flood tidal shoals, some still in suspended form and the

rest as bed load. When the flow through the channel is in the ebb stage, some

of the material which was transported through the channel to the bay shoals

may be transported back through the channel to the ebb shoals and beyond, and

"new" material (i.e. deposited from the littoral drift) will also be

transported out onto the ebb shoals and/or beyond. For inlets with certain

morphologic characteristics and strong ebb flow, some littoral material would

be transported as bed load in deep water past the inlet, while for inlets with

relatively small ebb flows subject to strong wave action at low tide, part of

the material in the littoral drift may effectively bypass the inlet and not

pass back and forth through the main channel.

Thus as noted by Bruun et al. (1978), there are essentially two ways by

which sediment (sand) is bypassed naturally around an inlet (Fig. 4.5a).

These two modes are referred to as bar bypassing in which sand is

predominantly transported from updrift to downdrift beach via the ebb shoal,

and tidal flow bypassing in which the material enters the channel and, under

the combined action of tidal currents and cross-flow (alongshore current), is

eventually transported downdrift. However, during this process of natural

transfer, particularly in the case of tidal flow bypassing, a certain fraction

of the sediment mass transported per unit time may end up in the interior,

bayward of the throat section, thus forming flood shoals.

Under natural conditions, inlets generally differ in character from those

modified, as for example in the case of Florida's east coast inlets prior to

their modification. These natural entrances and their associated shoals










are volumetric rates of sediment transport across these boundaries. The

algebraic sum of all the Q's equals the time-rate of change of sediment volume

within the box. For an illustrative example see Jones and Mehta (1978).

In reference to these issues, quantities of particular interest are the

volume of sediment presently stored in the ebb shoal, and the volume of

material trapped, either as a result of training works such as jetties, or as

a consequence of the opening of an artificial inlet and the growth of

associated shoals. There is also the related question of volumetric erosion

of the downdrift shoreline. These issues will be examined with specific

reference to major inlets on the east coast of Florida together with

additional examples from Georgia inlets, following some comments concerning

natural and artificial sediment bypassing at sandy inlets.



SEDIMENT BYPASSING

Natural Bypassing

It has been well established that waves striking obliquely along the

coastline cause a significant transport of sediment along the coastline in

what has been called "the littoral drift system." An inlet located along such

a coastline represents a discontinuity to the littoral drift system, and

although the exact processes of the interaction between the inlet and the

littoral drift system are not fully understood, the gross effects are; namely,

accumulation of sediment in the ebb and flood shoals and a considerable

sediment exchange between the inlet channel and the shoal complexes (Dean and

Walton, 1975, Byrne et al., 1974, and FitzGerald, et al., 1976).

A schematic representation of the sediment transport processes at an

inlet has been given by Bruun et al., (1978) and is shown in Fig. 4.4 (Winton

and Mehta, 1981). Sediment moving down the coast in the littoral drift system










approached long term equilibrium with the sand transport processes under

prevailing wave and tide environment. Due to the predominant northeast

direction of wave approach, the net longshore transport of sand along the

shoreline is from north to south. Typically, as demonstrated by Fineren

(1938), the characteristics of these inlets included a broad shallow ebb shoal

or ocean bar; perhaps with a channel incised through the bar. Table 4.1

demonstrates that the bar depth was typically 1 to 2 m, much too shallow for

navigational purposes. Although the channels through the bar were

considerably deeper, most of them were still too shallow for modern commercial

purposes. Additional serious navigational disadvantages of these natural

channels were their tortuous alignments and migrational tendencies.


Table 4.1. Natural Depths in Channels and on Ebb Shoals of Florida's East
Coast Inletsa

Inlet Depth on Bar Channel Depth
(m) (m)

Nassau Sound 1.2 6.4-8.2
Fort George 1.2 3.4-7.9
St. Augustine 1.8 3.1-9.1
Matanzas Nearly blocked 3.7-5.5
Mosquito Nearly blocked 2.7-7.9
Canaveral Bight 1.8 to 5.5 9.1-12.2
Indian River Blocked 2.1-2.4
St. Lucie 1.2 2.4-3.7
Jupiter Blocked 0.9-1.5
Lake Worth 0.9 0.9-2.7
New River 2.4 3.1-4.6
Hillsboro 0.8 0.9-1.2
Norris Cut Not affected by sand Shoal
Bear Cut 1.2 2.1-5.2
Cape Florida Channel Not affected by sand Coral reefs

aSource: Fineren (1938)










When an inlet of natural origin is trained by jetties, the associated

sedimentary volumes change until the bottom topography reaches a new con-

figuration, which can be considered to be approximately in equilibrium with

the prevelant currents and wave climate (Dean and Walton, 1975). Often, the

net accretion in the updrift beach fillet is of the same order of magnitude as

the corresponding erosion downdrift. The flood shoal may experience only

minor change in shoal volume. The most dramatic effect occurs at the ebb

shoal, which contains most of the stored material (Marino and Mehta, 1986).

Jetties, possibly coupled with a dredged channel, concentrate the ebb

flow and cause the shoal to move seaward into deeper waters (Fig. 4.5b).

Furthermore over the long term, a secular rise in mean sea level will cause

the nearshore waters to become deeper. The contribution to shoal volume, if

any, from sea level rise along Florida's east coast cannot be evaluated

easily; however, at all the jettied inlets, training is likely to be the

dominant factor. Given the same tide and offshore wave conditions, the

seaward shoal at a trained inlet can store a larger quantity of impounded

sediment (Figs. 4.6a,b) than prior to training. Indeed, in many cases, the

impounded volume associated with the ebb shoal due to training is the only

significant trapped quantity of practical significance (Marino and Mehta,

1986).



Artificial Bypassing

Sediment transfer systems are oftentimes necessary components in an inlet

improvement system for two reasons. First, the ability of a tidal inlet to

naturally flush material from its channel may not be adequate to meet

navigation requirements. Second, the improvement of a tidal inlet may

interfere with the inlet's ability to naturally bypass materials from one side


















FLOOD SHOALS:


B.AY

':BAY



BAY


Figure 4.5b.


IEL

R SHIFT


iEW EB SEA



NEW EBB SHOAL


Plan View Changes at an Inlet Due to Jetties and Dredged Channel:
Shoreline Response to Modification.


Bay


Barrier


Figure 4.6.


Ebb Shoal Elevation View: a) Natural Inlet, b) Trained Inlet (After
Marino and Mehta, 1988).










to the other; hence, shoreline erosion is frequently intensified in the

vicinity of the inlet. Figure 4.7 and Table 4.2 illustrate the locations and

types of sand transfer systems in Florida. Note that more than one transfer

system may be employed at an entrance; the principal method is listed first

and the others are enclosed in parentheses. At Canaveral Harbor Entrance a

moveable sand transfer plant designed two decades ago has not been built.

Perdido Pass, Alabama has been included since it can be physiographically

considered to be part of the Florida panhandle.

The transfer systems have been divided into six types as follows (Jones

and Mehta, 1977):


Type I: Hydraulic dredging from the inlet, navigation channel, shoal areas

or sand trap (excluding weir jetty systems).

Type II: Hydraulic dredging in the entrance vicinity from an impoundment

basin adjacent to a weir jetty.


Table 4.2. Sand Transfer Systems in Floridaa


Entrance Transfer
System

Ponce de Leon II (I)
Canaveral Harbor IV
Sebastian I
Jupiter I
Lake Worth III (I)
S. Lake Worth III (I)
Boca Raton I
Hillsboro II (I)
Mexico Beach VI (V)
East Pass II (I)
Perdido Pass II (I)

aSource: Jones and Mehta (1977)










Ki


Perdido East "
Pass Pass
Mexico Beach N
Inlet




0%


Figure 4.7.


/~-'---


-C'


S--Ponce de Leon 9V
0- Inlet
Canaveral Entrance
Harbor
Sebastian Inlet
S___; .' Jupiter Inlet
--: 7 __ Lake Worth
Inletn
South Lake
--- Worth Inlet
Boca Raton
S Inlet
\. -Hillsboro
Inlet

.4-- ,,


Locations of Several Sand Transfer Systems in Florida (After Jones
and Mehta, 1977).


General Direction
of Net Drift


Bay


Ocean


Figure 4.8. Sediment Volumes near an Inlet (After Marino and Mehta, 1988).










Type III: Fixed bypassing plant.

Type IV: Moveable bypassing plant.

Type V: Land-based transfer by dragline, truck, etc.

Type VI: Jet pump system.



The stability of a tidal entrance is generally thought to depend upon the

balance between the littoral movement of sediment which tends to close the

entrance, and the ability of the entrance to scour the sediment that has been

deposited in the channel. If an entrance cannot maintain a stable navigation

channel by its own flushing capability, then this must be supplemented by

artificial means. However, merely improving an entrance and undertaking an

artificial sand transfer program does not guarantee that navigable depths will

always occur through the entrance. Nor is there any guarantee that beach

erosion conditions on the downdrift side of the entrance will be measurably

improved. These depend upon the stability of the entrance, the manner in

which it naturally bypasses materials from the updrift to the downdrift side,

the method of artificial transfer, and the geomorphic characteristics of the

entrance. The direction of wave approach during the period when sand

deposition on the downdrift beach is carried out is quite important. If this

direction is such as to result in an updrift sand transport along the

shoreline, then a portion of the transferred material may be transported into

the channel, thus clogging it.

Observed entrance stability, based primarily on historic information for

tidal entrances shown in Fig. 4.7, is cited in Table 4.3. Also included in

this table are descriptions of the natural bypassing tendencies (tidal flow,

intermediate between tidal flow and bar, and bar) of the entrances as

determined by a method developed by Bruun (1966) using the ratio of the net










Table 4.3. Florida Inlet Stability and Bypassing Tendencya


Observed Bypassing
Entrance Stability Tendency

Ponce de Leon Fair Intermediate
Sebastian Good Tidal Flow
Jupiter Poor Bar
Lake Worth Fair Intermediate
S. Lake Worth Poor Bar
Boca Raton Poor Bar
Hillsboro Fair Bar
Mexico Beach Poor Bar
East Pass Good Intermediate
Perdido Pass Fair Intermediate

aSource: Jones and Mehta (1977)






Table 4.4. Florida Inlet Bypassing Effectivenessa


Entrance Naviagation Beach
Erosion

Ponce de Leon Fair Fair
Sebastian Good Good
Jupiter Fair Fair
Lake Worth Fair Fair
S. Lake Worth Fair Fair-Poor
Boca Raton Fair Fair-Poor
Hillsboro Good Fair-Poor
Mexico Beach Poor Fair
East Pass Good Fair
Perdido Pass Fair Fair

aSource: Jones and Mehta (1977)










annual littoral drift at an entrance to the maximum discharge through the

inlet during spring tide conditions. At entrances where the numerator

predominates, the offshore bar plays a major role in bypassing material. At

entrances where the denominator predominates, tidal flow bypassing occurs.

The ebb shoal or offshore bar in this latter case is usually limited in size

and volume.

Table 4.4 gives an evaluation of the bypassing effectiveness of each

entrance and its associated transfer system, as related to their combined

ability, i.e. natural and artificial, to aid in maintaining navigable depths

and in retarding downdrift erosion. These estimates are based upon shoreline

changes on both sides of the entrance, dredging data, and discussions with

individuals having local knowledge of the entrance behavior and shoreline

history. As a result, these estimates are essentially subjective, but are

believed to be fairly representative of actual performance. Unacceptable

bypassing effectiveness for prevention of beach erosion at several inlets in

Florida has led to strong recommendations for enhancing sand transfer

capabilities at these inlets (Dean and O'Brien, 1987a,b).



SEDIMENT VOLUMES NEAR AN INLET

Figure 4.8 shows a schematic of an inlet through a land barrier. This

description applies, for instance, to Florida's east coast inlet down to

Government Cut except Nassau Sound and Matanzas, which have no jetties or

dredged channel. Significant features are the sea or ebb shoal, A; bay or

flood shoal, B; updrift and downdrift beach fillets, C and D; and navigation

channel, E. For convenience in describing Florida's east coast inlets, the

updrift beach may be considered to be north and downdrift beach south of the

inlet. Among these features, the flood shoal is typically the most poorly










described area at most inlets, because it occurs in confined waters where

limited bathymetric information exists. Additionally, the history of dredging

or spoil deposition from the internal waterways is not documented well. The

beach fillets, which define alongshore distances corresponding to the updrift

and downdrift influences (up to points 1 and 2, respectively), of the inlet

are difficult to identify unambiguously. The dashed line between points 1 and

2 indicates shoreline position in the absence of the inlet. Point 2 is

particularly difficult to locate, with consequent limitation for the accuracy

of estimates of downdrift loss of sediment over the selected time interval.

At some inlets the ebb shoal distribution varies widely and shoal contours are

not defined clearly.



EVOLUTION OF EBB AND FLOOD SHOALS

Prior to evaluating the various volumes associated with an inlet, it is

instructive to make reference to the manner in which ebb and flood shoals

evolve at a newly cut entrance. Although each situation is obviously unique,

the following examples are illustrative of probable trends.

To trace the evolution of an inlet ebb shoal, a time history of the inlet

must be studied. St. Augustine Inlet, for example, has a unique history and

helps in understanding evolutionary trends as well as difficulties which are

typically encountered in precisely determining the shoal volume at any

particular point in time.

St. Augustine Inlet was cut 4 km north of an existing inlet in 1941.

Figure 4.9 depicts both the previous (1937) and recent (1985) shoreline and

shoal contours. Locations I and J represent the areas through which the old,

natural inlet meandered prior to the new inlet opening at location K, in

1940. The shoal contour lines delineate significant levels of sediment










annual littoral drift at an entrance to the maximum discharge through the

inlet during spring tide conditions. At entrances where the numerator

predominates, the offshore bar plays a major role in bypassing material. At

entrances where the denominator predominates, tidal flow bypassing occurs.

The ebb shoal or offshore bar in this latter case is usually limited in size

and volume.

Table 4.4 gives an evaluation of the bypassing effectiveness of each

entrance and its associated transfer system, as related to their combined

ability, i.e. natural and artificial, to aid in maintaining navigable depths

and in retarding downdrift erosion. These estimates are based upon shoreline

changes on both sides of the entrance, dredging data, and discussions with

individuals having local knowledge of the entrance behavior and shoreline

history. As a result, these estimates are essentially subjective, but are

believed to be fairly representative of actual performance. Unacceptable

bypassing effectiveness for prevention of beach erosion at several inlets in

Florida has led to strong recommendations for enhancing sand transfer

capabilities at these inlets (Dean and O'Brien, 1987a,b).



SEDIMENT VOLUMES NEAR AN INLET

Figure 4.8 shows a schematic of an inlet through a land barrier. This

description applies, for instance, to Florida's east coast inlet down to

Government Cut except Nassau Sound and Matanzas, which have no jetties or

dredged channel. Significant features are the sea or ebb shoal, A; bay or

flood shoal, B; updrift and downdrift beach fillets, C and D; and navigation

channel, E. For convenience in describing Florida's east coast inlets, the

updrift beach may be considered to be north and downdrift beach south of the

inlet. Among these features, the flood shoal is typically the most poorly










described area at most inlets, because it occurs in confined waters where

limited bathymetric information exists. Additionally, the history of dredging

or spoil deposition from the internal waterways is not documented well. The

beach fillets, which define alongshore distances corresponding to the updrift

and downdrift influences (up to points 1 and 2, respectively), of the inlet

are difficult to identify unambiguously. The dashed line between points 1 and

2 indicates shoreline position in the absence of the inlet. Point 2 is

particularly difficult to locate, with consequent limitation for the accuracy

of estimates of downdrift loss of sediment over the selected time interval.

At some inlets the ebb shoal distribution varies widely and shoal contours are

not defined clearly.



EVOLUTION OF EBB AND FLOOD SHOALS

Prior to evaluating the various volumes associated with an inlet, it is

instructive to make reference to the manner in which ebb and flood shoals

evolve at a newly cut entrance. Although each situation is obviously unique,

the following examples are illustrative of probable trends.

To trace the evolution of an inlet ebb shoal, a time history of the inlet

must be studied. St. Augustine Inlet, for example, has a unique history and

helps in understanding evolutionary trends as well as difficulties which are

typically encountered in precisely determining the shoal volume at any

particular point in time.

St. Augustine Inlet was cut 4 km north of an existing inlet in 1941.

Figure 4.9 depicts both the previous (1937) and recent (1985) shoreline and

shoal contours. Locations I and J represent the areas through which the old,

natural inlet meandered prior to the new inlet opening at location K, in

1940. The shoal contour lines delineate significant levels of sediment





































New Shoreline
.........Old Shoreline


New
---- Old


Shoal Contours
Shoal Contours


/ \T


0 1200m


Figure 4.9. Ebb Shoal Changes at St. Augustine Inlet, Florida (After Marino and
Mehta, 1987).










deposition above an "ideal" offshore profile. The ideal profile is defined as

the natural offshore profile in that local area, as if the inlet were not

present. It can be seen that as a result of the opening of a new inlet, the

previous 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 was completely closed by sand deposition in 1957. The

elongated shape of the recent shoal is believed to be due to the presence of a

predominant longshore current to the south. The narrowest part of the shoal

directly east of the inlet is evidence of the dredging done by sidecast

dredges in the shoal area since 1940. The large bulge adjacent to the south

jetty is a direct result of jetty construction in 1957. The shoreline since

construction has moved eastward approximately 750 m adjacent to the jetty.

This suggests jetty sand-trapping during seasonal reversals of the littoral

drift.

This inlet is a mere example of the manner in which ebb shoals form and

how the coastline responds to inlet formation. By constructing jetties of

sufficient length to stabilize an inlet, as was done at St. Augustine, the

shoals are maintained a significant distance away from the inlet. It may also

be noted that dredging seems to have significantly affected the shape of the

shoal. Where a channel has been dredged, the shoal is divided into two

distinct lobes, rather than one large mass as is the case for example at Boca

Raton Inlet, where there is no dredged channel.

Figure 4.10 presents a history of St. Lucie Inlet interior shoaling

volumes (Dean and Walton, 1975). As observed this inlet shoaled rapidly in

its earlier years and gradually approached a much smaller "equilibrium"

shoaling rate as represented by the slope of the right-hand sides of the

curves. The two curves represent shoaling over different areas considered as














: Trend Line for Shoaling Pattern In
Si St. Lucle Inlet (From 3.2 km North of
' Inlet to 1.6 km South of Inlet In I.C.W.W.)





E









M Trend Line for Shoaling Pattern
-,"In St. Lucle Inlet (Vicinity of
S 1.2 km Radius of Inet)
i | Trend Line for Shoaling Pattern
I ?| /in St. Lucle Inlet (Vicinity of
!-- 1.2 km Radius of Inlet)


1883 1890 1900 1910 1920 1!


YEAR


Figure 4.10.


Time-History of Sediment Deposition in the Interior of St. Lucle Inlet
(After Dean and Walton, 1975).


\
* Leon 0


Canaveral


SC.
0


-t. Pierce
t---i T St. Lucie
-- __ Jupiter
.... Lake Worth
South Lake Worth
Boca Raton
S-'_Hillsboro
----\ -Port Everglades
S/'.-Bakers Haulover
| Govemment Cut


Figure 4.11. Nineteen Inlets along Florida's East Coast.


cn


>C
m
2 "

0






E n
U)
01 M
o
Qw

Z co
< F--
0)




x
n
E










a "bay". The widely differing results are indicative of problems inherent in

flood shoal calculations.



SAND TRAPPING

Selected Inlets and Physical Environment

Nineteen inlets along the 580 km shoreline between St. Marys Entrance at

the Florida/Georgia border to Government Cut, Miami, are listed in Table 4.5

(see also Fig. 4.11). St. Johns River Entrance and Ft. George Inlet are two

separate inlets. Ft. George, a small riverine entrance, occurs immediately

north of St. Johns. They are characterized together by a single large ebb

shoal and are therefore treated here as a single inlet system. Eleven inlets

were opened artificially, although three (St. Augustine, Boca Raton and Port

Everglades) have replaced inlets of natural origin in the vicinity. The

remainder are known to have existed naturally since the earliest recorded

history. All presently have two jetties except Nassau Sound and Matanzas. No

training works occur at Nassau Sound. During 1976-77 a portion of the bay at

Matanzas was closed by a dike at a location where a storm-induced breakthrough

had occurred in 1964. Inlet hydraulics and sediment distribution were

influenced measurably by this closure operation (Hayter and Mehta, 1979).

The tidal range and nearshore wave energy are reliable descriptors of the

coastal physical environment. The semi-diurnal spring tidal range varies from

2.1 to 0.8 m (Table 4.5). A nearshore wave energy characterizing parameter

can be defined as the square of the product of the wave height and the period.

Annual average significant height and modal period may be selected for the

present purpose (Marino, 1986). The range of wave energy parameter values are

from 29.1 to 3.8 m2 sec2. Thus both the tidal range and the wave climate

exhibit some variability along the coast, although this variability is










Table 4.5. Florida's East Coast Inletsa

Inlet Origin Training Spring Wave
works tidal energy
range parameter
(m) (m2sec2)


St. Marys natural jetties 2.1 10.9
Nassau Sound natural none 1.9 10.9
St. Johns/ natural jetties 1.7 18.3
Ft. George
St. Augustine opened, 1940b jetties 1.6 18.7
Matanzas natural closures 1.5 20.6
Ponce de Leon natural jetties 1.3 26.7
Port Canaveral opened, 1950 jetties 1.2 24.0
Sebastian opened, 1948 jetties 0.9 28.7
Ft. Pierce opened, 1921 jetties 0.9 26.5
St. Lucie opened, 1892 jetties 1.0 29.1
Jupiter natural jetties 0.9 27.5
Lake Worth opened, 1917 jetties 0.8 14.6
South Lake Worth opened, 1927 jetties 0.8 15.0
Boca Raton opened, 1925b jetties 0.8 16.0
Hillsboro natural jetties 0.8 5.2
Port Everglades opened, 1926b jetties 0.8 5.2
Bakers Haulover opened, 1925 jetties 0.8 5.2
Government Cut opened, 1902 jetties 0.8 3.8


aSource: Marino (1988)
bReplacing a natural inlet in the vicinity; two near
cStorm breakthrough closure inside the bay by a dike


Port Everglades


relatively minor in a global context. From the point of view of tide and

waves, Florida's east coast environment has been classified as moderate

(Walton and Adams, 1976; Marino, 1986).

The net littoral drift is generally from north to south, although a local

reversal is suggested at some inlets. At St. Marys, the net southward drift

is believed to be 420,000 m3/yr, while near Government Cut it is on the order










of 15,000 m3/yr (Marino, 1986). While these estimates are admittedly rough,

the littoral drift rate in the stretch between St. Marys and Jupiter is

considerably larger than that in the stretch between Lake Worth and Government

Cut. There is thus a general correlation with wave energy, which is

relatively low in southern Florida due to the intervening influence of the

Bahama Banks.



Volumetric Calculation

St. Marys, St. Augustine and Lake Worth may be selected as illustrative

examples. Sediment volumes have been calculated for each site by routine

procedures based primarily on bathymetric information, making allowances for

complicated bathymetry or lack of adequate data (Marino and Mehta, 1986).

Relevant quantities listed in Table 4.6 are self-explanatory.



Summary of Results

Three noteworthy quantities are given in Table 4.7 for all nineteen

inlets. These include the most recent, available (post-training) estimate of

the ebb shoal volume, the total material trapped due to training during the

approximate period indicated, the corresponding change of volume downdrift and

the quantity of sediment disposed at sea. The trapped volume in each case

represents the sum of ebb shoal volume change, flood shoal volume change

(where computed), updrift beach fillet volume change, and material disposed at

sea or placed upland, but not on the beach. A positive number indicates

accretion and a negative number implies erosion.

At shorelines where the littoral drift is predominantly unidirectional,

the total volume of sediment trapped by the updrift beach fillet, the ebb

shoal and the flood shoal must equal the volume of sediment denied downdrift.










Table 4.6. Sediment Volumes at Three Florida Inletsa

St. Marys St. Augustine Lake Worth

Quantity Period Quantity Period Quantity Period
(x10-6m3) (yr) (x10-n3) (yr) (x10-m3) (yr)

Ebb shoal 89.2 1870 59.4b 1924 0.0c 1917
95.1 1974 83.3 1979 2.9 1967
Updrift -1.3 1870-1975 1.1 1937-1970 4.8 1883-1957
Downdrift 8.8 1857-1957 5.5 1924-1976 -0.7 1883-1957
Flood shoal -d 0.0 1940 0.0 1917
_d 0.5 1970 _d

Deposit-sea 9.4 1903-1985 0.0 2.1 1929-1985
-beach 0.3 1982 1.2 1940-1976 0.5e 1929-1985
-inland 0.0 0.0 0.9 1970-1985

aSource: Marino and Mehta (1988)
bOld inlet
CInlet opened in 1917
dNot calculated; believed to be small compared to ebb shoal
eExcluding 1.1 x 106m3 bypassed from updrift to downdrift beach, 1968-1986


However, no strong correlation between trapped volume and downdrift volume

change is apparent from the data in Table 4.7, although a general (but not

uniform) trend of decreasing magnitudes of both quantities from north to south

can be discerned. At four inlets St. Marys, Nassau Sound, St. Augustine and

Ponce de Leon downdrift beach fillet volume showed an apparent increase.

Notwithstanding the likelihood of the effect of local reversals in the

direction of littoral drift at these sites, it must be noted that the

downdrift volumetric changes calculated are very approximate. Considerably

lower confidence can be placed in these values than in the estimates of

material trapped.

Over the indicated 99-year period, Nassau Sound trapped 6.3 x 106m3,

despite the fact that no modifications have been made at this large entrance.










a "bay". The widely differing results are indicative of problems inherent in

flood shoal calculations.



SAND TRAPPING

Selected Inlets and Physical Environment

Nineteen inlets along the 580 km shoreline between St. Marys Entrance at

the Florida/Georgia border to Government Cut, Miami, are listed in Table 4.5

(see also Fig. 4.11). St. Johns River Entrance and Ft. George Inlet are two

separate inlets. Ft. George, a small riverine entrance, occurs immediately

north of St. Johns. They are characterized together by a single large ebb

shoal and are therefore treated here as a single inlet system. Eleven inlets

were opened artificially, although three (St. Augustine, Boca Raton and Port

Everglades) have replaced inlets of natural origin in the vicinity. The

remainder are known to have existed naturally since the earliest recorded

history. All presently have two jetties except Nassau Sound and Matanzas. No

training works occur at Nassau Sound. During 1976-77 a portion of the bay at

Matanzas was closed by a dike at a location where a storm-induced breakthrough

had occurred in 1964. Inlet hydraulics and sediment distribution were

influenced measurably by this closure operation (Hayter and Mehta, 1979).

The tidal range and nearshore wave energy are reliable descriptors of the

coastal physical environment. The semi-diurnal spring tidal range varies from

2.1 to 0.8 m (Table 4.5). A nearshore wave energy characterizing parameter

can be defined as the square of the product of the wave height and the period.

Annual average significant height and modal period may be selected for the

present purpose (Marino, 1986). The range of wave energy parameter values are

from 29.1 to 3.8 m2 sec2. Thus both the tidal range and the wave climate

exhibit some variability along the coast, although this variability is










Table 4.7. Florida Inlet Sediment Volumesa


Ebb Material trapped Downdrift Disposed
Inlet Shoal Volume Period Vol.change Vol.at sea
(xlO-6m3) (xlO-6n3) (yr) (x10- 63) (x10-6m3)


St. Marys 95.1 14.0 1857-1979 8.8 9.4
Nassau Sound 40.5 6.3 1871-1970 3.2 0.0
St. Johns/ 131.3 120.9 1874-1978 -23.4 15.7
Ft. George
St. Augustine 83.3 25.6 1924-1979 5.5 0.0
Matanzas 4.8 5.4 1963-1978 -0.2 0.0
Ponce de Leon 17.0 0.7 1925-1974 1.7 0.0
Port Canaveral 4.3 13.8 1953-1985 -0.8 7.5b
Sebastian 0.1 3.2 1924-1976 -0.2 1.4
Ft. Pierce 22.2 66.3 1882-1983 -35.9 2.0
St. Lucie 16.4 20.3 1888-1984 -34.7 0.0
Jupiter 0.3 -3.0 1883-1978 -2.4 0.0
Lake Worth 2.9 4.3 1883-1985 -0.7 2.1
South Lake Worth 1.1 1.5 1927-1979 -0.4 0.0
Boca Raton 0.8 1.3 1920-1981 ~ 0.0 0.0
Hillsboro -0.2c -1.7 1883-1967 -0.5 0.5
Port Everglades ~ 0.0 6.0 1927-1981 -0.5 2.1
Bakers Haulover 0.5 0.3 1919-1969 -0.5 0.2
Government Cut ~ 0.0 3.5 1867-1978 ~ 0.0 0.0


aSource: Marino and Mehta (1988)
bExcluding 15.9 x 106m3 dredged during
at sea


harbor construction and disposed


CNegative sign is indicative of a scour hole at the site


An approximately 0.3 m relative mean sea level rise which has occurred during

this period is a possible cause. Furthermore, modifications carried out at

St. Marys are believed to have influenced sand distribution at Nassau Sound.

At Jupiter and Hillsboro, there was actually a post-training loss of sediment,

although in both cases the volume lost was small in comparison with the gains










at inlets between St. Marys and St. Lucie, with the exceptions of Ponce de

Leon and Sebastian.

At four inlets St. Marys, St. Johns/Ft. George and Port Canaveral -

sizeable quantities of sediment have been disposed at sea over decades. The

type and quality of the disposed sediment were not investigated in this study;

hence no conclusion can be drawn regarding the potential suitability of this

sediment for such uses as beach replenishment. It is significant, however,

that a total of 40.9 x 1063 have been disposed offshore. This number does

not include, for example, an additional 15.9 x 106m3 which also were deposited

offshore during the construction of Port Canaveral harbor. It is not clear

how much of this material was derived from upland dredging.



EBB SHOALS

Florida Inlets

Ebb shoals at eight out of the nineteen inlets contain a total of 405.8

x 106m3 of sediment (Table 4.7). These eight inlets St. Marys, Nassau

Sound, St. Johns/Ft. George, St. Augustine, Ponce de Leon, Ft. Pierce and St.

Lucie thus contain nearly 97% of the ebb shoal sediment. Out of these, the

five northernmost inlets St. Marys, Nassau Sound, St. Johns/Ft. George and

St. Augustine store 350.2 x 106m3, or 83% of the total sediment. Clearly,

most of the stored sediment is found in northern Florida, with relatively

small contributions from the south. Below St. Lucie there is practically

negligible storage of sediment in the ebb shoals.

The observed variability in the ebb shoal volume, ranging from as high as

131.3 x 106m3 at St. Johns/Ft. George to almost zero at Port Everglades and

Government Cut, is indicative of the influences of a wide variety of physical

factors that determine ebb shoal configuration and volume. Prominent among










these factors are tidal range, wave climate and littoral drift, offshore

bathymetry, type of sediment, inlet and bay geometries and runoff. For the

east coast of Florida, tidal range, wave climate and littoral drift, and inlet

and bay geometries are more important. At least in some cases however, an

overriding influential factor, as one would suspect, is likely to be the

holocene processes which have led to nearshore sand deposition ultimately from

riverine sources. Quite simply, sand seems to be available at shorelines where

it was deposited in the first place.



Georgia Inlets

The inlets of Georgia are of particular interest since they are

contiguous to those of Florida's east coast inlets, and because their ebb

shoals store significant quantities of sand. In Table 4.8 nine major inlets

are listed including representative spring tidal range at each inlet, the

corresponding wave energy parameter, and ebb shoal volume. The tidal range

places this shoreline in the mesotidal regime, as opposed to Florida's east

coast which, with the exception of St. Marys area, is microtidal (Table

4.5). On the other hand, the wave energy parameter values suggest wave action

similar to that along the northern part of Florida's east coast (Table 4.5),

which is moderate. Overall, therefore, these nine Georgia inlets are much

more tide dominated than for example Sebastian through Boca Raton.

The ebb shoal volumes, ranging from 15.1 x 106 m3 to 191.0 x 106 m3, are

quite large, and with the exception of St. Catherines Sound are comparable to

northern Florida inlets between St. Marys and St. Augustine. The sum of these

volumes, 828.3 x 106 m3, is double that stored in Florida east coast ebb

shoals. The two southernmost inlets, St. Simons Sound and St. Andrew Sound,

together account for 376.6 x 106 m3 or 45% of the total.










Table 4.8. Georgia Inlet Ebb Shoal Volumesa

Inlet Spring Waveb Ebb
tidal energy shoal
range parameter volume
(m) (m2 sec2) (x 10-6 m3)

Nassau Sound 2.5 13.7 86.6
Ossabaw Sound 2.6 17.1 51.3
St. Catherines Sound 2.5 13.3 15.1
Sapelo Sound 2.5 15.6 165.8
Duboy Sound 2.4 14.2 33.0
Altamaha Sound 2.3 14.2 66.7
Hampton River 2.4 14.2 33.2
St. Simons Sound 2.3 12.5 185.6
St. Andrew Sound 2.3 9.5 191.0

aData generated by Millard Dowd, graduate student, University of
Florida.
bEnergy parameter values derived from Jensen (1983).


Ebb Shoal and Nearshore Environment

Following the opening of a new inlet or the training of a natural inlet,

the rate of growth of the ebb shoal is mainly contingent upon the rate of

supply of sediment from the littoral drift. The larger the drift, the faster

the rate at which the ebb shoal will develop to its new equilibrium size (Dean

and Walton, 1975). It may therefore be argued that, for example, northern

Florida inlets have nearly attained equilibrium, while the southern inlets

have not, given the significantly lower drift in the south compared to the

north. In other words, as mentioned previously the availability of sediment

can be a factor influencing variations in the ebb shoal size as well as the

volume of material trapped. It is, however, noteworthy that, as noted in the

case of St. Lucie Inlet (Fig. 4.10), when a new inlet is dredged or a natural

inlet trained, sediment trapping usually occurs rapidly initially, followed by

a much slower rate of entrapment. It is believed that most of the nineteen










Florida inlets considered have passed the stage of rapid entrapment, that they

are approaching equilibrium sedimentary distributions at a slow rate, and

that, in most cases, the quantities (ebb shoal volume and material trapped) in

Table 4.7 are close to those at equilibrium.

This hypothesis, i.e. that inlet sediment distribution is in equilibrium

with the governing forces due to tides and waves, would imply that variability

in littoral drift may not correlate measurably with variability in ebb shoal

volumes. Without evaluating this hypothesis further, however, it is

worthwhile noting some observations by assuming that one is dealing with ebb

shoals of equilibrium size.

The assumption of equilibrium ebb shoal size was used by Walton and Adams

(1976) to empirically relate the ebb shoal volume to the spring tidal prism,

considering the prism to be the characteristic parameter representing inlet

hydraulics, encompassing the effects of tidal range and inlet-bay geometry.

By further assuming the variability in wave energy to be relatively small, all

Florida east coast inlets were treated as being influenced by a similar wave

climate. The result was a power law expression indicating the ebb shoal

volume to be proportional to prism raised to the power 1.3, approximately.

However, there was significant data scatter about this trend. Such scatter

suggests that the ebb shoal volume may not be related uniquely to prism, and

that the influence of additional parameters must be considered. One possible

candidate is the inlet width-to-depth aspect ratio. The influence of this

parameter is suggested by the data presented in Table 4.9. Three Florida

inlets, Matanzas, Ponce de Leon and Ft. Pierce, are characterized by similar

values of prism, wave energy parameter and channel throat or minimum flow

area. There is a slight increase in prism from Matanzas to Ponce de Leon, and

a significant decrease in the aspect ratio. The data suggest a stronger










Table 4.9. Influence of Inlet Aspect Ratio on Ebb Shoal Volumea

Inlet Spring Wave Throat Width/ Ebb shoal
tidal energy area depth volume
prism parameter
(m3) (m2 sec2) (m2) (m3)


Matanzas 1.42 x 107 20.6 910 123 4.8 x 106
Ponce de Leon 1.63 x 107 26.7 1,170 75 1.7 x 107
Ft. Pierce 1.73 x 107 26.5 980 64 2.2 x 107

aSource: Marino and Mehta (1987)


correlation between increasing ebb shoal volume and decreasing aspect ratio,

than with increasing prism.

Notwithstanding the fact that Matanzas channel is untrained while both

Ponce de Leon and Ft. Pierce have jetties and dredged channels, it may be

inferred from Table 4.9 that given the same tidal prism, wave energy and inlet

throat area, a wide and shallow inlet will have a smaller ebb shoal than that

a narrower and deeper inlet. Although depth at the channel throat is by no

means uniquely related to the natural, shoal-free depths in the ebb shoal

region, it is reasonable to associate a shallow throat with shallow offshore

depths and a deep throat with deeper waters offshore. In the ebb shoal region,

currents are relatively weak compared with those in the channel, and the

prevailing bed shear stress is predominantly due to waves. The minimum flow

depth over the ebb shoal is therefore determined mainly by waves (Mehta and

Joshi, 1988). Any excess material that may deposit over the shoal will be

carried shoreward by wave action (Walton and Adams, 1976). Consequently, all

other conditions being equal, the thickness of stored ebb shoal sediment will

be greater at an inlet with a small aspect ratio than at one with a larger

ratio. The inlets of Table 4.8, where the sediment size is similar (~ 0.2-0.4

mm), appear to illustrate this process, although this concept requires further

consideration including the role of geomorphologic factors.
28










at inlets between St. Marys and St. Lucie, with the exceptions of Ponce de

Leon and Sebastian.

At four inlets St. Marys, St. Johns/Ft. George and Port Canaveral -

sizeable quantities of sediment have been disposed at sea over decades. The

type and quality of the disposed sediment were not investigated in this study;

hence no conclusion can be drawn regarding the potential suitability of this

sediment for such uses as beach replenishment. It is significant, however,

that a total of 40.9 x 1063 have been disposed offshore. This number does

not include, for example, an additional 15.9 x 106m3 which also were deposited

offshore during the construction of Port Canaveral harbor. It is not clear

how much of this material was derived from upland dredging.



EBB SHOALS

Florida Inlets

Ebb shoals at eight out of the nineteen inlets contain a total of 405.8

x 106m3 of sediment (Table 4.7). These eight inlets St. Marys, Nassau

Sound, St. Johns/Ft. George, St. Augustine, Ponce de Leon, Ft. Pierce and St.

Lucie thus contain nearly 97% of the ebb shoal sediment. Out of these, the

five northernmost inlets St. Marys, Nassau Sound, St. Johns/Ft. George and

St. Augustine store 350.2 x 106m3, or 83% of the total sediment. Clearly,

most of the stored sediment is found in northern Florida, with relatively

small contributions from the south. Below St. Lucie there is practically

negligible storage of sediment in the ebb shoals.

The observed variability in the ebb shoal volume, ranging from as high as

131.3 x 106m3 at St. Johns/Ft. George to almost zero at Port Everglades and

Government Cut, is indicative of the influences of a wide variety of physical

factors that determine ebb shoal configuration and volume. Prominent among










The role of bed shear stress in reference to the relationship between the

inlet aspect ratio and ebb shoal volume may be formalized via an illustrative

example. The critical shear stress is that value of the bed shear stress that

is exerted at the point of incipient grain motion. When the actual bed shear

stress exceeds the critical shear stress, the bed material is put into motion.

Jonsson (1966) noted that the wave friction factor, fw, is in general

significantly larger than the current friction factor, fc. The constitutive

expressions representing the shear stress due current, Tc, and waves, Tw are

'T = 0.5 pfcuc2 (1)


and

W = 0.5 pfwuw2 (2)


respectively, where p is the density of seawater, uc is the depth-mean flow

velocity due to current and uw is the near-bed velocity amplitude due to

waves.

For the problem at hand, it is sufficient to consider two inlets of the

same cross-section, but having different width over depth aspect ratio, W/D.

Let inlet 1 be 3 m deep by 400 m wide, and inlet 2 be 6 m deep by 200 m

wide. Thus both inlets have a cross-sectional area of 1,200 m2, but the

corresponding aspect ratios are 133 and 33, respectively. It can be shown that

the maximum ebb velocity through both the inlets will be the same because the

flow areas, and therefore the tidal prisms, are equal (Marino and Mehta,

1987). Let us assume that the velocity, uc over the ebb shoal is as well 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 rough-

ness, i.e. the maximum water particle displacement near the bed, Ab, divided

by the bed roughness, ds. fw can be estimated by using calculated Reynolds

Numbers of 2.85x106 and 1.33x106 and corresponding Ab/ds values of 2,264 and

1,586 for inlets 1 and 2, respectively (Marino, 1986). The f, values are

estimated to be 8.0x10-3 and 9.0x10-3 for inlets 1 and 2, respectively.

The current shear stress, Tc, and wave shear stress, Tw, are obtained for

the two inlets as follows:

Table 4.10. Bottom Shear Stress Calculation

Inlet D Tc Tw
(m) (N/m2) (N/m2)

1 3 0.18 3.23
2 6 0.18 1.62



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 wave shear stress is twice as much in the shallower

inlet, it follows 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), who 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.

30










REFERENCES


Bruun, P. (1966). Tidal Inlets and Littoral Drift, University Book, Oslo,
Norway.

Bruun, P., Mehta, A.J. and Jonsson, I.G. (1978). Stability of Tidal Inlets:
Theory and Engineering, Elsevier, Amsterdam.

Byrne, R.J., DeAlteris, J.T. and Bullock, P.A. (1974). Channel stability in
tidal inlets: a case study, Proc. 14th Coastal Engineering Conf., ASCE,
Copenhagen, Denmark, 1585-1604.

Dean, R. G. (1987). Additional sediment input to the nearshore region, Shore
and Beach, 55(3-4), 76-81.

Dean, R.G. and Walton, T. L. (1975). Sediment transport processes in the
vicinity of inlets with special reference to sand trapping, Estuarine
Research, L.E. Cronin ed., Vol. II, Academic Press, New York, 129-149.

Dean, R.G. and O'Brien, M.P. (1987a). Florida's east coast inlets shoreline
effects and recommended action, UFL/COEL-87/017, Coastal and Ocean. Engr.
Dept., Univ. of Fla., Gainesville.

Dean, R.G. and O'Brien, M.P. (1987b). Florida's west coast inlets shoreline
effects and recommended action, UFL/COEL-87/018, Coastal and Ocean. Engr.
Dept., Univ. of Fla., Gainesville.

Fineren, W.W. (1938). Early attempts at inlet construction on the Florida east
coast, Shore and Beach, 6(3), 89-91.

FitzGerald, D.M., Nummedal, D. and Kana, T.W. (1976). Sand circulation
pattern at Price Inlet, South Carolina, Proc. 15th Coastal Engineering
Conf., ASCE, Honolulu, 1868-1880.

Hayter, E.J. and Mehta, A.J. (1979). Verification of changes in flow regime
due to dike breakthrough closure. Proc. Coastal Structures. 79, ASCE
Alexandria, Virginia, 729-746.

Jensen, R.E. (1983). Atlantic coast hindcast, shallow-water, significant wave
information, WES Wave Information Studies No. 9, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, Mississippi.

Jones, C.P. and Mehta, A.J. (1977). A comparative review of sand transfer
systems at Florida's tidal entrances, Proc. Coastal Sediments '77, ASCE,
Charleston, South Carolina, 48-66.

Jones, C.P. and Mehta, A.J. (1978). Ponce de Leon inlet, Glossary of Inlets
Report No. 6, Rept. No. 23, Florida Sea Grant Program, Gainesville.

Jonsson, I.G., (1966). "Wave boundary layers and friction factors," Proc. 10th
Conf. on Coast. Engr., ASCE, Vol. 1, Tokyo, Japan, 127-148.

Marino, J.N., 1986. Inlet ebb shoal volumes related to coastal physical
parameters, UFL/COEL-86/017, Coast. and Ocean. Engr. Dept., Univ. of Fla.,
Gainesville.










Marino, J.N. and Mehta, A.J. (1986). Sediment volumes around Florida's east
coast tidal inlets, UFL/COEL-86/017, Coast. and Ocean. Engr. Dept., Univ.
of Fla., Gainesville.

Marino, J.N. and Mehta, A.J. (1987). Inlet ebb shoals related to coastal
parameters, Proc. Coastal Sediments '87, Vol. II, ASCE, New Orleans,
Louisiana, 1608-1623.

Marino, J.N. and Mehta, A.J. (1988). Sediment trapping at Florida's east
coast inlets, In: Hydrodynamics and Sediment Dynamics of Tidal Inlets,
D.G. Aubrey and L. Weisher (eds), Springer-Verlag, New York, 284-296.

Mehta, A.J. and Joshi, P.B. (1988). Tidal Inlet Hydraulics, Journal of
Hydraulic Engineering, 114(11), 1321-1338.

Olsen, E.J. (1979). Engineering report for the South Seas Plantation beach
improvement project, Contract No. 3287 Report, Tetra Tech, Jacksonville,
Florida.

Walton, T.L. and Adams, Wm.D. (1976). Capacity of inlet outer bars to store
sand, Proc. 15th Coast. Engr. Conf., ASCE, Vol. 2, Honolulu, Hawaii, 1919-
1937.

Winton, T.C. and Mehta, A.J. (1981). Dynamic model for closure of small
inlets due to storm-induced littoral drift, Proc. XIX Congress of IAHR,
Subject B(c), paper 2, New Delhi, India, 154-159.




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