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Storm-influenced sediment transport gradients on a nourished beach

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Title:
Storm-influenced sediment transport gradients on a nourished beach
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Book
Language:
English
Creator:
Elko, Nicole A
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University of South Florida
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Tampa, Fla
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Subjects / Keywords:
Planform evolution
Profile equilibration
Hurricanes
Nearshore sediment transport
Cross-shore sediment transport
Longshore sediment transport
Shore protection
Design
Construction
Sediment budget
Coastal management
Dissertations, Academic -- Geology -- Doctoral -- USF
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bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

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Abstract:
ABSTRACT: Beach nourishment provides an excellent opportunity for the study of intensified sediment transport gradients and associated morphological changes in a natural setting. The objectives of this study are to quantify and predict longshore and cross-shore transport gradients induced by 1) beach nourishment, 2) different storm wave conditions, and 3) the annual wave climate and long-term sediment supply. The details of sediment transport rates and gradients induced by gradual processes and high-energy events are analyzed on a macro-scale. Well-planned monitoring of the 2004 Upham Beach nourishment project in west-central Florida collected high-spatial and -temporal resolution field data. Three hurricanes passed by the project soon after nourishment was complete.Post-nourishment planform adjustment occurs immediately after nourishment via diffusion spit development at the end transitions. Thus, the initiation of planform adjustment may be abrupt, rather than gradual as pred icted by the typical diffusion models. Diffusion spit formation is dominant during relatively calm wave conditions on coasts with low wave heights and tidal ranges.Profile equilibration also may be an event-driven, rather than a gradual, process. Rapid profile equilibration following nourishment occurred not only due to hurricane passage, but also during a winter season. The duration between nourishment and the passage of the first high-energy event is an important factor controlling the time scale of profile equilibration.The passage of three hurricanes generated different wave conditions and induced different sediment transport directions, rates, and gradients due to their variable proximities to the project area. The direction of cross-shore transport was governed by wave steepness. Onshore sediment transport occurred during a storm event, in contrast with the concepts of gradual onshore transport during mild wave conditions and abrupt offshore transport during storm events, as ^cited in the literature.By formulating sediment budgets on various temporal and spatial scales, both event-driven and average transport rates and gradients can be resolved. Annual average transport rates for a region should not be arbitrarily applied to nourished beaches; rather, sediment budgets formulated with high-spatial and -temporal resolution field data should be formulated during the design phase of future nourishment projects.
Thesis:
Dissertation (Ph.D.)--University of South Florida, 2006.
Bibliography:
Includes bibliographical references.
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System requirements: World Wide Web browser and PDF reader.
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Mode of access: World Wide Web.
Statement of Responsibility:
by Nicole A. Elko.
General Note:
Title from PDF of title page.
General Note:
Document formatted into pages; contains 177 pages.
General Note:
Includes vita.

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aleph - 001795686
oclc - 154302154
usfldc doi - E14-SFE0001576
usfldc handle - e14.1576
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Storm-influenced sediment transport gradients on a nourished beach
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ABSTRACT: Beach nourishment provides an excellent opportunity for the study of intensified sediment transport gradients and associated morphological changes in a natural setting. The objectives of this study are to quantify and predict longshore and cross-shore transport gradients induced by 1) beach nourishment, 2) different storm wave conditions, and 3) the annual wave climate and long-term sediment supply. The details of sediment transport rates and gradients induced by gradual processes and high-energy events are analyzed on a macro-scale. Well-planned monitoring of the 2004 Upham Beach nourishment project in west-central Florida collected high-spatial and -temporal resolution field data. Three hurricanes passed by the project soon after nourishment was complete.Post-nourishment planform adjustment occurs immediately after nourishment via diffusion spit development at the end transitions. Thus, the initiation of planform adjustment may be abrupt, rather than gradual as pred icted by the typical diffusion models. Diffusion spit formation is dominant during relatively calm wave conditions on coasts with low wave heights and tidal ranges.Profile equilibration also may be an event-driven, rather than a gradual, process. Rapid profile equilibration following nourishment occurred not only due to hurricane passage, but also during a winter season. The duration between nourishment and the passage of the first high-energy event is an important factor controlling the time scale of profile equilibration.The passage of three hurricanes generated different wave conditions and induced different sediment transport directions, rates, and gradients due to their variable proximities to the project area. The direction of cross-shore transport was governed by wave steepness. Onshore sediment transport occurred during a storm event, in contrast with the concepts of gradual onshore transport during mild wave conditions and abrupt offshore transport during storm events, as ^cited in the literature.By formulating sediment budgets on various temporal and spatial scales, both event-driven and average transport rates and gradients can be resolved. Annual average transport rates for a region should not be arbitrarily applied to nourished beaches; rather, sediment budgets formulated with high-spatial and -temporal resolution field data should be formulated during the design phase of future nourishment projects.
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Planform evolution.
Profile equilibration.
Hurricanes.
Nearshore sediment transport.
Cross-shore sediment transport.
Longshore sediment transport.
Shore protection.
Design.
Construction.
Sediment budget.
Coastal management.
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Storm-Influenced Sediment Transport Gradients on a Nourished Beach by Nicole A. Elko A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Geology College of Arts and Sciences University of South Florida Co-Major Professor: Ping Wang, Ph.D. Co-Major Professor: Richard A. Davis, Jr., Ph.D. Robert G. Dean, Ph.D. Mark Rains, Ph.D. Mark Ross, Ph.D. Date of Approval: March 1, 2006 Keywords: planform evolution, profile equi libration, hurricanes, nearshore sediment transport, cross-shore sediment transport, l ongshore sediment transport, shore protection, design, construction, sediment budget, coastal management. Copyright 2006, Nicole A. Elko

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Dedication To James B. Jim Terry, the late Chief of Coastal Systems for Pinellas County, Florida.

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Acknowledgements Getting a Ph.D. while holding a full-time j ob makes for a lonely existence. Over the last year, I have spent most week night s in the office and most weekends at home working. The path from my house to the beac h, then south to Johns Pass and back, has been well trodden. If those sand grains c ould talk, many of the thoughts and emotions that led to this manuscript would surface. I want to sincerely thank my colleagues, advisors, friends, and family who have both guided and tolerated me throughout this journey. In particular, three individuals have pl ayed such a significant role that without them, my career and life would have taken a ma rkedly different path. The pillar of my academic existence, the person who listened to my ideas, who took the time and effort to review my writing, who provided thought-proving discussions, and who made me believe in my work is Dr. Ping Wang. I cannot e xpress my sincere gratitude to his undying devotion to my research. He responded with in days, if not hours, when I presented him with something to review. He came to the be ach to discuss while th e students surveyed. Our interaction truly exemplifies the advisor-student relationship. Another great contributor to my post-gradua te career is Dr. Ri chard Skip Davis, one of the most distinguished coastal geomor phologists in the world. I came to Florida nine years ago to learn from Skip. In my fi rst graduate class, Skip explained that hed started studying modern coastal geology to better understand the ancient rock record. He

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continues to guide my way as I study nears hore sediment transport and engineering to better understand modern coastal geology. Skip has been a mentor as much in his keen presence as in his kind acceptance when I grew away from the Geology Department and then back again. One of Skips best qualities, that was particularly helpful in the past few months, is his optimism. It helped me to finish without compromising my physical or emotional well being. The third individual I woul d like to acknowledg e is the late Jim Terry, to whom this document is dedicated. Jim gave me a special gift, his job. My dedication to my career increased dramatically when I was challenged to fill Jims shoes. Jim Terry was a quiet champion for the beaches of this area and a model to whom I strive. I have been enlightened by many othe rs. Dr. Bob Dean, one of the most distinguished coastal engineers in the world, inspired me to study the theory and practice of beach nourishment. Dr. Mark Rains and Dr Mark Ross helped me to realize the value of studying related sediment transport mechanisms. Peter Howd, Hilary Stockdon, Rob Holman, Meg Palmsten, and Abby Sallenger broadened my understanding about nearshore oceanography. The Board of Pi nellas County Commissioners, Will Davis, and many others with Pinellas County have suppor ted my research and my goal to finish despite working full time. Andy Cummings taught me many things about beach nourishment that I didnt learn in school. Dave Tidwell, Craig Tolliver, and A ndy McManus were our dedicated field assistants who surveyed tirelessly despite hurricanes and weekly, and sometimes daily, field work. Tom Payne inspired me to hustle taught me how to build a beach, and was

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my sanctuary. To my other emotional ba stions, Mom, Dad, John Elko, Noreen Buster, and Hilary Stockdon, thank you for cheering me on to the finish line!

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Table of Contents List of Tables iv List of Figures v Abstract x Chapter One: Introduction 1 Chapter Two: Study Area 10 Historic Morphodynamics 13 Nourishment History 21 2004 Nourishment 23 Construction 26 Chapter Three: Methodology 29 Literature Review 29 Field Data Collection 31 Chapter Four: Wave and Sediment Data Analysis 39 Wave Conditions 39 Sediment Grain Size and Composition 46 Chapter Five: Post-nourishment Planform Adjustment 51 Literature Review 51 Planform Adjustment 53 North Segment 53 Central and South Segments 54 Predicting Immediate Planform Adjustment 61 Shoreline Orientation Changes 62 Sediment Transport Rate 65 Conclusions 66 Chapter Six: Post-nourishment Profile Adjustment 68 Literature Review 68 Profile-shape Adjustment 69 North Segment 70 i

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Central and South Segments 70 Profile Equilibration 72 North Segment 72 Central and South Segments 74 Beach Slope 75 North Segment 77 Central and South Segments 79 Rapid Equilibration 80 Predicting Immediate Profile Adjustment 82 Discussion 83 Conclusions 86 Chapter Seven: Storm-induced Sediment Transport 87 Literature Review 87 Determining Sediment Transport from Beach Profiles 92 Storm Wave Conditions 96 Storm-induced Sediment Transport 97 North Segment 98 Central and South Segments 99 Hurricane Frances 100 Hurricane Ivan 100 Hurricane Jeanne 103 Longshore Gradients in Sediment Transport 106 Predicting Storm-induced Sediment Transport 110 Wave Steepness Analysis 110 SBEACH Simulations 114 Conclusions 119 Chapter Eight: Sediment Budget Formulation and Analysis 121 Literature Review 121 Previous Long Key Sediment Budgets 123 Sediment Budget Formulation 126 Spatial and Temporal Scales 127 Conceptual Budget 129 Littoral Cell Delineation 130 Application of Measured Values 134 Sediment Fluxes 136 Net Longshore Sediment Transport Rates and Gradients 138 Sediment Pathways 139 Sediment Budget Analysis 141 1996 2004 Sediment Budget 141 Shoreline Change Analysis 144 Northern Long Key, 1991 2004 146 Shoreline Maps 147 ii

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Short-term Sediment Budgets 150 2004 2005 Sediment Budget 151 Comparison of Sediment Budgets 154 Sediment Pathways 156 Impact of T-Groin Field 160 Conclusions 162 Chapter Nine: Conclusions 165 References 167 About the Author End Page iii

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List of Tables Table 2-1. Beach nourishment on northern Long Key from 1991 to 2005. 22 Table 3-1. Construction schedule for the three segments (Fig. 2-6) of the 2004 Upham Beach project. 33 Table 4-1. Maximum significant wave height (H s ) and the associated peak wave period (T p ) measured at the nearshore wave gauge during the three storms. 43 Table 6-1. Calculated beach slope () during the study period. 77 Table 7-1. Reproduction of Table 4-1. 97 Table 8-1. Summary of Q x net longshore transport rates, (m 3 /yr) calculated in the sediment budgets (Figs. 8-3, 8-5, and 8-7). 155 Table 8-2. Qualitative sediment transport pathway determination for Long Key. 158 Table 8-3. Conservative sediment transport estimate for Cell 1 with T-groins during the 2004 to 2008 nourishment interval. 161 iv

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List of Figures Figure 1-1. Gradual change, illustrated with cascading temporal scales, and event-driven change may lead to similar responses on similar spatial scales; however, distinct processes drive the different types of change. 2 Figure 1-2. Large-scale morphologic features that result from gradients in longshore sediment transport. 3 Figure 1-3. Examples of structures blocking longshore sediment transport and the resulting downdrift erosion. 4 Figure 1-4. Property damage on a non-nourished beach in Brevard County due to the 2004 hurricane season (source: Brevard County website). 5 Figure 1-5. Dredging and hydraulic placement of nourished sediment on beaches. 6 Figure 1-6. Schematic sketches of beach nourishment project evolution illustrating A) planform adjustment via longshore transport; B) profile equilibration via cross-shore transport (modified from Dean (2002)). 7 Figure 2-1. Location of Upham Beach on Long Key in Pinellas County, FL, illustrated with an early 1970s shoreline. 11 Figure 2-2. Process-response model and features of a drumstick barrier island illustrated on the 1873 NOS Historic Topographic Survey Sheet (T-sheet) of Long Key. 14 Figure 2-3. 1926 aerial photograph of northern Long Key showing the southerly migration of Blind Pass (c.f. Fig. 2-2), the northwest-southeast trending beach ridges, and the reduced ebb delta of Blind Pass. 17 Figure 2-4. Blind Pass and northern Long Key (Upham Beach) in a) 1957 and b) 1965 (note the structures built on the beach, shown with arrow). 19 v

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Figure 2-5. Blind Pass and Upham Beach in October 2003 depicting the stabilization of Blind Pass, the southern migration of the inlet, and the development of the back-barrier bay. 20 Figure 2-6. The planform design template of the 2004 Upham Beach nourishment project. 25 Figure 2-7. Construction of the 2004 Upham Beach nourishment project on July 28, looking north. 28 Figure 3-1. Proportion of fill remaining, M(t), along an initially rectangular planform (from NRC, 1995). 30 Figure 3-2. High spatial resolution field data on Long Key from the field-data collection portion of the study. 32 Figure 3-3. Weekly beach surveys conducted before, during, and after construction at profile R148 at the south limit of the 2004 Upham Beach nourishment. 34 Figure 3-4. Combined beach and offshore surveys at profile R148. 35 Figure 3-5. Shoreline maps for Upham Beach before and after nourishment, and after the passage of Frances, Ivan, and Jeanne. 37 Figure 4-1. Tracks of the four hurricanes that made landfall in Florida during 2004 and their proximity to the project area. 40 Figure 4-2. A) Significant wave height (H s ) and B) peak wave period (T p ) from July 18 to October 1, 2004 (gauge location shown in Fig. 3-2) measured in 4 m of water depth. 40 Figure 4-3. Wave and meteorological conditions at the study area during the month of September 2004. 42 Figure 4-4. Surf zone conditions during the passage of Hurricane Ivan at A) on Treasure Island, 1 km north of Upham Beach, and B) N. Redington Beach, 2 km to the north. 44 Figure 4-5. Wave spectra for the waves measured at the nearshore wave gauge during the passage of Hurricanes Frances, Ivan, and Jeanne. 46 vi

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Figure 4-6. Mean sediment grain size before (D N ) and after nourishment (D F ). The x-axis refers to distance from Blind Pass at the north end of the fill. 47 Figure 4-7. Example post-nourishment grain size frequency curves for A) the 20% of sediment samples that failed, and B) the 80% of samples that passed the FDEP Sand Rule test. 49 Figure 4-8. Example of typical grain size and composition distribution for the Florida Gulf peninsular beaches (from Davis, 1994). 50 Figure 5-1. Profile response after nourishment from: A) the north segment, B) the central segment, C) the south segment, and D) downdrift of the nourished area. 54 Figure 5-2. Contour map of the beach fill based on survey data from September 1, 2004. 56 Figure 5-3. Main diffusion spit extending from the wide, north segment of Upham Beach on August 27, 2004, note the numerous overwash tongues on the landward side. 57 Figure 5-4. Photos of diffusion spits on A) the 1998 Sand Key nourishment, and B) the 2002 Anna Maria Island nourishment. 60 Figure 5-5. Vector sum model of diffusion spit formation. 64 Figure 6-1. Beach-profile changes induced by Hurricane Frances: A) the north segment, B) the central segment, C) the south segment, and D) downdrift of the nourishment area. 71 Figure 6-2. Translated measured and calculated profiles from: A) north segment, B) central segment, C) south segment, and D) downdrift of the nourished area. 74 Figure 6-3. Time series of measured beach slopes for the 12 surveyed profiles in the A) north, B) central, and C) south segments. 78 Figure 6-4. R(t), from Eq. (6-4), following the 2004 Upham Beach nourishment. 84 Figure 7-1. Conceptual model of possible combinations of wave heights (H) and wave steepness (H/L) and the predicted cross-shore sediment transport. 91 vii

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Figure 7-2. Schematic diagram of storm-induced profile change, the cumulative sediment transport across the profile, right side of Eq. (7-5), and the cross-shore transport rate at the equilibrium point, q y (y eq ). 95 Figure 7-3. Morphologic response and measured sediment transport, right side of Eq. (7-5), at profile LK2 in the north segment due to the passage of Hurricane Frances. 99 Figure 7-4. Morphologic response and measured sediment transport, right side of Eq. (7-5), at profile LK5 in the center of nourishment due to the passage of Hurricane Frances. 101 Figure 7-5. Morphologic response and measured sediment transport, right side of Eq. (7-5), due to the passage of Hurricane Ivan at profile A) LK5A in the center segment of nourishment, and B) R160 on southern Long Key. 102 Figure 7-6. Morphologic response and measured sediment transport, right side of Eq. (7-5), due to the passage of Hurricane Jeanne at profile A) LK5 in the center segment of nourishment and B) R149, 300 m downdrift of the nourishment. 105 Figure 7-7. The longshore distribution of A) the longshore transport gradient (m 3 /m/event) and B) cross-shore transport (m 3 /m/event) for the nourishment area due to the passage of Hurricanes Frances, Ivan, and Jeanne, and during the post-Jeanne recovery period. 107 Figure 7-8. Fig. 7-1 with wave conditions from each of the three hurricanes and the post-Jeanne recovery and the resulting gradients in longshore and cross-shore sediment transport on the nourished beach. 110 Figure 7-9. Critical steepness analysis. 112 Figure 7-10. The Dean number, Eq. (7-1) calculated during the passage of the three hurricanes. 113 Figure 7-11. Measured and predicted profile response and measured and predicted cumulative sediment transport curves for profile LK5 during Hurricane Frances with A) D F = 0.44 mm and B) D = 0.3 mm. 116 viii

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Figure 7-12. Measured and predicted profile response and measured and predicted cumulative sediment transport curves for profile LK5 during Hurricane Jeanne with A) D F = 0.44 mm and B) D = 0.3 mm. 118 Figure 8-1. Sediment budget sources and sinks and boundaries for each of the four littoral cells. 132 Figure 8-2. Beach profile at R161 at the south end of Cell 3, illustrating stable performance since 1989, even after the 2004 hurricane season. 133 Figure 8-3. Sediment budget for Long Key from 1996-2004. 142 Figure 8-4. Shoreline change (dy/dt) downdrift of Upham Beach from LK7 to R165 from July 1997 to June 2004. 145 Figure 8-5. Preand post-nourishment shoreline maps illustrate the planform evolution from 1996 to 2004. 148 Figure 8-6. Upham Beach: A) post-nourishment 1991, illustrating the typical nourishment template extending to LK5 at the north end of the seawall, B) pre-nourishment 1996 (1995 photo), INSET: March 1995, erosion exposed sand bags at the public park, C) pre-nourishment 2000 (1999 photo) and D) pre-nourishment 2004 (2003 photo). 149 Figure 8-7. Sediment budget from 2004 to 2005 for Long Key. 152 Figure 8-8. Sand bar crest (black) and shoreline (red) positions along Long Key (map). 157 Figure 8-9. Sediment transport pathways illustrated on a 1997 aerial photo of Long Key. 159 ix

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Storm-influenced Sediment Transport Gradients on a Nourished Beach Nicole A. Elko ABSTRACT Beach nourishment provides an excellent opportunity for the study of intensified sediment transport gradients and associated morphological changes in a natural setting. The objectives of this study are to quantify and predict longshore and cross-shore transport gradients induced by 1) beach nourishment, 2) different storm wave conditions, and 3) the annual wave climate and long-term sediment supply. The details of sediment transport rates and gradients induced by gradual processes and high-energy events are analyzed on a macro-scale. Well-planned monitoring of the 2004 Upham Beach nourishment project in west-central Florida collected high-spatial and -temporal resolution field data. Three hurricanes passed by the project soon after nourishment was complete. Post-nourishment planform adjustment occurs immediately after nourishment via diffusion spit development at the end transitions. Thus, the initiation of planform adjustment may be abrupt, rather than gradual as predicted by the typical diffusion models. Diffusion spit formation is dominant during relatively calm wave conditions on coasts with low wave heights and tidal ranges. x

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Profile equilibration also may be an event-driven, rather than a gradual, process. Rapid profile equilibration following nourishment occurred not only due to hurricane passage, but also during a winter season. The duration between nourishment and the passage of the first high-energy event is an important factor controlling the time scale of profile equilibration. The passage of three hurricanes generated different wave conditions and induced different sediment transport directions, rates, and gradients due to their variable proximities to the project area. The direction of cross-shore transport was governed by wave steepness. Onshore sediment transport occurred during a storm event, in contrast with the concepts of gradual onshore transport during mild wave conditions and abrupt offshore transport during storm events, as cited in the literature. By formulating sediment budgets on various temporal and spatial scales, both event-driven and average transport rates and gradients can be resolved. Annual average transport rates for a region should not be arbitrarily applied to nourished beaches; rather, sediment budgets formulated with high-spatial and -temporal resolution field data should be formulated during the design phase of future nourishment projects. xi

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Chapter One Introduction Scientific research often focuses on processes occurring gradually over time, causing a response. Figure 1-1 shows cascading time scales from the century to the daily scale. Temporal scales imply gradual change because morphologic change occurs over time. These temporal scales also imply certain spatial scales (Fig. 1-1). A temporal scale that doesnt fit into this continuum is an event. A similar morphologic response may occur due to gradual change over time or it may occur relatively instantaneously as the result of a high-energy event. The magnitude of these event-driven changes will govern their spatial influence (Fig. 1-1). It is crucial to understand both types of change, gradual and episodic, because distinct processes drive morphologic change at these different time scales. Based on this concept, the research philosophy for this study is to understand morphologic changes caused by both gradual processes and high-energy events, and their implications on various spatial scales. Modern barrier islands represent a dynamic coastal environment where natural occurrences such as shoreline fluctuation and storm inundation are common. Human development of coastlines has attempted to fix the position of this dynamic system, turning these natural phenomena into human problems for which a solution is necessary. 1

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Figure 1-1. Gradual change, illustrated with cascading temporal scales, and event-driven change may lead to similar responses on similar spatial scales; however, distinct processes drive the different types of change. Macro-scale is defined within the island to feature spatial range. Natural, large-scale, morphologic variability occurs when there is a change in sea level, sediment supply, incoming wave energy, and/or tidal regime. These processes often induce sediment transport gradients in the longshore and cross-shore direction that ultimately result in coastal change. Figure 1-2 provides natural examples of the large-scale morphologic variability that results from gradients in longshore sediment transport. 2

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Figure 1-2. Large-scale morphologic features that result from gradients in longshore sediment transport. The need to understand and predict sediment transport rates and gradients was realized as early as the 1920s and 1930s when human development of the coast increased. Coastal structures, such as jetties, groins, and breakwaters, were built to protect property and maintain channels and harbors. When jetties block the natural movement of sand, longshore sediment transport rates are evident. Jetties trap sediment on the updrift side, causing a gradient in longshore sediment transport on the downdrift side. The impedance of longshore sediment transport at these structures often leads to detrimental downdrift effects. Several examples, such as the Ocean City, MD jetties (Leatherman, 1979), are shown in Figure 1-3. Significant updrift accretion is 3

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Figure 1-3. Examples of structures blocking longshore sediment transport and the resulting downdrift erosion. accompanied by dramatic erosion on the downdrift side of the structures. On some of these beaches, the downdrift sediment deficit has been remedied through beach nourishment. Since the 1970s, beach nourishment has become widespread and the preferred method of coastal protection. This is because beach nourishment is non-intrusive and it directly addresses the problem of a sediment deficit in the system. Nourishment doesnt rob Peter to pay Paul, an accusation commonly made about structures. Coastal structures are ubiquitous around the country (Fig. 1-3) and around the world, and today, so is beach nourishment. A good example of widespread beach nourishment occurs in the state of Florida. Florida has over 1300 km of sandy shoreline along the Panhandle, Gulf, and Atlantic 4

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coasts. 528 km of this shoreline is critically eroded and about 40% of the critically eroded shoreline is actively managed through beach nourishment (FDEP, 2005). In addition to promoting recreation, tourism, and natural habitat, beach nourishment protects upland infrastructure from storm damage. During the 2004 and 2005 hurricane seasons, nourished beaches in Florida protected coastal property and infrastructure more effectively than non-nourished beaches (Clark, 2005). Figure 1-4 illustrates damage to upland development along a non-nourished beach in Brevard County, FL, during the 2004 hurricane season. Nearby nourished beaches incurred little to no damage to upland structures due to wave action or beach erosion (Barker and Bodge, 2005). The importance of a wide protective beach is well known (NRC, 1995). Figure 1-4. Property damage on a non-nourished beach in Brevard County due to the 2004 hurricane season (source: Brevard County website). Beach nourishment involves the placement of sediment on a typically eroding beach to advance the shoreline seaward. Figure 1-5 shows some examples of dredging and the hydraulic placement of sand on beaches. Nourishment appears somewhat intrusive from this perspective; however, a nourished beach is constructed with the 5

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objective of approximating the natural system. Nourished beaches are essentially natural systems with a periodic, anthropogenic introduction of sediment. Figure 1-5. Dredging and hydraulic placement of nourished sediment on beaches. Generally speaking, a beach nourishment project is a large shoreline perturbation that eventually equilibrates with the surrounding system via longshore and cross-shore sediment transport (Dean, 1983). These forcing mechanisms influence the evolution of beach nourishment projects through planform evolution, i.e. longshore spreading, and cross-shore adjustment, i.e. profile equilibration (Fig. 1-6). Beach nourishment provides an excellent opportunity for the study of intensified sediment transport gradients and associated morphological changes in a natural setting. 6

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Figure 1-6. Schematic sketches of beach nourishment project evolution illustrating A) planform adjustment via longshore transport; B) profile equilibration via cross-shore transport (modified from Dean (2002)). Major advances in the technology of beach nourishment have been made since widespread projects were constructed in the 1970s (e.g., Dean, 1983; Hanson and Kraus, 1989; Dean, 1991; Dean and Yoo, 1992; NRC, 1995; Gravens, 1997; Dean, 2002). Several projects, which have been monitored throughout much of their lifetime (Everts et al., 1974; Wiegel, 1992; Stauble and Grosskopf, 1993; Leidersdorf, et al., 1993; Work and Dean, 1995; Ebersole, et al., 1996; Davis et al., 2000), have provided data to test simple, yet effective, models to predict general project performance. Due to the 7

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widespread use of beach nourishment, many interesting research opportunities exist within this burgeoning field. In the ongoing effort to confirm beach nourishment as an economically and technically-sound shore-protection practice, project performance monitoring is vital. Over the last several decades, beach nourishment has proven to be an effective solution to erosion problems in some areas, while elsewhere, the controversy over the technical merits of the practice continues. Just as the large-scale field experiments of the 1980s and 1990s (i.e., Birkemeier et al., 1981) improved the understanding of sediment transport and beach morphodynamics, beach-nourishment monitoring is important to improve the existing theories of post-nourishment beach performance. Well-planned performance monitoring helps to verify and improve project design and modeling, and to justify project necessity and re-nourishment intervals (Dean and Campbell, 1999). This study quantifies sediment transport gradients induced by the events of beach nourishment and storms. High spatialand temporal-resolution field data are used to examine morphologic changes at various temporal and spatial scales. The time-dependent sediment transport processes that govern morphologic change are analyzed with three specific research objectives. The objectives are to quantify and predict longshore and cross-shore transport gradients induced by 1) significant changes in shoreline orientation and beach slope due to nourishment, 2) different storm wave conditions, and 3) the annual wave climate and long-term sediment supply. These three objectives represent different time scales. The first two involve studying sediment transport in response to events. With the event of a beach 8

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nourishment, is transport gradual or immediate? What are the associated transport processes during storm events? The third objective involves studying gradual (long-term) longshore sediment transport at various time scales. The overall research philosophy is to understand the morphologic changes caused by both gradual process and high-energy events, and their implications on various spatial scales. In general, this study aims to augment the existing theory of post-nourishment beach performance by quantifying macro-scale sediment transport processes. 9

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Chapter Two Study Area The nourished beach in this study is located downdrift of a structured tidal inlet that has been nourished periodically over the last 30 years. Rapid changes that follow nourishment occur over short temporal and spatial scales. This creates an ideal natural laboratory for the study of longshore and cross-shore gradients in sediment transport. The study area is located in Pinellas County within the west-central Florida barrier-inlet complex (Fig. 2-1), which is bounded to the north and south by marshes and mangrove mangals, respectively. This low-energy region is subjected to mean wave heights of about 0.3 m (Tanner, 1960) and an average tidal range that is less than 1 m (NOAA, 2004). Dunes are also small on the natural portion of this coast, less than 4 m, due to low average wind speeds and low sediment supply. Along most of this region, the dunes have been removed in the process of urbanization. The low wave height and tidal range values result in a mixed-energy coast that displays a great diversity of barrier island morphologies (Davis, 1994). Some regions exhibit classic wave-dominated barriers, with long, narrow islands and few tidal inlets, whereas other areas have short and wide, drumstick barriers with closely spaced tidal inlets. The varied morphology is a product of the relative influence of waves and tides 10

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Figure 2-1. Location of Upham Beach on Long Key in Pinellas County, FL, illustrated with an early 1970s shoreline. Note the causeways which were constructed in 1926 and the dredge-and-fill canals in the back-barrier bay. (Davis and Hayes, 1984; Davis, 1989a) in which small changes in the influence of either parameter can result in significant changes in barrier island morphology. Sediment along the west coast of Florida has a bimodal distribution of predominantly fine quartz sand and gravel-sized carbonate that is mostly bivalves (Davis, 1994). The siliciclastic sediment originated in the southern Appalachians and the carbonate shells are produced in situ. Presently, this is a sediment-starved system in 11

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terms of terrigenous material (Davis, 1997). The little sand that is supplied to the coastal system via the upland drainage system is trapped in the estuaries rather than supplying the Gulf beaches. The typical weather conditions along this coast consist of prevailing breezes from the south during the summer. These summer conditions cause moderate longshore sediment transport from south to north. During the winter, cold fronts approach from the northwest about every seven to ten days. As a front approaches, winds are initially out of the south. A sharp change in wind direction from south to north occurs upon passage of the front. The passage of cold fronts generates relatively high-energy wind and wave conditions, with breaking wave heights of about 1 m and strong longshore sediment transport to the south. It is not uncommon for these weather conditions to persist for 48 hours or more. The continental shelf off the west-central coast of Florida is broad and flat with a slope of about 1:1000. The combination of this wide shelf and the fetch-limiting Gulf of Mexico results in depth-limited waves at the coast. Shoaling and refraction of these small waves occurs in the nearshore zone when the wave fronts interact with the irregularities of the coastline. The general northwest approach of wave energy drives regional net longshore sediment transport to the south. Several local reversals in sediment transport (Davis, 1994; 1999), as well as significant longshore transport gradients, result from variations in nearshore bathymetry and shoreline orientation. Occasionally, tropical storms impact the west coast of Florida. It is rare for a hurricane that entered the Gulf of Mexico from the southeast to turn abruptly to the 12

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east/northeast and impact the west coast of Florida. In fact, the last time a hurricane made direct landfall in Pinellas County was 1921. During the hurricane season of 2004, four strong hurricanes made landfall in Florida. This tied the 1886 record with Texas for the most hurricanes to hit one state in a single season (Bell et al., 2005). The 2004 hurricanes made landfall at some distance from, but with significant effects to, the study area. Historic Morphodynamics Long Key is a 7-km-long barrier island in southern Pinellas County that evolved from a drumstick barrier island to the present configuration (Fig. 2-1) over the last two centuries. Blind Pass, the tidal inlet to the north of Long Key, was a large, mixed-energy tidal inlet with a prominent ebb-tidal delta in the 1800s (Davis and Gibeaut, 1990). Even at this long-term scale, events are important. The first event that led to the change in morphology on Long Key was the Hurricane of 1848, which breached Johns Pass, 5 km to the north. Prior to this time, Long Key developed according to the drumstick barrier process-response model (Fig. 2-2). Long Key was oriented with the wide end of the drumstick to the north due to a local reversal in the southerly littoral drift. Drumstick barrier islands typically develop on mixed-energy coasts where a combination of wave and tidal processes shape the coastline (Hayes and Kana, 1976). As opposed to wave-dominated barrier islands, which are relatively long, straight and narrow, mixed-energy barrier islands are short in length, typically with one end wider than the other. The shape of these islands has been likened to that of a chicken drumstick 13

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Figure 2-2. Process-response model and features of a drumstick barrier island illustrated on the 1873 NOS Historic Topographic Survey Sheet (T-sheet) of Long Key. (Hayes et al., 1974). Such barriers are common and have been studied extensively in Alaska (Hayes et al., 1976), Massachusetts (Fitzgerald et al., 1989), South Carolina (Hayes and Kana, 1976), Virginia (McBride and Vidal, 2001), and the west coast of 14

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Florida (Davis, 1989b; 1994), as well as along the German Bight of the North Sea (Van Straaten, 1965; Fitzgerald et al., 1984). The coastal processes that shape drumstick barriers depend upon a well-developed ebb-tidal delta associated with the updrift inlet (Fig. 2-2). Waves approaching from the updrift direction are refracted around the ebb delta causing a local reversal in sediment transport near the updrift end of the island. Sediment that becomes trapped by this local reversal is deposited in the lee of the ebb delta in the form of swash bars that slowly migrate onshore. The swash bars fuse with the beach as ridge and runnel systems and over time a prograding beach ridge complex forms. Fitzgerald et al. (1984) note that a local sediment transport reversal is not necessary for swash bar attachment. In their model, the ebb delta configuration controls the location of bar attachment that may occur at any distance from the delta. Features commonly found on the updrift end of a drumstick barrier include wide accretional beaches, ridge and runnel systems representing the onshore movement of swash bars, and vegetated beach ridges alternating with low-lying wetlands that often contain cats-eye ponds (Hayes and Kana, 1976). As a result of the sediment-trapping mechanism at the ebb delta, the downdrift end of the barrier receives little or no sediment from longshore transport and tends to erode. Washover fans, patchy dunes on very narrow beaches, and marsh sediments exposed in the surf zone are common features of the downdrift, transgressive end of a drumstick barrier. The downdrift tip of the island often contains an accretional spit 15

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advancing in the direction of net sediment transport and encroaching on the adjacent tidal inlet. The National Ocean Service (NOS) Historic Topographic Survey Sheets (T-sheets) that were published in 1873 depict Long Key with the classic drumstick configuration and a prograding, triangular-shaped northern end (Fig. 2-2). Blind Pass had a prominent ebb-tidal delta that refracted wave energy resulting in onshore sediment transport illustrated by attached bars visible along the northern shoreline of Long Key. By the time the T-sheets were published, the hurricane of 1848 had already breached Johns Pass. This hurricane likely initiated the southerly migration of Blind Pass and subsequent erosion of the wide northern end of Long Key. After the hurricane, the cross-sectional area and tidal prism of Johns Pass increased and captured a significant portion of the tidal prism of Blind Pass (Mehta et al., 1976). The diminishing tidal prism of Blind Pass did not have sufficient energy to maintain its large ebb delta, which subsequently deteriorated. This instability resulted in the inlet migrating to the south in response to the dominant direction of longshore sediment transport. In 1873, Blind Pass was located nearly 2 km north of its present location and was already migrating to the south at the expense of northern Long Key. An aerial photograph from 1926 illustrates the southerly migration of Blind Pass (Fig. 2-3). Blind Pass migrated over 1 km to the south from 1873 to 1926 eroding the elaborate system of beach ridges; however, sediment was abundant in and around Blind Pass in the form of a reduced ebb delta and a prograding spit on southern Treasure Island. 16

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Figure 2-3. 1926 aerial photograph of northern Long Key showing the southerly migration of Blind Pass (c.f. Fig. 2-2), the northwest-southeast trending beach ridges, and the reduced ebb delta of Blind Pass. 17

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Despite this initial instability, the tidal prism of Blind Pass in 1926 was roughly 90% larger than the present condition (Becker and Ross, 1999). Causeway building that began in Boca Ciega Bay in 1926 (Fig. 2-1) and dredge-and-fill construction during the construction boom that began in the mid-1950s further reduced the tidal prism and accelerated the deterioration of Blind Pass (Davis and Barnard, 2000). Throughout Pinellas County, dredged sediment from the back-barrier environment was mounded to create subaerial land upon which causeways and homes were built. Dredge-and-fill construction (c.f. Figs. 2-1 and 2-3) reduced the surface area of the back-barrier bays that supplied the tidal inlets, thereby reducing their tidal prisms. The causeways, which connected the barrier islands to the mainland, compartmentalized the back-barrier bays and limited open circulation of tidal flow further reducing tidal prisms. In the study area, causeway and dredge-and-fill construction caused inlet instability. In 1926, Blind Pass was already decreasing in width and migrating to the south as a result of the opening of Johns Pass in 1848. Construction of the Treasure Island Causeway, Corey Causeway and the Pinellas Bayway in 1926 (Fig. 2-1) contributed to the decreasing tidal prism of Blind Pass, accelerating the southerly migration of the inlet. Dredge-and-fill construction reduced the surface area of Boca Ceiga Bay by nearly 30%. To prevent further inlet migration, the first of many stabilizing structures was built on northern Long Key in 1937 when a 27-m-long rock-pile jetty (Fig. 2-4A) was constructed on the south side of Blind Pass (Mehta et al., 1976). This beach was 18

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privately owned at the time by William W. Upham, but was donated to local government in a possible act of foresight in 1954, and is now called Upham Beach (Headrick, 1999). Figure 2-4. Blind Pass and northern Long Key (Upham Beach) in a) 1957 and b) 1965 (note the structures built on the beach, shown with arrow). When the first buildings were constructed on Upham Beach in the 1960s, the ebb delta of Blind Pass was collapsing and moving onshore, creating an abnormally wide beach. Condominiums were built on the dry beach, seaward of the dunes, and a seawall was constructed at the shoreline (Fig. 2-4B). Due to this poorly-located construction, erosion problems were imminent. Once the ebb delta collapsed and Upham Beach was no longer protected from wave energy, erosion began to dominate this region. Many structures were built in and around Blind Pass, creating a continuous line of seawalls, revetments, and jetties to stabilize the inlet (Fig. 2-5). The jetty on the north 19

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side of Blind Pass was extended to mitigate inlet shoaling; however, the jetty trapped most of the southerly longshore transport, exacerbating the erosion problem on Upham Beach. Despite this long jetty, Blind Pass continued to shoal due to low-energy tidal flows in the inlet and relatively high longshore transport rates from the north. Although spring tidal velocities exceed 0.8 m/s, Blind Pass is an unstable inlet evidenced by rapid shoaling that follows each dredging event (Tidwell, 2005). Presently, the inlet carries only about 5% of the tidal prism of Boca Ceiga Bay (Becker and Ross, 1999). Figure 2-5. Blind Pass and Upham Beach in October 2003 depicting the stabilization of Blind Pass, the southern migration of the inlet, and the development of the back-barrier bay. Also note that a northwest swell from a cold front is approaching the area with wave crests that are perpendicular to the Upham Beach shoreline orientation. The southern jetty of Blind Pass was also extended and a breakwater was added in hopes of reducing downdrift erosion, but Upham Beach has continued to erode. Although the ubiquitous structures in this region have stabilized the position of Blind 20

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Pass, they have resulted in the most highly modified inlet along Floridas west coast (Davis and Barnard, 2000) and one of the most rapidly eroding nourished beaches in Florida (Dixon and Pilkey, 1989; Elko et al., 2005). Upham Beach has essentially been stabilized in a seaward advanced position, creating a headland at the north end of Long Key (Fig. 2-5). The downdrift beaches have benefited from the erosion of northern Long Key since the mid-1800s (Elko and Davis, 2006). In summary, morphologic changes to Long Key over the last two centuries were initiated by natural events that altered the tidal regime of the adjacent tidal inlet (Elko and Davis, 2006). The deterioration of Blind Pass was initiated by the result of the hurricane of 1848, and then accelerated by anthropogenic influences. The large ebb-tidal delta eroded as a result of inlet deterioration, thereby removing the sediment sink that caused the updrift end of the barrier to prograde (Davis, 1989b). The shoreline now appears to be tending toward a straight configuration, as the island transforms from a drumstick barrier with a prograding updrift end and eroding downdrift end into a wave-dominated barrier with the opposite erosion/accretion pattern. Presently, the combined effect of long jetties at Blind Pass, a minimal ebb shoal, and periodic dredging of the inlet has largely eliminated natural sand bypassing around Blind Pass. This prevents an adequate sediment supply from reaching Upham Beach. Nourishment History Due to minimal bypassing around Blind Pass, the only mechanism of sediment delivery to Upham Beach is beach nourishment. Nourishment projects were constructed 21

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on northern Long Key at Upham Beach in 1975, 1980, 1986, 1991, 1996, 2000, and 2004. Typically, about 200,000 m 3 of material was placed on the northernmost 640 m of this 7-km long barrier (Table 2-1). The maximum berm width typically constructed was 115 m. The projects created a wide shoreline perturbation that spreads out rapidly. During the 1996 project, half of the planform area eroded within one year of placement (Elko et al., 2005). After two years, 83% of the nourished material had eroded. Longshore currents transport the nourished material to the downdrift beaches; thus, Upham Beach acts as a feeder beach for the rest of Long Key (USACE, 1999). A feeder beach is a nourishment project in which material is introduced at the updrift end of the littoral cell intended to receive fill (Hall and Watts, 1957; Everts et al., 1974; Gravens et al., 2003). Although material is not retained at Upham Beach, longshore transport distributes the fill to the rest of the project area. The Upham Beach nourishment plan was altered in 2000. The project length was extended, the nourishment interval was decreased from five to four years, and the nourishment volume was increased (Table 2-1). Table 2-1. Beach nourishment on northern Long Key from 1991 to 2005. Date of Upham Beach nourishment Volume (m 3 ) Length (m) (southern limit) Mar 1991 176,000 640 (LK5) May 1996 193,000 640 (LK5) Jan 2000 215,000 830 (LK6) Sep 2004 322,400 1080 (R148) Nov 2004 41,600 470 (LK4) Blind Pass is the preferred borrow area for Upham Beach nourishment projects, due to its proximity and sediment quality. The USACE dredging interval for Blind Pass 22

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is about eight years, whereas the renourishment interval for Upham Beach is now four years. Every other project utilizes an alternate borrow area, such as Pass-a-Grille Channel (Fig. 2-1), used for the 1989 nourishment, and Egmont Shoal, approximately 13 km south of the project area, used for the 1996 nourishment. Nourishing Upham Beach with sediment from Blind Pass acts as an alternate form of inlet sediment bypassing that might occur naturally if a substantial ebb shoal existed. Previous studies have concluded that between 64,500 and 86,000 m 3 (up to 40% of the total fill volume) of sediment erodes from Upham Beach during the first year after nourishment (CPE, 1992; Elko, 1999; USACE 1999; USACE, 2001). Positive volume change is routinely measured on the downdrift beach following nourishment, however the sediment budget for material eroding from the project area (Q out ) and material accreting downdrift (Q in ) has not been balanced, likely due to insufficient monitoring. 2004 Nourishment Project As mentioned above, the 2004 Upham Beach nourishment project extended beyond the typical limit at LK5 for an additional 400 m to R148 (Table 2-1). The project supplied an unprecedented amount of material, 322,400 m 3 (50% more than the previous nourishment in 2000). The 2004 project was designed with three distinct segments (Fig. 2-6): 1) the wide north segment, from Blind Pass to LK3A, 2) the central segment, from LK3A to LK5A, a large end transition that typically ties into the natural beach, and 3) the south segment, from LK5A to R148, part of which was nourished for the first time in 2004. The total project length in 2004 was 1080 m and the design berm elevation (B) 23

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was 1.8 m NGVD (National Geodetic Vertical Datum 1929, to which all elevations are referenced; zero m NGVD is roughly 0.15 m below present mean sea level). The 2004 beach fill was designed with a multiple slope that has become known as a turtle friendly design. A gently sloping berm is designed to minimize scarping and prevent overtopping of the berm, which leads to ponding in the backbeach. The 2004 Upham Beach project was designed with a wide flat berm that sloped at 1:30 (0.03) from elevation 1.8 to 0.75 m. The design then transitioned to a 1:20 (0.05) slope below 0.75 m (Fig. 2-6). The north and central segments had a maximum berm width of 140 m, the widest berm width ever constructed on Upham Beach, and an average nourishment volume density of 360 m 3 /m. The south segment had an average berm width of 40 m and an average volume density of 95 m 3 /m. To accommodate the additional project width, the fill was designed with two transitions: 1) the large transition in the central segment of fill that reduced the berm width from 140 m to 40 m over 260 m, and 2) the slight transition at the south end which tied in with the natural berm width of about 40 m. This design was implemented to provide advance mitigation for the planned T-groin field to be installed following nourishment. Five geotextile T-head groins were planned for construction on Upham Beach after the 2004 nourishment in an effort to improve the longevity of the nourishment project. The goal of the stabilization project is to maintain a beach of at least 12 m in the project area while avoiding downdrift erosion. The stabilization project was justified as necessary to maintain the public beach and protect property along the beachfront. The 24

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Figure 2-6. The planform design template of the 2004 Upham Beach nourishment project. goals of the T-head groin field are to maintain the beach, increase the nourishment interval, and ultimately utilize Blind Pass as the sole sediment source for future nourishment projects. If the stabilization project successfully maintains a 12-m wide 25

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beach, approximately 130,000 m 3 of sediment will be retained within the T-groin field. The remaining fill volume is required to provide sediment for the downdrift beaches. Permission for construction was granted from the Florida Department of Environmental Protection (FDEP) with the contingent that the structures would be removed if downdrift erosion occurred. The T-groin field installation had not yet been completed at the time of writing. Construction Elko (2005) describes the 2004 Upham Beach nourishment project in detail. The borrow area for the 2004 project was the Pass-a-Grille Channel and ebb shoal located 5 km south of Upham Beach (Fig. 2-1). This borrow area provided fill not only for the Upham Beach nourishment project, but also for the concurrent Treasure Island nourishment and the Pass-a-Grille Beach emergency project, which was constructed to repair damage from the 2004 hurricanes. In order to provide a sufficient volume of material, the pre-project channel alignment was straightened, cutting through the ebb shoal along the western portion of the Pass-a-Grille navigational channel. Nearly 600,000 m 3 of sediment were removed from the channel and shoal by a 24-inch (61-cm) cutterhead-suction dredge, the Charleston, of Norfolk Dredging Company. The average depth of water before dredging was 2.4 m and the borrow area was excavated to an average depth of 3.4 m. Material was pumped hydraulically to Upham Beach through more than 6,500 m of submerged pipeline located approximately 600 m offshore. The pipeline was left in place during dredge demobilizations due to stormy weather. 26

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Production rates were approximately 13,000 m 3 /day. The addition of a booster pump halfway along the pipeline increased production to 15,300 m 3 /day. Fill placement began on Upham Beach on July 28, 2004. Fill was placed from south to north (Fig. 2-7) in the opposite direction of net longshore transport. Placement from north to south was not possible due to environmental permit requirements that restricted the pipeline corridor location. In addition, the contractor was not permitted to generate turbidity above background conditions. To reduce turbidity, shore-parallel or longitudinal sand dikes were constructed to minimize the amount of sand slurry runoff entering the adjacent waters. The longitudinal dike was maintained at a length of at least 150 m in advance of the filling operation. Occasionally, it was necessary to construct a shore-perpendicular dike to control sediment runoff. A Y-valve was installed at the end of the shorepipe (Fig. 2-7) such that material could either be pumped Gulfward for dike construction or landward for beach construction. This method of construction resulted in little to no turbidity and minimal sand loss. Due to the passage of three hurricanes in September 2004, shortly after the completion of the project, 60 m of shoreline retreat occurred in twenty-seven days, or 2.2 m per day, along the widest portion of the project (Elko, 2005). A repair nourishment, authorized for Upham Beach following the storms, was completed on October 28, 2004. This renourishment repaired a section from Blind Pass to LK4 (Table 2-1) to the original design template. 27

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Figure 2-7. Construction of the 2004 Upham Beach nourishment project on July 28, looking north. 28

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Chapter Three Methodology Literature Review The proportion of material remaining in the beach nourishment project area over time, M(t), is an important overall parameter characterizing nourishment performance. M(t) can be determined by integrating the Pelnard-Considre (1956) diffusion equation, which will be discussed in detail in Chapter Five, over the length of a beach project (Dean, 1988). Figure 3-1 illustrates that M(t) decays exponentially indicating a rapid material loss immediately after construction. With the introduction of a large perturbation to a dynamic system, a significant initial adjustment should be expected. Initial changes occurring along the steep slope of the exponential decay curve should play a crucial role in determining the overall trend of project evolution. Thus, it is important to understand and quantify the processes that drive the immediate post-nourishment adjustment. Given the importance of the rapid initial adjustment, it is surprising that immediate high-resolution post-nourishment monitoring is typically not conducted. In addition, monitoring data are often collected without clear site-specific objectives for analysis (Weggel, 1995). Often, data produced from inadequately planned monitoring programs are unable to address the pertinent issues, and crucial performance questions 29

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Figure 3-1. Proportion of fill remaining, M(t), along an initially rectangular planform (from NRC, 1995). remain unanswered (NRC, 1995). Although frequent post-nourishment monitoring has been recommended (Davis, 1991; Davis et al., 1993, 2000; Gravens et al., 2003), post-nourishment monitoring surveys are normally conducted several months after completion of the project and annually thereafter (Leadon et al., 2004). The temporal resolution of these surveys is often not adequate to quantify immediate post-nourishment adjustment, particularly when high-energy events occur after nourishment. Understanding the immediate post-nourishment adjustment also has important management implications. Nourishment projects tend to be highly scrutinized by the public during construction and immediately after project completion (i.e., Pilkey and Clayton, 1989). Public education is important to explain the cost-benefit ratios of nourishment to storm protection. In addition, profile and planform adjustment must be explained to avoid misinterpretation of immediate project adjustment as a permanent loss of sand or a misuse of public funds (NRC, 1995; Elko, 2005). Thus, it is important to 30

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understand the physical processes and time scales governing adjustment during and immediately following construction when public interest is at its peak. Field Data Collection An intensive field-data collection program was initiated prior to construction of the 2004 nourishment project with the goal of understanding the processes governing immediate post-nourishment project adjustment in the longshore and cross-shore directions. Of course, the impact of four hurricanes was not anticipated, but was an interesting addition to the field data. Beach profiles, offshore bathymetry, planform configuration, and offshore waves were measured from June 2004 to September 2005. Figure 3-2 illustrates the high spatial resolution of the field data. Along Long Key, 25 profiles were surveyed regularly with the closest spacing of about 100 m within the nourished area. Profile spacing increased downdrift of the project where less short-term change was anticipated. Figure 3-3 illustrates the high temporal resolution of the beach surveys. Based on experience from previous monitoring efforts, the traditional wading-depth beach-profile surveys were extended to approximately -3 m. Wading profiles, which are typically surveyed to approximately -1.5 m, were extended to capture nearshore changes and measure profile equilibration. In general, the beach profile surveys extended offshore nearly to the depth of closure, which is approximately -3 m in southern Pinellas County (Wang and Davis, 1999). Below this depth, there is little sediment transport except 31

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Figure 3-2. High spatial resolution field data on Long Key from the field-data collection portion of the study. 32

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during extreme storm events. These wading beach-profile surveys followed level-and-transit procedures using an electronic total survey station. Thirty (30) surveys of the 21 profile lines were conducted during this study. Weekly beach profiles were surveyed before, during, and immediately after nourishment until October 8, 2004 (Fig. 3-3). Then, beach surveys were conducted every two weeks until September 2005. The pre-construction beach survey was conducted on June 6, 2004, and the post-construction surveys were conducted at different times along different segments. For profiles at the south end of fill, the post-construction survey was conducted on July 22, 2004, while for profiles on the north end of the fill, the post-construction survey was conducted on August 28, 2004 one month after the south segment was completed (Table 3-1). In the meantime, up to six weekly surveys were conducted along the central and south segments during construction of the north section of the project. As discussed in the following sections, significant beach profile changes were measured even at weekly intervals. Table 3-1. Construction schedule for the three segments (Fig. 2-6) of the 2004 Upham Beach project. Segment Completion date (2004) Completion to the passage of Hurricane Frances on September 5, 2004 (days) South July 22 45 Central July 28 39 North August 27 9 Repair October 28 n/a 33

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Figure 3-3. Weekly beach surveys conducted before, during, and after construction at profile R148 at the south limit of the 2004 Upham Beach nourishment. Surveys dates inside box were measured during construction. Quarterly bathymetric surveys extending to a water depth of approximately 5 m and 1,500 m offshore were also conducted using a synchronized precision echo sounder for water depth and RTK-GPS (Real Time Kinematic-Global Positioning System) for horizontal positions. Tidal water level variations were removed based on measurements from the wave gauge (Fig. 3-2). Twenty-five shore-perpendicular and three shore-parallel offshore survey lines were measured. Beach and offshore surveys were combined (Fig. 3-4). The jagged line along the offshore portion of the profile reflects the sampling interval of one point per second (1 Hz). The short, straight, line segments on the profile reflect linear interpolations between data gaps. Minimal change in the offshore portion of the surveys suggests that the beach surveys captured most of the nearshore changes and that little sediment was transported 34

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Figure 3-4. Combined beach and offshore surveys at profile R148. The transition from the wading profile to the jagged bathymetric profile is evident. offshore beyond about -3 m. This concurs with the depth of closure determined by Wang and Davis (1999). The spring-tide high water line, berm crest, dune and vegetation line, and other features (e.g., seawall) were mapped with the RTK-GPS mounted on an ATV (All Terrain Vehicle). The spring high water level can generally be identified in the field from a rack line left from the previous high tide. The operator slowly drives the ATV along the morphologic feature of interest while the RTK records position and elevation values every second, with a spatial sampling interval of 1.5 to 2 m. High water lines (hereinafter referred to as shorelines) were mapped prior to nourishment and after each 35

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storm event, and then overlain on digitally geo-referenced aerial photos. Resulting shoreline maps proved to be an invaluable management tool during the 2004 hurricane season (Fig. 3-5). A PUV directional wave gauge was deployed about 600 m offshore of the center of the Upham Beach nourishment project in approximately 4 m of water (Fig. 3-2). Wave conditions were sampled at 2 Hz for 512 samples (or 256 s) every 90 minutes. Tidal water levels were measured every 15 minutes. Sediment samples were collected by the nourishment contractor before and during construction in fulfillment of the U.S. Army Corps contract requirement. One hundred and eighty-seven sediment samples were obtained, representing every 1,500 m 3 of fill placed. The sampling locations were evenly distributed across the fill template in a 30-m grid. The sediment grain size analysis was performed with sieves that correspond with the phi units of -4.25, -2.25, -1.0, 1.25, 2.0, 2.75, 3.25, and 4.0 (19, 4.75, 2.0, 0.42, 0.25, 0.15, 0.10, and 0.06 mm). This sieving technique was required to conform with F.A.C. 62B-41.007(2) j and k, known as the "Sand Rule", which is an FDEP rule that defines the minimum quality of fill material. Per the Sand Rule, if more than 5% of the weight percentage of an individual sediment sample is retained on the -2.25-phi sieve, the sediment is considered unsuitable for nourishment (FDEP, 2001). The use of only eight sieves is not comparable to sediment analysis at -phi increments as is recommended in most particle-size analysis standards; however, this sieving technique was sufficient to determine the mean grain size of the nourished material. 36

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Figure 3-5. Shoreline maps for Upham Beach before and after nourishment, and after the passage of Frances, Ivan, and Jeanne. To determine the mean grain size for each beach-profile line, samples located 30 m to the north and south of the profile line were averaged. Frequency curves were plotted to provide an overview of the grain size distribution and sorting. Overall, the post-nourishment field data collection was well planned and successful, and allowed for analysis of the immediate post-nourishment response, as well 37

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as the effect of multiple storm impacts on a recently nourished beach. This is one of the most comprehensive field data sets ever collected for a nourishment project. The data were used to study of the mechanisms of post-nourishment planform adjustment and profile equilibration (Chapters Five and Six), to analyze storm-induced sediment transport gradients (Chapter Seven), and to determine a sediment budget from 2004 to 2005 (Chapter Eight), as well as in emergency management decision making following the hurricanes. 38

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Chapter Four Wave and Sediment Data Analysis Wave Conditions During the hurricane season of 2004, four strong hurricanes made landfall in Florida at some distance from the study area (Fig. 4-1). This tied the 1886 record with Texas for the most hurricanes to hit one state in a single season (Bell et al., 2005). The variable proximities and the wave and wind conditions generated by the passage of each hurricane affected the study area in different ways. The wave data were collected with a PUV directional gauge deployed approximately 600 m offshore in 4 m water depth (Chapter Three). The passage of Hurricane Charley on August 13, 2004 generated maximum peak wave periods (T p ) of about 8.3 s and significant wave heights (H s ) of up to 0.92 m at the project area (Fig. 4-2). Prior to the passage of Charley, two storm events beginning on July 16 and August 1, 2004 generated similar wave conditions. This indicates that the passage of Charley was not discernable as a hurricane at the study area. Following the passage of Charley, calm conditions were characterized by an average H s of 0.13 m. Fluctuation of the peak wave period between 3 s and 7.5 s (Fig. 4-2B) was a result of bimodal spectrum with a combination of swells (T p = 7.5 s) and locally generated wind waves (T p = 3.0 s) that is commonly observed in the Gulf of Mexico. 39

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Figure 4-1. Tracks of the four hurricanes that made landfall in Florida during 2004 and their proximity to the project area. Figure 4-2. A) Significant wave height (H s ) and B) peak wave period (T p ) from July 18 to October 1, 2004 (gauge location shown in Fig. 3-2) measured in 4 m of water depth. 40

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Due to the relatively low-energy conditions generated by the passage of Hurricane Charley, this event was not a primary focus of this study. Rather, the portion of the study that examines storm-induced change (Chapter Seven) focuses on the passage of Hurricanes Frances, Ivan, and Jeanne during the month of September 2004 (Fig. 4-3). Hurricanes Frances, Ivan, and Jeanne made landfall on September 5, 16, and 26, 2004, respectively. The eye of Hurricanes Frances and Jeanne passed within 50 and 80 km, respectively, of the project area, whereas that of Hurricane Ivan traversed the Gulf of Mexico greater than 500 km to the west (Fig. 4-1). Local sustained winds from the passage of Hurricanes Frances and Jeanne exceeded 15 m/s (Fig. 4-3) and a sharp change in wind direction occurred during their passage. Because the profile surveys were conducted before and after the storms, the influence of this change is not examined. The waves generated by the passage of Hurricanes Frances and Jeanne were typical of local wind-generated storm waves. Meteorological data reflect the distant passage of Hurricane Ivan. Wind speeds did not increase dramatically during the passage of Ivan suggesting that locally-generated waves and longshore currents would not be significant. Atmospheric pressure did not indicate the passage of a low-pressure system, defined as an event with barometric pressure less than 1010 mb (Hagemeyer and Almeida, 2002). The most obvious signal of the passage of Hurricane Ivan is the exceptionally high T p that exceeded 15 s at the study area (Fig. 4-2). The arrival of the long-period waves preceded the increase in H s by about one day. Waves generated by Hurricane Ivan were typical of waves propagating from a 41

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Figure 4-3. Wave and meteorological conditions at the study area during the month of September 2004. distant storm and becoming better organized with distance from the offshore source. These waves approached the project area as a well-organized, shore-normal swell. The pressure port on the wave gauge was later clogged due to sediment suspension and subsequently malfunctioned in November and December; however, wave conditions were measured during the previous winter season in 2003. Cold fronts generated high-energy events with the highest H s of 1.3 m. Several similar cold fronts occurred during the months following the repair nourishment in 2004, but wave data are not available. 42

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Breaking wave height (H b ) and wave steepness (H o /L o ) are calculated from measured significant wave height (H s ) from the wave gauge. H b is estimated from linear wave theory and wave shoaling. To determine H o /L o offshore wave height (H o ) is calculated based on the energy-flux method as )tanh(2khnHHo where )2sinh21(21khkhn and deep-water wave length is calculated from the measured wave period as L o = gT 2 /2. Wave steepness will be analyzed in detail in Chapter Seven. Table 4-1. Maximum significant wave height (H s ) and the associated peak wave period (T p ) measured at the nearshore wave gauge during the three storms. The mean wave conditions from December 2003 to February 2005 are also shown. The last two columns show calculated breaking wave height (H b ) and offshore wave steepness (H o /L o ). H s (m) T p (s) H b (m) H o /L o Frances, 9/6/04, max 1.7 8.8 2.2 0.014 Ivan, 9/16/04, max 1.0 11.8 1.6 0.004 Jeanne, 9/27/04, max 1.6 7.6 2.2 0.018 12/03 2/05, mean 0.3 5.8 0.5 0.005 The H s recorded during the passage of Hurricanes Frances and Jeanne was more than five times the mean H s measured from December 2003 to February 2005. The total energy of a wave is proportional to the square of the wave height. As such, the hurricanes introduced extremely high energy levels to the study area. The H s recorded during the passage of Hurricane Ivan was considerably lower than the waves generated by the passage of Hurricanes Frances and Jeanne; however, the longer period waves likely experienced more shoaling that the short period waves generated by Frances and Jeanne. Thus, breaking waves during the passage of Hurricane Ivan were also quite energetic. Figure 4-4 illustrates the high-energy surf zone conditions during the passage 43

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of Hurricane Ivan. This was a high-energy event, and not typical of swell conditions on this coast. Figure 4-4. Surf zone conditions during the passage of Hurricane Ivan at A) on Treasure Island, 1 km north of Upham Beach, and B) N. Redington Beach, 2 km to the north. The mean H b from December 2003 to February 2005 was 0.5 (Table 4-1), which is considerably higher than the commonly referenced mean annual breaking wave height for this region of 0.3 m (Tanner, 1960). Possible explanations for the higher estimate are that northern Long Key is a relatively high-energy section of the west coast of Florida, and that the 2004 hurricane season and higher than average storminess during the winter of 2004-2005 (Bell et al., 2005) increased the mean wave height. Alternatively, this H b 44

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determined from mean H s measured with the accurate nearshore wave gauge could be an improvement of the estimate of Tanner (1960). Offshore waves measured at the NOAA buoy (Station 42036) were not used in this study because of the lack of correlation between the offshore and nearshore wave data. Wave data from this buoy, located 56 km west of Clearwater, FL, recorded maximum significant wave heights of 5.7 m, 6.4 m, and 3.8 m for Hurricanes Frances, Ivan, and Jeanne, respectively. Offshore wave steepness was greatest for Hurricane Ivan. A comparison of these wave statistics to those measured at the study area (Fig. 4-3) illustrates that the offshore wave data were not representative of the wave conditions that impacted the project. This lack of correlation between offshore and nearshore waves is because the nearshore wave conditions during the passage of Hurricanes Frances and Jeanne were significantly influenced by local winds. Based on field observations, the visible nearshore wave climate was choppy with white capping due to local winds. A strong longshore current to the south was also observed. In contrast, local wind speed was low during the passage of Hurricane Ivan. Waves generated by Hurricane Ivan approached the study area as well-organized swell propagating from the offshore source. The significant reduction in wave height from the offshore gauge (6.4 m) to the nearshore gauge (1.0 m) resulted from energy losses due to bottom friction as the long-period waves propagated across the broad and flat west-Florida shelf. Wave spectra for Frances and Jeanne are wide and spread across relatively high frequencies indicating the early stage of wave development, or locally-generated wind 45

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waves (Fig. 4-5). The Ivan spectrum has a narrower peak in lower frequencies indicating a more developed, well-organized wave field. The morphologic response to these different wave conditions is examined in Chapter Seven. Figure 4-5. Wave spectra for the waves measured with the nearshore gauge during the passage of Hurricanes Frances, Ivan, and Jeanne. Sediment Grain Size and Composition Any study that analyzes sediment transport must first analyze the sediment characteristics. Figure 4-6 is a scatter plot of the mean grain size of the natural and nourished sediment samples collected before and after nourishment at the study area. The density of sediment samples was proportional to the volume density of nourishment in each segment, with the north segment receiving the highest volume density. The mean sediment grain size of the nourished (fill) material (D F ) was 0.52 mm (0.94 phi). The 46

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Figure 4-6. Mean sediment grain size before (D N ) and after nourishment (D F ). The x-axis refers to distance from Blind Pass at the north end of the fill. mean post-nourishment grain size for each beach-profile line ranged from 0.38 mm at LK1C to 0.66 mm at LK4A. The fill material was similar but slightly coarser than the native sand (D N = 0.45 mm) with the exception of the central segment from LK3 to LK5. The grain size of the material placed in this central segment is clearly coarser than the rest of the beach. The individual post-nourishment sediment samples ranged from a mean grain size of 0.3 to 0.9 mm. Most of these samples, about 75%, ranged from 0.3 to 0.6 mm. Of the remaining 25% of samples greater than 0.6 mm, 92% were located in the section between LK3 and LK5. The placement of relatively coarse sediments between LK3 and LK5 was 47

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unintentional, but was expected to improve nourishment performance in this rapidly eroding area. 20% of the post-nourishment sediment samples failed the FDEP requirement for beach-quality material (Chapter Three). These samples retained more than 5% of the total weight percentage on the -2.25-phi sieve (4.75-mm). The portion that did not pass the -2.25-phi sieve was noted to be shells and shell fragments. Example frequency curves for sediment samples that passed and failed the FDEP test indicate that the failing samples had a bimodal distribution with peaks in the granule to coarse-sand range and in the fineto very-fine sand range of the Wentworth size classification (Fig. 4-7A). The passing samples had a single peak in the fine to very-fine sand range (Fig. 4-7B). Figure 4-8 illustrates a bimodal sediment grain size distribution that is common on the west coast of Florida. The bimodal distribution is evident in the sediment size, composition, and shape. This is poorly-sorted material. With the exception of small amounts of mud and phosphorite, quartz and calcium carbonate dominate the sediment composition in this region. The calcium carbonate component is produced in situ and bivalves are the predominant form of skeletal material. The percentage of carbonate in this region ranges from 0 to 100%, depending on location and time (Davis, 1994). The quartz component originated in the southern Appalachians and has been reworked into very well sorted fine sand. The coarse fraction of the sediment is composed of small calcium carbonate shells in the granule size range (Fig. 4-7, inset). The shape of these grains is platy. Conversely, the fine fraction is composed of fine quartz sand. The quartz grains are spherical. These 48

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Figure 4-7. Example post-nourishment grain size frequency curves for A) the 20% of sediment samples that failed, and B) the 80% of samples that passed the FDEP Sand Rule test. Inset: coarse/granule concentration at profile LK5 on August 11, 2004. different compositions, sizes, and shapes of sediment will be transported differently. Typically, the coarsest sediments tend to become concentrated in high-energy locations. However, there has been little attention given to the transportability of platy grains or how to represent bimodal grain size distributions in nearshore morphologic change models. 49

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Figure 4-8. Example of typical grain size and composition distribution for west coast of Florida beaches (from Davis, 1994). The histogram shows the distinct bimodal distribution of coarse shell and fine quartz sand. 50

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Chapter Five Post-nourishment Planform Adjustment Literature Review One-line models that predict the long-term planform evolution of nourishment projects (Dean, 1983; Dean, 1996; Hanson and Kraus, 1989) have been developed from the Pelnard-Considre (1956) diffusion equation. In an idealized case of an initially rectangular planform, with project width Y and length l, on an infinitely long shoreline, the solution to the diffusion equation is 1241242),(lxGtlerflxGtlerfYtxy (5-1) where x and y are the longshore and cross-shore coordinates, respectively, and t is time. The longshore diffusivity, G, is dependent on wave height and sediment characteristics, ))(1)(1(8*25BhpsgKHGb (5-2) in which K is the sediment transport coefficient, H b is the breaking wave height, is the ratio of H b to water depth (h), s is the specific gravity of the sediment, p is the in-place sediment porosity, h is the depth of closure, and B is the berm elevation. During the diffusion process, the post-nourishment shoreline perturbation is smoothed by incoming 51

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wave energy that drives longshore transport. The beach fill gradually diffuses from a rectangular planform to a bell-shaped curve that spreads out to a straight shoreline eventually over time (Fig. 1-6A). Figure 1-6A is essentially a graphical representation of Eq. (5-1). The diffusion process leads to smooth end transitions over time (Dean, 1996); thus, the accepted theory indicates gradual, rather than episodic, change in response to the event of beach nourishment. Eq. (5-1) assumes small changes in shoreline orientation due to beach nourishment. The assumption is reasonable when applied to relatively large spatial scales. However, the substantial nourishment perturbation created along the local shoreline is particularly evident at the project ends where the transitions, which can be designed smoothly or abruptly, merge into the adjacent shoreline. The greatest shoreline orientation change obviously occurs at these end transitions. Here, local wave transformation patterns are altered and the gradients in longshore transport increase. This process often results in high end losses (Gravens et al., 2003) that occur immediately following construction. Because Eq. (5-1) represents long-term and large-scale diffusion, post-nourishment evolution at the end transitions may not be adequately described. Quantifying short-term, local project adjustment, such as transport gradients at end transitions, is essential in improving the present state-of-the-art predictive capabilities. The objective of this chapter is to understand the immediate planform response of a beach nourishment project. Specifically, the time scales and energy levels associated with initial project adjustment are examined on a fine-scale. This study will contribute to the understanding of processes governing immediate post-nourishment planform 52

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adjustment, particularly at end transitions. Results will also contribute to improved planform design considerations for rapidly eroding nourishment projects. Planform Adjustment Due to differences in construction schedules, fill templates, and morphologic responses in the different fill segments, planform adjustment results are presented separately for 1) the north segment and 2) the central and south segments of the fill. The downdrift segment, extending approximately 1000 m south of the fill (south of R148 to R151), was also analyzed. The locations of the fill segments and the beach profiles are illustrated in Figs. 2-6 and 3-2, respectively. North Segment Little morphological change occurred in the north segment between the completion of nourishment in this segment on August 27, 2004 and the passage of Hurricane Frances (Fig. 5-1A). Although strict turbidity requirements precluded fine sediment runoff, some fill material was transported to the south, predominantly in the swash zone, during construction. Erosion, e.g., in the form of scarping, took place in the loose sediment that was placed in the intertidal zone, for example in the longitudinal dikes. By the time construction of this segment was complete on August 27, a considerable volume of material had been transported to the south. Obviously, the post-construction survey for the north segment does not illustrate this volume loss because 53

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Figure 5-1. Profile response after nourishment from: A) the north segment, B) the central segment, C) the south segment, and D) downdrift of the nourished area. See Figures 2-6 and 3-2 for profile locations. Note that the post-nourishment survey dates are different for A (082704), B (072804), and C (072204). transport occurred during construction and prior to the post-construction survey. This transport contributed to the development of a spit, as discussed in detail in the following paragraphs. Central and South Segments Construction in the central and south segments of fill was completed on July 28 and 22, respectively, earlier than in the north segment. Planform adjustment began to 54

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occur soon after nourishment of the central and south segments was complete. About 40 days elapsed between completion of nourishment in the central and south segments and the passage of Hurricane Frances (Table 3-1). Calm wave conditions prevailed during this time (Fig. 4-2). The beach in the central and south segments prograded, as sediment that eroded from the north segment (under construction) was deposited in the nearshore and intertidal zones (Fig. 5-1B and C). In the downdrift region, offshore sand bars accumulated sediment and migrated onshore (Fig. 5-1D). Transport to the downdrift beaches during construction was also measured during the January 2000 Upham Beach nourishment, which took six months to construct due to oil contamination of the Blind Pass borrow area. By the time post-nourishment monitoring began in July 2000, the downdrift beaches had already accumulated almost 30,000 m 3 of sediment (11% of the total fill) (USACE, 2001). Deposition in the central segment was first measured on August 11, about two weeks after nourishment was completed there. Weekly survey data indicate the formation of a large interto supratidal sediment body. Contour maps derived from beach-profile surveys and morphologic mapping illustrate the sediment body extending over 300 m from profile LK4A to the south to LK6 (Fig. 5-2). It resembled a spit spreading, or diffusing, from the transition of the wide north segment of the planform. The post-nourishment shoreline position in the central segment is shown on the right side of Figure 5-3. The diffusion spit on the left side of Figure 5-3 represents deposition that occurred after construction was complete in this segment. In the aerial photo (Fig. 555

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Figure 5-2. Contour map of the beach fill based on survey data from September 1, 2004. Insert: aerial photo taken on August 12, showing the well-developed diffusion spit (outlined by dashed line) at the south end of the project and the development of the main diffusion spit at the transition between the north and central segments. The south spit had welded to the beach by September 1; thus, it is not shown on the contour map. 56

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2, insert), which was taken two weeks prior to Figure 5-3, the main diffusion spit was not fully developed; however, a similar spit was observed extending from the end transition of the south segment. This diffusion spit extended from the south end of the project at R148 shortly after the completion of the fill in the south segment. Only one survey line (R148) intersected this southern spit, so the spit volume cannot be accurately calculated. The southern diffusion spit was first documented on July 28, 2004 (Fig. 5-1C) only six days after construction of this section was complete. The diffusion spits extended to the downdrift shorelines (Fig. 5-2, insert), abruptly reducing the large shoreline orientation changes at the end transitions. Figure 5-3. Main diffusion spit extending from the wide, north segment of Upham Beach on August 27, 2004, note the numerous overwash tongues on the landward side. Formation of the diffusion spits suggests that substantial longshore transport of the nourished material, and therefore planform adjustment, occurred before construction 57

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of the entire nourishment project was complete. In other words, the diffusion process began during fill placement. The direction of spit formation reveals that the source of the sediment is from the northern end of the project. The dominance of shell material in the subaerial part of the main spit (Fig. 5-3) indicates that selective transport was important during the initial formation of this diffusion spit. Beach profiles surveyed on September 3, 2004 indicated that the main diffusion spit was composed of approximately 7,000 m 3 of sediment. The spit resulted in shoreline advancement of 8 to 16 m as compared to the immediate post-nourishment survey. During this time, the spit accreted to an elevation of over 1.3 m (Fig. 5-1B). The beach profiles prograded, essentially translating seaward. The post-nourishment profiles steepened slightly during spit formation due to the coarse shelly sediment. As shown in Figure 5-2, the shape of the diffusion spit and the associated runnel are depicted well by contours at elevations 1.0 and 0.7 m, respectively. These elevations also correlate with the shape of the spit shown on the beach profiles (Fig. 5-1B), confirming that the contour map revealed the spit morphology accurately. The modest storm event from August 1 to August 6 (Fig. 4-2), with wave heights reaching 0.6 m, only slightly higher than the annual average of 0.5 m, may have initiated and accelerated diffusion spit formation. The spit persisted through the relatively distant passage of Hurricane Charley when waves approached from the southwest. Net onshore transport occurred during this time of relatively calm wave conditions, as indicated by continued spit accretion (Fig. 5-1B) and numerous overwash tongues along the landward side of the spit (Fig. 5-3). The diffusion spit persisted for about 40 days and was 58

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dispersed during the passage of Hurricane Frances in early September. The substantial profile changes caused by the hurricane impacts are discussed in detail in Chapter Six. Similar diffusion spits were observed on the 2004 Treasure Island project, on the 2004 emergency nourishment project at Pass-a-Grille Beach, on the 2005 Venice Beach Nourishment, on the 2005 Sand Key Nourishment, and on the 1996 Upham Beach project. Diffusion spit formation occurred on the Pinellas County Sand Key nourishment in 1998, a nourishment project about 18 km north of Upham Beach. Development of the diffusion spit at the north end of the Sand Key project abruptly changed the shoreline orientation at the large end transition (Fig. 5-4A). A similar abrupt end transition that was constructed on Anna Maria Island in 2002 also resulted in diffusion spit formation (Figure 5-4B). The elevation and width of the Anna Maria Island spit increased for about one year until a storm event generated sufficient wave energy to overwash the feature and fill in the landward runnel/lagoon (Spadoni, pers. comm.). Kraus (1999) reported the formation of similar, but longer-term, spit development downdrift of the Corpus Christi Beach nourishment project in 1977. This is a bay-shore beach on the western side of Corpus Christi Bay. In the four years following nourishment, this diffusion spit extended over 500 m until reaching a causeway that prevented further extension. Note that the diffusion spits cited above formed on beaches with relatively low wave energy and low tidal range. 59

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Figure 5-4. Photos of diffusion spits on A) the 1998 Sand Key nourishment, and B) the 2002 Anna Maria Island nourishment. 60

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This study shows that diffusion spit formation occurs under a certain set of environmental conditions that are common on the west coast of Florida. They include low wave energy, low tidal range, infrequent storm events, and bimodal sediment grain size. Higher energy coastal environments would likely drive sufficient cross-shore sediment transport to preclude spit formation. In this case, initial planform adjustment would not result in an abrupt shoreline orientation change; rather, planform spreading would follow the gradual model of Figure 1-6A. In summary, diffusion spit formation is a common feature along low energy coasts during the initial planform adjustment at the end of a beach fill. Formation of a diffusion spit reveals the initial step in the diffusion model of Eq. (5-1). End transitions are smoothed abruptly by diffusion spit attachment to the downdrift shoreline, followed by net onshore sediment transport that redistributes deposited material above mean water level (Fig. 5-1B and C) resulting in overwash and landward migration of the spit. Predicting Immediate Planform Adjustment Various definitions and formation processes for spits exist in the literature. A spit is an elongated depositional feature extending in the direction of longshore sediment transport (Dean and Dalrymple, 2002). Sediment that forms a spit may be derived from nearby eroding headlands, discharge from rivers, or the landward movement of sand from inner shelf deposits (Davis and Fitzgerald, 2004). Spits extend alongshore in the direction of sediment transport as they simultaneously move onshore (Carter, 1988). Johnson (1919) observed that spit growth is most common on irregular coastlines where 61

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spit formation aids in smoothing the initially irregular coast. Findings from the present study support these definitions and suggest that a spit can also develop at the end transition of a beach nourishment project. Shoreline Orientation Changes Changes in shoreline orientation, due to nourishment are generally assumed to be small, in terms of the overall spatial scale (Dean, 2002). The increased beach width, y, is typically much less than project length, l. The average change in shoreline alignment due to nourishment is 2/tan l y (5-3) For the idealized nourishment project illustrated in Fig. 1-6A with y = 100 m and l = 4000 m, = 2.86. The analytical model of Eq. (5-1) assumes small changes in shoreline orientation due to beach nourishment. In this model, the linearization of the sediment transport equation is justified because sin(2) roughly equals 2 for small (less than 0.02% difference for the above example). However, the design template for many feeder beaches and erosional hotspots, or short nourishment projects, creates a relatively large shoreline perturbation. In the case of Upham Beach, the typically nourished north and central segments had a maximum berm width (y) of 140 m and a length (l) of 700 m, which yields a = 20.38. This large yields an 8.2% difference between 2 and sin(2) suggesting that a considerable error may result from the 62

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assumption of sin(2) 2. Abrupt end transitions that do not taper into the natural beach may have values of that approach 90. The assumption of small changes in shoreline orientation due to beach nourishment is problematic in this extreme example. In this study, the beach orientation and its change at the transition zone is measured directly from the GPS shoreline maps. The measured orientations, of the pre-nourishment shoreline (X) and of the design transition (T) from LK4A to LK5A are 35 and 57, respectively (Fig. 5-5). Thus, the measured is approximately 22, which is similar to the calculated from Eq. (5-3), as expected. This large is reduced abruptly upon formation of the diffusion spit. The measured of the diffusion spit was 45, considerably reducing the orientation difference from 22 o to 12 o (a 50% reduction). The orientation of the diffusion spit can be calculated from the orientation of the pre-nourishment shoreline and the design transition. Assuming that the orientations of the pre-nourishment shoreline and the design transition can be represented by two unit vectors, X and T respectively, the sum of the two unit vectors yields the vector of the diffusion spit S STX (5-4) In this case, X = 35 and T = 57, yields S = 46, which closely approximates the measured of 45. This simple model for determining the orientation of a potential diffusion spit can be utilized during the design process. This method will always predict 63

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Figure 5-5. Vector sum model of diffusion spit formation. The pre-construction shoreline (X) and the designed transition (T) are shown with the 1-m contour (from Fig. 5-2) that was measured on 9/1/04. The 1-m contour illustrates the diffusion spit (S). is the change in shoreline orientation from the pre-construction shoreline to the design template. The inset shows a schematic of the diffusion spit orientation as the vector sum of the transition and pre-construction shoreline orientations. diffusion spit formation; however, the angle of the vector sum becomes infinitely small as decreases. 64

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Ridge formation at the shoreline and the associated ponding that accompany diffusion spit formation are undesirable features in terms of sea turtle nesting, and often public perception. As such, beach nourishment projects may be designed to avoid diffusion spit formation. In particular, designing end transitions with a shoreline orientation similar to that of the predicted diffusion spit may reduce the likelihood of post-nourishment spit formation. Detailed modeling incorporating the computation of the gradient in longshore sediment transport is beyond the scope of this study. Sediment Transport Rate Kraus (1999) developed an analytical model for calculating the longshore sediment transport rate based on spit evolution. The model was based on formation of a diffusion spit that formed downdrift of the Corpus Christi Beach, Texas nourishment project. The model assumed that spit growth was induced by gradients in longshore transport. Another assumption was that the spit maintained a constant width, W, and prograded within a fixed vertical elevation, h + B, from the berm (B) to the depth of closure (h ). Based on the spit morphology, Kraus (1999) proposed the following equation to predict an annual average longshore transport rate, tVxtBhWQss)(* (5-5) where t is the time for the spit to elongate a distance of x s The volume of the spit, V s assumed to be a rectangular prism, is the product of W, h + B, and x s 65

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The 16-m wide diffusion spit that formed at Upham Beach extended 275 m in approximately one month. Substituting the morphologic parameters into Eq. (5-5) yields an annual longshore transport rate of about 180,000 m 3 which is considerably higher than the predicted rate for this region. V s can be calculated directly from beach profiles, and the concept presented in Eq. (5-5) can be applied more accurately with the field data collected in this study. On September 3, 2004 (37 days after nourishment), V s = 7,000 m 3 which yields a transport rate of 69,000 m 3 /year. This value of Q is in agreement with previous studies, which calculated annual sediment losses from the project during the first year after nourishment between 64,500 and 86,000 m 3 (Elko, 1999; USACE, 1999). This longshore transport rate is also considerably less than the Q determined from Eq. (5-5) due to the assumption of a rectangular-prism shaped spit. Conclusions Planform adjustment via diffusion spit formation abruptly reduces the large shoreline orientation change caused by beach nourishment. Diffusion spits form at end transitions and extend to the downdrift shoreline. Diffusion spit formation is dominant during relatively calm wave conditions on coasts with low wave heights and tidal ranges. Under these environmental circumstances, spit formation reveals the initial step in the diffusion model. Planform adjustment was initiated prior to profile equilibration, and it did not require high-energy conditions. Diffusion spit formation suggests that initial planform adjustment is abrupt as opposed to the gradual spreading model of Eq. (5-1). This finding improves the general 66

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understanding of planform evolution of beach nourishment projects. The orientation of a potential diffusion spit can be determined from a simple unit-vector sum model developed in this study. With this enhanced comprehension of longshore spreading, the design of future nourishment projects can be improved. To avoid spit formation, end transitions should be designed at the predicted shoreline orientation of the diffusion spit. 67

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Chapter Six Post-nourishment Profile Adjustment Literature Review Profile equilibration refers to the reduction of a steep nourished profile to a gentler characteristic, or equilibrium, profile (Fig. 1-6B). The equilibrium profile form that is frequently estimated with the simple model of Brunn (1954) and Dean (1977; 1991) 32Ayh (6-1) is dependent on sediment grain size. In Eq. (6-1), h is the water depth relative to mean sea level, y is the horizontal distance from the shoreline, and A is a scale parameter correlated with grain size (D). The A value can be determined graphically from Moore (1982), or according to Dean (1987) as 44.0067.0wA (6-2) in which A is in units of m 1/3 and w is the settling velocity, in units of cm/s, which can be determined from Hallermeier (1981) as 1.114Dw (6-3) Nourished beaches are almost always constructed with sediment that differs from the native grain size of the natural beach. Nourished beaches are also constructed on 68

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considerably steeper slopes than natural profiles. During the process of profile equilibration, most of the volume of placed material remains within the project area landward of the closure depth, and is simply redistributed across the profile. The dry beach width is usually reduced during this process (Fig. 1-6B). Profile equilibration time is considered one of the design issues for which design guidance is limited (Dean and Campbell, 1999). Presently, no cross-shore sediment transport models have been employed to accurately predict time scales of profile equilibration (Dean, 2002). The objective of this chapter is to understand the beach-profile response of a nourishment project that was impacted by storms. Specifically, the time scales and energy levels associated with profile equilibration are examined on a fine-scale to understand whether this process occurs gradually or immediately in response to an event. This study will contribute to the understanding of processes governing profile equilibration. Results will also contribute to improved profile design considerations for rapidly eroding nourishment projects. Profile-shape Adjustment As in Chapter Five, profile adjustment results are presented separately for 1) the north segment and 2) the central and south segments of the fill. The downdrift segment, extending approximately 1000 m south of the fill (south of R148 to R151), is also analyzed. The same four profiles from Figure 5-1 (except LK5A replaces LK5) are displayed in Figure 6-1 to illustrate these changes. Beach profile locations are illustrated in Figures 2-6 and 3-2. 69

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North Segment In the north segment, beach profiles maintained a steep post-construction slope for nine days until the passage of Hurricane Frances (Fig. 5-1A). The slight changes measured in the surf zone before the storms likely resulted from longshore sediment transport, which is consistent with southward growth of the diffusion spit. The newly constructed, wide, north segment of Upham Beach lost over 25 m of shoreline during the week of Frances passage (Fig. 6-1A). Significant profile change due to net cross-shore transport, e.g., offshore transport and formation of sand bars, as is typical during storms, did not occur along this portion of the fill. The profile-shape change was largely caused by net longshore transport, resulting in substantial volume loss (60 m 3 /m) over the entire profile. This section typically exhibits a monotonic beach profile, unlike the downdrift sections that contain a nearshore bar. This section is also characterized by large gradients in longshore sediment transport; however, the processes that preclude bar formation are unclear. The large longshore transport gradient is apparently dominant over offshore transport during storm events. Central and South Segments Nourishment was completed earlier in the central and south segments. Here, the steep post-construction slope persisted for up to 40 days after nourishment (Fig. 5-1B and C). During this time, the passage of Hurricane Charley generated up to a 0.9 m swell for a short time (Fig. 4-2), but did not induce sufficient cross-shore sediment transport to reduce the beach slope. Due to the passage of Frances, erosion within the intertidal zone 70

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Figure 6-1. Beach-profile changes induced by Hurricane Frances: A) the north segment, B) the central segment, C) the south segment, and D) downdrift of the nourishment area. See Figures 2-6 and 3-2 for profile locations. resulted in deposition on nearshore sand bars (Fig. 6-1B and C). Net offshore transport during the passage of the storm is responsible for the profile change. As compared to the north segment, little berm erosion took place in these segments. In fact, along the central segment, up to 8 m of berm progradation was measured (Fig. 6-1B), apparently benefiting from the erosion of the northern segment and dispersion of the material in the diffusion spit. Overall, the morphologic changes within the fill area caused by Frances resulted in reduction of the steep post-nourishment slope. Downdrift of the fill, the pre-storm sand bar was moved offshore in response to the passage of Hurricane Frances (Fig. 671

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1D). Otherwise, the profile shape, which was likely already in an equilibrium form, changed little. Profile Equilibration The processes and time scales of profile equilibration are important factors in understanding and predicting beach-nourishment evolution. To examine profile slope equilibration and to compare with the equilibrium shape of Eq. (6-1), the coordinates of the surveyed profiles were shifted, such that a vertical elevation of zero (z = 0) corresponded to a horizontal distance of zero (x = 0). This provided a comparison of changes in profile slope and shape, and essentially removed the erosion/accretion signal. The shifted surveyed profiles were compared with the calculated equilibrium profile (Fig. 6-2). Native (pre-nourishment) grain size, D N for each profile (Fig. 4-6), was utilized to determine the parameter A in Eqs. (6-1) through (6-3). Equilibrium profiles were calculated from x = 0 to at least x = 100 m. Then, the shape of the equilibrium profiles was compared to the pre-nourishment profiles, the post-nourishment profiles, and the post-storm (post-Jeanne, October 1, 2004) profiles. North Segment Equilibrium profiles calculated for the north segment were gentler than the oversteepened pre-nourishment profiles (Fig. 6-2A). Pre-nourishment profiles were exceptionally steep due to scour in front of the seawall in this location. The slope of the calculated equilibrium profile is similar to the pre-nourishment profile only along the 72

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offshore portion, as to be expected in the presence of a seawall. If the seawall did not exist in this region, erosion would continue to a point landward of the horizontal position of the seawall. This has been termed a virtual origin by Dean (1991). When the calculated equilibrium profile is translated landward 20 m (Fig. 6-2A), it approximated the slope and position of the 2004 pre-nourishment survey for LK2. Thus, the virtual origin for Upham Beach is located approximately 20 m landward of the existing seawall. This suggests that if the seawall did not exist, the shoreline would retreat landward to this location. As expected, post-nourishment profiles were steeper than both the pre-nourishment and equilibrium profiles. The beach was constructed according to the design template that required a 1:20 (0.05) slope below 0.75 m. Post-storm profiles in the north segment were similar to the calculated equilibrium profile suggesting that the wave energy generated by the passage of the hurricanes resulted in profile equilibration. Although the equilibrium profile calculated with Eq. (6-1) represented the post-Jeanne profiles quite well, it did not represent the pre-nourishment profiles along this seawalled segment. This shows that Eq. (6-1) is capable of predicting an equilibrium shape for this segment until the beach erodes to the seawall. It is also worth noting that the profiles in the north segment did, in fact, equilibrate. The steep post-nourishment slope was reduced despite the lack of obvious offshore sediment transport and deposition. Again, the large longshore transport gradients preclude offshore deposition. 73

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Figure 6-2. Translated measured and calculated profiles from: A) north segment, B) central segment, C) south segment, and D) downdrift of the nourished area. The long dashed line in (A) is the equilibrium profile translated 20 m landward. Central and South Segments Equilibrium profiles in these segments were similar but slightly steeper than the pre-nourishment profiles. Profiles in the central, south, and downdrift segments contained a substantial nearshore sand bar (Fig. 6-2B-D). This makes it difficult to compare the measured profile with the monotonic equilibrium profile of Eq. (6-1). Due to the presence of a sand bar on these profiles, the overall slope of the equilibrium profile was steeper than the pre-nourishment profile, specifically in the offshore segment. The 74

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calculated equilibrium profile provided a reasonable fit from the shoreline to the bar trough. On barred profiles, the region of the profile offshore of the bar crest often has a different equilibrium slope than that described in Eq. (6-1) (Inman et al., 1993; Wang and Davis, 1999). Post-nourishment profiles in the central segment of fill were substantially steeper than both the pre-nourishment and equilibrium profiles (Fig. 6-2B). In the south segment of fill, a narrow design berm (Fig. 2-6) and a nearshore bar resulted in fill placement between the berm and bar. Consequently, the post-nourishment profile tied in with the natural profile and was not as steep as along the north and central fill segments. The slope of the post-storm profiles was gentle with a large sand bar in the central and south segments, resembling the pre-nourishment profile slopes (Fig. 6-2B and C). This shows that the profiles returned to a pre-nourishment, or equilibrium, slope as a result of the storms. Thus, the wave energy produced during the month of September appears to have been sufficient to induce cross-shore transport resulting in profile equilibration of the nourished beach. Beach Slope To further quantify this apparent rapid profile equilibration, an overall beach slope () was calculated for all 106 measured and equilibrium profiles. This overall slope was measured via linear regression from mean high water (MHW = 0.12 m) to the toe of fill (-2.5 m). It is worth noting that the seaward limit of this calculation extends seaward of the bar. Although this calculation is not capable of representing the details of slope 75

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variations along the profile, the linear-regression slope represents the beach slope trend from the shoreline to the toe of fill. The measured equilibrium beach slope was measured (via linear regression) as the slope of the pre-nourishment beach profiles assuming that the beach was in equilibrium prior to nourishment. Pre-nourishment profiles are typically used to represent the natural beach slope, unless scour in front of a seawall has occurred (e.g., Fig. 6-2A). The calculated equilibrium beach slope was measured (via linear regression) from the profiles calculated with Eq. (6-1). Slope results are presented as average values for the north, central, and south segments of the fill, as well as the mean slope for the entire project (Table 6-1). Overall, the mean slope of the calculated equilibrium profiles ( eq ) was 0.034 and the mean slope ( m ) of the pre-nourishment profiles was 0.025. The slightly gentler pre-nourishment slope ( m ) is influenced by the presence of a nearshore sand bar as discussed in the following sections. When construction of the project was complete on August 27, the overall mean slope ( m ) was 0.078 (Table 6-1), indicating a steep post-nourishment slope, as expected. Nine days later, due to the passage of Hurricanes Frances, this m was dramatically reduced to 0.036, or less than half of the post-construction slope. The m decreased further due to the passage of Hurricanes Ivan and Jeanne, from 0.036 to 0.028; however, the slope reduction was much less than that induced by Frances. In fact, Hurricane Jeanne generated similar wave conditions to those generated by Frances (Fig. 4-3). 76

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However, the magnitude of beach change caused by these two events was quite different, with much more change induced by Frances. Table 6-1. Calculated beach slope () during the study period. Calculated Equilibrium ( eq ) Pre-nourishment (060404) Post-construction (072204 to 082704) Post-Frances (091004) Post-Jeanne (100104) Repair post-construction (102904) Winter (121304) North 0.033 0.026* 0.102 0.046 0.035 0.064 0.034 Central 0.032 0.023 0.075 0.035 0.027 0.055 0.031 South 0.037 0.026 0.041 0.023 0.020 Mean ( m ) 0.034 0.025 0.078 0.036 0.028 0.063 0.033 Pre-nourishment slope of LK2 and LK2A was omitted from this calculation due to scour in front of the seawall. North Segment As discussed earlier, no dry beach remained in the north segment prior to nourishment (Fig. 6-1A). The water depth directly in front of the seawall and associated riprap was approximately 0.5 m and increased to about 2 m within a short distance from the wall (< 30 m). When fill was placed in this region, a 1:20 (0.05) slope was constructed to about m, within the range of the construction equipment. Below m, the hydraulically placed fill settled at a slope of about 1:7 (0.14) resulting in an exceptionally steep post-construction m of 0.102 for the north segment (Table 6-1). This slope change at -1 m is evident in the post-nourishment survey (Fig. 6-1A). Figure 6-3 shows a time series of slope values from Table 6-1. The calculated equilibrium and pre-nourishment slopes (columns one and two) are represented as dashed and solid horizontal lines. When slope values return to this range following nourishment, 77

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Figure 6-3. Time series of measured beach slopes for the 12 surveyed profiles in the (A) north, (B) central, and (C) south segments. The calculated equilibrium and measured pre-nourishment slopes are shown as dashed and solid horizontal lines, respectively. 78

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profile equilibration has been achieved. Rapid reduction of this steep post-construction slope began during the first week after nourishment (Fig. 6-3A). The impact of Hurricane Frances resulted in a sharp drop of m from 0.102 to 0.046. Due to this high-energy event, approximately 90% of the total slope change necessary to achieve profile equilibration occurred. The post-Jeanne slope of 0.035 was similar to the equilibrium slope of 0.033. After passage of the storms, the beach slope in the north segment did not return to the pre-nourishment slope, rather it returned to the mean calculated equilibrium slope, eq (Fig. 6-3A). As stated above, the pre-nourishment profile was oversteepened due to scour in front of the seawall. Post-storm profiles, which were not yet experiencing the effects of the seawall, returned to the calculated equilibrium slope. Due to the absence of a nearshore bar, the monotonic equilibrium profile (Eq. (6-1)) represented the post-storm profile shape well. This explains the good fit between the post-storm profile and the calculated equilibrium profile (Fig. 6-2A), and also the agreement between the mean post-storm (100104) and the calculated equilibrium ( eq ) beach slopes (Table 6-1). Central and South Segments In the central segment of fill, the m was relatively constant at 0.075 for about 40 days after nourishment was complete on July 28 until the passage of Frances on September 5, 2004 (Fig. 6-3B). During this time, a diffusion spit formed in this region (Chapter Five). The formation of the diffusion spit and the resulting berm accretion are responsible for the slight increase of m during this period of relatively calm weather. 79

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Similar to the north segment, a sharp decrease of m from 0.075 to 0.035, was measured following the passage of Hurricane Frances. The post-Jeanne slope of 0.027 was similar to the pre-nourishment slope of 0.023 (Table 6-1). As mentioned previously, fill was mainly placed between the berm and bar in the south segment (Fig. 6-1C). Consequently, the post-nourishment profile was not as steep (Fig. 6-3C) as in the north and central fill segments. The post-nourishment m was constant at 0.041 for about 45 days, followed by a drop to 0.023 induced by the passage of Hurricane Frances. The slope decrease was not as dramatic as in the other segments due to the gentler post-nourishment m Overall, profile slopes in the central and south segments of fill returned to the pre-nourishment slope after passage of the storms (Fig. 6-3B and C). Although the magnitude of change was smaller than in the north segment, the trend of rapid equilibration was consistent. This shows that rapid equilibration occurred along the entire nourishment project, not only in the segment characterized by high erosion rates. Rapid Equilibration The slope-change patterns as shown in Figures 6-2 and 6-3 indicate that profile equilibration was controlled by high-energy wave events. The steep post-nourishment profile slope was flattened by the single event of the passage of Hurricane Frances, reducing the overall beach slope to nearly the pre-nourishment slope. Based on this morphologic response and the calculated beach slopes (Table 6-1), it is reasonable to 80

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conclude that profile equilibration was largely complete by October 1, 2004, 35 days after nourishment was complete. Rapid equilibration due to high-energy events is also supported by the cross-shore profile adjustment during the winter season following the repair nourishment. When the repair nourishment was complete on October 28, 2004, the measured overall slope m for the renourished profiles increased sharply to 0.064 in the northern segment and 0.055 in the central segment (Table 6-1, Fig. 6-3). The repair nourishment provides an excellent comparison because this project was not impacted by three strong hurricanes. Several energetic cold fronts, capable of generating waves exceeding 1.2 m, impacted the study area following the repair nourishment. Within six weeks, m decreased to 0.034 in the northern segment and 0.031 in the central segment, once again approaching the equilibrium slope. This rapid slope reduction following the repair nourishment was a result of the passage of the cold front events. This suggests that the event-driven equilibration that occurred following the initial nourishment was not simply an anomalous result influenced by the passage of three strong hurricanes. Event-driven profile equilibration also occurred during a winter season. This finding indicates that the time scale of profile equilibration depends on the duration between nourishment and first high-energy event. This portion of the research shows that profile equilibration is event-driven. It is not a gradual process that occurs over several years following nourishment. 81

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Predicting Immediate Profile Adjustment To examine the large-scale equilibration process over an entire nourishment project, Dean (2002) recommended comparing the volume remaining in the project area some time after nourishment (V t ) to the plan area remaining after nourishment (PA t ). When sediment is transported offshore to equilibrate the profile, the plan area decreases while the volume should remain relatively constant. As PA t diverges from V t over time, profile equilibration results. This concept, which incorporates the entire project area, reflects the overall equilibration process more comprehensively than analyzing the equilibration time based on individual profiles. From this concept, Dean (2002) proposed a calculation for profile equilibration time that resembles an exponential decay curve; however, it was noted that additional monitoring results are necessary to model this process. Dean (2002) also suggested that the ratio, )()(*BhPAVtRtt (6-4) should approach unity as the project evolves. Figure 6-4 illustrates R(t) for Upham Beach following the 2004 nourishment project. The increase in this quantity following the passage of Hurricane Frances indicates that a substantial portion of the total profile equilibration occurred as a result of this storm. Due to the passage of Frances, shoreline recession of up to 30 m reduced PA t from 86,000 m 2 to 70,000 m 2 whereas V t was only reduced from 294,000 m 3 to 279,000 m 3 This loss of nearly 20% of the plan area, and only 5% of the total volume, in nine days following nourishment suggests that a large portion of the nourished material was 82

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redistributed offshore, typical of profile equilibration. This phenomenon is evident in the shoreline maps (Fig. 3-5) when twice as much shoreline retreat occurred in response to the passage of Hurricane Frances as compared to that induced by Hurricanes Ivan and Jeanne. The large dry beach loss in such a short period of time is typically perceived as a dramatic loss by the public and should be incorporated into the planning and public education phase of the project (NRC, 1995; Dean, 2002; Elko, 2005). Following the passage of Hurricane Frances, R(t) continued to increase slightly (Fig. 6-4). This implies that overall cross-shore equilibration was achieved and that the project was continuously eroding due to longshore transport. This further confirms the finding that profile equilibration was largely complete due to the single event of the passage of Hurricane Frances, nine days after nourishment was complete. It is worth noting that the relatively high-energy conditions of H s = 1.7 m along this low-wave energy coast, which resulted in this rapid equilibration, would not be considered particularly energetic in many locations. These waves generated sufficient energy to transport sediment of D F = 0.5 mm offshore and equilibrate the steep post-nourishment profiles. Discussion This study measured rapid beach profile equilibration as a result of high-energy events immediately following nourishment completion. This response is different from the present general understanding, which suggests that profile equilibration continues for several years after nourishment (Dean and Campbell, 1999; Browder and Dean, 2000; 83

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Figure 6-4. R(t), from Eq. (6-4), following the 2004 Upham Beach nourishment. Dean, 2002). During other high-resolution monitoring programs in Pinellas County, profile equilibration was measured in approximately six months (Bortnick, 2000). The present study suggests that profile equilibration, along both barred and non-barred beaches, can be an event-driven, dramatic process rather than a process that occurs gradually as the project evolves. The rate of profile equilibration can considered a function of energy rather than time. Results from this study are contrary to the generally accepted notion that profile equilibration is a longer-term gradual process. Rapid initial profile evolution toward dynamic equilibrium was also measured in both mediumto large-scale laboratory experiments (Wang et al., 2003; Wang and Kraus, 2005). 84

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This study suggests that storm conditions may be required for profile equilibration to occur on a nourished beach, particularly in the offshore portion of the profile. By definition, transport to the depth of closure is only initiated during energetic conditions (e.g., Hallermeier, 1981). For sediment redistribution from a steep post-construction slope to a gentler slope that is relatively constant from the shoreline to the depth of closure, high-energy conditions are necessary. In the case of Upham Beach, transport to a depth of 2.5 to 3 m was induced during the passage of Hurricanes Frances and Jeanne during the month following nourishment. This finding should also be applicable to high energy coastal environments. Although wave energy is higher in these regions, the depth of closure is also deeper. To achieve profile equilibration, a high-energy event capable of transporting sediment to the depth of closure is necessary. As such, a higher-energy storm that the passage of Hurricane Frances experienced in this study would be required for profile equilibration on, for example, the northeast coast of Florida. The duration between the completion of nourishment and the first high-energy event to impact the project area is likely an important factor in determining the time scale of profile equilibration. The exponential decay model of Figure 3-1 may not apply. If significant profile adjustment does not occur until the passage of the first high-energy event, post-nourishment adjustment may behave as stasis, punctuated by rapid change, as opposed to a smooth decay curve. Profile equilibration should be considered complete once the slope is reduced to near the equilibrium, or pre-nourishment slope. Post-nourishment profile equilibration 85

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should demonstrate a clear trend of profile-shape changes (e.g., decreasing beach slope) and should not be confused with dynamic variations in profile shape without a distinctive trend. Overall, once R(t) stabilizes, profile equilibration should be considered complete. A combined analysis of individual beach-profile slope response and a time series analysis of Eq. (6-4) is a comprehensive method to determine profile equilibration time. Conclusions Profile shape and slope were relatively constant until the passage of Hurricane Frances on September 5, 2004 resulted in remarkable beach profile changes. Based on individual profile-shape analysis, calculated beach slopes, and Eq. (6-4), the steep post-nourishment slope equilibrated nearly to the pre-nourishment slope (for a barred beach) or the equilibrium slope (for non-barred beach) within weeks of construction. This equilibration was largely dominated by one high-energy event, Hurricane Frances. Hurricanes Ivan and Jeanne passed by later in September 2004 and resulted in much less overall profile-shape and slope change, as compared to the changes caused by Frances. These subsequent storms completed the profile equilibration process. This study shows that profile equilibration can be an event-driven process rather than a process that occurs gradually as the project evolves. For sediment redistribution from a steep post-construction slope to a gentler slope that is relatively constant from the shoreline to the depth of closure, high-energy conditions are necessary. Finally, the duration between nourishment completion and the passage of the first high-energy event appears to be an important factor controlling the time scale of profile equilibration. 86

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Chapter Seven Storm-induced Sediment Transport Literature Review The seasonal beach profile cycle in response to changing wave conditions was introduced by Shepard (1950). In general, high-energy conditions during the winter months result in a flat, eroded beach profile, whereas low-energy conditions during the summer months result in an accretionary beach with a well-developed berm. Assuming no longshore sediment transport gradient, net onshore transport leads to dry beach accretion, whereas net offshore transport results in beach erosion. The cross-shore sediment transport processes governing this cyclical pattern are associated with different time scales and energy levels; thus, onshore and offshore transport are considered two distinct modes of cross-shore transport that occur at markedly different time scales (Birkemeier, 1979; Dean et al., 2002). The seasonal profile cycle described above led to predictions of the direction of net sediment transport with the wave steepness parameter (H o /L o ). High steepness storm waves tend to induce net offshore sediment transport, whereas gentle swell waves have low steepness values and result in net onshore sediment transport. As such, a critical steepness value should exist that indicates the direction of net onshore and offshore 87

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transport. Early experiments produced a range of values for this critical wave steepness parameter from 0.0064 to 0.03 (Johnson, 1949; Rector, 1954; Saville, 1957). Dean (1973) noted the importance of sediment grain size and proposed that sediment is suspended by breaking waves to a height proportional to the wave height. If the fall time of the sand grains is less than (or greater than) half of the wave period, sediment is transported onshore (or offshore). It follows that the sediment fall velocity, w, is important in the determination of the transport direction. The parameter, w T HNod (7-1) called the Dean number, relates the fall velocity to the wave orbital motion, giving this parameter the potential to be an indicator for beach change. Several studies have recommended a critical value for the Dean number that separates accretion and erosion events. Using offshore significant wave height (H o ), Kraus et al. (1991) determined a value of 3.2. Using rms (root-mean-square) wave height (H rms ), Kriebel (1986) recommended a value of 2.3. Using breaking wave height (H b ), Wright et al. (1984) concluded that values less than 1.5 resulted in accretion and values greater than 5.4 led to erosion. The Dean number has also been used in many of the recent movable bed laboratory experiments as a parameter to assess the trend of net cross-shore transport (Smith and Kraus, 1991; Wang et al., 2002). Dean (1973) also introduced the relationship between variable wave steepness and sediment fall velocity to determine a critical steepness value 88

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gTwcLHcriticaloo (7-2) where c is a proportionality coefficient. Deep-water wave length is calculated from the measured wave period as L o = gT 2 /2. When the critical wave steepness (H o /L o ) exceeds the value on the right side of the equation, net offshore transport is predicted. Under calm or low critical steepness conditions, net transport is onshore. Proposed values for c have ranged from 1.7 to 5.5 (Dean, 1973; Allen, 1985; Kriebel, 1986; Larson and Kraus, 1989). Adopting the concept presented in Eq. (7-2), Kraus et al. (1991) developed an empirical wave steepness criterion 30007.0wTHLHcriticalooo (7-3) that was directly formulated with the Dean number. This relationship was verified with laboratory and field data. In this equation, net offshore transport is predicted when the critical wave steepness is less than the value on the right side of the equation. Eq. (7-3) is used to determine the transport direction in the SBEACH model (Larson and Kraus, 1989), a commonly used storm profile evolution model that is also used in this study. These relationships, used to determine the direction of cross-shore sediment transport, neglected the gravitational forcing from the slope of the beach profile. For a post-nourishment beach profile, the gravitational forcing induced by the steep slope may 89

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have significant influence on cross-shore sediment transport. In this case, the above parameters may not be directly applicable. In addition, Eqs. (7-1) through (7-3) illustrate that the critical value used to determine the transport direction can change if different sediment grain sizes are input while the wave conditions remain constant. In other words, grain size alone can control the direction of transport under certain wave conditions. In addition to the analytical relationships described above, process-based cross-shore sediment transport models have recently been developed. These models successfully simulate offshore transport during high-energy conditions, but onshore bar migration during calm conditions is predicted poorly (Thornton et al., 1996; Gallagher et al., 1998). All of the above studies display some predictive capability that relates increased wave height during storms to net offshore transport and sand bar formation (Komar, 1998), but less skill in predicting net onshore sediment transport. In other words, dramatic storm-induced changes are predicted more accurately than gradual longer term changes. At this time, an understanding of the processes that govern cross-shore transport remains rudimentary. In this study, a conceptual model (Fig. 7-1) illustrates the accepted sediment transport response to different combinations of wave height (H) and wave steepness (H/L). Numerous field and laboratory studies have confirmed that beaches erode under the influence of steep storm waves (high H and H/L) and recover during mild swell conditions (low H and H/L). Offshore transport occurs in response to a storm-event, whereas onshore transport occurs gradually. Furthermore, it is reasonable to assume that 90

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Figure 7-1. Conceptual model of possible combinations of wave heights (H) and wave steepness (H/L) and the predicted cross-shore sediment transport. small but steep waves, e.g., low-energy waves generated by local prevailing breezes, should not result in significant morphologic response due to cross-shore transport. High-energy, long-period waves, e.g., from a powerful distant storm, will result in high H and low H/L (Fig. 7-1). The direction of net cross-shore transport induced by these waves is not well documented in the literature and little field data appear to exist on this topic. Little attention has been given to relatively high-energy, long-period waves in laboratory experiments due to scaling restrictions. Designed accretionary waves with H s = 1 1.3 m and T = 10 11 s resulted in erosion in some wave tank experiments (Raynor and Simmons, 1964) and accretion in others (Kraus et al., 1992; Dette et al., 1995). It is also well known that substantial onshore transport in the form of overwash occurs during extreme storms when beaches are inundated by storm surge (Sallenger, 2000; Wang et al., in press). 91

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The storms that passed by the project area in September 2004 provided an excellent opportunity to test the conceptual model in Figure 7-1. Hurricanes Frances and Jeanne produced steep locally-generated storm waves to test the theory of offshore transport during high-energy storm events, and Hurricane Ivan was a distant storm that could help to answer the question of transport due to high-energy, long-period waves. The objective of this chapter is to assess storm-induced sediment transport processes based on preand post-storm beach profile surveys. Specifically, the magnitude and direction of cross-shore transport and the longshore gradients in longshore transport generated by the three major storm events during the 2004 hurricane season are determined. The relative importance and spatial and temporal variability of each transport process is examined. Then, several analytical models are tested to simulate the measured magnitude and direction of transport. Determining Sediment Transport from Beach Profiles Beach profiles were surveyed before and immediately after the wave conditions subsided following the passage of Hurricanes Frances, Ivan, and Jeanne (Chapter Three). This ensured high-temporal resolution surveys that measured beach profile response to the storms without significant post-storm recovery. The beach-profile spacing from Blind Pass to R151 was 150 m on average, providing high-spatial resolution surveys to resolve the trends in longshore and cross-shore sediment transport. The profiles extended to nearly -3 m, close to the closure depth. The following methodology, modified from Work and Dean (1995), is intended to provide a macro-scale estimate of transport from 92

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beach profile data, not a detailed examination of process-based transport across the profile (e.g., Inman and Bagnold, 1963). Longshore and cross-shore transport are analyzed with the conservation of sediment equation yqxqthyx (7-4) where h is the water depth, t is time, q x and q y are the local longshore and cross-shore volumetric sediment transport rates, respectively, at any point on the profile. x and y are the longshore and cross-shore coordinates, respectively. y is positive in the offshore direction and x is positive in the downdrift direction, to the south in this case. In general, local erosion is indicated by positive transport. Positive q y indicates offshore transport and local erosion, whereas negative q y indicates onshore transport and local deposition. Likewise, positive q x indicates downdrift (southerly) transport and local erosion. Eq. (7-4) is integrated across the active profile from y = 0 to y = y the landward and offshore limits of profile change (i.e., the closure depth), respectively, as ***000yyyyxyyqyxqyth (7-5) where the left side of the equation represents cumulative beach volume change, indicating the overall gradient in sediment transport. The last term, the cumulative cross-shore sediment transport, should be zero when integrated across the entire active profile to y Thus, the gradient in longshore sediment transport can be calculated as 93

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**00yyxxxQyxqyth (7-6) where Q x is the net longshore transport rate across the entire profile, expressed in units of m 3 /m for each storm event. Cross-shore sediment transport is the mechanism governing profile change in the absence of longshore transport gradients. When 0 xQx the first term on the right side of Eq. (7-5) is zero. When integrated from y = 0 to some arbitrary distance y offshore, Eq. (7-5) yields yyyqyqyth0)0()( (7-7) The last term in this equation is zero when the calculation begins at y = 0, the landward limit of active profile change. By this formulation, the local cross-shore transport rate at any offshore distance y can be determined. For example, the peak cross-shore transport is determined when Eq. (7-7) is integrated to the equilibrium point, y eq Hallermeier (1978) defined y eq as the cross-shore position where the depth remains the same before and after a storm. This point represents the profile crossing on storm profiles separating inshore erosion from offshore deposition. A schematic diagram (Fig. 7-2) illustrates the parameters and concepts presented in Eq.s (7-5) through (7-7). Storm-induced morphologic changes resulted in foreshore erosion and offshore deposition with the formation of a sand bar. The left side of Eq. (7-5) is represented by a cumulative sediment transport curve (right side vertical axis). 94

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Figure 7-2. Schematic diagram of storm-induced profile change, the cumulative sediment transport across the profile, right side of Eq. (7-5), and the cross-shore transport rate at the equilibrium point, q y (y eq ). Because the beach profile survey extends beyond y and sediment is conserved across the profile, the curve returns to zero at the offshore limit. The value of the curve at the equilibrium point, q y (y eq ), reflects the amount of cross-shore sediment transport that caused the adjacent erosion and deposition. Positive q y (y eq ) of 30 m 3 /m indicates net offshore transport. The slope of this curve represents the cross-shore transport gradient with a positive trend representing erosion and a negative trend representing deposition. Figure 7-2 also illustrates a negligible longshore gradient in longshore sediment transport. The total sediment transport curve returns to zero at the offshore limit indicating volume conservation across the profile and no longshore transport gradient. If the curve does not return to zero at the offshore limit, a positive or negative trend at the offshore limit is attributable to a gradient in longshore transport. This positive or negative offset actually represents the cumulative value of the longshore gradient in 95

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longshore transport across the profile. It is realized at the offshore limit as a residual value. To rigorously separate crossand longshore sediment transport by this method, knowledge of the cross-shore distribution of longshore sediment transport is required (Work and Dean, 1995). As mentioned previously, the details of transport across the profile are beyond the scope of this paper. If the effects of the longshore transport gradient are small, they can be removed, leaving only the cross-shore transport rates. Unfortunately, the effects of the longshore transport gradients in this region are large and this effect is difficult to remove. As such, the cross-shore transport rate is estimated from the cumulative transport curve at the equilibrium point, q y (y eq ), without attempting to remove the effect of the longshore transport gradient. By this method, the trend of total sediment transport across the profile is utilized to determine cross-shore sediment transport rates and longshore gradients in longshore transport. Storm Wave Conditions The passage of Hurricanes Frances, Ivan, and Jeanne is evident in the wave, water level, and meteorological conditions measured during the month of September 2004 (Fig. 4-3). The field data collection methodology and the wave data analysis are described in Chapters Three and Four, respectively. Table 4-1, which illustrates the wave heights, periods, and wave steepness generated by each of the storms, is reproduced here for convenience of reference (Table 7-1). Recall that the passage of Hurricanes Frances and Jeanne resulted in local wind-wave generation; whereas, waves generated by Hurricane 96

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Ivan over 500 km offshore approached the project area as a well-organized, shore-normal swell. Table 7-1. Reproduction of Table 4-1. H s (m) T p (s) H b (m) H o /L o Frances, 9/6/04, max 1.7 8.8 2.2 0.014 Ivan, 9/16/04, max 1.0 11.8 1.6 0.004 Jeanne, 9/27/04, max 1.6 7.6 2.2 0.018 12/03 2/05, mean 0.3 5.8 0.5 0.005 Wave steepness (H o /L o ) during the passage of Hurricanes Frances and Jeanne was up to four times higher than H o /L o during the passage of Hurricane Ivan (Table 7-1). H o /L o during Hurricane Ivan was actually 20% lower than the mean steepness. In fact, the long-period waves that preceded the increase in H s (Chapter Four) had a minimum steepness of 0.0003. The swell waves generated by Hurricane Ivan were not typical of swell conditions in this region (Fig. 4-4). H b during Hurricane Ivan was more than three times higher than the mean H b A somewhat skeptical hypothesis proposed prior to the passage of Ivan was that these relatively high-energy waves could result in onshore sediment transport due to their low steepness values, but as mentioned above, little data exist to confirm this hypothesis. Storm-induced Sediment Transport Cross-shore sediment transport and the longshore gradient in longshore transport are estimated from the morphologic response to the passage of the three hurricanes. Examples of morphologic changes due to the three storms are presented in the same 97

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format as Figure 7-2 with a curve representing the left side of Eq. (7-5) superimposed on the beach profile surveys. In contrast to Figure 7-2, all of the sediment transport curves from the nourished beach have a negative or positive trend at the offshore limit. This indicates that longshore transport gradients are important at the study area and that volume is not conserved in the cross-shore direction. North Segment Hurricane Frances caused profile equilibration along the nourished area as discussed in Chapter Six. In the north segment, the passage of Hurricane Frances resulted in foreshore erosion without associated offshore deposition (Fig. 7-3). In this case, the large positive residual at the offshore limit of the cumulative sediment transport curve indicates a large positive gradient in longshore sediment transport. This corresponds to an increasing longshore transport rate and a loss of sediment volume (erosion) at this location. Sediment is eroded from the profile and removed from the region, rather than being deposited offshore, and volume is not conserved across the profile. q y cannot be measured in this example due to the lack of a negative trend to the transport curve, indicating no offshore deposition. In the north segment, the morphologic response was similar for all three hurricanes, indicating consistently large longshore transport gradients and minimal cross-shore transport. As noted in Chapter Six, the beach profiles in the north segment equilibrated in response to the storms, but this 98

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Figure 7-3. Morphologic response and measured sediment transport, right side of Eq. (7-5), at profile LK2 in the north segment due to the passage of Hurricane Frances. equilibration was not accompanied by offshore deposition. The large gradient in longshore transport is dominant of over cross-shore transport during storm events. Central and South Segments The morphologic response in the central and south segments from LK4 to R148 is illustrated with example profiles from LK5(A) in the center of the nourishment. This region exhibited both longshore gradients in longshore transport and significant cross-shore transport. Examples from the downdrift beaches are also included to illustrate the longshore variability in transport gradients. 99

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Hurricane Frances The morphologic response to the passage of Hurricane Frances involved foreshore erosion and offshore deposition (Fig. 7-4). The sand bar/ridge is close to shore along this section of the beach. This is discussed in more detail in Chapter Eight. The initial positive trend to the cumulative sediment transport curve indicates erosion, and the negative residual indicates excess deposition. Volume was not conserved across the profile. The steep post-nourishment profile shape induced a strong cross-shore transport gradient causing rapid beach change. The passage of Hurricane Frances induced significant net offshore transport, measured as q y (y eq ). The negative residual at the offshore limit of the sediment transport curve indicates a large negative gradient in longshore transport. This corresponds to a decreasing longshore transport rate in this region and subsequent deposition. Hurricane Ivan Analysis of sediment transport induced by the passage of Hurricane Ivan is less straightforward. Hurricane Ivan resulted in foreshore deposition with up to 25 m of shoreline advancement that was not accompanied by significant offshore erosion or sand bar migration (Fig. 7-5A). The negative trend of the cumulative sediment transport curve indicates deposition, and the negative residual confirms that this deposition was not accompanied by offshore erosion. The negative residual at the offshore limit of the curve also indicates a negative gradient in longshore transport. This reveals that most of the sediment deposited during the passage of Hurricane Ivan was supplied from updrift rather 100

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Figure 7-4. Morphologic response and measured sediment transport, right side of Eq. (7-5), at profile LK5 in the center of nourishment due to the passage of Hurricane Frances. than from the cross-shore direction. Most of the deposition was a product of longshore transport supplying eroded sediment from the north segment. It is difficult to measure significant cross-shore transport from this morphologic response to the passage of Hurricane Ivan. A small amount of cross-shore transport can be measured from slight erosion of the foreshore and the seaward face of the sand bar. This sediment transport is realized as a small positive (offshore) and only slightly larger negative (onshore) trend along the cumulative transport curve (shaded areas, Fig. 7-5A). This pattern is consistent along the south and central segments as a result of the passage of Hurricane Ivan. Thus, most of the deposition due to the passage of Hurricane Ivan was 101

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Figure 7-5. Morphologic response and measured sediment transport, right side of Eq. (7-5), due to the passage of Hurricane Ivan at profile A) LK5A in the center segment of nourishment, and B) R160 on southern Long Key. 102

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the result of sediment supplied from longshore transport with a small amount of onshore transport. An example from southern Long Key is included to illustrate the morphologic response to Ivan in the absence of large longshore transport gradients. At profile R160, the passage of Hurricane Ivan induced minor profile-shape change with some berm deposition and onshore migration of the sand bar (Fig. 7-5B). Berm deposition was consistent along the study area. The negative trend of the cumulative sediment transport curve indicates deposition. The curve returns to zero at the offshore limit indicating a minimal longshore gradient in longshore transport. Thus, the measured transport was a result of a small amount of net onshore sediment transport. Minor net onshore transport was measured along the island in response to the passage of Hurricane Ivan with the exception of the north segment of the nourishment. Similar magnitudes of onshore transport were also measured throughout Pinellas County after the passage of Hurricanes Dennis and Katrina in 2005. Hurricane Jeanne In the central and south segments, sediment that was deposited in the foreshore zone during Hurricane Ivan was eroded and deposited offshore, forming a sand bar in response to the passage of Hurricane Jeanne (Fig. 7-6A). The initial positive trend to the cumulative sediment transport curve indicates foreshore erosion, and the negative residual indicates a negative gradient in longshore transport. The curve indicates that both cross-shore and longshore transport were significant along the central and south 103

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segments during the passage of Hurricane Jeanne. This sediment transport trend is similar, although slightly less in magnitude, to the transport generated by the passage of Hurricane Frances. Most of the profile equilibration occurred during the passage of Frances (Chapter Six) resulting in a larger magnitude of cross-shore and longshore transport. An example from the region downdrift of the nourishment project for the passage of Hurricane Jeanne is also included. Profile R149 is located approximately 300 m south of the south limit of nourishment. Foreshore erosion was accompanied by offshore sand bar deposition in this region (Fig. 7-6B). In this case, the positive trend to the cumulative sediment transport curve indicates foreshore erosion. The curve returns to zero at the offshore limit, suggesting a conservation of volume across the profile and a minimal gradient in longshore sediment transport. Here, the sand bar position was relatively constant before and after the storm. Note that the depth of closure in Figure 7-6B is relatively shallow at -2 m. This occurred occasionally for one of several possible reasons. The survey may not have extended to the depth of closure, or the storm waves may not have mobilized sediment below this depth at this particular location due to longshore variability in wave energy. To the south at profile R160, offshore sand bar migration was measured in response to the passage of Hurricane Jeanne. Thus, the longshore gradient in longshore transport has diminished downdrift of the nourishment, and cross-shore transport is the dominant storm-induced transport process. 104

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Figure 7-6. Morphologic response and measured sediment transport, right side of Eq. (7-5), due to the passage of Hurricane Jeanne at profile A) LK5 in the center segment of nourishment and B) R149, 300 m downdrift of the nourishment. 105

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Longshore Gradients in Sediment Transport Transport gradients determined for individual beach profiles are plotted to illustrate the spatial distribution of the longshore gradient in longshore transport and cross-shore transport (Fig. 7-7). For comparison, transport is also analyzed for the recovery phase during the 17 days of low-energy wave conditions that followed the passage of Hurricane Jeanne (10/1/04 to 10/18/04). During this time, wave conditions were similar to the annual mean conditions (Table 7-1). In response, the post-Jeanne profiles recovered as sediment that had been transported offshore during the storm slowly returned to the beach. Cross-shore and longshore transport rates for the recovery period were calculated to correlate with the 7-day time period between surveys used to determine the storm-induced transport rates. The large positive gradients in longshore transport along the north segment result in transport to the south and rapid erosion (Fig. 7-7A). The northernmost profile is protected from wave energy by a jetty and breakwater. This gradient becomes negative in the central and south segments and the longshore transport rate decreases, resulting in deposition from longshore sand transport. South of the nourishment the longshore transport gradient fluctuates about zero. Profiles south of R151 were not included in Figure 7-7 due to sparse data; however, the fluctuation about zero is consistent to the south end of the island (e.g., Fig. 7-5B). This general trend describes the longshore transport gradient generated by the hurricanes and during the recovery period with two notable exceptions. First, maximum longshore transport gradients were generated by Hurricane Frances because of the rapid 106

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Figure 7-7. The longshore distribution of A) the longshore transport gradient (m 3 /m/event) and B) cross-shore transport (m 3 /m/event) for the nourishment area due to the passage of Hurricanes Frances, Ivan, and Jeanne, and during the post-Jeanne recovery period. The transport rates are based on surveys measured approximately weekly. 107

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profile equilibration and high-energy wave conditions. The magnitude of the longshore transport gradient induced by Ivan was 60% less than the gradient induced by the passage of Hurricane Frances. Secondly, the only time large gradients were not generated in the north segment was during the low-energy recovery period following the passage of Hurricane Jeanne. Even the low wind speeds and normal wave angle of approach during the passage of Hurricane Ivan induced relatively large transport gradients along the north segment. This is due to the northwest/southeast shoreline orientation of Upham Beach. Wave energy that approaches from the northwest has perpendicular wave crests (Fig. 2-5) and southwest waves approach normal to shore. Thus, neither wave angle of approach drives longshore transport to the north. Wave refraction at the headland also induces longshore transport to the south, even when wave energy approaches normal to shore. To the south, the shoreline orientation is generally north-south, resulting in a decreased longshore transport gradient. Figure 7-7B illustrates the longshore distribution of cross-shore transport, q y (y eq ), calculated from Eq. (7-7). Cross-shore transport was negligible along the north segment with the exception of the northernmost profile. Downdrift of the north segment, positive q y (y eq ) indicates offshore transport due to Hurricanes Frances and Jeanne, whereas the small negative q y (y eq ) indicates a small amount of onshore transport during the passage of Ivan and during the post-Jeanne recovery period. The magnitude of net onshore transport induced by the passage of Hurricane Ivan was 60% less than the magnitude of net offshore transport due to Frances and Jeanne. The magnitude of net onshore transport 108

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induced by the passage of Hurricane Ivan was small. However, net onshore sediment transport was induced by Hurricane Ivan, not offshore transport as is expected during high-energy conditions. Similar magnitudes of onshore transport were induced by the high-energy swell conditions created by the passage of Hurricane Ivan and by the gentle swell condition during a post-storm recovery period. The different wave conditions for each of the three hurricanes and the post-Jeanne recovery period are plotted on the conceptual model from Figure 7-1 (Fig. 7-8). The measured differences in longshore and cross-shore sediment transport determined above are summarized by this figure. The passage of the three hurricanes, all of which generated relatively large H, resulted in large gradients in longshore transport. Only the low-energy conditions during the post-Jeanne recovery phase did not generate significant longshore transport gradients. Thus, wave energy, which is a function of H, governs the generation of longshore transport gradients in this region. As discussed above, the shoreline orientation and headland effect of Upham Beach drives longshore currents to the south regardless of the wave direction. Along the non-nourished beaches, longshore transport gradients were negligible. Cross-shore transport gradients were consistent alongshore, not specific to the nourishment project like the longshore transport gradients. The steep storm waves generated by the passage of Frances and Jeanne resulted in offshore transport (Fig. 7-8), whereas the swell (low steepness) waves generated by Ivan and during the post-Jeanne recovery period resulted in a small amount of onshore transport. Cross-shore transport was governed by wave steepness. Recall that the conceptual model indicates that 109

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Figure 7-8. Fig. 7-1 with wave conditions from each of the three hurricanes and the post-Jeanne recovery and the resulting gradients in longshore and cross-shore sediment transport on the nourished beach. offshore transport occurs in response to high-E events and onshore transport occurred gradually over time. This study has documented that onshore transport may occur on two distinct time scales, both in response to an event, as well as gradually. Thus, onshore sediment transport can be associated with high-energy events, not only with mild wave conditions as implied in the literature. Predicting Storm-induced Sediment Transport Wave steepness analysis Eqs. (7-1) through (7-3) are utilized to investigate whether the direction of cross-shore sediment transport determined from the beach profiles can be predicted from measured wave data. These equations include a dependency on the sediment fall 110

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velocity, w, which depends on grain size (Eq. (6-3)). The mean post-nourishment grain size (D F ) for each beach profile ranged from 0.38 to 0.66 mm, with the coarsest concentration of grains in the central segment of the nourishment (Fig. 4-6). The greatest amount of cross-shore transport was also measured in the central portion of the nourishment (Fig. 7-7). This is counterintuitive because coarser grain sizes lead to higher fall velocities and, theoretically, less sediment transport. For this reason, the mean D F of 0.52 mm was utilized to determine the sediment fall velocity in Eqs. (7-1) through (7-3) rather than the longshore distribution of D F A rationale for this apparent sediment transport inconsistency is discussed in the next section. The H o /L o exceeded the critical steepness parameter from the right side of Eq. (7-2) due to the passage of Frances and Jeanne by up to 70% (Fig. 7-9A). When H o /L o exceeds this critical steepness parameter, offshore transport is predicted. H o /L o did not exceed the critical steepness parameter from Eq. (7-2) due to Ivan, indicating onshore sediment transport. Similarly, the critical steepness predictor used to determine the direction of transport in the SBEACH model (Eq. (7-3)) also exceeded H o /L o by 70% during the passage of Frances and Jeanne, indicating offshore transport (Fig. 7-9B). H o /L o was exceeded for 6 and 10 hours during the passage of Frances and Jeanne, respectively. This direction indicator persisted for a sufficient amount of time to induce morphologic change given adequate transport. The critical steepness parameter did not exceed H o /L o during the passage of Hurricane Ivan, indicating onshore transport. The Dean number, Eq. (7-1), is another predictor of the transport direction (Fig. 7-10). In this study, erosion and accretion events are well separated by this simple 111

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Figure 7-9. Critical steepness analysis. The blue line represents the left side of the equation. The red dots represent the right side of A) Eq. (7-2) with c = 5.5 as recommended by Larson and Kraus (1989), and B) Eq. (7-3). When the value from the right side of Eq. (7-2)/(7-3) is less than/greater than H o /L o offshore transport is predicted. 112

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criterion. Net onshore transport is predicted at values less than 1.3. The precise value separating onshore and offshore transport is difficult to determine, but it appears to fall within the range (1.5 to 3.2) of the values predicted in the literature. Figure 7-10. The Dean number, Eq. (7-1) calculated during the passage of the three hurricanes. The horizontal dashed line separates onshore and offshore sediment transport events. In summary, the direction of transport predicted by Eq.s (7-1) through 7-(3) is supported by the morphologic response to the three hurricanes that passed by the study area in September 2004. According to the concept of critical wave steepness, onshore transport could be achieved by increasing the wave period while holding the wave height constant; however, little field data exist to prove this concept (Komar, 1998). Beach 113

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profiles and measured wave data collected in this study provide evidence for this statement. Relatively large breaking wave heights (1.6 2.2 m) generated by the passage of the three hurricanes were accompanied by variable wave periods. The shorter period waves (7.6 8.8 s) induced offshore transport, whereas the longer period waves (11.8 to 14.9 s) induced onshore transport. SBEACH simulations A series of numerical simulations of storm response is made to investigate whether the measured morphologic response can be predicted given the wave conditions for each event. The specific objective is to predict the measured direction and magnitude of cross-shore sediment transport for the different wave conditions with the SBEACH model (Larson and Kraus, 1989). SBEACH is a macro-scale, empirical model designed to predict the adjustment of beach fill to short period storm waves and to model the subsequent recovery process. The SBEACH model simulates the growth and movement of the berm and of sand bars. The direction of cross-shore transport is determined with Eq. (7-3). The magnitude of cross-shore sediment transport is a function of the wave energy dissipation per unit volume, calculated in the surf zone. Longshore sediment transport is neglected; rather, the model relies on volume conservation in the cross-shore direction. An important calibration parameter in SBEACH is the sediment transport rate coefficient, K. In SBEACH, increasing the K value increases erosion, resulting in the prediction of larger sand bars (Rosati et al., 1993). During model calibration in this 114

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study, variation in the K value altered the predicted profile shape minimally. The results presented here were simulated with the maximum allowable K value of 2.5 x 10 -6 m 4 /N, as recommended when coastal overwash is present. Measured wave, water level, and wind data (Fig. 4-3), post-nourishment sediment grain size (Fig. 4-6), and the pre-storm beach profile were also input into the model. Results from the north segment were omitted because of the large gradients in longshore sediment transport in this region. Model results were consistent along the central, south, and downdrift segments of the beach as illustrated with the typical simulation results at profile LK5 (D F = 0.44 mm). The SBEACH model correctly predicted the offshore direction of transport induced by the steep storm waves generated by the passage of Hurricanes Frances and Jeanne; however, the model did not reproduce the significant sand bar formation (Figs. 7-11A and 7-12A, black short-dashed lines). As expected, the predicted sediment transport curves (Figs. 7-11A and 7-12A, black dot-dashed lines) return to zero, indicting volume conservation across the profile (a model assumption). SBEACH underpredicted the measured magnitude of cross-shore transport by up to 90%. The model did not induce sufficient offshore transport. The underprediction of transport was not affected by the range of D F from 0.38 to 0.66 mm. In addition, SBEACH predicted no morphologic change when wave conditions from Ivan were used as input. Several sensitivity tests were conducted in an effort to better represent the magnitude and direction of cross-shore transport. Water levels, sediment grain size, wave height and period, and storm duration were altered to force onshore transport. The 115

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Figure 7-11. Measured and predicted profile response and measured and predicted cumulative sediment transport curves for profile LK5 during Hurricane Frances with A) D F = 0.44 mm and B) D = 0.3 mm. 116

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model did not predict onshore sediment transport in any of the sensitivity tests. Significant offshore transport was only simulated by decreasing the sediment grain size. A sensitivity analysis using a grain size of 0.3 mm essentially increased the K coefficient to a greater value than allowed by the model. This small change in grain size (about 30%) resulted in 1) morphologic changes that are reasonably close to those measured (Fig. 7-11B and 7-12B, black short-dashed lines) and 2) a significant change in the magnitude of sediment transport. Cross-shore transport rates (Fig. 7-11B and 7-12B, black dot-dashed lines) were not matched as successfully as the morphologic change. Although this is an unrealistic alteration to the model parameters, use of the decreased grain size can be rationalized. The relatively large mean post-nourishment grain size of 0.44 mm at this profile was a product of bimodal grain size distribution composed of fine quartz sand (~0.2 mm) and small shells and shell fragments (> 2 mm) (Chapter Four). The composition and shape of these grains made them more transportable than a homogenous distribution of spherical 0.5 mm grains, which was assumed by the model. The transportability of 0.3 mm spherical grains, as simulated by the SBEACH model, seems to be comparable to that of the nourished sediment composed of platy shells and spherical grains. Model parameters were also altered in an attempt to reproduce onshore transport during the Ivan simulations. When the sediment grain size was decreased in the Ivan simulations, SBEACH predicts significant offshore transport. Under no circumstances did SBEACH predict onshore sediment transport. This prediction of cross-shore transport in the direction opposite of the measured direction is somewhat perplexing 117

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Figure 7-12. Measured and predicted profile response and measured and predicted cumulative sediment transport curves for profile LK5 during Hurricane Jeanne with A) D F = 0.44 mm and B) D = 0.3 mm. 118

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because Eq. (7-3) predicted the correct direction of transport for Hurricane Ivan. Although the SBEACH model is intended to simulate bar formation under short-period storm-wave conditions, it is also intended to simulate post-storm recovery, e.g. onshore transport. The poor agreement of the measured and predicted morphologic changes during the Ivan simulations reinforces the conventional thinking that high-energy waves induce beach erosion. It is clear that the morphologic response to the passage of Hurricane Ivan was not reproducible with the SBEACH model. This analysis suggests that with an appropriate representation of sediment grain size, SBEACH is capable of predicting offshore sediment transport during steep storm-waves conditions, but it is less successful in predicting onshore transport. This analysis also highlights our rudimentary understanding of cross-shore sediment transport. Conclusions The three different hurricanes that passed by the project area in September 2004 generated different wave conditions due to their variable proximities to the project area. The passage of Hurricanes Frances and Jeanne resulted in locally-generated, steep, high-energy storm waves, whereas the passage of Hurricane Ivan resulted in low steepness, high-energy swell waves at the project area. Sediment transport directions, rates, and gradients were controlled by the different storm wave conditions. Large longshore sediment transport gradients at the nourished beach were governed by wave energy and shoreline orientation, as opposed to wave 119

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angle. In general, the net cross-shore transport direction was governed by wave steepness. Steep storm waves induced offshore sediment transport resulting in beach erosion; whereas, the low steepness waves caused onshore sediment transport. The magnitude of onshore transport was up to 60% less than the magnitude of offshore transport. Onshore transport was induced quickly under high-energy, low-steepness conditions (an event) as well as gradually during low-energy swell conditions. This conclusion contrasts with the concepts of gradual onshore transport during mild wave conditions and abrupt offshore transport during high-energy conditions, as cited in the literature. Critical steepness parameters correctly predicted the direction of cross-shore sediment transport during the three hurricanes. This study shows that the SBEACH model is quite sensitive to grain size and that the model cannot handle bimodal grain sizes. With an appropriate representation of sediment grain size, SBEACH is capable of predicting offshore sediment transport during steep storm-waves conditions, but is less successful in predicting onshore transport. 120

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Chapter Eight Sediment Budget Formulation and Analysis Literature Review Coastal sediment budgets quantify the sediment influx and outflux along a particular stretch of coastline for a specified time period. Sediment budgets are calculated by balancing the volumetric rate of change with the difference between the sediment sources and sinks. Thus, a conservation of mass approach is employed to achieve a balanced sediment budget. Sediment budgets essentially illustrate our level of knowledge of the overall coastal processes in a region. Ultimately, a sediment budget defines the surplus or deficit of sediment for the region (Rosati, 2005) and the coastal processes that cause the imbalance. Factors that are considered in a sediment budget typically include gross and net longshore sediment transport, onshore and offshore transport, beach erosion and accretion, beach nourishment, inlet bypassing and infilling, dredging, and other engineering activities. Sea level change also contributes to long-term sediment budgets by causing shoreline retreat or advance, changing sediment transport pathways, and modifying the spatial position of the budget boundaries. One of the most important factors in evaluating a coastal sediment budget is the determination of the magnitude and direction of net longshore sediment transport (Jarrett, 1991). Quantifying longshore 121

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transport is difficult due to a limited understanding of the numerous contributing coastal processes (Schoones and Theron, 1996; Wang, 1998); therefore, an indirect approach is often necessary to calculate transport rates (i.e., USACE, 1984; Inman and Bagnold, 1963). Along Floridas west coast, longshore sediment transport is particularly difficult to quantify due to the complicated transport gradients and the numerous local transport reversals (Davis, 1999). Sediment budgets are useful tools in nearly every aspect of coastal science and engineering, such as evaluating the natural evolution of the coast, designing future beach nourishment projects, understanding the impacts of potential structures, and developing inlet management plans. Quantification of the amount of sediment entering and leaving a segment of coast, the processes driving the transport, and determination of the transport pathways are important, yet often elusive, elements of sediment budget formulation. In fact, an unbalanced sediment budget provides useful information regarding the coastal processes that require additional study (Dolan et al., 1987). Inlets typically complicate coastal sediment budgets due to the numerous sediment sources, sinks, and transport pathways that they introduce. For example, ebb and flood currents, wave refraction and diffraction at the shoals and structures, and wave/current interactions influence the magnitude and direction of transport in the inlet sediment budget. In addition, inlets can capture the gross longshore sediment transport, or the inlet may bypass a portion of the longshore transport. Stabilized inlets have the potential to influence sediment transport patterns for many kilometers. These 122

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complicating flows and transport patterns often result in different possible formulations of the sediment budget for the adjacent beaches (Bodge, 1999). In the past, uncertainty in the sediment budget typically resulted in a range of values to approximate the transport rates and pathways (Mann, 1999; Bodge and Rosati, 2003). With improved surveying technology, sediment budgets can be calculated by directly quantifying volume change along a stretch of coast. A sediment budget is determined by the summation of the sources and sinks as, rRPVQQoutin (8-1) where Q in and Q out are known sources and sinks (both positive) to the region, V is the net volume change within each cell, representing beach erosion or accretion. V is calculated from beach profile surveys that preferably extend to the depth of closure. P represents nourishment, R represents dredging, and r is the residual. A balanced budget has zero residual. Previous Long Key Sediment Budgets Sediment budgets for Long Key with various spatial and temporal resolutions have been determined in the past (USACE, 1985; CPE, 1992; Elko, 1999). Longshore sediment transport rates were determined by different methods in each study. Three years of wind data collected from an inland gauge were used to calculate a wave climate by the USACE (1985). The wave data were input into the N-line model of Perlin and 123

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Dean (1983) to determine an average net longshore transport rate of 18,600 m 3 /yr to the south for Upham Beach. A sediment budget determined for Blind Pass by CPE (1992) utilized the method of Walton (1976) to estimate the magnitude and direction of net longshore sediment transport. Waltons method was developed to predict longshore sediment transport rates along Floridas coastline from wave climate data collected onboard U.S. Navy vessels. Assumptions of this data set include straight and parallel offshore contours, linear longshore energy flux, wave-domination, and no sheltering effects due to inlets. By Waltons method, northerly transport of 56,000 m 3 /yr predominates during the summer months, whereas 75,000 m 3 /yr of southerly transport occurs mainly from December until March. This yields a net longshore sediment transport rate in the vicinity of Blind Pass of 19,000 m 3 /yr to the south. Waltons method provides predicted, not actual, longshore sediment transport rates. The predicted rate may not apply when the model assumptions are violated, as when sediment supply is lacking, when the littoral cell is influenced by an inlet or other engineering activities, or when gradients in longshore transport exist. For example, a downdrift inlet may capture all of the south-directed transport from a littoral cell and not bypass any north-directed transport. In this case, the net longshore transport rate from the littoral cell could be as high as 75,000 m 3 /yr to the south. Tidwell (2005) and Tidwell and Wang (2006) analyzed sedimentation patterns at Blind Pass and determined that minimal deposition occurs in Blind Pass due to north-directed transport from Upham Beach because of 1) the lack of a sand source at Upham 124

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Beach and 2) the strong ebb current along the south side of the inlet channel that transports the limited north-directed transport offshore. Another sediment budget for Long Key was based on volume change calculated from historic shoreline positions from 1848 to 1998 (Elko, 1999). This budget yielded a similar net longshore transport rate to the above studies of 19,500 m 3 /yr to the south. Elko (1999) also calculated a short-term sediment budget from 1997 to 1998 that determined a southerly net transport rate of 75,600 m 3 from Upham Beach. The short-term budget yielded substantially higher transport rates due to the 1996 Upham Beach nourishment and increased storminess during the 1997-1998 El Nio winter (Elko et al., 2005). These significantly different transport rates highlight the importance of selecting the appropriate temporal scale for the sediment budget, particularly in regions with large transport gradients. The present study determined a sediment budget for Long Key to update and address unanswered questions from the previous budgets. This budget improves on previous studies by utilizing long-term offshore survey data to accurately quantify volume changes. A sediment budget for Long Key has not been determined since the nourishment plan was modified in 2000. In addition, previous budgets have focused on Blind Pass and Upham Beach, and have not adequately determined the downdrift sediment transport pathways from the Upham Beach feeder beach along Long Key. The main objective of this chapter is to accurately quantify annual longshore sediment transport rates, gradients, and pathways along Long Key at various spatial and temporal scales. With detailed data, it is possible to quantify the longshore transport 125

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gradients and the complex sediment pathways of material that erodes from Upham Beach. This study improves on the traditional sediment budget methodology by considering the cross-shore distribution of longshore sediment transport in the determination of budget pathways. Other objectives include the determination of the downdrift influence of the Upham Beach feeder beach, the recent performance of nourishment on Long Key, and the effect of the planned Upham Beach T-groin field on the downdrift beaches. Sediment Budget Formulation The sediment budget procedure implemented in this study is modified from various recommendations in the literature (Rosati and Kraus, 1999; Bodge and Rosati, 2003; Rosati, 2005) to address the objectives described above. The budget calculation in this study utilizes minimal assumed values; rather, the values used to calculate the budget are quantified from accurate surveys. The sediment budget formulation includes the following steps 1) determining spatial and temporal scales, 2) considering a conceptual budget, 3) delineating littoral cells, 4) applying known volume change, nourishment, and dredging values to littoral cells, 5) calculating longshore sediment transport rates to balance the budget, and 6) interpreting sediment transport pathways. This sediment budget methodology should be pertinent to other erosional hotspots with unknown transport pathways. 126

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Spatial and temporal scales First, a regional approach is considered to determine the spatial and temporal extents of the sediment budget. Bodge and Rosati (2003) recommended establishing the budget boundaries at some distance from the area of interest. In this case, the amount of bypassing around Blind Pass, estimated at up to 21,000 m 3 /yr in 1987 (CPE, 1992), has decreased to nearly zero since the collapse of the ebb shoal (USACE, 1999). The inlet is now a total littoral sink with no significant pathway for sediment bypassing. In addition, previous studies have concluded that little sediment is transported north from Upham Beach into Blind Pass (USACE, 1984; USACE, 1999; Elko, 1999; Tidwell, 2005). This littoral barrier is a logical choice for the northern boundary of the sediment budget. This will be considered an open boundary to allow a small amount of north-directed transport. On the south end of Long Key, Pass-a-Grille Channel has a well-developed ebb delta that unfortunately, is not surveyed. The navigational channel was surveyed in 2004 when it served as the borrow area for the Treasure Island/Long Key nourishment project. In addition, the downdrift barrier island, Shell Key, has never been surveyed. In order to calculate a budget with a high level of certainty, the jetty on the south end of Long Key, on the north side of Pass-a-Grille Channel, is selected as the southern boundary. This will be considered an open boundary because sediment bypassing is evident at this jetty. If the budget boundary was extended farther south, significant assumptions would be necessary due to the lack of survey data. The objectives of this sediment budget include quantification of average annual longshore transport rates and assessment of nourishment performance on Long Key. 127

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Nourishment began on Upham Beach in 1975, and is planned to continue for many years into the future. Thus, the time scale of the objectives requires that the budget analysis include multiple nourishments. Data availability is considered to determine an appropriate sediment budget time scale for the decadal planning scale under consideration. Preand post-nourishment monitoring surveys have been conducted annually since 1996 from Blind Pass to R150, extending up to 1 km south of the Upham Beach nourishment area. All of Long Key was surveyed in 1997 and 2001 as part of the FDEP monitoring program, which aims to collect beach surveys of the entire state of Florida every four years (Leadon et al., 2001). The surveys occurred one year after the 1996 and 2000 Upham Beach nourishment projects. In the present study, northern Long Key was surveyed weekly (Chapter Three). A long-term sediment budget time scale from 1996 to 2004 is selected based on this dataset. The long-term budget is not extended to 2005 due to the large volume of sediment placed in 2004 and the construction of the Upham Beach T-groin Project. Due to the large amount of accurate input data, several budgets with finer temporal scales are calculated from Blind Pass to R150 for the first year after each of the 1996 and 2000 nourishment projects, and a budget for all of Long Key is calculated for the first year after the 2004 project. The goal of the short-term budgets is to quantify net longshore transport rates and gradients following nourishment and assess nourishment performance over time. The budgets are also used to predict the effect of the T-groin field on future beach performance. The budgets and their variable spatial and temporal 128

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scales provide valuable insight to the coastal processes on Long Key since the 1996 Upham Beach nourishment. This achieves the goal of a long-term analysis encompassing multiple nourishment projects. Conceptual Budget After the boundaries and scales of the budget are determined, it is important to develop a conceptual model. A conceptual budget (Kana and Stevens, 1992) is a qualitative model of the coastal processes at a site that establishes the foundation of the sediment budget by identifying sources and sinks and the probable transport pathways. On northern Long Key, net longshore transport to the south dominates the coastal processes. As such, Upham Beach has been labeled a feeder beach for the rest of Long Key (USACE, 1999). A feeder beach is a nourishment project in which material is introduced at the updrift end of a coastal region intended to receive fill. Longshore transport distributes sand from this sediment source to the rest of the barrier island. Characteristics of feeder beaches, and of the Upham Beach project, include a deficit in the supply of littoral material, unusually high erosion rates, and longshore transport in a consistent, predominant direction (Gravens et al., 2003). Feeder beaches are often located downdrift of structured inlets that form a littoral barrier. The nourished material spreads out rapidly under the influence of waves, and the erosion rate slows through time. Elko et al. (2005) utilized high-resolution video imagery to determine that project evolution on Upham Beach followed a predictable pattern of exponential decay following the 1996 nourishment. 129

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Based on the feeder beach concept, the conceptual budget indicates that sediment placed on Upham Beach is transported to the south. The unknown elements in this concept are the transport pathways and the southern limit of feeder beach influence. Pass-a-Grille Beach, on the south end of Long Key, has been thought to benefit from the feeder beach (USACE, 1999). For that reason, this region had not been nourished or monitored since 1989. Gradual beach erosion during the last decade was overlooked because it was believed that the Upham Beach feeder beach was supplying Pass-a-Grille Beach with sand. Significant shoreline retreat along this already eroded beach during the 2004 hurricane season necessitated emergency nourishment in late 2004 (Elko, 2005). The lack of planning for Pass-a-Grille Beach nourishment clarified the need for a more detailed assessment of the influence of the Upham Beach feeder beach on the downdrift beaches of Long Key. Littoral Cell Delineation A sediment budget is divided into numerous littoral cells that denote the limits of smaller self-contained budgets (Dolan et al., 1987). An early sediment budget formulation from the California coast (Bowen and Inman, 1966) defined littoral cells as individual pocket beaches between rocky headlands with clearly identified sources and sinks. Along an open sandy coast, boundaries are not always as straightforward. Littoral cell boundaries may be based on geomorphology, beach performance, the level of uncertainty of the calculation, or engineered structures. Littoral cells range from 10s to 100s of meters for a local-scale budget and from 100s of meters to kilometers for 130

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regional-scale budgets (Rosati, 2005). In this case, littoral cell boundaries are based on recent beach performance and range from 0.6 to 3 km. Long Key is divided into four regions (Fig. 8-1) based on the magnitude and trend of erosion or accretion that occurred from 1996 to 2005. The area from Blind Pass to LK6 is Cell 1. This cell is characterized by rapid beach erosion and encompasses most of the traditionally nourished area. In 1996, 2000, and 2004, the south limit of nourishment was LK5, LK6, and R148, respectively (Chapter Two). Nourishment only exceeded Cell 1 in 2004. Cell 2 extends from LK6 to R152 because deposition in this region is obvious after nourishment. Due to frequent monitoring in this region, transport conditions are reasonably well known. This section of the beach has been accreting, apparently benefiting from nourishment to the north. Cell 3 extends from R152 to R161 because beach profiles in this region exhibit little overall morphologic change. This region has not been included in the long-term monitoring program for Long Key. The north portion of Pass-a-Grille Beach nourishment is included in this cell because profiles R160 and R161 have been stable since 1989 (Fig. 8-2), similar to the beach performance in Cell 3. Cell 4 extends from R161 to Pass-a-Grille Channel, where the beach has actually been eroding since 1996. The jetty at the south end of Cell 4 bypasses, rather than impounds, sediment. The boundaries and parameters of the littoral cells in this budget are shown in Figure 8-1. The landward boundary of the budget is the toe of the dune. The offshore 131

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Figure 8-1. Sediment budget sources and sinks and boundaries for each of the four littoral cells. boundary of the budget is the depth of closure. Offshore surveys, which were utilized to calculate volume change (V), extend to the depth of closure. The depth of closure for Long Key was established in Chapter Six at about -3 m. Although it is inevitable that sediment transport occurs across this boundary, it is difficult to quantify the sediment transfer from the active profile to the offshore region. Offshore changes are typically within the error of the surveying equipment (Fig. 8-2). In this study, it is assumed that a negligible volume of sediment is transported across this offshore boundary. Net cross-shore transport on the active profile is included in the volume change calculations. Onshore and offshore transport are not quantified separately. An analysis of cross-shore transport during the 2004 hurricane season is presented in Chapter Seven. 132

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Figure 8-2. Beach profile at R161 at the south end of Cell 3, illustrating stable performance since 1989, even after the 2004 hurricane season. It is important for cell boundaries to be consistent between the different budgets with varying temporal scales. Although the extent of nourishment changes through time, the littoral cell boundaries must be consistent. The littoral cell boundaries based on beach performance do not coincide with the monitoring limit (to R150) for Upham Beach or the nourishment limits at Pass-a-Grille Beach. This suggests that it is important to consider a regional approach and look beyond the pre-determined boundaries when defining littoral cells. In addition, the limits of monitoring and nourishment should be reviewed periodically. 133

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Application of Measured Values The next step in sediment budget formulation is the application of known volume change, nourishment, and dredging values to littoral cells. The net change in volume (V) for each littoral cell is determined by first quantifying the profile-volume change between surveys at the beginning and end of the sediment budget time period (V p in m 3 /m/yr). Then, the profile-volume change is applied over a distance, x i that is the sum of half of the distance to each adjacent profile, x i = x N /2 + x S /2 (m). V for the littoral cell is the summation of each of these profile volume calculations:. piVxV Profile spacing increased to the south with an average profile density per cell of one survey every 150 m for Cells 1 and 2, respectively, and one survey every 335 m in Cells 3 and 4 (Fig. 3-2). This high spatial resolution resulted in minimal error from spatial variability, i.e. longshore coverage less than cross-shore coverage. The surveys extend to the depth of closure such that V includes net cross-shore transport. Nourishment volumes (P) for the cells are calculated from post-construction monitoring surveys (USACE, 1999; USACE, 2001). Sediment placed on the beach in the form of nourishment is included in the beach surveys. Thus, when V exceeds P, the beach has accreted in addition to nourishment. Conversely, when V is less than P, nourished material has eroded from the cell. Surveys following the 1996 and 2000 projects were conducted one and six months after construction, respectively, whereas surveys following the 2004 project were conducted within one week of the final beach grading. The surveys conducted for the 2004 project were equivalent to payment surveys, used to determine the pay volume for 134

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the contract (herein referred to as post-construction surveys). Nourishment projects are typically constructed in segments that are approximately 300 m long. Once a section is complete, the construction operation advances to the adjacent beach and post-construction surveys of the completed section are conducted. The 1996 and 2000 surveys were monitoring surveys, which are typically conducted some time after construction is completed (herein referred to as monitoring surveys). Due to the large gradients in sediment transport on Upham Beach, significant changes often occur between the completion of construction of each section and the monitoring survey. This highlights the importance of using post-construction, rather than monitoring, surveys in budget calculation if possible. When post-construction surveys are used to calculate P, another factor must be introduced. Dredging losses, R, occur during construction. R is sediment that is transported out of the unfinished section prior to the post-construction surveys. R typically occurs in the form of sediment runoff during the pumping operation. R also occurs when sediment erodes from an unfinished section when construction is suspended due to inclimate weather, which in turn causes a higher transport rate. R is essentially the discrepancy between the volume of material dredged from the borrow area and the volume placed on the beach. Dredging losses are assumed to range from 10% to up to 100% of the nourished volume, depending on the dredging methodology and the weather conditions. In this case, a comparison of the post-construction beach surveys to the post-dredging borrow area surveys suggests that R was roughly 14%. Assuming that some dredging losses 135

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occur at the borrow area, R is estimated for each cell at 10% of P. Deposition in Cell 2 measured from weekly surveys conducted during construction of Cell 1 confirms this ratio for R. The necessity of R in the 2004 to 2005 sediment budget is illustrated with the following example. The sediment source of the diffusion spit that formed during construction of the 2004 nourishment (Chapter Five) was from runoff and erosion of the north segment that was under construction (R). This sediment was introduced after the post-construction survey; thus, it was necessary to include R, the source of this sediment, in the 2004 to 2005 budget. Dredging losses were not an issue in determining the 1996 and 2000 budgets because monitoring surveys are used to calculate volume change. By the time monitoring surveys are conducted once construction of the entire project is complete, P and R have been incorporated into the surrounding coastal system. An advantage to using monitoring surveys is that it is unnecessary to have knowledge of the construction methodology. A disadvantage is that project equilibration is typically underway by the time monitoring surveys are conducted. Sediment Fluxes The next step in this sediment budget formulation is determining Q in and Q out which represent sediment fluxes across the four boundaries of the littoral cells. The north and south boundaries of the overall sediment budget (Blind Pass and Pass-a-Grille Channel) are open. The sediment flux into Pass-a-Grille Channel is defined from the 136

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south-directed longshore transport rate to the south from Cell 4. Sediment flux into Blind Pass is estimated as 1,500 m 3 /yr. CPE (1992) assumed continual sediment flux into Blind Pass from Upham Beach as 3,500 m 3 /yr. In this study, it is assumed that significant transport into Blind Pass only occurs during the first two years following nourishment when sediment is available in the north segment. Two years after nourishment, the shoreline has retreated to the seawall and no sediment source is available for north-directed transport into Blind Pass. Thus, the annual average transport rate of 1,500 m 3 /yr accounts for about 6,000 m 3 of north-directed transport into Blind Pass in the beginning of a four year nourishment interval. In general, transport across the landward boundary can be a result of dune/bluff erosion, aeolian transport, or overwash. In this example, transport across the landward boundary is represented by aeolian transport out of the cell to the dune (Q dune ) and is quantified from beach surveys. Volume change landward of the toe of the dune (m 3 /m/yr) is calculated for each profile line and applied to the half-profile distance (m) on either side of the beach profile, as in the littoral cell volume change calculation. Transport across the seaward boundary, the depth of closure in this case, is assumed to be zero. This is a closed boundary; thus, this sediment flux does not contribute to the budget calculation. Onshore and offshore transport that occurs within the active portion of the profile is included in V. 137

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Net longshore Sediment Transport Rates and Gradients Transport across the longshore boundaries is represented by net longshore sediment transport (Q x ). Net longshore sediment transport rates have commonly been defined with the energy-flux method in sediment budget determination (i.e., Jarrett, 1991). Longshore transport rates were determined by three different authors using the energy-flux method in Oceanside, California (Dolan et al., 1987). Deep-water wave statistics were transformed to breaker heights and applied to the energy-flux method. Each author determined a different transport rate for the same region due to differences in wave gauge locations and the use of dated statistics. Longshore sediment transport rates were measured for the southeast coast of the United States and the Gulf Coast of Florida and compared to several empirical formulas including the energy-flux formula (Wang, 1998). Transport rates along these low-energy coasts were much lower than calculated rates from empirical formulas suggesting that researchers should be cautious when applying such formulas to low-energy shorelines. Rather than utilize longshore transport rates predicted by the energy-flux method, this study calculates longshore sediment transport using the concept introduced with Eq. (8-1). In this case, Q out is the sum of wind-blown transport out of the cell to the dune (Q dune ) and longshore transport out of the cell to the south in the direction of net transport (Q x ): Q out = Q dune + Q x By assuming that the residual in Eq. (8-1) is zero, net sediment transport rates for each cell are determined by solving Eq. (8-1) for Q x xduneinQRPVQQ (8-2) 138

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Measured values are input into the left side of Eq. (8-2) to determine the net longshore sediment transport (Q x ) for the cell. Gross sediment transport is also important to consider in this sediment budget because of the adjacent tidal inlets. It is assumed that the inlets capture the gross sediment transport. The north-directed component of transport into Blind Pass is small due to longshore transport to the south from Upham Beach. South-directed transport trapped by Pass-a-Grille Channel may be as high as 75,000 m 3 /yr based on the method of Walton (1976). Blind Pass and Pass-a-Grille Channel also trap the southand north-directed transport, respectively, from the adjacent barriers. This creates a sediment deficit in Cells 1 and 4. Due to these inlet effects, the potential transport for the region will not approximate the actual transport rate in Cells 1 and 4. Sediment Pathways In general, sediment pathways define the direction of, and often the processes driving, transport. Pathway determination can be made from local site knowledge, aerial photo analysis, field observations of tracer movement, changes in coastal morphology, and interpretation of shoreline response to structures. Transport pathway determination was the final step in this sediment budget formulation. Significant longshore transport to the south has been measured in previous sediment budget studies on Long Key (e.g., Elko, 1999). However, the detailed transport pathways have not been adequately determined. In this study, the general transport direction is defined in the conceptual budget, and then the magnitude and direction of 139

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sediment transport are calculated using Eq. (8-2). This provides an understanding of the total transport of sediment along the beach. In order to determine the sediment pathways, an evaluation of the distribution of transport, i.e. the cross-shore distribution of longshore sediment transport, is required. The details (pathways) of sediment transport in the nearshore are described by the cross-shore profile of Q x The Q x distribution is important in the effective design of jetties and groins, particularly notched structures (Bodge and Dean, 1987; Wang and Kraus, 2004) to insure proper sediment bypassing. The Q x distribution is important in sediment budget formulation even if the focus of the budget is the dry beach. For example, a littoral cell may be receiving sufficient sediment supply from Q x If the maximum Q x distribution coincides with the swash or inshore zone, and a mechanism for onshore transport exists, the dry beach should be stable to accretionary. Alternatively, the maximum Q x distribution may occur along the offshore sand bar. Without an onshore transport mechanism, the adequate sediment supply from Q x may not be realized on the dry beach. In this study, the Q x distribution within each littoral cell is determined qualitatively from beach profile surveys. With high temporaland spatial-resolution beach surveys, the regions on the profile of significant morphologic variability are apparent. These dynamic regions correspond with high transport rates, illustrating the active sediment pathways. The transport pathways are resolved by comparing the annual Q x supplying the littoral cell to the profile shape changes, which illustrate the transport pathways in cross-section, and then to aerial photos, which illustrate the pathways in plan 140

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141 view. This analysis enhances the traditional sediment budget formulation by resolving the details of the total sediment transport. Sediment Budget Analysis In this section, Eq. (8-2) is utilized to calculate sediment budgets on various spatial and temporal scales. Then, sedime nt pathways are determined, followed by a cursory analysis of the po tential future impact of the planned T-groin field. 1996 2004 Sediment Budget The net longshore sedime nt transport rate ( Q x ) of 42,000 m 3 /yr represents the average annual transport rate from Cell 1(Fig. 8-3). This rate is lik ely higher during the first year after nourishment, and then decr eases exponentially until the next nourishment event (Elko et al., 2005). Beach profiles indi cate that the beach eroded to the northern seawall at LK2 during the first year follo wing the 2000 nourishment (Fig. 8-3A) implying that no sediment is retained in Cell 1 (i.e. 100% erosion). Nourishment projects in 1996 and 2000 in Cell 1 yielded an annual nourishment rate ( P ) of 51,000 m 3 /yr. If 100% of the nourished material had eroded from this cell, Q x would have been similar to P The slightly lower Q x from Cell 1 indicates that some sediment was retained in the cell. Beach surveys illustrate a large scour pit ex tending 200 m from the seawall at LK2 in 1996 (Fig. 8-3A). Deposition in this area infilled the scour pit by 2004 explaining why Q x is lower than P The infilled scour pit and sediment retention in Cell 1 is the first evidence of improved nourishment performance through time.

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142 Figure 8-3. Sediment budget for Long Key from 1996-2004. Values are x 10 3 m 3 and variables are defined in Eq. (2). Example beach profiles from A) Cell 1, B) Cell 2, C) Cell 3, and D) Cell 4 illustrate the morphologic changes that accompany transport fluxes.

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The Q x of 26,300 m 3 /yr from Cell 2 is less than the value of Q x from Cell 1, indicating that the longshore transport gradient is decreasing to the south. Deposition and subaerial sediment accumulation in Cell 2 increased the beach width and overall profile volume. The shoreline advanced 18 m at R150 as the profile was essentially translated seaward (Fig. 8-3B). Sediment was transported onshore over time. This is an important transport mechanism that will be discussed in the following sections. The Q x in Cell 3 of 17,100 m 3 /yr is similar to the predicted net longshore transport rate for the region of 19,000 m 3 /yr (Walton, 1976). In Cell 3, less shoreline progradation was measured as compared to Cell 2 (Fig. 8-3C). Morphologic fluctuations were evident in the swash zone and on the nearshore and offshore sand bars. The nearshore sand bar was ephemeral. The positions of the shoreline and offshore sand bar, located about 150 m offshore, have been remarkably stable since 1989 (Fig. 8-2). A deep sand bar trough (< -2 m) has also been persistent in Cell 3. This feature likely precludes onshore transport from the offshore sand bar. Survey data indicate that the large Q x in Cell 4 from 1996 to 2004 was accompanied by substantial beach erosion, with up to 25 m of shoreline recession (Fig. 8-3D). As in Cell 3, the nearshore sand bar was ephemeral. Beach erosion occurred in conjunction with significant position and shape changes in the nearshore and offshore sand bars. The large Q x in Cell 4 from 1996 to 2004 can be attributed to the effect of Pass-a-Grille Channel trapping the south-directed component of longshore sediment transport. The terminal structure at the south end of this cell does not impound sediment; rather, 143

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sediment is transported around the jetty and into Pass-a-Grille Channel. The longshore current is influenced by the longshore component of the flood tidal flow. Pass-a-Grille Channel captures both the northand south-directed components of sediment transport, creating a sediment deficit in Cell 4. Overall, the 1996 to 2004 sediment budget reveals the substantial longshore sediment transport gradient along Long Key. Q x decreases from north to south, and then increases at the south end of the island (Fig. 8-3). Q x of Cell 3 compares with the predicted net transport rate for the region of 19,000 m 3 /yr to the south (Walton, 1976). Cell 3 is not critically eroding and not actively managed through beach nourishment. In Cells 1 and 4, which require periodic nourishment (active management), the Q x is greater than two times the predicted regional value. Clearly, Q x would be grossly underestimated by applying this regional average rate. In terms of regional sediment management, this suggests that sediment budgets that determine regional average transport rates are not sufficient to achieve the goal of managing critically eroded shorelines. Annual average transport rates for a region should not be arbitrarily applied to beaches that require active management. Shoreline Change Analysis To further assess the gradient in longshore sediment transport and its influence on beach performance, shoreline change downdrift of Cell 1 is examined. The shoreline change rate (dy/dt) is calculated from July 1997 to June 2004 (Fig. 8-4), prior to the 2004 nourishments and the hurricane season. Values of shoreline change in Cell 1 are too 144

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Figure 8-4. Shoreline change (dy/dt) downdrift of Upham Beach from LK7 to R165 from July 1997 to June 2004. The spatial rate of shoreline change determined by linear regression (red line) is .9 m/yr/km. negative to be plotted on Figure 8-4. South of Cell 1, dy/dt decreased at a spatial rate of -0.9 m/yr/km as determined from a linear regression. Overall, the decreasing trend of dy/dt to the south indicates that deposition immediately downdrift of the Cell 1 feeder beach is not consistent along Long Key. As the gradient in longshore sediment transport diminishes, less sediment is supplied to the downdrift beaches and dy/dt decreases. In Cell 2, the average dy/dt was 2.1 m/yr, confirming the substantial deposition suggested by the sediment budget (Fig. 8-4). The decreasing dy/dt within Cell 2 illustrates the transition from nearshore deposition in Cell 2 to stable beach performance 145

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in Cell 3. In Cell 3, the average dy/dt was 0.5 m/yr, confirming that this cell has been stable to accretionary. The shoreline position in Cell 3 is stable due to sediment supplied at the regional average transport rate. In Cell 4, dy/dt averaged -1.8 m/yr, confirming the erosional nature of this cell. The outlier in Figure 8-4 at approximately 6.6 km from Blind Pass is profile R164. This beach profile is located downdrift of a seawall that protects the concession building, the only building on Pass-a-Grille Beach. As the shoreline retreated to the seawall, downdrift erosion was exacerbated. Shoreline retreat in Cell 4 from 1997 to 2004 indicates that the benefit of the feeder beach extends only to Cell 3, more than 4 km to the south of Upham Beach (Fig. 8-4). Northern Long Key, 1991 2004 The performance of the 1991, 1996, and 2000 Upham Beach nourishment projects are analyzed to examine the effect of the altered Upham Beach nourishment plan and to determine the transport rates during the first year after nourishment. The nourishment plan was altered in 2000. The project length was extended, the nourishment interval was decreased from five to four years, and the nourishment volume was increased (Chapter Two). The longevity of the project should increase as the project length is increased (Dean, 2002). The long-term nourishment performance is examined by two methods: 1) comparing preand post-nourishment shoreline maps and 2) calculating sediment budgets for the first year after the 1996 and 2000 nourishment projects. Shoreline maps from 146

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1996 to 2004 illustrate the planform evolution of the Upham Beach nourishment project. Surveyed beach profile data is contoured at mean high water (MHW = 0.14 m, NGVD29) before and after nourishment. These shoreline maps (Fig. 8-5) illustrate 1) the maximum design planform following nourishment and 2) the eroded planform at the end of each nourishment interval: 1991 to 1996, 1996 to 2000, and 2000 to 2004. Shoreline Maps The southern limit of the 1991 fill was LK5 (Fig. 8-6A). By 1995, the shoreline at the public park between LK3 and LK5 had receded sufficiently to expose the sand bags that protect the concession building (Fig. 8-6B). The 1996 pre-nourishment condition downdrift of LK5 is represented (Fig. 8-5, black line) because the 1996 nourished planform had not yet spread out. Prior to the 1996 nourishment, erosion had flanked the seawall and was beginning to threaten the downdrift beach at LK6. The southern limit of fill in 1996 was also LK5. The nourishment interval was decreased to four years during this time. At the end of the 1996 to 2000 nourishment interval, the shoreline had once again eroded significantly along Upham Beach (Fig. 8-5, black/gray lines). In 2000, the seawall between LK5 and LK6 was exposed, but was not flanked. Downdrift of the fill, the shoreline position advanced over 10 m at R148. Prior to the 2000 nourishment, a nearshore sand bar was apparently supplying sediment to Cell 2 (Fig. 8-6C). Thus, decreasing the nourishment interval by one year in 2000 resulted in a wider pre-nourishment shoreline planform. 147

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Figure 8-5. Preand post-nourishment shoreline maps illustrate the planform evolution from 1996 to 2004. Sediment budgets for northern Long Key (2 km south of Blind Pass) for the one year following the 1996 and 2000 nourishments. Values are x 10 3 m 3 and variables are defined in Eq. (8-2). In 2000, the southern limit of the fill was extended to LK6 on the south end of the seawall, such that the fill buried the wall. At the end of the 2000 to 2004 nourishment interval (Fig. 8-5, blue lines), the planform was significantly farther seaward along the entire project than at the end of the previous nourishment interval (Fig. 8-5, compare gray 148

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to light blue line). The seawall between LK5 and LK6 did not become exposed during this nourishment interval (Fig. 8-6D). Figure 8-6. Upham Beach: A) post-nourishment 1991, illustrating the typical nourishment template extending to LK5 at the north end of the seawall, B) pre-nourishment 1996 (1995 photo), INSET: March 1995, erosion exposed sand bags at the public park, C) pre-nourishment 2000 (1999 photo) and D) pre-nourishment 2004 (2003 photo). The black arrows point to the seawall between LK5 and LK6 that becomes less exposed indicating improved nourishment performance through time. Prior to the 2004 project, the scour pit in front of the LK2 seawall had infilled, the LK5 seawall did not become exposed, and the pre-nourishment shoreline position was up to 50 m farther seaward than in 1996. This indicates that more sediment was retained on Upham Beach during the 2000 to 2004 nourishment interval than in the past. The increased volume, increased project length, and reduced nourishment interval improved the performance of the 2000 Upham Beach project from the 1996 condition. 149

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Short-term Sediment Budgets To further examine this improved nourishment performance and to determine post-nourishment longshore transport rates, sediment budgets for northern Long Key for the first year after nourishment were calculated for 1996 and 2000 (Fig. 8-5). Formulation of sediment budgets at these smaller spatial and shorter temporal scales, as compared to the long-term budget, provides information about transport rates and gradients in response to the event of beach nourishment. The one-year post-nourishment sediment budgets were developed following the same procedures as the long-term budget, but only calculated from Blind Pass to R150 due to limited survey data to the south. Cell 2A extends from LK6 to R150. The Q x from Cell 1 was higher during the first year after the 1996 and 2000 nourishments (Fig. 8-5) than the average annual Q x determined in the 1996 to 2004 budget (Fig. 8-3). Q x from Cell 1 was high following nourishment and likely decreased throughout the nourishment interval. The Q x from Cell 1 was higher following the 2000 project than the 1996 project (Fig. 8-5). The 1996 and 2000 projects had different lengths, but the littoral cell boundaries were consistent for the two budgets. Longshore spreading of the different-length projects across a constant boundary explains the different transport rates. Figure 8-5 illustrates that in 1996, the nourishment planform did not encompass all of Cell 1. A portion of the nourished sand was redistributed within Cell 1 as the planform spread out. In 2000, the southern limit of fill was LK6, at the southern boundary of Cell 1. The 2000 planform encompassed all of Cell 1 and spreading losses were transported directly into Cell 2A. 150

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151 This different spreading pattern is al so evident in Cell 2A. Deposition (V ) in Cell 2A was substantially higher following th e 2000 project due to spreading losses from Cell 1 that were transported direct ly into Cell 2A. Interestingly, Q x from Cell 2A was similar in both budgets. This is furt her evidence of the improved nourishment performance through time. The beaches immediately downdrift are accumulating sediment rather than bypassing the additional Q x from Cell 1. Cell 2A is maintaining a constant net transport rate during th e first year following nourishment. 2004 2005 Sediment Budget A sediment budget from 2004 to 2005 was calculated to determine whether nourishment performance has continued to im prove during the 2004 project. This budget is necessary to examine high-temporal resolution profile-shape fluctuations, which reveal the Q x distribution and the transport mechanis ms for the sediment pathway analysis. The southern limit of the 2004 Upham Beach nourishment was extended to R148 to provide advance mitigation for the T-groin field. An emergency nourishment project was also constructed in 2004 in Cells 3 and 4 (Chapter Nine). In Cell 1, dredging losses during nourishment and beach erosion following nourishment resulted in a Q x of 63,300 m 3 The beach did not recede to the northern seawall at LK2 during the first year followi ng the 2004 project (Fig. 8-7A) as in 1996 and 2000. This diminished erosion was a result of T-groin construction th at began in January 2005.

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152 Figure 8-7. Sediment budget from 2004 to 2005 for Long Key. Values are x 10 3 m 3 and variables are defined in Eq. (8-2). Example beach profiles from A) Cell 1, B) Cell 2, C) Cell 3, and D) Cell 4 illustrate quarterly morphologic changes that accompany the fluxes.

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The official monitoring surveys were conducted in December 2004, four months after the initial nourishment (Fig. 8-7A). Note that despite the repair nourishment, 30 m of shoreline recession occurred between the September 2004 post-construction survey conducted one week after nourishment and the December 2004 monitoring survey. This illustrates the importance of monitoring programs that survey beach as soon as possible following nourishment. One year after the 2004 nourishment, deposition in Cell 2 and the initial nourishment in this cell resulted in a large V. Beach profiles from 2004 to 2005 indicate nearshore deposition and shoreline progradation. At R149, which is over 300 m south of the nourished area, sediment was deposited on the sand bar and subsequently transported onshore (Fig. 8-7B). This trend of subaerial sediment accumulation was also observed in the long-term budget. Significant onshore transport occurs in this cell relocating sediment deposited on the sand bar to the beach. The Q x from Cell 2 and Cell 3 is similar to the predicted net longshore transport rate for the region (Walton, 1976). Beach profiles in Cell 3 do not indicate significant shoreline progradation as in Cell 2. At R157, little volume change occurred on the profile, but morphologic changes were evident in the swash zone and on the nearshore and offshore sand bars (Fig. 8-7C). There was no indication of onshore migration of the offshore sand bar. Interaction between the nearshore sand bar and beach was evident. The trend of minimal shoreline change (Fig. 8-4) accompanied by morphologic fluctuations in the swash zone and sand bars was also observed in the long-term budget. 153

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Despite the emergency nourishment in Cell 4, sediment eroded from this cell. The beach adjusted rapidly following nourishment as sediment was transported offshore resulting in significant morphologic changes on the offshore sand bar. This trend of beach erosion accompanied by sand bar variability was also observed in the long-term budget. As in the long-term budget, the large Q x in Cell 4 can be attributed to the effect of Pass-a-Grille Channel trapping the south-directed sediment transport. In 2004, more sediment was available to be transported to the south; thus, transport gradients were elevated due to nourishment. Comparison of Sediment Budgets A comparison of the above sediment budgets reveals a substantial longshore gradient in longshore sediment transport along Long Key on various spatial and temporal scales (Table 8-1). In the storm-induced sediment transport analysis (Chapter Seven), the longshore gradient in longshore transport decreased to the south in response to storm events (Fig. 7-7). With a larger spatial and longer temporal scale in the sediment budget analysis, the same trend is evident. The average annual Q x (1996-2004) from Cell 1 to Cell 3 is reduced by 60% over 4 km. The transport gradient then increases in Cell 4 because Pass-a-Grille Channel captures the south-directed sediment transport. The large transport gradient is consistent even when rates are averaged over several years. 154

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Table 8-1. Summary of Q x net longshore transport rates, (m 3 /yr) calculated in the sediment budgets (Figs. 8-3, 8-5, and 8-7). Cell 1996 2004 2004 2005 2000 2004 1996 1997 1 42,000 63,300 77,000 53,900 2 26,300 20,100 36,500* 36,000* 3 17,100 16,700 4 25,600 61,400 Only calculated to R150. During the first year following each of the nourishment projects, Cell 1 eroded at a considerably higher rate, up to 83% higher than the long-term average. This confirms that Q x is initially high following nourishment, and then decreases throughout the nourishment interval. Different transport rates from Cells 1 and 2 following the 1996, 2000, and 2004 projects were related to variable spreading losses that resulted from the different project lengths. Interestingly, the highest measured transport rate approximates the potential south-directed transport for the region of 75,000 m 3 /yr (Walton, 1976). To effectively manage and design beach nourishment projects, sediment budgets on various temporal scales are crucial. In particular, the transport rate in the year following nourishment, when transport gradients are elevated, will be considerably higher than the long-term annual average rate. The consistent transport rate of about 17,000 m 3 /yr from Cell 3 is also similar to the predicted Q x for the region (Walton, 1976). Cell 3 is the only region on Long Key that conforms to the assumptions of Waltons study of straight and parallel offshore contours, wave-domination, and no inlet effects. It is out of the influence of nourishment and inlets. The potential Q x should be a good estimate of the transport rate in Cell 3. The fact that this Q x was calculated independently with the method employed in this study 155

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validates the use of Eq. (8-2) to calculate transport rates. The lack of correlation between this regional prediction and the actively managed portions of Long Key (Cells 1 and 4) shows that detailed sediment budget analysis is a vital part of nourishment design and prediction. Average regional rates should not be applied to beaches that require periodic nourishment. Sediment Pathways The magnitude and direction of longshore sediment transport, Q x and the observed morphologic changes were described in the previous sections. The cross-shore distribution of Q x and consequently the dominant longshore transport pathways, were determined qualitatively by comparing these results for each cell with aerial photos. Figure 8-8 illustrates the offshore sand bar and shoreline positions along Long Key. The contour map and accompanying aerial photos illustrate the sand bar diverging from the swash zone near R148 at the southern limit of 2004 fill (Fig. 8-8A). The sand bar crest diverges from the shoreline with distance from Upham Beach. At the south end of Long Key, the offshore sand bar diffuses and merges with the ebb shoal. An ephemeral nearshore sand bar is often located between the shoreline and this offshore sand bar (Fig. 8-8B). This nearshore bar extends from R155 to R165. At the south end of Long Key, the deep marginal flood channel between the nearshore and offshore sand bars (Fig. 8-8C) is also important to the sediment transport pathways. Here, the nearshore sand bar wraps around the jetty, creating a transport pathway into Pass-a-Grille Channel. The cross-shore distribution of Q x is divided into two transport pathways 156

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Figure 8-8. Sand bar crest (black) and shoreline (red) positions along Long Key (map). The green swath to the south is the 2004 Pass-a-Grille Channel survey, which does not include the northern portion of the ebb shoal. Aerial photos: A) the offshore sand bar at R148, Nov. 2005 B) the offshore and inshore sand bar along southern Long Key, Nov. 2005 and C) deep marginal flood channel separating offshore bar (merges with ebb shoal) and inshore bar, Nov. 2003. Also shown in C is the bay-side subaerial beach on the south end of Long Key. 157

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defined in Table 8-2: 1) swash/inshore Q x (in the swash and along the inshore sand bar) and 2) offshore Q x (along the offshore sand bar). Table 8-2. Qualitative sediment transport pathway determination for Long Key. Cell Annual Q x Morphologic change to beach profiles Dominant transport pathways (direction) 1 42,000 Rapid erosion, no sand bar deposition Swash Q x (S) 2 26,300 Nearshore deposition, onshore migration of nearshore sand bar Swash Q x (S) Onshore transport 3 17,100 Stable profile, minor fluctuations in swash, nearshore and offshore bar regions 4 25,600 Beach erosion, sand bar migration Swash/inshore Q x (S) Offshore Q x (S) The sediment transport pathways are illustrated on a 1997 aerial photo of Long Key (Fig. 8-9). In Cell 1, sediment erodes rapidly and is transported to the south via longshore sediment transport. There is no offshore sand bar in Cell 1, suggesting that swash transport is dominant (Table 8-2). The sediment budget analysis revealed a substantial onshore transport mechanism in Cell 2 that causes subaerial accumulation of sediment supplied via swash and inshore transport. Cell 2 is a significant sediment sink for the sediment eroding from Upham Beach. Deposition in this area contributes to the decreasing transport gradient. In Cell 3, the sediment budget analysis revealed minimal shoreline change accompanied by morphologic changes in the swash and on the sand bars. Northand south-directed longshore transport occurs in these regions. The development of an inshore sand bar in Cell 3 introduces a new transport pathway. In Cell 4, the budget analysis indicated beach erosion accompanied by significant morphologic changes to the sand bars and no mechanism for onshore sediment transport. Sediment transported via swash transport and along the inshore sand bar in Cell 4 is 158

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Figure 8-9. Sediment transport pathways illustrated on a 1997 aerial photo of Long Key. Sand bars have been consistent over time. Pathways: 1) swash/inshore Q x (white), 2) offshore Q x (star blue), and 3) cross-shore transport (shore-perpendicular green/gray). 159

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transported around the jetty, and deposited along the south and bayside shorelines of southern Long Key. This transport pathway is evidenced a beach that has developed along the east bay shoreline of Long Key since 1997 making the two boat docks worthless (Fig. 8-8C). Longshore sediment transport along the offshore sand bar bypasses Cell 4 and is deposited on the ebb shoal. The persistent, deep trough (marginal flood channel) between the sand bars prevents significant onshore sediment transport from the offshore transport pathway. The sediment transport pathways and the pattern of shoreline change since 1997 (Fig. 8-4) indicate that subaerial accumulation becomes less prominent with distance from Upham Beach. The Upham Beach feeder beach has helped to maintain accretionary to stable beaches in Cells 2 and 3 since 1997. Sediment from Upham Beach was supplied to Cell 4, but the majority of sediment bypassed the beach due to the interaction of the inshore sand bar and the channel and the offshore sand bar and the ebb shoal. An insufficient amount of sediment has been retained on the beach in Cell 4. This is an important finding because the notion of Upham Beach as a feeder beach for Pass-a-Grille Beach has been promoted for decades (USACE, 1984). This study highlights the importance of periodic review of coastal management strategies using high-resolution survey data. Impact of T-groin Field Due to concerns that the planned T-groin field may cause downdrift erosion, the future impact of the structures is assessed with results from the sediment budget analysis. 160

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A conservative approach to this assessment assumes that all of the available sediment will erode from Upham Beach during the present nourishment interval from 2004 to 2008. The T-groin field is designed to be buried within the 2004 beach fill and to become exposed as the beach erodes. Once the advance nourishment erodes, the remaining volume of sand that will be retained by the T-groin field is predicted to be 130,000 m 3 (Chapter Two). Table 8-3 shows that the annual average Q x from Cell 1 from 2004 to 2008 will increase to 58,000 m 3 /yr as compared to the 1996 to 2004 average Q x of 43,600 m 3 /yr (Fig. 8-3). Table 8-3. Conservative sediment transport estimate for Cell 1 with T-groins during the 2004 to 2008 nourishment interval. Cell 1 P + R, 2004 361,900 Volume predicted to be retained by T-groins 130,000 Remaining volume to be transported out of Cell 1 231,900 (Mean Q x = 58,000 m 3 /yr) Sediment surplus in Cell 1 0 As an extra precaution an additional 25,000 m 3 of sediment was placed in Cell 2 during the 2004 project as advance mitigation for the potential downdrift impact from the structures. With the estimate of transport determined above and this additional nourishment, it is reasonable to conclude that the downdrift beaches of Long Key will be supplied with an equal or greater volume of sediment than in the past, despite the new structures. By the above rationale, it can be argued that all of the nourished material would erode during the 2004 to 2008 nourishment interval without the T-groins. This is unlikely for two reasons. First, the annual average Q x would be 90,500 m 3 /yr, which is 161

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likely too high for this region. Recall that the potential south-directed transport from Walton (1976) was 75,000 m 3 /yr. Second, nourishment performance improved from 1991 to 2004 based on the short-term budget analyses. The 2004 project was longer and provided more sediment than the previous projects. It is hypothesized that without the new T-groins, nourishment performance of Upham Beach would have continued to improve, resulting in a pre-nourishment shoreline configuration in 2008 that would be farther seaward than the pre-nourishment condition in 2004. In fact, Upham Beach may have retained up to 130,000 m 3 of sediment without the T-groins. The assumption that 100% of the available sediment will erode from Upham Beach during the 2004 to 2008 nourishment interval is unlikely; however, it provides a conservative estimate of the downdrift effect of the T-groin field. Conclusions High-resolution field data from 1996 to 2004 are used to calculate sediment budgets on various temporal and spatial scales that revealed more information than a typical regional sediment budget with average annual transport rates. The cross-shore distribution of longshore transport is inferred from morphologic variability along the profiles. The traditional sediment budget formulation is improved by resolving the details of the sediment transport pathways. The average longshore transport rate from Upham Beach is 42,000 m 3 /yr to the south. The longshore transport rate is up to 83% higher during the first year after nourishment, and then the transport rate decreases throughout the remainder of the 162

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nourishment interval. Thus, beach nourishment events elevate transport gradients. Longshore transport rates are reduced at longer temporal scales, but the large gradient is persistent. The large gradient in annual longshore transport decreases by 60% toward the south until transport approximates the predicted rate for the region (Walton, 1976) along the central portion of the island (Cell 3). This predicted rate only applies to the non-eroding Cell 3 that is out of the influence of inlets and nourishment. This shows that annual average transport rates for a region should not be arbitrarily applied to nourished beaches; rather, sediment budgets formulated with high-spatial and -temporal resolution field data should be formulated during the design phase of future nourishment projects. Stable beaches along central Long Key (Cell 3) benefit from the Upham Beach feeder beach, which influences beach performance over 4 km to the south. Pass-a-Grille Beach, on southern Long Key, is eroding because the south-directed transport bypasses the beach and is deposited inside the channel and on the ebb shoal. Upham Beach is not a feeder beach for Pass-a-Grille Beach as previously believed. This finding also highlights the importance of periodic review of coastal management strategies using high-resolution survey data. The nourishment performance on Upham Beach has improved since 1991 because the project length and total volume were increased and the nourishment interval was reduced from five to four years. The planned T-groin structures on Upham Beach should not result in downdrift erosion with the present four-year renourishment interval. Increased nourishment volume and project length in 2004 has provided sufficient 163

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sediment for transport to the downdrift beaches. The management strategy for Long Key over the next decade should include at least quarterly surveys of the entire island and continued renourishment every four years with the equivalent volume and length of the 2004 project. A feasibility study on the effect of extending the jetty on southern Long Key should also be considered. 164

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Chapter Nine Conclusions High-resolution field data are crucial to improve the understanding of the time-dependent sediment transport processes that govern changes in coastal morphology. A well-planned monitoring program that was conducted before, during, and immediately after construction of the 2004 Upham Beach nourishment project collected high-spatial and -temporal resolution field data. With this robust dataset, the details of sediment transport rates and gradients induced by gradual processes and high-energy events are analyzed on a macro-scale. Post-nourishment planform adjustment occurs immediately after nourishment via diffusion spit development at the end transitions. Thus, the initiation of planform adjustment may be abrupt, rather than gradual. Diffusion spit formation is dominant during relatively calm wave conditions on coasts with low wave heights and tidal ranges. Under these environmental circumstances, spit formation reveals the initial step in diffusion modeling of planform adjustment, improving upon the present understanding of planform evolution. Profile equilibration also may be an event-driven, rather than a gradual, process. Rapid profile equilibration following nourishment occurred not only as a result of hurricane passage, but also during a typical winter season. The duration between 165

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nourishment and the passage of the first high-energy event is an important factor controlling the time scale of profile equilibration. This is a significant contribution to the present predictive capability of post-nourishment profile adjustment. The passage of three hurricanes generated different wave conditions and induced different sediment transport directions, rates, and gradients due to their variable proximities to the project area. Gradients in longshore transport were largely governed by wave energy and local shoreline orientation, rather than offshore wave direction. The direction of cross-shore transport was governed by wave steepness, as opposed to a simple relationship with wave energy. Onshore sediment transport occurred during a storm event (high-energy swell waves), as well as during low-energy swell conditions. This contrasts with the concepts of gradual onshore transport during mild wave conditions and abrupt offshore transport during storm events, as cited in the literature. By formulating sediment budgets on various temporal and spatial scales, both event-driven and average transport rates and gradients can be resolved. It is crucial to quantify elevated transport gradients during the first year after nourishment (an event). Annual average transport rates for a region should not be arbitrarily applied to nourished beaches; rather, sediment budgets formulated with high spatialand temporal-resolution field data should be formulated during the design phase of future nourishment projects. In general, the analysis of sediment transport induced by gradual processes and high-energy events has led to an improved understanding of macro-scale morphologic changes in the coastal environment. 166

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References Allen, J.R., 1985. Field evaluation of beach profile response to wave steepness as predicted by the Dean model, Coastal Engineering, 9: 71-80. Barker, V.H., and Bodge, K.R., 2005. Impacts of the 2004 hurricane season on Brevard County, Floridas beaches, Shore and Beach, 73(2&3): 34-42. Becker, M.L. and Ross, M.A., 1999. A Model Study of Boca Ciega Bay, Johns Pass, and Blind Pass, Publication Report: No. CMHAS.FDOT.99.01, Center for Modeling Hydrologic and Aquatic Systems, Department of Civil and Environmental Engineering, University of South Florida, Tampa, Florida, 72p. Bell, G. D., Goldenberg, S., Landsea, C., Blake, E., Chelliah, M., Pasch, R., Mo, K., 2005. The 2004 North Atlantic Hurricane Season: A Climate Perspective, http://www.nhc.noaa.gov/2004atlan.shtml accessed February 6, 2006. Birkemeier, W.A., 1979. The effects of the 19 December 1977 coastal storm on beaches in North Carolina and New Jersey, Shore and Beach, 47(1): 7-15. Birkemeier, W.A., Dewall, A.E., Gorbics, C.S., and Miller, H.C., 1981. A users guide to CERCs Field Research Facility, U.S. Army Corps of Engineers, Coastal Engineering Research Center, Misc. Report No. 81-7, 118p. Bodge, K.R., 1999. Inlet impacts and families of solutions for inlet sediment budgets, Proceedings Coastal Sediments Reston, VA, ASCE, 703-718. Bodge, K.R., and Dean, R.G., 1987. Short-term impoundment of longshore transport, Proceedings Coastal Sediments Reston, VA, ASCE, 469-483. Bodge, K.R., and Rosati, J.D., 2003. Sediment Management at Inlets and Harbors. In: Ward, D.L.. (ed.), Coastal Engineering Manual, Part V, Coastal Project Planning And Design Chapter 6, Engineer Manual 1110-2-1100, U.S. Army Corps of Engineers, Washington, DC. Bortnick, B., 2000. Post-construction adjustment of nourished beaches: Examples from Pinellas County, Florida. Tampa, Florida: University of South Florida, Master's thesis, 90p. 167

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Bowen, A. J. and Inman, D. L., 1966. Budget of littoral sands in the vicinity of Point Arguello, California. TM-19, U.S. Army, Corps of Engineers, CERC, Washington, D.C. Browder, A.E. and Dean, R.G., 2000. Monitoring and comparison to predictive models of the Perdido Key beach nourishment project, Florida, USA. Coastal Engineering, 39 (2-4): 173-191. Brunn, P., 1954. Coast erosion and the development of beach profiles, Technical Memo No. 44, U.S. Army Corps of Engineers Beach Erosion Control Board. Carter, R.W.G., 1988. Coastal Environments, Academic Press Limited, San Diego, CA, 617 p. Clark, R.R., 2005. Impact of the 2004 North Atlantic hurricane season on the coast of Florida, Shore and Beach, 73(2&3): 2-9. Coastal Planning And Engineering, 1992. Blind Pass Inlet Management Plan. Boca Raton, FL: Coastal Planning and Engineering, Inc., 69 p. Davis, R.A., Jr., 1989a. Morphodynamics of the west-central Florida barrier system: the delicate balance between waveand tide-domination. Coastal Lowlands, Geology and Geotechnology. Dordrecht, The Netherlands: Kluwer, 225-235. Davis, R.A., Jr., 1989b. Management of drumstick barrier islands. Proceedings of the 6 th Symposium on Coastal and Ocean Management, Charleston, South Carolina, ASCE, 16p. Davis, R.A., Jr., 1991. Design of comprehensive beach nourishment monitoring projects, Proceedings of the 10 th Australasian Conference on Coastal and Ocean Engineering, Auckland, New Zealand, 335-338. Davis, R. A., Jr., 1994. Barriers of the Florida Gulf Peninsula. In: Davis, R. A., Jr. (ed), Geology of Holocene Barrier Island Systems, Berlin: Springer-Verlag, 167-206. Davis, R. A., Jr., 1997. Geology of the Florida Coast. In: Randazzo, A.F. and Jones, D.S. (eds.), The Geology of Florida, Gainesville, FL: Univ. Press of Florida, 155-168. Davis, R. A., Jr., 1999. Complicated littoral drift systems on the Gulf Coast of Peninsular Florida, Proceedings Coastal Sediments '99, Reston, VA: ASCE, 761-769. Davis, R. A., Jr. and Hayes, M.O., 1984. What is a wave-dominated coast?, Marine Geology, 60: 313-329. 168

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Davis, R.A., Jr., and Gibeaut, J.C., 1990, Historical Morphodynamics of Inlets in Florida: Models for Coastal Zone Planning, Florida Sea Grant College, Technical Paper 55, p.29-35. Davis, R.A., Jr., Terry, J.B., and Ryder, L., 1993. Design of beach monitoring programs with Florida examples, Proceedings of the 1993 National Conference on Beach Preservation Technology, Florida, 272-278. Davis, R.A. Jr. and Barnard, P.L., 2000. How anthropogenic factors in the back-barrier area influence tidal inlet stability: examples from the Gulf Coast of Florida, USA, Coastal and Estuarine Environments: Sedimentology, Geomorphology, and Geoarchaeology, Geological Society, London, Special Publications, 175: 293-303. Davis, R.A., Wang, P., and Silverman, B.R., 2000. Comparison of the performance of three adjacent and differently constructed beach nourishment projects on the Gulf peninsula of Florida. Journal of Coastal Research, 16: 396-408. Davis, R.A., Jr. and Fitzgerald, D.M., 2004. Beaches and Coasts. Blackwell Sci. Ltd., Malden, MA, 419 p. Dean, R.G., 1973. Heuristic models of sand transport in the surf zone. Proceedings of the 1 st Australian Conference on Coastal Engineering, Engineering dynamics in the surf zone, Sydney, Australia, 209-214. Dean, R. G., 1977. Equilibrium beach profiles: U.S. Atlantic and Gulf coasts. Ocean Engineering Technical Report No. 12, Dept. of Civil Engineering and College of Marine Studies, Univ. of Delaware. Dean, R. G., 1983. Principles of beach nourishment. In: Komar, P.D. (ed.), CRC Handbook of Coastal Processes and Erosion, Boca Raton: CRC Press, 217-232. Dean, R.G., 1987. Coastal sediment processes: Toward engineering solutions. Proceedings, Coastal Sediments : ASCE, 1-24. Dean, R.G., 1988. Engineering design principles. Short Course on Principles and Applications of Beach Nourishment. Gainesville, FL: Florida Shore and Beach Preservation Association, 42 p. Dean, R. G., 1991. Equilibrium beach profiles: characteristics and applications. Journal of Coastal Research, 7(1): 53-84. Dean, R. G., 1996. Beach nourishment performance: planform considerations. Shore and Beach, 64: 36-39. 169

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Dean, R.G., 2002. Beach Nourishment, Theory and Practice. Advanced Series on Ocean Engineering Volume 18. Singapore: World Scientific, 399 p. Dean, R.G. and Yoo, C., 1992. Beach Nourishment performance predictions. Journal of Waterway, Port, Coastal and Ocean Engineering, 118(6), 567-586. Dean, R.G. and Campbell, T.J., 1999. Recommended beach nourishment guidelines for the state of Florida and unresolved and related issues. FDEP Workshop on Beach Nourishment. Gainesville, FL, 10 p. Dean, R.G. and Dalrymple, R.A., 2002. Coastal Processes with Engineering Applications, Cambridge University Press, 475p. Dean, R.G., Kriebel, D.L., Walton, T., 2002. Cross-shore sediment transport processes. In: King, D. (editor), Coastal Engineering Manual, Part III, Coastal Sediment Processes Chapter 3, Engineer Manual 1110-2-1100, U.S. Army Corps of Engineers, Washington, DC. Dette, H.H., Newe, J. and Peters, K., 1995. Large Wave Flume experiments '93, Vol. I: Data report, wave data and beach profile surveys. Rep. No. 787, Leichtweiss-Inst., Tech. Univ. Braunschweig. Dixon, K. and Pilkey, O.H., 1989. Beach replenishment on the U.S. coast of the Gulf of Mexico. In: Magoon, O.T., et al. (eds.), Coastal Zone New York: ASCE, 2033-2045. Dolan, T. J., Castens, P. G., Sonu, C. J., and Egense, A. K., 1987. Review of sediment budget methodology: Oceanside littoral cell, CA, Proceedings Coastal Sediments Reston, VA, ASCE, 2, 1289-1304. Ebersole, B.A., Neilans, P.J., and Dowd, M.W., 1996. Beach fill performance at Folly Beach, South Carolina (1 year after construction) and evaluation of design methods. Shore and Beach, 64(1), 11-26. Elko, N.A., 1999. Long-term beach performance and sediment budget of Long Key, Pinellas County, Florida. Tampa, Florida: University of South Florida, Master's thesis, 176p. Elko, N.A., 2005. Management of a Beach Nourishment Project during the 2004 Hurricane Season, Shore and Beach, 73(2&3): 49-54. Elko, N.A., Holman, R.A., and Gelfenbaum, G., 2005. Quantifying the rapid evolution of a nourishment project with video imagery, Journal of Coastal Research, 21(4): 633-645. 170

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Elko, N.A. and R.A. Davis Jr., 2006. Morphologic evolution of similar barrier islands with different coastal management, Journal of Coastal Research, SI 39, 126-130. Everts, C., Dewalls, A.E., and Czeriak, M.T., 1974. Behavior of a beach fill at Atlantic City, NJ, Proceedings of the 14 th Annual Coastal Engineering Conference, ASCE, 1370-1388. Fitzgerald, D.M., S. Penland, D. Nummedal, 1984. Control of barrier island shape by inlet sediment bypassing: East Frisian Islands, West Germany, In: B. Greenwood and R.A. Davis, Jr. (eds.), Hydrodynamics and Sedimentation in Wave-Dominated Coastal Environments, Marine Geology, 60: 355-376. Fitzgerald, D.M., Ibrahim, N.A., and Humphries, S.M., 1989. Formation of beach ridge barriers along an indented coast: Buzzards Bay, Massachusetts. In: Magoon, O.T. et al., (eds.) Coastal Zone New York: American Society of Civil Engineers, 2997-3016. FDEP, 2001. Chapter 62B-41, Rules and Procedures for Application for Coastal Construction Permits, Effective 10-23-01, Sand Rule, http://www.dep.state.fl.us/beaches/publications/gen-pub.htm#Rules accessed February 6, 2006. FDEP, 2005. Critically eroded beaches in Florida, Florida Department of Environmental Protection, Bureau of Beaches and Coastal Systems, FDEPReport, http://www.dep.state.fl.us/beaches/publications/tech-rpt.htm accessed March 22, 2006, 73 p. Gallagher, E.L., Elgar, S., and Guza, R.T., 1998. Observations of sand bar evolution on a natural beach, Journal of Geophysical Research, 103(C2): 3203-3215. Gravens, M.B., 1997. Wave resolution effects on predicted shoreline positions. Journal of Waterway, Port, Coastal and Ocean Engineering, 123(1), 23-33. Gravens, M.B., Ebersole, B.A., Walton, T.L., and Wise, R.A., 2003. Beach Fill. In: Curtis, W. (editor), Coastal Engineering Manual, Part V, Coastal Project Planning And Design Chapter 4, Engineer Manual 1110-2-1100, U.S. Army Corps of Engineers, Washington, DC. Hagemeyer, B. C., and Almeida, R. A., 2002: Experimental Forecasting of Dry Season Storminess over Florida and the Southeast United States from the ENSO Signal using Multiple Linear Regression Techniques. 16th Conference on Probability and Statistics in the Atmospheric Sciences. Orlando, FL: American Meteorological Society, Paper J3.10. Hall, J.V., and Watts, G.M., 1957. Beach rehabilitation by fill and nourishment, Trans. Amer. Soc. Civil Engineers, 155-177. 171

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About the Author Nicole A. Elko received a B.S. in Environmental Resource Management from Penn State University in 1996 and a M.S. in Geology from the University of South Florida (USF) in 1999. She entered the Ph.D. program at USF in 1999. Nicole began working full-time for the U.S. Geologic Survey in St. Petersburg, FL in 2000. In 2002, Nicole started working for Pinellas County as the Coastal Coordinator. She has been managing federal and local beach nourishment and other coastal projects. In 2005, Nicole published two peer-reviewed journal articles in the Journal of Coastal Research and Shore and Beach. She has submitted another article to Coastal Engineering. In addition to frequent presentations to local environmental and political organizations, she has made paper presentations at national meetings of the American Geophysics Union, the Geological Society of America, Coastal Education and Research Foundation, the American Society of Civil Engineers, and the Florida Shore and Beach Preservation Association.