Dredging for Development

THEINTERNATIONAL ASSOCIATION OF PORTS AND HARBORS

DREDGING FOR DEVELOPMENT

COMMITTEE ON PORT & SHIPSAFETY,

ENVIRONMENT AND CONSTRUCTION

Report of the Dredging Task Force

(3th revised edition)

TO

THE17th IAPH CONFERENCE

BARCELONA SPAIN

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ABSTRACT

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The publication, "Dredging for Development,"is

the third edition of an introduetion to dredging for port development. The publication is particularly intended for government officials and port managers from developing countries and is written in non-technicallanguage. It discusses the nature of dredging, its importance and objectives, the processes of excavation, transport and disposal ofmaterial dredged and the types of materials encountered in dredging projects. There is a description ofvarious types of dredging equipment and factors affecting the choice of equipment. The processes normally involved in port development projects; e.g., planning, preliminary design, flnancing,final design and construction and subsequent operation and maintenance of completed projects are summarized. Furthermore, the publication emphasizes the environmental aspects of dredging and international agree-ments pertaining thereto. The appendices contain sections on typical dredging contract provisions,'a current report on port development activities and policies ofthe World Bank Group and the United Nations Economie and Social Commission on Asia and the Pacific.a listing of pertinent international organizations and lending institutions and a listing of relevant publicationswitha specific index of articles which have appeared in the journal, Terra et Aqua.

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TABLE OF CONTENTS

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ABSTRACT

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TABLE OF CONTENTS

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INTRODUCTION

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Preface . Acknowledgements . . Organization of Contents . 7 8 9

SECTION ONE - DREDGING INFORMATION

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The Dredging Process 11

The Importance ofDredging 11

Dredging Objectives 11

Types of Material to be Dredged 12

SECTION TWO - EQUIPMENT CONSIDERATIONS

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Types ofDredgers 13

Choice of Type of Dredger 25

Transport of Dredged Material...25 Disposal of Dredged Material... 26

SECTION THREE - PROJECT PROCESS

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Planning 27

Preliminary Design 28

Financing 28

Detailed Design 29

Execution or Construction . 29

Operation andMaintenance .. 29

SECTION FOUR - ENVIRONMENTAL ASPECTS

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Overview of Environmental Considerations 30

Water Related Impacts 30

Land Related Impacts . 31

Air Related Impacts 31

Disposal of Dredged Material . .. 31

Hazardous Material and Cargoes . _...................... 31

Socio-Cultural Impacts . 32

Environmental Monitoring . 32

International Agreements Regulating Pollution 32

APPENDIX A - DREDGING BY CONTRACT - USUAL PROVISIONS

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Bidding .

Conditions of Contract .

Continuity ofShipping Operations .

Inspeetion and Measurement of Operations .

Frequency of Dredging Operations .

Permits for dredging operations .

Employer-owned equipment .

APPENDIX B - THE ROLE OF THE WORLD BANK

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WORLD BANK INVOLVEMENT IN PORT DEVELOPMENT .

APPENDIX C - SITUATION IN ASIAAND TUE PACIFIC

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APPENDIX D - INTERNATIONAL BODIES AND ORGANIZATIONS

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International Advisory Bodies .

Addresses of Organizations . .

Development Banks .

Acronyms... . .

APPENDIX E - RECOMMENDED LIST OF PUBLICATIONS

ON DREDGING AND PORT DEVELOPMENT

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Books, Periodicals, Reports and Monographs .. . .... 45

Terra et Aqua Contents,Numbers 1-44... .. 49

Summaries of Pertinent Articles from Terra et Aqua 53

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INTRODUCTION

Preface

The International Association of Ports and Harbors (IAPH)has long been aware ofthe need

to provide public officials of developing nations

with an introduetion to the complexfield of dredgingwhich iswritten in non-technical language, coversthe main elements such an official mustbe aware of and a souree of basic information concerning the field of dredging technology. For this reason "Dredging for Development"was first presented to the IAPH membership and published in Terra et Aqua in 1983.Because ofthe interest shown bythe target audience and others, a second revised edition was published by IAPHas a separate publication in 1987.Once again,the response was most gratifying and confirmed our initial premise.

In view of this response and to report on significant developments, the IAPHDredging Task Force Sub-committee decided to undertake this third revised edition. The publication has been expanded once again from earlier versions and reorganized somewhat and reflects

comments received as weUas developments in equipment, contracting standards and particu-larly the justified sensitivities of the general population and lending institutions regarding the environment.

Itis not our intention to te ach anyone how,or even when,to perform dredging. Rather, we have attempted to point out some items which should be considered when dredging becomes a logicalor essential part of a port development project. Likewise,we have included some information on the need to consider subsequent operation and maintenance of port projects as it relates to dredging once the construction has been completed.

Therefore, this publication is an introduetion to the complex field of dredging. Dredging is essential to the construction and maintenance of navigation and port projects.The various aspects ofthe dredging process, the types of soils encountered on dredging projects, the equip-ment generallyemployed,the disposal of dredged material, the types and nature of contracting vehicles,the vital importance 0f environmental factors and issues related to financing such projects are all issues with which the navigation and port officials must at least be aware. These are the subjects presented in overview form in this publication.

While there are many publications and sourees ofinformation available to those who deal with

tbis field as a specialty,there was no single document designed especiaUyfor the managers,

planners and decision-makers. They,above all,

must have some basis of general awareness of dredging related issues and knowledge in order for them to direct and focus the actions oftheir staffs and an appreciation for these issues as they

ponder the feasibilityof developing navigation projects. +-' c Q)

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This publication is an attempt at providing this single document for those officials and mana-gers.It is not intended to be all inclusive,for that would take a major publication and one which most busy managers would not likelysee or have the time to peruse. It is intended th at this modest publication be readable, available and used bya wide audience ofnavigation and port managers and officials.

While this publication is basicallyconcerned with dredging, we recognize that this is only one aspect ofthe entire area ofport development and we have included several items dealing with port development in general. We also touch on port financing in a very general sense and present some information on port development which has been experienced in Asia and the Pacific regions.

We sincerely hope that this publication will provide a useful reference souree for officials and managers responsible for port projects. While our primary aim was to provide tbis information to developing nations, experience has shown th at many ports and port users in the developed nations have found this publication useful. Aswith any publication ofthis nature, we have tried to maintain a balance ofbrevity, readability and substance. We welcome your comments and suggestions for changes and improvements.Comments should be directed to:

Chairman,Dredging Task Force c/o IAPHGeneral Secretariat Kotobira Kaikan Building

2-8 Toranornon 1-chome,Minato-Ku Tokyo 105,JAPAN

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Acknowledgements

Anumber of dredging experts and organizations have provided information and generous assistance in the preparation, editing and printing ofthis 3rd edition ofthis publication.

Mr. R.C.W.Brouwer, President and Mr. J.A. Mulock Houwer,Secretary General ofthe International Association of Dredging Contrac-tors (IADC)have all provided gracious assistance and guidance. Once again the IADCassisted in the preparation, and the printing ofthis edition. Special thanks are given to

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Holland,IADC member companies and the World Bank who provided photographs and figures for this publication.

Particular mention is made of Mr.Herbert R.Haar, Jr., the long time chairman ofthe IAPH Dredging Task Force Sub-committee and strong advocate of education and environmental responsibility in dredging operations, who was a great help in this project as weIl the instigator of the original publication.

Mr. John Lethbridge ofThe World Bank; Mr. David P. Turner ofthe United Nations Economie and Social Committee for Asia and the Pacific;Mr. R. de Leeuw ofVolker Stevin and his colleagues at Nash Dredging in the UK;

Mr. J.J. Goudsmit, independent consultant; and Dr.Robert M. Engier ofthe U.S.Army Corps of Engineers Waterways Experiment Station all made significant contributions to this publica-tion. Similarly, Ms. V. Lorraine van Dam and the Central Dredging Association and Delft Univer-sity of Technology (DUT)assisted in providing reference mate rial which was liberally drawn upon.Further, I would like to thank my mentor,

Mr.W. R. Murden, Murden Marine, Ltd.,Prof. Kees D'Angremond of DelftUniversity of Technology and the IAPHDredging Task Force Sub-committee for reviewing the manuscript and suggesting improvements.

Charles W.Hummer, Jr.

Editor TheHague March 1991

Organization of Contents

This document is organized insuch awayasto allow the user togo fromoverviewinthe bodyof

the report tomoreselective information inthe appendices tofit the users' needs.Perhaps as important, itprovidessourees for more com-prehensive and detailedinformation on avariety of subjects related to dredging and port

development.

Sections 1 and 2provide a general overview of the subject of dredging. This mate rialwas adapted from a number of sourees but the primary references used were the manual "Port Maintenance, "(2)published bythe American Association of Port Authorities(AAPA),Annex I ofthe World Bank publication, "Environmental Considerations for Port and Harbor Develop-ment,"(10)and material from the course,

"Dredging and the Environment,"presented by

the Stichting Postakademisch Onderwijs Civiele

Techniek en Bouwtechniek and the Central Dredging Association in November 1989.The first two references are excellent additions to the library used byport officialswho are not experts in the complex subject of dredging.The latter is an excellent course which would be particularly useful to the technical department engineers and technicians of anyport or navigation authority.

The numbers in brackets refer to the referenced publication which is listed in Appendix E. Section 3 introduces the reader to the main aspects ofthe process which leads to develop-ment projects and the importance of these elements in the successful planning, design, financing and construction ofport projects.More detailed information on the usual contracting conditions,particularly as they relate to the standard contract conditions promulgated bythe Fédération Internationale des Ingénieurs-Con-seils(FIDIC)!15and the IADCFIDICUsers') Guidel20)is presented in Append, ixA.

The environmerital aspects are treated in Section 4,with particular reference to the London Dumping Convention(LDC)and theUnited

Nations Environmental Programme (UNEP)

Regional Seas Programme and the policies ofthe

World Bank and were drawn primarilyfrom the

World Bank publication cited above'P'. Consi d-eration ofthe environment and its proteetion is increasinglya paramount factor in designing

and executing port improvements and mainte -nance throughout the planning, design and

execution phases of a project.In most instances. environmental considerations are equal to the

technological, engineering and financial factors related to navigation projects and if adequately

considered earlyinthe process,cansmooth the

way to project financing and execution.

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Appendix B gives a current view ofThe World

Bank andthe agencies making up the World Bank Group.Additional informationregarding port development in developing nations is presented in Appendix C.This information was obtained fromUnitedNations Economie and Social Commission,Asia and Pacific (ESCAP),

courtesy of Mr.DavidL.Turner, Chief, Trans-port and Communications Divisionin Bangkok.It is presented to give the readers a perspective of navigation and port development in a segment of the community of developing nations.

Appendix Dlists the other international agencies involved in this work and addresses of organiza-tions which are useful to port officials.Appendix E contains a list of pertinent publications, periodicals, books and monographs; a complete index ofthe journal Terra et Aqua along with summaries of pertinent articles from Terra et Aqua.

A common thread which runs through the literature is the importance oftransportation to the economy of anynation. developed or developing.One pitfall which seems quite common is the failure to understand the interrelationship of all phases ofthe infrastruc-ture which often results in the failure to develop each in relation to the other. Several articles illustrate the point that developing nations may not have the expertise to handle major projects. It is therefore judicious that a competent consultant be engaged to prepare the project. The fee paid to the consultant may well prove to be one ofthe best investments made by the authorities concerned. However, for the long term, there is no question that the development of a training program by which local authorities can establish the necessary in-house staff of experts on dredging and environmental technologies is the best course of action.

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The

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ging Process

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A simple definition of dredging is that it is the

subaqueous excavation of soils and rock.The process consists ofthe excavation.transport and subsequent disposal or use of the material dredged. Since it occurs underwater. it is out of sight and generally the appreciation ofthe need for and complexity of dredging is little under-stood except by those actually connected with construction or maintenance ofprojects associated with navigation or one ofthe other purposes of dredging listed below. Another tendency is to consider only the excavation phase ofthe process and overlook the transportation and disposal phases. The process is so integrated that all must receive equal consideration and emphasis. Government planners and officials as well as the public often have little idea of the issues which must be considered in the planning.

design. construction and operation and mainte-nance ofnavigation projects. whether they be coastal or inland projects. For this reason, it is often prudent to provide some education ofthe process and the benefits and the potential impacts.

T

he Importance of Dredging

From the beginning of civilization and the evolution of established communities,there has been a need to transport people, equipment.

materials and commodities by water.This resulted in the requirement that the channel depths ofmany waterways be increased to provide access to ports and harbours. Virtually

all major portsinthe world require dredging to deepen access channels, provide turning basins and appropriate water depths along waterside facilities. Likewise,often these channels require frequent and regular maintenance dredging in order to provide adequate depths for using

vessels engaged in domestic and international commerce. Inthe case ofriverine navigation.

dredging is likewise required to construct and maintain vital navigation links to inland ports and facilities.Insumrnary,dredging plays a vital role in the economie and environmental aspects of most countries in the world.

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Thebasicobjectives of dredginginclude:

(1)Navigation.

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To maintain, to extend or otherwise improve waterways, harbours and channels. To create

harbours, basins, canals,marinas and other facilities for navigation.

(2) Flood control.

To improve or maintain the discharge or flow

capabilities ofthe rivers by deepening andJor natural waterways or by the realignment of watercourses or the construction of control structures such as dams, dykes or levees.

(3) Construction and reclamation.

To provide construction materials such as sand,

gravel.shell and clay or to provide landfills.

including the construction ofindustrial and.

residential are as. highways.darns, airports:

causeways and habitats for birds and other forms ofwildlife.

(4) Mining.

Toreeover minerals. gems. precious met als and fertilizers.

(5) Beach Nourishment.

To provide

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material for theproteetion and replenishment of beaches. including the construction of protective dunes.

(6) General.

To excavate for underwater foundations and for the emplacement ofpipelines or tunnels. To provide for flood control in swampy or lowland areas, where thatis environmentally acceptable.

To remove or remediate pollutants and improve

water quality.

Itis obvious th at dredging projects can and do

varyenormously with re gard to the purpose of

the project and the volumes and types of soil

which have to be moved. In the developing

countries serious problems may be encountered

with even small-soale dredgingjobs for which

local,low-cost solutions would be preferable, This is often more difficult than one would imagine at fust glance.

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Types of Material to be Dredged

Types ofmaterial to be dredged vary signifi-cantlyfrom project to project and within projects. The primary categories generally associated with dredging are: peats and organic soils,clays,silts,sands, corals, sandstones, gravels, boulders and cobbles,and rock. See the PIANCpublication on the classification ofsoils and rocks to be dredged for more detailed information.(25)

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_{Within each ofthese major categories are ranges}

ofparticle sizes and partiele nature and plasticity.The type ofmaterial determines the most etTectivedredging plant,the production rates, the likelihood of contamination, the potential disposal or end uses, and the charac-teristics atTectinghandling such as bulking, formation of clay balls, etc.The determination of types ofmaterials to be encountered in a project is made by the use ofsubsurface exploration and geophysical techniques in which a representa-tive set of samples is taken throughout the potentialor actual project dimensions. Since there is often vertical as well as horizontal distribution ofmaterial, samples are taken

Figure 2 - Large Cutter-he ad Dredger.

vertically to those depths planned for the project. These samples are then subjected to laboratory investigation to supplement their characteriza-tion with that from the visual observacharacteriza-tions usually taken at the time of sampling.There are significant risks involved when insufficient soil characterization data are collected.

As win be stated on a number of occasions,the geological or subsurface exploration taken during the feasibility or planning phase is generally insufficient for the level of detail required for the design and construction phase. These detailed sampling or exploration

programmes are required once the project alignment and definition approaches that which will ultimately be built. The ditTerencein the level of detail and the need for two occasions of exploration with their significant costs must be emphasized and understood by those in

management in addition to those in the technical statT.The costs involved with insuring adequate soil data are available in the two distinct phases, namely, feasibility and design and construction, are relatively minor when one considers the project costs and risk for large and unpredictable cost overruns.

production rates, therefore they can range from 50cubic metres to 4000 cubic metres per hour.

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SECTION TWO - EQUIPMENT CONSIDERATIONS

Asthe reader willobserve below,there are a

varietyof dredgers andmeans by which to

employ themdepending on thespecifics ofa particular project. Nosingle type of dredger or

system ofemploymentwillbe suitable for all projects. The quantity and type ofmaterial to be dredged, disposal alternative, availability of

equipment or costofmobilization are but some of the factors which playa part inthe ultimate decision.This section presents an overview ofthe subject.

Types of Dredgers

There are a number of schemes for describing types of dredgers. For the purpose of this publication the types of dredgers are described bythe three broad classifications of dredgers on the basis ofthe mode ofexcavation and opera-tion:mechanical dredgers, hydraulic dredgers,

and mechanicallhydraulic dredgers which utilize both basic elements in some combination. Within these three categories further subdivision

can be made on the basis of propulsion;that is,

those which are self-propelled either during the excavation phase, the transportation phase or both and those which are non-self-propelled.

The production rates for the dredger varies widely depending on the circumstances, the material to be dredged and the transport and disposal methods employed.Other factors such as weather and sea state, ship traffic,depth,

depth ofthe dredging face also affect dredging

Mechanical Dredgers

This category employs mechanical means forthe excavation ofmaterial and aregene rally similar totheequipment used fordrylandexcavation.

Examples ofmechanical dredgers are:

a.Grab or clamshell and dragline

These employeither rotating cabs ortixed

A-frame type barge-mounted equipment,which have hoisting and control systems and use

clamshell digging devices or buckets rigged on

cablesto excavate the material from the bottom and transport it verticallyout ofthe water and into barges for subsequent transport to a disposal area. Clamshell dredgers can be used in sandy,some types of clay,gravel,cobbles and some broken rock dredging situations. Theyare not particularly effective in fine silts which have a tendencyto run out ofthe bucket but are nonetheless used for this purpose in smaller jobs. One advantage of clamshell dredgers is their abilityto dredge in fairly deep waters and their abilityto do precise spot dredging either to remove isolated areas above grade in the channel or along docks and corners ofdocks. Depending on the type ofmaterial dredged,they

have moderate to low production rates. Theyare normallynon-self propelled and are flxed at the excavation site using anchors or spuds.

("I")

.-Figure3 •Dredger Types

DREDGER TYPES

MECHANICAL MECHANICAL

HYDRAULIC

HYDRAULIC

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GRAB/CLAMSHELL

DRAGLINE

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Figure4a-4b - Grab or ClamshellDredger

b.Backhoe

The backhoe is cornmon to drylandexcavators

and is increasingly being employedf0r dredging.

Asin the case above,theyare barge-rnounted for

dredging, gene rallynon-self-propelled and can

have moderate production rates. They ernployan

articulated excavation bucket mounted on an

articulated boom. Theygenerallyusehy

drauli-callyoperated rams for movement. positioning

and excavating. The mate rialisexcavated,

brought to the surface and placedinbarur-s for

transport to the disposal area. They ran diga

broad range ofmaterials such as;sand. vlays,

gravel. cobbles and fractured and unlrnrtured

moderately hard rock. Theydo have radius and

depth limitations but with somenewi-r mudels

increased excavating depths are pnssihh-. These

dredgers are likewise generallynon-sr-lf-propal

-led and require anchors or spudstuIix tlu-m at

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.-Figure 5- BackhoeDredger

c.Dipper

The dipper dredger is more or less a powered

shovel mounted on a barge. Olderversions used

arotating boom with a stick and shovel design.

I.ater designs incorporate the "whirley"or

rotating cab,luflingboom and a stick and bucket.

T1H'sedredgers use vertical spudsto anchor

thf'm to the bottorn and a digging spud at the rear

Ilrthevessel to provide resistance to the massive

!liggingforces ofthe bucket. Dipper dredges

rnrne in all sizes but thelargest modern such

dn-dge has a 15 cubic metre bucket. The dredger

opvrates byusing teeth on the lip ofthe bucket to

excavatethe materialfrom the bottom,oncethe

bucketisfull the dipper stick iswithdrawn

upwards andthe cab and boom rotated 50the

bucketis over the barge or scow,the bottorn of

the bucket is released thereby dumping the

contents ofthe bucketinto the barge. The

dredged material isthentransported tothe

disposal area in barges or scows,which maybe

either self-propelled or propelled byattendant

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particularly suited for dredging hard rock and highly compacted materials and have been used effectively in removing old subaqueous founda-tions from within the project. There are

limitations on dredging depths which can be dredged by dippers.Muchofthe work previously done by dipper dredgers is now done by

backhoes, although large dippers are still in use and compete quite effectivelywith other types of

d. Bucket-ladder

Bucket-ladder dredgers once comprised a major part ofthe European dredging fleet and are in fa ct the direct descendants of the historie mud mills.Theyuse a series ofbuckets mounted to an

endless chain loop. The loop ispowered causing

the buckets to tra velin such a manner as to scoop

the mate rial from the bottom,carry the mate rial

in the upright buckets up the ladder to the top of the ladder where the buckets then rotate into an upside down position thereby dumping their contents into a chute. The material is then sent

through the chutes to barges or scows alongside

the dredger. Likethe other mechanical dredgers,

barges or scows are used to transport the

dredged material to the disposal sites.They can

be effectively used in a wide variety ofmaterials up to and including soft rock mate rial. These dredgers were sometimes self-propelled to provide transport to the dredging site. They fell into disuse because oftheir low production rates, need for anchor lines which often interfered with navigation traffic and relatively high noise levels.

Figure 7a-7b - Bucket-ladder Dredger

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Figure 8-PlainSuction Dredger

Figure 9a-9b-Dustpan Dredger

THE DUST'JIIilN DREDGE

AConcept Design by MarineDesign Center

Hydraulic Dredgers

These dredgers use hydraulic centrifugal pumps to provide the excavating force. with or without mechanical cutters. and hydraulic transport force to carry slurried solids from the digging site.through a pipeline to the surface and thence through a discharge pipeline to the disposal site.

In some special cases hydraulic dredgers do dispose into barges for subsequent transport to the disposal site.

a. Plain suction

They can dig at great depths using ladder mounted centrifugal pumps to enhance

production at deeper depths. They are effective in unconsolidated materials such as sands and gravels and are used extensively in aggregate winning operations and large reclamation projects. Because oftheir inability to handle consolidated materials and their characteristic to produce small deep excavations. they are rarely suitable or used for channel or harbour construction projects. They can be both stationary or self-propelled, although self-pro-pulsion is not used during the excavation process. In suitable materials, they have high production rates.

b. Dustpan

A rather special type of suction dredger, called the dustpan dredge is used on river systems where there are high bed loads of sand and small gravel and which when conditions are right, form bars in the navigation channels. The dustpans are capable ofmoving large volumes of

mate rial from localized areas using a suction head shaped much like a dustpan. The mate rial is usually slurried by use of water jets along the top ofthe digging face ofthe dustpan, drawn into the suction head and up the suction pipeline, through the pump and thence through a relatively short floating discharge line. The mate rial is disposed into a portion ofthe river where high energy currents keep it in suspension and it is carried downstream and away from the constricting bar. They are not generally used for construction dredging and were originally designed for use in large river navigation systems where conditions are appropriate for their design and use.

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c. Water injection

Although this type ofprocess has been known for some time and utitized in special circumstances. the water injection dredger is finding some notabie successes primarily for maintenance dredging at the current time. The dredger uses water pressure to fluidize the material to be removed creating a dense fluid slurry. The slurry is then transported from the excavation site by means of currents either induced by the density gradient between the slurry and that ofwater . or by naturally occurring currents within the dredging site. such as tidal currents. This is a relatively low cost dredging technique which is limited to silts and unconsolidated clays and fine sands. The system can either be barge-mounted, either self-propelled or stationary or it can be a fixed structure associated with a quay where siltation is known to occur.

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N MechanicalJHydraulic Dredgers

These type dredgers include the real workhorses ofthe dredging industry. The cutter or cutter-head dredger, bucket-wheel dredger and trailing hopper dredger are representative of mechani-calJhydraulic dredgers. These dredgers are employed on construction and maintenance projects depending on the nature and quantities ofmaterial to be excavated.

a.Cutter-he ad and bucket-wheel dredgers Both the cutter-he ad and bucket-wheet dredgers use rotating mechanical devices. calledcutters, mounted ahead ofthe suction head toexcavate the mate rial into suitably sized material which is then sucked into the suction pipe as aslurry and pumped to the surface. Byuse ofpumps mounted on the ladder or structural devicewhichextends to the bottom these dredgers can dig effectively at depths approaching 25-30 metres or morein special cases.Theyare characterized byhigh production rates and the ability to effectivelydig silts,clays,sand, gravel, cobbles,fractured and sound rocks. Theyworkinastationary mode

Figure lOb - Water Injection Dredger

either on spuds or anchors. Some are self-pro-pelled to provide for transportation between werk-sites. They have flexible disposal alternati-ves and can either discharge into barges or, as is generally the case, through discharge pipelines to the disposal site.Byuse of booster pumps in the discharge lines, they can transport and dispose ofmaterials at considerable distances from the work site. Cutter-heads rotate along the axis ofthe suction pipe whereas hucket-wheel dredgers rotate perpendicular to the axisofthe suction pipe.The bucket-wheel is afairlynew technology and is used in cases wbere large amounts ofrubbish are found,and in mining applications.

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b.Trailing hopper dredgers

Trailing hopper dredges are self-propelled ships with hoppers or dredged mate rial storage internal to the hull, which have articulated dredging or drag arms which extend to the

bottom to be excavated. They dredge while

underway travelling at lowspeeds. The drag

head can be either passive or active. In the case

ofthe passive draghead, no addition power is

applied at the draghead and it depends on the scouring ofthe mate rial to be excavated by hydraulic currents induced at the drag head. The active draghead employs power to drive either cutters or water jets to excavate the material and aid in slurrying the mate rial. The weight of the drag system which maintains contact with the bottom material in either passive or active draghead then allows the mate rial to be

transported hydraulically as a slurry. In both

cases. the mate rial is hydraulically transported

through suction lines, through the centrifugal

pump and into the hoppers where it is retained

for transport and disposal.

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Trailing hopper dredgers are quite flexible in

terms ofthe mate rial to be dredged, its disposal

alternatives and the ability to work in protected

and unprotected waters. The material is

transported internally in hoppers within the vessel to a disposal site remote from the work site and either dumped through doors or valves in the hopper bottorn. or in the case of a split-hulled

vessel,out the bottom when the hull is split;or it

can be pumped from the hoppers through discharge lines to shore based disposal sites with

or without the use of booster pumps.

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These dredgers can dig effectivelyat depths ofup to 60 metres using pumps mounted on the drag arm close to the drag head.They are effective in silts,sands, clays and gravels but are not

gene rally used in rock dredging.They have

relatively high production rates. They have the additional advantage since they are

self-propel-led,theycan work in congested areas with

minimum disruption to ship traffic and can work in unprotected waters such as entrance channels far out to sea and under weather and sea conditions where stationary equipment is

somewhat limited.The trailing suction dredger

is unique in the sense that it uses its self-propul-sion during the excavation and transportation processes.

Figure 13c - Trailing Hopper Dredger(Splithull)

Other dredgers

There are other types of dredgers utilized,some

ofwhich fit into the above categories but are not described here. These are specialized tools developed for specific purposes such as

environmental clean-up, small maintenance

projects and mining and extraction operations.

Ofparticular note are modular or portable dredgers which can be truck hauled to the work sites. Those described above are gene rallythe categories and types used in major construction projects and routine operation and maintenance projects.

Figure 14 - Portable Mudcat Dredger

Choice

of Type

of Dredger

The choice of dredger used on a specific project depends on a number offactors. Type ofmaterial to be dredged is a primary factor. Hard rock dredging gene rally limits the types of dredgers to mechanical dredgers or cutter-head dredgers designed specifically for rock dredging. Where the material can be suitably dredged by several types of dredgers, then a more detailed consider-ation of operating parameters is required. Trailing hopper dredgers are able to work effectively in entrance channels where sea and traffic conditions make stationary plant less desirabie and effective. The location ofthe disposal are as and access to them mayalso play and important role in the decision on the most suitable and effective dredger type.Asstated above, cutter-head dredgers can pump long distances to remote disposal areas and do so, more or less, on a continuous basis.Hopper dredges under the same circumstances may spend a considerable time transporting material for disposal, particularly where water depths further increase haul distances and likewise, mechanical dredgers using barge or scows for disposal transport may require large numbers of barges and support equipment such as tugs and tenders. These factors require both technical and economie analysis in the decision process.

For instance, the most effective dredger may not. be available close to the work site and then mobilization time and cost must be factored into the decision. To give an approximate sense ofthe employment ofvarious types of dredges, recent data show that the share ofthe total dredging market in terms of volume for cutter-head dredgers is approximately 50%, for trailing hopper dredgers, 30%, for grab dredgers and backhoes, 10%, for bucket-ladder dredgers, 5%,

and for the remaining dredgers, 5%.

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In summary, there are a variety oftools or dredgers capable of being used on a project. All ofthe factors mentioned abovewillplay a part in selecting the most suitable equipment for a particular job, but ultimately, ifthe work is to be accomplished by contract, the competitive bidding processwilloften serve as the final decision mechanism.

Transport

of Dredged Material

The transport of dredged material is an integral part ofthe dredging process and is determined to a large extent on the type ofequipment employed and the disposal options available.Asdiscussed above, hydraulic suction and cutter head dredgers use pipelines to transport dredged materials to the disposal site. For long distances to the disposal areas one or more booster pumps may be required at intervals along the discharge line. Discharge lines may be floating or pontoon mounted, or can be submerged where floating lines would interfere with navigation or shore pipelines. Often, all three discharge lines may be used on the same project.

Mechanical dredgers must use barges or scows for transportation. In these cases, unless the barges are self-propelled, ancillary power vessels such as tugs or tenders are used to tow or push the disposal barges. These barges may be transported singly or in groups depending upon the power ofthe power vessels and sea condi-tions.The barges or scows used for disposal usually contain pockets in which the dredged material is placed. The material is unloaded from the barges by being dumped through the bottom either through cable or hydraulically operated doors or in the case of split-hulled barges by splitting the barge longitudinally.

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There are cases where the barges are unloaded using hydraulic pumps or mechanical equip-ment.

In the case of dustpan dredgers and water injection dredgers the transport of dredged material depends on the energy contained in the water currents which are induced either because of slurry to water density gradients or due to hydraulic currents in the waterbody itself, such as tidal or river currents.

Depending on the transport mode, costs for transport can be significant both in the case of hydraulic pumping or barge and scow opera-tions, to minimal as in the case of the use of natural forces such as currents.

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Disposal of Dredged Material

The ultimate step in the dredging process is to dispose or deposit the dredged material in a location away from that excavated. There are a number of disposal alternatives. The basic options are: open water, intertidal or shoreline and upland or on-shore sites.In each option there are further options to either confine the material or leave it unconfined. The option or options employed depend on a number offactors, such as; accessibility to the work site,type of dredger and transport system, whether the dredged mate rial contains contaminants, cost and environmental factors. It is always desirabie to use the dredged material for beneficial purposes. Such purposes may be to create fast land for subsequent construction purposes, use as aggregates, creation ofwildlife habitat, construction of shore proteetion features, beach nourishment or tofillabandoned mine or quarry excavations or even, when the material is suitable, for topsoil. When used for beneficial purposes there is gene rally a cost benefit to be achieved thereby reducing the actual cost for navigation purposes. Ifbeneficial uses are not possible,either because ofthe nature, volume or contamination ofthe dredged material. then disposal should be conducted in a manne r which creates minimum environmental damage,is cost effective and for which sites can be reasonably acquired.

The disposal of dredged mate rial should be considered early in the planning process both for construction and subsequent maintenance dredging. Adequate disposal sites should be planned and provided for the life ofthe project.

Asports become more congested after construc-tion, disposal sites can present a major problem for continued economie disposal ofmaintenance material. Many projects employ multiple disposal sites for various segments of the waterway system. For instance, entrance channels may use open water disposal sites for both construction and maintenance material. Inner harbours may use intertidal and upland sites. And in the case of developed harbours, many times contamination of bottom sediments can occur thereby requiring specially designed and constructed sites for contaminated sedi-ments.

SECTION THREE- PROJECT

PROCESS

This section is included in order to highlightthat

there is a processwhichis required for port

developmentand this process should bewell

thought outand understood at the outset. There

are manyspecialized books,reports and papers

onthe details of schemes successfullyused for

portdevelopmentsomeofwhich areincluded in the appendices. Perhaps the greatest change in the project development process is the need to consider the environmental consequences of such a project and to incorporate environmental proteetion concepts and costs from the beginning ofthe process. Lending institutions certainlynow require substantive and comprehensive

environmental assessments before theywill favorably consider applications for development funds. Simllarly,these same financial institu-tions have developed some excellentguidelines and means bywhich to fmance the initial environmental studies essential to sound development.

Consideration should be given to using an integrated or life cycle project management process and structure which involves all parties and disciplines from the outset. Planners; design, cost and construction engineers; dredging experts; environmentalists; economomists; financial planners;and transportation special-ists all playa part in the development process. The integrated project management process insures that all these players are involved throughout the process not only in their special phases ofthe project.The project evolves through the various disciplines but certainlyone closely impacts on the other and only through integration ofthe disciplines will the project avoid oversights and costlyerrors. Even

experienced organizations, such as the USCorps of Engineers in the United States and the

Rijkwaterstaat in Holland which have been responsible for port development projects for over a century,have concluded that their pll"orh could be significantly more efTectiveutilizing such an integrated approach.

Althoughthere are manyformats fortheport

projectdevelopment process, forthe purposes of

this publication a simplified and basic outlineis

used.The elements ofthis process are:

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1.Planning 2. Preliminary Design 3.Financing 4.Detailed Design 5.Executionor Construction 6.Operation andMaintenance In some cases, items 4.and 5. above are combined into a"designlconstruction phase," nonetheless there remain discrete sub-elements even in that case.

P

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anning

This is a broad term and appropriately so,for manyactivities must be taken into consideration during the planning or project formulation phase. Some ofthe basic elements ofthis phase are:

1.Isthe project consistent with the national

transportation development master plan? 2.Onthe basis oftotal transportation infrastruc-ture, does it make good investment sense? 3. Willthe project further the national socio-economie interests?

4-. Is the planning horizon sufficiently long both in hindsight data as well as future projections for use?

.i. Doesit incorporate the latest state-of-the-art interrnsofequipment, procedures and

rhroughput taking into account the abilityto ....cure scarce capital resources?

1,.Doesit consider alternatives and include an analysis oftrade-ofTs and cost and benefits for

«achofthe alternatives?

ï. Doesit adequately assess the short and long

term environmental consequences?

Focusing on the dredging aspects, such a

planning effort should consider some ofthe followingfactors:

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1. Do adequate data exist concerning hy

dro-graphy, morphology, geology,meteorology and

geography of the potential port development sites? Ifnot, these data sets are essential to evaluate potential design scenarios, proper

specifications for the works,good construction

estimates, maximum use ofnatural forces both

for construction and maintenance, such as

scouring currents, impacts of salt water intrusion, disposal alternatives and costs

therefore, and finally, the subsequent

mainte-nance requirements and costs.

2. Does there exist an adequate engineering staff to collect,analyze existing data or credibly direct the collection and analysis of such engineering data or should the use of consultants be

employed? If consultants are to be employed, on which elements? Is this an opportunity to train local engineers in these specialized engineering disciplines or gain practical experience? 0)

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3.Does the plan consider the disposal ofdredged

material for the construction and subsequent maintenance? Were sufficient options consi-dered to minimize transportation costs for the dredged material and to consider the potential impacts ofweather, sea state,etc. on the construction and maintenance processes? These are pretty basic factors to be sure, but often the understanding ofsite investigation and necessary data are not differentiated between the planning or feasibility process and the design

and construction process. In most cases,two

separate data sets are required. The latter and more detailed being that in the design phase where such data are essential to adequately specify the works in such a manner as to avoid unnecessary risk to the owner and to the

contractors. There are many instances where

preliminary site investigation data were inappropriately extrapolated into designs and specifications with costlyand unsatisfactory results.

Preliminary Design

Once the feasibility has been determined from the planning phase, a preliminary design is often

the next step.Itfurther focuses the development

ofthe project on the most sound engineering,

environmentally responsible and economie

alternative and avoids some ofthe pain of overlooking some critical engineering element. Further, it provides a productive adjunct to the planning documents required for the successful

acquisition offinancing. Italso provides another

series of cost estimates which will have more

basis than those used in earlyplanning

docu-ments. Itshould be pointed out that cost estimates should evolve and become more accurate as the project development process unfolds. Reliance on only the initial planning cost estimates can be another costlyexperience.This lesson is one for which developing nations should also be aware of.

Financing

It goes without saying, th at securing the

necessary financing for port development

projects is critical. However,ifthe planning and preliminary design phases are conducted

adequately, they provide the necessary basis on

which to credibly secure financing for the

project.Aswas pointed out earlier, many lending

institutions now require substantially greater consideration ofthe environmental aspects of

development. For example,The World Bank in.

its recent publication, "Environmental Consider-ations for Port and Harbor Development,"(10)

states:

"The World Bank attaches great importance to environmental aspects of development projects.

In the case of port and harbor developments,

ports and port authorities, consuIting firms and Bank port engineers and other staff are expected

to provide effective and thorough environmental

input into the project concept,preparation, detailed engineering, construction and opera -tion. This implies the need for adequate

environmental units within each ofthe bodies or agencies responsibIe for the project. "

The publication goes on to state: "The Bank:

-will not finance projects that cause severe or irreversibie environmental deterioration

without any mitigatory measures acceptable to the Bank....

-will not finance projects that unduly com -promise the public health and safety....

- will not finance projects that displace people or seriously disadvantage certain vulnerable groups without taking mitigatory measures acceptable to the Bank...

- will not finance projects that contravene any international environmental agreement to which the member country concerned is a party ... - willnot finance a project that could signifi-cantlyharm the environment of a neighboring country without the consent ofthat country ...

- endeavors to ensure that projectswith unavoidable adverse consequences for the environment are sited in areas where the environmental damage is minimized,even at somewhat greater costs....H

Accordingly,in addition to the traditional lending institution requirements, environmental aspects must be adequately considered in order to secure financing for port development and improvement projects.

Detailed Design

This phase presumes that all feasible alterna-tives have been considered and a single project has beenidentified which meets the economie, financial and environmental criteria established. The preliminary design is then developed into a detailed engineering design package. For the purposes ofthis publication,this detailed design package is the primary vehicle for developing a set of specifications suitable for soliciting international tenders from dredging contractors. Sufficient information must be contained as a re sult ofthe design to clearlydescribethe elements ofthe works and present to tenderers the data and information required for the preparation of a responsibie tender. Further-more, atthe end ofthe detailed design, a reliable

cost estimate should be in hand on whichtobase

an evaluation of such tenders.

Execution or Construction

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In orderto move into the execution or

construc-tion phase, aswas mentioned above,detailed

specifications andcontracting documents must beprepared and used to solicit tenders forthe actualconstruction ofthe works.AppendixA describesin detail the typical provisions and

conditionsfor suchcontracting documents. Of

noteisthe needto designate an "Engineer" and

"Contracting Official"bythe owner.In some cases,the Engineer function is performed by

qualified,knowledgeable and responsible consulting engineering firms.The selection of such a firm is another process which requires due care and attention. On the basis ofthe

tenders, evaluation is made and a contractor

selected for the execution ofthe works. Perhaps ofnote isthe need for the owner to ensure an adequate contract administration structure and construction inspeetion scheme is in place prior to the initiation ofthe execution or construction phase.

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Operation and Maintenance

The completion of the execution or construction phase has now provided the physical assets ofthe project. There is a need to have developed and in place an operations and maintenance scheme for the completed project and a clear definition between the construction and operation and maintenance phases. On large projects whére segments may be accepted as complete by the owner,maintenance mayeven be required on that completed segment before completion ofthe entire project. Much ofwhat is required for sueh a scheme can be drawn from the planning and engineering phases. But in the case of dredging, there seems to be a tendency to overlook or minimize the importance of subsequent

maintenance of completed navigation projects.

Maintenance costs can be significant and are recurring. Unless provision has been made to adequately maintain the project,its usewill be limited over a matter of time as natural forces such as siltation reduce project dimensions and limit the use and effectiveness ofthe project. Itis obvious that such limitationswillseriously

impact the abilityto meet financing obligations

and the primary project purposes. The mainte-nance scheme should include not only the main navigation features, but structural features such asbreakwaters. groynes,navigational aids and thelike.

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SECTION FOUR - ENVIRONMENTAL ASPECTS

Overview of Environmental

Considerations

Probably the most current and comprehensive reference for port and waterwaydevelopment on environmental matters is the World Bank

publication. "Environmental Considerations for

Port and Harbor Development"(10).It is readable

and provides an extremely useful "Checklist"as

weUas current information on and the original

international conventions.Muchofthis section is

drawn from this publication.

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Ashas been noted earlier, the environment and

its consideration are justifiably playing an increasing role in port and navigation project development. The days of development strategies being based solelyon economie and

engineering considerations are past. Certainly,

one can point out a myriad of cases where development has occurred to the detriment of

both short and long term environmental aspects.

Industrialized countries are paying a high price to remedy earlier environmental disregard, for

corrective action is far more expensive than

taking environmental1yresponsihle actions from

the outset of development projects. Unfortu-nately, dredging and dredgers have been singled out quite unreasonably as "destroyers ofthe

environment". In factodredging and dredgers in

the past were no different than most ofthe populations and techno logies that they served. There remains much emotional and ill-founded reaction to the dredging process as resulting in

environment al damage, per se.Most ofthe

dredged material involved in any project is uncontaminated and its disposal has often been and remains environmentaUy responsible and beneficial. Most of the emphasis has been and remains on the relatively smal1portion of dredged material which has been contaminated

from avarietyof sourees by a variety of

conta-minants. Extensive research on the disposal of

contaminated sediments has providedviabie and

environmental1y acceptable solutions. However,

the fact remains that because of public percep-tion and cases where dredging did result in

environmental damage in the past.strong

emphasis on environmental responsibilityis and

willlikely continue to be a majorconsideration

on development projects.

Afew words seem appropriate on how dredgers have and continue to foster this image of

"dredging is an environmental insult". Some

terms used by dredgers have come to have

pejorative connotations. "Spoil"and"sludge"

are perhaps two of those terms, which in the

public understanding are bydefinition bad. evil

or environmentally objectionable. In factomost of

what is dredged is environmentaUy clean mate rial and should be referred to in terms

which have more positive connotations. It is far

better to use the term. "dredged material or

sediments" than terms which have ingrained

objectionability. Similarly.dredgers use the term

"dump"or"dispose" in relationship to the

transport and placement of dredged materials.

Youwill note that in this report the term disposed is still used contrary to the point being made. but

old habits are hard to break. The point is.that

those of us in the business ofdredging or port and

waterway development have to rethink not only

the essence ofenvironmental considerations. but

the perception as well.

Development projects have some common problems related to the environment.

The primary categories can be summarised as

being:

Water Related Impacts Land Related Impacts

Air Related Impacts

Disposal of Dredged Material Hazardous materials and cargoes Socio-Cultural Impacts

Awareness and consideration ofthese categories must be part ofthe development process from

the outset.A recent survey ofworld ports by

IAPHconfirmed that the first four items are indeed considered to be major problems by the

ports. In the followingparagraphs a number of

the sub-elements of these categories will be

highlighted.

Water Related Impacts

These impacts include: impacts caused by

dredging andthe disposal of dredged mate rial,

the construction of piers,breakwaters and other

waterside structures. alteration ofharbor/port

shiptraffic patterns. ship discharges. spills of

hazardous substances. and waterfront industry

Those which relate to dredging can be further subdivided into the following elements: dispersal and settlement ofresuspended sediments,

effe cts ofblasting, results of altered bathymetry,

effects ofchanging shoreline configuration,loss ofbottom habitat and altered water currents and groundwater flow.Factors related to the

disposal of dredged mate rial are more compli-cated and will bediscussed separately.

Land Related Impacts

These impacts include: excavation forfill,

wetland damage and filling,loss of usabie uplands to expanding waterfront area, noise from port and harborside industry, effects ofdust and other airborne emissions,traffic burden projections, handling and disposal of solid shore generated wastes, runofffrom raw mate rial storage, waterfront drainage and industrial liquid wastes not discharged to the harbor. Those which relate to dredging are basically

those impacted bythe disposal of dredged mate rial.

Air Related Impacts

A good knowledge ofpreconstruction conditions is essential to forecast air related impacts. Such impacts may re sult from activities associated with industry which develops around the port or from airborne emissions from the port opera-tions themselves. Dredging is unlikely to contribute directlyto air related impacts except for the emissions from the prime movers of dredging plant, which gene rally are negligible when compared to the other factors.

Disposal of Dredged Material

Dredged materials can be broadlydivided into four categories:

1.Material derived from maintenance dredging of areas affected bysedimentation resulting from rivers or estuaries or land runoff

2. Material derived from maintenance dredging

of sand bars atthe entrances to harbours or channels.

3. Material derived from capital dredgingwithin a port.

4. Material derived fromcapital dredging of channels or outer harbour areas.

Because ofthe nature of activitiesaround ports such asagriculture, industry and municipalities,

the mate rial mostlikelyto contain significant

levels ofcontamination are those found in Category1.Accordingly,the disposal orthese materials is a focusof environmental concern. Category2 materials are farless likelyto be

contaminated and are often suitablybeneficially

used for beach nourishment andconstruction fill mate rial or aggregates. Category 3 materials are likely to contain significant levels of contamina-tion in the upper levels,with the underlying materials generally uncontaminated. Depending on the specific case,the upper levels maybe subject to restricted or special disposal alterna

-tives,while the uncontaminated underlying mate rial maybe disposed in open water, or beneficiaIlyon land. Category4 materials are also likelyto becontaminant free andtherefore can be disposed in open water, or beneficially

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It is the materials in Categories 1 and 3 which contain contaminants which are ofmost concern from an environmental viewpoint and are most likelyto fall within disposal restrictions set out in local or international agreements, statutes or conventions. The international conventions are limited to the disposal in the sea, with local restrictions, ifthey exist at all, either consistent with the international ocean disposal or

established to mitigate damage from intertidal or upland disposal. In either case,the project sponsor must consider disposal options which are environmentally sensitive and responsibie.

Hazardous

Material and Cargoes

Obviouslyport development may increase the handling ofhazardous materials and cargoes and the types of materials, their handling and storage, the disposal ofwastes associated with such cargoes are all factors which require

consideration in the overall assessment of potential environmental consequences.There is almost no relationship of these impactsto the dredging process, either construction or maintenance.

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Socio-Cultural Impacts

These impacts are more elusive but nonetheless important. Because the very best engineering,

highlylaudable environmental planning, and

extensive economie justification can all serve to

no avail ifwork practices, site selection or similar

factors such as visual and auditory factors run counter to socio-cultural standards and

traditions. Failure to consider such factors as

local tribal, cultural, ethnic, historical and religious traditions may essentially cancel any

benefits from the project.Again, this is an area

where the dredging process has little if any

impact,however, the disposal of dredged

material may weIl be involved in this area and should receive ample consideration.

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Environmental Monitoring

It is often important to have a pre-project

assessment ofthe characteristics ofthe

mate-rials to be dredged and the likely disposal sites.

Such characterizations permit the defmition of

disposal options;quantities ofmaterials suitably

disposed in each ofthe options;the dredging

equipment used not only in consideration ofthe disposal requirements, but also oftransportation to the disposal options and to minimize sediment

re-suspension and loss during dredging;

monitoring programs at both dredging and disposal sites; and mitigative measures that may

be required at the dredging or disposal sites.

Proper environmental monitoring ofthe dredging and disposal sites is likely to be a requirement either under permit or to be consistent with international convention.

Furthermore, post-construction monitoring of

disposal sites,both open water and upland are

essential to determine ifthe mitigatory measures are adequate to prevent serious environmental

harm. This is particularly true where c

ontami-nated dredged materials are involved.Such

monitoring is also useful in establishing a data

base for future work in the area where either

more or less stringent controlsrnaybe

appro-priate.

International

Agreements

Regulating Pollution

The oceans have long beenconsidered tohave a

limitlesscapacity to receive and absorb all

marmer ofwastes. Beginningin the 1950's, .

various scientists began towarnthat this limitless

capacity was running outandthat thevery

survivalofthe marine environment was indoubt.

Manyenvironmental groups began to demand

that aUwaste disposal in the marine

environ-ment cease.The initial focus was on disposal of

waste chemieals and nuclear wastes or incinera-tion at seas of waste organo-halogen com-pounds. Subsequently the disposal of sewage sludges and the large volumes of dredging matenals. particularly those from heavily industrialized urban eentres led to demands that

these materials also not be permitted to be ocean

disposed.Such demands were not limited to the

oceans; for example,in the early 1970's both the

United States and Canada limited the disposal of dredged material from the Great Lakes to confined shoreline or upland facilities with very

little material being permitted to open-water.

Beginning with the OsloConvention of 1974 and

the Paris Convention of 1978,the European

nations sought to limit the input of contaminants to the adjacent marine waters. The conventions

addressed international waters. Itwas accepted

that the disposal of dredged materials could occur provided the materials contained only

"trace quantities of contaminants". Materials

which are primarily sand, gravel or rock,from

areas of strong currents and are therefore not

likelyto contain significant concentrations of

fme-grained contaminated sediments and which are intended for beach nourishment or other forms ofshoreline proteetion should not have to

be tested.(Note:Fine-grainedsediments, such as

clays,have a tendency to sorb or bind

contami-nants thereby becoming contaminated bythese

bound contaminants, whereas sands do not ha ve

such characteristics.)

The intergovernmental convention of the

dumping ofwastes at sea, commonlycalled the

London Dumping Convention (LDC),adopted the

general philosophy and has manysimilar articles

ofthe OsloConvention and appliestoall

international waters.

The LDCcontains a series of Armexeslisting a

large number of chemieals andchemical

compounds which are deemed hazardous or

potentiaUyhazardous and therefore worthyof

regulation.Aswith the earlier conventions. the

LDCwas designed primarilyto regulare the

dumping ofchemicalor industrial wastos inthe

The regulation of dredged materials and their disposal inthe open ocean have revolved around

the following terrns: • trace contaminants • significant amounts • rapidly rendered harmless • toxic • persistent • bio-accumulative

The question then arises as to what

concentra-tions of such compounds can be considered

"tracé" or in such a forrn as to be "rapidly

rendered harmless. "The latter term arose from the chemical reactions that occur when various metal contaminated liquids are inter-mixed with

seawater and the elevated Ph and salinity rapidly

create insoluble metal compounds which are then not available to the biota.

The LOCguidelines on dredged mate rial disposal recommend:

• representative sampling

• measuring the general characteristics

• measuring the priority contaminants,

and

• biological testing, ifnecessary, to show that the material can be dumped so as not to cause acute chronic effects or bio

-accumulation in sensitive marine organism typical ofthe disposal site. Compliance with the London Dumping Conv en-tion and other pertinent international agree-ments is mandatory for those projects which wish financing from internationallending organizations such as The World Bank, see AppendixB.

UNEP Regional

Seas

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The Regional Seas Programme ofthe United

Nations' Environrnental Pro gramme inrespond

-ing toregional needs ofpollution control and marine and coastal resources management, is

moving towards a more detailed structure of

coordinated activity with emphasis on the development ofregionallegal agreements and

on the effective execution of action plans.

UNEP's Governing Council has defined the overall strategy ofthe Regional Seas Pro gramme as:

• promotion of international and regional conventions, guidelines and actions for the control of marine pollution and for the proteetion and management of aquatic

resources.

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• assessment ofthe state of marine pollution, ofthe sourees and trends ofthis pollution, and ofthe impact ofthe pollution of human health, marine ecosystems and amenities.

• coordination ofthe efforts with regard to the environment al aspects of the protee-tion, development and management of marine and coastal resources.

• support for education and training efforts to make possible the full participa-tion of developing countries in the proteetion. development and management of marine and coastal resources.

At present the programme covers ten regtons with the participation of over 120