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Evaluation of the suitability and efficacy of aragonite sand for beach nourishment

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Title:
Evaluation of the suitability and efficacy of aragonite sand for beach nourishment
Series Title:
UFLCOEL-2000004
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Altman, David, 1974-
Place of Publication:
Gainesville Fla
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Coastal & Oceanographic Engineering Program, University of Florida
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English
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xii, 148 leaves : ill. ; 28 cm.

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Subjects / Keywords:
Beach nourishment -- Florida ( lcsh )
Sediment transport -- Florida ( lcsh )
Aragonite -- Florida ( lcsh )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Thesis:
Thesis (M.S.)--University of Florida, 2000.
Bibliography:
Includes bibliographical references (leaves 142-147).
Statement of Responsibility:
by David Altman.

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UFL/COEL-2000/004

EVALUATION OF THE SUITABILITY AND EFFICACY OF ARAGONITE SAND FOR BEACH NOURISHNMENT
by
David Altman Thesis

2000




EVALUATION OF THE SUITABILITY AND EFFICACY OF ARAGONITE SAND
FOR BEACH NOURISHMENT
By
DAVID ALTMAN

A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA

2000




ACKNOWLEDGMENTS

I began my studies in the Coastal and Oceanographic Engineering Department at the University of Florida in August, 1998. First and foremost, I would like to express my heartfelt thanks to my advisor and supervisory committee chairman, Dr. Robert G. Dean; his relentless commitment and enthusiasm has been paramount to my success. My thanks are also extended to Dr. Daniel M. Hanes and Dr. Robert J. Thieke for serving on my committee and for their support and encouragement throughout the duration of this study. In addition, I would also like to thank the Office of Beaches and Coastal Systems of the Florida Department of Environmental Protection for the funding provided for this study. I would like to extend a most sincere thank you to the staff at the Coastal and Oceanographic Engineering Laboratory, in particular, Sidney Schofield and Jim Joiner. The time and effort they each provided are extremely appreciated. In addition, I would like to thank James MacMahan, Cris Weber, Sean Mulcahy, and Al Browder for their encouragement and technical assistance during the course of this study.
I would like to extend the warmest of thanks to my parents for their love and support throughout my college career. They have instilled in me the drive to succeed in all of my pursuits. Finally, I would like to thank Julie Verona for helping me to realize my goals in life. Her unwavering love, support, and confidence has been the guiding light in inspiring me to achieve my aspirations, and has motivated me to strive for new ones.




TABLE OF CONTENTS
A CKN OW LED GM EN TS .................................................................................................. ii
LIST OF TABLES ............................................................................................................ vi
LIST OF FIGURES .......................................................................................................... vii
ABSTRACT ...................................................................................................................... xi
CHAPTERS
I INTRODU CTION ........................................................................................................ 1
1. 1 General D escription ................................................................................................ 1
1.2 Quantifying Sedim ent Transport Characteristics ..................................................... 3
1.3 Previous Studies of Beach N ourishm ent Perform ance ............................................ 8
1.4 Theoretical Predictions of Beach Nourishment Planform Evolution ..................... 11
1.5 Scope of This Thesis ............................................................................................ 13
2 THEORY .................................................................................................................... 15
2.1 Introduction .......................................................................................................... 15
2.2 Governing Equations ............................................................................................ 15
2.3 Analytical Solutions ............................................................................................. 19
2.4 Num erical Solutions ................................................... ......................................... 25
2.5 Effects of Fall Velocity on Transport of Aragonite and Quartz Sediment ............ 29
2.5.1 Shape Factor ............................................................................................... 30
2.5.2 Determ ination of A-V alues ........................................................................ 31
2.5.3 Specific Gravity ......................................................................................... 31
2.5.4 Including Both Shape Factor and Specific Gravity ................................... 33
3 LITERATURE REVIEW OF PREVIOUS ARAGONITE STUDIES ..................... 35
3.1 Introduction .......................................................................................................... 35
3.2 Com position and Origin of Aragonite .................................................................. 35




3.3 Coastal Engineering Issues ................................................................................... 37
3.3.1 Coastal Engineering Properties Relating to Aragonite .................................. 37
3.3.2 Suitability Studies Based on Previous Field and Laboratory Experiments-41 3.3.3 Fisher Island Project ................................................................................... 46
3.4 Environm ental Issues ............................................................................................. 52
3.4.1 Im pacts to Sea Turtles ................................................................................. 52
3.4.2 Im pacts to Infauna Com m unities ................................................................ 55
3.4.3 Im plications to the Baham ian Environm ent ............................................... 56
3.5 Political Issues ...................................................................................................... 57
3.5.1 U .S. Protectionist Legislation ..................................................................... 57
3.5.2 State and Local Political Concerns ............................................................. 59
3.5.3 Baham ian Political Issues .......................................................................... 59
3.6 Sum m ary and Conclusion .................................................................................... 61
4 LAB ORATORY EXPERM EN TS ............................................................................ 63
4.1 Introduction ........................................................................................................... 63
4.2 Experim ental Equipm ent ....................................................................................... 64
4.2.1 W ave Basin ................................................................................................ 64
4.2.2 W ave Gage ................................................................................................. 66
4.2.3 Survey Technique ...................................................................................... 67
4.3 Test Preparation and D esign ................................................................................. 68
4.4 Experim ental Procedures ...................................................................................... 70
4.4.1 Beach N ourishm ent Perform ance Experim ent ............................................ 70
4.4.2 Sedim ent Transport Experim ent ................................................................ 74
4.4.3 Rapid Sand Analyzer Experim ent .............................................................. 75
4.5 Results .................................................................................................................. 76
5 ANALYSIS AND DISCUSSION OF LABORATORY RESULTS ........................ 77
5.1 Introduction .......................................................................................................... 77
5.2 Beach N ourishm ent Experim ent ........................................................................... 77
5.2.1 Shoreline Evolution and Volumetric Density Changes .............................. 78
5.2.2 Average Profile Evolution .......................................................................... 84
5.2.3 Proportion of Sand Rem aining ................................................................... 88
5.2.4 Quantifying the Sediment Transport Coefficient ....................................... 91
5.2.5 D iscussion of Beach N ourishm ent Experim ent .......................................... 96
5.3 Sedim ent Transport Experim ent .......................................................................... 97
5.3.1 Average Profile Evolution .......................................................................... 99
5.3.2 Volum etric D ensity Evolution ............................................ ..................... 103
5.3.3 Quantifying the Sedim ent Transport Rate ................................................ 106
5.3.4 Quantifying the Sediment Transport Coefficient ..................................... 109
5.4 Rapid Sand Analyzer Experim ent ...................................................................... 111
5.5 Com parison Between Laboratory Experim ents .................................................. 117




6 SUMMARY AND CONCLUSION ........................................................................ 120
6.1 Sum m ary of Investigation .................................................................................. 120
6.2 C onclusions ........................................................................................................ 12 1
6.2.1 Beach Nourishment Experiment .............................................................. 121
6.2.2 Sediment Transport Experiment .............................................................. 122
6.2.3 Rapid Sand Analyzer Experiment ............................................................ 123
6.3 Suggestions for Future Research ........................................................................ 124
APPENDICES
A BEACH NOURISHMENT EXPERIMENT SURVEY CONTOUR PLOTS .......... 126 B SEDIT\4ENT TRANSPORT EXPERIMENT SURVEY CONTOUR PLOTS ......... 133 LIST O F REFEREN CES ............................................................................................... 142
BIOGRAPHICAL SKETCH .......................................................................................... 148




LIST OF TABLES

iahk PAP
5.1 Percent Remaining After 60 Minute Testing Cycle ................................................ 88
5.2 K Values Obtained Through Theoretical Methods for the Quartz Beach ............. 110
5.3 K Values Obtained Through Theoretical Methods for the Aragonite Beach ....... 110 5.4 Summary of Comparative Quartz/Aragonite Grain Size Analysis ....................... 114
5.5 Shape Factor Effects on Fall Velocity To Determine A Quartz Equivalent ......... 115 5.6 Equivalent Quartz Diameter Including Shape Factor and Specific Gravity ......... 116




LIST OF FIGURES

Figure PAPe
1.1 Relationship Between the Longshore Component of Wave Energy Flux and the Immersed Weight of Longshore Transport for both Field and
Laboratory Studies, After Komar and Inan (1970) ................................. 6
2.1 Non-dimensional Shoreline Evolution for a Rectangular Beach Nourishment Planform, After Dean and Dalrymple (1999)........................ 21
2.2 Percentage of Material Remaining in Fill Area Versus Dimensionless Time, After Dean and Dalrymple (1999)............................................. 22
2.3 Initially Trapezoidal Planform on a Long Straight Beach......................... 23
2.4 Schematic Diagram for DNRBS Numerical Model, After Dean and Dalrymple (1999)....................................................................... 26
2.5 Definition of Terms Used in the DNRBS Numerical Model Formulation With Perturbed Contours, After Dean and Yoo (1991).............................. 27
2.6 Definition Sketch for Effect of Beach Nourishment on Contours ................ 28
2.7 Relationship Between Mean Grain Size Diameter and Settling Velocity For Varying Shape Factors............................................................ 30
2.8 Relationship Between Drag Coefficient and Reynolds Number .................. 32
4.1 Schematic Layout of the Wave Basin and the Initial Test Conditions at the University of Florida Coastal and Oceanographic Engineering
Laboratory............................................................................... 65
4.2 Particle Grain Size Distribution for Quartz Sediment Used throughout the Duration of this Study.................................................................. 66
4.3 Average Equilibrium Beach Profile of the Quartz Sediment ...................... 68
vii




4.4 Schematic of the Quartz/Aragonite Equilibrium Beach Profile Templates .......... 69
4.5 Schematic Layout of the Beach Nourishment Performance Experiment
and the A ssociated Fill D esign ............................................................................. 71
4.6 Sand Size Distribution of Aragonite and Quartz Fill ............................................ 73
4.7 Schematic Layout of the Wave Basin for the Sediment Transport
E xperim ent ............................................................................................................ 74
5.1 Shoreline Evolution of Quartz Nourishment After 0, 5, 9, 20, 40, and 60
M inutes of W ave A ctivity ..................................................................................... 78
5.2 Shoreline Evolution of Aragonite Nourishment After 0, 5, 9, 20, 40, and 60
M inutes of W ave A ctivity ..................................................................................... 79
5.3 Comparison of Change in Dry Beach Width After 60 Minutes of Wave
Activity for Quartz and Aragonite Test Nourishments ......................................... 80
5.4 Change in Quartz Volumetric Density After 0, 5, 9, 20, 40, and 60 Minutes
of W ave A ctivity ................................................................................................... 81
5.5 Change in Aragonite Volumetric Density After 0, 5, 9, 20, 40, and 60
M inutes of W ave A ctivity ..................................................................................... 82
5.6 Comparison of Loss in Volumetric Density After 60 Minutes of Wave
Activity for Quartz and Aragonite Test Nourishments ......................................... 83
5.7 Quartz Test Nourishment Average Profile Evolution After 0, 5, 9, 20, 40,
and 60 M inutes of W ave Activity ......................................................................... 85
5.8 Aragonite Test Nourishment Average Profile Evolution After 0, 5, 9, 20, 40,
and 60 M inutes of W ave Activity ......................................................................... 86
5.9 Comparison of Average Equilibrated Beach Profile of Aragonite and Quartz
Test Nourishments After 60 Minutes of Wave Activity ....................................... 87
5. 10 Percent Plan Area Remaining Over Time for Aragonite and Quartz Test
N ourishm ent Sections ........................................................................................... 89
5.11 Percent Volume Remaining Over Time for Aragonite and Quartz Test
N ourishm ent Sections ........................................................................................... 90
5.12 Determination of Sediment Transport Coefficient for Quartz Nourishment
Based on Percent Volume Remaining ................................................................... 92
viii




5.13 Determination of Sediment Transport Coefficient for Aragonite Nourishment
Based on Percent Volum e Remaining ................................................................... 93
5.14 DNRBS Simulation of Equilibrated Shoreline After 0, 5, 10, 20, 40, and 60
Minutes of Wave Activity Based on K Value Obtained (1.47) for Quartz
Nourishment Percent Volume Remaining ............................................................ 94
5.15 DNRB S Simulation of Equilibrated Shoreline After 0, 5, 10, 20, 40, and 60
Minutes of Wave Activity Based on K Value Obtained (1.20) for Aragonite
Nourishment Percent Volume Remaining ............................................................ 95
5.16 Sediment Transport Experiment Grain Size Distribution for Aragonite and
Q uartz Sands ......................................................................................................... 98
5.17 Average Profile Evolution of the Quartz Beach After 0, 30, 60, 90, 120, 180,
240, and 360 M inutes of W ave Activity ............................................................... 99
5.18 Average Profile Evolution of the Aragonite Beach After 0, 30, 60, 90, 120, 180,
240, and 360 M inutes of W ave Activity ............................................................. 100
5.19 Total Average Profile Evolution for the Quartz Beach ....................................... 101
5.20 Total Average Profile Evolution for the Aragonite Beach .................................. 102
5.21 Volumetric Density Evolution of the Quartz Beach After 0, 30, 60, 90, 120,
180, 240, and 3 60 Minutes of Wave Activity ..................................................... 104
5.22 Volumetric Density Evolution of the Aragonite Beach After 0, 3 0, 60, 90, 120,
180, 240, and 3 60 Minutes of Wave Activity ..................................................... 105
5.23 Longshore Sediment Transport Rate Evolution for the Quartz Test Section ...... 107 5.24 Longshore Sediment Transport Rate Evolution for the Aragonite Test Section. 108
5.25 Average Sediment Transport Rate Occurring Over Time for the Quartz and
A ragonite Test Sections ...................................................................................... 109
5.26 Comparison of the Settling Velocities for Varying Sand Diameters of Quartz
Quartz and Aragonite Sedim ent .......................................................................... 113
A. 1 Quartz Nourishment Survey Contour Plots After; a) 0 and b) 5 Minutes of
W ave A ctivity ...................................................................................................... 127
A.2 Quartz Nourishment Survey Contour Plots After; a) 9 and b) 20 Minutes of
W ave A ctivity ...................................................................................................... 128
ix




A.3 Quartz Nourishment Survey Contour Plots After; a) 40 and b) 60 Minutes of
W ave A ctivity ...................................................................................................... 129
A.4 Aragonite Nourishment Survey Contour Plots After; a) 0 and b) 5 Minutes of
W ave A ctivity ...................................................................................................... 130
A. 5 Aragonite Nourishment Survey Contour Plots After; a) 9 and b) 20 Minutes of
W ave A ctivity ...................................................................................................... 131
A.6 Aragonite Nourishment Survey Contour Plots After; a) 40 and b) 60 Minutes
of W ave A ctivity ...................................... .......................................................... 132
B.1 Quartz Sediment Transport Survey Contour Plots After; a) 0 and b) 30
M inutes of W ave A ctivity .................................................................................... 134
B.2 Quartz Sediment Transport Survey Contour Plots After; a) 60 and b) 90
M inutes of W ave A ctivity .................................................................................... 135
B.' ) Quartz Sediment Transport Survey Contour Plots After; a) 120 and b) 180
M inutes of W ave A ctivity .................................................................................... 136
BA Quartz Sediment Transport Survey Contour Plots After; a) 240 and b) 360
M inutes of W ave A ctivity .................................................................................... 137
B.5 Aragonite Sediment Transport Survey Contour Plots After; a) 0 and b) 30
M inutes of W ave A ctivity .................................................................................... 138
B.6 Aragonite Sediment Transport Survey Contour Plots After; a) 60 and b) 90
M inutes of W ave A ctivity .................................................................................... 139
B.7 Aragonite Sediment Transport Survey Contour Plots After; a) 120 and b) 180
M inutes of W ave A ctivity .................................................................................... 140
B.8 Aragonite Sediment Transport Survey Contour Plots After; a) 240 and b) 360
M inutes of W ave A ctivity .................................................................................... 141




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 Science
EVALUATION OF THE SUITABILITY AND EFFICACY OF ARAGONITE SAND FOR BEACH NOURISHMENT
By
David Altman
August, 2000
Chairperson: Dr. Robert G. Dean
Major Department: Civil and Coastal Engineering
With the increasingly common use of beach restoration, this study was prompted by the scarcity of quality offshore borrow areas and increased environmental concerns associated with offshore dredging, primarily along the South Florida coast, and the possible use of alternate materials and methods for beach nourishment. Aragonite is formed from calcium carbonate deposits and exists in abundance approximately 60 miles offshore of Florida's lower east coast in the Carribean, and is considered an excellent candidate as a material for beach nourishment.
After conducting an extensive literature review of all pertinent information relating to previous studies involving the use of aragonite for beach nourishment, a series of laboratory experiments was designed to compare the evolution and transport characteristics of quartz and aragonite sediments. The three main experiments discussed in this study xi




include the beach nourishment experiment, the sediment transport experiment, and the rapid sand analyzer test.
The results were analyzed using several approaches and revealed that the average profile, shoreline, and volumetric density equilibration of aragonite nourishments are comparable with, and somewhat superior to, compatible quartz nourishments. The proportion of fill material remaining within project limits was determined to be, on average, 10% higher for the aragonite nourishment section. Analysis of the sediment transport experiment revealed the longshore sediment transport for aragonite was substantially lower than that for quartz, and the direction of cross-shore sediment transport was found to be landward for the aragonite and seaward for the quartz test sections, respectively. These results were attributed primarily to an initial aragonite slope which was considerably milder than the quartz test section, and increased fall velocities of the aragonite sediment associated with a slightly larger grain size (0.30 mm) than that of quartz (0.25 mm) resulting in less suspension times. Based on the settling velocity measurements, aragonite was determined to perform as a comparable quartz equivalent that is 1. 11 times its initial diameter.
The results of the laboratory experiments conducted during this study demonstrated that aragonite is comparable to quartz sand and is suitable for future use in beach nourishment projects. The effectiveness and the ability of aragonite to perform as a nourishment material has been established and should exceed somewhat the predictions of nourishments employing comparable quartz fills.




CHAPTER 1
INTRODUCTION
1.1 General Description
The use of beach nourishment materials as a viable resource in stabilizing and controlling beach erosion is fast becoming the preferred solution in the long term beach erosion control program in the State of Florida. Beach restoration requires the delivery of large quantities of good quality sand to the eroded shoreline in a cost effective manner, while minimizing environmental and social impacts. Typically, in the past, this has been achieved by either the transfer of sand from: 1) an offshore borrow area or to a much lesser extent from 2) an inland source. However, in many places in the State of Florida, the availability of such materials is limited. In areas where there are offshore deposits of materials, the sediment grain size characteristics may be finer than the native, resulting in poor nourishment performance. In addition, the dredging of fine grained materials produces heavy siltation which in turn increases the amount of turbidity in the water. This can pose a potential threat to nearby coral reefs and other sensitive offshore resources. In particular, this concern appears to be more prevalent along the South Florida coast, i.e. Dade and Broward Counties, where the availability of good quality sand has been reduced and potential environental impacts are of prime concern.




2
Due to the lack of nearby sand resources for beach nourishment in South Florida, the possibility of transporting sand from remote areas is considered a feasible solution. One alternate material which is currently under consideration is aragonite sand. Aragonite, which exists in large abundance in the Carribean, appears to be of an excellent grain size distribution and could potentially have other physical characteristics which would make it a superior material for beach nourishment.
Oolitic aragonite is defined as small, round calcareous grains by the American Heritage Dictionary (Second Edition). For the purposes of this thesis, the deposits in the Bahamas and elsewhere will be referred to as either oolitic aragonite or simply aragonite, although they may contain substantial quantities of shell and coral. Monroe (1969) describes oolitic aragonite as being composed of pure calcium carbonate crystalized in the orthorhombic crystal system, exhibiting a smooth, spherical to ellipsoidal shape, and a distinct nucleus. In addition, the distribution of aragonite sands tends to be moderately to well sorted, meaning a large proportion of a sand sample would have similar sizes (Campbell, 1983). Typical quartz sand grains, on the other hand, are of irregular shape and may have a poorly sorted distribution. In this study the relative effects of the differing physical characteristics between aragonite and quartz sands on sediment transport and beach nourishment evolution will be explored.
In December of 1990, construction began on the first full-scale beach restoration project to utilize imported Bahamian aragonite sand in the United States. Fisher Island, located in Dade County and situated south of Miami Beach, was the recipient of the nourishment material. Prior to the nourishment, Fisher Island's 620 meters of shoreline was chronically eroding at a rate of 4 fl/yr due to the long south jetty of Government Cut




3
which prevented sediment transport from reaching Fisher Island. Studies performed nine months after construction concluded that the approximately 23,000 m3 of aragonite which was placed on the shoreline remained within the project area and the shoreline subsequently stabilized, exhibiting no net retreat. Despite the fact that the use of structures was employed in the design of this project, the nourishment, in all respects, exceeded expectations. Characteristically, beach restoration projects performed in a relatively small project area do not fare well. The main hypotheses behind the success of this project are threefold, a combination of 1) the structures designed to protect the nearshore seagrass communities also acted to stabilize and hold the material in place, 2) the aragonite sand is of superior physical and hydrodynamic characteristics which allow it to maintain a higher threshold to sediment movement and less time in suspension, and/or 3) some combination of the two aforementioned hypotheses. The present study will test the relevance of the second hypothesis in order to obtain a better understanding of the sediment transport processes associated with aragonite sand.
1 .2 Quantifying Sediment Transport Characteristics
Quantifying and comparing the sediment transport associated with aragonite and comparable quartz sand grains is extremely important in establishing the relative suitability of aragonite sands for beach nourishment. Sediment transport is defined as the movement of sediment in the nearshore region. Transport may occur in either the cross-shore direction, perpendicular to the beach face, or alongshore, parallel to the beach face. The transport which is directed parallel to shore is known as littoral drift or longshore sediment




4
transport. Littoral drift is due to, in large part, obliquely incident waves. These waves propagate and shoal towards the coastline at an angle resulting in a current directed alongshore. When the turbulence of the breaking waves suspends the sediment, the longshore current carries the suspended sediment downdrift. The durability and life expectancy of any beach restoration project is improved by the ability of the nourishment sands to both be more stable in the presence of wave breaking and to minimize suspension times once incipient motion has occurred. There have been numerous laboratory and field studies conducted throughout the past century to quantify the sediment transport of quartz sands in the nearshore ocean environment. Several of these results will be discussed in this section.
Early efforts to quantify sediment transport relate the amount of longshore energy flux of a wave, when arriving at the shoreline, as the direct mechanism causing sand transport. This theory is known as the 'Wave Energy Flux Method'. Perhaps the most noted study in this area is that of Inman and Bagnold (1963) where they theorized that the immersed weight longshore sediment transport rate I, in units of energy flux, is directly related to the longshore energy flux factor Ps, resulting in: 1I =KPI, (1. 1)
where K is known as the dimensionless sediment transport coefficient. Castanho (1966) developed a formula for littoral drift including the dual effects of current velocity and waves. In his representation of the energy flux factor, he includes the influence of wave steepness at the break point, the ratio of the breaking wave height to the breaking wave




5
length Hb/Lb, beach slope m, and bottom roughness c. In addition, Castanho (1966) distinguishes between the transport due to bed load from that due to sediment suspension. The final formula he proposed for the volumetric littoral transport rate Q, is:
S
y,(1 -p)tanO (1.2)
where y, is the submerged specific weight of the sand grains, p is the in-place porosity usually taken to be as approximately 0.35 for quartz sand grains, 0 is the natural angle of repose for the sediment, and s is a function dependent upon the three breaker types, i.e. plunging, spilling, and surging. The immersed weight longshore sediment transport I, and the volumetric transport rate Q, are related using the following expression: I=Y,(1 -P)Q, (1.3)
which is seen to be of equivalent form to Equation 1.1.
Komar and Inman (1970) simultaneously measured wave parameters and sediment transport at both El Moreno Beach in Mexico, and Silver Strand Beach on the California coast. Based on an array of remote sensors placed in the nearshore, detailed measurements of the direction and magnitude of wave energy flux were obtained. By compiling the data and comparing the results with those of Watts (1953) and Caldwell (1956) to Equation 1.1, they found that the field data best represented a value of 0.77 for the sediment transport coefficient, K. See Figure 1.1.




6
lt,8
FIELD
V) Walls (1953)
U) 107 Caldwell (1956)
Komar and Inman (1970)
0 El Moreno Beach
o Silver Strand Beach 0/ a o 106.
Cr
0 .0
o 05. LABORATORY
~ l0~ *Krumbein (1944)
VI Saville (1950)
o Shay and Johnson (1951) o' p Souvo e and Vincen 9 (1954)
, 0,' oSavage and Fairchild (1959-1970) o Price and Tomlinson (1968) Ao 135 '' "I 1 JI J _,,,i0 1o4 10 1o6 l0 08 109
P (ECn)t sin c. cosoci erg/sec cm
Figure 1.1 Relationship Between the Longshore Component of Wave
Energy Flux and the Immersed Weight of Longshore Transport for both
Field and Laboratory Studies, After Komar and Inman (1970).
The variability in the data presented in Figure 1.1 indicates that the use of one
specific number for K may be inappropriate. In actuality, K values can differ by an order
of magnitude. In Figure 1.1, it is evident that the K values obtained through laboratory
studies are significantly lower than those found in the field. The reason for this is subject
to much debate; however, one possibility is an intrinsic error in the laboratory data due to
scaling effects. When the model studies are scaled up to prototype size the beach sands
used are usually abnormally large (Dean and Dalrymple, 1999).




7
More recent studies of sediment transport were conducted by Dean et al. (1982) and Kamphuis, Davies, Nairn, and Sayao (1986). Dean et al. (1982) found from studying various field experiments that there is an inverse relationship of the sediment transport coefficient, K, with median sediment grain size, D50 Therefore, it may be argued that larger grain sizes can be associated with a net decrease in sediment transport. Building off this work Kamphuis et al. (1986) utilized dimensional analysis to determine an energy related sediment transport expression, resulting in:
7/2
mHb.
Q,=1.28 sin2a bs (1.4)
D 50
In this formula the sediment transport Q, in kg/s, is related to the breaking wave height Hb, breaking wave angle abs, beach slope m defined as the ratio of depth of breaking over the distance from the still water shoreline to the breakpoint, and the constant (1.28) is related to the S.I.. system and assumes salt water. From this expression, the sediment transport coefficient is calculated by:
K= 0.01y2MHb,]K (1.5)
D50
where K is taken to be the constant of 0.77 after Figure 1.1. In 1991, Kamphuis modified Equation 1.4 was to:

2 1.5 0.75 -025. 06
Q=,=2.27HbTP/ Mbs D50 sin 2a,

(1.6)




8
Here the influence of the wave period TP is included. This more recent representation of Equation 1.4 is based on an extensive, coherent set of laboratory experimental data. This expression has been found to correctly predict sediment transport over a wide range of grain sizes and for various field studies. Kamphuis (1991) found the scale effects for determining sediment transport to be rather small since the laboratory effects of beach slopes and grain sizes have a tendency to cancel each other out; however, aragonite is known to have differing hydraulic characteristics than quartz. The extent to which these new hydraulic characteristics would affect flow separation in the boundary layer of the smooth spherical particles has not been investigated as of yet. As a result, scaling effects associated with aragonite in the laboratory are expected, but the magnitudes are unknown at this time.
1.3 Previous Studies of Beach Nourishment Performance
Beach Nourishment is defined as the placement of large quantities of good quality sand on the foreshore and nearshore regions of a beach to advance the shoreline seaward. With decreasing usage of stabilizing structures, such as jetties and groins, beach restoration is fast becoming the method of choice to address chronic erosion problems on the coastlines. The earliest documented beach nourishment project was constructed in 1922 in Coney Island, New York. From 1922 to 1950 approximately 71 more projects were constructed in the United States. However, due to relatively little to no monitoring studies of these projects, limited knowledge was gained. A detailed overview of each project and its performance may be found in Hall (1952). This section is intended to address the




9
conclusions regarding basic nourishment parameters with respect to sand characteristics and placement region established over the past 50 years of beach nourishment.
In 1968, Berg and Duane studied the effects of particle size and distribution on the stability of an artificially filled beach along a recurved spit on the northern shore of Lake Erie, Pennsylvania. This was a small scale project, approximately 1000 feet in length, nourished with 17,000 cubic yards of sediment which was coarser than the native sands. Prior to the nourishment, the Peninsula was migrating downdrift and the shoreline was retreating landward at a rapid rate, resulting in a loss of high value property. The beach restoration project was commissioned in an attempt to either slow down or halt these processes. As a result of their monitoring studies, Berg and Duane (1968) found that the nourished region underwent minimal material loss and maintained a relatively stable profile. On the basis of these findings several conclusions were made. First, beaches composed of coarse sediment are more stable over time and tend to exhibit a decrease in erosion rates. Therefore, nourishing a beach with sediment with larger grain sizes than those existing on the beach results in a decrease in the erosion rate and a more stable profile. More recently, this finding has been investigated by Dean and Yoo (1992) and Donahue (1998), where they were able to both substantiate and, to some extent, quantify the positive effects of utilizing fill sand coarser than the native. Although these theories have withstood the test of time, and are widely accepted today, the effects of changing the hydraulic and physical characteristics of the sediment, while maintaining a uniform grain size distribution, on beach nourishment has not been studied adequately.
The performance of a beach nourishment project based on placement location has also been an area of interest. For the most part, beach nourishments are placed on the




10
foreshore from the berm to a designated specification for initial dry beach width and then tapered seaward in the cross-shore direction until the nourishment toe meets the natural bathymetry. Typically, the initial placement geometry is steeper than the equilibrium profile, resulting in a reduction of dry beach width during the equilibration and stabilization process. Obviously, aesthetically speaking, most clients and beach patrons would prefer to see the nourishment on the dry beach; however, there has been a considerable amount of time and effort devoted to the study of profile or "mound" nourishment. Profile nourishment is the placement of sand in the nearshore at some specified depth, within the active profile, with the hopes that through the constructive forces of wave action, the placed sand will eventually migrate landward and stabilize on the foreshore. Hall and Herron (1950), Browder and Dean (1997), Otay (1994), and Hands and Allison (199 1) all studied the migration patterns of underwater sea mounds. Although Hall and Herron (1950) and Browder and Dean (1997) found no significant migration either landward or seaward of the sea mounds, Hands and Allison (199 1) studied several mounds ranging in depth from 2.1 to 21.3 meters and were able to identify some movement characteristics. There findings indicated that sea mounds located in shallower depths in the nearshore have a significantly better chance of migrating landward than those located further offshore; however, the benefits associated with profile nourishment could not be quantitatively identified. To date, standard industry practice is to nourish the foreshore and allow for a recession due to equilibration in the design, rather than nourish the profile in the hopes that the material will eventually result in an additional dry beach width. One advantage of offshore placement is that sands of lesser quality may be employed resulting in decreased project costs.




1.4 Theoretical Predictions of Beach Nourishment Planform Evolution
A number of investigators have studied the evolution of beach nourishment projects in order to develop predictive techniques for the evolution and longevity of the project. Most notably, Pelnard-Considere (1956) applied the heat conduction equation to develop a one-line analytical planform model to describe the diffusive processes of beach nourishments. The heat conduction equation can be expressed as: dY =Gd2y
dt dx2 (1.7)
where y is the cross-shore coordinate to the anomalous beach, x is the longshore coordinate, t is time, and G is known as the longshore diffusivity coefficient and is defined as:
8(s-1)( -p)h+B)(1.8)
where K is the sediment transport coefficient shown in Figure 1.1, Hb is the breaking wave height, g is the acceleration of gravity, K is the ratio of breaking wave height to water depth, s is the specific gravity of the nourished material, p is the porosity, h. is the depth of closure, and B is the berm height. Dean (1983) found, on the basis of Equation 1.7 and Equation 1.8, that the longevity (t), or the expected life span, of any beach nourishment can be expressed as:




5/2 (1.9)
where 1 represents the total length of the project area. Equation 1.9 basically states that the performance of any project increases rapidly with an increase in project length.
Inspecting Equation 1.8, it is evident from the s and p terms that the hydraulic characteristics of the nourishment sands have a direct relationship to the diffusive characteristics of the nourishment. The grain size characteristics are also related to the diffusive nature of the nourishment and, as stated earlier, are a function of the sediment transport coefficient. Beach nourishment predictions on the basis of sediment compatibility have been investigated by Krumnbein and James (1965), James (1974), and Dean (1974) and a brief explanation of their findings will be offered in this section; however, previous studies on the effectiveness of beach nourishment on the basis of varying the hydraulic components of the sediment are limited.
Krumbein and James (1965) presented a method to compare the fill material with the native material through the respective log-normal grain size distributions in 4 units. They defined the relative compatibility of nourishment material on the basis of the percent of the borrow material which was common to the native sands. This approach is reasonable in that it neglects the finer fraction of the borrow material which may eventually be washed offshore; however, their method neglects the coarser borrow material which is larger than the native sands. Based on this work Dean (1974) adjusted the sediment distributions to account for the benefits associated with coarser than native material, and developed an overfill factor, K, to represent the amount of fill material required in cubic meters to be




13
placed on a beach to be equivalent to one cubic meter of native sands. Therefore, minimizing the proportion of fine sands in the fill material and maximizing the coarser than native sands will ultimately result in a decrease in the overfill factor keeping project costs to a minimum. James (1974) developed a numerical comparison of the borrow material to determine if the overfill ratio would result in either a stable or unstable beach. In addition, James (1974) predicted relative retreat rates of the nourishment based on his stability criterion. As stated earlier, it is widely accepted today throughout the field of coastal engineering that the evolution and associated benefits of beach nourishment projects are directly related to the compatibility and suitability of the fill material.
1.5 Scope of This Thesis
The goal of this thesis is to investigate and qualify the effectiveness and hydraulic suitability of utilizing aragonite sand for beach nourishment. A basic overview of the concepts associated with sediment transport and beach nourishment performance and evolution has been detailed within this chapter. Chapter 2 reviews existing theory including the governing equations and the analytical and numerical solutions which will be employed during the analysis section of this report. In addition, this chapter will include a finther investigation into the effects of fall velocity on sediment transport. Chapter 3 will provide an extensive literature survey of previous applications and studies of aragonite in the field of coastal engineering. An outline of the experimental apparatus, procedures, and test conditions applied in the laboratory will be presented in Chapter 4. Chapter 5 will address the results based on the findings in Chapter 4 and will include a brief discussion




14
on all pertinent information found herein. Chapter 6 concludes and summarizes the study, and identifies potential areas of future research.




CHAPTER 2
THEORY
2.1 Introduction
This chapter presents the various theoretical concepts which will be utilized to both implement and analyze all laboratory testing procedures throughout this study. Section 2.2 of this chapter presents the governing equations related to equilibrium profile geometry and conservation of sand. Furthermore, how these solutions may be applied to planform and beach nourishment evolution through sediment transport analysis will also be discussed. Sections 2.3 and 2.4 of this chapter address both the analytical and numerical solutions for beach nourishment evolution under wave action, respectively. The final section of this chapter examines the effects of fall velocity on transport of aragonite and quartz sediment.
2.2 Governing Equations
The basis for all equations governing the planform evolution of both regular and nourished shorelines includes the concept of an equilibrium beach profile. A profile is the cross sectional shape of a beach as it would look peering across the beach face. Typically, profiles are represented as a line in two dimensions with the elevation, displayed as the elevation difference from mean water to the bed, plotted versus the cross-shore distance, 15




16
directed positive offshore. A profile which is said to be in equilibrium is one in which the shape of the beach has reached a quasi uniform state as a direct result of the natural forces acting on the sand comprising the beach. Bruun (1954) and Dean (1977) studied various beach profiles along the coastal United States and Denmark and found an appropriate representation of a natural equilibrium beach profile of the form: h (y) =Ay 2/3 (2.1)
where h is the depth of the water at any cross-shore position, y, (taken positive seaward), and A is the non-dimensional profile scale parameter based on sediment size or fall velocity. Although this equation has limitations, most notably in representing bars, for the most part, it has been proven and is widely accepted throughout the field of coastal engineering as an acceptable description of equilibrium beach profiles.
One assumption which is usually made to aid in the formulation of sediment transport along beach systems is that cross-shore equilibration of the beach profile occurs rather rapidly, allowing the bulk of effort in examining evolution scenarios to be focused on the longshore direction. As a result, the three dimensional problem is simplified and the scope to investigate the transport associated with planform evolution is lessened. The next step in the formulation of planform evolution is the conservation of sand equation, or commonly referred to as the continuity equation. The continuity equation is: dV =dQ (2.2)
dt dx

where V denotes the volume density, the volume per unit width of beach, and Q is the net




17
longshore transport. By assuming both equilibrium beach profiles and the conservation of sediment in the system, a one-line relationship is established between the change in the shoreline position and the change in volume for each profile, as follows: dVdY(h, +B) (2.3)
dt dt
By canceling out the time dependence on the left and right side of Equation 2.3 and substituting into Equation 2.2, the change in shoreline position may be represented as a function of the gradient in transport, as follows:
(h,, +B) dx (2.4)
where in this case Q is taken to be positive to the right as an observer looks seaward. Therefore a positive gradient in transport will result in a loss of dry beach width while the form of the beach profile is maintained constant. On the other hand, a negative gradient in transport will result in a deposition on the beach face while again maintaining the form of the beach profile.
Referring to Chapter 1, the transport rate Q has been studied and characterized in many ways. For purposes of this study, all sediment transport will be expressed in terms of deep water wave characteristics. By first representing the transport rate as a function of the breaking wave conditions, assuming straight and parallel contours, and neglecting energy losses in deep water this transformation may be completed as follows after Dean and Dalrymple (1999):




K(EC cossinO)b5)
pg(s-1)(1 -p) (2.5)
where b denotes breaking wave conditions. Applying the conservation of energy equation and Snell's law to rewrite the breaking conditions in terms of deep water conditions we have:
(ECcosO) b =(ECgcos 0 (2.6)
and
sinO) =(sinO
C b C o (2.7)
where 'o' denotes deep water wave conditions, 0 represents the approaching wave angle, and C is the wave celerity. In order to express the remaining Cb term in the form of deep water conditions, various shallow water limits may be applied: Cb = (g b)l2, Hb = K k, and Lo = gT2/27t to obtain the depth of breaking, hb. By reinserting this expression into the equation for Cb:
0 2TcOSog3 0.2
Cb =( ) (2.8)
47cos~bK2
Approximating the cosine of the breaking wave angle to be unity, the final transport equation based solely on deep water wave conditions is:




KH24 0.6T 2cos1.2 sinO.
Q9 ~O2y. 0 (2.9)
8= 8(s -1)(1 -p)21" 'K' 29
The Pelnard-Considere (1956) heat conduction equation, Equation 1.7, is obtained by assuming small shoreline orientation changes in Equation 2.5 or Equation 2.9 and combining the result with the continuity equation yields an approximate relationship between the gradient in transport and the longshore diffusivity G, as follows:
dQ 2, y
dx dx2 (2.10)
where G is defined in Equation 1.8. The governing equations presented in this section will provide the reader with the necessary background to understanding the various analytical and numerical solutions for beach nourishment and planform evolution, due to sediment transport, presented in the next two sections of this chapter, respectively.
2.3 Analytical Solutions
Commencing with the governing equations established in the preceding section, namely the Pelnard-Considere equation, various analytical solutions can be applied to examine the efficacy and evolution of both a rectangular beach fill design and a trapezoidal beach fill design, which is essentially a rectangular design including end tapers. Since most beach nourishment projects may be approximated by a rectangular design, the linear




20
solution to Equation 1.7 becomes the superposition of many point solutions throughout the length of the project area. The solution for the change in shoreline position of an initially rectangular nourishment project as a function of longshore position x, and time t, becomes:
Y l 2x l 2x
y(x,t) =-(erf[I( + 1)] -er I(2 1A)]) (2.11)
2 4 1Ft I 4 t I
where 1 and Y are the initial project length and width of the project, respectively and 'erf []' is known as the error function and is defined as:
erf(z) =--2 f oe -U 2du (2.12)
where u is considered to be a dummy of integration. For a normal rectangular beach nourishment with no structures present, the solution can be shown to be symmetric about the centroid of the nourished area. A diagram demonstrating the shoreline evolution for a rectangular planform over a non-dimensional time period may be seen in Figure 2.1.




1 1 0
1' :4.0\ l
1 16.0
---- --------

t-:O
-1 -0.04
. t 0.11

Note:
Shoreline Positions are
"" '. *,Symmetric About xi(i2) = 0
------------ -------------

0 1 2 3 4
x/(&,2)
Figure 2.1 Non-dimensional Shoreline Evolution for a Rectangular Beach Nourishment Planform, After Dean and Dalrymple (1999)

By evaluating the solution for a rectangular planform given in Equation 2.11, it is possible to obtain an analytical expression for the expected longevity of the project. For this specified case the proportion of sand M(t), remaining within the project area may be represented as:
1 I/2
M(t) = -1 f 12Y(x,t)dy (2.13)
IT3)

,=12




Integrating this yields:
M(t)=V (e -( )-1)+erf(/ )
1V -1 (2.14)
This solution is presented in Figure 2.2 where the proportion of fill, M(t), remaining is plotted versus dimensionless time, (Gt)112/1.
Cn 0.5 1.0
a_ 1.0
E t=Time After Placement Ay0
V G=Along shore Diffusivity Initial
-o 1"Asymplote Fill
.. 0.5 -M 12 vGI Planfor
0.5
22
C2 U
n 0 1 2 3 4 5 6
Figure 2.2 Percentage of Material Remaining in Fill Area Versus
Dimensionless Time, After Dean and Dalrymple (1999)
From Figures 2.1 and 2.2 it is clear that initially there is a large net loss to the original rectangular planform, resulting in a decrease in the designed dry beach width; however, the loss rate reduces over time resulting in an average lower loss rate over the project life.
The Pelnard-Considere (1956) equation may also be applied to an initial trapezoidal planform on a long straight beach. As stated earlier and as illustrated in Figure 2.3, a trapezoidal nourishment is an initially rectangular planform with end tapers placed at both longshore limits of the project area.




I

-b -a 0 a b x
Figure 2.3 Initially Trapezoidal Planform on a Long Straight Beach
The analytical solution for the planform evolution of the trapezoidal beach fill is given by Walton (1994) as:

(2.15)

Y
y(x,t) = [(A -AX)erf(AX-A) -(A +AX)erf(AX+A)
2(B -A)

+(B +AX)erf(AX+B) -(B -AX)erflAX-B) + 2 [e -(A 2X2 +B )cosh(2AXB) -e -(A 2X2+A 2)cosh(2A 2X)]]
where A = a/2(Gt)12; B = b/2(Gt)112; X=x/a
Similar to the methodology used with the rectangular planform geometry, a solution to determine the proportion of material remaining, M(t), within the project area may be obtained,

Y

1




M(t) 1[erf(AX+A) -erf(AX-A)]
2 (2.16)
+1 B-AX)[erf(AX-A) -erf(AX-B)]
1 B -AX
+-(-[erf(AX-A) -er/(AX-B)]
2 B-A
1 B +AX
+-(B )[erf(AX+A) -er/(AX+B)]
2 B-A
+ 1 exp[-(AX-B)2]-exp[-(AX-A)2]
218(B -A)
+ 1 exp[-(AX+B)2] -exp[-(AX+A)2]
2 (B -A)
where A, B, and X are defined as above. The solution to Equation 2.16 is similar to that of Equation 2.14; however, the effects of the tapered ends result in an increase in the longevity of the nourishment project.
The rate at which a beach nourishment project spreads is directly related to the longshore diffusivity term G, and the inverse of the square of the project length 1. For the case of a rectangular nourishment it may be shown, via Figure 2.2, that the half-life, M(t) = 0.5, of any given project occurs for a dimensionless time term of 0.46. Therefore, a halflife t50 can be defined as: 12 12
tso50=(0.46)2 -=0.21G G (2.17)
All analytical solutions show that the determination of the efficacy of a beach nourishment project is dominantly due to the project length, 1. Since most nourishment projects are




25
designed for a given length of beach, this parameter usually remains somewhat fixed. Building off of this concept, for the purposes of this study, the project length of all laboratory experiments will remain constant while a determination is made as to how utilizing aragonite versus quartz sediment affects the longshore diffusivity term and ultimately changes the longevity and the efficacy of a nourishment project.
2.4 Numerical Solutions
Various numerical models have been developed to predict the planform evolution of beach nourishment projects. In this section, the rationale and solution for the DNRBS (Department of Natural Resources, Beaches and Shores) model will be employed. Although there are many models of greater complexity, this program is the main predictive technique used throughout the duration of this study. Therefore, this model will be described in greater detail, rather than describe other models which are not used in this investigation.
The DNRBS model developed by Dean and Grant (1989) is a one line model which is based on the diffusion equation and incorporates both the sediment transport equation and the continuity equation. A schematic diagram of the setup for the numerical model is presented in Figure 2.4. Figure 2.4 shows each grid cell location with the transport quantities, Q,, defined at the grid lines and the nourishment shoreline displacement, yi, defined at the grid mid-points. The transport and continuity equations are then solved explicitly as follows. The y values are considered to be fixed while the Q values are calculated as:




n+I 121 =Cq sin2(Pi -cb,)
KHb/ g[K
C .
qi 16(s-)(-p)
16 (s 1)(1 -p)

(2.18)

(2.19)

(2.20)

= ---tan-(yi -Y(i -1)
2 Ax
N
Reference Baseline For Shoreline \_

Figure 2.4 Schematic Diagram for DNRBS Numerical Model, After Dean and Dalrymple (1999)

where




27
where the terms in Equation 2.18 through 2.20 are defined in Figure 2.5. Figure 2.6 demonstrates the pre-and-post nourishment profiles.

North
\

h]
:7

Shoreline
I.
A
Region Influenced by Beach Nourishment
x

- y

h h,
h> h.

Deep Water Contour
N

A

Figure 2.5 Definition of Terms Used in the DNRBS Numerical Model Formulation with Perturbed Contours, After Dean and Yoo (1991)




b) Profile Through A-A
Figure 2.6 Definition Sketch for Effect of Beach Nourishment on
Contours
The subscripts in Equations 2.18 through 2.20 signify the grid locale while the superscripts are indicative of the time increment of wave activity, corresponding to t = nAt. The next step in the formulation is to update all Q'+l values and hold them fixed while the new y values are calculated as follows:
n+I n At n+l n+l
i i" Ax(h, +B) ) (2.21)
The stability criterion for this explicit method of solution is expressed in terms of the time step, At. This requires that the time step used in the program satisfy the following:
At_<.X (2.22)
2G
where G is defined in Equation 1.8.
Of course, as with all numerical models, appropriate boundary conditions must be set, namely: number and length of structures, long open coastline or a small island-like




29
coastline bordered by two inlets, or some combination of the aforementioned situations which requires-the formulation of adequate boundary and initial conditions. All of the testing procedures and pertinent boundary conditions associated with predicting the planform evolution using DNRBS will be described further in Chapter 4 of this report.
2.5 Effects of Fall Velocity on Transport of Aragonite and Quartz Sediment
The settling velocity, 6) is the maximum speed that a particle can fall in a fluid under the action of gravity. This is an extremely relevant parameter in determining the effectiveness of potential nourishment materials because the amount of sediment suspended in a water colun is directly dependent on the settling velocity. The faster a material can settle under the forces of wave activity and gravity, the less likely the sediment is to be transported by the dominant longshore and cross-shore currents, resulting in a net reduction in transport and erosion in the area in question. The theoretical concepts examined in this section consider the settling velocity as a function of two parameters. The first is the actual shape of the sediment and will be discussed in terms of the sediment shape factor after Vanoni (1975). The second is the ratios of the specific gravities of the respective sediments which is based on the work conducted by Rouse (1937). Once these parameters are quantified, the determination of the associated A-values can be calculated through the relationship found by Dean (1987; 1999) and used to determine an equivalent quartz diameter for aragonite sediment.




30
2.5.1 Shape Factor
The shape factor of a given sediment refers to the relative sphericity of the material. For example a sediment with a shape factor (s.f.) of 1.0 would be a perfect sphere, while an s.f. of 0.5 would be indicative of an irregular shaped grain. Figure 2.7, after work conducted by Vanoni (1975), demonstrates the relationship between mean grain size diameter, shape factor, and settling velocity for naturally worn quartz sand particles falling in distilled water at varying temperatures. Investigation of Figure 2.7 demonstrates that an increase in the shape factor, results in an increase in the settling velocities.
0 .... ...
C;--- 08 -. .05.,
0 0" .
0( 6q.. .0.1 0 0
.3......
Figure.2.7Relation..i: Betee MenGanSze .ie n
o........... Veoct for VaynSaeFatr
Thi phnmeo isdet h ac.httedagcefcetishge.. rrglrysae
grains~~~~~ whc anan0hm.upne3ntewte ounfrlne proso ieta
a ~ 3 uniform speia patce Sinc aragnit is known tob.aryuior0n peia




31
in shape, first it is assumed that the specific gravities of both substances is the same, and Figure 2.7 is used to calculate the settling velocities for quartz particles which have a shape factor which is 0.9 or nearly spherical. By allowing these velocities to be comparable to those consistent with aragonite, an equivalent quartz grain size may be calculated and normalized in order to determine the percentage increase due to shape factor alone.
2.5.2 Determination of A-Values
The determination of the associated A-values may be calculated through the relationship found by Dean (1987; 1999) which relates the s ediment profile scale parameter, A, to the settling velocity,
0 44
A =O.O67wfj (2.23)
This relationship has been utilized to calculate the profile scale factor for nearly spherical quartz grains after determining the settling velocity. Once the A-value has been determined the associated mean diameter can be found by linearly interpolating the "Summary of Recommended A Values (m 113)"~ found in Dean (1999). By normalizing the mean diameters to aragonite, the percentage increase of the diameters based on the shape factor, %,f. may be calculated.
2.5.3 Specific Gravity
The specific gravity of quartz sands is approximately 2.65, while the average of the various specific gravities for aragonite, based on published results, is 2.90. Specific gravity is defined as the ratio of the density of a substance divided by the density of water. Therefore, the greater relative density of aragonite should result in both an increase in settling velocities and an increase and an associated ability to withstand the motion induced




32
by currents. This can be explored further through the investigation of Figure 2.8, after work conducted by Rouse (1937), which is a plot of the resistance (drag) coefficient versus Reynolds Number.
I -- -7 j l -,T=
Ik I t! g-4--i
1. I,"<
Figure 2.8 Relationship Between Drag Coefficient and Reynolds
Number
The drag force FD, and the immersed weight of the assumed spherical sediment particle Ws, are:
2 2
CDpd Cf (2.24)
and
W =(O-O)gnd (2.25)
6




33
Equating Equation 2.24 and Equation 2.25 and solving for settling velocity, wf, yields:
(9"-l)gd (2.26)
3 CD
Assuming the drag coefficient, CD, to be the same for quartz and aragonite sands, the ratio of the settling velocities may be written in terms of their respective specific gravities:
Of p-1 (2.27)
Letting Pa=2.90 and p,=2.65 yields:
6)4
1.0 (2.28)
2.5.4 Including Both Shape Factor and Specific Gravity
Multiplying the percentage change in equivalent diameter due to specific gravity by the percentage change due to the shape factor (i.e. CD) will yield the total percentage change of the equivalent diameter. For example, defining the normalized quartz grain diameter for aragonite as the percentage change due to the shape factor alone, %s.f., (which assumed constant specific gravity), then,




%total=%5f% S.g. (2.29)
substituting,
%total =(I. 12)(1.08) = 1.21 (2.30)
or the equivalent calculated quartz diameter is 1.21 times that of the original aragonite median diameter.
The applications of calculating an aragonite/quartz equivalent grain size is twofold. First, quantifying a quartz equivalent grain size, provides a better overall understanding as to the predictive nature of the evolution of an aragonite nourished project. Most previous studies of beach nourishment performance have been carried out on quartz sand beaches, thus yielding considerable knowledge. Therefore, an aragonite/quartz equivalent enables researchers to apply the lessons learned in previous studies. Second, the process of identifying the settling velocities of aragonite and quartz sands of a compatible grain size will yield some insight into the different hydrodynamic characteristics between the two sediments and will allow for better performance predictions. The next chapter in this report will discuss all of the characteristics of aragonite sand and will include some previous studies which have been performed with the material to attempt to quantify the potential benefits, if any, of utilizing aragonite sand for fill material.




CHAPTER 3
LITERATURE REVIEW OF PREVIOUS ARAGONITE STUDIES
3.1 Introduction
The scarcity of nearshore nourishment materials, increased dredging costs, and a growing concern for environmental impacts caused by beach restoration has prompted this study to determine the potential use of aragonite sand as an effective alternative for beach nourishment material. The purpose of this chapter is to provide a comprehensive review of pertinent literature regarding the use of aragonite sand for beach nourishment. This survey will include all information relating the engineering, environmental, and political issues regarding the utilization and implementation of aragonite sand for beach restoration, as well documenting previously examined field studies and nourishment projects.
3.2 Composition and Origin of Aragonite
As stated earlier in Chapter 1, Monroe (1969) describes oolitic aragonite as being composed of pure calcium carbonate crystalized in the orthorhombic crystal system, exhibiting a smooth, spherical to ellipsoidal shape, and a distinct nucleus. Although the formation of oolitic aragonite is uncertain, several theories have been advanced. The organic theory suggests that aragonite originates through the precipitation of calcium 35




36
carbonate from seawater during periods of increased bacteriological activity. The occurrence of shell and shell fragments of various marine pelecypods and gastropods along with fragments of tubes made by burrowing marine worms known as Chaetopterus found in aragonite deposits tends to lend credence to this hypothesis (Monroe, 1969). Traditional inorganic theory suggests that aragonite forms where colder oceanic waters flow onto warm shallow waters precipitating the calcium carbonate around nuclei of various sorts (Monroe, 1969). This theory is also plausible considering that these conditions exist over the Bahama Banks, where extensive deposits of oolitic aragonite are found. Typically, these Bahamian deposits are generally made up of smooth, rounded, moderately sorted particles (CPE, 1997; USACE, 1987).
Deposits containing approximately 40-75 billion cubic yards of aragonite, located 50 miles from Miami, Florida, have been leased by the Bahamian government to Marcona Ocean Industries since the 1960's. Marcona constructed an eighty-five acre island, Ocean Cay, as their base of operations, and promptly began commercially mining the aragonite (Slatton, 1986). The operations at Ocean Cay consist of dredging the material with a cutterhead suction dredge, screening for rocks and impurities, stockpiling on Ocean Cay, and eventually loading and transporting the aragonite by ship to the U.S. mainland, where Marcona has holdings at various ports along the Florida coast (Steve Dowd-Marcona representative, personal communication, 1999). Although the use of aragonite for beach restoration has been limited, it is widely employed in various industrial applications, including the manufacture of Portland cement and glass, agricultural lime, a filtration media, fine aggregate, flue gas desulferization, and as an additive for animal and poultry feed (Slatton, 1986).




3.3 Coastal Engineering Issues
Although aragonite has been proven to possess numerous beneficial qualities and uses to the industrial field, the use of Bahamian aragonite for purposes of beach nourishment is limited. This section will explore the engineering issues regarding oolitic aragonite and its potential to perform as a quality beach nourishment material. This will include a discussion of the coastal engineering properties of aragonite and its suitability to perform as a nourishment material based on previous laboratory and field studies. In addition, this section will incorporate a review of the Fisher Island project, which to date is the only beach nourishment project in Florida to employ the use of oolitic aragonite sand.
3.3.1 Coastal Engineering Properties Relating to Aragonite
There are several advantageous characteristics aragonite possesses which lead to its consideration of the sediment as a beach nourishment material. These properties will be detailed in the following section.
Grain Siz
The average grain size of aragonite sand is generally larger than that of quartz sand, native to Florida beaches. Average aragonite grain sizes are approximately 0.30 mm, while quartz sand is usually in the vicinity of 0.20 nim for most South Florida beach sands and fill materials (Cunningham, 1966). Although data which explicitly relate grain size with beach face slope of aragonite beaches are not available, this increase in grain size will provide a steeper, more stable slope, and accompanying foreshore, when placed on a beach composed of finer grained material. Settling tube analyses indicate that aragonite behaves




38
as a hydraulically coarser material than quartz grains of equivalent geometric size (Campbell, 1983). Further studies suggest that aragonite perforins as quartz sand with an equivalent grain size which is 1.36 times coarser than that measured by sieve analysis (Olsen and Bodge, 1991). Coarser sediments tend to either be able to withstand the destructive forces to a greater extent than finer grained sands, or the constructive forces have a larger positive effect (Dean, 1999). This has been documented by the Beach Erosion Board in 1933, which found steeper New Jersey beaches were comprised of coarser grained materials, and was subsequently observed by Bascom (1951), who positively correlated beach face slope with grain size for California beaches. On the basis of this parameter alone, less volume of beach fill is needed to provide a desired design dry beach width of a nourishment project, ultimately, reducing construction costs (Slatton, 1986). Grain Shap-e
As stated earlier, aragonite is generally smoother and more rounded to elliptical in shape than quartz sand. This higher sphericity has been expected to result in less sediment transport based on settling velocity. To date, measurements of sand shape are not included in coastal engineering analyses due to the difficulties in predicting the transport of sand; however, through a qualitative assessment, it is evident that a more angular sediment (such as quartz) will encounter more friction after suspension, causing it to settle slower than a smooth rounded material (such as aragonite). Obviously, the associated transport should also be increased because the longer a sediment remains in suspension the further the sand grain is displaced (Dean, 1999). Therefore, according to this theory, aragonite should experience less time in free suspension, which should reduce the transport rates.




SpecificGravity
The specific gravity of oolitic aragonite Bahamian sands has an average value of 2.90 (ranging from 2.88 to 2.92 in the literature), while the specific gravity of quartz is approximately 2.65. Specific gravity is defined as the ratio of the density of a substance divided by the density of water. Therefore, the greater relative density of aragonite should result in an increase in settling velocities and a greater ability of the sediment to withstand the motion due to currents. (Cunningham, 1966). As proven by Inman and Bagnold (1963), and followed by Dean's (1973) sediment transport models which show that the longshore sediment transport rate is inversely proportional to the specific gravity of the material which, ultimately, should increase the life of the nourishment project due to a reduction in end losses (Dean, 1999).
Natural Adhesion
Aragonite has been observed to possess a natural adhesive quality. The compaction of the sediment is greater than that of sand; however, it remains soft enough to permit digging by hand (Slatton, 1986). No evidence of concretion has been observed in the stockpiles at Ocean Cay, and it seems rather unlikely that aragonite would form beach rock (Beachler, 1995; USACE, 1985). Although the genesis of this adhesive quality is uncertain, it is assumed that this unique characteristic should provide a greater resistance to erosion while permitting sea water to infiltrate the foreshore of the swash zone (Cunningham, 1966). This hypothesis has yet to be explored, prompting further exploration in-the laboratory. In addition, environmental issues regarding the ability of sea turtles to nest in adhesive aragonite sand is of prime concern and will be discussed later in this chapter.




G~radation
Aragonite sand, as stated earlier, is moderately sorted, which means that the sediment exhibits a moderate spread in its grain size distribution curve. It is extremely high in quality and contains small quantities of pebbles, silts, and/or clays (Cunningham, 1966). In addition, the Marcona operation at Ocean Cay includes a screening and washing procedure to remove any foreign objects or rocks which may have been dislodged by the dredge, and also eliminates most silt size grains (Slatton, 1986). This is a desirable property in any beach restoration project. First, the community receives a uniform, safe, rock free beach. Secondly, the removal of silts and clays is expected to reduce turbidity related impacts near offshore reefs and in the surf zone (Beachler, 1995). The placement of the sand would produce turbidity; however, the amount and duration would be significantly less than dredging from an offshore borrow site (CPE, 1985). This can be attributed to aragonite's low concentration of silts, on the order of 0.5 to 2%, when compared to that of quartz sand in the vicinity of Broward County, which generally contains from 3% to 10% silts in certain places (CPE, 1985). Moreover, eliminating the need to dredge from an offshore site, drastically reduces the potential to harm offshore reef communities (Beachler, 1995). Finally, the moderately sorted grain size distribution allows the engineer to predict, with some certainty, how the design will perform over time since in traditional nourishments fine grains of sand could be carried offshore, resulting in unforeseen losses.
Aragonite sand is bright white in color and is the main reason the Bahamas are known for their "beautiful white sand beaches". Aesthetically, nourishing with aragonite




41
would result in an attractive beach and could help bolster tourism for that municipality. However, the white sand reflects solar radiation more than quartz resulting in cooler temperatures (Cunningham 1966). There has been some concern as to whether this could adversely affect the ability of loggerhead sea turtles to reproduce, which will be addressed in Section 4 of this chapter.
3.3.2 Suitability Studies Based on Previous Field and Laboratory Experiments
A number of laboratory and field studies conducted to test the suitability of aragonite as a beach nourishment material date back to the mid 1960's. The purpose of this section is to review these studies and their findings in detail to assess both the effectiveness of the aragonite sand and to determine appropriate areas for future research. PMVer Park Beach Field StudIn 1965-66 the first small scale prototype study designed to test the effectiveness of oolitic aragonite as a beach nourishment material was conducted in Pepper Park Beach in St. Lucie County, Florida by the Union Carbide Corporation (Monroe, 1969). Pepper Park Beach is located approximately two miles north of the Fort Pierce Inlet. This particular test site was chosen because of the favorable prevailing stability in the foreshore slope and the compatibility of the grain size distribution, at mid-tide level, with that of aragonite (Cunningham, 1966). The basis for this experiment assumed that over the span of a few years beaches tend to exhibit either accretional or erosional trends; however, shorter time cycles exist which induce both deposition and erosion allowing for the assessment of the performance of the test material to these prevailing processes of the environment (Cunningham, 1966). Pepper Park beach was observed to accrete from




42
September to February, when the dominant net littoral transport is from the south, and erode slightly over the remainder of the year when the swell direction and associated transport is from the north (Cunningham, 1966).
The procedure consisted of placing 1,000 tons (approximately 588 cy, using a conversion factor of 1.7 tons per cy as proposed by CPE, 1997) of aragonite sand, of 0.30 nim mean grain size diameter over a beach length of 200 ft, and an equivalent volume of native sand from the adjacent backshore at comparable locations on the foreshore of Pepper Park Beach. The materials to be tested were placed, in equal increments, at the top of the foreshore, thereby allowing the uprush of successive high tides to naturally disperse the sediment which provided space to place the next load. The slopes of the test beaches were not artificially graded, enabling the natural wave activity to shape the respective profiles of both test beaches. The experiment was designed to commence at the beginning of the erosional cycle in order to observe and compare the relative erosion rates of both the aragonite test beach and the native nourishment beach. (Cunningham, 1966).
The monitoring of the experiment consisted of daily inspections of estimated breaking wave height, period of breaking waves, distance in feet below lowest berm of the mean high water line, wind velocity and direction, precipitation in the previous 24 hours, and general appearance of the test beaches (i.e. ridges, troughs, shell deposits, sand mixing, etc.) (Cunningham, 1966). Profile and sampling surveys were conducted every seven days and were carried out to the 5 foot depth contour every 14 days (Cunningham, 1966). This schedule was to continue until adequate information regarding the utility of aragonite as a beach nourishment material could be satisfactorily ascertained (Cunningham, 1966).




43
Unfortunately, the results of this experiment were inconclusive. Due to an unusually low tidal cycle over the course of the experiment, the test materials were forced to be moved 15 feet closer to the ocean than originally planned (Cunningham, 1966). However, Cunningham did find the aragonite nourishment test site remained slightly more stable than the native sand site over a six month investigation period. Nonetheless, due to the small amount of fill material and inadequate controls, the results proved inconclusive in determining the effectiveness of aragonite as a nourishment material (Olsen and Bodge, 1991).
Oolitic Aragonite and Quartz Sand* Laboratory Co=arison Under Wave Action
Prompted by the aforementioned field study, the Coastal Engineering Research Center (CERC) began investigating the potential of new sources of suitable beach fill material for use in beach nourishment purposes, specifically for the South Florida coast. CERC conducted saltwater wave tank tests whereby both a quartz sand beach and an aragonite beach were tested simultaneously under wave action (Olsen and Bodge, 1991).
This laboratory test setup and procedure described by Monroe (1969), consisted of a 96 foot long, 18-inch wide flume partitioned in the center by a separating wall in order to simultaneously test the aragonite and quartz sand beaches under similar wave activity using artificial sea water. The mean grain size diameter of the aragonite was 0.27 mm and was comparable to the grain size diameter of the quartz material. The profiles of both beaches were initially scraped to establish the same initial equilibrium conditions, and were subjected to differing wave heights ranging from 0.18 to 0.53 feet. The wave periods varied from 1. 19 to 5.06 seconds. After all runs were complete, a final test was conducted




44
simulating beach nourishment. Throughout the test series, profiles were measured periodically and graphed comparatively.
The analysis of the experimental results consisted of the calculation and graphical comparison of the cross-shore sediment transport for both materials. The profiles of both beaches were found to maintain a similar shape and the calculated transport rates based on profile analysis were comparable. The results of the experiment generally indicate that, from a hydraulic standpoint, the aragonite material is as good a beach material as quartz sand, if the wave climate of the beach to be nourished does not require sand sizes outside of the range of oolitic aragonite available (Monroe, 1969). Thus, beaches with native quartz grain sizes comparable to aragonite may be considered as potential candidates for future aragonite nourishment. In addition, Monroe states that future nourishment projects employing aragonite sediment depend on the ability to place the sediment at a cost competitive with traditional sand sources. Furthermore, since the materials used had prototype size characteristics and were tested in a small-scale laboratory setting, no accurate correlation to a prototype wave climate could be established (Monroe, 1969). Evaluation of Oolite Araganite for Beach Nourishment in South Florida, USACE 1995
In 1985, the U.S. Army Corps of Engineers conducted laboratory tests to further explore the suitability of aragonite sand for beach nourishment in South Florida. These experiments included abrasion evaluation, wet/dry testing in fresh and sea water, dissolution testing to simulate acid rain conditions, detailed microscopic constituent determination, x-ray diffraction analysis, bulk specific gravity, and absorption (Olsen and Bodge, 1991).




45
The abrasion tests were performed in a split wave tank. After representing approximately two years in nature, the Corps found some breakdown of shell fragments and cemented oolitic aragonite. However, the amount of material that was abraded was relatively small, and no difference was observed between the aragonite-only side of the flume and the aragonite-quartz (equal volume) side (Beachler, 1995).
The possibility that aragonite could dissolve when subjected to the conditions found on Florida's beaches was also of concern. There have been speculations that acid rain and/or freshwater discharges from adjacent inlets could result in an increase in acidic conditions that could act to chemically dissolve and remove the calcium from the calcite particles, which make up aragonite (CPE, 1985; USACE, 1985; Beachler 1995). This prompted the USACE (1985) to perform wet/dry testing of aragonite in fresh and sea water, and solution testing of aragonite for acidic rain conditions with a ph of 4.6. The results of this experiment demonstrated that no apparent dissolution of the aragonite occurred for any of the prescribed conditions (Beachler, 1995).
The USACE concluded from these experiments that aragonite "appears to be suitable for beach renourishment material" (Olsen and Bodge, 1991). Moreover, these tests showed that aragonite's physical characteristics are superior to those of quartz sand which should correlate to an increase in nourishment performance and resulting longevity (Olsen and Bodge, 1991).
Abrasion Testing
The Mohs hardness of aragonite sand ranges from (3.5 to 4.0) while the hardness of quartz sand is classified as 7.0 (Beachler, 1995). This difference between the two materials has led to some concern regarding the relative durability and resistance of the




46
aragonite to abrasion when in contact with the harder more angular shaped quartz sand. Dean (1989), following the Corps study in 1985, found that aragonite in a quartz/aragonite sand mixture, subjected to artificial tumbling in a salt water solution, abraded more rapidly than just a pure aragonite sample. However, the aragonite demonstrated an ability to "season" rapidly, such that most of the abrasion occurred during the initial tumbling of the sample, with subsequent minimal abrasion occurring thereafter. One plausible conclusion to this experiment is that the abrasion of the aragonite may be minimized by nourishing beaches made up of less native quartz sediment, or in areas of high native calcium carbonate concentrations (Olsen and Bodge, 1991). In addition, if this abrasion factor can be quantified, in the future an allowance could be provided in the design of any nourishment project from inception, to account for this loss of sediment.
3.3.3 Fisher Island Project
Background
In December of 1990, construction began on the first full-scale beach restoration project to utilize imported Bahamian aragonite sand in the United States. Fisher Island, located in Dade County and situated south of Miami Beach, was the location of the nourishment project. Fisher Island was created in 1904 when the southern tip of what is now known as Miami Beach was breached to provide a navigation channel, known as Government Cut (Olsen and Bodge, 1991). After the channel was created, jetties were placed on the south end of Miami Beach and on the north end of Fisher Island, isolating the island from the predominantly southerly littoral drift, resulting in a net loss of sediment supply to the system. Records indicate that since the completion of the navigation project




47
in 1904, the island's Atlantic coastal shoreline has retreated an average of about 4 ft/yr (Olsen and Bodge, 199 1).
Fisher Island, today, is a well developed, private residential and resort community consisting primarily of large upscale condominium complexes. Naturally, the community and owner of the resort facilities recognized the need to nourish the beach to prevent the on-going erosion and to enhance the area. Olsen Associates, Inc. (1991) investigated several options that would best suit all involved. Due to the scarcity of offshore borrow areas, the environmental concerns regarding utilizing upland sources, the owner's enthusiasm to create a tropical beachfront atmosphere, and the minimal volume requirements needed to support the project (when compared to typical beach nourishment projects) made the use of imported Bahamian aragonite sand an excellent candidate (Olsen and Bodge, 199 1).
Detailed Site Characteristics
As a result of the isolation of Fisher Island from the net littoral drift, created by the Government Cut jetties, the island's southern border eroded 600 to 850 feet before it was stabilized by a revetment and terminal jetty in the early 1980's (Olsen and Bodge, 199 1). In contrast to most of Fisher Island's shoreline, the northern 250 feet of shoreline has remarkably remained stable over the past 90 years and has produced a small downdraft fillet. This is due to a shadow effect that is caused by wave sheltering by Government Cut's south jetty, which is consistent with the predominant northeast wave direction. Further grid-based wave refraction analysis, conducted by Bodge (1989), suggests that the shadow effect results in a nodal point, approximately 500 to 1500 feet south of the southern jetty. This results in a small net northerly littoral drift to the north of the nodal point, and




48
a rapid increase in the southerly drift to the south of the nodal point. This rapid increase in southerly drift has been estimated to be on the order of 120,000 cy/yr at the south end of Fisher Island. The pre-project dry beach width ranged from 20 to 46 feet along the southern 250 feet of shoreline, and less than 10 feet along the south-central 850 feet of shoreline (Olsen and Bodge, 1991). Although the southern terminal groin is successful in retaining some of the net southerly littoral drift, sand does bypass into Norris Cut, to the south, where it is eventually lost to ebb and flood tidal currents. The shadow effect causes sand to be transported northward where it becomes impounded at the base of the southern Government Cut jetty and eventually recirculates around clockwise where it returns to the shoreline approximately 1500 feet downdrift. These littoral drift scenarios result in Fisher Island representing its own littoral cell (Olsen and Bodge, 1991). Olsen Associates, Inc.(1 992) found seagrass beds about 130 feet seaward of the mean high water line in the southern half of the island, and in scattered clusters 50 to 90 feet seaward from NMWL on the northern half. They determined that for environmental safety, precautions were required in order to prevent encroachment of the nourishment material on the seabeds. Project Desig
The project was designed to nourish the Fisher Island shoreline with Bahamian aragonite sand, while both protecting the natural seagrass beds and the integrity of the nourishment itself. Olsen and Associates (1991) solved this problem through the use of "tuned" structures. Tuned structures, basically, refer to structures designed to force the beach planfonn to equilibrate to a shape that it would not have otherwise. The "tuned" structures consisted of 6 T-head groins spanning the length of the project, approximately 620 m, to create classical pocket beaches bounded by artificial headlands. The structures




49
shape and size were mainly determined by the location of the seabeds, and the orientation was "tuned" to the incident wave direction to increase fill stability (Olsen and Bodge, 1991). The expected benefits of this design were threefold. First and foremost, the artificial headlands would prevent the encroachment of the aragonite on the seagrass beds; secondly, they would act to stabilize the actual nourishment itself; and finally, from an aesthetics point of view, the beaches would resemble the stabilized beaches of the Mediterranean, which worked nicely with the upland structures architecture (Olsen Associates, Inc., 1992).
Project Construction
Construction began in December 1990 and was completed by March 1991. Once the rock structures were in place, the beach fill placement phase of the project commenced. The aragonite was barged approximately 60 miles (one-way) to the site in 2000 short ton loads (1178 cy) from Marcona Ocean Industries base of operations in Ocean Cay, Bahamas (Olsen Associates, Inc., 1992). The aragonite was offloaded by a conveyer and directly transferred into dump trucks at a berthing location on the north side of the island where it was then transported to the project area and subsequently placed (Olsen Associates, Inc., 1992).
Specifics regarding the placed aragonite and its characteristics according to Olsen Associates Inc. (1992) include:
Compaction- The computed post-construction in place volume of aragonite at the site was 25,000 cy, 42,950 short tons were imported, including a 6% moisture content, which Marcona assumes to correspond to 0.74 cy/ton in a natural, noncompacted state. From this estimation, approximately 31,800 cy are estimated to




have been placed on Fisher Island, which correlates to a compaction of 21.4%.
Turbidity- The greatest turbidity occurred during the construction of the T-head groins; however, turbidity 150 ma offshore never exceeded the critical value of 29 NTU. Relatively small levels of turbidity from the placed aragonite resulted in nearshore white cloudiness of the water, but disappeared completely within hours
after the cell was filled.
* Grain Size- The median grain size of the placed aragonite was 0.27 mm. with 3%
finer than 0.107 mim and less than .5% finer than 0.074 mm. (i.e. minimal amounts of silts and clays). This sediment is slightly coarser than the native median grain
sizes ranging from 0.21 to 0.24 mm.
* Beach Slope- Olsen Associates assumed that the aragonite would perform 1.36
times its mean diameter which converted to a 0.37 mm quartz equivalent. Utilizing equilibrium beach face relationships (Bascom, 195 1), this value yields beach slopes ranging from 1:7.4 to 1:10 for low to moderate wave energies. Field studies conducted at the site measured an average post-project beach slope of 1:9.0 on the foreshore. This measurement did not include the beach profiles directly adjacent
to the structures which would have yielded non-representative results. Project Performance
Monitoring of the project included both physical engineering performance statistics as well as the impact of the project on the environment. To date, performance results for both categories appear to be extremely positive.
In October 1991, approximately 9 months after construction was complete, observations conducted by Olsen Associates, Inc. indicated there was no net shoreline




51
retreat anywhere within the project area. This is extremely positive because typically, due to profile equilibration, one would expect beach recession. The data for the first six months of the project indicate some apparent losses at the southern end; however these losses were comparable to gains found on the northern end. This net northward shift of the planform is indicative of a net northerly littoral drift, which, as of yet, remains unexplained. Overall, the project performed as anticipated, and the results of the 3 year monitoring study found that there was no apparent loss of net volume. This was determined to be due, in large part, to the stabilizing structures constructed at the site (Olsen Associates, Inc., personal communication).
Environmental impact studies, conducted post-construction, were performed to determine the effects of the use of aragonite on sea turtle nesting (specifically loggerhead sea turtles native to the region) and the potential implications of the project on the benthic and infaunal communities. Results of a joint three year study, conducted by Wetlands and Ecological Services and the Department of Biological Sciences at Florida Atlantic University, indicate that aragonite sand temperatures were approximately 20 C cooler than traditional native Florida quartz sands, which extended incubation times by 5 or 6 days and may have altered the natural sex ratios of the sea turtles. Sex determination of sea turtles is known to be temperature dependent. Average temperatures in the observed hatcheries, on Fisher Island, ranged from 27-3 10C and could result in a preponderance of male loggerhead hatchlings. However, the study also found that gas exchange, oxygen and carbon dioxide levels, water potentials, and grain size distribution were similar between the aragonite and the quartz hatcheries. Although, the beach eventually became more compacted, sea turtles continued to nest on the beach and no significant differences were




52
found in hatchling mass and carapace size between nesting sands despite the difference in incubation periods. In addition, no significant differences were found in hatching success, mortality, or emergence success between the two hatcheries. Therefore, the study concluded that aragonite sand beach nourishment had no significant impact on sea turtle nesting; however, additional studies on the impact of aragonite on nest temperatures would be beneficial (Milton, et. al., 1995).
Sediment characteristics which affect benthic and infaunal communities include grain size distribution, organic content, and silt/clay content. The similarity between aragonite and quartz sand properties should ensure a suitable substrate for the native Florida benthic and infaunal environment (Cummings and Fisher, 1995). Moreover, studies at Fisher Island indicate that similar species compositions exist between both the aragonite beach and adjacent quartz sand beaches (Cummings and Fisher, 1995; CSA, 1992 and 1993).
3.4 Environmental Issues
The possible environmental effects of utilizing Bahamian aragonite sand for beach restoration in South Florida are substantial. Specific areas of concern include the ramifications on sea turtles native to the Florida Coast, infaunal communities, and the potential implications to the Bahamian environment.
3.4.1 Impacts to Sea Turtles
There are five different species of sea turtles that nest on southeast Florida beaches; however, for the purposes of this report, the emphasis will be on loggerhead turtles since




53
they represent 95-97% of all nests on Florida's beaches annually (Flynn, 1992; CPE, 1994). The main emphasis will be on the effects of sediment characteristics on sea turtle populations, and the effects of aragonite on nesting and hatching success rates.
Effects of Sediment Characteristics on Sea Turtle Populations
A viable sea turtle population is dependent upon the ability of the sediment to foster a "good nesting beach." A "good" nesting beach allows for adequate gas exchange, has a proper moisture content, and suitable grain size to permit successful chamber construction (Cummings and Fisher, 1995; Mortimer, 1982). In addition, other positive characteristics include a low silt/clay content, low salinity, low levels of organic carbon, high sphericity of the sand grains, and proper compaction properties to permit successful nest building (Cummings and Fisher, 1995).
Proper gas exchange is required for the development of sea turtle embryos. The developing embryos depend on gas diffusion to obtain oxygen and lose carbon dioxide. The amount of gas diffusion in the sediment depends on several factors. These include the amount and size of spaces between adjacent sand gains, temperature, and moisture content (Cummings and Fisher, 1995). Compacted sands have a higher moisture content which results in lower gas diffusion rates, and increased temperatures result in higher gas diffusion rates (Lutz et al., 1991). The optimum moisture content to induce successful hatching and embryonic growth is 25% (McGehee, 1990). Sufficient moisture content is necessary because if the sediment is too dry the eggs will be dehydrated, while increased moisture is detrimental, as well (Kraemer and Bell, 1980).




54
Studies have shown that incubation temperatures affect the hatching success, the rate of embryonic development, and the sex of the hatchlings (Cummings and Fisher, 1995). During early stages of embryonic development the incubation temperature is related to the net radiation at the surface of the beach, and the heat capacity and conductance of the sand (Packard and Packard, 1988). The ability to absorb and radiate heat is influenced by the sediment's color, texture, composition, water content, and the relative depth of the nest (Cummings and Fisher, 1995). The optimal temperatures for producing healthy loggerhead turtles ranges from 26-32'C with mortality rates increasing drastically for values outside this range (Cummings and Fisher, 1995). Incubation temperatures also affect the development rate of the embryos. Lower temperatures tend to slow down development resulting in longer incubation periods, while higher temperatures act to accelerate embryonic development, hence shortening incubation periods (Cummings and Fisher, 1995). Incubation temperatures are also widely believed to determine the sex of sea turtles (Lillycrop and Howell, 1996). Higher temperatures tend to produce more females, while lower temperatures tend to primarily produce males (Mrosovsky, 1988). Due to this apparent phenomena, a pivotal temperature has been established at 29-30'C, at which a 1: 1 male/female sex ratio is established (Lillycrop and Howell, 1996). It is important to mention that the study of temperature dependent sex ratio hatchlings in loggerhead sea turtles is still in the developmental stages and a definitive range has yet to be reached. Some studies have found that the sex determination is related to the time of year of incubation- whether the eggs were laid early or late in the season. In addition, there seems to be some uncertainty whether the male/female ratios are a function of environmental or genetic predisposition.




Effects of Aragonite on Nesting and Hatching Success Rates
All studies indicate that aragonite appears to be a suitable material for successful sea turtle nesting and incubation. The median grain size, moderate sorting, and the low silt/clay content of aragonite all fall well within the limits of optimal nesting and hatching success rates (Olsen and Bodge, 1991). Aragonite appears to have no effect on embryonic development or hatching success when compared to native Florida sands. In addition, the similarity in the grain size distributions between aragonite and quartz sands yields negligible differences in gas diffusion and moisture content (Miller-Way et al., 1987). Moreover, aragonite does not adversely affect the hatchling's ability to successfully emerge from the nest, or subsequently hinder the crawl back to the sea (Cummings and Fisher, 1995). However, aragonite has been proven to affect the temperatures and resultant durations of the sea turtle incubation periods. This could potentially alter the sex ratios of the loggerhead sea turtle population native to South Florida (Cummings and Fisher, 1995). To date, definitive results from studies which compare the sex ratios of the hatchlings incubated on an aragonite beach with those incubated on a comparable native Florida beach have not been attained.
3.4.2 Impacts to Infauna Communities
Sediment characteristics which affect infaunal communities include grain size distribution, organic content, and silt/clay content (Cummings and Fisher, 1995). All studies show that the aragonite characteristics are comparable to those of native Florida beaches, suggesting that aragonite will be a suitable material for the native Florida infauna. In addition, studies revealed that many of the species of infauna found in the Bahamas are




56
native to Florida, as well (CSA, 1992 and 1993). The potential for the introduction of foreign born exotics entering through the use of aragonite is expected to be minimal. This may be due to the fact that the Gulf Stream reaches both areas, carrying similar larvae along it's path, oolitic aragonite already exists in South Florida in minimal quantities, and the climatic, geologic, and geographic conditions are practically the same for both areas (USACE, 1987).
3.4.3 Implications to the Bahamian Environment
Several precautions have already been taken by Marcona Ocean Industries in order to protect the Bahamian environment. Prior to mining, a buffer zone was created to conserve offshore natural resources, and a large settling basin was constructed to limit the amounts of suspended material from the stockpiling operations at Ocean Cay. Moreover, frequent biological surveys are conducted in the area to assess and monitor the impacts of the mining facility on the environment. Based on these studies it appears that the mining operations at Ocean Cay have minimal effects on the Bahamian fauna. Studies of the surrounding seagrass beds, coral reefs, anemones, and filter feeding bivalves adjacent to the dredging operations yielded no visible signs of siltation, burial, or sediment related decline (Cummings and Fisher, 1995). Observations of excavated sites revealed the presence of seagrass and algae which was not present prior to excavation (Rehrer, 1977). In addition, the mining operations do not appear to impact the sea turtle or shore bird nesting sites on adjacent islands (Rehrer, 1977). Due to the relatively strong tidal currents surrounding the aragonite deposits, elevated turbidities and siltations associated with the




57
dredging operations were confined to within a half mile west of Ocean Cay (Rebrer, 1977; Cummings and Fisher, 1995).
3.5 Political Tssues
The potential use of aragonite as a beach nourishment material for South Florida is dependent upon the successful resolution of various political concerns involving both the Local, State, and Federal U.S. Governments and the Bahamian Government. This section will introduce these political issues in an attempt to stimulate thought as to plausible solutions.
3.5.1 U.S. Protectionist Legislation
The delivery and utilization of imported aragonite sand for purposes of beach nourishment is subject to U.S. laws regarding international shipping and trade. These laws, which include the Buy American Act (41 U.S.C. Section 10b), the Jones Act (46 U.S.C. Section 292), and the Shipping Act (46 U.S.C. Section 883), are designed to protect U.S. industries from unfair competition from foreign businesses; however, in actuality, there are provisions in these laws which could pose a serious threat to the use of aragonite in South Florida (Higgins, 1995).
The Buy American Act was amended in the Water Resources Development Act of 1986 to allow the acquisition of foreign beach fill only if domestic sources are unavailable for environmental or economic reasons (Higgins, 1995). This means that aragonite could technically be used in nourishment projects if all other offshore deposits are exhausted, or




58
pose adverse environmental impacts which make the aragonite a more economic solution. Environmental pressure, of late, to provide increased buffer zones to limit the dredge's operational capacity around reefs, and growing dissatisfaction with marginal beach nourishment performance of projects which used small grain sizes, has acted to increase dredge travel distances, thus increasing the costs. When the economics favor importing Bahamian aragonite compared to U.S. owned dredging operations, the Buy American Act will allow the importation of aragonite. Therefore, economics appears to be the key to permitting aragonite's use.
Both the Jones and Shipping Acts prohibit foreign owned vessels from engaging in U.S. coastwise commerce, which may be interpreted as not allowing a foreign owned dredge to transport materials to the U.S. for beach nourishment (Higgins, 1995). The implications of this are extremely important in determining the economics of aragonite beach restoration projects. The allowance of foreign owned dredges to fairly compete for the acquisition and transportation of Bahamian aragonite to South Florida beaches could drastically reduce project costs (Higgins, 1995). If competition is not allowed then aragonite, most likely, will not be considered an economic alternative until all offshore borrow areas have been either completely exhausted or until the regulatory agencies pass bills prohibiting dredging around reefs.
In addition, environmental concerns regarding the use of aragonite have forced regulatory agencies to take a stance against the use and implementation of aragonite until more study results are available. These environmental issues which were discussed earlier include sea turtle nesting and hatching and potential infauna impacts. As preliminary environmental studies begin to cast the impacts of aragonite's use in a beneficial light, it




59
is assumed that these regulatory agencies will take a less restrictive stance with respect to aragonite (Higgins, 1995).
3.5.2 State and Local Political Concerns
Florida has one of the most proactive, comprehensive beach management programs in the nation (Higgins, 1995). The Florida Department of Environmental Protection, which is authorized to request state and federal appropriations for beach and inlet projects, is responsible for maintaining stable beaches. For this reason it is believed that political concerns, on state and local levels, mainly address economic and environmental considerations. If the use of aragonite becomes economically feasible and environmentally sound, then the State would welcome the use of aragonite for beach nourishment (Higgins, 1995). In addition, pressure at the local level to seriously consider aragonite for beach nourishment is mounting due to jurisdictional disputes regarding the lack of suitable and economic offshore resources (Higgins, 1995).
3.5.3 Bahamian Political Issues
The mining and exportation of aragonite sand is controlled by the Bahamian Government. The sale of the aragonite must not only serve the best interests of the U.S. and Florida, but the Bahamas as well. Higgins (1995) outlines several issues, with respect to the Bahamian Government, that must be met before the Bahamas regards the sale of aragonite as in their best interests. First, the dredging operations must not adversely affect their environment. Secondly, the importation of Bahamian aragonite by the U.S. must result in significant monetary benefit to the Bahamas. Finally, and possibly most




60
important, the export of aragonite to benefit Florida beaches and tourism must not come at the expense of Bahamian tourism.
Environmental concerns are important for both the U.S. and the Bahamas, but the Bahamian Government will undoubtedly demand that assurances be granted that the mining of aragonite sand will not be harmful to commercially important species of fish and lobster as well as seagrass beds, coral reefs, and infaunal communities.
Concessions for the sale of aragonite are expected to provide a substantial economic benefit to the Bahamian Government. The Bahamians will probably charge a severance tax on the aragonite by the cubic yard (Higgins, 1995). This issue could affect the economic viability of aragonite's use for beach nourishment.
Tourism is the main source of income for the Bahamas. If the Bahamians consider that selling aragonite to preserve and enhance Florida beaches will result in decreased tourism to the Bahamas, it is unlikely that they would agree to selling. The U.S. and Florida should assure the Bahamian Government that the resulting "white sand beaches" on the Florida shores will act as an advertisement for Bahamian beaches, that could actually serve to bolster tourism both in Florida and the Bahamas.
The aragonite deposits located on the Great Bahama Banks are owned by the Bahamian Government. The use of aragonite as beach fill for Florida shores is contingent upon the consent of the Bahamians. Higgins (1995) stresses the importance of high-level discussions with Bahamian Government officials to address and ease their concerns, and to initiate pertinent studies to quantify these issues.




3.6 Summaiz and Conclusion
Bahamian oolitic aragonite appears to be a suitable material for beach nourishment in South Florida. However, its utilization is dependent upon several issues which must be resolved before any major projects can be constructed. The issues regarding the application of aragonite include the engineering capabilities, environmental impacts, and political concerns associated with the use of the sediment.
From an engineering standpoint, studies have indicated that beach nourishment experiments employing aragonite sand have typically performed as well as or better than native quartz sands. Cunningham (1966) and Monroe (1969) found that aragonite and quartz sand beaches subjected to wave activity performed similarly. In addition, Olsen and Bodge (199 1) found that aragonite performs as quartz sand with an equivalent grain size that is 1.36 times coarser. This is significant since coarser sediments tend to withstand destructive forces to a greater extent than finer ones allowing for the maintenance of steeper beach slopes. In addition, coarse sediments can resist sediment motion resulting in decreased sediment transport rates. Although some laboratory studies have been conducted to test the efficacy of aragonite as a beach nourishment material, studies to quantify the relative transport rates of aragonite sand have been limited. Ideally, information regarding the comparison of sediment transport rates of aragonite and quartz sand beaches could prove extremely beneficial in predicting the potential benefits of aragonite beach restoration projects.
Based on available environmental data, aragonite appears to be a suitable material for the nourishment of South Florida beaches. Aragonite has been proven to not adversely




62
affect sea turtle nesting sites, hatching success, or emergence success. Studies have also shown that aragonite is a suitable sediment for Florida native infauna, and the introduction of foreign species to the Floridian ecosystem is expected to be minimal. In addition, the mining operations at Ocean Cay have resulted in negligible turbidity effects, and in some areas, have increased and induced seagrass growth where there was none prior to excavation. Moreover, turbidity levels associated with placed aragonite pose a significantly less threat to offshore coral reefs and seagrass communities. Although aragonite was shown to decrease incubation temperatures resulting in increased incubation periods, it is not known to what extent this affected the sea turtle populations or gender ratios. By all accounts, biologists concede this is an area of study that warrants further investigation; however, the overall impact to sea turtles appears to be minimal.
Political concerns related to the importation of aragonite for beach nourishment purposes need to be addressed. Assurances need to be provided to the Bahamian Government that the mining and utilization of aragonite for Floridian beach restoration projects will not negatively impact the Bahamian environment nor Bahamian tourism. Secondly, the U.S. needs to relax restrictions regarding foreign competition in dredging and transportation operations in order to reduce the current economic burden of replenishing beaches with aragonite. Finally, as jurisdictional disputes over diminishing offshore borrow areas become more significant, it is believed that local pressures will influence the State and Federal Governments to relax these restrictions, thereby allowing imported Bahamian aragonite for nourishment of Florida's shores at a reasonable cost.




CHAPTER 4
LABORATORY EXPERIMENTS
4.1Introdcin
The results of the literature survey have prompted a laboratory study to compare the relative beach nourishment properties and longshore sediment transport characteristics of sediment native to Florida beaches with those of aragonite. All experimental studies utilized a typical quartz sand of uniform grain size to provide a basis for transport and compatible sediment along South Florida beaches. The first experiment conducted was a beach nourishment performance test where quartz fill sediment compatible to the native was compared to a similar grain size aragonite fill on an adjacent beach under wave activity. Both nourishment sections were tested for their longevity and plan area remaining at various time intervals throughout the life of the project. In addition, the DNRBS numerical model was employed to try and predict the eventual equilibrium planform of the nourishment region. This experiment allowed for detailed conclusions to be drawn regarding the effectiveness and suitability of nourishing native Floridian beaches with aragonite sediment. The second experiment conducted was designed to obtain a better understanding of the transport characteristics of aragonite sand and how those qualitative and quantitative values compare with those for quartz sand under similar wave action. The




64
conclusions drawn from this experiment should aid in determining the basic effective spreading losses of any nourishment project employing aragonite sand, and should yield some information as to how the equilibrated aragonite beach and associated profile will continue to perform over time. All tests were conducted in the three dimensional wave basin in the Coastal and Oceanographic Engineering Laboratory at the University of Florida.
4.2 Experimental Equipment
4.2.1 Wave Basin
The wave basin dimensions are: 17.5 m wide, 15 m long, and 26 cm deep. The basin is equipped with a snake-like wavemaker consisting of 88 paddles and is capable of producing oblique monochromatic wave trains. To minimize lateral wave diffraction, two artificial wave guides consisting of concrete blocks were placed on either side of the wave paddles and extended landward. The guides perform- as artificial wave rays, and the guide on the west (updrift) side of the beach was sealed to ensure no loss of sediment to the littoral cell and thus performed as a perfect littoral barrier. In addition, a sealed concrete groin was placed in the center of the beach extending from the beach seaward to a depth of -26 cm to act as a partition between adjacent beaches for all experiments. The angle of the groin was such that it was facing directly into the incoming waves to minimize the interaction of the waves with the structure. A schematic layout of the wave basin is presented in Figure 4. 1. Initially, shoreward of the wave maker, a sandy beach is located consisting of uniform quartz sediment of 0.25 mm median grain size diameter. See Figure




65
4.2 for the quartz grain size distribution which will be used throughout the duration of all
experiments. A constant water level of 26 cm was maintained within +0.3 cm by a float
triggered pump during all testing.
SNAKE WAVE MAKER
NO -r --- ----------
\WAVE RAY I
I I
I I
'WAVE GUIDE
I I
t
., _,JEC
I I
7' I -m I
S I I
SI I
~ I I
~~ LI1ORAL BARRIER
II
west-side east-side
LrlMORAL CELL LITIMORAL CELL
Figure 4.1 Schematic Layout of the Wave Basin and the Initial Test Conditions at the University of Florida Coastal and Oceanographic Engineering Laboratory




'0
)0 --10 - -
10 --.- -------------------!0 - - - -
10
0

-breakerline
water line/berm zone
riedi66 diameter:= 0.:25: im:::
- - -- -

10 10'
Grain Size [mm]

Figure 4.2 Particle Grain Size Distribution for Quartz Sediment Used Throughout the Duration of this Study
4.2.2 Wave Gage
A capacitance type wave gage was used during the experiments to measure the wave heights. The gage was calibrated by measuring the gage output at two known still water levels. The wave measurements were then taken at an intermediate distance from the beach to the wave paddles and the voltage differences were then recorded using Global Lab software in the laboratory, which ran for approximately twenty minutes collecting data continuously. Once complete, the maximum and minimum voltages were converted into




67
wave heights. The laboratory results document that the waves were a period, T, of 1. 13 seconds, deep water wave height, H, of 3.35 cm, breaking wave height of 5.5 cm, and a deep water obliqueness, (x, of 150. These conditions were maintained throughout the duration of all experiments.
4.2.3 Survey Techn" .
Upon the conclusion of each incremental time period of wave activity, the water level is raised from 26 cm to 30 cm, which is the maximum berm elevation, and a dark string is placed along the waterline over the entire beach width. This line represents the +4 cm contour. The water level is then lowered by 2 cm, representing the +2 cm contour. Followed by the +1 cm contour and the mean water line elevation contour line. Then these contours are mirrored below the mean water line resulting in contours of -1 cm, -2 cm, and
-4 cm. This process is then continued as the water is lowered every 2 cm until the water level reaches a depth of 8 cm. Finally, the last contour line, -26 cm which is the basin floor, is documented during the analysis of the survey. The result is a field of sand contours at elevations of +4 cm, +2 cm, +1 cm, 0 cm, -1 cm, -2 cm, -4 cm, -6 cm, -8 cm,
- 10 cm, 12 cm, 14 cm, 16 cm, 18 cm and -26 cm. Once the survey is complete, a Kodak digital camera is used to photograph the contour lines to import into Surfer software where it is digitized for later analysis.




4.3 Test Preparation and Desig

After the establishment of uniform wave conditions, the wave maker was activated for 8 hours. The resulting beach was surveyed along three profiles and assumed to be in equilibrium with the aforementioned wave characteristics. Analysis of the survey and the resulting beach profiles across the width of the beach yielded an average profile. Figure
4.3 represents the equilibrium beach profile of the quartz sediment.
2 - --- - --- ---( -ro---2 ------------ ------------ ---------.2
W
2-10 --------------------------- ----------- - -- -
CI
W N
-12 [ - - - - - - - - - - - - - - - - A - - - -\ - -

Cross-Shore Distance, Y[m]
Figure 4.3 Average Equilibrium Beach Profile of the Quartz Sediment




69
The existing beach was then returned to its initial state by standard scraping techniques, and molded to the equilibrium condition established during the first stage of this procedure. The process of scraping clean the bed forms followed by molding the beach to the aforementioned equilibrium beach profile was performed at the end of each experiment, namely the beach nourishment experiment and the sediment transport experiment, thereby providing the initial conditions for the next testing procedure. The molded template was constructed out of standard half inch plywood and consists of both an upper (onshore) and lower (offshore) profile section. Each section was manually fitted with a carpenter level to ensure proper vertical elevations. Figure 4.4 is a diagram of the quartz/aragonite equilibrium beach profile templates.
5
Onshore Section Offshore Section
37
2
-2- Water Line
N
e-5
= -6 > -7
()

0 0.25 0.5 0 75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3
Cross-Shore Distance, y[m]
Figure 4.4 Schematic of the Quartz/Aragonite Equilibrium Beach Profile Templates




4.4 Experimental Procedures
4.4.1 Beach Nourishment Performance Experimen
The beach nourishment performance test has been designed to develop a better understanding of the relative longevity of nourishment projects employing aragonite vs. quartz sediments. Utilizing the wave basin in a confined laboratory environment, affords the opportunity to test both a quartz fill section, compatible with the native, alongside an aragonite fill section of comparable grain size characteristics. The beach was divided by a complete littoral barrier into two separate sections to prevent any mixing of sediments, see Figure 4.1. After the beach was scraped and molded with the templates, the wave maker was activated for 3 hours to allow the initial prenourished beach to be in complete equilibrium with the incoming wave direction. Contrary to actual field nourishment designs, the test fill was designed specifically to induce sediment transport. This is achieved by exaggerating the angle between the tapered ends of the shore parallel fill and the initial dry beach, while reducing the length of the fill section. The signal that is produced by instituting this type of design and subjecting it to monochromatic wave activity should be large enough such that relative correlations may be drawn between the transportability of nourishment projects implementing quartz fill compatible with the native with that of aragonite fill. Figure 4.5 is a schematic layout of the beach nourishment performance experiment and associated fill design.




SNAKE WAVE MAKER
1 \ WAVE RAY
- -F ------ --------AI
WAVE GUIDE \ I
- '
' I
S!
aLrFORAL BARRIER i
a QUARTZ SAND FILL
, I
Fu 4 i
artz thtiv Asscite FilDsg
III
I II
I
The total project area of the design was 3 mn for each fill. The maximum berm elevation of the nourishment was made to conform with the existing +4 cm berm height. The center rectangular section was 1.5 mn long with two 0.75 mn tapers on either side. The berm, and associated dry beach width of the nourishment, extended seaward to the 6 cm depth contour, a distance of 0.64 mn. From that point the toe of the fill was configured to meet the bed at a 2:1 horizontal to vertical slope. The total extension seaward of the entire nourishment, including the toe, was to approximately the -8 cm depth contour line, a distance of 0.85 mn.
The placement of the nourishments was conducted in such a manner as to not adversely affect the preexisting beach planform. This was performed by inserting 3/4 inch




72
dowels at each intersection point, i.e. all of the comers, through the beach and down to the floor of the basin. The berm height was then established by using a rotating laser. Once complete, the dowels were cut at the proper height and fitted with 2x2 inch ribbing which acted as the basic skeleton of the nourishment. After the form was in place, the fill material was placed inside the project area with a moisture content of approximately 25 percent. Compaction was performed by rudimentary techniques and the final form of the nourishment was smoothed by running a piece of plywood over the ribbing. Finally, the outer mold was dismantled and fill material was compacted into the holes left by the dowels.
Based on sieve analysis, it was found that the aragonite sediment obtained from Marcona Ocean Industries had a mean grain size of 0.30 mm. Before the aragonite could be placed in the nourishment section, the sediment was manually sieved, removing a portion of the coarser sediments. The resulting grain size distributions of the aragonite and the quartz nourishment fill size distribution are presented in Figure 4.6. From Figure 4.6, it is evident that the mean diameter of the aragonite sands is slightly larger than that of the quartz. This was intentional to account for the larger percentage of finer material in the aragonite. Due to the larger portion of fines in the aragonite, it is assumed that the small increase in the mean diameter will result in these two nourishment materials being approximately comparable in size characteristics.




10.2 10' 100 101
Grain Size [mm]
Figure 4.6 Sand Size Distribution of Aragonite and Quartz Fill
The testing procedure commenced with a pre-nourishment survey followed by a post nourishment survey at time, t, equal to 0 minutes. Monochromatic waves, of the aforementioned characteristics, were then run over time intervals of 5, 9, 20, 40, and 60 minutes with post surveys conducted after each time period. The interpretations of the results of these surveys will be presented in Section 4.5 of this report and the analysis of these results will be presented in Chapter 5.

I i' -f' r I I I I I I I I .
I-- - - I-: -: I -: '-: :
- J 1 -, ,- - - - -

AraQuarte
-,_ _IL L

T




4.4.2 Sediment Transport Experiment
The sediment transport experiment was performed to understand the relative differences and similarities between the transport properties of quartz and aragonite sands. Basically, both beaches are prepared to be initially out of equilibrium with the oblique incoming wave activity. By monitoring the beaches over time, the respective transport characteristics of each sediment can be determined as the beaches evolve and equilibrate. Figure 4.7 represents the layout of the wave basin for this experiment. From Figure 4.7, it is evident that the basic setup was maintained throughout all testing procedures; however, the quartz sand in the eastern most compartment was completely removed and filled with aragonite. This formed two distinct beaches, one composed of quartz sediment and the other of aragonite, separated by the center littoral barrier.
SNAKE WAVE MAKER
- -r
t~i\ WAVE RAY 65
WAVE GUIDE
55 =OR BARRIER
I
Quartz Sand Aragonite Sand
I!
ws-ieLITTORAL CELL LITTORAL CELLeatsd
Figure 4.7 Schematic Layout of the Wave Basin for the Sediment Transport Experiment




75
After the aragonite was placed, the basin was filled to allow the aragonite to saturate and eventually settle. Once the aragonite was compacted to a similar state as the quartz beach, both beaches were raked to remove any preexisting bed forms and configured with the profile templates shown in Figure 4.4. Testing commenced with an initial survey immediately after the beaches were molded at time, t, equal to 0 minutes with subsequent surveys conducted after 30, 60, 90, 120, 180, and 240 minutes of monochromatic waves. The interpretations of the results of these surveys will follow in Section 4.5 of this report and the analysis of these results will be presented in Chapter 5.
4.4.3 Rapid Sand Analyzer Experiment
A Rapid Sand-Analyzer (RSA) was utilized to obtain the settling velocity characteristics of quartz and aragonite sands of the same diameter. The Rapid Sand Analyzer, located at the University of Florida's Coastal and Oceanographic Engineering Laboratory, is a large settling tube which is 254 cm. in length and approximately 30 cm in diameter. The tube was filled with fresh water at 20T. The bottom of the tube is fitted with a pan which collects the sediment. This pan is supported by three thin wires attached to an electronic scale which measures the cumulative weight of the material as a function of time. The sample is placed in a holding compartment at the top portion of the tube which automatically opens when testing begins. The quartz and aragonite samples were also sieved through Standard Sieve Numbers 30, 40, 50, 60, 80, 100, 120, 140, and 160. The proportion of material remaining on each sieve was then separated and saturated for 24 hours to remove any air pockets which would hinder the settling of the samples. Once complete, each sample was placed into the RSA and the average settling velocity for each




76
size range was calculated. The results and analysis of this experiment will be presented in Chapter 5 of this report.
4.5 Res Its
Analysis of the beach nourishment experiment and the sediment transport experiment will be conducted in a similar manner. Once all testing procedures were complete, the digitized Surfer plots of each survey were analyzed to calculate the sediment transport rates and the proportion of nourishment material remaining after each time period for each respective beach. This was accomplished by calculating the volumetric changes under the initial survey from each subsequent profile which produced an average estimate of the transport characteristics over time. If all the sand in the littoral cell was conserved then all of the positive changes should equal all of the negative changes. Similar methods are employed to evaluate the relative compatibility of each experiment such that quantitative comparisons may be drawn for the two sediments. Analysis of these experiments, presented in Chapter 5, are based on the various survey plots presented in Appendix A of this thesis.
The rapid sand analyzer test results will be analyzed by plotting the settling velocities of each sediment of known grain size against one another such that a correlation between the two can be reached. The values obtained to determine a proper quartz equivalent grain size for aragonite will be determined and compared to those values found through theory outlined in Chapter 2. In addition, these values will also be compared to the quartz equivalent found by Olsen and Bodge (1991) for aragonite sediment.




CHAPTER 5
ANALYSIS AND DISCUSSION OF LABORATORY RESULTS
5.1Introd1ucio
The objective of this chapter is to present and discuss the results of the laboratory experiments. The main features of interest are the determination of the relative effectiveness of aragonite with respect to quartz sands include profile and planform evolution, volumetric changes, sediment transport rates and characteristics, and the effects of settling velocity on these parameters. Section 5.2 presents the results of the beach nourishment experiment. The results from the sediment transport experiment and the settling velocity experiment follows in Sections 5.3 and 5.4, respectively.
5.2 Beach Nourishment Experiment
The beach nourishment experiment was conducted to determine the potential effectiveness of nourishing a native quartz beach with compatible aragonite sediment. The evolution of two similar nourishment sections were compared, each consisting of compatible quartz and aragonite sands. The project areas were each evaluated by comparing the shoreline evolution and volumnetric density changes within the nourishment region, associated profile evolution, proportion of fill material remaining over time, and 77




78
DNRBS simulations to quantify the sediment transport coefficient, K, for both the quartz and aragonite nourished beaches.
5.2.1 Shoreline Evolution and Volumetric Density Changes
Figures 5.1 and 5.2 present the shoreline evolution of the quartz and aragonite nourishment sections, respectively. These plots were generated by interpolating the digitized shoreline data collected for each survey conducted throughout the course of the experiment.
-itial Shoreine
Potuishmr, t=Omin
t = 5 minutes
t = 9 minutes
t = 20 mines
058.. . .'. .. . . t =40 minues
t = 60 minAes
0.6 -- -_ -- . .
0.4 - r
C,,,,I-0.2!
U)I I
-0.2 L i
1 2 3 4 5 6 7 8
Longshore Distance, X[m]
Figure 5.1 Shoreline Evolution of Quartz Nourishment After 0, 5, 9, 20, 40, and 60 Minutes of Wave Activity




0.4 ~ ~ ~ -- --0 .2 - - - - - -
-021 1
0 1 2 3 4 5 6 78
Lorgshre Distamce, )qm]
Figure 5.2 Shoreline Evolution of Aragonite Nourishment After 0, 5, 9, 20, 40, 60 Minutes of Wave Activity
Examination of Figures 5.1 and 5.2, reveals interesting details regarding the beach nourishment shoreline evolution of aragonite and quartz sands. First, it is interesting to note that in the evolution of each nourishment, initial perturbations in the design tend to be maintained throughout the life of the project. Secondly, the resulting dry beach width initially decreases rather rapidly, but tends to stabilize over time for each nourishment. Finally, the resulting total change in dry beach width for the quartz and aragonite




80
nourishments is remarkably similar. This is evident in Figure 5.3 which denotes the change in dry beach width over the 60 minute duration of the experiment for each test section.
I I
-e- Aragonte Nrishmnt
Quatz Nowjdshmeda
0.1 -- Project-Area
0
-0- -- -- - - --"
o 3 35 4 4.5 5 5.5
I
Longshore Distance Wthin the Project Area, X[m] Figure 5.3 Comparison of Change in Dry Beach Width After 60 Minutes of Wave Activity for Quartz and Aragonite Test Nourishments
The average recession for the aragonite and quartz nourishments occurring within the 1.5 m center rectangular design section was -0.44 m and -0.46 m, respectively. The associated dry beach recession within the tapered regions of the projects were also




81
comparable for each sediment, as is evident in the correlation of the curves below 3.5 m and above 5 m in Figure 5.3.
The changes in volumetric density for the quartz and aragonite nourishments is presented in Figures 5.4 and 5.5, respectively. These figures were generated by summing the volumes across each profile line for every survey and referencing them to the initial prenourishment conditions of each beach. There are a total of 182 profile lines across each test beach with an approximate longshore spacing of 0.05 m between profiles.

Aongshore [Distarme, X[m] Figure 5.4 Change in Quartz Volumetric Density After 0, 5, 9, 20, 40, and 60 Minutes of Wave Activity




0 1 2 3 4 5 6 7 8
AJongshore Distance, X[m]
Figure 5.5 Change in Aragonite Volumetric Density After 0, 5, 9, 20, 40, and 60 Minutes of Wave Activity
An evaluation of Figures 5.4 and 5.5 to determine the total loss of volumetric density within the rectangular region of the nourishment planforms is presented in Figure 5.6. Calculating the average maximum loss of volumetric density, AV [m3/m], for the aragonite and quartz nourishments over the 60 minute duration of the experiment yields values of -0.0342 and -0.0371 m3/m, respectively.




6 3 3.5 4 4.5 5 5.5
"J Longshore Distance Wthin Project Area, X[m]
Figure 5.6 Comparison of Loss in Volumetric Density After 60 Minutes of Wave Activity for Quartz and Aragonite Test Nourishments

Although the shoreline recession shows a higher correlation than the change in volumetric density between the quartz and aragonite nourishment sections, similar trends exist, as is evident in Figures 5.1 through 5.6. In both cases each nourishment first exhibited a rapid recession which eventually stabilized after approximately 40 minutes of wave activity. The magnitudes of these recessions, occurring after each time interval for both test beaches, were also comparable. In addition, the fact that initial perturbations in




84
the nourishment design were maintained throughout the testing procedure, for each beach, was evident in both the change in shoreline position and volumetric density.
5.2.2 Average Profile Evolution
The average profile evolution of both the quartz and aragonite test nourishments will be presented in this section. The profiles were generated by averaging each profile line within the rectangular portion of the nourishment section over each time interval. As stated in Chapter 4, the rectangular portion of the project length was 1. 5 m. The spacing between profile lines was approximately 0.05 mn resulting in 31 profile lines across the length of the rectangular nourishment. Figures 5.7 and 5.8 present the average profile evolution for the quartz and aragonite test nourishments, respectively.
The evolution of the nourishment profiles, for both test sections, demonstrate the initial rapid equilibration of the nourished profile, followed by a general stabilization which occurred after approximately 40 minutes of wave activity. The relative similarity in the steepness of the foreshore slope is also evident. The equilibrated aragonite and quartz profiles occurring after 60 minutes of wave activity are presented in Figure 5.9. From Figure 5.9, it is interesting to note the foreshore slopes, from the berm elevation, B of 4 cm. to the depth of closure, h. of approximately -8 cm, of each profile is practically identical; however, at a depth, z of -2 cm, the aragonite profile maintains a slightly steeper slope.




N
-20 - - - - - -
-2 4 ----28
0 50 1.C 150 20 250 30 35 1 450
Cross-Shore Distance, Y[cm] Figure 5.7 Quartz Test Nourishment Average Profile Evolution After 0, 5, 9, 20, 40, and 60 Minutes of Wave Activity




Cross-Shore Distance, Y[cm]

Figure 5.8 Aragonite Test Nourishment Average Profile Evolution After 0, 5, 9, 20, 40, and 60 Minutes of Wave Activity




CO,
-2>
0a0 10 10 20 20)0 5 0 5 0
W -6 - - - - T C ro s S h r D i-n e -Y - - - - --cm -] - - -
Figur -. Coprio of Avrg Eqiibae Bec Prfl of Argnt an Quartz--- ---- ---appears o be slihtly moerstableatrdept s anging from-.5c o-. m ute
analysis of the roportion of and remain win ahont proe aredwiceha wilhe
presented in Section 5.2.3, and the determination of the associated sediment transport coefficient for each nourishment is still necessary in order to ascertain a thorough hypothesis as to the complete efficacy and suitability of the aragonite nourishment section.