ALTERNATE MATERIALS FOR THE NOURISHMENT OF
September 30, 2003
Bureau of Beaches and Wetland Resources
Department of Environmental Protection
Tallahassee, FL 32399
ALTERNATE MATERIALS FOR
THE NOURISHMENT OF FLORIDA'S SHORELINES
September 30, 2003
Bureau of Beaches and Wetland Resources
Department of Environmental Protection
Tallahassee, FL 32399
Robert G. Dean
Department of Civil and Coastal Engineering
University of Florida
Gainesville, Florida 32611
TABLE OF CONTENTS
LIST OF TABLES ........... ....... ............................ . ........... v
LIST OF FIGURES ................................... ................ vi
EXECUTIVE SUMMARY ................... ...... ......................... ES-1
1 INTRODUCTION ............................................. 1-1
2 ARAGONITE CHARACTERISTICS ................................2-1
2.1 General Characteristics ................ ...................... 2-1
3 WAVE BASIN EXPERIMENTS ...................................3-1
3.1 General ................. ................................. 3-1
3.2 Sediment Origin and Characteristics ............................. 3-1
3.3 Measurements ................ ............ ..... ........... 3-1
3.4 Beach Nourishment Experiments ..................... ..........3-3
3.4.1 Shoreline Evolution ............................. ........ 3-3
3.4.2 Volume Evolution .......................................3-3
3.4.3 Beach Profiles ............ .......................... 3-9
3.5 Transport Characteristics Based on Oblique Wave Approach
to Straight Beaches ..................... ... .................. 3-10
3.5.1 Sediment Characteristics ............................... 3-10
3.5.2 Initial Profile Distributions .............. ............... .3-10
3.5.3 Volumetric Evolution and Transport Rates ...................3-13
3.5.4 Discussion of Effects of Initial Beach Profiles ................ 3-13
4 WAVE TANK EXPERIMENTS .....................................4-1
4.1 General ................................................... .4-1
4.2 Wave Tank and Sediment Characteristics ........................ 4-1
4.3 Wave Characteristics Tested ................................4. -2
4.4 Results ................. ...................................4-2
4.4.1 Quartz Test 1 (First Quartz Test) .................. ............... 4-2
4.4.2 Test 2 (Second Quartz Test) .........................................4-3
4.4.3 Test 3 (Third and Final Quartz Test) ........................ .4-3
4.4.4 Test 4 (First Aragonite Test) ............................. 4-5
4.4.5 Test 5 (Second Aragonite Test) .......................... .4-5
4.4.6 Test 6 (Third and Final Aragonite Test) ..................... 4-5
4.5 Summary of Wave Tank Test Results ............................4-7
5 CEMENTATION TESTS ........................................ 5-1
6 ABRASION TESTS ............................................... 6-1
6.1 General .................................................. 6-1
6.2 Abrasion Apparatus ....................................... 6-2
6.3 Abrasion Test Methods and Results ............................. 6-3
6.4 Discussion of Laboratory Tests .............................. 6-4
6.5 Time Scale Relating Tumbler Results to Surf Zone Conditions ........ 6-8
6.5.1 Energy Dissipated on Sediments in Tumbler Experiments ....... .6-8
6.5.2 Energy Dissipated Within the Surf Zone ....................6-10
6.6 Summary and Conclusions From Abrasion Tests ...................6-11
7 ALTERNATE MEANS OF DELIVERING SEDIMENT
TO FLORIDA'S SHORELINES ..................................7-1
7.1 G general .... ........ ................... ............... 7-1
7.2 Sediment Delivery Through Barges or Ore Carriers ................. 7-1
7.3 Sediment Delivery Transiting Significant Wave Conditions ...........7-1
7.4 Delivery Costs by Pipeline Slurry From Interior Sources.............. 7-5
7.4.1 General ...................................... ........7-5
7.4.2 Scenarios Considered .......................... ......... 7-5
7.5 A Hybrid System "Mixing" Barging and Slurry Delivery .............7-8
8 MODERN DREDGE CAPABILITIES ..................... .........8-1
8.1 General ...................................... .............. 8-1
8.2 Pipeline Dredges ................. ......................... 8-1
8.3 Hopper Dredges ................... .......................... 8-2
8.4 Advances From the Dredging Industry .......... ...................8-3
9 SEA TURTLES AND OTHER POTENTIAL
BIOLOGICAL CONCERNS ............................................... 9-1
9.1 Sea Turtles .............................................. 9-1
9.1.1 Introduction .............. ..... .........................9-1
9.1.2 Experimental Design ............... .................... 9-2
9.1.3 Results .................... .................... ...... 9-2
18.104.22.168 Temperatures ........ ........... ............... 9-2
22.214.171.124 Gas Exchange ................................. 9-4
126.96.36.199 Hatching Success and Hatchling Mortality .............9-4
188.8.131.52 Hatchling Morphology .............................9-5
9.1.4 Overall Summary of the Fisher Key Monitoring
on the Effects of Aragonite on Sea Turtles ................... 9-5
9.2 Other Potential Biological Concerns ...... .......................9-6
10 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS ...........10-1
10.1 Summary and Conclusions .............. ....................... 10-1
10.2 Recommendations .... ...... .............................. 10-2
11 GENERAL REFERENCES ........................................11-1
APPENDIX A MECHANICS OF HYDRAULIC DREDGING AND
SLURRY TRANSPORT .................. ................ ... A-1
A.1 Introduction ............. ... ................................ A-i
A.2 Slurry Transport by Pipeline ................................... .A-1
A.2.1 Relationship Between Slurry Specific Gravity and
Volumetric Concentration of Solids ............................ A-1
A.2.2 Relationship Between Volume Concentration in
Pipeline and Volume in Place ............................... .A-2
A.2.3 Velocities Required for Non-Depositional Conditions .............. A-3
A.2.4 Allocation of Total Head Produced by the Dredge Pump(s) .......... A-4
A.2.5 Components of Energy Requiring Consideration in the Intake
and Discharge Lines ....................................... A-4
A.2.5.1 Increase in Energy Due to the Increasing Elevation
of the Solids ....................................... A-4
A.2.5.2 Velocity Head Required to Accelerate Slurry .............. A-5
A.2.5.3 Entrance Head Losses .............................. A-5
A.2.5.4 Friction Head Losses in Intake and Discharge Lines......... A-5
A.2.6 Suction Limitations in the Intake Line .......................... A-7
A.2.7 Ladder Pump .......................................... A-7
A.2.8 Booster Pumps ............................................ A-8
A.3 Energy Considerations ........................................... A-9
A.3.1 Total Horsepower Requirements ............................. A-9
A.3.2 Pump Characteristics and Efficiency ........................... A-10
A.3.3 Matching Pump Characteristics and Dredging Requirements ........ A-10
A.4 Practical Considerations: The Dredge Efficiency ...................... A- 1
A.5 Energy Requirements and Costs of Dredging ......................... A-11
A.6 Pipeline Life .................................................. A-12
A.7 Examples Illustrating Material Presented in This Appendix .............. A-12
A.7.1 Example 1. Dredge Production Limitations Imposed by Intake Line A-12
A.7.2 Example 2. Maximum Production for Each Dredging Depth ....... A-12
A.7.3 Example 3. Dredge Production vs. Pumping Distance ............. A-14
LIST OF TABLES
4.1 Wave and Sediment Characteristics in Wave Tank Tests ......................4-1
6.1 Characteristics of Sediment Samples Tested and Nomenclature ................6-3
6.2 Aragonite Component of Sample 1: Sample 1 is a Mixture
of Quartz and Aragonite .............................................. 6-5
6.3 Sample 2 Tests: Sample 2 Contained Only Aragonite ....................... 6-6
6.4 Aragonite Component of Sample 3: Sample 3 is a Mixture of
Quartz and Aragonite ............................................... 6-7
6.5 Sample 4 Tests: Sample 4 is Aragonite Only ............................ 6-8
7.1 Examples of Unit Costs for Barge Shipments of Coal on Rivers ................7-2
7.2 Ore Vessels Suitable for Transporting Sand Under Energetic Wave Conditions ... .7-2
7.3 Costs of Sediment Obtained From a Distant Source Including
Loading and Unloading ................................ .... ...........7-3
7.4 Characteristics of and Results From Slurry Pipeline Scenarios .................7-6
7.5 Values of Coefficients in Equation (1) .................................. 7-7
7.6 Example Costs for Pumping 2 Million Cubic Yards Annually
Over a 10 mile Distance ................................................7-8
8.1 World Ranking of Four U.S. Major Dredging Companies
and Numbers of Dredges ................... ........................... 8-1
9.1 Temperature Characteristics of Hatchery Nests and Control Areas ..............9-3
9.2 Hatching Success in the Two Sediment Hatcheries and Natural Nests ........... 9-4
LIST OF FIGURES
3.1 Wave Basin Layout For Nourishment Test Series ...........................3-2
3.2 Grain Size Distributions for Aragonite and Quartz, Nourishment Test Series ...... 3-2
3.3 Planform Evolution for Quartz Beach. Beach Nourishment Experiment ......... 3-4
3.4 Planform Evolution for Aragonite Beach. Beach Nourishment Experiment ....... 3-4
3.5 Comparison of Quartz and Aragonite Longshore Distributions of Shoreline
Changes After 60 Minutes of Testing. Beach Nourishment Experiment. ........ 3-5
3.6 Volumetric Density Changes for Quartz Beach. Beach Nourishment Experiment .3-6
3.7 Volumetric Density Changes for Aragonite Beach. Beach Nourishment
Experiment ....................................................... 3-6
3.8 Comparison of Quartz and Aragonite Longshore Distributions of Volume
Changes After 60 Minutes of Testing. Beach Nourishment Experiment ......... 3-7
3.9 Comparison of Percent Volume Remaining Within Placement Area for
Quartz and Aragonite Experiments. Beach Nourishment Experiment ............3-7
3.10 Best Fit Sediment Transport Coefficient (K) Value for Quartz Experiment.
Beach Nourishment Experiment ........................................3-8
3.11 Best Fit Sediment Transport Coefficient (K) Value for Aragonite Experiment.
Beach Nourishment Experiment .........................................3-8
3.12 Evolution of Average Beach Profiles. Quartz Experiment. Beach
Nourishment Experiment ..............................................3-9
3.13 Evolution of Average Beach Profiles for Aragonite Experiment. Beach
Nourishment Experiment ............................................. 3-9
3.14 Comparison of Quartz and Aragonite Average Profiles After 60 Minutes of
Testing. Beach Nourishment Experiment ................................3-10
3.15 Experimental Arrangement for Sediment Transport Experiment ............... 3-11
3.16 Grain Size Distributions for Quartz and Aragonite. Sediment
Transport Experiment ............................................. 3-11
3.17 Evolution of Average Quartz Profile. Note Profile Becomes Milder in Slope.
Sediment Transport Experiment ....................................... 3-12
3.18 Evolution of Average Aragonite Profiles. Note Profile Becomes Steeper.
Sediment Transport Experiment ........................................3-12
3.19 Longshore Distribution of Volume Density Evolution for Quartz Sediment.
Sediment Transport Experiment ......................... ............. 3-14
3.20 Longshore Distribution of Volume Density Evolution for Aragonite Sediment.
Sediment Transport Experiment .................... .... ................ 3-14
3.21 Longshore Distributions of Sediment Transport Rate Evolution for Quartz Sediment.
Sediment Transport Experiment ....................................... -15
3.22 Longshore Distributions of Sediment Transport Rate Evolution for Aragonite
Sediment. Sediment Transport Experiment ................................3-15
3.23 Comparison of Average Quartz and Aragonite Sediment Transport Rates
Over Period of Experiment. Sediment Transport Experiment ................. 3-16
4.1 Quartz and Aragonite Grain Size Distributions. Wave Tank Tests ..............4-2
4.2 Profile Evolution Along Center of Wave Tank. Quartz Sediments, Test I ....... .4-3
4.3 Profile Evolution Along Tank Centerline. Quartz Sediments, Test 2 ............4-4
4.4 Profile Evolution Along Tank Centerline. Quartz Sediments, Test 3 ............4-4
4.5 Profile Evolution Along Tank Centerline. Aragonite Sediments, Test 4 ..........4-5
4.6 Profile Evolution Along Tank Centerline. Aragonite Sediments, Test 5 ......... 4-6
4.7 Profile Evolution Along Tank Centerline. Aragonite Sediments, Test 6 ......... .4-6
5.1 Photograph of Drained and Undrained Aragonite Samples After
Seven Months Exposure to the Elements ................. ....................5-2
5.2 Photograph of Samples After Fifteen Months of Exposure .................... 5-2
5.3 Stockpile of Aragonite Stored Outside UF Coastal Laboratory
for More than a Year ............................................... .. 5-3
6.1 Tumblers Used in Abrasion Tests .............................. ....... 6-2
6.2 Percentage Change in Mean Diameter as a Function of Tumbling Time ......... .6-4
6.3 Definition Sketch of Element of Sediment in Tumbler ....................... 6-9
7.1 Comparisons of Shipping Costs for Grain and Ore by Panamax Vessels.
The Upper Curve Applies to Grain ......................................7-3
7.2 Comparison of Charter Rates for Various Ore Carriers ................... ... 7-4
8.1 Schematic of Cutterhead Pipeline Dredge .............................. .8-2
8.2 Schematic of a Hopper Dredge ....................................... 8-3
9.1 Photograph of Fisher Island Which Extends From Government
Cut Southerly to Norris Cut ........................................... 9-1
9.2 Layout of Fisher Key Showing the Seven Stabilization Structures ..............9-2
9.3 Incubation Times for the Two Sediment Types and Three Year
Monitoring Period ...................................................9-4
A.1 Relationship Between Slurry Concentration by Volume and
Slurry Specific Gravity for Normal Sands and Sea Water .................... A-2
A.2 Minimum Velocities for Non-deposition vs Slurry Concentration
and Sediment Size. Pipe Diameter of 20 inches ........................... A-3
A.3 Hazen-Williams Coefficient, C, vs Slurry Concentration and Sediment Size. Pipe
Diameter of 20 inches ............................................... A-6
A.4 Distance Between Pumping Stations vs Volume Concentration,
C, for Several Pipe Diameters .........................................A-8
A.5 Distance Between Pumping Stations vs Volume Concentration, Cv
for Several Sediment Sizes ...........................................A-9
A.6 Illustration of Pump and Dredge System Characteristics .................... A-10
A.7 Production Rate vs Dredging Depth, Various Intake Pipe Sizes,
Sediment Diameter = 0.5 mm, Volume Concentration, Cv = 0.2 .............. A-13
A.8 Production Rate vs Dredging Depth, Intake Pipe Size = 24 inches,
Sediment Diameter = 0.5 mm, Volumetric Concentration, Cv = 0.20
and Variable to Maximize Production .................................. A-13
A.9 Maximum Production Rate vs Maximum Pumping Distance for Two Sand Sizes
and Various Dredging Depths. Total Available Horsepower = 2400 .......... A-14
The availability of offshore sediments for beach nourishment is becoming limited in some
areas of Florida and this limitation will increase geographically with time. The purpose of this
report is to explore the feasability of using alternate sediments or sediments from non-
traditional sources for the nourishment of Florida's beaches. Specifically, the suitability of
Aragonite as a beach nourishment material and the transport of sediments from inland or
distant or deep water offshore sources are examined.
Laboratory tests have investigated and compared the following characteristics of Aragonite
relative to Quartz: (1) Beach profile shapes, and (2) Longshore sediment transport. The beach
profile tests established that Aragonite behaves quite similarly to Quartz in profile shape. Two
types of longshore sediment transport tests were conducted in a wave basin. The first
mimicked beach nourishment in which the transport was driven by planform protuberances in
the shoreline and showed that the two types of materials had similar transport characteristics.
The second set of tests were planned to evaluate transport characteristics with the waves
arriving at an angle to an initially straight beach. Inadvertently, the Aragonite profiles were
constructed at a slope considerably milder than the Quartz profiles. This resulted in greater
transport of the Quartz, and although the original objectives of these particular tests were not
realized, this finding of greater transport for steeper slopes is considered valuable to beach
Aragonite is considerably less resistant to wear than Quartz. Abrasion tests were conducted to
determine the capability of Aragonite to maintain its size characteristics when placed in an
energetic environment in the presence of Quartz particles. It was found that, over the
laboratory testing time (more than 450 hours), no reduction in Aragonite size was detectable.
An approximate conversion factor to allow interpretation of these laboratory testing times in
terms of Florida surf zone exposure was developed and resulted in an approximate surf zone
time of approximately 21 years.
Costs were evaluated of transporting sediment from interior sources by a combination of
pipeline and/or barge or from distant sources using an ore transport vessel. The ranges of
resulting costs are considered reasonable for beach nourishment.
Sea turtle and other monitoring data from the only sizable Aragonite beach nourishment
project in Florida were reviewed. With minor additional care, it is concluded that Aragonite
can be used for beach nourishment without adverse effects to the environment.
In summary, this study concludes that Aragonite is a suitable sediment for beach nourishment
and that sediment delivery from inland or, by ocean transport can be reasonably cost and
environmentally effective. Local cost components will vary from project to project.
ALTERNATE MATERIALS FOR
THE NOURISHMENT OF FLORIDA'S SHORELINES
This report presents a synthesis of the investigations conducted under the project "Alternate
Materials for the Nourishment of Florida's Shorelines". The overall objective of the project was
to investigate and report on the feasibility and costs of employing non-traditional sediment types
and sources for nourishment purposes. Traditionally, nourishment materials have originated from
locations offshore of the Florida shoreline in water depths ranging up to 60 feet. The presence of
reefs, primarily along Florida's lower east coast, limited traditional sediment sources and other
environmental concerns have caused interest in non-traditional sources, including inland sources,
Aragonite from the Carribean and elsewhere and sediments from deeper water than has been
This study included both laboratory investigations and an examination of information available
in the relevant literature. The laboratory studies included wave basin and wave tank studies of the
transport and profile characteristics of Aragonite in comparison with quartz sediment, tendency
for Aragonite to cement, and the durability of Aragonite. The literature studies have examined
published characteristics of Aragonite, the costs to access both Aragonite and other materials
from sources different than normally used and the potential environmental effects of using
Aragonite as a beach nourishment material.
A list of relevant publications is provided in the References section of this report.
2. ARAGONITE CHARACTERISTICS
2.1 General Characteristics
"Aragonite" sediments are nearly 100% Calcium Carbonate (CAC03) and are typically found in
marine areas with warm waters. Oolitic Aragonite, so-called because the sediment grains are
"egg shaped", is a particular form of Aragonite and is formed by precipitation of CAC03 out of
solution. Unlike most substances, CAC03 has the property that the solubility decreases with
increasing temperature. Thus, for example in the Bahamas, as the water temperature increases
due to solar radiation in shallow waters, CAC03 is precipitated, increasing the size of individual
particles. A cross-section through an oolitic particle reveals growth rings similar to tree rings.
Other types of Aragonite, obtained from the Caribbean, include broken coral and shells. Usually
an Aragonite sample will include oolitic and other forms of Aragonite.
Somewhat surprisingly, Aragonite is slightly more dense than quartz and the other more common
components of sediment found on Florida's beaches. The specific gravity of Aragonite ranges
from 2.75 to 2.88 compared to 2.65 for quartz. This characteristic alone is desirable for beach
nourishment since more dense sediments tend to be more stable. Similarly, as will be discussed
later, the "egg shape" characteristic results in a higher fall velocity which is also a desirable
beach nourishment material characteristic. However, in some climates, Aragonite tends to
cement forming "beach rock". This undesirable characteristic is due to the process of Aragonite
dissolving as a result of rainfall which is undersaturated with CAC03 and precipitating to cement
grains together during a period of evaporation which causes the water to become supersaturated
with CAC03 and then precipitate which cements adjacent particles. Also, Aragonite is not as
durable as quartz, with the hardness of Aragonite on the Moh scale being 3.5 to 4.0 as compared
to 7 for Quartz. These and other properties of Aragonite will be presented and discussed in
greater detail later in this report. The natural color of Aragonite is whiter than most natural
sediments on Florida's beaches.
3.0 WAVE BASIN EXPERIMENTS
Altman (2000) carried out his Master of Science thesis in conjunction with this project. Two
basin tests were conducted in the wave basin at the Coastal Engineering Laboratory of the
University of Florida. The basin was partitioned into two longshore segments such that tests of
Aragonite and Quartz could be carried out simultaneously with the same wave characteristics
affecting two halves of the basin. In general, the experiments were configured to induce sediment
transport and by monitoring the evolution of the sediment geometry under wave action, the
transport characteristics of the two sediments could be quantified and compared. Each of these
experiments is discussed in greater detail below.
The dimensions of the wave basin at the Coastal Engineering Laboratory of the University of
Florida are: length: 15.0 meters, width: 17.5 meters, depth: 26 cm. A wavemaker is located along
one end of the basin and consists of 88 individual paddles hinged at the bottom of the basin. Each
of the paddles can be adjusted to be slightly out of phase from its neighboring paddle and the
stroke (range of movement) of each paddle can be adjusted independently of the neighboring
paddle. The capability to adjust the phases of the paddles allows the wave direction to be
controlled. Periodic waves encompassing the range from approximately 1 second to 4 seconds
can be generated.
The characteristics selected for the basin experiments were: wave height: 3.4 cm, wave period:
1.1 seconds, and deep water wave direction: 150. Concrete block wave guides were used to
minimize diffraction at the ends of the wavemaker and to partition the basin. A Quartz beach was
placed in the segmented areas over which the nourishment projects were configured. Figure 3.1
shows the initial planform arrangement for the first test series.
3.2 Sediment Origin and Characteristics
The Aragonite sediment was obtained from Marcona Ocean Industries in Jacksonville, FL and
originated from Ocean Key in the Bahamas and the Quartz material was obtained from a quarry
located near Gainesville. Upon receipt, the Aragonite was coarser than the Quartz sediments and
through sieving and removing the larger size components of the Aragonite, the resulting grain
size characteristics of the Aragonite and Quartz were approximately the same as presented in
The wave characteristics and evolution of the placed sand were documented. The primary
purpose of the wave measurements was to ensure that the waves affecting the two partitioned
areas were the same. For this purpose, a mobile capacitance wave gage was used and could be
placed at any location in the basin. The strokes of the individual wave paddles were adjusted
SNAKE WAVE MAKER
- r\----- WAVE RAY
IsI \j WAVE RAY
LT'ORAL CELL LITTORAL CELL
Figure 3.1. Wave Basin Layout For Nourishment Test Series.
10------ --- --- I ------ 1
a a ., . I I IA go
S0 -. -o.. .T- .-- ..---. -- --
0 - - -a I I a- I- - ---- -
I0 I -I I I -I I - - I I I I I I I I I i- J
a I I I I I I a I I I I I I i
.. . --- .-- ... - .. ... . . ..... ...-... .. .. .-L
0 10 10- a 10 I I I
leI I I a Ie a I a Ia aa aa IIaI
Grain Size [mm]
Figure 3.2. Grain Size Distributions for Aragonite and Quartz,
Nourishment Test Series. I I I
a I I I a. I a a a I a a a a a a Il I
i a a I a a a a IIa
a l a I I I. I I I 1 aala i I l a I I
I i I II II I a lI la a I I I a
aI I I I I I IaI I I I I I Ii, I I I I al l
1.111. I a a o laa- a I I I Ill
a I' 11111 I 1111 Ill I a a I all
---t-~~t r~~------ -r--1--------)----------I-
I I I I aI I I
I I l a a al Ial a i-a II 11 1 1I I I I I ala
l l a II aIa I i a '1 I I" I I Ial
a a i I a"a1111 a I I I I l
--ra-v,----a?1aa---- -----CI-'1 C
a a .111 a 1"*a I -a a i a "
-.. . . .. a a. . ..
a a "a iI i a a a I a 1i" I II I I I la
-I a ItlI Il I I I I I I I III II
I I ll al l l I I I I I lI I I I I
l l Ia a I I a I I I I
I I I 1 I I I I a I I I l
I a i 1I I I I a a I I I a I
I I 1 .1 111 + I I I , I I 1 I I I +
I I I I I I I I I
Grain Size [mm]
Figure 3.2. Grain Size Distributions for Aragonite and Quartz,
Nourishment Test Series.
until the waves at a location just outside the area influenced by the placed sediment were
The evolution of the placed sediment was documented with a rotating laser and a graduated staff.
The rotating laser is mounted on a tripod, leveled and "paints" a sheet of red light at a uniform
elevation in the vicinity of the laser. The elevations at monitored locations were established by
simply placing the graduated staff at that location and reading the staff at the elevation of the
laser sheet. These elevations and their horizontal locations were read into a tape recorder and
later transferred to form a data base, a procedure which allowed one person to carry out the
3.4 Beach Nourishment Experiments
This experiment commenced with the Aragonite and Quartz sediments in the two halves of the
wave basin configured as trapezoidal beach nourishment projects as shown in Figure 3.1. These
projects were then subjected to the same waves simultaneously and measurements of the
evolving sediment geometry documented by surveying at the following times: 5 minutes, 9
minutes, 20 minutes, 40 minutes and 60 minutes.
3.4.1 Shoreline Evolution
The shoreline evolution of the Quartz and Aragonite nourishments are presented in Figures 3.3
and 3.4, respectively. A comparison of the longshore distribution of the changes in dry beach
widths for the two materials at the conclusion of testing (60 minutes) is presented in Figure 3.5.
It is seen that there are no substantial differences in the shoreline evolution confirming that the
two sediments performed equally in this beach nourishment test series.
3.4.2 Volume Evolution
The evolution of the volumetric density (volume per unit beach length) of the Quartz and
Aragonite nourishments are presented in Figures 3.6 and 3.7, respectively. A comparison of the
longshore distribution of the changes in volumetric density for the two materials at the
conclusion of testing (60 minutes) is presented in Figure 3.8. It is seen that, although there are
greater differences in the volume density changes than for the planform changes (Figure 3.5), the
differences appear as distributional rather than magnitude differences.
Figure 3.9 presents a comparison of the proportion of material placed remaining within the
placement area for the two sediments over the 60 minute testing duration. Consistent with
previous results, no major differences between the two sediments are evident.
A final volumetric analysis was conducted to provide an objective basis for comparing the
response of the two materials by determining the best-fit sediment transport coefficient, K, for
the two experiments using the numerical model DNRBS. These results are presented in Figures
3.10 and 3.11. As before, no major differences are evident.
L ?2 3 4 5
Figure 3.3. Planform Evolution for Quartz Beach.
Beach Nourishment Experiment.
1 2 .3 4 5 4 7
Longshore Distance, X[m
Figure 3.4. Planform Evolution for Aragonite Beach.
Beach Nourishment Experiment.
* 1 t1Or.*
I I -tb N
I I I - I nt-OhAf
---------- ------]- 40 MhtftI-~~ ---. Ialno
'p I- .~ I ,~~ l
I 4 i" It
-! ,., ~
.. .. .. ..
- ragoritr lajtmert
. I . Q rtzHua ml r
S' 5 as
Longshore Dstae Wthn the ,Project Area, Xm]
2-- -- -----. ;Pi-----.A.-.q; *-. -- ;- -
-s \ ... I
S3 35 4 4S S5
Longshore Distance Wthin the Poject Area, XIm]
Figure 3.5. Comparison of Quartz and Aragonite Longshore
Distributions of Shoreline Changes After 60 Minutes of Testing.
Beach Nourishment Experiment.
0.~2 . -2 .38
Alo rg Di state, Xfr
Figure 3.6 Volumetric Density Changes for Quartz Beach.
Beach Nourishment Experiment.
-- - -- ,- - - |-
0 1 2 3 .4 6 7
Alngshore Distance, X[mj
oa o "---L -- -I---) .--i o o i---~ i~---
Figure 3.7. Volume Density Changes for Aragonite Beach.
Beach Nourishment Experiment.
-------------------------- ---- --
C Z -- ...... .. -- ...-...-.-- ...-.---.- -.- ............ ...- .... .--
..... ----- ------ ---------.-* ---- --
....... ,.... ... .
Time in Minutes
Figure 3.9. Comparison of QuaPercent Volume Remainite Long Withinore
DistribuPlacement Area for Quartz Chane Aragonite Experiments.
Testing. Beach Nourishment Experiment.
04 ------ - - "- -. - - --- - -----
. .-.-.-. .... .... .. .. .. ........ .. .. ............ .. ......
ao--.--...-~~, -. - ... .- -- - - -- - - -
nims in Mirutes
Figure 3.9. Comparison of Percent Volume Remaining Within
Placement Area for Quartz and Aragonite Experiments.
Beach Nourishment Experiment.
-- ----- --. --- -- - --- ...... 4 .......-'-------------- ---- -
.M D - - - - - - A : - - - - - - - - - - -
- - - - --- - --- - -
40 - - - - - - - - - -- - - -
iI I-- - 1 - - - - - - - -
Beach Nourishment Experiment.
S' d-X- HM-nd Qute Pln VSM
----- --------- -------- --
S-------- -------,------------------- .-
I I I I
--. K= 1.47
70-------- . ^ ---------------- ..... --------------------
S-----....-.-- ......... ...--.... ................... .. ......
4 I o o
10--------- -.. ... .
I I I II
40 -- - - - -- 8
0I ........ ......... J.... .------- --- - ---- ---- --... ... -----..
a0 10 20 o O
Tima in Mirntes
Figure 3.10. Best Fit Sediment Transport Coefficient (K) Value for
Quartz Experiment. Beach Nourishment Experiment.
: : M-ew M &MMauPlngaPmV
so ---....- .... ---- ......---- ...---....--.... ......... -------
\ K K=1.20
0.......I.... .... -..... .......... ....................... ....
2D 40-----.-.-----------.- -.-.---. ---------------- .---------------
10.......... .......... ---- ------- --.-. --------.----------------
me In Mites
"rirm In Mnute
II0 '- '
"' '' l .a. .. .. .. a' .. . l. . . l. . . I' . .
3.4.3 Beach Profiles
Considerable care was taken to ensure that the initial beach profiles for the adjacent beach
nourishment projects were the same. The beach profiles were monitored and the average beach
profile evolutions for the Quartz and Aragonite are shown in Figures 3.12 and 3.13, respectively.
Figure 3.14 superposes the two profiles at the conclusion of the 60 minute testing period.
.. i "-M .-...... .. --
-4- --.-------;- -----. .. I. ... .. .I u- -
Experiment. Beach Nourishment Experiment.
12 ------------------- -- -- --- ---.--- --- ---
ie ............. ...... ...... ..... ...... -........... ......*-.o
--- 4-- - .............. ..-..... ....
I-- --- --- i -----
M I m r .2 is Ia M I =a d i
w. : u :.. ,- ;:: .. I
C ss&-Shore Ehstance, Y c1n]
Figure 3.12 Evolution of Average Beach Profiles. Quartz
Aragonite Experiment. Beach Nourishment Experiment.
S -Pa NMNmi,-rt ,
. .. -' -- ... . . ... . .. . . .. . . -, . . ..- -. . .
.... -..- ------
a).- -.-- .-- -T-- -- --- .-. .-.- --- -- .------ --- -
-2 ..... .. .......... ........ --------
SO .1W 1W 200 3M 350 4W 4W
W., usseb DEtewanoe% Ycm
Figure 3.13. Evolution of Average Beach Profiles for
Aragonite Experiment. Beach Nourishment Experiment.
S-r Angonne Press
4Figure 3.1. .. Compare. .s .. of Quar. -t .and Ar e PAverage
Pro Wates er Line utes of Testg.
I3.5 Transport Characteristics Based on Oblique Wave Approach to Straight Beaches
As described earlier, this second experiment was conducted with two straight beaches in the
partitioned basin with oblique waves as presented in Figure 3.15. The transport was calculated
alignment parallel to the incoming waves.
. . .. ... . ..
...... r ..... .. ... ......... ............. ... .. .. ......
. . I -- I
ra ----------- 4 -1-----4----i----i-------- -i......-
1. IS. W 4W 4W 5O
Cr1 Sediment Characteristics
AFigure 3.14. Comparison of Quathe grain size distributions for thez and Aragonite and Quartz sediments used in this
experiment are presented in Figure 3.16. Experiment.
3.5.2 Initial Profile Distributions n Oblique Wave Approach to Straight Beaches
Anintentionally) for, this experiment I t was found tat te init two straight beaes in te
partitioned basin with oblique waves as presented in Figures 3.17 and 3.18 for the transport was calculated Aragonite
basprofile becamon the hanges in ovwhereas the Quartz profile becamthe milderach as in slope. The average hing itial
Aragonite profile to the 4 cm depth is 1:12.5 whereas the corresponding slope for the Quartz
3.5.1 Sediment Characteristics II I
Aprofil is 1 a fto of 5grain sze dstriti ons for th Aronite ato in itial proiles at su dierent
3.5.2slopes was unintended and had a significant effect on the transport rates.
and evolving profiles are presented in Figures 3.17 and 3.18 for the Quartz and Aragonite
profiles, respectively. It is seen that over the six hour testing period, the average Aragonite
profile became steeper whereas the Quartz profile became milder in slope. The average initial
profile is 1:5, a factor of 2.5 greater. The construction of the two initial profiles at such different
slopes was unintended and had a significan--- t .effect on the transport rates.
slopes was unintended and had a significant effect on the transport rates.
SNAKE WAVE MAKER
-i v -- --... .... --
\* WAVE RAY
\ WAVE GUIDE
I WAVE GUIDE-
a Quartz Sand. Aragonite Sard
LITTORAL CELL LITORAL CELL
Figure 3.15. Experimental Arrangement for Sediment Transport Experiment.
10o 10 1o0
Grain Size [mn]
Figure 3.16. Grain Size Distributions for Quartz and Aragonite.
Sediment Transport Experiment.
Im I I P I '&.. i i l l
I I a I I \ I i I I a a
a m a Aigg m ) a alma, Sg -a a
I I i i o I i i e i t *
.. . ...*T111.. -- -.. - T ......... .. . . -
i I I'\ I ( i
S. .t.it. as a i 1. I I Il m L
1 1 a I I I a I a a a a ,
I 11 I I I I I I I I I I 9 l 1 0 1 t I I
S I I I i I I a I 1 a
...... ........t. .. .... .....a*.a.............----..--... a.a..
i I a a a m, ,, a 5 a a a im aI a I -s I Is
I I I I i I I I I I I I I
a I I Ia ImII I a a I
*...... -... t ..... .... .- -.. ,I I I------- --0- -- s I l a..-
5 a I am im l I a a sg ae I I a a a a aa
Ia a a i i i i a i a I
aI I I I I I Ia I I I
S a a a a a I I I a a a
S I I I i * 1
a a a a a a aaat a a ama, a a1 a I a111
Ia a a m a ,,I I I I I mIa, a a a a I
a a I a al a a a I I I Ia I t- I
S I a I I I -I
a a a a a a a I i a a I a IaIa
I I a I I I I I I
a I a aml a a a a Ia m a a a a m gas
a i a a lm I a a 1 1 1 1
------I-1--r~ T~---1-- r 9---I------------------ ------r-,rr.
a a 5 i as s l i a I m-aaa a a a a 55
a a ml11 sas i a akiC as 1a 5 as a am
a *s11 a aP l~) is as 5 5 a 1,.. a aa
'I ,*- a, h a I a alas
-,kM Sa unM -o 0 min
------r--------r-I------------ IA----- 0 '
S; ms. m O es
Af e L r o U' -m s 120 4D
S. Wate.ine -e 1n-2nuee
S-- --r --- T-im 1le 80nlute
------ - -. -. .---.. -m-s24 -
..... ..... ..... .... ... ....
- 2D*3 --- ------. ---* ----..* .. -* -L. .---- .. --- .. ^ I-- -
S -- --------
1 I I I I m
1 ...... ..... ... ---. -------------- -- m rinut
0 so 10 ISO 2M 25 3M 35 4w 4W
Cross Shre Dstane, Ycm]
Figure 3.1. Evolution of Average Profile te ole
n -| n a 3 e 12
.," u :1.e= | 0 minutes
WOW .14 I .
---------------- ------------- ---- ----- ----- ------ -- -
Figure 3.18. Evolution of Average Aragonite Profiles. Note Profile
:- - - --- -
3.5.3 Volumetric Evolution and Transport Rates
The volumetric density evolutions for the Quartz and Aragonite beaches are presented in Figures
3.19 and 3.20, respectively. The transport rates for the Aragonite and Quartz beaches were
calculated from the information in Figures 3.19 and 3.20 and the continuity equation and are
presented in Figures 3.21 and 3.22, respectively. Finally, the average transport rates over the
period of the experiment are shown in Figure 3.22.
3.5.4 Discussion of Effects of Initial Beach Profiles
As noted, the construction of the two initial beach profiles at such different slopes was
unintended. Because the beach nourishment basin study had established that, with the same
initial beach profiles, the transport rates were approximately the same, the only conclusion that
can be drawn here is that the milder initial slopes of the Aragonite were responsible for the
markedly lower transport rates compared to those for the Quartz sediments. Thus, this
experiment was serendipitous in the sense that while the cause of the transport difference was not
the goal of the experiment, the results found were more significant that those of the original
This finding that the sediment transport rates are higher on steeper beaches than on beaches of
milder slopes is consistent with our knowledge of the physical principles governing sand
transport in rivers and has considerable significance to profile construction in beach nourishment
projects and in the interpretation of the evolution of such projects. In particular, beach
nourishment profiles are almost always constructed with slopes steeper that equilibrium. The
higher sediment transport rates associated with these steeper slopes will result in a more rapid
project evolution during the equilibration period of the profiles. Our studies have shown that the
planform equilibration times associated with beach nourishment projects is on the order of 3
years. Although the overall magnitude of this effect warrants further investigation, it provides
support for constructing the profiles with milder slopes. An additional contribution of this
finding is in the interpretation of some erosional hot spots. That is, if a segment of a nourishment
project is constructed at a steeper slope than the adjacent segments, it is expected that the
transport rates would be greater along the steeper portions of the project resulting in nonuniform
rates of volume change and hence, one or more erosional hot spots. The profile data associated
with the mid-island erosional hot spot on Captiva Island appears to be consistent with this cause.
04 ----- -- r ------ 11--------- -- ----------- ----~ `--- ... ......
0 1 2 3 4 7
Alongshore Distance, X[m]
Figure 3.19. Longshore Distribution of Volume Density Evolution
for Quartz Sediment. Sediment Transport Experiment.
0 1 l 2 3 4
O ------ ----- -------I -I
8 ,-.-;; ---------;-----------
04 --------~-- -- --- ,~-~--------- -----~--------- ~ ------- - - - - -
I. 1 2 3 4" 5 "a : "
Alongshore Distance, X[nq
Figure 3.20. Longshore Distribution of Volume Density Evolution
for Aragonite Sediment. Sediment Transport Experiment.
1 : 2 .3 ...-4
Alongshore Distance, X[m]
6 7 8
Figure 3.21. Longshore Distributions of Sediment Transport Rate
Evolution for Quartz Sediment. Sediment Transport Experiment.
1 --- 1n-- I I I I I I I
--- t a n
8~~~~ ~ -, -~aaf -- ---------- -- -- -- -- -- -- -- -- --- -- ---
15 It I I I*
S-------------- ----------- ----------"- -- - -
S ....... - ..-- .. -. --- .-------. .- ---- ------- -- -
i i' i I I I I I
I I i I I II
2e . . . .'. . .'. ..""" . . + .
\~ \ \ !
3 4 5
Alongshore Distance, X[m]
6 7 a
Figure 3.22. Longshore Distributions of Sediment Transport Rate
Evolution for Aragonite Sediment. Sediment Transport Experiment.
-w0n*l % I
.- t1m l ... .
--- - - t
2 $-- l - -.-,I. -- ,
1 I I
Time in Minutes
Figure 3.23. Comparison of Average Quartz and Aragonite Sediment Transport Rates
Over Period of Experiment. Sediment Transport Experiment.
4.0 WAVE TANK EXPERIMENTS
Although the wave basin experiments examined the beach profiles associated with Quartz and
Aragonite sediments, additional larger scale wave tank tests were conducted to compare the
associated profile characteristics.
4.2 Wave Tank and Sediment Characteristics
The wave tank in which these tests were conducted is approximately 15.5 m long, 60 cm wide
and 90 cm deep. The waves are generated by a periodic piston type wavemaker with a maximum
stroke of 20 cm and a minimum period of 1.4 seconds. For a particular wavemaker stroke, the
wave height generated increases with decreasing wave period. For purposes here, the wave
period was maintained at its minimum and the wave height was varied by adjusting the stroke to
obtain the desired wave height. The water depth was maintained at 35.4 cm. Table 4.1 presents
the wave and sediment characteristics associated with these experiments.
The relatively large quantities of sediment required for these experiments precluded obtaining
Quartz and Aragonite sediments with closely matching grain size characteristics. The median
diameter of the quartz sediments was 0.23 mm and that for the Aragonite sediments was 0.30
mm. The grain size distributions are compared in Figure 4.1
Wave and Sediment Characteristics in Wave Tank Tests
Test Wave Water Wave Initial H/wf T Sand Type and Median Size
Period Depth Height, H* Slope (mm)
(sec) (cm) (cm)
1 1.4 35.4 4.2 1:15 0.92 Quartz: 0.23
2 1.4 35.4 10.0 1:15 2.20 Quartz: 0.23
3 1.4 35.4 15.0 1:15 3.33 Quartz: 0.23
4 1.4 35.4 7.0 1:15 0.90 Aragonite: 0.30
5 1.4 35.4 10.0 1:15 1.29 Aragonite: 0.30
6 1.4 35.4 15.0 1:15 1.94 Aragonite: 0.30
*In horizontal section of tank
10-2 10' 10 101
Falling Speed (cm/s)
Figure 4.1. Quartz and Aragonite Grain Size Distributions.
Wave Tank Tests.
4.3 Wave Characteristics Tested
Three experiments were conducted for each sediment. As shown in Table 4.1, these tests
encompassed the range of dimensionless fall velocity parameter, H/wf T from 0.92 to 3.2 in
which H is the wave height, w1 is the sediment fall velocity and T is the wave period. The fall
velocity parameter has been shown to distinguish between profile types usually referred to as
"summer" and "winter" with a characteristic of the summer profile that it is nearly monotonic
and a characteristic of the winter profile is the presence of a noticeable bar.
The profile evolution was documented by profiling along three lines: the tank centerline and 20
cm on either side of the centerline.
The results of the wave tank studies are presented and discussed below.
4.4.1 Quartz Test 1 (First Quartz Test)
The results for the central profile for Test 1 are presented in Figure 4.2. The value of the fall
velocity parameter for this case is H/w/ T = 0.92 which is below the value required for the
generation of a bar. It is seen that, as expected, a bar is not present in this profile. Rather the
sediment transport was onshore resulting in the development of a berm.
--- t=22.2 min
-30 --- t=140.7 min
-*-- t=240.2 min
Figure 4.2. Profile Evolution Along Center of Wave Tank.
Quartz Sediments, Test 1.
4.4.2 Test 2 (Second Quartz Test)
The results for the central profile for Test 2 are presented in Figure 4.3. The value of the fall
velocity parameter for this case is H/wf T = 2.20 which is near the intermediate case for bar
formation. Examining Figure 4,3, it is seen that a small bar has formed. For this case, sediment
has been transported both landward and seaward resulting in both a berm and sediment
transported offshore to form the bar.
4.4.3 Test 3 (Third and Final Quartz Test)
The results for the central profile for Test 3 are presented in Figure 4.4. The value of the fall
velocity parameter for this case is H/wf T = 3.30 a value for which a bar is expected.
Examining Figure 4.4, it is seen that a substantial bar and a small berm have formed. For this
case, sediment has been transported both landward and seaward resulting in both a berm and
sediment transported offshore to form the bar; however, most of the sediment transport has been
100 200 300 400 500 600 700
Figure 4.3. Profile Evolution Along Tank Centerline.
Quartz Sediments, Test 2
Figure 4.4. Profile Evolution Along Tank Centerline.
Quartz Sediments, Test 3.
4.4.4 Test 4 (First Aragonite Test)
The results for the central profile for Test 4 are presented in Figure 4.5. The value of the fall
velocity parameter for this case is H/wf T = 0.90 a value for which bar formation is not
expected. Examining Figure 4.5, it is seen that substantial onshore sediment transport has
occurred resulting in construction of a berm and a minimal bar, ie the profile is essentially
monotonic. Comparison of the results of this test with those for the counterpart for the Quartz
tests as shown in Figure 4.2 establishes that although the profiles are not identical, they are quite
10 T-1.4 s
-10 __ STILL WATER LEVEL,___ 9
---. t=22.2 min
-30 -.-.- t=140.7 min
t- t188.9 min
-- t=240.2 min
0 100 200 300 400 500 600 700 800
Figure 4.5. Profile evolution Along Tank Centerline.
Aragonite Sediments, Test 4.
4.4.5 Test 5 (Second Aragonite Test)
The results for the central profile for Test 5 are presented in Figure 4.6. The value of the fall
velocity parameter for this case is H/wf T = 1.29 a value which is near the limit for bar
formation. Examining Figure 4.6, it is seen that both a berm and bar have been constructed.
Comparison of the results of this test with those in Figures 4.2 and 4.3, the values of
H/wf T which bound the value of 1.29 for this test, it is seen that the profiles in Test 5 are
intermediate to the two Quartz tests.
4.4.6 Test 6 (Third and Final Aragonite Test)
The results for the central profile for Test 6 are presented in Figure 4.7. The value of the fall
velocity parameter for this case is H/wf T = 1.94 a value for which bar formation is expected.
Examining Figure 4.7, it is seen that the dominant sediment transport has been directed seaward.
100 200 300 400 500 600 700
Figure 4.6. Profile Evolution Along Tank Centerline.
Aragonite Sediments, Test 5.
--- t=22.2 min
-30 --- t=140.7 min
-- t=240.2 min
-40 I I S i
0 100 200 300 400 500 600 700 800
Figure 4.7. Profile Evolution Along Tank Centerline.
Aragonite Sediments, Test 6.
--- t=22.2 min
-- t=140.7 min
- t=188.9 min
--- t=240.2 min
Comparison of the results of this test with those for the Quartz test with the closest value of
H/wf T as shown in Figure 4.3 suggests that even the smaller value of H/wf T associated
with the Aragonite tests compared with that for the Quartz test, the Aragonite profiles are more
barred than would be expected based only on the fall velocity parameter.
4.5 Summary of Wave Tank Test Results
Although comparison of the profile results from Tests 2 and 6 are somewhat unexpected in the
sense that the profiles from Test 6 are more barred in character than those from Test 2 even
though the H/wf T value for Test 6 is less than that for Test 2, overall the results are supportive
of the generally similar profile characteristics for Aragonite and Quartz based on the fall velocity
The profile results established in this report are consistent with those of Monroe (1969) who
compared laboratory beach profiles formed of Quartz and Aragonite with approximately the same
sediment size and when acted upon by the same waves. Monroe found that the profiles in the two
sediments were quite similar.
5.0 CEMENTATION TESTS
Tests to evaluate the tendency for Aragonite to cement were conducted. Aragonite was subjected
to the outdoor elements and was observed for tendencies to cement. These small scale tests of
cementation were based on outdoor "pan" tests in which both pans contained Aragonite and one
pan was drained and one was undrained, allowing rain water to pond. The purpose of these small
scale tests was to determine whether, under the conditions tested, Aragonite would tend to form
"beach rock" as occurs in some semi-arid climates. Beach rock is the result of rain dissolving the
calcium carbonate and then during the evaporative phase of this solution, the calcium carbonate
precipitates as a cement to bond the adjacent particles together. Dissolution would tend to occur
as a result of the more acidic rain water rather that immersion in salt water and thus the
previously described pan tests to determine cementation will also serve as tests of potential
dissolution. Figure 5.1 presents photographs of the pans in which drained and undrained
Aragonite sediments had been exposed for approximately seven months (since March 2002).
After this period of exposure, neither of the pans indicated any properties of significant
cementation. In the "drained" pan, there was a very slight crust in the surface, but this was so
weak that it was difficult to detect. Figure 5.2 presents photographs of the drained and undrained
tests after fifteen months of exposure. The properties of the sediments in the two pans was
approximately the same as after seven months of exposure. That is, the drained sample was
characterized by a very weak surface crust, but the strength of this crust was such that it would
not interfere with normal beach activities, including turtle nesting.
In addition to the pan tests described above, an experiment of opportunity was available. The
Aragonite that was used for the wave tank tests (Chapter 4 of this report) was removed from the
tank and placed outdoors adjacent to the University of Florida Coastal Engineering Laboratory.
The exact date at which this placement outdoors is not known; however, the material was located
outdoors for more than a year. Figure 5.3 presents a photograph of this Aragonite. There is
absolutely no surface cementation of this sediment although the outer two to three inches of this
sediment is more consolidated than the sediments inside this layer. This consolidation is rather
weak. It is envisioned that this stockpile of Aragonite will remain in its present position for the
foreseeable future and its tendency to cement will be evaluated periodically on an informal basis.
Figure 5.1. Photograph of Drained and Undrained Aragonite Samples
After Seven Months Exposure to the Elements.
Figure 5.2. Photograph of Samples After Fifteen Months of Exposure
Figure 5.3. Stockpile of Aragonite Stored Outside UF Coastal Laboratory
for More Than a Year.
6.0 ABRASION TESTS
The purpose of the abrasion tests was to determine, through laboratory experiments, the
qualitative degree to which Aragonite can withstand the physical interaction when interacting
with sediments which may include native Florida Quartz. Additionally, a method is presented to
interpret the laboratory testing time in terms of exposure time within the surf zone. As noted
previously, the hardness of Aragonite on the Moh Scale is 3.5 to 4 as compared to a Moh value
of 7 for Quartz.. The Moh scale is a measure of the resistance of a mineral to being scratched by
another mineral and was established by the German mineralogist Friedrich Moh in 1822. Moh
selected 10 minerals and established their relative capability to scratch one another and assigned
a number ranging from 1 to 10 based on his tests. A diamond has the greatest resistance to being
scratched and was assigned a Moh value of 10. Talc was the most easily scratched and was
assigned the lowest Moh value of 1. However, the Moh scale is only relative and is not linear, ie
a mineral with a Moh scale of, say 8 is not necessarily twice as resistant to scratching as a
mineral with a Moh scale of 4.
A sediment being scratched by another sediment removes mass (or volume) from the sediment
being scratched and is thus a form of abrasion or wear. It is noted that other hardness scales
exist, including the Brinell and Vickers scale; however, these scales are more a measure of the
relative abilities of materials to indent one another due to a prescribed contact force. Based on the
processes to which Aragonite grains would be subjected in an active surf zone, it appears that the
Moh hardness scale is more relevant than either of the other two scales.
Of course, a substantial portion of the native sediments on Florida beaches are formed of calcium
carbonate in the form of shell and coral fragments, etc. Inspection of these fragments, which are
usually larger than most quartz fragments may show considerable signs of wear. However, there
is no basis to determine the length of time that a particular shell fragment, for example, has been
exposed to the abrasive surf zone elements. An additional factor in discussing wear is that larger
particles are more subject to wear than are smaller particles.
If a nourishment sediment decreases in size through abrasion, it will perform less effectively in
maintaining a beach since smaller sediments form a milder slope and are transported in the
alongshore direction more rapidly. Thus, it is relevant to determine the relative wear properties
of: (1) Aragonite when interacting with the harder Quartz, and (2) Aragonite when interacting
only with Aragonite. However, the wear experienced by a sediment particle in a laboratory
environment can only be extrapolated to a surf zone environment in an approximate manner
since there is no established and verified basis for stating that ifX percent wear occurred under Y
hours of laboratory testing, the same wear would occur in Z years under field conditions. Thus,
the results presented here should be considered as a step toward improved understanding of the
wear properties of Aragonite that can only be established fully through large scale beach
nourishment projects in a variety of wave energy settings.
6.2 Abrasion Apparatus
The abrasion tests were conducted in "tumblers" developed for polishing rocks. A photograph of
the two tumblers used in these abrasion tests is presented in Figure 6.1. The tumbler consists of a
sealed container into which the sample is placed with water and the container is rotated slowly,
thereby subjecting the sample sediments to physical contact as they are alternatively raised in the
tumbler and then fall under the action of gravity causing interaction with the various sediment
components within the sample. When these devices are employed for polishing rocks, an
abrasion agent (usually different sizes of Carborundum) is added to expedite the abrasion
process. The initial phase of this process is conducted with a coarse abrasion agent and is
followed by successively finer abrasion agents with the final agent being very fine to result in a
polishing effect. As will be apparent, in the present sets of "paired" tests, a mixture of Aragonite
and Quartz is placed in one of the pair of tumblers and only Aragonite is placed in the other
tumbler of the pair. Additionally, replicate tests were conducted such that one set of samples
(Aragonite/Quartz and Aragonite) were tested as a pair and a second set (Aragonite/Quartz and
Aragonite) comprised a second pair.
Figure 6.1. Tumblers Used in Abrasion Tests.
6.3 Abrasion Test Methods and Results
The application here employed two tumblers into which sediment samples of known size
distributions were placed. As noted, one of the tumblers also included Quartz sediment as an
abrasion agent. The rationale of tumbling Aragonite with and without Quartz is that for large
nourishment projects, less interaction of the placed Aragonite with Quartz will occur. The
tumblers in which the tests were conducted were Model 45C Lortone tumblers and were of the
size to accommodate up to 4 pounds of sediment. The dimensions of these tumblers are:
Diameter = 5.5 inches and depth = 3.5 inches.
The abrasion experiments consisted of tumbling sediment/water mixtures for various times
followed by grain size analyses to quantify any reduction in grain size. Salt was added to the
water in the tumblers to achieve an ocean salinity, ie approximately 35 parts per thousand by
weight. The sediment placed in each tumbler comprised approximately one-fourth of the tumbler
volume and the water approximately one-fourth of the total volume such that the sediment water
mixture occupied approximately one-half of the tumbler volume.
To standardize terminology, sediment samples are numbered as indicated in Table 6.1. Samples
S1 and S3 are mixtures of Aragonite and Quartz with S3 planned as a replicate test of S1. The
sediments in samples S2 and S4 are Aragonite only with tests on S4 designed as a test replicate
of S2. The experiments consisted of: (1) Sieving the samples to obtain a size distribution, (2)
Tumbling the sample sediment/water mixture for a particular length of time, and (3) Drying and
sieving the sample to determine its grain size distribution to establish any change in sediment
size. For the mixtures of Aragonite and Quartz, the size distributions of the two components were
determined before mixing the sediments, followed by the procedure described above. After each
sieving, it was assumed that the Quartz grains did not abrade and thus that the Quartz grain sizes
were the same in each sieve size fraction. For each size fraction, this allowed subtraction of the
original Quartz weight from the total in that size fraction and the remaining weight of the
Aragonite in each size fraction to be deduced. Although the grain size distributions were
determined in this process and these results will be presented here, the analysis results will be
focused primarily on changes in the mean diameter.
Characteristics of Sediment Samples Tested and Nomenclature
Sample Pair Characteristics
S1 1 A Mixture of of Quartz (405.3 gms) and Aragonite (313.4 gms)
S2 Aragonite Only (500.4 gms)
S3 2 A Mixture of of Quartz (255.5 gms) and Aragonite (252.9 gms)
S4 Aragonite Only (500.7 gms)
The results of the tests for the four samples are presented in Tables 6.2, 6.3, 6.4, and 6.5 for
Samples S1, S2, S3 and S4, respectively. Each of these tables presents the sieve numbers used in
the tests, the effective size of the sediment for each sieve employed in calculating the average
sediment size, the weight of sediment remaining on each sieve, the total weight of the Aragonite
component of the sample as determined in each test and the mean grain size at the conclusion of
that particular test. For the final tests on Samples S3 and S4, the sieving was conducted twice on
each sample and the results are reported in Tables 6.4 and 6.5 as Hours 464 (1) and 464 (2). It is
seen that the sieving is reasonable reproducible. Figure 6.2 presents a plot of the percentage
change in mean sediment diameter for the various samples as a function of cumulative testing
6.4 Discussion of Laboratory Tests
Referring to the change in mean grain sizes at various testing times in Tables 6.2, 6.3, 6.4 and 6.5
and Figure 6.2, it is clear that during the total durations of the tests, 226 hours for Samples S1
and S2 and 464 hours for Samples S3 and S4, abrasion has not been detectable. In general, the
samples showed some increase in mean grain size. This is interpreted as due to a minor amount
of cementation that occurred during the drying of the samples. If this is the case, there is no
reason that after the first drying, the size should continue to increase due to cementation in
successive tests. Inspecting the results with this consideration, there is still no discernable trend
with Samples S1 and S2 showing slight increases and Samples S3 and S4 showed no significant
changes in diameter. At the conclusions of the tests, the mean sediment sizes were within 4 % of
their original sizes.
In summary, my interpretation from the tests conducted and reported here is that there is no
significant abrasion to the Aragonite particles over the length of the tests conducted. Rather it is
believed that there was minor increase in size due to cementation.
) ....... ; ........ ........ ................... ................. .--- '--- S m i
-*4- Sample Si
E 6 -.. ...... ... SampleS2 "
S:......... ........................... Sam ple S3 .-
S 4 .... \ .. ............ ...... - Sample S4 ..
c .. ...-.-...--.....-..--... ........--
2 2 .: ---- .......... -------. .. .
ra . ........ .. .......... .... . .. ...... . ....... .. I ...... ........ ........
U 0 ..... .. .. .... ..... ..... : ....... .. .. ..... . .
0 100 200 300 400 500
Total Testing Time (Hours)
Figure 6.2. Percentage Change in Mean Diameter
as a Function of Tumbling Time.
Aragonite Component of Sample 1
Sample 1 is a Mixture of Quartz and Aragonite
Sieve No. Effective Weight (gms) Remaining on Sieve After Tumbling for
Diameter (mm) Various Times (Hours)
Applied to Each
Sieve 0 2 10 34 226
30 0.625 38.8 47.7 45.1 43.4 40.8
40 0.508 36.6 41.2 39.6 43.3 41.8
60 0.335 116.5 116.3 113.4 108.8 113.7
100 0.1995 39.4 84.6 86.7 86.2 92.4
120 0.137 16.1 10.8 11.4 10.9 4.7
Pan 0.0625 16.0 15.6 17.3 16.9 15.1
Total Weight (gms) 313.4 316.2 313.5 309.6 308.5
D, (mm) 0.328 0.345 0.339 0.340 0.340
Mean Diameter, D, (mm)
Percent Change in Mean 0 5.18 3.35 3.65 3.65
Sample 2 Tests
Sample 2 Contained Only Aragonite
Sieve No. Effective Weight (gms) Remaining on Sieve After Tumbling for Various
Diameter Times (Hours)
to Each Sieve 0 2 10 34 226
to Each Sieve
20 0.900 45.1 54.2 47.1 45.8 46.3
30 0.718 19.1 22.3 20.1 19.3 19.4
40 0.508 57.1 61.9 61.3 64.5 66.6
60 0.335 198.1 183.6 184.2 182.3 185.1
100 0.1995 137.4 132.4 138.3 141.6 140.9
120 0.137 20.8 25.5 23.2 20.8 16.8
Pan 0.0625 22.8 29.4 30.2 26.5 26.7
Total Weight (gms) 500.4 0.372 504.7 500.8 501.8
(mm) 0.362 0.372 0.361 0.363 0.366
Mean Diameter, D, (mm)
Percent Change in Mean 0 2.76 -0.28 0.27 1.10
Aragonite Component of Sample 3
Sample 3 is a Mixture of Quartz and Aragonite
Sieve Effective Diameter (mm) Weight (gms) Remaining on Sieve After Tumbling
No. Applied to Each Sieve for Various Times (Hours)
0 2 34 464 (1) 464 (2)
20 0.900 24.9 26.7 29.4 24.6 24.5
30 0.718 10.3 12.7 12.5 11.4 11.3
40 0.508 31.9 35.5 38.6 33.5 34.1
60 0.335 93.5 91.0 89.9 86.3 86.5
100 0.1995 66.8 64.2 64.3 66.5 66.1
120 0.137 13.0 12.0 8.3 12.7 12.3
Pan 0.0625 12.5 14.7 12.3 15.2 15.3
Total Weight (gms) 252.9 256.8 255.3 250.2 250.1
n D ( 0.369 0.378 0.391 0.369 0.369
Mean Diameter, D, (mm)
Percent Change in Mean Diameter 0 2.4 5.96 0 0
Sample 4 Tests
Sample 4 is Aragonite Only
Sieve No. Effective Weight (gms) Remaining on Sieve After Tumbling for
Diameter Various Times (Hours)
to Each Sieve 0 2 34 464 (1) 464(2)
20 0.900 48.9 53.9 52.3 51.4 51.4
30 0.718 19.6 22.2 21.0 20.5 20.3
40 0.508 58.0 62.8 65.0 60.3 59.8
60 0.335 187.4 179.9 182.8 178.5 178.7
100 0.1995 135.9 135.4 142.7 134.6 136.1
120 0.137 25.2 23.4 15.4 25.9 25.9
Pan 0.0625 25.7 28.9 27.5 31.2 30.0
Total Weight (gms) 500.7 506.5 507.4 502.4 502.2
Mean Diameter, D, (mm) 0.365 0.344 0.372 0.366 0.366
Mean Diameter, D, (mm)
Percent Change in Mean 0 -5.75 1.92 0.30 0.30
6.5 Time Scale Relating Tumbler Results to Surf Zone Conditions
The objective of this section is to develop a basis for converting tumbling time of sediments into
an equivalent time for surf zone conditions. Stated differently, if a sediment sample were
tumbled for one hour, what is the approximate equivalent time in the surf zone on the basis of
equal energy expended on the sediments? Clearly, due to the complexity of the problem, any
quantification of this relationship will represent an approximation. In order to establish the
desired relationship, it is necessary to develop equations for the rate of energy expended on the
sediments for the two environments: tumblers and surf zone.
6.5.1 Energy Dissipated on Sediments In Tumbler Experiments
Consider the system shown in Figure 6.3 and a sediment element at radius r. This parcel is lifted
a distance: rsin 0c before it cascades down to the centerline of the tumbler where 0. is the
Figure 6.3. Definition Sketch of Element of
Sediment in Tumbler.
limiting sediment slope. The average energy expended on this particle in one rotation of the
tumbler, ETumbler is
x R 3
ETmbler = Psgbsin9 Jr2dr dO = pgbsinO, c
in which p, is the mass density of the sediment, g is gravity, b is the width of the tumbler, r and
0 are the radial and azimuthal cylindrical coordinates, respectively and R is the tumbler radius.
This energy dissipation occurs every rotation, ie in a rotational period, T, so the average energy
expended on the sediments per unit time, ETumbler is
* psgbsin9 tR3
ETumbler T 3
and the rate of energy dissipation per unit sediment mass exerted by the tumbling process on the
sediments, eTmblt (the basis for the surf zone relationship to be developed later) is
* gsin0, R
eTumbler T 3
6.5.2 Energy Dissipated Within the Surf Zone
The most direct approach to developing an expression for the wave energy dissipation per unit
sediment mass is to consider the rate at which wave energy enters the surf zone per unit length of
beach and then later in the development, to consider an efficiency factor representing the
proportion of this wave energy that is expended on the sediments. The rate at which energy
enters the surf zone per unit beach length is
Waves = ECG = pg
in which E is the wave energy per unit surface area, Cg is the group velocity and, for shallow
water can be approximated as Cg = ghb p, is the water mass density, Hb and hb are
breaking wave height and water depth, respectively considered to be related by Hb = K hb where K
= 0.78. Considering a beach nourishment project with sediment mass, M, per unit beach length,
the average wave energy dissipated per beach length per unit sediment mass, ewaves is
E Waves Ewaves p. gHV b F
as M pV p, 8V
in which V is the nourishment sediment volume per unit beach length (M = pV)and F is an
efficiency factor relating the ratio of the wave energy dissipation rate on the sediments to the
total wave energy dissipation rate.
The equivalent time scale, tR, is obtained on the basis of the times in the two environments
required to dissipate the same energy on the sediments, ie
eTumbler tTumbler ewaves twaves
from which a time ratio, tR, can be established as
t twves erumbler 8 psVR sin qp
tR umbler e 3 pTH ghF
which is dimensionless. The interpretation of the above is that one hour of tumbler testing would
be equivalent to the number of hours in the surf zone given by the above expression. The
following example will provide a quantitative estimate of this ratio, tR. Consider the following
values: p, /Pw = 2.65, Hb = 2 ft., V = 2,700 ft3/ft, R = 0.33 ft., 0, = 10, T = 2 s, hb = 2.0/0.78 =
2.56 ft.and F = 0.05. For these condition, the ratio, t, 400 In other words, for the average
sediment particle within the surf zone, each hour of tumbling is equivalent to approximately 400
hours of surf zone time.
There are several issues relating to the interpretation of the above results. The reason that the
time factor, tR is so large is that even though the energy expended on the sediments in the
tumbler is so small, the nourishment sediment volume associated with a beach nourishment
project per unit length, V, is so large and only a small portion of the total sediments (the surface
sediments) are exposed to the energy dissipation at any one time. Although if this were actually
the case, these exposed sediments would wear and the next layer would be exposed, etc. In
reality there is substantial mixing and, in areas where a substantial longshore sediment transport
exists, the nourishment sediments will become intermixed and/or partially or completely covered
by native sediments. This can be observed in areas where sand has been placed and which has
characteristics (color, size, etc.) which are visually distinct from the native sediments. After a
year or so, the surficial sediments within the active surf zone are usually indistinguishable from
the native sediments documenting that much of the nourishment sediments have been "capped"
by the native sediments, albeit temporarily. Of course as the volume of the nourishment project
decreases due to spreading along the shoreline, more and more nourishment sediments are
activated and eventually all of the nourishment sediments would be exposed to the wave energy.
The main point is that the nourishment sediments would not be acted upon by the waves
continuously, so the effects of only a portion of the nourishment volume being acted upon at any
one time is not of great consequence. In summary, everything considered, the above conversion
factor of 400 appears a reasonable approximation considering the uncertainties in the processes.
6.6 Summary and Conclusions From Abrasion Tests
Based on the abrasion tests reported here, it is evident that Aragonite is not subject to rapid
wasting when tumbled for substantial lengths of time in the presence of Quartz. It appears that
there was some cementation in the drying of the samples which, on the average, caused some
minor(average 2 to 3 percent) increase in the mean size of the sieved sediments. The
equivalency developed indicates that for representative Florida nourishment projects, one hour of
tumbler time is equivalent to approximately 400 hours of surf zone time. Thus the tests
conducted here are equivalent to up to 21 years of exposure under typical surf zone conditions.
7.0 ALTERNATE MEANS OF DELIVERING SEDIMENT TO FLORIDA'S
The most often used approaches to providing beach nourishment materials are through dredging,
either by pipeline or hopper dredges. These dredges remove suitable sediment from the ocean
floor and whereas pipeline dredges deliver the sediment continuously from removal to delivery
point, hopper dredges store the sediment in the hull, transit to the delivery location and then
usually pump the sediment to the shoreline in a "batch" mode. Alternate means could be by barge
or ore carrier from a distant location or through pipelining the material from an interior source.
Hauling sediment by trucks is also a feasible approach; however, heavily laden trucks are noisy,
disruptive to normal traffic flow and can cause wear to the highways and thus are not considered
further here. The two types of alternate means that are considered here are transport by barges
across sheltered waters, ore carriers for exposed waters and pipelines for sediment delivered from
7.2 Sediment Delivery Through Barges or Ore Carriers
Low freeboard barges can be used to deliver bulk goods in waters which are sheltered from
significant wave action. Also if the waterway geometry is suitable, a number of such barges can
be connected and pushed by a single tug for improved economy. These approaches are used, for
example, for river conveyance and in the intracoastal waterway. However, it is anticipated that
most sediment that would be delivered to Florida's beaches from distant sources would be
exposed to a substantial wave environment and would require a hull suitable for energetic wave
environments. Nevertheless, to provide a basis for comparison, some barge transportation costs
(based on coal transport) are provided below. These cost bases have been converted to cubic
yards of sand for greater relevancy to our interests here.
Table 7.1 lists several examples of costs per ton and costs per cubic yard (in 1997 $) for coal
deliveries by barges to power plants located on rivers. The conversion from the original cost units
in $ per ton were transformed to $ per cubic yard by considering a coal specific gravity of one-
half that of sand and equal porosities. The cost information presented in Table 7.1 reflects
economies of scale and, as noted, are applicable only for sheltered waters.
7.3 Sediment Delivery Transiting Significant Wave Conditions
If the sediment delivery system is to include areas where the waves can be substantial, the most
appropriate mode of delivery will be in a vessel outfitted with a ship type hull of the form used
for shipping ore and grain. These types include the Handymax, Panamax, and the Capesize
vessels. The overall characteristics of these vessels are summarized in Table 7.2.
Examples of Unit Costs for Barge Shipments of Coal on Rivers
Power Plant Origin of Coal Distance barged Cost per Ton of Cost per Cubic
Name (Miles) Coal yard of sand
West Virginia 354 3.31 6.60
Ghent Indiana 280 4.59 9.20
West Virginia 442 2.37 4.75
Kentucky 224 3.30 6.60
Ohio 50 0.87 1.75
Monongahela Pennsylvania 5 0.38 0.75
Power Company West Virginia 50 0.87 1.75
Pennsylvania 5 0.38 0.75
Ohio 50 0.87 1.75
Ore Vessels Suitable for Transporting Sand Under Energetic Wave Conditions
Type Vessel Approximate Rating in Dead Weight Tons
Handy and Handymax 15,000 to 50,000
Panamax 50,000 to 65,000
Capesize 70,000 to 100,000
The term "dead weight tons" refers to the total weight that a vessel could carry when fully
loaded, including cargo, fuel, water, stores and crew and is expressed in long tons (2,240 pounds
per long ton). For approximate application purposes, the amount of cargo that can be carried by a
vessel is approximately 80% to 90% of the dead weight ton rating of that vessel.
The cost of fuel in transporting cargo is approximately 40% of the total cost. Thus, the distance
over which the cargo is shipped is a significant, but not an overiding factor in the total cost. As
shown in Figure 7.1, the costs of shipping "clean" dry bulk such as grains is greater per ton than
that for ore which would apply for sand.
Drycargofreight rates. Panamax
Figure 7.1 Comparisons of Shipping Costs for Grain and
Ore by Panamax Vessels. The Upper Curve Applies to
The paragraphs below develop approximate costs per cubic yard to deliver sand from a fairly
distant source to Florida's shorelines. The basis for these estimates will be a Panamax ore carrier
which could transport approximately 40,000 yd3 to 45,000 yd3 of sediment. The costs will be
developed for several distances from the placement locations. Thus, the cost estimates include a
fixed component, plus a transit cost which depends linearly on the distance from the origin to the
Costs of Sediment Obtained From a Distant Source Including Loading and Unloading
Cost Component Cost Estimate ($/ Cubic Yard)
Cost of Extracting and Transporting $4.00
Sediment to Loading Point
Loading and Unloading Sediment and $ 3.00
Transportation to Placement Location
From Table 3, the sum of the estimated fixed cost components related to transportation in is
$ 7.00 per cubic yard. It is emphasized that these are estimates only and will vary with a
particular application. The additional costs of a particular application depend on the round trip
transit distance from the source to the destination and return. As seen in Figure 7.1, the charter
rates for a Panamax type vessel over the period 2001 through 2002 has fluctuated between $
6,800 per day and $ 12,000 per day. Adopting a reasonably representative daily rate of $ 10,000,
the average costs per cubic yard were determined as:
Cost per cubic yard = $ 7.00 + $ 0.17 x (One way distance in 100 miles).
US ulf IJapan 54,000 t
Rlchards Bay ILe Hawvre -70000 t
I I I I I I I I I I I I I
Average time charter rates for bulk carriers
18 000 --,Modem Handymax 35 months tic
S0(del. I redel. Pacific)
17000 J ,- Modem Panamax TIC rates (basis 12
15000 Modem Captsize
12 months tic
5000. I I II
01100 07/00 01101 07101 01102 07102 01103
Figure 7.2. Comparison of Charter Rates for Various Ore Carriers.
Thus, the costs associating with transiting in the process of delivering the sediment and returning
to the supply point are relatively small. For example, the additional transiting costs for a one way
distance of 400 miles would be $ 0.68 per cubic yard. The total costs would require including any
severance costs of the sediment which may apply for a particular project.
It is emphasized that these rates are based on international costs and may be higher if the
provisions of the Jones Act are required although it is my understanding that the Jones Act would
not be in effect for shipment of sediment to the United States.
7.4 Delivery Costs By Pipeline Slurry From Interior Sources
Sediment can be delivered over great distances by pipelines as a water/sediment mixture termed a
"slurry". Some coal slurries have been pumped in excess of 1,000 miles! As discussed
previously, the delivery of large quantities of sediment by pipeline from the interior of the State
is one alternative and is examined in this section.
There are several operating principles and limitations related to pumping slurries, a discussion of
which will aid in evaluating options. A sand water slurry can be pumped in concentrations by
volume up to approximately 30%. For concentrations greater than 30%, a significant risk exists
of progressive sedimentation in the pipeline which will eventually lead to shutdown of the
operation through clogging. For a given sized sediment, slurry concentration and pipe size, a
minimum velocity is required in order to avoid deposition in the pipeline. This minimum velocity
increases with increasing sediment size, concentration and pipe size. Standard dredge pumps and
the associated piping can only generate and withstand a certain pressure at the discharge of the
dredge pump. As the pressure drops along the pipeline primarily due to pipe friction, it is
necessary to install booster pumps in order to maintain the minimum velocity. Booster pumps
and pipelines are expensive and pipelines wear due to the abrasive sediment conveyed with the
greatest wear located on the bottom of the pipe. Thus, in order to minimize pipe replacement and
associated expense, the pipes are rotated to maximize life.
To provide an estimate of the economics of slurry pumping, for a 24 inch diameter slurry
pipeline pumping a sediment of 0.3 mm at a maximum concentration of 30%, booster pumps
would be required approximately every 1.0 miles. Reducing the slurry concentration to 10%
increases the required booster pump spacing to approximately 2.4 miles. Approximately 1,500
horse power is required to deliver the 30% concentration 1 mile and the cost of a pump and
electric motor to deliver this slurry is approximately $ 800,000. The cost of the 24 inch dredge
pipe for a length of 1.0 mile is approximately $ 264,000. The power costs are relatively small, on
the order of $ 0.03 per cubic yard per mile. Pumping a lesser concentration would reduce the
numbers and total costs of the power plants and pumps. The following sections consider four
scenarios of volumetric concentration.
7.4.2 Scenarios Considered
In order to obtain a more complete range of estimated costs of pumping slurries, four scenarios
are considered and the results developed into useful relationships. The characteristics of these
four scenarios and the pumping quantities and costs are summarized in Table 7.4. The costs are
based on pumping over a one year period and over a ten mile distance with 50% pumping time.
Characteristics of and Results From Slurry Pipeline Scenarios
Pipe Slurry Slurry Unit Minimum QTOT QSED Booster Total Pump,
Diameter Concentrati Weight Velocity Pump Motor and Pipe
Scenario (inches) on by (lbs/ft3) (ft/s) (cfs) (yd3/hour) Spacing Costs for 10 miles
Volume (Miles) (Millions of$)
1 12 0.1 73 8 6.3 129 1.2 6.4
2 12 0.3 93 10 7.9 486 0.8 10.0
3 24 0.1 73 11 34.5 708 2.4 3.2
4 24 0.3 93 14 44.0 2,700 1.0 8.0
Table 7.4 (Continued)
Characteristics of and Results From Slurry Pipeline Scenarios
Based on 50% Pumping Time for One Year Over a Distance of Ten Miles
Scenario Annual Fixed Costs Total Pumping Costs @ Total Sediment Total Unit Cost
(Millions of $) $ 0.08/KWH Pumped ($/yd3)
(Millions of $) (Millions of yd3)
1 0.83 0.370 0.57 0.65
2 1.19 0.83 2.13 0.39
3 0.58 1.01 3.1 0.32
4 1.06 3.90 11.8 0.33
The results in Table 7.4 establish that there are fixed costs and costs that are linearly related to
the quantity of sediment pumped. These results can be organized into an equation of the
Annual Cost in Millions of $ = a + b VED
in which the coefficients a and b depend on the scenario being considered and VSED is the
volume of sediment pumped over that year in millions of cubic yards. The values of the a and b
coefficients for the four scenarios are presented in Table 7.5.
Values of Coefficients in Equation (1)
Scenario Coefficient a Coefficient b
(Millions of $) (Millions of $/Million yd3)
1 0.83 0.65
2 1.19 0.39
3 0.58 0.32
4 1.06 0.33
The results in Table 7.5 will be illustrated with an example. Suppose it is wished to configure the
optimum system to pump 2 million cubic yards per year using one of the systems in the four
scenarios summarized in Table 7.4. Table 7.6 summarizes the results. Inspection of the results in
Table 7.6 indicates that the 24 inch pipeline operating at a 30% concentration is the least cost.
Recalling that these results are for a pumping distance of 10 miles, it appears that delivery of
sediment by pipeline is economically feasible, if not optimal.
It is emphasized that the costs presented in this section do not include real estate acquisition costs
nor sediment severance fees which could be appreciable.
Example Costs for Pumping 2 Million Cubic Yards Annually Over a 10 mile Distance
Scenario Fixed Costs Pumping Costs Total Annual Costs Unit Cost
(Millions of $) (Millions of $) (Millions of $) ($/yd3)
1 0.83 1.3 2.13 1.07
2 1.19 0.78 1.97 0.99
3 0.58 0.64 1.22 0.61
4 1.06 0.66 1.72 0.86
7.5 A Hybrid System "Mixing" Barging and Slurry Delivery
Previous sections have considered sediment transportation by pipeline slurries and barges or ore
carriers. Considering the cost advantage of transportation by barge including the lack of or
minimal initial capital investment, lack of right of way concerns, etc, it appears desirable to use a
barge mode of transportation where practical. Considering the availability and location of the
Intracoastal and Okeechobee Waterways in Florida, it is worthwhile to consider a hybrid system
in which a slurry pipeline would be used to transport the sediment from a quarry to the
Okeechobee Waterway and then barges to transport the sediment to the destination point.
Although consideration of such a system is beyond the scope of this study, it is suggested that
this possibility may be appropriate for some particular projects.
8.0 MODERN DREDGE CAPABILITIES
As easily accessible deposits of suitable sediments are reduced, extraction from deeper waters
becomes more attractive which may extend the limits of the existing dredge fleet. This section
reviews the capacities of existing dredges. A more detailed treatment of the mechanics of
dredging is provided in Appendix A.
Dredges remove sediment from the seafloor and deliver it to a beach to be nourished. As the
extraction depths increase, physical limitations of the dredge system reduce the efficiency of the
extraction process or require additional equipment, each or both of which can increase the costs.
Within the U. S. dredging fleet, there are 214 cutter suction pipeline dredges and 22 trailing
suction hopper dredges. Of these, as of 2001, 78 dredges were owned by the four largest U. S.
dredge companies as shown in Table 8.1.
World Ranking of Four U. S. Major Dredging Companies and Numbers of Dredges
Company World Ranking Number of Dredges
Great Lakes Dredge and 6 29
Weeks Marine 13 18
Manson 14 18
Bean 25 13
More than 95% of sediment delivered for beach nourishment projects are provided by pipeline or
hopper dredges. Thus, these two types of dredges are reviewed below.
8.2 Pipeline Dredges
This type dredge delivers sediment from the source to destination through a pipeline, hence its
name. The sediment is accessed from the seafloor by a pipe with either an open end (called a
suction dredge) or a rotating cutter head to facilitate dislodgement of the sediment. Suction head
dredges are used primarily and most effectively for cases in which the material is very weak such
as a soupy mud. Therefore, almost all beach nourishment projects in which pipeline dredges are
used employ a cutter head. Figure 8.1 presents a schematic of a cutter head dredge. Pipeline
dredges are most efficient in cases where there is a substantial thickness of suitable sediment, say
at least 6 to 8 feet thick, the pumping distances are short and the water is reasonable shallow. As
noted previously, for long pumping distances, intermediate pumping stations called "booster
pumps" will be required which will increase the pumping costs. Cutter head dredges are also
favored over hopper dredges in cases where the geometry of the borrow area may be complex as
can be the case when limited by reefs or sediments with an unacceptable rock content.
PUMP. MOTORS. ETC.
Figure 8.1. Schematic of Cutterhead Pipeline Dredge. (From Richardson, 1976).
Under ideal conditions, a cutterhead may be able to deliver sediment for a cost as low as $ 2.00
per cubic yard. In less than ideal conditions including long pumping distances, costs can be as
high as $ 20.00 per cubic yard.
The presently available cutter dredge fleet includes dredges that can extract sediments to depths
in excess of 100 feet. However, these dredges would require a ladder pump which would increase
the cost. Although the additional cost per cubic yard due to extracting sediment from deep water
would depend on many factors, it is estimated that the cost of extracting sediment from a depth
of 100 feet would add approximately $ 2 to $ 3 per cubic yard compared to more normal dredge
depths of 40 to 60 feet. There is no practical limit of distance from the source to the destination.
However, as a rule of thumb, booster pumps will be required every mile to two miles of pumping
distance and each booster pump will add approximately $ 1.00 per cubic yard to the sediment
8.3 Hopper Dredges
Hopper dredges are the more suitable type of equipment for long distances from the extraction to
delivery point, when the suitable sediment is available only in relatively thin layers and the
borrow area is reasonably extensive and linear in extent. A schematic of a hopper dredge is
shown in Figure 8.2. The sediment is conveyed from the ocean floor to the dredge by one or two
pipes (termed "drag arms") which extend from the ocean floor up to the dredge. This loading
operation is conducted while the dredge moves at approximately 2 to 3 knots. The sediment
water mixture ranges from approximately 10% to 30% of sediment by volume and is discharged
into the hull of the hopper dredge where the sediment settles out and the excess water flows over
the gunwales of the dredge returning to the sea. Once fully loaded, the dredge transits to the
delivery point at a speed of 6 to 8 knots. Most hopper dredges can extract sediment from depths
up to 60 feet with some having capacities up to 80 feet. However, as discussed for pipeline
dredges, the costs increase with increasing depths.
G AR DRAGHEAD
Figure 8.2. Schematic of a Hopper Dredge. (From Richardson, 1976).
Upon arrival at or near the delivery point, the hopper dredge can pump its sediment load directly
to the beaches or simply discharge it onto the ocean floor from which the sediment would need to
be rehandled to place it upon the beach. Not all hopper dredges are configured for direct pumpout
to the beaches; however, this is becoming more common in order to meet beach nourishment
needs. Most dredges in the U. S. fleet have storage capacities of 3,600 cubic yards; however, the
Long Island hopper dredge, owned by Great Lakes Dredge and Dock Company, can store and
convey 16,000 cubic yards to the destination.
The world's largest hopper dredge is the Vasco da Gama which can dredge in water depths up to
430 feet. This dredge is owned by Jan de Nul, is registered in Belgium and has a storage capacity
of 43,200 cubic yards. No unit cost estimates are available for sand extraction by this dredge
8.4 Advances From the Dredging Industry
Dredging industry representatives have stated that they are capable and ready to develop and
provide any dredging capability that can be shown to provide a reasonable economic return.
Thus, as the need for additional sediments for beach nourishment materializes, there are several
scenarios that can be envisioned. The option selected will likely depend on costs, political issues
and regulatory concerns. One option is the extraction from deeper and deeper water. A second is
the importation of sediments from outside US waters or from quarries located inside the State by
pipeline or barge or a combination. These latter two options have been addressed in Section 7 of
this report. However, it is reasonable to consider that the dredging industry has the interest,
capability and resources to accommodate deeper water needs for sediment extraction if this is the
direction taken by the designers of beach nourishment projects and if there is sufficient demand
to make this effort economically attractive.
9.0 SEA TURTLES AND OTHER POTENTIAL BIOLOGICAL CONCERNS
9.1 Sea Turtles
A major concern over the use of Aragonite for beach nourishment is the impact on Sea Turtle
nesting. The first full scale Aragonite beach nourishment project in Florida was constructed in
1991 with substantial monitoring and comparison of the effects of Aragonite and native Florida
sand. These results are summarized here.
In 1991 the first full scale beach nourishment project using Aragonite was constructed on Fisher
Island in Florida. This was a fairly small project comprising 42,950 cubic yards along 2,060 feet
of shoreline (Olsen and Associates, 1995). This shoreline lies between Government Cut to the
north and Norris Cut to the south and was stabilized by seven structures, see Figure 9.1 and 9.2.
A thorough sea turtle monitoring
project was conducted to identify
differences between the
Aragonite and natural Florida
beach sands. Due to the short
length of the project, nests were
relocated from Juno Beach to two
hatcheries on Fisher Island. One
of these hatcheries contained
Aragonite and one contained
natural Florida sand. In addition,
natural nests on the Aragonite
beaches were monitored. The
monitoring was conducted
through the Rosenstiel School of
Marine and Atmospheric
Sciences at the University of
Miami and reported by Lutz, et al
(1993). The sections below
summarize the results of this
study which included nest
temperatures, gas exchange,
hatchling success and hatchling
Figure 9.1. Photograph of Fisher Island Which Extends From
Government Cut Southerly to Norris Cut.
9.1.2 Experimental Design
The moniotring design encompassed
one year ofpre-nourishment and
three years of post-nourishment
results. Three temperature probes
were placed in each relocated nest at
9 inches, 12 inches and 18 inches
below the surface. These
temperatures were compared with
temperatures from control areas
placed at the same depths but at a
distance from each nest. The gas
content in each nest was sampled via
a small diameter polyethylene tube
placed in the center of each nest.
The relocated nests were monitored
for hatchling success defined as
hatchlings which emerged from their
eggs, but not necessarily their nests
and mortality of hatchlings which
were those hatchlings which pipped
their egg shells but were unable to
escape from their nests.
As expected, because Aragonite is
of lighter color than most natural
Florida beach sand, it was found that
the temperatures were lower, on
average, in the Aragonite nests. The
interest in temperatures is that the
sex of reptiles is known to depend
on the incubation temperature.
Turtle eggs incubated at
temperatures below approximately
280 C produce predominantly males
and incubation temperatures above
320 C produce predominantly
females. Table 9.1 summarizes the
Figure 9.2. Layout of Fisher Key Showing the Seven
Stabilization Structures. From Olsen, Associates, 1993.
findings with respect to temperature over the three year period. It is seen that there is substantial
interannual variability in both the Aragonite and Florida sand temperatures. The averages ranged
from 27.5 o C to 31.70 C for the "Average Florida Nest" and from 25.50 C to 30.80 C for the
"Average Aragonite Nest" over the three year period. On average, over the three year period, the
temperature of the Aragonite nests was 28.40 C compared to the average of 30.1 C for the
Florida beach sand, a difference of 1.70 C. It is seen that there is substantial interannual variation
in the incubation times (Figure 9.3), in fact more than the differences between the average
incubations for the Aragonite and Florida beach sands although there is a consistent bias between
the two sands. In addition to skewing the sex ratios, lower nest temperatures increases the
incubation period and thus the potential for egg predation. Comparison of the incubation times in
Figure 9.3 with the temperature data in Table 9.2 demonstrates the effect of average temperature
on incubation times. The gender of the hatchlings was not determined. Therefore it is not
possible to quantify any bias in the numbers of male versus female hatchlings for the two types
sediments. Finally, with regard to the temperature and gender issue, if the eggs were relocated to
hatchery areas, the temperature could be controlled to replicate that of the natural sands on a
Temperature Characteristics of Hatchery Nests and Control Areas
(From Lutz, et al, 1993)
Variable Temperature for Year
1991 1992 1993
Average Florida Control 32.00 C 30.80 C 31.80 C
Florida Control Range 27.50 C to 36.50 C 26.60 C to 32.70 C 30.70 C to 32.70 C
Average Aragonite Control 30.00 C 28.40 C 30.40 C
Average Aragonite Range 28.50 C to 31.00 C 26.20 C to 30.60 C 29.60 C to 31.40 C
Average Florida Nest 31.00 C 27.50 C 31.70 C
Florida Nest range 29.50 C to 32.50 C 26.00 C to 34.40 C 30.00 C to 35.00 C
Average Aragonite Nest 29.00 C 25.50 C 30.80 C
Aragonite Nest Range 28.00 C to 30.00 C 22.20 C to 32.00 C 29.20 C to 32.20 C
184.108.40.206 Gas Exchange
Based on comparison of 60
results of the gas exchange Days to
and reported values on (+/ .E.) 55
natural beaches in the
literature, it was concluded 5o
that Aragonite was a suitable
220.127.116.11 Hatching Success
and Hatchling Mortality
The hatching success for the Figure 9.3. Incubation Times for The Two Sediment Types and
three years is presented in Three Year Monitoring Period. From Lutz, et al, 1993.
Table 9.2 for the three years
of studies including both incubation areas and the natural nests in the Aragonite. It is seen that all
of the hatching success data are quite high. Moreover, there are no evident differences between
the Aragonite and Florida sand results.
Hatching Success in the Two Sediment Hatcheries and Natural Nests
(From Lutz, et al, 1993)
Year Nest Characteristics
Aragonite Hatchery Florida Sand Hatchery Natural Nests in Aragonite
1991 91.7% 92.7% 77.0%
1992 86.8% 91.0% 95.1%
1993 96.2% 84.0% (*94.5%) 97.0%
* Hatching success if Nest J (which had an atypically high mortality) is eliminated from the data.
The average mortality of hatchlings were found to be approximately the same for the two types
sand, ranging from 2.5% to 5.6% for Aragonite and 2.2% to 9.0% for Florida sand. The upper
limits for both types sediment was due to one nest in each sediment type in 1993 and if these two
nests are not included the ranges decrease from 2.5% to 2.7% for Aragonite and 2.2% to 2.7% for
18.104.22.168 Hatchling Morphology
The lengths, widths, weights and any tendencies for abnormalities of the hatchlings were
examined. No significant abnormalities were identified in any of these characteristics.
9.1.4 Overall Summary of the Fisher Key Monitoring on the Effects of Aragonite on Sea
The most effective summary that can be provided of this thorough and authoritative study of the
effects of Aragonite on sea turtle nesting is to quote the "Conclusions" section of the final (1993)
"1- We were able to confirm that aragonite sand registered 1.4-2 degrees Celsius
lower temperatures than Florida silicate throughout the three year period.
2- The temperatures registered during the middle third of incubation (when
gonadal differentiation occurs in loggerhead sea turtles) correspond to male and
female producing ratios of both sands.
3- Although incubaton periods were significantly longer in aragonite nests in
1992 and 1993, no significant differences were reported between aragonite and
Florida nests in 1993.
4- No significant differences between both sands were found in grain size, water
potential or gas exchange. SEM photographs revealed that aragonite sand is oval
shaped while Florida sand is angular, this could potentially make Florida sand
5- We found no correlation between aragonite sand compactability and nesting
6- No significant differences were found in hatching success, mortality,
hatchling size or morphology between the two sands.
7- We found no ill effects by the use of Bahamian aragonite as a nesting
substrate for Loggerhead Sea Turtle (Carreta carreta) nests. All the physiological
parameters of egg development such as incubation times, gas exchange,
hatchling size and mass, were within the normal limits reported in the literature.
Hatching success and emergence were both above the average reported in the
literature. However, we must caution that sand temperatures are regulated by
extrinsic environmental factors (such as atmospheric temperatures, rainfall, etc.)
and since aragonite sands are cooler than Florida silicate, incubation times and
sex ratios could be affected negatively in cooler climates."
9.2 Other Potential Biological Concerns
Concerns other than sea turtles associated with the Fisher Island beach nourishment project were
addressed through biological monitoring by Continental Shelf Associates, Inc. and Olsen
Associates, Inc (1995). The monitoring included sea grass beds, hard bottom communities both
offshore and on the adjacent jetties and benthic macroinvertrebrates associated with the intertidal
and subtidal beach.
It was found, as expected, that there was a decrease in the sea grass beds; however, this was less
than one-half of the permitted decrease. Otherwise, although there was considerable variability in
the data, there were no identifiable trends in the monitoring results that could be related to the
use of the Aragonite for beach nourishment.
10. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
10.1 Summary and Conclusions
This report is based on laboratory studies and a literature review and has evaluated the suitability
of Aragonite for beach nourishment and has developed estimated costs to deliver sediments from
Laboratory experiments conducted in the University of Florida Coastal Engineering Laboratory
have demonstrated that equivalents can be established between Quartz and Aragonite such that
they perform approximately the same within the beach system. A series of these laboratory
experiments was conducted in a wave tank with the emphasis on equilibrium beach profiles and
cross-shore sediment transport. Others were conducted in a wave basin with the primary focus on
the longshore sediment transport characteristics. One approximate equivalent for the two types of
sediment is simply the average or median grain size of the two types of sediments; however, a
slightly better equivalent is the fall velocity. Aragonite has a slightly greater density than Quartz
(approximately 2.8 vs 2.65) and one type of Aragonite (oolitic Aragonite) is more streamlined (or
rounded) than Quartz, thus having a faster fall velocity resulting in a more stable beach sediment
for the same size compared to Quartz.
Cementation tests were conducted over a period of fifteen months with drained and undrained
samples exposed to the environment. It was found that the drained sample formed a very weak
surface structure, but certainly the strength of that structure was not sufficiently large to affect
normal beach activities including sea turtle nesting. As expected, no cementation was apparent in
the undrained sample.
Laboratory abrasion tests were conducted with a mixture of Quartz and Aragonite and Aragonite
alone. No significant abrasion was detectable for durations in excess of 400 hours of laboratory
testing which is approximately equivalent to 21 years of exposure in the surf zone with a
typically sized beach nourishment project in Florida.
Costs of barging sediment in sheltered and unsheltered waters by barges and ore carriers,
respectively were examined. The costs of barging sediment over long distances are quite low if
accomplished by coupling barges together such that only one propelling vessel is required. These
costs are in the range of several dollars per cubic yard even for cases of transportation distances
exceeding several hundred miles. Transportation by ore carriers was based on international rates
resulting in estimates on the order of $ 8 to $ 9 per cubic yard. One caveat is that this estimate
does not include extra costs if the transportation is regulated by the Jones Act which could
escalate the costs substantially; however, it is my understanding that the provisions of the Jones
Act will not apply for the types of transportation operations envisioned here.
Transportation of particles by slurries is well developed with some coal slurries transported over
distances greater than 1,000 miles. The costs per cubic yard to transport sand slurries from an
inland quarry to coastal areas was estimated for several scenarios of slurry concentrations and
pipe sizes. Depending on the system characteristics investigated, booster pumps can be required
along the pipeline at spacings ranging from 1.0 to 2.4 miles. The substantial initial costs
associated with slurry transport argue for use of other transport modes where possible. One
option that was considered, but not explored further was a combination of slurry system to
transport the sediment to a waterway where the more attractive barge mode of transport can be
It is stressed that costs presented in this report do not include components associated with land
acquisition, initial cost of the transportation system nor severance fees.
The 1991 beach nourishment project on Fisher Key was constructed with Aragonite and was
monitored for potential impact on sea turtles and other nearshore biota. Overall, the conclusions
were that Aragonite was a suitable material for beach nourishment in Florida.
It is recommended that more detailed cost estimates be developed with an emphasis on accessing
sediment from an inland borrow pit in reasonably close proximity to the Okeechobee Waterway
such that a relatively short slurry pipeline can transport the sediment from the quarry to a loading
point for barges. From this location, the sediment would be transported either east or west
through this waterway to its destination.
11.0 GENERAL REFERENCES
Altman, D. (2000) "Evaluation of the Suitability and Efficacy of Aragonite Sand for Beach
Nourishment", Master of Science Thesis, Department of Civil and Coastal Engineering,
University of Florida.
Beachler, K. E. (1995) "Bahamian Aragonite: Can it Be Use on Florida's Beaches? Engineering
Issues", Proceedings National Conference on Beach Preservation Technology, pp. 43-66.
Bodge, K. R. and E. J. Olsen (1992) "Aragonite Beachfill at Fisher Island, FL", Shore and
Beach, Vol.60, No.1, pp.3-8.
Coastal Planning and Engineering (1997) "Dade County Alternate Sand Source Investigation",
Prepared for Jacksonville District, U. S. Army Corps of Engineers.
Coastal Planning and Engineering (1994) "Feasibility Study for the Use of Aragonite Sand For
Beach Renourishment in Broward County", Unpublished.
Continental Shelf Associates and Olsen Associates, Inc. (1995) "Fisher Island Beach
Nourishment Project: Biological Monitoring Final Report", Prepared for Island Developers, Ltd.
Cummings, S. and L. Fisher (1995) "Bahamian Aragonite: Can it Be Use on Florida's Beaches?
Environmental Issues", Proceedings National Conference on Beach Preservation Technology, pp.
Flynn, B. (1992) "Beach Nourishment, Sea Turtle Nesting, and Nesting Relocation in Dade
County, FL", Proceedings, National Conference on Beach Preservation Technology, pp. 381 -
Herbich, J. B., Editor (2000) "Handbook of Dredging Engineering", Second Edition, McGraw
Hill, New York, NY
Higgins, S. H. (1995) "Bahamian Aragonite: Can it Be Use on Florida's Beaches? Political
Issues", Proceedings National Conference on Beach Preservation Technology, pp. 26-42.
Lillicrop, L. S. and G. L. Howell (1996) "The Impacts of Aragonite Use in the Nourishment of
Dade County and Other Southeast Florida Shore Protection Projects", Proceedings National
Conference on Beach Preservation Technology, pp. 60-74.
Lutz, P. L., A. A. Schulman, and S. L. Milton (1993) Fisher Island Sea Turtle Project: Final
Report 1993", Division of Marine Biology and Fisheries, Rosenstiel School of Marine and
Atmospheric Science, University of Miami, Miami, FL.
Milton, S., P. Lutz and A. Schulman (1995) "The Suitability of Aragonite as a Nesting Substrate
for Loggerhead Sea Turtles (caretta caretta)", Proceedings National Conference on Beach
Preservation Technology, pp. 179 180.
Monroe, F. F. (1969) "Oolitic Aragonite and Quartz Sand: Laboratory Comparison Under Wave
Action", U. S. Army Corps of Engineers, Coastal Engineering Research Center, 1 (69): 26 pages.
Olsen, E. J. and K. R. Bodge (1991) "The Use of Aragonite as an Alternate Source of Beach Fill
in Southeast Florida", Proceedings, Coastal Sediments '91, ASCE, pp. 2130-2145.
Olsen Associates, Inc. (1995) "Fisher Island, Florida: Beach Restoration: Physical Monitoring
Report No. 4", Jacksonville FL.
Oman, H. (1986) "Energy Systems Engineering Handbook", Prentice-Hall, Inc., Englewood
Pankow, V. R. (1987) "Dredging Applications of High Density Polyethylene Pipe", Proceedings,
19th Dredging Seminar, Center of Dredging Studies, TAMU-SG-88-103, Texas A and M
University, College Station, Texas.
Richardson, T. W. (1976) "Beach Nourishment Techniques, Report 1: Dredging Systems for Beach
Nourishment From Offshore Sources", Hydraulics Laboratory, U. S. Army Waterways Experiment
Station, Vicksburg, MS.
Slatton, R. D. (1986) "Aragonite: An Alternative Beach Nourishment Solution", Florida Shore
and Beach Preservation Association, pp. 25-32.
Turner, T. M. (1996) "Fundamentals of Hydraulic Dredging", ASCE Press, Second Edition, New
York, NY, 258 pages.
Wasp, E. J., J. P. Kenny, and R. L. Gandhi (1977) "Solid-Liquid Flow: Slurry Pipeline
Transport", Trans Tech Publications, ISBN 0-87849-016-7, Germany.
MECHANICS OF HYDRAULIC DREDGING
AND SLURRY TRANSPORT
MECHANICS OF HYDRAULIC DREDGING AND SLURRY TRANSPORT
Dredges remove sand from the seabed and both lift the sand to a higher elevation, thereby
increasing its potential energy, and transport the sand over distances which can be fairly long.
Both the increase in potential energy and friction losses occurring in the transport to a distant
location require energy. Additionally, with the main dredge pump on the vessel, a limitation
exists on the pump intake due to the vapor pressure of water and the related concerns of pump
and intake line cavitation. It will be seen that in conveying the sand water mixture, called a
"slurry", a minimum water velocity is required to ensure that progressive deposition does not
occur in the pipeline resulting in eventual clogging. Since coarser sediments have higher fall
velocities than finer sediments, the required velocities in the pipeline to ensure no deposition are
greater for the coarser sediments. The energy required for transporting the slurry increases with
the approximate square of the velocity, thus requiring greater energy for the larger sediments
which, as we have seen, are preferable for beach nourishment. A second relationship of interest
to be shown is that since the energy requirements depend on pipe size, the energy required to
pump a certain volume of sand is inversely related to the diameter of the discharge line. Of
course, larger dredges and thus larger pipelines are usually justified for the larger volume
projects, on the order of 1 million cubic yards (0.77 million cubic meters) or greater. These and
other factors and mechanisms related to slurry transport are considered in greater detail below.
The objective of this appendix is to introduce the essential hydraulic and energy fundamentals
related to dredging and slurry transport. An understanding of the material presented in this
chapter should equip the Reader with the basics and essentials for preliminary analysis of energy
requirements for a dredging project. Although the focus is on pipeline dredges, the same
fundamentals apply to hopper dredges. This appendix is not intended to provide an exhaustive
treatment on dredging, thus the Reader is encouraged to access more complete references for
additional information and will find the following very informative (Turner, 1996; Wasp, et al
1977: Herbich, 2000)
A.2.0 SLURRY TRANSPORT BY PIPELINE
A.2.1 Relationship Between Slurry Specific Gravity and Volumetric Concentration of
The slurry (water and sand mixture) specific gravity, SGL, and volumetric proportion of solids,
Cv, are related by
SG = SG (1 C) + SG C =SG + C (SG SGw) (A-l)
in which SGL, SGw and SG, are the specific gravities of the slurry, water and sediment,
respectively. Figure A.1 presents this linear relationship between volumetric concentration and
slurry specific gravity for a sediment specific gravity of 2.65, the usual approximate value for
quartz and other common materials including shell and a sea water specific gravity of 1.03. Note
that a volumetric concentration of 30% is equivalent to a slurry density of 1.52 and is the upper
practical limit of design sediment concentrations transported by pipeline.
Slurry Concentration by Volume, C,
Figure A.1. Relationship Between Slurry
Concentration by Volume and Slurry
Specific Gravity for Normal Sands and Sea
A.2.2 Relationship Between Volume Concentration in Pipeline and Volume in Place
As shown, the quantity of sediment transported in the slurry can be defined in terms of the
sediment volume concentration, Cv, or the slurry specific gravity, SGL. Considering the sediment
concentration by volume in the slurry discharge through the pipeline, Cv, the volume rate at
which sediment is transported is simply Q Cv where Q is the total discharge. When this slurry is
discharged and allowed to dewater, the resulting volume will contain a proportion of pore spaces,
p. Thus, the volumetric rate at which the "in-place" sediment volume is being delivered, Q1, is
in which p is the non-dimensional porosity, and is on the order of 0.3 to 0.4 for normal
consolidation packing densities. We will have occasion to use this expression later in this
appendix. In applying Equation (A-2), it is necessary to use the average concentration by volume
which differs from the design value as will be discussed later.
.... .... . ... .. ... .... ...
A.2.3 Velocities Required for Non-Depositional Conditions
As mentioned previously, the velocities in the intake and discharge lines must be sufficiently
large to prevent progressive deposition. Most of this sediment transport occurs in the suspension
mode, although a portion is by bed load on the bottom of the pipe, Since large sediment particles
have higher fall velocities than small particles, it is logical that larger particles require higher
velocities than finer particles in order to avoid progressive deposition. Additionally, as would be
anticipated, the required velocities for non-deposition, VR, are larger for higher sediment
concentrations and larger pipeline diameters. Figure A.2 presents results adapted from Turner
(1996) and quantifies the velocities required to avoid deposition for various normal beach
nourishment sized sediments in a pipeline of 20 inch diameter. It is seen that the velocities range
from approximately 8 feet/sec to 18 feet/sec for sediment sizes varying from 0.1 mm to 10 mm
diameter for a maximum volumetric concentration of 0.3. As noted, the required velocity for
non-deposition, VR(D), increases with pipe diameter, and is given by Turner as
VR(D)= VR(20)(0 )-' (A-3)
o5 * *........... .... ... ...... ........... ... ............... . se g S I o .......
e 14 : .: ....:---. -. ::_-
S: Sed S;ze 0 3 mm
Sed Size 0.1 mm
0.0 0.1 0.2 0.3
Slurry Volume Concentration, CV
Figure A.2 Minimum Velocities for Non-deposition vs
Slurry Concentration and Sediment Size. Pipe Diameter
of 20 inches. Adapted From Turner (1996).
in which D is the pipe diameter in inches and VR (20) is the required velocity for non-deposition
from Figure A.2 for a pipeline diameter of 20 inches. As an example, consider a sediment of 0.3
mm diameter at a volumetric concentration, Cv = 0.20 (corresponding to a slurry specific gravity
of 1.35) to be transported in a 40 inch pipeline. The required velocity for a 20 inch pipeline from
Figure A.2 is 12.4 ft/sec. Thus, the required velocity for a 40 inch pipeline is
R(40) = 12.4 (0).5 = (12.4)(1.41) = 17.5ft/sec (A-4)
A.2.4 Allocation of Total Head Produced by the Dredge Pump(s)
The total head provided by the dredge pump(s) is allocated to increase potential energy of the
solids and water and to account for energy losses. The increase in potential energy is manifested
by the increase in elevation of the solids from the seafloor to the final discharge point whereas
the energy losses are distributed along the flow path from the intake to the discharge point. Each
of these is discussed below with the losses expressed in terms relating to the hydraulic head,
V2/2g where g is gravity.
A.2.5 Components of Energy Requiring Consideration in the Intake and Discharge Lines
A.2.5.1 Increase in Energy Due to the Increasing Elevation of the Solids
The hydraulic head, hSG, required to lift the solids from the seafloor to the dredge pump a vertical
distance, h1, expressed in terms of the slurry specific gravity, SGL and that of water, SG,, is
h= (SG -SGw)h, (A-5)
where, as before, SGL is the specific gravity of the slurry, SGw is the specific gravity of the
water, and hi is the vertical distance from the sea floor to the dredge pump intake and it has been
assumed that the vertical location of the dredge pump intake is at the mean water line. If the
dredge pump were located at an elevation, h', above the mean water line, the head required
hsG = (SGL -SG) h,+SGLh' (A-6)
Additionally, since the discharge elevation will be at a distance, ZD above sea level, this
additional hydraulic head, hD, a requirement which occurs on the discharge side of the dredge
hD =SG Z (A-7)
D L D
A.2.5.2 Velocity Head Required to Accelerate Slurry
In preparation for discussion of energy losses in the pipeline, the velocity head is a term that is
common to all hydraulic problems and represents the head, measured in units (for example, we
will use feet) of fresh water, required to accelerate the slurry from a state of rest to the velocity
in the pipeline. This velocity head for our slurry flow is given by
H =-SG (A-8)
v 2g L
where g is gravity.
A.2.5.3 Entrance Head Losses
The entrance losses are expressed as
He=K -SGL (A-9)
in which Ken is the entrance loss coefficient. A reasonable value of unity may be taken for the
entrance loss coefficient.
A.2.5.4 Friction Head Losses in Intake and Discharge Lines
Friction losses may be represented in terms of several established relationships. The two most
popular are the Darcy Weisbach equation and the Chezy equation, each of which is expressed
below. The Darcy Weisbach relationship is
H- V2 (A-10)
in which f is the so-called Weisbach Darcy friction factor and is non-dimensional and is the
pipeline length and this equation can be applied to determine the losses in both the intake and
discharge lines. The Chezy equation is
in which C is the Chezy coefficient and has units of square root of length over time. Comparing
the above two equations, it is evident that f and C are related by
It is seen that each of the above equations contains an empirical coefficient. Approximate values
of these coefficients depend on the pipeline size and the concentration of the slurry. Turner
(1996) represents the head loss in feet of water, hL, for slurry transport as
hL = 0.0109 ( 100) 1.s5
C D 1.165
in which e is the pipeline length, C is the Hazen-Williams coefficient which depends on sediment
size and slurry specific gravity as shown in Figure A.3, D is the pipeline diameter in inches and,
V is the average pipeline velocity in feet per second. It is seen that the velocity exponent in Eq.
(A.13) is slightly less than the value of 2 which appears in the other head loss relationships. Eq.
(A.13) is applicable for calculating losses in the intake and discharge lines.
Slurry Volume Concentration, Cv
Figure A.3. Hazen-Williams Coefficient, C, vs Slurry
Concentration and Sediment Size. Pipe Diameter of 20
A.2.6 Suction Limitations in the Intake Line
Perhaps somewhat surprisingly, water has a characteristic similar to a tensile strength which is
represented by the vapor pressure. If the pressure in water is lowered below that value, the water
will be transformed into a vapor (boil). This characteristic of water imposes limitations on the
minimum pressure which can occur in the intake line of the dredge. The pressure at the dredge
intake can only be lowered to a pressure equivalent to approximately 5 feet of water (320 psf).
This leaves approximately 28 feet for the various head losses and potential energy increases on
the suction side of the dredge. It is instructive to examine the consequences imposed by this
Suppose that the dredging depth is h,, and that the specific gravity of the slurry is SGL. The total
available head, hTi, required to elevate the solids and the slurry and provide the additional head
hr = 28feet = ht(SGL SGw) + SGL (1.0 + Ken) + hL (A-14)
in which the various terms are expressed by equations given earlier. Several examples will be
presented later to illustrate the significance of this equation. It can be seen that an upper limit on
the volumetric concentration, (Cv)max, for a given dredging depth, hi, can be expressed that,
without any velocity would cause vapor pressure to occur at the pump intake, by setting the
velocity to zero in the above equation as
in which all head loss terms have been set equal to zero and the normal sea water and sand
specific gravities have been used. Of course, the actual maximum volumetric concentration in the
intake line would be significantly less that the value given by Eq. (A-15) due to the head losses
associated with the minimum velocity required for non-deposition.
A.2.7 Ladder Pump
The limitations imposed on intake conditions by the vapor pressure of water can be avoided by
the use of a so-called "ladder pump" which is a submerged pump mounted on the ladder
reasonable near the intake. The purpose of the ladder pump is to produce a positive pressure on
its discharge side and thus on the intake side of the main dredge pump. It is reasonable for the
ladder pump to produce on the order of one-half the horsepower of the main dredge pump.
Ladder pumps are especially effective for relatively deep water dredging.
A.2.8 Booster Pumps
For a particular dredging scenario, including a given horsepower dredge and pipeline size, with
increasing discharge pipeline lengths, the maximum possible pipeline velocity decreases to a
value such that with greater lengths, the maximum possible velocity will be less than that
required for non-depositional conditions. For such cases and those in which the head losses and
associated reduced production decrease efficiency to less than desired, one or more booster
pumps may be introduced into the discharge line. In the beach nourishment applications of
interest here, the booster pump may be floating, mounted on a jack up barge or located on land.
In cases where a single booster pump is to be installed, it is customary to locate it approximately
40% of the distance to the end of the discharge pipeline (Turner, 1996). The reason is to avoid
concerns of cavitation in the intake of the booster pump. Most dredge pumps produce 200+ feet
of head and booster pumps must be spaced to prevent the head from being reduced to a value that
would result in cavitation in the intake of the next booster pump. Figure A.4 presents the
required distances between pumping stations for a sediment size of 0.5 mm and various pipeline
sizes. In this figure, the velocities have been taken as the minimum to prevent non-deposition.
Figure A.5 presents similar information for a 24 inch pipeline and three sediment sizes. It is seen
from these two examples that there are some advantages (greater spacing of pumping stations) of
using larger pipelines; however, these advantages are not as much as might be expected. This is
due, in part, to the higher velocities required for non-deposition in the larger pipelines.
'.. i Sediment Diameter =0.5 mm
0 ') : : . . .. ........ . .. . .
|.10000 ".. . ...-... ... . .. .....
0.0 0.1 0.2 0.3
Volume Concentration, Cv
Figure A.4. Distance Between Pumping Stations vs
Volume Concentration, Cv for Several Pipe Diameters.
Pipe Diameter = 24 inches
0 :d .'
0.0 0.1 0 0.3
Volume Concentration, Cv
Figure A.5. Distance Between Pumping Stations vs
Volume Concentration, Cv for Several Sediment Sizes.
A.3.0 Energy Considerations
A.3.1 Total Horsepower Requirements
The total horsepower requirement, HP, is given by
HP= YLQ(hT+ hL) YLQH (A-16)
where the 550 factor converts feet pounds per second to horsepower and H is the total head
delivered by the pump. The first term in the parenthesis represents the increase in potential
energy of the slurry as its elevation is increased from the ocean floor to the discharge point and
the second term represents the total head losses in the intake and discharge lines. The product YL
Q H is the rate at which the number of weight units are being increased in head due to the
dredging process. It is emphasized that the discharge term included in this expression (Q) is the
total water and slurry volumetric discharge.
A.3.2 Pump Characteristics and Efficiency
The operating characteristics of all centrifugal pumps are described by operating curves
expressed in terms of discharge and head produced by the pump at various pump rotation speeds
in revolutions per minute (RPM). The two solid lines in Figure A.6 are examples of these curves.
These curves are provided by the pump manufacturer and for a pump rotating at a particular
speed, the greatest discharge would be with zero head imposed on the pump as represented by the
intersection of the "curve" with the horizontal axis in Figure A.6. With increasing head imposed
on the pump, the discharge decreases until it becomes zero at the intersection of the curve with
the vertical axis. Obviously, the horsepower produced by the pump at either of these two limits is
zero. The output horsepower of the pump can be computed for any location along the curve by
simply applying Eq. (A-16).
Pipe Dia.i= 24 inches
S.......Sedsi. Size = 02 mm
S00 Discharge Line = 1 mile
.': Intake Ladder= 100feet
S200 ., ,0 Dredging Depth 40 feet
0 10 20 30 40 50 60 70 80
Pump Discharge (cfs)
Figure A.6. Illustration of Pump and Dredge System
A.3.3 Matching Pump Characteristics and Dredging Requirements
Consider a given dredging scenario with the dredging depth, pipeline size and length and slurry
concentration established. The controls available to the dredge operator are the rotation speed of
the pump and the slurry density through control of the proximity of the intake to the sand bank
being accessed. The minimum discharge is that associated with the minimum velocity to
maintain non-depositional conditions whereas the maximum discharge is that which would
produce cavitation at the intake to the dredge pump (Section A.2.6). As the discharge increases
from the minimum, the overall head requirements depend approximately on the square of the
discharge in the pipeline and can be calculated by equations presented previously in this
appendix. The example in Figure A.6 is for the case of a 24 inch pipeline, a sediment diameter of
0.2 mm, an intake line of 100 feet, a discharge line of 1 mile, a dredging depth of 40 feet and
volumetric sediment concentrations of 0.1 and 0.3. The two discharge-head relationships are
shown as the dashed lines. For each of these lines, the lower point is that associated with non-
depositional conditions and the upper point is controlled by the suction pressure at the intake. It
is seen that a dredge pump of 500 RPM or 700 RPM could be used to pump a volumetric
concentration, Cv of 0.1; however, for Cv of 0.3, the velocities would be below that required for
non-deposition at 500 RPM and thus a RPM of 700 is required. The discharge and head that
would occur are defined by the intersection of the curves for the pump characteristics and the
dredge system curves (the dashed curves in Figure A.6). As an example, for 700 RPM, the
discharge of 41 cfs and 35 cfs would occur for Cv values of 0.1 and 0.3, respectively.
A.4.0 Practical Considerations: The Dredge Efficiency
Although previous considerations in this appendix have represented sand slurry concentrations as
uniform along the pipeline and constant with time, the nature of the dredging operation is such
that such conditions are not possible. A practical approach to account for these unsteady and non-
uniform conditions along the pipeline is to define a "dredge efficiency" which is less than unity
and is to be applied to the design quantities to determine the production quantities. The
appropriate dredge efficiency for a particular project will depend on its conditions; however,
Turner (1996) recommends a range of 0.4 to 0.5. The cause of this inefficiency is that, for
various reasons, it is impossible for the dredge to continuously access sand at the design
concentration, Cv, which should be considered a maximum and that to be applied for determining
limitations in the pipeline (Section A.2.6). However, dredging quantities should be based on the
product of the design concentration and the dredge efficiency.
A.5.0 Energy Requirements and Costs of Dredging
To complete the energy story, it is useful to examine the conversion efficiency of diesel fuel to
horsepower and also to consider other possible sources of energy for dredging. Energy, E, is
equal to the product of power, P, acting over a time interval, t (E = P t) and can be expressed in
terms of horsepower hours, kilowatt hours, etc. For costing purposes, it is also useful to express
the energy requirements for a certain project in terms of the number of gallons of diesel to
transport a cubic yard of sand to its intended location. It is noted that in the United States, there
are now several dredges powered by electricity.
The following equivalencies exist (Oman, 1986): 1 Kilowatt hour (KWH) = 0.746 Horsepower
hour (HPH), 1 gallon of Diesel fuel = 0.045 Horsepower hour. These relationships allow us to
express the energy usage in common terms which are independent of the current cost of fuel. In
addition, dredge pump efficiencies are on the order of 70% and must be taken into account.
A.6.0 Pipeline Life
A moving slurry is an abrasive agent and will cause wear (erosion) of the conveying pipeline.
Slurry pipelines can be constructed of either steel or High Density Polyethylene (HDPE). The
costs to replace and the resistance to wear of these two materials differ with the HDPE more
wear resistant than steel. Wear tends to occur along the lower elevations of the pipe cross-section
due to the concentration of materials there and thus the operating life of pipelines can be
extended by rotating the pipelines thereby distributing the wear around the perimeter of the pipe.
In a laboratory test, Pankow (1987) found that the erosion of a HDPE pipe varied between 1%
and 30% of the wall thickness due to conveying 2.6 million cubic yards and that the amount of
erosion depended more on the size and angularity of sediment than the volume of material.
A.7.0 Examples Illustrating Material Presented in This Appendix
A.7.1 Example 1. Dredge Production Limitations Imposed by Intake Line
This example considers the limitations imposed on the dredge production imposed due to the
vapor pressure and the minimum velocities to maintain non-depositional conditions discussed in
Section A.2.6. For this example, we consider a volumetric concentration, Cv of 0.2, a sediment
diameter of 0.5 mm, three different intake pipeline diameters, a ladder length of 100 feet and a
range of dredging depths. The results are presented in Figure A.7 where it is seen that in general
with increasing dredging depth, the required head (of the total 28 feet available) to lift the
sediments increases leaving less head for the velocity head related terms and resulting in a
decrease in dredge productivity. As the dredging depth increases, the velocity necessarily
decreases and eventually falls below the value required to maintain non-depositional conditions
which is the upper limitation of the dredging depth plotted. It is recalled that for this example, we
have maintained the slurry volumetric concentration, Cv constant and have not considered any
dredge pump power limitations. For example, it would certainly require greater horsepower for
the 48 inch intake line and the associated productivity than for the 24 inch intake line and its
productivity. In most cases, the smaller dredges will be specified for the smaller dredging depths.
One avenue available to the dredge operator to dredge in greater water depths than presented in
Figure A.7 is simply to reduce the sediment volumetric concentration for the larger dredging
depths. Additionally, to maximize production, the dredger will usually attempt to pump the
maximum concentration allowable for each dredging depth. This will be explored in the
A.7.2 Example 2. Maximum Production for Each Dredging Depth
This example differs from Example 1 in that the slurry concentration will be varied with each
dredging depth to obtain maximum dredge production. The case of a 24 inch pipeline will be
presented and compared with the productions obtained with a 24 inch pipeline as considered in
Example 1. All other variables will be kept the same. The results are presented in Figure A.8
0 10 20 30 40 50
Dredging Depth (ft)
Figure A.7 Production Rate vs Dredging Depth, Various Intake Pipe
Sizes, Sediment Diameter = 0.5 mm, Volume Concentration, Cv = 0.2.
Note: Maximum Dredging Depth Shown Controlled By
Note: Ma:rur Dredging Depth Sh:wn Controlled By
Minimum Velocity for Non-deposition for Case of....
Constant C = 0.2;
n i -,- i --- 1 ; i : i -,- i i -
0 10 20 30 40 50
Dredging Depth (ft)
60 70 80
Figure A.8. Production Rate vs Dredging Depth, Intake Pipe Size
= 24 inches, Sediment Diameter = 0.5 mm, Volumetric
Concentration, Cv = 0.20 and Variable to Maximize Production.
...... ...... ...... Note: M-aximum Dredging Depth Shown Controlled by
.......:. .......:. ....... ..... ......
.......4. M nium Velocity.for. Nondeposition.............
. .... . .. ... ....... .. ...... ...... . ..... ....... .. .... :.. ....... ... ... ...... .. ...... ... . ...... .... .. ......
. . .
P ,. ... .. .
'P i.2 nh
Pipe Dia. = 12 inches
I f I ; I
where it is seen that the production at the smaller dredging depths are greater due to the increased
slurry concentrations; however, the differences decrease with greater depths. Additionally,
because the concentrations are reduced with greater depths, it is possible to dredge to a greater
depth than is possible with the fixed concentration, Cv = 0.2. For the case in which dredge
production is maximized, the slurry concentration varies from 0.3 at the smaller depths to 0.135
at a depth of 80 feet, the maximum shown in Figure A.8.
A.7.3 Example 3. Dredge Production vs Pumping Distance
In this example, the productivity and pumping distance of 24 inch intake and discharge lines are
examined for the case of sediment sizes of 0.2 mm and 0.5 mm and for the case of 2,400
Horsepower available. The results are presented in Figure A.9 for various dredging depths which
are annotated on the individual points. The production has been maximized by adjusting the
sediment concentration as illustrated in the previous example. A discussion of the results in
Figure A.9 will assist in understanding some of the interrelationships. First, a direct result of the
smaller friction losses for the smaller sediment, is that for a particular dredging depth, the smaller
sediment is pumped a greater distance with a higher production rate. The break in slope at
approximately 35 feet is a result of the reduction in slurry concentration for greater depths and a
slurry concentration, Cv = 0.3 for depths less than 35 feet. Finally, the increasing pumping
distances for the greater depths is a result of the smaller velocities required in the intake line to
reduce the velocity head losses to accommodate a greater head required to lift the sediments a
greater distance and the associated reduced losses per unit discharge pipe length.
3000 : : : : : : : : :
5 f (Dredging Depth)
S: Sed Size =
0200 .....- ..... ... .. . .' ..
. : : ft
: ..... .: :
i I ; I i : I I i ; I : ,
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Maximum Pumping Distance (ft)
Figure A.9. Maximum Production Rate vs Maximum Pumping
Distance for Two Sand Sizes and Various Dredging Depths. Total
Available Horsepower = 2400.