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Developing a Seawall Algorithm for the DNR Model with Application to the Oceanside, California, Coastline


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DEVELOPING A SEAWALL ALGORITHM FOR THE DNR MODEL WITH APPLICATION TO THE OCEANSID E, CALIFORNIA, COASTLINE By GABRIEL A. PERDOMO A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2004

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Copyright 2004 by Gabriel Perdomo

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ACKNOWLEDGMENTS I thank my wife for giving me her indispensable and unconditional support in every goal that I have strived to accomplish. I thank my daughter for giving me the inspiration to be a better person. I thank my parents for providing me with the morals, commitment, and attitude for excellence that has led me to achieve my childhood dreams. I thank my two sisters for making me a proud older brother. I also thank everyone who offered me assistance, guidance, and their friendship (both inside and outside the classroom) throughout my years at the University of Florida. Most of all, I would like to thank God, for He has given me all who I have mentioned above, and all the other gifts that I am so blessed to have in my life. iii

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TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES............................................................................................................vii LIST OF FIGURES.........................................................................................................viii ABSTRACT.....................................................................................................................xiii CHAPTER 1 INTRODUCTION........................................................................................................1 Overview.......................................................................................................................1 Project Scope................................................................................................................2 Enhancements to the DNR Model................................................................................3 2 SITE CHARACTERIZATION....................................................................................6 Shorelines.....................................................................................................................6 Beach Profiles...............................................................................................................7 Development of Wave Conditions................................................................................8 Tides...........................................................................................................................10 El Nino Southern Oscillation......................................................................................11 Development of Oceanside Harbor Breakwaters and Groins.....................................11 Dredging, By-passing, and Nourishment Events........................................................13 Sources/Sinks..............................................................................................................15 Rivers, Creeks, and Lagoons...............................................................................15 Background Erosion............................................................................................16 Even-odd analysis........................................................................................16 Historic shoreline change.............................................................................18 Longshore Sediment Transport...................................................................................20 North Breakwater Fillet..............................................................................................21 Historic Volume Changes...........................................................................................22 Seawalls......................................................................................................................23 Method of Defining Seawall Positions................................................................23 Description of Seawalls Found Within the Project Area.....................................24 iv

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3 DNR MODEL.............................................................................................................51 Shoreline Position.......................................................................................................51 Longshore Sediment Transport...................................................................................52 Wave Setup.................................................................................................................53 Run-up........................................................................................................................54 Overtopping Propagation............................................................................................55 Forces..........................................................................................................................55 Input Parameter Cell Definitions................................................................................56 4 SEAWALL MODEL..................................................................................................60 Theory.........................................................................................................................60 Profile Definitions...............................................................................................60 Profile Changes...................................................................................................63 Longshore Transport Modification......................................................................65 Along-shore Boundary Conditions......................................................................66 Seawall/ Nourishment Sensitivity Tests.....................................................................66 Case 1: One Seawall, No Nourishments.............................................................67 Case 2: No Seawalls, One Nourishment.............................................................68 Case 3: One Seawall, One Nourishment............................................................69 Case 4: Two Seawalls, One Nourishment..........................................................71 5 OCEANSIDE MODEL DATA..................................................................................88 Input............................................................................................................................88 Main Input File....................................................................................................88 Constants.............................................................................................................88 Total Depth..........................................................................................................89 Groins..................................................................................................................89 Initial Shoreline...................................................................................................90 Nourishment........................................................................................................92 Seawalls...............................................................................................................93 Sources/Sinks......................................................................................................94 Waves..................................................................................................................96 Background Erosion..........................................................................................100 Output.......................................................................................................................100 6 RESULTS.................................................................................................................110 Sensitivity Analysis..................................................................................................110 Alongshore Wave Variation..............................................................................111 Fill Factor..........................................................................................................111 Offshore Loss Coefficient.................................................................................112 v

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Calibrated Shoreline Planform Results.....................................................................112 Historical Runs..................................................................................................113 Forecast Results.................................................................................................114 Damage Comparisons...............................................................................................116 7 CONCLUSIONS......................................................................................................129 LIST OF REFERENCES.................................................................................................131 BIOGRAPHICAL SKETCH...........................................................................................134 vi

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LIST OF TABLES Table page 2-1. Tide level record at the NOAA/NOS/CO-OPS La Jolla Tide Gage.........................29 2-2. Nourishment dates, locations, and volumes (yd 3 ) within the project area...............30 2-3. Sediment discharge rates by rivers and streams (yd 3 /yr)..........................................31 2-4. Location and sediment contributions used in the DNR simulations for the Santa Margarita River, the San Luis Rey River, and the Loma Alta Creek......................31 2-5. Shoreline change rates north of Oceanside Harbor..................................................32 2-6. Shoreline change rates south of Oceanside Harbor..................................................32 2-7. North fillet volume accumulation rates....................................................................32 2-8. Volume change rates................................................................................................32 4-1. Input parameters for seawall sensitivity test cases...................................................74 5-1. Cross-shore location and effective lengths of breakwaters and groins along the Oceanside coastline................................................................................................101 5-2. Seawall input parameters for the Oceanside and Carlsbad shorelines...................102 5-3. Source/sinks at the north and south breakwaters....................................................104 vii

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LIST OF FIGURES Figure page 1-1. Overview of site..........................................................................................................4 1-2. Oceanside Beach at the Oceanside Municipal Pier....................................................5 2-1. Three historical reference shorelines for the Carlsbad, Oceanside, and Camp Pendleton coast......................................................................................................33 2-2. Comparison of the equilibrium beach profile used in the DNR model to an actual SANDAG profile of the Oceanside coastline........................................................33 2-3. The nine wave gages and the 90 computational sites used to create the 50 wave records....................................................................................................................34 2-4. Mean wave height and mean period for each of the nine BOR wave gages............35 2-5. Maximum wave height by station for the 50 wave records......................................35 2-6. Mean local wave angle with respect to the local shoreline orientation for the 50 wave records at the nine wave gages.....................................................................36 2-7. Chronological development of Del Mar Boast Basin and Oceanside Small-Craft Harbor....................................................................................................................37 2-8. Nourishment placements and times for beaches downcoast of Oceanside Harbor..38 2-9. Timeline of significant historical events that occurred along the project area coastline.................................................................................................................39 2-10. Comparison of the actual initial 1934 and final 1998 shorelines...........................40 2-11. Total change in shoreline position from May 1934 to April 1998.........................40 2-12. Results of the even-odd analysis from 1934 to 1998 for the Oceanside coastline.41 2-13. Even-odd analysis results and background erosion rates north and south of Oceanside Harbor complex from 1934 to 1972.....................................................41 2-14. Even-odd analysis results and background erosion rates north and south of Oceanside Harbor complex from 1972 to 1998.....................................................42 viii

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2-15. MSL shoreline position in 1934, 1972, and 1998...................................................42 2-16. Average annual rate of change between the 1934, 1972, and 1998 shorelines......43 2-17. California Coastal Record Project, Image 9032. Parking area at the southern end of Carlsbad State Beach adjacent to the north Agua Hedionda discharge jetty.....43 2-18. Maptech Mapserver image of the Agua Hedionda discharge jetties and Carlsbad State Beach.............................................................................................................44 2-19. California Coastal Record Project, Image 9017. Rocky cliffs just north of the elevated concrete walkway that spans Carlsbad State Beach................................45 2-20. California Coastal Record Project, Image 9011. Erratic portion of seawall along Carlsbad.................................................................................................................45 2-21. California Coastal Record Project, Image 9005. Armoring at The Point, Carlsbad, and Buena Vista Lagoon discharge point..............................................................46 2-22. California Coastal Record Project, Image 9002. Well-organized rubble seawall that spans from Buena Vista Lagoon to Loma Alta Creek, Oceanside.................46 2-23. California Coastal Record Project, Image 8985. South Pacific Street bridge crossing over Loma Alta Creek discharge point, Oceanside.................................47 2-24. California Coastal Record Project, Image 8971. Well-organized portion of rubble seawall that spans north of Loma Alta Creek to The Strand, Oceanside...............47 2-25. California Coastal Record Projects Aerial Photograph, Image 8963. Emergency Revetment along The Strand, Oceanside...............................................................48 2-26. California Coastal Record Projects Aerial Photograph, Image 8952. North Pacific Street curb along The Strand that acts as a landward erosion barrier, Oceanside...............................................................................................................48 2-27. California Coastal Record Project, Image 8948. Timber and rubble rip-rap seawall that armors North Coast Village, Oceanside.............................................49 2-28. California Coastal Record Project, Image 8946. North Pacific Street bridge crossing over the San Luis Rey River discharge point, Oceanside........................49 2-29. California Coastal Record Project, Image 8944. North Pacific Street curb landward of Oceanside Small Craft Harbor, Oceanside........................................50 3-1. Possible changes in sediment amounts within a cell................................................59 4-1. Critical volume, V c per unit width. The critical volume is the entire area shown in brown.....................................................................................................................75 ix

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4-2. Volume per unit width for an aerial beach seaward of the seawall (y N y sw )..........75 4-3. Initial volume per unit length for a seawall in the surf zone (y N < y sw )....................76 4-4. Volume change for a fictitious shoreline retreat with locations shown in both global and local coordinates..............................................................................................76 4-5. Total sediment transport fronting a seawall for four planar beach slopes and several wave conditions.....................................................................................................77 4-6. Graphical representation of positive transport and y sw (I) < y N (I-1) at the start of the seawall....................................................................................................................78 4-7. Input parameters for Case 1......................................................................................78 4-8. Case 1b: One seawall, no nourishment. Shoreline evolution.................................79 4-9. Case 1b: One seawall, no nourishment. Shoreline position by cell........................79 4-10. Input parameters for Case 2....................................................................................80 4-11. Case 2a: No seawall, one nourishment, no breakwater. Shoreline evolution......80 4-12. Case 2a: No seawall, one nourishment, no breakwater. Shoreline position by cell.81 4-13. Case 2b: No seawall, one nourishment, one breakwater. Shoreline evolution.....81 4-14. Case 2b: No seawall, one nourishment, one breakwater. Shoreline position by cell..........................................................................................................................82 4-15. Input parameters for Case 3....................................................................................82 4-16. Case 3a: One seawall, one nourishment, no breakwater. Shoreline evolution.....83 4-17. Case 3a: One seawall, one nourishment, no breakwater. Shoreline position by cell..........................................................................................................................83 4-18. Case 3b: One seawall, one nourishment, one breakwater. Shoreline evolution...84 4-19. Case 3b: One seawall, one nourishment, one breakwater. Shoreline position by cell..........................................................................................................................84 4-20. Input parameters for Case 4....................................................................................85 4-21. Case 4a: Two seawalls, one nourishment, no breakwater. Shoreline evolution..85 4-22. Case 4a: Two seawalls, one nourishment, no breakwater. Shoreline position by cell..........................................................................................................................86 x

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4-23. Case 4b: Two seawalls, one nourishment, one breakwater. Shoreline evolution.86 4-24. Case 4b: Two seawalls, one nourishment, one breakwater. Shoreline position by cell..........................................................................................................................87 5-1. May 1934 shoreline and straight initial shoreline..................................................105 5-2. Sediment budget north and south of Oceanside Harbor.........................................105 5-3. OReilly hindcast wave gage locations and approximate -12-m contour...............106 5-4. Mean peak wave angle and mean effective wave angle from the 50 wave records for each of the nine wave station.........................................................................106 5-5. Depth contours along the study area shown in 5-fathom intervals.........................107 5-6. The shore normal direction used in the OReilly wave computations and the shore normal directions determined from the 1934, 1972, and 1998 surveys...............108 5-7. Mean peak wave angle and mean effective wave angle results from the wave transformation to the 1934 shoreline orientation.................................................108 5-8. The local wave angle with respect to the 1934 shoreline for all the OReilly wave calculation locations within the study area..........................................................109 6-1. RMS error between the predicted and the measured shorelines south of the harbor in 1972, 1998, and for both combined based on the V-shaped wave angle variation as a function of the local wave angle at Agua Hedionda Lagoon........118 6-2. RMS errors for different fill factors and different values of offshore loss coefficients, c.......................................................................................................119 6-3. The RMS error as a function of LST rates for various offshore loss coefficients..120 6-4. Shoreline planform results referenced to the actual 1934 initial shoreline............121 6-5. Annual shoreline change rates................................................................................122 6-6. Historical shoreline evolution.................................................................................123 6-7. Historical shoreline planform evolution without breakwaters for waves developed with the harbor presence......................................................................................124 6-8. Historical shoreline planform evolution without breakwaters for wave angles adjusted to remove harbor effects........................................................................124 6-9. Forecast final shoreline position with breakwaters................................................125 6-10. Forecast shoreline evolution with breakwaters....................................................125 xi

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6-11. Forecast final shoreline position if breakwaters were removed in 1998..............126 6-12. Forecast shoreline evolution if breakwaters were removed in 1998....................126 6-13. Forecast final shoreline position if breakwaters never existed.............................127 6-14. Forecast shoreline evolution if breakwaters never existed...................................127 6-15. Forecast monthly overtopping events with breakwaters, removing breakwaters in 1998, and if breakwaters never existed................................................................128 xii

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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 DEVELOPING A SEAWALL ALGORITHM FOR THE DNR MODEL WITH APPLICATION TO THE OCEANSIDE, CALIFORNIA, COASTLINE By Gabriel A. Perdomo May 2004 Chair: William G. McDougal Cochair: Robert G. Dean Major Department: Civil and Coastal Engineering The Oceanside Littoral Cell spans the southern coast of California from La Jolla Canyon to Dana Point. Our study examined the portion of the Oceanside Littoral Cell from Agua Hedionda Lagoon in Carlsbad, to a point 14.5 km (9.0 mi) north of the Oceanside Harbor along the Camp Pendleton shoreline. The coastline along this reach has historically experienced a variety of changes (including construction of the Oceanside Harbor, urbanization of coastal lands, changes in sediment supply, coastal stabilization structures, and sand removal and placement) that have significantly influenced the shoreline position. Our objective was to estimate the shoreline impacts attributable to Oceanside Harbor by applying the DNR model. To accomplish this, shoreline characteristics within the project area were defined. A seawall algorithm (that tracks volume change and then solves for the shoreline position) was added to the DNR model. Verification results for the seawall algorithm are given. Wave run-up, bore propagation, and force calculations were also added to the DNR model. Shoreline evolution and xiii

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damage results were examined for 50 different wave cases for two 60-year forecast simulations with and without breakwaters. Results for the with-breakwater case show that if current natural processes and human practices continue into the future, the shoreline will erode back to the seawall, causing progressively more overtopping and damage events along the Oceanside coastline. Results for the no-breakwater forecast case give significantly less damage, and show the shoreline stabilizing to a future equilibrium position that is shaped somewhat like the 1934 measured shoreline. xiv

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CHAPTER 1 INTRODUCTION Overview The Oceanside littoral cell spans the southern coast of California from La Jolla Canyon to Dana Point. This cell is 86.1 km (53.5 mi) long, and is defined by natural coastal features such as rivers, creeks, lagoons, and cliffs; as well as man-made features including beach nourishments, seawalls, groins, jetties, and breakwaters. This study examines only a portion of the Oceanside Littoral Cell. The project area includes the shorelines of Carlsbad, Oceanside, and Camp Pendleton. The southern boundary is the north Agua Hedionda Lagoon discharge jetty, in Carlsbad. This structure is approximately 8.5 km (5.3 mi) south of Oceanside Harbor. The northern boundary is approximately 14.5 km (9.0 mi) north of the Oceanside Harbor, along the Camp Pendleton shoreline. Over the past 60 years, the coastline along this reach has experienced a variety of changes. The most significant change was the construction of the Del Mar Boat Basin in 1942, and the subsequent expansions to form what is now Oceanside Harbor. Other factors that contributed to shoreline change include a decrease in sediment supply, coastal stabilization structures, and sand removal and placement. Oceanside Harbor and its protecting structures have had a significant influence on the shoreline. Construction of the Del Mar Boat Basin in 1942 was a major littoral barrier to the downdrift beaches. The updrift breakwater of the Del Mar Boat Basin began trapping sediment, and a fillet developed north of the harbor. The fillet increased 1

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2 in size, and sediment attempted to bypass the harbor. Meanwhile, urbanization of coastal lands and construction of flood control structures decreased the sediment discharge from the Santa Margarita and San Luis Rey rivers into the Oceanside littoral system. The trapping of littoral material by the harbor and the reduction of river sediment supply have been attributed to severe erosion on the beaches downcoast of Oceanside Harbor. To reduce erosion damage, shoreline stabilization structures were constructed along the Oceanside and Carlsbad coastlines (USACE, 1991c). Aerial photography of the Oceanside area is available before 1942. These historical photographs show the shoreline before significant human intervention. Figure 1-2 shows the Oceanside Pier in June 1938 and January 1953 (11 years after the initial construction of the Del Mar Boat Basin). The two photographs are shown at a similar scale. The pier is longer in 1953 than in 1938 because of the reconstruction and lengthening of the pier in 1947 after its partial destruction by a storm in 1942. Comparison of the two photographs indicates significant shoreline recession. Project Scope Our general objective was to estimate the shoreline impacts attributable to Oceanside Harbor. The historical influence of the breakwaters was examined with the DNR model to estimate harbor impact on the coastline relative to a no breakwater condition. Results yield the influence of sediment volume trapped by the north breakwater and long-term shoreline position changes. For lack of necessary data over the past 70 years, certain historical conditions and their components (including wave height and direction, river contributions, dredging, bypassing, beach nourishments, bluff erosion, and water levels) had to be synthesized. As a result, the model predicts the

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3 relative long-term results for conditions with and without breakwaters, as opposed to a detailed outcome. Damage attributable to the harbor can then be determined by comparing damage results with and without harbor processes. Shoreline modeling determined the historical influence of the breakwaters and estimated the damage events 50 years into the future with and without the harbor present. Completion of these objectives involved the following tasks: Determining wave and water-level conditions for the period of simulation Determining sediment sources, sinks, dredging, bypassing, and nourishments Developing information on initial shoreline configuration, description of structures, beach profiles, and sediment characteristics Specifying a damage-cost function related to calculated hydrodynamic responses Using a Monte Carlo simulation to determine the statistical estimates of responses. Enhancements to the DNR Model To accomplish these goals, the DNR model had to be modified to allow for the inclusion of seawalls and revetments in the study area. The seawall routine allowed the DNR model to more realistically model shoreline responses for armored beaches. Development of the seawall algorithm was a major component of our study. Therefore, development and verification of the seawall routine is described in detail. A subroutine was also added to the DNR model to quantify the damage resulting from overtopping events at seawalls. This routine calculated run-up, bore propagation behind the seawall, and the forces on a vertical-faced structure.

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4 Figure 1-1. Overview of site. U.S. Army Corps of Engineers (USACE), Los Angeles District (1994), Oceanside Shoreline, Oceanside, San Diego County California: Chapter 2.0 The Study Area, Reconnaissance Report, Main Report, pp. 2-2.

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5 Figure 1-2. Oceanside Beach at the Oceanside Municipal Pier. A) June 1938. B) January 1953.

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CHAPTER 2 SITE CHARACTERIZATION This chapter discusses the physical characteristics of the study area (including shoreline position; beach profiles; wave climate; tides; El Nino; Oceanside Harbor breakwaters and groins; dredging, by-passing, and nourishment events; sources and sinks; background erosion; north breakwater fillet formation; historical volume changes; and seawalls). This chapter presents findings from previous studies performed along this coastline, and procedures used to define these characteristics for use in the DNR model. Shorelines The U.S. Army Corp of Engineers, Los Angeles District, provided three measured shorelines for the study area: 1) 1934 pre-harbor shoreline, 2) 1972 shoreline, and 3) 1998 shoreline (Ryan, 2002). These shorelines were referenced to a baseline located approximately 650 m (2,100 ft) inland of the shoreline at the Agua Hedionda discharge jetties in Carlsbad. The baseline has a bearing of 325. The 1934 shoreline was digitized from three U.S. Coast and Geodetic Survey sheets. The surveys were performed between March 1934 and May 1934 in three sections from Carlsbad to San Mateo Point: Carlsbad to Santa Margarita River; March to April 1934. Hydrographic Survey #5648. Santa Margarita River to Las Flores; April to July 1934. Hydrographic Survey #5606. Horno Canyon to San Mateo Point; May 1934. Hydrographic Survey #5605 6

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7 This shoreline is assumed to be Mean Tide Level (MTL). The USACE (Ryan, 2003) provided the 1972 shoreline, which was with respect to mean sea level (MSL). Plan views of survey plots were scanned and analyzed. The 1998 shoreline was taken from a LIDAR survey conducted in April 1998 and represents the shoreline referenced to MTL. The southern boundary of the study area is located the north Agua Hedionda discharge jetty. The northern boundary is located 24.1 km (15.0 mi) upcoast of the Agua Hedionda discharge jetty, which is approximately 14.5 km (9.0 mi) north of the Oceanside Harbor Complex in Camp Pendleton. The 1934 and 1998 shorelines surveys extended past the northern boundary. However, the 1972 shoreline survey stopped approximately 4 km (2.5 mi) short of the upper boundary. Figure 2-1 shows the three shorelines. These will be discussed later in greater detail. Beach Profiles In the DNR model, the beach profile is defined by the Brunn/Dean equilibrium beach profile. The equilibrium profile is based on constant wave energy dissipation per unit volume of surf zone. This profile definition has been well documented and widely used in coastal engineering, and is given as 23hAy (2.1) where h is the still water depth along the profile, A is the profile coefficient related to the sediment diameter, and y is the cross-shore distance along the profile (Dean and Dalrymple, 2002). Figure 2-2 shows a comparison between a SANDAG profile representative of the Oceanside coastline and the Brunn/Dean equilibrium profile. The figure shows that the equilibrium beach profile provides a good fit to the SANDAG profile.

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8 Development of Wave Conditions O'Reilly (2004) developed the wave conditions. The waves were estimated from statistical analyses of historical wave data. The primary source of these data was the Coastal Data Information Program (CDIP) buoy located offshore of Oceanside. The wave records only spanned five years of measurements, which is short for the development of 50-year wave records. The data were subdivided into three wave groups: 1) north swell, 2) south swell, and 3) local seas. Each of these was analyzed as an independent population and then further categorized by the season (fall, winter, spring, or summer) and whether the event was during an El Nino year. For each of these groups, typical storm hydrographs were developed. The magnitude of the hydrograph was changed to correspond to different magnitude events. The magnitudes of the events were selected in accordance with the extreme value statistics for the specific population. The wave simulations algorithm proceeded in the following order and repeated every hour for 50 years to generate a 50-year wave record: Determining if an El Nino year Determining season. Making a Monte Carlo selection of the event magnitudes for each population. Generating the wave hydrographs. Superimposing the hydrographs into a single wave time series. Transforming the waves to the -12-m (-40-ft) contour. The initial plan for the shoreline model was to use predicted waves at a number of locations along the study area to drive the longshore sediment transport (LST). Nine stations, determined by taking the average of ten alongshore locations near the stations

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9 along the -12-m (-40-ft) contour, were selected that spanned the study area. The locations of the nine wave stations and the 90 computation sites are shown in Figure 2-3. Figure 2-4 shows the mean values of each of the 50-year wave records (438,000 individual wave conditions) for the nine wave stations. The study area is located from alongshore distance x = 0 to 24,100 m (0 to 79,000 ft) in Figure 2-4. The two heavy, vertical, black lines mark the location of the Oceanside Harbor breakwaters. The mean significant wave heights and mean peak periods are nearly constant along the study area. The average significant wave height is 0.66 m (2.2 ft) and the average peak period is 10.7 s. South of the Agua Hedionda discharge jetty, the wave heights and periods decrease because of the Carlsbad Canyon. However, these decreases are only 8% of the mean significant wave height and 7% of the average peak period. The maximum wave heights for each 50-year time series are shown in Figure 2-5. The average maximum is 6.2 m (20.3 ft) with little variation in the alongshore direction. Figure 2-6 shows the mean local wave angle with respect to the local shoreline orientation. This figure shows that significant variations exist in the local wave angle. North of the harbor, the local wave angle varies from -2 to -11. Local wave angles are defined such that negative angles drive the LST to the south. The LST is approximately linear with respect to the wave angle for small wave angles with a constant wave height. A wave angle change from -2 to -11 results in a variation in LST by more than a factor of five. The historical shorelines north of the harbor do not support this large variation in longshore transport. South of the harbor there is a 6 variation in the local wave angle. This variation south of the harbor is more probable and could be associated with the Carlsbad Canyon.

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10 Using the wave time series with the wave heights, periods, and local wave angles characterized in Figures 2-4 and 2-6 does not lead to reasonable shoreline predictions. The waves have a significant amount of longshore variation that can result in local convergences and divergences in the LST. As a result, necessary modifications were made to the wave data to achieve realistic shoreline modeling results. These modifications are discussed in Chapter 5. Tides Tides along the southern California coastline are of the mixed semi-diurnal type, consisting of two high and two low tides each of different magnitude (USACE, 1994a). The tidal characteristics for La Jolla (Latitude: 32 52.0' N, Longitude: 117 15.5' W), referenced to mean lower low water, are shown in Table 2.1. These data are a result of 18 years of measurements at La Jolla by the National Oceanic and Atmospheric Administration (NOAA). At La Jolla, a difference of 0.02 ft exists between MTL and MSL. Therefore, MSL and MTL will be assumed equal for this project. NOAA 1 provides the harmonic constituents to calculate the tide. These are the amplitude, epoch, and the speed for each component. Amplitude is one-half the range of a tidal constituent in meters, epoch is the phase lag of the observed tidal constituent relative to the theoretical equilibrium tide in degrees referenced to UTC (GMT), and speed is the rate change in the phase of a constituent, expressed in /hr. The speed is equal to 360 divided by the constituent period expressed in hours. The tide is then computed as follows, 1 NOAA/NOS/CO-OPS Water Level Data Retrieval Page (http://co-ops.nos.noaa.gov/cgi-bin/co-ops_qry_direct.cgi?stn=9410230+LA+JOLLA%2C+PACIFIC+OCEAN+%2C+CA&dcp=1&ssid=WL&pc=P2&datum=NULL&unit=0&bdate=20030201&edate=20030201&date=1&shift=0&level=-4&form=0&host=&addr=68.18.240.2&data_type=har&format=View+Data)

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11 (2.2) =1Tide{cos[()()]}IiiiAstE i where A i is the amplitude (m), s i is the speed (/hr), t is the time (hrs), and E i is the epoch (). These values are given for each tidal component. El Nino Southern Oscillation The El Nino Southern Oscillation (ENSO) episodes are inter-annual large-scale oscillations in circulation and temperature distribution occurring in the Pacific Ocean. El Nino occurrences last from one to three years and occurred approximately every 14 years on average for the past century. Analyses suggest that ENSO episodes create a +0.3 m (+1 ft) tidal departure. ENSO periods increase the probability of experiencing more severe winter storms, and as a result, increase the likelihood of coincident storm waves and higher storm surge (USACE, 1994a). In the model, the MSL is increased +0.3 m (+1 ft) during ENSO episodes. Development of Oceanside Harbor Breakwaters and Groins The Oceanside coastline features several jetties, groins, and breakwaters. Initial construction of the harbor included two converging breakwaters extending offshore to the -6-m (-20-ft) contour. The north breakwater was 640 m (2,100 ft) long and the south breakwater was 396 m (1,300 ft) long. In 1957, these two breakwaters were extended to reduce the rate of sediment accumulation within the harbor. The upcoast breakwater was extended approximately 274 m (900 ft) on the same alignment and another 427 m (1,400 ft) in the down coast direction bringing its total length to 1,325 m (4,350 ft). The downcoast breakwater had 76 m (250 ft) removed from its seaward end and was then rebuilt 115 m (380 ft) bringing the total length to 433 m (1,420 ft) (Clancy, 1972).

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12 After 1960, shore-perpendicular structures downcoast of the Del Mar Boat Basin were built to control the flow of sediment near the harbor. In 1961, a 120 m (400 ft) long groin extending 90 m (300 ft) into the ocean at the upcoast side of the San Luis Rey River was built. From March to June of the same year, the south jetty of the recently constructed Oceanside Small-Craft Harbor complex was constructed to a length of 266 m (873 ft); and in 1962, the south jetty was lengthened on the shoreward end 39 m (127 ft). Also in 1962, the 216 m (710 ft) north groin was built. This structure was a submerged groin that formed the upcoast side of the entrance channel to the Small Craft Harbor. In July 1968, the south groin at the San Luis Rey River was extended approximately 158 m (518 ft) bringing its total length to 280 m (918 ft) (Clancy, 1972). In 1973, the south jetty was extended 114 m (375 ft) seaward bringing its total length to 419 m (1,375 ft). Figure 2-7 shows a chronological summary of the harbor development. Structures were also constructed on Oceanside Beach. In 1952, two 76-m (250-ft) long groins were built on Oceanside Beach extending out to the mean sea level. One was located at the south property line of Wisconsin Avenue and the other was located 305 m (1,000 ft) downcoast of Wisconsin Avenue (Clancy, 1972). The rubble rip-rap base of the Oceanside Municipal Pier may also act as a groin during high-energy storm events. Presently, the only structures having a significant effect on the longshore littoral transport in the Oceanside area are the north breakwater and south breakwater (the new south jetty) at Oceanside Harbor, the south groin just north of the San Luis Rey River, and potentially the base of the Oceanside Municipal Pier during significant storm events (USACE, 1994b). These structures are all rock rubble mound structures.

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13 Dredging, By-passing, and Nourishment Events The years immediately after the initial construction of the Del Mar Boat Basin were characterized by drastic changes in shoreline position north and south of the harbor. Sediment accumulated in a fillet north of the north breakwater. On the beaches south of the harbor, erosion became a problem. Furthermore, a shoal developed across the entrance channel to the harbor decreasing its depth and width. With time, it became apparent that to maintain the channel at its design dimensions and to prevent erosion damage to the beaches downcoast, sand would have to be artificially by-passed around the harbor (Clancy, 1972). The construction of the Del Mar Boat Basin began in 1942 and marked the beginning of a number of dredgings that would occur at this site. The initial cutting of the harbor required the removal of 1,150,000 m 3 (1,500,000 yd 3 ) of sediment. The U.S. Navy conducted a second dredging in 1945, removing 167,000 m 3 (219,000 yd 3 ) of sediment from the entrance channel. The material from these two dredgings was taken to an inland disposal site. In 1957, the U.S. Navy once again dredged material from the harbor entrance. The 612,000 m 3 (800,000 yd 3 ) of removed sediment was placed on the downcoast beaches from approximately 9 th Street to 6 th Street to alleviate some severe erosion problems that were threatening the street and sewer line (Clancy, 1972). This marked the first by-passing of sediment from the harbor to Oceanside Beach. Table 2-2 summarizes the nourishment dates, locations, and volumes for beaches downcoast of the harbor. Figure 2-8 shows the location and times of all nourishments in the project area. Starting in 1960, sediment was regularly by-passed to beaches south of the harbor. In 1963, the Army Corp of Engineers completed the construction of the Oceanside Small

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14 Craft Harbor. The total material dredged from the site was approximately 2,900,000 m 3 (3,800,000 yd 3 ), which was placed on the downcoast beaches. Nourishment placement patterns along Oceanside beach have varied since they began in 1957. The source of sediment for the following nourishments was Oceanside harbor. Before 1971, the center of gravity of by-passed sediment was located about 2.1 km (7,000 ft) downcoast the south breakwater near the Oceanside Municipal Pier (USACE, 1991b). These are shown in red in Figure 2-8. From 1971 to 1990, the center of gravity of the beach nourishments was positioned approximately 3.4 km (11,000 ft) downcoast of the south breakwater seaward of Hayes Street (USACE, 1991b). These are shown in blue in Figure 2-8. In 1992 and 1993, two nourishments were placed seaward of Tyson Avenue, which is approximately 2.4 km (8,000 ft) downcoast from the south jetty. From 1995 to 1998, the dredged material was placed nearshore in -4.6 to -7.6 m (-15 to -25 ft) of water depth seaward of Oceanside Boulevard, which is approximately 4.0 km (13,000 ft) south of the south jetty. Sediment dredged from the harbor and placed on the beaches from 1999 to 2003 was again placed seaward of Tyson Avenue on Oceanside Beach (Ryan, 2003). The Tyson Avenue nourishments are shown in green and the nearshore Oceanside Boulevard nourishments are shown in orange in Figure 2-8. From 1995 to 2001, several nourishments took place on the beaches within the project area where the sediment source was not from Oceanside Harbor. In June 1995, sediment was taken from the Santa Margarita River Desiltation project and placed seaward of Oceanside Boulevard. In March 1997, sand was taken from an inland source as part of the Sand-for-Trash project and placed seaward of Oceanside Boulevard. In

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15 September 1997, the US Navy Homeporting project took sand from North Island and nourished the beach seaward of Oceanside Boulevard (Coastal Frontiers Corporation, 2003). These three nourishments are shown in black in Figure 2-8. In 2001 sediment was taken from an offshore borrow pit and placed along Carlsbad and Oceanside beaches for the SANDAG nourishment project. These were the only two SANDAG beach nourishments that occurred in our project area, and they are shown in gray in Figure 2-8. From 1988 to 1999, six nourishments were placed on Carlsbad State Beach as sediment was back-passed from the Agua Hedionda discharge channel (Coastal Frontiers Corporation, 2003). These nourishments were placed from Acacia Avenue to Oak Avenue and are shown in purple in Figure 2-8. Sources/Sinks Rivers, Creeks, and Lagoons During the period before the construction of the Del Mar Boat Basin, rivers, streams, and lagoons served as significant sources of sand to the littoral system after major storm and flood events (USACE, 1991a). However, urbanization of the upper watersheds and the implementation of flood control systems reduced the amount of sediment carried into the littoral system from these potential sources. The two major rivers in the project area are the San Luis Rey River and the Santa Margarita River. During the time period between 1900 and 1938, the deltas of the Santa Margarita and the San Luis Rey Rivers built the beach seaward (USACE, 1991a). Recently, these rivers have not contributed significant amounts of sediment to the littoral system. Other smaller potential sediment sources within the project area are Loma Alta Creek and Buena Vista Lagoon. As with the Santa Margarita and the San Luis Rey Rivers, these other contributors have seen a dramatic decrease in their discharge rates

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16 since the construction of the harbor because of urbanization and a reduction in major storm events. Table 2-3 provides a summary of sediment contribution estimates from several studies performed on the Oceanside littoral cell. The river sources used in the DNR simulations include the Santa Margarita River, San Luis Rey River, and Loma Alta Creek. The values listed in Table 2-3 from the various studies were averaged to determine the representative sediment contribution to the littoral system from the Santa Margarita River and the Loma Alta Creek. However, for the San Luis Rey River, the two studies that concluded a sediment contribution of 268,000 m 3 /yr (351,000 yd 3 /yr), which seems excessively disproportionate to the values used in previous studies of the Oceanside coastline, were discarded and the remaining values were averaged. Buena Vista Lagoon was not considered a sediment source, as it does not contribute sediment into the littoral system because of the weir that was constructed at its discharge point to artificially maintain the lagoon at 1.8 m (5.8 ft) above mean sea level (USACE, 1994a). The locations and final values used for the three sediment sources are listed in Table 2-4. Background Erosion Background erosion is a long-term coastal phenomena resulting in chronic shoreline retreat. The coastline at Oceanside has experienced background erosion over the past 70 years. This section discusses methods for quantifying background erosion and shoreline recession for use in the DNR model. Even-odd analysis The analyses are based on the three shorelines discussed above in the Shoreline Position section of this chapter. Figure 2-10 shows the measured shorelines for 1934 and 1998 north and south of the harbor at Oceanside where two things become evident.

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17 First, the breakwaters at the harbor act as a littoral barrier to the longshore sediment transport. The net transport is to the south causing impoundment of sand north of the harbor and erosion to the south beaches. Second is that north of the harbor in Camp Pendleton, the shoreline has retreated in the past 60 years in spite of the fillet that has formed because of the north breakwater (Figure 2-11). The recession that has occurred north of the harbor shows that the coastline within the project area (north and south of the harbor) has experienced background erosion. An even-odd analysis is used to separate the effects of the harbor and the background erosion (Dean and Dalrymple, 2002). The purpose of the even-odd analysis is to separate out those shoreline changes that are symmetric about a point on the coastline (and probably not attributable to the structure) and those that are attributable the presence of the coastal structure (Dean and Dalrymple, 2002). The analysis separates shoreline changes, y s into an even and an odd function, y e (x) and y o (x) respectively, where the x-axis is the alongshore axis. For a specific distance north of the north breakwater, +x, and the same distance to the south of the south breakwater, -x, the even values of shoreline position change are the same, y e (+x) = y e (-x). For the odd component, y o (+x) = -y o (-x). The even function approximately represents the ongoing changes in shoreline position in the absence of a coastal feature, and the odd function approximates the change in shoreline associated with the coastal feature. The total change in shoreline position at any location along the coast is the sum of the even and the odd functions: ()()()seoyxyxyx (2.3) Results for the even-odd analysis using the changes in shoreline position from 1934 to 1998 are shown in Figure 2-12. The even function (shown in red) shows that erosion,

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18 not attributable to the structures, occurred during this time period along the natural shoreline north of the harbor and along Oceanside beach. The shoreline changes attributable to the harbor are seen in the odd function (shown in blue) with accretion north of the harbor and erosion south of the harbor. In conclusion, the coastline within the study area has experienced background erosion. Incorporating the intermediate 1972 shoreline into the even-odd analysis allows for a comparison of background erosion from 1934 to 1972 and then from 1972 to 1998. To make a direct comparison, the total background erosion for each time period was converted into annual recession rates. Figures 2-13 and 2-14 show results for the even-odd analysis and the recession rates for the two time periods. These two figures show that most of the background erosion that occurred from 1934 to 1998 actually occurred from 1934 to 1972. Historic shoreline change The Camp Pendleton shoreline north of the harbor, beyond the range of influence of the north breakwater, has experienced minor human intervention. This section of the coast provides an indication of the historical natural shoreline response for the project area. Figure 2-15 shows the historical shoreline positions in 1934, 1972, and 1998. The survey for the 1972 shoreline ended approximately 4 km (2.5 mi) downcoast of the northern project boundary. The total average change between 1934 and 1998 for the shoreline north of the Oceanside Harbor was -26.2 m (-86.0 ft). This means that a net recession occurred in spite of the fillet that formed in response to the north breakwater. Table 2-5 shows the historical shoreline change rates between surveys for the Camp Pendleton shoreline. Notice that most of the erosion occurred before 1972. Table 2-5 also seems to show a discrepancy in conservation of sand since the changes from 1937 to

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19 1972 and 1972 to 1998 do not sum to the change from 1934 to 1998. The reason for this is the lack of survey data for the 1972 shoreline for the upcoast 4 km (2.5 mi) of the project area. Toward the northern boundary of the project area (Figure 2-10), the 1934 and the 1998 shorelines are almost parallel. This suggests that the historical rate of shoreline retreat has been uniform along this section of the coast. Figure 2-16, which is the average rate of shoreline change, shows that the average annual rate of shoreline recession between 1934 and 1998 was about 0.6m/yr (2 ft/yr). As previously mentioned, most of this shoreline retreat occurred between 1934 and 1972, with a small amount of accretion from 1972 to 1998. If this accretion is neglected, then the average rate of recession for 1934 to 1972 is linearly approximated as 1934197219341998(19981934)-1.0m/yr (-3.4ft/yr)(19721934)dydydtdt (2.4) This result is in agreement with the even-odd analysis for the 1934 to 1972 time period (Figure 2-13). Figure 2-16 shows that most of the erosion south of the harbor also occurred between 1934 and 1972. Table 2-6 shows the shoreline change rates for the coastline south of the harbor. By comparing Table 2-6 to Table 2-5, it is apparent that the recession rates were significantly higher to the south of the harbor. Figure 2-16 shows that the annual recession rate for the entire coast south of the harbor from 1934 to 1972 was 1.4 m/yr (4.6ft/yr). For the 5.5 km (3.4 mi) immediately south of the harbor, the shoreline recession rate was much greater at 2 m/yr (6.6 ft/yr). The recession rate decreased significantly from 1972 to 1998 because of the routine Oceanside Harbor by-passing/nourishment projects that took place during this time period. However, although

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20 the recession rates decreased from 2 m/yr (6.6 ft/yr) to 0.5 m/yr (1.6 ft/yr), the shoreline continued to retreat despite the nourishment efforts. If present practices are continued, shoreline recession will continue into the future; and the seawalls and properties along the Oceanside coastline will progressively experience more overtopping events, and consequently, greater damage. In the DNR model runs, a uniform background erosion of -1.1 m/yr (-3.5 ft/yr) was assumed over the entire open coastline from 1934 to 1972 and no background erosion after 1972. This rather simplistic assumption follows from the three shoreline surveys and results from the even-odd analysis. Longshore Sediment Transport The net longshore sediment transport for the Oceanside coast is approximately 153,000 m 3 /yr (200,000 yd 3 /yr) to the south. However, published values of LST from various studies--which include both analyses of historical wave statistics (north swell, south swell, and local seas) and analyses of sediment accumulation rates in the fillet north of the harbor and in the harbor itself--yielded varying results. Furthermore, several studies suggested long-term variations in LST over the past 90 years. Hales (1978) determined a net LST rate for the Oceanside Littoral Cell of 76,000 m 3 /yr (100,000 yd 3 /yr) to the south based on wave statistics. Marine Advisors (1960) and Inman and Jenkins (1983) also employed wave statistics to determine the LST rates in this area. Marine Advisors found a net southerly transport of 165,000 m 3 /yr (216,000 yd 3 /yr), and Inman and Jenkins found a net southerly transport of 194,000 m 3 /yr (254,000 yd 3 /yr). A study by Tekmarine, Inc. (1987) gave a net southerly LST of 81,000 m 3 /yr (106,000 yd 3 /yr) at Oceanside Harbor. Moffat and Nichol (1990) performed the most comprehensive determination of LST in the Oceanside Littoral Cell. This study predicted

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21 a net southerly LST rate of 76, 000 to 191,000 m 3 /yr (100,000 to 250,000 yd 3 /yr) from 1945-1977. From 1978-1987, data analysis gave the net southerly transport rate to be from 0 to 31,000 m 3 /yr (0 to 40,000 yd 3 /yr), which is a substantial decrease form the pervious time period. North Breakwater Fillet As previously mentioned, a fillet developed to the north of the north breakwater. This fillet began forming immediately after the initial construction of the north breakwater in 1942 and extends 8.9 km (5.5 mi) north of the harbor. The sediment rate of retention has been quantified as approximately 38,000 m 3 /yr (50,000 yd 3 /yr) (USACE, 1994a). The volume of the sediment in the north fillet can be estimated from the 1934, 1972, and 1998 shorelines. The volume estimates are based on a closure depth of 7.6 m (25 ft) and a berm elevation of 4.3 m (14 ft). These volumes are converted to annual rates of accumulation, noting that the fillet began forming after the north breakwater was constructed in 1942 (Table 2-7). The net longshore transport significantly exceeds these accumulation rates. Since the placement of the north breakwater in 1942, only a portion of the transport has been impounded. The rest of the transport is carried into the harbor, by-passed around the harbor, or lost offshore. The values in Table 2-7 are lower than the estimate of 38,000 m 3 /yr (50,000 yd 3 /yr) published by the U.S. Army Corps of Engineers. Also, it is surprising that the accumulation rates are higher in more recent times. Based on the above discussion, an average accumulation rate of 31,000 m 3 /yr (40,000 yd 3 /yr) is used for the north fillet. Immediately to the south of the south breakwater, the shorelines in the 1934, 1972, and 1998 surveys do not show the development of a fillet or an eroded area. This is a

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22 result of sheltering behind the breakwater, longshore transport reversals, and sediment retention between the breakwater and the San Luis Rey groin. Historic Volume Changes The measured shorelines from Figure 2-10 provide an opportunity to estimate the total changes in sediment volume north and south of the harbor. For these estimates, the closure depth is defined as 7.6 m (25 ft) and the berm elevation is defined at 4.3 m (14 ft). The resulting volume change rates are summarized in Table 2-6. For the full reach north of the harbor including the fillet, the average shoreline recession, as previously mentioned, from 1932 to 1998 was -0.4 m/yr (-1.3 ft/yr). North of the harbor, there was an annual loss of .5 m 3 /m/yr (-1.4 yd 3 /ft/yr) from 1934 to 1998. This volume change rate includes the fillet accretion updrift of the north breakwater. Moving farther north out of the fillet, the recession rate over this period was approximately -0.6 m/yr (-2 ft/yr), which is a removal of -8.3 m 3 /m/yr (-3.3 yd 3 /ft/yr). South of the harbor there was a substantial loss of sediment each year (Table 2-8). Before 1972, the sediment eroded at a rate of -16.6 m 3 /m/yr (-6.6 yd 3 /ft/yr). Although by-passing and nourishments occurred regularly from 1972 to 1998, this stretch of coastline still resulted in a deficit of -7.3 m 3 /m/yr (-2.9 yd 3 /ft/yr) during that time period. Again it should be noted that these results predict that future loss of sediment will continue to occur south of the harbor if the current by-passing and nourishment practices are continued. This will lead to increasing overtopping events and more severe damage with time.

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23 Seawalls Method of Defining Seawall Positions The Oceanside and Carlsbad coastlines are heavily armored with seawalls. Rubble, timber, and concrete structures protect many private properties and public lands along the shoreline. The cross-shore locations and alongshore lengths of the armoring was estimated using three references: 1. Maptech Mapserver ( http://mapserver.maptech.com ), 2. California Coastal Record Project aerial photographs by Kenneth Adelman (http://www.californiacoastline.org), and 3. AutoCAD files provided by the USACE (Ryan, 2002). All of the seawalls from the Agua Hedionda discharge jetties to Oceanside Harbor can be seen in the California Coastal Record Project aerial photographs. Figure 2-17 shows an aerial photograph of the shoreline just up-coast of the north Agua Hedionda discharge jetty. A rubble rip-rap seawall protects the parking lot at the south end of the Carlsbad State Beach; and a vertical concrete seawall, which serves as an elevated walkway, spans the length of the Carlsbad State Beach. The Maptech Mapserver website was used to find the alongshore locations and lengths of the seawalls. Running the cursor over the images on this web site gives the longitudinal coordinates along the coast. Figure 2-18 shows the same area as Figure 2-17 in an over-head view with Maptech Mapserver. The parking lot adjacent to the jetty and the rubble rip-rap seawall between the parking lot and the beach are visible. Using the intersection between the shoreline and the north Agua Hedionda discharge jetty as the initial reference point, the longitudinal coordinates from Maptech were converted into alongshore distances. The alongshore distances were then translated to corresponding

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24 cell locations. Gaps in the seawalls and seawalls less than 50 m (165 ft) were omitted since the cell width resolution is 100 m (330 ft). As a result, the structures appear as continuous seawalls of varying type, cross-shore position, and height. To determine the cross-shore position of the seawalls, CAD files provided by the USACE, Los Angeles District, were used. These files include a 2001 Eagle Aerial definition of the landward edge of sand. Upon comparison between the Eagle Aerial line and the aerial photographs, it was concluded that the landward edge of sand defines the seaward edge of the seawalls. Therefore, the cross-shore location of each seawall is defined as the distance from the Eagle Aerial 2001 landward edge of sand to the baseline. To model overtopping events along Oceanside, the crest elevation for each seawall must be known. The crest elevation is the vertical distance from the mean tide level (MTL), which is the reference datum, to the top of the seawall. These elevations were obtained by using a combination of two sources: 1) the GIS study performed along the Oceanside coastline, and 2) a Lidar survey performed for the Oceanside littoral cell. Using these two references gave the elevations at the top of the seawalls with reasonable accuracy. The GIS and the Lidar surveys were taken from the NAVD88 reference datum, which is approximately 0.78 m (2.57 ft) below the MTL datum. Therefore, conversions were made accordingly. Description of Seawalls Found Within the Project Area The final results of the seawall analysis revealed that the entire coastline between the Agua Hedionda discharge jetties and the Oceanside Harbor is armored in one form or another (small gaps less than 50 m are neglected). The continuous seawall from the north discharge jetty at Agua Hedionda to the south breakwater at Oceanside Harbor is divided into many sub-seawalls. A sub-seawall is defined as a change in armoring type (vertical

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25 structure or rubble rip-rap), and therefore a change in slope, within the continuous seawall. The first stretch of the seawall is located in Carlsbad. It is erratic in cross-shore distance and type as it spans across Carlsbad Beach and a number of private properties. The seawall begins as a protective structure for the parking lot just north of the Agua Hedionda discharge jetties mentioned above (Figure 2-17). This first sub-seawall is a rubble rip-rap structure that extends north from the Agua Hedionda jetty. The second sub-seawall is a vertical concrete structure that serves as an elevated walkway and spans along the length of Carlsbad State Beach to Walnut Avenue (Figure 2-17). The third Carlsbad sub-seawall is a rubble rip-rap structure located at the up-coast end of the elevated walkway directly seaward of the Tamarack Beach Resort in Carlsbad. Immediately north of the third Carlsbad sub-seawall is a rocky cliff with an elevation of approximately 14 m (45 ft) (Figure 2-19). Although no man-made structures exist seaward of this cliff from Pine Avenue to Oak Avenue, the cliff itself acts as a seawall. During significant storm events, the cliff itself may erode and contribute sediment to the littoral system. However, the sandy beach will not erode past the cliff in the same manner as it would if no cliff existed. Therefore, this stretch of coastline is modeled as if it were entirely armored by a seawall. Moving up-coast from Oak Avenue to the Buena Vista Lagoon, the coast is heavily armored as protection for many private properties (Figure 2-20). Significant variation occurs in the cross-shore position and type of seawalls along this shoreline. Some of the variations in cross-shore position occur within a 100 m (330 ft) span, so the average cross-shore position was used for each cell. Furthermore, several properties located on

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26 this stretch of the Carlsbad coastline do not have seawalls. The buildings on these lots are constructed higher up on the slope that connects Ocean Street to the beach. The buildings themselves or their foundations will prevent erosion to occur landward of them. For this reason, and the fact that many of these unarmored properties are less than 50 m (165 ft) in width and bounded by seawalls on both sides, this shoreline is considered armored at the location of the buildings. The final Carlsbad sub-seawall is up-coast of the Army Navy Academy and adjacent to Buena Vista Lagoon. This armoring is located along The Point and consists of rubble rip-rap (Figure 2-21). Just north of this seawall is a small gap in armoring where Buena Vista Lagoon discharges in to the Pacific Ocean (Figure 2-21). This discharge point cannot be modeled in its actual configuration because its size is too small (approximately 50 m). More accurate results are obtained when the Buena Vista Lagoon discharge cell is modeled as a seawall rather than a gap with no armoring. This assumption is appropriate since Buena Vista Lagoon is maintained at 1.8 m (5.8 ft) above mean sea level (MSL) by the presence of a weir that spans the lagoon mouth (USACE, 1994a). Continuing upcoast past Buena Vista Lagoon is the Oceanside coastline, where the remaining section of the seawall spans from the lagoon to the Oceanside Harbor. The entire coast of the city of Oceanside is armored and consists of seven sub-seawalls. The first sub-seawall is a long, rubble rip-rap structure that spans the southern coastline of Oceanside (Figure 2-22). This structure extends from Buena Vista Lagoon across St. Malo to Buccaneer Beach (which is adjacent to Loma Alta Creek). A gap exists in the seawall where Cassidy Street intersects the coastline. However, this gap is too small

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27 (approximately 30 m) to be included in the model. The rubble seawall contains a discontinuity point at the Loma Alta Creek discharge point (Figure 2-23). However, the foundation of the South Pacific Street Bridge, which crosses over Loma Alta Creek, provides a landward erosion barrier similar to the cliffs previously mentioned in Carlsbad. North of Loma Alta Creek, the rubble rip-rap structure continues up-coast to just south of Tyson Street Beach Park. This sub-seawall is divided it into two sections. The first section is a uniform structure that spans from Loma Alta Creek to Wisconsin Avenue across many private properties (Figure 2-24). The second section--comprising the northern portion of this seawall--is very unorganized rubble rip-rap, and was labeled by the USACE (1994b) as emergency revetment placed along The Strand. Figure 2-25 shows a section of this emergency revetment. The fourth Oceanside sub-seawall is not an actual seawall. The curb that separates Oceanside Beach from The Strand is a landward erosion barrier that is susceptible to overtopping and damage (Figure 2-26). The curb extends up the coast to North Coast Village. Just south of the San Luis Rey River is the armoring that protects North Coast Village. This sub-seawall is a 150-m (492-ft) vertical timber structure with rubble toe protection that projects farther seaward that the adjacent seawalls to the north and the south (Figure 2-27). This anomaly in the shoreline increases the possibility of overtopping and damage at North Coast Village relative to the adjacent shorelines. The San Luis Rey River discharge is a discontinuity in the shoreline similar to the Loma Alta Creek discharge point. However, North Pacific Street Bridge, which crosses

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28 over San Luis Rey River, provides a landward erosion barrier (Figure 2-28). Therefore, the foundation to this bridge is the sixth sub-seawall. The curb of North Pacific Street north of the bridge marks the seventh Oceanside sub-seawall. This section is very similar to the curb and street erosion barrier that spans the northern portion of Oceanside beach just south of the North Coast Village. The curb extends from the San Luis Rey River groin to the South Breakwater at Oceanside Small Craft Harbor (Figure 2-29).

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29 Table 2-1. Tide level record at the NOAA/NOS/CO-OPS La Jolla Tide Gage 2 Tide Levels Given in Feet La Jolla Mean Higher High Water (MHHW) 5.33 Mean High Water (MHW) 4.60 Mean Tide Level (MTL) 2.75 Mean Low Water (MWL) 0.90 Mean Lower Low Water (MLLW) 0.00 2 NOAA/NOS/CO-OPS La Jolla Tide Gage

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30 Table 2-2. Nourishment dates, locations, and volumes (yd 3 ) within the project area. Nourishment Location Date Downcoast End Upcoast End Volume (yd 3 ) Volume (m 3 ) Jun 1942 Inland Fill 1,500,000 1,149,000 May 1945 Inland Fill 219,000 167,000 Nov 1957 9 th Street 6 th Street 800,000 612,000 Aug 1960 9 th Street 6 th Street 410,000 313,650 Aug 1961 9 th Street 6 th Street 481,000 367,965 Jan 1963 North Coast Village Loma Alta Creek 3,800,000 2,907,000 Aug 1965 9 th Street 3 rd Street 111,000 84,915 Mar 1966 3 rd Street Ash Street 684,000 523,260 Jul 1967 3 rd Street Tyson Street 178,000 136,170 Apr 1968 San Luis Rey River Wisconsin Avenue 434,000 332,010 Aug 1969 San Luis Rey River 3 rd Street 353,000 270,045 May 1971 3 rd Street Wisconsin Avenue 552,000 422,280 Jun 1973 Tyson Street Wisconsin Avenue 434,000 332,010 Nov 1974 Ash Street Whitterby Street 560,000 428,400 Jun 1976 Ash Street Whitterby Street 550,000 420,750 Nov 1977 Ash Street Whitterby Street 318,000 243,270 Apr 1981 Hayes Street 863,000 660,195 Feb 1982 Hayes Street 922,000 705,330 Jan 1984 Hayes Street 475,000 363,375 Jan 1986 Hayes Street 450,000 344,250 Jan 1988 Hayes Street 220,000 168,300 Feb 1988 Acacia Avenue Oak Avenue 118,000 90,335 Jan 1990 Hayes Street 249,000 190,485 Feb 1991 Acacia Avenue Oak Avenue 25,000 18,933 Feb 1992 Tyson Street 188,000 143,820 Dec 1993 Tyson Street 483,000 369,495 Feb 1994 Acacia Avenue Oak Avenue 75,000 57,241 Jan 1995 Nearshore Placement (Oceanside Blvd.) 161,000 123,165 Jun 1995 Oceanside Blvd. 40,000 30,600 Feb 1996 Acacia Avenue Oak Avenue 106,000 108,630 Feb 1996 Nearshore Placement (Oceanside Blvd.) 162,000 123,930 Jan 1997 Nearshore Placement (Oceanside Blvd.) 130,000 99,450 Mar 1997 Oceanside Blvd. 1,000 765 Sep 1997 Oceanside Blvd. 102,000 78,030 Mar 1998 Nearshore Placement (Oceanside Blvd.) 315,000 240,975 Mar 1999 Tyson Street 187,000 143,055 Apr 1999 Acacia Avenue Oak Avenue 203,000 154,935 Feb 2000 Tyson Street 327,000 250,155 Feb 2001 Tyson Street 80,000 108,630 Feb 2001 Acacia Avenue Oak Avenue 142,000 61,200

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31 Table 2-2. Continued Nourishment Location Date Downcoast End Upcoast End Volume (yd 3 ) Volume (m 3 ) Jul 2001 Vista Way Wisconsin Avenue 421,000 322,065 Sep 2001 Carlsbad Village Dr Buena Vista Lagoon 225,000 172,125 Jan 2002 Tyson Street 400,000 306,000 Feb 2003 Tyson Street 438,000 335,070 Table 2-3. Sediment discharge rates by rivers and streams (yd 3 /yr). Discharge Rates yd 3 /yr CCSTWS 88-3 Simons/Li (1988) Simons/Li (1985) Inman Jenkins (1983) Brownlie Taylor (1981) CCSTWS 84-4 USACE LAD (1984) CCSTWS 90-1 Moffat/Nichol (1990) Moffat Nichol (1977) DNOD (1977) Brownlie and Taylor (1981) Simons, Li and Assoc. (1988) Santa Margarita River 11,430 15,000 24,000 11,000 2,000 20,000 900 15,000 11,300 19,000 San Luis Rey River 6,540 23,000 37,000 18,000 351,000 11,000 20,000 351,000 12,500 11,000 Loma Alta Creek 565 ----1,000 ----Buena Vista Lagoon 0 ----0 ----Table 2-4. Location and sediment contributions used in the DNR simulations for the Santa Margarita River, the San Luis Rey River, and the Loma Alta Creek. Sediment Source Sediment Volume (yd 3 /yr) Sediment Volume (m 3 /yr) Alongshore Location Santa Margarita River 13,000 9,900 2000 m upcoast of the north breakwater San Luis Rey River 17,000 13,000 2000 m downcoast of the north breakwater Loma Alta Creek 800 610 5500 m downcoast of the north breakwater

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32 Table 2-5. Shoreline change rates north of Oceanside Harbor. Shoreline Change Shoreline Change Rate Time Interval (m) (m/yr) Comments 1934 to 1972 -30.0 -0.79 1972 Survey Incomplete 1972 to 1998 +9.4 +0.37 1972 Survey Incomplete 1934 to 1998 -26.2 -0.40 Table 2-6. Shoreline change rates south of Oceanside Harbor. Shoreline Change Shoreline Change Rate Time Interval (m) (m/yr) 1934 to 1972 -16.4 -0.44 1972 to 1998 -5.5 -0.21 1934 to 1998 -22.0 -0.34 Table 2-7. North fillet volume accumulation rates. Time Interval Accumulation Accumulation (yd 3 /yr) (m 3 /yr) 1942 to 1972 11,500 8,800 1972 to 1998 26,100 20,000 1942 to 1998 18,300 14,000 Table 2-8. Volume change rates. South of Harbor North of Harbor Time Interval (m 3 /yr) (m 3 /m/yr) (m 3 /yr) (m 3 /m/yr) Comments 1934 to 1972 -128,400 -16.6 --1972 Survey Incomplete 1972 to 1998 -61,200 -7.3 --1972 Survey Incomplete 1934 to 1998 -109,300 -12.8 -50,500 -3.5

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33 Figure 2-1. Three historical reference shorelines for the Carlsbad, Oceanside, and Camp Pendleton coast. Figure 2-2. Comparison of the equilibrium beach profile used in the DNR model to an actual SANDAG profile of the Oceanside coastline.

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34 Figure 2-3. The nine wave gages and the 90 computational sites used to create the 50 wave records.

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35 Figure 2-4. Mean wave height and mean period for each of the nine BOR wave gages. The two black lines on the plot show the locations of the north and south breakwaters. Figure 2-5. Maximum wave height by station for the 50 wave records. The two black lines on the plot show the locations of the north and south breakwaters.

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36 Figure 2-6. Mean local wave angle with respect to the local shoreline orientation for the 50 wave records at the nine wave gages. The two black lines on the plot show the locations of the north and south breakwaters.

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37 Figure 2-7. Chronological development of Del Mar Boast Basin and Oceanside Small-Craft Harbor. U.S. Army Corps of Engineers (USACE), Los Angeles District (1991b), State of the Coast Report, San Diego Region: Chapter 7, Application of Beach Change Models, Coast of California Storm and Tidal Wave Study (CCSTWS) Volume 1 Main Report.

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38 Figure 2-8. Nourishment placements and times for beaches downcoast of Oceanside Harbor.

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39 Figure 2-9. Timeline of significant historical events that occurred along the project area coastline.

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40 Figure 2-10. Comparison of the actual initial 1934 and final 1998 shorelines. Figure 2-11. Total change in shoreline position from May 1934 to April 1998.

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41 Figure 2-12. Results of the even-odd analysis from 1934 to 1998 for the Oceanside coastline. Figure 2-13. Even-odd analysis results and background erosion rates north and south of Oceanside Harbor complex from 1934 to 1972. The background erosion rate is the even function shown in red.

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42 Figure 2-14. Even-odd analysis results and background erosion rates north and south of Oceanside Harbor complex from 1972 to 1998. The background erosion rate is the even function shown in red. Figure 2-15. MSL shoreline position in 1934, 1972, and 1998.

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43 Figure 2-16. Average annual rate of change between the 1934, 1972, and 1998 shorelines. Figure 2-17. California Coastal Record Project, Image 9032. Parking area at the southern end of Carlsbad State Beach adjacent to the north Agua Hedionda discharge jetty.

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44 Figure 2-18. Maptech Mapserver image of the Agua Hedionda discharge jetties and Carlsbad State Beach.

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45 Figure 2-19. California Coastal Record Project, Image 9017. Rocky cliffs just north of the elevated concrete walkway that spans Carlsbad State Beach. Figure 2-20. California Coastal Record Project, Image 9011. Erratic portion of seawall along Carlsbad that consists of rubble rip-rap, vertical structures, and home foundations.

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46 Figure 2-21. California Coastal Record Project, Image 9005. Armoring at The Point, Carlsbad, and Buena Vista Lagoon discharge point. Figure 2-22. California Coastal Record Project, Image 9002. Well-organized rubble seawall that spans from Buena Vista Lagoon to Loma Alta Creek, Oceanside.

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47 Figure 2-23. California Coastal Record Project, Image 8985. South Pacific Street bridge crossing over Loma Alta Creek discharge point, Oceanside. Figure 2-24. California Coastal Record Project, Image 8971. Well-organized portion of rubble seawall that spans north of Loma Alta Creek to The Strand, Oceanside.

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48 Figure 2-25. California Coastal Record Projects Aerial Photograph, Image 8963. Emergency Revetment along The Strand, Oceanside. Figure 2-26. California Coastal Record Projects Aerial Photograph, Image 8952. North Pacific Street curb along The Strand that acts as a landward erosion barrier, Oceanside.

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49 Figure 2-27. California Coastal Record Project, Image 8948. Timber and rubble rip-rap seawall that armors North Coast Village, Oceanside. Figure 2-28. California Coastal Record Project, Image 8946. North Pacific Street bridge crossing over the San Luis Rey River discharge point, Oceanside.

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50 Figure 2-29. California Coastal Record Project, Image 8944. North Pacific Street curb landward of Oceanside Small Craft Harbor, Oceanside.

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CHAPTER 3 DNR MODEL This chapter briefly explains the theory behind the one-line DNR model. For a more detailed discussion, see Dean and Grant (1989). First a background on one-line models is presented, along with the equations used to calculate longshore sediment transport and shoreline position. This is followed by a discussion on wave set-up, run-up, overtopping, and force estimates as implemented in the DNR model for this project. Shoreline Position The DNR model is a one-line model, meaning the model predicts the evolution of one contour (Dean and Grant, 1989). The most common contour to track is the shoreline, which is typically divided into a number of equally spaced cells. A one-line model assumes that the beach profile shape remains constant. Shoreline position change from one time step to the next is a function of the change in volume within a cell between consecutive time steps. The change in volume, in turn, is a function of gradients in longshore sediment transport and additions or subtractions in sediment from sources or sinks in the cell. The DNR model determines the change in shoreline position using the Brunn rule. Two requirements are necessary to apply the Brunn rule for the new equilibrium profile: 1) The profile shape does not change with respect to the water line, and 2) The sand volume in the profile must be conserved (Dean and Dalrymple, 2002). Once equilibrium occurs, the shoreline position change, y, is given by 51

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52 *VyhB (3.1) where V is the volumetric change, h is the closure depth, and B is the berm elevation. Longshore Sediment Transport Gradients in the sediment flux result in a change in volume. If the longshore sediment transport (LST) entering a cell is greater than the LST exiting the cell, then the cell experiences sediment accretion and the shoreline advances seaward. Conversely, if the LST exiting the cell is greater than the LST entering the cell, then the cell experiences a reduction in sediment volume and the shoreline retreats landward. If erosion or accretion occurs, then the profile simply translates landward or seaward. Since the profile shape is always the same, tracking one point on the profile is sufficient for defining the entire profile. Figure 3-1 shows various terms that can influence the volume of sediment in a cell. Each cell is a local, small-scale littoral budget. The terms from Figure 3-1 can be summarized in the conservation of mass (volume) equation, *inout[()][()] s syxhBQQQtV N (3.2) where y is the change in shoreline position for time interval t, x is the alongshore length of the cell, Q in and Q out are the LST at the boundaries of the cells, Q ss is a source/sink, and V N is the volume associated with nourishment or mining. The terms h and B are the closure depth and the berm elevation. Their sum gives the vertical range of the active profile. This equation is written for each cell to get a complete one-line description of the shoreline. To apply Equation 3.2, the LST must be specified. The DNR model implements a variation of the CERC formula (SPM, 1984),

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53 (cossin(1)(1) ) g bKQECgsp (3.3) where Q is volume transport, is the water density, g is the acceleration due to gravity, s is the specific gravity of the sediment, p is the sediment porosity, and K is a dimensionless empirical transport coefficient. The terms in the parenthesis with the subscript b are evaluated at the breaker line. The term E is the wave energy density, C g is the group celerity of the waves, and is the wave local angle relative to the shoreline. Using linear wave theory, conservation of energy flux, and Snells Law for refraction, Equation 3.3 may be written 2cossin 8(1)(1)bKQnHsp C (3.4) where C b is the wave celerity evaluated at the breaker line and n is the ratio of the group velocity to the wave celerity. The advantage of Equation 3.4 is that only C b is evaluated at the breaker line while all other terms may be evaluated at any arbitrary depth outside the breaker line. The DNR model proceeds by first calculating Q at each cell boundary. The angle is the local wave angle and incorporates the influence of the shoreline orientation at the cell. With Q known and all sources/sinks and nourishments specified, Equation 3.2 is solved. The solution technique is an explicit, forward, finite difference scheme. Time steps are made small enough to ensure numerical stability. Wave Setup If the water depth as the seawall is greater than zero, then wave setup at the seawall is calculated as

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54 238316 s wBLswhhh BL (3.5) In which s w is the setup at the seawall, h BL is the still water depth at the breaker line, h sw is the still water depth at the seawall, and is a breaker index. This setup equation is valid for depth profiles that increase monotonically with distance offshore. The influence of wave reflection is not included. Run-up The run-up is calculated using different formulations for a vertical face and a rubble slope. For a vertical face, the height of the run-up, R a is taken as the height of a standing wave crest. uswTRH (3.6) where H sw is the incident wave height at the seawall. This is added to the tide T and wave setup to get the total height of the run-up at the seawall. For a rubble slope, the run-up is calculated as (CIRIA/CUR, 1991) (3.7) 0.410.721.50.881.52.841.352.84swuswswHRHH in which is the surf similarity parameter defined as 1/222/swmmHgT (3.8) where m is the slope of the structure face (), g is the acceleration due to gravity, and T V:1Hm m is the mean wave period. Data for this project are given as peak period, T p An approximate conversion is T m = 0.83T p (CIRIA/CUR, 1991).

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55 Overtopping Propagation Overtopping occurs when the height of the run-up exceeds the crest elevation of the seawall. Overtopping creates the potential for damage to structures from flooding and direct water forces. Cox and Machemehl (1986) present a simple model for propagation of a bore behind the seawall when overtopping occurs. The height of the bore, H, is given as 21/212uoRE x HA (3.9) where R u is the run-up height, E o is the crest elevation of the structure, and x is the distance behind the seawall. The term is a coefficient with a recommended value of = 0.1. The term A is defined as (3.10) 3/21/2(1)A gT where g is the acceleration of gravity and T is the wave period. The bore height is a maximum at the seawall crest (x = 0) and decreases in height rather quickly as the bore propagates landward of the seawall. The magnitude of the excess run-up determines the distance of the bore propagation (R u E o ). In the DNR model, if overtopping occurs, the bore height is calculated at the seawall crest, and then every 5 m (16 ft) behind the seawall until the bore height diminishes to H = 0. Forces If a propagating bore impacts a structure, wave forces develop. These forces are estimated as outlined in Ramsden and Raichlen (1990), 22max(1)2F 2 f NH (3.11)

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56 where f max is the per unit width of the structure, is the weight density of the water, and N F is the Froude number. The value of the Froude number is taken to be N F = 1.8, which follows the data given in Ramsden and Raichlen (1990). Input Parameter Cell Definitions This section explains the methods used in defining characteristics within a cell of the DNR model. These characteristics include shoreline position, seawall location, longshore sediment transport rate, shore perpendicular structures (breakwaters, jetties, and groins), beach nourishments, and sediment sources/sinks. These definitions are important to define the study area as accurately as possible in the model. The definitions of shoreline position, cross-shore seawall location, and groin lengths are referenced to the baseline. The baseline is an imaginary line typically located landward of the shoreline with an azimuth similar to that of the shoreline between the boundaries of the study area. The baseline is then segmented into equally spaced intervals that define each individual cell. The baseline origin marks one boundary of the study area and is defined at cell 1. The positive direction along the base coordinate is defined as left to right when facing offshore. Perpendicular lines are then projected from the baseline to define the shoreline position, cross-shore seawall locations, and the seaward tip of shore perpendicular structures. The study area is sub-divided into cells, which are equally spaced across the domain. The upper boundary is cell I max which is the last cell in the domain. The upper and lower boundaries are not referenced by the direction of transport; rather they are designated by the location within the domain. For the purposes of this project, the cells are all 100 m (330 ft) in width.

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57 Shoreline positions are defined at the midpoint of each cell. The representative shoreline distance for each cell is found by interpolating the shoreline position at the boundaries for each cell. The number of shoreline position values is equal to the total number of cells from the lower boundary to the upper boundary. Shoreline position is entered in feet from the baseline. Cross-shore seawall positions are defined in a similar manner as shoreline positions. Representative cross-shore seawall positions are found by interpolating the seawall positions at the boundary of each cell and are defined at the midpoint of those cells. The seawall position value is the same for the entire cell. In the along shore orientation, seawalls represent armoring of the entire cell at the specified cross-shore distance from the baseline. Cross-shore seawall location is entered in feet from the baseline. Longshore sediment transport (LST) is defined at the boundaries between cells. As a result, there is one more LST value along the reach than there are cells. LST values are positive if the transport is moving from the left to the right of an observer facing offshore. Likewise, transport is negative if it is moving from the observers right to left. The lower boundary is the location of the first LST value, Q(1), and the upper boundary of the reach is the location of the final LST value, Q(I max +1). LST rate is measured in cubic yards per year. Groins are defined in both the alongshore and the cross-shore directions. Groins is the general term used to describe any shore perpendicular structure capable of blocking the movement of sediment alongshore, and includes breakwaters, jetties, and groins. In the alongshore, groins are defined at the boundaries between cells. The cell whose lower

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58 boundary marks the location of the groin designates the LST. For example, a groin located in cell 100 is placed in the boundary between cells 99 and 100. In the cross-shore direction, groin lengths are given as the distance from the baseline to the seaward tip of the groin. This length is measured in feet. Beach nourishment input includes the alongshore location, nourishment volume, time of placement, and a fill factor. In the alongshore, nourishment projects are defined with an upper cell and a lower cell. The nourishment volume is then placed uniformly on the coast between the lower and upper cell. Beach nourishment volumes are given in cubic yards. The nourishment is placed at the specified time (in hours). The fill factor is the portion of the nourishment volume that remains in the littoral system. Sediment sources and sinks are defined as a uniform addition or removal of sediment within the assigned cell. The volume change is an annual rate that remains constant throughout the duration of the model run. Sediment sources and sinks include river contributions, bluff contributions, offshore sediment deflection, sediment removal, and background erosion. Sources/sinks are given in yd 3 /ft/yr.

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59 Figure 3-1. Possible changes in sediment amounts within a cell.

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CHAPTER 4 SEAWALL MODEL The DNR model has been modified to include influences from seawalls. If a seawall is in the surf zone, then the surf zone width increases, the longshore sediment transport (LST) is reduced, and the shoreline cannot retreat landward of the seawall cross-shore location. In this chapter, the seawall algorithm is described and examples are presented to show the performance of the seawall routines. Theory Profile Definitions The DNR model is a one-line model that tracks the cross-shore position of the shoreline in response to alongshore gradients in the LST. Along seawalls, the actual shoreline position cannot retreat landward of the seawall location. Therefore, a modification is necessary in the one-line model to determine the shoreline response where the shoreline position becomes fixed. The modification implemented into the DNR model is that for cells with seawalls, the volume of sediment seaward of the seawall is tracked rather than the shoreline position. The cross-shore profile must be known to determine this volume of sediment. As mentioned in Chapter 2, the beach profile in the DNR model is defined by the Brunn/Dean equilibrium beach profile. The equilibrium profile is based on constant wave energy dissipation per unit volume of surf zone and has been well documented and widely used in coastal engineering. The equilibrium beach profile is given as 23hAy (4.1) 60

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61 where h is the still water depth along the profile, A is the profile coefficient related to the sediment diameter, and y is the cross-shore distance along the profile (Dean and Dalrymple, 2002). The shoreline position corresponds to y = 0; and the depth of closure, h = h correspond to the width of the active littoral zone, y = y To distinguish between global cross-shore position and local profile position, the subscript L is applied to variables that refer to the local coordinate system of the beach profile. The global coordinates begin at the baseline as the origin, and the local coordinates begin with the shoreline position of the equilibrium beach profile as the origin. The global cross-shore distance from the baseline to the shoreline position is defined as y = y N The shoreline position in reference to the local coordinates of the equilibrium beach profile occurs at y L = 0. Other variables used in the local coordinate system are y *L which is the cross-shore width of the active littoral, y aL which defines the cross-shore shoreline displacement when y sw > y N and y swL which is the distance from the shoreline position landward of the seawall to the seawall. A critical location for the profile is when the equilibrium profile shoreline position is defined at the location of the seawall. If the shoreline is seaward of the seawall (y N y sw ), then a sub-aerial berm/beach exist seaward of the seawall. If the profile is landward of this critical point (y N < y sw ), then no sub-aerial berm/beach exist seaward of the seawall, and there is a finite water depth fronting the seawall. The volume of sediment calculated at this critical shoreline position is referred to as the critical volume for the profile. If the volume of sand in the profile exceeds the critical volume, then a sub-aerial beach exists seaward of the seawall. If the volume of sediment in the profile is less than the critical volume, then a finite water depth exists at the

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62 seawall. Figure 4-1 shows this critical condition. For an equilibrium profile, the critical volume is 53****[()(0.6)]cswLLVyhByhAyd x (4.2) where V c is the critical volume, y sw is the cross-shore distance from the baseline to the seawall, y *L is the width of the active littoral zone, h is the closure depth, B is the berm elevation, and dx is the cell width. Figure 4-2 shows the condition where the profile of sand exceeds the critical volume (y N > y sw ). For this case, the volume is 53****[()(0.6)]NLLVyhByhAyd x (4.3) where y N is the cross-shore shoreline position seaward of the seawall. This equation is similar to the equation for critical volume. The only difference is that the berm extends seaward of the seawall to the actual shoreline. For this case, the change in shoreline position associated with the volume tracking within the profile is the same as the shoreline position change calculated by profile translation: *VyhB (4.4) Excess volume, V E is defined as the actual volume minus the critical volume, EVVV c (4.5) If V E > 0, then a sub-aerial beach exists seaward of the seawall. If V E < 0, no beach exists and water fronting the seawall. The V E < 0 case is more complex than the V E > 0 case and leads to the modification of tracking the sediment volumes as opposed to simply solving for the shoreline position change with profile translation.

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63 Figure 4-3 shows an example where the seawall is in the surf zone. The submerged profile is still defined as an equilibrium beach profile, but the origin of the profile is displaced landward of the seawall. This landward translation results in an increase in water depth and flattening of the profile at the seawall. The cross-shore position referred to as y N is actually a fictitious shoreline position, since the actual shoreline cannot retreat onshore beyond the seawall location. However, this fictitious shoreline position is crucial in defining the profile and the volume. The volume of sediment within a cell for the case where the V E < 0 is (4.6) *****[() ()()0.6()]swLaLswLswaLVyhByyhhhyhyd x where y aL is the distance from the fictitious shoreline position to the cross-shore seawall location. 32swaLhyA (4.7) Profile Changes In the preceding section, the volumes of sediment in the profile were determined for the cases with and without a beach fronting the seawall. In this section, the change in shoreline position is determined as a function of the change in sediment volume. As previously mentioned, in a one-line model, shoreline changes are driven by gradients in the longshore transport. In a cell, if the transport entering the cell exceeds the transport leaving of the cell, then accretion occurs and the shoreline advances seaward. Conversely, if a deficit exists between the boundaries of a cell, then erosion occurs and the shoreline retreats landward. This same principal applies along a seawall, with the exception that if V E < 0, the fictitious shoreline retreats or advances as opposed

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64 to the actual shoreline position, which is fixed at the seawall. This results in a change in water depth fronting the seawall. Consider the change in sediment volume in a cell to be V. For a one-line model, neglecting sources/sinks and nourishments, this is simply () inoutVQQ t (4.8) where Q in is the transport going into the cell, Q out is the transport leaving the cell, and t is the time interval. V can be positive or negative. If the excess volume is positive, then a beach is fronting the seawall, and there is a one-to-one relationship between volume and shoreline position given by (4.9) *()()nonoVVVyyhBdx where the subscript o, or old, refers to the initial condition at a time step; and the subscript n, or new, refers to final condition (initial time step + t). The old shoreline, y n is the same as y N at the new location in global coordinates, and the new shoreline, y o is the same as y N at the old location in global coordinates. Using Equations 4.8 and 4.9 gives an estimate of the new shoreline position. When the excess volume is negative, there is no dry beach fronting the seawall, and the volume change is still given as nVVV o (4.10) except the volumes are defined by Equation 4.6. The volumes V n and V o depend on the location of the fictitious shoreline. The location y o is known, and the value for y n must be determined that satisfies Equation 4.10. Consider Figure 4-4, which gives a graphical representation of -V E and -V based on the longshore transport gradient where the fictitious shoreline retreats from y o to y n

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65 For convenience, the shoreline position change is expressed in local coordinates. Using Equation 4.4, the volume change is defined as 535353**{0.6[()()()]}LswLaLswLaLLVAyyyyyy dx (3.27) The only unknown variable in Equation 3.27 is y aL which cannot be solved for explicitly. Therefore, the DNR model iteratively solves for y aL using a numerical technique. Longshore Transport Modification A seawall that is in the surf zone modifies LST. On a beach with no seawall the waves break across the surf zone and are completely dissipated at the shoreline. All of the wave power, or momentum, is available for generating longshore currents and sediment transport. With a seawall in the surf zone, the waves break as they propagate across the surf zone, but still have a finite height when they reach the seawall. The wave energy may be dissipated at a rubble seawall or reflected back offshore at a vertical seawall. Either way, the associated wave power does not lead to the development of longshore currents. As a result, the LST on a beach with a seawall in the surf zone is generally less than for the same beach with no seawall. Ruggiero and McDougal (2001) presented an analytical solution for the LST on a plane beach that supports this argument. The response was more complex because partial standing waves developed from reflected waves. It was also found that the reflected wave causes the incident wave to break approximately 10% farther offshore. Never-the-less, the general observation was that the farther out into the surf zone a seawall is located, the greater the reduction in LST. Figure 4-5 shows the LST as a function of seawall location for four planar beach slopes. The position of the seawall was relative to the location of the breaker line if no

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66 seawall was present. In each case, the LST decreased as the seawall position moved farther offshore. The milder the beach slope, the wider the surf zone became and the influence of the partial standing wave increased. In Figure 4-5, the seawall reduction factor, R sw was approximated as 1swLswswblLyRaBy (4.11) where y swL and y blL are the seawall and breaker line locations in local coordinates, B sw is the increase in surf zone width because of reflection from the seawall (B sw = 1.12), and a is the slope of the linear approximation. A value of a = 1.0 was used which yields no LST when the seawall is seaward of the breaker line. Along-shore Boundary Conditions The seawall flux boundary conditions are located at the cell boundaries. Every seawall has one more longshore sediment transport value, Q, than y sw values. This extra transport value marks the boundary where LST makes the transition from a cell that does not contain a seawall to a cell that is armored by a seawall. There is an additional transport modification that may occur at the ends of the seawall. If the seawall is in the surf zone, then the updrift boundary of the seawall can act as a groin and block the LST (Figure 4-6). At this updrift location, the DNR model refers to the groin routine. The end of the seawall can completely block LST until the updrift shoreline advances seaward of the end of the seawall, or the groin can be leaky and allow partial transport before the shoreline reaches the end of the groin. Seawall/ Nourishment Sensitivity Tests This section shows the functionality of the seawall routines in the DNR model by examining a variety of hypothetical cases. The base conditions for the tests are:

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67 Straight initial shoreline located at y N = 0. Constant wave of height H 0 = 0.61 m (2 ft) and period T = 12.1 s. Shore-normal wave angle 0 = -3 (causing transport to move from right to left). A study area of 241 cells. Duration of simulation = 50 yrs. The variables are a 150-m (500-ft) breakwater, a beach nourishment at time t = 10 yrs (varies in location by case depending on seawall locations), and the presence of one or more seawalls. Table 4-1 gives input parameters for each case. The letters a and b in the case titles show whether or not a breakwater exists for that particular simulation: no breakwater for cases that are denoted with an a and one 150-m (500-ft) breakwater at cell 120 for cases that are denoted with a b. The cases that do not contain a breakwater do not experience a disruption in the longshore sediment transport, and thus do not result in erosion. Case 1: One Seawall, No Nourishments Case 1 incorporates one seawall with a cross-shore location at the initial shoreline position. No nourishment is included for this test. Figure 4-7 gives a graphical representation of the input parameters for Case 1. Case 1a is not presented in Table 4-1, as the results are unimportant. Case 1a consists of one seawall and no breakwater or beach nourishments. Consequently, no forcing is present that would cause the shoreline to accrete or erode. The result for Case 1a is a straight final shoreline identical to the straight initial shoreline. Figure 4-8 shows the evolution of the shoreline at the 1-yr, 5-yr, 10-yr, 30-yr, and 50-yr time steps for Case 1b, and Figure 4-9 shows the shoreline position at pre-selected cells for every time step. These two figures display the shoreline response when

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68 interacting with a seawall in an area experiencing a gradient in longshore sediment transport attributable to the breakwater. It should be noted that the present version of the DNR model does not include diffraction, so the shoreline response close to shore-perpendicular structures is not simulated accurately. Figure 4-8 presents an important verification on the behavior at the ends of a seawall. If the shoreline immediately updrift recedes landward past the seawall, the updrift end of the seawall acts as a groin, thus blocking transport. In this simulation, the breakwater acts as the primary sediment trap blocking all transport. Once the shoreline upcoast of the seawall retreats landward of the seawall, the updrift end of the seawall becomes a secondary block in the sediment transport. The shoreline between the breakwater and the seawall then continues to adjust its orientation without any supply in sediment to these cells until the shoreline aligns with the incoming wave angle. This behavior mimics the response of a shoreline between groins. While this is occurring, erosion continues downdrift of cell 100 because of the lack of sediment reaching those cells. Case 2: No Seawalls, One Nourishment Case 2 is a simple case with one nourishment and no seawalls. This case is designed to check the functionality of the nourishment routine by isolating it from the seawall routines. Figure 4-10 gives a graphical representation of the input parameters for Case 2. Figures 4-11 and 4-13 show the evolution of the shoreline for the 1-yr, 5-yr, 10-yr, 30-yr, and 50-yr time steps for Cases 2a and 2b, respectively. Figures 4-12 and 4-14 show the shoreline position at pre-selected cells for every time step for Cases 2a and 2b, respectively. These figures show the nourishment spreading effects as time progresses

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69 after the implementation of nourishment projects, both in an area with no disturbance in LST (Case 2a) and in an area experiencing reduced LST (Case 2b). Figure 4-13 shows that the same volume of sediment is placed for every nourished cell. The cells within the nourishment bounds have a nourished planform that is parallel to the shoreline planform immediately before the nourishment event. Case 3: One Seawall, One Nourishment Case 3 combines one seawall and one nourishment. The nourishment spans the updrift half of the seawall, and then extends an equal distance upcoast across the unarmored shoreline. Figure 4-15 gives a graphical representation of the input parameters for Cases 3a and 3b. Figure 4-16 shows the shoreline evolution for Case 3a for the 1-yr, 5-yr, 10-yr, 30-yr, and 50-yr time steps. The nourishment at the 10-yr time step causes the shoreline to move seaward between cells 100 and 115. As the simulation continues after the 10-yr mark, the nourishment spreads out in the form of a normal distribution in accordance to the one-line Pelnard-Considere model that predicts alongshore diffusion. Since there is no erosion to expose the seawall, the seawall has no influence. Figure 4-17 shows the shoreline position as a function of time at a number of cells along the seawall and beyond the ends of the seawall. The results also show the spreading of the nourishment with no influence from the seawall. Case 3a is in agreement with the results of Case 2. Figure 4-18 shows the shoreline evolution for Case 3b, which includes a breakwater at cell 120 that causes erosion in the area of the seawall for the 1-yr, 5-yr, 10-yr, 30-yr, and 50-yr time steps. The results of Figure 4-18 shows the updrift end of the seawall acting as a groin when the shoreline updrift recedes landward of the seawall.

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70 This is in agreement with the results at the seawall updrift end for Case 2b. Figure 4-18 also shows an interesting result important in the seawall model verification. Notice the point in the shoreline position at year 10 that occurs at the upcoast end of the seawall. This point seems to represent an error, or a discontinuity, in the beach nourishment. However, since the shoreline had already retreated back to the armoring before the placement of the nourishment (notice that in the 5-year planform the shoreline position is already landward of the updrift end of the seawall), progressively varying water depth exists seaward of the seawall, increasing from the updrift to the downdrift ends of the seawall. The volume of nourishment assigned to each cell along the seawall first goes toward filling the profile to the critical volume. Once that critical volume is achieved, the shoreline advances seaward in accordance to profile translation. The point in the nourishment project at cell 105 represents the boundary between the end of the seawall, where a water depth existed before the nourishment (from the fictitious retreat of the shoreline landward of the seawall), and the open, unarmored coastline. Figure 4-19 shows the shoreline position by cell for Case 3b and gives a good representation of the seawall effect on shoreline response in a sediment-starved system. Cell 115 (represented by the green line in the figure) is the closest to the breakwater and therefore begins to erode first and more severely than the other cells. Between the 10-yr time step (when the nourishment occurs) and the 15-yr time step, shoreline advance occurs at this cell. This advance is a result of the spreading effect of the nourishment as it reaches cell 115. The consequent shoreline retreat is from the sediment eroding away because of the lack of transport at that location. However, since the sediment becomes essentially trapped between the breakwater and the updrift end of the breakwater, the

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71 erosion rate decreases dramatically toward the end of the simulation as the shoreline aligns itself to the wave angle. Conversely, cell 80 (represented by the yellow line) is the cell farthest from the breakwater. This cell is the last of the specified cells to start eroding, and its distant location from the nourishment causes only a small advance in the shoreline position as the nourishment spreads out along the coast. The erosion downdrift of the seawall mentioned previously because of the updrift end of the seawall acting as a groin is evident for those cells downcoast of the seawall in Figure 4-19. Case 4: Two Seawalls, One Nourishment The main focus of Case 4 is to isolate the shoreline response in gaps between seawalls. To examine the shoreline behavior between seawalls, two seawalls each 1,500 m (4900 ft) long and 1,000 m (3300 ft) apart are examined. Also, a beach nourishment is placed at the 10-yr time step that spans beyond both ends of the updrift seawall. This configuration allows an examination of the shoreline behavior along a seawall fronted by water and at the ends of seawalls. Figure 4-20 gives a graphical representation of the input parameters for Cases 4a and 4b. Figure 4-21 shows the shoreline evolution for the 50-yr simulation for Case 2a. It is rather uneventful and similar to Figure 4-16. Once again, since no breakwater is included for this case, there is no erosion. Therefore, the nourishment moves the shoreline seaward, and the seawalls have no effect. As time progresses, the beach nourishment spreads out along the coast. This is also shown in Figure 4-22. Figure 4-23 shows the shoreline response with an updrift breakwater. The shoreline position from the middle of the updrift seawall to the breakwater is similar to that same relative location in Figure 4-18. These results reinforce the conclusions from

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72 Case 3b. Continuing downcoast from the midpoint of the updrift seawall, the shoreline position seaward of the seawall continues to increase slowly to the boundary of the nourishment with only a small dip at the downcoast end of the seawall. As previously mentioned, the sediment volume from the nourishment must first provide a profile with the necessary sediment to reach the critical volume before the shoreline can advance seaward. The shortage of sediment for transport (attributable to the breakwater in this case) results in a progressive removal of sediment from the updrift (adjacent to the sediment sink) to the downdrift direction to satisfy continuity, and in turn, progressively greater depths fronting the seawall in the updrift direction. Consequently, more and more of the nourishment volume must go toward reaching the critical volume along the seawall from the downdrift to the updrift direction of the seawall. The resulting gradual increase in shoreline advance is a result of these processes. The small dip at the downcoast end of the seawall shows that immediately before the nourishment, the shoreline at that downcoast end of the seawall had already reached the seawall resulting in water depth at that boundary. This means that more sediment volume is necessary to reach the critical volume in those cells, and the resulting shoreline is landward of cells that had less water depth fronting the seawall at the time of the nourishment. This behavior was discussed for the results of Case 3b. The shoreline response downdrift of the second seawall is similar to the results downdrift of the seawall in Case 3b. The only other difference between Case 4b and Case 3b is that now the shoreline must orient itself to the direction of the incoming waves not just between the first seawall and the breakwater, but also between the two seawalls

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73 since the updrift end of the downcoast seawall will also act as a groin once the shoreline recedes landward of the seawall. Figure 4-24 shows the shoreline position by cell for Case 4b. These figures give an accurate description of erosion rates in relation to distance downdrift from the breakwater and proximity to a seawall. Figure 4-24 agrees with previous conclusions for shoreline response from the nourishment spreading out along the coast over time. As the nourishment spreads, temporary shoreline advances are evident in cells affected by this behavior.

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74 Table 4-1. Input parameters for seawall sensitivity test cases. Case Groin (yes/no) Groin (cell) Nourishment (yes/no) Nourishment (cells) Seawalls (yes/no) 1st Seawall (cells) 2nd Seawall (cells) 1b yes 120 no -yes 100 to 110 -2a no -yes 90 to 110 no --2b yes 120 yes 90 to 110 no --3a no -yes 100 to 110 yes 95 to 105 -3b yes 120 yes 100 to 110 yes 95 to 105 -4a no -yes 85 to 110 yes 65 to 80 90 to 105 4b yes 120 yes 85 to 110 yes 65 to 80 90 to 105

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75 Figure 4-1. Critical volume, V c per unit width. The critical volume is the entire area shown in brown. Figure 4-2. Volume per unit width for an aerial beach seaward of the seawall (y N y sw ).

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76 Figure 4-3. Initial volume per unit length for a seawall in the surf zone (y N < y sw ). Figure 4-4. Volume change for a fictitious shoreline retreat with locations shown in both global and local coordinates.

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77 Figure 4-5. Total sediment transport fronting a seawall for four planar beach slopes and several wave conditions shown by different line types. A) Slope, m = 1:10. B) Slope, m = 1:02. C) Slope, m = 1:50. D) Slope, m = 1:100. Ruggerio, P. and W.G. McDougal (2001), An Analytic Model for the Prediction of Wave Setup, Longshore Currents and Sediment Transport on Beaches with Seawalls, Coastal Engineering: An International Journal for Coastal, Harbour and Ocean Engineers, Volume 43, pp. 161-182.

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78 Figure 4-6. Graphical representation of positive transport and y sw (I) < y N (I-1) at the start of the seawall. The shoreline is shown in blue and the seawall is shown in red. This case means the seawall act as a groin and blocks transport (Q(I) = 0) as it forms a discontinuity in the shoreline. Figure 4-7. Input parameters for Case 1.

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79 Figure 4-8. Case 1b: One seawall, no nourishment. Shoreline evolution. Figure 4-9. Case 1b: One seawall, no nourishment. Shoreline position by cell.

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80 Figure 4-10. Input parameters for Case 2. Figure 4-11. Case 2a: No seawall, one nourishment, and no breakwater. Shoreline evolution.

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81 Figure 4-12. Case 2a: No seawall, one nourishment, no breakwater. Shoreline position by cell. Figure 4-13. Case 2b: No seawall, one nourishment, one breakwater. Shoreline evolution.

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82 Figure 4-14. Case 2b: No seawall, one nourishment, one breakwater. Shoreline position by cell. Figure 4-15. Input parameters for Case 3.

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83 Figure 4-16. Case 3a: One seawall, one nourishment, no breakwater. Shoreline evolution. Figure 4-17. Case 3a: One seawall, one nourishment, no breakwater. Shoreline position by cell.

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84 Figure 4-18. Case 3b: One seawall, one nourishment, one breakwater. Shoreline evolution. Figure 4-19. Case 3b: One seawall, one nourishment, one breakwater. Shoreline position by cell.

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85 Figure 4-20. Input parameters for Case 4. Figure 4-21. Case 4a: Two seawalls, one nourishment, no breakwater. Shoreline evolution.

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86 Figure 4-22. Case 4a: Two seawalls, one nourishment, no breakwater. Shoreline position by cell. Figure 4-23. Case 4b: Two seawalls, one nourishment, one breakwater. Shoreline evolution.

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87 Figure 4-24. Case 4b: Two seawalls, one nourishment, one breakwater. Shoreline position by cell.

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CHAPTER 5 OCEANSIDE MODEL DATA This chapter describes the general content of the input/output (I/O) files and the specific values used for the Oceanside simulations. Input files define the groins, initial shoreline, nourishments, seawalls, sources/sinks, waves, and background erosion. The current version of the DNR model requires that input variables be defined in English units. Output files contain the saved variables that define the results of the simulation. The data displayed in the output file are also given in English units. Input Main Input File The main input file must have the name InputMain and must be in the same directory as the DNR executable. This input file provides the full paths and names for all other input files. Constants The Constants input file provides information about the sediment and other run parameters that remain unchanged throughout the simulation. These include the longshore sediment transport coefficient (K = 0.35), gravitational constant (g = 9.81 m 2 /s or 32.18 ft 2 /s), specific gravity of the sediment (usually defined for sand as 2.65), sediment porosity (usually defined for sand as 0.35), sediment grain size, the profile coefficient for an equilibrium profile, and a breaker index ( = 0.78). 88

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89 Total Depth The total depth input file provides the closure depth and berm height at each cell. The present version of the DNR model requires these values to be uniform. Some variability exists in published closure depth values for this region of the coast north of San Diego. The United State Army Corps of Engineers (USACE, 1991b) estimated a 9.1-m (30-ft) closure depth in the Oceanside area. Boswell et al. (2004) found the closure depth equal to 7.6 m (25 ft). The 7.6-m (25-ft) closure depth value will be used since this is a more recent result. The berm elevation is 4.3 m (14 ft) (USACE, 1991b). Groins Groin lengths are defined as the perpendicular distance from the baseline to the seaward tip of the structure. As discussed in Chapter 2, structures defined in the groins input file include breakwaters, jetties, and groins. The only structures presently affecting littoral transport in the project area are the north and the south breakwaters at Oceanside Harbor, the San Luis Rey River groin, and the rubble base of the Oceanside Municipal Pier. The lengths of the north and south breakwaters were taken from the USACE shoreline definition AutoCAD files provided by Ryan (2002). The effective lengths of these two structures were defined as the perpendicular distance from the baseline to the point on the structure farthest from the baseline. The lengths for the San Luis Rey River groin and the base of the Oceanside Municipal Harbor were found using the Maptech Mapserver website. First, the distance between the shoreline and the tip of the structures was found by converting the latitude and longitudinal coordinates of these locations to distances. Next, the actual shoreline positions were referenced to the 1998 shoreline to find the total distance from the baseline to the tips of these two structures. The change in

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90 shoreline position from 1934 to 1998 was then incorporated to give the length of the structures referenced to the initial 1934 shoreline position. The structures may be defined as impermeable or leaky. An impermeable structure blocks all longshore transport until the shoreline position is seaward of the tip of the structure. Leaky, or permeable, groins only block a portion of the transport. This amount is based on the fraction of the breaker zone blocked by the groin. In the groin input file, the location, length, date of installation, and groin type are specified for each groin or breakwater. For the Oceanside simulations, groins are considered leaky and breakwaters are impermeable. Table 5-1 shows the effective lengths these structures used in the model runs. The effective length of the San Luis Rey River groin is approximately 100 m (330 ft) shorter than its actual length because of sand passing through or over the groin. It should also be noted that at a groin, the shoreline angle is based on the tip of the groin rather than the down drift cell. Normally, the orientation of the cross-shore distance between one cell and its adjacent downdrift cell defines the shoreline angle. However, when a groin is present, the shoreline angle is defined by the orientation between the tip of the groin and the cross-shore position of the adjacent, updrift cell. This results in a local modification of the transport at a groin. Initial Shoreline The DNR model can use the actual shoreline or a straight initial shoreline as an initial configuration. Using the actual shoreline requires that the wave heights and directions be accurately known along the shoreline. Furthermore, these wave characteristics are required at a detailed scale in the alongshore direction to avoid

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91 interpolation errors. Small inaccuracies in the wave estimates can lead to large errors and dominate the results in the long-term simulations. It has been observed that on most open coastlines, the alongshore wave conditions with respect to the local shoreline orientation tend to be uniform. If the local waves are uniform, then referencing to the local shoreline is equivalent to taking a straight initial shoreline and spatially constant wave conditions. The change in shoreline position over time is computed using this straight shoreline as the initial shoreline. The changes are then added to the actual initial shoreline position to give the actual predicted shoreline position. This approach is less sensitive to small inaccuracies in wave conditions and is the approach recommended by Dean (2001) for shoreline modeling. This is the technique employed for the Oceanside simulations. However, the conditions at Oceanside are somewhat atypical. Carlsbad Canyon results in an alongshore variation in local wave conditions. This influence is included in the DNR model and discussed later in the waves section. The actual initial shoreline for the historical runs is the May 1934 survey, which is shown in Figure 5-1. For the forecast runs, the initial shoreline is the April 1998 Lidar survey. The variation of the wave angles resulting from the Carlsbad Canyon at the southern end of the study area necessitates a modification of the wave direction in this area. This adjustment was developed for the 1934 to 1998 calibration runs using the 1934 shoreline as the initial condition. Since the model was calibrated for the 1934 initial shoreline, the 1998 shoreline was defined with respect to the 1934 shoreline for the forecast runs. This preserves the calibration coordinate system. The forecast runs do not

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92 begin with a straight initial shoreline. Instead, they begin with the position of the 1998 shoreline relative to the 1934 shoreline. The initial shoreline input file is also used to specify the computational cell length (must be constant), the number of cells, and the orientation of the local beach alignment with respect to north. For the present version of the model, all characteristics must be defined in English units. Nourishment The DNR model can address multiple nourishments at arbitrary times and locations. For each nourishment, the total volume of fill, the cells in which the fill is placed, and the date of the placement must be specified. It is assumed that the total volume of each individual nourishment is evenly divided among the cells. Cases with longshore variations in the fill volume may be addressed through multiple fills placed at the same time. The nourishments input file defines the alongshore extent of the nourishment (first and last cell), volume (yd 3 ), placement time (hr), and fill factor. The fill factor is the relationship between the total volume of sediment in the beach nourishment and the volume of sediment that remains as part of the littoral system. The smaller the fill factor, the more sediment is lost from the littoral system. If all the sediment remains in the littoral system, the fill factor is equal to 1.0. Conversely, if all the sediment from the nourishment is lost from the littoral system, the fill factor is equal to 0.0. A comparison between native and the fill sediments revealed that the median sediment size used as nourishment is smaller than the native sediment size located at Oceanside Beach (USACE, 1984). Because of this difference in sediment size, a fill factor with a value less than one is expected. Beach monitoring by Coastal Frontiers

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93 Corporation (2004) resulted in a fill factor approximation of 0.8. For this project, a fill factor of 0.7 provides the best shoreline predictions. A detailed explanation of the historical nourishment locations and volumes was presented in Chapter 2. For the nourishment input in the forecast simulations, the recent practices are assumed to continue in the future. The average dredged volume from the harbor from 1992 to 2003 had been 184,600 m 3 /yr (241,500 yd 3 /yr). This is the volume used for the future nourishments. Figure 2-8 shows the historical nourishment patterns, which reveals three major placement areas shown by the red, blue, and green lines. Future nourishments placements are assumed to alternate repeatedly between these three areas for the duration of the simulations. At the southern end of the project area, several nourishments occurred that were associated with back-passing at Agua Hedionda Lagoon. In the forecast simulations, the back-passing rates are 38,000 m 3 /yr (50,000 yd 3 /yr). These nourishments are placed in the area denoted by the purple lines in Figure 2-8 along the Carlsbad shoreline. Seawalls The DNR model can accommodate multiple seawalls along the reach. At each cell with a seawall, the cross-shore location, height, and slope of the wall are given. Since the cells are 100 m wide, the seawalls are fit into cells by rounding their lengths accordingly either up or down. Furthermore, small spaces, or gaps in armoring, and very short seawalls (less than 50 m) are omitted. If the slope is set to 99, the model assumes a vertical wall. The water depth/berm elevation at the seawall is also specified. Berm elevation is given as a negative number and water depth as a positive number. Elevations in the DNR model for the Oceanside simulations are referenced to MSL.

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94 The seawall height, or crest elevation, is the vertical distance from MSL to the top of the seawall. These elevations are obtained from two sources: 1) The GIS Study performed at Oceanside and 2) The Lidar Survey performed for the Oceanside littoral cell. These two references enable estimates of the elevations at the top of the seawalls with reasonable accuracy. This is important for the calculation of overtopping events. The GIS and the Lidar Surveys are taken from the NAVD88 reference, which is approximately 0.78 m (2.57 ft) below the MSL reference datum. Therefore, conversions are made accordingly. This topic was discussed in Chapter 2. The cross-shore distance used for the seawall data input is a function of the initial shoreline position. If the actual initial shoreline is used, then the actual distance from the baseline to the seawall defines the seawall cross-shore position. If a straight initial shoreline is used, the cross-shore seawall distance is relative to the distance from the shoreline being referenced. In the Oceanside simulations, the initial shoreline is straight and referenced to the 1934 shoreline. Therefore, cross-shore seawall locations, y sw are the distances from the actual seawall locations, y swa to the 1934 shoreline positions, y 1934 (y sw = y swa y 1934 ). Table 5-2 shows the seawall parameters for the project area. For details on the specifications of the seawalls along the Carlsbad and Oceanside coastlines, refer to Chapter 2. Sources/Sinks Sources and sinks are gains or losses of sediment from the littoral system to or from external sources. Sources or sinks may be specified for any cell. A source may be used to account for sediment influx from a river or sand introduced to a down drift beach by bar by-passing. A sink may be used when there is shoreline retreat and the eroded sediment is finer than the native material. A portion of this finer sediment will be

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95 removed from the littoral system. A sink may also be used at an up drift breakwater to account for by-passing sediment or loss to the offshore. Sources and sinks are specified as volume per unit length per year. This definition is convenient for shoreline recession. For point processes, such as the sediment added by rivers, the total volume of sediment added in one year must be divided by the cell length to get the per unit length value for the cell. Input parameters for river sediment contributions for the project area are described in Chapter 2. Another important source/sink consideration is in the by-passing boundary condition at Oceanside Harbor. The DNR model does not include inlet processes as the sediment passes the entrance to the harbor. By-passing may be included as a source/sink by removing the source nourishment sediment from one or more specified cells. At Oceanside Harbor, a source/sink is placed updrift of the north breakwater and also downdrift of the south breakwater. The strength of the sources/sinks is estimated from a sediment budget at the breakwaters. In Figure 5-2, Q is the longshore sediment transport (LST) rate, Q d is the dredging rate (the main source for downdrift nourishments), Q f is the accumulation rate in the fillet north of the breakwater, and Q o is the rate sediment is lost to the offshore. The amount of sediment lost to the offshore is a function of the LST rate (Q o = cQ), where c is a constant. Table 5-3 is an example of the sources/sinks for an annual longshore transport rate of 153,000 m 3 /yr (200,000 yd 3 /yr). The rate of accumulation in the north fillet was discussed in Chapter 2. The sediment from the north breakwater may be transported into the harbor, develop a shoal at the harbor entrance, by-pass the harbor, or be jetted by

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96 currents into deeper water. In Table 5-3, it is assumed that the volume of sediment in the harbor is in equilibrium and the offshore loss coefficient is c = 0.05. The dredged volume of sediment removed from the harbor must have been supplied from either the north or south side of the harbor. The available sediment from the north side has been estimated, so the remainder must be provided south of the harbor. This is the source/sink strength for the south breakwater. The volume change rates for the areas marked 1 and 2 in Figure 5-2 are as follows: 1-(--)f oodVQQQQQQdt f (5.1) 2() f odfodfdVQQQQQQQQQcQQdt d (5.2) In the cell north of the harbor, the volume change rate is not a function of the LST rate. This is a result of the fillet accumulation rate being given as a constant based on limited field observations. At the cell south of the harbor, the updrift fillet accumulation rate is constant and the annual dredging rate is also constant, so the rate of volume change is weakly dependent on the LST through the term Q o = cQ. A consequence of these harbor boundary conditions is that the shoreline response is insensitive to the magnitude of the LST. In a one-line model, shoreline changes are driven by gradients in longshore processes. Waves The waves are the most complex input file. The waves define the time step, run duration, and to a great extent, the mode in which the DNR model executes. The DNR model can be run in three modes, which are specified by the type of wave data: 1) Waves that are constant in space and time, 2) Waves that are constant in space and variable in

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97 time, and 3) Waves that are variable in space and time. The complexity and computational effort increases with each of these cases. In each case, the specified wave data are the height (either significant or RMS), period, direction, and water depth. For the case of waves that are constant in space and time, just a single, constant wave condition is provided. Some variation may be added to this constant wave to account for seasonal variations in direction by adding an annual sinusoidal change in the dominant wave direction. For waves that are uniform in space and variable in time, a single time series of waves is provided. This constant in space, variable in time condition is the wave case used for the Oceanside project. For waves that are variable in space and time, wave time series are provided at several wave stations along the reach. The waves at these stations are linearly interpolated to provide wave conditions at each computation cell at each time step. Waves that are variable in space and time significantly increase the run time for the model. The wave input is also used to define the time step, run duration, and the length of the wave time series. If the run duration exceeds the length of the wave time series, the time series is repeated from the beginning. This process will repeat up to a maximum of five times. In the present version of the DNR model, the time step must be one hour. The wave hindcast series, provided by OReilly are given at nine wave stations along the study area at the -12-m (-40-ft) contour. These are shown with respect to the April 1998 shoreline in Figure 5-3. The wave records from OReilly provide hourly estimates of significant wave height, H s peak wave period, T p peak wave direction, p radiation stress, S xy and water depth change from El Nino events. Radiation stress is determined by summing the radiation stresses at each wave frequency and direction in the

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98 spectrum to get a total integrated value. This is important because it quantitatively determines the direction and magnitude of the LST. The LST equation in the DNR model uses H s and T p to compute the transport rather than directly using S xy The peak wave direction is slightly different than the direction of the integrated radiation stress. The local wave angle, eff which corresponds to the radiation stress direction, is determined by equating the integrated radiation stress with the computed radiation stress using H s and T p This is done for every hour of wave data in the 50-year records. Figure 5-4 shows a comparison of p and eff The average difference between the two is rather small (1.3), and this definition of wave direction is consistent with the LST formulation in the DNR model. The Carlsbad Canyon causes the offshore profile to become steeper. This is seen in Figure 2-3 where the -12-m (-40-ft) depth contour becomes closer to the shoreline from Oceanside Harbor to Agua Hedionda. This longshore variation in depth can also be seen in Figure 5-5, where the depth contours are given in 5-fathom intervals. The depth contours not being parallel to the shoreline introduces two difficulties: 1) The DNR model is a one-line model and assumes that the profile is the same at all alongshore locations, and 2) The wave angles referenced to the -12-m (-40-ft) contour are not the same as those referenced to the shoreline. Figure 5-6 shows the shore normal directions used in the 90 OReilly wave computation locations and the shore normal directions determined from the 1934, 1972, and 1998 surveys. The orientation for the waves is based on NOS hydrographic surveys conducted in the 1970's and early 1980's (O'Reilly, 2004). North of the harbor, an offset exists of approximately 2. South of the harbor, the difference is more significant and

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99 varied. To partially account for this difference, the waves are transformed to the 1934 shoreline orientation since the 1934 shoreline is the initial shoreline condition used in the model simulations. The transformation applies a three-step procedure: 1) Refract the OReilly waves back out to deep water, 2) Convert to the 1934 shoreline orientation, and 3) Refract the waves back into the -12-m (-40-ft) contour. Results for this transformation are shown in Figure 5-7. North of the harbor, local wave angles are very similar. South of the harbor, there is a nearly constant 2 difference. Figure 5-8 shows the local wave angle with respect to the 1934 shoreline for all OReilly wave calculation locations in the study area for one wave case (not the average of all 50 simulations). The head of Carlsbad Canyon comes close to the shoreline approximately 1,200 m (3,900 ft) south of Agua Hedionda Lagoon, which is outside of the project area. However, this anomaly affects processes occurring within the model bounds. The canyon causes the distance from the shoreline to the -9-m (-30-ft) contour to decrease almost linearly from Carlsbad Canyon to Oceanside Harbor. At the Oceanside pier, the -9-m (-30-ft) contour is approximately 750 m (2,500 ft) offshore, and at Agua Hedionda the -9-m (-30-ft) contour is approximately 600 m (2,000 ft) offshore. The result is that the -9-m (-30-ft) contour has an angle of 1.3 with respect to the shoreline. This causes a mean variation in wave direction south of the harbor. The variation in mean direction is estimated by the piecewise linear approximations shown in Figure 5-8. North of the harbor, a great deal of variability exists. The blue line north of the harbor is the mean for all computational sites. The pink line is the location and local wave angle for Station 6. The wave time series at Station 6 is used in the project simulations, so the local wave angle variation south of the harbor is expressed

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100 with respect to the wave directions north of the harbor. The variable wave direction at the southern end of the study area is explicitly included within the DNR model. This relationship between the highly variable wave directions north of the harbor and the wave directions south of the harbor is discussed in Chapter 6. North of the harbor, waves are taken to be uniform in space and variable in time for the model simulations. A great deal of variability exists in the wave direction north of the harbor, so a single shoreline orientation was selected which gave the appropriate LST (153,000 m 3 /yr or 200,000 yd 3 /yr) at a location north of the harbor that was outside the influence of human intervention near the northern part of the project area. LST rates were discussed in Chapter 2. Background Erosion As mentioned earlier, the background erosion input file creates a gradient in the longshore sediment transport to simulate a specified shoreline retreat. This method of defining background erosion was not used in the Oceanside simulations. Output The output file specifies which variables are to be saved (including shoreline positions, areas, volumes, and transport rates). The time interval and/or locations at which these values are saved are specified in this file. The DNR model automatically saves a shoreline position output file, a run summary file, and an error message file. For the Oceanside project, an overtopping and bore propagation file was also saved.

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101 Table 5-1. Cross-shore location and effective lengths of breakwaters and groins along the Oceanside coastline. Structure Cross-shore Location (Cell) Effective Length from Baseline (ft) Effective Length from Baseline (m) Oceanside Pier 65 -482 -147 San Luis Rey Groin 78 -95 -29 South Breakwater 86 636 194 North Breakwater 96 1860 567

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102 Table 5-2. Seawall input parameters for the Oceanside and Carlsbad shorelines. Cell y from 1934 Straight Initial Shoreline (ft) MTL Seawall Elevation (ft) Seawall Slope Depth at Toe (ft) MTL Backshore Elevation (ft) SW Description 1 -211.62 10.23 0.5 -14.0 10.23 Rubble 2 -196.44 20.83 0.5 -14.0 33.13 Rubble 3 -184.74 20.83 99.0 -14.0 35.43 Vertical seawall walkway 4 -193.23 20.83 99.0 -14.0 40.73 Vertical seawall walkway 5 -188.40 20.83 99.0 -14.0 46.33 Vertical seawall walkway 6 -184.44 20.83 99.0 -14.0 46.93 Vertical seawall walkway 7 -177.09 20.83 99.0 -14.0 46.33 Vertical seawall walkway 8 -174.96 20.83 99.0 -14.0 45.63 Vertical seawall walkway 9 -186.17 20.83 99.0 -14.0 45.93 Vertical seawall walkway 10 -174.94 20.83 99.0 -14.0 48.23 Vertical seawall walkway 11 -169.17 20.83 99.0 -14.0 48.63 Vertical seawall walkway 12 -185.92 20.83 99.0 -14.0 47.93 Vertical seawall walkway 13 -186.02 43.33 0.5 -14.0 43.33 Rubble 14 -199.81 25.93 99.0 -14.0 25.93 High cliff 15 -223.55 25.93 99.0 -14.0 25.93 High cliff 16 -222.20 17.93 99.0 -14.0 17.93 Home foundations 17 -233.64 17.93 0.5 -14.0 17.93 Rubble 18 -242.74 16.93 99.0 -14.0 16.93 Private vertical seawall 19 -249.28 12.53 0.5 -14.0 32.73 Rubble 20 -256.23 24.53 99.0 -14.0 25.13 Private vertical seawall 21 -258.53 16.93 99.0 -14.0 18.73 Home foundations 22 -252.39 18.73 0.5 -14.0 38.43 Rubble 23 -221.04 15.83 99.0 -14.0 18.43 Private vertical seawall 24 -220.67 16.43 0.5 -14.0 37.23 Rubble 25 -254.15 9.43 0.5 -14.0 9.43 Bridge over Buena Vista Lagoon 26 -277.77 10.43 0.5 -14.0 10.43 Rubble 27 -266.25 11.43 0.5 -14.0 12.43 Rubble 28 -246.98 11.43 0.5 -14.0 11.43 Rubble 29 -248.77 11.43 0.5 -14.0 12.43 Rubble 30 -255.60 13.43 0.5 -14.0 15.43 Rubble 31 -267.22 12.43 0.5 -14.0 13.43 Rubble 32 -290.70 12.43 0.5 -14.0 14.43 Rubble 33 -316.78 14.43 0.5 -14.0 16.43 Rubble 34 -334.52 15.43 0.5 -14.0 16.43 Rubble 35 -366.82 13.43 0.5 -14.0 15.43 Rubble 36 -373.41 11.43 0.5 -14.0 13.43 Rubble 37 -351.67 13.43 0.5 -14.0 14.43 Rubble

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103 Table 5-2. Continued Cell y from 1934 Straight Initial Shoreline (ft) MTL Seawall Elevation (ft) Seawall Slope Depth at Toe (ft) MTL Backshore Elevation (ft) SW Description 38 -335.60 11.43 0.5 -14.0 13.43 Rubble 39 -321.33 15.43 0.5 -14.0 15.43 Rubble 40 -320.28 12.80 0.5 -14.0 12.43 Rubble 41 -324.31 12.00 0.5 -14.0 11.43 Rubble 42 -440.84 10.60 99.0 -14.0 11.43 Bridge over Loma Alta Creek 43 -299.51 12.90 0.5 -14.0 12.43 Rubble 44 -284.15 15.50 0.5 -14.0 17.43 Rubble 45 -282.10 15.80 0.5 -14.0 17.43 Rubble 46 -286.87 14.80 0.5 -14.0 16.43 Rubble 47 -296.83 15.80 0.5 -14.0 13.43 Rubble 48 -334.37 12.80 0.5 -14.0 17.43 Rubble 49 -373.33 15.50 0.5 -14.0 17.43 Rubble 50 -396.43 13.43 0.5 -14.0 14.43 Rubble 51 -413.39 11.43 0.5 -14.0 11.43 Rubble 52 -428.55 11.43 0.5 -14.0 13.43 Rubble 53 -405.33 13.43 0.5 -14.0 13.43 Rubble 54 -366.06 11.43 0.5 -14.0 11.43 Rubble 55 -369.01 11.20 0.5 -14.0 11.43 Rubble 56 -389.85 11.20 0.5 -14.0 9.43 Rubble 57 -406.51 11.20 0.5 -14.0 9.43 Rubble 58 -420.75 11.20 0.5 -14.0 9.43 Rubble 59 -430.30 11.20 0.5 -14.0 9.43 Rubble 60 -434.78 11.20 0.5 -14.0 9.43 Rubble 61 -455.35 11.20 99.0 -14.0 10.43 Curb 62 -482.27 11.20 99.0 -14.0 10.43 Curb 63 -506.80 11.20 99.0 -14.0 10.43 Curb 64 -525.75 11.20 99.0 -14.0 9.43 Curb 65 -537.58 11.20 99.0 -14.0 9.43 Curb 66 -544.38 11.70 99.0 -14.0 9.43 Curb 67 -552.60 11.70 99.0 -14.0 9.43 Curb 68 -569.35 11.70 99.0 -14.0 10.43 Curb 69 -569.69 11.70 99.0 -14.0 10.43 Curb 70 -560.51 11.70 99.0 -14.0 9.43 Curb 71 -574.73 11.70 99.0 -14.0 9.43 Curb 72 -592.60 11.70 99.0 -14.0 9.43 Curb 73 -596.29 11.70 99.0 -14.0 9.43 Curb 74 -524.60 11.70 99.0 -14.0 9.43 Curb

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104 Table 5-2. Continued Cell y from 1934 Straight Initial Shoreline (ft) MTL Seawall Elevation (ft) Seawall Slope Depth at Toe (ft) MTL Backshore Elevation (ft) SW Description 75 -447.94 14.80 99.0 -14.0 11.43 Timber vertical SW 76 -666.33 14.80 99.0 -14.0 11.43 Timber vertical SW 77 -781.12 9.43 99.0 -14.0 9.43 Bridge 78 -602.95 13.30 99.0 -14.0 9.43 Curb 79 -540.18 13.30 99.0 -14.0 9.43 Curb 80 -506.21 14.30 99.0 -14.0 9.43 Curb 81 -488.18 13.30 99.0 -14.0 9.43 Curb 82 -492.07 14.20 99.0 -14.0 9.43 Curb 83 -435.57 13.80 99.0 -14.0 9.43 Curb 84 -283.44 13.80 99.0 -14.0 9.43 Curb 85 -164.43 13.80 99.0 -14.0 9.43 Curb Table 5-3. Source/sinks at the north and south breakwaters. Longshore Transport (yd 3 /yr) North Fillet (yd 3 /yr) North BW Source/Sink (yd 3 /yr) Dredging (yd 3 /yr) Offshore Losses (yd 3 /yr) South BW Source/Sink (yd 3 /yr) 200,000 40,000 -160,000 241,500 10,000 -91,500

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105 Figure 5-1. May 1934 shoreline and straight initial shoreline. Figure 5-2. Sediment budget north and south of Oceanside Harbor.

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106 Figure 5-3. OReilly hindcast wave gage locations and approximate -12-m contour. Figure 5-4. Mean peak wave angle and mean effective wave angle from the 50 wave records for each of the nine wave station.

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107 Figure 5-5. Depth contours along the study area shown in 5-fathom intervals.

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108 Figure 5-6. The shore normal direction used in the OReilly wave computations and the shore normal directions determined from the 1934, 1972, and 1998 surveys. Figure 5-7. Mean peak wave angle and mean effective wave angle results from the wave transformation to the 1934 shoreline orientation.

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109 Figure 5-8. The local wave angle with respect to the 1934 shoreline for all the OReilly wave calculation locations within the study area. This data is representative of only one of the wave records with values similar to the mean of the 50 wave records.

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CHAPTER 6 RESULTS This chapter presents preliminary results for the Oceanside shoreline simulations. Sensitivity analyses results are presented for the alongshore wave variation, the nourishment fill factor, and the offshore loss coefficient. Calibration results are evaluated by comparing calculated shorelines with the 1972 and 1998 measured shorelines. After calibration, the model was run to estimate the historical responses from 1934 to 1998 with and without the harbor. Forecast runs were made for the period from 1998 to 2058 with and without the harbor that included damage estimates. Sensitivity Analysis A number of DNR runs are conducted to determine the sensitivity to input parameters. The calibration simulations begin with the measured 1934 shoreline, and end in 1998. The RMS errors between the predicted and measured shorelines in 1972 and 1998 are computed. Results lead to the refinement of several input parameters, and the process is repeated until the RMS error is minimized. Seawall locations, initial and final shorelines, and nourishment volumes and placement locations are available from previous studies, so these parameters are not adjusted. Although guidance for other input variables, such as the nourishment fill factor, offshore loss of sediment at the north breakwater, and local wave angle can be taken from other published studies, the actual processes that define these characteristics are not as well known. Therefore, calibration is necessary for these parameters to achieve satisfactory results. 110

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111 Alongshore Wave Variation The alongshore variation in wave direction follows from the discussion in Chapter 5. Figure 5-8 shows a V-shaped variation in local wave angle south of the harbor. The local wave angle at Agua Hedionda, which is the southern end of the V, is estimated to be -6. The wave input for the entire coast is referenced to Station 6, which is north of the harbor and has an average local wave angle of -4. However, the local wave angles for the entire reach north of the harbor show significant variations. Using Station 6 as the reference presents an obstacle since it may or may not be a good representation of local wave angle north of the harbor. Furthermore, the local wave angle adjustments south of the harbor are dependent on the constant value chosen for the coastline north of the harbor. The variation in local wave angles north of the harbor does not greatly influence the shoreline planform evolution north of the harbor. However, since the shoreline south of the harbor is dependent on the local wave angle of Station 6, adjustments are necessary to achieve reasonable results. Figure 6-1 shows the RMS error between the predicted and the measured shorelines south of the harbor in 1972, 1998, and for both combined based on the V-shape wave angle variation south of the harbor as a function of the local wave angle at Agua Hedionda Lagoon. The reference local angle at Agua Hedionda is changed from -3 to +3. The optimum local wave angle at Agua Hedionda in terms of minimizing the RMS error for all 50 wave runs is +1. This result suggests that the local wave angle at Agua Hedionda is equal to +5 the local wave angle at Station 6, which is -4. Fill Factor The fill factor is the portion of nourishment that remains in the littoral system. Coastal Frontiers (2004) determined a fill factor of FF = 0.8 from field surveys

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112 conducted at Oceanside Beach. Figure 6-2 shows the RMS errors for the shoreline south of the harbor for different fill factors. Results are given for three longshore sediment transport (LST) rates and for a range of offshore loss coefficients. The offshore loss coefficient was discussed in Chapter 5. A fill factor of FF = 0.7 gives the best agreement with the shoreline data. Offshore Loss Coefficient Inman and Jenkins (1983) assumed that 20% of the longshore transport on the north side of the harbor was either trapped or lost offshore. In the present analysis, the trapping by the north breakwater and the offshore losses are separated. The trapping in the north fillet is taken as 30,600 m 3 /yr (40,000 yd 3 /yr). The loss to the offshore is considered to be a portion of the longshore transport. It is expected that the greater the LST, the greater the amount of sediment that is deflected to the offshore. Results from Inman and Jenkins (1983) showed that offshore loss is approximately 4% of the net transport for a net transport of 194,200 m 3 /yr (254,000 yd 3 /yr) and a fillet-trapping rate of 30,600 m 3 /yr (40,000 yd 3 /yr). Figure 6-3 shows the RMS error as a function of LST rates for various offshore loss coefficients. At all LST rates, the lowest RMS error occurs for zero offshore loss. At a LST of 152,900 m 3 /yr (200,000 yd 3 /yr), the RMS error difference between c = 0.00 and c = 0.05 is approximately 0.6 m (2 ft), which is not a significant difference. Since it is recognized that offshore losses do occur, an offshore loss coefficient of c = 0.05 is used for the Oceanside simulations. Calibrated Shoreline Planform Results A range of LST rates exist, which in combination with reasonable choices for other input information, yields similarly accurate estimates for the predicted shorelines. The

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113 shoreline response is rather insensitive over long periods of time to the magnitude of the LST since shoreline changes are primarily attributable to gradients in the LST rather than the magnitude of the transport. Using constant values for the accumulation rate of the north fillet, the by-passing of the harbor, and the harbor dredging combine to reduce the sensitivity of the shoreline response with respect to the magnitude of the LST. Therefore, published values for LST are used as guidance. As discussed in Chapter 2, reported LST rates range from approximately 76,000 to 191,000 m 3 /yr (100,000 to 250,000 yd 3 /yr) with a typical value of 153,000 m 3 /yr (200,000 yd 3 /yr). A LST of 153,000 m 3 /yr (200,000 yd 3 /yr) is used in the DNR model runs. Historical Runs Historical runs are from 1934 to 1998. Figure 6-4 shows the shoreline positions in 1972 and in 1998. The figure gives the RMS errors north and south of the harbor and the combination of the 1972 and 1998 RMS errors. Comparison of the measured and calculated shorelines shows good results north of the harbor. The RMS error for 1972 is 13.1 m (43.0 ft) and the RMS error for 1998 is 18.3 m (60.0 ft). The combined RMS error for the shoreline north of the harbor is 15.9 m (52.2 ft). South of the harbor, the agreement is reasonable between the measured and the calculated shorelines. The RMS errors for 1972, 1998, and the combination of the two dates are 22.0 m, 20.6 m, and 21.3 m (72.1 ft, 67.6 ft, and 69.9 ft), respectively. A substantial amount of the error occurs between the San Luis Rey river groin and the south breakwater. The DNR model does not include wave modifications associated with breakwaters, so less accurate result near breakwaters are expected. Figure 6-5 shows the annual shoreline recession rates for the periods 1934 to 1972, 1972 to 1998, and 1934 to 1998. The 1934 to 1972 and 1934 to 1998 measured and

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114 predicted shoreline change rates are in good agreement both north and south of the harbor. The main differences occur near the breakwaters where the DNR model does not include breakwater effects. The measured changes for 1972 to 1998 show significant alongshore variation not seen for the other time intervals. The DNR model approximates the trends in the result, but does not capture all of the variation. Figure 6-6 shows the shoreline positions as a function of time. Figure 6-6 (A) is the actual shoreline position, and Figure 6-6 (B) is the change in position from an initial straight shoreline. Both plots show recession of the shoreline north of the harbor. Closer to the north breakwater, the shorelines do not show development of a fillet. Since little shoreline change occurs, the fillet growth must approximately balance with the shoreline recession, offshore losses, and by-passing. South of the harbor, the dominant response is major shoreline retreat from 1942 to the mid-1950s. In 1957, by-passing and nourishments began and the shoreline immediately shows a decrease in erosion rate. Figure 6-7 shows the historical shoreline response without breakwaters. The planform approaches an equilibrium shape that is somewhat similar to the 1934 pre-harbor shoreline. The delta shape in the shoreline is located at the south breakwater rather than near the San Luis Rey groin. The waves were developed and calibrated for conditions with the harbor present. If the harbor had not been present, the V-shape in the local wave angle may have terminated near the San Luis Rey groin rather than the south breakwater. The resulting shoreline evolution for this case is shown in Figure 6-8. The final shoreline result is quite similar to the 1934 planform. Forecast Results The initial shoreline in the forecast runs is the measured 1998 shoreline. However, the 1998 shoreline position is referenced to the 1934 shoreline, which is the coordinate

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115 system used for the wave calibrations. The run duration is 60 years to estimate the damage costs for 50 years from 2008 to 2058. Input for the forecast runs is very similar to input for the historical runs. It is assumed that the processes that occurred in the recent past will continue to occur into the future. Historic dredging and nourishments are assumed to continue at the same magnitudes and time intervals. Figure 6-9 shows the predicted 2058 shoreline position. The 1998 shoreline is shown for reference. The fillet to the north of the harbor continues to grow. The volume of sediment in the fillet corresponds to 60 years of accumulation at a rate of 30,600 m 3 /yr (40,000 yd 3 /yr). South of the harbor, significant shoreline recession exists between Buena Vista Lagoon and the Oceanside Pier. The shoreline retreats back to the seawall and significant overtopping events occur. Figure 6-9 shows that if the natural processes such as the LST rate and human influences such as by-passing and nourishment continue to occur in the future as they have in the recent past, erosion will continue and the shoreline will retreat back to the seawall. This will result in a dramatic increase in the number of overtopping events and damage potential. Figure 6-10 shows the shoreline planform evolution in 10-yr intervals. Minor shoreline changes occur north of the harbor. However, the shoreline south of the harbor retreats back to the seawall. To estimate the influence of the breakwaters, simulations without breakwaters are done for two cases: 1) Assuming the breakwaters were removed in 1998 and the 1998 shoreline was taken as the initial shoreline, and 2) Assuming the breakwaters were never constructed and the 1934 shoreline was taken as the initial shoreline. Figure 6-11 shows the shoreline position in 2058 if the breakwaters were removed in 1998. For reference, the measured 1934 and 1998 shorelines are also shown. The 2058 shoreline

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116 configuration is somewhat similar to the 1934 shoreline. The evolution of the shoreline for this case is shown in Figure 6-12. Figures 6-13 and 6-14 show the same results if the breakwaters never existed. Damage Comparisons The economic analyses for damage costs are based on the largest overtopping event that occurs each month. It is possible that many months will not have any overtopping events. The DNR model actually determines the overtopping events every hour. These are then sorted to select the largest event each month. The number of overtopping events is determined for the forecast simulations with and without the breakwaters in place. The without-breakwaters simulations are done for two cases: 1) Assuming the breakwaters are removed in 1998 using the 1998 shoreline as the initial shoreline and 2) Assuming the breakwaters were never constructed with the 1934 shoreline as the initial shoreline. With breakwaters, 39,272 hourly overtopping events and 4,168 monthly events occur. For the same simulation conditions with the breakwaters removed in 1998, 11,345 hourly events and 1,789 monthly events occur. For the case where breakwaters were never installed, 1,298 hourly events and 305 monthly events occur. For the case with breakwaters there are approximately 30 times as many hourly events and 14 times as many monthly events compared to the case where breakwaters were never installed. This is a significant difference and indicates the potential magnitude of the harbor on future shoreline stability and the need for increased nourishment. Figure 6-15 shows the number of monthly overtopping events for each cell with and without breakwaters. These results are for wave case 38, which has a net longshore transport rate approximately equal to the rate for all 50 wave cases. Many more

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117 overtopping events occur with the breakwaters, and they occur from cells 30 to 60. For the case where no breakwaters were installed, the damage was distributed from cells 40 to 47.

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118 Figure 6-1. RMS error between the predicted and the measured shorelines south of the harbor in 1972, 1998, and for both combined based on the V-shaped wave angle variation as a function of the local wave angle at Agua Hedionda Lagoon.

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119 A B C Figure 6-2. RMS errors for different fill factors and different values of offshore loss coefficients, c. A) Transport, Q = 229,000 m 3 /yr. B) Transport, Q = 134,000 m 3 /yr. C) Transport Q = 38,000 m 3 /yr.

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120 Figure 6-3. The RMS error as a function of LST rates for various offshore loss coefficients.

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121 Figure 6-4. Shoreline planform results referenced to the actual 1934 initial shoreline. A) 1972. B) 1998.

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122 Figure 6-5. Annual shoreline change rates. A) 1934 to 1972. B) 1972 to 1998. C) 1934 to 1998.

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123 Figure 6-6. Historical shoreline evolution. A) Referenced to actual shoreline positions. B) Change from a straight initial shoreline.

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124 Figure 6-7. Historical shoreline planform evolution without breakwaters for waves developed with the harbor presence. Figure 6-8. Historical shoreline planform evolution without breakwaters for wave angles adjusted to remove harbor effects.

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125 Figure 6-9. Forecast final shoreline position with breakwaters. Figure 6-10. Forecast shoreline evolution with breakwaters.

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126 Figure 6-11. Forecast final shoreline position if breakwaters were removed in 1998. Figure 6-12. Forecast shoreline evolution if breakwaters were removed in 1998.

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127 Figure 6-13. Forecast final shoreline position if breakwaters never existed. Figure 6-14. Forecast shoreline evolution if breakwaters never existed.

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128 Figure 6-15. Forecast monthly overtopping events with breakwaters, removing breakwaters in 1998, and if breakwaters never existed.

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CHAPTER 7 CONCLUSIONS Our objective was to estimate the shoreline impacts attributable to Oceanside Harbor. To accomplish this, the shoreline characteristics within the project area were defined. Since the Oceanside and Carlsbad coastlines are almost entirely armored by seawalls, a seawall algorithm was added to the DNR model and then calibrated. Run-up, bore propagation, and force calculations were also added to the DNR model. Simulations were made for the time period from 1934 to 1998 to calibrate the model. Then two 60-year forecast cases were examined to estimate the future impacts of the harbor: 1) With breakwaters, and 2) Without breakwaters. To model the shoreline, it was necessary to correctly specify the variables that define the project area. Most of the coastline characteristics (including the historical shoreline positions, beach nourishments, by-passing/dredging rates, river sediment contributions, and structures) have been studied and documented. For these, the published results defined the input. Other input parameters needed to be simulated, including the background erosion rates and local wave angles. The wave input file included derived values for the wave heights based on historical buoy data and simulated values for the wave direction. These simulated wave angle values were necessary to correctly define the local incoming wave angles. Finally, several parameters were the result of calibration and sensitive analyses, including the offshore loss coefficient and the nourishment fill factor. 129

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130 A seawall algorithm for the DNR model was developed and examples were presented to verify the model. To incorporate the seawall routine into the DNR model, which normally tracks the shoreline position, adjustments were made that allowed the model to track the change in sediment volume along a seawall. The algorithm then calculates the shoreline position from the change in volume assuming an equilibrium profile and the incorporated reduced transport seaward of the seawall. The verification of the seawall algorithm provides insight on how the routine interacts with the nourishment and groin subroutines. Once the characteristic site input data were gathered and the DNR model modified to accommodate seawalls and calculate the run-up, bore propagation, and forces; the impact of the harbor breakwaters was examined. Two forecast simulations were made that spanned 60 years into the future. One included the breakwaters, by-passing, and nourishments and the other one did not. Results for the with-breakwater condition show that if the current natural processes and human practices continue into the future, the shoreline will erode back to the seawall causing progressively more overtopping and damage events along the Oceanside coastline. Results for the without-breakwater conditions shows the shoreline equilibrating to a final shoreline position that is similar to the shape of the 1934 measured shoreline.

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LIST OF REFERENCES Boswell, M.K. (2004), Closure Depth and Beach Profiles for Southern California Beaches, University of Florida Master of Science Report, Department of Civil and Coastal Engineering, 41 pp. Brownlie, W.R., and B.D. Taylor (1981), Sediment Management of Southern California Mountains, Coastal Plains, and Shorelines Part C, Coastal Sediment Delivery by Major Rivers in Southern California, California Institute of Technology, Environmental Quality Laboratory Report No. 17 C, Pasadena, California, 314 pp. CIRIA/CUR (1991), Manual on the Use of Rock in Coastal Shoreline Engineering, CIRIA Special Publication 83/CUR Report 154, A.A. Balkema Publishers, pp. 246-252. Coastal Frontiers Corporation (2003), SANDAG 2002 Regional Beach Monitoring Program Annual Report, Chatsworth, CA, 105 pp. + app. Cox, J.C, and J. Machemehl (1986), Overload Bore Propagation Due to an Overtopping Wave, Journal of Waterway, Port, Coastal, and Ocean Engineering, Volume 112, No. 1. Dean, R.G. (2001), Beach Nourishment: Theory and Practice Advance Series on Ocean Engineering, World Scientific Publishing Co, Singapore. Dean, R.G., and R.A. Dalrymple (2002), Coastal Processes with Engineering Applications, Cambridge University Press, Cambridge, 475 pp. Dean, R.G., and J. Grant (1989), Development of Methodology for Thirty-Year Shoreline Projections in the Vicinity of Beach Nourishment Projects, University of Florida Master of Science Thesis, Department of Coastal and Oceanographic Engineering Department, Gainesville, FL, 153 pp. Hales, L.Z. (1978), Coastal Processes Study of the Oceanside, California Littoral Cell, Final Report, U.S. Army Corp of Engineers, Waterways Experiment Station, Misc. Paper H-78, Vicksburg, MS, 464 pp. Inman, D.L., and S.A. Jenkins (1983), Oceanographic Report for Oceanside Beach Facilities, prepared for the city of Oceanside, 206 pp. 131

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132 Marine Advisors (1960), Design Waves for Proposed Small Craft Harbor at Oceanside, California prepared for the U.S. Army Corp of Engineers, Los Angeles District, La Jolla, CA. Ramsden, J.D., and F. Raichlen (1990), Forces on Vertical Wall Caused by Incident Bores, Journal of Waterway, Port, Coastal, and Ocean Engineering, Volume 116, No. 5. Ruggerio, P. and W.G. McDougal (2001), An Analytic Model for the Prediction of Wave Setup, Longshore Currents and Sediment Transport on Beaches with Seawalls, Coastal Engineering: An International Journal for Coastal, Harbour and Ocean Engineers, Volume 43, pp. 161-182. Shoreline Protection Manual (1984), 4 th Edition, Volumes I and II, U.S. Army Corp of Engineers, Waterway Experiment Station, Government Printing Office, Washington, DC. Simons, Li and Associates (1985), Analysis of the Impact of Dams on Delivery of Sediment From the Santa Margarita River, California. U.S. Bureau of Reclamation, Lower Colorado Region, Boulder City, Nevada. Simons, Li and Associates (1988), River Sediment Discharge Study, San Diego Region, U.S. Army Corps of Engineers, Los Angeles District, Coast of California Storm and Tidal Waves Study (CCSTWS) Report No. 88-3, 4 Volumes. Tekmarine, Inc. (1987), Oceanside Littoral Cell, Preliminary Sediment Budget Report, U.S. Army Corp of Engineers, Los Angeles District, Coast of California Storm and Tidal Waves Study (CCSTWS) Report No. 87-4, 36 pp. + Appendices. U.S. Army Corps of Engineers (USACE), Los Angeles District (1984), Geomorphology Framework Report, Dana Point to the Mexican Border, Coast of California Storm and Tidal Wave Study (CCSTWS) Report No. 84-4, 75+ pp. U.S. Army Corps of Engineers (USACE), Los Angeles District (1991a), State of the Coast Report, San Diego Region: Chapter 6, Sources, Transport Modes, and Sinks of Sediments, Coast of California Storm and Tidal Wave Study (CCSTWS) Volume 1 Main Report. U.S. Army Corps of Engineers (USACE), Los Angeles District (1991b), State of the Coast Report, San Diego Region: Chapter 7, Application of Beach Change Models, Coast of California Storm and Tidal Wave Study (CCSTWS) Volume 1 Main Report. U.S. Army Corps of Engineers (USACE), Los Angeles District (1994a), Oceanside Shoreline, Oceanside, San Diego County California: Chapter 2.0 The Study Area, Reconnaissance Report, Main Report.

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133 U.S. Army Corps of Engineers (USACE), Los Angeles District (1994b), Oceanside Shoreline, Oceanside, San Diego County California: Coastal Engineering Appendix, Reconnaissance Report, Economic Appendix, Environmental Evaluation, Real Estate Appendix.

PAGE 148

BIOGRAPHICAL SKETCH Gabriel Alejandro Perdomo graduated from Dr. Phillips High School, in Orlando, in May 1996. He was accepted to the University of Florida (UF) and began his undergraduate studies in Civil Engineering in August 1996. During his undergraduate studies, Gabriel Perdomo worked under the supervision of Dr. Kurt Gurley, studying the effects of hurricane-force winds on structures. In May 2001, he graduated with a Bachelor of Science degree in civil engineering, with an emphasis on structural engineering. In August 2001, Gabriel Perdomo began graduate studies at UF in structural engineering, but changed his degree program in January 2002 to coastal engineering. In July 2002, he began work on a project (with William G. McDougal and Robert G. Dean) that focused on modeling the Oceanside, CA coastline to determine the effects of Oceanside Harbor on the beaches downcoast. On completing the project, Gabriel Perdomo graduated from the coastal engineering program at UF with a Master of Science degree in May 2004. 134


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Title: Developing a Seawall Algorithm for the DNR Model with Application to the Oceanside, California, Coastline
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Material Information

Title: Developing a Seawall Algorithm for the DNR Model with Application to the Oceanside, California, Coastline
Physical Description: Mixed Material
Copyright Date: 2008

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Holding Location: University of Florida
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DEVELOPING A SEAWALL ALGORITHM FOR THE DNR MODEL WITH
APPLICATION TO THE OCEANSIDE, CALIFORNIA, COASTLIE\T















By

GABRIEL A. PERDOMO


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

UNIVERSITY OF FLORIDA


2004

































Copyright 2004

by

Gabriel Perdomo
















ACKNOWLEDGMENTS

I thank my wife for giving me her indispensable and unconditional support in every

goal that I have strived to accomplish. I thank my daughter for giving me the inspiration

to be a better person. I thank my parents for providing me with the morals, commitment,

and attitude for excellence that has led me to achieve my childhood dreams. I thank my

two sisters for making me a proud older brother. I also thank everyone who offered me

assistance, guidance, and their friendship (both inside and outside the classroom)

throughout my years at the University of Florida. Most of all, I would like to thank God,

for He has given me all who I have mentioned above, and all the other gifts that I am so

blessed to have in my life.





















TABLE OF CONTENTS


page


ACKNOWLEDGMENT S ................. ................. iii...__ ....


LI ST OF T ABLE S ............. ............ .............. vii...


LIST OF FIGURES ............. ........... ..............viii...


AB STRAC T ......__................ ........_._ ........xi


CHAPTER


1 INTRODUCTION ................. ...............1.......... ......


Overview ................. ...............1.................

Proj ect Scope .................... ............... ...............2......
Enhancements to the DNR Model .............. ...............3.....


2 SITE CHARACTERIZATION .............. ...............6.....


Shorelines .............. ...............6.....
Beach Profiles ............... ...... ._ ...............7....
Development of Wave Conditions. .....__.....___ ..........__ ............
Tides .............. .... ....... ............1
El Nino Southern Oscillation............. .._..... .. ..__ ............___........1

Development of Oceanside Harbor Breakwaters and Groins............__.. ...............1 1
Dredging, By-passing, and Nourishment Events .......___..........._. ................1 3
S ourc es/ S inks .........._.... .....___ ...............15..
Rivers, Creeks, and Lagoons ...._. ......_._._ .......__. ............1

Background Erosion ........._. ........_. ...............16....
Even-odd analysis .............. ...............16....
Historic shoreline change ...._. ......_._._ ......._. .............1
Long shore Sediment Transport............... ...............2
North Breakwater Fillet ........._. ....... .__ ...............21....
Historic Volume Changes............... ...............22
Seaw alls ................. ....... .. ..............2
Method of Defining Seawall Positions ............... .. ........... ......_.._..........2
Description of Seawalls Found Within the Proj ect Area. ........._.._... ................24













3 DNR MODEL ............. ...... .__ ...............51..


Shoreline Position............... ... ..............5

Long shore Sediment Transport............... ...............5
W ave Setup ............. ...... ._ ...............53...
Run-up .............. .... ...............54..
Overtopping Propagation............... ..............5
Forces............ ........... ... ...............5

Input Parameter Cell Definitions ................ ...............56................


4 SEAWAL L MODEL ................. ...............60........... ....


Theory ............... .... ...............60.......... .....
Profie Definitions .............. ...............60....

Profie Changes ................... .... ...............6

Long shore Transport Modiaication ................. ...............65........... ...
Along-shore Boundary Conditions ................. ...............66........... ....
Seawall/ Nourishment Sensitivity Tests .............. ...............66....
Case 1: One Seawall, No Nourishments............... ..............6
Case 2: No Seawalls, One Nourishment............... ..............6
Case 3: One Seawall, One Nourishment .............. ...............69....
Case 4: Two Seawalls, One Nourishment ................ ................ ......... .71


5 OCEANSIDE MODEL DATA .............. ...............88....


Input ................. ........... .. ...............88......
Main Input File ................. ...............88........... ....
Constants .............. ...............88....

Total Depth ................. ...............89.................
G roins .............. ...............89....
Initial Shoreline .............. ...............90....
Nourishment .............. ...............92....
Seawalls ................. ...............93........... ....
Sources/Sinks .............. ...............94....
W aves .............. ...............96...

Back ground Erosion ................. ...............100......... ......

Output ................. ...............100......... ......


6 RE SULT S ................. ...............110......... ......


Sensitivity Analysis ................. ...............110......... ......

Along shore Wave Variation ................. ...............111................
Fill Factor ................ .. .... ....... ...............111......
Offshore Loss Coefficient ................. ...............112................













Calibrated Shoreline Planform Results ......__. ..........._. ............... 112 ....
Historical Runs ................. ...............113_._._.......
Forecast Results ......__................. ...............114......

Damage Comparisons ......__................. .........__..........11


7 CONCLUSIONS .............. ...............129....


LI ST OF REFERENCE S ................. ...............1 1......... ....


BIOGRAPHICAL SKETCH ................. ...............134....... ......


















LIST OF TABLES


Table pg

2-1. Tide level record at the NOAA/NO S/CO-OP S La Jolla Tide Gage ................... ......29

2-2. Nourishment dates, locations, and volumes (yd3) within the project area. ..............30

2-3. Sediment discharge rates by rivers and streams (yd3/yr) ................. ................ ...31

2-4. Location and sediment contributions used in the DNR simulations for the Santa
Margarita River, the San Luis Rey River, and the Loma Alta Creek. .....................31

2-5. Shoreline change rates north of Oceanside Harbor. ............. .....................3

2-6. Shoreline change rates south of Oceanside Harbor .................... ...............3

2-7. North fillet volume accumulation rates. ............. ...............32.....

2-8. Volume change rates. ............. ...............32.....

4-1. Input parameters for seawall sensitivity test cases. ................... ............... 7

5-1. Cross-shore location and effective lengths of breakwaters and groins along the
Oceanside coastline. ............. ...............101....

5-2. Seawall input parameters for the Oceanside and Carlsbad shorelines. ..................102

5-3. Source/sinks at the north and south breakwaters ................. ........_.._........._104


















LIST OF FIGURES


Figure pg

1-1. Overview of site. ................. ...............4......... ....

1-2. Oceanside Beach at the Oceanside Municipal Pier. ............. .....................

2-1. Three historical reference shorelines for the Carlsbad, Oceanside, and Camp
Pendleton coast. ............. ...............33.....

2-2. Comparison of the equilibrium beach profile used in the DNR model to an actual
SANDAG profile of the Oceanside coastline. ......____ ... ....._ ................33

2-3. The nine wave gages and the 90 computational sites used to create the 50 wave
records. ........... ..... ._ ...............34...

2-4. Mean wave height and mean period for each of the nine BOR wave gages. ...........35

2-5. Maximum wave height by station for the 50 wave records. .............. ...............3 5

2-6. Mean local wave angle with respect to the local shoreline orientation for the 50
wave records at the nine wave gages. ............. ...............36.....

2-7. Chronological development of Del Mar Boast Basin and Oceanside Small-Craft
H arbor. ............. ...............37.....

2-8. Nourishment placements and times for beaches downcoast of Oceanside Harbor..38

2-9. Timeline of significant historical events that occurred along the proj ect area
coastline. ............. ...............39.....

2-10. Comparison of the actual initial 1934 and final 1998 shorelines. ..........................40

2-11. Total change in shoreline position from May 1934 to April 1998. ........................40

2-12. Results of the even-odd analysis from 1934 to 1998 for the Oceanside coastline. 41

2-13. Even-odd analysis results and background erosion rates north and south of
Oceanside Harbor complex from 1934 to 1972 ................. ................ ....._.41

2-14. Even-odd analysis results and background erosion rates north and south of
Oceanside Harbor complex from 1972 to 1998............... ...............42..










2-15. MSL shoreline position in 1934, 1972, and 1998............... ..................4

2-16. Average annual rate of change between the 1934, 1972, and 1998 shorelines......43

2-17. California Coastal Record Project, Image 9032. Parking area at the southern end
of Carlsbad State Beach adj acent to the north Agua Hedionda discharge j etty.....43

2-18. Maptech Mapserver image of the Agua Hedionda discharge j etties and Carlsbad
State Beach............... ...............44.

2-19. California Coastal Record Project, Image 9017. Rocky cliffs just north of the
elevated concrete walkway that spans Carlsbad State Beach ............... ...............45

2-20. California Coastal Record Project, Image 9011. Erratic portion of seawall along
Carl sbad. ............. ...............45.....

2-21. California Coastal Record Project, Image 9005. Armoring at The Point, Carlsbad,
and Buena Vista Lagoon discharge point. ............. ...............46.....

2-22. California Coastal Record Project, Image 9002. Well-organized rubble seawall
that spans from Buena Vista Lagoon to Loma Alta Creek, Oceanside. ................46

2-23. California Coastal Record Project, Image 8985. South Pacific Street bridge
crossing over Loma Alta Creek discharge point, Oceanside. ............. .................47

2-24. California Coastal Record Project, Image 8971. Well-organized portion of rubble
seawall that spans north of Loma Alta Creek to The Strand, Oceanside............_...47

2-25. California Coastal Record Project's Aerial Photograph, Image 8963. Emergency
Revetment along The Strand, Oceanside. .............. ...............48....

2-26. California Coastal Record Project's Aerial Photograph, Image 8952. North
Pacific Street curb along The Strand that acts as a landward erosion barrier,
Oceanside. .............. ...............48....

2-27. California Coastal Record Project, Image 8948. Timber and rubble rip-rap
seawall that armors North Coast Village, Oceanside............... ...............4

2-28. California Coastal Record Project, Image 8946. North Pacific Street bridge
crossing over the San Luis Rey River discharge point, Oceanside........................49

2-29. California Coastal Record Project, Image 8944. North Pacific Street curb
landward of Oceanside Small Craft Harbor, Oceanside ................... ...............50

3-1. Possible changes in sediment amounts within a cell. ............. .....................5

4-1. Critical volume, Vc, per unit width. The critical volume is the entire area shown in
brow n. ............. ...............75.....











4-2. Volume per unit width for an aerial beach seaward of the seawall (ys 2 ysw)..........75

4-3. Initial volume per unit length for a seawall in the surf zone (ys < ysw). .................. .76

4-4. Volume change for a fictitious shoreline retreat with locations shown in both global
and local coordinates............... ..............7

4-5. Total sediment transport fronting a seawall for four planar beach slopes and several
wave conditions. ............. ...............77.....

4-6. Graphical representation of positive transport and ysw (I) < yN (I-1) at the start of the
se awall ................. ...............78........... ....

4-7. Input parameters for Case 1.............. ...............78....

4-8. Case lb: One seawall, no nourishment. Shoreline evolution. ............... ...............79

4-9. Case lb: One seawall, no nourishment. Shoreline position by cell........................79

4-10. Input parameters for Case 2............... ...............80...

4-11. Case 2a: No seawall, one nourishment, no breakwater. Shoreline evolution. .....80

4-12. Case 2a: No seawall, one nourishment, no breakwater. Shoreline position by cell.81

4-13. Case 2b: No seawall, one nourishment, one breakwater. Shoreline evolution.....81

4-14. Case 2b: No seawall, one nourishment, one breakwater. Shoreline position by
cell............... ...............82..

4-15. Input parameters for Case 3.............. ...............82....

4-16. Case 3a: One seawall, one nourishment, no breakwater. Shoreline evolution.....83

4-17. Case 3a: One seawall, one nourishment, no breakwater. Shoreline position by
cell............... ...............83..

4-18. Case 3b: One seawall, one nourishment, one breakwater. Shoreline evolution...84

4-19. Case 3b: One seawall, one nourishment, one breakwater. Shoreline position by
cell............... ...............84..

4-20. Input parameters for Case 4............... ...............85...

4-21. Case 4a: Two seawalls, one nourishment, no breakwater. Shoreline evolution. .85

4-22. Case 4a: Two seawalls, one nourishment, no breakwater. Shoreline position by
cell............... ...............86..










4-23. Case 4b: Two seawalls, one nourishment, one breakwater. Shoreline evolution.86

4-24. Case 4b: Two seawalls, one nourishment, one breakwater. Shoreline position by
cell............... ...............87..

5-1. May 1934 shoreline and straight initial shoreline. ............. .....................0

5-2. Sediment budget north and south of Oceanside Harbor ................. ................ ..105

5-3. O'Reilly hindcast wave gage locations and approximate -12-m contour. ..............106

5-4. Mean peak wave angle and mean effective wave angle from the 50 wave records
for each of the nine wave station. ................ ....___ .....__ ...........0

5-5. Depth contours along the study area shown in 5-fathom intervals.........................107

5-6. The shore normal direction used in the O'Reilly wave computations and the shore
normal directions determined from the 1934, 1972, and 1998 surveys. ..............108

5-7. Mean peak wave angle and mean effective wave angle results from the wave
transformation to the 1934 shoreline orientation. ................ ...................0

5-8. The local wave angle with respect to the 1934 shoreline for all the O'Reilly wave
calculation locations within the study area. .............. ...............109....

6-1. RMS error between the predicted and the measured shorelines south of the harbor
in 1972, 1998, and for both combined based on the V-shaped wave angle
variation as a function of the local wave angle at Agua Hedionda Lagoon. .......1 18

6-2. RMS errors for different fill factors and different values of offshore loss
coefficients, c. ................ ...............119..............

6-3. The RMS error as a function of LST rates for various offshore loss coefficients..120

6-4. Shoreline planform results referenced to the actual 1934 initial shoreline. ...........121

6-5. Annual shoreline change rates. .............. ...............122....___ ....

6-6. Historical shoreline evolution. .................._____ ...............123....

6-7. Historical shoreline planform evolution without breakwaters for waves developed
with the harbor presence. ............. ...............124....

6-8. Historical shoreline planform evolution without breakwaters for wave angles
adjusted to remove harbor effects. .............. ...............124....

6-9. Forecast final shoreline position with breakwaters. ............. ....................12

6-10. Forecast shoreline evolution with breakwaters. ............. ....................12











6-11. Forecast final shoreline position if breakwaters were removed in 1998. .............126

6-12. Forecast shoreline evolution if breakwaters were removed in 1998. ...................126

6-13. Forecast final shoreline position if breakwaters never existed. ................... .........127

6-14. Forecast shoreline evolution if breakwaters never existed ................. ...............127

6-15. Forecast monthly overtopping events with breakwaters, removing breakwaters in
1998, and if breakwaters never existed ................. ...............128........... ..
















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

DEVELOPING A SEAWALL ALGORITHM FOR THE DNR MODEL WITH
APPLICATION TO THE OCEANSIDE, CALIFORNIA, COASTLIE\T

By

Gabriel A. Perdomo

May 2004

Chair: William G. McDougal
Cochair: Robert G. Dean
Major Department: Civil and Coastal Engineering

The Oceanside Littoral Cell spans the southern coast of California from La Jolla

Canyon to Dana Point. Our study examined the portion of the Oceanside Littoral Cell

from Agua Hedionda Lagoon in Carlsbad, to a point 14.5 km (9.0 mi) north of the

Oceanside Harbor along the Camp Pendleton shoreline. The coastline along this reach

has historically experienced a variety of changes (including construction of the Oceanside

Harbor, urbanization of coastal lands, changes in sediment supply, coastal stabilization

structures, and sand removal and placement) that have significantly influenced the

shoreline position. Our objective was to estimate the shoreline impacts attributable to

Oceanside Harbor by applying the DNR model. To accomplish this, shoreline

characteristics within the project area were defined. A seawall algorithm (that tracks

volume change and then solves for the shoreline position) was added to the DNR model.

Verification results for the seawall algorithm are given. Wave run-up, bore propagation,

and force calculations were also added to the DNR model. Shoreline evolution and










damage results were examined for 50 different wave cases for two 60-year forecast

simulations with and without breakwaters. Results for the with-breakwater case show

that if current natural processes and human practices continue into the future, the

shoreline will erode back to the seawall, causing progressively more overtopping and

damage events along the Oceanside coastline. Results for the no-breakwater forecast

case give significantly less damage, and show the shoreline stabilizing to a future

equilibrium position that is shaped somewhat like the 1934 measured shoreline.















CHAPTER 1
INTTRODUCTION

Overview

The Oceanside littoral cell spans the southern coast of California from La Jolla

Canyon to Dana Point. This cell is 86.1 km (53.5 mi) long, and is defined by natural

coastal features such as rivers, creeks, lagoons, and cliffs; as well as man-made features

including beach nourishments, seawalls, groins, jetties, and breakwaters. This study

examines only a portion of the Oceanside Littoral Cell. The proj ect area includes the

shorelines of Carlsbad, Oceanside, and Camp Pendleton. The southern boundary is the

north Agua Hedionda Lagoon discharge j etty, in Carlsbad. This structure is

approximately 8.5 km (5.3 mi) south of Oceanside Harbor. The northern boundary is

approximately 14.5 km (9.0 mi) north of the Oceanside Harbor, along the Camp

Pendleton shoreline.

Over the past 60 years, the coastline along this reach has experienced a variety of

changes. The most significant change was the construction of the Del Mar Boat Basin in

1942, and the subsequent expansions to form what is now Oceanside Harbor. Other

factors that contributed to shoreline change include a decrease in sediment supply, coastal

stabilization structures, and sand removal and placement.

Oceanside Harbor and its protecting structures have had a significant influence on

the shoreline. Construction of the Del Mar Boat Basin in 1942 was a major littoral

barrier to the downdrift beaches. The updrift breakwater of the Del Mar Boat Basin

began trapping sediment, and a fillet developed north of the harbor. The fillet increased









in size, and sediment attempted to bypass the harbor. Meanwhile, urbanization of coastal

lands and construction of flood control structures decreased the sediment discharge from

the Santa Margarita and San Luis Rey rivers into the Oceanside littoral system. The

trapping of littoral material by the harbor and the reduction of river sediment supply have

been attributed to severe erosion on the beaches downcoast of Oceanside Harbor. To

reduce erosion damage, shoreline stabilization structures were constructed along the

Oceanside and Carlsbad coastlines (USACE, 1991c).

Aerial photography of the Oceanside area is available before 1942. These

historical photographs show the shoreline before significant human intervention. Figure

1-2 shows the Oceanside Pier in June 1938 and January 1953 (11 years after the initial

construction of the Del Mar Boat Basin). The two photographs are shown at a similar

scale. The pier is longer in 1953 than in 1938 because of the reconstruction and

lengthening of the pier in 1947 after its partial destruction by a storm in 1942.

Comparison of the two photographs indicates significant shoreline recession.

Project Scope

Our general obj ective was to estimate the shoreline impacts attributable to

Oceanside Harbor. The historical influence of the breakwaters was examined with the

DNR model to estimate harbor impact on the coastline relative to a no breakwater

condition. Results yield the influence of sediment volume trapped by the north

breakwater and long-term shoreline position changes. For lack of necessary data over the

past 70 years, certain historical conditions and their components (including wave height

and direction, river contributions, dredging, bypassing, beach nourishments, bluff

erosion, and water levels) had to be synthesized. As a result, the model predicts the










relative long-term results for conditions with and without breakwaters, as opposed to a

detailed outcome.

Damage attributable to the harbor can then be determined by comparing damage

results with and without harbor processes. Shoreline modeling determined the historical

influence of the breakwaters and estimated the damage events 50 years into the future

with and without the harbor present. Completion of these obj ectives involved the

following tasks:

* Determining wave and water-level conditions for the period of simulation

* Determining sediment sources, sinks, dredging, bypassing, and nourishments

* Developing information on initial shoreline configuration, description of structures,
beach profies, and sediment characteristics

* Specifying a damage-cost function related to calculated hydrodynamic responses

* Using a Monte Carlo simulation to determine the statistical estimates of responses.

Enhancements to the DNR Model

To accomplish these goals, the DNR model had to be modified to allow for the

inclusion of seawalls and revetments in the study area. The seawall routine allowed the

DNR model to more realistically model shoreline responses for armored beaches.

Development of the seawall algorithm was a major component of our study. Therefore,

development and verification of the seawall routine is described in detail. A subroutine

was also added to the DNR model to quantify the damage resulting from overtopping

events at seawalls. This routine calculated run-up, bore propagation behind the seawall,

and the forces on a vertical-faced structure.
























Harbor


Cadlsbad


L~rucedle






Encinites;













Figure 1-1. Overview of site. U.S. Army Corps of Engineers (USACE), Los Angeles
District (1994), "Oceanside Shoreline, Oceanside, San Diego County
California: Chapter 2.0 The Study Area", Reconnaissance Report, Main
Report, pp. 2-2.

























Figure 1-2. Oceanside Beach at the Oceanside Municipal Pier. A) June 1938. B)
January 1953.


~i4'"
''"~C- :..~--il~
-i-~i;_















CHAPTER 2
SITE CHARACTERIZATION

This chapter discusses the physical characteristics of the study area (including

shoreline position; beach profiles; wave climate; tides; El Nino; Oceanside Harbor

breakwaters and groins; dredging, by-passing, and nourishment events; sources and sinks;

background erosion; north breakwater fillet formation; historical volume changes; and

seawalls). This chapter presents findings from previous studies performed along this

coastline, and procedures used to define these characteristics for use in the DNR model.

Shorelines

The U. S. Army Corp of Engineers, Los Angeles District, provided three measured

shorelines for the study area: 1) 1934 pre-harbor shoreline, 2) 1972 shoreline, and 3)

1998 shoreline (Ryan, 2002). These shorelines were referenced to a baseline located

approximately 650 m (2,100 ft) inland of the shoreline at the Agua Hedionda discharge

jetties in Carlsbad. The baseline has a bearing of 325008'38".

The 1934 shoreline was digitized from three U.S. Coast and Geodetic Survey

sheets. The surveys were performed between March 1934 and May 1934 in three

sections from Carlsbad to San Mateo Point:

* Carlsbad to Santa Margarita River; March to April 1934. Hydrographic Survey
#5648.

* Santa Margarita River to Las Flores; April to July 1934. Hydrographic Survey
#5606.

* Horno Canyon to San Mateo Point; May 1934. Hydrographic Survey #5605









This shoreline is assumed to be Mean Tide Level (MTL). The USACE (Ryan, 2003)

provided the 1972 shoreline, which was with respect to mean sea level (MSL). Plan

views of survey plots were scanned and analyzed. The 1998 shoreline was taken from a

LIDAR survey conducted in April 1998 and represents the shoreline referenced to MTL.

The southern boundary of the study area is located the north Agua Hedionda

discharge jetty. The northern boundary is located 24. 1 km (15.0 mi) upcoast of the Agua

Hedionda discharge j etty, which is approximately 14.5 km (9.0 mi) north of the

Oceanside Harbor Complex in Camp Pendleton. The 1934 and 1998 shorelines surveys

extended past the northern boundary. However, the 1972 shoreline survey stopped

approximately 4 km (2.5 mi) short of the upper boundary. Figure 2-1 shows the three

shorelines. These will be discussed later in greater detail.

Beach Profiles

In the DNR model, the beach profie is defined by the Brunn/Dean equilibrium

beach profie. The equilibrium profie is based on constant wave energy dissipation per

unit volume of surf zone. This profie definition has been well documented and widely

used in coastal engineering, and is given as

h = Ay- (2.1)

where h is the still water depth along the profile, A is the profile coefficient related to the

sediment diameter, and y is the cross-shore distance along the profile (Dean and

Dalrymple, 2002). Figure 2-2 shows a comparison between a SANDAG profile

representative of the Oceanside coastline and the Brunn/Dean equilibrium profile. The

figure shows that the equilibrium beach profile provides a good fit to the SANDAG

profile.









Development of Wave Conditions

O'Reilly (2004) developed the wave conditions. The waves were estimated from

statistical analyses of historical wave data. The primary source of these data was the

Coastal Data Information Program (CDIP) buoy located offshore of Oceanside. The

wave records only spanned five years of measurements, which is short for the

development of 50-year wave records. The data were subdivided into three wave groups:

1) north swell, 2) south swell, and 3) local seas. Each of these was analyzed as an

independent population and then further categorized by the season (fall, winter, spring, or

summer) and whether the event was during an El Nino year. For each of these groups,

typical storm hydrographs were developed. The magnitude of the hydrograph was

changed to correspond to different magnitude events. The magnitudes of the events were

selected in accordance with the extreme value statistics for the specific population. The

wave simulations algorithm proceeded in the following order and repeated every hour for

50 years to generate a 50-year wave record:

* Determining if an El Nino year

* Determining season.

* Making a Monte Carlo selection of the event magnitudes for each population.

* Generating the wave hydrographs.

* Superimposing the hydrographs. into a single wave time series.

* Transforming the waves to the -12-m (-40-ft) contour.

The initial plan for the shoreline model was to use predicted waves at a number of

locations along the study area to drive the longshore sediment transport (LST). Nine

stations, determined by taking the average of ten alongshore locations near the stations










along the -12-m (-40-ft) contour, were selected that spanned the study area. The

locations of the nine wave stations and the 90 computation sites are shown in Figure 2-3.

Figure 2-4 shows the mean values of each of the 50-year wave records (43 8,000

individual wave conditions) for the nine wave stations. The study area is located from

along shore distance x = 0 to 24,100 m (0 to 79,000 ft) in Figure 2-4. The two heavy,

vertical, black lines mark the location of the Oceanside Harbor breakwaters. The mean

significant wave heights and mean peak periods are nearly constant along the study area.

The average significant wave height is 0.66 m (2.2 ft) and the average peak period is 10.7

s. South of the Agua Hedionda discharge j etty, the wave heights and periods decrease

because of the Carlsbad Canyon. However, these decreases are only 8% of the mean

significant wave height and 7% of the average peak period. The maximum wave heights

for each 50-year time series are shown in Figure 2-5. The average maximum is 6.2 m

(20.3 ft) with little variation in the alongshore direction.

Figure 2-6 shows the mean local wave angle with respect to the local shoreline

orientation. This figure shows that significant variations exist in the local wave angle.

North of the harbor, the local wave angle varies from -2o to -110. Local wave angles are

defined such that negative angles drive the LST to the south. The LST is approximately

linear with respect to the wave angle for small wave angles with a constant wave height.

A wave angle change from -2o to -11o results in a variation in LST by more than a factor

of Hyve. The historical shorelines north of the harbor do not support this large variation in

longshore transport. South of the harbor there is a 6o variation in the local wave angle.

This variation south of the harbor is more probable and could be associated with the

Carlsbad Canyon.










Using the wave time series with the wave heights, periods, and local wave angles

characterized in Figures 2-4 and 2-6 does not lead to reasonable shoreline predictions.

The waves have a significant amount of longshore variation that can result in local

convergences and divergences in the LST. As a result, necessary modifications were

made to the wave data to achieve realistic shoreline modeling results. These

modifications are discussed in Chapter 5.

Tides

Tides along the southern California coastline are of the mixed semi-diurnal type,

consisting of two high and two low tides each of different magnitude (USACE, 1994a).

The tidal characteristics for La Jolla (Latitude: 320 52.0' N, Longitude: 1170 15.5' W),

referenced to mean lower low water, are shown in Table 2.1. These data are a result of

18 years of measurements at La Jolla by the National Oceanic and Atmospheric

Administration (NOAA). At La Jolla, a difference of 0.02 ft exists between MTL and

MSL. Therefore, MSL and MTL will be assumed equal for this project.

NOAA1 provides the harmonic constituents to calculate the tide. These are the

amplitude, epoch, and the speed for each component. Amplitude is one-half the range of

a tidal constituent in meters, epoch is the phase lag of the observed tidal constituent

relative to the theoretical equilibrium tide in degrees referenced to UTC (GMT), and

speed is the rate change in the phase of a constituent, expressed in o/hr. The speed is

equal to 3600 divided by the constituent period expressed in hours. The tide is then

computed as follows,


SNOAA/NOS/CO-OPS Water Level Data Retrieval Page (http://co-ops.nos.noaa.gov/cgi-bin/co-
ops_qry_direct.cgi?stn=94 10230+LA+JOLLA%/2C+PACIFIC+OCEAN+%/2C+CAdc=&ssid= WL&pc
=P2&datum=NULL&unit=0&bdate=2003 020 1&edate=20030201l&date=1l&shift=0&level=-
4&form-0&host=&addr-68. 18.240.2&data~type=har&format= View+Data)










Tide = [ q {cos[(s,)(t) + E,] (2.2)


where A, is the amplitude (m), s, is the speed (o/hr), t is the time (hrs), and E, is the epoch

(o). These values are given for each tidal component.

El Nino Southern Oscillation

The El Nino Southern Oscillation (ENSO) episodes are inter-annual large-scale

oscillations in circulation and temperature distribution occurring in the Pacific Ocean. El

Nino occurrences last from one to three years and occurred approximately every 14 years

on average for the past century. Analyses suggest that ENSO episodes create a +0.3 m

(+1 ft) tidal departure. ENSO periods increase the probability of experiencing more

severe winter storms, and as a result, increase the likelihood of coincident storm waves

and higher storm surge (USACE, 1994a). In the model, the MSL is increased +0.3 m (+1

ft) during ENSO episodes.

Development of Oceanside Harbor Breakwaters and Groins

The Oceanside coastline features several jetties, groins, and breakwaters. Initial

construction of the harbor included two converging breakwaters extending offshore to the

-6-m (-20-ft) contour. The north breakwater was 640 m (2, 100 ft) long and the south

breakwater was 396 m (1,300 ft) long. In 1957, these two breakwaters were extended to

reduce the rate of sediment accumulation within the harbor. The upcoast breakwater was

extended approximately 274 m (900 ft) on the same alignment and another 427 m (1,400

ft) in the down coast direction bringing its total length to 1,325 m (4,350 ft). The

downcoast breakwater had 76 m (250 ft) removed from its seaward end and was then

rebuilt 115 m (380 ft) bringing the total length to 433 m (1,420 ft) (Clancy, 1972).









After 1960, shore-perpendicular structures downcoast of the Del Mar Boat Basin

were built to control the flow of sediment near the harbor. In 1961, a 120 m (400 ft) long

groin extending 90 m (300 ft) into the ocean at the upcoast side of the San Luis Rey River

was built. From March to June of the same year, the "south j etty" of the recently

constructed Oceanside Small-Craft Harbor complex was constructed to a length of 266 m

(873 ft); and in 1962, the south j etty was lengthened on the shoreward end 39 m (127 ft).

Also in 1962, the 216 m (710 ft) north groin was built. This structure was a submerged

groin that formed the upcoast side of the entrance channel to the Small Craft Harbor. In

July 1968, the south groin at the San Luis Rey River was extended approximately 158 m

(518 ft) bringing its total length to 280 m (918 ft) (Clancy, 1972). In 1973, the south jetty

was extended 114 m (375 ft) seaward bringing its total length to 419 m (1,375 ft). Figure

2-7 shows a chronological summary of the harbor development.

Structures were also constructed on Oceanside Beach. In 1952, two 76-m (250-ft)

long groins were built on Oceanside Beach extending out to the mean sea level. One was

located at the south property line of Wisconsin Avenue and the other was located 305 m

(1,000 ft) downcoast of Wisconsin Avenue (Clancy, 1972). The rubble rip-rap base of

the Oceanside Municipal Pier may also act as a groin during high-energy storm events.

Presently, the only structures having a significant effect on the longshore littoral

transport in the Oceanside area are the north breakwater and south breakwater (the new

south j etty) at Oceanside Harbor, the south groin just north of the San Luis Rey River,

and potentially the base of the Oceanside Municipal Pier during significant storm events

(USACE, 1994b). These structures are all rock rubble mound structures.









Dredging, By-passing, and Nourishment Events

The years immediately after the initial construction of the Del Mar Boat Basin were

characterized by drastic changes in shoreline position north and south of the harbor.

Sediment accumulated in a fillet north of the north breakwater. On the beaches south of

the harbor, erosion became a problem. Furthermore, a shoal developed across the

entrance channel to the harbor decreasing its depth and width. With time, it became

apparent that to maintain the channel at its design dimensions and to prevent erosion

damage to the beaches downcoast, sand would have to be artificially by-passed around

the harbor (Clancy, 1972).

The construction of the Del Mar Boat Basin began in 1942 and marked the

beginning of a number of dredgings that would occur at this site. The initial cutting of

the harbor required the removal of 1,150,000 m3 (1,500,000 yd3) Of sediment. The U.S.

Navy conducted a second dredging in 1945, removing 167,000 m3 (219,000 yd3) Of

sediment from the entrance channel. The material from these two dredgings was taken

to an inland disposal site. In 1957, the U.S. Navy once again dredged material from the

harbor entrance. The 612,000 m3 (800,000 yd3) Of removed sediment was placed on the

downcoast beaches from approximately 9th Street to 6th Street to alleviate some severe

erosion problems that were threatening the street and sewer line (Clancy, 1972). This

marked the first by-passing of sediment from the harbor to Oceanside Beach. Table 2-2

summarizes the nourishment dates, locations, and volumes for beaches downcoast of the

harbor. Figure 2-8 shows the location and times of all nourishments in the proj ect area.

Starting in 1960, sediment was regularly by-passed to beaches south of the harbor.

In 1963, the Army Corp of Engineers completed the construction of the Oceanside Small-









Craft Harbor. The total material dredged from the site was approximately 2,900,000 m3

(3,800,000 yd3), which was placed on the downcoast beaches.

Nourishment placement patterns along Oceanside beach have varied since they

began in 1957. The source of sediment for the following nourishments was Oceanside

harbor. Before 1971, the center of gravity of by-passed sediment was located about 2. 1

km (7,000 ft) downcoast the south breakwater near the Oceanside Municipal Pier

(USACE, 1991b). These are shown in red in Figure 2-8. From 1971 to 1990, the center

of gravity of the beach nourishments was positioned approximately 3.4 km (1 1,000 ft)

downcoast of the south breakwater seaward of Hayes Street (USACE, 1991b). These are

shown in blue in Figure 2-8.

In 1992 and 1993, two nourishments were placed seaward of Tyson Avenue, which

is approximately 2.4 km (8,000 ft) downcoast from the south jetty. From 1995 to 1998,

the dredged material was placed nearshoree" in -4.6 to -7.6 m (-15 to -25 ft) of water

depth seaward of Oceanside Boulevard, which is approximately 4.0 km (13,000 ft) south

of the south j etty. Sediment dredged from the harbor and placed on the beaches from

1999 to 2003 was again placed seaward of Tyson Avenue on Oceanside Beach (Ryan,

2003). The Tyson Avenue nourishments are shown in green and the nearshore Oceanside

Boulevard nourishments are shown in orange in Figure 2-8.

From 1995 to 2001, several nourishments took place on the beaches within the

project area where the sediment source was not from Oceanside Harbor. In June 1995,

sediment was taken from the Santa Margarita River Desiltation proj ect and placed

seaward of Oceanside Boulevard. In March 1997, sand was taken from an inland source

as part of the Sand-for-Trash project and placed seaward of Oceanside Boulevard. In










September 1997, the US Navy Homeporting proj ect took sand from North Island and

nourished the beach seaward of Oceanside Boulevard (Coastal Frontiers Corporation,

2003). These three nourishments are shown in black in Figure 2-8.

In 2001 sediment was taken from an offshore borrow pit and placed along Carlsbad

and Oceanside beaches for the SANDAG nourishment proj ect. These were the only two

SANDAG beach nourishments that occurred in our proj ect area, and they are shown in

gray in Figure 2-8. From 1988 to 1999, six nourishments were placed on Carlsbad State

Beach as sediment was back-passed from the Agua Hedionda discharge channel (Coastal

Frontiers Corporation, 2003). These nourishments were placed from Acacia Avenue to

Oak Avenue and are shown in purple in Figure 2-8.

Sources/Sinks

Rivers, Creeks, and Lagoons

During the period before the construction of the Del Mar Boat Basin, rivers,

streams, and lagoons served as significant sources of sand to the littoral system after

major storm and flood events (USACE, 1991a). However, urbanization of the upper

watersheds and the implementation of flood control systems reduced the amount of

sediment carried into the littoral system from these potential sources. The two maj or

rivers in the proj ect area are the San Luis Rey River and the Santa Margarita River.

During the time period between 1900 and 193 8, the deltas of the Santa Margarita and the

San Luis Rey Rivers built the beach seaward (USACE, 1991a). Recently, these rivers

have not contributed significant amounts of sediment to the littoral system.

Other smaller potential sediment sources within the proj ect area are Loma Alta

Creek and Buena Vista Lagoon. As with the Santa Margarita and the San Luis Rey

Rivers, these other contributors have seen a dramatic decrease in their discharge rates









since the construction of the harbor because of urbanization and a reduction in maj or

storm events. Table 2-3 provides a summary of sediment contribution estimates from

several studies performed on the Oceanside littoral cell.

The river sources used in the DNR simulations include the Santa Margarita River,

San Luis Rey River, and Loma Alta Creek. The values listed in Table 2-3 from the

various studies were averaged to determine the representative sediment contribution to

the littoral system from the Santa Margarita River and the Loma Alta Creek. However,

for the San Luis Rey River, the two studies that concluded a sediment contribution of

268,000 m3/yr (351,000 yd3/yr), which seems excessively disproportionate to the values

used in previous studies of the Oceanside coastline, were discarded and the remaining

values were averaged. Buena Vista Lagoon was not considered a sediment source, as it

does not contribute sediment into the littoral system because of the weir that was

constructed at its discharge point to artificially maintain the lagoon at 1.8 m (5.8 ft) above

mean sea level (USACE, 1994a). The locations and final values used for the three

sediment sources are listed in Table 2-4.

Background Erosion

Background erosion is a long-term coastal phenomena resulting in chronic

shoreline retreat. The coastline at Oceanside has experienced background erosion over

the past 70 years. This section discusses methods for quantifying background erosion

and shoreline recession for use in the DNR model.

Even-odd analysis

The analyses are based on the three shorelines discussed above in the "Shoreline

Position" section of this chapter. Figure 2-10 shows the measured shorelines for 1934

and 1998 north and south of the harbor at Oceanside where two things become evident.









First, the breakwaters at the harbor act as a littoral barrier to the longshore sediment

transport. The net transport is to the south causing impoundment of sand north of the

harbor and erosion to the south beaches. Second is that north of the harbor in Camp

Pendleton, the shoreline has retreated in the past 60 years in spite of the fillet that has

formed because of the north breakwater (Figure 2-11). The recession that has occurred

north of the harbor shows that the coastline within the proj ect area (north and south of the

harbor) has experienced background erosion. An even-odd analysis is used to separate

the effects of the harbor and the background erosion (Dean and Dalrymple, 2002).

The purpose of the even-odd analysis is to separate out those shoreline changes that

are symmetric about a point on the coastline (and probably not attributable to the

structure) and those that are attributable the presence of the coastal structure (Dean and

Dalrymple, 2002). The analysis separates shoreline changes, Ays, into an even and an

odd function, Aye(x) and Ayo(x) respectively, where the x-axis is the alongshore axis. For

a specific distance north of the north breakwater, +x, and the same distance to the south of

the south breakwater, -x, the even values of shoreline position change are the same, ye(+x)

= ye(-x). For the odd component, yo(+x) = -yo(-x). The even function approximately

represents the ongoing changes in shoreline position in the absence of a coastal feature,

and the odd function approximates the change in shoreline associated with the coastal

feature. The total change in shoreline position at any location along the coast is the sum

of the even and the odd functions:

Ay, (x) = Ay, (x) + Ay, (x) (2.3)

Results for the even-odd analysis using the changes in shoreline position from 1934

to 1998 are shown in Figure 2-12. The even function (shown in red) shows that erosion,









not attributable to the structures, occurred during this time period along the natural

shoreline north of the harbor and along Oceanside beach. The shoreline changes

attributable to the harbor are seen in the odd function (shown in blue) with accretion

north of the harbor and erosion south of the harbor. In conclusion, the coastline within

the study area has experienced background erosion.

Incorporating the intermediate 1972 shoreline into the even-odd analysis allows for

a comparison of background erosion from 1934 to 1972 and then from 1972 to 1998. To

make a direct comparison, the total background erosion for each time period was

converted into annual recession rates. Figures 2-13 and 2-14 show results for the even-

odd analysis and the recession rates for the two time periods. These two figures show that

most of the background erosion that occurred from 1934 to 1998 actually occurred from

1934 to 1972.

Historic shoreline change

The Camp Pendleton shoreline north of the harbor, beyond the range of influence

of the north breakwater, has experienced minor human intervention. This section of the

coast provides an indication of the historical natural shoreline response for the proj ect

area. Figure 2-15 shows the historical shoreline positions in 1934, 1972, and 1998. The

survey for the 1972 shoreline ended approximately 4 km (2.5 mi) downcoast of the

northern project boundary. The total average change between 1934 and 1998 for the

shoreline north of the Oceanside Harbor was -26.2 m (-86.0 ft). This means that a net

recession occurred in spite of the fillet that formed in response to the north breakwater.

Table 2-5 shows the historical shoreline change rates between surveys for the Camp

Pendleton shoreline. Notice that most of the erosion occurred before 1972. Table 2-5

also seems to show a discrepancy in conservation of sand since the changes from 1937 to









1972 and 1972 to 1998 do not sum to the change from 1934 to 1998. The reason for this

is the lack of survey data for the 1972 shoreline for the upcoast 4 km (2.5 mi) of the

proj ect area.

Toward the northern boundary of the proj ect area (Figure 2-10), the 1934 and the

1998 shorelines are almost parallel. This suggests that the historical rate of shoreline

retreat has been uniform along this section of the coast. Figure 2-16, which is the average

rate of shoreline change, shows that the average annual rate of shoreline recession

between 1934 and 1998 was about 0.6m/yr (2 ft/yr). As previously mentioned, most of

this shoreline retreat occurred between 1934 and 1972, with a small amount of accretion

from 1972 to 1998. If this accretion is neglected, then the average rate of recession for

1934 to 1972 is linearly approximated as

dy9417 y94-98(98-94 = -1.0m/yr (-3 .4ft/yr) (2.4)
dt dt (1972 -1934)

This result is in agreement with the even-odd analysis for the 1934 to 1972 time period

(Figure 2-13).

Figure 2-16 shows that most of the erosion south of the harbor also occurred

between 1934 and 1972. Table 2-6 shows the shoreline change rates for the coastline

south of the harbor. By comparing Table 2-6 to Table 2-5, it is apparent that the

recession rates were significantly higher to the south of the harbor. Figure 2-16 shows

that the annual recession rate for the entire coast south of the harbor from 1934 to 1972

was 1.4 m/yr (4.6ft/yr). For the 5.5 km (3.4 mi) immediately south of the harbor, the

shoreline recession rate was much greater at 2 m/yr (6.6 ft/yr). The recession rate

decreased significantly from 1972 to 1998 because of the routine Oceanside Harbor by-

passing/nourishment proj ects that took place during this time period. However, although









the recession rates decreased from 2 m/yr (6.6 ft/yr) to 0.5 m/yr (1.6 ft/yr), the shoreline

continued to retreat despite the nourishment efforts. If present practices are continued,

shoreline recession will continue into the future; and the seawalls and properties along

the Oceanside coastline will progressively experience more overtopping events, and

consequently, greater damage.

In the DNR model runs, a uniform background erosion of -1.1 m/yr (-3.5 ft/yr) was

assumed over the entire open coastline from 1934 to 1972 and no background erosion

after 1972. This rather simplistic assumption follows from the three shoreline surveys

and results from the even-odd analysis.

Longshore Sediment Transport

The net longshore sediment transport for the Oceanside coast is approximately

153,000 m3/yr (200,000 yd3/yr) to the south. However, published values of LST from

various studies--which include both analyses of historical wave statistics (north swell,

south swell, and local seas) and analyses of sediment accumulation rates in the fillet north

of the harbor and in the harbor itself--yielded varying results. Furthermore, several

studies suggested long-term variations in LST over the past 90 years.

Hales (1978) determined a net LST rate for the Oceanside Littoral Cell of 76,000

m3/yr (100,000 yd3/yr) to the south based on wave statistics. Marine Advisors (1960) and

Inman and Jenkins (1983) also employed wave statistics to determine the LST rates in

this area. Marine Advisors found a net southerly transport of 165,000 m3/yr (216,000

yd3/yr), and Inman and Jenkins found a net southerly transport of 194,000 m3/yr (254,000

yd3/yr). A study by Tekmarine, Inc. (1987) gave a net southerly LST of 81,000 m3/y

(106,000 yd3/yr) at Oceanside Harbor. Moffat and Nichol (1990) performed the most

comprehensive determination of LST in the Oceanside Littoral Cell. This study predicted









a net southerly LST rate of 76, 000 to 191,000 m3/yr (100,000 to 250,000 yd3/yr) fTOm

1945-1977. From 1978-1987, data analysis gave the net southerly transport rate to be

from 0 to 31,000 m3/yr (0 to 40,000 yd3/yr), which is a substantial decrease form the

pervious time period.

North Breakwater Fillet

As previously mentioned, a fillet developed to the north of the north breakwater.

This fillet began forming immediately after the initial construction of the north

breakwater in 1942 and extends 8.9 km (5.5 mi) north of the harbor. The sediment rate of

retention has been quantified as approximately 38,000 m3/yr (50,000 yd3/yr) (USACE,

1994a).

The volume of the sediment in the north fillet can be estimated from the 1934,

1972, and 1998 shorelines. The volume estimates are based on a closure depth of 7.6 m

(25 ft) and a berm elevation of 4.3 m (14 ft). These volumes are converted to annual

rates of accumulation, noting that the fillet began forming after the north breakwater was

constructed in 1942 (Table 2-7). The net longshore transport significantly exceeds these

accumulation rates. Since the placement of the north breakwater in 1942, only a portion

of the transport has been impounded. The rest of the transport is carried into the harbor,

by-passed around the harbor, or lost offshore.

The values in Table 2-7 are lower than the estimate of 38,000 m3/yr (50,000 yd3/r

published by the U. S. Army Corps of Engineers. Also, it is surprising that the

accumulation rates are higher in more recent times. Based on the above discussion, an

average accumulation rate of 31,000 m3/yr (40,000 yd3/yr) is used for the north fillet.

Immediately to the south of the south breakwater, the shorelines in the 1934, 1972,

and 1998 surveys do not show the development of a fillet or an eroded area. This is a









result of sheltering behind the breakwater, longshore transport reversals, and sediment

retention between the breakwater and the San Luis Rey groin.

Historic Volume Changes

The measured shorelines from Figure 2-10 provide an opportunity to estimate the

total changes in sediment volume north and south of the harbor. For these estimates, the

closure depth is defined as 7.6 m (25 ft) and the berm elevation is defined at 4.3 m (14 ft).

The resulting volume change rates are summarized in Table 2-6. For the full reach north

of the harbor including the fillet, the average shoreline recession, as previously

mentioned, from 1932 to 1998 was -0.4 m/yr (-1.3 ft/yr). North of the harbor, there was

an annual loss of -3.5 m3/m/yr (-1.4 yd3/ft/yr) from 1934 to 1998. This volume change

rate includes the fillet accretion updrift of the north breakwater. Moving farther north out

of the fillet, the recession rate over this period was approximately -0.6 m/yr (-2 ft/yr),

which is a removal of -8.3 m3/m/yr (-3.3 yd3 ft/yr).

South of the harbor there was a substantial loss of sediment each year (Table 2-8).

Before 1972, the sediment eroded at a rate of -16.6 m3/m/yr (-6.6 yd3/ft/yr). Although

by-passing and nourishments occurred regularly from 1972 to 1998, this stretch of

coastline still resulted in a deficit of -7.3 m3/m/yr (-2.9 yd3/ft/yr) during that time period.

Again it should be noted that these results predict that future loss of sediment will

continue to occur south of the harbor if the current by-passing and nourishment practices

are continued. This will lead to increasing overtopping events and more severe damage

with time.









Seawalls

Method of Defining Seawall Positions

The Oceanside and Carlsbad coastlines are heavily armored with seawalls. Rubble,

timber, and concrete structures protect many private properties and public lands along the

shoreline. The cross-shore locations and alongshore lengths of the armoring was

estimated using three references:

1. Maptech Map server (http://map server. maptech.com),

2. California Coastal Record Proj ect aerial photographs by Kenneth Adelman
(http://www.californiacoastline.org), and

3. AutoCAD files provided by the USACE (Ryan, 2002).

All of the seawalls from the Agua Hedionda discharge j etties to Oceanside Harbor

can be seen in the California Coastal Record Project aerial photographs. Figure 2-17

shows an aerial photograph of the shoreline just up-coast of the north Agua Hedionda

discharge j etty. A rubble rip-rap seawall protects the parking lot at the south end of the

Carlsbad State Beach; and a vertical concrete seawall, which serves as an elevated

walkway, spans the length of the Carlsbad State Beach.

The Maptech Mapserver website was used to find the alongshore locations and

lengths of the seawalls. Running the cursor over the images on this web site gives the

longitudinal coordinates along the coast. Figure 2-18 shows the same area as Figure 2-17

in an over-head view with Maptech Mapserver. The parking lot adj acent to the j etty and

the rubble rip-rap seawall between the parking lot and the beach are visible. Using the

intersection between the shoreline and the north Agua Hedionda discharge jetty as the

initial reference point, the longitudinal coordinates from Maptech were converted into

alongshore distances. The alongshore distances were then translated to corresponding









cell locations. Gaps in the seawalls and seawalls less than 50 m (165 ft) were omitted

since the cell width resolution is 100 m (330 ft). As a result, the structures appear as

continuous seawalls of varying type, cross-shore position, and height.

To determine the cross-shore position of the seawalls, CAD files provided by the

USACE, Los Angeles District, were used. These files include a 2001 Eagle Aerial

definition of the landward edge of sand. Upon comparison between the Eagle Aerial line

and the aerial photographs, it was concluded that the landward edge of sand defines the

seaward edge of the seawalls. Therefore, the cross-shore location of each seawall is

defined as the distance from the Eagle Aerial 2001 landward edge of sand to the baseline.

To model overtopping events along Oceanside, the crest elevation for each seawall

must be known. The crest elevation is the vertical distance from the mean tide level

(MTL), which is the reference datum, to the top of the seawall. These elevations were

obtained by using a combination of two sources: 1) the GIS study performed along the

Oceanside coastline, and 2) a Lidar survey performed for the Oceanside littoral cell.

Using these two references gave the elevations at the top of the seawalls with reasonable

accuracy. The GIS and the Lidar surveys were taken from the NAVD88 reference datum,

which is approximately 0.78 m (2.57 ft) below the MTL datum. Therefore, conversions

were made accordingly.

Description of Seawalls Found Within the Project Area

The final results of the seawall analysis revealed that the entire coastline between

the Agua Hedionda discharge jetties and the Oceanside Harbor is armored in one form or

another (small gaps less than 50 m are neglected). The continuous seawall from the north

discharge jetty at Agua Hedionda to the south breakwater at Oceanside Harbor is divided

into many sub-seawalls. A sub-seawall is defined as a change in armoring type (vertical









structure or rubble rip-rap), and therefore a change in slope, within the continuous

seawall.

The first stretch of the seawall is located in Carlsbad. It is erratic in cross-shore

distance and type as it spans across Carlsbad Beach and a number of private properties.

The seawall begins as a protective structure for the parking lot just north of the Agua

Hedionda discharge jetties mentioned above (Figure 2-17). This first sub-seawall is a

rubble rip-rap structure that extends north from the Agua Hedionda jetty. The second

sub-seawall is a vertical concrete structure that serves as an elevated walkway and spans

along the length of Carlsbad State Beach to Walnut Avenue (Figure 2-17). The third

Carlsbad sub-seawall is a rubble rip-rap structure located at the up-coast end of the

elevated walkway directly seaward of the Tamarack Beach Resort in Carlsbad.

Immediately north of the third Carlsbad sub-seawall is a rocky cliff with an

elevation of approximately 14 m (45 ft) (Figure 2-19). Although no man-made structures

exist seaward of this cliff from Pine Avenue to Oak Avenue, the cliff itself acts as a

seawall. During significant storm events, the cliff itself may erode and contribute

sediment to the littoral system. However, the sandy beach will not erode past the cliff in

the same manner as it would if no cliff existed. Therefore, this stretch of coastline is

modeled as if it were entirely armored by a seawall.

Moving up-coast from Oak Avenue to the Buena Vista Lagoon, the coast is heavily

armored as protection for many private properties (Figure 2-20). Significant variation

occurs in the cross-shore position and type of seawalls along this shoreline. Some of the

variations in cross-shore position occur within a 100 m (330 ft) span, so the average

cross-shore position was used for each cell. Furthermore, several properties located on









this stretch of the Carlsbad coastline do not have seawalls. The buildings on these lots

are constructed higher up on the slope that connects Ocean Street to the beach. The

buildings themselves or their foundations will prevent erosion to occur landward of them.

For this reason, and the fact that many of these unarmored properties are less than 50 m

(165 ft) in width and bounded by seawalls on both sides, this shoreline is considered

armored at the location of the buildings.

The final Carlsbad sub-seawall is up-coast of the Army Navy Academy and

adj acent to Buena Vista Lagoon. This armoring is located along "The Point" and consists

of rubble rip-rap (Figure 2-21). Just north of this seawall is a small gap in armoring

where Buena Vista Lagoon discharges in to the Pacific Ocean (Figure 2-21). This

discharge point cannot be modeled in its actual configuration because its size is too small

(approximately 50 m). More accurate results are obtained when the Buena Vista Lagoon

discharge cell is modeled as a seawall rather than a gap with no armoring. This

assumption is appropriate since Buena Vista Lagoon is maintained at 1.8 m (5.8 ft) above

mean sea level (MSL) by the presence of a weir that spans the lagoon mouth (USACE,

1994a).

Continuing upcoast past Buena Vista Lagoon is the Oceanside coastline, where the

remaining section of the seawall spans from the lagoon to the Oceanside Harbor. The

entire coast of the city of Oceanside is armored and consists of seven sub-seawalls. The

first sub-seawall is a long, rubble rip-rap structure that spans the southern coastline of

Oceanside (Figure 2-22). This structure extends from Buena Vista Lagoon across St.

Malo to Buccaneer Beach (which is adj acent to Loma Alta Creek). A gap exists in the

seawall where Cassidy Street intersects the coastline. However, this gap is too small










(approximately 30 m) to be included in the model. The rubble seawall contains a

discontinuity point at the Loma Alta Creek discharge point (Figure 2-23). However, the

foundation of the South Pacific Street Bridge, which crosses over Loma Alta Creek,

provides a landward erosion barrier similar to the cliffs previously mentioned in

Carlsbad.

North of Loma Alta Creek, the rubble rip-rap structure continues up-coast to just

south of Tyson Street Beach Park. This sub-seawall is divided it into two sections. The

first section is a uniform structure that spans from Loma Alta Creek to Wisconsin Avenue

across many private properties (Figure 2-24). The second section--comprising the

northern portion of this seawall--is very unorganized rubble rip-rap, and was labeled by

the USACE (1994b) as emergency revetment placed along The Strand. Figure 2-25

shows a section of this emergency revetment.

The fourth Oceanside sub-seawall is not an actual seawall. The curb that separates

Oceanside Beach from The Strand is a landward erosion barrier that is susceptible to

overtopping and damage (Figure 2-26). The curb extends up the coast to North Coast

Village.

Just south of the San Luis Rey River is the armoring that protects North Coast

Village. This sub-seawall is a 150-m (492-ft) vertical timber structure with rubble toe

protection that proj ects farther seaward that the adj acent seawalls to the north and the

south (Figure 2-27). This anomaly in the shoreline increases the possibility of

overtopping and damage at North Coast Village relative to the adj acent shorelines.

The San Luis Rey River discharge is a discontinuity in the shoreline similar to the

Loma Alta Creek discharge point. However, North Pacific Street Bridge, which crosses









over San Luis Rey River, provides a landward erosion barrier (Figure 2-28). Therefore,

the foundation to this bridge is the sixth sub-seawall. The curb of North Pacific Street

north of the bridge marks the seventh Oceanside sub-seawall. This section is very similar

to the curb and street erosion barrier that spans the northern portion of Oceanside beach

just south of the North Coast Village. The curb extends from the San Luis Rey River

groin to the South Breakwater at Oceanside Small Craft Harbor (Figure 2-29).









Table 2-1. Tide level record at the NOAA/NOS/CO-OPS La Jolla Tide Gage2.
Tide Levels Given in Feet La Jolla
Mean Higher High Water (MHHW) 5.33
Mean High Water (MHW) 4.60
Mean Tide Level (MTL) 2.75
Mean Low Water (MWL) 0.90
Mean Lower Low Water (MLLW) 0.00


2 NOAA/NOS/CO-OPS La Jolla Tide Gage









Table 2-2. Nourishment dates, locations, and volumes (vd3) within the project area.


Nourishment Location
Downcoast End Upcoast End
Inland Fill
Inland Fill


Volume
(yd3)
1,500,000
219,000
800,000
410,000
481,000
3,800,000
111,000
684,000
178,000
434,000
353,000
552,000
434,000
560,000
550,000
318,000
863,000
922,000
475,000
450,000
220,000
118,000
249,000
25,000
188,000
483,000
75,000
161,000
40,000
106,000
162,000
130,000
1,000
102,000
315,000
187,000
203,000
327,000
80,000
142,000


Volume
(m3
1,149,000
167,000
612,000
313,650
367,965
2,907,000
84,915
523,260
136,170
332,010
270,045
422,280
332,010
428,400
420,750
243,270
660,195
705,330
363,375
344,250
168,300
90,335
190,485
18,933
143,820
369,495
57,241
123,165
30,600
108,630
123,930
99,450
765
78,030
240,975
143,055
154,935
250,155
108,630
61,200


Date
Jun 1942
May 1945
Nov 1957
Aug 1960
Aug 1961
Jan 1963
Aug 1965
Mar 1966
Jul 1967
Apr 1968
Aug 1969
May 1971
Jun 1973
Nov 1974
Jun 1976
Nov 1977
Apr 1981
Feb 1982
Jan 1984
Jan 1986
Jan 1988
Feb 1988
Jan 1990
Feb 1991
Feb 1992
Dec 1993
Feb 1994
Jan 1995
Jun 1995
Feb 1996
Feb 1996
Jan 1997
Mar 1997
Sep 1997
Mar 1998
Mar 1999
Apr 1999
Feb 2000
Feb 2001
Feb 2001


9th Street
9th Street
9th Street
North Coast Village
9th Street
3rd Street
3rd Street
San Luis Rey River
San Luis Rey River
3rd Street
Tyson Street
Ash Street
Ash Street
Ash Street


6th Street
6th Street
6th Street
Loma Alta Creek
3rd Street
Ash Street
Tyson Street
Wisconsin Avenue
3rd Street
Wisconsin Avenue
Wisconsin Avenue
Whitterby Street
Whitterby Street
Whitterby Street


Hayes Street
Hayes Street
Hayes Street
Hayes Street
Hayes Street
Acacia Avenue Oak Avenue
Hayes Street
Acacia Avenue Oak Avenue
Tyson Street
Tyson Street
Acacia Avenue Oak Avenue
Nearshore Placement (Oceanside Blvd.)
Oceanside Blvd.
Acacia Avenue Oak Avenue
Nearshore Placement (Oceanside Blvd.)
Nearshore Placement (Oceanside Blvd.)
Oceanside Blvd.
Oceanside Blvd.
Nearshore Placement (Oceanside Blvd.)
Tyson Street
Acacia Avenue Oak Avenue
Tyson Street
Tyson Street
Acacia Avenue Oak Avenue


















_I j j


Table 2-3. Sediment discharge rates by rivers and streams (yd3iy)



Discharge ~ ~ aRi
Rates

Santa
Margarita 11 430 15 000 24 000 11,000 2,000 20 000 900 15 000 11 300 19 000
River
San Luis Rev
6,540 23 000 37 000 18,000 351,000 11 000 20,000 351,000 12 500 11 000
River
Loma Alta
565 -- -- -- -- 1,000 -- -- -
Creek
Buena Vista
0 --- --- 0------
Lagoon


Table 2-2. Continued


Nourishment Location
Downcoast End Upcoast End
Vista Way Wisconsin Avenue
Carlsbad Village Dr Buena Vista Lagoon
Tyson Street
Tyson Street


Volume
(yd3)
421,000
225,000
400,000
438,000


Volume
(m3>
322,065
172,125
306,000
335,070


Date
Jul 2001
Sep 2001
Jan 2002
Feb 2003


Table 2-4. Location and sediment contributions used in the DNR simulations for the
Santa Margarita River, the San Luis Rey River, and the Loma Alta Creek.


Sediment Sediment
Volume Volume
(vd3/Vr) (m3/Vr)


Sediment
Source
Santa Margarita
River
San Luis Rey
River
Loma Alta
Creek


Alongshore
Location


13,000

17,000


9,900 2000 m upcoast of the north breakwater

13,000 2000 m downcoast of the north breakwater

610 5500 m downcoast of the north breakwater


800














































Table 2-8. Volume change rates.
~South of Harbor North of Harbor
Time Interval Comments
(m3/yr> (m3/m/yr) (m3/yr) (m3/m/yr)
1934 to 1972 -128,400 -16.6 -- -- 1972 Survey Incomplete
1972 to 1998 -61,200 -7.3 -- -- 1972 Survey Incomplete
1934 to 1998 -109,300 -12.8 -50,500 -3.5


Table 2-5. Shoreline change rates north of Oceanside Harbor.
Time Interval Shoreline Change Shoreline Change Rate Comments
(m) (m/y r)
1934 to 1972 -30.0 -0.79 1972 Survey Incomplete
1972 to 1998 +9.4 +0.37 1972 Survey Incomplete
1934 to 1998 -26.2 -0.40


Table 2-6. Shoreline change rates south of Oceanside Harbor.
Time Interval Shoreline Change Shoreline Change Rate
(m) (m/yr)
1934 to 1972 -16.4 -0.44
1972 to 1998 -5.5 -0.21
1934 to 1998 -22.0 -0.34


Table 2-7. North fillet volume accumulation rates.
Time Interval Accumulation
(yd3/yr)
1942 to 1972 11,500
1972 to 1998 26,100
1942 to 1998 18,300


Accumulation
(m3/r
8,800
20,000
14,000



































2500 5000 7500 10000 12500 15000
Alongshore O~stance (m)


17500 20000 22500 25000


Figure 2-1. Three historical reference shorelines for the Carlsbad,
Pendleton coast.


Oceanside, and Camp


1,000 2,000 3,000 4,000 5,000 6,000


7,000 8,000


Cross-Shore Dsisance (ff)

Figure 2-2. Comparison of the equilibrium beach profile used in the DNR model to an
actual SANDAG profile of the Oceanside coastline.









Ocnthlip idEdel 14tdr than Site. 12m depth centou.


llzs





33~15



33 1

ModPI :Tlle.
Alonrg~ps hre Arft ag 5:ws '

-11765 -117 -17 5 -1175 175 -1174 -11735 -1173 -11725
Lorigitude
Figure 2-3. The nine wave gages and the 90 computational sites used to create the 50
wave records.


JJII




























































I~maxHs


10

09

OB

07


S06







03

02

01


00' 1 I I 1 1'
-10 000 -6,000 0 5,000 10,000 15,000 20,000 25,000 30,000

Alongshore Oistance (m)

Figure 2-4. Mean wave height and mean period for each of the nine BOR wave gages.
The two black lines on the plot show the locations of the north and south
breakwaters .


80


70






S50


~40


~30


20


10


00 I II
-10,000 -5 000 0 5,000 10,000 15,000 20,000 25,000 30

Alongshore D stance (rn)

Figure 2-5. Maximum wave height by station for the 50 wave records. The two black
lines on the plot show the locations of the north and south breakwaters.



































120 0
-10,000


10,000 15,000 20 000 25,000


Figure 2-6. Mean local wave angle with respect to the local shoreline orientation for the
50 wave records at the nine wave gages. The two black lines on the plot show
the locations of the north and south breakwaters.






















~~5;'
$~B, a~.~J
j~L
B : c,~_~"~'
r I;
N,7
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7
SC~E
1~DD Q 20140 ~~
9~~1-- 7~------ ~ --- ---


1


LEGENo
ma 1973
sege 19
1942
m1958
[III 1961
IEE1962
malE 1988-


Figure 2-7. Chronological development of Del Mar Boast Basin and Oceanside Small-
Craft Harbor. U.S. Army Corps of Engineers (USACE), Los Angeles District
(1991Ib), State of the Coast Report, San Diego Region: Chapter 7,
Application of Beach Change Models", Coast of California Storm and Tidal
Wave Study (CCSTWS) Volume 1 Main Report.
















00n0
0 O O
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S2500 5000 7500 10000 12500 15000 17500 20000 22500 25000
Alongshore O~stance (m)


Figure 2-10. Comparison of the actual initial 1934 and final 1998 shorelines.







200


150


100



S50





-60


-100


-160


-200
0 2500 5000 7500 10000 12500 15000 17500 20000 22500 25000



Figure 2-11. Total change in shoreline position from May 1934 to April 1998.

















-34-98 Even
-34-98 Odd


10000 -8000 -6000 -4000 -2000


2000 4000 6000 8000 10000


O~stance from Harbor (m)

Figure 2-12. Results of the even-odd analysis from 1934 to 1998 for the Oceanside
coastline.


8000 -7000 -6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000 6000 7000 800[
Distance from Harbor (m)


9000


Figure 2-13. Even-odd analysis results and background erosion rates north and south of
Oceanside Harbor complex from 1934 to 1972. The background erosion rate
is the even function shown in red.























-72-98 Even
-72-98 Odd


10


3




2





~1

a

Po
r,
o
m
r
P1
ol
V,



Z




3
90C


-8000 -7000 -6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance from Harbor (m)


Figure 2-14. Even-odd analysis results and background erosion rates north and south of

Oceanside Harbor complex from 1972 to 1998. The background erosion rate

is the even function shown in red.








-193



650


~-1972
















450





0 2500 5000 7600 10000 12500 15000 17500 20000 22500 25000

Nlongshore Olstance (m)


Figure 2-15. MSL shoreline position in 1934, 1972, and 1998.













--1934-1972
--1934-1998
--1972-1998


















O 2500 5000 7500 10000 12500 15000 17500 20000 22500 25000
Nlongshore O~stance (m)

Figure 2-16. Average annual rate of change between the 1934, 1972, and 1998
shorelines.


Figure 2-17. California Coastal Record Project, Image 9032. Parking area at the
southern end of Carlsbad State Beach adj acent to the north Agua Hedionda
discharge jetty.







44


















Figre2-8.Ma tehMpevriaeothAgaHdoddicrejtisan

Carlsad Sate each



































Figure 2-19. California Coastal Record Project, Image 9017. Rocky cliffs just north of
the elevated concrete walkway that spans Carlsbad State Beach.


rlgure L-Lu. aInormla Loastal Kecora rrojet, Image voi1. trrauce pornon or seawall
along Carlsbad that consists of rubble rip-rap, vertical structures, and home
foundations.









































Figure 2-21. California Coastal Record Project, Image 9005. Armoring at The Point,
Carlsbad, and Buena Vista Lagoon discharge point.


:LWUIEi'Y~I :~ '~"F5ij~~C1':. .
'r` '`~ `I;':. rL~C*- -.~C :L


rlgure L-Lz. aInormla Loastal Kecora rrojet, Image youur well-orgamlzea ruoole
seawall that spans from Buena Vista Lagoon to Loma Alta Creek, Oceanside.


































*il!
**. ~ *


figure 2-23. Calformla Coastal Record Project, Image 8985. South Pacitic Street bridge
crossing over Loma Alta Creek discharge point, Oceanside.


r figure L-m4. aInormla Loastal Kecora rrojet, Image rri 1 w ell-orgamlzea pornon or
rubble seawall that spans north of Loma Alta Creek to The Strand, Oceanside.







48














Fgr2-25 aionaCatlRcr rjctsAra htgah mg 93
Emrec evtetaog h tadOenie


figure L-Lo. aInornia Loastal Kecora rrojet s Nenall rnorograpn, Image warL IUonnI
Pacific Street curb along The Strand that acts as a landward erosion barrier,
Oceanside.

































Figure 2-27. California Coastal Record Project, Image 8948. Timber and rubble rip-rap
seawall that armors North Coast Village, Oceanside.


igure 2-28. California Coastal Record Project, Image 8946. North Pacific Street bridge
crossing over the San Luis Rey River discharge point, Oceanside.



































C.


Figure 2-29. California Coastal Record Project, Image 8944. North Pacific Street curb
landward of Oceanside Small Craft Harbor, Oceanside.















CHAPTER 3
DNR MODEL

This chapter briefly explains the theory behind the one-line DNR model. For a

more detailed discussion, see Dean and Grant (1989). First a background on one-line

models is presented, along with the equations used to calculate longshore sediment

transport and shoreline position. This is followed by a discussion on wave set-up, run-up,

overtopping, and force estimates as implemented in the DNR model for this proj ect.

Shoreline Position

The DNR model is a one-line model, meaning the model predicts the evolution of

one contour (Dean and Grant, 1989). The most common contour to track is the shoreline,

which is typically divided into a number of equally spaced cells. A one-line model

assumes that the beach profile shape remains constant. Shoreline position change from

one time step to the next is a function of the change in volume within a cell between

consecutive time steps. The change in volume, in turn, is a function of gradients in

longshore sediment transport and additions or subtractions in sediment from sources or

sinks in the cell.

The DNR model determines the change in shoreline position using the Brunn rule.

Two requirements are necessary to apply the Brunn rule for the new equilibrium profile:

1) The profile shape does not change with respect to the water line, and 2) The sand

volume in the profile must be conserved (Dean and Dalrymple, 2002). Once equilibrium

occurs, the shoreline position change, Ay, is given by









AV
Ay = (3.1)
A+B

where A~is the volumetric change, h* is the closure depth, and B is the berm elevation.

Longshore Sediment Transport

Gradients in the sediment flux result in a change in volume. If the longshore

sediment transport (LST) entering a cell is greater than the LST exiting the cell, then the

cell experiences sediment accretion and the shoreline advances seaward. Conversely, if

the LST exiting the cell is greater than the LST entering the cell, then the cell experiences

a reduction in sediment volume and the shoreline retreats landward. If erosion or

accretion occurs, then the profile simply translates landward or seaward. Since the

profile shape is always the same, tracking one point on the profile is sufficient for

defining the entire profile.

Figure 3-1 shows various terms that can influence the volume of sediment in a cell.

Each cell is a local, small-scale littoral budget. The terms from Figure 3-1 can be

summarized in the conservation of mass (volume) equation,

Ay[Ax(Ax+ B)] = [(Qm, eont > s]At +V, (3.2)

where Ay is the change in shoreline position for time interval At, Ax is the alongshore

length of the cell, Q,n and Qo,, are the LST at the boundaries of the cells, Qss is a

source/sink, and Vu~ is the volume associated with nourishment or mining. The terms h*

and B are the closure depth and the berm elevation. Their sum gives the vertical range of

the active profile. This equation is written for each cell to get a complete one-line

description of the shoreline.

To apply Equation 3.2, the LST must be specified. The DNR model implements a

variation of the CERC formula (SPM, 1984),










Q = (EC, cos B sin 8)b (3.3)
pg(s -1)(1 p)

where Q is volume transport, p is the water density, g is the acceleration due to gravity, s

is the specific gravity of the sediment, p is the sediment porosity, and K is a

dimensionless empirical transport coefficient. The terms in the parenthesis with the

sub script b are evaluated at the breaker line. The term E is the wave energy density, C, is

the group celerity of the waves, and B is the wave local angle relative to the shoreline.

Using linear wave theory, conservation of energy flux, and Snell's Law for

refraction, Equation 3.3 may be written


Q = n H2 COS BSin8 Ob (3.4)


where Cb is the wave celerity evaluated at the breaker line and n is the ratio of the group

velocity to the wave celerity. The advantage of Equation 3.4 is that only Cb is evaluated

at the breaker line while all other terms may be evaluated at any arbitrary depth outside

the breaker line.

The DNR model proceeds by first calculating Q at each cell boundary. The angle B

is the local wave angle and incorporates the influence of the shoreline orientation at the

cell. With Q known and all sources/sinks and nourishments specified, Equation 3.2 is

solved. The solution technique is an explicit, forward, Einite difference scheme. Time

steps are made small enough to ensure numerical stability.

Wave Setup

If the water depth as the seawall is greater than zero, then wave setup at the seawall

is calculated as










rl, = (hL-h) hL(3.5)
8 + 3r 16

In which rs, is the setup at the seawall, hBL is the still water depth at the breaker line, hs,,

is the still water depth at the seawall, and r is a breaker index. This setup equation is

valid for depth profiles that increase monotonically with distance offshore. The influence

of wave reflection is not included.

Run-up

The run-up is calculated using different formulations for a vertical face and a

rubble slope. For a vertical face, the height of the run-up, Ra is taken as the height of a

standing wave crest.

R,, = Hs, + rT + r (3.6)

where Hs,,- is the incident wave height at the seawall. This is added to the tide r, and


wave setup r to get the total height of the run-up at the seawall. For a rubble slope, the

run-up is calculated as (CIRIA/CUR, 1991)

0.725Hsw 5<1.5
R,, = 0. 8850 41H,, 1.5 < 5 < 2.84 (3.7)
1.35Hcw 5> 2.84

in which 5 is the surf similarity parameter defined as


5= (3.8)


where m is the slope of the structure face (mV : 1H ), g is the acceleration due to gravity,

and T,;;is the mean wave period. Data for this project are given as peak period, T,. An

approximate conversion is T,;;= 0.83 T, (CIRIA/CUR, 1991).









Overtopping Propagation

Overtopping occurs when the height of the run-up exceeds the crest elevation of the

seawall. Overtopping creates the potential for damage to structures from flooding and

direct water forces. Cox and Machemehl (1986) present a simple model for propagation

of a bore behind the seawall when overtopping occurs. The height of the bore, H, is

given as


H = ~,-E a (3.9)
1+a 2A


where R,, is the run-up height, Eo is the crest elevation of the structure, and x is the

distance behind the seawall. The term a is a coefficient with a recommended value of a

= 0.1. The term A is defined as

A = a(1 + a)3/ g /T (3.10)

where g is the acceleration of gravity and Tis the wave period.

The bore height is a maximum at the seawall crest (x = 0) and decreases in height

rather quickly as the bore propagates landward of the seawall. The magnitude of the

excess run-up determines the distance of the bore propagation (R,, Eo). In the DNR

model, if overtopping occurs, the bore height is calculated at the seawall crest, and then

every 5 m (16 ft) behind the seawall until the bore height diminishes to H = 0.

Forces

If a propagating bore impacts a structure, wave forces develop. These forces are

estimated as outlined in Ramsden and Raichlen (1990),


fmax =1 + NF) 7]H' (3.11)










where fm, is the per unit width of the structure, yis the weight density of the water, and

NF is the Froude number. The value of the Froude number is taken to be NF = 1.8, which

follows the data given in Ramsden and Raichlen (1990).

Input Parameter Cell Definitions

This section explains the methods used in defining characteristics within a cell of

the DNR model. These characteristics include shoreline position, seawall location,

longshore sediment transport rate, shore perpendicular structures (breakwaters, jetties,

and groins), beach nourishments, and sediment sources/sinks. These definitions are

important to define the study area as accurately as possible in the model.

The definitions of shoreline position, cross-shore seawall location, and groin

lengths are referenced to the baseline. The baseline is an imaginary line typically located

landward of the shoreline with an azimuth similar to that of the shoreline between the

boundaries of the study area. The baseline is then segmented into equally spaced

intervals that define each individual cell. The baseline origin marks one boundary of the

study area and is defined at cell 1. The positive direction along the base coordinate is

defined as left to right when facing offshore. Perpendicular lines are then proj ected from

the baseline to define the shoreline position, cross-shore seawall locations, and the

seaward tip of shore perpendicular structures.

The study area is sub-divided into cells, which are equally spaced across the

domain. The upper boundary is cell Ims, which is the last cell in the domain. The upper

and lower boundaries are not referenced by the direction of transport; rather they are

designated by the location within the domain. For the purposes of this proj ect, the cells

are all 100 m (330 ft) in width.










Shoreline positions are defined at the midpoint of each cell. The representative

shoreline distance for each cell is found by interpolating the shoreline position at the

boundaries for each cell. The number of shoreline position values is equal to the total

number of cells from the lower boundary to the upper boundary. Shoreline position is

entered in feet from the baseline.

Cross-shore seawall positions are defined in a similar manner as shoreline

positions. Representative cross-shore seawall positions are found by interpolating the

seawall positions at the boundary of each cell and are defined at the midpoint of those

cells. The seawall position value is the same for the entire cell. In the along shore

orientation, seawalls represent armoring of the entire cell at the specified cross-shore

distance from the baseline. Cross-shore seawall location is entered in feet from the

baseline.

Longshore sediment transport (LST) is defined at the boundaries between cells. As

a result, there is one more LST value along the reach than there are cells. LST values are

positive if the transport is moving from the left to the right of an observer facing offshore.

Likewise, transport is negative if it is moving from the observer' s right to left. The lower

boundary is the location of the first LST value, Q(1), and the upper boundary of the reach

is the location of the final LST value, Q(I;;;a+1). LST rate is measured in cubic yards per

year.

Groins are defined in both the alongshore and the cross-shore directions. "Groins"

is the general term used to describe any shore perpendicular structure capable of blocking

the movement of sediment alongshore, and includes breakwaters, jetties, and groins. In

the alongshore, groins are defined at the boundaries between cells. The cell whose lower









boundary marks the location of the groin designates the LST. For example, a groin

located in cell 100 is placed in the boundary between cells 99 and 100. In the cross-shore

direction, groin lengths are given as the distance from the baseline to the seaward tip of

the groin. This length is measured in feet.

Beach nourishment input includes the alongshore location, nourishment volume,

time of placement, and a fill factor. In the alongshore, nourishment projects are defined

with an upper cell and a lower cell. The nourishment volume is then placed uniformly on

the coast between the lower and upper cell. Beach nourishment volumes are given in

cubic yards. The nourishment is placed at the specified time (in hours). The fill factor is

the portion of the nourishment volume that remains in the littoral system.

Sediment sources and sinks are defined as a uniform addition or removal of

sediment within the assigned cell. The volume change is an annual rate that remains

constant throughout the duration of the model run. Sediment sources and sinks include

river contributions, bluff contributions, offshore sediment deflection, sediment removal,

and background erosion. Sources/sinks are given in yd3 ft/yr.








59












Offshore Source/Sink
Shoreline Posit on C


M ning/Nourishment


Figure 3-1. Possible changes in sediment amounts within a cell.















CHAPTER 4
SEAWALL MODEL

The DNR model has been modified to include influences from seawalls. If a

seawall is in the surf zone, then the surf zone width increases, the longshore sediment

transport (LST) is reduced, and the shoreline cannot retreat landward of the seawall

cross-shore location. In this chapter, the seawall algorithm is described and examples are

presented to show the performance of the seawall routines.

Theory

Profile Definitions

The DNR model is a one-line model that tracks the cross-shore position of the

shoreline in response to alongshore gradients in the LST. Along seawalls, the actual

shoreline position cannot retreat landward of the seawall location. Therefore, a

modification is necessary in the one-line model to determine the shoreline response

where the shoreline position becomes fixed. The modification implemented into the

DNR model is that for cells with seawalls, the volume of sediment seaward of the seawall

is tracked rather than the shoreline position.

The cross-shore profie must be known to determine this volume of sediment. As

mentioned in Chapter 2, the beach profie in the DNR model is defined by the

Brunn/Dean equilibrium beach profile. The equilibrium profile is based on constant

wave energy dissipation per unit volume of surf zone and has been well documented and

widely used in coastal engineering. The equilibrium beach profile is given as

h = Ay2/ (4.1)









where h is the still water depth along the profie, A is the profie coefficient related to the

sediment diameter, and y is the cross-shore distance along the profie (Dean and

Dalrymple, 2002). The shoreline position corresponds to y = 0; and the depth of closure,

h = h*, correspond to the width of the active littoral zone, y = y*.

To distinguish between global cross-shore position and local profie position, the

subscript "L" is applied to variables that refer to the local coordinate system of the beach

profile. The global coordinates begin at the baseline as the origin, and the local

coordinates begin with the shoreline position of the equilibrium beach profile as the

origin. The global cross-shore distance from the baseline to the shoreline position is

defined as y = yN. The shoreline position in reference to the local coordinates of the

equilibrium beach profile occurs at yL = 0. Other variables used in the local coordinate

system are y*L, which is the cross-shore width of the active littoral, yaL, which defines the

cross-shore shoreline displacement when ys,, yN, and ysitL, which is the distance from

the shoreline position landward of the seawall to the seawall.

A critical location for the profile is when the equilibrium profile shoreline position

is defined at the location of the seawall. If the shoreline is seaward of the seawall /

ys,,-), then a sub-aerial berm/beach exist seaward of the seawall. If the profile is landward

of this critical point / ys,,), then no sub-aerial berm/beach exist seaward of the

seawall, and there is a finite water depth fronting the seawall.

The volume of sediment calculated at this critical shoreline position is referred to as

the critical volume for the profile. If the volume of sand in the profile exceeds the critical

volume, then a sub-aerial beach exists seaward of the seawall. If the volume of sediment

in the profile is less than the critical volume, then a finite water depth exists at the









seawall. Figure 4-1 shows this critical condition. For an equilibrium profie, the critical

volume is

Vc = [ysw(A2 + B)+(y,,Az 0.6Ay, 5/3 )]dx~ (4.2)

where Vc is the critical volume, ysw is the cross-shore distance from the baseline to the

seawall, y*L is the width of the active littoral zone, h* is the closure depth, B is the berm

elevation, and dx~ is the cell width.

Figure 4-2 shows the condition where the profile of sand exceeds the critical

volume (ys > ysw). For this case, the volume is


V'= [yh,( +B)+(y~, -0.6Ay, 3)]dx (4.3)

where yN is the cross-shore shoreline position seaward of the seawall. This equation is

similar to the equation for critical volume. The only difference is that the berm extends

seaward of the seawall to the actual shoreline. For this case, the change in shoreline

position associated with the volume tracking within the profie is the same as the

shoreline position change calculated by profie translation:

AV
Ay = (4.4)
A+B

Excess volume, VE, iS defined as the actual volume minus the critical volume,

VE = V Vc (4 .5)

If VE > 0, then a sub-aerial beach exists seaward of the seawall. If VE < 0, no beach exists

and water fronting the seawall. The VE < 0 case is more complex than the VE > 0 case

and leads to the modification of tracking the sediment volumes as opposed to simply

solving for the shoreline position change with profile translation.










Figure 4-3 shows an example where the seawall is in the surf zone. The submerged

profile is still defined as an equilibrium beach profile, but the origin of the profile is

displaced landward of the seawall. This landward translation results in an increase in

water depth and flattening of the profile at the seawall. The cross-shore position referred

to as yur is actually a fictitious shoreline position, since the actual shoreline cannot retreat

onshore beyond the seawall location. However, this fictitious shoreline position is crucial

in defining the profile and the volume. The volume of sediment within a cell for the case

where the VE < 0 is

V = [y,,(A2 + B)+ (y,, ya,)(A2 hs)- 0.6(Ay,, hsy, )]dx ~ (4.6)

where yL is the distance from the fictitious shoreline position to the cross-shore seawall

location.


For=(, 3/2 (4.7)


Profile Changes

In the preceding section, the volumes of sediment in the profile were determined

for the cases with and without a beach fronting the seawall. In this section, the change in

shoreline position is determined as a function of the change in sediment volume.

As previously mentioned, in a one-line model, shoreline changes are driven by

gradients in the longshore transport. In a cell, if the transport entering the cell exceeds

the transport leaving of the cell, then accretion occurs and the shoreline advances

seaward. Conversely, if a deficit exists between the boundaries of a cell, then erosion

occurs and the shoreline retreats landward. This same principal applies along a seawall,

with the exception that if VE < 0, the fictitious shoreline retreats or advances as opposed










to the actual shoreline position, which is Eixed at the seawall. This results in a change in

water depth fronting the seawall.

Consider the change in sediment volume in a cell to be AV. For a one-line model,

neglecting sources/sinks and nourishments, this is simply

AV =(Q,, o,,)>At (4.8)

where Q,n is the transport going into the cell, Qour is the transport leaving the cell, and At

is the time interval. AV can be positive or negative. If the excess volume is positive, then

a beach is fronting the seawall, and there is a one-to-one relationship between volume

and shoreline position given by

AV = V,, V, = (7,, y, )(A2 + B)dx~ (4.9)

where the subscript o, or old, refers to the initial condition at a time step; and the

sub script n, or new, refers to Einal condition (initial time step + At). The old shoreline, yn,

is the same as yN at the new location in global coordinates, and the new shoreline, yo, is

the same as yN at the old location in global coordinates. Using Equations 4.8 and 4.9

gives an estimate of the new shoreline position.

When the excess volume is negative, there is no dry beach fronting the seawall, and

the volume change is still given as

AV = V,, V, (4 10)

except the volumes are defined by Equation 4.6. The volumes Vn and Vo depend on the

location of the fictitious shoreline. The location yo is known, and the value for yn must be

determined that satisfies Equation 4. 10.

Consider Figure 4-4, which gives a graphical representation of -VE and -AV based

on the longshore transport gradient where the fictitious shoreline retreats from yo to yn.










For convenience, the shoreline position change is expressed in local coordinates. Using

Equation 4.4, the volume change is defined as

AV = {0.6A[-(y., + y,,, y, )5/3 (swL aL y5/3 (*L )5/3 ]}dx (3.27)

The only unknown variable in Equation 3.27 is yat, which cannot be solved for explicitly.

Therefore, the DNR model iteratively solves for ye using a numerical technique.

Longshore Transport Modification

A seawall that is in the surf zone modifies LST. On a beach with no seawall the

waves break across the surf zone and are completely dissipated at the shoreline. All of

the wave power, or momentum, is available for generating longshore currents and

sediment transport. With a seawall in the surf zone, the waves break as they propagate

across the surf zone, but still have a finite height when they reach the seawall. The wave

energy may be dissipated at a rubble seawall or reflected back offshore at a vertical

seawall. Either way, the associated wave power does not lead to the development of

longshore currents. As a result, the LST on a beach with a seawall in the surf zone is

generally less than for the same beach with no seawall. Ruggiero and McDougal (2001)

presented an analytical solution for the LST on a plane beach that supports this argument.

The response was more complex because partial standing waves developed from

reflected waves. It was also found that the reflected wave causes the incident wave to

break approximately 10% farther offshore. Never-the-less, the general observation was

that the farther out into the surf zone a seawall is located, the greater the reduction in

LST.

Figure 4-5 shows the LST as a function of seawall location for four planar beach

slopes. The position of the seawall was relative to the location of the breaker line if no










seawall was present. In each case, the LST decreased as the seawall position moved

farther offshore. The milder the beach slope, the wider the surf zone became and the

influence of the partial standing wave increased.

In Figure 4-5, the seawall reduction factor, Rsw, was approximated as


R, = 1- a Bswb (4 11)


where yswL and yblL are the seawall and breaker line locations in local coordinates, Bsw is

the increase in surf zone width because of reflection from the seawall (Bsw = 1.12), and a

is the slope of the linear approximation. A value of a = 1.0 was used which yields no

LST when the seawall is seaward of the breaker line.

Along-shore Boundary Conditions

The seawall flux boundary conditions are located at the cell boundaries. Every

seawall has one more longshore sediment transport value, Q, than ysw values. This extra

transport value marks the boundary where LST makes the transition from a cell that does

not contain a seawall to a cell that is armored by a seawall. There is an additional

transport modification that may occur at the ends of the seawall.

If the seawall is in the surf zone, then the updrift boundary of the seawall can act as

a groin and block the LST (Figure 4-6). At this updrift location, the DNR model refers to

the groin routine. The end of the seawall can completely block LST until the updrift

shoreline advances seaward of the end of the seawall, or the groin can be leaky and allow

partial transport before the shoreline reaches the end of the groin.

Seawall/ Nourishment Sensitivity Tests

This section shows the functionality of the seawall routines in the DNR model by

examining a variety of hypothetical cases. The base conditions for the tests are:










* Straight initial shoreline located at ynr= 0.

* Constant wave of height Ho = 0.61 m (2 ft) and period T= 12. 1 s.

* Shore-normal wave angle ao = -30 (causing transport to move from right to left).

* A study area of 241 cells.

* Duration of simulation = 50 yrs.

The variables are a 150-m (500-ft) breakwater, a beach nourishment at time

t = 10 yrs (varies in location by case depending on seawall locations), and the presence of

one or more seawalls. Table 4-1 gives input parameters for each case. The letters 'a' and

'b' in the case titles show whether or not a breakwater exists for that particular

simulation: no breakwater for cases that are denoted with an 'a' and one 150-m (500-ft)

breakwater at cell 120 for cases that are denoted with a 'b.' The cases that do not contain

a breakwater do not experience a disruption in the longshore sediment transport, and thus

do not result in erosion.

Case 1: One Seawall, No Nourishments

Case 1 incorporates one seawall with a cross-shore location at the initial shoreline

position. No nourishment is included for this test. Figure 4-7 gives a graphical

representation of the input parameters for Case 1. Case la is not presented in Table 4-1,

as the results are unimportant. Case la consists of one seawall and no breakwater or

beach nourishments. Consequently, no forcing is present that would cause the shoreline

to accrete or erode. The result for Case la is a straight final shoreline identical to the

straight initial shoreline.

Figure 4-8 shows the evolution of the shoreline at the 1-yr, 5-yr, 10-yr, 30-yr, and

50-yr time steps for Case lb, and Figure 4-9 shows the shoreline position at pre-selected

cells for every time step. These two figures display the shoreline response when










interacting with a seawall in an area experiencing a gradient in longshore sediment

transport attributable to the breakwater. It should be noted that the present version of the

DNR model does not include diffraction, so the shoreline response close to shore-

perpendicular structures is not simulated accurately.

Figure 4-8 presents an important verification on the behavior at the ends of a

seawall. If the shoreline immediately updrift recedes landward past the seawall, the

updrift end of the seawall acts as a groin, thus blocking transport. In this simulation, the

breakwater acts as the primary sediment trap blocking all transport. Once the shoreline

upcoast of the seawall retreats landward of the seawall, the updrift end of the seawall

becomes a secondary block in the sediment transport. The shoreline between the

breakwater and the seawall then continues to adjust its orientation without any supply in

sediment to these cells until the shoreline aligns with the incoming wave angle. This

behavior mimics the response of a shoreline between groins. While this is occurring,

erosion continues downdrift of cell 100 because of the lack of sediment reaching those

cells.

Case 2: No Seawalls, One Nourishment

Case 2 is a simple case with one nourishment and no seawalls. This case is

designed to check the functionality of the nourishment routine by isolating it from the

seawall routines. Figure 4-10 gives a graphical representation of the input parameters for

Case 2.

Figures 4-11 and 4-13 show the evolution of the shoreline for the 1-yr, 5-yr, 10-yr,

30-yr, and 50-yr time steps for Cases 2a and 2b, respectively. Figures 4-12 and 4-14

show the shoreline position at pre-selected cells for every time step for Cases 2a and 2b,

respectively. These figures show the nourishment spreading effects as time progresses










after the implementation of nourishment proj ects, both in an area with no disturbance in

LST (Case 2a) and in an area experiencing reduced LST (Case 2b). Figure 4-13 shows

that the same volume of sediment is placed for every nourished cell. The cells within the

nourishment bounds have a nourished planform that is parallel to the shoreline planform

immediately before the nourishment event.

Case 3: One Seawall, One Nourishment

Case 3 combines one seawall and one nourishment. The nourishment spans the

updrift half of the seawall, and then extends an equal distance upcoast across the

unarmored shoreline. Figure 4-15 gives a graphical representation of the input

parameters for Cases 3a and 3b.

Figure 4-16 shows the shoreline evolution for Case 3a for the 1-yr, 5-yr, 10-yr, 30-

yr, and 50-yr time steps. The nourishment at the 10-yr time step causes the shoreline to

move seaward between cells 100 and 115. As the simulation continues after the 10-yr

mark, the nourishment spreads out in the form of a normal distribution in accordance to

the one-line Pelnard-Considere model that predicts alongshore diffusion. Since there is

no erosion to expose the seawall, the seawall has no influence. Figure 4-17 shows the

shoreline position as a function of time at a number of cells along the seawall and beyond

the ends of the seawall. The results also show the spreading of the nourishment with no

influence from the seawall. Case 3a is in agreement with the results of Case 2.

Figure 4-18 shows the shoreline evolution for Case 3b, which includes a

breakwater at cell 120 that causes erosion in the area of the seawall for the 1-yr, 5-yr, 10-

yr, 30-yr, and 50-yr time steps. The results of Figure 4-18 shows the updrift end of the

seawall acting as a groin when the shoreline updrift recedes landward of the seawall.









This is in agreement with the results at the seawall updrift end for Case 2b. Figure 4-18

also shows an interesting result important in the seawall model verification.

Notice the point in the shoreline position at year 10 that occurs at the upcoast end

of the seawall. This point seems to represent an error, or a discontinuity, in the beach

nourishment. However, since the shoreline had already retreated back to the armoring

before the placement of the nourishment (notice that in the 5-year planform the shoreline

position is already landward of the updrift end of the seawall), progressively varying

water depth exists seaward of the seawall, increasing from the updrift to the downdrift

ends of the seawall. The volume of nourishment assigned to each cell along the seawall

first goes toward filling the profile to the critical volume. Once that critical volume is

achieved, the shoreline advances seaward in accordance to profile translation. The point

in the nourishment proj ect at cell 105 represents the boundary between the end of the

seawall, where a water depth existed before the nourishment (from the fictitious retreat of

the shoreline landward of the seawall), and the open, unarmored coastline.

Figure 4-19 shows the shoreline position by cell for Case 3b and gives a good

representation of the seawall effect on shoreline response in a sediment-starved system.

Cell 115 (represented by the green line in the figure) is the closest to the breakwater and

therefore begins to erode first and more severely than the other cells. Between the 10-yr

time step (when the nourishment occurs) and the 15-yr time step, shoreline advance

occurs at this cell. This advance is a result of the spreading effect of the nourishment as

it reaches cell 115. The consequent shoreline retreat is from the sediment eroding away

because of the lack of transport at that location. However, since the sediment becomes

essentially trapped between the breakwater and the updrift end of the breakwater, the









erosion rate decreases dramatically toward the end of the simulation as the shoreline

aligns itself to the wave angle.

Conversely, cell 80 (represented by the yellow line) is the cell farthest from the

breakwater. This cell is the last of the specified cells to start eroding, and its distant

location from the nourishment causes only a small advance in the shoreline position as

the nourishment spreads out along the coast. The erosion downdrift of the seawall

mentioned previously because of the updrift end of the seawall acting as a groin is

evident for those cells downcoast of the seawall in Figure 4-19.

Case 4: Two Seawalls, One Nourishment

The main focus of Case 4 is to isolate the shoreline response in gaps between

seawalls. To examine the shoreline behavior between seawalls, two seawalls each

1,500 m (4900 ft) long and 1,000 m (3300 ft) apart are examined. Also, a beach

nourishment is placed at the 10-yr time step that spans beyond both ends of the updrift

seawall. This configuration allows an examination of the shoreline behavior along a

seawall fronted by water and at the ends of seawalls. Figure 4-20 gives a graphical

representation of the input parameters for Cases 4a and 4b.

Figure 4-21 shows the shoreline evolution for the 50-yr simulation for Case 2a. It

is rather uneventful and similar to Figure 4-16. Once again, since no breakwater is

included for this case, there is no erosion. Therefore, the nourishment moves the

shoreline seaward, and the seawalls have no effect. As time progresses, the beach

nourishment spreads out along the coast. This is also shown in Figure 4-22.

Figure 4-23 shows the shoreline response with an updrift breakwater. The

shoreline position from the middle of the updrift seawall to the breakwater is similar to

that same relative location in Figure 4-18. These results reinforce the conclusions from










Case 3b. Continuing downcoast from the midpoint of the updrift seawall, the shoreline

position seaward of the seawall continues to increase slowly to the boundary of the

nourishment with only a small dip at the downcoast end of the seawall.

As previously mentioned, the sediment volume from the nourishment must first

provide a profile with the necessary sediment to reach the critical volume before the

shoreline can advance seaward. The shortage of sediment for transport (attributable to

the breakwater in this case) results in a progressive removal of sediment from the updrift

(adj acent to the sediment sink) to the downdrift direction to satisfy continuity, and in

turn, progressively greater depths fronting the seawall in the updrift direction.

Consequently, more and more of the nourishment volume must go toward reaching the

critical volume along the seawall from the downdrift to the updrift direction of the

seawall. The resulting gradual increase in shoreline advance is a result of these

processes.

The small dip at the downcoast end of the seawall shows that immediately before

the nourishment, the shoreline at that downcoast end of the seawall had already reached

the seawall resulting in water depth at that boundary. This means that more sediment

volume is necessary to reach the critical volume in those cells, and the resulting shoreline

is landward of cells that had less water depth fronting the seawall at the time of the

nourishment. This behavior was discussed for the results of Case 3b.

The shoreline response downdrift of the second seawall is similar to the results

downdrift of the seawall in Case 3b. The only other difference between Case 4b and

Case 3b is that now the shoreline must orient itself to the direction of the incoming waves

not just between the first seawall and the breakwater, but also between the two seawalls







73


since the updrift end of the downcoast seawall will also act as a groin once the shoreline

recedes landward of the seawall.

Figure 4-24 shows the shoreline position by cell for Case 4b. These figures give an

accurate description of erosion rates in relation to distance downdrift from the breakwater

and proximity to a seawall. Figure 4-24 agrees with previous conclusions for shoreline

response from the nourishment spreading out along the coast over time. As the

nourishment spreads, temporary shoreline advances are evident in cells affected by this

behavior.






74


Table 4-1. Input parameters for seawall sensitivity test cases.
1st 2nd
Groin Groin Nouri shment Nouri shment Seawall s Seawall Seawall
Case (yes/no) (cell) (yes/no) (cells) (yes/no) (cells) (cells)
lb yes 120 no -- yes 100 to 110 -
2a no -- yes 90 to 110 no---
2b yes 120 yes 90 to 110 no---
3a no -- yes 100 to 110 yes 95 to 105 -
3b yes 120 yes 100 to 110 yes 95 to 105 -
4a no -- yes 85 to 110 yes 65 to 80 90 to 105
4b yes 120 yes 85 to 110 yes 65 to 80 90 to 105

















































I II1


Bsaseli na


Figure 4-1. Critical volume, Vc, per unit width. The critical volume is the entire area
shown in brown.


O yswYN
I I


YLIN


Bas eli ne


Figure 4-2. Volume per unit width for an aerial beach seaward of the seawall (ys 2 ysw).
















o YN YaPI


ftL~tYN


Baseline


Water Line!


Figure 4-3. Initial volume per unit length for a seawall in the surf zone (ys < ysw).


Globat y, y,


Yn + Y ye + y
I I




| | hT.


Figure 4-4. Volume change for a fictitious shoreline retreat with locations shown in both
global and local coordinates.











m = :10 in = 1 2
A B




Is* blHBS -.


ceaes 2b
E ;Ll~..~~asse 2b
0.2 0.4 0.8 02 ~ 0. 0.8 0.8




up m 9;1:50 1 1:10 0)





0~ Q ;f








several wave conditions shown by different line types. A) Slope, m = 1:10.
B) Slope, m =1:02. C) Slope, m =1:50. D) Slope, m =1:100. Ruggerio, P.
and W.G. McDougal (2001), "An Analytic Model for the Prediction of Wave
Setup, Longshore Currents and Sediment Transport on Beaches with
Seawarlls"ll`, Coastal Engineering: An International Journal for Coastal, Harbour
and Ocean Engineers, Volume 43, pp. 161-182.














































































BS 90 95 100 105 1 10 1 15 120
Cells (Each Cell Represents 100m)

Figure 4-7. Input parameters for Case 1.


78


Elaseline


Figure 4-6. Graphical representation of positive transport and ysw (I) < yN (I-1) at the
start of the seawall. The shoreline is shown in blue and the seawall is shown
in red. This case means the seawall act as a groin and blocks transport

(Q(I) = 0) as it forms a discontinuity in the shoreline.


Note: The breakwater is not drawn to
scale in the cross-shore direction.
No Nourishment












Initial Straight Shorefine


500ft Breakwater
(For Case lb only)


Seawall


















































































-20

-30

-n


-wu














O 0 0304



Time (yrsil


Figure 4-9. Case lb: One seawall, no nourishment. Shoreline position by cell.


-InRlal
Year 1
--Year 5
--Yzar 10
--Yzar 30
--Yzar 50


0 25 50 75 100 125 150 175 200 225 250

Cell


Figure 4-8. Case lb: One seawall, no nourishment. Shoreline evolution.


Cell 85
-Cell 95
-Cell l OS
-Cell 115


















Note: The nourishment and the breakwater are
not drawn to scale in the cross-shore direction. S~tBekae
No Seawall (For Case 2b only)




1,000.000 cu yd Nourishment
Occuring at Year 10O









Initial Straight Shoreline


75 BO BG 90 95 100 105
Cells (Each Cell Represents f00m)


Figure 4-10. Input parameters for Case 2.


110 115 120 125


25



20



16



10 i











-5



-10


--Innlal
Year 1
-Year 10
-Year so
-Year 50


0 25 50 75 100 125 150 175 200 225 250

Ceil


Figure 4-11. Case 2a: No seawall, one nourishment, and no breakwater. Shoreline
evolution.









































0 10 20 30 40 50

T~me (yrs)

Figure 4-12. Case 2a: No seawall, one nourishment, no breakwater. Shoreline position

by cell.


--Innlal
-Year 5
-Year 10
-Year 30
-Year 50


0 25 50 75 100 125 150 175 200 225 250

CeHl

e 4-13. Case 2b: No seawall, one nourishment, one breakwater. Shoreline
evolution.


Figur~





Cell 85
-Cell 95
-Cell 100
-Cell 115


T me (yrs)

Figure 4-14. Case 2b: No seawall, one nourishment, one breakwater. Shoreline position

by cell.


Note: The nourishment and the breakwater are
not drawn to scale in the cross-shore direction. 50tBe~ae

(For Case 3b only)




1,000,000 cu yd Nourishment
Occuring at Year 10









Initial Straight Shoreline

Seawall


75 80BS 9095 100 105
Cells (Each Cell Represents f00m)


Figure 4-15. Input parameters for Case 3.


110 115 120 125





CL 20


P1



-1


--Innlal
Year 1

-Year 10
***Year 30
-Year 50


0 25 50 75 100 125 150 175 200 225 250
Ceil


Figure 4-16. Case 3a:
evolution.









60h


Cell 80
-Cell 87
-Cell 92
-Cell 97
-Cell 102
-Cell 107
-Cell 115


0 10 20 30 40 50

n~me (yrs)

Figure 4-17. Case 3a: One seawall, one nourishment, no breakwater. Shoreline position
by cell.


One seawall, one nourishment, no breakwater. Shoreline


























































































30 1 03 0

T e(ys

Fiue41.Cs b n saal n orsmn, n rawtr hrln

poiinb el


-0
Year 1
-Year 5
-Year 10
-Year 30
-Year 50


0 25 60 75 100 125 150 175 200 225 250

Cell


Figure 4-18. Case 3b: One seawall, one nourishment, one breakwater. Shoreline

evolution.


Cell 80



--Cell 97
--Cell 102
--Cell 107
--Cell 115



















SO0ft Breah~water
Note: The nourishment and the breakwater ame (For Case 4b only)
not drawn to scale in the cross-shore direction.







1,000,000 cu yd Nourishment
Occuring at Year 10










Initial Straig~ht Shoreline

Seawall Seawall


75 85 95
Cells (Each Cell Represents f00m)


Figure 4-20. Input parameters for Case 4.


25



20



16



10 i












-5



-10


--Innlal
Year 1

-Year 10
-Year so

-Year 50


0 25 50 75 100 125 150 175 200 225 250

Ceil


Figure 4-21. Case 4a: Two seawalls, one nourishment, no breakwater. Shoreline
evolution.





































































\


25



20



15



0 10



5


Call 50
--Czll 60
--cell 72
--Cell 82
--Cell 87
--Cell 97
--cellio07
--Cell 115


0 10 20 30 40 50

n~me (yrs)

Figure 4-22. Case 4a: Two seawalls, one nourishment, no breakwater. Shoreline

position by cell.


--Innlal
Year 1


0 25 50 75 100 125 150 175 200 225 250

CeHl


Figure 4-23. Case 4b: Two seawalls, one nourishment, one breakwater. Shoreline
evolution.