• TABLE OF CONTENTS
HIDE
 Cover
 Title Page
 Report documentation page
 Foreword
 Table of Contents
 List of Tables
 List of Figures
 Introduction
 Field investigation
 Data analysis
 Physical model
 Potential solutions
 Model testing
 Summary and recommendations
 Appendix A: Storm surge flow...
 Appendix B: Depth correction for...
 Appendix C: Dimensionless transverse...
 Appendix D: Friction slope and...
 Appendix E: Determination of nearshore...
 Appendix F: Inlet bathymetry
 Appendix G: Wavemaker setting
 Appendix H: Weir calibration
 Appendix I: Roughtness element...
 Appendix J: Test results
 References






Group Title: UFL/COEL (University of Florida. Coastal and Oceanographic Engineering Laboratory) ; 84/004
Title: Coastal engineering investigation at Jupiter Inlet, Florida
CITATION DOWNLOADS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00076167/00001
 Material Information
Title: Coastal engineering investigation at Jupiter Inlet, Florida
Series Title: UFLCOEL
Physical Description: xv, 228 p. : ill., maps ; 28 cm.
Language: English
Creator: Buckingham, William T., 1961-
Jupiter Inlet District
Palm Beach County (Fla.)
University of Florida -- Coastal and Oceanographic Engineering Laboratory
Publisher: Coastal & Oceanographic Engineering Dept., University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1984
 Subjects
Subject: Sedimentation and deposition -- Florida -- Jupiter Inlet   ( lcsh )
Hydraulic models   ( lcsh )
Jupiter Inlet (Fla.)   ( lcsh )
Coastal and Oceanographic Engineering thesis M.S
Coastal and Oceanographic Engineering -- Dissertations, Academic -- UF
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 225-228).
Statement of Responsibility: by William T. Buckingham ; submitted to Jupiter Inlet District and Palm Beach County.
General Note: "March 1984."
Funding: 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.
 Record Information
Bibliographic ID: UF00076167
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 15746147

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Table of Contents
    Cover
        Cover
    Title Page
        Title Page
    Report documentation page
        Unnumbered ( 3 )
    Foreword
        Foreword
    Table of Contents
        Table of Contents 1
        Table of Contents 2
        Table of Contents 3
        Table of Contents 4
    List of Tables
        List of Tables 1
        List of Tables 2
    List of Figures
        List of Figures 1
        List of Figures 2
        List of Figures 3
        List of Figures 4
        List of Figures 5
        List of Figures 6
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Field investigation
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
    Data analysis
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
    Physical model
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
        Page 99
    Potential solutions
        Page 100
        Page 101
        Page 102
        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
        Page 124
        Page 125
        Page 126
    Model testing
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 141
        Page 142
        Page 143
        Page 144
        Page 145
        Page 146
        Page 147
        Page 148
        Page 149
        Page 150
        Page 151
        Page 152
        Page 153
        Page 154
        Page 155
        Page 156
        Page 157
        Page 158
        Page 159
        Page 160
    Summary and recommendations
        Page 161
        Page 162
        Page 163
        Page 164
        Page 165
        Page 166
        Page 167
        Page 168
        Page 169
    Appendix A: Storm surge flow velocity
        Page 170
        Page 171
        Page 172
        Page 173
        Page 174
        Page 175
    Appendix B: Depth correction for velocity measurements
        Page 176
        Page 177
        Page 178
    Appendix C: Dimensionless transverse velocity profiles
        Page 179
        Page 180
        Page 181
        Page 182
        Page 183
        Page 184
        Page 185
        Page 186
        Page 187
    Appendix D: Friction slope and bed roughness calculations
        Page 188
        Page 189
        Page 190
    Appendix E: Determination of nearshore wave directions
        Page 191
        Page 192
    Appendix F: Inlet bathymetry
        Page 193
        Page 194
        Page 195
        Page 196
        Page 197
        Page 198
        Page 199
        Page 200
    Appendix G: Wavemaker setting
        Page 201
        Page 202
        Page 203
        Page 204
        Page 205
        Page 206
        Page 207
    Appendix H: Weir calibration
        Page 208
        Page 209
    Appendix I: Roughtness element theory
        Page 210
        Page 211
        Page 212
    Appendix J: Test results
        Page 213
        Page 214
        Page 215
        Page 216
        Page 217
        Page 218
        Page 219
        Page 220
        Page 221
        Page 222
        Page 223
        Page 224
    References
        Page 225
        Page 226
        Page 227
        Page 228
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UFL/COEL-84/004


COASTAL ENGINEERING INVESTIGATION AT
JUPITER INLET, FLORIDA




by




William T. Buckingham


March 1984




Submitted to:

Jupiter Inlet District
and
Palm Beach County







REPORT DOCUMENTATION PAGE
1. Report No. 2. 3. Recipient'e Accession No.


4. Title and Subtitle 5. Report Data
March, 1984
COASTAL ENGINEERING INVESTIGATION AT JUPITER March, 1984
INLET, FLORIDA
7. Author(s) 8. Performing Organization Report No.
William T. Buckingham UFL/COEL-84/004

9. Performing Organization Name and Address 10. project/Task/Work Unit No.
Coastal and Oceanographic Engineering Department
University of Florida u. Contract or Grant No.
336 Weil Hall R-82-878
Gainesville, FL 32611 13. rype of Report
12. Sponsoring Organization Name and Address
Jupiter Inlet District Technical
Jupiter, FL
and
Palm Beach County 4.
Palm Beach, FL __
15. Supplementary Notes



16. Abstract

A fixed-bed hydraulic model of Jupiter Inlet, Florida, was
constructed for the purpose of testing measures designed to remedy
problems of sediment erosion and deposition in the inlet area. Both
tide-induced flows as well as waves were simulated in the model which
was built on an undistorted scale of 1:49. Model verification was based
on prototype measurements of waves, tides and currents. Results have
been interpreted in terms of the influence of various proposed remedial
schemes on flow velocity magnitude, distribution and wave height at
various locations within the study area. A stability parameter has been
utilized for evaluating the degree of sediment erosion or deposition at
a given location.

Various structural solutions were examined in the model. It is
proposed that, in the initial phase of solution implementation, sediment
removal/nourishment methods be used primarily to mitigate the existing
problems. New structures, as per model test results, should be
installed under subsequent phases, only if sediment management
procedures do not prove to be adequate. The currently followed
procedure of periodic sand trap dredging may be extended to include the
new dredging/nourishment requirements.

17. Originator's Key Words 18. Availability Statement
Erosion Sediment Management
Hydraulic Model Sedimentation
Inlet Hydraulics Tidal Entrance
Physical Model Tidal Inlet
19. U. S. Security Classif. of the Report 20. U. S. Security Classif. of This Page 21. No. of Pages 22. Price
Unclassified Unclassified 245


UNIVERSITY OF FLORIDA'
COASTAL ENGINEERING '
I^.:Archives/

















ABSTRACT

A fixed-bed hydraulic model of Jupiter Inlet, Florida, was

constructed for the purpose of testing measures designed to remedy

problems of sediment erosion and deposition in the inlet area. Both

tide-induced flows as well as waves were simulated in the model which

was built on an undistorted scale of 1:49. Model verification was based

on prototype measurements of waves, tides and currents. Results have

been interpreted in terms of the influence of various proposed remedial

schemes on flow velocity magnitude, distribution and wave height at

various locations within the study area. A stability parameter has been

utilized for evaluating the degree of sediment erosion or deposition at

a given location.

Various structural solutions were examined in the model. It is

proposed that, in the initial phase of solution implementation, sediment

removal/nourishment methods be used primarily to mitigate the existing

problems. New structures, as per model test results, should be

installed under subsequent phases, only if sediment management

procedures do not prove to be adequate. The currently followed

procedure of periodic sand trap dredging may be extended to include the

new dredging/nourishment requirements.

















TABLE OF CONTENTS


PAGE

FOREWORD................... ... ...... ....... .... .... .............. ii

ABSTRACT........................................................... ii

LIST OF TABLES .................................... .... viii

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

CHAPTER

I INTRODUCTION.................... ........ ...... ........ 1

1.1 Introductory Note.................................. 1

1.2 Inlet History...................................... 4

1.3 Problems of Present Concern........................ 4

1.4 Purpose and Scope of the Study..................... 11

1.5 Previous Studies............. .......... .......... 11

1.6 Selected Methodology................ ..... .... ...... 12

II FIELD INVESTIGATION............................... ..... .. 15

2.1 Overview .............. .......................... ... 15

2.2 Hydrographic Surveys............................... 15

2.3 Water Surface Elevations.......................... 19

2.4 Extreme High Water Levels.......................... 21

2.5 Flow Cross-Sections and Current Profiles............ 23
2.5.1 Instantaneous Velocity Profiles............. 23
2.5.2 Continuous Velocity Measurements............ 28

2.6 Drogue Study........................................ 29

2.7 Dye Studies........................................ 29

2.8 Wave Information.... ............................ 29












PAGE

2.9 Sediment Samples.................................. 33

2.10 Runoff ....................................... 36

2.11 Winds ......................... ................ 37

III DATA ANALYSIS............................................ 38

3.1 Overview........................................... 38

3.2 Hydrographic Surveys.............................. 38

3.3 Tide Records ............................ .. 41

3.4 Storm Surge.................. ................ 43

3.5 Analysis of Vertical Velocity Profiles............. 44
3.5.1 Vertical Velocity Profiles.................. 44
3.5.2 Depth-averaged Transverse Velocity
Profiles.................................... 47
3.5.3 Continuous Velocity Measurements............ 50
3.5.4 Discharge Computations...................... 50

3.6 Drogue Study...................................... 55

3.7 Dye Study......................................... 56

3.8 Wave Information.................................. 57

3.9 Sedimentary Analysis............................... 61
3.9.1 Procedure................ ................... 61
3.9.2 Interpretation of Sediment Analysis......... 64

3.10 Sand Budget........................................ 70
3.10.1 Overview................................... 70
3.10.2 Littoral Transport and Distribution......... 71
3.10.3 Sand Budget........ .......................... 76

3.11 Runoff........................................... 76

3.12 Wind............................................... 78

IV THE PHYSICAL MODEL....................................... 80

4.1 Model Facility..................................... 80

4.2 Model Scale..................................... 80

4.3 Model Construction................................. 82
4.3.1 Templates, Sand, and Concrete............... 82
4.3.2 Seawall, Channel, Jetty and Rip-Rap......... 85
4.3.3 Dredging Simulation......................... 85
4.3.4 Aesthetics................... .... ........ 85










PAGE

4.4 Instrumentation ................................... 86
4.4.1 The Wave Generator......................... 86
4.4.2 Capacitance Wave Gage....................... 89
4.4.3 Pumps, Weir Boxes, and Weir Gates........... 89
4.4.4 Current Meters.................. ... .... 9
4.4.5 Stilling Wells............................ 91

4.5 Calibration and Verification ...................... 91
4.5.1 Flow Calibration........................... 93
4.5.2 Tide Level Calibration.............. .......... 96

4.6 Roughness Elements ................. ............... 96

4.7 Calibration and Verification Results............... 97

V POTENTIAL SOLUTIONS............................................. 100

5.1 Overview ........................................... 100

5.2 Solution Options................................... 102

5.3 Solution Implementation.......................... 115
5.3.1 Portable Hydraulic Dredge................... 116
5.3.2 Jet Pump................... ................ 118
5.3.3 Bypassing Dredge............................ 120

5.4 Boat Wakes............................. .......... 122

VI MODEL TESTING.. ...................... .................... 127

6.1 Overview............................. .............. 127

6.2 Test Conditions..... ............................... 127
6.2.1 Initial Considerations..................... 127
6.2.2 Test Conditions............................. 128

6.3 Data Analysis.. .......................... ......... 133
6.3.1 Overview................................... 133
6.3.2 Procedure....................... 133

6.4 Test Results and Interpretation.................... 138
6.4.1 Overview.................................... 138
6.4.2 Results and Interpretation.................. 138
6.4.2.1 Problem Site A..................... 138
6.4.2.2 Problem Sites B and C.............. 142
6.4.2.3 Problem Sites D, E and F........... 148
6.4.2.4 Problem Site G..................... 150
6.4.2.5 Problem Sites H and I.............. 157

VII SUMMARY AND RECOMMENDATIONS .............................. 161

7.1 Summary........................................... 161













7.2 Recomendations.....................
7.2.1 North Bank..................................
7.2.2 South Bank..................................

7.3 Inlet Maintenance...............................

APPENDICES

A STORM SURGE FLOW VELOCITY..........................

B DEPTH CORRECTION FOR VELOCITY MEASUREMENTS.........

C DIMENSIONLESS TRANSVERSE VELOCITY PROFILES.........

D FRICTION SLOPE AND BED ROUGHNESS CALCULATIONS......

E DETERMINATION OF NEARSHORE WAVE DIRECTIONS.........

F INLET BATHYMETRY*...... ............................,

G WAVEMAKER SETTING.................................

H WEIR CALIBRATION .......................................

I ROUGHNESS ELEMENT THEORY...........................

J TEST RESULTS.............................. ....

REFERENCES........................................................


PAGE

162
163
166

168


170

176

179

188

191

193

201

208

210

213

225

















LIST OF TABLES


TABLE PAGE

2.1. Current Meter Positions for Continuous Time-Velocity
Measurements.......................... ................... 28

2.2. Wave Data for West Palm Beach............................ 34

2.3. Freshwater Inflow into the Three Forks of the Loxahatchee
River Estuary ............................................ 36

3.1. Tidal Ranges, Lags and Range Ratios Relative to Inlet
Mouth, January 26 February 2, 1983...................... 43

3.2. Maximum Discharge through Each Flow Cross-Section......... 55

3.3. Comparison of Normalized Drogue Velocities to Velocities
Obtained from Current Meter Measurement at C-2............ 50

3.4. Sedimentary Analysis.................................... .. 63

4.1. Verification of Flow Velocities.......................... 95

4.2. Verification of Tide Elevations........................... 9S

5.1. Dredge Summary Chart (Corps of Engineers, 1983)........... 117

C-1. Location of Dominant Flow along Each Cross-Section........ 18C

D-1. Friction Slope (Sf) and Bed Roughness (k) for Each
Flow Cross-Section............ .......................... 19'

D-2. Average Bed Roughness (k) Values......................... 190

E-1. Nearshore Wave Directions................................. 192

G-1. Paddle Phase Angles for Various Wave Approach Angles...... 207

H-1. Weir Calibration.......................................... 209

J-la. Bottom Velocities, Wave Heights and P Values during Ebb
Tide for the Existing Condition and the Condition under
Phase One. .....................**** **.... ................. 215

J-lb. Bottom Velocities, Wave Heights and P Values during a
1.5 m Storm Surge for the Existing Condition and the
Condition under Phase One................................. 216


viii












TABLE PAGE

J-lc. Bottom Velocities, Wave Heights and P Values during
Flood Tide for the Existing Condition and the Condition
under Phase One....................................... ... 217

J-2a. Bottom Velocities, Wave Heights and P Values at
Locations Shown in Fig. J-2 with the Groin
Remnants in Place......................... ............ 219

J-2b. Bottom Velocities, Wave Heights and P Values at
Locations Shown in Fig. J-2 with no Groin................. 219

J-3. Bottom Velocities, Wave Heights and P Values near the
Flow Deflector with and without a 6 m Gap as Shown
in Fig. J-3..... .... .... .......... ....... ... ....... 221

J-4. Bottom Velocities, Wave Heights and P Values Resulting
from the Placement of a Sill between the Groins at the
Dubois Park Beach........................................ 223

J-5a. Bottom Velocities, Wave Heights and P Values for the
Three Sill Schemes Shown in Fig. J-4 during a Flood Tide.. 223

J-5b. Bottom Velocities, Wave Heights and P Values for the
Three Sill Schemes Shown in Fig. J-4 during an Ebb Tide... 224

J-5c. Bottom Velocities, Wave Heights and P Values for the
Three Sill Schemes Shown in Fig. J-4 during a 1.5 m
Storm Surge (Flood Tide)..................................... 224

















LIST OF FIGURES


FIGURE PAGE

1.1. Location Map of Jupiter Inlet.............................. 2

1.2. Area Map of Jupiter Inlet.................................. 3

1.3. Example of Shoreline Erosion at the Inlet................. 6

1.4. Example of Bulkhead Failure at the Inlet................... 6

1.5. Problem Areas of Erosion and Accretion..................... 7

2.1. Boundaries of the Inlet Study Area......................... 16

2.2. Areas of Relative Erosion and Accretion between 1957
and 1979................................................... 17

2.3. Mean High Waterline Changes near Jupiter Inlet between
1883 and 1979............................................. 18

2.4. Locations and Dates of Operation of Tide Recorders,
Current Meters and Wave Gage............................... 20

2.5. A Sample Tide Record for Lighthouse Crossing C-4.
HW = High Water; LW = Low Water............................ 22

2.6a. Profile of Jetty Crossing C-1. MSL Refers to NGVD......... 24

2.6b. Profile of Culvert Crossing C-5............................ 24

2.6c. Profile of Main Channel Crossing C-2...................... 25

2.6d. Profile of Intracoastal Waterway Crossing C-3.............. 25

2.6e. Profile of Lighthouse Crossing C-4......................... 26

2.7. Positioning Procedure for Obtaining Velocity Profiles
(Hayter and Mehta, 1979)................................... 27

2.8. Cross-Sectional View of Procedure for Obtaining
Instantaneous Velocity Profiles and Continuous
Velocity Record (Hayter and Mehta, 1979)................... 27

2.9. Plot of Drogue Course over Time............................ 30











A. jun- PAGE

2.10. Design of Drogue........................................... 31

2.11. Elapsed Time Plot of Dye Movement, Nov. 18, 1982........... 32

2.12. Sediment Sample Sites..................................... 35

3.1. Illustration of the Change in Area of a Typical Main
Channel Cross-Section when the Sand Trap is Dredged........ 40

3.2. Cumulative Histogram of Wave Heights (cm) at Gage 2-A
over the Period September 30 November 7, 1982............ 42

3.3. Vertical Velocity Profiles for Jetty Cross-Section C-1
taken October 14, 1982 at 1830 Hours....................... 45

3.4. Logarithmic Plot of the Vertical Velocity Profiles for
Jetty Cross-Section C-1................................... 46

3.5. Plot of Transverse Depth-averaged Velocity Profile for
Jetty Cross-Section C-2................................... 48

3.6. Dimensionless Transverse Velocity Profile for Jetty
Cross-Section C-1.......................................... 49

3.7. Typical Current Meter Chart Record for Lagoon
Cross-Section C-5.... ............................... 51

3.8. Plot of the Product of the Depth-averaged Velocity
and the Depth at Each Location Against Dimensionless
Width K. Integration of this Plot Results in the
Instantaneous Discharge Through the Jetty
Cross-Section C-1 at 1830 hr on 10/14/82................... 53

3.9. Discharge Through Each Cross-Section Corresponding
to Maximum Discharge Through the Inlet Mouth............... 54

3.10. Plot of Concurrent Jupiter Inlet and West Palm Beach
Wave Data. Plot Indicates that All Waves may be
Described by Stoke's Second Order Theory................... 58

3.11. Comparison of Concurrent Wave Data for Jupiter Inlet
and West Palm Beach over the Period January 27-30, 1983.... 59

3.12. Zones of Similar Sedimentary Characteristics............... 62

3.13. Plot of Critical Velocity Versus Grain Size Based on
Shield's Diagram......................................... 66

3.14. Modes of Sediment Transport into Zones 3, 4, and 6;
and out of Zone 2 (ref. Fig. 3.13)........................ 67










FIGURE PAGE

3.15. Areas of Erosion (-) and Sedimentation (+)
Corresponding to Areas Requiring Nourishment and
Areas Acting as Sediment Sources in the Inlet.............. 69

3.16. Qualitative Illustration of Sand Transport towards the
Inlet Mouth during Both Stages of a Tidal Cycle............ 73

3.17. Sand Budget for Jupiter Inlet.............................. 77

4.1. Schematic Layout of the Physical Model..................... 83

4.2. Schematic Drawing of the Template Scheme to Reproduce
the Bathymetry in the Model................................ 84

4.3a. A View of the Model........................................ 87

4.3b. A View of the Model as Seen from Offshore .................. 88

4.4. A Typical Pump and Weir Box System Used in the Model....... 90

4.5. A Typical Weir Gate Used in the Model..................... 90

4.6. Stilling Well Scheme....................................... 92

4.7. Two Types of Weir Boxes Used in the Model.................. 94

5.1. Problem Areas of Erosion and Deposition.................... 101

5.2. Plan and Profile of the Existing Condition and Proposed
Solution to Problem Site A............... .............. 103

5.3. Existing Conditions and Proposed Solution for Problem
Sites B and C.............................................. 105

5.4. Plan and Profile of the Existing Condition and Proposed
Solution for Problem Site D (and subsequently,
Sites E and F).......................................... 108

5.5. Plan and Profile of the Existing Condition and Proposed
Solution for Problem Site G................................ 110

5.6. Three Offshore Sill Schemes Tested as Possible Measures
to Protect the Shoreline between Problem Sites G and H..... 112

5.7. Plan and Profile of the Present Condition and Proposed
Solution for Problem Site H (and subsequently, Site I)..... 114

5.8. Schematic of a Jet Pump (Jones, 1977)..................... 119

5.9. Three Possible Modes of Employing a Single Portable
Jet Pump at Jupiter Inlet................................. 121












FIGURE PAGE

5.10a. Maximum Wave Height as a Function of Ship Speed for
the Tug "Merryfield"; Length 13.5 m, Draft 1.8 m,
Beam 4 m, Displacement = 29 Tons (Sorensen, 1967).......... 125

5.10b. Maximum Wave Height as a Function of Ship Speed for
a Cabin Cruiser; Length 7 m, Draft 0.5 m, Beam 2.5 m,
Displacement = 3 Tons (Sorensen, 1967)..................... 125

5.10c. Wave Height as a Function of Ship Speed for the Fishing
Boat "Miss Dragnet"; Length 19.5 m, Draft 0.9 m,
Beam 3.9 m, Displacement = 35 Tons (Sorensen, 1967)........ 125

5.10d. Wave Height as a Function of Ship Speed for a Coast
Guard Cutter; Length 12.2 m, Draft 1.0 m, Beam 3.0 m,
Displacement = 10 Tons (Sorensen, 1967)..............***..* 126

5.10e. Wave Height as a Function of Ship Speed for City of
Oakland Fire Boat; Length 30.5 m, Draft 3.5 m,
Beam 8.5 m, Displacement =' 343 Tons (Sorensen, 1967)....... 126

6.1. Combinations of Wave Heights, Wave Directions and Tidal
Stages Resulting in 18 Conditions Considered for
Testing......... ................ ............... ...... 129

6.2. Photograph Indicating the Inability of Waves to
Penetrate into the Inlet on Ebb Tide....................... 131

6.3. Circulation Patterns within the Cove Area at Site A;
Ebb Tide ........... .................................. .... 139

6.4. Circulation Patterns near the Groin Remnants at Site A;
Flood Tide............................................... 139

6.5. Attenuation of Circulation Patterns upon Removal of
Groin Remnants at Site A; Flood Tide....................... 141

6.6. Flow Patterns Induced by the Implementation of a
Weir-groin at Site A; Flood Tide........................... 141

6.7. Indication of the Manner in which Flood Currents Attack
the North Shoreline (Site B).............................*. 143

6.8. Illustration of the Diversion of Ebb Flow such that it
does not Enter behind the Flow Deflector with no Gap;
no T-groin........................................******** 143

6.9. Resulting Flow Patterns due to a Gap in the Flow
Deflector; Ebb Tide, T-groin........................***... 145

6.10. Resulting Flow Patterns behind the Flow Deflector with
no Gaps; Ebb Tide, T-groin................................ 145


xiii










FIGURE PAGE

6.11. Flow Patterns Induced due to the Placement of a T-groin
along the North Shoreline at Site C; Ebb Tide.............. 147

6.12. Flow Patterns at the Mouth of the Dubois Park Lagoon;
Flood Tide................................................. 147

6.13. Flow Patterns at the Mouth of the Dubois Park Lagoon due
to the Placement of an Impermeable Structure at the West
End of the South Jetty Rock Extension; Flood Tide.......... 149

6.14. Proposed Backfill of the West Extension of the South
Jetty. White Layer Represents Gravel, Coal Represents
Sand Fill, Filter Cloth is not Shown....................... 149

6.15. Flow Patterns at Dubois Park Beach; Flood Tide............. 151

6.16. Flow Patterns at Dubois Park Beach Resulting from the
Placement of Two Curved Groins Extending from Each End
of the Beach; Flood Tide.......... ........................... 151

6.17. Flow Patterns Resulting from the Placement of an
Underwater Sill between the Two Groins Shown in
Fig. 6.16; Flood Tide...................................... 154

6.18. Flow Patterns Resulting from the Implementation of
Sill Plan b in Fig. 5.6; Flood Tide........................ 154

6.19. Flow Patterns Resulting from the Implementation of
Sill Plan a in Fig. 5.6; Flood Tide........................ 156

6.20. Flow Patterns Resulting from the Implementation of
Sill Plan c in Fig. 5.6; Flood Tide......................... 156

6.21. Flow Patterns in the Southshore Promontory Area;
Flood Tide............................. ................... 158

6.22. Flow Patterns in the Southshore Promontory Area;
Flood Tide................................................. 158

6.23. Flow Patterns in the Southshore Promontory Area due
to the Implementation of the Solution Scheme Proposed
for this Site; Flood Tide.................................. 160

7.1. Suggested Locations for Test Groins....................... 165

A-i. Dimensionless Maximum Velocity, u' as a Function of
Keulegan's Repletion Coefficient.......................... 171

A-2. Lag e in Degrees as a Function of Keulegan's Repletion
Coefficient K .................................. .... 173










FIGURE PAGE

B-1. Vertical Displacement of the Current Meter due to
Current-Induced Drag Forces................................ 176

B-2. Vertical Displacement of the Current Meter versus Flow
Velocity .......................#* ... ...* ......... ....... .... .. 178

D-1. Lateral Distribution and Cross-Sectional Average of Sf
at Jetty Cross-Section C-1, October 14, 1982,
1820 Hours ....... ................................ ...... 189

F-1. Inlet Mouth and Offshore Bathymetry. Horizontal Scale
is in Meters. Depths are in Feet Below MSL................. 194

F-2. Bathymetry of Main Channel Region (Note: Sand Trap
is Full)................................................... 195

F-3. Bathymetry of Dubois Park Lagoon........................... 196

F-4. Bathymetry of Area West of Main Channel where the
Inlet/Channel Splits into two Reaches of the
Intracoastal Waterway... ...... ........................ 197

F-5. Bathymetry of North Reach of the Intracoastal Waterway..... 198

F-6. Bathymetry of the West Reach of the Intracoastal
Waterway**..................... ............................ 199

F-7. Offshore Bathymetry....................................... 200

G-1. Flap-type Wavemaker...... ................................ 201

G-2. Flap-type Wavemaker Theory. Wave Height to Stroke Versus
Relative Depths (Dean, 1983)............................... 202

G-3. Schematic of Wavemaker Generating Waves in the x-y Plane... 203

G-4. Definition for Wave Direction 8............................ 204

I-1. Schematic of a Roughness Element in a Velocity Field....... 210

J-1. Locations of Measurements Made in the Model for the
Existing Conditions and those under Phase One.............. 214

J-2. Locations of Current Velocity and Wave Height Measurements
Made in the Model with and without the Remnants of the
Existing Northshore Groin.................................. 218

J-3. Locations of Current Velocity Measurements Made in the
Model near the Proposed Flow Deflector with and without
a 6 m Gap as Shown ........................................ 220

J-4. Locations of Current Velocity and Wave Height Measurements
Made in the Model for the Three Proposed Sill Schemes...... 222

















CHAPTER I

INTRODUCTION

1.1 Introductory Note

Jupiter Inlet is located in northern Palm Beach County on the

southeast coast of Florida, about 28 km south of St. Lucie Inlet and

km north of Lake Worth Inlet (Figs. 1.1 and 1.2). It is a natural

waterway connecting the Atlantic Ocean with the Loxachatchee River.

Along both banks of the inlet, erosion and sedimentation problems have

become a matter of concern in recent years. An investigation to examine

these problems and to recommend appropriate remedial measures was

conducted. This investigation is described here.

Although Jupiter Inlet is relatively small, it is important for iti

aesthetic and recreational values, its value as a prime residential

development, and because it is the primary waterway connecting the

Loxahatchee River Estuary to the Atlantic Ocean. The physical and

biological characteristics of the inlet are typical of other such

waterways in the general geographic location; the bottom consists

primarily of sand interspersed with sea grasses and occasional oyster

beds, and the shoreline vegetation consists mainly of pine, scrub oak

and mangrove. The inlet covers approximately 50 hectares that are

circumscribed by 8 km of shoreline. The average volume of water present

in the inlet at any one time is approximately 1 million cubic meters

(McPherson et al., 1982).
























\ "" "v- .

o Tollohassee
0


"' Goinesville \7
o






N Tampa





0 JUP TER
0 INLET

Palm Beacho

Miomi






Key West *'-'
Fig Location Map of Jupiter Inlet.

Fig. 1.1. Location Map of Jupiter Inlet.































































Fig. 1.2.


Area Map of Jupiter Inlet.












1.2 Inlet History

Jupiter Inlet has existed as a natural waterway for at least 300

years according to historical records (McPherson, et al., 1982). The

first such record, consisting of explorers charts, indicates the

presence of the inlet in the year 1671. Originally, the inlet served as

the only outlet for the Loxahatchee River, Lake Worth Creek and Jupiter

Sound (Fig. 1.2), and as one of several outlets for the St. Lucie and

Indian Rivers. The resulting discharge from these sources was of

sufficient magnitude to prevent closure of the inlet except in events of

severe storm action that sometimes resulted in temporary closure. The

creation of St Lucie Inlet in 1892, the Intracoastal Waterway between

Jupiter Sound and Lake Worth Creek in 1896 and Lake Worth Inlet in 1918

resulted in a diversion of much of the flow through Jupiter Inlet. As a

result of this loss of flow through the inlet, the frequency and

duration of inlet closure greatly increased until 1947 when a regular

inlet maintenance schedule, primarily consisting of dredging, was

initiated by the Jupiter Inlet District (Escoffier and Walton, 1979).

This schedule of periodic dredging has since prevented closure of the

inlet and has maintained it in a navigable state. However, there are

other inherent problems that have yet to be solved.

1.3 Problems of Present Concern

As is the case with any coastal inlet exposed to littoral drift

from one predominant direction, Jupiter Inlet is beset by, 1)

navigational difficulties due to hazardous wave and current action as

well as shoaling near the mouth of the inlet, and 2) beach erosion

downdrift (south) of the inlet. In addition, erosion of the shoreline,

including that which has been armored by bulkheads as well as that in










its natural state, has taken place at a noticeable rate along the inner

banks of the inlet. Figures 1.3 and 1.4 show examples of this

erosion. Problems of shoaling well inland of the inlet mouth have

occurred along the northern bend of the Intracoastal Waterway, in the

public marina located on the south shore of the inlet and in the Dubois

Park Lagoon. A hydraulic sand bypassing scheme has been satisfactorily

maintaining a navigable channel through the mouth and mitigating erosion

downdrift of the inlet; this study focuses on the problems of erosion

and sedimentation along the shoreline within the inlet. Figure 1.5

shows the locations of these problem areas.

Sites marked A through I are of particular concern. Along the

north shore (A, B and C) the overall problem is one of erosion. The

entire reach (with the exception of the northernmost portion of site C)

is bulkheaded to protect valuable residential property in the Jupiter

Inlet Colony. At site A there appears to be some problem in retaining

sand in front of the bulkhead to act as a buffer against wave attack and

currents. This area has been used as a recreational beach cum partially

sheltered cove (formed between the beach and the rocks forming the

western extension of the north jetty) by people using the clubhouse

nearby. Elsewhere along this reach, various segments of the bulkhead

(erected by the property owners) are in different states of repair.

While some segments appear relatively undamaged, in other areas cracks

have occurred and subsidence has become a problem. In some cases

segments of the outer protective sheeting have collapsed thus exposing

the piles and inner sheeting. At site B and adjacent reaches, waves and

strong currents are believed to be the cause of the damage. Sand at the

bulkhead toe has eroded away except in pockets where it offers

















































Example of Shoreline Erosion at the Inlet.


Fig. 1.4. Example of Bulkhead Failure at the Inlet.


7- ; -~


---- ilCI,


. z



















V
A


<-2
C,


0
C,
-2


Jupiter Inlet Colony


Dubois


0 100 200m
scale


r


L P
L. t rlo.~J_


Deposition Basins


,5 :\M \a Ar Erosion
..... .:.-.: ..:: Accretion


Fig. 1.5. Problem Areas of Erosion and Accretion.










protection against direct wave and current attack. At site C and

adjacent reaches bulkhead damage and shoreline erosion is believed to be

due to currents and boat wakes (resulting from traffic through the

Intracoastal Waterway). Wave activity is observed to be lower here.

Location D corresponds to the shoreline behind rocks which form the

western extension of the south jetty. Here, the sand has eroded away

leaving an erosion scarp. Some Australian pines have fallen as a

result. This area is heavily utilized as it is a part of the Dubois

Park. The lagoonal channel (site E) and a portion of the lagoon itself

(site F) have experienced shoaling due to sand deposition. The lagoon

serves as a drainage basin for a rather extensive watershed. The

channel is the only draining outlet for the lagoon into the inlet.

Furthermore, tidal exchange between the inlet and lagoonal waters is

essential for flushing and water renewal. Small boats use the channel

at high tide to commute between the inlet and upstream residential

areas. The topography and vegetation of the area have been conducive to

the use of the channel area for picnics and other recreational

activity. It is essential to maintain the channel and minimize shoaling

there or in the adjacent waters.

At site G a public beach has been created by providing two short

groin-like structures with a sandy beach in between. The beach consists

of a curved shoreline stabilized by concrete on which sand has been

deposited. In recent years there has been a depletion of the sand

here. It is believed that wave and current attack is responsible for

this problem. The problem is compounded by the concrete which causes

significant reflections of the wave energy and enhanced scour. The

shoreline west of the beach (G) has as well been stabilized by rocks and











concrete. There is, however, concern that continued wave and current

attack might penetrate these defenses and erode the land. At site H the

promontory between the marina and the inlet is rather narrow. It serves

as a parking lot and picnic area and its erosion must be prevented. At

site I, the problem is one of deposition (near the tip of the

promontory). This has reduced docking space in the marina along its

north bank. Two or three docks are now useless as the bottom is expose!

at low tide. Furthermore, deposition is beginning to constrict the

channel for boat access. The specific causes of and solutions to these

problems are the main focus of this study and are addressed individual;

in Chapters III and V but are presented briefly as follows.

It is apparent that the causative forces for sand transport and

attack on structures in the inlet area are contingent upon tide-induced

currents and waves. The latter include approaching swells from the

ocean as well as boat wake-induced waves. With respect to sand

transport, waves primarily provide a mechanism for resuspension while

currents can resuspend and also transport sediment. The relative

magnitude of the influences of currents and waves differ in different

locations. There are regions of strong main or primary currents and

also regions of secondary cells or eddies where the strength is

typically much lower. Waves from the ocean generally penetrate in a

manner such that the wave crest is more or less normal to the jetties.

However once inside, their direction is altered due to refraction

resulting from depth changes, as well as due to diffraction. Refraction

causes the crests to bend both towards the north as well as the south

shorelines in a manner such that the shorelines become exposed to a

relatively direct attack as waves break on the shore. Such a phenomenon













at inlet channels is not uncommon (COEL, 1970). Additional effects come

from diffraction which produces a fairly complex wave field within the

confines of the channel.

At site A, the importance of refracted and diffracted waves and

eddy currents as causative forces of erosion are in that order. At site

B it is currents and refracted waves. Main currents and boat wakes are

the causative forces of erosion at site C. At site D, it is currents

that exist during very high tides. At sites E and F the problem is not

of currents or waves but of sand input from erosion at site D during

very high tides. Refracted waves and eddy currents cause the erosion at

site G. Main currents and refracted waves result in the erosion at site

H while the deposition at site I is due to sediment transport due to

currents.

Solutions to these problems must therefore, 1) reduce current

strength and/or wave activity in areas of erosion, 2) supply sand in the

same areas and 3) reduce the sand supply in areas of shoaling. The

major ongoing activity of relevance is the periodic dredging of the sand

trap and the Corps of Engineers dredging basin (every 2-4 years on the

average) and the placement of the spoil downdraft of the inlet. This

activity has been beneficial in that it controls downdrift erosion and

keeps the inlet channel as well as the Intracoastal Waterway in a

navigable state. It is evident therefore that any proposed solutions

for the problems of erosion and shoaling must be viewed in conjunction

with the dredging and spoil deposition routine which must continue as

such.










1.4 Purpose and Scope of the Study

The purpose of this study was to formulate and recommend a remedial

scheme that would mitigate the problems of erosion and sedimentation at

Jupiter Inlet. Specifically, this scheme must consist of measures,

either structural or non-structural, that would: 1) eliminate or at

least substantially decrease erosion along the shoreline inland of the

inlet mouth and 2) minimize shoaling at specified problem areas within

the study area. The study consisted of, 1) field work in which

prototype data were collected and on-site inspections and observations

were made, 2) data analysis for evaluating the hydraulic and sedimentary

characteristics of the inlet, and 3) a physical model in which solution

options were tested.

1.5 Previous Studies

Very few previous studies can be found that have attempted to

address all of the problems associated with the maintenance of Jupiter

Inlet. Specifically, over the period in which this study was conducted,

no previous investigations related to the shoaling and erosion problems

inland of the inlet mouth were found. The primary issue addressed in

previous studies of the inlet area has been the problems associated with

beach erosion of Jupiter Island and shoaling in the immediate area of

the inlet mouth.

The U.S. Army Corps of Engineers published a survey of the inlet in

1966 proposing federal maintenance of the inlet channel as a connection

between the Intracoastal Waterway and the ocean together with a weir-

jetty at the north side of the inlet for transferring littoral drift

across the inlet. This proposal was not approved; channel maintenance

remained the responsibility of the Jupiter Inlet District and the north

jetty remained unchanged (Corps of Engineers, 1966).











The University of Florida Department of Coastal and Oceanographic

Engineering conducted a study of the inlet during the period 1967-1969

(COEL, 1969). This study was a combination of field, model, and office

investigations and again focused primarily on the problems of inlet

shoaling and erosion of the south beach. The conclusions reached in

this report consisted of recommendations to: 1) increase the lengths of

both the north and south jetties, 2) construct a weir section at the

north jetty that would direct littoral drift into an adjoining sand

trap, and 3) enlarge the overall sand trap volume near the mouth.

With the exception of studies documenting the bypassing of sand

from the sand trap to the south beach and periodic maintenance dredging

of the Intracoastal Waterway by the Corps of Engineers, there are

believed to be no published reports regarding recommended maintenance

procedures for the inlet since 1970.

1.6 Selected Methodology

Physical modeling is a recognized method for providing accurate

predictions of the performance of a particular design project. The fact

that such a model is a scaled-down version of its prototype allows for

accurate reproduction of the geometric, kinematic and dynamic

characteristics of the prototype. In addition, physical modeling allows

identification of problem areas and features that may not be of initial

concern in the prototype and which may have otherwise been overlooked.

The primary drawbacks are the costs and time of construction and

maintenance as well as considerable set-up time between the testing of

different situations in the model.

The type of model employed for this investigation was an

undistorted, fixed-bed model of the study area. An undistorted model










maintains the same scale ratio in both the vertical and horizontal

dimensions. Fixed-bed indicates that the prototype sediment transport

phenomena are not reproduced in the model. This combination of a fixed

bed and no distortion enables the simulation of tides, waves and

currents (the three primary components causing sediment transport in the

inlet) simultaneously with the necessary degree of overall accuracy

(Sager and Hales, 1976). While the actual sediment transport phenomena

were not modeled, the hydraulic forces which cause these phenomena were

simulated. This resulted in an understanding of the causes of the

problems at the inlet, rather than a mere reproduction of these

problems. The model served as the means by which remedial measures were

tested so as to predict their effectiveness and to expose any

detrimental side-effects that they may have caused. A more detailed

discussion of the physical model is presented in Chapter IV.

The three main phases of the study are presented as follows:

Chapters II and III discuss the data collection and analysis phase,

Chapter IV describes the model construction phase, and Chapters V and VI

present potential solutions developed for the inlet and the testing of

these solutions. Chapter VII presents a summary of the study and the

resulting recommendations. Nine appendices have been included.

Appendix A presents a procedure by which flow velocities corresponding

to a storm surge were calculated. Appendix B describes the depth-

correction factor applied to velocity profile measurements. Appendix C

presents dimensionless transverse velocity profiles obtained at four

cross-sections in the inlet and an interpretation of these profiles.

Appendix D describes the procedure by which friction slopes and bed

roughness calculations were carried out for each of the four






14


cross-sections. Appendix E provides an example of and the overall

results from'the calculations of the refraction of the predominant deep

water wave directions offshore of the inlet into shallow water.

Appendix F includes a map of the inlet bathymetry from which the model

was constructed. Appendix G presents the theory behind and practical

application of the "snake-type" wave generator that was used to produce

the directional waves determined in Appendix E. Appendix H describes

the procedure by which the weirs used in the model to simulate tidal

conditions were calibrated. Appendix I presents a discussion of the

theory behind and calculations made in determining the number and

location of roughness elements in a physical model. Finally, in

Appendix J, test results representing measurements and the stability

parameter are reported.

















CHAPTER II

FIELD INVESTIGATION

2.1 Overview

Data collection was carried out over a six month period from

September 1982 through February 1983. Tidal records were obtained and

velocity profiles, sediment samples, hydrographic surveys and drogue an

dye studies were carried out over the study area as defined by the

following boundaries: from the seaward limit of the study area

corresponding to a distance 1050 m offshore (ten inlet widths) to the

north and west limits as defined by the Intracoastal Waterway, and along,

the southern limit of the study area as determined by the south shore i

the inlet including the lagoon extending into the Dubois Park area.

These boundaries are shown in Fig. 2.1. The following paragraphs

describe the methods employed for data collection.

2.2 Hydrographic Surveys

Hydrographic survey information on the inlet was obtained from

various sources. This information included surveys of the bathymetry

seaward of the mouth as well as surveys of the entire inlet study area

up to + 1.5 m elevation; with the exception of the northwest shore area

and the southshore marina area which were surveyed during the field

study. Comparative historical surveys were also available which show

beach erosion over the past 100 years near the inlet as well as relative

erosion and accretion levels offshore in the last 30 years. An

interpretation of these data are provided in Figs. 2.2 and 2.3. In
























-f~..... Z


OCEAN
ATLANTIC


Fig. 2.1. Boundaries of the Inlet Study Area.






































ISOLINES OF EQUAL VERTICAL
CHANGE IDENTIFIED IN METERS
S EROSION
ACCRETION


-- 1957 MHW SHORELINE
1979 MHW SHORELINE
CONTOURS IN METERS.


Fig. 2.2. Areas of Relative Erosion and Accretion between 1957 and 1979.













ATLANTIC


OCEAN


A \,


o 200 '4om Mean High Water Line
scale -. 1883
------- 1929
1979

Fig. 2.3. Mean High Waterline Changes near Jupiter Inlet between 1883 and 1979.











addition, surveys were performed at cross-sections where velocity

profiles were taken (see Fig. 2.4) so as to provide accurate measurement

of the areas and depths at these cross-sections. Survey data were

available for the Intracoastal Waterway portion within the study area.

2.3 Water Surface Elevations

Variations of water surface elevations due to tides were obtained

by employing Stevens Type F gages at seven locations in the inlet.

These gages were leveled with reference to the 1929 NGVD and were

adjusted to provide continuous records over periods of eight days.

Every eighth day, the gages were reset and outfitted with new chart

paper. This procedure was continued over the six month data collection

period. A few problems, mainly due to equipment failure or otherwise,

were encountered. Tide gages were placed at each of the extreme

boundaries of the inlet as well as at locations near the problem areas

of erosion and deposition. Figure 2.4 shows the locations.

Gage T-1: This gage was located at the west end of the south jetty

cap defining the entrance to the inlet and the eastern boundary of the

study area.

Gage T-2A: This gage was located on a private dock on the north

bank of the inlet, corresponding to an area of erosion.

Gage T-2B: This gage was located on a dock in the marina located

in the southwest basin of the inlet, corresponding to an area subject to

shoaling.

Gage T-2C: This gage was located on a private dock situated on the

northeast bend where the inlet meets the northern reach of the

Intracoastal Waterway. This area also corresponds to one of erosion.
















































0 100 200m
scale


Tide Recorders
Sept. 82/Feb.83
--- Boundary Limit Cross-Sections
Oct 82
Continous Bendix Current Meter
Jan.83
Continous Current Meter
Jan.83
SWove Goge
Jan.83


Fig. 2.4. Locations and Dates of Operation of Tide Recorders, Current
Meters and Wave Gage.










Gage T-3: This gage was also located on a private dock, situated

on the east bank of the northern reach of the Intracoastal Waterway.

This location corresponds to the northernmost boundary of the study

area.

Gage T-4: This gage was located on a dock owned by the U.S. Coast

Guard situated at the west end of the north bank of the inlet and

corresponding to the westernmost boundary of the study area.

Gage T-5: This gage was located on a walkway overpassing the

lagoon immediately southwest of the inlet entrance and extending into

the Dubois Park area. This location represents the southernmost

boundary of the study area.

An example of a tidal record is shown in Fig. 2.5.

2.4 Extreme High Water Levels

High winds and relatively large atmo=nheric pressure gradients

associated with tropical storms and hurricanes can cause water levels in

the ocean as well as inside an inlet to be much higher than the

astronomical levels predicted by the National Ocean Survey Tide

Tables. This phenomenon is referred to as storm surge and may result in

the flooding of land areas near the ocean or an inlet. Such flooding is

especially severe if conditions conducive to storm surge occur during a

spring tide.

According to Bruun et al. (1962), for the coastal regions of North

Palm Beach County the return period for various levels of storm surge

greater than or equal to the level indicated is predicted as follows:

1.25 m or higher above MSL 6 7 years

1.5 m or higher above MSL 12 14 years

2.0 m or higher above MSL 20 22 years














Ir 00IU tcD
E Range Rang
S 80 HW


i 60- L
w 1
40

S 20

1929MSL
LW
-20 October 15-21,1982
LW Tide Gage 4
-400- I --IJ I -I I I I I I Io I' I A -I
0 48 72 96 120 144 l
ELAPSED TIME (Hours)
Fig. 2.5. A Sample Tide Record for Lighthouse Crossing C-4. HW High Water; LW L Low Water.










2.5 m or higher above MSL 34 36 years

3.0 m or higher above MSL 58 60 years

3.5 m or higher above MSL 100 years

2.5 Flow Cross-Sections and Current Profiles

Five locations were chosen for cross-sectional current velocity and

discharge measurements. These locations are indicated in Fig. 2.4. The

selection of four of these locations was based on the location of the

study area boundaries. The fifth cross-section (C-2) was chosen so that

in the event of measurement failure or error at C-l, C-2 could serve as

the control volume (between C-2, C-3, and C-4) boundary for the study

area. Each of the five locations corresponds to the positioning of a

tide gage.

Hydrographic surveys were obtained in detail at the cross-sections

with exception of C-5. The profile of cross-section C-5 consisted of a

rectangular culvert and was easily determined. The resulting profiles

and calculated areas are shown in Fig. 2.6.

2.5.1 Instantaneous Velocity Profiles

Vertical velocity profiles were obtained at representative points

across each of the cross-sections with the exception of C-5. The

measurements were obtained from a boat (the position of which was held

constant by a surveying crew) using an (model number 19089) Ott meter.

Measurements were made at every 0.5 m of depth at four locations along

each cross-section. Figures 2.7 and 2.8 illustrate the procedure used

in obtaining the velocity profiles. As expected, the strongest currents

were recorded at the mouth (C-l) where velocities approaching 2.2 meters

per second were obtained; the lowest values were recorded in the

Intracoastal Waterway (C-3) where the flow was visibly much slower.















MSL-



E,
ci-
E


.- I
0 25


Fig. 2.6a.


Jetty Crossin C-I
Area d 435m


I I
50 75


Profile of Jetty Crossing C-1.


I '
100 meters


MSL Refers to NGVD.


Dubois Park Culvert
Crossing C-5
Areoa4.2 m2


2 3 meters


Fig. 2.6b. Profile of Culvert Crossing C-5.


MSL-


- I
0 I












Main Channel Crossing C-2
Area = 490m2


-8-'- I I I I I I
0 25 50 75 100 125 150 meters

Fig. 2.6c. Profile of Main Channel Crossing C-2.


Intracoastal Waterway
Crossing C-3
Area 280m2


0- I I
0 25 50


75 meters
75 meters


Fig. 2.6d. Profile of Intracoastal Waterway Crossing C-3.


MSL-




























Lighthouse Crossing C-4
Area o490 m


- I I-' I I
0 25 50 75 100 125


I I I
150 175 200
meters


Profile of Lighthouse Crossing C-4.


Fig. 2.6e.


--~-
-------
------
----













Waterway


Bank -


Ai


Boat


Bearing


Fig. 2.7.


Positioning Procedure for Obtaining Velocity Profiles (Hayter
and Mehta, 1979).


ATidal Range
9 Tidal Range


Continous Record
Current Meter


Fig. 2.8.


Cross-Sectional View of Procedure for Obtaining Instantaneous
Velocity Profiles and Continuous Velocity Record (Hayter and
Mehta, 1979).












2.5.2 Continuous Velocity Measurements

In the last month of data collection, Marinco Inc. Type B-10

current meters were installed at all cross-sections with the exception

of C-5 where a Bendix Q-16 current meter was installed. These meters

provided a continuous current velocity record at a fixed position in

each cross-section. These data, combined with those of the tidal cycle

and geometry of each cross-section, were used to estimate the

corresponding time-discharge records for each cross-section using a

previously developed procedure (Hayter, 1979). The data collection was

fairly continuous over time; some interruptions occurred when the meters

became clogged with seaweed or fishing line and did not operate for a

period of some hours. Figure 2.8 gives a schematic of the placement

scheme for the continuous current meters, while Table 2.1 gives their

specific locations at each cross-section.


Table 2.1. Current Meter Positions for Continuous Time-
Velocity Measurements


Cross-Section No. Horizontal (m) Elevation* (m)


C-I 28 (from north jetty) 3.0

C-2 23 (from north bulkhead) 2.5

C-3 23 (from east shoreline) 1.0

C-4 19 (from north shoreline) 2.0

C-5 1.5 (center of culvert) 1.0


Relative to 1929 MSL










2.6 Drogue Study

A drogue study was carried out on November 18, 1982 during a flood

tide corresponding to a tidal elevation of +0.75 m at the inlet. The

primary purpose of these studies was to determine the direction and

magnitude of the flow as well as the locations of regions of high flow

velocities. Figure 2.9 provides an example of the resulting plot of a

drogue course over time. Three drogues were used consisting of 0.1 m

thick styrofoam circles with directional anchors extended approximately

one meter from the center by nylon rope (Fig. 2.10). Each drogue was a

separate color so that they could be distinguished when tracking their

separate paths. The drogues were launched from a boat at one minute

intervals and were tracked by aerial photography.

2.7 Dye Studies

Dye studies were carried out over the same two day period during

flood tides at the inlet. These studies served primarily to indicate:

1) mean flow directions in the channel, 2) regions along the banks where

flow circulation occurs as a result of eddies driven by the flow in the

main channel, and 3) relative degree of flow dispersion taking place at

the surface. Figure 2.11 provides a chronological series of dye study

observations as interpreted from aerial sketches and photographs. The

dye Rhodamine B (red in color), was injected near the north jetty while

Flourescein (a green dye), was injected at the south jetty.

2.8 Wave Information

A Viatran (absolute pressure transducer) wave measuring gage was

placed approximately 800 meters offshore of the inlet at a depth of

approximately 6 m. The gage recorded wave heights and periods for a

seventeen minute interval once every hour over the period































X ROUTE DISTIm) TIME() VEL.i/s)
SBOAT-013 232 160 1.45
BOAT-GI3 286 220 1.30
80AT-W13 345 280 1.23
013-014 150 175 0.86
G13-614 115 17S 065
W13.W14 177 175 1.00
014 016 180 180 1.00
G14-G01 91 180 0.51 *
W14 W16 189 180 1.05
016 .017 110 93 1.15
WIS6 -.W 70 95 0.74
017 .011 76 90 0.85
WIT .W18 70 90 078
018 -019 76 100 076
WIS -WIS 46 100 046
019 -020 107 155 069
WIS -W20 110 155 0.71
020 -022 61 310 0.20*
W20 -W22 100 310 0.33.
DROGUE PICKED UP AT THIS POINT
Fig. 2.9. Plot of Drogue Course over Time.


0 75 150Im
SC~l@


J


OCEAN






































V Directionol Anchor
SIDE VIEW


TOP VIEW


Fig. 2.10. Design of Drogue.










































Time 81,2S.3S am.
Elcsed Time 3.4mine.
(0)


Time 8*'36.20oa..
Elapsed Time 14.3 mins.
(d)


Times 8a29.50 sm.
Elapsed Time 7.mlinsr.
(b)


Time I39.00 .m.
Elopsed Time ?170mins.


Time a8 32.10 lm.
Elapsed Time 10.2 mise.
(c)


Time Is o42.50 am.
Elapsed Time 20.8 mini.
(f)


Fig. 2.11. Elapsed Time Plot of Dye Movement, Nov. 18, 1982.


~C_










January 27-30, 1983. In addition, data were obtained from a similar

permanently installed wave gage (one of nine comprising the University

of Florida Coastal Data Network) located offshore of West Palm Beach,

Florida (20 km south of the inlet), in 10 meters of water. As neither

of these gages measure wave direction, information on the predominant

directions from which waves reach inlet was derived from Volume 4 of the

Summary of Synoptic Meteorological Observations (SSMO) published by the

U.S. Naval Weather Service Command (1970). Table 2.2 provides a one

year summary of the wave climate at West Palm Beach including the period

in which the field investigations were made.

2.9 Sediment Samples

Sediment samples were taken from several locations at the inlet in

two phases. Each phase consisted of samples taken in a different

location and each was performed with a different objective in mind.

Fig. 2.12 indicates the location of all sediment samples taken. The

analysis of all samples taken is presented in Section 3.9. In the first

phase, samples were taken at specified locations as a means of

determining the nature and source of the sediment in areas where

deposition (shoaling) had occurred. Sample locations were chosen either

as areas of immediate deposition, areas adjacent to areas of deposition,

areas along the route over which the deposited sediment was transported,

or potential source areas of sediment. Locations denoted by numbers 1

through 21 in Fig. 2.12 indicate the sample sites in this phase.

The second phase of sediment sampling was conducted with the

purpose of determining the nature of the sand deposited in the sand trap

(and subsequently transferred to the south beach). Accordingly, samples

were taken at locations in and around the sand trap and were analyzed by












Table 2.2. Wave Data for West Palm Beach


April May June July August September October December January February March Average
1982 1982 1982 1982 1982 1982 1982 1982 1983 1983 1983 Value


Tavg 4.5 5.0 4.5 4.6 4.7 9.3 8.2 5.2 4.7 4.7 5.0 5.9
(sec)


Tmax 9.0 9.0 11.0 8.5 10.5 11.5 12.0 12.0 11.0 12.0 12.0 10.7
(sec)


Havg 0.30 0.52 0.25 0.21 0.25 0.33 0.52 0.76 0.4 0.75 0.52 0.43
(m)


Hmax 1.3 1.5 1.55 1.2 1.5 1.65 1.9 2.2 1.6 2.1 1.9 1.7
(m)


NOTE; No data were obtained for November, 1982.

Tavg average wave period

Tmax = maximum period

Havg = average wave height
avg maximum wave height
H maxinum wave height





















































-F---- z


0 100 200m
l I ll I
scale










0-@ COEL Sieve Analysis

Robert E.Owen and Assoc.
Sieve Analysis


Fig. 2.12. Sediment Sample Sites.




'












Robert E. Owen and Associates of West Palm Beach, Florida. Locations

denoted by numbers 22 through 32 in Fig. 2.12 indicate the sample sites

for this phase.

2.10 Runoff

Data concerning the contribution to the overall discharge through

the western boundary (Intracoastal Waterway) of the study area by

tributaries in the form of freshwater inflow were obtained from the U.S.

Geological Survey Water-Data Report (1981). Table 2.3 lists the

maximum, minimum and average daily discharge values for each tributary

as recorded for the water year October 1980 to September 1981. The

tributaries are grouped according to their contribution to one of the

three primary tributaries discharging directly upstream (west) of

Jupiter Inlet. These three primary tributaries, Canal C-18 and the

north and northwest forks of the Loxahatchee River, compromise the three

forks of the Loxahatchee River Estuary and are shown in Fig. 1.2.


Table 2.3. Freshwater Inflow into the Three Forks of the
Loxahatchee River Estuary


Maximum Daily Minimum Daily Average Daily
Discharge Discharge Discharge
Tributary (m3/sec) (m3/sec) (m3/sec)


Northwest fork
Kitchings Creek 0.63 0.00 0.14
Cypress Creek 7.41 0.03 1.12
Hobe Groves Ditch 4.67 0.01 0.20
Loxahatchee River at 16.21 0.20 1.61
State Road 206

North fork
Unmaned 1.87 0.00 0.10

Southwest fork
Canal-18 9.43 0.00 0.88










2.11 Winds

Data concerning the wind conditions at West Palm Beach were

obtained from records compiled by the National Climatic Center (NOAA,

1980-81). Maximum and average wind speed from different directions as

well as the percentage of occurrence of these speeds and directions were

compiled over the period January 1980 December 1981. The wind

conditions at the inlet should not differ much from those in the West

Palm Beach area.

Interpretation of the wind data reveals that velocities are greater

from the northeast sector but the duration and percentage of occurrence

are greater from the southeast sector. The yearly average wind velocity

from the northeast sector is about 18 km/hr while that from the

southeast sector is about 14.5 km/hr.

















CHAPTER III

DATA ANALYSIS
3.1 Overview

Data were analyzed and interpreted so as to provide information on

the hydraulic and sedimentary characteristics of the inlet. This

information yielded necessary input parameters for both the

computational procedures utilized and the physical modeling of the

inlet. In addition, this information provided for a better

understanding of the causes of the problems at the inlet. The following

paragraphs describe the procedures involved in the data analysis and

interpretation.

3.2 Hydrographic Surveys

The hydrographic survey of June, 1981, detailing the bathymetry of

the inlet helped in providing: 1) a general description of the

bathymetry of the inlet and surrounding areas, 2) an understanding of

the field observations and hypotheses regarding bathymetric trends in

the inlet, and 3) estimates of sediment volumes present at specific

locations within the inlet.

The survey of October, 1981, describing the bathymetry of the

offshore region immediately seaward of the inlet indicated the presence

of a relatively small ebb tidal shoal or bar. This corresponded with

observations made during the field investigation and compliments

estimates of the offshore bar volume made in this study (Section

3.10.2). These surveys along with aerial photographs also indicated



38










that shoaling had indeed occurred in the Dubois Park lagoon, the

southshore marina area and the bend in the Intracoastal Waterway.

Calculations (made from the surveys) of the volume of sand deposited in

the sand trap resulted in a value of 92,000 m3 and were found to be in

good agreement with prior sand trap dredging records which indicated an

average volume of 86,000 m3 between 1970 and 1979 (Jones, 1976).

The survey data were interpreted so as to determine bathymetric

profiles extending offshore of the inlet shoreline areas that have

undergone erosion. This provided the necessary information to calculate

sand volumes required to renourish these areas. The surveys also

indicated that (as detailed in Fig. 2.6c) the inlet area immediately

west of the mouth is progressively deeper from south to north across the

channel. This bottom feature causes waves entering the inlet to refract

towards the Dubois Park Beach, thereby accelerating the erosion rate

there. This phenomenon was first observed during the field-

investigation.

A cross-section of the "empty" sand trap was superimposed over a

representative cross-section of the inlet area where the trap is located

in order to determine the change in cross-sectional area when the trap

is dredged (Fig. 3.1). The resulting cross-sectional area, Ac, showed

an increase from 534 m2 to 708 m2. Calculations similar to those in

Appendix A based on tidal inlet relationships developed by Keulegan

(1967) were then made in order to determine the resulting change in

maximum flow velocity expected from the dredging of the trap. The

maximum flood velocity decreases from 1.95 m/sec to 1.65 m/sec while the

maximum ebb velocity decreases from 2.25 m/sec to 1.90 m/sec as a result

of dredging the sand trap according to the specifications of Fig. 3.1.


















0-



E -2-
Present Profile 6/24/81
SArea = 534 m2

I -4-

S\ / Profile After Dredging
E Area= 708m2 /
- -6- L------ _---J
0
Z


-8 I I I -
0 40 80 120 160 200

DISTANCE (m)

Fig. 3.1. Illustration of the Change in Area of a Typical Main Channel Cross-Section when the Sand Trap
is Dredged.










The effect of this decrease in flow velocity will be to decrease the

magnitude of the erosive forces along the shoreline while increasing the

likelihood of deposition in the trap (as opposed to areas further

inland). As the trap begins to fill up the cross-sectional area of the

inlet decreases and the flow velocities increase, thereby increasing the

magnitude of the erosive forces along the shoreline and decreasing the

tendency of deposition in the trap until conditions equivalent to those

when the trap is full exsit. As a result, it may be concluded that

conditions most conducive to erosion along the shoreline and deposition

of the eroded material further inland exist when the trap is full.

Based on this conclusion, model testing was limited to conditions

corresponding to the filled trap.

3.3 Tide Records

Data obtained at the seven tide gages were utilized in the

computation of inlet hydraulic parameters as well as in the calibration

of the physical model. Analysis of these data resulted in the

determination of tidal ranges at each gage, ratios of these ranges

relative to that of the inlet mouth (gage T-1), and lags of high water

and low water at each gage relative to high and low water at gage T-1.

These data are presented in Table 3.1. In addition, as an illustration,

a cumulative histogram of the tide record from gage 2A over the time

period September 30 to November 7, 1982 is provided in Fig. 3.2. Data

from the National Ocean Survey (NOS) Tide Tables indicate an average

tide range of 0.75 m and a spring tide range of 1.1 m for the inlet

vicinity. The tidal ranges measured corresponded well with the NOS

predictions in terms of magnitude (within 0.1 m) but were found to be

less comparable in terms of the time of occurrence (within 30 minutes).




















I00




z 80-
O
a:
U
0 60-

0



4O
U




200
S 40










30 50 70 90 110
RANGE (cm)


Fig. 3.2. Cumulative Histogram of Wave Heights (cm) at Gage 2-A over
the Period September 30 November 7, 1982.











Table 3.1. Tidal Ranges, Lags and Range Ratios Relative to Inlet
Mouth, January 26 February 2, 1983


Maximum Range Lag (High) Lag (Low)
Location Range (m) Ratio (min) (min)

Inlet Vicinity 1.10 0.90 -15 -10
Ocean*** 1.10 0.90 -48 -12
Gage T-1 1.22 1.00 0 0
Gage T-2A 1.05 0.86 4
Gage T-2B** 0.80 0.65 10 12
Gage T-2C 0.82 0.67 5 6
Gage T-3 0.76 0.62 29 16
Gage T-4 0.91 0.75 44 9
Gage T-5 0.43 0.35 234 151


*Relative to gage T-1.

Obtained from NOS prediction for Jupiter Inlet, Longitude 8005'
West Latitude 26*57' North.
*A*
Obtained from water level data from the offshore wave gage.
Negative sign indicates high or low tide occurred before that of
the inlet.
****Data obtained over the period January 19 January 26, 1983.


3.4 Storm Surge

Data from historical storm surge records were compiled by Bruun

et al. (1962) so as to provide a prediction of the return period for

various surge levels (Section 2.4). Normally, this information would be

used to determine a design storm surge level corresponding to a 50 or

100 year return period to be used as a worst-case condition for testing

in the model. However, because the solution options (Chapter V) were

all to be implemented within the inlet and not on the land area above

+1.5 m, a storm surge of +1.5 m, corresponding to a fifteen year return

period was chosen as the worst-case condition. In addition, the model










provides an accurate representation of the topography of the inlet study

area only up to an elevation of +1.5 m. As a result, a storm surge

greater than +1.5 m would not be accurately modeled and, therefore,

neither would the effects of such a surge on the proposed solution

options.

Field data similar to those obtained for normal flood and ebb flows

were not available for storm surge conditions. As a result hydraulic

relationships developed by Keulegan (1967) were utilized in order to

determine the resulting maximum flow velocities due to a 1.5 a storm

surge at the inlet. Appendix A presents relevant calculations by which

these flow velocities were determined.

3.5 Analysis of Vertical Velocity Profiles

3.5.1 Vertical Velocity Profiles

Figure 3.3 shows typical profiles of the vertical velocity

distributions for the jetty cross-section C-1. These measurements were

made on October 14, 1982 between 1800 and 1900 hours. However for the

purpose of further analysis it will be assumed that they represent

instantaneous values at time 1830 hours. Figure 3.4 presents a

corresponding logarithmic plot for the same profile. These profiles, as

well as most others obtained from the collected data, exhibited the

characteristic (for turbulent open channel flows) logarithmic velocity

decay with increasing depth. The depth-averaged velocities, u, for each

of the measurement locations, were determined by integrating (over the

depth of flow) the vertical velocity profiles, and are included in

Fig. 3.3.

At locations where the flow velocity exceeded approximately one

meter per second, the depths at which velocity measurements were taken





















0.7


-J 0.6 # 4
#3
o #2
r-
z 0.5



w /









0 meters

0.0 0.5 10 1.5 2.0 2.5
VELOCITY (mps)

Fig. 3.3. Vertical Velocity Profiles for Jetty Cross-Section C-I taken
October 14, 1982 at 1830 Hours.

























































U/u*


Logarithmic Plot of the Vertical Velocity Profiles for Jetty
Cross-Section C-1.


Fig. 3.4.











were corrected to account for horizontal displacement and the resulting

vertical displacement of the Ott current meter due to drag forces

associated with higher flow velocities. Appendix B presents the depth-

correction calculations.

3.5.2 Depth-averaged Transverse Velocity Profiles

Figure 3.5 shows a plot of depth averaged velocity, i, based on the

vertical profiles in Fig. 3.3, against the location of the profile as

measured from the indicated shoreline. The curve connecting these

points is assumed to represent a continuous transverse velocity profile

for the indicated cross-section. Values of G, profile position, and the

mean time corresponding to the cross-sectional velocity measurements

were non-dimensionalized and plotted in the manner shown in Fig. 3.6 in

order to present the results in a generalized manner. Similar plots for

the non-dimensionalized transverse velocity profiles obtained at each

cross-section are presented in Appendix C. The parameters describing

the tidal conditions corresponding to the measurements on which these

plots are based are defined as follows (Mehta and Sheppard, 1977):

W width of the flow cross-section at the time the vertical velocity

profiles were measured,

x distance from the shore on which the tide box was installed to the

location of the stations where the profiles were obtained,

K x/W dimensionless parameter to normalize the abscissa,

u3 vertically averaged horizontal velocity obtained from averaging the

vertical velocity profile measured at each station,

g = acceleration due to gravity,
































0.4




0.2 Date 10/14/82
Time: 1830
-- Flood Tide
w= 105m

0 0.4 0.8 I.2 1.6 2.0 2.4
i (m/sec)


Fig. 3.5. Plot of Transverse Depth-averaged Velocity Profile for Jetty
Cross-Section C-2.



























































Dimensionless Transverse Velocity Profile for Jetty Cross-
Section C-l.


Fig. 3.6.










R, = range of tide at the cross-section during the same stage of the

tidal cycle during which the velocity profiles were obtained (see

inset of Fig. 3.6),

v = u/gR = dimensionless parameter to normalize the ordinate,

TF or Tg time interval of flood or ebb tide (see inset of Fig. 3.6)

determined from the tide record by the gage at the cross-

section,

tl = time interval from the beginning of flood or ebb flow to the time

the velocity profiles were obtained, and

8 ti/TF or ti/TEg dimensionless parameter to determine during what

stage of flood or ebb tide the velocity profile was

measured.

3.5.3 Continuous Velocity Measurements

In each of the five cross-sections, continuous velocity

measurements were obtained over minimum time periods of 50 hours.

Figure 2.8 shows a typically located current meter. Records were

obtained over the period January 26 February 2, 1983. Current

magnitude and direction recorded on chart paper as shown in Fig. 3.7 by

the meter at cross-section C-5 were later digitized. Similar data for

the other four cross-sections were recorded in digital form. Table 2.1

lists the locations where the current meters were installed at each

cross-section.

3.5.4 Discharge Computations

The continuous velocity data were utilized in a single point-

velocity discharge computational procedure (Hayter, 1979) to obtain

continuous discharge records for each of the cross-sections. In

addition to the continuous velocity data, the computer program requires



















FLOOD

EBB


O 15 30 45 60 75 9C

TIME (mins)

Fig. 3.7. Typical Current Meter Chart Record for Lagoon Cross-Section C-5.


I I I I

Current Direction




Current Magnitude

S^


0.5











input in the form of water surface elevation, bed roughness and geometry

of each cross-section. If the bed roughness value of a specific cross-

section is unknown, the computer program has the capability to calculate

this value given the instantaneous measured water surface elevation and

discharge as well as the friction slope for the cross-section. The

instantaneous values for the discharge and the friction slope were

calculated from the vertical velocity profiles (see Fig. 3.8). The

corresponding water surface elevations were obtained from the tide

records. Friction slopes and bed roughnesses were determined as

described in Appendix D.

Table 3.2 presents the maximum flood and ebb discharges through

each cross-section and their time of occurrence relative to maximum

discharge at the inlet mouth. Figure 3.9 gives the flood and ebb

discharges at each cross-section at the time of maximum discharge at the

inlet mouth. The data included in Table 3.2 and Fig. 3.8 are based on

the results of the aforementioned computations.

Analysis of Fig. 3.9 reveals a considerable difference in the

discharge through the inlet mouth during ebb and flood flows. That the

discharge during ebb is much greater than that during flood is believed

to be due to two phenomena: 1) Discharge through the mouth during flood

flow is due entirely to tide-induced flow. Discharge through the mouth

during ebb flow, while due primarily to tide-induced flows, also

contains an additional contribution from the Loxahatchee River Estuary

in the form of freshwater runoff from inlet areas. 2) It is believed

that a significant contribution to the ebb discharge is made from the

reach of the Intracoastal Waterway extending west and south of the

inlet. Some of the water entering the larger Lake Worth Inlet south







53









1.0




0.8

Q=W Ohdk

0= Instantoneous Discharge
0.6- W= Instantaneous Width
5 = Instantaneous Deoth-Averaged Velocity
x h=Corresponding Instantaneous Depth


04-



0.2-

Date- 10/14/82
Time: 1830
Flood Tide
00' -1 I I I
0 20 4.0 6.0 8.0 100 12.0

h (m2/sec)


Fig. 3.8. Plot of the Product of the Depth-averaged Velocity and the
Depth at Each Location Against Dimensionless Width K.
Integration of this Plot Results in the Instantaneous
Discharge Through the Jetty Cross-Section C-1 at 1830 hr on
10/14/82.






















'7 125


S---- 200m

0 100 200 m


FLOOD TIDE EBB TIDE
1/28/83 e0614 1/28/8301136

Fig. 3.9. Discharge Through Each Cross-Section Corresponding to Maximum Discharge Through the Inlet Mouth.


170







55


during flood flow probably returns to the ocean through Jupiter Inlet

via the Intracoastal Waterway (van de Kreeke, 1976). The combined

effect of these three phenomena is considered to be of sufficient

magnitude so as to result in the observed difference in ebb and flood

discharge rates.


Table 3.2. Maximum Discharge through Each Flow Cross-Section


Ebb Flood
Maximum Maximum
Section Discharge Lag Section Discharge Lag
Number (m /sec) (Minutes) Number (m /sec) (Minutes)

C-1 1060 -- C-1 770 --
C-2 1060 -2 C-2 770 4
C-3 143 -12 C-3 200 101
C-4 936 -1 C-4 651 46
C-5 2 224 C-5 3 151


Data based on results from single point-velocity discharge
computation procedure (Rayter, 1979).

*Lag is in reference to time of maximum discharge at inlet mouth.
Negative sign means maximum discharge was earlier than that at the
inlet mouth.


3.6 Drogue Study

Drogue motion over time plots, such as that shown in Fig. 2.9,

revealed that flood flow is concentrated along the north bank of the

inlet. In addition, the paths indicated that the flood tidal velocity

vector exhibits a component normal to the shore. This component is

suggested by the fact that the drogues tended to drift towards the north

bank of the inlet as they travel westward. One drogue, as indicated in

Fig. 2.9, actually made contact with the shore, ceased its westward

movement, and had to be picked up. This characteristic of the flow is












believed to result in the deeper depths due to scouring along the north

bank as well as the shoreline erosion and bulkhead failure occurring in

this region.

Comparisons were made between the velocities of the drogues as they

drifted past cross-section C-2 and the velocities calculated from the

transverse velocity profile measured by a current meter at this

location. Drogue velocities in fact correspond to the velocity of their

anchor (see Fig. 2.10) and were therefore compared to the velocities at

that flow depth (1 m). Both velocities were normalized by dividing

by /V, where R is the tidal range and g is acceleration due to gravity,

to account for the difference in tidal range when the measurements were

taken. Table 3.3 provides the results of this comparison. As can be

seen, the agreement between the normalized velocities is good.


Table 3.3. Comparison of Normalized Drogue Velocities to Velocities
Obtained from Current Meter Measurement at C-2


Current Meter Velocity Drogue Velocity
(Oct. 14, 1982) (Nov. 18, 1982)
(Im depth, R 0.70 m) (Cross-Section C-2, R 0.86 m)


Drogue
Velocity Normalized Velocity Normalized
(m/sec) Velocity (m/sec) Velocity

0.80 0.31 W14-16 1.05 0.36
014-16 = 1.00 0.35



3.7 Dye Study

Dye progression over time provides a further indication of the

nature of flood flow through the inlet. Figure 2.11 supports the

conclusions reached from the drogue study (Section 3.6) that flood flow














is concentrated on the north bank at a location directly across from the

southshore marina. This phenomenon is clearly seen in the last two

frames of Fig. 2.11.

In addition, the dye study revealed eddy activity along the north

bank, just inland of the inlet mouth. This eddy formation is indicated

by the tendency of the dye to remain in that area only to become more

concentrated there; the dye did not begin to be transported inland until

14 minutes after injection. This phenomenon is especially noticeable

when one compares the westward transport rate of the dye on the

northshore to that of the dye on the southshore (see Fig. 2.11). This

eddy formation during flood, coupled with wave activity, serves as the

mechanism initiating sediment transport, and hence erosion, in this

region.

3.8 Wave Information

Wave data (significant height and period) at the location shown in

Fig. 2.4 were obtained over a period of only four days (January 27-30,

1983) and therefore could not be considered as representative over a

longer duration. Comparisons of similar data taken at a permanent wave

gage off of West Palm Beach at a depth of 10 m (COEL, 1983) over this

same four day period were made. The purpose of this was to determine if

the measured inlet waves were sufficiently comparable to those of West

Palm Beach so as to justify using the more representative wave record of

the latter in the model study.

Wave measurements were taken every hour at the inlet gage but only

every six hours at the West Palm Beach gage. Ten concurrent readings

were obtained from the two gages. The resulting data from these

readings are plotted in Figs. 3.10 and 3.11. Figure 3.10 (Shore



































(0
Q-
10-
-S


-3









-4
I6 4
0O





Fig. 3.10.


d10 10
d/gT2


Plot of Concurrent Jupiter Inlet and West Palm Beach Wave
Data. Plot Indicates that All Waves may be Described by
Stoke's Second Order Theory.








59



















--2


cr
















-4








West Palm Beach over the Period January 27-30, 1983.










Protection Manual, 1976) indicates that the non-breaking waves recorded

at both gages were in a transitional stage between deep and shallow

water and that they may be best described by employing Stokes' second

order theory. Waves described by Stokes' theory demonstrate crest

amplitudes that are greater and more peaked than their troughs. The

fact chat waves measured concurrently at the inlet and West Palm Beach

were all non-breaking and may be described by Stokes' theory indicates

that the waves at both locations were basically similar thereby

indicating that a more specific comparison of heights and periods is

justifiable. Figure 3.11 presents a plot of the dimensionless

parameter, H/gT2, where H is the significant wave height, g is the

acceleration due to gravity and T is the significant wave period. This

plot indicates that the wave conditions at both gages were reasonably

similar. This plot, along with the one shown in Fig. 3.10, provides

justification for using the West Palm Beach wave data as representative

of the prevailing wave climate at the inlet.

The West Palm Beach wave data were next used to determine the mean

and the maximum wave conditions (height and period) at the inlet. Wave

data were averaged monthly for the one year period as shown in Table

2.2. Values for the mean wave height and period were taken directly

from this averaged record as Hg .43 m, T 5.9 sec. The maximum wave

conditions were determined in the same manner as Hmax 1.7 m, and
"max
Teax = 10.7 sec.

Neither the wave gage at West Palm Beach nor the one at the inlet

provided directional information. As a result, the directions

corresponding to the highest frequency of incoming waves were determined

from volume 4 of the Summary of Synoptic Meteorological Observations











(SSMO) published by the U.S. Naval Service Weather Command (1970).

These directions were determined as Northeast, East, and Southeast; a

"wave fan" of 90". These waves are refracted from deep water so as to

align themselves with the shoreline (Dean, 1983). Refraction

calculations (Appendix E) resulted in a directional wave fan of

approximately 60.

3.9 Sedimentary Analysis

3.9.1 Procedure

The analysis of the sediment samples consisted primarily of

determining the median diameter D50 and the sorting coefficient

/D75/D2 of each sample. The median diameter of each sample provides a

description of the sediment size for the specific location and can often

give an indication of the source and mode of transport of that

sediment. The sorting coefficient provides an indication of the range

of grain sizes present at a specific location. A sorting coefficient

value of 1.0 1.3 indicates a well sorted (or poorly graded) sediment

sample while a value greater than 1.3 indicates a poorly sorted (well

graded) sample. Table 3.4 lists the results of sediment analyses for

each location. The results provide an indication of the sources and

mechanisms of the sediment deposition in the Dubois Park and southshore

marina areas.

Sample locations were grouped into eight different zones as shown

in Fig. 3.12. Values of median diameters and the sorting coefficient

for each sample in a given zone were averaged so as to provide a

representative description of the sediment in each zone. The values of

both of these sediment characteristics for the locations in each zone

were very similar and, as a result, averaging them did not significantly







62






N








-





": 0


S V


0 100 200 m

scale


Fig. 3.12. Zones of Similar Sedimentary Characteristics.









Table 3.4. Sedimentary Analysis


Sample D_____ Sample 050
Number (mm) /D25/D75 Number (mm) D2D75

1 well sorted 17 0.61 1.64
2 well sorted 18 0.25 1.37
3 well sorted 19 0.7 poorly sorted
4 0.3 1.89 20 0.9 1.57
5 0.62 2.36 21 0.42 1.51
6 0.38 1.54 22 0.88 1.74
7 0.36 1.51 23 0.77 1.61
8 *well sorted 24 0.75 1.56
9 0.37 1.53 25 1.00 1.57
10 well sorted 26 0.78 1.61
11 *well sorted 27 0.79 1.61
12 *well sorted 28 0.80 1.54
13 0.50 1.54 29 1.08 1.71
14 0.34 1.88 30 0.35 1.30
15 0.60 poorly sorted 31 0.36 1.96
16 0.43 1.45 32 0.50 2.0.


See Fig. 2.12 for locations of sample numbers.

*Indicates sediment primarily in the fine size range (less than
0.06 mm)


compromise the representative sediment characteristics of each zone.

These characteristics, and the sediment samples (as indicated in Fig.

2.12) included in that zone are presented as follows:

Zone 1: This zone consisted of sample numbers 14, 16, and 18. The mean

diameter for this zone was 0.34 mm while the sorting coefficient was

1.57.

Zone 2: This zone consisted of sample numbers 13, 15, and 17. The mean

diameter for this zone was 0.57 mm, while the sorting coefficient was

1.59.











Zone 3: This zone consisted of sample numbers 19, 20, and 21. The mean

diameter for this zone was 0.68 mm while the sorting coefficient was

1.51.

Zone 4: This zone consisted of sample numbers 1, 2, 3, 11, and 12.

Qualitative analysis of these samples (taken at a maximum depth of

0.5 m) indicated very fine sediment (less than 0.06 mm diameter) that

was well sorted (low sorting coefficient).

Zone 5: This zone consisted of sample numbers 4, 6, and 7. The mean

diameter for this zone was 0.35 mm while the sorting coefficient was

1.65.

Zone 6: This zone consisted of sample numbers 8, 9, and 10. The mean

diameter for this zone was 0.37 mm while the sorting coefficient was

1.50.

Zone 7: This zone consisted of sample numbers 22 through 30

(corresponding to the sand trap). The mean diameter for this zone

was 0.80 mm while the sorting coefficient was 1.59.

Zone 8: This zone consisted of sample numbers 31 and 32. The mean

diameter for this zone was 0.44 mm while the sorting coefficient was

1.99.

It should be noted that with the exception of zone 4, all zones

exhibited a relatively high sorting coefficient indicating the presence

of well graded sediments at each of these locations. As a result, only

the mean diameter values served to differentiate between the sediment

characteristics at each location.

3.9.2 Interpretation of Sediment Analysis

The mean diameter and sorting coefficient of the sediment in a

particular zone provide an indication of the sources and mode of












transport of the sediment in that zone. Flow velocities in each zone

act as the primary driving mechanism for sediment transport. By

evaluating the sediment characteristics and flow velocities in each

zone, hypotheses were made as to the causes of sediment deposition or

erosion in each zone. Figure 3.13 shows a plot of sediment size versus

velocity necessary to initiate transport (critical velocity), as based

on Shield's diagram for turbulent flows (Section 6.3.2), that was used

in part to base these hypotheses.

Zones 1, 2, 3 and 4: During a storm flood tide condition, water

floods over and behind the rock protection just west of the south jetty

(from zone 1 to zone 2). This water is channeled westward behind (south

of) the rocks, continually increasing in velocity (Fig. 3.14) and

results in the scouring of the sediment in zone 2. Velocities measured

in the model indicated prototype values of 1.10 to 1.80 m/sec in this

zone during storm conditions. These values are of sufficient magnitude

to initiate scour in zone 2. The relatively large grain size of the

remaining sediment in zone 2 suggests that primarily the finer grain

sizes are scoured from this zone. No erosion was observed in zone 1

indicating that there is no net transport of sediment in this zone over

time. Zone 1 was considered to be representative of the overall

sediment characteristics of the inlet region along the south jetty both

in mean diameter and sorting coefficient.

The channeled flow in zone 2 and the sediment that is scoured by

this flow are diverted into the Dubois Park lagoon where the sediment

would eventually settle out in zones 3 and 4. Velocities corresponding

to 0.75 to 0.90 m/sec measured in zone 3 indicate that only the

relatively larger grain sizes will remain in this zone. Analysis of the













































0 0.5 1 1.5
0.5 1.0 1.5


de, MEDIAN GRAIN SIZE(mm)


Fig. 3.13.


Plot of Critical Velocity
Shield's Diagram.


Versus Grain Size Based on


1.00




0.75


025


2.0















N








A


C,

1-
/-' '\



f. \ ^


..,





0 100 200m

scale


Fig. 3.14.


Modes of Sediment Transport into Zones 3, 4, and 6;and out
of Zone 2 (ref. Fig. 3.13).










sediment in zone 3 (D50 = 0.68 mm) substantiated the presence of larger

grain sizes there. When the lagoon widens rather abruptly into zone 4,

the flow velocity decreases to 0.1 to 0.2 m/sec. This decrease allows

the finer grains to deposit in this region. Qualitative analysis of the

sediment in zone 4 substantiated the presence of fine grain sizes

here. In addition, calculated volumes of erosion and deposition shown

in Fig. 3.15, indicate that the volume of sediment scoured from region 2

(N-2 = 1,500 m3) was of the same magnitude as that deposited in zones 3

and 4 (S-2 = 2,300 m3). These observations support the hypothesis that

the erosion of sediment from zone 2 serves as the source of sediment

deposition in zones 3 and 4.

Zone 5: At all stages of flood flow, sediment is transported into

the inlet. In regions of higher flow velocity, only the larger

particles are deposited; as the flow velocity decreases, finer particles

begin to settle out. This phenomenon is the primary factor in

determining the characteristics of the sediment found in zone 5.

Maximum velocities measured in the model 15 to 30 m off the south shore

of the inlet correspond to values of 0.50 to 0.80 m/sec in the

prototype. These velocites and the flow vortices they create near the

shoreline along with the previously mentioned wave action (Section 3.2)

are of sufficient magnitude to scour the finer sediments from the south

shoreline, and deposit them at locations further west within the inlet

area. Some of this finer sediment is redeposited along the south

shoreline during ebb flow but volume calculations (Fig. 3.15) and field

observations indicate a net state of erosion in zone 5. Analysis of

sample number 5 (Fig. 2.13), taken from the beach area of zone 5, gave a

mean grain size of 0.62 mm. This relatively high value of grain size

implies that the finer sediments have been gleaned from this zone.

































0N
-0 Im- N

!!!lm


AREA
S-I
S-2
S-3
S-4
N-I
N-2
N-3
N-4


SOURCE AREA (Shools)

AREA REQUIRING
NOURISHMENT (Scour)


VOLUME (m 3)
+92,000
+2,300
S1,000
+35,000
2,500
.- 1,500
2,000
700


Fig. 3.15. Areas of Erosion (-) and Sedimentation (+) Corresponding to
Areas Requiring Nourishment and Areas Acting as Sediment
Sources in the Inlet.










Zone 6: Flow yelocities measured in the model at the mouth of the

southshore marina correspond to values of 0.1 to 0.2 m/sec in the

prototype. These values are conducive to the deposition of sediment in

this zone. It is hypothesized that this deposition takes place during

both the flood and ebb flows. Sediment scoured from the south shoreline

of the inlet is deposited near the mouth of the marina, an area of low

flow velocities, during flood flow. Although most of this sediment is

transported back along the south shoreline during ebb flow, a small

portion of this sediment is carried into the marina. The low flow

velocities in the marina are of insufficient magnitude to resuspend the

sediment and transport the sediment out of the marina and, as a result,

a net state of deposition occurs there.

Zone 7: The relatively large grain sizes in this zone (D050 0.80

mm) would be expected due to the fact that the high flow velocities here

(1.6 to 1.8 m/sec) allow only the larger grain sizes to be deposited.

Zone 8: The relatively large grain sizes here (D50 0.44 mm)

result from the fact that the sediment deposited in zone 7 (the sand

trap) are mechanically bypassed to this zone. That the grain sizes here

are smaller than those in zone 7 is likely to be due to the fact that

some of the littoral drift (D50 = 0.25 mm) bypasses the inlet mouth and

deposits in this zone. This explanation is substantiated by the very

high sorting coefficients found in this zone.

3.10 Sand Budget

3.10.1 Overview

Examination and analysis of littoral drift estimates (Walton,

1976), hydrographic surveys (Corps of Engineers, 1966 and 1983) and

dredging records (Robert E. Owen & Associates, 1979; Corps of Engineers,












1983) for Jupiter Inlet provide the basis for an estimate of a sand

budget for the inlet. The basis for the formulation of the sand budget

are discussed in the following paragraphs.

3.10.2 Littoral Transport and Distribution

The predominant direction of littoral drift at the inlet is from

north to south; from June through August there is a northerly sand drift

(COEL, 1969). This drift is distributed in three general modes as it

reaches the inlet: it may be carried offshore by "jetted" ebb tidal

flows, it may naturally bypass the inlet by either bar-bypassing or

tidal flow bypassing, or it may be transported into and deposited in the

inlet.

As is the case with most inlets with jetties, a portion of the

littoral drift is believed to be lost offshore as it attempts to bypass

Jupiter Inlet. This is due to the jet action of the inlet caused by the

ebb tidal flow into the ocean. A portion of the drift may be directly

transported offshore as it bypasses the updrift jetty or it may first

enter the inlet and subsequently move offshore during ebb flow.

Some of the drift bypasses the inlet naturally via a process known

as bar-bypassing. In this process, littoral drift moves around the

mouth of the inlet in the form of a shifting sand bar. This phenomenon

usually results in a hindrance to navigation and is often mitigated by

jetties and maintenance dredging. It is believed that prior to 1966

seventy-five percent of the net littoral drift bypassed the inlet in

this manner (Corps of Engineers, 1966).

Littoral drift entering the inlet either settles out and remains in

the inlet, thereby resulting in shoaling of the inlet, or is eventually

transported down-drift by means of tidal flow bypassing. This latter


-------










form of transport is driven by the alternating ebb and flood tidal

currents which carry the sediment in and out of an inlet eventually

directing it down-drift of the inlet. While sediment will enter an

inlet during a flood current, it is constantly directed towards the

inlet mouth throughout the tidal cycle. During flood flow, the sediment

is directed towards the mouth by the flow converging on the mouth from

all seaward directions. During ebb flow, lateral mixing of the jet

induces eddy formations on each side of the mouth thus resulting in

nearshore currents directed towards the mouth from both sides. These

currents transport the sediment towards the mouth where it is deposited

only until the subsequent flood tide transports the material inside the

inlet (O'Brien, 1969). Figure 3.16 qualitatively illustrates this

process for Jupiter Inlet.

The refraction of waves by the sand bar near the inlet mouth as

well as by ebb currents results in the concentration of the wave energy

towards the mouth and currents directed towards the mouth from the surf

zone. Such waves also act to suspend sediment thereby providing the

initial mechanism for suspended sediment transport. These two phenomena

also result in the transport of sediment into an inlet (O'Brien, 1969).

Based on the intended effect of jetty lengthening since 1970 to

decrease the offshore bar volume, and based on field observations, it

would be expected that the inlet would exhibit primarily tidal flow

bypassing. This conjecture is supported by relationships developed to

quantitatively characterize inlet bypassing mechanisms and offshore bar

volume.

Bruun (1958) developed a "bypassing parameter" which characterizes

an inlet as tidal flow bypassing, bar-bypassing, or a combination of the

two as follows:








































OCEAN
FLOOD TIDE


OCEAN
EBB TIDE


Fig. 3.16.


Qualitative Illustration of Sand Transport towards the Inlet
Mouth during Both Stages of a Tidal Cycle.












r =s (3-1)
MT


where r is the bypassing parameter, MT is the net annual littoral drift

5 3
encountered by the inlet (1.76 x 10 m ) and a is the spring tidal
s
prism. Values of r greater than 100 indicate that the inlet undergoes

tidal flow bypassing while values of r less than 50 indicate bar

bypassing as the mechanism by which sand bypasses the inlet. Values of

r in between 50 and 100 indicate a combination of these two mechanisms,

weighted towards one or another depending on whether r is closer to 50

or 100. The value of ns may be estimated by the following relationship

(Mehta, et al., 1975):



as am(aOS)1/2 (3-2)
om


where Sm is the mean of the flood and ebb tidal prisms (1.205 x 107 m3),

aom is the tidal amplitude corresponding to the measured tidal prism

(0.4 m), and aos is the spring tidal amplitude (0.65 m). Substitution

of the appropriate values into equation (3-2) results in an Os value of

1.536 x 107 m3. Substituting the values for Qs and MT into equation (3-

1) results in an r value of 87. This value of r indicates a combination

of the two mechanisms of sand bypassing, tending slightly towards tidal

flow bypassing.

Walton and Adams (1976) developed a relationship between outer bar

volume and spring tidal prism for sandy inlets on moderately exposed (to

waves) coastlines as:











V 10.5 x 10-5 1.23 (3-3)
s


where V is the outer bar volume and fs as the spring tidal prism. For

Jupiter Inlet, this relationship indicates an outer bar volume of

71,000 m3. This corresponds to a low value for inlets on the east coast

of Florida, strongly indicating that Jupiter Inlet undergoes tidal flow

bypassing. The resulting sand budget also supports this conclusion.

This tidal flow bypassing mechanism is never fully operative because

approximately 70 percent of the sand entering the inlet settles in the

sand trap and is mechanically bypassed to the south beach during regular

maintenance dredging.

At this point it is worthwhile examining the relationship between

the spring prism 9s and the throat cross-sectional area of the inlet,

Ac. For inlets in sedimentary equilibrium, the well-known relationship

is (O'Brien, 1969)


Ac m bm (3-4)


where b and m are empirical coefficients. For inlets with two jetties

on the Atlantic Coast, mean values of b and m are 5.77 x 10-5 and 0.95,

respectively, where fs is measured in cubic feet and Ac in square feet

(Jarrett, 1976). For Jupiter Inlet, Qs 1.536 x 107 m3 -

5.43 x 108 ft3 and Ac = 435 m2 4,683 ft2 (cross-section C-1 in Fig.

2.4). For this value of Of, Eq. (3-4) yields Ac 11,461 ft2 which is

2.45 times larger than the actual area. Ninety-five percent confidence

limits have also been established by Jarrett (1976). These limits

indicate that while 11,461 ft2 is the mean value, the range can be

between 5,100 ft2 and 28,000 ft2. It is clear that the actual










cross-section is considerably smaller than the expected equilibrium

value. Erosion of the banks is not unexpected therefore, since the flow

section attempts to adjust to its equilibrium value.

3.10.3 Sand Budget

As previously stated, the net annual southerly littoral drift rate

near the inlet is 176,000 m3. Out of this amount 134,000 m3 is

estimated (from dredging records) to enter the inlet, 1500 m3 are lost

offshore without entering the inlet (Corps of Engineers, 1966), leaving

40,500 m3 of sand that is naturally bar bypassed each year.

Of the 134,000 m3 of sand entering the inlet, 92,000 m3 settle in

the sand trap, 35,000 m3 settle in the Intracoastal Waterway and

2,000 m3 are deposited in the southshore marina (in recent years).

Approximately 6,000 m3 of sand are transported out of the inlet during

ebb tidal flow and are lost offshore. The 92,000 m3 deposited in the

sand trap is mechanically bypassed to the south beach. Figure 3.17

provides a schematic drawing of the sand budget. In some cases records

of sediment accumulation were only available for periods greater than

one year. Data were interpreted in these cases, so as to determine a

corresponding yearly average of sediment accumulation. Specifically,

quantities of sediment dredged from the sand trap and the Corps of

Engineers deposition basin were divided by the time period between

successive dredgings to obtain yearly average accumulation of sediment.

3.11 Runoff

The contribution due to runoff in the form of freshwater inflow

from the three primary tributaries of the Loxahatchee River Estuary was

inherently included in the discharge calculations made from field

measurements. Analysis of the data presented in Section 2.10 provided








77















N


















"34



0 Maintenance DredBing'
176 Annual Rates in 1,000s
of cubic meters

0 100 200m
cale


L--j Deposition Basins
r----I
L----J




Fig. 3.17. Sand Budget for Jupiter Inlet.


0
C,


--~----~--











an indication of the net change in this contribution that may occur due

to maximum runoff conditions and the effect of this condition on the

tidal prism at the inlet. Summation of the maximum daily discharge

values in Table 2.3 results in a maximum freshwater contribution to the

discharge through the western boundary of the inlet of 40.22 m3/sec.

Assuming this value to be constant over one-half of the 12.4 hour tidal

cycle (equivalent to the time period over which a tidal prism is

defined) results in a total contribution of 9.0 x 105 m3 to the tidal

prism. This corresponds to 6% of the estimated spring tidal prism of

1.536 x 107 m3 (Section 3.10).

This value of 6% is considered to be much higher than the actual

contribution due to the following reasons: 1) the maximum contributions

of each tributary did not all occur on the same day although they were

all added together in this calculation and 2) the maximum contributions

from the north and northwest fork correspond to the period during which

Hurricane Dennis occurred (mid-August, 1981) which would result in a

much greater tidal prism in addition to the abnormally high freshwater

discharges. A more accurate estimate of the net change in the

freshwater contribution to the tidal prism at the inlet during maximum

runoff conditions is believed to be in the range of 2 to 3%. As a

result the additional contribution to the tidal prism due to maximum

runoff conditions was disregarded when determining the maximum flow

conditions over a tidal cycle.

3.12 Wind

While wind data are an essential characteristic in describing the

overall climatic conditions of an area, it was not considered as an

important factor in explaining the hydraulic and sedimentary phenomena











at the inlet. The water surface flows generated as a result of shear

stresses exerted by winds were assumed negligible when considered

relative to the magnitude of the tide-induced flows. Local wind-

generated waves are of insufficient magnitude to compound the effects

due to the longer waves entering the inlet from the ocean. In addition,

the inlet shoreline may be described as "low-lying" in terms of the

degree of exposure to wind and protection from the erosive forces of

wind is provided by trees surrounding the inlet. For these three

reasons, wind was not considered as an important characteristic to

replicate in the model.


















CHAPTER IV

THE PHYSICAL MODEL

4.1 Model Facility

The wave generator used in the study is classified as "snake-type"

and is of French manufacture (Sogreah Institute, Grenoble, France). The

stroke, phase angle and the frequency of the paddles can be varied to

produce wave fronts up to 600 from parallel to the generator face, up to

1.5 second wave periods, and with wave heights up to 10 cm. The

generator imparts these waves into a basin 50 m long and 35 m wide

(Macrae, 1977). A system made up of pumps, weir gates and weir boxes

was developed to provide a means to simulate flow conditions at the

inlet.

4.2 Model Scale

The model was constructed using an undistorted scale; the same

scale was used in both the vertical and horizontal direction. The

choice of scale was determined by a compromise between economics and the

technical requirements for similitude.

The economic aspects of choosing a scale consist primarily of

constructing the model within size limitations determined by the

dimensions of the modeling facility. The fact that the model was to be

undistorted narrowed the range of scale choices even further. In order

to maintain a reasonable vertical scale, so that phenomena dependent

upon vertical dimensions are accurately simulated, the scale should not

exceed 1:100. An undistorted scale of such magnitude results in a












considerably large plan (horizontal) area of interest, accompanied by

higher cost and considerable construction time (Sager and Hales, 1976).

Satisfying technical requirements for similitude involves achieving

and maintaining geometric, kinematic and dynamic similarities. In

addition, the range of scales to be considered had to be such that the

inertia of the fluid (water) would be predominant over the forces due to

viscosity and surface tension thereby preventing any scale effects

related to these two fluid parameters.

The physical nature of the model was such that the flow phenomena

would be dominated by inertial and gravitational forces. As a result,

similarity in the model was based on the Froude modeling laws. The

Froude number represents the ratio of inertial force to gravitational

force as V/Ig-, where V is a characteristic velocity, L is a

characteristic length and g is the acceleration due to gravity. This

ratio must have the same value in both the model and the prototype, and

can be expressed in terms of scales (relating the model to the

prototype) as nV 3 ingnL. A useful result of Froude modeling is that,

for an undistorted model, the velocity scale nV is equal to the square

root of the length scale, i.e. ny = /lln (since ng 1).

Having predetermined the approximate range of scales that would

satisfy both the economic and similarity criteria, a length scale of

nL 49 was chosen. This conveniently corresponds to a velocity scale

of nv = 7. Other scales (these are for an undistorted model only) were

obtained as follows (Bruun, et al., 1966):


3
Volume nV nL 117649
2
Cross-Section Area nA = nL = 2401











Time nT = nL/nv = 7

Discharge nq = n/n T = 16807

Slope nS = nL/nL 1 I

2
Roughness nf = nSnL/nV = 1


4.3 Model Construction

The area replicated in the model (Figs. 2.1 and 4.1) encompassed

the study area plus sufficient margins such that any boundary conditions

would not be altered as a result of: 1) the physical boundaries of the

model or 2) later modification of the study area. Construction of the

model consisted of the following four phases:

4.3.1 Templates, Sand, and Concrete

The construction of the model was based on a template scheme that

resulted in a fixed-bed, concrete bottom replica of the study area. The

templates, cut from masonite, corresponded to a grid system superimposed

over a topographic map of the study area up to plus 1.5 m elevaton. The

templates were cut and labeled according to their respective elevation

corresponding to their location on the grid. They were then placed on

the basin floor and leveled relative to mean sea level (1929 N.G.V.D.)

with surveying instruments. Appendix F gives the topographic map, which

was composed from several surveys.

The construction procedure consisted of filling each grid section,

measuring 1.2 m (0.6 m in locations requiring fine detail) by 2.4 m,

with sand. This sand was compacted and maintained at a level 5 cm below

the top of the templates. Concrete was then poured up to the template

levels and graded to produce continuous bathymetry. Figure 4.2 is a

schematic drawing of the template scheme. The sidewalls (boundaries) of

the model were formed from concrete building blocks.



















































=== WEIR GATE
WEIR BOX AND PUMP
TIDE RECORDER
o TIDE STILLING WELL
0 WAVE GAGE
-INLET SHORELINE


Fig. 4.1. Schematic Layout of the Physical Model.



















































2.4m-- |


Fig. 4.2. Schematic Drawing of the Template Scheme to Reproduce the Bathymetry in the Model.


00
4-




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