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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-
|
RSS
HIDE
