COASTAL SEDIMENT BUDGET FOR JUPITER INLET, FLORIDA

Transcription

1 COASTAL SEDIMENT BUDGET FOR JUPITER INLET, FLORIDA By KRISTEN MARIE ODRONIEC 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 2006

2 ACKNOWLEDGMENTS I greatly thank my supervisory committee, Dr. Ashish Mehta, Dr. Robert Dean, and Dr. Andrew Kennedy, for their assistance, guidance and insight throughout this research project. I would also like to express my gratitude to the Jupiter Inlet District for providing the financial resources needed to carry out this project. Thanks also go to Michael Grella of the Jupiter Inlet District for always providing prompt answers to my many questions and requests for information. I would also like to thank all of my fellow coastal engineering students and friends, whose support and distraction kept me sane. Finally, my ultimate thanks go to my family who were always there for me providing patience, understanding, encouragement and love. ii

3 TABLE OF CONTENTS page ACKNOWLEDGMENTS... ii LIST OF TABLES... vi LIST OF FIGURES... vii ABSTRACT... xi CHAPTER 1 INTRODUCTION Problem Statement Objective and Tasks Outline of Chapters SITE DESCRIPTION AND DATABASE Site Description and Recent History Site Description Recent History Beach Profile Data Ebb Shoal Volume Data Dredging Data Beach Nourishment Data Downdrift Beach Nourishment Volumes Updrift Beach Nourishment Volumes SHORELINE AND BEACH VOLUME CHANGES Shoreline and Beach Volume Change Calculation Methods Data Limitations and Uncertainties Data Uncertainties Corrections for Non-Closure of Profiles Corrections for Monument Relocation FDEP Intersurvey Interval: Shoreline Changes Sediment Volume Changes...20 iii

4 3.4 FDEP Intersurvey Interval: Shoreline Changes Sediment Volume Changes FDEP Intersurvey Combined Interval: Shoreline Changes Sediment Volume Changes Volume Change Sensitivity to Depth of Closure Volume Change Sensitivity to Depth of Closure: 1974 to Volume Change Sensitivity to Depth of Closure: 1986 to Volume Change Sensitivity to Depth of Closure: 1974 to JID Intersurvey Interval: Shoreline Changes Sediment Volume Changes JID Intersurvey Interval: Shoreline Changes Sediment Volume Changes JID Intersurvey Combined Interval: Shoreline Changes Sediment Volume Changes JID Intersurvey Interval: Shoreline Changes Sediment Volume Changes SEDIMENT BUDGET Sediment Budget Methodology Sediment Budget Equation Method for Evaluating Sediment Budget Effect of Length of Beach on Sediment Budget Calculations FDEP Sediment Budget Components JID Sediment Budget Components Sediment Budget Results SUMMARY AND CONCLUSIONS Summary Conclusions Recommendations for Further Work...57 APPENDIX A FDEP LONG BEACH PROFILES FOR MARTIN AND PALM BEACH COUNTIES...58 B JID BEACH PROFILES FOR PALM BEACH COUNTY...75 C STORMS NEAR JUPITER INLET, FLORIDA...82 iv

5 LIST OF REFERENCES...83 BIOGRAPHICAL SKETCH...85 v

6 LIST OF TABLES Table page 2-1 Beach profile data for Martin and Palm Beach Counties Jupiter Inlet ebb shoal volumes (Source: Dombrowski, 1994) Jupiter Inlet and interior sand trap dredging volumes Jupiter Inlet downdrift beach nourishment volumes Jupiter Inlet updrift beach nourishment volumes Annual mean sand volumetric transport rates in the eastern zone (Source: Patra & Mehta, 2004, p. 11) FDEP sediment budget components for long analysis FDEP sediment budget components for short analysis JID sediment budget components Short FDEP and JID sediment budget results...53 C-1 Storms occurring within 150 km of Jupiter Inlet...82 vi

7 LIST OF FIGURES Figure page 2-1 Jupiter Inlet connecting the Loxahatchee River forks to the Atlantic Ocean FDEP range monuments north and south of Jupiter Inlet Area map of Jupiter Inlet Photograph of Jupiter Inlet showing jetties and approximate location of sand trap Jupiter Inlet Management Plan recommended increase in nourishment beach length Sand trap and Intracoastal Waterway deposition basin from which sediment is dredged to be used as nourishment Schematic diagram defining depth of closure, where all offshore profiles converge to a certain depth Shoreline change rates for the period from 1976 to 1982 in Martin County and from 1974 to 1990 in Palm Beach County Unit volume change rates for the period from 1976 to 1982 in Martin County and from 1974 to 1990 in Palm Beach County Shoreline change rates for the period from 1982 to 2002 in Martin County and from 1990 to 2001 in Palm Beach County Unit volume change rates for the period from 1982 to 2002 in Martin County and from 1990 to 2001 in Palm Beach County Shoreline change rates for the combined period from 1976 to 2002 in Martin County and from 1974 to 2001 in Palm Beach County Unit volume change rates for the combined period from 1976 to 2002 in Martin County and from 1974 to 2001 in Palm Beach County Unit volume change rates calculated with varying depths of closure for the period from 1976 to 1982 in Martin County and from 1974 to 1990 in Palm Beach County...29 vii

8 3-9 Unit volume change rates calculated with varying depths of closure for the period from 1982 to 2002 in Martin County and from 1990 to 2001 in Palm Beach County Unit volume change rates calculated with varying depths of closure for the combined period from 1976 to 2002 in Martin County and from 1974 to 2001 in Palm Beach County Shoreline change rates for the period from 1995 to 1996 just south of Jupiter Inlet in Palm Beach County Unit volume change rates for the period from 1995 to 1996 just south of Jupiter Inlet in Palm Beach County Shoreline change rates for the period from 1996 to 1997 just south of Jupiter Inlet in Palm Beach County Unit volume change rates for the period from 1996 to 1997 just south of Jupiter Inlet in Palm Beach County Shoreline change rates for the combined period from 1995 to 2004 just south of Jupiter Inlet in Palm Beach County Unit volume change rates for the combined period from 1995 to 2004 just south of Jupiter Inlet in Palm Beach County Shoreline change rates for the period from 2001 to 2002 in Palm Beach County Unit volume change rates for the period from 2001 to 2002 in Palm Beach County Definition diagram displaying Jupiter Inlet along with all possible components in the sediment budget equation Sediment budget components specific to Jupiter Inlet Plot showing measurements of Jupiter Inlet s ebb delta volumes, highlighting the three that were chosen to construct a best-fit line Jupiter Inlet ebb tidal shoal depth contours for the year Jupiter Inlet ebb tidal shoal depth contours for the year Jupiter Inlet ebb tidal shoal difference in depth contours ( ) used for volume calculations...49 A-1 Profiles for Monument R-75 in Martin County...58 A-2 Profiles for Monument R-78 in Martin County...59 viii

9 A-3 Profiles for Monument R-81 in Martin County...59 A-4 Profiles for Monument R-84 in Martin County...60 A-5 Profiles for Monument R-87 in Martin County...60 A-6 Profiles for Monument R-90 in Martin County...61 A-7 Profiles for Monument R-93 in Martin County...61 A-8 Profiles for Monument R-96 in Martin County...62 A-9 Profiles for Monument R-99 in Martin County...62 A-10 Profiles for Monument R-102 in Martin County...63 A-11 Profiles for Monument R-105 in Martin County...63 A-12 Profiles for Monument R-108 in Martin County...64 A-13 Profiles for Monument R-111 in Martin County...64 A-14 Profiles for Monument R-114 in Martin County...65 A-15 Profiles for Monument R-117 in Martin County...65 A-16 Profiles for Monument R-120 in Martin County...66 A-17 Profiles for Monument R-123 in Martin County...66 A-18 Profiles for Monument R-126 in Martin County...67 A-19 Profiles for Monument R-1 in Palm Beach County...67 A-20 Profiles for Monument R-3 in Palm Beach County...68 A-21 Profiles for Monument R-6 in Palm Beach County...68 A-22 Profiles for Monument R-9 in Palm Beach County...69 A-23 Profiles for Monument R-12 in Palm Beach County...69 A-24 Profiles for Monument R-15 in Palm Beach County...70 A-25 Profiles for Monument R-18 in Palm Beach County...70 A-26 Profiles for Monument R-21 in Palm Beach County...71 A-27 Profiles for Monument R-24 in Palm Beach County...71 ix

10 A-28 Profiles for Monument R-27 in Palm Beach County...72 A-29 Profiles for Monument R-30 in Palm Beach County...72 A-30 Profiles for Monument R-33 in Palm Beach County...73 A-31 Profiles for Monument R-36 in Palm Beach County...73 A-32 Profiles for Monument R-39 in Palm Beach County...74 B-1 Profiles for Monument R-10 in Palm Beach County...75 B-2 Profiles for Monument R-11 in Palm Beach County...76 B-3 Profiles for Monument R-12 in Palm Beach County...76 B-4 Profiles for Monument R-13 in Palm Beach County...77 B-5 Profiles for Monument R-14 in Palm Beach County...77 B-6 Profiles for Monument R-15 in Palm Beach County...78 B-7 Profiles for Monument R-16 in Palm Beach County...78 B-8 Profiles for Monument R-17 in Palm Beach County...79 B-9 Profiles for Monument R-18 in Palm Beach County...79 B-10 Profiles for Monument R-19 in Palm Beach County...80 B-11 Profiles for Monument R-20 in Palm Beach County...80 B-12 Profiles for Monument R-21 in Palm Beach County...81 x

11 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science COASTAL SEDIMENT BUDGET FOR JUPITER INLET, FLORIDA By Kristen Marie Odroniec December 2006 Chair: Andrew Kennedy Major: Coastal and Oceanographic Engineering Three sediment budgets have been developed for Jupiter Inlet, a tidal entrance that connects the Atlantic Ocean to the Loxahatchee River in southeast Florida. These budgets cover varying lengths of shoreline updrift and downdrift of the inlet and are based on two sources of survey data. Two of the three budgets are based on Florida Department of Environmental Protection (FDEP) profile surveys covering periods of 1974 to 1986, 1986 to 2002, and 1974 to The third budget is based on surveys provided by the Jupiter Inlet District (JID) and covers the period of August 2001 to October The first budget covers a shoreline distance of approximately 26 km. The total period of 1974 to 2002 shows a net accumulation of sediment on the 8.53 km long downdrift beach of 122,600 m 3 per year. Since the shoreline distances north and south of the inlet are not equal, this sediment budget was believed to be the least accurate of the three. The second budget covers a shoreline distance of 14.5 km. This budget is believed to be more accurate in the respect xi

12 that it covers equal distances of north and south shorelines. It was determined that from 1974 to 2002 there has been a net accumulation of sediment on the 7.25 km long downdrift beach of 29,500 m 3 per year. The third budget covers a shoreline distance of about 1 km, with nearly equal distances north and south of the inlet. From August 2001 to October 2002, there has been a net accumulation of sediment on the downdrift beach of 65,600 m 3 per year. Due to the variability in the available ebb tidal delta volume data, two calculations of each of the three sediment budgets were made, one including delta volume change estimates and one excluding these estimates. The volumes given include the delta volume change estimates. When these changes are excluded from the calculations, net accumulated sediment volumes on the downdrift beach are about 2,100 m 3 per year higher than those given. It is recommended that profile survey data be taken yearly for Palm Beach County Monuments R-3 to R-21, which cover approximately equal shoreline distances updrift and downdrift of the inlet. Also, the area that the ebb tidal delta covers should be identified and also surveyed on a yearly basis. xii

13 CHAPTER 1 INTRODUCTION 1.1 Problem Statement Tidal inlets provide navigational access from the ocean to lagoons or bays for commercial and recreational purposes, and they also allow for the necessary exchange of waters, thus maintaining water quality and promoting life. However, some of the sediment that is transported along the coast often becomes trapped in the inlet channel during the flood tide and some is jetted far offshore during the ebb tide rather than being deposited on the shore as would normally occur in the absence of an inlet. This interruption in the longshore sediment transport causes shoreline erosion at beaches adjacent to the inlet (Dean and Dalrymple, 2002). Many inlets today have maintenance and management plans that were implemented in order to keep the channel open for navigation as well as to counteract the erosion that occurs at adjacent beaches. Jupiter Inlet in Florida is one such inlet that has an existing management plan due to its history of adjacent beach erosion as well as shoaling within the channel. In this study, the area surrounding this inlet was examined in order to determine the historical trend of beach and shoreline erosion and to assess the management plan for its effectiveness in regulating beach erosion. 1.2 Objective and Tasks The objectives of this study were 1) to develop a sediment budget to analyze the effects of the beach nourishment that has been carried out adjacent to Jupiter Inlet and 2) 1

14 2 to evaluate whether or not that nourishment has been successful in keeping the downdrift beach sufficiently nourished. The tasks undertaken for this study included: 1. Data compilation of the elements relevant to the sediment (sand) budget, including beach profiles, ebb shoal volumes, dredging volumes and nourishment volumes. 2. Determination of ebb shoal, dredging and nourishment data relevant to the locations and time periods being analyzed. 3. Calculation of the shoreline and volume change rates at the beaches adjacent to Jupiter Inlet. 4. Presentation of sediment budget equation specifically for Jupiter Inlet. 5. Assessment of the beach nourishment s efficacy after taking all data into consideration in the sediment budget equation. 1.3 Outline of Chapters Chapter 2 includes site description and a summary of the recent engineering history of the Jupiter Inlet area as well as a summary of beach profile and sand volume data compiled for use in the sediment budget analysis. Chapter 3 details methods used to calculate shoreline and volume changes of the beaches updrift and downdrift of Jupiter Inlet, describes the limitations of the profile data, and presents the shoreline and beach volume changes that took place within selected periods of time. The derivation of the sediment budget equation is given in Chapter 4, followed by the presentation of the quantities used in the sediment budget and an explanation of the results of the sediment budget. A summary of the study as well as conclusions and recommendations for further work are included in Chapter 5.

15 CHAPTER 2 SITE DESCRIPTION AND DATABASE 2.1 Site Description and Recent History Site Description Jupiter Inlet is a natural waterway maintained by the Jupiter Inlet District. The inlet connects the Loxahatchee River to the Atlantic Ocean, as shown in Figure 2-1. N km 0 1 Figure 2-1: Jupiter Inlet connecting the Loxahatchee River forks to the Atlantic Ocean In the present study, three separate sediment budget analyses have been conducted for Jupiter Inlet for varying shoreline distances. Figure 2-2 displays the shoreline surrounding the inlet and depicts the locations of the Florida Department of Environmental Protection s (FDEP) range monuments. The first analysis encompasses an expanse of shoreline nearly 26 km in length, with the study beginning at Monument R-75 in Martin County and continuing south to Monument R-40 in Palm Beach County. The second analysis covers a 14.5 km distance of shoreline, beginning with Monument R-112 3

16 4 in Martin County and ending just past Monument R-36 in Palm Beach County. The final analysis encompasses a much shorter distance of shoreline of just over 1 km, beginning at Monument R-10 in Palm Beach County just north of Jupiter Inlet and extending south to Monument R-15. Jupiter Inlet is located between Monuments R-12 and R-13 in northern Palm Beach County. It is approximately 26 km south of St. Lucie Inlet and about 19 km north of Lake Worth Inlet, as shown in Figure 2-3 (Dombrowski and Mehta, 1993). The Jupiter Inlet system consists of jetties at the north and south banks of the inlet, a navigational channel and an interior sand trap. The jetties and the location of the sand trap are displayed in Figure 2-4. Originally in 1922 the north and south jetties were each 120 m long and were built of rock. In 1929 both jetties were structurally strengthened and extended. The north jetty was extended 60 m and the south jetty 25 m. In 1956 a sheet-piled jetty 90 m long was constructed 30 m north of the pre-existing jetty. In 1967 the south jetty was extended by 30 m (Dombrowski and Mehta, 1993). Between 1996 and 1998, the seaward end of the south jetty was lengthened by 53 m with a hook in the southeastward direction (Mehta et al., 2005). Jupiter Inlet is approximately 112 m wide with a mean depth of 3.9 m at the jetties. Maintained through dredging, the navigational channel varies in width from about 206 m to 247 m and is also about 3.9 m deep (Patra, 2003). The interior sand trap located approximately 305 m westward of the inlet mouth is intended to maintain the channel, to nourish the beach downdrift of the inlet by placement of sand dredged from the trap, and to reduce the influx of sediment into the Loxahatchee River (Stauble, 1993) Recent History Jupiter Inlet has existed naturally for hundreds of years. Originally, it was kept open by the flow that passed through it from the Loxahatchee River, Jupiter Sound, and

17 5 Lake Worth Creek, closing intermittently due to natural events such as large storms (Grella, 1993). In more recent times, from the late 1800 s to the early 1900 s, the inlet closed more frequently than it had in the past due to the diversion of the natural flow caused by Lake Worth Inlet to the south and St. Lucie Inlet to the north. The inlet was occasionally dredged and reopened during this period, but it would again close because of the decreased flow through it (Dombrowski and Mehta, 1993). N km 0 1 Figure 2-2: FDEP range monuments north and south of Jupiter Inlet

18 6 Figure 2-3: Area map of Jupiter Inlet (Source: Buckingham, 1984, p. 3) N Sand Trap Jetties 0 km 1 Figure 2-4: Photograph of Jupiter Inlet showing jetties and approximate location of sand trap

19 7 The Jupiter Inlet District (JID) was created in 1921 for the purpose of preserving and maintaining the inlet and the Loxahatchee River. As mentioned, the first jetties were built in 1922 and extended in However, the inlet closed again despite these stabilization efforts (Grella, 1993). To keep the inlet open for navigation, periodic dredging of a sand trap to a depth of approximately 6 m below mean water level was implemented in Since that time the inlet has remained permanently open due to periodic dredging and maintenance of jetties. Since then, the jetties have been modified as mentioned, and the sand trap has been enlarged in order to reduce the entrance of littoral sediment into the inlet and to lessen the deposition of sediment further upstream of the trap (Mehta et al., 2005). 2.3 Beach Profile Data Two sources of data have been used to develop the three sediment budgets. The beach profile data used to conduct the analyses described in this report as the FDEP Sediment Budget were obtained from the Bureau of Beaches and Coastal Systems of the FDEP. Six sets of surveys consisting of beach profile data were obtained for Martin County and Palm Beach County. Three surveys within a period of nearly 30 years were found for each county. Ideally for this type of study the years in which the surveys were taken for each county would coincide, but matching survey dates were not available for Martin and Palm Beach Counties. The surveys that were found to be closest in dates were a 1976 survey for Martin County and a 1974 survey for Palm Beach County, a 1982 survey for Martin County and a 1990 survey for Palm Beach County, and a 2002 survey for Martin County and a 2001 survey for Palm Beach County. Table 2-1 lists the survey dates for each county as well as the beach profile type for each survey.

20 8 Table 2-1: Beach profile data for Martin and Palm Beach Counties County Survey Date Profile Type 1976 Wading profiles every monument; long profiles every third monument Martin 1982 Wading profiles every monument; long profiles every third monument 2002 Wading and long profiles every monument 1974 Wading profiles every monument; Palm Beach long profiles every third monument 1990 Wading and long profiles every monument 2001 Wading and long profiles every monument A wading profile consists of distance and elevation measurements of the dry beach and includes measurements as far offshore as can be reached by wading or swimming, which typically reaches approximately 1.5 m of water depth. A long profile is taken by a surveying vessel and consists of the offshore distance and depth measurements that cannot be reached by wading or swimming (Dean and Dalrymple, 2002). The long profiles have been plotted for the three survey dates for each county in Appendix A, from Monument R-75 in Martin County to Monument R-39 in Palm Beach County. The sediment budget analysis presented as the JID Sediment Budget uses beach profile data obtained from the Jupiter Inlet District (JID). The profile data obtained from JID were taken by Lidberg Land Surveying of Jupiter, Florida. Nine surveys were available for the JID sediment budget analysis. The first five were taken in May 1995, November 1995, May 1996, November 1996 and March These include Palm Beach County Monuments R-13 to R-17, which are south of Jupiter Inlet. The next three were taken in August 2001, June 2002 and October 2002 and include Monuments R-10 through R-21 in Palm Beach County. The last survey was taken in April 2004 and includes Monuments R-13 through R-17 in Palm Beach County, south of the inlet. The beach profiles based on the JID profile data have been plotted in Appendix B.

21 9 2.4 Ebb Shoal Volume Data Availability of Jupiter Inlet s ebb shoal volume measurements was limited. One record (Dombrowski, 1994) found contained eleven volume estimates taken in various years from 1883 to These volume measurements of the ebb shoal are presented in Table 2-2. Table 2-2: Jupiter Inlet ebb shoal volumes (Source: Dombrowski, 1994) Year Volume (m 3 ) , (inlet closed) , , , , , , , , ,530,000 A second source of ebb shoal volume data was found on the Palm Beach County Department of Environmental Resources Management website. This source contained survey data taken of the Jupiter Inlet ebb tidal shoal for the years 2000 and Based on these surveys, volume changes were estimated between the two years. 2.5 Dredging Data Jupiter Inlet has an extensive history of dredging. Even in the early 1900 s the inlet was dredged simply to keep it open. As mentioned, since then, periodic dredging has been implemented with the creation of the sand trap. For the time period covered in the sediment budget analyses, the material dredged from the inlet channel and the trap has been placed on the beach downdrift of Jupiter Inlet as nourishment. Volumes dredged from the channel and the trap between 1974 and 2004 are presented in Table 2-3. The

22 10 data were obtained from Michael Grella of JID (personal communication, March 20, 2006). The dredged sediment volumes between 1974 and 2001 within the limits of the sediment budget for Palm Beach County for the FDEP budget have an annual average value of approximately 34,800 m 3 over that total period. The dredged volumes in 2001 and 2002 within the limits of the sediment budget using the JID beach profiles have an annual average of about 48,500 m 3. Table 2-3: Jupiter Inlet and interior sand trap dredging volumes Year Dredged Volume (m 3 ) , , , , , , , , , , , , , , , , , , , Beach Nourishment Data Downdrift Beach Nourishment Volumes Records of downdrift nourishment events are shown in Table 2-4. The data were obtained from Michael Grella of JID (personal communication, March 20, 2006), from the Beach Erosion Control Project Monitoring Database Information System maintained by the Beaches & Shores Resource Center of the Florida State University, Tallahassee

23 11 and from a report prepared by Taylor Engineering for Palm Beach County (Albada and Craig, 2006). The volumes of sediment dredged from the inlet channel and the sand trap, as shown previously in Table 2-3, are taken to be equal to the volumes of sediment placed on the beach from the dredging, and therefore are included in the total nourishment volumes shown in Table 2-4. The Jupiter Inlet Management Plan, approved by JID in 1992, adopted 46,000 m 3 as the minimum sand volume to be placed on the downdrift beach annually (Grella, 1993). Prior to that plan, a section of the beach about 244 m in length just south of the jetty was used for the placement of nourishment. In order to increase the retention time of the same volume of sand, this length of beach was doubled to approximately 488 m as shown in Figure 2-5 (Mehta et al., 2005). The two key sources of sediment used for beach nourishment downdrift of Jupiter Inlet are the sand trap and the Intracoastal Waterway, as shown in Figure 2-6. The sand stored in the sand trap is dredged nearly every year. Also, excess sand is dredged from the Intracoastal Waterway by the U. S. Army Corps of Engineers as well as the Florida Inland Navigation District (FIND), and a portion of the dredged sediment is placed on the downdrift beach. The recommended plan for the nourishment of the beach is that the dredging of the sand trap be completed before the end of April each year and placed on the beach. If this volume is insufficient at that time, then dredging should be conducted in November instead. It has also been recommended that the Intracoastal Waterway be dredged and the sediment placed on the downdrift beach in April if the sand trap has been dredged in November, or in November if the sand trap has been dredged in April (Grella, 1993).

24 12 Table 2-4: Jupiter Inlet downdrift beach nourishment volumes Year Time of Year of Nourishment (If Available) Total Nourishment Volume Approximate Placement of Nourishment Source(s) of Sediment (m 3 ) ,744 Monument R-13 to R-14 Inlet/Sand Trap, Intracoastal Waterway ,733 Monument R-13 to R-14 Inlet/Sand Trap ,933 Monument R-13 to R-14 Inlet/Sand Trap, Intracoastal Waterway ,342 Monument R-13 to R-14 Inlet/Sand Trap ,873 Monument R-13 to R-14 Inlet/Sand Trap ,106 Monument R-13 to R-14 Inlet/Sand Trap ,078 Monument R-13 to R-14 Inlet/Sand Trap ,115 Monument R-13 to R-14 Inlet/Sand Trap, Intracoastal Waterway ,792 Monument R-13 to R-14 Intracoastal Waterway ,987 Monument R-13 to R-14 Inlet/Sand Trap ,466 Monument R-13 to R-14 Inlet/Sand Trap ,273 Monument R-13 to R-15 Intracoastal Waterway ,030 Monument R-13 to R-15 Inlet/Sand Trap ,681 Monument R-13 to R-15 Inlet/Sand Trap 1995 November 1995 to February ,530 Monument R-13 to R-15 Inlet/Sand Trap, Intracoastal Waterway 1995 Spring 461,635 Monument R-18 to R-19 Ebb Tidal Delta (Carlin Park) ,114 Monument R-13 to R-15 Inlet/Sand Trap ,987 Monument R-13 to R-15 Inlet/Sand Trap 2000 Contract Award February ,171 Monument R-13 to R-15 Inlet/Sand Trap, Intracoastal 2001 Contract Award February Contract Award February December 2001 to March January 2004 to March 2004 Waterway 112,948 Monument R-13 to R-15 Inlet/Sand Trap, Intracoastal Waterway 33,640 Monument R-13 to R-15 Inlet/Sand Trap 477,844 Monument R-18 to R-19 (Carlin Park) Borrow Area Approx. 3.2 km NE of Jupiter Inlet 127,681 Monument R-13 to R-15 Inlet/Sand Trap, Intracoastal Waterway

25 13 Figure 2-5: Jupiter Inlet Management Plan recommended increase in nourishment beach length (Source: Grella, 1993, p. 247) Figure 2-6: Sand trap and Intracoastal Waterway deposition basin from which sediment is dredged to be used as nourishment (Source: Buckingham, 1984, p. 7)

26 Updrift Beach Nourishment Volumes Some nourishment events have also occurred on the beach updrift of Jupiter Inlet for the time period under consideration for the FDEP sediment budget analyses. The volumes that were placed on the updrift beach are presented in Table 2-5. Based on Aubrey and Dekimpe, 1988, all except two of the updrift nourishment events that occurred through 1987 were placed within the bounds of Monument R-75 and Monument R-111 of Martin County. The first 1983 nourishment as well as the 1986 nourishment are known to have been placed just north of Jupiter Inlet in Palm Beach County, but the exact locations are uncertain. From the records obtained from the Beaches & Shores Resource Center, the 1995/1996 nourishment is known to have been placed between Monuments R-77 and R-106 of Martin County. A renourishment project was scheduled for 2001 for Jupiter Island updrift of the inlet, but no indication that the placement had occurred could be found (Tabar et al., 2002). Table 2-5: Jupiter Inlet updrift beach nourishment volumes Year Nourishment Volume Source of Data (m 3 ) ,618 Aubrey and Dekimpe, ,986 Aubrey and Dekimpe, ,872 Aubrey and Dekimpe, ,414 Michael Grella (personal communication, March 20, 2006) ,555 Aubrey and Dekimpe, ,916 Michael Grella (personal communication, March 20, 2006) ,704,957 Aubrey and Dekimpe, /1996 1,330,325 Beaches & Shores Resource Center

27 CHAPTER 3 SHORELINE AND BEACH VOLUME CHANGES 3.1 Shoreline and Beach Volume Change Calculation Methods Two main components that form the basis for the sediment budget for Jupiter Inlet are the updrift and downdrift beach volume change rates. In order to determine these rates, two computer programs that were developed by Dr. Robert Dean (personal communication, June, 2005) for use in an earlier development of a sediment budget for Sebastian Inlet, also located along the east coast of Florida (Dean, 2005), were modified and used. The first program inputs beach profile survey data. These surveys were obtained from the FDEP s Bureau of Beaches and Coastal Systems database and from records provided by the Jupiter Inlet District. The program organizes the input data for plotting profiles at each survey monument and calculates shoreline position changes and the unit volume (i.e., volume of sediment per unit beach width) changes for the determined time period based on these survey data. For each monument that has a long survey profile, the profile area between the water level (NGVD) and the sand surface from a selected (base line) position on land to the depth of closure is estimated by the trapezoidal rule. The change in area from one survey date to the next is then calculated in order to find accretion or erosion that has occurred at the monument in that period. This area change is then represented as the corresponding unit volume change for use in the second program. The second program analyzes the shoreline position and unit volume change calculations that are output from the first program, and determines the average shoreline 15

28 16 and volumetric changes per year. In order to determine the volumetric change per year, the unit volume change from an earlier survey date is subtracted from the unit volume change from a subsequent survey date. The unit volume change is then divided by the number of years in between the survey dates to obtain the unit volume change rate. In order to obtain the volume change rates for the intersurvey periods analyzed, the end-area method is used, which averages the unit volume change rates at each monument, and multiplies this rate by the distance between each monument. The second program also allows for the calculation of the volume change rate at user-specified points that need to be examined closely, for example, at the north and south boundaries of the inlet. From these two programs, the total volumetric rates of gain or loss of sediment are determined for the beaches updrift and downdrift of the inlet. These values are then used in the determination of the sediment budget, as described in Chapter Data Limitations and Uncertainties There are several uncertainties to be aware of when using beach profile survey data to calculate volumetric changes. As mentioned in Chapter 2, beach profile measurements are taken using two surveying processes, the first being the wading survey, and the second being the boat survey. The wading portion of the survey is conducted by a survey crew which uses standard land surveying equipment to determine the elevations of the dry beach, and as far offshore as is possible to reach by wading or swimming, typically up to about 1.5 m of water depth. Usually, a surveying vessel is used to obtain the offshore portion of the survey. This vessel commonly has a fathometer and a coordinate positioning system onboard so that the vessel s position can be correlated with depth measurements (Dean and Dalrymple, 2002). Early surveys, however, did not have the same level of technology that is used now, especially for the offshore portion of the

29 17 survey. Generally, vessels had to stay on the profile line visually by using the range poles, so errors were more prevalent in the offshore depth measurements Data Uncertainties Occasionally, there are discrepancies other than measurement errors in the beach profile survey data. For example, in the survey made in 1976 in Martin County, monument coordinates were missing for Monument R-84. It was documented in the FDEP database that the monument had been relocated after the 1976 survey and before the 1982 survey, so using the coordinates of Monument R-84 from the most recent survey, which is a common way to correct such a data omission, would have been inaccurate. Therefore, aerial photographs taken in 1972 and checked in 1975 for accuracy were inspected, and distances were scaled from Monuments R-83 to R-84 and from R-84 to R-85. Based on these distances, and on the coordinates of Monuments R- 83 and R-85 documented in the 1976 survey, coordinates for Monument R-84 were obtained by interpolation. This seemed the most reliable method because of the proximity in time between the aerials and the survey, and also because it took into account an estimate of the distance between the monuments, rather than assuming that the monuments were evenly spaced. An additional uncertainty occurred in the 1982 survey at Monument R-105 of Martin County. As mentioned, the early surveys only had long profiles recorded for every third monument; therefore R-105 should have had long profile measurements for each survey date. However, in 1982 the measurements were only taken to an offshore distance of about 45.7 m, with a corresponding maximum depth of -1.6 m. Because the depth of closure (which is the offshore limit of a volume calculation) was not reached in the measurements, a unit volume change could not be calculated at this location. Thus,

30 18 for the periods from 1976 to 1982 and from 1982 to 2002 in Martin County, the beach volume change rates had to be estimated based on unit volume changes at Monuments R- 102 and R-108 and averaged over the distance between these two monuments, which is a longer distance than the usual every third monument distance that was normally used for the other early survey calculations Corrections for Non-Closure of Profiles The depth of closure is a depth at which all beach profiles from any given time normally converge (and do not diverge significantly again beyond this depth), as exemplified in Figure 3-1 (Dean and Dalrymple, 2002). For the calculations made in the previously mentioned programs, the seaward distance corresponding to the depth of closure from the shoreline was used as a limit for the volume calculations. It can be seen from the beach profiles shown in Appendices A and B that there is non-closure of many of the profiles. These data suggest that there was probably some error in the 1976 and 1982 surveys from Martin County, and the 1974 survey from Palm Beach County. Shoreline Local depth of closure Figure 3-1: Schematic diagram defining depth of closure, where all offshore profiles converge to a certain depth

31 19 Because of the lack of obvious closure depth in the Martin County profiles, and questionable closure depth in the Palm Beach County profiles, a method other than visual inspection had to be used to determine a mean closure depth for each county. The standard deviation of the depths at every monument was calculated separately at the shoreline and at every 25 m distance offshore for each county. The depth of closure was chosen at the point where the standard deviation was the least. These closure depths were m at a 350 m distance from the shoreline in Martin County, and m at a 250 m distance from the shoreline in Palm Beach County. As described later, sediment volume analysis was extended by examining the effect of changing (increasing and decreasing) the depth of closure. This was done in order to make a quantitative assessment of the error introduced by selecting a particular depth of closure Corrections for Monument Relocation After the 1976 survey for Martin County and the 1974 survey for Palm Beach County, some of the monuments were relocated by FDEP, including Monument R-84 of Martin County as mentioned earlier. The first of the two programs used for the beach volume calculations accounts for monument relocation. It compares the monument coordinates from survey to survey, and if the coordinates differ, it calculates the distance between the monument s old location and its new location. If this distance exceeds m, then an appropriate shift is calculated and added algebraically to every distance measured along the profile of the original monument. 3.3 FDEP Intersurvey Interval: For the FDEP intersurvey interval of 1974 to 1986, shoreline change data were available for every monument. However, unit volume change rates for this interval could only be calculated for every third monument because in the earlier surveys, including the

32 and 1982 surveys for Martin County and the 1974 survey for Palm Beach County, long beach profiles were taken for only the first monument of a county and for every third monument thereafter. Therefore, the unit volume change rates could only be found for the long beach profiles, in which depths and distances were recorded up to the depth of closure Shoreline Changes Figure 3-2 displays the shoreline change rates for each monument for the period between the 1976 and 1982 FDEP surveys in Martin County, and between the 1974 and 1990 FDEP surveys in Palm Beach County. The largest rate of accretion of the shoreline updrift of Jupiter Inlet based on these data is almost 6.25 m per year at Monument R-84 in Martin County, and the largest rate of erosion of the updrift shoreline is nearly 4 m per year at R-105 in Martin County. The shoreline change rates on the updrift side of the inlet show accretion as well as erosion, with no obvious mean trend. Downdrift of Jupiter Inlet, the highest rate of shoreline accretion observed is around 2.4 m per year at Monuments R-25 and R-26 in Palm Beach County, and the highest rate of shoreline erosion is just over 2 m per year at R-29 in Palm Beach County. The shoreline change downdrift of the inlet for this time period tends to show trends of accretion with smaller amounts of erosion interspersed Sediment Volume Changes The unit volume change rates for each monument for the period between the 1976 and 1982 FDEP surveys in Martin County and for the 1974 and 1990 FDEP surveys in Palm Beach County are shown in Figure 3-3. The largest volumetric rate of accretion occurring updrift of Jupiter Inlet is about 22 m 3 /m per year at Monument R-84 in Martin County, and the largest volumetric rate of erosion updrift of the inlet is nearly 30 m 3 /m

33 21 per year at R-93 in Martin County. The unit volume change rates on the updrift side of the inlet show sections of the beach having high accretion as well as high erosion, where neither accretion nor erosion dominates. Downdrift of the inlet, the highest volumetric rate of accretion is almost 12 m 3 /m per year at Monument R-27, and the highest volumetric rate of erosion is just over 9 m 3 /m per year at R-36. The unit volume change rates downdrift of the inlet for this period show a small degree of erosion just past the inlet, with high accretion just past the erosional stretch. Further downdrift, accretion and erosion occur without a noticeable trend. 3.4 FDEP Intersurvey Interval: For the FDEP intersurvey interval of 1986 to 2002, shoreline change data were available for every monument. For Martin County, unit volume change rates for this interval could be calculated for only every third monument. Although the second survey of the interval is from 2002 and contains long beach profile data for every monument, the first survey of the interval is from 1982, which has long beach profiles for only every third monument. Therefore, the unit volume change could only be calculated for those monuments which had long beach profile survey data for both years. For Palm Beach County, the unit volume changes for this interval were calculated for every monument because the surveys were from 1990 and 2001, each of which had long beach profile surveys for every monument Shoreline Changes Figure 3-4 displays the shoreline change rates for each monument for the period between the 1982 and 2002 FDEP beach profile surveys in Martin County, and between the 1990 and 2001 FDEP surveys in Palm Beach County. Updrift of Jupiter Inlet, the highest rate of shoreline accretion is around 3 m per year at Monument R-10 in Palm

34 22 Beach County, with R-106, R-118, and R-120 having similarly high rates of accretion. The rate of shoreline erosion is comparatively small and does not even reach 0.5 m per year at any point. For this period, the shoreline change rate updrift of the inlet tends to be accretive. On the shoreline downdrift of Jupiter Inlet, the highest rate of accretion is around 5 m per year at Monument R-36 and nearly the same at R-31 in Palm Beach County. The highest rate of erosion is around 2.75 m per year at Monuments R-14 and R-23 in Palm Beach County. Erosion and accretion both occur up to about Monument R- 26, and past this point high accretion occurs Sediment Volume Changes The unit volume change rates for each monument for the period between the 1982 and 2002 FDEP beach profile surveys in Martin County and for 1990 and 2001 in Palm Beach County are displayed in Figure 3-5. Updrift of Jupiter Inlet, the highest rate of volumetric accretion is about 20 m 3 /m per year at Monument R-10 in Palm Beach County, with the next highest rate at R-120 in Martin County. These two locations displaying high volumetric accretion rates coincide with two of the locations showing high shoreline accretion rates. The largest rate of volumetric erosion updrift of the shoreline occurs at Monument R-12 of Palm Beach County, with a value of about m 3 /m per year. All other volumetric rates of erosion updrift of the inlet are below 8.5 m 3 /m per year, and few locations display erosion. For this period, similar to the shoreline change rates updrift of the inlet, the unit volume change rates tend to be accretive. Downdrift of the inlet, the highest volumetric rate of accretion is nearly 39 m 3 /m per year at Monument R-30 in Palm Beach County. The highest volumetric rate of erosion is nearly 20 m 3 /m per year at R-13 in Palm Beach County. The unit volume change rate

35 23 downdrift of the inlet shows drastic erosion immediately downdrift, and then it is mainly accretive for the rest of the beach length analyzed. 3.5 FDEP Intersurvey Combined Interval: For the FDEP intersurvey combined interval of 1974 to 2002, the shoreline change rates were calculated at every monument. However, the unit volume change rates could be calculated only for every third monument. For Martin County, the first survey for this interval is from 1976 and contains long beach profile survey data for every third monument, while the second survey is from 2002 and contains long beach profiles for every monument. For Palm Beach County, the first survey is from 1974 and contains long beach profiles for the first monument and every third monument thereafter, and the second survey is from 2001 and contains long beach profiles for every monument. Therefore, for both counties, unit volume change rates could be determined only for every third monument Shoreline Changes Figure 3-6 shows the shoreline change rates for the total time period analyzed, from 1976 to 2002 in Martin County and 1974 to 2001 in Palm Beach County. The shoreline change rates updrift and downdrift of Jupiter Inlet mainly show trends of accretion for this time interval. Immediately updrift and downdrift of the inlet, there is more variation, with erosion at Monuments R-12 and R-13 in Palm Beach County, but overall the shoreline is seen to have accreted. The highest rate of accretion updrift of the inlet is just over 2 m per year in Martin County, and the highest rate of erosion updrift is about 1.25 m per year in Palm Beach County at Monument R-12. On the shoreline downdrift of the inlet, the highest rate of accretion is around 2.5 m per year at Monument R-31, and the highest rate of erosion is almost 1.4 m per year. Downdrift of the inlet, erosion only

36 24 occurs over two small stretches of the shoreline, with the rest of the shoreline showing accretion Sediment Volume Changes The unit volume change rates from 1976 to 2002 in Martin County and from 1974 to 2001 in Palm Beach County are shown in Figure 3-7. Updrift of Jupiter Inlet, there are large stretches of volumetric accretion with one notable stretch of erosion from about Monument R-90 to R-105. The largest unit volume change rate showing erosion updrift of the inlet occurs at Monument R-12 in Palm Beach County and is nearly 14 m 3 /m per year. Downdrift of the inlet, there is a small amount of volumetric erosion adjacent to the inlet, at Monument R-15. Consistent with the trends that were displayed by the shoreline change rates for this period, the unit volume change rates also display mainly trends of accretion. Figure 3-2: Shoreline change rates for the period from 1976 to 1982 in Martin County and from 1974 to 1990 in Palm Beach County

37 25 Figure 3-3: Unit volume change rates for the period from 1976 to 1982 in Martin County and from 1974 to 1990 in Palm Beach County Figure 3-4: Shoreline change rates for the period from 1982 to 2002 in Martin County and from 1990 to 2001 in Palm Beach County

38 26 Figure 3-5: Unit volume change rates for the period from 1982 to 2002 in Martin County and from 1990 to 2001 in Palm Beach County Figure 3-6: Shoreline change rates for the combined period from 1976 to 2002 in Martin County and from 1974 to 2001 in Palm Beach County

39 27 Figure 3-7: Unit volume change rates for the combined period from 1976 to 2002 in Martin County and from 1974 to 2001 in Palm Beach County 3.6 Volume Change Sensitivity to Depth of Closure As mentioned, because the depths of closure were not obvious from the plots of the beach profiles, the standard deviation method was used to find the mean depth of closure for each county. Thus it was necessary to check for any significant sources of error introduced by assuming these values of the depth of closure. Depths of closure of -3 m and -4 m were used for computing sediment volumes to compare with those determined using the standard deviation-derived depths of closure. These two depths were chosen because they bracket the m used for Martin County and the m used for Palm Beach County. The -3 m depth represents an 18 % decrease from the original m for Martin County and only a 3.5 % decrease from the m for Palm Beach County. The -4 m depth introduces only a 9.3 % increase for Martin County and a 28 % increase for Palm Beach County.

40 28 For all time periods considered, specifically 1976 to 1982, 1982 to 2002 and 1976 to 2002 for Martin County and 1974 to 1990, 1990 to 2001 and 1974 to 2001 for Palm Beach County, the unit volume change rate differences between the -3 m depth of closure volumes and the standard deviation-derived depth of closure volumes were considerably larger in Martin County than in Palm Beach County. This can be attributed to the fact that the standard deviation-derived depth of closure of m for Palm Beach County is closer to -3 m than the standard deviation depth of m for Martin County. For the first and last time periods considered, which are 1976 to 1982 and 1976 to 2002 for Martin County and 1974 to 1990 and 1974 to 2001 for Palm Beach County, the unit volume change rate differences between the -4 m depth of closure volumes and the standard deviation depth of closure volumes were larger in Palm Beach County than in Martin County. This is because the standard deviation depth for Martin County is closer to -4 m than for Palm Beach County. Although the unit volume change rates do differ for each county when the depths of closure are varied, these differences are minor. This can be seen in Figures 3-8, 3-9, and Volume Change Sensitivity to Depth of Closure: 1974 to 1986 For the first period, from 1976 to 1982 in Martin County and from 1974 to 1990 in Palm Beach County, the unit volume change rates corresponding to all depths of closure are displayed in Figure 3-8. On average, the unit volume change rate differences found by subtracting the standard deviation depth volumes from the -3 m depth volumes were approximately 1 m 3 /m per year and m 3 /m per year, respectively. This means that within the first period of time considered, the unit volume change rate corresponding to -3 m is greater than the rate for m in Martin County, and the rate for -3 m is less than the rate for m in Palm Beach County. For the same time period, the rate

41 29 differences between -4 m depth volumes and the standard deviation depth volumes were on average about m 3 /m per year and 1.68 m 3 /m per year for Martin County and Palm Beach County, respectively. Therefore, the unit volume change rate corresponding to -4 m is less than the rate for m in Martin County and greater than the rate for m in Palm Beach County. Figure 3-8: Unit volume change rates using varying depths of closure for the period from 1976 to 1982 in Martin County and from 1974 to 1990 in Palm Beach County Volume Change Sensitivity to Depth of Closure: 1986 to 2002 For the second period from 1982 to 2002 in Martin County and from 1990 to 2001 in Palm Beach County, the unit volume change rates for all depths of closure are shown in Figure 3-9. The unit volume change rate differences found by subtracting the standard deviation depth volumes from the -3 m depth volumes were on average about 1.3 m 3 /m per year and 0.2 m 3 /m per year, respectively. This means that the rate corresponding to -3 m is greater than the rate for m in Martin County and is also greater than the rate

42 30 for m in Palm Beach County. The rate differences between -4 m depth volumes and the standard deviation depth volumes were about m 3 /m per year on average for Martin County and m 3 /m per year on average for Palm Beach County. This means that rates corresponding to -4 m are less than the rates corresponding to m in Martin County and m in Palm Beach County. Figure 3-9: Unit volume change rates using varying depths of closure for the period from 1982 to 2002 in Martin County and from 1990 to 2001 in Palm Beach County Volume Change Sensitivity to Depth of Closure: 1974 to 2002 The unit volume change rates for all depths of closure for the combined period from 1976 to 2002 in Martin County and from 1974 to 2001 in Palm Beach County are displayed in Figure The average unit volume change rate differences found by subtracting the standard deviation depth volumes from the -3m depth volumes were around 1.37 m 3 /m per year and m 3 /m per year for Martin County and Palm Beach County, respectively. This means that the rate corresponding to -3 m is greater than the

43 31 rate for m in Martin County, and that the rate for -3 m is less than the rate for m in Palm Beach County. The unit volume change rate differences between -4 m depth volumes and the standard deviation depth volumes were on average about m 3 /m per year for Martin County and 0.60 m 3 /m per year for Palm Beach County. Therefore, the unit volume change rates corresponding to -4 m are less than the rates for m in Martin County and more than the rates for m in Palm Beach County. Figure 3-10: Unit volume change rates using varying depths of closure for the combined period from 1976 to 2002 in Martin County and from 1974 to 2001 in Palm Beach County 3.7 JID Intersurvey Interval: For the JID intersurvey interval of May 1995 to May 1996, both the shoreline and the unit volume change rates were calculated just south of Jupiter Inlet for Monuments R- 13 to R-17.

44 Shoreline Changes The shoreline change rates at each monument are displayed in Figure 3-11 for the period between the 1995 and 1996 JID surveys in Palm Beach County. The highest accretion rate seen on this downdrift shoreline is about 9.4 m per year at Monument R- 13. The shoreline continues to show trends of accretion until about R-15, where it begins to be erosive. This continues to R-17 where the highest rate of erosion of 21.3 m per year is seen Sediment Volume Changes Figure 3-12 displays the unit volume change rates for each monument for the period between the 1995 and 1996 JID surveys in Palm Beach County. The shoreline is seen to accrete from Monument R-13 to R-15. The highest rate of volumetric accretion is just over 81 m 3 /m per year occurring at Monument R-13. Past Monument R-15, the shoreline is erosive, with the highest rate being 178 m 3 /m per year at Monument R JID Intersurvey Interval: For the JID intersurvey interval of May 1996 to March 1997, both the shoreline and the unit volume change rates were calculated for Monuments R-13 to R-17, just south of Jupiter Inlet Shoreline Changes Figure 3-13 displays the shoreline change rates at each monument for the period between the 1996 and 1997 surveys in Palm Beach County. The highest rate of accretion is seen to be just over 42 m per year at Monument R-13, just downdrift of the inlet. The highest rate of erosion is 28.5 m per year at Monument R-15. This stretch of shoreline is accretive directly downdrift of the inlet, starts to erode near Monument R-15, and then begins accreting again after Monument R-16.

45 Sediment Volume Changes The unit volume change rates for each monument for the period between 1996 and 1997 in Palm Beach County are displayed in Figure The largest rate of volumetric accretion occurs at Monument R-13, with a value of m 3 /m per year. The highest rate of volumetric erosion is m 3 /m per year at Monument R-15. This stretch of shoreline displays mostly erosion, with accretion occurring only at Monuments R-13 and R JID Intersurvey Combined Interval: For the JID intersurvey combined interval of May 1995 to April 2004, both the shoreline and the unit volume change rates were calculated just south of Jupiter Inlet for Monuments R-13 to R Shoreline Changes Figure 3-15 displays the shoreline change rates at each monument for the period between the 1995 and 2004 JID surveys in Palm Beach County. The only location where accretion occurs is at Monument R-13 where the rate is about 1.3 m per year. Over the rest of the length of shoreline there is a slightly erosive trend. The highest rate of erosion is 5.3 m per year and occurs at Monument R Sediment Volume Changes The unit volume change rates from 1995 to 2004 in Palm Beach County are shown in Figure Monument R-13 is the only location showing accretion, with a rate of about 19 m 3 /m per year. The rest of the shoreline from Monument R-14 to R-17 shows erosive trends. The largest rate of volumetric erosion is just over 32 m 3 /m per year at Monument R-15.

46 JID Intersurvey Interval: Shoreline and unit volume change rates for the JID intersurvey interval of August 2001 to October 2002 were calculated separately from the 1995, 1996, 1997 and 2004 JID data. This is because the 2001 and 2002 surveys included data for Monuments R-10 through R-21 whereas the other surveys included data only for Monuments R-13 to R-17, south of Jupiter Inlet. For the JID intersurvey interval of August 2001 to October 2002, both the shoreline and the unit volume change rates were calculated at every monument Shoreline Changes Figure 3-17 displays the shoreline change rates at each monument for the period between the 2001 and 2002 JID surveys in Palm Beach County. There are only profiles for three monuments on the updrift side of the inlet, at which the highest rate of accretion is approximately 3.4 m per year at Monument R-10 and the highest rate of erosion is nearly 3.75 m per year at R-12. On the shoreline downdrift of the inlet, the highest rate of accretion is seen to be just over 40 m per year at R-18, whereas the highest rate of erosion, which is also the only erosion seen over the analyzed distance, is only around 7 m per year at R-20. The downdrift shoreline displays a mainly accretive trend between 2001 and Sediment Volume Changes The unit volume change rates for each monument for the period between the 2001 and 2002 JID beach profile surveys in Palm Beach County are displayed in Figure Updrift of Jupiter Inlet, the highest rate of volumetric accretion is almost 11 m 3 /m per year at Monument R-10. The largest rate of volumetric erosion updrift of the inlet occurs at Monument R-12, with a value of just over 25 m 3 /m per year. Downdrift of the inlet, the highest volumetric rate of accretion is nearly 200 m 3 /m per year at Monument R-18.

47 35 Erosion on the downdrift side of the inlet is seen at only one monument, R-20, and is only approximately 3.75 m 3 /m per year. The unit volume change rate downdrift of the inlet shows accretion immediately downdrift, and the trend is mainly largely accretive for the rest of the analyzed beach length as well, with only one monument showing low rates of erosion. Figure 3-11: Shoreline change rates for the period from 1995 to 1996 just south of Jupiter Inlet in Palm Beach County Figure 3-12: Unit volume change rates for the period from 1995 to 1996 just south of Jupiter Inlet in Palm Beach County

48 36 Figure 3-13: Shoreline change rates for the period from 1996 to 1997 just south of Jupiter Inlet in Palm Beach County Figure 3-14: Unit volume change rates for the period from 1996 to 1997 just south of Jupiter Inlet in Palm Beach County

49 37 Figure 3-15: Shoreline change rates for the combined period from 1995 to 2004 just south of Jupiter Inlet in Palm Beach County Figure 3-16: Unit volume change rates for the combined period from 1995 to 2004 just south of Jupiter Inlet in Palm Beach County

50 38 Figure 3-17: Shoreline change rates for the period from 2001 to 2002 in Palm Beach County Figure 3-18: Unit volume change rates for the period from 2001 to 2002 in Palm Beach County

51 4.1.1 Sediment Budget Equation CHAPTER 4 SEDIMENT BUDGET 4.1 Sediment Budget Methodology This section presents the development of the sediment budget methodology applied to Jupiter Inlet. The elements included in the budget account for all possibilities of sediment entering, leaving or being stored within the area of consideration (Rodriguez and Dean, 2005). For Jupiter Inlet, the volumetric storage elements include the updrift and downdrift beach systems and the ebb tidal shoal. To fully illustrate the sediment budget methodology, the rates of volume change on the updrift and downdrift beaches will be described using all possible volume storage components as displayed in Figure 4-1. Later, the components that are unimportant to Jupiter Inlet will be deleted. The rate of volume gain for the updrift beach is described in Equation (4-1) and the rate of volume gain for the downdrift beach is described in Equation (4-2) as follows (Dean, 2005): dv dt UB = Q IN + Q OS, UB QEBB, UB QST, UB Q BB, UB (4-1) dv dt DB = Q OUT + Q Q Q Q + Q + Q OS, DB EBB, DB ST, DB BB, DB NOUR DR (4-2) where: dv dt UB or dv dt DB = volumetric rate at which sediment is accumulated in the updrift or downdrift beaches, respectively, 39

52 40 QIN or Q OUT = volumetric rate at which sediment enters the updrift beach or leaves the downdrift beach through littoral transport, respectively, Q OS, UB or QOS, DB = volumetric rate at which sediment enters the updrift or downdrift beaches through onshore transport, respectively, Q EBB, UB or QEBB, DB = volumetric rate at which sediment is accumulated in the ebb tidal shoal from the updrift or downdrift beaches, respectively, Q ST, UB or QST, DB = volumetric rate at which sediment is accumulated in the interior sand trap from the updrift or downdrift beaches, respectively, Q BB, UB or QBB, DB = volumetric rate at which sediment is accumulated in the back bay region from the updrift or downdrift beaches, respectively, QNOUR = annual average volumetric nourishment rate of the downdrift beach with sediment provided from outside of the system, and = volumetric rate at which sediment is dredged from the interior sand trap. QDR Combining Equations (4-1) and (4-2) yields the total volumetric rate at which sediment is stored on the updrift and downdrift beach systems: dv dt UB dv + dt DB = Q IN Q Q ST, UB OUT Q + Q ST, DB OS, UB Q + Q BB, UB OS, DB Q Q BB, DB EBB, UB + Q Q NOUR EBB, DB + Q DR (4-3) The sediment budget is based on the premise that, if the inlet were non-existent, the processes along the same shoreline distance updrift and downdrift of the inlet would be identical. Therefore, over the same longshore distances, the beaches updrift and downdrift should be eroding or accreting at the same rate (Dean, 2005). Theoretically, with no inlet, the volume changes on equal lengths of updrift and downdrift beaches would be equal; that is, each would be one half of the total volume change: dv dt UB dv = dt DB = 1 2 ( Q Q + Q + Q ) IN OUT OS, UB OS, DB (4-4) However, due to the presence of the inlet and sediment likely being transported into the inlet channel, not all sediment coming from the updrift side of the inlet is transported to the beach downdrift of the inlet. Therefore, the difference between the actual volume

53 41 change rate that has occurred on the downdrift beach and the theoretical volume change rate of the downdrift beach represents the yearly excess or deficit of nourishment that has been placed on the downdrift beach, as follows: dv 1 = (4-5) ( Q Q + Q + Q ) Q DIFFERENCE IN OUT OS, UB OS, DB dt DB 2 In this context, a positive Q DIFFERENCE value would indicate that there is a quantity of sediment on the downdrift beach in excess of the amount that would be there in the absence of the inlet, whereas a negative value would represent a deficit of sediment. Rearranging equation (4-3), it can be seen that: 1 IN 2 1 dv 2 dt ( Q Q + Q + Q ) DB OUT OS, UB dv + dt UB OS, DB dv + dt = EBB dv + dt ST dv + dt BB Q NOUR (4-6) where the following substitutions have been made for the ebb tidal shoal, sand trap, and back bay elements: dv dt dv dt dv dt EBB ST BB = Q = Q = Q EBB, UB ST, UB BB, UB + Q + Q + Q EBB, DB ST, DB BB, DB Q DR (4-7) For Jupiter Inlet, the volume changes of the sand trap are approximated as zero because the sediment that flows into the trap is then dredged and placed within the system as nourishment on the beach. This means that, on average, accumulation of sand in the trap is not counted as a loss to the beach. Consequently, the nourishment placed on the beach from the sand trap is eliminated from the equation as well because only

54 42 nourishment coming from outside of the system needs to be accounted for. Also, the backbay element is approximated to be zero because the sediment that flows into, out of, and is stored in that region is relatively small when compared with the other elements, as shown in the last row of Table 4-1. Q IN Q OS,UB Q NOUR,UB (dv/dt) UB Q BB Q ST Q EBB,UB Q EBB,DB Q DR,OFF Q NOUR,DB (dv/dt) DB Q OS,DB Q OUT Figure 4-1: Definition diagram displaying Jupiter Inlet along with all possible components in the sediment budget equation Records of ebb shoal volumes tend to be limited and their reliability is uncertain. For this reason the sediment budget will be computed twice, once including the ebb shoal volume change rate data, and once assuming the ebb shoal volume change rates to be negligible and therefore excluding them from the equation. With all the necessary volumetric elements being accounted for including the ebb shoal volume change rate, the excess (positive Q DIFFERENCE value) or deficit (negative

55 43 Q DIFFERENCE value) of nourishment on the downdrift beach of Jupiter Inlet is found based on the following equation: Q DIFFERENCE 1 dv dv dv = + QNOUR 2 dt DB dt UB dt EBB (4-8) It consists of only the volumetric rates of change occurring on the north and south beaches and in the ebb tidal shoal, as well as the volumetric rate at which nourishment from outside of the system is placed on the downdrift beach, as shown in Figure 4-2. The sediment budget equation for Jupiter Inlet in which the ebb shoal volume change rate is excluded is similar to equation (4-8) with the only difference being that it excludes the ebb shoal term as follows: Q DIFFERENCE 1 dv dv = + QNOUR 2 dt DB dt UB (4-9) Table 4-1: Annual mean sand volumetric transport rates in the eastern zone (Source: Patra & Mehta, 2004, p. 11) Transport from/to Volumetric rate (m 3 /yr) Net southward littoral drift 176,000 Entering the channel from littoral drift 46,000 Bar-bypassed around the inlet 128,000 Bypassed by dredging from JID a trap and 33,000 ICWW Tidally bypassed by entering and then 4,000 leaving the channel Ejected from the channel to offshore by 4,000 ebb flow b Transported offshore from drift by ebb 2,000 flow b Transported to ICWW channels north and 4,000 south of inlet Transported to central embayment 1,000 a Jupiter Inlet District. b Deposited seaward of the littoral system.

56 44 (dv/dt) UB Q EBB,UB Q EBB,DB Q NOUR,DB (dv/dt) DB Figure 4-2: Sediment budget components specific to Jupiter Inlet Method for Evaluating Sediment Budget In order to determine the rate of excess or deficit of nourishment being placed on the beach downdrift of Jupiter Inlet, several steps were followed. First, the beach profile data were collected from records available on the Florida Department of Environmental Protection s website and from records kept by the Jupiter Inlet District. The FDEP data were analyzed for two different shoreline distances updrift and downdrift of Jupiter Inlet. The first analysis conducted focused on a distance of 17.4 km north of the inlet, beginning at Monument R-75 in Martin County, and extending a distance of 8.53 km south of the inlet, ending at Monument R-40 in Palm Beach County. The second distance of shoreline that was analyzed covered equal distances of shoreline updrift and downdrift of the inlet, beginning at Monument R-112 in Martin County, 7.25 km north of the inlet,

57 45 and ending just past Monument R-36, 7.25 km south of the inlet. For each shoreline distance analyzed, the FDEP data were examined over three periods. The average periods were from 1974 to 1986, 1986 to 2002, and 1974 to These average periods were determined based on the survey dates that were available for each county, specifically 1976, 1982 and 2002 for Martin County and 1974, 1990 and 2001 for Palm Beach County. The JID data were analyzed for a short shoreline distance within Palm Beach County, beginning at Monument R-10 which is almost 0.56 km north of the inlet, and ending at R-15 which is approximately 0.50 km south of the inlet. The JID data were analyzed for one period only, from 2001 to From these beach profile data, values of the cumulative volumetric rates of change of sediment being stored on the updrift and dv downdrift beaches, dt UB dv and dt DB, respectively, for the defined distances and time periods were determined as described in Section 3.1. To calculate the rates of beach nourishment, records of nourishment on the updrift and downdrift beaches were collected. Because the sediment budget methodology is focused on analyzing the volumetric rates of change that occur on the downdrift beach and only accounts for changes that would occur naturally, nourishment on the updrift beach does not appear in the final sediment budget calculation. Therefore, volumetric rates of nourishment that had occurred on the beaches updrift of the inlet were subtracted from the values of volumetric rates of change of sediment stored on the updrift beach. The records of nourishment on the downdrift beaches were added into the sediment budget equation as Q NOUR in cases where the sediment used for nourishment came from outside of the beach system. The nourishment from outside of the beach system consisted mainly of sediment dredged from the Intracoastal Waterway deposition basin.

58 46 The sediment collected in this basin is believed to have come from sources other than directly from the inlet, including the channel and the Loxahatchee River system. Volumes dredged from the JID sand trap and from the ebb tidal delta to be used as nourishment on the downdrift beach were not included when calculating the final rates of nourishment in the sediment budget equation because both the sand trap and the delta were considered to be included in the system. Records of volume measurements of the ebb tidal shoal are scarce. Only one compilation of volume measurements was found (Dombrowski, 1994), and this included measurement estimations only through The early data show wide variability, and it is uncertain if this is due to volume changes actually experienced or due to limitations in the quality of surveys used to obtain the volumes. Three of the measurements relevant to the study time period were used to construct a best-fit trend line, as shown in Figure 4-3. The slope of this line displayed a slightly positive volumetric rate of change which was dv used as dt EBB in the sediment budget equation. Because there were very few reliable measurements, the ebb tidal shoal volumetric rate of change was assumed to be constant as obtained from the best-fit line for all periods analyzed in the sediment budget. The 2000 and 2001 ebb tidal shoal survey data that were taken from the Palm Beach County Department of Environmental Resources Management website were also analyzed to find a volumetric rate of change estimate in order to assess the accuracy of the above estimate. A grid was created in MATLAB, and using measurements from the surveys, interpolations were made to find depths at each point of the grid. From this depth-grid, contour plots were created for each year, as shown in Figures 4-4 and 4-5. As displayed in Figure 4-6, the 2000 depth elevations were then subtracted from the 2001

59 47 depth elevations in order to find the difference in depths between the two years. As the exact area of the ebb delta was uncertain, different areas were used to calculate the volume changes. These areas are shown as boxes in Figure 4-6. Examining the area contained in the large box, a volume of -52,200 m 3 was estimated, implying that the delta had eroded between 2000 and Adding together the volumes estimated from the three smaller boxes, a total volume of +15,208 m 3 was estimated, suggesting that the delta had accreted from 2000 to Based on these calculations, it is obvious that ebb tidal shoal volume estimates vary greatly in accordance with the assumption of the area that is considered to constitute the ebb shoal. This could explain the variability in the measurements that were found in Dombrowski (1994). It was also the reason that the sediment budgets were computed both with and without the ebb shoal component Jupiter Inlet Ebb Delta Volumes Best-fit line with a slope of 4, y = x - 8E Volume (m^3) Year Figure 4-3: Plot showing measurements of Jupiter Inlet s ebb delta volumes, highlighting the three that were chosen to construct a best-fit line

60 48 Figure 4-4: Jupiter Inlet ebb tidal shoal depth contours for the year 2000 Figure 4-5: Jupiter Inlet ebb tidal shoal depth contours for the year 2001

61 49 Figure 4-6: Jupiter Inlet ebb tidal shoal difference in depth contours ( ) used for volume calculations After deriving all of the volumetric quantities for the necessary sediment budget components, these quantities were inserted into the sediment budget equations derived in order to solve for Q DIFFERENCE. The sediment budget components are presented in Tables 4-2, 4-3, and 4-4 with the appropriate quantities inserted where required. As discussed in Chapter 2, the sediment budgets that were created based on the FDEP profile data are presented as the FDEP sediment budgets, and the sediment budget that was created using the JID profile data is presented as the JID sediment budget Effect of Length of Beach on Sediment Budget Calculations The result of a sediment budget equation may vary depending on the equal lengths of updrift and downdrift shoreline that are chosen for the analysis. By selecting short distances of shoreline updrift and downdrift of the inlet, the immediate effects on the