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Seasonal and Spatial Variability of Beach Morphodynamics at an Autonomous Tidal Inlet

Permanent Link: http://ufdc.ufl.edu/UFE0042820/00001

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Title: Seasonal and Spatial Variability of Beach Morphodynamics at an Autonomous Tidal Inlet Matanzas Inlet, Florida Atlantic Coast.
Physical Description: 1 online resource (291 p.)
Language: english
Creator: MALONE,KATHERINE KELLY
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: Geological Sciences -- Dissertations, Academic -- UF
Genre: Geology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

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Abstract: SEASONAL AND SPATIAL VARIABILITY OF BEACH MORPHODYNAMICS AT AN AUTONOMOUS TIDAL INLET: MATANZAS INLET, FLORIDA ATLANTIC COAST By Katherine Kelly Malone May 2011 Chair: Peter Adams Major: Geology A study of beach topography was conducted along a 1.6 km coastal reach adjacent to the Matanzas Inlet, Florida, an inlet that has not experienced any anthropogenic modification. This thesis describes the seasonal and spatial variability of the mean high water (MHW) shoreline position and cross-shore beach morphology, from January 2009 through February 2010. Results indicate that there is an alongshore variability in the behavior of shoreline position and beach morphology that may be related to the inlet mouth. Beach width and width variability are comparatively large in the southern region (within 500 meters immediately adjacent to the inlet), whereas seasonal signals in beach width are discernable only in the northern region (600 - 1600 meters from the inlet). The northern region displays high topographic variability on the upper beach, near to the proto-dune base line (PDBL); the southern region displays high topographic variability on the lower beach near the MHW shoreline. During summer, the northern portion steepens at the MHW shoreline; the southern portion becomes more gently sloped. Correlation analyses imply that there is some, albeit weak, association between changes beach morphology and offshore wave conditions.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by KATHERINE KELLY MALONE.
Thesis: Thesis (M.S.)--University of Florida, 2011.
Local: Adviser: Adams, Peter Nelson.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2012-04-30

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0042820:00001

Permanent Link: http://ufdc.ufl.edu/UFE0042820/00001

Material Information

Title: Seasonal and Spatial Variability of Beach Morphodynamics at an Autonomous Tidal Inlet Matanzas Inlet, Florida Atlantic Coast.
Physical Description: 1 online resource (291 p.)
Language: english
Creator: MALONE,KATHERINE KELLY
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: Geological Sciences -- Dissertations, Academic -- UF
Genre: Geology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: SEASONAL AND SPATIAL VARIABILITY OF BEACH MORPHODYNAMICS AT AN AUTONOMOUS TIDAL INLET: MATANZAS INLET, FLORIDA ATLANTIC COAST By Katherine Kelly Malone May 2011 Chair: Peter Adams Major: Geology A study of beach topography was conducted along a 1.6 km coastal reach adjacent to the Matanzas Inlet, Florida, an inlet that has not experienced any anthropogenic modification. This thesis describes the seasonal and spatial variability of the mean high water (MHW) shoreline position and cross-shore beach morphology, from January 2009 through February 2010. Results indicate that there is an alongshore variability in the behavior of shoreline position and beach morphology that may be related to the inlet mouth. Beach width and width variability are comparatively large in the southern region (within 500 meters immediately adjacent to the inlet), whereas seasonal signals in beach width are discernable only in the northern region (600 - 1600 meters from the inlet). The northern region displays high topographic variability on the upper beach, near to the proto-dune base line (PDBL); the southern region displays high topographic variability on the lower beach near the MHW shoreline. During summer, the northern portion steepens at the MHW shoreline; the southern portion becomes more gently sloped. Correlation analyses imply that there is some, albeit weak, association between changes beach morphology and offshore wave conditions.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by KATHERINE KELLY MALONE.
Thesis: Thesis (M.S.)--University of Florida, 2011.
Local: Adviser: Adams, Peter Nelson.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2012-04-30

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0042820:00001


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1 SEASONAL AND SPATIAL VARIABILITY OF BEACH MORPHODYNAMICS AT AN AUTONOMOUS TIDAL INLET: MATANZAS INLET, FLORIDA ATLANTIC COAST By KATHERINE KELLY MALONE A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORID A IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2011

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2 2011 Katherine K. Malone

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3 To my Dad

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4 ACKNOWLEDGMENTS I am in great debt to a number of friends and colleagues. First and foremos like to thank Peter Adams for his guidance and intellectual support throughout my committee members. I suffered a great loss with the death of my father in March 2008 just prior to beginning my degree program. He was a great inspiration to me as we shared a mutual love for nature and for science. At first, I thought I had lost my momentum but I gained it back and I felt close to my father in the process of scie to thank him for teaching me to appreciate things we cannot understand. Without continual encouragement from my mother to push through this difficult time, I could have never finished. Jessica Lovering and Shaun Kline encourage d me to think analytically and made me love coming to work every day. Rich Mackenzie taught me how to use the friends, especially Sean Keough. I could not have completed t his research without the field support of Earl Soeder, Tim Kirchner, and Derrick Newkirk; I am in great debt to the freedom to explore such a beautiful place.

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5 TABL E OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 LIST OF ABBREVIATIONS ................................ ................................ ........................... 10 ABSTRACT ................................ ................................ ................................ ................... 11 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 12 1.1 Previous Work ................................ ................................ ................................ .. 12 1.2 Problem Statement and Objectives ................................ ................................ ... 18 2 METHODS ................................ ................................ ................................ .............. 21 2.1 Study Site ................................ ................................ ................................ ......... 21 2.1.1 Historical Landform Changes ................................ ................................ .. 21 2.1.2 Site Descriptio n ................................ ................................ ....................... 21 2.2 GPS Surveys ................................ ................................ ................................ .... 22 2.3 Data Processing ................................ ................................ ............................... 23 2.3.1 Digital Ele vation Model Grid Generation ................................ .................. 23 2.3.2 Cross Shore Transect Generation ................................ ........................... 24 2.3.3 Cross shore Profile Interpolation ................................ ............................. 24 2.3.4 Shoreline Interpolation and Beach Width Calculation .............................. 25 2.3.5 Beach Slope Calculation ................................ ................................ ......... 25 2.3.6 Wave Conditions Data Processing ................................ .......................... 26 3 RESULTS AND ANALYSIS ................................ ................................ .................... 33 3.1 Shoreline Position / Beach Width ................................ ................................ ...... 33 3.1.1 Spatial Variation of Shoreline Position (Beach Width) ............................. 33 3.1.2 Temporal Variation of Shoreline Position (Beach Width) ......................... 34 3.2 Beach Morphology / Profile Shape ................................ ................................ ... 35 3.2.1 Spatial and Temporal Variation of Cross Shore Profiles ......................... 35 3.2.2 Analysis of Variation of Cross Shore Profiles ................................ ......... 36 3.2.3 Beach Slope Analysis ................................ ................................ .............. 37 3.3 Bea ch Response to Wave Forcing ................................ ................................ .... 38 3.3.1 Offshore Wave Climate During Observation Period ................................ 38 3.3.2 Shoreline Variation and Wave Heigh t ................................ ...................... 39

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6 4 DISCUSSION AND CONCLUSIONS ................................ ................................ ...... 62 4.1 Shoreline Position Variation With Distance From Inlet ................................ ...... 62 4.2 Seasonal Variability in Shoreline Position ................................ ......................... 62 4.3 Beach Morphology Variation Spatial and Temporal ................................ ....... 63 4.4 Relationship of Beach Response to Forcing ................................ ..................... 64 4.5 Summary ................................ ................................ ................................ .......... 64 APPENDIX APPENDIX : SUPPLEMENTARY FIGUR ES ................................ ................................ 66 LIST OF REFERENCES ................................ ................................ ............................. 287 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 291

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7 LIST OF TABLES Table page 2 1 Table highlighting mean high water and mean range for the area ..................... 27

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8 LIST OF FIGURES Figure page 1 1 Location map of Matanzas Inlet, North Florida Atlantic coast. ............................ 20 2 1 Time series of air photos illustrating ~4m/yr southward migration (net narrowing ~3m/yr) of the inlet during February 1995 January 2008. ............... 28 2 2 Example of survey pattern deemed most efficient at collecting a large aerial extent of data. ................................ ................................ ................................ ..... 29 2 3 Example of scatter diagram. ................................ ................................ ............... 30 2 4 Example of DEM grid (1m resolution) interpolated from scatter diagram and polygon ................................ ................................ ................................ ............... 31 2 5 Figure illustrating 30 shore normal transects within the 1.5 km reach of coast directly north of Matanzas Inlet. ................................ ................................ .......... 32 3 1 Complete record of surveyed, monthly MHW shoreline positions throughout the study reach. ................................ ................................ ................................ .. 41 3 2a Temporal beach width of transect 15 ................................ ................................ .. 42 3 2b Temporal beach width of transect 27 ................................ ................................ .. 43 3 3 Spatial summary of shoreline change rates over the observation interval. ......... 44 3 4 Histogram showing time at which beach width maximum is reached. ................ 45 3 5a Cross shore topographic profile variation at transect 15. ................................ ... 46 3 5b Cross shore topographic profile variation at transect 27. ................................ ... 47 3 6a Time series of survey profiles for transect 15 ................................ ..................... 48 3 6b Time series of survey profiles for transect 27 ................................ ..................... 49 3 7 Colormap illustrating cross shore and alongshore distributions of temporal topographic variation plotted as standard deviation. ................................ ........... 50 3 8a Figure illustrating MHW shoreline slope for transect 15. ................................ .... 51 3 8b Figure illustrating MHW shoreline slope for transect 27. ................................ .... 52 3 9 Alongshore compilation of MHW shoreline slopes for each survey plotted as connected lines. ................................ ................................ ................................ .. 53

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9 3 10 Temporal analysis of beach slopes broken up into two groups according to locati on. ................................ ................................ ................................ .............. 54 3 11 Combined spatial and temporal analysis of the MHW shoreline beach slope illustrated as a colormap. ................................ ................................ .................... 55 3 12 NDBC wave buoy 41012 data illustrating significant wave height (m), wave period (s), and wave direction (degT) during the survey interval. ....................... 56 3 13a Temporal analysis of MHW shoreline position change ra te plotted against average significant wave height for each survey interval at transect 15. ............ 57 3 13b Temporal analysis of MHW shoreline position change rate plotted against average significant wave height for each survey interval at transect 27. ............ 58 3 14a Cross plot illustrating the relationship between average significant wave height and MHW shoreline position migration rate at tra nsect 3. ........................ 59 3 14b Cross plot illustrating the relationship between average significant wave height and MHW shoreline position migration rate at transect 26. ...................... 60 3 15 Summary of analyses of potential correlation between shoreline change rate and offshore wave height (H S ). ................................ ................................ ........... 61

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10 LIST OF ABBREVIATIONS dGPS Differential Global Positioning System DEM Digital Elevation Model MHW Mean High Water, 0.45 m NGS National Geodetic Survey PDBL Proto dune Ba se Line UTM Universal Transverse Mercator

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11 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science SEASONAL AND SPATIAL VARIABILITY OF BEACH MORPH ODYNAMICS AT AN AUTONOMOUS TIDAL INLET: MATANZAS INLET, FLORIDA ATLANTIC COAST By Katherine Kelly Malone May 2011 Chair: Peter Adams Major: Geology A study of beach topography was conducted along a 1.6 km coastal reach adjacent to the Matanzas Inlet, Fl orida, an inlet that has not experienced any anthropogenic modification. This thesis describes the seasonal and spatial variability of the mean high water (MHW) shoreline position and cross shore beach morphology, from January 2009 through February 2010. Results indicate that there is an alongshore variability in the behavior of shoreline position and beach morphology that may be related to the inlet mouth. Beach width and width variability are comparatively large in the southern region (within 500 mete rs immediately adjacent to the inlet), whereas seasonal signals in beach width are discernable only in the northern region (600 1600 meters from the inlet). The northern region displays high topographic variability on the upper beach, near to the proto d une base line (PDBL); the southern region displays high topographic variability on the lower beach near the MHW shoreline. During summer, the northern portion steepens at the MHW shoreline; the southern portion becomes more gently sloped. Correlation a nalyses imply that there is some, albeit weak, association between changes beach morphology and offshore wave conditions.

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12 CHAPTER 1 INTRODUCTION On naturally occurring sandy beaches, beach morphology is influenced by waves and tides. While the influence of waves and tides are well documented on continuous, straight, and planar beaches [ Masselink and Short 1993; Wright and Short 1984 ; Wright et al 1985 ; Wright et al 1987], these effects are less well understood on beaches adjacent to tidal inlets. At tidal inlets, significant quantities of water and sediment are exchanged between the open ocean and the protected back barrier bay, resulting in hydrodynamic discontinuities (two way jets), and bathymetric discontinuities (ebb shoals and ebb tidal delt as) alongshore. The presence of these discontinuities disturbs the simple, predictable pattern of wave driven longshore sediment transport, which is critical to coastal morphologic evolution [ FitzGerald 1996]. The development of numerical models to simu late coastal geomorphic response to changes in wave climate, sea level rise, and terrestrial sedimentary inputs are currently being developed [ Ashton et al. 2001 ; Ruggiero et al. in press ] and their improvement will be supplemented by data sets documenti ng oceanic forcing and beach morphologic change at inlets. Quantifying shoreline variability is only one method of examining the behavior of the coastal system; scientific understanding and engineering solutions require quantitative information regarding the behavior of multiple relevant morphologic characteristics (e.g., beach width, slope, and volume change) to facilitate effective coastal planning [ Stive et al 2002]. 1.1 Previous Work Much of the scientific l iterature regarding beach volumetric change (erosion or accretion) has focused on seasonal variability, which has helped to advance our limited

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13 understanding of intermediate term (annual to decadal) advances and retreats of the shoreline [ Komar and Inman, 1970; Winant et al 1975; Dolan et al., 1 977; Aubrey, 1979; Hayes, 1980; E liot and Clarke 1982; Wright et al 1985 ; Larson and Kraus 1995; Stive et al., 2002; Ruggiero et al., 2003 ; List et al., 2006 ]. Through a series of case studies, Stive et al [2002] illustrate potential causes for varia bility in shoreline evolution through a range of different time and space scales (hours to years/~10 m 1 km). Although some qualitative observations and correlations between forcing and response a ttempt to describe the reasons behind shoreline variabili ty (i.e., wave, tide and surge conditions, and climate variations), the authors found it difficult to derive generic quantitative relationships that attempt to describe cert ain behavior [ Stive et al 2002]. Wright and Short [1984] predicted modal beach state and beach surf zone variability in terms of environmental conditions from 1979 1982 on shore environments exhibiting the full natural range of beach and surf zone morphodynamics. Although their study was limited to sites in Australia, their morpho dynamic states model has been shown to be applicable to other coasts with minor modifications. The results Short, 1979a, b; Wright et al., 1979a, b, 1982a, b, c; Short & Wright 1981; Wright 1981, 1982; Wright and Short 19 83] culminate in six generalizations that describe relationships among environmental conditions, sediment types, and morphodynamic states. Most applicable to this study, is their generalization that states beaches and surf zones may be dissipative, reflec tive, or in any of at least four intermediate states depending on local environmental conditions, sediments and wave conditions.

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14 Dissipative beaches are generally low in slope, wherein waves break offshore and continue to lose energy as they cross the wi de surf zone; dissipative beaches are highly effective in dissipating wave energy of incident waves. R eflective beaches are steep wherein dominantly incident waves break close to the shore and immediately wash up on the beach face. The authors elaborate upon these two end members with the addition of several intermediate beach morphologies [ Wright et al., 1978, 1979]. The occurrences of these intermediate beach states (longshore bar trough, rhythmic bar and beach, transverse bar and rip, and ridge runne l or low tide terrace) vary according to a dimensionless ratio of beach steepness to wave steepness known as the Iribarren number ( ) [ Wright and Short 1983]. Dissipative beaches are found to correspond to very low Iribarren numbers ( = 0.2 0.3), and reflective beaches occur at approximately > 2. The four intermediate stages are more difficult to assess in terms of Iribarren number because of widely ranging local conditions of bottom slope and wave parameters. It is valuable to be able to predict sh ort term fluctuations in these beach states, as the beach state is an important indicator of dominant surf zone processes that influence the likelihood of beach erosion or accretion [ Short and Hesp 1982 ; Wright 1981 ; Wright et a l., 1985 ]. There have b een numerous studies that attempted to correlate changes in beach morphology to event scale and seasonal changes in wave fields [e.g. Dubois, 1988; List et al. 2006; Quartel et al. 2008]. Such studies are valuable in establishing the magnitudes of shore line variability on the event and seasonal scales, which can be compared to long term shoreline retreat resulting from relative sea level rise.

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15 List et al. [2006] noted an intriguing mystery: how could one section of beach exhibit significant erosion du ring a storm consistent with the classic storm to fair weather transition, while an adjacent similar section of coast a few kilometers away remains unresponsive? Reversing storm hotspots are referred to as such because the erosion typical of coastal erosio nal hotspots is reversed by accretion of a similar magnitude to storm induced erosion within a few days or weeks of fair weather after a storm. The authors aimed to quantify the spatial and temporal characteristics of the observed pattern of storm induced erosional variability along with its associated post storm accretion of reversing storm hotspots. List et al. [2006] studied the large scale (tens of kilometers) variability of two sandy, uninterrupted, shorelines of the US east coast for three years, 45 km on Cape amphibious all terrain vehicles (ATVs) were used as a platform for GPS measurements during low tide. Data gathered included three dimensional shoreline positions of MHW Measurements were conducted at three intervals: pre storm, storm, and post storm for ype. Shoreline change was then found as the difference between shoreline positions surveyed on two dates. NDBC buoys provided additional wave and tide information for both locations. Reversing storm hotspot patterns suggest coherent processes acting ove r large distances. These processes control the degree to which sand is removed from the subaerial beach during storms. List et al. [2006] provide several hypotheses that

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16 attempt to explain the nature of these processes. Areas exhibiting reversing storm hotspot response may lack a nearshore bar prior to storm initiation, thereby allowing more wave energy to act upon the shore. This is in contrast to areas with one or more nearshore bar(s) that dissipate offshore wave energy; however, the responsible proc esses that act to alter the nearshore bars remain unknown. Additional hypotheses include effective underlying geologic framework and longshore variations in wave characteristics; however, preliminary wave modeling using SWAN [ Booij et al., 1999] fail to r eveal any longshore variation consistent with the pattern of reversing storm hotspots. The results of work demonstrate that storm induced hotspots may be the result of a variety of processes, and the response of the shoreli ne to storms is complicated and requires further understanding and research [ List et al ., 2006] Dubois [ 1988] sought to understand the nature of a cyclic beach along a shore segment of the Delaware coast, and presented evidence that attempted to expl ain how the wave regime affected beach topography and beach volume. The author conducted a beach survey along the south area of Dewey Beach in Delaware Seashore State Park where the long term beach erosion was between 0.6 0.9 m/yr [ Kraft et al., 1978]. Wa ve conditions, specifically mean monthly surge variability, were estimated from NOAA tide tables measured in the Indian River Bay near the Indian River Inlet. Six profiles, spaced 40 m apart, extending from a 200 m long baseline were surveyed one to three times a month from May 3, 1982 until June 1983. The author concluded that beach topography and beach volume varied with changes in wave regime in phase with winter and summer seasons. During the winter, when the magnitude and frequency of waves were high er, the beach shape was concave upward. Additionally, the concave upward profile

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17 was consistent with when the beach was at its maximum sediment volume. Dubois [1988] also found an inverse relationship between the mean monthly sediment volume and the mean monthly surge variability. High surge levels occurred with large waves, while low surge levels occurred with small waves. During the winter, surge variability was high and sediment volume was low. In the summer, surge variability was low and sediment v olume was high. Quartel et al. [ 2008 ] conducted monthly beach surveys over a 1.5 km reach of coast at Noordwijk, in The Netherlands, to investigate the dependence of seasonal variability in shoreline position and beach volume on offshore wave characteri stics. Seasonal patterns show a narrow, large volume beach in the summer, and a wide small volume beach at the end of the winter, in general agreement with seasonally averaged, offshore wave conditions. In spite of general seasonal agreement the daily to weekly averaged wave conditions did not show a clear, correlative relationship with beach response on the same time scale, which the authors attribute to antecedent morphology preceding storms [ Quartel et al 2008]. Fenster and Dolan [1996] used aerial photography to investigate the influence of inlets on beach morphodynamics at two locations along the Atlantic coast: one wave dominated site at the Outer Banks of North Carolina (11 photographs from 1949 1986), and one tide dominated site at the Virginia Barrier Islands (9 photographs from 1949 1989). While their study is limited to snapshots in time and is focused on large scale (5 15 km) beach morphodynamics, the authors concluded that (1) the barrier zone in which inlet processes dominate shoreline tr ends can extend to distances of up to 4 5 km

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18 from an inlet, and (2) the zone in which inlet related processes influence shoreline trends can extend to distances of up to 6 13 km [ Fenster and Dolan, 1996]. In a study aimed largely at understanding the hydrodynamic discontinuities and sediment interaction at modified coastal inlets, Dean [1988] implores the necessity to understand the complex behavior of naturally occurring inlets. This is not necessarily for navigational or recreational necessities, bu t because the associated effects of sand transport on adjacent shorelines depend substantially on longshore sediment transport. Dean believes being able to predict the detailed behavior of inlets must be the subject of considerable future research [ Dean 1988]. 1.2 Problem Statement and Objectives This thesis presents the results of a field based monitoring program that was conducted to: (1) quantify spatial and temporal variability of beach size and shape adjacent to a natural inlet, and (2) identify the forcing responsible for the morphologic changes observed. The study examines changes in shoreline position (beach width) for one vertical elevation datum mean high water ( MHW ) and beach profile change at 30 cross shore transects over 14 months (Jan uary 2009 February 2010) at Matanzas Inlet on the North F lorida Atlantic coast ( Fi g ure 1 1 ) Co rrelations between offshore wave conditions and the beach morphologic response are investigated to explore potential links between oceanic forcing and geomorp hic response A simple hypothesis motivates the research: tidal inlet dynamics exert a spatially limited influence on the temporal behavior of nearby shoreline position and beach morphology. This hypothesis can be addressed by targeting a series of que stions, which are used to guide the analyses in this thesis:

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19 1. How does the shoreline position (beach width) vary as a function of distance from an inlet? 2. Does the spatial variability in shoreline position (beach width) exhibit a seasonal variability ? 3. How does beach morphology (profile shape) vary as a function of distance from an inlet? 4. Does the spatial variability in beach morphology (profile shape) exhibit a seasonal variability ? 5. How do temporal trends in shoreline position (beach width) and beach morph ology (profile shape) correlate with offshore wave conditions, thought to dominate the forcing?

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20 Fig ure 1 1 Location map of Matanzas Inlet, North Florida Atlantic coast. The study area includes ~1600 m on the northern of the beach north of the inle t mouth.

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21 CHAPTER 2 METHODS 2.1 Study Site The Matanzas Inlet, located ~7.8 km south of the intersection of Florida routes 206 and A1A constitutes the southern end of Anastasia Island, a 24 km long barrier island on the North Florida Atlantic coast. It provides a connection between the Matanzas River and the Atlantic Ocean, and is the only inlet (of 19 on the Florida Atlantic coast) that has not experienced substantial anthropogenic modification [ Mehta and Jones 1977] 2.1.1 Historical Landform Changes This inlet has historical significance, as it is the site of Spanish Colonial Fort Matanzas, which was constructed in 1742 to protect the southern entrance into the Matanzas River and the city of St. Augustine. At the time of construction, the fort was si tuated at the mouth of the inlet to the Atlantic Ocean. Today, the inlet is located ~1200 m south of the Fort, testifying to its migration. According to historical maps, the northern shoreline of the inlet is migrating southward at ~4 m/yr (761 m/191 yrs) and the southern shoreline of the inlet is migrating southward at ~1 m/yr (229 m/191 yrs), netting a total narrowing of the inlet of ~3 m/yr [ Dunkle, 1964]. This behavior is evident from the time series of air photos shown in Fig ure 2 1. 2.1.2 Site Desc ription This study focused on the 1600 meter alongshore reach of intertidal beach on the north side of the Matanzas Inlet. The beach on the south side of the inlet is armored with riprap, for stabilization purposes and was not investigated in this study. The beach in the study reach varies in width (measured from dune base to 0 m elevation contour,

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22 NAVD 88) between ~40 100 meters. The width of the barrier island itself, at the study site, varies from ~300 500 meters. Tidal information was gathered from b enchmark sheets for station number benchmark sheet denotes a MHW of 0.45 m and MLW of 0.91 m resulting in a mean 2005; Weber et al., 2005]. 2.2 GPS Surveys A total of 14 monthly surveys were conducted between January 2009 and February 2010, during the lunar new moon phase at low tide. Specific details, including tide level and number of survey po ints collected, are provided in Table 2.1. The beach and northern inlet mouth were surveyed on foot with backpack mounted differential Global Positioning System (dGPS) Trimble TSC2 controllers and 5800 mobile backpack antennas connected to a consistently occupied HPB450 radio base station. The base station was set up over a Department of Environmental Protection monument (identification number: DEP J796) located at Easting: 477861.574 m, Northing: 3287070.280 m ( UTM Zone 17R ) Elevation: 6.312 m (NAVD 88) on the boardwalk of Fort Matanzas National Monument St. Augustine, Florida Several survey patterns were employed throughout the study. The survey pattern deemed most efficient at collecting a large areal extent of data consisted of various oblique tr ansects at which the controllers would collect no r thing, easting, and elevation values at each meter along the traverse. An example of the data point distribution collected durin g a typical survey is shown in Fig ure 2 2 and maps of the beach traverses, f rom each of the 14 site visits, are compiled in Appendix A 1 (Page 66)

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23 2.3 Data Processing Following each dGPS survey, elevation data were uploaded from the survey controllers into the Trimble Business software After being quality checked and, if n ecessary, corrected for elevation discrepancies, elevation data were organized in a spreadsheet and exported to comma separated values (.csv) ascii text files, which were considered to be a general format that could be imported into most data analysis soft ware. Periodically, hourly summary wave data (significant wave height, spectral Station 41012 (LLNR 845.3) St. Augustin e, FL 40NM ENE of St Augustine, FL ] for the St. Augustine mid shelf wave buoy (#41012). These data were used to compare with the shoreline position, and beach morphology characteristics after dGPS data processing. All analyses in this study were c onducted using MATLAB software by The Mathworks, Inc. 2.3.1 Digital Elevation Model Grid Generation For each of the 14 surveys conducted, the quality controlled dGPS data point clouds were initially plotted in scatter diagrams that use color to denote elev ation. An example of this plot is provided in Fig ure 2 3 and the complete set of 14 plots is provided in Appendix A 2 (Page 86) These scatter plots were produced with the Also shown in the example Fig ure 2 3 is the outline of the data polygon used to convert the data point clouds to regularly spaced Digital Elevation Model (DEM) grids described below. For each of the 14 surveys, a unique polygon was drawn to maximize the data coverage for each survey, while minimizing the error arising from interpolating

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24 elevations over a broad region where data may be absent. Each unique polygon is plotted on each of the point cloud scatter diagrams in Appendix A 2 (Page 86) Regularly spaced rectangular grids, of 1 m reso lution and of size sufficient to cover each survey polygon, were generated for each of the 14 surveys. The data point cloud and polygon for each survey were used to interpolate a topographic surface onto each grid. An example of the resulting DEM grid, s howing the unique survey polygon, is provided in Fig ure 2 4 and the complete set of 14 DEM grids is provided in Appendix A 3 (Page 94 ) These DEM grid plots were produced with the MATLAB script named 2.3.2 Cross Shore Transect Ge neration Thirty (30) shore normal transects within the 1.5 km reach of coast directly north of Matanzas Inlet were generated, along which MHW shorelines and topographic profiles could be interpolated ( Fig ure 2 5 ). Transects were anchored on a proto dune base line (PDBL), identified in the field to be the furthest seaward cross shore position where the lower dune is vegetated with pioneer species. For each transect, the PDBL occupies the position of 100 m from the landward transect end. Transects were 33 0 m long and spaced 50 m apart along the PDBL, with an along transect point spacing of 1 m. This procedure was executed with the MATLAB script named 2.3.3 Cross shore Profile Interpolatio n The 30 shore normal cross shore tra nsects were overlain onto each of the 14 survey DEM grids to interpolate cross shore topographic profiles along the transects. The cross shore coverage at each transect varies significantly over the survey series due to the range of low tide elevations dur ing which the surveys were conducted ( Table

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25 2 1 ) and restrictions imposed upon beach access for areas marked off as shorebird nesting habitat during April September of 2009. The complete set of 14 survey profiles as each of the 30 cross shore transects is provided in Appendix A 5 ( Page 1 3 8) These cross shore profile plots were produced with the MATLAB script named 2.3.4 Shoreline Interpolation and Beach Width Calculation MHW s hore line positions along each transect were deter mined by finding the shoreward most position of intersection between the interpolated topographic profile and the MHW elevation of 0.45 m NAVD88. Beach width was then determined by subtracting the position of the PDBL (100m) from the shoreline position. This procedure was repeated, for each of the 30 shore normal transects and for each of the 14 surveys, position calculations. It should be noted that 31 of the 420 (7.5%) shoreline calculations resulted in no value (NaN), because of mistakes in the data collection procedure during some of the surveys. 2.3.5 Beach Slope Calculation Calculation of b each slope is a n elusive task due to the fact that most beaches are not pla portion of the topographic profile being considered. In this thesis, the slope is quantified by calculating a least squares residual fit as a first order polynomial trend line to the portion of profile beginning 5 meters landward of the MHW shoreline position, and ending 5 meters seaward of the MHW shoreline position. This allows for consistency of slope calculation by linking to a datum derived portion of the beach i.e. the portio n on either side of the MHW shoreline.

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26 2.3.6 Wave Conditions Data Processing m, and located at [ 30.041 N 80.533 W need to convert to UTM ] off the coast of Saint Augustine, FL. Ava Station 41012 (LLNR 845.3) St. Augustine, FL 40NM ENE of St Augustine, FL ], standard meteorological data chronicles wave, wind, and solar radiation conditions. Present and historical data are available to download as a text (.txt) file. For the purposes of this project, wave height, dominant wave period, and wave direction were imported and analyzed with the MATLAB script named

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27 Table 2 1. Table highlighting mean high water a nd mean range for the area. Survey date, tide level and number of data points collected for St. Augustine Beach tidal station 2005; Weber et al., 2005]. Survey Date Tide Level (m) (NAVD 88) Number of Data Points Collected 1 1/16/2009 1.05 8,159 2 2/20/2009 0.75 12,025 3 3/24/2009 0.87 9,843 4 4/24/2009 1.02 10,669 5 5/22/2009 0.99 5,863 6 6/22/2009 1.14 12,386 7 7/21/2009 1.17 16,424 8 8/19/2009 1.14 1 1,996 9 9/17/2009 1.05 15,262 10 10/19/2009 0.99 11,564 11 11/18/2009 0.93 15,118 12 12/11/2009 0.93 12,364 13 1/15/2010 1.02 15,976 14 2/12/2010 0.96 12,470 St. Augustine Beach, Atlantic Ocean Mean Range = 1.35 m MHW = 0.45 m MLW = 0.9 m

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28 Fig ure 2 1 Time series of air photos illustrating ~4m/yr southward migration (net narrowing ~3m/yr) of the inlet during February 1995 January 2008. The blue dots are a consistently occupied line (later termed as the proto dune base line (PDBL)), occupyi ng the position of 100 m from the landward transect end

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29 Figure 2 2 Example of survey pattern deemed most efficient at collecting a large aerial extent of data. Various oblique transects collect northing, easting, and elevation values at each me ter along the traverse. All survey patterns are found in Appendix A 1 (Page 66)

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30 Figure 2 3. Example of scatter diagram. Each data point contains a northing and easting, while color to denotes elevation. Also shown is the dark black line that highl ights the unique polygon for this survey month. All scatter diagrams are found in Appendix A 2 (Page 86) Colorbar denotes elevation in meters (NAVD88).

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31 Figure 2 4. Example of DEM grid (1m resolution) interpolated from scatter diagram and polygon. All DEMs are found in Appendix A 3 (Page 94) Colorbar denotes elevation in meters (NAVD88)

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3 2 Figure 2 5. Figure illustrating 30 shore normal transects within the 1.5 km reach of coast directly north of Matanzas Inlet. Blue dots denote the proto dune base line (PDBL). PDBL is 100 m from the landward end of each transect.

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33 CHAPTER 3 RESULTS AND ANALYSIS In this chapter, the data compilations are presented, organized, and analyzed to address the specific research questions presented in section 1.2; namely, how does beach morphology vary within the vicinity of an inlet? More specifically, how do the shoreline positions ( beach widths) and cross shore profiles vary alongshore with respect to distance from the inlet? To do this, variations in shoreline p osition (beach width) and cross shore morphology throughout one year of observation are examined Then, wave forcing responsible is considered by correlating the changes witnessed on the beach with the offshore wave characteristics. 3.1 Shoreline Position / Beach Width 3.1.1 Spatial Variation of Shoreline Position (Beach Width) The complete record of surveyed, monthly MHW shoreline positions throughout the study reach, as well as mean shoreline position and standard deviation over the entire observation per iod, are presented in Fig ure 3 1 Beach widths are calculated by the PDBL, the morphologic feature that anchors the cross shore topographic analyses in this study. The most striking feature of Figure 3 1 is the abrupt change in shoreline position (beach width) in the vicinity of Transect 20, where the beach width more than doubles from ~40 m, in the northern portion of the reach, to ~90 m directly next to the inlet. The variability of shoreline position experiences a modest increase from the northern portion to the southern portion, as illustrated by the standard deviation values shown on Fig ure 3 1.

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34 3.1.2 Temporal Variation of Shoreline Position (Beach Wi dth) For each transect, a linear fit of shoreline position ( beach width ) through time rendered a shoreline change rate during the 14 month observation interval. Examples of these analyses, for the northern and southern portions of the study area, are provi ded in Fig ure s 3 2A and 3 2B respectively. Temporal variation plots of MHW shoreline position (beach width) for all transects can be found in Appendix A 4 (Page 108 Negative change rates denote a shoreward migration of the shoreline (beach narrowing) whereas positive change rates reflect a seaward migration of the shoreline (beach widening). The spatial summary of shoreline change rates over the observation interval is provided in Fig ure 3 3. Transects 1 17 and 23 25 reflect a beach narrowing, while transects 18 22 and 26 30 reflect beach widening over time. Values range from 11.9 cm/day (transect 13) to 14.7 cm/day (transect 28). For transects 1 17, change rates were negative, ranging from 11.9 cm/day (transect 13) to 2.1 cm/day (transect 1). T ransects 18 illustrates a change rate nearing zero (0.5 cm/day), as the shoreline variations transition from negative trends to a period of positive trends. Transects 18 22 display positive change rates, ranging from 0.5 cm/day (transect 18) to 10.6 cm/da y (transect 20). A brief aberration occurs at transects 23 25, as this portion of the inlet experiences a return to negative trends ranging from 0.3 cm/day (transect 25) to 3.4 cm/day (transect 24). Transects 26 30 return to positive change rates, rang ing from a minimum of 0.8 (transect 30), to including the greatest positive change rate in the data set of 14.7 cm/day (transect 28). Fig ure 3 4 is a histogram that shows the time at which each transect experiences maximum beach width over the survey inter val. Each bin corresponds to a survey date and contains the number of transects at which beach width was at its maximum for that

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35 interval. Transects 1 9 reach their maximum beach width during the summer months (June and July of 2009). Transects 10 19 re ach their maximums during the late winter months (February and March of 2009), with one exception during February 2010. For transects 20 30, the data do not behave consistently, as beach width maxima are reached during February 2009, July 2009, August 200 9, October 2009, November 2009, January 2010 and February 2010. 3.2 Beach Morphology / Profile Shape 3.2.1 Spatial and Temporal Variation of Cross Shore Profiles Examples of cross shore profiles for the 14 surveys are given in Fig ure 3 5A (Transect 15) an d Fig ure 3 5B (Transect 27) Also shown in Figures 3 5A and 3 5B, the cross shore distributions of temporal data coverage along each transect, and the cross shore distribution of the standard deviation of elevation along each transect. S imple observations of the cross shore profiles reveal that the northern portion of the study reach contains, generally, planar beach profiles (Transects 1 20), whereas profiles within the southern portion (Transects 21 30), adjacent to the inlet mouth, exh ibit a fair greater vertical relief. Another way of examining the time series of cross shore profile evolution is provided in Fig ure s 3 6A and 3 6B which display complete time series sets of 14 surveyed profiles at two specific transects. The cross shore topography is shown in color, and the migration of the shoreline is given as black dots. Locations of the PDBL are also provided (position 100 on all profiles), allowing for an uncomplicated display of beach width through time. The compilation of these diagrams for each of the transects is provided in Appendix A 5 (Page 138)

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36 3.2.2 Analysis of Variation of Cross Shore Profiles To better understand cross shore topographic profile variation at this site, standard deviation analyses were conducted. To account for the fact that not all profiles had equal coverage during all surveys, we establish a minimum number of observations, 10 out of 14 total surveys (71%), required to compute a meaningful standard deviation. These portions of the profiles are show n in red on the middle and lower panels of Fig ure s 3 5A and 3 5B The compilation of these diagrams is located in Appendix A 6 (Page 167) Low standard deviation values (0.01 0.44 m) reflect low variability, or a more stable profile; profiles with lo w standard deviation are typical of profiles farther from the inlet. High standard deviations (0.45 0.7 m) are characteristic of cross shore profiles where the variability about the mean is relatively high, and is typical of the profiles closer to the i nlet. Of particular interest are two characteristics of the standard deviation analyses: (1) Where are the greatest variations in elevation with respect to alongshore position within the study reach?, and (2) Where are the greatest variations in elevation with respect to cross shore position within the study reach, and how are the cross shore maxima in standard deviation distributed alongshore? These questions can be addressed by examination of Fig ure 3 7, in which both cross shore and alongshore distribut ions of temporal topographic variation are displayed as a colormap. The analysis of Fig ure 3 7 illustrates a seaward shift in the peak (maximum) standard deviation values as one moves from north to south, from lower to higher number transects, toward the i nlet. The highest standard deviation values, in the entire data set, are at the most seaward positions immediately adjacent to the inlet. At transects 1 18,

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37 the highest topographic variability occurs within 20 60 meters of the PDBL, whereas at transects 20 30, the highest topographic variability is 60 120 meters seaward of the PDBL. An isolated cloud of high variability, comparable in magnitude to the highest standard deviation values observed within the entire data set (> 0.5 m), occupies the upper beac h from transects 11 15. 3.2.3 Beach Slope Analysis Graphical examples of the MHW shoreline slope calculations, described in Section 2.3.5, are provided in Fig ure 3 8A and 3 8B for transects 15 and 27, respectively. The compilation of all slope calculati ons for each of the 389 MHW shorelines identified is provided in Appendix A 7 (Page 197) The high vertical exaggeration (75x) distorts the slope calculation, but also permits some general evaluation of beach slope change by simple inspection Fig ure 3 9 shows alongshore compilations of slopes for each survey (plotted as connected lines). In general, beach slopes are lower in the northern portion of the study reach (Transects 1 20), than in the southern portion (Transects 21 30) adjacent to the inlet. Fig ure 3 10 presents a simple temporal analysis of the beach slopes broken up into two groups according to location: the northern portion of the study reach (Transects 1 20) shown in blue, and the southern portion of the study reach (Transects 21 30) show n in red. Comparisons of the temporal means of the two groups illustrate that during the summer (July 2009, in particular), the two regions behave quite differently the northern portion steepens at the MHW shoreline, while the southern portion becomes m ore gently sloped. Also, it is striking that during the end of the observation period (Oct. 2009 Feb. 2010), the southern portion of the study reach witnesses a pronounced increase in MHW shoreline slope that is not found in the

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38 northern portion of the s tudy reach. A combined spatial and temporal analysis of the MHW shoreline beach slope is compiled as a colormap in Fig ure 3 11 3.3 Beach Response to Wave Forcing Wave data was obtained from the St. Augustine wave buoy number 41012, owned and operated by the National Data Buoy Center (NDBC). The buoy is a 3 meter discus buoy in 37.2 m of water located at Easting: 544990 and Northing: 3323463 (UTM Zone 17), off the coast of St. Augustine, Florida [ Station 41012 (LLNR 845.3) St. Augustine, FL 40NM ENE of St Augustine, FL 2011 ] Fig ure 3 12 wave heights, wave periods, and wave directions for the survey period. Also shown in Figure 3 12, are average significant wave height, average wave period, and modal wave direction for the survey interval 3.3.1 Offshore Wave Climate During Observation Period Wave heights range from 1 1.6 m during January, February, March, April, May, October, Novembe r, and December of 2009. During the quiescent summer period, wave heights range from 0.74 0.89 m, except for a storm event in August, which caused an increase in significant wave height average to 1.14 m. g the survey period. Event one was a storm that occurring around May 20, 2009. Significant wave heights of 5 m were recorded at the buoy. Additionally, there was a shift in modal wave direction from 57 degrees to 93 degrees (37 degrees and 73 degrees sh ore normal). The second event, Hurricane Bill, was a tropical depression that formed off the coast of Africa around August 15, 2009, tracked West Northwest, became a Category 4 hurricane (according to the Saffir Simpson Hurricane Scale) and dissipated A ugust 24, 2009; however, effects of the storm were recorded until August 28, 2009 as wave

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39 heights neared 3 m. The storm affected the East coast of the United States, Bermuda, Nova Scotia, and Newfoundland. Unfortunately, the buoy malfunctioned and did not record data from August 15, 2009 until August 25, 2009. Modal wave direction data for this period was recorded as 78 degrees shore normal. highly oscillatory significant wa ve heights from the end of October 2009 until February 2010. Average significant wave heights during this period ranged from 1.24 to 1.60 m, while average significant wave heights during January and February of 2009 were noticeably steadier, ranging from 0.99 to 1.17 m. 3.3.2 Shoreline Variation and Wave Height MHW shoreline position change rates, calculated as the difference of two monthly MHW shoreline positions divided by time between measurements, are plotted against average significant wave height ove r the interval between surveys. Examples are provided in Fig ures 3 13a (transect 15) and 3 13b (transect 27). Shoreline variation and wave height time series display for all 30 transects are provided in Appendix A 8 (Page 227) The most striking feature on Figures 3 13a and 3 13b are the significant wave height peak of ~1.6 m during the October/November 2009 interval. During this period, nearly all transects (except 17 22) experience a narrowing of the beach, ran ging from 0.1 to 0.4 m/day. From January through April 2009 survey period, average significant wave height increases from ~1 to 1.3 m. During this period, transects 1 7 demonstrate a similar seeming stepwise decrease in MHW shoreline position migration rate. The transition from the quiescent summer June/July/August 2009 interval to the August/September 2009 interval is interesting, in that significant wave heights jump

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40 from ~0.7 to ~1.1 m. The beach responds by narrowing in transects 1 21 and transects 24 27. Transect 18 behaves according to the accepted conceptual model of shoreline position change to wave height [ Dean, 1991]. When wave heights increase, the beach narrows. During the summer, when wave heights stabilize at relatively low heights, th e beach remains near equilibrium, hovering around 0 m/day of MHW shoreline position migration rates. Then, when wave heights increase between August and September 2009, the beach narrows, somewhat drastically, following its seemingly stable summer positio n. Wave heights calm between September/October 2009 and the beach responds by widening. Analyses of cross plots (average significant wave height vs. shoreline position migration rate of MHW) render inconsistent, yet intriguing, results. Results for two example transects (Transects 3 and 26) are provided in Fig ure 3 14, and illustrate the apparent negative correlation between the two variables. Cross plots between these two variables for each of the 30 transects can be found in Appendix A 9 (Page 257) Correlation coefficients, calculated for the proposed wave height shoreline change relationship for each of the 30 transects, are compiled in the upper panel of Fig ure 3 15. Of the 30 transects analyzed, 22 exhibit negative correlations between offsho re wave height and shoreline change. Results of the test of statistical significance ure 3 15. Of the 22 transects that exhibit a negative correlation, 7 (32%) transects have a t statistic which ex ceeds the critical t value for a statistically significant correlation at the 90% confidence limits.

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41 Fig ure 3 1 Complete record of surveyed, monthly MHW shoreline positions throughout the study reach, including mean shoreline position and standard de viation of entire observation period. The locat ion of transects are listed in F igure 2 5.

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42 Fig ure 3 2a. Temporal beach width of transect 15. A linear fit of the data rendered a change rate. Negative change rates denote a landward migration of the sho reline position.

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43 Fig ure 3 2b Temporal beach width of transect 27. A linear fit of the data rendered a change rate. Positive rates denote a seaward migration of the shoreline position.

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44 Fig ure 3 3 Spatial summary of shoreline change rates over the observation interval.

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45 Fig ure 3 4 Histogram showing time at which beach width maximum is reached

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46 Fig ure 3 5a Cross shore topographic profile variation at transect 15 illustrating the cross shore distributions of temporal coverage and cross sh ore distribution of standard deviation. A minimum number of nine surveys are required to complete a meaningful standard deviation; these are highlighted in orange.

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47 Fig ure 3 5b Cross shore topographic profile variation at transect 27 illustrating the cross shore distributions of temporal coverage and cross shore distribution of standard deviation. A minimum number of nine surveys are required to complete a meaningful standard deviation; these are highlighted in orange.

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48 Fig ure 3 6a Time series of survey profiles for transect 15. Cross shore topography is shown in color, and the migration of the shoreline is given in black dots. Colorbar denotes elevation in meters (NAVD88)

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49 Fig ure 3 6b Time series of survey profiles for transect 27. Cross sh ore topography is shown in color, and the migration of the shoreline is given in black dots. Colorbar denotes elevation in meters (NAVD88)

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50 Fig ure 3 7 Colormap illustrating cross shore and alongshore distributions of temporal topographic variation plot ted as standard deviation. Colorbar denotes standard deviation value.

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51 Fig ure 3 8a Figure illustrating MHW shoreline slope for transect 15 plotted as a trend line to the portion of the profile beginning five meters landward of MHW and five meters shor eward of MHW.

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52 Fig ure 3 8b Figure illustrating MHW shoreline slope for transect 27 plotted as a trend line to the portion of the profile beginning five meters landward of MHW and five meters shoreward of MHW.

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53 Fig ure 3 9 Alongshore compilation of MHW shoreline slopes for each survey plotted as connected lines.

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54 Fig ure 3 10 Temporal analysis of beach slopes broken up into two groups according to location. Blue denotes the northern portion (transects 1 20) of the study reach, and red denotes t he southern portion (transects 21 30) of the study reach. The green dotted line denotes the mean slope for all transects.

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55 Fig ure 3 11 Combined spatial and temporal analysis of the MHW shoreline beach slope illustrated as a colormap. Colorbar denotes beach slope.

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56 Fig ure 3 12 NDBC wave buoy 41012 data illustrating significant wave height (m), wave period (s), and wave direction (degT) during the survey interval. Bold black lines denote date at which a survey occurred. Also shown are the average wave height, average wave period, and modal direction for each survey interval [ Station 41012 (LLNR 845.3) St. Augustine, FL 40NM ENE of St Augustine, FL 2011 ].

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57 Fig ure 3 13a Temporal ana lysis of MHW shoreline position change rate plotted against average significant wave height for each survey interval at transect 15.

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58 Fig ure 3 13b Temporal analysis of MHW shoreline position change rate plotted against average significant wave height f or each survey interval at transect 27.

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59 Fig ure 3 14a Cross plot illustrating the relationship between average significant wave height and MHW shoreline position migration rate at transect 3 t test indicates that the correlation coefficie nt is statistically significant at the 90% confidence interval for this transect.

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60 Fig ure 3 14b Cross plot illustrating the relationship between average significant wave height and MHW shoreline position migration rate at transect 2 6 t tes t indicates that the correlation coefficient is statistically significant at the 90% confidence interval for this transect.

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61 Figure 3 1 5 Summary of analyses of potential correlation between shoreline change rate and offshore wave height (H S ) Upper panel shows the dominance of negative correlation coefficients over the transect series, implying a negative relationship between wave climate and shoreline change rate. Lower panel displays whose t statistic exceeds the critical t value (as determined by degrees of freedom /number of temporal observations ), have a correlation between the variables that is statistically significant at the 90% confidence limit.

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62 CHAPTER 4 DISCUSSION AND CONCLUSIONS B elow is a discussion of the results of this project. Conclusions are drawn that attempt to identify the validity of the hypothesis: tidal inlet dynamics exert a spatially limited influence on the temporal behavior of nearby shoreline position and beach mo rphology. To accomplish this, the research questions identified in section 1.2 are explicitly addressed. 4.1 Shoreline Position V ariation W ith Distance From Inlet How does the shoreline position (beach width) vary as a function of distance from an inle t? Results from this investigation indicate that s horeline position (beach width) varies considerably as a function of distance from the inlet. There is an abrupt change in beach width at a location 500 m north of the inlet T he beach width mo re th an doubles from ~40 m to ~90 m at this location Also, there is an increase in the variability of the shoreline position from a standard deviation value of ~10 m in the northern section of the study area to ~ 20 m in the southern portion of the study are a ( close to the inlet ) Therefore, the beach experiences increase s in width and width variability in the southern portion of the study area (within 500 m of the inlet ) which are likely to be associated with inlet sedimentary and hydraulic processes that control the morphology of the ebb shoal 4.2 Seasonal Variability in Shoreline Position Does the spatial variability in shoreline position (beach width) exhibit a seasonal variability ? Over the observation interval (Jan. 2009 Feb. 2010), an overall trend of b each narrowing is evident in the northern portion of the study area (at distances greater than ~650 m from the inlet ), whereas a more complex pattern is evident in the

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63 southern portion of the study area adjacent to the inlet. The portion of the beac h within ~650 m of the inlet contains two prominent areas of beach widening separated by a ~100 m band of narrowing. There is a seasonal signal between distances ~1450 m 1050 m from the inlet where beach widths reach their maximum during summer month s (June and July 2009), and between distances ~1000 m 550 m from the inlet where beach widths reach their maximum in late winter (February and March 2009). The spread in maximum beach width is difficult to characterize for the alongshore distance of 0 m 500 m from the inlet as maximum beach widths occur sporadically throughout the survey duration. Seasonal signals are more discernable for the northern portion of the study area, at distances greater than 600 m from the inlet. Sedimentary and hydraulic p rocesses associated with the inlet may be responsible for the lack of seasonal variability evident of shoreline position withi n the southern portion of the study area, at locations less than 600 m from the inlet 4.3 Beach Morphology Variation Spatial and Temporal How does beach morphology (profile shape) vary as a function of distance from an inlet? Does the spatial variability in beach morphology (profile shape) exhibit a seasonal variability? Beach morphology (profile shape) varies spatially and t emporally according to distance from an inlet. The northern portion of the study reach at distances greater than ~500 m from the inlet contain s gently sloped profiles, whereas, the southern portion of the study reach at distances within ~500 m of the i nlet contains comparatively steeper profiles. The greatest variation in topography occur s near the PBDL for the portion of the study reach greater than ~600 m from the inlet, whereas the southern portion of the study area, within ~500 m of the inlet exh ibit s increased temporal varia bility in topography towards the seaward end of the cross shore profile

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64 which can be identified as increased lower beach berm building behavior. Beach slopes are lower in the southern, portion of the study area as compared to the northern portion. During the summer months, the northern portion steepens at the MHW shoreline, whereas the southern portion becomes more gently sloped. Sedimentary and hydraulic processes associated with the inlet may influence beach morphology ( profile shape) within the southern portion of the study area 4.4 Relationship of Beach Response to Forcing How do temporal trends in shoreline position (beach width) and beach morphology (profile shape) correlate with offshore wave conditions, thought to dominate the for cing? It is difficult to discern a clear relationship between temporal trends in shoreline position and beach morphology and offshore wave conditions, from data collected in this study. Some transects (18, for example) appear to follow a proposed conceptual model relating shoreline position change rate to wave height [ Dean 1991 ], but other transects do not. This may be a result of the influence of the tidal inlet overprinting the influence of the wave forcing. The data indicate some association (negative correlation) of shoreline change with changes in offshore wave conditions; however, only 32% of the transects with negative correlation coefficients exhibited statistical significance of the proposed relationship. Henc e, the association is not strong enough to draw definitive conclusions correlating offshore wave conditions to observed shoreline position and beach morphological changes. 4. 5 Summary In summary, this study presents data that illustrate an abrupt change in the behavior of shoreline position and beach morphology at approximately 500 600m from a natural tidal inlet. A possible origin of this behavioral difference may lie in the dynamic

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65 behavior of the sedimentary and hydraulic mechanics of the subaq ueous ebb shoal on the seaward side of the tidal inlet. The presence of this bathymetric discontinuity may disrupt the pattern of longshore sediment transport, which is reflected as an alongshore inconsistency in beach behavior approximately 500 m from th e inlet. North of this inconsistency, the beach behavior can be considered to be influenced primarily by oceanic forcing, whereas south of the inconsistency, the beach is overwhelmed by the presence of the tidal inlet processes. In the future, the foll owing improvements to the project are suggested: (1) increase survey frequency (2) improve consistency of survey coverage, (3) extend observation period, as multiple years of data will provide a better handle on seasonality, and (4) gather nearshore wave d ata at multiple positions alongshore to obtain a clear signal of wave forcing in the nearshore region.

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66 APPENDIX : SUPPLEMENTARY FIG URES A 1

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287 L IST OF REFERENCES Ashton, A., A.B. Murrary, and O. Arnault (2001), Formation of coastline features by large scale instabilities induced by high angle waves, Nature 414 296 300. Aubrey, D.G (1979), Seasonal patterns of onshore/offshore sediment movement, Journal of Geophysical Research, 84 6347 6354. Booij, N., R.C. Ris, and L.H. Holthuijsen (1999), A third generation wave model for coastal regions 1. Model description and validation Journal of Geophysical Research 104 7649 7666. Dean, R.G. (1988), Sediment interaction at modified coastal inlets: processes and policies, in Hydrodynamics and Sediment Dynamics of Tidal Inlets Lecture Notes on Coastal and Estuarine Studies vol 29, edited by M.J. Bowman et al., pp. 412 439, Springer Verlag, New York. Dean, R.G. (1991), Equilibrium beach profiles: characteristics and applications, Journal of Coastal Research 7 (1), 53 84. Dolan, R., B. Hayden, and L. Vincent (1977), Sho reline forms and shoreline dynamics, Science 197 49 51. Dubois, R.N. (1988), Seasonal changes in beach topography and beach volume in Delaware, Marine Geology 81 79 96. Eliot, I.G. and D.J. Clarke (1982), Seasonal and biennial fluctuations in subaerial beach sediment volume on Warilla beach, New South Wales, Marine Geology 48 89 103. Fenster, M. and R. Dolan (1996), Assessing the impact of tidal inlets on adjacent barrier island shorelines Journal of Coastal Research 12 (1), 294 310. FitzGerald D. M. (1996), Geomorphic variability and morphologic and sedimentologic controls on tidal inlets Journal of C oastal R esearch 23 47 71. Guza, R.T. and D.L. Inman ( 1975 ), Edge waves and beach cusps. Journal of Geophysical Research 80 ( 21), 2997 3012. Hayes, M.O. (1980), General morphology and sediment patterns in tidal inlets, Sedimentary Geology 26 139 156. Komar, P.D. and D.L. Inman (1970), Longshore sand transport on beaches. Journal of Geophysical Research 75 (30), 5514 55 27.

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288 Kraft, J.C., E.A. Allen, and E.M. Maurmeyer (1978), The geological and paleogeomorphological evolution of a spit system and its associated shoal environments: Cape Henlopen Spit, Delaware, Journal of Sedimentary Petrology 48 (1), 211 226. La rson, M., Kraus, N.C. (1995), Prediction of cross shore sediment transport at different spatial and temporal scales, Marine Geology 126 111 127. List, J.H., A.S. Farris, and C. Sullivan (2006), Reversing storm hotspots on sandy beaches: spatial an d temporal characteristics, Marine Geology 226 (3 4), 261 279. Mehta, A.J., and C.P. Jones (1977), Matanzas Inlet glossary of inlets report #5, in Florida Sea Grant Program, Rep. 21 pp. 1 79, Coastal and Oceanographic Engineering Laboratory, Gainesv ille, Florida. Masselink, G., and A.D. Short (1993), The effect of tide range on beach morphodynamics and morphology: a conceptual beach model, Journal of Coastal Research 9 (3), 785 800. National Oceanographic and Atmospheric Association (2011), St. Augustine Beach, FL Station ID: 8720587 Station Information (3/16/2005), Retrieved from: http://tidesandcurrents.noaa.gov/station_info.s html?stn=8720587%20St.%20Aug ustine%20Beach,%20FL National Oceanographic and Atmospheric Association (2011), Station 41012 (LLNR 845.3) St. Augustine, FL 40NM ENE of St Augustine, FL (1/2 6/2011), Retrieved from: http://www.ndbc.noaa.gov/station_page.php?station=41012 Quartel, S., A. Kroon, B.G. Ruessink (2008), Seasonal accretion and erosion patterns of a microti dal sandy beach, Marine Geology 250 19 33. Ruggiero, P., P.D. Komar, W.G. McDougal, and R.A. Beach, (1996), Extreme water levels, wave runup and coastal erosion in Proceedings of the 25 th Coastal Engineering conference, pp. 2793 2805, American So ciety of Civil Engineers Orlando, Florida. Ruggiero, P., G. Gelfenbaum, C.R. Sherwood, J. Lacy, and M.C. Buijsman (2003), Linking nearshore processes and morphology measurements to understand large scale coastal change. In: Proceedings of Coastal Se Clearwater, Florida Ruggiero, P., R.A. Holman, and R.A. Beach (2004), Wave runup on a high energy dissipative beach, Journal of Geophysical Research, 109 C06025, doi:10.1029/2003JC002160.

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289 Ruggiero, P. and J.H. List, in press, Improvi ng accuracy and statistical reliability of shoreline position and change rate estimates, Journal of Coastal Research Ruggiero, P., M.C. Buijsman, G. Kaminsky, and G. Gelfenbaum, in press, Modeling the effect of wave climate and sediment supply variab ility on large scale shoreline change, Marine Geology Short, A.D. (1979a), Wave power and beach stages: a global model, In : Proceedings of the 16 th International Conference on Coastal Engineering 1162, Hamburg, Germany. Short, A.D ., and L.D. Wright (1981), Beach systems of the Sydney region, Australian Geographer 15 8 16. Short, A.D., and P.A. Hesp (1982), Wave, beach, and dune interactions in southeastern Australia, Marine Geology 48 259 284. Stive, M.J.F., S.G.J. Aar ninkhof, L. Hamm, H. Hanson, M. Larson, K.M. Winjber, R.J. Nicholls, and M. Capobianco (2002), Variability of shore and shoreline Evolution, Coastal Engineering, 47 211 235. Weber, K.M., J.H. List, and K.L.M. Morgan (2005), An operational mean h igh water datum for determination of shoreline position from topographic lidar data, U. S. Geological Survey Open File Report 2005 1027 Retrieved from: http://pubs.usgs.gov/of/2005/1027/index.html Winant, C.D., D.L. Inman, and C.E. Nordstrom (1975), Description of seasonal beach changes using empirical eigenfunctions. Journal Geophysical Research 80 (15), 1979 1986. Wright, L.D. (1981), Beach cut in relation to surf zone morphodynamics, In: Proceedings of the 17 th International Conference on Coa stal Engineering 996, Sydney, N.S.W. Wright, L.D. (1982), Field observations of long period surf zone oscillations in relation to contrasting beach morphologies. Australian Journal of Marine and Freshwater Research 33 181 201. Wright, L.D., J. Chappell, B.G. Thom, and J. Chappel (1978), Morphodynamic variability of high energy beaches, In : Proceddings of the 16 th Coastal Engineering Conference, American Society of Civil Engineers 1194, Hamburg, Germany. Wright, L.D. J. Chappell, B.G. Thom, M.P. Bradshaw, and P. Cowell (1979), Morphodynamics of reflective and dissipative beach and inshore systems: southeastern Australia, Marine Geology 32 105 140.

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290 Wright, L.D., B.G. Thom, and J. Chappell (1979b), Morphodynami c variability of high energy beaches, In : Proceedings of the 16 th International Conference on Coastal Engineering 1194, Hamburg, Germany. Wright, L.D., R.T. Guza, and A.D. Short (1982a), Dynamics of a high energy dissipative surf zone, Marine Geology 45 41 62. Wright, L.D., P. Nielsen, A.D. Short, and M.O. Green (1982b), Morphodynamics of a macrotidal beach, Marine Geology 50 97 128. Wright, L.D., P. Nielsen, A.D. Short, F.C. Coffey, and M.O. Green (1982c), Nearshore and su rf zone morphodynamics of a storm wave environments: Eastern Bass Strait, Australia, in Technical Report no. 82/3, Coastal Studies Unit, University of Sydney pp.154, Sydney, N.S.W. Wright, L.D. and A.D. Short (1983), Morphodynamics of beaches and surf zones in Australiam, In : KOMAR, P.D. (editor), Handbook of Coastal Processes and Erosion pp. 35 64, Boca Raton: CRC Press Wright, L.D. and A.D. Short (1984), Morphodynamic variability of surf zones and beaches: a synthesis, Marine Geology, 56 9 3 118. Wright, L.D., A.D. Short, and M.O. Green (1985), Short term changes in the morphodynamic states of beaches and surf zones: an empirical model, Marine Geology 62 339 364. Wright, L.D., A.D. Short, J.D. Boon, S. Kimball III, and J.H. List (1987 ), The morphodynamic effects of wave groupiness and tide range on a energetic beach, Marine Geology 74 1 20.

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291 BIOGRAPHICAL SKETCH Katherine Malone is originally from Annapolis, Maryland. She received a Bachelor of Arts in geological scie nce in 2008 from Mount Holyoke College, South Hadley, MA and received her Master of Science in geology from the University of Florida in the spring of 2011 Research interests include ocean waves, climate change, and barrier island and inlet morpho dynamics.