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Erosion, navigation and sedimentation imperatives at Jupiter Inlet, Florida: recommendations for coastal engineering management

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Title:
Erosion, navigation and sedimentation imperatives at Jupiter Inlet, Florida: recommendations for coastal engineering management
Series Title:
UFL/COEL (University of Florida. Coastal and Oceanographic Engineering Laboratory) ; 92/0
Creator:
Mehta, Ashish J.
Montague, Clay L.
Thieke, Robert J.
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College of Engineering -- Department of Civil and Coastal Engineering
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Gainesville
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Coastal and Oceanographic Engineering Department
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Subjects / Keywords:
Jupiter Inlet (Fla)
Inlets -- Florida
Spatial Coverage:
Jupiter Inlet

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Sponsor: Jupiter Inlet District 400 North Delaware Boulevard Jupiter, FL 33458
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This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.

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University of Florida
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University of Florida
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UFL/COEL-92/002

EROSION, NAVIGATION AND SEDIMENTATION IMPERATIVES AT JUPITER INLET, FLORIDA: RECOMMENDATIONS FOR COASTAL ENGINEERING MANAGEMENT
Tidal Inlet Management at Jupiter Inlet: Final Report
by
Ashish J. Mehta Clay L. Montague and
Robert J. Thieke
Additional Contributors: Michael DelCharco, Richard Faas, Scott Fears, Philip Harris, Earl Hayter, Ray Krone, Li-Hwa Lin and Trimbak Parchure
July, 1992
Sponsor:
Jupiter Inlet District 400 North Delaware Boulevard Jupiter, FL 33458




UFL/COEL-92/002

EROSION, NAVIGATION AND SEDIMENTATION IMPERATIVES AT JUPITER INLET, FLORIDA: RECOMMENDATIONS FOR COASTAL ENGINEERING MANAGEMENT Tidal Inlet Management at Jupiter Inlet: Final Report by
Ashish J. Mehta, Clay L. Montague and Robert J. Thieke
Sponsor:

Jupiter Inlet District Commission 400 North Delaware Boulevard
Jupiter, FL 33458

July, 1992




REPORT DOCUMENTATION PAGE
. Repot No. 3. Rti; plaWt Accu LO 30.
4. TItle and Subtitle 3. laport Date
EROSION, NAVIGATION AND SEDIMENTATION IMPERATIVES AT July, 1992
JUPITER INLET, FLORIDA: RECOMMENDATIONS FOR COASTAL
ENGINEERING MANAGEMENT
7. author(.) 8. Performing O gZ izton port ia.
Ashish J. Mehta, Clay L. Montague and Robert J. Thieke UFL/COEL-92/002
9. ?erforming Oranuzatmoa Name and Aderess 10. ProJectJ skiVork Unit Jo.
Coastal and Oceanographic Engineering Department University of Florida 11. conaOC or Crat Na.
336 Weil Hall C89-002
Gainesville, FL 32611 U. Typeo -t0port
12. Sponsorin 0rlOgsfzastiao Mame and Address
Jupiter Inlet District Commission Final Report
400 North Delaware Boulevard
Jupiter, Florida 33458 14.
14.
15. Supple e tary aotas
16. Abstract
In this final report on the investigation of the potentialities of improved coastal engineering management of Jupiter Inlet, Florida, three management-guiding issues were considered: better control of the erosion of the south beach, better navigation access and safety, and better control (reduction) of sediment influx into the inlet channel and upstream points in the Loxahatchee River estuary. The first two issues have been particularly outstanding, due to persistent concern for the inherent deficiencies in the protocol for sand pumping and placement on the beach that tends to erode away rapidly, and the concern for conditions for navigation of vessels in the proximity of the inlet in open waters. With regard to the third issue, despite the reasonably successful ongoing program to pump sand out of the borrow areas within the inlet channel, other areas such as some of the marinas in the inlet area, as well as the region of the Loxahatchee River west of the Florida East Coast Railroad bridge, have been experiencing slow but persistent sedimentation.
Contingent upon a series of coastal and environmental engineering investigations, a range of engineering actions that could mitigate erosion, navigation and sedimentation problems were considered. Based on the physical and ecological impacts that would be caused by these actions, two sets of action options that have net beneficial impacts due to action implementation have been proposed. The first is a set of interdependent action options that must be instituted ifiherently in a time-wise phased manner. The second is a set of independent action options which can be instituted as and when 17. Origiator's Key Words 18. Availability Stameent
Beach erosion
Inlet management
Jupiter Inlet
Loxahatchee River
Tidal entrances
19. U. S. Security Classif. of the report 20. u. s. Security Classit. of This ?age 21. No. of 15g5s :2. Price
Unclassified Unclassified 228




desired. For determining the overall feasibility of any action option, it will be necessary to weigh the technical benefits against costs, which are provided. It should be emphasized however that, considering the overwhelmingly observational nature of coastal science, the estimates of potential benefits are essentially and inherently subjective, and the costs very approximate, especially in cases where the desired technology is in the "bench" stage.




SYNOPSIS

In this final report on the investigation of the potentialities of improved coastal engineering management of Jupiter Inlet, Florida, three management-guiding issues were considered: better control of the erosion of the south beach, better navigation access and safety, and better control (reduction) of sediment influx into the inlet channel and upstream points in the Loxahatchee River estuary. The first two issues have been particularly outstanding, due to persistent concern for the inherent deficiencies in the protocol for sand pumping and placement on the beach that tends to erode away rapidly, and the concern for conditions for navigation of vessels in the proximity of the inlet in open waters. With regard to the third issue, despite the reasonably successful ongoing program to pump sand out of the borrow areas within the inlet channel, other areas such as some of the marinas in the inlet area, as well as the region of the Loxahatchee River west of the Florida East Coast Railroad bridge, have been experiencing slow but persistent sedimentation.
Contingent upon a series of coastal and environmental engineering investigations, a range of engineering actions that could mitigate erosion, navigation and sedimentation problems were considered. Based on the physical and ecological impacts that would be caused' by these actions, two sets of action options that have net beneficial impacts due to action implementation have been proposed. The first is a set of interdependent action options that must be instituted inherently in a time-wise phased manner. The second is a set of independent action options which can be instituted as and when desired. For determining the overall feasibility of any action option, it will be necessary to weigh the technical benefits against costs, which are provided. It should be emphasized however that, considering the overwhelmingly observational nature of coastal science, the estimates of potential benefits are essentially and inherently subjective, and the costs very approximate, especially in cases where the desired technology is in the "bench" stage.




TABLE OF CONTENTS
SYNOPSIS ............................................................. ii

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

........ ix

M AP CAPTIONS ....................................................... xi
LIST OF TABLES ...................................................... xiii
1. INTRODUCTION ..................................................... 1
1.1 Pream ble ....................................................... 1
1.2 Location and Description ............................................. 1
1.3 Historical Information ............................................... 4
1.4 Chronology of Important Early Events ..................................... 5
1.5 Recreation and Fishing .............................................. 9
1.6 Navigation ...................................................... 11
1.7 Concluding Comment .............................................. 14
2. MANAGEMENT ELEMENTS AND TIRE STATE OF THE INLET .................... 17
2.1 Management Imperatives ............................................ 17
2.2 Investigations ..................................................... 22
2.3 State of the Inlet ................................................... 25
2.4 Concluding Comments ............................................... 29

3. SUMMARY OF ENGINEERING ACTIONS AND THEIR PHYSICAL AND
IM PACTS ...........................................
3.1 Pream ble ........................................
3.2 Actions and Impacts .................................
L No New Action ...................................
1. Present Protocol ................................
1. 1. Impact on Navigation Access ....................
1.2. Impact on Navigation Safety ....................
1.3. Impact on Beach Erosion ......................
1.4. Impact on Interior Sedimentation ..................
1.5. Ecological Considerations ......................
H. Trap Dredging ...................................
2. Volumetric Rate of Dredging ........................
2. 1. Impact on Navigation Access ....................
2.2. Impact on Navigation Safety ....................
2.3. Impact on Beach Erosion ......................
2.4. Impact on Interior Sedimentation ..................
2.5. Ecological Considerations ......................
3. Frequency of Dredging ...........................
3. 1. Impact on Navigation Access ....................
3.2. Impact on Navigation Safety ....................
3.3. Impact on Beach Erosion ......................
3.4. Impact on Interior Sedimentation ..................
3.5. Ecological Considerations ......................
4. Trap Dimensions ...............................
4. 1. Impact on Navigation Access ....................
4.2 Impact on Navigation Safety .....................

ECOLOGICAL ............
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4.3. Impact on Beach Erosion ..................................... 35
4.4. Impact on Interior Sedimentation ................................. 35
4.5. Ecological Considerations ..................................... 36
III. South Beach Nourishment ........................................... 36
5. Volumetric Rate of Nourishment ..................................... 36
5. 1. Impact on Navigation Access ................................... 36
5.2. Impact on Navigation Safety ................................... 36
5.3. Impact on Beach Erosion ..................................... 36
5.4. Impact on Interior Sedimentation ................................. 37
5.5. Ecological Considerations ..................................... 37
6. Frequency of Nourishment ........................................ 37
6. 1. Impact on Navigational Access .................................. 37
6.2. Impact on Navigational Safety .................................. 37
6.3. Impact on Beach Erosion ..................................... 37
6.4. Impact on Interior Sedimentation ................................. 38
6.5. Ecological Considerations ..................................... 38
7. Placement Timing .............................................. 38
7. 1. Impact on Navigation Access ................................... 38
7.2. Impact on Navigation Safety ................................... 39
7.3. Impact on Beach Erosion ..................................... 39
7.4. Impact on Interior Sedimentation ................................. 39
7.5. Ecological Considerations ..................................... 39
8. Placement Location ............................................. 40
8. 1. Impact on Navigation Access ................................... 40
8.2. Impact on Navigation Safety ................................... 40
8.3. Impact on Beach Erosion ..................................... 40
8.4. Impact on Interior Sedimentation ................................. 41
8.5. Ecological Considerations ..................................... 41
I-V North Jetty .................................................... 42
9. Height of North Jetty ............................................ 42
9. 1. Impact on Navigation Access ................................... 42
9.2. Impact on Navigation Safety ................................... 42
9.3. Impact on Beach Erosion ..................................... 42
9.4. Impact on Interior Sedimentation ................................. 42
9.5. Ecological Considerations ..................................... 42
10. Length of North Jetty ........................................... 43
10. 1. Impact on Navigation Access .................................. 43
10.2. Impact on Navigation Safety ................................... 43
10.3. Impact on Beach Erosion ..................................... 43
10.4. Impact on Interior Sedimentation ................................ 44
10.5. Ecological Considerations .................................... 44
V South Jetty .................................................... 45
11. Height of South Jetty ........................................... 45
11. 1. Impact on Navigation Access .................................. 45
11.2. Impact on Navigation Safety ................................... 45
11.3. Impact on Beach Erosion ..................................... 45
11.4. Impact on Interior Sedimentation ................................ 45
11.5. Ecological Considerations .................................... 46
12. Length of South Jetty ........................................... 46
12. 1. Impact on Navigation Access .................................. 46
12.2. Impact on Navigation Safety ................................... 46
12.3. Impact on Beach Erosion ..................................... 46
12.4. Impact on Interior Sedimentation ................................ 47




12.5. Ecological Considerations .................................... 47
W. NaWgational Considerations ......................................... 47
13. Lighthouse and Jetty Beacons ...................................... 47
13. 1. Impact on Navigation Access .................................. 47
13.2. Impact on Navigation Safety ................................... 47
13.3. Impact on Beach Erosion ..................................... 47
13.4. Impact on Interior Sedimentation ................................ 48
13.5. Ecological Considerations .................................... 48
14. Channel M arkers ............................................. 48
14. 1. Impact on Navigation Access .................................. 48
14.2. Impact on Navigation Safety ................................... 48
14.3. Impact on Beach Erosion ..................................... 48
14.4. Impact on Interior Sedimentation ................................ 49
14.5. Ecological Considerations .................................... 49
15. Boat Speed ................................................. 49
15. 1. Impact on Navigation Access .................................. 49
15.2. Impact on Navigation Safety ................................... 49
15.3. Impact on Beach Erosion ..................................... 49
15.4. Impact on Interior Sedimentation ................................ 49
15.5. Ecological Considerations .................................... 49
VIL Outer Channel ................................................. 50
16. Eastward Channel ............................................. 50
16. 1. Impact on Navigation Access .................................. 50
16.2. Impact on Navigation Safety ................................... 50
16.3. Impact on Beach Erosion ..................................... 50
16.4. Impact on Interior Sedimentation ................................ 50
16.5. Ecological Considerations .................................... 52
17. Southeastward Channel .......................................... 52
17. 1. Impact on Navigation Access .................................. 52
17.2. Impact on Navigation Safety ................................... 52
17.3. Impact on Beach Erosion ..................................... 52
17.4. Impact on Interior Sedimentation ................................ 53
17.5. Ecological Considerations .................................... 53
VIII. Offshore Dredging .............................................. 53
18. Volumetric Rate of Dredging ...................................... 53
18. 1. Impact on Navigation Access .................................. 53
18.2. Impact on Navigation Safety ................................... 53
18.3. Impact on Beach Erosion ..................................... 54
18.4. Impact on Interior Sedimentation ................................ 54
18.5. Ecological Considerations .................................... 54
19. Frequency of Dredging .......................................... 54
19. 1. Impact on Navigation Access .................................. 54
19.2. Impact on Navigation Safety ................................... 54
19.3. Impact on Beach Erosion ..................................... 54
19.4. Impact on Interior Sedimentation ................................ 55
19.5. Ecological Considerations .................................... 55
20. Location of Dredging ........................................... 55
20. 1. Impact on Navigation Access .................................. 55
20.2. Impact on Navigation Safety ................................... 55
20.3. Impact on Beach Erosion ..................................... 55
20.4. Impact on Interior Sedimentation ................................ 55
20.5. Ecological Considerations .................................... 56
21. Placement of Dredged Material ..................................... 56




21. 1. Impact on Navigation Access ....
21.2. Impact on Navigation Safety .....
21.3. Impact on Beach Erosion .......
21.4. Impact on Interior Sedimentation .
21.5. Ecological Considerations ...... IX Interior Trap Dredging ..............
22. Location of Interior Trap ..........
22. 1. Impact on Navigation Access ....
22.2. Impact on Navigation Safety .....
22.3. Impact on Beach Erosion .......
22.4. Impact on Interior Sedimentation .
22.5. Ecological Considerations ......
23. Dimensions of Interior Trap .........
23. 1. Impact on Navigation Access ....
23.2. Impact on Navigation Safety .....
23.3. Impact on Beach Erosion .......
23.4. Impact on Interior Sedimentation .
23.5. Ecological Considerations ......
24. Volumetric Rate of Interior Trap Dredging
24. 1. Impact on Navigation Access ....
24.2. Impact on Navigation Safety .....
24.3. Impact on Beach Erosion .......
24.4. Impact on Interior Sedimentation .
24.5. Ecological Considerations ......
25. Frequency of Interior Trap Dredging ...
25. 1. Impact on Navigation Access ....
25.2. Impact on Navigation Safety .....
25.3. Impact on Beach Erosion .......
25.4. Impact on Interior Sedimentation .
25.5. Ecological Considerations ......
26. Material Placement ..............
26. 1. Impact on Navigation Access ....
26.2. Impact on Navigation Safety .....
26.3. Impact on Beach Erosion .......
26.4. Impact on Interior Sedimentation .
26.5. Ecological Considerations ......

4. RECOMMENDED ACTIONS, IMPACTS AND COSTS.
4.1 Introduction ..........................
4.2 Recommended Phased, Interdependent Actions ...
4.3 Recommended Independent Actions ...........
4.4 Impacts of Interdependent and Independent Actions 4.5 Comments on Management Options ...........
4.6 M onitoring ...........................
Nearshore rocky outcroppings ...............
Sea turtle nesting .......................
Intertidal vegetation (marshes and mangroves) .....
Seagrasses (submerged vegetation) .............
Salinity intrusion ........................

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APPENDIX A: COASTAL AND ENVIRONMENTAL ENGINEERING MANAGEMENT ELEMENTS
FOR SANDY TIDAL INLETS ...........................................
Al. Introduction .....................................................




A2. Shoaling due to Littoral Sand.......................................
A3. Elements in Inlet Management......................................
A4. Creation of Artificial Pathways......................................
AS. Effective Bypassing..............................................
A6. Environmental Considerations.......................................
A6. 1. The Inlet as a Passageway........................................
A6. 2. Rocky Outcroppings............................................
A6. 3. Beach Habitats: Sea Turtle Nesting..................................
A6. 4. Inside the Inlet: Critical Estuarine Habitats............................
A6.5. Intertidal Habitats.............................................
A6. 6. Submersed Vegetation...........................................
A7. Sea Level Rise Effects............................................
A8. Concluding Comments............................................
APPENDIX B: ENVIRONMENTAL SEDIENTOLOGY OF THE LOWER LOXAHATCHEE

RIVER ESTUARY AND JUPITER IMET B1. Summary....................
B2. Introduction..................
B3. The Problem..................
B4. Background..................
B5. Field and Laboratory Work....... B6. Data Analysis and Interpretation ...
B6. 1 Median Diameter Map 2......
B6.2 Coefficient of Sorting Map 3
B6.3 Coefficient of Skewness Map 4
B6. 4 Sediment Distribution Map S
B6.5 Analysis of Vibracores.........
B6. 6 Summary of Vibracoring.......
B7. Sedimentary Types and Sources .... B8. Patterns of Sediment Transport .... B9. Conclusions..................

B10. Recommendations for Future Work.....................................
APPENDIX C: LITTORAL DRIFT AND SEDIMENT BUDGET........................
C1. Littoral Drift.....................................................

Cl.)I Previous Estimates..................
Cl. 2 Dredging Data Analysis...............
Cl. 3 University of Florida Study.............
C1.3.1 General....................
CI.3.2 Estimated Annual Drift..........
C1.3.3 Estimated Monthly Drift .........
C1.3.4 Estimated Daily Drift...........
C1. 4 Characteristics of Littoral Drift in the Vicinity
C2. Sediment Budget.....................
C2.1 General..........................
C2. 2 Primary Distribution.................
C2. 3 Secondary Distribution and Return Flows ...
C2. 4 Total Distribution...................
C2.S Sources of Southward Sand Transfer ......

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of Jupiter Inlet . ............
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......................................151

APPENDIX D: PHYSICAL MODEL TEST RESULTS RELATED TO POSSIBLE
JETTY CONFIGURATIONS AND DREDGING...............................
D1. Introduction......................................................

96 98 98 103
104 104 105 105 106 106 106 107 108

.... ... .... ... ... .... ... ... 109




D2. Tass......................... ......
D3. Test Criteria......................................................
D4. Test Conditions....................................................
D4. 1 Jetty Modifications................................................
D4. 2 Elevated Jetty Modifications..........................................
D4. 3 Offshore Dredging................................................
D5. Test Results......................................................
D5.1 Jetty Modifications................................................
DS. 2 Example Calculation................................................
DS.3 Offshore Dredging.................................................
D6. Evaluation of Test Results..............................................
D6. 1 Jetty Length Modi~fi cations............................................
D6. 2 Elevated Jetties...................................................
D6. 3 Offshore Dredged Bottom.............................................
APPENDIX E: TIDES, CURRENTS AND SEDIMENTATION EFFECTS OF POTENTIAL
MODIFICATIONS ON FLOW AND SAND TRANSPORT IN THE LOXAHATCHEE RIVER.

El. Introduction .........
E2. Salinity Distribution .... E3. Model Application ..... E4. Model Results ........
E4. 1 Modification 1......
E4. 2 Modification 2 .
E4. 3 Modification 3 .
E4. 4 Modification 4 ..E4.5 Modifi cation S .
E4. 6 Modifi cation 6 .
E4. 7 Modification 7 .
E4. 8 Modijfication 8 . E5. Conclusions..........

............................................. 185

APPENDIX F: ENVIRONMENTAL ASSESSMENT .......
Fl. Preamnble...............................
F7. Sea Turtle Nesting.........................
F3. Offshore Rocky Outcroppings.................
F4. Mangroves..............................
FS. Seagrasses..............................
F6. Seagrass Mitigation........................

APPENDIX G: DESIGN CRITERIA FOR SEA TURTLE NESTING BEACHES............... 210
BIBLIOGRAPHY......................................................... 211

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LIST OF FIGURES
FIGURE PAGE
1. 1. Area map of Jupiter Inlet ................................................ 2
1.2. Backwaters of Jupiter Inlet .............................................. 3
1.3. 1913 survey showing the earlier location of Jupiter Inlet (U.S. Coast and Geodetic Survey,
1913) ....... ..... ........... .. ....... .. .. .. ......... ........... 3
1.4. Details of the original construction works at Jupiter Inlet in the year 1922 ................. 6
1.5. Cross -section of the jetties and approach channel constructed at Jupiter Inlet in 1922 .......... 7
1.6. Modifications made to the south jetty at Jupiter Inlet in 1967 . . . . . . . . . . . . 8
1.7. Layout of the navigation channel at Jupiter Inlet . . . . . . . . . . . . . . . . 13
2.1 Three water regions of Jupiter Inlet/Loxahatchee River relevant to the study ............... 18
2.2. Sand fillet and deficit at beaches contiguous to Jupiter Inlet ......................... 19
2.3. JID sand trap ..................................................... 20
2.4. Army Corps of Engineers sand borrow area in the Intracoastal Waterway, and the
lighthouse ....................................................... 21
2.5. Marinas of interest to the study .......................................... 23
2.6. Technical issues, physical impact studies and ecological impact studies for the
inlet management plan ................................................ 24
3.1. Inlet ebb shoal and offshore channel options .................................. 51
4.1. Action categories considered in relation to improvement in beach erosion management ........ 65 4.2. Action categories considered in relation to improvement in navigation management .......... 66
4.3. Action categories considered in relation to improvement in sedimentation management ........ 67 4.4. Present sand placement plan ............................................ 68
4.5. A revised sand placement plan ........................................... 69
4.6. A revised sand trap plan .............................................. 71
4.7. Raising the elevations of the two jetties ..................................... 73
4.8. Extended the south jetty ............................................... 74
4.9. Extended north jetty with a sand bypassing plant ................................ 75
4.10. Extended north jetty with an offshore sand fluidization system ....................... 76
4.11. A sand fluidization arrangement for the interior channel . . . . . . . . . . . . . 77
4.12. Beacons or danger signals at jetties ........................................ 79
4.13. Offshore navigation channel ............................................ 80
4.14. Interior sand trap ................................................... 81
A. 1. Barrier shoreline with sandy tidal inlets and littoral sand transport ..................... 97




A.2. Interception and modification of the littoral sand pathway by an inlet .. .. .. .. .. .. .. ... ...99
A.3. Natural and artificial sediment pathways in the inlet nearfield and channel................. 100
A.4. Control water area identifying the passive ebb shoal. .. .. .. .. .. .. ... .. ... .. ... ...102
B. 1. Textural classification of Loxahatchee Estuary and Jupiter Inlet bottom samples (Shepard, 1954).
Inset shows the descriptive terms. Sixteen samples (Appendix III -Table 1, in Mehta et al.,
1990b) did not plot within the 'sand' category and are shown on the diagram. These are
designated as 'mixed' samples in the text....................................... 112
C. 1. Proposed developments at Jupiter Inlet. The south channel shown has also been referred to as
the southeast channel elsewhere............................................. 127
C.2. Estimated percentages of quantities of southward and northward alongshore sediment transport ..129 C.3. Log -normal probability plot of annual longshore transport magnitudes (southward and
northward) from WIS hindcasts for the period 1956 -1975............................ 133
CA4. Estimated percentages of duration of occurrence of southward and northward alongshore
sediment transport...................................................... 134
C.5. Monthly net quantities of littoral drift estimated for the year 1967...................... 135
C.6. Percentage of net littoral drift each month, estimated from 20 years WIS wave data........... 138
C.7. Cumulative net southward longshore transport at Jupiter Wnet calculated from WIS hindcast
data for the year 1967 (increasing volume implies net southward transport)................ 140
C.8. Primary littoral drift distribution at Jupiter Inlet.................................. 141
C.9. Secondary littoral drift distribution at Jupiter Inlet................................. 144
C. 10. Return flows of littoral drift distribution at Jupiter Inlet. .. .. .. .. .. .. ... .. .. ... .. ..146
C. 11. Quantities of total distribution of littoral drift at Jupiter Inlet.......................... 148
C. 12. Percentage of total distribution of littoral drift at Jupiter Inlet.......................... 149
C. 13. Offshore borrow areas for beach nourishment projects at Jupiter (Aubrey and DeKimpe, 1988) .150 D. 1. Results from numerical simulation of shoreline evolution with a jetty length of 220 ft.......... 155
D.2. Jetty length vs. erosion distance with corresponding scale values (0, 1 ,-2,- 3)............. 156
D.3. Inlet flow patterns for normal condition and modification M: flood and ebb tides............. 157
DA4. Shoreline in the vicinity of Jupiter Inlet, March 11, 1945............................ 158
D.5. Shoreline in the vicinity of Jupiter Inlet, March 8, 1971............................. 159
D.6. Jetty modification A..................................................... 161
D.7. Jetty modification B..................................................... 161
D.8. Jetty modification C..................................................... 162
D.9. Jetty modification D..................................................... 162
D. 10. Jetty modification E..................................................... 163
D. 11. Jetty modification F..................................................... 163
D. 12. Jetty modification G..................................................... 164
D. 13. Jetty modification H..................................................... 164
D. 14. Jetty modification I...................................................... 165




D. 15. D. 16. D. 17. D. 18. D. 19. D.20.
D.21.
D.22.
D.23.
D.24.
E. 1.
E.2.

Jetty modification J.................................
Jetty modification K.................................
Jetty modification L.................................
Jetty modification M................................
Jetty modification N.................................
Jetty modification 0.................................
North jetty and south jetty elevation views and height modifications Physical model data collection points and dredged ebb shoal area. Baker's Haulover Inlet in 1966.........................
Baker's Haulover Inlet in 1981.........................
Proposed sand trap east of Florida East Coast Railroad bridge .... Original finite element grid for the Loxahatchee River estuary ....

E.3. Finite element grid for Modification 1 extension of the jetties. Only the ocean part of
the grid is shown....................................................... 190
EA4. Finite element grid for Modification 2. Only the ocean part of the grid is shown............. 191
E.5. Predicted tides at Jupiter Inlet for March 1-30, 1991, used for ocean boundary conditions........193
F. 1. Good sea turtle nesting beach near the Hilton Inn at Jupiter, Florida, looking north toward
Jupiter Inlet.......................................................... 200
F.2. Beach-slope profile south of Jupiter Inlet near the Hilton hotel at Jupiter, Florida
on three occasions in 1990 1991............................................ 201
F.3. Steep scarp discouraging to nesting seaturtles just south of the south jetty at Jupiter
Inlet, Florida, looking south toward the Hilton hotel............ ................... 202
FA4. Beach-slope profile just south of the south jetty at Jupiter Inlet, Florida on three
occasions in 1990 1991.................................................. 203
F.5. Location of rocky outcroppings in the vicinity of Jupiter Inlet, Florida (adapted from
Continental Shelf Associates, 1985; 1987; 1989b; 1989c)............................ 204
F.6. Drawing of Jupiter Inlet, Florida from Captain Miller, showing location of bottom rocks
just inside the inlet...................................................... 206
F.7. Location, canopy height, and number of miangroves in mangrove forests in the Loxahatchee
River estuary east of the railroad bridge........................................ 207
F.8. Location, density, and total weight of seagrasses in seagrass beds in the Loxahatchee
River estuary east of the railroad bridge........................................ 209
MAP CAPTIONS......................................................... 120
Map 1 Grab sample locations are shown by a closed circle, vibracore locations are shown by closed
triangles. Area west of the railroad bridge is designated Area 'A. Area east of the railroad bridge, including the mouth of Jupiter Inlet, is designated Area WB. Marine samples come
from Area 'C......................................................... 121

... . .. . 165
... . .. . 166
... . .. . 166
... . .. . 167
... . .. . 167
... . .. . 168
... . .. . 171
... . .. . 172
... . .. . 181
... . .. . 182
... . .. . 186
... . .. . 187




Map 2 Distribution of sediment median diameters, contoured in phi units. Since phi units bear an
inverse relationship to metric units, areas outlined by large phi values show fine-grained
material and low phi values show coarse -grained material. Fine-grained material is found
in patches in the Northwest and Southwest Forks of the Loxahatchee Estuary and on the
flood tidal delta in the central portion of the estuary. Median diameters increase
generally from the center of the estuary through the mouth of Jupiter Inlet............... 122
Map 3 Distribution of Trask sorting coefficients. Several areas of poorly -sorted sediment occur in
the Northwest and Southwest Forks and 1.0 unit contour intervals were used to delineate these areas. The remainder of the estuary and tidal inlet was contoured in 0.2 unit contour intervals
to emphasize small differences of sorting within generally well -sorted material............ 123
Map 4 Distribution of sediment skewness, e.g., degree of abnormality of sediment distribution.
Values less than 0.9 indicate an excess of material smaller than the modal diameter
(finely skewed) Values greater than 1. 1 indicate an excess of material larger than the
modal diameter (coarsely -skewed). Normal skew is shown by values between 0.9 1. 1. The
Northwest and Southwest Forks are finely -skewed and the central portion is normally -skewed.
A small patch of finely -skewectediment occurs off the entrance to the southern portion of
the Intracoastal Waterway, and a coarsely -skewed region exists offshore to the south of the
inlet mouth. A band of coarsely -skewed sediment extends through the North Fork eastward to
the north branch of the Intracoastal Waterway.................................. 124
Map 5 Textural distribution of bottom sediment types, classified according to Shepard (1954
Fig. B. 1)......................................................... 125




LIST OF TABLES

TABLE PAGE
1.1 Population of Palm Beach and Martin Counties (U.S. Army Corps of Engineers, 1966).......... 4
1.2 Recreational boat use in the Jupiter area (U.S. Army Corps of Engineers, 1966).............. 10
1.3 Jupiter Inlet recreational boating benefits (U.S. Army Corps of Engineers, 1966).............. 12
1.4 Reported loss and damage to small craft at Jupiter Inlet (U.S. Army Corps of Engineers,
1966)................................................................ 15
3.1 Considered actions and impacts.............................................. 31
4.1 Individual actions investigated and costs......................................... 64
4.2 Recommended actions..................................................... 70
4.3 Recommended actions, impacts and costs........................................ 82
4.4 Implementation dates of actions.............................................. 91
Cl Some estimates of annual littoral drift near Jupiter Inlet............................. 126
C2 JID and Army Corps dredging records for Jupiter Inlet (Dixon and Assoc. Engr.,
Inc., 199 1)........................................................... 130
C3 History of Jupiter Inlet and Intracoastal Waterway dredging and placement of disposal
material on the shoreline south of Jupiter Inlet (Continental Shelf Associates, Inc., 1989a)........131 C4 Estimated longshore transport values (Q cubic yards per year) for 20 year. period
1956-1975 (calculated from WIS wave hindcast data)............................... 132
CS Estimated percentage of duration of occurrence of southward and northward drift for
20 year period 1956-1975 (calculated from WIS wave hindcast data).................... 136
C6 Estimated net monthly littoral drift for the year 1967............................... 137
C7 Estimated monthly magnitudes of littoral drift, based on 20 years (1956-1975)
WIS wave data........................................................ 137
C8 Estimated monthly magnitudes of net southward and northward littoral drift based on
20 years (1956-1975) WIS wave data.......................................... 142
D1 Thirty year erosion volume calculations (M indicates million)......................... 160
D2 Jetty modifications...................................................... 169
D3 Raw data from the physical model, Test #41: NE waves, MSL, ebb flow, "normal"
conditions............................................................ 170




D4 Scales for navigational safety and erosion potential ratio calculations . . . . . . . . . 174
D5 Example of data for NE wave testing of Modification D .......................... 174
D6 Results of jetting modification tests ....................................... 175
D7 Results of jetting modification tests without SE sand supply factor related to jetty length ...... 176
D8 Comparison of wave heights (from NE and SE at MSL) with dredged and normal conditions ... 178
D9 Dredged ebb shoal condition wave height ratios at several points from numerical
and physical models ................................................ 178
El Estimated net sediment transport rates for existing system ......................... 192
E2 Estimated gross sediment transport rates for existing system ........................ 192
E3 Results from model runs for Modifications 3, 4, and 5 ........................... 195
E4 Results from model runs for Modifications 6, 7, and 8 ........................... 197
GI Needs of nesting sea turtles and habitat design considerations ................ ...... 210
G2 Summary of design criteria for sea turtle nesting beaches ......................... 210




1. INTRODUCTION

1.1 Preamble
The University of Florida (UF) undertook a coastal engineering management study for the Jupiter Inlet District (JID), for improving the engineering management protocols with respect to three main issues: beach erosion control, navigational safety, and control of sedimentation in the interior waters. The study was initiated on January 5, 1990. Five technical progress reports (Mehta et al., 1990a, 1990b, 1991la, 1991lb and 1991c), based on a two year investigation and cited in the bibliography section, form the basis of the recommended coastal engineering management plan. The purpose of this final report is to recap the main findings discussed in more detail in the technical reports, and to highlight the management plan recommendations. We begin by providing a brief background of the study area.
1.2 Location and Description
Jupiter Inlet is located at latitude 26056'35" N and longitude 80'0O4'18" W on the east coast of Florida in the northern part of Palm Beach County (Fig. 1. 1). It is about 26 km south of St. Lucie inlet and about 23 km north of Lake Worth inlet. It is a natural inlet connecting Loxahatchee River to the Atlantic Ocean. The backwaters of Jupiter Inet are shown in Fig. 1.2.
Long and narrow barrier islands is a characteristic feature of the coast in the vicinity of Jupiter Inlet. The barrier island north of Jupiter Inlet is called the Jupiter Island. The central portion of Jupiter Island, opposite the town of Hobe Sound, has been well-developed as a winter residence area over the past several decades. Many large and expensive homes are located near the beach in this area. The southern portion of Hobe Sound was less developed until the 1940's and the houses in this area were placed near the shore of Hobe Sound. Most of the individual properties extended coast to coast on the island, the width of which varied from 15 m to 50 mn at low water.
According to the U.S. census of 1940, Hobe Sound had a permanent population of 874. The excess floating population was estimated to be around 100 in summer and 1,000 in winter. The permanent population of Palm Beach County and Martin County has increased substantially over the past few years as may be seen from data given in Table 1. 1. Martin County is the adjoining county just north of the Palm Beach County.
The figures given for the years 1930 through 1990 are obtained from the Federal Census. The figures given for the year 2000 are estimates obtained from the Palm Beach County Planning Division and the Martin County Department for Community Development.




Figure 1. 1. Area map of Jupiter Inlet.
2




Figure 1.2. Backwaters of Jupiter Inlet.

Figure Li 1913 survey showing the earlier location of Jupiter Inlet (U.S. Coast and Geodetic Survey, 1913).




Table 1. 1: Population of Palm Beach and Martin Counties.

Year Palm Beach County Martin County
1930 51,800 5,100
1940 80,000 6,300
1950 114,700 7,800
1960 228,100 16,900
1970 349,000 28,000
1980 567,800 64,000
1990 863,500 115,200
2000 1,113,200a 1980
'Estimate; Palm Beach County Planning Division.
bEstijiate; Martin County Department of Community Development.
1.3 Historical Information
According to historical accounts, Jupiter Inlet has been in existence for at least over 300 years (U.S. Army Corps of Engineers, 1966). It is first shown on the explorers' maps in 1671 and other contemporary navigation charts. Originally, this was the only outlet for Loxahatchee River, Lake Worth Creek and Jupiter Sound. Part of the discharge from St. Lucie River and the southern part of Indian River was also diverted to the ocean through Jupiter Inlet. The total flow was sufficient to maintain adequate depth through the inlet except during severe storms when the inlet closed temporarily for short periods. This inlet has been known by several names (Dubois, 1981). First it was known as Hobe, or Jobe for a tribe of the aboriginal Jeaga Indians who lived near the inlet. On the Spanish maps, the river appeared as Jobe River, named for these Indians. The English interpretation of Jobe was Jove, which in turn became Jupiter. On the DeBralum map of 1770, it is given as Grenville Inlet, formerly Jupiter. Hobe or Hoe-Bay continues as the nearby Hobe Sound. All are apparently related terms. In early days, the inlet was at times several hundred km south of the present location. The map of the Fort Jupiter Reservation, dated 1855, shows the inlet in this position.
St. Lucie Inlet, the next inlet due north, was a man-made creation in the year 1892. The Intracoastal Waterway connected Jupiter Sound to Lake Worth Creek in 1896 and Lake Worth Inlet was created in 1918. These constructions diverted much of the flow away from Jupiter Inlet, which in turn resulted in more frequent closure of the inlet. Between 1896 and 1909, under a special emergency authority, the Federal Government reopened Jupiter Inlet three times. Local interests also reopened the inlet several times between 1896 and 1922. The JID, created in 1921 by a special act of the Florida Legislature, spent in excess of $400,000 improving and maintaining the inlet between 1922 and 1960.
Until the year 1922, Jupiter Inlet was a natural inlet without any man-made training structures at the inlet mouth. Under the combined effect of tidal flow through the inlet and the predominant littoral drift in the southward direction, the inlet joined the Atlantic Ocean with an orientation in the south-eastern direction (Fig. 1. 3). Mr. J.




C. Wagen, Chief Engineer of Lake Worth, Florida approved construction drawings in the year 1922, which included the following works at Jupiter Inet (Fig. 1.4).
1 Cutting a channel in the easterly direction across the sand barrier. The channel was to be 30 m wide at
bottom with 2.1 m depth below the mean low water level. This involved removal of about 2,800 m3 of
material.
2. -Provision of a barrier across the natural south-easterly channel, the crest elevation of the barrier being
1.5 m above mean low water level, in order to divert the tidal flow through the new opening.
3. Construction of two jetties, each 120 m in length, 100 m apart, one on the north side and the other on the
south side of the inlet. Typical cross-section of the jetty and the dredged channel are shown in Fig. 1.5.
The permit for the above construction works was issued on 20th April 1922 by Mr. Lansing H. Beach, Major General and Chief Engineer, U.S. Army. In 1922 JID built two parallel jetties about 107 m apart at the inlet. Subsequently, the jetties were extended and strengthened. In 1929, the north and south jetties were extended 60 m and 25 m, respectively. In 1941 a 2 m deep and 18 m wide channel was dredged close to the south jetty. In 1940 JID built an angular groin at the seaward end of the south jetty. The intended purpose was to increase current velocities and induce scouring between the jetties where closure of the inlet had recurred. However, the inlet again closed in 1942 and remained as such until 1947. Closure occurred due to a sand barrier about 90 m wide having a top elevation of 2.1 mn above mean low water. Since lID reopened the inlet in 1947, typically biannual maintenance dredging has kept the inlet open for small-craft navigation. In 1956, a 90 m long concrete capped sheet pile jetty was constructed 30 m north of the existing north jetty. In 1966 JID, working with a consulting engineering firm, initiated a 15-year improvement program intended to ultimately provide: (1) Landward extension of the existing bulkheads; (2) jetties at the seaward ends of the existing bulkcheads; (3) continued periodic maintenance dredging of the inlet channel; and (4) a trestle-mounted sand-transfer plant sited north of the north jetty (U.S. Army Corps of Engineers, 1966). Local interests estimated the cost of the 15-year program, including interim channel dredging maintenance, at about $800,000. Funds for the program were raised by taxes on property within the inlet taxing district. Palm Beach County contributed funds to JID periodically for fill placed on the south beach. A sand trap was dredged 300 m west of the inlet mouth in 1966. In the late 1960's, the jetties were modified. A "wing" on the seaward end of the south jetty was removed in 1967 in an effort to reduce shoaling within the inlet (Fig. 1.6). Both jetties were extended landward to prevent flanking. The present, about 60 m wide, channel requires regular maintenance dredging.
1.4 Chronology of Important Early Events
Year Event
1892 St. Lucie inlet was constructed by making an artificial cut through the barrier strip, about 10 km north of
Jupiter.
1896 A canal was excavated connecting Jupiter Sound and the headwaters of Lake Worth Creek with Lake Worth.




44,

'Dredging of Channel to Extend to 6 ft Depth In the Ocean

of Two Jetties

Spoil to be Deposited by Hydraulic Dredge \.

Figure 1.4. Details of the original construction works at Jupiter Inlet in the year 1922.




Scale 1' 10'

100__ MSL
I Variable
.... '....-.-t: ':.. ..''
I ~*:~ L..10
Typical Section of Channel, In Water
Scale 1' 10'
Variable
Typical Section of Channel, Through Ridge.
Scale 1' 10'
Figure 1.5. Cross-section of the jetties and approach channel constructed at Jupiter Inlet in 1922.




BID ITEM A --.
Remove Existing Sheet Pile and Cap to Elevation -10.00 ft, Within These Limits
SOUTH Jerry

BID ITEM B
Construct Approximately 100 Linear Feet of Steel Sheet Pile and Granite Jetty "
-,-Uj- Line~~jne
"~ 0I Lie100 200 ft PLAN

SECTION THRU JETTY

PILE CAP DETAILS

Figure 1.6. Modifications made to the south jetty at Jupiter Inlet in 1967.

-V
0C

0
0 to

A




1913
1922 Inlet moved approximately 1250 ft north to its present position. 1922 Permit was issued to Jupiter Inlet District by the Chief of Engineers, U.S. Army to dredge a channel and
construct two entrance jetties 122 m apart in order to provide a stable inlet with eastward flow direction. 1922 400 ft long jetties were constructed, 400 ft apart and a channel was dredged to meet 6 ft depth in the
ocean.
1926 North jetty was constructed at St. Lucie Inlet. Seawall constructed on Jupiter Island. 1929 North jetty extended by 200 ft and south jetty extended by 75 ft. 1936 100 ft wide, 8 ft deep channel was dredged. 1940 Inlet District constructed an angular groin at the seaward end of the south jetty. 1942 Inlet closed and remained closed until 1947. 1947 House Document No. 765 was submitted to the 80th Congress, 2nd session of the U.S. House of
Representatives.
1947 Inlet was reopened by dredging.
1957 Coastal Engineering Investigation at Jupiter Island were conducted by the University of Florida in order
to recommend the best methods of protecting Jupiter Island beaches.
1960 Coastal Engineering Investigation conducted by the University of Florida for recommending the alignment
of bulkhead along Jupiter Island beach.
1966 Sand trap was dredged 1000 ft west of the inlet throat. 1967 Angular groin at the seaward end of south jetty was removed and the jetty was extended by 30 m.
1.5 Recreation and Fishing
The Survey Report of 1966 (U.S. Army Corps of Engineers, 1966) mentions that the absence of a dependable, safe channel to the ocean through Jupiter Inlet restricted recreational crafts from full realization of potential boating benefits. Local boats had to await favorable conditions of tides and seas or travel via the Intracoastal Waterway to St. Lucie or Lake Worth (Palm Beach) Inlets in order to cruise or fish in the ocean. Information on the recreation boats in use in the Jupiter area in the year 1966 is given as an example in Table 1.2 (U.S. Army Corp of Engineers, 1966).
Frequently, small craft entering the ocean through Jupiter Inlet in the morning were compelled to return via Lake Worth or St. Lucie Inlets due to adverse weather or seas encountered on the return trips. Some local boatmen considered the hazard and inconvenience of using the Jupiter Inlet so great that they either kept their boats at West Palm Beach or no longer cruised or fish in the ocean. During optimum navigating conditions, normal controlling depths over the ocean bar limited recreational use to boats drawing less than I m. Even with favorable conditions of sea and swell, navigation was restricted to the hours of highest tide.
With the abundance of natural and improved inland waterways and the nearness of the Atlantic Ocean, recreational boating and sport fishing are two of the major local outdoor activities. Tourists and vacationers from




Table 1.2: Recreational boat use in the Jupiter area in 1966 (U.S. Army Corps of Engineers, 1966).
Average Percent of fleet using
Length (ft) draft (ft) Jupiter Inlet Other inletsa
Inboards:
Up to 26 1.0 to 3.0 48 78
26 to 40 2.0 to 4.0 27 94
40 and longer 3.5 to 6.0 0 100
Outboards.10 and 22 1.0 to 2.0 39 53
'Part or full time.
other parts of Florida and from many other states visit the area to enjoy fishing, boating, and other recreational activities. The following extract taken from the Survey Report of Jupiter Island (U.S. Army Corps of Engineers, 1966) describes the status of fishing:
"In the 1962-1963 season a fleet of 21 king mackerel launches, comprised of 8 local and
13 transient boats, operated through Jupiter Inlet when tide and seas permitted safe passage. This is about the same number as was based at Jupiter in 1933-1934, when the inlet was open and usable by such craft. Of the permanently based local fleet, 7 boats are used only for king mackerel fishing in local waters, and I boat fishes year-round for other species. Operators of the 7 local boats fish for king mackerel as a secondary or supplemental occupation. The remaining 13 transient vessels follow the migrating schools. The fleet experienced varying degrees of restriction during the 1962-1963 season when large schools of king mackerel were concentrated offshore in the northern part of Palm Beach County. Evaluated benefit to the Jupiter fishing fleet is based upon the alternative of operating the fleet from West Palm Beach bases. Information from the field study indicates that the additional daily operating cost would be $5 per boat (10 gallons of gasoline at $0.34, 1 quart of oil at $0.60, and $1.00 added for daily engine wear and maintenance cost).
Local boats fish about 45 days a year for king mackerel. Estimated annual savings in operating costs would be $225 per boat or $4,700 for the fleet. It is believed that the fleet size will remain
relatively unchanged regardless of inlet improvement.
The offshore waters of Palm Beach County support an important marine fishery. In recent
years, annual food-fish landings have averaged over 4 million pounds. King and spanish mackerel have constituted about 85 percent of the total catch. Most of the fish landings, which are principally ocean species, have been carried through Lake Work Inlet. However, in th6 1962-63




season, significant catches of king mackerel were brought in through Jupiter Inlet when weather
and seas permitted.
There are no public terminals or docks in the Jupiter area. However, three private
marinas provide berths for about 75 recreational and commercial craft. Covered dry storage for an additional 50 small recreational craft is also available. Commercial fish catches are unloaded at a marginal wharf and passed directly into waiting trucks. Available facilities, while privately owned, are generally open to all on equal terms. The closest marine railways are at West Palm Beach. Outboard craft may be serviced and repaired at local marinas. Existing facilities have highway connections and are adequate for present recreational and commercial small craft. Land has been acquired and plans have been prepared for two additional marinas in the vicinity of the inlet. Plans for one of these, announced in April 1964, would provide space for 350 boats at a
coast in excess of $500,000. Adequate space is available for future expansion of terminals.
Commercial fishing is an important industry of Palm Beach County. King mackerel is the
principal food fish landed, representing about 50 percent of the tonnage and dollar value of all food fish landed in the county in recent years. In the period 1958 through 1962, king mackerel fishing extends from December through March. During that period large schools n- migrate through the offshore waters. During the 1962-1963 season a fleet of over 50 inboard launches 5.2 to 7.6 m long, with maximum loaded drafts of 1.2 m, fished for king mackerel from Palm Beach County bases. The boats are operated by one- and two-man crews. All fish landed were processed through fishhouses in the West Palm Beach area. Fish landed through Jupiter Wet were trucked to West
Palm Beach for processing."
The Survey Report of 1966 also included projections of recreational boat traffic at Jupiter. These, even though dated, are given in Table 1.3 for illustration. Comparison of boat ownerships and population in Florida coastal counties shows that the per-capita ownership of recreational boats is greatly reduced as coastal counties increased in population. Therefore, per-capita ownership of recreational boats in Palm Beach County and the Jupiter Inlet area was expected to decrease from the rate of about 35 boats per 1,000 population in 1966 to about 15 boats per 1,000 population by 2017. The projected local fleet at Jupiter Inlet, as shown in Table 1.3, is based on 1S boats per 1,000 population in 2017 (1,469 boats). It would be interesting to compare the facts for the past years from 1967 to 1992 with the projections made in the year 1966. These data were not however readily available while compiling this report.
1.6 Navigation
A navigation channel 60 m wide and 3 m. deep has been considered from the Jupiter Inlet entrance to the 3 rn contour in the ocean. The length of this channel would be about 380 m (Fig. 1.7; note units in ft). Inside of




Table 1.3: Jupiter Inlet recreational boating benefits (U.S. Army Corps of Engineers, 1966).

Type of Boat
item Outboards Inboards
Runabouts Cruisers Charter To 26 ft. 26-40 ft. 40 + ft.
Depreciated value ---$600 $1,300 $8,000 $3,000 $7,000 $20,000
Percent return -----10 12 12 8 7 6
Unit return -------$60 $156 $960 $240 $490 $1,200
Percent restriction 11 11 15 12 14 22
Unit benefit -------$7 $17 $144 $29 $69 $264
Without improvement:
Local fleet 1964:
Number -----131 58 0 45 9 11
Benefit -----$920 $990 0 $1,300 $620 $2,900
Added fleet by 1967:
Number -----52 24 0 17 3 2
Benefit -----$364 $408 0 $493 $207 $528
Added fleet by 2017:
Number -----630 280 0 200 40 30
Benefit -----$4,410 $4,760 0 $5,800 $2,760 $7,920
With improvement:
Added fleet in 1967:
Number -----0 0 4 1 0 0
Benefita---- 0 0 $3,840 $240 0 0
Added fleet by 2017:
Number -----0 0 20 10 3 2
Benefita----- 0 0 $19,200 $2,400 $1,470 $2,400
Total number of boats
(Year 2017) ------761 338 20 255 52 43
(Year 1967) ------$1,284 $1,398 $3,840 $2,033 $827 $3,428
Total benefits (Year 2017) $5,330 $5,750 $19,200 $9,500 $4,850 $13,220

aFull unit return

Total
254 $6,730
98
$2,000
1,180 $25,650
5
$4,080
35
$25,470
1,469 $12,810 $57,850




Width 150' Depth 10.
-~~~ --- -

0 100 200 300 ft

Figure 1.7. Layout of the navigation channel at Jupiter Inlet.




the inlet, the navigation channel would be 45 m wide and 3 m deep. The 3 m depth of channel was based on the following clearances:
Mean low water 0.3 m
Wave trough 0.9 m
Underkeel clearance 0.6 m
Draft of vessel 1.2 m
The 60 m width of the channel would provide enough room for a two-way traffic of boats 12 m long and 4 m wide.
Principal difficulties result from inadequate depth across the ocean bar at the entrance to the inlet. During periods of low tide or high seas or swells, passage over the ocean bar is extremely hazardous if not impossible. Local interests reported that at least five lives were lost in the 5-year period from January 1958 to March 1963, from capsizing of outboard boats in and near the inlet. Reported loss and damage to small crafts at Jupiter are given in Table 1.4 for illustrative purposes. The principal damage was to outboards grounding on the ocean bar or capsizing in the inlet. Outboards capsized in the inlet sustained damage ranging from minor superficial damages to complete loss. Representative costs for outboard grounding damage were: propeller replacement $12; water pump repair $25; lower unit replacement $130; and windshield replacement, $65. With allowance for boat damage that would occur regardless of inlet improvement, and allowance for undisclosed damage, annual benefit from reduction of damage to boats was estimated at $1,300 in 1964, $1,500 in 1967, and $7,000 in 2017. Prevention of loss of life was not evaluated.
1.7 Concluding Comment
Since its inception in 1921, JID has been consistently involved in managing navigation through Jupiter Inlet and, therefore, has had to contend with the auxiliary but inter-related issues arising from managing for beach erosion and sedimentation. In recent years ecological stresses on the inlet and the Loxahatchee River estuary have increased substantially, hence any examination of the impact of improvements with regard to management for beach erosion, navigation and sedimentation must simultaneously consider physical processes together with environmental factors. The subsequent chapters are therefore focussed along these lines.
In a review of literature and data of this engineering nature, mixed use of fps unit system and the Sl system poses the usual problem of unit conversion. Following the contemporary convention, the SI system is used in the text, either by itself or together with the fps system, with some exceptions. On the other hand, fps unites have been retained in many figures and tables including, but not limited to, those derived from other sources. Necessary conversions are as follows:




Table 1A Reported loss and damage to small craft at Jupiter Inlet (U.S. Army Corps of Engineers, 1966).

Reported
Cause of damage and type cost

Name of boat or type

1957
Capsized Grounded
Broached (1 insured)
1958
Swamped Capsized (I life lost)
1959
Bent propeller

$150

Inboard cruiser Outboard Outboard
Outboard Inboard cruiser
Inboard cruiser
Inboard cruiser Inboard cruiser Outboard Outboard
Inboard cruiser Outboard Outboard Outboard Outboards Outboards

1960
Grounded cracked hull Grounded sand in engine Broached (passenger thrown from boat) Grounded

1961
Grounded
Grounded broken windshield Grounded cracked lower unit
Grounded (5 incidents) Broken propellers (6 incidents)

1962
Capsized Grounded, broken up
Propeller damage
1963
Grounded
Grounded Capsized (2 lives lost) Capsized (1 life lost)

Alumincraft outboard Richardson cruiser Inboard cruiser Outboard
Ruby 5 (commercial fishing) Inboard-outboard Outboard skiff Outboard

8,000
150




To Convert centimeters cubic meters cubic meters per sec kilometers meters

Into
inches cubic yards cubic feet per sec miles (statute) feet

For convenience of description the grain size is defined in terms of diameter, d, and 4 the unit where deemed necessary. The relationship between these two is: q0 = log2d.
The essential elements of the management issues specific to Jupiter Inlet, as well as the present state of the inlet from a coastal engineering perspective and described next in Chapter 2.

Multiply By
0.3937
1.308 35.31
0.6214
3.281




2. MANAGEMENT ELEMENTS AND THRE STATE OF THE INLET

2.1 Management Ihmperatives
As shown in Fig. 2. 1, the water areas in the inlet region relevant to the study can be conveniently divided into three sub-areas: Region 1 (beaches and offshore area influencing the inlet and vice versa), Region 2 (inlet channel between the ocean ends of the jetties and the Florida East Coast Railroad, or FECRR, bridge), and Region 3 (including the area bounded between the FECRR bridge S.R. 707 and Pennock Point). The Intracoastal Waterway runs through Region 2, which serves as the connection between Jupiter Sound and Lake Worth Creek. Three forks of the Loxahatchee River enter Region 3. From the standpoint of JID's requirements for this study, Regions 1 and 2 are particularly important, whereas the importance of Region 3 only lies in terms of processes and recommended actions that are particularly relevant to Region 2.
As a characteristic feature of the beaches adjacent to sandy tidal inlets subject to a net littoral drift, the shoreline in the vicinity of Jupiter Inlet has readjusted itself relative to what would occur in the absence of the inlet, to create a northern accretion fillet of sand, and a southern deficit of sand as shown in Fig. 2.2. To maintain a navigable channel through the inlet and control the beach sand deficit problem, since the late Forties a coastal engineering management protocol has in fact been in place at this inlet. Over the years, partly based on two previous studies carried out by UF in 1969 and 1984 (Coastal Engineering Laboratory, 1969; Buckingham, 1984), this plan has evolved to its present state. A key element of the plan includes maintaining the channel through periodic dredging of the designated sand trap (Fig. 2.3), and managing the beach south of the south jetty by placement of sand derived from the trap. This protocol is aided by a similar dredging and pumping operation by the Army Corps of Engineers to remove excessive sand from the Intracoastal Waterway (Fig. 2.4). An important function of the two jetties is to maintain a trained navigable channel. The periodic dredging of the sand trap also serves to minimize the influx of sand in the interior areas including the marinas located in Region 2 and the aquatic preserve in Region 3.
The above mentioned management protocol has been functional to the extent that it has prevented catastrophic problems such as a barrier breakthrough with respect to the erosion of the south beach, has maintained a navigable channel, and has prevented excessive sedimentation of the interior as would, for example, clog the inlet completely. Such a clogging by sand did in fact occur in the mid-Forties, before the inlet was managed along the present lines. Due to increasing demands on the inlet and adjacent beaches arising from recreational and other needs, JID decided to seek possible solutions to three outstanding engineering needs as follows:
1. The need to increase the retention time of the sand placed on the south beach and reduce the threat of a land barrier breakthrough ("flanking") immediately south of the south jetty.




S.R. 707

Region 1

0 500 1000 1500 meters
DepthsI I I Mtrs
Depths In Meters

Fig. 2.1 Three water regions of Jupiter Inlet/Loxahatchee River relevant to the study.




Fig. 2.2. Sand fillet and deficit at beaches contiguous to Jupiter Inlet.




Fig. 2.3. JID sand trap.




Fig. 2.4. Army Corps of Engineers sand borrow area in the Intracoastal Waterway, and the lighthouse.




2. The need to improve navigational safety, particularly as related to vessel passage in the area immediately offshore of the inlet, where accidents occasionally occur.
3. The need to reduce sedimentation in the interior areas, such as at the sites where the marinas are located (east of FECRR Bridge, along the south bank of the channel; Fig. 2.5).
2.2 Investigations
Seeking engineering solutions in regard to these needs must necessarily involve an examination of the potentialities for physical and associated ecological impacts. Thus, in addition to physical processes including waves tides, currents, salinity/fresh water, bottom sediment characterization and sediment transport (erosion, horizontal motion and deposition), as well as the present dredging protocol and navigational aids, assessments of the submerged vegetation (seagrass), mangroves (in Region 2), and rocky outcrops (in Regions 1 and 2) were carried out. Furthermore, sea turtle nesting, an ecological sensitive issue, was taken into consideration. These ecological "baseline" data were then used to make assessments of ecological consequences of all the principal physical impacts of the solutions considered. Fig. 2.6 shown the components and inter-relationships among the technical components of the study.
Based upon engineering investigations briefly noted next and described in the progress reports and related correspondence with JID, a suite of solution options based on what is practicable at Jupiter Inlet was considered, and in determining the choices, of the three primary issues -- beach erosion, navigational safety and sedimentation in the interior, where applicable the first two were weighed equally, while sedimentation, considered by JID to be a less problematic (i.e. more easily manageable) issue than the first two, was given a lesser weight. In every choice made the advantage or adversity of ecological impacts was considered. Summary descriptions of considered actions and their physical and ecological impacts follows a reference to the engineering investigations and finds in regard to the present state of Jupiter Inlet and the management protocol.
A cornerstone of this study was the series of coastal and environmental engineering investigations that were carried out to develop the technical bases for the selection of the engineering options. The basis for selecting the investigative methodology is rooted in the essential elements of inlet management elements as described in Appendix A (Mehta and Montague, 1991). The investigations themselves encompassed a number of field and laboratory measurements, and data analyses and interpretations, based upon these measurements as well as prior experience, technical knowledge and data (e.g. Chiu, 1975; Buckingham, 1984) available from other sources documented in the progress reports. In brief, the field studies included offshore wave measurement (over a 15 month period), tide and current measurements in Regions 1 and 2, bottom sediment sampling in all three regions, sand tracing studies in Regions I and 2, and seagrass and mangrove mapping in Region 2. A physical scale model of the inlet area (Region 1) was constructed and tested at LTF. In addition, a suite of numerical models was used as an aid in analyzing the data collected in this as well as several previous studies to develop an understanding of the physical processes, a sediment budget for the inlet region, and physical and ecological impacts of the solution options (actions) considered.




Fig. 2.5. Marinas of interest to the study.




Technical
Issues
Physical Impacts
Ecological Impacts

Fig. 2.6. Technical issues, physical impact studies and ecological impact studies for the inlet management plan.




It must be noted at this point that coastal and environmental engineering sciences are strongly observational in nature and, therefore, process-dependent technical conclusions must in turn rely on experience elsewhere with similar and dissimilar physical environments, and imposed engineering protocols. Mathematical and physical models, given their strengths and limitations in duplicating the physical phenomena, are essentially used as aids in arriving at rational engineering decisions, but they cannot, and should never be used as a sole basis for such decisions. No where in this study have we directly or directly implied that models have been either the sole or even the predominant basis of our engineering decisions. Neither should the reader anticipate or demand such an assertion.
2.3 State of the Wet
The main findings with respect to the existing physical setting and the management protocol are briefly as follows:
1. In comparison with several other inlets, e.g. St. Lucie Inlet, Jupiter Inlet is reasonably well behaved, and well managed by JID, hence improvements to the existing management protocol are highly desirable but not absolutely critical.
2. A conservative (on the higher side) estimate is that as a result of the presence of the inlet, about 14,000 yd3 (10,700 m3) of sand out a total of 230,000 y& (176,000 m3) Oong term annual mean) of net southward transport of sand are "lost" from the littoral transport zone to the offshore and the interior waters. This quantity, i.e. 14,000 yO (10,700 m3), amounts to an annual sand equity loss in regard to the beaches south of the inlet.
3. The shape and the volume of sand in the ebb shoal of the inlet change continually in response to the wave climate. The volume of sand tends to vary from season to season and year to year; estimates of the range of volume suggest that there are times when the volume is less than 500,000 y& (382,000 m3) when the wave activity is strong, to somewhat more than 1000,000 yd (765,000 m3) under milder wave conditions. Most of the sand is believed to be exchanged with the beach that the ebb shoal protects from heavy wave action; thus during more inclement times the ebb shoal supplies sand to the beach, while during calmer times the reverse process occurs.
4. The beach immediately south of the inlet is inherently prone to erosion, by virtue of the refraction and diffraction of waves that naturally occur in the vicinity of inlets, particularly those with jetties. The present sand dredging and pumping protocol to nourish the beach periodically is limited by: 1) the fact that some of the sand placed there returns to the channel by transport around the southjetty, 2) other sand moves southward, and 3) the retention time of the placed is low; the sand moves into the channel and also southward too rapidly in relation to the typical biennial placement schedule that has been usually (although not always, such as recently, when the inlet has been dredged annually) followed. Furthermore, the approximately 800 ft (240 m) stretch of the beach south of the south




jetty over which sand is typically placed appears to be somewhat short in length. Finally, no particular pumping season "windows" have been adhered to, although pumping is carried out during spring or summer for ease of dredging and transport of sand.
S. In addition to sand pumping from the interior borrow area or trap managed by JID (Fig. 2.3), the Army Corps of Engineers also pumps sand to the south beach from the Intracoastal Waterway (Fig. 2.4). Excluding those years when no sand was pumped to the beach, the total volume of sand pumped from the JID trap and the Corps trap has varied from as low as 30,000 yd3 (22,900 in3) in 1952, to as much as 209,000 yd3 (160,000 in3) in 1966. To date no specific frequency of pumping or minimum amount required to maintain the beach have been selected. A difficulty in such specifications is the annual variability in the condition of the beach, and the infilling rate of the traps. Furthermore, the Corps of Engineer's sand transfer protocol is merely fortuitous, since the Corps's principal need is to maintain the Intracoastal Waterway, as opposed to beach maintenance.
6. The present sand placement protocol is unrelated, placement- or timing-wise, to any considerations for sea turtle nesting habits. When the sand is placed such that steep, prograded beach profiles are established in the region immediately south of the south jetty, some turtle nests are lost due to relatively rapid erosion that typically occurs at these steep profiles. Relatively flat, tillable beaches that are supplied with sand on a regular basis for their stability are well suited to the Loggerhead sea turtles, which are endangered world wide.
7. Nesting sea turtles are an important ecological feature of the beaches north and south of Jupiter Inlet. Each year between the months of April or May and October, as many as 200 sea turtle nests are laid per kmn from Juno Beach to Jupiter Island. Management of sea turtle nesting beaches must address four main needs of nesting sea turtles: 1) access to nesting sites; 2) excavation of a nest to a depth of over 1 mn (3.3 ft); 3) incubation of each nest for 60 d; and 4) successful emergence of hatchlings (which must dig out of nests). Access to nesting sites should be enhanced by a uniform moderate beach slope (1: 10), without steep scarps, rising to a soft sand berm. Nest excavation and hatching emergence should be enhanced by the presence of excavatable sand (loose sand of compaction less than 35 kg/cm2 and not prone to crustal formations). Beach material should be coarse enough to prevent compaction, but it should not contain large rubble. Excavatable sand should be deep enough over any hard substrate to allow complete nest excavation (> 1.5 in, or about 5 ft, deep). Moreover, for sea turtle nesting to be successful, it is imperative that incubating nests not wash out before hatchlings emerge. Thus, whatever can be done to enhance beach profile stability, within the confines of the other criteria, should benefit sea turtles. In this regard, sand could be placed on the beach more than 30 days prior to the beginning of the nesting season to allow beach profile stabilization; the beach could be nourished more frequently (perhaps twice per year); and nourishment material could be placed away from hard structures that reflect wave energy, such as the south jetty (to avoid nest wash-out in the immediate vicinity of the jetty).




8. Submerged rocky outcroppings from the Anastasia formation form an important habitat for fishes and invertebrates in the nearshore zone all along the southeastern Florida coast. Rocky outcroppings may be especially important to spawning fishes. Few rocky outcroppings occur in the immediate vicinity of Jupiter Inlet, however, because of the accumulation of sand in the ebb shoal. This sand forms a shifting veneer over the rocks. Periodic storms bury and re-expose rocky outcroppings in the vicinity of Jupiter Inlet. At present, submerged rocky outcroppings appear approximately 1 km (0.6 mile) north of the inlet and northward. Other nearshore rocky outcroppings appear 1.2 km (0.75 mile) south of the inlet at Carlin Park. A small area of possible rocky outcroppings occurs about 1. 3 km (0. 8 mile) northeast of the inlet and a popular fishing site known as "Grouper Hole" is found 2 km (1.2 miles) due east of the inlet. A few exposed rocks occur directly inside the inlet mouth. Management considerations for rocky outcroppings include avoiding modifications that would bury rocks that have been exposed long enough to have developed diverse ecological communities. Long jetties may divert sand far downdrift and could conceivably contribute to the burial of some rocky communities. Jetties, however, are themselves artificial rocky habitat. They develop diverse ecological communities within a few years.
9. The inlet jetties have performed well in maintaining a stable navigation channel, thereby also protecting the adjacent land properties. However, the bulkheads separating land from water in many places along the interior banks are poorly designed and/or are in a poor condition. Also, too much concrete has been poured over parts of the Dubois Park beach, thus causing the hardened bank to reflect waves and hence erosion by sand transport away from the bank (Buckingham, 1984). In some places where bank protection is desirable, none exists. These conditions, coupled with significant boat wakes, have led to bank erosion in many places. Speeding boats are a major cause of the bank erosion problem. This erosion adds to the sediment at the bottom, thereby contributing to the reduction in navigable depths.
10. As to the causes of boat accidents that occur off the entrance, two types seem common; those in which the boat runs aground or is caught in wave action over the ebb shoal platform, and those in which the boat is attacked by waves abeam, typically from the northeast. Opinions on the need for improving navigational safety in this respect seem to vary; experienced navigators consider lack of navigation experience and hence judgment on the part of individuals as one of the principal causes of accidents. Coast Guard records show that alcohol related accidents also occur in this area.
11. A natural navigation channel maintained by the inlet currents typically exists off the inlet generally in the southeast direction, with depths on the order of 10 ft (3 in), but in places where the littoral sand pathway intersects the channel, depths are less and navigation more difficult. The channel shifts in response to seasonal changes in the wave climate, and the Coast Guard considers Jupiter Inlet to be hazardous to navigation. The maximum drafts of vessels presently plying the waters cannot easily justify a deep,




i.e. deeper than 10 ft (3 m) navigation channel offshore such as at Fort Pierce and Palm Beach Inlets, unless future traffic growth patterns suggest otherwise.
12. The JID trap has performed reasonably well over the years, although a potential for somewhat improving its efficiency exists. The trap catches sand that enters from the littoral drift around both the jetties, and also over the jetties during storms when wind and wave-induced storm surge raises the water level and inundates the seaward ends of the jetties. Sand transport around and over the north jetty is four to six times greater than that from the south. The amount of sand caught by the trap annually varies widely because of the corresponding wide variations in the littoral drift. Estimates indicate for example that in 1956 the net southward drift was 433,600 yd3 (332,000 m3), while in 1968 it was only 63,400 yd3 (48,500 m3). The gross southward and northward drifts for the same two years were, respectively, 473,300 yd3 (362,000 m3), 39,600 yd3 (30,000 m3) and 989,900 yd3 (757,000 m3), 35,500 yd3 (27,100 m3).
13. As the sand enters the channel, the larger grains (around 0.4 to 0.6 mm size) fall out into the JID trap, somewhat smaller grains fall into the Corps trap, and some of the finer material (0.15 to 0.25 mm) is transported westward past the FECRR bridge. In recent years, with continual sedimentation and consequent decrease in depths in Region 3, the sand influx past the bridge has slowed to around 1,000 yd3 (760 m3) to 2,400 yd3 (1,800 m3) per year. Region 3 is the zone of the Loxahatchee River estuary where sea and fresh waters mix and there is a naturally high potential for sedimentation. Sediments of a variety of compositions enter this zone from the different connecting water bodies, one of which is the inlet channel. It is believed that a not wholly insignificant source of sand here is material derived from the banks of the Loxahatchee River due to boat wake induced erosion.
14. Some of the sand that is not caught by the JID trap deposits in the area where the marinas are located (Fig. 2.5). A representative rate of sedimentation in this area is about 0.5 ft (15 cm) per year. This area happens to occur along the side of a slight meander in the Loxahatchee River, and is naturally prone to sedimentation. Two other marinas located eastward appear to be much less prone to sedimentation, as they are semi-enclosed basins with well-defined entrances.
15. Seagrasses in the Loxahatchee River estuary inside Jupiter Inlet are an important habitat for juvenile fishes and invertebrates. Seagrasses are also important in sediment stabilization, wave energy reduction, and storm surge attenuation. East of the FECRR bridge are about 5.5 ha of seagrass beds. About 24% of the shoreline east of the FECRR bridge is adjacent to a seagrass beds. About half of the seagrasses in the estuary east of the FECRR bridge and south of the S.R. 707 bridge (in the north arm of the Intracoastal Waterway) are in one bed along the south shore just south of the north arm of the Intracoastal Waterway. Generally seagrass density in the beds declines toward the west. Seagrass beds exist between depth extremes from exposure to air at low water to a critical depth for adequate light penetration. Gentle bathymetric slopes between these extremes can result in large expanses of




seagrass beds. Seagrasses are also killed by high temperatures (above 350C2), such as may occur in shallow tidepools. Moreover, they are perhaps sensitive to high frequency, high amplitude fluctuations in salinity, such as may occur west of the FECRR bridge. Management considerations for seagrasses include effects of inlet modifications on water level, tidal amplitude, salinity regime, sediment loading, and light penetration.
16. The mangroves of the Loxaliatchee River estuary are an important intertidal habitat for juvenile fish and invertebrates. Moreover, they help to stabilize sediments and protect shoreline property from the damaging effects of storms. About 4.9 ha of mangroves exist in the Loxahatchee River estuary east of the FECRR bridge. Approximately 55 % are in the Dubois Park lagoon. Another 40 % are in the south arm of the Intracoastal Waterway. About 38 % of the shoreline is lined with mangroves. Changes in mean water level, tidal range, or sediment loading can change the extent of mangroves in the area. Management for mangroves includes consideration of the effects of inlet modifications on these variables.
2.4 Concluding Commnents
Of the various sub-studies conducted and reported in the five progress reports, illustrative (but by no means all) sedimentological, modeling and ecological investigations are reproduced, partly or wholly, as appendices to this report as a mean of general information. Note that these studies formed a partial basis for the final development of the management recommendations, and should on no account be construed as the sole basis for the final development, in which other studies conducted within this project, as well as other projects plus experience elsewhere, were also considered.
Appendix B considers "bottom mapping" of the Jupiter Inlet/Loxahatchee River region of interest, while Appendix C discusses issues related to the littoral drift regime and sediment (sand) budget relevant to the study.
As an illustration of the basis for the development of quantitative decision matrices used as guides in evaluating the various technical issues, Appendix D is included to demonstrate the procedure by which physical model results related to various options for jetty modifications were initially examined using test data. The outcome, in the way of a decision matrix, was supplemented with other information, such as experiences elsewhere, as well as what would be practical at Jupiter Inlet, to develop the final management plan options.
In Appendix E, the manner in which one suite of mathematical models was used to examine the effects of jetty and other modifications on tides, currents and sedimentation is illustrated.
In Appendix F, an ecological assessment of the study region with reference to such factors as seagrass, mangroves, rocky outcrops and sea turtle nesting, are discussed. An attempt is made in Appendix G to propose some design criteria for sea turtle nesting beaches.
The engineering actions, per management plan, and their physical and ecological impacts are summarized in Chapter 3 next.




3. SUMMARY OF ENGINEERING ACTIONS AND THEIR PHYSICAL AND ECOLOGICAL IMPACTS
3.1 Preamble
The considered actions, including the so-called no new action option, and associated impact investigations, led to the development of a matrix which formed the rationale for making the choices for the recommended management plan. The matrix is presented in Table 3.1 (see also Fig. 2.6), and the 130 impact "boxes" in the matrix, identified by row and column numbers, are noted in what follows.
3.2 Actions and Impacts
L No New Aaion
1. Present Protocol
1. 1. Impact on Navigation Access
The present practice of trap dredging appears to be adequate to meet the requirements of
maintaining a navigation channel in the interior (Region 2). The presence of the ebb shoal restricts traffic to some extent, and the Coast Guard cautions against navigation through this inlet. However, experienced navigators familiar with the inlet have been able to well negotiate through the natural passage (in Region 3) that typically occurs between the deeper offshore waters and the jetties. Navigation depths in the aquatic
preserve (Region 3) are likely to continue to decrease, although at a very slow rate.
1.2. Impact on Navigation Safety
The frequency of accidents reported, primarily in the region offshore of the jetties, is unlikely to
reduce. In 1988 for example, five accidents, including one alcohol related were reported. Total damage was around $25,000. Note however, that according to the Coast Guard, only about 10% of the accidents
are typically reported.
1.3. Impact on Beach Erosion
The retention time of sand placed on the south beach is relatively short such that sand placed there
moves elsewhere at a rate that is faster than desired, and the public shore facilities are periodically threatened. This concern, and the concern for a breakthrough of the barrier at the point of maximum shoreline erosion remain, since this stretch of the shoreline is unlikely to build up (accrete) without a
different set of engineering actions.
1.4. Impact on Interior Sedimentation
Sedimentation problem in Region 2 is reasonably well managed, although the marinas are not well
served by the present dredging practice. They are required to finance their own dredging, because the depths at many boat slips tend to reduce and make these slips commercially useless. The problem there




Table 3.1: Considered actions and impacts.

ACTIONS

IMPACTS

z z
0 0
z z p .i
ouJ. .'Q.
0w 0
CATEGORY SUB-CATEGORY = "
I. No New Action 1. Present Protocol 1.1 1.2 1.3 1.4 1.5
2. Volumetric Rate 2.1 2.2 2.3 2.4 2.5
I. Trap Dredging 3. Frequency 3.1 3.2 3.3 3.4 3.5
14. Trap Dimensions 4.1 4.2 4.3 4.4 4.5
5. Volumetric Rate 5.1 5.2 5.3 5.4 5.5
1H. South Beach
6. Frequency 6.1 6.2 6.3 6.4 6.5
Nourishment
7. Placement Timing 7.1 7.2 7.3 7.4 7.5
18. Placement Location 8.1 8.2 8.3 8.4 8.5
IV. North Jetty 9. Height 9.1 9.2 9.3 9.4 9.5
10. Length 10.1 10.2 10.3 10.4 10.5
11. Height 11.1 11.2 11.3 11.4 11.5
V. South Jetty
12. Length 12.1 12.2 12.3 12.4 12.5
VI. Navigational 13. Lighthouse 13.1 13.2 13.3 13.4 13.5
Considerations 14. Channel Markers 14.1 14.2 14.3 14.4 14.5
15. Boat Speed 15.1 15.2 15.3 15.4 15.5
VII. Outer 16. Eastward Channel 16.1 16.2 16.3 16.4 16.5
Channel 17. Southeastward Channel 17.1 17.2 17.3 17.4 17.5
18. Volumetric Rate 18.1 18.2 18.3 18.4 18.5
VIII. Offshore 19. Frequency 19.1 19.2 19.3 19.4 19.5
Dredging 20. Location 20.1 20.2 20.3 20.4 20.5
21. Placement 21.1 21.2 21.3 21.4 21.5

IX. Interior Trap
Dredging

22. Location 23. Dimensions 24. Volumetric Rate 25. Frequency 26. Material Placement

I IJi




appears to be dual; one is their naturally unfavorable site which is prone to sedimentation. The other is that finer fractions of incoming sand continue to be transported upriver beyond the JID trap. Sedimentation in Region 3 will continue, but the present rate of influx past the FECRR bridge, about 1,000 yd3 (800 in3), possibly as high as 2,400 yd3 (1,800 in3) is considerably lower than the rate of influx about two decades
ago. In due course the depths in Region 3 may become unacceptably shallow for navigation.
1.5. Ecological Considerations
The present practices of sand disposal on the south beach require diligent transplanting of sea turtle
nests following beach nourishment. This involved about 8 nests during 1990 nourishment activities. Risks to turtles that nest in new material placed immediately south of the south jetty include the possibility of nest washout from wave reflection off the south jetty during storms. Moreover, steep erosional scarps
sometimes form just south of the jetty that may discourage some turtles from nesting.
Present practices of dredging and nourishment just south of the south beach may periodically bury
rocks that become exposed from intermittent beach erosion immediately south of the south jetty. These rocks would not be exposed were it not for the considerable erosion and they do not remain exposed long enough to develop diverse biological communities. The exposed rocks of Carlin Park and elsewhere more
than 1 km (0.6 mile) from the inlet are unlikely to be measurably affected by current practices.
The interior sedimentation now occurring may in due course increase the area suitable for
seagrasses by increasing the total area between low water and the critical depth for light penetration.
Likewise, the area suitable for mangroves may increase along interior shores that receive sediments. The proces of stabilizing interior shoals may be enhanced by planting seagrasses and mangroves on some shoals. Unfortunately, salinity and other water quality conditions may fluctuate too drastically over shoals west of the railroad bridge to allow the full development of seagrass beds. This may not be as much of a
problem for mangroves, however, which may become established despite fluctuations in water quality.
HI. Trap Dredging
2. Volumetric Rate of Dredging
2. 1. Impact on Navigation Access
A larger dredging rate (e.g. a minimum of 60,000 yd3/yr vs. 45,000 yd3/yr; or 45,900 xn3/yr vs.
34,400 m3/yr) will generally require a longer operation period for the dredging equipment. Channel access may therefore be slightly restricted for somewhat longer time periods during dredge operation. A larger rate may also imply a larger trap size (see Section 4. 1), in which case access may be improved slightly
provided uneven shoaling does not occur.




2.2. Impact on Navigation Safety
Effects are similar to those on navigation access. Larger dredging rates may reduce safety slightly if dredging equipment is required to operate mn channel for longer time periods. Associated larger trap sizes will tend to improve access.
2.3. Impact on Beach Erosion
Increases in the dredging rate itself are not expected to directly affect beach erosion. However they do imply larger nourishment rates, which would tend to decrease erosion effects (Section 5.3; also Harris, 1991). Reduction or absence of trap dredging would tend to reduce beach erosion since more sand would tend to bypass the system naturally, possibly at the expense, of course, of a navigable channel.
2.4. Impact on Interior Sedimentation
Increases in the dredging rate, particularly since they imply an increase in trap size (Section 4.4), are expected to reduce interior sedimentation, since more sand is trapped at the inlet mouth. This assumes that sand influx from the system boundaries is not changed by other actions.
2.5. Ecological Considerations
The impacts from dredging at Jupiter, Florida pertain primarily to volume of material dredged per dredging event, trap location, dredging frequency, and material disposal. The type of material removed from the trap per se is not presently an environmental issue since it consists of unstable sand of very low organic content and limited ecological production, diversity, or habitat value. Increasing the volume from, say, 43,000 yd3/y ( a mean value based on earlier years of dredging) to 60,000 yd3/y (33,000 m3/y to 46,000 m3Iy) is unlikely to create an issue involving the material being dredged as long as it continues to be unstable sand suitable for beach nourishment and is collected from within defined trap boundaries.
Death of biota from entrainment in the dredge is possible, including death of sea turtles. Increasing the volume dredged or frequency may increase the opportunity for entrainment of biota. However, since the material being dredged is itself neither biologically rich nor an attractive habitat for fragile organisms, significant entrainment may be limited to the happenstance entrainment of a few of the organisms passing through the inlet during dredging. Dredged material could be monitored to assess the significance of death through entrainment.
Increasing the volume of dredging will necessitate either more frequent dredging or greater volumes dredged per event. Larger dredges -- perhaps associated with higher volume events -- are likely to entrain more and larger biota. Furthermore, high volume-per-event dredging suspends more material in the vicinity of the dredge and creates a larger sediment plume, but does so less frequently than lower volume-per-event dredging.




Nevertheless, with high volume events, the plume of suspended sediment is more likely to reach sensitive habitat. Sediment suspended in the water reduces light penetration to submerged surfaces, such as submerged rocks and seagrass beds in the vicinity of the dredge. Light reduction may reduce primary productivity of attached algae and seagrasses for the period of dredging. Subsequent sedimentation of suspended materials may occur on the sedentary animals and plants living on submerged rock or seagrass beds that are reached by the sediment plume.
Sediment screens around the dredge should reduce any impact from sediment plumes. If sediment screens are used, impacts on seagrass beds and submerged rocks in the vicinity of the dredging are not likely to be a significant addition to the natural fluctuation of suspended sediments in the vicinity of the trap.
3. Frequency of Dredging
3. 1. Impact on Navigation Access
Increases in the trap dredging frequency (e.g. from once/two years to once/year to twice/yr to semi-continuous) will, in general, tend to improve navigational access by constantly inhibiting the growth of shoaling regions to restrictive dimensions. However, high-frequency dredging operations (i.e. semicontinuous) will also impose certain access restrictions since the dredging equipment will be in place for the majority (or the entirety) of the operational year.
Provided a cost effective fluidization system can be installed in the trap, a continuous, or "as needed" sand transfer operation can be achieved. Presently such a system is not available, but ongoing experiments may lead to a commercially available system in five or six years.
3.2. Impact on Navigation Safety
Effects are similar to those in Section 3. 1, although are expected to be only slight. Increased frequency may promote safety minimally by reducing shoaling, with the drawback of a potentially nearpermanent obstruction during semi-continuous operations.
3.3. Impact on Beach Erosion
Increasing frequency tends to reduce south beach erosion only though the nourishment process (Section 5.3). Otherwise effects are expected to be minimal. Reduction in frequency may promote more natural bypassing (at the expense of increased shoaling and reduced navigational access).
3.4. Impact on Interior Sedimentation
Although the total annual rate is more significant in reducing interior sedimentation, increased dredging fr-equency will, in general, aid in this process by providing a buffer against longer term variability in shoaling rates.




3.5. Ecological Considerations
The fr-equency, intensity, and style of dredging are inter-related. Ecological impacts relate primarily to the volume of material dredged per event as outlined in Section 2.5. Infrequent dredging will necessarily involve more volume per event. This may require longer event durations and heavier equipment. At the other extreme, nearly continuous dredging requires a sand pump and fluidizer bed, but the disturbance and volumes moved at any one time are much lower. Continuous sand pumping will likely minimize local ecological impact. Unlike intermittent dredging, continuous pumping does not cause a sudden perturbation of the area that requires a period of recovery. Moreover, entrairnent of passing biota is unlikely in a sand fluidizer system and sediment plumes at the dredging site may be all but eliminated if fluidized sand is pumped out from below.
4. Trap Dimensions
4. 1. Impact on Navigation Access
.Two trap sizes are proposed: 1) a length of approximately 1,020 ft (310 m) and width of roughly 220 ft (65 in); or 2) a larger trap with a length extension of 1, 120 ft (340 m) and a width of 270 ft (80 in). Access will in general be improved with the larger trap since deeper conditions will prevail for a longer time period. Although the projected filling rates are estimated to be 20 % higher than existing conditions for the larger trap, but only 5 % higher than existing for the smaller trap, this difference is accounted for by the trap size.
4.2. Impact on Navigation Safety
Effects are similar to those on navigation access. A larger trap with deeper conditions will tend to reduce shoaling and improve safety, although this is not likely to be a major effect.
4.3. Impact on Beach Erosion
Increased trap size implies a larger nourishment rate (Section 5.3) which will tend to reduce erosion. Aside from this, the trap size will have little direct effect on beach erosion.
4.4. Impact on Interior Sedimentation
An increase in trap size will, in general trap more sand at the inlet mouth and thus reduce interior sedimentation. Sediment modelling simulations indicate that the larger trap configuration will reduce the net sediment flux past the FECRR bridge by around 23 % over existing bathymetry. The smaller trap size will only reduce the net flux by around 4 %.




4.5. Ecological Considerations
Increasing the trap dimensions is expected to have little impact by itself. This assumes that the type
of material within the new dimensions is unstable sand, suitable for beach nourishment, that no rock must be removed by blasting to achieve these dimensions, and that the tidal prism does not change after dredging
the larger trap.
The tidal prism controls such aspects as water level, tidal range, current, and salt transport.
Changes in the tidal prism may cause changes in intertidal and submerged vegetation, and in salt transport up the northwest fork of the Loxahatchee River. Results of the hydrodynamic model constructed as part of this study indicate no measurable impact of the present or proposed trap dimensions on salinity intrusion
or tidal flows to the limits of the model boundaries.
At present the bottom in the western part of the trap is underlain by hard rock, which will have
to be removed by way of capital dredging, a one-time operation lasting perhaps a few days. This removal
in itself should create no significant ecological impacts.
III. South Beach Nourishment
5. Volumetric Rate of Nourishment
5. 1. Impact on Navigation Access
The rate of annual sand placement on the south beach is not expected to Fignificantly affect
navigational access if considerations involving timing and location are observed (Sections 7.1, 8. 1).
Placement of large amounts of sand close to the south jetty may result in substantial sediment flux into the inlet as observed in tracer and drogue studies. Placement of sand under or prior to storm conditions may
cause large initial profile adjustment with potential shoaling of the outer channel.
5.2. Impact on Navigation Safety
In the same manner as the discussion on navigational access, the rate of annual sand placement
on the south beach is not expected to significantly affect navigational safety if considerations involving
timing and location are observed (Sections 7.2, 8.2).
5.3. Impact on Beach Erosion
Erosion of the south beach is crucially dependent on the rate of beach nourishment. In general,
larger nourishment rates will reduce beach erosion (subject of course to the availability of sand to be dredged, which may be altered by other actions such a jetty modifications). For example, a nourishment rate of 45,000 yd3/yr (34,400 m3/yr) has be shown to not offset the persistent sediment deficit and to generally permit critical levels of erosion to occur. A minimum rate of 60,000 yd3/yr (46,000 m3/yr) has been shown to make up the deficit and simulations indicate this rate will also provide an effective buffer




against natural variability in the transport rates. Coordination of nourishment from the Army Corps of Engineers trap with material dredged from the JID trap will expedite the attainment of this larger rate.
5.4. Impact on Interior Sedimentation
Effects of the nourishment rate on interior sedimentation are expected to be minimal provided considerations of timing and location are observed (Sections 7.4, 8.4) in order to prevent conditions which promote a large influx of material into the inlet channel.
5.5. Ecological Considerations
An increase in nourishment volume, say from 43,000 yd3/y to 60,000 yd3/y (33,000 m3/y to 46,000 m3Iy), would enhance the slope and stability of the beach profile for sea turtle nesting and for ecological communities of nearby beaches and dunes. Assuming all of this material can be placed sufficiently north of the nearshore rocky outcroppings at Carlin Park, impact of this added sand to rocky outcroppings should be low, unless storms redistribute some of this sand over these rocks (see Section 7.5).
6. Frequency of Nourishment
6. 1. Impact on Navigational Access
No significant effects are expected provided considerations of timing and location are observed (Sections 7. 1 and 8. 1), particularly for the case of near-continuous bypassing, if and when this protocol is undertaken.
6.2. Impact on Navigational Safety
No significant effects are expected provided considerations of timing and location are observed (Sections 7.2 and 8.2), particularly for the case of near-continuous bypassing, if and when this protocol is undertaken.
6.3. Impact on Beach Erosion
The effect of nourishment frequency on beach erosion is connected with the issue of nourishment timing and is particularly significant in the context of the natural variability in the longshore transport. Highly infrequent nourishment (i.e. once/two years) exposes the beach to greater risk of possible successive large transport years with subsequently greater erosion. Increasing the frequency of dredging reduces such risk. Semi-continuous dredging minimizes such risk, and also affords the flexibility of modifying bypassing rates to accommodate the natural variability in the transport conditions.
Although the Corps' dredging and sand pumping operations are independent of those of JID, coordination between the two dredging operations so as to actually effect a twice per year pumping needs to be considered. Given the May-October non-pumping window during peak sea turtle nesting season,




pumping by JID in April (around the usual time chosen by JID in the past) and Corps in November (often the time chosen by the Corps in the past) has potential advantages for retention of the beach sand. Firstly, pumping sand by JID and the Corps at the same time, e.g. in April, may amount to rapid rate of erosion of excessively placed sand at one time. Secondly, Corps pumping in November would serve as a feeder beach, supplying sand to the areas further south without the high risk of re-transport of sand into the inlet, since the wave then are from the northeast.
6.4. Impact on Interior Sedimentation
Effects of the nourishment frequency on interior sedimentation are expected to be minimal provided considerations of timing and location are observed (Sections 7.4, 8.4) to prevent a large influx of material into the inlet channel, particularly for the case of near-continuous bypassing.
6.5. Ecological Considerations
As with dredging (Section 2.5), nourishment events of lower frequency will usually involve more volume per event, a greater perturbation of the beach, larger sediment plumes, and longer ecological recovery time. One or two events per year might have less impact than one event every two years, though many of the benefits of increasing nourishment frequency probably don't accrue until nearly-continuous or at least twice per year sand pumping is achieved. Nearly-continuous sand pumping involves much smaller disturbances and volumes moved at any one time. Such pumping will liely minimize local ecological impact.
It is unclear how nesting sea turtles will respond to continuous sand pumping, however. If the effects of piping sand to the beach are subtle (sound is within background frequencies and amplitudes, turbidity plumes are within background turbidities), impact on sea turtle behavior may be negligible. Careful monitoring of sea turtle reactions may be required, but the ecological benefits of sand pumping in providing stable, suitable beach profiles for nesting may offset any small effects of pumping activities during the nesting season. It may be necessary to turn off continuous pumping during the peak egg-laying season (May through August). Even so, continuous pumping may be advantageous for appropriate beach profiling prior to the nesting season.
7. Placement Timing
7. 1. Impact on Navigation Access
Placement of large quantities of sand on the beach near the south jetty during or just prior to periods of large northerly transport may result in significant amounts of sediment flux into the entrance channel. Similarly, placement of large amounts of sand during or just prior to major storm events may result in large amounts of erosion or large scale profile adjustment with potential shifts in the offshore channel as well.




7.2. Impact on Navigation Safety
Effects are similar to those on navigational access. Safety may be impacted by entrance shoaling due to sediment influx following placement during intense northerly transport (particularly near southjetty), or by offshore channel shifting due to sediment placement during or before storm events.
7.3. Impact on Beach Erosion
Timing of nourishment significantly effects shoreline evolution, and is mitigated by the turtle nesting window (May through October) during which placement of dredged material on the south beach is not permitted. Placement after the window will subject the nourished material immediately to winter storms with subsequent large-scale profile adjustment, and has been shown to result in small summer beach volumes. Nourishment prior to the window is seen to result in large summer beach volumes; winter storms then act on a beach which has already achieved a large degree of profile equilibrium and less erosion would then tend to occur.
A possibility exists for selecting two rather than a single sand placement time. Two choices include pre-May (e.g. April) and post-October (e.g. November) periods. While sand placed during the latter period will in general have a lower retention time than the former, a more continuous, and therefore more desirable, sand pumping protocol would be established. In consonance with past practices, the JID trap would be utilized in April, and the Corps trap in November. In this way, there would be a lower pile up of sand on the beach; hence lesser amount would be transported into the inlet following the April placement. The November placement would serve as a feeder beach for the beaches further south of the inlet. Due to the direction of wave action, this sand would not typically move into the inlet.
7.4. Impact on Interior Sedimentation
Timing effects are significant to interior sedimentation if large amounts of material are placed near the southjetty during summer conditions with northerly transport. Field studies have shown that substantial amounts of sediment can enter the inlet under such conditions, and may aggravate interior shoaling. Similar effects may occur if sand is placed near the southjetty during intense wave conditions which suspend large amounts of sand. Two placements per year, e.g. in April and in November, could reduce the influx of sediment as noted in Section 7.3.
7.5. Ecological Considerations
The main ecological consideration in the timing of beach nourishment is the sea turtle nesting season. A stable and gentle beach profile is needed prior to and throughout the nesting season. Furthermore, disturbance from nourishment activities must be minimized during the season. Peak egglaying activity is from May through August, but earlier and later activity by some individuals is common. Eggs require roughly 2 months to hatch. To account for these factors, the U.S. Fish and Wildlife Service




includes the period from March 1 through November 30 as the sea turtle nesting season in the vicinity of Jupiter Inlet.
8. Placement Location
8. 1. Impact on Navigation Access
Options for locations of placed material include 1) immediately south of the south jetty, 2) roughly 1/4 mile (0.4 m) south of the south jetty, and 3) at multiple points spanning the above distance and extending downcoast. Navigational access will tend to be impacted most severely by placement close to the south jetty, particularly if the timing is such that conditions are most conducive for "leakage" of sand into the channel. If a continuous system is employed, monitoring of wave climate and transport to identify such conditions is essential to avoid the wasted effort of pumping sand which will tend to immediately re-enter the inlet. Dispersed placement may also impact outer channel access to a lesser degree, since less profile disequilibrium will exist and smaller initial fluctuations would be expected.
8.2. Impact on Navigation Safety
Effects are similar to those for navigational access. Safety may be impacted by channel shoaling resulting from placement of sand close to the south jetty. Concentrated placements of sand will cause a high degree of profile disequilibrium and initial shifting, with potential impact on the outer channel.
8.3. Impact on Beach Erosion
Placement of sand close to the south jetty in conjunction with summer transport conditions (i.e. placement prior to the turtle nesting window) will tend to increase beach erosion, since the sand is typically lost into the inlet channel. Placement further downcoast, although apparently "sacrificing" the beach immediately south of the jetty, will, in the case of pre-window timing, tend to reduce beach erosion since the sand replenishes the exposed sections of beach upon adjustment. A 10% increase in the retention time of placed sand may be achieved by a proper redesign of the presently followed placement plan. This placement configuration should not, however be considered with post-window timing since the winter storm conditions would tend to most severely impact the unprotected beach immediately south of the jetty, resulting in critical erosion. Thus if the Corps is encouraged to place its material in November, that material should be placed within the first around 800 ft (240 m) of the south jetty, in accordance with the present practice.
In general, spatially and temporally more dispersed placement than at present will tend to reduce erosion effects over concentrated placement, since initial profile adjustment losses will be minimized.




8.4. Impact on Interior Sedimentation
Interior sedimentation will tend to be increased by scenarios which involve placement of sand close to the south jetty. This is particularly true for continuous bypassing systems, in which failure to monitor wave conditions to identify circumstances which encourage sediment influx (i.e. northward transport) will tend to increase interior shoaling. Nourishment further downdrift will tend to inhibit dredged sand reentering the inlet. Dispersed placement will also reduce this influx by reducing initial profile shifts, although this effect will be minimal for placement at any substantial distance from the south jetty.
8.5. Ecological Considerations
Beach Profile: From the standpoint of sea turtle nesting, the nearshore and onshore beach profile should be maintained with a slope similar to that of nearby unimpacted areas where sea turtles nest. This is roughly 1 unit of rise for every 10 to 20 units of run in the zone from mean sea level to 100 ft (30 m) toward land. Placement of material within these limits prior to the nesting season will enhance the beach as a sea turtle nesting area if neither the profile changes (develops steep scarps) nor the beach erodes during the nesting period.
Placing the material close to the swash zone at several points along the beach (rather than high on the beach at only one point) uses more of the natural surf energy rather than heavy machinery to distribute the sand along the beach. This may improve the development of a natural beach profile composed of natural sand-grain sizes. By reducing the need for heavy sand-moving and tilling equipment on the beach, this approach should also minimize the disturbance to the ecological community of the intertidal beach, including sea turtle nests, should any have been laid prior to nourishment.
Longshore Placement: Naturally, from the standpoint of offsetting beach erosion, placing beach nourishment material just south of the south jetty is logical. After nourishment, however, wave refraction, diffraction and reflection off the south jetty may rapidly alter the post-nourishment beach profile and cause sudden sand erosion. Since beach nourishment can make the profile attractive to nesting sea turtles, the beach immediately south of the south jetty (approximately the first tenth of a mile or 160 m) may become an "attractive nuisance" for nesting sea turtles. Nests laid in this area may wash out before they hatch. Nests laid here should be relocated or the area should be effectively fenced to keep sea turtles from nesting in this short stretch of beach. The construction of a "dog-leg" or "hooked" extension of the south jetty may obviate some of this concern, however (see Section 12.5).
Nearshore rocky outcroppings appear at Carlin Park, 3/4 mile (1.2 kin) to the south of Jupiter Inlet. To protect these rocks, beach nourishment material should be placed between the south jetty and sufficiently north of the rocks to avoid directly covering them with sediment from nourishment operations. If the amount of material placed is greatest nearer the south jetty, and tapers off toward the Carlin Park rocks, impact on these rocks should be minimized to near zero. However, it is always possible that a storm may shift sand over these rocks at some future date, a recurring natural process.




IV. North Jetty
9. Height of North Jetty
9. 1. Impact on Navigation Access
The seaward end of the concrete-capped north jetty has a step-like structure; section I, the
seaward-most, 275 ft (84 m) long section has an elevation of 6.9 ft (2.1 m) with respect to NGVD. The next landward segment, section II is 175 ft (53 m) long and is 2 ft (0.6 mn) higher. Landward of section II is the remainder of the jetty, section III, which is 2 ft (0.6 m) higher than section 11. This jetty has served well in maintaining navigational access to the inlet, but during times of storm surge water and sand are transported over the jetty, particularly sections I and 11, which causes sedimentation in the inlet interior.
Raising these two sections would mitigate this problem. For example, in accordance with test results from the physical model study, section I may be raised by 3 ft (0.9 m) and the effect monitored. Further, section II may be raised by 3 ft (0.9 mn) as well. These modifications are however not likely to impact navigational
access.
9.2. Impact on Navigation Safety
Raising sections of the north jetty will not measurably impact safety of navigation since navigation
through this inlet is feasible only under non-extreme conditions.
9.3. Impact on Beach Erosion
Raising sections of the north jetty may have a beneficial effect with respect to beach erosion on
the south side, as sand bypassing may increase during storm conditions.
9.4. Impact on Interior Sedimentation
The purpose of raising section of the north jetty is to reduce sand influx. The very roughly
estimated 3 % reduction by raising section I and an additional 5 % by raising section II would amount to a reduction on the order of 5,000 yd3 (3,800 mn3) per year. This number is believed to be conservative and the actual saving may be higher. Such a reduction would have two advantages: 1) it would mean a reduction in the cost of dredging of the JID trap (as well as the Corps of Engineers trap), and 2) it would reduce the problem of sedimentation in the marina area, which is presently estimated to be on the order
of 0.5 ft (0. 15 m) per year.
9.5. Ecological Considerations
Increasing the height of the north jetty by 3 ft (0.9 mn) could have positive ecological benefits if
by blocking sand entry to the inlet during periods of higher water, sand bypassing actually increases.
Greater sand bypassing would reduce the volume of dredging necessary inside the inlet and would reduce the necessity to actively nourish the beach. If, however, the effect of blocking the sand during higher water




levels is simply to build the ebb shoal, dredging will still be required to replace eroded sand along the south beach. If such is the case, the environmental impact on the south beach will be the same as without the increased jetty height, and some of the dredging impact may simply be shifted from the existing traps inside the inlet to the ebb shoal or elsewhere (perhaps to an area where impacts have not yet been evaluated).
10. Length of North Jetty
10. 1. Impact on Navigation Access
Physical model study results indicate that the possibilities of extending the north jetty are along a curvature in the southeastern direction. The purpose of such an extension would be, firstly to improve navigation by increasing the sheltering effect of the jetty against wave action, and secondly to reduce sediment influx into the inlet by improving bypassing around the inlet. Model results suggest that for the sheltering effect to be effective in the channel, the jetty extension would have to be well in excess of 200 ft (61 in). A 400 ft (122 m) extension would materially improve navigational accessibility. The likely amount of reduction of sand influx, if at all in the long run, is uncertain.
10.2. Impact on Navigation Safety
Extending the north jetty along a southeastward curvature by 400 ft (122 in), would be expected to impact navigational safety in a positive manner by measurably reducing the wave heights in the channel to less than one-half the present.
10.3. Impact on Beach Erosion
Extending the north jetty is likely to increase downdrift beach erosion adjacent to the south jetty by creating a *sand shadow", in spite of the fact that: 1) model results indicate an extension would increase the sheltering of the area immediately south of the south jetty, and 2) calculations suggest that there may be a slight (but perhaps statistically insignificant) reduction in sand influx into the inlet. The reason for the possibility of increased erosion immediately south of the south jetty is that north jetty extension would cause the littoral sand pathway to be diverted seaward, the extent of diversion being dependent on the length of the curved, southeastward extension of the jetty.
A length of extension greater than 50 ft (15 mn) may result in a measurable increase in erosion. For a 400 ft (122 m) extension for example, the deficit of sand on the south beach, presently estimated to be on the order of 0.24x106 yd3 (0. 18xl06 mn3), could increase to as much as 0.9x106 yd3 (0.69x106 mn3). Since however the fraction of the net littoral sand transported into the inlet per unit time may also decrease (certainly not increase), this added erosion may pose a sand management problem. At Boca Raton Inlet for example, ebb shoal dredging has been carried out to mitigate increased downdrift beach erosion caused by a 180 ft (55 mn) extension of the north jetty.




Given this possibility, caution is warranted in any plan to lengthen the north jetty without additional measures including the installation of a sand bypassing system for transferring sand on as needed basis. Such a system could include a fixed bypassing plant such as at Palm Beach inlet (however one with an improved mechanical and aesthetic design and efficiency), or a fluidization system. A system of the latter type is currently being tested at Oceanside Harbor in California. The technical viability of this system, proven theoretically and in laboratory experiments, remains to be checked thoroughly in the field. Even if proven in the field, a commercially available system is unlikely to be available over the next onehalf decade.
10.4. Impact on Interior Sedimentation
Calculations suggest that, a 400 ft (122 in) extension on the north jetty would initially reduce the influx of sand in the inlet by about 25 %. It is unclear if this advantage would be retained however, after the shoreline north of the north jetty eventually achieves a new equilibrium configuration. Experience elsewhere suggests that in fact the eventual reduction in sand influx, in the absence of any active bypassing system, may not be significant.
10.5. Ecological Considerations
Although a safer navigation channel will result and some sand may be prevented from entering the inlet (obviating some dredging), increasing the length of the north jetty by any amount in excess of 50 ft (15 in) will measurably exacerbate the beach erosion south of the south jetty, even if natural sand bypassing is improved by this jetty modification. Longer jetties will send by-passed sand further to the south before it comes ashore to build beaches. Calculations suggest that the point where the sand pathway reattaches itself to the shore would move southward such that the distance between the southjetty and the reattachment point would increase by about 25 % over the present for a 400 ft (122 in) extension. Hence, maintenance of the south beach near the south jetty will require more movement of sand by continuous pumping or heavy machinery. The impacts of beach nourishment have been covered in Sections 5.5, 6.5,
7.5, and 8.5.
As noted, longer extensions of the north jetty will push bypassed sand even further south and lengthen the eroding zone south of the south jetty. A 400 ft (122 in) extension of the north jetty could perhaps cause bypassed sand to cover the rocky outcroppings at Carlin Park 3/4 mile (1.2 kin) to the south.
On the positive side, however, jetty extensions will provide some additional rocky substrate for the development of habitat similar to that provided by natural nearshore rocky outcroppings in the area. Presently many fishes and invertebrates use the rocks of the existing jetties as habitat. Additional habitat will likely result in additional use at Jupiter Wet. The positive aspects of these additions, however, would accrue to the placement of many kinds of artificial reef structures offshore of Jupiter Inlet without the concomitant negative effects of beach erosion.




Another important consideration ofjetty extension in general is the potential for impact on the tidal
prism. The tidal prism controls such things as water level, tidal range, current, and salt transport. Changes in the tidal prism may cause changes in the location and productivity of intertidal and submerged vegetation, and changes in salt transport up the northwest fork of the Loxahatchee River. Results of the hydrodynamic model constructed as part of this study however indicate no measurable impact of considered
jetty extensions on salinity intrusion or tidal flows to the limits of the model boundaries.
V. South Jetty
11. Height of South Jetty
11. 1. Impact on Navigation Access
Raising the height of the south jetty, presently 5.5 ft (1.5 m) high with respect to NGVD, e.g. by
3 ft (0.9 m) as suggested by the physical model study, will not materially affect navigational access.
11.2. Impact on Navigation Safety
Raising the height of the south jetty, e.g. by 3 ft (0.9 in), will not measurably influence
navigational safety.
11.3. Impact on Beach Erosion
Raising the height of the south jetty, e.g. by 3 ft (0.9 in), could somewhat reduce beach erosion
immediately south of the jetty, as this would reduce the transport of sand over the jetty during significant storms. Field evidence however suggests that the transport of sand around the jetty which occurs over each flood tide is not insignificant, and that this transport around may be a greater contributor to beach erosion than transport over the jetty during storms. Via this mechanism the erosion is believed to be particularly significant when material dredged from the interior areas is placed on the south beach. Given these conditions, the efficacy of reducing beach erosion by sand transport into the interior by raising the jetty is likely to decrease rapidly with increasing height, and the added benefit of raising the jetty to a height greater than 3 ft (0.9 m) may be negligible. At this height, sand influx may reduce by about 2,000 yd3
(1,500 in3). This estimate is conservative and the actual reduction may be higher.
11.4. Impact on Interior Sedimentation
Comments made under Section 11.3 also hold in this case, namely that raising the south jetty by
any height greater than e.g. 3 ft (0.9 m) may not measurably reduce the rate of interior sedimentation
further.




11.5. Ecological Considerations
Increasing the height of the south jetty will have much the same ecological impact as increasing the height of the north jetty (see Section 9.5). By achieving its intended purpose of preventing overtopping of sand during periods of very high water, less trap dredging and beach nourishment may be required. Greater height, however, may increase wave reflection during periods of simultaneously very high water and high winds from the southeast. This may cause increased scour of the beach just south of the south jetty, thus exacerbating the present problem of unstable beach profiles just to the south of the south jetty during the sea turtle nesting season (see Section 7.5). Perhaps by using a gentle angle for the south sidewall of the jetty e.g. by riprap placement, this problem could be somewhat reduced.
12. Length of South Jetty
12. 1. Impact on Navigation Access
Lengthening the south jetty, optimally by a 175 ft (53 mn) *hooked" extension, and coupled with a 3 ft (0.9 m) rise is not expected to measurably alter navigational access, as long as this extension is either linear along the direction of the existing jetty, or in the southeastern "hooked" direction.
12.2. Impact on Navigation Safety
Lengthening the south jetty as noted in Section 12. 1 is not likely to alter the present level of navigational safety.
12.3. Impact on Beach Erosion
Model results and related considerations suggest that, for example, up to 175 ft (53 m) extension of the south jetty as a southeastward dog-leg or hook would reduce erosion immediately south of the south jetty by enhancing the region sheltered against wave action, and by reducing the (sand-laden) water movement around the modified jetty, and promote retention of beach sand. Extensions greater than this length on the other may interrupt the littoral sand pathway which would diminish the overall beneficial effect of extension as noted, although experience at Baker's Haulover Inlet, where however the drift is much smaller, suggests that at appropriate locations considerably longer south jetty extensions can be very effective in retaining sand. In Fig. 2.2 the approximate position of the shoreline that would exist in the absence of the inlet is shown. Note that the north jetty protrudes much more into the ocean than the south jetty relative to the no-inlet shoreline. Thus as long as the south jetty remains "shorter" than the north jetty, the latter will predominantly determine the erosion deficit and shoreline orientation of the south beach by way of its "shadow" effect when the beach-eroding waves occur from the northeast.




12.4. Impact on Interior Sedimentation
By virtue of the type of beneficial extensions of the south jetty noted in Section 12.3, the same
extensions would reduce sand influx into the inlet. The required annual dredging of the sand trap with a
raised and extended south jetty could reduce by up to 10,000 yd3 (7,700 in3).
12.5. Ecological Considerations
Unlike lengthening the north jetty (see Section 10.5), lengthening the south jetty by 175 ft (53 mn)
should have overall positive ecological effects if these modifications achieve their intended purposes of reducing beach erosion and reducing sand flow into the inlet from the south. These benefits accrue from the more stable beach profile that should result just south of the south jetty, the reduced necessity for dredging traps inside the inlet, and the reduced need for beach nourishment. The impacts from dredging are covered in Sections 2.5, 3.5, and 4.5. The impacts of beach nourishment have been covered in Sections 5.5, 6.5, 7.5, and 8.5. The value to nesting turtles of stable beach profiles immediately south of the south jetty have been covered in Section 8.5. In addition, as with the north jetty extension, extension of the south
jetty will provide more substrate for ecological development of rocky habitat.
Impact from the suggested south jetty modifications on existing rocky outcroppings or ecological
productivity and diversity in the Loxahatchee River is unlikely. Results of the hydrodynamic model constructed as part of this study indicate no measurable impact (less than 0.5 ppt change in either direction)
of proposed jetty extensions on salinity intrusion or tidal flows to the limits of the model boundaries.
I. Navigational Considerations
13. Lighthouse and Jetty Beacons
13. 1. Impact on Navigation Access
The lighthouse (Fig. 2.4), although not managed by JID, occurs within the study area and serves
to identify Jupiter from offshore. While it alone can not be used for navigation in the inlet area, its role
to identify Jupiter Inlet as a navigational access is evident.
Addition of two beacons,on eat each tip of the jetties, in accordance with Coast Guard
specifications, would improve navigation access (siting). See also Section 14. 1.
13.2. Impact on Navigation Safety
The lighthouse is not a means to ensure navigational safety, which must be considered by other
means. Beacons at jetty tips may not measurably improve navigation safety however, since a fair number
of accidents appear to be occurring offshore of the jetties. See also Section 14.2.
13.3. Impact on Beach Erosion
The lighthouse has no tangible bearing on the problem of beach erosion. Same for beacons.




13.4. Impact on Interior Sedimentation
The lighthouse has no tangible impact on sedimentation in the interior region of the inlet. Same for beacons.
13.5. Ecological Considerations
Operation of the lighthouse has no known local ecological impact; however, somewhat wild speculation may include a possible effect on navigation by migrating animals into and out of the inlet. It is unknown how most migratory animals in the sea navigate. Sea turtles, for example, probably recognize beaches by their features, and they and other organisms may detect dissolved materials emanating from inlets. It is known that sea turtles can be discouraged by lights turning on and off directly on the beach as they come ashore to lay eggs. On the other hand, it is possible that sea turtles and other organisms (perhaps manatees) have come to recognize the coast of Florida from far offshore just as vessels do -- by noticing the pattern of lights at night along the coast. Failure to operate the Jupiter light may require a period of adjustment by sea turtles and other migratory animals that can detect the light.
Beacons on the jetties could conceivably disorient a small number of both adult and hatching sea turtles that appear very near to the jetties. If lights are installed with appropriate consideration of the Florida Department of Natural Resources Sea Turtle Protection Plan guidelines for permanent lighting, this effect should be negligibly small and permissible.
14. Channel Markers
14. 1. Impact on Navigation Access
At present all channel markers occur well within the inlet; there are no markers either at the seaward end of the inlet or in the offshore area. Note that this inlet has been designated by the Coast Guard to be hazardous to navigation. Therefore, any changes in the existing arrangement will to some extent be the management responsibility of JID. As noted in Section 13. 1, If changes must be made, then it appears that marking the tips of the two jetties by beacons (one at each jetty) will be useful to navigators as identifiers of Jupiter Inlet. 'Me beacons, per Coast Guard specifications, should be operated on a regular basis; they should not be programmed to operate as indicators of entrance accessibility, e.g. as related to weather and sea conditions.
14.2. Impact on Navigation Safety
Addition of beacons as entrance markers will not materially alter the present degree of navigational safety in the inlet area.
14.3. Impact on Beach Erosion
There is no tangible correlation between the installation of channel markers and beach erosion.




14.4. Impact on Interior Sedimentation
There is no tangible correlation between channel markers and the rate of sedimentation in the interior areas.
14.5. Ecological Considerations
The placement of simple markers to identify the channel should have minimal ecological impact. If the markers include anti-fouling treatments, a small associated impact can be expected on sensitive organisms, however this would be a minuscule addition to the total surface area covered by anti-fouling paints in the vicinity of Jupiter Inlet. Markers without anti-fouling treatments will add to the substrate for rocky-shore ecological communities, but again this would be a tiny additional effect.
15. Boat Speed
15. 1. Impact on Navigation Access
The issue of boat speed regulation is not directly associated with access to navigation.
15.2. Impact on Navigation Safety
Regulation of boat speeds is obviously linked to navigational safety. Regulation of boat speed especially in the seaward area of the inlet is unquestionably important to improvement of safety.
15.3. Impact on Beach Erosion
There is no significant association between boat speed and beach erosion at this inlet. However, wakes from boats are known to increase damage to poorly designed bulkheads and cause localized beach erosion. This issue was examined in the study by the University of Florida in 1984 (Buckingham, 1984). Bulkheads west of the Jupiter Inlet Colony club house as well as the Dubois Park beach are vulnerable to boat wakes. In addition, boat wakes are believed to cause bank erosion, e.g. in the vicinity of the lighthouse.
15.4. Impact on Interior Sedimentation
The role of boats in causing bank erosion has been established in this study in an indirect way. Regulating boat speed in the interior waters is considered to be important for example in reducing navigable depths the wider region of the Loxahatchee River estuary west of FECRR bridge (Region 3).
15.5. Ecological Considerations
Reducing boat speeds would have positive benefits to the manatees that use the inlet as a passageway. Throughout coastal Florida, many manatees are killed or injured by boats each year. It is possible that other organisms also are harmed by fast-moving boats, including sea turtles. By reducing boat




speeds through the inlet, the potential for such injuries and deaths in Jupiter Inlet will be reduced. Idle
speeds would be best, though any reduction in boat speed would have some positive effect.
Vii. Outer Channel
16. Eastward Channel
16. 1. Impact on Navigation Access
The 10 ft (3 m) deep eastward outer channel through the ebb shoal (Fig. 3. 1) should enable better
navigational access to vessels that require this much minimum depth and direction of passage. At Jupiter Inlet even the largest vessels presently plying the waters do not require such a deep channel, except where the ebb shoal restricts navigation, particularly during lower stages of tide. In such cases this channel will open up a new passage between the ocean and the inlet. The utility of such a channel will also depend on
the future traffic growth including vessel draft.
16.2. Impact on Navigation Safety
The eastward channel should improve the navigational safety of vessels presently negotiating the
inlet and expectedly reduce the chances of accidents which reportedly occur due to shallow depths over the
ebb shoal.
16.3. Impact on Beach Erosion
Dredging of the eastward outer channel should be on the order of 20,000 y&3 to 40,000 yd3
(15,300 m:3 to 30,600 in3) from the shallow portions of the channel. Maintenance dredging frequency is likely to be high; with dredging once a year in spring (e.g. in April or May), the channel may maintain itself through summer, but will undoubtedly fill up during the fall and winter months. The rate of infilling could be higher that of a southeastward outer channel. Dredging of the ebb shoal for this purpose will interrupt the littoral drift to some extent. Regular dredging (e.g. every April or May) and placement of the dredged material on the downdrift beach is a feasible option for maintaining fair weather (summer) access but the consequences of this operation to beach stability must be monitored, and the plan to maintain this channel discontinued if adverse effects with respect to shoreline stability are reported. The channel is not likely to increase wave action at the beach in any drastic way, and the net sand loss may not occur on an
annual basis, unless for example dredging is also carried out during fall or winter.
16.4. Impact on Interior Sedimentation
The eastward outer channel is not likely to impact sedimentation in the interior of the inlet in any
measurable way.




Figure 3. 1. Inlet ebb shoal and offshore channel options.
51




16.5. Ecological Considerations
An eastward channel through the ebb shoal area should have minimal impact on nearshore rocky outcroppings, and sea turtle nesting, assuming initial and maintenance dredging do not occur during the turtle nesting season. If the channel affects the tidal prism, salinity intrusion and the ecological production and diversity of submerged and intertidal ecosystems in the Loxahatchee River estuary may be affected. However, channel dredging through the ebb shoal outside the inlet jetties is unlikely to measurably impact the tidal prism.
The process of dredging and maintaining such a channel will have the impacts of dredging and placement of material in proportion to the amount of dredging required. These impacts have been described in the relevant sections of this report.
17. Southeastward Channel
17. 1. Impact on Navigation Access
A 10 ft (3 m) deep outer southeastward channel (Fig. 3. 1) will not provide a new access route to the inlet as it is designed to be along the orientation of the present access. Dredging will be necessary only in certain portions where the littoral sand attempts to cross the channel. Dredging this access should not disturb the wreckage of an ancient vessel which is believed to be strewn along a path which is close to this channel.
17.2. Impact on Navigation Safety
Dredging out those areas (ebb shoal) where shoaling normally occurs should improve navigational safety, but the improvement may not be as significant as that at the eastward channel, since along most of the southeastward channel length the depths are adequate for navigation for presently negotiating vessels.
17.3. Impact on Beach Erosion
Capital dredging is likely to be around 30,000 yd3 (23,000 m3). This amount could be greater than that for the eastward channel. It is important to note, however, that the mass of sediment to be dredged is less unevenly distributed in the southeastward channel than in the eastward channel; in the latter case the smaller amount is concentrated over a smaller area and hence technically provides a greater barrier to navigation than in the case of the southeastward channel. As in the case of the eastward channel noted in Section 16.3, a summer channel can be maintained by dredging every April or May. The presence of this channel is not likely to alter wave action at along the affected beach south of the inlet, but the infilling rate of the channel may not be less than that of the eastward channel; hence no advantage may be gained during the fall and winter months. The presence of the channel coupled with regular dredging and placement of the dredged material on the south beach will increase shoreline oscillations but may not result in a net erosion on an annual basis, unless dredging is also carried out in fall or winter.




17.4. Impact on Interior Sedimentation
The southeastward channel is not likely to impact sedimentation in the interior of the inlet in any
measurable way.
17.5. Ecological Considerations
While no channel would have the least ecological impact, because a southeastward channel will
follow a natural flow pattern, it may require significantly less initial and maintenance dredging than an eastern channel, even though calculations do not point to any significant reductions. As with an eastward channel (see Section 16.5), a southeastward channel is not expected to measurably alter the tidal prism,
and hence should not impact the ecological production and diversity in the interior of the estuary.
VII Offshore Dredging
18. Volumetric Rate of Dredging
18. 1. Impact on Navigation Access
Sediment budget calculations suggest that the presence of the inlet results in some "loss" of sand
in the sense that the net volume of sand moving southward as littoral drift on the annual basis is reduced as this sand bypasses the inlet. About 7,000 yd3 (5,400 in3) are not trapped by JID borrow area or the Corps of Engineers borrow area. A very approximate estimate suggests that about the same amount moves offshore. The latter amount may actually fluctuate from -7000 yd3 (-5,400 mn3), i.e. a net onshore transport from the ebb shoal area or elsewhere, to perhaps as much as 2 1,000 yd3 (16, 100 mn3). On a long term basis (e.g. decadal) the total annual loss is thus estimated to be 1,4000 yd3 (10,700 mn3). This amount represents
an annual loss of sand equity to the beach south of the inlet.
Given the evidence which possibly suggests that the offshore bathymetry undergoes a decadal
oscillation in the sand volume, as well as considering the cost of dredging, a practical approach would require that around 140,000 to 150,000 yd3 (108,000 to 115,000 in3) be dredged from the offshore to account for 100% sand bypassing requirement by JID. Dredging of this amount of sand should be carried out after identifying a suitable site which does not cause a measurable interruption of the littoral flow of
sand, or is potentially harmful to the nearby beaches.
Note that an eastward channel corresponding to this sand volume would have to be about 250 ft
wide by 22 ft deep (76 rn x 6.7 in), which is too large to be justified for navigational needs, and is likely to pose a high risk as far as its impact on the beach south of the inlet is concerned. Therefore the required 150,000 yd3 (115,000 in3) should not be dredged from the ebb shoal by way of an eastward channel. The
same general argument holds for the southeastward channel.
18.2. Impact on Navigation Safety
Dredging in the offshore area is not likely to impact navigational safety in a negative manner.




18.3. Impact on Beach Erosion
A potential exists for enhanced beach erosion depending on the selected site for dredging. As noted in Section 18.1 dredging 150,000 yd3 (115,000 in3) to create, for example, a channel through the ebb shoal is likely to cause a major adverse impact. Even if the dredged sand is placed on the beach, there is likely to be a significant oscillation of the shoreline position during the months following dredging.
18.4. Impact on Interior Sedimentation
Offshore dredging is not likely to impact sedimentation in the interior of the inlet in any measurable way.
18.5. Ecological Considerations
Dredging in the offshore shoal may help restore and maintain the beach to the south of the south jetty, although for a comparatively short period. If this action helps to maintain stable and gentle beach profiles during the sea turtle nesting season, this will have some positive ecological benefits. As with the trap dredging (see Section 2.5), however, other impacts also occur.
Ecological damage from sediment plumes during dredging may not be as likely in the offshore area as they are in the traps inside the inlet. The suspended sediment may be able to dissipate more widely, thus diluting any impacts to some degree. Furthermore, ecological communities in the immediate area are likely to be less productive than the seagrasses inside the inlet and are also likely to be more tolerant of shifting sediments, a phenomenon that occurs routinely in the sandy offshore areas. No seagrasses are likely to be in the immediate path of the plume, although this should be monitored and sediment screens employed if necessary. Dredging in the offshore area will not impact the tidal prism.
19. Frequency of Dredging
19. 1. Impact on Navigation Access
As noted in Section 18. 1, dredging in the offshore area may be carried out once every 10 years. A shorter interval may prove to be uneconomical as the amount to be dredged after n number of years is equal to 14,000 yd3 (10,800 mn3) x n. There is also the concern for impacts on the beach due to the uncertainty in the behavior of the offshore bathymetry over shorter time intervals.
19.2. Impact on Navigation Safety
The frequency of dredging is not likely to impact navigational safety; however see Section 21. 1.
19.3. Impact on Beach Erosion
As mentioned in Section 18. 1, ebb shoal dredging to create a wide and deep eastward (or in some other direction, e.g. southeastward) outer channel can not be justified. The site ultimately selected for




dredging should be in an area which is shown to have a relatively stable bottom. Site selection must be based on further searches for offshore sources of beach compatible sand, since the present data are inadequate for making a rational decision with regard to site selection. See also 21.3.
19.4. Impact on Interior Sedimentation
There is no significant relationship between the offshore dredging frequency and sedimentation in the interior region of the inlet; see however 21. 1.
19.5. Ecological Considerations
Ecological considerations pertaining to the frequency of offshore dredging are the same as for the trap dredging covered in Section 2.5. More frequent dredging of smaller volumes per event may reduce local ecological impact, while allowing the collection of a sufficient volume of unstable sand. Less frequent dredging of a larger volume could require dredging more stabilized and ecologically productive sand communities in order to achieve the target volume. If sufficient unstable sand is available, the differences between dredging, for example, once ten years or once every year may not be particularly consequential.
20. Location of Dredging
20. 1. Impact on Navigation Access
As noted in Sections 18.1 and 19.3, dredging of a major offshore access channel in the ebb shoal area is likely to impact beach stability and, furthermore, a wide and deep channel is not required at this inlet.
20.2. Impact on Navigation Safety
No strong correlation is expected between navigational safety and offshore dredging location as envisaged and noted in 18. 1; see however Section 2 1. 1.
20.3. Impact on Beach Erosion
As noted in Section 19.3 the offshore sand borrow site should be carefully chosen to minimize impact on the beach.
20.4. Impact on Interior Sedimentation
There is no significant relationship between offshore dredging frequency and sedimentation in the interior region of the inlet; see however Section 2 1. 1.




20.5. Ecological Considerations
Although offshore dredging may reduce the necessity to dredge traps inside the inlet by an equal volume, it is not clear that the net ecological impact from dredging in the offshore area is any less. A beneficial impact may actually occur if sufficient quantities of unstable (mobile) sand are found at a suitable site which does not impact the beaches by increasing the wave energy reaching the beach. Furthermore, the location of the dredging site is of great importance. For the dredging in the offshore area to meet its main objective, dredged material must be suitable for placement on the beach. Therefore it must consist of sand of sufficiently large grain size and low organic content. For sand, low organic content is correlated to low ecological productivity. Thus dredging sand suitable for beach nourishment also reduces ecological impact at the dredging site.
To provide suitable sand for beach nourishment and to minimize damage to existing ecological communities in the offshore area, sand should be removed from the unstable parts of the bottom. Unstable areas, however, are likely to be those presently dissipating wave energy that would otherwise reach the beach or inlet. Hence the importance of selecting the optimal borrow site. Identifying the minimum-impact location on the offshore site also requires some ecological observation of the site.
21. Placement of Dredged Material
21. 1. Impact on Navigation Access
Some of the sand placed on the beach immediately south of the inlet is known to be transported into the inlet around the south jetty. This transport decreases the depth at the JID trap more rapidly than desired, and can be construed as impacting on access to navigation, even though this effect is not thought to be highly significant. Note that the south beach is the most appropriate site to place beach compatible sand dredged from the offshore area. Modification of the south jetty for reducing interior sedimentation, as noted under Section 11.4, and reducing beach erosion as noted under Section 11.3 are related to this issue.
21.2. Impact on Navigation Safety
The linkage between navigational safety and placement of sand dredged from the offshore area is not likely to be significant; however see Section 21. 1.
21.3. Impact on Beach Erosion
The material dredged from the offshore area should be placed on the beach downdraft of the inlet. Note that this condition imposes an additional requirement for location of the offshore borrow area in terms of the compatibility of the borrow material as a beach fill. Material unsuitable for placement on the south beach should not be considered for dredging.




21.4. Impact on Interior Sedimentation
Calculations show, for example, that the net amount of sand transported per unit time is doubled
if the median grain size is decreased from 0.50 mm to 0.20 mm. Thus for instance an annual, net sediment influx of 78,000 yd3 (60,000 in3) would increase to 166,000 yd3 (127,000 mn3). Therefore finer the
material, the greater the likelihood of increased sediment in the interior area.
21.5. Ecological Considerations
Assuming the nature of the material dredged from the offshore area is suitable for placement along
the beach, the ecological considerations are the same as for the other aspects of beach nourishment. These are covered in Sections 5.5, 6.5, 7.5, and 8.5. If the offshore material is not suitable for beach nourishment, the main ecological advantage of offshore dredging will be lost. Furthermore, another site for disposal of the material will have to be found. This site must avoid covering offshore rocky
outcroppings.
IM. Interior Trap Dredging
22. Location of Interior Trap
22. 1. Impact on Navigation Access
Following a suggestion made during the mid-Seventies (Chiu, 1975), a third sand trap (i.e. in
addition to the JID trap and the Corps of Engineers dredging site) may be created and located immediately eastward of the FECRR bridge. The earlier proposal called for a trap on the west side of the bridge which is a more suitable location than east of the bridge; however, the area west of bridge is now an aquatic preserve. The purpose of the third trap would be to control the accretion of littoral sand in the wider region of the Loxahatchee River estuary west of the bridge, i.e. in Region 3. Calculations indicate that at present about 1,000 yd3 (800 mn3) of (0.50 mmn) littoral sand is transported west of the railroad bridge. Note that the precise amount is not known; it is conceivable that at times the influx increases to as much as 2,400 yd3 (1,800 in3) of 0.20 mm sand. In so far as the trap is designed to control sediment buildup west of the
railroad bridge, its impact on navigational access should be beneficial.
22.2. Impact on Navigation Safety
It is unlikely that the proposed trap location will impact navigational safety beneficially or
otherwise in any significant way; there could be a minor positive impact on safety due to the availability
of greater depths.




22.3. impact on Beach Erosion
Dredging in this particular location will have little impact on beach erosion. Bank erosion in the vicinity is unlikely to be impacted in a major way, although the possibility of some impact cannot be ruled out.
22.4. Impact on Interior Sedimentation
As note in Section 22. 1, the main purpose of the proposed third trap is to control the influx of littoral sand into the wide area of the Loxahatchee River west of the FECRR bridge. The location is thus appropriately selected to be at the eastern end of Region 3 where sedimentation is a matter of concern.
22.5. Ecological Considerations
Because the environmental portion of this study did not involve the area west of the Florida East Coast Railroad bridge, specific knowledge of the ecological impacts of trap location are not possible. In general, however, it is important to avoid dredging at sites that contain seagrasses or are in close proximity to seagrass beds. Dredging operations should perhaps employ the use of sediment screens to block sediment plumes from reaching seagrass beds. As stated in Section 2.5, suspended-sediment plumes temporarily reduce seagrass productivity through reduced light. Subsequent settlement of the plume may bury some organisms.
23. Dimensions of Interior Trap
23. 1. Impact on Navigation Access
The considered trap dimensions are 500 ft (152 m) width centered laterally across the Loxahatchee River, 200 ft (61 m) length along the axis of the river and 12 ft (3.7 m) depth below NGVD. Such a depth is also maintained in the nearby Intracoastal Waterway. These trap dimensions do not suggest a strong positive or negative impact on access to navigation.
23.2. Impact on Navigation Safety
The proposed trap dimensions will not materially alter navigational safety in the area.
23.3. Impact on Beach Erosion
The proposed trap dimensions will not have any tangible bearing on beach erosion. However, there exists some possibility of local bank erosion; hence if and when the trap is dredged its stability must be monitored by periodic surveying.




23.4. Impact on Interior Sedimentation
The trap size is considered to be sufficiently large to contain a sizeable fiction of the incoming littoral sediment. Mathematical model calculations indicate that the net movement of sand further to the west should decrease by up to 50 % relative to the present movement noted in Section 22. 1. The degree of reliability of this assertion is, to a fair (but not the sole) extent dependent upon the model's ability to make accurate predictions. Since the model has been shown to yield reasonable results with respect to sand transport in the area of the JID trap as well as estimates of sand transport past (westward) of the FECRR Bridge, the basis for accepting model results does exist. On the other hand, at present the Intracoastal Waterway in the vicinity of the proposed trap does not seem to shoal significantly; an observation that seemingly counters model prediction. We must however note two mitigating physical factors: 1) the natural depths in the area of the proposed trap are somewhat lower than those of the proposed trap, and therefore there is likely to be a natural tendency to "fill up the hole", and 2) one is dealing with very small rates of shoaling of the trap in any event.
23.5. Ecological Considerations
Generally, interior traps of smaller surface area should carry less ecological impact than larger traps. Depth is less important. The majority of ecological activity in most estuarine sediments is found in the upper ft (30 cm) or so and diminishes considerably below that point. Since dredging will involve more than a ft (30 cm) of depth in any scenario (other than the no new action scenario), the impact of depth is ecologically relatively unimportant compared to the surface area of the trap. Smaller surface areas will yield lower ecological impact.
24. Volumetric Rate of Interior Trap Dredging
24. 1. Impact on Navigation Access
The volumetric rate of trapping given the range of present rate of influx in Section 22.1 and trap efficiency given in Section 23.4 would range from 500 to 1,200 yd3 (380 to 920 m3). This trapping mode has no tangible bearing on navigational access. Dredging may be once every ten years.
24.2. Impact on Navigation Safety
The volumetric sand trapping rate in the proposed trap will have no measurable impact on navigational safety.
24.3. Impact on Beach Erosion
The volumetric sand trapping rate in the proposed trap will not impact beach erosion. The concern for some local bank erosion is noted in Section 23.3.




24.4. Impact on Interior Sedimentation
Calculations indicate that the rate of shoaling of the wider region of the Loxahatchee River west of the FECR1R bridge (Region 3) has been decreasing steadily over the past two decades. Thus the possibility exists that with a continuation of this trend, coupled with an effort to trap more sand at the JID trap as noted in Section 2.4, could reduce the movement of sand into this area from the littoral drift, and hence diminish the need for maintaining the proposed trap.
24.5. Ecological Considerations
In general the comments about volumetric rate of trap dredging in Section 2.5 are applicable here. However, the material to be dredged is likely to contain a much greater number of biota (perhaps several orders of magnitude greater) that could be damaged by entrainment in the dredge. These are the estuarine epifauna and infauna: polychaete worms, clams, burrowing crustacea, and fish (e.g., certain gobies). The possible volumetric rate of about 10,000 yd3 (7,600 mn3) in 10 years is relatively small compared to the dredging that occurs in the JID and Corps traps, however, the type of material to be dredged should be considerably more ecologically productive.
Results of the hydrodynamic model constructed as part of this study indicate no measurable impact of the proposed interior trap on salinity intrusion or tidal flows to the limits of the model boundaries.
25. Frequency of Interior Trap Dredging
25. 1. Impact on Navigation Access
From Section 23.1 and the fact that the existing mean depth to the bottom at the site is less than the proposed depth means that the dredging interval can be shown to be on the order of a decade. Navigational access will be restricted only during those times when dredging is actually being carried out.
25.2. Impact on Navigation Safety
Any significant relationship between navigational safety and the frequency of dredging in the proposed trap is not evident.
25.3. Impact on Beach Erosion
No significant correlation is expected between beach erosion and the proposed trap dredging frequency. However, some local bank erosion may occur, for which monitoring will be required.
25.4. Impact on Interior Sedimentation
The decadal dredging frequency at the proposed trap would be more than adequate to maintain the up to 50 % trapping efficiency of the trap noted under Section 22. 1.




25.5. Ecological Considerations
The comments about the frequency of trap dredging given in Section 2.6 are applicable here also, but the intensity of the effects may be somewhat magnified since the ecological community in the sediment may stabilize and become very productive between dredging events. For estuarine sediments, the best option may be to allow an intermediate recovery between dredging events rather than either maintaining a high dredging frequency that is more continuously disruptive, or planning a lower frequency that produces a greater perturbation and a longer recovery time. This is presumably not as important an issue in the existing traps east of the Florida East Coast Railroad bridge, since they are composed of relatively unproductive, unstable sand that is unlikely to ecologically stabilize between dredging events.
Analysis of a dynamic ecological simulation model of infaunal recovery may help to determine inappropriate frequencies of dredging of interior traps. With additional research support, a model of a hypothetical infaunal community could be developed and so analyzed.
26. Material Placement
26. 1. Impact on Navigation Access
Any significant relationship between navigational access and the placement of material from the proposed trap is not evident. Placement should be accomplished in such a way so as not to impact channels.
26.2. Impact on Navigation Safety
Any significant relationship between navigational safety and the placement of dredged material is not evident, as long as the material is not placed in the navigation channels or nearby.
26.3. Impact on Beach Erosion
No significant correlation is expected between beach erosion and the placement of dredged material. It is expected that this material will be unsuitable for beach nourishment.
26.4. Impact on Interior Sedimentation
The actual placement of the material should be accomplished so as not to allow material to impact channels, hence there should be no impact.
26.5. Ecological Considerations
Material may not be suitable for beach nourishment because sediment size may be too small and organic content too great. If so, alternative disposal sites will have to be found. Depositing the material on land may be expedient, but will not positively benefit the estuary. On the other hand, it may be possible to use this material to build shallow zones elsewhere in the Loxahatchee River estuary, possibly in Region 3, and plant seagrasses, marshes, or mangroves on them. It is necessary to assess the likelihood of success




of such plantings in advance, however. Placement of material in the estuary, however, is likely to produce a large sediment plume. This could perhaps be adequately controlled by sediment screens, which should also be tested in advance.




4. RECOMMENDED ACTIONS, PACTS AND COSTS

4.1 Introduction
The decision rationale given in Chapter 3, coupled with practical engineering considerations relevant to Jupiter Inlet, were used to develop a series of individual recommended actions and associated costs. These actions are relative to the present coastal engineering protocol, which would require no new action. The individual actions and costs are listed in Table 4.1. Note that a given action may impact beach erosion, navigation as well as sedimentation in the interior. This interdependence between the thre management characterizing (improvement) issues and the actions is shown by box diagrams in Figs. 4.1, 4.2 and 4.3. The costs are inherently approximate; in particular, the costs of such one-time purchase items as the sand fluidization system are uncertain. While annualization. is based on a 50 year item life, even the expected life of a fluidization system is not quite known. Given these uncertainties as well as the questionability in projecting dredging and other annual costs in future at an appropriate interest rate (8% has been assumed here), the validity of the given costs beyond a 10 year period for dredging etc is speculative.
Two categories of "cumulative" actions for the proposed management plan are considered -- those that are interdependent and therefore must be carried out in a certain sequence or phases, and those that are mutually independent (Table 4.2). These are described next.
4.2 Recommnended Phased, Interdependent Actions
Pl. This action entails a revision of the sand dredging and placement protocol by lID, and a concomitant recommendation to the Army Corps of engineers to revise their dredging schedule. In order to minimize the south beach erosion problem, a minimum of 60,000 yd3 (49,000 in3) must be pumped to the south beach, each year. The actual amount, by way of combined total for the JID trap and the Corps trap, should not be allowed to decrease below this amount in a given year, assuming, of course, that this amount is available from the two traps.
Note that the recommended volume of 60,000 yd3 (49,000 mn3) is the minimum for beach stability; the actual amount in the trap (or traps) may be larger, in which case the need to maintain a certain depth in the trap (- 20 ft or -6.1 m. n the JID trap, and -12 ft or 3.7 m. in the Corps maintained Intracoastal Waterway) would mean that the actual volume pumped to the beach each year may be larger than the minimum, as often has been the case.
We also recommend that a sand placement plan that is different from that at present (Fig. 4.4) be tried as a way to increase the retention time of placed sand. A possible plan is shown in Fig. 4.5 in which the sand is shown to be spread out over a wider section of the public beach than the existing stretch. We suggest implementation of the proposed plan initially on a trail basis during a pre-summer (before the end of April) placement of sand. Monitoring of the beach subsequent to sand placement will provide grounds for making a decision as to the rate of success of the project. It must be borne in mind, however, that a single placement trial




Table 4.1: Individual actions investigated and costs.

Action Cost Basis Annualized
Description ($) Costa
($)

JID Trap Expansion Dredging 60,000 yd3/yr
Raise Elevation of South Jetty Maintenance Raise Elevation of North Jetty Maintenance
South Jetty Extension by 175 ft Maintenance
North Jetty Extension by 400 ft Maintenance Fixed Sand Bypassing Plant Maintenance Fluidizer System Maintenance Offshore Dredging 150,000 yd3 Dredge Offshore Channel 40,000 yd3/yr Navigational Aids Maintenance Additional Sand Trap 10,000 yd3, Every 10 years

500,000 250,000
60,000
3,000
80,000
4,000
500,000 80,000
1,100,000
12,000
3,500,000 150,000
3,650,000
2,500,000 300,000 3,600,000

950,000

40,000 5,000 40,000

One-Time Annual One-Time Annual One-Time Annual One-Time Annual One-Time Annual One-Time Annual One-Time Annual 10 Years Annual One-Time Annual 10 years

41,000 250,000
291,000
4,900 3,000
7,900 6,500 4.000
10,500 41,000 8,000
49,000
90,000 102,000 436,000 150,000
586,000 204,000 100,000
304,000 143,000 620,000

3,300 5,000
8,300
7,300

aOne-time costs annualized at 8% interest, 50 year life. bCapital plus maintenance dredging.




,,, I I I-- I.. 1I II I
I I II
Volume FrequeFeuncyy Timing Placement Bue Feqecessing
Iternatives
I
II
Idixd ant Fluidizer Ix System
Fig. 4.1. Action categories considered in relation to improvement in beach erosion management.




Fig. 4.2. Action categories considered in relation to improvement in navigation management.




Fig. 4.3. Action categories considered in relation to improvement in sedimentation management.




PACEMtIO CATION
yic
P s-NORISHMENT Fig. 44RENE Present sand placement plan.
Fig. 4.4. Present sand placement plan.




URISHMENT INE
ALTERNATIVE FOR
-PLACEMENT OF DREDGED SAND
SOUTHWARD LIMIT OF PUBLIC BEACH

Fig. 4.5. A revised sand placement plan.




Table 4.2: Recommended actions.

Recommended Phased, Interdependent Actions
P1 Trap dredging and sand placement protocol modification.
P2 P1 + raising north and south jetty elevations and extend south jetty.
P3A P2 + north jetty extension and installation of beach sand bypassing
facility.
P3B P2 + Installation of a sand fluidizer system in the channel.
Recommended Independent Actions
Ii Modification of Corps trap dredging protocol.
12 Regulating boat speed.
13 Placement of beacons.
14 Dredging offshore navigation channel.
is Offshore dredging for sand equity.
16 Interior trap dredging.
may not yield all answers, given the episodic nature of beach sand transport. Additional trials may therefore be required.
A possibility of enhancing the efficiency of sand trapping exists by expanding the size of the existing trap somewhat, as shown in Fig. 4.6. We recommend that the suggested length-wise expansion be carried out first, followed by width-wise expansion at a later date only if length increase does not show any measurable increase, e.g. around 15 %, in trapping. If and when width-wise expansion of the trap is carried out, its impact on the stability of Dubois Park beach and the bulkheads in the area must be monitored. Furthermore, the trap should be consistently dredged to -20 ft (-6.1 m), even without any expansion. At the western end of the trap rocky bottom prevents dredging to full 20 ft (6.1 m); therefore these rocks must be removed by capital dredging, to "clean out" the bottom.
The JID trap should be preferably dredged by or before the end of each April, prior to the peak sea tur tle nesting season. If at times insufficient sand accumulates in the trap for this dredging window, then dredging in early November may be carried out. The Corps is encouraged to dredge each November during those years when the JID trap is dredged in April. At other times, the Corps is encouraged to dredge before the end of April.
Since any action be the Corps would be independent of that by JID, we have also listed the above recommended action by Corps as independent action Il.




Fig. 4.6. A revised sand trap plan.




P2. This action is in addition to P1, and involves raising the seaward end of the two jetties by 3 ft (0.9 in), and lengthening the south jetty by 175 ft (53 m) (Figs. 4.7 and 4.8). Although these three actions can be implemented separately, it is recommended that they be carried out simultaneously. If for financial reasons for example, it is decided to carry out the works piecemeal, then we recommend that the north jetty be raised first (to reduce incoming sand from the north), then raise the south jetty (to reduce incoming sand from the south), and finally extend the south jetty as shown.
P3A. This action is in addition to P2, involving an extension of the north jetty by 400 ft (122 m) as shown in Fig. 4.9, coupled with the installation of a sand bypassing plant in order to prevent the extended jetty from causing further erosion of the south beach. In order to maintain the south beach, a minimum of 60,000 yd3 (49,000 Mn3) sand must be annually pumped to the south beach. The sand "catching" efficiency of the bypassing plant may not exceed about 75 %. This being the case, dredging of the JID trap would not be eliminated entirely.
An alternative to the fixed sand bypassing plant is a fluidizer system shown in Fig. 4. 10. The fluidization pipes will have to buried at least 6 ft (1.8 m) below the surface of the sandy bottom. The applicability of this system to this type of an environment is pending experiments presently being conducted at Oceanside Harbor, California, by the Army Corps of Engineers.
It should be noted that since it is unlikely that accumulation of sand in the interior will be entirely eliminated by way of this action, any decision concerning the need to remove the "access" sand from the trap will depend primarily on navigation considerations. However, a secondary consideration would be that an "empty" and larger trap will be more efficient than a filled, smaller trap in catching the fine sand that will continue to be transported past the trap, even though perhaps at a lower than present rate. Therefore the proposed protocol of dredging from a larger trap must be continued, even though the required frequency of dredging may be lower.
P3B. This action, involving the installation of a fluidizer sand bypassing arrangement in the general area of the JID sand borrow area (Fig. 4. 11) must be considered as an alternative to P3A for practical reasons, since it would be impractical and costly to maintain more than one sand bypassing arrangement at Jupiter Inlet. This essential constraint means that P3A, which is meant to improve navigation via the extended north jetty, must be weighed against P313, which is meant to better manage the south beach.
4.3 Recormmended Independent Actions
It. The recommendation to request the Corps to coordinate their dredging and sand pumping activity with that of JID is described under action Pl. As noted there, since the Corps' activity has different objectives than JID, and inasmuch as the Corps is an independent entity, any action by the Corps to work with JID must be considered as an action that is jurisdictionally independent of the JID's management plan.




Fig. 4.7. Raising the elevations of the two jetties.




4
Fig. 4.8. Extended the south jetty.

SEAWAU




Fig. 4.9. Extended north jetty with a sand bypassing plant.
75




FLUIDIZER PIPES (200 FT LONG 1:25 SLOPE)

- -~ ~ ~ I
_ ,'
- k I

Fig. 4.10. Extended north jetty with an offshore sand fluidization system.




>1

2t
4,-.

Fig. 4. 11. A sand fluidization arrangement for the interior channel.

k-11 4"




12. Regulating boat traffic is within the jurisdiction of the Marine Patrol and the Coast Guard, hence it must be considered as an independent action.
B. The placement of beacons on the jetty tips per Coast Guard specifications is recommended as shown in Fig. 4.12. Or, as an alternative, international danger signals on the north jetty. When the signals are lit the inlet would be closed to navigation.
M. A possible configuration of the offshore navigation channel is shown in Fig. 4.13.
15. Offshore dredging of 150,000 yd3 (115,000 m3) every 10 years to mitigate the loss of sand from the beaches south of the inlet is an independent action. Evidently, the sand must be beach quality.
16. Dredging a third trap at the site shown in Fig. 4.14 can be considered independently of the plans for other dredging, jetty modifications or sand bypassing arrangements.
4.4 impacts of Interdependent and Independent Actions
Table 4.3 (matrix) summarizes the recommended actions and their costs based on cost data given in Table 4. 1. The impacts corresponding to the matrix "boxes" are noted in this section. Note that a number corresponding to a scale of -10 (extremely adverse impact) to + 10 (extremely beneficial impact) is included within parentheses for each "box". These numbers are a semi-quantitative representations of the opinion of the authors. They should not be applied by other parties without due consideration to all of the rationale used in their development. This rationale is briefly summarized in the what follows, but is contained more completely in the earlier part of this report and particularly, the progress reports (see bibliography) and other communications with the JID during the course of this project.
Pl. 1 Revising the dredging and sand placement protocols will have no major bearing on the issue of navigation access, even though annual or bi-annual hydraulic dredging could, at least in principle, hinder boat traffic. A potential reduction in the sand being carried east of the JID trap would however have a slightly beneficial effect.
P1.2 Revising the dredging and sand placement protocols is unlikely to impact navigation safety in a measurable way, even though annual or bi-annual dredging could, at least in principle, "come in the way" of boat traffic.
P1.3 Modification of dredging and sand placement protocols should improve retention of sand on the south beach and hence reduce erosion. Improvement by revising the sand placement protocol is likely to be brought about by two factors: 1) less sand placed in an area where the "excess" sand is easily washed away by wave action in the vicinity of the south jetty, and 2) more sand placed in an area further south, where past records indicate retention




-V

Fig. 4.12. Beacons or danger signals at jetties.
79







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44 "o tv 81




Table 4.3: Recommended actions, impacts and costs.
Actions Impacts Costs
Navigation Navigation Beach Interior Ecological Amount Basis Annualizeda
Access Safety Erosion Sedimentation Considerations ($) ($)
P1 P1.lb(+1)c P1.2(0) P1.3(+3) P1.4(+5) P1.5(+3) 500,000 One-Timed 41,000
250,000 Annual 250
291,000
P2e P2.1(+1) P2.2(0) P2.3(+5) P2.4(+6) P2.5(+7) 1,140,000 One-Time 93,400
265,000 Annual 202000
295,400
P3Af P3A.1(+3) P3A.2(+8) P3A.3(+6) P3A.4(+6) P3A.5(+6) 4,640,000 (Fixed Plant) One-Time 529,400
415,000 Annual 352000
881,400
3,640,000 (Fluidizer) One-Time 297,000
302,000 Annual 3 000
599,000
P3Bg P3B. 1(0) P3B.2(0) P3B.3(+5) P3B.4(+6) P3B.5(+ 10) 3,640,000 (Fluidizer) One-Time 297,000
302,000 Annual 302000
599,000
Ii I1.1(+1) 11.2(0) 11.3(+4) 11.4(+2) I1.5(+2) N.A.h N.A. N.A.
12 12.1(0) 12.2(+8) I2.3(+3) 12.4(+3) I2.5(+3) N.A. N.A. N.A.
13 I3.1(+6) I3.2(+5) I3.3(0) I3.4(0) I3.5(-1) 40,000 One-Time 3,300
5,000 Annual 500
8,300
14 I4.1(+5) 14.2(+3) I4.3(0) 14.4(0) I4.5(0) 620,000 Annual 620,000
15 15.1(0) 15.2(0) 15.3(+1) 15.4(0) I5.5(+l1) 950,000 10 Years 143,000
16 I6.1(+1) I6.2(+1) I6.3(0) I6.4(+6) I6.5(-2) 150,000 10 Years 22,600
aOne-time costs analyzed at 8% interest, 50 year life. bSee comments on impacts for all such "boxes". cOn a scale of -10 (extremely adverse impact) to +10 (extreme benefit). dThis cost has been added for simplicity to the one-time costs of actions P2, P3A and P3B, even though these cumulative actions are not meant to be instituted at the same time; see Table 4.4.
eSaving of 15,000 yd3/yr dredging. A fixed sand bypassing system or a fluidizer system are technical options. gThis action as an alternative to action P3A. hCosts not applicable to JID.




to be more efficient. We do not anticipate shoreline recession in the critical zone to increase by virtue of the revised placement procedure over and beyond the present scenario; however, a major storm episode could cause drastic erosion irrespective of any selected sand placement protocol. If post-project monitoring of the beach suggests measurable adverse effects (in terms of retention time or shoreline position change), then this protocol must be revised again. Consistent annual (or bi-annual) dredging will provide a greater buffer against episodic events, and larger (over long term) dredging volumes, i.e. 60,000 yd3/yr (49,000 m3/yr) or more, placed on the beach should lead to larger beach volumes throughout the year. Dredging prior to the non-pumping (May-October) window should produce better summer beach conditions.
PIA This protocol will enable a more consistent maintenance of depths in the interior, and somewhat reduce sand deposition in the marina area. If as noted under action PI the trap is increased in width, its impact on the adjacent banks, specifically the Dubois Park beach ( which has been excessively hardened by concrete such that any sand deposited there is transported offshore by reflected wave action, thus causing the beach to lose the sand) and the bulkheads (many of which seem to have been poorly constructed and/or are in a poor state of repair) protecting private and public lands in the area must be monitored for any adverse impacts.
P1.5 The major ecological improvement here is on sea turtle nesting. Nesting turtles should benefit from greater quantities of sand per year added more frequently, at effective times of year, and spread out farther along the south beach. The sand derived from the JID trap (and the Corps trap) is typically suitable for sea turtle nesting. If nourishment is done according to the criteria for sea turtle nesting beaches outlined in Appendix G, sea turtles should benefit considerably from this action. An increase in death of biota via entrainment in the dredge will accompany any increase in dredging, however. This negative effect should be small relative to the positive effect on nesting sea turtles (based on biomass lost versus biomass gained). Spreading the nourishment farther alongshore may allow better retention of sand and hence a more stable and uniform beach profile for nesting sea turtles. If the design developed in this study is followed, the spreading zone will not extend far enough to the south to affect rocky outcroppings at Carlin Park. Increasing the JID trap dimensions in the manner described in this report should have no perceptible impacts on any of the ecological impacts that we have considered. The suggested new dimensions impact an area of high current and constantly shifting sand. Our model studies have indicated no significant effect of increased dimensions and dredging of the JID trap on ecologically important parameters in the interior.
P2.1 The recommended jetty modifications will not add to, or take away from, the present navigation access in any major way, but the reduction in sand influx should slightly improve access, e.g. in the marina area and the Intracoastal Waterway.
P2.2 The recommended jetty modifications should not measurably alter the present degree of navigation safety in the inlet area.