Number 130 | March 2013
THEORY VS REALITY testing the ‘pilferer’ draghead
SCIENCE VS PRECONCEPTIONS Lough Foyle’s two disposal sites
EXPECTATIONS VS FACTS silt concentrations at Maasvlakte 2
ET Maritime Solutions for a Changing WorldTERRA AQUA TERRA ET Membership list IADC 2013 AQUA Through their regional branches or through representatives, members of IADC operate directly at all locations worldwide Africa Dredging and Contracting Rotterdam b.v., Bergen op Zoom, Netherlands Editor Guidelines for Authors BKI Egypt for Marine Contracting Works S.A.E., Cairo, Egypt Dredging and Maritime Management s.a., Steinfort, Luxembourg Marsha R. Cohen Dredging and Reclamation Jan De Nul Ltd., Lagos, Nigeria Dredging International (Luxembourg) SA, Luxembourg, Luxembourg Terra et Aqua is a quarterly publication of the International Association of Dredging Companies, Dredging International Services Nigeria Ltd., Ikoyi Lagos, Nigeria Dredging International (UK) Ltd., East Grinstead, UK Nigerian Westminster Dredging and Marine Ltd., Lagos, Nigeria Dredging International N.V., Zwijndrecht, Belgium Editorial Advisory Committee emphasising “maritime solutions for a changing world”. 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Cover Terra et Aqua is published quarterly by the IADC, The International Association © 2013 IADC, The Netherlands A survey ship with a specially developed silt profiler – designed and constructed in 2009 and owned of Dredging Companies. The journal is available on request to individuals or All rights reserved. Electronic storage, reprinting or by the Port of Rotterdam – follows a trailing suction hopper dredger at work to measure active and organisations with a professional interest in dredging and maritime infrastructure abstracting of the contents is allowed for non-commercial surface plumes. This was an integral part of the extensive monitoring programme at the Maasvlakte 2 projects including the development of ports and waterways, coastal protection, purposes with permission of the publisher. expansion project in Rotterdam (see page 20). land reclamation, offshore works, environmental remediation and habitat restoration. ISSN 0376-6411 The name Terra et Aqua is a registered trademark. Typesetting and printing by Opmeer Drukkerij bv, For a free subscription register at www.terra-et-aqua.com The Hague, The Netherlands. PEFC/30-31-372 Contents 1
contents
EDITORIAL 2
EROSION BEHAVIOUR OF A DRAGHEAD 3 ARNAUD VERSCHELDE, Cees van Rhee AND Marc van den Broeck
The IADC Young Author’s Award-winning paper verifies the agreement between the theoretical calculations for a new toothless draghead and the real situation when the draghead is being used.
DREDGING AND DISPOSAL AT LOUGH FOYLE, NORTHERN IRELAND 10 DAVID CLOSE, ANTHONY BATES, ROBIN MORELISSEN AND CAROLINE ROCHE
Is it possible for an in-site disposal area to be environmentally and economically preferable to an offshore disposal site? Real-time monitoring says yes, there are numerous benefits to the disposal of dredged material in-site.
The Monitoring Programme for the Maasvlakte 2 20 Construction at the Port of Rotterdam – PART II WIL BORST, TIEDO VELLINGA AND ONNO VAN TONGEREN
Given the inter-dependence of the underwater food chain from benthic fauna and algae to shells, worms, fish and birds, a new modelling strategy was instituted to evaluate the effects of enhanced silt concentrations during dredging.
Building with nature BOOKS / PERIODICALS REVIEWED 33
Thinking, acting and interacting differently Innovation is the keyword of two new publications, “175 Ideas on the Future of the Fehmarnbelt Region” and “Building with Nature”; and Facts About Subsea Rock Installation and Facts About Initiating Hydraulic Fill Projects as well.
SEMINARS / CONFERENCES / EVENTS 34
Plans for 2013 include two IADC Seminars on Dredging & Reclamation in Brazil and Delft; WODCON in Brussels; WEDA in Hawaii; the World Ocean Council Sustainable Ocean Summit in Washington and many other water-related events. 2 Terra et Aqua | Number 130 | March 2013 EDITORIAL
Education and the dissemination of information about state-of-the-art dredging and maritime construction stand high on the list of the priorities of the International Association of Dredging. With this in mind IADC publishes Terra et Aqua, the Facts About series, Dredging for Development and other books. IADC also supports the publication of third- party books such as Hydraulic Fill Manual, Clarksons’ The Dredger Register and FIDIC’s Form of Contract for Dredging and Reclamation Works.
Educational outreach is also achieved by organising seminars worldwide. The first of 2013 will be the International Seminar on Dredging and Land Reclamation, to be held in Búzios, Brazil in April. Brazil was chosen because of the enormous amount of activity going on in Latin America. That will be followed by the IHE-UNESCO seminar in Delft, an annual event that informs young Peter de Ridder professionals doing advanced water-related studies specifically about dredging. Ultimately this President, IADC helps increase knowledge of sound dredging techniques in emerging nations. In both these seminars, the instructors are dredging experts with both academic and professional credentials.
Looking further forward, a reprisal of the “Early Contractor Involvement Forum” is planned for the autumn in Kuala Lumpur, Malaysia. This Forum, successfully held in London in 2011, is an interactive event which stimulated surprising, sometimes controversial, dialogues amongst participants. The Forum examines the full scope of maritime construction projects. It explores the possibilities for the exchange of knowledge and experiences between clients, consultants and contractors even before the launch of a project.
As part of the IADC Seminar in Búzios, a site visit will take place to the development of TX2 terminal of Superporto do Açu, a project of LLX Logística, in São João da Barra (Brazil).
To execute successful dredging operations means finding the optimal working methods. To find these optimal methods demands extensive research and modelling and these are then tested by practical application and trials. The articles in this issue of Terra et Aqua clearly demonstrate the applied science of dredging: One is the IADC Young Author’s Award paper from CEDA Dredging Days in Abu Dhabi which reports the results of measuring the theoretical productions of “the pilferer” draghead with reality as it was used for a dredging project at the River Scheldt, Belgium. Two other articles focus on environmental monitoring under very different circumstances – one at disposal sites in Lough (lake) Foyle in Northern Ireland and the other at the land reclamation site of the Maasvlakte 2 in the Netherlands. Quite different projects, but both demanded scientific accuracy and verification of results.
The beauty of dredging – and the challenge – remains this intersection of engineering theory, research and modelling with practical application to site-specific circumstances. And that practical application is what makes dredging the backbone of the world’s economic engine – providing goods and energy and new land, and creating millions of jobs at ports, harbours and elsewhere. Erosion Behaviour of a Draghead 3
ARNAUD VERSCHELDE, Cees van Rhee AND Marc van den Broeck
EROSION BEHAVIOUR OF A DRAGHEAD
ABSTRACT research. This article originally was published results was the so-called “pilferer” draghead in the Proceedings of the CEDA Dredging (see Figures 1 and 2), which is based on the A draghead known as “the pilferer”, based Days 2012 in Abu Dhabi and is reprinted here principle of erosion and can remove small on the principle of erosion, was invented by in an adapted version with permission. layers of soil without really touching the river- DEME dredging company. Using the concept or seabed. This would allow careful dredging of van Rhee (2010) the erosion behaviour of without damaging the buried cables. this particular draghead was investigated. INTRODUCTION The erosion rates created by the flow velocity The draghead is the part of the dredging along the seabed are calculated using In 2010 DEME (Dredging, Environmental and excavating system that is in touch with the potential flow theory. Certain assumptions Marine Engineering) wanted to tender for a seabed. Most dragheads excavate soil from were made during the use of this theory. dredging project at the River Scheldt in Belgium. the seabed with the help of jet water flow These assumptions were validated in a At this project site two 50kV electricity cables and a number of teeth. The pilferer draghead Computational Fluid Dynamics (CFD) model were buried which could not be touched, yet is designed without teeth and with jets that using OpenFOAM. The CFD model also gave dredging works needed to be done in their have a relatively low jet water velocity (up to a better understanding of the flow field of a vicinity. As a result of years of erosion from 10 m/s). These jets are positioned in such a draghead during the erosion process. With river flow and other natural effects, the depth way that their only purpose is to create a these theories the productions of the erosion of these cables was not precisely known. higher water flow to the draghead for better head were calculated and compared to reality. Therefore careful dredging was recommended. transport of the eroded sand particles. The Agreement between calculations and the real DEME wanted to make use of one of their erosion is set up by a flow along the seabed situation is promising. The theory explained in existing vessels without much extra equipment which is created by the suction effect of the this research can also be used to describe the onboard and therefore they decided to centrifugal pump. This topic was a research erosion behaviour of other types of dragheads. develop a specialised type of draghead. The project as part of an MSc study in the Section Offshore and Dredging Engineering at Delft The author wishes to thank C. van Rhee, University of Technology, carried out under Professor, Delft University of Technology, Above: Unlike traditional dragheads, the so-called the guidance of Professor C. van Rhee and Section Dredging Engineering, Faculty “pilferer” draghead is designed without teeth, and with started in March 2011. For describing the Mechanical, Maritime and Materials jets with a relatively low jet water velocity. The pilferer is erosion behaviour of the pilferer draghead Engineering, and M. van den Broeck, Head based on the principle of erosion and can remove small actually three main ingredients are necessary: Research, Method, Production and layers of soil without really touching the river- or 1 erosion theory Engineering department, DEME, Zwijndrecht, seabed. This allowed for careful dredging of the bed of 2 flow velocities along the seabed Belgium for their contributions to this the River Scheldt without damaging buried cables. 3 groundwater flow 4 Terra et Aqua | Number 130 | March 2013
Figure 1. A 3D drawing of the pilferer draghead. The draghead is designed without teeth but with jets with a relatively low jet water velocity, which are positioned so that they purposefully create a higher water flow to the draghead for transporting the eroded sand particles.
These three subjects were each investigated the erosion behaviour of other types of was the most consistent with the real separately and brought together at the end dragheads can also be investigated. situation. This is one of the reasons why the of the research for describing the erosion van Rhee theory was used for this research. behaviour of the pilferer draghead. In this EROSION THEORY article, first a description is given of erosion The research started by comparing several The theory of van Rhee (2010) is based on the theory, then how the flow velocities along the erosion theories in a literature study. Three theory of van Rijn (1984). The theory of van Rijn seabed evolve are explained, next the ground- erosion theories were found to be appropriate (1984) can only be used for erosion created water flow theory is clarified, and finally these for this research. These were the theory of by low velocities (< 10 m/s). With the three subjects are combined to explain the van Rijn (1984), the theory of Visser (1995) adjustments of van Rhee, this theory can be final erosion behaviour of the draghead. and the theory of van Rhee (2010). Visser used for erosion created by higher flow (Bisschop, Visser, van Rhee and Verhagen, velocities (≥ 10 m/s). Because during dredging Although in this research only the erosion 2010) compared these theories with his the flow velocities that are encountered are behaviour of the pilferer draghead was theory and measurements and came to the higher than 10 m/s, the van Rhee theory investigated, using the theory explained here, conclusion that the van Rhee theory (2010) (2010) was preferred for this research. The
Figure 2. Two views of the pilferer with a close-up of the waterjets. (3) ! !.! ! !.! 𝜃𝜃 − 𝜃𝜃!" (3) ! ∗ ! where: 𝜙𝜙 = 0.00033 ∙ 𝐷𝐷 ∙ !.! 𝜃𝜃 !" (3) ! (3) Erosion Behaviour !of a Draghead 5!.! 𝜃𝜃 − 𝜃𝜃!" (3) = dimensionless! particle!.! ! diameter ∗ ! ! !.! where: 𝜙𝜙 = 0.00033 ∙ 𝐷𝐷 !∙.! !" ! !.! !" ! !" 𝜃𝜃 − 𝜃𝜃! !.! !" ! 𝜃𝜃 !.! 𝜃𝜃 − 𝜃𝜃 ∗ ! = adapted∗ critical! ! Shields parameter∗ 𝜃𝜃 − 𝜃𝜃 ! ∗ ! where: 𝜙𝜙 where:= 0.00033 ∙ 𝐷𝐷 = ∙ !"𝜙𝜙 dimensionlesswhere:= 0.00033 ∙ 𝐷𝐷 particle∙ ! diameter𝜙𝜙 = 0.00033 ∙ 𝐷𝐷 ∙ !" 𝐷𝐷! 𝜃𝜃 𝜃𝜃!" (3) 𝜃𝜃 = dimensionlessThis!" adapted particle= critical ∗ diameter dimensionless = Shields adapted parameter particle critical= diameter Shields is dimensionless different ! parameter!.! from particle van Rijn (3) diameter in that it takes into (3) 𝜃𝜃 𝐷𝐷 ! !.! 𝜃𝜃 − 𝜃𝜃!" ! ! ∗! ! ! !.! account a hydraulicwhere: gradient and𝜙𝜙 = the0.00033 slope∙ 𝐷𝐷 angle.∙ !" The adapted critical Shields parameter!.! is: ∗ = adapted critical∗ ShieldsThis =!" adapted adaptedparameter critical critical ! Shields Shields = parameterparameter!"!.! adapted𝜃𝜃 −𝜃𝜃 𝜃𝜃!" critical is different Shields from parameter van Rijn in ! that it takes into 𝐷𝐷 𝐷𝐷 𝜃𝜃where: = dimensionless𝜙𝜙∗! = 0. 00033particle∙𝜃𝜃𝐷𝐷 diameter∗ ∙ ! ! (4)!.! !" other theories! were not set up to deal with ! account a ahydraulic hydraulic 𝐷𝐷gradient gradient and the and slope the !" slope! angle.! The adapted∗ critical𝜃𝜃 − 𝜃𝜃Shields parameter is: This!" adapted critical ShieldsThis!" parameter adapted critical is Shields different! parameterwhere: from van isRijn𝜃𝜃 different in !"that from 𝜙𝜙it takes= van0.00033 Rijninto in∙ 𝐷𝐷 that∙ it takes! into 𝜃𝜃 ∗ = dimensionlessadaptedThis critical adapted particle Shields diameter parametercritical Shields parameter is different!" from van Rijn in that it takes into these high flow𝜃𝜃 velocities. The van Rhee theory angle.𝐷𝐷 The adapted critical!" Shields parameter! is: 𝜃𝜃 ! ! ! 𝜃𝜃 (4) account a hydraulic gradientaccount and a!the hydraulic slope! angle. gradient𝜃𝜃 The and !adapted the slope sin!"critical angle.𝜙𝜙 − 𝛽𝛽ShieldsThe adapted𝑣𝑣 parameter𝑛𝑛 − critical𝑛𝑛 𝐴𝐴 is:Shields parameter is: This!"∗ adapted = !" critical adapted accountShields critical!" parameter Shields a hydraulic!" =parameter is different dimensionless gradient from van and Rijn particlethe in thatslope it diameter takes! angle. into The adapted critical Shields parameter is: (2010) is based on the following equation:where: 𝐷𝐷𝜃𝜃 𝜃𝜃 = 𝜃𝜃 𝜃𝜃 + ! ∙ ! (4) !" account! a 𝜃𝜃hydraulic gradient and the slope! !angle.sin 𝜙𝜙 (4)The adapted𝑘𝑘 1 critical− 𝑛𝑛 ∆Shields! ! parameter! is: This!" adapted critical Shields parameter = !"!" is different adapted!" sin from𝜙𝜙 critical −van𝛽𝛽 Rijn Shields𝑣𝑣 in that𝑛𝑛 −𝜃𝜃it takes𝑛𝑛parameter𝐴𝐴 into (4) where: 𝜃𝜃 ∗ 𝜃𝜃 (4) (4) = (1)account gravitational(1) a hydraulic gradient acceleration 𝐷𝐷and! the slope sin𝜃𝜃! angle.𝜙𝜙=−𝜃𝜃 The𝛽𝛽 adapted𝑣𝑣! 𝑛𝑛! −critical𝑛𝑛!+𝐴𝐴 Shields! ∙ parameter! is: (1) ! (1) !!"! ! !" !!" sin 𝜙𝜙 𝑘𝑘 1 − 𝑛𝑛 ∆ where: sin 𝜙𝜙 − 𝛽𝛽 𝑣𝑣This𝜃𝜃 𝑛𝑛= adapted𝜃𝜃− 𝑛𝑛𝜃𝜃 𝐴𝐴 critical+ !Shields∙! ! parameter(4) is different from van Rijn in that it takes into where: = !" median !" = particle gravitational size !"diameter! accelerationsin sin𝜙𝜙 −𝜙𝜙𝛽𝛽 𝑣𝑣𝑘𝑘!𝑛𝑛 −1 𝑛𝑛− 𝑛𝑛𝐴𝐴! ∆! ! ! ! where:where:𝜃𝜃 = 𝜃𝜃 + 𝜃𝜃! ∙𝜃𝜃!" = 𝜃𝜃!"! + ∙ !" !" sin 𝜙𝜙 − 𝛽𝛽 𝑣𝑣 𝑛𝑛 − 𝑛𝑛 𝐴𝐴 𝐸𝐸 − 𝑆𝑆 𝐸𝐸 − 𝑆𝑆 𝑔𝑔 𝐸𝐸 − 𝑆𝑆 sin 𝜙𝜙 𝑘𝑘account1 − 𝑛𝑛 a hydraulic∆ gradient!! ! !! and the slope! angle. The adapted critical Shields parameter is: ! ! 𝑣𝑣! = = gravitationalwhere: acceleration ! sinsin𝜙𝜙 −𝜙𝜙 𝛽𝛽 𝑣𝑣𝑘𝑘 𝑛𝑛1 − 𝑛𝑛 𝐴𝐴∆ 𝜃𝜃 = 𝜃𝜃 !" + ! ∙ ! 𝑣𝑣 = 𝑣𝑣! = !! ! ! ! ! ! ! = median particle!" !"size diameter where:where: = gravitational𝜌𝜌 !"1 − 𝑛𝑛 − = 𝑐𝑐acceleration where: bed= = sheargravitational gravitational stress acceleration acceleration 𝜃𝜃 = 𝜃𝜃 + ! ∙ ! 𝜃𝜃 sin 𝜙𝜙 𝑘𝑘 1 − 𝑛𝑛 ∆ (4) where:where: 𝜌𝜌 1 −𝜌𝜌𝑛𝑛 1−−𝑐𝑐𝑛𝑛 − 𝑐𝑐 𝐷𝐷 𝑔𝑔 = median particle size diameter sin 𝜙𝜙 𝑘𝑘 1 − 𝑛𝑛 ∆ (3) = erosion velocity 𝑔𝑔 = = =median mediangravitational bedparticle particle shear size acceleration size =stressdiameter diameter gravitational acceleration = erosion = velocity median particle = size𝑔𝑔!" Shields diameter parameter = ! !.! = = erosion erosion velocity velocity !" 𝐷𝐷 = bed shear stress !" ! ! ! ! = settling𝑔𝑔 flux 𝜏𝜏 !" = = bed bedmedianshear shear stress particle stress! size diameter! !.! 𝜃𝜃 − 𝜃𝜃 !" !" sin 𝜙𝜙 − 𝛽𝛽 𝑣𝑣 𝑛𝑛 − 𝑛𝑛 𝐴𝐴 ! = settling flux 𝐷𝐷 𝐷𝐷𝑔𝑔 = Shields !where:parameter = median= ∗ particle! size 𝜃𝜃diameter= 𝜃𝜃 + ∙ 𝑣𝑣 !" = bed shear stress where: 𝑔𝑔 𝜙𝜙 = 0.00033 ∙ 𝐷𝐷 ∙ !" ! ! ! ! = = settling settling flux flux = =pick-up 𝐷𝐷 pick-up flux flux = 𝜏𝜏 = !" critical= = Shields Shields Shields Shieldsbed parameter shear parameter parameter stress = = ! !=! ! ! !!!" ! 𝜃𝜃 sin 𝜙𝜙 𝑘𝑘 1 − 𝑛𝑛 ∆ 𝑣𝑣 𝑣𝑣 𝑆𝑆 𝜃𝜃 𝜏𝜏 𝐷𝐷𝜏𝜏 = dimensionless !" = particle =! ! bed diameter shear gravitational stress acceleration = Shields parameter = = = Shields critical parameter Shields = parameter ! ! !" = = pick-up pick-up flux flux = =density density of particles of particles 𝜃𝜃 = = critical critical Shields𝐷𝐷 Shields parameter parameter!!!! ! !!!"! !! !! 𝐸𝐸 𝜏𝜏 !" 𝜃𝜃 = =𝜏𝜏𝜃𝜃 angle critical !of internal Shields friction parameter!! !! !!!!!" 𝑆𝑆 𝑆𝑆 = density of water 𝜃𝜃 ∗ = =angle of adapted internal criticalfriction = Shields = Shields parameter median parameter particle =size diameter = density of particles! = density of water 𝐷𝐷𝜃𝜃!" = = anglecritical angle of Shields internal of internalparameter friction!!! ! friction! !!!" = density of𝜌𝜌 particles𝜃𝜃 = critical Shields!" = parameter =𝜃𝜃 ! slope!!! angle! !angle! !of!" internal𝜏𝜏 𝑔𝑔friction ! IADC Secretary General𝐸𝐸 René Kolman (right) presents = porosity of the settled bed 𝜃𝜃 𝜃𝜃 This!" = adapted slope criticalangle Shields parameter = bed is shear different stress from van Rijn in that it takes into 𝐸𝐸 ! = porosity of the settled𝜙𝜙 bed 𝜃𝜃!" = = angleslope slope angleof internal angle!" friction ! = = density density of water of𝜌𝜌 water !" = angle of internal =friction𝜃𝜃𝜙𝜙 slope angle 𝐷𝐷 = critical! Shields parameter!!!! ! !!!" the Young Authors 𝜌𝜌Award to! Arnaud Verschelde at = =near-bed near-bed volumetric volumetric concentration concentration 𝜙𝜙 = 𝜙𝜙 account permeability= = apermeability hydraulic permeabilityslope 𝜃𝜃angleat atgradientmoment moment at moment and ofof ofthedilatation dilatation slope!" angle. The adapted critical Shields parameter is: 𝜌𝜌 𝑛𝑛! 𝜃𝜃 𝛽𝛽 𝛽𝛽𝜙𝜙 = 𝜃𝜃 Shields parameter = CEDA Dredging Days !in Abu Dhabi, = December porosity 2012. of the settled= settling bed velocity = = permeability =porosity permeabilityat moment at moment𝜏𝜏 of dilatationat of moment dilatation of dilatation (4) ! = porosity of! the = settled settling bed = velocity slope angle = 𝛽𝛽! porosity = porositypermeabilityat moment!" at moment at ofmoment = dilatation of dilatation of angledilatation of internal friction ! 𝜌𝜌 𝑐𝑐 𝜙𝜙 ! 𝛽𝛽 𝑘𝑘𝛽𝛽 𝜃𝜃 𝜌𝜌 𝑘𝑘 = = porosity =constant porosityat describing moment at single of moment dilatation =particle of or dilatation critical Shields ! parameter! ! ! ! !" ! = near-bed volumetric! concentration = permeability! at moment! = of dilatation constantporosity atdescribing moment𝜃𝜃 singleof dilatation! particle orsin continuum𝜙𝜙 − 𝛽𝛽 mode𝑣𝑣 𝑛𝑛 stability− 𝑛𝑛!𝐴𝐴! ! !! 𝑛𝑛 ! = near-bed𝑤𝑤 volumetric concentration ! 𝑘𝑘 = 𝑘𝑘where:𝑛𝑛𝑘𝑘 constant describing single = particle!" slope!" orangle continuum mode stability 𝑛𝑛 With certain𝛽𝛽 assumptions and sub-calculations ! = continuum relativeconstant𝜙𝜙 mode sediment describing stability density single𝜃𝜃 = particle = 𝜃𝜃 or continuum+ mode! ∙ stability! = settling velocity 𝑛𝑛 ! =𝐴𝐴𝑛𝑛! constant = constantdescribing describing!" single = particle single angle or particlecontinuumsin of𝜙𝜙 internal or𝑘𝑘 continuummode 1friction− 𝑛𝑛stability∆ mode stability ! ! = settling velocity ! = porosity at𝑛𝑛 moment𝑛𝑛 of dilatation (2) 𝜃𝜃 = permeability!!!!! at moment of dilatation IADC YOUNG AUTHORS𝑐𝑐 AWARD (van Rhee, 2010)𝑘𝑘 equation (1) can be rewritten = relative= = =relative sediment relative gravitationalsediment sediment density density density acceleration == = 𝑐𝑐 𝐴𝐴 =∆𝐴𝐴 is the Shields relative = parameter sediment relative𝛽𝛽 and sedimentdensity is a non-dimensional == density! !!!!! slope = number angle for describing the bed shear ! = constant1 describing𝐴𝐴 ! single particle or continuum! mode! !! stability PRESENTED AT CEDA DREDGING! DAYS to: ! ! ! 𝐴𝐴 ! ! = median particle𝜙𝜙 = size! porositydiameter!!!! !at!! moment!! of dilatation 𝑤𝑤 𝑛𝑛 𝑣𝑣 = ! ! 𝜙𝜙 𝑔𝑔∆𝐷𝐷stress.∆ −is 𝑐𝑐the𝑤𝑤 If Shields the critical parameter Shields! and parameter is a non-dimensional is! exceeded! number then the for initiationdescribing of the motion bed shearof the ABU DHABI, UAE, DECEMBER𝑤𝑤 12-13 2012 1 −∆𝑛𝑛 is− the𝑐𝑐 isShields the 𝑔𝑔𝜃𝜃Shieldsis theparameter Shields parameter parameter and𝑘𝑘 and is isaand non-dimensionala non-dimensionalis a non- = !!! permeability number for forat describing moment describing of the dilatation the bed bed shear shear = relative sediment∆ ∆sandstress. density is theparticles If =the Shields = critical will bed start parameterShields shear (Miedema, parameter𝛽𝛽 stress and 2008). is a Theis non-dimensional exceeded critical valuethen!! theof initiation in number equation of motion (4)for is describing multiplied of the the bed shear 𝐴𝐴 𝜃𝜃 (2)!" ! = 𝜃𝜃!" constant describing single particle or continuum mode stability stress.stress.(2) If the If dimensional𝐷𝐷by critical the a term critical (2)whichShields number ! Shields! !includes!! 𝑛𝑛parameter for parameter thedescribing slope! angle the = is andbedis exceeded exceeded an porosityextra term thenthen whichat themoment the isinitiation importantinitiation of dilatation ofat highofmotion motion erosion of the of the 𝜃𝜃 𝜃𝜃 stress.sand particles If = the will critical Shields start (Miedema, Shields parameter𝑘𝑘 2008).parameter =!" The critical valueis exceeded of in equation then the (4) isinitiation multiplied of motion of the The International Association of Dredging Companies (IADC) is the Shields! parameter and is𝜃𝜃shearvelocities. a non-dimensional stress. This If thelast!! criticalterm is number Shieldsa multiplication parameter for𝜃𝜃 describing of the hydraulic the gradient bed𝜃𝜃 shear that is present during ! ∆1 ! 𝟏𝟏 !sand! particlessand particles𝜏𝜏by will a term willstart which start (Miedema, includes (Miedema, the slope 2008). = 2008). angle = The Theand relative an criticalcritical constantextra! sediment term valuevalue whichdescribing of of isdensity importantin in equation singleequation = at high particle(4) erosion(4)is multiplied is or multiplied continuum mode stability 𝟏𝟏 𝐴𝐴 ! !"!" ! ! presented its Best Paper Award for a Young Author for the 𝑣𝑣 = 𝒆𝒆 ! ! 𝜙𝜙 𝑔𝑔∆𝐷𝐷𝒑𝒑− 𝑐𝑐 𝑤𝑤 𝒃𝒃 𝒔𝒔 sandvelocities.is particlesexceeded This last thenwill term thestart is initiationa 𝑛𝑛 multiplication(Miedema,𝜃𝜃 𝜃𝜃of motion of 2008). the hydraulic!" The critical gradient𝜃𝜃 thatvalue is present of ! in!during! equation (4) is multiplied 1𝒗𝒗−=𝑛𝑛stress.− 𝑐𝑐 𝟎𝟎If the𝒃𝒃 critical𝝓𝝓 𝒈𝒈∆ Shields𝑫𝑫 − 𝒄𝒄by𝒘𝒘 aparameter term𝜃𝜃erosion which = includes is exceededwith critical the a constant. slope Shields then angle The theparameter hydraulic and initiation! !an!! gradient !extra𝜃𝜃!! !"of term resultsmotion which from of isthe the important dilatant behaviour at high erosion 𝟏𝟏 − 𝒏𝒏 − 𝒄𝒄 by a term which includes!! !!!!! the slope angle =and an relativeextra term sediment which density is important = at high erosion 28th time at the CEDA Dredging Days on December 13, If this equation𝜃𝜃 is solved one can calculate the byoferosion the a term sand whichparticles with includes willa isconstant. startthe (Miedema,Shieldsthe The slope hydraulic parameter angle gradient and results anand extra fromis𝜃𝜃 a term thenon-dimensional dilatant which behaviour! is! important number at high for erosion describing the bed shear velocities.from This the =!upperlast term part! angle of ∆is the a ofmultiplication soil internal𝐴𝐴 that is subjected friction of the to the hydraulic flow. gradient𝜃𝜃 that is present!!!!! during sand particles will startvelocities. (Miedema, This!" 2008).last!! term∙!"!! !!The! ! is criticala multiplication value of of in the equation hydraulic (4) isgradient multiplied that 𝜃𝜃 is present during 2012 in Abu Dhabi, to Mr. Arnaud Verschelde for his paper erosion velocity. w , the settling velocity, in velocities.2008).𝜃𝜃fromThe slope the The 𝜃𝜃upper angle critical This part of the valuelastof thesoil term ofsoil is rapidly that inis equationais multiplicationchangingsubjected (4) duringto the flow.the of dredging the hydraulic process of gradient erosion. This that is present during s erosion ! =! ∙ with!!!! a slope constant.stress. angle If The is the the hydraulic criticalShields gradient Shieldsparameter results parameter and from is a non-dimensionalthe dilatant is exceeded!! behaviour number then the for initiationdescribing of the motion bed shear of the by a term which includeserosion the slopeproblem angle with is encountered and a constant. an𝜃𝜃 extra by dividing The∆term hydraulic whichthe erosion is importantzonegradient into several results at high subparts from erosion and the constantly dilatant behaviour “Erosion Behaviour of a Draghead”. Mr. Verschelde started equation (2) was set to 0 for this research erosionis𝜙𝜙The! !multiplied slope!!!! ! angle by ofa term the with soil which is a rapidly constant. includes changing 𝜃𝜃the The during hydraulic the dredging gradient process results of erosion. from This the dilatant behaviour velocities. This last term fromis a!! multiplication the!problemcalculating! !upper !! =ispart! !encounteredthe ! oferosionof!! permeabilitythe !the!sand soil and hydraulicby dividingthatslopeparticlesstress. is angleat subjected themoment gradientIf subsequently erosionthewill critical startofto zonethat thedilatation (seeinto (Miedema,isflow.Shields presentseveralFigure 3).parametersubparts during This 2008). calculation and !" constantly The is was exceededcritical value then theof initiation in equation of motion (4) is of multiplied the his studies at Delft University of Technology in 2006. because it was assumed that settling would slope𝛽𝛽!! ∙ !angle!!! and an extra term𝜃𝜃 which is 𝜃𝜃 from the! !upper!fromcalculatingdone!! part! numerically the of upperthe the erosion bysoil part solving and that of slope theequation is subjectedsoilangle (5). thatsubsequently This is to subjectednumerical the (see flow. Figurecalculation to the 3). Thisflow. was calculation done with thewas help In 2009 he obtained his bachelor degree of Marine not occur, only erosion. In equation (2) liesThe slope∙ important! angle = ! of at! ∙ thehigh!! porosity!soil erosion! by is arapidly term velocities.atsand moment whichchangingparticles This of lastincludes dilatation duringwill start the the (Miedema,dredging slope angleprocess 2008). and !"of Theerosion. an criticalextra This term value which of in is equation important (4) atis highmultiplied erosion erosion with a constant.𝑘𝑘doneof Thethe numerically Newton-Raphson hydraulic by solvinggradient method. equation results (5). fromThis numerical the dilatant calculation behaviour was done 𝜃𝜃 with the help !! !!!!! The slopeproblem angleThe is encountered ofslope the angle soil isby of rapidlydividing the soilby changinga theis term rapidly erosion which during changing zone includes into the severalduring dredging the slope subpartsthe process dredgingangle and and ofconstantly process anerosion. extra of term Thiserosion. which 𝜃𝜃 This is important at high erosion Technology. He continued his studies with a Master’s the difference with the van Rijn theory. The termof! the is Newton-Raphson a =multiplication constantvelocities. of method. the describing hydraulic This gradient single last term particle is aor multiplication continuum(5) mode of stability the hydraulic gradient that is present during from the! !upper!!! part! problem of thecalculating soil is thatencounteredproblem𝑛𝑛 is the subjected erosion is encountered by and dividingto theslope flow. byangle the dividing erosion subsequently the zone erosion (seeinto Figure several zone into3). subparts This several calculation andsubparts constantly was and constantly 𝜃𝜃 degree in Offshore and Dredging Engineering. In 2011 he van Rijn pick-up function∙ adapted for high- that is present during erosionvelocities.1 ! This with last term is a multiplication(5) of the hydraulic gradient that is present during = relativeerosion sediment ! density with != ! a constant.! The hydraulic gradient results from the dilatant behaviour The slope angle of thecalculating soildone is rapidly numerically thecalculating𝐴𝐴 erosion changing by theand solving erosion duringslope equation angle theand! dredging !slope subsequently(5).𝜙𝜙 𝑔𝑔This ∆angle𝐷𝐷 −process 𝑐𝑐numerical 𝑤𝑤subsequently!− (see𝑣𝑣 !of= 0 erosion.calculationFigure (see 3). This Figure wasThis done calculation 3). with This the calculation helpwas was graduated from the Delft University of Technology Faculty speed erosion using the new critical Shields a constant. 1 − 𝑛𝑛1 −!𝑐𝑐 !! ! ! !! erosion! !! !! ! !with! a constant. The hydraulic gradient results from the dilatant behaviour problem is encountereddone by numericallyof dividingthe Newton-Raphsondone is the numerically by Shieldserosion solving parameter method.zone equationby solving into ! and several !(5). 𝜙𝜙equationis aThis!𝑔𝑔 non-dimensional∆ 𝐷𝐷subparts!− numerical𝑐𝑐 (5).!𝑤𝑤 !− This! 𝑣𝑣and= 0 numericalconstantlycalculation number for calculation wasdescribing done was thewith beddone the shear helpwith the help of 3ME (Mechanical, Maritime and Materials Engineering). parameter is used in this expression (2). The ∆ from1 − the𝑛𝑛 − !upper𝑐𝑐 ! part! ! !! of the soil that is subjected to the flow. ! ∙ !!! (5) His graduation project was developed in cooperation with adapted functioncalculating is defined the as erosion follows:of the and Newton-Raphson slopeofThestress. angle the hydraulic Newton-RaphsonIf subsequently the gradientcritical method. Shieldsresults (seefrom method. from Figureparameter the the! !upper 3).!! This! part! is exceededcalculationof the soil then that was the is initiationsubjected of to motion the flow. of the 𝜃𝜃 The slope angle∙ of the soil is rapidly changing during the dredging process of erosion. This Dredging International, part of the DEME (Dredging, done numerically by solving equationdilatant (5).behaviour This fromnumerical the1 The upper calculationslope !part ofangle wasof the done soil with is rapidly the help changing(5) (5)during the dredging process of erosion. This sand particles willproblem start (Miedema, is !encountered 2008).!"! The! by critical! dividing value theof erosion in equation zone (4) into is multiplied several subparts and constantly ! ! 𝜙𝜙 𝑔𝑔∆𝐷𝐷 − 𝑐𝑐 𝑤𝑤 − 𝑣𝑣 = 0 Environmental and Marine Engineering) group. In 2012 of the Newton-Raphson method.the soil that is subjected1 − 𝑛𝑛 to −problemthe𝑐𝑐 flow. Theis encountered 𝜃𝜃 by dividing the erosion zone into several subparts and constantly by a term which (3) includescalculating1 the !slope the1 angleerosion !and and an extra slope term angle which subsequently is important at (see high Figure erosion 3). This calculation was calculating ! (3) the𝜙𝜙 !erosion!(5)!𝑔𝑔 ∆𝐷𝐷 − !and𝑐𝑐!𝑤𝑤 slope! − 𝑣𝑣 !angle= 𝜃𝜃0 subsequently (see Figure 3). This calculation was his graduation project was selected as best graduation ! !.! (3) slopevelocities. angle ofThis the last soil term!is rapidly !is 𝜙𝜙a changing multiplication𝑔𝑔! ∆𝐷𝐷 !− 𝑐𝑐 𝑤𝑤 of− the𝑣𝑣 hydraulic= 0 gradient that is present during !" ! !.! 1 −done𝑛𝑛 − 𝑐𝑐numerically1 − 𝑛𝑛 − 𝑐𝑐 by solving equation (5). This numerical calculation was done with the help project of 2011-2012 by the Dutch engineers society ! !.! 𝜃𝜃 − 𝜃𝜃 during !"the dredging processdone of erosion. numerically by solving equation (5). This numerical calculation was done with the help ! ∗ ! ! !.! ! (3) where: 𝜙𝜙 = 0.00033 ∙ 𝐷𝐷 ∙ ! ∗ 1 erosion𝜃𝜃 − 𝜃𝜃 ! with! ! a constant.! The hydraulic gradient results from the dilatant behaviour KIVI (Koninklijk Instituut van Ingenieurs) Niria. He is where:where: 𝜙𝜙 =!" 0.00033 ∙ 𝐷𝐷 ∙ ! 𝜙𝜙 !!𝑔𝑔∆!𝐷𝐷!!!−! 𝑐𝑐of𝑤𝑤 the− ofNewton-Raphson𝑣𝑣 the= 0 Newton-Raphson method. method. 𝜃𝜃 ! !!" ! !.! 1 − 𝑛𝑛 −from𝑐𝑐𝜃𝜃 the upper part of the soil that is subjected!" to the flow. (5) presently a Project Engineer Automation at DEME.= dimensionless = dimensionless= particle dimensionless diameter particle diameter particle diameterThis problem !! ∙ is!! encountered!!! by dividing!.! 𝜃𝜃 the− 𝜃𝜃 (5) ! ∗ ! where: The slope angle𝜙𝜙 of= the0.00033 soil is∙ 𝐷𝐷 rapidly∙ changing!" during the dredging process of erosion. This = adapted critical = adapted Shields critical parameter Shields parameter erosion zone into several subparts and 𝜃𝜃 ! ∗ ∗ = adapted critical Shields parameter 1 1 ! 𝐷𝐷 = problem dimensionless is encountered particle by dividing diameter the erosion zone into several! 𝜙𝜙 !subparts𝑔𝑔∆𝐷𝐷 − !and𝑐𝑐!𝑤𝑤! !constantly− 𝑣𝑣!! = 0 The purpose of the IADC Young Authors! Award is to 𝐷𝐷! constantly calculating the erosion and slope ! ! ! 𝜙𝜙! 𝑔𝑔∆𝐷𝐷 − 𝑐𝑐 𝑤𝑤 − 𝑣𝑣 = 0 This!" adapted critical ThisShields!" adapted parameter critical Shields is different parameter from vancalculating is Rijndifferent in the that from erosion it takesvan and Rijn into slope in that angle it takessubsequently into1 − 1𝑛𝑛 (see−−𝑛𝑛 𝑐𝑐 Figure− 𝑐𝑐 3). This calculation was stimulate the promotion of new ideas𝜃𝜃 and to encourage This𝜃𝜃 adapted critical Shields parameter ∗ is = angle subsequently adapted critical (see Figure Shields 3). Thisparameter account a hydraulic gradient and the slope! angle. The𝐷𝐷 adapted!done critical numerically Shields byparameter solving equation is: (5). This numerical calculation was done with the help young professionals under the age of 35 working in the differentaccount from a hydraulic van Rijn in gradient !"that it takes and into the! slope!"calculation angle. The was adapted done numerically critical byShields solving parameter is: 𝜃𝜃 This!" adapted𝜃𝜃 of the critical Newton-Raphson(4) Shields parameter method.(4) is different from van Rijn in that it takes into dredging industry and related fields. It is presented each 𝜃𝜃 ! account a hydraulic gradient and the slope!" angle. The adapted critical Shields(5) parameter is: year at selected conferences at the recommendation of the ! sin 𝜙𝜙 − 𝛽𝛽 !𝑣𝑣! 𝑛𝑛! −sin𝑛𝑛! 𝐴𝐴𝜙𝜙 − 𝛽𝛽 𝑣𝑣! 𝑛𝑛! − 𝑛𝑛! 𝐴𝐴 𝜃𝜃 (4) !" !" !" !" ! Conference Paper Committee. Thewhere: winner receives € 1,000 where: 𝜃𝜃 = 𝜃𝜃 𝜃𝜃+ =! ∙𝜃𝜃 ! + ! ∙ ! 1 Dredging profile at the beginningsin of𝜙𝜙 calculation𝑘𝑘 1 −Final𝑛𝑛 dredgingsin∆ 𝜙𝜙 profile𝑘𝑘 after1 − the𝑛𝑛 numerical∆ calculation𝜙𝜙! 𝑔𝑔∆𝐷𝐷 − 𝑐𝑐!𝑤𝑤! − 𝑣𝑣! = 0 ! ! ! ! ! ! and a certificate of recognition. The paper may = then be gravitational =acceleration gravitational acceleration !"1 − 𝑛𝑛 !"− 𝑐𝑐sin 𝜙𝜙 − 𝛽𝛽 𝑣𝑣 𝑛𝑛 − 𝑛𝑛 𝐴𝐴 where: 𝜃𝜃 = 𝜃𝜃 + ! ∙ ! published in Terra et Aqua, IADC’s quarterly journal. = median particle = sizeSuction mediandiameter mouth particle size diameter Suction mouth sin 𝜙𝜙 𝑘𝑘 1 − 𝑛𝑛 ∆ 𝑔𝑔 𝑔𝑔 = gravitational acceleration = bed shear !" stress = bed shear stress 𝐷𝐷!" 𝐷𝐷 = median particle size diameter Interval = Shields parameter𝑔𝑔 = Interval = Shields𝜏𝜏 parameter = Initial sandbed!" = bed shear stress 𝜏𝜏 ! 𝐷𝐷 ! Sand bed = critical Shields parameter !!!! = ! Sand!! bed!" Shields parameter = 𝜃𝜃 = critical𝜃𝜃 Shields parameter!!!! ! !!!" 𝜏𝜏 = angleMiddle ofline internal friction Middle line ! Figure 3. Division of = the dredging angle of!" internal friction ! ! !" !" 𝜃𝜃 𝜃𝜃 = critical Shields parameterDredging! !! profile!! profile𝜃𝜃 into several intervals. = slope angle = slope angle𝜙𝜙 !" = angle of internal friction 𝜙𝜙 = permeability at moment𝜃𝜃 of dilatation = permeability𝛽𝛽 at moment of dilatation = slope angle 𝛽𝛽 ! = porosity at moment𝜙𝜙 of dilatation ! = porosity𝑘𝑘 at moment of dilatation = permeability at moment of dilatation 𝑘𝑘 ! = constant describing𝛽𝛽 single particle or continuum mode stability = constant𝑛𝑛 describing single particle or continuum! = mode porosity stability at moment of dilatation 𝑛𝑛! 𝑘𝑘 = relative sediment density = = constant describing single particle or continuum mode stability = relative𝐴𝐴 sediment density = 𝑛𝑛! !!!!! 𝐴𝐴 !!!!! ∆ is the Shields parameter and is a non-dimensional = !! relative number sediment for describing density = the bed shear is the Shields parameter and is a non-dimensional! 𝐴𝐴number for describing the bed shear ! ! ∆ stress. If the critical Shields! parameter is exceeded then the initiation of! motion!! of the stress. If the critical Shields𝜃𝜃 parameter is exceeded∆ is then the Shieldsthe initiation parameter of motion and is aof non-dimensional the !! number for describing the bed shear 𝜃𝜃 sand particles will start (Miedema, 2008).!" The critical value of in equation (4) is multiplied stress. If𝜃𝜃 the critical Shields parameter is exceeded then the initiation of motion of the sand particles will startby (Miedema,a term which 2008). includes!" The the critical slope𝜃𝜃 valueangle ofand anin extraequation term (4) which is multiplied is important at high erosion 𝜃𝜃 sand particles will start (Miedema, 2008). The critical value of in equation (4) is multiplied by a term which includesvelocities. the slope This angle last term and isan a extramultiplication term which of theis important hydraulic atgradient high𝜃𝜃 erosion that𝜃𝜃!" is present during velocities. This last term is a multiplication of the hydraulicby a term gradient which𝜃𝜃 includes that is present the slope during angle and an extra term which is important at high erosion erosion with a constant.velocities. The hydraulic This lastgradient term resultsis a multiplication from the dilatant of the behaviour hydraulic gradient𝜃𝜃 that is present during erosion with a constant.!! ! !The!!! hydraulic gradient results from the dilatant behaviour !! !!!!! from the! !upper∙ !!! part! of the soil thaterosion is subjected to withthe flow. a constant. The hydraulic gradient results from the dilatant behaviour ! ! ! from the! !upper∙ !!! part! ofThe the slope soil thatangle is ofsubjected the soil isto rapidly the flow. changing ! ! ! !during the dredging process of erosion. This The slope angle of theproblem soil is rapidlyis encountered changing by duringdividingfrom the the the dredging erosion! !upper∙ !!! part!zoneprocess of into the of several soil erosion. that subparts is This subjected and constantly to the flow. problem is encounteredcalculating by dividing the erosionthe erosion and slopezoneThe angleinto slope several subsequently angle subparts of the (see soil and Figure is constantly rapidly 3). This changing calculation during was the dredging process of erosion. This problem is encountered by dividing the erosion zone into several subparts and constantly calculating the erosiondone and numerically slope angle by subsequently solving equation (see Figure(5). This 3). numerical This calculation calculation was was done with the help calculating the erosion and slope angle subsequently (see Figure 3). This calculation was done numerically by ofsolving the Newton-Raphson equation (5). This method. numerical calculation was done with the help done numerically by solving equation (5). This numerical calculation was done with the help of the Newton-Raphson method. (5) of the Newton-Raphson method. 1 ! (5) ! ! ! ! (5) ! ! 𝜙𝜙 𝑔𝑔∆𝐷𝐷 − 𝑐𝑐 𝑤𝑤 − 𝑣𝑣 = 0 1 ! 1 − 𝑛𝑛 − 𝑐𝑐 ! ! ! ! 1 ! ! ! 𝜙𝜙 𝑔𝑔∆𝐷𝐷 − 𝑐𝑐 𝑤𝑤 − 𝑣𝑣 = 0 𝜙𝜙! 𝑔𝑔∆𝐷𝐷 − 𝑐𝑐!𝑤𝑤! − 𝑣𝑣! = 0 1 − 𝑛𝑛 − 𝑐𝑐 1 − 𝑛𝑛! − 𝑐𝑐! (3) ! !.! ! !.! 𝜃𝜃 − 𝜃𝜃!" where: 𝜙𝜙! = 0.00033 ∙ 𝐷𝐷∗ ∙ ! 𝜃𝜃!" = dimensionless particle diameter
∗ = adapted critical Shields parameter 𝐷𝐷! This!" adapted critical Shields parameter is different from van Rijn in that it takes into 𝜃𝜃 ! account a hydraulic gradient and the slope!" angle. The adapted critical Shields parameter is: 𝜃𝜃 (4)
! sin 𝜙𝜙 − 𝛽𝛽 𝑣𝑣! 𝑛𝑛! − 𝑛𝑛! 𝐴𝐴 where: 𝜃𝜃!" = 𝜃𝜃!" + ∙ sin 𝜙𝜙 𝑘𝑘! 1 − 𝑛𝑛! ∆ = gravitational acceleration = median particle size diameter 𝑔𝑔 = bed shear stress 𝐷𝐷!" = Shields parameter = 𝜏𝜏 ! 𝜃𝜃 = critical Shields parameter!!!! ! !!!" = angle of internal friction 𝜃𝜃!" = slope angle 𝜙𝜙 = permeability at moment of dilatation 𝛽𝛽 = porosity at moment of dilatation 𝑘𝑘! = constant describing single particle or continuum mode stability 𝑛𝑛! = relative sediment density = 𝐴𝐴 !!!!! ∆ is the Shields parameter and is a non-dimensional!! number for describing the bed shear stress. If the critical Shields parameter is exceeded then the initiation of motion of the 𝜃𝜃 sand particles will start (Miedema, 2008). The critical value of in equation (4) is multiplied 𝜃𝜃!" by a term which includes the slope angle and an extra term which is important at high erosion velocities. This last term is6 aTerra multiplication et Aqua | Number of the hydraulic130 | March gradient 20𝜃𝜃13 that is present during erosion with a constant. The hydraulic gradient results from the dilatant behaviour !! !!!!! from the! !upper∙ !!! part! of the soil that is subjected to the flow. The slope angle of the soil is rapidly changing during the dredging process of erosion. This problem is encountered byequation dividing (5). the This erosion numerical zone calculation into several was subparts and constantlySuction mouth Expansion calculating the erosion anddone slope with angle the help subsequently of the Newton-Raphson (see Figure 3). This calculation was done numerically by solving equation (5). This numerical calculation was done with the help method. Draghead of the Newton-Raphson method. (5) (5) Suction mouth 1 ! 𝜙𝜙! 𝑔𝑔∆𝐷𝐷 − 𝑐𝑐!𝑤𝑤! − 𝑣𝑣! = 0 1 − 𝑛𝑛! − 𝑐𝑐! Sand bed FLOW VELOCITIES ALONG THE SEABED Contraction Middle line of For erosion to occur a flow along the seabed, suction mouth Sand bed
which picks up the sand particles and brings Middle line of them to the suction mouth, must be present. suction mouth This flow is created by the pressure difference Figure 4. Potential (green) lines and flow (blue) lines at Figure 5. Illustration of contraction and expansion of between the inside and the outside of the the suction mouth of the draghead. the flow (here outer flow lines are shown). draghead. This pressure difference is set up by the centrifugal pump of the trailing suction hopper dredger. The problem of determining moving further away from the suction mouth. flow comes from two directions. The losses the evolution of the flow velocities along the The potential lines combined with the erosion created by the contraction and expansion of seabed was solved with the potential flow theory described in the first part of this article a flow are described by Carnot (Becker, 1977). theory. The assumption of the pattern of the can determine the final seabed profile and potential flow lines and the corresponding the geometric production of the draghead. The vacuum formula calculates the flow velocity changing seabed profile are shown in Figure 4. To determine the potential lines, first a in the suction pipe. By the relationship between In this figure the potential lines are drawn calculation was made of the flow created by the diameter of the suction pipe and the suction when the flow comes from the left-hand side the centrifugal pump. This flow was calculated opening, the flow velocity at the suction only. This is done for clarity of the picture. with the help of the vacuum formula for a opening could be predicted. The evolution of centrifugal pump. This formula consists of a the flow velocities along the seabed could then In reality, the flow comes from the left- and pressure head, a velocity head and an elevation be found with the help of the potential lines right-hand sides. The assumption was made head. The velocity head includes extra losses shown in Figure 4. This was done by taking that these flows will interfere and on the of the flow going to the centrifugal pump. the calculated flow velocity under the suction middle line of the suction mouth there will be For the frictional losses the Wilson model for mouth, calculating the length of the no flow. This explains the horizontal path of inclined flow was used (Matousek, 2004). corresponding potential line and then frequently the dredging profile in Figure 4. Also some calculating the length of the potential lines turbulence will occur when the flow enters Other frictional losses are created by the (see Figure 4) and the corresponding flow the suction mouth of the draghead. contraction of the flow coming from outside velocity at that position. This made it possible the draghead and going to the suction to predict the flow velocities along the seabed
In Figure 4, V0 is the undisturbed flow going mouth. When the flow enters the suction necessary for creating erosion.
to the suction mouth and Vm is the mixture mouth and goes through the draghead, the
velocity. SOA is the suction opening at the left flow expands again going to the suction pipe. For the pilferer draghead three possible suction hand side and SO is the suction opening at A simple drawing of this process is shown in openings were made: 20 cm, 10 cm and 5 cm. B (7) the other side of the draghead. x is an Figure 5. This is again for the clarity of the For the 20-cm suction opening realistic results indication of the potential line with an ! figure shown for the flow going from one were found for the flow velocity under the 𝜙𝜙 !! 𝑥𝑥 increasing indices for the potential𝜙𝜙 =lines ∙ tan direction to the suction mouth. In reality the suction mouth with the theory described here. It should be noted that the in the formulas𝜋𝜋 (6)𝑦𝑦 and (7) represents the same potential lines
(the green lines) as defined in𝟏𝟏 Figure 4. The groundwater flow can be found by superposition of formulas (6) and (7). The𝝓𝝓 coordinate system for defining the groundwater flow of the pilferer draghead was chosen as follows:
(a) Side cross section (b) Front cross section
Figure 6. Cross-section of the CFD results with the flow velocities of the pilferer draghead.
(8)
𝜙𝜙! !! 𝑥𝑥 − 0.5𝑏𝑏 𝜙𝜙 = − ∙ tan where: 𝜋𝜋 𝑦𝑦 b = width of the suction mouth of the draghead.
(9)
𝜙𝜙! !! 𝑥𝑥 + 0.5𝑏𝑏 𝜙𝜙 = ∙ tan 𝜋𝜋 𝑦𝑦 (10)
𝜙𝜙! !! 𝑥𝑥 − 0.5𝑏𝑏 𝜙𝜙! !! 𝑥𝑥 + 0.5𝑏𝑏 𝜙𝜙 = − ∙ tan + ∙ tan 𝜋𝜋 𝑦𝑦 𝜋𝜋 𝑦𝑦 Erosion Behaviour of a Draghead 7
For smaller suction openings (10 and 5 cm), no realistic results were produced. This can be explained by the fact the flow velocities under the suction mouth can increase to high values (locally this can be higher than 30 m/s) and the Wilson model is not developed to work with such high accelerations of the Figure 7. Detailed view of flow. Therefore it was decided to use a the suction mouth with the Computational Fluid Dynamics (CFD) model. flow velocities and This model was also necessary to check corresponding legend. whether the assumptions made in the beginning of this research were correct. For the CFD modelling the programme OpenFOAM calculation set to 45 degrees. This is done reduced. If the stability of the sand particles is was used. The Navier Stokes equations were because then the draghead is perpendicular lower, the sand can be eroded more easily. solved using the RANS (Reynolds Average to the seabed. According to the calculations Therefore the groundwater flow theory is Navier Stokes) method. This solution was this situation gives the highest geometric examined here to see if this flow is great done with the help of the SIMPLE FOAM productions. This is an effect that was also enough to increase the erosion process. solver of the OpenFOAM CFD library (SIMPLE experienced in the field. = Semi-Implicit Pressure-Linked Equations). Figure 8 shows approximately what the Note that the bottom line in Figure 6 is kept groundwater flow in the width of a draghead In Figure 6 some pictures of the CFD calculation fixed. This line represents the seabed. Also one looks like. The function describing the results are given. Some results of the CFD can see that in Figure 6a there is more flow groundwater flow going from left to right calculation of the flow velocities in and around coming from the left-hand side than from the was deduced as: the draghead are shown when the draghead right-hand side. This is because at the left the (6) is perpendicular to the seabed. These are two suction opening is bigger, allowing more flow (6) cross-sections of the pilferer draghead; one to pass. In reality the seabed will deform and 𝜙𝜙! !! 𝑥𝑥 𝜙𝜙 = − ∙ tan cross-section from the side (see Figure 6a) and the flow will be coming more from the right- The function is the same𝜋𝜋 for the𝑦𝑦 flow going one cross-section from the front (see Figure 6b) hand side than is shown in Figure 6a. from right to left, except for a sign difference: of the draghead. These cross-sections are Therefore, for this research, the flow velocity (7) taken at the middle line of each side. Figure 7 just under the suction mouth is taken and the (7) gives a more detailed view of the suction other flow velocities in the erosion affected 𝜙𝜙! !! 𝑥𝑥 mouth and its flow velocities calculated with zone are calculated with the potential flow 𝜙𝜙 = ∙ tan the CFD programme OpenFOAM. In these theory. Combining thisIt shouldtheory with be the noted theory that Itthe should be in noted the that formulas𝜋𝜋 the in (6) 𝑦𝑦the formulasand (7) (6) represents the(7) same potential lines calculations the flow velocities are calculated explained under “Erosion(the Theory” green above, lines) it wasas definedand (7) in represents Figure the 4. sameThe potentialgroundwater lines (the flow can be found by superposition 𝟏𝟏 ! for a flow velocity set up by the pump. The scale now possible to determine the seabed profile. green𝝓𝝓 lines) as defined in Figure𝜙𝜙 4. The!! ground-𝑥𝑥 of formulas (6) and (7). The coordinate𝜙𝜙 =system∙ tan for defining the groundwater flow of the next to each picture in Figure 6 indicates the pilfererIt shoulddraghead be wasnoted chosenwater that flow the as can follows: be in found the byformulas𝜋𝜋 super-position (6)𝑦𝑦 andof (7) represents the same potential lines values of the flow velocities. The closer to the GROUNDWATER FLOW(the green lines) asformulas defined (6) and in (7).Figure The coordinate 4. The groundwatersystem for flow can be found by superposition color red, the higher the flow velocity. The flow During the excavation process of sediment defining the 𝝓𝝓groundwater𝟏𝟏 flow of the pilferer velocity set up by the pump is here 10 m/s. from the seabed, groundwaterof flowformulas is (6) anddraghead (7). The was chosencoordinate as shown system in Figure for 9. defining the groundwater flow of the present. This groundwater flowpilferer moves draghead was chosen as follows: These values were taken from the real measured towards the suction opening of the draghead In Figure 9, ‘b’ represents the width of the pump flow velocities onboard DEME’s trailing creating an area under the suction mouth at draghead. With the help of Figure 9 and suction hopper dredger Jade River. The average which the stability of the sand particles is formula (6), it was deduced that the flow suction opening used for the calculation shown here is 20 cm. The local accelerations of the flow going under the suction mouth into the draghead were also noticed in the CFD results (see red area in Figure 6). For smaller suction openings, this effect was even more noticeable, which agreed with the assumptions made in X the beginning of the research (the contraction expansion of the flow shown in Figure 5 and Excavating profile and groundwater Y and the local accelerations created by these from underneath a draghead without jets effects). The inclination angle of the suction Figure 9. The definition coordinate system for pipe according to the ship is for this Figure 8. Groundwater flow lines of a draghead. determination of ground-water flow.
(8)
𝜙𝜙! !! 𝑥𝑥 − 0.5𝑏𝑏 𝜙𝜙 = − ∙ tan 𝜋𝜋 𝑦𝑦 where: (8) b = width of the suction mouth of the draghead. 𝜙𝜙! !! 𝑥𝑥 − 0.5𝑏𝑏 𝜙𝜙 = − ∙ tan where: 𝜋𝜋 𝑦𝑦 b = width of the suction mouth of the draghead.
(9)
𝜙𝜙! !! 𝑥𝑥 + 0.5𝑏𝑏 𝜙𝜙 = ∙ tan 𝜋𝜋 𝑦𝑦 (9) (10) 𝜙𝜙! !! 𝑥𝑥 + 0.5𝑏𝑏 𝜙𝜙𝜙𝜙!= ∙!tan! 𝑥𝑥 − 0.5𝑏𝑏 𝜙𝜙! !! 𝑥𝑥 + 0.5𝑏𝑏 𝜙𝜙 = − ∙ tan𝜋𝜋 𝑦𝑦+ ∙ tan 𝜋𝜋 𝑦𝑦 𝜋𝜋 𝑦𝑦 (10)
𝜙𝜙! !! 𝑥𝑥 − 0.5𝑏𝑏 𝜙𝜙! !! 𝑥𝑥 + 0.5𝑏𝑏 𝜙𝜙 = − ∙ tan + ∙ tan 𝜋𝜋 𝑦𝑦 𝜋𝜋 𝑦𝑦 (7)
8 Terra et Aqua | Number 130 | March 2013 𝜙𝜙! !! 𝑥𝑥 (7) 𝜙𝜙 = ∙ tan 𝜋𝜋 𝑦𝑦 It should be noted that the in the formulas𝜙𝜙! ! !(6)𝑥𝑥 and (7) represents the same potential lines (the green lines) as defined in Figure𝜙𝜙 = 4. The∙ tan groundwater flow can be found by superposition It should be noted that the 𝟏𝟏 in the formulas𝜋𝜋 (6)𝑦𝑦 and (7) represents the same potential lines of formulas (6) and (7). The𝝓𝝓 coordinate system for defining the groundwater flow of the (the green lines) as defined in Figure 4. The groundwater flow can be found by superpositionDredging profile pilferer draghead was chosen 𝟏𝟏as follows: of formulas (6) and (7). The𝝓𝝓 coordinate system for defining0.3 the groundwater flow of the pilferer draghead was chosen as follows: 0.25 Suction mouth 0.2 Movement of draghead of the draghead 0.15
0.1 (7) 0.05 ! 𝜙𝜙 !! 𝑥𝑥 𝜙𝜙 = ∙ tan 0 It should be noted that the in the formulas𝜋𝜋 (6)𝑦𝑦 and (7) represents the same potential lines (the green lines) as defined in Figure 4. The groundwater flow can be found by superposition 𝟏𝟏 -0.05 of formulas (6) and (7). The𝝓𝝓 coordinate system for defining the groundwater flow of the Dredging depth in metres pilferer draghead was chosen as follows: -0.1
-0.15
-0.2 Figure 10. Calculated -10 -5 0 5 10 dredging profile for a suction Dredging length in metres opening of 10 cm.
going from left to right can be described with behaviour of the draghead only gave a slight of the draghead. Closer to the suction the following equation: improvement to the real situation. The calculated openings the flow velocity will rapidly geometric productions matched the real increase. If the amount of intervals chosen (8) 3 (8) productions a few m per hour more. Still this is too small, the acceleration of the flow 𝜙𝜙! !! 𝑥𝑥 − 0.5𝑏𝑏 theory was(8) an improvement of the calculations going to the suction mouth is overestimated. 𝜙𝜙 = − ∙ tan in comparison to the real production. The final This results in erosion rates that are too high. where: 𝜋𝜋 𝑦𝑦 where: 𝜙𝜙! !! 𝑥𝑥 − 0.5𝑏𝑏 calculation of the geometric productions is With the help of the MATLAB code the b = width of the suction𝜙𝜙 = mouth− ∙ tanof the draghead. where: b = width of the𝜋𝜋 suction mouth𝑦𝑦 of the explained in the next paragraph. correct amount of intervals was found. b = width of thedraghead. suction mouth of the draghead. This was done by searching for a number of CALCULATION OF THE EROSION intervals at which the dredging profile did not (8) The groundwater flow going from right to left BEHAVIOUR OF THE DRAGHEAD change anymore. If the amount of intervals is deduced𝜙𝜙! in! !the𝑥𝑥 − same0.5𝑏𝑏 manner and is the The theories described above were combined exceeded this number and the calculated 𝜙𝜙 = − ∙ tan where: following𝜋𝜋 formula:𝑦𝑦 in a MATLAB (9)calculation model. With this dredging profile remained unchanged, the b = width of the suction mouth of the draghead. model the removed amount of sediment was correct amount of intervals was determined. 𝜙𝜙! !! 𝑥𝑥 + 0.5𝑏𝑏 (9) 𝜙𝜙 = ∙ tan (9) calculated. The dredging profile was set up by Figure 10 shows a calculated MATLAB 𝜋𝜋 𝑦𝑦 𝜙𝜙! !! 𝑥𝑥 + 0.5𝑏𝑏 calculating the slope and the erosion velocity example of the dredging profile. 𝜙𝜙 = ∙ tan at a certain distance(10) between the boundaries of 𝜋𝜋 𝑦𝑦 (9) Superposition of the formulas (8) and (9) gives the erosion affected zone. These boundaries One should assume in Figure 10 that the ! !! ! !! 𝜙𝜙! !! 𝑥𝑥𝜙𝜙+ 0.5𝑏𝑏 𝑥𝑥 − 0.5𝑏𝑏 𝜙𝜙 𝑥𝑥 + 0.5𝑏𝑏 (10) the𝜙𝜙 = equation𝜙𝜙∙ tan= − (10).∙ tan + ∙ tan were determined with the help of the draghead is located at position 0 of the x-axis. 𝜋𝜋 𝜋𝜋𝑦𝑦 𝑦𝑦 𝜋𝜋 𝑦𝑦 ! !! ! !!corresponding potential lines and transport The calculated dredging profile shown in 𝜙𝜙 𝑥𝑥 − 0.5𝑏𝑏 𝜙𝜙 (10) 𝑥𝑥 + 0.5𝑏𝑏 𝜙𝜙 = − ∙ tan + (10)∙ tan parameter T. Figure 10 was done for a median particle size 𝜙𝜙! !! 𝑥𝑥𝜋𝜋− 0.5𝑏𝑏 𝜙𝜙! 𝑦𝑦!! 𝑥𝑥 + 0.5𝑏𝑏𝜋𝜋 𝑦𝑦 (11) diameter D of 300 (μm11 )and an average 𝜙𝜙 = − ∙ tan + ∙ tan 50 𝜋𝜋 𝑦𝑦 𝜋𝜋 𝑦𝑦 ! suction opening of 10 cm. (This suction 𝜙𝜙 − 𝜙𝜙!" Formula (10) was already deduced by Professor ! opening was taken at the middle line of the 𝑇𝑇 = !" Vlasblom of Delft University of Technology in The distance between the𝜙𝜙 boundaries of the pilferer draghead.) The maximal flow velocity 2004. His method of deducing the equation erosion-affected zone were divided into a along the seabed was calculated to be 15.5 m/s. was never published. This formula was used certain amount of intervals. These intervals This was calculated with the help of the CFD to describe the groundwater flow at several needed to be made small enough so as not to model and the potential flow theory. For this positions in the erosion affected zone with the have an overestimation of the calculated example a soil layer of 11 cm is removed and the help of the potential lines shown in Figure 4. geometric production. This phenomenon is production was calculated to be 786 m3/hour. The implementation of the groundwater flow explained by the fact that the flow velocity In reality the production varied between 784 theory in the final calculation of the erosion slowly increases going to the suction openings and 794 m3/hour for this case. Erosion Behaviour of a Draghead 9
Another case that was investigated was for an average suction opening of 5 cm. The CONCLUSIONS dilatancy of sediment at high flow velocities maximum flow velocity along the seabed was during erosion. Van Rhee achieves this by 30 m/s according to the CFD model. The During this research on the erosion taking the van Rijn pick-up function (van Rijn, median particle size diameter was 310 μm. behaviour of the pilferer draghead, several 1984), valid for low-velocity erosion, and The productions were in the range of 800 to topics were investigated. The main topics of modifying it to deal with high-velocity 820 m3/hour. The calculated production was investigation were erosion, flow effects regimes. This modification is done by 816 m3/hour with a corresponding removed along the seabed during dredging and changing the critical Shields parameter. soil layer of 14 cm. groundwater flow. These were analysed together to describe the final erosion During this research the limitations of the Several other cases were investigated and behaviour of the pilferer draghead. Some Wilson model were encountered. For small further agreement between the calculations elements such as the jet flow and the suction openings where the flow locally and the real situations were found to be groundwater flow do not affect the results accelerates strongly, the model could not be good. The maximum D50 particle size diameter of this research significantly. Still they gave a used anymore. Therefore a CFD model was dredged with the pilferer draghead was 400 μm. small improvement of the calculated results chosen instead. In the beginning of this compared to the real values. research certain assumptions were made Later on it was decided to add a jet system to regarding the contraction and expansion of the pilferer draghead to create an extra water It can, however, be concluded that the the flow. These effects were found back in flow to the suction mouth of the draghead. erosion theory and the theory describing the the CFD model. The CFD model thus gave a It was assumed that this jet flow would not flow velocities along the seabed have a good understanding of the flow behaviour create erosion because of its low flow velocity strong influence on the results of the of the pilferer erosion draghead during (≈10 m/s), but this was not investigated and calculations of the erosion behaviour of the dredging. so it is not clear whether the jet flow actually draghead. The fact that the calculations and does or does not create erosion. The jet flow reality are matched quite accurately shows The pilferer draghead finished its job was taken into account in the calculation of that the van Rhee erosion theory (van Rhee, successfully at the River Scheldt in Belgium the dredging profile according to the jet flow 2010) is pointing in the right direction for without damaging any buried cables. concept of Pani and Dash (1983). This gave describing erosion in dredging practice. This After this job the contractor, Dredging only a slight improvement in the calculated can be explained by the fact that the van International, part of the DEME group, production values as compared to the real Rhee theory takes into account the effect of patented this erosion draghead. values.
REFERENCES Talmon, A.M. and van Rhee, C. (2010). Method. Longman Scientific and Technical, Harlow, ”Sedimentation and erosion of sediment at high Essex, England. Anderson, J.D. (1995). Computational Fluid Dynamics: solids concentration”, 18th International Conference The Basics with Applications. McGraw-Hill, New York, on Hydrotransport, Bedfordshire, UK, pp. 211-222. Visser, P.J. (1995a). “Application of sediment USA. transport formulae to sand-dike breach erosion, Van der Veer, P. (1978). Calculation methods for Communications on hydraulic and geotechnical Becker, E. (1977). Technische Strömungslehre. two-dimensional groundwater flow, Ph. D. thesis, Delft engineering, report no.94-7”, Delft University of Teubner, Stuttgart, Germany. University of Technology, Delft, the Netherlands. Technology, Delft, the Netherlands.
Bisschop, F., Visser, P.J., van Rhee, C. and Verhagen, H.J. Van Prooijen, B.C. and Winterwerp, J.C. (2010). Visser, P.J. (1995b). Breach growth in sand-dikes, (2010). “Erosion due to high flow velocities: a “A stochastic formulation for erosion of cohesive Ph.D. thesis, Delft University of Technology, Delft, description of relevant processes“, 32nd International sediments”, Journal of Geophysical Research, the Netherlands. Conference on Coastal Engineering, Shanghai, vol.115, C01005. China. Voogt, L., van Rijn, L.C. and van den Berg, J.H. Van Rhee, C. and Bezuijen, A. (1992). “Influence (1991). “Sediment transport of fine sands at high Matousek, V. (2004). Dredge pumps and slurry of seepage on stability of sandy slopes”, Journal of velocities”, Journal of Hydraulic Engineering, ASCE, transport, lecture notes Delft University of Geotechnical Engineering, vol.118(8), pp. 1236-1240. vol.117, pp. 869-890. Technology, the Netherlands. Van Rhee, C. (2010). “Sediment entrainment at Wilson, W.C. (1989). Mobile-bed friction at high Miedema, S.A. (2008). “An analytical method to high flow velocity”, Journal of Hydraulic shear stress, Journal of Hydraulic Engineering, determine scour”, WEDA XXVII / Texas A&M 39, Engineering, ASCE, vol.136(9), pp. 572-582. ASCE, vol.825(115), pp. 824-829. St. Louis, Missouri, USA. Van Rijn, L.C. (1984). “Sediment pick-up functions”, Winterwerp, J.C., De Groot, M.B., Mastbergen, D.R. Pani, B and Dash, R. (1983). “Three-dimensional Journal of Hydraulic Engineering, ASCE, vol.110, and Verwoert, H. (1990). “Hyperconcentrated single and multiple free jet”, Journal of Hydraulic pp. 1494-1502. sand-water mixture flows over flat bed”, Journal of Engineering, ASCE, vol.109, pp. 254-269. Hydraulic Engineering, ASCE, vol.116, pp. 36-54. Van Rijn, L.C. (1984). “Sediment transport, Part II: Roberts J., R. Jepsen, D. Gotthard and W. Lick Suspended load transport”, Journal of Hydraulic Winterwerp, J.C., Bakker, W.T., Mastbergen, D.R. (1998). Effects of particle size and bulk density Engineering, ASCE, vol.110, pp. 1613-1641. and van Rossum, H. (1992). “Hyperconcentrated on erosion of quartz particles, Journal of sand-water mixture flows over erodible bed”, Hydraulic Engineering, ASCE, vol.124(12), Versteeg, H.K. (1995). An Introduction to Journal of Hydraulic Engineering, ASCE, vol.118, pp. 1261-1267. Computational Fluid Dynamics; The Finite Volume pp. 1508-1525. 10 Terra et Aqua | Number 130 | March 2013
DAVID CLOSE, ANTHONY BATES, ROBIN MORELISSEN AND CAROLINE ROCHE
Redcastle licensed Disposal Site Proposed McKinney’s Bank Disposal Site Port of Londonderry
Lough Foyle
DREDGING AND DISPOSAL AT LOUGH FOYLE, NORTHERN IRELAND
ABSTRACT Londonderry Port and Harbour Commissioners 007° 04.5’ West; it is still shown on the owns the copyright in reports by Anthony D current Admiralty navigation charts although The Port of Londonderry is located at the point Bates Partnership, Deltares and Aquafact that it is annotated as disused (Figure 1). of discharge of the River Foyle into Lough Foyle, were commissioned for the purpose of the lake on the western boundary of Northern relocating the silt disposal site. The authors Until 1977, when the Port’s bucket dredger and Ireland, and is an important strategic business in wish to thank LPHC for consenting to the use self-propelled hoppers were withdrawn from the North of Ireland, which serves the entire of images and extracts from those reports for service, quantities in the range of 86,220 m3 region and promotes economic growth and use in the technical paper presented here. to 180,090 m3 of mixed dredged materials stability. Historically the Port disposed of the were disposed of at the traditional site and in entirety of its dredging requirement at the 1977/78 1.055 million m3 were disposed of “traditional” disposal site within Lough Foyle. INTRODUCTION with no adverse effects within Lough Foyle. Because of changes in the dredging regime, In 1982 a volume of 324,750 m3 and in 1983 new licensing was required. The local shell- The Port of Londonderry is located at the point some 263,053 m3 were removed from the fisheries then objected to the increase in disposal of discharge of the River Foyle into Lough channels and berths and were either disposed at the currently used inshore disposal site at Foyle, the lake on the western boundary of of at the traditional site or else dispersed Redcastle and expressed a preference for Northern Ireland (opening photo) and is an during dredging. That is, this large volume of alternative sites, principally McKinney’s Bank. important strategic business in the North of material remained within Lough Foyle. The Port with the shellfishery industry under- Ireland, which serves the entire region and took to apply for the alternative (McKinney’s promotes economic growth and stability. Routine maintenance dredging from 1984 to Bank) site and an additional modelling exercise Historically the Port disposed of the entirety of 1994 was sporadic and was considered was then commissioned for this alternative site. its dredging requirement at its “traditional” unlikely to have exceeded 100,000 m3 per The monitoring programme demonstrated disposal site within Lough Foyle. This site had annum. In 1993/94 the Port moved its main that the changed regime of regular small-scale been in use since the 19th century and was base of operations from the constrained dredging and disposal of all dredged sediments centred at approximately 55° 09.5’ North, confines of the city to new berths and shore at the new McKinney’s Bank disposal site has facilities at Lisahally. The new facility was no significant detectable effect on water quality supported by a deepened access channel or seabed sediment characteristics within the Above: A Google Earth image of the North coast of through Lough Foyle (see Figure 2), which Lough (lake), other than within the immediate Northern Ireland, with top left the north Atlantic Ocean was dredged during the winter of 1993/94. environs of the licence area. It also demonstrated and top right the Channel. The Port of Londonderry is clearly the numerous benefits to the disposal located at the point of discharge of the River Foyle into In support of the new access channel, 2D of dredged material within the Lough. Lough Foyle on the western boundary of Northern Ireland. mathematical modelling was undertaken and Dredging and Disposal at Lough Foyle, Northern Ireland 11
Disused former Redcastle disposal site
Current licensed DAVID CLOSE disposal site (MEng, BEng (Hons), DMS, CEng, MICE) is a Consultant with Cwaves and is based in London. He is a specialist Maritime Civil Engineer with extensive worldwide experience of port, marina and coastal engineering, and dredging and land reclamation projects. He was the lead Partner from the Anthony Bates Partnership on the Londonderry Incorrectly charted project. disposal site
ANTHONY BATES (CEng, MICE) is a Chartered civil engineer and senior partner in specialist dredging consultants Figure 1. Location of Current Redcastle Disposal Site. Large Circle shows Actual Licensed Area. Anthony D Bates Partnership. Together with his partners, he provides advice in dredging and related projects across the world, mainly a variety of options for disposal were within the Lough Foyle sediment cell and the to ports and harbours, but also to industry, investigated including land reclamation and Natural Heritage Directorate (the predecessor governments, water authorities, law firms and beach recharge. One of the favoured sites for of the Northern Ireland Environment Agency) private companies. He has served on a variety disposal was near to the mouth of the Lough at objected strongly to the material being of professional committees and PIANC working McKinney’s Bank (Figure 2). Modelling proved removed and lost to the sediment system, groups. Today he focuses mainly on expert that the proposed McKinney’s Bank site would but the views of the fishermen prevailed. witness assignments and input to projects have been suitable for disposal of whatever where his experience is of special value. arose from the capital dredging without Since the deepening of the access channel, causing any adverse effects within the Lough. the Port has had a regular maintenance ROBIN MORELISSEN dredging requirement for the channel received his MSc degree in Civil Engineering However, following objections from the Lough’s amounting to about 95,000t annually which from the University of Twente, The fishing industry, an agreement was reached has been disposed of mainly (80,000t) Netherlands. Since 2001, he has been that the capital dredged materials (a paid offshore by contract dredgers with the working at Deltares as a senior researcher/ volume of some 728,060 m3) be disposed of balance (15,000t) being disposed of at the consultant on coastal hydrodynamics, outfalls at sea far outside of the Lough (Figure 2). This Redcastle disposal site (shown at the centre and dredging-related topics. He has a wide action removed material from circulation of Figure 1) by the Port’s own dredger. experience in (multi-disciplinary) projects world-wide concerning coastal hydrodynamics and marine impacts. He also has a key role Offshore in developments around the coupling of Disposal Site near and far field models and advanced modelling techniques in engineering practice used in dredge plume studies and recirculation studies for industrial outfalls.
CAROLINE ROCHE Dredging Site obtained her PhD in 2004 in Marine Science from the National University of Ireland, Proposed Galway. Her PhD thesis focused on the McKinney’s Bank impacts of dredge material disposal on a Disposal Site disposal site in Inner Galway Bay. Since then she has been working with AQUAFACT International Services Ltd., an environmental consultancy based in Galway. She has consulted on a variety of projects including dredging and disposal operations, offshore wind farms and harbour developments and specialises in assessing the impacts of human activity on the benthos. Figure 2. Location of Dredging Site, McKinney’s Bank and the Licensed Offshore Disposal Site. 12 Terra et Aqua | Number 130 | March 2013
which is outfitted with bottom doors. This vessel is capable of maintaining the channel depth of the Port’s recent annual requirement of 80,000t without the need for periodic contract dredging. The offshore disposal site (see Figure 2), which has taken the majority of the dredged sediment since the Lisahally berths were created, is a round trip of approximately 65 km from the Redcastle disposal site with consequentially substantial energy consumption and associated carbon emissions. Therefore, to keep sailing times, and hence costs, down the Port has sought (from 2008 to 2010) to re-establish the former practice of disposal within the Lough.
In practice, this would mean the disposal of up to 80,000t annually at the Redcastle site. Figure 3. The Port of Londonderry’s trailing suction hopper dredger Lough Foyle. However, dredging and disposal would be regular – no more than one trip per day, five days per week – such that no more than a The major part of the maintenance dredging Cooperative after trial shellfish dredging in 1994. couple of thousand tonnes a week would be has been undertaken by contract dredgers in The trial shellfish dredge established that the relocated within the Lough. This is in sharp single campaigns as required by conditions nearest known shellfish beds were located contrast to the contract dredging situation, within the Port and Harbour, with a smaller 1000 m (oysters) and 3500 m (mussels) away when up to 15,000t was sometimes disposed amount removed by the Port’s own dredger and it was concluded (Anthony D Bates of within the Lough in only a few days. – originally the Mary Angus and, now, the Partnership, 1994) that the site was the best Lough Foyle – to keep the channel clear practicable environmental option (BPEO). The proposal to keep the dredged sediment between the more substantial and more Despite establishing the disposal site in within Lough Foyle would be in line with the general contract maintenance dredging dialogue with the Lough Foyle fishing industry stated preference of the NIEA’s predecessor campaigns. No contract dredging has been much commercial shellfishery development (Connor J, 1995) and various official bodies, carried out since the Port acquired the Lough has subsequently taken place up to and, it is “… to retain dredged sediment within the Foyle in 2010. Until recently, sand dredged by understood, even within the boundaries of coastal cell or sediment transport system from the Port dredgers was not disposed of, but is the licensed disposal site. which it is removed.” It is, however, a change landed ashore for beneficial use. from recent practice and would require going Note that the existing Redcastle licensed through the full FEPA (Food and Environmental The current inshore site at Redcastle within sediment disposal site is not correctly shown Protection Act) licensing process. Lough Foyle has been licensed since 1995 for on the current Admiralty Chart 2511 in respect the disposal of 15,000t annually by the Port’s of either location or size (see Figure 1). It is THREE-DIMENSIONAL MODELLING own small dredger so that the Port can deal incorrectly charted as a 400-m diameter circle An extensive data collection and modelling with the smaller amounts of continuous with its centre 100 m east of the licensed exercise (Deltares, 2009) was conducted from maintenance dredging for which contract location but its licensed size is actually much 2008 to 2009. A dedicated Delft 3D-FLOW dredging would be prohibitively expensive. bigger; it is a 0.25 nautical mile radius (926-m model was developed for Lough Foyle with Consequently, the Port now utilises two diameter) circle. The disposal of maintenance a high level of detail in the areas of interest licensed disposal sites: material at the two existing (Redcastle and (i.e., dredged sediment disposal sites). To - offshore at 55° 17.5’ North, 06° 40.0’ West, offshore) sites was previously covered by the demonstrate the predictive value of the and issue of two separate licences but, more hydrodynamic model, the model was calibrated - inshore at 55° 08.9’ North, 07° 06.5’ West recently and logically, has been amalgamated and validated with field measurements of (the Redcastle site). under a single licence. water levels and three-dimensional current measurements (see Figure 4, which shows a The location of the current Redcastle site was PROPOSALS TO EXPAND USAGE OF vector plot and comparison with the model established after extensive consultation with, THE REDCASTLE DISPOSAL SITE current predictions and field measurements). amongst others, the Foyle Fisheries As mentioned above, the Port recently purchased These measurements were collected in Commission and the Greencastle Fishermen’s the trailing suction hopper dredger renamed transects around the area of interest in a Cooperative Society, and the Foyle Shellfish Lough Foyle (previously, Saeftinge) (Figure 3), survey campaign dedicated to this study. Dredging and Disposal at Lough Foyle, Northern Ireland 13
Sedimentation (m)
Disposal Site
Figure 4. Samples of Model Current Vector Plots, and a Comparison of Model Figure 5. Sedimentation in Metres after One Year (15,000 tonnes Silt disposed of at Current Predictions and Field Current Measurements. Redcastle).
Furthermore, other data sources, including suspended sediment concentrations are modelling shows that after one year, the excess water level data, salinity data (conductivity, expected compared to the existing dredging sedimentation resulting from the full dredging temperature and density (CTD) profiles) and regime involving a contractor dumping high operation is limited to a number of patches with sediment concentration data, were used to volumes in a short period of time. Because of sedimentation over 1 mm on shallow areas further validate the model’s predictive value. the increased amount of annually discharged inland of the disposal site and on the north This calibration and validation has sediment, the sedimentation as a result of the shore of the Lough and that the discharged demonstrated that the developed model was new dredging regime inevitably shows an sediment will be transported away from the very capable of replicating the present increase compared to the old regime. disposal site. A few patches are expected to behaviour of the natural system and predicting have a local sediment layer thickness up to a expected future effects of proposed different The model showed that the impacts of few tens of millimetres, but most patches will dredging regimes. increased sedimentation >10mm were mainly have a thickness of a few millimetres. restricted to an area local to the disposal site The modelling exercise presented the existing (see Figure 6). The majority of the additional THE REGULATORY CONTEXT situation (15,000t per annum) and showed annual sedimentation is expected in the East Sediment contamination the patterns of redistribution of sediment channel, with a typical layer thickness of 5 mm. The normal regulatory process for the disposal within Lough Foyle from the disposal ground of dredged sediment requires a demonstration at Redcastle as an “excess” quantity above Because the local shellfisheries objected to the that the sediment is within acceptable limits background levels (see Figure 5). Other increase in disposal at Redcastle (see below), set out by OSPAR (Convention for the simulations were carried out for the situation additional modelling of disposal at a potential Protection of the Marine Environment of the of 60,000t and 80,000t disposed of annually alternative site at McKinney’s Bank was required. North East Atlantic). This is done by testing at Redcastle. The sedimentation pattern after one year sediments for their physical and chemical (long-term simulation) of disposal of 80,000t properties. Samples were taken for testing The modelling showed that as a result of the at McKinney’s Bank is presented in Figure 7. from the access channel (see Figure 8), which infrequent sediment discharges at the disposal is the source of the proposed maintenance site location in the new regime, the dredging- In this case, approximately 50% of the dredging. induced suspended sediment concentrations discharged sediments are predicted to be can be increased in the direct vicinity of the transported out of the Lough because of the The samples were tested and tested against disposal site, but only for short periods. Lower close vicinity of the Lough’s entrance. The the widely accepted CEFAS “Action Levels” 14 Terra et Aqua | Number 130 | March 2013
Sedimentation (m) Sedimentation (m)
Disposal Site
Sediment Monitoring Area 3 Sediment Disposal Site Monitoring Area 2
Sediment Monitoring Area 1
Figure 6. Sedimentation in Metres after One Year (80,000 tonnes Silty Sand disposed Figure 7. Sedimentation in Metres after One Year (80,000 tonnes Silty Sand disposed of of at Redcastle). at McKinney’s Bank).
shown in Table I (CEFAS is the UK Government’s shellfishers to apply in the future for the an application was made for disposal of all Centre for Environment, Fisheries and Aqua- alternative (McKinney’s Bank) site and an the Port’s 80,000t of maintenance dredging culture Science). The CEFAS guideline action additional modelling exercise was then at the existing Redcastle disposal site because levels for the disposal of dredged material are commissioned for this alternative site. it was feared that unresolved national (Ireland/ not statutory contaminant concentrations for United Kingdom) jurisdiction concerns at the dredged material but are used as part of a Notwithstanding the preference expressed by proposed new McKinney’s Bank site would weight of evidence approach to decision- the shellfishery industry for an alternative site, delay licensing. making on the disposal of dredged material to sea. Table II shows the results of the testing.
Lough Foyle ENVIRONMENT AND FISHERIES Disposal Site After the modelling was complete, a Sample No 8 presentation was made to principal consultees Sample No 7 – NIEA (Northern Ireland Environment Agency), DARD (Department of Agriculture and Rural Sample No 6 Development) and the Loughs Agency. The Navigation Channel Sample No 5 Loughs Agency recommended that the Port discuss the results with the commercial Sample No 4 shellfisheries and open a dialogue. This was Sample No 3 done, but despite the prediction of only minor Muff Sample No 2 impact, the shellfisheries expressed a preference for alternative sites, principally Sample No 1 McKinney’s Bank. This is approximately the Navigation Channel same location rejected by fishery industry for Black Brae disposal of capital dredging in 1993. It is important to note that the new site now Lisahally proposed was identified by the shellfishers Wharf themselves. The Port undertook with the Figure 8. Locations of Access Channel Sediment Samples. Dredging and Disposal at Lough Foyle, Northern Ireland 15
The fishery industry’s expected objections to Table I. CEFAS Contaminant Action Levels. this licence application were received and a Action Level 1 Action Level 2 meeting to discuss the situation was attended Contaminant (μg/g wet weight) (μg/g wet weight) by NIEA, LPHC, the Loughs Agency and the Port’s consulting engineers, Anthony D Bates Arsenic (As) 10 25-50 Partnership (ADBP). At the meeting, a Mercury (Hg) 0.15 1.5 compromise FEPA Licence for 30,000t annual Cadmium (Cd) 0.20 2.5 disposal in Lough Foyle was agreed upon Chromium (Cr) 20 200 together with the agreement to proceed with an application for full disposal at McKinney’s Copper (Cu) 20 200 Bank. Nickel (Ni) 10 100 Lead (Pb) 25 250 Ultimately, however, the monitoring Zinc (Zn) 65 400 requirements attached to the 2010 FEPA Licence for disposal of 30,000t annually at the Organotins (TBT, DBT, MBT) 0.10 1.0 current Redcastle site proved financially too PCBs Sum of ICES 7 0.010 – onerous for the relatively small increase in PCBs Sum of ICES 25 congeners 0.020 0.20 disposal tonnage and the Port decided Oil (petroleum hydrocarbons) 100 – therefore to revert to the previous licensed Sum of DDT 0.001 – tonnage, which did not require monitoring to be conducted. The 2010 FEPA Licence was Dieldrin 0.005 – accordingly varied back to 15,000t at Redcastle and 65,000t offshore. The existing disposal area is located on potential disposal locations, the depth of sediment in ENVIRONMENTAL CONSIDERATIONS oyster ground, relaid mussel ground and the disposal site at any one time will not vary AT REDCASTLE undifferentiated ground. The disposal of from what is present under the existing regime CEFAS had carried out a baseline survey of sediment on any of these grounds will impact (approximately 1.0-1.5 m). The larger quantity the shellfish resource in Lough Foyle on behalf on the resident fauna within the area. While of sediment disposed under the proposed of the Loughs Agency in 2007. Figure 9 shows the proposed quantities of sediment (60,000t new disposal regimes will result in a larger a distribution map of oyster and mussel grounds or 80,000t annually) are larger than is disposed quantity of sediment being dispersed over the resulting from the CEFAS study. Oyster of currently (15,000t), given the much larger Lough over a one-year period. However, these ground was typified not only by the presence timeframe over which the sediment is disposed levels are all less than 10 mm deep. The of oysters but also of suitable shell cultch. of in the proposed new disposal regimes, tidal specific impacts of this sediment dispersal on movements and variation in individual cargo the key shellfish species is discussed below. Large areas of the Lough are in use for mussel relaying (i.e., farming) and there are also considerable stocks of wild mussels either Table II. Sediment Sampling Results. naturally settled or remnants of previous Contaminant Sample Sample Sample Sample Sample Sample Sample Sample relaying exercises. Mussels are relaid onto / Compound 1 2 3 4 5 6 7 8 ground that has been cleaned by (mussel) Mercury ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ dredging. A total of approximately 32% of the Lough’s entire surface area is occupied by Aluminium ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ relaid mussels, a quarter of which was Arsenic ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ considered unproductive (CEFAS, 2007). Cadmium ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Approximately 42% of the Lough can be Chromium ✗ ✗ ✗ ✓ ✓ ✓ ✓ ✓ characterised as oyster grounds, more than half of which contained significant amounts Copper ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ of oysters during the 2007 CEFAS survey. Lead ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Nickel ✗ ✗ ✗ ✓ ✓ ✓ ✓ ✓ Additional species such as green crabs Zinc ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ (Carcinus maenas), whelks (Buccinum PCBs ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ undatum), cockles (Cerastoderma edule), palourde clam (Tapes senegalensis) and the Organotins ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ trough shell (Spisula solida) were recorded Notes: Tick indicates below CEFAS Action 1 Levels. during the CEFAS (2007) survey. Cross indicates exceedance of CEFAS Action Level 1 but still substantially below CEFAS Action Level 2. 16 Terra et Aqua | Number 130 | March 2013
Table III. Summary of Critical Thresholds for Oyster (Ostrea edulis) Beds. matter. The tolerance thresholds of mussels are summarised in Table IV. Species Parameter Optimum Range Maximum Tolerated Tolerant of short periods Mussels are very tolerant of extremely high Suspended of high turbidity. <100 mg/ℓ turbidities (see Table IV). Although incidental sediment excess turbidities higher than 100 mg/ℓ do occur Ostrea edulis 750 mg/ℓ (larvae) near the disposal site (see Figures 6 and 9), 10-20 mm (adult) <3 mm excess turbidity never exceeds 10 mg/ℓ for more Sedimentation (larvae after attachment) than 5% of the time (over a 14-day spring- 1-2 mm (larval settlement) neap tidal cycle) except in a very small area near the disposal location. This will not have any impact on mussels (adults, larvae or spat). Table IV. Summary of Critical Thresholds for Mussel (Mytilus edulis) Beds. Increased Disposal at Redcastle Site Species Parameter Optimum Range Maximum Tolerated The model demonstrated, in the main, the 50-100 mg/ℓ <1867 mg/ℓ (field) viability of disposal at Redcastle. Some concerns Suspended <250 mg/ℓ (5 weeks) <10,000 mg/ℓ for 3 weeks about the spat of native oysters were raised Mytilus edulis sediment <400 mg/ℓ (turbid estuaries) (adult in lab conditions) but these could potentially have been overcome by the implementation of a closed season. Sedimentation 10-20 mm (short time) Sedimentation nowhere reaches lethal levels for mussels, except at the sediment disposal site and its immediate vicinity. Impacts of the Oysters grounds (Figure 9). However, note that the dredging plume on mussel beds in Lough Oyster larvae appear to tolerate relatively high threshold is also exceeded in the current Foyle are therefore considered negligible. suspended sediment concentrations, as high disposal regime, although in a smaller area, as 400-800 mg/ℓ (Germano and Cary, 2005). but this has not impeded recruitment of ENVIRONMENTAL CONSIDERATIONS They require a clean, hard substratum (e.g., oysters to date (CEFAS, 2007). AT ALTERNATIVE MCKINNEY’S BANK oyster shell or shell cultch) for attachment, but DISPOSAL SITE can tolerate thin layers of deposited sediments, Furthermore, modelling results should be Figure 7 shows the sedimentation in metres perhaps up to 1 mm. After attachment, oyster considered against the prevailing natural after one year following the disposal of larvae can tolerate deposition of 2-3 mm, but background sedimentation in the area, which 80,000 tonnes of sandy silt at McKinney’s thicknesses >3-5 mm are likely to have some could be in the same order of magnitude or Bank. (For ease of reference, the locations of negative effects (Germano and Cary, 2005). more. In addition, storm events in the Lough, sediment monitoring sites imposed by the Table III summarises the tolerance thresholds which is mostly rather shallow, are expected licence are also shown on this image to show for oysters. to wipe the oyster shells clean of built-up their correlation with predicted sediment areas.) sedimentation. Adult oysters will not be affected by the dredging Oysters plume, as excess turbidities >10mg/ℓ are not Mussels Adult oysters will not be affected by the sustained more than 5% of the time (over a Previous studies on the effects of suspended sediment plume, as excess turbidities >10 mg/ℓ 14-day spring-neap tidal cycle) almost anywhere sediments on adult mussels (Mytilus edulis) are not sustained for more than 5% of the time in the Lough and sedimentation nowhere reaches have shown that they are capable of coping (over a 14-day spring-neap tidal cycle) almost lethal levels for adult oysters (see Table III), except with extreme high concentrations of anywhere in the Lough, and sedimentation at the disposal site and its immediate vicinity. suspended material (Kiørboe et al., 1980). nowhere reaches lethal levels for adult oysters. The ability for mussels to effectively utilise Larval settlement of oysters (which usually Larval settlement of oysters (which usually suspended food particles for growth is takes place during the summer months, takes place during the summer months: optimal at concentrations below 50 mg/ℓ and June-September) is, however, sensitive to June-September) is, however, sensitive to concentrations above 100 mg/ℓ result in sedimentation levels >2 mm. The model sedimentation levels greater than 1-2 mm weight loss (Prins and Smaal, 1989). calculations show that this threshold is (Table III). The model calculations show that in exceeded over an area up to approximately both proposed disposal regimes at Redcastle Mussels can protect themselves from 5 km2 within the Lough, overlapping only for (i.e., 60,000t and 80,000t annually), this overloading by temporarily closing their valves a small part with potential oyster grounds. sedimentation threshold is exceeded over an and when given sufficient time (months), Therefore, relocating the disposal site to area of approximately 10-15 km2 within the which may be expected to be the case in McKinney’s Bank causes no significant impact Lough (Figure 6), partly overlapping with Lough Foyle, they can adapt their gills and on oysters. In fact, the relocation of the some of the current and potential oyster palps to higher concentrations of suspended disposal site would result in significant Dredging and Disposal at Lough Foyle, Northern Ireland 17
Disposal at McKinney’s Bank Clearly sedimentation and, therefore, impacts throughout the Lough are significantly lower if the alternative McKinney’s Bank disposal site is used rather than the existing Redcastle disposal site.
LICENSING Following the encouraging predictions of the modelling in relation to the published knowledge concerning shellfish response, application was made for a licence to dispose of 60,000t annually at the McKinney’s Bank disposal site.
As is standard procedure, the application was subject to widespread consultation. No objections were received that were judged by NIEA to be of sufficient concern to justify refusal. However, as a precautionary measure, it was agreed that prior to the issue of a licence a programme of monitoring should be agreed between the Port, NEIA and the Loughs Agency. Figure 9. Shellfish Resource in Lough Foyle (adapted from CEFAS, 2007). The agreed monitoring programme specified that turbidity levels be continuously monitored at a fixed station for a period commencing one improvements with respect to potential adverse turbidities. Although incidental excess turbidities month prior to the commencement of dredging effects on the settlement of oyster larvae over 100 mg/ℓ do occur in the vicinity of the and for three months thereafter. The location compared to the use of the Redcastle site. McKinney’s Bank disposal site, excess turbidity finally agreed for monitoring was: Glenburnie never exceeds 10 mg/ℓ for more than 5% of Light at 55° 10.41’N, 007° 1.56’W. Mussels the time (over a 14 day spring-neap tidal cycle) Impacts of the dredging plume from the except in an area limited to the McKinney’s It was further agreed that 20 bed samples be McKinney’s Bank disposal site on mussel beds in Bank disposal site. This will not have any impact collected on a grid basis from three locations Lough Foyle are considered negligible. Mussels on mussels (adults, larvae or spat). Sedimentation (approximately seven per site). The sampling are known to be very tolerant of extremely high nowhere reaches lethal levels for mussels. sites selected were those identified by the modelling process as the potential areas of highest deposition. The analysis of these samples was to determine if the particle distribution in the selected areas had been changed significantly during the initial six months of dredging and disposal.
In October 2010 a formal application was therefore made for the disposal of 60,000t annually at the McKinney’s site. Following a tendering procedure, a contract for monitoring was awarded to the Fisheries & Aquatic Ecosystems Branch of the Northern Ireland Agri-Food & Bioscience Institute (AFBI) for the provision, installation and operation of a fixed instrument. This was a fixed continuous turbidity monitor of the type “Hydrolab MiniSonde MS5”. The instrument was installed on 02 December 2010 to measure the following parameters: temperature; luminescent Figure 10. Turbidity and Local Tide at the Glenburnie Light Monitoring Station (AFBI, 2011). conductivity; and luminescent dissolved oxygen. 18 Terra et Aqua | Number 130 | March 2013
Turbidity data (smoothed, 3h rolling average) in Lough Foyle normalised across sites
Figure 11. Turbidity (measured by optical backscatter) and Local Tide Height (above instrument) at Monitoring Stations within Lough Foyle. (All turbidity data have been normalised to a certified Figure 13. Results of ‘Before’ and ‘After’ Sediment Sampling and reference instrument for optimum comparability, and smoothed using a 3-hour rolling average.) Testing at Site 1.
Upon installation of this instrument and the Fortunately, as a result of the extensive Figure 11 presents the results recorded at that initial bed sampling NIEA granted a licence for monitoring stations in the Lough, it was possible time (AFBI, 2011). The data indicates that tidal the period 01 January to 31 December 2011 to interpolate between data sets routinely flow, as well as spring and neap cycles, are the for 60,000 tonnes. Dredging and disposal collected by AFBI at other locations within the dominant influence on the patterns of turbidity. operations by the Port dredger commenced Lough and mathematically deduce a substitute Disposal activities at McKinney’s Bank disposal on 11 January 2011. On 07 January 2011 the data set sufficient for the purpose of site have occurred on neap tides but have not instrument was attended to download the monitoring the effect of dredging and disposal. caused any notable increase in turbidity levels. collected data, but unfortunately it was found that the instrument attached to the Glenburnie Data from 07 January to 17 February 2011 To understand the effect of the dredging and Light had malfunctioned – a failure of the was downloaded twice to minimise the risk of disposal activity on turbidity levels the records wiping mechanism caused an interference with further failures – once on 11 January 2011 obtained from the Glenburnie Light site (see the optical turbidity measurement. As a result, and again on 17 February 2011. No further Figure 10) were compared with contemporary the data collected was not deemed reliable. malfunction of the instrument was noted. records from two regular monitoring sites elsewhere within the Lough known as Lough Foyle North and South (see Figure 11). The results for all three sites are provided in Figure 13. The results of the second testing of seabed sediments at three sites were also favourable. The location of the three sites from which samples were taken is shown approximately in Figure 7.
The AFBI report (2012) provides the results of the sediment analysis and those results for Area 1 are provided in Figure 13. The results of testing at the other two sites also record no significant change in the characteristics of the seabed sediments. In fact, the AFBI report states that, “The three monitoring areas displayed statistically different sediment characteristics with subtle differences in the amount of fine material entrained within the samples. The differences were however consistent and stable; no statistical difference in the sediment composition or structure was Figure 12. Locations of AFBI’s Permanent Lough Foyle Monitoring Stations. detected over time”. Dredging and Disposal at Lough Foyle, Northern Ireland 19
CONCLUSIONS whereas the records of disposal available to AFBI disposal site has no significant detectable are comprehensive, the records of dredging effect on water quality or seabed sediment These conclusions regarding the effect of are not and hence it has not been possible to characteristics within the Lough, other than dredging and disposal are based on reports by attempt any meaningful correlation between the within the immediate environs of the licence AFBI on the results of monitoring of turbidity act of dredging and turbidity levels. On the basis area. levels and other effects at Glenburnie Light in of the limited dredging activity data that has Lough Foyle. Glenburnie Light was chosen as been examined, AFBI opine that there may be The clear benefits of disposal of dredged a monitoring point as it is considered to be a a weak but detectable affect. However, it is material within the Lough include: convenient location at which the effect of apparent that any affect is small in relation to • the retention of sediment within the Lough; dredging and disposal, if any, could be the much stronger effects coming from the • a large reduction in the carbon footprint of observed. The objective of the monitoring of natural forces of tidal flow and wind generated the disposal activity; turbidity levels at the Glenburnie Light was to waves over the many shallow areas of the Lough. • reduced dredging cost, and determine whether or not the disposal of • the opportunity for maintenance dredging to sediments during routine maintenance dredging Other causes of sediment suspension, such as be carried out by the port using local labour activity causes any significant increase in high fluvial flows, the navigation of deep with consequent benefit to the local economy. turbidity relative to the ambient conditions in draught vessels and the action of trawling areas of the Lough that are remote from the when harvesting shellfish, can also be expected In all probability there is also a benefit to dredging. The conclusion was that it does not, to have significant localised effects. Of these, fisheries as a result of the modest, but regular as is clear from examination of the recorded from unrecorded observations, it will not be reworking of the seabed sediments in areas of results that are illustrated in Figure 12. surprising if trawling has the greatest effect, but dredging and disposal with consequent increase as this has not been measured, it is not certain. in the availability of nutrients for shellfish and The AFBI report states, “The combination of mobile species. This begs the question, why in instrumental water quality monitoring and The results of monitoring seabed sediments at the past have local fishing interests been so sediment analysis did not identify any three potential sediment receptor sites do not intransigent in resisting change when science significant transport (in the water column) or record any significant effect caused by the has predicted no significant adverse effect? deposition of sediment in the monitored areas dredging and disposal activities. The AFBI report during or for the three months after the states that, “There has been no statistically The result of this unfounded attitude has dredge disposal activity.” detectable change in the sediment composition been excessive cost and energy consumption, or structure at the three monitoring areas over particularly associated with the channel It is apparent that the state of the tide is the time. The sediments from all three areas were deepening in 1993, when objections from predominant influence on sediment characterised the same at the beginning, fisheries interests resulted in all dredged suspension and, furthermore, it is also clear middle and end of the monitoring period. material being disposed of outside of the that the level of suspension caused by tidal No significant changes in any of the sediment Lough at a site so distant from the area of flow, particularly mid-flood and mid-ebb flow, fractions were detected indicating that there dredging as to be closer to Scotland than to is much greater than the effect of the disposal had been no deposition of fresh material Ireland. This situation persisted for of dredged material. Occasional high resulting from the dredge disposal.” maintenance dredging until the issue of the terrestrial fluvial flows were also shown to new licence in January 2011. Hopefully, result in raised levels of suspended sediments. In summary, the monitoring programme has henceforth, a more balanced approach that demonstrated that the changed regime of recognises the wider interests, not only of No correlation between dredging, disposal and regular small-scale dredging and disposal of all fisheries, but also of the environment, the turbidity levels has been identified. However, dredged sediments at the new McKinney’s Bank local community and commerce will prevail.
REFERENCES Quality and Sediment Monitoring, prepared by AFBI Connor J (1995). Internal Memorandum to Bleakley R, Fisheries and Aquatic Ecosystems Branch for Environment Service, DoENI, File DU19/94, 03 January Anthony D Bates Partnership, March 2012. 1995. AFBI (2011a). Lough Foyle Dredge Disposal Monitoring 2011 - Environmental Monitoring Anchor Environmental (2003). Literature review of Deltares (2009) Sediment Dispersion Monitoring – Interim Report, prepared by AFBI Fisheries and effects of resuspended sediments due to dredging Lough Foyle, Report H5087, Delft, May 2009 Aquatic Ecosystems Branch for Anthony D Bates operations. Prepared for Los Angeles Contaminated Germano JD & Cary D, 2005, Rates and Effects of Partnership, February 2011. Sediments Task Force, Los Angeles, California. Sedimentation in the Context of Dredging and Anchor Environmental, California, June 2003, 140 pp. Dredged Material Placement, DOER Technical Notes AFBI (2011b). Lough Foyle Dredge Disposal Collection (ERDC TN-DOER-E19), U.S. Army Engineer Monitoring – Environmental Monitoring – February Anthony D Bates Partnership (1994). Disposal of Research and Development Center, Vicksburg, Instrumental Data Update, prepared by AFBI Dredged Material, Review of Options, Best Practicable Mass., 12 pp. Fisheries and Aquatic Ecosystems Branch for Environmental Option, Somerset, November 1994. Anthony D Bates Partnership, February 2011. Kiørboe T, Mohlenberg, F and Nohr, O (1980). CEFAS (2007). Baseline Survey of Shellfish Resources Feeding, Particle Selection and Carbon Absorption in AFBI (2012). Lough Foyle Dredge Disposal in Lough Foyle. Final Report, December 2007, CEFAS Mytilus edulis in Different Mixtures of Algae and Monitoring – Environmental Monitoring – Water Contract Report C2697, 80 pp. Resuspended Bottom Material, Ophelia 19:193-205. 20 Terra et Aqua | Number 130 | March 2013
WIL BORST, TIEDO VELLINGA AND ONNO VAN TONGEREN
THE MONITORING PROGRAMME FOR THE MAASVLAKTE 2 CONSTRUCTION AT THE PORT OF ROTTERDAM – PART II
ABSTRACT “Voordelta”, whereas low concentrations are Regarding monitoring strategy for silt: Because found further offshore. Owing to the residual statistical analysis of silt measurements, owing This is the second article in a series on the current along the Dutch coast, silt is mainly to the high variability and spatial autocorrelation, monitoring programme at Maasvlakte 2 in transported in north-north-eastern direction. is complicated, a decision was made to the Netherlands. The first article appeared in Because of the Coriolis force (the deflection of develop a new modelling strategy, model Terra et Aqua, number 129, December 2012 moving objects caused by the rotation of the supported monitoring, which is explained and and described the framework of the Earth), the silt remains close to the shore. discussed further in this article: All of the monitoring of Maasvlakte 2 following the measurements gathered are input for the Environmental Impact Assessment and A heavy storm has a large effect on the validation of a numerical model (MoS2). discussed the juvenile fish survey and the concentration of silt in the water column; the possible mismatch between cockles and algal higher waves cause silt to be released from Concerning the effects on the food chain: The bloom. This second article focuses on the the seabed. Only after some time will such silt dredging operations at sea for the construction monitoring aspects of silt (fines or SPM in the return into the seabed, for example as a result of MV2 lead to extra fine particles from the water column) resulting from the construction of the activity of benthic fauna, which is more trailing suction hopper dredger (TSHD) overflow. of Maasvlakte 2 and the possible effects on active in summer than in winter. An increased Silt, being part of the suspended particulate the benthic communities (mid and far field). flow velocity (during ebb and flood) also brings matter (SPM) in the water makes it turbid, silt in suspension from the thin fluffy layer on with the result that the algae in the water the seabed that is present during slack tide. (phytoplankton) receive less light. This allegedly INTRODUCTION slows down the growth of the algae and their Because of the expected effects of enhanced silt spring bloom (peak) shifts to a later time. The aspects that will be described are: the silt concentrations on the food chain, a condition in the water column along the Dutch coast; was included in the permit for the construction Were this to happen, less food would be the monitoring strategy for silt; and the of Maasvlakte 2 that silt should be monitored. available for small creatures (zooplankton) in the effects on the food chain. water and those living on or in the seabed, such as shells and worms. This zooplankton Silt in the water column is extremely variable Above: A survey ship with a new silt profiler – designed and the benthic fauna are, in turn, eaten by in space and time. High concentrations of and constructed in 2009 and owned by the Port of fish. Birds, diving ducks in particular, also feed suspended silt as well as high concentrations Rotterdam – is sailing behind a working trailing suction on benthic fauna. Other birds, such as gulls, in the seabed are found along the coast. hopper dredger to measure active and surface plumes enjoy fish. Reduced growth in algae may thus The highest concentrations are in the region as part of the extensive monitoring programme at the have possible consequences for the whole south of Scheveningen, especially in the Maasvlakte 2 expansion project. food chain. Therefore understanding how the The Monitoring Programme for the Maasvlakte 2 Construction at the Port of Rotterdam – Part II 21
Sand mining Wil Borst earned a MSc, Civil Eng, at Delft University of Technology in 1974 and began his Overflow career with De Weger International, followed by Svasek BV. He is a consultant Silt in water column on many projects related to port structures, graven dry docks, cooling water intake structures, offshore supply base and Transparency Algae coastal protection and dredging all over the world. In 1987 he took over Catchability of prey Biomass zooplankton Biomass worms etc. Biomass bivalves Netherlands Dredging Consultants. From 1991-2002 he was a part-time lecturer at the Groningen State Polytechnic. He is a founding member of Blue Pelican Biomass fishes Associates. In 2005 he was engaged by the Maasvlakte 2 organisation to assist Fish-eating birds and seals Waders Eiders, Scoters, Scaups in drafting the EIA and is now responsible for monitoring the possible effects on the Figure 1. Possible cause and effect chain initiated by extra fines (silt) in the water column. marine environment.
TIEDO VELLINGA SPM is distributed before, during and after environment. Also the effect of silt in the obtained his degree in Civil Engineering construction is important. By comparing these sediment on the benthic organisms is more (coastal engineering) at the Delft University SPM patterns, any (negative) effects of sand direct. These organisms would perhaps have of Technology in 1979. Since then he has extraction will become apparent (Figure 1). to work harder to filter the extra silt out of been working for the Port of Rotterdam the water, thereby ingesting less food and, as Authority in the fields of infrastructure and Since benthic species are less variable within a result, show less growth. Most species have water management. He is currently the year (between seasons) than algae a clear preference for certain grain sizes and Professor, Ports and Waterways at Delft (phytoplankton) and zooplankton (small mud contents in the sediment. University of Technology, Director animals floating in the water column and Environmental Monitoring at Maasvlakte 2, moving particularly with currents), the effects SILT MONITORING and project leader for the development and of large-scale interventions by human activities In-situ silt measurements implementation of the Environmental Ship (for example sand mining) on benthic species For silt concentrations, the question is not of Index, a World Ports Climate Initiative. are better indicators for changes in the coincidental (high) values at a certain time in a He is an expert on port environmental management and sediment management.
ONNO VAN TONGEREN TSHD SOURCE NEAR FAR received an MSc Biology in Vegetation terms FIELD FIELD Science, Microbiology and Soil Science in 1976 and a PhD in Mathematics and Background Composite Natural Sciences in 1988, both from turbidity Background New turbidity Radboud University, Nijmegen, the Background turbidity Netherlands. From 1985 to1994 he PASSIVE conducted scientific research in theoretical plume biology at NIOO/Centre for Limnology. Since 1994 to the present he has been a consultant and owner at Data-Analyse Ecologie (www.dataneco.nl) and in 2005 ACTIVE Dispersement of the passive Sand he started working as a subcontractor for plume plume (fine fraction < 63 μm) Extraction due to sand extraction by (TSHD) Haskoning and since 2007 is directly pit Trailing Suction Hopper Dredger employed by them. From 2006 to the Source -> Near field -> Far field present, he has been engaged by the 5,000 x 3,000 m Port of Rotterdam for monitoring the Figure 2. Schematic presentation of the passive and active plumes (fines) coming from the TSHD overflow. Both active possible effects of the construction of and passive plume were taken into account in the scenario calculations for the EIA. The surface plume is not been Maasvlakte 2. shown here, but is also included in the studies.
22 Terra et Aqua | Number 130 | March 2013
usual statistical methods without knowing Silt survey (2007) 100 points / 20 lines the preceding history would make the (randomised pattern) (perpendicular to the coast) interpretation of the measurements difficult or impossible. Hence, using only the 2 (~30 x 150 km ) measurements as prescribed in the permit might make it impossible to measure and distinguish any effect or consequences of the sand extraction for MV2.
The permit under the Earth Removal Act states that measurements must be taken every 14 days in three representative transects (imaginary lines) perpendicular to the coast. Along those three lines vertical silt profiles Borrow areas Rotterdam should be taken. The Port of Rotterdam (POR) and their experts doubted if the effect of the sand extraction on the Dutch coast could be measured reliably in this way. More emphasis on the changes in the spatial distribution of Figure 3. Set-up of silt measurements based on the scenario calculations (EIA, upper limit approach) The survey extent silt was considered to be necessary. In concert includes affected and non-affected (control) areas. with the relevant authorities, the permit series (every fortnight) were substituted by a more extensive survey over a larger area along the certain place, but long-term deviations which fluctuations in the volumes of silt brought coast, but limited to three campaigns per year could possibly be caused by the construction from the rivers and from the coastal waters in which 100 points would be investigated. of Maasvlakte 2 (MV2). Only when these of Zeeland, Flanders and France, might they The extent of the area was, amongst other long-term deviations could not be explained come from the MV2 construction. considerations, determined by the initial by, for example, fluctuations in the climate or Silt measurements at sea are not so easy to mathematical modelling of the Environmental incidental peaks, such as heavy storms or high carry out and to interpret. Simply using the Impact Assessment (EIA).
Sampling near Terra Nova 2009/7/29
TSM Average TSM Average TSM Average
Figure 4. Left, Sailing behind a working TSHD (Ostsee). Right, Example of the measurements (TSM - total suspended matter) following the TSHD Volvox Terra Nova. In the TSM records the active and the surface plumes are clearly visible. The red line is the path of the Terra Nova, the blue line is the track of the BRA-7, the survey vessel. The diagrams on the bottom left side indicate the current speed and direction taken from the ADCP. The Monitoring Programme for the Maasvlakte 2 Construction at the Port of Rotterdam – Part II 23
The locations were divided over approximately 20 transects with at least four points per transect, divided over four depth classes. In the area around the sand extraction pit, the transects are longer and thus contain more sampling stations (Figures 2 and 3).
In 2007 three baseline silt survey campaigns were carried out by POR, i.e., in the same timeframe and on the same locations as the juvenile fish survey (April, June and October) (see Terra et Aqua, nr. 129, December 2012). The sampling route and the 100 locations were randomised as much as possible taking into account the available contract time of the vessel, the sailing distances, the tidal conditions (not all shallow samples at low tide) and so on. The frequency of sampling was changed in 2009 to six times 50 locations (for each campaign a different subset of the 100 locations) as the Figure 5. The new silt profiler (designed and constructed in 2009 and owned by POR) is being placed overboard. coupling with the juvenile fish monitoring was no longer necessary. In this way a better spread in time was obtained and possible problems with spatial autocorrelation were reduced.
In order to obtain more information about the physical processes in the coastal zone additional measurements were taken in certain areas of interest, starting with a 13-hour measurement (one tidal cycle) along a transect in Noordwijk in November 2007. In 2009 the changes during the tidal cycle at the Noordwijk transect were studied twice (spring tide and slack tide cycle) during two full tidal cycle (26 hrs). More 13-hour measurement campaigns at different locations followed in later years.
Furthermore, measurements were taken during a storm (ad hoc decision in December 2010 to sail again), as well as following behind trailing suction hopper dredgers dredging at the sand borrow area in order to measure the extent and fate of the plume generated by the overflow (Figure 4). Also in 2013 silt measurements will be carried out.
EQUIPMENT In the 2007 survey the measurements were taken by the silt profiler owned by the Port of Rotterdam (POR). The observations over the vertical profile were performed with the following devices: - Two optical backscatter sensors with different ranges of SPM (suspended particulate matter) concentrations Figure 6. New silt profiler with all its sensors. 24 Terra et Aqua | Number 130 | March 2013
After the silt measurement baseline study of 2007 it was decided to improve the measurements by building a new profiler. Mid- July 2009 the new profiler was tested and put in operation in the survey of July and thereafter up until the present (Figure 5). This new profiler measures, depending on the lowering speed, at least once in each 10 cm of the vertical profile.
The new profiler (Figure 6) has the following extra equipment: - A Wetlab ACS spectrophotometer, measuring Figure 7. The crew of the Euro cutter Jade/BRA-7, the survey vessel used by the POR from 2007 to the present, were a continuous spectrum in the range of able to go to sea at wind forces of 8 or 9 on the Beaufort scale (BF). Most ships can only conduct their research at a visible light to estimate the concentrations maximum of 5 BF. of dissolved substances and SPM. - A LISST - 1000 probe, measuring particle size distributions and SPM concentrations in the - Transmission probe for the highest SPM - Chlorophyll sensor (fluorescence) vertical profile including the concentration concentrations - Pressure sensor of the SPM. - Conductivity sensor, from which the salinity is - Temperature sensor - An altimeter (echo sounder) to measure the computed after correction for temperature - Three Niskin water samplers, volume 1.8 litre height of the profiler above the seabed and and press each to be able to close the bottom Niskin water
Alongshore velocity ADV Cross-shore velocity ADV Temperature [˚C] Chlorophyll height [m]
velocity [ms-1] velocity [ms-1] Salinity [PSU] Chlorophyll [ugL-1]
SBS ADV [counts] downcast LISST Extinction upcast height [m]
OBS CTD [FTU] extinction particle size (log10) particle size (log10)
Figure 8. High SPM values measured during stormy conditions. The various simultaneously measured values are presented, i.e. alongshore and cross-shore velocity by ADV, temperature and salinity, Chlorophyll, SBS (sound backscatter) of the ADV (counts) and OBS (optical backscatter, FTU), LISST Extinction and particle sizes during up- and downcast. Please note that, when the OBS is going in overload (too much TSM, red and blue line in the lower left graph), the ADV (same graph) still records and so does the LISST, hence high values of TSM can still be evaluated correctly. Expected tidal current (kn) TIME (GMT) Measured waveheight (cm) Expected tidal current (kn) TIME (GMT) Measured waveheight (cm) Expected tidal current (kn) TIME (GMT) Measured waveheight (cm) and directions at Noordwijk, at IJmuiden and Euro Channel and directions at Noordwijk, at IJmuiden and Euro Channel and directions at Noordwijk, at IJmuiden and Euro Channel IJmuiden & Euro Channel 11:43:34 IJmuiden & Euro Channel 15:47:24 IJmuiden & Euro Channel 23:55:01 Seapoint 125 (OBS) Seapoint 125 (OBS) Seapoint 125 (OBS)
Measured waterlevels (cm MSL) Measured waterlevels (cm MSL) Measured waterlevels (cm MSL) IJmuiden & Scheveningen IJmuiden & Scheveningen IJmuiden & Scheveningen
Depth vs FTU’s Depth vs FTU’s Depth vs FTU’s
Figure 9. Part of a series of measurements under ”normal” weather conditions showing the influence of the tidal current on the distribution of the TSM in the water column. Recordings taken from a 13-hour cycle near Noordwijk. The strength and direction of the current, the direction and the position with respect to the tide is also given as well as the tidal cycle.
sampler precisely on a pre-determined TRIOS sensor (watercolour, incoming and used as a survey vessel for the silt measurements) height close to the seabed. reflected spectra of sunlight). The validation, (Figure 7) and the POR’s staff who carry out - An ADV probe to measure current speed elaboration and further analysis of the the silt measurements even go to sea at wind and direction. gathered data are done by POR staff in concert forces of 8 or 9 on the Beaufort scale (BF) and with external specialists. conduct their research under these difficult Part of the equipment is also a dedicated dGPS conditions. Most survey ships in the past, as far system, a detachable Acoustic Doppler Current Bad weather and silt as available data is concerned, return to port Profiler (ADCP) and, in 2007 only, a portable The crew of the Jade/BRA7 (the fishing vessel at wind force in excess of 5 BF. Because of the BRA7’s ability to endure wind forces of 8 or 9 BF, researchers were able to get a much better understanding of the effects of storms at sea and the sediment that is brought up from the seabed as a result of wind and wave action.
The data appears to indicate that the silt concentrations during a storm can increase by a factor of between 10 and 100, because the fine particles from the bottom are turned up and over by the energy exerted by the waves and end up in the water column as a result (Figures 8 and 9). As a contrast, the variation of the average amount of fines over the vertical caused by the tide is a factor 2 (for this location the range is between 10 and 20 mg/l).
New insights in the Rhine ROFI` One of the striking things noted during the silt monitoring along the Dutch coast is the great influence exerted by the hugely variable volume of fresh water that flows into the sea. Fresh water continuously enters the North Sea coming from the River Rhine through de Nieuwe Waterweg and the Haringvliet, creating a Region of Freshwater Influence (ROFI). The Dutch call this phenomenon the “Coastal River” which in the USA is a called a “River Figure 10. The ROFI in front of the Dutch coast. The figure shows an overview of the results of the scenarios studied. Plume”. The ROFI interacts directly with the In all figures (during high water) the salinity structure in the top layer by the 28, 30 and 32 PSU isohalines is indicated. transport of SPM along the coast (Figure 10). Furthermore the size and the location of the stratification by phi (ø), the potential energy anomaly of the water column (0 = completely mixed), and the total amount of energy required to mix the water column in the Dutch In his PhD thesis Gerben de Boer described coastal zone. The direction and speed of the wind are indicated in the figures. From Masters thesis, Joost van Wiechen. the importance of changes in stratification of 26 Terra et Aqua | Number 130 | March 2013
the ROFI on a theoretical basis. During slack to set up a new monitoring method to provide (but not necessarily limited to observations tide, there are currents perpendicular to the much greater insight into the distribution of using satellites) is used for these adjustments. coast, which cause downwelling or upwelling. the (extra) silt off the Dutch coast. The basis The surface of the sea is observed regularly His only proof of the existence of upwelling for determining the amounts of SPM is an from satellites, amongst which MERIS, the was one remote sensing image in which innovative method based on a combination satellite that passes over once a day and that cooler water was visible in a zone along the of numerical models and measurements: supplied the images that are used in the MV2 coast. The measurements made by the POR, MoS2 (which stands for Model-Supported model. The MERIS satellite stopped working in particularly the 13- and 26-hour measurements Monitoring) of SPM in the North Sea. The April 2012, many years after its predicted life were used to study the ROFI and the decision was based on an earlier pilot project, time. The MODIS satellite images are a proper movement of SPM in the ROFI. The behaviour TnulTSM (Baseline Total Suspended Matter) in replacement. The pictures encompass the of the ROFI is extremely variable in terms of which the POR participated in the review of whole of the North Sea in the (visible) light time and space (both location and size). the results and the funding. spectrum. Hence data is only available when there is no cloud coverage, although partly In one of the POR’s 26-hr measurements Using the Deltares numerical models (DELFT-3D) clouded pictures are still useful (Figure 11). the upwelling was clearly visible in the at ten-minute intervals, the water movement measurements. The measurements and the is calculated with input of real weather data Based on the colour of the water, an estimate analysis of the results have provided a better and information on river outflows. Next the can be made of the quantity of SPM (silt and understanding of this phenomenon. Also sediment transport model (DELWAQ) calculates algae) present in the topmost metres of the turbulence in the water, particular in the ROFI how much silt is released from the seabed water column. dominated areas, is a source of uncertainty in and how the silt rises and falls in the water the numerical models. A number of TU Delft column. Both models are huge: The amounts The combination of data with model results is students cooperated with the POR and Deltares, of grid cells in the model are approximately referred to as data assimilation. The technique in their master thesis research, to see if they 300,000 and 160,000 for the hydrodynamic used by Deltares is ensemble Kalman filtering. could explain, analyse and measure the and silt model, respectively. All computations This Kalman ensemble filtering is also used for upwelling and the water turbulence. for one year, after investing in new Linux weather forecasts. In addition to or instead of clusters, take a week computing time. data-assimilation, the team at Deltares also MODEL SUPPORTED MONITORING applies parameter assimilation: Using the OF SPM, A NEW METHOD However good the numerical models might be, same principles, parameters of the model are In consultation with and following approval they always deviate from reality. The models adjusted in the ensemble Kalman filtering, from the authorities, the decision was made can be adjusted on the basis of observations leading to different parameter values in space (in 2008, before the start of the sand extraction) (data assimilation). Data from remote sensing (differences between regions) and in time (seasonal differences).
This ultimately leads to increasingly better models, which produce the most reliable results. This method must lead to a smaller margin of error and provide more insight into the different SPM flows. The procedure has been tested and it proved that the new monitoring model, the satellite observations and the measurements at sea provide a reliable picture and that it is possible to produce SPM maps and silt atlases. Finally, the uncertainty is still present regarding what happens deeper in the water column. For this reason, the model results are validated using the POR’s in-situ measurements at sea (2007, 2009-2013). A B Furthermore, all other relevant available data from the Dutch Ministry of Infrastructure and the Environment, Rijkswaterstaat (RWS) and Figure 11. a) Result of the optical analysis of a satellite image partially covered with clouds projected on the schematisation other parties, e.g., temperature, salinity (CTD of the Southern North Sea of the MoS2 model; b) Part of a satellite image (on a different date) showing the variation series, Ferry box measurements, Tow fish and so of colours in the surface waters from which (amongst others) the amount of SPM in the top layer can be estimated. on) are used to validate the model (Figure 12). The Monitoring Programme for the Maasvlakte 2 Construction at the Port of Rotterdam – Part II 27
Figure 12. This schematic representation shows the three pillars on which the MoS2 model is based. Model results are in this case Delft3D combined with Earth Observations and calibrated and validated by in situ measurements. The validation is on independent in-situ data (gathered by POR), not used for the calibration of the model outcome.
After combining and assimilating a year’s data, the SPM distribution maps can be made, for example as weekly or monthly averages of the silt concentrations. These maps are put into a silt atlas and can be used when deducing possible ecological effects of the sand extraction. Apart from that the POR receives all generated data on each grid point of the models on a hard disk in which a whole year’s output (at one hour intervals) is available. These can be looked at as time series in either 2 or 3-dimensional space. The silt atlases can subsequently be used to check the predictions of the EIA (Figure 13).
The first concept silt atlas for 2007 has been published in early 2012. The experience gained when creating this atlas will be incorporated into an updated version of the MoS2 method. In the new setup atlases for the years 2003 through 2008, becoming available in the second quarter of 2013, will be prepared.
Results so far At the end of 2012 a new model setup of MoS2 was ordered from Deltares in which all the previous lessons learnt were incorporated. The new results of the improved MoS2-II model will start with all available data from 2003 continuing until 2008.
Figure 13. Example page from the SPM Atlas for 2007. On the top row the MERIS surface layer SPM values (averaged over the time period of one week) that are used as input, the deterministic values of SPM in the surface layer and the resulting assimilated SPM surface values just after the assimilation. The second row: the Root Mean Squared differences (standard deviations) between MERIS and the assimilated model results, the deterministic SPM at the bottom and the resulting SPM at the bottom layer after assimilation. Furthermore the tide at Noordwijk 10 and the Significant wave height at the Europlatform are shown. The period for which the pictures are shown is the light pink band shown in the lower two figures. 28 Terra et Aqua | Number 130 | March 2013
Figure 14. Examples of some worms found in the box core samples.
A provisional analysis shows that there BENTHOS AND SEABED COMPOSITION The second group are the creatures that live appears to be no evidence of significant Monitoring benthos on or just above the seabed: the epifauna. increases in the SPM concentrations outside More than 300 species of benthic organisms Well-known examples include shrimp, hermit the borrow area on the basis of the in-situ live in and on the bottom of the North Sea. crabs, crabs and starfish. The spatial variation filed measurements of 2009, 2010, 2011 and Most of these are invertebrate organisms. and the variation between years are large. 2012. This means that, in accordance with the Within the benthos, a distinction is made Within just a few metres, the composition of EIA and the Appropriate Evaluation, only between two groups. First of all the creatures the marine benthos can be completely minor effects, if any, can be expected on the living in the seabed: the infauna. The infauna different. A species can decrease in an area of Natura 2000 areas of the North Sea coastal includes many species of worms, such as several km2 and at the same time increase in a zone and the Wadden Sea. The expected clam worms, tube worms and bristle worms. nearby area. This variation in space and time, proof of this will be available in 2013 when The worms vary in size from 1 millimetre to especially the spatial autocorrelation in the new MoS2-II model results will be available 10 centimetres (Figure 14). Many shellfish also changes, is a complicating factor in the and can be compared with the in-situ live in the seabed, such as cockles, otter shells analysis of the effects of the sand mining. measurements. and razor shells. In order to determine the effects of the extra silt released as a result of the sand extraction, BACI (Before After Control Impact) study baseline measurements were made in the spring of 2006 and 2008 for the whole area, including the reference areas. During and after the peak of sand mining the benthic fauna was sampled again in 2010, 2011 and 2012. In 2009 a baseline survey in the borrow area, with a finer mesh, was carried out. This only concerned the area that will be investigated after the sand extraction is finished (2013) in order to find out if the benthos is recovering well, how recolonisa- tion is taking place and on what time scale.
Study design The study of the effects of extra silt on the benthic fauna was designed like a so-called Figure 15. The basic principle of a BACI (Before After Control Impact) design. The control area is used to estimate the Before After Control Impact (BACI) design autonomous development. The impact area is assumed to follow the same development. The difference between the The basic principle of such a BACI design is expected end situation in the impact area and the real situation is the effect. shown in Figure 15. The Monitoring Programme for the Maasvlakte 2 Construction at the Port of Rotterdam – Part II 29
about 50 kilometres wide, at right angles to the coast (Figure 16, left).
The second baseline measurement of the benthos took place in 2008 and had a more elongated shape (Figure 16, right). This modification was based on new additional impact scenario study result that indicated that the fines from the sand extraction would be transported more towards the coast over a longer stretch.
The boundaries were at Petten and Westkapelle (Walcheren) approximately a length of 200 km and the width of the survey area was reduced to a maximum 35 km. Thus the area under consideration is now similar to the area of the silt survey, which started in 2007 and was Figure 16. The extent of survey area in 2006 (first baseline survey, left) and in 2008 and thereafter (right). based on the new impact scenario study. The T1, T2 and other surveys were repeated during the sand extraction in 2010, 2011 and The autonomous development in a so-called very well before, so a more complicated 2012 in the same area as the 2008 survey. control area is estimated as the difference analysis of the changes in spatial pattern of between the situation before sand mining the species was also planned and carried out Field and laboratory methods and the situation during and after the sand by POR in 2012. The samples from the seabed are taken using mining (brown). In the impact area the a box corer (infauna) and a benthic sledge same amount of autonomous change is In order to be able to demonstrate relatively (infauna, and epifauna in particular larger expected. small changes, given the great natural species). These two surveys are carried out variation in the benthos, the number of independently from each other with different Apart from the autonomous development samples has to be large. survey vessels; the MS Arca (2006), MS Luctor there is also an effect of the sand mining in (2008, 2009 and 2010) and the BRA7 (2011 and the impact area. This effect can be estimated The first baseline measurement of the benthos 2012) for the box core sampling by NIOO and from the change in the impact area and the was carried out in 2006 (Figure 16, left). the MS Isis for the benthic sledge by IMARES. change in the control area. The extent and The area sampled was between IJmuiden and A Reinecke box corer of 32 cm diameter and the shape of the impact area were not known Schouwen-Duiveland (~100 km) and was added weight of 200 kg was used (Figure 17).
After taking small sediment samples, the benthos samples are sieved over a one- millimetre mesh. The residue is collected in a bottle and fixated by adding pH-neutralised formaldehyde (formalin).
In the laboratory, the organisms are sorted under a stereomicroscope and counted and weighed per species. Species composition per sample, spatial distribution of species and groups of species, density (numbers per m²) and biomass (ash-free dry weight per m²) are derived from the collected data.
Figure 17. Reinecke box corer on the left and the first version of the benthic sledge on the right. Both photographed onboard the survey vessel MS Arca (2006 baseline study). 30 Terra et Aqua | Number 130 | March 2013
Figure 18. Discussions on identification of a particular species from the box core sample. This sequence of photos was taken during the ringtest ordained by POR (2012). The particular species lying in the petri dish are shown enlarged when viewed under the microsope and on the screen. Also shown are various text book pictures of the same species that form the reference of the determination.
The box corer surveys and laboratory work and rarer infaunal species which have a lower The benthic sledge is dragged over the were carried out by the Netherlands Institute density. In this way, information is obtained to seabed and, in this way, cuts a strip about for Ecological Research (NIOO-KNAW). supplement that from the box corer samples. 10 centi-metres wide, 7-10 centimetres deep The 2011 samples have been processed by A benthic sledge is less standard than a box over a “controlled” length of approximately two other laboratories (IECS from the UK and core. The benthic sledge used consists of a 150 metres, thus sampling ~15 m2 of seabed. Koeman & Bijkerk, the Netherlands) (Figure 18). metal mesh cage fixed to a sledge. The base The material ends up in the cage and the plate of the sledge is fitted with two vertical water that flows through it ensures that sand Sampling with the aid of the benthic sledge blades and a horizontal, sloping blade forming and other small particles, including the tiniest focuses mainly on the epifauna and the larger the knife (Figure 19). worms and juvenile molluscs, are rinsed out of
Figure 19. This series of pictures shows the benthic sledge, with equipment and catch unsorted and sorted, onboard one of the survey vessels. The Monitoring Programme for the Maasvlakte 2 Construction at the Port of Rotterdam – Part II 31
Figure 20. Benthic sledge with extra equipment. The changes include extra weight at the bottom, removal of the spoiler, restriction on the free movement of the arm of the counting wheel, echo sounders (altimeters) on both sides plus the attachment of a motion sensor on top of the sledge (heave, pitch and roll recording). The drawback of this operation is that the sledge now has to be employed using an umbilical cord for powering the equipment and storage of the recorded data on a PC onboard the survey vessel.
the sample. The result is a sample that contains mechanic counting wheel. Consequently, an was rather straightforward, although the the larger species of infauna and epifauna. extensive research programme was initiated patterns looked complicated at first sight. From this sample, that contains a large by the POR and resulted in adaptations to the Canonical Correspondence Analysis (CCA) amount of dead shells and other by-catches, regular benthic sledge of IMARES as well as revealed that most of the changes in the the live organisms are taken and processed. mounting sensors to register the underwater control and impact area were not related to movements of the sledge while being towed. silt. Only a rather low percentage (ca. 10%) Onboard the survey ship Isis, density, biomass, This has increased the accuracy of the actual of the spatial and temporal variation could be distribution and size category are determined. calculated (cutting) length of the knife attributed to explanatory variables. Afterwards, in the laboratory, the ash-free dry through the seabed (Figure 20). weight is determined. The benthic sledge Time accounted for ca. 3.5% of the variation provides information on, for example, the However, one of the lessons learnt so far is in the species data (not related to silt) and the numbers of cockles, nuns, beach shells, mussels, that the spatio-temporal variation appeared percentage of the variation in space and time lesser sand eels and gobies. This research was to be so large, that the sampling error is of that could be attributed to silt was only 1.1%. contracted out to IMARES (Yerseke, the minor importance. However, a clear and significant, although Netherlands). During the first survey (2006) small, effect of the increase of the silt with the benthic sledge concern arose about Results so far contents in the impact area is present: its efficiency to cut sufficiently deep (10 cm) After statistical analysis of the box core data Mussels, Baltic clam, dog whelks, some bristle over the full length accounted for by the with CANOCO (ter Braak) the interpretation worms and polychaetes increased in the high impact area. Many other changes, as well in the control area as in the impact area, could not be related to silt. These relatively small changes can be explained by considering the conceptual model explained in Figure 21.
The silt concentration in the bed and the SPM in the water column increase towards the shore (black line). The underlying assumption is that during and after the sand mining the silt increases (dashed line). Each species is
Figure 21. Conceptual model of a few of the species abundant along the silt gradient perpendicular to the Dutch coast. Offshore, on the left-hand side, the coast is on the right. In reality over 300 species are present along this gradient. 32 Terra et Aqua | Number 130 | March 2013
represented as a bell-shaped curve and its abundance, although definitely influenced by CONCLUSIONS predicted ranges for the Natura 2000 areas other environmental variables too, is assumed designated as the North Sea coastal zone and to depend on the silt concentration along the The aspects that were described here focus Wadden Sea. The expected proof of this will gradient. Changes in silt content (SPM and on the silt in the water column along the be available in 2013 when the new MoS2-II sediment, black dashed line) lead to a shift in Dutch coast; the monitoring strategy for silt; model results will be available and can be the optimum location and the spatial range and the effects of silt on the food chain. compared with the in-situ measurements. over which the species occur. Owing to the high variability and spatial autocorrelation, statistical analyses of silt Other changes in the course of monitoring Apart from temporal changes not related to measurements are complicated. Consequently, involved adaptations to the regular benthic silt, species in the control area are not a decision was made to develop a new sledge owned by IMARES. These included affected. Species in the low impact area are modelling strategy – model-supported equipping the sledge with additional sensors restricted to a narrower zone and move in monitoring. All of the measurements that are to register the underwater movements of the offshore direction. In the high impact area gathered are input for the validation of a sledge while being towed. This has increased some species (for example, the red one) numerical model (MoS2). the accuracy of the actual calculated (cutting) disappear, but they still can move to the low length of the knife through the seabed. impact area. Only near to the coast the A new model set-up of MoS2 was ordered increase in silt concentrations leads to an from Deltares at the end of 2012 and all the Regarding the statistical analysis of the box increase or the appearance of species that previous lessons learnt were incorporated. core data with CANOCO, the patterns looked were rare or absent before the sand mining. The new model MoS2-II will start with all complicated at first sight, but the interpretation available data from 2003 and continues was actually rather straightforward. The through 2008. After 2008 the differences Canonical Correspondence Analysis (CCA) REFERENCES between the deterministic model run results revealed that most of the changes in the and the remote sensing and in-situ data will control and impact area were not related to
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Rapport Nummer: C026/07. NIOO-Monitor Taskforce Publication Series 2007-03. Datarapportage Nulmeting Maasvlakte 2. Baseline study Benthic thesis Technical University Delft. Keetels, G.H. (2012). Model setup, data assimilation communities 2006 (in Dutch). http://repository.tudelft.nl. and skill assessment: Model-supported Monitoring http://edepot.wur.nl/146578 of SPM in the Dutch coastal zone. Deltares Report Ter Braak, C.J.F. (1986). Canonical correspondence 1002611-000, February 2012. Vaarrapport benthic survey 2006 (in Dutch). analysis: a new eigenvector technique for (Sailing logs benthoc survey 2006). multivariate direct gradient analysis. Ecology 67 (5), Ghada, Y.H., El Serafy, Marieke A., Eleveld, Meinte http://edepot.wur.nl/148248 1167-1179 Blaas, van Kessel, Thijs, Van der Woerd, Hans J. and de Boer, Gerben (2012). Assimilating Remotely Monitoringsplan Aanleg Maasvlakte 2. (2008). Jongman, R.H.G., Ter Braak, C.J.F. and Van Tongeren, Sensed Suspended Particulate Matter in a 3D Projectorganisatie Maasvlakte 2, 15 augustus 2008 O.F.R. (1995). Data analysis in community and Transport Model of the Dutch Coastal Zone. Journal (bijgewerkt d.d. 30 september 2008). Definitief landscape ecology. Cambridge Univ. Press of Geophysical Research-Oceans, 2012. 9P7008.M1 (In Dutch only). http://www.maasvlakte2.com/kennisbank/2008-08 Blaas M., Eleveld, M.A., El Serafy, G.Y., van der Van Kessel, T., Winterwerp, J.C., van Prooijen, B., Monitoringsplan Aanleg Maasvlakte 2.pdf Woerd, H.J., van Kessel, T. and de Boer, G.J. (2008). van Ledden, M. and Borst, W.G. (2011). TnulTSM: Integration of remote sensing and Modelling the seasonal dynamics of SPM with a van Tongeren, O.F.R. and van Riel, R.C. (2007). modelling of total suspended matter in the Dutch simple algorithm for the buffering of fines in a MEP Slib: een schets van de gewenste opzet van coastal zone. Deltares Report 53618WL(Z4030), 66 pp. sandy seabed. Cont. Shelf Res. 31(10) S124–S134, een meetprogramma. Havenbedrijf Rotterdam N.V. doi:10.1016/j.csr.2010.04.008 April 2007. Blaas, M., Cronin, K., El Serafy, G.Y., Eleveld, M.A., Gaytan Aguilar, S., Friocourt, Y.F., Keetels, G.H., Van Prooijen, B., van Kessel, T., Nolte, A.J., Los, F.J., van Tongeren, O.F.R. and Dankers, P. (2008). de Reus, N.O. and van der Woerd, H.J. (2011). Boon, J.G., de Jong, W. and van Ledden, M. (2006). Meetrapport slibmetingen 2007, Nulmeting Composite atlas of SPM in the southern North Sea Impact sand extraction Maasvlakte 2, Mud Maasvlakte 2. 14 juli 2008, Havenbedrijf Rotterdam N.V. 2007; MoS2: Model-supported monitoring of SPM in transport, nutrients and primary production. Referentie; 9P7008.E0/R0002/902199/JEBR/Nijm. the Dutch coastal zone. Deltares, September 2011. Royal Haskoning, Svašek Hydraulics, WL | Delft Hydraulics report 9P7008.O9. van Wiechen, J. (2011). Modelling the wind-driven Blaas, M., Cronin, K., El Serafy, G.Y., Friocourt, Y.F., motions in the Rhine ROFI. March 2011, Masters Garcia Triana, I.D.T.F., Gaytan Aguilar, S. and Books / Periodicals Reviewed 33 books / periodicals reviewed
Facts about seagrass meadows and mangrove forests. Seabed landscaping as a tool Subsea Rock Installation An Information Update from the IADC – Number 3 – 2012 TWO NEW INFORMATION for restoring habitats that encourage biodiversity. Revitalising wetlands number 2012 What is typically meantFACTS by Subsea ABOUTdisperse the rock, the more difficult it becomes04 to ensure Rock Installation? An Information Updateplacement from accuracy. the IADC With the exploration and development Rock has been used for ports and coastal protection of oil and gas fields in increasingly deeper waters, new rock purposes for centuries – for dikes and breakwaters, groins placement technologies were needed to guarantee accuracy, in freshwater lakes, especially in low-lying areas such as deltas. and scour protection. During the past several decades the whilst the workability in more remote offshore locations UPDATES FROM THE IADC major dredging contractors have become increasingly had to be secure. involved in the development and execution of Rock Installation in marine environments. From the previously How did the dredging industry adapt used term rock dumping, today the term Subsea Rock to working at greater depths? Installation is commonly used to reflect the advanced To keep up with the pace of oil and gas field developments techniques that are being applied, in particular for the in deeper waters an entirely new solution was developed: Facts About Subsea Rock offshore oil and gas sector. A fall pipe, which could guide the rocks from the water Two types of Subsea INITIATINGRock Installation should be surface subsea to much greater depths. By the end of the distinguished: One is for shallow water and is typically used 1970s a steel, telescopic fall pipe was developed for Rock for coastal and embankment protection works and for scour Installation at water depths significantly exceeding 50 metres. protection for the offshoreHYDRAULIC oil, gas and wind energy Big diameter steel FILL fall pipes are, however, PROJECTS sensitive to large developments at up to 50 metres of water depths. The drag and gravity forces. Installation Though this book provides an exciting overview, with wonderful other is Rock Installation at greater water depths, usually In the mid-1980s an improved technique was developed ranging from 50 to 2,200 metres, and is most frequently based on a semi-open, flexible fall pipe consisting of a string applied for the offshore oil Whatand gas isindustry. hydraulic Fill? of bottomless, heavy plastic bucketsbe considered. along two Determining chains. At the characteristics of the available Hydraulic Fill is fill in which the materialsthe lower are end deposited of the stringby a a borrowremotely material operated, such propelled as type, grading and silt content is also flowing stream of water. This fill material will originate from a important as these may vary considerably. In some cases the How is Rock Installation implemented? vehicle (ROV) was attached. The ROV was equipped with borrow area or dredging site and be transported to the borrow material may need specific construction and/or At first the installation of rock was done from shore or by a sophisticated range of technologies such as camera, survey (Number 3, September 2012) illustrations, and a summary of what has been achieved, it is not the reclamation area by dredger, barge or pipeline. It is then treatment methods in order to become suitable fill material. hand from a flat deck barge.placed In theas a last mixture century of fill the materialfirst and positioningprocess water equipment. in the This flexible fall pipe design, in mechanical rock dumpingreclamation vessels were area. designed, Hydraulic built, Fill hascombination a wide variety with of the ROV,What installed kind on oa Fdynamically knoWled Ge about hydraulic tested and used for ever largerapplications maritime for works infrastructure worldwide, construction positioned projects. vessel, was able Fillto achieve is important? more accurate for port extensions as well as flood protection structures. placement of rock by correctingDetailed the off-setting knowledge caused from a bywide variety of disciplines in What kinds oF projects use hydraulic Fill? geotechnical engineering, hydraulic engineering and These vessels were typically self propelled and outfitted currents. The drag forces were lower and therefore the Hydraulic Fill is used for reclamation projects, which means mechanical engineering combined with practical know-how with a strengthened flat deck to load the rock, hydraulically system was less sensitive to rupture. This guaranteed a Facts About Initiating Hydraulic end. The partners in the programme are looking forward and outward land creation for a range of purposes – from building or and experience of dredging and filling techniques are all or mechanically operated “shovels”,extending anwhich airport were platform designed to landhigher for residential workability or as the semi-opencritical. andInsufficient flexible informationstring of about the technical to gradually push the rock recreationalover the side areas of the to industrialvessel, and construction buckets is such able as to an adjust its shapespecifications to the currents. of a reclamation project can lead to inadequate a series of anchors and winchesLNG plant for accurateor nuclear positioning. power station. OtherIn projectsthe early where 1990s DGPSand conflicting (Differential specifications, Global to construction requirements They were designed to handleHydraulic a large Fill range is used of arerock the sizes, restoration Positioning of eroded System) beaches was introducedthat cannot in the be offshore met and/or oil and to excessive costs for fill treatment and construction of coastline defences as well as for and testing. varying from gravel to large boulders weighing many gas and marine construction worlds: Differential drift of environmental and habitat restoration or creation, for These developments may frustrate the tender process, tonnes. the rock-laying fall pipe vessel with respect to the subsea instance, of wetlands. may cause serious problems during construction and quality Fill Projects offering guidelines, lessons learnt and practical tools. More about this This technique is still used frequently and is referred to pipeline or cable could be achievedcontrol by anddynamic may leadpositioning. to long-lasting, costly arbitration cases. as side-stone dumping. Side-stoneWhy is knodumpingWled is Gprimarilye about hTheydraulic success of Fill this technique Thehas provenformulation invaluable of generally as the accepted guidelines and used in water depths up to 50material metres, because and htheydraulic accuracy Filldredging projects industry has becomereasonable more and specifications more involved should be established. In this way of rock placement from theimportant? water surface is limited. The with the offshore energy industry,the client working can understandat ever greater and properly plan a reclamation No two situations are the same. The quality of the Hydraulic project and the consultants and contractors have adequate deeper the waters, the more the currents may influence and depths. Fill to be used is crucial to the quality of the end product. guidelines for design and quality control. The end product or application will have specific performance (Number 4, December 2012) innovative programme and the book are available at the website, requirements and the characteristics of the fill mass will What drives the desiGn philosophy oF a determine how well these performance criteria are met. hydraulic Fill project? The physical conditions of project areas may differ The design philosophy of a Hydraulic Fill project should
64797_FactsAbout.indd 1 dramatically. Wave climate, currents, water depth and subsoil match the anticipated loading23-08-12 response 15:04 of the fill mass to the conditions as well as the sensitivity of the environment and requirements imposed by the future use of the reclaimed land availability of fill at or nearby the site are essential factors to – all within the technical boundary conditions of the project. 4 pp. Available free of charge online www.ecoshape.nl
Pictured above: A trailer suction hopper dredger placing sand fill in a reclamation area by rainbowing. international association of dredging companies
65640_Facts about_nr4.indd 1 27-11-12 15:10 and in print.
In these two Facts About published in 2012, two very different types 175 Ideas on the Future of of dredging operations and dredged materials have been addressed: 175 ideas the Fehmarnbelt Region The subsea installation of rock and the use of hydraulic fill for land on the future of Creative ideas from the workshops at reclamation. Rock and hydraulic fill each have unique characteristics the Fehmarnbelt Fehmarnbelt Days 2012 which demand extensive knowledge of the substance, the water depths Region COMPILED BY THE STRING and the type of equipment which are appropriate for these materials. SECRETARIAT ON BEHALF OF
The technical engineering details of each of these types of material are Creative ideas from THE FEHMARNBELT DAYS the workshops at quite specific and each subject needs to be understood and appreciated Fehmarnbelt Days 2012 ORGANISERS on its own merits. Each of these Facts About defines the technical December 2012. 62 pages. Downloadable expertise that is necessary to execute these very different operations as PDF. successfully, the environmental concerns and the financial consequences. The very essence of Fehmarnbelt Days 2012 held in Hamburg and Facts About is an initiative of the International Association of Lübeck, Germany in September 2012 is now available as a book, Dredging Companies (IADC) to distribute up-to-date information on which consolidates 175 unique ideas from this meeting with the aim various maritime construction and dredging subjects. All are to inspire decision-makers, developers and innovators in the corridor downloadable as PDFs at www.iadc-dredging.com, under publications, from the Øresund Region to Hamburg, from Scandinavia to Germany. or by emailing the IADC Secretariat at [email protected]. More than 300 people participated in 19 different events over the three days of the forum. Their common objective was to help create Building with Nature the new Fehmarnbelt Region within the context of the future tunnel Building with nature EDITED BY VALERIE JONES between Denmark and Germany. Workshops, conferences and podium Thinking, acting and interacting differently 40 pages. 2012. EcoShape. debates generated countless, many innovative ideas that are meant to Hardcover. Many full-colour point the way towards a dynamic and integrated Fehmarnbelt Region illustrations. bound together by the Fehmarnbelt Fixed Link, which is scheduled to open in 2021. This so-called “Book of Ideas” was designed to serve as Beginning with an Introduction a guideline for the work of the various regional and national by Wim Kuiken, The governments as well as for the many cross-border stakeholders and Netherlands Commissioner for organisations in the region based on the many activities of the event. the Delta Programme, this compact book gives a clear explanation It attempts to point the way toward a common future, integrated about why the Dutch Delta plan was enacted into law and why the perspectives on regional development sustainable growth, labour EcoShape project, “Building with Nature”, is important. markets, infrastructure and scientific cooperation. It will, however, also encourage all stakeholders in public or private administration, politics EcoShape is a consortium of private sector partners, government agencies and business to think and act creatively when looking at the future. and knowledge institutes who have joined together to use their expertise to tackle the challenges of urbanisation, economic development, This publication was compiled by the STRING Secretariat on behalf of all sea-level rise and climate change with innovative approaches. The idea the Fehmarnbelt Days organisers. Queries concerning this publication is to think, act and interact differently. The book brings together the should be directed to STRING Secretariat, Region Sjælland, EcoShape team’s work during the last few years: The shift from building Alléen 15, 4180 Sorø, Denmark, Tel: +45 5787 5851. in nature to building with nature in mind from the very start. Projects that seek to nourish the coastline with ‘soft’ rather than ‘hard’ solutions. A copy of this publication can be downloaded free of charge at: The use of oyster reefs to protect tidal flats from erosion in estuaries. http://www.femern.com/material-folder/documents/2013-publications/ Coastal protection in the tropics in order to strengthen coral reefs, 175-ideas.pdf 34 Terra et Aqua | Number 130 | March 2013 seminars / conferences / events
IADC SEMINAR ON DREDGING & RECLAMATION and transport of materials such as steel, iron ore, oil, slag, granite APRIL 15-19, 2013 amongst others, as well as specialised companies to assist with ATLÂNTICO BÚZIOS CONVENTION & RESORT regulations and customs clearance. BÚZIOS, BRAZIL The port area of Açu will have a 2.9 kilometre-long bridge with The International Seminar on Dredging and Reclamation is being 10 docking berths, which will be able to accommodate the latest organised by the International Association of Dredging Companies generation of super-ships, including 380-metre-long Chinamax vessels (IADC), the premier organisation representing the private dredging with a reported capacity of 400,000 tonnes of cargo. industry, in Búzios, Brazil from April 15 to 19, 2013. The seminar includes a tour of the immense dredging project at Superporto do To appreciate the enormity of this project view this movie about the Açu, the biggest port complex of its type in the world, the largest project(s): http://www.youtube.com/watch?v=G8e2lscJXCg investment in port infrastructure in Latin America, in the country with the greatest GDP growth for a region. By Professionals for Professionals Dredging plays an essential role in world trade and economic and Why Brazil? Why now? social progress. To optimise the chances of the successful completion Latin America – and especially Brazil – is booming. And port of a project, contracting parties should, from the start, fully development and dredging is an essential element. Dredging in Latin understand the requirements of a dredging project. America has been steadily growing over the last few years including such mega-projects as the Superporto do Açu. And many more That’s why IADC developed this comprehensive Seminar for projects and works are going on or being planned for the near future. professionals in dredging-related industries – presented by professionals No wonder that ABD, Associação Brasileira de Dragagem – together from the major dredging companies. Since 1993 IADC, often in with other interested parties – has asked IADC to organise its co-operation with local universities and/or other associations, has informative and educational Seminar in Latin America for a second time. provided this Seminar combining classroom lectures and workshops with a site visit to a dredging project. Hundreds of past participants agree: Seeing is Believing: Site visit to Boskalis’ Superporto do this is a unique chance to receive invaluable hands-on experience. Açu project Part of the beauty of the IADC Seminar is getting out of the classroom Costs and early registration discount and into the field. In that context, seminar participants will be delighted The fee for the week-long seminar is € 2,950.- (VAT inclusive). that Boskalis, one of the world’s largest dredging companies, is allowing This includes all tuition, seminar proceedings, workshops and special us a close up view of their dredging site at the Superporto do Açu. participants’ dinner, but excludes travel costs and accommodations. Most likely one of their state-of-the-art dredging vessels will be Seminar participants can get a preferential rate at the hotel where the available for a visit. Seminar will be held (Atlântico Búzios Convention & Resort). Participants registering before 1 March 2013 will receive a € 200.- discount. The Superporto do Açu, a US$1.6 billion project developed by LLX, a logistics company, is an impressive effort to improve the freight For further information contact: transport infrastructure and support the country’s growing trade links Jurgen Dhollander, International Association of Dredging Companies with China, the U.S. and others. Deemed a one-stop-shop, the Tel.: +31 70 352 3334 90-kilometer square area (about 1.5 the size of Manhattan) will • Email: [email protected] provide everything necessary for the production, processing, storage www.iadc-dredging.com
WIND FARM DEVELOPMENT: in the offshore wind industry with two days of networking and EUROPEAN OFFSHORE 2013 open interactive discussions. APRIL 10-11, 2013 Attendees will be senior management from within the industry EDINBURGH, UK including: wind farm developers, wind farm operators, turbine manufacturers, engineers, consultants, ports and harbours, offshore Wind Farm Development: European Offshore 2013 will provide shipping companies, energy analysts and lawyers. Fees for the presentations and interactive discussions lead by senior representatives conference will be £1,495 (ex VAT). from the leading companies operating in the offshore wind sector. Key industry players and decision makers will be present to discuss For further information contact: the development and future of this significant renewable energy Justyna Korfanty source. This is an opportunity to enhance your network and gain Tel.: +44 207 981 2503 contacts from within the leading organisations making a difference • Email: [email protected] Seminars / Conferencestekst nog plaatsen/ Events 35
THE HYDRAULIC FILL MANUAL INTERNATIONAL A wide range of industries are involved in the use of marine space COURSE and resources, including shipping, oil and gas, fisheries, aquaculture, April 11-12, 2013 ports, mining, renewable energy, tourism, dredging, marine science/ PAO Post-Academic Onderwijs, Delft, The Netherlands technology, maritime law, insurance, finance, and others. The conference will address priorities for cross-sectoral industry leadership and This course covers the initiation, design and construction of hydraulic collaboration in ocean sustainability, including: ocean policy, regulations fill projects as described in the recently published Hydraulic Fill and governance; marine spatial planning; the role of industries in ocean Manual. Without proper hydraulic fill and suitable specialised and climate observations; biofouling and invasive species; fisheries and equipment, major infrastructure projects such as ports, airports, aquaculture interaction with other industries; cross-sectoral collaboration roads, industrial or housing projects cannot be realised. To date in responsible use of the Arctic; sound and marine life; cargo issues, port comprehensive information about hydraulic fill is difficult to find. waste reception facilities and marine debris; marine mammal interactions; the role of finance, insurance and legal sectors in ocean sustainability. The Hydraulic Fill Manual is a thoroughly researched book, written by Other cross-cutting topics critical to responsible industry operations in noted experts, which takes the reader step-by-step through the complex the marine environment will be developed as the programme evolves. development of a hydraulic fill project. This in-depth Manual will enable the client and his consultant to understand and properly plan a SOS sessions will be designed to provide the state of the knowledge reclamation project. It provides guidelines for design and quality control on these issues, including topic overviews, case studies and examples and allows the contractor to work to known and generally accepted of best practices. Limited opportunities are available for speakers to procedures and reasonable specifications. The ultimate goal is to realise address the themes above. Experts and thought leaders interested in better-designed, better- specified and less costly hydraulic fill projects. being considered as speakers are encouraged to contact the WOC.
The course is of particular interest to clients, consultants, planning SOS participants are primarily the senior management responsible for and consenting authorities, environmental advisors, contractors and environment and sustainability in companies and industry associations civil, geotechnical, hydraulic and coastal engineers involved in from a wide range of ocean industries. Other ocean stakeholders are dredging and land reclamation projects. For following this course welcome to participate, e.g., senior representatives of international some background knowledge in geotechnical engineering is required. organisations, government agencies, academic/research institutions CEDA, CUR and IADC are happy to support The Hydraulic Fill Manual and non-government organisations. International. The course leader will be Engineer Jan van ‘t Hoff (Van ‘t Hoff & Partners), one of the editors of the Manual. The course For further information contact: fee is € 990,00 excl. VAT and includes a copy of the Manual. • Email: [email protected] Participants will receive 10 PDH’s Bouw- en Waterbouwkunde http://www.oceancouncil.org/site/summit_2013/ (Construction and Maritime construction) study points.
For further information contact: WODCON XX http://pao-tudelft.nl/Infoaanvragen/2439/0/The_Hydraulic_Fill_Manual. JUNE 3-7, 2013 html SQUARE-BRUSSELS MEETING CENTRE, BRUSSELS, BELGIUM
Organised by CEDA on behalf of WODA (World Organisation of WORLD OCEAN COUNCIL Dredging Associations) which incorporates WEDA, CEDA and EADA, SUSTAINABLE OCEAN SUMMIT (SOS) 2013 WODCON XX, with the theme, “The Art of Dredging” will showcase April 22-24, 2013 some 120 technical papers over three days covering all aspects of dredging Washington, DC and maritime construction. All WODCON XX papers will be peer reviewed and provide up to date, relevant and high quality information. In 2050, what will the state of the ocean and the ocean business community be – and what must be done between now and then to ensure The Congress will also feature a technical exhibition and technical that both are healthy and productive? The Sustainable Ocean Summit visits. These technical programme elements will ensure a complete (SOS) 2013 is the only international, cross-sectoral ocean sustainability learning process, while various social events will allow participants to conference designed by and for the private sector, focused on Corporate meet fellow professionals from all over the world in a friendly and Ocean Responsibility. This is the World Ocean Council’s second SOS and inspiring atmosphere. The 2013 conference marks the XXth edition of builds on the highly successful SOS 2010, held in Belfast, Northern WODCON and coincides with the 35th anniversary of the current Ireland, which drew together more than 150 representatives from a WODA and its three component associations. wide range of ocean industries. The aim is to further advance leadership and collaboration amongst the diverse ocean business community in Topics of interest include but are not limited to the following broad addressing marine environment and sustainability challenges. areas: Method, Equipment & Techniques; Management of Sediments 36 Terra et Aqua | Number 130 | March 2013
(clean and contaminated); Environmental Issues; Regulatory Issues; progress that has created today’s market trends and also emerging Management and Economics; Alluvial and Deep Sea Mining. environmental issues. The conference will provide a forum for discussions between North, Central, South American and Pacific regions. For further information contact: Congrex Belgium - WODCON XX Organisation Office For further information contact: Tel.: +32 (0)2 627 0166, Fax: +32 (0)2 645 26 71 Tel.: +1 360 750 0209 • Email: [email protected] • Email: [email protected] www.cedaconferences.org/wodcon www.westerndredging.org
IADC SEMINAR ON DREDGING & RECLAMATION PORTS 2013 JUNE 24-28, 2013 AUGUST 25-29 2013 UNESCO-IHE DELFT, THE NETHERLANDS SEATTLE, WASHINGTON, USA
For (future) decision makers and their advisors in governments, port PORTS ‘13 – “Ports: Success through Diversification” – is the 13th in a and harbour authorities, off-shore companies and other organisations series of international port and harbour specialty conferences held on that have to execute dredging projects, the International Association a tri-annual basis since 1977. This year’s conference theme recognises of Dredging Companies will again organise the International Seminar the broad spectrum of factors that make ports so important to their on Dredging and Reclamation at UNESCO-IHE, Delft, The Netherlands. local, regional and national communities, including the broad missions To optimise the chances of the successful completion of a project, they support, such as moving cargo, providing recreational contracting parties should, from the start, fully understand the opportunities, serving as engines of economic development, and requirements of a dredging project. This five-day course strives to providing for stewardship of environmental resources. The PORTS provide an understanding through lectures by experts in the field and Conference series is internationally recognised as an outstanding workshops, partly conducted on-site in order to give the “students” opportunity to network with hundreds of leading practitioners, hands-on experience. An important feature of the Seminars is a trip to researchers and specialists in the port engineering profession. This visit a dredging project being executed in the given geographical area. year PORTS ‘13 has expanded to 3 full days, resulting in a 50 percent Each participant receives a set of comprehensive proceedings with an increase in opportunities to present ideas and experiences. extensive reference list of relevant literature and, at the end of the week, a Certificate of Achievement in recognition of the completion For further information see: of the coursework. Please note that full attendance is required for http://content.asce.org/conferences/ports2013/index.html obtaining the Certificate of Achievement. The fee for the week-long seminar is € 2,250.- (VAT inclusive). This includes all tuition, seminar proceedings, workshops and a special participants’ dinner, but COASTS, MARINE STRUCTURES AND BREAKWATERS excludes travel costs and accommodations. SEPTEMBER 17-20, 2013 EICC EDINBURGH, SCOTLAND, UK For further information contact: Jurgen Dhollander, International Association of Dredging Companies The Institution of Civil Engineers is pleased to announce the tenth in this Tel.: +31 70 352 3334 highly-regarded series of specialist conferences. This is an international • Email: [email protected] forum addressing the developments in offshore and nearshore energy www.iadc-dredging.com production, procurement, issues with coastal defence, and the construction, management and refurbishment of all coastal assets. Whilst retaining the historical coverage on shoreline structures, coastal processes, and WEDA 33 / TAMU 44 design and construction of breakwaters and related structures, the AUGUST 25-28, 2013 conference will also emphasise aspects at the civil and coastal engineering HILTON HAWAIIAN VILLAGE, HONOLULU, HAWAII interface, such as fluid loadings, resource modelling, interactions with the environment, construction, installation, cabling, servicing and maintenance. The theme of the Western Dredging Association’s 33nd Annual Western Hemisphere Dredging Conference and Texas A&M’s 44th Annual Dredging For further information contact: Seminar (WEDA 33/TAMU 44) is “So That Ships May Pass”. It will ICE Events Team, Institution of Civil Engineers focus on the Historical, Structural and Operational Development of One Great George Street Navigation throughout the Western Hemisphere. Included in the Westminster, London SW1P 3AA, UK dredging conversations will be the critical global economic need for Tel.: +44 (0)20 7665 222, Fax: +44 (0)20 7233 1743 dredging, the importance of enhancing the marine environment as • Email: [email protected] well as historical dredging developments, trends and the dredging www.ice-conferences.com/Upcoming-events/ICE-Breakwaters TERRA ET Membership list IADC 2013 AQUA Through their regional branches or through representatives, members of IADC operate directly at all locations worldwide Africa Dredging and Contracting Rotterdam b.v., Bergen op Zoom, Netherlands Editor Guidelines for Authors BKI Egypt for Marine Contracting Works S.A.E., Cairo, Egypt Dredging and Maritime Management s.a., Steinfort, Luxembourg Marsha R. Cohen Dredging and Reclamation Jan De Nul Ltd., Lagos, Nigeria Dredging International (Luxembourg) SA, Luxembourg, Luxembourg Terra et Aqua is a quarterly publication of the International Association of Dredging Companies, Dredging International Services Nigeria Ltd., Ikoyi Lagos, Nigeria Dredging International (UK) Ltd., East Grinstead, UK Nigerian Westminster Dredging and Marine Ltd., Lagos, Nigeria Dredging International N.V., Zwijndrecht, Belgium Editorial Advisory Committee emphasising “maritime solutions for a changing world”. It covers the fields of civil, hydraulic Van Oord Nigeria Ltd., Victoria Island, Nigeria Flota Proyectos Singulares S.A., Madrid, Spain Bert Groothuizen, Chair and mechanical engineering including the technical, economic and environmental aspects Heinrich Hirdes G.m.b.H., Hamburg, Germany Robert de Bruin of dredging. Developments in the state of the art of the industry and other topics from the Asia Irish Dredging Company Ltd., Cork, Ireland Beijing Boskalis Dredging Technology Co. Ltd., Beijing, PR China Jan De Nul (UK) Ltd., Ascot, UK René Kolman industry with actual news value will be highlighted. Boskalis Dredging India Pvt Ltd., Mumbai, India Jan De Nul n.v., Hofstade/Aalst, Belgium Heleen Schellinck Boskalis International (S) Pte. Ltd., Singapore Mijnster Zand- en Grinthandel bv, Gorinchem, Netherlands Martijn Schuttevâer • As Terra et Aqua is an English language journal, articles must be submitted in English. Dredging International Asia Pacific (Pte) Ltd., Singapore Nordsee Nassbagger-und Tiefbau GmbH, Bremen, Germany Hyundai Engineering & Construction Co. Ltd., Seoul, Korea Paans Van Oord B.V., Gorinchem, Netherlands Roberto Vidal Martin • Contributions will be considered primarily from authors who represent the various disciplines International Seaport Dredging Private Ltd., New Delhi, India Rock Fall Company Ltd., Aberdeen, UK Ann Wittemans of the dredging industry or professions, which are associated with dredging. Jan De Nul Dredging India Pvt. Ltd., India Rohde Nielsen, Copenhagen, Denmark • Students and young professionals are encouraged to submit articles based on their research. Jan De Nul Singapore Pte. Ltd., Singapore Sociedade Española de Dragados S.A., Madrid, Spain P.T. Boskalis International Indonesia, Jakarta, Indonesia Societa Italiana Dragaggi SpA ‘SIDRA’, Rome, Italy IADC Board of Directors • Articles should be approximately 10-12 A4s. Photographs, graphics and illustrations are Penta-Ocean Construction Co. Ltd., Tokyo, Japan Société de Dragage International ‘SDI’ SA, Lambersart, France P. de Ridder, President encouraged. Original photographs should be submitted, as these provide the best quality. PT Van Oord Indonesia, Jakarta, Indonesia Sodraco International S.A.S., Lille, France Toa Corporation, Tokyo, Japan Sodranord SARL, Le Blanc-Mesnil Cédex, France Y. Kakimoto, Vice President Digital photographs should be of the highest resolution. Van Oord (Malaysia) Sdn Bhd, Selangor, Malaysia Terramare Eesti OU, Tallinn, Estonia C. van Meerbeeck, Treasurer • Articles should be original and should not have appeared in other magazines or publications. Van Oord (Shanghai) Dredging Co. Ltd., Shanghai, PR China Terramare Oy, Helsinki, Finland Th. Baartmans An exception is made for the proceedings of conferences which have a limited reading public. Van Oord Dredging and Marine Contractors bv Hong Kong Branch, Hong Kong, PR China Tideway B.V., Breda, Netherlands Van Oord Dredging and Marine Contractors bv Korea Branch, Busan, Republic of Korea TOA (LUX) S.A., Luxembourg, Luxembourg P. Catteau • In the case of articles that have previously appeared in conference proceedings, permission Van Oord Dredging and Marine Contractors bv Philippines Branch, Manilla, Philippines Van Oord (Gibraltar) Ltd., Gibraltar N. Haworth to reprint in Terra et Aqua will be requested. Van Oord Dredging and Marine Contractors bv Singapore Branch, Singapore Van Oord ACZ Marine Contractors bv, Rotterdam, Netherlands P. Tison • Authors are requested to provide in the “Introduction” an insight into the drivers (the Why) Van Oord India Pte Ltd., Mumbai, India Van Oord Ireland Ltd., Dublin, Ireland Van Oord Thai Ltd., Bangkok, Thailand Van Oord Middle East Ltd., Nicosia, Cyprus behind the dredging project. Zinkcon Marine Singapore Pte. Ltd., Singapore Van Oord Nederland bv, Gorinchem, Netherlands IADC Secretariat • By submitting an article, authors grant IADC permission to publish said article in both the Van Oord nv, Rotterdam, Netherlands Australia + NEW ZEALAND Van Oord Offshore bv, Gorinchem, Netherlands René Kolman, Secretary General printed and digital version of Terra et Aqua without limitations and remunerations. Boskalis Australia Pty, Ltd., Sydney, Australia Van Oord UK Ltd., Newbury, UK Alexanderveld 84 • All articles will be reviewed by the Editorial Advisory Committee (EAC). Publication of an Dredging International (Australia) Pty. Ltd., Brisbane, QLD, Australia 2585 DB The Hague article is subject to approval by the EAC and no article will be published without approval Jan De Nul Australia Ltd., Australia Middle East NZ Dredging & General Works Ltd., Maunganui, New Zealand Boskalis Middle East Ltd., Abu Dhabi, UAE of the EAC. Van Oord Australia Pty Ltd., Brisbane, QLD, Australia Boskalis Westminster (Oman) LLC, Muscat, Oman Mailing address: WA Shell Sands Pty Ltd., Perth, Australia Boskalis Westminster Al Rushaid Co. Ltd., Al Khobar, Saudi Arabia P.O. Box 80521 Boskalis Westminster Middle East Ltd., Manama, Bahrain Europe Gulf Cobla (Limited Liability Company), Dubai, UAE 2508 GM The Hague Atlantique Dragage Sarl, St. Germain en Laye, France Jan De Nul Dredging Ltd. (Dubai Branch), Dubai, UAE The Netherlands Baggermaatschappij Boskalis B.V., Papendrecht, Netherlands Middle East Dredging Company (MEDCO), Doha, Qatar Baggerwerken Decloedt & Zoon NV, Oostende, Belgium National Marine Dredging Company, Abu Dhabi, UAE Ballast Ham Dredging, St. Petersburg, Russia Van Oord Gulf FZE, Dubai, UAE T +31 (0)70 352 3334 Baltic Marine Contractors SIA, Riga, Latvia F +31 (0)70 351 2654 BKW Dredging & Contracting Ltd., Cyprus The Americas Boskalis B.V., Rotterdam, Netherlands Boskalis International bv Sucural Argentina, Buenos Aires, Argentina E [email protected] Boskalis International B.V., Papendrecht, Netherlands Boskalis International Uruguay S.A., Montevideo, Uruguay I www.iadc-dredging.com Boskalis Italia Srl., Rome, Italy Boskalis Panama SA, Panama City, Panama I www.terra-et-aqua.com Boskalis Offshore bv, Papendrecht, Netherlands Compañía Sud Americana de Dragados S.A., Buenos Aires, Argentina Boskalis Sweden AB, Gothenburg, Sweden Dragabras Servicos de Dragagem Ltda., Brazil Boskalis Westminster Ltd., Fareham, UK Dragamex SA de CV, Mexcio City, Mexico Boskalis Westminster Marine (Cyprus) Ltd., Limassol, Cyprus Dravensa C.A., Caracas, Venezuela Boskalis Westminster Middle East Ltd., Limassol, Cyprus Dredging International de Panama SA, Panama Boskalis Westminster Shipping BV, Papendrecht, Netherlands Dredging International Mexico SA de CV, Veracruz, Mexico Please address enquiries to the editor. Brewaba Wasserbaugesellschaft Bremen mbH, Bremen, Germany Jan De Nul do Brasil Dragagem Ltda., Brazil Articles in Terra et Aqua do not necessarily DEME Building Materials NV (DBM), Zwijndrecht, Belgium Mexicana de Dragados S.A. de C.V., Mexico City, Mexico reflect the opinion of the IADC Board or Dragapor Dragagens de Portugal S.A., Alcochete, Portugal Stuyvesant Dredging Company, Louisiana, USA Dravo SA, Italia, Amelia (TR), Italy Van Oord Curaçao nv, Willemstad, Curaçao of individual members. Dravo SA, Lisbon, Portugal Van Oord Dragagens do Brasil Ltd., Rio de Janeiro, Brazil Dravo SA, Madrid, Spain Westminster Dredging (Overseas) Ltd., Trinidad
Cover Terra et Aqua is published quarterly by the IADC, The International Association © 2013 IADC, The Netherlands A survey ship with a specially developed silt profiler – designed and constructed in 2009 and owned of Dredging Companies. The journal is available on request to individuals or All rights reserved. Electronic storage, reprinting or by the Port of Rotterdam – follows a trailing suction hopper dredger at work to measure active and organisations with a professional interest in dredging and maritime infrastructure abstracting of the contents is allowed for non-commercial surface plumes. This was an integral part of the extensive monitoring programme at the Maasvlakte 2 projects including the development of ports and waterways, coastal protection, purposes with permission of the publisher. expansion project in Rotterdam (see page 20). land reclamation, offshore works, environmental remediation and habitat restoration. ISSN 0376-6411 The name Terra et Aqua is a registered trademark. Typesetting and printing by Opmeer Drukkerij bv, For a free subscription register at www.terra-et-aqua.com The Hague, The Netherlands. PEFC/30-31-372 Number 130 | March 2013
THEORY VS REALITY testing the ‘pilferer’ draghead
SCIENCE VS PRECONCEPTIONS Lough Foyle’s two disposal sites
EXPECTATIONS VS FACTS silt concentrations at Maasvlakte 2
ET Maritime Solutions for a Changing WorldTERRA AQUA