International Journal on Public Works, Ports & Waterways ... · 14 Sediment Resuspension and Cycling due to Wave Groups Samantha Kularatne Predicting the transport of sediments in

International Journal on Public Works, Ports & Waterways DevelopmentsNumber 94 • March 2004

International Association of Dredging Companies

Terra et Aqua – Number 94 – March 2004

Terra et Aqua is published quarterly by the IADC, The International Association of Dredging Companies.

The journal is available on request to individuals or organisations with a professional interest in the

development of ports and waterways, and in particular, the associated dredging work.

The name Terra et Aqua is a registered trademark.

Editor

Marsha R. Cohen

Editorial Advisory Committee

H.L.H. Smink H.W.J. Poiesz, Chairman A.G.M. Groothuizen

H.A.J. Fiers C.P.I.M. Dolmans P.G. Roland

H. De Vlieger R. Vidal Martin C. Meyvaert

IADC Board of Directors

R. van Gelder, President T. Tawara, Vice President C. van Meerbeeck, Treasurer

P.G. Roland M. Montevecchi G. Vandewalle

O.F. Verkerke

Please address inquiries to the editor.

Articles in Terra et Aqua do not necessarily reflect the opinion of the IADC Board or of individual members.

© 2004 IADC, The Netherlands

All rights reserved. Electronic storage, reprinting or abstracting of the contents is allowed for

non-commercial purposes with permission of the publisher.

ISSN 0376-6411

Typesetting and printing by Opmeer Drukkerij bv, The Hague, The Netherlands.

Cover:When large quantities of rock are not easily available for breakwaters and shore protection against waveaction, concrete armour units are the best solution. Recently a new, cost-efficient armour unit has beendeveloped (see page 3).

IADC

Constantijn Dolmans, Secretary General

Duinweg 21

2585 JV The Hague, The Netherlands

Tel. +31 (70) 352 3334, Fax +31 (70) 351 2654

E-mail: [email protected]

http://www.iadc-dredging.com International Association of Dredging Companies


1

CO N T E N T S

2 Editorial

3 Introduction of the Xbloc® Breakwater Armour Unit

Pieter B. Bakker, Martijn Klabbers and J.S. Reedijk

A new, six-sided concrete armour unit provides a cost-effective solution for the age-oldchallenge of protecting harbours and the shorelines from severe wave action.

12 The Exploitation of Cockle Shells

Martin Zwanenburg

At the CEDA Dredging Days conference “Specialist Dredging Techniques, InspiringDredging Solutions”, an IADC Young Authors Award was presented to a research paperon environmentally sensitive cockle dragheads.

14 Sediment Resuspension and Cycling due to Wave Groups

Samantha Kularatne

Predicting the transport of sediments in nearshore environments and their affect on coastalstability is essential. This paper, reporting on field experiments in this subject, won theIADC Young Authors Award at COPEDEC IV in Sri Lanka.

28 Books/Periodicals Reviewed

A CDROM on Dredging Operations and Environmental Research (DOER), and twobooks, one on the history of hydrography and the other, an overview of importantdredging projects, are discussed.

30 Seminars/Conferences/Events

Scheduled for 2004 are the new PAO Seminar on Environmental Aspects of Dredging, the WEDA XXIV in Orlando, Florida, and WODCON in Hamburg, Germany.


2

EDITORIAL

For many years the IADC has presented its International Seminar on Dredgingand Reclamation to postgraduate students and professionals in dredging relatedfields. One of the first questions asked during the seminar is: “What is Dredging?”It is a question that cannot be asked, nor answered, often enough. For while we inthe industry realise that dredging is an environmentally sound, high-tech tool foreconomic and social betterment, it should be clear to us by reading newspapersthat well-meaning citizens often see the situation differently.

How can we clarify what dredging means for the economy, the environmentand social well-being? A recent Associated Press article in January laments “witha public unconcerned about the health of the watery highways, Louisiana’s keyshipping routes are getting so bumpy and silted that some deep-draft ships are notable to make it into port”. Public indifference and even sometimes antagonismmust be addressed, and it is incumbent upon those of us in the field to confront theissues that cause concern.

International trade depends on dredging. Dredging helps develop ports andwaterways; it deepens existing harbours and builds new ports, thus improvingmarine transportation facilities. Dredging reclaims and creates land whereresidential, recreational and industrial complexes can be built to accommodatean ever-growing world population. Dredging makes it possible to lay pipelinesoffshore for gas and oil. There are a thousand and one ways in which dredgingimproves the economic climate of a country and through that brings socialimprovements by raising the standard of living for the indigenous peoples.

The articles that appear in Terra are often quite technical: they reflect theconfidence and the large financial investments that private dredging companiesplace in research and development. In addition, such events as the IADC YoungAuthors Awards, which are featured in this issue, are the industry’s way ofinvesting in young people. Perhaps more than anything when one examines thedredging industry, its overriding quality is its eye for tomorrow’s world. It is anindustry focussed on the future – developments in world trade and globalprosperity lean heavily on the availability of efficient maritime infrastructure fornow and for later.

Robert van GelderPresident, IADC Board of Directors

Abstract

Over the past two years Delta Marine Consultants hasdeveloped a new breakwater armour unit called Xbloc®.The new armour unit has proven to be reliable and easyto use leading to significant cost savings. The newarmour development included extensive 2-D and 3-Dphysical model tests, finite element stress calculations,prototype drop tests, a production and handlinganalysis, and placement studies.

Whereas originally concrete armour units were simpleheavy shapes, the development in the 1960s and 70sfocussed more and more on slender shapes. The advantage of slender shapes is the high hydraulicstability caused by improved interlocking. As theseshapes turned out to be vulnerable to breakage, a morerobust shape was developed in the 1980s. Althoughthis unit combined a relatively high hydraulic stabilitywith a robust shape, a new slender unit was developedin the 1990s with a slightly higher hydraulic stability buta larger vulnerability to breakage. Therefore, the mainfocus of the DMC armour unit development was tocreate a unit with a hydraulic stability that is comparableto the present state of the art units, but with a robustshape.

The reliability of the Xbloc® was proven during thephysical model tests. The structure proved difficult todamage, even at a significant exceedance of the designwave height. Furthermore the unit provides a largesafety margin between the start of damage and failureof the armour layer. The structural stability of thearmour unit was proven by the finite element stresscalculations and the prototype drop tests.

The Xbloc® (Figure 1) is easy to use because of thesimple mould, the simple handling and storage methodsand especially because of its easy placement on thebreakwater slope. The placement of the presentinterlocking armour units is subject to very stringentspecifications about the orientation of each armour unit.Obviously this decreases the speed of construction. No such specifications apply for the placement of thenew unit as it easily finds its position on the slope.

Introduction of the Xbloc® Breakwater Armour Unit

Pieter B. Bakker, Martijn Klabbers and J.S. Reedijk

Introduction of the Xbloc®

Breakwater Armour Unit

3

Pieter Bakker obtained his MasterDegree in Civil Engineering from theDelft Technical University in 2001.Since then he has been working atDelta Marine Consultants as a coastalengineer involved in many offshoreand coastal projects such as break-waters, artificial reefs, dredgingoperations, offshore wind farms,heat recirculation studies and portoperability assessments. Pieter B. Bakker

After gaining his bachelors degree in1994, Martijn Klabbers graduated fromDelft Technical University in CivilEngineering in 1998. Working ascoastal engineer for Delta MarineConsultants his experience includesthe design of harbours, breakwaters,causeways, shore protections andbeach replenishments, supervision ofphysical model tests and wave studiesincluding finite element diffractioncalculations. He has also done sitesupervision in various marineconstruction works overseas.

Martijn Klabbers

Bas Reedijk obtained his MasterDegree in Civil Engineering fromDelft Technical University in 1988, andjoined Delta Marine Consultants in1990 as a coastal engineer. He has beeninvolved in a large number of projectssuch as the Ramspol storm surgebarrier and various port and break-water projects all over the world.Since 2002 he is the head of theCoastal Department of Delta MarineConsultants.

Bas Reedijk

Introduction

Concrete armour units are generally applied in break-waters and shore protections (Figure 2). The function ofthe armour layer in these structures is twofold. Firstly itmust protect the finer material below the armour layeragainst severe wave action. Secondly the armour layermust dissipate the wave energy in order to reduce thewave run-up, overtopping and reflection. These twofunctions require a heavy, but porous armour.

A typical cross section of a breakwater armour layeris shown in Figure 3. The cross section of a shoreprotection is similar, but instead of a core, the soilmaterial is protected. In both structures, the armourlayer is placed on top of a filter layer which covers thefine material in the core of the breakwater (or the soilmaterial of the shore). This filter layer must prevent thatthe fine material washes away through the pores in thearmour layer. Near the seabed the armour layer isgenerally supported by a rock toe.

As the armour layer is an expensive part of the wholestructure, it is worthwhile to put effort in theoptimisation of the armour layer design. Depending onthe local situation it can be economical to apply a rockarmour layer, if sufficiently large rock is available nearthe site. If this is not the case, concrete armour unitsare the best solution. However as there are variousconcrete armour units available and the choice hasgreat financial consequences, the choice of the armourunits should be made carefully.

In this article, the development is described of a newconcrete armour unit called Xbloc®. This armour unit,which is reliable and easy to use leads to significantcosts savings as the concrete volume applied in thearmour layer is low. Although concrete armour unitscan be applied both in breakwaters and shore

protections, the focus in the remainder of this articlewill be on breakwater applications.

HISTORY OF BREAKWATER DEVELOPMENT

The development of breakwater construction is closelyrelated to the development of ports around the worldover the centuries. In the ancient times harbours wereconstructed in sheltered locations such as rivermouths, bays and areas sheltered by islands wherethe wave climate is calm.

In time nautical trade developed and more harbourswere built. Near more densely populated areas, portswere constructed in less sheltered locations where theport operations were hindered by the wave climate. In order to reduce the waves entering the harbourconstructions were made of wood, stone or evenconcrete. The constructions made in these daysinclude wooden pile rows, masonry quay walls andrubble mound structures. Over the years thesestructures have evolved into breakwaters as they arepresently known (Figure 4).

As ships became bigger, the required water depth inthe ports increased to cope with the increased draught.The location of the harbours therefore shifted seawardwhich resulted in increased wave exposure. Longerand wider breakwaters were required and as theyextended further seaward they were subjected tohigher waves.

In order to withstand these high waves breakwaterswere built that consisted of an outer layer — armourlayer — of large heavy rocks. However, the applicationof rock is limited as the maximum rock size is limitedand in some parts of the world no large size rock orgood rock quality was available. Therefore, for locationswhere a rock armour layer was impossible, concretearmour units were developed. Nowadays most of themajor ports in the world are protected using break-waters with concrete armour units.

Development of concrete armour units after 1950Before World War II the only concrete armour unitsthat were used were cubes. In a cube armour layer – just like a rock armour layer – the stability against thewave action is derived from the weight of the armourunits. Each block on the slope must be sufficientlyheavy to withstand the wave forces. Therefore thecubes in a breakwater armour layer are always heavyelements.

As opposed to stability owing to the armour unit’sweight, another stabilising mechanism was developedafter 1950 when armour units were developed whichare interlocking. Because of the more slender shapes,these armour units not only use the weight of each


4

Figure 1. The 4 m3 Xbloc® with one of the engineers.

individual element, but also of the surroundingelements. This leads to a higher hydraulic stability ofthe units. The first interlocking unit on the market wasthe Tetrapode (1950). Apart from the interlockingfeature, another advantage compared to the cube wasthe increased porosity of the armour layer which isrequired for wave energy absorption and reduction ofwave run-up.

In the period between 1950 and 1980 a number ofdifferent armour units were developed based on theprinciple of stability through the combination of unitweight and interlocking (Figure 5). In fact during thisperiod the armour units became more and more inter-locking as a result of the increasingly slender shapes.The best example of hydraulic stability is the Dolos(1963). Owing to the efficient interlocking propertiesof this block, the required unit weights reducedsignificantly compared to the simple cube elements.

Looking back at the development of the Dolos, it canbe concluded that one aspect was to a certain degreeoverlooked. As the units became more and more slender,the structural stability decreased as they becamevulnerable to breakage. Too much focus was put onhydraulic stability (interlocking) whereas structuralstability was undervalued. This became clear in 1978when the Sines breakwater in Portugal collapsed dueto broken armour units. The Dolos units applied wereso slender (for optimal interlocking) that they broke intopieces because of wave action. Once the elementswere broken, the interlocking mechanism vanished andthe entire armour layer failed.

In 1980 the Accropode was introduced. As this unitwas the first single layer armour unit, significant costsavings were made compared to the double layer units.This is illustrated in Figure 6.


5

Figure 2. Concrete armour units are generally applied in breakwaters (left, Scheveningen, The Netherlands) and shore protections

(right, Scarborough, U.K.).

Figure 3. Typical cross section of a breakwater armour layer.

Figure 4. The ancient Port Claudius near Ostia, Italy including

primitive breakwaters (±50 AD) ref. ABC-klubben.

Compared to the Dolos, the Accropode is a robust andbulky unit which is far less vulnerable to breakage. As the interlocking capacities were still relatively high,there was a good balance between hydraulic andstructural stability. Owing to this balance and the costssavings, the Accropode has been a successful unitsince its launch.

One of the latest developments has been the Core-loc®,which is a registered trademark of the US Government.Developed to repair damaged Dolos breakwaters theCore-loc® is a mix of the Dolos and the Accropodeshape. The configuration of the legs is similar to that ofthe Accropode while the shape of the legs has strongsimilarities with the Dolos. The hydraulic stability isslightly higher compared to the Accropode, but theslender shape of the unit makes it more vulnerable tobreakage. It therefore seems that the balance betweenstructural and hydraulic stability has been shifted againtowards hydraulic stability.

Uniformly placed armour unitsThe elements described above are all randomly placedunits. A whole different type of armour units is formedby the uniformly placed elements. Examples of suchelements are the Cob, the Shed, the Diahitis and theSeabee. These revetment-like elements gain theirstability not from their weight or from interlocking butfrom friction between the surrounding elements. As placement of these elements is very difficult underwater, they are normally only applied where construc-tion can be done above low water. Therefore no furtherattention is paid in this article to uniformly placed units.

DEVELOPMENT OF THE XBLOC®

Motive for development of the Xbloc® armour unitDuring a breakwater rehabilitation project on FregateIsland, the Seychelles, DMC made the detailed designand provided site assistance during execution of theworks. The armour layer applied consisted of Accropode units. Experiences on this project broughtup the idea to develop an improved armouring systembased on single layer application. The new unit shoulddecrease the weak points of the existing units whilemaintaining the strong points. The new unit should therefore have a right balancebetween hydraulic and structural stability. A strongfocus on a high hydraulic stability would result in aslender unit vulnerable to breakage. Therefore the unitshould have a hydraulic stability in the same order ofthe latest single layer armour units combined with ahigher structural stability.

Another starting point was to have a unit that is easy to apply for a contractor. The placement on the breakwaterslope should be easy, as this is considered one of the mainshortcomings of the existing single layer armour units.

Summarised, the main objectives for the Xbloc®

development were to create an armour unit that:– is applied in a single layer;– has a high hydraulic stability;– has a high structural stability;– is easy to produce and to handle;– is easy to place on the slope.


6

Figure 5. Overview of development of some widely applied

armour units.

Figure 6. Thickness of armour layer for double (top) and single

layer (bottom) armour units designed for equal conditions.

HydraulicStability

StructuralStability

2 layers

2 layers

2 layers

1 layers

1 layers

Cube

Tetrapode1950

Dolos1963

Accropode1980

Core-loc®

1995

tim

e

HYDRAULIC STABILITY TESTS

Physical model tests have been performed at DelftHydraulics in the new 2-D Scheldt flume and the 3-D Jo Vinje wave basin. During these tests, the stability ofthe armour units and the wave overtopping weretested. Furthermore during the 3-D tests, the influenceof oblique wave attack was investigated. In total 104tests were performed in 11 series, 4 of which during

Overview of development stepsThe Xbloc® development started in 2001 with abrainstorm session about shapes that would fulfil theobjectives described above. This creative processresulted in various shapes and concepts. The mostpromising shape of these looked in fact very similar tothe final shape of the Xbloc®. Only minor changes havebeen applied since, based on the development stepsthat were taken.

After the brainstorm session, the most promisingshape was tested in a small flume facility of DMC inorder to confirm that investments in the developmentof this shape were justified. As the results of thesepreliminary tests were very promising, the developmentwas continued. The different development phases andthe key results are shown in the Table I. A moredetailed description of the different tests and theirresults is given in the following sections. Thesedevelopment steps have lead to the Xbloc® as shownin Figure 7.

The Xbloc® can be applied in the range:– Unit height [D]: 1.3 to 3.9 m– Unit volume [V]: 0.75 to 20 m3

– Design wave height [Hs]: 3 to 10 m


7

Figure 7. Xbloc® dimensions.

Table I. Overview of different development phases.

phase 1: Investigation of Hydraulic StabilityTests performed Conclusions2D physical model tests at DMC flume December 2001 High hydraulic stability2D physical model tests at Delft Hydraulics October 2002 Limited wave overtopping due to porous armour layer3D physical model tests at Delft Hydraulics June 2003 Self repairing capacity instead of progressive failure2D physical model tests at Delft University of Technology

June 2003 High porosity of armour layer

phase 2: Investigation of Structural StabilityTests performed ConclusionsFinite Element Calculations June 2002 High structural stabilityPrototype Drop tests May 2003

phase 3: Investigation of Production and HandlingTests performed ConclusionsProduction of prototype moulds February 2003 simple mouldsProduction of 4m^3 prototype units March 2003 easy handling by simple sling technique or by forkAnalysis of casting options May 2003 compact storage possible on siteAnalysis of handling and storage options May 2003

phase 4: Investigation of Placement on Breakwater SlopeTests performed ConclusionsPlacement analysis June 2003 no requirements to orientation of units on the slope

easy placement by simple sling technique

phase 5: Comparison concrete use and costsTests performed Conclusions

Concrete volume comparison single layer units June 2003concrete savings up to 10% compared to other single layer units

Cost comparison based on case studies June 2003 Savings add up to millions of euros

fillet,r = D/19

D

D/3 D/3 D/3

DD

D/3

a b a b a

the 3-D tests. The cross sections of the two settingsare shown in Figure 8.

During the many series, the following parameters havebeen varied:– water depth;– wave height;– wave length;– wave steepness;– packing density of the units;– wave direction.

It must be noted that no demands were made aboutthe placement of the units on the slope. The elements

were quickly and easily placed on the slope after whichthe packing density was determined. This is in contrastto other single layer armour units, where the orientationof each unit on the slope has certain requirements.

During the tests it was observed that only at a severeexceedance (>20%) of the design wave height thestart of damage occurred. Furthermore, for a numberof tests it was observed that the hole left by a unittaken out of the armour layer was filled by the unitspositioned above this hole. Subsequently the armourlayer sustained the increased wave loading to the limit ofthe wave flume. It can therefore be concluded that anXbloc® armour layer is to a certain degree self repairing. The margins between the design wave height (whichwas based on a stability coefficient of Kd=16) and thestart of damage and the failure of the armour layer areshown in Figure 9.

Another important finding from the physical modeltests is the fact that the required packing density onthe slope is low. This is very favourable for the porosityof the armour layer and the wave runup and overtop-ping therefore are low. Furthermore the low packingdensity leads to large concrete savings.

Conclusions from the physical model tests:– The Xbloc® has a high hydraulic stability equal to the

present state of the art single layer armour units.– There is a large safety margin between the design

wave height and the start of damage and betweenthe start of damage and failure of the armour layer.

– The Xbloc® armour layer is to a certain degree selfrepairing.

– The wave runup and overtopping are limited due tothe porosity of the armour layer.

– Owing to the low packing density, the number ofunits required is low; this leads to faster construc-tion and lower concrete volumes used.


8

Figure 8. Cross section of 2-D model setup (top) and 3-D

model setup (bottom).

Figure 9. Wave impact on Xbloc® slope and key results on hydraulic stability

Waterlevel

Xbloc aromour layer

Xbloc aromour layer

Filter layer Dn 50 = 15 mm

Core Dn 50 = 10 mmToe Dn 50 = 25 mm

0.0520.07

1.30

0.03

0.30

m0.

75 m0.

95 m

0.34

filer layer

core

0.125

0.80

0.20 m0.022 m0.030 m

1:1.5

1:1.5

1:1.5

of both these tests confirmed that the structural stabilityof the Xbloc® is outstanding (Figures 11 and 12).

The conclusions of the Structural Stability tests werethat the Xbloc® has an outstanding structural stability.

STRUCTURAL STABILITY

The first tests performed to the structural stabilityof the Xbloc® were Finite Element calculations tocompare the stresses in the Xbloc® under 7 standardload cases with the stresses in the present state of theart armour units. The load cases applied consisted offlexure, torsion and a combination of these two. The main results of these calculations are shown inFigure 10. From these calculations it can be concludedthat the tensile stresses in the Xbloc® are low.

As a reality check of the calculations described above,prototype drop tests have been performed using 4 Xbloc® units of 4 m3. Concrete with a 28-daycompressible strength of 35 MPa was used to cast theunits. The test consisted of 2 different series. Firstlythree repetitive drop tests were performed in order tosimulate the loads due to the rocking movement of the armour units on the breakwater during severe waveattack. Secondly destructive free fall tests wereperformed with increasing fall heights. The results


9

Figure 10. Example of structural tests by Finite Element Calculations and the key results.

Figure 11. Tip Drop Test in reality.

Figure 12. Results of the various drop tests performed.

fllexure

fllexure &torsion

torsion

3.0

2.5

2.0

1.5

1.0

0.5

0.0Xbloc® Core-loc® Accropode

tens

ile s

tres

s [M

Pa]

Type of test Repetitions Drop Height Result

Hammer drop 10 40 cm Damage at 0.4 m

Ti[ drop 1 50 50 cm Nodamage

Tip drop 2 50 50 cm No damage

Free Fall test increasing Breakage at 2.5 m

Hammer Drop Test Tip Drop Test q Tip Drop Test 2 Free Fall Test

Fall height FFall height F Fall height F

Fall height F

Concrete base Concrete base Concrete base

Concrete base

PRODUCTION AND HANDLING

The prototype Xbloc® units were cast in a simplewooden mould and it was concluded that the unit isvery easy to cast owing to the large openings in themould. For large breakwater projects, steel formworkwill be used for repetitive casting. Although only onesteel prototype mould was made, there are variouscasting options and per project the most suitablecasting method can be chosen. In the Figure 13, threepractical casting options are shown.

The storage method of the Xbloc®s betweenproduction and placement on the breakwater slopewill depend completely on the local conditions(Figure 15). If space is scarce, very compact stacking isrequired whereas in case of sufficient area, very quickstacking will be preferred. If required, the Xbloc®s canbe stacked very compactly and if the soil conditionsare suitable, the units can be stacked in multiplelayers. The area required for stacking 100 4 m3 units in a double layer for example is approximately 13 m x 14 m.

The conclusions drawn from the Production andHandling analysis are:– The Xbloc® is easy to produce, handle and store;– The methods used for production, handling and

storage depend on local conditions and thepreferences of the contractor.

Handling of the Xbloc® can be done using varioustechniques with a sling, a forklift or a clamp. With the 4 prototype 4 m3 units, experience was gained withvarious practical sling techniques around the wholeblock, around the legs of the “X” and around the noseof the unit. It was found that the sling around the noseof the block was simple and stable. However a forkliftseems to be the most suitable equipment for handlingof the units. Using a forklift, the units can be rolled ontheir sides, transported and stacked in the storage area(Figure 14).


10

Figure 13. Various mould options for casting.

Figure 14. A forklift was the most suitable equipment for

handling the Xbloc.

Figure 15. Stacking the Xbloc® for storage, after production

and before placement.

Owing to the fact that breakwater construction is verycostly and that the armour layer is an expensive part ofit, these savings easily add up to millions of euros.

Conclusions

The Xbloc® is a new armour unit that fulfils all therequirements Delta Marine Consultants haddetermined to be necessary before the start of thedevelopment.

The Xbloc® is a single layer armour unit with a highhydraulic stability and a high structural stability. It iseasy to produce, to handle and to store. Because of itsinterlocking mechanism, it is easy to place on theslope.

Furthermore it was shown that application of theXbloc® armour unit leads to significant cost savings.Based on case studies, these cost savings primarilyresulted from the lower concrete volumes required.This makes the Xbloc® an economically attractivealternative to other state of the art armour units.

PLACEMENT ON BREAKWATER SLOPE

The placement of single layer armour units on a break-water (or shore protection) slope is of key importanceas the placement of the presently available unitsdetermines to a large degree their hydraulic stability.If the orientation of these units is not correct, theeffectiveness of the interlocking mechanism issignificantly reduced and the armour layer might notbe stable under the design conditions. Therefore strictspecifications are applied for the placement of theseunits. This makes placement a tedious and expensiveprocedure, as blocks have to be picked up repeatedlyin order to place them in the specified orientation.

As opposed to these placement specifications, therequirements for an Xbloc® slope are:1) the packing density on the slope, and 2) the restriction that it may not be possible to remove

any unit from the slope without touching thesurrounding blocks.

Because of the new shape of the Xbloc®, each of the 6 sides of the unit is efficiently interlocking. Thereforethe blocks easily find a position that fully activates theinterlocking mechanism. This was observed during thehydraulic model tests where technicians of DelftHydraulics placed the armour units. As a result of thefact that the Xbloc® interlocks so easily, the secondrequirement is easily met (Figure 16).

An extensive placement analysis was performed usingscale models and slings. The objective of this analysiswas to confirm that the required packing densitiescould be achieved with a sling. It was found that therequired packing densities could easily be met. It wasfurthermore found that the sling technique around theleg of the “X” of the element was most suitable (Figure 17). Based on this analysis, it can be concludedthat the first requirement can easily be met.

COMPARISON OF THE CONCRETE USE

A general comparison has been made of the concreteuse of the Xbloc® compared to other concrete armourunits. For varying wave heights, the concrete use wasdetermined based on the required unit size and thepacking density of the armour units. It was concludedthat the Xbloc® can lead to concrete savings of morethan 10% compared to other single layer armour unitsand even more compared to double layer armour units.

Apart from this theoretical analysis, a detailed costcomparison has been made based on various casestudies. Although the relative cost savings dependon the local boundary conditions and prices for eachproject, the use of Xbloc® armour units did lead tosignificant savings in each of the case studies.


11

Figure 16. Because of their 6-sided shape, units placed on a

slope easily interlock.

Figure 17. Handling the Xbloc® with a sling around the nose

was the most suitable technique for placement.

AWARDS PRESENTATION

At the CEDA Dredging Days held in November 2003,an IADC Young Authors Award was presented toMartin Zwanenburg for his paper ‘The Exploitation ofCockle Shells’.

During the presentation at the closing ceremony ofthe conference, IADC Secretary General ConstantijnDolmans noted, “Innovation in finding dredging

solutions is of the utmost importance. It is a goal thatall IADC member companies strive for. We encouragesuch innovation within our industry, and certainly in theup and coming generation of young researchers. Sinceresearch is an integral part of the competitive process,looking outside of the traditional dredging industry canbe just as important as looking within. Wherever usefulideas originate, the ultimate aim of dredging is toensure the expansion of prosperity, with due respectfor environmental issues. Dredging plays a significantrole in the search for sustainable economicdevelopment and papers such as this one are part ofthe process of stimulating further research andattaining this goal”.

BACKGROUND OF THE PAPER

The cockle, which is considered a delicacy in southernEuropean countries, is dredged up by specialisedcockle ships. However, the dredging of the cocklesleaves tracks on the seabed, resulting in negative publicopinion toward the cockle branch. A reduction of thesetracks, together with a reduction of the required powerand an improvement in cockle quality is desired. The Dutch Producers Organisation of Cockle Fishermendecided to investigate the possibilities of adapting thecurrent design of the cockle-dredging draghead. The research was done at the University of TechnologyDelft, The Netherlands, Department of MechanicalEngineering.

The cockle dragheadThe cockles are fished with special ships equipped withan installation which looks in some respect like the


Martin Zwanenburg

The Exploitation ofCockle Shells

12

IADC Award 2003 Presented at CEDA Dredging Days,Amsterdam, The NetherlandsNovember 20-21 2003

The theme of the 2003 CEDA Dredging Daysconference held in conjunction with the Europort inAmsterdam was “Specialist Dredging Techniques,Inspiring Dredging Solutions”. As is customary theIADC at the recommendation of the CEDA PaperCommittee presents an award to the best paperwritten by a younger author. This year the PaperCommittee selected Mr. Martin Zwanenburg forhis research entitled “The Exploitation of CockleShells”. Mr. Zwanenburg, who works for theshipbuilder IHC Holland, was supported in his studyby Mr. J.D. Holstein of the Dutch ProducersOrganisation Cockle Fishermen of The Netherlandsand professors S.A. Miedema and W.J. Vlasblom ofUniversity of Technology Delft.

Figure 1. Cockle fishing ship and draghead.

draghead passes, but instead is sucked up. To achieveimprovements the jet water should be minimised and,if possible, the sand that is brought up by the bladeshould be reduced. For this reason the investigationfocussed on the design of the blade in order to achievethe required improvements and minimise tracking onthe seabed.

Serrated knivesSeveral configurations of serrated knives were testedto investigate whether or not it is possible to pick upthe cockles, whilst leaving the sand at the bottom.An unexpected difficulty was the phenomenon that, insome configurations, the teeth are blocked by the sandwhich then pushes the sand forward like a bulldozerblade (Figure 2).

The best results were obtained by a serrated knifeconsisting of straight round bars, connected to eachother at the back end, thus achieving an optimum flowthrough the serrated knife, with no use of jet water.Though the laboratory results were satisfying, practicalapplication not yet been determined. Extensive testson site are still required to determine the possibilitiesfor using serrated knives in cockle dragheads.

The entire text of this paper can be found in theProceedings of the CEDA Dredging Days,November 20-21 2003, Amsterdam.

dredging installation on a trailer suction hopper dredger(Figure 1). Via the dredging head, cockles and sand aresucked up and transported to a separation drum onboard the ship, in which the sand is separated from thecockles.

The cockles are kept on board and the sand and waterare drained back to the sea. Several scientific studieshave determined that there are no irreversable effectsto the seabed, however, because of other negativeopinions, the decision was still made to conduct furtherinvestigations.

The current design of the cockle draghead wasdeveloped at the end of the 1970s and made for highproduction and high sailing speeds. The dimensions ofthe cockle draghead differ for each ship, but the widthof the blade is determined by the law by the depart-ment of Agriculture and Fishery. The current blade isadjustable bin depth and cutting angle.

After completely examining the of the cockle draghead,it became clear that the use of jet water causes thedepth of the tracks. Reducing the jet water is notpossible in the current draghead design because thepulling forces are too high. From the flow pattern insidethe cockle draghead, it is clear that the sand which isbrought up by the blade does not resettle after the

The Exploitation of Cockle Shells

13

Two IADC YoungAuthors Awardsin 2003Each year, at selected conferences and at otherappropriate occasions, the International Associationof Dredging Companies grants awards for the bestpapers written by authors younger than 35 years ofage. At each appointed conference or occasion, the Paper Committee is asked to recommend aprizewinner whose paper makes a significantcontribution to the literature on dredging and relatedfields. The purpose of the IADC Award programmeis “to stimulate the promotion of new ideas andencourage younger men and women in the dredgingindustry”. The winner of an IADC Award receivesUS$ 1000 and a certificate of recognition, and thepaper if suitable is then published in Terra et Aqua.

In 2003 two such awards were presented. InSeptember one was presented at the COPEDEC VIheld at Colombo, Sri Lanka (see page 14). The secondwas presented last November at the CEDA DredgingDays in Amsterdam (See opposite page).

Figure 2. Configurations of the serrated knives.

Abstract

Field experiments conducted to explore sediment resuspension and cross-shore cycling in nearshoreenvironments are presented with special emphasis onthe influence of wave groups. Field data presented arefrom City Beach, Mullaloo Beach and Leighton Beachof Western Australia and Chilaw, Sri Lanka.Measurements include simultaneous measurementsof surface elevation, cross-shore current velocities andsuspended sediment concentrations collected justoffshore of the breaker zone. As it has been wellestablished, wave groups appear more capable ofresuspending sediments than incident waves. Resultsof cross-correlation and cross-spectral analysis show aconsiderable inconsistency especially in the direction ofcross-shore sediment flux on the frequency domain atdifferent locations and under different conditions. This lead to the hypothesis that there are additionalfactors such as local wave climate, grain size, beachslope and bed forms.

The author wishes to thank for Charitha Pattiaratchi of the Centre for Water Research, The University ofWestern Australia, for assistance in the preparation of this paper. The paper originally appeared in theProceedings of the COPEDEC Conference, Colombo,Sri Lanka, in September 2003 and is reprinted here inan adapted version with permission.

Introduction

One of the most important challenges facing coastalresearchers is to predict the transport of sediment innearshore regions directly influencing coastal stability.This is a prime socio-economic concern for coastalregions globally. Although nearshore sedimenttransport occurs mainly in the longshore direction,the smaller cross-shore transport plays a dominantrole in determining seasonal shoreline evolution,shelf morphology, and so on. Therefore, an improvedunderstanding of the processes of sediment suspensionand cycling within this highly dynamic region is essential

to make accurate predictions of cross-shore sedimenttransport and thus coastal stability.

Under wave-dominated conditions, which is commonwhen the tidal range is small, sediment resuspensionand transport is closely related to the local waveclimate. In general, three distinct regimes of local waveclimate can be identified: (a) periods of storm activity associated with passage of

frontal systems during winter (or during monsoonseason);

(b) periods of locally generated waves caused by seabreeze systems; and,

(c) swell wave activity during “calm” periods.

But storm or sea breeze systems occur over a shortduration and swell waves dominate the nearshorewave climate for longer periods. This highlights theneed to explore nearshore processes under swell waveconditions and is further emphasised by the fact that anearshore wave climate dominated by swell provideideal conditions for the presence of wave groups.

WAVE GROUPS

With any combination of waves a point will occurwhere all frequencies cancel and the resulting wavehas minimal amplitude. The set of waves between twoof these points is called a wave group (Figure 1).

Group bound long waveWhen there is an incoming swell, Munk (1949) andTucker (1950) first noticed the existence of longerwaves, of 2-3 min period, very similar to the envelopeof the visual swell, and suggested that the long wavesmay be caused by an excess of mass carried forwardby groups of high swell. Longuet-Higgins and Stewart(1962 and 1964) further explained it as a wave group,containing larger than average waves, which depressthe water surface and thereby force a long wave whichis defined as group bound long wave. Therefore, wavegroups are always associated with a group bound longwave (Figure 1).


Samantha Kularatne

Sediment Resuspensionand Cycling due to Wave Groups

14

The majority of previous studies on cross-shoresediment transport in nearshore regions have revealedthat the suspension of sand, and hence, the cross-shore sediment flux in the nearshore region occur in anevent-like manner over a range of time scales rangingfrom seconds (wind waves) to minutes (wave groupsor infragravity waves) (Brenninkmeyer, 1976; Hanesand Huntley, 1986; Sternberg et al., 1989; Osborne andGreenwood, 1993; Masselink and Pattiaratchi, 2000).However, these observations made under differentconditions covering various parts of the world appearnot to be very consistent especially with respect to thedirection of sediment flux (onshore or offshore) underdifferent time scales (wind waves, swell, infragravitywaves, and so on). Thus, an improved understanding of the governing factors of this inconsistency in thedirection of sediment flux (cycling) is important and hasyet to be resolved.

Field measurements of nearshore sedimentresuspension clearly show that the time series recordsof suspended sediment concentration indicatepronounced suspension events at low frequencies(Hanes and Huntley, 1986; Huntley and Hanes,1987; Hanes, 1991a; Osborne and Greenwood,1993; Masselink and Pattiaratchi, 2000; Smith andMocke, 2002). This enhances the assumption thatwave groups are more capable of stirring up sedimentparticles from the bed.

Figure 2 shows a comparison of time series records of cross-shore current velocity (u), envelope function of u and suspended sediment concentration fromMasselink and Pattiaratchi (2000), which clearlysuggest a correlation between wave groups andsuspended sediment concentration.

Furthermore, past investigations have suggested that,in most of the cases, at lower frequencies (wavegroups, infragravity waves) the cross-shore sedimentflux is in the offshore direction and it changes intoonshore direction under higher frequencies (windwaves, swell) (Huntley and Hanes, 1987; Hanes, 1988).However, contradicting results can also be found inliterature where offshore fluxes are evident at incidentfrequencies and vice-versa (Masselink and Pattiaratchi,2000; Smith and Mocke, 2002).

Deigaard et al. (1999) have investigated the influence of the group bound long wave on sediment re-suspension using a mathematical model. Theydeveloped a model in which the turbulent boundarylayer flow was simulated through a mixing lengthmodel and the suspended sediment was modelled bythe advection diffusion equation. It was found that thenet cross-shore sediment transport depends on thegrain size and the magnitude of transport. In mostcases (with exception of very intensive transportconditions) the bound long waves were found to give a

Sediment Resuspension and Cycling due to Wave Groups

15

Sam Kularatne (left) receiving the IADC Young Authors Award

from Mr. Hans Poiesz, Chairman of the IADC Public Relations

Committee, at the COPEDEC VI in Sri Lanka, September 2003.

IADC Award 2003

Presented at the COPEDEC VI,Colombo, Sri Lanka September 15-19 2003

At the sixth International Conference on Coastaland Port Engineering in Developing Countries(COPEDEC), held this past September in Colombo,Sri Lanka, Samantha Kularatne was presented withan IADC Young Dredgers Award. Mr. Kularatnegraduated with a B.Sc. (Engineering) with first class(honours) specialised in Civil Engineering from theUniversity of Peradeniya, Sri Lanka in 1998.From October 1998 to May 1999 he worked as aResearch Engineer at Lanka Hydraulic Institute Ltd.,Sri Lanka. He received a Master of Engineering inCoastal Engineering from the National University ofSingapore in 2001 and worked as a ResearchEngineer at the Institute of Hydrodynamics andWater Resources, Technical University of Denmarkfrom September 2001 to March 2002. Since April2002 he is working on a Ph.D. in CoastalOceanography at the University of WesternAustralia.

negative contribution to the sediment transport, andthe bound long waves could even change the directionof the net suspended sediment transport, opposite todirection of wave propagation. Their study wasrestricted to plane bed (sheet flow conditions).

Therefore, the objectives of the present study are to:a) undertake field measurements of sediment

resuspension and cycling caused by wave groupsunder a variety of conditions (differing wave climate, grainsize, beach slope, bed forms, and so on), to definefactors governing the direction of cross-shoresediment flux on frequency domain;

b) develop a numerical model to explore the sameproblem in more detail, taking into account theinfluencing factors separately and comparing the output with field measurements. In this paper,the initial results of this study are presented.

METHODS

Field investigationsField measurements providing the basis for the presentstudy on influence of wave groups on nearshoresediment resuspension were carried out at number oflocations:– City Beach, Mullaloo Beach, Leighton Beach –

Western Australia (Figure 3) and – Chilaw, Sri Lanka (Figure 4) covering a range of

different conditions.

All the measurements were conducted just offshore ofthe breaker zone.

Data on surface waves, currents and suspended sandconcentrations were collected using the “S” probe, an instrument package developed at the Centre forWater Research, University of Western Australia.


16

short waves (formwave group) mean water

levelbound long wave

envelope function

Figure 1. Wave groups and group bound long wave.

Figure 2. Time series of: (a) cross-shore current velocity u (solid line), envelope function of u (thick dashed line) and lowpass-filtered

u (thick solid line); and (b) suspended sediment concentration c 0.05m from the bed (solid line) and lowpass-filtered c (thick solid

line) (Masselink and Pattiaratchi, 2000).

The “S” probe consists of a Paroscientific Digiquartzpressure sensor (located 0.35 m above the bed), Neil Brown ACM2 acoustic current meter together withthree optical back scatterance (OBS) turbidity sensors.The two-dimensional horizontal velocity at 0.20 mabove the sea bed is recorded by the current meterwhile the OBS sensors record the concentration profileat three levels: 0.025 m, 0.125 m and 0.275 m, abovethe sea bed (Figure 5).

Bed profiles were surveyed using a total station whilesediment samples collected at the field site wereanalysed to determine the median grain size. The meangrain sizes off Chilaw, Sri Lanka were found to be 0.2 mm and along Western Australia (Mullaloo Beachand City Beach) it was relatively coarser (0.3 mm).

Additional details of field measurements can be foundin Masselink and Pattiaratchi (2000) and Pattiaratchi et al. (1999).

Numerical modellingA numerical model was developed to further explorethe influence of wave groups on nearshore sedimentresuspension and cycling. The simulation of waves(hydrodynamics) is based on Boussinesq typeequations. The classical Boussinesq theory providesa set of equations for surface water waves in thecombined limit of weak nonlinearity and weakdispersion, which represents shallow water wavesof moderate amplitude quite well. The standardBoussinesq equations for variable water depth werefirst derived by Peregrine (1967), who used depth-averaged velocity as a dependent variable. But theassumption of weak frequency dispersion effectsmakes the equations perform well only within shallowwater and invalid in intermediate and deep water.

Novel forms of Boussinesq equations extending thevalidity to intermediate and deep water were achievedby improving the linear dispersion characteristics of theweakly dispersive model (Madsen et al., 1991; Nwogu,1993). Nwogu (1993) used the velocity at a certaindepth as a dependent variable and the equationssimulate intermediate water much better than thestandard equations. Despite their improved dispersionrelationship, the extended Boussinesq equations arestill restricted to situations with weakly nonlinearinteractions.

Adapting the approach of Nwogu (1993), but making noassumption of small nonlinear effects, Wei et al. (1995)derived a new set of Boussinesq equations that includeadditional nonlinear dispersive terms. Not only can theequations be applied to intermediate water depth, butalso they can simulate wave propagation with strongnon-linear interactions. These equations derived by Weiet al. (1995) provide the base for the wave model usedin the present study (Funwave1D).

17

Figure 3. Study areas off Perth, Western Australia.

Figure 4. Study area off Chilaw, Sri Lanka.

The numerical modelling of the process will primarilybe achieved using a modified version of Funwave1D,an open source distribution from the Centre for AppliedCoastal Research, University of Delaware, described inKennedy et al. (1999). This software is developedbased on the fully nonlinear Boussinesq model of Weiet al. (1995) and a source function method is used ingenerating required input wave signal (Wei et al., 1999).The directional wave spectra or the time series recordof the input surface elevation can be directly fedthrough the source function method. Both wavebreaking and run-up (shoreline) are parameterisedwithin the original code (Kennedy et al. 1999).

The model simulates time varying surface elevationand horizontal (cross-shore) velocity over desiredbottom topographies. The surface elevation recordand the bottom topography obtained through fieldmeasurements are directly input into the modelallowing a highly realistic simulation of the nearshorehydrodynamics. This model has been extensivelyvalidated against laboratory data and has been usedfor field simulations by Chen et al. (2000).

The sediment transport model developed by Bagnoldand Bailard (1981), which predicts instantaneoustransport rates of bed load and suspended load iscoupled with the hydrodynamic model in order toobtain the cross-shore sediment flux.

This enhances separate exploration of the influence ofdifferent parameters governing the direction of cross-shore sediment cycling on frequency domain using thedata gathered through field experiments as well as forsome hypothetical wave signals.

DATA ANALYSIS AND RESULTS

Field investigationsThe role of wave groupiness on sedimentresuspension was investigated by comparing timeseries records of cross-shore current velocity, the wavegroupiness envelope and suspended sedimentconcentration. The groupiness envelope wascomputed by lowpass-filtering the modulus of thecross-shore current record at 0.01 Hz (List, 1991).Figure 6 presents time series records obtained fromChilaw, Sri Lanka during the initiation of an afternoonsea breeze and clearly indicates the correlationbetween wave groups and the sediment resuspension.Whereas Figure 7 the time series records of cross-shore velocities and suspended sedimentconcentrations, from the same location but during themonsoon season, does not show any clear evidence ofpronounced groupiness as strong wind waves couldpresumably destroy any particular pattern. A similar setof data records from the City Beach, Western Australia


18

Figure 5. ‘S’ probe, an Instrument package consist of a Paroscientific Digiquartz pressure, Neil Brown ACM2 acoustic current meter

together with three optical backscatterance (OBS) turbidity sensors. All data for this paper was obtained from this instrument

package.

Pressure sensor

EM current meter

OBS

in sediment resuspension and cross-shore cycling. The results obtained for the data records presented inFigure 6 are shown in Figure 9 (Chilaw, Sri Lanka).Auto-spectra of the cross-shore current and sedimentconcentration records (Figure 9a) identify the dominantfrequencies and Figure 9b presents cross-correlation

(summer 1992) gathered during an afternoon seabreeze also indicate that the complexity of wind wavescould destroy any marked groupiness (Figure 8).

Cross-correlation and cross-spectral analyses wereperformed to quantify the different aspects involved


19

Figure 6. Time series of: (a) cross-shore current velocity u (solid line) and envelope function of u (thick dashed line);

and (b) suspended sediment concentration c 0.05m from the bed (solid line) and lowpass-filtered c (thick dashed line) (Chilaw, Sri

Lanka – 18-01-96).

Figure 7. Time series of: (a) cross-shore current velocity u (solid line) and envelope function of u (thick dashed line); and (b)

suspended sediment concentration c 0.05m from the bed (solid line) and lowpass-filtered c (thick dashed line) (Chilaw, Sri Lanka -

13-05-96 – during monsoon season).

between the groupiness envelope and the low-passfiltered cross-shore current. Figure 9c describes themost important result of the present project; the co-spectrum between the time series of cross-shorecurrent and sediment concentration which portrays thedirectional variation in cross-shore sediment flux in thefrequency domain. Finally, the cross-correlationbetween the groupiness envelope and low-passfiltered sediment concentration (Figure 9d) providesinformation on the relationship between the two timeseries.

Figure 9a shows that the dominant peak for cross-shore current at 0.06 Hz and for sedimentconcentration at 0.005 Hz. This indicates that moresediment was stirred up at low frequencies (wavegroups) which is evident from Figure 6. A strongpositive relationship between the groupiness envelopeand the lowpass filtered cross-shore current velocity isevident from Figure 9b and this enhances the fact thatthere was no distinct formation of a group bound longwave. Figure 9c shows the most interesting resultwhich is contrary to the original explanation for thedirection of sediment flux (e.g. Huntley and Hanes,1987). Here, the cross-shore sediment flux is offshoreat high frequencies (swell) and onshore at lowfrequencies (wave groups). Figure 9d further provesthat the cross-shore current velocity and the sedimentconcentration have a strong positive correlation with atime lag of 20s.

Results of similar analysis (cross-correlation and cross-spectral) for data collected from the same location (off Chilaw, Sri Lanka) during a period of much calmersea conditions (in the morning with more pronouncedgroupiness) on the same day (Figure 10), were found to be the complete opposite to Figure 9 (especially Figure 9c) where cross-shore sediment flux is onshoreat higher frequencies (swell) and offshore at lowerfrequencies (wave groups) (Figure 10c is in accordancewith the original explanation; e.g. Huntley and Hanes,1987). This confirms the influence local waveconditions have on sediment resuspension and thedirection of cross-shore sediment flux on frequencydomain. Further, a strong negative correlation betweenthe envelope function and the low-pass filtered cross-shore current record (Figure 10b) proves the presenceof a group bound long wave under a wave climate withimproved wave groupiness (Longuet-Higgins andStewart, 1964).

Comparison of the envelope function of cross-shorecurrent record and sediment concentration obtained atMullaloo, Western Australia is presented in Figure 11,and again it is apparent that higher sedimentconcentrations occur with the passage of wave groups.Results of the cross-correlation and cross-spectralanalysis for this data (Figure 12) are in line withFigure 10 where cross-shore sediment flux is onshoreat higher frequencies (swell) and offshore at lowerfrequencies (wave groups) (Figure 12c) but in complete


20

Figure 8. Time series of: (a) cross-shore current velocity u (solid line) and envelope function of u (thick dashed line);

and (b) suspended sediment concentration c 0.05m from the bed (solid line) and lowpass-filtered c (thick dashed line)

(City Beach, Western Australia – 23-01-92 – with an afternoon sea breeze).


21

Figure 9. (a) the normalised auto-spectra of cross-shore currents (u- solid line) and nearbed suspended sediment concentration

(c - dashed line); (b) cross-correlation between: an envelope function of u and lowpass-filtered u; (c) the co-spectrum between

u and c; and, (d) envelope function of u and lowpass-filtered c (Chilaw, Sri Lanka – 18-01-96 at 16:30 hrs).



u and c; and, (d) envelope function of u and lowpass-filtered c (Chilaw, Sri Lanka – 18-01-96 at 11:40 hrs).

(a) (b)

(c) (d)

(a) (b)

(c) (d)

onshore

offshore


22

Figure 11. Time series of: (a) cross-shore current velocity u (solid line) and envelope function of u (thick dashed line); and

(b) suspended sediment concentration c 0.05m from the bed (solid line) and lowpass-filtered c (thick dashed line);

GF-ut – groupiness factor calculated based on u (Mullaloo, Western Australia – 18-04-93).



u and c; and, (d) envelope function of u and lowpass-filtered c (Mullaloo, Western Australia – 18-04-93).

(Figure 12c). Further, the most dominant peak ofsediment concentration appears to occur at acomparatively higher frequency (0.025 Hz) (Figure 13a).All these differences and deviations of the direction ofcross-shore sediment flux on frequency domainvindicate the inconsistency of the process underdifferent conditions (wave climate, grain size, beachslope, bed forms, and so on).

Numerical analysisRecords of water surface elevation obtained at alocation offshore of breaker zone (water depth of3.4 m) off Leighton Beach, Western Australia (Figure 3)were used as input signal for the numerical modelexplained in the “Methods” section. Figure 14a showsa time series record of the surface elevation measuredat the field and Figure 13b presents the correspondingfiltered signal which is the input signal for the model.

The model layout is shown in Figure 15. The averagesediment size is 0.1 mm and the beach slope is 1:30.Waves were generated at a constant depth of 3.4 mand the model output of surface elevation, cross-shorecurrent velocity (depth averaged) and the suspendedsediment concentration, 0.55 m from the bottom at awater depth of 1.2 m are presented in Figure 16.

disagreement with Figure 9 (especially Figure 9c).Data for Figures 9 and 10 were collected from Chilaw,Sri Lanka where average grain size is finer comparedto Mullaloo, Western Australia.

Figure 12a indicates that the dominant peak forsediment concentration occurs at a low frequencycorresponding to wave groups and Figure 12dreconfirms the correlation between wave groups andsediment concentration with a strong positive relationwith a lag of 63 s. Further, Figure 12b demonstrates astrong negative relation between the groupinessenvelope and the lowpass filtered cross-shore currentvelocity and such an out-of-phase relationship indicatesthe presence of the group bound long wave (Longuet-Higgins and Stewart, 1964).

Results of a similar analysis conducted for a set of datagathered at the same location (Mullaloo, WesternAustralia) on a different day are presented in Figure 13.

Though it depicts the same trend in cross-shoresediment flux (offshore at low frequencies and onshoreat higher frequencies) (Figure 12c and 13c) it can beseen that offshore flux begins to occur at much higherfrequency (Figure 13c) than in the previous case


23



u and c; and, (d) envelope function of u and lowpass-filtered c (Mullaloo, Western Australia – 03-04-93).

As described in the “Methods” section, the sedimentconcentration (transport) is modelled using Bagnold andBailard (1981) model and the results show that highersuspended sediment concentrations occur with thepassage of waves of higher amplitude (Figure 16).

Results of cross-spectral and cross-correlation analysisperformed for the output from the numerical model arepresented in Figure 17. It is evident that dominantpeaks for both cross-shore currents and sedimentconcentration occur at the incident wave frequency(~0.1 Hz) and this further proves the lack ofrepresentation of the influence of wave groups.The need for proper simulation of low frequency

oscillations (wave groups) is confirmed again inFigure 17c as the cross-shore sediment flux is towardsonshore almost throughout the whole frequencydomain.

Conclusions

This paper summarises the results of measurementscollected to explore sediment resuspension and cyclingcaused by wave groups in nearshore environments.Field data obtained at different locations (MullalooBeach, City Beach, Leighton Beach – Western Australiaand Chilaw – Sri Lanka) under different conditions were


24

Figure 14. (a) Time series of surface elevation recorded off Leighton Beach, Western Australia. (b) Filtered signal of the surface

elevation which is the input to the numerical model.

waves

3.4m

1.2m

slope- 1:30

Figure 15. Model layout.

1987)., However, the results of Masselink andPattiaratchi (2000) and Smith and Mocke (2002), as wellas the results of the present study indict that this patternmay be reversed (e.g. Chilaw, Sri Lanka – Figure 9).

This reversal can occur at the same site within a fewhours with a change in local sea conditions (Figures 9and 10). Wave climate was observed to be changedfrom rather calm conditions to conditions dominatedby wind waves caused by an afternoon sea breeze. This explains the influence of local wave climate onthe nearshore sediment resuspension and cycling.

The inconsistency in results obtained at differentlocations can also be influenced by the change inother parameters governing sediment resuspension.Grain size could be a decisive factor which has a directinfluence on sediment resuspension and transport, andin the present study a range of mean sediment sizeswere observed at different locations. Deigaard et al.(1999) emphasised the influence of grain size on netcross-shore sediment transport with a numerical studyon net sediment transport under wave groups.

The bottom slope and the ripple geometry too couldhave a considerable bearing on sediment resuspension

analysed in an attempt to understand the factorsinfluencing sediment resuspension and cross-shorecycling.

The presence of pronounced wave groups depends onthe local wave climate. Calm sea conditions dominatedby swell have been identified as the ideal conditions forformation of well-defined wave groups and coastalwaters forced by local winds (monsoons (winter) orafternoon sea breeze) do not appear to havepronounced wave groups. Far less pronounced wavegroupiness could be observed under monsoonconditions or conditions surrounded by afternoon seabreeze. From the results obtained at all the locations,when wave groups were apparent, a significant relationbetween wave groups and suspended sedimentconcentrations could be observed. This further provesthe well-established assumption that wave groups aremore capable of stirring up sediments and keepingthem up in suspension than incident waves.

The direction of cross-shore sediment flux in thefrequency domain, it is generally postulated that thereis onshore transport at higher incident frequencies(wind waves, swell) and offshore transport at lowerfrequencies (wave groups) (e.g. Huntley and Hanes,


25

Figure 16. Model output at water depth of 1.2 m (a) surface elevation (b) depth averaged cross-shore current velocity (c) suspended

sediment concentration at 0.55m from the bottom.

and cycling forced by wave groups (on frequencydomain) as has been documented (Vincent et al., 1991;Villard et al., 1999; Vincent and Hanes, 2002).

The simple numerical model described in this paper isan attempt to develop a comprehensive model tosimulate sediment resuspension and cross-shoresediment cycling in a nearshore environment. The finalobjective of this numerical study is to develop a modelthat is capable of conducting separate exploration ofthe influence of different parameters governingsediment resuspension and the direction of cross-shore sediment cycling on the frequency domain(covering wind waves, swell, wave groups, and such).

References

Bagnold, R.A. (1966). “An approach to the sediment transport problem from general

physics”. Geological Survey Prof. Paper 422-I, Washington DC,

USA.

Bailard, J.A. (1981). “An Energetics total load sediment transport model for plane

sloping beach”. Journal of Geophysical Research, 86(C11),

10,938-10,954.

Brenninkmeyer, B.M. (1976). “In situ measurements of rapidly fluctuating, high sediment

concentrations”. Marine Geology, 20, 117-128.

Chen, Q., Kirby, J., Dalrymple, R., Kennedy, A., Thornton, E.and Shi, F. (2000). “Boussinesq modelling of waves and longshore currents under

field conditions”. In Proceedings of 27th International Conference

on Coastal Engineering, 651-663.

Deigaard, R., Jakobsen, J.B. and Fredsoe, J. (1999).“Net sediment transport under wave groups and bound long

waves”. Journal of Geophysical Research, 104(C6), 13,559-13,575.

Hanes, D.M. and Huntley, D.A. (1986). “Continuous measurements of suspended sand concentration in

a wave dominated nearshore environment”. Continental Shelf

Research, 6, 585-596.

Hanes, D.M. (1991a).“Suspension of sand due to wave groups”. Journal of

Geophysical Research, 96(c5), 8911-8915.

Huntley, D.A. and Hanes, D.M. (1987). “Direct measurement of suspended sediment transport”.

Coastal Sediments ’87, ASCE, 723-737.


26



u and c; and, (d) envelope function of u and lowpass-filtered c (Results of the numerical model for field data collected off Leighton

Beach, Western Australia).

Villard, P.V., Osborne, P.D. and Vincent, C.E. (1999). “Influence of wave groups on sand resuspension over bedforms

in a large scale wave flume”. Proceedings of the Fourth

International Symposium on Coastal Engineering and Science

of Coastal Sediment Processes CS99, New York, 367-376.

Vincent, C.E., Hanes, D.M. and Bowen, A.J. (1991). “Acoustic measurements of suspended sand on the shoreface

and the control of concentration by bed roughness”. Marine

Geology, 96, 1-18.

Vincent, C.E. and Hanes, D.M. (2002). “The accumulation and decay of near-bed suspended sand

concentration due to waves and wave groups”. Continental Shelf

Research, 22, 1987-2000.

Wei, G., Kirby, J.T., Grilli, S.T. and Subramanya, R. (1995). “A fully non-linear boussinesq model for surface waves: I.

Highly non-linear, unsteady waves”. Journal of Fluid

Mechanics, 294, 71-92.

Wei, G., Kirby and J.T., Sinha, A. (1999). “Generation of waves in Boussinesq models using a source

function method”. Coastal Engineering, 36, 271-299.

Kennedy, A., Chen, Q., Kirby, J. and Dalrymple, R. (1999). “Boussinesq modelling of wave transformation, breaking and

runup”. I:1d. Journal of Waterway, Port, Coastal and Ocean

Eng., 126(1): 39-47.

List, J.H. 1991). “Wave groupiness variations in the nearshore”.

Coastal Engineering, 15, 475-496.

Longuet-Higgins, M. and Stewart, R. (1962). “Radiation stress and mass transport in gravity waves, with

application to ‘surf beats’”. Journal of Fluid Mechanics, 13,

481-504.

Longuet-Higgins, M. and Stewart, R. (1964). “Radiation stresses in water waves: a physical discussion, with

applications”. Deep-Sea Research, 11, 529-562.

Madsen, P.A., Murray, R. and Sorensen, O.R. (1991). “A new form of Boussinesq equations with improved dispersion

characteristics”. Coastal Engineering, 15, 371-388.

Masselink, G. and Pattiaratchi, C. (2000). “Tidal asymmetry in sediment resuspension on a macrotidal

beach in northwestern Australia”. Marine Geology, 163, 257-274.

Munk, W.H. (1949). “Surf beats”. Trans. American Geophysical Union, 30, 849-854.

Nwogu, O. (1993). “An alternative form of the Boussinesq equations for nearshore

wave propagation”. Journal of Waterway, Port, Coastal Ocean

Engineering, 119, 618-638.

Osborne, P.D. and Greenwood, B. (1993). “Sediment suspension under waves and currents: time scales

and vertical structure”. Sedimentology, 40, 599-622.

Pattiaratchi, C., Masselink, G. and Wikramanayake, N. (1999). “Sea breeze effects on coastal processes”. Proceedings of Fifth

International Conference on Coastal and Port Engineering in

Developing Countries (COPEDEC V), 37-48.

Peregrine, D.H. (1967). “Long waves on a beach”. Journal of Fluid Mechanics, 27, 815-827.

Smith, G.G. and Mocke, G.P. (2002). “Interaction between breaking/broken waves and infragravity-

scale phenomena to control sediment suspension transport in

the surf zone”. Marine Geology, 187 (3-4), 329-345.

Tucker, M.J. (1950). “Surf beats: sea waves of 1 to 5 minutes’ period”. Proc. Royal

Society, A207, 565-573.


27

As it Was – Highlights of Hydrographic History, from the Old Hydrographer’s Column: “HydroINTERNATIONAL” Volumes 1 – 6. GTIC bv, Lemmer, The Netherlands, 2003.Soft cover, A-4, 118 pp, colour illustrations.

by Steve Ritchie and others

For any reader with the slightest interest in surveyingthe sea bottom, its history and technology, this book isa pleasant and relaxing way to read through the subject.The volume begins with a piece entitled, “Periploi,”which discusses the earliest known sailing directions— which were made over a thousand years before thefirst charts — and finishes with an article on “UnderseaTrilateration – North Sea,” which discusses the mea-surement of the proximity of pipelines to productionplatforms. The other 46 articles, by Steve Ritchie andseven colleagues, literally cover the waterfront andmuch under the water as well.

Ritchie opines that Lucas Janzoon Waghenaer ofEnkhuizen is the true hero of hydrography, since hewas the first professional seaman to compile and printpaper charts designed specifically for his fellowmariners. One column centers around this hero. Othercolumns feature other “heroes,” such as Tadaka Inouof Japan, and Edward Halley, the seventeenth centuryastronomer of Halley’s Comet fame. The book hasprofiles of many individuals that played major roles inthe field.

The author/editor writes with a style that belies thetechnological subject matter. This makes reading historyand technology an enjoyable experience, and theknowledge that the reader gains comes easily and canbe divided into many sessions, as time permits.

The articles grew out of columns that were publishedin the magazine, Hydro INTERNATIONAL. The first of these columns was published in February 1997. The author, Steve Ritchie, set out to describe howthings were done before the advent of such aids as

electronic ship fixing, GPS and side scan sonar. It wasnot long before he realised that the use of other guestauthors was necessary to fill in the areas where hisown experience was lacking. This resulted in a seriesof columns that drew on a variety of experts in thefield.

The author states that he may be accused of beingpresumptuous in his selection of highlights, but that hisintention was to show the wonderful story the historyof hydrography. He hopes that these articles will“encourage others to delve further to expose manyhidden gems”. The book is illustrated profusely, and thechoice of illustrations provides excellent examples ofearly charts, the heroes in the field, and other graphicsthat are very well done.

It is rare to find a technically oriented publication thatshould serve as a great piece to have available fornightly recreational reads, and a fine alternative toevenings in front of the telly.

This book can be obtained from:GITC bvP.O. Box 1128530 AC Lemmer, The Netherlands or by contacting:[email protected]

Dredging Operations and Environmental Research,Program Products, Volume II (FY1997 – FY20*02)CDROM, requires Windows 95 or later, browser version3.0 or later and Adobe Acrobat Reader.

US Army Engineer Research and Development Center (ERDC)

This is the second of the CDROM presentationsprepared and distributed by the US Army Corps ofEngineers as a unique and effective way to transfer thetechnology and results of the Corps dredging researchprogramme. Volume II covers the results of the first sixyears of Dredging Operations and Environmental


Charles W. Hummer, Jr.

Books/PeriodicalsReviewed

28

results emanating from the ambitious and long-standingresearch programmes.

The CDROM is available at no cost from:Engineer Research and Development CenterAttn: CEERD-EM-D, 3909 Halls Ferry RoadVicksburg, Mississippi 39180-9981 USA

The Dynamics of DredgingPlacer Management Corp., Irvine, California, USA, July 2002. Hardbound, 6” x 9”, 413 pp, illustrated, bibliography and index. US$ 65 plus shipping

by Mort J. Richardson

According to the author, this book is an outgrowth ofthe research and preparation of an issue of the WorldDredging/Mining & Construction magazine to select theten major dredging programmes of the twentiethcentury and the most significant advancements indredging technology.

The book covers a broad spectrum of subjects and isdivided into 12 chapters, a 6-part appendix, a photosection, bibliography and index. An appreciation for thecontents can be garnered from the table of contents. – History of Dredging– Major Dredging Projects of the 20th Century– Dredge Types & Descriptions– Maintenance Dredging– Reservoir Maintenance Dredging– New Construction Dredging– Reclamation Dredging– Environmental Dredging– Dredge Mining– Technology Development– Dredging Research

Clearly the book has an eclectic selection of subjectmatter, and although the author states that the bookarose from the selection of ten major dredgingprogrammes of the twentieth century, only a smallportion of the book is devoted to these projects, listingsixteen projects in four pages and aggregating alldredging in Japan to a single paragraph. The selectionsraise the awkward question of why some subjectswere selected and others not. Nonetheless the bookdoes contain a collection of interesting facts and doesserve as a compendium on dredging with a rich varietyof colourful illustrations.

This book can be obtained from:World Dredging/Mining & ConstructionP.O. Box 17479Irvine, CA 92623-7479 USAtel. +1 949 553 0836, fax +1 949 863 9261email: [email protected]

Research (DOER) programme from 1997 to 2002 andreplaces the earlier Volume I entirely. The auto-play dischas a seven-part menu which includes: Welcome,Message, Mission, History, DOER Products, Creditsand Exit.

The Message is from eminent dredging scientist, Dr. Robert M. Engler, Director of the DOER Program.Mission describes in the briefest of terms the naviga-tion mission of the Corps of Engineers and the rele-vance of the DOER Program to fulfilling that mission.The History tab refers to the history of DOER and itsantecedent and corollary research programmes. DOERProducts are divided into two subsections; namely,DOER Products, Fiscal Year 1997 – 2003 and Links toother programmes. The DOER Product Review isfurther divided into a narrated auto-play slide showsummarising the DOER Program and its researchareas; a manually operated slide show of the samematerial; downloadable PDF files of research reports anda 6.5 minute narrated video tour of the Corps hopperdredge Wheeler. The Links section brings the viewer tothe Internet links associated with the corollary Corpsdredging research programmes; – Dredging Operations Technology Support (DOTS), – Center for Contaminated Sediments (CCS) and the – Long Term Effects of Dredging Operations (LEDO)

Program.

The CDROM does a superb job of presenting thecurrent products of the DOER Program and allowingaccess to many, if not most, of the products generatedby the other Corps-sponsored dredging researchprogrammes. It is notable that the Corps EngineerResearch and Development Center at Vicksburg,Mississippi has developed this state-of-the-art media totransfer the very significant and important research

Books/ Periodicals Reviewed

29

Volume II of the DOER CDROM.

Asia Pacific Maritime 2004Singapore Expo, Singapore

March 24-26 2004

Targeted at both the Marine Engineering and Portsindustry sectors, Asia Pacific Maritime 2004 is a uniquecomprehensive international trade and technologyexhibition, covering the full range of commercialmaritime equipment, facilities, operations and services.The exhibition is aimed at Port Authorities, ship ownersand builders, and maritime specialists.

For further information contact:Daniel Chan or Ng Chuan YongReed Exhibitions Pte, Ltd.51 Changai Business Park Central 2#07-91 The Signature, Singa6ore 480066tel. +65 6789 8800, fax +65 6789 7711email: [email protected]

Seminar on Environmental Aspects of DredgingPAO Civil Engineering and Construction

Delft, The NetherlandsMay 13-14 2004

Dredging is a necessary activity in society’s develop-ment. Under the right circumstances it is also a veryuseful tool for remedying past environmental interfer-ences. By its very nature, however, the act of dredgingand relocating dredged material is an environmentalimpact. It is, therefore, of the utmost importance to beable to determine whether any planned dredging willhave a positive or negative impact on our environment.Evaluation of environmental impact should examineboth the short- and long-term effects, as well as thesustainability of the altered environment.

This two-day Seminar gives an overview of theenvironmental aspects of dredging and state-of-the-art

dredging techniques. Topics included are:– Players, Processes and Perspectives;– Conventions, Codes and Conditions: Marine

Disposal and Land Disposal;– Investigation, Interpretation and Impact;– Machines, Methods and Mitigation;– Reuse, Recycle or Relocate,– Effects, Ecology and Economy– Frameworks, Philosophies and the Future.

Besides presentations on these subjects, participantswill be challenged in case studies to apply the principlesdiscussed in order to get a full understanding of thescope and importance of the environmental aspects ofdredging projects, the management of dredged material,and effects of environmental guidelines.

The Environmental Seminar is a joint effort of theInternational Association of Dredging Companies(IADC) and the Central Dredging Association (CEDA). It is part of the curriculum of PAO Civil Engineering and Construction, the foundation for postgraduateeducation of the Technical University of Delft in The Netherlands. The Seminar is aimed at consultantsin dredging related industries, and professionals fromdifferent governmental bodies such as municipalities,district water boards, ports and harbour authorities andcentral government.

Course material includes the seven book series ofGuides entitled “Environmental Aspects of Dredging”.The course fee is € 790, including these books, lecturenotes, coffee, tea and lunches. Travel costs and lodgingare not included.

For further information contact:PAO Civil Engineering and ConstructionP.O. Box 5048, 2600 GA Delft, The Netherlandstel. +31 15 278 4618, fax +31 15 278 4619email: [email protected]


Seminars/Conferences/Events

30

numeric modelling; geo-technical aspects; beachnourishment; beneficial uses; and wetlands creationand restoration.

For further information contact:Dr. Ram K. MohanBlasland, Bouck & Lee, Inc., 326 First Street, Suite 200Annapolis, MD 21403tel. +1 410 295 1205, fax +1 410 295 1209email: [email protected]

Dr. Robert E. RandallDept. of Civil Engineering, Texas A&M UniversityCollege Station, TX 77843tel. +1 979 862 4568, fax +1 979 862 8162email: [email protected]

Mr. Stephen Garbaciak, Jr.Blasland, Bouck & Lee, Inc.200 South Wacker Dr, Suite 3100Chicago, IL 60606tel. +1 312 674 4937, fax +1 312 674 4938email: [email protected]

29th ICCE 2004 Congress Centre of the National Civil

Engineering Laboratory (LNEC), Lisbon, Portugal

September 19-24 2004

The Organising Committee of ICCE 2004 and thePortuguese coastal engineering community arepleased to announce the 29th International Conferenceof Coastal Engineering (ICCE), continuing thesuccessful conference series which is the world’spremier forum on coastal engineering and relatedsciences.

Original papers will be presented on theory,measurement, analysis, modelling and practice of thefollowing topics: Coastal processes and climatechange; oceanography, meteorology, morphodynamicsand sediment processes, macro and micro tidalregimes, extreme events, coastal waves, effects oncoastal management; flood and coastal defenceengineering including beach management andnourishment, coastal and beach control structures,construction techniques and performance; flood riskmanagement; recreation, industrial activity, waterquality, wetlands and estuaries, sustainability,environmental economics; ports and harbours includingsiltation, dredging and dredged material re-use,navigation channels, optimisation, wave-structureinteractions, breakwater monitoring, coastalinteractions; and coastal legislation, planning andcooperation.

Ports 2004Westin Galleria

Houston, Texas, USAMay 23-26 2004

The Ports 2004 Conference, "Port Development In The Changing World," will be the tenth in a series ofinternational port and harbour development specialtyconferences held on a tri-annual basis since 1977. This conference is co-sponsored by the Ports andHarbors Committee of the American Society of CivilEngineers (ASCE), Coasts, Oceans, Ports and RiversInstitute (COPRI); and the U. S. Section of thePermanent International Navigation AssociationCongress (PIANC). The conference will be cohosted bythe Port of Houston Authority (PHA).

This four-day conference will cover subjects involvingport and harbour access; terminal facilities such assecurity systems, cargo handling, cruise ships;environmental issues such as dredging and sedimentmanagement; transportation planning; and projectdelivery such as design-build-own-operate and public-private partnerships. There will be at least two technicalfield tours. In addition a number of technical shortcourses will be on offer given by experts in the field.

For further information contact:Ms. Christina Childs, Conference Managere-mail: [email protected] – World Headquarters1801 Alexander Bell Drive Reston, Virginia 20191-4400 USAtel. +1 800 548 2423 or +1 703 295 6030fax +1 703 295 6144

WEDA XXIV & TAMU 36 Dredging SeminarWyndham Palace,

Orlando, Florida, USAJuly 6-9 2004

The twenty-fourth Western Dredging AssociationAnnual Meeting and Conference and the thirty-sixthTexas A&M Dredging Seminar will be held in July atthe Wyndham Palace, Orlando, Florida. The conferencewill provide an in-depth technical programme based on the theme, “Unique Dredging Projects”. It providesa unique forum for discussions amongst dredgingcontractors, port authorities, government agencies,environmentalists, consultants, academicians, and civiland marine engineers.

Topics of interest include but are not limited to: dredgingand navigation; dredging systems and techniques; newdredging equipment; surveying; cost estimating;dredging and navigation; project case studies; auto-mation; inland dredging; contaminated sediments;

Seminars/ Conferences/ Events

31

For further information contact:ICCE 2004 Secretariat, c/o LNEC - DIEAGAv. do Brasil, 101, 1700-066 Lisbon, Portugaltel. +351 21 844 3483 or 844 3900fax +351 21 844 3014e-mail: [email protected]

World Dredging Congress XVIICCH - Congress Centrum,

Hamburg, GermanySeptember 27-October 1 2004

Every three years leading experts meet in a differentpart of the world for the World Dredging Congress(WODCON). The congress is held under the auspicesof the World Dredging Association which is comprisedof the WEDA, CEDA and EADA. In 2004 it will takeplace in Hamburg, organised by CEDA on behalf ofWODA, and co-sponsored by the Ministry of EconomicAffairs, Free and Hanseatic City of Hamburg, and the Department of Port and River Engineering and the Shipbuilding, Machinery & Marine TechnologyInternational Trade Fair (SMM 2004) which will runsimultaneously. The theme of the conference will be“Dredging in a Sensitive Environment”.

The programme will consist of Technical sessions withhigh quality peer-reviewed papers and a specialEnvironment Day focussed on environmentalchallenges and solutions. An Academic session, withcontributions by young scientists, continues CEDA’ssupport of young professionals. Technical visits in andaround Hamburg including views of the Port ofHamburg are planned.

At this conference an IADC Young Authors Award willbe presented to the best paper by an author youngerthan 35 years of age recommended by the TechnicalPaper Committee.

For further information contact:www.woda.org orCEDA, P.O. Box 488,2600 AL Delft, The Netherlandstel. +31 15 278 3145, fax +31 15 278 7104email: [email protected]

International Conference on Coastal Infrastructure Hong Kong Convention and Exhibition Centre

November 22-24 2004

The International Conference on Coastal InfrastructureDevelopment - Challenges in the 21st Century, jointlyorganised by the Hong Kong Institution of Engineers(HKIE) Civil Division and Works Branch of theEnvironment, Transport and Works Bureau,

The Government of the Hong Kong SAR, China aims atproviding a forum for sharing knowledge, experienceand creative ideas among worldwide engineers,academics, environmentalists, developers and financialmanagers in delivering coastal infrastructure projectswith due consideration of the technical, social,environmental and financial perspectives. A number ofpanel discussion sessions with invited speakers will beorganised to address current issues related to coastalinfrastructure development.

For further information contact: www.hkie.org.hk/cv/COASTAL2004email: [email protected]

Call for PapersHYDRO4

Galway, IrelandNovember 2-4 2004

The Hydrographic Society, presently devolving into theInternational Federation of Hydrographic Societies(IFHS), is to hold its 14th biennial internationalsymposium in Galway, Ireland from 2-4 November2004. Proceedings, which will also include a majorexhibition of equipment and services, workshops, fielddemonstrations and anticipated visits by specialistsurvey vessels, are being co-sponsored by severalleading international survey and maritime organisations.

The main theme of the HYDRO4 symposium is “Diversity”. The aim is to provide a forum foraddressing the use of hydrographic expertise for non-traditional survey applications in new seagoingoperations, while conversely exploring potentialbenefits for exploiting non-traditional survey techniqueswithin the hydrographic profession itself. Related technical issues and topics will include:Bathymetry, Coastal Zone Management and Protection,Data Acquisition and Management, Electronic Charting,GIS and Positioning.

300-word English-language abstracts of proposedpapers, by disk or email in Word 2000 format, arerequired by 31 March 2004. They should be submittedto the Symposium organising committee from whomfurther general details are also available.

For further information and submissions contact:Hydro474 Callington Road, Saltash, Cornwall PL12 6DY, UK tel. +44 (0)1752 843461, fax: +44 (0)1752 848267 email: [email protected]


32

Africa

Ballast Ham Dredging (Nigeria) Ltd., Ikeja-Lagos, NigeriaNigerian Westminster Dredging and Marine Ltd., Lagos,Nigeria

The Americas

ACZ Marine Contractors Ltd., Brampton, Ont., CanadaBallast Ham Sucursal Argentina, Capital Federal, ArgentinaBallast Ham Dredging do Brazil Ltda, Rio de Janeiro, BrazilDragamex SA de CV, Coatzacoalcos, Mexico

Asia

Ballast Ham Dredging India Private Ltd., Mumbai, IndiaBallast Ham Dredging bv Singapore Branch, SingaporeDredging International Asia Pacific (Pte) Ltd., SingaporeHyundai Engineering & Construction Co. Ltd., Seoul, KoreaJan De Nul Singapore Pte. Ltd., SingaporeTOA Corporation, Tokyo, JapanVan Oord ACZ B.V., Dhaka, BangladeshVan Oord ACZ B.V., Hong Kong, ChinaVan Oord ACZ B.V., SingaporeVan Oord ACZ Overseas B.V., Karachi, Pakistan

Middle East

Boskalis Westminster M.E. Ltd., Abu Dhabi, UAEGulf Cobla (Limited Liability Company), Dubai, UAEJan De Nul Dredging, Abu Dhabi, UAEVan Oord ACZ Overseas B.V., Abu Dhabi, UAE

Australia

Ballast Ham Dredging Pty. Ltd., Brisbane, QLD, AustraliaDredeco Pty. Ltd., Brisbane, QLD., AustraliaVan Oord ACZ B.V., Victoria, NSW, Australia

Europe

ACZ Ingeniører & Entreprenører A/S, Copenhagen, DenmarkA/S Jebsens ACZ, Bergen, NorwayAtlantique Dragage S.A., Nanterre, FranceBaggermaatschappij Boskalis B.V., Papendrecht, NetherlandsBallast Ham Dredging Ltd., Camberley, United KingdomBallast Ham Nederland bv, Gorinchem, NetherlandsBoskalis B.V., Rotterdam, NetherlandsBoskalis International B.V., Papendrecht, NetherlandsBoskalis Westminster Aannemers N.V., Antwerp, BelgiumBoskalis Westminster Dredging B.V., Papendrecht, NetherlandsBoskalis Westminster Dredging & Contracting Ltd., CyprusB.V. Bedrijfsholding L. Paans en Zonen, Gorinchem,Netherlands

Draflumar SA., Neuville Les Dieppe, FranceDRACE (Grupo Dragados S.A.), Madrid, SpainDravo S.A., Madrid, SpainDredging International N.V., Zwijndrecht, BelgiumDredging International (UK), Ltd., Weybridge, United KingdomHeinrich Hirdes GmbH, Hamburg, GermanyJan De Nul N.V., Aalst, BelgiumJan De Nul Dredging N.V., Aalst, BelgiumJan De Nul (U.K.) Ltd., Ascot, United Kingdom

Mijnster Beheer B.V., Gorinchem, NetherlandsN.V. Baggerwerken Decloedt & Zoon, Oostende, BelgiumSociedad Española de Dragados S.A., Madrid, SpainSodranord S.A.R.L., Le Blanc-Mesril Cédex, FranceTerramare Oy, Helsinki, FinlandTideway B.V., Breda, NetherlandsTOA (LUX) S.A., Luxembourg

Van Oord N.V., Rotterdam, NetherlandsVan Oord ACZ Ltd., Newbury, United KingdomWasserbau ACZ GmbH, Bremen, GermanyWestminster Dredging Co. Ltd., Fareham, United Kingdom

Membership List IADC 2004Through their regional branches or through representatives, members of IADC operate directly at all locations worldwide.

International Association of Dredging Companies

Documents

International Journal on Public Works, Ports & Waterways ... · 14 Sediment Resuspension and Cycling due to Wave Groups Samantha Kularatne Predicting the transport of sediments in