Title Page
 Table of Contents
 List of Tables
 List of Figures
 Features of residential canal...
 The canal design problem
 Canal design objectives, guidelines,...
 Site characteristics, available...
 Field measurements, instrumentation...
 The numerical canal network...
 Design of trial canal network and...
 Design alternatives and example...
 Summary, conclusions and recom...
 Appendix A
 Appendix B
 Biographical sketch

Title: Hydraulic measurements, data analysis, and rational design procedures for residential tidal canal networks /
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00097475/00001
 Material Information
Title: Hydraulic measurements, data analysis, and rational design procedures for residential tidal canal networks /
Physical Description: xxxiii, 603 leaves : ill. ; 28 cm.
Language: English
Creator: Morris, Frederick W
Publication Date: 1978
Copyright Date: 1978
Subject: Canals -- Florida   ( lcsh )
Canal ecology   ( lcsh )
Civil Engineering thesis Ph. D
Dissertations, Academic -- Civil Engineering -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Thesis: Thesis--University of Florida.
Bibliography: Bibliography: leaves 592-601.
Additional Physical Form: Also available on World Wide Web
General Note: Typescript.
General Note: Vita.
Statement of Responsibility: by Frederick W. Morris IV.
 Record Information
Bibliographic ID: UF00097475
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000065656
oclc - 04361997
notis - AAH0870


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Table of Contents
    Title Page
        Page i
        Page ii
        Page iii
        Page iv
    Table of Contents
        Page v
        Page vi
        Page vii
        Page viii
        Page ix
        Page x
    List of Tables
        Page xi
        Page xii
        Page xiii
    List of Figures
        Page xiv
        Page xv
        Page xvi
        Page xvii
        Page xviii
        Page xix
        Page xx
        Page xxi
        Page xxii
        Page xxiii
        Page xxiv
        Page xxv
        Page xxvi
        Page xxvii
        Page xxviii
        Page xxix
        Page xxx
        Page xxxi
        Page xxxii
        Page xxxiii
        Page 1
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        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
    Features of residential canal systems
        Page 33
        Page 34
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    The canal design problem
        Page 105
        Page 106
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        Page 128
    Canal design objectives, guidelines, criteria and constraints
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
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        Page 159
    Site characteristics, available information, preliminary site investigations and field surveys
        Page 160
        Page 161
        Page 162
        Page 163
        Page 164
        Page 165
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    Field measurements, instrumentation and results
        Page 188
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    The numerical canal network model
        Page 283
        Page 284
        Page 285
        Page 286
        Page 287
        Page 288
        Page 289
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    Design of trial canal network and variability of design elements
        Page 394
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    Design alternatives and example of modification of an existing canal design
        Page 482
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    Summary, conclusions and recommendations
        Page 518
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    Appendix A
        Page 534
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    Appendix B
        Page 551
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    Biographical sketch
        Page 602
        Page 603
        Page 604
        Page 605
Full Text






JUNE 1978


The opportunity to study under, and learn from, a man who is both

a superb teacher and an experienced and knowledgeable researcher is

not the fortune of every graduate student. Such an opportunity was

extended by Dr. Bent A. Christensen to the author, for which he is

sincerely appreciative. The canal research project was enriched in

many ways by the independent field projects which were made possible,

in large part, through his expertise and experience.

The author would like to also extend his thanks to Dr. Wayne

Huber for serving on his committee and providing guidance in the areas

of pollution transport and hydrology. Dr. Zoran R. Pop-Stojanovic,

representing the Mathematics Department, has also served on the author's

committee and is thanked for his participation.

Bob Snyder, a philosopher, craftsman, and imagineer, has provided

a unique kind of guidance which will never be forgotten. The author

is proud to have had him serve on his committee, and acknowledges that

whatever has been achieved on this project is due in large part to his

perception and innovative ideas. Bea Snyder, whose enthusiasm for the

research was no less encouraging, also deserves special recognition

for her part in the success of the project.

The author owes a special debt to his fellow graduate students

who committed many hours and days of their time to the field trips and

the inevitable reduction of data upon their return. Among the many

students who volunteered to participate, and did their best to ensure

that the work would be done efficiently and well, were Jerry Piccolo,

Geoff Slack-Smith, Ray Walton, Tim Middleton, Clark Clement, Ho-Shong

llou, Tom Langley, Tom Souers, Brian Swenty, Jim Diubac, Ron Chernik, and

Rachel Christensen.

The author wishes to especially thank Carol Dillard and Dave

Bloomqvist for their excellent and very professional drafting, and John

Daniels and Ken DeCosta for their assistance in the preparation of the

illustrations in this dissertation. Their cooperation during the last

days and hours is very much appreciated.

The photography and artwork provided by Ron Franklin, Lise Johnson,

and Carol Ashcraft, has been especially important and always on time.

Working with outmoded and temperamental equipment, they still consistently

produce the highest quality artwork, vital to our research presentations.

The author would like to acknowledge the financial aid provided

by the Office of Sea Grant (NOAA), the State University System of

Florida Sea Grant Program, the Board of Regents of the State University

System, and the Board of Commissioners of Palm Beach County. In

addition, the availability of a graduate assistantship for the entire

span of the canal project is greatly appreciated.

The Northeast Regional Data Center (NERDC) computer was used for

all of the canal design simulations. The assistance of the Center for

Instructional Research (CIRCA) in the form of consultation on many

related computer projects over the past three years is also gratefully


The majority of the typing was carefully and expertly accomplished

by Dona Hlatche r and Al ice Morea.u, to whom the author is partLicularly

ii l

grateful. The additional typing by Rhonda Downing and Susan Olson, is

much appreciated.

No project of this magnitude could be successfully accomplished

without the assistance of capable laboratory technician and handyman.

The author appreciates the effort and cooperation of Leonard White in

helping to keep equipment operational.

Finally, and most importantly, I would like to thank my wife,

Susan, and Holly, Fred, and Abby, for their cooperation and the sacrifice

of our time together. The completion of this work was dependent upon

their understanding and support, and I am proud of them.


ACKNOWLEDGEMENT............ . . . . . .

LIST OF TABLES . . . . . .

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

NOTATION . . . . . . . . .

ABSTRACT . . . . . . . . .


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

1.1 Background . . . . . . . . . .
1.2 Problems Associated With Canal Development ..
1.3 Present State of Canal Design ....
1.4 Objectives of the Canal Design Research
Project . . . . . . . . . .
1.5 Field Observations . . . . . . . .
1.6 Numerical Modeling . . . . . . . .
1.7 Organization of the Chapters .. . . .....


2.1 Governing Features of Tidal Canal Systems
2.2 The South Atlantic and Gulf Coastal Zone .
2.3 Climate . . . . . . . . .
2.4 Physical Features of Floridian Canal Systems

2.4.1 Types of Canals . . . . . .
2.4.2 Canal Banks . . . . . . .
2.4.3 Tidal Characteristics . . . . . .
2.4.4 Tidal Energy . . . . .
2.4.5 Secondary Currents . . . . . .
2.4.6 Dispersion Coefficients, Flushing
Time, and Models . . . . . .
S2.4.7 Stratification . . . . .
2.4.8 Geology . . . . . . . . . General Features . . . . . Bank and Bottom Materials . .
2.5 Water Quality . . . . .











2.5.1 Variability of Salinity, Water
Temperature, and DO . . . . . .
2.5.2 Sources of Pollution in Canal Systems Sources and Effects of

Pollution Residential Wa Septic Tanks Boats and Mari

. . . . . 68
iter Use . . . 69
. . . . . . 70
nas . . . . 73

2.6 Ecosystem Components ....


Algae and Plants .. ..
Lawn Grasses .. . ...
Mangroves ....
Turtle Grass .. . ...
Marsh Grass ...

3 THE CANAL DESIGN PROBLEM . . . . . . .105

Overall Objectives of Canal Design
Development Considerations . .
Legislative Considerations . .

. . . 106
. . . 107
. . . .. 108

3.3.1 Federal Authority . . . . . ... .109
3.3.2 State Authority . . . . . . .112 Geographic Areas of
Particular Interest . . .. .113 Special Flood Hazard Areas . . 114 State Legislation . . . ... .115

3.3.3 Regional and Local Authority . . ... .117

3.4 Permitting Procedure .. . . . . . . 118


4.1 Formulation of Design Objectives . . . ... .129
4.2 Design Guidelines, Criteria and Constraints . . 135


5.1 Fixed Characteristics . . . .

5.1.1 Topography and Drainage . .
5.1.2 Tidal Range . . .
5.1.3 Climate . . . . . .
5.1.4 Hydrology and Water Resources
5.1.5 Vegetation . . . . .
5.1.6 Soils . . . . .

. . . 162

. . . . 162
. . . . 164
. . . 165
. . . 167
. . . 169
. . . 171

. . 129

5.2 Alterable Characteristics . . . .. .. . 173

5.2.1 Drainage ........ . . . 173
5.2.2 Pollution Sources . . . ... .. .174
5.3 Preliminary Site Investigations, Field Surveys
and Instrumentation . . . ... .. ... 175

5.3.1 Objectives of Field Work . . . ... 176
5.3.2 The Monitoring and Sampling Problem . . 177
5.3.3 Measurement Requirements for Tidal
Canals . . . . . . . . 180


Desirable Specifications for Canal Ins
station . . . . . . .
Instrumentation and Support Equipment
the Hydraulic Laboratory . . .



Used by

Tide Recording . . . . . . .
Distance Measurements . . . . .
Depth Recording .. . .
Current Measurements
Wind Recording . . . . . . .
Salinity Measurements . . . . .
Water Temperature Measurements . . .
Dissolved Oxygen Measurements . . .
Dye Concentration Measurements . . .

. 191

. 192
. 194
. 200
S 203
. 203
S. 204

6.3 Reduction and Analysis of Field Observations . 210

6.3.1 Reduction and Presentation of Tidal
Data and Bathymetry . . . . ... 211
6.3.2 Reduction and Presentation of
Current Readings . . . . .. 212
6.3.3 Reduction and Presentation of
Wind Data .... ........... 213
6.3.4 Reduction and Presentation of
Salinity Data . . . . . . .213
6.3.5 Reduction and Presentation of
Dye Concentration Data . . . ... 214

6.4 Field Observations in Floridian Canals .



Variability Studies . . . .
Design Modification and Improvement
Surveys . . . . . . .
Longitudinal Dispersion Studies .
Comprehensive Field Surveys . .. Loxahatchee River Field Surv 57 Acres Field Surveys .

. . 221

. . 223

. . 224
. . 227
. . 229

ey . 230
. . 234



Chapter Page


7.1 Development of the One-Dimensional Models . . 284
7.1.1 Definitions of Canal Network
Geometry . . . . . . . 284
7.1.2 One-Dimensional Hydrodynamics ...... 287
7.1.3 One-Dimensional Mass-Transport . . .. .289
7.1.4 Boundary Conditions . . . . ... 292
7.1.5 Numerical Methods . . . . . . 294 Finite-Difference and Finite-
Element Methods . . ... .294 Hybrid Computer Approach ... 296 Second Upwind Differencing
Method . . . .. . . 298 Method of Characteristics
Techniques . . . . .. .299 Method of Second Moments ... 300
7.2 Development of the Three-Dimensional Model . . 301

7.2.1 Tidal Velocities . . . . . ... 303
7.2.2 Wind-Induced Circulation . . . ... .304
7.2.3 Secondary Currents . . . . ... 309
7.2.4 Density-Induced Currents . . . ... .313
7.2.5 Three-Dimensional Mass-Transport
Coefficients . . . . . ... 315 Diffusion and Dispersion Coef-
ficients and Transport
Mechanisms . . . ... 316 Longitudinal and Lateral
Diffusion Coefficients . .. 318 Vertical Diffusion Coefficient .320

7.3 Development of Three-Dimensional Numerical
Model .. . . . . . . . ... 322

7.3.1 Layout of Geometry . . . . . . 324
7.3.2 The Velocity Field . . . . ... 327 Tidal Velocities . . . ... 327 Wind-Induced Circulation ... 329 Secondary Currents . . . .. .330 Density Currents . . . ... 332

7.3.3 Dispersive Terms in the Transport
Equation . . .. ....... .. .333 Longitudinal Dispersion Term . 334 Lateral and Vertical Disper-
sion Terms . . . ... 334

7.3.4 Lateral Inflows . . . . . . .. 336


7.3.5 Decay Coefficients .... . . . . 337
7.3.6 Boundary Conditions ...... .. . . 338
7.4 Model Accuracy, Stability and Convergence
Criteria . . .. .... . . . 341
7.4.1 Velocity Stability Criteria . . . 342
7.4.2 Dispersion Stability Criteria .... 346
7.4.3 Convergence Criteria ...... . . 348
7.5 Model Verification with Field Data ...... 350
7.5.1 Case No. 1: Big Pine Key Canal III . 351
7.5.2 Case No. 2: 57 Acres Canal Network . 353
7.5.3 Case No. 3: Loxahatchee North Canal . 362
7.6 Application of the Model ...... .. . . 364

DESIGN ELEMENTS . . .... ..... . 3 394

8.1 Outline of the Overall Design Process .... 394
8.2 Quantifying Design Constraints ...... . 396
8.3 Quantifying Design Criteria ... .. . . 399
8.4 Trial Canal Design . . . . . . . 400
8.4.1 Topographic Site Map . . . . .. 400
8.4.2 Storms, Hydrographs and Pollutographs . 401
8.5 Variability of Parameters in a Straight Reach .403
8.6 Variability of Parameters in Three Dimensional
Mass-Transport . . . . . . . . 405
8.6.1 Effect of Wind-Induced Circulation . . 406
8.6.2 Effect of Density- and Wind-Induced
Circulation ..... . . .. . 409

8.7 Variability of Canal Network Design Elements . 411
8.7.1 Design Tests . . .... .. . . 412
8.7.2 Simple Comb-Structured Canal (System A). 413
8.7.3 Comb-Structured Canal with Lake .... .415
8.7.4 Comb-Structured Network with Bends . . 416
8.7.5 Simple Network with Two Tidal Entrances .418
8.7.6 Summary of Observation on Network
Design Elements . . .... . 420


9.1 Introduction to the Example . . ..... 482
9.2 Description of Existing Canal System . . .. .482
9.3 The Canal Network Model . . . . . ... .483
9.4 Simulation Objectives . . . . . . . 485
9.5 Flushing Under No-Wind Conditions . . ... .486

Chapter Page

9.6 Design Alternatives . . . . . . . 488

9.6.1 Flushing With Wind . . . . ... .488
9.6.2 Flushing With Additional Tidal Prism 491
9.6.3 Comparison of Effects of Steady and
Variable Wind . . . . . ... .494


10.1 Summary . . ..... ... . . .. . 518
10.2 Conclusions . . . . . . . ... 524
10.3 Recommendations for Future Research . . .. .530

APPENDIX A . . . . .. . . . . . . .. . 536

APPENDIX B . . ... ............... . .553

REFERENCES ... .. . . . . . . . . 592

BIOGRAPHICAL SKETCH ....... . . . . . .602


Table Page

1.1 Inventory of Large-Scale Developments in Florida . .. 28

1.2 Criteria for Canal Design Without Consideration
of the Environment . . . . . . . . . 29

2.1 Chances of Hurricane Force Winds in Floridian
Cities in Any Given Year . .. . . . . . 79

2.2 Mean, Maximum, and Minimum Values of Salinity,
Water Temperature, and Dissolved Oxygen in
Floridian Canals . . . . . . . . . 80

2.3 Summary of Possible Sources of Pollution to
Canal Surface Waters . . . . . . . . 81

2.4 Harmful Effects of Pollutants on Canal Waters
and Environment . ... . . . . . ... 82

2.5 Common Population Densities, Residential Areas . . . 83

2.6 Average Residential Water User Characteristics . . .. 84

2.7 Domestic Sewage Volume and BOD . . . . . ... 85

2.8 Average Characteristics of Municipal Sewage ...... 86

2.9 Relationships for Variability of Domestic
Sewage from Areas of Moderate Size . . . . .. 87

3.1 Examples of Canal Design Objectives, Guide-
lines, Criteria, and Constraints . . . . .. 121

3.2 The Development Process . . . . . . . ... 122

3.3 Environmental Checklist Worksheet: A
Selected List . . . . . . . .. . 123

3.4 Government Decision Making .. . . . . . ... 125

3.5 Partial List of Federal Laws Regulating Canal
Development . . .. ... . . . . . 125

3.6 Authorities to be Utilized and State Agencies
Involved in Activities Related to Canal
Development . . . . . . . ..... .126

Table Page

3.7 State of Florida Criteria for Class III Waters . . . 127

3.8 Checklist for Regulatory Information . . . . .. 128

4.1 Balancing Environmental and Economic Costs and
Benefits . . . . . . . . . 139

4.2 Principal Design Objectives Relating Particularly
to Residential Canal Design. . .. . . . .... 140

4.3 Decision-Making Agencies or Institutions with an
Interest in Coastal Development . . . . . . 141

4.4 Summary of Comments Relative to Canal Design
Guidelines Received from Federal Agencies
in Response to a Request (December 4, 1974)
for Comments on the Need for Research on Canal
Performance . . . . ..... . . .. 142

4.5 Design Guidelines for Dredge-Fill Structures,
Established by U.S. Army Corps of Engineers
and Florida Department of Environmental
Regulation . . . . . .. .. . . . . 145

4.6 Design Guidelines Relative to Canal Design for
Various Kinds of Ecosystems in South Florida,
by Associated General Contractors . . . .... .146

4.7 Guidelines and Standards for Coastal Projects.
Elements applicable to residential canal systems . 151

4.8 Design Guidelines Relative to Canal Design by
Planners and State Agencies . . . . . . 155

4.9 The Rational Approach to Canal Design, Snyder
Oceanography Services . . . . . . 159

5.1 A Checklist of Principal Site Characteristics
Relative to Canal Design . . . .. . . 185

5.2 Relationship Between Desired Information,
Information Derived by Engineering Analysis,
and Variables Measured During Field Surveys . ... 186

6.1 List of Field Equipment and Instrumentation,
Which Can be Used for Each of the Measured
Variables in Table 5.2. . .. . . .. ... 241



6.2 Preliminary Site Investigations and Field Surveys
Conducted by the Hydraulic Laboratory (Univer-
sity of Florida) During the Canal Design Research
Project . ........................

6.3 Summary of Results of Dispersion Measurements by the
Hydraulic Laboratory (University of Florida)
During 1975 . . . . . . . . . . .

7.1 Typical Measured Canal Parameters ......

7.2 Comparison Between Horizontal Water Surface Assumption
and Harleman and Lee's Hydrodynamics Model ..

7.3 Constant Parameters for Three-Dimensional Model
Test Canal . . . . .

7.4 Parameters for Big Pine Key Canal III Case No. 1 .. ...

7.5 Parameters for 57 Acres, Case No. 2 .....

7.6 Parameters for Loxahatchee North Canal, Case No. 3 .

8.1 Elements of Design . . . . . . . . . .

8.2 Typical Canal Design Constraints .. . . ......

8.3 Examples of Typical Canal Design Criteria ....

8.4 Standard Data Set for First Test Canal . . .....

8.5 Parameters for Three-Dimensional Model Test Canal .

8.6 Dimensions and Parameter Values for Network
Simulations . . . . . . . . . . .

8.7 Comparison of Concentration Values in Systems A and
D Under No Wind and East Wind Conditions ...

8.8 Variability Tests on Design Elements .. . . .....

9.1 Relative Calculated Times to Reduce Bottom Concen-
tration at the Two Slowest-flushing Dead-ends
to 10 Percent of Their Initial Value, Arranged
in Order of Decreasing Flushing Time, for the
Example Canal Design . . . . . . .

9.2 Summary of Simulations of the Original, the Trial
and Some Alternative Canal Network Designs . . .






Figure Page

1.1 Example of Bayfill Development in Florida . ... . .30

1.2 Example of Intertidal Development in Florida ...... 0.

1.3 Example of Inland Canal Development in Florida . . . 31

1.4 Average Values of Dissolved Oxygen Concentrations
in Canal Systems in Florida, August, 1974 ...... 32

2.1 Florida's Coastal Zone as Defined by the Florida
Coastal Coordinating Council in 1971 . . . . .. 88

2.2 A Geometric Classification for Types of Canals . . .. 89

2.3 Typical Cross-section of Conventional Residential
Canal .... . . . . . . . . . . 90

2.4 Proposed Canal Cross-section with Same Area as
the Conventional Canal Section Shown in
Figure 2.3 .... . . . . . . .. ... 91

2.5 Classification of Florida Tides . . . . . ... 92

2.6 Types of Tides ........ . . . .... . 93

2.7 Velocity Profile Measured During Loxahatchee
North Canal Field Survey, June, 1977 .. . . . . 94

2.8 Secondary Current and Resulting Helical Flow
in Canal Bend . . . . .. ........ . 95

2.9 Monthly Surface and Bottom Water Temperatures,
Salinity and DO . . . . . . . .... . 96

2.10 Generalized Locations of Landforms in Florida . . . 98

2.11 Index to Principal Geologic Structures in Florida . .. 99

2.12 General Layering of the Bedrock Formations Below
Southern Florida from Ocala (North) to Florida
City (South) . . . . . . . . . . 100

2.13 Location Map for Sources of Data Used by Bailey
(1976) . . . . . . . . ... . . . 101

2.14 Topographic (7 1/2 min quadrangle) Map for Loxahatchee
River Canals . . . . . . . . . . 102


2.15 Location Map for Frenchman's Canal and 57 Acres Canal
Sites . .. .. . .. . . . . . . 103

2.16 Typical Bank Section Across Canal Showing Filter
Mound and Swale, From 57 Acres Canal Design . . . 104

5.1 Location Map of Weather and Meteorological Sta-
tions in Florida . .... ........ . 187

6.1 Typical Stilling Well and Water Level Recorder Box
for the Tide Measurements . . . . . . 246

6.2 Dimensions of Velocity Meter Tower with Adjustable
Carriage, Designed and Built by Snyder Ocean-
ography Services . . . ... . . .247

6.3 Velocity Meter Tower Set-up in Canal .. ... . . .. .248

6.4 Lower Part of Velocity Meter Tower Showing Carriage
with Probe Holder and Adjustable Legs .... ..... 249

6.5 Detail of Probe Holder Carriage on Velocity Meter
Tower, with Probe Installed . . . .... . . 250

6.6 Three Velocity Meter Towers installed in the
Loxahatchee North Canal . . . ... . .. 251

6.7 Electrical Conductivity of Seawater as a Function
of Temperature . ... .......... ... 252

6.8 Fluorometer with Continuous Sampling Arrangement
and Strip Chart Recorder on Work Boat . . . ... .253

6.9 Pressurized Dye Injection Device Constructed by
Snyder Oceanography Services . . . ... . .254

6.10 Diagram of Continuous Flow Dye Sampling System .. ... .255

6.11 Use of Short Length of PVC Pipe for Sampling Water-
Tracing Dye from Moving Boat at 3 ft Depth . .... 256

6.12 Gunwale Support for 3 and 6 ft Water Sampling Tubes . 257

6.13 Example of Plotted Velocity Components from Measure-
ments by Electromagnetic Current Meter . . 258

6.14 Relationship of Density of Seawater (g/ml) to Salin-
ity (ppt) and Temperature (oC) . . . ..... . 259



6.15 Example of Plotted Salinity, Velocity, and
Dye Concentration Profiles . . ... . . .... 260

6.16 Photochemical Decay Rhodamine WT Atlantic
Beach, North Carolina, September, 1974 . . .... .261

6.17 Example of Vertically-Averaged Dye Concen-
tration Profiles . . . . . . . . . 262

6.18 Example of Continuous Dye Concentration
Profile . . ... ............... . 263

6.19 Topographic (7 1/2 min quadrangle) Map for
Cudjoe Gardens Canal System . . . . . ... .264

6.20 Location Map for Venus Waterway Canal System ...... 265

6.21 Layout of Cudjoe Gardens Canal System, Cudjoe
Key, Florida, with Canal Designation
Letters Established for October 1974
Hydrographic Survey . . . . . ... . .266

6.22 Layout of Venus Waterway Canal System and
Location of Venus Waterway Terminus . . . ... .267

6.23 Layout of Frenchman's Canal . . . . . . .268

6.24 Layout of 57-Acres Canal Network Showing
Locations Used to Designate Reaches for
1975 Dispersion Studies . . . . . . . 269

6.25 Layout of Loxahatchee River North Canal,
Showing Locations of Tide Range and
Velocity Meters .... . . . . . . . .270

6.26 Vertical Salinity Profiles, Loxahatchee
North Canal, Showing Presence of Density
Wedge Near the End of an Ebb Tide
(Date: 770613; Time: 1249-1334) . . ... . .271

6.27 Vertical Salinity Profiles, Loxahatchee
North Canal, Showing the Beginning of
a Density Wedge After Low Tide. (Date:
770615; Time: 1550-1700) . . . . . . . 272

6.28 Vertical Salinity Profiles, Loxahatchee
North Canal, Showing a Remnant Salt Dome
Near the Dead-end at Mid-Flood Tide.
(Date: 770613; Time: 1639-1750) . .. ...... .273



6.29 Measured Dye Concentration at 3 ft Depth
Along Centerline. 57 Acres Canal
System, Palm Beach County, FL. Date:
770720; Time: 1935 . .. . . . . . .... . 274

6.30 Measured Dye Concentration at 3 ft Depth
Along Centerline. 57 Acres Canal
System, Palm Beach County, FL. Date:
770721; Time: 0105 . . . . .... ..... . 275

6.31 Measured Wind Velocity, 57 Acres Canal
System, October, 1977 . . . . . . .. . 276

6.32 57 Acres Site Plan Showing Location of
Electromagnetic Current Meters for
October, 1977 Velocity, Salinity,
and Water Temperature Measurements . . . . 277

6.33 57 Acres Site Plan Showing Location of
Electromagnetic Current Meters for
October, 1977 Dye Dispersion
Measurements . .. . . . . . . . . 278

6.34 Measured Dye Concentration at 3 ft Depth
Along Centerline. 57 Acres Canal
System, Palm Beach County, FL. Date:
771021; Time: 0420 . . . . . . . . 279

6.35 Measured Dye Concentration at 3 ft Depth
Along Centerline. 57 Acres Canal
System, Palm Beach County, FL. Date:
771021; Time: 1045 . . . . . . . . . 280

6.36 Measured Dye Concentration at 3 ft Depth
Along Centerline. 57 Acres Canal
System, Palm Beach County, FL. Date:
771020; Time: 0330 .. . . . . . . . .281

6.37 Measured Dye Concentration at 3 ft Depth
Along Centerline. 57 Acres Canal
System, Palm Beach County, FL. Date:
771020; Time: 0950 .. . . . . . . . 282

7.1 Definition Drawing of Canal Network . . . . ... .375

7.2 Theoretical Wind-Induced Vertical
Velocity Profile . . . . . . . . ... 376



7.3 Comparison Between Observed and Theoretical
Wind-Induced Vertical Velocity Profiles,
With and Without Width Correction (N = 0.002
ft2/sec) 57 Acres . . ............... . 377

7.4 Comparison Between Observed and Computed Lateral
Velocities Induced by Bend in South Loop of
57 Acres System . . . . . . . . . 378

7.5 Schematic Drawing of a Salt Wedge Entering a
Canal Showing Definitions . . . . . . ... .379

7.6 Comparison of Observed and Computed Velocity
Profiles for Loxahatchee River Site . ... .... 380

7.7 Schematic Layout of Canal Network Showing Features . . 381

7.8 Cell Structure in Reach . . . . . . . . 382

7.9 Cell Structure in Junction . ... . . . .. .383

7.10 Schematic Layout of Bend . . . . . . . 384

7.11 Schematical Canal for Three-Dimensional Model Tests .. 385

7.12 Typical Longitudinal Sections and Cross-sections,
Big Pine Key Canal III, Florida (EPA, May 1975) . . 386

7.13 Case No. 1: Observed and Predicted Concentration
Profiles for Big Pine Key Canal III . . . ... .387

7.14 Model Layout of Reaches and Junctions in 57 Acres
System . . . . ... . . . ... . 388

7.15 Case No. 2: Observed and Predicted Concentration
Profiles for 57 Acres, July, 1977 . . . . ... .389

7.16 Measured Dye Concentration at 3 ft Depth Along
Centerline, Reach AD, Low Tide, 57 Acres
Canal System, October, 1977 . . . .. . .. 390

7.17 Case No. 2: Observed and Predicted Concentration
Profiles for 57 Acres, October, 1977 . . . ... 391

7.18 Variation of Vertical Dispersion Coefficient With
Time and Wind Speed at Mid-Point of Reach 1
(Figure 7.14), 57 Acres, October, 1977 . . ... .392




7.19 Case No. 3: Comparison Between Observed and
Computed Concentration for Loxahatchee
River North Canal, June, 1977 . . . .

8.1 Steps in Formulating a Trial Canal Design . .

8.2 Sinuous Bank Design for 57 Acres Project . . .

8.3 First Test Canal Network - -

8.4 Variability of

8.5 Variability of

8.6 Variability of

8.7 Variability of

8.8 Variability of

8.9 Variability of

8.10 Variability of

8.11 Variability of

8.12 Variability of

Tidal Entrance Time Decay
. . . . . . . . 437

Tidal Amplitude, a . . . . . .. 438

Canal Length, L . . . . . . 439

Dimensionless Canal Length . . ... 440

Bottom Width, b .. . . . . . . 441

Inverse Side Slope, s .. . . . . . 442

Lateral Inflow Rate, qI .. . .. 443

Lateral Inflow Concentration,
. . . . . . 444

Mean Tidal Depth, d . . . . 445

8.13 Variability of Nikuradse's Equivalent
Sand Roughness, k . . . . . ..

8.14 Variability of Dimensionless Dispersion
Coefficient, K . . . . . . .

8.15 Second Test Canal Network

8.16 Variability of Low Tide Concentration Pro-
files for Various Branch Canal Locations

8.17 Variability of High Tide Concentration Pro-
files for Various Branch Canal Locations

8.18 Case 1W: Initial Concentrations, c. = 100
ppm, Background Concentration, c 5
ppm Fifty Tidal Cycles . .


. . 393

. . 43-4

. . 435

. . 436

. . . 446

. . . 447

. . . 448

. . . 449

. . . 450

. . 451



8.19 Case 2W; Initial Concentrations, c. = 5
ppm, Background Concentration, cW =
100 ppm Fifty Tidal Cycles .. . . . ...

8.20 Case 3W: Lateral Inflow Distribution Along
Length of Canal Fifty Tidal Cycles .. . ....

8.21 Case 4W: Lateral Inflow Distribution Along
Upper Half of Canal Fifty Tidal Cycles ...

8.22 Case 5W: Lateral Inflow at Dead-end -
Fifty Tidal Cycles . . . . . . .

8.23 Case IS: Effect of Salt Wedge With Initial
Concentration, c. = 100 ppm, Background
Concentration, cRW = 5 ppm Fifty
Tidal Cycles . . . . . . . .

8.24 Case 2S: Effects
Tidal Cycles .

. . . 455

of Salt Wedge With Initial
c = 5 ppm, Background
CRW = 100 ppm Fifty

8.25 Case 3S: Effect of Salt Wedge With Lateral
Inflow Distribution Along Length of
Canal Fifty Tidal Cycles . . . .

8.26 Case 4S: Effect of Salt Wedge With Lateral
Inflow Distribution Along Upper 1/2 of
Canal Fifty Tidal Cycles .. . ...

8.27 Case 5S: Effect of Salt Wedge With Lateral
Inflow Distribution at Dead-end Fifty
Tidal Cycles . . . . .

8.28 Four Simple Network Design Elements Tested
with the Mass-transfer Model, CANNET3D




. . . . 461

8.29 Test Canal and Lot Dimensions .. . .....

8.30 Test Canal Cross-section . . . . . . . .463

8.31 Layout and Dimensions of System A .. . . . ... .464

8.32 Values of Surface and Bottom Concentrations
for No Wind at Junctions and Dead-ends at
High Tide After Thirty Tidal Cycles,
System A . . . . . . . . .

. . . . 465



8.33 Values of Surface and Bottom Concentration for
West Wind, at Junctions and Dead-ends at
High Tide After Fifty Tidal Cycles,
System A . . . . . . . . . .

8.34 Values of Surface and Bottom Concentration for
Three Wind Conditions in Reach Number 1 at
High Tide After Thirty Tidal Cycles,
System A . . . . . . . . . .

8.35 Values of Surface and Bottom Concentration for
East Wind, at Junctions and Dead-ends at
High Tide After Thirty Tidal Cycles,
System A . . . . . . . . . . .

. 466

. 467

. 468

8.36 Values of Surface Concentrations for Three
Wind Conditions at Dead-end of Reach Number
1 and Junction 2 versus Number of Tidal
Cycles from Beginning of Simulation,
System A . . . . . .. . . . . 469

8.37 Layout and Dimensions of System B . . . . . . 470

8.38 Values of Surface and Bottom Concentrations for
No Hind at Junctions and Dead-ends at High
Tide After Forty-eight Tidal Cycles,
System B . . . ..... . . . . . . 471

8.39 Values of Surface and Bottom Concentrations
for Three Wind Conditions in Reach Number 3
at High Tide After Forty-eight Tidal
Cycles, System B . . . . . . .. ..... .472

8.40 Values of Surface and Bottom Concentrations for
West Wind at Junctions and Dead-ends at High
Tide After Forty-eight Tidal Cycles,
System B . . . . . . . . . .

8.41 Values of Surface and Bottom Concentrations for
East Wind at Junctions and Dead-ends at High
Tide After Forty-eight Tidal Cycles,
System B . . . . . . . . . .

8.42 Layout and Dimensions of System C .. . ....

8.43 Values of Surface and Bottom Concentrations for
Upstream Wind, at Junctions and Dead-ends at
High Tide After Fifty Tidal Cycles,
System C...... . . . . .

. . . 473

. . . 474




8.44 Layout and Dimensions of System D .. ...

8.45a Values of Surface Concentrations for
No Wind at Junctions and Dead-ends
at High Tide After Fifty Tidal Cycles,
System D . . . . . . . . .

8.45b Values of Bottom Concentrations for
No Wind at Junctions and Dead-ends
at High Tide After Fifty Tidal Cycles,
System D ....... . . . . . . .479

8.46a Values of Surface Concentrations for East
Wind, at Junctions and Dead-ends at High
Tide After Fifty Tidal Cycles, System D . . ... .480

8.46b Values of Bottom Concentrations for East
Wind, at Junctions and Dead-ends at High
Tide After Fifty Tidal Cycles,
System D . . .... ............. . .481

9.1 "Existing" Example Canal System . ... . . ... .499

9.2 Layout of Model Network . . . . . . . ... 500

9.3 Cross-sectionally Averaged Concentration
Profiles in the 8 ft deep Original Canal
Network After Fifty Tidal Cycles, With a
Steady Wind of 5 mph From the East
(Run No. 827) . . . . .

9.4 Cross-sectionally Averaged Concentration
Profiles in the 8 ft deep Trial Canal
Network After Fifty Tidal Cycles, for No
Wind and No Lake (Results of Run No. 443) . .

9.5 Cross-sectionally Averaged Concentration
Profiles in the 4 ft deep Alternate Canal
Network After Fifty Tidal Cycles, for No
Wind and No Lake (Results of Run No. 486) .

. 501

9.6 Cross-sectionally Averaged Concentration
Profiles in the 8 ft deep Trial Canal
Network After Fifty Tidal Cycles, With a
Steady Wind of 2 mph from the East and
No Lake (Results of Run No. 32) . . .

. . . 504


9.7 Cross-sectionally Averaged Concentration
Profiles in the 8 ft deep Trial Canal
Network After Fifty Tidal Cycles, With
a Steady Wind of 5 mph from the East and
No Lake (Results of Run No. 444) . . . . . 505

9.8 Cross-sectionally Averaged Concentration
Profiles in the 4 ft deep Alternate
Canal Network After Fifty Tidal Cycles,
With a Steady Wind of 5 mph from the
East and No Lake (Results of Run No. 182) ...... 506

9.9 Cross-sectionally Averaged Concentration
Profiles in the 12 ft deep Alternate
Canal Network After Fifty Tidal Cycles,
with a Steady Wind of 5 mph from the
East and No Lake (Run No. 728) . . . . . ... 507

9.10 Semilogarithmic Plots of Laterally Averaged
Bottom Concentration at the Dead-ends of
Canals R2 and R12 versus Number of Tidal
Cycles in the 8 ft deep Trial Canal
Network After Fifty Tidal Cycles, With a
Steady Wind of 5 mph from the East and
No Lake (Run No. 444) . . . . . . . . .508

9.11 Semilogarithmic Plots of Laterally Averaged
Bottom Concentration at the Dead-ends of
R2 Canals versus Number of Tidal Cycles
for Various Combinations of Depths 4, 8
and 12 ft and East Winds with Velocities
of 0, 2, and 5 mph (Results of Run Nos.
32, 182, 444, 553, and 728) . . . . . . . 509

9.12 Semilogarithmic Plots of Laterally Averaged
Bottom Concentration at the Dead-ends of
R12 Canals versus Number of Tidal Cycles
for Various Combinations of Depths 4,
8, and 12 ft and East Winds with Velocities
of 0, 2, and 5 mph (Results of Run Nos.
32, 182, 444, 553, and 728) . . . . ... .510

9.13 Cross-sectionally Averaged Concentration
Profiles in the 8 ft deep Trial Canal
Network After Fifty Tidal Cycles, With
No Wind and a Lake with a Surface Area
of 15 percent of Canal Network Surface
Area (Run No. 726) .. . . . . . . . . 511




9.14 Cross-sectionally Averaged Concentration
Profiles in the 8 ft deep Trial Canal
Network After Fifty Tidal Cycles, With
No Wind and a Lake with a Surface
Area of 30 percent of Canal Network
Surface Area (Run No. 451) . . . . . . ... .512

9.15 Cross-sectionally Averaged Concentration
Profiles in the 4 ft deep Alternate
Canal Network After Fifty Tidal Cycles,
with No Wind and a Lake with a Surface
Area of 30 percent of Canal Network
Surface Area (Run No. 553) . . . . . . .. 513

9.16 Cross-sectionally Averaged Concentration
Profiles in the 8 ft deep Trial Canal
Network After Fifty Tidal Cycles, with
East Wind of 5 mph and a Lake With
Surface Area of 30 percent of Canal
Network Surface Area (Run No. 524) . . . . .. 514

9.17 Semilogarithmic Plot of Laterally Averaged
Bottom Concentration at the Dead-ends
of Canals R2 and R12 versus Number of
Tidal Cycles for 4 ft deep Alternate
Canal Network After Thirty and Fifty
Tidal Cycles, with Lake Surface Area of
30 percent of Network Surface Area and
with a Steady Wind of 5 mph from the
East (Run No. 633) . . . . . . . . ... .515

9.18 Semilogarithmic Plots of Laterally Averaged
Bottom Concentration at the Dead-ends of
R2 Canals versus Number of Tidal Cycles
for Various Combinations of Depths 4, and
8 ft and East Winds With a Velocity of
5 mph (Results of Run Nos. 451, 524, 553,
633 and 726) . . . . . . . . . . . 516

9.19 Cross-sectionally Averaged Concentration
Profiles in the 8 ft deep Trial Canal
Network After Fifty Tidal Cycles, with a
Variable Wind Speed and Direction and No
Lake (Results of Run No. 308). . . . . .. 517



a tidal amplitude, (L)

a constant of integration

A cross-sectional area, (L2)

A surface area of canal, (L2)


A(k) function defined by Equation (7.31)

b bottom width, (L)

B top width. (L)

B(z) width correction factor, dimensionlesss)

c turbulent time mean concentration dimensionlesss)

I concentration of lateral inflow, dimensionlesss)

cRW background concentration in receiving waterbody, dimensionlesss)

c' fluctuation from turbulent time mean concentration,

c initial concentration, dimensionlesss)

c, concentration at or near peak, dimensionlesss)

C Chezy coefficient, (L /T)

d depth, (L)

db thickness of bottom layer, (L)

d mean tidal depth, (L)

D depth of reach, (L)

D offset distance of bend from straight center-line, (L)

etx longitudinal turbulent mass flu.: or diffusion coefficient,



e lateral turbulent mass flux or diffusion coefficient, (L2/T)
etz vertical turbulent mass flux or diffusion coefficient, (L2/T)

e exponential constant 2.718

E dispersion coefficient, (L2/T)

potential energy, (FL)

Ek layer averaged vertical dispersion coefficient, (L2/T)

Ek layer averaged, Richardson number dependent, vertical dispersion
coefficient, (L2/T)

Ep longitudinal dispersion coefficient, (L2/T)

E longitudiual diffusion/dispersion coefficient, (L2/T)
E lateral diffusion/dispersion coefficient, (L2/T)
E vertical uiffusion/dispersion coefficient, (L2/T)
E background dispersion coefficient, (L-/T)
E photon energy, (L2 /T2
f Coriolio parameter, (1/T)

frequency, (1/T)

F( ) exact solution of partial differential equation

P( ) numerical approximation to partial differential equation

F I( ) function defined by Equation (7.34)

F 4( ) function defined by Equation (7.35)

Fl(k) layer averaged form of FI( )

F (k) layer averaged form of F4 ( )

g acceleration due to gravity, (L/T2)

h Planck's '",,stant, (FLT)

6.6256 x 10-34 Js

i number of reach (Chapter 7)

number of segment

j nunher ol reach (Chapter 7)


number of lateral layer

k Nikuradse's equivalent sand roughness, (L)

number of vertical layer

K dimensionless dispersion coefficient

decay coefficient, (1/T)

K constant associated with an initial value (Chapter 9),

KR reach uniform decay coefficient, (1/T)

K wind drag coefficient, dimensionlesss)

length scale of turbulent eddy, (L)

a characLtristic length of the cross-section of a canal, (L)

L length of reach, (L)

length scale of convective period, (L)

distance between injection point and sampling point

Ld length of decay of secondary current, (L)

L length of saltwater wedge, (L)

M mass of pollutant released, (M)

N number of tidal cycles

N Avogadro's number (mol )
)3 -1
6.02252 x 1023 mol

Nu number of upstream reaches Equation (7.1.2)

N vertical -momieiLtum transfer coefficient, (L2/T)

N constant defined by Equation (7.26)

p variable used in Section 7.1.3

permissible deviation from background velocity Equation (7.40)

P power available from tidal prism, (FL/T),
P atmospheric pressure, (M/LT-)
q lateral inflow per unit length, (L2/T)

xxvi i

Q discharge, (L /T)

Qu discharge at upstream section of reach, (L /T)

Q mean discharge, (L3/T)

r radius of bend, (L)

r rate of production or loss of substance, (1/T)

R hydraulic radius, (L)

width of volume in cell after convective step, (d

Ri Richardson number, dimensionlesss)

R dimensionless width of distribution in cell

s inverse side slope, dimensionlesss)

sL inverse side slope of left bank, dimensionlesss)

sR inverse side slope of right bank, dimensionlesss)

t time, (t)

temperature (C)

t elapsed time to measurement of peak concentration
t' time since low tide, (T)

t* time corresponding to c*, (T)

T tidal period, (T)

TF flushing time, (T)

T time to peak, (T)
TR mean residence time, (T)

U mean, steady, uniform velocity of flow, (L/T)

u cross-sectional mean velocity, (L/T)

uD dispersion velocity in x-direction, (L/T)
uD dispersion velocity in y-direction, (L/T)

uD dispersion velocity in z-direction, (L/T)

uF velocity of front of saltwater wedge, (L/T)


, (T)


usm mean velocity in the salt wedge, (L/T)

u* bed shear velocity, (L/T)

u' turbulent fluctuation from time mean velocity in x-direction,

u. densimetric velocity, dimensionlesss)

u4 constant defined by Equation (7.43)

v lateral velocity component (L/T)

vck layer averaged secondary current, L/T)

V volume of tidal prism upstream of section, (L )

V transfer volume due to wind, (L )

W width of reach, (L)

w vertical velocity component, (L/T)

w wind speed, (L/T)

w' turbulent fluctuation from upstream section of reach, (L)

x longitudinal distance from upstream section of reach, (L)

x' distance from tidal entrance, (L)

X distance, (L)

XD longitudinal dispersion distance, (L)

y lateral coordinate direction

depth, (L)

z vertical coordinate direction


Greek Letters

a included angle between radii to ends of a curved reach, (rad)

Y unit weight of water, (F/L )

3 partial derivative operator

A change

At time increment, (T)

Ax longitudinal spatial increment, (L)

Ay lateral spatial increment, (L)

Az vertical spatial increment, (L)
Ap,Ap incremental density, (M/LT-)

p elevation of water surface from the mean depth, (L)

6 angel u'-teen wind and positive :-direction of reach, (degrees)

K von Karman's constant = 0.4 dimensionlesss)

T universal constant = 3.141593

pp density, (M/L3)
0 variance

t density function used in oceanography

T time decay coefficient at tidal entrance, (1/T)

s surface longitudinal wind shear stress, (M/LT2)

T shear stress in x-direction with respect to x-direction, (M/LT2
T shear stress in y-direction with respect to x-direction, (H/LT2)
T shear stress in z-direction with respect to x-direction, (IM/LT2)

T bed shear stress, (F/L2)

4(Ri)- function of Richardson number, dimensionlesss)

t0 tidal frequency, (1/T)



av average over two time layers

b bottom layer

f variables in freshwater layer above saltwater wedge

k longitudinal direction

LT low tide

m spatial mean value

max maximum value

p previous time level (Section 7.2.3)

RW receiving waterbody

s variables in saltwater wedge



t tidal variables

TE tidal entrance

w wind variables

0 node at upstream section of reach

1 node adjacent to upstream node of reach

base of layer

-1 base of top layer

2 node, two away from upstream node of reach

top surface of layer

Superscr ipts

n- time level

turbulent time mean value

value of variable at intermediate step


Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment
of the Requirements for the Degree
of Doctor of Philosophy



Frederick W. Morris IV

June 1978

Chairman: Dr. B. A. Christensen
Major Department: Civil Engineering

A rational approach to the design of residential canal networks

through the formulation of design objectives, guidelines, and

quantitative criteria is developed. The legislative constraints

currently in effect are summarized, and recent environmental guidelines

relevant to the design of residential tidal canal networks are reviewed,

particularly as they apply to Southeast and Gulf states. An overview of

the important climatological, hydrodynamic, and water quality features

of canal systems is given as a basis for understanding the hydrodynamics

of tidal canals and tidal canal networks. A general approach to canal

design through the formulation of design objectives, guidelines, quan-

titative criteria, and engineering constraints is outlined. The

evaluation of canal site characteristics is described, together with

appropriate measurement requirements, techniques, and instrumentation

and support equipment.

Field measurements conducted during the development of the canal

design project are shown to have had a fundamental influence on the


development of a three-dimensional mass-transport mathematical model

for canal networks. The characteristics of the model, a separate

project developed simultaneously with the canal design project, are

described. The unique features of the model include its capability of

modeling wind-induced circulation, density currents associated with a

saline wedge, and helical flows induced by bends in the canals. Field

measurements conducted from 1974 through 1977 are summarized, and their

implications are discussed. The verification of the model with field

data is demonstrated to be consistent with data from two different

canal systems in Florida.

The variability of an equilibrium concentration profile with

canal geometry, a time constant associated with transport of mass away

from the tidal entrance, lateral inflow of mass along the canals,

roughness, and the longitudinal dispersion coefficient are shown by

numerical simulation. The response of simple canal network design

elements, in terms of rate of flushing, to changes in channel depth,

speed and direction of wind, and tidal prism are shown. The flushing

of canals and canal networks is demonstrated to be primarily dependent

on the wind. The design alternatives for the improvement of flushing

in a traditional residential canal network are illustrated by means of

an example.




Florida's rapid growth over the past three decades has been

accompanied by a large demand for residential dwellings in the coastal

zone. In particular, the demand for waterfront property has led to the

dredging of many residential canal networks along both the Atlantic and

Gulf Coasts, and these canals have often been built without consideration

of the natural conditions at the site. Large canal projects constructed

in ecologically sensitive areas have destroyed aquatic nurserys, removed

natural barriers to storm tides, disrupted surface water flows, and

polluted bays and coastlines. As a result, canals have received a

sinister reputation which, while deserved in many cases, should not be

universally applied. As shown herein, canals networks can be designed

to maintain their water quality without adverse effect on the environ-

ment, using only natural forces.

1.1 Background

The story of residential canal development in Florida begins early

in this century, when the state was still considered a frontier and men

were preoccupied with converting the land to a more habitable and com-

mercially useful form. Residential canals were not being constructed in

those years, but patterns of land use were developing which would

intensify through several stages of growth and culminate in the

grandiose waterfront land development schemes of the 1950's and 1960's.

Florida is a subtropical peninsula overlying a deep, layered,

limestone aquifer. Its coastal lowlands extend far inland, and its

southern part is dominated by vast wetlands which extend westwards to a

marshy coastline. This marsh and swampland has been viewed by suc-

cessive generations of inhabitants as an impediment to progress, some-

times even as a wasteland, which had to be conquered and transformed to

"useful" property. This perceived need developed into a dream which,

supported by money and the policy of the state and federal governments,

spawned the Everglades drainage canal projects (begun in 1880), federal

flood control canal projects (1907 through 1970), and the residential

canal projects following the Second World War. Thus, during the first

fifty to seventy-five years after statehood had been acquired in 1845,

trends in land use were being established which would not be changed

until the "environmental decade" -- the 1970's. During the early years

of statehood the development ot remote areas and wetlands was encouraged

by federal and state governments through direct sales and grants of

federal and state lands to homesteaders.

In 1869 the completion of the railway to Miami provided a

transportation link with the north which would bring thousands of set-

tlers and eventually hundreds of thousands of tourists into the state,

and would carry agricultural products out to the markets in the rest of

the country. In 1911 the "first swamp salesman" [Carter, 1974, p. 69],

Richard J. Bolles, introduced the contract method of selling, on an

installment basis, land that had been reclaimed by the state and sub-

divided, but was unimproved. This enterprise, which resulted in many

law suits and investigations, became a national scandal. The state was

then faced with a dilemma; if it desired to continue the drainage of

wetlands, it could do so only by promoting the sale of state lands. But

these sales easily attracted gullible buyers, and seemed by their very

nature to encourage fraud. The decision was made, drainage continued,

and a policy was established which led inexorably to substantial alter-

nation of Florida's natural features.

In 1913 a promoter from Indiana, Carl Fisher, who had bought a home

in Miami, began what was to become the first large scale dredging and

filling project in Florida. This was located on Miami Beach, then a

long barrier beach across Biscayne Bay from Miami. To complete this

project a thousand acres of mangrove were filled with six million cubic

yards of bay bottom [Redford, P., 1970, in Carter, 1974, p. 75]. While

this was not a canal development, the dredge and fill technique was

demonstrated by this venture to be both feasible and profitable.

While the state was carrying out its plan for drainage of the

Everglades, and Fisher was constructing waterfront lots on Biscayne Bay,

another large-scale project was taking shape in south Florida. Barron

G. Collier, a New Yorker who had a winter home near Fort Myers on the

west coast, was buying large tracts of land in and around the Big

Cypress watershed southwest of Lake Okeechobee. In return for a promise

to complete the Tamiami Trail, a road across the Everglades between

Tampa and Miami, he was encouraged by the state to pursue his plans for

development of his 900,000 acre holdings. The highway was completed in

1926 by the State Road Department after eleven years of tortuous work in

the swamps, but little development was accomplished in this portion of

the state until the 1960's.

In 1962 draglines, bulldozers, and tree-crushers began extensive

alteration of a site near the coast, in what had by then become Collier

County. By 1974 an irregular area had been leveled for a distance of

twenty-five miles north and south across the Big Cyrpess swamp, and

major canals, discharging incredible volumes of freshwater from the

development area, had been opened to Naples Bay, Rookery Bay, and Fahka

Union Bay. By 1974 a grid of 171 miles of undeveloped canals and 807

miles of undeveloped roads had been constructed on this property. These

smaller canals were connected to the Fahka Union Canal ten miles up-

stream from its mouth and to the Golden Gate Canal three miles from

Naples Bay (Carter, 1974, pp. 236-240].

A study of the area by the Environmental Protection Agency (EPA)

[1973] showed that dredging had drastically increased runoff to the

canals, thereby decreasing the area of potential inundation by surface

waters during the wet season with subsequent undesirable ecological side

effects [EPA, 1973, p. 11-3). The canals had lowered the groundwater

table by two to four feet, significantly increasing saltwater intrusion;

intercepted surface flow and drastically decreased the time for surface

water to reach the receiving water, which affects ecosystems dependent

on a steadier supply of freshwater and diverts minerals and nutrients

directly to the estuarine waters; reduced primary productivity in

cypress forests and wet prarie ecosystems; increased the drying rate on

the forest floor, leading directly to increased spreading of wildfires;

and caused subsidence of organic soils [EPA, 1973, Chapters I through

VIII. While these effects are extreme, due to the immense size of the

development and its ecologically sensitive location, they are never-

theless typical and illustrate many of the adverse effects often

associated with poorly sited and improperly designed canal developments.

During the first half of the twentieth century, then, development in

Florida was encouraged by the state and was largely unregulated. After

the Second World War a huge retiree market was discovered and feverishly

exploited. The out-of-state market, particularly for waterfront pro-

perty, continued to grow into the 1970's attracting persons approaching

retirement, younger people making long-term investments toward retire-

ment, and speculators [Carter, 1974, p. 29]. The sudden awakening of

citizen consciousness to the environmental stress brought on by this

exploitive style of development, and the subsequent introduction of

protective legislation and enactment of new regulations stemming from

the National Environmental Policy Act (NEPA, 1969), appears to have

finally caused large developers to attempt to design pleasant and

environmentally acceptable new communities.

The large-scale developments, some of which were conceived before

the "environmental decade", are listed in Table 1.1 [Florida Trend

Magazine, June, 1974, in Carter, 1974, pp. 32-33]. This shows the

extensive acreage involved and the current and ultimate population

figures for which the developers were planning. Not all of these

developments are sited directly in the coastal zone, but many can be

identified as residential canal developments and all will have a major

effect on water resources.

Due to past abuses, caused in some instances by lack of knowledge

of the consequences of crude construction practices, and in others by

greed, present-day development regulations affect everyone, from owners

of small properties to large land development corporations, who desires

to alter a coastal area for any reason. Recently the regulatory process

in Florida has been somewhat simplified to permit relatively insignif-

icant dredge and fill for maintenance, and the construction of small

improvements, with a minimum of delay. The overall approach taken by

the regulatory agencies in the 1970's, however, has been one of caution

and deliberation.

In retrospect, it is not difficult to understand why such an

attitude has evolved, nor can one find much fault with the intentions of

the citizens and the government in this regard. While in the past some

development in the coastal zone has been carried out with good judgement

and accommodation of all the known environmental factors, examples of

such development are few. The more spectacular and environmentally

inconsiderate examples remain as major liabilities with regional effects

that will continue to cost the citizens, the state, and the federal

government much in terms of corrective measures and maintenance (for

example, see Carter, [1974, pp. 236-240]).

1.2 Problems Associated With Canal Development

There are many ways in which canal systems can be classified. For

a preliminary discussion of Floridian residential canals three principal

types of waterfront canals may be distinguished, following Barada and

Partington [1972] and Lindall and Trent [1975]:

1. bay-fiZ or finer-j'ill canals, which are constructed

below mean low tide by dredging and filling shallow bay

bottoms (Figure 1.1).

2. intertidal developments, which are constructed by dredge-

and-fill between mean low and mean high water; in many

cases, these canals are located in mangrove or salt marsh

ecosystems, in bays, estauries, lakes, or other wetlands

(Figure 1.2).

3. inland or upland canals, which are developed by

excavating land which is above mean high tide and

connecting the canals to natural channels, lakes, rivers,

or other natural or artificial waterways (Figure 1.3).

Residential canal systems are usually constructed by dredging in a

manner which maximizes the density of housing lots and is most con-

venient for the developer, the fill being used to elevate the land

surface to meet state criteria for hurricane tide and flood protection.

In the process of construction, dredges have excavated mangrove, grasses

and trees from the channel locations and covered vegetation in the areas

designated for landfill, often destroying estuarine nurseries over vast

areas. In the Florida Keys the process has been similar, although in

that region the Key Largo limestone substrates and higher elevation,

upland Miami oolite would first be cut with narrow, parallel, vertical

ditches to a depth of perhaps ten to fifteen feet. Then the area be-

tween the ditches would be blasted and dredged into long, straight,

vertical-walled channels. In the process of dredging, the bottoms of

the channels were overturned and clouds of silt were carried out to

nearby tidal waters, where they were deposited to smother large areas of

bottom life. Dredge and fill is now carefully regulated in Florida, and

spoil banks must be located where they cannot leach into tidal waters.

But if the dredging process itself is not carefully controlled, bottoms

may be cut through sediments into underlying bedrock, creating zones for

transfer of denser saltwater and possible pollutants into the aquifer.

Examples are cited by Griffin (1977, in Morris et al, 1977b, Appendix A,

pp. 8, 10, 15]. In addition "wavy" longitudinal bottom profiles will

result if the dredge operator follows the tidally-fluctuating water

surface as a reference level.

Two physical features which have been singled-out for particular

attention by previous investigators are the depth of canal and the

possible presence of a sill. A sill is often created when the canal is

first dredged before connection to the "receiving" waterbody. In its

most general form, however, a sill is a relatively shallow section at

any location in the canal which impedes the circulation in the bottom

waters inside the canal.

In general, it has been observed that "deep" canals are not

adequately flushed by tidal action and that the "lower layer acts as a

trap for sediments and organic detritus" [Polis, 1974, p. 21]. Polls

[1974, p. 23] and Barada and Partington [1972, p. 10) reported results

of an investigation in which thermal stratification was formed in all

canals investigated which were deeper than fifteen feet. A sharp den-

sity interface was measured at depths between ten to twelve feet in such

canals, with indications of less turbidity, anaerobic conditions, and

the presence of hydrogen sulfide in the region below the interface.

This stratification was reported to be "apparently due almost entirely

to depth, regardless of proximity to open water or canal configuration"

[O'Hara, J., 1971 in Barada and Partington, 1972, p. 10].

Canals that are too shallow can also have poorer flushing charac-

teristics, and limited navigability as well. Writing about residential

canal systems in the Florida Keys, Chesher observed:

Canals should be deep enough that boat traffic will
not disturb the bottom and shallow enough for good
biological productivity. This depth varies from one
area to the next and depends on the substrate and
the flushing characteristics of the canal. Five
feet is probably Loo shallow for most arjes. Canals

of this depth have poor flushing characteristics
over long distances... Boats can disturb the bottom
in depths of less than five feet, thus increasing
turbidity and damaging bottom communities.
Chesher [1974, p. 2].

In searching for a simple method by which "good" and "bad" canals

can be separated, governmental agencies have found that in general the

vertical dissolved oxygen profile (or surface and bottom values) can be

related statistically to the mean depth. Figure 1.4, for canals in

Florida, and similar relationships for North Carolina canals [EPA,

1975b, p. 11; Walton, G.F., 1976, p. 142] shows such a trend, which

seems to indicate that this is not a local condition. The EPA recom-

mended that "an appropriate canal depth for shallow draft pleasure craft

should be no more than four to six feet below mean low water", based on

measurements of vertical dissolved oxygen (DO) profiles and numerical

flushing models [EPA, 1975b, p. 5]. The one-dimensional dispersion

model used in making this determination, which is based on very

restrictive assumptions, and the cases which were simulated, were not

realistic enough to encourage wide acceptance of this oversimplified


A sill in a canal acts as a trap for the bottom, denser water and

fluidized sediments, and suppresses vertical mixing. Since vertical

mixing is the principal means by which reaeration of the bottom waters

is effected, the accretion of flocculentt sediments and organic detrital

matter" [Polis, 1974, p. 38] results in a sustained demand for oxygen

which can lead to anaerobic conditions and the release of hydrogen

sulfide. The same effect, on a smaller scale, occurs in deep holes.

Effective wind mixing can lower this interface somewhat, but it is

generally recommended that sills be removed from such canals.

Improper canal construction can also significantly affect coastal

aquifers and drainage. The aquifers, or underground freshwater storage

areas, are characterized by an interface with the seawater which

intrudes into the aquifer to an underground distance which depends on

the freshwater head above the piezometric head line. As this head

decreases, the saltwater interface moves upward and inward farther into

the aquifer. This relationship is known as the Ghyben-Herzberg prin-

ciple, from independent research on saltwater encroachment made by

Badon-Ghyben [1888] in Holland and Herzberg [1901] in Germany. In their

investigations into the equilibrium relationship between the shape and

position of the freshwater/saltwater interface, a simple expression for

the ratio of water table elevation above mean sea level to the interface

depth below sea level was derived under simplifed but realistic condi-

tions. Considering the difference in the density between fresh and

saltwater, it was shown that the depth of the interface below mean sea

level is about forty times the height of the freshwater table above it.

The effect of a canal is to bring tidal waters farther inland, and

sometimes also to substantially increase drainage from inland areas,

both of which can significantly increase saltwater intrusion. This

effect, however, may not be observed until many years after the canal

system is opened to the tide since the flow through a porous aquifer is

extremely slow.

The quality of the water in tidal canals can be characterized by

many different chemical and/or biological parameters. Whether it is

simply a measurement of dissolved oxygen, or whether it has been in-

directly indicated by a fish kill, the water quality has been observed

to be degraded in many instances in all regions of the state. This

occurs primarily when the water circulation, and the resulting flushing

action, are not of sufficient magnitude throughout the canal network to

maintain dissolved oxygen throughout the water column and to carry

undesirable pollutants out to the receiving waterbody. It is because

circulation is the basic mechanism for maintenance of water quality that

this canal design project has concentrated on a comprehensive descrip-

tion of the hydrodynamics in tidal canal networks.

The circulation or movement of water in a tidal canal network is

governed principally by the geometry of the channels and the tide, the

wind, and density gradients. In Florida the tidal effect is small

compared to other coastal areas, the mean amplitude ranging from less

than about 3 ft on the west coast to 2.5 ft or less in the Keys to about

2 to 3 ft on the lower east coast; since the tide is mixed, alternate

tidal cycles are even smaller in amplitude. The tidal energy flux into

a typical 80 ft wide Florida canal is about 4 hp per mile, corresponding

to a 2 ft tidal range. This means that the energy available from the

tides for mixing in Floridian canals is relatively small. However, if

more than one tidal entrance can be provided, and if these entrances can

be separated far enough to provide a tidal elevation differential, then

flushing can be substantially improved.

Wind provides a surface movement which is often accompanied by a

return flow in the lower layer, and sometimes a three-layered flow,

which effectively increases vertical mixing. When winds are relatively

steady and directed along the channel, the geometry of the channel

induces secondary, helical currents which mix surface water downward and

bring bottom water to the surface, also increasing vertical mixing.

Density gradients, on the other hand, inhibit vertical mixing across the

density interfaces. There are, thus, several phenomena which combine to

give a variety of circulation patterns, which once understood, can be

used to advantage in designing a canal network which will optimize

flushing throughout.

The favorable effect of wind on mixing in Floridian canals has been

recognized in most studies of the causes of water quality variations.

Alignment of the channels with prevailing land breezes can keep surface

debris from collecting in finger canals and can induce a vertical circula-

tion inward along the bottom, but canals are not usually aligned purposely

with the wind. EPA recommended that "orientation of canals should take

into account prevailing wind direction so that flushing/mixing would be

enhanced and wind drift of floating debris minimized" [EPA, 1975b,

p. 6].

In canals with oxygen-depleted bottom waters, most aquatic life can

only inhabit the upper, oxygenated layer. If these bottom waters are

suddenly driven to the surface, as they might be if a storm with strong

winds oriented in the direction of the canal channel were to induce

upwelling, mass mortality of these aquatic organisms could result.

Griffin [in Morris, et al, 1977b, Appendix A, p. 5] suggests that this

could be the cause of a recurring fish kill in a Key Largo canal.

Another aspect of canal design which has been mentioned in the

literature is bank and bottom stability. The effect of water velocity

on suspension and deposition of sediments has been quantified for

various channel cross-sectional, shapes, and is a factor in the analysis

of inlet stability. Velocities which are too low are accompanied by

deposition of sediments, particularly in deep holes. Sediments may

consist of sand and clays eroded upstream by faster-moving currents, or

organic material consisting of dead aquatic life or plant detritus. A

given channel geometry is characterized by a stable cross-section which

neither accretes nor erodes, and which adjusts itself on a long-term

basis to changes in the quantity of water flowing. Thus, another element

which must be considered in the canal design process is the stability of

the channel.

Vegetation acts as a natural zone for deposition since velocities

become very small among the roots and stems of aquatic plants. These

zones are often referred to as "nutrient traps"; a certain nutrient flux

is required for growth of a particular type of vegetation, but excessive

nutrients can lead to algal blooms, oxygen depletion, fish kills, and

subsequently worsening conditions (a form of positive feedback).

Water quality in canals is also adversely affected by pollutants

introduced from various sources along the boundaries of the canal

system. The major sources of canal pollution are stormwater runoff,

septic tanks, sewage treatment plant effluent, and boats and houseboats.

The contents of these pollutants vary widely and have been the subject

of numerous studies.

Stormwater runoff contains materials which collect on streets,

roofs, and lawns and are channeled into drains, storm sewers, and drain-

age ditches. They include chemicals such as insecticides, herbicides,

and fertilizers; animal wastes and sewage; oil and grease; chemical

products from cleaning operations; garbage, refuse and trash; and dead

or dying vegetation washed into the canals from storms. These pol-

lutants are either flushed out, or accumulate on the surface or in

bottom sediments, depending on the flushing ability of the canals. The

quantity of urban runoff water can be reliably predicted from analyses

of soil characteristics and the percent of developed surface area, for

various size storms in a given drainage basin, and some data are avail-

able for typical nutrient and bacterial contents of urban runoff. State

legislation has established limits for many chemical constituents for

various classes of water.

As of 1972, "more than half of Florida's canal-type developments

utilized septic tanks for municipal sewage disposal" [Barada and

Partigan, 1972, p. 20]. In many systems, however, either soil condi-

tions or the elevation of the canal waters reduce the efficiency of

septic tanks to such a degree that virtually untreated sewage is being

leached into the waterways through the sides of the canals. This

problem was particularly acute in the Florida Keys in the early 1970's;

a land use planning study had determined that none of the soil in Monroe

County was suitable for this mode of sewage treatment, while approxi-

mately 90 percent of the residences in the Keys were utilizing it

[Smith, Milo, and Associates, 1970, in Barada and Partington 1972, p.

29]. In addition, septic tanks in locations with high water tables are

often prone to overflow during heavy rains.

Sewage treatment effluents from both public and private plants

evidently have been a problem in many canal systems in Florida. As

communities expand, these facilities often are not upgraded and easily

become overloaded. While legislation provides definite guidelines and

limits for the operation of such facilities, these usually stop at

requiring secondary treatment. This criterion still does not remove

dissolved phosphates, nitrates, and other chemical contaminants, which

in many cases are oxygen-demanding materials. However, enforcement is

difficult due to the many point sources that do exist, or can exist in a

new development. The EPA recommended that "no sewage plant effluent or

other point-source discharges should be discharged directly into finger-

fill canal waters. Discharges into surface waters should be sufficient-

ly distant from the canals to ensure that the effluent is not carried

into the canal systems by tidal currents" [EPA, 1977b, p. 5].

Boats and houseboats have, in the past, been permitted to discharge

sewage directly into the canals and have been a source of gasoline and

oil wastes, bilge-water, garbage, and refuse. Regulations in particular

areas may require pump-out facilities for household wastes, since pol-

lution from petroleum products cannot be effectively controlled by

relying only on canal flushing.

However, in a study of fifty canal systems in the Florida Keys, of

which forty-four were man-made canals, Chesher arrived at the following


Disadvantages which have been alleged but which are
unsubstantiated in the Florida Keys by this or other
studies include such things as excessive nutrients
from fertilizer runoff, excessive transmission of
heavy metals and pesticides from residential areas
into ambient water, widespread disruption of marine
communities by increased turbidity from dredging
activities, hazardous levels of septic tank seepage
into canals, accumulation of organic muck on the
bottom of canals, low dissolved oxygen levels from
septic tank pollution and stagnation, and others.
These allegations were investigated during this
study but no evidence for their support could be
found. Pesticide accumulation was found in some
canals but was also present in natural man-made
canals and was not obviously correlated with pop-
ulation density.
(Chesher, 1974, p. 12].

Apparently, there has been some disagreement on the seriousness of this


The major problems which have been identified with Florida's

residential canal developments have been listed here along with some

conflicting data and opinions. In many instances these problems can be

eliminated or reduced to meet state requirements with proper canal

siting and channel design. The design, however, must take into account

the existing site characteristics, and must be thorough in considering

all possible effects on the water quality in the canal system as well as

the ability of the canal system to maintain itself. In addition, the

more extensive question regarding the canal system's effects on the

water quality in the receiving waterbody must also now be considered, as

required for any permit.

1.3 Present State of Canal Design

Snyder [1976b] has summarized the adverse effects of canal design

criteria which are established for the convenience of the developer and

without regard for the environment (Table 1.2). If design criteria

comprise only navigable depths to the shoreline, maximization of front

footage, increased lot elevation, minimum commitment of property to

water (i.e. canal) area, rapid drainage of stormwater, and simplified

surveying and construction methods, the results will almost certainly be

destruction of habitat and degradation of water quality both in the

canal system and its environs. It will subsequently be shown how

reconsideration of canal design criteria can eliminate all of the

objectionable features of residential canal systems, at properly

selected sites.

Present canal design is often planned to primarily satisfy the

objectives of the developer. His interests are chiefly economic,

although he must also contend with new regulations requiring that water

quality standards be met and there be no significant adverse effect on

the environment. But what tools are available whi(h will enable him to

predict the operational characteristics of his design? The regulatory

agencies can evaluate a canal plan on a subjective basis from past

experience, by looking at the gross features of the plan and noting

those which obviously will not permit adequate circulation, or will

destroy habitat, or which may introduce high levels of pollutants into

the receiving waters. Crude calculations of flushing based on tidal

prism methods and an assumption of homogeneity in the water column can

be made. At best, up until now, existing one-dimensional models might

be used to evaluate the circulation and concentration of conservative

substances in simple canal geometries under no wind conditions. Such

evaluations, based on inadequate models, can give grossly distorted


1.4 Objectives of the Canal Design Research Project

In 1975 the Office of Sea Grant, National Oceanographic &

Atmospheric Administration and the Board of Regents of the State of

Florida University System awarded a three-year contract to the

University of Florida through the State University Sea Grant Program,

supplemented by a three-year grant by the Board of Commissioners of Palm

Beach County, to study the hydrodynamics and transport properties of

residential finger canal networks in the coastal zone and to develop an

objective canal design procedure and a canal design manual.

One of the principal objectives of the canal design research pro-

ject was to describe the various characteristics of canals which deter-

mine their suitability or unsuitability in a variety of locations. A

second overall objective was to develop a means whereby the operation of

a canal system, either existing or planned, can be evaluated or predicted.

With a predictive capability, and an optimizing procedure which will

permit a designer to improve his plan in a systematic manner, the design

and evaluation of tidal canal systems can evolve from an essentially

random, subjective process to an objective engineering process.

The research project was organized into live principal topics or

sub-areas for investigation:

1. Evaluation of those characteristics of Floridian canals

which must be considered in canal designs, and integration

of these characteristics into the design process.

2. Field measurements and data analysis to support the

modeling efforts, including an evaluation of the detail

and extent of data collection required for design


3. Physical (hydraulic) modeling for determination of the

basic hydraulic and pollutant transport characteristics

of canal channels.

4. Numerical (computer) modeling for simulation of water

circulation and dispersion of pollutants in canal systems.

5. Decision modeling for evaluating canal performance and

finding optimal canal network designs.

These topics, which are discussed individually in more detail in

the following chapters, are closely interrelated. The physical,

climatic, geological and biological characteristics of a canal site and

the quality of the water (both existing and predicted) constitute some

of the primary limiting factors in the canal design, and affect every

facet of planning for a development. Initially, each of these factors

must be properly described and interrelated, and the interrelationships

between the canals and these factors must be considered at every step of

the canal evaluation process.

The design of a new canal system, or the redesign of an existing

canal system, requires certain specific measurements at the site. For

either application, the types of field data required may be categorized

as follows:

1. data for an analysis of the performance of an existing


2. data for input into the hand calculations and numerical

modeling which are part of the design process, consisting


a) data defining the geometry of the existing system,

b) data defining the ranges and the interrelationships

of the forcing functions (tide, wind, and salinity

and temperature gradients),

c) data for calibrating the numerical model (the

forcing-function data plus measurements of dispersion).

One of the most important objectives of this study was to review the

types of instrumentation available and to recommend those types which

would be most suitable for the identified data requirements.

The field measurement portion of a given design project affects, to

a significant degree, the quality of every other portion of the study,

as well as the final recommendations. Very little substantive work can

be accomplished without correct and complete data on all significant

variables, and extrapolation of results beyond the bounds of the data

base can be quite risky. Therefore, the plans for data acquisition must

be made carefully and with all due consideration of the existing condi-

tions at the site and the needs of the designer.

Physical modeling is essentially a research tool used for

determining basic flow and dispersion characteristics for theoretical,

simplified situations. Also, physical models are very useful for

complementing research conducted with numerical models, since one type

of model can simulate effectively at different levels of spatial detail

and time than the other. While hydraulic modeling can be a very useful

design tool, it is an expensive and time-consuming approach for the

one-time evaluation of a particular project and cannot be considered as

a tool which could be made available on a practical basis to canal

designers [Morris, Walton, and Christensen, 1977a]. Instead, numerical

models are more flexible and more easily used by engineers, designers,

and planners.

Numerical modeling is the technique used in this project for sim-

ulating the operation of a canal design. Once a model has been cali-

brated and verified, it provides the means by which changes in a given

design can be assessed.

Decision modeling provides the designer with an ability to improve

his design in steps which will optimize one or more selected parameters.

For example, if a given design does not provide an adequate degree of

flushing, this decision capability will guide the designer to a modifi-

cation in the design which will improve the flushing without recourse to

random trial and error methods. The objective of this portion of the

canal research project, therefore, was to develop the necessary facil-

ities for ensuring that designers, planners, and regulatory engineers

can use the numerical models effectively in developing optimal canal

designs. The effectiveness of this portion of the project obviously

depended upon the quality of data and the numerical model.

1.5 Field Observations

The objectives of the field work associated with this project were:

to determine the significant features of tidal canal
hydrodynamics and the transport of substances by
convection and diffusion, for purposes of developing
a numerical mass-transport model.

to develop effective measurement techniques and
determine the types of instrumentation and support
equipment required for evaluating development sites
and existing canal networks.

to obtain the data necessary, for verification of the
numerical model for particular sites

Depending on the information and data required at a particular

phase of the canal design, field operations may be conveniently divided

into "preliminary site investigations" and field surveys". The former

refers to field work which is required for obtaining qualitative plan-

ning information about the site. This type of information includes any

conditions which will limit field measurements, unusual conditions which

may require additional measurements or special equipment, and locations

of benchmarks for surveying. Field surveys, on the other hand, are

designed to obtain quantitative information such as the actual magni-

tudes of physical and environmental data for design calculations and

numerical models. Both of these general types of field observations

have been conducted by the author in support of the canal design pro-


In addition to the principal investigator and the numerical modeler,

it is advisable to include in the site investigation team several other

well qualified scientific persons to provide opinions on characteristics

not familiar to the principal investigator. A biologist or ecologist

should be available to make observations relating to water quality,

aquatic life, and vegetation; a geologist to look at soils, sediments,

and the geologic structure of the site; an oceanographer or coastal

engineer who can relate shoreline topography to the features of the

water circulation; and a representative of the State Department of

Natural Resources, to provide comments on the suitability of the site

for development. The developer and the canal designer should not assume

that they can by themselves learn all they need to know about a site,

but instead can learn much from people with qualifications in other

scientific disciplines.

There are basically two kinds of information and data that can be

obtained for a site. Usually a search will reveal earlier reports on

the same area, or perhaps at the same site, which may provide useful

historical perspective. Particularly useful are data on previous land-

forms, including land elevations and waterbody depths, and water

quality, which may reveal trends toward improvement or degradation at

the site. Aerial photographs are also a good source for historical

information. The investigator should obtain the chronology of land

ownership, which may lead to additional information about past condi-

tions at the site.

There is a need for both long-term field surveys and short-term,

intensive field surveys. Most natural variables, such as tide, wind and

rain have long as well as short periodicities which may be significant.

Some variables, such as water velocity, salinity, and temperature struc-

ture in a canal, need to be interrelated on a short period basis during

a tidal cycle, and these variables require short, intensive surveys.

The principal investigator and the field survey team need to have a

definite, well-organized plan before any survey is conducted. This will

ensure that no essential measurements are missed, at least due to lack

of planning.

1.6 Numerical Modeling

Today there are many numerical models available for simulating

hydrodynamics, transport phenomenon and water quality for almost every

conceivable type of waterbody. A number of these models have been used

so often that the results obtained are, unfortunately, accepted without

question. This has led, in some instances, to the application of

models to problems for which they were completely unsuitable, since each

model is designed under a specific set of assumptions and for a specific

range of variables which may be entirely different from those required

for the problem at hand. In addition, there has also been some tendency

to develop both oversimplified models, and over-elaborate models in

which complex techniques are used to approximate terms which have only a

relatively small influence in a particular situation, and which there-

fore can usually be neglected considering the quality of the input data

or the accuracy of the other inherent approximations and assumptions.

A distinction is usually made between hydrodraulic or hydrodynamic

models and water quality models, because they are usually developed

independently by different persons working in substantially different

disciplines. The user of the models will also frequently have developed

his expertise and experience in a discipline related to one or the other

of these areas, but not both. Thus, the limits within which each model

has been designed, that are established by the basic assumptions in the

mathematical development, the approximations inherent in the numerical

method, and the accuracy of the field data used in calibrating the model,

may not be fully appreciated by the user.

For example, a frequent over-simplification is to assume that the

hydrodynamics can be reproduced by a one-dimensional model. This would

be a fatal mistake for the analysis of canal networks, in which external

influences such as the wind and density gradients produce multi-layered

flows which are predominant over tidal influences. Similarly, some

hydrodynamic models are too elaborate for this application. For

example, models based on the full dynamic equations are not required

when the surface slope of the canal discharge is very small, as it is in

the low energy tidal canals characteristic of Florida's coastal zone.

Thus, one of the principal goals of the numerical modeling portion

of the canal design research project was to develop a predictive

three-dimensional model that would incorporate the physically important

factors in canal hydrodynamics and mass-transport. Furthermore, the

model had to be relatively inexpensive to run, so that it would be

feasible to iterate a canal design through trial configurations toward

an optimal solution. The input of boundary conditions, such as the tide

and fresh water or pollutant inflows, had to be simple, but flexible

enough to accommodate a wide variety of possible applications.

Likewise, the specification of the other forcing functions had to be

flexible to permit either time-carrying field conditions or fixed design

conditions to be applied.

The calibration of a numerical model for a particular site can

often be a very difficult task, relying on a great amount of field data.

A second goal of the numerical modeling portion was therefore to struc-

ture the model with a minimum of calibration coefficients. A model that

fulfills the goals of the project was developed by R. Walton (1978].

1.7 Organization of The Chapters

'lie principal features of typical Lidal canal systems in Florida

are summarized in Chapter 2. This section considers the climatic condi-

tions, geology, physical and hydrodynamic features, and water quality

found in developed areas along the coast of Florida. The regional and

seasonal variability of these features is an important consideration in

determining the types of coastal areas which would be relatively accep-

table for canal development.

Canal design in Florida is guided by legislation, the economics of

development, and environmental considerations. To some extent, it is

also influenced by past design practices, some of which, both good and

bad, have become widely accepted in practice through continued use. In

Chapter 3 these factors are outlined and discussed as they pertain to

present day design objectives and limitations.

Chapter 4 describes the initial planning for canal design in terms

of criteria, guidelines, and constraints. Design objectives are defined

as the qualitative guidelines under which the canal designer and the

developer cooperate to produce a set of quantitative design criteria.

These criteria are established by considering various suggested guide-

lines that have been developed from consideration of problems which have

been identified with canals in the past.

The first step in planning a canal development is an evaluation of

the characteristics of the site. Chapter 5 distinguishes between fixed

site characteristics and alterable site characteristics, and describes

sources of published information on regional data which are applicable

to this problem. Then, preliminary site investigations are described in

terms of their objectives and the monitoring and sampling problem. A

general discussion of the measurement requirements for tidal canals

completes this Chapter.

The results of the field work guided the development of the basic

features of the canal design model. Chapter 6 begins with a description

of desirable specifications for canal instrumentation, and then

describes the instrumentation and support equipment used by the

Hydraulic Laboratory in the canal design research project. The re-

duction and presentation of field data follows. The field procedures

carried out by the author for the Hydraulic Laboratory are next

described, with some observations on the results. A specific analysis

of the results of the comprehensive dye dispersion experiments, however,

has been incorporated into a discussion of the calibration of the

numerical model at the end of Chapter 7.

The development and features of the numerical model of mass-

transport in low energy canal networks, a research project conducted by

R. Walton in conjunction with the project described herein, are sum-

marized in Chapter 7. The characteristics of one- and three-dimensional

mathematical models, the development of the three-dimensional numerical

model, and its stability are covered in some detail, but not completely,

as the work is not that of the author. The chapter concludes with a

discussion of the verification of the model, with some explanation by

the author of the field results as they pertain to this aspect of the


In Chapter 8 an overall design process is described. This process

begins with the development of quantitative design constraints and

criteria, specific examples of which are given. Design elements

are described, and some general guidelines as to their use in

synthesizing canal networks are tabulated. The variability of both the

one- and three-dimensional numerical models is shown for variations in

geometry and boundary conditions, which gives some insight into the

operation and design of tidal canals and canal networks. The final part

of Chapter 8 describes some of the features of basic canal design

elements: the comb-structured network, the "lake," bends, and a simple

system with two tidal entrances and a nodal point. These are simulated

using the CANNET3D model, and the results are compared in terms of

relative flushing time.

An example consisting of a hypothetical "existing" canal network

and some tests to find its optimal depth and flushing characteristics

are developed in Chapter 9. General simulation objectives are described

as well as several methods for quantifying the flushing characteristics

of a given network. The resulting concentration profiles after fifty

tidal cycles, under no-wind and mild-wind conditions, and with and

without additional tidal prism, are compared. The chapter concludes

with a discussion of the relative effect of constant and variable winds.

Chapter 10 is a summary of the project, together with conclusions

and recommendations.

Table 1.1 Inventory of Large-Scale Developments in Florida.

\.,rlh I.oIlon Lh li

-ili-f K0ll. h S'hun1

ramei K mh {;r+,i(+

lortool St Oln.

Pur Ith lohn

Ppr1 St 0h,!
I 0, 1.o h ith0 r I 011id1
S0b1,l0,l H'hlndo H
101 1. i

Hpi rig b) ?hf St'd

N. + > i *I .

0 1 ila l d r m

S, ii I++ o0, j 0

lo. -1on IlrooIup.r

L. l0.00 l.j.1.,llll

110 1I ol,
Sr1 01 1(. Larpor

i b, .l p,

( (k 1( C .i$ nl

II. Ir 1 1r. (1 1 ,1 ,

It 0 0, II sI 1 1r 01

I ( 1, 1 A

Ir+ ft+ to o ,+ I IN ely ment +.
i0 1 0 1r J iluh r hr

I+ I ,,: ,I l p r t
0 1
11 110101 en

1, I' >1,1
I 1,001 2 ++

y +++ {+ bz, l l.i.rnt p ite
iiir ill1,1011.
ii-i nlt. l~li Ini (.ha in (vy
*id II

I) . uls1 n m Inl Ind a ~lk, t

001.00~riII1 n
0a10 0101111

*l ,l 0.1.
+++ + b,++ 4 u. n +

+ "+ + (-Ir i 4 m ++q

Irnd re ;
I lndIrI
II++ II I, + +m,,,0 I
+ + O+ + I I'V++. I
ru n+[ +ir+ ]rt l.+Jd t+ >r

++ +++.++I a I l( i sn ( .rl

0, ,Is+l. I,,~t I rd ( rl

i :11 l r I ,

) ( +l + ,

Source: Carter, 1974, pp. 32 & 33.

i.4 re.age

'wl +'
Ir rrlh

4 I i0

1ll 11. 1

4 1 .
I li
i" tll

a ll
4 J

1i 111
.... u

,+ lu+

I-l, 4.:


i io i* b

:I Oil)
i *41. -

1 150
+, .r i

+, ,+
$ +,+o


;<, uu

,z :+su

+, 4+L,1
. +; l
I If+0 +

N+ Ulrhmale
unIdl pop
uml'' POP

"u '. j~ u

U 0

0 0

,* 00 110*1T0
liol a iu1I

j4* in 1l000
ti v510 i~
nl iii Id sU n

ii ,nlu

5u Ot+c
1 ) JOo,
11o 110


l -i5O1H


IJ~ ?-

U4 1000


be: unu
( iD

i5 ,
25 lkJU





5 a00

I hO





*,; ivrri
,1 lilili
ill iillo


S -l

OJ "







H m




0 0

o 0



4m 4

4 44
0 4<00-

% 5s

5 Sos^
a 5 c o

05 C ~

't0 O

4V 4<'

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z< o5

-z 0

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o <<0 Li

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^fA- c...^ -_.;, '. .-., _'.

- -- ., -. . -1 -~ ^ -- *-- '--- : 1.,. .^*- .~ t :.. .L~ -. / .
^ + .....* -" .M-" *
..... 5 r
-,i^-s^^?^' ~" ~~~C4 J^ *- ^^-^fc
~~~ C& -r b4

t, "'""-
-s --~, S. -
r~ -r-

' 4:----

...- -.. ;. ...
r" -- "- -
F e--i rE.'-m:_pl.... .. -D.. n.. F F d .

Figure 1.1 Example of Bayfill Development in Florida.

4 .

e . ,,

." -
,~s ~cr. ** ,
* 3* *4
I- -.- *
- s ." ""* -, ..

. : . 't *-. *" ;
S .
:Qt .

Figure 1.2 Example of Intertidal Development in Florida.

Figure 1.3 Example of Inland Canal Development in Florida.


o AUGUST 1974

\ ater Quality

-- o

w 2

0 2 4 6 8 10 12 1t I I 0 2 2

DEPTH (feet)

IUGUbT l17)
,,o s, llsl ,,im=,

13 *-I 5 II) 0

W- 2i 55 id

II 114 O- 4S 0

0i2 u 10 1 2 14 16 ,C
i'i 24 II -I ?I 12

n 0 3 3 1 0 3 32
Canal Systems in Florida, August 197 (Source: EPA,

1975b, p. 12). I I 0
2 2 I2 45 22-I3 7 12 22 02 22
*D 23 22 2202 02 3l i 22 2

Figure 1.4 Average Values of Dissolved Oxygen Concentrations in

Can2 2 Systems in Florida, august 1974 (Source: EPA,
1975b, p. 12).



This section combines a literature review with a general,

qualitative explanation of the hydrodynamics and water quality of tidal

residential canal systems along the south Atlantic and Gulf Coasts. The

examples and data are taken somewhat at random from the existing infor-

mation for Floridian canals. It should be noted that canals primarily

constructed for navigation, flood control, irrigation, mosquito control,

and other such purposes are not specifically covered, as the problem of

residential canal design is being addressed. Of course, the physical

principles governing the operation of tidal canals do not vary with

their purpose, but rather with their form and location, so that many of

the concepts presented here can be applied in other contexts.

2.1 Governing Features of Tidal Canal Systems

The hydrodynamics of tidal canals are governed by the combined

effects of canal system layout, channel geometry, climate, tidal range

and period, wind, the saltwater/freshwater balance, water circulation,

and certain geological features. Water quality is dependent on the

hydrodynamics, but does not affect the flow in the canal, and thus can

be used as an indicator of the effectiveness of the circulation in

mixing and flushing pollutants from the canal system.

A given canal system is part of the surrounding ecosystem, which

has terrestrial, marine, and atmospheric components. Thus, there are

many interactions between the canal system and the other parts of its

natural surroundings. However, the mass-transport characteristics of a

canal system may be effectively described in terms of a pollutant with a

first-order decay, with the influence of the ecosystem being limited to

the physical forcing functions (tides, winds, and salinity and tempera-

ture gradients), the effect of vegetation on runoff, and the interaction

of water currents with bank and bottom materials. Since the basis for

the canal model is the hydrodynamic laws and the mass-transport of a

substance without interactions, the numerical model could be adapted at

a later time for the evaluation of water quality dynamics.

2.2 The South Atlantic and Gulf Coastal Zone

Lying between latitudes 24030' and 310 North, and longitudes 800

and 87030' West, Florida has 1,266 miles of general coastline or over

9,000 miles of detailed coastline (including all indentations and the

shores of islands). Of the general coastline, 593 miles border the

Alantic Ocean and the remaining 673 miles lie on Florida Bay and the

Gulf of Mexico [Corps of Engineers, 1971, p. dl; Carter, 1974, p. 1).

The coastal zone as defined by the Florida Coastal Coordinating Council

11971) is shown in Figure 2.1. The definition of the coastal zone is

based on population density rather than on the topography of the area.

It is a political definition, not a physical one.

The Atlantic shoreline of Florida consists of a series of sea

islands and barrier islands separated from the mainland by the contin-

uous Intracoastal Waterway. North of Jacksonville the sea islands

border salt marshes, while to the south as far as Miami the barrier

island chain, which is broken by 14 of the 57 inlets on the Florida

coast, is backed by low tidal marsh or lagoons. These barrier islands

vary considerably in their dimensions and the degree of development,

from wide flat beaches with 10 to 20 ft high dunes to narrow sand strips

fronting seawalls. Some of the inlets open into extensive estuaries,

while others formed by storms breaching the barrier islands have no

associated estuary or bay.

The Florida Keys may be divided into three distinct groups. The

long, narrow keys occurring at the northern end of the chain are coral,

the irregularly shaped Keys in the center portion are Miami oolite

(limestone), and the lower Keys consist of oolite interspersed with

patches of mangrove. The ocean bottom to the east of the Keys is a

nearly flat sheet of limestone extending from one-half to one mile

offshore. The side facing Florida Bay is similar, with scattered man-

grove located in the bay to the west of the upper Keys.

Most of the Gulf shoreline from Florida Bay northward to Anclote

Key (at the Pinellas/Pasco County line) consists of offshore barrier

islands, beginning with the Ten Thousand Islands at the south end of the

peninsula. The southern part of this coastline is characterized by

extensive networks of tidal creeks and mangrove swamps. Shallow tidal

lagoons lie between the offshore islands and the mainland. These bar-

rier islands are separated by shallow, natural passes which in some

instances have been extensively improved for navigation.

North from Anclote Key to Apalachee Bay the coast completely

changes character. The barrier beaches are replaced by low, flat tidal

marshes, and the slope of the bottom offshore is very slight. Beginning

with the sand spits at the west end of Apalachee Bay the coastline again

becomes predominantly a series of beaches on the mainland. These

beaches are generally wide, with 10 to 15 ft sand dunes. [Information

primarily from Corps of Engineers, 1971, p. dl].

2.3 Climate

Climate is an important consideration in the design of a canal

system because wind, precipitation and storms affect the circulation of

water in the canals. In addition, cloud cover affects the air and water

temperature and the productivity of the canal biota.

The climate of Florida is categorized as transitional between

temperate and subtropical in the extreme northern interior of the state,

and tropical in the Florida Keys. The climate is controlled and mod-

erated primarily by the latitude, proximity to the Atlantic Ocean and

the Gulf of Mexico, and the 4,400 square mile surface area of inland

lakes. The summer season throughout the state is relatively long, warm

and often humid, while the winters are comparatively mild due to the

southern latitude and warm coastal waters. The Gulf Stream has a

warming effect on the east coast because winds prevail from the ocean.

Florida has abundant rainfall. Host localities receive over 50

inches per year, except the Florida Keys which average about 40 inches

per year. A typical year can be subdivided into two "rainfall seasons"

throughout all of the state except the Panhandle. On the peninsula

portion more than one-half of the yearly precipitation usually falls

from June through September, which climatologists call the "rainy"

season. The other eight months comprise a relatively dry season. In

the Panhandle a secondary rainfall maximum occurs in late winter and

early spring. In addition, the distribution of rainfall with a given

year is quite uneven. During the rainy season the probability that rain

will fall oil any particular da.y is about 50 pler-enL, while during tile

remainder of the year rain may be expected to fall on one or two days

during the week.

The seasonal distribution of rainfall varies from north to south.

On the peninsula this distribution is dominated by a large amount of

summer rainfall and the rather abrupt start and end of the summer rainy

season. In the Panhandle there are two times of high rainfall, one in

late winter or early spring and the other during the summer. The time

of lowest rainfall occurs in October, and secondary low quantities occur

in April or May.

Local showers or thundershowers are common in summer. Many

localities average more than eighty of these storms in a year, while

some experience more than a hundred. These showers are generally quite

heavy, up to three inches in two hours and ten inches in twenty-four

hours. The more severe storms are occasionally accompanied by high,

damaging winds. However, typical summer storms are of relatively short

duration and even in the rainy season rainfall usually occurs less than

10 percent of the time.

While Florida normally has substantial rainfall during a year,

portions of the state have also experienced severe droughts. These dry

periods, which may last longer than a month, occur even during the

normal time of the rainy season, resulting in excessively low water

levels in reservoirs and aquifers.

Over the southern part of the peninsula winds prevail from the

southeast and east. In the remaining part of the state they are some-

what erratic, but predominately north in winter and south in summer.

The months with the highest winds are March and April, and high local

winds of short duration are generally associated with thunderstorms in

summer and with cold fronts in other seasons. Tornados have occurred at

all times of the year, but they usually do not cause extensive damage.

Tropical storms, and particular hurricanes, are another matter. A

tropical storm is any storm that produces high winds (above 34 knots)

and therefore has destructive potential. A hurricane is a tropical

storm with maximum winds of 64 knots or more. From 1885 through 1977,

67 tropical storms and 86 hurricanes have entered or significantly

affected Florida (Environmental Data Service, (monthly) to 1977]. The

average number of tropical storms is 1.7 per year, with a variation of

from none to 5 in any year. Florida has not experienced more than 3

consecutive years without a tropical storm, nor more than 5 consecutive

years without a major hurricane.

The probability that hurricane force winds will impact a particular

Floridian city in any year is summarized in Table 2.1. This probability

varies from a low of one in one-hundred at Jacksonville to a high of one

in seven at Key West and Miami. In the ninety-three years of record,

only ten or eleven hurricanes have passed inland on the west coast in

the area from Cedar Key to Fort Nyers. Along the coast from Jacksonville

to St. Augustine the first recorded hurricane was experienced in 1964.

The probability of experiencing a tropical storm increases as the

hurricane season develops. In August and early September hurricanes

normally approach from the east or southeast, while in late September

through October hurricanes generally approach from the western

Carribbean into the Gulf of Mexico. Wind gusts of up to 155 mph have

been recorded (accuracy unknown), but anemometers do not usually survive

winds in this range. Wind speeds up to 200 to 250 mph have been

calculated based on the extent of damage in the most intense recorded

hurricane. It is estimated that sustained winds of over 150 mph are

experienced in Florida approximately every seven years. Very heavy

rainfall occurs within tropical storms, over 20 inches in 24 hours

having been occasionally measured. The average hurricane rainfall,

however, usually does not exceed 8 inches in 24 hours.

The sky is overcast about one-third of the possible sunlight hours

during a year, ranging from a value of less than forty percent in

December and January to less than thirty percent in April and May. In

general, hours of sunshine in the southern part of the state exceed that

for the northern part. The contrast between the amount of daily sun-

light in New York and Miami is substantial. In December, the number of

sunlight hours in Miami averages sixty-six percent and in New York

fifty-one percent, but Miami receives an average of 317 langleys on a

horizontal surface while New York receives an average of only 116

langleys [Bradley, 1974, pp. 45-70].

2.4 Physical Features of Floridian Canal Systems

2.4.1 Types of Canals

A bay-fill canal network can be laid out in any shape the developer

chooses, since wetlands are flat and can be dredged at any location.

Intertidal and upland canals, on the other hand, will usually be laid

out with some conformance to local topography unless the developer is

willing to pay for additional earth moving. Present federal and state

regulations regarding work and construction in tidal areas require that

alterations to the environment be minimized, so that designs that do

take advantage of the existing topography will encounter the least

resistance to development, both physical and political.

Christensen [in Christensen and Snyder, 19781 has classified existing

straight canals into five major groups, and added borrow pits as a sixth

category for consideration of flushing characteristics:

Group No. Descript ion

1 Flow-through canal
2 Simple dead-end canal
3 Higher-order finger canal
4 Comb-structured canal system
5 Canal with lagoon (basin)
6 Borrow pits

These six classifications are diagrammed in Figure 2.2. Complex networks

may be obtained by combining one or more of these groups, with or without

curves. A flow-through canal (or canal reach) is one that maintains a

flow of water at its two open boundaries, in contrast to a

simple dead-end canal, which has only one boundary open to flow. The

latter is often associated with poor water quality because velocities

become small near dead-ends, sediments fall out of suspension more

easily, and surface debris tends to accumulate in the dead-ends unless a

favorable steady wind is able to carry this debris out. The flow in the

vicinity of a dead-end is complicated by upward or downward water move-

ment when two- and three-layer wind-induced flows occur in the channel.

A higher-order finger canal network is one which has one or more

branches joining the main channel. If these branches are dead-end

canals, the system is said to be second order. As additional branches

are added to the first-level branches the order of the system increases,

and it is called an upward-branching system.

A canal network with many relatively short, parallel, closely

spaced dead-end branches or fingers is a comb-strturtured network. These

fingers may be straight or curved, as shown in Figure 1.1. A canal with

a lagoon or basin at one end, such as a marina, has somewhat special

characteristics. Since the volume of water associated with the tidal

prism which will flow into a tidal canal basin is a linear function of

the surface area of the basin, velocities in the channels connecting a

basin to the receiving waterbody will increase as the basin area is

increased, which in turn will increase mixing and flushing in the con-

necting channels. The location and sizes of lagoons or boat basins are

therefore an important design element in a canal network.

2.4.2 Canal Banks

In the past, canal channels have often been constructed with

vertical bulkheads, not only to hold the fill from the channels but to

maximize the lot size and number of lots within the available develop-

ment area. Vertical bulkheads (shown in Figure 2.3) are convenient for

mooring boats, especially deep-draft vessels. Although they provide an

adequate environment for certain sessile organisms, they have a number

of serious disadvantages. One of the most serious is the susceptibility

of the bulkhead, if not designed properly, to erosion at the toe due to

boat wakes and to runoff and undermining on the landward side. They

also reflect boat wakes back into the channel, which can cause dangerous

navigation conditions.

The more desirable trapezoidal channel shape, which is similar to a

natural channel with sloping banks (Figure 2.4) is not often found in

residential canal developments. Substantially greater widths are

required to permit a navigable section along the centerline, which

utilizes land area that would otherwise be available for housing lots.

The banks may either be cut directly into the upland soils at slope

that will be stable for the design channel velocities, or may be estab-

lished at some arbitrary slope and riprapped. If constructed on native

soil, they should be vegetated to provide soil stability and to dissi-

pate the energy in boat wakes.

2.4.3 Tidal Characteristics

The relatively small range of tides around the coast of Florida,

and the resultant low level of energy available from this source for

mixing and flushing of pollutants, has already been mentioned. Along

the coast of Florida all of the three major types of tides are en-

countered, as shown in Figure 2.5. Examples of each type are given in

Figure 2.6. Mixed tides exhibit alternate high and low values of

substantially different elevations, which can have the effect of

decreasing the flushing action on alternate tidal cycles.

At the beginning of the canal research project it was not known

whether the slope of the water surface due to the tidal wave would be

significant or not, although it was suspected that it would be quite

small. Attempts to measure the slope with tide gauges showed it to be

of the order 105 to 106 or less. Therefore, a comparison of tidal

elevations at the end of a 5,000 ft straight canal was made using two

different one-dimensional numerical models, one including the momentum

equation (which takes this effect into account) and one that assumes

that the water surface is always horizontal [Walton, in Morris, Walton

and Christensen, 1978]. The water surface elevations and velocities

compared within 2 percent, which was concluded to be sufficient justi-

fication for ignoring the surface slope considering that the combined

measurement accuracy for tidal elevations, current velocities, dye

studies, and predictions using numerical models would he significantly

lower. The physical explanation that justifies the horizontal water

surface assumption is that the tidal elevation changes relatively slowly

over a tidal half period, on the order of 3 ft/6.21 hour or 0.008 fpm.

2.4.4 Tidal Energy

Part of the energy brought into the canal system by the tide is

expended in overcoming frictional resistance and in mixing, while the

remainder is stored as potential energy for the next half tidal cycle.

The total potential energy stored in the tidal prism in a given canal

system after a flood tide is

E = yVa (2.1)


E = potential energy, (FL)

y = unit weight of water, (F/L3)

V = volume of tidal prism, (L3)

a = elevation of centroid of tidal prism

= amplitude of tide, (L)

The total power, or rate of energy storage, in horsepower is found by

dividing by the half-tidal period and the conversion factor for Ib-ft/sec

to hp

p V a (2.2)
x 3600 x 550

2.64 x A x 2a x a
42 x 3600 x 550
12.42 x 3600 x 550

= 1.041 x 105 x a2 A (hp)

where the units of a and A are ft and ft respectively and
P = power available from tidal prism, (FL/T)

T = Lidal period, (sec)

A = surface area of canal, (L2)

Thus, the power available for flushing on the ebb flow at any location in

the canal system is given by Equation (2.2), using the mean tide surface

area upstream (in the direction away from the tidal entrance) of that

location for A For example, in one large system studied by the
Hydraulic Laboratory, the 57 Acres canal system in Palm Beach County, on

the intracoastal waterway, the mean tidal amplitude is approximately

1.25 ft, the total surface area is about 4,300,000 ft2 (98.7 acres), and

the power available is 70 hp. The available power from stored tidal

energy in the 1700 to 2400 ft long west coast finger canals studied by

the Hydraulic Laboratory varies between I and 2 hp. This energy is

supplemented by energy from the wind and salinity gradients for


As the tidal wave travels into the canal system it will progres-

sively lose some of its energy and it will take a finite time to reach

locations within the canal system. Measurements by the Hydraulic

Laboratory in the 57 Acres canal system, using tide gauges, showed a

tidal elevation difference of 0.04 ft and a lag of 0.8 hours at slack

tide over a distance of 7780 ft from one entrance, and a tidal elevation

difference of 0.01 ft and a lag of 0.6 hours at slack tide over a dis-

tance of 9695 ft. The calculated water surface slopes at maximum tidal

discharge over these distances were 5 x 105 and 3 x 105 respectively

[Walton, et al, 1975b, p. 59].

Since the tide loses energy as it progresses up a dead-end canal

system, there is, at least theoretically, a limited distance over which

it will be effective in mixing. This may be called the tidal excursion

distance, x', which can he theoretically calculated if it is assumed

that there is no mixing of the flood tide with the resident water.

Conceptually, under these circumstances the flood tide pushes the resi-

dent water toward the dead end and the tidal prism, awL, fills the

entrance end of the canal to a distance x' or

(d + a) wx' = 2awL

x 2a L (2
d +


d = mean (mid-tide) depth, (L)

L = length of canal, (L)

By this concept the maximum possible value of the excursion distance is

the length of the canal, when a equals d In an eight-ft deep canal,

with tidal amplitude equal to 1, the excursion distance by this formula

would be 0.22 L.

2.4.5 Secondary Currents

It is known that secondary currents occur in straight channels as a

result of turbulent velocity fluctuations and the normal stress produced

by turbulence [Schlichting, 1968, p. 576; Ikeda and Kikkawa, 1976].

Velocity measurements taken by the Hydraulic Laboratory in a canal

several miles up the Loxahatchee River indicate that even in a straight,

2200 ft dead-end canal the flow is not at all uniform in any of the

coordinate directions (Figure 2.7). Some lateral nonuniformity in the

depth, and transverse wind components, contribute to the formation and

maintenance of the secondary flows that are observed there. Further

evidence of the presence of secondary flows is a series of evenly-

spaced, dome-shaped shoals along the banks of the canal that are

uncovered at low tide.

Secondary currents of much greater significance from the viewpoint

of mixing also occur in bends, producing velocities an order of magni-

tude greater than those produced in straight reaches. These currents

are formed by the effect of the centrifugal force exerted on the water

particles due to higher velocities at the surface than at the bed. This

results in a superelevation of the water surface on the outside of the

bend and lower elevation on the inside of the bend, and secondary cur-

rent flowing downward on the outside and upward on the inside. The

superposition of the secondary flow on the primary water movement

results in a helical water particle path, as shown in Figure 2.8.

Secondary flows are an important design element because they are

instrumental in vertical mixing.

2.4.6 Dispersion Coefficients, Flushing Tme and Models

The ability of a canal system to flush pollutants to the receiving

waterbody, and thereby to maintain water quality in the canals, is

fundamentally related to the way in which incoming natural energy is

distributed and used in the canal system. Principally, energy is

brought into a canal system by the tides and the wind. A secondary

source is freshwater inflow and the resulting salinity gradients. In

describing the spatial and temporal changes of energy it is convenient

to employ descriptions of the circulation of the water and the distri-

bution of pollutant concentration gradients, to which, in turn, the move-

ment and spreading of pollutants can be directly related.

The movement of the water convects pollutants, while concentration

gradients cause the pollutants to distribute themselves in the direction

that will tend to reduce these gradients. In turbulent flow, which is

the type of flow almost always found in open channels, the local circu-

lation is characterized by the presence of velocity fluctuations in all

directions, and transverse and vertical eddies. Together these fluctua-

tions and eddies cause turbulent mixing.

The "flushing time" of a canal may be considered as the time

required to replace the polluted water in the canal with unpolluted

water (Bowden, 1967, p. 19]. The "residence time" has been generally

defined as the time that a particle of water remains in the canal before

it is exchanged with another particle from outside the system. The

following expression for the flushing time, TF, or the mean residence

time, TR, can be derived by ignoring the dynamics of the circulation and

the details of the flushing process and assuming that steady state

conditions prevail (i.e., that the pollutant is removed at the same rate

as it is introduced).

TF = = (2.4)


V = mean volume of polluted water to be removed, (L )

Q. = mean rate of removal of polluted water, (L3/T)

The "mixing half-life" of the canal would be given by T /2. Equation

(2.4) has been derived by neglecting the mixing of incoming polluted

water with the resident canal water and ignoring any density-induced net

circulation (stratified flow) or wind influence. Because of the assump-

tions involved, flushing and residence times calculated in this way are

meaningless for tidal canals.

Many more sophisticated "flushing time" models have been devised,

most of which involve assumptions of complete mixing over at least some

part of the waterbody. For example, in "tidal prism" methods it is

assumed that all of the water entering on the flood tide becomes com-

pletely mixed with the resident water in the canal, while in "segmented"

models [Ketchum, 1951] complete mixing is assumed to take place succes-

sively in segments with lengths determined by the tidal excursion.

Still another variation is to introduce an "exchange ratio," which

effectively reduces the volume over which mixing is assumed to take

place. While such models attempt to take the variation of salinity into

account, and will in some cases provide results to the correct order of

magnitude, there are still too many assumptions involved to give a

reliable estimate of flushing time for tidal canals.

Longitudinal dispersion is one of the processes by which a mass of

some dispersant, e.g. a pollutant, is spread out, mixed, and thus

diluted in a flow of water, the others being molecular diffusion and

turbulent diffusion. The term "dispersion" applies to spreading that is

controlled by spatial velocity gradients, in contrast to "diffusion"

which is spreading caused by random temporal fluctuations. Thus, dis-

persion is caused by nonuniform transverse and vertical velocity profiles.

In turbulent flow in natural waterways it has been found that the velocity

gradients are far more important in determining the dispersion rate in a

given canal than either molecular diffusion or turbulent diffusion,

which are essentially random and therefore not occurring in any particular


In the derivation of the one-dimensional convective-dispersion

equation for turbulent flow

a a a ac
t(Ac) + (Auc) = (AE ) Ar (2.5)
t x x+ Ar x p(2.5)

c(x,t) = concentration, dimensionlesss)

A = cross-sectional area, (L2)

u(x,t) = spatial mean velocity, (L/T)

E = longitudinal dispersion coefficient, dimensionlesss)

r = rate of production or removal of pollutant

mass, (1/T)

it is assumed that the dispersion process can be approximately described

by a one-dimensional Fickian-type diffusion equation. Under this assump-

tion, in theory, the variance of the concentration distribution of a

conservative dispersant in steady flow should increase linearly with

time. For uniform steady flow a variety of analytic solutions are

available for the concentration distribution as a function of location,

time, and the characteristics of the source of the dispersant. For

example, the solution for an instantaneous plane source of dispersant

uniformly distributed over the cross-section of a channel is given by

Ii (X Ut)
c(x,t)= ---2exp [ 4Et (2.6)
pA(4nEt)12 4Eet


M = mass of pollutant injected, [m)

p = density of solution, (M/L )

X = distance from point of injection of dispersant, (L)

t = elasped time since injection, (T)

U = mean (steady, uniform,) velocity of low from

injection point to sampling point, (L/T)

This equation indicates that the pollutant has a Gaussian distribution

in the x-direction for all time and the peak concentration is always at

x = Ut, and decreases with time according to

c = (2.7)
pA 4nEIt

The centroid of the dispersing cloud is also at x = Ut, and the variance

of the distribution of concentration is given by o2 = 2 E2t [Holley and

Harleman, 1965, pp. 59-601.

This solution, and others similar to it for continuous sources, in

one-, two-, or three-dimensions, form the basis for the design and

analysis of a great many dispersion experiments. The objective of a

dispersion experiment is to determine a value for the coefficient EP

from measurements of tracer distributions. One form of the dispersion

coefficient EQ is [Taylor, 1954; Elder, 1959]

E2 = KRu (2.8)


K = dimensionless dispersion coefficient

R = hydraulic radius (L)

u = bed shear velocity, (L/T)

The dimensionless dispersion coefficent K is an empirical coefficient

which is independent of the depth and roughness of the channel, but a

function of the regularity of the channel; low values of K correspond to

straight regular canals while high K values correspond to irregular

curved and meandering systems.

Besides the restriction that the mean velocity of flow must be

approximately constant over the period of a dispersion experiment, there

is a further limitation described by Fischer (1967b, pp. 192 and 207].

For dispersion to be described by the diffusion equation (i.e. the

Fickian equation) it is necessary that the motion of each tracer par-

ticle not be dependent on its initial velocity. The period during which

this is true is called the "Taylor" period. The initial period after

injection of the tracer material is called the convectivee" period, and

Fisher found that the criterion for use of the one-dimensional convec-

tive-dispersion equation and a Taylor-type dispersion coefficient

(Equation 2.8) is that the distance downstream from the point of tracer

injection to the sampling point should be [Fischer, 1967b, p. 213)

2 U
L > 1.8 -- (2.9)
R u


L = distance between injection point and sampling

point, (L)

2 = a characteristic length of the cross-section

= distance from the point of maximum surface velocity

to the most distant bank, (L)

For example, in an 80 ft wide canal, 8 ft deep, with a uniform trans-

verse velocity distribution, a mean flow velocity of 0.2 fps, and u

typically 0.05 fps, L is 1450 ft. Thus, if the canal in which the study

is to be conducted is 1500 ft or less in length, the tracer must be

well-mixed across the channel near the dead-end for the experimental

results to be valid.

One-dimensional convective-dispersion models have been available

since the late 1960's and have been applied to the simulation of pol-

lutant dispersion in rivers and in estuaries. While there are many

reviews of the capabilities of a variety of numerical models (for

example, see Grimsrud et al [1976] and Lombardo [1973]), the conmnents by

EPA, [1975b, pp. 207-209] on the process of selecting a model for appli-

cation to flushing in tidal canals are most pertinent here. EPA began

by reviewing the Feigner and Harris [1970] version of Water Resources

Engineers' San Francisco Bay model, called the Dynamic Estuary Model

(DEN). This had been incorporated into the Stormwater Management Model

(SW h), University of Florida 1973 version [Metcalf and Eddy, 1971),

which was used for EPA's initial canal flushing simulations. The fact

that diffusion and dispersion were not incorporated into these models

finally led EPA to choose the Columbia River Model (CRN) version of the

original Water Resources Engineers model [Callaway et al, 1970] for

simulating flushing in canals, but since this is only a one-dimensional

model it could not simulate canal flushing properly (Walton, in Morris,

Walton, and Christensen, 1978, p. 342-343].

The effect of mixing in numerical models is expressed in terms of

various coefficients. The mixing coefficients associated with turbu-

lence, and obtained by averaging turbulent velocity fluctuations over

time, are called turbulent diffusion, turbulent diffusivity, or eddy

diffusivity coefficients, usually expressed in each of the coordinate

directions. The mixing coefficients evaluted by spatial averaging are

called dispersion coefficients. In particular, one-dimensional cross-

sectionally averaged models use a longitudinal dispersion coefficient,

which is usually found to be related primarily to lateral velocity

gradients (Fischer, 1967b, p. 189]. The magnitudes of vertical and

lateral diffusion and longitudinal dispersion coefficients vary with

location and time in a tidal waterbody.

Models can be programmed to accommodate variable coefficients, but

often a constant will be used because it is too difficult, time-

consuming, and/or expensive to measure the dispersion at various

locations and times in a given waterbody. The development of laboratory

and field experiments to quantify dispersion coefficients for steady

(river) and oscillating (estuary) flow may be traced through the work of

H.B. Fischer, which was reviewed in Fischer [1973].

Many experiments have been conducted in rivers [Nordin and

Sabol, 1974] and estuaries [EPA, 1975b, p. 30] in an attempt to relate

measured dispersion characteristics to the geometry and flow charac-

teristics of the waterbody. The experiment is usually conducted by

placing a tracer, that is, a neutrally buoyant solution of some material

such as a dye or a radioactive element, that can be detected in very

small concentrations, at a prescribed location and time in the waterbody

and then measuring the resulting concentration distribution downstream

at one or more subsequent times. These measurements are subject to a

great many subjective decisions and experimental variables, which can

result in a relatively wide range of experimental values. The investi-

gator usually concludes that the longitudinal dispersion coefficient is

primarily a function of the shear velocity and the hydraulic radius, or

equivalently a function of the flow velocity, depth, and roughness of

the channel.

The use of a two- or three-dimensional numerical model based on

tidal-, salinity-, and wind-induced circulation and diffusion, such as

the model by Walton (see Chapter 7), for evaluating the flushing time of

a complex canal network provides, in addition to a more realistic simu-

lation of water circulation, the advantage of allowing for realistic

pollutant inflow distributions. Thus, for example, the effect of an

unusually large pollutant point loading of limited duration can be

evaluated only by a model that can simulate the circulation and dif-

fusion over successive tidal cycles.

The design of a dye experiment is dictated by the kinds of

coefficients used in the model, which in turn depends on the number of

spatial dimensions in the model. It has been found by the Hydraulic

Laboratory that it is impractical to attempt to measure turbulent

diffusion coefficients due to the complexity and variability of the

circulation in a canal, and the alternate approach of releasing a tracer

and estimating coefficients from the resulting concentration profiles

over successive tidal cycles has been adopted. The limitations of this

approach are discussed in Section 7.5.2.

2.4.7 Stratification

When the vertical salinity and temperature gradients in a canal are

very small, the canal is said to be "well-mixed". However, when these

gradients are sufficiently large to affect the circulation in the canal,

then the flow is called density- or temperature-induced. When the

gradients become so large that two distinct layers of water form, one

above the other over a significant length of the canal, the conditions

are called "stratified".

A distinction between gradient-induced flow and stratified flow

should always be maintained, as they describe two different phenomena.

When stratification occurs the two water masses tend to form an inter-

face sloping downward and inward into the canal. In this case the

denser water mass is often referred to as a "saline wedge."

A salinity profile is adequate for showing the shape of a density

profile provided the water temperature is relatively constant. However,

the density of seawater varies with both salinity and temperature, and

therefore density should be used when vertical temperature differences

of greater than about 5C are measured at a station.

Density gradients and stratification are indicators of the relative

stability of water masses. If the water is well-mixed, the vertical

density profiles will be straight vertical lines. If it is completely

stratified and in equilibrium, with the less dense water mass wholly

above the other more dense layer, the vertical density profile would

consist of two vertical profiles of different value, one representing

each water mass, and a relatively sharp change from one value to the

other at the interface. A sudden decrease in density with depth would

indicate that the waterbody was unstable and in the process of over-

turning. In practice, one usually sees a more gradual change in density

with change in depth and it is necessary to examine several vertical

density profiles over a period of time to determine whether there is a

tendency toward stratification or not.

Salinity gradients can also occur when fresh river water interacts

with saline tidal water near the mouth of a canal, and both are intro-

duced into the canal system on the flood tide. It is also possible for

canal waters that are not well flushed to increase their salinity

locally through evaporation and form local density gradients which will

further inhibit flushing. This might occur, for example, near a dead-

end that is located far from the tidal entrance of a canal system, if

little circulation is taking place.

Salinity gradients and/or stratification commonly occur in

Floridian canals during the wet (summer) season due to runoff from

rainstorms. Figure 2.9c from Lindall, Fable, and Collins [1975,

pp. 82-83] shows the change in the salinity difference between surface

and bottom stations in a Tampa Bay canal system (Figure 2.9a) during

October, 1971 and August and September, 1972. The maximum salinity dif-

ference shown here is 4.5 ppt in October, 1971 at station 3. It will be

noted that water temperature was close to uniform at all times except in

January and February in this set of data (Figure 2.9b) and that DO

gradients (Figure 2.9d) tended to form during the summer months when

salinity gradients formed. It will also be noted that after the rainy

season subsided (October) the canals destratified again.

The effect of a large density gradient in the vicinity of the

salinity interface is to reduce vertical diffusion, which suppresses

vertical mixing. If a saline wedge remains in a canal over a period of

time, perhaps fluctuating in position but not permitting much of the

bottom waters to be exchanged, pollutants could be trapped under the

saline layer and anoxic conditions can result at the bottom.

If conditions are favorable for stratification in a particular

canal, the salt water has a tendency to remain together as a unit over

many tidal cycles. On a flood tide the saline wedge displaces the

lighter, less dense water. On the ebb tide, the elevation of the salt

wedge at the tidal entrance falls in response to the change in the

elevation of the salt water in the receiving waters. Due to frictional

retardation of the movement of the wedge out of the canal, a salt water

dome is frequently observed in the canal at low tide. The hydrodynamics

of the salt wedge movement will be discussed in Chapter 7.

2.4.8 Geology

The geology of a site controls the movement of surface water,

subterranean water, and indirectly the stability of canal channels

through the potential for erosion or deposition at a site. In con-

sidering a site for development, geologic data are used to obtain

1. the potential water supply. The depth to the aquifer

and its potential rate of supply are of importance

in determining whether onsite water supply will be


3. surface water runoff patterns. Runoff is directed

by the topography of the site and the infiltration

rate is controlled by the type of ground cover at

a particular location, and the geologic formation

under the surficial deposits.

4. construction requirements. For construction it is

necessary to determine the characteristics of the

soil, such as its physical formation, granular con-

tent, weight-bearing capacity, and its thickness.

5. canal deposition or erosion rates. The erosion or

deposition of canal bank and bottom material is a

function of the characteristics of the material,

the geometry of the channel, and the water velocity. General Features

Alternating periods of high and low sea level created the landforms

of Florida. The coastline is characterized by geologic features which

are generally parallel to the coast, which implies that the sea has had

much to do with shaping this region [Puri and Vernon, 1964, p. 12]. In

fact, by thorium dating it has been determined that the main body of the

Florida peninsula was formed about 190,000 years ago [Veri, et al,

p. 18] when the peninsula was below sea level and layers of limestone

were being formed by the sea. "Today the sea level is rising again at a

rate of three inches per 100 years, and land building processes are

active along the shore and on the ocean floor" [Parker and Cooke,

1944, in Veri et al, 1975, p. 16].

The generalized landforms of Florida have been divided into the

Northern Highlands, Central Highlands, Coastal Lowlands, and the

Southern Zone or Distal Lowlands, as shown in Figure 2.10 [Puri and

Vernon, 1964, pp. 7-13]. The geologic structures and stratiography of

the state are highly variable from one region to another (for example,

see Figure 2.11) but for a general view of the primary peninsular

bedrock formations and the two principal aquifers, the Biscayne Aquifer

and the Floridan Aquifer, see Figure 2.12. As can be surmised from the

latter figure, each site will have a unique stratigraphy which will have

to be investigated for a particular development.

As far as water resources are concerned, limestone is the most

important geologic component of the state. There are 800 miles of

limestone extending from Key West to Tallahassee, in layers up to 12,000

ft thick above a granite base [Veri, et al, 1975, p. 18]. Limestone is

composed of calcium carbonate which, in Florida, is deposited in various

ways to produce different types such as oolitic limestone and marl.

Groundwater erodes these limestone deposits by dissolving the calcium,

the rate of erosion being on the order of one foot thickness each 800 to

1,000 years, a fairly rapid rate [Veri, et al, 1975, p. 19].

Five types of limestone are formed in Florida:

1. Oolitic limestone. This type is formed in shallow

mud seas by the precipitation of calcium carbonate

from the ocean water around a small nucleus, such as

a shell, and then cementing together of the small


2. Bryozoan limestone.

3. Coral Reef (Key Largo) limestone.

4. Coquina limestone.

5. Marl. This type is formed by excretion of calcium

carbonate by marine organisms in salt water. It is

a fine-textured, clay-like deposit that can become

hardened over a period of time and, because of a

lack of pore spaces, becomes relatively impervious

[Veri, et al, 1975, p. 18].

Surficial deposits in Florida consist of organic soils and a

variety of types of sand. Pamlico sand is usually highly permeable,

Talbot and Penholoway sands less permeable, and the organic soils and

marl are the least permeable of all. Pervious surfaces are, of course,

the best for aquifer recharge, while the impervious materials limit

percolation and result in higher runoff. Since organic soils absorb

large quantities of surface water until they become saturated, they gen-

erally contribute to runoff only during heavy rainstorms [Veri,

et al, p. 19].

Marl is relatively impervious and has poor aquifer potential.

Rainfall runs off marl to lower elevations, forming lakes in depres-

sions. The bearing capacity for building varies with thickness of the

layer, and there is some potential for shrinking or swelling.

Pamlico sands are highly permeable and are usually found in layers

from one to two feet thick. Their water-bearing capacity is low, and

they shift easily with the wind and erode easily by water when not

revegetated. The physical characteristics and aquifer potential of

other South Florida geological formations are summarized by Veri et al

[1975, pp. 20 and 24]. Bank and Bottom Materials

The magnitude of the bank and bottom roughness, and variations in

the roughness with location in the canal network, control in part the

dissipation of energy used to overcome friction. The effect of friction

on the flow may either be quantified from measured vertical velocity

profiles or predicted, for a proposed canal network, from estimates of

mean velocity, hydraulic radius, and tidal characteristics at the site.

The beds of the Floridian canals surveyed by the Hydraulic

Laboratory consisted either of silt or sand, except in the Florida Keys

where broken pieces of limestone deposited by the dredging process are

also found. The banks of natural channels have been observed to be made

of mostly sand or sandy soil. The stability of these beds and banks is

dependent upon the grain size distribution and velocities in the channel.

Beds and banks tend to adjust to the quantity of flow in the channel,

and the geometries of inlets and channels, i.e., the depths, side slopes,

and widths, must be designed for stability under the expected range of

flow in a given channel. In addition, the effect of boat traffic on the

stability of channel geometry must be considered during design.

Bed and bank samples were taken in the 57 Acres system and in

Frenchman's canal, located about two miles south of Jupiter inlet on the

Intracoastal Waterway (ICW). The samples were measured by sieve

analysis, and with a hydrometer when a significant portion of the sample

passed through the finest sieve available. For each of the samples the

grain size distribution was plotted and the value of d35%/ was selected

as the effective grain size, de, where the percentage is the percentage

of materials in the sample finer than the given grain-size.

Using the MIT soil descriptions, all bank samples were found to be

medium or fine sands, some of which were cemented by organic materials.

The bottom sample group consisted of both cohesive and noncohesive

samples. The six cohesive samples consisted of medium silts and coarse,

medium, and fine clays, while the noncohesive samples ranged from fine

to medium sands. The effective grain sizes on the banks ranged from

0.18 to 0.24 mm while the bottom sizes ranged from 0.11 to 0.30 mm

(sand) and from .00024 to .0075 mm (silt). There was no significant

difference between the samples from the two different locations.

2.5 Water Quality

The water quality in Florida's residential canals may be

characterized by a wide variety of constituents. The most significant,

from the viewpoint of the canal designer, is dissolved oxygen. The

State has established criteria for five classes of water, each of which

is defined in terms of measured dissolved oxygen (see Section

Dissolved oxygen could be simulated with the numerical model (CANNET3D)

developed for the canal design project by specifying local sources and

sinks and decay rates in the appropriate cells in the network.

2.5.1 Variability of Salinity, after Temperature, and DO

The literature on the environmental effects of canals and dredged

holes contains data on salinity, temperature, and dissolved oxygen which

are useful to the canal designer. Some of this literature was first

reviewed for a study of the environmental impact of borrow pits in

Maryland estuarine water (Polis, 1974]. lie summarized reports on work

in Texas, Florida, North Carolina, Maryland, Delaware, and New Jersey.

Later Bailey [1977] extended this literature survey to 1976, specifi-

cally for Floridian canals.

In order to quantify the variability of salinity, water

temperature, and dissolved oxygen in Florida's residential canals,

several studies with representative data have been chosen from each of

the principal coastal areas of the state. Included with these results

are published and previously unpublished data collected by the Hydraulic

Laboratory in support of this project. It is emphasized that these data

are only a sample and far from being a comprehensive selection.

Figure 2.13 shows the approximate locations of the sites at which

the compiled data used for the variability summary are located. Each

location is shown in detail in the reports referenced in Section 1.4 of

Morris, Walton, and Christensen [1978]. Studies made in the same

general area, but not in the same canal system, are designated by small

letters "a" and "b". It should be realized that canal systems of

varying size and age are located in many other coastal communities in

Florida besides those indicated in Figure 2.13.

The mean, minimum, and maximum values for each parameter, compiled

from a selected set of data, is herein cautiously presented as an

indication of the variability of that parameter in Florida. These

values have only limited usefulness and must not be taken as a valid

sample, but can be viewed as an indication of the extent of variation of

salinity, temperature, and dissolved oxygen in canals in various regions

of Florida. While the data are presented separately for the "wet"

season (June through September) and the "dry" season (October through

May) and for different geological areas, there are many potential dis-

crepancies in the composite data bases. Since five sets of investi-

gators were involved (with collaboration between Bailey and the

Hydraulic Laboratory, but essentially separate measurement efforts),

there were five different sets of instruments, five different sizes of

data bases, and several stages of transcription and analysis for each

data base with the involvement of at least five different analysts.

Most important of all, however, is the fact that the differences in

physical features of the canals, water circulation dynamics, and

variations in location and time within the canal system are totally

ignored in this collection. The mean, maximum, and minimum values of

the three variables are summarized in Table 2.2. The standard devia-

tions of these data are not available since the original data are not

all published.

The salinity varies, in the canals represented by this collection

of data, from a minimum of 5.3 ppt several miles up the Loxahatchee

River (Figure 3.14) to a maximum of 40 ppt in the Frenchman's canal

system (Figure 2.15). The former value results from a great deal of

mixing with river water. The latter, somewhat higher than the salinity

of ocean water, may be caused by high evaporation over a slow moving,

poorly mixed portion of the canal waters, or by leaching of minerals

from the walls or bottom of the canals. Other explanations are proposed

by Griffin [in Morris, et al, 1977b, Appendix A, pp. 7-10]. The high

values of salinity could also be attributed to measurement error. In

any case, as will be discussed in more detail later, the more

interesting consideration with regard to salinity is whether or not it

varies with depth in different locations in the canal system. Since

density is directly proportional to salinity, zones of different

salinity will, if not arranged in stable layers, induce density currents

which tend to stabilize the waterbody. Since density currents will

advect pollutants in the water, just as will any other currents, these

should be taken into consideration in a predictive model when signi-

ficant in the prototype. If a waterbody has no variations in density it

is said to be homogeneous or well mixed, a simplification frequently,

and sometimes unjustifiably, introduced in the development of numerical


Water temperature in the canals included in Table 2.2 varies between

21 and 370C. The winter or "dry" season temperature band lies completely

below the summer, or "wet" season band, as would be expected. As is the

case with salinity gradients, vertical gradients in temperature can also

induce density currents which must be included in a model if they are

found to be significant in the prototype. Due to the decrease in

density with increasing temperature (a rate of 34 x 10-5 ppt per IC at

30C), the water column tends toward stability when heated from above,

and toward instability when the surface cools suddenly.

Dissolved oxygen (DO) in the canals in Table 2.2 varies from 0 to

16.3 ppm. It is generally accepted that a minimum of 4 ppm (Section

17-3, Florida Administrative Code) or 5 ppm (in the opinion of some

biologists) is necessary to support fish and most other aquatic

creatures. It has frequently been observed in both wetland and upland

canals, that anaerobic (approaching zero ppm DO) conditions can develop,

particularly at the bottoms of deep canals or holes. These conditions

develop whenever the supply of oxygen from the surface of the water is

not sufficient to replenish that which is consumed in the water colunn,

either by the respiration of aquatic life or by decomposition of organic

materials. If sufficient oxygen is not provided at the bottom,

anaerobic decomposition of organic will occur accompanied by the

release of hydrogen sulfide gas. At night, oxygen in the water is

depleted by respiration, while during the day it is restored by

photosynthesis. Thus, the DO criteria set by the state are expressed

as not less than an average value of 5 ppm over a period of twenty-four


The saturation concentration of dissolved oxygen in water decreases

with increasing temperature and salinity from about 14.6 ppm in fresh-

water at 0C to about 6.1 ppm in 36 ppt seawater at 30C. The rate at

which oxygen is taken up by water at the surface, the reaeration rate,

is proportional to the difference between the saturation value of DO and

the actual value near the surface. The reaeration rate increases as the

turbulence of the water increases, due to entrainment. Sinks of DO

include respiration and, more importantly, the oxygen demand of benthic

materials. This will be on the order of 0.05 g-02/m2/day [Isaac (1965)

and Servizi, et al (1969), in Polis, 1974, p. 44] depending on the type

of material being oxidized, and increases with temperature. A transient

sink of considerably greater magnitude occurs upon a sudden resuspension

of bottom sediments, which can be caused by dredging or by a storm. It

is evident that anaerobic conditions occur naturally at some locations

in natural channels, but the state regulations for dissolved oxygen in

canal waters permit lower limits only if their prior existence can be


Low DO concentrations have been associated with fish kills in

Floridian canals. It is thought that fish kills caused by low DO can

result only when fish become trapped in a canal or cannot find their way

out of a confined area, such as in a dead-end canal, since it is known

that they will tend to abandon an area of deteriorating DO long before

lethal conditions prevail.

Bailey (1977] has attempted to find statistical relationships

between water quality parameters and the physical characteristics of the

forty-six canals included in his data set. For the parameters listed in

Table 2.3 these results may be summarized as follows:

1. Regression equations for average and minimum dis-
solved oxygen concentrations explained ninety-one
and eighty-eight percent, respectively, of the
observed variabilities
[Bailey, 1977, p. xiii).

2. A simple water quality index would not be adequate
to classify these canals, since the first principal
component explains just twenty-nine percent of the
total variability of these water quality parameters.
[Furthermore,] the first three components or factors
can account for [only] sixty-three percent of the
differences in water quality...
[Bailey, 1977, p. 107-110).

The results in the second statement above come from a principal

component analysis, a statistical technique that identifies the

parameters that vary the most throughout a data set and quantifies how

much of the variability in the data can be accounted for by successive

linear combinations of the variables.

Bailey also used a canonical (linear combinations) correlation

analysis, that indicates the amount of correlation or association

between a series of linear combinations of data from two data subsets.

Bailey's canonical analysis indicated a substantial association between

water quality parameters, and the physical characteristics. Specifically,

it was found that,

3. a. large [surface area] canal systems tend
to have higher average dissolved oxygen

b. increases in canal width increase average
oxygen levels; but [increases in] the
product of canal depth and cummulated
tidal amplitude tends to reduce the oxygen
[Bailey, 1977, P. 168].

Bailey's results are covered in some detail here because they appear to

be the most comprehensive statistical analysis of canal data yet

attempted, and because the analysis illustrates a very important concept.

The results show that, while interesting and plausible relationships

between variables and combinations of variables do exist in the data,

there is still missing an explanation of the fundamental physical proces-

ses and cause-and-effect relationships at work in even a simple, straight,

dead-end canal. Thus, when it becomes necessary to explain these results

on an objective basis, one can only resort to conjecture. The method

provides no guidance for canal design except an analysis procedure which

will permit the canal designer to predict the results of his design on a

statistical basis, under the assumption that the effects of environ-

mental variables that are omitted either from the designer's model or

from Bailey's model are the same, and that all variables are within the

ranges of data in Bailey's model.

2.5.2 Sources of Pollution in Canal Systems

In recent years the term "pollution" has often been used, and

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